SU468446A3 - The method of decontamination of radioactive liquids - Google Patents

Description

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This invention relates to a method for deactivating radioactive liquids with mineral substances.

Methods are known for the deactivation of radioactive liquids using ion exchanges, which are subject to regeneration. However, as a result of the regeneration, radioactive liquids are obtained that need to be decontaminated.

There is also known a method of processing.

radioactive liquids, consisting in the chemical deposition of radioactive ions. The precipitate obtained is filtered off and stirred with hot bitumen, until a homogeneous mixture is obtained. With

during this operation, the water present is evaporated and the mass is stored in steel drums. The separation of precipitation by filtration is difficult, it requires large installations. Besides

In addition, the precipitate must be dewatered by freezing and thawing in order to give it a better filtering ability. i All specified known methods are not

are specific to radioactive ions. For this reason, ion exchangers are impacted to a large extent by such ions that are not desired to be extracted (sodium, calcium or magnesium ions). Sediments may also contain predominantly such ions that are undesirable to extract (such ions are always present in the water to be decontaminated).

The proposed method is specific for radioactive ions. According to the proposed method for extracting radioactive ions present in insignificant amounts in polluted liquids, the liquid is brought into contact with a mineral that includes several compounds from the group: barium salt, metal sulfide and copper ferrocyanide. The ions of sodium, calcium, magnesium, iron, aluminum are not thus extracted, while the radioactive ions are extracted from the liquids to be purified.

Experiments have shown that different

inorganic substances have specific torbtional characteristics. This appears when these substances come in contact with a solution of u, containing radioactive ions and, in particular,

ions in quantities that are defined. The term sorption includes any of the means by which an ion can be transferred from a solution to a solid substance of mineral origin that is in contact with the solution.

Sorption can be carried out, for example, by isotope exchange, the formation of mixed crystals and in particular precipitation, co-precipitation and subsequent precipitation. The problem of deactivating radioactive liquids is of particular relevance to the extraction of the following ions: strontium, cesium, cobalt cerium, ruthenium, sake and antimony.

The process according to the invention is preferably sorbed: strontium - with barium salt; radium - a salt of barium or sulfido metal; zorium — a salt of barium or a metal sulphide; ruthenium - salt of barium, metal sulfide KL ferrocyanide copper; antimony - with barium salt, metal sulfide or copper ferrocyanide; cesium ferrocyanide copper.

These salts can be used in the form of simple or offset salts.

Barium sulphate is obtained by mixing at room temperature an equal volume (solutions) of barium chloride and sulfuric acid.

sour sodium. the precipitate is formed and filtered out, and without washing BbicyuJHBaioT at 1OO C. The resulting powder product is used to determine sorption characteristics, expressing (5 cu (x coeff (KI impedance Kd, which is defined as the ratio between the ion concentration on the sorbent (1 g) and ion concentration in rast-eore (per 1 ml.). Experiments were performed with

earth-mineralized water, to which radioactive ions were added, as defined, and 40 parts per 1 million altsi. The following Kd values were obtained. : dl strontium - 7, for - 27 and

turf .- 284. After adding sulfuric acid to the water used for the tests, for example to lower the 3N to 2, the Kd values increased: for strontium - 195O, for the sake of - ZOOO and

Deri - 66OO.

The sorption mechanism may be superior to the following facts: if pure barium sulphate had sorption properties, there would be no difference between the Kd values before and after the addition of sulfuric acid. However, the addition of sulfuric acid is necessary to achieve good.

sorption. On the other hand, as can be easily proved with the help of a control solution, in a solution of sulfate ions, derived from added sulfuric acid, is not enough to lower the solubility of the products — strontium and sake, when they are deposited in small quantities.

The reason why strontium and radium are sorbed more efficiently after the addition of sulfuric acid is probably due to the occurrence of co-precipitated with newly formed barium sulphate. Indeed, barium ions are already present in the barium sulphate (not subjected to precipitation) and are formed together with sulphate ions, in solution, an additional amount of barium sulphate precipitating on the barium sulphate that already existed before. In the course of this formation, strontium, radium and cerium are subjected to co-precipitation.

Kd values can be significantly increased by preparing barium sulphate in the manner described above, but with an excess of barium ions. The Kd values obtained in this way are summarized in Table 1. Further, it is possible to increase the sorption properties of sulfuric acid barium by activating it, for example, by adding sodium nitrate during the precipitation of barium sulphate. The concentration of sodium nitrate should be such that it is in the range of 1 sodium ion per 1 barium ion to 1 sodium ion per 24 bari ion. Other concentrations of sodium nitrate do not have a favorable effect on the sorption capacity of sodium sulfate.

As mentioned above, an excess amount of barium ions in the sorbent composition in the form of barium sulphate is necessary for good sorption properties. Although the ratio of 3 barium ions to 1 HOIJ provides good sorption, it should be noted that a further increase in the proportional amount of barium ions is not accompanied by a more improved sorption properties. Co-generation has a very high selectivity, for example, there is practically no deposition of calcium. Test water: demineralized water containing strontium, radium and cerium and 4O parts per million calcium, to which sulfuric acid was added until the pH reached 2. Table Water for testing did not contain sulfuric acid. Barium sulphate is activated by adding 1 volume of sodium nitrate to 3 volumes of barium chloride during the production of barium sulphate. Similar experiments with demineralized water, to which sodium and magnesium ions were added, showed that these ions are not subjected to co-precipitation. Co-precipitation occurs during the formation of freshly formed barium sulphate. The newly obtained barium sulphate can also be formed, from any soluble barium salt, by the addition of ions. Good results have been obtained using barium carbonate in sulfate-containing medium. In this way, fresh barium sulphate is formed and co-precipitation of strontium is achieved, for the sake of cerium. Using the same water for testing, barium carbonate sorption was first carried out under the same conditions of acidity of the medium (pH 2 by adding sulfuric acid), as in the case of sulfuric acid barium, then in the medium in which sodium sulfate is found. The obtained values of the Kd coefficient are listed in Table 2. Test water: demineralized water containing strontium, radium and cerium, and 4O parts per 1 million calcium. pH 2 was reached in the indicated medium. Barium carbonate - commercially available. Table 2

The data table. 2 indicate that in a 0.1N sodium sulfate solution, the results of barium carbonate sorption are comparable to those for barium sulfate with a Ba / So molar ratio of 3/1.

Due to the fact that it is not always cost-effective to process large volumes of wastewater in the environment

the form of 0.1n. Sodium sulphate solution, according to the proposed method, it is recommended to treat the mentioned volumes on the ion exchanger, and liquids obtained after regeneration, obtained after the ion exchanger treatment, further process with barium carbonate.

Ruthenium and antimony must also be sorbed on barium carbonate. So with h) az, in the case of the mentioned ions there is no need to use metal sulphides if barium soda is used. However, such co-precipitation on barium salts, which is successful in the presence of strontium, sake and cerium, cannot be achieved with all ions, it is desirable to extract .. For example, cobalt can be precipitated with better results tatami using manganese sulphide, copper sulphide and iron sulphide. Ruthenium and antimony are also precipitated by these sulphides. In accordance with the proposed method, the mentioned metal sulfides in this case should be prepared with an excess of sulfide, and sorption should be carried out under conditions of an almost neutral medium (for example, at pri 5). This is explained by the fact that in a strongly acidic medium sulfide ions will release gaseous hydrogen sulfide. The values of the Kd coefficient obtained are given in Table 3 for the following cases: Manganese sulphate prepared using equal amounts (by volume) of manganese sulphate and sodium sulphide; manganese sulphate prepared using an excess of ions, sulfide {2 volumes of sodium sulphide per 1 volume of manganese sulphate); sulfur iron prepared using two volumes of sodium sulfite, 1 volume of iron sulfide. Test water: demineralized water containing cobalt, ruthenium and antimony and 40 parts per 1 million calcium.

T a b l and c a 3

Cerium and radium will also be sorbed on sulphides. Thus, metal sulfide can be used to extract water and these elements from. Regarding the relationship between sulfides and metal ions in the sorbent, we note that

The sorption of radioactive ions, which form insoluble sulphides, coming from the liquids after the regeneration of ion exchangers, has also been investigated in the direction of using metal sulphides. Excellent results were necessary excess sulphide ions. Preferably the ratio is 2/1. A further increase in the proportional amount of sulfide ions does not lead to an improvement in the results. When sulfide is used, the sorption mechanism is based on the formation of a precipitate. Due to the fact that alkaline earth sulphides are soluble in water, calcium and magnesium, which are usually present in the waters to be decontaminated in large quantities, will not precipitate. Thus, this sorption mechanism is very selective. However, alkali metal ions affect the sorption of cobalt on metal sulfides. Experiments performed with water to test the same composition, to which sodium c. Was also added. an amount of 100 parts per 1 ppm was shown for iron sulfide, prepared as above, that K4 value for cobalt is 7800 instead of 30,000. However, sorption of cobalt can be significantly improved by adding calcium chloride during the precipitation of iron sulfide. The concentration of calcium chloride to be added can be changed in the range of 1 calcium ion to 1-18 iron ions. The effectiveness of the effect of such activation on the cobalt sorption is shown in Table 4. Test water: demineralized water containing cobalt {ruthenium and antimony), 4O parts per 1 million, calcium and 100 hours per 1 million sodium. (Table 4 was obtained by ferrous sulfides of natural origin, such as troilite and pyrite. Sorption of cerium, for cobalt, ruthenium and antimony on troilite from water waste after regeneration, the ion exchange is shown in Table 5. 6l of liquids after regeneration containing 2 M chloride sodium and 0.05 M calcium chloride, to which sodium sulphate was added to achieve a concentration of 0.1 N., were measured from the south of troilite. Table 5 The data in Table 5 show that troilite can be successfully used to treat aqueous radioactive Non-cesium or strontium-free liquids. Obviously, if cesium or strontium is present, troilit can be used provided there is an additional sorbent for these ions. Cesium sorption is preferably carried out using copper ferrocyanide, which can be prepared by mixing 2 volumes of copper sulphate with 1 volume of ferrocyanide iron. This product holds almost 100% of the total cesium ions. If necessary, copper ferrocyanide can be absorbed by activation achieved by adding chloride Calcium to copper sulfate during the preparation of copper ferrocyanide. The above considerations indicate the selectivity of the products mentioned. Thus, using barium salts, metal sulfide and copper ferrocyanide, it is possible to extract radioactive ions from radioactive water. However, these products must be in a form that would facilitate their use in industrial process equipment, for example, columns and precipitators with agitators. The proposed method, these substances are obtained using the preparative method. Sulfides: iron sulfide, copper sulfide and manganese sulfide already have a granular structure, and barium sulfate and barium carbonate are obtained in the form of fine powder, which is unsuitable for use in column equipment. A suitable structure for use may be imparted to barium sulfate by preparing it as a mixed product. Thus, barium sulfate and copper ferrocyanide are obtained in the form of a mixed substance with a good structure in the form of granules, which can be used for the simultaneous extraction of strontium, for the sake of cerium, as well as cesium, ruthenium and antimony. To obtain such a mixed substance, ZOO volumes of 1 M sodium sulfate are added to 150 volumes of a 0.1 M copper sulfate solution. With stirring, 945 volumes of a 1 M barium chloride solution are added to this mixture. Then, 75 volumes of a 0.1 M potassium ferrocyanide solution are added to the resulting barium sulfate precipitate and vigorously stirred for 2 minutes. The resulting precipitate is then left to form for 1-2 hours. before separating it by filtration. Then, without washing, the precipitate is dried at 1OO C. The resulting dense, filtered precipitate is crushed to obtain grains of the desired size (not passing through a sieve with 80 mesh cells). The granular material has the following theoretical composition: 97.7% barium sulphate with a molar ratio Ba / SO. 3/1 and 2/3% of copper ferrocyanide, having a molar ratio between Cu and TeCCN) of 1: 1. The granules are then placed in a column through which the water used for the test is passed. The values of the K? 1 coefficient thus obtained are listed in Table 6. The same example was repeated, but with the addition of sodium nitrate in an amount that provides the ratio of 3 barium ions to 1 sodium ion. The same example is repeated with the difference that calcium chloride is used instead of sodium nitrate in an amount that provides a ratio of 3 barium ions to 1 calcium ion.

Test water: demineralized water containing strontium, radium, cerium, and cesium, 100 hours per 1 million. The value of the Kd for radium has not been determined. Mixed sorbents in the form of barium sulphate and manganese sulphide also have a good granular structure, however, manganese sulphate in this case only provides the structure of barium sulphide. Another sorbent that can be used in accordance with the proposed method is barium carbonate and copper ferrocyanide. Unlike a mixed product containing barium sulphate, this mixed salt based on carbonate barium still remains a fine powder, so that the contact between the mixed product and the wastewater to be treated must be unitized using unit loads. The sorbent should be prepared, for example, as follows. 1 volume of 1 m of barium chloride solution is mixed with 1 volume of 1 M sodium carbonate solution and left to

ten

sodium and ZO part of 1 million. Calcium, to which he added sulfuric acid to pi until it reached a pH of 2.

T a b l and c a 6

Table for obtaining a uniform precipitate. In addition, 1 volume of 1 M potassium ferrocyanide solution is added to 2 volumes of 0.1 Mipac T of copper sulfate and also left. until a uniform precipitate is obtained. Then both sludge is stirred each separately, mixed and dried without prior washing. This method provides a mixed sorbent consisting of 91% barium carbonate, having a molar ratio of Ba and CO 1: 1 and 9% of copper ferrocyanide, having a molar ratio of Sy „and Fe (CN) of 1: 1. idо Kd value. The center of this Sorbent is determined using the same test method as in the beam presented in Table 6. The results are shown in table.7. The pH value was obtained in the above medium (5 g of the sorbent was shifted from 1 liter of solution for 15 minutes, then centriuged).

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Ruthenium, antimony and cobalt will also be sorbed on this sorbent. Table 7 presents the excellent results obtained in an environment characterized by the presence of 0.1 n. sulfuric acid solution. As already established, it is not always cost effective to treat large volumes of wastewater in an environment - Oh, 1n. sulfuric acid solution. For the same reason, it is recommended by the proposed method to treat radioactive wastewater using ion exchangers and to treat liquids obtained after preliminary treatment of radioactive wastewater on ion exchangers on this sorbent.

As a sorbent, concentrated saline is effective, which must be available due to the need to deactivate

liquids after ion exchangers regeneration.

It should be noted that ion exchangers have already been proposed repeatedly to deactivate radioactive liquids. However, to date, their use has not been justified by practical considerations, as problems have arisen related to the deactivation of liquids,

The results of Table 8 show that sorption, especially strontium, is a function of the sulfate concentration. Concentration of 0 n. sodium sulfate is

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after regeneration of ion exchange B. These fluids are, in fact, concentrated salt brines.

solutions containing radioactive ions. With the help of an offset sorbent consisting of barium carbonate and copper ferrocyanide, the wastewater after the regeneration of ion exchangers can be easily and efficiently treated without any additional difficulties.

The sorbent is used in a sulphate medium if strontium is present in the composition of the wastewater to be decontaminated. The concentration of sulphate was found to influence the sorption of various radioactive ions. The effect of sulfate in various concentrations in the case of the use of the described sorbent in the form of barium carbonate with copper ferrocyanide is reflected in Table 8. The water used for the tests contained sodium chloride (2 M calcium chloride concentration (0.05 M concentration;) along with measurable amounts of cesium, strontium, cerium, radium, cobalt, ruthenium, and antimony. 3 g of sorbent was added to 1 liter of water, used for testing, and stirred for 1 hour before filtering.

Table8

preferred, since higher concentrations should lead to increased calcium sulfate formation. Carbonate is usually soluble in acidic

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medium, so pH values above 3.5 are noted. although the experiments described above were carried out with a mixed sorbent containing 91% barium carbonate and 9% copper ferrocyanide. The water used for the test contained sodium chloride (2 M concentration) and chloride

Table 9 indicates that ruthenium and antimony are sorbed by both components, while cesium is sorbed mainly by copper ferrocyanide. On the other hand, cerium and radium are sorbed mainly by barium carbonate. The ratio in the mixed sorbent should be considered especially carefully for the case of absorption of strontium and cobalt. It was found that in order to obtain a good sorption of strontium, in the composition of the mixed south of the sorbent, at least 9O% of barium carbonate must be present. As for cobalt, the same proportion gives good results, however, it is possible to increase the proportional ratios between the components to st and amp; due to the content of 85% barium carbonate and 15% copper ferrocyanide. However, referring to the radiological toxicity of strontium, a mixed sorbent containing at least 9 O% barium carbonate is preferred to ensure the sorption of the maximum amount of strontium.

The following are additional examples of the sorption of radioactive ions present in the stock / 1 bones after the regeneration of ion exchangers used to deactivate radioactive wastewater.

468446

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calcium (0.2 M concentration) in addition to cesium, strontium, cerium, radium, cobalt, ruthenium and antimony. Sodium sulphate was added until a concentration of 0 N was reached. The sorbent was added in an amount equivalent to the content of 7 g per 1 liter of water.

T a b and c a 9.

Sewage fluid containing the following metal ions: boron - 2 hours per

1 million, manganese - 0.16 parts per 1 million, iron - 0.2 parts per 1 million, magnesium - 1.15 parts per 1 million, silicon - 2.55 parts per 1 million , calcium - 41 hours per 1 million, sodium - 112 hours per 1 million, strontium 0, 06 hours per 1 million and potassium - 6.4 hours per 1 million, in addition to the following isotopes : cerium - 144, rute) sy - 1 O6, cesium - 137, zirconium - 95, tubium-95, cobalt - 58, cobalt - 6O, manganese -

54, strontium - 9O, having RP 3,

passed through a column containing synthetic ion-exchange resin in sodium form (trade name Amberlite IR - 120). After passing 350 volumes of waste liquid, the water was decontaminated to the following extent,%: strontium 9O - 99.7, ruthenium OO6 - 95.6, cesium 137-94.1, cobalt 58 - 1OO, cobalt 6O - 98.3, cerium

144 - 1OO, zirconium 95 and niobium 95 1OO, manganese 54 - 1OO. Then the ion exchange resin was subjected to regeneration using 6 volumes of 4 M sodium chloride solution. rI environment increase

to 3.5 and add sodium sulfate to achieve a concentration of 0.1 N. 1O mixed sorbent containing 91% barium carbonate and 9% ferrocyanide

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copper was added to 1.5 liters of effluent with quenched composition, stirred for 1 hour and centrifuged for 10 minutes. After processing, it was found that the degree of deactivation was,%: 95.1 for gamma emitters, 98.7 for beta emitters and 98.6 for strontium 9O.

Sewage liquid of another composition

contained ions of the following metals: boron - 1 part per 1 million, manganese - O, O9 parts per 1 million, iron - 1.3 hours per 1 million, magnesium - 0.9 hours per 1 million. , silicon - 2h. for 1 million, aluminum - 1.95 parts for 1 million; calcium - 61.5 parts for 1 million, sodium 38 parts for 1 million, strontium - 0.1 parts for 1 million and potassium - 6.5 hours, per 1 million, in addition to the following isotopes;

cerium - 144, ruthenium - 1O6, cesium - 137 zirconium - 95, niobium - 95, cobalt - 58 cobalt - 60, manganese - 54 and strontium - 90, were passed through a column containing the same ion exchanger as in the previous example. After passing 615 volumes of waste fluid, it turned out that the degree of water deactivation was%: 94.8 for gamma beta emitters and 97.8 for strontium - 90. The ion exchanger was then regenerated using 12.5 volumes of 2 M sodium chloride solution . The pH of the liquid obtained after regeneration was raised to 6.5 by the addition of sodium hydroxide. Sodium sulfate was also added until reaching

concentration 0.1 n. Yg of a mixed sorbent containing 91% barium carbonate and O% copper ferrocyanide was added to 2 liters of waste liquid of the above composition, stirred for 1 hour and filtered. Then the water was checked for residual radioactivity. It was found that the degree of deactivation was,%: 97.7 for gamma-beta emitters and 9O-99.8 for strontium. The last example suggests that strontium decontamination is more effective at pH 6.5.

The above sorbents can also be used to extract other radioactive ions, which

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may be present in the radioactive 4, waters of some species. Such ions include uranium, plutonium and iodine. Experiments have shown that uranium and plutonium can be extracted using cm & ns sorbent composed of barium sulphate and metal sulphide. On the other hand, iodine can precipitate from copper sulphide and copper iodide. In this case, copper sulphide should be precipitated in the presence of an excessive amount of copper ions. If iodine is present in radioactive liquids, from which ruthenium, cobalt and antimony should also be extracted, sulfur copper should be prepared first with an excess of copper ions, and then with an excess of sulfide ions. Both copper sulphides in the form of granules can be mixed. Then they will delay iodine with ruthenium, cobalt and antimony.

The proposed method can be used in many different cases. As an example, we point out that radium can be extracted from solutions characterized by a high concentration of sodium. Such solutions occur among the waste liquids resulting from the separation operation after the actinium is obtained from the source. Such solutions have a 6 M sodium concentration and contain radium in quantities worthy of extraction. To achieve this goal, a mixed sorbent containing 5% of barium sulphate is prepared, with the ratio between Ba and IPO. 2/1, and

5O% manganese sulfur, and the ratio between manganese and sulfur 1/1. The dense precipitate obtained as a result of filtration was dried to con / ZOO C and then crushed to grains, the size of which corresponded to the requirements of use in certain clonns of a certain size. More than 99% of the ions of ions were separated from solutions with an increased koH concentration of sodium ions.

 Table I indicates the preferred activated sorbents for removing radioactive ions from liquids contaminated with such ions.

17 According to the proposed method, other ions, such as uranium, plutonium, iodine, zirconium, niobium and manganese, can also be sorbed. The subject matter of the invention is 1. A method for deactivating radioactive liquids, the contamination of which does not exceed the activity of 1 curie per cubic meter, from radioactive impurities by passing a liquid through a sorbent containing a barium salt, characterized in that in order to increase the efficiency

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Table 10: Purification; use a mixed sorbent containing at least. .50% barium salt and copper ferrocyanide, and the process is carried out in a sulphate medium, the pH of which is less than 8, 2. The method according to claim 1, I distinguish, u and with the fact that barium sulfate is used as barium salt 35 a ratio of 2-3 barium ions to the ion S O, 3. The method noffn.lu2, which is also distinguished by the fact that BaSO ,, is used as the salt of barium 40, the pH of the sulfate medium being 5-8