CHELATED Fe(II) ACTIVATED PERSULFATE OXIDATION OF PHENOL: EXPERIMENTAL OPTIMIZATION, REACTION KINETICS AND MECHANISM

The potential oxidation of phenol by chelated ferrous ion activated persulfate (PS) at 10 degrees C is systematically investigated to determine the optimal experimental condition (PS/chelate/Fe(II)/phenol molar ratio) and to estimate reaction kinetics and mechanism for phenol oxidation. In comparison with sodium tripolyphosphate (STPP) and ethylenediaminetetraacetic acid (EDTA) chelate, citric acid (CA) chelated Fe(II) performs as a most effective activator for persulfate activation and subsequently phenol oxidation. A CA/Fe(II) molar ratio of 1/5 is found to be the lowest acceptable ratio to maintain sufficient quantities of Fe(II) activator in solution. Excess Fe(II) content leads to more persulfate consumption and less phenol oxidation, owning to the competition for sulfate radicals between Fe(II) and phenol. In general, phenol depletion is significantly increased with increasing persulfate dosage, but deceased with increasing phenol dosage. The PS/CA/Fe(II)/phenol molar ratio of 100/10/50/1 is evaluated as the optimum experimental condition, resulting in almost complete phenol depletion after 15-min reaction. The reaction rate constant ((1.72-7.17) x 10(-3) s(-1)) of phenol oxidation by CA-Fe(II) activated persulfate is evaluated with a simple mechanism following the pseudo-first-order reaction kinetics. Furthermore, the major intermediate product p-benzoquinone is formed during the phenol oxidation. Single Fe(II) activation mode has no ability of achieving phenol mineralization, however, it achieves almost complete removal of phenol within 15 min under optimal condition without the help of other activation modes.