Study on air cooling process for limonite magnetization roasting

As an effective technical approach for processing complex and refractory iron ores, Suspension magnetization roasting is of great significance for the efficient utilization of difficult-to-process limonite resources. To investigate the feasibility of magnetization roasting followed by air cooling for limonite, systematic experiments are conducted using the Baozipu limonite from Kunming Iron and Steel as the research subject. Through systematic condition-specific experiments, optimal magnetization conditions for limonite are established at a reduction temperature of 580 ℃, roasting duration of 5 minutes, and H₂ concentration of 30%. The magnetically separated concentrate obtained after nitrogen-protected cooling achieved an iron grade of 57.92% with a recovery rate of 87.94%. Further research is carried out on the air cooling process of the roasted ore, with particular attention being paid to the influence of oxidation time and temperature on the oxidation behavior of magnetite in an air atmosphere. The results reveal that at an oxidation temperature of 300 ℃ for 3 min, magnetite is almost completely oxidized, with the cooles product being predominantly composed of strongly magnetic maghemite and a minor amount of weakly magnetic hematite. With prolonged oxidation time or increased temperature, the hematite content is observed to gradually rise while the maghemite content decreased, though maghemite is maintained as the dominant phase. By controlling the oxidation conditions, the dominance of maghemite in the air-cooled product could be maintained, thus ensuring favorable magnetic properties. The findings are considered to provide a viable technical solution for the efficient utilization of complex and low-grade limonite resources, contributing to the sustainable development of refractory iron ore reserves.