Unveiling the Neglected Roles of Chloride and Sulfate in the Removal of Nitro Compounds by Sulfidated Zero-Valent Iron/Ferrous Ion Systems
Shiwen Sun, Xueran Xu, Xiaofei Jiang, Yuhang Yue, Yinshun Dai, Xiaowei Yang, Qi Xiu, Liangfeng Duan, Shan Zhao
Abstract
Ferrous ions (Fe 2+ ) can effectively promote the removal of pollutants by sulfidated zero-valent iron (S-ZVI), but the role of anions coexisting with Fe 2+ was often ignored. This study systematically compared the performances of S-ZVI/FeCl 2 and S-ZVI/FeSO 4 systems for chloramphenicol (CAP) and nitrobenzene (NB) removal. The results showed that FeCl 2 and sulfidation had a synergistic promoting effect on the reaction, but FeSO 4 could not promote the removal of nitro compounds by S-ZVI. Liquid chromatography/mass spectrometry (LC/MS) and UV–vis analysis showed that only the nitro group was reduced during the removal of CAP and NB. The results of batch experiments showed that both NaCl and Na 2 SO 4 could effectively promote the reaction, but the promotion effect of Na 2 SO 4 weakened with the decrease of pH. X-ray photoelectron spectroscopy (XPS) analysis showed that Fe 2+ could promote the adsorption of SO 4 2– on the surface of S-ZVI. A possible mechanism was proposed: Fe 2+ could maintain a low pH level because of hydrolysis, which promoted the adsorption of Cl – and SO 4 2– on the surface of S-ZVI. Cl – promoted the reaction because of its pitting corrosion, while SO 4 2– competed with nitro groups for the adsorption sites. Our findings suggest that the coexisting anions are quite essential in the removal of nitro compounds by S-ZVI/Fe 2+ systems.