Recovery of low grade haematite via fluidised bed magnetising roasting: investigation of magnetic properties and liberation characteristics

The separability of low grade haematite from Tangshan was investigated experimentally via fluidised bed magnetising roasting. To better understand the separation mechanisms, the magnetic properties of the products (magnetite or maghemite) made from reduction roasting or reduction-oxidation process were investigated. The liberation behaviour was analysed through beneficiation results and theoretical models. It was found that several parameters such as temperature and roasting time would influence the reduction process; however, the magnetic susceptibility of the reduced sample is mainly determined by the content of the magnetic component. The beneficiation results are mainly influenced by the magnetic properties, magnetic field and grinding size. For the reduction products, i.e. low grade magnetite, the best results occurred when the applied magnetic field was 119.4 kA m(-1) and the particle size was -0.048 mm, with the iron grade of the concentrate being 62.5% and the recovery rate being 91.1%. The produced magnetite can be reoxidised to maghemite at temperatures below 300 degrees C, and the concentrate grade is improved when the reduced samples are reoxidised at 200 degrees C. For the reoxidised samples, a preferential breakage effect appeared during the grinding process, and Hsih's model with a detachment factor of 0.3 was observed to provide a good fit for their liberation characteristics.