NaHCO₃-promoted olivine weathering with H₂ generation and CO₂ sequestration in alkaline hydrothermal system

Hydration of Fe(II) bearing minerals, such as olivine ((Mg,Fe)SiO₄), potentially generate hydrogen (H₂). However, because of the low Fe(II) dissolution rate, the H₂ production rate is usually low. We have recently proposed a novel system to promote H₂ production and simultaneous CO₂ storage in hydrothermal conditions via NaHCO₃-enhanced olivine weathering. The present study reports the role of NaHCO₃ on both H₂ production from olivine hydration and on minerals generations on laboratory experiments in CO₂-rich (0.5 mol/L NaHCO₃) and CO₂-free hydrothermal conditions at pH range of 8-11. The highest H₂, HCOOH yields and carbonation rate reached at the CO₂-rich experiment with lower alkaline pH at 8.25. The addition of high concentration NaHCO₃ decreased pH from 10.92 to 8.25, whereas olivine and brucite dissolutions were accelerated. Thus, more Fe(II) was released from olivine and brucite, and H₂ production was accelerated. At higher pH range, olivine dissolution was promoted, but brucite dissolution was suppressed in both CO₂-rich and CO₂-free conditions. This study suggests H₂ production was promoted with the presence of HCO₃ ^-, but not the pH variation. The consumption of Fe(II)-bearing brucite was important in enhancing H₂ production during olivine hydration process.