Mineralogical evidence for H2 degassing during serpentinization at 300°C/300bar

Evolution of Fe redox state in serpentine during subduction

“…These observations indicate that olivine-hosted Fe becomes oxidized as water is reduced during serpentine crystallization (Berndt et al, 1996;McCollom and Bach, 2009;Seyfried et al, 2007). Recent studies have shown that the increase of the serpentinization degree of the peridotite is correlated with an increase of the magnetite mode and Fe 3+ /Fe Total ratio of the serpentine (Andreani et al, 2013;Marcaillou et al, 2011). These observations imply that the serpentinites that constitute the upper oceanic lithosphere and which are ultimately subducted are highly oxidized relative to mantle peridotites.…”

“…The serpentinization of ultra-mafic rocks is associated with magnetite formation Oufi et al, 2002), while the fluids discharged from serpentinites can be H 2 and CH 4 rich (Charlou et al, 2002;Marcaillou et al, 2011). These observations indicate that olivine-hosted Fe becomes oxidized as water is reduced during serpentine crystallization (Berndt et al, 1996;McCollom and Bach, 2009;Seyfried et al, 2007).…”

“…The Fe 3+ /Fe Total was derived directly from the variogram of Wilke et al (2001). This variogram was reproduced by measuring three powdered standard compounds namely olivine ( VI Fe 2+ ), andradite ( VI Fe 3+ ) and sanidine ( IV Fe 3+ ), previously characterized in other studies (Andreani et al, 2013;Marcaillou et al, 2011;Muñoz et al, 2013).…”

Experimental Perspectives of Mineral Dissolution and Precipitation due to Carbon Dioxide-Water-Rock Interactions

“…Luquot et al (2012) showed that CO 2 may be converted into reduced carbon when injected in a ferrous iron-bearing sandstone reservoir, resulting in the precipitation of poorly-crystallized graphite. In mafic and ultramafic reservoirs, the oxidation by H 2 O of the ferrous iron component of olivine or pyroxene can result in H 2 production (Stevens and McKinley 2000;Marcaillou et al 2011). In CO 2 -poor experiments, a part of the CO 2 is reduced to methane and possibly more complex carbon compounds (McCollom 2013).…”

Hydrothermal Steel Slag Valorization—Part II: Hydrogen and Nano-Magnetite Production

“…In this context, Malvoisin et al (2013) proposed to recover part of the steelmaking energy stored chemically in steel slags using a novel process which produces high-purity hydrogen through the hydrothermal oxidation of steel slags. This process is inspired from the abiogenic geochemical process of native dihydrogen (H 2 ) formation operating at midoceanic ridges (Charlou et al, 2002;Marcaillou et al, 2011). Under these hydrothermal conditions (350 • C−500 bar), ferrous iron-bearing magnesium silicates are hydrated and oxidized by hot seawater.…”