Hydrophobicity has to be imparted to most minerals in order to float them. In order to achieve this, surfactants known as collectors are added to the pulp and time is allowed for adsorption during agitation in what is known as the conditioning period. Collectors are organic compounds which render selected minerals water-repellent by adsorption of molecules or ions on to the mineral surface, reducing the stability of the hydrated layer separating the mineral surface from the air bubble to such a level that attachment of the particle to the bubble can be made on contact.

Collector molecules may be ionising compounds, which dissociate into ions in water, or non-ionising compounds, which are practically insoluble, and render the mineral water-repellent by covering its surface with a thin film.

Ionising collectors have found very wide application in flotation. They have complex molecules which are asymmetric in structure and are heteropolar, i.e. the molecule contains a non-polar hydrocarbon group and a polar group which may be one of a number of types. The non-polar hydrocarbon radical has pronounced water-repellent properties, whereas the polar group reacts with water.

Ionising collectors are classed in accordance with the type of ion, anion or cation that produces the water-repellent effect in water. This classification is given in Figure 12.4.

Figure 12.4: Classification of collectors (after Glembotskii et al., 1972)

The structure of sodium oleate, an anionic collector in which the hydrocarbon radical, which does not react with water, constitutes the non-polar part of...