Typical Ion Exchange Capacities of Zeolites

1
Typical Ion Exchange Capacities of Zeolites
2
Selectivity Series for Zeolite A

• Zeolite A
• AggtTlgtNagtKgtNH4gtRbgtLigtCs
• ZngtSrgtBagtCagtCogtNigtCdgtHggtMg
• Used in detergents for water softening (replacing
  Ca2 and Mg2 with Na)

3
Ion-exchange isotherms for Li, K, Ag, and Ca
on zeolite NaA at 25 C Total concentration in
aqueous phase 0.1 N
4
Figure . Ion-exchange isotherms on zeolite X,
sodium form. X equivalent fraction in zeolite, X
equivalent fraction in solution.
5
Zeolites as Detergent Builders

• Detergent Builders The prime function of
  phosphates in detergents is to reduce the
  activity of the hardness ions, Ca2 and Mg2, in
  the wash water by complexing. Zeolite ion
  exchangers in powder form replace Ca2 and Mg2
  in thes olution with ions such as Na. Heavy-duty
  detergents employ the sodium form of Type A
  zeolite for this purpose in low or zero-phosphate
  formulations. The zeolite powder is incorporated
  into the detergent powder during formulation.
  Large amounts of zeolite are used in this
  application.

6
SEM Micrographs of Clinoptilolite sample from
Gördes (MANISA)
7
Selectivity Sequence of Clinoptilolite( according
to different literature)
8
Uses of Clinoptilolite in Ion Exchange

• Removal of Ammonium ion (NH4) from wastewater
• Removal of radioactive 137Cs and 90Sr2 from
  radioctive waste streams
• Removal of heavy metals like Pb2 and
• Cd2 from wastewaters (potential )

9

• WHY REMOVAL OF AMMONIUM IS NEEDED ?
• ? toxic to fish aquatic life
• ? contribute to explosive algal growth
  promoting eutrophication
• ? dissolved oxygen reduction
• ? corrosive to certain metals materials of
  construction
• detrimental effect on disenfection of water
  supplies
• allowable concentration at 180 C and pH5-7 ? 2
  mg/l

10
Zeolites in radioactive waste treatment

• Removal Cesium and Strontium Radioisotopes 
• Because of their stability in the presence of
  ionizing radiation and in aqueous solutions at
  high temperatures, molecular sieve ion exchangers
  offer significant advantages in the separation
  and purification of radioisotopes.
• Their low solubility over wide pH ranges,
  together with their rigid frameworks and
  dimensional stability and attrition resistance,
  have endowed zeolites with properties which
  generally surpass those of the other inorganic
  and organic ion exchangers.
• The high selectivities and capacities of several
  zeolites for cesium and strontium radioisotopes
  resulted in the development of processes
  currently used by nuclear processing plants.

11
Equipment Types

• Batch
• Fixed bed
• Fluididized bed
• Continuous countercurrent

12
Batch Operations
Stirred tanks are used for batch contacting,
with an attached strainer or filter to remove the
resin beads from the solution after equilibrium
conditions are approached. Agitation is mild to
avoid resin attrition, but sufficient to achieve
complete suspension of the resin.
13
Fixed Bed Operation

• Semicontinuous and continuous systems are, with
  few exceptions, practiced in columns.
• Most columnar systems are semicontinuous since
  flow of the stream being processed must be
  interrupted for regeneration.
• Columnar installations almost always involve the
  process stream flowing down through a resin bed.
  Those that are upflow use a flow rate that either
  partially fluidizes the bed, or forms a packed
  bed against an upper porous barrier or
  distributor for process streams.

14
An industrial ion-exchange column a)
Distributor b) Resin c) Collector
15
Figure Examples of strainers used for industrial
water-softening plants A) Simple plate strainer
B) Double strainer for two-chamber floating
beds
16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
Fixed Bed Cycle

• Sorption(loading)
• Backwash
• Regeneration
• Rinsing

20
Sorption(loading)

• Impurities are removed, or valuable constituents
  recovered, from a process stream during the
  adsorption step, which is also referred to as
  loading or exhausting the resin.
• Performance is rated primarily on meeting
  objectives for completeness of removal.
• Performance is also rated on operating capacity,
  frequency of regeneration, and operational costs.
• Variables affecting performance include resin
  selection, solution chemistry, operating
  conditions, and equipment design. All are
  interrelated in varying degrees.
• Completeness of removal improves by using a resin
  more selective for that constituent. Using a
  resin having a selectivity substantially greater
  than required for the process stream generally
  results in lower operating capacity, more
  frequent regenerations, higher operating costs,
  and higher capital investment. For example,
  strong acid rather than weak acid cation
  exchangers are used to soften water supplies

21
Operating Capacity in fixed bed operation

• is defined as proportion of total(equilibrium)
  capacity used during the exchange process,
  depends on
• Concentration and types of ions to be sorbed
• Rate of percolation
• Temperature
• Depth of resin bed
• Type, concentration and quantity of regenerant

22
(No Transcript)
23
Backwash

• Process streams may contain small suspended
  particles which are collected on top of the
  resin bed, and penetrate deeper down causing an
  increase pressure drop across the bed.
• Water is passed up through a bottom distributor
  at a flow rate sufficient to expand the resin bed
  by 50100, and exits the top of the column No
  resin, other than a small amount that may have
  undergone physical degradation, should escape the
  unit as long as the column was designed to
  accommodate that degree of expansion . Tap water
  may be used as backwash. Backwash frequency
  varies from one installation to another

24
Regeneration

• The regeneration step is also called elution..
• Regeneration is of much shorter duration than the
  adsorption step.
• The combined time for backwashing, regeneration,
  and rinse is usually not longer than two hours.
  The time is shortened using a smaller volume of
  regenerating chemicals at a higher concentration,
  or by increasing the regenerant flow rate.
• Flow rates commonly used for regeneration in
  terms of bed volumes (BV) are between 4 6 BV/h,
  but 2 BV/h is preferred in many cases

25

• Cation exchangers are regenerated with mineral
  acids when used in the H form.
• Sulfuric acid is preferred over hydrochloric
  acid , HCl, in many countries because it is less
  expensive and less corrosive.
• However, the use of hydrochloric acid is the
  best method of overcoming precipitation problems
  in installations which deionize water with high
  concentrations of barium or calcium compared to
  other cations.
• A 4 acid concentration is common, although
  sulfuric acid regenerations may start as low as
  0.81 to minimize calcium sulfate precipitation.

26

• Strong base anion exchangers must be regenerated
  with sodium hydroxide when used in the OH- form.
• Potassium hydroxide is a more expensive
  alternative.
• Weak base anion exchangers may be regenerated
  with solutions of ammonium hydroxide , NH4OH, or
  sodium carbonate , Na2CO3, although NaOH is more
  common. The most common concentration for basic
  regenerating solutions is 4.

27
Co-flow and coounterflow regeneration
28

• Mixed-bed resins cannot be regenerated until the
  two resins are separated by backwashing. Each
  resin is regenerated separately. The cation
  exchanger should not be in contact with the NaOH
  solution used for the anion exchanger. The anion
  exchanger should not be in contact with the acid
  solution used to regenerate the cation exchanger.
  

29
Rinsing

• When transfer of the required volume of
  regenerating solution to the column has been
  completed, a small amount of regenerating
  solution occupies space immediately above the
  resin bed, between resin particles in the bed,
  and within the resin particles.
• It must be displaced with water before the column
  can be returned to the adsorption step.
• Rinsing should begin at the same flow rate as
  used during regeneration and continue at that
  rate until a volume of water equal to 12 bed
  volumes has been used. After that, the flow rate
  is increased to the rate normally used during the
  adsorption step, and continued at that rate until
  the effluent is of satisfactory quality, as
  determined by pH, conductivity, or resistivity. .
  

30
(No Transcript)
31
The Himsley contactor has a series of trays, on
each of which the resin beads are fluidised by
the upward flow of liquid. Periodically, the flow
is reversed to move incremental amounts of resin
from one stage to the stage below. The batch of
resin at the bottom is lifted to the wash column,
then to the regeneration column, and then back to
the top of the ion exchanger column for re-use.
32
Higgins contactor operates as a moving, packed
bed by using intermittent hydraulic pulses to
move incremental portions of the bed from the
contacting section, where ion exchange takes
place, up around and down to the backwash
section, down to the regeneration section, and
back up through the rinse section to the
contacting section to repeat the cycle. Liquid
moves counter-currently to the resin
33
Mixed Bed Operations
34
Mixed Bed Ion Exchange
35
Figure Mixed-bed ion-exchange system a)
Breather b) Raw water distributor c) Sodium
hydroxide distributor d) Intermediate collector
e) Strainer rack
 
36
Figure . Small-scale water softener a) Control
unit b) Resin c) Solid salt d) Saturated brine