Phase transformation during roasting process and magnetic beneficiation of oolitic-iron ores

Oolitic-iron ore material is one of the most important iron resources in China. However, due to its low grade of Fe, poor liberation of iron minerals and high impurities, no satisfactory processing method has been developed to effectively utilize it for the practical applications. In this work, a coal-based reductive roasting method was applied, where the detail mineral phase transformation and reduction area during magnetic roasting process was quantitatively investigated. Then, low intensity magnetic separation was performed. The results showed that roasting time significantly affected Fe recovery, with a minor influence on Fe content of concentrate. Fe recovery increased from 10 to 60 min before starting to decrease slightly. This may result from the formation of weakly magnetic FeO or Fe3O4-FO (solid-melt-body), where the reduction degree increased gradually from 10 to 50 min. During the roasting process, the mineral phase Fe2O3 changed to Fe3O4, but the original oolitic structure and mineral embedding relation were hardly evolved. This research could enhance our understanding regarding the microscopic view of magnetic phase transformation, and provide help for commercial development of such refractory iron ores.