What is a limitation of the ion exchange softening process?

• A. A decrease in the sodium content if the ion exchanger is regenerated with sodium chloride
• B. Ion exchange is a selective method of softening
• C. An Increase in the sodium content if the ion exchanger is regenerated with sodium chloride
• D. It will remove the total hardness (the sum of carbonate and noncarbonate hardness)

Answer: (C)

Ion exchange softening replaces calcium and magnesium in the water with sodium on the resin. When the resin is regenerated with sodium chloride, sodium ions are recharged onto the resin and calcium and magnesium are released into the regenerant. That means the softened water ends up with a higher sodium concentration. This increase in sodium is a common limitation because it can be undesirable for people on low-sodium diets, can affect taste, and may influence downstream processes or corrosion control. To cope, operators might blend with lower-sodium water or use alternative regeneration schemes or technologies. The other statements either misstate the sodium change, describe a property rather than a limitation, or imply full hardness removal in all cases, which isn’t guaranteed.