Study on Volume Reduction of Contaminated Soil by Radioactive Cesium Using Magnetic Separation

This study intends to develop a new volume reduction method of the soil that is contaminated by radioactive cesium. The volume reduction process by the magnetic separation method is described as follows. First, the soil constituent particles with different particle sizes such as gravel, sand and clay are separated by classification. In this method, the clay, which mainly adsorbs cesium, is separated from the soil. Then, the magneto-Archimedes method is applied to the clay, that utilizes the difference of magnetic susceptibility of substances. The clay minerals consist of two principle types, 1 : 1 and 2 : 1 type. The 1 : 1 type clay mineral is diamagnetic and weakly adsorbs small amount of cesium, whereas the 2 : 1 type clay mineral is paramagnetic and strongly adsorbs a large amount of cesium. The recovery of paramagnetic 2 : 1 type clay mineral by superconducting magnet enables selective separation of high-dose soil. It will reduce the volume of contaminated soil. In this study, the separation of 1 : 1 and 2 : 1 type clay mineral by the magneto-Archimedes method was investigated. It was confirmed that it was possible to separate between 1 : 1 and 2 : 1 type clay mineral effectively. Based on the result, the magneto-Archimedes method was applied to the actual contaminated soil in Fukushima. It was shown that there was a possibility that the volume reduction of contaminated soil could be reduced.