What they are
Weak acid cation (WAC) exchange resins remove cations associated with alkalinity (temporary hardness). WAC resins typically employ carboxylic acid functional groups (RCOO–), and are regenerated with sulphuric or hydrochloric acid. Similar to SAC resins, WAC resins swap cations for hydrogen ions, resulting in slightly greater acidity in the treated stream.
What they're used for
WAC resins are used for demineralization and dealkalization applications. Their high affinity for divalent cations ions (Ca2+ and Mg2+) makes them a good choice for applications demanding the removal of hardness ions associated with alkalinity. For high temporary hardness applications, a WAC resin can be used ahead of a SAC resin in a two-step IX process. Additionally, WAC resins tend to have relatively high oxidation resistance and mechanical durability, making them a good choice for streams containing oxidants such as hydrogen peroxide and chlorine, among others.
