SOLIDIFICATION OF BOF SLAGS MODIFIED BY PYROMETALURGY AND SUBMITTED AT DIFFERENT COOLING RATES

Antonio Malynowskyj,Marcelo Breda Mourão,Fabiano Ferreira Chotoli,João Batista Ferreira

doi:10.4322/2176-1523.1549

Abstract

In a scenario of blast furnace slag shortage, the use of BOF slag (Blast Oxygen Furnace) as a partial substitute in cement production is a low cost alternative. In this paper, BOF (Blast Oxygen Furnace) slag samples were melted in an experimental electric arc furnace (EAF), with different modifiers materials (Al top dross reject, slag from FeSi iron alloy production, et al.) with different rates of additions, subject to differentiated cooling in specifically designed experimental apparatus. The objective was to search the formation of different phases formed during a process of BOF slag modification, for different materials additions containing Al2 O3 and SiO2 and subjected to different cooling conditions. Modified slags, with basicity (CaO/SiO2 ) below 1.1 and Al2 O3 contents less than 5%, subjected to cooling rates up to 21Â°C/s, favor the formation of crystalline phases; no amorphous phases were detected in this trial. Modified slag tests with basicity below 1.2 and Al2 O3 content between 10.0% and 12.5% favor both the formation of crystalline (majority) and amorphous phases (between 25% and 30%). The influence of the cooling rate up to 21Â°C/s on amorphous phase formation in this trial was not conclusive.

Highlights

Slag from the BOF process usually accounts for between 9 and 15% of liquid steel production, and is an important component in the primary refinery stage of a steelworks
The chemical compositions for the fifteen tests slag modification are presented in Table 2, parameterizing the quantities of CaO, SiO2, FeO, MgO, MnO, Fe2O3 and Al2O3 values in 100%, which are used for thermodynamic simulation as previously stated
The main conclusions can be summarized as follows: 1. Solidification of BOF modified slag resulted in several predominant crystalline phases: Olivine solid solution, Melilite and RO phase, and solid precipitate of Merwinite

Summary

Introduction

Slag from the BOF process usually accounts for between 9 and 15% of liquid steel production, and is an important component in the primary refinery stage of a steelworks. Blast furnace slag is the most used in cement production, due to the favorable proximity of its chemical composition to that of Portland cement, besides having satisfactory hydraulic reactivity. In Brazil, steel production is stagnant, but civil construction, a major consumer of cement, is being demanded, so that the substitution of blast furnace slag for BOF slag would be a low cost strategic response. The BOF slags, they present chemical components common to Portland cement have serious restrictions regarding their use in the construction industry due to the expansion caused by the oxidation of Iron (Fe0 and Fe+2) and CaO-free and MgO-free expansion effect after hydration [6]. In the HBM process described by Yao-Hung Tseng et al, oxygen and SiO2 are injected into the liquid slag in order to reduce basicity and inhibit the formation of CaO-free and MgO-free, enabling this material for many applications [7]

Methods

Results

Discussion

Conclusion