What’s Foam Separation?

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Foam separation uses a bubbled gas and surfactant to remove components from liquid mixtures. It can be used to extract precious metals, proteins, and impurities from water. Foam separation can be performed as batch or continuous operations and is used in wastewater treatment systems.

Foam separation is a process of removing a component of a liquid mixture by using a bubbled gas and surfactant to collect the material. A surfactant is a chemical that helps produce foam without chemically reacting with the solution. Many materials can be removed from liquids using foam separation methods, including precious metals, proteins, and impurities from water.

Another term for foam separation is adsorbent bubble separation. Adsorption means that a material settles on the foam surface without a chemical reaction having occurred. Foam has a surface tension, and in some cases molecular polarity, which attracts the desired material to the surface of the foam.

There are a number of chemical methods of extracting gold from ore, but many of them involve toxic chemicals and waste products. Gold can be extracted from a liquid mixture using air or nitrogen and a foam-producing surfactant. The foam exiting the equipment is enriched in gold, which can then be separated by centrifuges that push the gold and remove the foam.

The separation of proteins and oils can be done with foam separation equipment. Surfactants attract the desired product to the foam interface in preference to organic or oily molecules over water molecules. Foam systems can use non-reactive nitrogen gas instead of compressed air to prevent any oxidation reactions of the air with the desired materials.

Wastewater treatment systems often use scum separation steps to remove solids from the water stream. Larger solids can be removed by gravity or centrifuge operations, but fine solids must also be removed to meet treated water standards. Air can be bubbled along with a surfactant to create a foam layer that rises to the top of the foam tank. Fine solids will be adsorbed on the foam, which may overflow the tank or be foamed from the top.

Foam separation can be performed as batch or continuous operations. Batch processes will place the liquid mix in a processing tank and produce foam until most of the product has been removed. Product analysis can determine when machining is complete and equipment can be re-filled and the process repeated.
Continuous production systems add the mix to the bottom of the vessel or to a side point. Air or other gas and surfactant are added to the bottom and are mixed as the gas moves to the top. The foam will either be carried to the top of the tank or to a collection point on the side above the liquid level. Further processing can remove surfactant from the desired product stream.

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