Adsorption Studies on Clay Minerals. VI. Alkali Ions on Attapulgite

Merriam, C. Neale; Thomas, Henry C.

doi:10.1063/1.1742726

Cited by 15 publications

(4 citation statements)

References 3 publications

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“…In the second procedure, both isotopes 6 Li and 7 Li were considered in the starting seawater solution, and the selective adsortion of each one on clay mineral surfaces was calculated form the mass action law, by using two separate half reactions:

^{7} {Li}^{+} + X \Rightarrow^{7} LiX (log K = - 0.0 8)

^{6} {Li}^{+} + X \Rightarrow^{6} LiX ({log K}_{k a o l} = - 0.0 713; {log K}_{v e r m} = - 0.0 679)

where the ratio between the equilibrium constants was constrained to be equal to the alpha factionation factor, given by Zhang et al . [], and log K values were taken from the PHREEQC database [ Merriam and Thomas , ].…”

Section: Methodssupporting

confidence: 87%

Tracking the weathering of basalts on Mars using lithium isotope fractionation models

Fairén

Losa-Adams

Gil-Lozano

et al. 2015

Geochem Geophys Geosyst

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Lithium (Li), the lightest of the alkali elements, has geochemical properties that include high aqueous solubility (Li is the most fluid mobile element) and high relative abundance in basalt‐forming minerals (values ranking between 0.2 and 12 ppm). Li isotopes are particularly subject to fractionation because the two stable isotopes of lithium—7Li and 6Li—have a large relative mass difference (∼15%) that results in significant fractionation between water and solid phases. The extent of Li isotope fractionation during aqueous alteration of basalt depends on the dissolution rate of primary minerals—the source of Li—and on the precipitation kinetics, leading to formation of secondary phases. Consequently, a detailed analysis of Li isotopic ratios in both solution and secondary mineral lattices could provide clues about past Martian weathering conditions, including weathering extent, temperature, pH, supersaturation, and evaporation rate of the initial solutions in contact with basalt rocks. In this paper, we discuss ways in which Martian aqueous processes could have lead to Li isotope fractionation. We show that Li isotopic data obtained by future exploration of Mars could be relevant to highlighting different processes of Li isotopic fractionation in the past, and therefore to understanding basalt weathering and environmental conditions early in the planet's history.

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^{7} {Li}^{+} + X \Rightarrow^{7} LiX (log K = - 0.0 8)

^{6} {Li}^{+} + X \Rightarrow^{6} LiX ({log K}_{k a o l} = - 0.0 713; {log K}_{v e r m} = - 0.0 679)

Section: Methodssupporting

confidence: 87%

Tracking the weathering of basalts on Mars using lithium isotope fractionation models

Fairén

Losa-Adams

Gil-Lozano

et al. 2015

Geochem Geophys Geosyst

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“…Another interesting point shown in Figure 2 is that the selectivities of alkali cation exchange on attapulgite (Merriam andThomas, 1956, Marshall andGarcia, 1959) also fit the model, although it is not a 2:1 clay mineral. On the other hand, the selectivity of alkali cation exchange on a natural zeolite did not fit the model (data not shown).…”

Section: Cross Validationmentioning

confidence: 95%

“…Figure 2. The comparison of the measured log Kv ~ with the log K ~ predicted from the amount of tetrahedral and octahedral charge for the following exchange reactions (with the source of exchange data in parentheses), Attapulgite: Na ~ K (Na replaced by K), Na ~ Rb, Na ~ Cs (Marshall and Garcia, 1959;Merriam and Thomas, 1956); Belle Fourche mont. : Na K (Shainberg et al, 1987); Bayard mont.…”

Section: Cross Validationmentioning

confidence: 99%

“…For Upton Wyoming and Chambers montmorillonites, both exchange data and chemical analysis were obtained from Gast (1972). For others, the tetrahedral and octahedral charges were calculated from the total elemental analysis data from 4"---1954; (10) Foster, 1963;(11) Gast, 1972;(12) Grim and Guven, 1978;(13) Kittrick, 1973;(14) Laird, 1987;(15) Lagaly, 1982;(16) Mattigod and Sposito, 1978;(17) Merriam and Thomas, 1956;(18) Norrish, 1973;(19) Senkayi et al, 1985;(20) Shirozu and Bailey, 1966;(21) Schultz, 1969;(22) Sterte and Shabtai, 1987;(23) Van Olphen and Fripiat, 1979;(24) Weaver and Pollard, 1973;(25) Weir, 1965;(26) this study.…”

Section: Layer Chargementioning

confidence: 99%

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

Harsh

1992

Clays and clay miner.

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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.

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