Abstract: Fluorinated sludge, as the main byproduct of refined production in the semiconductor industry, is a hazardous solid waste. In the process of co-treating fluorine-containing sludge in cement kilns, the fluorine, phosphate, and various heavy metal ions contained in the fluorinated sludge will inevitably be introduced into the cement raw material at the same time. These ions will significantly affect and change the calcination process and properties of cement raw material minerals. However, there are few studies on the impact of their coexistence on the properties of cement clinker. Therefore, this paper systematically studied the synergistic influence mechanism of fluorine, phosphate, and heavy metal ions co-doping on the calcination process, microstructure, and hydration characteristics of tricalcium silicate (C₃S). The results show that compared with the single doping of phosphorus, the co-doping of phosphate and heavy metal ions is not conducive to the firing of C₃S, while the co-doping of fluorine, phosphate, and heavy metal ions has a significant synergistic promoting effect on the firing of C₃S, while significantly improving the symmetry of C₃S crystal structure, resulting in more defects of different types on the surface of C₃S minerals. Compared with the single doping ofphosphorus, the co-doping of phosphate and heavy metal ions is beneficial for improving the initial and later hydration rates of C₃S, reducing the aspect ratio of rod-shaped hydrated calcium silicate (C-S-H). The effect of co-doping of fluorine, phosphate, and heavy metal ions on the hydration performance of C₃S depends on the doping ratio of each ion. However, as the doping amount of each ion increases, the acceleration period of C₃S hydration will be continuously delayed, and the co-doping of the three ions will promote the increase of the aspect ratio of rod-shaped C-S-H.

Key words: tricalcium silicate, co-doping, synergistic influence, phosphorus, hydration heat, hydration product