Stage leaching of a complex polymetallic sulfide concentrate: Focus on the extraction of Ag and Au

•Cu and Zn were efficiently extracted by oxygen pressure leaching with H2SO4.•Pb was effectively extracted by carbonate transformation–silicofluoric acid leaching.•Ag and Au were effectively extracted by nickel catalyzed thiosulfate leaching.•This process neither released sulfur dioxide nor used cyanide.

A novel staged leaching process has been reported in this paper to extract Ag and Au and their associated valuable metals including Cu, Zn and Pb from a complex polymetallic sulfide concentrate with high Fe, As and Sb. The Ag in this concentrate primarily occurs in tetrahedrite, and Au is also partly encapsulated by sulfide minerals. At first, 98.2% of Cu and 95.8% of Zn were extracted by oxygen pressure leaching with sulfuric acid, and then 95.7% of Pb was extracted by silicofluoric acid leaching. After these two stages of leaching, the dissolution for both Ag and Au was negligible, and the overall leaching of Fe, As and Sb reached 91.6%, 71.1% and 48.8%, respectively. Ag was concentrated in silicofluoric acid leach residue primarily as Ag2S while Au became more accessible to lixiviant. Afterwards, 96.8% of Ag and 94.7% of Au in the residue were extracted by two-step countercurrent nickel catalyzed thiosulfate leaching. The silver in the final residue mainly occurred in antimonate and arsenate, and most of the remaining gold was encapsulated by pyrite and these oxysalts.