Article ID: ISIJINT-2019-049
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–FeOx–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.