Electrostatic separation

Electrostatic separation:

Electrostatic separation is a process that uses electrostatic charges to separate crushed particles of material. An industrial process used to separate large amounts of material particles, electrostatic separating is most often used in the process of sorting mineral ore. This process can help remove valuable material from ore, or it can help remove foreign material to purify a substance. In mining, the process of crushing mining ore into particles for the purpose of separating minerals is called beneficiation.

Generally, electrostatic charges are used to attract or repel differently charged material. When electrostatic separation uses the force of attraction to sort particles, conducting particles stick to an oppositely-charged object, such as a metal drum, thereby separating them from the particle mixture. When this type of beneficiation uses repelling force, it is normally employed to change the trajectory of falling objects to sort them into different places. This way, when a mixture of particles falls past a repelling object, the particles with the correct charge fall away from the other particles when they are repelled by the similarly charged object.

Principle of operation:

A process called "electrostatic beneficiation", which means charging them with static electricity and separating them by passing them through an electric field, as pictured in the next figure.

An electrostatic beneficiator works because different minerals have different electrostatic affinities -- will absorb different amounts of charge depending upon their composition, and hence are deflected different amounts by an electric field. After grains are sieved by size, they are placed through a beneficiator. After a few passes through beneficiators, we have separated different minerals fairly well. (There's no change in physical or chemical identity; there's only separation of minerals.)

Beneficiators typically use free-fall of grains through electric fields. However, some beneficiators slide the grains down a ramp, and some put them across a rotating drum with a certain electrostatic charge so that grains of a certain affinity will stick to the drum and others will fall to the ground due to gravity or the centrifugal force. Thus, beneficiation separates minerals according to their electrostatic affinity, as well as their different densities (with gravity or the centrifugal force).

The grains are charged by any of the following methods: charging the screen that sieves them, or charging another surface which they slide over, or a diffuse electron beam as they fall. The charging method can depend upon which minerals we want to separate, since different minerals have different responses to different methods (and indeed to different temperatures, too).

The resultant material is collected in different bins whereby the enriched portion of the desired mineral is called the "concentrate" and the rest of the output is called the "gangue" or "tailings".

While on Earth we're usually interested in just one mineral and one bin, on the Moon we will often be interested in using more of the material. With an electrostatic beneficiator we could have multiple bins at the bottom, as the mineral stream will split up into multiple streams depending upon the degree of attraction or repulsion of each mineral.

The electrostatic separation of conductors is one method of beneficiation; another common beneficiation method is magnetic beneficiation. Electrostatic separation is a preferred sorting method when dealing with separating conductors from electrostatic separation non-conductors. In a similar way to that in which electrostatic separation sorts particles with different electrostatic charges magnetic beneficiation sorts particles that respond to a magnetic field. Electrostatic beneficiation is effective for removing particulate matter, such as ash from mined coal, while magnetic separation functions well for removing the magnetic iron ore from deposits of clay in the earth.