Simultaneous oxidation of roxarsone and adsorption of released arsenic by FeS-activated sulfite.

The conventional oxidation-adsorption methods are effective for the removal of roxarsone (ROX) but are limited by complicated operation, toxic residual oxidant and leaching of toxic metal ions. Herein, we proposed a new approach to improve ROX removal, i.e., using the FeS/sulfite system. Experimental results showed that approximately 100% of ROX (20 mg/L) was removed and more than 90% of the released inorganic arsenic (As(V) dominated) was adsorbed on FeS within 40 min. This FeS/sulfite system was a non-homogeneous activation process, and SO4·-, ·OH and 1O2 were identified as reactive oxidizing species with their contributions to ROX degradation being 48.36%, 27.97% and 2.64%, respectively. Based on density functional theory calculations and HPLC-MS results, the degradation of ROX was achieved by C-As breaking, electrophilic addition, hydroxylation and denitrification. It was also found that the released inorganic arsenic was adsorbed through a combination of outer-sphere complexation and surface co-precipitation, and the generated arsenopyrite (FeAsS), a precursor to ecologically secure scorodite (FeAsO4·2H2O), was served as the foundation for further inorganic arsenic mineralization. This is the first attempt to use the FeS/sulfite system for organic heavy metal removal, which proposes a prospective technique for the removal of ROX.