Abstract: Continuous or semi-continuous ion exchange treatment, such as desalination, is achieved by utilizing a column packed with a heterogeneous thermally regenerable ion exchange resin in a single bed divided into a loading zone, a heat displacement zone above the loading zone, and a resin regeneration zone above the heat displacement zone. In operation, feed liquid flows upwardly through the loading zone and the treated liquid is removed. Loaded resin is transferred from the loading zone to the regeneration zone, the resin bed then being displaced downwardly, counter-current to the flow of feed liquid. A hot regeneration liquid, which may be a portion of the treated liquid, is passed through the loaded resin in the regeneration zone for thermal regeneration of the resin.