Research:

Kinetic isotopic fractionation by Diffusion

This research involves measurements of the isotopic fractionation of various dissolved species due to diffusion in silicate and aqueous fluids. The goal is to understand the phenomenon of kinetic isotopic fractionation by diffusion in condensed media, and the implications for the structure and behavior of dissolved complexes.

We expect the research to provide isotopic fingerprints for diffusive transport in geologic systems. Our results so far, indicate that the magnitude of fractionation of Li isotopes during aqueous diffusion is much smaller than predicted by theory or previous experimental estimates (see Richter et al. 2006; link below). This is due in part to Li diffusing as an aqueous complex. Further sets of experiments comparing diffusion in normal water to diffusion in heavy water should allow the direct calculation of the average number of waters in the hydration sphere of Li.

We are investigating isotopic fractionation of other elements, including K and the noble gases, during diffusion in water and across semi-permeable membranes. The results of experiments will provide feedback to molecular dynamic models of water and ion complexes. We are also investigating isotopic evidence of diffusive exchange between mafic and silicic silicate melt in natural systems.

Publication

Richter, FM, Mendybaev, RA, Christensen, JN, Hutcheon, ID, Williams, RW, Sturchio, NC and Beloso Jr., AD (2006) Kinetic isotopic fractionation during diffusion of ionic species in water. Geochimica et Cosmochimica Acta, v.70(2), pp.277-289.