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

Xu, Shihe; Harsh, James B.

doi:10.1346/ccmn.1992.0400511

Cited by 38 publications

(17 citation statements)

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“…Recently, following Pearson's HSAB theory (1963, 1968), Xu & Harsh (1992) demonstrated that the alkali cation selectivity of the 2:1 clays could be quantitatively predicted from the net tetrahedral and octahedral charge of the mineral, which behaves as ligand, and from the absolute electronegativity and softness of the exchangeable cations. Cations and ligands are generally Lewis acids and bases, respectively, of different strengths: for example, alkali metal cations are hard, Zn 2+ and Pb 2+ are borderline, and Hg 2+ and Cd 2+ are soft acids, while OH-and H20 are hard, NO~ and SO~-are borderline, and CN-and CO are soft bases.…”

Section: Pb 2+mentioning

confidence: 99%

“…The variability between Zn 2+-and pb2+-treated smectites in the interlayer water content depends both upon cation electrostatic features and upon smectite layer charge localization. The greatest water content was observed in Cation exchange between metals from interstitial solutions and 2:1 phyllosilicates is a major process affecting the retention of toxic contaminants in the vadose zone and influencing both plant growth and water quality.Recently, following Pearson's HSAB theory (1963, 1968), Xu & Harsh (1992) demonstrated that the alkali cation selectivity of the 2:1 clays could be quantitatively predicted from the net tetrahedral and octahedral charge of the mineral, which behaves as ligand, and from the absolute electronegativity and softness of the exchangeable cations. Cations and ligands are generally Lewis acids and bases, respectively, of different strengths: for example, alkali metal cations are hard, Zn 2+ and Pb 2+ are borderline, and Hg 2+ and Cd 2+ are soft acids, while OH-and H20 are hard, NO~ and SO~-are borderline, and CN-and CO are soft bases.…”

mentioning

confidence: 99%

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The influence of layer charge on Zn²⁺ and Pb²⁺ sorption by smectites

et al. 1996

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pB 2+ABSTRACT: Two smectites with different layer charge localization were used to characterize the chemical and structural aspects of minerals treated with 1.9 x 10 .2 M and 1 M heavy metal solutions (Zn 2 § and pb2+). Natural and treated smectites were analysed by: (1) X-ray powder diffraction first at 25~ and relative humidity of 60% and then at increasing temperature up to 400~ (2) thermogravimetric and differential thermal analysis; (3) X-ray fluorescence; (4) atomic absorption and UV visible spectrophotometries. The sorption of both metals depends on 2:1 layer features and is enhanced when the total layer charge is mostly due to substitution in the octahedral sheet. The variability between Zn 2+-and pb2+-treated smectites in the interlayer water content depends both upon cation electrostatic features and upon smectite layer charge localization. The greatest water content was observed in Cation exchange between metals from interstitial solutions and 2:1 phyllosilicates is a major process affecting the retention of toxic contaminants in the vadose zone and influencing both plant growth and water quality.Recently, following Pearson's HSAB theory (1963, 1968), Xu & Harsh (1992) demonstrated that the alkali cation selectivity of the 2:1 clays could be quantitatively predicted from the net tetrahedral and octahedral charge of the mineral, which behaves as ligand, and from the absolute electronegativity and softness of the exchangeable cations. Cations and ligands are generally Lewis acids and bases, respectively, of different strengths: for example, alkali metal cations are hard, Zn 2+ and Pb 2+ are borderline, and Hg 2+ and Cd 2+ are soft acids, while OH-and H20 are hard, NO~ and SO~-are borderline, and CN-and CO are soft bases. Hard acids prefer to bind to hard bases, while soft acids prefer to bind to soft bases. The location of layer charge (X 1+) in smectite determines the strength of the clay ligand and can affect the selectivity of metals: smectite behaves as a soft base when the layer charge is located in the octahedral sites, while it behaves as a hard base

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Section: Pb 2+mentioning

confidence: 99%

mentioning

confidence: 99%

The influence of layer charge on Zn²⁺ and Pb²⁺ sorption by smectites

et al. 1996

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“…Following the HSAB theory of Pearson (Pearson, 1963(Pearson, , 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).…”

Section: Introductionmentioning

confidence: 99%

“…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). Since hard bases link preferentially with hard acids, and soft bases with soft acids, the smectite layer-charge location strongly affects the cation selectivity.…”

Section: Introductionmentioning

confidence: 99%

Effects of Exchange Cations and Layer-Charge Location on Cysteine Retention by Smectites

Brigatti

Lugli

Montorsi

et al. 1999

Clays and clay miner.

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Abstract--This study investigates the complexes formed between amino acids, which are the natural degradation products of organic matter, and smectites. Thus, the adsorption and desorption behavior of cysteine and Na-, Ca-, Cu-homoionic smectites with different layer-charge location, a montmorillonite, and a beidellite, were studied. The clay samples were treated with Na, Ca, and Cu 1 N solutions and then with a 0.2 M cysteine solution. To test smectite-cysteine stability at acidic pH, the solids obtained were repeatedly treated with distilled water acidified to pH = 5. All treated samples were characterized by thermal, X-ray diffraction, chemical, and infrared analyses. The results showed that: 1) Na-and Carich smectites adsorbed and retained small amounts of cysteine, and did not show interlayer cationcysteine complexes, whereas the amino acid was strongly retained in the interlayer by Cu-rich smectites; 2) d(001)-values for Na-and Ca-rich smectites showed little or no expansion, whereas for the Cu-rich smectites the intercalation of the organic molecule produced a swelling of the structure; 3) the interaction mechanism of homoionic smectites with cysteine in an aqueous medium occurs by weak interactions, (e.g., van der Waals interactions, hydrogen bonding, dipole-dipole interactions, and other electrostatic forces such as entropy-driven hydrophobic bonding), and/or by complexes involving interlayer cations and organic ligands. The formation of a stable chelate complex with the saturating ion permits cysteine to be adsorbed by Cu(II)-rich smectites and to be resistant to migration in soils and groundwaters.

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“…Deconvolution procedures assuming all lineshapes to be Lorentzian, were applied if the doublet was insufficiently resolved (Grandjean and Laszlo 1989;Delville et al 1991). Hectorite (from Hector, California), purified according to standard procedure (Fripiat et al 1982), is affected by isomorphous cationic substitution in the octahedral layer only (Xu and Harsh 1992). A montmorillonite sample (from Gonzales County, Texas) has 652 ' 80 mg/3 ml H20"CD3CN (95/5; V/V); T = 299 K.…”

mentioning

confidence: 99%