Weakly Acidic Cation (WAC) - De-alkalisation Flashcards
What do WAC resins primarily remove from water?
Calcium and magnesium associated with temporary hardness
This process also results in the removal of alkalinity.
What is the process called when alkalinity is removed by WAC resins?
De-alkalisation
What functional groups are present in WAC resins?
Carboxylic acid functional groups
What ion is exchanged for calcium ions in the WAC ion exchange process?
Hydrogen ions (H+)
What is formed when hydrogen ions are released during the exchange process?
Water and CO2
What is the chemical reaction for the exchange of calcium ions in WAC?
Ca(HCO3)2 + 2 resin-H → (resin)2-Ca + 2H2O + 2CO2
How are WAC ion exchanger units regenerated?
Using strong acids such as hydrochloric or sulphuric acid
What are the products of regeneration using hydrochloric acid?
2 resin-H + CaCl2
True or False: The effluent produced during regeneration is highly acidic.
False
What happens to the pH of water as it passes through the WAC?
The pH drops slightly
What form does temporary hardness take after the exchange process?
Carbonic acid (H2CO3)
What ions are not removed by the WAC process?
Permanent hardness ions such as magnesium and sodium salts
At what pH does the majority of dissolved carbon exist as carbonic acid?
Below pH six
What is the primary form of carbon that leaves the WAC resin bed?
Carbonic acid
How is CO2 removed from the water after the WAC process?
Using mechanical aeration or a degasser membrane system
What is the purpose of adding sodium hydroxide (NaOH) after degassing?
To adjust the water’s pH back to the target value
Fill in the blank: The water is now dealkalised, with all _______ removed.
Temporary hardness (alkalinity)
What alternative exchange ion can be used instead of hydrogen ions?
Sodium ions (Na+)
What is the regeneration solution used when sodium is the exchange ion?
Sodium chloride solution
What is the equation for the removal of temporary hardness using sodium as the exchange ion?
Ca(HCO3)2 + 2Resin-Na → (Resin)2-Ca + 2NaHCO3
True or False: Changing the exchange ion from H+ to Na+ doubles the volume of the resin.
True
What type of resin can also be used to remove calcium and magnesium?
Strongly acidic cation exchange resin
