Effect of the Addition of Ca(OH)₂,SiO₂,and Pyrite on the Shrinkage and the Metallization of Pellets Containing Coke during Firing

　Investigation has been caarried out on the effect of Ca(OH)₂, SiO₂, and pyrite addition on the shrinkage and the metallization of pellets during the reduction in coke bed.
　Four kinds of iron ore were used as test materials. The mixed powder of the test materials with fixed amounts of Ca(OH)₂, SiO₂, and pyrite, and 10wt% of coke was pressed in a die to make green pellets. The pellets were embeded in a crucible charged the coke powder to be reduced in vertical tube furnace at the temperature of 1200 to 1300℃.
　Ca(OH)₂ addition to the pellets was very effective for shrinkage because of the formation of a large amount of liquid phase in the pellets, and also for metallization because of the prevention of fayalite formation. The necessary amount of Ca(OH)₂ for the improvement of shrinkage and metallization depends on the origin of ore used and the reduction conditions. At a reducing temperature of 1250℃, for example, it was found that the addition of about 4wt% of Ca(OH)₂ was generally effective owing to the formation of slag containing a large amount of CaO.
　Prereduced pellets added CaO can be expected to have high fusibility in the melting process of pellets, because metallic iron is surrounded by slag with a low melting point and low content in FeO.
　SiO₂ addition was not favorable either from the viewpoint of strengthning and of the metallization of the pellets. Only 0.2wt% of pyrite was effective in pellet shrinkage, and pellet strength increased. However, desulphurization was needed because of remains of high percentage of sulphur after reduction.