Beds of ion exchange resins can efficiently remove ionised species from water by exchanging them for H+ and OH- ions. Ion exchange resins are sub-1 mm porous beads made of highly cross-linked insoluble polymers with large numbers of strongly ionic exchange sites. Ions in solution migrate into the beads; where, as a function of their relative charge densities (charge per hydrated volume), they compete for the exchange sites. Beads are either cationic or anionic. Strong cation resins are usually polysulfonic acid derivatives of polystyrene cross-linked with divinylbenzene. Strong anion resins are benzyltrimethyl quaternary ammonium hydroxide (Type 1) or benzyldimethlyethyl quaternary ammonium hydroxide (Type 2) derivatives of polysytrene cross-linked with divinylbenzene.

Beds of ion exchange resins are available either in cartridges or cylinders, which are replaced /removed from site for remote regeneration, or as an arrangement of tanks, vessels, valves and pumps, which allows on site regeneration of the ion exchange resins. Positively charged ions (e.g. calcium, magnesium) are removed by the cation resin by exchanging hydrogen ions for the heavier more highly charged cations. Once "exhausted" the cation resin is regenerated by exposing the resin to an excess of strong acid, usually hydrochloric (HCl).

Similarly, negatively charged ions (e.g.sulphate, chloride) exchange with hydroxyl ions on the anion resin. Anion resin is regenerated using strong sodium hydroxide solution (NaOH).

The very large surface areas of ion exchange resins makes them a potential breeding place for micro-organisms and can lead to the release of fines and soluble components.For these reasons, good quality resins should be used and bed volumes kept as small as reasonably possible. Filters are typically installed after the beds to trap fines and other particulate matter. Bacterial build up can be minimised by frequent recirculation of the water and by regular cartridge replacement.

Modern ion exchange plant design uses relatively small resin beds and frequent regeneration - this minimises the opportunity for microbial growth.

With suitable choice of resin, pretreatment and system design, ion exchange enables the lowest levels of ionic contamination to be achieved.

The NWT regeneration services take place off-site with regenerated “portable exchange” deionization tanks delivered through our service department. Please see our Portable Exchange Deionization page for more information.