Accelerating Natural CO2 Mineralization in a Fluidized Bed

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Accelerating natural CO2 mineralization in a fluidized bed Rajat Bhardwaj, J. Ruud van Ommen, Henk W. Nugteren, and Hans Geerlings Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b04925 • Publication Date (Web): 26 Feb 2016 Downloaded from http://pubs.acs.org on February 29, 2016

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Industrial & Engineering Chemistry Research

Accelerating natural CO2 mineralization in a fluidized bed Rajat Bhardwaj*, J. Ruud van Ommen, Henk W. Nugteren and Hans Geerlings Department of Chemical Engineering, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands; * E: [email protected]; T: +31 15 2782418. ABSTRACT: The presence of water is essential for the adsorption of CO2 on the serpentine particles. However, use of water in the slurry bed columns requires high energy inputs for maintaining temperature when operating above ambient temperatures. Moreover, separation, drying, handling and processing of the product stream will pose challenges and cost even more energy. Here, we show the proof of principle of CO2 sequestration on mineral particles in a fluidized bed using a moist CO2 stream. The setup allows wetting of particles while maintaining fluidization. Results show 50 % mineral conversion and 40 % CO2 conversion in 8 minutes at 1 bar and 90 °C.

Introduction: In nature, CO2 is removed from the atmosphere by photosynthesis and dissolution in water. Dissolved CO 2 is the source for (bio) chemical formation of carbonate rocks, but also an important agent for weathering of silicate rocks. During weathering in a carbonic acid rich environment, silicates react to silica and carbonates as mineralization products. Basic and ultrabasic rocks, formed at high temperatures, contain minerals that are largely unstable at atmospheric conditions and therefore show the highest weathering reaction rates. These minerals are mainly MgFe-Ca-silicates, such as olivines, pyroxenes and amphiboles. Their weathering reaction can be given in a simplified form as Mg-Fe-Ca-silicate + CO2  Mg-Fe-Ca-carbonate + silica

(1a)

and as an example in the specific case of forsterite (Mgolivine) as Mg2SiO4 + 2 CO2  2 MgCO3 + SiO2 forsterite + carbon dioxide  magnesite + silica

(1b)

The presence of water is essential for this reaction to proceed as CO2 can then be offered as HCO3- or CO32-, and a number of intermediate reaction products will be formed. One of these is the hydrous silicate serpentine, which can be formed according to 3 Mg2SiO4 + Mg2Si2O6 + 2 CO2 + 4 H2O  2 Mg3Si2O5(OH)4 + 2 MgCO3 + SiO2 forsterite + pyroxene + CO2 + H2O  serpentine + magnesite + silica (1c)

or in case no CO2 is present, directly from forsterite, pyroxene and water. Reactions of the form of eq (1) have been major contributors to permanent sequestration of CO2 on earth1,2. Therefore, accelerating natural CO2 mineralization could in potential be a viable solution for capture and storage of CO2. The

reactions as occurring in nature are too slow to be directly applied industrially for capture of CO2 from flue gas3-5. However, if the reaction rates can be significantly increased, such mineralization reactions could have high potential for capture and storage of CO2 at industrial point sources3-6. To achieve reasonable reaction rates, conditions must be such that liquid water is present7,8,9,10,11,12. Serpentine is the main component of serpentinite rock of which abundant and easy to mine deposits can be found all over the globe. When calcined between 610 °C and 790 °C its (OH)-groups are released, resulting in a reactive amorphous phase of an olivine-pyroxene composition13. As proposed by Steinfeld14, for biomass gasification, the thermal activation may be carried out using solar energy at locations where both resources are abundant, such as in the dry Oman Mountains, where released water could be a source of drinking water. Wet slurry columns have been used for carbonation reactions of silicate minerals5,7,15,16,17. However, the large amount of liquid in such columns requires high energy inputs for maintaining temperature when operating above ambient temperatures. Moreover, separation, drying, handling and processing of the product stream will pose challenges and cost even more energy. Fluidized beds offer enhanced mass and heat transfer, require less mass to be heated, yield dry and easier to handle products and therefore use significantly less energy compared to wet slurry columns. However, for achieving significant conversion yields under dry conditions, high pressures and temperatures will be required. The use of such conditions pose an economic challenge for the use of fluidized beds for the mineralization of serpentine. The operation of fluidized bed with wet mineral particles atmospheric pressures and moderate temperatures, can take the advantage(s) of both slurry columns and fluidized beds. However, a proof of such an approach is absent in the literature.

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This paper shows the proof of principle for CO 2 mineralization in a bed of mineral particles fluidized by a moist CO2 stream. Our reactor setup allows wetting of particles and fluidization simultaneously and therefore is capable of achieving appreciable mineral and CO2 conversion at 1 bar and 65 °C – 95 °C. Results show 50 % mineral conversion and 40 % CO2 conversion in 8 minutes at 1 bar and 90 °C. Materials and methods:

Serpentinite rock is obtained from Lizard Point, Cornwall, England. The sample contained 57 % lizardite (determined by QXRD), the rest being forsterite, tremolite, enstatite, chlorite and talc. Although most of those minerals may react with CO2 (see eq (1)), their reaction rates are too low to be used in an industrial process. By calcination of this serpentinite rock only lizardite is activated to form an amorphous phase that leaches Mg2+ ions to react with CO2. The other phases are therefore considered as nonleachable18. The bulk Mg content is 21.2 wt% (or 35.3 wt% MgO) as determined by XRF. The ground rock is thermally activated for 16 hours at 610 °C, resulting in a powder with an median particle diameter (d50) of 11.3 µm and a bulk density of 1160 kg/m3. For an analysis of particle size distribution, refer to Figure S1 (SI).

necessary to avoid agglomeration in the partially wet bed. Pure CO2 is wetted by passing it over a thermostatic water bath, and is then blown into the column to fluidize the serpentinite particles. The reactor is typically loaded with 45 g of calcined serpentinite and operated in batch mode at constant temperature during a predetermined time. Experiments were done at atmospheric pressure and temperatures between 65 °C and 95 °C. Product samples were taken out from the wellmixed bed at 0.05 m above its base. Samples were analysed by thermo-gravimetric analyzer (Mettler Toledo TGA/SDTA 851e). The TGA was operated in a N2 atmosphere from 25 °C to 950 °C with a temperature increase of 10 °C per minute. For a detailed description of methods, refer to Figure S2 (SI). Figure 1 (b) gives a schematic description of mechanisms for carbonate formation on the surface of serpentinite particles. The reaction steps have been detailed previously 7 and the kinetics of such reactions are generally believed to follow a shrinking core mechanism19. Whether this applies in this case as well could not be verified, however the overall reaction mechanism can be described as follows. Moisture in the input stream condenses in the form of a thin liquid film around the serpentinite particles. Because of the high 𝑝𝐶𝑂2 of the incoming stream, CO2 will dissolve in this water film and form species such as HCO3- and CO32-. This makes the water film acidic, a favorable condition to dissolve serpentine and produce Mg2+ ions at the surface of the particles. Precipitation of Mg-carbonates and silica is the last step of the carbonation reaction. The amount of CO2 reacted or captured by the carbonation reaction, 𝑚𝐶𝑂2 ,𝑐𝑎𝑝𝑡𝑢𝑟𝑒𝑑 , is obtained by measuring the weight loss (TGA analysis of the product) caused by the decomposition reaction of Mg-carbonate into periclase (MgO) and CO2, which takes place at temperatures higher than 300 °C. Knowing the amount of CO2 supplied, 𝑚𝐶𝑂2 ,𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑑 , which is the CO2 mass flow rate multiplied by the duration of the experiment, the CO2 conversion is given by 𝑋𝐶𝑂2 =

Figure 1: a) Activated serpentinite particles are fluidized by a CO2 gas stream saturated with water vapor. The progress of the mineralization reaction is monitored by thermo-gravimetric analysis (TGA) combined with mass spectrometry (MS). b) The inset shows the formation of the carbonate-silica product layer at the surface of the particles.

The experimental set-up, consisting of a glass column (0.5 m high and 0.025 m diameter) and a 1000 W halogen lamp (bulb length 0.3 m), mounted on a vibrating table with maximum frequency of 50 Hz, is shown in Figure 1a. The temperature of the column is regulated by a temperature controller with a feedback to the power of the lamp, allowing the temperature in the reactor to be maintained within ±2 °C of the pre-set temperature. Vibration is

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𝑚𝐶𝑂2 ,𝑐𝑎𝑝𝑡𝑢𝑟𝑒𝑑

(2)

𝑚𝐶𝑂2 ,𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑑

Similarly, the mineral conversion is given by 𝑋𝑚𝑖𝑛𝑒𝑟𝑎𝑙 =

𝑚𝑀𝑔2+,𝑟𝑒𝑎𝑐𝑡𝑒𝑑 𝑚𝑀𝑔2+,𝑎𝑣𝑎𝑖𝑙𝑎𝑏𝑙𝑒

=

𝑚𝐶𝑂2 ,𝑐𝑎𝑝𝑡𝑢𝑟𝑒𝑑 𝑚𝐶𝑂2 ,𝑐𝑎𝑝𝑡𝑢𝑟𝑒𝑑 𝑎𝑡 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦

(3) Extraction of magnesium (as Mg2+ ions) from magnesium silicate rocks during mineral carbonation is an important step prior to CO2 fixation as solid magnesium carbonate20,21,22,23. The maximum amount of magnesium that is available for reaction in the activated serpentinite raw material, 𝑚𝑀𝑔2+ ,𝑎𝑣𝑎𝑖𝑙𝑎𝑏𝑙𝑒 , and thus the maximum CO2 capture capacity, 𝑚𝐶𝑂2 ,𝑐𝑎𝑝𝑡𝑢𝑟𝑒𝑑 𝑎𝑡 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 , depends on the mineralogical composition of the serpentinite rock used. Among the minerals detected, only

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lizardite (a serpentine polymorph) is considered to contain leachable Mg2+ species. QXRD results allowed to calculate that although the whole rock analysis reports 21.2 % Mg, only 13.3 % Mg is leachable after complete activation or calcination. However, not all OH-groups from lizardite were released (9.35 % weight loss by TGA from 300 °C to 900 °C), as only 7.31 % weight loss upon calcination was recorded. The remaining 2.04 % was indeed recorded as weight loss by TGA from the activated sample for the same range of temperature (300 0C to 900 0C). This indicates that the efficiency of the activation process was 78%. Mg was leached from the calcined sample in an autoclave by suspending the powder in a solution of 0.1 M NaHCO3 in water for 5 hours at an L/S = 50, T = 140 °C and p = 30 bar. The concentration of NaHCO3 was kept low to assure that the pH could not increase to levels favorable for carbonate precipitations, as at 0.5 M and higher buffering of pH in the range of 6.5 – 7 was recordered24. The final Mg concentration in the leachate was 1.63 g/L. Other serpentinite samples were treated in the same batch and Mg concentrations of up to 2.87 g/L were found, indicating that saturation was not reached and carbonation did not occur in the sample used for this study. From the 1.63 g/L Mg in the sample is was calculated that the leaching efficiency was 61.4 %. This means that under practical conditions the highest achievable amount of Mg to react with CO2 is 0.614 of the 13.3 % of theoretical leachable Mg, which is 8.17 %. We will use this amount of Mg as 𝑚𝑀𝑔2+ ,𝑎𝑣𝑎𝑖𝑙𝑎𝑏𝑙𝑒 under practical conditions and use it as a benchmark for the fluidized bed experiments. If all this Mg reacts to form MgCO3, 14.87 g of CO2 is captured per 100 g of serpentinite, and the resulting product will contain 12.9 % CO2. In case the reaction product is hydromagnesite (Mg5(CO3)4(OH)24H2O), 100 g of serpentinite will capture at a maximum 11.89 g CO 2 and 6.08 g H2O (weight ratio CO2/H2O = 1.96). For the commonly encountered compound nesquehonite [MgCO33 H2O] this will be 14.87 g CO2 and 18.25 g H2O [ratio 0.81]. Note that if all Mg present in lizardite is taken as the benchmark, then these amounts will have to be multiplied by a factor 1.63 (being 1 / 0.614). Consequently, all mineral conversion calculated hereafter will become a factor 0.614 less, whereas the CO2 conversion will remain the same.

Results: Figure 2 shows typical TGA data for a sample of serpentinite obtained from the fluidized bed (loading 45 g) after 10 minutes of carbonation at a temperature of 90 °C. The graph shows three steps of mass loss. The first step, from 25 °C to the first flexure point at approximately 150 °C, corresponds to loss of free or loosely bound water. The second step, from 150 °C to 300 °C, depicts loss of weight corresponding to release of bound water. The last step corresponds to the release of CO2, which takes place above 300 °C (and taken up to 900 °C). This last step shows that it is indeed feasible to mineralize CO2 in a fluid bed reactor. Note that the current experiments were done at 1 bar with pure CO2, which is not flue gas.

From the data on Figure 2 it is calculated that 100 g serpentinite has captured 5.57 g CO2, 2.85 g fixed H2O and 6.53 g total H2O (after correction for the blank). From this, the x-ray amorphous reaction product could not be determined since the fixed water CO2/H2O ratio (1.95) points to hydromagnesite and the total water ratio (0.85) to nesquehonite. Assuming that samples taken from the fluidized bed contain significant amounts of moisture, hydromagnesite is taken in the following to calculate mineral conversion. For the example in Figure 2 this leads to a mineral conversion of 47 % and a CO2 conversion of 33 %. For the TGA of blank (activated) serpentinite sample and the detailed calculations on mineral and CO2 conversion refer to Figure S3 (SI) and Figure S4 (SI), respectively. 100 99

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Mass Loss < 150 °C: 4.34 % (free H2O)

97 96 95

Mass Loss 150 °C - 300 °C: 3.30 % (fixed H2O)

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Mass %

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Mass Loss 300 °C - 900 °C: 7.05 % (CO2)

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Figure 2: TGA analysis of a typical product sample of mineral carbonation. The experiment was conducted with 45 g of serpentinite particles in the fluidized bed at 90 °C with a CO2 flow at 0.42 L/min for a duration of 10 minutes (the experiment at 10 minutes in Figure 5). The first two steps indicate release of free and fixed water and the third step indicates release of CO2.

Next, the maximum achievable CO2 and mineral conversions with the current setup are further explored, as well as the influence of temperature and bed mass thereof. Figure 3 shows a significant increase of the mineral conversion as a function of the temperature inside the fluidized bed. As the CO2 flow rate is constant, also more CO2 must have been captured after 20 minutes when the mineral conversion increases. This is confirmed by the increasing CO2 conversion as shown in Figure 3. All experiments were

conducted with 45 g of activated serpentinite particles for a duration of 20 minutes. This increasing conversion with increasing temperature is attributed to a combined effect of improved kinetics and increased moisture content. A higher temperature not only leads to a higher reaction rate but in our experimental set-up also ensures the availability of enough water vapor for the formation of a condensation film on the surface of serpentinite particles. Because of ease and better controllability of operation, further experiments were carried out at 90 °C. Figure 4 shows an increase of the CO2 conversion with increase in bed mass inside the fluidized bed. These experiments were conducted at 90 °C for a duration of 20 minutes. The data show a perfect linear fit, which is also

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Industrial & Engineering Chemistry Research reflected by a nearly constant mineral conversion for the three experiments (40.7 %; 41.0 % and 40.6 %, in agreement with the value found at 90 C in Figure 3.).This means that the carbonation reaction is independent of the bed mass within the experimental range. A larger bed mass increases the residence time of CO2 in the reactor and enables contact between gas and solids. This result suggests that it is possible to scale up the size and loading of the fluidized bed, which will be required for an industrial setup operating at much larger bed masses.

Mineral Conversion (□) / % CO2 Conversion () / %

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Figure 3: The effect of the operating temperature of the fluidized bed on the mineral conversion (squares) and CO2 conversion (diamonds). Experiments were conducted with 45 g of activated serpentinite particles for 20 minutes.

continuous operation, the residence time of the serpentinite should be in the order of ten minutes. The conversion reaction takes place at the surface of the lizardite particles and the products form a layer on this surface shielding the lizardite from the CO2/H2O reactant. At a certain time shielding becomes dominant and the mineral conversion will not further increase as can be seen in Figure 5a. In this case, the maximum conversion is in the order of 50%, but this depends on the particle size and the removal of product fines by attrition of the particles in the bed. Fines which are collected at the exit of the reactor contain approximately 19 % CO2. When applying the same calculation as for the bed samples, mineral conversion of over 200 % is found (refer to Figure S5 in (SI) for calculation). This can be explained by strong attrition inside the fluidized bed, causing the reaction products to wear off from the surface of serpentinite particles. The pure reaction products according to equation 1b, adjusted by hydration, would contain 26 % or 28.5 % CO2 for nesquehonite or hydromagnesite respectively. This shows that these fines consist predominantly of reaction products. It also means that because of the loss of reaction products, actual conversions for bed samples are higher than calculated. Attrition in the bed makes new surfaces available for reaction and therefore assists the carbonation reaction. By promoting attrition and tuning the particle size, the efficiency of the bed may be further improved. (a) 60

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Figure 4: The effect of bed loading (mass of particles) on CO2 conversion. The mineral conversion was found to remain constant at around 41 %, in agreement with the value found at 90 C in Figure 3. Experiments were conducted at 90 °C for 20 minutes.

(b) 80

Figure 5a shows the variation of mineral conversion with time in a bed with 45 g of activated serpentinite and a constant CO2 flow of 0.42 L/min. To measure the conversion with time, samples were taken every two minutes after a steady temperature (90 °C) was reached. The detailed procedure is explained in the, refer to Figure S2 (SI). The graph shows that approximately 50 % CO 2 conversion of the serpentinite can be achieved under the given conditions (temperature, particle size, gas flow). This means that in practice approximately 7.5 g CO2 can be captured per 100 g of the used activated serpentinite rock. Most of the mineral conversion in the fluidized bed takes place within the first ten minutes of operation. Hence, in a

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Figure 5: Variation of the mineral conversion (a) and CO2 conversion (b) of batch reactor fluidized bed carbonation with increasing time. Samples are withdrawn after every two minutes and analysed by TGA. Starting bed mass is 45 g and operating temperature is 90 °C. The conversion values are cumulative with time.

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However, the composition of the fines shows that under the present conditions the bed material will become enriched in inert serpentinite components and therefore removal of the fines alone and addition of new bed material will not be sufficient to operate the bed. Some replacement of the bed to remove the non-reactive components will have to be carried out as well. The attrition mechanism is a big advantage of the fluidized bed approach compared to the use of slurry columns. Figure 5b shows the cumulative CO2 conversion for the same experiments. During the first four minutes, when most of the minerals react, approximately 70 % of the supplied CO2 has reacted. After that, when less mineral reactions take place, the CO2 conversion gradually decreases with time and most of the supplied CO2 will leave the bed unreacted. This value gives an indication of the optimum column operation time given a certain bed mass and CO2 flow rate for a required CO2 conversion under the experimental conditions. The optimal residence time for mineral particles and CO 2 are important characteristics for designing a reactor. While the residence time of mineral particles depends on the temperature through the reaction kinetics and availability of liquid water, the optimal residence time of CO2 is dependent on the rate of mineral conversion and total bed mass. Thus, the required values of residence times for mineral and CO 2 will decide reactor conditions (temperature, moisture content) and the size of the reactor. The present study indicates that the optimal residence time of minerals is in the order of 4 to 8 minutes, whereas the optimal column operation time to achieve CO2 conversions of 50 % and more is in the order of 2 to 4 minutes. With longer operation the overall CO2 conversion drops down steeply as the mineral conversion slows down. However, since these times are interdependent, decoupling would be beneficial for the design of an efficient mineralization reactor. This can be achieved by recirculating the gas or by using multiple fluidized beds in series. More efficient condensation of water near the exit of the fluidized bed may also have contributed to the formation of the fines that consist predominantly of reaction products. Good control over condensing water film on serpentinite particles will further facilitate optimization of mineral and CO2 conversion. Conclusions The current work shows a successful first step for using a fluidized bed to sequester CO2 by mineralizing activated serpentinite. The results presented in this paper show that maximum 7.5 g of CO2 can be sequestered by 100 g of the serpentinite used. It holds the promise that with a careful selection of rock (pure serpentine and high Mg leachability) and optimization of the operating conditions, CO2 sequestration capacity may be doubled or tripled. An integrated CO2 capture and sequestration process using a moist CO2 stream in a fluidized bed reactor is a feasible option and may be an attractive solution for capture of CO 2 from flue gas.

Supporting Information: Particle size distribution of activated serpentinite powder (Figure S1), experimental setup and procedure of experimentation (Figure S2), TGA of blank (activated) serpentine sample (Figure S3), calculation of mineral conversion and CO2 conversion (Figure S4), TGA of fines (Figure S5), . The Supporting Information is available free of charge on the internet at http: //pubs.acs.org.

Author information: Corresponding Author * Rajat Bhardwaj. Tel: +31-15-2782418. Email: [email protected]

Notes: The authors declare no competing financial interest.

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Vapor: a Feasibility Study for Carbon Dioxide Sequestration. Environ. Sci. Pollut. Res. 2015, 22, 13486. (10) Eikeland, E.; Blichfeld, A. B.; Tyrsted, C.; Jensen, A.; Iversen, B. B. Optimized Carbonation of Magnesium Silicate Mineral for CO2 Storage. ACS Appl. Mater. Interfaces 2015, 7, 5258. (11) Gadikota, G.; Swanson, E. J.; Zhao, H.; Park, A. H. A. Experimental Design and Data Analysis for Accurate Estimation of Reaction Kinetics and Conversion for Carbon Mineralization. Ind. Eng. Chem. Res. 2014, 53, 6664. (12) Bao, W., Li, H.; Zhang, Y. Selective Leaching of Steelmaking Slag for Indirect CO2 Mineral Sequestration. Ind. Eng. Chem. Res. 2010, 49, 2055. (13) McKelvy, M. J.; Chizmeshya, A. V.; Diefenbacher, J.; Béarat, H.; Wolf, G.; Exploration of the Role of Heat Activation in Enhancing Serpentine Carbon Sequestration Reactions. Environ. Sci. Technol. 2004, 38, 6897. (14) Piatkowski, N.; Wieckert, C.; Weimer, A.W.; Steinfeld, A. Solar Driven Gasification of Carbonaceous Feedstock-a Review. Energy Environ. Sci. 2011, 4, 73. (15) Huijgen, W. J. J.; Comans, R. N. J. Literature Review Report on Carbon Dioxide Sequestration by Mineral Carbonation. Energy research Centre of the Netherlands, Petten, 2003. (16) Fagerlund, J.; Nduagu, E.; Zevenhoven, R. Recent Developments in the Carbonation of Serpentinite Derived Mg(OH)2 Using a Pressurized Fluidized Bed. Energy Procedia, 2011, 4, 4993. (17) Werner, M.; Hariharan, S.; Mazzotti, M. Flue Gas CO2 Mineralization Using Thermally Activated Serpentine: from Single to Double-step Carbonation. Phys. Chem. Chem. Phys. 2014, 16, 24978. (18) O’Connor, W. K.; Dahlin, D. C.; Rush, G. E.; Gedermann, S. J.; Penner, L. R.; Nilsen, D. N. Aqueous Mineral Carbonation, Final Report. DOE/ARC-TR04, Office of Fossil Energy, US DOE, 2005. (19) Levenspiel, O. Chemical Reaction Engineering, third ed.; Anderson, W; Santor, K; John Wiley & Sons, New York, 1999. (20) Lackner, K. S. Carbonate Chemistry for Sequestering Fossil Carbon. Annu. Rev. Energ. Environ. 2002, 27, 193. (21) Lackner, K. S.; Butt, D. P.; Wendt, C. H. Progress on Binding CO2 in Mineral Substrates. Energy Convers. Manage. 1997, 38, 259. (22) Zevenhoven, R.; Teir, S.; Eloneva, S. Heat Optimization of a Staged Gas-Solid Mineral Carbonation Process for Long-Term CO2 Storage. Energy 2008, 33, 362. (23) Nduagu, E. I.; Highfield, J.; Chen, J.; Zevenhoven, R. Mechanisms of Serpentine–Ammonium Sulfate Reactions: Towards Higher Efficiencies in Flux Recovery and Mg Extraction for CO2 Mineral Sequestration. RSC Adv. 2014, 4, 64494. (24) Gadikota, G.; Matter, J.; Kelemen, P.; Park, A. H. A. Chemical and Morphological Changes During Olivine Carbonation for CO2 Storage in the Presence of NaCl and NaHCO3. Phys. Chem. Chem. Phys. 2014, 16, 4679.

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List of figure captions in manuscript: Figure 1: a) Activated serpentinite particles are fluidized by a CO2 gas stream saturated with water vapor. The progress of the mineralization reaction is monitored by thermo-gravimetric analysis (TGA) combined with mass spectrometry (MS). b) The inset shows the formation of the carbonate-silica product layer at the surface of the particles. Figure 2: TGA analysis of a typical product sample of mineral carbonation. The experiment was conducted with 45 g of serpentinite particles in the fluidized bed at 90 °C with a CO2 flow at 0.42 L/min for a duration of 10 minutes (the experiment at 10 minutes in Figure 5). The first two steps indicate release of free and fixed water and the third step indicates release of CO2. Figure 3: The effect of the operating temperature of the fluidized bed on the mineral conversion. Experiments were conducted with 45 g of activated serpentinite particles for 20 minutes. Figure 4: The effect of bed loading (mass of particles) on CO2 conversion. Experiments were conducted at 90 °C for 20 minutes. Figure 5: Variation of the mineral conversion (a) and CO2 conversion (b) of batch reactor fluidized bed carbonation with increasing time. Samples are withdrawn after every two minutes and analysed by TGA. Starting bed mass is 45 g and operating temperature is 90 °C. The conversion values are cumulative with time. Figure 5b shows the cumulative CO2 conversion for the same experiments. During the first four minutes, when most

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Accelerating Natural CO2 Mineralization in a Fluidized Bed

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