Synthesis of Different Manganese Oxides Using SO2/O2 Gas Mixtures at Different Temperatures

Abstract

The aim of this work is to study the kinetics and required operation conditions for the formation of various manganese oxides using the SO2/O2 gas mixture as the oxidant agent. This promising approach presents some obvious economical advantages over traditional pyrometallurgical routes. Experimental evidence demonstrate that increasing the temperature of the reaction allows modifying the oxidation potential, thus facilitating the oxidation product synthesis. However, at 25 °C by varying the SO2/O2 ratio and the gas mixture flow rate, it was not possible to modify this potential. It was also observed that manganese dioxide (MnO2) is formed between 20 and 50 °C (activation energy (Ea) = 14.33 kJ/mol), oxy-hydroxide of manganese (MnO·OH) is obtained between 55 and 65 °C (Ea = 25.14 kJ/mol), and manganese(II, III) oxide (Mn3O4) is produced between 70 and 90 °C (Ea = 12.44 kJ/mol). The magnitude of these activation energy values is characteristic of processes controlled by the diffusion of the gaseous reagents.