Separation of
the elements

How does diffusion dialysis work

Diffusion dialysis is a membrane separation process used to regenerate acids or bases or to replace special ions in a solution (“anion/cation exchange”).

The process is based on two different fluids flowing through two channels which are separated by a semi-permeable membrane.

In a simplified way, mass transport occurs from concentrated to diluted fluids until the concentration difference has been balanced out. With a selective membrane, certain components can be "separated out" from the concentrated fluid by increasing the resistance for other components.

Acid diffusion dialysis

The special feature of acid diffusion dialysis is the membrane used.

If acid is to be recovered from old process baths, an anion exchange membrane is used, through which only anions (negatively charged ions) can diffuse. Since the acid cation H+ is very small, it is carried along in anion diffusion, while the much larger metal cations are withheld. This selective membrane keeps two channels separate.

Fluid from the old process bath flows through one channel; demineralised water flows through the other. Thus, when fluid flows through the separate channels you achieve selective transport of anions and acid cations into the demineralised water.


To guarantee that diffusion dialysis will work, you need a dense ion-selective membrane. Thanks to a partnership started in 2015 between Fumatech BWT GmbH and Spiraltec GmbH, Spiraltec has exclusive access to the latest generation Fumatech BWT GmbH ion-conducting flat membrane films.
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