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Geochimica et Cosmochimica Acta 168 (2015) 133–150 www.elsevier.com/locate/gca
Lithium isotope fractionation during uptake by gibbsite
Josh Wimpenny a,⇑, Christopher A. Colla a, Ping Yu b, Qing-Zhu Yin a, James R. Rustad a, William H. Casey a,c
a Department of Earth and Planetary Sciences, University of California, One Shields Avenue, Davis, CA 95616, United States b The Keck NMR Facility, University of California, One Shields Avenue, Davis, CA 95616, United States c Department of Chemistry, University of California, One Shields Avenue, Davis, CA 95616, United States
Received 5 November 2014; accepted in revised form 8 July 2015; available online 15 July 2015
Abstract
The intercalation of lithium from solution into the six-membered l2-oxo rings on the basal planes of gibbsite is well-constrained chemically. The product is a lithiated layered-double hydroxide solid that forms via in situ phase change. The reaction has well established kinetics and is associated with a distinct swelling of the gibbsite as counter ions enter the interlayer to balance the charge of lithiation. Lithium reacts to fill a fixed and well identifiable crystallographic site and has no solvation waters. Our lithium-isotope data shows that 6Li is favored during this intercalation and that the solid-solution fractionation depends on temperature, electrolyte concentration and counter ion identity (whether Cl ,NO3 or ClO4 ). We find that the amount of isotopic fractionation between solid and solution (DLisolid-solution) varies with the amount of lithium taken up into the gibbsite structure, which itself depends upon the extent of conversion and also varies with electrolyte concentration and in the counter ion in the order: ClO4