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.

An ion-selective, dense membrane guarantees the operation of diffusion dialysis.

Thanks to a cooperation that has existed between FUMATECH BWT GmbH and Spiraltec GmbH since 2015, Spiraltec is the exclusive partner for the latest generation of ion-conducting flat membranes from Fumatech BWT GmbH. Through this cooperation we can rely on the support of FUMATECH BWT GmbH for all our R&D projects concerning membranes.

The special feature of bases diffusion dialysis is the membrane used. This selective membrane separates two channels from each other.

If bases are to be recovered from old process baths, a cation exchange membrane is used, through which mainly cations (positively charged ions) can diffuse.

It has been shown in practice that recovery of caustic solutions with cation exchange membranes actually works, although the OH- ions are much larger than the co-diffusing H+ ions in acid diffusion dialysis with anion exchange membranes. However, the diffusion velocities are lower than in acid diffusion dialysis.