Dissolution of Cu, Co and Ni from ocean nodules by l-ascorbic acid

Ferromanganese ocean nodules contain important transition metals like Cu, Co and Ni. They serve as an alternate source of these metals especially in countries like India, which does not have land-based resources of Co and Ni. The existing methods for metal dissolution from the nodules use highly acidic or alkaline media accompanied by strong organic or inorganic reducing agents at high temperature and/or pressure. In a clear variation to them, a single-stage metal dissolution method using l-ascorbic acid is described here. A well-known biological reducing agent, ascorbic acid; is shown to reduce Mn (IV) in nodules in a short time period of 30 min to accomplish almost 90% dissolution of Cu, Co and Ni, associated with Mn-rich phases. A detailed study of synthetic MnO2 reduction was carried out followed by nodule-leaching tests. Kinetics of the metal dissolution was studied and a model was developed to understand nodule-leaching process by ascorbic acid. The effect of solid/liquid ratio and particle size on the metal dissolution from the nodules by l-ascorbic acid was also investigated.