Deionised water is essentially water from which ions, such as cations from sodium, calcium, magnesium and potassium, and anions such as chloride, nitrates and sulphates have been removed. Water is often required to be deionised for applications such as scientific research where the elimination of impurities is essential.

With the latest technology it is now practical to achieve deionised water without the use of cation and anion resins regenerated with acid and caustic solutions; this technology is known as Continuous Electro-Deionisation or CEDi.

This method of producing deionised water is considerably safer and less harmful to the environment than the earlier use of chemicals, and is also extremely economical.

The CEDi cell is constructed from alternating layers of cation and anion permeable membranes; these ion selective membranes do not allow the passage of water only ions. On the outer sides of the stack are placed the cathode and anode electrodes. Feedwater flows into the stack and is split accordingly, between the feed/dilution chamber, the concentration chamber and the electrolyte compartment. The unwanted ions in the feedwater are exchanged onto the ion exchange resin and the applied DC potential draws the ions towards their respective electrodes. The cations move towards the cathode passing through the cation permeable membrane and into one of the concentration compartments. Further movement towards the cathode is halted by anion permeable membranes; the cations are neutralised by anions rejected from the other corresponding chambers. The rejected ions are flushed from the system in the concentrate stream.

For more information on the latest water purification systems that produce deionised water, click here.

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