2019-7-17 · 1 1Definitions: The term bioleaching refers to the conversion of an insoluble metal (usually a metal sulfide, e.g., CuS, NiS, ZnS) into a soluble form (usually the metal sulfate, e.g., CuSO4, NiSO4, ZnSO4). When this happens, the metal is extracted into water; this process is called bioleaching (48, 89). Because these processes are oxidations, this process may also be …