PNNL

Abstract

Hydrothermal synthesis is an important route to novel materials. The hydrothermal chemistry of materials is also an important aspect of geochemistry and a variety of waste remediation technologies. There is significant lack of information about the speciation of inorganic compounds under hydrothermal conditions. We applied x-ray absorption fine structure (XAFS) and x-ray imaging to define the Cu(I) speciation in a solution containing both solid and dissolved Cu phases at temperatures up to 325 degrees C. X-ray imaging of the various hydrothermal phases allows micro-XAFS to be collected from different phases within the heterogeneous solution. The complete structural characterization of a soluble bichloro-cuprous species was determined. In situ XAFS measurements were used to define the oxidation state and the first-shell coordination structure. The Cu-Cl distance was determined to be 2.12 A for the CuCl2- species and the complete loss of tightly-bound waters-of-hydration in the first shell was observed. The method can be used to test thermodynamic models of solubility and redox chemistry of a variety of different hydrothermal solutions.