Reduction characteristics of oily hot rolling mill sludge by direct reduced iron method

Oily hot rolling mill (HRM) sludge including high amount of iron was recycled by the direct reduced iron (DRI) method. The oil component in the HRM sludge which should be removed in order to reuse the sludge was thermally decomposed at the beginning of the reduction and acted as a reducing agent in the reaction by reducing the hematite (Fe₂O₃) and magnetite (Fe₃O₄) in the HRM sludge pellets into wustite (FeO). It was found that the oil component could participate in the reduction of the HRM sludge but additional reducing agent was needed to improve the metallization indicating the generation rate of metal Fe from the oily HRM sludge. When coke dust and blast furnace slag as an additive for reducing agent was applied, increase in the degree of metallization was observed. In the range of reaction temperature, 900-1150°C, metallization linearly increased with the elevation of temperature. Metallization showed sharp increase at the initial stage of the reaction while the increase began to level off after 30 min. To obtain the minimum requirement for acceptable DRI, 90% metallization, temperature must be kept above 1100°C and mole ratio of mixture of coke dust (C/Fe₂O₃) must be above 3.6.