Characterisation studies on swelling behaviour of iron ore pellets. (7th February 2018)

• Record Type: Journal Article
• Authors: Umadevi, T.; Kumar, A.; Karthik, P.; Srinidhi, R.; Manjini, S.
• Is Part Of: Ironmaking & steelmaking. Volume 45:Number 2(2018)
• Page Start: 157
• Page End: 165
• Publication Date: 2018-02-07
• Subjects: Iron ore pellet -- Swelling -- Silica -- Basicity -- Microstructure -- Physical and metallurgical properties; Iron industry and trade -- Periodicals; Steel industry and trade -- Periodicals; 669.1
• DOI: 10.1080/03019233.2016.1250043
• Languages: English
• ISSNs: 0301-9233

Abstract

Abstract : At JSW Steel Limited (JSWSL), pellets form the major part of the iron-bearing feed to corex and blast furnace. JSWSL produces low-basicity pellets ((CaO/SiO2 ) – 0.40 to 0.50). The quality of the pellet is affected by the raw material chemistry (gangue content), flux proportion and their subsequent heat treatment to produce the fired pellets. The raw material silica, limestone addition, i.e. basicity – CaO/SiO2 of pellet decides the mode, temperature and the amount of melt formed. The properties of the pellets are, therefore, largely governed by the form and degree of bonding achieved between ore particles and also by the stability of these bonding phases during the reduction of iron oxides. In the present study, laboratory pelletisation experiments have been carried out to know the effects of silica and basicity on the microstructure and swelling behaviour of pellets during reduction. Phase analysis was carried out using image analyser, and chemical analysis of oxide and slag phases was carried out using SEM–EDS. From the laboratory studies, it was observed that the swelling index of the pellets decreased with an increase in silica content due to the decrease in porosity. The presence of higher silica in pellet hinders the reduction step of haematite to magnetite at lower temperatures. Pellets with basicity range 0 to 0.1 exhibited lower swelling index due to the formation of high melting point fayalite phase and also at this basicity range the structure is held together by the seam-like compounds between Fe2 O3 and SiO2 primarily at high silica content. Higher swelling index was observed at the basicity range 0.3 to 0.7 due to the presence of low melting point calcium olivines (1115°C) between fayalite (FeSiO4 ) and dicalcium silicate (Ca2 SiO4 ). Low melting point slag phase enhances the swelling index of the pellets. Swelling index of the pellets considerably dropped between the basicity range 0.9 to 1.1 due to the formation of calcium ferrite phases with a close pore structure.