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Ion exchange resins are cla-sified as cation or anion exchangers. Both types are produced from the same basic organic polymers. The chemical behavior of the resin is determined by the particular ionizable group attached to the resin. The following is a list of five resin types that may be used by the Facility for metals along with the important characteristics of each. 1. Strong Acid Cation •- The important characteristics of this resin type are: The exchange capacity is not affected by the pH of the solution, it is tht least expensive resin, it is the most durable and its selectivity is low so it may pick up hardness in the water. 2. Weak Acid Cation - Important characteristics are: The exchange capacity is reduced at a solution pH below 6, it will tend not to pick up water hardness because the selectivity for heavy metal is higher and it is a more expensive resin than the strong acid but a smaller amount of reagents are needed to reverse the reaction and regenerate the resin. 3. Strong Base Anion - Important characteristics are: The exchange capacity is unaffected by solution pH, it is generally more expensive than the cation resins, it has a shorter functional life span than cation resins and the resin can be fouled by organics in the solution. 4. Weak Base Anion - Important characteristics are: The exchange capacity is reduced above a solution pH of 7, the resin cost is the same as the strong base anion, and less reagent is necessary for resin regeneration than for the strong base anion resin. 5. Heavy Metal Chelating Resins - Important characteristics are: It has a higher selectivity for heavy metals than does the weak acid cation resin so it can separate heavy metals from high levels of water hardness in the solution, reduced amounts of reagent are required for regeneration, it is the most expensive resin type, and removal of heavy metals is effective above a solution pH of 4. The ion exchange resins are housed in a canister which is attached to a drain pipe in the rinse tank (see Figure 2). The rinse solution flows through the canister, the metal is removed allowing the exiting water to flow to the sewer. When the exchange capacity of the canister (containing the resins) is reached, it is replaced by a fresh one. Saturated canisters are transported to the Facility and regenerated. Regeneration is accomplished by flushing the resins with a concentrated acid or base solution, depending on the resin type, which effec tively reverses the exchange reaction. A-3