Technetium sorption by anionexchange resins, inorganic sorbents, natural minerals and rocks. Effect of radiation. Precipitstion of sulfide. Solubility of sulfide.

1. Journal of Radioanalytical and Nuclear Chemistry, Articles, Vol. 157, No. 1 (1992) 3-14
SORPTION OF TECHNETIUM ON INORGANIC SORBENTS
AND NATURAL MINERALS
S. EL-WEAR,* K. E. GERMAN,** V. F. PERETRUKHIN**
*Ta/ura Nuclear Researche Center, Tripoli (Libya)
**Institute o f Physical Chemistry o f Acad. Scs USSR Leninski prospect,
31 Moscow, 117 915 (USSR)
(Received November 5, 1990)
The sorption behavior of the pertechnetate anion in various solid-solution systems under
aerobic conditions and pH 1.3-12.5 has been investigated. Batch techniques were employed.
On most of natural minerals only surface adsorption occurs. Rs-values were no larger than
2.0 m l o g= 1. Adsorption on various natural minerals and rocks such as sandstone, basalt,
granite, pyrite, peat and others are comparaed with the analogous processes on artificial
inorganic sorbents: titanium oxides (thermoxide-34, thermoxide-3), erystaline cadmium
sulfide, zirconium phosphate, and complex inorganic sorbents: antimony oxide - silicon
oxide - phosphorus pentoxide, antimony oxide - silicon oxide - aluminium oxide, lithium
oxide - manganese oxide - aluminium oxide - water, lithium oxide - titanium oxide chromium oxide - water. For comparison the sorption of Tc on some organic sorbents was
included. The solubility of T% S7 in water was measured to be 0.257 g/t. It has been shown
that preliminary irradiation of sorbents such as sandstone, peat and humic acid by -/-rays
with doses not less than 10 ~ rad results in the decrease of To(VII) sorption.
Introduction
All over the world no less than 19000 T B q o f 9 9 T c had already been p r o d u c e d in
nuclear reactors up to 1990. As considered, 10% o f this a m o u n t has been dissipated
in the e n v i r o n m e n t ) Estimations for the last years show that around 160 T B q o f
99Tc has
been released during atmospheric atomic b o m b t e s t i n g ) On the other hand,
as was m e n t i o n e d by G A R C I A - L E O N , the continuous increase o f 99 roTe.generator s
in nuclear medicine should be given a t t e n t i o n ) A l t h o u g h some authors consider this
c o n t r i b u t i o n o f 99Tc to the e n v i r o n m e n t to be negligible, 4 to our m i n d it should be
taken into account that all this t e c h n e t i u m penetrates the h u m a n surrounding through
the h u m a n b o d y .
So, ecological aspects o f Tc-chemistry n o w are o f increasing importance, and
consist o f p r o b l e m s o f To-determination, 3 - 7 volatilization,S-11 solubility m e a s u r e m e n t
and leaching, 12-17 sorption,1 s-20 and the diffusion o f Tc.21,22 Many problems in
Elsevier Sequoia S. A., Lausanne
Akaddmiai Kiad6, Budapest

2. S. EL-WEARet al.: SORPTIONOF TECHNETIUMON INORGANICSORBENTS
ecological aspects of Tc behavior have not yet been investigated. Only little information is available about the sorption of Tc in pure natural minerals of inorganic and
organic nature.In,21 This fact make~ it difficult to predict the behavior of Tc in the
environment. The behavior of Tc on some minerals and soils is of great importance,
particularly in peats, which is one of the main ingredients of the soil in Eastern
Europe, especially in the region of Chernobyl contamination. This problem has not
been studied at all. So we thought it necessary to concentrate on the following: (1)
investigation of To-behavior in natural waters in contact with a large number of natural
minerals, (2) modeling of Te-behavior in artificial minerals and inorganic sorbents in
comparison with organic sorbents, and (3) investigation of To-behavior on irradiated
natural sorbents.
Experimental
Technetium was obtained from the firm "Isotope", USSR, in the form of KTcO4
and transformed into NaTcO4 by means of cation exchange in the Laboratory of Radiochemical Research, Institute of Physical Chemistry, Academy of Sciences of the USSR. 2 a
Minerals
The sorption of 99To was studied on the artificial minerals, natural minerals and
organic ion-exchangers. The artificial minerals studied were: Thermoxide-34, Thermoxide-3,
GSK, ZrP, SPSC, SKK-AL, ISMA, ISTH-1, and Polysorb-1 (all from USSR), and some
inorganic sorbents from different countries: Chromosorb-P, Chromosorb-W (from USA),
and Celite-545 and Celite-C-22 (from UK). The natural minerals were: sandstone,
feldspar, bauxite, basalt, megrele, phosphorite, peat, pyrite and kaoline. All specimens
used-were obtained from deposits in the USSR.
The results were compared with the sorption of Tc on organic anion exchange resins:
AV-17 and VP-1AP (Table 6). All the minerals were crushed and sieved. The fraction
between 6 0 - 8 0 mesh was chosen. Prior to use, the particle fraction was washed several
times with distilled water until no dust was visible in washing water. Thereafter air
dried solids were used in the experiments.
Sorption experiments
For preparation of the pH 1.27, 6.46 and 12.6 solutions, 132 mg of NaTcO4 was
dissolved in one liter of dilute HNO3, distilled water and dilute NaOH, respectively.
For measuring the sorption ratio Rs, batch sorption experiments were performed
by shaking 1 g of the crushed and sieved minerals with 10 ml of Tc solution with dif-
4

3. S. EL-WEARet al.: SORPTION OF TECHNETIUMON INORGANICSORBENTS
ferent concentrations. Varying the contact time from 1 - 2 0 days for pH 1.27, from
1 - 1 3 days for pH 6.46 and from 1 - 7 days for pH 12.7 and 1 - 2 months for natural
minerals and other minerals.
Measurements of solubility
For explanation of sorption behavior of Tc on sulfuoric minerals it was necessary
to get the exact value of Tc2 $7 solubility, but this value was not available from the
literature. So we synthesized Te2 $7 for measuring its solubility. Equimolar quantities
of Na2S and NaTeO4 were stirred in a beaker for 30 minutes. The following reaction
explains the formation of To2 $7:
8H20 + 7Na2S + 2NaTcO4 a
9 Tc2S7, + 16NaOH
The precipitate was centrifuged and washed 10 times with distilled water and in
each washing was centrifuged at 8000 r.p.m, for 30 minutes. Distilled water was added
to the precipitate with stirring and the initial pH was 7. Five hours later the solution
became violet due to the formation of unknown intermediate technetium sulfides,
the UV-VIS spectrum is show0 in Fig. 1.
&
35200
- 1.6
I.
D
- 1.4
- 1.2
19250
- 1.0
J
.,
I
1
I
I
38
34
30
26
,
22
18
1/-,
13
)-
xlO-Scm-1
Fig. 1. UV-VIS spectrum of supernatant solution of technetium sulfide in water
After three days of stirring the solution became colorless and the pH value was
2.35 due to-the following reversible reaction:
Tc2S7 + 8 H 2 0
.
' 2HTcO4 + 7 H 2 S
The solution was centrifuged and the solubility of the precipitate was measured to
be 0.257 g/l.

4. S. EL-WEAR et al. : SORPTION OF TECHNETIUM ON INORGANIC SORBENTS
Measurement of radioactivity
Samples of 20/A were taken from each batch and dried on a paper disc and the
/3-activity of 99 Tc was measured by an NRQ-605 a - / 3 - 7 autometic instrument
(Tesla, Czechoslovakia), equipped with a stilbene scintillation/3-detector. The discrimination level of the pulse was chosen to provide the best efficiency for measuring
the soft/3-emission of 99 Tc. Relative technique was used.
Irradiation technique
An experiment has been done on sorption of Tc on irradiated minerals; sandstone,
peat and humic acid were 7-irradiated with a 6~
source for 20 hours. The absorbed
dose was 107 Rad at room temperature (See Table 8).
Calculations
The sorption ratio R s and R's was used in this work to describe the sorption
properties of the minerals. The following equations give the ratio of R s and R's:
Asolid
Vsolution
(1)
R s -Asolution
where A s o l i d
Vsolid
activity of the dried sorbent,
A s o l u t i o n - activity of the supernatant solution,
V s o l u t i o n -- volume of supernatant solution in ml,
Vsoli d
- weight of the dried sorbent in g.
-
V
R's
=
C1 - C2
--
(2)
.
W
C2
where V - volume of the solution,
W - weight of solid material used,
C1 - initial activity per ml of a given radioactive Tc in solution,
C2 - activity per ml for the solution after contact.
For the calculation of the solubility of Tc2S7, we used the following equation:
Is
CS
~
- -
Io
Vo
"
- -
Vs
~
Co
(3)

5. S. EL-WEAR et al.: SORPTION OF TECHNETIUM ON INORGANIC SORBENTS
where Cs - solubility of Tc2 $7,
Is - counts of Tc in solution,
Io - counts of Tc in standard,
Vs - aliquot volume o f Tc solution,
Vo - aliquot volume of Tc standard,
Co - concentration o f Tc in standard.
m
C 0 ~
v
where m - mass of Tc in standard,
v - volume of standard.
Results and discussion
The sorption experiments on 99 Tc were carried out with the minerals listed in
Tables 1, 5, 6 and 7. As can be seen in Tables 2, 3 and 4, the study of 99Tc sorption
on artificial minerals at pH of 1.27, 6.46, and 12.7 was carried out. As we have seen
from formulas 1 and 2, the values o f R's and Rs represent the molecular sorption and
the ionic sorption, respectively. The ionic sorption ratios o f the artificial minerals Rs,
were very small at all pH values. Small value appears on Thermoxide-34 at pH 6.46,
being equal to 3.2.
The GSK mineral showed R's values of 2.2, 1.25 and 0.57 at pH's of 1.27, 6.46,
J
and 12.7, respectively. Those values o f R s are due to the formation of a black precipitate of Tc2 $7. The precipitation increases with decreasing pH. Though the solubility product of CdS itself (SP = 3.6 9 10 - 2 9 in natural media is lower than the SP
o f Tc2S 7 at p H 2.35).
In acidic media a partial dissolution o f GSK (CdS) occurs, providing the increase
of S2 - ion concentration.
The R's-values are small too, but still higher than the ion exchange which is
represented by Rs-values. As is shown in Tables 2, 3 and 4, the R's-values are large
in neutral media and decrease in acidic and alkaline media.
T h e smallest Rs-values were obtained for the artificial inorganic minerals listed
in Table 5. From Table 6, it can be seen that Rs-values are very large on the organic
sorbents, AV-17 and VP-1AP, the largest one being observed at pH 6.46, which is
equal to 1.2 9 l0 s ml 9 mg -1

6. S. EL-WEAR et al.: SORPTION OF TECHNETIUM ON INORGANIC SORBENTS
Table 1
Formulas o f some minerals
Mineral
Thermoxide-34
Thermoxide-3
GSK
ZrP
SPSC
SKK-AI
ISMA
ISTH
Formula
Crystalline TiO 2 (high density)
Crystalline TiO~ (low density)
Crystalline CdS
ZrO 3 9 n P 3 0 * 9 k H 2 0
S b 3 0 s 9 nSiO 2 9 m P 2 0 s
A b 3 0 s 9 nSiO 3 9 m M e O 9 k i l O o A I 3 0 t
n L i 3 0 9 m M n O 3 9 1A130 t 9 kH=O
nLi=O 9 mTiO= 9 1CRO3 9 k H 3 0
Table 2
Sorption o f Tc o n artificial minerals a t pH 1.27
Mineral
Thermoxide-34
Thermoxide-3
Contact time, day
R~
4
8
20
< 0.05
4
< 0.05
0.3
2.94
8
20
GSK
4
8
20
ZrP
4
8
20
Rs after 90 days
2.9
9 10-1
2.2
o 10 "3
0.3
5.3
3.2
7.3
11.0
2.5
1.9
3.9
2.2
4.0
9 10 "3
9 10 -3
SPEC
4
8
20
<0.05
< 0.05
4.7
1.2
SKK-AI
4
8
20
0.26
< 0.05
4.4
3.26 9 10 -4
4
2.6
9 10 -3
2O
< 0.05
2.4
4
4
8
2O
< 0.05
1
3.6
7.6
o 10 -4
ISMA
8
ISTH-1

7. S. EL-WEAR et al.: SORPTION OF TECHNETIUM ON INORGANIC SORBENTS
Table 3
Sorption of Tc on artificial minerals at pH 6.46
Mineral
Contact time, day
R~
Rs after 90 days
Thermoxide-34
1
4
13
9.8
10.0
31.3
3.2
Therrnoxide-3
1
4
13
< 0.1
0.67
11.5
1.35 o 10- 3
GSK
1
4
13
1.5
0.7
13.4
1.25
ZrP
1
4
13
10.94
SPSC
1
4
13
4.5
11.0
9.4
1.6 o 10 -3
SKK-AI
1
4
13
1.45
0.6
10.5
6.1 o 10 -3
ISMA
1
4
13
<0.1
1
10.25
1.45 o 10 -3
ISTH-I
1
4
13
<0.1
1.9
11.1
1.3 o 10 -4
2,4 o 10 -2
The same behavior has already been described by other authors.24, 2 s The distribution coefficients o f Tc are investigated and described in Fig. 2 and we can see in this
figure that Tc is adsorbed very strongly at low acidity o f HNO3 and could be eluted
at high acidity o f HNO3.
Table 7 shows very small values o f R s in most o f the minerals and negligible ones
in the others for sorption o f 99Tc on natural minerals at pH 6.46, and at contact
times o f 1 - 2 months. Tc sorption by minerals decreases along the following series:
sandstone > feldspar ~ peat > basalt ~ bauxite ~ phosphorite > pyrite > megrele
kaoline. Table 8 shows the difference in the value o f Rs, for the non-irradiated
9

8. S. EL-WEAR et al.: SORPTION OF TECHNETIUM ON INORGANIC SORBENTS
Table 4
Sorpfion of Tc on artificial minerals at pH 12.7
Mineral
C0ntaef time, day
R~
Rs after 90 days
Thermoxide-34
1
2
3
7
0.36
0.02
0.73
1.0 o 10-4
Thermoxide-3
1
2
3
7
0.36
0.54
1.34
1.8
4.0 o 10 -4
GSK
1
2
3
7
0.13
0.85
2.16
0.57
ZrP
1
2
3
7
< 0.1
0.1
1
0.9
SPSC
1
2
3
7
<
<
<
<
SKK-A1
1
2
3
7
< 0.1
<0.1
1.1
ISMA
1
2
3
7
0.7
0.76
1.8
0.3
ISTH
1
2
3
7
0.3
0.6
2.4
1.9 ~ 10 -3
0.1
0.1
0.1
0.1
1.0 9 10 -3
-
1.2 9 10 - '
m i n e r a l s ( s a n d s t o n e , h u m i c acid a n d p e a t ) a n d t h o s e i r r a d i a t e d b y 3,-rays w i t h a dose
o f 107 rad. As we see h e r e , Rs-values f o r t h e i r r a d i a t e d m i n e r a l s are n e a r l y t w o t i m e s
l o w e r t h a n t h o s e for t h e n o n - i r r a d i a t e d m i n e r a l s . This d i f f e r e n c e c o u l d b e e x p l a i n e d
10

9. S. EL-WEAR et al.: SORPTION OF TECHNETIUM ON INORGANIC SORBENTS
Table 5
Sorption of Te on organic sorbents
Organic sorbent
pH
AV-17*
VP-1AP**
Contact time, day
Rs
Rs
1.27
1
4
8
20
412.7
528.8
499.6
738.3
2819
266
422
544.7
6.46
1
4
13
5.0 9 10"
1.2 9 lO s
1.2" 10 s
2496.8
2143.2
4525.1
1
2
3
7
6297
1.4 o 104
1.5 o 104
2.1 ~ 104
1920.3
2062.3
2087.3
2014.0
127
AV-17 lS analogous to DOWEX-1.
**VP-1At is a macroporous anionite which consists of two ion"
exchange groups: (1) N-methylpyridinium, (2) pyridine.
Table 6
Sorption of Tc on natural minerals at pH 6
Mineral
Contact time, month
Rs
Sandstone
t
2
2.57•
Feldspar
1
2
2.1 •
1.66_+0.3
Bauxite
1
2
1.01_+0.3
0.92•
Basalt
1
2
1.0 •
1.28_+0.3
Megrele
1
2
Phosphorite
1
1.05
Peat
1
1.89
Pyrite
1
0.32
Kaoline
0.1
<0.t
<0.1
<0.1
11

10. S. EL-WEAR et al. : SORPTION OF TECHNETIUM ON INORGANIC SORBENTS
&
1500~
1000
500
0
0
I
z,
2
,
I
6
i
D.
CHNo3mO|
Fig. 2. Distribution coefficient of technetium on AV-17 anion exchanger in nitric acid media
Table 7
Sorption of Tc on minerals at pH 6.46
Mineral
Contact time,
month
Chromosorb-P (USA)
Chromosorb-W (USA)
Celite-545 (UK)
Celite-C-22 (UK)
1
1
I
1
R~
<
<
<
<
0.1
0.1
0.1
0.1
Rs
5
6
4
4
9 10 -4
9 10- 4
9 10 -s
9 10- 5
Table 8
Sorption of Tc on irradiated minerals
Mineral
Sandstone
Sandstone
Humic acid
Humic acid
Peat
Peat
12
Concentration of Tc,
mg/1
Contact time,
day
Rs
(irradiated)
Rs
(non-irradiated)
132
1.32
132
1.32
132
1.32
5
5
5
5
5
5
1.05
0.72
2.12
2.01
1.2
0.84
2.26
1.8
4.2
4.0
2.9
1.0

11. S. EL-WEARet al.: SORPTION OF TECHNETIUM ON INORGANIC SORBENTS
by the elimination of the active chemical group in the case of peat and humic acid and
may be due to some changes in the chemical composition of the impurities in the ease
of sandstone. So we can say that a very small part of Tc produced during nuclear
tests in the atmosphere was absorbed by soils around the test site.
Conclusions
The 99Tc(VII) is n o t reduced and sorbed on the inorganic minerals and peat studied
in solution in the presence of oxygen. SO To(VII) can easily penetrate the environment
through natural waters.
After irradiation with doses n o t less than 107 rads the inorganic minerals and peat
decrease the sorption ratio of To(VII).
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14