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Fluorspar (CaF2) is commonly used to control the fluidity of slag in ladle-refining of steel. However, because it is desirable to reduce CaF2 consumption because of its environmental impacts, the industrial waste material such as white mud (WM) was investigated as a potential substitute for fluorspar. Steel sample (Fe-0.3C-0.9Mn-0.3Si-0.03Al-0.05S, mass pct) was melted in a high-frequency induction furnace, followed by additions of ladle slag (CaO-Al2O3-SiO2-5MgO-xCaF2, CaO/Al2O3=3, x = 0 to 10 mass pct) and fluxing agent (WM) at 1823 K (1550 °C). The desulfurization experiments were carried out by reducing CaF2 content in the ladle slag and increasing the addition of WM. Ladle slag with added WM showed an overall mass transfer coefficient of sulfur (kO) equivalent to or higher than that of conventional 10 mass pct CaF2-containing ladle slag. In a slag melting experiment based on DIN 51730 standard, the melting rate of mixed slag increased with the amount of WM added, which is considered to have a positive effect on the initial desulfurization rate. In addition, adding WM provided sulfide capacity of the slag equivalent to that of CaF2-containing slag. Consequently, the use of WM yielded slag having $$k_{{\text{O}}}$$ k O equivalent to or higher than that of conventional ladle slag with 10 pct CaF2, and thus, WM shows promise as a partial replacement for fluorspar.