Kinetics of Calcium Leaching from Particulate Steelmaking Slag in Acetic Acid Solution

In order to reduce CO₂ emission, the CO₂ sequestration using particulate steelmaking slag in water is world widely being studied through a Ca-carbonation method. As consequence, the improved efficiency of Ca leaching from the steelmaking-slag particles contributes significantly to increasing the amount of fixed CO₂. Therefore, in this study, for the purpose of understanding the Ca leaching from steelmaking slag particles, the rate of Ca leaching in week acidic solution was analyzed by several leaching kinetics models such as the shrinking core model and the logarithmic rate law. In addition to Ca, the leaching rate of Fe which is one of the major elements was also investigated. The Ca and Fe leaching process with stirring could be fitted well by logarithmic rate law. Moreover, by the observation using SEM-EDX, it was observed that the residue after acetic acid leaching was porous material with the pores blocked. From these results, it was revealed that the mass transfer in the products blocking the pore surface of slag particles was very likely to be the rate-controlling step of Ca leaching. In fact, promoting mass transfer by ultrasonic irradiation could enhance the rate of Ca leaching remarkably. While the Ca leaching ratio reaches 56.6% at 300 min without ultrasonic irradiation, the leaching ratio reaches 57.3% just for 30 min leaching with ultrasonic irradiation. This study reveals that promoting the mass transfer in the products blocking the pore surface of slag particles is important for increasing the rate of Ca leaching.