Effect of CaO/SiO2 and MgO/Al2O3 on the Metallurgical Properties of Low Boron-Bearing High-Alumina Slag

For optimizing the operational efficiency and productivity within blast furnace processes, a profound understanding of the viscous flow characteristics of CaO–SiO2–MgO–Al2O3–B2O3 slag systems is of paramount importance. In this study, we conducted a comprehensive investigation into the influence of the CaO/SiO2 and MgO/Al2O3 ratios on the viscosity, break point temperature (TBr), and activation energy (Eη) of low boron-bearing high-alumina slag. Concurrently, we elucidated the underlying mechanisms through which these ratios affect the viscous behavior of the slag by employing a combination of analytical techniques, including X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and thermodynamic modeling using the Factsage software. The experimental findings reveal that, as the CaO/SiO2 ratio increases from 1.10 to 1.30, the slag viscosity at 1773 K decreases from 0.316 Pa·s to 0.227 Pa·s, while both the TBr and Eη exhibit an upward trend, rising from 1534 K and 117.01 kJ·mol−1 to 1583 K and 182.86 kJ·mol−1, respectively. Conversely, an elevation in the MgO/Al2O3 ratio from 0.40 to 0.65 results in a reduction in slag viscosity at 1773 K from 0.290 Pa·s to 0.208 Pa·s, accompanied by a decrease in TBr from 1567 K to 1542 K. The observed deterioration in slag flow properties can be attributed to an enhanced polymerization degree of complex viscous structural units within the slag matrix. Ultimately, our study identifies that an optimal viscous performance of the slag is achieved when the CaO/SiO2 ratio is maintained at 1.25 and the MgO/Al2O3 ratio is maintained at 0.55, providing valuable insights for the rational design and control of blast furnace slag systems.