An empirical rate equation for the partial removal of manganese from solution using a gas mixture of sulfur dioxide and oxygen

The oxidation of soluble manganese by SO2–O2 gas mixtures is known to occur via complicated reaction pathways. An empirical equation was derived for the rate of manganese precipitation from solution as a function of the gas composition, the concentrations of dissolved sulfur and O2, and the solution temperature and pH. The relationships between the rate of manganese precipitation and each of these parameters were obtained from batch tests.The influence of SO2 was described by both the SO2 content of the gas mixture and the concentration of the dissolved sulfur arising from the dissolution of the SO2 gas. The rate of manganese precipitation was found to be first order with respect to the dissolved O2 concentration and inversely proportional to the pH of the solution. An Arrhenius relationship was used to relate the solution temperature to the rate of precipitation, from which an activation energy of 23.5 kJ/mol was calculated. The manganese(II) concentration had little influence on the rate at concentrations above 500 mg/L.The rate equations for each of the operating parameters were combined into a single empirical rate equation for manganese precipitation, which described all of the batch data and was also applicable to manganese precipitation in continuous mode.