Contribution of Mineralogical Phases on Alkaline Dissolution Behavior of Steelmaking Slag

Abstract

To suppress alkaline elution from steelmaking slag through microstructure control, in this study, several mineralogical phases identified in industrial steelmaking slag were synthesized, and their dissolution behaviors were investigated. The results indicated that in addition to free CaO and free MgO, 2CaO·SiO₂-3CaO·P₂O₅ (C₂S–C₃P) is another reason for alkaline elution from steelmaking. To suppress the amount of C₂S–C₃P in steelmaking slag, reducing the slag basicity by the compositional modification of slag at the hot stage was considered. To determine the optimum composition, the contribution of newly formed primary crystalline phases must be clarified. Some primary crystalline phases in the CaO–SiO₂–FeO_x–MgO–Al₂O₃ system were synthesized, and their dissolution behaviors were evaluated. The results indicated that the formation of α-CaO·SiO₂ (α-CS), β-CaO·SiO₂ (β-CS), 3CaO·2SiO₂ (C₃S₂), 2CaO·MgO·2SiO₂ (C₂MS₂), and 3CaO·MgO·2SiO₂ (C₃MS₂) must be restrained in slag modification. Based on the results, a slag with multiple components and low basicity was synthesized, and the suppression of alkaline elution by reduction of slag basicity and microstructure control was confirmed. Moreover, a method to predict Ca dissolution and pH change during the dissolution of slag by the combination of each crystal phase was proposed.