Magnetically iron ore represented ferromagnetic minerals belonging ferrimagnetic material having a magnetic domain structure. The magnetic domain is a small area of ​​spontaneous magnetization that exists inside the magnetite without an external magnetic field. Its volume is about 10 -15 m 3 Contains about 10 15 atoms. Each magnetic domain has a certain spontaneous magnetization direction, and the spontaneous magnetization directions of the magnetic domains are inconsistent. From a macroscopic point of view, the magnetizations of the magnetic domains cancel each other out, so the whole is not magnetic. When the applied magnetic field is gradually increased, the magnetic domains whose spontaneous magnetization direction coincides with the direction of the applied magnetic field are enlarged until the other magnetic domains are swallowed, and the magnetite exhibits strong magnetic properties. After the magnetite is magnetized by the external magnetic field, the applied magnetic field is removed, and its magnetic properties do not completely disappear, but a part of the residual magnetism is retained. This is due to the fact that the magnetic domain cannot be restored. In addition, the magnetism of magnetite is also related to the shape and particle size of the particles. In terms of shape, the long strip is stronger than the spherical magnet; in terms of particle size, the coarse particles are stronger than the fine particles.

The magnetic properties of ferromagnetic minerals have the following effects on the magnetic separation process:

(1) Since ferromagnetic minerals such as magnetite are strong in magnetic properties, they can be recovered by using a lower magnetic field.

(2) magnetite particles to retain a residual magnetism will be magnetized, when the particle size finer. Particles will attract each other to form a magnetic flux or group. The magnetic cluster is not easy to disperse, and if it contains gangue particles, the grade of the magnetic product is lowered. If there is a magnetic cluster in the ore feeding of the classification operation, the classification efficiency is lowered. This is an adverse effect of magnetic agglomeration. In this case, a demagnetizer can be used to eliminate residual magnetism and destroy magnetic agglomeration.

(3) micro-fine magnetite particles of weak magnetism, and suffered larger resistance in the water during moving, and therefore requires a large magnetic force during recovery, and flow easily washed away, resulting in the loss of metal. It can be seen that the grinding process should minimize over-grinding.

(4) If the monomer in the grinding process is not sufficiently dissociated, the continuous particles of magnetite and gangue will appear. Although the gangue is mostly a non-magnetic mineral, because the magnetite is very magnetic, it is subjected to a magnetic force that can bring its associated gangue into the magnetic product, which reduces the grade of the magnetic product. If this part of the continuum is to be separated from the magnetic product, fine sieving, flotation, re-election or other sorting methods are required.

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