Mechanisms for solubilization of cobalt,copper and nickel from Indian Ocean nodules at near neutral pH by a marine isolate

Polymetallic ocean nodules offer an alternative source for extracting valuable strategic metals like Cu, Co and Ni. A novel biodissolution process was carried out, employing the cell-free spent growth medium from a marine organism (Bacillus M1) isolated from nodules; and Cu, Co and Ni solubilization from the nodules was observed to be beyond the theoretical solubility limits at near neutral pH. Different characterization techniques revealed the presence of phenolic substances in the spent growth medium, which might have formed soluble complexes with the transition metals. The low prevailing E_h redox value in the medium suggested a strong reducing environment, favoring the reductive dissolution of the oxides. A correlation study of dissolution of Cu, Co and Ni with that of Mn and Fe in the nodules was made to investigate the mechanisms of metal solubilization by the marine isolate. Under the influence of a strong reducing environment coupled with complexation by a phenolic substance present in the spent growth medium, Mn and Fe oxides were solubilized from the nodules, resulting in concomitant dissolution of Cu, Co and Ni associated with them in the nodules.