CO2 Fixation in Ca2+-/Mg2+-Rich Aqueous Solutions through Enhanced Carbonate Precipitation

In this work, the possibility of achieving fixation of CO 2 using Ca and Mg ions was tested and verified. Concentrated seawater from desalination plants, subsurface brines, industrial effluents with high hardness, and/or natural seawaters that are rich in Ca 2+ and Mg 2+ could all be potential aqueous sources. Theoretical analyses indicated that the carbonation reaction could be enhanced by raising the pH or the CO 2 partial pressure. Experiments using synthesized seawater confirmed this possibility. Over 90% of the Ca 2+ and Mg 2+ ions in the seawater could be converted by precipitation in the forms of MgCO 3 and dolomite [MgCa(CO 3 ) 2 ], and the kinetics of the process was found to be quite acceptable. It was found that 1 m 3 of natural seawater could fix about 1.34 m 3 or 2.65 kg of CO 2 (gas volume, standard conditions), and the potential of concentrated seawater is 2–3 times this value. Even if the annual CO 2 emissions of the entire world were captured in this way, the concentration of Ca 2+ /Mg 2+ in natural seawater would change at only the part-per-million scale, such that the ecological effects could be negligible. This idea has great potential for application. It might be able to realize not only the permanent fixation of CO 2 but also the production of large amounts of carbonate byproducts.