Synthesis of new carbazole derivative extractants and study on extraction of perrhenate/pertechnetate

It is very necessary to remove radioactive TcO4- from nuclear waste because TcO4- is harmful to the environment and public health due to the extremely high mobility and long-term radioactivity. In this paper, four carbazole derivative extractants L1-L4 were synthesized, and their extraction behavior for ReO4- (as an analog of radioactive TcO4-) was preliminarily studied in the chloroform-HNO3 system. Compared with L1-L3, L4 showed excellent extractability toward ReO4-, and D-Re is more than 100 at pH = 2 when the initial concentration of L4 is 50 mmol/L, with the high selectivity for ReO4- over other competition anions due to the pre-organized cavity of L4 matching the size of ReO4-. L4 also showed the high SFRe(VII)/U(VI)(5000). And more, ReO4- could be easily and efficiently stripped from the loaded organic phase by Na2CO3 solution with about 100% of the stripping yield. The mechanism was further studied by NMR, HRMS, and theoretical calculation, and the results found that the process of ReO4- extracted by L4 conformed to the anion-exchange extraction model, and the extraction compound is [H2L2+.ReO4-][NO3-]. Finally, the distribution ratio (4-33) of TcO4- by L4 is better than ReO4- (1-5). This research provides a new idea for the design of extractants for efficient separation of TcO4-.

Automated summary

This paper investigates a new carbazole derivative extractant for efficient extraction and stripping of radioactive TcO4-. The results demonstrate that the extractant exhibits excellent extraction performance and selectivity, and the extraction mechanism is revealed through experimental and computational studies.