Studies on the Production of Ferro-Silico-Manganese Alloy in Arc Furnace from Polymetallic Sea Nodule

Polymetallic sea nodule contains 1.1% Cu, 1.15% Ni, 0.076% Co, 5.4% Fe, 22.3% Mn & others. World-wide research is progressing on sea nodules as an alternative future source of minerals. The current Indian program of work considers direct smelting of sea nodules to recover manganese, Cu, Ni and Co for better process, economic viability & environmental consideration. The processes developed so far are mainly based on hydrometallurgical methods which generate very dilute leach solution and the downstream processing becomes difficult. In such a scenario direct reduction smelting process is proposed in this paper to recover manganese as Fe-Si-Mn alloy from sea nodule. The ferro-silico-manganese alloy is extensively used in the steel industry as deoxidizer. The direct smelting of nodules was carried out on 1 kg scale in electric arc furnace to have Cu, Ni and Co alloy and Mn rich slag. The slag obtained during smelting has MnO: 45%, SiO2: 27%, FeO: 2%, CaO: 4%, some Al2O3 & MgO. This manganese rich slag was further treated in 50 kVA arc furnace to produce Fe-Si-Mn alloy. A number of experiments were carried out with charge consisted of first stage Mn rich slag, coke and dolomite with holding time 15-45 minutes, temperature of melt ranged from 1450 - 1550oC.The composition of Fe-Si-Mn alloy obtained is in the range of Mn: 60-65%, Si: 13-17%, C: 1-2%, S: 0.003% and balance iron which is acceptable grade for industrial use. A manganese recovery of about 78% was achieved.