DISSOLUTION KINETICS OF CALCIUM ALUMINATE IN STEELMAKING SLAGS

Abstract

Inclusion removal is critical for the production of clean steel. A better understanding of removal processes require knowledge of the effect of process parameters on dissolution kinetics. The present research focuses on the kinetics of calcium aluminate inclusion dissolution in relevant steelmaking slags that contain CaO, Al2O3 and SiO2. In-situ observation of inclusion dissolution in slag is conducted using a high temperature, confocal scanning laser microscope (HT-CSLM). The particles used in this experimental work are produced in the laboratory and the production technique is explained in detail. The change in particle size is recorded with time and the effects of temperature, slag composition and inclusion morphology are investigated. The images are extracted from video and they are analysed to record the change in equivalent radius of a single particle during the dissolution process. The original and normalized dissolution data is used to determine the dissolution mechanism and to improve existing dissolution models. It has been found that an increase in temperature increases the dissolution rate. At 1550°C and 1600°C, there is no product layer formation at the slag-inclusion interface and so, the dissolution process is faster. Slag composition shows a significant influence on the dissolution kinetics due to differences in the dissolution driving force and viscosity. Additionally, the dissolution rate depends on the morphology of inclusion as available reaction sites vary significantly. Rate limiting steps are discussed based on the shrinking core model and diffusion in stagnant fluid model. It is shown that the rate limiting step for dissolution is the diffusion v through a product layer at 1500°C whereas it is mass transfer in slag at 1550°C and 1600°C. The diffusion coefficient of alumina is obtained by applying a one-dimension diffusion model. The calculated results varied between 5.5×10-11 and 2.6×10-10 m2/s depending on experimental conditions. Slag viscosity was found to be an important parameter for the modelling of the dissolution process. A modification to the correlation between the correction coefficient and slag viscosity was proposed. This modification improved the prediction of the dissolution path for calcium aluminate and alumina inclusions in steelmaking slags. This novel study provides an understanding of dissolution mechanisms and it offers data on the dissolution rate of CA2 inclusions in the slags related to the process of steelmaking. The results from this work can be used by steelmakers to aid in process design.