On the use of ammoniacal/ammonium thiosulphate for gold extraction from a concentrate

The use of ammonium thiosulphate as leaching agent for gold from a flotation concentrate has been studied. The gold content in the concentrate was 95 g/t, whereas the main mineralogical species were chalcopyrite, pyrite, pyrrhotite, tennantite and sphalerite. The experimental variables studied were: (i) Cu(II) concentration (0–6.5 g Cu(II) (added) per liter of leaching solution), (ii) thiosulphate concentration (0.1–0.7 M), (iii) pH (9–10) and (iv) pulp density (10–40%). Best gold dissolution (94%) was obtained at 0.05 M Cu(II), 0.3 M S2O32−, pH 10 and 10% pulp density after 15 h, whereas cyanidation gives the same yield but after about 46 h of reaction.