National Metallurgical Laboratory has developed a reduction roast-ammonia Leach-solvent extraction-electro winning process operational at pilot sale for the recovery of Cu, Ni and Co from sea nodules of Central Indian Ocean. This paper describes the effect of the various process parameters in reduction roasting on the leach recoveries of Cu, Ni and Co with the use of both liquid and gaseous reductants. For this purpose, reduction roasting experiments on sea nodules has been carried out at laboratory scale. Leach recoveries in excess of 95% for Cu & Ni and 75% for Co could be achieved under optimum conditions with both liquid and gaseous reductants.


Polymetallic sea nodules are one of the potential sources of valuable metals such as Cu, Ni, Co and Mn. Considerable information is available in the literature about the various extraction techniques for these metals from ocean nodules. Extraction methods include both hydrometallurgical processes such as acid leaching, ammonia leaching and reductive leaching (including high temperature pre-treatment like reduction or sulphation roasting) and pyrometallurgical processes such as, smelting, chlorination-vaporization and seggregation. A modified Caron" s process (Caron 1924) comprising of a reduction roasting step prior to ammonia leaching has been adopted at National Metallurgical Laboratory, India at pilot scale for the processing of manganese nodules. The present paper deals with the reduction roasting of sea nodules at laboratory scale. The objective of roasting in the processing of manganese nodules is two fold:

  • to liberate Cu, Ni and Co associated with the complex iron and manganese phases [goethite, ferroxyhyte, ferrihydride, todorokite, birnessite, δ-MnO2 etc.] (Rakesh Kumar, Ray and Biswas 1992, Rakesh Kumar, Das, Ray and Biswas 1991 and 1994). and

  • to selectively reduce the oxide phases of Cu, Ni and Co to elemental form to make them amenable to leaching.

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