Phosphorus distribution between carbon-saturated iron at 1350 °C and lime-based slags containing Na2O and CaF2

Abstract

The Corex process is capable of consistently producing hot metal with very low silicon contents (<0.1 pct), and as a consequence, its hot metal is ideally suited for the external removal of phosphorus. Various studies have shown that small additions of Na2O significantly enhance the ability of lime-based slags to dephosphorize liquid iron. Additions of fluxes (such as CaF2) may be required to ensure that the slags remain fluid during treatment. The aim of the present investigation was to study the dephosphorization capabilities of lime-based slags from the CaF2-CaO-Na2O-SiO2 system. Phosphorus containing slag and carbon-saturated iron was equilibrated in carbon crucibles at 1350 °C under a carbon monoxide atmosphere. It was confirmed that additions of Na2O increase the phosphate capacity of silicate and lime-based slags considerably. Additions of CaF2 to Na2O containing lime-based slags increase the activity coefficient of P2O5 and, therefore, decrease the phosphate capacity thereof. These slags have high phosphate capacities and low melting points, yielding them suitable as effective reagents for dephosphorization, and even desulphurization, of hot metal at relatively low temperatures. However, CaF2 additions to these slags should be limited.