Immobilization of thorium over fibroin by polyacrylonitrile (pan)

Waste Management, Vol. 17, No. 1, pp. 87-89, 1997 © 1997 Elsevier Science Ltd All rights reserved. Printed in Great Britain 0956-053X/97 $17.00 + 0.00

Pergamon PII: S0956-053X(97)00025-1

TECHNICAL NO TE

IMMOBILIZATION OF THORIUM OVER FIBROIN BY POLYACRYLONITRILE (PAN)

Mahmoud A. A. Aslani,* Sema Akyil and Meral Eral Ege University Institute of Nuclear Sciences, 35100 Bornova-lzmir, Turkey

ABSTRACT.This report describes a process for immobilization of thorium over fibroin, which was used as a bio-adsorbant, by polyacrylonitrile. The amounts of thorium in aqueous solutions which may be leached in various aqueous ambients were detected by a spectrophotometer. The results show that polyacryionitrile processes are feasible to immobilize spent fibroins. The leachability of the materials immobilized with polyacrylonitrile can meet the requirements of storage and final disposal. The leachability of thorium ions from immobilized spent fibroin was rather low for 8 months. © 1997 Elsevier Science Ltd

INTRODUCTION

their conversion into stable monolithic forms by polymerization will minimize the potential for radionuclides to leak into the environment during storage, transportation and disposal. 5 Organic polymers of various types have been used to condition aqueous liquid waste treatment residues, although, to a much lesser extent than cement or bitumen. Several types of thermosetting polymers such as polystyrene, polyester, epoxide, and urethane have been used to produce solid waste forms. In most cases, the use of an organic polymer as the immobilization matrix requires the waste to be dried before mixing. Thermoplastic polymers such as polyethylene can be used for the immobilization of radioactive concentrates by heating them until they become liquid then mixing them with the waste in a similar manner to bituminization. 6 We have investigated sorption of thorium on silk fibroin from aqueous solutions and the residues of thorium leach solutions as actual waste in an earlier study. 7 In that study, we have pre-examined desorption of adsorbed thorium on fibroin, and have observed that the thorium was desorbed in a water and acid media in a short time (approximately 2 weeks). This study describes the process for immobilization of spent fibroins with polymer in which polyacrylonitrile has been investigated in the immobilized process.

In the atomic energy industry, the treatment and management of high level liquid waste (HLLW) are the most serious problems. In fission products, the most soluble and long-lived radioactive isotopes are 137Cs and 9°Sr, therefore, the fixation of these isotopes into insoluble materials is the most valuable to security against the management of HLLW.I The management of radioactive wastes has been investigated mainly in the glass solidification. The vitrified solids containing a variety of radioactive elements with various half-lives must be stored or disposed for a considerable time. Also, these products have some disadvantages, i.e. low thermodynamic stability and high leachability of Cs and Sr. Therefore, alternative waste solids are underdeveloped such as supercalcine ceramics and synroc, which have more stable properties than the vitrified solids. 2'3 Various ceramic products have been developed as an alternative to borosilicate glasses for the disposal of high-level radioactive waste. 4 The nuclear industry generates considerable amounts of spent ion-exchange resins which may require further treatment prior to safe disposal. Owing to the fact that spent resins are small beads or powder materials and have a strong exchange capability, RECEIVED 21 NOVEMBER 1996; ACCEPTED 1 APRIL 1997.

EXPERIMENTAL

*Corresponding author. Fax: 00-90-232-3886757, E-mail: aslani@ egeuniv.ege.edu.tr

Materials Native silk was obtained from the Silk Industry Research Centre, Bursa, Turkey. Polyacrylonitrile (PAN) was obtained from the AKSA Industry of

Acknowledgements--We

are grateful to Bursa Silk Research Center and AKSA Industry o f Acrylic Chemistry, Istanbul, Turkey for their assistance.

87

M. A. A. ASLANI ET AL.

88

Acrylic Chemistry, Istanbul, Turkey. Arsenazo III and Th(NO3)a.5H20 Merck Company and all other chemicals were of reagent grade.

I Spent

Fibroin (O.lo)

I ~1

I~

I

Solutionof Binding Polymer (0.1g)

[

I(60 Minutes, Mixing l 70°C)

Preparation of Fibroin

4,

I F°rmati°n as Plate I

The native silk was cut with scissors into lengths of approximately 0.5 cm. Then, native silk was degummed with soap mixed for 2h at 99-100°C. The degummed silk was filtered, washed thoroughly with deionized water, and air-dried. Thus, fibroin which was enclosed with sericin, is saved, s

4,

I I

,sF

I

Washingwith

[

Deironized Water 4,

Treatment of Fibroin with Waste Solution The thorium uptake capacity of fibroin was calculated as 2.15mmol/g by Aslani. 7 The activity of aqueous effluents for waste arising from research and training studies was reported as 10-6-10 -1 Ci / m3.9 In this study, we prepared a solution of thorium-232 with 10-7 Ci / m 3 (1000ppm) activity. The fibroin was suspended in 50 ml of this solution. The suspension was stirred continuously in a batch system at 30°C for 24h. The mix was filtered and the loaded fibroin waste was pre-dried. Then, the residual thorium in filtrate was determined via a spectrophotometer using the Arsenazo III method (Z=658nm, e = 1.0883x 1051/mol.cm) by using a Shimadzu UVVis 260 Recording Spectrophotometer (Fig. 1).s

Immobilization of the Spent Fibroin The principle scheme of preparation of the covered fibroin containing polyacrylonitrile as a binding polymer is shown in Fig. 2. In this immobilization process, PAN is used as binder polymer. The spent fibroin was added to the PAN solution and mixed at 70°C for 1 h. Then the final products were formed as thin plates and washed with deionized water and dried at ambient temperature. This principle preparation scheme (Fig. 2) can be practically used for any spent adsorber or resin. The spent adsorber or resin can be mixed directly with the solution of binding polymer. The final product can be shaped as grains, membranes etc. From an economical point of view, it is worth mentioning that even some industrially produced PAN can be used to cover spent adsorbers. The covered adsorbers can be modified by altering the degree of cross-linking of the polymer, using

Fibroin

Filter

.......... "B Spent Fibroin

(Ambient Temperature) 4,

I

Storage

[

FIGURE 2. Scheme of the simplified experimental stages in the preparation of ISF.

suitable co-polymers, or by changing the composition and temperature of the coagulation bath.

Leaching Tests of Immobilized and Non-immobilized Spent Fibroin (ISF) The leachability tests were carried out using 250 ml of tap and ground water and 0.1M HNO3 + 3.6 M NaNO3 at ambient temperature. The amount of thorium in solution was determined every week for 8 months and 2 weeks for immobilized and nonimmobilized spent fibroin, respectively. Thorium in aqueous solution was determined by the Arsenazo III method.

RESULTS AND CONCLUSION Table 1 shows the leaching results from non-immobilized fibroin after 2 weeks. As shown in this table, the amounts of leached thorium in the tap, the ground and 0.1 M HNO3 + 3.6 M NaNO3 mediums were rather high in a short time. Thorium amounts of ISF and the leaching mediums are shown in Table 2. Since ISF is insoluble in water and has a high resistance to the diffusion of water, nitrates, etc., the leachability of ISFs was not detected during 8 months in these mediums. TABLE 1

Immobilization

/Pr°cess

]

The Leaching Results from Non-immobilized Fibroin after 2 weeks

Sample Amounts of Th No. on fibroin (ppm) l 2 3

FIGURE 1. Treatment process of spent fibroin by immobilization.

375 375 375

Leaching medium

Leached Th (ppm)

Tap water Ground water 0.1 M HNO3 + 3.6M NaNO3

2.50 16.30 66.26

IMMOBILIZATION OF THORIUM OVER FIBROIN

89

TABLE 2 Th Amounts of ISF and the Leaching Mediums

Sample no. 1 2 3 4 5 6 7 8 9

Weight (g)

Thickness (ram)

Amount of Th on fibroin (ppm)

Leaching medium

2.03 2.50 2.37 1.64 1.96 1.87 2.14 1.69 2.00

1.70 1.85 1.20 1.20 1.20 0.80 1.25 1.00 1.20

960.64 960.64 960.64 474.39 474.39 474.39 117.37 117.37 117.37

Tap water Ground water 0.1 M HNO3 + 3.6 M NaNO3 Tap water Ground water 0.1 M HNO3 + 3.6 M NaNO3 Tap water Ground water 0.1 M HNO3 + 3.6 M NaNO3

Even t h o u g h the m i n i m u m detection limit o f spect r o p h o t o m e r i c analysis is 0 . 1 2 / z g T h / m l , no Th was d e t e c t e d as being leached f r o m i m m o b i l i z e d fibroin by polyacrylonitrile. W e r e c o m m e n d this process as feasible to i m m o bilize spent a d s o r b e n t s o r resins arising f r o m nuclear i n d u s t r y a n d the l e a c h a b i l i t y o f the i m m o b i l i z e d f o r m s o f spent a d s o r b e n t with p o l y a c r y l o n i t r i l e will meet the r e q u i r e m e n t s o f storage, t r a n s p o r t a t i o n a n d final disposal. W e f o u n d t h a t p o l y a c r y l o n i t r i l e is very suitable for solidification o f Th a n d the i m m o b i l i z e d f o r m s o f spent a d s o r b e n t were fairly stable up to a b o u t 100°C. The i m m o b i l i z a t i o n o f the r a d i o n u c l i d e s , especially the long-lived Th, w o u l d be effective for the solidific a t i o n after p a r t i t i o n i n g o f H L L W . F o r this reason, this described process for s t o r a g e a n d final d i s p o s a l o f spent a d s o r b e n t o r resins is r a t h e r c h e a p a n d rapid. Also, it was seen t h a t this i m m o b i l i z a t i o n process p r e v e n t e d s p r e a d to the e n v i r o n m e n t b y an external f a c t o r d u r i n g s t o r a g e because o f the 0.5 cm lengths o f fibroin used. Therefore, in o u r o p i n i o n , the u p t a k e o f c o n t a m i n a t e d fibroin into h u m a n a n d a n i m a l f o o d c h a i n w o u l d be prevented. In the following stages o f waste m a n a g e m e n t , the i m m o b i l i z e d fibroin with P A N w o u l d be s t o r e d in a smaller v o l u m e as plate, a n d thus the T h l o a d e d

fibroin f r a g m e n t s w o u l d be collected t o g e t h e r as one smaller piece using this i m m o b i l i z a t i o n process.

REFERENCES

1. Kanno, T. and Mimura, H. Ion-exchange properties ofzeolites and their application to processing of high-level liquid waste. IAEA-TECDOC-337 0985). 2. Hsu, C., Mimura, H., Tenman, M. and Kanno, T. Solid phase reactions of denitrated precipitates for high-level liquid waste with zeolites. Nucl. Sci. J. 23:2 (1986). 3. Dutta, N. C. and Bhattacharyya, D. K. Immobilization of yttrium over crystalline titania. J. Radioanalytical and Nuclear Chemistry 204:167-172 (1996). 4. Hsu, C., Mimura, H. and Kanno, T. Synthesis of Haiiyne by reaction between sodium lanthanum molybdeum oxide and nepheline. Nucl. Sci. J. 23:4 (1986). 5. Fan, X., Luo, S., Lin, M., Jiang Y., Li H., Li, X., Tan, G., Zhang, Y. and Wang, L. Immobilization of spent resins with polymers. IAEA-TECDOC-568 (1990). 6. Williamson, A. S., Hild, W. and Cowlam, S. K. Treatment and conditioning of spent ion exchange resins from research reactors, precipition sludges and other radiactive concentrates. IAEA-TECDOC-689 (1993). 7. Aslani M. A. A. PhD Thesis, Ege University, Institute of Nuclear Sciences (1996). 8. Aslani, M. A. A. and Eral, M. Investigation of uranium recovery from dilute aqueous solutions using silk fibroin. Biological Trace Element Research. Humana Press 43--45:737-743 (1993). 9. Dumas D. O,, Wakerley M. W., Plumb G. R. and Tsyplenkov, V. S. Minimization and segregation of radioactive wastes, technical manual for the management of low and intermediate level wastes generated at small nuclear research centres and by radioisotope users in medicine, research and industry. International Atomic Energy Agency TECDOC-652 (1992).