Reduction Rate of Cr2O3 in a Solid Powder State and in CaO-SiO2-Al2O3-CaF2 Slags by Fe-C-Si Melts.

Abstract

In order to understand effective conditions to recover chromium from stainless steel-making slags, the kinetic behavior of Cr 2 O 3 reduction by iron-carbon melts were investigated at various conditions by using solid Cr 2 O 3 powder and Cr 2 O 3 -CaO-SiO 2 -Al 2 O 3 -CaF 2 slags. The effect of temperature on the reduction rate of solid Cr 2 O 3 was fairly large and the apparent activation energy was about 180 kJ mol Ϫ1. The overall reduction of solid Cr 2 O 3 was considered to be controlled by a chemical reaction step. For reduction of Cr 2 O 3 in slag, the addition of CaF 2 to slag and of silicon to iron melt promoted the reduction rate, but the reduction of Cr 2 O 3 powder was retarded by the silicon addition. The kinetic behavior of reduction of Cr 2 O 3 in slag could be well simulated by the kinetic reaction model proposed previously. As a result, it was found that the overall reduction rate of Cr 2 O 3 in slag was controlled by the mass transport in the slag phase.

A Mathematical Model for the Reduction Stage of the AOD Process. Part II: Model Validation and Results

“…Similar observations have been made with stainless steel slags by Görnerup & Lahiri 33) and Nakasuga et al 26,27) …”

“….............. (5) Nakasuga et al 26,27) have studied the recovery rate of chromium from stainless steel slag using a kinetic reduction reaction model proposed by Shibata et al 28) In these studies, it was suggested that the reduction rate of Cr2O3 increases with increasing temperature. Görnerup & Lahiri 29) reported that increased temperature both decreased the incubation time and increased the reduction rate of Cr2O3.…”

A Mathematical Model for the Reduction Stage of the AOD Process. Part I: Derivation of the Model

“…However, much less attention has been paid to the reduction stage. Although numerous studies have been conducted on the emulsification of slag [31][32][33][34][35][36][37][38][39][40][41][42] and reduction of slag 18,[43][44][45][46] as separate research fields, a phenomena-based model capable of combining the present knowledge of both phenomena has not been previously discussed in the literature.…”

“…78) Unlike in the PFR used to describe the plume zone, the influence of CaO, MgO and Al2O3 has been taken into account in the surface element. CaF2 was considered here as the calcium ion, similar to Nakasuga et al 45) The relevant equations for activity coefficients of FeO (51) …”

Reduction Behavior of EAF Slags Containing Cr2O3 Using Aluminum at 1793 K

“…3) Nakasuga et al found that the transfer rate of chromium from the CaO-SiO 2 -Al 2 O 3 -CaF 2 slag to the Fe-C-Si melt was controlled by the mass transport in the slag phase during the entire period of reaction. 4) Recently, Miyamoto et al suggested that the reduction of Cr 2 O 3 by carbon in steel melt would be controlled by mass transfer of chromium in the CaO-SiO 2 -5wt%FeO-MgO-Al 2 O 3 slags and could mainly be affected by the product of liquid fraction and activity of Cr 2 O 3 in the slags. 5) In these studies, the reductant is a solid or liquid carbon and the content of Cr 2 O 3 was relatively high from about 10 to 35 wt% in the slags.…”