Viscous flow and crystallization behaviors of p-bearing steelmaking slags with varying fluorine content

Abstract

The role of fluorine in the CaO-SiO2-MgO-Al2O3-FetO steelmaking slags was investigated through analyzing the viscous flow and crystallization behaviors of the slags. It was found that the viscosity decreased with increasing CaF2 content, which resulted from the decrease of the degree of polymerization (DOP) of the structures, as proved by O1s X-ray photoelectron spectroscopy (XPS) and magic angular spinning nuclear magnetic resonance (MAS-NMR) analysis. The continuous cooling transformation (CCT) diagrams of the primary crystals were also constructed. The results showed that CaF2 addition promoted the transformation of the primary crystal from spinel (MgFe2O4) to flourapatite (Ca5(PO4)3F, which was beneficial to the further enrichment of phosphorus. According to 19F MAS-NMR results, F- ions mainly coordinate with Ca2+ ions to form Ca-F bond. Furthermore, considering the greater stability of P-O-Ca than that of Si-O- Ca bonds, most of the F- ions behave as F-Ca-O-P band, which thus enhanced the formation of Ca5(PO4)3F. Additionally, the non-isothermal crystallization kinetics was further analyzed and the activation energy for the primary crystal growth was derived.