Manganese nodule contains 13-26% manganese in oxide/hydroxide form. Copper, nickel and cobalt together vary between 1.5 to 2.5%: Over last several decades processes have been developed for four metals (Cu, Ni, Co and Mn) or three metals (Cu, Ni and Co) recovery from nodules. The processes for four metal recovery are based on acid leaching in the presence/absence of reductants like S02 and charcoal. The processes for three metal recovery are primarily based on ammoniacal leaching routes in the presence of reductants. Under ammoniacal conditions the extent of manganese extraction during leaching depend on nature of buffering agent (ammonium carbonate, ammonium chloride and ammonium sulphate) and reductant. In ammonia-ammonium sulphate medium with sulphur based reductants like MnS04, FeS04 (NH4)2S03 and elemental sulphur about 20-30% manganese dissolves during leaching step. In order to recover manganese, both the leach liquors as well as the residue need to be treated. From the leach residue manganese can be recovered by pyrometallurgical as well hydrometallurgical routes. Manganese dioxide, manganese salts or electrolytic manganese metal can be produced through aqueous route. In the present paper various options for manganese recovery from nodules are described.


Manganese dioxide forms the major matrix of nodules and its percentage varies between 13 to 24%. Manganese nodules containing about 1.5% of Cu+Ni+Co considered as low grade nodules contain about 13% Mn whereas nodules having ~2.0 to 2.5% of Cu+Ni+Co contain 18-24% Mn. The hydrometallurgical processes are either acid or ammonia based. A number of reviews have summarized the hydrometallurgical routes developed to recover metal values in acid and ammoniacal medium (Agarwal et. al., 1976; Fuerstenau and Han, 1977; Huberd, 1980; Monhemius, 1980; Fuerstenau and Han, 1983; Benjamin et.al, 1985a, 1985 b; Das and Anand, 1997; Han, 1997).

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