What they are
Strong acid cation (SAC) exchange resins are among the most widely used resins. They are composed of a polymer matrix to which anionic functional groups are bound, such as sulphonate (SO3–). SAC resins are regenerated with either a sodium salt solution (Na2+) for softening applications, or with an acid (H+) for demineralization applications.
What they're used for
SAC resins are used extensively for softening applications, and are very effective at complete removal of hardness ions such as magnesium (Mg+) or calcium (Ca2+). They may also be used in split-stream dealkalization, where two SAC beds operate in parallel, the first as a softener that produces an alkaline solution, and the second as a demineralizer (in the H+ form), with the result that alkalinity is removed from the blended stream. Certain varieties of SAC resins have also been developed for applications demanding removal of barium and radium from drinking water or other streams. SAC resins can be damaged by oxidants and fouled by iron or manganese, so care must be taken to avoid exposure of the resin to these materials.