Phosphate-Based Reactive Membranes for Uranium Isotopic Screening

This study describes the application of reactive membranes for the isolation and concentration of uranium from circumneutral pH solutions by ultrafiltration. The reactive membranes were prepared by grafting a uranium-selective polymer layer via ultraviolet-initiated radical polymerization from the surfaces of poly(ethersulfone) ultrafiltration membrane supports. Dynamic uranium binding capacity measurements were conducted using the reactive membranes housed in an inline filter column, and column breakthrough data were fitted to theoretical models. The experimental data were best described by the Thomas model, indicating that uranium sorption was a reaction rate-limited process. Fitted model parameter values were compared with the results from batch experiments, where similar reaction rate constants were obtained for loading from solutions at pH 4 and 6. The maximum uranium binding capacity of the reactive membrane decreased in the presence of multiple competing ions, from 7.8 +/- 0.3 mg g-1 in deionized water to 3.6 +/- 0.2 mg g-1 in simulated seawater at pH 6. Alpha spectroscopy pulse-height spectra of uranium-loaded reactive membranes were analyzed. Peak energy resolutions measured as full width at half-maximum of 70 +/- 8 and 65 +/- 5 keV were obtained from samples loaded with uranium from DI and seawater solutions. The results of this study provide an approach for a rapid, on-field screening of liquid samples to complement existing techniques and accelerate sample analyses.