Equilibrium barium isotope fractionation between minerals and aqueous solution from first-principles calculations

Barium isotopes could be a novel tracer in low-temperature geochemical processes such as the Ba cycle rivers and oceans. Equilibrium isotope fractionation between Ba-hosting minerals aqueous solution is of great importance for applications geochemistry, but it remains poorly constrained. In this study, we performed first-principles calculations based on density functional theory (DFT) to determine equilibrium (103ln?mineral-Ba_aq 137Ba/134Ba). The structural properties Ba2+ are well predicted by molecular dynamics (FPMD) simulation 121 snapshots extracted from FPMD trajectories estimate reduced partition function ratio (? factor or 103ln? 137Ba/134Ba) Ba2+. decreases sequence aragonite > calcite ? witherite barite. ? dominantly determined force constant, which affected both average BaO bond length coordination number. Our results show that 103ln?aragonite-Ba_aq 103ln?witherite-Ba_aq 0.36‰ ?0.02‰ at 300 K, respectively, consistent with experimental studies equilibrium. depletion heavy observed natural corals relative seawater suggests kinetic effects play an important role during coral growth. 103ln?barite-Ba_aq only ?0.17‰ indicating limited caused removal stemmed inorganic barite precipitation. Overall, factors calculated study provide guideline geochemistry.