『Abstract
Plagioclase is one of the most abundant sources of calcium in
the earth's crust, and it may play an important role for CO2 storage. This study address' the carbonation
of anorthite-rich plagioclase (An67-An73) in a system with fluid
transport, and under stagnant conditions.
A combined approach of flow-through column and batch experiments
has been used. Experimental conditions ranging from 100 to 250
℃ and 20 to 120 bar and different preparations of the starting
material were applied. The overall carbonation reaction consists
of plagioclase dissolution coupled to a number of precipitation
reactions. The flow-through column experiments at 250 ℃ showed
stoichiometric dissolution of the plagioclase. Al-hydroxide (“proto
Al-hydroxide”) nucleated on the plagioclase as the first phase
to precipitate. A secondary porosity development between the shrinking
plagioclase and the enclosing “proto Al-hydroxide”. Calcite, as
the second phase to precipitate, filled the primary pore space.
A reaction front was developed separating the zone at the inlet
where all the plagioclase had dissolved and the less reacted outlet
of the column. Redissolution of the calcite and formation of euhedral
boehmite crystals occurred when a sufficient amount of plagioclase
had dissolved. Clay minerals were not precipitated in the column
experiments. Between 11% and 30% of the plagioclase was dissolved
within 72-168 h of reaction. A much higher extent of plagioclase
dissolution was observed in the high pressure experiments compared
to the low pressure. However, a smaller share of the released
Ca was trapped as calcite in the high pressure experiments. Both
observations are consistent with a more rapid progression of the
dissolution front at high pressure.
The batch experiments from below the detection limit to 91% was
observed within reaction periods of 24-72 h. Crystallinity of
the feldspar was the most important factor contributing to increased
reaction rates. A general positive effect of increasing temperature
on the conversion is observed for all materials, whereas pressure
and the addition of CaCl2 did not have any
effect.
The carbonation of plagioclase at stagnant conditions is slow
compared to olivine at temperatures around 200 ℃. However, industrial
operations involving high fluid flows of CO2-water
mixtures induce gradients in pH or solute concentrations, which
may lead to increased reaction rates and changes in porosity/permeability.』
1. Introduction
2. Methods
2.1. Samples
2.2. Experimental procedures
2.2.1. Flow-through column experiments
2.2.2. Batch experiments
2.3. Analytical methods
2.2.1. Total carbon analyses (TC)
2.3.2. X-ray fluorescence (XRF)
2.3.4. X-ray diffraction (XRD)
2.3.4. Petrography
2.3.5. Electron microprobe
2.3.6. Particle size analyses
2.3.7. Specific surface area (BET)
2.3.8. Water analyses
2.4. Geochemical modelling
3. Results
3.1. Flow-through column experiments
3.1.1. Reaction textures
3.1.2. Aqueous chemistry
3.2. Batch experiments
3.2.1. Solid reaction residues/products
3.2.2. Aqueous chemistry
3.3. Degree of conversion
4. Discussion
4.1. Reaction mechanism
4.2. Stoichiometric dissolution coupled with precipitation
4.3. Effect of material properties
4.4. Physical and chemical experimental parameters
4.4.1. Pressure and fluid flow
4.4.2. Temperature
4.4.3. Addition of CaCl2
4.5. Implications for CO2 storage
5. Conclusions
Acknowledgments
Appendix A. Supplementary data
References