Leaching of metals from Indian ocean nodules in SO2-H2O-H2SO4-(NH4)2SO4 medium

Studies have been carried out for extraction of Cu, Ni, Co, Zn and Mn with simultaneous avoidance of iron dissolution during leaching of manganese nodules in an aqueous SO2-H2SO4(NH4)(2)SO4 system. The leaching parameters such as sulphuric acid concentration, ammonium sulphate concentration, time and pulp density were varied to study their effect on extraction of metals and precipitation of iron. It was observed that the presence of both sulphuric acid and SO2 was required for maximum recovery of Cu, Ni, Co, Zn and Mn. The iron in solution decreased with increase in ammonium sulphate concentration. The optimum conditions established for maximum metal extractions were: pulp density 20%, time 3 h, temperature 363 K, SO2 60 g l(-1), sulphuric acid 3.0% (v/v) and ammonium sulphate 100 g l(-1). Under these conditions the recoveries from a typical nodule sample were: 88.5% Cu, 99.8% Ni, 91.8% Co, 97.8% Zn, 99.6% Mn with iron extraction of 2.4%. Nodules containing different percentage of metal contents were also tested under the established conditions and it was observed that the dissolution of iron varied between 2.4 and 4.9% with no significant variations in recoveries of Cu, Ni, Co, Zn and Mn. (C) 1999 Published by Elsevier Science B.V. All rights reserved.