Abstract
Tannic acid-type organic composite adsorbents (PA316TAS, AR-01TAS, PYRTAS, WA10TAS, WA20TAS, and WA30TAS), combined with hydrolyzed and sulfonated tannic acid (TAS) and porous-type strongly basic anion-exchange resin (PA316), benzimidazole-type anion-exchange resin embedded in high-porous silica beads (AR-01), pyridine-type anion-exchange resin (PYR), acrylic-type weakly basic anion-exchange resin (WA10), or styrene-type weakly basic anion-exchange resins (WA20 and WA30) for simultaneous removal of various kinds of radionuclides in river water were successfully synthesized. The adsorption behavior of twelve kinds of simulated radionuclides (Mn, Co, Sr, Y, Ru, Rh, Sb, Te, Cs, Ba, Eu, and I (I− and IO3−)) on these composite adsorbents has been studied in real river water at room temperature. PA316TAS adsorbents showed much higher distribution coefficients (Kd) for all metal ions. TAS structure has more selective adsorption ability for Mn, Co, Sr, Y, Cs, Ba, Eu, and IO3−. On the other hand, Y, Ru, Rh, Sb, Te, Eu, I (I− and IO3−) were adsorbed on both PA316 and TAS structures. To evaluate the validity of these mechanistic expectations, the respective chemical adsorption behaviors of Mn, Co, Sr, etc. and PA316TAS adsorbent were examined in river water ranging in temperature from 278 to 333 K. As was expected, one adsorption mechanism for Mn, Co, Sr, Cs, and Ba systems and two types of adsorption mechanisms for Y, Ru, Rh, Sb, Te, Eu, I (I− and IO3−) systems were observed. On the other hand, the precipitation of Mn, Co, Y, Ru, Rh, Te, and Eu was formed by ozonation for river water, that is, ozone can transform Mn, Co, Y, Ru, Rh, Te, and Eu ions into the insoluble precipitates. Hence, one straight line for Sr, Cs, Ba systems and two types of straight lines for Sb, I (I− and IO3−) systems were obtained in river water treated with ozone. The chromatography experiments of Cs, Sr, I (I− and IO3−) were carried out to calculate their maximum adsorption capacities. The obtained maximum adsorption capacities of Cs, Sr, and I− mixed with IO3− were 1.7 × 10−4 (Cs), 1.8 × 10−3 (Cs/O3), 7.8 × 10−5 (Sr), 5.6 × 10−4 (Sr/O3), 5.4 × 10−2 (I− and IO3−), 3.1 × 10−2 (I− and IO3−/O3) mol/g - PA316TAS. It was discovered that the maximum adsorption capacities of I− and IO3− for the composite adsorbent is unprecedented high and the capacity become much greater than an order of magnitude, compared with those of previous reports. This phenomenon suggests the formation of electron-donor-acceptor (EDA) complexes or pseudo EDA complex. Based on these results, it was concluded that the combined use of tannic acid-type organic composite adsorbents and ozone made it possible to remove simultaneously and effectively various kinds of radionuclides in river water in the wide pH and temperature ranges.
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