Reaction of Nonaqueous Phase TCE with Permanganate

摘要

Oxidative treatment of trichloroethylene(TCE)in the form of dense nonaqueous-phase liquid(DNAPL)by potassium permanganate(KMnO_4)was investigated in a series of batch tests.The study focused on understanding the fundamental mechanisms of oxidative removal of DNAPL TCE by permanganate oxidation.Dissolution experiment for DNAPL TCE has been performed as a control experiment in the absence of KMnO_4.DNAPL TCE dissolved into the aqueous phase until it reached the saturation concentration of 1200 mg/L(9.16 X 10~(-3)M)at 20 deg C.The rate of dissolution of DNAPL TCE was proportional to the volume of the DNAPL.In the presence of KMn04,the experimental results showed that the amount of TCE oxidized during the reaction was increased continuously as [MnO_4~-] decreased even though the rate decreased as [MnO_4~-] decreased.It was apparent that more DNAPL TCE was removed with a faster rate for higher initial permanganate concentration.At high permanganate concentration,the aqueous concentration of TCE was kept low and practically constant by the chemical reaction between aqueous TCE and MnO_4~-.However,as MnO_4~-was consumed in the system,the aqueous concentration started to increase until it reached solubility.From experimental observation,1.56-1.78 mol of MnO_4~-was consumed per mole of TCE oxidized.Furthermore,2.85-2.98 mol of Cl~-was released to the solution per mole of TCE oxidized.Since the complete mineralization of TCE requires 2.0 mol of MnO_4~-and releases 3 mol of Cl~-per mol of TCE oxidized,the observed stoichiometric factors indicated incomplete mineralization of TCE,but nearly complete dechlorination.Enhancement factor due to chemical reaction was quantified experimentally.The enhancement factor was shown to be a function of the molar ratio of MnO_4~-to TCE in the system,and hence varied during the reaction period.