Journal of Nuclear and Radiochemical Sciences, Vol. 5, No. 1, pp. 7-10, 2004

RevisedIon Exchange Studies of Cerium (III) on Uranium Antimonate
M. V. Sivaiah,a K. A. Venkatesan,b P. Sasidhar,*, c R. M. Krishna,a and G. S. Murthyaa

Nuclear Chemistry Section, Andhra University, Visakhapatnam-530 003, India
Fuel Chemistry Division, Indira Gandhi Centre for Atomic Research, Kalpakam-603 102, Indiac
Safety Research Institute, Atomic Energy Regulatory Board, Kalpakkam-603 102, Indiab

Received: December 15, 2003; In Final Form: April 4, 2004
Ion exchange of cerium on uranium antimonate (USb) from nitric acid medium was studied. The distribution
coefficient of ~19,000 mL/g was obtained for ion exchange of cerium in 0.1 M nitric acid and it decreased withincrease in the concentration of nitric acid. Rapid ion exchange of cerium in the initial stages of equilibration
followed by the establishment of equilibrium occurs after one hour. Ion exchange data were fitted into both
Langmuir and Freundlich adsorption models using non-linear regression. The enthalpy change accompanied byion exchange of cerium was determined by the temperature variation method. The performance of the ion
exchanger under dynamic condition was assessed by following a breakthrough (BT) curve and the BT curve wasfitted using Thomas equation.

1. Introduction
Radioactive liquid wastes are generally composed of major
quantity of non-radioactive component contaminated withminor amounts of hazardous gamma emitting radionuclides
such as 137Cs, 90Sr, 154Eu, 144Ce etc. Separation and concentration of the radioactive components from a large volume ofradioactive waste minimize the volume of the radioactive fraction that is to be safeguarded for long time. Major gains
achieved by the isolation of radioactive fission products are thereduction in occupational exposure, minimal radiation degradation to structural materials and chemicals used, lowsecondary waste generation, and reduction in the cost of
disposal. Further, the other larger fraction of treated component can be either disposed or handled without serious hazards.
It is well recognized that only inorganic exchangers/sorbents
can withstand to very high radiation dose levels without muchdegradation and they also exhibit unprecedented selectivity forfission products. 1−4 Several inorganic sorbents were foundsuitable for the separation of chemically toxic and radiotoxic
metal ions from various waste streams.1−4 Recent reviews by
Clearfield2 and Lehto and Harjula4 describe about the latest
developments in inorganic sorbents and their applications to
the treatment of nuclear waste. They have also indicated thatnot many sorbents are effective in the separation of fission
products especially strontium from acidic liquid wastes andhave suggested the need to develop new inorganic sorbents toaccomplish these tasks. Thus, we have prepared several inorganic sorbents in the recent past and evaluated for the removalof fission products especially 137Cs, 90Sr, and 154Eu from acidic
streams.5−10
Hydrous antimony oxides and binary metal antimonates are
excellent candidates for the separation of fission products
especially divalent strontium-90 and trivalent rare earths from
acidic waste streams.11−14 Several insoluble binary metal antimonates containing titanium,12−14 zirconium,15 tin16 etc. weresynthesized and the ion exchange properties of them werereported. In addition, it was shown that the pyrochlore structure of antimonates could be tuned to the desired ion exchange
selectivity by substituting various cations such as W6+, Nb5+
*Corresponding author. E-mail: sasidhar@igcar.ernet.in. FAX:
+91-4114-280165.

into the framework of the parent compound.12 Antimonates
were also studied for the chromatographic separation of a
mixture of metal ions of identical charge, separation of trivalent actinides from lanthanides, and for the separation offission products.14 But so far, to the best of our knowledge,
antimonate-containing uranium has not been evaluated for the
uptake of fission products. However uranium based inorganic
ion exchangers such as uranium phosphate were indeed reported
by Pekarek and Veseley17 and studied for the sorption of various
metal ions.
Thus, we have prepared uranium antimonate (USb) andstudied the sorption of cesium, strontium, and europium.9, 10
Selectivity of USb was found to be in the order Eu3+ > Sr2+ >Cs+ and the rate of sorption of europium on USb found to becontrolled by the diffusion of europium in the solid phase(diffusion coefficients (D i) = ~10−8 cm2 s−1). Sequential chromatographic separation of 137Cs, 90Sr, and 154Eu from nitric acidmedium was also performed.10 In this paper we report the ion
exchange properties of cerium on USb. Effect of various parameters such as time, temperature, concentrations of nitric acid,and metal ion on the distribution coefficient was reported. The
performance of the sorbent under dynamic condition wasassessed by following the breakthrough curve up to the entire
range (i.e. C/Co = 1), where C is the effluent radioactivity at
various intervals of time and Co is the initial radioactivity of
the feed.
2. Experimental
Materials. Potassium pyroantimonate (KSb(OH) 6 ) anduranyl nitrate were obtained from E. Merck. 144Ce radioisotope
was separated from the spent fuel solution by the proceduredescribed in Reference 18. All the other chemicals and reagentswere of analytical AR grade.
Preparation of Uranium Antimonate. Uranium antimonate was prepared by the procedure described elsewhere. 9
Briefly it involves drop wise addition of 200 mL of 0.05 M
uranyl nitrate to a hot solution of 200 mL of 0.1 M potassium
pyroantimonate. The precipitate thus obtained was heated to
60˚C for about 12 hours and allowed to age in the motherliquor overnight. It was then filtered, washed thoroughly with
distilled water and dried at 60˚C. This dried product was
ground, sieved and converted to H+ form by passing 1 M nitric© 2004 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 05/10/2004

8

M. V. Sivaiah

J. Nucl. Radiochem. Sci., Vol. 5, No. 1, 2004+

acid into a column packed with the particles of USb. The H
form of USb was then washed with distilled water till pH of
the effluent was neutral, which is subsequently used for all theion exchange studies.
Ion Exchange Studies. Variation of distribution coefficient(Kd, mL/g) of cerium with the concentration of nitric acid wasstudied by equilibrating 0.05 g of the sorbent (USb) with 10
mL of the solution containing nitric acid (varied from 0.1 M to
2.0 M) spiked with 144Ce radioactive tracer. After 6 hours ofcontact, an aliquot was taken from the supernatant and theradioactivity was measured using well-type NaI(Tl) scintillation detector. The distribution coefficient was calculated using
eq 1
V
m

13

Ai–Af
Af

68

Kd =

(1)

where A i and A f are the radioactivity per mL of an aliquot
before and after equilibration, respectively. V (in mL) and m(in g) are the volume and mass of the sorbent taken for equilibration, respectively.
The rate of uptake of metal ions from nitric acid wasstudied, at 300 K, by contacting 0.05 g of the sorbent with 10
mL of the solution containing 0.1 M nitric acid, 10 mg/L of Ce(III) ion spiked with 144Ce tracer. At various intervals of time,shaking was stopped and aliquot was drawn from the supernatant. From the measurement of activity at a time t, the metal
ion exchanged was calculated. Similar experiment was
performed when the concentration of cerium was increased to
100 mg/L.
Cerium ion exchange isotherm was obtained by equilibrating, at 300 K, 0.05 g of the sorbent with 10 mL of the solution containing 0.1 M nitric acid and the varied amounts ofcerium ion (from 10 mg/L to 1000 mg/L) spiked with 144Cetracer. After 6 hours, shaking was stopped and the activity ofsupernatant was measured as described earlier. From theinitial and final activity, the amount of cerium exchanged by
the USb was calculated.
Effect of temperature on the distribution coefficient of
cerium on USb was studied by equilibrating 0.05 g of thesorbent with 10 mL of 0.1 M nitric acid solution containing
200 mg/L of cerium ion spiked with 144Ce tracer. After 6 hours
of contact between sorbent and solution, the distribution coefficient was measured as described above. Similar experiments
were performed at various temperatures from 300 K to 323 K.
Column Studies. Breakthrough experiment was performedby packing a slurry containing 1.0 g of the sorbent into a column of radius 0.25 cm provided with sintered disc at the bottom. The column was conditioned with nearly 10 bed volumesof 0.1 M nitric acid. The feed solution composed of 1.1 × 10−3
M cerium (III) ion spiked with 144Ce tracer in 0.1 M nitric acid.

This was passed into a column at the flow rate of 0.20 mL/min.
Various fractions of the effluent were collected until the ratioof effluent activity (C) to initial activity (Co) equals to one.
The ratio of C/Co, called as breakthrough, was plotted against
the volume of the solution passed in to the column to obtain abreakthrough curve. Cerium was eluted with 5 M nitric acid at
a flow rate of 0.1 mL/min and 1 mL fractions were collected
for obtaining the material balance.
3. Results and Discussion
The rate of uptake of cerium on USb from 0.1 M nitric acidis shown in Figure 1. Rapid ion exchange was observed in theinitial stages of equilibration followed by saturation occurs
within three hours. The experimental data was fitted toLagergren equation of the form
a t = a e (1 −e −kt )(2)where a t and a e are the amount of cerium exchanged at a time tand equilibrium respectively and k is the Lagergren first order
rate constant. Non-linear regression of the experimental datausing eq 2 results in a rate constant of 0.154 ± 0.005 min−1 and
0.112 ± 0.022 min−1 for the exchange of cerium from 0.1 M nitricacid containing cerium of 10 mg/L and 100 mg/L respectively.
Plot of distribution coefficient (Kd) of cerium as a functionof the concentration of nitric acid is shown in Figure 2. Kdvalues decreased from 18,943 mL/g to 6 when the concentration of nitric acid was increased from 0.1 M to 2 M. If thesorption of Ce3+ on USb involves ideal ion exchange mechanism as shown in eq 3, then the plot of logKd against log[H+a ]should result in a slope of –3 according to eq 6.
3++
3H+s + Ce a3+ →← Ces + 3Ha

K=

(3)

+ 3
[Ce3+
s ] [H a ]3++ 3[Cea ] [H s ](4)

logKd = logK + 3 log[H+s ] – 3 log[H+a ](5)

logKd = logK’ – 3 log[H+a ](6)

where the subscripts ‘a’ and ‘s’ represent aqueous and sorbent
phase respectively and Kd is defined by eq 1. Since the ion
exchange reaction was carried out in trace level concentrationof cerium ion, the magnitude of [H+s ] may be assumed as unaltered and hence K’ is constant. Log-log plot for the sorption of
cerium on USb is shown in Figure 2. A slope of –2.6 obtained
is an indicative to the adherence to ideal ion exchange mechanism for the sorption of cerium on USb. A slight deviationfrom the theoretical slope of –3 could be due to the calculation

16

144

Ce tracer
V/m = 200 mL/g
Temp = 300 K
Slope = - 2.6
Eq. time = 6 hr

10000

2

-1

100 mg/L; χ = 2.9300; k = 0.112 ± 0.022 min
Lagergren equation fit-1

2

10 mg/L; χ = 0.0010; k = 0.154 ± 0.005 min

12-1

Kd /mL g

Amount of Ce(III) exchanged /mg g -1

100000[HNO3 ] = 0.1 M; V/m = 200 mL/g; Temp = 300 K

8

1000

100

4
10

0

1

0

100

200

300

400

Time /min3+

Figure 1. Uptake of Ce by USb from 0.1 M nitric acid.

500

0.1

[HNO3 ] /M

1

Figure 2. Variation of distribution coefficient of cerium (III) with
[HNO3] on USb at 300 K.

Ion Exchange Studies of Cerium (III)J. Nucl. Radiochem. Sci., Vol. 5, No. 1, 2004

to eqs 7 and 8 using non-linear regression and the coefficientsobtained are shown in Figure 3. From the χ2 values of thefitting, it can be seen that the data were described better by
Freundlich isotherm in the entire range. However, when theequilibrium concentration of cerium was less than 500 mg/L,
the data adheres to Freundlich equation, above which, itfollows Langmuir adsorption model in the high cerium
concentration range.
The plot of logKd against 1/T is shown in Figure 4 and thestandard enthalpy change (∆H o) accompanied by the sorptionof cerium can be evaluated10, 20 using eq 9
logKd =KLbCS
CE =(Langmuir equation)
1 + KLCS(7)

CE = KF [CS]β (Freundlich equation)(8)

where CS is the amount of metal ion present in solution phaseat equilibrium (mg/L), CE is the amount of metal ion in theexchanger phase (mg/g), KL (in L/mg) and KF (in L/g) are theLangmuir and Freundlich adsorption constants, respectively, b
is the apparent ion exchange capacity (mg/g) and β (0 < β < 1)is the measure of heterogeneous interaction of the Ce 3+ withthe sorbent. When β = 1, the sorbent is said to be homogeneous and all the sites are indistinguishable with respect to theenergy of sorption. The Freundlich and Langmuir constants
can be related to energy of adsorption 19 and thus it was
regarded as a measure of affinity of the metal ion towards thesorbent. It can be easily shown from eq 7 that at high values ofCS, the value of CE approaches the magnitude of b. Thus b was
found to be ~35 mg/g from Figure 3. The isotherm was fitted–∆H o2.303 R

13

68

based on concentration terms instead of activity used in eq 6.
Similarly, log-log plot for the sorption of Cs+ on USb haveresulted 10 in a slope of –0.9 in accordance with ideal ion
exchange mechanism, while considerable deviation from theexpected value was observed10 for Sr2+ (slope = –1.6) and Eu3+
(slope = –2.4) sorption on USb.
Ion exchange isotherm of cerium on USb is shown in Figure
3. The amount of metal ion loaded on to the solid phaseincreased with increase in the concentration of metal ion inaqueous phase, followed by saturation. The experimental data
was fitted with non-linear Langmuir and Freundlich isothermsof the form given in eqs 7 and 8, respectively,

Cerium concentration in sorbent /mg g -1

1
+ constantT(9)where R is the gas constant. From the slope of the linear fit
shown in Figure 4, ∆H o was found to be 10.2 kJ/mol. The
endothermicity observed for the ion exchange of cerium could
be due to the requirement of the energy for dehydrating watermolecules surrounding Ce3+ ion in the aqueous phase before
sorption. ∆H o obtained for the ion exchange of Ce3+ is higher
than the enthalpy observed 10 for the sorption of Sr 2+ (9.9kJ/mol) on USb but lower than Eu3+ (32 kJ/mol) sorption.
The break through (BT) curve for the exchange of ceriumon USb is shown in Figure 5. It can be seen from the figurethat 1% BT, 50% BT, and 100% BT occur after passing 11 bed
volumes (BV), 39 BV, and 83 BV of the feed solution, respectively. The ion exchange data under dynamic conditions wasanalyzed using Thomas equation21 of the form shown in eq 10,
which has been widely used for describing BT curves.22−24
Ce1=
C o 1 + e (K (q m – C V ))/Q
T

40

o

(10)

o

where,
35

Ce = Cerium concentration in the effluent (mg/L) - Variable
Co = Cerium concentration in the feed (mg/L) = 154 mg/L
KT = Thomas rate constant (L min−1 mg−1)
qo = Maximum amount of cerium that can be loaded on
USb (mg/g) under the specified conditionm = Mass of the adsorbent (g) = 1.0 g
V = Throughput volume (L)Q = Flow rate (L/min) = 0.2 × 10−3 L/min

Expermental
Freundlich model
Langmuir model

30
25[HNO3 ] = 0.1 M
V/m = 200 mL/g
Temp = 300 K

20
15Freundlich modelχ2 = 14.23
β = 0.206
K F = 9.82

105Langumuir Modelχ2 = 21.36
b = 34.40
KL = 0.110

0
0

200

400

600

800
-1

Cerium concentration in solution /mg L

Figure 3. Variation of the amount of cerium in the solid phase withconcentration of cerium in solution.

3.30

Non-linear regression of the BT data using Thomas equation isshown in Figure 5. The fitting constants KT and qo for the ion
exchange of cerium on USb under the specified conditions arefound to be 9.3 × 10−5 L min−1 mg−1 and 7.6 mg/g, respectively.
Marked difference of experimental capacity between dynamic
absorption conditions, 7.6 mg/g, and batch experiments, 35
mg/g, could be due to the insufficient contact time given for
1.0[HNO3 ] = 0.1 M[Ce(III)] = 200 mg/L
V/m = 200 mL/g

3.28

0.8

Experimental data
Thomas equation fito∆H = 10.2 kJ/mol

Ce / Co

3.26

log(K d )

9

3.24
3.22
3.20

0.6

[HNO3 ] = 0.1 M-3[Ce(III)] = 1.1 × 10 M
Weight of Resin = 1.0 g
Bed Volume = 1.14 mL
Flow Rate = 0.20 mL/min

0.4

0.2

3.18

0.0
3.16
3.10

3.15

3.20

1000/T /K

3.25

3.30

3.35

-1

Figure 4. Plot of log Kd against 1/T for the ion exchange of cerium
on uranium antimonate.

0.00

0.02

0.04

0.06

0.08

0.10

0.12

Throughput Volume /L

Figure 5. Break through curve for the ion exchange of cerium on
USb fitted using Thomas model.

10

J. Nucl. Radiochem. Sci., Vol. 5, No. 1, 2004

M. V. Sivaiah
References

Counts/10000 /min-1

6[HNO3 ] = 5.0 M[Ce(III)] loaded = 7.6 mg
Weight of Resin = 1.0 g
Bed Volume = 1.14 mL
Flow Rate = 0.10 mL/min

4

ELUTION PATTERN
2

0
0

2

4

6

8

10

12

14

16

18

20

Bed volumes of 5.0 M HNO3 /mL

Figure 6. Elution pattern of cerium from USb with 5 M nitric acid.

the ion exchange of cerium on USb under dynamic conditions.
The loaded cerium can be eluted using 5 M nitric acid and theelution pattern is also shown in Figure 6. More than 90% of
cerium was eluted with in six BV and quantitative elution wasobserved with in 20 BV.
4. Conclusions
Ion exchange of cerium from nitric acid medium on USb wasstudied as a function of various parameters. Rapid absorption
in the initial stages of equilibration followed by the establishment of equilibrium occurs after one hour and the first order
rate constant was found to be of the order of 1.2 × 10−1 min−1.
Kd of 18,943 mL/g obtained for the ion exchange from 0.1 M
nitric acid and it decreased with increase in the concentration of
nitric acid. Slope (= –2.6) obtained from logKd – log[HNO3]
plot indicated that sorption of cerium by USb can be presumed
to follow ideal ion exchange mechanism. Freundlich modelseems to fit the ion exchange isotherm when the equilibrium
concentration of cerium was less than 500 mg/L while
Langmuir adsorption model was preferred in the later stage.
From, non-linear regression of the experimental data using
Langmuir equation, the apparent experimental capacity, b, wasfound to be 34.4 mg/g. The enthalpy change (∆H o) accompanied for the ion exchange was found to be –10.2 kJ/mol, indicating that heat energy required for dehydrating watermolecules surrounding Ce3+ for their entry in to USb. At 100%
BT, the ion exchange capacity was found 7.6 mg/g for cerium,
which was quantitatively eluted using 5 M nitric acid.
Acknowledgements. The author (M. V. Sivaiah) is gratefulto Atomic Energy Regulatory Board (AERB), Government ofIndia for providing fellowship and thankful to Dr. P. R.
Vasudeva Rao, Associate Director, Chemical Group, IGCAR
for providing the facilities.

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