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Ion exchange(ionex)

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Separation method based on exchange of dissolved ions onfunctional groups fixed on matrix .

Ionex (ion exchanger (IX)) - compound able to exchange ions

inorganic (zeolites) and organic materials, nowadays mainly

functionalised organics polymers

Cation exchanger - ionex exchanging positive charged ions

Anion exchanger - ionex exchanging negative charged ions

Chelating ionex - dissolved species are captured by coordinationbonding with ionex. More selective.

Ion exchange

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• enable to capture ions from very diluted solutions and

concentrate them

• selective - special ion exchangers designed to separate only one

type of ions (e.g. nitrates).

Advantages

Disadvantages

- additional chemicals necessary (regeneration) - waste solutions formation

- low efficiency in case of high concentration

- fouling of columns - pretreatment necessary

- risk of biological contamination

- periodically interrupted

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Ion exchangers• inorganic or organic materials , today mainly synthetic

polymers (polystyrene, polyacrylate) (resins)

• form of particles (spheres) – particle size has influence to the kinetics and pressure drop in IX column

• IX matrix – wide polymer molecule forming IX particle

strong base resin – anion exchanging

strong acid resin – cation exchanging

http://www.purolite.cz

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capacity

• amount of active groups (multiplied by its charge) in IX relatedto the IX volume (val.dm-3) or mass in dry state (val.kg-1) – totalcapacity

• operating capacity – number of active groups in given volumeused in given process

IX - characteristics

selectivity

• preferred bonding of specified ion based on affinity towards IXactive group

degree of swelling

• osmotic pressure causes expansion of matrix (active groupsfixed in IX decrease its concentration by attracted water)

• volume changes are important from technological point of view

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Column operation

• most frequent arrangement (filter press principle)

• equilibrium at each level => low output concentrations

• working cycle

sorption – capture of ions

regeneration – displacement of captured ions

rinsing – remaining parts of reg. solution

backwash – to eliminate resin compaction + suspended items removal

IX column: A inlet; B outlet of treated water; C rinsing inlet; Drinsing outlet; E reg. soln inlet; F reg. soln. outlet; G flow distribution

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Treatment of wastes

• radioactive item concentration and repository

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Treatment of wastes

• heavy metal contaminated waste water

• decontamination of ground water

Metsep process pro regeneration of waste HCl in IX column for Zn and Fe separation.

http://www.remco.com/ixidx.htm

old circuit boards treatment

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Membrane separation processes

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Fundamental principle – selective transport of componentsacross the membrane by the driving force. Ions, molecules,colloids, etc. can be transported.

Membrane – nonideal semi permeable barrier with preferredtransport of one component from entering stream to product stream

permeability– amount of flux across the membrane

selectivity– ability to separate various items

Membrane separation processes

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Advantages• separation of components without change of state at ambient

temperature

• simple automation and continuous process

• simple arrangement – easy scalable

• low energy consumption related to “classical methods”

• zero-emission technological blocksDisadvantages/limitation

• membrane poisons

• compounds solubility – precipitation on membrane surface

• membrane material requirements, price

• used membrane treatment

concentration polarisation

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Membrane categorization

• symmetric

structure and pore size same across all membrane thickness

usually formed by one type of material

• asymmetric

separation layer on porous support

one or more materials (composite)

structure

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Membrane modules

• flat sheet

a) sheet fixed in frame

b) circular disc

• tubular (tubular module) –

similarity to candle filtration

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Membrane modules II

• spiral wound - membranes scrolled

• hollow fiber

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polymer or ceramics

Membrane material

D dialysis, EP electrophoresis, GS gas separation, MF microfiltration, NF nanofiltration, RO reverse osmosis, UF ultrafiltration

(Sterlitech™) PolyethersulfoneUltrafiltration Membrane

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Membrane processes

membrane process scheme

feed

concentrate (retentate)

permeate (diluate)

driving force process

conc. gradient diffusion, osmosis, dialysis, pervaporation

pressure gradient reverse osmosis, ultrafiltartion, microfiltration

el. potential electrodialysis, electrogravitation, electrophoresis,

temperature gradient thermoosmosis, membrane destilation

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Pressure membrane processes

driving force - external pressure gradient over membrane

Process pore size [nm]/ rejected compound size [D]

smallest rejected compounds

MF

UFNFRO

50-1000 nm

3-50 nm/1000-106 D1-3 nm/200-1000 Dpod 1 nm / pod 200 D

suspension, miocroorganisms, colloidsmacromolecules, organic comp.multivalent saltssalts

MF -microfiltration, UF - ultrafiltration, NF - nanofiltration, RO - reverse osmosis

• for waste treatment the most frequent application RO/NF(ions separation) andUF (organic polutants separation)

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Pressure membrane processes

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Reverse osmosis

galvanic Ni plating rinsing water regeneration

http://www.gewater.com/library/tp/771_Application_of.jsp

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UltrafiltrationUse significantly lower pressure (0,1-1MPa)

than RO - low price

suitable for organics polutants (oil, ink, etc.)

UF FEED

Typical ultrafiltration flexographic ink feed.Total solids % : 0.5-2; average 0.75 Suspended solids (mg/l) : 300-10,000; average 5,600PH : 5.6-9.3; average 7.5 Chemical Oxygen Demand : 8,000-80,000; average 4,000 Biological Oxygen Demand : 3,340 - 66,000; average 31,000

UF PERMEATE

Typical ultrafiltration of flexographic ink permeates.Total solids % : 0.6-0.62; Suspended solids (mg/l) : 4-40; average 23PH : 4.6-9.3; average 6.8 Chemical Oxygen Demand : 8,00-9,300; average 3,700 Biological Oxygen Demand : 160-6,000; average 2,900

UF CONCENTRATE

Typical practical concentrates of approximately 25% total solids can be achieved via Prep-Tec tubular ultrafiltration systems. Final solids levels of > 30% total solids have been achieved at the expense of more intensive membrane cleaning procedures

Prep-Tec UF system 2m3 / den

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Electromembrane processes

separation of charged ions by migration in electric field.

driving force - electric field

electrodialysis (ED) and electrodeionisation (EDI),

electrophoresis, membrane electrolysis, electrogravitation

suitable for low concentrated solutions treatment

often applied in connection to pressure membrane process

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Ion exchange membranes

ion exchange (ion selective) membrane - foil or sheet prepared from

ion exchanger

main task isn’t ion exchange but selective transport across

charge of active groups in membrane is compensated by ions with

opposite charge - counterions

occurrence of membrane defects causes penetration of ions charged

as active groups fixed in membrane

similarly to ion exchangers:

Cation selective - enables transport of positive charged ions

Anion selective - enables transport of positive charged ions

bipolar - (special kind) membrane consisting from cation and anion

selective layers

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Ione exchange membrane structure

With respect to the structure and preparation way:

Homogeneous - produced by incorporation of active groups to the

polymer film. They are formed only from ion exchanging material.

Most often based on styrenne or vinylpyridine copolymers,

crosslinked by divinylbenzene.

Heterogeneous - dispersion of ion exchanger material in inert

support. Inert support provide mechanical properties and IX material

provide ionic selectivity. Distribution of IX material and optimal

balance between inert matrix and IX material are crucial points in

membrane preparation.

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Electrodialysis

application of direct electric current on dissolved ions cause

migration of ions to the opposite charged electrode.

ion selective membrane enable transport of ions with only one

polarity - cation and anion selective membrane forms together

chambers:

diluate chamber - treated stream

concentrate chamber - stream with concentrated solution

electrodialyser contain hundreds of membrane chambers

arrangement - „filter press“, periodically contains diluate and

concentrate chambers

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Electrodyalysis scheme

D - diluate chamber, K- concentrate chamber, AM - anion selective membrane, KM - cation selective membrane

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Application of electrodialysis

• sea water desalination

• recycling of rinse water in galvanoindustry

• waste water treatment and chemicals recycling in chemical

industry

• radioactive solutions treatment

• desalination of organics compounds (glycerine, CMC)

www.mega.cz

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Electrodialysis limitations• concentration polarisation

• fouling of chambers and membrane surface

• membrane poisons

• limiting current density

• pressure drop

Possible operation modes

Continuous Batch

Operation:• batch• feed and bleed• one-pass

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Electrodialyser

spacer - separation of membranes

Single parts together forms stack

possible arrangement of diluate flow space

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Electrodialyser ED-IIType: ED-II-2/200

Nr. of installed membranes 200 cell pairs, (max. effective area 166 m2)

Dimension of the membrane 400 x 1600 mm, effective 320 x 1300 mm

Membranes– RALEX AM, CM 200 + 210 pieces

Dimension of the spacer 810 x 1610 mm, thickness 1 mm

Spacers– work., electr., inter. 400 + 4 + 2 pieces, PE

Electrode frame and sealing 2 pieces PP 10 mm, 2 pieces EPDM 1 mm

Electrodes– anode, cathode 4 pieces, Ti + Pt (Ru), stainless-steel

End plates (frames) 2 pieces, PP 20 mm and stainless-steel

Dimensions, weights 500 x 960 x 1750 mm, empty 600 kg, w.water850 kg

Operation limits: ED-II-2/200

DC el. power max. 400 V / 120 A

Pressure inlet / outlet,difference operational 50 kPa, max. 80 kPa / max. 10 kPa

Flow D, K approx. 10 m3/hr at 50 kPa, E min. 3 m3/hr

Temperature operationapprox. 30oC, max. 40oC

TSS max. 10µm, max. 10 ppm

F-, (Cl-) max. 5 ppm in electrode solution

MEGA a.s.

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Electrodialysis of Ni rinse water

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Electrodialysis with bipolar membrane

Special arrangement of electrodialyser. Water dissociate inside bipolar membrane and H+ a OH- ions are introduced to the neighboring chambers

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Electrodeionisation (EDI)combination of ion exchange and electrodialysis

continuous process for highly diluted solutions

diluate chamber filled with ion exchanger (mixed bed or selective)

ion exchanger increase conductivity of diluate chamber

ion exchanger is continually regenerated by OH- a H+ ions

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Electrodeionisation (EDI)

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Summary

• all mentioned methods have their own advantages and limitations

• suitable application of any methods need individual judgment

• efficiency increase by methods combination

• in case of waste treatment methods is desired formation of commercially attractive products.

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Recommended literature

• Ullmann's Encyclopedia of Industrial ChemistryPublished by Wiley-VCH Verlag GmbH & Co. KGaA

• Perry's Chemical Engineers' Handbook, by Robert H. Perryand Don W. Green McGraw-Hill Inc.

• best available techniques – BAT, reference documents BREF http://eippcb.jrc.es/