57. Elution Behavior of Tc and Re through a Tc-selective Chromatographic Resin Column

Shigeo Uchida and Keiko Tagami

Keywords: technetium, rhenium, yield tracer, ICP-MS, elution behavior

Technetium-99 has been determined in environmental samples to understand the behavior of Tc in the environment. To measure ⁹⁹Tc in environmental samples, a chemical separation and purification of the nuclide from interfering elements is required, because the concentration in the environment is very low. There are several yield tracers for ⁹⁹Tc measurement, such as ^95mTc, ^99mTc, ⁹⁷Tc and Re. From a practical point of view, Re is a convenient yield monitor because it is cheap and has no interference on ⁹⁹Tc counting by ICP-MS. In this study, we performed tracer experiments to compare the elution behavior of Tc and Re through a Tc-selective chromatographic resin (TEVA resin) column under various conditions.

Two hundred and fifty mL of pure water or tap water were adjusted to 0.1 M HNO₃ with conc. HNO₃. The solution spiked with ⁹⁹Tc and Re was passed through the column. Next, the column was washed with 40 mL of 1, 2, 4 or 8M HNO₃. Finally, Tc and Re retained in the column were stripped with 10 mL (5 mL x 2) of 12M HNO₃. The loading solutions and the nitric acid solutions were allowed to drain completely and the eluate was collected into polyethylene vials for the measurement of ⁹⁹Tc and Re by ICP-MS.

The elution behaviors of Tc and Re are listed in Table 12. The recovery was defined as the ratio of the amount of the nuclide in each fraction to that in the sample solution. There was no difference in each nuclide's behavior between pure water and tap water. When the solution was introduced into the column, Re was extracted onto the resin together with Tc. Then the column was washed with 8 mL of 1, 2, 4 or 8M HNO₃ for 5 times (total 40 mL). When 1M HNO₃ was used, Re remained on the resin as well as Tc did. With 2M HNO₃, Re was gradually removed and it was found in the third 8 mL wash fraction but Tc was not found in the eluates. When solutions of higher nitric acid concentrations than 4M HNO₃ were used, Re was removed from the resin easily and was found in the first 8 mL.

Since the distribution coefficient of Re between the resin and nitric acid solution was almost half the value of that of Tc over a wide range of nitric acid concentrations from 0.1M to 8M HNO₃, Re could be removed with less than 40 mL of 2M HNO₃. Thus, when the TEVA resin is applied for Re separation, less than 1M HNO₃ should be used for washing the column to avoid Re losses. For stripping, as seen in Table 12, with 8 mL of 8M HNO₃ both Tc and Re can be completely removed from the resin.

From the results, it was concluded that the TEVA resin showed high selectivity for Re, similar to that for Tc. When concentrations of nitric acid solutions of 1M and 8M were used for washing and stripping, respectively, the elution behaviors of Tc and Re were the same. This indicated that Re could be used as a yield tracer for Tc in environmental water samples.

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