Sorption of 137Cs and 90Sr Ionic Species on Soil of Various Types

Sorption of ¹³⁷Cs and ⁹⁰Sr ionic species on soils with different agrochemical features was studied. The dependence of ¹³⁷Cs sorption on peaty-bog soil on the ratio of the solid and liquid phases shows that sorption occurs by the ion-exchange mechanism. The correlation between the potassium content in soils and     

Effect of basic chemical characteristics of soils on mobility of radionuclides in them

Interplay between the basic chemical characteristics of soils of the Belarussian Polessie and the tightness of fixation of Chernobyl-derived ¹³⁷Cs and ⁹⁰Sr in them is studied. The mobility of radionuclides in the soil proved to be controlled essentially by the soil type and organic matter content. In the investigated soils, nonexchange sorption of ¹³⁷Cs and exchange sorption of ⁹⁰Sr dominate.     

Acid Deactivation of Soils with Ammonium Fluoride To Remove 137Cs

Leaching of ¹³⁷Cs from various contaminated clay soils with fluoride-containing mineral acid solutions was studied. It was demonstrated that the use of fluorides offers advantage over chlorides and nitrates. The decontamination mechanism was studied by infrared spectroscopy. Conditions for simultaneous removal of ¹³⁷Cs and ^238,239Pu with fluoride-containing nitric acid solutions were optimized.     

Vertical transfer of137Cs in peat soils fallen out as a consequence of the chernobyl accident

On the basis of measurements of the specific radioactivity of soil specimens sampled with a small step along their deposition, depth profiles are plotted for the curves of the vertical change in ¹³⁷ Cs in peat soils not treated since the Chernobyl accident. A theoretical analysis is provided for the plotted profiles that shows that the vertical transfer of ¹³⁷ Cs in these soils is described adequately within the framework of a model that accounts for the processes of diffusion and convection of the radionuclide in the soil solution and its sorption by the solid phase of the soil. The parameters of the model are determined and a prediction is given for the migration character of ¹³⁷ Cs.Institute of Solid State Physics, Academy of Sciences of Belarus, Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 1, pp. 33–38, January–February, 1995.     

Decontamination of 137Cs-contaminated sandy soils by a combination of separation of finely dispersed fraction by sedimentation in water with reagent treatment

Possibilities of reagent decontamination of sandy soils contaminated with ¹³⁷Cs are considered. Treatment with a 2 M H₂SO₄ solution for 7 h at 80°C and liquid-to-solid ratio (L : S) of 2 : 1 results not only in complete recovery of the finely dispersed fraction but also in additional leaching of ¹³⁷Cs from particles of sandy size, with the decontamination factor reaching ∼60–70. The reagent treatment is the most efficient at L : S from 3 : 1 to 4 : 1 after preliminary separation of finely dispersed particles by sedimentation in water.     

Desorption of 90Sr and 137Cs from Flood Plain Deposits of the Sozh River and Rocks of the Adjacent Catchment Areas

Desorption of ⁹⁰Sr and ¹³⁷Cs from flood plain warps, meadow sod, humus-containing sandy loam, peat, clays, limonite, meadow marl, and friable rocks of the adjacent catchment areas (moraine clay, loam, sandy loam) was studied. ¹³⁷Cs is sorbed the most strongly on clays by the mechanism of isomorphic ion-exchange incorporation into the crystal lattice of montmorillonite-type minerals. ¹³⁷Cs is also tightly fixed on buried and peaty soils due to association with the poorly mobile species of humic acids and humin. The strong fixation of ⁹⁰Sr on amorphous iron hydroxides is caused by its association with poorly soluble ferrite-type minerals. Sorption of ⁹⁰Sr on peaty soils can be attributed to their association with aluminum and iron-containing organomineral complexes. ¹³⁷Cs sorbed on flood plain warps, sandy loams, and loams exhibits increased mobility and is leached with all the tested desorbing solutions. These deposits apparently contribute maximally to the redistribution of radiocesium over flood plain and the adjacent catchment areas. The desorption efficiency of cations of the desorbing solutions decreases in the order Cs⁺ > K⁺ > Fe^{3 +} > NH₄ ⁺ > Ca^{2 +} > H⁺ for radiocesium and Fe^{3 +} > Sr^{2 +} > K⁺ > H⁺ > Ca^{2 +} > NH₄ ⁺ for radiostrontium.     

Cesium-137 of Chernobyl origin in lake–river systems of Eastern Fennoscandia: 30 years after the accident

Contamination of waters of lake–river systems after many-year migration of ¹³⁷Cs in water bodies was studied. In lakes with the ¹³⁷Cs fallout density lower than 8 kBq m^–2, the radionuclide concentrations in water after 24–29 years did not exceed 2–3 Bq m^–3, and at a fallout level of 37 kBq m^–2 it was in the range 11–34 Bq m^–3. The natural half-clearance time Т of lake waters from ¹³⁷Cs was 6–7 years at the exposure of up to 20 years. The ¹³⁷Cs migration in the lake–river systems that occurred during ~30 years did not lead to structural changes in the water contamination: The initially low ¹³⁷Cs level in lake waters did not become high, and vice versa. Among rivers feeding Lake Ladoga, the ¹³⁷Cs level in the Vuoksa River is ~3 times higher than in waters of the Volkhov and Svir rivers. During the period 1988–2015, 21.3 TBq of ¹³⁷Cs was supplied to Lake Ladoga with Vuoksa waters. The Vuoksa source from the Saima lake system with increased contamination with ¹³⁷Cs of Chernobyl origin leads to long-term supply of this radionuclide to Lake Ladoga.     

Artificial radioactivity of the White Sea

Vertical profiles of ¹³⁷Cs in bottom sediments collected from various sites of the White Sea are reported. From these profiles, the ¹³⁷Cs inventory in the bulk of sediment was estimated to be 270–3300 Bq m^?2, and the surface contamination of sediment, 7.1–46.5 Bq kg^?1. In the most of the sediment cores, ¹³⁷Cs was detected to a depth of >20 cm. The highest activity of ¹³⁷Cs was usually observed in the 1–2-cm layer. The mean specific radioactivity of ¹³⁷Cs in the seawater was 4.1 Bq m^?3.     

Reconstruction of Global 137Cs Concentration in Lake Onega

The dynamics of global ¹³⁷Cs content in Lake Onega in the past 25 years was reconstructed. Based on a sorption-diffusion model of ¹³⁷Cs behavior in the lake water-bottom sediment system, the decontamination of the lake water from ¹³⁷Cs as influenced by natural factors was analyzed.     

From global <Superscript>137</Superscript>Cs to determinations of the sedimentation rate in deep lakes and sea estuaries

Sedimentation rate in deep lakes and estiaries of the Baltic, Pechora, and Laptev Seas was determined using global ¹³⁷Cs as a sedimentogenesis marker. The sedimentation rate in Lake Ladoga and Levinson- Lessing Lake was 0.3–3 mm year^?1, and that in estuaries of the Baltic, Pechora, and Laptev Seas was 0.74–1.76, 1.0, and 3.3–5.0 mm year^?1, respectively. At a sedimentation rate of >1–2 mm year–1, the concentration peaks of global and “Chernobyl” ¹³⁷Cs in the bulk of the bottom sediments do not overlap, and the sedimentation rate is estimated for each kind of nuclides separately. At a sedimentation rate of <1 mm year^?1, “Chernobyl” ¹³⁷Cs + ¹³⁷Cs from dumping into sea mask in the bottom sediments the subsurface maximum of the global ¹³⁷Cs concentration and prevent the sedimentation rate determination. The use of ¹³⁷Cs for sedimentation rate determinations is appropriate for the poorly studied shelf zone of Russian Arctic seas.     

Effect of Site-Specific Parameters on the Transfer of 137Cs and 90Sr into Freshwater Fishes1,2

The content of ¹³⁷Cs in fallout, fish, and water was measured with the aim to study the role of site-specific parameters on the transfer of ¹³⁷Cs into fishes. The temporal changes of 137Cs and 90Sr in various types of fishes were studied at two sites of Lake Saimaa. The ¹³⁷Cs content in fishes in the Ukonvesi area, which is the north-western part of the lake, was clearly lower than that in the southern parts of the lake, in Ala-Saimaa, although the fallout of ¹³⁷Cs to the Ukonvesi area was somewhat higher than that to Ala-Saimaa. The fallout in 1986 was about 6 kBq m^{- 2} to the Ukonvesi area and about 3 kBq m^{- 2} to the southern parts of the lake. The ¹³⁷Cs content in fishes was the highest in 1988-1989 in Ala-Saimaa, approximately 700 Bq kg^{- 1}, while that in the Ukonvesi area was only about 300 Bq kg^{- 1}, where the values were the highest in 1987. In Ukonvesi the ¹³⁷Cs content in fishes decreased rapidly, being already in 1990 almost at the same level as in 2000. In the southern parts of the lake the decrease in the ¹³⁷Cs content in fishes was much slower. Also the ⁹⁰Sr content in fishes in Ukonvesi was lower than that in Ala-Saimaa. The ¹³⁷Cs content of the water in the Ukonvesi area decreased rapidly, being about 7 Bq m^{- 3} in 1998, while that in the lower areas of the lake was still 15 Bq m^{- 3} in 2000. The ⁹⁰Sr content in water was approximately the same at the both sampling sites (7-8 Bq m^{- 3}). The water chemical parameters, such as potassium, total phosphorus, total nitrogen, chlorophyll a, and electrical conductivity were significantly higher in Ukonvesi than in Ala-Saimaa.     

Radioactive Fallout and Accumulated Level of Soil Surface Contamination with 90Sr and 137Cs around St. Petersburg in 1954-1999

Systematic data on radioactive atmospheric fallout in 1954-1999 and accumulated levels of contamination of the soil-vegetable cover with ⁹⁰Sr and ¹³⁷Cs around St. Petersburg, estimated on 1998, are presented. Comparative analysis is made of these data and directly obtained data on the vertical distribution of these radionuclides in the surface horizon (0-25 cm) of soddy-podzolic sandy loam soil: the levels of surface contamination with ^90Sr and ¹³⁷Cs were found to be 580±90 and 6500±600 Bq m^-2 on 1998. Before April 28, 1986 the ⁹⁰Sr and ¹³⁷Cs radioactivity in the investigated region corresponded to the global level. After Chernobyl accident the contamination levels with ⁹⁰Sr and ¹³⁷Cs increased, respectively, from 1200 to 1280 (by 6.3%) and from 2400 to 7050 Bq m^-2 (by a factor of 2.9). The ⁹⁰Sr and ¹³⁷Cs vertical distributions throughout the soil profile are considerably different: ¹³⁷Cs is practically totally fixed in the surface horizon, its activity being exponentially declining; whereas the stock of ⁹⁰Sr in horizons 0-10 and 0-25 cm represents only 22 and 59% of the integral accumulated inventory of ⁹⁰Sr in the soil (990 Bq m^{- 2}). The activity ratio of ¹³⁷Cs to ⁹⁰Sr in the atmospheric fallout in 1963-1985 was 1.85±0.42, and in river water in the same period, ca. 0.18, suggesting higher mobility in the soil of ⁹⁰Sr as compared to ¹³⁷Cs, and, therefore, higher rate of self-cleaning of the surface soil horizon with respect to ⁹⁰Sr.     

Recycling of Transmutation Targets in the Presence of Impurity Isotopes of Starting Nuclides

Relations were obtained for calculating the concentrations of impurity isotopes of starting nuclides ⁹⁸Tc, ¹²⁷I, ^133'134'137Cs in recycling ⁹⁹Tc, ¹²⁹I, ¹³⁵Cs targets, respectively. Conditions of removing ⁹⁸Tc from the transmutation cycle in a single irradiation run were found. The content of ¹²⁷I in the targetattains an equilibrium value, thus making unnecessary isotopic separation of iodine. For isotopic separation of cesium, a decrease of the initial content of ¹³⁷Cs in the ¹³⁵Cs target to 1% is sufficient. The ¹³³Cs and ¹³⁴Cs nuclides preserve steady-state concentrations for a long period, and for this reason the activity grows insignificantly, depending on the ¹³⁷Cs accumulation, which makes unnecessary isotopic separation of cesium from irradiated targets.     

Sorption of 137Cs and 90Sr by potassium production wastes, clay-salt slimes

Sorption of ¹³⁷Cs and ⁹⁰Sr by clay-salt slimes from model aqueous salt solutions (4.0–40.0 g l^?1 NaCl + KCl) was studied under static conditions. The influence of the sorption parameters (time, specific consumption, salt content) on the efficiency of the ¹³⁷Cs and ⁹⁰Sr recovery with finely dispersed sorbents was studied. The activity of the aqueous salt solution decreases by two orders of magnitude owing to the recovery of ¹³⁷Cs.     

Sorption-diffusion model of 137Cs uptake by a water body bottom in estimations of water contamination

For a sample including 22 lakes, the ¹³⁷Cs concentrations in water were determined by the sorption-diffusion model. The ¹³⁷Cs levels in waters of lakes of the Kola Peninsula and Karelian Isthmus are satisfactorily described by the suggested model at the distribution coefficient K _d of 4000 L kg^?1 and diffusion coefficient D of 1.0 × 10^?7 cm² s^?1 for 2–4-year exposure. For mid-latitude lakes, the ranges of K _d and D of ¹³⁷Cs were 6000–1200 L kg^?1 and 1.0 × 10^?7–0.2 × 10^?7 cm² s^?1, respectively. The ¹³⁷Cs concentration in water is determined by the major contribution of silts, which are characterized by high K _d of ¹³⁷Cs and by large thickness of sediments on the bottom of lake hollows, to the watter-bottom sorption system. After 2-year exposure of “Chernobyl” ¹³⁷Cs in lakes, its inventory in water relative to the amount that fell out in 1986 did not exceed 14% for deep lakes and 2–3.6% for shallow lakes.     

Influence of calcium ion concentration on the selective sorption of 137Cs with illite

The ¹³⁷Cs sorption and desorption equilibrium between illite and a solution containing 0.5 mM K⁺ and 1 to 100 mM Ca²⁺, determined using a kinetic method with direct measurement of the radioactivity in the sorbent solid phase, was attained within 20–25 days. The kinetic curves of the ¹³⁷Cs sorption onto/desorption from illite, normalized on the maximal sorbed radioactivity, almost coincided at different Ca²⁺ concentrations. An increase in the ¹³⁷Cs distribution coefficient (K _d) with a decrease in the Ca²⁺ concentration did not exceed 60% and was due exclusively to the influence of the solution ionic strength. With an increase in the Ca²⁺ concentration from 1 to 100 mM, the fraction of ¹³⁷Cs extracted with 1 M CH₃COONH₄ (α_Ex) decreased from 24.1 to 14.8%.     

Leaching Decontamination of Soil of the 5th Block of the Vasil'evskii Island District (St. Petersburg) from 137Cs

Leaching decontamination of soil taken from the 5th block of the Vasil'evskii Island district (St. Petersburg) from ¹³⁷Cs with Na2EDTA, HNO₃, and FeCl₃ aqueous solutions was studied. The highest degree of decontamination (60%) was reached in leaching ¹³⁷Cs with solutions containing equimolar amounts (0.02 M) of FeCl₃ and NH₄Cl at the liquid to solid phase ratio V/m = 20 l/kg. The distribution factor of cesium between the soil and eluate Ds/l is equal to 12. This distribution factor practically coincides with that obtained in leaching decontamination of the soil collected from Bryansk oblast but is significantly lower than the distribution factor for the soil taken from Gur'ev oblast. This difference in Ds/l reflects specificity in mineral composition of these soils.     

Sorption of <Superscript>137</Superscript>Cs from seawater onto resorcinol–formaldehyde resin

Sorption of ¹³⁷Cs from seawater onto a selective cation exchanger based on resorcinol–formaldehyde resin was studied. The maximal distribution coefficient of ¹³⁷Cs at the ratio S: L = 1: 1000 is (4.1–4.5) × 10³ cm³ g^–1. The sorption-selective characteristics of the resin are negatively affected by alkaline earth meal ions. In the dynamic regime, the operation life of the resorcinol–formaldehyde resin exceeds 700 bed volumes with more than 95% efficiency of cesium sorption. More than 95% of ¹³⁷Cs is eluted with a 1–3 M HNO₃ solution. The eluate volume does not exceed 10 bed volumes.     

Concentrating Radiocesium with Selective Sorbents

The dynamic characteristics of ¹³⁷Cs sorption with the sorbent based on NaX zeolite and copper(II) and antimony(V) ferrocyanides were studied. At a rate of filtration of active solution (2 ×10⁵ Bq l^{- 1 137}Cs) of 50-200 column volumes per hour, the degree of sorption (S) was 95.0-99.8%. The optimum filtration rate of the solution containing radioactive cesium was determined to be 75 column volumes per hour. Up to 6000 column volumes with the specific activity of 6.2 Bq l^{- 1} with respect to ¹³⁷Cs was passed. In this case, the sorption was 96.0-98.0%. At the optimum filtration rate, the initial activity of the solution does not affect the point of ¹³⁷Cs localization in the column volume. An increase in the filtration rate to 200 column volumes per hour results in smearing of the sorption front, with a decrease in the ratios of the sorbent activities at the top and bottom parts of the column from 15.4 to 3.9.     

Removal of volatile 137Cs and 131I compounds from an air flow

The removal of volatile ¹³⁷Cs and ¹³¹I compounds from an air flow on various filtering elements was studied. ¹³¹I₂ and ¹³⁷CsOH are sorbed on basalt wool, but the degree of their recovery is low: ～86 and 90–93%, respectively, at the basalt wool bed height of 15–18 cm. The use of a cascade of bubblers in combination with a column packed with basalt wool allows virtually complete (>99.9%) removal of ¹³¹I and ¹³⁷Cs in the form of ¹³¹I₂, ¹³⁷Cs¹³¹I, and ¹³⁷CsOH from an air flow.