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Bisulfite triggers fast oxidation of organic pollutants by colloidal MnO2

Sun, Bo, Xiao, Zhongjin, Dong, Hongyu, Ma, Shangchen, Wei, Guangfeng, Cao, Tongcheng, Guan, Xiaohong
Journal of hazardous materials 2019 v.363 pp. 412-420
EDTA (chelating agent), Lewis acids, absorbance, bisulfites, calcium, humic acids, magnesium, manganese, manganese dioxide, oxidation, pH, pollutants, reducing agents, spectroscopy, synergism, water treatment
Colloidal MnO2 is the most reactive phase of Mn(IV) while HSO3⁻ is a common reductant in water treatment. This study shows that the presence of HSO3⁻ resulted in significant increase in the decomposition rate of organic contaminants by colloidal MnO2. The degradation rate of contaminants in the MnO2/HSO3⁻ process dropped with elevating pH and a proper MnO2/HSO3- molar ratio was critical for efficient decomposition of contaminants. The time-resolved spectroscopy of manganese species, the influence of pyrophosphate on UV absorbance spectra, and the relative rate constants of contaminants oxidation in MnO2/HSO3⁻ process suggested that the synergetic effect of HSO3⁻ and colloidal MnO2 arose from the generation of Mn(III)aq, which could oxidize contaminants rapidly. The presence of pyrophosphate, ethylenediaminetetraacetic acid, and humic acid depressed the degradation of contaminants in MnO2/HSO3⁻ process by complexing with Mn(III)aq, buffering the solution or competing with contaminants for Mn(III)aq, and/or inhibiting the consumption of bisulfite. However, Ca²⁺ and Mg²⁺ accelerated the oxidation of contaminants in MnO2/HSO3- process by enhancing the reduction of MnO2 by HSO3-. The good negative correlation of the O/N or H Mulliken charges of organic contaminants with their removal in MnO2/HSO3⁻ process suggested that organic contaminants were oxidized by Mn(III)aq via electrophilic attack.