Cadmium Mobility with Persulfate Chemical Oxidation: Effects of Soil Properties and Activation Methods

Abstract

The potential effects of persulfate in situ chemical oxidation (ISCO) on metals and on long-term groundwater quality is an important issue because of the potential risks to public health and to the environment. Application of persulfate and its activation amendments to soil and groundwater can lead to complex interactions, altering geochemical conditions and processes, thereby affecting metals mobility. The mobility of cadmium sorbed on three soils varying in physical–chemical properties was investigated after chemical oxidation by unactivated and activated persulfate using mixed batch reactors. Each of the three soils was treated with two different concentrations of persulfate, 2.1 mM and 42 mM, and different activation amendments that included Fe(II), Fe(II)-EDTA, and high pH. Resulting solutions were analyzed for soluble cadmium after 48 h and 6 months. Results show that cadmium mobilization varied with the persulfate activation method and the soil type. The maximum amount of cadmium was mobilized with Fe(II)-EDTA activation and the least amount of cadmium was mobilized with high pH activation. In addition to Fe(II)-EDTA activation, cadmium was more mobile in soil with low soil organic carbon and low mineral content. Enhanced cadmium desorption at low pH and formation of soluble cadmium-EDTA complexes are the main mechanisms of cadmium mobilization from soils with persulfate ISCO.