Remediation of Contaminated Fine-grained Soil by Freezing and Ion Exchange Effect

Abstract

It is extremely difficult to remediate contaminated fine-grained soils by the conventional methods. However, the use of freeze-thaw was proposed for this purpose. This method utilizes the ice segregation phenomena in a frost susceptible soil. Soluble contaminants in the pore structure in a soil can be removed easily by the method than by the conventional method. However, it is extremely difficult to remove adsorbed contaminants on soil's surface even by this method. In order to overcome this problem and improve the method, ion-exchange reaction was proposed. The purpose of this study is to demonstrate the combined effect of freeze-thaw and ion-exchange for remediation of fine-grained soil.A series of freeze-thaw tests were conducted to remove natural potassium ions from Kizuchi clay by changing freezing conditions such as temperature gradient, freezing speed, type of freezing and the number of repetition of freeze-thaw. As for washing agent, pure water, 0.37 and 0.10mol/L of ammonium acetate solutions were compared. The test specimen was frozen from the bottom side to top direction while washing agent was supplied from the top side. The specimen was thawed almost instantly and the drainage was taken from the bottom side of the specimen to measure potassium level. Furthermore, the distribution of potassium concentration was measured in the freeze-thawed specimen. The potassium concentration was obtained by atomic absorption spectrometry.Conclusions are as follows; (1) Ammonium acetate solution was effective to remove natural potassium in the freeze-thaw process but pure water was not. (2) Level of potassium concentration in the drainage increased with the repetition of freeze-thaw. (3) Remediation efficiency was increased with greater temperature gradient, slower freezing speed and increased number of repetition.