Oxidation of pentachlorophenol in manganese oxide suspensions under controlled Eh and pH environments

Abiotic oxidation of pentachlorophenol (PCP) by manganese(IV) oxide (MnO2) was examined in orderto understand the physiochemical environment(s) where PCP oxidation occurs. An Eh-pH potentiostat was used to simulate natural groundwater environments where MnO2 (0.025 g L(-1)) and PCP (0.020 g L(-1)) suspensions were incubated from Eh -300 to 300 mV and pH 4.5 to 7.0. The pH-Eh region where maximum PCP sorption occurred corresponded to the same region where the greatest concentrations of soluble Mn(II) where measured (Eh > -100 mV and pH <5.0). Reduced Mn species [Mn(II,III)] released by reductive dissolution were readsorbed and restricted further abiotic oxidation of PCP by the MnO2 surface. A greater transformation of PCP to primarily tetrachloro-1,4-benzoquinone (p-chloranil) and smaller amounts of lesser chlorinated phenols occurred under increasing pH and Eh conditions.