How can foam properties be utilized to separate mixtures?
The surfaces of gas bubbles in a foam attract hydrophobic particles to their surfaces.
Froth flotation is a process for separating hydrophobic materials from hydrophilic. The mining industry uses flotation to concentrate ores.
A crusher grinds the ore to fine particles less than 100 µm in size. The various minerals then exist as separate grains.
Mixing water with the ground ore forms a slurry. Adding a surfactant makes the desired mineral hydrophobic. A stream of air produces bubbles in the slurry.
Hydrophobic particles attach to the air bubbles, which rise and form a froth on the surface. Centrifuging removes the mineral from the froth.
The minerals that do not float into the froth (the tailings) may undergo further stages of flotation. This recovers valuable particles that did not float the first time.