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Ion Exchange Behavior of the Febex Bentonite. 1. Na/K, Na/Mg and Na/Ca Experimental Exchange Isotherms

Published online by Cambridge University Press:  21 March 2011

F.J. Huertas ,
P. Carretero ,
J. Delgado ,
J. Linares  and
J. Samper
F.J. Huertas
Affiliation:
Department of Earth Sciences and Environmental Chemistry, Estación Experimental del Zaidín, CSIC, Profesor Albareda 1, 18008 Granada, Spain
P. Carretero
Affiliation:
E.T.S. de Ingenieros de Caminos, Canales y Puertos, Universidade da Coruथa, Campus de Elviथa s/n, 15192 A Coruथa, Spain
J. Delgado
Affiliation:
E.T.S. de Ingenieros de Caminos, Canales y Puertos, Universidade da Coruथa, Campus de Elviथa s/n, 15192 A Coruथa, SpainEmail: delgado@iccp.udc.es
J. Linares
Affiliation:
Department of Earth Sciences and Environmental Chemistry, Estación Experimental del Zaidín, CSIC, Profesor Albareda 1, 18008 Granada, Spain
J. Samper
Affiliation:
E.T.S. de Ingenieros de Caminos, Canales y Puertos, Universidade da Coruथa, Campus de Elviथa s/n, 15192 A Coruथa, Spain
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Abstract

Na/K, Na/Mg, and Na/Ca exchange isotherms have been experimentally determined for the FEBEX bentonite. Na-homoionized FEBEXbentonite was reacted at room temperature with mixedsalt dissolution of NaCl/KCl, NaCl/MgCl2, or NaCl/CaCl2, while keeping a total cation normality of 0.5 eq L-1. Isotherm exchange experiments were performed using ten (duplicated)experimental points, which cover the complete range of the corresponding binary equivalent fractions. Results indicate that for the Na/K exchange reaction, Vanselow coefficients are larger than one, what is in agreement with the tendency of the smectite of having greater affinity for K than for Na. The exchange constant decreases as K progressively replaces Na in the smectite. This tendency ends when the equivalent fraction of potassium, EK, reaches a value of around 0.250.3. From this point to higher K contents, it remains nearly constant irrespective of EK but slightly decreasing again at values near one. The Vanselow selectivity coefficient for the Na/Mg isotherm indicates a preference for the divalent cation. It is nearly constant (Kv ≍ 5.6) for EMg < 0.6, but increases up to 10.2 for a nearly Mg-saturated smectite.

The Na/Ca exchange resembles that of Na/Mg, although the selectivity coefficients are larger (Kv ≍ 7.0 for ECa < 0.6). The comparison of the selectivity coefficients for the Na/Mg and Na/Ca exchange reactions indicates that the smectite has a slightly higher affinity for Ca than for Mg. This result is consistent with those observed for the Wyoming bentonite.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 663: Symposium – Scientific Basis for Nuclear Waste management XXIV , 2000 , 589
Copyright
Copyright © Materials Research Society 2001

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References

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