Kinetics of reductive leaching of manganese oxide ore using cellulose as reductant

The kinetics of reductive leaching of manganese from a low-grade manganese oxide ore were studied using cellulose as reductant in dilute sulfuric acid medium. It was found that when the stirring speed was higher than 200 r/min, the effect of gas film diffusion on manganese extraction efficiency could be neglected, and the kinetic behavior was investigated under the condition of elimination of external diffusion influence on the leaching process. Effects of leaching temperature, mass ratio of cellulose and ore, and the sulfuric acid concentration on manganese extraction efficiency were discussed. The kinetic data were analyzed based on the shrinking core model, which indicated that the leaching process was dominated by both ash layer diffusion and chemical reaction at the initial stage, with the progress of leaching reaction, the rate-controlling step switched to the ash layer diffusion. It was also concluded that the sulfuric acid concentration had the most significant influence on the leaching rate, the reaction orders with respect to the sulfuric acid concentration were 2.102 in the first 60 min, and 3.642 in the later 90 min, while the reaction orders for mass ratio of cellulose and ore were 0.660 and 0.724, respectively. An Arrhenius relationship was used to relate the temperature to the rate of leaching, from which apparent activation energies were calculated to be 46.487 kJ/mol and 62.290 kJ/mol at the two stages, respectively. Finally, the overall leaching rate equations for the manganese dissolution reaction with cellulose in sulphuric acid solution were developed. The morphological changes and mineralogical forms of the ore before and after the chemical treatment were discussed with the support of SEM and XRD analyses.