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.