Synthesis and characterization of a novel Fe3O4-loaded oxidized biochar from pine needles and its application for uranium removal. Kinetic, thermodynamic, and mechanistic analysis

Abstract

This work investigates the fabrication of magnetic biochar (pncm) and Fe₃O₄-loaded oxidized biochar (pncom) obtained from pine needles for uranium removal. Adsorbent properties were characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) techniques. Using batch-type experiments the effect of the uranium concentration, solution pH, contact time, temperature and ionic strength on the uranium adsorption was investigated. The results showed better adsorptive properties for pncom, particularly in the acidic pH range. The experimental adsorption data were found to be well fitted with the Langmuir isotherm and the pseudo-second order kinetic model. For pncom, the maximum adsorption capacity obtained applying the Langmuir isotherm model was found to amount 2.6 mol/kg at pH 6 and 25 °C. Spectroscopic data indicated that the U(VI) adsorption was associated with the formation of inner-sphere complexes. Regeneration and reusability studies were performed with 0.1 M Na₂CO₃. After four cycles, the % relative adsorption and the desorption for pncom decreased from 99.5% to 87.2% and 99.6%-62.6%, respectively. The present results show that magnetization of oxidized pine needle biochar improves significantly the adsorption characteristics regarding the uranium removal from aqueous solutions.

Keywords: Adsorption isotherms; Kinetics; Magnetized pine needle biochar; Mechanism; Uranium.