Investigation of methods for removal and recovery of manganese in hydrometallurgical processes

Abstract

Manganese is a major impurity which needs to be removed in many hydrometallurgical processes while some waste solutions are also important secondary manganese sources. Precipitation methods were investigated for the removal and recovery of manganese from a typical nickel laterite waste solution. Hydroxide precipitation alone was not an attractive option for the recovery and removal of manganese to very low levels due to its poor selectivity. Carbonate precipitation could be used for partial recovery of manganese from the waste solutions, but not desirable for removal of manganese to very low levels due to substantial co-precipitation of calcium and magnesium. Aeration at appropriate pH or using pure oxygen did enhance manganese removal, but this approach remains either kinetically slow or expensive due to the cost of oxygen. The oxidative precipitation with SO 2/air is very promising for both removal and recovery of manganese from laterite waste solutions and was investigated in detail to identify optimum conditions. It was found that solution pH was the most critical factor for maximising the rate of the oxidative precipitation with little co-precipitation of magnesium and calcium impurities. The SO 2/air (O 2) system worked efficiently in a nearly neutral pH range of 6–7, indicating that the system was favourable for treatment of metallurgical waste solutions. SO 2/air (O 2) ratio is another important factor for maximising the oxidising capacity of the SO 2/air (O 2) system and the utilisation of SO 2 and O 2 reagents with minimum consumption of base reagents for neutralisation. In this paper, potential commercial applications of these methods and their constraints are discussed.