Kinetics and mechanism of mineral carbonation of olivine for CO2 sequestration

Mineral carbonation (MC) is one of the most important methods to sequester CO2 due to the advantages of permanently storage and abundant mineral resources. This work was designed to investigate the MC chemistry and kinetics in order to further develop carbonation technology. The comprehensive effects of all factors on MC of olivine were investigated. The mechanism of the reaction has been elucidated and can vary under different conditions. With high addition of sodium salts and high CO2 partial pressure (Pan), the rate of MC was controlled by chemical reaction between H+ and olivine no matter how the other variables were changed. The H+ concentration in the void between the well-crystallized carbonates formed by carbonation and the non-reacted olivine was believed to be the same as that in the aqueous bulk solution. The decrease in particle size, increase in temperature, HCO3- concentration and ionic strength in solution can dramatically enhance the carbonation. With little addition of sodium salts, the MC was controlled by diffusion through the Si-rich layer surrounding the olivine core. In contrast, with high addition of sodium salts but low P-CO2, the MC was controlled by diffusion through the dense carbonate layer. The addition of sodium bicarbonate can dramatically increase the ionic strength and aid the dissolution of Si to temporarily aqueous H4SiO4 followed by decomposition to amorphous silica and consequently the removal of Si-rich layer. Under low P-CO2, there was a limited supply of CO32- ions, which resulted in the formation of a dense and poorly porous carbonate layer between a layer of well-crystallized carbonates and non-reacted olivine.