X-ray absorption spectroscopy study of solvation and ion-pairing in aqueous gallium bromide solutions at supercritical conditions

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 [GaBrn(H2O)4 − n](aq)3 − n (n = 2, 3 or 4) tetrahedral complexes.