A new insight into iron ore oxidized pellets prepared by steel belt roasting process

Abstract

The steel belt roasting process has the advantages of low cost, small footprint, and high thermal efficiency, making it widely used in the smelting of ferroalloys such as ferrochrome, ferromanganese, and ferroniobium. However, its application in preparing iron ore oxidized pellets has not been sufficiently explored. The optimal thermal process conditions for magnesium-containing oxidized pellet preparation by steel belt roasting machine were investigated based on the roasting properties of high-magnesium iron concentrate and typical iron concentrate. The results indicate that, for the blending scheme of 70 wt.% high-magnesium iron concentrate and 30 wt.% typical iron concentrate, the appropriate preheating temperature for pellets is 950–975 °C and the suitable roasting temperature is 1250–1275 °C, during which the compressive strength of pellets can exceed 2500 N pellet⁻¹. During the steel belt roasting process, SO₂ is primarily released in the preheating zone, and the maximum exhaust gas temperature in the roasting zone can reach 637 °C. High-temperature sulfur-containing exhaust gas causes oxidation corrosion, sulfide corrosion, and deformation of the steel belt. To enhance the steel belt longevity, it is recommended to appropriately reduce the wind velocity in the preheating zone and roasting zone, while also decreasing the ratio of pellet bed height to hearth layer height. By adopting the system of “low wind velocity, thin pellet bed, fast steel belt speed,” the exhaust gas temperature can be reduced to 463 °C. The prepared pellet maintains a compressive strength of 2607 N pellet⁻¹ and exhibits excellent metallurgical properties.