『Abstract
Occurrences of the mineral dawsonite (NaAl(OH)2CO3) after natural CO2 accumulation
support suggestions that this mineral may contribute to long-term
storage of CO2 in geological formations.
Knowledge of the reactivity of dawsonite is crucial to better
understand its role as a CO2 storage host.
Here the results of free-drift batch dissolution rate experiments
at 22, 60 and 77℃ performed on synthesized dawsonite are presented.
Based on previously reported dawsonite dissolution rate data at
circumneutral conditions and the present experiments, it is suggested
that the dissolution rates can be expressed by two parallel mechanisms
according to r+ = k1aH+v + k2,
where aH+ denotes
the proton activity. The The rate coefficient k1
(22℃) and order with respect to the proton activity v were estimated
from the 22℃ dataset to be 10-4.48±0.48 and 0.982±0.15,
respectively, at the 95％ confidence level. The rate coefficient
for the pH-independent region k2 (77℃) was
found to be approximately 10-6.89 from the maximum
R2 = 0.95 for the rate equation using the 77℃ dataset.
The k2 value was however uncertain because
of the few data points in the transition into the pH-independent
region. The apparent activation energy Ea
for the proton-promoted mechanism was estimated to 49.43 kJ/mol,
increasing to 63.82 kJ/mol for the data points approaching pH
independence. From the trends of data points for the 22 and 77℃
data series, it is likely that the difference in rates between
22 and 77℃ increases further at higher pH.』
1. Introduction
2.Materials and methods
2.1. Preparation and characterization of synthetic dawsonite
2.2. Reaction rates, experimental procedure
2.3. Thermodynamic calculations
3. Experimental results
3.1. Element release stoichiometry from the synthetic material
3.2. The dissolution rate of dawsonite
3.3. BET specific surface area changes
3.4. Total Inorganic Carbon (TIC) from selected experiments
4. Discussion
4.1. Were rates affected by the affinity of the reaction?
4.2. Why did rates slow down at far-from-equilibrium conditions
and constant pH?
4.3. Fitting the data to an empirical rate law with respect to
pH
4.4. Comparisons of rates with the earlier reported Hellevang
et al. (2005) data
5. Conclusions
Acknowledgments
Appendix A
References