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| Titel |
Direct nano-scale observations of CO2 sequestration during brucite (Mg(OH)2) dissolution |
| VerfasserIn |
J. Hövelmann, C. V. Putnis, H. Austrheim, E. Ruiz-Agudo |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250064437
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| Zusammenfassung |
| Mineralization of CO2 is regarded as the safest and most permanent option for carbon
sequestration (e.g., O’Connor et al. 2005). So far, research has been concentrated on the
carbonation of silicates such as olivine ((Mg,Fe)2SiO4) and serpentine (Mg3Si2O5(OH)4).
However, also the less common hydroxide mineral brucite (Mg(OH)2) has recently become a
focus of interest, owing to its much higher reactivity relative to silicate minerals at low
temperature and P CO2 conditions(e.g., Zhao et al. 2010; Schaef et al. 2011). Utilization of
brucite for carbon sequestration requires an in-depth understanding of the associated reaction
mechanisms from the macro- to the nano-scale. Therefore, we have conducted a
series of in-situ and ex-situ Atomic Force Microscopy (AFM) experiments enabling
direct nano-scale observations of dissolution and precipitation features on brucite
(001) cleavage surfaces. In particular, we tested the effects of pH (2-12), aqueous
NaHCO3 concentration (1μM – 1M) and P CO2 (0-1 bar) on brucite dissolution and
carbonation.
Brucite dissolution proceeded by the formation and spreading of etch pits with equilateral
triangular shapes. Measured etch pit spreading rates increased with decreasing
pH (from 0.030±0.008 nm/s at pH 9 to 0.70±0.07 nm/s at pH 2) and increasing
NaHCO3 concentration (from 0.038±0.004 nm/s in 1μM to 0.38±0.07 nm/s in 1M
solution). In pure NaHCO3 solutions (pH 7.2-9.3) secondary phase precipitation was
relatively minor. Enhanced precipitation was observed in slightly acidified NaHCO3
solutions (pH 5) as well as in solutions that were equilibrated with 1 bar CO2 (pH 4).
Nucleation predominantly occurred in areas of high dissolution such as larger step edges.
Initially, nucleating particles were only 1-2 nm and weakly attached to the brucite
surface as they could be easily pushed away by the scanning tip during in-situ AFM
experiments. Growth of the particles was observed after ex-situ AFM experiments
lasting for several hours. The size of individual particles increased to about 100
nm within 16 h. Lateral spreading of the particles was rather limited. Instead, we
observed the formation of particle clusters reaching total heights of up to 1 μm
after 32 h. SEM-EDX investigations confirmed that the precipitate is an Mg-rich
carbonate phase (probably hydromagnesite). Our results contribute to an improved
understanding of the mechanism of aqueous brucite carbonation at low temperature
and P CO2 conditions and to a further understanding of carbonation reactions in
general.
References
O’Connor, W. K., Dahlin, C. L., Rush, G. E., Gerdemann, S. J., Penner, L. R. and
Nilsen, D. N. (2005), Technical Report DOE/ARC-TR-04-002, Albany Research
Center.
Zhao, L., Sang, L., Chen, J., Ji, J. and Teng, H. H. (2010), Environ. Sci. & Technol., 44,
(1), 406-411.
Schaef, H. T.; Windisch, C. F.; McGrail, P. B.; Martin, P. F.; Rosso, K. M. (2011),
Geochim. Cosmochim Acta, 75, 7458-7471. |
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