Kinetics of the Iron(II)- and Manganese(II)-Catalyzed Oxidation of S(IV) in Seawater with Acetic Buffer: A Study of Seawater Desulfurization Process

Kinetics of iron(II)and manganese(II)-catalyzed oxidation of S(IV) in seawater were studied here to provide theoretical support for the flue gas desulfurization process (SFGD). Experiments were carried out with artificial seawater and acetic buffer. Results indicated that the reaction order with respect to dissolved oxygen is zero. However, the reaction order with respect to S(IV) is variable: second-order under uncatalyzed condition (4.0 ≤ pH ≤ 7.0); first-order under Fe(II)-catalyzed oxidation (2.5 ≤ pH ≤ 3.5); first-order (4.0 ≤ pH ≤ 5.0) and second-order (5.5 ≤ pH ≤ 5.9) under Mn(II)-catalyzed oxidation. The different S(IV) dependence could be attributed to different metal speciation at different pH values. Also, acetate is found to have significant inhibition effect on Mn(II)-catalyzed oxidation in high ion strength solution. The strong catalytic effect of Fe(II) and Mn(II) ions on S(IV) oxidation could lead to new ideas for the design of SFGD systems.