RU2622647C1 - Method of processing processed ion exchange resins - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method for processing spent ion exchange resins involves grinding the resin grains to a particle size of not more than 500 mcm, preparing 18-22% of a suspension of ground resin in an alkali solution at a concentration of 5-50 g/l, oxidizing the slurry in the reactor by supplying air to the oxidation zone in conditions of the supercritical state of water at a temperature of 480-580°C and a pressure of 235-245 atm, the withdrawal of gaseous oxidation products in the form of water vapour, CO₂ and N₂, the removal of solid reaction products in the form of an aqueous suspension, the oxidation of solid reaction products in an additional reactor when air is supplied to the oxidation zone under supercritical water conditions at a temperature of 480-580°C and a pressure of 235-245 atm, condensation of water vapour, separation of gaseous, solid and liquid phases.

EFFECT: invention allows to reduce energy costs for grinding, to shorten the grinding time.

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Description

The invention relates to the field of processing ion-exchange resins that have exhausted their resources in the processes of ion-exchange extraction of cations and anions from water, including radionuclides at nuclear facilities. Spent ion-exchange resins (OIS) are spherical particles of a cross-linked polymer with a diameter of 0.5-1.5 mm, including those that may contain radionuclides. OICs are stored both in a dry state and in temporary storage tanks under a layer of water. OIDs containing radionuclides must be conditioned after temporary storage.

There is a method of localizing OICs in a dry or wet state by incorporating them into a solid matrix of blast furnace slag by adding sodium hydroxide with a concentration of 100-150 g / l. For good compatibility, the components should be thoroughly ground (to particle sizes less than 0.075 mm) and mixed (RU 2243162, 10.06.2004).

The disadvantage of this method is the large volume of the resulting mixture, which significantly increases the cost of permanent storage.

A known method for the joint processing of OIS and liquid radioactive waste (LRW) by mixing them, the LRW being fed to the mixture in the form of a hot bottoms at t ~ 110 ° C, perlite is added, the mixture is kept for 3-16 days until curing (RU 2384903, 11/20/2009).

The disadvantages of the method are the same - a large amount of waste coming to permanent storage, and the corresponding high cost of storage.

A known method of processing OIC, involving the reduction of the mass of the resin. For this, the OICs are mixed in a reactor with powdered metallized fuel and an oxidizing agent, an incendiary composition is added, and a polymer oxidation reaction is carried out. OIS burns in the reactor at 96-98% with the formation of a monolithic product suitable for long-term storage (RU 2114471, 06.27.1998).

The disadvantages of the method are the formation of secondary gaseous radioactive waste, which receives part of the radionuclides from the resin, as well as the high porosity of the product (up to 50%), which complicates and increases the cost of its permanent storage.

Known methods for processing OICs based on the chemical oxidation of a polymer by strong oxidizing agents at high operating temperatures.

In the method according to patent RU 2062517, 06/20/1994, nitric acid with a concentration of up to 12 M / L is used as an oxidizing agent, the process is carried out in an autoclave at a temperature of 250 ° C.

In the method according to patent RU 2412495, 02.20.2011 sulfuric acid with a concentration of up to 1700 g / l is used as an oxidizing agent, the process is carried out in an autoclave at a temperature of up to 340 ° C. The resulting product is subject to monolithic binders.

The main disadvantage of these methods is the use of aggressive reagents, the formation of a large amount of aggressive liquid waste, requiring special processing.

In the method according to US Pat. No. 5,558,783, 09/24/1996, the oxidation of various organic substances, including mixed radioactive waste, is carried out under the supercritical state of water in a single-stage process by heating the supplied oxidizing reagent to a supercritical or higher temperature.

The disadvantage of this method is the need to heat the supplied oxidizing reagent to a supercritical or higher temperature, which leads to a significant increase in the cost of the equipment necessary for this and an increase in energy consumption.

A known method of oxidizing an OIS under the conditions of a supercritical state of water, which involves wet grinding of resin grains to a particle size of 1-45 μm, alkali is added to the resulting suspension to a pH of 10.5-11.0, then liquid-phase oxidation of the suspension is carried out when air is fed into the oxidation zone in supercritical water conditions at a temperature of 450-550 ° C and a pressure of 230-250 atm, removal of gaseous oxidation products, separation of solid and liquid phases by filtration (RU 2465665, 10.27.2012).

The disadvantages of the method are the significant energy costs for thin wet grinding of resin grains to a particle size of 1-45 microns, which dramatically complicates and increases the cost of processing the resins.

The objective of the present invention is to develop an integrated method for processing OICs providing efficient processing of OICs with lower energy costs for grinding on cheaper equipment with a reduction in grinding time, without energy costs to maintain the oxidation process, without the use of aggressive chemicals when achieving a high degree of reduction in the mass of secondary waste and no toxic emissions.

The technical result consists in the efficient processing of OICs, reducing energy costs for grinding, using cheaper equipment, reducing grinding time, eliminating additional energy costs for maintaining the oxidation process, refusing to use aggressive chemicals when achieving a high degree of reduction in the mass of secondary waste and the absence of toxic emissions.

Achievable technical result is ensured by the described method of processing spent ion-exchange resins, including grinding, including wet, resin grains to a particle size of not more than 500 microns, preparation of an 18-22% suspension of ground resin in an alkali solution at a concentration of 5-50 g / l, oxidation slurry in the reactor at an intake air in an oxidation zone under conditions of supercritical water condition at a temperature of 480-580 ° C and a pressure of 235-245 atm, removal of gaseous oxidation products in the form of water vapor, CO ₂ and N _2, the withdrawal of solid products in D ktsii in the form of an aqueous slurry of solid oxidation of the reaction products in the reactor at the additional supply of air in an oxidation zone under conditions of supercritical water condition at a temperature of 480-580 ° C and a pressure of 235-245 atm, condensation of water vapor, the separation of the gaseous, solid and liquid phases.

The grinding of resin grains is carried out by a planetary mill. Grinding the initial resin to larger particles allows the use of cheaper equipment, several times lower energy costs and reduce grinding time.

When using supercritical water oxidation technology, the maximum allowable size of oxidizable particles depends on how they are fed into the reactor, their chemical properties, size and design of the reactor assembly. To ensure the completeness of oxidation of larger OIC particles, a two-stage oxidation is proposed - initially in the main supercritical water oxidation reactor (SCWO) and the subsequent oxidation of incompletely oxidized particles in an additional SCWR reactor installed on the solid particle withdrawal line from the main reactor.

Using the method of supercritical water oxidation under the stated conditions ensures the complete conversion of organic substances into harmless gaseous products of CO ₂ and N ₂ with the formation of metal oxides and hydroxides deposited in the form of solid particles. The oxidation reaction is exothermic, which allows, with a sufficient concentration of OIS in the suspension, to exclude the supply of heat from the outside, i.e. significantly reduce energy costs for processing IPOs.

The process parameters indicated in paragraph 1 are necessary and sufficient to obtain the claimed technical result.

The following is a specific embodiment of the invention.

Example

The spent ion-exchange resin of the KU-2 brand was subjected to processing after 1.5 years of its operation in the water treatment plant of the TPP. ANOVA analysis (before and after grinding) showed the following granule size distribution (see table).

Crushing of OIS was carried out in a planetary mill in the form of a suspension in a solution of NaOH at a concentration of 5 g / L. Based on the balance of energy in the oxidation of OICs, the estimated mass concentration of the suspension of OICs is 20%. The grinding process led to the following fractional composition of the OIC particles (see table).

The concentration of the solid phase (crushed OIS granules) in the suspension remained the same - 20%, the suspension was a light cream-colored mixture, which almost completely precipitated upon standing for 60 minutes.

Previously, the reactor was heated to a temperature of 540 ° C and air was pumped into it to a pressure of 225 atm. The suspension was supplied in portions of 20 ml into the main reactor of a supercritical water oxidation unit with a volume of 4.8 liters. As a result of the oxidation reaction, the pressure in the reactor increased to 240 atm, and the temperature to 565 ° C. After 30 seconds of exposure, the gaseous reaction products were withdrawn until the pressure was reduced to 225 atm, followed by condensation of water vapor. Next, the cycle of air injection and suspension feeding was repeated. After 5 cycles, the solid reaction products were withdrawn to an additional reactor heated to a temperature of 560 ° C, into which air was then supplied to a pressure of 200 atm. After 60 seconds of exposure, the gaseous reaction products were withdrawn from the additional reactor with a pressure decrease from 240 atm to 120 atm, followed by condensation of water vapor. Then, the solid reaction products were withdrawn from the additional reactor to the solid waste collector with a pressure drop of up to 40 atm.

The appearance of the suspension of solid waste is a slightly turbid fine suspension, after one hour of settling, it is transparent with a fine precipitate. Water condensate is a clear, colorless liquid. The resulting suspension is directed to filtering. The solids content during filtration is 1.6 g / l. To control the completeness of the oxidation of organic substances, the chemical oxygen demand (COD) was determined using the bichromate method. For the initial suspension, the OIS was 98.4 g / l O ₂ . For a suspension of solid waste - 28 mg / l O ₂ , for aqueous condensate - 11 mg / l O ₂ .

As can be seen from the above example, as a result of the implementation of the inventive method provided almost complete oxidation of the OIS.

As a result of the claimed method, the following types of secondary waste were obtained: sludge in the form of a finely dispersed suspension of metal oxides and a coke-like residue in a solution of sodium chloride and sulfate containing 0.8% of the dry filtered residue by weight of the initial resin weight and water condensate. The sludge can then be cemented and sent for permanent storage.

Thus, the present invention allows to obtain a technical result, which consists in processing OIC with lower energy costs for grinding on cheaper equipment with a reduction in grinding time, without energy costs to maintain the oxidation process, without the use of aggressive chemicals when achieving a high degree of reduction in the mass of secondary waste and the absence of toxic emissions.

Claims (1)

A method for processing spent ion-exchange resins, including those contaminated with radioactive elements, including grinding, including wet, resin grains to a particle size of not more than 500 microns, preparing an 18-22% suspension of the crushed resin in an alkali solution at a concentration of 5-50 g / l , oxidation of the suspension in the reactor when air is supplied to the oxidation zone under conditions of supercritical water at a temperature of 480-580 ° C and a pressure of 235-245 atm, removal of gaseous oxidation products in the form of water vapor, CO ₂ and N ₂ , output of solid reaction products to form in dispersion, oxidation of the solid reaction products in the reactor at the additional supply of air in an oxidation zone under conditions of supercritical water condition at a temperature of 480-580 ° C and a pressure of 235-245 atm, condensation of water vapor, the separation of the gaseous, solid and liquid phases.