Investigation of cooling processes of molten slags to develop multilevel control method for cleaner production in mineral wool

Abstract

Direct use of molten slags in production of mineral wool is considered a positive approach for large-scale absorption of this waste, both economically and environmentally. However, this application has been limited by the poor production stability caused by the complex and variable compositions and properties of molten slags. To improve it, this study developed a novel multilevel control method based on molecular dynamics simulations and experimental investigation of structure and thermophysical properties of molten slags during cooling processes over a broad basicity range. The structural analysis showed as the basicity increased, the Si-related network was depolymerized and the Al-related structure was polymerized, and as a comprehensive result the degree of polymerization of melt decreased. The reflection of this structural change on the process properties was the flowing and crystallization abilities of molten slags increased. Especially, the viscous flow activation energy decreased from 188.43 to 185.15 kJ/mol and the critical cooling rate increased from 5 to 30 °C/s. The mineral wool prepared from molten slags with basicity of 0.8 showed the optimal morphology and mechanical properties overall, with the fibrosis rate of 91%, the mean fiber diameter of 5.39 μm, the tensile strength of 2518 MPa. We further analyzed the relationship between structure, rheological and crystallographic properties, and product quality. Based on these, method of determining initial composition, temperature schedule, and cooling rates for cleaner and high-efficient production was developed from the structural simulation, viscosity-temperature curve and time-temperature-transformation curve.