Ab initio evaluation of boron isotope fractionation factors in Salt Lake Brine

<p indent="0mm">Boron isotopes have found extensive applications in fields such as source tracing and paleoenvironmental research. It is important to obtain accurate boron isotope equilibrium fractionation factors between different boron species in brine to study boron isotope geochemistry in salt lakes. These boron species include boric acid (B(OH)₃), borate ion (B(OH)₄⁻) and polyborate ion B₃O₃(OH)₄⁻, B₃O₃(OH)₅²⁻, B₄O₅(OH)₄²⁻ and B₅O₆(OH)₄⁻. In this study, the boron isotope equilibrium fractionation factors between B(OH)₃ and B(OH)₄⁻ and polyborate ions in brine were accurately calculated by quantum chemical calculation method, and the effects of anharmonic effect and solvation effect on the calculation results were corrected. According to the results, the equilibrium boron isotope fractionation factors between B(OH)₃ and B(OH)₄^– and polyborate ions are as follows: <italic>α</italic>_3-4<italic> </italic>= 1.0286, <italic>α</italic>_3-334<italic> </italic>= 1.0389, <italic>α</italic>_3-335<italic> </italic>= 1.0717, <italic>α</italic>_3-45<italic> </italic>= 1.0889, <italic>α</italic>_3-56<italic> </italic>= 1.1180, <italic>α</italic>_4-334<italic> </italic>= 0.9545, <italic>α</italic>_4-335<italic> </italic>= 0.9849, <italic>α</italic>_4-45<italic> </italic>= 0.9728, <italic>α</italic>_4-56<italic> </italic>= 0.9711. The identification of these fractionation factors provides foundational data and theoretical insights into the boron isotope fractionation occurring during the transport of boron in salt lakes brine.