The Heterogeneity of the Charge Density in Montmorillonites

Stul, M.S

doi:10.1346/ccmn.1974.0220505

Cited by 87 publications

(64 citation statements)

References 11 publications

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“…Using alkyl ammonium ions of increasing chain length, Lagaly and Weiss (1976) characterized about 200 montmorillonites into six groups based on layer charge distribution. Using a similar technique, Stul and Mortier (1974) found that Wyoming bentonite had 9 and Camp Berteau montmorillonite 6 interlayer-cation density classes, the former being the most heterogeneous of the six montmorillonites examined. They found that no layer-charge density class dominated the physicochemical properties of these materials and that ionic substitution was discontinuous, its contribution to the gross SCD being different for each sample.…”

Section: Classification Of the Heterogeneity Of Chargementioning

confidence: 99%

Charge Heterogeneity in Smectites

Talibudeen

1983

Clays and clay miner.

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The heterogeneity of sites for Ca---~K exchange was examined by microcalorimetry in the <0.2-/zm fractions of some selected smectites. Six groups of sites, ranging in exothermic exchange enthalpy (-d(AHx)/dx) from 5.7 to 10.9 kJ/eq were identified. In Wyoming bentonites, only three groups with enthalpies of 5.7 to 7.5 kJ/eq were distinguished, although in the 0.2-1.0-p~m fraction, a 10.7-kJ/eq group was also observed. Redhill and Camp Berteau smectites contained, in addition, groups with enthalpies of 8.7-10.9 kJ/eq, but a New Mexico sample only had groups with the higher values. Thus, the exchange enthalpies of four main groups of sites (reclassified from those observed) appear to be inversely related to the extents of interlayer expansion in the samples by the adsorption of polar molecules. Consequently, a 'true montmorillonite,' such as a <0.2-/~m Wyoming bentonite, contains only fully expanding layers with -d(AHx)/ dx values between 5.7 and 7.5 kJ/eq. As such, it is less heterogeneous and should have a much greater swelling capability than Camp Berteau montmorillonite which has, in addition, groups with exchange enthalpies of 8.7 and 10.3 kJ/eq.

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Section: Classification Of the Heterogeneity Of Chargementioning

confidence: 99%

Charge Heterogeneity in Smectites

Talibudeen

1983

Clays and clay miner.

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“…Lee et al (1989) found that water sorption by TMA limited the sorption of aromatic molecules larger than benzene by TMA-smectites. Sheng et al (1997) found that the heterogeneous charge density of smectites noted by Stul and Mortier (1974) leads to micropores with a heterogeneous size distribution in TMPA-smectites. Similarly, Sheng and Boyd (1998) examined mixed Ca/TMPA-smectites and found that TMPA cations function as nonhydrated interlayer pillars, and organic-solute adsorption occurs predominantly on the siloxane surfaces and is not associated with the TMPA cations.…”

Section: Introductionmentioning

confidence: 99%

Sorption of Benzene, Toluene, Ethylbenzene, and Xylene (BTEX) Compounds by Hectorite Clays Exchanged with Aromatic Organic Cations

Jaynes

Vance

1999

Clays and clay miner.

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Abstract--Adsorptive-type organoclays, where hydrocarbons adsorb directly to the siloxane surfaces, were studied to find new organic cations and to determine the parameters that produce effective sorbents. Organoclays were prepared from hectorite by cation exchange with small, aromatic organic cation salt solutions. Trimethylphenylammonium (TMPA) chloride was obtained and iodide salts of commerciallyunavailable aromatic cations were synthesized and used to prepare organoclays. An aqueous mixture of benzene, toluene, ethylbenzene, and xylenes (BTEX) consistent with the composition of unleaded gasoline was used in sorption isotherms to compare the sorptive properties of the organoclays. Only the TMPA, methylphenylpyridinium (MPPyr), and trimethylammonium indan (Indan) organoclays were effective BTEX sorbents. Organoclays prepared from methylpyridinium (MPyr), trimethylammonium biphenyl (Biphenyl), and trimethylammonium fluorene (Fluorene) were poor sorbents. The MPPyr and TMPA organoclays preferentially sorbed ethylbenzene, whereas the Indan organoclay preferentially sorbed benzene and toluene. Langmuir-type sorption isotherms for the TMPA, MPPyr, and Indan organoclays implied surface adsorption, whereas linear isotherms suggested that partitioning was the sorptive mechanism for the MPyr, Biphenyl, and Fluorene organoclays. Water hydrating the small MPyr cation and the larger bulk of the Biphenyl and Fluorene cations may have blocked BTEX access to the interlayer siloxane surfaces. Although the rather bulky MPPyr and Indan cations produced effective organoclays, compact size and low hydration are organic cation properties that typically yield effective adsorptive-type organoclays.

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“…Ae = 46.5/ 2~:'/~z = the equivalent area or the area available per Dabco charge, and A~ = the cross-sectional area of the cation. ~:' = ~ • 383/950, in which ~ = 0.314~/(Si,A1)4010 (Stul and Mortier, 1974), and 950 = the microequivalents of Dabco in a simply exchanged Dabco-Moosburg clay. Therefore, h = 7.75 A and 8.86 A for Ar = 40 and 28/~z, respectively.…”

Section: Resultsmentioning

confidence: 99%