RU2205461C2 - Method for recovering and decontaminating radioactive industrial products and/or industrial wastes - Google Patents

Abstract

FIELD: metallurgy. SUBSTANCE: upon dissolving source industrial products and/or industrial wastes product obtained is treated with lime slurry, hydrate sediment is separated and brought out to mother waters of barium chloride and sulfuric acid, ionic proportions being as follows: SO $\genfrac{}{}{0ex}{}{\text{2-}}{\text{4}}$ /Ba²⁺ = -1-6 and Ca²⁺/Ba²⁺≤5. Then solution of iron trichloride in the form of waste waters is introduced in addition into pulp formed in the process. Upon processing pulp with trichloride iron solution in the amount of 0.5- 5 kg of iron per 1 sq. m of mother waters it is treated again with lime slurry. EFFECT: reduced radioactivity of filtrates due to enhanced joint precipitation of radionuclides and cakes. 1 cl, 3 tbl

Description

 The present invention relates to the field of metallurgy and can be used for the neutralization and decontamination of radioactive intermediate products and / or production wastes containing Th-232 and its daughter products (Ra-228, Ra-224), as well as REE, Fe, Cr, Mn , Al, Ti, Zr, Nb, Ta, Ca, Mg, Na, K, etc. The invention can be used for processing multicomponent polymetallic intermediates containing natural radionuclides, industrial products and / or production wastes and formed at various stages of the technological processes of complex refin ing loparite, zircon, ilmenite concentrates, slimes dump ferrovolframovogo production tails wet magnetic separation titanomagnetikov, red mud aluminum production, waste from the processing of columbite, ferroniobium et al.

 A known method of processing (Recycling of the process of chlorination of loparite // Non-ferrous metallurgy, 1987, 1, p. 32-33) of radioactive waste production - spent melt salt irrigation filter of the process of chlorination of loparite concentrates, which consists in leaching the melt by pouring it into water, mixing chloride pulps with barium chloride solutions, sulfuric acid, heating the pulp and supplying steel scrap to restore ferric iron to ferrous and increase the pH to 2.5-3.5; treating the pulp with milk of lime to pH 4.5-5.0, and then with a 0.5% solution of polyacrylamide, filtering and washing the precipitate; drying the sludge and subsequent removal for burial in the storage of special waste (CSW).

 The known method allows to increase the degree of concentration of thorium and its content in the "cakes" sent for burial; the degree of extraction of thorium from the solution into the precipitate - radioactive cake exceeds 99.9%.

 The reasons that impede the achievement of the technical result indicated below when using the known method include the unsatisfactory degree of deactivation of the solutions due to the high radioactivity of the filtrates after separation of the thorium-containing precipitate.

 Of the known analogues, the closest in technical essence and the achieved result to the proposed method is a known method for processing and neutralizing radioactive intermediate products and / or production waste (Concentration of chloride waste from processing loparite concentrates // Non-ferrous metals, 1995, 12, p. 53-56), which is selected as a prototype.

According to the prototype method, the initial waste and / or intermediate products are dissolved, the resulting solution (pulp) is treated with BaCl ₂ solution, sulfuric acid and milk of lime, followed by filtration of the pulp, separation of the mother liquor from the oxyhydrate sulfate precipitate and its disposal in the special waste storage. The known method allows you to localize thorium and translate it into a form convenient for long-term storage (in the storage of special waste).

 The reasons that impede the achievement of the technical result indicated below include an unsatisfactory degree of purification - decontamination from daughter radionuclides of a series of thorium-232, in particular from Ra-224 and Ra-228. This is due to the incomplete coprecipitation of radium with precipitation of barium sulfates, calcium and metal oxyhydrates.

 The claimed technical solution is aimed at solving the problem of increasing the degree of decontamination of solutions. The technical result that can be obtained by implementing the claimed invention is to reduce the radioactivity of the filtrates after separation of the radioactive cakes by increasing the degree of coprecipitation of natural radionuclides of the Th-232 series, in particular Ra-224 and Ra-228 with radioactive fallout - cakes.

 The specified technical result in the implementation of the claimed method is achieved by the fact that in the known method of processing and neutralizing radioactive waste and / or industrial products, including their processing with a solution of barium chloride, sulfuric acid and milk of lime, separation of the solution from the radioactive deposit and its disposal, the peculiarity lies in the fact that the processing of milk of lime is carried out immediately after dissolution of the original industrial products and / or production waste, barium chloride and sulfuric acid DYT in the mother liquor after separation of the hydrate precipitate, then the resulting pulp is further added a solution of iron chloride (III).

The peculiarity lies in the fact that the mother liquor is treated with barium chloride and sulfuric acid at ionic ratios SO ₄ ^2- / Ва ²⁺ = 1 ... 6 and Са ²⁺ / Ва ²⁺ ≤5;
the peculiarity lies in the fact that a solution of iron (III) chloride is introduced in an amount of 0.5-5.0 kg of iron per 1 m ^{3 of the} mother liquor;
the peculiarity also lies in the fact that as a solution of iron chloride, "washing" wastewater is used;
the peculiarity, in addition, also lies in the fact that after the introduction of a solution of iron (III) chloride into the pulp, it is again treated with milk of lime.

 Ceteris paribus, the proposed method, characterized by new methods of performing actions and a new order of performing actions, using certain substances, without which it is impossible to implement the method itself, with new modes and parameters of the process, provides a technical result in the implementation of the claimed invention.

 Checking the patentability of the claimed invention shows that it corresponds to the inventive step, as it should not be obvious to specialists.

The analysis of the prior art indicates that in the book, magazine and patent literature there is no information on the processing and disposal of radioactive waste and / or intermediate products from thorium and its daughter decay products - radium by sequential processing of the initial solutions (pulp) first with milk of lime, then separation precipitate with barium chloride, sulfuric acid at an ionic ratio of SO ₄ ^2- / Ва ²⁺ = 1 ... 6 and Ca ²⁺ : Ва ²⁺ ≤5, after which iron (III) chloride is added to the suspension (pulp) in an amount of 0 , 5-5,0 kg Fe / 1 dm ³ of the mother liquor, Using the solution as ferric chloride (IV) wastewater - obmyvochnyh enterprise water formed during treatment for washing sites for equipment and the like, and if needed - additional processing of milk of lime, slurry by filtration and removal of radioactive sludge in special waste storage.

 An analysis of the totality of the features of the claimed invention and the result achieved in this case shows that there is a well-defined causal relationship between them, expressed in the fact that the implementation of the processing and neutralization of radioactive waste and / or industrial products under the strictly defined above conditions, conditions and process parameters: the sequence of operations, the presence of new actions, the introduction of certain substances in the field, defined by the ratio of reagents, and a strictly defined order Ia reagents provide increased degree of deactivation due to the decrease of radioactivity of the filtrates after the separation of radioactive deposits by increasing the degree of natural radionuclides coprecipitation number of Th-232, in particular Ra-228 and Ra-224 with and hydrate precipitation-kekami oxyhydrate.

 In violation of the above process modes, sequence of actions, etc. the above technical result is not achieved. It should be noted that the established causal relationship does not explicitly follow for specialists and does not follow from the literature on the chemistry and technology of vanadium and its compounds.

 Information confirming the implementation of the invention with obtaining the above technical result, as well as a comparison of the effectiveness of the known (prototype) and the proposed technical solutions are given in the examples.

Examples
The following were used as radioactive production wastes, intermediates and industrial products: spent salt melting irrigation melts and REE melts of the chlorination of loparite concentrates (Solikamsk), solutions from leaching of primary scandium concentrates, rare-earth concentrates obtained from the complex processing of tetrachloride production wastes titanium; by-products from processing and pre-concentration of tailings of wet magnetic separation of titanomagnetics (Kachkanar), red mud from alumina production (Kamensk-Uralsky), waste from chlorine processing technology for zircon concentrates (Glazov) and dump sludge from ferro-tungsten production (Chelyabinsk) .

Example 1. Comparison of the effectiveness of the known prototype and the proposed methods
Radioactive waste containing, wt.%: 2.5 ThCl ₄ , 20 AlCl ₃ , 7 LnCl ₃ , as well as impurities TiCl ₄ , NbCl ₃ , TaCl ₅ , NaCl, KCl, MgCl ₂ , CaCl ₂ , water-insoluble residue (5% ), was dissolved at W: T = 4: 1 water. With the resulting chloride pulp, comparative tests were conducted on the effectiveness of decontamination and determining the performance of the prototype and the proposed method.

According to the known method, the pulp was heated to 75 ± 5 ^o C and treated with 200 l of a 10% solution of barium chloride and 50 l of a 78% solution of sulfuric acid, after which it was neutralized with calcium hydroxide to a pH of 8.0 ± 0.5, filtered on equal to the filter press. In the filtrate, α-radioactivity was measured by the emanation method, after which it was sent for re-neutralization according to the described scheme. The deactivation process was repeated until the radioactivity of the filtrate was 1 eq mg of thorium / dm ³ .

According to the proposed method, the pulp was treated with calcium hydroxide to a pH of 7.0-8.5 and filtered on a frame filter press. The mother liquor was treated with 50 l of a 10% solution of barium chloride and 10 l of a 78% solution of sulfuric acid, after which 2 m ^{3 of} iron-containing wastewater with an iron concentration of 0.8 t / m ³ (0.59 kg of iron) was introduced into the pulp / m ³ stock solution) and again treated with calcium hydroxide to a pH of 8.0 ± 0.5. Then the pulp was filtered, α-radioactivity was measured in the filtrate by the emanation method and dumped into the sewer.

 In all tests, the fallout was taken to the radioactive waste storage facility.

 In total, six experiments were carried out: three - according to the known and three - according to the proposed methods. The results of comparative tests are presented in table 1.

Example 2. The rationale for the treatment of mother liquor-pulps after the introduction of BaCl ₂ and H ₂ SO ₄ an additionally determined amount of FeCl ₃
1.0 kg of spent molten salt irrigation filter of the process of chlorination of liparite containing,%: 1.9 Th; 10.2 Fe (III); 7.8 Al; 12.3 REE, leached in 4.0 DM ³ water. The resulting pulp was treated with a solution of calcium hydroxide to pH 8 and filtered.

The mother liquor after separation of the hydrated precipitate was divided into seven portions of 500 cm ³ ; 0.5 dm ^{3 of the} mother liquor was treated with 10 cm ^{3 of a} 10% solution of barium chloride and 0.5 cm ^{3 of a} 78% solution of sulfuric acid, mixed, then a certain amount of iron-containing wastewater with a concentration of _Fe = 0 was introduced into the pulp 8 g / dm ³ , i.e. a certain amount of iron was introduced per 1 dm ^{3 of the} mother liquor.

After the introduction of iron, the pulp was treated with milk of lime to pH 8.0 ± 0.5, the volumes of all samples were brought to the same level with water and filtered. In the filtrate, α-radioactivity was measured by an emanation method. In the "idle" experiment (Run 0) radioactivity was measured mother liquor (without introducing FeS1 ₃₎ diluted to the same volume of water. The activity of this solution was 397.4 equiv. mg thorium / dm ³ The results of the experiments are summarized in table 2.

Example 3. The justification of a certain sequence - the need for the introduction of BaCl ₂ and H ₂ SO ₄ after preliminary processing of the initial pulp with milk of lime and the subsequent separation of the radioactive precipitate of the sum of the oxyhydrates of Th, Fe (III), A1, REE, etc.

The pulp obtained after leaching the melt of the salt irrigation filter of the composition indicated in Example 1 was processed according to three options:
1. by the proposed method;
2. Barium chloride and sulfuric acid were introduced before treatment with milk of lime;
3. Barium chloride and sulfuric acid were introduced after treatment with milk of lime, but before separation of the hydrated precipitate.

The radioactivity of the filtrate according to the proposed method amounted to three options:
1. 0.64 equiv. mg Th / dm ³ ;
2.832 equiv. mg Th / dm ³ ;
3. 1324.0 equiv. mg Th / dm ³ .

Example 4. The rationale for the introduction of a solution of FeCl ₃ after appropriate treatment with milk of lime and introduction into the mother liquor BaCl ₂ and H ₂ SO ₄
The pulp obtained after leaching the melt of the salt irrigation filter of the composition indicated in Example 1 was treated in two ways:
1. by the proposed method;
2. Iron chloride was introduced into the solution before treatment with calcium hydroxide.

The radioactivity of the filtrate according to the proposed method in two ways was:
1. 0.59 equiv. mg Th / dm ³ ;
2.774.6 eq. mg Th / dm ³ .

Example 5. The rationale for the need for a certain ratio of SO ₄ ^2- / Ba ^{2+ and} Cr ²⁺ / Ba ²⁺ ≤5
Radioactive salt waste containing, wt.%: 1.9 Th, 12.3 REE, 10.2 Fe (III), 7.8 Al, up to 50% ΣNaCl, KCl, MgCl ₂ , CaCl ₂ , impurities of other metals, dissolved at a ratio of waste: water = 1: 4. The resulting pulp was treated with milk of lime (100 g / dm ³ CaO) to pH 8.0 ± 0.5, the radioactive precipitate of thorium oxyhydrate and other metals was separated from the mother liquor containing CaCl ₂ , MgCl ₂ , NaCl, KCl and water-insoluble radionuclides (in the ionic form) of the Th-232 series, in particular, the "not captured" oxyhydrate precipitates Ra-228 and Ra-224.

This mother liquor was sequentially treated with BaCl ₂ , H ₂ SO ₄ , FeCl ₃ and milk of lime to a pH of 8.0 ± 0.5. During the experiments, the molar ratio of H ₂ SO ₄ : BaCl ₂ (ionic ratio of SO ₄ ^2- / Ba ²⁺ ) from 0.9 to 6.5 and the ionic ratio of Ca ²⁺ / Ba ²⁺ from 0.29 to 6 were used. 3. Under these conditions, 12 experiments were carried out, and experiments 1-7 were performed under optimal conditions by the proposed method. The results of all experiments are summarized in table 3.

 Thus, the results of comparative tests (experiment 1) and the data of experiments to study the influence of various factors on the degree of decontamination of waste and the residual radioactivity of purified solutions indicate that under optimal conditions for the implementation of the process according to the proposed method, a high (tens and hundreds of times higher, than by the known method) the degree of neutralization of solutions from radioactive metals.

Claims (1)

A method for processing and neutralizing radioactive industrial products and / or production waste, including their dissolution, treatment with barium chloride, sulfuric acid, lime milk, separation from the solution of radioactive fallout and their disposal, characterized in that the treatment with lime milk is carried out immediately after dissolution of the initial industrial products and / or industrial waste, barium chloride and sulfuric acid is introduced into the mother liquor after separation of the precipitate when hydrated ion ratios SO ₄ ^2- / Ba ²⁺ = 1 ÷ 6 and Ca ²⁺ / Ba ²⁺ ≤5, then of razovavshuyusya pulp mixed with iron wastewater, taken in an amount to provide an introduction to the mother liquor of 0.5-5.0 kg of iron in the form of its chloride per 1 ^m3 of the mother liquor, whereupon the pulp is again treated with lime milk.

Images