ARTICLE pubs.acs.org/crystal
Monitoring the Effect of Mineral Precursor, Fluid Phase CO2 H2O Composition, and Stirring on CaCO3 Crystallization in a Supercritical— Ultrasound Carbonation Process Ana M. Lopez-Periago,† Roberta Pacciani,‡,§ Lourdes F. Vega,‡,§ and Concepcion Domingo*,† †
Instituto de Ciencia de Materiales de Barcelona, Consejo Superior de Investigaciones Científicas (ICMAB-CSIC), Campus de la UAB s/n, Bellaterra, E-08193 Spain ‡ MATGAS Research Center, Campus de la UAB s/n, Bellaterra, E-08193 Spain § Carburos Metalicos, Air Products Group, C/Aragon 300, Barcelona, E-08009 Spain ABSTRACT: This study focuses on the evaluation of the different factors that affect the particle size distribution of precipitated calcium carbonate formed in a wet supercritical CO2 carbonation process and on the conversion rate from two different Ca2+ precursors (Ca(OH)2 or CaO). The operating factors investigated include the composition of the fluid phase (CO2/H2O) in contact with the solid precursor, the calcium cation source, and the stirring mode (no agitation, vertical mechanical, and ultrasound). The calcium carbonate particles were fabricated in batch mode in a stainless steel reactor filled with the solid precursor, water, and scCO2 at 130 bar and 40 °C. The particle size was estimated using scanning electron microscopy, while the precipitated solid phase composition was determined by a quantitative characterization method based on X-ray diffraction. The conversion of CaO or Ca(OH)2 to CaCO3 varied from 50 to >90 wt % depending on the reactor fill level and the existence of a rich-water phase in equilibrium with the scCO2-rich fluid. It was found that micrometric particles were precipitated in systems containing a large quantity of water in the fluid phase, while nanometric calcite was formed when using a reduced water percentage. The use of ultrasound stirring accelerated the kinetics of the carbonation process, thus increasing the calcium carbonate yield. The highest conversion rates were obtained using CaO as the solid precursor.
’ INTRODUCTION Calcium-containing inorganic minerals exhibit a strong reactivity to carbon dioxide (CO2) and can be favorably recrystallized into calcium carbonate (CaCO3) in the presence of water. The understanding of the carbonation reaction of portlandite (Ca(OH)2), quicklime (CaO), or minerals containing these compounds in contact with water and CO2 is of paramount importance due to the wide range of processes in the chemical, geochemical, and biological areas in which this reaction takes place.1 In the chemical industry, precipitated calcium carbonate (PCC) is the most produced white pigment worldwide, as it is used in the pulp and paper, paint, plastics, textile, and detergents industries, among others.2 4 Furthermore, the reaction of portlandite with CO2 is a valuable process used to tailor Portland calcium-rich cements, determining their hydraulic and mechanical properties and overall permeability.5 In geological applications, the carbonated material is used as a borehole cement to enhance the confining properties of wells and plugs for underground disposal of hazardous waste contaminated with heavy metals or even radioactive compounds,6 as well as for the storage of CO2 in oil or gas reservoirs, deep saline cavities, and flood basalts for greenhouse emissions mitigation.7 On the other hand, carbonates are also important precursors for solid adsorbents r 2011 American Chemical Society
used in processes of in situ removal of CO2 at high temperature, such as in the sorption-enhanced reaction process for high purity H2 production or from the flue gases of fossil fuel power plants.8 Industrially, PCC is produced through a gas solid liquid atmospheric carbonation route, which consists in bubbling gaseous CO2 through a concentrated aqueous slurry of Ca(OH)2 (slaked lime) in stirred reactors. Natural carbonation of Ca(OH)2 is a well-known phenomenon associated with the weathering of alkaline rocks, which plays an important role in the cycle of atmospheric CO2, or with the resistance of cement-based materials placed in humid environments. The atmospheric carbonation of Ca(OH)2 is a slow process, mainly due to the relatively low solubility of CO2 in water. In this respect, accelerated carbonation methods using supercritical carbon dioxide (scCO2) as a reactant in stirred systems have been described for the production of PCC9 14 and the formation of dense and low-pH cements.15 17 Moreover, it is worth pointing out that, in geological CO2 storage, injected CO2 in contact with the container is found under supercritical conditions. Received: July 14, 2011 Revised: September 21, 2011 Published: October 17, 2011 5324
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Figure 1. Schematic diagram of the experimental apparatus used for the carbonation reaction describing configurations 1 and 2.
The aim of this work is to give an accurate description of portlandite carbonation using scCO2 under experimental conditions relevant to industrial accelerated carbonation processes (stirred reactors) and natural carbonation in concrete or geological storage (nonagitated systems). The study of the extent of carbonation in the presence of scCO2 and water was performed by varying the calcium-source mineral (portlandite or quicklime), the reaction time, and the number of phases (one or two) for the water CO2 mixture in the reactor controlled by the relative concentration of each component. Results obtained in systems using ultrasound stirring were compared to nonagitated systems and with systems stirred using a conventional mechanical apparatus. Sonochemical processing, which is technically simple and can operate under ambient conditions, has been proven to be a useful technique for the preparation of novel materials with unusual structure and properties.18 Conventionally, sonication has been often used to influence crystallization of calcium carbonate from an aqueous solutions, which affects not only the nucleation rate and the particle size but also the relative amounts of precipitated polymorphs.19 21 The use of ultrasound combined with scCO2 is a nonconventional approach, which has already been successfully applied to accelerate supercritical extraction processes and for particle size control in different precipitation methods.22 28 Conversion to calcite was quantitatively calculated using X-ray diffractometry (XRD). Results were corroborated by thermogravimetry (TG). Morphological characterization was performed using scanning electron microscopy (SEM).
’ EXPERIMENTAL SECTION Materials. Analytical grade calcium hydroxide (Ca(OH)2 or portlandite, samples labeled P_) and calcium oxide (CaO or quicklime, samples labeled Q_) were purchased from Merck and Sigma-Aldrich, respectively. Ca(OH)2 slurries with a Ca2+ concentration of 2.7 mol L 1 were obtained either by redispersion of dry Ca(OH)2 in distilled water or by heterogeneous phase precipitation following hydration of CaO in a process known as lime slaking. Fresh slurries were prepared 2 h before being used in each experiment. CO2 (99.995%) was supplied by Carburos Metalicos S.A., Air Products Group (Spain).
Equipment and Procedure. Figure 1 shows a schematic drawing of the high-pressure apparatus used for carbonation. Experiments were carried out in a 110 mL reactor (Autoclave Engineer) operated in batch mode at the constant pressure (P) of 130 bar supplied by a syringe pump (ISCO 260D). The reactor was charged with a solid Ca2+-source and water in two different configurations. In the first design (configuration 1), suspensions of Ca(OH)2 (200 g L 1) or CaO (151 g L 1) in water were added to the reactor up to a filling level of 9 vol % (10 mL) or 27 vol % (30 mL). In the second set of experiments (configuration 2), the Ca2+ source and the liquid phase were placed physically separated in the reactor: 1 g of dry solid, either Ca(OH)2 or CaO, was placed at the bottom of the vessel, and a small amount of water (between 0.2 and 0.5 mL) was sprinkled on cotton wool placed in the middle of the reactor. In this configuration, the CO2 added to the system was expected to flow through the cotton- wool supporting the water and to dissolve the water until saturation. The effect of the stirring method was studied using three different setups: the first series of experiments was performed without agitation (na), the second one with vertical mechanical stirring (vm, MagnetDrive III with a 6 blade Ruston turbine impeller rotating at either 150 or 300 rpm), and the third one with ultrasonic agitation (us, Fisher Scientific, frequency 42 kHz and power 70 or 90 W). Once sealed, the vessel was heated up to a working temperature of 40 °C and CO2 was added until reaching 130 bar to start the carbonation reaction. After allowing the reagents to react for either 20 or 60 min, the reactor was depressurized rapidly and the suspensions recovered at this stage were filtered and dried under vacuum at 50 °C. Characterization. The precipitated powder was analyzed by XRD with a Rigaku Rotaflex RU200 B instrument. The diffraction patterns were recorded from 2θ = 20 to 60° with a step scan of 0.02° counting for 1 s at each step. X-ray diffractometry was used to identify the relevant calcium phases (CaCO3 and Ca(OH)2 or CaO). These phases were, then, quantified by using the relative intensity ratio (RIR) method described elsewhere.13,27 The accuracy of the method was verified by subjecting some of the samples to TG analysis using a Perkin-Elmer 7 instrument. The morphological analysis was performed with a SEM QUANTA FEI 200 FEG-ESEM.
’ RESULTS AND DISCUSSION The experimental conditions employed in each set of experiments and the phase composition of the precipitated samples, 5325
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Table 1. Operating Conditions Using Experimental Configuration 1 (Figure 1) and Results on Calcite Yield (wt %)a sample
a
Ca2+ source
Ca2+ (mol)
H2O (mol)
CO2 (mol)
fill level (vol %)
t (min)
stirring mode
stirring power
calcite (wt %)
1
Ca(OH)2
0.027
0.47
1.64
9
20
na
2
Ca(OH)2
0.027
0.47
1.64
9
60
na
3
Ca(OH)2
0.027
0.47
1.64
9
20
vm
150 rpm
64
4
Ca(OH)2
0.027
0.47
1.64
9
60
vm
150 rpm
68
5
Ca(OH)2
0.027
0.47
1.64
9
20
us
70 W
83
6
Ca(OH)2
0.027
0.47
1.64
9
60
us
70 W
86
7
Ca(OH)2
0.027
0.47
1.64
9
20
us
90 W
84
8 9
Ca(OH)2 CaO
0.027 0.027
0.47 0.47
1.64 1.64
9 9
60 20
us na
90 W
88 22
10
CaO
0.027
0.47
1.64
9
60
na
11
CaO
0.027
0.47
1.64
9
20
vm
150 rpm
64
12
CaO
0.027
0.47
1.64
9
60
vm
150 rpm
73
13
CaO
0.027
0.47
1.64
9
20
us
70 W
97
14
CaO
0.027
0.47
1.64
9
60
us
70 W
99
15
Ca(OH)2
0.081
1.41
1.32
27
20
na
5
16 17
Ca(OH)2 Ca(OH)2
0.081 0.081
1.41 1.41
1.32 1.32
27 27
60 20
na vm
150 rpm
20 34
18
Ca(OH)2
0.081
1.41
1.32
27
60
vm
150 rpm
65
19
Ca(OH)2
0.081
1.41
0.95
27
20
vm
300 rpm
67
20
Ca(OH)2
0.081
1.41
1.32
27
60
vm
300 rpm
70
21
Ca(OH)2
0.081
1.41
1.32
27
20
us
70 W
33
22
Ca(OH)2
0.081
1.41
1.32
27
60
us
70 W
77
23
Ca(OH)2
0.081
1.41
1.32
27
20
us
90 W
77
24
Ca(OH)2
0.081
1.41
1.32
27
60
us
90 W
84
25 47
41
Ca2+ [mol], H2O [mol], and CO2 [mol] indicated the amount of Ca(OH)2 and fluids in the reactor at the starting point of the experiments.
Table 2. Operating Conditions Using Experimental Configuration 2 (Figure 1) and Results on Calcite Yield (wt %)a sample
a
Ca2+ source
Ca2+ (mol)
H2O (mol)
CO2 (mol)
t (min)
stirring mode
stirring power
calcite (wt %)
25
Ca(OH)2
0.013
0
1.77
60
us
26 27
Ca(OH)2 Ca(OH)2
0.013 0.013
0.011 0.011
1.77 1.77
20 60
na na
28
Ca(OH)2
0.013
0.011
1.77
20
vm
150 rpm
29
Ca(OH)2
0.013
0.011
1.77
60
vm
150 rpm
57
30
Ca(OH)2
0.013
0.011
1.77
20
us
70 W
53
31
Ca(OH)2
0.013
0.011
1.77
60
us
70 W
64
32
Ca(OH)2
0.013
0.011
1.77
20
us
90 W
63
33
Ca(OH)2
0.013
0.011
1.77
60
us
90 W
67
34 35
CaO CaO
0.018 0.018
0 0.011
1.77 1.77
60 20
us us
70 W 70 W
5 24
36
CaO
0.018
0.011
1.77
60
us
70 W
37
CaO
0.018
0.030
1.77
20
na
38
CaO
0.018
0.030
1.77
60
na
39
CaO
0.018
0.030
1.77
20
vm
150 rpm
40
CaO
0.018
0.030
1.77
60
vm
150 rpm
89
41
CaO
0.018
0.030
1.77
20
us
70 W
85
42
CaO
0.018
0.030
1.77
60
us
70 W
92
70 W
7 49 55 48
33 82 91 88
Ca2+ [mol], H2O [mol], and CO2 [mol] indicated the amount of Ca(OH)2 and fluids in the reactor at the starting point of the experiments.
expressed as weight percentage [wt %] of calcium carbonate, are shown in Tables 1 and 2 for configurations 1 and 2 (Figure 1), respectively. For calcium carbonate, the polymorphic, morphologic, and particle size control is, most of the time, provided by adding certain macromolecular additives.29 34 The study of the
extent of carbonation of calcium-based minerals in the presence of scCO2 and water was performed by varying several process parameters, not including the addition of additives:35 38 (a) Ca2+-source mineral, added as either portlandite or quicklime; (b) mole ratio of the reagents, Ca2+/H2O/CO2; (c) reactor filled 5326
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Figure 2. Calculated weight percentage of CaCO3 in two samples obtained in the scCO2/Ca(OH)2 slurry (9 vol %) system, treated with vertical mechanical stirring (sample 3) and ultrasonic agitation (sample 5) during 20 min, analyzed using (a) TG weight loss and (b) the RIR method applied to X-ray normalized diffraction patterns.13,27
Figure 3. Schematic representation of the different steps occurring in the carbonation reaction. First, either Ca(OH)2 (a) or CaO (b) was dispersed in water and Ca(OH)2 tiny hexagonal platelets were formed. The drawing in part c indicates reaction (black arrow) and diffusion (blue arrow) steps, with the platelike portlandite precursor symbolized by shaded hexagons, and CaCO3 by cubes, indicating the rhombohedral morphology of the precipitated crystals.
level with the water/solid suspension, between 1.1 1.2. In contrast, the growth of the predominant (2,1, 1) face in scalenohedral calcite is inhibited for solutions under identical conditions of supersaturation but with more stoichiometric [Ca2+]/[CO32 ] ratios.46,47 Hence, the rhombohedral morphology was favored by enhancing the concentration of the CO32 anion in the scCO2 medium, which reduced the ratio of Ca2+ excess with respect to a conventional CO2 gas carbonation process. In the experiments performed applying ultrasound stirring, the main mechanism responsible for the high attained conversion was related to the intense agitation caused by acoustic streaming, and from the shearing forces, jets and shock waves produced by cavitational collapse in the water-rich phase.48 50 Moreover, applying ultrasonic agitation also causes significant mixing and turbulent motion in both the liquid phase and the suspended solids. Finally, collisions between growing crystals can produce abrasive surface effects and small fragments in the precipitated CaCO3 (Figure 4c, f, and i), which favor further dissolution of Ca(OH)2 and enhance the diffusion of newly formed Ca2+b (step ii*) in the slow stage of the reaction. Hence, for both filling levels and both stirring methods (mechanical and ultrasound), the conversion of Ca(OH)2 to carbonate was higher in the ultrasound treated samples than in the mechanically stirred ones. Furthermore, conversions were clearly higher for the agitated systems than for the nonagitated one (Figure 5a) with slurries prepared from either Ca(OH)2 or CaO. For a 9 vol % filling level, conversions in the fast (20 min) and slow (60 min) reaction stages were similar for both mechanical and ultrasound agitated systems, while for nonagitated systems the conversion of Ca(OH)2 to CaCO3 at 20 min was ca. half of the value reached after 60 min (Figure 5a). Besides the stirring
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Figure 5. Schematic representation of the different carbonation percentages attained for Ca(OH)2 (samples P_) and CaO (samples Q_) slurries (reactor fill level 9 or 27 vol % using configuration 1) treated with scCO2 during 20 and 60 min (Table 1) using (a) different stirring modes (na, no agitation; vm, vertical mechanical at 150 rpm; us, ultrasound at 70 W) and (b) different stirring powers (150 and 300 rpm in vm or 70 and 90 W in us).
mode, an increase of the level of filling of the overall reactor volume from 9 to 27 vol % also influenced the conversion to carbonate. By comparing data for portlandite suspensions (samples P_ in Figure 5a) carbonated using different reactor filling levels, lower conversions were obtained for the highest filling level after both 20 and 60 min, although the effect was more evident in the fast reaction step. For runs performed with stirred systems with a filling level of 27 vol %, the conversion after 20 min was ca. 50% of the value attained after 60 min, while it was nearly 100% in the 9 vol % filled reactor. With the same stirring method, the reduction of the CaCO3 yield in the first fast stage of the carbonation reaction with the increase of volume occupied by the liquid phase was related with a loss of stirring efficiency, thus indicating a predominant kinetic control ruled by Ca2+ diffusion (step ii in Figure 3c). To corroborate this finding, the stirring speed was increased from 150 to 300 rpm in experiments performed with the 27 vol % filled reactor, while the power in the ultrasound bath was increased from 70 to 90 W (Table 1). At 300 rpm or 90 W, the attained conversions were similar to those obtained for the 9 vol % filled reactor at 150 rpm or 70 W, respectively (Figure 5b). In the 9 vol % filled reactor agitated with the ultrasound bath, increasing the power from 70 to 90 W did not significantly modify the conversion (Figure 5b), suggesting that the reaction was controlled by Ca2+ dissolution (step i in Figure 3c) rather than by diffusion (step ii in Figure 3c). 5329
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Figure 6. Precipitated calcite particles at 60 min corresponding to samples in Table 2 originated from Ca(OH)2: (a) 27, (b) 29, (c) 31; and CaO: (d) 38, (e) 40, (f) 42.
A completely different scenario was observed for nonstirred systems at both filling levels, where low conversion degrees were achieved (Figure 5a). Due to the absence of agitation, the process was likely controlled by Ca2+ diffusion (step ii in Figure 3) from the very early stages of the reaction. In contrast, attained conversions with the 9 vol % filled reactor after 60 min were twice the values reached in the 27 vol % filled reactor (Table 1). These differences could not be exclusively attributed to Ca2+ diffusion, since in both systems the mole ratio Ca2+/H2O was similar (1:18). The main difference between the two systems was the volume of water through which CO32 must diffuse (step v) to reach the Ca2+b cations, which were situated near the Ca(OH)2 particles placed mainly at the bottom of the reactor in the nonagitated system. For the 27 vol % filled reactor, the water volume for CO32 diffusion was three times that of the 9 vol %, and therefore, mass transport resistance was also an important parameter. Moreover, the Ca2+/CO2 mole ratio in the highly filled reactor (1:16) was almost four times lower than that in the 9 vol % filled reactor (1:60), thus reducing the driving force for crystallization. Finally, for experiments performed using configuration 1 (Figure 1, 9 vol %), neither the CaCO3 conversions after 20 and 60 min (Figure 5a) nor the particles morphology (Figure 4a f) were significantly affected by the different Ca2+ source. Factors Affecting Conversion and Morphology in Configuration 2. Further experiments were performed with a system consisting of wet CO2 and dry Ca(OH)2 or CaO (Table 2) and, therefore, having in the reactor a fluid phase mostly composed by CO2 (configuration 2 in Figure 1). At the working temperature, the amount of H2O in the CO2-rich phase was quite small (yH2O = 4.7 10 3)51 and the CO2 properties could be approximated fairly well by those of pure CO2. The volume of added water (0.2 mL or 0.011 mol for Ca(OH)2 and 0.5 mL or 0.030 mol for CaO, respectively) was calculated as to be in a slight
excess of the minimum amount necessary to saturate the CO2 at the working pressure and temperature (ca. 0.15 mL). Moreover, it should be taken into account that the carbonation of portlandite produces 1 mol of water for each mol of reacting CO2 (Ca(OH)2 + CO2 S CaCO3 + H2O). Therefore, the water content of the reacting fluid increased throughout the carbonation reaction. Nevertheless, solid portlandite was mostly in contact with a scCO2 phase saturated with water, instead of a CO2-saturated water phase, as it was in the first series of experiments performed using configuration 1. Morphological analysis indicated that in all cases rhombohedral submicrometric calcite particles were precipitated (Figure 6). Previous work performed on the morphological control of calcite precipitated by carbonation of slaked lime47 has shown that the presence of submicrometric particles points toward calcite precipitation by the Ca(OH)2 surface route. In this route, nanometric particles of amorphous calcium carbonate are first precipitated in the lime surface. Dehydration and reorganization of this precursor is a slow process that requires a passage in solution to nucleate dehydrated calcite. In media with a reduced amount of water, like the one used in experiments performed following configuration 2, the interaction of the new nucleated tiny calcite particles with the substrate surface makes their interfacial free energy decrease, thus diminishing their tendency to grow and stabilizing the fine particles. Hence, a large population of nanometric particles (ca. 0.1 0.2 μm) was observed in the SEM images together with a few micrometric crystals (>1 μm). The conversion of Ca(OH)2 or CaO to CaCO3 via scCO2 requires the presence of water, since a significant transformation did not take place in experiments performed in a totally dry CO2 atmosphere (samples 25 and 34 in Table 2, respectively). In a first series of experiments (samples 26 36), the volume of water added to the reactor (0.2 mL or 0.011 mol) was calculated to be in a slight excess of the water necessary to saturate the CO2 at the working pressure and temperature (ca. 0.15 mL). For systems 5330
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and ultrasound stirred systems, the high conversion values indicated predominant control of Ca(OH)2 dissolution, at least in the first fast stage of the reaction. Due to the lack of a significant water-rich liquid phase when using scCO2 containing dissolved water as the gas phase in contact with the solid precursor, the conversion values were less affected by the stirring method. Calcite with rhombohedral morphology was precipitated using both configurations. However, larger particles (1 3 μm) were obtained by carbonating slurries than by carbonating wet solid reagents, in which a nanometric system was precipitated. Moreover, strong CaCO3 yield variations were found between the powders precipitated from either Ca(OH)2 or wet CaO in the gas solid configuration. Under similar stirring conditions, the reactivity of wet CaO was higher than that of the slaked lime prepared using commercial dry Ca(OH)2. Figure 7. Schematic representation of the different conversion percentages attained for Ca(OH)2 (samples P_) and CaO (samples Q_) dry reagents carbonated with wet scCO2 using configuration 2 treated with scCO2 during 20 and 60 min (Table 2) using different stirring modes (na, no agitation; vm, vertical mechanical at 150 rpm; us, ultrasound at 70 or 90 W).
starting with solid Ca(OH)2 (samples 26 33), the reaction stopped at a conversion value of ca. 50 60 wt %, progressing to slightly higher values only for ultrasound agitated systems (Figure 7). Increasing the ultrasound power from 70 to 90 W did not have any apparent effect on the conversion degree. Under similar experimental conditions (0.2 mL of water added to the reactor), the conversion percentage to calcite was significantly smaller for systems starting from CaO than for those involving Ca(OH)2 (Table 2). This was attributed to the requirement of CaO to transform into Ca(OH)2 by water absorption before being able to be carbonated. Hence, the 0.018 mol of CaO in the medium need 0.32 mL of water to form Ca(OH)2 in the 1:1 stoichiometric reaction (CaO + H2O f Ca(OH)2). As a consequence of the lack of water, the precipitated system was a mixture of CaO, Ca(OH)2, and a small amount of CaCO3. In a next series of experiments, the amount of added water was increased to a value of 0.5 mL (0.030 mol). For CaO reagent, addition of a stoichiometric amount of water results in the formation of a dry powder made up of Ca(OH)2 crystals. Slight excess of water leads to the formation of a slaked lime putty. Under these conditions, the transformation to calcite from freshly (in situ) formed Ca(OH)2 was almost completed (>90 wt %) even after the first 20 min of reaction (Figure 7), indicating that the carbonate layer around the reacting particles was likely not formed.52 It has been pointed out that the addition of water to CaO forms a colloidal slaked lime putty of high reactivity, while dried Ca(OH)2 did not retain the original colloidal behavior due to an effect of orientated aggregation during drying, which results in an increase of particle size and a reduction in surface area.53
’ CONCLUSIONS Supercritical gas liquid solid and wet gas solid systems were experimentally investigated in the precipitation process of calcium carbonate. In the two-phase fluid system, the carbonation reaction took place in the liquid phase and both the conversion degree and the kinetics were highly influenced by the stirring method. The low conversion values obtained for the nonagitated samples indicated that the reaction kinetics was controlled by ion diffusion. On the contrary, for mechanically
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
’ ACKNOWLEDGMENT The financial support of the Spanish government under projects Ingenio 2010 CEN-20081027 (CDTI), CTQ2008-05370/ PPQ, and MAT2010-18155 is gratefully acknowledged. Additional support for this work has been provided by the Generalitat of Catalonia under project 2009SGR-666 and by Carburos Metalicos. ’ REFERENCES (1) Ridgwell, A.; Zeebe, R. E. Earth Planet. Sci. Lett. 2005, 324, 299–315. (2) Xanthos, M. In Calcium Carbonate, in Functional Fillers for Plastics; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, 2005; doi: 10.1002/3527605096.ch16. (3) Li, L.; Collis, A.; Pelton, R. J. Pulp Pap. Sci. 2002, 28, 267–273. (4) Mathur, K. K.; Vanderheiden, D. B. In PVC: compounds, processing and applications; Lutz, J. T., Jr., Grossman, R. F., Eds.; Marcel Dekker: New York, 2001; Chapter 5, pp 114. (5) Huet, B.; Tasoti, V.; Khalfallah, I. Energy Procedia 2011, 4, 5275– 5282. (6) Huertas, J.; Hidalgo, A.; García-Gonzalez, C. A.; Domingo, C. Appl. Clay Sci. 2009, 42, 488–496. (7) Ingram, K. D.; Daugherty, K. E. Cem. Concr. Compos. 1991, 13, 165–170. (8) Choi, S.; Drese, J. H.; Jones, C. W. ChemSusChem 2009, 2, 796–854. (9) Gu, W.; Bousfield, D. W.; Tripp, C. P. J. Mater. Chem. 2006, 16, 3312–3317. (10) Montes-Hernandez, G.; Renard, F.; Geoffroy, N.; Charlet, L.; Pironon, J. J. Cryst. Growth 2007, 308, 228–236. (11) Domingo, C.; García-Carmona, J.; Loste, E.; Fanovich, A.; Fraile, J.; Gomez-Morales, J. J. Cryst. Growth 2004, 271, 268–273. (12) Domingo, C.; Loste, E.; Gomez, J.; García, J.; Fraile, J. J. Supercrit. Fluids 2006, 36, 202–215. (13) Lopez-Periago, A. M.; Pacciani, R.; García-Gonzalez, C.; Vega, L. F.; Domingo, C. J. Supercrit. Fluids 2010, 52, 298–305. (14) Regnault, O.; Lagneau, V.; Schneider, H. Chem. Geol. 2009, 265, 113–119. (15) Van Ginneken, L.; Dutre, V.; Adriansens, W.; Weyten, H. J. Supercrit. Fluids 2004, 30 (2), 175–188. (16) García-Gonzalez, C. A.; Hidalgo, A.; Andrade, C.; Alonso, M. C.; Fraile, J.; Lopez-Periago, A. M.; Domingo, C. Ind. Eng. Chem. Res. 2006, 45, 4985–4992. 5331
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Crystal Growth & Design
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dx.doi.org/10.1021/cg200895q |Cryst. Growth Des. 2011, 11, 5324–5332
