Nitrate-Dependent, pH Neutral Bioleaching of Ni from an Ultramafic Concentrate

This study explores the possibility of utilizing bioleaching techniques for nickel extraction from a mixed sulfide ore deposit with high magnesium content. Due to the ultramafic nature of this material, well-studied bioleaching technologies, which rely on acidophilic bacteria, will lead to undesirable processing conditions. This is the first work that incorporates nitrate-dependent bacteria under pH 6.5 environments for bioleaching of base metals. Experiments with both defined bacterial strains and indigenous mixed bacterial cultures were conducted with nitrate as the electron acceptor and sulfide minerals as electron donors in a series of microcosm studies. Nitrate consumption, sulfate production, and Ni released into the aqueous phase were used to track the extent of oxidative sulfide mineral dissolution; taxonomic identification of the mixed culture community was performed using 16S rRNA gene sequencing. Nitrate-dependent microcosms that contained indigenous sulfur- and/or iron-oxidizing microorganisms were cultured, characterized, and provided a proof-of-concept basis for further bioleaching studies.MAS