Characteristics and mechanisms of controlled-release KMnO4 for groundwater remediation: Experimental and modeling investigations

Abstract

Controlled release materials (CRMs) are emerging oxidant delivery techniques for in-situ chemical oxidation (ISCO) for groundwater remediation. Successful implementation of CRM relies on good understandings of the kinetics and mechanism of controlled release of reactive agents. In this study, batch experiments and model simulations were conducted to explore the impacts of CRM properties (composition and size) and environmental conditions (temperature, pH, water volume and anions) on KMnO4 release from KMnO4 -paraffin controlled release beads. Experimental results indicated that higher KMnO4: paraffin mass ratio resulted in shorter release longevities and higher release rate. Larger bead resulted in lower release rate, longer release longevity, and more KMnO4 released. Higher incubation temperature resulted in higher release rate and shorter release longevity, but did not affect the total mass of KMnO4 released. Acidic pH decreased the total mass of KMnO4 released while alkaline pH did not affect KMnO4 release. The presence of SO42−, CO32−, Cl− and Br− had negligible impacts on KMnO4 release. A dissolution-diffusion conceptual model was developed. The above experimental observation and the associated controlled release mechanisms can be qualitatively explained by the conceptual model. A more detailed two-film boundary mathematical model was developed to simulate KMnO4 release process. Comparison of modeling results with experimental data suggest that the new mathematical model gave a good quantitatively predication. Overall, this study shows that properly designed CRM can sustain release for years, thus representing a cost-effective and low-maintenance groundwater remediation technology. Both CRM properties and environmental conditions significantly affect the release kinetics and longevity, therefore these factors should be considered in the design and maintenance of CRM-based ISCO system.