Hydrothermal carbon dioxide fixation in magnesium hydroxide and serpentine: Effects of temperature and pH

Abstract

This study investigated hydrothermal fixation of CO2 in serpentine or magnesium hydroxide as one of the compounds containing Mg at an initial CO2 pressure of 7.1 MPa. The carbonation of magnesium hydroxide gave primarily magnesite and the yield increased with increasing initial pH and increasing temperature, reaching 97.9 % at 473 K. Carbonation of serpentine also gave magnesite, and the yield initially increased and then slightly decreased with increasing temperature. Both low and high initial pH enhanced serpentine carbonation at 573 K and the yield of magnesite reached 12.7 % at an initial pH of 1.0. Estimation of chemical species indicated that both the dissolution of serpentine via the action of H+ and the formation of magnesite from MgHCO3+ and Mg2+ via the release of H+ were important reactions. Hydrothermal serpentine carbonation is a promising CO2 fixation method for naturally abundant mineral rocks without expensive additives.