Elsevier

Hydrometallurgy

Volume 164, September 2016, Pages 154-158
Hydrometallurgy

Removal of iron from sythetic copper leach solution using a hydroxy-oxime chelating resin

https://doi.org/10.1016/j.hydromet.2016.06.004Get rights and content

Highlights

  • Iron removal is a common process in hydrometallurgy of non-ferrous metallic ores.

  • A hydroxy-oxime resin, named Z-Fe, has adsorption preference to Fe over Cu.

  • Cu adsorbed could be stripped from the resin using dilute sulfuric acid solution.

  • Oxalic acid is efficient for stripping Fe(III) from loaded resin Z-Fe.

  • 89.83% Fe removal rate were obtained from closed circuit processing.

Abstract

Iron removal is a common procedure in hydrometallurgy of non-ferrous metallic ores. Chemical precipitation and solvent extraction are currently the main methods employed for separation of iron from copper leach solution. However, chemical precipitation methods have the problem of producing large amounts of iron precipitates, and/or requiring high temperature and high pressure conditions for precipitation. The precipitates are difficult to separate from the solution. Emulsification is a general problem for solvent extraction, which causes loss of extractants and contamination of the electrolyte. A common problem for solvent extraction and chelating ion exchange processes is the difficult iron stripping process. Therefore, finding an efficient and environmentally friendly method for iron removal is of great significance. In this paper, new processes of using ion exchange resins to remove iron from copper leach solution have been investigated.

Salicylic acid, amino carboxylic acid, amino phosphonic acid and hydroxy-oxime resins were employed to adsorb iron from a synthetic copper leach solution containing 40 g/L of Cu2 + and 36 g/L of Fe3 +. It was found that a hydroxy-oxime resin, named Z-Fe, has excellent adsorption selectivity on Fe3 +. Desorption behavior of the resin was studied by two step elutions using dilute H2SO4 and oxalic acid solution, respectively. After optimizing the adsorption-elution processes, the extent of removal of iron from the simulated copper leach solution using resin Z-Fe was 89.83%, while copper recovery could reach 100% in closed circuit processing.

Introduction

As one of the most abundant elements in the Earth's crust, iron always coexists with nonferrous metals in their ore bodies. The removal of iron is a necessary process in the production of pure nonferrous metals. Copper leach liquors must be purified to remove iron and other impurities before being sent to copper electrowinning. Chemical precipitation and solvent extraction (SX) are currently the main commercial processes for iron removal in the metallurgy of nonferrous metals.

Initial attempts of iron removal were to precipitate iron as hydroxides, which are gelatinous, and poorly filterable (Tainton and Leyson, 1924). It is well known that solid–liquid separation and washing processes are improved if the precipitate is dense with a crystalline character and has reasonably large particle size. By using hot, dilute solutions to prevent supersaturation which results in high nucleation rate and precipitation of small particles, crystalline precipitate of coarse particle size typically forms.

The jarosite process was the first iron removal method that realized the production of a filterable iron residue in commercial practice, and is still the most widely used process in nonferrous metal industry today. The first patents of jarosite processes were reported by Asturiana de Zinc (Asturiana de Zinc, 1964), Norzinc (Det Norske Zinkkompani, 1965) and Electrolytic Zinc Company of Australasia (Electrolytic Zinc of Australasia, 1970). Ferric ion precipitates slowly from weak acidic sulfate solutions in the form of crystalized AFe3(SO4)2(OH)6 under high temperatures, as illustrated below:3Fe3++A++2SO42+6H2O=AFe3SO42OH6+6H+

A+ could be a cation of K+, Na+, or NH4+. In Jinchuan Nonferrous Metal Company, the iron concentration in copper leach liquor was lowered from 16 g/L to < 0.05 g/L at pH 1.4–1.6 and temperature above 95 °C using a jarosite process (Jarosite Process Testing Group of Jinchuan Metallurgy Plant, 1980). One advantage of jarosite processes is the removal of SO42  ion and other impurities from the leach solution, and their disadvantages are elevated temperature operation to form well crystallized ferric vitriols for fast filtration and the production of large amount of dregs.

Goethite processes remove iron from acidic leaching solutions under relatively low temperature compared with jarosite processes in the form of goethite α-FeOOH by means of the Vieille-Montagne Process (Societe de la Vieille Montagne, 1968). To prevent the formation of Fe(OH)3 colloid, Fe(III) concentration is usually required to be < 1 g/L, which means the leach liquors should be diluted.

Another major iron removal process by precipitation is the hematite process as practiced at the Iijima Electrolytic Zinc Plant in Japan (Tsunoda et al., 1973). First iron in the solution is reduced to the ferrous state, and is then oxidized by oxygen under high temperature and pressure (1.8–2.0 Mpa) to precipitate the iron as hematite, as shown below:4FeSO4+O2+4H2O=2Fe2O3+4H2SO4

The advantage of the hematite process is that it produces a small amount of iron residue with 50%–60% iron content, which can be sold as steel making material or cement additive.

Other iron precipitation processes, such as the paragoethite process (Loan et al., 2006), Zincor process (Claassen et al., 2002) and phosphate process (Yang et al., 2012), were also explored by researchers.

Although precipitation processes are most widely employed for iron removal, the disposal of solid iron residues represents an environmental drawback. Solvent extraction and ion exchange processes are increasingly being used for iron control (Flett et al., 1996).

The phosphate group has a strong affinity and selectivity for Fe(III). In the past decades, bis(2-ethylhexyl)phosphoric acid (D2EHPA) (Sato et al., 1985, Biswas and Begum, 1998) and tributylphosphate (TBP) (Miralles et al., 1992, Sahu and Das, 2000, Sarangi et al., 2007, Liu et al., 2014) were used as extractants to remove Fe(III). As a mixture of four trialkyl-phosphine oxides, Cyanex 923 was used to extract Fe(III) from acidic chloride solutions in xylene (Saji et al., 1998).

Ligands containing an oxime group and pyridine ring are popular in coordination chemistry. The majority of the metal complexes of these ligands have been prepared in the last decades. The donor atoms of the 2-pyridyl oximes in metal complexes are the nitrogen atoms of the oxime and the pyridyl groups. The extractive Fe(III) removal from chloride solutions in the presence of Cu(II) and Zn(II) with 2- and 4-pyridyl ketoximes was reported by Parus et al. (Parus et al., 2011).

The volatile diluents like kerosene used in SX exhibit disadvantages such as high volatility and toxicity (Kislik, 2012), which cause evaporation and pollution, respectively. Ionic liquids were introduced as diluents due to their excellent properties such as chemical stability, water immiscibility and negligible vapor pressure which would avoid solvent losses providing a total recyclability. Furthermore, it was found that ionic liquids are advantageous over traditional organic diluents as they exhibit better extractability (Yoon et al., 2010). The selective removal of iron from industrial and synthetic solutions containing mainly Cu(II)/Fe(III) using the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [bmim][Tf2N] as the diluent and 1,1,1-trifluoro-2,4-pentanedione (TFA) as the extractant was investigated by E. Quijada-Maldonado et al. (Quijada-Maldonado et al., 2016) However, some researchers think that the hydrolysis of ionic liquids is not always green (Swatloski et al., 2003).

Similar to solvent extraction, a specific/chelating ion exchange resin is generally used for iron removal from copper electrowinning solutions. Chelating ion exchange resins have reactive groups binding with metal ions through the formation of complexes. It is recognized that commercial chelating ion exchange resins used for iron removal are structurally iminodiacetic, picolylamine, sulphonated phosphonic, or aminophosphonic, which have strong affinity for the ferric ion. Due to the strong acidic nature of copper electrowinning solutions, only the phosphonic resins are suitable for this application (Shaw et al., 2006). The phosphonic group likely acts as the specific chelating group for Fe(III) ion in these resins (Chiarizia et al., 1997). Adsorption of ferric ion onto these resins is an ion exchange with hydrogen ions, and for the case of a sulfate based electrolyte can be described by the following equation, where R represents the chemistry of the resin not involved in ion exchange:Fe2SO43+6HR2FeR3+3H2SO4

The Diphonix resin is a sulfonated diphosphonic resin used for iron removal. One of the disadvantages of Diphonix resin for iron removal lies in the difficulty associated with stripping iron from the loaded resin. One elution process developed for this resin involved reducing the bound ferric iron to ferrous iron using a solution containing sulphurous acid and copper ions, created by bubbling SO2 gas through copper electrolyte (Gula et al., 1996). Aqueous diphosphonic acid was tested to be effective in eluting iron from the loaded Diphonix resin (Chiarizia et al., 1997).

As aforementioned, chemical precipitation and solvent extraction are currently the main methods employed for iron removal from copper leach solutions. However, chemical precipitation methods have the problem of producing large amounts of iron precipitates, and/or requiring high temperature conditions for precipitation. The precipitates are difficult to separate from the solutions. As to solvent extraction, emulsification is a general problem, and causes loss of extractants and contamination of the electrolyte. A common problem for solvent extraction and chelating ion exchange processes is the difficulties in iron stripping owing to the strong bonding between chelating groups and ferric ion (Liu et al., 2014, Chiarizia et al., 1997, Gula et al., 1996). Therefore, finding an efficient and environmentally friendly method for iron removal is of great significance. In this paper, new processes of using ion exchange resins with excellent elution properties to remove iron from a synthetic copper leach solution have been investigated.

Section snippets

Experimental

According to the chemical composition of the copper leach liquor from a copper mine in Southern China, simulated leach solution containing 40.0 g/L of copper and 36.0 g/L of iron was prepared with analytic reagents CuSO4·5H2O and Fe2(SO4)3·6H2O for iron removal experiments. Sulfuric acid or sodium hydroxide solution was used to adjust solution pH when needed.

In a resin adsorption test, 25 mL simulated copper leach solution and certain amount of resin were added into a 250 mL conical flask with a

Adsorption tests

The major metal ions in the simulated copper leach solution are Cu2 + and Fe3 +. To selectively adsorb Fe3 + from the solution, the resin employed should have group(s) with special bonding power to it. However, there is no effective theory for selecting or designing resins with specific adsorption capability to Fe3 + ion by now. From the knowledges of inorganic and analytical chemistry, it is known that Fe3 + ion has strong bonding preference with OH and PO43  ions. And from the exploration of

Conclusions

New processes of using ion exchange resins to remove Fe(III) from a synthetic copper leach solution have been investigated. Salicylic acid resin SA, amino carboxylic acid resin D851, amino phosphonic acid resins D405 and LSC-500, and hydroxy-oxime resin Z-Fe were employed to adsorb iron from the solution containing 40 g/L of Cu2 + and 36 g/L of Fe3 +. It was found that hydroxy-oxime resin Z-Fe has the most selective adsorption behavior for iron from copper leach solution compared with other resins.

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