f-Block element separation mediated by carboxylated Fe₃O₄ nanoparticles as robust adsorbents in acidic systems

Citric acid functionalized magnetic nanoparticles (CA-MNP) were synthesized and studied for sorption of two representative trivalent lanthanide and actinide ions (Eu³⁺ and Am³⁺). The material was characterized using various analytical techniques such as FTIR, SEM, TEM and zeta potential measurement etc. which indicated successful synthesis of magnetic nanoparticles and citric acid coating on its surface. The uptake study indicated efficient sorption of Eu³⁺ (76.7%) and Am³⁺ (60.9%) at optimum concentration of CA-MNP) 2.5 mg mL^- 1. Sorption of metal ion onto the substrate was confirmed by EDXRF results. The sorption process indicated better kinetics for Eu³⁺ compared to previously reported studies and both the radionuclides were found to be following pseudo-second order rate kinetics. The rate constants were found to be 4.76 × 10^- 9 mg g^- 1 min^- 1 and 2.45 × 10^- 7 mg g^- 1 min^- 1 for Am³⁺ and Eu³⁺, respectively. Thermodynamic study indicated ΔG values as - 15.8 kJ mol^- 1 and - 17.9 kJ mol^- 1 for Am³⁺ and Eu³⁺, respectively indicating the spontaneity of the sorption processes. Stripping with different reagents viz. 0.1 M EDTA, 0.1 M oxalic acid, 0.1 M Na₂CO₃, and 0.1 M HNO₃ indicated best results with 0.1 M EDTA. >99% of loaded Eu³⁺ is stripped in two stripping cycles while stripping of Am³⁺ requires more number of cycles to quantitatively strip the loaded radionuclide.