Hydration/dehydration and ion complexation in hydrothermal solutions

Abstract

The present work is dedicated to the study of dehydration and ion pair formation in hydrothermal ion-rich solutions. The objectives are to describe at the molecular scale these processes, and relate them to the macroscopic properties of the solvent water. Thanks to the combination of x-ray synchrotron techniques (x-ray absorption spectroscopy and small angle x-ray scattering), and to the design of a high-pressure and high-temperature set-up, local order in ZnBr2 aqueous solutions is studied. The evolution of ion pair formation (between Zn2+ and Br- ions) with temperature, pressure and ion concentration is shown. Furthermore, the influence of density fluctuations (characteristic of supercritical conditions) on this ion interaction is explained. This work is a good candidate to show the efficiency of synchrotron measurements as a complement to other spectroscopies, especially in the case of hydrothermal solutions where the experimental conditions are challenging.