Nickel complexation as an innovative approach for nickel-cobalt selective recovery using sulfate-reducing bacteria

Highlights: • Similar solubility challenges Ni-Co selective recovery from mine-impacted waters. • Ni exposure to sulfate reducing bacteria resulted in higher Ni solubility than Co. • Higher Ni solubility was attributed to complexation with extracellular material. • Proteomic analysis identified extracellular proteins present at each metal system. • A new approach for separation: Ni complexation vs. Co sulfide precipitation founded. This study evaluated the differences in nickel (Ni) and cobalt (Co) solubility in the presence of sulfate reducing bacteria (SRB) to evaluate the feasibility of selective recovery of both metals from mine-impacted waters. A series of sulfate reducing activity tests with Ni, Co and both metals showed that up to 99 % Ni remained soluble despite the availability of sulfide for precipitation, while Co sulfide precipitation always occurred (over 84.5 %). The characterization of proteins in the liquid phase of the experiments revealed that some proteins were only produced in the experiments where Ni displayed higher solubility, suggesting their involvement in metal complexation. Some functions of these proteins included maintaining Ni homeostasis, acting as metalloenzymes and containing Ni-binding ligands. Desulfomicrobium baculatum, Stenotrophomonas maltophilia, and Desulfovibrio magneticus, were the main responsible species producing these proteins.