Highly efficacious entrapment of Th (IV) and U (VI) from rare earth elements in concentrated nitric acid solution using a phosphonic acid functionalized porous organic polymer adsorbent

It is challenging to extract Th (IV) and U (VI) from rare earth elements (REEs) in concentrated acidic solution. Herein, a nanoporous polymer adsorbent P (DVB-VPA) bearing phosphonic acid groups has been synthesized by solvothermal copolymerization of divinylbenzene (DVB) and vinylphosphonic acid (VPA). The maximum adsorption capacity (qmax) for Th (IV) and U (VI) onto P (DVB-VPA) was estimated to be 354.6 and 216.5 mg g−1 at 298 K in 4 mol L−1 of hydrogen nitrate media, which were much larger than most of the adsorbents reported previously. Besides, P (DVB-VPA) exhibited a good selectivity for Th (IV) and U (VI) from REEs in concentrated nitric acid solution, since the values of the selectivity for Th (IV) and U (VI) over La (III), Ce (III), Eu (III), Nd (III) and Sm (III) were 82.2% and 72.5%, respectively. XPS analysis revealed that the adsorption mechanism was achieved through the complexation of PO ligands anchored onto the polymer skeleton of P (DVB-VPA) with thorium and uranium. Due to P (DVB-VPA) showed a larger binding force toward Th (IV) than U (VI), both q max and selectivity for Th (IV) in concentrated hydrogen nitrate media was larger than those for U (VI) on P (DVB-VPA), which has been confirmed by DFT calculations.