• energy-dispersive XAS;
  • radiolysis;
  • oxidation/reduction;
  • hydrothermal fluid

Radiolysis-induced effects on aqueous tungsten ions are observed to form a precipitate within seconds upon exposure to a synchrotron X-ray micro-beam in a WO3 + H2O system at 873 K and 200 MPa. In situ Fe K-edge energy-dispersive X-ray absorption spectroscopy (ED-XAS) measurements were made on Fe(II)Cl2 aqueous solutions to 773 K in order to study the kinetics of high-temperature reactions of Fe2+ and Fe3+ ions with transient radiolysis species. The radiolytic reactions in a fluid sample within a hydrothermal diamond anvil cell result in oxidation of the Fe2+ ion at 573 K and reduction of Fe3+ at temperatures between 673 and 773 K and of the Fe2+ ion at 773 K. The edge-energy drift evident in the ED-XAS data directly reflects the kinetics of reactions resulting in oxidation and/or reduction of the Fe2+ and Fe3+ ions in the aqueous solutions at high temperatures. The oxidation and reduction trends are found to be highly consistent, making reliable determinations of reaction kinetics possible.