Ion Exchange, as the name suggests, is the exchange of ions between ionized species in the water with ion exchangers such as H+ and OH- ions. The process is reversible and the column can be regenerated by washing through excess ions.
How does it work?
Water is passed through beds of ion exchange resins where the ions in solution migrate into the beads. Here, as a function of their relative change densities (charge per hydrated volume), they compete for the exchange sites. The resins themselves are sub 1 mm porous beads made of highly cross-linked insoluble polymers with large numbers of strongly ionic exchange sites.
Deionization beads are either cationic or anionic and exchange either H+ ions for cations (e.g. Na+, Ca2+ and Al3+) or OH- ions for anions (e.g. Cl-, NO3- and SO42-). The hydrogen ion from the cation exchanger unites with the hydroxyl ion of the anion exchanger to form pure water.
Beds of ion exchange resins are available as cartridges or cylinders and are typically used for a period of time before being replaced. This happens when cations and anions have replaced most of the H+ and OH- active sites in the resin. Once the packs are exhausted, they can be regenerated by washing through with an excess of desirable ions using strong acids and bases. This reverses the whole process and removes the unwanted cations and anions however this requires the use of harsh chemicals.
Why is ELGA better?
In all deionization processes there is a risk that weakly ionized impurities will elute from the resins and into your application as they approach exhaustion. This is because, after a period of use, the ion exchange capacity of a purification pack starts to be exhausted and these compounds are released first, even before the resistivity has fallen below 18.2 MΩ-cm. ELGA’s patented PureSure® technology prevents this.
PureSure® is a double purification pack and monitoring system which ensures accurate results and uninterrupted workflow. The secondary purification pack retains any organics and silica that may be released by the first purification pack as it approaches exhaustion, providing you with the time to change the consumable without impacting on your results. Not only does it help to guarantee your water purity, you have increased security and advanced warning of usable purification pack life.
Benefits and limitations
✓ Removes dissolved inorganic ions, giving resistivity up to 18.2MΩ.cm (at 25oC) and <1 ppb total ionic contamination
✓ Regenerated by deionization using acid and bases
✓ Cost-effective water purification solution
⨯ Does not effectively remove bacteria, organics, particles or pyrogens
⨯ Finite capacity - once all ion sites are occupied, ions are no longer retained