Eu(III) adsorption/desorption on Na-bentonite: Experimental and modeling studies

In this paper, the physico-chemical, titration and Eu(III) adsorption/desorption characteristics of a purified Na-bentonite have been measured. Potentiometric titration at three ionic strengths (0.01, 0.1 and 0.5 mol/L NaCl) at 25 °C indicates that the point of zero charge (PZC) of the Na-bentonite increases with decreasing ionic strength. The parallel titration curves at three ionic strengths were interpreted by considering a layer site and two edge hydroxyl sites in the framework of surface complexation model. The adsorption/desorption of Eu(III) on the Na-bentonite was investigated by a batch experimental method. pH adsorption edges of Eu(III) in the absence and presence of CO2 at variable Eu(III) concentrations (6.74 × 10−8 and 3.33 × 10−6 mol/L) were collected and reasonably interpreted by a surface complexation model. Adsorption and desorption isotherms at pHs 4.04 ± 0.05, 6.01 ± 0.05, 6.53 ± 0.05 and 7.46 ± 0.05 indicate that the adsorption/desorption of Eu(III) on the Na-bentonite is reversible. The adsorption isotherms of Eu(III) were successfully reproduced by the proposed model.