What is the higher cost regenerant that is 2-5 times more expensive than NaCl?

Potassium Chloride (KCl) is recognized as a higher-cost regenerant, typically priced at 2-5 times more than Sodium Chloride (NaCl). The use of KCl as a regenerant in water softening processes is favored by some because it does not introduce sodium into the water, which can be beneficial for certain health concerns or environmental considerations.

KCl is often marketed as a low-sodium alternative for individuals on sodium-restricted diets, yet its higher cost can be a limiting factor for widespread use. The other substances listed are either not used as regenerants in the same way or are not considered higher-cost options relative to NaCl. For example, Calcium Chloride and Magnesium Sulfate are mainly utilized in specific industrial or agricultural applications rather than for typical water softening processes. Sodium Bicarbonate also does not serve the same purpose as a regenerant in this context, making Potassium Chloride the most suitable and appropriate answer for this question.