Certification Action Line: Ion and cation exchange resins

April 1, 2016

Certification Action Line features questions and answers typical of those appearing in Water Quality Association certification examinations. Some answers may not satisfy everyone or every condition.

1. List four symptoms of potential problems that may occur in an ion exchange system that has been in service for a long period of time.

2. Name the two types of ion exchange resins and polarity of the ions each attracts.

3. True or False: All resins basically have the same color.

4. True or False:  The lower the cross-linking of a resin, the physically weaker the bead is, resulting in poorer chemical and physical stability.

5. What is the particle size distribution of the standard cation exchange resin?

6. True or False: Most cation resins are specified at 30,000 grains of exchange per cubic foot of resin at a salting level of 15 pounds per cubic foot.

7. True or False: The ion exchange softening process reduces the total dissolved solids of a water supply.

8. What is meant by an equilibrium shift in the regeneration cycle?

9. What percentage of brine solution is generally used to cause this equilibrium shift when the water softener resin is regenerated?

10. Studies show that ion exchange resin has a preference for one ion over another. This preference depends on what three factors?



  1. Hardness leakage
  2. Iron leakage
  3. Loss of capacity
  4. Excessive pressure loss across the resin bed

2. Cation resin attracts positively charged ions. Anion resin attracts negatively charged ions.

3. False

4. True

5. 16/40 U.S. mesh

6. True

7. False

8. An equilibrium shift occurs when a very high concentration of weakly held cations are exposed to the resin. This causes the more strongly held cations to be displaced or replaced because they are overwhelmed by the higher concentration of other surrounding cations.

9. 10 to 12 percent


  1. Ionic charge. Most resins will hold polyvalent ions more strongly than monovalent ions.
  2. Molecular weight. Resins will hold onto the ion with the greater atomic or molecular weight much more tightly than one     with a lesser weight.
  3. Solution concentration. The higher concentration of an ion will force more of those ions onto the resin.

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