The aim of this study is to develop a method of heat treatment for removal of Cs from the contaminated soil. This development can reduce the concentration of Cs in the soil to acceptable levels for the use as civil work materials. In a simulative experiment using clay (Bentonite) containing non-radioactive Cs for evaluating Cs removal, heightened CaO/SiO_2 ratio effectively prevent the soil from melting thereby achieving dramatically higher Cs removal rate under the conditions of high temperatures with the addition of chloride as a reaction accelerator. Based on this finding, we carried out heat treatment tests using actually contaminated soil which contained 10,000 Bq/kg of radioactive Cs and a chloride as an accelerator. Through this practice, Cs in the samples of higher CaO/SiO_2 ratio successfully volatilized showing much lower residual radioactive Cs concentration than the clearance level (100Bq/kg).
