X-ray Absorption Spectroscopy Study of Solvation and Ion-Pairing in Aqueous Gallium Bromide Solutions at Supercritical Conditions

Abstract : X-Ray Absorption Spectroscopy measurements have been performed both at the Ga and Br K-edges on aqueous GaBr3 solutions. The isobaric experiments have been recorded at 30 MPa from ambient temperature to 670 K for two GaBr3 concentrations (0.017 and 0.17 mol/dm3). At room temperature, Ga3+ and Br- ions are fully solvated, surrounded by water O atoms at 1.97 Å (Ga-O) and 3.37 Å (Br-O). When the temperature is elevated, Ga3+ cations precipitate as gallium oxy-hydroxide colloids while Br- anions remain solvated. With a further increase in temperature, the gallium solid precipitates remarkably re-dissolved (25% and 50% for 0.017 and 0.17 mol/dm3 respectively), due to the formation of (n=2, 3 or 4) tetrahedral complexes.