Gallium isotope fractionations between several important Gallium- bearing minerals and aqueous solutions

Abstract

This study predicts the equilibrium isotope fractionation factors for some important Ga-bearing species, including major minerals, aqueous solutions and gas phase systems. Equilibrium isotope fractionations of Ga are investigated by using first-principles quantum chemistry method at B3LYP/6-311+G(d) level. The isotope fractionation factors of minerals Orthoclase, Albite, Quartz, Kaolinite, Forsterite, Montmorillonite, Gibbsite, Cassiterite, Aragonite, Sphalerite and Calcite are calculated with the method of the volume variable cluster model (VVCM). The 1000ln(RPFR)s of these minerals decrease in the following order: Orthoclase>Albite>Quartz>Kaolinite>Forsterite>Montmorillonite>Gibbsite>Cassiterite>Aragonite>Sphalerite>Calcite. The solvation effect of Ga3+-bearing aqueous species is modeled by the water-droplet method. The 1000ln(RPFR)s of Ga3+-bearing aqueous species decrease in the order of [Ga(OH)4]->[Ga(OH)3]>[Ga(OH)]2+>[Ga(OH)2]+>[Ga(H2O)6]3+. The calculation results show that equilibrium isotope fractionations of Ga between different minerals, solutions and gas phases are appreciable. Among solid minerals, gallium isotope fractionation has the largest value between orthoclase type and calcite type minerals. Ga isotopic fractionation value between these two minerals can reach 3.18 per mil at 100 °C. Ga isotope fractionation between Ga-bearing aqueous species and minerals are important to give some information about the different geochemistry processes such as surficial geochemistry. This study has provided those important Ga isotope fractionation factors.