Manganese metallurgy review. Part II: Manganese separation and recovery from solution

Various methods for manganese separation and recovery from solution are reviewed, which are potentially applicable to leach solutions of secondary manganese sources, particularly nickel laterite waste effluents. The main methods include solvent extraction, sulfide precipitation, ion exchange, hydroxide precipitation and oxidative precipitation. These methods are briefly compared and assessed for both purification of manganese solutions and recovery of manganese from the solutions in terms of their selectivity, efficiency, reagent costs and product quality. The strategies for co-recovery of valuable metals including nickel and cobalt are discussed.Among these methods, oxidative precipitation with cheap oxidants such as SO2/O2 mixture is highly selective for recovery of manganese and the most promising method recommended for future research and development. Solvent extraction with cheap extractants is next for selective extraction of manganese, purification of manganese solutions or co-recovery of other valuable metals. The cost of base needed for neutralisation in solvent extraction is a major consideration. Carbonate precipitation is more selective for manganese than hydroxide precipitation with respect to magnesium impurity. Manganese carbonate is a favourable form for further processing to final manganese products, but its applicability will largely depend on the relative concentrations of manganese to magnesium and calcium impurities. Sulfide precipitation and ion exchange offer useful means for purification and/or co-recovery of other base metal impurities.