A study of the efficiency and enhancement of electro-kinetic extraction of a heavy metal from contaminated soils /

Recent laboratory studies have reported on the success of electro-kinetic extraction of heavy metals from contaminated test samples, and have suggested that this would be a useful in-situ remediation technique. However, field studies have shown limited success and some contradictory results. The basis for successful application appears to be a judicious choice of soil type and parametric constraints.In this study, the surface charges of two soils (kaolinite and illite soils) are used as the primary control in the investigation of electro-osmotic extraction of lead---introduced as a contaminant into the soils. Four types of soils were used: pure kaolinite, illite soil, illite and sand as a mixture, and kaolinite and sand as a mixture. The contaminating lead concentrations, ranging from 100 mg/kg to 5000 mg/kg, were all below the CEC (cation exchange capacity) of the pure soils and their mixtures.Electro-kinetic extraction tests showed that more than 60% of Pb was transported to the cathode in kaolinite, while there was little removal in the illite or sand/illite mixtures. Laboratory results demonstrated that the surface charges of the soils had important effects on the electro-kinetic extraction.In addition, a modified technique, based on electro-chemical processes, was developed to maximize the contaminant extraction and to minimize precipitation at the cathodic region. The study's approach relies on combining electro-kinetics with conditioning fluids and acidification of the cathodic reservoir to enhance the efficiency of contaminant removal. An experimental testing program indicated that the success of electro-kinetic removal was governed by the quantity of H+ ions available in the system. It was also noticed that the hydraulic conductivity (in the same direction of electro-osmotic flow), the conditioning fluid, and acidification of the cathodic reservoir had positive effects on the removal of lead, while the OH- ions produced at the cathode and/or other anions induced during the acidification of the cathodic reservoir had negative effects on lead removal.A modified model, based on interaction energies, was also presented for ion distribution next to the soil particle surface. The removal predictions of this model, through isotherm values, were compared with the results from batch equilibrium tests. A good correlation was noted