Interactions of Perrhenate (ReO) and Pertechnetate (TcO) with the Uranyl Ion (UO) in Acetonitrile Solution: Spectroscopy and Theoretical Calculations

The co-extraction of pertechnetate (TcO) along with the uranyl ion (UO) is a problematic issue that complicates the Plutonium Uranium Reduction EXtraction (PUREX) process for reprocessing spent nuclear fuel. Unfortunately, research on the interactions of TcO with UO is very scarce. This work quantitatively investigated the interactions of TcO and its analog ReO with UO in acetonitrile with 0.5% water content by spectrophotometric titrations including UV-Vis absorption and Raman spectroscopies. UO and TcO/ReO form complexes of 1 : 1 to 1 : 3 molar ratios, in which the stability constants of the UO-TcO complexes are slightly higher than those of the UO-ReO complexes. The structures of the complexes of UO with TcO/ReO are modeled by DFT calculations. The DFT calculations indicate that the TcO/ReO anions are monodentate coordinated with UO. The UV-Vis and Raman spectra of the complexes are simulated, and it is found that the second solvation shell needs to be explicitly taken into account in the DFT calculations in order to obtain Raman spectra comparable to the experiments. The results in this work help understand the co-extraction behavior of TcO with UO in spent nuclear fuel reprocessing.