Background

Electric arc furnace steelmaking, also called EAF, typically uses Direct reduced iron or ferrous scrap as the feed materials. In the electric arc furnace lime (calcium) is added to remove silicates and phosphorus. With the addition of oxygen the ferrous materials are essentially melted, while the remaining material is changed to oxide forms. The slag by-product, also called EAFS, contains relatively constant levels of these oxides and variable amounts of iron, calcium and silicon oxides. Monitoring the FeO levels indicates the efficiency of the process, while monitoring the ratio of CaO to SiO₂ gives information on the basicity of the slag. The slag is then collected and either refined to be fed back into the steelmaking system, or sold as an aggregate. The high iron and low silicate content and hardness of the EAFS make it unsuitable as a cement raw material, but make it an excellent aggregate in asphalt and construction usage.