Recovery of soluble manganese from electrolyte manganese residue using a combination of ammonia and CO2

To minimize the environmental impacts of electrolyte manganese residue (EMR) and to recover the valuable manganese element, precipitation of the soluble manganese from EMR using ammonia bubbled with CO2 was investigated. Precipitation behaviours in the presence of ammonia with or without CO2 are discussed by comparison. It was found that the process using a combination of ammonia and CO2 results in better precipitation of manganese, yielding MnCO3 as observed by XRD analysis. The molar ratio of ammonia to manganese and the strength of bubbling and agitation with CO2 were studied as parameters affecting the recovery of manganese. The optimal experimental conditions for the recovery of manganese were found to be an ammonia-to-manganese molar ratio of 3:1, CO2 bubbling at a rate of 2 L/min for 2 min, and agitation at 190 rpm at 298 K for 12 min. Under these conditions, a manganese recovery of 94.2% was obtained. Kinetic analysis indicated that the order of the reaction and the energy of activation for the precipitation of manganese are approximately 2.2 and − 56.7 kJ/mol, respectively.