Bioprocessing of polymetallic Indian Ocean nodules using a marine isolate

Polymetallic Indian Ocean nodules offer a lucrative resource for valuable strategic metals like Cu, Co and Ni. A novel bioleaching process to recover those metals from the nodules at near-neutral pH and ambient temperature is presented in this paper. The significant role of in situ microorganisms and their by-products in solubilization of valuable trace metals from the nodules was studied and is discussed. A marine organism was isolated from the nodules and characterized, both physiologically and morphologically. The isolate was observed to grow well in artificial seawater medium, at neutral pH, 30 °C and 0.25 M NaCl concentrations and showed $MnO_2$ reducing activity. The growing culture as well as the cell-free growth supernatant of the isolate was employed in bioleaching studies of the nodules, and leaching efficiency was observed to follow the same trend in both the cases. It can be inferred that the metabolites produced during growth of the microorganism played a primary role in the bioleaching process. The initial concentrations of Co, Cu and Ni in the polymetallic ocean nodules were 17, 114 and 115 ppm, respectively, for 1% pulp density. Around 45% Co and 30% of Cu and Ni were dissolved at pH of 8.2 in 10 h. Co recovery by bioleaching was comparable to that obtained in concentrated acidic solutions. It was also found that increasing the pH of the growth supernatant to about 13 markedly improved the leaching efficiency