Overlooked Role of Sulfur-Centered Radicals During Bromate Reduction by Sulfite

In this work, the kinetics and mechanisms of the reductive removal of BrO3- by sulfite in air atmosphere were determined. BrO3- could be effectively reduced by sulfite at pH(ini) 3.0-6.0, and the reduction rate of BrO3- increased with decreasing pH. The coexisting organic contaminants with electron-rich moieties could be degraded, accompanied with BrO3- reduction by sulfite. The reaction stoichiometries of -Delta[sulfite]/Delta[bromate] were determined to be 3.33 and 15.63 in the absence and presence of O-2, respectively. Many lines of evidence verified that the main reactions in the BrO3-/sulfite system in air atmosphere included the reduction of BrO3- to HOBr and its further reduction to Br-, as well as the oxidation of H2SO3 by BrO3-to form SO3 center dot- and its further transformation to SO4 center dot-. Moreover, SO4 center dot- rather than HOBr was determined to be the major active oxidant in the BrO3-/sulfite system. SO(3)(center dot-)played a key role in the over-stoichiometric sulfite consumption because of its rapid reaction with dissolved oxygen. However, the formed SO3 center dot- was further oxidized by BrO3- in the N-2 atmosphere. BrO3- reduction by sulfite is an alternative for controlling BrO3- in water treatment because it was effective in real water at pH(ini) <= 6.0.