Generation Transport and Uses of Mill Scale Sep23

Generation Transport and Uses of Mill Scale...

Generation Transport and Uses of Mill Scale  Mill scale is the flaky surface of hot worked steel and is formed by the oxidation of the steel surface during reheating, conditioning, hot rolling, and hot forming operations. It is one of the wastes generated in steel plants and represents around 2 % of the produced steel. It is a hard brittle coating of several distinct layers of iron oxides formed during the processing of steel and composed mainly of iron oxides and may contain varying amounts of other oxides and spinels, elements and trace compounds. It flakes off the steel easily. Characteristics of mill scale Mill scale is normally present on rolled steel and is frequently mistaken for a blue coloured primer. The very high surface temperature combined with high rolling pressures result in a smooth, bluish grey surface. Under visual inspection, mill scale appears as a black metal powder made up of small particles and chips. Its physical state is solid and powdered. The specific gravity of mill scale is in the range of 5.7 to 6.2. Mill scale’s melting point is around 1370 deg C and boiling point is around 2760 deg C. It has a stable state and is insoluble in water and alkalis but soluble in most of strong acids. It is normally classified as non dangerous waste material. Fig 1 shows a small pile of mill scale. Fig 1 Small pile of mill scale  The size of the mill scale normally varies from dust size in microns up to usually 6 mm. The average mill scale obtained during the hot working of steels has iron content ranging from 68 % to 72 %. The iron in the mill scale is present in different chemical forms as given below. Magnetite, Fe3O4,...