Physical Separation Technologies

Question 1

Cyclone separator

Answer 1

A form of density separation.

• Upward flow of air
• Feed material to be classified is transferred to the fluidising air stream
• Material w/ higher density than air is disengaged at the bottom (at disengaging hopper)
• Material w/ lower density than air is carried by the ascending vortex out of the top of the classifier

Question 2

Dense medium separation

Answer 2

A form of density separation.

• Bath of fluid with proper density, aka heavy media. Commonly used: Magnetite, Ferrosilicon, a mixture of the two, or CaCO3.
• The heavy media is kept in constant circulation inside a rotating drum.
• Feed material to be classified is immersed in the bath.
• Material with lower density than that of the bath will float.
• Material with higher density than that of the bath will sink.

Question 3

Jigging

Answer 3

A form of density separation.

• Water is pulsated up and down.
• A vertical force of alternating direction is created.
• Material is re-layered into different layers under this force.
• High density particles are settling down to the bottom layer quickly.
• Lower density particles are settling slowly in the upper layer.

Question 4

Shaking table

Answer 4

A form of density separation.

• Deck of almost rectangular shape, slightly inclined (< 6°), covered with riffles.
• The feed end of the table is lower than the concentrate end.
• Wash water is added. The direction of the water on the table is perpendicular to that of the riffler.
• The table is shaking along its long axis.
• => Helps denser materials ascend and move towards the concentrate.
• Lower density particles won’t be able to ascend and they will flow over the tailings end.

Question 5

What is density separation?

Answer 5

• Density separation is based on the principle that different materials in the waste may have different densities.
• If multiple materials w/ different densities are placed in a liquid with an intermediate density, it’s possible to separate them based on their specific gravity.
• With the aid of centrifugal force, flotation, jigging, shaking, etc.

Question 6

What is magnetic separation?

Answer 6

• A process in which magnetic material is extracted from a mixture using a magnetic force.
• Separates ferromagnetic and paramagnetic materials from non-magnetic materials.
• Magnetic separators using permanent magnets generate fields of low magnetic intensity only. Theses work well in removing ferrous materials.

Question 7

Magnetic separator

Answer 7

A form of physical separation.

• 60 rpm, 0.6x gravity.
• Separates (weak) magnetic (ferrous) scrap from non-magnetic materials.
• The powdered impure ore, in the form of a thin layer, is allowed to fall on a rubber belt which moves horizontally over two rollers, one of which has an electromagnet attached to it.
• As the ore particles roll over the belt, the magnetic component in the ore gets attracted to the magnet.
• => Gets collected in a heap while the non-magnetic component forms a separate heap.

Question 8

Eddy current separator

Answer 8

A form of magnetic separation.

• 1500-6000 rpm, 1500x gravity.
• Separates non-ferrous metals (incl. SS) from non-metals.
• A magnetic rotor with alternating polarity spins rapidly inside a non-metallic drum, driven by a conveyor belt. As non-ferrous metals pass over the drum, the alternating magnetic field creates eddy currents in the non-ferrous metal particles, repelling the material away from the conveyor.
• While other materials drop off at the end of the conveyor, the non-ferrous metals are propelled forward over a splitter for separation.
• Ferrous metals must be removed beforehand since they become hot inside the eddy current field and could damage the feed belt.