Water softening process - Base Exchange process

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It is the most simple and used process. Water obtained by using this process has a hardness of 0-2⁰. Water is softened by exchanging Ca²⁺ and Mg²⁺ ion with the help of zeolite. That’s why it is also called Zeolite or permutit process. While water is passed into Zeolite the ions are exchanged. Zeolite is the Hydrated silicate of sodium and aluminium. The general formula is:

(Na₂O)_x(Al₂O₃)_y(SiO₂)_z(H₂O)_n

Let, Zeolite = Z = (Al₂O₃)_y(SiO₂)_z(H₂O)_n

For temporary hardness:

Ca(HCO₃) + Na₂O.Z --> CaO.Z+ Na₂CO₃ + H₂O

Mg(HCO₃) + Na₂O.Z --> MgO.Z + Na₂CO₃ + 2H₂O

For permanent hardness:

CaSO₄ + Na₂O.Z --> CaO.Z + Na₂SO₄

MgSO₄ + Na₂O.Z --> MgO.Z + Na₂SO₄

MgCl₂ + Na₂O.Z --> MgO.Z + NaCl

Process:

Zeolite are taken into the tank. Then hard raw water is entered into the inlet pipe. While water comes to the contact of Zeolite in Zeolite bed, the water softened. Then soft water is collected from  downward outlet.

Regeneration:

When water is softened by this process for many times Zeolite is exhausted. For this reason, Zeolite is not used for every time while softening water. 10% NaCl is used through the Zeolites and the Zeolites are regenerated again.

CaO.Z + 2NaCl --> Na₂O.Z + CaCl₂