Adsorption of uranium(VI) from aqueous solution using phosphonic acid-functionalized silica magnetic microspheres

The phosphonic acid-functionalized silica magnetic microspheres (PA-SMM) were successfully synthesized for U(VI) adsorption. The PA-SMM exhibited higher adsorption capacity for U(VI) compared to unmodified silica magnetic microspheres due to the high affinity of phosphonic acid groups with U(VI). The adsorption was dominated by inner sphere surface chelation and kinetically followed the pseudo-second-order equation. The adsorption isotherms fitted well to the Langmuir model, with the maximum adsorption capacity of 76.9 mg/g at 298 K and pH 5.0. Thermodynamic parameters indicated the endothermic and spontaneous nature of U(VI) adsorption. The PA-SMM could be regenerated using 0.2 M EDTA-0.5 M HNO3 as the eluent.