Leaching Studies of Deep-Sea Manganese Nodule with Ferrous Sulfate Solutions

Improved extractions of valuable elements such as Mn, Cu, Ni and Co have been obtained by acidified ferrous sulfate leaching of deep-sea manganese nodule from the Pacific Ocean. This leaching is based on an oxidation-reduction reaction shown as : MnO_2+2(Fe)^<2+>+4H^+=(Mn)^<2+>+2(Fe)^<8+>+2H_2O MnO_2 in the nodule growth layer is reduced to (Mn)^<2+> by the aid of (Fe)^<2+> ions in the leaching solution, thus releasing valuable elements contained in Mn phase of the nodule. Better Mn extractions together with Cu, Ni and Co were obtained in solutions of 0.05M FeSO_4 and 0.05M H_2SO_4 in 1.5 hour of leach time in comparison with poor extraction obtained in the 0.05M H_2SO_4 leaching solutions without FeSO_4. Extractions of Mn, Cu, Ni and Co decreased gradually in the solutions at higher FeSO_4 concentration range over 0.05M due to deficiency in H_2SO_4 and hydrolysis of the (Fe)^<3+> ions produced through the above leaching reaction. Equi-extractive contour lines are also presented on FeSO_4-H_2SO_4 diagram showing concentration limits of both FeSO_4 and H_2SO_4 in the solution to obtain better extractions in the FeSO_4 leaching as well as optimum leaching conditions.