Influence of Pellet Basicity (CaO/SiO₂) on Iron Ore Pellet Properties and Microstructure

摘要

In JSW steel limited Pellets form the major part of the iron bearing feed to Corex and Blast Furnace. These two iron making units demand high strength, lower reduction degradation index pellets to maintain good permeability of the bed to achieve high productivity and lower fuel rate. To produce good quality of pellets certain additives are important. JSWSL produces basic pellets with basicity (CaO/SiO_(2)) 0.40 to 0.50. The quality of the pellet is affected by the type of the raw materials, gangue content, and flux proportion and their subsequent treatment to produce pellets. The limestone addition, i.e. basicity–CaO/SiO_(2) 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. Hence in production of acid, basic and fluxed pellets, characterization of the bonding and crystalline phases is of prime importance in understanding the basis for the production of pellets of desired quality. To understand the influence of limestone addition (basicity) on iron ore pellets microstructural, physical and metallurgical properties basket trials have been carried out with different level of basicity from 0.08 to 1.15. From the test result it was clear that pellet properties were influenced by the bonding phases present in the pellet. The tumbler index increased from 93.15 to 95.38% and cold crushing strength increased from 176 to 264 kg/p with increase in pellet basicity from 0.08 to 1.15. This effects result from microstructural differences appeared from the flux addition. RDI of the pellet decreased initially from 16.3 to 10.9% in the pellet basicty range from 0.08 to 0.33 and again increased from 10.9 to 13.6 with increase in pellet basicty from 0.33 to 1.15. This effect is due to the change in structural properties of the pellet during reduction. Pellet with basicity 0.33 showed good physical as well metallurgical properties due to bonding phases present in the pellets.