TABLE OF CONTENTS Ion exchange systems are used primarily to remove inorganic ions from wastewater streams. These systems consist of steel or fiberglass-reinforced plastic columns packed with synthetic resins. The resins contain ionic functional groups to which exchangeable ions are attached. Ion exchange resins are called anionic if they exchange negative ions ( 
, 
, 
, CI -) and cationic if they exchange positive ions (Fe +3,Pb +2,Cd +2,Ca +2,NH +4, etc.).
In cation exchange, cations are removed from solution by exchanging for sodium or hydrogen ions, known respectively as the sodium and hydrogen cycles. Cation exchange can be expressed generally as follows [22]:
Sodium cycle: Na 2 R + M 2+ = M R + 2Na +
or
Hydrogen cycle: H 2 R + M 2+ = M R + 2H +
where: R represents the resin and M represents a divalent contaminant cation exchanged.
Anion exchangers work on opposite charges than cation exchangers, removing anions from solution and replacing them with hydroxyl ions (OH -), thus:
R(OH) 2 + A 2- = RA + 2OH -
where: R represents the resin and A represents a divalent contaminant anion exchanged.
As can be seen by looking at the right hand sides of the equations above, the resin becomes increasingly depleted of innocuous ions and increasingly loaded with contaminant ions. When an...
