Characterization of direct reduced iron for reduction and elimination of sulfur using calcium carbonate

In the ironmaking process, sulfur is one of the most important elements to consider. Sulfur weakens a steel product and creates unexpected situations. In this study, calcium carbonate was used as an additive in the coal-based reducing process to investigate the extent of the reduction in the sulfur content of fabricated direct reduced iron (DRI). The experimental conditions were 900, 1000, and 1100 °C with 1 or 3 h retention times. The calcium carbonate was added at 0, 5, 10, and 20 wt% of the anthracite coal. The extent of reduction and metallic Fe content of the DRI were dominated by temperature and retention time. When the calcium carbonate content was increased to 5 wt%, the metallic Fe content was proportionally enhanced to a value of 62.38 wt%, which was the highest among all the cases examined. However, the metallic Fe content decreased as the quantity of calcium carbonate was increased from 5 to 20 wt% owing to the effect of saturated CO2 gas. In the case of sulfur content, as more calcium carbonate was applied in the reaction, less sulfur was detected. The calcium oxide from the decomposition of calcium carbonate captured the sulfur and hindered the infiltration of sulfur into the DRI during the reduction reaction. Calcium carbonate was confirmed to be an effective material for removing sulfur during the production of DRI.