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.
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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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