Highly efficient extraction of uranium from strong HNO3 media achieved on phosphine oxide functionalized superparamagnetic composite polymer microspheres

Abstract

Recovery of uranium from strongly acidic solutions using magnetic nanoparticles as adsorbents is very important for sustainable nuclear energy, due to their superparamagnetic character and high adsorption efficiency for uranium. However, it is still a challenging task to develop magnetic nanoparticles for the removal of uranium from strongly acidic media, since most of the magnetic nanoparticles have poor acid resistance. Herein, superparamagnetic microspheres Fe₃O₄@SiO₂/P(TRIM–VPA) bearing phosphine oxide groups have been developed successfully by distillation–precipitation polymerization of trimethylolpropane trimethacrylate (TRIM) and vinylphosphonic acid (VPA). Amazingly, Fe₃O₄@SiO₂/P(TRIM–VPA) could still show a record-breaking maximum adsorption capacity (q_max) of 60.4 mg g⁻¹ for uranium even in 4 mol L⁻¹ of HNO₃ with a good selectivity of 61.2% in strong HNO₃ solution containing 11 coexisting ions. More importantly, the structure, uranium adsorption capacity and selectivity of the adsorbent in strong HNO₃ media did not change obviously even after soaking in 4 mol L⁻¹ of HNO₃ for 24 h, indicating that the prepared magnetic adsorbent had excellent acid resistance. Also, the magnetic adsorbent could be recovered conveniently by magnetic force and reused at least six times without obvious decrease in adsorption capacity. The phosphine oxide groups were responsible for the good adsorption capacity for uranium in strong HNO₃ solution, which was confirmed by XPS analysis and DFT method. To the best of our knowledge, this work reports the first example for effective extraction of uranium from strong HNO₃ solution by employing functionalized magnetic nanoparticles as adsorbents.