Functionalized graphene nanoplatelets: a promising adsorbent for solid-phase uranium extraction

Abstract

Graphene nanoplatelets (GNPs) were functionalized with an organic ligand to prepare materials for selective extraction of uranium from acidic solution. The effects of di-2-ethylhexylcarbamoylethylbutyl phosphonate (DEHCEBP) ligand concentration on the structure of the final solids and the effect on its extraction capacity were investigated in materials with 0.3, 0.5, 0.8, 1.0 and 1.2 mmol of organic ligand per gram of solid. Raman spectroscopy and X-ray diffraction analysis confirm that impregnation does not modify the carbon network and interlayer distance of the GNPs. As shown with nitrogen adsorption–desorption experiments, the amidophosphonate ligand first fills the micropores then the mesopores of the support while the ligand concentration increases. Acidic uranium solutions with high sulfate content were used to simulate the composition of ore treatment leaching solutions. Increasing the ligand concentration inside the graphene leads to an increase of the equilibration time in batch extraction experiments. This suggests that the DEHCEBP molecules form multiple layers in the materials containing the highest ligand contents. The results also suggest that the ligands located inside the micropores remain inaccessible for extraction. Maximum extraction capacities of the material with 1.2 mmol g⁻¹ to 0.3 mmol g⁻¹ DEHCEBP ranged respectively from 108 mg to 18 mg of uranium per gram of solid. This indicates the high potential of these functionalized graphene nanoplatelets for solid phase uranium extraction.