Effect of Calcareous Material Particle Size via Separate Grinding on the Burnability and Microstructure Development of Portland Cement Clinker

Based on the separate grinding process for raw meals in the cement industry, raw meal samples with different particle size characteristics were prepared by controlling the fineness of calcareous components. The results show that the fineness of the calcareous components has a significant influence on the burnability of the clinker and that a critical threshold exists (80 μm sieve residue (R80μm) = 15%). When the particle size exceeds this critical value, the particle size effect becomes dominant, leading to a nonlinear and sharp increase in f-CaO content. As the proportion of coarse particles larger than 200 μm increases, the f-CaO content rises markedly, with a greater impact than that of 80 μm particles. Microscopic analysis of the clinker reveals that with coarsening of the calcareous components (increase in R80μm), alite (C3S) content decreases, whereas belite (C2S) and f-CaO contents gradually increase and exhibit enrichment. Based on diffusion-controlled kinetics, a semi-empirical reaction kinetics model, f-CaO = A·exp(Ea,0+k·R80 μm)RT·(R80μm)n, was developed by introducing the apparent activation energy parameter Ea(R80μm) as a function of particle size. The model exhibited excellent goodness of fit (R2 > 0.95), with an intrinsic activation energy Ea,0 = 18.7 kJ·mol−1 and an incremental coefficient k = 0.28 kJ·mol−1·%−1. Validation experiments yielded a relative error of 4.3%. This model quantifies the coupled effects of temperature and particle size, providing quantitative guidance for balancing grinding energy consumption and sintering energy consumption.