CHARACTERIZING GELATION AND RELEASE DYNAMICS OF SLOW-RELEASE PERMANGANATE GEL FOR TRICHLOROETHYLENE PLUME TREATMENT IN POROUS MEDIA

Trichloroethylene (TCE) is one of the commonly found toxic organic compounds in groundwater around the world. The pollutant can persist in groundwater for decades and may pose a long-term source of groundwater contamination. Efforts have been made to develop a slow-release permanganate gel (SRP-G), a modified in-situ chemical oxidation remediation scheme, that can slowly release permanganate (MnO₄^-) from gel formed in situ after spreading upon injection as a solution via wells. This study aims to develop low-temperature SRP-G solution with increased gelation lag times and strong gel formation in saturated porous media in situ through batch and column tests.

It was hypothesized that low temperature conditions can increase gelation lag time, allow inclusion of larger amount of colloidal silica and KMnO₄ in well-injectable SRP-G solution, and increase size and strength of gel and release duration of MnO₄^- in saturated sands. SRP-G solutions were prepared by mixing variable mass (g) of 99+% ACS KMnO₄ with 20 mL 40 wt% colloidal silica (Alfa Aesar 43110 by Thermo Fisher Scientific) at 24 ^oC and 4 ^oC. The gelation lag times with KMnO₄ concentrations of 30 g/L and 60 g/L were 542 and 71 minutes for 4 ^oC SRP-G, respectively, and 230 and 32 minutes for 24 ^oC SRP-G, respectively, indicating that the low-temperature condition attenuated the gelation kinetics. The flowrates from the columns decreased significantly from 1mL/min to 0.78 mL/min after the injection of SRP-G solution and increased gradually as MnO₄^- was released as outflows, indicating the gel formation in situ and MnO₄^- release from the gel formed in the saturated sandy media with flow. Cumulative release and mass flux data also showed that the release duration increased with the low-temperature SRP-G injection. These results suggested that the low-temperature SRP-G can form larger and stronger gel with higher KMnO₄ concentration in saturated porous media with flow and can yield longer release duration compared to room-temperature SRP-G injection, thus warrant further characterization of spreading, gelation, and release of SRP-G with larger 3-dimentional flow-tank experiments.