Effects of nitrate additives in soil decontamination using Cs-free mineralization

Shimoyama, Iwao   

Cs-free mineralization is a decontamination method to remove radiocesium from soil by converting clay minerals to different minerals through chemical reaction with additives, and its efficiency considerably depends on reagents. In this work, nitrate reagents were used to decrease processing temperatures. Weathered biotite (WB) which sorbed non-radioactive Cs was used as model soil. WB was heated with an additive for two hours and analyzed using X-ray fluorescence and X-ray diffraction after rinsing with water and drying. When calcium nitrate was added, Cs removal ratio reached to 100%at 450C in Ar atmosphere, and this achieves significant decrease of processing temperature as compared with the cases of chloride reagents. In the case of NaCl or KCl addition, ion exchange was the major Cs removal process at 700C, whereas in the case of NaNO or KNO addition, phase transformations were induced at 634C under vacuum, which suggests that Cs removal process depends on the anion in the reagent. In the case of calcium nitrate, the phase transformation temperature decreased to approximately 500C, however, ion it is presumed that ion exchange was the major Cs removal process at 450C because WB was preserved at this temperature.