Influence of basicity and MgO content on metallurgical performances of Brazilian specularite pellets

• Limestone and magnesite were used to modify the basicity and MgO content.
• RI and RDI were improved with increasing basicity.
• At a basicity range of 0.2 to 0.8 abnormal swelling occurred.
• Addition of MgO increased RI and decreased RSI and RDI.

Influence of basicity (CaO/SiO2 ratio) by adding limestone and MgO content in the form of magnesite on metallurgical performances of Brazilian specularite pellets was investigated. Pellets with varying basicity (0.12 to 1.20) and MgO content (0.08% to 3.0%) were studied for RI (reducibility index), RSI (reduction swelling index) and RDI (reduction degradation index) tests. SEM (scanning electron microscope) with EDS (energy dispersive spectrometry) and optical microscope were employed to test the microstructure and chemical analysis of iron oxide and slag of fired pellets. Meanwhile, measurement of the microstructure of reduced pellets after RSI and RDI tests was also carried out by using an optical microscope. With increasing basicity or MgO content, RI and RDI were improved. In the basicity range of lower than 0.20 or higher than 0.80, pellets exhibited low RSI. In the basicity range of 0.20 to 0.80, abnormal swelling occurred and RSI was higher than 20%, which attributed that more amount of low melting point slags appeared at this basicity range. Due to the presence of MgO that decreased the amount of liquid phases, with increasing MgO content, RSI was restrained. The basicity between 0.20 and 0.80 should be avoided during producing pellets using Brazilian specularite due to the abnormal swelling.