nai

Project Progress

Over the past year PhD student Pamela Hill (ESS, UCLA) and COI Schauble, with assistance from Anat Shahar, Ed Young, and Eric Tonui, have continued experiments with diethyl ether/aqueous solution mixtures aimed at measuring the effects of solution chemistry and oxidation state on iron-isotope fractionations. Initial results are shown in Figure 1. The data show the change in ⁵⁶Fe/⁵⁴Fe fractionation between iron (Fe³⁺) dissolved in aqueous solutions of varying HCl concentration (at constant total HCl + HNO₃ acidity), and FeCl₄^— dissolved in a coexisting, immiscible ether solution. The results show a definite drop in ether/aqueous fractionation as chloride concentration increases. This result is consistent with theoretical modeling by Ms. Hill and the COI’s previous work (Schauble et al., 2001, GCA v. 65, p. 2487-2497), which found that ⁵⁶Fe/⁵⁴Fe tends to decrease in complexes with Fe-Cl bonds, relative to complexes and minerals with Fe-O bonds. As the activity of chloride in the solution increases, more Fe-Cl complexes form, and the aqueous solution more closely resembles the FeCl₄^—-bearing ether solution. These results are significant for astrobiology because they demonstrate that non-redox processes can fractionate iron isotopes at equilibrium, and suggest that bond partner effects may play a role in causing differences between biological and inorganic fractionations.

Ongoing work will include reversal experiments with isotopic spikes to demonstrate the attainment of equilibrium, and the addition of Fe₂⁺ (ferrous iron) to the aqueous solutions to investigate reduction/oxidation effects.

Pamela Hill will be presenting initial results of her research at the 2006 Goldschmidt conference in Melbourne, Australia.

{{ 1 }}