Extraction mechanism of Tc(IV) by Di-(2-ethylhexyl)phosphoric acid (HDEHP)

Di-(2-ethylhexyl)phosphoric acid, HDEHP, is a well-known extractant used for metal ion extraction in an industrial scale and for research work. Understanding metal extraction mechanisms is crucial for accurate interpretation of data obtained from solvent extraction experiments. The extraction mechanism of many metals by HDEHP has been determined. However, the mechanism for Tc(IV) extraction by HDEHP has not been specifically described in the literature and various assumptions have been made on the identity of the extracted Tc(IV) complex, without convincing demonstration. This work reports that TcO(OH)(DEHP)(HDEHP) is the Tc(IV) complex extracted by HDEHP into dodecane from an aqueous solution of 3 M NaClO4 at pH 2, with one HDEHP dimer participating in the extraction and one proton undergoing transfer from the HDEHP into the aqueous phase. The proposed mechanism agrees with other established metal hydroxide mechanisms and follow overall extraction trends for tetravalent metals with HDEHP.

Automated summary

HDEHP is a commonly used extractant for metal ion extraction, and this study identifies the Tc(IV) complex extracted by HDEHP under specific conditions.