The Flotation Process

Flotation, or more specifically “froth” flotation, is a physico-chemical method of concentrating ground ores. The process involves chemical treatment of an ore pulp to create conditions favorable for the attachment of pre-determined mineral particles to air bubbles. The air bubbles carry the selected minerals to the surface of the pulp, there forming a stabilized froth which is skimmed off and from which the pre-determined mineral particles are recovered. Other minerals remain submerged in the pulp.

History of Flotation Development

The earliest patent relating to the mineral flotation process is that of Haynes in 1860. his recognition of the differences in wettability of various minerals by water and oil formed the basis for a number of “oil” flotation processes. During the next fifty years, there principal stages of flotation development occurred:

Bulk oil flotation used the fact minerals of metallic luster are preferentially wetted by oil the presence of water – consequently passing into the interface between the oil and water – while the water – wetted gangue (worthless rock) drops out. This process requires large amounts of oil – usually one part for each part of are.

Skin flotation used the fact that when finely ground dry ore was gently brought into contact with still water, the metallic particles tended to float more than did the gangue. This process was developed between 1890-1915. However, both skin and bulk oil flotation were made obsolete by the froth flotation process.

As early as 1902, it was recognized that gas bubbles could an ideal buoyant medium for carrying oiled sulfide mineral particles to the surface of an ore pulp. The and other investigators generated bubbles by chemical action, or by applying a partial vacuum above the ore-water pulp. Ballot, Sulman, and Picard (1905) used a rising stream of air bubbles and thus reduced the quantity of required. This process, when applied in acid pulps and with non-selective oils used as collectors, proved to be an economic method of concentrating many sulfide ores.
However, it was inapplicable to many complex ores, such as those Cu-Fe, Cu-Pb-Zn-Fe, Pb-Zn-Fe, Cu-Zn-Fe, and Cu-Ni-Fe.

The need to treat such complex sulfide ores – as well as non-sulfide ores – resulted in the development both of more selective reagent combinations and of more selective reagent combinations and of more efficient flotation equipment. Modern flotation is considered to have begun in 1923, when C. H. Keller discovered the use of xanthates as collectors for sulfide minerals.

Through math model in 1978, Klimpel illustrated the importance of kinetics in flotation. He separated the overall effect of a reagent or operating condition change into two portions: (1) the potential recovery achieveable with the system at long time of flotation, “R”, and (2) a measure of the rare at which this potential can be achieved, “K”.

In 1979, Hansen and Meyer developed a collector to enhance recovery of oxidized coal. This collector gave flotability to weathered or naturally oxidized coal fines, allowing these particles to attach to air bubbles, with no resultant increase in ash content.