Modification of microstructure of LD slag for recovery of hybrid flux material

Abstract

The Basic Oxygen Furnace steel making process produces BOF slag (LD slag) at a rate of about 125 kg/t. The LD slag contains about 18% Fe in wustite and dicalcium ferrite and about 45% CaO. These minerals are an excellent source of alternative flux material for the steel industry. Through slag modification and in-depth characterization studies, investigations were carried out to develop a material that could be utilized as an alternative flux material. Detailed characterization studies were conducted using SEM-EPMA and XRD to identify the changes in the crystal structure, phase distribution, grain size and liberation size of minerals. The grain size of phases was found to be between 10-150 ­­­­­µm for normally cooled slag and 20-250 µm for slowly cooled slag. It was also shown that slow cooling promotes the formation of an additional phase which is essentially the dicalcium silicate phase (C2S) with some amounts of FeO and MgO in the crystal lattice. Overall, it was observed that about 50% of the LD slag could be recovered as alternative flux material containing approximately 30% CaO and 30% Fe content. This alternative flux material is an excellent source of material for use in steel industries because of its low melting slag formation.