Magnetic Separation


MAGNETIC SEPERATION

Magnetic separation is a process in which magnetically susceptible material is extracted from a mixture using a magnetic force. This separation technique can be useful in mining iron as it is attracted to magnet. Magnetic separators exploit the difference in magnetic properties between the ore minerals and are used to separate either valuable minerals from non-magnetic gangue, e.g. magnetite from quartz, or magnetic contaminants or other valuable minerals from the non-magnetic values.

All materials are affected in some way when they are placed in a magnetic field. Materials can be classified into two broad groups, according to whether they are attracted ( or ) repelled by a magnet.

  1. Diamagnetic are repelled along the line of magnetic force to a point where the field intensity is smaller. The forces involved here are very small and diamagnetic substances can’t be concentrated magnetically.
  2. Paramagnetic are attracted along the lines of magnetic force to points of greater field intensity. Para magnetic field materials can be concentrated in high intensity magnetic separators.

Examples: Illmenite ( FeTiO3), Rutile (TiO2), Wolf Amite ((Fe , Mn)WO4), Monazite ( Rare earth phosphate), Siderite (FeCO3), Chromites (FeCr2O4), Hematite (Fe2O3).

The unit of measurement of Magnetic Flux density or Magnetic Induction (B),( the number of lines of force passing through a unit area material) is the Tesla(T).

Field Intensity (H)

Field intensity is the magnetic force which induces the lines of force through a material. It is denoted by H and it has the units Ampere/ meter. The intensity of magnetization ( M A/m) of a material relates to the magnetization induced in the material and

B = µ0(H+M) ……..(1)

Where µ0 – permeability of free space
µ0= 4 π × 10-7 T m/A In vaccum, M=0, and it is extremely low in air,

such that eqn (1) becomes
B= µ0(H) ...…...(2)

Magnetic Susceptibility(S)

It is the ratio of the intensity of magnetization produced in the material to the magnetic field which produces magnetization i.e,

S= M/H …….(3)

Combining eqns (1) and (3)

B= µ0 H(1+S)
Or
B= µ µ0 H

Where
µ = 1+S, and it is a dimensionless number known as relative permeability

Types of Magnetic Separators

Magnetic separators can be classified into low and high intensity machines, which may be further classified into dry feed and wet feed separators.

Low intensity Magnetic Seperators

Low intensity separators are used to treat ferromagnetic minerals and some highly paramagnetic minerals. Low intensity wet separation is now widely used for purifying the magnetic medium in the dense medium separation process, as well as for the concentration of ferromagnetic sands.

Drum Separators

Drum separators are the most common missions in current use for cleaning the medium in dense medium separation circuits and are widely used for concentrating finely ground iron ore.

Counter Rotation Drum Seperators

Where the field flows in the opposite direction. This type is used in roughing operations.

Counter Current Separators

In this tailings are forced to travel in the opposite direction to the drum rotation and are discharged into the tailing chutes. This type of separator is designed for finishing operations on relatively fine material, of particle size less than about 250 micro meters.

High Gradient Separators

In order to separate paramagnetic minerals of extremely low magnetic susceptibility, high magnetic forces must be generated. These forces can be produced by increasing the magnetic field strength, and in conventional high-intensity magnetic separators use is made of the ferromagnetic properties of iron to generate a high B-field (induced field) many hundreds of times greater than the applied H-field, with a minimum consumption of electrical energy.

Reference

Mineral Processig Technology by B.A. Wills

Question and answers

1. What is magnetic separation?
Ans. Magnetic separation is a process in which magnetically susceptible material is extracted from a mixture using a magnetic force.


2. What are the examples of paramagnetic minerals?
Ans. Illmenite ( FeTiO3), Rutile (TiO2), Wolf Amite ((Fe , Mn)WO4), Monazite ( Rare earth phosphate), Siderite (FeCO3), Chromites (FeCr2O4), Hematite (Fe2O3).


3.What is the unit of magnetic flux?
Ans. Tesla (T).


4.What are the low intensity magnetic separators?
Ans. Drum separator, Counter Rotation drum separator, Counter current separator.


5.What is meant by magnetic field intensity?
Ans. Magnetic Field intensity is the magnetic force which induces the lines of force through a material. It is denoted by H and it has the units Ampere/ meter.

More pages