PH influence on 2,4,6-trichlorophenol degradation by ferrate(VI)

Abstract

The influence of pH on 2,4,6-trichlorophenol (TCP) degradation by ferrate(VI) (Fe(VI)) was investigated comprehensively, including influence of pH on the speciation and stability of TCP and Fe(VI), impact of pH on the efficiency of degradation of TCP by Fe(VI), and effect of pH on the kinetics of TCP degradation by Fe(VI). The stability of TCP decreases with increasing pH on account of the ionization principle of the weak acid. Fe(VI) is more stable in the alkaline solution due to the lower redox potential of Fe(VI) and the equilibrium shifting of Fe(VI) decomposition. The degradation efficiency of TCP decreases with increasing pH, however the degradation efficiency was found to rise slightly at pH 9.50, which may be explained by the fact that the oxidation potential and stability of Fe(VI) are strongly pH-dependent. The rate constants for the reaction of TCP with Fe(VI) decreased non-linearly from 143.81 to 1.77 M−1 s−1 with increasing pH (7.00–10.50) owing to pH dependence of the oxidation ability of Fe(VI) and the speciation of Fe(VI) and TCP. The kinetic studies were found to be first order with respect to both Fe(VI) and TCP, and the activation energy of the reaction was determined to be 33.22 kJ mol −1. The reaction between the protonated species of Fe(VI) and deprotonated TCP occurs fastest among four parallel reactions of Fe(VI) with TCP. The results indicate that Fe(VI) has the significant potential to remove TCP, and pH has a strong influence on TCP degradation by Fe(VI).