The charge obtained by the ore particles in a corona electric field

The charge obtained by a spherical ore particle in a corona electric field is usually expressed by the following formula:

Where r - the radius of the ore, m;
——Air dielectric constant, F/m,

- ionic charge, equal to 1.6 × 10 ^-19 C;
n - the ion concentration in the corona electric field, ie the number of ions per m ³ ;
K ——Ion mobility, m ² / V•s, at 1 standard atmospheric pressure, K is 1~2×10 ⁴ m ² / V•s is equivalent to 15~30m ² /s;
t - discharge time, s.
If the ion concentration in the electric field is n=10 ¹⁴ ions/m ³ , from the above formula, let t=10 ^-3 , 10 ^-2 and 10 ^-1 seconds, the corresponding charge of the ore particles can be obtained as the maximum value. 6% of Q _max , 45% and 90%.
The time relationship required for the ore particles to charge in the corona field to reach a maximum charge value Q _{max is} listed in the following table.

For coarse-grained minerals less than 2 mm to 0.1 mm, it is required to be able to charge a large charge value (Q _max ) (at least 50% Q _max ) in the corona field, which is due to the larger size of the ore in the drum The centrifugal force and gravity component on the electric separator are also large, especially for non-conductor ore particles, such as not adsorbing more charge from the corona field and thus generating a larger mirror suction. However, it is inevitably mixed into the conductor product due to excessive centrifugal force and gravity, which affects the sorting effect; but for the conductor, it is not affected because the adsorbed charge can be transmitted away through the grounding electrode as soon as possible.
For ore particles smaller than 0.1 mm, the particle size is small and the mass is small. Under the same charging condition, it is larger than the surface charge, but if it is at the same rotation speed of the drum type electric separator (equal to coarse particles) ), its centrifugal force is almost 1000 times smaller. If it is like a sort of coarse grain, it will also be charged with a large amount of electricity, and the resulting specular suction will be larger. This will inevitably bring the opposite to the conductor ore. As a result, especially the intergranular interaction of fine particles (less than 0.1 mm) is very large, and it is extremely difficult to separate from the fine particle group, so the charge required for sorting fine particles is much smaller than that of coarse particles. That is, the time for charging should be shorter.
According to the nature and characteristics of the above coarse particles and fine particles, in particular, the difference in the amount of charge required is required, and different electrode structures must be employed for this purpose. In addition, there must be significant differences in operating conditions, mainly in the voltage and the rotational speed at which the centrifugal force is generated. The coarse particles require a high voltage, the rotational speed is small, the fine particles require a low voltage, and the rotational speed is high.

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