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Alkali Cation Selectivity and Surface Charge of 2:1 Clay Minerals

Alkali Cation Selectivity and Surface Charge of 2:1 Clay Minerals,10.1346/CCMN.1992.0400511,Clays and Clay Minerals,Shihe Xui,James B. Harsh

Alkali Cation Selectivity and Surface Charge of 2:1 Clay Minerals   (Citations: 10)
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Abstract--A critical demand,in environmental,modeling,and a desirable but elusive goal of research on the ion exchange,properties of the charged,solid surface has been to determine,the selectivity coefficient from,fundamental,properties of the ions and,surface. We developed,a Hard and,Soft Acid and,Base (HSAB) Model to describe exchangeable,cation selectivity on solid surfaces. Our previous,work,has shown that the model,quantitatively,describes alkali cation exchange,on clay minerals,in terms of the absolute etectronegativity and softness of the exchangeable,cations and two fitting parameters: a and/3. This study was conducted,to determine,the relationship between,a and/3 and surface charge characteristics of 2:1 clays. The layer charge and,cation selectivity of seven smectites,and one vermiculite,were,used. The regression of log K ~ against four combinations,of charge properties was performed,and the appropriate relationship between a,/3, and surface charge was selected based on both statistical criteria (R 2) and their consistency with the assumptions,of the HSAB model. The selected model,was then cross-validated using separate cation exchange,data from,the literature. It was found that a and/3 are linearly related to the amount of charge arising from mineral tetrahedral and octahedral sites, respectively. These results make it possible to predict the alkali cation selectivity of 2:1 clay minerals,from,their chemical,composition data and the alkali cation properties. Key Words--Hard/soft acid/base model, Ion exchange, Isomorphic substitution, Layer charge, Lewis acid, Lewis base, Smectite, Surface complexation, Vermiculite.
Journal: Clays and Clay Minerals - CLAYS CLAY MINER , vol. 40, no. 5, pp. 567-574, 1992
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    • ... concept has been taken farther and used to quantitatively derive thermodynamic equilibrium constants for cation exchange from electronegativities and softness parameters (Xu and Harsh, 1990b) Indeed, these quantitative predictions have been ‘‘verified’’ (Xu and Harsh, 1990a) for series [1] interacting with several clay minerals, and the computed parameters used to posit specific adsorption mechanisms operant in the exchange reactions (Xu and ...
    • ... due to the larger size (r in Table 1) of the Cs1 cation, resulting in an overall free energy change that strongly favored K1 (Fig. 1). These results are very reasonable in a physicochemical sense, and they are also the conditions implied by the thermodynamic energy balance depicted in Fig. 2. We do not exclude the possibility of partially covalent interactions between Cs1 and smectite surfaces, but we do disagree with assertions (Xu and Harsh, ...

    Brian J. Teppenet al. Hydration Energy Determines Isovalent Cation Exchange Selectivity by C...

    • ...Following the HSAB theory of Pearson (Pearson, 1963, 1968) the interlayer cations and the silicate layer of smectites can be considered Lewis acids and bases, respectively (Xu and Harsh, 1992)...
    • ...The location of the layer charge determines the strength of the Lewis base: smectite behaves as a soft base when the layer charge is located in octahedral sites, whereas it behaves as a hard base when the charge is located in the tetrahedral sheet (Xu and Harsh, 1992)...

    Maria Franca Brigattiet al. Effects of Exchange Cations and Layer-Charge Location on Cysteine Rete...

    • ...These values are in agreement with the literature (Xu and Harsh 1992)...
    • ...Xu and Harsh (1990b, 1992) used the softness values given by Parr and Pearson (1983)...

    M. Auboirouxet al. Hard and Soft AcidBase Model Applied to Bivalent Cation Selectivity on...

    • ...interlayer cations can be considered as Lewis bases and acids respectively (Xu and Harsh, 1992...
    • ...base and vermiculite as a hard base (Xu and Harsh, 1992)...

    D. Malferrariet al. Sorption kinetics and chemical forms of Cd(II) sorbed by amino acid cy...

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