Study on adsorptive property of bentonite for cesium

Abstract

Characterization and adsorption analysis of the bentonite samples were studied by scanning electron microscopy (SEM), energy disperse spectroscopy (EDS), Fourier transformed infrared (FTIR) spectroscopy, and X-ray diffraction (XRD). SEM, EDS, FTIR, and XRD results showed that the ion exchange is one of the adsorption mechanisms of Cs⁺ onto bentonite and the Al–O–H and H–O–H groups of the bentonite might participate in the Cs⁺ adsorption process. The effect of the contact time, different concentrations of Cs⁺, pH value, and bentonite dosage on the adsorption of Cs⁺ onto bentonite were examined. The study results showed that cesium ions could be effectively adsorbed by bentonite. The adsorption equilibrium was established after 24 h. The distribution coefficient decreased from 1614.57 to 84.93 mL/g, but the adsorption capacity increased from 8.71 to 21.79 mg/g when the initial Cs concentration increased from 100 to 500 mg/L. The distribution coefficient and adsorption capacity for the cesium ions increased with an increase of solution pH in the range of 3 and 11 except for a little decrease at pH 7. The distribution coefficient increased from 66.54 to 3498.62 mL/g, but the adsorptive capacity decreased from 23.48 to 2.86 mg/g with an increasing amount of the adsorbent from 0.25 to 0.5 g. Adsorption isotherms fitted with Freundlich models well. Thermodynamic studies indicated that the sorption capacity of the sorption of cesium ions onto bentonite became weak with a temperature increase and showed the sorption of cesium ions onto bentonite was exothermic.