Weak Acid Cation Exchange Resin
Weak acid cation resins (WAC) are polymer beads containing carboxylic acid groups. The ion exchange behavior of these groups depends on the pH of the water.
In hydrogen form, they retain cations associated with bicarbonate and help reduce water alkalinity. Changes in ionic form can also change the volume of the resin beads.
Technical Specifications
| Polymer structure | Crosslinked acrylic / methacrylic polymer |
|---|---|
| Functional group | Carboxylic acid |
| Ionic form | H⁺ |
| Appearance | Spherical beads |
| Total exchange capacity (H⁺) | 4.07 eq/L |
| Moisture retention (H⁺) | 44.9–54.3% |
| Particle size | 320–1415 µm |
| Uniformity coefficient | 1.56 |
| Specific gravity | 1.165 |
| Particle density | 1.17 g/mL |
| Shipping weight | 738–788 g/L |
Application and use
- In dealkalization, hydrogen-form resin removes cations associated with bicarbonate; downstream carbon dioxide removal is considered in the process design.
- Before full demineralization, a weak acid stage can reduce the load on a following strong acid cation bed when the water composition suits this arrangement.
- In selected softening duties, the conversion and regeneration cycle must be defined together with the free space required for bed swelling.
Frequently asked questions
Can hydrochloric acid be replaced directly with sulfuric acid?
Do not retain the same regeneration settings. Calcium sulfate may precipitate during sulfuric acid regeneration; a grade-specific procedure is needed.
Why can residual hardness remain while alkalinity decreases?
Hydrogen-cycle weak acid treatment does not remove every hardness salt in the same way. Noncarbonate hardness can remain even when dealkalization is working.
When should a weak-acid resin be considered?
It is useful to evaluate when hardness is associated with substantial alkalinity. The inlet hardness-to-alkalinity relationship and outlet target determine whether a following strong-acid stage is needed.
Why must vessel freeboard be checked?
Bead volume changes when ionic form changes. The amount and direction of swelling are grade specific and must fit the vessel and backwash arrangement.
Is a degasser required after dealkalization?
Hydrogen-cycle treatment of bicarbonate produces carbon dioxide. The need for degassing depends on the downstream water-quality target and process arrangement.