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Title: Dynamics of Magnesite Formation at Low-Temperature and High pCO2 in Aqueous Solution

Abstract

Like many metal carbonate minerals, despite conditions of supersaturation, precipitation of magnesite from aqueous solution is kinetically hindered at low temperatures, for reasons that remain poorly understood. The present study examines precipitation products from reaction of Mg(OH)2 in aqueous solutions saturated with supercritical CO2 at high pressures (90 atm and 110 atm) and low temperatures (35 °C and 50 °C). Traditional bulk characterization (X-ray diffraction) of the initial solid formed indicated the presence of hydrated magnesium carbonates (hydromagnesite and nesquehonite), thermodynamically metastable phases that were found to slowly react during ageing to the more stable anhydrous form, magnesite, at temperatures as low as 35 °C (135-140 days) and at a faster rate at 50 °C (56 days). Undetected by bulk measurements, detailed examination of the precipitates by scanning electron microscopy (SEM) showed that magnesite is present as a minor component at relatively early reaction times (7 days) at 50 °C. In addition to magnesite dominating the solid phases over time, we find that mangesite nucleation and growth occurs more quickly with increasing partial pressure of CO2, and in electrolyte solutions with high bicarbonate content. Furthermore, formation of magnesite was found to be enhanced in sulfate-rich solutions, compared to chloride-rich solutions.more » We speculate that much of this behavior is possibly due to sulfate serving as sink of protons generated during carbonation reactions. These results support the importance of integrating magnesite as an equilibrium phase in reactive transport calculations of the effects of carbon dioxide sequestration on subsurface formations at long time scales.« less

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1222084
Report Number(s):
PNNL-SA-105262
KC0302060
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Environmental Science & Technology, 49(17):10736-10744
Country of Publication:
United States
Language:
English

Citation Formats

Qafoku, Odeta, Dixon, David A., Rosso, Kevin M., Schaef, Herbert T., Bowden, Mark E., Arey, Bruce W., and Felmy, Andrew R. Dynamics of Magnesite Formation at Low-Temperature and High pCO2 in Aqueous Solution. United States: N. p., 2015. Web. doi:10.1021/acs.est.5b02588.
Qafoku, Odeta, Dixon, David A., Rosso, Kevin M., Schaef, Herbert T., Bowden, Mark E., Arey, Bruce W., & Felmy, Andrew R. Dynamics of Magnesite Formation at Low-Temperature and High pCO2 in Aqueous Solution. United States. doi:10.1021/acs.est.5b02588.
Qafoku, Odeta, Dixon, David A., Rosso, Kevin M., Schaef, Herbert T., Bowden, Mark E., Arey, Bruce W., and Felmy, Andrew R. Thu . "Dynamics of Magnesite Formation at Low-Temperature and High pCO2 in Aqueous Solution". United States. doi:10.1021/acs.est.5b02588.
@article{osti_1222084,
title = {Dynamics of Magnesite Formation at Low-Temperature and High pCO2 in Aqueous Solution},
author = {Qafoku, Odeta and Dixon, David A. and Rosso, Kevin M. and Schaef, Herbert T. and Bowden, Mark E. and Arey, Bruce W. and Felmy, Andrew R.},
abstractNote = {Like many metal carbonate minerals, despite conditions of supersaturation, precipitation of magnesite from aqueous solution is kinetically hindered at low temperatures, for reasons that remain poorly understood. The present study examines precipitation products from reaction of Mg(OH)2 in aqueous solutions saturated with supercritical CO2 at high pressures (90 atm and 110 atm) and low temperatures (35 °C and 50 °C). Traditional bulk characterization (X-ray diffraction) of the initial solid formed indicated the presence of hydrated magnesium carbonates (hydromagnesite and nesquehonite), thermodynamically metastable phases that were found to slowly react during ageing to the more stable anhydrous form, magnesite, at temperatures as low as 35 °C (135-140 days) and at a faster rate at 50 °C (56 days). Undetected by bulk measurements, detailed examination of the precipitates by scanning electron microscopy (SEM) showed that magnesite is present as a minor component at relatively early reaction times (7 days) at 50 °C. In addition to magnesite dominating the solid phases over time, we find that mangesite nucleation and growth occurs more quickly with increasing partial pressure of CO2, and in electrolyte solutions with high bicarbonate content. Furthermore, formation of magnesite was found to be enhanced in sulfate-rich solutions, compared to chloride-rich solutions. We speculate that much of this behavior is possibly due to sulfate serving as sink of protons generated during carbonation reactions. These results support the importance of integrating magnesite as an equilibrium phase in reactive transport calculations of the effects of carbon dioxide sequestration on subsurface formations at long time scales.},
doi = {10.1021/acs.est.5b02588},
journal = {Environmental Science & Technology, 49(17):10736-10744},
number = ,
volume = ,
place = {United States},
year = {Thu Sep 17 00:00:00 EDT 2015},
month = {Thu Sep 17 00:00:00 EDT 2015}
}
  • The formation of magnesite was followed in aqueous solution containing initially added Mg(OH)2 equilibrated with supercritical carbon dioxide (90 atm pressure, 50°C) in the presence of introduced magnesite particles and minor components, Co(II). As expected, the introduction of magnesite particles accelerated the formation of magnesite from solution. However, the formation rate of magnesite was even greater when small concentrations of Co(II) were introduced, indicating that the increased rate of magnesite formation in the presence of Co(II) was not solely due to the addition of a growth promoting surface. Detailed analysis of the magnesite particles by scanning electron microscopy (SEM), transmissionmore » electron microscopy (TEM), energy dispersive spectroscopy (EDS), and atom probe tomography (APT) revealed that the originally added Co(II) was concentrated in the center but also present throughout the growing magnesite particles. Addition of the Co(II) in different chemical forms (i.e. as solid phase CoCO3 or Co(OH)2) could alter the growth rate of magnesite depending upon the addition of bicarbonate to the starting solution. Geochemical modeling calculations indicate that this difference is related to the thermodynamic stability of these different phases in the initial solutions. More broadly, these results indicate that the presence of even small concentrations of foreign ions that form carbonate compounds with a similar structure as magnesite can be incorporated into the magnesite lattice, accelerating the formation of anhydrous carbonates in natural environments.« less
  • No abstract prepared.
  • Aqueous solutions of lithium chloride are an excellent model system for studying the dynamics of water molecules down to low temperatures without freezing. The apparent dynamic crossover observed in an aqueous solution of LiCl at about 220 to 225 K [Mamontov, JPCB 2009, 113, 14073] is located practically at the same temperature as the crossover found for pure water confined in small hydrophilic pores. This finding suggests a strong similarity of water behavior in these two types of systems. At the same time, studies of solutions allow more effective explorations of the long-range diffusion dynamics, because the water molecules aremore » not confined inside an impenetrable matrix. In contrast to the earlier incoherent quasielastic neutron scattering results obtained for the scattering momentum transfers of 0.3 {angstrom}{sup -1} {le} Q {le} 0.9 {angstrom}{sup -1}, our present incoherent neutron spin-echo measurements at a lower Q of 0.1 {angstrom}{sup -1} exhibit no apparent crossover in the relaxation times down to 200 K. At the same time, our present nuclear magnetic resonance measurements of the diffusion coefficients clearly show a deviation at the lower temperatures from the non-Arrhenius law obtained at the higher temperatures. Our results are consistent with a scenario in which more than one relaxational component may exist below the temperature of the dynamic crossover in water.« less
  • No abstract prepared.