Nickel losses have been observed from leach liquors obtained during extraction of metal values from ocean nodules using ammonium sulphite. Studies have been carried out to establish the reasons for such losses. Behaviour of Ni(II) in the following systems was studied: (a) NH3(NH4)(2)SO3- (b) NH3-partially oxidised (NH4)(2)SO3 using oxygen-H2O, and (c) NH3-partially oxidised (NH4)(2)SO3 using MnO3-H2O. Nickel added during or after reduction of MnO2 in NH3-(NH4)(2)SO3 solution resulted in its precipitation as a crystalline compound. The XRD pattern showed discrete peaks but did not correspond to any compound cited in ASTM. Detailed work of DT-TGA and chemical analysis supported the formation of Ni0.75Mn0.25(NH3)(4)S2O6 . 2 H2O in nodule leach liquor.