Photochemical Oxidation of Arsenic(III) to Arsenic(V) using Peroxydisulfate Ions as an Oxidizing Agent

Abstract

The photochemical oxidation of arsenic, As(III), to the less toxic As(V) using peroxydisulfate ions (S2O8(2-)) as the oxidizing agent under UV light irradiation was investigated. The photochemical oxidation of As(III) to As(V) assisted using peroxydisulfate ions (KPS) proved to be a simple and efficient method, and the rate of oxidation for As(III) was exceptionally high in accordance with the concentration of KPS. In this study, the UV light intensity was of primary importance for the dissociation of the KPS in generating sulfate anion radicals (SO4(-*)). Upon intense UV light irradiation, very efficient oxidation was achieved due to the complete decomposition of KPS into SO4(-*) radicals which favor a higher reaction rate. Subsequent pH variation from 3 to 9 was seen to have no influence on the photolytic cleavage of KPS, and hence, the reaction was unaltered. There was also no significant effect from the continuous purging of oxygen or dissolved oxygen before the reaction as the air-equilibrated condition was found to be sufficient for efficient oxidation. However, the continuous purging of nitrogen substantially reduced the reaction rate (20%), confirming that the dissolved oxygen plays a role in this reaction, although at high concentrations of KPS, this situation was overcome. Humic acid was also found to have no detrimental effect on the reaction rate, even at 20 ppm concentration. The resultant SO4(2-) obtained in this studywas,thus, not considered a pollutant. Moreover, there was no need for a sensitizer or other metals with highly alkaline conditions that are normally used in conjunction with KPS. Natural solar light could also effectively oxidize As(III) at room temperature. This simple technique was, thus, considered a cost-effective and safe method for the oxidation of As(III) to As(V).

Preparation, characterization and application of a Ce–Ti oxide adsorbent for enhanced removal of arsenate from water

“…Especially, TiO 2 has attracted much interest because As(III) can be oxidized to As(V) in UV-illuminated TiO 2 suspension [13]. Since As(V) adsorbs more strongly on most adsorbents than As(III), the pre-oxidation of As(III) to As(V) is normally required to enhance As(III) removal [15,16]. Therefore, the nanocrystalline TiO 2 is not only an effective adsorbent for arsenic, but also an efficient photocatalyst for As(III) [13].…”

Treatment of Arsenite‐Contaminated Water by Electrochemical Advanced Oxidation Processes

“…Most of the treatment technologies are effective in arsenate removal but it is not fully successful in the removal of arsenite . Therefore, it is necessary to oxidize arsenite to arsenate for its effective removal …”

Peroxymonosulfate Improves the Activity and Stability of Manganese Oxide for Oxidation of Arsenite to Arsenate

“…In peroxosulfate‐based AOP systems, sulfate radicals (SO 4 ) can be formed through activation of PMS by UV, heat, and catalysts . For example, peroxosulfate‐based chemicals activated by UV and Fe 2+ rapidly oxidized As(III) . As a result of lower energy consumption and its recycling ability, activation of PMS by manganese oxides has attracted a lot of attention compared to UV light, thermal radiation, and transition metal ion catalysts such as Fe 2+ , Co(II), Cu(II), Mn(II), Ni(II), and Ce(III) .…”