MadSci Network: Other
Query:

Re: Does a water softener increase sodium in the drinking water ?

Area: Other
Posted By: Nick Bourbaki, Collective Enigma Elucidator
Date: Mon Jan 20 21:15:35 1997
Message:

Yes, it does..

Hard water is caused by the presence of divalent cations, namely calcium (Ca++) and magnesium (Mg++) - both of which have 2 positive charges when in solution. These ions are the predominant cause of scale in pipes. They also react with the fats in soaps to cause that unpleasant 'cakey' feeling while washing in the shower. Calcium is the more common of the two as it comes from calcium carbonate or limestone which is common in many areas. Sodium, on the other hand, only has one positive charge (Na+), and does not cause the ill-effects of calcium or magnesium.

Water softeners remove calcium and magnesium by "replacing" them with sodium. The process makes use of the positive charges of the ions. The softener usually contains a negatively charged resin which is periodically flooded with sodium ions from a tank of brine. The sodium ions associate with the negative charges on the resin. When hard water runs through the resin, the calcium and magnesium ions are also attracted to the negative resin, now populated with sodium ions. Sodium is used because the larger, divalent cations can readily displace them from the surface of the resin. Every ion of Ca++ of Mg++ displaces two atoms of Na++ into the water.

The resin is periodically regenerated by exposing it to the brine solution. Under these conditions the overwhelming excess of sodium ions displaces the Ca++ and Mg++ that have bound to the resin.

A good tutorial on water purification and treatment can be found at the Good Water Company.


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