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

Abstract

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.

Keywords: As removal; Nascent active sulfur; PH adjustment; Residual sulfide elimination; SO(2) multi-roles.