Carbon dioxide sequestration: Chemical and physical activation of aqueous carbonation of Mg-bearing minerals and pH swing process (2005)

According to the United States Environmental Protection Agency (US EPA), carbon dioxide, the key greenhouse gas, was emitted to the atmosphere from fossil fuel combustion in the United States at nearly 5,788 MMT in 2003, amounting to more than 80 % of the total CO 2 emission in the country.The United States is also the world's largest emitter of carbon dioxide, releasing nearly 25 % of worldwide CO 2 emissions.Although policy-makers and the media frequently claim that the effects of elevated atmospheric carbon dioxide levels on global warming are uncertain, there is enough scientific evidence being mounted to support the claim that anthropogenic greenhouse gas emissions are heating the Earth's surface.In their recent report, the National Academy of Sciences Committee testified that human activities are causing increases in surface air temperatures and subsurface ocean temperature.Thus, to ensure the continued use of fossil fuels, it is essential to reduce CO 2 emissions from fossil fuel conversion plants and stabilize CO 2 levels in the atmosphere.The containment of carbon dioxide involves several steps including CO 2 separation, transportation, and sequestration.This study addresses the sequestration step, employing mineral carbonation.Specifically, mechanistic and kinetic characteristics of aqueous iii carbonation of Mg-bearing minerals, which underline the methodology development for mineral sequestration of CO 2 , were explored.Mineral carbonation is achieved through mimicry of natural inorganic chemical transformation of CO 2 , such as the weathering of rocks and dissolution of CO 2 in seawater/saline waters to form bicarbonates.This sequestration process presents a safe and permanent method of CO 2 containment that is based on chemical fixation of CO 2 in the form of geologically and thermodynamically stable mineral carbonates.The total accessible amounts of the Mg-bearing minerals were estimated to significantly exceed the worldwide coal reserves.However, little has been known regarding the fundamental characteristics of CO 2 -mineral reactions to allow a viable CO 2 mineral sequestration technology to be developed.Screening of mineral samples for their application in the CO 2 mineral sequestration scheme identified both olivine and serpentine to be the viable candidates.According to the experimental results, the chemically enhanced aqueous carbonation of serpentine showed promising results.From the investigation of serpentine dissolution in various solvents, it was found that a mixture of 1 vol% orthophosphoric acid, 0.9 wt% of oxalic acid, and 0.1 wt% EDTA greatly enhanced the Mg leaching process of ground serpentine while preventing the precipitation of Fe(III) on the surface of the mineral particles.When this acidic solvent was used for the aqueous mineral carbonation, the overall process was limited by the rates of dissolution of CO 2 and dissociation of carbonic acid, rather than the dissolution rate of the mineral.Fan, for his priceless guidance, encouragement, and support throughout this work.His enthusiasm and drive has been a constant source of inspiration.