Multi-roles of SO2 to enhance the removal of arsenic from wastewater in sulfidation processes

Sulfidation has been an efficient method for arsenic (As) removal from acid wastewater, yet it is inefficient under neutral and weak acid conditions. The higher pH values resulted in the formation of the unstable As-S precipitates, especially employing Na2S as the vulcanizing agent as it can increase the pH value dramatically. Here, we found that SO2 exhibited excellent multi-roles in As removal when applying H2S-sulfidation method. The acidification effect of SO2 lead to the decreasing of pH values, guaranteed the stable As-S precipitates formation. Through the SO2 pre-treatment method, the results indicated that the pH values decreased from 7 to 2.8, with the increased H2S utilization efficiencies for As(III) removal from 20.9% to 92.0%. Moreover, SO2 post-treatment not only increased the As(III) removal efficiency, but also eliminated the excessive sulfides in solution. The reaction mechanism analysis indicated that the liquid comproportionation reaction between SO2 and excessive sulfides plays a vital role. The generated nascent sulfur (N-S0) can adsorb arsenic species and promote the agglomeration of As(III)-S precipitates. Furthermore, the SO2 and H2S co-treatment exhibited excellent As(V) removal performance. This study provides a new alternative method to improve the H2S-sulfidation process with SO2 for As removal from wastewater. [Display omitted] •SO2-coupled H2S was firstly reported to enhance the As removal efficiency.•SO2 regulated the As-S species to accelerate precipitation by adjusting the pH.•SO2 eliminated the excessive S(-II) increasing the stability of precipitates.•The nascent sulfur (N-S0) exhibited adsorption performance for As-S species.•The N-S0 provided active interfaces to accelerate the reduction of As(V).