Pressure leaching of copper minerals in perchloric acid solutions

The leaching of covellite (CuS), chalcocite (Cu₂S), bornite (Cu₅FeS₄), and chalcopyrite (CuFeS₂) was carried out in a small, shaking autoclave in perchloric acid solutions using moderate pressures of oxygen. The temperature range of investigation was 105° to 140°C. It was found that covellite, chalcocite, and bornite leach at approximately similar rates, with chalcopyrite being an order of magnitude slower. It was found that chalcocite leaching can be divided into two stages; first, the rapid transformation to covellite with an activation energy of 1.8 kcal/mole, followed by a slower oxidation stage identified as covelite dissolution with an activation energy of 11.4 kcal/mole. These two stages of leaching were also observed in bornite with chalcocite (or digenite) and covellite appearing as an intermediate step. No such transformations were observed in covellite or chalcopyrite. Two separate reactions were recognized as occurring simultaneously for all four minerals during the oxidation process; an electrochemical reaction yielding elemental sulfur and probably accounting for pits produced on the mineral surface, and a chemical reaction producing sulfate. The first reaction dominates in strongly acidic conditions, being responsible for about 85 pct of the sulfur released from the mineral, but the ratio of sulfate to elemental sulfur formed increases with decreasing acidity. Above 120°C the general oxidation process appears to be inhibited by molten sulfur coating the mineral particles; the sulfate producing reaction, however, is not noticeably affected above this temperature. For chalcopyrite, activation energies were determined separately for the oxygen consumption reaction and for the production of sulfate, with values of 11.3 and 16.0 kcal/mole respectively. This paper is based upon a thesis submitted by F. LOEWEN in partial fulfillment of the requirements of the degree of M.A. Sc. in Metallurgical Engineering at The University of British Columbia.     

Fluidised-bed anodic dissolution of chalcocite

The anodic dissolution of chalcocite (Cu₂S) has been investigated using a fluidised-bed anode technique. Results obtained for a variety of electrolytes and experimental conditions indicate that the fluidised-bed anodic dissolution of chalcocite occurs via the formation of an intermediate copper sulphide, viz., “blue-remaining” covellite, Cu_1.1S.In sulphuric acid electrolyte the dissolution of chalcocite is inhibited after about 50% copper extraction by the vigorous evolution of oxygen gas at the platinum feeder anode.In both sulphuric acid-sodium chloride and sulphuric acid-potasium bromide electrolytes, the dissolution of chalcocite occurs to 95% copper extraction in two stages. The first stage involves the formation of Cu_1.1S, as is the case for the sulphuric acid electrolyte, while the second stage is attributed to the reaction between chloride (or bromide) and Cu_1.1S.     

Cupric chloride leaching of model sulfur compounds for simple copper ore concentrates

To learn more about the leaching characteristics of simple copper ore concentrates, the leaching behavior of cupric sulfide (CuS) and cuprous sulfide (Cu₂S) was studied. These compounds serve as model compounds for covellite and chalcocite, respectively. With aqueous saline cupric chloride solutions above 100 °C, dissolution of both compounds is rapid, but does not proceed to completion on a stoichiometric basis. The course of the leaching can be explained with a solution model based on thermodynamic considerations and recognition of certain side reactions. The model is based on consideration of the complexes formed by various ionic species in solution and their effect on the observed extent of reaction near equilibrium. The leaching process was found to be enhanced by elevated temperatures, high chloride concentrations, and acidity. Limited leach times also were found to be advantageous. At dilute copper concentrations, leaching reactions could be driven closer to completion than with higher concentrations, as predicted by the model. For process reasons, it is desirable to convert all copper (II) in solution to copper (I). Routes for accomplishing this are reviewed.     

中条山低品位铜矿地下溶浸的研究

对中条山铜矿峪铜矿的低品位含铜矿石进行了可浸性研究,试验结果表明,经过86h的浸出,单独使用硫酸时铜的浸出率只有68.98%;若加入3.14g/L的Fe3+,可使铜的浸出率提高到74.34%;若再加入5g/L的NaCl助浸,铜的浸出率则可提高到79.98%。化学物相和光学显微图像分析表明,氧化铜的浸出很快就可完成,辉铜矿和斑铜矿也以较快的速度降解为蓝辉铜矿和铜蓝,而铜蓝的浸出反应比较缓慢。     

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.     

低品位次生硫化铜矿的细菌浸出研究

在硫酸体系中 ,对含有辉铜矿、蓝辉铜矿和铜蓝的低品位次生硫化铜矿的Fe3+ 浸出和细菌浸出进行了研究 ,通过对浸出过程的动力学进行分析 ,揭示了次生硫化铜矿的浸出过程和细菌浸出的作用机理 ,得出了细菌浸铜主要以间接机理进行的结论 ,提出了加快铜浸出速率的 2条途径。     

Dissolution of bornite in sulfuric acid using oxygen as oxidant

Leaching of natural bornite in a sulfuric acid solution with oxygen as oxidant was investigated using the parameters: temperature, particle size, initial concentration of ferrous, ferric and cupric ions, and using microscopic, X-ray and electronprobe microanalysis to characterize the reaction products. Additionally, stirring rate, pH and P_O2 were varied. Dissolution curves for percent copper extracted as a function of time were sigmoidal in shape with three distinct periods of reaction: induction, autocatalytic and post-autocatalytic which levelled off at 28% dissolution of copper. The length of the induction period was not reproducible, causing the dissolution curves to be shifted with respect to time. The dissolution curves in the autocatalytic and post-autocatalytic regions were reproducible, and this property was utilized to treat much of the kinetic data. The iron dissolution curves had four dissolution regions. An initial small but rapid release of iron to solution preceded the three periods just given for copper dissolution. Aside from this initial iron release, the iron and copper dissolution curves were almost identical.Stirring rate had no effect on dissolution of copper above 400 min^?1 nor did oxygen flow rate in the range 20–40 cm³/min. Dissolution rate was slightly dependent on oxygen partial pressure for P_O2 < 0.67. Hydrogen ion concentration had no effect except that sufficient acid was required to prevent hydrolysis and precipitation of iron salts.The dissolution rate was directly dependent on the reciprocal of particle diameter indicating possible surface chemical reaction control, but the activation energy of 35.9 kJ/mol (8.58 kcal/mol) for the autocatalytic region of copper dissolution is slightly too small for that, though not unreasonable. Initial addition of Fe²⁺ had a rather complex effect and markedly enhanced dissolution of copper, as also did initial addition of Fe³⁺. Microscopic analysis showed nuclei of two new phases, covellite and Cu₃FeS₄, in the induction region. The new phases grow rapidly in the autocatalytic stage, which is controlled by nuclei formation and chemical reaction. The post-autocatalytic region is characterized by complete transformation of bornite into covellite on the particle surfaces and Cu₃FeS₄ as an internal product with an X-ray spectrum very similar to that of chalcopyrite. The post-autocatalytic region is controlled by autocatalytic growth of newly formed phases. Further reaction beyond the autocatalytic region (percent copper dissolution > 28%) occurs so slowly with oxygen as oxidant that it was not studied.The rate of copper dissolution appears to be controlled by the rate of iron dissolution. Using that and the other experimental evidence a mechanism for reaction is proposed in which iron-deficient bornite, Cu₅Fe_?S₄, is formed on the surface by initial preferential iron dissolution. Labile Cu⁺ diffuses into this from Cu₅Fe_?SO₄ and unreacted bornite to produce CuS on the surface. Depletion of labile Cu⁺ ions from Cu₅FeS₄ produces Cu₃FeS₄ in the interior of the mineral particles.     

Kinetics of the dissolution of scheelite in aqueous Na4EDTA solutions

The reaction kinetics of the dissolution of pure scheelite (CaWO₄) particles in aqueous Na₄EDTA solutions were studied at atmospheric pressure. As expected, the dissolution rate increased with decreasing initial particle size and with increasing temperature and Na₄EDTA concentration. Further, the dissolution rate decreased as the initial solid-liquid ratio and the ionic strength of the solution were increased. The experimental results do not support the conventional shrinking-core model for a single irreversible reaction. A new shrinking-core model for multiple reactions, composed of a noninstantaneous reversible reaction (scheelite dissociation into the ions Ca²⁺ and WO ₄ ²⁻ ) and an instantaneous irreversible reaction (formation of Ca-EDTA complex), was presented. The observed dependency of the dissolution rate on the relevant operating variables was the same a the theoretical predictions based on the present shrinking-core model. The activation energy was 49800 J mol⁻¹. These findings justify the validity of the assumed kinetic model with the multiple reactions as the rate-controlling step. The dissolution rate expression was obtained as a function of the initial particle size, initial solid-liquid ratio, Na₄EDTA concentration, temperature, and ionic strength of the solution.     

Dissolution of Cu2S in aqueous edta solutions containing oxygen

The mechanism of the reactions taking place in the heterogeneous system: synthetic polydispersive Cu₂S-ethylediaminetetraacetic acid (EDTA)—O₂—H₂O has been investigated. The partial pressure of oxygen and pH of the solution were found to exert a significant effect on the process kinetics. The dissolution rate does not depend, in practice, on the agitation rate and the EDTA concentration exerts an influence only at higher partial oxygen pressures.Dissolution of Cu₂S in aqueous EDTA solutions proceeds in two steps with the formation of CuS as an intermediate. In acid and neutral solutions the final products of dissolution are elementary sulphur and Cu(EDTA)^2- complex ion. The activation energy ΔE = 10.4kJ/mol (2.4 kcal/mol) suggests a diffusion controlled process. In alkaline solutions sulphur is oxidized to the sulphate ion and the dissolution process is kinetically controlled, ΔE = 41.4 kJ/mol (9.9 kcal/mol).     

Leaching kinetics of digenite concentrate in oxygenated chloride media at ambient pressure

The leaching of digenite concentrate in CuCl₂-HCl-NaCl oxygenated solutions is very rapid. From the effect of variables on the leaching rate and measurements of the concentrations of cuprous and cupric species in the solution as a function of time, it was concluded that the leaching in O₂ atmosphere proceeds by the attack of cupric ions on the copper sulfides to produce cuprous ions which are subsequently oxidized to cupric by the O₂ present in the system. The kinetic study showed that the leaching proceeds in two sequential stages. In the first stage, the digenite is transformed to covellite, and in the second stage, the covellite is dissolved to copper and elemental sulfur. In the first stage, the fraction of copper extracted varied linearly with time according to α=k _l t, whereas in the second stage, the dissolution of covellite was well represented by a shrinking core model controlled by diffusion through a porous product layer kinetic equation: 1−2/3α _cv−(1−α _cv)^2/3=k _cv t. The calculated activation energies were 15.8 and 80.0 kJ/mol for the first and second stages, respectively. These results were explained by an electrochemical mechanism of digenite dissolution.     

The effect of contact of copper sulphide grains on the initial rate of leaching in oxygenated sulphuric acid solution

The initial stage of leaching of chalcocite, bornite, and chalcopyrite as well as chalcocite-chalcopyrite and bornite-chalcopyrite mixtures in oxygenated aqueous sulphuric acid was investigated at 368 K. It was determined that chalcopyrite accelerates the rate of copper leaching from chalcocite due to grain contact between chalcocite and chalcopyrite. In contrast, chalcopyrite decreases the rate of dissolution of bornite.     

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.     

Treatment of a Nigerian covellite ore. Part I: Dissolution kinetics study by ammonia solution

In the present work, the leaching kinetics of covellite ore in ammonia solution was studied and the following variables, the solution concentration, reaction temperature and particle size were considered. A kinetics model representing the effects of these variables on the leaching rate was developed and it was ascertained that the leaching rate increases with increasing solution concentration, reaction temperature and decreasing particle size. At optimal conditions, 75.1% of covellite ore was reacted within 120 min and the leaching reaction was diffusion controlled by surface chemical mechanism. The calculated activation energy of 56.98 kJ/mol supported the proposed dissolution process.     

Oxygen pressure leaching of white metal

Sulfuric acid–oxygen pressure leaching of white metal was investigated at laboratory scale as an alternative to the pyrometallurgical Peirce–Smith converting to produce metallic copper. The main variables studied were temperature, concentration of sulfuric acid, partial pressure of oxygen, and time of leaching. The results indicated that most of the sulfur in the white metal is oxidized to sulfate in the range 105 °C to 150 °C. The concentration of sulfuric acid over 0.05 M, and oxygen partial pressure over 608 kPa had little effect on the dissolution of copper. The temperature was the most significant variable; below 130 °C copper dissolution was incomplete after 5 h of leaching while at 150 °C the dissolution was complete in 90 min. The dissolution of white metal proceeded in two stages through the formation of CuS as an intermediate compound and the kinetics of copper dissolution was analyzed by considering two consecutive reactions controlled by chemical reaction. The activation energies for the first and second stages were determined as 55 and 88 kJ/mol, respectively.     

Oxidative roasting of covellite with minimal retardation from the CuO⋅CuSO4 film

Copper (II) sulfide can be efficiently converted to the oxide at lower temperatures than normally required in aerobic roasting by a new method involving programed environment roasting (PER). When heating was conducted in absence of oxygen up to about 650°C, and then nitrogen was replaced by air, the sulfide was easily converted to oxide without need for further increase in temperature. Traditional oxidative roasting of chalcocite required a temperature range of 800° to 850°C for conversion to tenorite. Unlike the situation with conventional roasting, CuSO₄ was not detected in the X-ray diffractogram of the product obtained with the PER method above 625°C. Also, the amount of CuO ⋅ CuSO₄ significantly decreased as the halt temperature in the PER process increased from 600° to 700°C. Apparently the shell of copper oxysulfate is impervious to oxygen and/or sulfur dioxide and delays the formation of tenorite until the sulfate and oxysulfate are decomposed. If the oxysulfate stage were bypassed with an inert atmosphere, then, even if small amounts of this salt were formed upon introducing the oxidant, it would decompose at an appreciable rate and the impedance of its thin film to gaseous transport would be considerably diminished. By contrast, the accelerating effect of externally added iron on the oxidative roasting of covellite was confined to the low temperature reactions and hence iron promoted the extent of sulfate formation. Iron did not, however, lower the thermal requirement for complete oxidation of CuS or Cu₂S because it had virtually no effect on the thermal decomposition of CuO ⋅CuSO₄.     

Kinetics of dissolution of cobalt oxides in acidic media

The kinetics of dissolution of cobalt oxides Co₂O₃ and Co₃O₄ in aqueous solutions of acids (H₂SO₄, EDTA) is experimentally studied. Dissolution rate W increases with the temperature or the EDTA concentration. The reaction orders of dissolution for hydrogen ions in sulfuric acid and EDTA (dlogW/dpH = 0.5 ± 0.1) and for anions (dlogW/dlog[An ⁻] = 0.5 ± 0.1) are determined. A specific feature of the dissolution kinetics in EDTA is a maximum in the dissolution rate of the cobalt oxides at pH −1. The activation energy of the process E _a is 70 kJ/mol in H₂SO₄ and 60 kJ/mol in EDTA. The modeling of the process shows that the CoOH⁺ ion is a surface particle controlling the dissolution rate in mineral acids and the CoHY⁻ ion, in the complexone.     

The dissolution of chalcopyrite in ferric sulfate and ferric chloride media

The literature on the ferric ion leaching of chalcopyrite has been surveyed to identify those leaching parameters which are well established and to outline areas requiring additional study. New experimental work was undertaken to resolve points still in dispute. It seems well established that chalcopyrite dissolution in either ferric chloride or ferric sulfate media is independent of stirring speeds above those necessary to suspend the particles and of acid concentrations above those required to keep iron in solution. The rates are faster in the chloride system and the activation energy in that medium is about 42 kJ/mol; the activation energy is about 75 kJ/mol in ferric sulfate solutions. It has been confirmed that the rate is directly proportional to the surface area of the chalcopyrite in both chloride and sulfate media. Sulfate concentrations, especially FeSO₄ concentrations, decrease the leaching rate substantially; furthermore, CuSO₄ does not promote leaching in the sulfate system. Chloride additions to sulfate solutions accelerate slightly the dissolution rates at elevated temperatures. It has been confirmed that leaching in the ferric sulfate system is nearly independent of the concentration of Fe³⁺, ka[Fe³⁺]^0.12. In ferric chloride solutions, the ferric concentration dependence is greater and appears to be independent of temperature over the interval 45 to 100 °C.     

辉铜矿湿法冶金新工艺

针对辉铜矿含铜高、含硫低等特点,采用巴西辉铜矿进行了详细的试验研究,开发了一种湿法冶金新工艺,采用常压、加压联合流程直接生产阴极铜,铜总浸出率大于99%,回收率大于98%.     

Recovery of copper from chalcocite by means of the pyridine and chloride ion donor systems

Recovery of copper from natural chalcocite by means of pyridine—hydrochloric acid mixtures and pyridine solutions of pyridine hydrochloride is described. The systems were found to be effective media for leaching of chalcocite. Total copper recovery is reached after 15 minutes at 60°C.