Results and Discussion
Separation Using Anion-SR
Good recovery of I(as 129I-) from the Anion-SR was observed in the 3 M NaOH solution, but only minor amounts of IO3(as 127IO3-) were recovered (Table 27.1). The percent recoveries did not appear to be dependent on the reductant because good recoveries of Iand poor recoveries of IO3were observed regardless of the presence or absence of NaHSO3. This result supports the expectation that 129Iis extracted and 127IO3is not extracted by the Anion-SR, as 127IO3was not reduced to 127Iby NaHSO3 in 3 M NaOH solution, and the isotopic exchange reaction between 127IO3and 129Iand reduction from 127IO3to 127Iwere negligible at least for 1 day. It is reported that 129I in seawater offshore of Fukushima is mainly 129Iregardless of the presence of large amounts of natural 127IO3.
In the diluted HCl solution at pH 2, 129I and 127I were recovered in the presence of the reductant and were not recovered without the reductant (Table 27.1). Both the isotopes behaved similarly in this case despite the difference in the initial chemical species, 129Iand 127IO3-. In contrast, the experiments using 1 μg 127Iin the diluted HCl solution at pH 2 without the reductant and standing, higher recovery of 127I-, 72 ± 6 %, was obtained. Although the influence of the Iamount on recovery cannot be wholly denied, it is possible that a considerable amount of 129Iwould be changed to another chemical species in the diluted HCl solution in a day. In addition, the changed chemical species and IO3were reduced to Iby the reductant in this experimental condition. Consequently, inorganic iodine species were analyzed at pH 2 with the reductant, and only Iwas analyzed in 3 M NaOH. It is possibly to apply speciation methods to analyze Iand IO3-, depending on the solution conditions.
When 1 g pine bark was combusted by the electric furnace without control, smoking was observed at the temperature range from 200 o to 300 oC, especially at 240 oC. Therefore, a stepwise and slow rate of temperature increase was introduced. When smoking was observed, the gap of the setting temperature was decreased and holding time at the temperature was prolonged. Finally, smoking was not observed by the controlled rising temperature program shown in Fig. 27.3, in which the increments of 50 oC for 20 min from 100 oC to 200 oC, and in increments of 15 oC for 20 min from 200 oC to 300 oC.
Tetramethyl ammonium hydroxide solutions containing known amounts of Ior IO3were prepared to make calibration curves for the DRC-ICP-MS measurement. However, the counts of mass number 127 for IO3were essentially at background levels, which indicated that measurement of IO3in 2 % TMAH solution was not available in our instrument. It is considered that I is vaporized as I2 by the combustion and I2 is trapped in an alkaline solution as I-. Therefore, the calibration curve was prepared from Isolutions.
Combustion experiments of pure pine bark sample and pine bark samples spiked with 50 μg I as Ior IO3were performed and the amounts of 127I in the traps were determined by DRC-ICP-MS with the calibration curve previously mentioned
Fig. 27.3 Optimized rising temperature program
Table 27.2 Recovered I (μg) in the traps by the combustion method
(Table 27.2). Greater than 90 % recovery was obtained for both Iand IO3spiked samples in the first trap. This result suggested that the chemical species of I in the traps was Iregardless of the initial chemical species.
To analyze 129I in the contaminated water from FDNPS, separation of I from radionuclides such as 137Cs and 90Sr using Anion-SR and measurement by DRCICP-MS are convenient and effective. As a solution condition, a diluted HCl solution of pH 2 with reductant was required to analyze inorganic iodine species using Anion-SR.
To analyze 129I in tree samples from FDNPS, a combustion method is suitable. Both Iand IO3were vaporized by combustion and trapped in the 2 % TMAH solution as Iwith high recovery (>89 %). Anomalous combustion was avoided by the stepwise and slow temperature increase in the range from 100 o to 300 oC.