Study on the Separation of Thorium and Lanthanide Ions by Oligoaromatic Amide Extractant
The separation of actinides from lanthanides is a critical control segment in the last stage of the nuclear fuel cy-cle,and it is also a worldwide challenge due to the extreme similarity of physicochemical properties of actinides and lantha-nides.Therefore,it is of great significance to find a new and effective separation method.In order to realize effective separa-tion of lanthanides and actinides,the paper employed liquid-liquid extraction method to investigate the extractability and influ-encing factors of extractants 1(oligoaromatic amide pentamer),2(oligoaromatic amide trimer)and 3(oligoaromatic amide di-mer)for La3+,Ce3+,Pr3+,Nd3+,Sm3+,Gd3+,Yb3+,Lu3+and Th4+.The extraction performance and re-extraction property of extractant 1 were discussed.The results show that among the 9 selected metal cations,extractants 1,2,and 3 had the high-est extractability for Th4+,with 88.6％,56.4％,and 44.1％,respectively.However,their extractabilities for the 8 lantha-nide ions were all low and did not differ significantly.Among the separation factor(SF)of Th4+and other 8 metal ions on ex-tractant 1,the largest separation factor is SFTh/Sm,the smallest separation factor is SFTh/Lu,and the average value of separation factor is 21.9,which has the ability to efficiently separate Th4+from the 9 metal ions,while extractants 2 and 3 do not.The extractant coordination number was directly proportional to its extractability,and Th4+is the most affected.The metal ion prop-erties can affect its extractability too.The extractability of extractant 1 for Th4+increased first and then decreased as the pH in-creased.The maximum extraction capacity and complex-ratio of extractant 1 and Th4+are 0.105 g·L-1and 1∶1,respective-ly.When the concentration of hydrochloric acid is 2.5 mol·L-1,the re-extractability of the loaded organic phase on extract-ant 1 can reach more than 93％.By studying the separation performance of the new extractants for lanthanides and actinides,it is helpful to design more excellent extractants.
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