[Oxidation kinetics of pentachlorophenol by manganese dioxide].

Experiments were conducted to determine oxidation kinetics of pentachlorophenol (PCP) using manganese dioxide (MnO2) as an oxidant. The influence of cosolutes (e.g. inorganic ions and organic substances) on the reaction kinetics was also assessed. When simulating the kinetics of PCP with n-order reaction model by a non-linear curve fitting approach, the reaction order n is over 0.999, which suggests that the first order reaction model fit the degradation kinetics of PCP. The apparent rate constant k(obs) values are 2.86 h(-1) for the centrifugation method and 2.14 h(-1) for the ascorbic acid method by non-linear fitting the kinetics of PCP for 0.5 h reaction using pseudo-first-order model under the 95% confidence limits. The addition of bivalent metal ions causes the considerable reduction of the apparent rate constants. The significant effect on the k(obs) of PCP occurs when the concentration of Mn2+ above 2% of the initial MnO2 is added as the co-solute, but no significant influence on the k(obs) of PCP for the presence of other ions. The presence of caffeic acid, syringic acid or gallic acid reduces the reaction rate of PCP significantly. Oppositely, no considerable decrease of k(obs) is observed in experiments with the addition of cinnamonic acid, coumaric acid, ferulic acid or ortho (para)-hydroxybenzoic acid. These experimental results demonstrate that the decrease of PCP adsorbed to MnO2 considerably or the action of competing against PCP reacted with MnO2 is the dominant factor that slows down the transformed rate of PCP oxidation by MnO2.