Enhanced Removal of Hexavalent Chromium in the Presence of H2O2 in Frozen Aqueous Solutions

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• 作者：Kitae Kim ; Jaesung Kim ; Alok D. Bokare ; Wonyong Choi ; Ho-Il Yoon ; Jungwon Kim
• 刊名：Environmental Science & Technology
• 出版年：2015
• 出版时间：September 15, 2015
• 年：2015
• 卷：49
• 期：18
• 页码：10937-10944
• 全文大小：417K
• ISSN：1520-5851

文摘

The reductive transformation of Cr(VI) to Cr(III) by H₂O₂ in ice was compared with that in water. The reduction of Cr(VI) was significant at 鈭?0 掳C (ice), whereas the reduction efficiency was very low at 25 掳C (water). This enhanced reduction of Cr(VI) in ice was observed over a wide range of H₂O₂ concentration (20鈥?000 渭M), pH (3鈥?1), and freezing temperature (鈭?0 to 鈭?0 掳C). The observed molar ratio of consumed [H₂O₂] to reduced [Cr(VI)] in ice was in close agreement with the theoretical (stoichiometric) molar ratio (1.5) for H₂O₂-mediated Cr(VI) reduction through proton-coupled electron transfer (PCET). The synergistic increase in Cr(VI) reduction in water by increasing the H₂O₂ and proton concentrations confirms that the freeze concentration of both H₂O₂ and protons in the liquid brine is primarily responsible for the enhanced Cr(VI) reduction in ice. In comparison, the one-electron reduction of Cr(VI) to Cr(V) and subsequent reoxidation of Cr(V) to Cr(VI) is the major reaction mechanism in aqueous solution. The reduction efficiency of Cr(VI) by H₂O₂ in the frozen aqueous electroplating wastewater was similar to that in the frozen aqueous deionized water, which verifies the enhanced reduction of Cr(VI) by freezing in real Cr(VI)-contaminated aquatic systems.