Structure and aggregation behavior of pertechnetate/perrhenate in organic phase in the extraction by tributyl phosphate

The extraction of pertechnetate (TcO 4 − ) and perrhenate (ReO 4 − ) by tributyl phosphate (TBP) has been extensively studied, but the structure of the extracted species is subject to debate. In this work, the extraction behavior of TcO 4 − and ReO 4 − from both HNO 3 and HCl media by TBP in n -dodecane was studied by examining the effects of acid concentration, extractant concentration, and temperature on the extraction. The two anions displayed similar extraction behavior in both the HNO 3 and HCl systems, where the distribution ratio of TcO 4 − was slightly higher than that of ReO 4 − . The measurement of water content in the organic phase and dynamic light scattering were carried out, which in combination with the extraction behavior indicated that ReO 4 − was extracted as [H + ReO 4 − (H 2 O) 8 ·(TBP) 4 ] and formed microemulsions in the organic phase. Theoretical calculations were performed on the structure of both [H + ReO 4 − (H 2 O) 8 ·(TBP) 4 ] and [H + TcO 4 − (H 2 O) 8 ·(TBP) 4 ]. The TBP molecules interacted with the [H + ReO 4 − (H 2 O) 8 ] and [H + TcO 4 − (H 2 O) 8 ] clusters through hydrogen bonding between H 2 O and the O=P groups, i.e., ReO 4 − and TcO 4 − underwent outer-sphere coordination with TBP in the organic phase. Results in this work provide valuable insights into the structures of ReO 4 − and TcO 4 − extracted into the organic phase by TBP, and also assist in the analysis of TcO 4 − species in the PUREX process.