Recycling iron from oolitic hematite via microwave fluidization roasting and magnetic separation

Abstract

Oolitic hematite is an iron ore resource with complex refractory characteristics, abundant reserves, and significant recycling value. In this study, a clean and innovative microwave fluidization roasting method was developed. Iron concentrate with an iron grade of 58.72% and iron recovery of 89.32% was obtained via microwave pretreatment at 1050 °C for 2 min, followed by magnetization roasting at 650 °C for 5 min at a CO content of 30% and total gas volume of 700 mL/min. A vibrating-sample magnetometer analysis indicated that the saturation magnetization increased from 0.33 A·m2/kg for the raw ore to 42.52 A·m2/kg for the roasted products. Scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed that microwave pretreatment promoted the formation of microcracks at the interfaces between minerals, offering the advantages of a rapid reaction and phase transformation during the magnetization roasting. X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy analyses indicated that the iron mineral phase was selectively transformed from weakly magnetic hematite into strongly magnetic magnetite and that the iron mineral was effectively recycled from the roasted samples via magnetic separation.