Leaching of manganese deep ocean nodules in FeSO4–H2SO4–H2O solutions

Studies have been carried out to determine maximum extraction efficiency of Co, Ni, Cu and Mn from manganese deep ocean nodules in FeSO4–H2SO4–H2O solutions and to maximise Co, Ni, Cu and Mn concentrations in the resulting leach liquors. The leaching parameters such as sulphuric acid concentration, liquid-to-solid ratio, temperature, time and grain size of nodules were varied to study their effect on metal extraction. The optimum conditions established were as follows: stoichiometric amount of FeSO4, 1.6-fold excess over stoichiometric amount of H2SO4, 90 °C, l/s of 7:1, grain size ≤1000 μm. Under these conditions, more than 85% of Co and 90% of Ni, Cu and Mn could be extracted within 30 min. The leach liquors contained approximately 146 mg Co/L, 1.63 g Ni/L, 1.69 g Cu/L and 30 g Mn/L.