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Effect of microwave pre-treatment on the magnetic properties of Ludwigite and its implications on magnetic separation

To improve magnetic separation and recovery for Ludwigite, the influences of microwave radiation on the heating characteristics, microstructure, magnetic properties and the magnetic separation of Ludwigite are investigated. The magnetizations of untreated and microwave-treated samples with various microwave powers are analyzed using vibrating sample magnetometer. It is found that magnetite is an active material, while ascharite and serpentine are inactive materials. The heating rate of magnetite is faster than those of ascharite and serpentine, resulting in temperature gradient and internal stress among different components in Ludwigite. The effect of microwave power on the internal stress for mineral phases is positive. The internal stress significantly induces intergranular fractures and facilitates mineral liberation. After microwave treatment from 0 to 4 kW exposed for 40 s, serpentine is dissociated and the crystallinity of magnetite is increased, which leads to the saturation magnetization of samples increasing from 12.39 to 24.51 emu/g. Compared with untreated ore, the energy demand for microwave-treated Ludwigite is only about 0.44 kWh/kg, the grade of iron concentrate of microwave-treated Ludwigite increases from 48.56% to 58.06% and iron recovery increases from 69.44% to 96.35%, respectively. It can be concluded that microwave radiation has a positive effect on magnetic properties of Ludwigite and is conducive to magnetic separation from non-magnetic minerals with low energy consumption, thereby obtaining high iron recovery.