Leaching kinetics of manganese from pyrolusite using pyrite as a reductant under microwave heating

Abstract

• Microwave heating was applied to the hydrometallurgical reduction leaching of pyrolusite. • Compared with conventional heating, microwave heating could improve manganese leaching rate and save energy. • The reduction leaching kinetics behavior of pyrolusite by microwave heating was studied. Microwave heating was applied to leaching of manganese from pyrolusite using pyrite as reductant. The leaching parameters on manganese extraction, such as mass ratio of pyrite and pyrolusite, H 2 SO 4 concentration, liquid to solid ratio, reaction temperature, were investigated. The results displayed that under the optimum parameters of mass ratio of pyrite and pyrolusite of 0.25, H 2 SO 4 concentration of 1.6 mol/L, liquid to solid ratio of 10 ml/g, reaction temperature of 353 K, the leaching time of 3 h, Mn extraction rate reached 93.03%. Under the same conditions, Mn extraction rate was only 75.84% by conventional heating, The Mn leaching rate obtained by microwave heating was 17.19% higher than that obtained by conventional heating. Moreover, the leaching data was successfully verified based on unreacted shrinking core model. A shift in the rate control step was found. The leaching rate control step was determined by surface chemical reaction within 0 ~ 100 min and by diffusion through product layer within 100 ~ 180 min, respectively, the apparent activation energy was 30.95 kJ/mol and 53.03 kJ/mol, separationly, and the apparent rate equation was respectively expressed as: 1 - 1 - r 1 / 3 = 46.71 m F e S 2 / m M n O 2 0.7154 H 2 S O 4 0.3042 V L / M S 0.7821 e x p - 30950 / R T t 1 - 3 1 - r 1 - r 1 2 / 3 + 2 1 - 1 - r r - r 1 1 / 3 = 387000 m F e S 2 / m M n O 2 1.4498 H 2 S O 4 0.6093 V L / M S 1.2043 e x p - 53030 / R T t