Electro dialysis is used whenever solutions, which contain dissolved electrically charged ions, have to be concentrated or diluted. The electrolyte separation of solutions which contain electrical uncharged molecules, like e.g. sugar, proteins and so on, is also possible. The electro dialysis process is driven by the electrical potential.
For conditioning, the solutions are pumped through the membrane stack and at the electrodes, a direct current voltage will be applied. The positively charged salt ions (cations) follow the electrical field and flow to the cathode, the negatively charged ions (anions) flow to the anode.
A membrane stack for electro dialysis consists of a series of cells, which are separated from eac h other by alternating anions and cations exchange membranes. The stack is completed by a anode and a cathode and fixed in a clamping device which looks similar to a filter press.
The positively charged ions are able to pass the cations exchange membrane, but they cannot pass the following anions exchange membrane and are retained. Vice versa the negatively charged ions are able to pass the anions exchange membrane and are retained at the cations exchange membrane. Hence, ions are concentrated (concentrate) in every second cell whereas the ions of the neighboring cells are removed (diluate).
By supply and drain connections at the cell frame, the diluate and concentrate flow can be pumped through the cells of the membrane stack.
OSMO Membrane Systems engineers and produces customized electro dialysis plants for all kinds of applications. The design of the plants is based on a modular conception: series connection of stacks means a higher grade of desalination, whereas parallel connection of stacks means a higher volume flow.
Field of application of electrodialysis
- Acid recovery
- High concentration of brines
- Desalination of brackish water
- Nitrate removal of potable water
- Reduction of operating costs of ion exchanger plants by upstream desalination with electro dialysis
- Conditioning of reverse osmosis concentrate to reach a plant recovery of more than 95%
- Concentration of Sea water for table salt production
- Reclaiming of materials out of rinsing baths (Cu, Ni, Zn, Cd, and so on)
- Reclaiming of hardening salts out of rinsing baths of heat treatment (NaNO3, KNO3, NaNO2)
- Reclaiming of acids out of rinsing baths of the battery and accumulator production
Waste water conditioning
Combined with thermal processes like evaporation or cristallisation, waste water with very high salt content (e.g. FGD waste water) can be disposed with little residues