An experimental study of the solubility of Gallium(III) oxide in HCl-bearing water vapour

The solubility of β-Ga2O3(s) in HCl-bearing water vapour was measured at temperatures between 150 and 400 °C and pressures up to 257 bar. These measurements indicate that Ga(III) oxide dissolves in significant concentrations in water vapour, and that its solubility depends on fHCl and fH2O. At low fHCl, the dominant gallium gas species is Ga(OH)3(g), whereas at high fHCl, Ga(OH)Cl2(g) predominates. Gallium(III) oxide solubility increases exponentially with increasing pressure at 350 and 400 °C due to the formation of the hydrated clusters, GaOHCl2(H2O)n(g), where n = 1–7. The logarithms of the dissolution constants for the reaction, 0.5Ga2O3(s) + 1.5H2O(g) = Ga(OH)3(g), are −7.70 ± 0.30 and −7.93 ± 0.30 at 350 and 400 °C, respectively, and for the reaction, 0.5Ga2O3(s) + 2HCl(g) = GaOHCl2(g) + 0.5H2O(g), are −0.32 ± 0.29, 0.03 ± 0.20, and −2.59 ± 0.15 at 150, 200, and 400 °C, respectively.The data obtained in this study were used to determine the partitioning of Ga between vapour and liquid at temperatures between 150 and 350 °C, and a pH for the liquid ranging from 0 to 10. The estimated partition coefficient (Kd) decreases with increasing temperature, and reaches a maximum value of ∼100 at 150 °C and ∼25 at 200 °C at a pH of ∼4. The values are very similar to those estimated from data for geothermal wells in Iceland and hot springs in the Kamchatka Peninsula.