Zeolite means boiling stone.

Principle:

Zeolite is hydrated sodium alumino silicate capable of exchanging reversible sodium ions for hardness producing ions in water. It is also use as softening of water. For water treatment we can use sodium zeolite ie. $Na_{2}Ze$

$Na_{2}O.Al_{2}O_{3}.xSio_{2}.yH_{2}O--\rightarrow$ Hydrated sodium alumino silicate.

Reactions-

$CaCl_{2}+Na_{2}Ze--\rightarrow CaZe+2NaCl$

$CaSO_{4}+Na_{2}Ze--\rightarrow CaZe+Na_{2}SO_{4}$

$Ca(HCO_{3})_{2}+Na_{2}Ze--\rightarrow CaZe+2NaHCO_{3}$

$MgCl_{2}+Na_{2}Ze--\rightarrow MgZe+2NaCl$

$MgSO_{4}+Na_{2}Ze--\rightarrow MgZe+Na_{2}SO_{4}$

$Mg(HCO_{3})_{2}+Na_{2}Ze--\rightarrow MgZe+2NaHCO_{3}$

$FeSO_{4}+Na_{2}Ze--\rightarrow FeZe+Na_{2}SO_{4}$

$MNSO_{4}+Na_{2}Ze--\rightarrow MnZe + Na_{2}SO_{4}$

FeZe and MnZe is not regenerated so it is not ideal for Mn and Fe

Regeneration-

When zeolite bed is saturated with Ca & Mg ions, they can be regenerated & reused. For regeneration we used chemical like Brine (conic.NaCl), Sodium nitrate $(NaNO_{3})$, sodium sulphate $Na_{2}SO_{4}$

NaCl is widely used because it has low m,ole wt. & obtained product is highly soluble. They can be readily soluble. Also they can be readily rinsed out from zeolite bed.

high pressure

Exhausted Ze + Brine------$\rightarrow$ Regenerated Ze+Washing

$CaZe+2NaCl--\rightarrow Na_{2}Ze+CaCl_{2}$

$MgZe+2NaCl--\rightarrow Na_{2}Ze+MgCl_{2}$

Advantages:-

i) Very low hardness of less than 15 ppm.

ii)Equipment is compact & occupying at less space.

iii) Different hardness is automatically adjusted.

iv) It is work under pressure.

v) Ions simply exchange with Na ion

Disadvantages:-

i) As compared to the lime soda process the dissolved solid is more in zeolite process since calcium & magnesium salts are replaced by sodium salts.

The presence of bicarbonate & carbonate generate $NaHCO_{3}$ & $Na_{2}CO_{3}$ in softened water. This alkalinity in water is not desirable since in boiler it leads to caustic embrittlement due to formation caustic soda.