Ion Exchange

Ion exchange units that replace calcium and magnesium ions from water are known as water softeners. They may also remove varying amounts of other inorganic pollutants such as metals, but they will not remove organic chemicals, pathogens, particles, or radon gas. Water softener units work most efficiently with particulate-free water.

Principles of Ion Exchange to Soften Water- Calcium and magnesium ions are atoms having a positive electrical charge, as do sodium and potassium ions. Ions of the same charge can be exchanged. In the ion exchange process, a granular substance (usually a resin) that is coated with sodium or potassium ions comes into contact with water containing calcium and magnesium ions. Two positively charged sodium or potassium ions are exchanged (released into the water) for every calcium or magnesium ion that is held by the resin. This “exchange or trade” happens because sodium or potassium are loosely held by the resin. In this way, calcium and magnesium ions responsible for hardness are removed from the water, held by the resin, and replaced by sodium or potassium ions in the water. This process makes water “soft.” Eventually, a point is reached when very few sodium or potassium ions remain on the resin, thus no more calcium or magnesium ions can be removed from the incoming water. The resin at this point is said to be “exhausted” or “spent,” and must be “recharged” or “regenerated.”

Ion Exchange Unit Components- A water softener can be as simple as a tank to hold the exchange resin, together with appropriate piping for raw (inlet) and treated (outlet) water. Modern water softeners include a separate tank for the brine solutions used to regenerate the resin, additional valves to back-wash the resin, and switches for automatic operation.