Effect of adding limestone on the metallurgical properties of iron ore pellets

• A comparative study was made between limestone-fluxed and non-fluxed pellets.
• Reducibility, softening, swelling, cracking, LTD and CCS were parameters of interest.
• Reducibility, swelling and cracking were increased when limestone was added.
• Softening temperature and CCS and LTD indices were decreased with limestone addition.
• However, all the parameters were within the acceptable range for blast furnace use.

In order to produce high-quality pellets with good reducibility and superior softening and melting properties, certain additives are important. One of the most common fluxing materials for iron ore pellet production is limestone, which is mainly calcium oxide (CaO). In this study, the effect of adding limestone on the metallurgical properties (reducibility, swelling, cracking, softening temperature, Low-Temperature Disintegration, Cold Crushing Strength) of acid iron ore pellets was investigated using a comprehensive set of metallurgical laboratory tests.The dynamic reducibility test under unconstrained conditions showed a higher final degree of reduction in limestone-fluxed pellets compared to non-fluxed ones. Also in the reduction–softening test under load, the fluxed pellets reduced to a higher final degree of reduction, although they started to soften at a somewhat lower temperature. Swelling and cracking of the pellets during dynamic reduction were slightly increased by the addition of limestone, but not remarkably. Adding limestone slightly decreased the Cold Crushing Strength and increased the formation of fines in the hematite to magnetite reduction stage in the LTD test. However, all four parameters (CCS, LTD, swelling, and cracking) are within the acceptable range for blast furnace use.