1. Softening of Water : Softening can be done in two ways
External Treatment
Zeolite Process
Ion Exchange Process
Internal Treatment
Colloidal Conditioning
Phosphate Conditioning
Carbonate Conditioning
Calgon Conditioning
Treatment with Sodium Aluminate

2. Ion Exchange Process :
Cations like Ca2+ and Mg2+ and anions like Cl- and SO42- can be removed by cation and anion exchange resins.
Resins containing -COOH, -SO3H are capable for exchanging their H+ ions to cationic portion of minerals. It is called cation exchanger.
Resins containing –NH2 , NHCH3 are capable for exchanging the anionic portion of the minerals. It is called anionic exchanger.

4. Process :
Water is passed through cation and anion exchanger respectively.
Water coming out side from anion exchanger is completely free from cations and anions.
It is known as deionised water or demineralised water and it is pure as distilled water.

5. Regeneration :
Cation exchange resins are regenerated by passing a dilute solution of HCl through them.
Rca + 2HCl RH2 + CaCl2
Anion exchange resins are generated by passing a dilute solution of NaOH.
R’Cl2 + 2NaOH R’(OH)2 + 2NaCl

6. Advantages : Disadvantages :
Highly acidic or alkaline water can be treated.
Water of nearly zero hardness can be obtained.
Disadvantages :
Equipment is costly and expensive chemicals are needed.
If water contains turbidity then the output of process is reduced.

7. Internal Treatment: 1) Colloidal Conditioning :
This colloidal Substances get coated over the scale forming particles and thus the coalescence of this particles to a compact scale is prevented.
Thus the scale formed remains loose and non- sticky and can be easily removable.
starch and glue are colloidal conditioning agents.

8. Internal Treatment: 2) Phosphate Conditioning :
Scale formation can be avoided by adding sodium phosphate to boiler water.
Phosphate reacts with Ca and Mg salts and formed easily removable sludge.
3CaSO4 + 2Na3PO Ca3(PO4)2 + 3Na2SO4
If water is
- acidic then trisodium phosphate is used
- alkaline then sodium dihydrogen phosphate is used
- neutral then disodium hydrogen phosphate is used

9. 1) Electrodialysis :

10. Ions present in saline water migrate towards the oppositely charged electrodes because of applied E.M.F.
Movements of ions takes place through ion selective membranes.
Compartments with even number are filled with pure water and compartments with odd numbers filled with concentrated brine water when the process finish.
Thus the salinity from the water can be removed.

11. When two solutions of different concentration are separated by a semi permeable membrane, flow of solvent takes from a region of low concentration to high concentration, until the concentration is equal both sides. This process is called osmosis and reverse process is called reverse osmosis.
The driving force in this phenomenon is called osmotic pressure.
By this method pure water is separated from sea water.
Membranes used are cellulose, acetate, cellulose butyrate etc.