02
Track 02 · Water treatment
IER: ion exchange resin
Softening and demineralization on resin beads, regenerated with salt, acid or caustic.
How it works
Resin beads carry functional groups that hold ions. As water passes, ions in the water swap places with ions on the resin. Softening replaces calcium and magnesium with sodium. Demineralization uses cation resin in H⁺ form and anion resin in OH⁻ form.
A mixed bed combines both resins in one vessel to reach very high purity. Once saturated, the resin is regenerated with salt, acid or caustic.
When to use it
- Softening for boilers, cooling water, or ahead of RO on hard water.
- Cation-anion trains for high-volume demineralized water from a low-TDS feed.
- Mixed bed for polishing after RO or a cation-anion train.
Common mistakes
- Sizing resin on average water quality instead of the worst case.
- Regenerating at the wrong concentration, with too little contact time or poor rinsing.
- Iron, chlorine and organics fouling or shortening resin life.
- Poor separation before regeneration, or poor remixing after it, in a mixed bed.
- Not tracking ion leakage at the end of the cycle.
Related notes
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