Effect of pH and ionic strength on sorption of Eu(III) to MX-80 bentonite: batch and XAFS study

Sorption of radionuclides on MX-80 bentonite has been studied extensively because of its high sorption capacity and low penetrability. Herein, MX-80 bentonite was characterized by acid-base titration, XRD and FTIR in detail. The sorption of Eu(III) from aqueous solution to MX-80 bentonite was investigated as a function of contact time, solid content, ionic strength and pH under N-2 conditions. The experimental data was performed with the diffuse layer model (DLM) with the aid of FITEQL 3.1 code. The site densities are 2.52 x 10(-4) mol/g for [ XOH] and 1.54 x 10(-4) mol/g for [ YOH], and acidity constants as pK(a) are pK(xo)- = 6.772, pK(yOH2+) = - 1.68, and pK(YO-) = 4.145. The sorption of Eu(III) on MX-80 bentonite consists of YOEu2+ species at low pH values and XOEu(OH)(+) species at high pH values. The sorption isotherms were simulated by Langmuir, Freundlich and Dubini-Radushkevich (D-R) models, respectively, and the results indicated that Langmuir model fitted the sorption data better than the Langmuir and D-R models. XAFS technique was applied to characterize the local structural environment of the adsorbed Eu(III), and the results indicated that Eu(III) was bond to 0 atoms at a distance of about 2.43 angstrom as Y/XO-Eu2+ at low pH values.