ELECTROLYTIC OXIDATION OF ARSENOPYRITE SLURRIES

Arsenopyritic (FeAsS) gold ore is usually refractory because cyanide s olution cannot react with the gold, which is locked within the sulphid e lattice. Destruction of the arsenopyrite lattice by electrolytic oxi dation is a possible low temperature pretreatment option for refractor y arsenopyritic gold ore. Slurry electrolysis of arsenopyrite particle s on an inert anode was tested in a cell partitioned into anolyte and catholyte sections with a felt diaphragm. Current densities arising fr om particle-anode collision were less than a few hundred muAcm-2, whic h is insufficient current for any practical application. Hence, mediat ed electrolysis by a dissolved redox couple in the anolyte was tested. Fe(II) is initially dissolved in the anolyte from crushed arsenopyrit e prior to oxidation. Fe(II) is anodically oxidised to Fe(III), which can be reduced at the arsenopyrite particle surface causing dissolutio n. The reaction produces an increasing amount of Fe(II) available in a repetitive cycle for re-oxidation at the anode at an increasing curre nt density. This mode of reaction could readily oxidise a 10 wt % slur ry above 49-degrees-C (taken to 30 kC or about 50% oxidation of the ma terial) with current densities in the range 10 - 30 mAcm-2 in this tes t cell. In the presence of the couple Cl2-Cl-, significant oxidation w as possible at 25-degrees-C but there was wastage of current because c hlorine built up in the anolyte and so could be reduced at the cathode . This effect became unimportant above 49-degrees-C because the reacti on of chlorine with the mineral was then much faster, limiting any bui ld up of chlorine in the anolyte. In the present cell configuration, r ates of slurry oxidation were much lower than those obtainable with a mineral electrode. To reduce energy costs, a better designed cell is n eeded which would increase the oxidising potential at the slurry-parti cle surface.