Solubilization of cobalt from ocean nodules at neutral pH-a novel bioprocess

Abstract

A marine organism (Bacillus M1) isolated from Indian Ocean manganese nodules was characterized. The organism grew well in artificial seawater medium, at near neutral pH, 30°C and 0.25 M NaCl, and showed MnO₂-reducing activity. Growing cultures of Bacillus M1 as well as cell-free spent liquor from fully-grown cultures were employed to extract metals from the nodules. The spent liquor of cultures of the organism could dissolve around 45% cobalt (Co) at a pH of 8.2 in 2 h. Co recovery by this treatment was comparable to that in acidic leaching with 2.5 M hydrochloric acid solutions, and was independent of pulp density (w/v ratio). The amount of Co dissolved was beyond the thermodynamic solubility limit in aqueous solution at a pH of 8.2. It is inferred that the metabolites present in the spent liquor played a pivotal role in complexing the Fe (III) phase, solubilizing Co in the process. Partial characterization of spent liquor by spot tests, UV visible spectroscopy and FTIR spectroscopy, showed the presence of siderophore-like phenolic compound(s) with an attached carboxyl group that might form soluble organic complexes with Fe (III).