Kinetics of the sulfidation of chalcopyrite with gaseous sulfur

The sulfidation of chalcopyrite with gaseous sulfur in the temperature range of 325 °C to 400 °C occurs with the formation of covellite and pyrite as the final products. The rate of sulfidation depends strongly on the temperature, with nearly complete conversion in less than 30 minutes at 400 °C. Microscopic analysis of partially and completely reacted particles showed that the sulfidation proceeded topochemically, with a shrinking core of unreacted chalcopyrite surrounded by successive layers of FeS₂ and CuS. The experimental data exhibited an induction period at the beginning of the reaction. An electrochemical mechanism is proposed for the sulfidation reaction, which involves simultaneous diffusion of Cu⁻ and electrons through the product layers. The rate data showed that the fraction reacted is well represented by a shrinking-core model controlled by the reaction occurring at the chalcopyrite-pyrite interface, resulting in the conversion-vs-time relationship 1−(1−X)^1/3=k(t−t _ind). An activation energy of 98.4 kJ/mol was determined for the temperature range of 325 °C to 400 °C.     

The action of sulfur trioxide on chalcopyrite

Chalcopyrite reacts readily with SO₃ at about 100°C to form water-soluble sulfates; the reaction is approximately: 3CuFeS₂+26SO₃→3CuSO₄+FeSO₄+Fe₂(SO₄)₃+25SO₂ The presence of about 4 pct O₂ in the gas phase greatly accelerates the reaction presumably due to the complete transformation of ferrous into ferric sulfate in an extremely porous form: 2CuFeS₂+17SO₃+1/2O₂→2CuSO₄+Fe₂(SO₄)₃+16SO₂ A stoichiometric mixture of SO₂+1/2O₂ behaves towards chalcopyrite in nearly the same way as SO₃ although only in the temperature range 350° to 700°C.     

Interaction of pentlandite, chalcopyrite, and pyrrhotine with elementary sulfur: II. Sulfidizing of chalcopyrite

The results of the second part of the study into the sulfidizing of the main sulfide minerals of copper-nickel ores, namely, pentlandite, chalcopyrite, and pyrrhotine, by elementary sulfur are presented. The phase compositions of the sulfidizing products are examined by scanning electron microscopy and electronprobe microanalysis, and a mechanism is proposed for the sulfidizing of chalcopyrite under near-equilibrium conditions.     

Interaction of pentlandite,chalcopyrite, and pyrrhotine with elementary sulfur: I. Sulfidizing of pentlandite

The first part of the study into the sulfidizing of the major minerals of copper-nickel ores, namely, pentlandite, chalcopyrite, and pyrrhotine, by elementary sulfur is presented. The phase composition of the sulfidizing products is determined by scanning electron microscopy and electron-probe microanalysis and is then used to propose a mechanism for the sulfidizing of pentlandite under near-equilibrium conditions.     

Interaction of pentlandite,chalcopyrite, and pyrrhotine with elementary sulfur: III. Sulfidizing of nickel-containing pyrrhotine

The sulfidizing of the main sulfide minerals of copper-nickel ores, namely, pentlandite, chalcopyrite, and pyrrhotine, by elementary sulfur is studied. The phase compositions of the sulfidizing products are examined by scanning electron microscopy and electron-probe microanalysis, and a mechanism is proposed for the sulfidizing of nickel-containing pyrrhotine under near-equilibrium conditions.     

Reduction of SO2 to elemental sulfur over rare earth-iron catalysts

With coal gas as a reducing agent, the catalytic reduction of SO2 to sulfur in the flue gas produced in metallurgical processes was studied over catalysts of rare earth-Fe/Al2O3 (REFe/Al2O3). The catalytic activity of the REFe/Al2O3 catalyst on the reduction of SO2 to sul-fur was investigated based on kinds and the contents of rare earths and different preparation method of the catalyst. Additionally, the mecha-nism of this catalytic reduction reaction was also explored. Results showed that different rare earth imposed different effect on the activity of the Fe/Al2O3 catalyst. Especially, the addition of Sm and Dy greatly improved the catalytic activity of Fe/Al2O3. The yield of sulfur over SmFe/Al2O3was increased to 86.62% at 360 ℃, which was 40.5% higher than that over Fe/Al2O3at the same temperature; and the sulfur yield over DyFe/Al2O3was increased to 91.62% at 400 ℃, 26.4% higher than that over Fe/Al2O3. The catalytic activity of REFe/Al2O3 was somehow dependent on the content of rare earth. For SmFe/Al2O3, the content of Sm was optimized to be about 1.0 wt.%. The rare earth catalyst prepared with different methods also showed varied activity. The sulfur yield over rare-earth transition metal catalysts follows the order: Sm and iron solution mixing impregnationSm first, then iron solution impregnationiron first, then Sm solution impregnation. The reaction mechanism of SO2 reduction to sulfur with coal gas was proposed to be an intermediate mechanism.     

Leaching of marine manganese nodules by acidophilic bacteria growing on elemental sulfur

This article describes the bioleaching of manganese nodules by thermophilic and mesophilic sulfuroxidizing bacteria, in which oxidized sulfur compounds are biologically produced from elemental sulfur added to liquid medium and are simultaneously used to leach nodules. The thermophile Acidianus brierleyi solubilized the manganese nodules faster at 65 °C than did the mesophiles Thiobacillus ferrooxidans and Thiobacillus thiooxidans at 30 °C. Leaching experiments with A. brierleyi growing on elemental sulfur were used to optimize various process parameters, such as medium pH, initial sulfur-liquid loading ratio, and initial cell concentration. The observed dependencies of the leaching rates at a pH optimum on the initial amounts of elemental sulfur and A. brierleyi cells were qualitatively consistent with model simulations for microbial sulfur oxidation. Under the conditions determined as optimum, the leaching of nodule particles (−330+500 mesh) by A. brierleyi yielded 100 pct extraction of both copper and zinc within 4 days and high extractions of nickel (85 pct), cobalt (70 pct), and manganese (55 pct) for 10 days. However, the iron leaching was practically negligible.     

The leaching of chalcopyrite with ferric sulfate

The leaching kinetics of natural chalcopyrite crystals with ferric sulfate was studied. The morphology of the leached chalcopyrite and the electrochemical properties of chalcopyrite electrodes also were investigated. The leaching of chalcopyrite showed parabolic-like kinetics initially and then showed linear kinetics. In the initial stage, a dense sulfur layer formed on the chalcopyrite surface. The growth of the layer caused it to peel from the surface, leaving a rough surface. In the linear stage, no thick sulfur layer was observed. In this investigation, chalcopyrite leaching in the linear stage was principally studied. The apparent activation energy for chalcopyrite leaching was found to range from 76.8 to 87.7 kJ mol⁻¹, and this suggests that the leaching of chalcopyrite is chemically controlled. The leaching rate of chalcopyrite increases with an increase in Fe(SO₄)_1.5 concentration up to 0.1 mol dm⁻³, but a further increase of the Fe(SO₄)_1.5 concentration has little effect on the leaching rate. The dependency of the mixed potential upon Fe(SO₄)_1.5 concentration was found to be 79 mV decade⁻¹ from 0.01 mol dm⁻³ to 1 mol dm⁻³ Fe(SO₄)_1.5. Both the leaching rate and the mixed potential decreased with an increased FeSO₄ concentration. The anodic current of Fe(II) oxidation on the chalcopyrite surface in a sulfate medium was larger than that in a chloride medium.     

The leaching of chalcopyrite with ferric chloride

A comparative study of electrochemical leaching and chemical leaching of chalcopyrite was done to elucidate the leaching mechanism of chalcopyrite with FeCl₃. The leaching rate of chalcopyrite exhibits a half order dependency on the FeCl₃ concentration, whereas it is independent of the FeCl₂ concentration. The mixed potential of chalcopyrite exhibits a 72 mV · decade⁻¹ dependency upon FeCl₃ concentration; no influence on the mixed potential was observed by the addition of FeCl₂. In FeCl₃ solutions acidified with HC1, the predominant chemical species of Fe(III) was found to be FeCl ₂ ^u+ from equilibrium calculations. The concentration of this species is approximately proportional to the amount of FeCl₃ added to the solutions. Based on these observations, an electrochemical mechanism is proposed which involves the oxidation of chalcopyrite and the reduction of FeCl ₂ ⁺ , the predominant species of Fe(III). By converting the leaching rate to electric current density,i, 140 mV · decade⁻¹ dependency of mixed potential,E, against logi is obtained. This dependency of the chemical leaching of chalcopyrite with FeCl₃ as well as its activation energy agree with those for electrochemical leaching. These findings strongly support the electrochemical mechanism of FeCl₃ leaching of chalcopyrite. Formerly Graduate Student, Kyoto University     

The leaching of chalcopyrite with cupric chloride

A comparative study of electrochemical leaching and chemical leaching of chalcopyrite was performed mainly at 343 K to elucidate the leaching mechanism of chalcopyrite with CuCl₂. Also, the morphology of the leached chalcopyrite surface was studied by using a single chalcopyrite crystal. The leaching with CuCl₂ produced a porous elemental sulfur layer on the chalcopyrite surface, showing a similar morphology to that produced during leaching with FeCl₃. The leaching kinetics were found to be linear over an extended period, followed by an acceleration stage, as a result of an increase in the reaction surface area. The leaching rate of chalcopyrite was proportional to C(CuCl₂)^0.5, whereas it was inversely proportional to C(CuCl)^0.5. The mixed potential of chalcopyrite exhibited a 66 mV decade⁻¹ dependency upon C(CuCl₂), and—69 mV decade⁻¹ upon C(CuCl). Based on these observations together with other findings, an electrochemical mechanism involving the oxidation of chalcopyrite and CuCl ₋ ² and the reduction of CuCl⁺ was proposed. The Tafel plot between the mixed potential and the current density obtained by converting the rate of chemical leaching gave a straight line whose slope was in good agreement with that of the electrochemical leaching. These findings strongly support the electrochemical mechanism of chalcopyrite leaching with cupric chloride.     

Surface Effects in Sulfidation Reactions

Abstract

Pure iron and an Fe–41 wt% Ni alloy are reacted at temperatures in the range 793–1073 K with H₂–H₂S–N₂ atmospheres corresponding to equilibrium P _S2 levels from 6.5 × 10^?5 to 0.65 Pat The kinetics of iron sulfidation are intermediate in form to linear and parabolic rate laws. The instantaneous parabolic rate constant is found to increase with extent of reaction until a constant value is reached. For fixed equilibrium sulfur pressures, the instantaneous rate increases with hydrogen sulfide partial pressure; for fixed hydrogen sulfide partial pressure, the instantaneous rate decreases as the equilibrium sulfur pressure is increased. It is demonstrated that hydrogen sulfide is the reactant species. A Langmuir-Hinshelwood kinetic model based on the slow dissociation of adsorbed hydrogen sulfide accounts satisfactorily for the unusual gas-phase compositional effects, and also for the rate at which the reacting system approaches steady state. Similar effects are found for the Fe–41%Ni alloy, where nickel sulfide whisker formation results from localized catalysis of the hydrogen sulfide dissociation reaction.     

Chlorination of chalcopyrite concentrates

The chlorination behaviors of two chalcopyrite concentrates and their pure constituents in Cl₂+N₂ were investigated by thermogravimetric analysis (TGA) in nonisothermal conditions up to 1000 °C. The effect of temperature on the reaction of chlorine with both concentrates was studied between 170 °C and 300 °C under isothermal conditions. The effects of gas flow rate, chlorine content of the gas mixture, and reaction time on the reaction rate were also investigated. The reaction products were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results showed that the kinetics of chlorination of chalcopyrite concentrates generating chlorides of Cu, Pb, Zn, Fe, and S was rapid at about 300 °C. The iron and sulfur chlorides were volatilized, leading to a residue containing valuable metal chlorides.     

Galvanic conversion of chalcopyrite

Galvanic interaction between particulate chalcopyrite (CuFeS₂) and copper results in the rapid conversion of chalcopyrite to chalcocite. The effects of temperature, surface area, concentration of sulfuric acid and agitation were systematically evaluated. The kinetics were found to be controlled by a steady-state current flow controlled by the effective anodic and cathodic surface areas involved in the galvanic couple. The experimental activation energy was 11.5 and stoichiometric data and reaction products have been characterized. The overall kinetic system has been evaluated based upon an electrochemical model.     

Chloride leaching of chalcopyrite

Two new process flowsheets have been developed which combine chloride leaching of copper from chalcopyrite with solvent extraction, to selectively transfer copper to a conventional sulfate electrowinning circuit. Chloride leaching with copper(II) as oxidant offers significant advantages for copper including increased solubility and increased rates of leaching. Both process flowsheets were similarly designed with a two stage counter-current leach but differ with respect to iron deportment. The goethite model flowsheet includes sparging of air or oxygen to the second leach stage to aid precipitation of iron as goethite (FeOOH). The hematite model flowsheet precipitates iron as hematite (Fe₂O₃) downstream from the leach in a dedicated autoclave. A mass balance has been completed for both process flowsheets and this determined the concentrations of copper and iron species in feed liquor returning to the leach following copper solvent extraction.The optimum leach extraction conditions were determined by varying grind size, temperature and residence time for both leach model scenarios. Leach tests were conducted using a chalcopyrite concentrate from Antamina in northern Peru, which contains a low to moderate amount of gangue material. The hematite model was also examined using a Rosario concentrate from Chile which contained chalcocite in addition to chalcopyrite and significant pyrite. Leach tests based on the hematite model were successful in achieving copper extractions > 95% in 4–6 h at 95 °C after fine grinding the concentrate (P₉₀ = 41 μm). However, copper extraction exceeded 99% from the finely ground Rosario concentrate (P₉₀ = 37 μm). In the goethite model leach tests, 89% copper extraction was achieved under optimum conditions in the atmospheric conditions tested.     

High-Temperature Sulfidation of Mo-Nb Alloys

Ｂｅｃａｕｓｅｏｆｔｈｅｉｎｃｒｅａｓｉｎｇｕｔｉｌｉｚａｔｉｏｎｏｆｍｅｔａｌｓａｔｈｉｇｈｔｅｍｐｅｒａｔｕｒｅｉｎｉｎｄｕｓｔｒｉａｌａｔｍｏｓｐｈｅｒｅｓｃｏｎ－ｔａｉｎｉｎｇｓｕｌｆｕｒａｎｄｉｔｓｃｏｍｐｏｕｎｄｓ，ｔｈｅｐｒａｃｔｉｃａ...     

Equilibria associated with cupric chloride leaching of chalcopyrite concentrate

The leaching of chalcopyrite in aqueous cupric chloride solutions is treated with a thermodynamic model which incorporates the equilibria associated with the formation of various cupric, cuprous and ferrous chloride complexes. The precipitate from a refluxing slurry of elemental sulfur and aqueous cuprous and ferrous chlorides contained predominantly covellite (CuS) and a small amount of pyrite (FeS₂). Mössbauer spectra indicate that there was no chalcopyrite formation. Cupric chloride leaching experiments on both chalcopyrite concentrate and cupric sulfide indicated that the extent of cuprous ion formation in these aqueous cupric chloride solutions is controlled by the thermodynamics of the equilibrium:

$\text{CuS+Cu}{}^{\mathrm{2+}}\text{? 2 Cu}{}^{\mathrm{+}}\text{+S}{}^0$

Conditions which favor the desired complete reduction of cupric ion are discussed.     

Leaching studies of chalcopyrite and sphalerite with hypochlorous acid

Laboratory studies have been conducted on the leaching of chalcopyrite and sphalerite with hypochlorous acid. The effects of stirring speed, temperature, pH, and hypochlorous acid concentration on the leaching rates have been determined. In addition, the leaching mechanisms have been resolved by analyzing the concentrations of the reaction products. It has been found that more than 90 pct extraction of both chalcopyrite and sphalerite can be achieved in one hour using less than 0.3 molar hypochlorous acid at room temperature. The primary leach products of chalcopyrite and sphalerite were sulfur and sulfate in the mole ratios of 1 to 1 and 2 to 1, respectively. A mixed kinetic model was applied to explain the leaching rates of chalcopyrite while a diffusion model was applied to explain the leaching rates of sphalerite. The mixed kinetic model involved steady-state diffusion of hypochlorous acid through the sulfur layer by a chemical reaction at the reaction interface. Good agreement between these models and the leaching rates of both minerals was obtained.