Solubility of the hydrated Mg-carbonates nesquehonite and dypingite from 5 to 35 °C: Implications for CO 2 storage and the relative stability of Mg-carbonates

Anna L. Harrison, Vasileios Mavromatis, Eric H. Oelkers, Pascale Bénézeth

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Hydrated Mg-carbonate minerals form during the weathering of ultramafic rocks, and can be used to store atmospheric CO 2 to help combat greenhouse gas-fueled climate change. Optimization of engineered CO 2 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 [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 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 CO 2 , and for the first time allow assessment of the saturation state of dypingite in aqueous solutions.

Original languageEnglish
Pages (from-to)123-135
Number of pages13
JournalChemical Geology
Volume504
DOIs
Publication statusPublished - 20 Jan 2019

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Carbonates
Carbon Monoxide
solubility
Solubility
carbonate
Carbonate minerals
Weathering
mineral
weathering
Phase transitions
Saturation (materials composition)
Metastable phases
Batch reactors
ultramafic rock
hydration
Greenhouse gases
Climate change
Hydration
Minerals
Dissolution

Keywords

  • CO sequestration
  • Dissolution-reprecipitation
  • Dypingite
  • Mg-carbonates
  • Mineral phase transformation
  • Mineral solubility
  • Nesquehonite
  • Ultramafic mineral weathering

ASJC Scopus subject areas

  • Geology
  • Geochemistry and Petrology

Cite this

Solubility of the hydrated Mg-carbonates nesquehonite and dypingite from 5 to 35 °C : Implications for CO 2 storage and the relative stability of Mg-carbonates. / Harrison, Anna L.; Mavromatis, Vasileios; Oelkers, Eric H.; Bénézeth, Pascale.

In: Chemical Geology, Vol. 504, 20.01.2019, p. 123-135.

Research output: Contribution to journalArticleResearchpeer-review

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abstract = "Hydrated Mg-carbonate minerals form during the weathering of ultramafic rocks, and can be used to store atmospheric CO 2 to help combat greenhouse gas-fueled climate change. Optimization of engineered CO 2 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 [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 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 CO 2 , and for the first time allow assessment of the saturation state of dypingite in aqueous solutions.",
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AB - Hydrated Mg-carbonate minerals form during the weathering of ultramafic rocks, and can be used to store atmospheric CO 2 to help combat greenhouse gas-fueled climate change. Optimization of engineered CO 2 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 [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 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 CO 2 , and for the first time allow assessment of the saturation state of dypingite in aqueous solutions.

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