World steel production from Electric Arc Furnace (EAF) route has surpassed more than 400 million tons and continues to grow as an important route for steelmaking as raw material flexibility, better quality, higher scrap recycling and increased energy efficiency are realized. In particular, in North America there is a strong tendency in the mini-mills to improve the quality range to produce flat products that compete with integrated mills.The desulphurization of liquid steel with ladle refining slag is one of the most important refining reactions in the entire steelmaking process. Except for a few steel grades such as ball bearing steel where the sulphide precipitates aid the cutting operation, sulphur is considered to be a major impurity as it increases brittleness and decreases weldability and corrosion resistance of steel. The two key levers of sulphur removal are metallurgical thermodynamics and kinetics. While from the thermodynamic standpoint, sulphide capacity (Cs) & sulphur partition ratio (Ls) are the defining parameters, slag/metal reaction controls the kinetics of sulphur removal. Only a very good understanding of these two levers allows efficient control over the desulphurization process. Lime is the most common desulphurizing agent due to its low cost, good sulphide capacity, and convenience in storage and transportation. However, the formation of high melting phases makes attainment of proper lime dissolution a challenging task. Thus, the operators face a lot of difficulties in preventing lime from getting lumped under prevalent operating conditions, which results in inefficient desulphurization of liquid steel.
Dastur Innovation Labs (DIL) along with Process Metallurgy Research Labs at the University of Toronto has been working on the area of waste reuse/recycling over the past few years and have come up with few innovative ideas: one of them being utilization of an aluminium industry waste named Red Mud (RM) as a fluxing agent for aiding the desulphurization process.
The present work depicts how and why RM can be effectively utilized as a flux in the steel industry and potentially generate significant cost savings by partial replacement of lime (CaO). Based on the principles of high temperature thermochemistry, alternative fluxing reagents were designed which can promote the sulphide capacity of slag as well as kinetically enhance the desulphurization process by lowering its melting point.