Ab initio thermodynamics of magnesium carbonates and hydrates in water-saturated supercritical CO2 and CO2-rich regions

Abstract

ab initio thermodynamics is used to determine how free energies of magnesium carbonates and hydrates in a CO 2-rich environment change with water concentration across a range temperature and pressure relevant to geochemistry and carbon sequestration (275 K to 375 K and pCO 2 of 1 to 210 bar). The methodology is based on first principles densityfunctional theory (DFT) calculations of the total energies and vibrational entropy of periclase, magnesite, brucite, nesquehonite, and hydromagnesite coupled to the experimental chemical potentials of CO 2 and H 2 O. The impact of water in supercritical CO 2 (scCO 2), even though less than 1% at saturation, is found to have a significant impact on the stability of hydrated carbonate minerals. Hydromagnesite and nesquehonite are found to be more thermodynamically stable than periclase and brucite in water-saturated scCO 2 and hence may be expected to result kinetically from carbonation of these minerals during CO 2 sequestration. Under dehydrating conditions nesquehonite destabilizes rapidly, whereas hydromagnesite is much more likely to persist in a CO 2-rich environment, consistent with the observations that hydromagnesite is widespread in nature and nesquehonite is relatively rare.

Solubility of the hydrated Mg-carbonates nesquehonite and dypingite from 5 to 35 °C: Implications for CO2 storage and the relative stability of Mg-carbonates

“…The stoichiometry of minerals in terms of their Mg:C ratios and Mg:H 2 O ratios also 528 governs the efficiency of CO 2 sequestration; a Mg:C of 1:1 such as provided by nesquehonite, lansfordite [MgCO 3 •5H 2 O], and magnesite is most efficient. In dry conditions, such as in subaerially stored ultramafic mining wastes (Bea et al, 2012;Wilson et al, 2014), or near the injection of supercritical CO 2 in the subsurface (Schaef et al, 2011(Schaef et al, , 2013Chaka et al, 2016), the availability of water may be a limiting factor for carbonate precipitation (Schaef et al, 2011(Schaef et al, , 2013Harrison et al, 2015Harrison et al, , 2016, therefore carbonates that consume less water during their formation, such as dypingite, hydromagnesite, and magnesite, are desirable. The anhydrous carbonate, magnesite, is the ideal carbon sink in terms of stability, water requirements, and efficiency (Power et al, 2017).…”

“…The multitude of potential metastable hydrated 69 phases complicates prediction of Mg-carbonate formation and thus the stability of the CO 2storing phase (Königsberger et al, 1999;Hopkinson et al, 2008Hopkinson et al, , 2012Hänchen et al, 2008;Montes-Hernandez et al, 2012;Kristova et al, 2014). To reduce some of the ambiguity in the prediction of Mg-carbonate mineral formation under various conditions, in this study we determine the solubility of nesquehonite [MgCO 3 •3H 2 O] and dypingite [Mg 5 (CO 3 ) 4 (OH) 2 •(5 or)8H 2 O], two commonly observed products of carbon mineralization in ultramafic materials (Wilson et al, 2006(Wilson et al, , 2011(Wilson et al, , 2014Boschi et al, 2009;Zhao et al, 2010;Pronost et al, 2011;Schaef et al, 2011;Bea et al, 2012;Loring et al, 2012;Montes-Hernandez et al, 2012;Assima et al, 2012Assima et al, , 2014cHövelmann et al, 2012;Felmy et al, 2012;Beinlich and Austrheim, 2012;Schaef et al, 2013;Harrison et al, 2013aHarrison et al, , 2015Harrison et al, , 2016Harrison et al, , 2017Power et al, 2013aPower et al, , b, c, 2014bKristova et al, 2014;McCutcheon et al, 2016;Chaka et al, 2016;Garcia del Real et al, 2016;Highfield et al, 2016;Gras et al, 2017;McCutcheon et al, 2017), and the transformation process that converts nesquehonite to dypingite. Both nesquehonite and dypingite are readily formed during reaction of Mg-rich minerals with CO 2 at ambient te...…”

Mechanisms controlling the Mg isotope composition of hydromagnesite-magnesite playas near Atlin, British Columbia, Canada

“…However, its formation in low temperature environments is unlikely to occur on short timescales (Hänchen et al, 2008;Saldi et al, 2012), thus making the hydrated Mg-carbonates the targets for CO2 storage at near Earth's surface temperatures. Although hydromagnesite, dypingite and nesquehonite are common products of ultramafic rock weathering (Assima et al, 2014;Bea et al, 2012;Boschi et al, 2009;Chaka et al, 2016;Felmy et al, 2012;Garcia del Real et al, 2016;Gras et al, 2017;Highfield et al, 2016;Hövelmann et al, 2012;Kristova et al, 2014;Loring et al, 2012;Montes-Hernandez et al, 2012;Pronost et al, 2011;Schaef et al, 2011;Zhao et al, 2010), previous studies on their formation that used Mg isotope systematics suggested a continuous exchange of Mg isotopes between the solid and the fluid phase at ~25 o C (e.g., Mavromatis et al, 2012;Shirokova et al, 2013). Similar observations were made based on the δ 13 C value of the solid and the dissolved inorganic carbon composition of the forming fluid (Mavromatis et al, 2015) and likely reflect the high reactivity of these…”

XPS Study on the Stability and Transformation of Hydrate and Carbonate Phases within MgO Systems

“…Chaka et al [ 14 ] underline that the amount of water in the environment where the carbonation occurs strongly influences the transformation path of the HMCs and their stability, and they relate this to carbon storage and the sequestration potential.…”