Magnetic fluid static separation process (1)

(1) Magnetic Floatation and Magnetic Fluid Characteristics First look at two experiments.
[Experiment 1] The magnetic iron ore broken into fine particles, coal-oil as solvent, oleic acid as dispersant, water made slightly lighter than the magnetic fluid. When the magnetic fluid is placed in the beaker and the head of the horseshoe-shaped permanent magnet lying on the side is approached, the "climbing phenomenon" of the magnetic fluid can be seen immediately (the magnetic fluid close to the magnet pole rises into a slope) When the horseshoe was removed, the "climbing phenomenon" disappeared immediately.
[Experiment 2] A certain amount of the above-mentioned magnetic fluid was placed in a test tube, and a certain amount of clean water was placed and placed above the pole of the electromagnet. Since there is no electricity, no external magnetic field is present, but less than the density of the magnetic fluid is water, so the magnetic fluid in the upper aqueous layer; which time a glass spheres (density 2.7 g / ^cm3, 10 mm diameter) and a copper ball (The density is 8.9 g / cm ³ , the diameter is 8 mm), these two balls will naturally sink to the bottom. After that, the electromagnet is energized. When the current value is gradually increased, the first thing is that the water rises and the water and magnetic fluid are translocated. When the current is further increased, it can be seen that both the glass ball and the copper ball are suspended above the magnetic fluid. When the power is turned off, the external magnetic field disappears and everything returns to its original state.
From the phenomena appearing in the above two experiments, the characteristics of the magnetic fluid can be seen:
(1) The magnetic fluid itself is a magnetic medium. It is like a solid magnet and is constantly adsorbed in the magnetic field where it has the largest magnetic flux.
(2) The magnetic fluid is subjected to an external magnetic field force, and attempts to discharge the position where the magnetic flux is at the maximum occupied by other weak magnetic particles or non-magnetic particles. This is manifested by the phenomenon of "weighting" the liquid, or "apparent density" with a certain value.
(3) Since the magnetic fluid always exists at the maximum magnetic flux of the external magnetic field, it can be "suspended" in the open bottom container without falling. With this characteristic, a bottomless sorting tank can be made to make the light minerals The top of the tank overflows and the heavy mineral falls out of the sorting tank, separating the minerals by density and magnetic properties.
(4) Changing the magnetic pole shape of the external magnetic field, the minerals with different (or similar) density and specific magnetic susceptibility can be separately suspended in the sorting tank, and then the components of the positioning suspension are separately extracted to achieve sorting. The purpose of the component mineral raw materials.
(2) Principle of movement of ore particles in the magnetic fluid of the wedge-shaped magnetic pole system
The wedge-shaped magnetic pole system is one of the simplest and most common magnetic pole systems. The movement of the ore particles in the magnetic fluid in the system can be decomposed into three spatially orthogonal coordinate axes of X, Y and Z. As shown in Figure 1.

The ore particles may move in the direction of the three axes of X, Y and Z, but the movement along the vertical Y axis is the most important movement, and the ore particles are mainly layered by it. The following mainly studies the movement in the Y-axis direction. [next]
A. The ore particles move vertically in the Y-axis direction. In Figure 1, it is assumed that a trough body made of a non-magnetic material (for example, plastic) is placed in a horizontally wide and narrow wedge-shaped magnetic pole gap. A static paramagnetic salt solution is contained in the tank. Since the magnetic field strength in the magnetic pole gap gradually increases from top to bottom, the degree of "heavy" of each horizontal layer in the paramagnetic salt solution is also different from top to bottom, that is, the "visual density" of each horizontal layer will also be from above. It gradually grows bigger. It is conceivable that minerals with different densities will also be suspended in layers. Suspension is the result of static balance. Therefore, we discuss the stress of the ore particles in the magnetic pole gap according to the static balance.
Let ρ, ρ ₀ represent the density of ore G and solution in the magnetic fluid, respectively, ton / m ³ ;
X and X ₀ represent the specific magnetic susceptibility of the ore particles and the solution, respectively;
H represents the magnetic field strength where the ore is located, am/meter;

ΔV represents the volume of the ore particles, m ³ ;
g represents the acceleration of gravity, m/s ² ; the direction is positive.
The gravity of the ore particles in the gravitational field is ρΔVg, and the buoyancy of the medium is -ρ ₀ ×ΔVg; the magnetic field received in the magnetic field

The C value is a characteristic value of the suspended height of the ore particles in the magnetic fluid. If the C values ​​of the two ore particles are the same, their suspension height in the magnetic fluid is also the same.

When the relationship can satisfy the condition of Equation 3, the ore particles will be suspended at a height that satisfies the condition of Equation 3 (i.e., at a certain Y coordinate), otherwise the ore particles will move up or down. [next]
B The horizontal movement of the ore particles in the X-axis direction The horizontal movement of the ore particles in the X-axis direction is due to the uneven magnetic field strength in the X-axis direction of the spatial plane of the ore particles. The reason is that although the sorting space (magnetic pole gap) is composed of two parallel lines, since the longitudinal length of the magnetic pole is always limited, the edge effect generated by the magnetic pole ends causes the magnetic field to be uneven in the X-axis direction. Sex. This non-uniformity is manifested by the magnetic field strength in the middle of the magnetic pole gap being greater than the two sides of the magnetic field gap, so that the generated magnetic field force Æ’ X is directed from both sides of the gap to the center of the gap, and the generated magnetic thrust F _{X is} directed from the center of the gap to both sides of the gap, such as Figure 2 shows.

Since the magnetic thrust has a large dry magnetic field force, that is, F _X - Æ’ _x = positive value, in the sorting process, when the ore particles are suspended at their respective heights, they start to move from the center of the gap along the x-axis direction. Movement on both sides of the gap. This is the second behavior caused by the magnetic field force of the magnetic particles when sorting in the paramagnetic salt solution - horizontal x axial motion behavior. This kind of behavior can be used in mineral processing to design an intermediate feed type magnetic hydrostatic separator, as shown in Figure 3.

If the sorting machine is required to discharge material at one end (discharge light product) and feed the other end, the x-axis of the magnetic pole can be at an angle to the horizontal plane, so that the magnetic pole gap forms a chute.
In order to explain the reason why the ore particles can move to only one end after the magnetic pole is tilted, the ore particles G are subjected to force analysis in the magnetic pole gap in this state, as shown in FIG.

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