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Methods of water
treatment part 2
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Types of ion exchangers
Anionic (exchange anions)
Cationic (exchange cations)
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Polymer ion exchange resin
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Ion exchange in column
A
Exchanger saturated with ion B
Exchanger saturated with ion A
B B B + A
A A
B
B +A A
B
I II III IV V
OperationRegeneration
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Use of ion exchange in water technology
Softening
Strong acid (SA) exchanger in Na+ form
Dealkalization
Weak acid (WA) exchanger in H+ form
Demineralization
Strong acid in H+form Strong base (SB) in OH- form
Mixed bed exchanger
Nitrate removal
Strong base in Cl- form
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Strong acid cation exchanger
-SO3- functional group Exchange cations
Use
For softening in Na+ form
As a first step of demineralization in H+form
Selectivity:Ca2+>Mg2+>Na+ >H+
Water temperature up to 120 oC
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Softening with strong acid exchanger
Ca2+
>Mg2+
>Na+
>H+
Mg(HCO3)
2NaNO3
Na2SO4
CaCl2
2 NaCl
2 NaHCO3
NaNO3
MgSO4
Totalhardenss =0
Process control:TH =0
Na+
Ca2+
Mg2+
Na+
HCO3-
Cl-
SO42-
NO3-
Na+
HCO3-
Cl-
SO42-
NO3-
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Uses of water softening
Removes total hardness and prevents
scaling
Constant water quality
Inexpensive treatment
Used for:
Boilers
Cooling plants
Drinking water
Industry
Home appliances (dish washers etc.)
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Strong base anion exchanger
Functional group -N(CH3)3
+
-N(CH3)2(CH2CH2OH)+
Exchanges anionsUses
As second step in demineralization inOH- form
Selectivity:SO4
2- >NO3- > Cl- > HCO3
- > OH-
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Application of demineralizationby ion exchange
For production of demineralized (distilled)water
For high pressure boilers
For different types of industries
More and more replaced by reverse osmosiswhich consumes less chemicals
Mixed bed ion exchange (less than 1 S/cmeffluent )
Regenerated separately
Separated by difference in density (strong acidexchanger is heavier)
Strong
acid H+
form
Strong
base OH-
form
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Principle of mixed bed operation
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Reverse osmosis desalination
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Typical RO desalination plantscheme
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Seawater composition inMediterranean (mg/L)
Chloride (Cl-) 21.200Sodium (Na+) 11.800Sulfate (SO4
2-) 2.950Magnesium (Mg2+) 1.403Calcium (Ca2+) 423Potassium (K+) 463Bicarbonate(HCO3
-) 145Bromide (Br-) 155Borate (BO3
3-
)
72Iodide (I-) 2Total dissolved solids
(TDS) 38.600
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Desalination of sea and brackishwater with RO