Efficient soil decontamination via rapid ion exchange in vacuum

Soil from Fukushima contaminated with radioactive Cs was effectively decontaminated through heat treatment with NaCl under vacuum. Although the decontamination ratio was about 10% after heat treatment at 1073 K in atmospheric conditions, the decontamination ratio reached over 90% after heat treatment at 1073 K under vacuum. Under atmospheric conditions, NaCl induced phase transformation in clay minerals, whereas under vacuum, decontamination progressed through rapid ion exchange in clay minerals. It was revealed that rapid ion exchange in vacuum is facilitated by the sublimation of NaCl and the expansion of interlayer spacing during heating. Differences in interlayer spacing during heat treatment under atmospheric and vacuum conditions were explained by deprotonation and the resulting changes in layer charge. The novel phenomenon we discovered is a promising solution for the decontamination of soil contaminated with radioactive Cs.