J.RADIOANAL.NUCL.CHEM.,LETTERS
164
(4) 211-220
(1992)
R A D I U M R E M O V A L F R O M AQUEOUS SOLUTIONS BY V A R I O U S L Y S U P P O R T E D LIGANDS
P. Benzi,
R. Righetti,
P. Volpe
Dipartimento
di C h i m i c a G e n e r a l e ed Organica U n i v e r s i t ~ di Torino, C.so Massimo d ' A z e g l i o 48, 10125 Torino,
Received Accepted
2 January 10 January
Applicata, Italy
1992 1992
A set of ligands loaded on v a r i o u s supports have been tested to remove radium from aqueous solutions. Crown ethers have dem o n s t r a t e d i n e f f i c i e n c y in all cases, while open chain ligands (podands) have shown satisfactory d i s t r i b u t i o n c o e f f i c i e n t s and uptake rates in p a r t i c u l a r conditions. Hypotheses to explain the p h e n o m e n o n are b r i e f l y discussed.
INTRODUCTION Radium
is the most d a n g e r o u s
also owing complete radium
to its gaseous
removal
life should scientists.
processes
drinks
therefore
In some cases
difficulties problem.
reduction
concerning
The of
human
be the aim of the e n v i r o n m e n t a l
(e.g. p h o s p h a t i c
from various prevent
radioisotope,
the partial
and anything
have been d e v e l o p e d
radioisotopes
I
or at least
from foods,
natural
and solid decay products.
fertilizers)
to e x t r a c t
matricesl-3;
from a r e a s o n a b l e
211
chemical
the natural in others,
solution
many
of the
EIsev~r Sequo~ & A., ~u~nne
Akaddm~i Kiad6, Budape~
BENZI et al.: RADIUM REMOVAL FROM AQUEOUS SOLUTIONS
For e x a m p l e w a t e r s
from natural
sources
sometimes
c o n t a i n r a d i u m over the limit r e c o m m e n d e d by ICRP and even if m a n y attempts have been m a d e to e x t r a c t r a d i u m for p o t a b i l i z a t i o n ,
up to now the r e s u l t s o b t a i n e d are 4,5 as n e e d e d for p r a c t i c a l a p p l i c a t i o n
not as u s e f u l
In fact m e t h o d s suitable
based on the c o p r e c i p i t a t i o n
for small d i m e n s i o n w a t e r
same h a p p e n s
supplies
for reverse o s m o s i s methods,
commercialization for the r a d i u m
are not
and the
w h i l e the
of systems p a t e n t e d in the last years
selective
c o m p l e x a t i o n has been forbid-
den by the US EPA b e c a u s e of t h e i r t o x i c i t y 6. At p r e s e n t
some studies are in progress,
BaSO 4, A I 2 0 3 or MnO 2 v a r i o u s l y lets,
ion e x c h a n g e r s
able m e m b r a n e s ,
using
supported
(plastic pel-
or active charcoal)
or s e m i p e r m e -
and s a t i s f a c t o r y
results
are e x p e c t e d 7.
The aim of our study is the search for a system able to uptake r a d i u m specific
ligands
(and e v e n t u a l l y
cules have been tested, been o b t a i n e d
but s a t i s f a c t o r y
in p a r t i c u l a r with
chain p o l y e t h e r s porting agents
its daughters)
s u p p o r t e d on solid matrix.
by
Many mole-
results have
two ligands,
open
that have been u s e d r e c e n t l y as t r a n s -
in p h a s e t r a n s p o r t
catalysis:
Kryptofix8 , cal-
5 (1,11-bis(8-quinolyl-oxy)-3,6,9-trioxaundecane
led "K" in our work, and t r i s ( 2 - m e t h o x y e t h o x y e t h y l ) a m i "T" , s u p p o r t e d on three d i f f e r e n t porous
ne 9 , c a l l e d beds
(Amberlite XAD-4,
A m b e r l i t e XAD-8
and K i e s e l g e l
40 ) .
EXPERIMENTAL A m b e r l i t e XAD-4 Chem., stadt
Buchs
and XAD-8 were p r o v i d e d
(CH), the K i e s e l g e l
(D). The open chain ligands
crown ethers
(18C6, DB18C6,
Darm-
(K and T) and the
and 24C8) 212
by F l u k a
40 by E. Merck,
were p r o v i d e d by
BENZt et al.: RADIUM REMOVAL FROM AQUEOUS SOLUTIONS
E. Merck,
Darmstadt
"Th~ R a d i o c h e m i c a l trate.
Center",
The radium
obtained liters
(D). R a d i o i s o t o p e
solution
by d i s s o l v i n g
of d i s t i l l e d
2.4x10-9M
used
(Resins
of the isotope
to obtain
30-70 Mesh
20-50 Mesh
for the Kieselgel), water,
methanol
oven at 70 ~
with
in 5% w / w p r o p o r t i o n
the ligand
the bed volume
dried by R o t a v a p o r Preliminary loadedresins combination
in 5 of
of methanol;
and dried
dissolved
the m i x t u r e
by treating
was
then
0.500 g of each
15.0 ml of r a d i o i s o t o p e
g of loaded porous
in 4
of the uptake grade of the
was o b t a i n e d
kinetics
into an
then treated
under vacuum.
evaluation
with
for the
were p r e v i o u s l y
overnight,
for 24 h in p o l y e t h y l e n e
reactions
was
a concentration
air-circulating
shaking
(UK) as 226Ra ni-
in the e x p e r i m e n t s
and Kieselgel;
w a s h e d with d i s t i l l e d
times
by
(19.7 Bq ml-1).
The beds resins,
Amersham
an amount
water
was p r o v i d e d
vials.
has been p e r f o r m e d bed with
solution
and
Study of the
by treating
600.0 ml of radium
20.00
solu-
tion. Radioactivity by counting
measurements
for 30 min triplicate
of the r e m a i n i n g
solution
,tillation Analyzer samples
berra Packard) tain
present
of the 226Ra
of merit
only,
Liquid
adding
glass
for the alpha
(Can-
vials 5.
in order to ob-
In this counting
its al-
region
is >98.5% with
of 3500 and a b a c k g r o u n d
213
Scin-
to the
cocktail
separating
particle
out
(1.00 ml)
from the peaks due to its progeny,
in the solution.
the e f f i c i e n c y
~*
Packard),
scintillator
in high p e r f o r m a n c e
the m e a s u r e
figure
(Canberra
of the LSA have been chosen
alpha-emission ways
aliquotes
in a 2 2 0 0 C A / L L C M
10.0 ml of InstaGel
Windows
on 226Ra were carried
of 2-2.3
a
cpm.
BENZI et al.: RADIUM REMOVAL FROM AQUEOUS SOLUTIONS
RESULT
AND
DISCUSSION
The r e s u l t s uptake Table
by v a r i o u s l y
ethers
equilibrium ethers ionic
ligands
was
due to their
crown
is s i m i l a r
removal
tions w h i c h between
yield
attribute
Van
on r a d i u m
is shown
in
satisfactory The
affinity
yields
choice
of the c r o w n
to the K + ion,
to that of radium. seems
to s u p p o r t
the u p t a k e
to the
in
whose
By c o n t r a s t
the
considera-
compatibility
der W a a l s radius of %he e l e m e n t and the 10 diameter , a highly selective mechanism.
hole
alternative
explanation
by o b s e r v i n g an a b i l i t y
to c a p t u r e the
in the
ligand
of this
behavior
that T on K i e s e l g e l ,
that of
ble that
show neither
nor r e p r o d u c i b i l i t y .
radius
the small
the
supported
screening
I.
Crown
than
of the p r e l i m i n a r y
Ra 2+, has
support cases
alone.
which
otherwise
an u p t a k e
yield
Therefore,
considered
shows
lower
it is p o s s i -
the c a t i o n
(crown or T) a c o m p l e x
An
can be g i v e n
forms w i t h
according
to the e q u i -
librium: 2+ Ra
which
solut
seems
+ Ligandbound
shifted
In an a t t e m p t chromatography Kieselgel-T the l i q u i d
~
Complex
bound
to the left.
to v e r i f y
analysis
experiment, phase.
~
this h y p o t h e s i s ,
was
performed
checking
Significant
for
amounts
liquid
in the case
of
the amino g r o u p of T w e r e
found
in solution. For m o r e attention uptake
quantitative
only
yield
Figures function
of
(greater
I-4
studies,
on the four
(a)
time
than
show
for
systems
we have that
focused
show
our
the b e s t
30%).
the
solution
the four 214
activity
ligand-support
as a systems,
in
BENZI et al.: RADIUM REMOVAL FROM AQUEOUS SOLUTIONS
E 1200 f~ u
a)
>
<
1000
800 ,
eq
0 9'
J
l
I
100
200
1 300
100
200
I
I
t,min 300 400 I"
40O
o o
v
o
~I 10 I
Fig.
I. V a r i a t i o n of specific a c t i v i t y vs. time (a) and ig (C-Ceq) vs. time (b) for the system A m b e r l i t e XAD 4 - K TABLE
Percent
I
radium uptake of v a r i o u s l y (Batch 24 h, 2.4x10-9M,
Ligand
supported pH=4.5)
ligands.
Matrices XAD - 4
XAD - 8
Kieselgel
No ligand
17.3(2.2)%
12.2(1.8)%
29.2(4.3)%
Ligand
K
32.0(3.2)%
20.0(3.3)%
56.5(4.7)%
Ligand
T
49.8(2.2)%
68.5(2.7)%
13.0(1.6)%
18-Crown-6
22.3(12.1)%
18.2(8.0)%
8.5(4.2)%
DB 18-Crown-6
25.2(11.3)%
12.1(6.4)%
13.0(7.5)%
24-Crown-8
36(13.4)%
11 .2(4.1)%
19.4(9.3)%
215
BENZI et al.: RADIUM,REMOVAL FROM AQUEOUS SOLUTIONS
IE 1200 ~L U
a)
>: >
< I000
800
o
600
o
- eq
.1 100
0
l 200
1 300
400 t,min
0
100
200
300
1
I
I
400
9 84
o o
o
o i
o
o
E~
T 10 o
Fig.
2. V a r i a t i o n of s p e c i f i c a c t i v i t y vs. t i m e (a) a n d ig (C-Ceq) vs. t i m e (b) for the s y s t e m A m b e r l i t e XAD 4 - T
while
Figs
logarithm the
same
first
the
show
the
corresponding
concentration The
(Co-Ceq)
linearity
of t h e
plot versus
plot
of t h e time
points
for to a
mechanism.
statement in one
suggests step
to c o m p a r e
complex
tribution
(b)
systems.
only
possible fixed
of
order
This curs
1-4
on the
the
probably
bonded
influence
by c o m p a r i n g
coefficients
that
the
216
ligand.
of
the
uptake
of d i f f e r e n t
the u p t a k e Then
support
rates
ligands
and
it on the
bonded
ocis the disto
BENZI et al.: RADIUM REMOVAL FROM AQUEOUS SOLUTIONS
E
1200 b
ol
-~ looo -~ ~j <
[
800 J-t
0
100
0
100
9~
200
300 t,min 200 30O
I
I
o
I
Fig.
the
3. V a r i a t i o n of s p e c i f i c a c t i v i t y vs. t i m e (a) a n d ig ( C - C e q ) vs. t i m e (b) for the s y s t e m A m b e r l i t e XAD 8 - T
same
ferent
support
or of
the
In T a b l e
2 the d i s t r i b u t i o n s
(radiumsolid/radiumsolu c a l c u l a t e d as:
t)
k = t -I !n were
A 0 = initial
tion
at e q u i l i b r i u m
listed
for
XAD-4 (system uptake
same
ligand
bonded
to d i f -
supports.
the
has 2).
rate
the
concentration, and
at
constants
k
time
Aeq t,
and A t = concentra-
respectively,
are
considered.
loaded
The greater and yield
uptake
D
(A 0 - A e q ) / ( A t - Aeq)
systems
been
and
coefficients
with
K
(system
efficiency
of
c a n be e x p l a i n e d
217
I)
and w i t h
system in t w o
2 both ways:
T in
BENZI et al.: RADIUMREMOVALFROM AQUEOUSSOLUTIONS
IE 1200 O. U
1000
8O0
600 eq c
I
I
0
200
400
i0, Fig.
4.
than
- the b o n d i n g
of
stronger
of
\
activity vs. time (a) a n d (b) for t h e s y s t e m K i e s e l g e l
K
- T is b e t t e r
The
o\
Variation of specific ig (C-Ceq) vs. t i m e -
I
600 t,m.in
than first
system
K in r a d i u m
the
in o t h e r
complex
radium-T
or to X A D - 4
is in c o n t r a s t
it m u s t
be c o n c l u d e d
with
the
results
that
the
equi-
librium: K-radium ( )solid is s h i f t e d
to the
is
systems.
hypothesis
4; t h e n
uptake
--~ ~--
right. 218
(K-radium)
solut
BENZI et al.: RADIUM REMOVAL FROM AQUEOUS SOLUTIONS
TABLE
2
R a d i u m d i s t r i b u t i o n c o e f f i c i e n t s and u p t a k e rates for v a r i o u s l y l o a d e d resins System
D
I(K-XAD4)
0.47
1.6 + 0.2
2(T-XAD4)
1.00
1.1
+ 0.1
3(T-XAD8)
2.17
3.1
+ 0.2
4(K-Kiese!gel)
1.30
0.5 + 0.3
The a b i l i t y of resins
k x102,
as supports
systems
2 (XAD-4,
non-polar)
polar).
The two supports d i f f e r
40 A for the first m a t r i x A computer complex
simulation
a diameter
and 3
is c o m p a r e d in
(XAD-8, w e a k l y
also in pore diameter:
and 220 A for the second one.
of the Ra2+-T i n d i c a t e s
of about 8 A; therefore,
likely that the i n f l u e n c e of this p a r a m e t e r concern
the uptake
f i c i e n t of X A D - 8
min-1
rate.
The g r e a t e r
is p r o p a b l y
for this
it is not does not
distribution
connected
coef-
to the s t r e n g t h
of the bond f o r m e d due to the polar nature of the m e t a l l i g a n d complex. Finally, which
it is p o s s i b l e to o b s e r v e
that system 4,
shows a s a t i s f a c t o r y u p t a k e yield,
by c o n t r a s t
slow in the removal of Ra 2+ from the solution. slowness,
which
denotes
a high a c t i v a t i o n
c a t i o n capture by the ligand, nary
studies
on lead removal
greater
energy
from solutions,
than values p r e v i o u s l y
other c h e l a t i n g From removal
This for
is shown also in p r e l i m i -
for Pb 2+ the u p t a k e yield by K on K i e s e l g e l high,
is
even if is very
o b t a i n e d with
systems 11
this p r e l i m i n a r y
selection
from w a t e r we c o n c l u d e
as T and K, s u i t a b l y
supported, 219
of ligands
for radium
that o p e n - c h a i n show p r o p e r t i e s
ligands which
BENZI et al.: RADIUM REMOVAL FROM AQUEOUS SOLUTIONS
encourage
us to continue the experiments.
final aim is to treat neutral waters,
Even if the
the e f f e c t of the
c o n c e n t r a t i o n of anions and of a n t a g o n i s t c a t i o n s should be c o n s i d e r e d before p e r f o r m i n g
flow e x p e r i m e n t s .
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