Acta Phys. -Chim. Sin. ›› 2015, Vol. 31 ›› Issue (5): 843-851.doi: 10.3866/PKU.WHXB201503202


Extraction Mechanism and Selectivity of UO2(NO3)2 in Tributylphosphine Oxide-Ionic Liquid System

LIU Hai-Wang, SHEN Xing-Hai, CHEN Qing-De   

  1. Beijing National Laboratory for Molecular Sciences, Fundamental Science on Radiochemistry and Radiation Chemistry Laboratory, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China
  • Received:2015-01-13 Revised:2015-03-19 Published:2015-05-08
  • Contact: SHEN Xing-Hai
  • Supported by:

    The project was supported by the National Natural Science Foundation of China (91226112).


The extraction of UO2(NO3)2 from aqueous solution was investigated using trioctylphosphine oxide (TOPO) and tributylphosphine oxide (TBPO) in ionic liquids (ILs) (CnmimNTf2, n=2, 4, 6, 8). A third phase was formed in the TOPO-C2mimNTf2 and TOPO-C4mimNTf2 extraction systems, whereas the extracted species of TBPO-CnmimNTf2 (n=2, 4, 6, 8) were well soluble in all ILs. The influence of the concentrations of the extractant, nitric acid, and salt on the extraction efficiency was also investigated. Adding HNO3 to the aqueous phase decreased the extraction efficiency. The effect of salt indicates the presence of a cation-exchange mechanism in the extraction. The addition of NO3 - in the aqueous phase increased the extraction efficiency of U, which indicates that NO3 - participates in the extraction. Selective extraction research indicates that TBPO-C4mimNTf2 exhibits good selectivity for U at low acid concentration despite the significant extraction efficiency on Zr at high acid concentration. After removing U, TBPO-C4mimNTf2 still showed high selectivity for Nd at low acid concentration. We also confirmed the difference of the extraction mechanisms among TBPO-CnmimNTf2 by quantitative measurement of NNO3 - in ILs, electrospray ionization mass spectroscopy (ESI- MS), and UV spectroscopy. There are two extraction species (UO2(TBPO)3(NO3)+ and UO2(TBPO)32+) and the proportion of UO2(TBPO)3(NO3)+ increases from C2mimNTf2 to C8mimNTf2.

Key words: Uranium, Ionic liquid, Extraction third phase, Extraction selectivity, Extraction mechanism


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