Functionalized Magnetic Silica Nanoparticles for Highly Efficient Adsorption of Sm from a Dilute Aqueous Solution.

Separation of Sm from a dilute solution via conventional solvent extraction is often plagued by emulsion and third phase formation. These problems can be overcome with functionalized magnetic nanoparticles that can capture the target species and be separated from the raffinae phase rapidly and efficiently on application of a magnetic field. Magentic silica nanoparticles (FeO/SiO) were synthesized by a modified Stöber method and functionalized with carboxylate (FeO/SiO/RCOONa) and phosphonate (FeO/SiO/RRPONa) groups to achieve high adsorption capacity and fast adsorption kinetics. The adsorbents were characterized by X-ray diffraction analysis, transmission electron microscopy, BET measurements, magnetization property evaluation, Fourier infrared spectroscopy, and thermogravimetric analysis. Equilibrium adsorption of Sm on FeO/SiO/RCOONa particles was attained within 10 min and within 20 min on FeO/SiO/RRPONa nanoparticles. The kinetic data were correlated well with a pseudo-second-order model. Adsorption capacities of FeO/SiO/RCOONa and FeO/SiO/RRPONa were 228 and 180 mg/g, respectively. The recovery of the adsorbed Sm using 2 mol/L HCl as desorption agent was evaluated. The adsorption mechanism is discussed based on FTIR analysis, carboxylate group/Sm molar ratio, phosphonate group/Sm molar ratio, and pH. The adsorbents show significant potential for Sm recovery in industrial applications.