Evaluation of a chloride-based Zr isolation strategy using a tributyl phosphate (TBP)-functionalized extraction resin.

Introduction: The remarkable stability of the Zr-DOTA complex has been shown in recent literature. The formation of this complex appears to require Zr-chloride as the complexation precursor rather than the more conventional Zr-oxalate. In this work we present a method for the direct isolation of Zr-chloride from irradiated Y foils.

Methods: Zr, Zr, and Y were prepared by 16 MeV proton irradiation of Y foils and used for batch-extraction based equilibrium coefficient measurements for TBP and UTEVA resin. Radionuclidically pure Zr was prepared by 14 MeV proton-irradiation of Y foils. These foils were dissolved in concentrated HCl, trapped on columns of TBP or UTEVA resin, and Zr-chloride was eluted in <1 mL of 0.1 M HCl. For purposes of comparison, conventionally-isolated Zr-oxalate was converted to Zr-chloride by trapping, rinsing, and elution from a QMA cartridge into 1 M HCl. Trace metal analysis was performed on the resulting Zr products.

Results: Equilibrium coefficients for Y and Zr were similar between UTEVA and TBP resins across all HCl concentrations. K values of <10 mL/g were observed for Y across all HCl concentrations. K values of >10 mL/g were observed at HCl concentrations >9 M for Zr, falling to K values of <10 mL/g at low HCl concentrations. Zr-chloride was recovered from small columns of TBP in <1 mL of 0.1 M HCl with an overall recovery efficiency of 89 ± 3% (n = 3). An average Y/Zr separation factor of 1.5 × 10 (n = 3) was obtained. Trace metal impurities, notably Fe, were higher in TBP-isolated Zr-chloride compared with Zr-chloride prepared using the conventional two-step procedure.

Conclusion: TBP-functionalized resin appears promising for the direct isolation of Zr-chloride from irradiated Y targets. Excellent Zr recovery efficiencies were obtained, and chemical purity was sufficient for proof-of-concept chelation studies.