J. Avraamides

The leaching of copper from sulphur activated chalcopyrite with cupric sulphate in nitrile-water mixtures☆

If chalcopyrite is roasted with sulphur at 400–450°C pyrite and idaite or bornite are produced. Bornite plus pyrite are also prepared by roasting a 1:1 mixture of chalcopyrite and covellite. These copper-iron sulphides were leached with acidified aqueous cupric sulphate solutions containing acetonitrile or hydracrylonitrile and the results are compared with leaching with acidified cupric chloride in brine. The nitrile route has the advantage of a less corrosive sulphate medium for subsequent copper recovery processes. Bornite appears to be the most attractive product from the roasting of sulphur and chalcopyrite because much of its copper can be readily leached. Iron reports to the solution only in the latter stages of extraction. Up to 80% of the copper in this bornite is leached with CuSO4/RCN/H2O at 60°C. Copper is recovered from the resulting cuprous sulphate solution by electrowinning with inert anode. The products are copper cathodes and cupric sulphate, which is recycled. The leach residue may be used to reactivate further chalcopyrite or is leached of its copper by established routes.

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.

The electrochemical oxidation of gold telluride (AuTe2) in perchloric acid solutions

Although gold tellurides are important sources of gold in several areas in the world, little attention has been paid to understanding how they might be processed. This paper describes an electrochemical study of the oxidation of one gold telluride, namely calaverite (AuTe2) in acid solution. The principal technique in this study was cyclic voltammetry. Up to a potential of 0.5 V (sce), the reaction products are gold metal and HTeO+2, as is predicted from the E-pH diagram. At potentials above 0.75 V (sce), the reaction products are gold metal and solid tellurous acid which partially passivates the calaverite surface. Tellurous acid is soluble in 1.0 M perchloric acid, being thermodynamically unstable. Under appropriate conditions an oscillating electrochemical reaction is observed. At lower pHs (up to about 2), the telluryl ion is observed. Above this pH, up to about 3, tellurous acid and gold are the preferred products.

An application of acetonitrile leaching and disproportionation.: Refining segregated copper from roasted concentrates and ores

Pure copper with > 99% recovery has been obtained on a laboratory scale from a variety of copper sulfide concentrates by the following steps. An oxidative roast at 800–900°C to remove sulfur; reduction of the calcine, preferably but not necessarily under segregation roasting conditions at 650–750°C, to generate particulate copper; screening, in the case of segregation roasting, to partially separate from magnetite the over-size carbon which is coated with copper, gold and silver; selective dissolution in acetonitrile-water of the copper from both fractions; then thermal disproportionation of the copper(I) sulfate solution to remover pure copper powder. At least 80% of the silver and > 98% of the copper is recovered by this new concept. Cyanidation of leach residues recovers > 99% of the copper, > 90% of the silver and 80% of the gold, without interference from the iron in the residue. The method has been applied to the product of a segregation roast of refractory copper ores (TORCO process), to the product of a double roast of copper concentrates (Opie-Coffin process) and to the product of a non-segregation reductive roast of a dead roasted concentrate (USBM process). It is also applicable to calcines reduced in a blast furnace. Successful scale up could result in a low cost process for producing copper from copper concentrates. The energy requirements promise to be less than 6000 kJ as 25 psig steam per kg copper, if effective use of steam from the exothermic roasts can be achieved.

An electrochemical study of reduced ilmenite carbon paste electrodes

The anodic dissolution of reduced ilmenite has been studied using the carbon paste electrode technique. To understand the polarization behaviour of reduced ilmenite, the polarization behaviour of iron oxide and iron powder carbon paste electrodes has also been investigated. It was shown that synthetic rutile and reduced ilmenite promoted the anodic dissolution of iron.

Leaching of silver with copper(ii) ions in aqueous acetonitrile solutions: solubility of salts and equilibrium constant measurements in sulphate media

Silver metal may be oxidised by copper(II) ions in acidified aqueous acetonitrile. The extent of reaction was shown to be directly related to the proportion of acetonitrile in solution and to the sulphuric acid concentration up to about 5% v/v. The solubility of silver sulphate was measured in a variety of acetonitrile—water compositions containing varying amounts of sulphuric acid. Increasing temperature had little effect on either equilibrium constant values or solubility of silver sulphate in the range 25–50°C. Suitable leaching conditions were defined from the data collected and a process flowsheet in proposed for the recovery and refining of silver. Silver powder can be obtained from the leach solutions via distillation to remove the acetonitrile.

The use of ethylenediammonium chloride as an aeration catalyst in the removal of metallic iron from reduced ilmenite

Laboratory scale experiments were conducted on the removal of metallic iron from reduced ilmenite. A mechanically stirred aeration vessel was used to determine the iron leaching ability of aerated water in the presence of ethylene diammonium chloride catalyst. The efficiency of the aeration catalyst, ethylene diammonium chloride, was then compared to the standard ammonium chloride catalyst used in industry to remove metallic iron from a reduced ilmenite matrix. Through the use of ethylenediammonium chloride as a catalyst it was found that the same rate of iron removal could be achieved as with ammonium chloride while the molar concentration of ethylene diammonium chloride was only 75% of that of ammonium chloride. It was also found that the ethylenediammonium chloride catalyst produced a slightly faster leaching rate at a temperature of 80 to 90°C. Finally, through increasing the oxygen partial pressure of the gas flow to 100%, at the same total gas flow rates both the ammonium chloride and ethylenediammonium chloride slurries were leached at much faster rates.

The iodine−propanenitrile−water system. Effects of added salts on distribution coefficient and conductivity

Distribution coefficients for iodine in the propanenitrile-water solvent system were measured as a function of the nature and concentration of various added metal halides. BothNaCl and KI at concentrations between 1 and 3 M had a positive effect on the distribution coefficient. Zinc halides, particularly zinc iodide, tended to lower the distribution coefficient significantly and also raised the conductivity of the organic phase. These studies suggest that the two-phase solvent system is suitable for application in a zinc-iodine battery.