Bioleaching of Tetrahedrite by Iron‑ and Sulfur‑Oxidizing Bacteria

This study describes the bioleaching of a flotation concentrate by acidophilic iron- and sulfur-oxidizing bacteria at ambient temperature in shake flasks. The concentrate was prepared from polymetallic Ag–Cu–Sb–siderite ores from Rožňava (Slovakia) and consisted of tetrahedrite and siderite, with small amounts of chalcopyrite, pyrite, and quartz. Biologically driven Cu and S extraction was significantly greater than the extraction in the abiotic control. The oxidation of 1 mol of tetrahedrite (nominally Cu10+Cu22+Sb43+S132−) to produce sulfate involved the transfer of 122 mol of electrons. The stoichiometry of the reaction was confirmed by gas analyses and the concentration profiles of the oxidation products and can be described by the equation Cu12Sb4S13 + 122Fe3+ + 52H2O → 12Cu2+ + 4Sb5+ + 13SO42− + 122Fe2+ + 104H+. The rate of bacterial ferrous iron oxidation highly exceeded that of the chemical reduction of Fe3+ at the tetrahedrite surface, as indicated by the high Fe3+-to-Fe2+ ratio in the leaching liquors. The sulfur entity (S2−) of tetrahedrite was oxidized ultimately to sulfate. After 120 days of tetrahedrite bioleaching, the concentration of Cu in the leaching liquor exceeded 4 g L−1, which is equivalent to > 80% metal yield. While the recovery of Cu and S increased proportionally with time, the Sb concentration approached 40 mg L−1 and subsequently decreased, which indicates the formation of secondary antimony minerals. Electron microprobe analyses of the solid residues showed that the alteration products are distinctly depleted in Cu and S and enriched with Sb and Fe when compared to the primary tetrahedrite.