title: Dynamics of Magnesite Formation at Low Temperature and High pCO2 in Aqueous Solution.
abstract: Magnesite precipitation from aqueous solution, despite conditions of supersaturation, is kinetically hindered at low temperatures for reasons that remain poorly understood. The present study examines the products of Mg(OH)2 reaction in solutions saturated with supercritical CO2 at high pressures (90 and 110 atm) and low temperatures (35 and 50 °C). Solids characterization combined with in situ solution analysis reveal that the first reaction products are the hydrated carbonates hydromagnesite and nesquehonite, appearing simultaneously with brucite dissolution. Magnesite is not observed until it comprises a minor product at 7 days reaction at 50 °C. Complete transition to magnesite as the sole product at 35 °C (135 days) and at a faster rate at 50 °C (56 days) occurs as the hydrated carbonates slowly dissolve under the slightly acidic conditions generated at high pCO2. Such a reaction progression at high pCO2 suggests that over long term the hydrated Mg-carbonates functioned as intermediates in magnesite formation. These findings highlight the importance of developing a better understanding of the processes expected to occur during CO2 storage. They also support the importance of integrating magnesite as an equilibrium phase in reactive transport calculations of the effects of CO2 sequestration on geological formations at long time scale.
authors.affiliation: Pacific Northwest National Laboratory , P.O. Box 999, MS K8-96, Richland, Washington 99352, United States.
authors.forename: Odeta
authors.initials: O
authors.lastname: Qafoku
authors.affiliation: Department of Chemistry, The University of Alabama , Shelby Hall, Tuscaloosa, Alabama 35487, United States.
authors.forename: David A
authors.initials: DA
authors.lastname: Dixon
authors.affiliation: Pacific Northwest National Laboratory , P.O. Box 999, MS K8-96, Richland, Washington 99352, United States.
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Rosso
authors.affiliation: Pacific Northwest National Laboratory , P.O. Box 999, MS K8-96, Richland, Washington 99352, United States.
authors.forename: Herbert T
authors.initials: HT
authors.lastname: Schaef
authors.affiliation: The Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory , Richland, Washington 99354, United States.
authors.forename: Mark E
authors.initials: ME
authors.lastname: Bowden
authors.affiliation: The Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory , Richland, Washington 99354, United States.
authors.forename: Bruce W
authors.initials: BW
authors.lastname: Arey
authors.affiliation: Pacific Northwest National Laboratory , P.O. Box 999, MS K8-96, Richland, Washington 99352, United States.|Washington State University , Pullman, Washington 99164, United States.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Felmy
mesh_terms: D001272:Atmosphere / Q000737:chemistry; D002245:Carbon Dioxide / Q000737:chemistry*; D003080:Cold Temperature; D008274:Magnesium / Q000737:chemistry*; D008276:Magnesium Hydroxide / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D010313:Partial Pressure; D012996:Solutions; D013818:Thermogravimetry; D014961:X-Ray Diffraction
chemical_list: D012996:Solutions; C005479:magnesium carbonate; D002245:Carbon Dioxide; D008274:Magnesium; D008276:Magnesium Hydroxide