Modification of magnetic properties of siderite ore by microwave energy

The modification of the magnetic properties of mineral components in siderite ores by microwave heating results in increasing the efficiency of their magnetic separation. Pre-treatment in a microwave oven with maximum power of 900 W of weakly paramagnetic ore (25.1% Fe, 9.6% SiO2) was realized with the samples (100 g) of iron spathic ore of particle size 0.5-1 mm from Nižná Slaná in Slovakia. After 10 min of heating an essential change in the magnetic properties of the ore samples occurred, and after 15 min, a rapid increase of magnetic susceptibility value was observed, showing the intensive decomposition of siderite. Changes in magnetic properties were confirmed by the measurement of magnetic susceptibility and by chemical analyses, and X-ray diffraction method confirmed the formation of new strongly magnetic mineral phases. Finally, after 40 min of heating, a microwave sintering of powder grains in the form of agglomerates with molten mass was observed. The result of energy-dispersive X-ray (EDX) analysis showed the oxidic character of the phase consisting of complex oxides and metal iron and from the chemical analysis results: Fetotal 45.4%, Femetal 7.1%, SiO2 15.5%. After microwave treatment, the samples were subjected to the separation in magnetic field with maximum induction of 0.17 T, where at 15 min heated sample the 97.6% recovery of Fe was obtained.