- Email: [email protected]
The sorption of 90Sr from natural waters by alginates
Appl. Radiat. Isot. Vol. 47, No. 9/10, pp. 88%888, 1996
Pergamon PII: S0969-8043(96)00081-4
Copyright © 1996ElsevierScienceLtd Printedin Great Britain.All rights reserved 0969-8043/96 $15.00+ 0.00
The Sorption of 9°Sr from Natural Waters by Alginates Y U . A. S A P O Z H N I K O V .1, S. N. K A L M Y K O W , I. P. E F I M O W a n d V. P. R E M E Z 2 ~Radiochemical Division~Department of Chemistry, M. V. Lomonosov Moscow State University, Moscow V-234, 119899, Russia and 2Compomet Cantec, 5, 8th Marta Street, Ekaterinburg 620219, Russia The analytical applications of alginates, obtained from the marine algae Laminaria, for the pre-concentration of 9°Sr from natural waters was studied. The sorption capacity for strontium in the samples investigated reached 30 mmol kg- 1. The alginate sorbents were tested with sea water from the north-western part of the Black Sea over a wide range of salinity. The limit of detection for 9°Sr in sea water with a salinity of 15°/'oo < 1 mBq dm -a. The sorbents described are waste products of alginate manufacture and have a relatively low cost which considerably reduces the total costs of the analysis. Copyright © 1996 Elsevier Science Ltd
Introduction The determination of low concentrations of 9°Sr in natural waters is impossible without its pre-concentration. At present the most widespread pre-concentration method for many radionuclides from natural waters is a sorption procedure which permits their rapid concentration from large volumes of sample. For mCs and ~37Cs the introduction of the ferrocyanide based sorbents (Remez and Sapozhnikov, 1996) has provided a near specific sorbent that has largely replaced other pre-concentration methods. Unfortunately, for 9°Sr pre-concentration no such perfect and practical sorbent exists, sorbents based on crown ethers do show good specificity but are very expensive, and many investigators have used conventional precipitation methods. Attempts have been made to use manganese dioxide as a sorbent for the pre-concentration of 9°Sr from sea water (Sapozhnikov et al., 1992; Shipman, 1966) but the sorption capacity and the selectivity appear to be low. A high efficiency of alginates to remove radionuclides such as 9°Sr and 226Ra from animals or humans has been observed (Vanderborght et al., 1972). Alginic acids are natural polysaccharides, composed of B-D-mannuronic and U-L-guluronic acid residues, which make up 70-90% of the biomass of brown algae, such as L a m i n a r i a . They are colourless or slightly coloured substances, with molecular masses ranging from 3.5 x l0 s up to 1.5 x 10 6, which have many industrial uses. At the request of the Arkhangelsk' Algae Plant (Arkhangelsk, Russia) we have investigated the *To whom all correspondence should be addressed.
practical use of alginate-containing wastes as sorbents for radionuclides. We have carried out studies of the sorption of 9°Sr and t37Cs on more than 20 different kinds of alginate manufacturing wastes. These studies have included measurements of the sorption kinetics, the influence of the salt background and other factors. For all the samples investigated the sorption capacity for 9°Sr was higher than that for J37Cs. The maximum sorption capacity for 9°Sr in the alginate samples investigated was 30 mmol kg-R The main tests of alginate sorbents for 9°Sr extraction from natural waters were carried out in July 1995 in the north-western part of the Black Sea. In this region, which includes the Dnieper-Boug Gulf, 9°Sr concentrations are largely controlled by ingress from the Dnieper river which is subject to radioactive pollution as a result of the Chernobyl accident in 1986. The salinity of the water samples studied had a wide range of salinity, 2.84-17.56%o, thus providing widely differing concentrations of competitive ions.
Experimental The alginate preparations used were obtained from the Arkhangelsk' Algae Plant (Arkhangelsk, Russia) in the form of solid dried slices of marine algae which had a complicated and ill-defined form. The acid pre'-treatment of L a m i n a r i a at the Algae plant ensured the absence of low molecular mass organic compounds. The main component of the alginate sample is cellular tissue which firmly holds alginates. Water samples, 120-240 dm 3, were collected during a research vessel cruise. The samples were 'spiked' with the 3'-ray emitting isotope S5Sr as a tracer of
887
888
Yu. A. Sapozhnikov et al.
chemical yield. The water was then allowed to flow by gravity through a column, 20 cm high × 6.5 cm diameter, constructed of polyvinyl chloride, flied with 150 g of sorbent. After passage of the water sample, the column was disassembled and the sorbent removed and dried. After the research vessel cruise, the sorbent was analysed for SSSr by non-destructive 7-spectrometric measurements using a Ge(Li) detector (DGDKl15V, Russia) coupled to an AMA-03F (Russia) multi-channel analyser. After counting, the samples were loaded into alund crucibles and ashed in an furnace at 500°C for 20 h. The residue was spiked with strontium and yttrium carrier (20 mg) and treated with concentrated nitric acid and hydrogen peroxide. The insoluble residue was isolated by filtration. Yttrium was separated by addition of ammonium hydroxide. The filtrate was evaporated to 20 ml and placed in a liquid scintillation vial. The solutions were counted for 100 min steps during 120--150h to re-establish the radioactive equilibrium. The 9°Sr in the samples was determined by Cherenkov counting of the high-energy B-particles from the daughter 90y using a standard liquid scintillation counter. The limit of detection of 9°Sr in a 240 dm 3 sample of sea water with a salinity of 15%o, passed at a rate of 1 dm 3 min - l through 150 g of sorbent, was < 1 mBq dm-3. For comparison, at a number of the measurement stations a 9°Sr preconcentration was also carried out using manganese dioxide as the sorbent. The latter is the sorbent usually used for the preconcentration of radium from sea water, but it also has some capacity to adsorb strontium (Sapozhnikov et al., 1992; Shipman, 1966).
Results and Discussion The results obtained using the SSSrtracer were used to determine the relationship between the sorption of strontium and the salinity of the water sample. For alginate the relationship had the form D = (63.55 __+10.0) - (2.95 ___0.79)S where D is the sorbed strontium as % of the total; S is the salinity (%o), the correlation coefficient for this relationship was 0.91: For manganese dioxide the dependence on salinity had the form D = (22.30 + 2:23) -- (1.17 + 0.17)S with a correlation coefficient of 0.95. Obviously, the sorption capacity of the alginate sorbent is essentially higher than that of manganese dioxide, The sorbents described are wastes from alginate manufacture and their cost price is quite low, U.S.$, 4 k g - 1 and this makes the whole analysis considerably cheaper. The present work discusses only the analytical applications of these alginate wastes, however, they can also be used for the decontamination of waters in nuclear facilities, or as additives to forage for animals living in polluted territories.
References Sapozhnikov Yu. A., Eftmov I. P., Sapozhnikova L. D. and Remez V. P. (1992) Strontium-90 determination in surface waters of northwestern Black Sea. Vestnik MSU., Ser. 2. Khim. 33, 395. Shipman W. H. (1966) Determination of Strontium-90 in seawater after concentration by manganese dioxide. Analyt. Chem. 38, 1175, Vanderborght O., Colard J. and Boulenger R. (1972) Human faecal ~6Ra excretion shortly after alginate treatment. Hlth Phys. 23, 240.
Pergamon PII: S0969-8043(96)00081-4
Copyright © 1996ElsevierScienceLtd Printedin Great Britain.All rights reserved 0969-8043/96 $15.00+ 0.00
The Sorption of 9°Sr from Natural Waters by Alginates Y U . A. S A P O Z H N I K O V .1, S. N. K A L M Y K O W , I. P. E F I M O W a n d V. P. R E M E Z 2 ~Radiochemical Division~Department of Chemistry, M. V. Lomonosov Moscow State University, Moscow V-234, 119899, Russia and 2Compomet Cantec, 5, 8th Marta Street, Ekaterinburg 620219, Russia The analytical applications of alginates, obtained from the marine algae Laminaria, for the pre-concentration of 9°Sr from natural waters was studied. The sorption capacity for strontium in the samples investigated reached 30 mmol kg- 1. The alginate sorbents were tested with sea water from the north-western part of the Black Sea over a wide range of salinity. The limit of detection for 9°Sr in sea water with a salinity of 15°/'oo < 1 mBq dm -a. The sorbents described are waste products of alginate manufacture and have a relatively low cost which considerably reduces the total costs of the analysis. Copyright © 1996 Elsevier Science Ltd
Introduction The determination of low concentrations of 9°Sr in natural waters is impossible without its pre-concentration. At present the most widespread pre-concentration method for many radionuclides from natural waters is a sorption procedure which permits their rapid concentration from large volumes of sample. For mCs and ~37Cs the introduction of the ferrocyanide based sorbents (Remez and Sapozhnikov, 1996) has provided a near specific sorbent that has largely replaced other pre-concentration methods. Unfortunately, for 9°Sr pre-concentration no such perfect and practical sorbent exists, sorbents based on crown ethers do show good specificity but are very expensive, and many investigators have used conventional precipitation methods. Attempts have been made to use manganese dioxide as a sorbent for the pre-concentration of 9°Sr from sea water (Sapozhnikov et al., 1992; Shipman, 1966) but the sorption capacity and the selectivity appear to be low. A high efficiency of alginates to remove radionuclides such as 9°Sr and 226Ra from animals or humans has been observed (Vanderborght et al., 1972). Alginic acids are natural polysaccharides, composed of B-D-mannuronic and U-L-guluronic acid residues, which make up 70-90% of the biomass of brown algae, such as L a m i n a r i a . They are colourless or slightly coloured substances, with molecular masses ranging from 3.5 x l0 s up to 1.5 x 10 6, which have many industrial uses. At the request of the Arkhangelsk' Algae Plant (Arkhangelsk, Russia) we have investigated the *To whom all correspondence should be addressed.
practical use of alginate-containing wastes as sorbents for radionuclides. We have carried out studies of the sorption of 9°Sr and t37Cs on more than 20 different kinds of alginate manufacturing wastes. These studies have included measurements of the sorption kinetics, the influence of the salt background and other factors. For all the samples investigated the sorption capacity for 9°Sr was higher than that for J37Cs. The maximum sorption capacity for 9°Sr in the alginate samples investigated was 30 mmol kg-R The main tests of alginate sorbents for 9°Sr extraction from natural waters were carried out in July 1995 in the north-western part of the Black Sea. In this region, which includes the Dnieper-Boug Gulf, 9°Sr concentrations are largely controlled by ingress from the Dnieper river which is subject to radioactive pollution as a result of the Chernobyl accident in 1986. The salinity of the water samples studied had a wide range of salinity, 2.84-17.56%o, thus providing widely differing concentrations of competitive ions.
Experimental The alginate preparations used were obtained from the Arkhangelsk' Algae Plant (Arkhangelsk, Russia) in the form of solid dried slices of marine algae which had a complicated and ill-defined form. The acid pre'-treatment of L a m i n a r i a at the Algae plant ensured the absence of low molecular mass organic compounds. The main component of the alginate sample is cellular tissue which firmly holds alginates. Water samples, 120-240 dm 3, were collected during a research vessel cruise. The samples were 'spiked' with the 3'-ray emitting isotope S5Sr as a tracer of
887
888
Yu. A. Sapozhnikov et al.
chemical yield. The water was then allowed to flow by gravity through a column, 20 cm high × 6.5 cm diameter, constructed of polyvinyl chloride, flied with 150 g of sorbent. After passage of the water sample, the column was disassembled and the sorbent removed and dried. After the research vessel cruise, the sorbent was analysed for SSSr by non-destructive 7-spectrometric measurements using a Ge(Li) detector (DGDKl15V, Russia) coupled to an AMA-03F (Russia) multi-channel analyser. After counting, the samples were loaded into alund crucibles and ashed in an furnace at 500°C for 20 h. The residue was spiked with strontium and yttrium carrier (20 mg) and treated with concentrated nitric acid and hydrogen peroxide. The insoluble residue was isolated by filtration. Yttrium was separated by addition of ammonium hydroxide. The filtrate was evaporated to 20 ml and placed in a liquid scintillation vial. The solutions were counted for 100 min steps during 120--150h to re-establish the radioactive equilibrium. The 9°Sr in the samples was determined by Cherenkov counting of the high-energy B-particles from the daughter 90y using a standard liquid scintillation counter. The limit of detection of 9°Sr in a 240 dm 3 sample of sea water with a salinity of 15%o, passed at a rate of 1 dm 3 min - l through 150 g of sorbent, was < 1 mBq dm-3. For comparison, at a number of the measurement stations a 9°Sr preconcentration was also carried out using manganese dioxide as the sorbent. The latter is the sorbent usually used for the preconcentration of radium from sea water, but it also has some capacity to adsorb strontium (Sapozhnikov et al., 1992; Shipman, 1966).
Results and Discussion The results obtained using the SSSrtracer were used to determine the relationship between the sorption of strontium and the salinity of the water sample. For alginate the relationship had the form D = (63.55 __+10.0) - (2.95 ___0.79)S where D is the sorbed strontium as % of the total; S is the salinity (%o), the correlation coefficient for this relationship was 0.91: For manganese dioxide the dependence on salinity had the form D = (22.30 + 2:23) -- (1.17 + 0.17)S with a correlation coefficient of 0.95. Obviously, the sorption capacity of the alginate sorbent is essentially higher than that of manganese dioxide, The sorbents described are wastes from alginate manufacture and their cost price is quite low, U.S.$, 4 k g - 1 and this makes the whole analysis considerably cheaper. The present work discusses only the analytical applications of these alginate wastes, however, they can also be used for the decontamination of waters in nuclear facilities, or as additives to forage for animals living in polluted territories.
References Sapozhnikov Yu. A., Eftmov I. P., Sapozhnikova L. D. and Remez V. P. (1992) Strontium-90 determination in surface waters of northwestern Black Sea. Vestnik MSU., Ser. 2. Khim. 33, 395. Shipman W. H. (1966) Determination of Strontium-90 in seawater after concentration by manganese dioxide. Analyt. Chem. 38, 1175, Vanderborght O., Colard J. and Boulenger R. (1972) Human faecal ~6Ra excretion shortly after alginate treatment. Hlth Phys. 23, 240.