Foaming agents are mostly anisopolar surfactants, slightly soluble in water, and relatively stable in composition. Commonly used ones include:
(1) No. 2 flotation oil (No. 2 oil) is a deep yellow oily liquid with a pine wood aroma. It is turpentine oil obtained by steam distillation of pine resin, followed by hydration with sulfuric acid and alcohol. It has strong foaming properties and can produce a large amount of uniform foam with appropriate viscosity.
(2) Eucalyptus oil is a distillation product of eucalyptus leaves. Its main component is eucalyptol (C₁₀H₁ 18O). Its foaming ability is not as good as turpentine oil, the foam is brittle, and it has good selectivity.
(3) Camphor oil is the crude oil obtained by distillation of camphor tree branches, leaves, and roots. It is the general term for the residual oil after camphor extraction. It is divided into three types: white oil, red oil, and blue oil. White oil can be used as a substitute for turpentine oil and has good selectivity; red oil produces more viscous foam; blue oil has both foaming and collecting abilities, but poor selectivity. (4) Cresolic acid is a byproduct of the coking industry. Its foaming ability is weaker than turpentine, the foam is brittle, and it has good selectivity.
(5) Higher alcohols are byproducts of the chemical and petroleum industries. They have moderate foaming properties and good selectivity.
(6) No. 4 flotation oil, a synthetic foaming agent, has more than twice the foaming ability of turpentine, good selectivity, and is easily soluble, easily washed off, and unaffected by pH value and water hardness.