Low-temperature slow-release permanganate gel for groundwater remediation: Dynamics in saturated porous media.

Due to its adverse health and environmental impacts, groundwater contamination by toxic organic compounds such as chlorinated solvents is a global concern. The slow-release permanganate gel (SRP-G) is a mixture of potassium permanganate (KMnO 4) and colloidal silica solution. The SRP-G is designed to radially spread after injection via wells, gelate in situ to form gel barriers containing permanganate (MnO 4 −), and slowly release MnO 4 − to treat plumes of chlorinated solvents in groundwater. This study aimed to characterize the effects of temperature on the dynamics of SRP-G in saturated porous media. In gelation batch tests, the viscosity of ambient-temperature (24 °C) SRP-G with 30 g/L-KMnO 4 was 21 cP at 70 min, 134 cP at 176 min, and peaked at 946 cP to solidification at 229 min. The viscosity of low-temperature (4 °C) SRP-G with 30 g/L-KMnO 4 was 71 cP at 273 min, 402 cP at 392 min, and peaked at 818 cP to solidification at 485 min. A similar pattern, e.g., increased gelation lag time with low-temperature SRP-G, was observed for SRP-Gs with 40 g/L, 50 g/L, and 60 g/L KMnO 4. In flow-through tests using a glass column filled with saturated sands, injection rates, spreading rates, and release durations were 0.6 mL/min, 46 mm/min, and 33 h for KMnO 4 (aq), 0.2 mL/min, 2 mm/min, and 38 h for ambient-temperature SRP-G, and 0.4 mL/min, 16 mm/min, and 115 h for low-temperature SRP-G, respectively. These results indicated that the injectability, injection rate, and gelation lag time of SRP-G and the size, release rate, and release duration of MnO 4 − gel barriers can be increased at low temperatures. The low-temperature SRP-G scheme can be useful for treating large or dilute dissolved plumes of chlorinated solvents or other pollutants in groundwater. [Display omitted] • Slow-release permanganate gel (SRP-G) is a mixture of potassium permanganate and colloidal silica solution. • SRP-G solution spreads, gelates, and slowly releases permanganate in saturated porous media. • Cooling increases injectability, gelation lag time, spreading, release rate, and release duration of SRP-G in porous media. • Low-temperature SRP-G can be effective for treating large or dilute plumes of chlorinated solvents in groundwater. • Low-temperature SRP-G scheme can be used with other treatment agents to reduce different pollutants in groundwater. [ABSTRACT FROM AUTHOR]