Low temperature and limited water activity reveal a pathway to magnesite<i>via</i>amorphous magnesium carbonate

Mergelsberg, Sebastian T.; Kerisit, Sebastien N.; Ilton, Eugene S.; Qafoku, Odeta; Thompson, Christopher J.; Loring, John S.

doi:10.1039/d0cc04907g

Cited by 21 publications

(32 citation statements)

References 22 publications

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“… 4 A recent work demonstrated that magnesite could precipitate under low water activity but not in the bulk solution. 59 Theoretical calculation using MD and metadynamics (MetaD) revealed that certain anions and solvent molecules could facilitate the dehydration of the Mg 2+ –water complex and foster precipitation of high Mg–carbonate phases. 60 Our experimental data support this calculation result with ethanol affecting the Mg hydration shell and enhance the dehydration of the Mg 2+ –water complex.…”

Section: Discussionmentioning

confidence: 99%

Low-Temperature Synthesis of Disordered Dolomite and High-Magnesium Calcite in Ethanol–Water Solutions: The Solvation Effect and Implications

et al. 2021

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How dolomite [CaMg(CO 3 ) 2 ] forms is still underdetermined, despite over a century of efforts. Challenges to synthesizing dolomite at low temperatures have hindered our understanding of sedimentary dolomite formation. Unlike calcium, magnesium’s high affinity toward water results in kinetic barriers from hydration shells that prevent anhydrous Ca–Mg carbonate growth. Previous synthesis studies show that adding low-dielectric-constant materials, such as dioxane, dissolved sulfide, and dissolved silica, can catalyze the formation of disordered dolomite. Also, polar hydrophilic amino acids and polysaccharides, which are very common in biomineralizing organisms, could have a positive role in stimulating Mg-rich carbonate precipitation. Here, we show that disordered dolomite and high-magnesium calcite can be precipitated at room temperature by partially replacing water with ethanol (which has a lower dielectric constant) and bypassing the hydration barrier. Increasing the ethanol volume percentage of ethanol results in higher Mg incorporation into the calcite structure. When the ethanol volume percentage increases to 75 vol %, disordered dolomite (>60 mol % MgCO 3 ) can rapidly precipitate from a solution with [Mg 2+ ] and [Ca 2+ ] mimicking seawater. Thus, our results suggest that the hydration barrier is the critical kinetic inhibitor to primary dolomite precipitation. Ethanol synthesis experiments may provide insights into other materials that share similar properties to promote high-Mg calcite precipitation in sedimentary and biomineral environments.

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Section: Discussionmentioning

confidence: 99%

Low-Temperature Synthesis of Disordered Dolomite and High-Magnesium Calcite in Ethanol–Water Solutions: The Solvation Effect and Implications

et al. 2021

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“…39 Similarly, the faster kinetics of MgCO3 precipitation measured within the nanoconfined water environments, compared to the bulk solution, was explained in terms of the reduction in coordinating water molecules (fewer than six) for Mg 2+ . 40 To quantify the ability of each additive in Table 1 to promote the Mg 2+ dehydration process, we have conducted CµMD simulations of electrolyte solutions where the separation between Mg 2+ and X nwas kept at approximately 4.5 nm by imposing a harmonic potential with a force constant of 1000 kJ.mol -1 between the magnesium and the counterion ion. This corresponds to the formation of SSHIP and allows us to evaluate the ability of solution additives to stabilize the undercoordinated Mg 2+ states.…”

Section: Resultsmentioning

confidence: 99%

Solution additives promoting the onset of MgCO3 nucleation

Toroz

Song

Uddin

et al. 2021

Preprint

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Formed via aqueous carbonation of Mg2+ ions, the crystallization of magnesite (MgCO3) is a promising carbon capture and reuse technology, albeit limited by the slow precipitation of MgCO3. Although magnesite is naturally abundant, forming at low temperature conditions, its production is an energy-intensive process due to the temperatures required to prevent the formation of hydrated phases. The principle difficulty arises from the very strong Mg2+···H2O interaction, raising barriers to dehydration. Using atomistic simulations, we have investigated the influence of thirty additive anions (Xn–, n = 1–3), ranging from simple halides to more complex molecules, on the first two steps of MgCO3 aggregation from solution: Mg2+ dehydration and Mg2+∙∙∙CO32– pairing. We have computed the thermodynamic stability of solvent shared ion pairs, Mg2+···H2O···Xn–, and contact ion pairs, Mg2+···Xn–, with Mg2+ to reveal the propensity of solution additives to inhibit Mg2+∙∙∙CO32– formation. We have determined the stabilization of undercoordinated hydrated Mg2+ states with a vacant coordination site to which CO32– can bind, subsequently initiating MgCO3 nucleation or Mg2+ incorporation into the crystal lattice. Extensive molecular dynamics simulations of electrolyte solutions containing Na2CO3 with different sources of Mg2+, MgCl2, MgSO4 and Mg(CH3COO)2, further shows that the degree of dehydration of Mg2+ and the structure of prenucleation MgCO3 clusters changes depending on the type counterion. Through a fundamental understanding of the role of solution additives in the mechanism of Mg2+ dehydration, our computational study can rationalize previously reported experimental observation of the effect of solvation environments on the growth of magnesite. This understanding may contribute to identifying solution composition conditions that could promote the low-temperature CO2 conversion into MgCO3.

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“…Two eigenvectors from these analyses accounted for approximately 99.95% of the variance for all data sets, suggesting that the measured spectra can be reliably represented by two components. The first component, C1, is assigned to AMC with minimum absorbance between 715 and 770 cm –1 . The second component, C2, represents magnesite with a clear CO deformation band , between 715 and 770 cm –1 but minimal absorbance for the HOH bend of adsorbed H 2 O between 1600 and 1700 cm –1 .…”

Section: Methodsmentioning

confidence: 99%

“…This MCR-ALS calculated the relative concentrations of both C1 and C2 as a function of time. The relative concentrations of C1 and C2 for the experiment at 25 °C were converted to moles of AMC and magnesite, respectively, by assuming that the experiment started with a hypothetical 1 g sample of unreacted forsterite and ended with a mole percent of forsterite consumed based on an ex situ high energy X-ray diffraction (heXRD) and pair distribution function (PDF) analyses of the postreacted sample that used a molar density for dry amorphous SiO 2 . The heXRD and PDF analyses for the experiment at 25 °C are detailed in Mergelsberg et al The heXRD and PDF analyses were not available on the postreacted samples for the experiments performed at 40 and 50 °C.…”

Section: Methodsmentioning

confidence: 99%

“…An example of surprising reactivity in thin H 2 O films that has received much recent attention is the growth of magnesite (MgCO 3 ) at relatively low temperatures during the carbonation of forsterite (Mg 2 SiO 4 )a relatively reactive mineral in basalts with high carbonation potentialin wet scCO 2 . ,− This is unexpected since magnesite growth in bulk solution is relatively slow due to a high activation barrier related to the large hydration enthalpy and low water exchange rate of Mg 2+ . − Yet, forsterite was recently shown to react to form magnesite via an amorphous magnesium carbonate intermediate (AMC; MgCO 3 · x H 2 O, 0.5 < x < 1) in thin H 2 O films within just days to weeks at 25 °C in liquid CO 2 …”

Section: Introductionmentioning

confidence: 99%

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Thin Water Films Enable Low-Temperature Magnesite Growth Under Conditions Relevant to Geologic Carbon Sequestration

Kerisit

Mergelsberg

Thompson

et al. 2021

Environ. Sci. Technol.

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Injecting supercritical CO2 (scCO2) into basalt formations for long-term storage is a promising strategy for mitigating CO2 emissions. Mineral carbonation can result in permanent entrapment of CO2; however, carbonation kinetics in thin H2O films in humidified scCO2 is not well understood. We investigated forsterite (Mg2SiO4) carbonation to magnesite (MgCO3) via amorphous magnesium carbonate (AMC; MgCO3·xH2O, 0.5 < x < 1), with the goal to establish the fundamental controls on magnesite growth rates at low H2O activity and temperature. Experiments were conducted at 25, 40, and 50 °C in 90 bar CO2 with a H2O film thickness on forsterite that averaged 1.78 ± 0.05 monolayers. In situ infrared spectroscopy was used to monitor forsterite dissolution and the growth of AMC, magnesite, and amorphous SiO2 as a function of time. Geochemical kinetic modeling showed that magnesite was supersaturated by 2 to 3 orders of magnitude and grew according to a zero-order rate law. The results indicate that the main drivers for magnesite growth are sustained high supersaturation coupled with low H2O activity, a combination of thermodynamic conditions not attainable in bulk aqueous solution. This improved understanding of reaction kinetics can inform subsurface reactive transport models for better predictions of CO2 fate and transport.

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Low temperature and limited water activity reveal a pathway to magnesiteviaamorphous magnesium carbonate

Abstract: Forsterite carbonated in thin H2O films to magnesite via amorphous magnesium carbonate during reaction with H2O-bearing liquid CO2 at 25 °C. This novel reaction pathway contrasts with previous studies that...

Cited by 21 publications

References 22 publications

Low-Temperature Synthesis of Disordered Dolomite and High-Magnesium Calcite in Ethanol–Water Solutions: The Solvation Effect and Implications

Low-Temperature Synthesis of Disordered Dolomite and High-Magnesium Calcite in Ethanol–Water Solutions: The Solvation Effect and Implications

Solution additives promoting the onset of MgCO3 nucleation

Thin Water Films Enable Low-Temperature Magnesite Growth Under Conditions Relevant to Geologic Carbon Sequestration

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