Preparation of Red Iron by Magnetization Roasting-Hydrothermal Method Using Ultra-Low-Grade Limonite

Abstract

Iron is one of the most important strategic materials in national production, and the demand for iron ore is huge in the world. High quality iron ore reserves have been almost exhausted, and it is necessary to develop a technology that utilizes low-grade iron ore. Limonite is a representative low-grade iron ore due to its complex mineral and elemental composition. In this paper, the union process was employed to separate the iron elements in low-grade limonite. Firstly, a rough iron concentrate was obtained under 1.0 T of magnetic field intensity and −0.074 mm > 94.84% of grinding fineness; then, the rough iron concentrate was magnetization roasted under a temperature of 700 °C, 60 min of retention time, 3 wt% of biochar consumption, and 0.15 T of magnetic field intensity. The grade of iron concentrate was 59.57% and the recovery of iron was 90.72%. Finally, the red iron pigment was produced via a high temperature hydrothermal method in order to increase the additional value of this ultra-low-grade limonite. The optimal parameters were 10.0 g/L of solution acidity, a 200 °C reaction temperature, 5 h of reaction time, and a 6:1 solid-to-liquid ratio. The reaction mechanism was also discussed.