Effect of DTPA on the extractions of actinides(III) and lanthanides(III) from nitrate solution into TODGA/n-dodecane

For the separation of trivalent lanthanides [Ln(III)] and actinides [An(III)], the chelating agent, diethylenetriamine-N,N,N',N'',N''-penta-acetic acid (DTPA), was used to decrease selectively the distribution ratios (D) of An(III) between TODGA/n-dodecane and nitrate solution. The D values of An(III) and Ln(III) decrease with an increase of the pH of the aqueous phase. Their dependencies for light Ln(III) are different from those for medium and heavy Ln(III), which implies that the complexing ability of DTPA(5-) with Ln(III) is different from each other. The calculation of D values was performed using dissociation constants of H(5)DTPA and the formation constants of Ln-DTPA. Their results suggested the existence of Ln(III) ions without any complexation at the intermediate stage of the extraction reactions and demonstrated the curvilineal relation of D with pH in Ln-TODGA-DTPA extraction system. Americium(III) and Cm(III) form more stable 1 : 1 complex with DTPA(5-) and show lower D values than light Ln(III), it is expected to have a high separation against light Ln(III). The separation factors (SF), D-Ln/D-Am and D-Ln/D-Cm, determined varied within the range of 1-60.