Redox changes of iron in brucite under hydrothermal conditions and low-T H2 production

The main objective of this proposal is to conduct in situ Fe K-edge XANES and X-ray diffraction measurements at controlled oxygen fugacity to characterize the Fe(II)/Fe(III) distribution in ferrian brucite at T up 600 °C and to infer whether its formation can be accompanied by H2 production. Ferrian brucite, (Mg0.8FeIII0.2)(OH)1.8O0.2, has recently been synthesized at 200 °C by hydrothermal alteration of ferroan brucite, (Mg0.8FeII0.2)(OH)2, a mineral found in serpentinites. Ferrian brucite is isostructural to brucite with ferric iron replacing ferrous iron in octahedral position, charged balance by H vacancies. Indeed synthetic brucite (ferroan and ferrian) is prone to oxidation and carbonation in air what renders sample post-mortem characterization unreliable. For this purpose, we propose to use the resistively heated diamond anvil cell (RH-DAC) set-up developed at BM23, which was successfully used in our previous works for the study of ferrous – ferric iron mineral transformation.