RU2396614C1 - Method of decontaminating natural and manmade objects contaminated with radionuclides - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves treatment of an object with an agent which contains humis acid and then removal of radionuclide contaminants from the solutions. If there is no natural water containing fulvic acid (FA) available, treatment is carried out artificially using a weak sulphuric acid solution (pH 2.0-3.0) with a microadditive of fulvic acid complexon (up to 100 mg/l). Under normal conditions, the process of cleaning the soil and thickening the decontaminated layer must continue to a depth of not less than 70 cm.

EFFECT: more efficient decontamination of soil beyond humid climatic zones, simplification and lower cost of the decontamination method.

3 cl

Description

The invention relates to the decontamination of natural and man-made objects in areas of contamination with radionuclides as a result of accidents at nuclear power plants, in nuclear industry enterprises.

A known method of decontamination of natural and technogenic objects by processing (irrigation) with a solution of humic substances (Lishtvan I.I. Shenets A.V. Smelovsky V.E. Results of factory technology for decontamination using humic preparations. Abstracts of the report of the interstate conference "Radionuclide Chemistry and Metal -ions in natural objects "Minsk, 1992, pp. 94-95). The humic preparation is obtained by treating the extract from peat with alkaline solutions, followed by its oxidation. The composition of the solution mainly includes humic acid (80-85%) as well as polyphenols, fulvic acids (FC) and minerals. The disadvantage of this method is its inefficiency, since the polyphenols present in solutions reduce the degree of sorption of radionuclides by humic acids. In addition, the preparation of an aqueous solution of humic substances from peat is a laborious operation.

Water suitable for decontamination, containing mainly fulvic acids from humic substances (since they are readily soluble in water), is found in many areas: in tundra and taiga lowlands, such as the woodlands of the Russian Plain and Western Siberia. River, lake and partially ground waters with fulvic acids are diagnosed by the color of strong tea (from here Black Lake, Meshchera, Chernaya Rechka St. Petersburg, etc.). In permafrost regions, such river waters are also possible in mountainous conditions, for example, the Amalat River on the Vitim Upland. For specific areas, diagnostics are possible as a result of routine routine studies, landscape and geochemical mapping, aerial photos, interpretation of aerial photographs.

Theoretically, the use of humic complexes as soil reagents for the flushing regime created in soils opens up real prospects for success in this area. FC complexon is a product of natural biogeochemical processes of podzol formation, provides vertical migration of metals in the soil profile, activates the movement of uranium by tens of meters in ore-containing strata during PV and is undoubtedly capable of “trapping” radioactive and other chemical toxicants below the root layer (only 1 m below the earth’s surface). The ion-exchange (absorption) capacity of one and a half oxides and clay fractions of rocks of the aeration zone is, as a rule, immeasurably higher than the weighted amounts of technogenic pollution of the soil cover. As a result of this, it is possible to confidently predict the strong binding of “squeezed” toxicants by natural sorbents below the layer to be cleaned and the low probability of contamination of groundwater with them. GK-complexon (humic acids) can actively participate in detoxification of soil, as it has the ability to sorb not only metals, but also bind organic ecotoxicants - various pesticides, organochlorines (dioxins), polycyclic aromatic hydrocarbons (benzopyrene) and others subsequently exposed gradual microbiological degradation. Fulvic acids (PC complexons) are part of the humus plant growth stimulants and contribute to this preservation and even increase the fertility of the soils being cleaned.

The closest technical solution to the proposed one is a method of decontamination of natural and technogenic objects infected with radionuclides, including treating objects with water containing humic acids, followed by removal of radionuclide contaminants from solutions, the treatment being carried out with natural waters of humid climatic zones containing fulvic acids in an amount of at least 60 mg / l at pH 3.5-6.5 (RU No. 2088988, G21F 9/28, publ. 08.27.1997).

The known method is used in the decontamination of any natural and man-made objects in the presence of water sources with fulvic acids next to them (lake, river, swamp water). Water is pumped to the surface of a contaminated object. Monitoring the degree of cleaning of objects is carried out radiometrically. Natural waters of humid climatic zones, containing fulvic acids of at least 60 mg / l at pH 3.5-6.5, have strong tea color, are widely distributed in regions of Russia with humid climates and contain on average in mg / l:

Fulvic Acids 5.6-134.0 Na ⁺ 1.8-2.5 K ⁺ 1.2-2.5 Sa ⁺⁺ 4.7-11.4 Mg ⁺⁺ 2.0-7.9 SO ₄ ^- 1.0-21.1 Cl 0.7-6.1

The disadvantage of this solution is that its practical use is limited only by the limits of humid climatic zones when the content of fulvic acids in natural waters is not less than 60 mg / l and pH 3.5-6.5. This solution cannot be effectively applied if there are no sources of FC-containing natural waters in the vicinity.

The present invention is aimed at achieving a technical result, which consists in increasing the effectiveness of soil disinfection outside of humid climatic zones by using artificially prepared weak sulfuric acid with a pH of 2.0-3.0 with microcomponent FC complexon to dissolve radionuclides while simplifying and cheapening the decontamination method .

The specified technical result is achieved by the fact that in the method of decontamination of natural and man-made objects infected with radionuclides, which includes treating the soil object with an agent containing humic acids, followed by removal of radionuclide pollutants from solutions, out of the reach of natural waters containing fulvic acids, up to three soil objects are treated times by adding 5 g / m ² fulvic acids to the surface of the soil object in the form of a weakly acid solution with a fulvic acid fraction of up to 100 g / m ³ at pH 2.0-3.0 or in the form of sprayed on a moistened with weak sulfuric acid solution with a pH of 2.0-3.0 in a volume of up to 10 l / m the surface of the soil object of a dry deactivating preparation, which is a mixture of humic substances enriched in fulvic acid fraction up to 60 wt.%.

Moreover, under normal conditions, the process of cleaning soil and increasing the thickness of the disinfected layer should last no less than 70 cm, and in zones of development of permafrost and a small thickness of the thawed surface layer, its cleaning from radionuclides is an irrigation (sprinkling) of soil with deactivating FC solutions and suction the resulting radioactive liquid by needle filters.

These features are significant and are interconnected with the formation of a stable set of essential features sufficient to obtain the desired technical result.

The invention is described below in essence.

The total area of the Russian territory with a humid climate is very large, which allows us to count on a significant reduction in the costs necessary to clean the country's environment from radioactive and chemical toxicants. However, such a technical solution cannot be effectively applied in the absence of sources of FC-containing natural waters in an accessible vicinity. This limitation, however, can be successfully overcome by using a specially prepared solvent based on the PK reagent or its modifications.

In addition, such large-scale natural objects as soil cover and surface soils can, under favorable conditions, be sufficiently economically cleaned of radioactive contamination and without the cost of subsequent chemical operations to concentrate toxicants released from soil and their disposal.

First of all, this concerns territories with a sufficiently powerful aeration zone, measured in meters. The sorption-capacitive parameters of the rocks of such zones are large, which allows for the rapid disinfection of the upper soil layer by “squeezing” radioactive contaminants below the root layer and permanently burying toxicants transported down to “eternal times”. In this case, the above chemical operations or excavation and removal of soil contaminated with radionuclides will not be required, followed by its purification in the factory. Encouraging results in this area were obtained in the 90s during field experiments on the disinfection of soils contaminated with radionuclides of the Chernobyl spectrum.

To decontaminate soils in any climatic conditions, including in the absence of accessible sources of FC-containing natural waters, depending on the degree of pollution, they add up to three times 5 g / m ^{2 of} fulvic acids (FC) or in the form of their weakly acid solution (FC up to 100 g / m ³ , pH 2.0-3.0), or by spraying a dry deactivating preparation, which is a mixture of humic substances, which is enriched in the fulvic acid fraction (up to 60 wt.%). In the second case, the introduction of a dry reagent should be accompanied by primary wetting (up to 10 l / m) of the disinfected land masses with a weak sulfuric acid solution (pH 2.0-3.0), followed by the use of atmospheric precipitation toxicants (rain and melt water) for the regime of vertical migration. Under the influence of the FC complexon, uranium and other radionuclides are “squeezed” into the lower layers of the aeration zone, where they are firmly sorbed by rock-forming minerals. The use of humus FC-reagent allows avoiding the excavation of soil contaminated with toxicants, enhances the fertile properties of the soil layer and will contribute to the production of environmentally friendly food on cleaned agricultural land.

In areas with the development of permafrost, the problem of cleaning soils from radionuclides by using a humic FC preparation can also be solved quickly and economically. At a low power of the thawed soil layer, it is advisable to transfer the radionuclides into the liquid phase by irrigating the surface of the contaminated area with a FC solution (FC up to 100 mg / l; pH = 2.0) while organizing the suction of the resulting radioactive solutions with needle filters (well-known designs should be used as needle filters) ) Concentrations of radionuclides that occur during the subsequent processing of these solutions are subject to disposal.

It is recommended to treat the soil object at least three times by adding fulvic acids to the surface of the soil object in the form of a solution or a dry deactivating preparation. As a deactivating composition, a weakly sulfuric FC solution (H ₂ SO ₄ = 5 g / m ² ; pH 2.0-3.0, FC up to 100 g / m ³ ) is recommended.

The values indicated in the application parameters were determined based on the following considerations:

1. One of the main environmental pollutants in the sphere of influence of radiation hazardous objects is uranium. In laboratory and field tests of the FC complexon, positive results on the extraction of metal from uranium-containing minerals into the liquid phase were achieved in a wide range of the content of humic reagent in it - from 50 to 500 mg / l. To obtain economically justified guaranteed success in the conversion of uranium from a solid phase to a working solution, it was experimentally established that a concentration of FA in this solution of 100 mg / l is sufficient.

At this concentration, the uranium leached from the ore mass is able to move together with solutions in ore-bearing rocks for tens of meters, being in a water-dissolved state, most likely in the form of associates with fulvic acid molecules.

As shown by the studies of G.M. Varshal (GEOCHI RAS), even at insignificant concentrations of fulvic acids in water, other pollutant radionuclides ( ¹⁰⁶ Ru, ^l44 Ce, ⁹⁰ Sr, ¹³⁷ Cs) pass into the dissolved state by 80% even after a single treatment of natural and technogenic objects (patent No. 2088988).

2. The relatively low degree of acidity of decontamination solutions (pH 2-3) is preferable for two reasons:

- these pH values are characterized by the presence of fulvic acids in the form of dominant monomeric forms with a weight average molecular weight close to 300. This activates the development of complexation processes of FAs with environmental metal pollutants;

- the low content of sulfuric acid in the working decontamination solutions dramatically reduces the risk of contamination of the soil with sulfate ion. The optimal thickness of the soil to be cleaned is 70 cm (the average penetration into the soils of the root system of the grass cover).

With an average porosity of water-permeable rocks of the aeration zone equal to 20%, the total pore volume will be approximately 140 dm ³ / m ² . In this case, the average amount of FA in the decontamination solution filling the pores will be 0.1 g / dm ³ × 140 dm ³ = 14 g / m ² (≈15 g / m ² ).

3. Soil-polluting components are usually concentrated in the near-surface part of the soil or in the upper third of the layer to be decontaminated (70: 3 = 23.3 cm). With a single treatment of the soil cover with a solution of fulvic acids (5.0 gFK / m ² ), coarse cleaning of toxicants with squeezing them into the underlying rocks is guaranteed to undergo only its upper third.

With triple soil treatment, a more complete decontamination is achieved. As a result of the recommended cleaning regime, the upper third of the layer to be cleaned will be washed 3 times, the underlying layer below it will be washed 2 times, and the lowest one will be washed 1 time, taking out all the pollution accumulated in the soil with FC solutions that leak down below 70 cm.

4. When focusing mainly on precipitation, the amount of FA required for soil cleaning in dry form (15.0 gFK / m ² ) is applied to the soil during autumn plowing or to moist soil after initial autumn rains.

5. To carry out soil decontamination, you can use FC preparations with any initial concentration of FC in them, but from an economic point of view, it is preferable to use more concentrated products in order to reduce transport costs. To date, the technology for the industrial production of FC reagent with the stable production of humic extracts containing at least 60 wt.% FC has been developed.

Thus, the use of a humus deactivating FC preparation in a dry or dissolved state significantly expands (compared with the scope of patent No. 2088988) the possibility of prompt cleaning of the environment of radionuclides, heavy metals and other toxicants.

Claims (2)

1. The method of decontamination of natural and man-made objects infected with radionuclides, including treating the soil object with an agent containing humic acids, followed by removal of radionuclide contaminants from solutions, characterized in that, out of the availability of natural waters containing fulvic acids, the soil object is processed up to three times by making the surface of the soil fulvic object to 5 g / m ² as slabosernokislotnogo solution of fulvic acids fraction to 100 g / m ³ at a pH of 2.0-3.0, or in the form of dustable th on moistened slabosernokislotnym solution at pH 2.0-3.0 in volume to 10 L / m of the soil surface object deactivating dry preparation comprising a mixture of humic substances, fulvic acids enriched fraction to 60 wt.%. 2. The method according to claim 1, characterized in that the process of cleaning the soil object and increasing the power of the disinfected layer is carried out to a depth of not less than 70 cm