Particle magnetics are the basic basis for magnetic separation and are important raw material characteristics for determining the magnetic induction strength and sorting efficiency of magnetic separators.

Magnetic separation practice shows that magnetic separation is extremely easy to sort magnetic minerals and gangue (such as quartz , calcite, etc.), but it is difficult to sort magnetic minerals and continuous organisms. Because the ratio of the magnetic susceptibility of magnetic minerals to gangue is extremely different, the difference in the magnetic susceptibility ratio between the living body, the magnetic mineral and the continuum is relatively small. In an example magnetic minerals, dissociate sufficiently, the magnetic susceptibility of the component to be separated than about 800, even if the living body is present (if the magnet containing 30% of ore), the bulk magnetic susceptibility of magnetite compared with students not more than 30 . Taking the weak magnetic minerals as an example, the specific magnetic susceptibility of the wolframite , cassiterite and quartz is 8.3×10-7, 6.3×10-8, 1.3×10-7 m3/kg, and the difference in the absolute value of the magnetic susceptibility is only It is a single digit. When the cassiterite or quartz contains different amounts of black tungsten ore and becomes a continuous body, the ratio of the magnetization of the black tungsten ore to the cassiterite or quartz is smaller, so the separation of tungsten and tin is difficult. The relationship between the content of the black tungsten ore in the continuous body and the ratio of the magnetization of the wolframite and quartz or cassiterite is shown in the following table:

The above table is only a case of black tungsten ore. When the continuous body contains more than 10% black tungsten ore, it is very difficult to separate the continuous body from the pure black tungsten ore, because the ratio of the magnetic susceptibility of the separated components is less than 3 ~5, and this value is the critical value that is proven to be effective in sorting weak magnetic minerals. This is an important reason for the low efficiency of weak magnetic mineral separation.

There are three measures to solve this problem: First, proper fine grinding to reduce the content of continuum. However, over-grinding should be avoided, and fine grinding can be produced by over-grinding, resulting in inefficient sorting. The second is to narrow the difference in the size of the selected materials, that is, according to the particle size classification or screening into several levels, and then the respective levels are separately sorted, which can improve the sorting efficiency of the magnetic difference small minerals. The third is to use a magnetic separator with a relatively uniform magnetic force distribution. The sorting efficiency of materials with a slightly wider particle size range and a slightly lower magnetic ratio can still be higher.

When selecting a strong magnetic ore, in addition to the magnetic susceptibility of the particles, the remanence and coercivity that are retained after removal from the magnetic field have an effect on the sorting process. Due to the remanence and coercive force, fine particles and fine particles are magnetically agglomerated. If the magnetic agglomeration is selective, pre-enrichment is obtained before the formal magnetic separation. When the magnetic separation is performed, only the magnetic agglomerates and the gangue are separated, and the efficiency of the selection is improved. However, magnetic agglomeration inevitably brings some non-magnetic impurities into the agglomerates, which reduces the sorting index. In addition, when the magnetically selected product also needs to be ground, graded or even re-magnetically selected, the magnetic agglomerates cannot be sufficiently dispersed, which has an adverse effect on these operations.

In the usual magnetic selection, the selection factor is not only related to the magnetic susceptibility of the particles, but also related to the particle size, density, shape, etc., which leads to a decrease in the selectivity of the magnetic separation. According to the magnetic susceptibility gradient sorting method, "pure" magnetic separation is performed only according to the magnetic susceptibility of the raw material, regardless of the properties of other raw materials.

The non-uniform magnetic field is filled with a colloid-like magnetic fluid, and the magnetic field gradient causes the magnetic fluid to produce a concentration gradient, thus also producing a density gradient. When the particles to be selected are in a magnetic field of a density gradient, they are subjected to mutually perpendicular magnetic forces and gravity, and the particles move to a position where the magnetic susceptibility of the particles and the magnetic susceptibility of the magnetic fluid are equal.

According to research, the magnetic susceptibility of the particle is exponentially related to the magnetic field strength which changes with the position X. Therefore, in a gradient magnetic field, a numerical value in which the magnetic susceptibility changes with X is obtained, that is, the magnetic susceptibility of the magnetic fluid is generated. Gradient, resulting in a new magnetic susceptibility gradient sorting method.

According to the magnetic force, gravity and viscous resistance of the particles to be selected in the magnetic fluid, the equation of motion of the particles can be written. When gravity settles. Due to the action of the magnetic force, the particles also move in the horizontal direction. If the settling time is large enough for the particles to reach static, the horizontal displacement at this point will bring the particles in equilibrium. Solving the static equation and obtaining the magnetic susceptibility of the magnetic fluid at this time

This method is a "pure" magnetic separation method, and the sorting effect is related to the magnetic susceptibility, and other factors such as particle size, density, and shape. Since the magnetic susceptibility of the magnetic fluid varies greatly, from ferromagnetic to diamagnetic, the range of magnetic susceptibility of the corresponding sorting particles can also be greatly varied. The disadvantage is that the establishment of a magnetic susceptibility gradient takes a long time.

In the magnetic susceptibility gradient sorting process, colloidal magnetic fluids with different magnetic susceptibility K1 and K2 are added into the sorting chamber, and the particles ABC are introduced into the fluid during use. The magnetic susceptibility of the particle A is small, causing A to move to the left side of the sorting chamber to form a reverse magnetic trap. The magnetic susceptibility of the particles C is large, causing C to move to the right side of the sorting chamber to form a paramagnetic trap. The magnetic susceptibility of the particles B is between the two, causing B to move to the right side of the fluid layer 1. The final granule ABC can be obtained from the corresponding discharge port.

In the actual magnetic beneficiation process, grinding operation is required to achieve different mineral particles from the solution, and then achieved according to the magnetic particles is effectively differences sorting, to ensure that the work is a useful base metal concentrate grade and recovery .

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