An investigation on the use of coal gangue and coal gasification slag as reducing agent in synergistic utilization of steel slag for higher-activity supplementary cementitious materials

To explore the synergistic effect of iron recovery and the hydration reactivity of the residue, steel slag was heated and reduced at different temperatures using coal gangue and coal gasification slag as reducing agents. The resulting aluminosilicates were then quenched in water. The content of Fe in reduced ferroalloys and water quenching residues is determined. X-ray diffraction, infrared spectroscopy, microcalorimeter , etc. were used to analyze the phase changes and hydration activity of water quenching residues. The results show that the increase of reduction temperature can significantly improve the iron recovery rate, reaching a maximum of 98.5 %, and an iron grade of 98 %. When the reduction temperature is below 1450 ℃, the mineral phases in the water quenching residues are mainly merwinite and gehlenite . With the temperature increase to 1450 ℃ and 1500 ℃, the phases of merwinite and gehlenite disappeared. At this time, the water quenching residues is mainly composed of glass phase. The increase of reduction temperature leads to an increase of the glass content in the water quenching residues, enhancing the hydration activity. The cumulative heat release of cement hydration reaction is greater when high reduction temperature water quenching residues is added. The compressive strength development rate of water quenching residues cement is higher than that of reference cement. After 28 d, the compressive strength of cement prepared with 30 wt% water quenching residues (reduced at 1400 ℃) reaches 90 % of the reference cement strength . • Using coal gangue and gasification slag to reduce iron oxides in steel slag. • Achieved 98.5 % iron recovery and 98 % purity by high-temperature reduction (1500 °C). • Substantial glass-phase formation in residues enhances hydration activity above 1450 °C. • 30 % residue-containing cement achieves 90 % strength of conventional cement at 28 days.