The effect of CaO on the crystallization properties and viscosity of synthetic silicomanganese waste slag for mineral wool production

The production of mineral wool from silicomanganese slag is a new way of resource utilization of metallurgical wastes. The crystallization and viscosity properties of waste slag are the basis of the production of mineral wool. In this study, four synthetic silicomanganese slag with various CaO contents were investigated for their crystallization tendency and viscosity. The crystallization behavior and the viscosity of the samples have been investigated by using a confocal laser scanning microscopy (CLSM) and a viscometer, respectively. The type and morphology of crystalline phases were determined by using scanning electron microscopy (SEM) with an Energy Dispersive Spectrometer (EDS). The experimental results show that the crystallinity of silicomanganese slag increases with the increase of CaO content. The crystallinity of Sample 1 is very poor, and the final sample is glass phase. In the crystallization process of Sample 2, the crystallization is not obvious, drift and grow, and finally the liquid phase in the slag continuously precipitates into fine grains. At 1350 °C, irregular crystals appeared in Sample 3, which gradually cooled down, and the number and volume increased rapidly. When the temperature is 1375 °C, many fine crystals appear in the Sample 4. These crystals are also irregular and can move freely. When the temperature is 1350 °C, the crystal grows up gradually and appears rectangles and squares, and the fluidity of crystal becomes worse. The main precipitates of Sample 2 and Sample 3 were elongated anorthite, and the precipitate of Sample 4 was cubic melilite. Furthermore, the viscosity of silicomanganese slag increases with the addition of CaO, and the main reason for the increase of slag viscosity is the precipitation of crystal in slag. When the crystal is small and has fluidity, it has little effect on viscosity. Once the crystal is fixed and grows up, however, the viscosity increases rapidly.