Theoretical and Experimental Study on Vanadium Isotope Fractionation among Species Relevant to Geochemistry

Abstract

The application of vanadium (V) stable isotopes to trace various geological and biological processes is an emerging field. Vanadium can exist in several redox states and in various coordination environments, such that its isotopic composition could be used to trace its exchange between different phases during these processes. In order to provide a basis for interpreting natural data, we have computed theoretical isotope fractionation factors of V among various species relevant to geological and biological environments. To validate the accuracy of the calculations, we performed laboratory experiments to evaluate the V isotopic fractionation between organic and aqueous phases. The laboratoryscale experiment via liquid−liquid extraction with the aqueous phase of V in HCl and the organic phase of dicyclohexano-18-crown-6 (DC18C6) in 1,2-dichloroethane was performed. The magnitude of the isotope fractionation factor for the 51 V/ 50 V ratio between the aqueous and organic phases, which was found to vary between −0.1 and +1.35‰ depending on HCl molarity, is well explained by our theoretical isotope fractionation factors (ln β) obtained by the density functional theory method for V(IV) model molecules. We have also estimated the relative effect of the nuclear field shift (NFS) effect and the conventional mass-dependent isotope fractionation, where the NFS effect was found to be marginal (∼0.025‰) on the V isotope fractionation. This theoretical approach is applied to obtain ln β for various V species relevant to geological and biological environments which are discussed with regard to understanding natural variations of the V isotopes.

Vanadium in the Environment: Biogeochemistry and Bioremediation

“…Coupled V–Fe isotope analysis has also shown that V in silicate minerals was released during chemical weathering and adsorbed on colloidal Fe (oxyhydr)­oxides, which were transported by water flow along the latosol profile . When V migrated between the aqueous and organic phases, the V isotope fractionation factor for the 51 V/ 50 V ratio varied between −0.1 and +1.35‰ …”

Rapid determination of V isotopes with MC-ICP-MS: new developments in sample purification

“…[10][11][12][13][14][15][16][17][18][19][20][21] Vanadium isotope compositions are generally reported as d 51 V values, which are the deviations of V isotope ratios relative to AA-V solution: 10 d 51 V = [( 51 V/ 50 V sample )/ ( 51 V/ 50 V AA ) − 1] × 1000&. Large V isotope fractionations have been predicted by theoretical and experimental studies, [22][23][24] and observed in natural samples, which implies their wide application to study geological processes. The distinct d 51 V in chondritic meteorite, 25,26 Martian, 27 lunar, 28 and terrestrial materials 29,30 were proposed to reect V isotope fractionation during planetary differentiation in the Solar System and the formation of the Moon.…”