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Phsicochemical Treatment of Hazardous Wastes - Chapter 6

Năm 1881, Fenton được công bố một mô tả ngắn gọn các đặc tính oxy hóa mạnh mẽ của một hỗn hợp của hydrogen peroxide và các muối kim loại màu. Hỗn hợp này được gọi là thuốc thử Fenton, và phản ứng đã trở thành được biết đến như phản ứng của Fenton. Ban đầu, Fenton áp dụng phản ứng oxy hóa các axit hữu cơ như formic, lactic, glycolic, tartronic, saccharic, malic, mucic, glyceric, benzoic, picric, dihydroxytartaric, dihydroxymaleic, và acetylenedicarboxylic (Fenton, 1900). Trong trường hợp không có muối kim loại màu, sự xuống cấp tiền thu được hydro. | 6__ Fenton s Reagent 6.1 Introduction In 1881 Fenton published a brief description of the powerful oxidizing properties of a mixture of hydrogen peroxide and ferrous salts. This mixture became known as Fenton s reagent and the reaction has become known as the Fenton s reaction. Initially Fenton applied this reaction to oxidize organic acids such as formic glycolic lactic tartronic malic saccharic mucic glyceric benzoic picric dihydroxytartaric dihydroxymaleic and acetylenedicarboxylic Fenton 1900 . In the absence of ferrous salt the degradation of hydrogen peroxide proceeds at very slow rates with little or no oxidation of the organic acids Fenton 1899 1900 . In addition Cross et al. 1900 further confirmed that ferrous salts significantly enhance the kinetics of hydrogen peroxide decomposition. Goldhammer 1927 investigated the effect of Fenton s reagent on phenols and found that for each equivalent of Fe2 three equivalents of H2O2 were decomposed. They also noted that in concentrated hydrogen peroxide solutions each mole of Fe2 decomposed 24 equivalents of hydrogen peroxide. Haber and Weiss 1934 were the first to propose that free radicals existed as intermediates during the chemical reactions in solution. The next year Haber and Weiss further investigated the Fenton chemistry and concluded that Fenton s reaction can be expressed as a series of chain reactions with reaction pathways dependent on the concentration of the reactants. The study disproved the original theory of Fenton s reaction which suggested that the interaction between an intermediate six-valent iron-oxygen complex and hydrogen peroxide was the most significant reaction step. In 1934 Haber and Weiss proposed that breaking rate of chain length was increased at lower pH so the propagation cycle was extended before termination. The concentration of free hydroxyl radicals was determined to be directly proportional to the concentration of hydrogen peroxide. Baxendale and Wilson 1957 reported