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

Abstract

Hydrated Mg-carbonate minerals form during the weathering of ultramafic rocks, and 2 can be used to sequester atmospheric CO 2 to help combat greenhouse gas-fueled climate change. Optimization of engineered CO 2 sequestration and prediction of the composition and stability of Mg-carbonate phase assemblages in natural and engineered ultramafic environments requires knowledge of the solubility of hydrated Mg-carbonate phases, and the transformation pathways between these metastable phases. In this study, we evaluate the solubility of nesquehonite [MgCO 3 •3H 2 O] and dypingite [Mg 5 (CO 3) 4 (OH) 2 •(5 or 8)H 2 O] and the transformation from nesquehonite to dypingite between 5°C and 35°C, using constanttemperature, batch-reactor experimentals.. The logarithm of the solubility product of nesquehonite was determined to be:-5.03±0.13,-5.27±0.15, and-5.34±0.04 at 5°C, 25°C, and 35°C, respectively. The logarithm of the solubility product of dypingite, never reported before, was determined to be:-34.95±0.58 and-36.04±0.31 at 25°C and 35°C, respectively, with eight waters of hydration. The transformation from nesquehonite to dypingite was temperature-dependent, and was complete within 57 days at 25°C, and 20 days at 35°C, but did not occur during experiments of 59 days at 5°C. This phase transformation appeared to occur via a dissolution-reprecipitation mechanism; external nesquehonite crystal morphology was partially maintained during the phase transformation at 25°C, but was eradicated at 35°C. Together, our results facilitate the improved evaluation of Mg-carbonate mineral precipitation during natural and engineered ultramafic mineral weathering systems that sequester CO , and 20 for the first time allow assessment of the saturation state of dypingite in aqueous solutions. 21

Synthesis of magnesium carbonate hydrate from natural talc

“…The morphology of these magnesium carbonate hydrate particles produced by talc carbonation was visualized by SEM, and the representative images are presented in Figure 1. As can be observed, the magnesium carbonate hydrate particles exhibited four different microscopic morphologies [22][23][24]. In Figure 1a, the needle-like particles were produced, and the axis diameter was in the range of 0.3-0.8 µm.…”

Crystal structure of nesquehonite, MgCO₃·3H(D)₂O by neutron diffraction and effect of pH on structural formulas of nesquehonite

“…Numerous approaches to CO 2 sequestration have extensively been studied (Park and Fan, 2004;Rendek et al, 2006;Kelemen and Matter, 2008;Assayag et al, 2009;Montes-Hernandez et al, 2009;Felmy et al, 2012;Farhang et al, 2016;Noiriel and Daval, 2017). Magnesium carbonates, therefore, offer attractive possibilities for the permanent and safe geological storage of CO 2 (Hänchen et al, 2008;Ferrini et al, 2009;Ballirano et al, 2010;Harrison et al, 2019). In the MgO-CO 2 -H 2 O system at temperatures ranging from 0 to 60°C, the thermodynamically stable phases are brucite Mg(OH) 2 and magnesite MgCO 3 (Königsberger et al, 1999).…”

A combined Raman, Fourier transform infrared, and X‐ray diffraction study of thermally treated nesquehonite

“…[1] Natural nesquehonite is associated with weathering of ultramafic rocks; besides, it is found in caves and coal mines, whereas its formation has been reported in Mg-rich mining waste stockpiles depending on the environmental conditions. [2][3][4] Recent studies showed that nesquehonite can be the product of CO 2 mineralization under low pressure conditions. [5,6] The main advantage of nesquehonite in being a potential permanent storage for CO 2 emissions is that at least 30% of its structure consists of CO 3 2−.…”

“…[9][10][11][12][13][14] Nesquehonite exhibits excellent physical and chemical properties for building materials [5,6,8,15,16] and can be potentially used for industrial purposes as acoustic or insulation panels. [6] The chemical formula of nesquehonite has been proposed either as MgCO 3 •3H 2 O or as Mg (HCO 3 ) (OH)•2H 2 O [9][10][11][12][13][14] ; the second one assumes the presence of HCO 3 − and OH − in the nesquehonite structure.…”

“…Raman and Fourier transform infrared spectroscopy (FT-IR) studies of raw nesquehonite have confirmed the presence of OH − in its structure [12,13,17] ; however, the presence of HCO 3 − has yet to be defined by spectroscopic [9,18,19] or by X-ray diffraction (XRD) studies [1,11] and remains questionable. Over the time, it has been suggested that there are two structural isomers of nesquehonite, [12,13,20] with the pH being the key factor for which isomer is formed.…”