title: Enhanced Removal of Hexavalent Chromium in the Presence of H2O2 in Frozen Aqueous Solutions.
abstract: 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 -20 °C (ice), whereas the reduction efficiency was very low at 25 °C (water). This enhanced reduction of Cr(VI) in ice was observed over a wide range of H2O2 concentration (20-1000 μM), pH (3-11), and freezing temperature (-10 to -30 °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.
authors: Korea Polar Research Institute (KOPRI) , Incheon 406-840, Korea.
authors: Kitae
authors: K
authors: Kim
authors: Department of Environmental Sciences and Biotechnology, Hallym University , Chuncheon, Gangwon-do 200-702, Korea.
authors: Jaesung
authors: J
authors: Kim
authors: School of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH) , Pohang 790-784, Korea.
authors: Alok D
authors: AD
authors: Bokare
authors: School of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH) , Pohang 790-784, Korea.
authors: Wonyong
authors: W
authors: Choi
authors: Korea Polar Research Institute (KOPRI) , Incheon 406-840, Korea.
authors: Ho-Il
authors: HI
authors: Yoon
authors: Department of Environmental Sciences and Biotechnology, Hallym University , Chuncheon, Gangwon-do 200-702, Korea.
authors: Jungwon
authors: J
authors: Kim
mesh_terms: D002857:Chromium / Q000302:isolation & purification*; D004595:Electroplating; D004777:Environment; D005615:Freezing; D006861:Hydrogen Peroxide / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D017665:Hydroxyl Radical / Q000737:chemistry; D007053:Ice; D012996:Solutions; D013997:Time Factors; D062065:Wastewater / Q000737:chemistry; D014867:Water / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*
chemical_list: D002857:Chromium; D006861:Hydrogen Peroxide; D017665:Hydroxyl Radical; D007053:Ice; D012996:Solutions; D062065:Wastewater; D014867:Water; D014874:Water Pollutants, Chemical; C074702:chromium hexavalent ion