Hydrochloric acid-hydrogen peroxide leaching and metal recovery from a Greek zinc-lead bulk sulphide concentrate

Abstract

A zinc-lead bulk sulphide concentrate from Kirki (Greece) was leached in aqueous solution with HClH 2O 2at atmospheric pressure and 95°C to extract up to 97% zinc, 40% lead, 80% silver and less than 12% iron after 6 h. Highly pure PbCl 2 crystallized from the leach filtrate on cooling. Sulphur was oxidized to the elemental form; its loss as sulphate ion in solution and residue was 7.5%. During leaching no emission of H 2S or SO 2 was detected. Conditions were determined for producing a pregnant solution (130 g/L Zn) low in iron and lead, to facilitate zinc extraction by electrolysis. Leaching experiments were conducted at 40% solids, 0.55 g HCl and 0.26 g H 2O 2 per gramme concentrate in a 1-L reactor. After a second leaching of the residue in aqueous solution with HCl (1 M) for 1 h at 90°C, the residual lead sulphate was extracted, so that total lead recovery was over 98%. Other values, such as silver and sulphur, could be recovered by additional treatment of either the leach solution or leach residue.