Hardness of Water : The capacity of water which restricts the formation of lather with soap is called hardness of water.
It is due to the presence of bicarbonates chlorides and sulphates of calcium and magnesium in water.
Permutit method for removal of permanent hardness of water This method is also called zeolite/ permutit process. Hydrated Sodium Aluminium silicate is zeolite/permutit. For the sake of simplicity, Sodium Aluminium Silicate (NaAlSiO4) can be written as NaZ. 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. Zeolite is the hydrated silicate of Sodium and Aluminium. The general formula is (Na4O)x (Al4O3)y (SiO2)z (H2O)n.
Let, Zeolite = Z = (Al2O3)y (SiO2 )z (H2O)n
CaSO4 + Na2.Z ➝ CaZ + Na2SO4
MgCl2 + Na2.Z ➝ MgZ + 2NaCl
Na2Z(s) + M++(aq) ➝ MZ(s) + 2Na+(aq)
Where M = metal.
Zeolite is taken into the cement tank. Then hard raw water is entered into the inlet pipe. When water comes in contact with zeolite, water is softened. Zeolite is not used for every time while softening water. 10% NaCl is used through the Zeolites and the Zeolites are regenerated again.
MZ(s) + 2NaCl(ag) ➝ Na2Z(s) + MCl2(ag)