Removal of 3,4-dichlorophenol from water utilizing ferrate(VI): Kinetic and mechanistic investigations, and effect of coexisting anions

3,4-dichlorophenol (3,4-DCP) has been detected in industrial and domestic effluents, posing adverse effects on human health. Herein, ferrate (Fe(VI)) oxidation of 3,4-DCP was systemically and comprehensively investigated by determining its kinetics, mechanisms, and effect of anions. pH dependence of reaction kinetics was strong and the second-order reaction rate constant k varied nonlinearly from (342.82 ± 21.81) M-1s-1 to (8.21 ± 0.27) M-1s-1 with an increase in pH from 6.5 to 10.5, whereas its temperature dependence was quite weak. The individual species-specific second-order rate constants for the reaction were obtained using least-squares regression approach. Protonated Fe(VI) has higher reactivity than its unprotonated specie while 3,4-DCP is just the opposite, leading to the reaction of HFeO4- with 3,4-DCP- occurring fastest among four parallel reactions. Significantly, 3,4-DCP removal kinetics was inhibited by coexisting anions. Meanwhile, efficiency of 3,4-DCP removal by Fe(VI) at different Fe(VI) concentrations, solution pH, and coexisting anions was determined. Furthermore, eight intermediates of 3,4-DCP oxidation were identified, and a detailed mechanism involving hydroxylation, substitution, dechlorination, and ring-opening steps of Fe(VI)/3,4-DCP reaction was proposed. Removal of 3,4-DCP was enhanced in authentic waters, demonstrating that Fe(VI) could be regarded as an efficient technology for removing 3,4-DCP from water.