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CaO–MgO–Al₂O₃–SiO₂–Cr₂O₃ diopside glass–ceramics were prepared from blast furnace slag, low-carbon ferrochromium alloy slag, and quartz sand by the melting method. The prepared glass–ceramics were characterized by differential thermal analysis (DTA), X-ray diffraction (XRD),scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS), and X-ray photoelectron spectroscopy (XPS). The effect of Cr₂O₃, a nucleating agent, in the crystallization process of diopside glass–ceramics was studied. The results show that chromium is present in glass–ceramics as Cr³⁺ and Cr⁶⁺, and Cr³⁺ accounts for more than 80% of the chromium contents. When the mass percentage of Cr₂O₃ in glass–ceramics is less than 1.60%, a small amount of diopside phase is precipitated during heat treatment, and Cr³⁺ is dispersed in the diopside phase. When the mass percentage of Cr₂O₃ reaches or exceeds 1.60%, Cr³⁺ preferentially forms the magnesia chrome spinel phase, which further induces the in situ growth of diopside. The leaching concentration of chromium meets the Chinese national standard, indicating that diopside glass–ceramics can effectively solidify the heavy metal chromium, and this fact makes the application of glass–ceramics feasible.