Pure water leaching soluble manganese from electrolytic manganese residue: Leaching kinetics model analysis and characterization

Electrolytic manganese residue (EMR) is a solid waste that generated in electrolytic manganese metal production, which would not only contaminate the environment due it contains soluble manganese, but occupy a large amount of farmlands as well. Hence, recovering manganese from EMR using economical method is the key to achieve the targets of resource recycling and solid waste harmless treatment. In this paper, pure water was used to leach soluble manganese out from EMR. Leaching kinetics model of manganese were established and examined, characteristics of EMR before and after leaching were analyzed by XRF, XRD, EPMA-WDS and SEM. The results revealed that the apparent activated energy (E) during the leaching processes was 11.17 ± 2.02 kJ/mol and the slope in fitting line of Arrhenius equation was −1.343, which indicated that the leaching kinetic model was appropriate and the rate determining step was diffusion process, that is, Mn2+ migrate into bulk solution from diffusion layer. The main crystal phases in EMR are quartz (SiO2) and calcium sulfate (CaSO4·nH2O) (n = 0.5 or 2), but the distribution relationship between SiO2 and CaSO4·nH2O was not regular. Mn is in the form of “film” covered in CaSO4 bar in EMR. High temperature and high volume of water could promote Mn2+ transport process. The optimal leaching condition was S:L (Solid : Liquid)1:4, temperature was 24 °C and the agitation rate was 300 r/min when combined the cost and efficiency, and 83.35 % soluble manganese can be leached out from EMR.