Development and characterization of colloidal silica-based slow-release permanganate gel (SRP-G): Laboratory investigations

The SRP-G exhibited a two-phase increase in viscosity: a lag phase characterized by little increase in viscosity followed by a short gelation phase. Gelation lag times of SRP-G solutions increased (from 0.5 h to 13 d) with decreasing KMnO4 concentrations (from 25 to 8 g L−1). Permanganate release from gelated SRP-G increased with increasing KMnO4 concentrations, and was characterized as asymptotic release with initial peak (0.9-2.2 mg min−1) followed by more attenuated release. Gelation lag times of SRP-G flowing in sands (linear velocity = 2.1 m d−1) increased (1, 3, and 6 h) with decreasing KMnO4 concentrations (25.0, 23.0, and 22.9 g L−1). Permanganate release from gelated SRP-Gs continued for up to 3 d and was characterized as asymptotic release with an initial peak release (∼1.2 g min−1) followed by more attenuated release over 70 h. Dilution of SRP-G by dispersion in porous media affects gelation and release kinetics. Increasing the silica concentration in the SRP-G may facilitate gelation and extend the duration of MnO4- release from emplaced SRP-G in porous media.