Specific H₂S Release from Thiosulfate Promoted by UV Irradiation for Removal of Arsenic and Heavy Metals from Strongly Acidic Wastewater

Abstract

The removal of arsenic and heavy metals (HMs) from strongly acidic wastewater by hydrogen sulfide (H2S) is an efficient method. However, traditional sulfuration reagents (Na2S, FeS, CaS, etc.) rapidly release H2S under acidic conditions via spontaneous hydrolysis, leading to serious H2S pollution. Herein, a H2S release process employing thiosulfate as a sulfuration reagent was proposed to eliminate H2S pollution. We found that thiosulfate can release H2S with specificity both in the dark and under ultraviolet (UV) irradiation under acidic conditions. In the absence of arsenic/HMs, H2S is not released because the formed H2S is consumed by a thiosulfate decomposition product, sulfite, or by its photolysis. In the presence of arsenic/HMs, H2S is released because the formed H2S immediately reacts with arsenic/HMs to generate sulfide precipitates rather than being consumed. The efficiency of transforming thiosulfate to H2S under UV irradiation is 2.5-fold the efficiency in the dark, because UV irradiation promotes the transformation of “effective sulfur” in thiosulfate molecules to form H2S through the transformation of HS· and S2O3 • – radicals. Moreover, more than 99.9% of arsenic/HMs were removed from strongly acidic wastewater without producing H2S pollution under UV irradiation. This thiosulfate-based H2S-specific release process solves the problem of H2S pollution under acidic conditions.

Direct and indirect oxidation removal of chloride ions from sulfuric acid wastewater using photoactivated PMS/PS: efficiency and mechanism

“…9 Recently, considerable attention has been paid to the improvement effect of UV light on sulfide precipitation for arsenic. [10][11][12] Under UV irradiation, abundant free radicals will be produced and act on the surface of arsenic sulfide slags, leading to enhanced efficiency and settleability. Owing to these research studies, selective removal of arsenic and heavy metals has been achieved.…”

Deep purification of copper from zinc sulfate solution using controllable aging FeS nanoparticles through slow-release sulfide precipitation

“…These encompass the capability for selectively extracting metals, rapid reaction kinetics, achieving higher product quality, and the potential for recycling precipitates through smelting [9]. Still, conventional ionic sulfidizing agents exhibit rapid spontaneous hydrolysis and sulfur ion release in aqueous solutions, resulting in low sulfur utilization efficiency, severe product intermixing, and fine particle size that hinders settling [10]. The key to addressing these issues is the slow-release rate of S 2ions, as it can provide a lower sulfur ion saturation in the solution, allowing sufficient time for the binding of other metal ions with sulfur ions [11].…”

Sulfur-Containing Radical Anions Formed by Photolysis of Thiosulfate: Quantum-Chemical Analysis

“…20 The main products of S 2 O 3 2− photodegradation in water are elemental sulfur S 8 , sulfite and sulfate anions, tetrathionate S 4 O 6 2− , and hydrogen sulfide. 29,30,35,36 When photolysis was performed in air-saturated solutions, the formation of colloids was observed. 20 The colloid is an analogue of Raffo sol 37 consisting mainly of polymeric sulfur S n (n = 6−14, mainly S 8 ), hydrogen sulfide, sulfur dioxide, and long-chain polythionic acids H 2 S n O 6 .…”