Efficient capture of actinides from strong acidic solution by hafnium phosphonate frameworks with excellent acid resistance and radiolytic stability

Abstract

A kind of unconventional metal–organic framework (UMOF), hafnium phosphonates (HfP) with different molar fractions P/(P + Hf), were synthesized via a template-free, one-pot method by the reaction between hafnium chloride octahydrate (HfOCl2·8H2O) and amino tris(methylenephosphonic acid) (ATMP); the structure, sorption behaviors for actinides, acid resistance and radiolytic stability of the synthesized materials were then investigated. The results reveal that the materials were amorphous and porous, and HfP with a higher molar fraction P/(P + Hf) exhibited a higher sorption capacity for Th(IV) and U(VI). In 3 mol/L HNO3, Kd values of HfP for Th(IV) and U(VI) were 5.84 × 104 and 5.09 × 103 mL/g, respectively, indicating superiority to other MOF materials in strong acidic solution. The Kd values for tracer amounts of radioactive 239Pu and 237Np were 1.19 × 104 and 6.68 × 103 mL/g in 4 mol/L HNO3, respectively. This is the first case of applying MOF materials to capture transuranic elements from a strong acidic medium. Moreover, the materials were quite stable when dipped into strong acidic solutions, while their sorption performances were unexpectedly enhanced after irradiated by high dosage γ-rays in air. All the results support its anticipated application as actinide sorbents in many practical nuclear processes.