An ion exchange water softener is one of the most common components of a water treatment. Its function is to remove scale-forming calcium and magnesium ions from hard water. In many cases soluble iron (ferrous) can also be removed with softeners.
A standard water softener has four major components: a mineral tank, resin (filter media), a brine tank (pellet salt tank) to hold sodium chloride, and a control head.
The resin tank contains treated ion exchange resin made out of small beads of polystyrene that could be 8%, or 10% (best quality) cross-linked. The resin bead exchange sites adsorb sodium ions and displace multivalent cations during regeneration with 6-10% solution of NaCl from the brine tank.
The resin has a greater affinity for multivalent ions such as calcium and magnesium than it does for sodium. Thus, when hard water is passed through the resin tank in service, calcium and magnesium ions adhere to the resin, releasing the sodium ions until equilibrium is reached.
When most of the sodium ions have been replaced by hardness ions, the resin is exhausted and must be regenerated. Regeneration is achieved by passing a concentrated NaCl solution draw from the brine tank, through the resin tanks, replacing the hardness ions with sodium ions.
The resin’s affinity for the hardness ions is overcome by the concentrated NaCl solution. The regeneration process can be repeated indefinitely without damaging the resin.
