Cationic Effects of Calcium, Ferrous and Magnesium on Dephosphorization Ability of CaO-SiO₂-FeO-MgO Slag System

Designing an appropriate composition of dephosphorization slag is crucial for effectively reducing phosphorus content in steels and facilitating the development of high-quality steel products. In this study, we conducted dephosphorization equilibrium experiments to elucidate the cationic effect of Ca²⁺, Fe²⁺, and Mg²⁺ on dephosphorization behavior through Raman and ³¹P MAS-NMR spectroscopy. The results indicate that the addition of CaO, MgO, and FeO induces a consistent transformation from Q²(Si), Q¹(Si), and Q¹(P) units to Q⁰(Si) and Q⁰(P) units, resulting in a reduction in the degree of polymerization of the slag. The dephosphorization rate exhibits a nearly linear increase with CaO and MgO content, reaching its maximum value upon adding 30 mass% FeO. This phenomenon confirms that excessive addition of Fe²⁺ has an adverse impact on the dephosphorization ability of slag, which can be attributed to a reduced stability of PO₄ groups. Moreover, when Fe^(II)/(Mg + Ca) is within 0.5, increasing NBO of molten slag is beneficial for improving dephosphorization rate.