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The viscosity, melting proprieties, and molten structure of the high-Al silicon–manganese slag of SiO2–CaO–25 mass% Al2O3–MgO–MnO–K2O system with a varying MgO and K2O content were studied. The results show that with the increase in MgO content from 4 to 10 mass%, the measured viscosity and flow activation energy decreases, but K2O has an effect on increasing those of slags. However, the melting temperature increases due to the formation of high-melting-point phase spinel. Meanwhile, Fourier transform infrared (FTIR) and X-ray photoelectron spectra (XPS) were conducted to understand the variation of slag structure. The O2− dissociates from MgO can interact with the O0 within Si–O or Al–O network structures, corresponding to the decrease in the trough depth of [SiO4] tetrahedral and [AlO4] tetrahedral. However, when K2O is added into the molten slag, the K+ can accelerate the formation of [AlO4] tetrahedra, resulting in the increase in O0 and O− and the polymerization of the structure.

The effect of TiO2 and the MgO/Al2O3 ratio on the viscosity, heat capacity, and enthalpy change of CaO–SiO2–Al2O3–MgO–TiO2 slag at constant heat input was studied. The variation of slag structure was analyzed by the calculation of activation energy and FTIR spectrum measurements. The results showed that the heat capacity and enthalpy change of the slag decreased with the increase of TiO2 content. Under constant heat supply, the fluctuations in slag temperature were relatively apparent, and the temperature of slag increased as the TiO2 content increased. The viscosity of slag decreased due to the increase in slag temperature. Increasing the MgO/Al2O3 ratio could decrease the temperature and viscosity of slag. The effect of increasing the MgO/Al2O3 ratio on the viscosity was more pronounced than the decreasing temperature caused by increasing the MgO/Al2O3 ratio. The apparent activation energy decreased with increasing TiO2 content and MgO/Al2O3 ratio. The Ti–O bonds formed with TiO2 addition, and the Ti–O bonds were weaker than Si–O bonds, which resulted in the decrease in heat capacity and viscosity of slag.

The potassium removal capacity of BaO-bearing blast furnace slags was investigated. The influence of basicity (CaO/SiO 2 ), Al 2 O 3 and BaO content on potassium removal capacity was analysed by combining with the activity of K 2 O in slag. The relationship between optical basicity and potassium removal capacity of slag was also studied. The results showed the temperature and basicity had a great influence on the potassium removal capacity. The increasing temperature and basicity made the reduction reaction of K 2 O enhance, leading to a significant decrease in potassium removal capacity. The activity of K 2 O in slag decreased with Al 2 O 3 content increasing, which inhibited the reduction reaction of K 2 O, leading to the increase in potassium removal capacity. BaO had a slight effect on the potassium removal capacity, and the remaining K 2 O content in slag decreased with BaO content increasing from 0% to 5%. The higher optical basicity was, the weaker potassium removal capacity was.