Dept. of Environmental Science and Engineering
Oregon Health & Science University
When assessing the feasibility of in situ chemical oxidation (ISCO) for treatment of a contaminated site, knowledge of the oxidation rates of the contaminants to be treated is critical. While kinetic data for the reactions of permanganate (MnO4-) with chlorinated solvents such as trichloroethylene (TCE) and perchloroethylene (PCE) are available, there is a lack of kinetic data for the reactions of MnO4- with many other environmental contaminants. To help fill these data gaps, an efficient method of determining rate constants for oxidation of contaminants by MnO4- was developed. This method uses UV spectroscopy to analyze decreasing concentrations of MnO4- at 525 nm (an absorbance maximum of MnO4-) in the presence of excess contaminant. A complication of this method is that colloidal manganese dioxide (MnO2), a product of MnO4- reduction, also absorbs at 525 nm. It is shown here that (for the reaction times of interest) the colloidal MnO2 particles are small enough that they behave according to Beerâs Law of absorbance. Because the particles follow Beerâs Law, it was possible to separate the absorbance of MnO2 from the absorbance of MnO4-. Rate constants of four chlorinated ethylenesâPCE, TCE, cis-1,2- dichloroethylene (cis-DCE), and trans-1,2-dichloroethylene (trans-DCE)âobtained with this method fall within the range of previously published rate constants, many of which were obtained by using gas chromatography to analyze decreasing concentrations of the chlorinated ethylenes in the presence of excess MnO4-. After this validation, the UV spectroscopy based method was used to determine oxidation rate constants for 22 other contaminants from the chemical classes of chlorinated alkanes, oxygenates, fuels, phenols, and pesticides. It was determined that many of the phenols and some pesticides have reactivities with MnO4- that are similar to (or faster than) the chlorinated ethylenes. Because chlorinated ethylenes have been treated successfully in the field using ISCO technology with MnO4-, it is likely that phenols and some pesticides could also be treated successfully with this technology. To provide a basis for predicting rate constants for compounds not studied, kinetic data generated from this study along with kinetic data obtained from the published literature were analyzed to determine whether quantitative structure-activity relationships (QSARs) exist for the reaction of compounds with MnO4-. A general descriptor that characterizes the reactivity of MnO4- with all compoundsâregardless of chemical structureâwas not found. Within chemical classes, however, the reactivity of the chlorinated ethylenes with MnO4- correlated strongly to reactivity of these compounds with ozone, possibly indicating similar mechanisms of oxidation for the two oxidants. Satisfactory descriptors were not found for compounds belonging to the BTEX or oxygenate classes. Because the training set of the QSARs developed for the substituted phenols consists of both phenolate ions and protonated phenols, the correlations cannot be used for predictive purposes outside the pH condition studied.
OGI School of Science and Engineering
Waldemer, Rachel, "Determination of the rate of contaminant oxidations by Permanganate: Implications for in situ chemical oxidation (ISCO)" (2004). Scholar Archive. 19.