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Electrostatic Separation

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Electrostatic Separation


Electrostatic separators can be split into high tension and electrostatic types and listed as follows:



High tension rolls (HTR)


Examples of HTRs are manufactured by Mineral Technologies , and have been used in electrostatic separation of dry conductor and non conductor minerals for many years. Current HTRs employ a 10 inch diameter roll compared to the older 6 inch rolls, which allow for greater surface contact time.


They use the different surface electrical conductivities of various minerals to effect a separation. Dry and heated feed is distributed at a controlled rate at the top of a spinning stainless steel roll and subjected to a high tension electrical field between an negatively charged electrode wire and the earthed roll. Conductor grains lose their charge immediately to the roll and discharge at a trajectory determined by their mass and velocity, while non conductor grains hold their charge and are pinned to the roll. The non conductors are subsequently are thrown off the roll or removed by a brush mounted at the rear of the roll. An alternating current wiping electrode located behind the roll also assists in non conductor removal.


Operating variables include:




Corona Stat and Carrara Separator rolls


These are a relatively recent development of HTR, and due to their greater efficiency have generally replaced the traditional HTR in mineral sand separation dry mills. Examples of which are the Carrara Separator manufactured by Mineral Technologies and Corona Stat, manufactured by Ore Kinetics and have been used to enhance the electrostatic separation of dry conductor and non conductor over and above that achieved by HTRs.


They differ from HTRs in that they have two electrodes, namely the wire of the HTR and a plate type electrode similar to that of the electrostatic plate separator, as shown in the diagram below, such to some extent they combine the two machines.

Electrostatic plates

Examples of electrostatic plates are manufactured by Mineral Technologies and are typically used after HTRs to counteract the effect of grain size (HTRs and rolls tend to throw coarse non conductors into the conductor product due to their greater mass and momentum derived from the spinning roll).


There are no moving parts on an electrostatic plate, with the feed being distributed and moving down an inclined and curved metal plate surface by gravity. A negatively charged electrode shaped like an commonly called a muffler creates an electrostatic field between its surface and the plate, causing fine non conductor grains to be lifted up and discharge from the plate such that they can be split from the bulk of conductors and coarse grained non conductors. The gravitational and electrical forces involved are smaller than those in the HTR and the separation is generally less efficient overall, but the opposite in terms of the effect of grain size to that of the HTR. An electrostatic plate normally consists of five stages of conductor cleaning.


Operating variables include:



Screen plates


Examples of electrostatic plates are manufactured by Mineral Technologies. Screen plates are sometimes used on non conductor rich feeds for final cleaning and are similar to electrostatic plates, but employ a screen on the lower half of the plate, which is also at a flatter angle then the normal plate. Conductor grains pass through the screen and thus unload the separator while coarse non conductors cannot and discharge separately with the lifted fine non conductors. Operating variables are similar to plates, except that the plate / screen area ratio can be adjusted to suit.