Unexpected ultrafast elimination of uranium and europium from aqueous solutions with magnetic bio-CaCO3

Abstract

In this investigation, the magnetic bio-CaCO3 were synthesized and elimination of uranium and europium from aqueous solutions. The prepared magnetic composite underwent a series of characterization analyses, such as Transmission electron microscope (TEM), Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), which prove that the magnetic particles are successfully modified on bio-CaCO3. Surprisingly, it was found that coating the bio-CaCO3 with Fe3O4 not only increased the distance between the calcium carbonate nanosheets but also ensured the presence of FeO active groups on the bio-CaCO3 surface. The sorption of U(VI)/Eu(III) on the magnetic bio-CaCO3 as a function of the pH, adsorbent dose, shaking time, co-existing ions, and the temperature was investigated using batch experiments. The effect of pH was investigated showing optimum sorption at pH 5 for U(VI) and Eu(III). The adsorption kinetics is relatively fast and can reach equilibrium in 60 to 90 min, and the pseudo-second-order rate equation preferentially fits the kinetic distribution, suggesting chemisorption was involved. The maximum adsorption amounts were 122.66 mg·g−1 for U(VI) and 130.62 mg·g−1 for Eu(III) at pH 5.0 and 298 K. The adsorption mechanism, which was evaluated with XRD, FTIR, SEM-EDS, and XPS, demonstrated that the functional groups (OH, -NH2, CO32− and OFe) and the increased hierarchical distances were primarily responsible for the improved adsorption ability. This paper highlights magnetic bio-CaCO3 as potential, eco-friendly and ultrahigh-efficiency materials for uranium and europium pollution cleanup.