Low-Temperature Carbon Mineralisation and Hydrogen Production in Basalt

Hydrogen generation has been observed under conditions relevant to subsurface carbon mineralization, however, conditions that promote H₂ production and its relevance to carbon mineralization remain understudied. In low-temperature (50°C) batch experiments with CO₂-charged North-Atlantic-seawater and mid-ocean ridge basalt (MORB) glass, hydrogen and methane were produced and carbonates were formed.  DNA extraction was attempted by 16S rRNA gene amplification was unsuccessful. Accordingly, no evidence was found for microbial presence that could explain formation of the reduced gases. Here, we quantify CO₂ mineralization, H₂ and CH₄ production in experiments under mild conditions (50°C and 1.5 bar pCO₂) relevant to subsurface carbon mineralization using the Carbfix method with MORB and seawater. Significant H₂ production was not observed in higher temperature (130°C) experiments, conflicting with earlier studies. We provide evidence for H₂ and CH₄ production via water rock reactions (i.e., low temperature serpentinization) using aqueous cation concentrations, x-ray diffraction data and FTIR data of reaction products. Findings of this work have implications for pilot-scale studies injecting CO₂-charged seawater into basalt formations, such as the Seastone project in southwest Iceland by Carbfix. This study highlights key variables to analyze in such studies to assess reduced gas formation, which can be sources of metabolic energy for microbial communities, a potential source of H₂ for energy or feedstock use, or an additional reaction pathway for injected CO₂. Findings from this work have implications for scaling carbon mineralization projects as they grow in importance in response to global warming.