Neptunium and Plutonium uptake by LN-series resins in halide media.

Neptunium (Np) and plutonium (Pu) exhibit multiple oxidation states with substantially different coordination and extraction behavior that complicate their separation in acidic media. Extraction chromatography using acidic organophosphorus extractants offers an alternative to solvent extraction while reducing the need for bulk organic solvents, but the behavior of Np and Pu on the LN-series resins in hydrochloric acid (HCl) and hydrobromic acid (HBr) remains largely uncharacterized. Here, we investigate the uptake of Np in HBr and Pu in both HCl and HBr on commercial LN and LN2 resins. Batch weight distribution ratios, uptake kinetics, and column separations were evaluated as functions of acid type and concentration. Plutonium exhibited strong uptake from HCl over the investigated acidity range under redox-conditioning conditions intended to favor Pu(IV), whereas Np uptake measurements in HCl were not reproducible, potentially reflecting oxidation-state instability. In HBr, Np showed substantial retention on both resins, consistent with predominantly Np(IV) behavior, while Pu exhibited limited uptake consistent with bromide-mediated reduction to predominantly Pu(III). Plutonium uptake from HCl and Np uptake from HBr were rapid on both resins with initial uptake plateaus generally reached within ≈ 120 s under the investigated kinetic conditions. A mixed Np/Pu feed was separated using 0.5-mL LN resin columns. Alpha spectrometry showed no detectable Np in the Pu fraction or Pu in the Np fraction. Additional matched single-element column experiments involving uranium (U) and americium (Am) yielded ≈ 95 - 100% recoveries and supported conceptual U/Np/Am and U/Pu/Am schemes requiring future mixed-feed validation. Collectively, these results characterize Np uptake from HBr and Pu uptake from HCl and HBr on LN and LN2 resins and support high-recovery separations for analytical and small-scale radiochemical applications.