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

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, H2SO4 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, H2SO4 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 similar to 100 min and by diffusion through product layer within 100 similar to 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(FeS2)/m(MnO2)](0.7154)[H2SO4](0.3042)[V-L/M-S](0.7821)exp(-30950/RT) t 1 - 3(1 - r/1 - r(1))(2/3) +2(1 - (1 - r)(r - r(1))(1/3)) = 387000[m(FeS2)/m(MnO2)](1.4498)[H2SO4](0.6093)[V-L/M-S](1.2043)(exp)(-53030/RT) t

Automated summary

The study demonstrated that under microwave heating, the extraction rate of manganese was significantly higher compared to conventional heating method. The verified leaching data supported this result, and a shift in the rate control step was observed, indicating differences in the leaching mechanism between the two heating methods.