Mixing Resins – How to Avoid Calcium Carbonate Fouling of Drain LinesBy: Michael Urbans
Mixing cation & anion resin in a single tank.
This blog is about mixing sodium form cation and chloride form anion resins in a single tank. Not mixed bed resin, which is hydrogen (H) form cation and hydroxide (OH) form anion.
These are the resins we’re discussing:
- Anion Resin – Chloride form specialty resin used to remove sulfates, nitrates, tannins, alkalinity
- Cation Resin – sodium form softening resin used to remove hardness – calcium, magnesium
When these resins are in separate tanks the cation is ahead the anion tank. The hardness minerals are removed before the water goes through the anion resin. Both are regenerated with sodium chloride (NaCl) – salt. Sodium (Na) exchanges with hardness minerals; chloride (Cl) exchanges with anions – sulfate, nitrate, etc. Use of this common regenerant (salt) creates the opportunity to combine cation and anion in one tank. Anion resin is lighter and rests at the top of the resin bed; cation is beneath it.
Calcium Carbonate may form if the water hardness is above 6-8 grains.
- The ion “exchange” happens during regeneration. The undesired cation minerals (calcium, magnesium) are being washed away and anion salts (exact contaminant depends on desired outcome) are also being washed away. These “waste” products foul the anion resin and combine to create calcium carbonate, a cement like substance which can block the drain line.
How to avoid the problem.
- Use separate tanks for cation and anion.
- Add phosphoric acid to the brine. By acidifying the calcium remains in solution.
- Pro Res Care Easy Feeder (Manufactured by Pro Products may purchase direct or from local supplier)
- Res Up Feeder (Manufactured by Clack – purchase only from local supplier)
How to repair.
- Clean the drain line by breaking up the calcification.
- Portions of seal pack and injectors my need to be replaced. Best to rebuild the valve before putting back in service.