Solvent extraction of chromium and cadmium from contaminated soils

Abstract

A new process to remediate soils contaminated with heavy metals is proposed, which is potentially useful for both in situ recovery as well as for treatments of excavated soils and sediments. This process is essentially a solvent extraction with chelating agents, but it differs from other methods proposed previously since it uses benign, environment-friendly and water-soluble solvents. In fact, their previous works have shown that the main difficulty in using conventional solvent extraction for soil remediation is the insufficient contacting between soil and solvents, due to the preferential absorption of water on the soil, and the fact that the solvents that were used were mostly water insoluble. This difficulty was overcome here by making suitable (i.e. water insoluble) solvents and complexing agents water soluble, via mixing them with water-soluble solvents. Using this method, contaminants can be extracted rapidly and efficiently. Then, contaminants as well as solvents can be separated from the water by adding a water-insoluble solvent to the system. As a result, the authors do not observe the formation of stable emulsions, which would otherwise occur when treating excavated soils and sediments. All the solvents can be chosen to be environmentally acceptable, and can subsequently be removed from themore » soil by a water wash. The new extraction process was first demonstrated by removing iron from Vesuvian soils, finding that removal was fast and thorough, even at high concentration levels. Then, the new process was applied to extract chromium (VI) from an Appalachian soil, containing 15% of organic materials, which had been previously spiked with about 25 ppm of metal ions.« less