Cuprous hydrometallurgy Party VI. Activation of chalcopyrite by reduction with copper and solutions of copper(I) salts

Chalcopyrite is reduced by solutions of copper(I) sulfate and copper(I) chloride to chalcocite (Cu₂S) and bornite (Cu₅FeS₄) whilst the iron reports to the solution. Factors which affect the rate and efficiency of reduction are examined. The reaction is rapid on fresh surfaces of chalcopyrite but slows markedly as a film of chalcocite or bornite forms. The reduction in the presence of copper metal goes to completion and gives a material which is more readily leached by oxidising agents than is chalcopyrite. Thus 99% of the copper in the reduced chalcopyrite is leached when copper(II) sulfate in aqueous acetonitrile is the oxidising agent, whereas only 30% of the copper is leached from pure chalcopyrite under similar conditions. Concentrated solutions of copper(I) salts are less effective in reducing CuFeS₂ in a heterogeneous solid-liquid reaction than is copper metal in a “galvanic” solid-solid reaction. Solutions of copper(II) sulfate plus concentrated copper(I) sulfate in dilute acetonitrile (4 M) containing copper sheets are an effective reductant for chalcopyrite.     

Ferric chloride leaching of sulphidized chalcopyrite

Reactions between chalcopyrite and elemental sulphur at between 320°C and 400°C produce various combinations of covellite, nukundamite (Cu_5,5 FeS_6,5, and pyrite depending on the sulphur content of the products. If all the contained copper is transferred to covellite, and iron to pyrite, at least 95% of the copper can be leached by ferric chloride with negligible iron dissolution at up to 70°C. At above 70°C, iron is extracted from pyrite. When nukundamite is present, the iron and copper contents of this compound are leached simultaneously, and the consequent loss of selectivity is further enhanced at above 70°C by attack of pyrite. The increased rates of copper extraction obtained following sulphidation result from both the breakdown of chalcopyrite and a greater porosity.     

Cuprous hydrometallurgy Part IV. Rates and equilibria in the reaction of copper sulphides with copper(II) sulphate in aqueous acetonitrile

Copper(II) sulphate in solutions of aqueous acetonitrile leaches copper from copper sulphides to form stable copper(I) sulphate solutions. Covellite and chalcopyrite are oxidised and leached more rapidly in the early stages of leaching with acidic CuSO₄/CH₃CN/H₂O than with acidic iron(III) sulphate in water. A redox equilibrium between copper(I) sulphate, copper(II) sulphate and partially leached solid copper sulphide, Cu_xS, is established. The equilibrium concentration of Cu₂SO₄ and the value of x in Cu_xS, in solutions saturated with CuSO₄, are interdependent if the acetonitrile concentration is constant. This behaviour is considered in terms of the structural and electrochemical changes which occur, in the solids Cu₂S and CuS, as leaching proceeds. According to the activities of acetonitrile, of copper(I) sulphate and of copper(II) sulphate, i.e. according to the redox potential of the solution, CuS either can be oxidised by copper(II) sulphate to a less copper-rich copper sulphide and even to sulphur, or reduced by copper(I) sulphate to a more copper-rich sulphide, up to Cu₂S, in acidic solutions containing CuSO₄, Cu₂SO₄, CH₃CN and water. This observation leads to an easy method of generating Cu₂S from CuS or from sulphur.     

Utilisation of native microbes from a spent chalcocite test heap

A variety of acidophilic iron and/or sulphur-oxidising microbes capable of growth on several substrates (chalcopyrite, pyrite, ferrous ion, sulphur, glucose) in the range 30–60 °C were recovered from a spent chalcocite/chalcopyrite/pyrite heap. Several isolates exhibited tolerance to salt, up to 5 g/L NaCl, and to the metals nickel, cobalt, zinc and copper at up to 50 g/L.Leaching tests on chalcopyrite concentrate indicated higher copper yields when native isolates were employed, compared with the laboratory reference strains Acidithiobacillus ferrooxidans (DSM 583) and Sulfobacillus thermosulfidooxidans (DSM 9293). After 30 days, several native isolates had leached 20–30% more copper than the abiotic controls during experiments conducted at 45 °C. The results demonstrate that the native isolates are potential bioleaching candidates, adapted to diverse growth conditions.     

Process mineralogy of suspended particles from a simulated commercial flash smelter

Polished sections of pyrometallurgical intermediate products from a simulated commercial flash furnace were examined by reflected light microscopy, scanning electron microscopy-energy dispersive spectrometry and electron backscatter analysis, and microprobe analysis for phase and textural relationships. The smelter feed is a copper concentrate from a porphyry copper deposit. The concentrate consists primarily of chalcopyrite, bornite, and pyrite with smaller amounts of covellite, chalcocite, molybdenite, magnetite, galena, and sphalerite. The flash furnace reactions for pyrite and chalcopyrite can be observed by reflected light microscopy. Reacted angular particles of pyrite exhibit successive rims of fibrous pyrrhotite and hematite or magnetite. Reacted angular chalcopyrite particles show successive rims of bornite, digenite, and chalcocite. Spherical particles, formed by the complete melting of former pyrite and chalcopyrite particles, consist of variable amounts of granular pyrrhotite with magnetite rims and minor hematite. Spherical particles, formed by the complete melting of former chalcopyrite particles, exhibit exsolution intergrowths with varying proportions of intermediate solid solution, bornite, digenite, and chalcocite, and have rims of hematite, magnetite, and copper-iron spinel. Electron microprobe analyses show that the iron oxides contain significant copper and minor zinc in their structures. Sphalerite and molybdenite do not show evident mineralogical reactions.     

Process mineralogy of suspended particles from a simulated commercial flash smelter

Polished sections of pyrometallurgical intermediate products from a simulated commercial flash furnace were examined by reflected light microscopy, scanning electron microscopy-energy dispersive spectrometry and electron backscatter analysis, and microprobe analysis for phase and textural relationships. The smelter feed is a copper concentrate from a porphyry copper deposit. The concentrate consists primarily of chalcopyrite, bornite, and pyrite with smaller amounts of covellite, chalcocite, molybdenite, magnetite, galena, and sphalerite. The flash furnace reactions for pyrite and chalcopyrite can be observed by reflected light microscopy. Reacted angular particles of pyrite exhibit successive rims of fibrous pyrrhotite and hematite or magnetite. Reacted angular chalcopyrite particles show successive rims of bornite, digenite, and chalcocite. Spherical particles, formed by the complete melting of former pyrite and chalcopyrite particles, consist of variable amounts of granular pyrrhotite with magnetite rims and minor hematite. Spherical particles, formed by the complete melting of former chalcopyrite particles, exhibit exsolution intergrowths with varying proportions of intermediate solid solution, bornite, digenite, and chalcocite, and have rims of hematite, magnetite, and copper-iron spinel. Electron microprobe analyses show that the iron oxides contain significant copper and minor zinc in their structures. Sphalerite and molybdenite do not show evident mineralogical reactions.     

Copper recovery from chalcopyrite concentrates by the BRISA process

The technical viability of the BRISA process (Biolixiviación Rápida Indirecta con Separación de Acciones: Fast Indirect Bioleaching with Actions Separation) for the copper recovery from chalcopyrite concentrates has been proved. Two copper concentrates (with a copper content of 8.9 and 9.9 wt.%) with chalcopyrite as the dominant copper mineral have been leached with ferric sulphate at 12 g/L of ferric iron and pH 1.25 in agitated reactors using silver as a catalyst. Effects of temperature, amount of catalyst and catalyst addition time have been investigated. Small amounts of catalyst (from 0.5 to 2 mg Ag/g concentrate) were required to achieve high copper extractions (>95%) from concentrates at 70 °C and 8–10 h leaching. Liquors generated in the chemical leaching were biooxidized for ferrous iron oxidation and ferric regeneration with a mixed culture of ferrooxidant bacteria. No inhibition effect inherent in the liquor composition was detected. The silver added as a catalyst remained in the solid residue, and it was never detected in solution. The recovery of silver may be achieved by leaching the leach residue in an acid-brine medium with 200 g/L of NaCl and either hydrochloric or sulphuric acid, provided that elemental sulphur has been previously removed by steam hot filtration. The effect of variables such as temperature, NaCl concentration, type of acid and acidity–pulp density relationship on the silver extraction from an elemental sulphur-free residue has been examined. It is possible to obtain total recovery of the silver added as a catalyst plus 75% of the silver originally present in concentrate B (44 mg/kg) by leaching a leach residue with a 200 g/L NaCl–0.5 M H₂SO₄ medium at 90 °C and 10 wt.% of pulp density in two stages of 2 h each. The incorporation of silver catalysis to the BRISA process allows a technology based on bioleaching capable of processing chalcopyrite concentrates with rapid kinetics.     

Mineralogical changes occurring during the ferric lon leaching of bornite

The reaction products formed during the leaching of bornite in either ferric chloride or ferric sulfate media depend on the leaching conditions as well as the particle size of the bornite. The extent of dissolution is always more vigorous in the ferric chloride system and increases with increasing temperature in either system. The reaction initially involves the rapid outward diffusion of copper to form slightly nonstoichiometric bornite (Cu_5-xFeS₄), chalcopyrite, and covellite. The non-stoichiometric bornite is progressively converted to a Cu₃FeS₄ phase, which varies considerably in its composition, and to covellite. Although the reaction at low temperature terminates at the Cu₃FeS₄ phase, leaching at higher temperatures results in further dissolution to elemental sulfur and soluble Cu²⁺ and Fe²⁺. The leaching ofmassive bornite illustrates the complexities of the leaching reaction more clearly than is observed for the finelypaniculate bornite. In leached massive bornite, a distinct covellite zone appears in the Cu₃FeS₄ phase; as well, chalcopyrite exsolution lamellae rimmed by a copper sulfide (possibly digenite) appear in the covellite zone, in the Cu₃FeS₄ phase, and in the nonstoichiometric bornite. The experimental leaching results, especially those involving massive bornite, are generally consistent with the mineralogical trends produced by supergene alteration of bornite ores, but a significant difference is that the Cu₃FeS₄ phase does not correspond closely to the mineral idaite.     

Cuprous hydrometallurgy : Part II. The electrowinning of copper from cuprous sulphate solutions containing organic nitriles

Copper can be won with low power consumption from an acidified cuprous sulphate solution containing organic nitriles in a one electron process to give smooth non-dendritic copper cathodes and cupric sulphate at the inert anode. A diaphragm is necessary if cupric sulphate is allowed to concentrate in the cell. In the presence of an organic nitrile in water, cuprous sulphate is stable and cupric sulphate oxidises copper to cuprous sulphate. A scheme for refining crude copper to cathode copper without casting anodes is proposed. Various inert anode materials are compared.     

Cupric chloride leaching of a complex copper/zinc/lead ore

A complex Cu/Zn/Pb ore from Cayeli, Turkey, was reacted with cupric chloride solutions under different conditions. Energies of activation were calculated for dissolution of copper (37 kJ mol^?1), iron (33 kJ mol^?1, zinc (26 kJ mol^?1) and lead (7.5 kJ mol^?1, values which indicate diffusion control of the reaction, probably through the sulphur layer formed round each particle. Particle size/leaching relationships corroborated microscopic assessments and indicated that chalcopyrite dissolved at a very low rate. Calculation of Fe:Cu ratios of metal leached showed considerable dissolution of pyrite from finely-ground ($\text{d}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{≈ 3?5 μ}\text{m}$) ore. Examination of residues using SEM X-ray fluorescence line scan techniques revealed little attack of large pyrite crystals, suggesting that fine pyrite particles in complex relationship with the sphalerite and chalcopyrite were dissolving.     

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.     

Leaching of bornite in acidified ferric chloride solutions

In an acidified ferric chloride solution, bornite leaches in two stages of reaction with the first being relatively much more rapid than the second; the first terminates at 28 pct copper dissolution. The first-stage dissolution reaction is electrochemical and is mixed kinetics-controlled; ferric-ion transfer through the solution boundary layer and reduction on the surface to release Cu²⁺ into solution are both important in controlling the rate. The concentration of labile Cu⁺ in the bornite lattice governs the potential of the surface reaction, and, once Cu⁺ is depleted from the original bornite, stage-I reaction ceases. The solid reaction intermediate formed is Cu₃FeS₄. Minute subcrystallites formed at the latter part of stage I leach topochemically in stage II. This reaction which commences at 28 pct Cu dissolution is characterized by a change in mechanism at about 40 pct copper dissolution, though the overall chemical equation for reaction is unchanged in stage II; cupric and ferrous ions and sulfur as a solid residue are products of reaction. The region 28 to about 40 pct Cu dissolution is designated as a transition period to stage-II reaction. Reaction rate in this period is interpreted as being controlled by reduction of Fe³⁺ on active product sulfur surface sites, and hence the reaction rate is controlled by the rate of nucleation and growth of sulfur on the Cu₃FeS₄ intermediate surfaces. Strain in the Cu₃FeS₄ crystal lattice is released during this period by diffusion from the lattice of Cu⁺ remaining from the labile copper initially present in the bornite. After about 40 pct Cu dissolution the rate of reaction is controlled by diffusion through the fully formed sulfur layer in an equiaxial geometrically controlled reaction.     

Rational Processing of Refractory Copper-Bearing Ores

The results of material composition studies of four samples of refractory copper-bearing ores of the Uzelga deposit are presented along with the results of studies of technological solutions to increase their processing parameters. The refractoriness of ores is associated with a thin dissemination up to micron size and close interbreedings of ore and rock minerals. Iron sulfides are presented by a wide range of minerals: pyrite and marcasite, melnikovite, arsenic pyrite, and arsenopyrite; sooty melnikovite has an increased flotation activity. The grinding of iron sulfides from 89 to 29% is followed by a proportional increase in easily floatable rock minerals to 45% and clay to 9%. These properties make these sulfides difficult to process and retain ore refractoriness to the flotation concentration. The content of copper sulfides in ore samples varies from 3.32 to 7.29%; the relative portion of copper sulfide in a form of tennantite in different samples of deposit varies from 29 to 93%. Copper is also present in a form of chalcopyrite and bornite. The best flotation activity of tennantite can be seen in a neutral and slightly acidic medium, in contrast with the standard flotation regime for chalcopyrite and bornite with butyl xanthate in a high-alkaline calcareous medium. Free grains of copper minerals can be selectively extracted into intercycled concentrates during grinding of no more than 60% of the class–71 μm. The technology of flotation in a low-alkaline medium with M-TF selective sulfhydril collector in the intercycle copper flotation and refinement cycle of the copper concentrate is developed for refractory copper-bearing ores with a variable tennantite content. Aeration is applied to suppress the flotation activity of melnikovite, which makes it possible to attain 80% copper recovery into a conditional copper concentrate. The fine inclusions of bornite, tennantite, chalcopyrite, and sphalerite into pyrite makes it rational to obtain copper–pyrite and copper–zinc–pyrite products with a yield up to 12% for pyro- and hydrometallurgical processing, along with the isolation of enriched copper concentrates.     

Developments in Selective Flotation of Complex Copper-Lead-Zinc

Sulphur dioxide has been successfully used as a depressant for galena and sphalerite in selective copper flotation of complex fine-grained sulphide ores. Dosage of the gas demands care and that is why it is not used as often as it could be. The sulphur dioxide gas has been replaced by a solution of sulphur dioxide forming salt with improved selectivity. Easy dosage of the reagent and use of selective copper mineral collectors has demonstrated better process control with upgraded products. On an Australian Cu-Pb-Zn ore the key to improved process was the finding that gangue minerals of the ore have buffer capacity to allow the stagewise addition of acidic reagent solution and still maintain the narrow pH range of selective separation of chalcopyrite and galena even with simple manual process control.

On a Russian Cu-Pb-Zn ore good selectivity against galena and sphalerite was obtained in the flotation of bornite and chalcopyrite as a high grade copper concentrate. Stagewise grinding-flotation with three grinding steps were used to obtain reasonable liberation of copper minerals and to maintain the optimum selectivity.     

Leaching of chalcopyrite with ferric ion. Part III: Effect of redox potential on the silver-catalyzed process

This study examines the effect of redox potential on silver-catalyzed chalcopyrite leaching. Leaching tests were carried out in stirred Erlenmeyer flasks with 0.5 g chalcopyrite mineral, 1 g Ag/kg Cu and 100 mL of a sulphate solution of Fe³⁺/Fe²⁺ (with redox potential ranging between 300 and 600 mV Ag/AgCl) at pH 1.8, 180 rpm and 35°C or 68 °C. Unlike uncatalyzed leaching, an increase of the redox potential increased copper dissolution in the presence of silver ions, as the regeneration of Ag⁺ requires a high concentration of oxidizing agent, Fe³⁺. Additionally, the high reactivity of the mineral surface when silver was present could have been responsible for inhibiting the nucleation of hydrolysis products of Fe³⁺ on it. Excessive addition of silver transformed the chalcopyrite surface into copper-rich sulphides such as covellite, CuS, and geerite, Cu₈S₅, preventing the formation of CuFeS₂/Ag₂S galvanic couple and the recycling of silver ions.     

Hydrothermal purification and enrichment of Chilean copper concentrates. Part 2: The behavior of the bulk concentrates

The hydrothermal treatment of Chilean Codelco-type copper concentrates with copper sulfate solutions was investigated as a mean of removal of impurities and subsequent increase of the copper assay. The behavior of the mineral phases (digenite, chalcopyrite, covellite, bornite, pyrite and sphalerite) was similar to those obtained in previous works from pure mineral samples. An almost complete transformation of bornite, chalcopirite, covellite and sphalerite into Cu_2 ? xS phases was obtained at 225 °C–240 °C. The highest degree of elimination (around 80%) of impurities was in Zn, Cd, Tl and Bi. An intermediate elimination (40–70%) was achieved for Pb and Te, with only moderate elimination (20–40%) of Mo, Hg, Sb and As. Temperature was the variable having the greatest influence on the elimination of the impurities. A concentrate containing 33% Cu, 33% S, 22% Fe and 2% Zn was converted to a highly enriched concentrate containing 70% Cu, 19% S and 3% Fe. The advantages of a concentrate of this type would include: (1) raising by more than twice the smelting capacity due to the high copper content, (2) generation of a minimum amount of slag, (3) reduction by almost 50% in sulfur emissions, (4) substantial reduction of wastes containing hazardous metals and, finally (5), retention of the option to hydrometallurgical copper recovery since the neo-formed Cu_2 ? xS phases are more reactive than chalcopyrite to the chemical or biochemical leaching.     

The kinetics of dissolution of bornite in acidified ferric sulfate solutions

Sintered disks of synthetic bornite were dissolved in acidified ferric sulfate solutions at temperatures ranging from 5δ to 94δC. The dissolution occurs in two stages; in the first a nonstoichiometric bornite with up to 25 pct deficiency of copper is formed. In the second, the nonstoichiometric bornite is converted to chalcopyrite and elemental sulfur, which accumulates on the disk surface. At temperatures below 35°C, the reaction follows parabolic kinetics and stops at the nonstoichiometric bornite stage. At higher temperatures it continues through to chalcopyrite and follows linear kinetics. Both the parabolic and linear processes have activation energies of 5 to 6 kcal per mole. At higher temperatures the sensitivity of the reaction rate to changes in stirring velocity indicates control by diffusion through the liquid boundary layer. Natural and synthetic bornite dissolve by the same process and at essentially the same rate.     

Leaching of chalcopyrite with ferric ion. Part IV: The role of redox potential in the presence of mesophilic and thermophilic bacteria

This paper reports a study on the effect of redox potential in chalcopyrite bioleaching in the presence of iron- and sulphur-oxidizing bacteria. Bioleaching tests were carried out in stirred Erlenmeyer flasks at 180 rpm, with 0.5 g of chalcopyrite mineral, 99 ml of a sulphate solution of Fe³⁺/Fe²⁺ (with the redox potential ranging between 300 and 600 mV Ag/AgCl) at pH 1.8 and 1 ml of a mesophilic (35 °C) or thermophilic (68 °C) culture. The overoxidation of the leaching solution, due to the activity of iron-oxidizing microorganisms (Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans and Sulfolobus BC), favoured the precipitation of jarosite on chalcopyrite surfaces followed by passivation. Iron- and sulphur-oxidizing microorganisms, such as A. ferrooxidans and Sulfolobus BC adapted for 4 months to elemental sulphur as the sole energy source, recovered their iron-oxidizing ability after being in contact with Fe²⁺.     

Hydrothermal purification and enrichment of Chilean copper concentrates: Part 1: The behavior of bornite,covellite and pyrite

The nature and basic kinetics of the hydrothermal reactions of bornite, covellite and pyrite with copper sulfate solutions were investigated, as a previous study on the behavior of the bulk Chilean copper concentrates. The reaction of bornite produced digenite at < 160 °C and djurleite above this temperature. The reaction products formed a continuous, non porous layer. The rates were of zero order with respect [Cu²⁺]_(aq), and the activation energy was ～ 100 kJ/mol. Covellite was transformed to digenite at < 200 °C and to chalcocite (Q and M) at > 200 °C. The reaction was characterized for an irregular nucleation and growth of the products, which were non-protective. The order with respect the [Cu²⁺]_(aq) was 0.6 and the activation energy ～ 110 kJ/mol. The pyrite reaction was significant at > 200 °C and extensive at 240 °C. It produced a mixture of digenite/chalcocite-Q, with small amounts of djurleite. The transformation has a high Philling–Betworth ratio (～ 1.6), causing the break of the product layers. The reaction order and the activation energy were also 0.6 and ～ 110 kJ/mol, respectively. The rate of the bornite reaction should be controlled by solid-state ionic diffusion, whereas for covellite and pyrite the rates should be limited by electrochemical processes. Towards the hydrothermal transformation, the reactivity of the main phases present in Chuquicamata-type concentrates was: bornite > chalcopyrite > covellite > sphalerite > pyrite.     

Leaching of chalcopyrite with Brønsted acidic ionic liquid

A Brønsted acidic ionic liquid 1-butyl-3-methyl-imidazolium hydrogen sulphate ([bmim]HSO₄) and its aqueous solutions were used for the leaching of chalcopyrite concentrate at ambient pressure under air in the temperature range of 50 to 90 °C. Copper extraction increased from 52% to 88% as the ionic liquid concentration in solution increased from 10% (v/v) to 100%. Copper extraction was very low at temperatures below 70 °C, but increased significantly at temperatures from 70 to 90 °C, suggesting a high activation energy for the chemical reaction. Elemental sulfur formed a solid layer surrounding the surface of unreacted core during the leaching to affect the reagent diffusion and limit the leaching rate. Hydrogen ion, released by the ionic liquid, and dissolved oxygen were determined to be foremost responsible for the oxidative leaching of chalcopyrite. Compared with leaching of chalcopyrite in acidic aqueous sulphate solutions, the pure ionic liquid and its aqueous solutions exhibited easier leaching of chalcopyrite at higher temperatures which is attributed to increasing the oxygen solubility and transfer of dissolved oxygen to speed up the oxidation reaction.