Temperature regulation for calcined magnesite tailing in basic magnesium sulfate cement: Mechanisms from hydration kinetics and products performance

This study investigates the influence of calcination temperature (650 °C, 750 °C, 850 °C) of magnesite tailings on the hydration properties, microstructure and performance of basic magnesium sulfate cement (BMSC) prepared using the calcination products. Through isothermal calorimetry, compressive strength tests, water resistance evaluation and hydration products analysis, the influencing mechanism was systematically investigated. The results indicate that a lower calcination temperature (650 °C) resulted in the greatest specific surface area and the reactivity of α -MgO in the calcined magnesite tailings. The setting time, hydration rate, and microscopic morphology of the 5·1·7 phase were predominantly influenced by reactivity variation from calcination temperature. Lower calcination temperatures led to the formation of magnesia with higher reactivity. This higher reactivity shortened the setting time of BMSC, advanced the acceleration period and facilitated the formation of the 5·1·7 phase with higher aspect ratios. In contrast, the cumulative heat of hydration, compressive strength, water resistance, and content of hydration products reached their optimum values when the tailings were calcined at 750 °C, which can be attributed to the highest α -MgO content achieved at this temperature. An excessive calcination temperature (850 °C) resulted in substantial formation of Mg(OH) 2 , which was detrimental to strength development. The BMSC prepared from magnesite tailings calcined at 750 °C exhibited excellent mechanical properties and water resistance, and reduced carbon emission and energy consumption by more than 60 % compared to Portland cement and about 30 % compared to conventional BMSC, demonstrating its feasibility and environmental benefits for BMSC production.