Selective molybdenum removal from simulated acidic high-level liquid waste by a synergistic electrostatic-coordination resin for yellow-phase risk mitigation.

The formation of a water-soluble molybdate-rich yellow phase is a critical hazard in high-level liquid waste (HLLW) vitrification because it reduces glass durability, increases melter corrosion, and limits waste loading. Herein, a hierarchically porous amidoxime-polyamine resin, AOMA-PEI, was developed for selective molybdenum removal from acidic HLLW before vitrification. The material was constructed from a poly(acrylonitrile-co-methyl acrylate) resin through amidoximation and covalent grafting of branched polyethyleneimine, generating sites for electrostatic enrichment and coordination binding of anionic molybdate species. AOMA-PEI exhibited a maximum measured Mo(VI) uptake of 1805.57 mg g-1 and maintained Mo(VI) uptake in 3 M HNO3 and after 500 kGy γ irradiation. In simulated HLLW containing radioactive 99Mo at 3.24 Ci L-1 and competing fission-product ions, the resin achieved > 99% Mo removal while suppressing the uptake of most coexisting ions. Fixed-bed experiments confirmed its feasibility for continuous-flow pretreatment. XPS and EXAFS results were consistent with Mo interactions involving O- and N-containing environments, while DFT calculations indicated more favorable adsorption energetics for the coupled-site model than for individual-site models. These results demonstrate that AOMA-PEI is a promising pretreatment adsorbent for reducing the yellow-phase-forming molybdenum inventory and improving HLLW feed compatibility for vitrification.