Sodium-Lithium Exchange Equilibria on Vermiculite at 25° and 50°C

Abstract

Abstract-Sodium-lithium exchange equilibria between dilute aqueous chloride solutions and 0.2-62/z Transvaal, South African vermiculite were studied at 25 ~ and 50~ using a dialysis technique. The K content of the vermiculite was reduced to < 1% of the exchange capacity of 2.14 me/g by exhaustive extraction using Na-tetraphenylboron. The thermodynamic equilibrium constants and in turn the standard free energies and heats of exchange were evaluated from the equilibrium selectivity coefficients at the two temperatures. The standard entropy of exchange, AS ~ was calculated according to the relationship AG ~ = AH ~ --TAS ~ Similar results were obtained for Na ~ Li and Li ~ Na exchange at 25~ thus confirming the reversibility of the reaction.Sodium preference increased with Na saturation of the vermiculite and equilibrium selectivity coefficients ranged from 6-0 to 22.0 at 25~ In comparison, selectivity coefficients for Na-Li exchange on montmorillonite ranged from 1.0 to 2.0 and became smaller with increasing Na saturation. The standard free energy and heat of exchange on vermiculite at 25~ were-1444 and-5525 cal mole -1, respectively, resulting in a AS ~ value of-13.7 e.u. This relatively large entropy change is probably due to differences in ion hydration in the solution and surface phases.

Ion Exchanged Vermiculites with Lower Expansion Onset Temperatures

“…This is in agreement with previous study which also showed that the quantity of water released was 9 more than expected from the dehydroxylation of vermiculite itself [43]. In K-vermiculite, all typical vermiculite features had disappeared and the lattice had drastically collapsed [7]. By the same token, the typical well-ordered mica-like structure reflection at 2θ = 8.74° (10.10 nm) was mostly observed (Fig.…”

“…The frequency of the shaker was adjusted to 200 rpm (rotations per minute). For these experiments, 50 g of vermiculite were weighed out and enough salt was added to prepare 250 ml of saturated salt solution: vermiculite selectivity rises with increase of the preferred ion loading [7,28]. The ion-exchanged vermiculites were washed thoroughly with distilled water until all chloride anions were quantitatively removed.…”

“…Unlike the potassium cations in biotite, the hydrated interlayer ions (usually magnesium ions) in the vermiculite layers are easily exchanged [5][6][7][8][9]. Palabora vermiculite, like other commercial types, shows considerable variability in both composition and cation exchange capacity (CEC).…”

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

“…: Na-Cs (Maes and Cremers, 1978); Chambers mont. : Na Cs (Cremers and Thomas, 1968) and Li ~ Na (Gast and Klobe, 1971); hectorite: Na ~ Cs (Maes and Cremers, 1978); Otay mont. : Na ~ K (Shainberg et al, 1987) and Na ~ Cs (Maes and Cremers, 1978); Polkville mont.…”

“…: Na ~ K (Shainberg et al, 1987) and Na ~ Cs (Maes and Cremers, 1978); Polkville mont. : Na ~ K (Shainberg et al, 1987); Transvaal vermiculite: Na ~ Li (Gast and Klobe, 1971); Utah bentonite: Na ~ K (Tabikh et al, 1959) and Na ~ Rb (Kunishi and Heald, 1968); Upton mont. : Na K (Shainberg et al, 1987); Wyoming bentonite: Na ~ Li (Tabikh et al, 1960).…”