Recovery of gold and silver from plumbojarosite-containing hematite tailings by alkaline pretreatment and cyanidation

Synopsis

The tailings from the sulphatizing roasting of Spanish complex pyrites consist of an impregnation of ferric sulphate, argentian plumbojarosite and minor amounts of anglesite and elemental sulphur in a porous hematite matrix. The gold and silver contents are 1–4 g/t and 50–150 g/t, respectively. A two-step alkaline pretreatment and subsequent cyanidation was investigated.

The effects of prior conditioning with CaCO₃, the NaCN concentration, particle size, temperature and basic aspects of the alkaline decomposition of the plumbojarosite were looked at. Extensive batch testing showed that 85–90% Ag and 90–95% Au can be recovered by: (1) a first pretreatment with CaCO₃ at pH 5–5.5; (2) a second pretreatment with CaO at 60°C, pH 11–12, for 60 min; and (3) cyanidation at 60°C for 30 min. The reagent consumption was 25–60 kg/t CaCO₃, 25–35 kg/t CaO and 0.2–1.5 kg/t NaCN.