Sizes reduction technologies


Size reduction or communication is an important step and may be used

• To produce particles of required sizes and shapes
• To liberate valuable mineral so that it can be concentrated.
• To increase the surface area available for chemical reaction.

It is often said that the efficiency of energy utilization during fragmentation of solid particles is only about 1% with respect to the new surface created. Energy consumption represents major cost in the mineral processing operation.

Crushing and grinding are size reduction methods. Crushing is applied to subsequent size reduction down to about  25mm. In grinding finer size is produced. Grinding or milling is an important size reduction method. In grinding force is applied by a medium which could either balls  or rods .Both dry and wet grinding is done Wet  grinding has the following characteristics.

• It requires less power
• It does not need dust central equipment.
• Wet grinding uses more steel grinding media to  mill the material/per ton of product, as a result there occurs increase in erosion of the lining material.
• Water is required for wet grinding.

Material balance is important to determine

• Amount of water in a milling circuit
• % solid in slurry (slurry is a mixture of solid in water )

Both information are needed to determine the pump capacity to transport slurry.
In wet milling water/solid ratio is important to control the viscosity of slurry. Too dilute slurry will lead to excessive wear of the medium .Too high a solid concentration results in cushioning of the medium. Percent solid in slurry can be determined by

(1)

                                                 
   is density of solid and slurry respectively. For example   if  and   then slurry contains 33.3% solid according to equation 1.

Wet milling gives the following advantages:

• Less power requirement
• Required pollution as compared with dry milling.

After wet milling the milled product is classified by a hydro cyclone in to undersize (also termed underflow) and oversize (overflow) . The overflow is taken to the plant for concentration operation, for example  flotation The undersize is  recirculated after milling in a  ball mill  for further separation .

The interested reader may see the references for more details.