Ammoniacal leaching of roast reduced deep-sea manganese nodules

The paper describes the reduction-roast ammonia leach process developed at NML for recovery of copper, nickel and cobalt from polymetallic sea nodules. A brief account of the development of a two stage ammoniacal leaching scheme with a prior pre-conditioning step is given. The necessity of monitoring redox potential in the first stage leaching to control cobalt recovery has been emphasized. Based on the two stage leaching scheme, recycle leaching has been carried out to generate leach liquor having suitable composition for the subsequent solvent extraction–electrowinning operation. The average recovery of metals in 16 cycles of leaching has been found to be 92% Cu, 90% Ni and 56% Co.