Producing magnetite concentrate from iron tailings via suspension magnetization roasting: A pilot-scale study

In the process of iron ore beneficiation, a considerable amount of iron was lost to the tailings, resulting in the waste of resources and environmental pollution. In this study, an innovative technology of pre-concentration followed by suspension magnetization roasting and low-intensity magnetic separation (PSRM) was used to recover iron from iron tailings. The iron grade of the roasted feed ores was increased from 15.68% to 33.19% by pre-concentration process. Subsequently, the suspension magnetization roasting was performed to transform the weak magnetic minerals into magnetite, and magnetite concentrate was obtained via low-intensity magnetic separation. The effects of feeding rate, roasting temperature, reducing gas CO flow rate, and fluidizing gas N-2 flow rate during suspension magnetization roasting were investigated, and the pilot-scale equipment was conducted for 72 h continuously under the optimum roasting conditions. The phase transformation and magnetic property variations of the minerals before and after roasting were analyzed by X-ray diffractometer (XRD) and vibrating sample magnetometer (VSM), respectively. The results showed that an iron concentrate with iron grade of 63.04% and total iron recovery of 48.40% was obtained under the optimum roasting conditions: feeding rate of 111.70 kg/h, roasting temperature of 550 degrees C, CO flow rate of 4.0 m(3)/h, and N-2 flow rate of 2.0 m(3)/h. The hematite and siderite in tailings were transformed into magnetite with an average magnetic conversion rate of 86.46%. This innovative PSRM technology provides an important reference for the resource utilization of solid waste and the recovery of iron from iron tailings.