RU2586072C1 - Method of localising radioactive contaminants - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method for localisation of radioactive contamination, for example, in area of burial of radioactive wastes, and can be used for cleaning of ground waters from dissolved therein radioactive radium-226 (²²⁶Ra). Disclosed method includes setting migration of radioactive groundwater geochemical barrier from solid filler, iron oxide and working components, when dissolving being allocated sulphate-ion SO₄ ^-2 and cation Ba⁺². Radium-226 is fixed in crystal lattice of formed radiobarite (Ba, Ra)SO₄. Substance containing sulphate-ion used is gypsum, substance containing Ba⁺² cation is witherite in molar ratio 1:1-1.15 in the form of a 1-3 mm fraction. Iron oxides used are goethite and/or haematite with fraction 2-5 mm. Filler used is crushed stone from non-carbonate magmatic rocks: granite or diorite or dunite, or diabase fraction 1-5 cm. Substance containing Ba⁺² cation can also be barite in form of fraction 2-5 cm, ratio of component placed in netted boxes fitted in drains, wt%, is as follows: filler 60-70; gypsum 10-15; witherite 10-15; barite 1-2; goethite and/or haematite 5-10.

EFFECT: technical result is reduction of radiation of ground waters due to fixation in solid form of radioactive radium directly in water-bearing layer.

10 cl, 2 dwg

Description

The invention relates to methods for the localization of radioactive contaminants, for example, in the radioactive waste burial zone, and can be used to purify groundwater from radioactive radium-226 dissolved in them ( ²²⁶ Ra).

Methods for preventing environmental pollution by toxic and radioactive metals are known, see, for example, RF patent No. 2075125, op. 03/10/1997. The method is as follows. Studies of the location and migration directions of contaminated carbonate uraniferous waters are carried out. Then, a buffer layer of acidic rocks (mainly sulfides) and a barrier of granular fine clays are successively laid in the path of the migration flow. With the passage of uranium-bearing waters of the buffer layer, a change in the water regime occurs and, as a result, the restoration of the uranyl ion by reducing agents that migrate in the water. Due to the inertia of the system, uranium does not settle in the layer, but concentrates on the sorption geochemical barrier. This method does not allow the fixation of radioactive radium.

Also known "Kopeikin V.A. The method of localization of radioactive contamination of soil and groundwater "(RF patent No. 2069905, op. 27.11.1996), which consists in the fact that around the place of pollution create a waterproof protective shell of sodium silicate and clay, inside the source of pollution drill holes into which 0 , 1% salt solutions, wells are arranged in a hexagonal order, salt solutions containing calcium ions, phosphoric acid anions and iron or manganese sulfate are sequentially introduced into the wells of odd rows, and the solution with the even rows is first introduced with oli of ferrous or manganese sulfate, and then solutions of salts containing calcium ions and phosphoric acid anions are added. Radionuclides (r / n) are deposited directly on the geochemical barrier that is created inside the RAW repository at the moment of contact of the dissolved r / n with calcium and phosphate ions and with iron (or manganese) and hydroxyl ions. During their interaction, these calcium and phosphoric acid ions give a poorly soluble mineral phase - apatite, whose crystal lattice contains due to isomorphism r / n present in groundwater; others r / n are sorbed on simultaneously formed (also poorly soluble) mineral phases of hydroxides and oxides of iron or manganese.

A known method of protection from water migration of a technogenic radionuclide ⁹⁰ Sr due to its isomorphic crystallochemical entry into the crystal lattice of newly formed, practically insoluble apatite (Kopeikin V.A. Method for the localization of radioactive soil pollution. RF Patent, No. 1806411 of July 9, 1990 - prototype) . The method consists in creating on the tracks in the soil 90-strontium ⁽⁹⁰ Sr) migration together with groundwater geochemical barriers by separate administration in the wells drilled aqueous salt solutions. The first in the direction of movement of strontium-90 is an aqueous solution of salts containing an alkaline earth metal cation — barium or calcium ions. The second in the direction of travel of strontium-90 is the mineral acid anion — sulfate ions or phosphate ion. In this case, due to the supply of calcium oxide and phosphate (or dihydrogen phosphate) potassium to the wells, apatite is formed. Dissolved radioactive strontium enters the crystal lattice of newly formed apatite due to isovalent isomorphism. This method does not prevent the water migration of radionuclide radium-226. In addition, the above solutions provide for a large amount of work on drilling wells.

The objective of the invention is the prevention of water migration of dissolved radium by fixing it in the crystal lattice of a newly formed insoluble compound.

EFFECT: reduced groundwater radioactivity due to solid fixation of radioactive radium directly in the aquifer.

To achieve this result, a method for the localization of radioactive contamination is proposed, which consists in setting up a geochemical barrier on the paths of radioactive groundwater migration with fixing the radionuclide in the solid mineral phase that is insoluble in water, while the geochemical barrier to radium-226 is made of solid filler, iron oxide, and workers components, upon dissolution of which sulfate ion SO ₄ ^-2 and Ba ^{+ 2} cation are released, and radium-226 is fixed in the crystal lattice of the formed (Ba, Ra) SO ₄ radio barite.

Wherein:

- as a substance containing a sulfate ion, gypsum CaSO ₄ × 2H ₂ O is used;

- as a substance containing a cation of Ba ⁺² , Witerite BaCO _{3 is used} ;

- gypsum and witerite are used in a molar ratio of 1: 1-1.15;

- gypsum and witerite are used in the form of a fraction of 1-3 mm;

- goethite FeOOH and / or hematite Fe ₂ O ₃ fractions of 2-5 mm are used as iron oxides;

- gravel of a fraction of 1-5 cm is used as a filler;

- carbonate-free igneous rocks are used as a filler: granite, or diorite, or dunite, or diabase;

- the ratio of the components of the geochemical barrier, wt.%, is:

filler 60-70

gypsum 10-15

witerite 10-15

barite 1-2

goethite and / or hematite 5-10

- All components are placed in mesh boxes installed in drains.

In figures 1 and 2 shows the dependence of the solubility of Viterite BaCO ₃ and barite BaSO ₄ from the pH of the aqueous solution.

The method is as follows.

To prevent water migration of dissolved radium into the zone of radioactive contamination with radium-226 necessary for the formation of an insoluble compound, which will include radium, solid components. They can be pre-laid in the area of radioactive, contaminated with radium, water. The task of these compounds is to isolate the initial complexes and ions into the aqueous solution, which in the future will give the necessary insoluble minerals, where radium will enter isomorphically.

Natural minerals are used as initial components, which should create a geochemical barrier to radium.

To fix the radionuclide radium-226 perform a geochemical barrier (GB) of solid mineral materials.

The practical setting of the geochemical barrier in the general case is as follows.

Around the storage of radioactive waste containing radium, a wall is laid in the ground, which is filled with clay material. The lower boundary of the trench, which is filled with clay, is located 3-4 meters below the groundwater level. The trench is filled with clay to the level of the day surface.

In this clay wall in the ground, drains are made in the ground on the path of a possible exit of groundwater, through which groundwater can leave. It is in these drains that a geochemical barrier to radium is placed.

In practice, filler, iron oxides and working components are placed in metal mesh boxes installed in drains, upon dissolution of which sulfate ion SO ₄ ^-2 and Ba ^{+ 2} cation are released.

As a filler, gravel of a fraction of 1-5 cm from non-carbonate igneous rocks is used - granite, or diorite, or dunite, or diabase, or mixtures thereof.

The main requirement is the absence of carbonates in the gravel, as they can react with the sulfate ion. The width of such a box is 2-3 meters wider than the width of the drain, since it should cover everything possible for the migration of radioactive water. The lower boundary of this "mesh box" should be located below the low-water level of groundwater by 3-4 m.

The upper boundary of the box should overlap the flood level of groundwater also by 3-4 m.

The filler prevents adhesion of the remaining components of the RB.

In these boxes are placed:

- as a substance containing a sulfate ion, gypsum CaSO ₄ × 2H ₂ O,

- and as a substance containing a Ba ^{+ 2} cation, witerite in a molar ratio of 1: 1-1.15.

The ratio of the added components is proportional to their atomic weights: gypsum CaSO ₄ · 2H ₂ O — molecular weight 172.17 grams; WiterO BaCO ₃ 197.35 grams; barite - BaSO ₄ 233.40 grams.

Therefore, the weighted amounts of viterite and gypsum should be related as 197.35: 172.17 = 1.146. In practice, you can take 1: 1 by weight, or take Viterite 15% more than gypsum.

Both components (gypsum and witerite) should be added as a sand fraction, 1-2 mm in size.

Gypsum does not record dissolved radium, but only adds the first of the geochemical barrier to the composition of radioactive groundwater.

Witerite (BaCO ₃ ), upon dissolution of which into radioactive water, receives another component (Ba cation ^{+ 2} ), and gives a newly formed radio barite (Ba, Ra) SO ₄ - an insoluble product, in the crystal lattice of which radium enters due to isovalent isomorphism, thereby passing into an insoluble state, since the radius of the Ba ion is ⁺² = 0.138 nm, and the radius of the ion is Ra ⁺² = 0.152 nm. This can be compared to chemisorption.

Since the formation of a geochemical barrier requires a sulfate ion, which exists only in an oxidizing environment, it is necessary to add iron oxides to the composition of the barrier - hematite minerals Fe ₂ O ₃ , goethite FeOOH in the form of a sand fraction of a fraction of 2-5 mm placed in a box to the entire height, since below the level of groundwater, the sulfate ion passes into the HS ^- ion. It is for the creation of oxidizing conditions in the barrier region that iron oxides are needed.

To fix radium in the form of a radio barite (Ba, Ra) SO ₄ , only gypsum and witerite are actually needed. Hematite and goethite with barite are needed precisely to create a geochemical environment where SO ₄ ^-2 ions exist.

In addition to these minerals, barite (10-15% of the weight of witerite) can be added to the composition of the geochemical barrier as a fraction of 2-5 cm. This barite will absorb dissolved radium, but not form a radio barite. In addition, desorption of radium from the surface of barite is possible.

This is confirmed by figures 1 and 2, which show that barite is practically insoluble in water, while witerite is highly soluble, especially in an acidic and neutral environment.

The geochemical role of barite is to be a possible center of crystallization, it should contribute to the formation of nuclei of a new radio barite. The source of barium cation - Ba ⁺² will be witerite.

Practically the ratio of the components, wt.%, Is

filler 60-70

gypsum 10-15

witerite 10-15

barite 1-2

goethite and / or hematite 5-10

and will depend on the specific installation conditions of GB.

To confirm the feasibility of the method, a series of experiments was carried out.

The tests were carried out as follows.

I. 1 gram of a mixture of witerite and gypsum in the form of a powder was placed in a Teflon tube and at room temperature in a statistical mode 20 ml of the liquid phase was poured. It was prepared by mixing 10 ml of a standard standard solution containing ²²⁶ Ra and 10 ml of surface natural water. This liquid mixture had a pH of 6.8-7.0, and during the process of absorption of radium, the pH did not noticeably change.

After 4, 24, 72, and 192 hours, the solid phase was separated from the liquid phase by centrifugation, and an aliquot of a 1 ml solution was taken from model sorption systems to determine the specific activity of radium. Then, with periodic stirring, stirring was continued.

After 8 days of contact, the phases were again separated in a centrifuge. After that, the liquid phase was analyzed for radium content. The solid phase was pre-washed with 2 ml of distilled water and examined by the method of successive extracts on the absorption strength of ²²⁶ Ra. Distilled water, 1 M ammonium acetate solution and hydrochloric acid were used. The volume of extractant was 20 ml, the extraction time was 24 hours.

Then the phases were separated by centrifugation and the liquid phase was selected to determine the specific activity of ²²⁶ Ra. The measurements were carried out on an Alpha-1 instrument by the emanation method with a detection limit of ²²⁶ Ra of about 0.07 Bq and a determination uncertainty of 15%.

Based on the data obtained, the degree (%) of radionuclide recovery was calculated.

The results showed that the components presented for testing have a high degree of absorption of ²²⁶ Ra, which varies, with different phase contact times, in the range from 86.4 to 100 and from 99.4 to 100% for solutions with an initial specific activity of 422.762 Bq / L and 24.949 kBq / L.

The highest levels of radium absorption are observed after 4 hours of phase contact, and after the exposure time, the activity of radium in the liquid phase was lower than the sensitivity of the emanation method for its determination (0.07 Bq). Radium is absorbed firmly, while the proportion of radium capable of desorbing is not more than 5.5% of the sorbed amount.

The effective durable absorption of radium from solutions with radium concentrations far exceeding the permissible sanitary standards for industrial water (from 1000 to 50,000 intervention levels) indicates a high sorption capacity of the presented samples of the geochemical barrier to radium. This opens up the prospect of using these compounds as a geochemical barrier to the migration of radium in natural and anthropogenic ecosystems.

The process of formation of the radio barite includes the following phases.

Gypsum dissolution CaSO ₄ × 2H ₂ O = Ca + ² + SO ₄ ^-2 + 2H ₂ O.

Dissolution of Viterite BaCO ₃ = Ba + ² + CO ₃ ^-2 .

The interaction of barium ions and sulfate ion: Ва ⁺² + SO ₄ ^-2 = BaSO ₄ cr.

Dissolved radium enters into the crystal lattice of this newly formed barite, due to isovalent isomorphism, thereby passing into a stationary state.

Tests have shown that the use of barite (BaSO ₄ ) contributes to the extraction of radium from groundwater only due to sorption, since the solubility of barite over the entire pH range is extremely small - 10 ^-4.75 mol / l (2 mg / l, Fig. 1). Witerite (BaCO ₃ ) is soluble in alkaline and acidic waters - 0.1 mol / L at pH 8.3 and 10-2.8 mol / L at pH≥10 (≥20 mg / L. Fig. 2).

II. Calculation of the starting components and experimental results.

Two radium-226 containing stock solutions were prepared.

The first solution with a specific activity of the liquid phase of 422.762 Bq / l and the second solution with a specific activity of the liquid phase of 249.49 kBq / l.

Weight amounts of components were taken based on molar ratios. Mineral samples were ground in a mortar to a fraction of 1-2 mm.

1st experience. According to a possible reaction, witerite and iron sulfide - pyrite - BaCO ₃ + FeS ₂ mixed 10 g of witerite and 3 g of pyrite. Since pyrite is very poorly soluble, the result of the experiment is almost negative. After 192 hours, the degree of extraction of radium from the first solution with a specific activity of the liquid phase of 422.762 Bq / L was 60.6% and 85.9% of the second solution with a specific activity of the liquid phase of 249.49 kBq / L.

After treatment with 1 M hydrochloric acid, 21.33% radium from the first solution and 18.8% from the second solution are desorbed back into the solution.

2nd experience. According to a possible reaction of BaCO ₃ + CaSO ₄ · 2H ₂ O, 10 g of witerite and 9 g of gypsum were mixed. After 192 hours, the degree of extraction of radium from the 1st solution was 93.6% and 99.9% from the 2nd solution.

Desorbed back into the solution after treatment with 1 M hydrochloric acid 0.45% and from a 2nd solution of 0.06% radium.

3rd experience. According to a possible reaction, BaCO ₃ + CaSO ₄ · 2H ₂ O + FeS ₂ mixed 10 g of witerite, 9 g of gypsum and 3 g of pyrite. After 192 hours, the degree of extraction of radium from the solution was 100% from the first solution and 99.9% from the second.

After treatment with 1 M hydrochloric acid, 0.10% radium from the 1st solution and 0.14% radium from the second solution are desorbed back into the solution.

4th experience. According to a possible reaction, BaSO ₄ + FeS ₂ mixed 30 g of barite and 15 g of pyrite. After 192 hours, the degree of extraction of radium from the solution was 98.3% from the first and 99.9% from the second solution.

After treatment with 1 M hydrochloric acid, 2.48% of the first and 1.62% of the second are desorbed back into the solution.

5th experience. According to a possible reaction, BaSO ₄ + CaSO ₄ · 2H ₂ O mixed 30 g of barite and 22 g of gypsum. After 192 hours, the degree of extraction of radium from the first solution was 93.1% and 99.7% from the second.

After treatment with 1 M hydrochloric acid, 0.97% of radium from the first and 0.52% from the second solution are desorbed back into the solution.

The result of the experiments is the conclusion about the need for mandatory use of viterite BaCO ₃ and gypsum CaSO ₄ · 2H ₂ O.

Boxes of metal mesh that will cover the drains should be filled with crushed stone from carbonate-free igneous rocks by 60-70%. The remaining volume is filled with 5–10% hematite and / or goethite and 10–15% each with viterite and gypsum. In the amount of 1-2%, barite can be added.

The use of the invention will reduce the level of radioactive contamination of territories infected with radiation to the current radiation safety standards and prevent the water migration of radium. This will contribute to improving the ecology of the region and preventing radiation damage to the population. In this case, radioactive radium is not extracted from groundwater to the earth's surface, and the geochemical barrier to radium is carried out from available natural minerals.

Claims (10)

1. The method of localization of radioactive contamination, which consists in setting up a geochemical barrier on the paths of radioactive groundwater migration with fixation of the radionuclide in the solid mineral phase formed in water insoluble, characterized in that the geochemical barrier to radium-226 is made of solid filler, iron oxide and working components upon dissolution of which sulfate ion is released $$S{O}_{\mathrm{four}}^{-2}$$

and cation Ba ⁺² , and radium-226 is fixed in the crystal lattice of the resulting radio barite (Ba, Ra) SO ₄ . 2. The method according to p. 1, characterized in that the gypsum CaSO ₄ · 2H ₂ O is used as the substance containing the sulfate ion. 3. The method according to p. 1, characterized in that as a substance containing a Ba ^{+ 2} cation, Witerite BaCO _{3 is used} . 4. The method according to PP. 2 and 3, characterized in that gypsum and witerite are used in a molar ratio of 1: 1-1.15. 5. The method according to PP. 2 and 3, characterized in that gypsum and witerite are used in the form of a fraction of 1-3 mm. 6. The method according to p. 1, characterized in that goethite FeOOH and / or hematite Fe ₂ O ₃ fractions of 2-5 mm are used as iron oxides. 7. The method according to p. 1, characterized in that as a filler using crushed stone fractions of 1-5 cm 8. The method according to PP. 1 and 7, characterized in that as a filler using carbonate-free igneous rocks - granite, or diorite, or dunite, or diabase. 9. The method according to p. 1, characterized in that the ratio of the components of the geochemical barrier, wt.%, Is:
filler 60-70
gypsum 10-15
witerite 10-15
barite 1-2
goethite and / or hematite 5-10. 10. The method according to p. 1, characterized in that all components are placed in mesh boxes installed in the drains.

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