Adsorption of bivalent ions (Ca(II), Sr(II) and Co(II)) onto FEBEX bentonite

Abstract The sorption of the bivalent ions Ca, Sr and Co onto the Spanish “FEBEX” bentonite, converted to its Na-form was analysed. Several batch experiments were carried out to study, the effects of pH, ionic strength and radionuclide concentration on the uptake of these bivalent elements, independently. Results showed that the sorption behaviour of Ca and Sr is very similar both from a qualitative and quantitative point of view. The main sorption mechanism for Ca and Sr on the Na–montmorillonite is the ionic exchange and sorption is linear in the whole range of concentrations investigated. The mean logarithm of selectivity coefficient, with respect to Na, obtained from the above-mentioned sorption studies, considering trace concentrations of these elements, is 0.65 ± 0.11 and 0.66 ± 0.06 for Ca and Sr, respectively. However, a small contribution due to surface complexation at the clay edge sites (SOH) had to be considered to fit adequately the sorption results obtained at pH higher than 8 and higher ionic strengths. The sorption behaviour of Co is quite different from that observed for the previous elements. The pH-dependence of Co sorption on the clay is significantly more noticeable, indicating a major contribution of surface complexation at the edge sites. Sorption due to ionic exchange becomes more evident when the ionic strength decreases. The value of the logarithm of the selectivity coefficient, with respect to Na, used in the simulations was 0.62 ± 0.13. The sorption isotherms with Co indicated the existence of two different complexation sites (weak and strong) that were accounted for in the final modelling.

[1]  M. Bradbury,et al.  Sorption of Eu on Na- and Ca-montmorillonites: Experimental investigations and modelling with cation exchange and surface complexation , 2002 .

[2]  Adell,et al.  On the Applicability of DLVO Theory to the Prediction of Clay Colloids Stability. , 2000, Journal of colloid and interface science.

[3]  Brown,et al.  Surface Precipitation of Co(II)(aq) on Al2O3 , 1997, Journal of colloid and interface science.

[4]  Trainor,et al.  Adsorption and Precipitation of Aqueous Zn(II) on Alumina Powders. , 2000, Journal of colloid and interface science.

[5]  M. Bradbury,et al.  A mechanistic description of Ni and Zn sorption on Na-montmorillonite Part I: Titration and sorption measurements , 1997 .

[6]  Werner Stumm,et al.  Specific Chemical Interaction Affecting the Stability of Dispersed Systems , 1970 .

[7]  D. Sparks,et al.  Investigation of Ni Sorption on Pyrophyllite: An XAFS Study , 1996 .

[8]  G. A. Parks,et al.  Molecular Structure and Binding Sites of Cobalt(II) Surface Complexes on Kaolinite from X-Ray Absorption Spectroscopy , 1994 .

[9]  Garrison Sposito,et al.  The surface chemistry of soils , 1984 .

[10]  G. Gaines,et al.  Adsorption Studies on Clay Minerals. II. A Formulation of the Thermodynamics of Exchange Adsorption , 1953 .

[11]  M. Bradbury,et al.  Modelling the sorption of Zn and Ni on Ca-montmorillonite , 1999 .

[12]  M. Schlegel,et al.  Sorption of Metal Ions on Clay Minerals: II. Mechanism of Co Sorption on Hectorite at High and Low Ionic Strength and Impact on the Sorbent Stability , 1999 .

[13]  M. Bradbury,et al.  A mechanistic description of Ni and Zn sorption on Na-montmorillonite Part II: modelling , 1997 .

[14]  M. Avena,et al.  Proton Adsorption and Electrokinetics of an Argentinean Montmorillonite , 1998 .

[15]  Mikazu Yui,et al.  Diffusion behavior for Se and Zr in sodium-bentonite , 1994 .

[16]  R. J. Hunter.  The interpretation of electrokinetic potentials , 1966 .

[17]  A. Maes,et al.  Thermodynamics of transition metal ion exchange in montmorillonite , 1975 .

[18]  M. Bradbury,et al.  Analysis of the porewater chemical composition of a Spanish compacted bentonite used in an engineered barrier , 2004 .

[19]  D. Oscarson,et al.  Diffusion of14C in dense saturated bentonite under steady-state conditions , 1994 .

[20]  K. Combs,et al.  Cobalt(II) Oxide Solubility and Phase Stability in Alkaline Media at Elevated Temperatures , 1999 .

[21]  José Linares,et al.  Experimental kinetic study of the smectite-to-illite transformation , 1996 .