Sustainable valorization of coal gasification slag through optimized grinding kinetics: Composite cement compressive strength enhancement and environmental assessment

The utilization of industrial solid wastes for the preparation of supplementary cementitious materials (CGS) has great development potential and helps to solve the problems of resource shortage and environmental pollution. In this paper, the mechanically activated coal gasification slag (CGS) scheme was optimized based on the grinding kinetic model, and the intrinsic connection between particle characteristics, activity index, and CGS-composite cement properties was established. The hydration mechanism of CGS-composite cement was explored by characterization techniques such as XRD, FTIR, TG-DTG, and SEM. The results showed that the distribution index n, fractal dimension D and SSA were the key parameters affecting the activity index of CGS particles and the properties of composite cement. At a grinding time of 55 min, the distribution index n of CGS was 1.04, fractal dimension D was 2.41, SSA was 614.6 m²/kg, the activity index reached a peak of 99.3 %, and the compressive strength of the prepared composite cement at 28 days was 42.4 MPa. The ground CGS-composite cement showed a higher molar mass ratio of Ca to Si as compared with that of the unground group. C-(A)-S-H and AFm hydration products had higher polymerization and denser microstructures than the unground group, suggesting a synergistic hydration effect between the ground CGS and the cement. In addition, the environmental and economic impact assessment showed that by replacing 30 % of cement, embodied energy (EE) was reduced by 17.96 %, global warming potential (GWP) by 24.46 %, and cost by 22.56 %. The study promotes the development of the solid waste recycling industry and helps to achieve the goals of efficient resource utilization and environmental protection.