Electrostatic Separation - PDF

ELECTROSTATIC SEPARATION  INTRODUCTION The electrostatics equipment consists of an earthed mild steel roll also called a rotor. It is equipped with an electrode assembly with a rectified DC voltage of up to 50 kV. The electrode assembly ionized the surrounding air to prod...

ELECTROSTATIC SEPARATION  INTRODUCTION The electrostatics equipment consists of an earthed mild steel roll also called a rotor. It is equipped with an electrode assembly with a rectified DC voltage of up to 50 kV. The electrode assembly ionized the surrounding air to produce electron charges-corona The electron charges produced are used to spray the ore particles to be delivered unto the roll. ELECTROSTATIC SEPARATOR THE PRINCIPLES OF OPERATION The non-conducting mineral particles receive the electric charges and largely retain them and the large surface charges get them attracted to and pinned to the positively charged rotor surface. On the other hand, conducting mineral particles receive the charges and rapidly dissipate them unto the rotor and they continued approximately in a path they would have taken without the charge. High tension separators takes in feeds containing particles with sizes between 60 and 500 µm diameter  THE PRINCIPLES OF OPERATION Particle size has effects on the separation behaviour since the surface charges influence on a coarse non conducting grain is lower in relation to its mass in comparison to the effect on a fine grain. Thus a coarse non conducting grain is more readily thrown from the roll surface instead of been pinned to it and are misplaced into the conducting fraction. Similarly, the finer particles are more influenced by surface charges and the non-conducting fractions often contain some fine misplaced conducting particles  CONDUCTING AND NON- CONDUCTING MINERALS Examples of non-conducting minerals pinned to the rotor are: apatite, barite, calcite, corundum, garnet, gypsum, kyanite, monazite, scheelite, sillimonite, spinel, tourmaline, zicon, quartz Examples of conducting minerals thrown from the rotor are: Cassiterite, chromites, diamond, fluorspar, galena, gold, hematite, ilmenite, limonite, magnetite, pyrite, rutile, sphalerites, stibnite tantalite, wolframite  AREAS OF APPLICATION Electrostatic separation is used in all plants that process heavy mineral sands bearing zircon, rutile , and monazite. In addition, the cleaning of special iron ore and cassiterite concentrates as well as the separation of cassiterite-scheelite ores are conducted by electrostatic methods. Electrostatic separation enables the separation of a wide range of minerals and this example, separating Pyrite from Silica Sand, provides a good example of the separation process. A feed of conducting (Pyrite FeS2) and non-conducting (Silica Sand SiO2) powders is fed via a vibratory feeder onto an earthed, stainless-steel roll revolving at a pre-determined rate. A strategically positioned electrode assembly, at around 20° from the vertical, charges the feed at a high voltage (20 – 30 KeV). As the mineral particles leave the vibratory feeder and land on the roll, two behaviours are observed: Conductors (i.e. Pyrite) – lose their charge and are thrown by centrifugal force off the roll; Non-Conductors (i.e. Silica Sand) – have an image change and are pinned on the roll and discharged by a brush (see Figure 1);  ASSIGNMENTS Watch the YouTube Video Electrostatic Separations to appreciate the procedure