Efficiency of biological versus mesoporous adsorbents for gadolinium removal from wastewater

Gadolinium application in industry and medicine results in generation of large volumes of gadolinium-containing wastewater, which can present hazard for humans and environment. Adsorption proved to be an efficient way of metal removal from wastewater. Two adsorbents of different origin, yeast biomass and titanosilicate ETS-10, were applied for gadolinium removal from synthetic wastewater under different experimental conditions. Several analytical techniques, including scanning electron microscopy and X-ray diffraction were used for adsorbents characterization. The maximum removal of gadolinium by both adsorbents was achieved at pH 3.0. By studying kinetics, the applicability of the pseudo-first-order model for the description of gadolinium adsorption on analyzed adsorbents was shown. Langmuir and Freundlich adsorption isotherms were used to explain the equanimity of the sorption process. The Langmuir model showed its applicability for the explanation of the equilibrium data obtained for yeast biomass, while Freundlich model was more applicable for mesoporous material. The maximum sorption capacity of titanosilicate ETS-10 (234 mg/g) significantly overpassed the value obtained for yeast biomass (98 mg/g). The relevant thermodynamic parameters, standard free energy, enthalpy change, and entropy change were calculated to understand the nature of the adsorption process. For both adsorbents the process was spontaneous and heat-taking. Fourier transform infrared spectroscopy reaved the role of functional groups in gadolinium removal. Tested adsorbents maintained high adsorption capacity during three sorption-desorption cycles.