Technical principle of electrodialysis operation
Electrodialysis is the process of separating electrolytes from water under the influence
of DC electric field by ion exchange membrane.
First, the basic principle and characteristics of
Electrodialysis in alternating many ion exchange membranes, divided into small room.
When the raw water enters these cells, the ions in the solution will be directed
migration under the action of the DC electric field. The cation membrane only allows the
cation to pass through the anion, and the anion only allows the anion to pass through
the cation. As a result of these cells into fresh room a little water containing ions,
known as freshwater. The chamber adjacent to the fresh water chamber becomes a
concentrated water chamber where large quantities of ions are gathered, and the effluent
is called concentrated water. Thus, the ions are separated and concentrated, and the
water is purified.
There are similarities and differences between electrodialysis and ion exchange:
(1) although the working media of ion separation are all ion exchange resins, the former
is a flake like film, while the latter is spherical particles;
(2) from the mechanism, which belongs to the ion transfer replacement ion exchange, ion
exchange resin occurs in the process of ion exchange reaction. Electrodialysis is an ion
selective displacement, and ion exchange membrane plays an important role in ion
selective permeation and interception. Therefore, ion exchange membranes should be
called ion selective permeation membranes more precisely;
(3) working medium electrodialysis need not be regenerated, but power consumption; and
the working medium of ion exchange must be regenerated, but no electric energy
consumption. The treatment of wastewater by electrodialysis is characterized by no
consumption of chemicals, simple equipment and convenient operation.
The application of electrodialysis method in wastewater treatment
Electrodialysis desalination was first used to produce drinking water and industrial
water, condensed water waterand salt, and other unit technology combination high pure
water, but also get more extensive application in wastewater treatment.
In wastewater treatment, according to the technical characteristics of electrodialysis
operation has two types: one is from the ion exchange membranes are arranged alternately
into common electrodialysis process, mainly used for simple separation of contaminant
ions from wastewater, or contaminant ions in wastewater and non electrolyte pollutant
separated, then the other methods of treatment; another is a special electrodialysis
consisting of composite membrane and cation membrane deposited process to produce H+ and
OH- ions by electrode reaction polarization in the composite film and the electrode
chamber, producing acid and alkali from waste water.
At present, electrodialysis method in wastewater treatment practice in the most commonly
used are: 1) treatment of papermaking wastewater, the alkali recovery from solution,
recovery of lignin from dilute solution; 2) separated from the wastewater containing
metal ions and concentration of surplus metal ions, then concentrate for further
processing or recycling: 3) separation of radioactive elements from radioactive waste;
4) produced from mirabilite waste sulfuric acid and sodium hydroxide; 5) produced from
pickling waste sulfuric acid and deposition of heavy metal ions; 6) electroplating
wastewater and waste liquid, containing Cu2+, Zn2+, Cr (IV), wastewater Ni2+ and other
metal ions are suitable for electrodialysis method of processing, is widely used in the
recovery of nickel from nickel plating wastewater, showed that many factories in
practice, this method can be used to realize the closed cycle. Electrodialysis equipment