The co-precipitation of copper and zinc with lead jarosite

The formation of lead jarosite, Pb_0.5Fe₃(SO₄)₂(OH)₆, in the presence of dissolved copper and/or zinc results in a significant substitution of these metals in the jarosite phase; the co-precipitation is most pronounced in sulphate media but also occurs, to a lesser degree, in chloride solutions. The copper and/or zinc substitute for iron, and under extreme conditions the product approaches beaverite, Pb(Cu,Zn)Fe₂(SO₄)₂(OH)₆, in structure and composition. The extent of co-precipitation increases sharply with increasing concentrations of dissolved CuSO₄ or ZnSO₄ and slightly with either an increasing stoichiometric ratio of PbSO₄/Fe³⁺ or increasing ionic strength. The co-precipitation of copper or zinc is not significantly affected by acid concentration although the yield of product declines with increasing concentration of H₂SO₄. The extent of reaction is relatively insensitive to reaction temperatures in the range 130–180°C and to reaction times in excess of 2 h. Copper is strongly co-precipitated in preference to zinc from solutions containing both metals. Other divalent base metals such as Co, Ni and Mn are also co-precipitated with lead jarosite although not to the same degree as copper or zinc.     

On the Role of Dilution on Selective Hydrolytic Precipitation from Bimetallic Solutions: Zn–Ni Sulfate Solution

This paper introduces and discusses some potential effects of dilution in aqueous precipitation processes. The response of a sulfate solution comprising of 0.3 mol L^?1 Zn and 0.015 mol L^?1 Ni diluted with NaOH solution has been simulated. Considerable changes in separation pH, separation potential and precipitating minerals, have appeared after dilution. An increase in separation pH from 6.86 to 7.45 due to 100 times dilution has been predicted. It has also been revealed that the selectively precipitable zinc decreases from 89.4 to 85.7 % as a result of dilution. The products of zinc precipitation from undiluted and 100 times diluted solutions should be ZnO and Zn₄(OH)₆SO₄, respectively, according to equilibrium analysis. Despite the acceptable agreement of experimental results, the full agreement has been restricted in some cases by kinetic difficulty of ZnO precipitation and local high pH zone effect that has led to nickel co-precipitation.     

Potentiostatic studies of the influence of temperature on lead-silver anodes during electrowinning and decay period

The electrochemical behaviour of the Pb-0.7% Ag anode has been investigated in zinc sulphuric acid electrolyte containing 5, 8, 12?g/L Mn²⁺ by electrochemical measurements at different temperatures of 35°C, 40°C, 45°C. It was observed by cyclic voltammetry before electrolysis that temperature increase from 35°C to 45°C resulted in a decrease in the oxidation peak I (Pb → PbSO₄) and an increase in the oxygen evolution peak II (2H₂O → O₂?+?4H⁺?+?4e). At 2.01?V/SHE, the current densities of Pb-0.7% Ag anode in sulphuric acid solution containing 8?g/L Mn²⁺ at 35°C, 40°C and 45°C increased from 26.5 at 35°C to 28.5 and 37.7?mA/cm² at 40 and 45°C, respectively. In the presence of ZnSO₄ addition to the sulphuric acid solution, the anodic current of oxygen evolution at 2.01?V/SHE decreased by ～ 18% at 40°C. After 2?h of potentiostatic polarisation in the presence of zinc sulphate addition at 2.01?V/SHE, electrochemical Noise Measurements showed that the admittance (corrosion rate) of the Pb-0.7% Ag anode in the zinc electrolyte increased with the increase in temperatures during decay. This tendency was also confirmed by linear polarisation and impedance measurements.     

Copper removal by chelating adsorption in solution purification of hydrometallurgical zinc production

Use of the chelating adsorbent CuWRAM® in the copper removal step of hydrometallurgical zinc process has been studied. This adsorbent contains 2-(aminomethyl)pyridine groups anchored on a polyamine-silica composite and it binds copper and other transition metals by a chelating adsorption mechanism. Equilibrium binding capacity of metal sulfates and sulfuric acid from synthetic and authentic ZnSO₄ process solution was determined at 25-90 °C using batch adsorption measurements. The copper removal efficiency was tested using a laboratory-scale fixed-bed column.Results of the equilibrium measurements show that the selectivity of CuWRAM® is sufficient for feasible separation of copper in the presence of 250-fold zinc excess. Increasing the operation temperature from 25 °C to 60 °C affects only slightly the binding capacity of copper and at the same time decreases the capacity of zinc. In column separation, increasing temperature substantially improves copper removal efficiency from the ZnSO₄ process solution. The improvement is mainly due to enhanced intra-particle mass transport. The positive effect is further amplified by marked decrease in viscosity of the feed solution. The optimum temperature for copper removal appears to be around 60 °C. According to the results of this study, copper can be separated from the authentic ZnSO₄ solution by the chelating adsorbent, while nickel, cobalt and cadmium must be separated by means of conventional methods like cementation with zinc dust. A process scheme is proposed for the solution purification step in the zinc process.     

Selective hydrogenation of benzene to cyclohexene over monometallic ruthenium catalysts in the presence of Ce02 and ZnS04 as co-modifiers

The monometallic Ru catalysts with the CeO2 without calcination and ZnSO4 as co-modifiers gave a cyclohexene yield of 58.5% at the optimum nominal CeO2/Ru molar ratio of 0.15. Moreover, this catalyst had a good stability. The chemisorbed （Zn（OH）2）3（ZnSOa）（H20）3 salt on Ru surface, which was formed by the CeO2 reacting with ZnSO4, created the new Ru active sites suitable for the formation of cyclohexene and improved the selectivity to cyclohexene. In addition, the Zn2＋ in the aqueous phase could form a stable complex with cyclohexene, stabilizing the cyclohexene in the liquid phase and improving the selectivity to cyclo- hexene. The calcination treatment of CeO2 was not beneficial for the enhancement of the selectivity to cyclohexene since it is difficult for the CeO2 calcinated to react with ZnSO4 to form the （Zn（OH）2）3（ZnSO4）（H20）3 salt.     

Kinetics and mechanism of the oxidative dissolution of a zinc sulphide concentrate in ferric sulphate solutions

The kinetics of the oxidative dissolution of a zinc sulphide (sphalerite) concentrate was studied. It was observed that the dissolution of the concentrate continued beyond 90% conversion in two hours at 80°C. The kinetics of dissolution are successfully described by an electrochemical mechanism in which the charge transfer from the solid to the oxidant is rate-limiting. The rate of reaction is proportional to the sum of the concentrations of the Fe³⁺ (aq) and FeHSO₄²⁺ complexes with a reaction order of one-half. The addition of Fe (II) to the solution had an indirect effect on the reaction rate, by decreasing the concentrations of the electro-active ions. Addition of ZnSO₄ did not affect the reaction rate.     

The hydrometallurgical treatment of zinc silicate ores

A novel hydrometallurgical procedure is described for the recovery of zinc from zinc silicate ores which have high acid-soluble zinc and silica contents. The process is conducted in a continuous concurrent manner at atmospheric pressure and temperatures of 50 to 95°C. The ore is leached with spent electrolyte from an electrolytic zinc plant to a final pH of approximately 2 to dissolve zinc and the soluble silica. The pH of the leach solution is then raised to 4 to 5.5, using a neutralizing agent, to precipitate and coagulate the colloidal silica. Finally the coagulated silica is filtered from the solution and washed. The resulting filtrate is treated conventionally for electrolytic zinc production. This process solves in a simple way the difficult problem of precipitating large concentrations of colloidal silica(e.g. 25 g SiO₂ per liter) in a readily filterable and easily washed form. The process has been tested at up to the 5 tons per day scale on ores containing willemite and on a laboratory scale with ore containing hemimorphite and smith-sonite. D.ELSNER was Formerly Senior Research Officer, Risdon Diversion, Electrolytic Zinc Company of Australasia Limited, Melbourne, Victoria, 3000, Australia.     

Passive and transpassive anodic behavior of chalcopyrite in acid solutions

The electrochemical oxidation of CuFeS₂ in various acid solutions was studied using electrodes made from massive samples. The primary techniques employed were potentiodynamic polarization and constant potential experiments supplemented by capacitance measurements. It was the purpose of this study to investigate the behavior of: (1) several sources of CuFeS₂ in H₂SO₄ electrolytes, and (2) a single source of CuFeS₂ in various dilute acids. Electrochemical characterization of CuFeS₂ from various locations was performed in 1 M H₂SO₄ which showed significant differences in their behavior. All samples exhibited passive-like response during anodic polarization. The current density in this passive region was reproducible and showed differences of up to two orders of magnitude between samples from different sources which has been attributed mainly to the presence of impurities in some of the samples. During anodic polarization CuFeS₂ was found to be sensitive to pH at higher potential, but insensitive at low potential in sulfate solution. In addition, current decay measurements at constant potential in the low potential-passive region were found to follow the Sato-Cohen (logarithmic) model for solid film formation. Based on current and mass balance measurements, two intermediate sulfide phases appeared to form in the sequence CuFeS₂→S₁→S₂. At higher potentials, in the transpassive region, the observed increase in current is compatible with the decomposition of water to form chemisorbed oxygen which releases copper and forms sulfate ions.     

Electrical conductivity of acidic sulfate solution

The electrical conductivities of the aqueous solution system of H₂SO₄-MSO₄ (involving ZnSO₄, MgSO₄, Na₂SO₄, and (NH₄)₂SO₄), reported by Tozawaet al., were examined in terms of a (H₂O) and H⁺ ion concentration. The equations to compute the concentrations of various species in aqueous sulfuric acid solutions containing metal sulfates were derived for a typical example of the H₂SO₄−ZnSO₄−MgSO₄−(Na₂SO₄)−H₂O system. It was found that the H⁺ ion concentrations in concentrated sulfuric acid solutions corresponding to practical zinc electrowinning solutions are very high and remain almost constant with or without the addition of metal sulfates. The addition of metal sulfates to aqueous sulfuric acid solution causes a decrease in electrical conductivity, and this phenomenon is attributed to a decrease in water activity, which reflects a decrease in the amount of free water. The relationship between conductivity and water activity at a constant H⁺ ion concentration is independent of the kind of sulfates added. On the other hand, any increase in H⁺ ion concentration results in an increase in electrical conductivity. A novel method for the prediction of electrical conductivity of acidic sulfate solution is proposed that uses the calculated data of water activity and the calculated H⁺ ion concentration. Also, the authors examined an extension of the Robinson-Bower equation to calculate water activity in quarternary solutions based on molarity instead of molality, and found that such calculated values are in satisfactory agreement with those determined experimentally by a transpiration method.     

Evaluation of zinc sulfate electrolytes by cyclic voltammetry and electron microscopy

A cyclic voltammetric technique has been developed for approximating the quantities of active chemical species present in zinc sulfate electrolytes. The experimental apparatus consisted of a Pyrex “H” cell, an aluminum cathode encased in a Teflon holder, a carbon anode and a mercurous sulfate reference electrode. Voltammograms were obtained using industrial, purified neutral leach solution (Cominco Ltd., Trail, BC) acidified to give a final concentration of 0.77 M Zn⁺⁺ and 1 M H₂SO⁴. The polarization curves were then evaluated and used as reference standards to compare with results obtained when various organic and inorganic additions were made. The deposit morphologies obtained for short-time cathodic cycles were also studied with the aid of a Scanning Electron Microscope. Changes in concentrations of glue in the 5 to 10 ppm range and of antimony in the 5 to 10 ppb range were detected using the techniques described.     

The evidence for a miscibility gap in the Fe3O4-ZnFe2O4 system—A review

There is an increasing amount of evidence indicating the existence of a miscibility gap in the solid solution of the spinels zinc ferrite (franklinite) (ZnFe₂O₄) and magnetite (Fe₃O₄). Several types of information on the solid state chemistry of this system have been assessed, including measurements of the dependence of activity, lattice constant, conductivity, magnetization, and Mössbauer spectrum on the composition of the solid solution. The indicated miscibility gap is imminent at a temperature of about 1100 K and, for several hundred degrees below this, is bounded by two phases that contain 0.12 and 0.30 mole fraction magnetite. These characteristics of the solvus curve are confirmed by the analysis of a geological specimen. The cation distribution as a function of composition has been calculated from the lattice parameter data and is confirmed by Mössbauer spectroscopic measurements. The miscibility gap was found to occur between two largely normal spinels that contain little tetrahedrally coordinated Fe³⁺. Due to the existence of this incipient immiscibility during the roasting of zinc concentrate, there are greater losses of zinc to the ferrite than would otherwise occur.     

Insight into leaching of rare earth and aluminum from ion adsorption type rare earth ore: Adsorption and desorption

Clay minerals are inferred to be the primary host materials for ion-exchangeable rare earth in ion adsorption type rare earth ore(IAREO).During the rare earth leaching process,the adsorption and desorption reactions of the cations controlling the leaching process continue to occur at the clay minerals-leaching agent solution interface.In order to understand the leaching mechanism and behavior of rare earth and co-leached aluminum,adsorption,competitive adsorption,and desorption experiments were ...     

Electrochemical polarization and passive film of a cryogenic and non-magnetic steel in aqueous solution

The corrosion behaviour of the austenitic steel Fe-23Mn-4Al-5Cr-0.3C in different aqueous solutions of pH-0.8 to 15.3 and the corrosion protection mechanism induced by adding Al or Al and Cr have been investigated by electrochemical measurements and AES/XPS analysis. The corrosion behaviour of Fe-Mn base steel have been compared with those of mild steel, cryogenic 9 % Ni steel, stainless steels 1Cr13 and 1Cr18Ni9Ti. The addition of manganese to mild steel is very detrimental to the corrosion resistance. Fe-25Mn steel passivates with difficulty even in such neutral aqueous electrolytes as 1 M Na₂SO₄ solution. The addition of 5 % aluminum to Fe-25Mn steel confers passivity to the steel in neutral or oxidizing, chloride-free solution. The addition of 5 % Cr to Fe-Mn-Al steel further improves resistance to corrosion. The passivity of Fe-23.5Mn-4Al-5Cr-0.3C steel in aqueous electrolytes tested is superior to that of 9 % Ni steel and approximate to that of 1Cr13 stainless steel. The corrosion resistance is probably imparted by a thin barrier film of oxides. The outer part of the passive film formed on the surface of Fe-23.5Mn-4Al-5Cr-0.3C steel in 1 M Na₂SO₄ solution is enriched in Al³⁺, Cr³⁺ and Fe³⁺, and this means that the film is probably made up of a mixture of Al₂O₃, Cr₂C₃ and Fe₂O₃.     

过氧化氢-钛-氟化物体系褪色光度法测定熔盐中氟

在pH 3.2～3.5的硫酸介质中,Ti与氟离子络合形成H₂TiF₆,使Ti与H₂O₂生成的黄色络合物(TiO·H₂O₂)SO₄褪色,且褪色的程度与氟离子含量呈线性关系,据此提出了一种褪色光度法测定熔盐中氟含量的方法。试样采用氧化锌、碳酸钠和石英砂的混合熔剂熔融,经水浸取、过滤后,分取适量样品溶液,加入二氧化钛溶液,用硫酸调节pH值,加入双氧水溶液进行反应15 min后在波长410 nm处测定吸光度。氟含量在0.5～6μg/mL时,校准曲线呈线性关系,相关系数r=0.999 6,方法检出限为0.35 μg/mL。测定0.5 μg/mL的氟,5倍的SO₄^2- 、10倍的Na⁺、20倍的K⁺和Cl^-不干扰测定,熔盐样品中的Ca²⁺、Fe³⁺、Mg²⁺因其在试样熔融后已被沉淀分离,也不干扰测定。用本法对海绵钛厂镁电解车间2个熔盐样品中氟进行测定,结果与氟离子选择电极法和极谱法一致,相对标准偏差（n=5）分别为2.2%和4.2%。     

Characterization and alkaline decomposition–cyanidation kinetics of industrial ammonium jarosite in NaOH media

A complete characterization was carried out on a jarositic residue from the zinc industry. This residue consists of ammonium jarosite, with some contents of H₃O⁺, Ag⁺, Pb²⁺, Na⁺ and K⁺ in the alkaline “sites” and, Cu²⁺ and Zn²⁺ as a partial substitution of iron. The formula is: [Ag_0.001Na_0.07K_0.02Pb_0.007(NH₄)_0.59(H₃O)_0.31]Fe₃(SO₄)₂(OH)₆. Some contents of franklinite (ZnO^·Fe₂O₃), gunninguite (ZnSO₄·H₂O) and quartz were also detected. The jarosite is interconnected rhombohedral crystals of 1–2 μm, with a size distribution of particles of 2–100 μm, which could be described by the Rosin–Rammler model.The alkaline decomposition curves exhibit an induction period followed by a progressive conversion period; the experimental data are consistent with the spherical particle with shrinking core model for chemical control. The alkaline decomposition of the ammonium jarosite can be shown by the following stoichiometric formula:NH₄Fe₃(SO₄)₂(OH)_6(s)+3OH_(aq)⁻→(NH)_4(aq)⁺+3Fe(OH)_3(s)+2SO_4(aq)²⁻.The decomposition (NaOH) presents an order of reaction of 1.1 with respect to the [OH⁻] and an activation energy of 77 kJ mol⁻¹. In NaOH/CN⁻ media, the process is of 0.8 order with respect to the OH⁻ and 0.15 with respect to the CN⁻. The activation energy was 46 kJ mol⁻¹. Products obtained are amorphous. Franklinite was not affected during the decomposition process. The presence of this phase is indicative that the franklinite acted like a nucleus during the ammonium jarosite precipitation.     

The corrosion of lead anodes in copper electrowinning

The steady-state corrosion rate of 0.4 pct As-10 pct Sb-Pb anodes in H₂SO₄ copper electro-winning electrolytes was studied. The corrosion rate increases markedly with increasing acid strength and current density, although the corrosion per pound of copper electrowon is affected only slightly by current density. Several ions such as Cu⁺², Mg⁺², Al⁺³, SiO₃ ^-2 and Na+ have no effect on the corrosion while Fe+S and Ni+2 ions have moderate inhibiting effects. Strong corrosion inhibition is brought about by introducing small amounts of Co*2 into the solution or by substituting a Ca-Pb alloy for the conventional antimonial lead anodes.     

Zinc recovery from zawar ancient siliceous slag

Zinc is found to exist in Zawar ancient slag in India mainly as the silicate phases hemimorphile, Zn₄(OH)₂Si₂O₇·H₂ O, and willimite, Zn₂SiO₄, and also as the hydrozycarbonate phase hydrozincite, Zn₅(CO₃)₂(OH)₆. Various processing techniques show that the non-silicate mineral can be easily leached by acid. Willemite and the hemimorphite phase can also be leached by acid. However, zinc recovery apparently is poor; this phenomenon has been ascribed to chelation or adsorption of Zn²⁺ by colloidal/polymeric silicic acid. Neutralisation, coagulation and precipitation of silicic acid by Al³⁺ ions distinctly improve zinc recovery. The “fast leaching” technique, which makes use of the water-starved nature of the silicate—acid system shows distinct promise. Recovery of zinc of more than 80% is reported.     

Leaching of Cu2O with aqueous solution of sulfur dioxide

Leaching of Cu₂O with aqueous SO₂ solution is significant, since during the dissolution process, precipitation of copper as Chevreul’s salt also takes place under appropriate conditions. The dissolution is controlled by surface reactions and proceeds through both aqueous SO₂ and acid dissolution paths. An overall rate equation based on the above premise has been found to agree well with the experimental data. At pH values higher than 1.8, precipitation of copper as Chevreul’s salt takes place after about 10 minutes of leaching. The extent of the precipitation depends upon the pH, SO₂ concentration, initial Cu²⁺ concentration, and sulfate concentration in the leaching solution.     

A partial equilibrium model to characterize the precipitation of ferric ion during the leaching of chalcopyrite with ferric sulfate

A partial equilibrium model has been developed and used to characterize the conditions under which precipitation of ferric ion occurs during the dump leaching of chalcopyrite ores. The precipitates which have been considered include amorphous Fe(OH)₃, α-FeOOH (goethite), and Na⁺, K⁺, Ag⁺, Pb²⁺, and H₃O⁺ jarosites. Solution of the model equations makes possible the determination of the concentrations of the solution species during leaching of the mineral. The concentration product for Fe(OH)₃ (am) and α-FeOOH was calculated for changing solution concentrations and compared with the solubility product constants to determine when precipitation would be expected thermodynamically. The K⁺, Na⁺, Ag⁺, and Pb²⁺ concentrations that would be necessary to satisfy the solubility product constants for the corresponding jarosites were calculated for various initial concentrations and varying amounts of O₂ consumption. Formerly Graduate Assistant, Ames Laboratory USDOE and Department of Chemical Engineering, Iowa State University, Ames, IA 50011     

The oxidation of thiosulfates with copper sulfate. Application to an industrial fixing bath

This paper presents the transformation of thiosulfate using Cu(II) salts, such as copper sulfate, at pH between 4 and 5. The nature and kinetics of this process were determined. In the experimental conditions employed, the reaction between thiosulfates and Cu(II) ions produces a precipitate of CuS and the remaining sulfur is oxidized to sulfate, according to the following stoichiometry: 1 mol thiosulfate reacts with 1 mol Cu²⁺ and 3 mol H₂O, generating 1 mol copper(II), 1 mol sulfate and 2 mol H₃O⁺. In the kinetic study, the apparent reaction order was ≈ 0 with respect to H₃O⁺ concentration, in the interval 1.0 · 10^? 4–1.0 · 10^? 5M H₃O⁺; of order 0.4 with respect to Cu²⁺ in the interval 0.21–0.85 g L^? 1 Cu²⁺; and of order 0 with respect to S₂O₃^2? in the interval 0.88–2 g L^?1 S₂O₃^2?. The apparent activation energy was 98 kJ mol^? 1 in the interval 15–40 °C. On the basis of this behavior an empirical mathematical model was established, that fits well with the experimental results. The thiosulfate transformation process using copper(II) sulfate was applied to an industrial fixing bath that proceeded from the photographic industry; after this, the resulting effluent contained less than 10 mg L^? 1 of thiosulfates.