High temperature dielectric properties of ludwigite and its effect on microwave heating process

To liberate magnetite from ludwigite, the dielectric properties of ludwigite are investigated by cavity perturbation method at 2.45 GHz from 20 to 800 degrees C. The results show dielectric properties of ludwigite with temperature can be divided into three stages: at the first stage (20-200 degrees C), the dielectric constant (epsilon '), dielectric loss factor (epsilon ") and loss tangent (tan delta) increase approximately by 4.55, 47.31 and 38.89%, respectively, at the second stage (200-500 degrees C), epsilon ' increases slowly by 5.19%, while epsilon " and tan delta gradually decrease, at the third stage (500-800 degrees C), epsilon ' first increases rapidly by 6.21% at 500-700 degrees C and then increases slowly beyond 700 degrees C, epsilon " and tan delta fluctuate slightly. Meanwhile, the penetration depth (D-p) decreases significantly at 20-200 degrees C and decreases slightly at 200-500 degrees C, but decreases substantially again at 500-700 degrees C, and finally is closed to the constant value beyond 700 degrees C. The heating rate of magnetite is faster than those of ascharite and serpentine, which results in the formation of intergranular fractures to promote the liberation of magnetite from ludwigite by microwave heating.