Study On Surface Magnetization Of Weakly Magnetic Iron Minerals

Weakly magnetic fine particles of iron minerals, because of its fine grain size, large specific surface and low magnetic susceptibility, are difficult to separate from gangue minerals effectively by conventional mineral processing methods.In this paper, the mineral surface were coated by strong magnetic particles to expand the magnetic differences between minerals, it could increase the mineral's separability. On the basis of summary and analysis a large number of relevant literature, systematical experiments had been carried out to magnetize two weakly magnetic iron minerals-siderite and hematite.Magnetization of siderite was achieved through the reaction of Fe2+ from the self dissolved siderite and external addition of NaOH. The results showed that the temperature was an important factor of magnetization of siderite surface, and 60℃was regarded as the optimal temperature.The recovery of siderite increased to 88.8% through magnetic separation after magnetization reaction in comparison with a recovery of 26.9% without surface magnetization. The reaction condition was determined as the reaction time of 10 minutes, reaction temperature of 60℃and the NaOH dosage of 0.15mol/L. Vibrating sample magnetometer (VSM) and scanning electron microscope were used to characterize the siderite before and after the process of surface magnetization. After the process of magnetization, the the magnetic moment per unit mass (σs) of siderite increased to 2.569 A·m2·kg-1 from 0.652A·m2·kg-1, also fine particles Fe3O4 were observed coating on the surface of siderite. XPS analysis discovered Fe2P3/2 electron binding energy changed after process, which proved the formation of Fe3O4 on the surface of siderite.Magnetic Fe3O4 particles were formed by air oxidation method in pulp and were coated on the surface of hematite. The main magnetization reaction mechanism is the hydrolyses of Fe (Ⅱ) and Fe (Ⅲ) ions in alkaline pulp to form Fe3O4 crystalline grains. The effects of amount and proportion Fe2+ and Fe3+, concentration of ammonia, reaction time and pulp temperature on the surface magnetization of hematite were investigated. At the pulp temperature of 50℃for reaction of 10 minutes by adding Fe (Ⅱ) 0.012mol/L and ammonia 0.15mol/L, the recovery of hematite increased to 95.2%by magnetic separation in comparison with a recovery of 68% without surface magnetization. Vibrating sample magnetometer (VSM) and scanning electron microscopy (SEM) were used to characterize the hematite before and after the process of magnetization. After the process of magnetization, the magnetic moment per unit mass (σs) of hematite increased increased to 1.415 A·m2·kg-1 from 0.694 A·m2·kg-1; also ultrafine magnetic particles were observed coating on the surface of hematite.The experiments on tailings of iron ore indicated that fine weakly magnetic minerals which contain siderite could be magnetized with the self dissolved Fe element in pulp.