Effects of CaF2 and ilmenite on dissolution behavior of lime in Al2O3-CaO-SiO2 slags

The effects of CaF2 and ilmenite on dissolution rate and diffusivity of CaO in calcium alumino-silicate based slag in a temperature range of 1500-1600 degrees C were studied by using the rotating disk/cylindcr technique. The effect of rotation speed on the rate of dissolution in the base slag indicated that mass transfer in liquid slag played a significant role in controlling the dissolution. At a constant rotation speed, the effect of 5 wt% addition of fluxes to the slag on the dissolution rate was investigated at various temperatures. While CaF2 had the highest effect, addition of ilmenite increased the rate of dissolution significantly. The diffusivity of lime in these slags was quantified using the dimensionless mass transfer correlations for rotating disk/cylinder in the melt. The diffusivity values were deduced using the data on dissolution rate and solubility of lime in the slags. The measured diffusivity in base slag at 1500 degrees C was found to be about 1.32 x 10(-5) cm(2)/s and increased to 3.07 x 10(-5) cm(2)/s at 1600 degrees C. Addition of 5 wt% CaF2 increased the diffusivity by a factor of 3 to 5, while 5 wt% ilmenite increased the diffusivity by a factor of 2 to 3 in the temperature range of 1500 to 1600 degrees C. The two examined fluxes reduced the activation energy of diffusion.