Separate bed vs mixed bed
Demineralization therefore requires using at least two types of ion exchange resins to produce deionized water. One resin will remove positively charged ions and the other will remove negatively charged ions.
In a dual bed system, the cation resin is always first in line. As city water enters the tank filled with cation resin, all positively charged cations are attracted to the cation resin bead and exchanged for hydrogen. The negatively charged anions are not attracted to the cation resin bead and pass through. For example, let’s 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. The chloride has a negative charge and therefore will not attach itself to the cation Resin bead. The hydrogen, which has a positive charge, will attach itself to the chloride ion, forming hydrochloric acid (HCl).The resulting effluent from a SAC exchanger will have a very low pH and a much higher conductivity than the incoming feed water.
The effluent from the cation resin will consist of strong and weak acids. This acidic water will then enter a tank Filled with anion resin. The anion resin will attract negatively charged anions such as chloride and exchange them for hydroxyl.The result is hydrogen (H+) and hydroxyl (OHD), which forms H20
In reality, a dual bed system does not produce true H20 due to “sodium leakage”. If sodium leaks past the cation Exchange tank, then it combines with hydroxyl to form sodium hydroxide, which has a high conductivity. Sodium Leakage occurs because sodium and hydrogen have a very similar attraction to the cation resin bead and Sometimes the sodium ion does not exchange itself for a hydrogen ion.
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. 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.
How are ions measured?
Ions conduct electricity. Electrical current passes through water using ions as stepping -stones to pass current from One conductive ion to another. As a result, by measuring the electrical conductance of water can tell us what the ionic content of the water is. Fewer ions in the water will make the passage of electricity more difficult. Therefore, Water with a lower conductivity value is considered more “deionized” than water with a high conductivity value.