Ion exchange resins
  • Ion exchange resins

Ion exchange is a process in which, under certain conditions, resin attracts a positive or negative ion in a solution to reject another ion of the same sign. The majority of resins are manufactured from a polymer and have the appearance of granules or globules.

Resins can be classified in two categories:

  • cation exchange resins
  • anion exchange resins.

Cation exchange resins can be sub-divided into two groups, according to whether the exchange occurs in a high or low acidity environment. Anion exchange resins are distinguished according to the high or low alkalinity of the medium.

Ion exchange is the basis of procedures used for clearly defined applications such as water softening. Resin action can be perturbed by all types of impurity, and care must be taken to ensure that some of the water to be treated does not contain solids in suspension, and its turbidity must be low.

Water turbidity is induced by particles of inorganic materials (and its colour results from the presence of such particles).

Furthermore, resin regeneration must be obtained using very high purity salt (sodium chloride).

Water softening involves exchanging calcium and magnesium ions with sodium ions fixed by the resin. When there are no more, the resin must be regenerated. This regeneration phase is essential. The solution obtained from the sodium chloride gives an inverse ion exchange. A softener incorporating ion exchange resins reduces water hardness resulting from the presence of calcium and magnesium ions. It is measured by its hydrotimetric titre(HT) expressed in °f. For example, 1°f corresponds to a concentration of Ca++ ions of 4.008mg/L. Water, the titre of which is between 15 and 25°f is worth softening. Above 25°f, softening is strongly recommended.


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