Impact of Persulfate Chemical Oxidation on Soil Properties and Metal Mobility

Persulfate In situ chemical oxidation (ISCO) is a useful technology for remediation of organic contaminants at hazardous waste sites. Application of persulfate ISCO to sites with metal co-contaminants or with high natural metals concentrations presents a complex challenge to remediation. Addition of persulfate and amendments can lead to complex interactions in the subsurface, altering geochemical conditions and processes, thereby affecting metals mobility. Limited research has been conducted to investigate these complex interactions and their ultimate impact on risk associated with the treated site. The objectives of this research were to evaluate the impact of unactivated and activated persulfate on geochemical properties and on metal mobility, and to understand the mechanisms that cause metal mobilization under conditions created by persulfate ISCO.;Laboratory studies with controlled, bench-scale batch-reaction systems were employed to examine these interactions. Three field soils with different characteristics were used to study the impact of unactivated and activated persulfate (activated with Fe(II), Fe(II)-EDTA, and high pH) on the soil properties (i.e., soil organic carbon, Fe and Mn content, pH, oxidation reduction potential (ORP), and cation exchange capacity (CEC). Release of two metals -- cadmium (non-redox sensitive metal) and chromium (redox sensitive metal) from soils following unactivated and activated persulfate treatment was determined to study the mechanisms of metal mobilization.;The results of this research indicate that persulfate oxidation can promote changes in the soil properties and metal mobility, and these changes depend on the soil type and the amendment used for activation of persulfate. Different mechanisms, which included desorption and dissolution of metals at low pH, destruction of sorption sites, formation of soluble metal-organic complexes, and oxidation of metal, were responsible for metal mobilization based on the characteristics of the metal, nature of the soil, and the persulfate application (i.e. unactivated or activated).;Results of this research emphasize the importance of performing comprehensive geochemical evaluations of a site and careful selection of activation methods to avoid potential deleterious effects of persulfate ISCO on constituents of subsurface and metal mobility.