Recycling of steel plant mill scale via iron ore sintering plant

Abstract

During the processing of steel in steel mills, iron oxides will form on the surface of the metal. These oxides, known as mill scale, occur during continuous casting, reheating and hot rolling operations. Mill scale is a valuable metallurgical raw material since it contains 65–70% iron. JSW Steel Ltd is a 7 Mtpa integrated steel plant and generates 270 t of mill scale per day. Most of the materials of steel plant wastes are recycled through sinter making in most of the countries. Because of its physical, chemical and mineralogical properties, it can be used as a raw material in a process like sintering. The mill scale contains high amounts of Fe and low amounts of silica and alumina. Thus, recycling it through the sintering process helps in the saving of raw materials like iron ore and limestone. This paper presents preliminary findings of a study that investigates the potential for recycling steel mill scale in the sintering process. Experiments were conducted using the mill scale in sinter making from 0 to 70 kg/t of sinter. The total Fe and FeO contents of the sinter increased with the increase in mill scale addition. The sinter productivity decreased with the increase in mill scale addition due to a decrease in sinter bed permeability. The sinter strength and sinter mean size initially increased and reaches a maximum at mill scale addition of 40–50 kg/t of sinter and afterwards declines with the increase in mill scale addition. Sinter reduction degradation index and reducibility decreased with the increase in mill scale addition due to the increase in FeO content. Except sinter productivity, other desired sinter properties can be obtained with the use of 40–50 kg mill scale per tonne of sinter.