Study on Volume Reduction of Cesium Contaminated Soil by High Gradient Magnetic Separation: Design of Magnetic Filters

The superconducting magnetic separation was examined to reduce the volume of cesium contaminated soil by the Fukushima Daiichi nuclear power plant accident. By using superconducting high gradient magnetic separation, silt and clay with high radioactive concentration due to the large particle surface area per unit mass can be further separated into high-dose 2:1 type and low-dose 1:1 type clay minerals selectively. Here, we examined filter conditions to improve the magnetic separation performance in farmland soil that is rich in organic matter. The results of magnetic separation of uncontaminated soil suggested that the separation selectivity of 1:1 and 2:1 type clay minerals was larger with the filters with smaller wire diameter. On the other hand, it was found that it was difficult to magnetically separate 0-20 μm particles even with the filters with small wire diameter and high selectivity. To solve this problem, magnetic separation was performed under the same conditions on actual contaminated soil that was highly classified into 0-20 μm and 20-75 μm particles. As the result, it was found that the radioactivity can be further reduced by removed high-dose 0-20 μm particles and targeting the 20-75 μm particles.