Reductive leaching of valuable metals from indian ocean nodules by bacillus circulans

In the present investigation B. circulans, a heterotrophic microorganism has been used for the recovery of copper, nickel and cobalt from Indian Ocean nodules. The organism after reviving in growth medium and gradual adaption on sea nodules, was used for the bioleaching studies in shake flasks under a range of conditions such as pH, pulp density, particle size of nodules and temperature. The leaching of metals was found to be 92% Cu, 73% Ni, 72% Co, 38% Mn and 17% Fe in 25 days at 5% (w/v) pulp density (PD), 2 pH and 35°C. XRD identification of the leach residue showed the presence of some lower and mixed oxidation phases of manganese and some unaltered iron phases. Surface morphology of the bioleach residue was examined by SEM. The process may be accompanied by direct enzymatic action of bacteria leading to reduction of Mn (IV) to Mn (II) and Fe (III) to Fe (II) releasing the valuable metals from the host lattice for leaching in acidic conditions.