title: Development and characterization of colloidal silica-based slow-release permanganate gel (SRP-G): laboratory investigations.
abstract: Slow-release permanganate (MnO4(-)) gel (SRP-G) is a hyper-saline KMnO4 solution that can be used for treating large, dilute, or deep plumes of chlorinated solvents in groundwater. Ideally, the SRP-G injected into aquifers will slowly gelate to form MnO4(-) gel in situ, and the gel will slowly releases MnO4(-). Objectives of this study were to develop SRP-G using colloidal silica as gelling solution, characterize its gelation and release kinetics, and delineate its dynamics in a saturated sandy media. 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 0.5h to 13d) 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=2.1md(-1)) increased (1, 3, and 6h) with decreasing KMnO4 concentrations (25.0, 23.0, and 22.9 g L(-1)). Permanganate release from gelated SRP-Gs continued for up to 3d and was characterized as asymptotic release with an initial peak release (∼1.2 g min(-1)) followed by more attenuated release over 70h. 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.
authors.affiliation: Department of Geological Sciences, Ohio University, Athens, OH 45701, United States. Electronic address: leee1@ohio.edu.
authors.forename: Eung Seok
authors.initials: ES
authors.lastname: Lee
authors.affiliation: Department of Geological Sciences, Ohio University, Athens, OH 45701, United States.
authors.forename: Neha
authors.initials: N
authors.lastname: Gupta
mesh_terms: D003102:Colloids / Q000737:chemistry*; D005782:Gels / Q000737:chemistry*; D007700:Kinetics; D007753:Laboratories; D017895:Manganese Compounds / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D016062:Porosity; D011196:Potassium Permanganate / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry*; D013997:Time Factors; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: D003102:Colloids; D005782:Gels; D017895:Manganese Compounds; D010087:Oxides; D011196:Potassium Permanganate; D014867:Water; C048856:permanganic acid; D012822:Silicon Dioxide
keywords: Chlorinated ethylene; Colloidal silica; Gel; Groundwater; KMnO(4); Remediation; Slow-release system