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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