Mineral carbon sequestration is a crucial area of research in both environmental protection and industry. While much of the existing research has focused on the direct carbon sequestration of minerals to enhance cementation properties, there is a gap in understanding the interface micro-structure evolution of mineral powder particles during the carbonization process for the use of supplementary cementing materials. This study delves into the investigation of three calcium silicate minerals found in steel slag, examining the single-particle carbonization reaction rate and the micro-evolution process of the reaction interface at a micron scale. The goal is to uncover the differences and mechanisms behind the carbon fixation reaction rates of these three calcium silicate minerals.

Three types of calcium silicate minerals, namely γ-C₂S, β-C₂S, and C₃S, were prepared using the sintering method. A time gradient experiment was conducted on these minerals, and the evolution of multi-scale products was observed and analyzed through various microscopic techniques. Quantitative analysis using XRD and TG-DTG was employed to compare the carbon sequestration rates of the three minerals, and reaction equations were constructed through fitting analysis. The morphology, crystal structure, and growth characteristics of calcium carbonate products during the carbon sequestration reactions of the three minerals were analyzed using SEM, TEM, and crystal size calculations. The correlation between the differences in carbon sequestration rates among the three minerals and the evolution of micro-structure was elucidated.

γ-C₂S had the highest carbon sequestration rate, which was 47.40% after 2880 min of carbon sequestration, reaching 92.65% of the theoretical carbon sequestration, and still had an exposed reaction surface at the later stage of the reaction. During the carbon sequestration process of β-C₂S, the carbon sequestration rate increases and the particle size, grain size and structure distribution of the product calcium carbonate aggregate are relatively stable. C₃S has the highest carbon sequestration rate. Due to its high reactivity, C₃S stagnates rapidly after 5 min, and then the carbon sequestration rate increases slowly, but the crystal shape of surface calcium carbonate products changes with time.

The carbon sequestration reaction processes of γ-C₂S and β-C₂S conform to BoxLucas1 model. The first 60 min is the rapid carbon sequestration stage of γ-C₂S and β-C₂S, and the inflection point of reaction rate reduction occurs in 180 min and 360 min respectively, and the reaction plateau begins at 360 min. The carbon sequestration reaction of C₃S is consistent with the nuclear shrinkage reaction model, and almost stops after 5 min. The calcite produced by the three minerals tend to grow on the (104) rhomboid plane, and the growth of calcite is controlled by the competition between grain growth and grain size reduction.

γ-C₂S and β-C₂S carbon fixation product calcium carbonate is mainly calcite, C₃S carbon fixation product calcium carbonate also contains relatively more aragonite. The growth of calcium carbonate products on the surface of γ-C₂S particles shows a transition from epitaxial growth to mantle growth. The epitaxial growth in the early stage leads to more reaction surfaces and increases the grain size of calcite. The growth of calcium carbonate products on the surface of β-C₂S particles is from mantle growth to epitaxial growth. The mantle growth in the early stage leads to denser nucleation, and the reaction ability is poor in the later stage, but the grain size development is more stable. On the surface of C₃S, calcite and aragonite are mixed, and the composite structure of acicular aragonite and brick calcite hinders the gas-solid contact reaction.

The development rules of carbon sequestration rate of γ-C₂S and β-C₂S are similar, and both conform to BoxLucas1 model; The calcium carbonate crystals on the surface of the two C₂S particles are dominated by calcite, and tend to grow more preferentially on the (104) thermo-dynamically stable surface. The calcium carbonate on the surface of γ-C₂S particles grows from mantle to epitaxial. The epitaxial growth in the early stage leads to a larger reaction contact surface, and it still has reactive activity in the late stage, and the calcite grain size is larger. However, β-C₂S epitaxial growth to mantle growth, the early mantle growth led to denser nucleation, the late reaction ability is poor, the grain size development is more stable. Due to its high calcium content, C₃S has the fastest carbon sequestration reaction at the initial stage, and quickly stops after 5 minutes of reaction, which conforms to the nuclear shrinkage reaction model. C₃S presents different product evolution rules: In the early stage of carbon sequestration reaction, acicular aragonite and cubic calcite on the surface of C₃S are mixed, and its dense structure causes premature stagnation of carbon sequestration reaction. As the reaction proceeds, aragonite is transformed into calcite.