RU2458418C1 - Method for removing transition metals and radionuclides from solutions containing complexing agent - Google Patents

Abstract

FIELD: power industry.

SUBSTANCE: method for removing transition metals and radionuclides from solutions containing complexing agent including circulation of cleaned solution through anionite, converted to shape of complexing agent, with simultaneous recovery of that agent and with its further return to the main volume of cleaned solution at maintaining optimum ranges of pH and temperature values of cleaned solution. Hydroxyethylidenediphosphonic acid is used as complexing agent. Volume distribution coefficients of trace contaminants of ions of transition metals and radionuclides between cleaned solution and anionite in the form of complexing agent and dependences of volume distribution coefficients on equilibrium pH values of cleaned solutions are determined; at that, optimum ranges of pH values of solutions are determined from dependences of volume distribution coefficients of ions of metals and radionuclides on anionite in the form of complexing agent on equilibrium pH values of cleaned solutions and maintained during cleaning in the range corresponding to maximum values of volume distribution coefficients of trace contaminants of ions of transition metals and radionuclides between cleaned solution and anionite, and temperature of solution on anionite is maintained in upper limits corresponding to rated values of anionite as to thermal stability.

EFFECT: invention allows improving sorption efficiency, enlarging the capacity of sorbents in the form of complexing agents as to metals.

3 cl, 10 tbl

Description

The invention relates to nuclear and thermal energy, in particular to sorption purification of solutions containing a complexing agent from transition metals and radioactive elements. The invention can be used in the practice of chemical decontamination and washing of equipment and circuits of nuclear power plants (NPP), for the purification of liquid radioactive waste.

The operation of nuclear power plants is accompanied by the accumulation on the internal surfaces of the first contours of radioactive contamination (RE). This leads to an increase in the dose rate of gamma radiation from the equipment, complicates the conduct of preventive maintenance. The formation of the radiation environment is caused by the processes of adsorption, sorption and coprecipitation of radionuclides formed in the coolant on the corrosion deposits of the primary circuit. The composition of radionuclides includes products of neutron activation of structural materials (CM) elements of the circuit and fission products (PD) of uranium, which enter the coolant from the surfaces and from the shells of fuel elements (TVEL) of the reactor core. Among the measures aimed at normalizing the radiation situation, improving the conditions for maintaining the water-chemical regimes of the circuits, there are decontamination, the purpose of which is to remove RE / Technologies for ensuring radiation safety at facilities with nuclear power plants: Monograph / Under total. ed. V.A. Vasilenko. - St. Petersburg: LLC "Research Center" Morinteks ", 2010, pp. 153-154, 122-129 /.

The accumulation of deposits is associated with the processes of corrosion KM. The most widely used in nuclear energy are austenitic and pearlitic steels. In addition to iron, chromium (Cr), nickel (Ni), cobalt (Co), manganese (Mn), molybdenum (Mo), titanium (Ti), niobium (Nb), and others contain metals. The content of metals in steels is different. Corrosion products (PCs) are mixed transition metal oxides (PM), which are deposited by approximately 98% on the surfaces of the circuit and AZ fuel elements. The oxides mainly include magnetite (Fe ₃ O ₄ ), magemite (γ-Fe ₂ O ₃ ), hematite (α-Fe ₂ O ₃ ). Oxides can correspond to spinel structures, for example: FeO · Cr ₂ O ₃ ; NiO · Cr ₂ O ₃ ; FeO · α-Fe ₂ O ₃ ; CoO · Fe ₂ O ₃ and others. Quantitatively, the composition of oxides is determined by iron and nickel / N.I. Ampelogova, Yu.M. Simanovsky, A.A. Trepeznikov. Decontamination in nuclear power. - M.: Energoizdat, 1982, p. 38, 76-78 /.

The resulting radionuclides are included in the structure of oxides in the form of cations: ⁶⁰ Co ²⁺ , ⁵⁸ Co ²⁺ , ⁵⁹ Fe ²⁺ , ⁵⁹ Fe ³⁺ , ⁵¹ Cr ³⁺ , ⁵⁴ Mn ²⁺ , ⁶⁵ Zn ²⁺ , etc. The main contribution to radiation doses are introduced by long-lived nuclides: ⁶⁰ Co, ⁵⁸ Co, ⁵⁴ Mn, ⁶⁵ Zn / Peak M., Segal M. Chemical decontamination of pressurized water reactors in the UK. - Nuclear technology abroad. 1984, No. 12, pp. 26-27 /.

The greatest effects on reducing the dose rate levels of ionizing radiation from nuclear power equipment are achieved using chemical decontamination processes, when REs are removed from surfaces by dissolving PC deposits, for which solutions of mineral, organic, complexing acids (complexones) and their salts are used. The effectiveness of chemical action on oxides is increased by introducing reducing or oxidizing agents into acidic solutions. Among the characteristics of solutions, iron intensity or the maximum concentration of iron retained in solutions are distinguished, since iron determines the composition of PC, as well as the stability or stability of the compounds of metal cations (Me) with anions or ligands (L) of acids. The stability of MeL compounds in solutions is characterized by instability constants (pK), defined as negative decimal logarithms of the ratio of the product of concentrations of metal ions [Me] and ligands [L] to the concentration of compounds [MeL] formed in solutions.

The larger the pK value, the more stable the MeL compound in solution.

Long-term studies aimed at finding solutions of reagents with greater iron intensity and stability of MeL compounds have shown the advantages of using complexon solutions. Anions of complexing agents form more stable compounds with PM cations in comparison with anions of mineral (nitric, phosphoric) and organic (acetic, oxalic, citric) acids. The difference in stability reaches 10-15 orders of magnitude / N.I. Ampelogova, Yu.M. Simanovsky, A.A. Trapeznikov. Decontamination in nuclear power. - M.: Energoizdat, 1982, p. 123-130, Table 9.5 p. 126 /.

Monoamine and polyamine complexones of an aliphatic series with carboxyl groups, primarily ethylenediaminetetraacetic acid (EDTA) and solutions based on it, have found the greatest application in the dissolution of PC oxides. The stability of the compounds of metal cations with complexones (metal complexonates), the forms of complexonates depend on the pH of the solutions, the presence of other reagents in the solutions, etc. / N.M. Dyatlova, V.Ya. Temkina, K.I. Popov. Complexones and complexonates of metals. M .: "Chemistry", 1988, pp. 99-105, 456-458 /.

Regardless of the composition of the solutions, chemical decontamination technologies include: introducing reagent solutions into the primary circuit; ensuring their circulation, chemical, thermophysical parameters of the processes of dissolution of PC and RE; withdrawal of spent solutions; bringing the quality of the water in the circuit to standardized cleanliness indicators. The "underwater" stone of decontamination is their final stage. The solution commonly used in technology is the drainage of waste solutions. At the same time, their circulation is stopped. Drainages take a considerable time, during which suspensions of PCs with radionuclides are deposited in separate areas, especially dead ends. Subsequent filling of the NPP circuits with high purity water (VHF) to dilute the residual solutions, resuming circulation to mix them, repeating the drains to bring the water quality to purity standards, cannot ensure the effective removal of settled sediment / V.M.Sedov, A.F. Nechaev, V.A. Doilnitsyn, P.G. Krutikov. Chemical technology of coolants of nuclear power plants. - M .: Energoatomizdat, 1985, p. 264-266 /. This leads to a deterioration in the results of lower levels of RE. Mass transfer of PC suspensions along the circuit when the nuclear power plant is brought to power after deactivation can lead to a decrease in the coolant flow rate in the reactor and, as a result, to temperature anomalies in the AZ / N.I. Ampelogova, Yu.M. Simanovsky, A.A. Trapeznikov. Decontamination in nuclear power. - M.: Energoizdat, 1982, p .98-199 /.

A disadvantage of technologies in which solutions are drained is the formation of large volumes of highly active liquid radioactive waste (LRW). They are subject to collection, further processing in order to clean from the RE, localization of radionuclides in forms suitable for storage in the form of solid radioactive waste (SRW). Since all stages of processing require significant costs, reducing the volume of LRW is recognized as one of the priority areas for improving nuclear decontamination technologies / Decontamination of Nuclear Facilities to Permit Operation, Inspection, Maintenance, Modification or Plant Decommissioning. International Atomic Energy Agency, Vienna, 1985. Technical Reports Series, No. 249, page 41-43 /.

It was repeatedly noted that a decrease in LRW volumes during nuclear power plant deactivation is possible when solutions are cleared of reagents, metals and radionuclides on ion-exchange filters. The implementation of this approach requires consideration of both the properties of the reagents and the characteristics of the dissolution of the PC. If you select and justify the forms of ion exchangers that can effectively remove PM and radionuclides during the dissolution of PCs, the volumes of LRW discharges and their volumetric activity can be significantly reduced /J.A.AYRES. DECONTAMINATION OF NUCLEAR REACTORS and EQUIPMENT. THE RONALD PRESS COMPANY. NEW YORK, 1970, page 568-571 /.

The selection of filter loading for solving such problems depends on the nuclear power plant decontamination technologies that regulate the requirements, which are justified in the laboratory, and then specified in an industrial environment. First of all, these include the compositions (formulations) of solutions that should effectively dissolve PCs with allowable corrosion losses of CM. Reagent concentrations, pH values of solutions, their allowable ranges are important. They affect sorption processes. In domestic practice, nuclear-grade ion-exchange resins are used to clean water coolants: strongly acidic cation exchanger KU-2-8 hS; strongly basic anion exchange resin AB-17-8 hS. Analogs of these gel ion exchangers are AMBERLIGHT-IRN77 cation exchanger, AMBERLITE-IRN78 anionite / V. M. Sedov, A. F. Nechaev, V. A. Doilnitsyn, P. G. Krutikov. Chemical technology of coolants of nuclear power plants. - M .: Energoatomizdat, 1985, pp. 132-133 /.

Given the wide variety of chemical formulations, the forms of MeL compounds in solutions, today there are no unambiguous solutions for choosing filter loads, ion exchangers and their forms, applicable for all technologies. Even for the same solutions, recommended downloads often vary significantly. Examples of the use and study of the processes of sorption removal of PM from solutions and coolants are known.

So, in order to reduce LRW volumes and clean coolants to norms, sorption methods are used at the end of nuclear power plant deactivation. The removal of PM and sludge is carried out on mechanical and ion-exchange filters, or only ion-exchange, after drains and a decrease in the salt content of solutions in the circuit to 1 g / l or less / V.M.Sedov, A.F. Nechaev, V.A. Doilnitsyn, P .G. Krutikov. Chemical technology of coolants of nuclear power plants. - M .: Energoatomizdat, 1985, p. 267 /. This allows you to reduce the volume of LRW, but is not a fundamental solution to the problems associated with the conduct of drainage.

When deactivating baskets for transporting fuel assemblies, solutions of mineral acids HNO ₃ + HF with concentrations of 0.5-1.0 and 0.05% by weight. To remove metals (Fe, Cr) and radionuclides from solutions, strongly acid cation exchange resin in the H ⁺ form is used. The purification of the solutions is combined with the dissolution of RE / AAMIR HUSAIN. A process for decontaminating stainless steels to release limits. - Nuclear technology, vol. 85, apr. 1989, page 66-73 /.

From solutions of organic oxalic acid (H ₂ C ₂ O ₄ ), which is widely used in the decontamination of nuclear power plants, ⁶⁰ Co, nickel and mono-, divalent cations of other radionuclides are effectively sorbed by KU-2 cation exchanger in the H ⁺ form. At the same time, trivalent iron and chromium cations are mainly sorbed on anionite AB-17 / N.I. Ampelogova, Yu.M. Simanovsky, A.A. Trapeznikov. Decontamination in nuclear power. - M.: Energoizdat, 1982, pp .98-200, 206 /.

For cleaning solutions containing a complexing agent obtained by deactivating the reactor loop in IAE I.V. Kurchatova, used separate layers of sulfonated coal and ion exchangers: KU-2 in the H ⁺ form, AB-17 in the OH ^- form. Decontamination was carried out with a solution of EDTA and citric acid with agent concentrations of 2 and 1 g / l at an initial pH of 3.0. It was shown that sorption of iron from solutions occurs mainly on cation exchange resin and, to a lesser extent, on anion exchange resin / T.Kh. Margulova. The use of complexones in the power system. - M .: Energoatomizdat, 1986, p. 241 /.

Known are the results of studies of the sorption of iron from condensate in the presence of Trilon B (a disubstituted sodium salt of ethylenediaminetetraacetic acid) on anion exchange resin AB-17-8 hC. The capacity of anion exchange resin for iron complexonate was estimated at 4.8 g / l, and for EDTA from 100 to 120 g / l / T.Kh. Margulova. The use of complexones in the power system. - M.: Energoatomizdat, 1986, pp. 229-230 /.

The CAN-DECON loop decontamination process developed for nuclear power plants with a heavy water coolant, including sorption purification of solutions containing ethylenediaminetetraacetic, citric, and oxalic acids, was widely used. The total concentration of acids corresponds to 1-2 g / l. Upon decontamination, the solutions are purified on ion exchangers for the regeneration of reagents. Filter loading includes cation exchange resin (90%) and anion exchange resin (10%) / Alexander P. Murray. Modeling nuclear decontamination processes. - Nuclear Technology, vol. 77, may 1987, page 197 /.

In practice, it was found that EDTA, which forms strong complexes with PM, including Fe ³⁺ , is reluctant to give them to cation exchange resin, which leads to an increase in the concentration of iron in solution. The pH of the solution increases, which worsens the conditions for the binding of Fe ³⁺ to the complex with EDTA, since the acidic environment is optimal for this process / N.M. Dyatlova, V.Ya. Temkina, K.I. Popov. Complexones and complexonates of metals. M .: "Chemistry", 1988, pp. 457-458 /. This necessitates dosing an additional amount of EDTA into the circuit, which does not exclude the precipitation of complexon, poorly soluble in water, in dead ends and complicates the final cleaning of the coolant.

A method for removing PM from solutions containing a complexing agent having an equilibrium constant with Fe ³⁺ ions above 10 ²² (or an instability constant greater than 22), which consists in using an anion exchange resin with this complexing agent or its salt, and circulate the purified solution through such an anion exchange resin / EP No. 0135276. A method for removing transition metals from solutions containing a complexing agent. Westinghouse Electric Corporation, 1983, paragraph 1 of the formula /. This method is the closest to the claimed and adopted as a prototype.

The method uses anion exchange resin converted to a complexing agent, which is ethylenediaminetetraacetic acid or an alkali metal salt of an acid (claim 2). Requirements for the type of ion exchange resin are not presented. The description of the method indicates that any anion exchange resin is suitable for using the method. Anion exchange resin is converted into a complexing agent by passing EDTA salt solution through it until the pH of the resulting solution is less than 6.0 (paragraph 3 of the formula). The transition metal removed on such an anion exchange resin is ferric ion (paragraph 4 of the formula). The temperature of the solution is maintained in the range from 40 to 100 ° C (paragraph 5 of the formula). The lower temperature limit is justified by the poor solubility of EDTA. Its violation can lead to the loss of complexon from the solution on the surfaces of the circuit, which is undesirable. The EDTA solution also contains citric and oxalic acid (paragraph 6 of the formula). The pH of the cleaned solutions, as indicated in the description of the method, is not significant. It is noted that usually it corresponds to a range from 2 to 2.5 for most decontamination solutions, due to the acidity of the reagents.

The disadvantages of the prototype method are as follows.

1. Anion-exchange resin, converted into the form of ethylenediaminetetraacetic acid (paragraphs 2 and 3 of the formula), allows you to remove only Fe ³⁺ ions from solutions (claims 1 and 4 of the formula), but does not allow you to remove Fe ^{2+ ions} from the reducing solutions.

It was previously found that the sorption of Fe ^{2+ ions} on anion exchangers in the EDTA form is impossible, since it is accompanied by gas evolution and rupture of the sorbent column. This is associated with an increase in the reducing ability of Fe ^{2+ ions} in the phase of this form of anion exchange resin, which leads to the decomposition of water / V.M.Sedov, A.F. Nechaev, V.A. Doilnitsyn, P.G. Krutikov. Chemical technology of coolants of nuclear power plants. - M .: Energoatomizdat, 1985, p. 258 /.

At the same time, the use of reduction potentials of metal ions in a low oxidation state underlies a number of modern “low-concentration” processes for the decontamination of nuclear power circuits. Their abbreviation adopted by the IAEA classification is “LOMI” (low oxidation metal ion). Technologies developed in the UK and have been widely used since the 80s of the last century. The main reagents of the solutions are a complexing agent and a metal ion in a low oxidation state, which is used as a reducing agent that increases the dissolution efficiency of PC. Use divalent ions of vanadium, chromium, iron / Peak M., Segal M. Chemical decontamination of water-cooled reactors in the UK. - Nuclear technology abroad. 1984, No. 12, pp. 30-31 /. Accordingly, the effective sorption removal of metal ions in a low oxidation state, including Fe ²⁺ , from solutions of complexing agents is one of the urgent problems associated with the improvement of decontamination technologies that cannot be solved by the prototype.

2. The second disadvantage of the prototype is the limitation associated with the pK values of complexes with PM. The method is applicable for the removal of metal ions, the instability constant of which with a complexing agent is higher than 22 (paragraph 1 of the formula).

From data on instability constants / N.I. Ampelogova, Yu.M. Simanovsky, A.A. Trapeznikov. Decontamination in nuclear power. - M .: Energoizdat, 1982, pp. 123-130, Table 9.5, p. 126 / it follows that anion exchange resin in the EDTA form will not effectively sorb Co ²⁺ , Ni ^{2+ ions} , the pK values of which with EDTA are determined values of 16.31 and 18.62, which is lower than 22. Moreover, it was found that radionuclides ⁶⁰ Co, ⁵⁸ Co largely determine the activity of deposits of PC and, therefore, solutions during decontamination, and nickel is one of the elements that determines the composition of loose PC in the circuits / Peak M., Segal M. Chemical decontamination of pressurized water reactors in the UK. - Nuclear technology abroad. 1984, No. 12, pp. 26-27 /.

The very determination of the instability constants of metal complexes is a separate and complex task. The pK values depend on many factors, including the composition of solutions and pH values. The stability of the complexes is affected by the presence in solutions of guest ligands accompanying the main host ligand (in the prototype EDTA). As "guests" use citric, tartaric and other acids. As a result, the values of the instability constants of metal complexonates obtained by different researchers differ significantly from each other. Thus, the known pK values for ethylene diamine tetraacetate Cr ³⁺ , namely 23.0 and 12.8, differ by 10 orders of magnitude (10 ¹⁰ ) / N.M. Dyatlova, V.Ya. Temkipa, K.I. Popov. Complexones and complexonates of metals. M .: "Chemistry", 1988, pp. 100-101, 104 /.

3. The disadvantages of the prototype is the low adaptability of the preparation of anion exchange resin for sorption of PM. To transfer the resin to the EDTA form, it is recommended that a two-substituted EDTA sodium salt, Trilon B, be passed through it (paragraph 3 of the formula). This is due to the low solubility of EDTA in water. At 20 ° C it is 283 mg / l, and at temperatures from 60 to 70 ° C it is from 1.2 to 2.0 g / l / N.M. Dyatlova, V.Ya. Temkina, K.I. Popov . Complexones and complexonates of metals. M .: "Chemistry", 1988, pp. 122-123 /. The capacity, for example, of anion exchange resin AB-17 - 8 hC according to EDTA is from 100 to 120 g / l / T.Kh. Margulova. The use of complexones in the power system. - M.: Energoatomizdat, 1986, pp. 229-230 /. Considering the capacity of the ion exchanger and the solubility of EDTA, at least 430 liters of complexon solution must be passed through it to prepare 1 liter of resin at 20 ° C. The use of the disubstituted sodium salt of EDTA (Trilon B), the solubility of which is higher and is 108 g / l at 20 ° C, slightly improves the preparation process, which follows from example 1 of the prototype. At the same time, 30-40 liters of ion exchangers are required for cleaning solutions during nuclear power plant decontamination per 1 m ³ of the circuit volume / Peak M., Segal M. Chemical decontamination of pressurized water reactors in the UK. - Nuclear technology abroad. 1984, No. 12, p. 33 /. The volumes of industrial NPP circuits range from hundreds to thousands of cubic meters. Given the low manufacturability of the preparation of anion exchange resin in the EDTA form, the preparation of the required amounts of anion exchange resin requires special technological systems and considerable time.

4. Another disadvantage of the prototype is the instability of the regeneration of the complexing agent in the cleaned solution during the removal of PM ions.

When passing through anion exchange resin in EDTA form containing a solution of Fe ³⁺ , oxalic, citric and ethylenediaminetetraacetic acids, acid concentrations and their ratios in the solution after the filter are constantly changing. Oxalic acid and partially citric acid are adsorbed on the anion exchange resin, and EDTA is washed off (prototype example 3). Thus, in the solution after the filter, designed for the following acts of dissolution of PC and RE, the ratio of the concentration of the ligands of “guests” and “host” changes and is unstable, which affects the stability of PM complexes with EDTA and the dissolution conditions of PC / N.M. Dyatlova, V.Ya. Temkina, K.I. Popov. Complexones and complexonates of metals. M .: "Chemistry", 1988, pp. 100-101, 104 /.

The objective of the present invention is to provide a method for removing transition metals and radionuclides from solutions containing a complexing agent on ion exchangers, allowing:

- increase the efficiency of sorption of transition metals and radionuclides from solutions containing complexing agents;

- expand the range of transition metal ions and radionuclides that can be removed from solutions containing various complexing agents on ion-exchange resins in the process of decontamination of NPP circuits;

- to provide the ability to effectively remove transition metal ions and radionuclides from solutions of complexing agents, additionally containing reducing agents;

- expand the pH range of solutions that meets the conditions for the effective removal of PM and radionuclides from solutions containing complexing agents;

- increase the capacity of the form of anion exchange resin on the main, exhausting the capacity of the ion exchanger sorbate, respectively, increase the efficiency of regeneration of complexing agents in solutions during their purification from transition metals and radionuclides during deactivation.

To solve the problem and achieve the technical results in a method of removing transition metals from solutions containing a complexing agent, including circulation of the solution to be purified through anion exchange resin, previously converted into the form of a complexing agent, with the simultaneous regeneration of this agent and its subsequent return to the main volume of the solution to be purified at maintaining optimal ranges of pH and temperature of the solution being cleaned, it is proposed:

- as a complexing agent for the modification of anion exchange resin, use one of the complexones with phosphonic groups — alkyl diphosphonic complexone, namely hydroxyethylidene diphosphonic acid (OEDP);

- determine the volumetric distribution coefficients of microimpurities of transition metal ions and radionuclides between the solution to be cleaned and the anion exchange resin in the form of a complexing agent and the dependence of the volume distribution coefficients on the equilibrium pH values of the solutions to be purified;

- the optimal range of pH values of solutions is determined from the dependences of the volume distribution coefficients of metal ions and radionuclides on the anion exchange resin in the form of a complexing agent on the equilibrium pH values of the solutions to be cleaned and maintained during the cleaning process in the range corresponding to the maximum values of the volume distribution coefficients of microimpurities of transition metal ions and radionuclides between the cleaned solution and anion exchange resin;

- maintain the temperature of the solution on the anion exchange resin in the upper limits corresponding to the passport data of the anion exchange resin for heat resistance;

- as the anion exchange resin, which is converted into the form of a complexing agent, use strongly basic anion exchange resin in the OH ^- form.

The use of HEDP for ion exchange purification of solutions containing various agents, including complexing agents, from transition metals and radionuclides has not been previously studied and has not been studied. Ethylenediaminetetraacetic acid used in the prototype is a polyamine complexone and refers to complexones with carboxyl groups / N.M. Dyatlova, V.Ya. Temkina, K.I. Popov. Complexones and complexonates of metals. M .: "Chemistry", 1988, p. 122 (EDTA) and p. 204 (OEDF) /.

The inventive method of removing transition metals and radionuclides from solutions containing complexing agents on anion exchange resin in the form of an alkyl diphosphonic complexon, for example, HEDP, is carried out as follows.

Previously, in laboratory conditions, the indicators of sorption removal of PM cations and radionuclides from solutions are determined:

- volume distribution coefficients (K _p ) of microimpurities of metal ions between the cleaned solutions and forms of ion exchangers and the dependence of K _p on the chemical composition and the equilibrium pH values of the cleaned solutions;

- the optimal range of pH values of solutions from the dependences of the volumetric distribution coefficients of metal ions and radionuclides on the anion exchange resin in the form of a complexing agent on the equilibrium pH values of the solutions to be purified, corresponding to the maximum values of the volumetric distribution coefficients of microimpurities of transition metal ions and radionuclides between the solution to be treated and the anion exchange resin;

- the exchange capacity of the forms of ion exchangers in relation to the main, exhaustive capacity of the ion exchanger sorbate.

In the prototype method, these characteristics were not considered and not defined.

The values of volume distribution coefficients allow us to estimate the volumes of solutions that can be maximally passed through an ion exchanger before the elution (washing off) of elements previously sorbed on the ion exchanger. The more K _p , the greater the volume of solutions can be passed through the ion exchanger before the start of elution. The volume distribution coefficient is related to the volume of the eluent, corresponding to the maximum of the elution curve, by the ratio:

- объем раствора, отвечающий максимуму кривой элюирования;Where

- the volume of solution corresponding to the maximum of the elution curve;

V _eff - effective filter load;

To _p - volume distribution coefficient of the element;

ε is the fraction of the free volume of the filter / O. Samuelson. Ion exchange separation in analytical chemistry. Chemistry Publishing House, Moscow, 1966, Leningrad, p. 120-121 /.

To determine K _p you can use one of the methods with the use of radioactive indicators, which is as follows. Prepare solutions with predetermined concentrations of reagents and various initial pH values. PH adjustment is carried out by alkaline agents. One of the labels of radionuclides ⁵⁹ Fe, ⁵¹ Cr, ⁶⁰ Co is introduced into the solutions and the initial activity is determined. Then, the swollen resin in the test form is added to the solutions. Under static conditions, the solution is kept with the ion exchanger until the radionuclides balance between them, stabilizing the activity of the solutions. Fix the equilibrium pH and activity of the solutions. The volume distribution coefficient (K _p ) of trace metal ions between the solution and the ion exchanger is calculated by the formula:

where N ex., N equ. - the initial and equilibrium activity of the solution according to the corresponding radionuclide, imp./min · ml; V resin, V solution - the volume of resin and solution, ml.

The plots of the dependence of the volumetric distribution coefficients of microimpurities of transition metal ions and radionuclides on the anion exchange resin in the form of a complexing agent on the equilibrium pH values of the purified solutions are constructed.

Based on the dependencies, the optimal pH range of the solutions to be removed is determined to remove PM metals and radionuclides from them, which corresponds to the maximum values of the volume distribution coefficients of microimpurities of PM ions and radionuclides between the solution to be purified and anion exchange resin.

To determine the capacity of the forms of ion exchanger, it is kept in a solution with a known concentration of iron. The capacity is calculated by the difference in the concentrations of impurities in the solution before and after the establishment of ion-exchange equilibrium between them according to the equation:

where SOE is the sorption capacity of the ion exchanger by impurity, g / l of ion exchanger;

C ₁ and C ₂ - the initial and final concentration of the impurity, g / l;

V is the volume of the solution in contact with the ion exchanger, l; V _IONITE - the volume of swollen ion exchanger, l.

Before cleaning the solutions, the anion exchange resin is converted into the required form. The authors of the proposed method experimentally found that the most effective sorption of PM and radionuclides on ion exchangers in the form of complexones occurs when using strongly basic anion exchangers, for example, anion exchangers AB-17-8 hC, AMBERLIGHT-IRN78. The conversion of anion exchangers into the form of alkyl diphosphonic complexones, for example, HEDP, can be carried out under dynamic or static conditions: in the first case, passing a concentrated HEDP solution through a layer of anion exchange resin in the OH ^- form until the pH of the solution flowing from the column (eluate) is equal to pH stock solution (eluent); in the second, introducing a concentrated HEDP solution into the above commercial water above the layer of anion exchange resin in the OH ^- form and keeping the ion exchanger until the pH value stabilizes above the commercial water.

Given the high solubility of HEDP (up to 600 g / l at 20 ° C) / N.M. Dyatlova, V.Ya. Temkina, K.I. Popov. Complexones and complexonates of metals. M .: "Chemistry", 1988, pp. 206-207 /, translation in static conditions is more simple and convenient. The swollen strongly basic anion exchange resin in the OH ^- form is washed several times with VHF. By introducing a portion of OEDP into a known volume of VHF, a concentrated OEDP solution is prepared. Based on the obtained concentration of complexon, the volume of solution required to convert the anion exchange resin into the form of complexon is calculated. When carrying out the calculation, the complexion anionite capacity is taken into account. For example, for AB-17-8 hC, it was experimentally determined by the authors as ~ 97.5 g of HEDP per liter of swollen ion exchanger. The calculated volume of the HEDP solution in portions (to exclude excessive heating of the resin) is added to the anion exchange resin with stirring over stirring water. Anion exchange resin is kept in solution. The pH of the solution over the ion exchanger is periodically monitored. After stabilization of the pH of the solution in the acidic region (~ 2 ÷ 3), the form of anion exchange resin is ready for use. The exposure time does not exceed several (1 ÷ 3) hours.

Anion exchange resin in the HEDP form is loaded into an ion-exchange column (filter). A solution containing a complexing agent and a transition metal ion, for example, Fe ³⁺ or Fe ²⁺ (in the case of a solution reducing medium) is purified on anion exchange resin, and the solution is heated to temperatures corresponding to the upper limits of the passport data of the anion exchange resin on heat resistance. For example, for anion exchange resin AB-17-8 hС up to 60-70 ° С / Ionites. Anionites. Specifications - OST 95 291-86 /. A part of the solution is circulated from the volume to be cleaned, for example, the NPP circuit, through a filter with the return of the eluate (filtrate) after it to the volume of the circuit (bypass cleaning). The linear rate of filtration of solutions is maintained in the range recommended for sorption processes (optimally from 15 to 25 m / h).

During the cleaning process, the pH of the solution to be cleaned and the concentration of PM removed from the solution are periodically monitored in the circuit. The pH of the solution in the circuit should correspond to the range of maximum values of the volume distribution coefficients of the distribution of PM ions between the ion exchanger and the solution. For the sorption of Fe ³⁺ , Fe ²⁺ , Co ²⁺ , Cr ³⁺ on AB-17-8 hC in the HEDP form from solutions containing HEDP, the optimal pH range was determined by the authors from 2.5 to 6.0. If the pH of the solution deviates from the optimal range, it is adjusted by introducing an alkaline agent or acid into the circuit, which can be used as a concentrated OEDP solution.

Purification of the solution is completed at the beginning of elution from the filter of previously sorbed transition metal ions that maximize the capacity of the anion exchange resin in the form of a complexing agent, as the concentration of these transition metals in the solution being cleaned (before the filter) becomes equal to the concentration of metals after the filter. In the case of dissolution of PC oxides formed in an aqueous coolant on the surfaces of austenitic and pearlitic steels, iron is such a transition metal. When dissolving the oxides of titanium or zirconium with sorbates that maximize the capacity of the anion exchange resin, titanium or zirconium will be, respectively. The amount of anion exchange resin necessary for the complete removal of a metal ion from solutions of known volume is determined from the PM anionite capacity and the expected maximum concentration of sorbate upon dissolution of mixed transition metal oxides. For iron ions, the static exchange capacity of AB-17-8 hC in the HEDP form was determined by the authors with an average value of 17.5 g / l, and dynamic - by ~ 15 g / l.

The advantages of the inventive method are illustrated by experimental data obtained in laboratory conditions to determine the main indicators characterizing the possibility of sorption processes for the removal of PM cations and radionuclides from solutions containing complexing agents on anion exchangers in the form of complexing agents for the prototype method and the claimed.

Examples of the proposed method and its comparison with the prototype method.

Tables 1, 2, 3 show the data on volume distribution coefficients (K _p ) of microimpurities of Fe ³⁺ , Cr ³⁺ , Co ²⁺ cations from solutions containing EDTA, citric and oxalic acid on anion exchange resin in the form of EDTA, obtained by the authors for prototype method.

Tables 4, 5, 6, 7 show the data on the volume distribution coefficients (K _p ) of microimpurities of Fe ³⁺ , Cr ³⁺ , Co ²⁺ cations, as well as Fe ²⁺ from solutions containing HEDP, on anion exchange resin in the form of HEDP for the proposed method.

Test conditions: static, T = 20 ÷ 25 ° C, V _solution = 100 ml, V _resin = 2 ml. The pH values of the EDTA solutions were adjusted by introducing ammonia (NH ₄ OH), HEDP solutions by introducing ammonia or, when studying the sorption of Fe ^{2+ ions} , hydrazine (N ₂ H ₄ ) and ammonia. To prepare the forms of ion exchangers we used gel strongly basic anion exchange resin of the AB-17-8 hC grade in the OH ^- form. Translation of the anion exchange resin in the form of EDTA was carried out under dynamic conditions with a solution of Trilon B according to paragraph 3 of the formula of the prototype method. The transfer of anion exchange resin into the OEDP form was carried out under static conditions.

Table 1 Prototype method. _P ⁵⁹ K Fe ³⁺ ions on the anion trace AB-17-8 emergencies in EDTA-form depending on the pH of the composition equilibrium quantities solutions g / L: EDTA + 1.4 1 ₃ H Cit + 1 H ₂ C ₂ O ₄ (CAN-DECON process solution - initial solution). No. p / p Solution composition pH ref. pH equal to Lg K _p one Starting + NH ₄ OH 3.45 3,50 2.68 2 Starting + NH ₄ OH 4.45 4.10 2.20 3 Starting + NH ₄ OH 5.37 4.89 1.30 four Starting + NH ₄ OH 6.27 5.54 0.90 5 Starting + NH ₄ OH 7.87 6.06 0.15

table 2 Prototype method. K _p trace ⁶⁰ Co ²⁺ ions on the anion AB-17-8 emergencies in EDTA-form depending on the pH of the composition equilibrium quantities solutions g / L: EDTA + 1.4 1 ₃ H Cit + 1 H ₂ C ₂ O ₄ (CAN-DECON process solution - initial solution). No. p / p Solution composition pH ref. pH equal to Lg K _p one Source 2.82 3.07 1.14 2 Starting + NH ₄ OH 3.35 3.45 1.12 3 Starting + NH ₄ OH 3.85 3.96 0.99 four Starting + NH ₄ OH 4.40 4.72 1.05 5 Starting + NH ₄ OH 5.03 5.27 0.95 6 Starting + NH ₄ OH 6.18 6.08 0.92 7 Starting + NH ₄ OH 7.88 6.70 0.67 8 Starting + NH ₄ OH 8.63 8.04 0.84

Table 3 Prototype method. K _p trace ⁵¹ Cr ³⁺ ions on the anion AB-17-8 emergencies in EDTA-form depending on the pH of the composition equilibrium quantities solutions g / L: EDTA + 1.4 1 ₃ H Cit + 1 H ₂ C ₂ O ₄ (CAN-DECON process solution - initial solution). No. p / p Solution composition pH ref. pH equal to Lg K _p one Source 2.82 3.06 1,60 2 Starting + NH ₄ OH 3.35 3.38 1.77 3 Starting + NH ₄ OH 3.85 3.84 1.75 four Starting + NH ₄ OH 4.40 4,56 1,53 5 Starting + NH ₄ OH 5.03 5.14 1,52 6 Starting + NH ₄ OH 6.18 6.00 1.12 7 Starting + NH ₄ OH 7.88 6.55 1,62 8 Starting + NH ₄ OH 8.63 7.86 1.23

Table 4 The inventive method. K _p trace ⁵⁹ Fe ³⁺ ions on the anion AB-17-8 Disaster HEDP-form depending on the pH values of equilibrium composition of the solutions in g / l: 2.0 HEDP (stock solution). No. p / p Solution composition pH ref. pH equal to Lg K _p one Source 2.12 2.10 4,50 2 Starting + NH ₄ OH 3.70 2.96 4.95 3 Starting + NH ₄ OH 5.90 3.21 4.66 four Starting + NH ₄ OH 7.34 4.23 4.88 5 Starting + NH ₄ OH 8.10 5.23 4.77 6 Starting + NH ₄ OH 8.88 6.55 4.86 7 Starting + NH ₄ OH 9.80 9.31 1.20

Table 5 The inventive method. K _p trace ⁶⁰ Co ²⁺ ions on the anion AB-17-8 Disaster HEDP-form depending on the pH values of equilibrium composition of the solutions in g / l: 2.0 HEDP (stock solution). No. p / p Solution composition pH ref. pH equal to Lg K _p one Source 2.62 2,50 2.70 2 2 g / l HEDP + N ₂ H ₄ 4,55 3.12 2.77 3 2 g / l HEDP + N ₂ H ₄ + NH ₄ OH 6.57 3.33 2.70 four 2 g / l HEDP + N ₂ H ₄ + NH ₄ OH 7.35 4.82 2.97 5 2 g / l HEDP + N ₂ H ₄ + NH ₄ OH 8.00 6.34 2.79 6 2 g / l HEDP + N ₂ H ₄ + NH ₄ OH 8.25 6.60 2.70 7 2 g / l HEDP + N ₂ H ₄ + NH ₄ OH 9.60 8.83 1.73

Table 6 The inventive method. K _p trace ⁵¹ Cr ³⁺ ions on the anion AB-17-8 Disaster HEDP-form depending on the pH values of equilibrium composition of the solutions in g / l: 2.0 HEDP (stock solution). No. p / p Solution composition pH ref. pH equal to Lg K _p one Source 2.20 1.97 1.20 2 Initial + 0.60 g / l N ₂ H ₄ 4.05 2.72 2.00 3 Initial + 0.60 g / l N ₂ H ₄ + NH ₄ OH 6.80 2.95 3.40 four Initial + 0.60 g / l N ₂ H ₄ + NH ₄ OH 7.40 3.42 4.16 5 Initial + 0.60 g / l N ₂ H ₄ + NH ₄ OH 7.54 5.65 4.10 6 Initial + 0.60 g / l N ₂ H ₄ + NH ₄ OH 8.82 6.52 3.70 7 Initial + 0.60 g / l N ₂ H ₄ + NH ₄ OH 8.14 6.58 3.65 8 Initial + 0.60 g / l N ₂ H ₄ + NH ₄ OH 8.72 7.20 2.70

Table 7 The inventive method. K _p trace ⁵⁹ Fe ²⁺ ions on the anion AB-17-8 Disaster HEDP-form depending on the equilibrium pH of the solution containing the HEDP, hydrazine hydrate, ammonia. No. p / p The composition of the solution, g / l pH ref. pH equal to Lg K _p one 5 OEDP + 1.9 N ₂ H ₄ -H ₂ O 3.23 2.78 3.80 2 5 HEDP + 1.9 N ₂ H ₄ · H ₂ O + NH ₄ OH 6.78 4.49 3.60 3 5 HEDP + 1.9 N ₂ H ₄ · H ₂ O + NH ₄ OH 7.11 5.73 3.20 four 5 OEDP + 2.4 N ₂ H ₄ · H ₂ O + NH ₄ OH 7.09 6.03 3.20 5 5 HEDP + 1.9 N ₂ H ₄ · H ₂ O + NH ₄ OH 7.50 6.32 2,30 6 5 OEDP + 2.4 N ₂ H ₄ · H ₂ O + NH ₄ OH 7.96 6.97 1,50 7 2.5 OEDP + 1.2 N ₂ H ₄ · H ₂ O 6.00 3.15 3.95 8 1 OEDP + 0.4 N ₂ H ₄ · H ₂ O 4.49 3.21 3.85

The differences in the oxidation states of iron cations in Tables 1, 4, 7 are explained by the fact that they correspond to the redox potential of the media from which iron is adsorbed.

Table 8 shows the experimental data on the determination of SOE of anion exchanger AB-17-8 hC in the HEDP form by iron from solutions containing HEDP. Test conditions: static, V solution = 100 ml, V ion exchanger = 2 ml.

Table 8 The inventive method. Change in iron concentration in composition solutions, g / l: 5 OEDPK + 2.2 N ₂ H ₄ · H ₂ O + NH ₄ OH in contact with anion exchange resin AB-17-8 hC in OEDP form from the equilibrium pH and temperature of solutions . pH ref. T, ° С C _Fe , ref., Mg / l The contact time of the solutions with the ion exchanger (hour), the concentration of Fe in the solution (mg / l). pH equal to SOY on Fe, g / l 6 8 eleven 13 26 36 47 68 84 186 209 2.04 twenty 640 523 446 410 375 298 1.99 17.1 3,54 twenty 729 558 473 437 419 354 3.32 18.7 4.17 twenty 740 602 507 502 482 415 3.69 16,2 4.95 twenty 751 598 512 488 410 417 4.26 16.7 6.30 twenty 765 600 410 500 430 440 4.92 17,2 8.44 twenty 745 544 532 368 6.42 18.8 9.55 twenty 739 586 567 359 8.38 19.0 6.30 70 765 462 390 382 400 4.70 18.2 5.96 70 400 151 78 85 80 4.45 16,0

The authors experimentally established:

1. Volumetric distribution coefficients of transition metal cations (Fe ³⁺ , Co ²⁺ , Cr ³⁺ ) from solutions of EDTA + H ₃ Cit + H ₂ C ₂ O ₄ on anion exchange resin in the EDTA form (Tables 1, 2, 3) much less K _p for the same cations from OEDP solutions on anion exchange resin in the OEDP form (Tables 4, 5, 6) at all equilibrium pH values of solutions. The obtained data on the distribution coefficients were not predictable, since they do not correlate with the values of the instability constants of complexes with transition metal cations (pK) known from the literature. The strength of cobalt complexes with OEDP is inferior to the strength of complexes with EDTA by at least seven orders of magnitude (10 ⁷ times) / N.I. Ampelogova, Yu.M. Simanovsky, A.A. Trapeznikov. Decontamination in nuclear power. - M .: Energoizdat, 1982, Table 9.5 p. 126 /. At the same time, the authors found that the cobalt selectivity of the anion exchanger in the OEDP form or the cobalt sorption strength on this anion exchanger is not less than 65 times the sorption strength on the anion exchanger in the EDTA form, which follows from the data in Tables 2 and 5.

2. The claimed form of anion exchange resin exhibits a higher selectivity to all the studied PM ions and radionuclides, which are included in the corrosion deposits of the PC circuits and determine the dose rate levels from the equipment, in comparison with the prototype anion form. The revealed regularities indicate that a significantly larger solution volume can be passed through anion exchange resin in the OEDP form until the metal elution.

3. High values of K _p cations of transition metals and radionuclides on the claimed form of anion exchange resin remain in the pH range of solutions from 2.5 to 6.0 (tables 4, 5, 6, 7). On the contrary, the sorption of PM on anion exchange resin in the EDTA form (prototype method) sharply worsens even with insignificant pH shifts of solutions from the acidic region to the alkaline region, which is expressed in a decrease in K _p values (Tables 1, 2, 3).

4. The capacity of anion exchanger AB-17-8 hC in the HEDP form for iron is greater than the capacity of the anion exchanger in the EDTA form. The static exchange capacity of anion exchange resin in the HEDP form was determined by the authors with an average value of 17.5 g per liter of swollen ion exchanger (Table 8), and a dynamic exchange capacity of at least 15 g / l. The dynamic exchange capacity of anion exchange resin in the EDTA form, equal to 4.8 g / l / T.Kh. Margulova. The use of complexones in the power system. - M .: Energoatomizdat, 1986, pp. 229-230 /, inferior to the OEDP form by more than three times.

Thus, the claimed form of anion exchange resin provides the removal of more PM cations from solutions during the dissolution of PC oxides, and, accordingly, increases the efficiency of regeneration of active agents, including complexing agents, when PC and RE are dissolved. This is confirmed by a change in the pH values of solutions containing iron, after their exposure in contact with anion exchange resin AB-17-8 hC in the HEDP form, which is expressed in the shift of the pH of the solutions to the acid region from pH _ref. up to pH _{equal to} .

5. An increase in the temperature of solutions containing complexones from 20 to 70 ° C significantly reduces the time to reach equilibrium between the ion exchanger and the solution from about 200 hours to 10, which indicates an improvement in the kinetics of PM sorption on anion exchangers in the form of complexing agents with increasing temperature (Table. 8). Therefore, in order to increase the efficiency of sorption of PM and radionuclides, regeneration of complexones upon dissolution of PCs, the temperature of solutions containing complexing agents, when they are purified on anion exchange resins in the form of complexon, must be maintained within the upper limits of the passport limitations of ion exchangers on heat resistance. So, for anion exchange resin AB-17-8 hC, it is not higher than 70 ° C and in the range from 60 to 70 ° C. A decrease in temperature is not critical, but significantly increases the time required to remove PM from solutions containing complexing agents.

6. The pH values of solutions containing complexing agents, in which effective and stable removal of PM (Fe ³⁺ , Fe ²⁺ , Co ²⁺ , Cr ³⁺ ) and radionuclides on anion exchange resin in HEDP form is possible in order to regenerate agents and maintain optimal PC dissolution conditions are in the range from 2.5 to 6.0.

Changes in the pH of the solutions in the specified range for the proposed method compared with the prototype method does not significantly affect the possibility of sorption removal of transition metals and radionuclides from solutions. Maintaining optimal pH values of solutions containing complexing agents in the process of cleaning solutions and surface decontamination is greatly simplified.

7. On the claimed HEDP form of anion exchange resin from solutions containing, along with complexing agents, reductants (N ₂ H ₄ ), effective removal of Fe ^{2+ ions is also} achieved (Tables 7, 8), which, as indicated above, is essentially impossible anion exchange resin in the EDTA form. Thus, when using the HEDP form of anion exchange resin, a number of PM cations that make up the PC, which can be effectively removed on the ion exchanger, are significantly expanded in comparison with the prototype method.

The most pronounced differences in the selectivity of the EDTA form of the anion exchanger of the prototype method and the claimed HEDP form during sorption of PM cations and radionuclides on them from solutions containing complexing agents, at comparable equilibrium pH values of the purified solutions, are seen from the obtained experimental data presented in Table 9 . The table shows the values of the volumetric distribution coefficients of trace amounts of metal cations, and not the logarithms of their values, used for the convenience of constructing graphical dependences of K _p on the pH of solutions. Experimental conditions: static, T = 20 ÷ 25 ° C, V _solution = 100 ml, V _resin = 2 ml. Adjustment of the pH value of the initial solution of 2.5 g / l EDTA + 0.25 g / l N ₂ H ₄ was carried out by the introduction of ammonia (NH ₄ OH).

It was found that the selectivity of strongly basic anion exchangers, for example, AB-17-8 hC anion exchange resin converted to the form of alkyl diphosphonic acids, for example, to the HEDP form, is two to four orders of magnitude higher than the selectivity of the EDTA form of the anion exchange resin and radionuclides (Table 9).

Table 9. The values of K _{p the} trace amounts of PM ions (Fe ³⁺ , Co ²⁺ , Cr ³⁺ ) between solutions of the composition, g / l: 1.4 EDTA + 1 H ₃ Cit + 1 H ₂ C ₂ O ₄ and anion exchange resin AB-17- 8 h in the EDTA form (prototype method) and solutions of OEDP composition 2 and anion exchange resin AB-17-8 hC in the HEDP form (inventive method) at different equilibrium pH values. Ion PM Prototype method The inventive method The composition of the solution, g / l pH equal to To _r The composition of the solution, g / l pH equal to To _r Fe ³⁺ 1.4 EDTA + 1 H ₃ Cit + 1 H ₂ C ₂ O ₄ 3.41 4.7 · 10 ² 2 OEDF 3.21 4.6 · 10 ⁴ 1.4 EDTA + 1 H ₃ Cit + 1 H ₂ C ₂ O ₄ 4.10 1.5 · 10 ² 2 OEDF 4.23 7.6 · 10 ⁴ 1.4 EDTA + 1 H ₃ Cit + 1 H ₂ C ₂ O ₄ 4.89 1,810 2 OEDF 5.23 5.910 ⁴ 1.4 EDTA + 1 H ₃ Cit + 1 H ₂ C ₂ O ₄ 6.06 1.3 2 OEDF 6.55 7.310 ⁴ Co ²⁺ 1.4 EDTA + 1 H ₃ Cit + 1 H ₂ C ₂ O ₄ 3.07 1.410 2 OEDF 3.12 6.010 ² 1.4 EDTA + 1 H ₃ Cit + 1 H ₂ C ₂ O ₄ 3.96 9.7 2 OEDF 3.33 5.010 ² 1.4 EDTA + 1 H ₃ Cit + 1 H ₂ C ₂ O ₄ 5.27 9.0 2 OEDF 4.82 9.4 · 10 ² 1.4 EDTA + 1 H ₃ Cit + 1 H ₂ C ₂ O ₄ 6.08 8.4 2 OEDF 6.34 6.210 ² Cr ³⁺ 1.4 EDTA + 1 H ₃ Cit + 1 H ₂ C ₂ O ₄ 3.06 4.010 2 OEDF 2.95 2.6 · 10 ³ 1.4 EDTA + 1 H ₃ Cit + 1 H ₂ C ₂ O ₄ 3.84 5.710 2 OEDF 3.42 1.5 · 10 ⁴ 1.4 EDTA + 1 H ₃ Cit + 1 H ₂ C ₂ O ₄ 4,56 3.4 · 10 2 OEDF 5.65 1.3 · 10 ⁴ 1.4 EDTA + 1 H ₃ Cit + 1 H ₂ C ₂ O ₄ 6.00 1.3 · 10 2 OEDF 6.52 5.110 ³

Also, as a result of experiments, it was found that the claimed alkyl diphosphonic form of strongly basic anion exchangers, for example, HEDP form, allows efficient removal of PM and radionuclides from reducing solutions containing EDTA, for example, from solutions of the composition EDTA + N ₂ H ₄ + NH ₄ OH. The volume distribution coefficients of Fe ²⁺ cations on the anion exchange resin in the HEDP form from solutions containing EDTA and a reducing agent are presented in Table 10. Test conditions: static, T = 20 ÷ 25 ° C, V _solution = 100 ml, V _resin = 2 ml . Adjustment of the pH value of the initial solution of 2.5 g / l EDTA + 0.25 g / l N ₂ H ₄ was carried out by the introduction of ammonia (NH ₄ OH).

Table 10 The inventive method. K _p trace ⁵⁹ Fe ²⁺ cations on the anion AB-17-8 Disaster HEDP-form depending on the equilibrium pH of the solution containing EDTA, the composition, g / l 2.5 EDTA + 0,25 N ₂ H ₄ + NH ₄ OH. No. p / p The composition of the solution, g / l pH is _equal lg K _p one 2.5 EDTA + 0.25 N ₂ H ₄ 3.08 3,50 2 2.5 EDTA + 0.25 N ₂ H ₄ + NH ₄ OH 3.45 3.49 3 2.5 EDTA + 0.25 N ₂ H ₄ + NH ₄ OH 4.07 3.07 four 2.5 EDTA + 0.25 N ₂ H ₄ + NH ₄ OH 4.67 2.90 5 2.5 EDTA + 0.25 N ₂ H ₄ + NH ₄ OH 6.32 3.02 6 2.5 EDTA + 0.25 N ₂ H ₄ + NH ₄ OH 8.35 2.60

It was experimentally found that the effective removal of Fe ²⁺ on the claimed form of anion exchange resin from reducing solutions containing EDTA is possible and effective in the range of equilibrium pH solutions from 3.0 to 6.0. Changes in the pH of solutions in the indicated range slightly affect the selectivity of the HEDP form of the anion exchange resin with respect to Fe ²⁺ and, therefore, do not significantly affect the sorption of this cation.

The experiments also revealed the possibility of removing PM and radionuclides on the claimed form of anion exchange resin from solutions containing, along with complexing and reducing agents, ligands of various mineral or organic acids. It was found that the introduction of ligands of acetic, citric, and nitric acids into solutions of complexones, for example, HEDP, EDTA, does not lead to a deterioration in the characteristics of sorption processes of PM and radionuclides on anion exchangers in the HEDP form, and in some cases, on the contrary, as a result of the presence of additional ligands in solutions is the improvement of sorption characteristics. For example, volumetric distribution coefficients of trace impurities of Fe ²⁺ cations from solutions with the composition of 2.5 g / l HEDP + 1.25 g / l CH ₃ COONH ₄ +0.75 g / l N ₂ H ₄ on anion exchange resin AB-17-8 hС in the HEDP form in the range of equilibrium pH of solutions from 4.00 to 5.50 vary in the range from 5.1 · 10 ⁴ to 1.3 · 10 ⁴ . These values are not less, and in some cases, greater than the values of K _p for Fe ³⁺ and Fe ²⁺ cations, which were determined by the authors for sorption on anion exchange resin in HEDP form from solutions containing:

- OEDP + NH ₄ OH;

- HEDP + N ₂ H ₄ + NH ₄ OH;

- EDTA + NH ₄ OH;

- EDTA + N ₂ H ₄ + NH ₄ OH.

Fundamentally, in the inventive method, in contrast to the prototype method, no restrictions are introduced associated with the values of the instability constants of complexes formed by complexing agents that are part of solutions with transition metal ions. The prototype method extends to the sorption of PM ions only, specifically Fe ³⁺ , having the instability constants of compounds in solutions above 22. In the present method, the OEDP complexes with Fe ²⁺ (MeH ₂ L, MeHL) and Co ²⁺ (MeH ₂ L , MeHL) correspond to instability constants of 5.31 and 9.05 for Fe ²⁺ ; 5.29 and 9.36 for Co ^{2+ /} N.I. Ampelogova, Yu.M. Simanovsky, A.A. Trapeznikov. Decontamination in nuclear power. - M.: Energoizdat, 1982, p. 123-130, Table 9.5 p. 126 /. From the same source it follows that the instability constant of the Cr ³⁺ complex with HEDP has not yet been determined, which does not interfere with the effective sorption of Cr ³⁺ on the claimed form of anion exchange resin and is confirmed by the data in Table 6. Advantages that are revealed during sorption of Cr ³⁺ from solutions containing complexing agents follow from the known data on the contribution of the ⁵¹ Cr radionuclide to the dose rate of gamma radiation from solutions upon deactivation of the first nuclear power circuit immediately after shutting down the reactor. The contribution of ⁵¹ Cr is in the range of 30-50%.

Thus, the inventive method of removing transition metals and radionuclides from solutions containing complexing agents on a strongly basic anion exchange resin converted to an alkyl diphosphonic complexone, for example hydroxyethylidene diphosphonic acid (OEDP), provides:

- improving the efficiency of sorption of transition metals and radionuclides from solutions containing complexing agents;

- expansion of a number of transition metal ions and radionuclides that can be removed from solutions containing various complexing agents on ion-exchange filters in the process of decontamination of nuclear power plants;

- the ability to effectively remove transition metal ions and radionuclides from solutions of complexing agents, additionally containing reducing agents;

- expanding the pH range of solutions that meets the conditions for the effective removal of PM and radionuclides from solutions containing complexing agents;

- an increase in the capacity of the form of anion exchange resin on the main, exhausting the capacity of ion exchanger sorbate, respectively, increase in the efficiency of regeneration of complexing agents in solutions during their purification from transition metals and radionuclides during deactivation.

An additional advantage of the claimed form of anion exchange resin is the convenience of its preparation by introducing a concentrate of a HEDP solution into the ion exchange water and holding in static conditions until equilibrium occurs. Preparation does not require special technological systems and equipment; it is easily feasible in separate containers made of materials that are inert with respect to HEDP solutions, for example, polymer ones.

The proposed method can be used for chemical decontamination and washing the contours of nuclear power and heat power plants. The method provides the possibility of sorption purification of solutions and LRW containing complexones, reducing agents, ligands of mineral or organic acids, reducing the amount and volumetric activity of LRW, reducing the cost of receiving, storing and processing waste.

Claims (3)

1. A method for removing transition metals and radionuclides from solutions containing a complexing agent, comprising circulating a solution to be purified through anion exchange resin, previously converted into a complexing agent, with the simultaneous regeneration of this agent and its subsequent return to the main volume of the solution to be purified, while maintaining optimal ranges of pH and temperature of the solution to be purified, characterized in that hydroxyethylidene diphosphonic acid is used as a complexing agent, o the volume distribution coefficients of microimpurities of transition metal ions and radionuclides between the solution to be purified and the anion exchange resin in the form of a complexing agent and the dependence of the volume distribution coefficients on the equilibrium pH values of the solutions to be purified are determined, the optimal pH range of the solutions being determined from the dependences of the volume distribution coefficients of metal ions and radionuclides on the anion exchange resin in the form of a complexing agent from equilibrium pH values of the purified solutions and support in p the purification process in the range corresponding to the maximum values of the volumetric distribution coefficients of microimpurities of transition metal ions and radionuclides between the solution to be cleaned and the anion exchange resin, and the temperature of the solution on the anion exchange resin is kept in the upper limits corresponding to the passport data of the anion exchange resin on heat resistance. 2. The method according to claim 1, characterized in that as the anion exchange resin, which is converted into the form of a complexing agent, a strongly basic anion exchange resin in the OH ^- form is used. 3. The method according to claim 1, characterized in that the optimal range of pH values of the solutions is 2.5-6.0.