Rapid and Highly Efficient Preconcentration of Eu(III) by Core-Shell Structured Fe3O4@Humic Acid Magnetic Nanoparticles

In this study, humic acid-coated Fe3O4 magnetic nanoparticles (Fe3O4@HA MNPs) were synthesized using a chemical coprecipitation method and characterized in detail. The XRD analysis results showed that HA coating did not change the phase of Fe3O4 cores. The TEM image suggested that Fe3O4@HA MNPs had nearly uniform size without the observation of aggregation. The Fe3O4@HA MNPs were stable in solution and could be easily separated from aqueous solution using a magnetic separation method. A batch technique was adopted to investigate the removal efficiency of Fe3O4@HA MNPs toward Eu(III) under various environmental conditions. The kinetic process of Eu(III) sorption on Fe3O4@HA MNPs reached equilibrium within < 30 mm. The fast sorption kinetics and high sorption amount were attributed to the plentiful surface sites provided by the surface-coated HA macromolecules. The Fe3O4@HA MNPs was able to remove similar to 99% of Eu(III) in aqueous solution at pH 8.5. Except for SO42- anions, the coexisting electrolyte ions had no significant competition effects on the removal of Eu(III) by Fe3O4@HA MNPs. The obvious sorption-desorption hysteresis suggested that the removal of Eu(III) was dominated by inner-sphere surface complexation. The sorption isotherm agreed well with the Langmuir model, having a maximum sorption capacity of 6.95 x 10(-5) mol g(-1). The leaching test showed that the Eu(III)-loaded Fe3O4@HA colloids were capable to maintain high thermodynamic stability for long aging times. The findings herein suggested that Fe3O4@HA MNPs could be potentially used as a highly effective material for the enrichment and preconcentration of radionuclide Eu(III) or other trivalent lanthanides/actinides in geological repositories or in nuclear waste management.