RU2246550C1 - Method for reprocessing of thorium-containing radwastes - Google Patents

Abstract

FIELD: rare, dispersed and radioactive metal metallurgy, in particular hydrometallurgy.

SUBSTANCE: invention relates to method for reprocessing of polymetal, multicomponent, thorium-containing radwastes, formed when reprocessing of various mineral, containing rare-earth elements, Nb, Ta, To, V, Zr, Hf, W, U, etc. Method includes treatment of solution and/or slurry with alkaline agent; introducing of sulfate-containing inorganic compound solution and barium chloride; treatment of obtained hydrate-sulfate slurry with iron chloride-containing solution, and separation of radioactive precipitate from solution by filtration. As alkali agent magnesia milk containing 50-200 g/dm² of MgO is used; treatment is carried out up to pH 8-10; sodium sulfate in amount of 6-9 g Na₂SO₄/dm² is introduced as solution of sulfate-containing inorganic compound; barium chloride solution is introduced in slurry in amount of 1.5-3 g BaCl₂/dm². Hydrate-sulfate slurry is treated with solution and/or slurry containing 0.8-16 Fe³⁺/dm² (as referred to starting solution) of iron chloride, followed by treatment with high molecular flocculating agent and holding without agitation for 0.5-2 h. Radioactive precipitate is separated from mother liquor, washed with water in volume ratio of 0.5-2:1; then washed with sodium chloride-containing solution and/or slurry in volume ratio of 0.5-2:1; radioactive precipitate is removed from filter and mixed with mineral oxides in amount of 0.5-0.8 kg MgO to 1 kg of precipitate. Formed pasty composition is fed in forms and/or lingots and presses with simultaneous heating up to 80-120⁰C.

EFFECT: filtrate with reduced radioactivity due to increased codeposition coefficient of natural Th-232-group radioactive nuclide, in particular Ra-224 and Ra-228, with radioactive precipitates.

10 cl, 1 ex

Description

The present invention relates to the field of metallurgy of rare, scattered and radioactive metals, in particular to hydrometallurgical methods for processing polymetallic, multicomponent, thorium-containing radioactive waste generated during the processing of various mineral raw materials containing REE, Nb, Ta, Ti, V, Zr, Hf, W , U, etc. The invention can be used in the processing, disposal and decontamination of salt waste from chlorination processes of loparite and / or zircon and / or titanium concentrates.

There is a method of processing thorium-containing radioactive waste - waste from the chlorination process of loparite concentrates (Non-ferrous metals, 1993, No. 12, p.30-31; See also: Journal of Applied Chemistry, 1990, t.63, p.946. Dep. VINITI 10.10. 1989, No. 6183 - B 89). The known method consists in the sorption extraction of thorium by macroporous phosphoric acid cation exchangers of the KFP type, followed by desorption of thorium from cation exchange resin with carbonate-containing solutions, precipitation of thorium compounds from the eluate to obtain, after drying and calcination, concentrates containing 90-98% ThO ₂ for deactivation of solutions from daughter products - Ra- 228 and Ra-224 - the operation of processing the initial pulp H ₂ SO ₄ (Na ₂ SO ₄ ) and BaCl ₂ is provided (Journal of Applied Chemistry, 1990, v.63, p.946). However, as the results of special studies and tests have shown, the introduction of this operation in the “head” of the process does not provide the required degree of decontamination of solutions, and therefore additional operations of decontamination of filtrate solutions after sorption columns are required. Ultimately, this leads to the formation of a large amount of secondary radioactive waste (RW) to be disposed of in a special waste storage facility (CSW).

Known (“Method for the extraction of thorium from solutions" Application No. 9302707/26 with priority from 05/11/1993. MKI C 01 F 15/00. Publ.: Bull. No. 18. 1995, p.27) a method of processing thorium-containing radioactive waste ( See also: Radiochemistry, 1996, vol. 38, issue 1, pp. 60-65; Non-ferrous metallurgy, 1995, No. 7-8, pp. 30-33. RZhMet. 1996, ZG128), which consists in the selective extraction of thorium coprecipitation with precipitations of Ba (Ca) SO ₄ from solutions containing REE, rare, scattered, non-ferrous metals. The method involves treating the initial solution with alkali metal and / or ammonium chloride and / or hydrochloric acid to obtain a solution saturated with the total amount of metal chlorides, introducing into the solution first a water-soluble sulfate-containing inorganic compound, then a water-soluble barium salt in quantities ensuring the establishment of molar ratios SO ₄ / Ba≥1.1 and BaSO ₄ / Th≥30; separation of the radioactive residue from the solution.

The known method allows with high selectivity to extract thorium from solutions containing 0.01-0.1 g / DM ³ thorium and other metals. However, at a thorium concentration of more than 0.1 g / dm ³ , a very large consumption of barium salts and sulfate-containing inorganic compounds (Na ₂ SO ₄ ) is required, which leads to the formation of a large amount of precipitation - secondary RAW to be disposed of, while the required degree of decontamination of solutions from Ra-228 and Ra-224 are not achieved due to the adsorption and coprecipitation of thorium with the BaSO ₄ precipitate and the blocking of the surface of barium sulfate by Th ⁴⁺ ions.

Of the known analogues, the closest in combination of essential features is a method for processing thorium-containing radioactive waste, including treating solutions and / or pulps with an alkaline reagent, introducing solutions of a sulfate-containing inorganic compound and barium chloride, treating hydrated sulfate pulp with a solution containing iron chloride, and separating the radioactive deposit from solution by filtration (RU 2205461 C2, IPC G 21 F 9/30, publ. 05/27/2003, p. 1 column 1, p. 5 example 3, option 3, example 4, option 2).

The disadvantage of this method is the prototype is an unsatisfactory degree of purification - decontamination of solutions from daughter radionuclides of a series of thorium-232, in particular from Ra-224 and Ra-228, which is associated with incomplete coprecipitation of radium with precipitates of barium sulfate, calcium and metal oxyhydrates. Another disadvantage of the known method - the prototype is associated with the need for the removal of radioactive fallout in the storage of special waste (CSW), the construction and operation of which requires large capital costs.

The claimed technical solution is aimed at solving the problem of improving environmental and radiation safety.

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 fallout by increasing the degree of coprecipitation of natural radionuclides of the Th-232 series, in particular Ra-224 and Ra-228 with the fallout, as well as in localization radioactive metals (thorium and its decay products) and their conversion to a radiation-safe form - non-dusting water-insoluble solidified state, resistant to atmospheric precipitation, soil and underground water, no adverse effects on human health and the maintenance personnel and suitable for further storage without causing ecological damage to the environment.

The specified technical result in the implementation of the claimed method is achieved by the fact that in the known method of processing thorium-containing radioactive waste, including the treatment of solutions and / or pulps with an alkaline reagent, the introduction of solutions of sulfate-containing inorganic compounds and barium chloride, the treatment of hydrated sulfate pulp with a solution containing iron chloride, and separation of radioactive sludge from the solution by filtration, as an alkaline reagent is used at a concentration magnesia milk MgO 50-200 g / dm ^3, v abotku lead to pH 8-10, the sulphate solution as inorganic compounds are sodium sulfate in an amount of 6-9 g of Na ₂ SO ₄ / dm ^3, and then introduced into the slurry of barium chloride solution in an amount of 1.5-3 g VaSl ₂ / dm ³ , hydrated sulfate pulp is treated with a solution containing iron chloride in an amount of 0.8-16 g Fe ³⁺ / dm ^{3 of the} initial solution and / or pulp, treated with a high molecular weight flocculant and kept without stirring for 0.5-2 hours, radioactive the precipitate is separated from the mother liquor, washed first with 0.5-2 volumes of water per 1 about the volume of the precipitate, then with a solution and / or suspension containing magnesium chloride in an amount of 1-2 volumes per 1 volume of sediment, the radioactive precipitate from the filter is unloaded and mixed with magnesium-containing oxide mineral materials taken in an amount of 0.5-0.8 kg MgO per 1 kg of sediment, the resulting pasty composite mixture is placed in molds and / or molds and pressed while heating to 80-120 ° C.

The peculiarity lies in the fact that a suspension prepared on the basis of magnesium-containing oxide mineral materials, for example asbestos waste, is used as magnesia milk.

The peculiarity lies in the fact that pre-heat-treated natural mineral materials, industrial products and / or asbestos waste with a particle size of less than 100 microns are used as magnesium-containing oxide mineral materials.

The peculiarity lies in the fact that a solution of Na ₂ SO ₄ with a concentration of 50-200 g / dm ^{3 is} used as a sulfate-containing inorganic compound.

The peculiarity lies in the fact that as a solution of barium chloride, a solution with a concentration of 50-200 g of BaCl ₂ / dm ^{3 is used} .

The peculiarity lies in the fact that, as a solution and / or suspension of magnesium chloride, a suspension is obtained, obtained by reacting magnesium-containing oxide mineral materials, for example, asbestos waste products, with a solution of hydrochloric acid.

The peculiarity lies in the fact that, as a solution and / or suspension of magnesium chloride, the suspension formed during the purification of the exhaust gases from Cl ₂ and / or Hcl with magnesian milk is used.

The peculiarity lies in the fact that a solution with a concentration of 10-100 g of FeCl ₃ / dm ³ is used as a solution of iron chloride.

The peculiarity is that as a solution of iron chloride, workshop wastewater is used, which is formed during the washing of production sites and equipment, with an iron content of 5-2 g / dm ³ .

The peculiarity lies in the fact that as a solution of high molecular weight flocculant use a solution of polyacrylamide with a concentration of 0.01-0.2%.

Ceteris paribus, the proposed method, characterized by new methods of performing actions and a new order of actions, using certain substances, without which it is impossible to implement the method itself, 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.

An analysis of the prior art indicates that there is no information in the book, magazine and patent literature on the processing of thorium-containing radioactive waste by sequentially treating the initial solutions (pulp) first with an alkaline reagent, then with solutions of sodium sulfate, barium chloride, and then introducing into the pulp a solution containing iron chloride, filtering the pulp, washing the precipitate, first with 0.5-2 volumes of water per 1 volume of precipitate, then with a solution and / or suspension containing magnesium chloride in an amount of 1-2 volumes per 1 vol the volume of sediment, mixing the radioactive sediment with magnesium oxide mineral materials, pressing, heating and obtaining blocks.

An analysis of the totality of the features of the claimed invention and the technical 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 process of processing thorium-containing radioactive waste in the strictly defined above conditions, modes and parameters of the process: sequence of operations, availability new actions, the introduction of certain substances, defined by the ratio of reagents, and a strictly defined order of introduction of reagents provide an increase in the degree of decontamination and a decrease in the radioactivity of the filtrates after separation of the radioactive fallout by increasing the degree of co-precipitation of natural radionuclides of the Th-232 series, in particular Ra-228 and Ra-224 with hydrated, sulfate and oxysulfate precipitates, the localization of radioactive metals and their conversion to environmentally friendly form - non-dusting water-insoluble cured state, resistant to atmospheric precipitation, groundwater and subsoil water, without harmful effects on public health Nia and staff and suitable for further storage without causing environmental and radiation damage to the environment.

In violation of the above ratios of reagents, a strictly defined order of introduction of reagents, mixing modes, process conditions, 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 data on the chemistry and technology of rare and rare-earth metals.

Information confirming the implementation of the invention with obtaining the above technical result is shown in the example.

Example

The following solutions were used as solutions containing natural radionuclides for experiments: spent melts of a salt irrigation filter for the chlorination of loparite concentrates.

Solutions 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%), - dissolved in water at W: T = 4: 1. 1 dm ³ pulps were treated with magnesia milk to a pH of 9.0 ± 0.5, then 40 dm ^{3 of a} solution containing 100 g / dm ^{3 of} sodium sulfate, 25 dm ^{3 of a} solution containing 100 g / dm ³ of barium chloride were treated, followed by the pulp was injected with 0.8 dm ^{3 of a} solution containing 5 g / dm ³ Fe ³⁺ . Then the pulp was treated with a 0.1% solution of polyacrylamide, the pulp was kept without stirring for 1 hour and filtered, the radioactive precipitate was separated from the mother liquor, washed first with 1.5 volumes of water per 1 volume of precipitate, then with a solution containing 1 mg of magnesium chloride, 5 volumes per 1 sediment volume, the precipitate was mixed with magnesium-containing oxide mineral materials taken in the amount of 600 g MgO per 1 kg of precipitate, the resulting paste-like composite mixture was placed into molds and pressed while heating to 100 ° C.

Studies and tests have shown that the process of decontamination of solutions from natural radionuclides by the proposed method makes it possible to deactivate radioactive waste to established standards, and the transfer of radioactive fallout into the cured state ensures their environmentally safe storage without harming the environment, public health and staff: obtained in accordance with the proposed method, the "blocks", as shown by tests, are resistant to temperature fluctuations s medium (-50 to + 50 ° C) not raise dust, water insoluble and resistant to precipitation, soil and groundwater.

Claims (10)

1. A method of processing thorium-containing radioactive waste, including treating solutions and / or pulps with an alkaline reagent, introducing solutions of a sulfate-containing inorganic compound and barium chloride, treating the hydrated sulfate pulp with a solution containing iron chloride, and separating the radioactive precipitate from the solution by filtration, characterized in that Magnesia milk with an MgO concentration of 50-200 g / dm ³ is used as an alkaline reagent; treatment is carried out to a pH of 8-10; as a solution of sulfate-containing inorganic soy distinctions, a solution of sodium sulfate is introduced in an amount of 6-9 g of Na ₂ SO ₄ / dm ³ , then a solution of barium chloride in an amount of 1.5-3 g of BaCl ₂ / dm ³ is introduced into the pulp, the hydrated sulfate pulp is treated with a solution containing iron chloride in an amount of 0.8-16 g Fe ³⁺ / dm of the initial solution and / or pulp, treated with a high molecular weight flocculant and kept it without stirring for 0.5-2 hours, the radioactive precipitate is separated from the mother liquor, washed first with 0.5-2 volumes water per 1 volume of sediment, then a solution and / or suspension containing magnesium chloride in an amount of 1-2 volume per 1 sediment volume, the radioactive precipitate from the filter is unloaded and mixed with magnesium-containing oxide mineral materials taken in an amount of 0.5-0.8 kg MgO per 1 kg of precipitate, the resulting paste-like composite mixture is placed in molds and / or molds and pressed simultaneous heating to 80-120 ° C. 2. The method according to claim 1, characterized in that as a magnesia milk use a suspension prepared on the basis of magnesium-containing oxide mineral materials, such as asbestos production waste. 3. The method according to claim 1, characterized in that the pre-heat-treated natural mineral materials, industrial products and / or asbestos waste with a particle size of less than 100 microns are used as magnesium-containing oxide mineral materials. 4. The method according to claim 1, characterized in that a solution of Na ₂ SO ₄ with a concentration of 50-200 g / dm ^{3 is} used as a sulfate-containing inorganic compound. 5. The method according to claim 1, characterized in that a solution with a concentration of 50-200 g BaCl ₂ / dm ³ is used as a solution of barium chloride. 6. The method according to claim 1, characterized in that as the solution and / or suspension of magnesium chloride using a suspension obtained by the interaction of magnesium-containing oxide mineral materials, for example, asbestos waste products, with a solution of hydrochloric acid. 7. The method according to claim 1, characterized in that the suspension and suspension of Cl ₂ and / or Hcl with magnesian milk are used as a solution and / or suspension of magnesium chloride. 8. The method according to claim 1, characterized in that as a solution of iron chloride use a solution with a concentration of 10-100 g FeCl ₃ / DM ³ . 9. The method according to claim 1, characterized in that as the solution of iron chloride using workshop wastewater generated during washing of production sites and equipment with an iron content of 5-2 g / DM ³ . 10. The method according to claim 1, characterized in that as a solution of high molecular weight flocculant use a solution of polyacrylamide with a concentration of 0.01-0.2%.