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

The extraction of pertechnetate (TcO4-) and perrhenate (ReO4-) 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 TcO4- and ReO4- from both HNO3 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 HNO3 and HCl systems, where the distribution ratio of TcO4- was slightly higher than that of ReO4-. 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 ReO4- was extracted as [H+ReO4-(H2O)(8)center dot(TBP)(4)] and formed microemulsions in the organic phase. Theoretical calculations were performed on the structure of both [H+ReO4-(H2O)(8)center dot(TBP)(4)] and [H+TcO4-(H2O)(8)center dot(TBP)(4)]. The TBP molecules interacted with the [H+ReO4-(H2O)(8)] and [H+TcO4-(H2O)(8)] clusters through hydrogen bonding between H2O and the O=P groups, i.e., ReO4- and TcO4- underwent outer-sphere coordination with TBP in the organic phase. Results in this work provide valuable insights into the structures of ReO4- and TcO4- extracted into the organic phase by TBP, and also assist in the analysis of TcO4- species in the PUREX process.

Automated summary

The extraction behavior of TcO4- and ReO4- by TBP in n-dodecane from HNO3 and HCl solutions was investigated. The results indicated that TBP interacted with [H+ReO4-(H2O)(8)] and [H+TcO4-(H2O)(8)] clusters through hydrogen bonding, suggesting the outer-sphere coordination of ReO4- and TcO4- with TBP in the organic phase.