In the same way that Reverse Osmosis plants are dependent on the RO membranes, Deionisers are very dependent on the performance of the Ion Exchange resins within.
During the life span of Ion exchange resins, the performance of the resins will change. This is a factor of the physical condition of the resins and the level of fouling that the resins have on them.
Water Softener Resins
Water Softeners contain a strong gel Cation resin. These resins do not in general lose their capacity to exchange out the water hardness, but they do over the course of time break down physically.
It is possible for softener resins to become fouled with Iron if the pre treatment is inadequate, but this can be removed with an acidic rinse.
In conventional Two Bed Deionisers there is normally a gel cation resin and a particular type of anion resin depending on the duty of the Deioniser.
The cation resin will provide a good life span but will degrade physically after approximately 5 to 7 years.
Anion Resins
Depending on the type of Deionised water and PH required, different Anion resins can be used. Anion resins are prone to fouling and because of this a macro-porus Anion resin is often used in this application. Anion resins do break down physically but they also lose their capacity to exchange anion impurities out of the water being treated. This is a progressive thing which tends to increase when the resins are 3 to 5 years old.
Because of the costs involved in both labour and materials, clients will often continue to operate deionisers with resins that are beyond their useful working life. This in many cases is a false economy as the effects are a decreased volume of Deionised water produced with an increased volume of regeneration effluent discharged and an increased volume of regeneration chemicals consumed.
Fouled anion resins can be cleaned to remove what is typically organic fouling. This is achieved by mixing up a solution containing 2% caustic soda and 10% brine. Ideally the solution should be at a temperature circa 40 degrees Centigrade. The solution is pumped into the resin and left to soak overnight. In rinsing out the next day a strong discoloured effluent should be seen.
Specialist Chelte Resins
Specialist Chelate resins are available for the removal of heavy metals. These are very effective in ensuring that waste stream outfalls are within consent limits. These types of resins need to be regenerated in a very defined way. The service run impurities are removed with hydrochloric acid whilst the resins are put into the sodium form by a counter flow regeneration.
Specialist Chelate resins are available for the removal of heavy metals. These are very effective in ensuring that waste stream outfalls are within consent limits. These types of resins need to be regenerated in a very defined way. The service run impurities are removed with hydrochloric acid whilst the resins are put into the sodium form by a counter flow regeneration.
The quality of Ion Exchange resins used in the first place is fundamental and critical. Cheaper resins can be purchased from the Far East, but they are so fundamental to the efficient operation of the Deioniser that it is not worth taking the risk.