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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

Harrison, AL; Mavromatis, V; Oelkers, EH; Bénézeth, P; (2019) 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. Chemical Geology , 504 pp. 123-135. 10.1016/j.chemgeo.2018.11.003. Green open access

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Abstract

Hydrated Mg-carbonate minerals form during the weathering of ultramafic rocks, and can be used to store atmospheric CO2 to help combat greenhouse gas-fueled climate change. Optimization of engineered CO2 storage 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 [MgCO3·3H2O] and dypingite [Mg5(CO3)4(OH)2·(5 or 8)H2O] and the transformation from nesquehonite to dypingite between 5 °C and 35 °C, using constant-temperature, batch-reactor experiments. 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 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. This is the first reported dypingite solubility product. 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 in natural and engineered ultramafic mineral weathering systems that sequester CO2, and for the first time allow assessment of the saturation state of dypingite in aqueous solutions.

Type: Article
Title: 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
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.chemgeo.2018.11.003
Publisher version: https://doi.org/10.1016/j.chemgeo.2018.11.003
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Mg-carbonates, CO2 sequestration, Mineral solubility, Ultramafic mineral weathering, Mineral phase transformation, Dissolution-reprecipitation, Dypingite, Nesquehonite
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10064741
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