Radiometric evaluation of diglycolamide resins for the chromatographic separation of actinium from fission product lanthanides

Actinium-225 is a potential Targeted Alpha Therapy (TAT) isotope. It can be generated with high energy (>= 100 MeV) proton irradiation of thorium targets. The main challenge in the chemical recovery of Ac-225 lies in the separation from thorium and many fission by-products most importantly radiolanthanides. We recently developed a separation strategy based on a combination of cation exchange and extraction chromatography to isolate and purify Ac-225. In this study, actinium and lanthanide equilibrium distribution coefficients and column elution behavior for both TODGA (N,N,N',N'-tetra-n-octyldiglycolamide) and TEHDGA (N,N,N',N'-tetrakis-2-ethylhexyldiglycolamide) were determined. Density functional theory (DFT) calculations were performed and were in agreement with experimental observations providing the foundation for understanding of the selectivity for Ac and lanthanides on different DGA (diglycolamide) based resins. The results of Gibbs energy (Delta G(aq)) calculations confirm significantly higher selectivity of DGA based resins for Ln(III) over Ac-III in the presence of nitrate. DFT calculations and experimental results reveal that Ac chemistry cannot be predicted from lanthanide behavior under comparable circumstances.