Ion Exchange

In water treatment this process adds and removes ions from water. In general a plastic bead (called resin) is used as the exchange site. The bead is permanently charged and attracts ions of the opposite charge. Each ion in the water has a different affinity for the resin. Those with greater affinity will replace those with less affinity.

Example-If a resin is coated with sodium ions and water with calcium is run through the resin, the calcium ions will replace any sodium ions that are attached to the resin because they have a greater affinity for the resin than do the sodium ions. This exchange of places (from the water to resin and from the resin to water) removes calcium from the water and replaces it with sodium.

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