8/14/2019 Ion Exchange.pdf
1/26
Ion Exchange
8/14/2019 Ion Exchange.pdf
2/26
Ion exchange
Ion exchange is an adsorption phenomenon where the
mechanism of adsorption is electrostatic. Electrostatic forces
hold ions to charged functional groups on the surface of the
ion exchange resin. The adsorbed ions replace ions that are
on the resin surface on a 1:1 charge basis. For example:
8/14/2019 Ion Exchange.pdf
3/26
8/14/2019 Ion Exchange.pdf
4/26
Applications of ion exchange in water & wastewater
Ca, Mg (hardness removal) exchange with Na or H.
Fe, Mn removal from groundwater.
Recovery of valuable waste products Ag, Au, U Demineralization (exchange all cations for H all anions
for OH)
Removal of NO3, NH4, PO4(nutrient removal).
8/14/2019 Ion Exchange.pdf
5/26
Ion Exchangers (types)
Natural: Proteins, Soils, Lignin, Coal, Metal oxides,
Aluminosilicates (zeolites) (NaOAl2O3.4SiO2).
Synthetic zeolite gels and most common -polymeric resins
(macroreticular, large pores).
8/14/2019 Ion Exchange.pdf
6/26
Polymeric resins are made in 3-D networks by cross-linking
hydrocarbon chains. The resulting resin is insoluble, inert and
relatively rigid. Ionic functional groups are attached to this
framework.
8/14/2019 Ion Exchange.pdf
7/26
8/14/2019 Ion Exchange.pdf
8/26
These resins are generally manufactured by polymerizing
neutral organic molecules such as sytrene (to form polystrene)
and then cross-linked with divinyl benzene (DVB). Functional
groups are then added according to the intended use. For
example the resin can be sulfonated by adding sulfuric acid to
get the structure shown above.
8/14/2019 Ion Exchange.pdf
9/26
8/14/2019 Ion Exchange.pdf
10/26
Divinylbenzene
8/14/2019 Ion Exchange.pdf
11/26
Ion Exchange Resin:
8/14/2019 Ion Exchange.pdf
12/26
Resin classification:
Resins are classified based on the type of functional group
they contain and their % of cross-linkages
Cationic Exchangers:
- Strongly acidic functional groups derived from strong acids
e.g., R-SO3H (sulfonic).
- Weakly acidic functional groups derived from weak acids,
e.g., R-COOH (carboxylic).
8/14/2019 Ion Exchange.pdf
13/26
Anionic Exchangers
- Strongly basic functional groups derived from
quaternary ammonia compounds, R-N-OH.
- Weakly basic - functional groups derived from primary
and secondary amines, R-NH3OH or R-R-NH2OH.
8/14/2019 Ion Exchange.pdf
14/26
Ion Exchange
Ion Exchange Process exchanges undesirable ions contained in
the raw water with more desirable ones that produces
acceptable BFW (BoilerFeed Water).
For example, in the sof teni ng pr ocess, calcium and
magnesium ions are exchanged for sodium ions. In
dealkalization, the ions contributing to alkalinity (carbonates,
bicarbonates, etc) are removed and replaced with chloride
ions. Demineralizationin this process replaces all cations with
hydrogen ions (H+), and all anions with hydroxyl ions (OH)
making pure water (H+ +OH).
8/14/2019 Ion Exchange.pdf
15/26
The ion exchange material needs to be regenerated after a
period of operation.
The operating period will differ from process to process andwill depend to some extent on the amount of impurities in the
water and the required purity of the treated water.
8/14/2019 Ion Exchange.pdf
16/26
Regeneration
Regeneration is accomplished in three steps
1. Back washing
2. Regenerating the resin bed with regenerating chemicals
3. Rinsing
8/14/2019 Ion Exchange.pdf
17/26
Ion exchange unit
8/14/2019 Ion Exchange.pdf
18/26
8/14/2019 Ion Exchange.pdf
19/26
8/14/2019 Ion Exchange.pdf
20/26
8/14/2019 Ion Exchange.pdf
21/26
Under operating conditions the raw water is introduced
through the top connection and distributor. The water flows
through the resin bed where ion exchange takes place.
The treated water is removed via the bottom connection.
Under regeneration operation, raw water as backwash is
introduced through the bottom connection and removed from
the top connection.
8/14/2019 Ion Exchange.pdf
22/26
8/14/2019 Ion Exchange.pdf
23/26
This is done by introducing a stream of raw water at the top
connection and removing it from the bottom connection. This water
is also disposed to waste.
Normally ion exchange units are installed in pairs. When one is
operating the other is being regenerated.
An automatic switch over of electronically controlled valves takes
the pair of units through the correct cycles at the prescribed time
intervals, without disrupting the treating process
8/14/2019 Ion Exchange.pdf
24/26
Ion Exchange
The interior is generally treated to protect the tank against corrosion
from the salt.
The units are normally of the downflow type, and the size and
volume of the units are dictated by the hardness of the water and the
volume of treated water needed to be produced between each
regeneration cycle.
Resin is supported by an underdrain system that removes the treated
water and distributes brine evenly during regeneration. Minimum
depth of resin should be no less than 24 inches above the underdrain.
8/14/2019 Ion Exchange.pdf
25/26
Ion Exchange
Ion-exchange does not alter thewaterspH or alkalinity.
The stability of the water is altered due to the removal of calcium
and magnesium and an increase in dissolved solids.
For each ppm(parts permillion) of calcium removed and replaced
by sodium, total dissolved solids increase by 0.15 ppm.
For each ppm of magnesium removed and replaced by sodium, total
dissolved solids increase by 0.88 ppm.
8/14/2019 Ion Exchange.pdf
26/26
Special Ion Exchangers - Commercially Available