Effect of Co60 irradiation on the degradation and mineralization of sulfonated aromatic compounds in aqueous solutions.

As sulfonated aromatic compounds are widely used in industry, they have frequently been detected in aquatic environments. This study evaluated the degradation and mineralization of 2,6-naphthalenedisulfonic acid disodium salt (2,6-NS), sodium 2-naphthalenesulfonate (2-NS), benzenesulfonic acid sodium salt (BS), and 4-vinylbenzene sulfonate sodium (4-VBS) by exposing aqueous solutions of these compounds to Co60 irradiation. The radiolytic degradation of these pollutants was found to follow pseudo-first-order kinetics. The dose required to achieve 90% degradation (D90) of these four sulfonated compounds was 0.480 (2,6-NS), 0.390 (2-NS), 0.194 (BS), and 0.280 kGy (4-VBS). The chemical radiolytic yield (G) decreased as the absorbed dose increased; moreover, the chemical structures of these compounds affected their radiolytic efficacy. No significant reduction in radiolytic degradation was observed in the presence of inorganic anions (SO, Cl). The radiolytic degradation efficiency was higher when hydrogen peroxide (HO, a hydroxyl radical (OH) promoter) was added. The results also showed that combining HO, persulfate anions (SO, a sulfate radical anion (SO) promoter), or NO gas (a OH radical promoter) with the sulfonated compounds enhanced the radiolytic mineralization yield and process by reducing the required irradiation energy. In terms of the Co60/O system, at an absorbed dose of 12 kGy, the total organic carbon (TOC) removal efficiency was almost 70%, resulting in the observed release of SO anions. In addition, the concentration of dissolved oxygen decreased and the pH was lowered. Based on these results, irradiation with Co60 was found to be a useful tool to remedy wastewater containing sulfonated aromatic compounds.