Investigation on the Coal-Based Direct Reduction of Mill Scale Pellets: Statistical Modeling and Characterization Studies

Abstract

The feasibility of producing direct reduced iron from pellets made up of mill scale by utilizing coal as a reductant has been investigated. The chemical and morphological characterization studies reveal that the mill scale contains around 71% Fe and comprises of a mixture of iron oxide phases such as magnetite and hematite with a little amount of wustite. The reduction study of the mill scale pellets has been carried out using the statistical design of experimental approach employing the response surface methodology. Under optimum conditions such as a temperature of 1246 °C, a time of 1.52 h, and coal-to-mill scale ratio of 0.58, around 88–89% metallization is obtained. Similarly, around 84% of metallization can be achieved at a temperature around 1150 °C, time of about 1.5 h with coal-to-mill scale ratio of 0.59. The characterization studies of the reduced pellets using X-ray diffraction and optical microscopy show the sequential growth of the metallic phase as the reducing parameters are increased. The properties of the mill scale pellets are found to match the desired specification for the direct reduction process, and the reduction behavior of the pellets as a function of temperature, time, and coal-to-mill scale ratio suggests that iron making from mill scale through this route is a promising process.