Extraction of metals from manganese nodules of the Indian Ocean by leaching in aqueous solution of sulphur dioxide

Abstract

A low grade manganese nodule sample from the central Indian Ocean basin was leached in aqueous SO 2solution whereby the tetravalent oxide of manganese was rapidly reduced and extracted along with cobalt, nickel, zinc, iron and copper. The extraction of all these metal ions and particularly of iron and copper depended upon the actual amount of SO 2 present (in moles) per unit weight of nodule sample. This is usually represented by a term ‘R’ which is characteristic of a particular nodule sample. It was observed that by choosing a suitable value of R and the period of leaching, more than 85% of Mn, Ni, Co and more than 75% of Cu could be extracted with small recovery of Fe. Though the extractions of metal values were extremely fast in the initial stage, a longer leaching period helped in in-situ separation of Fe. The particle size of the ground nodule sample and the environment of leaching appear to be critical factors for optimum recovery of metal values. A temperature higher than 40°C was found to be unsuitable for maximum extraction of important metals.