Preparation of salt-activated cementitious materials from high-temperature activated iron tailings and micromechanism

Abstract In this study, iron tailings were subjected to high-temperature activation at 600, 800, and 1 000 ℃, and then compounded with slag, cement, and sodium sulfate to prepare a salt‑activated cementitious material. The activation mechanism of the high-temperature activated iron tailings and their mechanism of action in the sodium sulfate-activated cementitious system were revealed by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and maximum intensity projection (MIP) characterization techniques. The results show that activation at 800 ℃ can transform kaolinite, chlorite, and nontronite in iron tailings into highly active amorphous substances, increasing the specific surface area and enhancing the pozzolanic activity. After incorporation of the activated iron tailings, the fluidity of the material decreases with increasing activation temperature, while the setting time first shortens and then slightly prolongs. Compared with the unactivated system, the material incorporating 800 ℃-activated iron tailings exhibits increases in compressive strength at 3, 7, and 28 d of 17.6%, 23.6%, and 21.9%, respectively, and increases in flexural strength of 15.0%, 15.6%, and 12.4%, respectively. This system has a porosity of 11.94% and a water absorption of 3.37%, with low proportions of capillary and large pores and a dense microstructure. Further microscopic analysis reveals that Na₂SO₄ reacts with Ca(OH)₂ to form NaOH, increasing the alkalinity of the paste and promoting the dissolution of active components from the iron tailings and slag. These dissolved components participate in the reaction, continuously generating ettringite and C-(A)-S–H gels. As the hydration age increases, the hydration products continuously accumulate, making the material structure gradually denser, thereby effectively enhancing the strength.