An experimental and thermodynamic study on reduction smelting of sea nodules to recover valuable metals

Sea nodule contains appreciable quantities of valuable metals such as Cu, Ni, Co and Mn. In order to develop an alternate process to the existing hydrometallurgical process, an attempt has been made at National Metallurgical Laboratory by direct reduction smelting of sea nodule to recover these metals. Sea nodule of composition 1.1% Cu, 1.15% Ni, 0.076% Co, 5.4% Fe and 22.3% Mn was directly smelted in presence of coke as reductant to get Cu-Ni-Co alloy, which can be further processed to recover Cu, Ni, Co in the pure form. Initial smelting experiments on 0.5 kg scale were optimized with respect to temperature, holding time and coke concentration. The above smelting trail results were corroborated with thermodynamic analysis to design the experiments which were found to be in good agreement with the experimental results. The smelting of sea nodule was further optimized on 20 kg scale using double electrode 50 kVA AC electric arc furnace. Though it was found difficult to control iron in the alloy, an optimum recovery of 90% Cu, 92% Ni and 86% Co was achieved with 7% coke and 4% quartz in the charge. Since part of the iron is removed in the alloy, the manganese rich slag having high Mn/Fe ratio is further treated to produce standard grade Fe-Si-Mn