Reductive Leaching of Manganese Nodule Using Saw Dust in Sulphuric Acid Medium

Single-step reductive dissolution studies were carried out to extract Mn, Cu, Ni and Co values from manganese nodules of Indian Ocean using a cellulosic low-cost reductant (sawdust) in sulphuric acid medium. The leaching conditions were optimized for maximum extractions by varying experimental parameters such as time, amount of reductant, sulphuric acid concentration, temperature, and pulp density. It was observed that both acid as well as reductant were essential to successfully dissolve most of the desired metal values. 99.5% Mn, 99.1% Cu, 99.6% Ni, 93% Co and 64.6% Fe were dissolved under the conditions: pulp density 10% (wt/v), amount of sawdust 0.5 g/g of nodule, acid 5% (v/v), temp 105 °C, time 2 h. The enriched leach liquor was obtained following lock cycle technique. The composition of solution taken for purification was: 98.2 g/L Mn, 4.1 g/L Cu, 5 g/L Ni, 336 ppm Co with 12.3 g/L Fe. Precipitated bulk sulphides of Cu, Ni, Co and crystallized MnSO₄·H₂O were the two products obtained after Fe removal from the solution. A schematic flow sheet was suggested. The complete process comprised of simple hydrometallurgical unit operations.