Light Metals 2012

Bauxite samples from Boke-Mine, Guinea, West Africa, were investigated by TG-DSC, TG-MS, dilatometry and laser flash analysis. The sample showed mass-loss steps due to the dehydration of aluminum hydroxides and iron hydroxides. Sintering of the samples starts at around 800°C. The thermal diffusivity values were between 1.2 to 0.6 mm2/s for the temperature range RT to 300°C.

The process of leaching diasporic bauxite in sodium aluminate solution is the most popular method to produce alumina in Chinese alumina industry. A new consistent kinetic model for gibbsite leaching process model has been developed in our previous work. This paper aims to study the application of the new model for the diaspore leaching in industrial alkali solution. The model equation was numerically integrated applying the fourth-order Runge-Kutta technique. Nonlinear regression analysis was carried out to estimate the unknown model parameters by comparing numerical solutions with available experimental data. The new model which considers the fractal geometry of the shrinking diaspore particles and the residual aluminium concentration in particles, is more consistent with the leaching process of the diaspore particles distributing in a narrow size range than the particles with the wide range of the size distribution.

Overview of our research on ‘structure and reactivity’ of gibbsite and boehmite under varied conditions of mechanical activation, e.g. milling energy and presence of a second phase is presented. Bulk and surface changes induced in the solids by milling are characterized in terms of morphology, particle size distribution, specific surface area and nature of porosity, crystallite size and zeta potential. Results on enhanced amorphisation of gibbsite in presence of a second phase (quartz, hematite etc), changes in zeta potential of gibbsite due to loss of texture during milling and anomalous decrease in surface area of boehmite during milling are reported. Reactivity of the activated solids in sodium hydroxide and variation in thermal transformation temperatures is correlated with physicochemical characteristics of the samples and plausible explanation for the observed correlations presented. Significance of the results with specific reference to bauxite and alumina processing in Bayer process is highlighted.

This paper proposes a “mechanical activation-homogeneous digestion” technology as a strengthening method for diasporic bauxite digestion process of alumina production. Effects of digestion temperature, digestion time and mechanical activation speed on digestion performance of diasporic bauxite were investigated by using “homogeneous digestion” equipment, and the digestion kinetics of diasporic bauxite was studied as well. The results indicate that the mechanical activation can greatly improve the digestion performance of diasporic bauxite, digest mine with larger particle size. The optimal mechanically activated digestion temperature is 20°C lower than that of direct digestion. The relative digestion rate of alumina goes up to above 97% when digested at 245°C for 60 minutes with a mechanical activation speed of 80rpm.The apparent activation energy of mechanically activated digestion is 57.30kJ/mol, 21.09kJ/mol lower than the direct digestion. The kinetic equation of mechanically activated digestion is (1−η)−1/3−1=1.5532x10−4exp(4.764x105/T)t.

The crystallized layer that compounds the bauxite’s geological profile from NE Pará was ore dressed through the processes of crushing, screening, washing and grinding, in order to reach the same size distribution of that in the alumina production industry. After the preparation process, the sample (90%, < 0.21 mm) containing 5.3% reactive silica and 47.2% available alumina was submitted to mechanochemical activation with different kinds of reagents (CaO, Ca(OH)₂, CaCO₃, CaO+HCl), in different concentrations, which resulted in the formation of a calcium aluminum hydrosilicate (hydrogarnet). This phase was formed in the first 30 min of grinding with the use of CaO and Ca(OH)₂. However, chemical characterization showed that the principal phase obtained, katoite hydrogarnet, had high aluminum content in its chemical composition thus proving that its formation is not good for the Bayer process.

This paper investigates the changes of phase and apparent morphology under the combined effects of an intense magnetic field and temperature field. The effect of different roasting conditions on the digestion and settling performance of high-iron diaspore is also studied here. The results indicated that roasting pretreatment under high magnetic fields can change the microstructure of bauxite, hence improving its digestion properties. The optimum roasting conditions in intense magnetic field for high-iron bauxite are: the roasting temperature is 500°C, roasting time is 60min and the magnetic field intensity is 9T. The digestion rate of alumina for roasted ore is 71.82% when digested at 210°C for 60min with the digesting liquor ratio of 1.69, which is ~20% higher than that of raw ore. The settling performance of the digested slurry is also improved significantly when using roasted bauxite treated in intense magnetic field.

The effect of lime addition on the predesilication and digestion properties of a gibbsitic bauxite in industrial Bayer liquor at different temperatures was investigated in the present paper. Lime increases the desilication efficiency of gibbsitic bauxite during the predesilication process, which promotes the conversion of sodalite and cancrinite to hydrogarnet in the presence of CO₃2−. Lime slightly decreases the alumina digestion rate of gibbsitic bauxite at both 145 °C and 245 °C when the lime dosage is 2 wt%. However, the soda consumption during the digestion process is decreased due to lime addition, especially at the higher temperature. Lime can also promote the conversion of aluminogoethite to hematite during the digestion process, which improves the digestion property of aluminogoethitic alumina in the gibbsitic bauxite.

Technological investigations were carried out based on the Bayer process. Predesilication characteristic of the bauxite, the effects of digestion temperature and retention time, concentration of Na₂O and amount of CaO addition on Al₂O₃ digestion efficiency in Bayer process, the settling characteristics of the red mud were determined. The bauxite in the northern region of China is diasporic type with high silica (in 6–15% SiO₂). The main silica minerals in the bauxite are kaolinite and chamosite. The presence of high silica causes high bound-soda losses in the red mud in the Bayer process, but a part of silica content in the bauxite was in the form of chamosite, the bound-soda losses can be greatly reduced with chamosite mineral by using Bayer process. Therefore, it is necessary to study digestion characteristics of the special diasporic bauxite and settling separation properties of the red mud by Bayer process.

Until now, the domestic diasporic bauxite resources is the primary supplied bauxite for alumina production, and Bayer, dressing Bayer, sintering, mixed combination and serial combination processes are parallel used to produce alumina product in China. At the same time Chinese diasporic bauxite resources was seriously depleted recently with the greatly increasing of alumina capacity. In this paper, depending on current diasporic bauxite conditions, the raw material, energy consumption and raw materials & fuel cost are studied for processing different grade diasporic bauxite with different production processes, at same time the raw material, energy consumption and raw materials & fuel cost are discussed at same A/S for different processes, in order to provide references to economical usage of Chinese bauxite resources for Chinese alumina industry.

ETI Aluminium can process nearly 550.000 tons of bauxite and produce 250.000 tons of alumina per year. The south region of Turkey produces boehmitic bauxite at various alumina/silica ratio. The reserve of Morcukur Bauxite in this region is about 6.000.000 tons of high reactive silica content.ETI started producing bauxite from the Morcukur deposits in 2007 because of easy handling and lower cost. 60,000 tons of Morcukur bauxite have been produced from this mine but could not be used because of red mud settling problems. After XRF, XRD, Goethite/Hematite ratio, Organic content (TOC) analysis, autoclave efficiency (Parr Reactor) and settling performance tests, 10 %–40 % Morcukur bauxite has been processed in 2011 with a strict laboratory and process control. Results from grinding, digestion and red mud settling performance in the process and laboratory are discussed in this paper.

With some two to four tonnes of bauxite residue arising for every tonne of aluminium produced, the management of bauxite residue (or Red Mud) has always been a significant issue for the aluminium industry. However, the tragic fatal incident in Ajka, Hungary in October 2010 has reinforced the need for safe and effective management of storage areas globally.For the past five years the International Aluminium Institute has been involved in research into the management of bauxite residue and in 2011 created a set of voluntary objectives recommending that best practices are adopted to ensure that the Hungarian incident is never repeated elsewhere.This paper will review the current and best practices of bauxite residue management.

To produce alumina with high quality, competitive costs and high efficiency on caustic recover with low flocculant consumption has been a challenge for the filtration area in Alunorte. This area has 3 chains each with 5 washers for 7 production lines where together, handles about 4,4 Mtpy of red mud. Specifically at production lines 6 & 7, the washer chain has only high rate settlers and apart from that, they receive bauxite from Mineração Bauxita de Paragominas. The combination of these two aspects results on lower density in the settler underflows. One of the actions to increase underflow solids content was to replace the conventional polyacrylate flocculant by another one which could be capable to increase the density in the washer underflows. Among other trials were gotten good results from the use of FLOMIN OL 99 polymer in lab tests as well as in the plant. The discussion of these results is the main propose of this paper

The results of pressure filtration testing demonstrates that a standard design FLSmidth AFP IV™ filter press can dewater red mud from initial feed concentrations of between 30–44 wt% and produce final cakes containing 67 – 70 wt% solids. This paper outlines various factors affecting the filtration rate and final cake solids concentration such as feed solids concentration, slurry temperature and feed pump delivery rate/pressure relationship as well as the configuration of the filter plates. The results are presented for different bauxite grades. Additional testing was performed to obtain filter cakes containing 75 wt% cake solids by evaluating high-pressure filtration at 30 – 60 bar using both recessed plate and membrane plate configurations. The tests demonstrate that high-pressure filtration above 30 bar can produce 75 wt% solids.

The wet red mud yard in Guizhou Branch of CHALCO is closed when it is used up to 1370m altitude, and it’s difficult to construct the new red mud yard within a short term because of the difficulty in land requisition, so, in order to ensure the continuity of alumina production, it’s required to expand the volume of the existing wet red mud yard by dry method, so as to extend its service life. Based on tests and studies on the basic performances of red mud filtration cake, the author in this article gives introductions of technologies on red mud dewatering, transportation, spreading out & stacking, reinforcing of weak red mud layer, recycle of waste water in red mud yard, and flood control & drainage etc. It’s shown by study achievements that good economical and social & environmental benefits can be obtained by using dry-method volume expansion technology for wet red mud yard.

ETI Aluminum has capacity to process 541,000 tons of bauxite, produce 250,000 tons of alumina per year and generate approximately 260,000 tons of red mud. Red mud slurry is disposed at 30 % (w/w) solids and less than 3 g/L Na₂O.ETI is focusing its efforts in maximizing extraction efficiency in digestion and improving decomposers yield. The red mud area is one of the most important topics that require serious study in terms of handling, recovery and environmental impact.A study has been initiated to determine red mud characterization, settling performance and separation strategies. XRF, XRD, TG/DTA, IR, SEM/EDX, BET and PSD analysis have been conducted to define red mud physical and chemical characteristics. Many settling tests have been performed to select the most suitable and economic flocculant that provides the best compaction, overflow clarity with an acceptable settling rate and enhanced rheology. Also ETI might face red mud disposal area problems in the following years. ETI has initiated a fast track program towards the improvement of the dewatering of red mud and increase disposal area life time.

Alumina is produced from khondalite hosted bauxite of Indian origin in the Alumina refinery employing the time tested Bayer’s Process. In the process, about 40% of unwanted elements are rejected as undigested sand and red mud. During the whole cycle; major, minor, trace and RE elements in these litho-units get redistributed, either depleted or enriched. Khondalite, the source rock of bauxite, is rich in silica, moderate in alumina and iron with minor titanium. Bauxite becomes rich in alumina and iron with subordinate titanium and negligible silica. After alumina recovery from bauxite, most of the valuable metals including REE get accumulated in the refinery rejects. The studies, while establishing the extent of various metals dispersed in khondalite, bauxite, undigested sand, red mud and alumina also reveals the state of enrichment of valuable metals in undigested sand and suggests possible means to recover some of them.

Solving the problem of large-scale utilization of Bayer process bauxite residue (red mud) becomes more and more vital for an increasing number of alumina refineries around the globe. Till now, in spite of the fact that many technically sound process routes have been developed, only a few of them have been implemented due to favorable local economic and market conditions. Being a complex and poor ore for extraction of iron, alumina and titanium, treated red mud has to compete with other low cost materials; this is often uneconomic. In this paper the most promising utilization directions are discussed and focus areas for research by the world scientific community are outlined.

Red Mud, a by-product generated from the caustic leaching of bauxite to produce alumina in the Bayer Process, causes serious environmental problems and is considered as a hazardous industrial waste. A novel process has been developed for production of Pig Iron from NALCO Red Mud by employing Plasma Smelting Technology. Red Mud containing 15–40% Fe₂O₃ was subjected to Thermal Plasma Smelting by use of Extended Arc Plasma Reactor at a temperature of 1600°C for a period of 30 minutes and high quality Pig Iron was produced. Effect of various process parameters like basicity, amount of reductant, plasmagen gas, input electric power and reduction time for recovery of Pig Iron has been studied and optimized. Basicity of 0.3, reduction time of 25 minutes at 12.5 kW power was found to be optimum for maximum recovery of pig iron (70%) from Red Mud in 1kg scale.

Boehmite precipitation is a new alternative way from sodium aluminate solutions to alumina, however, the too small particle size becomes one bottleneck for this methods replacing the current production route. Growth and agglomeration of crystals are the main factors influencing product size. The results show that the growth rate of boehmite is in a low range from 0.08 to 2.4 μm/h. Thus, agglomeration of boehmite is a major means to enlarge the particle size of precipitation products from sodium aluminate solutions. By means of laser particle size analyzer and powder attrition index analyzer, the agglomeration efficiency was represented by combining agglomeration degree and attrition index. The influences of seed ratio, temperature, the molar ratio of Na₂O to Al₂O₃ and organic additives on agglomeration were investigated. The alcohol type additives PPG increases precipitation ratio and agglomeration degree, but reduces the strength of products and makes attrition index increase.

The suspension and dispersion of Al(OH)₃ particles in seed precipitation tank, which may affect the quality and output of alumina besides the deposit on the bottom of the tank, is one of the key steps in Bayer process. In order to solve these problems, the solids concentration profiles of Al(OH)₃ particles were investigated by cold water experiments under simulated industrial conditions. The results showed that, the mixing uniformity in the whole tank improved with the increase of impeller off-bottom clearance when used the impeller of small diameter (D / T ⩽ 0.6), and it deteriorated when enlarged the impeller (D / T = 0.65 ~ 0.7). The mixing effects can be improved by increasing the impeller diameter and stirring speed, meanwhile the influence of impeller off-bottom clearance was weakened. But the impeller diameter and stirring speed should be controlled in appropriate ranges for the consideration of power consumption and mixing efficiency.

Boehmite was prepared from supersaturated sodium aluminates solutions with ethanol-water solvent. The results of thermo-gravimetric analyzer and XRD showed that the product was mixture of boehmite and gibbsite, and the mass ratio of gibbiste and boehmite varied greatly with different process conditions. This work presents the effects of mass ratio of ethanol and temperature on the precipitation rate and phase compositions of alumina hydrate. The ratio of AlOOH in the product increased significantly with the increase of mass ratio of ethanol because the precipitation of gibbsite was restrained. When the solvent was pure ethanol, the ratio of AlOOH in the product reaches the peak of 90%. Ethanol reduces the free caustic concentration and increases initial supersaturation coefficient significantly. The boehmite activation energy of precipitation in ethanol solvent was 13.7 kJ/mol, indicated that ethanol reduces effectively energy barrier of boehmite from sodium aluminate solutions and it was controlled by diffusion process.

It has been proved that crystal growth modifier (CGM) can improve particle size distribution (PSD) and the alumina production. However, few researches were reported on whether CGM has an effect on the structure of sodium aluminate liquors. In order to provide fundamental guidance to the application of CGM to seed precipitation, the effect of CGM on the structure of synthesized sodium aluminate liquors was studied. It is shown that there is no new characteristic peak and obvious shift in the Raman spectrum of the liquors after adding a certain amount of CGM. By constructing a comparison function and using calculation function of the software of Raman spectrometer, it is found that CGM might have micro effect on the structure of sodium aluminate liquors via changing the concentration of principal ion Al(OH)₄-in the liquors.

ETI Aluminum is an integrated facility that produces sandy alumina by processing boehmitic bauxite. With the development of aluminum smelting technology and greater attention given to environmental protection, the quality requirements of alumina are much strict. ETI has initiated a study to meet smelter grade alumina specifications of its internal electrolysis customer. The old precipitation circuit at ETI alumina refinery was converted to sandy alumina. The change involved modifications to existing tanks and flows to obtain proper hydrate agglomeration. The challenge has been to improve and control particle size distribution without losing precipitation yield and product quality. ETI has been able to reduce its minus 44 micron particles from approximately 40 % to 6–8 % by means of controlling the precipitation circuit parameters such as, alumina supersaturation, seed charge, temperature and classification. Improvements in hydrate occluded soda and attrition index were obtained.

In the last 40 years, stationary calciners have permanently replaced rotary kilns in existing alumina refineries and are being installed in all new Greenfield alumina refineries producing smelter grade alumina.In the 1960’s two separate and different approaches to stationary alumina calciners were going through research and development. Alcoa developed a fluid flash system and VAW, together with Lurgi (today Outotec) the Circulating Fluid Bed (CFB) calciner. Both developments had the same targets, but took different approaches to create more efficient calcination systems. Without any joint effort, the industrial stages of both developments were introduced to the industry at the same time.This paper describes the significant steps of the development that both calcination systems went through to reach an industrial stage and the risks and failures that both took. Furthermore the differences and common goals of both approaches are analyzed and described.

In the international literature it is possible to find references of optimized refractory materials for lining circulating fluidized bed alumina calciners. However, unexpected failures of these refractories are still relatively common, impacting in many ways the results of alumina refineries. Due to the importance of this subject, this work addresses the performance analysis of a refractory material which faced harsh operational conditions and resulted in a short life. “Post-mortem” techniques, “in situ” observation and properties evaluation were used to study the materials’ behavior. Based on the obtained results, a discussion related to the better performance potential of distinct refractories is presented, highlighting that based on the variety of different features these materials have, significant improvements of calciner refractory life can still be attained.

Research work on new types of castable refractory, pre-casted assembly parts and thermal insulation materials, with resistance to high wear, thermal shock and erosion and low thermal conductivity, were done to solve problems of high system energy consumption, cracking and spalling of partial lining and mismatch of furnace top material and hanging material and so on, caused by unreasonable design of domestic Al(OH)₃ dilute phase fluidized bed roasting furnace lining. Several difficult problems such as the matching of different materials, preservation of dilatation joint between different zones and reasonable mechanical distribution of lining were solved. A full set of techniques including construction, furnace lining drying, lining maintenance and corresponding standards were developed according to the properties of lining materials and features of the furnace type. Using the ideas of furnace integration and new theory of furnace lining, we have solved the key technologies of high-efficiency and energy-saving for furnaces. The achievements have been applied to domestic Al(OH)₃ dilute phase fluidized bed roasting furnaces to reduced energy consumption by one thousand MJ per ton of alumina, thus making a furnace lining with higher production, lower energy consumption and less exhaust gas emission.

Environmental performance of the Gas Suspension Calciners for Alumina installed at QAL and Yarwun in Queensland, Australia, is secured by fabric filters.Gas Suspension Calciners equipped with Fabric Filters represents today’s State of the Art of stationary calciners for Alumina.This paper describe the development of the fabric filter technology relevant for this application including selection of filtration medium from an environmental and cost efficiency point of view.A three year R&D project has demonstrated that in all relevant aspects 10 m long bags can be used for general filter performance within the standard design rules of FLSmidth A/S, Airtech — Air Pollution Control. Purge pressures as low as 1.5 to 2 bar g has proven sufficient at “Standard Conditions”.FLSmidth has been offering filters with 10 m long bags to customers worldwide in Alumina and Cement market segment since quite some time.Five fabric filters orders or ESP conversions have been received so far with 10 m long bags.

The conditions of technique to prepare α-alumina by calcination from aluminum hydroxide were optimized using a central composite design (CCD) of response surface methodology (RSM). A quadratic equation model for field was built and effects of main factors and their corresponding relationships were obtained. The statistical analysis of the results showed that in the range studied the field of α-alumina was significantly affected by the calcination temperature and calcination time. According to results from analysis of variance (ANOVA), the value of the determination coefficient (R2=0.9890) indicates that the model was a good fit that 98.90% of the variation could be explained well by the model. The value of the adjusted determination coefficient (adj.R2=0.9811) was also very high to advocate for a high significance of the model. The optimized calcination conditions were as follows: the calcination temperature 1206.81 °C and the calcination time 2.06 h respectively. Under these conditions the field of α-alumina was 95.93%. In addition, the sample was characterized by X-ray Diffraction (XRD).

Two major impurities in Smelter Grade Alumina, SGA, directly impact the bath chemistry of smelting customers. Aluminum fluoride is consumed in great quantities to neutralize the impact of calcium and sodium that enter the process. Consumption solely for the neutralization of excess CaO and Na₂O generates surplus bath. The resulting cyrolitic material can then only be consumed by the primary aluminum industry. In this paper the author discusses points of concern from the perspective of customers with regard to %CaO, %Na₂O, and the ratio of between %CaO and %Na₂O. Conclusions include the impact that the growth of surplus cryolitic bath will have upon producers of SGA.

There has been a wide range of joint ventures within resource industries. The author has had direct experience in a number and a keen observer of others. This paper builds on a previous paper that examined the rationale for, history and observations as to the success of longer term joint ventures within the aluminium industry.In this paper options for the structure of joint ventures are discussed.

The technological and heat engineering substantiation for a new process arrangement for nepheline production using the sintering process is presented. In this process desilication of aluminate liquor and evaporation of a soda liquor is combined in one stage. As a result the thermodynamic performance (exergic efficiency) increased from 70 to 90% and the steam requirement decreases 1.6 together with improvements in operational reliability of equipment.

The influence of Na₂O on phase composition, self-powder and alumina leaching properties of calcium aluminate slag was investigated by XRD, laser particle size analyzer and chemistry analysis method, and the measure of eliminating the adverse impacts of Na₂O on calcium aluminate slag was proposed. The results show that when the mass percent of Na₂O is 3% and less than 3%, the main phase of slag are Ca₁₂Al₁₄O₃₃ and γ-Ca₂SiO₄, the self-powder rate of slag is above 90%, the alumina leaching rate is above 80%. The leaching rate which is 75.6% is evidently decreased when the content of Na₂O is 4%. Decreasing the mole ratio of CaO to Al₂O₃ of slag containing 4% of Na₂O, the alumina leaching rate is 83.5% when the mole ratio of CaO to Al₂O₃ is 1.53, the adverse effect of Na₂O on the slag is basically eliminated, the calcium aluminate slag meets alumina leaching requirements.

The influence of TiO₂ on the phase composition, self-powder and alumina leaching properties of calcium aluminate slag was investigated by XRD, laser particle size analyzer and chemistry analysis methods, and the measure of eliminating the adverse impacts of TiO₂ on calcium aluminate slag was proposed. The results show that when the mass percent of TiO₂ is 2% or less than 2%, the main phases of slag are Ca₁₂Al₁₄O₃₃ and γ-Ca₂SiO₄, the self-powder rate of slag is above 95%, the alumina leaching rate is above 85%. The alumina leaching rate is gradually decreased when the TiO₂ content is above 2%, the leaching rate is 80.1% with 3% of TiO₂, and the leaching rate is only 73.4% with 5% of TiO₂. To add CaO into containing 5% TiO₂ of slag, the alumina leaching rate is 84.1% when the mole ratio of CaO added to TiO₂ is 1.25, the adverse effects of TiO₂ on the slag is basically eliminated, the calcium aluminate slag meets alumina leaching requirements.

Research on the leaching performance of fly ash of Shanxi, Chongqing and Western Inner Mongolia. Analyze the existing forms, crystallinity and package situation of Al-Si phase in fly ash from different areas by using SEM and XRD. Effect of fractionation of Al-Si phase in fly ash on the leaching performance from the view of mechanism was investigated as well. Leaching experiments and analysis indicate that: the leaching rates of Al203 in fly ash from the there different areas are 97.41%, 68.94% and 23.61% respectively, under the conditions of solid-liquid ratio 1:20, rotary speed 500rpm, leaching time 120min, sulfate concentration 20%, particle sizes −74µm. Leaching performance of fly ash in Western Inner Mongolia is better than that in other two areas. The main reason for different leaching performance of fly ash from different areas is the difference in crystallinity, encapsulated glass phase of Al-Si phase in fly ash. The crystallinity for Western Inner Mongolia is 75.98%, while there is no non-crystalline phase in fly ash from other tow areas, The average FWHM of XRD diffraction peak of Al-Si phase are 0.641, 0.3324 and 0.1107, respectively. The crystallinity of fly ash in Western Inner Mongolia is worst among the there areas, and its content of glass phase is also lowest among them, so its activity is obviously higher than that of other two areas.

The main phases of the reduction slag from magnesium production by vacuum aluminothermic reduction using dolomite and magnesite as materials and using Al-Si alloy as reductant are CaO·2Al₂O₃ and 2CaO·SiO₂. It also has amount of unreacted Si. The Al₂O₃ content of reduction slag is about 55% and SiO₂ is about 10%. When leaching Al₂O₃ with a mixture solution of sodium hydroxide and sodium carbonate, Si and SiO₂ would enter into leaching solution and has a negative effect on Al₂O₃ leaching. The effect of Si and silicide on leaching Al₂O₃ from magnesium smelting reduction slag was studied in laboratory. The results show that total Si and partial SiO₂ would enter into leaching solution and react with NaAl(OH)₄ to form (Na₂O·Al₂O₃·SiO₂)₆·27H₂O which is present in leaching residue and makes a loss of Al₂O₃.

Local shortages of bauxite in recent years present a challenge to the development of sustainable aluminum industry in China. Coal fly-ash from coal-fired power plants is rich in Al₂O₃ content with potential use as a resource for alumina refinery. This paper will describe recent investigation in extracting Al₂O₃ from coal fly-ash using an acid sintering-leaching process. Thermal weight loss testing against temperature is first carried out to find out an appropriate sintering temperature so as to avoid heavy volatilization of the coal fly ash — H₂SO₄ (98 %) mixture. Then, the mixture is subjected to sintering at 220 °C, dissolving in water at 85 °C, adjusting alkali level in solution by CaCO₃, removing iron by KMnO₄ and MnSO₄, precipitating Al₂(SO₄)₃·17H₂O particles, and heating-treated at 850 °C to produce Al₂O₃ powders. The rate of recycling Al₂O₃ can reach 70 – 90 % with relative lower processing temperature and less solid residues.

A Process for production of novel synthetic crystalline porous alumino silicate Zeolite Na-P consisting of the oxides of silicon and aluminium represented by the formula a Na₂O:Al₂O₃: b SiO₂,wherein a = 0.1–1.0 and b = 2.2–5.0 has been developed from three different raw materials viz. Sodium Aluminate Liquor/Spent Liquor/Alumina Tri-hydrate of NALCO’s Alumina Refinery, Damanjodi, Orissa. Zeolite Na-P was produced by preparing a gel by mixing Sodium Silicate, Sodium Aluminate Liquor/Spent Liquor/Alumina Tri — hydrate, autoclaving the gel at 80–150 Degree Celsius for a period of 2 hrs to 4 days under static or stirred condition, quenching the resultant crystalline material in cold water, separating the catalyst formed, washing with water, drying the solid catalyst at a temperature of 80–120 Degree Celsius for a period of 3–12 hrs to obtain the product which can be used as a builder material for detergent formulation.

The whole process of extracting alumina from coal fly ash was trailed by experimentation. Alumina was prepared with sintering, leaching, separating, precipitation with ammonia water and calcination units. The effects of the sintering temperature and the sintering time, molar ratio of ammonium sulfate and alumina in fly ash and the size of fly ash on the extracting efficiency of alumina in fly ash were studied. The extracting efficiency of alumina can reach 95% under the optimum conditions.

Both the low-concentration SO₂ and Bayer red mud do harm to the environment seriously.In this paper, it focuses on the absorption of low-concentration SO₂ with red mud. It studies on the absorption by roasted red mud and non-roasted red mud, and the experiments are intensified by ultrasonic wave of 20 kHz at different ultrasonic power. Through the single factor experiment and orthogonal test, the results were analyzed by the chemical and XRD analysis technology. The conclusion shows that the desulfurization and dealkalization processes can be intensified by ultrasonic wave. The amount of desulfurization reaches 36.7 ml/g. The optimal conditions are: liquid-solid ratio is 9:1; stirring speed of impeller is 250 rpm; gas flow is 0.1 m3/h; the ultrasonic power is 550 W. But the alkali amount of red mud dealkalizated still can not meet the national standard of cement production, and it needs the further processing to subsequent use.

Today, Bayer process is the basic method for producing alumina from bauxite. Bauxite does not only contain alumina but also contains iron, silicon, titanium and other impurities. Impurities are also dissolving with alumina in hot caustic solution and results to scale formation on several sections of the process. Because of the changing working conditions on different parts of the Bayer process, scale formation occurs having different characteristics at different parts of the process. Scales must be cleaned periodically due to the decreasing heat transfer efficiency and increased energy costs due to scale build up on the heat exchanger surfaces. As the characteristics of the scales are changing form one section to another there is not only one effective solution to remove all kind of scales. The purpose of this study is to find effective chemical compositions for acid cleaning of TiO₂ containing scales on Bayer process.

This study aims to compare, on an industrial scale, of the effect of the direct chill (DC) and continuous casting (CC) fabrication processes of AA1050 rolled and annealed sheets. Characterization of their microstructure and texture evolution from the as-cast condition up to the end condition of a deep-drawn cup was carried out. Stamping tests were performed to identify which process presents best performance. Different microstructures were obtained for the studies processes: the DC material was more homogeneous, both in terms of intermetallic distribution and grain size. The mechanical properties of the CC material were slightly higher than those for the DC material. Forming Limit Diagram (FLD) of the homogenized CC material presented the best results.

The strengthening effects of hot/cold rolling and surface mechanical attrition treatment (SMAT) on aluminium alloy were investigated in this paper. Before performing the rolling processes, aluminium sheets were treated using SMAT on both sides for 40 min at room temperature. The parameters for the hot/cold rolling process included a range of operating temperatures (−200 °C to 480 °C) and percentages of thickness reduction (up to 85%). Then the mechanical properties of rolled samples of different thicknesses were studied. Tensile test results showed that the higher the percentage of reduction in thickness, the higher the strength of the rolled samples that could be obtained. Considering the yield and tensile strength, rolling at room temperature with 80% thickness reduction was the optimum condition for AA2024-T3 in this article, in which the yield and ultimate tensile strength were increased by 54% and 79% respectively. It was also found that the ductility was also enhanced according to the operating temperature.

The present paper investigated the morphology and chemical phases of interfacial layer of Copper/Aluminum clad sheet by scanning electrical microscope equipped with energy dispersive X-ray detector and X-ray diffraction, also measured the mechanical property through micro-hardness test. The results are that the interfacial bonding is enhanced and the thickness of interfacial layer increases with mismatch speed ratio rising. The improved interfacial bonding can be found from the tensile fracture. The formation of intermetallic compound (IMC) is promoted by the significant element diffusion at high speed ratio. For sample annealed at 400 °C for 20 min, the formation of IMC is negligible, but the fracture lies between compounds. The micro-hardness on the interface decreases with speed ratio increasing. The study shows that the improvement of microstructure and mechanical property and formation control of IMC of Copper/Aluminum clad sheet can be achieved using asymmetrical roll bonding with high speed ratio.

Aluminum utilization is growing at a steady rate reaching 40 million tons per year considering remelt and semis. Among semis, aluminum rod accounts for approximately 10% of the worldwide consumption, mainly for power transmission. Numerous aluminum alloys have been developed and utilized for various mechanical applications and welding purposes. Many rod alloys are difficult to produce and require highly experienced operators and the most advanced machinery and technical know-how. In the form of wire, from molten metal to 3.2 mm wire, the situation becomes even more critical and only the latest Properzi C.C.W (Continuous Cast Wire) technology provides new possibilities within this industrial field. The Author explores state-of-the-art aluminum rod equipment and the range of application for the C.C.W. technology which allows the production of 1xxx — 2xxx — 3xxx — 4xxx — 5xxx — 6xxx — 7xxx — 8xxx series aluminum alloys for many industrial and specialty applications.

The propagation of high intensity ultrasonic wave in the solids can greatly affect the material properties. In this paper, the deformation characteristics of the ultrasonic vibration forging were investigated. For the ultrasonic vibration forging, the ultrasonic wave propagates in the specimen during the forming process. A detailed analysis and understanding of the mechanism of improvement is not possible on the basis of conventional experimental observations because ultrasonic vibration processing phenomenon occurs at a high speed. Hence, in order to study the mechanism of ultrasonic vibration forging, the finite element modeling was performed by using Abaqus/explicit. The metal flow of the ultrasonic vibration forging is totally different from the conventional one, and there is no “drum” effect in the forming process, which is the main characteristic in the conventional forging. Moreover, the stress and equivalent plastic strain distributions after the ultrasonic vibration forging process were explored.

The recycling process of aluminum scraps commonly contains high amount of impurities, especially Fe content which results in degraded properties compared with the primary aluminum production. The refinement of Fe-intermetallic compounds becomes increasingly important to extend the utilization of recycled aluminum. In this study, a thermo-mechanical process of Al-(2.2–2.3)mass%Si-0.9mass%Mg-(1.0–2.0)mass%Fe alloys by caliber rolling process was performed to investigate the refinement of Fe-intermetallic compounds and the mechanical properties. Fine fragmented Fe-intermetallic particles from around 200nm were achieved after 95% caliber rolling. The caliber rolling can effectively improve mechanical properties with good ultimate strength of 345–360MPa and high elongation of 15–25% in comparison with the as-cast l%Fe specimen with low ultimate strength of 269MPa and low elongation of 1.5%.

Induction heating is commonly used in the re-heating of aluminum billets before forging or extrusion. Powerful finite element modeling (FEM) tools are available to assist in the design of such processes; however, such models should be validated by comparison with analytical solutions or experimental results to ensure accuracy.Induction heating experiments have been performed using a number of different coil designs and work piece dimensions at 50 Hz. Aluminum alloys with different electrical conductivities have been used, i.e. 6060 and A356. Process parameters such as: current, power, magnetic field, electrical conductivity, etc. have been measured with high precision instrumentation. Experimental data are presented and compared with equivalent 1D analytical and 2D axial symmetric FEM modeling results.The effect of frequency on the induction heating process is reviewed using the validated analytical and FEM models. Some recommendations are given with respect to appropriate modeling techniques, boundary conditions and numerical mesh sizes.

The evolution of plasticity of heat treatable alloys in W temper is important for an efficient stress releasing by stretching or compression (Tx51 and Tx52 tempers) but also for some special hardening operations that combine cold working and ageing practices. For the alloys that have a significant natural ageing, the environment temperature has an important influence. In order to evaluate the influence of this temperature, the mechanical properties and the microstructure were investigated at various temperatures between −10 and + 80 °C and ageing time between 0 and 80 h on plates in alloy EN AW 2024, using standard tensile tests, electronic microscopy and X Ray diffraction. The results demonstrate that from many standpoints (mechanical properties, plasticity, electrical conductivity, microstructure etc.) the ageing transformations end before the limit of 96 hours that is considered as standard.

A novel technique for preparing in-situ Al-TiB₂ and Al-Al₃Ti composites by electroslag remelting (ESR) process was developed in this paper. The microstructure and phases of the composites were investigated by SEM and XRD. The aim of present work was to verify the feasibility of in-situ synthesis of Al-TiB₂ and Al-Al₃Ti composites by ESR process which had unique advantages in promoting fluoride salt-metal reaction efficiency. The reactant concentration and reactant contact area was improved greatly in the metal molten pool during ESR process leading to a totally complete reaction. The experiment results demonstrate that TiB₂ and Al₃Ti particulates disperse uniformly in the aluminum matrix and the mean particle size becomes much smaller compared with the conventional casting method.

Computational thermodynamics is a powerful tool for alloy design as well as process optimization. The quality of the predictions is dependent on the quality of the thermodynamic database that is used. In this paper the development of a new thermodynamic database for Aluminum alloys is described. Examples of calculations for different kinds of Aluminum alloys and their applications are shown using the database and comparing where possible against experimental data, thereby validating its accuracy.

Semisolid processing is considered as an attractive and promising manufacturing method for producing near net-shape metal products that have reduced porosity and shrinkage. In this study, the fluidity of Al-Si-Mg alloy slurry was evaluated by injection into a spiral metallic mold. Image analysis showed that solid particles in specimens became small and spherical with increasing shear rate on the gate. Fluidity was increased with increasing shear rate, with decreasing particle size and with particle roundness. Furthermore, particle roundness has a greater effect on fluidity than particle size.

Precipitation of the θ′ (Al₂Cu) phase was examined in Al-(1.75-x) at.%Cu-x at.%Ag alloys. In alloys containing trace Ag the θ′ precipitates formed T- or cross-shaped arrays of sympathetically-nucleated arrays similar to those reported in binary Al-Cu alloys. However, in alloys with equal atomic levels of copper and silver the θ′ plates formed at specific sites on dislocation loops alongside preexisting γ′ (AlAg₂) precipitates. The dislocation loops appeared to dissociate at these sites in a manner which would provide a stacking fault that was isostructural with the θ′ precipitate. Energy dispersive X-ray (EDX) mapping showed that the dislocation loops were silver-enriched at the sites where the θ′ phase eventually precipitated and that a silver atmosphere remained after precipitation of the θ′ plates.

Controlled diffusion solidification (CDS) involves mixing two precursor alloys at different thermal mass and subsequently casting the resultant mixture into near net shaped cast components. The process enables casting of Aluminum wrought alloys into near net shaped components by circumventing the problem of hot tearing by obtaining a non-dendritic morphology of the primary Al phase. The study presents the favorable process and alloy parameters to enable sound shaped casting of 7050 Al wrought alloy (Al-Zn-Mg-Cu) by the CDS process along with the mechanical tensile properties under various heat treatment conditions. The tilt pour gravity casting process was used for this study to demonstrate the ability to cast high integrity components with high strength and ductility.

This study was conducted with the intention of investigating a new experimental alloy, namely the 396 alloy which belongs to the Al-Si near-eutectic cast alloy group and contains about 11%Si. In the light of the above, the main purpose of the work is to report on the changes observed in the mechanical and/or machinability criteria resulting from the effects of the presence of two levels of Cu, namely 2.25% and 3.5%; and of the effects of two levels of Mg, namely 0.3 and 0.6%. In addition to the preceding, the effects of Mg-free alloys and Sr-modification on these same alloys were also investigated.

This study has methodically characterized the iron based intermetallic phases evolving during solidification of Al-Si binary alloys as a function of solidification cooling rate and and composition of Fe in the alloys. Contrary to the predictions of the evolution of only the ß (Al,Si,Fe) in these alloys by all commercial thermodynamic phase diagram simulation tools, the dominant phases were mostly the α (Al,Si,Fe) intermetallic phases and significantly vary in nature and type with the process parameters. The results from this study will further enable better design of the Al-Si alloys with an in-depth understanding of the evolution of the intermetallic phases and methodologies to prevent or modify the same in the final cast components.

In this paper, Low frequency electromagnetic field and air knife are applied simultaneously to produce large-size AA 7055 aluminum alloy ingots during DC casting. Moreover, the effects of low frequency electromagnetic field and air knife on the macro-physical fields during DC casting and the microstructure and crack in the ingots are studied and analyzed by the numerical and experimental methods. Comparison of the calculated results indicate that applying electromagnetic field can modify the direction and increase the velocity of melt flow and homogenize the distribution of temperature in the sump, and applying air knife can homogenize the distribution of temperature and decrease the stress and strain in the solidificated ingots. Further, the microstructure of the billet is refined remarkably and the crack is eliminated by applying electromagnetic field and air knife during DC casting because of modification of the macro-physical fields.

This article aims to investigate the grain refining response of Sr-modified A356.2 alloy with various Al-Ti, Al-B and Al-Ti-B master alloys at different levels. Thermal analysis was used to evaluate the interactions between Sr and B, and between Sr and Ti. Microstructure was examined using optical microscopy and EPMA technique. Impact properties were evaluated for both as-cast and heat-treated conditions. The results reveal that adding B with levels higher than 0.1% leads to formation of particles containing predominantly B and Sr, such as SrB₆. The Sr-B interaction may postpone grain refinement of the alloy containing 0.02–0.1%B. It is also observed that the Al-Ti-B and Al-4%B types of master alloy have a greater influence on the grain refining of the A356.2 alloy than does Al-10%Ti. The grain size of the alloy decreases rapidly with an increase in boron-content for the lower levels of boron addition.

Micro-focus X-ray technology was utilized to evaluate the influence of solidification velocity and hydrogen content on the volume fraction, number density and sizes of pores in the directionally solidified A356 castings. The results indicate that hydrogen content has a significant influence on porosity formation. When hydrogen content is low, few small irregular-shape pores were observed indicating the dominate impact of solidification shrinkage. While in high hydrogen specimens, many large spherical pores were found. The pore size distribution also shows dual populations. The group of large pores is formed in the liquid far from the solidification front. The group of small pores is formed near the solidification front. When hydrogen content is high, increasing solidification velocity (from 0.1mm/s to 0.2mm/s) not only decreases volume fraction of porosity but also significantly reduces the maximum pore sizes of large pores

Al-Si alloys exhibit large grain structure when Al-Si alloy melt is solidified in sand moulds due to low cooling rate provided by the mould. Ti-based grain refiner (Al-Ti-B) is known to be less-effective to refine grain structure of Al-Si alloys due to formation of Ti-Si phase. Recently, we have developed an effective novel grain refiner (NGR) for aluminium-silicon sand casting alloys. Effectiveness of grain size under slow cooling conditions has been investigated. For comparative purposes, a range of sand casting alloys with NGR addition have been produced. The results show that the addition of novel grain refiner reduces the grain and eutectic size significantly for all these alloys at lower cooling rate <0.5 °C/s. As a result of fine primary Al grains, the porosity and elongation in the solidified alloys is notably improved.

A good understanding of the kinetics of evolution of solid phases during solidification of hypereutectic aluminum alloys is a key factor in controlling the as-cast microstructure and, in turn, enhancing the service properties of industrial alloys.A study was performed to evaluate the solidification kinetics for two hypereutectic Al-19%Si alloys with the addition of 3%Cu and 3%Cu+1%Mg.This study included thermodynamic calculations of the solidification process using the FactSage™ 6.2 software package, as well as experimental thermal analysis, and neutron diffraction. The study revealed kinetics of solid Al, solid Si, Al₂Cu, and Mg₂Si evolution, as well as an individual effect of Cu and Mg alloying additions on the solidification path of the Al-Si system.

Hyper-eutectic Al-Si alloys composed of low-density materials with excellent castablity are good candidates for aerospace and automobile applications. Our efforts over the last few years have demonstrated that such hyper-eutectic Al-Si alloys with no primary silicon phase but with a eutectic microstructure that assumes nano-fibrous morphology for the eutectic silicon phase can be grown by directional solidification. In pursuit of this effort, more hyper-eutectic Al-Si alloys containing ultra-refined primary and eutectic silicon phases have been grown by an alternate casting method known as shape casting. The process of this fabrication and the microstructure of the resulting alloys are presented here.

The columnar — to — equiaxed transition (CET) was investigated in Al-Cu alloys (Al-lwt%Cu, Al-4.5wt%Cu, Al-15wt%Cu and Al-33.2wt%Cu) solidified directionally from a chill face in a vertical setup. The CET occurs when the temperature gradient in the melt ahead of the columnar front reach critical values. Also, we investigate correlations between structural parameters (grain size) with Vickers microhardness measurements in the directionally solidified samples. We observed that the Vickers microhardness is greater in the equiaxed zone than in the columnar or columnar to equiaxed transition (CET) zone, additionally, is greater on the edges of the samples than in the centre. Also, we determined that the grain size increases from the columnar to equiaxed structure.

Design tools to simulate the manufacturing processes applied to aluminum components require computationally efficient finite element methods. While static processes such as casting employ implicit techniques, dynamic processes such as forging may only be modeled with explicitly. A commonplace practice to expedite explicit simulations is to employ time or mass scaling, which can lead to unexpected thermal-mechanical behaviour in coupled analyses. In both cases, the development of fully coupled thermo-mechanical simulations necessitates the use of a constitutive model that is capable of defining the flow stress as a function of temperature, strain, and strain rate. In this work, a material model for as-cast A356 is presented and applied in a range of fully coupled deformation models. Implicit and unscaled explicit models will be compared to explicit models with large amounts of scaling. Strategies for applying a material model to minimize error and maximize computational effort are discussed.

Deformation of polycrystalline materials results in a heterogeneous distribution of dislocation structures that are dependent upon the local character of the microstructure. 7xxx series aluminum alloys are particularly complex because of the wide range of particles and solute atoms that are in the material. High temperature deformation results in a microstructure that may be essentially free from dislocation structures at one position but have relatively high dislocation content at another position. Electron backscatter diffraction was used to quantify and map the dislocation density tensor at various positions through the metal. Subsequent annealing resulted in the development of recrystallization nuclei that were also observed by EBSD and related to the measured dislocation structure.

Microstructural changes of DC-cast 5xxx series Al-Mg-Mn alloy modified with Zn addition occurring during the homogenization treatments were studied through the thickness of a rolling ingot. The homogenization treatments included: low temperature annealing at 430 °C for 12h and high temperature homogenization at 550 °C for 16h. Microstructure evolution was followed by electrical resistivity measurements, optical microscopy, SEM and TEM characterization and microanalysis. During the homogenization, decomposition of the supersaturated solid solution, present in the as-cast state, occurred. Distribution of the precipitates was dictated by segregations and could be related to the partition coefficients of alloying elements. It was found that during the high temperature homogenization not only dissolution processes occurred, but also precipitation of new phases.

The 7003 Al alloy was prepared by equal channel angular extrusion process (ECAP), which microstructures were characterized by transmission electron microscope (TEM). Results showed that dislocation density increases obviously and the average grain size decreases with increasing passes of ECAP. However, after the fourth pass of ECAP, average grain size fails to decrease remarkably and the microstructure is still inhomogeneous. Some parallel micro-bands and the second phase MgZn2 are present in the alloy during annealing.

AA6082 aluminum alloy is used as constructional material for highly loaded automotive parts thus increasing of yield stress and ductility is of a great importance. Database of mechanical properties, processing parameters and chemical compositions for hot extruded profiles of the alloy was obtained. A CAE neural networks individual and spatial analyses was performed to determine the influences of processing parameters and alloying elements, e.g. Mg, Si, Mn, Fe, and Cu, on mechanical properties. The results of the analyses revealed a new understanding of their influences, and the possibility of increasing the mechanical properties if processing parameters and correlations between chemical elements were closer to the optimum values. Optimization was carried out in order to increase yield stress and elongation simultaneously. In practice, the obtained values for mechanical properties have confirmed the optimized values of influential parameters as correct.

Hot compression at 573K under different strain rates was conducted on DC cast Al-15% Si alloy. The effect of strain rate on the microstructure development was investigated. Microstructureal characteristics and deformation behavior of Al-15% Si alloy were discussed by analyzing of flow curves, optical microscope and electron back-scattering diffraction (EBSD). The results show that the peak and steady-state stresses are influenced by increasing of strain rate. The alpha-Al dendrits are almost disappeared and Si particle distribute homogeneously in the Al matrix with less of them cracked under every strain rate. The size of continuous dynamic re crystallized (CDRXed) grains decreases and the volume fraction of these grains increases with the strain rate increases. It is also observed that the fraction of HABs increases gradually and that of LABs decreases considerably as strain rate increases. It is realized that deformation under high strain rate help for CDRX to occur.

2197 (Al-Li-Cu-Zr-Mn) alloy has been processed by High-pressure torsion (HPT) at applied pressure P of 2GPa and different shear strain γ in the range of 3 turns and 10 turns. Optical microscope (OM) and transmission electron microscope (TEM) provided the detail information of grain size and microstructure of the alloys. Vickers indentation analysis was used to evaluate the micro-hardness of deformed samples. Tension test was employed to obtain the strength σ_b and elongation δ at room temperature. The result show that nice microstructure and properties are achieved when the pressure is 2GPa and the shear strain γ is 10 turns, for the grain sizes in the range of 0.1~0.4 μm, micro-hardness up to 163HV0.2, and σ_b at 591.005 MPa and elongation δ of 8.52%, higher than the peak aging treatment (T8) state of 474.7MPa.

In this study the role of Mg, Si-co-clusters formed during long-term natural aging on the artificial aging behavior was investigated by hardness measurements for the alloys AA6061 and AA6060. It was found that kinetics and age hardening response of artificial aging at common temperatures (e.g. 170 °C) are lowered by a strong presence of co-clusters, but enhanced at high temperatures (e.g. 250 °C) for AA6061. Co-cluster formation in the alloy AA6060 increases the age hardening response at 170 °C, but barely influences kinetics in both temperature regions. The co-cluster dissolution was analyzed by a model based on temperature dependent reversion of the hardness, which showed similar activation energies for both alloys. It is supposed that the different behavior of the alloys AA6061 and AA6060 can be explained by solute-vacancy interactions.

The effect of elastic stress on the microstructure of 7075 Al alloy aged at 433 K for 1 hour was investigated using hardness testing, along with transmission electron microscopy (TEM). Results indicate that the microhardness can reach 175HV after a 25MPa elastic compressive stress aging treatment; while it decreases to 151 HV if the elastic tensile stress is applied to the specimen. TEM observation demonstrates that MgZn₂ precipitates formed in all experimental samples. The elastic compressive stress inhibits the formation of fine precipitates at the grain boundary.

The present paper shows the variation in softening of 3003 alloy during annealing at final product gauge caused by fluctuation of Mn in solid solution prior to the anneal. The fluctuations of Mn in solid solution mainly are attribute in ingot preheat and/or hot rolling practice changes.The control of Mn in solid solution prior final anneal is necessary to achieve stable mechanical properties in back annealed tempers (-H2X) of 3003 alloy.

Al-Si-Ni alloys can be considered as a coarse two-phase system where a hardening effect is caused by load transfer to an interconnected rigid network of eutectic Si and aluminides. In the course of a solution treatment the contiguity of the eutectic phase is reduced, which leads to a decrease of strength. However, solution treatment is necessary to obtain a high supersaturation of elements in the Al-solid solution, which contribute to high-temperature strength due to precipitation hardening. Despite Ostwald ripening, the distribution of secondary precipitates is still dense enough to act as dislocation obstacles, as was confirmed by TEM-analysis. This work discusses the influence of heat treatments on the elevated-temperature strength of Al-Si foundry alloys with Ni and analyzes the active strengthening mechanisms. In order to investigate the effect of a solution treatment on the high-temperature strength of Ni-containing Al-Si foundry alloys, the tensile properties of various eutectic alloys were determined at 250°C after long-time exposure to test temperature.

The microstructure and tensile properties of the extruded Al-12.7Si-0.7Mg alloy aged at 160°C, 180°C and 200°C were investigated. The precipitates in different aging conditions have been characterized by regular and high resolution transmission electron microscopy (TEM and HREM) aiming at understanding the strengthening mechanisms. It was shown that the alloy after T6 treatment exhibits good ductility and much higher proof strength as well as tensile strength compared to 6063 alloy in general. The results have revealed that the strength changes by altering the precipitates size and volume fraction. The strengthening was attributed to be the combining effect of particle, grain boundary and precipitation strengthening.

The flow and filling characteristics influence product quality of high pressure die castings. A planar jet of liquid aluminum is formed at the ingate due to its high inlet velocity. The ingate design triggers the flow characteristics of the jet. Analytical investigations show that the process of drop formation at the liquid planar free jet is dominated by atomization at the ingate. Numerically, high-pressure die casting is attacked by a Volume of Fluid approach. Drop formation at the phase interphase cannot be captured by the numerical model since drops are much smaller than feasible grid spacing. Global spreading of the free jet in the casting mold is well pictured by this first numerical simulation. Experimentally the process is studied by water modeling validating the numerical results. The observed flow characteristics are discussed in comparison to product quality results observed in Al pressure die casting parts of the similar design.

In this paper, we present results of testing from sheet metal forming trials using pulsed electrohydraulic technology. Pulsed electrohydraulic forming is an electrodynamic process, based upon high-voltage discharge of capacitors between two electrodes positioned in a fluid-filled chamber. Electrohydraulic forming (EHF) combines the advantages of both high-rate deformation and conventional hydroforming; EHF enables a more uniform distribution of strains, widens the formability window, and reduces elastic springback in the final part when compared to traditional sheet metal stamping. This extended formability allows the fabrication of aluminum panels that are difficult to make conventionally even of EDDQ steel, and it thereby vastly improves the number automotive weight reduction opportunities. The paper presents discoveries regarding chamber design, electrode erosion, forming, and results of finite element multiphysics simulations of system performance.

Aluminum foils produced by cold rolling are able to show defects caused by primary particles that are formed along center line segregation. These particles are formed during casting process where some parameters are critical. In the same way, aluminum extruded parts are also able to show defects caused by intermetallic phases. They were used billets of AA6351 alloy (Al-Mg-Si) produced by “Direct Chill” and also sheets of AA8011 alloy (Al-Fe-Si) produced by “Twin Roll Casting”. Samples were submitted to a chemical etching based on methanol and iodine whose target is corrodes only aluminum matrix. Thus, intermetallic phases were analyzed using optical microscopy and SEM and EDS. Beyond, X-Ray Diffraction analysis were performed as well. On AA8011 alloy, they were identified the phases β-FeSiAl₅ and α- Fe₂SiAl₈ in as-cast samples, that are hazardous to final foil because they do not dissolve during homogenization treatment. On AA6351 alloy, they were identified the phases Mg₂Si and α-(Fe, Mn)₃Si₂Al₁₅. The identification of these phases contributed to process optimization.

The deformation behavior of Al-1Si and Al-11Si aluminum alloy in hot tensile procedure from 200°C to 450°C was investigated in this study. The results indicated that the flow stress was strongly dependent on second phase particles of δ (Al₃CuNi), Q (Al₅Cu₂Mg₈Si₆), τ₁ (Al₉FeNi) and Si particles. At 200°C to 300°C, the yield and ultimate tensile strength of Al-11Si were higher than Al-1Si. It can be found that the mount of intermetallic δ particles increasing will increase the deformation resistance whereas Si particle is detrimental. However, at elevated temperatures, Al-1Si would exhibit a higher elongation at 450°C but Al-11Si was higher than Al-1Si after 400°C. Microstructural observations showed Si particles would restrain the failure of matrix and increase the ductility.

Factors that influence the tensile mechanical properties of Al-7Si-Mg alloys A356/7 are critically analyzed. Different casting methods (SSM-HPDC, gravity die casting and investment casting), chemical composition variations and different temper conditions are considered. It is shown that the casting method employed has an influence on the primary α-Al structure, but does not influence the age-hardening response. The most important elements that influence mechanical properties are magnesium and iron. An equation to convert Vickers hardness to 0.2% proof stress in different temper conditions using the strain hardening exponent is proposed. Linear correlations between hardness, strength and (at% Mg-content available for precipitation hardening)1/2 are found. It is shown that ASTM Standard B969-10 needs to be revised.

7075-T6 aluminum alloy plates were subject to FSP with various tool rotational speeds (1230, 1450 and 1670 rpm) followed by different heat treatments (natural aging and T4T6 treatments). The influences of tool rotational speeds and aging treatments on the microstructures and tensile properties were discussed. The experimental results showed that the tensile strength of FSPed specimens with various tool rotational speeds were close. After aging treatments, higher tool rotational speeds (1670 rpm) had an embrittlement phenomenon on the SZ due to the contribution of low element bands (LEBs) and precipitates. EPMA analysis showed that the LEBs are low element distributions, such as Zn, Mg, Cu. Decreasing the tool rotational speeds, the LEBs were not obvious and restrained the brittle behavior to improve the ductility. Compared with natural aging, after T4T6 treatments, the tensile strength of FSP specimens with all tool rotational speeds was improved obviously.

A varied range of aluminum profile shapes are produced by hot extrusion and the die typically used is steel AISI H13. The quality and dimensions of the extruded pieces are determined by tribological and surface conditions of the die-bearing surface. Dies for hot extrusion require good metallurgical characteristics and chemical stability against hot aluminum. Experiments were conducted to evaluate the performance of specimens treated with conventional nitriding, and the ion nitriding process. Microstructural characterization, X-ray diffraction profiles, and wearing tests were carried out on the surface of H13 specimens. The ion nitriding process showed advantages over the conventional nitriding process, including productivity and tooling life.

High strength AA2219 aluminum alloys have gathered wide acceptance in aeronautic and aerospace applications mainly due to their excellent mechanical properties, high corrosion resistance and good weldability. However, these alloys have poor as welded joint strength. The loss of strength is due to melting and quick resolidification, which renders all the strengthening precipitates to dissolve. One way of improving strength is through the modification of weld microstructures. The refinement of fusion zone microstructure helps in improving the mechanical properties of weld metal. The present study has investigated the influence of Tibor additions on the structure and mechanical properties of AA2219 gas tungsten arc (GTA) weldments. Full penetration GTA welds were prepared using alternating current (AC). It was observed that grain size was decreased with increasing amounts of Tibor. The observed grain refinement was shown to result in an appreciable increase in fusion zone hardness.

The possibility of using linear friction welding (LFW) to produce high quality joints on an aerospace grade aluminium alloy (AA2024) was evaluated. In this solid state joining process the bonding of two flat edged components is achieved through frictional heating, induced by their relative reciprocating motion, under an axial compressive force. The Al joints were subjected to microstructural and mechanical characterization, including hardness and tensile tests. S-N probability curves were also computed after preliminary axial fatigue tests. No post-weld heat treatment was performed. The microstructural analyses showed substantially defect-free joints, with a relevant plastic flow in the thermo-mechanically altered zone. Maximum hardness decrease in the joint zone was approximately only 5% in respect to the base material. The joint efficiency was about 90% with respect to the ultimate tensile strength, with a slight reduction in the elongation to failure. Good fatigue performances were also detected.

The welding process introduces heat, plastic deformation, and chemical variation into the weld joints and alters the microstructure, strength, and ductility of the welded region. In this research, two plates of Al 2139-T8 alloys were welded together by friction stir welding (FSW). An evaluation of the crystallographic texture, grain size, and morphology of the grains in the FSW region, in comparison to those of the grains outside of the weld region, was made by scanning electron microscopy (SEM) and electron backscattered diffraction. In addition, the quasi-static tensile behavior of samples from the FSW region and those from outside of the FSW region was characterized by in-situ tensile experiments in the SEM with digital image correlation. It was found that the ultimate tensile strength was greater in the samples from outside FSW region and the elongation was greater for samples from the FSW region. The full results of the effect of the FSW on the Al2139 microstructure and tensile behavior will be discussed in detail.

In this investigation Al-Zn-Mg alloy AA7039 was friction stir welded (FSW) successfully employing a rotary speed of 635 rpm and welding speed of 75 mm/min, in order to elucidate the effect of FSW on mechanical and corrosion properties. The yield and ultimate tensile strength of the joint were found lower than the base material while ductility of FSW joint was found higher than the base material. The joint efficiency of friction stir welded joint was 85.59 %. The microstructure and other unique features associated with different zones of FSW joints were studied by optical and scanning electron microscopy. SEM study of fracture surfaces revealed that fracture is triggered by the breaking of secondary precipitates (MgZn₂). Weld nugget of FSW joint was found to be susceptible to corrosion than HAZ and base metal. The current density for WNZ and HAZ were ∼8.5 and 2.8 times higher than that of the base metal.

In this study a friction stir welded AA2017 is post weld heat treated at 500 °C for holding time of 20, 40 and 60min then quenched in water and naturally aged. The effect of post weld heat treatment on the microstructure and hardness is investigated across the transverse cross section of the weld. Experimental results showed that the PWHT causes abnormal grain growth of the grain structure mainly near to the advancing side of the weld. The grain size increases with the increase of the holding time however the region near to the retreating side of the weld retained its fine grain structure. EBSD has been used to examine the microstructure and texture before and after PWHT. EBSD investigation showed that the grain growth is texture dependant as grain growth occurs in some grains of (B+C) texture component while in the adjacent grains of texture components B- does not occur.

Closed aluminum foams fitted thin-walled circular tubes was investigated for its energy absorption characteristics. Compression test was carried out to obtain the representative quasi-static stress-strain curves. The deformation characteristic (foam, tube and their combination) was analyzed. The results indicated that the deformation mode of aluminum foam and tube changed after combine. Foam-tube configuration absorbed more energy than the sum of foam and tube due to the interaction between tube and filler which contains friction, extrusion, crack formation and growth. In addition, the energy absorption of foam-tube configuration was 6 times of aluminum foams. The experiment results reflected that the foam-tube configuration was a potential energy absorber candidate for car industry and transportation cask.

This paper analyses the dependence of the structures of foamed Al-Si alloy on the process parameters. It takes the aid of back propagation (BP) neural network theory to build the nonlinear mapping relations between the crucial process variables and the quality of pores. Then by the integrating BP neural network and genetic algorithm (GA), the optimized process parameters for high porosity of foamed Al-Si alloy can be searched. The comparisons between experiment results and neural network simulation results show that GA-based on BP method can predict the porosity with higher prediction accuracy. The effects of viscosity on the foam ability are also important. The mechanism of thickening agent has been analyzed theoretically.

Al-Mg wrought alloys such as Al-2.6Mg, Al-4.6Mg and Al-4.6Mg- 1Si were friction stir welded and a subsequent thermal exposure was carried out in this study. The effects of elements addition and exposure temperature on the microstructural stability of welded zone were investigated. A grain refinement was found in the weld zone of each alloy and the average grain size of friction stir welded Al-2.6Mg, Al-4.6Mg and Al-4.6Mg- 1Si was 10.1µm, 7.4µm and 4.7µm, respectively. Thermal exposure caused drastic coarsening of grains in the stirred zone and abnormal grain growth initiated at some preferred sites such as upper surface and bottom. The volume fraction of coarsening grains increased with increasing exposure temperature; however an unexpected decrease in grain size was found at 550°C in compare to 500 °C. Besides, the addition of Mg and Si deteriorated the thermal stability of grain structure in stirred zone.

Al metal foams manufactured by the powder-method have been investigated. Compression tests were performed on the same sample at increasing deformation steps: at each stage the sample was observed by X-ray computerized tomography. A geometric evaluation of porosity on many sections was performed by calculating, for each pore, its area, equivalent diameter, perimeter and circularity.

Aluminum smelting plants emit gaseous and particulate fluoride, sulfur dioxide (SO₂), carbon oxides (CO and CO₂), perfluorocarbons (CF₄ and C₂F₆), and other by-products of aluminum electrolysis processes. Potroom fugitive emissions intensity for some of these pollutants (most notably, fluorides) is strongly correlated with potroom work activities and work practices (e.g., anode change operations, metal tapping practices, pot hood placement, etc.). Therefore, work practice standardization and potroom personnel education regarding the impact of their day-to-day activities on smelter emissions are important components of pollution control and prevention strategy.This work introduces a low-cost video emissions monitoring technique utilized at Alcoa that allows overlaying real-time emissions measurements (e.g., HF, SO₂, dust, etc.) on video recordings of specific work activities. The developed capability is used to more effectively and uniformly communicate the impact of work practices on plant environmental performance. Specific examples of high-impact work practices are presented and discussed.

The general use of high amperage cells in the last decade has created new challenges for Gas Treatment Centers (GTCs). Aluminum production capacity increases proportionally with the applied electric intensity. This leads to more waste heat by joule’s effect which increases the cell outlet gas temperature. The cell gas temperature also depends on the ambient temperature. In hot climates, gas temperature at the cell outlet could reach 190°C. In such situations, it has become necessary to cool the gases before treatment by HF adsorption on alumina in order to protect the filtration media and to improve the overall scrubbing performance of fluorides. Several technologies have been developed and applied in recent years: dilution air cooling, water atomization in the upstream ducts and heat exchangers. The paper will present a technical and economical comparison of the various gas cooling technologies.

Reduction of fluoride emissions is necessary today as a result of production growth and/or increasingly demanding environmental regulation contexts.Over 40% of roof vent emissions are generated by the pot during periods when pot hoods are open. These periods are therefore targeted for improvement, which is usually obtained by significantly increasing pot exhaust flow while the hoods are opened.The Rio Tinto Alcan solution, patented since 2007 [1], the Jet Induced Boosted Suction system, trialed and now rolled-out on AP22 potlines in Tomago, has been scaled up to fit AP3X technology. This has led to implementation of an industrial demonstration on a 36-pot section in the Alma smelter, including automatic pot hood opening detection. The operational and environmental performance of the system was evaluated during the trial. At the same time, the design and proof of concept of an AP60 version has taken place in LRF, preparing for future evaluation as part of the AP60 Jonquière project.

During the production of aluminum in conventional prebake Hall-Héroult electrolysis, anodes have to be replaced on a regular basis. The anode butts are usually placed on uncovered trays for transportation, a practice that contributes to overall hydrogen fluoride (HF) emission. Anode tray covers developed by Alcoa were implemented at the Deschambault smelter to significantly reduce these fluoride emissions and an Alcoa-STAS R&D team developed a modified version of anode tray covers for the greenfield Alcoa Fjardaál plant.In 2009, the Alcoa-STAS R&D team designed and fabricated an experimental test garage to allow the accurate full-scale in-plant measurement of temporal HF emissions from cooling anode butt trays.Over the last two years, comparative measurements were performed on covered and uncovered anode trays in a manner to allow estimation of the overall impact of covered trays back to zero time, or initial butt removal from the pot. This paper presents results from these studies.

Aluminum electrolysis is known as more energy consumption and more pollution. The DC power of aluminum electrolysis before the technology of aluminum reduction cells with a new-type of cathodes design being applied in China was over 13000 kWh/t. After 2010, nearly all the aluminum smelters have began to use the technology of new type of cathode design and 500–700 kWh/t of aluminum reduction can be achieved easily. The DC power of aluminum electrolysis is nowadays 12100~12300 kWh/t. 11800 kWh DC energy power of an aluminum reduction cell in Chuangyuan Smelter is achieved. In present paper, Research and application of energy saving technology are given, and a new anode technology is presented. By using the new technology of anode, cathode and narrow central channel, the energy consumption will be decreased greatly.

During this decade the energy market is changing rapidly and new smelter projects may face large ranges of energy block size, significantly different energy prices and environmental regulations. To provide more choice in this complex and changing situation, Rio Tinto Alcan announced two years ago a new strategy of developing flexible solutions. On the same platform have been developed cells at very high productivity and cells with low energy consumption. This strategy has been delivered with the APXe and AP60 cells, able to operate with the same framework in the range 500–600 kA with energy efficiency between 12.0 and 13.2kWh/kg. This new development incorporates an environmental dimension, aiming to reduce dramatically the air emissions of future smelters. The prototype results have confirmed the feasibility of such ambitious targets and shown that innovation is a key factor to develop the cell of 2020’s, at low energy consumption and reduced environmental footprint.

The energy saving technologies applied in Chinese aluminum reduction are reviewed in this paper. The energy saving technology development in China in the aluminum reduction field could be divided into three stages. The first stage was retrofit of Soederberg cells to prebaked anode cells and technology development of large amperage prebaked anode cells, which happened mainly in 1990’s. The second stage was wide applications of the large amperage prebaked cell technology and the improvement of such relevant technologies as physical fields simulation, cell control systems and high quality anode and cathode manufacturing etc., which covered the first 6–7 years of this century. The third stage has lasted up to now, which mainly focused on the energy saving in the present prebaked cells by cell cathode and lining structure modifications and high performance operation and control system applications.

Perforation on the anode block is a new way of energy conservation. The bubbles under the anode block can be eliminated from the holes, and the energy consumption is reduced. The physical and mathematical models of perforated anode and bubble layer were established, and the thickness of the anode bubble layer and temperature field, electric field and thermal stress field were simulated. The simulation results show that the thickness of the bubble layer is 1.28cm of the perforated anode, reduced by 0.72cm compared to a normal anode, of which corresponding voltage is less than 240mV; the minimum temperature of anode block is 704.3°C, and the temperature distribution in a horizontal plane presents a wave shape due to the holes; the voltage drop of the perforated anode is 379mV and the current density distribution of the perforated anode and ordinary anode are consistent; the maximum of thermal stress is 17.4MPa in the perforated anode, which is far less than the allowable stress. The perforated anode industrial was conducted on three cells. The average cell voltage of perforated anodes decreases 229mV than the traditional reduction cell after long-term operation, which is agreed with the theoretical calculation.

In a prebake aluminium reduction cell, the continuous electrochemical and chemical oxidation of the anodes requires regular replacement of anodes in a predetermined sequence. It is important to maintain cell stability and thermal balance during the anode exchange.The higher amperage operation at Dubai pushed the ‘anode current density’ towards the anode effect threshold limit. Moreover during anode removal, this threshold limit is challenged causing a higher likelihood of AE. Therefore, the anode setting logic was revamped in order to improve the energy balance whilst operating at an anode current density greater than lA/cm2. An optimum utilization of resistance set point combined with an automated down movement of anodes prior to anode removal was introduced. Thereby it improved the thermal balance resulting in a reduction in anode effect frequency by 29% and cell voltage by 9 mV.This paper describes the methodology of optimising the energy balance during anode setting

The Alouette aluminium smelter at Sept-Iles, Quebec was commissioned in 1992 with a nominal capacity of 215,000 tonnes per year based on AP30 cells operating 264 pots at 300 kA. Since that time, the plant has expanded considerably, and in 2005 a new potline of 312 pots was added plus an 18 pots test section. The cells currently operate slightly over 370 k Amp with plant capacity now at 600,000 tonnes per year. In the quest for higher productivity and profitability, Alouette is planning a transition to 400 kA based on the use of new, high-amperage, low-energy (LE) AP cells, referred to as AP40LE. In designing this new cell, certain lining, rodding procedures and materials of construction were modified. The main performance objectives and the development steps towards introducing the AP40LE pots and plans for bringing all production lines to 400kA are described in this paper.

The adverse impact of anode setting on the current efficiency (CE) is well known in the aluminum industry, although few published studies exist. When a cold anode is lowered into the bath, it immediately quenches a layer of frozen bath on the bottom surface that may extend to the metal pad. It takes time, energy, and bath motion to melt this layer. Until then, the anode current distribution is uneven and the bath motion is disrupted around the newly set anodes. These effects are hypothesized to lead to higher noise and lower CE.The paper summarizes experiments, conducted at Alcoa Warrick, during which anodes pre-heated to 480–510°C (bottom surface) were set in a few pots over 60 days. The studies suggest potential to double the rate of load up, reduce energy consumption by 40 kWh/mt, and increase CE by 0.5–1%. Approaches to supply hot anodes are discussed.

In view of the existing status with aluminum overcapacity and lower aluminum price in China, many companies adopted various measures to reduce the production cost and the energy consumption, but there has been no a normalization theory and method as yet. Aimed at the existing status and the market demand, this paper puts forward the evident effects of energy-saving and consumption-reduction in aluminum reduction pot using new thermal insulation pot lining design, application of optimal cathode structure, reduction of horizontal current device, proper application of new lining materials and proper combination of relevant process parameters based on the finite element software ANSYS and using the thermal field simulation software of international simulation Prof. Mr. Dupuis as the calculation method, combining the actual production data. Practice proves that the above-mentioned method combining design, simulation and experiment can become the effective and feasible way to achieve low energy consumption, low cost and high profit.

In this paper one low voltage energy-saving technology for aluminum reduction cell is developed by SAMI, this technology can largely reduce horizontal current in the metal pad and improve the MHD stability of the cell. Some industrial testing results of this technology by SAMI and its application on different type cells in Chinese smelter are finally presented to illustrate how their contributions is to make D.C. power consumption close to 12000 kWh/t-Al without current efficiency loss compare to the prior technology.

Since the first Pot Tending Machine commissioned by ECL™ 50 years ago, all the new options, tools and technical solutions have been conceived and designed only to meet with smelters’ challenges: reduce energy consumption and consequently allow significant cost savings and ensure safe and secure operations.In close collaboration with MATTEI, a world-class air compressor designer and manufacturer, ECL™ has then developed and equipped its Pot Tending Machine with a new standard of air compressor: the twin air compressor. Instead of just one big energy-intensive compressor, two smaller and lighter compressors are in most cases used separately (anode changes), except for tapping operation. By running them alternately at only 82% of their full capacity, there are definite energy savings with the additional benefit of a longer operational life for the compressor. Furthermore, the size and weight of this new standard greatly ease maintenance operations.

In the first half year of 2011, PFC investigation has been conducted on five potlines whose line currents are at the range of 200~350kA. The total aluminum output is 1.35 million tons per year. Both PFC caused by anode effects and PFC unrelated to anode effects were monitored and calculated. C₃F₈ was observed during anode effects for the first time and its peaks were at the same location as C₂F₆ and CF₄ at the timetable. The weigh ratio of C₃F₈/CF₄ was 4.19%, and that of C₂F₆/CF₄ was 11.61%. C₃F₈ was observed only in the monitoring of two potlines and no C₃F₈ in the other three potlines. Concentration curves of C₃F₈ were plotted with C₂F₆. Percentage of Non Anode Effect PFC (NAE-PFC) of five potlines was calculated. The highest was 92.8% while the potline has the lowest anode effect frequency (AEF) and its AEF is 0.01 AEs/cell-day.

The aluminium industry is today the primary source of perfluorocarbon (PFC) to the atmosphere. These gases have a lifespan of several thousand years, and a greenhouse warming potential (GWP) 6500–10000 times that of CO₂. It is therefore of essential to understand, and reduce, the PFC emissions.Controlled potential electrolysis with gas analysis was utilized to study the PFC production in a laboratory cell during regular electrolysis conditions, and during anode effects. A 3-electrode setup with an Al reference electrode was utilized to monitor the anodic voltage. The combination of Mass Spectrometry (MS) and Fourier Transformed Infrared Spectroscopy (FTIR) was used to characterize the off gas. Traces of CF₄ were found in the anode gases at anodic voltages as low as 2.9 V VS the Al reference electrode, confirming that the PFC production can occur unrelated to the anode effect. However C₂F₆ was only detected during anode effects.

Point feeders have volumetric chambers that periodically deliver ore to cells through holes pneumatically broken into the crust layer. The period of feeder actuations is controlled by the logic employed to regulate bath alumina concentration. The time evolution of bath alumina concentration is mostly a function of the rates of alumina consumption and feeder mass charge, but is also influenced by other events such as crust seal breaks/leakages, and plugged or semi-plugged feeder holes. PID modulated In Situ feed logic addresses variable non-feeder ore related events to control alumina concentrations at targeted levels. Frequent underfeed and overfeed episodes are avoided. The In Situ ore feed concept has been successfully tested in the Dyna/Marc cell simulator at a targeted 2.30 % alumina concentration demonstrating both increased current efficiency (CE) and decreased kWh/kg compared to presently employed methodologies. Anode/cathode distances (ACD) can also be accurately measured using In Situ % alumina predictions.

Aluminum reduction cells typically use about 1.9 kg of alumina in order to produce 1 kg of aluminum. Hence, for modern reduction cells operating in the 350 to 400 kA range, 5000 to 6000 kg of alumina is fed to reduction cells on a daily basis. However, no information is available in an on-line fashion about the alumina properties fed to the pot. Alumina feeding control systems assume that alumina properties are constant for all pots within a potroom and also over time. Therefore, these control systems aim at controlling alumina concentration dissolved in the bath without accounting for the time varying effects of alumina properties and/or pot condition on alumina dissolution. Based on sampling campaigns, this paper presents evidences of time varying alumina properties impacting its dissolution rate and also proposes a novel approach in order to measure on-line, at the pot, parameters that are related to alumina dissolution.

Over the course of 30 years the Process Control softwares have narrowed the variations of individual reduction cells. The volume of data available for day-to-day management of the potlines have increased considerably while the number of technical personnel per pot and per potline have been considerably reduced.Combining the tools and principles of Continuous Improvement with in-depth knowledge of Reduction Process Control systems allows for a new generation of Potline Process Optimization techniques. These techniques, powered by new generation data integration software, can breathe a new life in the Energy and Environment Performance of all smelters. They can show their owners a new trend for improvement and demonstrate strong care to the local communities without mobilizing expensive capital resources and additional people. How much can we expect? What does it require in terms of Human and System capabilities? Where do we start and how far can we improve?We will bring an innovative answer by describing a new tool: the Variability Matrix.

In the aluminium reduction technology there is no full awareness concerning the dependence of technical-economic indices (TEI) including anode paste (AP) consumption on the changes of raw materials properties and technology parameters. Availability of this information could improve the effectiveness of the reduction technology control.In the paper the multivariate statistical treatment of anode paste consumption depending on the electrolysis parameters is applied. Using principal component analysis the parameters which greatly influence on the anode paste consumption are determined.Statistical models for paste consumption for single potroom and for comparison of the results between rooms are received. Anode paste consumptions if the parameters changed by three Standard deviations are calculated.

Alstom’s new pot feeding system (Alfeed) was successfully installed and commissioned on Emal’s 756 pots during 2009–2010.The Alfeed system consists of 15 km distribution and pot airslides, manufactured in standard sections for maximum ease of installation and use.Alfeed on Emal is connected to 8 enriched alumina silos, each feeding two sections with 48 pots. Each section is 300 m long. The nominal flow rate to each pot is >200 kg/h, and to each section >10 ton/h.The main issue encountered during start-up was dusting from the pot’s alumina hopper lids. Small puffs of dusty air would leak through a narrow opening, eventually leading to build-ups of alumina on the superstructure. This was resolved through implementation of a clamp to the lid as well as a gasket.As with all new systems, some challenges were encountered as well as possibilities for optimisation. These are discussed in detail in the paper.

Alumar which is one of Alcoa units, by following a corporate vision, is pursuing ways to reduce greenhouse gas emissions.Normally, the pot voltage is used to detect the anode effect events every 1 to 10 seconds. With the continuous improvements on the computer performance to handle faster scan data, we are able to read the pot voltage every 100 milliseconds. Our attempt is to use this fast scan data to distinguish the normal and the pre-anode effect voltage period.An algorithm has been created to detect this behavior, based on the speed of the voltage increase.With simulation we observed that 60 to 70% of the anode effects are predicted by the new algorithm. The other 40 to 30% are ignored in order to reduce false detections. Only 2 to 10% of the predictions do not really result in anode effects. The accuracy is strongly associated with the noise. The average voltage of prediction is 5.19V where the normal computer detection is 8V. The predictor was tested during one month in 102 pots indicating that we can predict the anode effect events from 7 to 20 seconds prior to its occurrence. These tests resulted in a reduction of 30% of time above 8 volts and 20% reduction in anode effect/potday.

The chemistry of sulphur in carbon anodes is not fully understood, especially its influence on the electrolysis parameters. The results of this study are indicative of an important link between the sulphur content in the anode material and the carbon consumption as well as the current efficiency during aluminium electrolysis. By performing a laboratory scale investigation of different carbon anodes with sulphur contents ranging from 1.97 to 3.82 wt% S in addition to graphite anodes with sulphur content close to zero, it was found that increasing sulphur content contributes significantly to a decrease in the current efficiency and a rise in the carbon consumption. When going from 0 to 3.82 wt% S, the current efficiency decreased from 92 to 85% (1.8 % per 1 wt% S), and the carbon consumption rose from 108 to 128% (5.2 % per 1 wt% S).

It is well known that the system NaF-AlF₃, which constitutes the “backbone” of the electrolyte used in primary aluminium manufacture, forms Na+, F-, and a number of fluoro-aluminate anion complexes in the molten state. Since mainly the Na+ ion carries electric current, the aluminium-containing complexes must diffuse towards the cathode, resulting in concentration gradients in the cathode boundary layer. Starting from a structural model for the melt containing five anion species, it was possible to calculate the concentration gradients of the individual ions using the Stefan-Maxwell equation for diffusion in a multi-component system. Generally, AlF₄- and Al₂F₇- were transported towards the cathode, while F- and AlF₆3- moved away from the cathode. For NaF/AlF₃ molar ratios higher than 2.0, AlF₅2- moved towards the cathode, while it diffused away from the cathode in more acid melts.

The anode processes of carbon electrodes in 49 wt% Na₃AlF₆ — 21 wt% K₃AlF₆ — 30 wt% AlF₃-Al₂O₃ (saturated or free) melts were studied in a wide range of potentials by cyclic voltammetry. Two electrolysis processes were observed on the cyclic voltammogram traces. It is considered that the first process corresponds to the discharge of oxide ions (or residual oxide ions), and the discharge of fluoride ions occur after the discharge of oxide ions, leading to the anode effect. As the potential increases, the second process occurs with the emission of Perfluorocarbon (PFC) gases. Compared to the cyclic voltammogram trace obtained from the traditional electrolyte for aluminium industry 84 wt% Na₃AlF₆ — 11 wt% AlF₃ — 5 wt% CaF₂ — Al₂O₃ (saturated), it can be seen, as the addition of a large amount of AlF₃ and the decrease of electrolysis temperature, the current density of the second process increases obviously. The performance of low temperature aluminium electrolysis increases the risk of a larger emission rate of PFCs.

Sustained, stable operation of low-temperature, potassium-cryolite-based aluminum electrolysis in 20 and 100 ampere cells fitted with vertical metal anodes and wetted cathodes was performed. The current efficiency, the amount of consumed alumina, and the amount of aluminum produced during electrolysis were calculated based on the measured amount of oxygen evolved on the anode. The purity of the recovered aluminum was analyzed throughout electrolysis. The cell voltage anomalies caused by the presence of sodium fluoride in the electrolyte were studied using a quasi-reference electrode.

Effects of K and Na on expansion of cathode carbon block were studied through an improved instrument for measurement of expansion rate. For a 30% graphitic cathode block, based on the results, in KCl-NaCl electrolysis system K and Na are reacting with graphite and forming graphite intercalation compounds (GICs) during penetration from surface to inside of the cathode block, and K plays more important role in expansion and penetration than Na. The results show that for a NaF-AlF₃-Al₂O₃ system, containing 7% Al₂O₃ and with CR = 6.5, during electrolysis at 1000°C the expansion rate of the 30% graphitic cathode block is increased from 0.47% to 0.82% with 0 to 7% KF addition to the electrolytes. It is also shown that the expansion due to K and Na penetration in cathode becomes lower with increasing content of graphite in cathode material, and that expansion of fully-graphitized cathode is very low.

Al-Sc Alloys have attracted much attention in recent years due to their great potential in many advanced applications. In this work, Al-Sc alloys were prepared on liquid Al cathode in KF-AlF3-Sc₂O₃ (CR=1.22) melts during reduction process. Scanning electron microscope (SEM) and Inductively coupled plasma atomic emission spectroscopy (ICP-AES) showed that the primary Al₃Sc were highly faceted and Sc contents were 0.44 and 0.73 wt.% in the alloys produced at 750 °C with current density of 0.5 and 1.0 A/cm2, respectively. At 1.0 A/cm2, Sc content increased to 0.95 wt.% at 800 °C and 1.27 wt.% at 850 °C. But higher mass loss from the melts was found with increased operating temperatures. Cyclic Voltammetry and Linear Sweep Voltammetry studies demonstrate that the reduction of Sc3+ occurs at liquid Al cathode and Al₃Sc formation is electrochemically irreversible. In addition, the effect of ultrasound on the Sc distribution was also investigated.

Liquidus temperatures for the primary crystallization of the molten salt system Na₃AlF₆-K₃AlF₆-AlF₃ for aluminium electrolysis were determined by thermal analysis. The data were fitted to an empirical equation: <math display='block'> <mrow> <mi>T</mi><mo>=</mo><mn>3478</mn><mo>&#x2212;</mo><mn>1867</mn><mo>&#x00D7;</mo><msup> <mrow> <mo stretchy='false'>[</mo><mi>K</mi><mi>R</mi><mo stretchy='false'>]</mo> </mrow> <mrow> <mn>0.12</mn> </mrow> </msup> <mo>&#x2212;</mo><mn>12.97</mn><mo>&#x00D7;</mo><msup> <mrow> <mo stretchy='false'>[</mo><mi>A</mi><mi>l</mi><msub> <mi>F</mi> <mn>3</mn> </msub> <mo stretchy='false'>]</mo> </mrow> <mrow> <mn>1.14</mn> </mrow> </msup> <mo>+</mo><mn>3.538</mn><mo>&#x00D7;</mo><mo stretchy='false'>[</mo><mi>A</mi><mi>l</mi><msub> <mi>F</mi> <mn>3</mn> </msub> <mo stretchy='false'>]</mo><mo>&#x00D7;</mo><msup> <mrow> <mo stretchy='false'>[</mo><mi>K</mi><mi>R</mi><mo stretchy='false'>]</mo> </mrow> <mrow> <mn>0.98</mn> </mrow> </msup> <mo>&#x2212;</mo><mn>0.505</mn><mo>&#x00D7;</mo><msup> <mrow> <mo stretchy='false'>[</mo><mi>A</mi><mi>l</mi><msub> <mi>F</mi> <mn>3</mn> </msub> <mo stretchy='false'>]</mo> </mrow> <mrow> <mn>1.24</mn> </mrow> </msup> <mo>&#x00D7;</mo><msup> <mrow> <mo stretchy='false'>[</mo><mi>K</mi><mi>R</mi><mo stretchy='false'>]</mo> </mrow> <mrow> <mn>1.23</mn> </mrow> </msup> </mrow> </math>$$T = 3478 - 1867 \times {[KR]^{0.12}} - 12.97 \times {[Al{F_3}]^{1.14}} + 3.538 \times [Al{F_3}] \times {[KR]^{0.98}} - 0.505 \times {[Al{F_3}]^{1.24}} \times {[KR]^{1.23}}$$ where T is the liquidus temperature in °C and the square brackets denote wt% of components in the system Na₃AlF₆-K₃AlF₆-AlF₃. with [KR]=K₃AlF₆/(K₃AlF₆+Na₃AlF₆) The composition limitations are 20%<AlF₃<30%, and 15%<KR<30%. The isothermal diagram of the molten salt system Na₃AlF₆-K₃AlF₆-AlF₃ was obtained in this composition limitation.

Since the 1990’s, DUBAL has engaged in self-development of proprietary aluminium reduction technology. DX and DX+ technologies, both being in-house designed, modeled, tested and optimized, are the latest products of this development process. In quest to decrease capital cost per tonne, DUBAL designed DX+ technology and started up five demonstration cells between June and August 2010. DX+ cells are similar to DX cells, but larger in size: the productivity per square metre of potroom is increased by more than 17%. This paper describes the DX+ cell design evolution from DX technology. It also summarizes the on-target performance achieved by the DX+ demonstration pots during their first year of operation at 420 kA. DX+ technology has been selected for the EMAL Phase II project. The project FEED study, completed in June 2011, is based on one potline of 444 DX+ pots. The design allows for an operating amperage increase to 460 kA.

Another significant step in the AP30 development has been successfully demonstrated; one that further enhances productivity. After the AP39 technology validation, an enhanced operating point has allowed cells to operate above 400 kA without decrease in energy efficiency. Since July 2010, these cells, now referred to as AP40, operate at St Jean de Maurienne in the range of 400–405 kA with specific energy consumption below 13150 kWh/t. Achieving this performance required an extensive review of operational aspects including busbar capability, operational quality, and process control. Also essential was the use of an “operating window” approach to determine the optimal operating point. By following a cell development methodology over two years, results have demonstrated a high level of process performance (anode effect frequency, current efficiency and energy consumption). Measurement campaigns have confirmed the excellent level of pot robustness.

The major factors affecting the profit of an enterprise are the price of the product, the price of raw materials and energy consumed, depreciation of fixed assets, labor cost, output and process consumptions, etc. In this paper, based on a cost-volume-profit (CVP) analysis method and the process techniques of aluminium production, a series of techno-economic analysis and optimization models for the production of the aluminium smelter enterprises are built. The models can be used for the aluminium smelters in various market situations to get the optimum technical parameters of production, which are necessary for obtaining the greatest economic benefit. Thus, it will guide the aluminium smelters in different market environment, according to their own conditions, to adopt different technical parameters of production to maximize the gains and to minimize the losses. We also have studied the optimization of potline current of a 300 kA aluminium smelter by the models as an example.

Between 2 December 2009 and 2 January 2011, all 756 DUBAL DX technology cells in Phase I of the EMAL smelter in Abu Dhabi were successfully commissioned. This represented the culmination of DUBAL DX technology fast-track development from prototyping to large scale industrialization. The process began with the design and engineering phase in 2004, followed by commissioning of five prototype pots in 2005, a demonstration line of 40 pots in 2008 and finally the commissioning of the giant smelter at EMAL Phase I in 2009/2010. The commissioning and normalization of the pots at EMAL Phase I were very smooth, without a single lining incident. This was achieved through excellent team work and coordination between the various teams at all stages (pot preparation, preheat, start-up and normalization). The rapid and stable commissioning also demonstrated the robustness of DX technology. Both potlines at EMAL Phase I are now operating at 353 kA and are achieving excellent performances: 96.0% current efficiency and 13.0 kWh/kgAl for more than 18 months since start-up.

On the 2nd of December 2009, Emirates Aluminium (Emal) commenced its journey of starting 756 Dubal DX technology reduction cells. This undertaking was successfully completed on the 2nd of January 2011, thirteen months later, resulting in an average start-up rate of 13.3 pots per week. This sets a new benchmark for Greenfield Smelters. This remarkable achievement was possible due to an efficient work organization, with committed and experienced employees. The pot start-up rate and pot technical results give measures of the success by which the task was accomplished.This article provides insights into the experiences gained and systems used by the Reduction Operations Team, in managing the organizational complexities of commissioning the largest Greenfield Smelter start-up to date.

Dubai Aluminium commenced operation in 1979 with 3 potlines, each with 120 D18 technology cells. While more advanced cell technologies have since been developed and implemented at Dubal, the original D18 cell technology has continued to be updated and improved so that it remains a vital contribution to the overall smelter production.This paper updates the progress1 of the original D18 cell technology at Dubal over the past few years, and its contribution towards the plant total hot metal output of >1 million tonnes per year.The four D18 potlines have been combined into two potline circuits, and additional busbars were added to all cells to reduce the external voltage drop and specific energy consumption. The original centre-break feeding design has gradually been replaced with a pseudo-point feeding design, and the anode size has been gradually increased so that it is now the largest for this technology. Other changes such as improved noise control logic, review of the anode set adder, and various changes to the alumina feed logic have enabled the D18 cell technology to reach the target amperage of 200kA and its subsequent stabilisation and optimisation at this milestone.

In early January 2011 the decision was taken to perform an emergency shutdown of the newly converted prebake potlines of Kubikenborg Aluminium AB (Kubal). This was due to power interruptions that resulted in bath shrinkage, which was followed by the onset of random anode failures in numerous cells when attempts were made to re-energize the potline.The present paper covers the methods for restarting the potline. These methods were first considered and tested on one or two pots to evaluate the individual method, taking into consideration the availability of trained personnel; cell limitations and logistics; metal purity for existing customer supply commitments; environmental regulations; and speed of restart.In addition, the paper will provide the criteria used to select the appropriate re-start procedure for different cell conditions and the results obtained by each of the methods used.

In November 2010, Ormet Primary Aluminum Corporation announced an aggressive plan of restarting two potlines before the end of the 1st quarter of 2011. In order to accomplish this goal several key factors were utilized including the experience of the plant personnel, management of anodes and bath generation at startup, initial power and chemistry control of the pots, and the fact that the shutdown of the lines was efficient and controlled. The total time from the restart announcement until all 344 pots were brought on took only 92 days, and the time from when the first line was energized until the final pot was cut in on the second line took only 71 days. This paper will discuss the key factors and obstacles that had to be overcome to allow Ormet to achieve this goal while also striving for safety as no recordable accidents occurred during the restart.

Due to the considerable number of VSS cells (more than 60 % of the total capacity), RUSAL continues to develop the Søderberg process successfully. Alumina point feeding systems (APF) and dry gas scrubbers were introduced, and anode paste production was modernized in the Krasnoyarsk smelter. The amperage was increased in all VSS potlines. These actions have increased the aluminium production efficiency and environmental sustainability. Besides, the company’s Engineering and Technological Centre (ETC) has successfully fulfilled the R&D program creating the new modification of VSS technology (so-called “Eco-Søderberg”) reaching a new environmental standard. The results of these and other activities of the company from 2004 to 2010 are shown in the present article.

Within the framework of the second modernization stage (since 2005), UC RUSAL began an “Environmentally friendly Søderberg” project. The strategic goal was to create a competitive cell.

This paper describes a useful experience, which was conducted duringlast year’s start-up and potroom operation regarding a sick cell treatment in an aluminum smelter in Iran, which we will call smelter X in this paper. Different parameters in the potroom have influence on cell stability, which need to be considered all together. Metal pad stability is the main concern for a smooth operation in an aluminum smelter to reach a low noise level and a high current efficiency. One of smelter X’s aluminum reduction cells, which was started with good and smooth operating parameters, turned into a sick cell with a very high noise level two months after its start up. A special team started to monitor, test, analyze and try different strategies to bring the cell back to normal condition. This paper is a summary of the aforementioned challenge, team endeavor, possible solutions and final results to overcome this problematic issue.

The well-known cryoscopy equation for binary systems was extended to the ternary system NaF-AlF₃-B, where B is a substance present in small amounts. It is shown that the depression in the liquidus temperature for a given molar fraction of B depends on the direction in which B influences the activity of NaF, as well as on the NaF/AlF₃ molar ratio. This implies that it is difficult to estimate the effect on the liquidus temperature of contaminants in the Hall-Héroult bath. The three-component cryoscopy equation can be regarded as a theoretical justification of the cross-terms used in most empirical equations for calculating the liquidus temperature. New cryoscopic data are given for the system Na₃AlF₆-CaF₂ as well as for some substances that are normally present in only small amounts, and empirical equations containing cross-terms between these substances and aluminium fluoride are suggested.

Since the 1960s SINTEF has, in collaboration with the Nordic aluminium smelters, developed methods for sampling and analysis of fluoride. Unlike conventional Potentiometric analysis, this methodology involves detection of fluoride in acidic media. At low pH, the electrode kinetics is improved, resulting in faster analysis. By masking of the fluoride leakage from the ion-selective electrode, the sensitivity of the method is improved. Standard addition methodology is applied for improved analytical performance. The acidic media makes it possible to perform a direct analysis of fluoride in biological samples. In this way, fluoride is extraced from the biological matrix by the acid. The high sensitivity requires low sample masses used and thus does not interfere with the fluoride detection at the ion-selective electrode. This is far more efficient than the conventional approach of ashing the sample at elevated temperatures. Acid extraction can also be applied to filter dust samples.

During the last decades, many efforts were spent to investigate different aspects of the Hall-Héroult process in order to improve its design and operation. However, many questions remain unanswered due to the complexity of the process and the hostile environment. One of the still unclarified questions is the mechanism of the transport of CO/CO₂ gas between the active electrolysis sites and the bubble-evolving anode pores. Generally, during electrolysis in aqueous systems, the generated gas is dissolved and transported through the electrolyte, especially when the anode is impermeable. However, the solubility of CO₂ in the molten cryolite is poor and the anodes, used in aluminum industry, are highly porous. In this paper, different mechanisms of the CO/CO₂ transport between the gas generating anode — bath interface and the bubble releasing sites are examined. The majority of the anode gas seems to be transported through a thin superficial layer of the porous anodes, while transport via the molten bath and gas adsorption by the anodes plays a secondary role

Consumable carbon anodes are used in the electrowinning of aluminium by the Hall-Heroult process and in other proposed processes for electrowinning in molten salts. Emissions of CO₂ may be eliminated by introducing an inert oxygen evolving anode, which however will require a higher anode potential. By introducing natural gas or hydrogen to the anode the CO₂ emissions can be reduced and the anode potential can be lowered. Laboratory experiments were carried out in a modified Hall-Heroult electrolyte with excess AlF₃ at 850 °C. Anodes of platinum, tin oxide and graphite were tested during electrolysis at constant current, with the supply of argon, methane and hydrogen through or at the anodes.Laboratory studies showed that by introducing both hydrogen and methane separately through a porous SnO₂ anode in molten Na₃AlF₆-AlF₃-Al₂O₃ (4.5 wt.%) at 850 °C the anode potential was found to be lowered by several hundred millivolts for a limited time during electrolysis.

Potassium Aluminum Fluoride obtained as a byproduct in the aluminum grain refiners and master alloys production may be used as an additive to the aluminum reduction process. The component leads to a considerable reduction in the liquidus temperature, and maintains other important parameters such as electrolyte conductivity and solubility of alumina. Both, laboratory tests and semi industrial trials in a 100A cell have been conducted in order to test the suitability of this new additive to the electrolytic process, with positive results. Potassium Aluminum Fluoride can be also used as a basic component of the low-temperature electrolyte for aluminum electrolysis.

Experimental in situ Raman spectra are presented for potassium, sodium and mixed fluoroaluminate melts. More acidic melts with cryolite ratio (CR) below 2 are accented. The cation-dependent ratio of integral band intensities is assigned to specific interactions of potassium cations with low coordinated fluoroaluminates. For alumina containing melts, the effect of potassium on the stoichiometry of predominating oxofluoroaluminate anion is observed indirectly. Density functional theory is employed to investigate the behavior of different fluoroaluminates (including dimers) and their associates formed by alkali metal cations.

The purity test is one of the key parameter for aluminum fluoride material used in aluminum smelting process. Aluminum fluoride is added to the reduction cell to react with alumina impurities such as CaO and Na₂O and to generate more alumina (Al₂O₃) and cryolite to the reduction cell. Good quality of AlF₃, usually having purity between 89 to 93%, has to be measured accurately, through a quick and safe method. This study provides several solutions for measuring the AlF₃ purity by instrumental methods such as NMR, XRF dilution, SEM and XRF standard as an alternative for the wet chemical methods. This approach is applicable also for Al₂O₃/ AlF₃ mixed samples.

Raman spectra of NaF-AlF₃-NaCl melts with the compositions in aluminum electrolysis practice are recorded by using the ultraviolet laser source. A kind of sealed sample cell was used to improve the measuring precision. The ionic structure of the melts with different cryolite ratio (molar ratio between NaF and AlF₃) and NaCl contents was studied. The effect of the composition and temperature was analyzed. The results show that with the addition of the NaCl to the acidic NaF-AlF₃ melts, the relative contents of the Al-F entities have been changed greatly. It is thought that the relative contents of the complex ions are also greatly influenced by the temperature.

The primary aluminum industry has achieved good progress over the past decade in reducing GHG emissions associated with metal production. The reductions have been tracked through well documented protocols for the measurement of GHGs associated with production processes as well as established inventory accounting methodologies, vetted by stakeholders from within and outside the industry. These protocols and inventory methodologies are currently in the process of being updated to reflect new findings and changes in the industry over the past decade, to further enhance the accuracy and robustness of GHG accounting for the aluminum industry. This paper discusses the revisions being considered and the factors driving the changes.

Ventilation in process buildings is key to proper smelter function. Correctly engineered systems to evacuate surplus thermal energy from process areas and allow optimized rates of air change are essential, will assure the good functioning for the lifecycle of the process and allow the demonstration of conformity with occupational hygiene standards. Computational fluid dynamic simulations can demonstrate to end users and assist engineers, coupled with traditional calculations and physical modeling, in the optimization of mill ventilation reducing total installed costs while assuring that the proper solution is in place for the complete lifecycle of the process equipment.

Aluminium Bahrain (Alba) is one of the largest producers of primary high quality aluminium in the world, and continues to consider further expansions such as the planned new line 6. In parallel the amperage on the existing AP30 pot lines 4 and 5 will be increased further.A vary typical bottleneck in the amperage creep projects concerns limitations on gas flow and temperature to the existing gas treatment centers (GTCs). Cooling can be provided by adding dilution air, or water injection, but in both cases additional scaling, HF emissions and higher costs are expected, as well as the potential for reduced lifetime of filter bags due to increased hydrolysis.A new way to consider is to install heat exchangers that are integrated into each compartment in the existing GTCs (IHEXs) to cool the potgas. Stable heat transfer and pressure drop, and successful avoidance of scaling are demonstrated. The performance is compared to the HEX data collected for 26 months at Alcoa Mosjøen.

Fluidization is an engineering unit operation that occurs when a fluid (liquid or gas) ascends through a bed of particles, and these particles get a velocity of minimum fluidization V _mf enough to stay in suspension, but without carrying them in the ascending flow. As from this moment the powder behaves as liquid at boiling point, hence the term “fluidization”. This operation is widely used in the aluminum smelter processes, for gas dry scrubbing (mass transfer) and in a modern plant for continuous alumina pot feeding (particles’ momentum transfer). The understanding of the alumina fluoride rheology is of vital importance in the design of fluidized beds for gas treatment and fluidized pipelines for pot feeding.This paper shows the results of the experimental and theoretical values of the minimum and full fluidization velocities for the alumina fluoride used to project the state of the art round non-metallic air-fluidized conveyor of multiples outlets.

In the aluminium industry today, smelters often have to rely on more than one alumina supplier. This creates diversity in the properties of smelter grade alumina (SGA). A method has been developed to compare the HF formation from aluminas containing different amounts of water. The water content of the different aluminas was determined by loss on ignition tests (LOI) and thermal gravimetric analysis (TGA). Further, the aluminas were added to a cryolitic melt kept in a gas tight furnace with a constant nitrogen flow rate. The HF concentration in the off gas during the alumina additions was measured in-situ using a tunable diode laser. A correlation between the quantity of water found from LOI characterisation and the amount of HF formed has been found. It was also found that in this laboratory setup, all types of water contribute to HF formation; structural hydroxyl, physisorbed and chemisorbed water.

‘Potroom dust’ comprises one of the major sources of particulate emissions from a smelter to the environment. With regulatory emission limits for particulates continually tightening, there is a need for smelters to understand the sources and pathways by which dust is generated in a potroom. Only armed with this understanding can smelters develop targeted strategies to counter these emissions. Methodologies to sample and analyse the composition of potroom dust (both settled on surfaces and airborne) have been applied in four smelters. By taking samples across a range of potroom locations and elevations, an overall compositional picture of dust can be built and visualised for any potroom. In general, settled dust is dominated by cover material and alumina — the role of each, however, is influenced by the granulometry of cover and how alumina is delivered to the pot. In contrast, airborne dust in a potroom is typically dominated by bath-related compounds.

The effect of alumina feeding and pot suction rate on the amount and composition of fine particles in raw gases has been investigated. Particle size distribution of ultra-fines (Di < 10 μm) were measured in real time and the chemical composition of particle size groups were analyzed. Mass distribution of dust in fumes from cells under different operational condition were calculated from density estimates based on measured currents which again were converted to particle number impacts and compared to weighted samples. EDS analysis and HR ICP-MS revealed a significant increase in contaminant level for particles with a Di > 0.75 μm. The findings indicate that particles with Di < 1.2 μm consist mainly of quenched bath fumes, NaAlF₄, Na₅Al₃F₁₄, partly converted to Na₃AlF₆ and A1₂O₃. Particles with Di > 1.2 μm exhibit significant levels of contaminants, presumably entrained particles from the combustion of anode carbon and alumina feed.

A mathematical model of magnetohydrodynamic (MHD) effects in an aluminium cell using numerical approximation of a finite element method is presented. The model predicts the current distribution in the cell and calculates the Lorentz force from the external magnetic field in molten metal for cathode blocks with different surface inclinations.The findings indicated that the cathode surface inclinations have significant influence on cathode current density and Lorentz field distribution in the molten metal. The results establish a trend for the current density and associated MHD force distributions with increase in cathode inclination angle, φ. It has been found that cathode with φ = 5° inclination could decrease 16 to 20% of Lorentz force in the molten metal.

Electromagnetic forces in the electrolyte and metal pad region of aluminum reduction cells affect the metal/electrolyte flow pattern and hence the cell performance, indicated by current efficiency and specific energy consumption. Numerical simulation has become an effective tool for analyzing such complex physics. In this paper, an electromagnetic and MHD study conducted for an 86 kA end-to-end potline is described. A detailed three-dimensional electromagnetic model was built in commercial ANSYS software package and steady state MHD (velocities and metal heave) in the cell were computed using CFX software. Magnetic field from the model was validated with the plant measurements. Various busbar configurations were analyzed using the developed model. The results show that new magnetic compensation designs effectively improve the magnetic field, the metal flow profile and the metal heave, thereby providing conditions for improving cell performance.

In this paper, a coupled modeling algorithm of electro-magnetic field of reduction cells has been systematically introduced. With this algorithm, magnetic fields of cells at different locations in the potline and under different potline status are computed. It is found that Bx pattern in the cells is generally identical for cells at different locations, while their By and Bz vary both in distribution and in values. With adjacent cell being bypassed, US-bypassed cell has bigger adverse influence on the operating cell than that from the DS-bypassed cell. Entry cells are more stable than those exit cells. If one cell is bypassed, its influence on non-adjacent operating cells decreases drastically with operating cells standing between. Of all factors on cell stability, Bz pattern and |Bz|_ave values play the biggest role.

A finite element model has been developed to examine the electromagnetic field and interface wave of electrolyte/aluminum melt in aluminum reduction cell with the novel cathode structure. The edge-based method is used to solve the Maxwell equations. The results show that the current density distribution in the novel cathode structure aluminum reduction cell becomes more uniform than the traditional cells, weak horizontal current appears on the convex surface, and weakened the longitudinal waves of molten aluminum. The voltage drop of the whole novel aluminum reduction cell has reduced. The result shows that the movement of molten aluminum affected by the electromagnetic force dominates and two reverse eddies in horizontal plane arise in aluminum reduction cell. The velocity and amplitude of molten aluminum wave reduce in the novel cathode structure aluminum reduction cell.

As the principal character of flow pattern, the vortex distribution plays a dominant role in the flow behavior of aluminum reduction cells, thereby affecting the cell performance. Based on the commercial CFD software CFX12, the method of vorticity and swirling strength was introduced to analyze vortex structures of the bath and metal phases quantificationally in a 300 kA cell, in which both the influences of electromagnetic forces (EMFs) and gas bubbles were included. Research results prove that, compared with velocity vector distribution and streamline picture, it can provide more flow field information with the above method, which may help to the optimization of alumina feeding points configuration. Vortexes usually occur as reverse symmetrical pairs. The single factor comparative study shows that the EMFs tend to trigger large vortexes near the upstream side, while gas bubbles mainly stir the bath and generate small ones around anodes.

A phenomenological model for the creation and transport of anodic gas bubbles in Hall-Héroult cells is presented. Due to the large variation in length scales and bubble topology, a multiscale approach is introduced in which molecular gas is assumed to be formed as supersaturated CO₂ in the electrolyte. This paper describes models and constitutive relations that are intended for the simulation of anodic bubbles, ranging from the generation of molecular gas species through Faraday’s law and subsequent bubble nucleation, to the evolution of macroscopic bubbles by means of a Volume of Fluid (VOF) model. The coupling between macro- and micro scales is performed by means of a population balance. The complete model is implemented in ANSYS FLUENT.The model is applied to a 2D-cross section of a lab scale electrolysis cell, showing that essential properties are well represented by the proposed approach. Finally, the influence of Lorentz forces on the global bubble behaviour is investigated.

Gas generated beneath anodes in aluminum electrolytic cells play an important role for the circulation of the bath, alumina mixing, and heat balance. Those bubbles cause an extra voltage drop, which is strongly affected by the amount and shape of the bubbles beneath anodes. Consequently, understanding the dynamic behavior of bubbles in aluminum electrolytic cells has been a major research focus worldwide in recent decades.This paper presents a numerical investigation of the motion of a single bubble beneath an anode. Using a 2-dimensional geometry of part of a real cell, the motion of different sized bubbles has been simulated. It was found that the bubble size affects bubbling dynamics significantly as is measured by bubble shape, sliding velocity beneath anodes and bubble induced turbulence. Simulations have been also conducted using an air-water system to check its relevance to the CO₂-cryolite system.

Primary aluminium is produced increasingly in regions where there is a scarce supply of clean and fresh water. A self sustainable, secure supply of fresh water is of strategic importance for aluminum smelters. Desalination plants can be installed in combination with gas-fired power plants, and it is shown that part of the natural gas consumed for production of water in the desalination process can be replaced with waste heat from the aluminium smelter pot gas. Besides, installation of heat exchangers allows a significant downsizing of Gas Treatment Centers as well as improved control of stack fluoride emissions. It is shown that a compact, robust double-effect desalination plant can provide the water required during predicted variations in water consumption and profitably use wasted heat for a typical AP40 smelter. The corresponding calculated cost of water is comparable to the cost of water available commercially.

With the increase of the cell capacity, the busbar length, the current load in each busbar and the magnetic field intensity around the cell are all increasing consequently, so are the electromagnetic forces on each busbar and the thermoelectric stress inside them. As a result, big displacements occur on busbars and even worse, the insulation bricks are crushed by busbar movement. Displacements of busbars lead to deformation of flexes, which may be detrimental to cell life. The displacement of the longest and highest-current branch is taken as study object, its displacement and stress status are studied systematically.

The mechanical performance of pot-to-pot busbars is intimately linked to the temperature and thermal expansion of conductors. With amperage creep, busbars are typically running hotter than they were at start-up, so that adequate temperature fields for both standard and bypass conditions must be considered to accurately represent the thermal stresses acting over the system.To assist smelters to evaluate the performances of busbars systems under realistic operating conditions, a methodology was developed using ANSYS™-based numerical simulation, where the temperature field obtained from a thermal-electrical model is applied as a load to a thermal-mechanical model. The bolted connections at the shunting-clamping stations, the weld plates and the contact mechanics between bars are taken into account explicitly.A test case based on a demonstration busbar system is presented and the typical impact of line current and selected operational procedures on thermal-mechanical performance and reliability of specific design features is discussed.

The key to the chemical reaction necessary to convert alumina to metallic aluminium is the running of an electrical current through the cryolite/alumina mixture. The process requires the use of direct current, only around 4 volts but the amperage is very high, generally in the range of 180,000 to 350,000 amperes or more. In the meantime, various interventions are required on the electrolysis cells to complete the smelting process: handling of wasted and new anode, crust breaking, alumina feeding…, interventions mainly performed by the Pot Tending Machine (PTM), electrically connected to the ground.Thus contact with electricity while performing on the potlines may result in hazardous situation such as short circuit of the Pot Tending Machine and/or serious and fatal injuries for the operator (electrocution due to high voltage up to 2,000 volts). Hence the importance of the electrical insulation of the driver’s cabin, the tools trolley and the tools themselves to avoid often irreparable situations.To prevent such risks and above all to make the work environment safer, ECL™ designed an efficient device able to monitor the insulation level to earth and giving an audible and visual indication of abnormally low insulation values: the CANDI™ system solution.

Modern smelters have made the reduction process efficiency and safety a key issue: produce more, faster in a safer environment. By designing and developing highly technical automated machines, equipment suppliers greatly help and support smelters in their objective. However it must be acknowledged that despite such innovation, human remains at the very heart of any operation (reduction process, operations on anode handling in the furnace area or rodding shop) and has a significant impact on it.To avoid production losses, reduce maintenance cost and increase safety reflexes of the crane operators in case of emergency, ECL™ has recently endowed its PTM simulator with some new revolutionary functions. The operator, facing a double screen on which a 3D virtual environment is generated, will be now equipped with some 3D glasses putting him in a total virtual reality (Cabin rotation, cranes translations).Well trained, the operator will fully contribute to improve production and increase safely of the smelter.

A potline open circuit can be a dangerous and catastrophic event. It results in a high power DC arc, which can not extinguish itself unless the conversion substation is tripped. It can escalate into an explosion: the arc energy can injure any operators in the vicinity or can damage not only the equipment in question but potentially anything within proximity. The consequences can include freezing of the potline.To manage this risk, the potline must be protected against the danger of open circuit fault. A dedicated system is required to provide effective protection: quick tripping of the rectifying groups is triggered when the open circuit trend is detected. In order to avoid inappropriate potline switching off, the protection system settings must always be optimized according to the operating conditions (potline amperage, potline restart after shutdown, number of stopped pots, etc.).An overview of the potline open circuit phenomena is explained.

Discrete logistics studies has proven to be a low cost tool to evaluate and implement technologies and lower the risk of investments into large scale infrastructural projects. So far this tools have not been used much with similar complexity as in other industries in order to evaluate design issues, feasibility questions and bankability. This paper describes how simulation tools do have an impact on capex and opex. What effect simulation has on optimizing interaction between smelter units and processes for additional cost savings. Finally how the use of simulation tools help to achieve “lean thinking” in new smelters or upgrades while at the same time lowering the risk of such innovations.

Extended electrical power interruptions often result in the shutdown and restart of aluminum cells in potlines. Cooling cells to ambient temperature causes irreversible and non-repairable damage to the carbon cathode lining, and ultimately causes the formation of numerous, often deep, cooling cracks on the surface of cathode blocks and in the seams between blocks and ultimately shorten potlife. It had been proposed that these cracks are caused because the strain setup by thermal gradients in the cooling cathode lining exceeds the strain capacity of the cathode, but heretofore there has been no supporting evidence to support this hypothesis.New ANSYS® based thermal cooling models, (2D+ full cell slice model, 3D full side slice model and a 3D full cell quarter) were developed to determine the cathode cooling rates, the differences in the temperature gradients and the resultant stress from cooling cathodes for 24 to 48 hours. The results indicate significant temperature gradients and corresponding stress develop during cooling to cause cracking of the cathode blocks. Reducing the aluminum metal level in cells during cooling was found to reduce the level of stress and thus reduce, if not eliminate the cathode surface cracks.

The modern primary aluminium industry is continuously aiming to reduce the cell energy consumption and the harmful cell emission rates. In order to optimize both aspects, a comprehensive understanding and prediction of the electrolysis cell mass and energy balance must be obtained.Traditionally, many cell heat balance models have presented limited considerations on the mass balance, reactions above the cavity crust and cell duct flow.The thermal balance model presented in this paper is entirely based on the first law of thermodynamics. The extended cell control volume that includes the hooded cell space is adopted. This new approach allows automatic accounting for important exothermic reactions and the study of the impact of duct gas flow rate on the energy balance.A user-friendly software tool for studying the cell energy balance was developed. The new modeling tool is applied to assess the mass and energy consumption rates of different cell technologies.

Current efficiency is one of the most important technical and economic parameters. Current efficiency loss is due to dissolved aluminum reacting with the anode bubbles by the back reaction, which is assumed to be responsible for the largest part of current efficiency loss in Hall-Héroult aluminum reduction cells. The magnetichydrodynamics flow in cells can be seen as a gas-liquid-liquid flow by neglecting the mina effect of alumina particles. An current efficiency predictive model (CEPM) was developed based on multiphase multicomponent flow. The model takes the flow in cells as a three-phase(the bath, the metal, and the anode bubbles) and multicomponent problem(the bath phase: bath species and dissolved Al species; the anode-bubble phase:CO₂ and CO), which is able to incorporate the mechanism of current efficiency loss in cells. The model was calibrated by a 160kA cell and validated by a 300kA cell. This study provides a new approach for predicting current efficiency of aluminum reduction cells.

Continuous measurement of individual anode currents in Hall-Héroult cells is now becoming practical. It has the advantage of early warning of anode effects and possibly improvements in current efficiency and operation (e.g. warning of anode burn-off). The paper describes the approach of Wireless Industrial Technologies which entails a “master-slave” arrangement with a slave measuring the magnetic field produced by the current in each anode rod each second and the masters wirelessly communicating the data to a computer. With this system there is no direct contact with the anode rods and thereby no interference with normal pot operations such as when changing anodes. Such a system has been under test at a smelter in the USA since December, 2010. A second smelter will be conducting tests of the system by the time of the Orlando conference. Experience with this system is described and projections made concerning potential economic benefit.

Since the introduction of prebaked anodes technology in Hall-Héroult process, anode setting has become one of the routine work practices. As all anodes in different parts of the cell are changed in turn at short regular intervals, the operation is always subject to a different degree of disturbances. This paper presents a dynamic thermal model that can be used to simulate the impact of anode setting on the local thermal balance and hence the overall operating condition by incorporating individual anode current signals as model inputs. This is done by discretizing the bath into multiple subsystems based on the position of each anode. The model can predict the local thermal conditions during the increase of current pick up of a newly replaced anode when based on online measurements of current distribution. A model incorporated with anode current distribution as model inputs can be employed as a foundation for future development of an online fault diagnostic system to help isolating other disturbances, hence improve early detection of impending abnormal conditions.

Compared with the traditional cathode structure cell, the new cathode structure cell can restrain the level fluctuations of aluminum liquid, effectively reduce polar distance and decrease cell voltage, it makes greatly electricity saving into reality. In this paper, using cold water model experiment based on principle of similitude to study the level fluctuations by anode gas disturbance, and investigate the rules of level fluctuations in new cathode structure electrolytic cell. Numerical simulation of the anode structure with Fluent was also carried out. Simulation results are basically consistent with experimental results, which can verify possibilities of using Fluent to investigate fluctuations in the interface of cell. According to the analysis of experimental data, the empirical formula of amplitude are obtained by using dimensional analysis, which are associated to a variety of material factors, operating factors, equipment factors. After the theoretical analysis, Dimensionless equation is in good agreement with experimental results.

Energy saving receives more and more attention because of high energy price and environment requirement. The flow field and interface wave of new structure cell by Chaclo were studied by ANSYS and CFX combination. The results show that the maximum velocity of traditional cells is 26.7 cm/s and the maximum velocity of new structure cell is 21.2 cm/s. The maximum velocity is reduced. The interface wave of traditional cells is between −2.19cm and 3.41cm and that of new structure cell is between −1.15cm and 2.50cm. The interface wave is weakened by 34.82%. The industrial practice shows that the anode-cathode distance of new structure cell can be reduced without current efficiency loss in comparison with traditional cells.

In this work full scale DC casting trials of 6xxx alloy were performed. The purpose of the trials was to study the effect of the grain refiner amount on the critical casting speed at which hot tearing occurs during DC casting of extrusion ingots. Four addition rates of grain refiner were used. For each amount of grain refiner the speed of casting was increased step by step after each half meter of casting until hot tears formed in the centre of the ingots. Two alloys, AA6060 and AA6082, and one diameter, Ø203mm (8”) were investigated. The effect of water amount on centre cracking was also investigated. The results have shown that the critical casting speed for centre cracking is highly dependent on the grain refiner addition level. Even though no further grain refiner effect could be observed in the trials high addition rates did still influence the critical casting speed. The effect of water amount on centre cracking was not significant.

Grain refiners are currently used in casting aluminum alloys to reduce the grain size and to produce equiaxed grains during solidification of the alloys. Using inoculants to refine grains makes alloys castable but produces several disadvantages, including particle agglomerates, local defects, and impurities. In contrast, ultrasonic vibrations can be used in the place of grain refiners to refine grains without the disadvantages of using inoculants. In this study, high intensity ultrasonic vibrations were applied during solidification of pure aluminum. The grains of pure aluminum treated using ultrasonic vibrations were compared to the grains obtained using the TiB₂ grain refiner. It was found that the grain size in the pure aluminum ingots subjected to ultrasonic vibrations was comparable to those with the addition of grain refiners.

The microstructure changes using the ultrasonic vibration process method and Al-P refiner on permanent mold castings of hypereutectic aluminum alloy (Al-20Si) were studied using optical microscopy. The Al-P refiner refined the primary silicon phase from a large polyhedral shape to a smaller polyhedral shape, but had no effects on the morphology of the eutectic silicon phase. However, in samples subjected to ultrasonic vibration during the solidification process, both primary and eutectic silicon phases were significantly refined and modified respectively. Furthermore, the aluminum phase was also significantly changed. Small polyhedral silicon particles and globular aluminum grains were formed in the region near the probe (zone one). In the region far away from the probe (zone two), the primary silicon refined as in zone one, while the partly eutectic phase changed to globular alpha aluminum phase and polyhedral silicon phase.

In this publication we report on our efforts to develop a mathematical model and the necessary material database that allow predicting physical and material property changes that occur in aluminum casting alloys in response to precipitation-hardening heat treatment. We use the commercially available finite element software ABAQUS and an extensive database that was developed specifically for the aluminum alloy under consideration — namely, A356.2 alloy. The model produces multiple outputs at each node including the thermal history of the component that develop in the component and mechanical properties.

An aluminium casthouse casts aluminium in charges (or drops). These charges are made to particular customers’ ordered chemistry specification. The ability for a casthouse to accurately and consistently produce charges inside the customers’ specification is crucial for productivity. In addition, it is important that a casthouse can accurately and consistently measure the real composition of each charge.In this paper the sources of uncertainty in the chemistry are classified and discussed. The use of a model to study sensitivities on the predicted process capability (Cpk) from changes in charging accuracy, conditions during analysis, sampling and adjustment is demonstrated. The model can be used as a tool to identify improvement potentials.

The frozen mold that is fabricated by refrigerating the mixture of sand and water has many advantages to improve the working environments such as noise, vibration, dust and bad smell. The fluidity might be the key issue to spreading this technique to light metals such as aluminum and magnesium because a frozen mold has the possibility to accelerate solidification due to its large cooling ability. In this study, the fluidity of an aluminum alloy (AC4CH) cast in the frozen mold, and the effect of water content of frozen mold on the fluidity was investigated. It is revealed that the AC4CH aluminum alloy has better fluidity against the frozen mold rather than the conventional green sand mold. The flow length of aluminum alloy cast into the frozen mold was influenced by the water content of frozen mold, and increased with decrease in the water content. The good fluidity can be achieved by the mold with the low temperature decrease property.

In this paper, cast house operation is considered as a true example of a Flexible Manufacturing System (FMS), where a target product mix is achieved by adapting both process parameters and production plans, respectively. The examples presented here were initiated by challenging cast house operation situations. The results derived from the simulation scenarios were used to propose mitigating measures and to corroborate suggested solutions. From the components of the simulation tool-set, further models are built. As is often required, these models can be configured and applied to, among others, cast house design, production planning and operations decision support. Moreover, they can be used for operator training.In-depth knowledge of cast house operations and dynamic process modeling has been turned to a practical engineering tool which is regularly used by Bechtel’s Mining & Metals “Center of Excellence” (COE) group to deliver recommendations and results to clients in global aluminum smelter projects.

It is well known that ultrasonic melt treatment (UST) provides many benefits to casting processing, especially for the refinement or modification of as-cast structure. There is a lack for systematic studies on Al-Si alloys, although a number of reports are available on hypo-eutectic A356-type and hyper-eutectic (18–24 wt% Si) alloys, showing primary Al or Si refinement. In this paper, the effect of UST on the formation of microstructure was systematically analyzed in hypo-eutectic, near-eutectic and hyper-eutectic Al-Si alloys, including commercial piston alloys. The results show that UST usually results in the refinement of grains and primary Si particles when it is applied in a proper temperature range, while ultrasonic treatment during the whole solidification processing leads to coarsening effect on eutectic Si phase or primary Si particles.

The benefits of accurate measurement of furnace heel and full furnace weights are well accepted in terms of increasing % right first time batching, increasing productivity and eliminating short casts however the practical realization of a robust system has been problematic. The development of the BatchPilot system, which has overcome these difficulties, is described. To date 47 systems are in operation in 20 casthouses world wide and the most recent innovations include a fully automated weighing capability and down line integration of the output data into the customer management data network.

Fives Solios have developed an innovative new generation electromagnetic metal moving system called GENIOS that can be incorporated within new installations or retrofitted to existing furnaces. It can be fitted simply and safely to a wide range of furnace types using a patented modular interface and mounting concept.The prototype system is being trialed on a 70 tonne capacity static holding furnace at a large modern re — melting facility in Europe. In this particular case, the system is configured to stir, aid silicon dissolution and transfer to a dedicated continuous casting machine. The trials are in progress and expected to be completed during 2011.This paper will give an overview of the development of the concept and technology. It will also include a brief review of the performance of the prototype and general operational experiences together with comparisons with traditional technology.

Low-temperature Oxyfuel technology provides lower peak flame temperatures and a more uniform heat flux and temperature profile in the cast house furnace. The objectives with the technology are to improve melt rates, save energy, reduce dross formation and to reduce NOx and CO₂ emissions. The paper will discuss operational results, process optimizations and economy from installations in reverberatory melting furnaces, mixing furnaces and tiltable rotary furnaces. The theory behind the technology will be described including reference to CFD simulations and laboratory testing. Low-temperature Oxyfuel is used by a number of aluminium producers including Hydro Aluminium, Sapa Heat Transfer AB, Stena Aluminium and others.

Over the past several years, many aluminum processors in North America have used unique, inherently non-wetting, non-reactive, micro-porous refractory products from Westmoreland Advanced Materials, Inc. to line their melting and holding furnaces, as well as their molten metal transport systems. These manufacturers have experienced significant energy and maintenance cost savings through the use of this unique refractory technology. A review of the technology that was used to develop these unique refractory products, along with specific examples of the energy and maintenance cost savings from several customers are presented.

Deterioration of metal quality caused by contamination (e.g. coatings) is an issue in remelting of aluminium scrap. Therefore molten metal quality from remelting sheet material with and without coating is compared. In the experiments the crucibles are placed inside a resistance furnace to ensure that the charges are melted under the same conditions at the same time, measuring temperature and hydrogen. The melts was subjected to (i) settling overnight (ii) blowing air through a porous plug for 2.5 min to generate oxides (iii) settle overnight and adding turnings and (iv) adding carbon. The bifilm index is used as a measure of metal quality. The results show a statistically significant difference in the quality of the samples comparing coated and non-coated for all the melt treatments (i) – (iv), even if the charge material only contained approximately 0.4 % coat.

In recent years oxy-fuel combustion has become an increasingly attractive alternative as a heating source when melting aluminium. A newly developed Low Temperature Oxy-fuel burner from Linde Gas was investigated and compared to a conventional cold air-fuel burner in an instrumented pilot scale furnace. Measurements and heating trials of aluminium samples were done for four different case studies. 3-dimensional CFD models using the commercial software package ANSYS Fluent were developed to attain additional knowledge and to demonstrate CFD as a viable tool to model aluminium melting furnaces. Good agreement was found between the numerical models and the measurements where the difference in heat transfer between the two burner technologies was clearly demonstrated.

Cast house operations involving molten aluminum processing and furnace charging result in dross generation. This undesirable residue is composed mainly of metallic aluminum and oxides, and engenders costs exceeding 1000 US$ per MT of dross.Considering that no batch-to-batch measurements of dross weight are generally performed in the cast house, the task of dross reduction has always been complicated since the key process parameters and batch preparation practices affecting dross are not well known. As such, a new integrated weighing device was developed to continuously measure dross generation. The data generated will be used not only to follow-up on long-term furnace performance, with respect to dross generation, but also to complete a statistical analysis aimed at identifying key dross contributors.This paper describes the industrial dross weighing strategy that was developed, as well as the equipment that was installed in a Rio Tinto Alcan (RTA) cast house.

Reducing the formation of dross is important for a sound economic result in aluminium casthouses. In order to reduce the amount of dross the main drivers affecting the dross creation need to be identified. The first step towards identifying these drivers is to measure the dross amount on a charge basis. With a sufficiently large data set it is possible to apply statistical methods to correlate different process variables and the dross amounts. It is also possible to rank the different variables and identify those that are the most important for dross formation. In this paper multivariate statistical analysis is used to correlate the various input variables and dross formation on a charge basis and to identify the most important drivers for dross formation.Examples from two remelt extrusion ingot casthouses and a primary extrusion ingot casthouse are given and discussed.

Graphite filters have previously been employed based on petrol coke. Wetting between molten aluminium and graphite is studied. Al₃C₄ is formed at the interface between aluminium and graphite. In filtration of aluminium inclusions such as Al₃C₄ formed in the hall electrolysis are removed. Wetting between aluminium and Al₃C₄ (graphite) is determined in kinetic studies in the higher temperature range 1000–1200°C. The results are extrapolated down to temperatures employed in the industry around 700°C. The contact angle between aluminium and graphite decreases with time. It may be divided into three stages: removal of an oxide layer on aluminium, formation of Al₃C₄ at the interface, finally giving an equilibrium value for Al-Al₃C₄. This value is found to be around 126° at 700°C.

The major cost factor in the production of fused refining fluxes is raw materials and in particular the cost of potassium chloride, which because of its role in fertilizer production has been subject to large price increases in the period 2008–2009, having risen by more than 350%. As demand for potash for world food production and bio-fuels is increasing again with the recovery in the global economy further price rises are expected, with the price having risen already by 43% from November 2010 to July 2011. A program of work has been undertaken to develop an alternative flux based on a ternary system comprising magnesium chloride and potassium chloride; where the potassium chloride is partially replaced with sodium chloride. The results of a study of the thermodynamics together with laboratory measurement of viscosity, and differential thermal analysis are presented.

Removal of inclusions from aluminum is a critical step during the production of high quality aluminum alloys. Electromagnetic purification method for the removal of inclusions has been proposed to complement the existing methods, and many researchers have devoted a lot of effort to studying the electromagnetic inclusion removal process. It has been widely published that high frequency electromagnetic field is limited in the depth of penetration into the molten metal thereby rendering the separation method ineffective. The contribution of the high circulatory fluid flow associated with such high frequencies has also been reported to be negative. The effect of wall temperature to the electromagnetic inclusion removal process has also not been clearly established. This study presents new results that show that, fluid flow contributes greatly in the presence of lower wall temperature to remove particles during high frequency (63 kHz) EM purification of aluminum, contributing to overcoming skin depth effect in small and large crucibles.

Regular monitoring of the melt quality is employed in Aluminum cast house production where optimized processes and high quality are required. A well established method for the quantitative measurement of non-metallic inclusions is the LiMCA system. In this method, inclusions flowing together with the liquid Aluminium through a 300μm orifice of a submerged glass tube are detected due to their high electrical resistance. The LiMCA system can identify the size, typically in the range between 20μm and 300μm and number of particles in the liquid Aluminium. Increasing product quality standards have resulted in demands to monitor particles even smaller than 20μm. This paper reports results of a parametric study to assess the capability of the LiMCA system to monitor non-metallic inclusions in the particle size range of 10–20μm through changing the orifice hole size and by adjustment of the basic measurement parameters.

Current methods to quantify metal quality suffer from disadvantages in complexity, expense or response time. One method suggested to provide a real-time quantitative assessment of metal quality is the use of filtrate weight-time curves produced by filtering the metal through a porous disk filter. The slope and overall shape of this curve should indicate the level of inclusions present in the metal.Hydro Aluminium increasingly employs such methods to assess the quality of both Aluminium und Magnesium alloys. Several different types of crucible and porous disk filter are used. Due to the increasing importance of this assessment method a better understanding of the importance of variations in the permeability of the filter was considered necessary. This paper describes a device to measure the permeability of the filter discs. It also gives details of trials conducted to quantify the effect of variations in filter permeability on the filtrate weight — time curves.

Impurity control in the production of Al alloys is very important for achieving desired alloy properties. There has been an increasing impurity concentration (particularly nickel and vanadium) in the coke used in the primary Al production which ends up in the Al alloys. V can be removed in the casthouse through boron treatment. Ni, however, is a non-reactive element and difficult to be remove. There is currently no technique available in the casthouse to remove Ni. The current paper describes an exploratory study of Ni removal from Al melt. A literature review on the available techniques for the removal of Ni impurity from Al melt was carried out; followed by a systematic thermodynamic analysis of various Al-Ni-X systems for possible formation of Ni-containing phases in Al melt. Laboratory experiments were carried out to test the possible systems identified from the thermodynamic analysis.

The surface quality of as-cast strip is a key factor in the production of strips produced by Horizontal Single Belt Strip Casting process (HSBC). Aluminum alloys were cast on an HSBC simulator, using different casting atmospheres at meniscus region, including preheated air and pure oxygen. The strip’s bottom surface was analyzed in order to evaluate the effect of casting atmosphere on strip surface quality. The preheated air or oxygen was injected into the hollowed backwall refractory and was released through the orifices on the bottom of the refractory, close to the back-wall meniscus region. The purpose was to flush out the ambient air entrained above the moving substrate. The possibility of eliminating surface defects caused by air pockets’ on the strip’s bottom surface and improving surface quality by controlling the casting atmosphere in the meniscus region were confirmed. The surface profiles of the sand-blasted substrates and those of the related strips were analyzed using 3D Profilometry. The interfacial heat fluxes through using an oxygen atmosphere at the upstream meniscus were also enhanced greatly, as compared to the casting process using a graphite coating on the substrate. A novel way for improving strip surface quality with high attendant interfacial heat fluxes is now proposed for the HSBC process.

Surface defects formation and their effects on the surface quality of aluminum direct-chill cast sheet ingots have been investigated by metallographic examinations and mathematical modeling. The influence of process variables such as alloy composition, casting speed and lubricant on the surface defects especially extruded surface segregation layer has been determined. The metallographic study for collected samples of plant trials involved visual, micro-examinations and macrosegregation analysis. A 2-D mathematical model has been developed to characterize the thermal, solidification, interdendritic strain and macrosegregation distributions. Also, the model contained a new approach to evaluate qualitatively the macrosegregation formed during dendritic solidification. The model predications were compared to measurements from collected samples to verify the model, where a good agreement was obtained. The model predications illustrate that all the process variables tested have an observed effect on the surface quality by different levels. The mathematical analysis of strain fields as well as metallographic study has been used to explain and discuss the effects of different process variables on the surface quality.

The thickening of the bottom part of DC cast rolling slabs, butt-swell, is a well known problem in the aluminium business. The slabs are scalped, normally in the rolling plant, prior to rolling to a absolute rectangular shape. The rolling mill therefore prefers rolling slabs with geometry close to rectangular from the casthouse. Due to geometry specifications from the rolling mills the supplier casthouse has to cut off the bottom part of the slab before shipping. The bottom cut length is typically 0.3–0.6m (1–2’) depending on the thickness and casting speed.Extensive research has been done on the basic mechanisms of butt-swell and the phenomenon is today well understood. The thickening in the bottom is due to the absence of pull-in which is a thickness reduction phenomenon during the stationary phase of DC casting of rolling slabs. It is impossible to avoid butt-swell when using moulds with fixed geometry. To eliminate the butt-swell flexible moulds are developed. In this technology the mould shape is gradually changed during the initial stages of casting in such manner that the rolling slabs will be rectangular from start to end of cast.This technology has been in industrial use since 1997 within Hydro casthouses. In addition to eliminating the butt-swell this technology allows for a large degree of freedom when choosing casting speed. Conventional moulds are designed to give rectangular slabs for a given casting speed, while the technology described in this paper may be adapted to any relevant casting speed.This paper describes the basic principles behind the technology, a description of the equipment, and the operational experience so far.For 600mm thick ingots flexible moulds typically reduce the total scrap rate in the casthouse with more than 5% compared to conventional moulds with fixed geometry.

Stress relief treatment is often required prior to sawing aluminum DC cast products in order to prevent crack formation and significant safety concerns due to the presence of high residual stresses generated during casting. Numerical models have been developed to compute these residual stresses and yet have only been validated against measured surface distortions. In the present contribution, the variation in residual strains and stresses have been measured using neutron diffraction in two AA6063 grain-refined cylindrical billet sections cast at two casting speeds. The measured residual stresses compare favorably with the numerical model, in particular the depth at which the axial and hoop stresses change sign. Such results provide insight into the development of residual stresses within castings and show that the stored elastic energy varies linearly with the casting speed, at least within the range of speeds that correspond to production conditions.

On April 20, 2010, an explosion rocked the Deepwater Horizon in the Gulf of Mexico. Resulting in the deaths of 11 workers. Over 400,000 pages of evidence were collected during the investigation for the root cause of the explosion[5].“What emerges is stark and singular fact: crew members died and suffered terrible injuries because every one of the Horizon’s defenses failed on April 20. Some were deployed but did not work. Some were activated too late, after they had almost certainly been damaged by fire or explosions. Some were never deployed at all.[l]”Parallels with the aluminium industry standout when comparing the Deepwater Horizon disaster (e.g., violent explosions, damaged equipment, worker deaths and worker injuries). The list of aluminium industry catastrophes is not short: Binzhou Weiqiao Aluminum (Photo2), Reynolds Alabama, Alcan France, etc.Aluminium plants, just as deepwater oil rigs, value training and safety measures to prevent accidents from occurring. But, on April 20, 2010 every safety measure employed failed, could the safety measures employed in a casthouse to prevent a molten metal steam explosion fail too?

To clarify the mechanism of hot tearing in the ingot produced by direct chill (DC) casting, the mechanical properties and the deformation behaviors of pure Al and Al-4.5 mass% Cu alloys in the semi-solid state were investigated by a new tensile test method. The tensile strength and elongation on the Al-4.5 mass% Cu alloy decreased remarkably at the temperature above the solidus. And in situ observation, the healing by the liquid flow into the crack was observed at a high temperature range in the semi-solid state. Pure Al exhibited very high ductility until near the liquidus temperature. The deformation behaviors in the semisolid state of both alloys were classified into four stages based on their mechanical properties, fracture surface morphologies, and in situ observations on the tensile tests. The brittle temperature ranges in which hot tearing occurred in both alloys were determined. These data obtained from the tensile test in the semisolid state could be applied to several simulations.

Hot tear susceptibility in VDC casting is strongly affected by the chemical additions of alloys, hardeners and grain refiners. This paper assesses a few different approaches to reducing hot tearing in the cast house. Grain refinement is one commonly used approach, including dosing at cast start. Another technique is to control the alloy content, through the additions of Si, Mg, Mn or Fe which can influence the type and amount of intermetallics present during the final stages of solidification when hot tearing occurs. This paper summarizes experimental findings which assess the influence of additions on a hot tear rating, particularly in 6xxx series alloys. Strategies which could be used in the cast house are discussed. While changes to the bulk metal can have consequences for alloy specification and quality control, additions at cast start could be used to reduce scrap from hot tearing without changing the composition of the saleable product.

An adaptive controller for keeping a ball mill working stably and efficiently is proposed in this paper. The controller is based on fuzzy logic control strategy by developing a method of adjusting the quantification and proportion factors. The selection of these factors makes a big influence on the static and dynamic performances of the controller. This new control strategy is implemented in Albras Anode Plants. The controller program was developed with ladder language and runs on programmable logical controller (PLCs) from Allen Bradley. Anode plants are operating with ball mills which are being controlled by fuzzy controllers, and the noise, that is the control variable is working around the established operation point. The results demonstrate the effectiveness and viability of the system that hereafter will be implanted for other processes of the anode plant.

Anodes produced using under calcined coke (or Low Real Density Coke) are reported to have less and homogeneous reactivity of all anode components following baking, which results in lower carbon consumption and less carbon dust in pots. Increased butt thickness due to lower carbon consumption provides opportunity for amperage creep in Reduction lines. Aluminium Bahrain (Alba) has unique arrangement of an in-house coke calcining operation with carbon plants for anode manufacturing. This gives Alba an added advantage of lower fuel consumption in calciner on use of under calcined coke for anode production. Alba used this opportunity and a trial batch of under calcined coke was produced at calciner with lower Real Density of 2.04 g/cm3. Anodes manufactured using this under calcined coke was tested in a trial group of pots for 3-anode cycles. This paper discusses the quality of anodes produced using under calcined coke and their performance in pot rooms.

The first single line 60 tph green anode plant ever was successfully commissioned at the Qatalum smelter. This green anode plant was designed to fulfil the anode requirements of the 585,000 tpy metal capacity smelter.The single process line is based on the Rhodax® technology for dry mix preparation and the IMC® technology for the paste mixing/cooling already demonstrated at Sohar Aluminium at 36 tph capacity. For Qatalum, new equipment, including crusher, coke preheating screw, continuous paste mixer/cooler and vibrocompactor, had to be designed, optimized and fine tuned to suit the 60 tph production level without compromising the anode quality and the plant reliability.High capacity green anode plants contribute to lower the CAPEX of greenfield or brownfield smelter projects.This paper describes the technical challenges that were met to realize such high production capacity and summarizes the operation performance achieved during one year of industrial production.

ALCOA Lista has experienced a period with a very high number of anode problems, mainly occurring as spikes, hanging anode ends, leak in stud holes, vertical cracks and dusting. The anode problems hindered a planned amperage increase. A systematic plant audit conducted by R&D Carbon revealed clear root causes that were responsible for the anode problems. The plant management and operation team swiftly implemented the recommendations of the plant audit and subsequent plant optimization. The major actions included a mixer revamp and adaptations of recipe formulation and mixing conditions. Today, the number of anode problems is down to 20 per week (2.4 per week in potroom 3). The major actions are discussed in this document, which had a significant impact on the plant performance figures (current efficiency, carbon consumption, energy consumption and bubble noise) that eventually allowed a substantial increase of the line current from 120 to 128.5 kA.

The two long term trends in the aluminum industry that will have the most effect on anode quality requirements are scarcity of good quality calcined coke for anode production and the current creep by pot lines. In ALBA the pot rooms have gradually increased the line current to increase aluminium metal production. Therefore there was need to improve baked anode quality and net carbon consumption so that the butts thickness at increased line current will be maintained. In ALBA, for a given set of raw materials, baked anode density in the range of 1.580–1.585 g/cm3 was normal. With in-house research, baked anode density of 1.600–1.605 g/cm3 was achieved by optimization of ultra fine content in Ball Mill Product, along with other process parameters of Green Anode Plant. The paper discusses the work done on the optimization of the Paste Plant’s dry aggregate recipe & process parameters and results achieved over a period of one and half years.

At Lanzhou smelter, there are more than 11 mainly delayed coke suppliers. The range of calcined coke real density was between 1.99 and 2.06kg/cm3, the resistivity was 480 – 570µΩ.m, and the operating cost of rotary kiln was high due to the short life of tuyere nozzles and chamber lining. The apparent density of green anode was low and the deviation was ±0.05kg/cm3 because of variation in the recipe and process parameters. There was very much dust in the cells and the net carbon consumption was about 450kg/t.Al. By blending delayed coke, adjusting calcining process parameters and optimizing the recipe and process parameters of green anode manufacturing, the quality of calcined coke improved. The tuyere nozzles and chamber lining were not distinctly destroyed in the past 8 months, the quantity of dust in the cells has decreased, and the net carbon consumption has reduced to nearly 420 kg/t.Al. This paper describes the work done on the optimization of green anode processing and the results achieved in the past one year.

As part of the worldwide biggest greenfield project, the two open top anode bake furnaces of EMAL were started up in 2010 to reach an annual production capacity of 450’000 tons of baked anodes. Two furnaces are installed with 64 sections, 9 flues and 8 pits that are equipped with 4 fires each. An unprecedented combination of outstanding anode quality and furnace performance figures could be achieved. This document highlights the distribution of key anode properties, furnace productivity and energy consumption. Furnace design and operational challenges to reach today’s standards are discussed.

Over the past decades, emission control has consistently been a major issue for the developed, aluminium consuming world. Environmental facilities like Fume Treatment Centres have been retrofitted to paste plants and carbon bake furnaces throughout the world. The emerged countries have seen a great increase in aluminium consumption and for all greenfield smelters, the addition of FTC’s has been mandatory. Danieli Corns’s experience in FTC’s extends from retrofit projects in e.g. the EU and Australia up to LSTK projects in developing countries such as the Middle East and India. This article describes how existing FTC’s have performed over the past decades in terms of environmental performance and maintenance requirement. For recent projects, specific circumstances of execution in greenfield situations are discussed. In addition, developments in FTC technology and future prospects are presented.

Voerde Aluminium GmbH (Voerdal) is operating a 36 section Kaiser type furnace for the production of anodes since more than 40 years. Due to the continuous amperage incease in the potline, the baking furnace capacity had to be increased by 10% in the given boundary conditions of the furnace size and government permission for the maximum flow gas volumes and emissions.Voerdal and the system designer jointly developed new control strategies to ensure the boost of anode production. This was achieved mainly by implementation of new control modules which integrate the FTC (fume treatment centre) feedback values into the overall control strategy.This paper explains the functional principles of these control strategies and describes the implementation phases. Finally, it outlines the actual results achieved.

Conventional anode baking firing and control systems are composed of several mobile pieces of equipment with their own local controller to manage the high speed local tasks. Redundant central control units synchronize the actions of each local controller.A fast real time Ethernet network implementation allows simplifying the existing control system architecture: it uses only one real time central controller and remote Inputs/Outputs for each mobile piece of equipment.The robustness and reactivity of the control as well as the required safety loops are preserved. The maintenance and day to day operation are simplified.Furthermore, real time network and accurate time synchronisation between the pieces of equipment open new perspectives to improve the baking process management and to enhance safety.

As a baking furnace ages, cracks and openings develop in the furnace which allow outside air to enter. Unless proper corrective actions are implemented, gas consumption can increase, final baking temperatures can decrease, and baked anode properties can deteriorate. In this paper, methods are presented for improving the efficiency of fuel utilization for aging furnaces, and thereby lowering fuel consumption, while maintaining or improving anode finishing temperatures and anode properties.

The energy saving technologies for anode manufacturing have been developed and applied in the anode production processes in Jinan Aohai Carbon Products Corporation Ltd. The surplus heat from shaft calciners is recovered for heating pitch and mixer and power generation as well. The baking furnace structure and the lining materials have been improved so as to get reasonable anode occupation efficiency and less heat loss. The heating curves for anode baking are finely adjusted and controlled for completely burning of the volatiles in the green anodes for less energy input into the baking furnace. Based on the technology application mentioned above a great energy saving and benefit to the plant environment have been achieved in Aohai anode plants.

The petroleum refining industry has historically categorized petroleum cokes as fuel, anode, or needle grade cokes. The term “anode grade coke” has been used as a broad definition by the aluminum industry to describe delayed coke with a sponge structure containing relatively low levels of metals like vanadium (typically <400ppm) and low to moderate levels of sulfur (0.5–4.0%). These classifications are less relevant today due to the much wider range of cokes used in anode blends. This paper will present a review of the growing range of coke qualities used in anode blends. Shortages of traditional quality anode coke are driving calciners and anode producers to use cokes with a much wider range of properties. Cokes previously regarded as unsuitable for anode production are being used routinely in blends at varying levels and this trend will continue. Examples are given on how smelters are dealing with changing coke quality.

Calcined petroleum coke (CPC) is a major raw material for smelting anodes. The anode quality plays an important role in the smelter productivity and profitability. Since the beginning, the CPC from different Indian suppliers has been used in National Aluminium Company Ltd.This paper presents the quality of CPC from different sources and their influence on anode quality. Anode bench scale studies have also been carried out by blending CPC from different sources and assessment of anode quality.

The preparation of prebaked anodes from coal using solvent extraction technology was investigated. Several bituminous coals were extracted with methylnaphthalene-based solvent under pressurized nitrogen atmosphere at 653K, and ash-free and high purity coal extract (Hypercoal, HPC) was obtained. It was found that the HPC can be utilized as an additive for binder pitch of anode manufacturing; the HPC improves the coke yield of the pitch and reduces the ash content of the binder. It was also found that a suitable modified HPC was self-sinterable, and was successfully molded and carbonized without binder pitch to result of dense carbon specimen. These results suggest the possibility for coal-based raw materials for prebaked anodes

Laboratory scale anodes were manufactured with a fixed coke and six binder pitches having different primary quinoline insoluble (QI) between 9 and 22%. Binder matrices were also made for CO₂ and air reactivity tests. Three of them were commercial products and the others were made experimentally, and none of them contained mesophase. Softening point of these pitches was around 110°C. The pitch with the largest amount of primary QI showed higher coking value, and thus it gave higher bulk density of baked anode. The increase in bulk density improved compressive strength. Electrical resistivity, which decreased with increasing bulk density, was not deteriorated by the larger amount of primary QI in pitch. Despite the high QI content, no acceleration of oxidation in CO₂ and air was observed in the binder matrix tests. These results showed that the pitch with high primary QI is more favorable as a binder pitch for anode.

The increasing price of coke raw materials and a shortage in local supply for anode manufacture has presented a long term challenge for aluminum smelters with added cost into the metal product. The aim of this work is to search alternative carbon raw materials to replace part of traditional coke raw materials or technology to reduce the material costs for the prebaked anodes. Some calcined anthracite was selected as a starting material chemically pretreated to remove its impurities. The pretreated anthracite was added to the carbon mixtures, formed, and baked into the anode samples using the process used in the existing industry. The air-reactivity and anode consumption were tested. The anode samples were also characterized using XRD and SEM to investigate microstructure and inner pores. The results show that the anodes with anthracite additions of 10 – 20 wt. % are promising for potential application. In addition, ultrasound is found to reduce the anode consumption due to its effect on removing the CO₂ gas bubbles.

Anode construction is a challenging process for Søderberg Cells. In order to reestablish the full plant capacity at Alcoa Pocos de Caldas, located in the southern part of Brazil, it was necessary to develop a new process to bake anodes within the potrooms environment. Using reduced amperage as baking element and controlling the current passing through each of fifty stubs, it was possible to assembly new anodes with quality and proper condition for optimum cell operations. This paper describes the sequence of activities applied for bake-in of new Søderberg anodes, the techniques implemented to monitor and control the baking process and finally the outcome after pot start-up.

The cathode is a set of items with a high cost in the primary aluminum production, this set is usually composed of carbon materials, refractory and insulating materials, which have their basic raw materials extracted from nature. There is great concern about cathode performance, this with respect to cathode life and energy efficiency, several works have been performed in order to maximize the cathode life thereby avoiding costs and waste, more commonly known as SPL (spent pot lining) as well as an hazardous waste to the environment and has a high cost for recycling.In this paper, the main findings extracted from pot autopsies will be presented as an important methodology to maximize cathode life at Votorantim Metais (CBA).

Carbon products used in aluminium electrolysis pots are generally based on coal-tar pitch or resin binders. Coal tar pitch is considered by the new European chemicals legislation REACH (Registration, Evaluation, Authorization and Restriction of Chemicals) as very high concern product, and it is carcinogenic classified. Phenol, a typical component of resin binders used in carbon products, is also carcinogenic classified. In face of these hazards, solutions that guarantee a clean and safe environment for the workers have to be found. Last year a 100% clean ramming paste NeO2 has been introduced, based on a new binder type containing no CMR product (CMR: carcinogenic, mutagenic or toxic for reproduction) and no hazardous substance. This paste was fully anthracitic. Since then, Carbone Savoie made developments to complete its Green range with a 100% clean semi-graphitic grade of ramming paste, using the same type of binder and with a 100 % clean glue, which could be used at different locations in the pot. Characteristics of these new products will be presented.

The collector bar sealing is an important procedure for cathode construction. The material selection and the installation techniques have to be very well managed in order to obtain a high performance pot with low cathode voltage drop and long lifetime.A new cathode block-to collector bar sealing material has been developed in Novelis Ouro Preto, southern of Brazil, aiming to achieve better electrical resistance and handling during application. This material, so-called LRM2, contains iron powder instead of traditional carbonaceous paste.In this paper, a comprehensive study comparing the traditional carbonaceous with iron-powder gluing is presented. The collector bar-to cathode sealing showed that iron powder techniques do not show meaningful difference on pot voltage when compared with cast iron and can improve the handling procedures during operation.

Dry barrier mix (DBM) has been successfully tested as a replacement for barrier bricks in several reduction cell technology types and has been adopted as standard practice in all three of the Chinese cell technologies.DBM reacts with cathodic bath in-situ to form a glass-like barrier which retards the further penetration of bath components, protecting the lighter insulation from contact with the bath. Laboratory “cup tests” and plant trials show that silicate based DBM formulations are more effective than anorthite formulations or conventional refractory aggregates in formation of the glassy barriers. Cell bottom temperatures remain stable over the lifetime of the cell, indicating the barrier formation protects the insulating value. Cell autopsies show partial penetration of the DBM with barrier formation and preservation of the bottom portion of the DBM. Cell lining life is at least equivalent to that of brick barrier cells.

Volatile matter (VM) analysis of green petroleum coke is an important measurement for determining the calcination behavior and properties of calcined coke. Green cokes with high VM (>12%) are more difficult to calcine and result in a higher porosity and lower bulk density in calcined coke. This paper will review current methods for measuring the VM of green coke based on the ASTM quartz method, the platinum crucible method, and the macro thermo-gravimetric (TGA) method. Detailed experimental results comparing the quartz crucible and macro TGA methods are presented in the paper. When used in combination with a high speed rotor mill, automated TGA equipment offers significantly improved speed and precision, as well as the capability for simultaneous measurement of ash and moisture contents.

Physical properties of coke particles including particle shape and size distribution have direct effects on their packing density. In the present work, effects of particle shape and size distribution on vibrated bulk density (VBD) of dry coke samples have been investigated. Discrete Element Method (DEM) has also been used to simulate the vibration process. Results showed that the shape and size distribution of particles influence the bulk density of coke and these parameters can be used to describe the packing density of coke particles. In general, mixed samples provide higher VBD than mono-size samples and as the fraction of coarse particles increases vibrated bulk density increases. However, existence of 10 wt.% of fine particles to fill the pores between coarse particles is essential. Simulation results were also reasonably consistent with experimental data. Finally, it is noteworthy that a well-tailored DEM model is capable of predicting the particle rearrangement and density evolution during the vibration process.

Vibrated Bulk Density (VBD) of calcined petroleum coke is widely utilized as one measure of quality and is useful for quantifying binder demand in the anode production process of the aluminum reduction industry. ASTM D4292–10 is one of the methods used widely by the carbon and aluminum reduction industries to measure VBD. Recently the carbon producer and consumer industries have jointly worked together to increase the reliability and benefit of this method. Geopyc is a semi-automated device that potentially yields better precision compared to traditional vibrator device specified in D4292. This paper presents an innovative use of the Geopyc instrument in measuring VBD, the results of which correlate well with D4292; especially to the 28x48 Tyler Mesh size fraction. This novel sample preparation does not involve complicated roll crushing steps as specified in the ASTM method(s) and thus simplifies the method while improving the accuracy and precision.

Computed tomography has been used in recent years to gather information on carbon anodes which can be used to calibrate numerical models dedicated to simulate the anode forming process. To this end, samples with diameters varying from 50 mm up to 300 mm and cored from an industrial anode have been scanned in a Somatom Sensation 64. A correlation was established between the CT scan results and the apparent density. To validate the correlation, an extended campaign was performed on 50 mm diameter samples cored in 20 different anodes with the advantage of using possibly different raw materials. In addition to the CT scan results, the apparent and real densities have been experimentally measured to estimate the porosity level. Similarly to the apparent density, a correlation between the CT scans results and the porosity has been proposed.

Anode quality assessment has become largely focused on laboratory tests undertaken on anode core samples. This is important, giving valuable insight to many anode quality problems and their potential causes. Anode “structural integrity” is, however, a critical anode property that is not directly assessed by these traditional anode core tests. Structural integrity is best described as how well a baked anode has been made, as evidenced by the visual appearance of the anode structure. Several methods have been used previously to visually assess anode structures, including optical image analysis. While these methods can highlight individual structural detail and features, they are not well suited to assessing overall anode structural integrity. This paper will outline a simple method for assessing baked anode structural integrity that uses USB macroscopy to evaluate anode quality and diagnose problems.

The objective of the present work is to achieve a better understanding of anode thermal shock fracture in the early stage after an anode change in the electrolysis cell. In order to show the mechanisms leading to anode fracture and crack propagation, a thermo-mechanical model of the thermal shock experienced by an anode when it is positioned in the pot was developed. The model allows calculation of stresses and strains within the anode, as function of time. The time interval of the modelling lasts for 1 hour after the anode change.

Anode electrical resistance is more and more recognized as a key parameter for pot operation, as the carbon material itself contributes close to 50% of the anode assembly voltage drop. Factors such as raw materials, forming and baking conditions are sources of significant variation in anode properties, including anode resistance. Anode resistance will vary within an anode and between anode batches, causing voltage differences up to several tens of millivolts. The current method for resistivity measurement is based on core sampling of a small number of anodes in limited locations and may not be representative of the global anode resistance. The current study proposes a non destructive method that reproduces the current distribution in service and provides immediate results. Such results could be used to improve anode resistance and help potrooms cope with anode batch variability.

Increases in the vanadium and nickel content of anode grade coke in recent years have predictably affected smelter metal quality. This has now reached the point where some smelters struggle to meet traditional metal purity specifications. New metallurgical studies have shown that metal specifications for impurities such as vanadium and nickel may be unnecessarily restrictive.

Anti-oxidation coating for carbon anode in aluminum electrolysis was studied in this paper. Different compounds of the anti-oxidation coating had different effects on carbon anode. The results showed that hot weight loss rate of coated anode was lower 10–30% than that of uncovered anode. The compounds of the anti-oxidation coating were optimized by SEM and tests of hot weight loss. It was proved that the anti-oxidation coating had great inoxidizable effects on carbon anode, and it was no influence on normal aluminum electrolysis.

This paper continues of a review given in 1999 and resumes practices to treat the waste from used cathodes of the primary aluminium industry. The waste cathode lining consists of a carbon part and a refractory part. Spent potlining contains water-soluble fluorides and small amounts of leachable cyanides, and is therefore classified as hazardous.

Cathode materials used in aluminum reduction cell today are of porous structure. This work is aimed to have better control of the cathode quality through quantitatively analyzing the pore structure and its correlation to the penetrated sodium (metallic Na and NaF). The cathode samples were made of graphite aggregate and pitch, and formed with various pressures (12 – 36 MPa). Image analysis was applied to characterize their porous structures. XRD and SEM-EDS were used to analyze the penetrated sodium in the cathode samples. When the forming pressure was 20 MPa, the cathode density got to its maximum value (1.58 g/cm3) with the minimum total porosity (21.96 %) and the least pore number (549). When the forming pressure rose from 12 MPa to 36 MPa, the pore connectivity was from 9.81 % up to 37.95 % while the shape factor increased from 1.98 to 2.21 and the depth of sodium penetration became longer from 6 mm to 30 mm. In addition, ultrasound applied can reduce the penetrated sodium in the cathode.

The carbon cathode is considered as the main component of the aluminum reduction cell. It provides the electrical contact that is essential for electrolysis as a result of holding molten electrolytic bath together with aluminum. Hence, its performance is crucial in electrolysis process. X-ray microtomography was used to compare different virgin cathode materials, as well as those that had been used in laboratory-scale aluminum reduction cells. Results demonstrated significant differences in terms of bath penetration and metallic inclusions. X-ray microtomography was shown to be a powerful tool for 3-D characterization of cathode materials.

Creep of ramming paste was studied from ambient to operational temperature in order to characterize its mechanical behaviour as used in the peripheral joint of aluminium electrolysis cells. Two types of uniaxial creep test over a specified stress level were performed on two inch samples: tests at room temperature for samples baked at different temperatures and test at temperatures close to the sample baking temperature. It is concluded that at certain baking temperatures and given stress level, three types of creep, called primary, secondary and tertiary, take place successively. In addition, at lower baking temperatures (200 °C), the creep level is larger in comparison with creep at higher baking temperatures. Also, for specified baking temperature, creep strain obtained by high temperature testing is larger than creep strain obtained by room temperature testing. These results give new insights on the ramming paste behaviour in aluminium electrolysis cell.

Graphite cathode materials are nowadays used in aluminum reduction process where KF-AlF₃-based melts may serve as an alternative electrolyte. In this work, wetting angles of KF-AlF₃-based melts on graphite cathode materials were measured using a modified sessile drop method. A fresh drop of the melt was injected through a BN tube on to the samples surface, and then the wetting angles were photographed against time elapsed. It was found that the wetting angles on the full graphitic and graphitized cathode samples were larger than those on the semi-graphitic at 750 °C, and their values changed with varying alumina content (3–5 wt%), cryolite ratio (1.2–1.5) and time (0–20 min). The melt penetration profiles on the cross-sections of the melt-graphite interface after wetting tests were also inspected using SEM-EDS technique. In addition, ultrasound was introduced into the cathode through a stainless steel rod and its effect on the wetting of melts was investigated.

The fundamentals of formation of aluminum carbide were studied by aluminum-carbon diffusion couple experiment. The diffusion couples consisted of liquid aluminum and graphitized carbon, and the diffusion couple experiments were performed at temperatures 1000–1200°C in stagnant argon atmosphere. The formation of aluminum carbide layer at the solid-liquid interface was confirmed by X-ray diffraction and electron and optical microscopy. The kinetics of the formation of the carbide layer was investigated in detail and formation of carbide by solid-gas reactions is discussed.

Cathode wear has become one of the major challenges for the life time of high amperage aluminum reduction cells due to the use of graphitized cathodes. The fundamentals of the cathode wear are still a matter of debate, and a laboratory procedure for testing of cathode materials is desired. Here, we present a laboratory electrolysis cell, which has been designed for cathode wear tests of industrial cathode materials. The formation and transport of aluminum carbide have been considered to be an important factor for cathode wear, and the laboratory test cell was designed in such a way that the cathode is exposed directly to the electrolyte. Aluminum carbide formed at the cathode may dissolve directly into the electrolyte. Here we present the study of the cathode wear of a commercial high density graphitic material, where the influence of the cathode surface morphology, diffusion and hydrodynamics in the electrolyte, have been in focus. The cathode wear and the penetration of electrolyte into the cathode were investigated by optical and electron microscopy. The influence of current density, hydrodynamics and transport of carbide in the electrode are discussed in relation to the experimental results.

High quality graphite cathode carbon blocks require low resistivity, strong resistant erosion to molten salts and liquid aluminum in the aluminum electrolytic cells. High quality cathode materials can decrease cathode voltage and then reduce the power consumption, and improve service life of the cell. Applying hot mould technology under 40 MPa pressure, different amounts of petroleum coke in anthracite mixtures is graphitized in graphitizing furnace. By the X-ray diffraction parameters, density, compressive strength and resistivity drop are measured. The experimental results show that compressive strength and volume density of graphite blocks containing 30% of petroleum coke are 1.366 g/cm3 and 4.8 MPa, respectively, resistivity drop from 114µΩm to 13µΩm, mostly in accordance with block production requirements.

Electrolysis expansion of pitch, modified by furan, phenolic-aldehyde and epoxy, based TiB₂-C composite cathodes in [K₃AlF₆/Na₃AlF₆]-AlF₃-Al₂O₃, melts were investigated, and TGA was used to study dynamics of pyrolytic process about various modified pitch. The results show that, compared with electrolysis expansion of unmodified pitch based composite cathode, pitch modified by furan, phenolic-aldehyde and epoxy based composite cathodes all exhibit lower electrolysis expansion which are 1.61 %, 1.62 % and 1.68 % respectively. The maximum depressed amplitude can reach 13.77 %. Apparent activation energy (AAE) concerning pyrolysis process of pitch is related to electrolysis expansion of composite cathodes. The higher the AAE, the lower the electrolysis expansion, and the AAE of unmodified pitch is 47.21 kJ/mol, while the AAE of pitch modified by furan, phenolic-aldehyde, and epoxy are 66.25 kJ/mol, 57.07 kJ/mol and 63.24 kJ/mol severally. The values of them can account for test result of electrolysis expansion mentioned above.

The article deals with the technology of producing an aluminium-wettable coating in the process of electrolysis of cryolite-alumina melts. This technology has been implemented under laboratory conditions by electrodeposition of boron on the surface of the carbon-titanium cathode.The presence of a 100–500 µm near-surface layer of boride-carbide compounds, synthesized in the process of a 20–42 hour electrolysis, is confirmed by X-ray diffraction and SEM-EDS analyses.

Electrodeposition of TiB₂ coating provides a convenient and low-cost way in preparation of TiB₂ material. In this paper, TiO₂ and B₂O₃ were selected as the active components, KF-LiF as the supporting electrolyte, Ti4+ ions and B3+ ions reduction processes in TiO₂-B₂O₃-LiF-KF melts were investigated by cyclic voltammograms. Then electrodeposition of TiB₂ onto graphite substrate was carried out from TiO₂-B₂O₃-LiF-KF melts at 800 °C by using CCP (continuous current plating) and PCP (pulsed current plating). The TiB₂ coatings prepared by PCP exhibit uniform, dense and metallic surface with good dherence to the substrate, but with more cracks. compared with those obtained by CPC.

A series of compounds with the general formula (Cu₆₅Ni₂₀Fe₁₅)_97.7O_2.3 were prepared by high energy ball milling and evaluated as inert anodes for aluminum electrolysis at 700°C. All compounds had the same nominal composition but O₂ was introduced at different moments during the milling operation. All compounds show the presence of an fcc phase (γ-phase). Upon heat-treatment at 1000°C during the subsequent powder consolidation, the added O reacts with Fe to form more or less well dispersed Fe₂O₃ precipitates. Dry oxidation tests at 700°C showed that the material oxidation behavior strongly depended on the moment when O₂ is added. The best results were obtained when O₂ is added after the γ-phase is formed. The use of this anode for Al electrolysis in low-temperature (700°C) KF-AlF3 electrolyte for 20 h showed that the cell voltage is stable at ca. 4.2 V and the Cu contamination of the produced Al is 0.2 wt.%. In this case, the size, dispersion and concentration of Fe₂O₃ precipitates in the consolidated powder are optimized to promote the formation of a protective NiFe₂O₄ layer on the anode surface.

Two-step sintering process was adopted to prepare NiFe₂O₄ matrix inert anode for aluminum electrolysis in this research. In the process of synthesizing NiFe₂O₄ spinel, Fe₂O₃ and NiO powders as raw materials added additives were synthesized at 1000 °C for 6h. Through crushing and screening, adding NiFe₂O₄ nanopowder, particle gradation and compression molding, the nickel ferrite matrix ceramic inert anode was sintered secondarily at 1300 °C for 6h. The effect of NiFe₂O₄ nanopowder content on the density and porosity, bending strength and impact toughness was investigated in details. The results showed the addition of NiFe₂O₄ nanopowder had considerable influence on the properties of NiFe₂O₄ matrix ceramic inert anode. Inert anodes had the best comprehensive properties while adding 30 wt% nanopowder. The values of density and porosity were 4.86 g/cm3 and 3.5% respectively, the value of bending strength was 42.47 MPa and the value of impact toughness was 3.31 J/cm2.

The samples with small amounts of MnO₂ (0, 0.5, 1.0, 2.5 wt%, respectively) were prepared via ball-milling process and two-step sintering process from commercial powders (i.e. Fe₂O₃, NiO and MnO₂). Microstructure features, phase transformation, the early-stage sintering behavior and mechanical properties of Mn-doped NiFe₂O₄ samples have been investigated. Results indicate that the reduction of MnO₂ into Mn₂O₃ and following the reduction of Mn₂O₃ into MnO existed in sintering process. No new phases are detected in the matrix, the crystalline structures of ceramic matrix are still NiFe₂O₄ spinel structure. MnO₂ addition can promote the sintering process. The temperature for 1 wt% MnO₂-doped samples to reach the maximum shrinkage rate is 59 °C lower than that of un-doped samples.

A kind of cermet inert anode for Al electrolysis based on NiFe₂O₄ had been studied in this paper. Firstly, the effect of NiFe₂O₄ pre-sintering temperature on properties of inert anodes was researched, and then the appropriate technological conditions were determined by the orthogonal test. The properties such as density, conductivity, corrosion rate, mechanical property and thermal shock resistance have been used as controlling parameter to obtain the optimum technological condition. The inert anode sized Φ50mm×15mm is prepared and tested as anode for 10h Al electrolysis in laboratory. This anode behaves good corrosion resistance to cryolite molten salt. The result gives that the corrosion rate of the anode was 1.5x10−4g•cm−2•h−1 after the 8 h electrolysis, and the purity of the aluminum gained from Al electrolysis test was 92 %~93 %. The analysis shows the main contaminations in the raw aluminum are Fe, Ni and Ag.