Removal of radioactive iodine and cesium species from rainwater by a pot-type water purifier, and chemical and physical analysis of radioactive components in rainwater

A pot-type water purifier captured 98% of the nonradioactive iodine and iodide when an ion-exchange resin and activated carbon were used. Approximately 93.8% of ¹³¹I, 74 to 84.5% of ¹³⁴Cs, and 75 to 81.1% of ¹³⁷Cs in rainwater were captured after six repeated purifications using the purifier. The remaining 6.2% of ¹³¹I was not removed by isotope exchange with nonradioactive I^- or by reduction to I^- using Na₂S₂O₄. Approximately 19% of ¹³¹I, 40% of ¹³⁴Cs, and 33% of ¹³⁷Cs were adsorbed on the silica gel. Analysis of the removal rates of 73% for the mixed ion exchange resin, 59% for the silver ions, and 18% for the silver nanoparticle-bound clay indicated that the content of ¹³¹I adsorbed particles components was 23%. The concentration ratio of radioactive components in rainwater decreased from 5.9 to 1.4 upon ultrafiltration with a YM-1 membrane filter, indicating that a soft aggregation of the aerosol occurred. The IP and γ-ray spectrum analysis of the filter produced a cottonlike image of ¹³¹I. Analysis of the TEM image and its electron diffraction pattern indicated the aggregation of a small fraction of the SiO₂ aerosol. The coagulation of radioactive components in rainwater using I-adsorbed SiO₂ nanoparticles may be due to the exchange of the ¹³¹I isotope with I in I-SiO₂ and the adsorption of ¹³⁴Cs⁺ and 1³⁷Cs⁺ on the surface of SiO₂ or the precipitation of the ¹³¹I-adsorbed aerosol and ¹³⁴Cs- and ¹³⁷Cs-adsorbed aerosols. (author)