Alan J. Parker

Solvation of ions. Part XXIX. Ionic conductances in acetonitrile-water and pyridine-water mixtures

The limiting conductance of various salts of Na+, Ag+, Cu+, Cu2+ and Ph4As+ in acetonitrile-water (AN-H2O) and pyridine-water (Py−H2O) mixtures are reported. Single ion values are calculated for AN-H2O mixtures using the TATB assumption [λo(Ph4As+) = λo(Ph4B−)]. The trends observed for the limiting Walden products (λoη) of the electrolytes and individual ions are discussed in terms of specific ion-solvent interactions and the structural effects of the solvent mixtures.

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.

Solvation of ions. Some applications. IV A novel process for the recovery of pure silver from impure silver chloride

Silver chloride is exceptionally soluble in dimethylsulfoxide saturated with calcium chloride at 25°C. Solutions containing up to 196 gl−1 silver as Ca(AgCl2)2 have been prepared. If 30–40% by volume of water is added to such solutions, then pure silver chloride is precipitated almost quantitatively. The silver chloride can be easily converted to pure (99.99%) silver metal either by melting at 1100°C with excess sodium carbonate as flux, or by reducing with hydrogen at 300–400°C, or by reducing an aqueous suspension with zinc dust. The water added to the DMSO solution can be recovered by distillation and both it and the CaCl2-DMSO bottoms are recycled for further leaching. This leads to a fast and cheap process for obtaining silver from crude silver chloride, or from materials containing silver in a form that can be converted to silver chloride. Applications to an anode slimes leach residue, a silver halide teaching laboratory residue, and the silver chloride cake from a gold refinery are demonstrated.

Anodic dissolution of silver, copper, palladium and gold in dimethylsulfoxide-halide solutions

The anodic behaviour of silver, copper, palladium, gold, platinum and glassy carbon (GC) electrodes has been studied in concentrated halide solutions in dimethylsulfoxide (DMSO) using linear sweep voltammetry, coulometry, chronoamperometry and X-ray diffraction. Parallel studies in perchlorate and aqueous solutions were used to interpret the data. Only solution oxidation was observed at Pt and GC, but Ag, Cu, Pd and Au were found to oxidize more readily in DMSO than in aqueous solution. The relative merits of DMSO and aqueous halide solutions for the electrorefining of these metals are discussed briefly.

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.

Recovery of copper powder from copper concentrates and from solutions of copper(II) sulfates using sulfur dioxide and aqueous acetonitrile

Copper concentrates can be sulfation roasted and leached with water to produce impure solutions of copper(II) sulfate. Copper sulfites are precipitated from aqueous copper(II) sulfate solutions with soluble salts of sulfurous acid like (NH4)2SO3 or Na2SO3. The water insoluble copper sulfites dissolve in acetonitrile—water (AN/H2O) and reduce Cu2+ to give acidic solutions containing up to 2.4 M Cu+ as Cu2SO4. Removal of acetonitrile by steam and disproportionation, gives up to 75 g pure particulate copper per litre of such solutions. Conditions for the recovery of Chevreuls salt from solution using different sulfite bases and for its dissolution in CuSO4/AN/H2O are determined. It is shown that both temperature and the molar ratios of Chevreuls salt and CuSO4 are important in the efficiency and stoichiometry of the dissolution reaction. Methods of separating copper and nickel from solutions of copper(II) and nickel sulfates, and of recovering copper from dilute (< 0.1 M) solutions of copper(II) sulfate, are suggested. A flow-sheet which combines these reactions and methods to recover copper from sulfation roasted chalcopyrite concentrates is proposed.

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.

Cuprous hydrometallurgy: Part VIII. Solvent extraction and recovery of copper(I) chloride with organic nitriles from an iron(III), copper(II) chloride, two-step oxidative leach of chalcopyrite concentrate

Water-immiscible organic nitriles selectively extract copper(I) chloride as CuCl from aqueous chloride solutions. The distribution coefficients for the extraction of metal chlorides are in the order Ni2+ ⪡ Fe2+ < Na+ < Cu2+ ≈ Co2+ < Cu+ ⩽ Fe3+. The equilibrium Cu2+ + Fe2+ ⇌ Cu+ + Fe3+ lies strongly to the right in nitrile solutions containing a small amount of water. When volatile nitriles containing some water are used as extractants, CuCl may be recovered from the organic phase by stripping the solvent with steam. Pure CuCl, suitable for reduction to electrolytic-grade copper, is precipitated from the residual aqueous phase. A process is demonstrated for the recovery of pure CuCl from chalcopyrite concentrate, in which a two-stage, iron(III), copper(II) chloride leach is used to maximize the amount of CuCl relative to CuCl2 formed in solution.

Removal of iron and formation of copper(i) from solutions containing iron(ii) and copper(ii) by addition of chloride ion or acetonitrile

Abstract Solutions of Cu(II) and Fe(II) establish the redox equilibrium Cu(II) + Fe(II) ⇌ K Cu(I) + Fe(III) which is displaced to the right by addition of either Cl− or acetonitrile (AN). Log K varies from −10.5 in water to about −2.5 in 4 M NaCl or AN, allowing iron to be removed selectively from copper (II) solutions either by solvent extraction with Versatic acid or by precipitation as goethite or j jarosite. To establish the required conditions Eh-pH diagrams have been developed for the CuH2OCl and CuH2OANSO42-systems at 25°C and 90°C. It is demonstrated that the catalytic effect of Cu(II) on the oxidation of Fe(II) to Fe(III) by O2 is dependent on the concentration of Cl− or AN and on the position of this redox equilibrium. Applications to removing iron from hydrometallurgical solutions are discussed and tested.