6-_D_D_Mishra_electrostatic.PDF - RawMaterials D.D.Misra 1...

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Electrical Separation of Mineral  Raw Materials  D.D. Misra  The feasibility of using electrostatic properties to  e ffect separation between different mineral particles was  known long back 1 , but for two main reasons little progress was  made : (a) The electrical equipment was unreliable, high voltage  generators (induction types) had small capacities, and were  useless under conditions of high humidity; (b) proven application5:  of the process were limited, and many of the separations could  be performed more efficiently and cheaply in other ways.  Electrostatic separation  However, with advances in electrical technology, particularly  in the rectification of alternating current to obtain a. pteady  high voltage direct current, electrostatic separation became popular,    Instead of feeding the material onto a direct charged rotating  cylinder, it was fed onto an earthed rotating cylinder charged by  induction, using a charged electrode insulated from the metal  framework. Besides simplifying the process from the point of view  of the necessary insulation, this changeover made the process safer  for the operators. The electrostatic separators which were mainly  being used for the separation of metallic sulphides from the  siliclous gangue minerals, were driven from their primary market  with the advent of froth flotation. Concentrated research efforts  in U.S.A. on the electrical concentration of rutile from the beach  sands during the World War II resulted in the modern electro- dynamic separator, and the renaissance of electrical separation as  an important minerals beneficiation technique.  Large - scale applications of the electrodynamic technique  now found in the recovery of heavy minerals from beach sand deposits  in the separation of cassiterite, and recently in the upgrading  of specular hematitic iron ores 2 . Table 1 gives the types of  electrical separation equipments used and the examples of the  typical mineral separations for which they are used1. 
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- 2 -  Further research efforts will undoubtedly reveal other  Special areas in minerals beneficiation field where the electro- dynamic method can, alone or in combination with other methodse  do a job that cannot be done by the conventional methods alone.  The process being a dry  one,  makes  it particularly attractive in  areas where process water is scarce  and/or costly to process.  Table 1 : Electrical separation Methods  Types  Electrodynamic (current  fields)  Electrostatic (static  fields)  Typical equip- ment  Typical mineral  separation  Rotors with discharging  electrodes  Hematite - silicates  Rutile  - Zircon 
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