This article was downloaded by: [University of Notre Dame Australia]On: 02 May 2013, At: 02:13Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

Solvent Extraction and Ion ExchangePublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/lsei20

INTERFACIAL ADSORPTION OF 2-HYDROXY-5-NONYLBENZOPHENONE OXIME IN STATIC ANDVIGOROUSLY STIRRED DISTRIBUTION SYSTEMSHitoshi Watarai a & Keiko Sasabuchi aa Department of Chemistry, Faculty of Education, Akita University, Akita, 010, JapanPublished online: 25 Jun 2007.

To cite this article: Hitoshi Watarai & Keiko Sasabuchi (1985): INTERFACIAL ADSORPTION OF 2-HYDROXY-5-NONYLBENZOPHENONE OXIME IN STATIC AND VIGOROUSLY STIRRED DISTRIBUTION SYSTEMS, Solvent Extraction and IonExchange, 3:6, 881-893

To link to this article: http://dx.doi.org/10.1080/07366298508918546

PLEASE SCROLL DOWN FOR ARTICLE

Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form toanyone is expressly forbidden.

The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses shouldbe independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly inconnection with or arising out of the use of this material.

SOLVENT EXTRACTION AND ION EXCHANGE, 3(6), 881-893 (1985)

INTERFACIAL ADSORPTION OF 2-HYDROXY-5-NONYLBENZOPHENONE

OXIME IN STATIC AND VIGOROUSLY STIRRED DISTRIBUTION SYSTEMS

Hitoshi Watarai* and Keiko Sasabuchi

Department of Chemistry. Faculty of Education

Akita University. Akita 010. Japan

ABSTRACT The interfacial adsorption of 2-hydroxy-5-nonylbenzo­phenone oxime (LIX65N) at a n-heptane/water interphase was exam­ined under static and vigorously stirred conditions. varying theaqueous pH from 2 to 12. In static systems. the pH and the con­centration dependences of the interfacial tension were analysedon the basis of the Gibbs equation. The acid dissociation equi­librium at the interface was evaluated. In vigorously stirredsystems. the interfacial adsorption was observed as a reversi­ble. reproducible decrease of the organic phase concentration inresponse to stirring. A Langmuir isotherm was applicable forthe adsorption of neutral LIX65N in acidic condition. Thegreater adsorption of the anionic form of LIX65N occurring inalkaline condition required an alternative isotherm.

INTRODUCTI ON

The distribution ratio of an extractant is one of the im­

portant parameters which determine the distribution ratio and

the extraction rate of metal ions. The distribution of the

881

Copyright © 1985 by Marcel Dekker,lnc. 0736-6299/85/0306.Q88I $3.50/0

Dow

nloa

ded

by [

Uni

vers

ity o

f N

otre

Dam

e A

ustr

alia

] at

02:

13 0

2 M

ay 2

013

882 WATARAI AND SASABUCHI

extractant is usually not affected by the extent of shaking or

stirring of the aqueous and organic phases present in the sys­

tem. However. we recently found out a remarkable decrease in

organic phase concentration, when the organic phase/alkaline

aqueous phase system containing an-substituted dithizone (1)

or the chloroform/acidic aqueous phase system containing a

1. 10-phenanthro1ine derivative (2) were vigorously stirred.

In this study, the effect of stirring on the distribution

of 2-hydroxy-5-nony1benzophenone oxime (LIX65N). an extractant

successfully used in hydrometa11urgy, was examined and the inter­

facial adsorption of LIX65N in the stirred system was evaluated.

EXPERIMENTAL

Chemicals

LIX65N (Henkel) was purified as sodium salt and its purity

was checked by silica gel TLC (3). n-Heptane (Wako. G.R.),

used as organic phase solvent. was purified by distillation

after a preliminary purification treatment with nitric acid and

sulfuric acid mixture. All other reagents were garanteed rea­

gent grade chemical and were used as purchased.

The pH of the aqueous phases was controlled by perch10ric

acid, acetate buffer (0.002M) and sodium hydroxide. The ionic

strength was maintained at 0.1 by sodium perchlorate.

Stirring Experiment

The effect of stirring on the distribution of LIX65N was

measured by means of the distribution apparatus reported else­

where in detail (2), (4). Fifty m1 of LIX65N in n-heptane and

an equal volume of aqueous phase were introduced into a 200 m1

three necked flask. which was immersed in a water bath thermo-

Dow

nloa

ded

by [

Uni

vers

ity o

f N

otre

Dam

e A

ustr

alia

] at

02:

13 0

2 M

ay 2

013

2-HYROXY-5-NONYLBENZOPHENONE OXIME 883

stated at 25 ± O.loC. By using a Teflon phase separator

(Kokuboseiki Co.) and.a peristaltic pump. the n-heptane phase

was continuously drawn out at the flow rate of 7.5 ml/min and

transfered through Teflon tubing to the flow cell (50 ~l) of a

spectrophotometer, and then returned to the flask. Thus the

change in organic phase concentration was recorded as a trans­

mittance change at the absorption maximum wavelength of 320 nm.

The stirring speed was monitored by an ONO SOKKI digital tacho­

meter HT-431. The pH of the aqueous phase was measured by a

Beckman Research pH Meter. The transmittance change increased

with increase of the stirring speed, but showed an almost con­

stant value above 4500 rpm. Hence, the experiments here re­

ported were conducted at about 5000 rpm.

Interfacial Tension

The interfacial tension of the heptane/water system con­

taining LIX65N was measured by the drop volume method at

25 ± O.l"C. by applying the Harkins-Brown correction (5).

RESULTS AND DISCUSSION

Interfacial Adsorption in Static System

In preliminary experiments. the interfacial tensions at the

n-heptane/water interface were measured as a function of the

LIX65N concentration in the range from 10-6M to 10-2M (M =mol/l) under acidic (pH = 3.2) and alkaline (pH = 12.0) condi­

tions. A lowering of interfacial tension with concentration was

observed for both systems. This lowering was larger in alkaline

system than that in acidic system. indicating the higher inter­

facial activity of the dissociated form of the reagent. In the

alkaline system the LIX65N adsorbed at the interface is expected

Dow

nloa

ded

by [

Uni

vers

ity o

f N

otre

Dam

e A

ustr

alia

] at

02:

13 0

2 M

ay 2

013

884 WATARAI AND SASABUCHI

to be predominantly dissociated (pKa ; 8~70 (6)). To evaluate

the acid dissociation equilibrium at interface. the pH

dependence of the interfacial tension was examined using very

dilute organic solutions. In Fig. 1. the interfacial pressure,

n. calculated from YO - y, where YO and y refer to the inter­

facial tensions in absence and in the presence of LIX65N, is

plotted against the LIX65N concentration. The linear correla-

pH =10.66

14

12

~10

Eu

28>­

1J

K 6

l.

2

o 4 6

Cor rE'lation between

8 10

lOS [H Llo / M

the interfacial

pH=1..32

pressure]( and

18

L1X 65N concentration

FIGURE 1. Interfacial pressure n vs LIX65N concentration plotat various aqueous pH's.

Dow

nloa

ded

by [

Uni

vers

ity o

f N

otre

Dam

e A

ustr

alia

] at

02:

13 0

2 M

ay 2

013

2-HYROXY - 5-NONYLJENZOPIIENONE OX1ME 885

6

E 5

Olo

4

3

logma--<>--------0--- oa

e

pH dependences of and log( m -rTId He)

2 3 4 5 9

pH

log m(o)

10 11 12

FIGURE 2. Dependences of log m (0) and log (m - ma) (e) on pH.

tion observed for each pH can be represented by:

TT = m [HL]o (1)

where m (dyn/M'cm) is the slope of the streight lines going

through the experimental points of Fig. 1 and [HLJ o is LIX65N

concentration in organic phase. Logarithmic values of the slope

m are plotted in Fig. 2 against pH. In the acidic region. log m

is constant (log ma), whereas in an alkaline region log (m - mal

tends to increase with pH. The slope of the plot approaches the

value of one at high pHs. This result can be explained with the

help of the Gibbs adsorption isotherm which formulates the rela­

tionship between the interfacial concentration and the interfac­

i a1 pressure:

[HL]o

RT(2)

where [HL]i and [L-]i indicate the interfacial concentrations of

the neutral and anionic forms of LIX65N. By defining the appar-

Dow

nloa

ded

by [

Uni

vers

ity o

f N

otre

Dam

e A

ustr

alia

] at

02:

13 0

2 M

ay 2

013

886 WATARAI AND SASABUCIII

ent dissociation constant at interface of HL, Ka', which in­

cludes the bulk phase hydrogen ion concentration and the distri­

bution constant between interface and organic phase of HL, K',

by:

K 'a

K'

[n i [H+J

[HL Ji

[HL 1i

[HLJ o

(3)

(4)

m = RTK' + RTK' .

the slope m will be represented by the equation:

Ka '(5)

The first term in eq. (5), RTK', is independent of the hydrogen

ion concentration, and it is equal to mao Thus, we can obtain:

log (m - mal = pH + log RTK'Ka'· (6)

Equation (6) explains the observed pH dependence of log m shown

in Fig. 2. From the observed value of ma = (2.5 ± 0.2) x 104

dyn'cm-l'M- l, K' = (1.0 ± 0.1) x 10-3 cm was calculated. Then,

eq. (6) allowed to make estimate of pKa' as 9.0 with an uncer­

tainty of 20 %. This means that more than 99 %of the LIX65N

adsorbed at interface exists in the dissociated form at pH

higher than 11. These results allows to estimate the distribu­

tion constants of HL and L- between the interface and the aque­

ous phases by using the distribution constant between bulk

phases [HLJo/[HLJ = 4.90 x 105 (7) as [HLJi/[HLJ = 4.9 x 102 cm

and [L-Ji/[L-J = 9.5 x 102 cm.

Interfacial Adsorption in Stirred System

Some typical results showing the influence of the stirring

on the bulk concentration of the organic reagent are shown in

Fig. 3. At pH = 2.20, the transmittance at 320 nm increases

Dow

nloa

ded

by [

Uni

vers

ity o

f N

otre

Dam

e A

ustr

alia

] at

02:

13 0

2 M

ay 2

013

2-HYROXY - 5-NONYLBENZOPHENONE OXUIE 887

Ec

oNl""l

l1JuCI'll

El/lCI'll'­.....

RE'Cordlng time

w

~: t==a.1---0

Ul_l===Ul.,. t=::" ~~ I--

'"

'"

~

1 min. pH=2.20

->-- 1-'- Q.I'll 0Ul Ul~ ~

""

c-

pH=lO.551'-------1'

2lmin.

FIGURE 3. Examples of the transmittance changes caused by stir­ring in acidic and alkaline conditions.

Dow

nloa

ded

by [

Uni

vers

ity o

f N

otre

Dam

e A

ustr

alia

] at

02:

13 0

2 M

ay 2

013

888 WATARAI AND SASABUCHI

soon after the starting of stirring and reaches a constant

value. When the stirring is stopped. it reverts to the initial

value. At pH = 10.55. a similar behavior is observed, but the

extent of transmittance increase is larger and the time required

to reestabl ish the initial value after interrupting the stir­

ring is longer than that in acidic conditions. This may be due

to the formation of a more stable emulsion in alkaline condi­

tions.

The absorbance decrease caused by stirring is plotted in

Fig. 4 against pH as 6A/A x 102, where 6A and A refer to the ab­

sorbance decrement and to the absorbance under no stirring, res­

pectively. The pH dependency shown in Fig. 4 follows the same

trend as that obtained for the interfacial pressure (Fig. 2).suggesting a preferencial interfacial adsorption of thedissociated LIX65N also in the stirred system.

The dependence of 6A on the absorbance under stirring A'

had different feature in acidic and alkaline conditions

(Fig. 5). The 6A vs A' curve at pH = 3.2 showed a saturation

effect. while at pH = 11.9 6A continued to increase with A'.

These effects may be explained by the following scheme

where HL and L- are adsorbed at the interface:

HL i~:

HL Io I

~'L"'"1

HL

1l

bulkorganic

interface bulkaqueous

Neglecting the amount of LIX65N in the bulk aqueous phase. the

total amount is represented by:

(7)

Dow

nloa

ded

by [

Uni

vers

ity o

f N

otre

Dam

e A

ustr

alia

] at

02:

13 0

2 M

ay 2

013

2-HYROXY-5-NONYLBENZOPHENONE UXlHE

70

60

50~....~

N 400

)(

«<, 30«"q

20

10

00 2 4 6 8 10 12 14

pH

Percent aqe decrease in the organic phase

absorb ance cause o by stirring

[L1X65N]= 1.5xlO-4M

889

Figure 4. Percentage decrease in the organic phase absorbancecaused by stirring vs pH plot at [LIX65N] = 1.5 x 10-4M.

Where [HL]t (M) is the total initial concentration in the organ­

ic phase. Vo (ml) the volume of organic phase. and Ai (cm2) the

total interfacial area in the dispersed system. Assuming thatthe interfacial concentration [HL]i (mol cm-2) obeys the Langmuirisotherm:

[HL]iab[HL]o

1 + b[HL]o(8)

Dow

nloa

ded

by [

Uni

vers

ity o

f N

otre

Dam

e A

ustr

alia

] at

02:

13 0

2 M

ay 2

013

890 WATARAI AND SASABUCHI

0.2

0.1 pH=3.2

1.51.00.5oO.L--------:-'::-~---.--L-------l

Adsorption isotherm of LIX65N at thesti rr ed n-hept ane/wat er interface[L1 X65N 1:(0.3 - 3.0) X10·4M

FIGURE 5. Adsorption isotherms of LIX65N in the dis~ersed

n-heptane/water system; [LIX65N] = (0.3 - 3.0) x 10- M.

the ~A in acidic condition is related to the absorbance under

stirring A' by:

Vo------M sAi 103

1 c 1(-+ ----)

a .. ab A'(9)

Dow

nloa

ded

by [

Uni

vers

ity o

f N

otre

Dam

e A

ustr

alia

] at

02:

13 0

2 M

ay 2

013

2-HYROXY-S-NONYLBENZOPHENONE OXIME 891

where £ is the molar apsorptivity at 320 nm. a is the interfac­

ial concentration at saturation and ab is the same meaning with

K' defined by eq. (4). The 6A vs A' curve at pH = 3.2 of Fig. 5was analysed according to eq. (9) and the linear relationship

was obtained as:

1 1~ = 4.62 + 1. 71 ~ (corr. coeff. = 0.999). (10)

From the intercept and the slope the values. aA i = 3.18 x 10-6

mol and abA i = 2.92 x 10- 2 1 were obtained. Using a = 1.75 x

10- 10 mol cm-2 (7). Ai = 1.8 x 104 cm2 was calculated. which

corresponds to 50 ml of bulk phase completely dispersed as

spherical droplets of 0.16 mm diameter. Furthermore. the value

of Ai allowed the calculation of ab as 1.6 x 10- 3 cm. which

agreed with K' = 1.0 x 10-3 cm obtained from the interfacial

tension measurement and confirmed the interfacial adsorption

mechanism in the stirred system.

In alkaline condition. the simple Langmuir isotherm was not

applicable. As shown in Fig. 5. the adsorbed amount of L- at

pH = 11.9 continuously increases by increasing the LIX65N con­

centration. Instead of the linear correlation between 1/6A vs

l/A' obtained at pH = 3.2. an apparently linear correlation be­

tween (1/6A)2 vs l/A' was in this case obtained:

1 1---2-- = 0.52 + 5.88 ---- (corr. coeff. = 0.998) (11)

6A A'

This correlation suggests that the interfacial area Ai increases

with [L-]i' The interfacial adsorption of significant amounts

of the anionic form of LIX65N may reduce the coalescence rate of

the dispersed drops. because of the electrostatic repulsion be­

tween drops and the reduced mobility of the interface.

Dow

nloa

ded

by [

Uni

vers

ity o

f N

otre

Dam

e A

ustr

alia

] at

02:

13 0

2 M

ay 2

013

892

CONCLUSIONS

WATARAI AND SASABUCHI

In the present study. the significant interfacial absorp­

tion of LIX65N in the vigorously stirred system was concluded aswell as in the static system. The interfacial activity of the

S-hydroxyoxime is due to the long hydrophobic group of -C9H19

and the two hydrophilic groups of -OH. or -0- in the dissocia­

ted form. and C = N-OH.

The determination of-the interfacial concentration of the

extractant in the stirred system. which has been accomplished

by the present method. will greatly help the elucidation of the

interfacial reaction mechanism in the metal extraction kinetics.

ACKNOWLEDGEMENTS

The authors thank Prof. N. Suzuki of Tohoku Univ. for sup­

port in experimental facilities. Kokuboseiki Co. for providing

the Teflon phase separator and Henkel (Japan) Ltd. for providing

LIX65N reagent. Part of this work was financially supported by

the Grand-in-Aid for Scientific Research from the Ministry of

Educat ion. Japan (No. 59.540.353-1984).

REFERENCES

( 1) H. Watarai and H. Freiser. J. Am. Chem. Soc. 105. 191 ( 1983).

(2) H. Watarai. J. Phys. Chem. 89. 384 (1985).

(3) A. W. Ashbrook. J. Chromatogr. lQl. 141 (1975).

(4) H. Watarai. L. Cunningham and H. Fre i ser , Anal. Chem. 54.

2390 (1982).

Dow

nloa

ded

by [

Uni

vers

ity o

f N

otre

Dam

e A

ustr

alia

] at

02:

13 0

2 M

ay 2

013

2··HYROXY - 5-NONYLBENZOPHENONE OXIME 893

(5) J. L. Lando and H. T. Oakley. J. Colloid Interface Sci. 25,

526 (1967).

(6) K. Akiba and H. Freiser, Anal. Chim. Acta 136. 329 (1982).

(7) I. Kome s ewa, T. Otake and A. Yamada. J. Chern. Eng. Jpn . .11.130 (1980).

Received by Editor

February 22, 1985

Dow

nloa

ded

by [

Uni

vers

ity o

f N

otre

Dam

e A

ustr

alia

] at

02:

13 0

2 M

ay 2

013