Solvent extraction of An(III) and Ln(III) using TODGA in aromatic diluents to suppress third phase formation

Abstract The extraction of nitric acid, trivalent actinides and lanthanides with N,N,N′,N′-tetra-n-octyl-3-oxapentanediamide (TODGA) dissolved in the aromatic diluents 1,4-diisopropylbenezene and tert-butylbenzene was studied. Nitric acid extraction proceeds along the formation of 1:1 and 2:1 HNO3-TODGA adducts. An(III) and Ln(III) distribution ratios were determined as a function of nitric acid, TODGA and Ln(III) concentrations. Distribution ratios are approximately an order of magnitude lower in aromatic diluents compared to aliphatic diluents. No third phase formation was observed when contacting the solvent with an aqueous phase containing 1.5 mol/L Er(NO3)3 in 2–4.3 mol/L HNO3. Slope analysis indicates the formation of 1:3 and 1:4 M(III):TODGA complexes. Using TRLFS, the formation of a previously unknown 1:2 complex in organic phases loaded with Ln(III) was observed for the first time.