Continuous foam separation is a chemical process closely related to foam fractionation in which foam is used to separate components of a solution when they differ in surface activity. In any solution, surface active components tend to adsorb to gas-liquid interfaces while surface inactive components stay within the bulk solution. When a solution is foamed, the most surface active components collect in the foam and the foam can be easily extracted. This process is commonly used in large-scale projects such as water waste treatment due to a continuous gas flow in the solution.
There are two types of foam that can form from this process. They are wet foam (or kugelschaum) and dry foam (or polyederschaum). Wet foam tends to form at the lower portion of the foam column, while dry foam tends to form at the upper portion. The wet foam is more spherical and viscous, and the dry foam tends to be larger in diameter and less viscous. Wet foam forms closer to the originating liquid, while dry foam develops at the outer boundaries. As such, what most people usually understand as foam is actually only dry foam.
The setup for continuous foam separation consists of securing a column at the top of the container of solution that is to be foamed. Air or a specific gas is dispersed in the solution through a sparger. A collecting column at the top collects the foam being produced. The foam is then collected and collapsed in another container.
In the continuous foam separation process a continuous gas line is fed into the solution, therefore causing continuous foaming to occur. Continuous foam separation may not be as efficient in separating solutes as opposed to separating a fixed amount of solution.