Acidic Ferric Sulphate Solutions Research Articles

Acid Leaching of Uranium from Weathered Uraniferous Black Shale

This paper describes the chemical leaching of uranium from weathered black shale by using sulfuric acid(H2SO4) and acidic ferric sulfate (Fe2 (SO4)3 solutions as lixiviants. The black shale sample was radioactive in nature dueto the presence of uranium and its decay radio-isotope products like 226Ra, 214Pb and 214Bi. The γ-activity of natural 235Uwas 97.6 ± 1.34 Bq Kg-1. The shale sample showed 48±1% porosity with bulk density of 1.38 ± 0.015 g/ cm3. The mainminerals identified in the weathered shale sample were quartz, illite, microcline (K-feldspar), anorthite (Ca-feldspar),gypsum and hematite. A mixed layer illite-smectite phase at 10.8Å was also detected indicating the weathering of clayminerals present in the shale sample. The shale sample was polymetallic in nature and contained 0.005% U3O8, 0.24%V2O5, 0.038% NiO, 0.012% CuO, 0.037% CeO2 and 0.019% ZnO on dry matter basis. The shale sample was organiccarbon rich and contained 19.60% C, 1.25% N and 2.50% H, which indicated the presence of nitrogenous hydrocarboncompound(s). Uranium was present in the tetravalent oxidation state (U4+) in the shale matrix. A series of leachingexperiments were conducted in shake flasks and percolation column for uranium dissolution from black shale with andwithout acidic ferric sulfate solutions of pH 1.5 and pH 2.0 at 30±2 °C. Uranium leaching efficiency was mainly attributedto the concentrations of H2SO4 and Fe3+ ions in the leaching solutions. Uranium dissolution from the weathered blackshale mainly attributed to redox reaction of U4+ to U6+ with Fe3+ as an oxidant in acidic leaching environment.

The interaction of Ag+ with synthetic chalcopyrite in the presence of Fe3+ and Cu2+ in sulfuric acid solutions

Silver (Ag+) and cupric (Cu2+) ions are known to be catalysts for oxidation of chalcopyrite (CuFeS2) in acid solutions. The present study investigates the interaction between Ag+ and Cu2+ with synthetic chalcopyrite under oxidative conditions in acidic ferric (50 mM Fe3+) sulfate solutions. After addition of Ag+ (e.g. concentration 20 mg/L) to solutions containing Cu2+, the oxidation rate of chalcopyrite increased from 1.08 × 10−6 to 12.65 × 10−6 A/cm2. In contrast, addition of 5 and 50 mM Cu2+ to solutions containing Ag+ decreased the chalcopyrite oxidation rate from 20.79 × 10−6 to 12.65 × 10−6 and 19.50 × 10−6 A/cm2, respectively. Oxidative chalcopyrite leaching tests results were in good agreement with those of the electrochemical tests above. X-ray photoelectron spectroscopy showed higher insensitivity of Ag 3d in leaching residue containing Cu2+ than residue without Cu2+. S 2p spectra analysis indicated the highest percentage of the disulfide form when leached in the Fe3+-Cu2+-Ag+ system, which suggests a synergistic effect of Cu2+ and Ag+ in the conversion of monosulfide to disulfide in chalcopyrite.

Synchrotron Radiation XRD Investigation of the Fine Phase Transformation during Synthetic Chalcocite Acidic Ferric Sulfate Leaching

The fine phase transformation process of chalcocite (Cu2S) leaching in acidic ferric sulfate solution was studied by leaching experiments and synchrotron radiation X-ray diffraction (SRXRD) tests. The results showed that the dissolution process of chalcocite was divided into two stages. In the first stage, Cu2S was firstly transformed to Cu5FeS4 and Cu2−xS, then the galvanic effect between Cu5FeS4 and Cu2−xS accelerated the dissolution process of Cu1.8S → Cu1.6S → CuS, and finally Cu5FeS4 was also transformed to CuS. While in the second stage, CuS was transformed to elemental sulfur, which formed the passivation layer and inhibited the leaching of chalcocite. Specifically, Cu5FeS4 was detected during the chalcocite leaching process by SRXRD for the first time. This research is helpful for revealing the detailed leaching process of chalcocite.

Ferric sulphate leaching of metals from waste printed circuit boards

Leaching of copper and other metals (i.e., Ni, Ag and Pd) from waste printed circuit boards (WPCBs) in acidic ferric sulphate solutions was studied. The effects of concentration of H2SO4 (0.05–1M), Fe(III) (0.05–0.5M) and temperature (20–80°C) on the extent and kinetics of extraction of metals were investigated using response surface methodology. Under the suitable conditions, high extractions of copper (i.e., ≥98%) were readily achieved over a leaching period of 120min. The kinetic data derived from the shrinking particle model for copper were used as the response for the analysis of data. All the leaching parameters were statistically significant within an order of temperature>[Fe(III)]>[H2SO4] and increasing their levels had positive influence on the leaching kinetics. The activation energy for extraction of copper was found to be 18.3kJ/mol. In addition to copper, nickel extractions were also high (i.e., up to 92.5% over 120min) whilst silver and palladium extractions were limited to ≤21.4% and ≤69.4%, respectively. Further tests indicated that increasing the solids ratio from 1% to 15% w/v had a deleterious influence on the leaching of metals apparently due to limited availability and rapid depletion of Fe(III) at high solids ratios. The supply of air/oxygen (2L/min) or H2O2 (585mg/L) for in-situ regeneration of Fe(III) improved the leaching of copper by ≈35% over 180min, with oxygen being the most effective. This indicates the requirement for the continual regeneration of Fe(III) in the leaching medium. The addition of chloride (25.6–116.5g/L Cl−) was found to promote the leaching of metals, particularly silver and palladium with their almost complete extraction (≥99% Ag/Pd) over 120min. These findings suggest that acidic ferric sulphate solutions can be suitably used as a potent lixiviant system for the extraction of metals from WEEE.

Precipitation of Iron Oxyhydroxides and Basic Sulphates from Bioleach Liquors Generated by Thermophilic Micro-Organisms

Thermophilic micro-organisms are known to oxidise pyrite and other iron sulphide minerals resulting in the production of acidic ferric sulphate solutions. In this study, the leach liquors generated from such bacterial oxidation were aged through a forced hydrolysis process to yield various iron oxyhydroxides and sulphates. The forced hydrolysis was carried out under a pH range of 1.9 to 9.0. Upon completion of aging, the precipitates generated were characterised using powder X-Ray diffractrometry. The XRD analyses revealed a production of a variety of iron oxyhydroxides and basic iron sulphates. The nature of these precipitates was influenced by the pH conditions used during aging. Jarosite compounds were precipitated under acidic conditions, whilst aging under more basic conditions led to the precipitation of iron oxyhydroxides. These findings may find application in forecasting the phase boundary conditions for Fe(III) precipitation in biogeochemical processes and provide an insight into the tackling of problems associated with the treatment and management of acid mine drainage.

Leaching and kinetic modelling of low-grade calcareous sphalerite in acidic ferric chloride solution

The leaching kinetics of a low grade-calcareous sphalerite concentrate containing 38% ankerite and assaying 32% Zn, 7% Pb and 2.2% Fe was studied in HCl–FeCl 3 solution. An L 16 (five factors in four levels) standard orthogonal array was employed to evaluate the effect of Fe(III) and HCl concentration, reaction temperature, solid-to-liquid ratio and particle size on the reaction rate of sphalerite. Statistical techniques were used to determine that pulp density and Fe(III) concentration were the most significant factors affecting the leaching kinetics and to determine the optimum conditions for dissolution. The kinetic data were analyzed with the shrinking particle and shrinking core models. A new variant of the shrinking core model (SCM) best fitted the kinetic data in which both the interfacial transfer and diffusion across the product layer affect the reaction rate. The orders of reaction with respect to ( C Fe 3+ ), ( C HCl), and ( S/ L) were 0.86, 0.21 and − 1.54, respectively. The activation energy for the dissolution was found to be 49.2 kJ/mol and a semi-empirical rate equation was derived to describe the process. Similar kinetic behavior was observed during sphalerite dissolution in acidic ferric sulphate and ferric chloride solutions, but the reaction rate constants obtained by leaching in chloride solutions were about tenfold higher than those in sulphate solutions.

Morphology of chalcopyrite leaching in acidic ferric sulfate media

Two-dimensional computer simulations based on percolation theory were used to explain the morphology associated with atmospheric chalcopyrite leaching in acidic ferric sulfate solution. The aim of this study was to understand the differences in observed morphology between chalcopyrite residues leached with and without pyrite in the leach environment. The study of chalcopyrite morphology is of interest because there are no records of similar investigations available. Simulations showed high copper extractions from chalcopyrite when surface atoms were mobile leading to agglomeration of like atoms and the formation of highly porous mineral structures. High degrees of surface mobility are associated with active anodic behavior. The simulated morphology was consistent with previously observed residue morphology from chalcopyrite leach experiments in the presence of pyrite. Thus it was found that the enhanced recoveries and peculiar morphology observed during pyrite catalyzed leaching are attributable to active anodic behavior. Conversely, the simulations also showed that the recovery of copper was low when surface atoms were effectively locked in place resulting in mineral passivation. The simulation morphology obtained in this case was also consistent with experimental results of chalcopyrite leached without the presence of pyrite which have shown non-porous film like product layers.

Silver-catalyzed bioleaching of low-grade copper ores. Part II: Stirred tank tests

A study of the effect of different variables (inoculation, aeration, silver complexants, [Ag], [Fe 3+], temperature and chemical activation stage) on the silver-catalyzed bioleaching of two different low-grade copper ores has been carried out in stirred tanks. The catalyzed bioleaching process was greatly affected by bacterial activity. Aeration and the use of different complexing agents (thiosulfate and thiosulfate plus cupric ions) did not enhance but also did not inhibit the copper kinetics in the silver-catalyzed process. On the contrary, the presence of 5 g/L Cl − inhibited the catalytic effect of silver. The effect of silver concentration was tested on two different low-grade copper ores in the range between 10 and 500 mg Ag/kg for the lower K-ore and between 1.4 and 35.7 g Ag/kg Cu for the PVD ore, the former with a higher content of copper. Silver catalysis was effective for both ores but the PVD ore was basically unaffected by silver concentration in the range studied. Maximum copper extractions and copper dissolution rates were obtained with a very small amount of silver (3.6 g Ag/kg Cu). In all cases, the copper recovery was at least twice that in the absence of silver (∼ 30%). High ferric concentrations have been tested in the absence and in the presence of silver. The presence of silver was essential to improve the copper extraction from chalcopyrite in acidic ferric sulfate solutions. However, bioleaching experiments conducted with silver and 1 g/L Fe 3+ produced lower copper extractions (20%) compared to experiments where ferric iron was absent (55%). The copper dissolution in the silver-catalyzed lower K-ore bioleaching is temperature dependent, with an optimum temperature around 35 °C. The activation energies of the copper dissolution process were 109.7 and 20 kJ/mol in the ranges of temperature between 15 and 28 °C and 28 and 45 °C respectively. The chemical activation stage establishes optimum conditions that promote higher copper extractions in the presence of silver.

Studies on leaching of massive rich copper ore in acidic ferric sulfate solutions

Representative samples of Küre (Turkey) massive rich copper ore were leached in acidic ferric sulfate solutions in order to recover copper and its associated metals (Zn, Co, Ni) present in the ore. The effects of leaching time, ferric ion concentration, acid concentration, solid/liquid ratio, temperature and silver sulfaste addition on metal leaching recoveries were investigated. Optimum leaching conditions and leaching kinetics were determined. Formation of elemental sulfur, which creates a diffusion barrier, was elucidated. In order to remove the retarding effect of elemental sulfur, silver ions were introduced to the leach medium and significant improvements were observed, especially in copper dissolution. Activation energies were found to be 36.7 kJ/mole for Cu and 43.3 kJ/mole for Zn dissolutions. The rate‐controlling step was found as the diffusion of ferric ions into the solution filling the pores of sulfur layer formed on the surface of partially leached ore particles.

Microwave-Assisted Dissolution of Pyrite in Acidic Ferric Sulfate Solutions

The use of microwaves in synthetic chemistry has gained greatly in importance in the past 10 years. An observed accelerating effect of microwaves on reactions rates has been explained either by a specific microwave effect or by a superheating phenomenon. This paper considers the dissolution of pyrite mineral in acidic ferric sulfate solutions in the absence and presence of microwaves. For this purpose, a computer-controlled microwave experimental apparatus was designed in our laboratory. The experiments show that the reaction rate between pyrite and acidic ferric sulfate solution is chemically controlled and that the reaction order with respect to each Fe3+ and H2SO4 is equal to 0.5 for both classical and microwave heating; thus, the reaction mechanism is not affected by microwave irradiation. At the same time, the activation energies calculated as 33.43 and 18.72 kJ/mol in the classical and microwave systems, respectively, reveal the net effect of microwave on the activation energy.

Enhancement of chalcopyrite leaching by ferrous ions in acidic ferric sulfate solutions

The effects of ferrous ions on chalcopyrite oxidation with ferric ions in 0.1 mol dm −3 sulfuric acid solutions were investigated by leaching experiments at 303 K in nitrogen. With high cupric ion concentrations, the chalcopyrite oxidation was enhanced by high concentrations of ferrous ions and copper extraction was mainly controlled by the concentration ratio of ferrous to ferric ions or the redox potential of solutions. Ferrous ions, however, suppressed the chalcopyrite oxidation when cupric ion concentrations were low. A reaction model, which involves chalcopyrite reduction to intermediate Cu 2S by ferrous ions and oxidation of the Cu 2S by ferric ions, was proposed to interpret the results.

The phenomenology and the mathematical modeling of the silicone-supported chemical oxidation of aqueous sulfide to elemental sulfur by ferric sulphate

When pumping a sulfide solution through a silicone cylinder immersed in a solution of ferric sulfate, a cloud of elemental sulfur is formed in the ferric sulfate if the pH of the sulfide solution is below about 8.5. The elemental sulfur subsequently sediments as orthorhombic α-sulfur particles. H 2 S(aq) diffuses through the pores of the hydrophobic silicone membrane and simultaneously reacts to become sulfur. This was confirmed by a mass balance between the amount of sulfide removed from the sulfide solution and the amount of solid product formed in the ferric solution. During the experiment, the pH of the non-buffered sulfide solution rises up to a maximum of 8.5; this is explained by the continuous protonation of HS caused by the removal of H 2 S(aq). The pH of the strongly acidic (pH 1.5) ferric sulfate solution hardly decreased. A mathematical model has been developed to quantify the phenomena related to the removal of H 2 S(aq). The model has been succesfully validated with the data of batch experiments. An Arrhenius-like relationship was found between the process temperature and the overall mass transfer coefficient K. A sulfide oxidation rate of 2.5 g S/dm 3 .day was predicted for a plug flow reactor. The integration of the novel process with biological sulfate reduction was studied.

Chemical oxidation kinetics of pyrite in bioleaching processes

Bio-oxidation experiments with Leptospirillum bacteria were used to determine the chemical oxidation kinetics of pyrite in acidic ferric sulphate solutions (0.1–0.2 M) at 30°C and pH 1.6. The proposed method is applicable because the oxidation of pyrite with Leptospirillum bacteria consists of two sub-processes: (i) Pyrite is chemically oxidized with ferric iron to sulphate and ferrous iron, (ii) Ferric iron is regenerated by the bacterial oxidation of ferrous iron with oxygen. The kinetics of the two sub-processes are mutually independent. It was found that the chemical oxidation rate of pyrite increases with increasing ferric to ferrous iron concentration ratios ([Fe 3+]/[Fe 2+]). An empirical kinetic equation appropriately described the chemical oxidation kinetics of pyrite with ferric iron. It also predicts low pyrite oxidation rates at relatively low [Fe 3+]/[Fe 2+] ratios (<500), which agrees with the reported low rates under similar conditions in (sterile) chemical batch experiments. The advantage of using Leptospirillum bacteria to determine the chemical oxidation kinetics of pyrite (or other minerals) at moderate conditions is that the bacteria maintain an extremely high [Fe 3+]/[Fe 2+] ratio (up to 2×10 4) and at a constant level, whereas in (sterile) chemical batch experiments a steep decrease of the high initial ratio will occur in a few minutes due to the production of ferrous iron. This explains why observed bacterial oxidation rates of pyrite are a factor of 10 to 20 larger than maximum observed (sterile) chemical oxidation rates.

Dissolution of sphalerite (ZnS) in acidic ferric sulfate solution in the presence of manganese dioxide

This paper describes a new approach for examining the kinetics and mechanism of zinc dissolution from sphalerite concentrate in acidic ferric sulfate solution in the presence of manganese dioxide. A literature search was performed to access the possible action of the two oxidizing agents, i.e., ferric ion and manganese dioxide. The possibility of galvanic coupling between ZnS and MnO2 and the cyclic action of the redox couple, Fe2+/Fe3+, on these two minerals were theoretically examined based on corrosion principles. Expressions for the mixed potential (Em) and the mixed current (im) were derived for the relevant corrosion and galvanic couples. Leaching experiments were conducted to establish which of the above phenomena is operative during leaching. The results indicated that the dissolution mostly occurs by the action of ferric ion on ZnS producing ferrous ions. The presence of MnO2 enables a quick conversion of ferrous to ferric, which maintains the rate of Zn dissolution. The process has promising features for commercial exploitation.

Kinetic anomalies of dissolution of sphalerite in ferric sulfate solution

During the leaching of several sphalerite concentrates in acidic ferric sulfate solution, the dissolution rate of zinc decreases with time and overall conversion does not exceed 305. The growing elemental sulfur layer on the surface of each particle was found to be the cause of this passivation. To eliminate this phenomenon, a small addition of lignosulphonate (1 g/l) into the leaching solution was found to be effective. A conversion of over 60% was obtained.

高温におけるＦｅ２（ＳＯ４）３溶液の加水分解に関する湿式冶金学的研究（第３報） 高温におけるＦｅ２（ＳＯ４）３溶液の加水分解に及ぼすＭｇＳＯ４の影響

Solubilities of magnesium sulphate in sulphuric acid solutions and hydrolysis of acidic ferric sulphate solutions of various concentrations with the addition of magnesium sulphate have been investigated in an autoclave at temperatures of 185°C and 200°C.The results obtained were as follows:1. Solubilities of magnesium sulphate increased with an increase in sulphuric acid concentrations in solutions, while at the same sulphuric acid concentration, solubilities of magnesium sulphate at 185°C were slightly higher than that at 200°C.2. Solubilities of magnesium sulphate in sulphuric acid solutions at temperatures of 185°C and 200°C were represented by the following emnirical formulas:Mg2+ (g/l)=4.981+3.044×10-1 [H2SO4 (g/l)]-4.651×0-1 [H2SO4 (g/l)] 2at a tenlperature of 185°CMgSUP>2+ (g/l)=2.962+2.947×10--1 [H2SO4 (g/l)]-3.889×10-4 [HH2SO4 (g/l)] 2 at a temperature of 200°C3. When the hydrolysis of ferric sulphate soulutions was at equilibrium, the concentration of ferric ion increased with an increase in that of sulphuric acid in solutions, while at the same sulphuric acid concentration, the concentration of ferric ion decreased considerably with an increase in the addition of magnesium sulphate.4. In the hydrolysis of acidic ferric sulphate solutions, ferric oxide, Fe203, was precipitated at lower sulphuric acid concentrations, and ferric basic sulphate, Fe (OH) SO4, was precipitated at higher concentrations of sulphuric acid, while hydrolysis and precipitation of ferric oxide increased withthe addition of magnesium sulphate in the ferric sulphate solutions.5. At a temperature of 185°C in the absence of magnesium sulphate, hydrolysis and precipitation of ferric oxide occurred up to the sulphuric acid concentration of 55.8g/l or below, and at 55.8g/l or above, ferric basic sulphate was precipitated. When respectively about 15g/l Mg2+ion and 30g/l Mg2+ion as magnesium sulphate were added in the ferric sulphate solutions, hydrolysis and precipitation of ferric oxide occurred up to the sulphuric acid concentration of 76.5g/l and 100.5g/l.6. At a temperature of 200°C in the absence of magnesium sulphate, hydrolysis and precipitation of ferric oxide occurred up to the sulphuric acid concentration of 69.3g/l or below, and at 69.3g/l or above, ferric basic sulphate was precipitated. When respectively about 15g/l Mg2+ion and 30g/lMg2+ion as magnesium sulphate were added, hydrolysis and precipitation of ferric oxide occurred up to the sulphuric acid concentration of 82.1g/l and 105.1g/l.7. When magnesium sulphate was added in solutions, empirical formulas of the ferric ion concentration and the sulphuric acid concentration over the stable region of ferric oxide were as follows. at a temperature of 185°Clog [Fe3+ (g/l)] =5.30 log [H2SO4 (g/l)]-9.61 about 15g/l Mg2+ion as magnesium sulphate log [Fe3+ (g/l)] =5.46 log [H2SO4 (g/l)] -10.24 about 30g/l Mg2+ion as magnesium sulphate at a temperature of 200°Clog [Fe3+ (g/l)] =5.09 log [H2SO4 (g/l)] -9.46 about 15g/l Mg2+ion as rnagnesium sulphate log [Fe3+ (g/l)] =5.74 log [H2SO4 (g/l)] -11.02 about 30g/l Mg2+ion as magnesium sulphate

高温におけるＦｅ２（ＳＯ４）３溶液の加水分解に関する湿式冶金学的研究（第４報） 高温におけるＦｅ２（ＳＯ４）３溶液の加水分解に及ぼすＮａ２ＳＯ４の影響

Hydrolysis of acidic ferric sulphate solutions of various concentrations with the addition of sodium sulphate has been investigated in an autoclave at temperatures of 185°C and 200°C.The results obtained were as follows:1. When the hydrolysis of ferric sulphate solutions was at equilibrium, the concentration of ferric ion increased with an increase in sulphuric acid concentrations, while at the same sulphuric acid concentration, the concentration of ferric ion decreased considerably with an increase in the addition of sodium sulphate.2. In the absence of sodium sulphate, hydrolysis and precipitation of ferric oxide, Fe2O3, occurred at lower sulphuric acid concentrations, and ferric basic sulphate, Fe (OH) SO4, was precipitated at higher concentrations of sulphuric acid, while with the addition of sodium sulphate in the ferric sulphate solutions, hydrolysis and precipitation of sodium jarosite, NaFe3 (SO4) 2 (OH) 6, occurred at higher concentrations of sulphuric acid.3. At a temperature of 185°C, when respectively about 7.5g/l Na+ ion, 15g/lNa+ ion and 30g/l Na+ion as sodium sulphate were added in the ferric sulphate solutions, hydrolysis and precipitation of ferric oxide occurred up to the sulphuric acid concentration of 22.8g/l or below, 29.7g/l or below and 48.3g/l or below, while at those or above, sodium jarosite was precipitated.4. At a temperature of 200°C, when respectively about 15g/l Na+ion and 30g/l Na+ ion as sodium sulphate were added in the ferric sulphate solutions, hydrolysis and precipitation of ferric oxide occurred up to the sulphuric acid concentration of 36.5g/l or below and 60.4g/l or below, while at those or above, sodium jarosite was precipitated.

高温におけるＦｅ２Ｏ３‐ＳＯ３‐Ｈ２Ｏ系状態図 高温におけるＦｅ２（ＳＯ４）３溶液の加水分解に関する湿式冶金学的研究について（第２報）

Hydrolysis of acidic ferric sulphate solutions of various concentrations has been investigated in an autoclave at temperatures of 150°, 170°, and 220°.The results obtained were as follows:1. When hydrolysis of ferric sulphate solutions was at equilibrium, the concentration of ferric ion increased with an increase in the sulphuric acid concentration in solutions, while at the same sulphuric acid concentration, the concentration of ferric ion decreased considerably with an increase in temperature.2. In hydrolysis of ferric sulphate solutions, ferric oxide, Fe203, was precipitated at lower concentrations of sulphuric acid, and ferric basic sulphate, Fe (OH) SO4, was precipitated at higher concentrations of sulphuric acid.3. At a temperature of 150°, hydrolysis and precipitation of ferric oxide occurred up to the sulphuric acid concentration of 53.4g/l, and above 53.4g/l, ferric basic sulphate was precipitated. Empirical formulas of the ferric ion concentration and the sulphuric acid concentration in solutions were as follows. up to the sulphuric acid concentration of 53.4g/l, log [Fe3+ (g/l)]=3.24log [H2SO4 (g/l)]-4.44 above 53.4g/l, log [Fe3+ (g/l)]=0.45 log [H2SO4 (g/l)] +0.454. At a temperature of 170°C, hydrolysis and precipitation of ferric oxide occurred up to the sulphuric acid concentration of 54.8g/l, and above 54.8g/l, ferric basic sulphate was precipitated. Empirical formulas of the ferric ion concentration and the sulphuric acid concentration in solutions were as follows. up to the sulphuric acid concentration of 54.8g/l, log[Fe3+ (g/l)]=4.07log[H2SO4(g/l)]-6.32 above 54.8g/l, log [Fe3+ (g/l)] =1.24log [H2SO4 (g/l)]-1.425. At a temperature of 220°C, hydrolysis and precipitations of ferric oxide and ferric basic sulphate occurred in wider concentration of sulphuric acid between 58.2g/l and 67.1g/l. Therefore the sulphuric acid concentration which allowed single precipitation of ferric oxide or ferric basic sulphate was not determined exactly. The sulphuric acid concentration, 67.5g/l, was determined from the point of intersection of the curved line of stable region of ferric oxide and that of ferric basic sulphate. up to the sulphuric acid concentration of 67.5g/l, log [Fe3+ (g/l)]=3.31 log [H2SO4 (g/l)]-5.91 above 67.5g/l, log [Fe3+ (g/l)]=1.43 log [H2SO4 (g/l)]-2.336.Equilibrium diagrams in the system, Fe2O3-SO3-H2O, at the temperatures of 150, 170, and 220°C were established from the experimental data.

Silver-catalysed hydrometallurgical extraction of copper from sulfide ores from Indian mines

Addition of silver greatly accelerated the rate and extent of copper dissolution from chalcopyrite ores in the process of leaching with acidic ferric sulfate solution. The solubility of copper depended on silver- and ferric ion concentrations, pulp density, pH and temperature. The mineralogy of ores was probably the most important factor since the extent of copper extraction in the presence of Ag + from different samples varied under identical conditions. It was thought that the presence of other metal ions in the ores might have influenced extraction rates catalysed by silver. This was confirmed by pretreatment of ore particles with other metal ions, which exhibited either a positive or no effect on subsequent leaching of copper with solutions containing Ag +.

第二鉄イオンによる黄鉄鉱の溶解速度に及ぼす溶存酸素の影響

Kinetics of pyrite oxidation in acidic ferric sulfate solution in the presence of dissolved oxygen was studied in the ternperature range of 313-333K. The effects of concentration of Fe2+, Fe3+, H+ and dissolved oxygen on oxidation rate were examined. All experiments were carried out isothermally in a batch reactor. The results are as follows:(1) The oxidation of pyrite with dissolved oxygen hardly occur under the experimental conditons studied.(2) The oxidation of ferrous ions with dissolved oxygen heterogeneously proceeds at the surface of pyrite, and the reaction orders for Fe2+, Fe3+ and dissolved oxygen are found to be 1, -1 and 1.2 respectively.(3) The reaction mechanism of pyrite oxidation with ferric ions in the presence of dissolved oxygen is as follows: Ferric ions react with pyrite to form ferrous ions, ferrous ions thus formed are oxidized to ferric ions with dissolved oxygen.(4) A reaction model consisting of the pyrite oxidation with ferric ions and the ferrous ions oxidation with dissolved oxygen was proposed and this model fits satisfactory with the experimental results.