Leaching kinetics of pyrolusite from manganese–silver ores in the presence of hydrogen peroxide

The leaching kinetics of pyrolusite from manganese–silver ores in sulfuric acid solution in the presence of hydrogen peroxide has been investigated. It is found that the H2SO4 concentration has the most important influence on the leaching rate. A reaction order of 0.95 for hydrogen ions is obtained at 0.55–1.6 mol/L H2SO4 concentration. The leaching rate is clearly improved with increasing H2O2 concentration although the effect is eroded by the decomposition of H2O2, which is catalyzed by MnO2. The leaching rate strongly depends on the stirring speed below 950 r/min. The particle size also distinctly affects the leaching process; the leaching rate is directly proportional to the inverse of the square of the average initial particle diameter. The effect of temperature is not apparent and the manganese can be extracted at room temperature in the presence of H2O2. The leaching process follows the kinetic model 1−(2/3x)−(1−x)2/3=kt and the apparent activation energy is determined to be 4.45±0.3 kJ/mol at 30–60 °C. It is concluded that the leaching process of pyrolusite from Mn–Ag ores in acidic sulfuric solution in the presence of H2O2 is controlled by diffusion through an insoluble layer composed of the associated minerals.