Absorption of SO2 from a Gas-Air Mixture by Solutions Containing Iron Compounds

Abstract

The chemisorption of sulfur(IV) oxide (SO2) from air by natural aqueous media containing iron (Fe) ions is a current area of research interest. At the same time, studies of SO2 absorption from gases with higher concentrations of SO2 and at high temperature by solutions containing Fe compounds are not enough to predict the purification process of industrial waste sulfur-containing gases. This study investigated SO2 absorption from a gas-air mixture by solutions containing Fe compounds under near-industrial conditions, viz., froth mode of bubbling, SO2 concentrations in the gas-air mixture about 0.21–4.05 g/m3, and temperatures of 22°C–80°C. The experimental results showed that a rise in process temperature, SO2 concentration in the gas phase, the Fe species, and the initial pH of the absorbing solutions lead to an increase in the rate and efficiency of SO2 removal. It was determined that SO2 absorption by an Fe(II)- and Fe(III)-containing solution (initial pH=7.85) consists of three stages: (1) induction, (2) increase in absorption rate, and (3) decrease in absorption rate. Absorption of SO2 occurred efficiently only in the presence of Fe(OH)2 in the solution (the maximum rate of SO2 absorption reached 100%). Replacing Fe(OH)2 with Fe(OH)3 led to a decrease in the absorption rate by more than four times. This was caused by heterogeneous catalytic oxidation on the surface of Fe(OH)2 accompanied by the formation of peroxide compounds. The proposed mechanism of heterogeneous catalytic oxidation is discussed in reference to the available information in the literature.