Removal from Industrial Wastes: A Review

Ind. Eng. Chem. Res. 2009, 48, 6145–6161

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REVIEWS Iron and Copper Recovery/Removal from Industrial Wastes: A Review Archana Agrawal,* S. Kumari, and K. K. Sahu Metal Extraction and Forming DiVision, National Metallurgical Laboratory, Jamshedpur-831007, India

Surface finishing of steel sheets and strips for the removal of iron oxide scale generates a huge amount of waste sulfate/chloride pickle liquor. Similarly large quantity of bleed stream is generated in the electrolysis industries due to the build up of acidity and metal impurity. The nature of the waste generated has become complex and hazardous in nature. Their impacts on ecological bodies are noticeable due to their toxic nature which is an alarming issue to the environmentalist. Hence, their treatment before disposal is mandatory. With the increasing demand for metals in industry and the depletion of land based resources, the focus of the research community is on the development of new approaches for the recovery of metal values from waste and recycle the water back to the system or dispose of it safely. This paper is a critical review on the waste streams generated from iron and steel industries and copper electrorefining industries. Various aspects on the metal value recovery from these wastes are being dealt with. The main focus is on iron recovery from waste pickle liquor and copper recovery from copper electroplating/electrorefining units by solvent extraction methods. Various solvents used for metal extraction are discussed here. 1. Introduction With the increase in the consumption of metal in various forms such as galvanized steel and other electroplated items, a large number of industries have come into operation and generate huge amount of liquid wastes such as waste acid pickle liquor and spent electrolyte, wash, and rinsewater. Pickle liquor is an acid solution or mixture of acids used to treat formed steel. Different mineral acids such as sulfuric, hydrochloric, hydrofluoric acid, phosphoric acid, and their mixtures have been used for pickling purposes.1 Iron and steel parts are generally pickled to clean the surface by chemically removing the iron, a scale formed with time on steel surfaces. Normal steels are usually pickled in 15-20% hydrochloric acid at 60-70 °C or in 20-25% sulfuric acid at 95-100 °C. When the steel is pickled with hydrochloric or sulfuric acid, the oxide scale dissolve to give iron(II)/iron(III) chlorides or sulfates leading to the generation of huge amounts of iron and acid containing pickle liquor. Such a huge quantity of acid and metal values become a source for major environmental pollution, and their disposal is recognized as an area where pollution prevention needs serious efforts. The general method in practice for such waste disposal is the following: neutralization of acid, precipitation of metal values, and disposal of the sludge generated on precipitation and in some cases evaporation or pyrohydrolysis of the pickle liquor. These practices are now being questioned increasingly with the stringent environmental regulation passed by the Ministry of environment and forest (MoEF), related to solid waste disposal and discharge of effluent into the river streams. Hence, it is worthwhile to develop a process to produce iron values like iron salt and powder and also prepare value added materials like ferrites from the combination of these wastes, besides recycling of the acid thereby meeting the environmental regulations. Similarly in the electrorefining unit of a copper plant,2 a dual reaction takes place during electrorefining where copper is simultaneously dissolved electrolytically from a * To whom correspondence should be addressed. E-mail: [email protected]. Phone no.: 0657 2345058. Fax: 06572345213.

relatively impure anode and the plating of relatively pure copper onto a cathode in a copper sulfate, sulfuric acid electrolyte. The copper anode contains a number of impurities that are separated from the copper during the electrorefining process. Typical impurities are precious metals, nickel, lead, iron, selenium, tellurium, arsenic, antimony, and bismuth. Most of the impurities form an insoluble slime, which falls to the bottom of the cell and is normally treated for byproduct metal recovery. However, some of these impurities, notably antimony and bismuth, are soluble in the electrolyte and accumulate in the electrolyte as the electrorefining proceeds. If left unchecked, antimony and bismuth present in the electrolyte will increase to the point where they contaminate the copper cathode. It is therefore necessary, and in fact a general practice in copper electrorefining, to remove antimony and bismuth from the electrolyte. Iron is another metal usually present in copper electrolyte. It is well-known that iron causes two undesirable phenomena during copper electrorefining, namely reduction of Fe3+ to Fe2+ which consumes current, thus reducing current efficiency and Fe3+ reacts with the reduced copper causing corrosion of the copper cathode especially at the surface where the Fe2+ is more apt to be oxidized.3 This is particularly a problem for cathodes employing copper suspension loops. Therefore, it is desirable to maintain dissolved iron levels to a minimum and to prevent electrolyte oxidation during copper electrorefining. In view of the criticality of the concentration of the above elements in copper electrolyte solutions, a part of this impurity rich electrolyte is bled off intermittently. This bleed stream need a proper treatment by removing impurities such as antimony, bismuth, and iron arsenic for further recycling of the electrolyte or for the recovery of metal values such as Cu, Ni, As, etc. as salts or pure metals for various other uses. Hence waste streams from copper electrorefining units, in the copper plating industry, can be used as a secondary source for the recovery of Cu, Ni, and other associated valuable metals. Thus there is a need for a method to produce base metals in a profitable yet environmentally safe manner. Copper producers, like all other base metal producers, have long practiced technology that was effective for converting ore to finished

10.1021/ie900135u CCC: $40.75  2009 American Chemical Society Published on Web 06/02/2009

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products, but this technology must now meet ever-increasingly stringent environmental regulations. To meet these demands, copper producers must re-examine their overall processing technology to either retrofit their existing technology or to introduce methods to recover the metal values from various wastes generated during the process. Several processes have been proposed for treating the spent copper bleed streams either to recycle the stream back to the system or to recover metal values from the stream.4-6 In one such method, the removal of antimony and bismuth from copper refining electrolyte is done by passing the solution through a series of electrowinning cells where antimony and bismuth are removed in their elemental form. The ion exchange process has also been used for the removal of antimony and bismuth but was found uneconomical. Several other methods have been tried for the extraction and separation of metals such as copper, nickel, and arsenic, and solvent extraction has been found suitable and capable of removing metals from such complex and highly acidic systems. This review covers the solvent extraction methods and various solvents for the extraction of iron from chloride and sulfate waste pickle liquor (WPL) and recovery of copper and nickel from copper bleed streams (CBS). 2. Iron Recovery from Waste Pickle Liquor Iron is present as an undesirable constituent in waste pickle liquor of the iron and steel industries, galvanizing industries, and zinc electrolysis units. Since iron is one of the major constituents of waste pickle liquor and is a cause to disqualify the pickle liquor for recycling after a few cycles, its proper disposal/utilization is of immense importance. Similarly during zinc electrolysis, iron is present in the solubilized form along with zinc which is a severe impurity in zinc solution and must be removed before electrolysis. During galvanizing of steel goods which are most often coated with zinc to protect their surfaces against atmospheric corrosion, zinc films are deposited by immersing steel items in molten zinc at around 450 °C. In order to obtain a high quality zinc film, pretreatment of the steel surface is required, including several processes such as degreasing with a hot alkaline solution, rinsing with water, pickling with HCl 20%, rinsing, and fluxing with zinc and ammonium chlorides. In the pickling step, hydrochloric acid is consumed during the process, but the concentration of chloride ions does not change. As a result, the spent pickling solution contains zinc and iron, present mainly in the form of iron(II), which forms appropriate chlorocomplexes. Typical metallic concentrations lie in the range 20-120 g/L for zinc and 100-130 g/L for iron, whereas the hydrochloric acid concentration lies in the range 1-6 mol/L.7 Besides this, the solution may contain other heavy metals such as Pb, Ni, Cu, Mn, etc. at low concentration. Thus, this effluent has a strong hazardous character and needs to be treated before disposal.8 The spent hydrochloride pickling solution is conventionally processed by the Ruthner process in which the hydrochloric acid is evaporated and granules of iron oxide are formed in a fluidized bed at temperatures above 600 °C. However, the presence of more than 500 ppm of zinc disturbs the process.8-12 The development of a clean process allowing the recovery of zinc under conditions that permit the recovery of electrolytic grade metal would reduce the effluent toxicity and recover the component of higher added value. There are various options which have been tried to combat with the iron and zinc in waste pickle liquor WPL and Various Leach Liquors. Neutralization of WPL is one of the most common methods used in many of the steel industries. The literature shows that iron is removed from iron containing solutions by precipitation13 as goethite14,15 or

hematite16,17 under optimized conditions, but in most existing electrolytic zinc plants, the method for iron removal involves its precipitation as jarosite.18-23 However, this process is disadvantageous due to the high cost of impounding jarosite in controlled tailing ponds; otherwise, the exposure of such residue, contaminated with heavy metals such as Zn, Se, In, Ge, and sulfur, to atmospheric conditions will cause environmental problems.24-26 In order to overcome these problems, it is required to remove iron and zinc from aqueous solutions as marketable products such as zinc oxide which can be used by pharmaceutical industries and pure hematite that can be used as a pigment or as raw material in steel making or magnet making industry. Pure zinc oxide and hematite can be produced if iron and zinc are removed from aqueous solutions by any hydrometallurgical process such as ion exchange and solvent extraction with selective extractants. Solvent extraction and membrane based solvent extraction have received considerable attention and have been proven to be very efficient in the removal and separation of FeCl2 and ZnCl2 from HCl.27-35 With regard to the separation of zinc(II) from solutions containing hydrochloric acid, Cierpiszewski et al.11 studied the behavior of different extractants in the separation between zinc and iron concluding that solvating extractants led to better extraction results than other analyzed compounds. In fact, tributyl phosphate (TBP) is the most suitable reagent and enables both the extraction of zinc(II) from HCl solutions and subsequent stripping with water.9,11,36 Samaniego et al.37 studied the kinetics of the extraction of zinc(II) from high acidic medium using TBP as extractant in a membrane assisted solvent extraction. Service water was used for the stripping of loaded Zn. A mathematical model that considers diffusion through the organic membrane as the main kinetic resistance was developed, and the membrane mass transport coefficient was estimated by means of the parameter estimation tool gEST (from gPROMS) to obtain a value of Km (membrane mass transfer coefficient) ) 3.89 × 10-4 m/h. Simulated results agreed satisfactorily with experimental data, thus confirming the validity of the kinetic model and parameters. However, some fundamental problems of such separation have been described by Cierpiszewski et al.,11 Regel et al.,9 Regel-Rosocka et al.,38 and Regel-Rosocka et al.39 The problem concerned with the spent pickling solutions containing zinc(II) and iron have been studied in details using TBP at different phase ratio by Rozenblat et al.40 In another study, Magdalena and Szymanowski41 studied the extraction of Zn(II) from spent pickling solution containing Fe(II) with tributyl phosphate (TBP). They observed the transfer of Fe(II) along with zinc(II) to the strip solution which may be due to physical transport of Fe(II) into the solvent which could be effectively scrubbed with water from the loaded organic before stripping zinc. There are only a few studies on the recovery and reuse of dissolved iron(II) in spent pickling solution. Generally, after acid extraction, the Fe(II) ions present in waste pickle liquor were oxidized in Fe(III) ion by some suitable reagent, which is further subjected to extraction. Thus attempts have been made to oxidize Fe(II) by various means. 3. Methods Used to Oxidize Fe(II) to Fe(III) It is possible to oxidize Fe(II) biotically (bacterial oxidation) or abiotically (chemical oxidation). Recently studies have been cited on the biotic oxidation of iron oxidation using various microbes, which can work in sulfuric acid medium at room temperature,34-44 and the oxidized solution is then treated to produce valuable ferric iron products. In this system, the


microbial oxidation of ferrous iron(II) by mesophile T. ferrooxidans lasted for a week even when the solution pH was adjusted to an optimum of pH 2 by adding aqueous NH4OH solution. A heat treatment of the microbially oxidized pickling solution at 160 °C for 8 h resulted in the formation of ammonia-jarosite (NH4 Fe3(OH)6(SO4)2), which can be used as a raw material in the production of iron oxides. The microbial oxidation of ferrous iron(II) in sulfuric acid pickling solution occurs according to following reaction: 2FeSO4(aq) + 1/2O2(aq) + H2SO4(aq) f Fe2(SO4)3(aq) + H2O(aq) (1) According to Nyavor et al.,45 the ferric ion and cell concentration also effects the oxidation of ferrous ion by T. ferrooxidans. Ferric ion competitively inhibited ferrous ion oxidation by the bacteria. The inhibitory effect of ferric ion was however reduced by increasing the cell concentration. Microbiological oxidation using Thiobasillus ferrooxidans can also be used in hydrometallurgy and various desulfurization process, being quite an undemanding organism, requiring only a few mineral nutrients which usually can be obtained from the surrounding rock. Nowaczyk et al.46 studied the microbiological oxidation of the waste ferrous sulfate using Thiobacillus ferrooxidans bacteria. Osaki47 studied the kinetics of ferrous ion oxidation with crystalline human ferrooxidase (ceruloplasmin) under various condition at 30 °C. The abiotic (chemical) oxidation of Fe(II) can be done by using different chemicals, thus oxidation by dissolved oxygen can proceed along with two parallel pathways, first homogeneous oxidation in a solution containing no surfaces and second via hetrogeneous oxidation in a suspensions. In a homogeneous solution the Fe(II) oxidation rate greatly increases in the reduction potential. For this reason, the rate of homogeneous oxidation is highly pH dependent.48,49 In heterogeneous suspensions, Fe(III) oxyhydroxide surfaces are well-known to catalyze the oxidation of Fe(II).50-55 Barnes et al.48 studied the zeta potential as a tool alongside kinetic experiments to delineate between various plausible mechanisms for the hetrogenous oxidation of Fe(II) by dissolved oxygen. Fe(II) were oxidized into Fe(III) using chlorine gas56 according to the following reaction: 3FeSO4 + 3/2Cl2 f Fe2(SO4)3 + FeCl3

(2)

Several trials have been carried out with other known oxidizers such as hydrogen peroxide and oxygen,56 as shown by the following reactions respectively: 2FeSO4 + H2O2 + H2SO4 f Fe2(SO4)3 + 2H2O

(3)

4FeSO4 + O2 + 2H2SO4 f 2Fe2(SO4)3 + 2H2O

(4)

Drawbacks of using hydrogen peroxide as an oxidizing agent are its high cost and low availability of H2O2. Because of the slow kinetics of the oxidation of the Fe(II) into Fe(III) reaction in the atmospheric oxygen supply, there is a need for a catalyst for the reaction to take place at temperatures below 723 K. Satisfactory results were obtained with nitric acid as an oxidizing agent in both the presence and absence of sulfuric acid. The oxidation process59-66 yields the following reactions: 3FeSO4 + 4HNO3 f Fe2(SO4)3 + Fe(NO3)3 + NO + 2H2O (5) 3FeSO4 + 6HNO3 f Fe2(SO4)3 + Fe(NO3)3 + 3NO2 + 3H2O(6)

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6FeSO4 + 9HNO3 f 2Fe2(SO4)3 + 2Fe(NO3)3 + 3HNO2 + 3H2O (7) 6FeSO4 + 2HNO3 + 3H2SO4 f 3Fe2(SO4)3 + 2NO + 4H2O(8) This oxidation of iron(II) sulfate by nitric acid is a fast reaction. It is also found that depending upon the aqueous phase conditions such as anionic species present, acidity, and acid present different species of iron are found which have a prominent role during the extraction process. Thus Belaustegi et al.59 found the formation of various species of iron in the presence of chloride, bromide, or fluoride ions in the aqueous phase such as FeCl2+, FeCl3, FeBr2+, FeBr2+, FeF2+, FeOH2+, Fe(OH)2+, Fe(OH)4-, etc. Similarly according to Deep et al.60 species like FeHSO42+, FeSO4+, and Fe(SO4)2- are found when H2SO4 is present in the aqueous phase. Finally after oxidation of Fe(II) to Fe(III), various methods such as methods like ion exchange separations, hydrothermal precipitation, solvent extraction, etc. have been used for the extraction of iron from aqueous streams. 4. Extraction and Removal of Fe(III) Although there is very scant literature on iron extraction by ion exchange resins mainly due to the fact that stripping of extracted iron is very difficult, and in some cases, the resin is degenerated and has to be disposed of. However few researchers have attempted to extract iron from dilute solutions. Maranon et al.61 compared two ion exchange resins, Lewatit MP-500 and Lewatit M-504, to remove iron and zinc from an acid picking bath. Stocks et al.62 tested DOWEX MSA-1, a strong base anion exchange resin in chloride form, to separate iron and zinc from waste pickle liquor. Dingman et al. and Kabay et al.63,64 pointed out that using ion-exchange resin is an effective procedure for removing the metals present in industrial effluents. Riveros65 evaluated six commercial cation exchange carboxylic resins and analyzed the effect of the resins’ morphology and the acidity of the -COOH group on the extraction of Fe(III) from acid sulfate media. Lee et al.66 studied Diphonix resin to remove iron from cobalt sulfate solution and used titaneous sulfate solution for elution to investigate the possibility of using this reagent as a reducing agent in the elution of iron. The fixed bed ion exchange requires a high investment costs for the resin. Besides, the eluted metal ion has no further use since it is in a very dilute form. Solvent extraction is another hydrometallurgical process that is extensively used in the extraction and recovery of metals and acids from aqueous solutions. A variety of extractants have been developed to date with much improved extraction properties, better selectivity, and stability under quite harsh conditions. Since pickling is done either by sulfuric acid or by HCl generating two types of waste pickle liquor, i.e. sulfate and chloride waste pickle liquor. 4A. Extraction of Iron(III) from Sulfate Medium. By Acidic Extractant. a. Phosphoric Acids. Demopoulos et al. studied extraction of iron(III) from sulfate solution by mono(2ethyl hexyl) phosphoric acid.67 While extracting iron(III) from sulfuric acid solution with Kelex 100 and phosphorus acid extractants, it was observed by Demopoulos et al.68 that no synergism is observed when Kelex100-M2EPHA mixtures are used. Fortes et al.69 carried out separation of iron from indium in sulfuric acid media using di-(2-ethylhexyl) phosphoric acid (D2EHPA) diluted in isoparafin. The results showed that D2EHPA can be effectively used to separate indium and iron

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from acid solutions. Lupi et al.70 carried out reductive stripping in vacuum of Fe(III) from D2EPHA using special high grade (SHG) zinc powder as a reducing agent. Principe et al.71 investigated the solubility and stability of several organophosphoric acid extractants in the light of the selection of suitable extractants for iron(III) solvent extraction as a potential iron rejection route in zinc processing. Suarez et al.72 investigated the extraction of iron(III) from acidic sulfate solution by PENRECO(R) 170 ES a new diluent which offer advantages such as improved solvency power, more complete phase disengagement, and reduced losses in aqueous stream, with reduction of over 50% in diluent usage after one year, compared with the paraffinic diluents. Principe et al.73 investigated the iron(III) removal from strong zinc sulfate-sulfuric acid solution by comparing the performance of octylphenyl acid phosphate (OPAP) and di-(2-ethylhexyl) phosphoric acid (D2EPHA). Principe et al.74 studied the use of OPAP, a mixed extractant consisting of mono- and di-octylphenyl phosphoric acids, is described as a potentially suitable extractant to selectively extract Fe(III) from concentrated ZnSO4 (90 g/L Zn) H2SO4 (50 g/L) solutions, followed by stripping of Fe(III) with 4-6 N HCl. OPAP was found to exhibit very low solubility degradation characteristics with minimal zinc antisulfate coextraction. OPAP seems to have the lowest sulfate carryover than any other extractant previously proposed for iron extraction from strong acidic solutions. While investigating the stripping of iron(III) loaded OPAP with HCl Principe et al.75 found that OPAP was an excellent extractant for the preparation of concentrated iron chloride strip solutions. b. Phosphonic acids. Alkylphosphonic acid monoalkyl esters such as 2-ethylhexyl 2-ethylhexyl-phosphonic acid (HEHEHP) are one type of solvent which can extract Fe(III) effectively from sulfate solution.76-78 Gao et al.79 studied the kinetics and mechanism of solvent extraction of iron(III) with n-octane solution of 2-ethylhexyl phosphonic acid mono 2-ethylhexyl ester (HEHEHP, HA) and explained the catalytic role of trioctyl phosphine oxide (TOPO) and sodium dodecyl sulfonate (SDS) on the kinetic process. The results indicate that TOPO decelerates the extraction rate of iron(III) with HEHEHP, but SDS accelerates it. c. Phosphinic Acids. The industrial utility of any iron solvent extraction process is generally measured by the feasibility of the extractant regeneration. Deep et al.80 studied the separation of Fe(III) from a tannery filtrate using Cyanex 272. They found this solvent to be efficient for the extraction of Fe(III) with the possibility of its easy regeneration using dilute sulfuric acid. Another report81 indicated the application of Cyanex 272 for the extraction and removal of iron from cobalt liquor. Both of the quoted studies, however, dealt only with a dilute solution of iron (up to 0.5 g/L). Deep et al.82 used a mixture of partially neutralized Cyanex 272 and TBP for the extraction of Fe(III) from the sulfuric acid medium containing high iron content. They observed that during extraction of Fe(III) by the solvent, a proportional amount of H+ ion is released in to the aqueous phase thus stopping further mass transfer. Fe3+ + 2(HR)2 S FeR3(HR) + 3H+

(9)

(HR)2 ) Cyanex 272 dimer

(10)

Thus, the solvent was partially neutralized to circumvent the problem. An equivolume addition of TBP in the extractant solution was required to attain satisfactory phase separation characteristics. The proposed extractant mixture extracts Fe3+ over a fairly wide range of the aqueous phase pH with a good loading capacity. Speciation studies have ascertained the mech-

anism of the iron extraction under the test conditions, i.e., Fe3+ ) 0.80 M, pH ) 1.2. The speciation data have also contributed to the determination of other physical parameters, namely the stoichiometry of the extracted complex, the thermodynamic extraction constant, and the heat of reaction. The stripping of the extracted metal ion is easily achieved using 2 M H2SO4, which can be cited as one of the biggest advantages of the proposed extraction system over DEHPA and Ionquest 801 extractants. The extractant solution also provides a fair selectivity to the extraction of Fe3+ in the presence of some commonly associated metals, namely Cr3+, Co2+, Ni2+, Cu2+, and Zn2+. Biswas et al.83 investigated the kinetics of the forward and backward extraction of Fe(III) from sulfate medium using a Lewis cell operated at 3 Hz and flux method of data treatment. Biswas et al.84 studied the interfacial adsorption property of purified Cyanex 272 and its characteristics toward Fe(III) from sulfate medium. Luo et al.85 investigated the mass transfer behaviors of Cd(II), Fe(III), Zn(II), and Eu(III) in the sulfuric acid solution using microporous hollow fiber membrane (HFM) containing bis(2,4,4-trimethylpentyl) monothiophosphinic acid (Cyanex 302). Naik and Dhadke86 investigated the distribution equilibrium of iron(III) between bis-(2-ethylhexyl) phosphinic acid dissolved in hexane, and acidic nitrate media has been investigated as a function of the concentration of extractant in the organic phase and the concentration of hydrogen ion and iron(III) in the aqueous phase. Senapati et al.87 studied the extraction of iron using 0.2 M Cyanex 272 (partially neutralized) as the extractant from sulfate solution. Demopoulos et al.68 studied the synergistic extraction of iron(III) from sulfuric acid solution using a mixture of Kelex 100 with phosphorus acid (HR): D2EHPA, PC-88A, or Cyanex 272. Nagaosa et al.88 carried out measurement of dimerization constants and distribution constants of bis-(2-ethylhexyl) phosphinic acid (PIA-8) in three kinds of diluents by a potentiometric two-phase titration technique and extracted iron(III) from 1.0 mol/dm3 ammonium sulfate solution by PIA-8 in heptane. Ajgaonkar et al.89 developed a rapid method for the solvent extraction separation of iron(III) and aluminum(III) from other elements with Cyanex 302 in chloroform. d. Carboxylic Acids. A study reported by Muhl et al.90 of the separation of iron(III) and aluminum by solvent extraction using aliphatic monocarboxylic acid (PC Saure Fi) from chloride and sulfate leach liquors produced by the acid leaching of aluminosilicate ore an alternative to the Bayer process for pure aluminum manufacture. van der Zeeuw et al.91 studied the extraction of iron(III) with Versatic 10. Several possiable species both dimeric and trimeric and containing both covalently bound carboxylate group and solvating molecules and possibly also hydroxyl groups were indicated. Meanwhile, extracting iron(III) from sulfate solution a relation between the extraction temperature and coefficient of distribution of various metals between aqueous phase and kerosene solution of Versatic acid has been invesigated by van der Zeeuw.92 Using a mathematical procedure, it was established that with increasing temperature the distribution coefficient changes if the composition of the metal-Versatic complex is temperature dependent. In the case of trivalent iron, a reversible increase in distribution coefficient occurs when the temperature is raised. It is suggested that this is due to a reversible depolymerization of the complex. Doyle et al.93 reported that iron(III) can be stripped from carboxylate solution with dilute H2SO4 (10-40 g/L) at 100 °C under atmospheric pressure to give geothite or basic sulfates. The structure of the iron carboxylate complexes within the organic phase is also discussed, along with the influence of these


structures on the stripping and nature of the hydrolysis products. Fletcher et al.94 studied the use of the tertiary aliphatic carboxylic acid, Versatic 911 (Shell Chemicals) for the removal of iron from base metal solution at about pH 2. Developments on the application of carboxylic extractants for the extraction of metal ions have been extensively reviewed by Rice et al.95 and Pouillon et al.96 506 nm. Quantitative studies proved difficult owing to side reaction such as adsorption of iron onto glassware, instability of the organic phase color due to the auto reduction of iron(III) by thiocyanate, slow extraction kinetics, and hydrolysis of ferric iron in the aqueous phase. Rice et al.96 attempted to apply slope analysis for the extraction of iron(III) from thicyanate media with Versatic 911 using equation derived for a 1:1 phase ratio. Wang et al. have studied the extraction of iron(II) with napththenic acid.97 Xue et al.98 conducted studies for the removal of iron from sulfate solutions using Eichrom’s Dipex extractant, PP′-di(2-ethylhexyl) methanediphosphonic acid (H2DEH[MDP]). They found that 99% of Fe(III) can be extracted effectively and selectively using this extract from a highly acidic solutions. The separation factor, Fe/Zn, was 106. More than 90% of the iron in a loaded organic can be recovered in an aqueous solution by reductive stripping. A process for the preparation of high purity iron compounds for use in ferrite manufacture by substoichiometric extraction with the sodium salt of a C6 to C10 aliphatic monocarboxylic acid has been patented and described by Muhl.99 Preston et al.100 studied the idea that pyridinecarboxylate esters caused appreciable synergistic shifts in the pH50 values for the extraction of some divalent base metals by solutions of Versatic 10 acid in xylene. For n-octyl 3-pyridinecarboxylate, the synergistic shifts decreased in the order Ni > Co > Cd > Cu ≈ Fe > Mn > Zn, and for the commercial extractant Acorga DS 5443A, in the order Ni > Cu > Co > Fe > Cd > Mn > Zn. No synergistic effects were observed for divalent lead, calcium, and magnesium. On the basis of the pH50 values obtained, several possible practical metal separations are suggested. No loss of metal-loading capacity was found when the organic phases were contacted with 1 M sulfuric acid for prolonged periods at 30 °C. Doyle et al.101-104 and Gindin et al.105 have done an extensive study on the extraction and stripping of Fe(III) from various acidic solutions. Basic Extractant. The extraction of iron(III) and other metals with amines when the metal is present in aqueous sulfate solutions has been studied by several authors. Seeley and Crouse106 and Seeley and McDowell107 determined the distribution coefficients for Fe(III) in the liquid-liquid extraction system containing Primene JM-T-toluene vs aqueous ammonium sulfate (and sodium sulfate) as a function of sulfate, acid, Fe(III), and amine sulfate concentrations. Kinetic study for this system indicated that equilibrium was largely achieved in 1 h; although some changes, possibly in the nature of the extracted species, occur up to approximately 20 h. Extraction isotherms show a slope of 1 at low loadings, indicating the same degree of selfassociation in both organic and aqueous phases, while the amine sulfate/iron ratio appears to approach 2.5 ( 0.25 at saturation loading. Results obtained by varying the sulfate concentration matrix indicates the formation of an aqueous complex of ferric ammonium sulfate which depresses iron distribution to the organic phase. The degree of aggregation of the amine sulfate, derived from iron distribution coefficient dependence on amine sulfate concentration data, is shown to be approximately 10. The results obtained by several authors108,109 show that the extraction of iron(III) by amine sulfates may be related to an adduct formation reaction and not an anion exchange reaction as suggested in the previous work.110 Alguacil et al.111 carried

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Figure 1. Possible structure for the amine sulfate-Fe(III) complex at high amine concentration.107

out experiments in order to define the iron(III) extraction equilibrium in the liquid-liquid system amine Primene 81R sulfate-kerosene vs aqueous iron(III) sulfate solution as a part of a process in which iron(III) is eliminated from aluminum sulfate solution by the technique of liquid-liquid extraction. According to the experimental data, the following extraction reation at 50 °C and higher temperature is suggested: Fe2(SO4)3aq + 2H2Oaq + 3(RNH3)2SO4org S 3(RNH3)2SO4·(Fe(OH)SO4)2org + H2SO4aq (11) On the basis of the UV visible spectrum of the isolated iron(III)-amine primene 81R complex, the following structure (Figure 1) was suggested where two iron(III) atom was complexed with three amine sulfate. These results were compared with the results obtained by other authors with different amine sulfates,107-109,111 because it has not been shown whether the nature of the extracted species is dependent only on the class of amine (i.e., primary, secondary, tertiary) or rather dependent on the structure of a specific amine. There is very little information on the behavior and characteristics of this reagent for extraction studies of this nature. Coleman et al.112 have concluded that the combination of amine and organic diluents should be considered as the effective extractant rather than the amine alone. For this purpose diluent may be considered not merely as a carrier but as a participant in the extraction process. There are many examples of the influence of the diluent properties on the extraction of metallic ions from different aqueous solution by amines.112-114 Alguacil et al.115,116 studied the influence of the diluents on the extraction of iron(III) from aluminum sulfate solutions by the amine primene 81R sulfate. Mitani et al.117 extracted the complexes of iron(III) with L-tartaric acid which is formed in aqueous solution at various pH values with (methyl) trioctylammonium chloride (TOMAC, R3R′ NCl) in toluene. The complex species before and after extraction have been characterized by various techniques. Solvating/Neutral Extractant. Deep et al.118 proposed the separation of Fe(III) and Cr(III) by liquid-liquid extraction with 0.50 M Cyanex 923. Fe(III) was selectively extracted from the mixed H2SO4 and NaCl medium leaving pure Cr(III) in the raffinate. Separation of iron(III), copper(II), and zinc(II) from a mixed sulfate/chloride leach liquor bearing 11.8 kg/m3 iron, 24.8 kg/m3 copper, 0.23 kg/m3 zinc, 3.8 kg/m3 cobalt, 35.2 kg/ m3 nickel, 176.3 kg/m3 chloride, and 48.9 kg/m3 sulfate was carried out by Sarangi et al.119 using solvent extraction. Iron, copper, and zinc extraction studies were carried out using TBP, LIX 841, and Cyanex 923 in kerosene, respectively. Iron loaded TBP, copper loaded LIX 841, and zinc loaded Cyanex 923 were stripped with water, H2SO4, and water, respectively. Samaniego et al.120 studied the kinetics of the nondispersive extraction and stripping of zinc chloride from spent pickling effluents using TBP as selective extractant and service water as stripping agent. Batch experiments were performed to analyze the influence of the initial metal concentration on the rate of zinc chloride separation. It was observed that there is no significant influence of the initial metal concentration on zinc extraction.

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Chelating Extractants. Simpson et al.121 studied the solvent extraction of iron(III) by means of the commercial salicyaldoxime LIX 860 and its influence on copper(II) extraction from sulfuric acid. Extraction experiments wre carried out at varying equilibrium time, temperature, extractant concentration, pH of the aqueous phase, and concentration of ferric and cupric ions in the solution. Since LIX 860 is an acidic extractant, the extraction reaction for Fe(III) is expressed as (eq 12) Feaq3+ + 3HRorg S FeR3org + 3Haq+

(12)

Thermodynamically, this reaction was found to be endothermic with dHo ) 8.6kJ/mol. The authors of this work also studied the extraction of Cu(II) by this extractant and found the preferential extraction of Cu(II) than Fe(III). Mixed Extractant or Synergistic Mixtures. Demopoulos et al.122 studied the synergistic extraction of Fe(III) from H2SO4 solutions, with a maximum at 130-150 g/L H2SO4, which is observed when using a mixture of Kelex 100 with dialkyl phosphorus (HR) acids: D2EHPA, PC-88A, or Cyanex 272. No synergism, however, is observed when a Kelex 100-M2EPHA mixture is used. The synergism is attributed to the formation of mixed metal-Kelex100-HR-sulfate complexes. Meng et al.123 carried out a kinetic study of iron(III) extraction from sulfate solutions using primary amine N-1923 and a TBP modified rotating disk diffusion cell (RDC) after cell calibration. The result showed that the rate-limiting step in the extraction process is chemical reaction at the interfaces. Demopoulos and Gefvert124 reported the use of a mixed reagent consisting of 7-alkylated 8-hydroxy quinoline (Kelex 100) and di-(2-ethylhexyl) phophoric acid (D2EHPA) for iron removal from sulfuric acid solution (50 < H2SO4 < 200 g/L). Synergism was observed both in terms of iron(III) loading and extraction rate. Demopoulos and Pouskouleli67 extended to mixture of Kelex 100 with other alkyl phosphorous acid, namely mono-2-ethylhexyl phosphoric acid, 2-ethylhexyl phosphoric acid 2-ethylhexylester (PC88A), and bis(2,4,4- trimethyl pentyl) phosphoric acid (Cyanex 272). During the course of experimentation, M2EHPA was found as an excellent extractant for iron(III); hence, the potential of using M2EHPA for iron(III) removal from industrial sulfuric acid leach solution was further investigated. Studies have been made on the formation of molecular complexes by addition of neutral extractants to the alkylphosphoric acid.125 Hsu et al.126 observed that no synergism was found in the extraction of Fe(III) by alkylphosphoric acid ester with addition of neutral extractant. Yu and Chen127 pointed out that the synergism was found in the extraction of Fe(III) by the addition of tertiary amine to 2-ethylhexyl 2-ethylhexylphosphoric acid (HEHEHP) or dialkylphosphonic acid in the organic phase as solvent. It was also found that the amount of sulfuric acid required for stripping of Fe(III) extracted was also reduced when mixed solvent was used. Chen et al.128 observed that a mixed solvent system consisting of a mixture of primary and secondary amines with neutral donor solvents such as 2-octanol and TBP enhanced the extraction and the stripping of Fe(III) from the sulfate system. With the addition of TBP in the primary amine solution, Fe is extracted as (FeOHSO4)(RNH3)2SO4 · TBP, which is schematically shown in Figure 2. For a primary amine alone as the solvent, the extraction species is Fe(SO4)3(RNH3)3. Thus iron is extracted as an unhydrolysed iron sulfate complex FeSO4+ with the dissociated amine sulfate. Stripping of extracted iron from primary amine is possible only with concentrated sulfuric acid, but addition of TBP results in the steric effect that hinders the extraction of unhydrolyzed iron. In the meantime, the direct coordination ability of the donors enhances the extraction of

Figure 2. Schematic representation of the proposed extraction species of Fe(III) with primary amine and TBP.

partially hydrolyzed iron. This also improves the stripping percentage of the loaded iron. The mechanism of Fe(III) extraction by such a mixed system was also proposed as given below: Fe3+ + H2O S Fe(OH)2+ + H+

(13)

Fe(OH)2+ + SO42- + TBP S Fe(OH)SO4 · TBP (14) Fe(OH)SO4 · TBP + (RNH3)2SO4 S Fe(OH)SO4 · (RNH3)2SO4 · TBP (15) Similarly a mixture of HDEHP and primary amine in n-octane was found to extract Fe(III) by the formation of reverse micelles. It is proposed that extraction and stripping within this mixed solvent involves the exchange of H3O+ with Fe(H2O)3+ at the water-oil interface of the reverse micelle. Stripping was possible by dilute H2SO4. The following reaction has been proposed for Fe(III) extraction with the mixture of HDEHP and primary amine as follows. Fe3+ · TBP + SO42- + mHA + n(RNH3)2SO4 f (Fe(SO4)A)[(RNH3)2SO4]n(HA)(m-1) + H+ (16) Fe3+ + SO42- + H2O + mHA + n(RNH3)2SO4 f [Fe(OH)(SO4)][(RNH3)2SO4]n(HA)m + H+ (17) The values of n and m in eqs 15 and 16 depend on the acidity of the aqueous feed. The solvent mixtures containing monoalkylphosphoric acid mixed with TRPO or RNH2128 and 2-ethylhexyl 2-ethyl-hexyl-phosphonic acid mixed with tertiary amines129,130 were also studied for the extraction and stripping of Fe(III). 4B. Extraction of Iron(III) from Chloride Medium. Acidic Extractant. a. Phosphoric Acids. Biswas et al.131 investigated the solvent extraction of Fe(III) from chloride solution by D2EHPA dissolved in kerosene over a wide range of aqueous acidity as a function of phase contact time, Fe(III), HCl, H+, and Cl- concentration in aqueous phase, D2EHPA concentration in organic phase, and temperature. The dependencies of Fe(III), HCl, H+, Cl-, and D2EHPA vary with the extraction condition used which indicates that the composition of Fe(III) species in both the aqueous and the organic phases vary with the HCl or Cl- concentration in the aqueous phase. Principe et al.136 studied the solubility and stability of several organophosphoric acid extractant in light of the selection of suitable extractants for iron(III) solvent extraction as a potential iron rejection route in zinc processing. Sato et al.133 studied the extraction of Fe(III) from sulfate, chloride, and nitrate medium by D2EHPA. They observed that rate of Fe(III) extraction was fast in chloride and nitrate medium as compared to sulfate medium. Thus D2EHPA combines with Fe(III) by solvating reaction at high acidic condition in Cl- and NO3- and can be expressed by eqs 18 and 19. In HCL : Fe(a)3+ + 3Cl(a)- + 3/2(HX)2(O) S Fe(Cl)3 · 3HX(O) (18)

Ind. Eng. Chem. Res., Vol. 48, No. 13, 2009 3+

In nitric acid : Fe(a)

-

+ 3NO3(a) + /2(HX)2(O) S Fe(NO3)3·3HX(O) (19) 3

They also confirmed that dependence values of extraction rate on hydrogen ion and D2EHPA concentration are in the first and inverse first orders. b. Phosphonic Acids. Didi et al.134 studied the effect of chain length of alkane-1-hydroxy-1,1′-methyldiphosphonic acids on the iron(III) liquid-liquid extraction. Lee et al.135 investigated the separation of iron and nickel from a spent FeCl3 etching solution by solvent extraction using Alamine 336, MIBK, and PC-88A as extractants and highest extraction percentage of iron was obtained with Alamine 336. c. Phosphinic Acids. The extraction of Fe(III) from hydrochloric acid solution has been investigated using Cyanex 923 (TRPO) in xylene by Saji et al.136 It was observed that extraction of iron(III) increases with increasing concentration of both hydrochloric acid and extractant. The extraction behavior of Fe(III) was compared with other metal ion: titanium(IV), chromium(VI), and vanadium(V), which are associated with iron in ilmenite leach liquors. The stripping percentage of Fe(III) with hydrochloric acid from the loaded Cyanex 923 was found to decrease with an increase in acid concentration. Remya et al.137 investigated the solvent extraction separation of titanium(IV), vanadium(V), and iron(III) from simulated waste chloride liquors of titanium minerals processing industry by trialkylphosphine oxide Cyanex 923 (TRPO) in kerosene as extractant. d. Carboxylic Acids. Preston and du Preez138 studied the separation of some bivalent metals by a mixture of versatic 10 and pyridinecarboxylate. They found that using pyridinecarboxylate esters causes appreciable synergistic shifts in the pH50 values for the extraction of some divalent base metals by solutions of Versatic 10 acid in xylene. For n-octyl 3-pyridinecarboxylate, the synergistic shifts decreased in the order Ni > Co > Cd > Cu ≈ Fe > Mn > Zn, and for the commercial extractant Acorga DS5443A, in the order Ni > Cu > Co > Fe > Cd > Mn > Zn. No synergistic effects were observed for divalent lead, calcium, and magnesium. On the basis of the pH50 values obtained, several possible practical metal separations are suggested. No loss of metal-loading capacity was found when the organic phases were contacted with 1 M sulfuric acid for prolonged periods at 30 °C. A process for the preparation of high purity iron compounds for use in ferrite manufacture by substoichiometric extraction with sodium salt of a C6 to C10 aliphatic monocarboxylic acid has been described by Mu¨hl et al.139 The feed is commercially pure iron (from a carbonyl process) is dissolved in hydrochloric acid. The loaded solvent is scrubbed with pure FeCl3 from a bleed of strip liquor. Stripping is achieved with NaOH solution. The work is based upon the order of cation extractant reported by Gindin.140 The mechanism of iron extraction has also been investigated.141 Basic Extractant. Nasu et. al142 studied the extraction of iron(II) and iron(III) as their anionic thiocyanate complexes with tetrabutylammonium ions in chloroform. Costa et al.143 studied solvent extraction of iron(III) from hydrochloric acid solutions using N,N′-dimethyl-N,N′-diphenylmalonamide (DMDPHMA) and N,N′-dimethyl-N,N′-diphenyltetradecylmalonaamide (DMDPHTDMA). A mechanism for iron(III) extraction from chloride media by DMDPHMA and DMDPHTDMA is proposed, and a comparison between their extraction behavior and involved mechanisms for both chloride and nitrate media is being considered as well. Stripping of the loaded Fe is a major problem encountered. In this study, the authors observed that, for similar aqueous solutions, the percentage of iron(III)

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stripping from DMDPHMA strongly depends upon the organic diluent used. Iron(III) can be completely recovered by simple contact with water if 1,2-dichloroethane is used as diluent. But when toluene was used, iron(III) was just partially stripped, and there was no stripping of iron when CCl4 was used as diluent. The partial iron(III) stripping efficiencies obtained for DMDPHMA in toluene or in tetrachloromethane can be due to a lower solubility of the metal-ligand adducts in the organic media, since when those diluents were involved, a yellow solid appeared after extraction of iron(III) from the initial aqueous solutions for some cases. Lee et al.144 investigated the solvent extraction equilibrium of FeCl3 from hydrochloric acid solution with Alamine 336. Solvent extraction reaction depended on the ratio of initial concentration of Alamine 336 to FeCl3. When the concentration of Alamine 336 was in excess to that of FeCl3, the extractant reacted as a dimer. When the initial concentration ratio of Alamine 336 to FeCl3 was below three, ferric chloride was extracted by monomeric extractant. They also studied the chemical equilibrium in ferrous chloride acid solution. The solvent extraction behavior of FeCl2 with Alamine 336 was explained with the distribution of Fe(II) species. The predicted pH values for the FeCl2-HCl-H2O system agreed well with those experimentally measured at 25 °C. Costa et al.145 investigated a new, simple, and effective method for iron(III) extraction from acidic chloride solution involving the use of a N,N,N′,N′-tetrasubstituted malonamide, N,N′-dimethyl-N,N′dibutylmalonamide (DMDBMA). The behavior of this ligand toward iron(III) extraction was investigated for different experimental conditions with a particular emphasis on the influence of HCl, LiCl, and legand concentrations. Paiva et al.146 studied the application of N,N′-tetrasubstituted malonamides to the recovery of iron(III) from chloride solution. They observed that Fe(III) extraction depends on the HCl concentration in the aqueous phase and suggested that the extraction could either be by an anionic pair mechanism (eq 20) HmLm+·mCl(org)- + FeCl4(aq)- S (HmLm+)·(2m - 1)Cl-·FeCl4(org)- + Cl(aq)-HmLm+·mCl(org)- + FeCl4(aq)- S (HmLm+)·(2m - 1)Cl-·FeCl4(org)- + Cl(aq)- (20) or by salvation mechanism (eq 21) L(org) + HFeCl4(aq) S L·HFeCl4(org)L(org) + HFeCl4(aq) S L·HFeCl4(org) (21) Miguel et al.147 describes the extraction of Fe(III) and several other metal ions from 1 to 4 M HCl media by Adogen 364, a commercial trialkylamine. Solvating/Neutral Extractant. The extraction of iron(III) from hydrochloric acid solution by ethyl ether was one of the earliest systems studied in inorganic chemistry. As early as 1892, Rothe148 recognized the possibilities of this process. Tri-n-butyl phosphate (TBP) and methyl iso-butyl ketone (MIBK) have been used by several investigators for the extraction of iron(III) from hydrochloric acid solutions. Specker and Cremer149 were the first to report data on the extraction of iron(III) chloride with TPB. They used TBP (1-5%) dissolved in benzene and concluded that the species extracted are FeCl3 · 3TBP from 4 N and HFeCl4 · 2TBP from 6-9 M HCL solutions. Majumdar and De150 reported quantitative extraction of iron(III) from 3-6 M HCl using 100% TBP. The metal concentration used in their studies was 0.92 kg/m3. They too reported the extracting species to be FeCl3 · 3TBP from 2 M and HFeCl4 · 2TBP from 6 M acid solutions. Thornhill et al.151 described the separation of irom

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(∼2 kg/m3) from HCl solutions (160 kg/m3) containing iron, cobalt, copper, and nickel obtained from nickel matte leaching, using 2 vol % TBP as the solvent. Ishimori et al.152 reported the extraction of iron at higher concentrations using TBP. They observed that distribution coefficient values were lower compared to those obtained at microlevel iron concentrations and that they are independent of the acid concentration. Other investigators have also reported the extraction of iron(III) from chloride solution using TBP.153-156 The extraction of FeCl3 from HCl solutions using MIBK was investigated as a function of iron and HCl concentrations by Song et al.157 Iofa et al.158 reported the extraction of Fe(III) using MIBK from 1.5 M HCl solutions. They observed that the distribution coefficient increased with temperature in the range 5-60 °C. Yamamura et al.159 described a process for the extraction of iron from ilmenite leach liquors. From a solution containing 235 kg/m3 FeCl3 and 159 kg/m3 of HCl, in addition to other metals, iron(III) was extracted in 3 stages using a 1:1 MIBK-benzene solvent mixture. Chiba and Kimura160 described a process for the production of high-purity iron oxide from waste acid pickle liquor using MIBK. They observed that HFeCl4 is the extracting species. The extraction was carried out at macrolevel concentration of iron from about 5.5 M HCl medium. A few authors have reported the use of MIBK for iron extraction at higher concentration of both iron and HCl. Rao et al.161 found third phase formation and poor phase disengagement while extraction of iron(III) from concentrated solution. Reddy et al.162 investigated TBP and MIBK as a suitable solvent for extraction of iron(III) at about 1 M iron(III) concentration. Thomas et al.163 studied the selective extraction of iron(III) from waste chloride liquor of titanium mineral processing industry using tributyl phosphate (TBP) in kerosene as an extractant. The results demonstrate that iron(III) is extracted into kerosene as HFeCl4 · 2TBP represented as in eq 22 3+

Feaq

+

-

+ Haq 4Claq + 2TBPorg S HFeCl4 · 2TBPorg (22) 164

Pospiech et al. investigated the separation of Fe(III) from acidic aqueous solutions containing Mn(II), Ni(II), Co(II) and Cu(II), 1 M HCl, and 2.0 M NaCl with 3.6 M TBP. Extraction of Fe(III) was found to be 99.8%. Fe(III) forms various complexes, and at around a 4.0 M Cl- concentration, Fe(III) exists as FeCl2+, FeCl2+, FeCl3, and FeCl4-. Hence, Fe(III) is extracted by different mechanisms such as by adduct formation (eq 23), FeCl3(aq) + TBP(org) S FeCl3·TBP(org)

(23)

ionic association with the anionic complexes (eq 24), FeCl4(aq)- + H(aq)+ + TBP(org) S FeCl4TBPH(org)+ (24) and by ionic association with the cationic complexes (eq 25). FeCl2(aq)- + Cl(aq)- + TBP(org) S FeCl2+Cl-TBP(org) (25) The extraction behavior of Fe(III) and Ti(IV) from acid chloride solutions has been investigated by Saji et al.165 using 3-phenyl-4-benzoyl-5-isoxazolone (HPBI) in xylene as an extractant. The results demonstrate that these metal ions are extracted into xylene as Fe(PBI)3 and TiO(PBI)2. Remya et al.166 carried out solvent extraction separation of titanium(IV) and iron(III) from multivalent metal chloride solution using 3-phenyl-4-acyl-5-isoxazolones as a reagents. Regel-Rosocka et al.167 studied the iron(II) transfer to the organic phase during zinc (II) extraction from spent pickling solution with tributyl phosphate (TBP). A hypothesis on the mechanism of Fe(II) transport is proposed. Grzeszczyk et al.168 studied the extraction

of zinc(II), iron(II), and iron(III) with a solution of dibutylphosphonate (DBBP) from hydrochloric acid solution. Iron (II) was only slightly extracted by DBBP. The transfer of iron(III) was effective, due to the neutral chlorocomplex at high Cl- and HCl concentration. Chelating Extractants. Rabah et al.169 discusses a method to recover copper and iron and some of their valuable salts from spent hydrochloric acid used to clean up dirty car radiators and to recycle the acid using LIX 860. Mixed Extractant. Hirato et al.170 investigated the usage of a mixture of D2EHPA-TBP in kerosene in the stripping of Fe(III). It was found that this mixture is effective in stripping of Fe(III) and that less concentrated acid solution is required as a stripping agent. They examined the role of TBP critically in the improvement of Fe(III) stripping from the mixed solvent by extracting HCl with TBP and the spectrum of Fe(III) loaded organic phases. The results of spectrum analysis indicated that in the presence of HCl, Fe(III) is liberated from D2EHPA in a mixed solvent by forming a complex with TBP by the following mechanism: Stripping of Fe(III) from organic solution containing D2EHPA alone can be represented as FeR3(RH)n(o) + 3H+ ) Fe3+(aq) + (3 + n)RH(o) (26) R ) D2EHPA, (o) and (aq) are Fe(III) in the organic and aqueous phases, respectively. Stripping of Fe(III) from the mixed solvent containing D2EHPA and TBP can be represented as TBP(o) + HCl(aq) ) (TBP:HCl)(o)

(27)

3(TBP:HCl)(o) + FeR3(RH)n(o) ) (TBP:FeCl3)(o) + (3 + n)RH(o) + 2TBP (28) (TBP:FeCl3)(o) ) TBP(o) + FeCl3(aq) 171

(29)

Reddy et al. carried out the extraction of iron(III) at about a 1 M concentration from hydrochloric acid solution using tri-nbutyl phosphate (TBP), methyl-iso-butyl ketone (MIBK), and their mixtures as a solvent. It was found that a solvent mixture consisting of 70% TBP and 30% MIBK was found suitable to achieve faster phase separation with no third phase formation. The two solvents, when used together, were also found to exert a synergistic effect on iron(III) extraction. Sandhibigraha et al.172 studied the solvent extraction of Fe(III) from aqueous hydrochloric acid solution using D2EPHA, PC-88A, Cyanex -272, and their mixture. While studying the salt effect, it was observed that sodium sulfate and sodium chloride lower the extraction efficiency of Fe(III) and sodium nitrate enhanced the extraction efficiency. Synergism was observed with binary mixture of extractants. Sahu and Das173 investigated the extraction of Fe(III) from chloride solution at a macrolevel concentration by different solvents such as tri-n-butyl phosphate (TBP), D2EHPA, and their mixture in various proportions at different acid concentrations. The synergistic extraction of iron(III) with a mixture of TBP and D2EPHA was studied and results were compared with that of the extraction by individual solvent alone. An increase in the concentration of the synergist, TPB, in the D2EPHA-TBP solvent system resulted in an increase in the synergistic coefficient value. Sahu and Das174 also studied the extraction of concentrated Fe(III) from acid chloride solution with MIBK, TBP, D2EHPA, and their mixture in various proportions, at different acid concentrations. On comparing the extraction of Fe(III) with mixed and individual extractant, it was found that both D2EHA-MIBK and D2EPHA-TBP mixtures exhibited synergism, the latter


having better extraction ability. They also observed that stripping of Fe(III) from D2EHPA-MIBK loaded solvent is better than that of D2EHPA-TBP. Voshkin et al.175 describe the extraction of Fe(III) using binary extractants based on quaternary ammonium bases and dialkyl phosphoric acids. Reddy et al.176,177 reported a solvent extraction process for the recovery of high purity chloride from the titanium minerals processing industry using a mixed-solvent system consisting of TBP and MIBK. They found that a solvent mixture consisting of 70 vol % TBP and 30 vol % MIBK was found suitable for extraction of Fe(III) from a chloride solution. Nearly 99.4% extraction and 100% stripping could be achieved in five stages. The problem associated with individual usage of MIBK and TBP could be overcome by using their mixture with a synergistic effect in the extraction of iron(III). In another study, Imura et al.178 examined the extraction behavior of iron(III) with 4-isopropyltropolone (Hipt) in various solvents in both the presence and absence of 3,5-dichlorophenol (DCP) as a synergist. They observed a great enhancement in the extraction of iron(III) with Hipt after the addition of 3,5-dichlorophenol as a hydrogen donor and heptanes and cyclohexane as efficient synergists. Equilibrium studies of a heptanes system has demonstrated the formation of adduct complexes of iron(III) chelates such as Fe(ipt)3 · nDCP (n ) 1-3) and reagents such as Hipt · nDCP (n ) 1, 2). The overall extraction equilibrium can be expressed as Fe3+ + 3Hiptorg + nDCPorg S Fe(ipt)3·nDCPorg + 3H+ (30) Shuqiu and Chen179 studied the extraction of iron(III) from sulfate solution by tertiary amine and 2-ethylhexyl 2-ethylhexylphosphonic acid or dialkylphosphonic acid. They also observed that the extraction and stripping ability of the solvent improved by the addition of trialkyl amine, and dilute sulfuric acid was found to be sufficient to strip the loaded iron from the solvent. The authors suggested that the active hydrogen atoms in the tertiary amines play an important role in the extraction of iron by phosphonic and phosphinic acid by the formation of a molecular association, in a low acidity solution as shown below.

(33) HA S H+ + AFor primary and secondary amine and for tertiary amine the acid will dissociate as The amine sulfate formed will associate with HA as (R3NH)2SO4 + HA f (R3NH)2SO4·HA

(34)

As seen in eq 31, a cyclic structure is formed by the active hydrogen atoms in primary and secondary amines and the phosphoric acid, which is not found in the case of the tertiary amine since there is no hydrogen atom to form any bond. Thus at a higher acidity, tertiary amine forms an amine salt so there is no synergism in the extraction of Fe(III) by a mixture of tertiary amine and a phosphoric acid. Chang et al.180 studied several types of commercial extractants for the separation of iron from zirconium in concentrated HCl solution. TBP and a

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mixed extractant (D2EHPA and Kelex 100) extract iron in concentrated HCl solution, but the separation of iron from zirconium is poor. Aliquat 336 extracts iron very effectively in concentrated HCl solution, and the separation of iron from zirconium is excellent for HCl concentrations between 3 and 4 M. Bartkowska et al.181 studied the extraction of zinc(II), iron(III), and iron(II) with TBP and its binary mixture with D2EHPA and Cyanex 302 from hydrochloric acid solution. Iron(III) was strongy extracted by TBP and its binary mixtures with DEHPA and Cyanex 302, and the extraction fell in the following order: binary mixture with DEHPA or Cyanex 302 > TBP > DEHPA . Cyanex 302. Fe(II) did not interfere during extraction of Zn(II). Thus zinc extraction with a binary mixture of the extractants could be written as (2 + n)(HL)2o + 2Znw2+)(ZnL2)2·n(HL)2o + 4Hw+ (35) Iron(II) was not extracted by the considered extractants. There was an increase in Zn(II) extraction with TBP and the TBP-DEHPA mixture in the presence of Fe(II). It was also observed that the tendency to take water by TBP could be decreased by adding acidic extractant such as D2EHPA or Cyanex 302. 5. Extraction of Copper and Nickel from Copper Bleed Streams As already discussed above, CBS contain an appreciable amount of Cu and Ni and are not taken care of properly since a huge amount of metal value is lost. Nowadays, the treatment of wastewater constitutes a crucial part of most industrial processes. Due to very strict legislation, companies have been forced to decrease the concentration of certain metal ions in the effluent streams. The most common form of effluent treatment involves the precipitation of metal as hydroxide, basic salt, or sulfide. But, metal-containing hydroxide and sulfide sludge from precipitation processes causes a severe problem since those products are rarely processed for metal recovery. In the copper industry, the electrolyte which is discarded intermittently is decopperized to remove copper until the concentration of Cu and Ni becomes same; then at this stage, either the mixed salt is crystallized out or it is further decopperized to get copper with other impurities. The black acid is further recycled. However in this method, the metal values are not recovered completely making the CBS treatment costly. Second the concept of recovery-reuse-recycling of metal containing waste makes these wastes a good secondary source for metal recovery. Various methods have been developed to date such as solvent extraction (SX), ion exchange, supported liquid membrane technology (SLM), etc., each of them having their own advantages and disadvantages. However, metals in pure form can be obtained by using SX. In view of the industrial and economic importance of these metals, there is a great need to separate and recover them using cost-effective commercial extractants. Literature survey reveals that liquid-liquid extraction has been applied extensively for the separation and recovery of copper, cobalt, and nickel. During the last two decades, the commercial availability of copperselective extractants has proposed a particular stimulus to the use of solvent extraction a hydrometallurgical unit operation in processing of copper containing leach liquor.182-185 These leach liquors arise through hydrometallurgical processing of raw materials such as lean grade ores, spent catalysts, scrap, complex sulfides, etc. Presently, more than 20% of the total world production of copper is achieved through the solvent extraction route.186

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In the process of developing extractants for copper recovery, various reagents with little variation in their structure and composition have been introduced into the industry under trade names LIX 64N, LIX 84 (Henkel), SME 529 (Shell), P17, P50, P5300 (Acorga), and Kelex 100 (Ashland). Among the various copper extraction reagents, LIX 64N was used on the commercial scale in a number of copper industry operations.187 Calligaro et al.188 studied the extraction of copper, nickel, cobalt, zinc, and iron from solution using LIX 64N in kerosene. The order of extractability as a function of pH was Cu(II) < Fe(III) < Ni(II) < Zn(II) < Co(II). Amal et al.189 established conditions for purification of copper-containing waste solution (on a plant scale employing mixer settlers) using LIX 84. The extractionstripping reaction of copper with a chelating reactant can be described as follows: Cuaq2+ + 2RHorg S R2Cuorg + 2Haq+

(36)

190

In China, LIX 84 is being used in four plants to produce copper from oxide ores. In addition, many LIX reagents were also used earlier for the extraction, separation, and recovery of copper, nickel, and zinc mostly from ammoniacal sulfate solutions using LIX 87QN, LIX 54, LIX 973, LIX 984, and LIX 34, respectively.191-197 Of the LIX reagents, LIX 84198 was used commercially for extraction and also for selective removal of copper ions from aqueous solutions using modified silica beads impregnated with LIX 84I.199,200 Also, it was used for the recovery of nickel and separation of nickel and copper from ammoniacal solutions through coextraction and selective stripping.201,202 Alguacil and Cobo203 studied the coextraction of copper and nickel from ammoniacal/ammonium carbonate aqueous media using LIX 973N diluted with Iberfluid. Basically, LIX 973N is a mixture of 5-alkylsalicylaldoxime and 2-hydroxy5-alkylaceto-phenone oxime, with the aldoxime in excess. The influence of equilibration time, temperature, equilibrium pH, and extractant concentration on the extraction of both metals has been studied. It was observed that neither copper nor nickel extraction is sensitive to temperature and equilibrium pH; however, nickel extraction needs a contact time of 20 min to reach equilibrium as compared to 5 min for copper. In addition, nickel extraction depends greatly on the extractant concentration in the organic phase. For a solution containing 3 g/dm3 each of copper and nickel and 60 g/dm3 ammonium carbonate, conditions were established for the coextraction of both metals, ammonia scrubbing, and selective stripping (with H2SO4) of nickel and copper. In ammoniacal medium, the extraction of Cu and Ni by LIX 973 can be shown as follows: Me(NH3)4aq2+ + 2HRorg S MeR2org + 2NH4aq+ + 2NH3aq (37) Using the appropriate extractant concentration, the yield (extraction stage) for both metals is near 100%, whereas the percentage of nickel and copper stripping is also almost quantitative. Reddy et al.204 studied the extraction of nickel(II) from sulfate solutions using LIX 84I as an extractant. The percentage extraction behavior of Cu(II), Ni(II), and Zn (II) was greatly dependent on equilibrium pH of the aqueous phase. Thus the extraction of Cu(II) started at pH > 0.2 and reached quantitative amounts at equilibrium pH ∼ 4. Under these conditions, the extraction of Ni(II) and Zn(II) was nil. Carlos et al.205 studied the statistical modeling of the equilibrium in the solvent extraction of copper from sulfuric acid and ammoniacal sulfate solutions by mixtures of LIX 64N and SME 529. This study employed an incomplete threelevel factorial design involving four variables, viz., the copper

and sulfuric acid or ammonia concentrations in the aqueous phase and the concentrations of the two extractants in the organic phase. The equilibrium models showed that the active oximes in LIX 64N and SME 529 are completely compatible as regards the extraction of copper without any synergistic effects between the reagents being observed. The percentage of copper extracted increases with increased extractant concentration in the organic phase but is affected adversely by increased sulfuric acid and copper sulfate concentrations in the aqueous phase. As expected, the equilibrium extraction of copper is influenced by the nature of the diluents, and thus, a higher copper extraction was observed with mixtures of LIX 64N and SME 529 when MSB-210 was used as diluents as compared to Escaid 100. This may be attributed to the fact that a higher aromatic content gave a lower degree of oxime aggregation. It was also found that the copper loading efficiency of the reagents was high when the extraction was done from ammoniacal solutions86.6% and 89.4% Cu in the diluents MSB-210 and Escaid 100, respectivelyswhereas extraction from sulfuric acid solution was only 47% for MSB 130 and 43.4% for Escade 100 as diluent. It was also observed that copper loading efficiencies greater than 100% were obtained when the aqueous copper concentration is high in ammoniacal media. This overloading is attributed to the uptake of ammonia by the hydroxyoximes and can be expected to increase with increasing aromatic content of the diluent, as in the case of Escaid 100 where the oxime aggregation is decreased. One of the new chelating extractants in this field is MOC 45 (oxime derivative) developed by ALLCO Chemical.206 There is limited information on the use of MOC 45. Amores et al.207 have studied the application of MOC for copper extraction from sulfate solutions. The species extracted into the organic phase were reported to be CuR2 and Cu(HR2)2. Rao et al.208 have studied the extraction and recovery of copper from a solution containing 0.1 M each of copper and sodium sulfate using MOC 45 as the extractant. An increase in equilibrium pH and extractant concentration increases the percentage extraction of metal ion. The extracted species appears to be CuR2. Much effort has been devoted to the production of suitable ligands and diluents for the complexation and extraction of copper and nickel ions.209 The efficiency of the extraction may be improved by a discerning choice of organic solvent, counterion, and pH.210 D2EHPA is a commercially used phosphoric acid. It has been widely used in liquid-liquid extraction for the separation and purification of liquid effluents containing various metals.211-215 Extraction of copper using D2EHPA has been shown to occur by an interfacial reaction mechanism. It was assumed that the extraction of metal ions took place mainly by reaction with extractant molecules adsorbed at the interface and not by reaction in the bulk liquid, on account of the high interfacial activity of D2EHPA and its low solubility in the aqueous solution. In addition, it was suggested that the overall extraction rate was mainly controlled by diffusional resistance in the immediate vicinity of the interface.216 D2EHPA and PC-88A are considered to be suitable liquid cation exchanger for separation of Zn, Cu, Mn, Co, and Ni.217-221 Thakur et al.222,223 has reported that the separation factor between Co and Ni increases with increase in loading of Co, and similarly, the separation factor between Cu and Co increases with the loading of Cu while the separation factor between Mn and Co decreases with the loading of Mn in the PC-88A system. They also investigated the distribution of Mn, Cu, Co, and


Ni, i.e., distribution coefficient (D) against initial aqueous acidity (Hi) at various initial concentration (Ci) of metals, using PC-88A in kerosene and utilized the data to derive the mathematical models of their extraction behavior. Extraction of copper using D2EHPA has been shown to occur by an interfacial reaction mechanism. It was assumed that the extraction of metal ions took place mainly by reaction with extractant molecules adsorbed at interface and not by reaction in bulk liquid, on account of high interfacial activity of D2EPHA and its low solubility in the aqueous solution. In addition, it was suggested that the overall extraction rate was mainly controlled by diffusional resistance in the immediate vicinity of the interface.223 Belkhouche et al.224 studied the extraction of Cu(II) and Ni(II) from acetate media with D2EPHA under optimal conditions. Cu and Ni were extracted from the acetate media as CuCH3COOR · HR and NiCH3COO · (H2O)2 · R. These species were in agreement with the one proposed in other media with the same reagent whereas the infrared and UV spectroscopic methods confirm the structure of the metals complex, formed in the organic phase. Cu(II) is extracted as an m-merized complex into an organic phase with small D2EHPA concentration which can be represented by the following general equation: Mn+ + (n + x)/2(H2R2) S MRn·xHR + nH+

(38)

where M is Cu or Ni, H2R2 represents the dimeric form of DEHPA in n-heptane, and the bar indicates the species in the organic phase. However, in acetate medium, the extraction is represented as Cuaq2+ + CH3COOaq- + (H2R2) S CuCH3COOR·HR + Haq+(39) Niaq2+ + CH3COOaq- + 2H2O + 1/2(H2R2) S NICH3COO·(H2O)2·R + H+ (40) Sarangi et al.225 studied the separation of iron(III), copper(II), and zinc(II) from a mixed sulfate/chloride leach liquor bearing 11.8 kg/m3 iron, 24.8 kg/m3 copper, 0.23 kg/m3 zinc, 3.8 kg/m3 cobalt, 35.2 kg/m3 nickel, 176.3 kg/m3 chloride, and 48.9 kg/ m3 sulfate using TBP, LIX 84I, and Cyanex 923 in kerosene, respectively. The use of mixed extractant system in liquid-liquid extraction of metal ions had received significant development. An increase of the extraction efficiency has been observed due to synergistic enhancement.226 A synergistic effect on the extraction of the metals is seen in mixed extractant systems, suggesting the formation of a mixed complex containing both extractants.227 Preston in 1982219 studied the extraction of Cu(II) and Ni(II) from acetate media with D2EHPA under the optimal conditions. Improved extraction of divalent transition metal ions was found with mixtures of an oxime of aliphatic aldehydes and an organophosphoric acid, and the enhancement of extraction was found to increase in the order Fe(II) > Co(II) > Cu(II) > Ni(II). The synergism was greater for nickel extraction and the selectivity of cobalt over nickel shown by an organophosphoric acid alone such as D2EHPA was reversed.221,228-230 Previous studies by De Ketelaere,231 Van de Voorde et al.,232 and Zhang et al.233 were focused on the extraction of nickel(II) with combinations of organophosphoric or phosphinic acids and chelating oximes. Those combinations of extractants also enhanced the distribution coefficient of Ni(II). Ketoximes are weaker

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extractants than the aldoximes but are more readily stripped at lower acidic levels. Replacing an organophosphoric acid by a phosphinic acid increased the selectivity, but the kinetics of the nickel extraction was slower. Synergism has also been observed when pyridinecarboxylate esters and carboxylic acids have been combined.234,235 By adding pyridinecarboxylate esters to carboxylic acids, substantial shifts were found in the pH 0.5 values for the extraction of Ni(II) and Co(II). Previous studies also showed that the introduction of certain anion ligands to the aqueous solution containing metal ions, such as acetate ions, greatly improved the extraction efficiency.236,237 Gu et al.236 also studied the influence of the addition of acetate ions to an aqueous solution containing Co(II) ions. D2EHPA was used as the extractant, and a low odor paraffin solvent (LOPS) was used as the diluent. Higher percentage extractions were observed in the presence of acetate ions. They suggested that the water molecules in the hexa-aqueous cobalt(II) complex are replaced by the ligand. This ligand-cobalt(II) complex reacts quickly with the extractant and therefore enhances the reaction rate. Furthermore, the anionic ligand has a hydrophobic-hydrophilic molecular structure; therefore, it shows a surface-active property. The ligand-metal complex tends to gather at the aqueous-organic interface more than the hydrated metal ions do. In this way, the metal ions are relatively concentrated at the membrane interface. This is favorable for the kinetics of the membrane extraction process and is called ligand-accelerated liquid membrane extraction. The results presented in this article however always deal with equilibrium conditions, so the kinetic aspect was not studied. The ligand effect in the liquid membrane extraction could in practice result in shorter contact times being necessary between the phases. In the case of wastewater treatment by means of liquid membranes, certain useful ligands may already be present in the effluent and as a result improve the separation process. Sarkar and Dhadke237 also studied the extraction of cobalt (II) in the presence of acetate ions. Cyanex reagents were used as extractants diluted in toluene. Sole and Hiskey238 determined the metal to reagent ratio to be 1:2 for Cyanex 272 [bis-(2,4,4-trimethylpentyl) phosphinic acid], Cyanex 302 [corresponding monothiophosphinic acid], and Cyanex 301 [corresponding dithiophosphinic acid] while Sarkar and Dhadke237 revealed a 1:1 ratio for Cyanex 301 with cobalt(II). The plot of log D versus log[acetate] also showed that acetate ions were present in the organic extract in the ratio 1:2 for Cyanex 272 and 302 while it was 1:1 for Cyanex 301. These findings received additional support from their IR-spectral studies in contradiction to the results of Gu et al.236 Nakashio et al.239 used 0.1 M (Na, H) acetate buffer as a model solution in the studies of Cu(II) extraction equilibriums with 2-ethylhexyl phosphonic acid mono-2ethylhexyl ester dissolved in n-heptane or toluene. More recently, sodium acetate was also used in model solutions by Simonin et al.240 To study the effects of salts on the kinetics of extraction of cobalt(II) and zinc(II) by D2EHPA dissolved in n-dodecane, De Ketelaere231 also found that higher extraction levels were obtained for the transport of nickel(II) when acetate ions were added to the aqueous phase. Shibata et al.241 also investigated the leaching-solventextraction-electrowinning method for the extraction of Cu2+ as a closed system and lessened the waste generation from the process. On the basis of their investigation, they have reported the extraction mechanism of Cu2+ with EHO (2-ethylhexanal oxime) from the leach solution obtained after leaching copper

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sulfide ores with ferric chloride solution. The extractant EHO was found to be very effective in the separation of Cu2+ from the leached solution containing Fe2+, Fe3+, and Zn2+ at a chloride ion concentration of 3.5 mol/dm3 without any interference from Fe3+ and Zn2+. The stages and phase ratio (A/O) required to attain the desired Cu2+ recovery were estimated to be two-stage countercurrent extraction with the phase ratio (A/ O) of 1.5. The loaded Cu was stripped with water in six stages at an O/A of 1.8. Thus by the extraction and stripping operation, 10 g/dm3 Cu2+ could be purified and concentrated to 25 g/dm3 Cu2+. 6. Conclusion This paper gives an overview on the iron and copper recovery/ removal from industrial wastes with more stress on the liquid wastes such as sulfate/chloride pickle liquor from iron and steel manufacturing and the bleed streams generated in the electrolysis industries. In both these types of waste streams, there is a buildup of acidity and metal impurity in due course of time. The nature of waste generated becomes very complex and hazardous. Hence, it becomes mandatory for industries to treat these wastes before disposal. The current practice of acid neutralization and precipitation of the metallic contents as sludge leads to the loss of the metal value present, and the burden of sludge disposal still remains a big issue due to the possibility of leaching of metals from the sludge and its effect on the environment in the long run. Hence the idea of the 3R’s, i.e. recover-recycle-reuse, of these wastes has become the main focus of the research community leading to the development of new approaches for the recovery of metal value from waste and recycling the water back to the system or disposing of it safely. In this paper, various aspects on iron recovery from waste pickle liquor and copper recovery from copper electroplating/ electrorefining units by solvent extraction methods have been discussed. Various types of solvents used for metal extraction such as cationic, anionic, chelating, mixed solvents, and binary solvents have been discussed. With the development of a newer variety of solvents, extraction of copper has become quite feasible and easy. However, iron recovery by solvent extraction remains a difficult job because 100% stripping of the loaded iron is quite difficult although there are several good extractants for iron. Acknowledgment The authors wish to thank the Director, National Metallurgical Laboratory, for his kind permission to publish this paper. Literature Cited (1) Agrawal, A.; Kumari, S.; Ray, B. C.; Sahu, K. K. Extraction of acid and iron values from sulphate waste pickle liquor of a steel industry by solvent extraction route. Hydrometallurgy 2007, 88, 58. (2) Nyirendar, L.; Phiri, W. S. The removal of nickel from copper electrorefining bleed-off electrolyte. Miner. Eng. 1998, 11 (1), 23. (3) Agrawal, A.; Bagchi, D.; Kumari, S.; Pandey, B. D. An overview of process options and behavioural aspects of the copper values recovered from copper bleed stream of a copper smelter developed at NML. Miner. Process. Extr. Metall. ReV., in press. (4) Shibata, J.; Hashiuchi, T.; Kato, T. Tamano refinery’s new processes for removing impurities from electrolyte. In The Electrorefining and Winning of Copper; Proceeings of the 116th Annual Meeting, Denver, CO, Feb 2426; Hoffman, J. E., Bautista, R. G., Ettel, V. A., Kudryk, V., Wesel, R. J., Eds.; AIME: Pennsylvania, 1987; p 99. (5) Toyabe, K.; Segawa, C.; Sato, H. Impurity control of electrolyte at Sumitomo Nihama Copper refinery. In The Electrorefining and Winning of Copper; Proceeings of the 116th Annual Meeting, Denver, CO, Feb 24-

26; Hoffman, J. E., Bautista, R. G., Ettel, V. A., Kudryk, V., Wesel, R. J., Eds.; AIME: Pennsylvania, 1987; p 117. (6) Nagai, T.; Yama Zaki, N.; Kobayashi, M. Purification of copper electrolyte by solvent extraction. In 11th Meeting on Electrolytic Metallurgy Symposium on SolVent Extraction, July 1979; p 27. (7) Jha, M. K.; Kumar, V.; Singh, R. J. Solvent extraction of zinc from chloride solutions. SolVent Extr. Ion Exch. 2002, 20 (3), 389. (8) Ortiz, I.; Bringas, E.; Romań, M. F.; San and Urtiaga, A. M. Selective separation of zinc and iron from spent pickling solutions by membrane-based solvent extraction: process viability. Sep. Sci. Technol. 2004, 39, 1. (9) Regel, M.; Sastre, A. M.; Szymanowski, J. Recovery of zinc(II) from HCl spent pickling solutions by solvent extraction. EnViron. Sci. Technol. 2001, 35, 630. (10) Kirschling, P.; Nowak, K.; Miessiac, I.; Nitsch, W.; Szymanowsky, J. Membrane extraction-stripping process for zinc(II) recovery from HCl solution. SolVent Extr. Res. DeV. 2001, 8, 135. (11) Cierpezewski, R.; Miesiac, I.; Regel-Rosocka, M.; Sastre, A. M.; Szymanowki, J. Removal of zinc (II) from spent hydrochloric acid solutions from zinc hot galvanizing plants. Ind. Eng. Chem. Res. 2002, 41, 598. (12) Mishonov, I. V.; Alejski, K.; Szymanowski, J. A contributive study on the stripping of zinc (II) from loaded TBP using an ammonia/ammonium chloride solution. SolVent Extr. Ion Exch. 2004, 22, 219. (13) Dutrizac, J. E. The physical chemistry of iron precipitation in the zinc industry. In Lead-Zinc-Tin’80, TMS-AIME World Symposium on Metallurgy and EnVironment Control, Las Vegas, NV, February 24–28, 1980; Cigan, J. M., Mackey, T. S., O’Keefe, T. J., Eds.; TMS-AIME: Warrendale, PA, 1980; p 532. (14) Boxal, J. M.; James, S. E. Experience with the goethite process at National Zinc. In Iron Control in Hydrometallurgy; Dutrizac, J. E., Monhemius, A. J., Eds.; Ellis Horwood: Chichester, 1986; p 676. (15) Torfs, K. J.; Vliegen, J. The Union Miniere Goethite process: plant practice and future prospects. In Iron Control and Disposal; Dutrizac, J. E., Harris, G. B., Eds.; The Canadian Institute of Mining, Metallurgy and Petroleum: Montreal, Canada, 1996; pp 135-146. (16) Ropenack, A. V. Hematitesthe solution to a disposal problemsan example from the zinc industry. In Iron Control in Hydrometallurgy; Dutrizac, J. E., Monhemius, A. J., Eds.; Ellis Horwood: Chichester, 1986; p 730. (17) Onazaki, A.; Kuramochi, S. The Versatic acid processsa solution in the zinc industry. In Iron Control in Hydrometallurgy; Dutrizac, J. E., Monhemius, A. J., Eds.; Ellis Horwood: Chichester, 1986; p 297. (18) Steintveit, G. Treatment of zinc leach plant residue by the jarosite process. In AdVances in ExtractiVe Metallurgy and Refining; IMM: London, 1971; p 521. (19) Haigh, C.; Wood, J. Jarosite process boosts zinc. World Miner. 1972, (Sept), 34. (20) Arregi, V.; Gordon, V.; Steintveit, A. R. The jarosite processspast, present and future. In Lead-Zinc-Tin’80, TMS-AIME World Symposium on Metallurgy and EnVironment Control, Las Vegas, NV, February 24– 28, 1980; Cigan, J. M., Mackey, T. S., O’Keefe, T. J., Eds.; TMS-AIME: Warrendale, PA, 1980; p 97. (21) Scott, J. D.; Donyina, D. K. A.; Mouland, J. E. Iron-the good with the badsKidd Creek zinc plant experience. In Iron Control in Hydrometallurgy; Dutrizac, J. E., Monhemius, A. J., Eds.; Ellis Horwood: Chichester, 1986; p 666. (22) Tamargo, F. J.; San, M.; Valcarcel, M. R. Asturiana de zinc: more than 30 years of experience with jarosite process. In Iron Control and Disposal; Dutrizac, J. E., Harris, G. B., Eds.; The Canadian Institute of Mining, Metallurgy and Petroleum: Montreal, Canada, 1996; pp 93100. (23) Buban, K. R.; Collins, M. J.; Masters, I. M. Zinc and Iron Control: Overview Iron Control in Zinc Pressure Leach Processes. J. Met. 1999, 51 (12), 23. (24) Berg, D.; Borve, K. The disposal of iron residue at Norzink and its impact on the environment. In Iron Control and Disposal; Dutrizac, J. E., Harris, G. B., Eds.; The Canadian Institute of Mining, Metallurgy and Petroleum: Montreal Canada, 1996; p 627. (25) Garcia, A.; Valdez. Jarosite disposal practices at the Penõles zinc plant. In Iron Control and Disposal; Dutrizac, J. E., Harris, G. B., Eds.; The Canadian Institute of Mining, Metallurgy and Petroleum, Montreal: Canada, 1996; p 643. (26) Welham, N. J.; Malatt, K. A.; Vukcevic, S. The stability of iron phases presently used for disposal from Metallurgical systems-A Review. Miner. Eng. 2000, 13 (8-9), 911. (27) Galan, B.; Urtiaga, A. M.; Alonso, A. I.; Irabien, A.; Ortiz, M. I. Extraction of anions with Aliquat 336: chemical equilibrium modeling. Ind. Eng. Chem. Res. 1994, 22, 1765.

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ReceiVed for reView September 10, 2008 ReVised manuscript receiVed March 16, 2009 Accepted March 27, 2009 IE900135U

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