In situ chemical oxidation schemes for the remediation of ground water and soils contaminated by chlorinated solvents.

摘要

This study investigates various aspects of in situ chemical oxidation (ISCO) schemes based on MnO₄−. Batch experiments show that the interaction between MnO₄− , and sediment solids will not only consume the reactant, but also can release toxic metals into ground water. Various column and flow tank experiments were conducted to examine the capacity and efficiency of the oxidation scheme. Oxidation was capable of destroying chlorinated ethylenes in aqueous phase. MnO₄− oxidation performs better in removal of residual DNAPL than pooled DNAPL. In zones of high NAPL saturation, Mn oxide precipitates causing pore plugging and permeability reduction. These changes potentially could cause the remedial action to fail. In an effort to mitigate the precipitation, experiments have been carried out to investigate possibilities of delaying the formation of colloidal Mn oxide and to remove the precipitates once formed. The investigation begins with the identification of the Mn oxide mineral structure and the determination of the chemical properties of the solid. Phosphate ion was added to the reaction in an attempt to slowdown colloidal formation due to its high charge and the tendency to sorb on surfaces. The results indicate that the presence of phosphate ion can lower the rate of colloid formation. However, the magnitude of effects due to the addition of phosphate is limited by the ionic strength increase and the pzc (point of zero charge) of the mineral. The dissolution kinetics of birnessite was evaluated using solutions of citric acid, oxalic acid, and EDTA. The results showed that the addition of an organic acid could greatly increase the dissolution rate of birnessite. The dissolution mechanism involves proton and ligand-promoted dissolution and reductive dissolution. A permanganate reactive barrier system (PRBS) was designed and a proof-of-concept experiment was carried out in the laboratory. The experiment demonstrated how the PRBS could delivery MnO ₄− at a stable, constant, and controllable rate. This idea could be developed as a long-term reactive barrier for the remediation of chlorinated solvents in plume.