Effect of Additives (Alumina, Magnesia or Calcium Fluoride) on Dissolution Rate of Solid CaO into Calcium Silicate Based Slags

Abstract

A study was undertaken to understand dissolution behavior of solid CaO particles into molten slags. Experiments were carried out to determine the effects of the basicity (CaO (mass%) / SiO₂ (mass%)) and the kinds of additives (Al₂O₃, MgO or CaF₂) on the dissolution rate of the rotating cylindrical CaO sinter into the ternary calcium silicate based slags at 1823 K. (Contact materials: graphite, Atmosphere: Ar)
The dissolution rate increased with increasing rotation velocity of the cylindrical CaO sinter. It was found that the dissolution rate was highest with the CaO-SiO₂-CaF₂ slag so that CaF₂ was proved as a good flux material. The dissolution rate of CaO increased with lowering slag basicity for the all slag system. However, this tendency was found to be weaker with the CaO-SiO₂-Al₂O₃ system than the others due to the significant viscosity increase in the lower basicity region.
The observation of the interface between CaO and each slag indicated that the dicalcium silicate (Ca₂SiO₄) phase was formed for all the slag systems. Further, the additive elements of Al and Mg were condensed in the interlayer between the Ca₂SiO₄ and the CaO phases as the calcium aluminates and the magnesia. On the other hand, in the case of fluorine containing system, solid phase precipitation was not observed in the interlayer. The results of CaO dissolution experiments indicated these interlayers also affected the dissolution rates. The CaO dissolution was retarded with the CaO-SiO₂-MgO system, compared to the other two kinds of systems. It could be explained by the magnesia precipitation in the interlayer.