The effects of amidophosphonate ligand immobilization method on the uranium extraction efficiency of functionalized silica

Abstract

The effects on the uranium extraction efficiency of the functionalization method of three kinds of functionalized silica materials were evaluated in low sulfate (pH = 2) and high sulfate (pH = 1) solutions, with compositions representative of typical effluents from uranium mines and leaching solutions from uranium ore treatment, respectively. Silica supports were functionalized with amidophosphonate moieties either by peptide grafting or by non-covalent impregnation. Prior to impregnation, the surface of the silica supports was modified with either alkyl chains or ionic liquid groups. The selectivity of the modified silica supports for uranium was determined in the presence of iron and molybdenum as competing cations. Our results show that both incorporation methods yield materials with good extraction efficiency and selectivity in low sulfate solutions. EXAFS data indicate that uranyl species have to first be desulfurized to be extracted by the phosphonate ligand. This process appears more energetically favorable for the impregnated ligands than for the grafted ones under high sulfate conditions; likely because the grafted ligands compete less efficiently with the bidentate sulfates coordination in uranyl coordination sphere.