Embed Size (px)
Citation preview
J.RADIOANAL.NUCL.CHEM.,LETTERS 165 (4) 243-253 (1992)
EFFECT OF ALKALI METALS, ALKALINE EARTH METALS AND LANTHANIDES ON THE ADSORPTION OF URANIUM ON ACTIVATED CHARCOAL FROM AQUEOUS SOLUTIONS
R. Qadeer, J. Hanif, M. Saleem*, M. Afzal*
Pakistan Institute of Nuclear Science and Technology, P.Oo Box No. 1356~ Islamabad, Pakistan
*Department of Chemistry, Quaid-i-Azam University, Islamabad, Pakistan
Received 3 April 1992 Accepted 17 April 1992
Effects of alkali metals, alkaline earth metals and some lanthanides on the adsorp- tion of uranium on activated charcoal from aqueous solutions have been studied. These effects are correlated with the ionic radii of metal ions present in the solu- tions. Adsorption capacity, X m and binding energy contant, K for uranium adsorption were calculated from the Langmuir equation. The mean energy of adsorption, E s was cal- culated from adsorption energy constant, K, values determined from the Dubinin- Radushkevich isotherm equation. Wavelength dispersive X-ray fluorescence spectrom, etry was used for measuring the uranium concentration.
INTRODUCTION
Activated charcoal, due to its selective adsorption,
high radiation stability and high purity, is often used
for the separation of metal ions from solutions in nu-
*Author for correspondence.
243 Elsevier Sequoia S. Ao, Lausanne Akad~miai Kiad6, Budapest
QADEER et al.: ADSORPTION OF U ON ACTIVATED CHARCOAL
clear industry. The adsorption of uranium on solids has
been the subject of several investigations 1-9. The
present communication describes the effect of alkali
metals, alkaline earth metals and some lanthanides on
the adsorption of uranium on activated charcoal from
aqueous solutions.
EXPERIMENTAL
The chemicals used in this study were activated
charcoal (BDH, No. 33032), uranyl nitrate (Riedel de
Haen, No. 31638), nitrates of lanthanum, samarium, gado-
linium, dysprosium, and erbium (Rare earth products,
99.999%), barium nitrate (Fluka, No. 11787), calcium
nitrate (Fluka, No. 21194), cerium nitrate (Fluka, No.
2100a), lithium nitrate (Fluka, NO. 62574), rubidium ni-
trate (Fluka, No. 84010), sodium nitrate (Fluka, No.
7175a) and strontium nitrate (Fluka, No. 85900).
Instruments
Siemens wavelength dispersive X-ray fluorescence
(WDXRF) spectrometer SRS-200, was used for measuring the
uranium concentration. Emund Buhlar-SM25 Shaker was used
for shaking sample solutions at a constant speed of 150
r.p.m.
Procedure
The adsorption of uranium in the presence of alkali
metals, alkaline earth metals and lanthanides was car-
ried out by a batch technique at room temperature
(21• ~ . 100 mg of activated charcoal in 250 ml re-
agent bottles containing known amounts of uranium and
244
QADEER et al.: ADSORtrHON OF U ON ACTIVATED CHARCOAL
TABLE I
Instrumental conditions for measuring uranium concentration
Spectrometer
Tube
Detector
Crystal
Collimator
Tube voltage
Tube current
Radiation path
Analyte line
LBG (2@ value)
Pak (2@ value)
HBG (28 value)
Counting time
Siemen's SRS-200
Cr-target
Scintillation, NaI(TI)
LiF-100
Fine, 0.15 ~
50 kV
50 mA
Air
U L ]
25.98
26.18
26.38
40 sec at all 2 @ values
fixed concentrations of alkali metals, alkaline earth
metals and some lanthanide elements were shaken for I h
(equilibration time). The solutions were then filtered
and concentration of uranium before and after shaking
was measured by a WDXRF spectrometer under conditions
given in Table 1. The sample solutions were placed into
the spectrometer in 0.1 mm thick walled polyethylene
bottles 10'11 The amount of uranium adsorbed (g) per g
of activated charcoal in the presence of alkali metals,
alkaline earth metals and lanthanides were calculated
and plotted against equilibrium concentration, C s t Figs I-3.
245
QADEER et al.: ADSORPTION OF U ON ACTIVATED CHARCOAL..
2 0 1 / / / , ~ �9 ~o c~ ~ 1 / / / / / ,, u ~o R~
V// / / " ~ !~ Na m Uin Li
3
Equil.conc.,gll
Fig. I. Adsorption isotherms of uranium in alkali metals
~ I / / / o~ureU 1//I" �9 0~0 Bo
I / / / o o 'o
Equil, conc. ,gl[
Fig. 2. Adsorption isotherms of uranium in presence of alkaline earth metals
RESULTS AND DISCUSSION
Figures I-3 show the effect of alkali metals Li, Na,
Rb, Cs, alkaline earth metals Ca, Sr, Ba and lanthanides
Er, Dy, Gd, Sm, La on the adsorPtion of uranium on ac-
tivated charcoal from aqueous solutions. In these inves-
246
OADEER et al.: ADSORPTION OF U ON ACTIVATED CHARCOAL
~ 3 0
20
<E
10
/ ~ ~ ~ i ~ e LUG
u U in Dy m U i n Er
i I l I __ , I i t 2 3 4
E.quit. conc., g / 1
Fig. 3. Adsorption isotherms of uranium in different lanthanides
tigations the concentration of uranium was varied from
1000 ~g ml -I to 6000 ~g ml -I, while the concentration
of all other metals was fixed at 1000 ~g ml -I It is
obvious from Figs I-3 that the presence of these metals
in solutions has reduced the adsorption of uranium on
activated charcoal. The adsorption of uranium is lowered
because these metals are coadsorbed along with uranium
on activated charcoal. The decrease in uranium adsorp-
tion has been observed in the order of, Li + > Na + >
Rb t > Cs t for alkali metals; Ca 2+ > Sr 2§ > Ba 2+ for al-
kaline earth metals and Er3+~> Dy 3+ > Gd 3+ > Sm 3+ > La 3+
for lanthanides. The values of ionic radii for the above
mentioned elements are in the order of Li + < Na + < Rb +
< Cs § for alkali metals; Ca2+ < Sr 2+ < Ba 2+ for alkali-
ne earth metals and Er 3+ < Dy 3+ < Gd 3+ <Sm 3+ < La 3+
for lanthanides. Itiis concluded that the elements with
small ionic radii have a greater effect of decreasing
uranium adsorption on activated charcoal as compared to
247
7 o, 0 . 1 8 - 6, o Pure U . J
�9 U in Cs
�9 U in R b 7/~ .0,0 N /////
6,
3" 012
006
QADEER cLal.: ADSORPTION OF U ON ACTIVATED CHARCOAL
n v I z I r I v ~0 1 2 3 4
C$, g/[
Fig. 4. Langmuir plot for the adsorption of uranium in presence of alkali metals
the elements having larger ionic radii. This is to be
expected since ions with smaller radii would interact
more strongly with the charcoal surface.
The data of Figs 1-3 fit well the Langmmir equation.
A typical Langmuir plot is shown in Fig. 4. The iso-.
therms drawn in Fig. 4 are represented by the following
equation:
C C s _ 1 + _ss (1 )
(x/m) K X X m m
where X = maximum adsorption capacity, m
K = binding energy constant,
(x/m) = amount of metal ion adsorbed per g of
solid,
C = equilibrium concentration of metal ion. S
248
QADEER et al.: ADSORPTION OF U ON ACTIVATED CHARCOAL
TABLE 2
Langmuir isotherm constants for the adsorption of uranium in the presence of alkali metals, alkaline earth metals
and lanthanide elements along with ionic radii
U in presence X K Ionic radii, of m
Alkali metals
Li + 24.69 5.10 0.68
Na + 26.19 5.60 0.97
Rb + 26.77 7.19 1.47 +
Cs 27.50 8.69 1.67
Pure U(VI) 28.79 11.12 -
Alkaline earth metals
C a2+ 25.90 2.64 0.99
Sr 2+ 25.95 4.57 1.12
Ba 2+ 28.30 5.02 1.34
Pure U(VI) 29.39 9.47 -
Lanthanides
Er3+ 24.03 1.45 0.881 3+
Dy 25.06 1.64 0.908
Gd3+ 25.30 2.14 0.938
Sm3+ 26.28 2.70 0.964
La3+ 27.45 3.68 1.016
Pure U(VI) 29.94 8.72 -
The values of X m and K calculated from the slopes and
intercepts of the Langmuir plots are given in Table 2.
It can be seen from this Table that the values of X and m
249
QADEER et al.: ADSORPTION OF U ON ACTIVATED CHARCOAl,
K for the adsorption of uranium in the presence of alka-
li metals, alkaline earth metals and landhanide follow
a sequence similar to that discussed earlier.
The mean energy of adsorption, E ; defined as the s
free energy change when one mol of ion is transferred
to the surface of the solid from infinity in solution,
for uranium in the presence of alkali metals, alkaline
earth metals and lanthanides is calculated using the
relation 12-13 .
S s = (-2K') -I/2- (2)
Where K' is calculated from the Dubinin-Radushkevich
(D-R) isotherm equation. The linearized D-R equation is
in X = in X - K'e 2 (3) m
Where e = RT in (1+I/Cs) ,
C s = equilibrium concentration of uranium,
R = gas constant (kJ deg -I mol-1) ~
T = absolute temperature (K),
K' = constant related to the adsorption energy
(mol 2 Kj-2),
X m = adsorption capacity of the adsorbent per
unit weight,
X = amount of uranium adsorbed per gram of solid.
A typical plot of in X against 2, for the adsorp-
tion of uranium in the presence of alkali metals is
shown in Fig. 5. From the slopes and intercepts, the
values of K' and X m, for the systems under study were
calculated and their values are given in Table 3. The
250
QADEER et al.: ADSORPIION OF U ON AC'IIVATED CHARCOAL
TABLE 3
D-R isotherm parameters and mean energy of adsorption of uranium in the presence of alkali metals, alkaline
earth metals and lanthanides
U in presence of X K' E , kJ mol -I m s
Alkali metals
Li + 23.81 0.063 2.81
Na + 25.38 0.060 2.88
Rb + 25.48 0.051 3.13
Cs + 27.19 0.035 3.78
Pure U(VI) 28.22 0.029 4.15
Alkaline earth metals
C a2+ 24.56 0.133 1.94
Sr 2+ 25.53 0.080 2"50
Ba 2+ 26.89 0.056 2.98
Pure U(VI) 29.42 0.023 4.66
Lanthanides
Er3+ 22.40 0.259 1.39 3+
Dy 23.24 0.213 1.53
Gd3+ 24.22 0.171 1.71
Sm3+ 24.83 0.122 2.02
La3+ 26.15 0.087 2.40
Pure U(VI) 28.62 0.030 4.08
values of Es, calculated from Eq. (2) are also given
in Table 3. This Table shows that E increases as the s
ionic radius, of the metal ion increases. The change in
251
QADEER et al.: ADSORPTION OF U ON ACTIVATED CHARCOAL
39
2.5 O! n U inL i
2 , - t I T l i 4 8 12
E 2
Fig. 5. D-R plot for the adsorption of uranium in presence of alkali metals
E s with the ion size is in line with the previous argu-
ment where smaller ions would decrease E to a larger s
extent.
REFERENCES
I. R.E. Byler, L.A. Meclaine, U.S. Atomic Energy Com- mission Report No. TID-7508, (1955) 47.
2; I.A. Kuzin, V.P. Taushkan.ov, V.C. Aleshechkin, Radiokhimiya, 4 (1962) 832.
3. V.S. Roslyakov, M.P. Ezhova, Radiokhimiy_a, 8 (1966) 360.
4. U. Keiji, Y.-Masahiro, K. Minoru, Kokai, 67 (1976) 217.
252
QADEER et al.: ADSORPTION OF U ON ACTIVATED CHARCOAL
5. E. Taskaev, D. Apostolov, J. Radioanal. Chem., 45 (1978) 65.
6. M. Hidetoshi, Kobunshi, 30 (1981) 193.
7. J. Halena, S. Lech, P. Karol, P. Grazyna, Przem. Chem., 64 (1985) 429.
8. K. Shunsaku, F. Ayako, M. Yoshitaka, T. Norio, S. Koji, H. Takhahiro, W. Hideo, K. Takao, O. Kenta, Shikoku Kogyo Gijutsu Shikensho Kenkyu Hokoku, 11 (1987) 37.
9. M. Saleem, M. Afzal, R. Qadeer, J. Hanif, Sep. Sci. Technol., (in press) (1992).
10. M. Afzal, J. Hanif, I. Hanif, R. Qadeer, M. Saleem, J. R~dioanal. Nucl. Chem., 139 (1990) 203.
11. M. Saleem, M. Afzal, J. Hanif, R. Qadeer, I. Hanif, J. Radioanal. Nucl. Chem., 142 (1990) 393.
12. G.F. Cerofoline, Surf. Sci., 24 (1971) 391.
13. J.P. Robson, J. Phys. Chem., 81 (1969) 2720.
253
