Thermodynamics of the simultaneous desulfurization and dephosphorization processes of hot metal with CaO- and BaO-based slags bearing MnO

Abstract

The technical feasibility of the simultaneous desulfurization and dephosphorization process of hot metal with high basicity slags of the BaO‐BaF2 system is discussed from the thermodynamic point of view. The partition ratios as well as the degrees of removal of sulphur and phosphorus from the hot metal obtained after a single refining step with BaO‐saturated slags have been compared to those achieved when typical hot metal pretreatment slags of the system CaO‐CaF2‐SiO2 (double saturated with CaO and 3CaO•SiO2) were used. The experiments were carried out in graphite crucibles at 1573 K, under CO atmosphere. Considering that both the desulfurization degree and the dephosphorization degree of hot metal achieved with BaO‐based slags, around 95 %, were much higher than those obtained when CaO‐based slags were used, maximum 45 %, it was concluded that the simultaneous desulfurization and dephosphorization process of hot metal with high basicity BaO‐BaF2 slags is technically feasible. It has been verified also that the high basicity BaO‐based slags led to manganese recovery degrees as high as 86 % and prevented at the same time the undesirable oxidation of carbon from the metal phase.

Dephosphorisation of hot metal containing moderate amounts of chromium with CaO–FeOx–Cr2O3–CaF2 slag

“…Based on the reviews above, although there have been a number of studies on the dephosphorisation of Cr-containing hot metal, concerns related to high toxicity of Ba-containing slag [10], generation of toxic SiF 4 gas caused by a high concentration of CaF 2 [13] and low dephosphorisation ratio, have limited their application in actual production. In addition, most of the reports focused on the dephosphorisation of high-chromium hot metal and thus do not provide effective guidance for the dephosphorisation of hot metal containing moderate concentrations of chromium.…”

“…Zhao et al performed thermodynamic calculations and experiments for dephosphorisation of hot metal containing Cr and Ni at 1673 to 1684 K using CaO-based slag, resulting in a dephosphorisation ratio of 36% [9]. Cruz et al found a low (maximum 45%) dephosphorisation efficiency of hot metal using CaO-based slags bearing MnO, which is much lower than using BaO-based slags [10]. From these studies, it can be concluded that the dephosphorisation efficiency is relatively low and mostly lower than 60% for Cr-containing hot metal without the addition of high basicity BaO.…”