A mixed bed DI tank contains which components?

• A. Cations and Anions
• B. Only Cations
• C. Only Anions
• D. Water and minerals

Answer: (A)

A mixed bed DI tank uses both cation and anion exchange resins together to remove all ions from water. The cation resin swaps positive ions (like calcium, magnesium, sodium) for hydrogen ions, while the anion resin swaps negative ions (like chloride, sulfate, bicarbonate) for hydroxide ions. The hydrogen from the cation resin and the hydroxide from the anion resin combine to form water, so the water becomes highly deionized. If only one type were present, you'd remove either cations or anions, but not both, leaving mineral ions in the water. Hence, the tank contains both cations and anions.