Abstract: Two types of direct carbonization methods of BOF slag, and their influencing factors and kinetics mechanism were summarized. The possible rate-limiting step for hotstage carbonation treatment of slag is the diffusion of CO₂ through the product layer to the unreacted zone inside the particle. The increase of temperature can accelerate the diffusion rate of CO₂, and the decrease of particle size of slag can reduce the thickness of product layer that inhibits the diffusion, thus which can contribute to enhancement of CO₂ sequestration and improvement of conversion rate during hot-stage carbonation treatment of slag. The main controlling step for aqueous carbonation treatment is the diffusion of calcium from the inside to the surface of steel slag. Reducing the particle size of steel slag and destroying the product layer by ultrasonic vibration are the most effective ways to accelerate the diffusion leaching of calcium. Due to the high temperature of steel slag from the converter, and both carbonization methods have some limitations, it is considerable to combine the two ways. The slag with high temperature is carbonized by hot-stage carbonation treatment at elevated temperature during cooling. By reducing the particle size of steel slag and increasing the CO₂ pressure, the CO₂ sequestration and calcium conversion rate are improved. Fixing a part of calcium through hot-stage carbonation and then performing aqueous carbonation is beneficial for shortening the aqueous carbonation time. After the steel slag is cooled and continued to be milled, aqueous carbonation treatment is carried out. Combined with size optimization and ultrasonic utilization, the steel slag can be carbonized to the maximum extent, which is more promising for energy save and emission reduction.

Key words: BOF slag, hot-stage carbonation, aqueous carbonation, kinetics, diffusion