Journal of Nuclear and Radiochemical
Sciences, Vol. 5, No.1, pp. 7-10, 2004
Ion Exchange Studies of Cerium (III) on Uranium Antimonate M. V. Sivaiah, K. A. Venkatesan, P. Sasidhar, R. M. Krishna, and G. S. Murthy aNuclear Chemistry Section , Andhra University, Visakhapatnam-530 003, India bFuel Chemistry Division , Indira Gandhi Centre for Atomic Research, Kalpakam-603 102, India c Safety Research Institute, Atomic Energy Regulatory Board, Kalpakkam-603 102, India Received: Ion
December
exchange
of
coefficient increase
in
the
by
Langmuir
was
cerium
April
antimonate
nitric
acid.
of
equilibrium models
determined
condition
from
ion
exchange
Rapid
ion
occurs
of
cerium
hour.
Ion
after
especially
divalent
acidic
waste
monates synthesized reported.
for
containing
variation
method.
following
and the
ion
insoluble
exchange
rare
earths metal
could
be tuned
by substituting
various
tin
properties
shown
that
are
products
binary
zirconium,
it was
the
author . E-mail:
from anti
were
with
equilibration
fitted
into
both
accompanied
performance
curve
actinides
and
by
of
the
BT
the
ion
curve
was
by Pekarek metal
[email protected].
2004
The
Japan
the
Selectivity
Society
separation
phosphate
of
knowledge,
evaluated
uranium
and studied
of
the
USb
rate by
(diffusion matographic
for the
based
inorganic
were indeed
reported
for the sorption
the
was
exchange such
as
of various
performance assessed by (i.e.
various
of
Sr,
distribution
of the following C/Co
on
temperature, the
of
where
time
this
USb.
Eu3+
USb
in
> Sr2+ >
found
the
solid
paper
we
Effect
of various
report
concentrations
of
coefficient
was
dynamic curve
C is the
and
order on
and
europium.
to be phase
cm2 s-1). Sequential chroand Eu from nitric acid
sorbent under the breakthrough
= 1),
intervals
In
cerium
in the
europium
(Di= •`10-8 of Cs,
of
on
be
(USb)
and
europium
performed.10
time,
ion
to of
diffusion
antimonate
strontium,
found
sorption
properties
metal
range
also
uranium
cesium,
was of
coefficients separation
medium
eters
prepared
effluent
Co is the
initial
the
ion
param-
nitric
acid,
reported. condition up to the
The was entire
radioactivity
at
radioactivity
of
feed.
2. Experimental
Materials. Potassium pyroantimonate (KSb(OH)6) and uranyl nitrate were obtained from E. Merck. Ce radioisotope was separated from the spent fuel solution by the procedure described in Reference 18. All the other chemicals and reagents were of analytical AR grade. was
of Uranium prepared
it involves nitrate
drop
water
ground,
sieved
and
addition of 200
It was
then filtered,
and dried
at 60•Ž.
and converted
Radiochemical
on Web 05/10/2004
wise
solution
Uranium described
of 200
Sciences
anti-
elsewhere.9 mL
of 0.05
M
mL of 0.1 M potassium
The precipitate thus obtained 12 hours and allowed to age
overnight.
distilled
Antimonate.
by the procedure
to a hot
pyroantimonate. 60•Ž for about
of Nuclear
as uranium
have
of
and
controlled
the
the
of a of triva-
of our
has not been
However
sorption
Preparation
FAX:
Published
we
studied
and
such
for
to the best
uranium products.
separation
ions.
Thus,
Cs+
and
so far,
and Veseley
Antimonates separation
charge,
lanthanides, But
of fission
compound.
chromatographic
of identical
from
ion exchangers
uranyl
as W6+, Nb5+
ions
products.
uptake
Briefly
ion exchange
for the
antimonate-containing
were
cations
of the parent
studied
of metal
fission
struc-
to the desired such
lent
monate
of them
the pyrochlore
framework
mixture
were
etc.
+91-4114-280165. •¬
of
change
The
distribution
it decreased
stages
data
(BT)
The
and
initial
enthalpy
a breakthrough
also
liquor *Corresponding
acid
exchange
temperature by
studied.
nitric
in the
the
assessed
antimonates
of fission
and trivalent
titanium,
In addition,
metal
separation
Several
was
M
equation.
and binary
the
strontium-90
streams.
ture of antimonates selectivity
oxides
0.1
The
Radioactive liquid wastes are generally composed of major quantity of non-radioactive component contaminated with minor amounts of hazardous gamma emitting radionuclides such as Cs, Sr, Eu, Ce etc. Separation and concentration of the radioactive components from a large volume of radioactive 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 the reduction in occupational exposure, minimal radiation degradation to structural materials and chemicals used, low secondary 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 much degradation and they also exhibit unprecedented selectivity for fission products. Several inorganic sorbents were found suitable for the separation of chemically toxic and radiotoxic metal ions from various waste streams. Recent reviews by Clearfield and Lehto and Harjula describe about the latest developments in inorganic sorbents and their applications to the treatment of nuclear waste. They have also indicated that not many sorbents are effective in the separation of fission products especially strontium from acidic liquid wastes and have suggested the need to develop new inorganic sorbents to accomplish these tasks. Thus, we have prepared several inorganic sorbents in the recent past and evaluated for the removal of fission products especially Cs, Sr, and Eu from acidic streams. antimony
one
in
regression.
into
candidates
medium
exchange
were
Hydrous
acid
cerium
non-linear
1. Introduction
excellent
nitric of
using by
was
4, 2004
(USb)
for
adsorption was
dynamic
Thomas
Form:
obtained
of
establishment
under
using
uranium
mL/g
Freundlich of
exchanger
on
In Final
concentration
the
and
exchange
fitted
cerium
of •`19,000
followed
ion
15, 2003;
washed This
to H+ form
was heated to in the mother thoroughly
dried
product
by passing
with was
1 M nitric
S
J. Nucl.
acid
into
form
Radiochem.
a column
of USb
the effluent
packed
was was
ion exchange
Sci., Vol. 5, No.1, with
then
washed
neutral,
which
2004
the particles with
Sivaiah
of USb.
The
H+
distilled
water
till pH of
is subsequently
used
for all the
studies.
Ion Exchange Studies. Variation of distribution coefficient (Kd, mL/g) of cerium with the concentration of nitric acid was studied 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 Ce radioactive tracer. After 6 hours of contact, an aliquot was taken from the supernatant and the radioactivity was measured using well-type NaI(T1) scintillation detector. The distribution coefficient was calculated using eq 1
Kd=Ai-Af/Af [V/m](1)
Effect
of temperature on USb
sorbent
with
was
10 mL
200 mg/L
of cerium
of contact
between
on the studied
of 0.1
by
distribution
coefficient
equilibrating
M nitric
ion spiked
acid
with
3. Results The
and Discussion
rate of uptake
is shown
in Figure
initial
stages
within
three
Lagergren
where Ai and Af 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 was studied, 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 Ce 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 of cerium ion (from 10 mg/L to 1000 mg/L) spiked with Ce tracer. After 6 hours, shaking was stopped and the activity of supernatant was measured as described earlier. From the initial and final activity, the amount of cerium exchanged by the USb was calculated. cerium
This was passed into a column at the flow rate of 0.20 mL/min. Various fractions of the effluent were collected until the ratio of 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 a breakthrough 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.
0.05
solution
Ce tracer.
of
of cerium L Rapid
of equilibration hours.
from
followed
The
equation
on USb
ion exchange
0.1 M nitric
was observed by
experimental
saturation data
acid in the
occurs
was
fitted
at=ae(1-e-kt) where
at and
and
equilibrium
rate
constant.
using
eq
0.112 •} acid
ae are the
(2) amount
respectively Non-linear
2 results 0.022
containing
for
cerium
of cerium and
constant
the exchange of
exchanged
at a time
Lagergren
first
k is the
regression
in a rate
mine
to
of the form
10 mg/L
of of
the
experimental
0.154 •}
0.005
of cerium and
100
from mg/L
t
order data
min-1 0.1
and
M nitric
respectively.
Plot of distribution coefficient (Kd) of cerium as a function of the concentration of nitric acid is shown in Figure 2. Kd values decreased from 18,943 mL/g to 6 when the concentration of nitric acid was increased from 0.1 M to 2 M. If the sorption of Ce3+ on USb involves ideal ion exchange mechanism as shown in eq 3, then the plot of logKd against log [Ha] should result in a slope of -3 according to eq 6. 3H+s
Ce3+a •¬Ce3+s
+ 3H+a
K = [Ce3+s]/[Ce3+a] [H+a]3/[H+s]3
(3)
(4)
logKd = logK + 3 log[H+s]- 3 log[H+a]
(5)
logKd = logK' - 3 log[H+a]
(6)
g of the
containing After
6 hours
the distribution
coef-
Column Studies. Breakthrough experiment was performed by 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 volumes of 0.1 M nitric acid. The feed solution composed of 1.1 x 10-3 M cerium (III) ion spiked with Ce tracer in 0.1 M nitric acid.
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 concentration of 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 deviation from the theoretical slope of -3 could be due to the calculation
Figure
Figure 2. Variation of distribution coefficient of cerium (III) with [HNO3] on USb at 300 K.
ficient were
was
measured
performed
t.
sorbent
and solution,
as described
at various
above.
temperatures
Uptake of Ce3+ by USb from 0.1M
Similar from
experiments
300 K to 323 K.
nitric acid.
Ion Exchange Studies of Cerium (III)
J. Nucl.
based on concentration terms instead of activity used in eq 6. Similarly, log-log plot for the sorption of Cs+ on USb have resulted in a slope of -0.9 in accordance with ideal ion exchange mechanism, while considerable deviation from the expected value was observed for Sr2+(slope = -1.6) and Eu3+ (slope = -2.4) sorption on USb. Ion exchange 3.
isotherm
of cerium
The
amount
increased
with
increase
in the concentration
phase,
followed
by saturation.
non-linear
Langmuir
aqueous was
fitted
of metal
with
of the form
given
ion
on USb
loaded
is shown
on
to the
The
in Figure
solid
phase
experimental
data
and Freundlich
non-linear
regression
obtained
in Figure
3.
are shown
fitting,
it can
Freundlich
isotherms
adheres Langmuir of
can
(Freundlich
phase
Langmuir
and
is the
apparent
is the
measure
the
can
found
of
all the
be
related as
the
to
KL
(8)
amount L/mg)
R is the
shown
in
by
However,
when
the
less
than
500
above in the in
mg/L,
which,
high
it
cerium
Figure
(ƒ¢H•¬) accompanied
evaluated
gas
Figure
using
eq
by
4 and the
the
sorption
9
of
of CE approaches mg/g
from
from
Figure
the
molecules
are
the
sorption. ƒ¢H•‹
of
(0
the
Ce3+
magnitude The
ion
to
the
constants thus
it was
towards
at high of b.
with
homoge-
respect
and metal
b
< ƒÀ < 1)
be
Langmuir
eq 7 that
3.
ion L/g)
to
with and
of the
the
in
is said
adsorption
shown
metal
and ƒÀ
interaction
affinity
be
respectively,
indistinguishable
of
phase
KE (in
(mg/g)
Freundlich
energy
easily
of and
sorbent
constant
the
values Thus
isotherm
was
of
due
than
constant.
to
the
was
(9)
kJ/mol)
on
USb
the
of Ce3+
obtained
enthalpy
for
ion
ion
in the ion
lower
of
the
10.2 of
for
aqueous
the
fit The
cerium
could water
phase of
is higher
of
kJ/mol)
before
Ce3+
sorption
Eu3+ (32
linear
kJ/mol.
dehydrating
exchange
for
than
be
exchange
energy
the
slope
to
the
observed10 but
the
found
for
requirement
surrounding
the
From
4, ƒ¢H•‹ observed
in solution
constants,
capacity
are The
to
be •`35
(in
present
adsorption
= 1, the
sites
be
ion
heterogeneous
a measure
It can value
metal
exchange
When ƒÀ
sorption.
sorbent. Cs,
ion
of
regarded
is shown
of the
better
(7)
equation)
CE is the
(mg/g),
and
energy
of
Freundlich
sorbent.
neous
amount (mg/L),
exchanger
against 1/T
= [-ƒ¢H•‹/2.303R]1/T +
endothermicity CS is the
equilibrium
was
values
described
equation, model
change
be
logKd
where CE = KF[Cs]ƒÀ
at
of cerium
adsorption
logKd
enthalpy
of cerium
were
range.
plot
standard
the x2
range.
to Freundlich
9
in eqs 7 and 8, respectively,
CE= KLbCs/ 1 + KLCs(Langmuir equation)
where
in the entire
2004
and the coefficients
From
the data
concentration
data
The
that
isotherm
equilibrium the
be seen
concentration
ion in
Sci., Vol. 5, No.1,
to eqs 7 and 8 using
follows
of metal
Radiochem.
Sr2+
(9.9
sorption.
The break through (BT) curve for the exchange of cerium on USb is shown in Figure 5. It can be seen from the figure that 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 was analyzed using Thomas equation of the form shown in eq 10, which has been widely used for describing BT curves.
b was fitted
Ce/Co =
1/1+e(K•¬(qom-CoV))/Q(10)
where, Ce
= Cerium
concentration
in the
Co = Cerium
concentration
in the feed
KT = Thomas qo
= Maximum USb = Mass
V
= Throughput
Q
= Flow
shown
found Marked
Figure 4. on uranium
Plot of log Kd against 1/T antimonate.
of cerium in the solid phase with
for the ion exchange
of cerium
on 10-5
difference
absorption mg/g,
cerium
of
could
be
due
that
be
g
=1.0
BT
data
fitting USb
10-3
loaded
on
7.6 the
under mg-1
using
the and
Thomas KT and
7.6
insufficient
and
equation qo for
specified
batch contact
the
conditions
mg/g,
capacity
mg/g,
Figure 5. Break through curve USb fitted using Thomas model.
L/min
constants
experimental
to
can
(g)
L min-1
conditions,
mg/L
mg-1)
condition
= 0.2 •~
of the The
- Variable
=154
(L)
(L/min)
5.
(mg/L) (mg/L)
specified
adsorbent
regression
of
the
volume
rate
to be 9.3 •~
(L min-1 of cerium
under
of the
in Figure
exchange
constant amount
(mg/g)
m
Non-linear
Figure 3. Variation of the amount concentration of cerium in solution.
rate
effluent
is ion are
respectively.
between
dynamic
experiments, time
for the ion exchange
given
of cerium
35 for
on
10
J. Nucl.
Radiochem.
Sci.,
Vol. 5, No.1,
2004
Sivaiah References
Figure
6.
Elution pattern of cerium from USb with 5 M nitric acid.
the ion exchange The
loaded
elution
pattern
cerium
was
observed
4.
of cerium
cerium
on USb
can be eluted
is also
eluted
shown
with
under
using
in Figure
in six BV
dynamic
conditions.
5 M nitric 6.
More
acid
and the
than
90%
and quantitative
elution
of was
with in 20 BV.
Conclusions Ion
exchange
studied in
as
the
ment rate
of cerium
a function
initial of
stages
Kd of
of
equilibrium
constant
nitric
acid
nitric
acid.
and
to be
with
(=-2.6)
to
fit
the
concentration Langmuir
Langmuir found
equation, to
for
cating
which
the
34.4
mg/g.
ion
exchange
heat
was
exchange quantitatively
of
The
energy
surrounding ion
was
enthalpy found
required Ce3+ for
eluted
their was using
-
the 500 in
entry found
presumed model
equilibrium
the
while
later
stage.
data
(ƒ¢H•‹) -10.2
using b, was
accompa-
kJ/mol,
indi-
dehydrating
water
in to USb. 7.6
5 M nitric
1. M of
capacity,
change
for
0.1
mg/L
experimental
to be
min
log[HNO3]
can be Freundlich
when than
order
10-1
concentration
experimental
was
capacity
USb
was
establishfirst
from
logKd
preferred the
apparent
be
molecules BT,
the
the that
isotherm less
the the
1.2 •~
in the
cerium by mechanism.
regression
of
from
was
by and
USb absorption
exchange
increase
exchange
model
non-linear
ion
obtained
cerium
adsorption
From,
nied
ion of
order
the
on
Rapid
hour
of the
plot indicated that sorption of to follow ideal ion exchange seems
one
for
it decreased
medium
followed
after
obtained
Slope
acid
parameters.
equilibration
found
mL/g
nitric
various
occurs
was
18,943
from
of
mg/g
At for
100%
cerium,
acid.
Acknowledgements. The author (M. V. Sivaiah) is grateful to Atomic Energy Regulatory Board (AERB), Government of India for providing fellowship and thankful to Dr. P. R. Vasudeva Rao, Associate Director, Chemical Group, IGCAR for providing the facilities.
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