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Title: Ab initio thermodynamics of magnesium carbonates and hydrates in water-saturated supercritical CO 2 and CO 2 -rich regions

Authors:
; ;
Publication Date:
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
OSTI Identifier:
1358936
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Chemical Geology
Additional Journal Information:
Journal Volume: 434; Journal Issue: C; Related Information: CHORUS Timestamp: 2017-10-03 21:36:03; Journal ID: ISSN 0009-2541
Publisher:
Elsevier
Country of Publication:
Netherlands
Language:
English

Citation Formats

Chaka, Anne M., Felmy, Andrew R., and Qafoku, Odeta. Ab initio thermodynamics of magnesium carbonates and hydrates in water-saturated supercritical CO 2 and CO 2 -rich regions. Netherlands: N. p., 2016. Web. doi:10.1016/j.chemgeo.2016.04.005.
Chaka, Anne M., Felmy, Andrew R., & Qafoku, Odeta. Ab initio thermodynamics of magnesium carbonates and hydrates in water-saturated supercritical CO 2 and CO 2 -rich regions. Netherlands. doi:10.1016/j.chemgeo.2016.04.005.
Chaka, Anne M., Felmy, Andrew R., and Qafoku, Odeta. 2016. "Ab initio thermodynamics of magnesium carbonates and hydrates in water-saturated supercritical CO 2 and CO 2 -rich regions". Netherlands. doi:10.1016/j.chemgeo.2016.04.005.
@article{osti_1358936,
title = {Ab initio thermodynamics of magnesium carbonates and hydrates in water-saturated supercritical CO 2 and CO 2 -rich regions},
author = {Chaka, Anne M. and Felmy, Andrew R. and Qafoku, Odeta},
abstractNote = {},
doi = {10.1016/j.chemgeo.2016.04.005},
journal = {Chemical Geology},
number = C,
volume = 434,
place = {Netherlands},
year = 2016,
month = 9
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1016/j.chemgeo.2016.04.005

Citation Metrics:
Cited by: 2works
Citation information provided by
Web of Science

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  • An ab initio thermodynamic framework for predicting properties of hydrated magnesium carbonate minerals has been developed using density-functional theory linked to macroscopic thermodynamics through the experimental chemical potentials for MgO, water, and CO2. Including semiempirical dispersion via the Grimme method and small corrections to the generalized gradient approximation of Perdew, Burke, and Ernzerhof for the heat of formation yields a model with quantitative agreement for the benchmark minerals brucite, magnesite, nesquehonite, and hydromagnesite. The model shows how small differences in experimental conditions determine whether nesquehonite, hydromagnesite, or magnesite is the result of laboratory synthesis from carbonation of brucite, and whatmore » transformations are expected to occur on geological time scales. Because of the reliance on parameter-free first principles methods, the model is reliably extensible to experimental conditions not readily accessible to experiment and to any mineral composition for which the structure is known or can be hypothesized, including structures containing defects, substitutions, or transitional structures during solid state transformations induced by temperature changes or processes such as water, CO2, or O2 diffusion. Demonstrated applications of the ab initio thermodynamic framework include an independent means to evaluate differences in thermodynamic data for lansfordite, predicting the properties of Mg analogs of Ca-based hydrated carbonates monohydrocalcite and ikaite which have not been observed in nature, and an estimation of the thermodynamics of barringtonite from the stoichiometry and a single experimental observation.« less
  • Phase equilibria in mixtures containing carbon dioxide, water, and chloride salts have been investigated using a combination of solubility measurements and thermodynamic modeling. The solubility of water in the CO2-rich phase of ternary mixtures of CO2, H2O and NaCl or CaCl2 was determined, using near infrared spectroscopy, at 90 atm and 40 to 100 °C. These measurements fill a gap in the experimental database for CO2 water salt systems, for which phase composition data have been available only for the H2O-rich phases. A thermodynamic model for CO2 water salt systems has been constructed on the basis of the previously developedmore » Mixed-Solvent Electrolyte (MSE) framework, which is capable of modeling aqueous solutions over broad ranges of temperature and pressure, is valid to high electrolyte concentrations, treats mixed-phase systems (with both scCO2 and water present) and can predict the thermodynamic properties of dry and partially water-saturated supercritical CO2 over broad ranges of temperature and pressure. Within the MSE framework the standard-state properties are calculated from the Helgeson-Kirkham-Flowers equation of state whereas the excess Gibbs energy includes a long-range electrostatic interaction term expressed by a Pitzer-Debye-Hückel equation, a virial coefficient-type term for interactions between ions and a short-range term for interactions involving neutral molecules. The parameters of the MSE model have been evaluated using literature data for both the H2O-rich and CO2-rich phases in the CO2 - H2O binary and for the H2O-rich phase in the CO2 - H2O - NaCl / KCl / CaCl2 / MgCl2 ternary and multicompontent systems. The model accurately represents the properties of these systems at temperatures from 0°C to 300 °C and pressures up to ~4000 atm. Further, the solubilities of H2O in CO2-rich phases that are predicted by the model are in agreement with the new measurements for the CO2 - H2O - NaCl and CO2 - H2O - CaCl2 systems. Thus, the model can be used to predict the effect of various salts on the water content and water activity in CO2-rich phases on the basis of parameters determined from the properties of aqueous systems. Given the importance of water activity in CO2-rich phases for mineral reactivity, the model can be used as a foundation for predicting mineral transformations across the entire CO2/H2O composition range from aqueous solution to anhydrous scCO2. An example application using the model is presented which involves the transformation of forsterite to nesquehonite as a function of temperature and water content in the CO2-rich phase.« less
  • No abstract prepared.
  • We investigate the liquid structure, ion hydration, and some thermodynamic properties associated with the rigid geometry approximation to water by applying ab initio molecular dynamics simulations (AIMD) with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional at T = 320 K. We vary the rigid water geometry in order to locate a class of practical water models that yield reasonable liquid structure and dynamics, and to examine the progression of AIMD-predicted water behavior as the OH bond length varies. Water constrained at the optimal PBE gas phase geometry yields reasonable pair correlation functions. The predicted liquid phase pressure, however, is large ({approx}8.0 kbar).more » Although the O-H bond in water should elongate when transferred from gas to the condensed phase, when it is constrained to 0.02, or even just 0.01 {angstrom} longer than the optimal gas phase value, liquid water is predicted to be substantially overstructured compared to experiments. Zero temperature calculations of the thermodynamic properties of cubic ice underscore the sensitivity toward small variations in the O-H bond length. We examine the hydration structures of potassium, chloride, and formate ions in one rigid PBE water model. The results are in reasonable agreement with unconstrained AIMD simulations.« less
  • In geologic carbon sequestration, while part of the injected carbon dioxide will dissolve into host brine, some will remain as neat to water saturated super critical CO2 (scCO2) near the well bore and at the caprock, especially in the short-term life cycle of the sequestration site. Little is known about the reactivity of minerals with scCO2 containing variable concentrations of water. In this study, we used high-pressure infrared spectroscopy to examine the carbonation of brucite (Mg(OH)2) in situ over a 24 hr reaction period with scCO2 containing water concentrations between 0% and 100% saturation, at temperatures of 35, 50, andmore » 70 °C, and at a pressure of 100 bar. Little or no detectable carbonation was observed when brucite was reacted with neat scCO2. Higher water concentrations and higher temperatures led to greater brucite carbonation rates and larger extents of conversion to magnesium carbonate products. The only observed carbonation product at 35 °C was nesquehonite (MgCO3 • 3H2O). Mixtures of nesquehonite and magnesite (MgCO3) were detected at 50 °C, but magnesite was more prevalent with increasing water concentration. Both an amorphous hydrated magnesium carbonate solid and magnesite were detected at 70 °C, but magnesite predominated with increasing water concentration. The identity of the magnesium carbonate products appears strongly linked to magnesium water exchange kinetics through temperature and water availability effects.« less