Electrodissolution of nickel sulphide concentrates in ferrous chloride solutions

Abstract

A 3 M ferrous chloride solution of pH 1.5 and operated at 72° C was found suitable to electro-oxidize nickel sulphide concentrates containing the following constituents in wt.%: nickel 20, iron 8, magnesium 10, silicon 8, sulphur 11 and copper 0.83.

The percentages of dissolution for 16 A h at current passed (current density 20–120 mAcm⁻² with respect to graphite) were in the ranges: Ni 90–70; Cu 70–50 and Mg 20–15. The changes in mol % of the final (mainly elemental) sulphur to initial sulphide-sulphur were in the range of 50 to 25. On the other hand the mole ratio of initial to final iron decreases, and this relates to the precipitation of hydroxides. Corresponding to these changes, the X-ray diffraction patterns detected the presence of elemental sulphur and hydrated oxides of iron and magnesium. The anolyte pH and electrode potential were followed during the electro-oxidation experiments.

Experiments were carried out to establish the feasibility of separating copper from nickel chloride-copper chloride mixtures at 75° C. It was possible to separate copper whose concentration was 5 gl⁻¹ or above while that of nickel was 75 gl⁻¹. The cathodic polarization curves for copper, nickel and hydrogen discharge from their individual and binary mixtures were used to predict the conditions required to avoid copper-nickel alloy deposition, and the efficiencies of deposition.