H   R R   OH Ca SO₄ Ca   R R   SO₄ H OH H   R R   OH Na Cl Na   R R   Cl H OH WATER TREATMENT PROCESSES DOE-HDBK-1015/2-93 Principles of Water Treatment CH-04 Rev. 0 Page 14 Ion Exchange Summary (Cont.) Resin beads are long-chain cross-linked polymers that contain sites occupied by exchangeable ions.  The general order of affinity serves as a useful guide in understanding many ion exchange processes. Cation and anion resins are named according to the identity of the ion occupying the exchange sites, such as hydrogen, hydroxyl, and chloride.  Mixed-bed resins are used to remove both cations and anions. The effectiveness of any ion exchanger is directly related to the relative affinities between a resin and different ions.  In order of decreasing strength, the relative affinities between a cation resin and various cations are: Ba    > Sr    > Ca    > Co    > Ni    > Cu    > Mg    > Be +2 +2 +2 +2 +2 +2 +2 +2 Ag   > Cs    > Rb   > K       NH   > Na   > H   > Li + + + + + + + +              Similarly, the relative affinities of the anion resin for various anions are: SO   > I  > NO   > Br  > HSO   > Cl  > OH  > HCO   > F  4 3 3 3 -2 - - - - - - - - The higher the relative affinity the more effective the ion exchanger.  This effectiveness is expressed by the Decontamination Factor. The reaction for removal of NaCl and CaSO  by a mixed-bed ion 4 exchanger such as one containing HOH resin is as follows: