Effects of divalent-cation iron and manganese oxides on the luminescence of free lime and free magnesia

Identification of free lime (f-CaO) and free magnesia (f-MgO) is vital for the effective reuse of steelmaking slag in road construction because f-CaO and f-MgO can cause road expansion. In the present study, we present a method to rapidly identify f-CaO and f-MgO likely to cause road expansion by investigating CL spectra of CaO and MgO containing FeO and MnO because MnO and FeO are major components dissolved in f-CaO and f-MgO. The CL peaks related to Mn²⁺ (600 nm for CaO and 755 nm for MgO) showed the highest intensities. The intensity of the peak at 600 nm for CaO containing 10 mass% MnO was the lowest for f-CaO and was 2.5-times lower than that for f-CaO, whose luminescence was captured in 15 s. MgO with 5 mass% MnO and 20 mass% FeO was found to show the lowest intensity for f-MgO that is responsible for road expansion, and its CL intensity was 10-times lower than that of f-MgO, whose luminescence was captured in 2 s. Therefore, we can identify the f-CaO and f-MgO likely to cause road expansion by capturing CL colors of the peaks related to Mn²⁺ at the exposure time of approximately 40 s. The method presented here will contribute to the effective reuse of steelmaking.