Uranium(VI) complexation with trans-1,2-cyclohexanediaminetetraacetic acid in solution: thermodynamic and structural studies

Abstract

Interaction between uranium(VI) and aminopolycarboxylic acids could significantly influence the chemical behavior of uranium(VI) in the processing and disposal of nuclear wastes. Trans-1,2-cyclohexanediaminetetraacetic acid (CDTA) is a commonly used aminopolycarboxylic acid, but its complexation with uranium(VI) has not been sufficiently studied. In this study, stability constants of CDTA protonation and U(VI)-CDTA complexes at different temperatures were measured by potentiometry. Their enthalpies and entropies were obtained from van’t Hoff plots. As a result, four U(VI)-CDTA species, UO₂(H₂CDTA), UO₂(HCDTA)^-, UO₂CDTA^2- and UO₂(OH)CDTA^3-, were identified at pH 3-6 and their coordination modes in solution were demonstrated by thermodynamic studies. The proposed coordination modes of UO₂(H₂CDTA) and UO₂(HCDTA)^- in solution differ from the reported crystals; the former is bidentate bonding with one carboxylate and the latter is tridentate bonding with iminodicarboxylate.

Graphical Abstract

Keywords:

• Uranium(VI)
• CDTA
• thermodynamic
• coordination mode
• potentiometry

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China under Grant No. 21976165, No. U1830202, and No. 11675156.