Rare Metal Technology 2023

Ionic clays (an important resource for rare earth elements (REEs)) are formed by natural weathering of REE-bearing minerals and adsorption of liberated REEs onto the clay surface. Most ionic clays around the world including those from southern China mainly contain light REEs. Here, a unique ionic clay from south America which is rich in heavy REEs, including dysprosium (Dy), is used as the feed. A desorption process using ammonium sulfate as the lixiviant is developed. The effect of operating parameters including lixiviant concentration, pH, liquid-to-solid ratio, and temperature is investigated, and optimum conditions are determined. The characterization results show that this ionic clay comprises three modes of REEs, including ion exchanged REEs physically adsorbed on the surface, hydrolyzed REEs chemically adsorbed on the surface, and mineralized (non-desorbable) REEs within the clay. Mechanistic investigations show REE desorption/adsorption is controlled by the pH and sulfate ions in the system.

Rare Earth Elements have grown in importance over the years because of their applications in electronics, rechargeable batteries, renewables, and the defense industry. The recycling of neodymium and dysprosium contained in NdFeB magnets from the End-of-Life electronics will improve the total supply of neodymium and dysprosium in the future. However, due to the use of expensive and hazardous acids (hydrochloric or sulfuric), no mature and economically feasible technologies have been identified for recycling NdFeB magnet powders. The extraction process utilizes a two-stage process. The NdFeB powders go through wet ball mill grinding to pretreat with sodium hydroxide (NaOH) solution to form rare earth hydroxides. The rare earth hydroxides then go through leaching in mild acids. The leaching efficiencies of HCl and citric acid were investigated. As a result, a leaching efficiency of 69% for Nd and 100% for Dy was achieved after 60 min of milling with 3.5 mL of 4.0 M NaOH and 60 min of leaching with 100 mL of 0.5 M citric acid into the solution phase. Subsequently, 100% of iron (Fe) content can be removed out of the solution. Finally, neodymium and dysprosium can be separated using multi-stage acid stripping. This work resulted from an SBIR Phase I program funded by The U.S. Defense Logistics Agency, Contract SP4701-19-P-0048, awarded to Advanced Cooling Technologies, Inc. (ACT).

Rare earth elements are critical for sustainability applications; yet, their extraction, separation, and smelting remain environmentally and economically tedious. Conventional rare earth processing consists of a sequence of physical beneficiation, hydrometallurgical, and metallothermic or electrolytic processes to produce pure metals and alloys. Environmental impacts are concentrated in impurities management and material separation. Recently, sulfide-based separation chemistries have been shown to offer higher separation effectiveness than legacy hydrometallurgical methods at a fraction of the cost and energy usage. However, previous experimental studies have only employed synthetic feedstocks of mixed rare earth oxides or FeNdB magnets. Herein, we consider rare earth element separation from monazite mineral using sulfidation. We explore the use of iron and alkaline-earth compounds as separation additives to enable separation of rare earth elements and sequestration of normally occurring radioactive materials in parallel with de phosphorylation. Preliminary experimental results indicate that the addition of iron during rare earth mineral sulfidation is a promising method to promote selectivity, potentially enabling targeted rare earth element extraction and production.

The importance of rare earth metals for clean energy technology and the threat to their supply has prompted several researchers to consider alternative techniques to mining. One strategy that is gaining traction in this area is recycling. Various studies have shown that the magnet-to-metal method, in which rare earth metal is leached from the magnet, is a potential way to obtain recycled mixed rare earth metal that may be used as a precursor for the manufacturing of rare earth magnets. This study will evaluate the leaching behavior of rare earth magnets in a liquid metal leaching and distillation recycling method. These data and prior leaching studies will form the basis of a model of leaching mass transfer kinetics. Models of distillation for magnesium and one other leaching agent can be used for scale-up reactor engineering.

Nd-Fe-B magnets find wide range of applications due to its high magnetic properties. At its end-of-life, huge quantity of scrap Nd-Fe-B magnets are generated, which are promising alternative resource for rare earth elements (REEs). Recycling of scrap Nd-Fe-B magnets will mitigate the demand supply gap of REEs. Thus, the present paper reports development of feasible hydrometallurgical flow sheet to recover REEs from Nd-Fe-B magnets. The process consists of roasting of magnets with 20% NaCl at 750 °C for 2 h followed by water leaching of the roasted mass at 75 °C for 60 min to produce REEs containing leach liquor. About 99.9% REEs was recovered, and the left residue contained Fe, which was further calcined at 600 °C for 2 h to get red oxide pigment.

During electrorefining, copper is purified from impure anodes by dissolving the anodes in an electrolyte and plating on the cathodes. All insoluble components are precipitated to the bottom of electrolytic cells in the tankhouse or cellhouse. These settled insoluble components are called anode slimes. They contain copper, tellurium, selenium, bismuth, silver, gold, and traces of platinum group metals, such as platinum and palladium. Traditionally, these valuable metals are recovered in partial pyro- and hydrometallurgical processes. This paper presents an innovative 100% hydrometallurgical process: Wang’s process. It can be tailored to target the recovery of specific critical metals. This novel process would not only eliminate all by-products from current precious metals plants, but also significantly increase revenues from copper electrorefinery operations.

The world platinum group metals (PGMs) reserves and the recovery of PGMs secondary resources are discussed in this review. For many countries, the low reserves, large consumption, and high external dependence of PGMs are common problems nowadays. Therefore, the recycling of catalysts which contain PGMs has become an important method to alleviate the shortage of resources. This paper mainly introduces the pyrometallurgical recovery and enrichment process of spent automotive catalysts, including plasma melting and metal capture method, which has the advantages of high enrichment rate, large-scale, and short process, and iron, copper, and lead are often used as metal collectors to capture and recover PGMs. The advantages and disadvantages of different technologies are summarized, and the improvement and progress of PGMs recovery process are prospected, which provide a new idea for green and efficient recovery of spent automotive catalysts.

Crystallization of cobalt sulfate within a typical hydrometallurgical process for the recycling of Ni-Mn-Co oxide or Ni-Co-Al oxide Li-ion batteries has been investigated. The cobalt sulfate salt was obtained by eutectic freeze crystallization (EFC) from a synthetic acidic cobalt strip liquor after solvent extraction. The ternary phase diagram of CoSO₄–H₂SO₄–H₂O was first established by the mixed-solvent electrolyte (MSE) model to predict and reveal the changes in the system during the freezing process and to assess the conditions required for EFC. Batch EFC experiments were then conducted for the cobalt strip liquor, which contained a low concentration of impurities. It is shown that with suitable control of supersaturation, seeding, and stirring, pure ice and salt crystals can be recovered as separate phases at the eutectic temperatures, with the crystalline salts in the form of a heptahydrate. The crystallization process can be described using the ternary phase diagram, but with certain deviations. The deviations might be related to insufficient data at the low temperatures in the MSE model and acid entrapment in crystals during the crystallization process. Finally, the performance of the EFC process has been compared to that of an evaporative crystallization (EC) using the same strip liquor. It was found that the CoSO₄·7H₂O product obtained by EFC was of slightly higher quality considering purity and crystal shape compared to that from EC.

In this era of modernisation, the demand of metals is increasing as well as limitation of primary resources created a huge gap between demand and supply. In this connection, attempt has been made to recover Pb, Sn, and Cu from waste PCBs of computer hard disc using pre-treatment followed by hydrometallurgical techniques. In PCBs, encapsulation of epoxy sheets hinders dissolution of metals. Therefore, initially PCBs were depopulated, and then, using pre-treatment techniques, i.e. size reduction and wet gravity separation, mix metal concentrate was obtained. This obtained concentrate was used further for developing various metal recovery processes and optimisation of various process parameters. The experimental results indicate ~ 99% recovery of metals using suitable leachates. The obtained data is presented and validated to develop a process flow-sheet. This work will be productive for the researchers, students, and industrialists working in this area.

A clean method of extracting tungsten, yttrium, and uranium from tantalum—niobium ore located in the Muchinga province of Zambia has been developed. Tungsten is selectively extracted by roasting with alkaline at 700 and 750 °C followed by leaching in water to solubilize alkaline tungstate. The alkaline leach residue is cured with sulphuric acid to sulphate uranium and yttrium which are then leached out in acidic media. The effects of sulphation temperature, time, and particle size were studied. Yttrium was recovered from leach solution via precipitation with oxalic acid in which yttrium oxalate with purity of more than 99 wt% was obtained. Uranium was recovered from the leach solution through precipitation with sodium hydroxide. Extraction of tungsten, yttrium, and uranium from the material concentrated tantalum oxide by two times. A process flowsheet was developed based on optimised test works.

Recently, a new eco-friendly electrolytic process using a metal cathode followed by vacuum distillation was developed to produce high-purity Mg metal from MgO. In this study, the viability of this novel Mg metal production process using primary and secondary resources containing MgO as a feedstock was examined. In the electrolysis experiments, an average current of 1.44 A was applied to the electrolysis cell at 1043 K for 12.5 h using Cu cathode and graphite anode in an Ar gas atmosphere. The electrolysis yielded Mg–Cu alloys of 14.0–14.4 mass% Mg with an average cell potential of 2.43–2.67 V and current efficiency of 89.6–92.4%. Vacuum distillation of the Mg alloys, obtained after the electrolysis, at 1300 K for 10 h yielded Mg metals with a purity of 99.994–99.999%. Therefore, this study demonstrated that the production of high-purity Mg metal from various resources that contain MgO through the novel Mg metal production process is feasible.

Limited metal resources and significant environmental hazards urged researchers for finding sustainable technology for recycling of waste printed circuit boards (PCBs) to recover metals. Therefore, the present paper is focused on the recovery of copper (Cu) from waste PCBs using mechanical pre-treatment followed by hydrometallurgical processing. Initially, depopulated PCBs were pre-treated to get enrich copper in metallic concentrate. Further, experiments were carried out with varying different process parameters, i.e. acid concentration, oxidant concentration, time, etc., to obtain optimized condition for efficient Cu leaching from metallic concentrate. It was found that 99.9% Cu was leached using 20% H₂SO₄ at 75 °C in the presence of 20% H₂O₂ within 120 min maintaining 100 g/L pulp density. The obtained leach liquor could be used for electro-winning to recover pure copper metal.

The first step of phosphoric acid production consists of leaching phosphate-containing material (mainly from primary resources) with sulfuric acid. During this step, a wide range of metallic elements are also leached, leading to high concentrations of impurities in phosphoric acid. Solvent extraction is the suitable technology to reach a high extraction efficiency of phosphoric acid while minimizing impurity co-extraction. In the case of an extraction solvent containing a mixture of n-tributyl phosphate (TBP) and di-iso-propyl ether (DiPE), titanium(IV) is co-extracted with phosphoric acid. In order to reduce titanium(IV) co-extraction, it is of great interest to understand the mechanisms involved at the liquid–liquid interface, which is controlled by the speciation. This paper gives an overview on the speciation of titanium(IV) in non-complexing media in order to get relevant information to investigate the titanium(IV) speciation in concentrated phosphoric acid.

In the current study, catechol functionalized chitosan, C-Cat, was investigated for selective solid-phase extraction of germanium. Germanium is one of the critical elements because of its growing demand, supply risk, and inefficient production. The current Ge production processes, such as chlorination-distillation and solvent extraction, suffer from high energy requirements, high chemical consumptions, impurities co-extractions, and waste stream generations. The adsorbent was synthesized via Schiff's base reaction. The adsorbent morphology was different from the chitosan due to surface modification. C-Cat adsorbed Ge selectively in the presence of competitive ions with K_d values of 10,832.0 mL/g at pH 3 and 7417.6 mL/g at pH 4. The selectivity for Ge was also observed in Ge-spiked coal fly ash leachate. The distribution coefficients were correlated with metal hydrolysis constants, and linear free-energy relationships were developed for C-Cat. These LFERs can be used to predict the selectivity of C-Cat using the metal hydrolysis constants.

This article presents a two-stage, eco-friendly hydrometallurgical route for the recovery of gold from the delaminated metallic layers of waste mobile phone Printed Circuit Boards (PCBs). The downsized PCBs were treated with an organic solvent dimethylacetamide (DMA) for the separation of metallic fraction from non-metallic glass fibre. The liberated metallic sheets are used for the selective dissolution of copper in an aqueous leaching reagent. Influence of various parameters such as type of leaching reagent, the concentration of the solution, temperature, time, and pulp density is optimized for the effective leaching (almost 100%) of copper. Results show that 3 M nitric acid is a suitable reagent for copper leaching but gold remained in solid residue. In the second stage, the separated residue is used for the recovery of gold by sulphuric acid with a combination of halide salt. Results have shown that almost 92% of gold is recovered at the optimized parameters. Solvent extraction with 0.1M tertiary amide reveled the selective and quantitative recovery of gold from gold leach solution.

Herein, the leaching of molybdenum and rhenium from the molybdenite roasting flue dust in H₂SO₄ was studied. The parametric studies showed that leaching performed at a pulp density, 10 wt./vol.%; H₂SO₄ concentration, 1.0 M; temperature, 90 °C; and time, 90 min was sufficient to yield 96% molybdenum and 93% rhenium. The leaching process significantly improved by raising the temperature from 30 °C to 90 °C, indicating an exothermic dissolution of refractory metals. Whereas the leaching kinetics indicated that the reaction mechanism changed from diffusion-controlled to chemically controlled, which was further confirmed by the apparent activation energy evaluated to be Ea(Mo), 35.5 kJ/mol, and Ea(Re), 21.5 kJ/mol.

One of the most harmful air contaminants is nitrogen oxides (NO_X) produced usually in combustion processes. To reduce the effluents, the most effective technology to date is selective catalytic reduction (SCR) where nitrogen oxides are reduced into nitrogen to be released freely. Due to the increasingly strict environmental regulations, the demand for SCR catalysts has increased, and inevitably, the necessity of disposal of those spent catalysts has increased accordingly. Most catalysts for stationary applications contain around 0.5–1.5% wt V₂O₅ and 7–10% wt of WO₃ in a TiO₂ glass fiber matrix, and due to the environmental burden of disposal and the necessity of finding secondary sources for vanadium (V) and tungsten (W), the recycling of spent SCR catalyst becomes a pressing issue for current research. During this investigation, different tertiary amines were used and compared to observe the effectiveness in the extraction of vanadium and tungsten from spent SCR catalyst, the enrichment process was optimized and the loaded organic (9 times concentration) went through a crowding process where vanadium was replaced by tungsten to obtain highly pure tungsten loaded organic. The crowding parameters such as crowding agent, concentration, and pH were optimized.

Selenium is an important mineral for plants and living organisms. Trace amounts of selenium are needed for our everyday functions; however, when large amounts are consumed, it becomes really dangerous with adverse health effects; as a result of this, its removal has been the focus of many studies over the past decades. The mining and refining industries release the most amounts of selenium which are present in their wastewater in most cases. This paper will discuss the removal of selenium from chloride media by adsorption using biobased materials. Data analysis revealed that the adsorption rate of selenium on lignin progressed via the pseudo-second-order rate model. Adsorption isotherm model studies indicate that the adsorption of selenium by lignin followed the Freundlich adsorption isotherm. Other thermodynamic data were calculated to examine the nature and efficiency of selenium removal from chloride media.

The present paper is focused on the application of environment-friendly processes on metals adsorption using bioadsorbent. A huge amount of effluents is generated in electronic manufacturing/ recycling industries containing various metals such as Cu, Cr, Pb, Zn, and Ni. An exhaustive review has been made based on varieties of adsorbents, targeted metals, and medium. The objective of this review is to find out low-cost, easily available, potential adsorbent for metal reclamation. The present paper is engrossed in ‘Bioadsorption’ as a vital tool for metal recovery. It includes various classified bioadsorbent with their mode of action, adsorption capacities, and feasibility. It gives an overview to researchers and industrialists to find out potential bioadsorbents for further research in effluent treatment and metal recovery. Based on the salient features of developed processes, recommendation for suitable processes has also been made.

The formation of zinc oxide particles of different hierarchical morphologies was investigated. By performing elemental analysis on samples extracted from the supernatant solution during precipitations yielding two distinctly different morphologies, the consumption of zinc ions was used to follow the liquid-to-solid phase formation. While a rapid Zn-ion consumption was synonymous with the formation of predominantly oxygen terminated flower-shaped ZnO-particles, with half of the zinc ions being precipitated during the first minute, less than 10% of the zinc ions were converted to sea urchin-shaped ZnO-particles (with mixed terminations) after 1 min of the reaction. The unique ZnO-particle morphologies may therefore be related to the precipitation rates, which can be further explored as a tool for understanding how ZnO-particles with differently facetted surfaces form. Interestingly, the different formation rates remained with identical patterns when 0.5 g/L cellulose (0.005 wt%) was added to the reactions as nucleating agent for improved yields. The controlled formation of specific functional ZnO-particle surfaces is an important method for recycling inexpensive zinc waste from batteries to high value materials useful in a variety of catalytic applications.

The development of sulfide-based chemistry and physical separation has opened the way for new industrial production methods. A new route for the production of micron sized metallic tungsten particles from natural wolframite (Fe, Mn)WO₄ and scheelite CaWO₄ is presented. Sulfidation of mineral concentrates allows for the breaking of the tungstate crystal structure into a mix of sulfides containing tungsten disulfide WS₂. The thermal instability of WS₂ at high temperature allows for its selective thermal reduction to metallic tungsten particles under inert atmosphere.

The increasing demand for pure barite as a precursor in oil and gas drilling mud cannot be over-emphasized. Despite the abundance of this mineral in Nigeria, its exploration has been facing neglect because of the lower quality that could not meet the American Petroleum Institute (API) standards. Consequently, the treatment of a Nassarawa State barite mineral through acidic and alkaline leaching techniques was purified using a Denver flotation cell at pH 9. At optimal conditions, a leaching efficiency of 87.6% was achieved. In addition, the specific gravity of the purified barite product (BaSO₄: 96-900-4486, melting point = 1465 °C) gave 4.42 g/cm³ close to the API standard of 4.48 g/cm³. The product as characterized is therefore recommended for use as local drilling mud in the oil and gas industries to sustain the continuous operation in industries, thereby supporting human and capital development of Nigeria among others.

Recovery of precious and valuable metals from WPCBs faces challenge due to heterogeneous mixture of organic substrates and metal sheets. Pyrolysis is a promising and effective method for easing the separation of metals and organic substrates in WPCBs by transforming the organic substrates into high calorific products of oil and gases. In this study, the pyrolysis of WPCBs has been examined while investigating the effect of parameters, such as temperature, heating rate, and N₂ flow rate. The pyrolysis process was optimized using response surface methodology with a central composite design (CCD). The results showed that a quadratic model explained adequately the nonlinear behavior of the modeled response with an \({R}^{2}\) value of 0.98, showing that the model was adequately adjusted to the experimental data. The effect of each parameter and their interaction were discussed, and a variety of methodologies (metal analysis by ICP, XRD, SEM, and FTIR) were used to characterize the solid pyrolized WPCBs.

Lithium ore is one of the most sought after minerals of the twenty-first century due to its versatile application and specific application in sustainable energy. With the high development and increase in electronic equipment, small-scale power storage, and new energy industry, the consumption and demands for lithium are on a continuous rise. Nigeria is a country with abundant mineral resource deposits where lithium ore of several kinds have been identified to be deposited in not less than five states across the country. This paper gives an overview on characterization and beneficiation of Nigerian lithium ore reporting the work done so far and identifying the knowledge gap for advancement in the research of lithium ore in Nigeria.

In recent years, tantalum is being increasingly researched as a replacement for coatings for high-temperature applications. Tantalum is a refractory metal with low recycling rate of less than 1% because most tantalum secondary recovery techniques are primarily meant for recovery of other elements. In this study, the objective is to review various potential methods for recycling of tantalum coated steel composite, either at its end of life or for coating refurbishment purposes when coating is damaged. Tantalum can be recovered by both pyrometallurgical and hydrometallurgical methods, or a combination of the two, and it usually involves a whole process development with multiple steps for separation and purification from other elements. The main factor for selecting the best recovery method is dependent on the materials which are mechanically or chemically bonded with tantalum. This review summarizes various methods to recover tantalum from different secondary sources like tantalum capacitors, tantalum mill products, and tantalum in chemical processing industry. Lastly, we comment on the best method to recover tantalum from tantalum coated scrap.

ITO is vital materials in preparing semiconducting film for electronic display screens, which contains 80–95 wt% of indium oxides. However, indium is a tare dispersion in Earth’s crust with an average abundance of 0.02 ppm, which is quite difficult to recover extract from primary ores. Then ITO wastes were high-quality secondary resource for indium recovery. In this paper, a novel process for the separation and recovery of indium oxides from ITO waste targets via roasting under CO–CO₂ atmosphere is proposed. The effect of roasting parameters on the indium volatilization and phase transformation was conducted using thermomechanical analysis, XRD, SEM, etc. The results showed that the indium volatilization was 95.2 wt% under optimal experimental conditions. In₂O₃ was selectively reduced to In₂O and volatile as gaseous phase above 900 ℃, then indium can be separated and collected as disproportionation products.

In order to fundamentally improve the recovery rate of vanadium in the process of sodium roasting-water leaching of vanadium slag with high chromium content, it is very important to study the evolution mechanism of vanadium-containing phases. XRD was used to characterize the phase evolution of vanadium-containing phases with roasting time. At the beginning of roasting, the vanadium-containing phases basically were not changed, V³⁺ still formed FeV₂O₄ with Fe²⁺ and O²⁻. After 10 min, FeV₂O₄ began to be oxidized, V³⁺ was oxidized to V⁴⁺/V⁵⁺. When the roasting time reached 15 min, the oxidized V⁵⁺ started to react with Na₂CO₃ to form soluble vanadate sodium. After 50 min, the diffraction peaks of sodium vanadate increased sharply. After 90 min, almost all FeV₂O₄ was converted to Na₃VO₄, NaV₃O₈, and NaVO₃.

Calcification roasting-acid leaching is a clean vanadium extraction process, but the recovery rate of vanadium is low. Therefore, this study proposed the enhanced extraction process of vanadium slag by calcination with CaO and MgO. The effects of the roasting and leaching process on vanadium recovery and the change of impurity content in vanadium extraction tailings were studied. The results show that under the conditions of roasting temperature of 850℃, roasting time of 2 h, and pH of 2.5, the leaching efficiency of vanadium can reach 93.8% by roasting with the mixture of CaO and MgO. Compared with the calcification roasting-acid leaching process, the leaching efficiency of vanadium can be significantly increased, and the yield of vanadium extraction tailings and the contents of sulfur and calcium also can be reduced by the calcium-magnesium composite roasting process. Such a process shows great potential in improving vanadium recovery and cleaner production.

In the basic oxygen furnace (BOF) steelmaking process, large quantities of slag are generated, which are sometimes used as by-products. However, in many cases, BOF slag is landfilled and thus seen as waste. Typically contained elements are chromium, manganese, and phosphorus aside from the main slag formers, such as oxides of iron, calcium, and silicon. Following sustainability goals, a major target is the recovery of these elements by modifying the phase formation during cooling to generate artificial minerals which are separable in a subsequent beneficiation step. The paper describes investigations on the formation of mineral phases depending on the additives Al₂O₃ and TiO₂ during slag cooling. The results are compared with the thermodynamic calculation program FactSage. In addition, the enrichment of valuable metals in mineral phases was evaluated with EDX mappings of the scanning electron microscope.