Mechanism of sulfite enhanced As(III) oxidation in the As(III)-Fe minerals under ambient conditions.

Iron (Fe) minerals are known to be effective adsorbents for arsenic (As). However, the effects of sulfur species formed from the reductive dissolution of Fe minerals on the transformation of As(III) during the redox fluctuations processes under ambient conditions were poorly understood. Herein, we synthesized the As(III)-Fe minerals using sodium arsenite and ferric nitrate to investigate the effects of sulfur species on As(III) transformation in the As(III)-Fe minerals. Experimental results showed that sulfite rather than elemental sulfur and thiosulfate significantly accelerated As(III) oxidation. The oxidation rate of As(III) increased markedly from 0.0050 to 0.0168 min-1 with the increase of sulfite concentration from 0.5 to 2.0 mM. Sulfate radicals (SO4 •- ) and hydroxyl radicals (• OH) were identified as the dominant reactive species for As(III) oxidation. Besides, the underlying mechanism of Fe(II)/Fe(III) cycling for enhancing As(III) oxidation was further explored in the homogeneous Fe(II)/sulfite systems. Finally, interactions between sulfite and soil components induced radical formation, leading to As(III) oxidation in the soil environments. This study gives new insights into As(III) transformation co-existed with Fe minerals and sulfur species, which shed light on developing remediation strategies for regulating As contamination in temporarily flooded soils. ENVIRONMENTAL IMPLICATION: "New Insights into the Mechanism of Sulfur Species Induced As(III) Oxidation in the As-Fe Minerals" This study systematically explored the coupled effects between sulfur species and Fe minerals on As(III) transformation in the As-Fe-minerals under oxic conditions, which showed that sulfite significantly accelerated As(III) oxidation to As(V) via the enhanced formation reactive oxygen species (e.g., SO4 •- and • OH). This study shed light on the development of remediation strategies in the contaminated soils with toxic pollutants via introducing sulfur species. We strongly believe this study is of great interest to environmental scientists and chemical engineers, especially those who works on the remediation of contaminated sites and wish to explore the high-efficiency strategies for the control of toxic pollutants like As.