Flotation is the process of choice when products of finest grain sizes are to be processed. In these size ranges the properties of the product which are otherwise important for normal separation process recede into the background, and are overshadowed by the greatly increased surface area.

Basics

The possibility of separating various substances with froth flotation procedures is opened up by the various influences which can be effected on the surfaces with the assistance of agents which make the particles hydrophobic. These are known as "collectors" in the lexicon of the flotation specialist. Through chemical and / or physical adsorption they are joined with the (usually polar) ends of the molecules at the surface, whereby their covalent end protrudes into the aqueous medium. The adsorption of the collector molecules can in many instances be influenced with additives which can be either supportive or inhibitive in effect. In these cases one speaks of "activators" and "inhibitors or "depressors". Air is injected to move the hydrophobized substance to the surface of the pulp. Further reagents must be added which facilitate the particles adhering to the gas bubbles and which hold in a layer of froth the products which have moved to the water / air interface surface. These reagents, consisting of a hydrophilic and a hydrophobic group, are referred to as frothing agents. The pH value also plays an important role in the three-phase interface surface reactions; pH must also be set at the optimal value. The optimal combination of reagents and their quantities must be determined in the laboratory for each material which is to be processed. Today there are suitable reagents available for virtually every problem.

History of Flotation

It was only at the middle of the nineteenth century that the phenomenon of the varying degrees of wettability of minerals with oil and water aroused the interest of the mining engineer. In 1869 W. Haynes patented a process for ore enrichment which was based on the fact that ore particles adhere in the oil/water interface. The first patent which exhibited all the technical characteristics of a modern flotation process, however, was awarded to the Bessel brothers, two Germans, in 1877.Development continued step-by-step from that point. Various methods for gas bubble generation or injecting air were developed and patented. These developments were accompanied by progress in chemistry, as well. A number of substances were found which could be utilized as collectors and frothing reagents. In combination with depressors and activators, such as sodium cyanide and copper sulfate, they made possible selective flotation even of complex systems.

The development of regents for processing of coal pulps started with tar based products and lead to the environmentally sound aliphatic alcohols in general use today.