Gravity concentration

This technique is deployed if valuable and heavy iron minerals are free from associated light gangue minerals or waste rock. It is the simplest method of ore dressing and depends on the fact that in general the metallic compounds have a higher specific gravity than the gangue, and hence settle faster in a steam of water. Gold panning is the simplest illustration of the procedure. On a larger scale, it is carried on in jibs where ore is placed on a screen and a pulsating stream of water forced through the screen, causing the lighter gangue to be washed out. Another form of gravity concentrator is the table, consisting of a surface with longitudinal ridges, which is given a jerking end-to-end motion (возвратно-поступательное движение) while a stream of water flows across it laterally.

As it was mentioned above, the common iron ore minerals have usually high specific gravity (hematite: 5.1, magnetite: 5.2 and siderite: 3.8) as compared to the most common associated gangue minerals like, quartz (2.65), limestone (2.75), and clay (2.63).

Effectiveness of gravity concentration depends on proper feed preparation, which includes crushing, screening and grinding to ensure feed of proper size to a particular unit operation, which affects the separation efficiency of the machine, as it enhances the viscosity of the pulp before subsequent treatment.