Kinetics of manganese reduction leaching from weathered rare-earth mud with sodium sulfite

The kinetics of manganese reduction leaching in an acidic medium from a weathered rare-earth mud (WREM) were investigated. Using sodium sulfite as a reductant, the effect of reaction temperature, mechanical agitation rate, sulfuric acid dosage, and feed particle size on leaching kinetics were examined. The leaching process can be described by the shrinking-core model. An apparent activation energy of 11.5 kJ/mol for manganese reduction leaching is estimated. The diffusion of reactants and leaching products through a porous ore matrix was found to be the rate-limiting step. An empirical equation relating the manganese leaching rate constant with feed-particle size and leaching temperature was established. It was found that the smaller the feed-particle size or the higher the leaching temperature, the faster the leaching proceeds, as anticipated. The kinetic process exhibited a self-catalysis characteristic of Mn2+ in the mud. This finding suggests that Mn(III,IV) in the mud was rapidly reduced to Mn2+ during the initial stage of leaching.