Direct moist carbonation of brucite-rich serpentinized dunites: An alternative to the carbonation of heat-activated serpentine

Abstract

Widely abundant peridotite and serpentinized rocks are foreseen as a potential sink for anthropogenic CO2. However, energy-intensive pretreatments (heat activation and grinding processes) as well as high temperature and pressure carbonation conditions are required for obtaining significant reaction yields. This represents significant challenges for its industrial implementation. In this work, direct moist carbonation of brucite-bearing serpentinized dunites under moderately low-pressure conditions (10 bar) in the 50-185 °C temperature range was studied. The formation of different carbonate phases is mainly controlled by the reaction temperature. At 145 and 165 °C, a complete hydromagnesite to magnesite conversion was observed at only ≤4h of reaction. The main limiting factor of the carbonation reaction was mostly attributed to the depletion of brucite. A maximum of 98gCO2/kgrock was fixed by magnesite at 145 °C during 4 h of reaction. The estimated extraction of Mg from lizardite and/or forsterite was estimated to be up to 6.9%, based on the obtained carbonation exceeds what would be estimated if only brucite reacted, considering a Fe-free brucite. This might explain the changes in the dehydration behavior of lizardite upon carbonation. A near maximum carbonation yield was obtained at 165 °C after only 2h of reaction. Brucite carbonation rate is significantly slower at 185 °C, which is attributed to the decreasing thermal stability of hydromagnesite. Results from this work suggest that sourcing and grinding brucite-bearing serpentinized dunites for mineral carbonation is a promising alternative to that of heat-activated lizardite. Moreover, strategically sourcing brucite-rich serpentinized dunites would likely increase the obtained carbonation yield under identical carbonation conditions.