Production and Characterization of Encapsulated Potassium Permanganate for Sustained Release as an in Situ Oxidant

Potassium permanganate (KMnO4) has been widely applied as an oxidant for in situ remediation of contaminated groundwater and soil. This study describes the creation and characterization of encapsulated KMnO4 particles, the purpose of which is to serve as a material that can be specifically targeted and delivered to a contaminant source zone for optimal oxidative destruction of the contaminant. Multinuclear particulate KMnO4 with a mean equivalent spherical diameter of 15 (± 8.6) μm was incorporated into a paraffin wax matrix and then pulverized, resulting in completely or partially encapsulated particles with a mean equivalent spherical diameter of 874 (± 377) μm. Paraffin wax is biodegradable and insoluble in water, and yet is very soluble in most hydrophobic contaminants, including chlorinated solvents such as perchloroethylene (PCE). Thus, KMnO4 is released very slowly into water from the encapsulating matrix, but the oxidant is rapidly released into PCE. The release kinetics of KMnO4 from the encapsulated particles into water were characterized by an initial rapid release (<10 min), followed by significantly sustained release in later stages. The estimated times for 90% release of the oxidant were 1.6 months, 19.3 years, and 472 years for paraffin wax to KMnO4 mass ratios of 1:1, 2:1 and 5:1, respectively. The encapsulated KMnO4 particles preferentially accumulated at the PCE-water interface, and the KMnO4 was rapidly released into pure phase PCE (∼3 min) as the paraffin wax completely dissolved.