Speciation of Technetium Dibutylphosphate in the Third Phase Formed in the TBP/HNO 3 Solvent Extraction System.

The speciation of technetium in the nitric acid/dibutylphosphoric acid (HDBP)- n -dodecane system was studied by extended X-ray absorption fine structure (EXAFS) spectroscopy and theoretical methods. Tetravalent technetium, produced by the hydrazine reduction of TcO 4 - in 3 M HNO 3 , was extracted by HDBP in n -dodecane (30% by volume). During extraction, the splitting of the organic phase into a heavy phase and a light phase was observed. EXAFS analysis is consistent with the presence of Tc(NO 3 ) 3 (DBP)(HDBP) 2 in the light phase and Tc(NO 3 ) 2 (DBP) 2 (HDBP) 2 in the heavy phase. Density functional theory calculations at the B3LYP/6-31G* level confirm the stability of the proposed species and indicate that stereoisomers -mer- and fac-Tc(NO 3 ) 3 (DBP)(HDBP) 2 for the light phase and cis- and trans-Tc(NO 3 ) 2 (DBP) 2 (HDBP) 2 for the heavy phase] could coexist in the system (in the n -dodecane solution). Mechanisms of formation of Tc(NO 3 ) 3 (DBP)(HDBP) 2 and Tc(NO 3 ) 2 (DBP) 2 (HDBP) 2 are proposed.