A Review of Multi-phase Slag Refining for Dephosphorization in the Steelmaking Process

Wenhui Lin,Qing Liu,Shuqiang Jiao,Xiaoming Feng,Jiankun Sun,Kaixiao Zhou

doi:10.3389/fmats.2020.602522

Wenhui Lin, Qing Liu + Show 4 more

Open Access

https://doi.org/10.3389/fmats.2020.602522

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Abstract

Dephosphorization has always been a challenging task in the steelmaking process. In the traditional studies, CaO-based steelmaking slag was usually treated as a homogeneous liquid phase to analyze the dephosphorization equilibrium between molten slag and hot metal (slag/metal). In fact, the slag shows a coexisting state of both liquid and solid at steelmaking temperature. In recent years, multi-phase slag refining has been proposed and proved to be an efficient technique to improve the utilization of solid lime and the dephosphorization efficiency in steelmaking practices. The present review focuses on hot issues for the multi-phase slag refining, including the dissolution of solid lime to the molten slag, the formation of 2CaO·SiO2 and phosphorus-rich solid solution of 2CaO·SiO2-3CaO·P2O5, as well as the phosphorus distribution ratio between the solid and liquid phases in the multi-phase slag. In addition to the discussion on thermal and kinetic factors of dephosphorization, the necessity of further research is proposed on the dissolution behavior of phosphorus-rich solid solution and phosphorus redistribution in the slag of high temperature, high basicity and high FeO in the final stage of converter steelmaking. Then, a more applicable dynamic model of dephosphorization could be expected considering the equilibrium not only between molten slag and liquid metal but also among the phases of the multi-phase slag in steelmaking process. Furthermore, the modelling work is beneficial for the fine control of the BOF process and the development of intelligent manufacturing in steelmaking industry.

Highlights

Dephosphorization is always the major but challenging task in the steelmaking process
The present review focuses on hot issues for the multi-phase slag refining, including the lime dissolution into the molten slag, the formation of 2CaO·SiO2 and 2CaO·SiO2-3CaO·P2O5 solid solution, and the distribution ratio of phosphorus between the solid and liquid phases in the slag, as well as the modeling of dephosphorization by multi-phase slag
From the perspective of traditional research, increasing FeO content can facilitate the dephosphorization by promoting the dephosphorization reaction (Equation 6) which occurs at the slag-metal interface; and from the perspective of multiphase slag refining, it can be explained that the formation of CaO-FeO phase promotes the transfer of P2O5 from the liquid slag to the solid phase, thereby forming more P-rich solid solution and increasing the solid-liquid phosphorus distribution ratio (L′p) in the slag

Summary

INTRODUCTION

Dephosphorization is always the major but challenging task in the steelmaking process. The equilibrium distribution ratio (L′P) of phosphorus between the solid solution and the liquid phase in the slag was proposed, which increased with the increment of the total Fe content, but irrelevant to the valency of Fe. In addition, no dependence of L′P on temperature and basicity was observed (Inoue and Suito, 2006b). The researchers from SMS group and GTT company (Khadhraoui et al, 2018; Khadhraoui et al, 2019) proposed a new approach to establish a dephosphorization model, by coupling a new thermodynamic database developed for industrial steelmaking slag to FactSage for the phase equilibrium calculation, and the phorsphorus distribution (L′P) between the C2S-C3P solid solution and the liquid slag was regressed based on the experimental data of (Ito and Sano, 1983; Suito and Inoue, 2006; Suito and Inoue, 1984b) and introduced to the total LP equation. There are some common limitations for the exiting models, due to the lack of thermodynamic and kinetic details of multi-phase slag reactions in the final stage of BOF process

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DISCUSSION

CONCLUSIONS