Mobility Enhancement of Mn Oxide during Permanganate Oxidation of TCE

Abstract

Manganese (Mn) oxide precipitation during in situ permanganate oxidation of organic compounds can cause pore clogging, reduce permeability, and increase resistance to mass transfer. Stability of Mn oxide is required to enhance oxidation effectiveness. Batch tests were conducted at eight polyphosphate (PP) to permanganate () mass ratios (0 to 8) at three MnO4−1 concentrations (500, 1000, or 2000 mg/L) for identifying mass ratios to maximize stability of Mn oxide produced in the presence of trichloroethylene (TCE). In general, stability of Mn oxide was the maximum at mass ratio of approximately 4. Three column tests were designed to investigate the impact of PP on overall removal of 4.6 or 7.0 g TCE emplaced as nonaqueous phase liquid within the column porous media. Water flush, chemical flush using alone (1000 mg/L), and chemical flush using (1000 mg/L) and PP (4000 mg/L) were conducted. Mass removal of TCE and changes in media permeability were estimated over a period of 78 to 312 h (12 to 49 pore volumes [PVs]). Column tests demonstrated enhanced removal (~90%) of TCE during chemical flush with and PP in 12 PVs as compared with approximately 64% during ‐only flush and approximately 26% during water flush. Pressure drop changes across the column captured change in media permeability and revealed that water flush and PP and flush caused significantly lower flow resistance as compared with ‐only flush. These results indicate that PP was capable of mobilizing Mn oxide away from the reaction zones, thereby reducing pore clogging and enabling better and long‐term contact between TCE and the aqueous phase.