In order to study the effect of the change of MgO/Al2O3 on the viscosity and thermodynamic properties of the chlorinated blast-furnace slag, the CaO-SiO2-MgO-Al2O3-TiO2-CaCl2 slag system was taken as the research object, and the viscosity change rule of the chlorinated high-titanium slag was studied by using the rotating cylinder method. The thermal stability of the chlorinated high-titanium slag was quantitatively analyzed by calculating the extreme heat release rate (EHRS) of the chlorinated high-titanium slag. At the same time, the qualitative and quantitative analysis of the high-titanium slag containing chlorine was carried out by combining FTIR and Raman spectroscopy, and the mechanism of the influence of MgO/Al2O3 on the viscous flow characteristics of the high-titanium slag containing chlorine was revealed. The results show that when the alkalinity (R2) of the fixed slag is 1.15, when MgO/Al2O3 is in the range of 0.40–0.66, the viscosity of the high-titanium slag containing chlorine presents a significant decreasing trend with the gradual increase of MgO/Al2O3, and the viscous flow activation energy of the slag decreases from 98.75kJ · mol−1 to 95.21kJ · mol−1. The heat capacity and enthalpy change of slag decrease with the increase of MgO/Al2O3, but the change rule of slag extreme heat release is opposite to that of heat capacity and enthalpy change. When MgO/Al2O3 increases, the slag extreme heat release increases from 13.413 kJ to 15.172 kJ. The content of simple structural units Q0 and Q1 of silicate tetrahedron in the slag gradually increases, the content of complex structural units Q2 and Q3 gradually decreases, and the average amount of non-bridging oxygen decreases from 1.94 to 1.79, indicating that Al2O3 acts as a network maker in the internal network structure of the slag. The increase of MgO/Al2O3 destroys the complex silicate tetrahedron structure in the slag, reducing the degree of polymerization of the slag silicate network. In addition, the transmissivity of [SiO4]4− tetrahedron, [AlO4]4− tetrahedron and T-O-T bond bending vibration band in the slag shows a decreasing trend. Within the scope of the experiment, the increase of MgO/Al2O3 can effectively improve the fluidity of the chlorine-containing blast-furnace slag and improve the thermal stability of the chlorine-containing blast-furnace slag.
