Surfactants and Flotation

The flotation of sohd particles on a liquid medium depends on the contact angle, which can be changed by the addition of surfactants. A familiar elementary chemistry demonstration consists of making a needle float on the surface of water by coating it in wax. Subsequent addition of a household detergent sinks the needle. 

The ore particles then float to the surface where they are recovered by skimming [51]. Flotation of this kind is also used as a purification procedure for sludges and effluents. 

Example 3.5 In flotation, for a sohd particle to float on a liquid surface, the upward pull of the meniscus around it (reflected in 9) must at least balance the weight of the particle. Any natural tendency of the particles to float or not float, depending on 0, can be modified by adding oils or surfactants to alter the interfacial properties. A mineral particle that does not float (a) can be floated by adding surfactant (b) as follows. 

Consider a cube-shaped mineral particle (sides of length L= 100 pm) placed on the surface of a container of water of surface tension y = TL mN/m. 

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