Effect of chelating agent on the oxidation rate of PCP in the magnetite/H2O2 system at neutral pH

The effect of chelating agents on the Fenton heterogeneous oxidation rate of pentachlorophenol (PCP) in the presence of magnetite (Fe3O4) Was investigated in opened batch reactor at neutral pH. Six kinds of chelating agents (CA) were selected including EDTA, CMCD, oxalate, tartrate, citrate and succinate. The PCP oxidation rate in the Fenton-like system was significantly improved by using chelating agents at neutral pH. This observation was supported by the increased concentration of chloride produced by the degradation of PCP. The enhancement factor of heterogeneous oxidation rate was found to be not correlated with that of dissolved iron amount. However, the propagation of homogeneous reaction by the dissolved iron contributed to the improvement of the whole oxidation rate. In homogeneous Fenton system (dissolved Fe2+ or Fe3+), EDTA-driven Fenton reaction showed the highest oxidation rate, while oxalate seems to be more efficient in heterogeneous Fenton system (Fe3O4). In fact, EDTA can bind more strongly than oxalate to magnetite surface and compete more actively than H2O2 or PCP for the sorption on the surface active sites. Decrease in H2O2 decomposition rate value was observed when EDTA is previously adsorbed on the catalyst surface. The surface mechanism of oxidant with iron sites on the catalyst surface appears to be the rate-determining step in heterogeneous Fenton system. (C) 2009 Elsevier B.V. All rights reserved.