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Sintered diopside glass ceramics were successfully prepared from mixtures of blast furnace slag, fly ash and mining tailing. Results showed that sample C2 with relatively low iron oxides and mass ratio of CaO/SiO2 possessed the highest bending strength value among samples. A low content of iron oxide enhanced densification degree because pores were developed by reduction of ferric oxide into ferrous oxide. Moreover, a low CaO/SiO2 mass ratio also greatly promoted the densification process by prolonging the sintering time and delaying the crystallisation. In addition, sample C1 developed by one-stage sintering had a worse mechanical performance than that obtained by two-stage sintering although they had the same crystals. For all samples, despite of different compositions and sintering processes, the main crystal phases are augite and diopside ferrian.

Glass–ceramic samples were prepared from a mixture that was composed of blast furnace slag, tailing and coal fly ash. FactSage software was used to calculate the batch viscosity and plot of the CaO–Al2O3–SiO2–6 wt-%MgO system phase diagram. The main mechanical properties, crystal morphology and crystalline phase transition of glass–ceramics were investigated as functions of batch viscosity, binary basicity (CaO/SiO2) and Al2O3 content by differential thermal analysis, X-ray diffraction, SEM-EDX and Fourier transform infrared spectroscopy techniques. Research results indicate that Al3+ cations play different roles in samples with various binary basicity values and Al2O3 contents for the formation of [AlO4] tetrahedral or [AlO6] octahedral structure, which is different from the role of Ca2+ ones. With the increase in binary basicity, the formula of high performance has a trend toward higher Al2O3 content region.

Metallurgical slag, quartz sand and coal fly ash were used as the raw materials for preparation of glass–ceramics according to their compositions and characteristics. Under different mole ratios of (CaO+MgO)/SiO2, the crystallisation mechanism, microstructure and main mechanical properties of glass–ceramics were systematically investigated through differential thermal analysis, X-ray diffraction, scanning electron microscopy, mechanical and chemical properties test. The results indicate that MgO plays the same role of CaO. The crystallisation activation energy Ea and crystallisation temperature Tp decrease as the increase in (CaO+MgO)/SiO2 ratio. It is found that when (CaO+MgO)/SiO2 ratio is 0·64 and sintering lasts for 1 h at 996°C, main phase of diopside can be obtained with the best mechanical properties and chemical durability, such as bending strength 110 MPa, microhardness 6·5 GPa, mass loss rate of 0·25 and 0·1% as acid resistance and alkali resistance respectively.