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

Abstract

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.