Influence of magnetite concentrate morphology on oxidation and sintering rates of pellet during induration

Abstract

This study investigates the influence of the morphology of concentrate on the oxidation and sintering rates of magnetite pellets during induration and its impact on the indurated pellets' quality. Various morphologies of concentrates were obtained by ball milling (BM) and high-pressure grinding rolls (HPGR). Pelletizing and induration processes were carried out at different temperatures and times. After a comparative study of the physical characteristics of concentrate powders, the effect of morphology was evaluated through thermal behavior during induration. The physical, microstructural, and strength properties of pellets were also investigated. The HPGR concentrate had angular and elongated-shaped particles with a broad particle size distribution, while the BM particles had a more rounded morphology, and their size distribution was narrower. Results showed that BM and HPGR magnetite pellets are oxidized between 270 and 950 °C. HPGR pellets oxidize slower than BM pellets. Cold compressive strength (CCS) was increased by induration time, although porosity was reduced. HPGR pellets had less porosity than BM pellets; however, their CCS was significantly higher. For pellets indurated at 1200 °C, the difference in CCS between HPGR and BM pellets increased with an increment in the induration time and reached 80 kg/pellet in 20 min. The microstructural analysis took place on the concentrate powder and pellets fracture surface. It was found that HPGR powder sinters faster than BM powder due to its angular shape and broad particle size distribution.