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.