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The Flotation Process

Copper flotation process      Until the invention of the flotation process, the extraction of metal depended upon being able to hand-pick the material in order to be economical. Taking copper as an example, previously, that meant that using low-grade ores - with less than four percent metal content - would not be practical. In the present, however, available ores are typically even lower in metal content. The current product from mines may typically yield at best 2 percent to as low as 0.8 percent of the metal, as fine particles of the mineral thinly distributed throughout the rock. One hundred tons of ore contains 99 percent waste material that must be separated to produce one ton of copper.

      The flotation process depends on the properties of minerals by which their surfaces differ in the degree by which their surfaces can be wetted, and  takes best advantage of such differences by suitable choice of the solution.

1898 Flotation Process Patent Illustration
Illustration of an early flotation process
from the 1898 British Patent No.21948 by the Elmore brothers

      Ore is first ground into a powder, which is introduced to a series of tanks (known as flotation cells) holding a solution containing oils, constantly agitated, through which air is pumped. In the resulting froth. The particles of copper minerals adhere to the raft of air bubbles on the surface, while the  majority of the worthless rock (known as the gangue) sinks. The valuable material is skimmed from the surface froth; the waste material is removed from the bottom of the tank.

      With careful control of the chemical conditions in such flotation cells, the results can be selective for the desired product.

      The huge amount of material that must be handled for a relatively small yield requires huge plants, fed continuously,  operated by large companies able to make the huge capital investment involved.

     See also:
     Flotation Process Patent 1898 by Alexander and Francis Elmore
Sixty Centuries of Copper