Friday, August 10, 2012

Gravity Separation or Lavigation

This method of concentration of ore is based on the difference in densities of the metallic ore and gangue particles powdered ore is treated with a stream of running water when the lighter gangue particles are washed away and heavier ore particles are left behind.

Two common methods for Gravity separation are as follows:

(i).        Wilfley’s Table Method:  A Wilfley Table used for the purpose is a slopping table with top corrugated or riffled in the direction of the slope. The crushed ore is fed on the top of table, which is kept vibrating all the time. A stream of water is made to flow across the table at right angles to the slope. At each jerk the lighter gangue particles are thrown upward and are carried across the table by the stream of water. At the same time the heavier particles (ore) move towards the bottom of table. A good deal of separation takes place by the time the ore particles reach the bottom. This method is particularly suitable for dense eres like cassiterite (SnO2) and hematite (Fe2O3).
(ii).       HydrulicClassifier Method:  Hydrulic Classifier is a conical reservoir fitted with a hopper at the top and a pipe at bottom, Powered ore is dropped through the hopper and the powerful stream of water is forced in through the pipe below. Lighter gangue particles are carried force in, through the pipe below. Lighter gangue particles are carried away by the current of water and the heavier ore particles collect in the apex of conc. the conical shape helps in reducing the velocity of water and thus ore particles are prevented from being carried away by water.