Abstract:The reaction of wollastonite (CaSiO 3 ) with CO 2 in the presence of aqueous solutions (H 2 O) and varied temperature conditions (296 K, 323 K, and 333 K) was investigated. The educts (CaSiO 3 ) and the products (CaCO 3 and SiO 2 ) 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 CaSiO 3 to CaCO 3 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 CO 2 in the reservoir.

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Wollastonite can be used as cementitious material, for example in carbon capture and storage (CCS application). The interaction of wollastonite (CS) and pure CO 2 in the presence of H 2 O at temperature (333 K) relevant to injection conditions for CCS were investigated within the joint BMWi research project CLUSTER. The reaction which describes the formation of wollastonite during metamorphism, is reversed. Wollastonite reacts in the presence of CO 2-pressure under aqueous conditions to form calcium carbonate and amorphous silicon oxide. To determine the driving force for this reaction it is important to investigate the impact of CO 2 pressure (p) and temperature (T). The reaction kinetics of the carbonation reaction of wollastonite is strongly dependent to temperature. At 333 K and 2 MPa CO 2 the C CS reaction is fast (≤ 24 h). The chemical composition of wollastonite was analyzed by X-ray fluorescence. To determine the conversion rate of the reaction quantitatively powder X-ray diffraction with Rietveld method were applied. For further application, it is important to understand the specific reactions during the carbonation. Therefore, the influence of different treatments on wollastonite raw material (hydrochloric acid, acetic acid and temperature), before the carbonation experiments, on the carbonation reaction were investigated. The conversion of wollastonite, depending on temperature, was performed successfully. It could be proven, that aragonite acted as seed crystal for further aragonite formation. Furthermore, indications for the formation of aragonite out of amorphous CaCO 3 were observed.