Home water softeners

Among the three-dimensional silicates are the zeolites, which contain cavities or tunnels in which Na+ or Caz+ ions may be trapped. Synthetic zeolites with made-to-order holes are used in home water softeners. When hard water containing Ca2+ ions flows through a zeolite column, an exchange reaction occurs. If we represent the formula of die zeolite as NaZ, where Z represents a complex, three-dimensional anion, the water-softening reaction can be represented by the equation... 

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Most home water softeners are based on ion-exchange resins. The first ion-exchange materials used in softening water were naturally occurring polymeric aluminum silicates called zeolites. At present, synthetic zeolites are also used for this purpose. Today, most... 

Most home water softeners work by replacing the calcium and magnesium ions of the tap water with sodium ions. This softened water, therefore, contains increased levels of sodium ions. 

Common table salt is the most important commercial sodium compound. It is used in ceramic glazes, metallurgy, soap manufacture, home water softeners, highway de-icing, herbicides, fire extinguishers, and resins. 

Figure 30F-1 Schematic of a home water softener. During the charging cycle, the valves are in the positions shown. Salt water from the storage reservoir passes through the ion-exchange resin to waste. Sodium ions from the salt water exchange with ions on the resin to leave the resin in the sodium form. During water use, the valves switch and hard water passes through the resin where the calcium, magnesium, and iron cations replace the sodium ions attached to the resin.

Ion exchange is a process in which one type of ion in a compound is exchangedfor a different type cation for cation and anion for anion. For example, calcium, iron, and magnesium ions can be removed from water by being exchanged for sodium ion. This can be done in a bucket or a bag, much like a home water softener... 

Using synthetic detergents is one way to combat the problem of hard water and bathtub ring. Another way is to simply remove the cations responsible for the hard water before they reach the house. You can accomplish this feat through a home water softener (see Figure 17-4). 

Home water softeners use ion exchange to replace Ca and from hard" water with Na (Box 13-2). 

Hard water has a high concentration of calcium and magnesium ions. Focusing on the calcium ion, a common home-water-softening process is based on a reversible chemical change that can be expressed by Na2Ze(s) + Ca (aq)... 

Dnring the regeneration process, a large excess of sodium chloride must be used—several pounds for a home water softener. Appreciable amounts of dissolved sodium chloride can be introduced into sewage by this route. 

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