A macromolecular N,N-dichlorosulfonamide as oxidant for residual sulfides

A redox copolymer, a macroporous poly(S/DVB) resin bearing N,N-dichlorosulfonamide groups, was used to remove residual sulfides from aqueous solutions by its oxidation to non-toxic products. The resin contains 8.2 meq active chlorine/g and shows strong oxidizing properties. It was employed in static and flow processes for treatment of sulfide solutions containing 32, 100 or 320 mg S2−/dm3. The effects of various parameters on the reaction course have been studied (molar ratio of the reagents, alkalinity of the reaction media, flow rate in column processes). The data showed that the reactive copolymer easily oxidizes sulfides––it was possible to reduce the concentration below 10 μg S2−/dm3. During oxidation processes the formation of two end products was confirmed––these were sulfates (in majority) and sulfur which causes the turbidity of the effluents. The reaction conditions to eliminate sulfur formation were sought. To utilize the polymer-bonded active chlorine with good efficiency, it was necessary to maintain a suitable level of alkalinity of the influx. The exhausted copolymer contained unsubstituted sulfonamide groups. It could be regenerated with a slightly acidified sodium chlorate(I) and reused for further processes.