In an ion exchange process, what is used to regenerate a depleted softener?

In an ion exchange process, sodium chloride (brine) is used to regenerate a depleted water softener. The softening process involves the exchange of calcium and magnesium ions in water for sodium ions from the resin in the softener. Over time, the resin becomes saturated with calcium and magnesium ions, which need to be removed for the softener to continue functioning effectively.

To regenerate the ion exchange resin, a concentrated solution of sodium chloride is introduced to the system. The high concentration of sodium ions in the brine solution allows for the sodium ions to displace the calcium and magnesium ions on the resin, effectively restoring its ability to soften water. This regeneration process is essential for maintaining the efficiency of the water softening system and ensuring that it can continue to provide soft water for use.

The other options do not serve the same purpose in an ion exchange context; potassium chloride, while it can also be used for regeneration, is less common and generally more expensive than sodium chloride. Calcium hydroxide and magnesium sulfate would not effectively regenerate a softener, as they would introduce additional hardness rather than replenishing the sodium ions needed for the softening process.