Preparation And Characterization of Sponge Iron

Abstract

Studies on reduction behavior of hematite iron ores with coal procured from different mines were undertaken to achieve better quality of sponge iron. Majority of the iron ores contain high iron and low alumina as well as silica contents. All of these iron ores are free from the deleterious elements (S, P, As, Pb, alkalies etc.). The size of iron ore is very important for reduction reaction. It has been observed that rate of reduction reaction of iron oxide increases with decrease in size of ore. It is observed that for very small size particle, reduction velocity is independent of the diameter whereas for medium size particle it is inversely proportional to (d) diameter of the particle and for larger size it is proportional to 1/d2. The reduction of iron oxide is performed under controlled atmosphere. Slowly reductants diffuse inside solid body and oxygen gets removed. It was observed that the iron oxide changes its phases from hematite to magnetite, magnetite to wustite and finally to metallic iron. The degree of reduction is influenced by the coal in the reduction zone area inside the kiln if good quality coal is used. The carbon and oxygen combine together to form carbon monoxide which is used as a reducing gas for the iron ore. The metallic layer thickness gets diminished due to the volatile matter present in coal. An increase in the thickness of product iron layer offers more resistance to the diffusion of carbon and reducing gas and prevents it to interact with the surface of unreduced iron oxide. Iron ore lumps shows lower degree of reduction than the corresponding fired pellets (small size iron ore). Coal becomes more reactive and occupies less volume in kiln if it has high volume of fixed carbon as well as volatile material in its composition. This results in increase of fusion temperature, good quality and high production of sponge iron. In this work the variables which influence the quality of sponge iron to achieve different grades of sponge iron has been studied and presented in subsequent chapters.