MnFe₂O₄-graphene oxide magnetic nanoparticles as a high-performance adsorbent for rare earth elements: Synthesis, isotherms, kinetics, thermodynamics and desorption

In recent decades, considerable amounts of rare earth elements have been used and then released into industrial wastewater, which caused serious environmental problems. In this work, in order to recycle rare earth cations (La³⁺ and Ce³⁺) from aqueous solutions, MnFe₂O₄-Graphene oxide magnetic nanoparticles were synthesized and after characterization studies, their adsorption isotherms, kinetics, thermodynamics and desorption were comprehensively investigated. Characterized was performed using XRD, FE-SEM, FT-IR, Raman spectroscopy, VSM, BET and DLS. REE adsorption on MnFe₂O₄-GO was studied for the first time in the present work and the maximum adsorption capacity at the optimum condition (room temperature and pH = 7) for La³⁺ and Ce³⁺ were 1001 and 982 mg/g respectively, and the reactions were completed within 20 min. In addition, the adsorption data were well matched with the Langmuir model and the adsorption kinetics were fitted with the pseudo-second order model. The thermodynamic parameters were calculated and the reactions were found to be endothermic and spontaneous. Moreover, the Dubinin-Radushkevich model predicted chemical ion-exchange adsorption. Desorption studies also demonstrated that MnFe₂O₄-GO can be regenerated for multiple reuses. Overall, high adsorption capacity, chemical stability, reusability, fast kinetics, easy magnetic separation, and simple synthesis method indicated that MnFe₂O₄-GO is a high-performance adsorbent for REE.