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Understanding Soft Water Chemistry Jan 20, 2015

Coming soon in the October issue of Water Technology, Jeff Franks writes about sodium chloride, NaCl,

as well as potassium chloride, KCl. In this article, Franks begins by asking readers if they know just how much

salt can fit in a cubic foot of resin and why this point of reference, with special regards to NaCl, is important for

everyone in the field of water to know — especially for those in the water softener industry.


Franks explains that eight percent DVB gel cation resin contains a capacity between 1.9 and 2.0 meq/ml of resin

as variation can occur during the manufacturing process; manufacturers will publish this range of resin in their spec sheets/technical specifications.


If these units were converted into grains per cu. ft., a cubic foot of eight percent DVB gel ion exchange resin

for water softeners (when new) has 31,499 to 43,683 grains per cu. ft.; meaning if the ion exchange process

was 100 percent effective during regeneration, clarifies Franks, 7.3 lbs./cu ft. of NaCl salt would completely

regenerate the resin.


"The term stoichiometric is used to state that the theoretical maximum chemical exchange has occurred" declares

Franks, "So if we lived in a perfect world where perfect chemical exchanges could occur between a salt solution

and ion exchange resin, then there would be absolutely no reason to regenerate a water softener above a salt

dosage of 7.3 lbs./cu. ft."