Journal of Radioanalytical and Nuclear Chemistry, Vol. 270, No.3 (2006) 559–566

Kinetic studies for sorption of some metal ions from aqueous acid solutions onto TDA impregnated resin E. Metwally* Nuclear Chemistry Department, Hot Labs Center, Atomic Energy Authority, Cairo, Egypt (Received March 7, 2006)

Kinetic studies for sorption of uranium, thorium and cobalt ions from hydrochloric acid solutions using tri-dodecyl amine (TDA) loaded on Amberlite XAD4 (polystyrene resin supplied by Rohm and Haas) using the batch technique, have been evaluated and assessed. Analysis of the respective data in accordance with three kinetic models revealed that the particle diffusion mechanism is the rate determining step, and the sorption for each metal ion on the impregnated sorbent follows the first order reversible kinetics. Values of the first order rate constants, rate constants of intraparticle transport, and the particle diffusion coefficients for the studied ions were determined. Sorption isotherms, which have been evaluated from the distribution coefficients for these ions, were found in good fit with the Langmuir and Freundlich isotherms.

Introduction Solvent impregnated resin (SIR) extraction technique has been proposed as a technological alternative to solvent extraction and ion-exchange techniques for metal separation and recovery,1 combining the advantages of both systems. Comprehensive works dealing with sorption and separation of metals with solvent impregnated resins has been carried out.2–22 Different extractants were used in these studies such as acidic organophosphorus extractants, e.g., di(2-ethyl hexyl) phosphoric acid (HDEHP), cyanex 272, PC-88A; neutral extractants, e.g., tri-n-butyl phosphate (TBP) and basic extractants, e.g., tri-n-octylamine (TOA). These extractants were impregnated on different supports like XAD resins, silica gel, kieselguhr, and activated carbons. The stability of impregnated resins depends principally on the type of support used and the nature of the organic reagent retained. In the present work, sorption of uranium, thorium and cobalt ions from acid medium using tri-dodecyl amine (TDA) loaded on a macroporous polymeric resin (XAD4) as a supporting material has been investigated with the batch kinetics and the equilibrium data obtained. Different models were applied for kinetic study for the sorption of the studied elements. Experimental Chemicals and reagents Reagent grade TDA (>95% purity, Merck) was used as extractant without further purification. Amberlite XAD4 resin (Rohm and Haas) was used as a macroporous polymeric support. It is made of styrenedivinylbenzene copolymer with a specific surface area

of 750 m2/g, an average pore diameter of 40 Å, and a particle size of 20–50 µm. The resin was washed with distilled water and acetone several times in turn, and dried at 50 °C. Stock solutions of U(VI), Th(IV) and Co(II) (~10–3M) were prepared by dissolving UO2Cl2.2H2O, Th(NO3)4.4H2O and CoCl2.2H2O (Prolabo) in distilled water, respectively. All the experimental procedures are explained in Reference 23. All chemicals used were of analytical grade. Preparation of impregnated resin Impregnated resins were prepared using a dry impregnation method.24 The procedure of the impregnated resin preparation is mentioned in Reference 25. An appropriate volume of 0.2M TDA solution in nhexane was mixed with a weighted amount of the resin for 1 hour. The diluent was then evaporated at 50 °C for 24 hours. The concentration of TDA in the prepared impregnated resin was determined from the amount of HCl sorbed by shaking the impregnated resin with 0.1M HCl, and is given as moles of TDA per kg of dry impregnated resin.25 Kinetic studies Samples of TDA-impregnated resin were contacted with 5 ml of the aqueous solution containing the metal ion at the desired concentration. Weight of the impregnated resin used was 0.05 g for studying U(VI) and Th(IV) ions and 0.1 g for studying Co(II) ions. A magnetic stirrer at a medium speed for 24 hours was applied at room temperature (25±1 °C). After the chosen time intervals the uranium and thorium samples were analyzed using spectrophotometry. 60Co sample was assayed radiometrically.

* E-mail: [email protected] 0236–5731/USD 20.00 © 2006 Akadémiai Kiadó, Budapest

Akadémiai Kiadó, Budapest Springer, Dordrecht

E. METWALLY: KINETIC STUDIES FOR SORPTION OF SOME METAL IONS FROM AQUEOUS ACID SOLUTIONS

Sorption isotherms Sorption isotherms for U(VI), Th(IV) and Co(II) on the TDA impregnated sorbent were investigated. In this study, 0.5 g TDA impregnated resin was agitated with 25 ml metal ion solutions of varying concentrations. The concentration of the ion sorbed onto the impregnated resin at equilibrium, qe (mg.g–1) was calculated by:

qe = (C0 − Ce )

V m

(1)

where C0 and Ce are the initial and equilibrium concentrations of the metal ion(s) in mg.l–1, respectively, V is the volume of the aqueous solutions (l), and m is the weight of the TDA impregnated resin used (g). Results and discussion

Kinetic studies Preliminary investigations carried out on the rate of sorption for uranium, thorium and cobalt ions onto XAD4 impregnated with TDA solution indicated that the uptake of uranium or thorium reaches ~95% after 24 hours of contact. After this time, the curves began to level off. Whereas the uptake of cobalt reaches 72% after 24 hours. The extraction mechanism of the studied ions from acid media have been published elsewhere.23,26–28 Figure 1, represents the amount of U(VI), Th(IV) and Co(II) ions sorbed onto TDA impregnated resin at room temperature. It had been recognized that the characteristics of the surface of the sorbent and, hence, its diffusion resistance played an important role in the rate of sorption and accordingly the overall transport of the solute. Therefore, an appropriate kinetic model is required to assess the changes of sorption of the studied ions with time. For this purpose, three kinetic models have been applied and evaluated. The first model used, was the first order Lagergren equation which was applied for sorption kinetics:29 log(qe − qt ) = log qe −

kt 2.303

(2)

where qe (mg.g–1), is the concentration of the ion sorbed at equilibrium, qt (mg.g–1) is the concentration of the ion sorbed at time t, and k is the overall rate constant.

560

Fig. 1. Amounts of uranium (a), thorium (b) and cobalt (c) ions sorbed onto TDA impregnated resin at room temperature

It could be observed from Figs 1 and 2 that the sorption of U(VI), Th(IV) and Co(II) ions had followed the Lagergren equation over the entire period of investigation. The slope of these plots is shown in Fig. 2. The values calculated for the first order rate constants for U(VI), Th(IV) and Co(II) ions were equal to 0.169, 0.116 and 0.21 h–1, respectively.

E. METWALLY: KINETIC STUDIES FOR SORPTION OF SOME METAL IONS FROM AQUEOUS ACID SOLUTIONS

Polynomial regression data of Fig. 2c Y = A + B1.X Parameter A B1 R2 (COD) 0.99252

Value 0.74706 –0.09147 SD 0.01716

N 3

Error 0.02338 0.00794 P 0.005514

Secondly, the kinetics of sorption of U(VI), Th(IV) and Co(II) on the TDA impregnated resin were also evaluated by the Morris-Weber equation:30

qt = K d t

(3)

where qt is the concentration of the sorbed ion (mg.g–1) at time t, and Kd is the rate constant for the intraparticle transport (mg.g–1.h–0.5). According to this model, a graphic plot for qt versus t could predict the sorption mechanism. If a straight line (passing through the point of origin) is obtained, therefore, sorption of the ions onto the impregnated sorbent followed a diffusion mechanism. In this case, the slope of the linear plot indicates the rate constant of the intraparticle transport (Kd). Figure 3a represents the Morris-Weber relationship. It could be seen that this relationship fits good up to 5 hours, and then deviates. The slope of the linear plot obtained from the initial stage is shown in Fig. 3b. The values of Kd calculated for the sorption of U(VI), Th(IV) and Co(II) ions from Figs 3 to 5, were found equal to 11.025, 9.915 and 2.028 mg.g–1.h–0.5, respectively. The third model suggested by HELFFERICH,31 has been applied to interpret the experimental results. The parameters involved in this model were calculated by: ∞

Fig. 2. Lagergren plot for the kinetic modeling of uranium (a), thorium (b) and cobalt (c) ions sorbed onto TDA impregnated resin at room temperature Polynomial regression data of Fig. 2a Y = A + B1.X Parameter A B1 R2 (COD) 0.99699

Value 1.543 –0.0735 SD 0.00638

N 4

Value 1.6148 –0.05061 SD 0.01923

N 4

or

Error 0.00782 0.00285 P 0.00151

Error 0.01923 0.00444 P 0.00761

F =1−

exp[− n 2 Bt ] 2∑ 2 n π 6

∞

1

(4)

(5)

n =1

where

Polynomial regression data of Fig. 2b Y = A + B1.X Parameter A B1 R2 (COD) 0.98483

⎡ − Di tπ 2 n 2 ⎤ 6 1 F = 1 − 2 ∑ 2 exp⎢ ⎥ r02 π n =1 n ⎢⎣ ⎥⎦

B=

π 2 Di r02

(6)

where F is the fractional attainment of equilibrium at time t, Di is the effective diffusion coefficient of metal ion, r0 is the radius of the particles of the impregnated sorbent, n is an integer = 1,2,3, …, and B is the time constant. Bt values as derived from Eq. (5), and the values of F were obtained from the REICHENBURG’s table.32 A plot for Bt versus time, t, for the sorption of U(VI), Th(IV) and Co(II) ions onto the impregnated sorbent was employed to distinguish between the film and the particle diffusion-controlled sorption mechanisms (Fig. 6). These plots were found linear for

561

E. METWALLY: KINETIC STUDIES FOR SORPTION OF SOME METAL IONS FROM AQUEOUS ACID SOLUTIONS

uranium, thorium and cobalt ions and the straight lines pass through the origin. These results indicated that the sorption of the studied ions on the TDA impregnated sorbent obeyed a particle diffusion mechanism. The values of the slope can be used to calculate the effective diffusion coefficient for the studied ions, using Eq. (6). The diffusion coefficients calculated are, in fact, a measure for the mean interdiffusion coefficient of the various species involved in the sorption processes. The diffusion coefficient values (Di) calculated for sorption of U(VI), Th(IV) and Co(II) ions were equal to 6.327.10–11, 3.275.10–11 and 7.389.10–11 cm2/h, respectively. These values agree with that published in the literature.33

Fig. 4. Morris–Weber plot for the kinetic modeling of thorium ions sorbed onto the TDA impregnated resin (a) and as linear plot (b) Parameters of Fig. 4b Parameter B R 0.99751

Value 9.91592 SD 1.84106

Error 0.4342 N 4

P 0.00231

Sorption isotherms

Fig. 3. Morris–Weber plot for the kinetic modeling of uranium ions sorbed onto the TDA impregnated resin (a) and as linear plot (b) Linear regression data of Fig. 3 Y = A + B. X Parameter A B R 0.99972

562

Value 0.00692 11.02539 SD 0.13657

N 3

Error 0.37204 0.26309 P 0.01519

Sorption isotherms obtained from sorption of U(VI), Th(IV) and Co(II) ions from 6M HCl, HNO3 and 9M HCl, respectively, onto TDA impregnated resin are shown in Fig. 7. It could be observed that the isotherms obtained are regular, positive, and concave towards the concentration axis. The initial rapid sorption indicated a slow approach to equilibrium with higher metal ion concentrations. The distribution of the studied ions between the solid-liquid interface at equilibrium, has been applied with Langmuir and Freundlish isotherm models.

E. METWALLY: KINETIC STUDIES FOR SORPTION OF SOME METAL IONS FROM AQUEOUS ACID SOLUTIONS

The equations of the Langmuir isotherm could be written in linear form:

Ce ⎛⎜ 1 ⎞⎟ ⎛⎜ 1 ⎞⎟ Ce = + qe ⎜⎝ Q 0b ⎟⎠ ⎜⎝ Q 0 ⎟⎠ and in non-linear form: Q 0bCe qe = 1 + bCe

(7)

(8)

where qe is the amount of the ion sorbed per unit weight of sorbent (mg.g–1), Ce is the equilibrium concentration of the solute in the bulk solution (mg.l–1), Q0 is the monolayer adsorption capacity (mg.g–1) and b is the constant related to the free energy of adsorption (b α e–∆G/RT).

Fig. 6. Reichenberg plot for the kinetic modeling of uranium (a), thorium (b) and cobalt (c) ions sorbed onto TDA impregnated resin Linear regression data of Fig. 6a Y = A + B. X Parameter A B R 0.99655

Value –0.03805 0.10195 SD 0.01342

N 4

Error 0.01643 0.006 P 0.00345

Linear regression data of Fig. 6b Y = A + B. X Fig. 5. Morris–Weber plot for the kinetic modeling of uranium ions sorbed onto the TDA impregnated resin (a) and as linear plot (b) Linear regression data of Fig. 5 Y = A + B. X Parameter A B R 0.99984

Value –0.01151 2.02895 SD 0.03358

N 4

Error 0.03152 0.02574 P 1.60862E-4

Parameter A B R 0.99992

Value –0.00112 0.05277 SD 0.00146

N 4

Error 0.00117 4.60353E-4 P <0.0001

Linear regression data of Fig. 6c Y = A + B. X Parameter A B R 0.99886

Value 0.00897 0.11906 SD 0.01773

N 5

Error 0.01164 0.00328 P <0.0001

563

E. METWALLY: KINETIC STUDIES FOR SORPTION OF SOME METAL IONS FROM AQUEOUS ACID SOLUTIONS

Also, the Freundlich equations may be written in linear form:

qe = K F Ce1 / n and in non-linear form: 1 log qe = log K F + log Ce n

(9)

(10)

where qe is the amount of the solute sorbed per unit weight of the sorbent (mg.g–1), Ce is the equilibrium concentration of the solute in the bulk solution (mg.l–1), KF is the constant indicative of the relative sorption capacity of the sorbent (mg.g–1) and 1/n is the constant indicative of the intensity of the sorption processes. The Langmuir and Freundlich isotherms for sorption of the studied ions on the impregnated sorbent are presented in Figs 8 and 9, respectively. The straight lines obtained indicate that sorption of U(VI), Th(IV) and Co(II) ions fit with the two investigated isotherms. Table 1 illustrates the Freundlich and Langmuir parameters calculated for sorption of U(VI), Th(IV) and Co(II) and the correlation coefficient values (R2) for these ions. The data obtained from the Freundlich isotherm suggest that the sorption processes could not be restricted for a specific class of sites and assume surface heterogeneity. The slopes of the Freundlich plots were found less than unity, which indicate that the sorption of these ions onto the TDA impregnated sorbent is a concentration-dependent process. Also, the monolayer capacity (Q0) for sorption of the studied elements was found in the order: cobalt > thorium > uranium ions.

Fig. 7. Isotherm plot of uranium and thorium ions (a) and cobalt ions (b) sorbed onto impregnated sorbent

Table 1. Langmuir and Freundlich parameters data for the sorption of uranium, thorium and cobalt ions from HCl media onto TDA impregnated sorbent Metal ion U(VI) Th(IV) Co(II)

564

Q0, mg.g–1 5.83 13.75 25.20

Parameters for Langmuir model b R2 ×10–3 l,g–1 98.7 0.996 54.3 0.990 2.55 0.997

Parameters for Freundlich model Ka

KF

n–1

R2

0.576 0.746 0.064

1.507 1.281 3.461

0.331 0.456 0.227

0.962 0.975 0.989

E. METWALLY: KINETIC STUDIES FOR SORPTION OF SOME METAL IONS FROM AQUEOUS ACID SOLUTIONS

Fig. 8. Langmuir isotherm for the sorption of uranium (a), thorium (b) and cobalt (c) ions onto TDA impregnated resin

Fig. 9. Freundlich isotherm for the sorption of uranium (a), thorium (b) and cobalt (c) ions onto the TDA impregnated resin

Polynomial regression data of Fig. 8a Y = A + B1.X

Polynomial regression data of Fig. 9a Y = A + B1.X

Parameter A B1 R2 (COD) 0.9962

Value 1.7346 0.17131 S 0.15642

N 5

Error 0.11748 0.00611 P <0.0001

Parameter A B1 R2 (COD) 0.96299

Value 1.33882 0.07272 SD 0.44876

N 4

Error 0.30898 0.00509 P 0.00486

Parameter A B1 R2 (COD) 0.97531

Value 15.51349 0.03968 SD 4.85447

N 7

Value 0.10767 0.45604 SD 0.04395

N 4

Error 0.08761 0.05131 P 0.01242

Polynomial regression data of Fig. 9c Y = A + B1.X

Polynomial regression data of Fig. 8c Y = A + B1.X Parameter A B1 R2 (COD) 0.99701

N 4

Error 0.06305 0.04596 P 0.01868

Polynomial regression data of Fig. 9b Y = A + B1.X

Polynomial regression data of Fig. 8b Y = A + B1.X Parameter A B1 R2 (COD) 0.99031

Value 0.17827 0.33158 SD 0.05238

Error 2.88544 9.71876E-4 P <0.0001

Parameter A B1 R2 (COD) 0.98931

Value 0.5393 0.22758 SD 0.01219

N 6

Error 0.03895 0.01183 P <0.0001

565

E. METWALLY: KINETIC STUDIES FOR SORPTION OF SOME METAL IONS FROM AQUEOUS ACID SOLUTIONS

Conclusions The use of macroporous material XAD4 (polystyrene divenyl benzene) and impregnated it with TDA solution for the sorption of uranium, thorium and cobalt ions from hydrochloric and nitric acid solutions, was found feasible from the sorption isotherms and kinetic data obtained. Applying this system with three different kinetic models revealed that the particle diffusion mechanism was the rate-determining step for the entire sorption processes. The values of the first order kinetic constants, constants of interparticle transport, and the particle diffusion coefficients of these ions were calculated. The equilibrium isotherms for sorption of the studied ions have been modeled successfully using the Langmuir and Freundlich isotherms. The kinetics data obtained provided valuable information about the sorption mechanisms involved and could be helpful for the design of the improved solvent impregnated resin (SIR) investigations. References 1. A. WARSHAWSKY, Ion Exchange and Solvent Extraction, Vol. 8, J. A. MARINSKY and Y. MARCUS (Eds), Marcel-Dekker, New York, 1981, p. 229. 2. J. L. CORTINA, A. WARSHAWSKY, Ion Exchange and Solvent Extraction, Vol. 13, J. A. MARINSKY and Y. MARCUS (Eds), Marcel-Dekker, New York, 1997, p. 195. 3. R. S. JUANG, Proc. Nat. Sci. Counc. ROC(A), 23 (1999) 353. 4. A. M. EL-KAMASH, A. A. EL-SAYED, H. F. ALY, J. Radioanal. Nucl. Chem., 253 (2002) 489. 5. A. M. EL-KAMASH, N. S. AWWAD, A. A. EL-SAYED, Arab J. Nucl. Sci. Appl., 37 (2004) 31. 6. A. M. EL-KAMASH, A. A. EL-SAYED, H. F. ALY, Arab J. Nucl. Sci. Appl., 36 (2003) 73. 7. R. S. JUANG, M. L. CHEN, Separ. Sci. Technol., 32 (1997) 1017. 8. W. FAUBEL, New Separation Chemistry Techniques for Radioactive Waste and Other Specific Applications, L. CECILLE, M. CASARCI and L. PIETRELLI (Eds), Elsevier, Amsterdam, 1991, p 73. 9. P. K. MOHAPATRA, S. SRIRAM, V. K. MANCHANDA, L. P. BADHEKA, Separ. Sci. Technol., 35 (2000) 39.

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10. M. YAMAURA, H. T. MATSUDA, J. Radioanal. Nucl. Chem., 224 (1997) 83. 11. J. SHIBATA, S. MATSUMOTO, Program and Abstracts of the International Rare Earths Conference, Rare Earths’98, WA, Australia, 1998, p. 67. 12. Z. WANG, G. MA, D. LI, Solvent Extr. Ion Exch., 16 (1998) 813. 13. S. AKITA, K. HIRANO, Y. OHASHI, H. TAKEUCHI, Solvent Extr. Ion Exch., 11 (1993) 797. 14. M. ROVIRA, J. L. CORTINA, J. ARNALDOS, A. M. SASTRE, Solvent Extr. Ion Exch., 16 (1998) 1279. 15. I. VILLAESCUSA, N. MIRALLES, J. DE PABLO, V. SALVADO, A. SASTRE, Solvent Extr. Ion Exch., 11 (1993) 613. 16. J. L. CORTINA, N. MIRALLES, M. AGUILAR, A. M. SASTRE, Hydrometallurgy, 36 (1994) 131. 17. E. P. HORWITZ, M. L. DIETZ, R. CHIARIZIA, H. DIAMOND, S. L. MAXWELL, M. R. NELSON, Anal. Chim. Acta, 310 (1995) 63. 18. Y. WAKUI, S. A. NDIAYE, H. MATSUNAGA, T. YOKOYAMA, K. AKIBA, Anal. Sci., 14 (1998) 299. 19. ZHANG-YUQIN, Uranium Mining Metallurgy, 18 (1999) 65. 20. C. H. LEE, K. S. CHOI, J. S. KIM, K. C. CHOI, K. Y. JEE, W. H. KIM, J. Korean Chem. Soc., 45 (2001) 304. 21. J. H. CHEN, Y. Y. KAO, C. H. LIN, Separ. Sci. Technol., 38 (2003) No. 15. 22. J. KRAMER, W. L. DRIESSEN, K. R. KOCH, J. REEDIJK, Separ. Sci. Technol., 39 (2004) No. 1. 23. A. SH. SALEH, M.Sc. Thesis, Ain Shams University, 2004, p. 64. 24. A. WARSHAWSKY, Ion Exchange and Solvent Extraction, Vol. 8, J. A. MARINSKY and Y. MARCUS (Eds), Marcel-Dekker, New York, 1981, p. 229. 25. E. METWALLY, A. SH. SALEH, H. A. EL-NAGGAR, J. Nucl. Radiochem. Sci., 6 (2005) 119. 26. W. A. ABBASI, M. STREET, Solvent Extr. Ion Exch., 16 (1998) 1303. 27. E. METWALLY, A. SH. SALEH, H. A. EL-NAGGAR, J. Nucl. Radiochem. Sci., 6 (2005) 1. 28. M. W. ABDEL RAOUF, A. M. EL-KAMASH, Arab J. Nucl. Sci. Appl., 38 (2005) No. 3. 29. J. I. HUH, D. I. SONG, Y. W. JEON, Separ. Sci. Technol., 35 (2000) 243. 30. W. J. WEBER, J. C. MORRIS, J. San. Eng. Div. ASEC, 899 (1963) 31. 31. F. HELFFERICH, Ion Exchange, McGraw-Hill, New York, 1962. 32. D. REICHENBURG, J. Am. Chem. Soc., 75 (1953) 589. 33. D. MOHAN, K. P. SINGH, Water Res., 36 (2002) 2304.