Theoretical study for uranium isotope fractionation caused by biotic reduction

Abstract

Microbial uranium reduction from hexavalent to tetravalent is of interest in terms of bioremediation and paleontology. During microbial reduction, heavier isotopes are more concentrated in tetravalent products, whereas abiotic reductions show various isotopic trends. In this study, to clarify the isotope fractionation mechanism of biological reduction, theoretical calculations of the equilibrium isotope fractionation coefficient for each elementary reaction was carried out using relativistic ab initio method. We also introduce a steady-state model and interpret the experimental values obtained by the Rayleigh fitting in biotic and abiotic reductions.Microbial uranium reduction from hexavalent to tetravalent is of interest in terms of bioremediation and paleontology. During microbial reduction, heavier isotopes are more enriched in tetravalent products, whereas abiotic reductions show various isotopic trends. In this study, to clarify the isotope fractionation mechanism of microbial reduction, theoretical calculations of the equilibrium isotope fractionation coefficient for each reaction step were carried out using relativistic ab initio method. We also introduced a steady-state model and interpreted the experimental values obtained by the Rayleigh fitting in biotic and abiotic reductions.