Oxidation of Sulfite in Pulp and Paper Mill Effluents, 1994 Environmental Conference Proceedings

P. Ramamurthy, R. Harland, J.G. Dorica

The catalytic oxidation of sulfite ions in bleached chemi-mechanical pulp (BCMP) mill effluents was investigated. The initial sulfite concentration was typically 550 – 1200 mg/L. Ferric chloride and ferric sulfate were found to be effective catalysts, while salts of cobalt and manganese, activated carbon and lime did not exhibit catalytic activity. A reaction time of about one hour was sufficient to reduce the sulfite concentration from 6.9 mM (550 mg/L) to 0.5-1 mM (40-80 mg/L), at temperatures above 400C with 0.3 mM of iron (48.6 mg/L of FeCl3).

Under the conditions tested, the reaction followed a zero order with respect to sulfite, at SO3(^2-) concentrations above about 2.5 mM (200 mg/L). At lower concentrations, the reaction kinetics shifted to first order. The COD reduction during oxidation corresponded to the decrease in sulfite indicating that during the reaction period there was no other loss of oxygen demand. The sulfite oxidation should facilitate activated sludge treatment since the sulfur is converted to a stable, highly-oxidized state.