Evaluation of As(III) Removal and Corresponding Species Regulation Mechanism from Sulfide-Abundant Arsenic Solution with Potential Application in Smelting Wastewater

Abstract

H₂S treatment is a potential method to remove As from smelting wastewater. However, it was difficult to achieve the high concentration As containing wastewater to standard through H₂S one-step treatment. Meanwhile, the sulfide-abundant conditions after H₂S treatment changed the As species and the pH condition, which put forward challenges for removing As deeply. In this study, we developed an H₂S-modification method to prepare sulfide nanoscale zero-valent iron (S-nZVI) to improve the acid resistance and the adsorption performance of adsorbents for As in sulfide-abundant conditions. The results showed that the H₂S-modification method expanded the pH windows with excellent As(III) removal efficiency from 3 to 7, and at pH value of 3, the As(III) removal efficiency reached 99%. Under pH = 3, the concentration of iron released from nanomaterials decreased from 200 to 20 mg/L, which is attributed to the protection of the surface by the FeS_x layer. Moreover, through H₂S-sulfidation, H₃AsO₃ (As-O species) transformed to As-S species, which were more challenging to remove than As-O species. In As(III)-S(-II) solution, S-nZVI adsorbed 95% of As(III) in the range of pH 1–5, and the excessive S(-II) could react with Fe(III) to accelerate the cycle of Fe(III)/Fe(II). This improved the efficiency of the Fenton reaction to enhance the oxidation of As(III). Furthermore, consumption of the S(-II) could promote the transformation from As-S species to As-O species. Thus, excellent acid resistance and the synergy with S(-II) made S-nZVI holds great potential to be applied in As(III) removal.