Effect of varying Al2O3 contents of CaO-Al2O3-SiO2 slags on lumped MgO dissolution

This study utilized the single hot thermocouple technique to examine the dissolution behavior of lumped magnesium oxide (MgO) in CaO-Al2O3-SiO2 ternary slags. The aluminum oxide (Al2O3) content in the slag (C/S = 1) varied from 10% to 30%; the MgO sphere with a diameter of 1 mm was placed in molten slags at 1,550 degrees C. Results showed that the dissolution rate decreased as the Al2O3 content increased up to 20%. Over 20% Al2O3, MgAl2O4 was formed at the interface of MgO and it did not fully melt at 30% Al2O3. The dissolution behavior and the formation of MgAl2O4 were analyzed by a phase diagram provided by Factsage 7.0 software. In the case of less than 20% Al2O3 content, apparent sphere radii were measured; the shrinking core model was then applied to understand the dissolution mechanism. The dissolution rate of both slags was controlled by boundary layer diffusion. The dissolution rate at 20% Al2O3 slag appeared to fit the behavior to the boundary layer diffusion, although it deviated during the middle stage of the dissolution because of MgAl2O4 formation. The 10% Al2O3 slag fitted well to the boundary layer diffusion curve; the obtained diffusion coefficient was 0.94 x 10(-9)m(2)/s.