Preferential leaching of cobalt, nickel and copper from cobalt-rich ferromanganese crusts with ammoniacal solutions using ammonium thiosulfate and ammonium sulfite as reducing agents

Preferential ammoniacal leaching of Co, Ni and Cu from cobalt-rich ferromanganese crusts under reducing conditions was performed using ammonium thiosulfate and ammonium sulfite as reducing agents. The effects of reducing agent concentration, initial pH, leaching time, temperature and the combined concentration of ammonium thiosulfate and ammonium sulfite on the extraction of Mn, Fe, Co, Ni and Cu were investigated. The extraction of Co, Ni and Cu with ammonium sulfite was better than that with ammonium thiosulfate. The extraction of Fe was not observed in the experiments. When ammonium thiosulfate was used as the reducing agent the extraction of Mn decreased with increasing initial pH. However, the extraction of Co, Ni and Cu was not so high. An increase in ammonium thiosulfate concentration and leaching temperature increased the Mn extraction. When ammonium sulfite was used as the reducing agent Mn was precipitated and appeared in the residue as (NH4)(2)Mn(SO3)(2) . H2O.