Indian Journal of Chemical Technology Vol. 10, May 2003, pp. 3 11 -320

Articles

Mass transfer analysis of the extraction of Nickel(II) by emulsion liquid membrane

Mousumi Chakraborty*", Chiranj ib Bhattacharyah & Siddhartha Dattab

" Departme nt of Che mi cal Engineering, S V Reg ional Co llege of Engineeri ng &Technology, Sura t 395 007 . Ind ia

hDepartment o f Chemica l Engineering, Jadavpu r Uni versity. Kolkata 700 032, India

Received 15 Julv 2002; revised received 17 January 2003; accepted 20 February 2003

A mathematical model for batch extraction of Nickei(II) with emulsion liquid membrane (ELM) from a dilute sulphate solution and from industrial wastewater, using di-(2-ethylhexyl) phosphoric acid (D2EHPA) as extractant and hydrochloric acid as stripping agent is reported. The model considers a reaction front within the emulsion globule and assumes an instantaneous and irreversible reaction between the solute and the internal reagent at the membrane internal droplet interface. Batch experiments are performed for separation of Nickei(II) from aqueous sulphate solution of initial concentration in the range of 100-75 mgJL. The influence of Nickei(II) concentration on the distribution coefficient at pH 3.5 is co-related by a semiempirical model, which has been used for simulation of the extraction process. The simulated curves are found to be in good agreement with the experimental data.

A variety of separati on problems have been investigated over the last three decades by usmg emul sion liquid membrane (ELM) processes . Compared to conventional processes, ELM processes have certainly some attracti ve features e.g. simple operation, high effic iency, ex tracti on and stripping in one stage, larger interfac ial area, scope of continuous operati on, etc. The applications include hydrometallurgical recovery of metal ions 1-

6, removal

of weak ac ids and bases from wastewater7-

11, and

application in biochemical and bi omedical fi e lds 12-14

•

ELMs are usuall y fo rmed first by making an emul sion of two immiscible phases and then di spersing the emulsion in a third phase (continuous phase). The liquid me mbrane phase refers to the phase which separates the encapsulated phase in the emul sion and the ex ternal continuous phase which are, in general, completely mi scibl e.

There are two types of transport mechani sms. In the first mechani sm, called carri er-facilitated transport mechanism, a carri er is incorporated in the me mbrane phase to increase the mass transfer rates5

. In the second mechanism, the solute firs t dissolves in the membrane phase near the ex ternal interface and then diffuses through it to the inward region of e mul sion drop in the disso lved state and is released in to the internal phase by reversing the solution process. Thus

*For correspondence (E- mail: mousumi_chakra @yahoo.com; Fax: 026 1 3228394).

a concentration gradient is maintained across the me mbrane7

.

A number of mathematical models have been developed over the years to describe the mechanism of solute transfer th rough emulsion liquid membranes . Based on the homogeneous distribution of non­circulating internal droplets w ithin the globule, Ho et al. 15 formulated the advancing reaction front model. The membrane soluble solute di ffuses th rough the g lobule to a reaction front where it is removed by an instantaneous and irreversible reaction with the internal reagent . As the reagent is consumed by reaction, thi s reaction front advances into the g lobule. Stroeve and Yaranas i16 and Fales and Stroeve 17

extended the approach of Ho et a/. by including an additi onal mass transfer res istance in the continuous phase. Kim et al. 18 assumed an additional thin liqu id me mbrane layer, which contained no internal droplets.

An alternate approach has been taken by Teramoto et al. 19 and Bunge and Noble20

. They incorporated reaction revers ibility in describing the transport process in the emulsion g lobule. Chan and Lee 11

assumed reaction equilibrium to ex its in both the internal and external continuous phases. They also incorporated the overall mass transfer res istance in their model. The reversibl e model was later extended by Braid et a/. 2 1 to predi ct the ex trac tion rate fo r multico mponent systems.

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Nickel, copper and chromium are the three most commonly used metals for electroplating. The wastewater of electroplating industries contains Nickel(II) ions. Kulkarni et al. 22 have used ELM application for the recovery of Nickel(II) using D2EHPA as a carrier. Katsushi et al. 23 have shown that the use of a mixture of commercial extractant LIX63-DOLPA has a high synergistic effect on the ex traction of Nickei(II) in the ELM system compared to the LIX63-D2EHPA mixture. Serga et al. 24 found that app li cation of direct current to ex trac tion system contributes to the complete extraction of Nickei(II) using D2EHPA as carri er. Recently Kulkarni et al. 25

have studi ed the recovery of Nickci(II) usi ng methane sulphonic ac id (MSA) as a strippant.

There still exists some scope for better insight into Nickei(II) recovery by ELM process. In thi s paper the effects of initial solute (N ickel) concentrati on in feed phase, internal reagent concentration, treat ratio and volume fraction of internal phase on the extraction of Nickei(II) are sys tematically in vestigated usi ng D2EHPA as a ex tractant. In view of this, application of thi s technique is investi gated for removal of Nickei(II), from wastewater using di-(2-ethylhexyl) phosphoric acid (D2EHPA) as ex tractant, Sorbitan mono-oleate (Span 80) as surfactant, kerosene as membrane phase and hydrochlori c ac id as stripping solution. Here, di-(2-ethylhexyl) phosphoric acid (D2EHPA) faci litates the transport o f Nickei(IT) and Nickei(II) ion is simultaneously changed by internal reagent, hydrochloric ac id, to nickel chloride which has a low solubility in membrane phase, so that concentration grad ient of Nickei(II) between two aqueous phases is mai ntained.

Experimental Procedure Simulated feed

For the study of transport of Nickei(II) ions through emulsion liquid membrane, nickel sulphate (99.99% pure, Merck make) is used.

Industrial feed characteristics Local electroplating company supplied the

industrial feed. The feed contains large concentration of Nickel(II) and trace amount of copper(II), chromium(III) and iron(II). Industri al feed composition is summarized in Table I.

Commercial kerosene of specific gravity 0.798 and boiling poi nt range 145-250°C is used as membrane phase. The extractant used is D2EHPA [CAS No. 298-07-7] hav ing 98.5% purity, Span 80 (Sorbitan

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Indian J. Chem. Techno!., May 2003

Table !- Summary of experimental cond itions for ELMs batch tests

Vo lume Carrier(D2EH P A) Diluent (11-heptane) Surfactan t (Span 80) Kerosene

Vo lume Nickel(ll) pH Buffer (NaAc-HAc)

Vo lume Ac idi ty

Membrane phase (Oil) 25 mL 10% V/V 5% V/V 5% V/V 80% V/V

Exterior phase (Water) 450 mL 100-200 ppm 1- 6 0.05 mo i/L

Interior phase (Water) 25mL IN (HCI)

Industrial feed composition Ele ments Cone. (ppm )

Ni Cr Fe Cu 900 45 40 50

For preparati on o f aqueous soluti ons double d istilled water has been used.

monooleate containing 0 2 based moieties) as surfactant ; 11-heptane as a diluent and stabi li zer for the membrane phase. Sodium acetate-Acetic acid (NaAc­HAc) is used as a buffer (to maintain pH) for ail the ex peri ments.

Method Emulsion IS prepared by emu lsifying aqueous

soluti on of ac id (s trip phase) with an organic phase (membrane phase) . The membrane consists of varying proportions of surfactan t Span 80, extractant D2EHPA, and diluent (n-heptane ). The mixer is st irred at 5000 rpm for 15 min using a homogenizer (s ix blade turbine impeller of 30 mm diameter) to form a uniform mixture. Then the internal strip phase is added. The contents are again stirred at 5000 rpm for 15 min. An excellent milky-white and stable emulsion is obtained. The emul si on is dispersed in feed phase CO!ltaining nickel ions from wh ich nickel is to be ex tracted. A six-blade paddle impeller of 50 mm diameter rotating at 500 rpm is used for stirring. For measuring speed of the agitator and homogeni ser a hand tachometer hav ing a range of 0-10000 rpm has been used.

Samples of about 5 mL are withdrawn from the extmctor at different intervals of time and are filtered through a sintered glass plug to separate emulsion and aqueous feed phase. At the end, the emul sion phase is

Chakraborty et al.: Nickel(II) extraction by emulsion liquid membrane

separated from feed phase by gravity separation in a separating funnel and finally the emulsion is broken down by heating to 80°C for the analysis of strip phase.

Analysis Samples of aqueous phase, containing nickel, have

been analyzed by a spectrophotometer (CE1020, 1000 series manufactured by CECIL) according to the standard methods26.

Results and Discussion Mechanism of Nickel(II) extraction process using ELM

The equations given below show the extraction and stripping reactions of Nickel(ll) occurring in ELM process, where RH represents the protonated form of an extractant (D2EHPA, in this study). D2EHPA IS

known to dimerize in nonpolar aliphatic solvents.

Formation of the complex:

Ni 2+ + 2 (HRh = NiRiHRh + 2 H+ ... (1)

Stripping reaction:

NiR2(HRh + 2H+ = Ni 2+ + 2(HRh ... (2)

Eq. (1) represents the complexation reaction, which occurs at the membrane-external phase interface, while Eq. (2) shows stripping reaction at the membrane-internal aqueous phase interface. A schematic presentation of the liquid membrane globule and simultaneous extraction and stripping mechanism in ELMs is exhibited in Fig. 1.

Mathematical description In the present study, an unsteady-state

mathematical model is proposed for the separation and concentration of Nickei(II) ions using liquid surfactant membranes based on the advancing front model developed by Ho et al. 15

• According to this mathematical formulation, at the outer interface of the emulsion globules, solutes (Nickel ions) from the external phase reacts with the carrier contained in the membrane phase, thus forming a complex. The complex diffuses through the membrane phase until it is removed by an instantaneous and irreversible chemical reaction with the reagent (HCl solution) contained in the internal droplets . The solute cannot penetrate into the globule beyond those droplets ,

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2

ex. phase org. phase in. phase

2(HR) 2

NiR2(HR) 2

(HR)l: dimer of carrier

Fig. !-Simultaneous extraction and st ripping mechanism m ELMs

which are completely depleted of internal reagent, because the solutes are immediately removed by reaction with the internal reagent. Hence, there exists a sharp boundary or a reaction front separating the inner region containing internal reagent and no solute from the outer region where the internal reagent has been totally used up by reaction with the complex. As time progresses, more and more reagent is used up and the radius of the unreacted inner core shrinks. The concentration of solutes at the surface of the reacted core is zero. The following assumptions have been made in developing the present model.

(i) The size distribution of emulsion globules is uniform. No coalescence or redispersion occurs between the globules in which the encapsulated droplets are uniformly distributed.

(ii) There is no internal circulation within all emulsion globules due to the presence of surfactants and the small dimension of the globules.

(iii) The solute reacts with the internal reagent irreversibly and instantaneously at the reaction front. As the reaction proceeds, the reaction front shrinks towards the core of the globules.

(iv) Both the important effects of resistance in the external boundary layer and the membrane are taken into account in the model.

(v) The breakage and the swelling of the emulsions are neglected.

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A diagram of the model showing the above assumptions is given in Fig. 2.

The rate of the solute diffusion in emulsion globules can be described by the following equations: The material balance for the solute in the membrane phase

... (3)

where (RJ(t)< r < R, t>o) (4)

t=O, C=O, (r..:;,R) (5)

r=RJ(t), C=O, (t~O) (6)

At r=R, C=CoCe, (t~O) (7)

The material balance for the solute in the extemal phase is

-v dCe e dt

=lvD acl R e ar r = R

... (8)

t=O, Ce =Ceo ... (9)

The material balance of the solute at the reaction front is

-- -n RJ ¢C d (4 3 ) dt 3

= 4n RJ2 D acl e ar r=RJ(t)

(10)

t = 0, Rr = R (II)

The above equations can be transformed into dimensionless form by defining

r RJ Del TJ=- x=- r =-2-,

R' R' R c Ce c

g=-, h=-, m=-, Ceo Ceo Ceo

... (12)

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Indian J. Chern . Techno!., May 2003

External phase

.- - ---Ex(emol botrldary layer ; ' ............ /

I

I

Memtnne~

Rea<.iion frort

/

Fig. 2-Schematic diagram of the model

Then the diffusion equation becomes:

a8 = _ 1 a CTJ2 ag ) or (1-¢)TJ2 o7J oTJ ... (13)

at (X <TJ < 1, r > 0)

r =0, g =0, (TJ..:;, I) (14)

TJ = x, g =0, (r~O) (15)

TJ = 1 then g = Coh at ( r ~ 0) (16)

The material balance equation in the external phase is:

dh = _ Ea8

dr aT/ TJ =I . .. (17)

r = 0, h = 1 .. . . (18)

The material balance equation at the reaction front is as follows :

dx 1 ag = ----

dr ¢ m aTJ TJ =x . .. (19)

r=O, X =I . . . (20)

The coupled Eqs (13), (17) and (19) have been solved by numerical computation using an implicit finite difference technique. A central difference scheme has been used for integration along the dimensionless

Chakraborty eta/.: Nickel(II) extraction by emulsion liquid membrane

radial distance. The grid sizes in r and X directions

have been chosen by trial and error to obtain good convergence. As none of the three equations can be solved independently, an iterative process has been adopted for each time step. The computational steps for each time step are as follows:

(i) Values of hand X have been assumed to be

equal to those in the previous time step.

(ii) The assumed values of h and X have been

substituted in Eq. (13). Simultaneous linear algebraic equations having a tridiagonal matrix of coefficients obtained by representing Eq. (13) in finite difference form have been solved by matrix inversion and multiplication method to obtain g as a function of X.

(iii) Whether the values of X and g thus obtained

satisfy Eq. (19) was checked. If they did not, a new estimate for X was made and the process

from step 2 onward was repeated until the matching was satisfactory.

(iv) h has been calculated from Eq. ( 17) and the

calculated and assumed values of h have been matched by an iterative process similar to that adopted in step 3 for solving X.

Estimation of model parameters Emulsion globule size

The emulsion globule size (Sauter mean) ts calculated by using the following correlation of Ohtake et al. 27

... (21)

The value of the interfacial tension between membrane and external phase is determined by a tensiometer and found to be 23.5 dyne/em. The value of d32 was calculated to be 0.1 em.

Effective diffusivity The value of the Effective diffusivity of D2EHPA­

Metal complex in the membrane phase is determined by the correlation of Wilke and Chang28

:

Dill (117.3xi0 -' 8 )(!J! M )

05 T _:_ _____ ....:...._-,--____ m 2 /s

0 .6 J.lm V c

... (22)

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The solvent assoctat10n factor 1Jf has been taken as 1.0. The viscosity of the membrane phase is determined to be 0 .0025 kg/ms and the molar volume of the complex is estimated by additive volume principle29 to be 0.5125m3/kg.mol. The molecular weight of kerosene is determined by obtaining distillation data, and the average molecular weight of the membrane phase is calculated to be 142.2. The value of diffusivity of the complex in the membrane phase thus obtained is 3.17 X 10- IO m2/s.

The effective diffusivity of the complex in the emulsion is obtained by the Jefferson-Witzell-Sibbitt correlation 30

, which in the present study becomes

D . =104 D [4(1+2p) 2 -n]cm2/s e[f m 4(l+2p)2

... (23)

I

where, p=0.403(¢) 3 -0.5 ... (24)

From the above equation effective diffusivity of the complex is found tO be 0.7832 X 10- IO m2/s.

Distribution coefficient Values of the distribution coefficient are calculated

from the experimental data at pH 3.5. The logarithm of the distribution coefficient is correlated with the logarithm of the aqueous phase equilibrium solute concentration by the linear regression method.

The equation obtained is,

co= 56.23 c ~ l.ll ... (25 )

where C0 = di stribution coefficient of the solute

(Nickel) between membrane and external phase, C5 =

equilibrium solute concentration in the aqueous phase, mg/L.

The logarithmic values of the distribution coefficient are plotted aga inst logarithmic values of the equilibrium aqueous phase concentration, C5, as shown in Fig. 4. It can be observed from the figure that at low concentration in the aqueous phase ( < 5 mg/L), the curves slightly deviate from linearity. However, under the present experimental conditions the concentration range in the aqueous phase is always much higher than this limit value and the

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distribution coefficients of Ni(ll) ions throughout the extraction run can be considered to fo llow Eq. (25).

The variables for the numerical calculations are initial solute [Nickel(II)] concentration in feed phase, internal reagent concentration, treat ratio and volume fraction of internal phase. The experimental data obtained for different values of the above variables are compared with the simulated curves as shown in Figs 5 to I 0. The operating conditions of the extraction runs and the calculated values of the different dimensionless variables are shown in Table 2. The parameters, De. R0 and C0 used in the simulation are calculated as mentioned above.

Effect of feed phase Nickel (II) concentration It is found from Fig.5 that the fraction of sol ute

[Nickel (II)] extracted is higher with a lower initial external phase solute concentration. This is due to a higher distribution coefficient for a lower initial external phase solutes concentration. However, it has been found that the time taken by the complex to reach the center of the emulsion globule remains almost unaffected and is only marginally higher with a lower initial external phase solute concentration.

Effect of internal reagent concentration From Fig. 6, it is evident that a variation in the

concentrations of stripping phase acid (0.5-1.0 N) does not effect the removal of Nickel(II) at the beginning of the process. However, towards the end of the process, extraction is more effective when a more concentrated stripping acid is used. This is because at the beginning of the process, extraction into the membrane phase is independent of the composition of the stripping phase and is mainly controlled by the continuous phase resistance. But at the later stage owing to high H+ concentration in the stripping phase, reaction rate in stripping phase is more than the reaction in membrane phase and the capacity of the internal phase as a sink for metal ion increases and, therefore, the solute penetrates at a faster rate inside the emulsion globu les. This increases the diffusional distance necessary for the complex to reach the reaction front inside the emulsion globule. It thus increases the mass transfer resistance, thereby decreasing the extraction rate. The reaction front movement is shown in Fig. 7.

1:.1fect of treat ratio The treat ratio is defined as ratio of emulsion phase

vol ume (Ve) to aqueous feed phase volume (V) . The

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Indian J. Chern. Techno!., May 2003

0.9 -2 0.8 0 i=

0.7 u ~

0.6 !< w

0.5 ;/!.

0.4

0.3 0 2 4 6

pH

Fig. }--Extraction profile of nickel (II) from a pure salt solution

Fig. 4-Distribution coefficients as a function of equilibrium aqueous phase solute concentration

.c;;

c.i 1.2 z • Ellj>Oriment.ai.Ceo-100 fnlj/1 0

Ellj>Oriment.ai.Ceo-150 fnlj/1 u • w -Thecrobcai.Ceo=100fnlj/1 en < -Theoreticai.Ceo=150fnlj/1 ::1: a.. ..J < z Ill: 0.8 w

~ • • • • en en ~ 0.6 z Q • • • • en z w

0.-4 ::E i5 0 0 .05 0.1 0 .15 0 .2

DIMENSIONLESS TIME, "t

Fig . .5--Yariation of external phase nicke l ion concentration with initia l external phase nickel concentration

Chakraborty et a!. : Nickel(Il) extraction by emulsion liquid membrane Articles

Table 2-0perating conditions and parameters for the extraction runs

(Ro=0.05 em, D, = 0.7832 x 10' 10 m2/s, C0 = 56.23 C ~ 111 )

Sample

2 3 4

1.2 .c

u z 0 u w (/) c( J: c.. ...J 0.8 c( z 0: w t< w

0.6 (/) (/)

~ z 0 iii 0 .4 z w 0 :::E i5

Figure

5 6&7 8 9& 10

0.05

C,, (mg /L)

100,150 100 100 100

• .,__,Ci•Ul(N)

A E>cperirnerUI,Ci=0.5(N) -Theoreticoi,CF1 .0 (N)

-Theoreticol,CP0.5(N)

.. .. ..

• • • •

0.1 0 .15

DIMENSIONLESS TIME, 't

0.2

Fig. 6-Variation of external phase nickel concentration with internal reagent concentration

treat ratio is varied by changing the amount of emulsion added to the feed phase and keeping the volume of the later constant. Fig. 8 exhibits the time profile of the feed phase concentration of Nickel(II) at different treat ratios . The treat ratio is varied from 1:12 (£ = 0.25) to 1:9 (£ = 0.33). With increase in treat ratio (E) the volumes of both the carrier and the stripping agent increases. Therefore, the surface areas for mass transfer owing to the formation of a larger number of emulsion globules increases. Hence, a higher degree of extraction is obtained. However, it has been found that the reaction front movement is not affected. This is because in each emulsion globule, the quantity of solute reacti ng with the carrier at the globule surface and the amount of internal reagent remains unaltered with a change in the value of E.

Effect of volume fraction of internal phase With a decrease in the volume fraction of the

internal phase ( ¢ ), the amount of internal reagent

with the globule decreases, resulting in the consumption of most of the reagents in the early stage. This causes a faster advancement of the reaction front towards the centre of the globules

E q> Ci (N)

0.33 0.5 1.0 0.33 0.5 1.0, 0.5 0.33, 0.25 0.5 1.0 0.33 0.5, 0.3 1.0

0.9 -Ci=1 .0N

0 .8 - Ci=O.SN

)(

..; :::l 0.7 0 ~ !z 0.8

0

" ... 0.5 z 0 ;:: 0.4 u :i " 0.3

0.2

0.1

0 .000 0.018 0.036 0.054 0.072 0 .090 0.108

OIM::NSIONLESS TIME, 't

Fig. ?-Variation of reaction front progress with internal reagent concentration

.c

0 1.2 z • ~.E=O.:D 0 u .. E--.E=0.2S w - Th<creticai,Eo<l.:D (/) c( J:

- Th<creticai ,E-D.25

c.. ...J c( z Ill: w 0.8 t< w (/) .. .. (/) .. .. ~ z 0 .6 0 iii • • z • • w :::E i5 0.4

0 0.05 0.1 0.15 0.2

DIMENSIONLESS TIME, T

Fig. 8---Yariation of external phase nickel concentration with volume ratio of emul sion to ex ternal phase

(Fig. 9). The higher penetration leads to a lower extraction rate because of the longer diffusion path needed by the solute to reach the reaction front as shown in Fig. 10.

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0.9

0 .8 - Theoretical, '=0.5

0.7 - Theoretical. f=O.J

.; ::0 i5 0 .6 .. 0: 1-z 0.5 0 0: u. z

0.4 0 ;:: u .. w 0.3 0:

0.2

0 .1

0 .000 0.018 0.036 0.054 0.072 0.090 0.108

DIMENSIONLESS TIME, T

Fig. 9--Yariation of reaction front progress with volume fraction of internal aqueous phase

.. "I ------u • z Elq)erimental . t~.5 0 ... Experimental, t -<>.3 u w Theoretical, +=0.5 ., - Theoretical, t=0.3

< :r 0..

~ ..J < z 0 .8 a: ... w t- • ... ... ... )( w ., .,

0 .6 w ..J z • • 0 • • iii z w 0.4 ~ 0 0 0.05 0.1 0.15 0.2

DIMENSIONLESS TIME, T

Fig. LG-Yariation of external ph ~se nickel concentration with volume fraction of internal aqueous phase

Comparison between experimental and computed results

Table 3 shows the absolute deviation between experimental and theoretical values of the external phase solute concentration for each experi mental run . The average absolute deviations were found to be between 0.024 and 0.048 for an initial dimension less solute concentration (h) of 1.0. This shows that the simulated curves are in good agreement with the experimental data.

Conclusion An unsteady-state mathematical model is proposed

for the separat ion and concentration of Nickel(! I) ions

318

Indian J. Chem. Techno!., May 2003

using emulsion liquid membranes based on the advancing front model developed by Ho et al. 15,

neglects external phase mass transfer and the effect of membrane breakage, and has no adjustable parameter. The effects of variables, such as initial solute concentration in the external phase, internal reagent concentration, treat ratio, vo lume fraction of internal phase on external phase solute concentration as well as on the reaction fro nt movement are studied. The solute distribution coefficient is fo und to be infl uenced by the ex ternal phase solute concentration, and a semiempirical correlation between the distribution coefficient and the equi librium external phase Nickel(Il) concentration has been developed for use in the simul ation of model equations. The theoretical resu lts obtained by numerical solution of the model equations are found to be in good agreement with the experimental data. Coexisting ions (I ndustria l wastewater) copper(II), chromium(III) and iron(II) hardly affect the separation.

Nomenclature

c

r

R

Rr T

v

metal ion (nickel) concentration in saturated zone of emulsion globule, mol/L

initial internal reagent concentration in internal phase, moi!L

internal reagent concentration in internal phase, mol/L

metal ions concentration in external phase, moi/L

initial metal ion concentration in external phase, moi/L

effective diffusivity of metal ions in saturated zone of emulsion globules, m2/s

distribution coefficients of the solutes (nickel) between membrane and externa l phase

equi librium solutes concentrations in the aqueous phase, mg/L

radial coord inate in emulsion globules, m

radius of emulsion globules, m

reaction fro nt position, m

time, min

total volume of emulsion phase, L

volume of external phase , L

avg. molecular wt. of the membrane phase

Chakraborty eta/.: Nickel(II) extraction by emulsion liquid membrane Articles

Table 3---Absolute deviation between experimental and computed values of ex ternal phase solute concentration

Run

2

3

4

5

c Ill=-'

C,o

Greek Letters

r T} =­

R

x=f\ R

T

C"' =IOO mg/L 0.018

£= 0. 33 0.036

<p = 0.5 0.054

C; =I .O(N) 0.072 0.090 0.108 0.126 0.144

C,., = 150mg/L 0.018

£= 0. 33 0.036

<p = 0.5 0.054

C; =I.O(N) 0.072 0.090 0.108 0.126 0.144

C,., =100 mg/L 0.018

£= 0. 25 0.036

<p = 0.5 0.054

C; =l .O(N) 0.072 0.090 0.108 0.126 0.144

C,., =100 mg!L 0.018

£= 0. 33 0.036

<p = 0.5 0.054

C; =0.5(N) 0.072 0.090 0.108 0.1 26 0.144

C,, =100 mg!L 0.018

£= 0. 33 0.036

<p = 0.3 0.054

C;=I .O(N) 0.072 0.090 0.108 0.126 0.144

Absolute Average dev iation absolute deviation

0.088 0.048 0.069 0.037 0.028 0.037 0.032 0.046 0.050

0.040 0.037 0.015 0.010 0.017 0.045 0.060 0.052 0.060

0.090 0.044 0.037 0.035 0.047 0.070 0.070 0.070 0.058

0.010 0.024 0.025 0.045 0.020 0.010 0.030 0.022 0.030

0.010 0.025 0.035 0.015 0.010 0.010 0.030 0.040 0.050

'II= solvent association factor Jl rn= viscosity of the membrane phase Vc= molar volume of the complex

Maximum absolute deviation

0.088

0.060

0.090

0.045

0.050

¢ =volume fracti on of internal aq ueous phase in the emulsion

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