Directed precipitation of hydrated and anhydrous magnesium carbonates for carbon storage

Abstract

Magnesite is the most desirable phase within the magnesium carbonate family for carbon storage for a number of reasons: magnesium efficiency, omission of additional crystal waters and thermodynamic stability. For large-scale carbonation to be a viable industrial process, magnesite precipitation must be made to occur rapidly and reliably. Unfortunately, the formation of metastable hydrated magnesium carbonate phases (e.g. MgCO3·3H2O and Mg5(CO3)4(OH)2·4H2O) interferes with the production of anhydrous magnesite under a variety of reaction conditions because magnesite crystals are slower to both nucleate and grow compared to the hydrated carbonate phases. Furthermore, the reaction conditions required for the formation of each magnesium carbonate phases have not been well understood with conflicting literature data. In this study, the effects of both magnesite (MgCO3) and inert (Al2O3) seed particles on the precipitation of magnesium carbonates from a Mg(OH)2 slurry were explored. It was interesting that MgCO3 seeding was shown to accelerate anhydrous magnesite growth at temperatures (80-150 °C), where it would normally not form in short time scale. Since the specific surface areas of MgCO3 and Al2O3 seeding particles were similar, this phenomenon was due to the difference in the surface chemistry of two seeding particles. By providing a template with similar chemistry for the growth of magnesite, the precipitation of anhydrous magnesite was demonstrated. The effect of temperature on seeded carbonation was also investigated. A comparison with published MgCO3 precipitation rate laws indicated that the precipitation of magnesite was limited by either CO2 adsorption from the gas phase or the dissolution rate of Mg(OH)2.

Magnesium-based systems for carbon dioxide capture, storage and recycling: from leaves to synthetic nanostructured materials

“…Although 45 breakthrough results were reported recently for all the steps of the synthetic CO 2 cycle, 52,57,147,151 there is still large room for improvements. For what concerns the catalysis research, among all the possible reactions involving CO 2 , the synthesis of fuels has a principle 50 role.…”

Formation of magnesite and hydromagnesite from direct aqueous carbonation of thermally activated lizardite

“…The mechanism and the reaction pathways for the formation of the Mg‐carbonate phases are not fully understood . In the MgO‐CO 2 ‐H 2 O system, a wide range of Mg‐carbonate products including anhydrous (magnesite/MgCO 3 ) and hydrous metastable carbonates such as nesquehonite (MgCO 3· 3H 2 O), lansfordite (MgCO 3· 5H 2 O), artinite (Mg 2 CO 3 (OH) 2· 3H 2 O), dypingite (Mg 5 (CO 3 ) 4 (OH) 2· 5H 2 O), and hydromagnesite (Mg 5 (CO 3 ) 4 (OH) 2 .4H 2 O) and mixtures thereof are possible. For hydromagnesite, the stoichiometric ratio of Mg to carbon is 0.8, while for magnesite (MgCO 3 ) this ratio is 1.…”

“…For hydromagnesite, the stoichiometric ratio of Mg to carbon is 0.8, while for magnesite (MgCO 3 ) this ratio is 1. Magnesite is a targeted carbonate phase because of this higher ratio and also because it is thermodynamically the most stable carbonate . Nesquehonite is precipitated in aqueous solutions at low CO 2 partial pressures (below ambient pressure) and at low temperatures (25–55°C), whereas magnesite precipitation is not observed under these conditions .…”

CO2 Absorption and Magnesium Carbonate Precipitation in MgCl2–NH3–NH4Cl Solutions: Implications for Carbon Capture and Storage

“…When Mg 2+ is present, various forms of magnesium carbonates can precipitate from saturated solution [43][44][45]. of temperature and pressure.…”