Adsorption of gadolinium on activated charcoal from electrolytic aqueous solution

Journal of Radioanalytical and Nuclear Chemistry, Articles, Vol. 159, No. 1 (1992) 155-165

ADSORPTION OF GADOLINIUM ON ACTIVATED C H A R C O A L FROM ELECTROLYTIC AQUEOUS SOLUTION

R. QADEER,* J. HAN1F,* M. SALEEM, **§ M. AFZAL**

*Pakistan Institute of Nuclear Science and Technology, P.O. Box 1356, Islamabad (Pakistan)

** Department of Chemistry, Quaid-i-Azam University, Islanmbad (Pakistan)

(Received September 2, 1991)

Adsoprtion of gadolinium on activated charcoal has been studied as a function of shaking time, pH, concentration of adsorbate and temperature. Gadolinium adsorption obeys the Langmuir isotherm. A H ~ and A S ~ were calculated from the slope and intercept of the In KD 1/T plot. The influence of different cations and anions on gadolinium adsorption has been examined. The adsorption of other metal ions on activated charcoal has been studied under optimum conditions to check the selectivity of gadolinium adsorption. Consequently, gadolinium was removed from Ni, V, Zn, Cu, Rb, Sr and Mn. More than 97% of the adsorbed gadolinium on activated charcoal can be recovered with 35 ml o f3M HNO3 solution.Wavelength dispersive X-ray fluorescence spectrometer was used for measuring gadolinium concentration.

Introduction

The adsorption of gadolinium on solids is important for its preconcentration because it has numerous applications in electrical and nuclear industry. Previously its adsorption on silicon, 1 molybdenum,Z3 and tungsten 4~ surfaces have been examined but no data are available for its adsorption on activated charcoal. In this work an attempt has been made to study the adsorption behavior of gadolinium on activated charcoal and to illustrate the optimal conditions required for its preconcentration and separation.

Experimental

The chemicals used during this study were activated charcoal (BDH; item No. 33032); gadolinium nitrate (Rare Earth Product, 99.999%); cerium nitrate (Rare Earth Product, 99.999%); sodium nitrate (Fluka, item No. 71755); potassium chloride (Merck,

+ Aulhor for correspondence.

Elsevier Sequoia S. A. Lausanne Akad~mlai Kiad6, Budapest

R. QADEER et al.: ADSORPTION OF GADOLINIUM ON ACTIVATED CHARCOAL

item No. 7517123); cobalt nitrate (Fluka, item No. 60833); zinc nitrate (Fluka, item No. 96482); chromium nitrate (Fluka, item No. 27080); sodium acetate (Fluka, item No. 71179); sodium thiosulfate (Fluka, item No. 72049); sodium iodide (Fluka, item No. 71710); sodium chloride (Fluka, item No. 71378); sodium nitrate (Fluka, item No. 71755); sodium bromide (Fluka, item No. 71330) and ethylenediaminetetraacetic acid (Fluka, item No. 03610).

Siemens wavelength dispersive X-ray fluorescence spectrometer (WDXX....RbX3) SRS-200 with the following attachment: Cr X-ray tube; Soller slit with angular divergence 0.15~ LiF (100) crystal; NaI(T1) scintillation counter was used for measuring gadolinium concentration. The pH measurements were made with a digital pH meter Metrohm 605. Buffer solutions of different pH supplied by Fluka were used for pH study. An Edmund Buhler-SM25 shaker was used for shaking at a constant speed of 150 r.p.m.

Adsorption measurements were carried out by a batch technique at room temperature [(22 +-1)~ except where otherwise specified. A known amount of activated charcoal in 250 ml reagent bottles containing 10 ml of gadolinium solution were shaken for a given time period. The solutions were then filtered and concentration of gadolinium before and after shaking was measured by WDXRFS. The sample solutions were introduced into the spectrometer in 0.1 mm thick walled polyethylene bottles.7, 8 The percent adsorption and distribution coefficients (KD) were computed in the usual way. 9

Results and discussion

The adsorption of gadolinium on activated charcoal was studied as a function of shaking time. 10 ml of gadolinium solution (2000 ~tg/ml) was shaken with 100 mg of activated charcoal for different intervals of time ranging from 5 to 120 minutes. Figure 1 shows the variation of % adsorption and distribution coefficient (KD) with shaking time. The adsorption increases as shaking time increases and attains a constant value at around 60 min when adsorption equilibrium is reached. A 60 minute shaking time was selected for all further studies.

Figure 2 shows the influence of pH on the adsorption of gadolinium on activated charcoal 'Ihe percentage adsorption and distribution coefficient (KD) increase with increasing pH up to 4 and then start to decrease. Maximum adsorption occurs at pH 4, hence a buffer of pH 4 (Fluka, item No. 82560) was used for all further studies. The influence of pH on gadolinium adsorption can be explained in the following way. Up to pH 4, the adsorption of simple hydrolysis product species takes place. Beyond pH 4, due to coagulation, a dimer is formed which reduces the mobility of gadolinium ion,

156

R. QADEER eta 1.: ADSORPTION OF GADOLINIUM ON ACTIVATED CHARCOAL

" 60f = S5 2 120

J,lo 45

[ r 1 6 2 I 100 40 I 0 40 80 120

Shaking time, rain

Fig. 1. Adsorption of Gd on activated charcoal as a function of shaking time: curve 1 - adsorption, curve 2 - K D

-- lOO c 0

~ 8o "(3 <

- 300 -

o

60 - 200

40-

20 - / / 100

0 ~ I 0 0 2 4 8

pH

Fig. 2. Influence of pH o n Gd adsorption on activated charcoal: curve 1 - adsorption, curve 2 - K D

lower ing the adsorpt ion. 10 W h e n the pH approaches a va lue o f 7, the precipi tat ion starts

due to the format ion o f c o m p l e x e s in aqueous solution.

q-he effect o f gado l in ium concent ra t ion on the adsorpt ion was studied under the

op t imized condi t ions o f 60 minutes shaking time, 100 mg of solid and pH 4. The

157

R. Q A D E E R et al.: A D S O R P T I O N OF G A D O L I N I U M O N A C T I V A T E D C H A R C O A L

100 2000 c~

"1~ '~500 < 80

I \ \ 4 500

1000 2000 3000 4000 5000 6000

Concentration of Gd, jug/m[

Fig. 3. Effect o f G d concent ra t ion on its adsorpt ion on act ivated charcoal: curve 1 - adsorption, curve 2 - K D

d

10

"7 ~ s

'7 0 ~ 6

* 4 u

2

0 0 5 1.0 1.5 2.0 2.5 -

c s , x10-3 g / m r

Fig, 4, L a n g m u i r plot for Gd adsopr t ion on act ivated charcoal

concentration of gadolinium was varied from 1000 ~g/ml to 6000 gtg/mt. The results in Fig. 3 show that the percentage adsorption and K o decrease as the gadolinium concentration increases. The increase of gadolinium concentration leads to the formation of larger polymer particles, which leads to the lowering of adsorption. The results were then analyzed in terms of FREUNDLICH, n LANGMUIR 12 and

~58

R. QADEER et a l.: ADSORPTION OF GADOLINIUM ON ACTIVATED CHARCOAL

DUBININ-RUDUSHKEVICH (D-R) 13 isotherms. The data do not fit the

FREUNDLICH and D - R equations. A straight line was obtained in Fig. 4 when Cs/X/m was plotted against Cs; where Csis the equilibrium concentration of gadolinium

(g/ml), X is the amount of gadolinium adsorbed (g) and m is the amount of activated

F . y 8oo

i

Gd solution 300 "- �9 2000jag/m[

�9 3000,ug/ml f 250 �9 4000)Jg/ml

o 5000pg/ml /

200 , /

150

100

50

ID_ 280 290 300 310 320 330

Temperature, K

Fig. 5. Effect of temperature on Gd a d s o p r t i o n o n activated charcoal

charcoal (g). It follows that the adsorption of gadolinium on activated charcoal obeys the LANGMUIR isotherm.

Dependence of gadolinium adsorption on temperature was investigated. The

temperature was varied from 10 to 50 "C in steps of 10 ~ while the other parameters were kept constant. Figure 5 shows that K o increases with the increase of temperature. This increase may be due to a negative temperature coefficient or to a steep simultaneous decrease of real adsorption of the solvent. 14 The values of AH ~ and AS ~

are calculated from the slopes and intercepts of linear variation of In K o with reciprocal

159

R. Q A D E E R et al.: ADSORPTION OF GADOLINIUM ON ACTIVATED C H A R C O A L

x . -

_=

6 �9 3000)Jg/mt

�9 0 4000.~g/m[

I I I I l - ' c " ~ t ~,. 3.0 3.1 3.2 3.3 3,4 3.5 3.6

lIT, xlO -3 K -1

Fig. 6. Plot of In K D vs. I /T for Gd adsorption on activated charcoal

t e m p e r a t u r e l / T , ( F i g . 6 ) u s i n g t h e r e l a t i o n

A S ~ A H o l n K D = ' R - R T (1 )

T h e v a l u e s a r e g i v e n i n T a b l e 1. T h e f l e e e n e r g y o f s p e c i f i c a d s o r p t i o n A G ~ i s

c a l c u l a t e d u s i n g t h e e q u a t i o n

A G ~ = A H ~ - T A S ~ (2 )

Table 1 Thermodynamic parameters for gadolinium adsorption on activated charcoal

Gd eoncen- AHO, ASO, AG ~ kJ" mo1-1

trat ion , kJ �9 m o 1 - 1 kJ - K - 1 �9 mo1-1 p.g/ml 283K 293K 303K 313K 323K

2000 14.7574 0.1033 - 14.4765 - 15.5095 - 16.5425 - 17.5755 - 18.6085

3000 23.7865 0.1199 - 10.1452 - 11.3442 - 12.5432 - 13.7422 - 14.9412

4000 12.4377 0.0774 - 9.4665 - 10.2405 - 11.0145 - 11.7885 - 12.5625 5000 15.2478 0.0837 - 8.4393 - 9.2763 - 10.1133 - 10.9503 - 11.7873

1 6 0


IOOI- Cation added Z/r L z~ NIL

g ~ , , . . ~ �9 K 0.7~2 L ~ ' ~ ' ~ o No 1.031

40

20 1000 2000 3000 4000 5000

Concentration of Gd, pg /mt

Fig. 7. Variation of adsorption for Od in the presence of different cations

a~ 104 Cation added Z/r

O Gd �9 K 0?52 ,~ Co 22?7 �9 Na 1.031 c] Zn 2.703

103 ~ . I Ce 2.901 ~ ~ , . ~7 Cr 4.?62

102

10 I l I I m,. 1000 2000 3000 4000 5000

Concentration of Gd, ,ug/m[

Fig. 8. Variation of KD for Gd in the presence of different cations

161


AG ~ values are also given in Table 1. Positive value of AH ~ and the decrease in

AG ~ with increasing temperature show that the adsorption is more favorable at high temperature.

The influence of cations (Na, K, Co, Zn, Ce and Cr) on the adsorption of gadolinium on activated charcoal was investigated. The concentration of each cation was fixed as

A

80 '~

60

40 )-'-- ~7 r [_ ~ NO3

201 vEDTA I

Anion added ,', Gd �9 Acetate t3 Thiosutphate

1OO0 2000 3000 4000 5000 Concentration of Gd, jug/mr

Fig. 9. Variation of adsorption of Gd in the presence of different anions

1000 Ixg/ml and gadolinium concentration was varied from 1000 ~tg/ml to 5000 gg/ml. The results of these investigations are shown in Figs 7 and 8. It is concluded that the greater the ionic potential (Z/r) of the added cation, the smaller the adsorption of gadolinium except in the case of potassium. Similar observations have been reported .earlier. 9

We also examined the adsorption behavior of gadolinium in the presence of acetate, thiosulfate, chloride, bromide, iodide, nitrate and EDTA. The concentration of each anion was fixed as 1000 ~tg/ml and the concentration of gadolinium was varied from 1000 gg/ml to 5000 lxg/ml. The results are shown in Figs 9 and 10. The acetate ions enhanced the adsorption of gadolinium while the other anions reduced the adsorption of gadolinium. This shows that the anionic acetate complex of gadolinium is more strongly adsorbed on activated charcoal than gadolinium ions themselves. The decrease in the adsorption of gadolinium in presence of I-, CI-, Br- NOg, EDTA and thiosulfate ions may be explained by the lower affinity of their complexes for adsorption. The

162

R. QADEER eta 1.: ADSORPTION OF GADOLINIUM ON ACTIVATED CHARCOAL

,It

10 4 ̀

o

10 3

10 z

10 ~ . 1000 2000 3000 4000 5000

Concentration of Gd ,)Jg/ml

Fig. 10. Variation of KD for Gd in the presence of different anions

&

~ I00 I i 80 u~

"o <

60

40

20

Gd Ni V Zn Cu Rb Sr Mn

Meta ls Fig. 11. Adsorption of Gd and other metals from a mixture containing Gd, Ni, V, Cu, Rb, Sr, Ma

163


&

50

~ 4o

3O

20

10

0 0 10 20 30 40 50

Volume of e tuent , mt

Fig. 12. Elution of adsorbed Gd from activated charcoal with 3M HNO3 solution

Table 2 Percentage adsorption and K D values of other metals on activated charcoal at optimized conditions for Gd

Metal* Adsorption, % KD, ml/g

Dy 91.70 1104.82 Sm 85.00 566.67 Eu 85.90 609.22 Er 83.00 488.24 U 69.30 225.73 La 60.25 151.57 Y 49.85 99.40 Ce 49.40 97.63 Ba 25.40 34.05 Cr 18.55 22.77 Cd 13.65 15.81 Cs 13.60 15.74 Co 11.15 12.55 Ni 9.40 10.38 Zn 7.85 8.52 Mn 7.60 8.23 V 7.30 7.88 Sr 7.30 7.88 Ca 6.95 7.47 Rb 5.05 5.32

*Concentration of all cations fixed at 2000 ~tg/ml.

164


anions reduce the adsorption of gadolinium in the order of EDTA > NOg > C1- > Br- > I-. The influence of flouride, phosphate and oxalate ions on the adsorption of gadolinium could not be studied as they form insoluble precipitates with gadolinium

in aqueous solution. To check the selectivity of activated charcoal for adsorption of gadolinium, the

adsorption of Dy, Sm, Eu, Er, U, La, Y, Ce, Ba, Cr, Cd, Cs, Co, Ni, Zn, Mn, V, Sr, Cu and Rb on activated charcoal was examined under the optimum conditions for gadolinium. The results are given in Table 2. It is obvious from the data that Dy, Sin, Eu, Er, U, La, Y, Ce and Ba have rather high value of % adsorption and K D. So they would coadsorb along with gadolinium on activated charcoal. Cr, Cd, Cs, Co, Ni, Zn, Mn, V, Sr, Cu and Rb are poorly adsorbed; hence separation of gadolinium from these metals may be achieved. The separation factor for gadolinium is larger in the presence of Ni, V, Zn, Cu, Rb, Sr and Mn, because they have much lower K D values. The separation of gadolinium in the presence of these metals is shown in Fig. 11. The feasibility of using activated charcoal for preconcentration of gadolinium was further assessed by elution studies. This study was performed with 3M HNO 3 and the result

is shown in Fig. 12.

The authors are grateful to Mr. A. MAJEED for his cooperation and encouragement during this work. Services of Mr. M. KHAN are highly appreciated. Thanks are also due to Mr. RABBANI for typing the

manuscript.

References

1. E. V. BUZANEVA, A. A. VDOVENKOV, T. A. VDOVENKOVA, M. I. GORODYSKII, Poverkhnost., No 10 (1985) 56.

2. G. G. VLADIMIROV, G. A. RUMP, Poverkhnost., No. 10 (1986) 61. 3. G. A. RUMP, G. G. VLADIMIROV, T. T. MYAGKOEV, Poverkhnost. Fiz. Khim. Mekh., 3 (1988) 54. 4. F. M. GONCHAR, V. K. MEDVEDEV, T. P. SMEREKA, YA. B. LOZOVYJ, G. V. BAKIN, Fiz. Tverd.

Tela, 29 (1987) 2833. 5. F. M. GONCHAR, T. P. SMEREKA, S. I. STEPANOVSKIJ, G. V. BABKIN, Fiz. Tverd. Tela, 30 (1988)

3541. 6. G. BLIZNAKOV, TS. MARINOVA, A. POPOV, Izuch. Khim., 9 (1976) 203. 7. M. AFZAL, J. HANIF, I. HANIF, R. QADEER, M. SALEEM, J. Radioanal. Nucl. Chem., 139 (1990)

203. 8. M. SALEEM, M. AFZAL, J. HANIF, R. QADEER, I. HANIF, J. RadioanaL Nucl. Chem.., 142 (1990)

393. 9. S. M. HASANY, M. H. CHAUDHARY, J. Radioanal. Nucl. Chem., 84 (1984) 247.

10. M. B. ABRAMSON, M. J. JAYCOCK, R. H. OTTEWILL, J. Chem. Soc., 5 (1964) 5041. 11. M. A. RAUF, S. M. HASANY, M. I. HIJSSAIN, J. Radioanal. Nucl. Chem., 132 (1989) 397. 12. M. AFZAL, M. SALEEM, M. I. MAHMOOD, G. RAFIQ, H. AHMAD, Sei. Int. (LHR), 1 (1989) 165. 13. S. AKSOYOGLU, J. Radioanal. Nucl. Chem., 134 (1989) 393. 14. J. J. BIKERMAN, Surface Chemistry-Theory and Application, Academic Press Inc., New York, 1958, p.

294.

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Adsorption of gadolinium on activated charcoal from electrolytic aqueous solution