Injectable silica–permanganate gel as a slow-release MnO4− source for groundwater remediation: rheological properties and release dynamics

Abstract

Injectable slow-release permanganate gels (ISRPGs), formed by mixing aqueous KMnO₄ solution with fumed silica powders, may have potential applications in remediating chlorinated solvent plumes in groundwater. A series of batch, column, and two-dimensional (2-D) flow cell experiments has been completed to characterize the ISRPG and study the release of permanganate (MnO₄⁻) under a variety of conditions. The experiments have provided information on ISRPG rheology, MnO₄⁻ release dynamics and distribution in porous media, and trichloroethene (TCE) destruction by the ISRPG-released oxidant. The gel possesses shear thinning characteristics, resulting in a relatively low viscosity during mixing, and facilitating subsurface injection and distribution. Batch tests clearly showed that MnO₄⁻ diffused out from the ISRPG into water. During this process, the gel did not dissolve or disperse into water, but rather maintained its initial shape. Column experiments demonstrated that MnO₄⁻ release from the ISRPG lasted considerably longer than that from an aqueous solution. In addition, due to the longer release duration, TCE destruction by ISRPG-released MnO₄⁻ was considerably more effective than that when MnO₄⁻ was delivered using aqueous solution injection. In the 2-D flow cell experiments, it was demonstrated that ISRPGs released a long-lasting, low-concentration MnO₄⁻ plume potentially sufficient for sustainable remediation in aquifers.