Different Role of Bisulfite/Sulfite in UVC-S(IV)-O2 System for Arsenite Oxidation in Water

Abstract

It is of interest to use UV-sulfite based processes to degrade pollutants in wastewater treatment process. In this work, arsenic (As(III)) has been selected as a target pollutant to verify the efficacy of such a hypothesized process. The results showed that As(III) was quickly oxidized by a UV-sulfite system at neutral or alkaline pH and especially at pH 9.5, which can be mainly attributed to the generated oxysulfur radicals. In laser flash photolysis (LFP) experiments (λex = 266 nm), the signals of SO3•− and eaq− generated by photolysis of sulfite at 266 nm were discerned. Quantum yields for photoionization of HSO3− (0.01) and SO32− (0.06) were also measured. It has been established that eaq− does not react with SO32−, but reacts with HSO3− with a rate constant 8 × 107 M−1s−1.

Sulfite Poses a Risk of Hexavalent Chromium Rebound in Vadose Zone: A Challenge of the Stability of CrxFe1–x(OH)3

“…The abnormal paucity of SO 4 2– is incongruous with the prevalence of REDOX reactions on the surface of Cr 0.5 Fe 0.5 (OH) 3 , but it does correspond to the decrease in the proportion of Cr(VI). The anomalous decrease in both SO 4 2– and Cr(VI) percentage might be attributed to the competitive adsorption of a significant amount of instantaneously formed CrO 4 2– and SO 4 . − Both CrO 4 2– and SO 4 2– were desorbed from the surface of Cr 0.5 Fe 0.5 (OH) 3 . Subsequently, dissolved CrO 4 2– is reduced by dissolved sulfite under the catalysis of dissolved Fe(III) to form Cr(III) ions, which elucidates the notable release of Cr(III). SO 3 · − + SO 3 · − → normalS 2 normalO 6 2 − normalS 2 normalO 6 2 − + normalH 2 …”

“…However, the potential oxidation of Cr­(III) by the sulfite and oxygen system (S­(IV)-O 2 ) in the vadose zone has been overlooked. Due to the generation of reactive oxysulfur radicals, the potential oxidizability of S­(IV)-O 2 has garnered significant attention in recent years within the fields of atmospheric oxidation processes , and advanced water treatment technologies. − Unfortunately, the impact of S­(IV)-O 2 has not been given due consideration in the realm of environmental geochemistry. In fact, sulfite is widely present in soil, primarily due to bacterial growth on organosulfur compounds and chemolithotrophic growth on inorganic sulfur compounds .…”

Advanced electrocatalytic redox processes for environmental remediation of halogenated organic water pollutants

“…Reactive sulfur radicals are generated through dissociative reactions of persulfate, peroxomonosulfate, sulfate, or bisulfate to produce sulfate radicals, which are capable of assisting PFAS breakdown, 26,243,301,304 whereas the dissociation of bisulfite or sulfite anions produces sulfite radicals and hydrated electrons in strictly oxygen-free conditions. 113,301,[330][331][332] Addition of iodide, dithionite, or ferrocyanide to anaerobic electrolytes can aid the detachment mechanism to produce hydrated electrons. 260,333 Dissociation of dithionite will produce reductive sulfur dioxide radicals.…”

“…286 Oxidants are often radicals under aerobic conditions, such as the hydroxyl radical (˙OH, aqueous lifetime 0.02 μs), superoxide radical anion (OO˙ − , aqueous lifetime 1.3 μs), sulfate radical anion (SO 4 ˙ − , aqueous lifetime 30–40 μs), and sulfite radical anion (SO 3 ˙ − ), in addition to potent non-radical species, such as hydrogen peroxide (H 2 O 2 ) and singlet oxygen ( 1 O 2 , aqueous lifetime 3.5 μs). 285,287–301…”

“…Sulfite promotes the formation of SO 3 ˙ − , which is a mild oxidant 343 that reacts rapidly with oxygen to produce SO 5 ˙ − and subsequently SO 4 ˙ − and ˙OH radicals, which are stronger oxidants and can more effectively degrade organohalogen pollutants. 301…”