Development of Advanced In-situ Soil Remediation Method

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Electrokinetic soil remediation by electroosmosis and ionic migration is restricted to soluble substances. At a higher pH, the soil particles sorb more heavy metals, such as cadmium, than at a lower pH and the precipitation reactions of heavy metals are promoted. Both mechanisms make heavy metals immobile, rendering cleanup more difficult and electrokinetic extraction inefficient. Therefore, the acidification of soils is very important to increase the cleanup efficiencies of heavy metals, such as cadmium by electrokinetic method from contaminated soils. Meanwhile, hexavalent chromium is more mobile and easily soluble. Hexavalent chromium has high solubility in water and exists as chromate, monochromate or dichromate anions depending on the pH of the solutions. This hexavalent chromium is the chemical form requiring remediation. And then, hydrogen and cadmium ions transport in unsaturated soils are predicted with a simple numerical method in which electrical flow is coupled with hydraul … More ic flow, and the treatment for unsaturated soils are investigated. In this study, cadmium and hexavalent chromium transport are predicted with a simple numerical method in which electrical flow is coupled with hydraulic flow, and the sorption process in the soils is induced in the model. The results obtained this study are summarized as follows :The two-dimensional electrode configurations containing cathode surrounded by three or more anodes rapidly remove cadmium from soils compared with one-dimensional electrode configuration. Meanwhile, in the removal of hexavalent chromium from soils, the two-dimensional electrode configurations containing anode surrounded by three or more cathodes can be effectively utilized compared with one-dimensional electrode configuration. A larger electrode spacing increases the processing time required, and it was also found that a larger electric field strength reduced the processing time required. Hydrogen and cadmium ions move downward in unsaturated soils, particularly, move significantly downward against upper layer, sandy/clay, and lower layer, clayey/silty soils. However, remediation is applied successfully to unsaturated soils by coupled electric-hydraulic gradient. Less