Mineralogical Characterization of Leach Residues of a Pyritic Zn–Pb–Cu–Ag Concentrate

Abstract

The products formed during the two-stage countercurrent oxygen pressure leaching of a pyretic Zn-Pb-Cu-Ag bulk concentrate from New Brunswick have been examined mineralogically and chemically with special emphasis on silver. Silver reports in the final leach residue mostly as unleached argentian tetrahedrite and precipitated silver-bearing lead jarosite. Other silver carriers identified include silver-bearing PbSO4, unleached galena and basic iron sulphate gel particles containing silver sulphides. Screening and/or flotation of the leach residue yields a sulphur-sulphide fraction which contains most of the unleached argentian tetrahedrite. The tetrahedrite in this fraction contains ≍ 25% of the total silver in the system. Treatment of the remaining jarosite-rich fraction by reductive SO2 leaching converts the silver-bearing lead jarosite to silver-free PbSO4. The silver liberated during this reaction ultimately precipitates as large complex sulphide-sulphate capsule-like structures rimmed by silver sulphides.