Assessment and prediction of the transformation kinetics determining the environmental fate of contaminants of concern. Part I, Remediation of 1,2,3 - trichloropropane with zerovalent zinc. Part II, Prediction of the environmental fate of novel munitions compounds
Div. of Environmental & Biomolecular Systems
Oregon Health & Science University
The environmental fate of contaminants of concern (CoCs) is controlled—in part—by chemical degradation reactions. Often these reactions are not well understood, hindering efforts to limit associated risks to human health and the environment. In this study, the kinetics of CoC degradation are studied with respect to addressing two aspects of contamination mitigation: remediation and prevention. Part I concerns the legacy and emerging contaminant 1,2,3-trichloropopane (TCP) and the prospects for remediating contaminated groundwater by reduction (i.e., dechlorination) with zerovalent zinc (ZVZ). Part II concerns the development of kinetic models to evaluate the environmental persistence of novel energetic compounds under consideration for use in munitions formulations.
Part I—The kinetics of TCP reduction by ZVZ were studied in both bench-top and pilot-scale experiments in order to evaluate the prospects for treating TCPcontaminated groundwater with ZVZ. The kinetics of the reaction were found to be highly dependent on solution chemistry, especially pH and the presence of certain groundwater constituents. The results indicated that this influence is related to morphological and solubility-related changes to a ZnO shell on the surface of the ZVZ. The kinetics of TCP reduction using commercially-available, industrial-grade ZVZ were measured in batch-reactor and column experiments and, in most cases, found to be on the order of those produced by more expensive reagent-grade materials. The results of material testing were used to design and execute large, pilot-scale column experiments comparing the use of two ZVZ formulations at a TCP-contaminated site. Analysis of TCP removal kinetics during column operation, and assessment of the column fill material post-operation, support the viability of ZVZ for treating TCP-contaminated groundwater in an engineered treatment system such as a permeable reactive barrier. Part II—Progress was made toward developing models to predict the environmental degradation kinetics of energetic nitroaromatic compounds (NACs) by two fate processes, alkaline hydrolysis and reduction. For alkaline hydrolysis, it was determined that model development is hindered by lack of understanding regarding reaction mechanisms. To address this, potential mechanisms for 2,4,6-trinitrotoluene (TNT) and 2,4-dinitroanisole (DNAN) were evaluated using coordinated experimental kinetic measurements and molecular modeling calculations. The results suggest that the initial step in alkaline hydrolysis is Meisenheimer complex formation or abstraction of a methyl proton for TNT and Meisenheimer complex formation for DNAN.
For the reduction pathway, a predictive model in the form of a free energy relationship (FER) based on the Marcus theory of outer-sphere electron transfer was developed. The FER relates the rate constant for NAC reduction to the free energy of the reaction, which was calculated from one-electron reduction potentials (E1) determined using molecular modeling. The FER accurately describes NAC reduction kinetics for non-energetic compounds. The model was found to accurately predict newly measured rate constants for TNT and 2,4-dinitrotoluene, but not for DNAN. The inconstancy of the DNAN results was proposed to be related to the calculation of E1.
School of Medicine
Salter-Blanc, Alexandra J., "Assessment and prediction of the transformation kinetics determining the environmental fate of contaminants of concern. Part I, Remediation of 1,2,3 - trichloropropane with zerovalent zinc. Part II, Prediction of the environmental fate of novel munitions compounds" (2014). Scholar Archive. 3529.