What are the Different Types of Magnetic Separation Method?

Magnetic materials separation methods or techniques can be broadly classified into two categories, permanent magnets, and ferromagnetic materials. 

Permanent magnets are materials that have a strong magnetic field that does not disappear when the material is cut or broken. Ferromagnetic materials are materials that have a strong magnetic field that disappears when the material is cut or broken. There are many different methods or techniques used to separate magnetic materials.

This method is used to separate different types of ferromagnetic materials, such as steel, iron, and nickel. Another common magnetic separation technique is magnetic separation using solids. A strong magnetic field is used to attract the ferromagnetic materials to the poles of a magnet, while the permanent magnets are ripe. 

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Electrostatic Separation Method and Principle 

If one or more of the materials of the granular mixture can acquire a surface change on or just before entering an electrostatic field, the grains or particles of that material will be attached to the active electrode or repelled from it depending upon the sign of the charge on particles. 

Electrostatic separation is a method of separation of solid particles based on the differential attraction of charged particles under the influence of an electric field. The difference in different materials' electrical properties is responsible for such a separation.

Charging of grains is an essential step in this separator. Solid particles can receive a surface by one of the following methods:

(i) Electrification by bombardment.

(ii) Contact electrification.

(iii) Electrification by conductive induction.

Electrostatic by conductive induction is one of the major electrification mechanisms for the separation or concentration of solid materials by this method. When an unchanged solid particle is placed on a grounded conductor in the presence of an electric field the particle will rapidly acquire a surface change by induction.

A conductive particle acquires the same charge as the grounded conductor through its contact with the conductor while a dielectric particle is polarized and thus no net charge is generated on it.

As a consequence of this induction, the conducting particle will be repelled by the surface conductor. While the dielectric particle will be unaffected. Charging by conductive induction can be used to make a finite separation between relative conductors and non-conductors.

Separation by Conductive Induction 

In electrostatic separation, the difference in electrical properties of different materials is exploited to effect a separation.

The solids to be separated are fed onto a rotating drum either charged or materials from a hopper. The conductive particles in a minimal time will assume the potential of the rotating drum which is opposite to that of an active electrode and hence they get attached to the active electrode. The non-conductive material is repelled by the electrode and attracted by the drum. The non-conductive material falls down straight under the influence of gravity and is collected in a separate bin.

Magnetic Separation Technique

Principle of Magnetic Separation: Separation is a technique of separation of solid particles by a magnetic field. In this technique, materials having different magnetic attractions are separated by passing through a magnetic field. The difference in magnetic properties of different materials is responsible for such a separation.

Solids are Classified as 

(i) Diamagnetic Solids:- Which when placed in a magnetic field are repelled by it.

(ii) Paramagnetic solids:- When placed in a magnetic field are attracted by the magnetic field.

Therefore when a mixture of the above solids is subjected to/is passed through a magnetic field, magnetic solids are attracted toward it, and non-magnetic solids are repelled and collected in separate bins.

Magnetic separators are working for tramp-iron removal and concentration. Note: in this case, they are called eliminators. Magnetic separators are mainly two types 

(i) Magnetic Pulleys and (ii) Magnetic Drum.

Magnetic Pulleys Separators 

What is a magnetic pulley? A magnetic pulley/magnetic conveyor is used for the removal of tramp iron from products handled on a belt conveyor.

Magnetic pulleys having a diameter of up to 1500 mm and a width of up to 1500 mm are available. The belt speed ranges from 35 m/minute for a pulley of a diameter of 300 mm to 150 m/minute for a pulley of 1500 mm diameter. 

A magnetic pulley is incorporated into a belt conveyor at the discharge end. As the material is conveyed over this pulley, the magnetically inert non-magnetic material drops off the belt in a normal manner while the magnetic material adheres to the belt and falls off from the underside where the belt loses contact with the pulley.

The material to be separated must be supplied in the form of a thin layer to subject all the particles to a magnetic field of the same intensity.

Magnetic Drums Separators 

A magnetic drum separator consists of a rotating drum incorporated stationary magnet assembly. The magnet arc covers approximately 166 degrees towards the discharge side of the drum. The feed is admitted at the top and is allowed to fall on the rotating drum. 

The non-magnetic material is discharged in a normal manner while the magnetic material adheres to the drum and falls off the underside when the drum loses contact with the magnet assembly. 

Also Read: Defines Flows of Fluids 

Take these Notes is, Orginal Sources: Unit Operations-II, KA Gavhane