Kinetics and thermodynamics of Eu(III) adsorption onto synthetic monoclinic pyrrhotite

The adsorption of Eu(III) from aqueous solutions onto monoclinic pyrrhotite (M-Pyr) was studied by batch experiments under various experimental conditions. M-Pyr was synthesized and characterized by XRD, FT-IR, SEM and potentiometric titration. The macroscopic results showed that the adsorption of Eu(III) on M-Pyr was independent of ionic strength, indicating that inner-sphere surface complexation predominated their adsorption. The kinetic adsorption process was well described by pseudo-second-order model with high correlation coefficient (R2 > 0.999). The adsorption isotherms indicated that the adsorption of Eu(III) on M-Pyr fitted by Langmuir model was better than Freundlich model. The maximum adsorption capacity of Eu(III) on M-Pyr calculated from Langmuir model was 10.03 mg/g at pH 5.0 and 293 K. The thermodynamic parameters suggested that the adsorption of Eu(III) on M-Pyr was a spontaneous and endothermic processes. According to XPS analysis, the adsorption of Eu(III) on M-Pyr was mainly dominated by ion exchange and inner-sphere surface complexation at low pH and high pH conditions, respectively.