Determination of optimum blast furnace slag cooling rate for slag recycling in cement manufacture

Abstract

The crystallisation behaviour of molten blast furnace slag was observed in situ using the single hot thermocouple technique. Isothermal and non-isothermal experiments were conducted to construct the diagrams for time temperature transformation and continuous cooling transformation. The molten slag should be cooled at a minimum critical cooling rate of 10°C s⁻¹. During crystallisation, melilite is the main crystal phase and rankinite is the primary phase. The crystallisation mechanism of the melilite crystal phase involves one-dimensional direction growth with bulk nucleation, whereas the growth mechanism of the rankinite crystal phase is between the surface nucleation mechanism and the one-dimensional direction growth mechanism. The crystallisation activation energies of the melilite and rankinite crystal phases are 238.07±28.81 and 523.52±58.56 kJ mol⁻¹ respectively.

Keywords:

• Blast furnace slag
• Glassy
• Crystallisation
• Critical cooling rate