use of ultra and nanofiltration ceramic membranes for desalination 2004 desalination

8/18/2019 Use of Ultra and Nanofiltration Ceramic Membranes for Desalination 2004 Desalination

1/7

E L S E V I E R

Desa lination 168 2004 ) 207-213

DES LIN TION

www.elsevier.com/locate/desal

U se o f ultra and nanofi ltration ceram ic m em bran es

for desalination

S . C o n d o m a A .

L a r b o t b*, S a a d A l a m i Y o u n s s i b, M . P e r s i n a

aIns ti tu t Europ~en des Membranes ( IEM), UMR 5635 CNR S EN SC M U M II , CNRS,

1919 Route de Mende, 34293 Montpel l i er cedex 5 , France

bLabratoire des Mat~riaux, Catalyse et Environnement F ST de Mohamm edia, B P 20650, Mohammedia, M aroc

Tel . +33 (4) 67 61 33 88; F ax +33 (4) 67 61 33 85; email: larbot@[email protected]

R e c e i v e d 1 3 F e b r u a r y 2 00 4 ; a c c e p t e d 2 0 F e b r u a r y 2 0 0 4

b s t r a c t

T h e f il tr a ti o n t e s t s o f e l e c t r o l y te s o l u t i o n s p e r f o r m e d w i t h d i f fe r e n t c e r a m i c m e m b r a n e s s h o w t h a t s a lt re j e c ti o n

d e p e n d s o n p H , s a lt n a t u r e a n d c o n c e n t r a t i o n . A s i mp l e c o r r e l a ti o n b e t w e e n s t r e a mi n g p o t e n t i a l a n d r e j e c t io n r a t e s e x i t s

a n d c o n f i r m s t h a t s tr e a m i n g p o t e n t i a l i s a r e l e v a n t p a r a m e t e r t o c h a r a c t e r i z e t h e s u r f a c e c h a r g e o f f i lt e r in g ma t e r i a l

d u r i n g t h e f i l t ra t i o n p r o c e s s .

Keywords M emb rane; Filtration; Electric interactions; Streaming potential

1 . In trodu c t i on

Fresh wa te r i s ve ry impo r t an t f o r a ll a spec ts o f

l i f e . Was t ewa te r , b r ack i sh wa te r and s eawa te r

t r ea tmen t i s a goo d so lu t i on a s a sou rce o f f r e sh

wa te r . Amo ng a l l t he t e chn iques u sed fo r de sa li -

na t ion , p r e ssu re -d r iven mem bran e p roces se s have

an im por t an t pos it i on . I f r eve r se o smos i s i s

known a s a c l a s s i ca l p roces s fo r de sa l i na t i on ,

*Correspond ing au tho r .

nanof i l t ra t ion NF ) and eve n u l t ra f il t ra tion UF) ,

i f me mb rane po re d i am e te r s a re l owe r t han

10 nm , can a l so be used . Th e in te res t in UF i s due

to the impor tan t f lux obta ined . D esa l ina t ion per -

f o rm a n c e s o f c e r a m i c m e m b r a n e s d e p e n d o n t h e

concen t r a t i on o f i ons and on t he complex i ty o f

the m ed ium to be f i lt e red , bu t a l so on t he t ype o f

m e m b r a n e m a t e r i a l . C e r a m i c m e m b r a n e s c o m -

mo n ly u sed a r e gene ra l l y mad e o f me ta l ox ide s ,

wh ich have an ampho te r i c behav iou r ; t hen t he

e l ec tr i c su r f ace cha rge depend s on t he pH o f t he

Pres ented at the Eu roM ed 2004 con ference on Desalination Strategies in South Med iterrane an Countries: Cooperation

between M edi terranean Countr ies o f Europe a nd the Southern Rim o f the Medi terranean. Sponsore d by the European

Desalinat ion Socie ty and Of fice Na t ional de l Ea u Potable, Marrakech, Morocco, 30 Ma y- 2 June, 2004.

0 0 1 1 - 9 1 6 4 / 0 4 / - S e e f ro n t ma t t e r © 2 0 0 4 E l s e v i e r B . V . A l l r ig h ts r e s e r v e d

doi ;10 .1016/ j .desal .2004.06.189


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208 S. Condom et al. / Desalination 168 2004) 207 -21 3

f i lt ered solution [1-4]. Thus , a phen om eno n of

repuls ion or a t trac t ion occurs be tween the ionic

species present in the solut ion and the charged

membrane. Besides the electrostat ic effects, the

size of the f i l tered species is also an othe r para-

meter which sho uld be c onsidered, par t icular ly i f

the solut ion conta ins complexed cat ions wi th

mineral or organic l igands.

In thi s work w e d iscuss the ef fects f rom the

results obtained for the f i l t rat ion of different

sa line solut ions us ing several ceramic m emb ranes

prepared by the sol gel route We also present the

corre la t ion of the m em bran e se lect ivi ty in terms

of re ject ion wi th the sur face charge deve loped on

the material surface.

2 Experimental

2 1 Mem bran e description

The membranes tes ted were , respect ively ,

ma de o f y alumin a, CoAI204, and TiO2/ZnA1204

(Table 1). The con di t ions for the preparat ion of

the t h ree membranes have been p rev ious ly

discussed [5-7]. The f i l ter ing layers were created

using the sol gel route: the sols were dep osi ted by

s l ip- cas t ing on the sur face of a tubular suppor t in

c¢ alum ina (200 n m of pore diameter) .

2 2 Filtration pilo t

The f i l t ra t ion exper im ents were car r ied out o n

a laboratory pi lot scale . The capaci ty o f the tank

was 2 L , the work ing pressure was f ixed between

0 and 10 bars by m eans of a ni t rogen gas bot tle ,

and the veloci ty ra te of the f luid was around

2.5 m .s -~. The f i l ter ing mo du le ha d a tub ular

membrane 15 cm in length and 10 mm in outer

diameter for a 7 mm inner diameter ; the act ive

layer (surface area 26 cm2) was dep osi ted in the

inner par t of the suppor t . S t reaming potent ia l

measurements made pe r fo rm ed th rough the mem-

brane by me ans o f two s i lver wi res covered wi th

s i lver chlor ide used as reference e lect rodes . On e

Table 1

Main characterist ics o f the prepared mem branes

y-alumina CoA1204 ZnAI204

Pore diamete r nm 3.2 5 5.6

Cut-off D 2400 2000 1500

Wate r permea bility 1.2 5.7 3.5

L.h-l.m-2.bar l

was posi t ione d a t the axis o f the mem brane tube

and the sec ond near the oppo si te s ide of the tube.

The f i lt ered solut ions were prep ared w i th analy-

sis grade sal ts at a concentrat ion between 10 -3

and 10 -2 mol.L-1 or o ther pre cise concentrat ion.

The concen t r at i on o f t he pe rmea te was ob t a ined

by a tomic absorpt ion and ionic chromatography.

The pH of the solut ion was adjus ted wi th concen-

trate acid (HC1) or base (NaOH ) solut ions.

3 Results and discussion

3 1 Membrane characterization

The di f ferent mem brane s tes ted we re charac-

ter ized by scanning microscopy and ni t rogen

adsorpt ion/desorpt ion; thei r cut -of f was evaluated

from the rejec t ion rates obtaine d for the f i l t rat ion

of soluble PEG polym ers of ca l ibra ted molecular

weight . F ig . 1 shows the cross sect ion and the

surface views of the CoAI204 mem brane, which

is abou t 4 m thick.

3 2 Size effect

The resul t s obta ined for the y-a lum ina mem-

brane show that the re ject ion ra tes depend

st rongly on the nature of the f i l t ered sa l t

(Table 2). U nder our exper imental condi t ions , the

bes t re jec t ions w ere observed for the M A z sa lt ; on

the cont rary, bad re ject ions were obta ined wi th

M2A salts. These classical results are in agree-

ment wi th the e lect ros ta t ic model based on the

interact ion between the ions and the charged


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S. Cond om et al . / Desa lination 168 2004) 207-2 13

Table 2a

Rejection of salts on a ,/-alum ina m em bran e (C = 10 -3 moL L-l)

209

Cations R,

S042- CI- N O 3

pH

K ÷ 1 36 55 5.6

Na+ 20 50 70 5.5

Ca 2÷ 40 95 95 5.6

Cu2+ 45 97 97 5.5

Cd 2+ 40 97 97 5.6

Ni 2÷ 40 97 96 5.6

Table 2b

Effect of complexation on the reject ion o f sal ts on a y-alum ina membrane (C = 10-3 mol.L-1)

Metal sulfate R

Ligand Without

NT A EDTA o-phenantroline Polycarboxylate

pH

Cu 2÷ 45 - - 80 96

Cd 2. 40 53 80 97

Ni2÷ 40 80 85 95

99

95

Fig. 1. SEM of spinel CoA12 4 mem brane: (a) cross section, (b) surface view.

f i l t e r i n g m a t e r i a l [ 8 , 9 ] . A t n a t u r a l p H t h e y -

a l u m i n a m e m b r a n e i s p o s i t i v e l y c h a r g e d , a n d

t h e n d i v a l e n t c o i o n s M 2+ a r e r e p u l s e d m o r e t h a n

a m o n o v a l e n t o n e ( M + ) . T h e s a l t s w h i c h a r e

a s s o c i a t e d w i t h b o t h d i v a l e n t i o n s p r e s e n t a

m o d e r a t e r e j e c t i o n .

C o m m o n l i g a n d s c a n b e u s e d t o i m p r o v e t h e

r e j e c t i o n o f t h e s a l t a f t e r c o m p l e x a t i o n o f t h e


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210

S. Condom et aL / Desalination 168 (2004) 207 -213

1

....~ :.

80 ~ Ni2 ~ x3

NiX

~ 60 [ ~ W ligand: Phenantroline

4 0

20

0 - ~ - - - ~ * ~ - ~ --'~-~- 1 * I

0 2 4 6 8 10

pH

Fig. 2. pH effect on complexation of Ni~ with an o-

phenetroline igand.

nique leads sometim es to an uncorrected charge

of the material in the f il tration con dition, prob-

ably because the texture o f the powder and of the

mem brane is quite different. This is w hy different

authors have suggested using others methods

[10,11 ] for the surface c harge measu rement such

as the streaming potential, which is also in

relation with the surface charge and seem s more

representative of the real charge dev eloped on the

mem brane surface in the f il tration condition. The

streaming potential (SP) depends on the zeta

potential according to the Sm oluch ow sky relation

(1), but in fact the conductivity ~. must include

the surface conduc tivity, wh ich can beco me im-

portant for low pore size membranes.

cation; nevertheless, the size o f the ligand should

be enough and m ore important than the pore size

of the membran e to prevent the ligand to cross the

membrane. Table 2 show s the rejection increasing

of MSO4 salts from 40 to more than 90 af ter

complexing the cation with different l igands.

Generally the rejection rate also depe nds o n the

pH according to the stabili ty of the complex,

which is more impor tant for the high pH value in

Fig 2.

3.3. Streaming poten tial an d salt rejection

The surface charge of the material, which

depends on the pH of the f il ter ing material, is an

important parameter wh ich governs the eff iciency

of a m embrane process , especia l ly for removing

ionic species. Unfortunately, the d irect determi-

nation of the surface charge is not easy an d only

indirect methods exist . Among these, the zeta

potential determination that is l inke d to the sur-

face charge can be used to approach the surface

charge o f the material. In the p ast the authors

have determin ed the zeta potential f rom electro-

phoretic measurements performed with f ine

powder suspensions of the membrane mater ia l

dispersed in an electrolyte solution. This tech-

s e - g (

..~. (1)

In order to correlate the experimental rejec-

tions of ionic species with the m embran e surface

charge, we present the results obtained for the

rejectio n of classical n eutral salts (NaC1, Na2SO4)

and also for sodium pho sphates at different pH by

means of the three prepared membranes . The

exper imental measuremen t o f the

SP

is relatively

easily obtained by the relation SP = AE/AP

which is the slope of the curve AE vs. applied

pressure in the dynamic f il tration conditions.

Fig. 3. shows that the SP va lues depen d on the pH

of the f il tered solutions, and this behavior is

expected because the SP given by the Smolu-

chowsky relation depends on the zeta potential,

wh ich also depends on surface charge of the

mem brane. The v ariation of the surface charge of

the membrane can be expla ined by the ampho-

ter ic properties of the material used to prepare the

membrane. In Fig. 4 we also report the electro-

phoretic m obility o f the CoA1204 pow der m aterial

in the presence of the same salts . The comparison

of the SP and mobility variations are quite dif-

ferent, whic h confirms the surface charge deter-

mined f rom powder mobil i ty and SP measure-

ments are not similar for the same material.


5/7

S. Condom et al. / Desalination 168 2004) 207- 213

211

3

2

0

2

a)

* NaC1 • CaCI2

• Na2SO4 • CaSO4

5 7 9 ~1

v

pH

6

-2

.4

cNaC1 nC~J2 AI'4t2SO¢ eC ~0 4 •

7 pH 9 ~

b)

Fig. 3. Evolution of the streaming potential measured

through the membranes vs. pH for different electrolytes

C = 10 3 moL L-l). a)

COA1204

membrane, b) TiO2 +

Z n A 1 2 0 4 membrane.

2

.7 1

-3

-4

-5

[]

F i g . 4 . E l e c t r o p h o r e t i c m o b i l i t i e s o f C o A l 2 0 4 p a r t i c l e s v s .

p H f o r d i f f e r e n t e l e c t r o l y t e s ( C = 1 0 -3 m o l . L - ~ ) .

3 .4 . p H e f fec ts on sa l t re jec t ion

The v ar ia t ion o f the re ject ion ra tes o f the di f-

ferent sal ts is reported in Fig 5 where we also

observed that i t depend s on the p H of the f i l tered

solut ion; this is the co nse que nce o f the electr ical

interact ions develop ed between the ions and the

surface charges of the membrane. For the

CoAI204 and TiOz/ZnAI204 membranes , the

reject ion rates of the neutral sal ts associat ing a

mon ovalen t anion and a ca t ion mon o or divalent )

decrease when the pH values increase; never-

theless , no great changes o f R was observed for

CaC1a betwe en pH 4 and pH 8. On the cont rary,

the reject ion rates o f Na2SO4 were very low in

acid medium, but they increase for higher pH

values . Those behaviours may be expla ined

taking into account the evolut ion of the SP

measured for the f i l tered sal ts . For the posi t ive

values of the SP, the reject ion of the sal ts is

relat ively high and i t decreases as the SP value

decreases . W hen the pH of the solut ion reaches

the pH va lue where t he cha rge o f t he membrane

is zero

S P

= 0) , the re ject ion beco mes very low

and then increases for the pH v alues where now

the mem brane i s negat ively charged. In the case

of the f i l t rat ion o f CaC1 z solut ions, we observ ed

only the decrease o f the re jection, which i s a lso in

agreement wi th the SP var ia t ions . This proves

that the sur face charge of the mem brane remains

120

10o

. .

20

0

4 8 12

p H

Fig. 5. Evolution o f the rejection o f salts C = 10-3 M) vs.

p H f o r t h e T i O ff Z n A 1 2 0 4 m e m b r a n e .


6/7

212

S. Condom e t aL / Desal inat ion 168 2004) 207-213

positive in the pH range studied. This pheno-

menon is probably due to the strong specif ic

adsorption of the Ca2+ ion at the surface of the

membrane whatever the pH of the solut ion

according to the surface equilibr ia complexation:

• Acid pH:

MOH~ + C a 2+ -* M O -, C a 2+ + 2H +

• Basic pH:

M O - + Ca 2+ -. MO -, Ca 2+

Generally the correlation between the rejec-

tion values and the SP determinations are more

satisfying than w ith the mo bilit ies obtained from

the electrophoretic measu rements perfo rmed w ith

the pow der suspension Figs. 3 and 5).

For the filtration of salts that are not neutral, it

is necessary to consid er their acid-ba se proper-

ties. This is the case of the pho sphate salts where

the charge of the anion depends on the pH of the

filtered solution. The results of the experiments

performed w ith the COA1204 mem brane are

reported in Fig. 6. The rejection of the sodium

phosphate is very low at pH under 5, and the

cor responding SP of the membrane is a lso weakly

negative. The comparison with the SP obtained

with the NaCI salt for the acid pH proves the

adsorption of the phosphate ion on the surface,

o ~

60 sodiu

p h o s p h ~ 1 >~

n~ 40 -2 u~

20 - 3

0 ~ -4

2 4 6 8 10 12

pH

Fi 8 . 6 . Evolut ion o f the SP and o f the re ject ion of sodium

phosphate C = 10 -3 mol. L -I) vs. pH for the Co AI204

membrane.

wh ich then decreases its charge according to the

complexation equilibr ium.

MOH2 + + H2PO4 - M OH ;, H2PO4)

Betw een pH 5 and 8, an increase of the rejec-

t ion can be observed whereas the SP becomes

more and more negative. These results are in

agreement with the change of H2PO4 to HPO4 -

anion bearing two negative charges and the

development of strong interactions between the

divalent anion phosphate and the neg ative surface

charge of the mem brane.

4 C o nc l us i o ns

The eff iciency of a f i l tration process depends

on the com plexity o f the f il tered solution. In the

case of an ionic solution , the steric and electrical

interactions are the two main parameters which

must be considered. The steric effect depends on

the stabili ty of the formed com plex betwee n the

cation and the ligand. For sim ple electrolytes, the

rejection depend s o n the electr ical interactions,

which are controlled by the surface charge

develop ed on the f ilter ing material. Generally, the

streaming potential mea surement across the me m-

brane seems to be a good param eter to predict the

rejection rates of the salt instead of electro-

phoretic pow der mobility, wh ich sometimes is not

in agreem ent with salt rejection.

References

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use of ultra and nanofiltration ceramic membranes for desalination 2004 desalination

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