加速碳化对水化硅酸钙显微结构的影响

Effect of Accelerated Carbonation on Microstructure of Calcium Silicate Hydrate

废弃水泥石等固体废弃物碳酸化不仅能够永久固碳,还可实现固体废弃物的再利用,减少对环境的污染。水化硅酸钙(C-S-H)是最主要的可碳化成分之一。合成了钙硅(C/S)比为1.50的C-S-H,研究了加速碳化对其显微结构的影响。用Rietveld全谱拟合的方法和热重-质谱联用的方法对碳化产物进行定量分析,用扫描电镜、N2吸附和29Si固体核磁共振对碳化前后的显微结构进行表征。结果表明:在99.9%CO2,0.2 MPa压力下加速碳化2 h之后,生成了3种不同晶型的碳酸钙和硅胶,碳酸钙从300℃开始分解,文石和球霰石具有较低的分解温度,结晶良好的方解石分解温度较高;多孔结构硅胶具有更高的吸附能力,但C-S-H碳化后的平均孔径从10.33 nm减小到6.69 nm,比表面积由85.6 m2/g减小到67.7 m2/g,这是由于大量的结构致密的碳酸钙晶体堆积造成的;C-S-H双层硅氧链之间的Ca–O层逐渐脱去与CO2反应,硅氧四面体被质子化或与邻近的硅氧四面体链接,形成了聚合度更高的Q3和Q4结构。

Mineral carbonation of alkaline solid waste such as waste cement paste is a promising way for carbon capture and storage. The solid waste can be reused, leading to the reduction of environmental pollution. Calcium silicate hydrate（C-S-H） is one of the dominant mineral phases that can be carbonated. In this paper, C-S-H with C/S ratio of 1.50 was synthesized, and the mierostructure changes induced by accelerated carbonation were investigated. The carbonation products were characterized by the Rietveld refineness （QXRD）, and the microstructure was analyzed by scanning electron microscopy, nitrogen physisorption and nuclear magnetic resonance, respectively. The results indicate that the carbonation leads to the formation of calcium carbonate with three different polymorphs and silica gel Calcium carbonate begins to decompose at 300 ℃, aragonite and vaterite show a relatively low decomposition temperature, and well-crystallized calcite decomposes at a higher temperature. The average pore diameter decreases from 10.33 nm to 6.69 nm, and the specific surface area decreases from 85.6 mE/g to 67.7 mE/g due to the stack of dense calcium carbonate, The Ca-O decalcifies from inter layer of C-S-H and the residual silica tetrahedron protonates or links with other silica tetrahedron to form Q3 or Q4 with more polymerization degree.