Nanoscale analysis for the San Carlos olivine carbonation reaction mechanism (Arizona)

Carbon sequestration by reacting Mg and Ca containing minerals with CO 2 to form carbonates has many unique advantages. The reaction is thermodynamically favorable and occurs naturally, the amount of minerals is abundant, and carbonate products are stable. However, little is known so far, regarding the fundamental characteristics of CO2 mineral reactions, to allow a viable CO 2 mineral sequestration scheme to be developed.; The dissolution of olivine without physical activation was investigated to understand the reacted surface and olivine/reaction layer interface. The surface morphology changes between rinsed olivine after reaction and ultrasonicated reacted olivine. This indicated that the formation of a silica reaction layer that cracks and exfoliates from the olivine substrate. The structure and composition of the reaction layer (RL) reveals that amorphous SiO2 is the dominant phase with MgCO3 nanoparticles are embedded in the RL. However, most magnesite forms in the solution.; The chemical reactions with the liquid solution, structural transformation between olivine and RL, and mechanical development of RL must be understood. The driving force for the reaction is that Mg and O transport across olivine/RL interface and through the reaction layer. Therefore, the olivine structure transforms to amorphous SiO2 by a diffusion process, and carbon species penetrate and form magnesite particles in the RL. The stresses from the molar volume differences between reactants and products concentrate in the thin RL, cause cracking, curling, and spalling from substrate. Stress calculation shows the distribution of stress along the thin reaction layer. The general mechanism model describes that attacking solution into olivine, Mg and O transportation, reaction layer formation, the breaking of pieces of the RL by stresses.; The agitation of the RL by mechanical abrasion helps with removing the diffusion limiting SiO2 RL in order to promote further dissolution of the inner Mg containing layer of olivine. The reaction layer itself seems to be slightly oxygen deficient SiO2 using electron energy loss nanospectroscopy. In addition, hydrogen may penetrate into the reaction layer during carbonation, which changes the chemical bonding status of near surface of the RL.