Fig. 8-13 Molecular formula of the novel extractant 2,6-bis (3-(5,6-dialkyl-1,2,4-triazinyl) pyridine)

Fig. 8-14 Experimental results on extraction chromatography to separate Am and REEs I: column dead volume, II: feed solution, III: nitric acid / sodium nitrate solution, IV: dilute nitric acid, V: water. This figure shows that Am and REEs are almost completely separated from each other by our novel extractant-impregnated adsorbent. Almost 100% of Am and REEs were recovered, respectively, and REEs in Am were below the detection limit (0.5% or less of original Gd, for example).

In JAERI, the transmutation of long-lived nuclides has been studied in an effort to reduce long-term toxicity of high level radioactive waste. It is indispensable to establish practical techniques to separate and recover transuranium elements, especially americium (Am) and curium (Cm), for transmutation. The key point of the technique is the separation of Am and Cm from rare earth elements (REEs: yttrium and lanthanide elements). Am, Cm and REEs are trivalent cations; thus, they have very similar chemical properties. Using any of the separation techniques which have been developed up to now, recovered Am and Cm contain inevitably 0.3 to 20% of the original REEs. The amount of REEs concerned is quite massive (e.g., one-third of the weight of all elements contained in highly radioactive raffinate from reprocessing of light water reactor spent fuels), absorbs neutrons, and includes highly radioactive isotopes. Therefore, a practical technique is needed for separating massive quantities of REEs from Am and Cm as efficiently as possible for practical use in transmutation. Collaborating closely with the Institute of Research and Innovation, we have developed a novel separation technique based on a chromatographic method of extraction using an extractant-impregnated adsorbent. By this method, it is quite easy to obtain a large amount of material in theory when compared with a conventional solvent extraction method, and the product is expected to have very high purity. The distinctive feature of the current technique is the utilization of a novel chelating extractant (Fig. 8-13, the synthetic method was developed in Germany), which forms a complex with Am and Cm selectively to the REEs, as an impregnating extractant. From the experimental results (Fig. 8-14), it can be said that almost all Am was recovered without any REEs. It is expected that the current technique will be easily adapted to practical use with simple equipment. We hope that this result will provide a great break-through for the research and development of methods to reduce radio-toxicity of high level radioactive waste.

Reference Y.-Z. Wei et al., Separation of Am(III) and Cm(III) from Trivalent Lanthanides by 2,6-bistriazinylpyridine Extraction Chromatography for Radioactive Waste Management, J. Alloy. com., 374(1-2), 447 (2004).

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