LETTER TO THE EDITOR Journal of Radioanalytical and Nuclear Chemistry, Vol. 238, Nos 1 2 (1998) 19~201
60Co removal from aqueous solutions using charcoal R. M. Flores E., M. T. Olguin, M. Solache-Rios, S. C. Longoria G., S. Bulbulian Instituto National de Investigaciones Nucleares, Apdo. Postal 18-1027, Col. Escand6n, Del. Miguel Hidalgo, C~P. 11801, M~xico, D. F. Mexico (Received April 1, 1998)
Charcoal, treated in different ways, can be used in the separation of 6~ from aqueous solutions. The cobalt species involved in the process were identified by high voltage electrophoresis. The best results were obtained using thermally and chemically treated charcoal with a maximum retention of 1.24 mmol cobalt per gram. It was also found that the cobalt was not desorbed from the chemically treated charcoal when washed with distilled water. However, it was eluted from the charcoal with 2.3N hydrochloric solution. Samples containing 6~ were analysed during the sorption process by gamma-ray spectrometry.
Introduction Radioactive cobalt is a constituent of liquid radioactive waste produced in nuclear facilities. Removal of 6~ has been studied in different materials l 3 Charcoal is one of the most used adsorption materials, and is generally applied in industrial processes to eliminate color, smell and organic substances from water solutions, or to retain cations s u c h a s U 0 2 + 2 , Sr 2+ and Ce3+. 4 5 Industrially, charcoal is obtained by degrading wood through a distillation process. It can be activated under high temperatures (880-900 ~ producing compounds with large surface areas (1000m2/g), thereby increasing the adsorption capabilities regarding of gases, vapours and colloids. 6 Charcoal has also been treated to remove nickel, lead, tin, copper and chromium. 7 The aim of this work was to study the 6~ sorption and desorption processes in charcoal.
and 1.00N Co(NO3) 2. Solutions labeled with 6~ were used for the cobalt uptake process in the different charcoal samples. Glass columns of 2.5 cm in diameter packed with 20 g of various charcoal samples were utilised to remove 6~ from the water solution. The radioactive cobalt nitrate solutions were passed through the columns at a rate of 2 ml/min. Analytical grade reagents were used without further purification. 60Co
separation J?om water solutions
Maximum 606o retention: The maximum 6 0 C o retention in the columns were determined in each column using different 6~ concentrations. 50 ml of 0.01, 0.05, 0.10 and 0.50N Co(NO3) 2 solutions were passed through the columns filled either with chl or ch2, and 50 ml of 0.01, 0.05, 0.10, 0.30, 0.50, and 1.00N Co(NO3) 2 solutions, were passed through columns filled with ch3. Removal of 606'0 jCrom the charcoal samples:
Experimental
Material and equipment Commercial charcoal samples (20 g), 14 mesh, were treated as follows: (1) (Samples chl) washed with tap water; (2) (Samples ch2) washed with tap water and then heated for 4 hours at 100 ~ (3) (Samples ch3) washed with tap water and then treated with 40 ml of 2M NaOH solution for 24 hours. Finally filtered to remove the excess of NaOH solution and dried at 30 ~ for 10 minutes. 6~ was obtained by neutron irradiating cobalt nitrate for one hour in a TRIGA Mark III nuclear reactor with an approximate neutron flux of 1013 n ' c m 2.s 1 The irradiation was carried out in a fixed irradiation system. Cobalt was determined by gamma-spectrometry of 6~ measuring the 1.173 and 1.332MeV photopeaks with a NaI(T1) well type detector coupled to a monochannel analyser. 0.01, 0.05, 0.10, 0.30, 0.50,
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Charcoal sample ch3 resulting from the previous experiment treated with 0.01N Co(NO3)2, was used to study whether 6~ adsorbed could be removed from the charcoal. For this purpose, first 100ml of demineralized water and then 100 ml of 2.3N HC1 solution, were passed through the columns. 10 ml aliquots of the eluates were measured in a gammaspectrometry system using the 0.01N 6~ initial solution as a reference.
Identification
of 6060 species in solution:
60Co
species were identified in the initial 0.01N Co(NO3) 2 solution and in the 6~ containing HC1 solution obtained in the previous experiment. The solutions were analysed by high voltage electrophoresis. For this purpose, 1.0cm wide Whatman papers were impregnated with a supporting electrolyte solution (0.01N cobalt nitrate solution). The radioactive Co solution was deposited at the origin of the paper strip (0 cm). The voltage used was 2000 V for 30 minutes. Once the electrophoresis was completed the papers were
Elsevier Science B. K, Amsterdam Akad~miai Kiad6, Budapest
R. M. FLORESE. et al.: 6~
REMOVAL FROM AQUEOUS SOLUTIONS USING CHARCOAL
air dried and cut in 1 cm long fractions. 60Co w a s determined in each paper fraction by y-spectrometry.
30 25
1.4
=~
1.2
2O
1 O
0.8
-6
nr
O
o
E E
0.6
5
0.4
o 1
2
3
0.2
4
5
6
7
8
9
10
Aliquot number
0
,
0
0.2
0.4
0.6
0.8
1
r
Fig. 3. Percentage of radioactivity of6~ eluted with 2.3N HC1 from charcoal samples (chl r-l, ch2 9 and ch3 m)
Co(NO3) 2 concentration, N
Fig. 1. Maximum cobalt retention (mmol) versus concentration of the cobalt nitrate solutions in the charcoal samples (chl O, ch2 m, ch3 *)
80
*6
30
25
~
100
,m >
60
O "O
40
n-
2O
>
20
]~ IRR......
._o 0
,n o
cq
to
~o
o
c,l
Centimeter number, negative region
1
2
3
4
5
6
7
8
9
10
Fig. 4. Electrophoregrams of 0.01N Co(NO3)2 solution U ) and eluted fraction with 2.3N HC1 solution from charcoal sample (ch3,r-1)
Aliquot number
Fig. 2. Percentage of radioactivity of 6OCo eluted with water from charcoal samples (chl r-l, ch2 m)
Results and discussion
The results obtained for the maximum cobalt retention vs. concentration of the cobalt nitrate solutions are shown in Fig. 1. It was found that the maximum retention in the columns packed with samples chl and ch2 were 0.08 and 0.17 mmol of cobalt per gram of charcoal, respectively. In our working conditions at higher concentration these columns were not able to retain all 6~ from the solution. For sample ch3, saturation was not reached, even for Co(NO3) 2 solution. The maximum cobalt retention found was 1.2 mmol per gram. As it can be observed in Fig. 1, the retention of cobalt by the sample ch3 is much higher than for the other charcoal samples. Removal of 6~ from samples chl and ch2 are shown in Fig. 2. When washed with water 6~ was not eluted at all from the column filled with ch3, and 200
R. M. FLORES E. et al.: 6~
REMOVALFROMAQUEOUSSOLUTIONSUSINGCHARCOAL
approximately 40% was eluted from the columns containing the other two charcoal samples. The remaining 6~ on charcoal samples was desorbed with 2.3N HC1 solution. Most of the cobalt was removed from the column, as shown in Fig. 3, due to the pH value reduction. Figure 4 shows that Co species in the original 0.01N Co(NO3) 2 solution and in the eluted fraction with 2.3N HC1 solution from ch3 sample, were different. The species present in the original solution corresponds to the octahedral Co(H20)2+ as reported elsewhere. 8 6~ species found in the hydrochloric acid solution eluted from sample ch3, was a heavier species, probably a cationic polynuclear hydrolysed9 species located near the origin of the paper strip. The retention of 6~ on the chemically treated ch3 sample is probably due to the hydrolysis of cobalt when it is in contact with the
charcoal surface. Therefore It is important to notice that the formation of hydrolysis products of cobalt improves the retention of this element. Conclusions
The charcoal sample washed and treated with NaOH solution was found to be the best of three charcoal samples for cobalt retention. Cobalt was strongly sorbed on it. Its desorption was only possible when a strong HC1 solution was passed through the column. The hydrolysed cobalt species eluted with hydrochloric acid probably polynuclear species was different from that found in the starting cobalt nitrate solution. References
[COx(OH)y](xz~)+
1. A. A. AL SUHYBANI,J. Radioanal. Nucl. Chem., 141 (1990) 25. 2. I. GARC[A, M. SOLACHE-R[os, P. BOSCH, S. BULBULIAN, J. Phys. Chem., 97 (1993) 1249. 3. B. RABENSTORF,Acta. Chem. Scand., A40 (1986) 550. 4. R. QADEER, J. HANIF, Adsorpt. Sci. Technol., 11 (1994) 201. 5. R. QADEER, J. HANIF, Radiochim. Acta, 64 (1994) 259. 6. A. Mc. LAUGHLINLISA, Mc. S. LAUGHLINHUGH, Strategy, Eng. Chem. Prog., 90 (1992) 40. 7. R. M. FLORES, E. ACOSTA, A. M. BENAVIDES, Tratamiento de Aguas Residuales de la Industria Galvanoplfistica, Reporte T~cnico EN/95/96, ININ, M~xico, 1996. 8. F. A. COTTON, G. WILKINSON,Quimica Inorgfinica Avanzada, Limusa, M~xico, 1975. 9. C. F. BAES Jr., R. E. MESMER, The Hydrolysis of Cations, John Wiley and Sons, New York, 1976.
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