This document discusses water demineralization using ion exchange. It explains that demineralization removes inorganic salts by using cation exchange resins to convert dissolved salts to acids and anion exchange resins to remove these acids. The purpose is to reduce conductivity and control pH. It describes how cation resins exchange hydrogen for raw water cations and anion resins exchange hydroxyl for anions. Together this forms water and embeds the anions in the resin, removing other weak acids. Cation resins are regenerated with acid then washing, and anion resins are regenerated with sodium hydroxide then washing.

1. WATER DEMINERALIZATION
Ashwani Kumar
NMIT,Bengaluru

2.  Demineralization is the removal of essentially all
inorganic salts. In ion exchange demineralization
hydrogen Cation exchange converts dissolved
salts to their corresponding acids, and basic
anion exchange removes these acids.
 Purpose
 Removal of ionic substances
 Reduction of conductivity
 Control of pH

4. Demineraliser Resins
 Cationic resins exchange positively charged functional
groups, for undesirable positive ions.
 With their functional groups in the hydrogen form, R – H,
“R” represents the exchange resin and “H” represents the
attached hydrogen ion.
 Anionic resins exchange negatively charged functional
groups for any undesirable negative ion.
 The hydroxyl ion, OH- (R—OH) is commonly used as the
functional group in an anion resin.

5. Principle Of Demineralization
 The demineralizer system consists of one or
more ion exchange resin columns, including a
strong Cation unit and a strong anion unit. The
Cation resins exchange hydrogen for raw water
cations as shown below:

6.  The anion resins exchange hydroxyl for raw water anions.
 In the example, the acids resulting from the Cation exchange
process react with the anion exchange resin. As a result we
form water and the anions are embedded into the resin.
 Other weak acids are also removed because the resin is
strongly basic.

7. Ion Exchange Reaction
water.freshformresult weaAssolution.inionsby the
exchangedareresintheinionsthat theisresultnetThe
RR
:followsasisreactionnetThe
arrow.by theindicatedasreactionreversibleaisThis
H
:waterformto
combineresinzingdemineraliby thereleasedionsThe
ions.chlorideandionssodiumform
tosdissociateitwaterindissolvedisNaClWhen
--
2
2





 
OHHClRNaClNaOHRH
OHOH
ClNaNaCl OH

9. REGENERATION
 Cation exchange resins are regenerated by
treatment with hydrochloric or sulfuric acid,
then washing with water.
 Anion exchange resins are regenerated by
treatment with sodium hydroxide (NaOH), then
washing with water.

11. Fig Showing:
Demineralizer