Polymeric Structure Evolution Behavior Analysis of Aluminosilicate-Based Smelting Slag

The physical and chemical properties of the CaO–SiO2–Al2O3–MgO slag system depend on structure evolution caused by the synergistic mechanism among the components at high temperature, especially the structural complexity of the anion group. In this study, Si–O, Al–O, and Al–Si–O anion groups were found in the high-temperature slag systems at 1773 K. The [Si2O5]2− (Q3) structural unit of the silicate polymer changed to [Si2O6]4− (Q2), [Si2O7]6− (Q1), and [SiO4]4− (Q0) as the binary basicity (R2) and ω(MgO)/ω(Al2O3) increased, while there was a trend toward a simplified structure. That is, the stability of each structural unit weakened, and the relative content of non-bridging oxygen increased. As a result, the degree of polymerization of slag decreased, and the experimental results of the relative content of non-bridge oxygen can be fitted well with the calculations from the reference documents. At the same time, the number of Si–O–Al structural units gradually decreased. The 27Al-MAS-NMR spectroscopy results showed that the structure of aluminate changed from [AlO4]5− tetrahedral structure to [AlO5]7− pentahedral and [AlO6]9− octahedral structure, and the degree of polymerization of the slag decreased. Comprehensive analysis showed that basicity controlled within 1.2 with the ω(MgO)/ω(Al2O3) ratio; less than 0.55 allows for suitable fluidity and energy-saving ability, which is beneficial for the stable and smooth production of the blast furnace.