Exploring the fate of Fe(III) at hydrothermal conditions

Iron is the most abundant redox-active element in many rocks and geofluids. Yet, the redox chemistry of Fe in high temperature geofluids remains controversial. Comprehensive in-situ XAS results suggest that reduction of Fe(III) to Fe(II) occurs around 200 °C, yet thermodynamic modelling and the presence of minerals such as magnetite indicate that Fe(III) exists at higher temperatures. Redox-active materials in autoclaves from previous in-situ experiments may have affected the results; here we plan to use sealed silica capillaries to measure the speciation of iron in saline geofluids at temperatures over 200 °C.