ELECTROLYTIC OXIDATION OF ARSENOPYRITE SLURRIES

Arsenopyritic (FeAsS) gold ore is usually refractory because cyanide solution cannot react with the gold, which is locked within the sulphide lattice. Destruction of the arsenopyrite lattice by electrolytic oxidation is a possible low temperature pretreatment option for refractory arsenopyritic gold ore. Slurry electrolysis of arsenopyrite particles on an inert anode was tested in a cell partitioned into anolyte and catholyte sections with a felt diaphragm. Current densities arising from particle-anode collision were less than a few hundred muAcm-2, which is insufficient current for any practical application. Hence, mediated electrolysis by a dissolved redox couple in the anolyte was tested. Fe(II) is initially dissolved in the anolyte from crushed arsenopyrite prior to oxidation. Fe(II) is anodically oxidised to Fe(III), which can be reduced at the arsenopyrite particle surface causing dissolution. The reaction produces an increasing amount of Fe(II) available in a repetitive cycle for re-oxidation at the anode at an increasing current density. This mode of reaction could readily oxidise a 10 wt % slurry above 49-degrees-C (taken to 30 kC or about 50% oxidation of the material) with current densities in the range 10 - 30 mAcm-2 in this test cell. In the presence of the couple Cl2-Cl-, significant oxidation was possible at 25-degrees-C but there was wastage of current because chlorine built up in the anolyte and so could be reduced at the cathode. This effect became unimportant above 49-degrees-C because the reaction of chlorine with the mineral was then much faster, limiting any build up of chlorine in the anolyte. In the present cell configuration, rates of slurry oxidation were much lower than those obtainable with a mineral electrode. To reduce energy costs, a better designed cell is needed which would increase the oxidising potential at the slurry-particle surface.