Heavy-Media Separation &
Magnetic Separation

Heavy-Media Separation
What is known as the heavy-media separation or sink-float process is another method of concentrating ores and minerals by floating (but is actually rather different from the flotation method described previously). Here, the differences in specific gravity of the many minerals in the rock mined are used to reach the wanted separation of ore from gangue.

In the sink-float plant, ore which is coarsely crushed is fed into a suspension of finely ground ferrosilicon (or magnetite or any other heavy mineral) in water. This suspension is carefully maintained at a specific gravity between that of the desired feed and the unwanted minerals or gangue. As a result of this, the mineral components that are heavier sink, and are retained, while the lighter constituents float, and are discarded.

Magnetic Separation
Some low-grade iron ore can be treated using magnetic separation because all iron minerals are magnetic to some degree. In this process, the crude ore, which may grade less than 30% iron, is mixed with water and ground to a suitable fineness. The pulp is then passed over a revolving magnetic drum, to which the magnetic iron minerals adhere. While the gangue particles are discarded with the water they are scraped off and retained.

The magnetic portion is dewatered and filtered, but the concentrate produced is much too fine to be used in a blast furnace at a steel plant (the destination of most iron), so it is pelletized — mixed with a appropriate bonding agent and is rolled on a pan or in a drum until marble-sized, iron-rich balls are formed. These pellets are baked and dried, and then shipped out to steelmakers.

Other methods of metal recovery include photometric sorting – where the distinct light-reflection properties of metallic minerals are used to separate them from gangue minerals — and a variety of simple processes that are gravity-based.