Q. Write phosphate conditioning method for water softening with suitable chemical reactions. How it is different from soda lime method.
Phosphate conditioning: In high pressure boilers, scale formation can be avoided by adding sodium phosphate, which reacts with hardness causing substance of water, forming non adherent and easily removable soft sludge of calcium and magnesium phosphates, which can be removed by blow down operation.
3MCl2 + 2Na3PO4 = M3 (PO4)2 + 6NaCl
Where M = Ca+2 or Mg+2
Mainly employed phosphates are:
1. Sodium dehydrogenate phosphate (acidic) Na2HPO4
2. Disodium hydrogen phosphate (weakly acidic) Na2HPO4
3. Trisodium hydrogen phosphate (alkaline) Na3PO4.
Difference between phosphate conditioning and Lime-Soda method
This is internal treatment method.
This is external treatment method.
It just supplements the L-S process and is not meant to replace L-S.
It has its own importance and is meant that it is necessary.
In this appropriate sodium phosphates are added.
Calculated amount of L and S is added.