Ions are electrically charged atoms or molecules found in water that have either a net negative or positive charge. For many applications that use water as a rinse or ingredient, these ions are considered impurities and must be removed from the water. Demineralization therefore requires using at least two ion types exchange resins to produce deionized water. One resin will remove positively charged ions and the other will remove negatively charged ions. However, Ions conduct electricity. Notice, Electrical current passes through water using ions as stepping stones. By measuring the electrical conductance of water can tell us what the ionic content of the water is. Less ions in the water will make the passage of electricity more difficult. Water with a lower conductivity value is considered more deionized than water with a high conductivity value. Anyway, In a dual bed system, the cation resin is always first in line. All positively charged cations are attracted to the cation resin bead and exchanged for hydrogen, as city water enters the tank filled with cation resin.
The negatively charged anions are not attracted to the cation resin bead and pass through.
We have to examine calcium chloride in the feed water.
In solution, the calcium ion is positively charged and will attach itself to the cation bead and will release a hydrogen ion. Also, The chloride has a negative charge and therefore would not attach itself to the cation resin bead. Generally, whenever forming hydrochloric acid, The hydrogen, that has a positive charge, will attach itself to the chloride ion. The resulting effluent from a SAC exchanger will have a very low pH and a much higher conductivity than the incoming feed water. Now pay attention please. Most of the exchange sites on the cation and anion resin beads are used up and the tank no longer produces deionized water.
At this point, the resin beads require regeneration to prepare them for use again.
In a mixed bed system, the strong acid cation and strong base anion resin are intermixed.
This effectively makes the mixed bed tank act like thousands of dual bed units in one tank. The cation/anion exchange is taking place over and over within the resin bed. It’s a well Sodium leakage is addressed because of the sheer number of repeated cation/anion exchanges taking place. By using a mixed bed you can produce the highest quality of deionized water possible. You see, Ion exchange resins are used to produce deionized water. These resins are small plastic beads that are composed of organic polymer chains that have charged functional groups built into the resin bead. Each functional group has either a fixed positive or negative charge. Of course The effluent from the cation resin will consist of strong and weak acids. On p of that, This acidic water will thence enter a tank filled with anion resin. Now look. The anion resin will attract negatively charged anions similar to chloride and exchange them for hydroxyl. Essentially, The result is hydrogen and hydroxyl, that forms H20. Usually, Different ions are attracted to a resin bead with different strengths.
Calcium is more strongly attracted to a cation resin bead than sodium is.
The hydrogen on the cation resin bead and the hydroxyl on the anion resin bead do not have a strong attraction to the bead.
This is what allows ion exchange to take place. I know that the cations are exchanged for hydrogen, as positively charged cations flow across cation resin beads. As negatively charged anions flow across anion resin beads, likewise the anions are exchanged for hydroxyl. When you combine hydrogen and hydroxyl you form pure H20. In order to produce deionized water, cation resin is regenerated with Hydrochloric Acid. The Hydrogen is positively charged and therefore attaches itself to the negatively charged cation resin bead. On p of this, The anion resin is regenerated with sodium hydroxide. Hydroxyl is negatively charged and attaches itself to the positively charged anion resin bead. Ions with a positive charge are called Cations and ions with a negative charge are called Anions.