Ion exchange is a domestic mature technology, mainly applied for the deep desalination, the making of the high pure-water and the water softening after the reverse osmose and electrodialysis process.

The process works like this: Ion exchange resins (little beads that are charged) are coated with the replacement ions. In the case of water softening the beads are coated with Na+ and Cl-. In the case of deionization, they are coated with H+ and OH-. Water flows over the resin. The ions in the water are attracted to the resin. The ions in the water attach themselves to the resin, and knock off the ions that are already attached.