Fenton's oxidation of pentachlorophenol

The combination of H2O2 and Fe(II) (Fenton's reaction) has been demonstrated to rapidly degrade many organics via hydroxyl radicals. However, few studies have related hydroxyl radical generation rates with measured organic chemical degradation data. The goals of this work were to investigate the kinetics, stoichiometry, and intermediates of pentachlorophenol (PCP) degradation in the Fenton's reaction and to develop a mathematical model of this reaction system. Batch reaction experiments were performed to assess both initial transients and steady states, and special attention was given to the analysis of intermediates. Solutions of PCP (55 μM) and Fe(II) (200 μM) were treated with variable levels of H2O2 (<850 μM), and the concentrations of these reactants and their products were measured. Partial PCP degradation and near stoichiometric dechlorination were observed at low initial H2O2 concentrations. Higher H2O2 doses achieved at most 70% dechlorination even though nearly all of the PCP was degraded. The reaction intermediates tetrachlorohydroquinone and dichloromaleic acid accounted for up to 5% of the PCP degraded. Organic carbon mineralization (transformation to CO2) was not observed. The OH scavenging effects of the PCP-by-products mixture were characterized as a lumped parameter in the reaction kinetics model, which provided reasonable predictions of experimental results at different oxidant concentrations and reaction time.