Recovery of Cu, Ni and Co from Manganese Nodules can be achieved either through a hydrometallurgical route or through a combination of pyro-hydrometallurgical route. With a view to pursue the second option, synthetic Cu-Ni-Co-Fe matte having almost similar composition as is expected to be obtained by smelting-sulphidising of Ocean Nodules was prepared from pure metals. The dissolution behavior of synthetic matte was studied both in sulphate and chloride media. Almost complete dissolution of Cu, Ni and Co could be achieved by sulphuric acid leaching at elevated pressure in presence of oxygen. Ammonium sulphate was added during leaching to reject most of iron as ammonium jarosite in the leaching step itself. Hydrochloric acid leaching gave very low recovery of copper unless oxygen was purged into the leach liquor. Conditions were optimized for metal recovery by first leaching the matte with 2N hydrochloric acid at 90oC for one hour followed by purging oxygen at a flow-rate of 100 ml/min for three hours. Quantitative dissolution of Cu, Ni and Co could be achieved within half-an-hour during chlorination under ambient temperature conditions. However, all the iron associated with matte got dissolved while the sulphide sulphur got distributed as sulphate and elemental sulphur. The results obtained from the synthetic matte were comparable with the actual matte prepared from Ocean Nodules.
Two approaches which are generally followed for the development of processes to recover Cu, Ni and Co from the Ocean Nodules are:
dissolution in acidic/ammoniacal medium in presence/absence of reductants and
reduction of metal values through pyrometallurgical route to obtain white metal containing Cu, Ni, Co and Fe.
The alloy so obtained is then subjected to sulphidisation to get metal containing matte which is further treated through hydro-metallurgical route for metal dissolution and separation.
