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Weak acid cation (WAC) exchange resin is a type of ion exchange resin with carboxylic acid functional groups (RCOO–). Similar to strong acid cation (SAC) exchange resins, WAC resins swap cations for hydrogen ions, resulting in slightly greater acidity in the treated stream. WAC resins can exchange with bases such as NaOH and weak acid salts such as NaHCO3.

WAC resin or SAC resin can be divided into two types: gel type and macroporous type. In gel type, the bead of resin comprises the homogeneous gel. The gel type ion exchange resin has the characteristics of high capacity, high chemical efficiency, good mechanical stability, and translucent pseudocrystaline structure. In contrast, macroporous ion exchange resin has lower capacity but has a bimodal pore size distribution, higher mechanical stability, better resistance to oxidation, high temperature and opaque porous structure.

Iminodiacetic acid prepared by chloromethylation of polystyrene/divinylbenzene (DVB) matrix is one of the common functional groups in WAC resins. The WAC resin with the carboxyl group is prepared by copolymerization of acrylic or methacrylic acid with DVB. The degree of dissociation of the functional group corresponds approximately with the acetic acid. Therefore, the ion exchange capacity of WAC resins decreases rapidly with decreasing pH value. Even though with limited use, WAC resins are easier to regenerate than SAC resins.

WAC resins are used for demineralization and dealkalization applications. Their high affinity for divalent cations makes them a excellent choice for applications requiring the removal of hardness ions associated with alkalinity. In addition, WAC resins generally have relatively high oxidation resistance and mechanical durability, making them a good choice for streams containing oxidants such as hydrogen peroxide and chlorine. Amerigo Scientific offers WAC exchange resins for dealkalization of water, transition metals recovery, purification of antibiotics and amino acid, etc.