MnO2 generation mechanisms in the presence of phase transfer catalyst enhanced trichloroethene oxidation by permanganate

The remediation of trichloroethylene contaminated groundwater by permanganate-based in situ chemical oxidation is limited by MnO 2 formation. The application of phase transfer catalyst (PTC) is a promising alternative to enhance remediation efficiency, and the alleviation of MnO 2 generation is one of crucial capacities of PTC to promote oxidation. This work has emphatically elucidated the mechanism of MnO 2 alleviation by PTC, as well as the effectiveness which was researched by conducting batch and sand column experiments. The results indicated that the contents of MnO 2 suspended in aqueous phase and total manganese in the media were respectively decreased by 29.5% and 26.1% attributed to PTC addition. Although PTC could not be used as a chelator for Mn(Ⅲ) stabilization, the generation of dissolved Mn(Ⅱ) and Mn(Ⅲ) was promoted by PTC for less MnO 2 generation. Further studies illustrated that redox reactions would occur between dissolved Mn(Ⅱ)/Mn(Ⅲ) and TCE, which benefited TCE degradation. Moreover, Smaller particle size and improved colloidal stabilization of formed MnO 2 were achieved by PTC to minimize MnO 2 precipitation. Overall, effective alleviation of the MnO 2 generation and precipitation by PTC is collectively contributed from the promotion of dissolved Mn(Ⅱ) and Mn(Ⅲ) and the stabilization of MnO 2 formed in situ.