Next Article in Journal
Cloud Incubator Car: A Reliable Platform for Autonomous Driving
Previous Article in Journal
Designing the Mind of a Social Robot
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

The Conversion of Wollastonite to CaCO3 Considering Its Use for CCS Application as Cementitious Material

Institute for Geosciences and Geography, Martin-Luther-University of Halle-Wittenberg, Von-Seckendorff-Platz 3, 06120 Halle (Saale), Germany
*
Author to whom correspondence should be addressed.
Submission received: 21 December 2017 / Revised: 7 February 2018 / Accepted: 8 February 2018 / Published: 20 February 2018
(This article belongs to the Section Chemical and Molecular Sciences)

Abstract

:

Featured Application

Building materials and CCS.

Abstract

The reaction of wollastonite (CaSiO3) with CO2 in the presence of aqueous solutions (H2O) and varied temperature conditions (296 K, 323 K, and 333 K) was investigated. The educts (CaSiO3) and the products (CaCO3 and SiO2) were analyzed by scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), and differential scanning calorimetry with thermogravimetry coupled with a mass spectrometer and infrared spectrometer (DSC-TG/MS/IR). The reaction rate increased significantly at higher temperatures and seemed less dependent on applied pressure. It could be shown that under the defined conditions wollastonite can be applied as a cementitious material for sealing wells considering CCS applications, because after 24 h the degree of conversion from CaSiO3 to CaCO3 at 333 K was very high (>90%). As anticipated, the most likely application of wollastonite as a cementitious material in CCS would be for sealing the well after injection of CO2 in the reservoir.

1. Introduction

To reduce the amount of CO2 in the atmosphere (currently 403 ppm [1]) several possibilities need to be considered. One possible technology being investigated and discussed is carbon capture and storage (CCS). The goal of CCS is reducing CO2 emissions from burning of fossil fuel by storing considerable amounts in suitable deep geologic reservoirs. The reservoirs considered for injection could be on- or offshore formations which could be in part already former exploited gas fields [2]. After injection, the sealing of wells in deep geologic formations being considered for CCS must be sustainable. Therefore, the choice of a tight and durable cement, used for sealing, is critical. The material has to resist the extreme conditions at the point of injection considering pressure, temperature, pH, and the composition of aggressive fluids (chloride rich brines, supercritical (sc) CO2 accompanied with NO2 and SO2). The high amount of CO2 and the fluids will have a considerable impact on cement properties. Hence, the term carbonation is occupied in the literature as a post hydration reaction of cementitious materials [3,4]. Ordinary Portland cements (OPC) cannot be used under these conditions of well boring due to their instability. The current study describes carbonation as a curing method to obtain carbonates as reaction products. In the present study, a literature review describing the influence of CO2 on conventional hydrated cements as an alteration reaction is presented. Studies on the reaction of natural wollastonite with CO2 as curing method under different pressures and temperatures were investigated.
Although natural deposits are limited, wollastonite can be fabricated using a conventional cement rotary kiln production process. Wollastonite has a Ca:Si ratio of 1:1 and therefore during production a better CO2 balance than conventional cements with Ca:Si ratio 2:1 and 3:1 (Table 1, [5]).
Additionally, the CO2 will be consumed during the carbonation reaction thereby improving the CO2 balance by forming carbonates.
The interaction of wollastonite and CO2 [6] was investigated within the joint BMWi (German Federal Ministry for Economic Affairs and Energy) research project CLUSTER [7]. The project CLUSTER focusses on two main topics:
(I)
Potential impacts of temporal variations in CO2 stream composition and mass flow that occur in larger pipeline networks on transport, injection, and geological storage of CO2.
(I)
(II) Flexibility of individual steps and the whole CCS process chain in response to this temporal variability [8].
In nature, wollastonite is formed during metamorphism. The present study considers the back reaction by carbonation of wollastonite forming CaCO3 and SiO2 as a base [6]. The carbonation reaction of wollastonite is described as extremely slow in absence of water at low temperatures [9]. Yet at 333 K and ambient pressure the C ¯ C S reaction is fast (several hours up to one day) in presence of water [9]. Microstructure aspects of the carbonation were investigated by Villani et al. [10] and Sahu and DeCristofaro [11]. Both studies showed a carbonation from the surface to the center of the wollastonite grains, similar to the shrinking core model [12]. Wollastonite reacts in the presence of CO2 in aqueous conditions to calcite and amorphous silicon oxide:
CaSiO 3 + CO 2   H 2 O CaCO 3 + SiO 2 ( amorphous )
The chosen temperature (333 K) defined by the project CLUSTER [8] equates to the conditions in deep geological formations envisaged for CCS. Gartner and Hirao [9] and Longo et al. [13] found that the carbonation reaction strongly depends on the presence of water. Our experiments were performed under aqueous conditions, because aqueous solutions are expected to be present at the point of injection in wellbores.

1.1. Interaction of CO2 and Conventional Hydrated Cements

Carbonation (i.e., formation of CaCO3) in hydrated cements causes a decrease of the pH-value from approximately 13 to approximately 8. The calcium carbonate ( C C ¯ ) mostly appears in form of calcite but also as vaterite and aragonite [3,4]. Carbonation is responsible for volume changes and formation of carbonates, hemicarbonates and monocarbonates, which leads to changes in porosity and permeability, and the formation of a fracture network. Dissolution of phases also may occur [3,4]. Considering the chemical and mechanical stability for construction due to changes of the porosity, this process is very critical [3,4].
Therefore, extensive research on the influence of CO2 on OPC and wellbore cement was performed. Shi et al. [14] investigated the carbonation of white portland cement (wPc, CEM I 52,5 N) from Aalborg Portland A/S, Denmark, metakaolin (MK) and limestone (LS) mortars. Their mortars were hydrated for 91 days and exposed to a controlled atmosphere with one percent CO2 at 293 K and 57% relative humidity (RH) for 280 days. They found that the Portland cement had the highest CO2 binding capacity followed by limestone and metakaolin. Abdoulghafour et al. [15] and Luquot et al. [16] performed flow-through experiments with CO2 and brine on fractured Portland cement. Their experiments were carried out at 333 K and 10 MPa for more than 100 h. They found that the leakage potential is controlled by the aperture of the fracture. Ozyurtkan and Radonjic [17] investigated the effect of CO2 rich brine (two percent salt solution) on artificially fractured well-cement (class H) in a flow-through experiment over 30 and 100 days. After 100 days, a secondary fracture network was developed which was not present after 30 days. The secondary fractures caused higher leaching rates. The obtained data by Ozyurtkan and Radonjic [17] indicates a negative effect on porosity of cement under dynamic conditions which can be dependent on time. Yalcinkaya et al. [18], performed an experimental study on the dynamic alteration process of class-H wellbore cement caused by acidic brine. Their experiments confirmed leaching of Ca2+ from the reacted cement. Carey et al. [19] investigated the wellbore integrity and CO2-brine flow along the casing-cement. They performed flow-through experiments at 313 K and 14 MPa pore pressure for 394 h. The brine was a 50:50 mixture of scCO2 and 30,000 ppm NaCl-rich brine. They were able to confirm that degradation of Portland cement is slow. Barlet-Gouédard et al. [20] compared the behavior of a Portland cement with a Schlumberger CO2 resistant cement (SCRC) with expanding agent under CO2 geological storage environment (363 K, 28 MPa). They used brine containing 220 g/L NaCl. They focused on the expansion of the cement because fractures caused by the expansion are one possible occurrence of leakages. The simulated injection scenario presented by Barlet-Gouédard et al. [20] showed, that conventional Portland cement does not fulfill the requirements for the well integrity. Wigand et al. [21] performed flow-through experiments which simulated the diffusion of brine (1.65 M) and scCO2 from the interface between wellbore cement and caprock into a fracture-bearing Portland cement. The experiments were performed at 327 K with a pore pressure of 19.9 MPa and a confining pressure of 26.2 MPa for 174 h. They showed that the carbonation of the wellbore cement at first caused closing and blocking of pores and fractures but opened other fractures in the following process, which increased the permeability. The chemical interaction along the cement–sandstone interface with scCO2 was investigated by Nakano et al. [22]. They prepared a well composite sample consisting of casing, Portland cement and sandstone. The experiments were performed under 10 MPa and 323 K with a 0.5 M NaCl-brine. Their results indicate that the formation of carbonation layers act as a barrier to further CO2-attack. Zhang et al. [23,24] investigated the reaction of two different pozzolan-amended (Class F fly ash, with ~70% silica, alumina and Fe2O3, ~5% sulfate, and less than 20% CaO) wellbore cements (API RP 10B; 35 vol % pozzolan and 65 vol % pozzolan) being exposed to CO2 and H2S gas mixtures and brine (one percent NaCl) at 323 K and 15.1 MPa for 2.5, 9, 28 and 90 days. The samples of the pozzolan-amended wellbore cement with 35 vol % pozzolan showed higher resistance against H2S. Mito et al. [25] and Wolterbeek et al. [26] investigated the influence of CO2-induced reactions on the mechanical behavior of fractured wellbore cement (class-G Portland cement). They found that the reaction with CO2 did not produce further geomechanical weakening. In fact, samples with six weeks reaction time recovered peak-strength (83%) and increased frictional strength (15–40%). Kutchko et al. [27] investigated the reaction of hydrated well cement (class-H) with H2S-CO2 (21 mol % H2S) acid-gas for 28 days at 323 K and 15 MPa. The H2S added to the experimental setup resulted in significant formation of ettringite (interior region of the cement) and pyrite (carbonated rim of the cement). Although secondarily formed ettringite is known to cause cracking and strength loss, a mechanical damage caused by formation of ettringite was not found. Even the long-term cement corrosion in chloride-rich solutions was investigated by Bube et al. [27]. They performed leaching experiments and thermodynamic simulations on cement (OPC; CEM I 32,5 R; w/c ratio of 0.4) with brine (4.3 mol Mg2+, 0.41 mol Na+, 0.54 mol K+, 8.9 mol Cl, and 0.23 mol SO42−) for 200 days. Comparing the results of laboratory and full-scale experiments, they were able to establish a link between the results of short-term laboratory experiments to long-term full-scale experiments, using thermodynamic equilibrium calculations.
The above research shows that carbonation can negatively impact the sealing qualities of OPC wellbore cements. Therefore, alternative materials are required to ensure wellbore integrity during the subsurface storage of CO2. One such alternative is a cement based on wollastonite (CaSiO3), which will create a seal through a carbonation reaction. In this study, experimental work addressing wollastonite carbonation kinetics under in-situ conditions relevant for subsurface CO2 storage in aquifers or depleted reservoirs is presented.

1.2. Interaction of Wollastonite and CO2

CO2 has an impact on the stability of conventional hydrated cements. Therefore, the use of a cement, based on calcium silicate (CS) curing in the presence of CO2 ( C ¯ ), seems very promising [28,29,30]. Yet knowledge considering this approach is rather scarce.
Ashraf et al. [31] investigated the effects of high temperature (723–783 K) on calcium silicate-based cement (CSC), OPCs and OPCs with 20% fly ash. During the experiments, the OPCs showed a reduction of stiffness (60%), an increase of porosity (30%) and a loss of mass (13–15%) higher than the CSC (stiffness: 6%; porosity: 20%; mass loss: 3%). Huijgen et al. [32] investigated the mechanisms of aqueous wollastonite carbonation, using three different grain sizes (<38 µm, <106 µm and <500 µm) at short time intervals (5–60 min), a temperature range from 298 to 498 K and a pressure variation up to 4 MPa. A maximum conversion of 70% in 15 min at 473 K, 2 MPa CO2 partial pressure and with a particle size of <38 µm was achieved. They were able to show that the aqueous carbonation mechanisms of wollastonite, steel slag and olivine are generally similar, although they showed that wollastonite carbonation was rapid, relative to the carbonation of Mg-silicates. Longo et al. [13] showed that water has a huge impact on the carbonation reaction of wollastonite. Without water the wollastonite sample carbonated on the surface rather fast but after a carbonate monolayer was formed, the reaction comes to a standstill. The presence of water completely changes the reaction and caused ongoing carbonation. Daval et al. [33] investigated the carbonation reactions of wollastonite at conditions relevant to geologic CO2 sequestration in subsurface environments. They performed experiments in batch reactors at 363 K and 25 MPa. After carbonation, they found two reaction products: Calcite and a silica-rich phase. No other carbonate polymorph was found. Min et al. [34] performed carbonation experiments on wollastonite at typical geological storage conditions (333 K and 10 MPa). They investigated the microstructure of the carbonated wollastonite and found that after 20 h the reaction was controlled by the diffusion of water-bearing scCO2 across the product layer on wollastonite surfaces. A layer of amorphous SiO2 covered the surface of the wollastonite and functioned as a barrier.

2. Materials and Methods

To determine carbonation rates, several series of experiments were performed and different analytic techniques were applied. Educts and products were analyzed with powder X-ray diffraction (PXRD) and differential scanning calorimetry with thermogravimetry (DSC-TG) coupled with mass spectrometer (MS) and infrared spectrometer (IR). The chemical composition of the educts was analyzed with wave length dispersive X-ray fluorescence (XRF).

2.1. Materials

For the experiments, steel reactors with teflon liners from the company Büchi AG were used. According to the investigations of Huijgens et al. [32] (best conversion rate of 70% after 15 min at 473 K and 2 MPa) a sample material with a grain size <38 µm was chosen and the experiments were performed with 2 MPa. In this work, experiments at lower temperatures were performed because this work is connected to a specific CCS process, in which temperatures do not exceed 333 K. The used raw material (natural CaSiO3, calcium silicate, meta, reagent grade, <20 µm powder) was supplied by Alfa Aeser. The chemical composition of the used raw material was analyzed with an XRF spectrometer (Siemens SRS 3000, Table 1). As expected the main elements were Si and Ca, but in addition the raw material contained small amounts of Fe, Al, Mg, Mn, Ti, K, and Sr (Table 2), which is due to the natural origin of this material.
The pressure in the reactors was adjusted using an ISCO-pump (Teledyne ISCO, Model 500D Syring pump). CO2 was supplied by Westfalen AG and had a purity of 4.5 (99.995%).

2.2. Analytical Methods

The mineralogical composition of the raw materials was measured by PXRD (Panalytical X’PERT3 Powder with Pixcel 1D detector). The PXRD measurements were carried out with 45 kV and 40 mA. As apertures 0.04 rad soller slit and fixed slits (0.125° and 0.25°) were used. Diffractograms were recorded from 5° to 100° 2Θ with 49.725 s per step and stepsize: 0.013° 2Θ. For qualitative investigation the Highscore Plus Suite [35] and for quantitative phase analysis the Rietveld method [36] with Profex-BGMN [37,38] was used. To determine the amorphous content, 10 wt % rutile (Kronos 2900–TiO2; Rutile, supplied by KRONOS TITAN GmbH, Leverkusen, Germany) was added as internal standard. Chemical composition was analyzed with wave length dispersive X-ray fluorescence (SRS 3000; Siemens, Karlsruhe, Germany; Rh-tube; vacuum: 200 mbar; measurement, 30 s for each line). Therefore, melting tablets with 1 g sample material and 8 g Di-Lithium Tetraborate (FX-X100-2) supplied by FLUXANA (Bedburg-Hau, Germany) were prepared.
To investigate the degree of carbonation depending on pressure (p) and temperature (T), the contents of wollastonite accompanied by the increase of calcium carbonate and increase of the amorphous phase contents different approaches were applied to identify and quantify educts and products. For quantitative phase analysis, PXRD with the Rietveld method [36] and differential scanning calorimetry with thermogravimetry (DSC-TG; STA 449 F3 Jupiter, Netzsch, Selb, Germany) coupled with mass spectrometer (MS; QMS 403D Aeolos Netzsch; atom mass units 1 to 50 u were recorded) and infrared spectroscopy (IR; Tensor II with TGA-IR extension compartment from Bruker, Karlsruhe, Germany) were used. The thermoanalytical measurements were carried out from ambient temperature (296 K) to 1273 K (1000 °C) with a heating rate of 10 K per minute. For the DSC-TG measurements ~15 to ~25 mg sample material per measurement were used.
With DSC-TG/IR/MS the amount of X-ray amorphous content of CaCO3 in the product could be analyzed as well.
The content of carbonate was calculated from the mass loss associated with CO2:
CaCO 3 [ wt   % ] = mass   loss   CO 2   [ wt   % ] ( mass   CO 2   [ g / mol ] mass   CaCO 3   [ g / mol ] )
Microstructure of educts and products were characterized by SEM (JEOL JSM 6300 combined with X-Flash 5010 detector from Bruker; secondary electron pictures were taken with 15 keV; samples were sputtered with gold).

2.3. Experimental Setup

Carbonation of wollastonite at three different temperatures (296 K, 323 K, and 333 K) was investigated. As starting conditions 1 g sample material was mixed with 5 mL H2O in the steel reactor. 20 mL CO2 (5.5 MPa) were pumped by the ISCO-pump into the steel reactor, to obtain a pressure of 2 MPa inside the reactor. The temperature in steel reactors was adjusted by placing them in a drying chamber. For each temperature (296 K, 323 K, and 333 K) several experiments with different time intervals and constant pressure (2 MPa) were performed (Table 3).
In addition, a series of experiments with constant time and temperature but varied pressure were performed. The applied pressure ranged from 0.2 MPa to 5 MPa (Table 4).
To determine carbonation and reactions rates educts and products were analyzed by PXRD, DSC-TG/MS/IR and SEM.

3. Results and Discussion

The results of the quantification of the educts and products at different temperatures and pressures showed that temperature has a higher impact on the conversion of wollastonite to CaCO3 than applied pressure.

3.1. Microstructure (SEM)

For the microscopic analysis of the morphology of educts and products SEM was used. The raw material exhibited wollastonite grains, showing elongated crystals of 5–6 µm × 10–12 µm (Figure 1, white arrows).
The carbonated wollastonite still showed small and elongated (2.5 × 5 µm) wollastonite (Wo) crystals, covered with carbonate crystals (Figure 2a, white arrow). Yet aggregates of carbonate crystals (Cb, Figure 2b, white arrow) were observed in the micrograph shown in Figure 2 (white arrow).

3.2. PXRD Analysis

To quantify the carbonation reaction of natural wollastonite (Table 5), samples were measured with PXRD before and after the CO2 treatment. The results of the PXRD-analysis showed three crystalline phases (wollastonite, calcite, and aragonite) and an amorphous content, determined by adding 10 wt % of rutile as internal standard (Table 5 and Figure 3 and Figure 4) in the starting material and the reaction products as well.
In Figure 4, the wollastonite with the fastest and most advanced conversion to carbonates (24 h, 333 K, 2 MPa) is shown. The results at the quantification of all carbonation reactions of wollastonite at 2 MPa is shown in part 3.4 of this study.

3.3. DSC-TG/MS/IR Measurements

DSC-TG/MS/IR measurement of the raw material and the carbonated wollastonite were carried out to determine the entire content of water and carbonate in the material because X-ray amorphous carbonate could not be determined with PXRD, when additional amorphous phases (SiO2) are also present in the mixtures.
DSC-TG/MS/IR measurements as shown in Figure 5 were performed with the raw material. During the measurement, the sample lost 2.1% of its weight. 1.7 wt % were associated with CO2, which results in original content of 3.9 wt % carbonate in the sample (Figure 5, Equation (2)). At the beginning of the experiment only H2O were detected by mass spectrometry. The detected mass flow of H2O (Figure 5, green line) decreased from 400 K to 800 K. From 800 K to 1050 K only CO2 were measured by mass spectrometry. The mass flow of CO2 reached its maximum at approximately 1000 K (Figure 5, magenta line). The measured weight loss (Figure 5, black line) decreased slowly from 400 K to 850 K. Starting with the increased mass flow of CO2 the weight loss increased significantly (850 K to 1050 K). At temperatures higher than 1050 K, the mass of the sample did not change. The DSC-signal (Figure 5, blue line) showed amplitudes at 400 K and 1000 K, which were associated with the detected peaks of the mass flows of H2O (400 K) and CO2 (1000 K).
The results of the Rietveld analysis and the DSC-TG measurements of the raw material for the content of carbonate were in good agreement (Rietveld: 5%; DSC-TG: 4%).
DSC-TG/MS/IR measurements on the carbonated wollastonite, shown exemplarily in Figure 6, were performed. During the measurement, the sample lost 25.4% of its weight. 23.9% were associated with CO2, which resulted in original content of 54.8 wt % carbonate in the sample (Figure 6, Equation (2)). At approximately 400 K the mass spectrometer detected a peak of the mass flow of H2O (Figure 6, green line). The mass flow decreased rapidly until 500 K was reached. From 500 K to 750 K the mass flow of H2O rose again and held a plateau until 950 K. The IR analysis did also confirm the investigation of the releasing behavior of H2O from CaCO3. The mass flow of H2O decreased significantly at temperatures higher than 950 K. The detection of the mass flow of CO2 (Figure 6, magenta line) started at 800 K and increased slightly until 950 K was reached, then it formed a sharp peak until 1100 K was reached. At temperatures higher than 1100 K, the mass flow of CO2 was nearly zero. The measured weight loss (Figure 6, black line) decreased slowly until 900 K. Starting with the increase of the mass flow of CO2 the weight loss increased significantly (900 K to 1100 K). At temperatures higher than 1100 K, the mass of the sample did not change. The DSC-signal (Figure 6, blue line) showed a negative (endothermic) amplitude at 1100 K which was associated with the detected peak of the mass flow of CO2. At 1150 K the DSC-signal showed a positive amplitude, which could be ascribed to the formation of Ca2SiO4. PXRD-measurements were performed on the same sample which showed small contents of C2S (larnite, i.e., Ca2SiO4).
The results of the Rietveld method and the DSC-TG measurements of the carbonated wollastonite for the content of carbonate were again in good agreement (Rietveld: 50%; DSC-TG: 55%).

3.4. Discussion of the PXRD and DSC-TG/MS Results

The results of the PXRD-measurements with the Rietveld method and the DSC-TG/MS/IR-measurements were collected and plotted in three diagrams (Figure 7, Figure 8 and Figure 9). The quantity of the phases wollastonite (black squares), amorphous (blue triangles), calcite (magenta circles) and aragonite (green circles) were determined by the Rietveld method. The red circles symbolized the sum of calcite and aragonite and therefore the content of carbonate in the sample detected by PXRD. The amount of CaCO3 determined by TG measurements were shown by cyan circles.
In Figure 7, the carbonation of wollastonite at 296 K is shown with seven different reaction times. To show the good reproducibility several experiments were performed two times (Figure 7). At 296 K, the reaction was not completed after 144 h. The content of calcite (magenta circles), the amount of CaCO3 determined by TG measurements (cyan circles) and of the amorphous content (blue triangles) in the sample increased exponentially while the content of wollastonite (black squares) decreased similarly. No further aragonite (green circles) was formed (Figure 7).
At 323 K, a high degree of conversion (>90%) was already achieved after 48 h (Figure 8). The content of calcite (magenta circles), aragonite (green circles), the amount of CaCO3 determined by TG measurements (cyan circles) and the amorphous content (blue triangles) increased exponentially, while the content of wollastonite (black squares) decreased exponentially in an analog manner. At 24 h, the contents of calcite and aragonite almost reached the same amount (~20 wt %), while at the beginning of the experiment the content of calcite was higher (Figure 8, grey circles marked by arrows).
At 333 K, the conversion was nearly completed already after 24 h (Figure 9). The contents of calcite (magenta circles), aragonite (green circles) and the total amount of CaCO3 determined by TG measurements (cyan circles) and the amorphous content (blue triangles) increased exponentially, while the content of wollastonite (black squares) decreased exponentially. At 12 h the contents of calcite and aragonite almost reached the same amount (~20 wt %) whereas at the beginning (6 h and 18 h) of the experiment the content of calcite was higher (Figure 9, grey circles marked by arrows).
At each investigated temperature (296 K, 323 K, 333 K), an exponentially decrease of wollastonite was observed. This was also true for the increase of calcite and the amorphous content vice versa. At higher temperatures (323 K and 333 K), aragonite exhibited also exponential increase (Figure 8 and Figure 9).
An additional experiment was performed, in which the temperature (333 K) and time (6 h) were held constant and only the pressure varied. The results showed that the reaction was mostly independent of pressure (Figure 10).
At low pressure (0.2 MPa) the decrease of wollastonite was slower and newly formed aragonite was not observed. At higher pressures (>1 MPa) the carbonation of natural wollastonite showed no further dependence of the applied pressure (Figure 10). From 1 MPa to 5 MPa no differences considering the rate of wollastonite transformation were observed. However the formation of aragonite was dependent on pressure. From 0.2 MPa to 2 MPa the formation of aragonite increased, from 2 MPa to 4 MPa it was constant and from 4 MPa to 5 MPa the formation of aragonite decreased. Figure 11 shows this observation as normalized amount of the wollastonite conversion.
Considering the conversion of wollastonite to CaCO3 in the presence of water the reaction rate of the carbonation depended strongly on the temperature, at higher temperatures the reaction rate was significantly higher (Figure 7, Figure 8 and Figure 9).
A first order reaction was assumed because the reaction was only dependent on wollastonite. The amount of CO2 was one order of magnitude higher than the amount of wollastonite. This assumption could be supported by plotting ln (C) vs time (Figure 12) from which a linear dependency after a conversion of ~90% could be derived.
In Figure 13 the wollastonite hkl reflection (100) at 12 ° 2Θ decreased from 296 K to 333 K.
Considering the conversion rates from wollastonite to calcite the rate constants and activation energies could be estimated (Table 6).
The carbonation reaction of wollastonite starts at the surface of a grain and moves towards the center [10,11,34]. The reaction rate will decrease because of the growing layer thickness of CaCO3 between unreacted CaSiO3 and CO2. Consequently, low amounts (5% to 10%) of material will remain unreacted within experimental periods. At 323 K, the reaction rate is three times faster, whereas at 333 K the reaction rate increased by a factor of six (Figure 14). The values of the activation energy EA for the carbonation reaction ranged from 44 to 64 kJ·mol−1 (Table 6) depending on ∆T, with the latter being in a good agreement with the results reported in Brady [39] (~72 kJ·mol−1).
The carbonation rate of wollastonite at different temperatures (when ~10% of wollastonite were still present) showed a non-linear behavior (exponential decrease) of reaction time (Figure 14).
The p-T conditions in the steel reactor were thermodynamically not suitable [40] for the formation of aragonite. Although metastable aragonite formation can be stabilized in presence of Sr [41], the content of Sr in the material was very low (0.01 wt %). Despite in preliminary performed experiments no aragonite was formed when the carbonate was previously removed from the raw material. Therefore, it was assumed that the small content of aragonite in the raw material functioned as a seed crystal for further metastable aragonite growth.

4. Conclusions

Experiments considering the conversion of CaSiO3 to CaCO3 in aqueous conditions were performed at different temperatures and pressures. The kinetics of this reaction was strongly dependent on temperature (Figure 13). Pressure seemed not to be critical for reaction kinetics (Figure 10 and Figure 11). The degree of conversion, i.e., the amount of reaction products (amorphous and crystalline), could be determined by XRD and coupled DSC-TG/MS/IR analysis. Calcite, aragonite and amorphous CaCO3 and amorphous SiO2 were observed. Depending on the temperature a nearly complete reaction was achieved within the experimental periods of 1–144 h. Activation energies EA could be determined and were in better agreement with the values reported by Brady [39] compared to those given by Huijgen (22 kJ·mol−1 at <38 µm, 20 kJ·mol−1 at <106 µm, 16 kJ·mol−1 at <500 µm) [32].
At the defined conditions (333 K, 2 MPa) relevant for the point of injection of CO2, the carbonation reaction of wollastonite was already completed after 24 h (Figure 9). At lower temperatures, the carbonation reaction was rather slow (144 h at 296 K, Figure 7 and 48 h at 323 K, Figure 8). Hence, it could be proven that the use of wollastonite as a cementitious material suitable for sealing the borehole in CCS is applicable.
To characterize mineral association and their stability as well, the reaction at the interfaces between rocks and casing materials, more experiments at selected pressure, temperature and composition of formation waters will be performed. The long-term stability is still under investigation. As anticipated, the most likely application of wollastonite as cement in CCS would be for sealing the well after injection of CO2 in the reservoir. In that case, the wollastonite will be mixed with water and pumped into the well like conventional cement, mortar or concrete. The CO2 stored in the reservoir will cause the hardening and therefore the sealing of the borehole.

Acknowledgments

We want to thank the German Federal Ministry for Economic Affairs and Energy (BMWi; FKZ: 03ET7031D) for financial support and Sabine Walther for sample preparation and support on the SEM. The constructive comments and helpful suggestions of two anonymous reviewers are gratefully acknowledged. We acknowledge the financial support within the funding program Open Access Publishing by the German Research Foundation (DFG).

Author Contributions

The authors worked together in a research project. Herbert Pöllmann, Andreas Neumann, Kristoff Svensson and Christof Lempp conceived and designed the experiments. Kristoff Svensson and Andreas Neumann performed the experiments. Kristoff Svensson and Andreas Neumann analyzed the data. Kristoff Svensson, Andreas Neumann, Flora Feitosa Menezes, Herbert Pöllmann and Christof Lempp contributed ideas, knowledge and discussion. Kristoff Svensson, Andreas Neumann and Herbert Pöllmann wrote the Paper.

Conflicts of Interest

The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

References

  1. NOAA (National Oceanic and Atmospheric Administration); Earth System Research Laboratory. Trends in Atmospheric Carbon Dioxide. Available online: https://www.esrl.noaa.gov/gmd/ccgg/trends/ (accessed on 18 December 2017).
  2. Benson, S.M.; Orr, F.M., Jr. Carbon Dioxide Capture and Storage. MRS Bull. 2008, 33, 303–305. [Google Scholar] [CrossRef]
  3. Locher, F. Zement–Grundlagen der Herstellung und Verwendung, 1st ed.; Verlag Bau+Technik GmbH: Düsseldorf, Germany, 2000; p. 522. ISBN 978-3-7640-0400-2. [Google Scholar]
  4. Taylor, H.F.W. Cement Chemistry, 2nd ed.; Thomas Telford Publishing, Thomas Telford Services Ltd.: London, UK, 1997; p. 459. ISBN 0-7277-2592-0. [Google Scholar]
  5. Pöllmann, H. Mineralogical strategies to reduce CO2 in the fabrication of alternative cements. Ibausil Conf. Rep. 2015, 1, 111–129. [Google Scholar]
  6. Rice, J.; Ferry, J. Buffering, Infiltration, and the Control of Intensive Variables during Metamorphism. Rev. Miner. Geochem. 1982, 10, 263–326. [Google Scholar]
  7. Svensson, K.; Neumann, A.; Pöllmann, H.; Menezes, F.; Lempp, C. Curing by carbonatisation of Wollastonite. GDCh–Tag. Bauchem. 2017, 52, 80–83. [Google Scholar]
  8. CLUSTER. Joint Research Project CLUSTER. Available online: www.bgr.bund.de/CLUSTER/ (accessed on 18 December 2017).
  9. Gartner, E.; Hirao, H. A review of alternative approaches to the reduction of CO2 emissions associated with the manufacture of the binder phase in concrete. Cem. Concr. Res. 2015, 78, 126–142. [Google Scholar] [CrossRef]
  10. Vilani, C.; Spragg, R.; Tokpatayeva, R.; Olek, J.; Weiss, W. Characterizing the Pore Structure of Carbonated Natural Wollastonite. In Proceedings of the 4th International Conference on the Durability of Concrete Structures, West Lafayette, IN, USA, 24–26 July 2014. [Google Scholar]
  11. Sahu, S.; DeCristofaro, N. Solidia CementTM–Part One of a Two-Part Series Exploring the Chemical Properties and Performance Results of Sustainable Solidia CementTM and Solidia ConcreteTM; Solidia Technologies: Piscataway, NJ, USA, 2013; pp. 1–12. [Google Scholar]
  12. Abbasi, E.; Hassanzadeh, A.; Abbasian, J. Regenerable MgO-based surbent for high temperature CO2 removal from syngas: 2. Two-zone variable diffusivity shrinking core model with expanding product layer. Fuel 2013, 105, 128–134. [Google Scholar] [CrossRef]
  13. Longo, R.C.; Cho, K.; Brüner, P.; Welle, A.; Gerdes, A.; Thissen, P. Carbonation of Wollastonite(001) Competing Hydration: Microscopic Insights from Ion Spectroscopy and Density Dunctional Theory. Am. Chem. Soc. Appl. Mater. Interfaces 2015, 7, 4706–4712. [Google Scholar] [CrossRef] [PubMed]
  14. Shi, Z.; Lothenbach, B.; Geiker, M.R.; Kaufmann, J.; Leemann, A.; Ferreiro, S.; Skibsted, J. Experimental studies and thermodynamic modeling of the carbonation of Portland cement, metakaolin and limestone mortars. Cem. Concr. Res. 2016, 88, 60–72. [Google Scholar] [CrossRef]
  15. Abdoulghafour, H.; Gouze, P.; Luquot, L.; Leprovost, R. Characterization and modeling of the alteration of fractured class-G Portland cement during flow of CO2-rich brine. Int. J. Greenh. Gas Control 2016, 48, 155–170. [Google Scholar] [CrossRef]
  16. Luquot, L.; Abdoulghafour, H.; Gouze, P. Hydro-dynamically controlled alteration of fractured Portland cements flowed by CO2-rich brine. Int. J. Greenh. Gas Control 2013, 16, 167–179. [Google Scholar] [CrossRef]
  17. Ozyurtkan, M.H.; Radonjic, M. An experimental study of the effect of CO2 rich brine on artificially fractured well-cement. Cem. Concr. Compos. 2014, 45, 201–208. [Google Scholar] [CrossRef]
  18. Yalcinkaya, T.; Radonjic, M.; Willson, C.; Bachu, S. Experimental Study on a Single Cement-Fracture Using CO2 Rich Brine. Energy Procedia 2011, 4, 5225–5342. [Google Scholar] [CrossRef]
  19. Carey, W.J.; Svec, R.; Grigg, R.; Zhang, J.; Crow, W. Experimental investigation of wellbore integrity and CO2-brine flow along casing-cement microannulus. Int. J. Greenh. Gas Control 2010, 4, 272–282. [Google Scholar] [CrossRef]
  20. Barlet-Gouédard, V.; Rimmelé, G.; Porcherie, O.; Quisel, N.; Desroches, J. A solution against well cement degradation under CO2 geological storage environment. Int. J. Greenh. Gas Control 2009, 3, 206–216. [Google Scholar] [CrossRef]
  21. Wigand, M.; Kaszuba, J.P.; Carey, W.J.; Hollis, K.W. Geochemical effects of CO2 sequestration on fractured wellbore cement at the cement/caprock interface. Chem. Geol. 2009, 265, 122–133. [Google Scholar] [CrossRef]
  22. Nakano, K.; Ohbuchi, A.; Mito, S.; Xue, Z. Chemical interactionof well composite samples with supercritical CO2 along the cement–sandstone interface. Energy Procedia 2014, 63, 5754–5761. [Google Scholar] [CrossRef]
  23. Zhang, L.; Dzombak, D.A.; Nakles, D.V.; Hawthorne, S.B.; Miller, D.J.; Kutchko, B.G.; Lopano, C.L.; Strazisar, B.R. Characterization of pozzolan-amended wellbore cement exposed to CO2 and H2S gas mixtures under geologic carbon storage conditions. Int. J. Greenh. Gas Control 2013, 19, 358–368. [Google Scholar] [CrossRef]
  24. Zhang, L.; Dzombak, D.A.; Nakles, D.V.; Hawthorne, S.B.; Miller, D.J.; Kutchko, B.G.; Lopano, C.L.; Strazisar, B.R. Rate of H2S and CO2 attack on pozzolan-amended Class H well cement under geologic squestration conditions. Int. J. Greenh. Gas Control 2014, 27, 299–308. [Google Scholar] [CrossRef]
  25. Mito, S.; Xue, Z.; Satoh, H. Experimental assessment of well integrity for CO2 geological storage: Batch experimental results on geochemical interactions between a CO2-brine mixture and a sandstone-cement-steel sample. Int. J. Greenh. Gas Control 2015, 39, 420–431. [Google Scholar] [CrossRef]
  26. Wolterbeek, K.T.; Hangx, S.J.T.; Spiers, C.J. Effect of CO2-induced reactions on the mechanical behaviour of fractured wellbore cement. Geomech. Energy Environ. 2016, 7, 26–46. [Google Scholar] [CrossRef]
  27. Kutchko, B.G.; Strazisar, B.R.; Hawthorne, S.B.; Lopano, C.L.; Miller, D.J.; Hakala, A.J.; Guthrie, G.D. H2S-CO2 reaction with hydrated Class H well cement: Acid-gas injection and CO2 Co-sequestration. Int. J. Greenh. Gas Control 2011, 5, 880–888. [Google Scholar] [CrossRef]
  28. Bube, C.; Metz, V.; Bohnert, E.; Garbev, K.; Schild, D.; Kienzler, B. Long-Term cement corrosion in chloride-rich solutions relevant to radioactive waste disposal in rock salt–Leaching experiments and thermodynamic simulations. Phys. Chem. Earth 2013, 64, 87–94. [Google Scholar] [CrossRef]
  29. Jain, J.; Deo, O.; Sahu, S.; DeCristofaro, N. Solidia CementTM–Part Two of a Series Exploring the Chemical Properties and Performance Results of Sustainable Solidia CementTM and Solidia ConcreteTM; Solidia Technologies: Piscataway, NJ, USA, 2014; pp. 1–17. [Google Scholar]
  30. Jain, J.; Atakan, V.; DeChristofaro, N.; Jeong, H.; Olek, J. Performance of Calcium Silicate-based Carbonated Concretes vs. Hydrated Concretes under Freeze-thaw Environments; Solidia Technologies: Piscataway, NJ, USA, 2015; pp. 1–8. [Google Scholar]
  31. Ashraf, W.; Olek, J.; Atakan, V.; Hyungu, J. Effects of High Temperature on Carbonated Calcium Silicate Cement (CSC) and Ordinary Portland Cement (OPC) Paste. In Proceedings of the 5th International Conference on Durability of Concrete Structures, Shenzhen, China, 30 June–1 July 2016. [Google Scholar]
  32. Huijgen, W.J.J.; Witkamp, G.-J.; Comans, R.N.J. Mechanisms of aqueous wollastonite carbonation as a possible CO2 sequestration process. Chem. Eng. Sci. 2006, 61, 4242–4251. [Google Scholar] [CrossRef]
  33. Daval, D.; Martinez, I.; Corvisier, J.; Findling, N.; Goffé, B.; Guyot, F. Carbonation of Ca-bearing silicates, the case of wollastonite: Experimental investigations and kinetic modeling. Chem. Geol. 2009, 262, 262–277. [Google Scholar] [CrossRef]
  34. Min, Y.; Li, Q.; Voltolini, M.; Kneafsey, T.; Jun, Y.-S. Wollastonite Carbonation in Water-Bearing Supercritical CO2: Effects of Particle Size. Environ. Sci. Technol. 2017, 51, 13044–13053. [Google Scholar] [CrossRef] [PubMed]
  35. Degen, T.; Sadki, M.; Bron, E.; König, U.; Nénert, G. The Highscore suite. Powder Diffr. 2014, 29, 13–18. [Google Scholar] [CrossRef]
  36. Rietveld, H.M. A profile refinement method for nuclear and magnetic structures. J. Appl. Crystallogr. 1969, 2, 65–71. [Google Scholar] [CrossRef]
  37. Döbelin, N.; Kleeberg, R. Profex: A graphical user interface for the Rietveld refinement program BGMN. J. Appl. Crystallogr. 2015, 48, 1573–1580. [Google Scholar] [CrossRef] [PubMed]
  38. Bergmann, J.; Friedel, P.; Kleeberg, R. BGMN–A new fundamental parameters based Rietveld program for laboratory X-ray sources, it’s use in qualitative analysis and structure investigations. Comm. Powder Diffr. Int. Union Crystallogr. CPD Newsl. 1998, 20, 5–8. [Google Scholar]
  39. Brady, P.V. The Effect of Silicate Weathering on Global Temperature and Atmospheric CO2. J. Geophys. Res. 1991, 96, 18101–18106. [Google Scholar] [CrossRef]
  40. Salje, E.; Viswanathan, K. The Phase Diagram Calcite-Aragonite as Derived from the Crystallographic Properties. Contrib. Mineral. Petrol. 1976, 55, 55–67. [Google Scholar] [CrossRef]
  41. Sunagawa, I.; Takahashi, Y.; Imai, H. Strontium and aragonite-calcite precipitation. J. Mineral. Petrol. Sci. 2007, 102, 174–181. [Google Scholar] [CrossRef]
Figure 1. Secondary electron (SE) images of two elongated wollastonite grains (arrows, Wo). The grain on the left (a) is 6 × 12 µm, the grain on the right (b) 5 × 10 µm.
Figure 1. Secondary electron (SE) images of two elongated wollastonite grains (arrows, Wo). The grain on the left (a) is 6 × 12 µm, the grain on the right (b) 5 × 10 µm.
Applsci 08 00304 g001
Figure 2. Secondary electron (SE) images of carbonated wollastonite. A wollstonite grain with small crystals of carbonate on the left (a, Wo). An aggregate of carbonate crystals on the right (b, Cb).
Figure 2. Secondary electron (SE) images of carbonated wollastonite. A wollstonite grain with small crystals of carbonate on the left (a, Wo). An aggregate of carbonate crystals on the right (b, Cb).
Applsci 08 00304 g002
Figure 3. PXRD of Rietveld analysis [36,37,38] of the used raw material. Three crystalline phases and an amorphous content were determined by adding an internal TiO2-standard of known weight: wollastonite (cyan), calcite (magenta) and aragonite (purple).
Figure 3. PXRD of Rietveld analysis [36,37,38] of the used raw material. Three crystalline phases and an amorphous content were determined by adding an internal TiO2-standard of known weight: wollastonite (cyan), calcite (magenta) and aragonite (purple).
Applsci 08 00304 g003
Figure 4. PXRD of Rietveld analysis [36,37,38] of carbonated wollastonite (carbonated at 333 K, 2 MPa, with 24 h reaction time). Three crystalline phases and an amorphous content were determined by adding an internal TiO2-standard of known weight: wollastonite (cyan), calcite (magenta) and aragonite (purple).
Figure 4. PXRD of Rietveld analysis [36,37,38] of carbonated wollastonite (carbonated at 333 K, 2 MPa, with 24 h reaction time). Three crystalline phases and an amorphous content were determined by adding an internal TiO2-standard of known weight: wollastonite (cyan), calcite (magenta) and aragonite (purple).
Applsci 08 00304 g004
Figure 5. Result of the differential scanning calorimetry with thermogravimetry coupled with a mass spectrometer (DSC-TG/MS) measurement of wollastonite raw material (initial weight 20.3 mg). Measurement from 296 K to 1273 K with heating rate of 10 K/min. The weight loss (wt %) is shown by the black line and the DSC-signal (mW) by the blue line. The green line shows the mass flow (A) for H2O, and the magenta line the mass flow (A) for CO2.
Figure 5. Result of the differential scanning calorimetry with thermogravimetry coupled with a mass spectrometer (DSC-TG/MS) measurement of wollastonite raw material (initial weight 20.3 mg). Measurement from 296 K to 1273 K with heating rate of 10 K/min. The weight loss (wt %) is shown by the black line and the DSC-signal (mW) by the blue line. The green line shows the mass flow (A) for H2O, and the magenta line the mass flow (A) for CO2.
Applsci 08 00304 g005
Figure 6. Result of the DSC-TG/MS measurement of carbonated (at 2 MPa and 333 K for 24 h) wollastonite (initial weight 15.2 mg). Measurement from 296 K to 1273 K with heating rate of 10 K/min. The weight loss (wt %) is represented by the black line, the DSC-signal (mW) by the blue line. The green line shows the mass flow (A) for H2O, and the magenta line the mass flow (A) for CO2.
Figure 6. Result of the DSC-TG/MS measurement of carbonated (at 2 MPa and 333 K for 24 h) wollastonite (initial weight 15.2 mg). Measurement from 296 K to 1273 K with heating rate of 10 K/min. The weight loss (wt %) is represented by the black line, the DSC-signal (mW) by the blue line. The green line shows the mass flow (A) for H2O, and the magenta line the mass flow (A) for CO2.
Applsci 08 00304 g006
Figure 7. Carbonation of wollastonite at 296 K (23 °C, ambient), 2 MPa and aqueous conditions (H2O). The quantity of the phases wollastonite (black squares), amorphous (blue triangles), calcite (magenta circles) and aragonite (green circles) were determined by the Rietveld method. The red circles symbolize the sum of calcite and aragonite and therefore the content of carbonate in the sample detected by PXRD. The amount of CaCO3 determined by TG measurements are symbolized by cyan circles.
Figure 7. Carbonation of wollastonite at 296 K (23 °C, ambient), 2 MPa and aqueous conditions (H2O). The quantity of the phases wollastonite (black squares), amorphous (blue triangles), calcite (magenta circles) and aragonite (green circles) were determined by the Rietveld method. The red circles symbolize the sum of calcite and aragonite and therefore the content of carbonate in the sample detected by PXRD. The amount of CaCO3 determined by TG measurements are symbolized by cyan circles.
Applsci 08 00304 g007
Figure 8. Carbonation of wollastonite at 323 K (50 °C), 2 MPa and aqueous conditions (H2O). The quantity of the phases wollastonite (black squares), amorphous (blue triangles), calcite (magenta circles) and aragonite (green circles) were determined by the Rietveld method. The red circles symbolize the sum of calcite and aragonite and therefore the content of carbonate in the sample detected by PXRD. The amount of CaCO3 determined by TG measurements are symbolized by cyan circles. The ellipsoids with arrows depict the symbols, at which aragonite and calcite exhibite nearly the same amount.
Figure 8. Carbonation of wollastonite at 323 K (50 °C), 2 MPa and aqueous conditions (H2O). The quantity of the phases wollastonite (black squares), amorphous (blue triangles), calcite (magenta circles) and aragonite (green circles) were determined by the Rietveld method. The red circles symbolize the sum of calcite and aragonite and therefore the content of carbonate in the sample detected by PXRD. The amount of CaCO3 determined by TG measurements are symbolized by cyan circles. The ellipsoids with arrows depict the symbols, at which aragonite and calcite exhibite nearly the same amount.
Applsci 08 00304 g008
Figure 9. Carbonation of wollastonite at 333 K (60 °C), 2 MPa and aqueous conditions (H2O). The quantity of the phases wollastonite (black squares), amorphous (blue triangles), calcite (magenta circles) and aragonite (green circles) were determined by the Rietveld method. The red circles symbolize the sum of calcite and aragonite and therefore the content of carbonate in the sample detected by PXRD. The amount of CaCO3 determined by TG measurements are symbolized by cyan circles. The ellipsoids with arrows depict the symbols, at which aragonite and calcite exhibit nearly the same amount.
Figure 9. Carbonation of wollastonite at 333 K (60 °C), 2 MPa and aqueous conditions (H2O). The quantity of the phases wollastonite (black squares), amorphous (blue triangles), calcite (magenta circles) and aragonite (green circles) were determined by the Rietveld method. The red circles symbolize the sum of calcite and aragonite and therefore the content of carbonate in the sample detected by PXRD. The amount of CaCO3 determined by TG measurements are symbolized by cyan circles. The ellipsoids with arrows depict the symbols, at which aragonite and calcite exhibit nearly the same amount.
Applsci 08 00304 g009
Figure 10. Carbonation of wollastonite at 333 K (60 °C), aqueous conditions (H2O) and reaction time of 6 h. The pressure was varied from 0.2 MPa to 5 MPa. The quantity of the phases wollastonite (black squares), amorphous (blue triangles), calcite (magenta circles) and aragonite (green circles) were determined by the Rietveld method. The red circles symbolized the sum of calcite and aragonite and therefore the content of carbonate in the sample detected by PXRD. The amount of CaCO3 determined by TG measurements were symbolized by cyan circles.
Figure 10. Carbonation of wollastonite at 333 K (60 °C), aqueous conditions (H2O) and reaction time of 6 h. The pressure was varied from 0.2 MPa to 5 MPa. The quantity of the phases wollastonite (black squares), amorphous (blue triangles), calcite (magenta circles) and aragonite (green circles) were determined by the Rietveld method. The red circles symbolized the sum of calcite and aragonite and therefore the content of carbonate in the sample detected by PXRD. The amount of CaCO3 determined by TG measurements were symbolized by cyan circles.
Applsci 08 00304 g010
Figure 11. Conversion rate of wollastonite at different pressures and constant temperature (333 K) and time (six hours).
Figure 11. Conversion rate of wollastonite at different pressures and constant temperature (333 K) and time (six hours).
Applsci 08 00304 g011
Figure 12. Conversion rate of wollastonite plotted as ln (C) vs time.
Figure 12. Conversion rate of wollastonite plotted as ln (C) vs time.
Applsci 08 00304 g012
Figure 13. X-ray powder diffractograms of carbonated wollastonite, recorded at different temperatures (296 K, 323 K, 333 K). Pressure (2 MPa) and time (24 h) were constant. The carbonation rate increases at higher temperatures.
Figure 13. X-ray powder diffractograms of carbonated wollastonite, recorded at different temperatures (296 K, 323 K, 333 K). Pressure (2 MPa) and time (24 h) were constant. The carbonation rate increases at higher temperatures.
Applsci 08 00304 g013
Figure 14. Carbonation rate of wollastonite at different temperatures at varying reaction times. Higher temperature resulted in a faster carbonation rate. The reaction time showed a non-linear behavior (data points were fitted with an exponential function).
Figure 14. Carbonation rate of wollastonite at different temperatures at varying reaction times. Higher temperature resulted in a faster carbonation rate. The reaction time showed a non-linear behavior (data points were fitted with an exponential function).
Applsci 08 00304 g014
Table 1. Raw meal CO2-output of selected cement clinker phases. [5].
Table 1. Raw meal CO2-output of selected cement clinker phases. [5].
Phaseg of CO2 per g PhaseRaw Materials
C3S Alite0.583 CaCO3/SiO2–OPC
C2S Belite0.512 CaCO3/SiO2
CS Wollastonite0.38CaCO3/SiO2
C3A0.49CaCO3/Al2O3
CA0.28CaCO3/Al2O3
CA20.17CaCO3/Al2O3
C2F0.32CaCO3/Fe2O3
C2A0.41CaCO3/Al2O3
C4AF0.36CaCO3/Al2O3/Fe2O3
C3A3Cs Sulfoaluminate0.22CaCO3/Al2O3/CaSO4
Table 2. Chemical composition of the used raw material determined by Siemens SRS 3000.
Table 2. Chemical composition of the used raw material determined by Siemens SRS 3000.
Element (Oxides)Content (wt %; Normalized)
SiO250.55
CaO45.95
Fe2O30.52
Al2O30.52
MgO0.17
MnO0.13
TiO20.05
K2O0.03
SrO0.01
LOI 12.09
Total100.02
1 LOI: loss of ignition at 1323 K.
Table 3. Overview of performed series of experiments at constant pressure and varied time and temperature.
Table 3. Overview of performed series of experiments at constant pressure and varied time and temperature.
Temperature (K)Pressure (MPa)Reaction Time (h)
29620, 24, 48, 72, 96, 120, 144
32320, 6, 18, 24, 48
33320, 3, 6, 12, 18, 24
Table 4. Overview of performed series of experiments at varied pressure and constant time and temperature.
Table 4. Overview of performed series of experiments at varied pressure and constant time and temperature.
Temperature (K)Pressure (MPa)Reaction Time (h)
3330.2, 0.5, 1.0, 1.5, 2.0, 2.6, 4.0, 5.06
Table 5. Composition of the used raw material and carbonated wollastonite (24 h, 333 K), determined by powder X-ray diffraction (PXRD) and Rietveld refinement [38] (RwpRaw material: 7%, Rwpcarbonated wollastonite: 7%).
Table 5. Composition of the used raw material and carbonated wollastonite (24 h, 333 K), determined by powder X-ray diffraction (PXRD) and Rietveld refinement [38] (RwpRaw material: 7%, Rwpcarbonated wollastonite: 7%).
PhaseRaw MaterialCarbonated Wollastonite
Content (wt %)Content (wt %)
Wollastonite90 ± 14 ± 1
Calcite5 ± 129 ± 1
Aragonite1 ± 121 ± 1
Amorphous4 ± 145 ± 1
Table 6. Rate constants k and activation energies EA of CaSiO3/CaCO3 conversion.
Table 6. Rate constants k and activation energies EA of CaSiO3/CaCO3 conversion.
Activation EnergiesRate ConstantskJ/mol
EA (323–296 K)−3.79 × 10−6 ± 2.36 × 10−763.88 ± 0.2
EA (333–296 K)−3.32 × 10−5 ± 1.87 × 10−658.88 ± 0.6
EA (333–323 K)−5.42 × 10−5 ± 1.95 × 10−643.70 ± 2.0

Share and Cite

MDPI and ACS Style

Svensson, K.; Neumann, A.; Menezes, F.F.; Lempp, C.; Pöllmann, H. The Conversion of Wollastonite to CaCO3 Considering Its Use for CCS Application as Cementitious Material. Appl. Sci. 2018, 8, 304. https://0-doi-org.brum.beds.ac.uk/10.3390/app8020304

AMA Style

Svensson K, Neumann A, Menezes FF, Lempp C, Pöllmann H. The Conversion of Wollastonite to CaCO3 Considering Its Use for CCS Application as Cementitious Material. Applied Sciences. 2018; 8(2):304. https://0-doi-org.brum.beds.ac.uk/10.3390/app8020304

Chicago/Turabian Style

Svensson, Kristoff, Andreas Neumann, Flora Feitosa Menezes, Christof Lempp, and Herbert Pöllmann. 2018. "The Conversion of Wollastonite to CaCO3 Considering Its Use for CCS Application as Cementitious Material" Applied Sciences 8, no. 2: 304. https://0-doi-org.brum.beds.ac.uk/10.3390/app8020304

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop