Permanganate Treatment of DNAPLs in Reactive Barriers and Source Zone Flooding Schemes

Schwartz, Franklin W.

Ohio State Univ., Columbus, OH (United States)

关键词: Oxidizers;    Phosphates;    Specific Surface Area;    Oxidation;    Dissolution;   

DOI  :  10.2172/833724
RP-ID  :  EMSP-73745
RP-ID  :  FG07-00ER15115
RP-ID  :  833724

美国|英语

来源: UNT Digital Library

【 摘 要 】

This research involves a combined experimental modeling study that builds on our previous DOE-sponsored work in understanding how KMnO4 can be used with in situ cleanups of contaminated sites. The specific objectives of this study are (1) to describe how solid forms of KMnO4 behave in saturated media, (2) to undertake flow tank studies that examine the hydraulic impact of reaction products (especially MnO2) on the flux of water through the zone of contamination, and (3) to represent process understanding in flow and transport models. We have made excellent progress in addressing these issues through a variety of different laboratory and theoretical investigations, as well as work that summarizes the state of the science. In the space available for this report, we can only summarize the key findings of the study. Readers interested in additional details can refer to the papers that are listed at end of this report. There has been significant industrial interest in the use of KMnO4 schemes for the in situ destruction of various chlorinated solvents. Given our previous work that emphasized some of the problems associated with field applications of the method, we were invited to contribute to a special edition of Environmental & Engineering Geoscience that examined the effects of heterogeneity on in situ remediation schemes. Our review targeted the most common implementation namely the use of an injection/withdrawal system to circulate oxidants (e.g., potassium permanganate, hydrogen peroxide, and Fenton's Reagent) through a source zone containing a dense nonaqueous phase liquid (DNAPL). The review demonstrated with various examples (1) how the efficiency of chemical oxidation is highly dependent on physical and chemical heterogeneities, and (2) how effective delivery is essential for successful remediation. A summary of this work is provided here in Section 1 of the Chapter Methods and Results. We investigated the mineralogy of Mn oxides, and the possibilities of controlling the colloid growth and removing the solid precipitates by dissolution. We determined the chemical formula of the Mn oxide and identified as semi-amorphous potassium-rich birnessite. We also measured the surface properties of the Mn oxide like the specific surface area and point of zero charge (pzc) of the Mn oxide. These findings provide foundation for further investigation of the behavior of Mn oxide precipitates in the remediation environment. We utilized batch experiments to explore the feasibility of applying phosphate to slow down the formation of colloidal Mn oxide. Our results show that phosphate can slow down the formation of the colloids, especially early in the reaction. A model was proposed to describe the reaction process. Our study provides scientific background on the possibility to slow down the formation of colloid during the oxidation scheme by chemical additives. The dissolution kinetics of Mn oxide was evaluated in batch experiments using solutions of citric acid, oxalic acid, and EDTA. Organic acids dissolve Mn oxide quickly. Reaction rates increase with acid concentration, as tested with citric acid. The Mn oxide dissolution mechanism likely involves proton and ligand-promoted dissolution and reductive dissolution. We proposed two models describing the dissolution of Mn oxide by organic acids. The flow tank experiment confirmed the possibilities of restoring permeability damaged by Mn oxide precipitation. There seem to be good possibilities for using citrate and oxalate to control plugging created by the precipitation of Mn oxide. A more details summary of the work on the Mn oxide precipitates is provided here in Section 2 of the Chapter Methods and Results. Another important thrust of our research effort involved a detailed evaluation of the efficiency of TCE removal with time, and the space/time dynamics of the solid-phase oxidation reaction front (Section 3 of the Chapter Methods and Results). The approach involved a very large 3-D flow tank experiment. The progress of TCE destruction and the distribution of MnO2 precipitates were monitored using novel optical and chemical monitoring techniques. The results showed that the efficiency of the KMnO4 treatment of chlorinated solvents in the flushing scheme diminished with time due to the formation of low-permeability reaction zones in the TCE source and along the downstream edge of the TCE plume.