RU2516274C2 - Method of determining optimal parameters of dissolution of oxides of transition metals in solutions, containing complexing agent - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to method of determining optimal parameters of dissolution of oxides of transition metals in solutions, which contain complexing agent, and can be applied in atomic energy. As parameters, applied are volume coefficients of distribution of radioactive isotopes of transition metals, which determine composition of oxides, between solutions, which contain complexing agent, and strong-base anionites in form of said complexing agent (complexits) and balanced values of solution pH. Radioactive isotopes of transition metals are introduced into fixed volumes of analysed solutions, after which, fixed volumes of complexits are introduced into solutions. Initial and final activity of solutions is measured. Also measured are balanced values of pH of solutions. Ranges, satisfying optimal parameters, which must be supported in contours of NEP directly in the process of dissolution of oxides in the process of washing and deactivation of NEP contours, are determined by the results of measurements.

EFFECT: increased reliability of determination of optimal parameters of dissolution of oxides of transition metals in complexing agent solutions and absence of necessity of carrying out complex analyses of metals to determine concentration of metal cations in solutions of complexons.

2 cl, 2 dwg, 1 tbl

Description

The invention relates to nuclear energy and can be used to determine the optimal parameters for the dissolution of transition metal oxides in solutions of complexing agents used in chemical washing and decontamination of the circuits of nuclear power plants (NPPs).

The operation of nuclear power plants is accompanied by the accumulation of mixed transition metal oxides (PM) on the inner surfaces of the first contours of the radioactive deposits (PO), including insignificant amounts of radioactive isotopes of PM cations - radionuclides: ⁵¹ Cr ³⁺ , ⁵⁴ Mn ²⁺ , ⁵⁹ Fe ²⁺ , ⁵⁹ Fe ^{3 +} , ⁵⁸ Co ²⁺ , ⁶⁰ Co ²⁺ , ⁶³ Ni ²⁺ and others. Metal cations, which quantitatively determine the composition of oxides (Fe, Ni, Cr), are the main elements of structural materials (CM). Other elements are alloying additives in steels. The accumulation of RO leads to a decrease in the heat-hydraulic parameters of the plants, corrosion damage to equipment elements, and a deterioration in the radiation situation.

To remove PO, chemical washing and decontamination technologies are used using solutions that include reagents that effectively transform PM oxides into a dissolved state, form stable soluble compounds with metal cations, radionuclides and do not have significant corrosive effects on KM / M. Peak, M. Segal. Chemical decontamination of pressurized water reactors in the UK. - Nuclear technology abroad .: 1984, No. 12, p. 26-36 /.

The main amount of PO is removed from the NPP circuits when exposed to solutions of acid agents (mineral, organic, complexing acids) on oxides. The advantages of complexing agents (complexones) over mineral and organic acids are known. If the latter are characterized by a higher dissolution rate of oxides, then complexones form significantly more stable soluble compounds (complexonates) with PM cations, which reduces the likelihood of back deposition of metals and radionuclides from solutions on the surface of CMs. The parameters characterizing the stability of the compounds of metal cations (Me) with anions or ligands (L) of acids in solutions are the instability constants (pK), determined by the negative decimal logarithms of the ratio of the product of the concentration of metal ions [Me] and ligands [L] in solutions to the concentration formed in solutions of the compounds [MeL].

$$pK=-\lg ([Me]\times [L])/[MeL](\mathrm{one})$$

The larger the pK value, the more stable it is in solutions of the MeL / N compound. I. Ampelogova, Yu.M. Simanovsky, A.A. Trapeznikov. Decontamination in nuclear power. - M.: Energoizdat, 1982, p. 123-130, Table 9.5 p. 126 /. The stability ("strength") of the compounds of the ligands of complexing agents with PM cations depends on the pH of the solutions, the composition of the solutions, the presence of other reagents besides complexones, for example, reducing agents, organic acids, etc.

Also distinguishing characteristics of complexon solutions include their “capacity” for PM cations or maximum concentrations of metal cations achieved and retained in solutions upon dissolution of PM oxides. A general pattern has been established - the larger the pK value of the complexonates, which means that the [MeL] compounds are the most stable, the higher the concentration of PM cations in the /Т.Х solutions. Margulova. Chemical cleaning of heat power equipment. - M .: "Energy", 1969, pp. 38-40 /, / N.M. Dyatlova, V.Ya. Temkina, K.I. Popov. Complexones and complexonates of metals. - M .: "Chemistry", 1988, pp. 99-105, 456-458 /. For mono-solutions of complexones used to dissolve PM oxides, for example, the best-known ethylenediaminetetraacetic acid (EDTA) and its two-substituted sodium salt Trilon B, the dependences of the change in the pK values of the complexonates of transition metal cations on the pH of the solutions are determined. The most stable compounds of EDTA with the Fe ³⁺ cation are formed in the range of pH of solutions ~ 1.5–2.0. For the Fe ²⁺ cation, pH ~ 5.0 corresponds to the maximum values of the instability constants of complex compounds in EDTA mono-solutions. Subject to the noted pH ranges, which are optimal for dissolving iron oxides in EDTA and Trilon B mono-solutions, the highest concentrations of Fe ³⁺ and Fe ²⁺ cations are achieved in solutions. These PM cations quantitatively determine the elemental composition of hematite (Fe ₂ O ₃ ) and magnetite (Fe ₃ O ₄ ) - iron oxides, which are formed in nuclear power plant circuits with an aqueous coolant. In the case of deviations of the pH values of mono-solutions of complexones from the optimal values, the stability of the compounds [MeL] decreases, which leads to a decrease in the concentration of PM. The dissolution of iron oxides in mono-solutions of EDTA and Trilon B is accompanied by a shift in the pH of the solutions from acidic to alkaline, in which the strength of the complexonates of iron cations is lower. At a certain pH value, the complexation ceases altogether, the pH value and the concentration of complexon, iron in solutions stabilize. Such a solution has to be discharged, although there is still enough free complexon / T.X. Margulova. Chemical cleaning of heat power equipment. - M.: “Energy”, 1969, pp. 38-40 /. Thus, the determination of authentic optimal parameters for the dissolution of PM oxides, namely, the pH ranges of solutions containing complexing agents, in which complexones form the most stable compounds with transition metal cations, and the “capacity” of complexon solutions for PM are used to the greatest extent, has a significant effect on the final results of the washing and decontamination of nuclear power plant circuits and their economic efficiency.

It was shown that the introduction of additional agents, for example, reducing agents or organic acids, into the solutions of complexones leads to an improvement in the performance of solutions. When reductants, for example, hydrazine (N ₂ H ₄ ) are introduced, the structures of iron oxides “become loose” due to the reactions of reduction of Fe ³⁺ cations to Fe ^{2+ /} В.М. Sedov, A.F. Nechaev, V.A. Doilnitsyn, P.G. Krutikov. Chemical technology of coolants of nuclear power plants, - M .: Energoatomizdat, 1985, p. 252 table 5, 1, p. 258 /. The introduction of organic acids (oxalic - H ₂ C ₂ O ₄ , citric - H ₃ Cit, etc.) helps to maintain the pH of the solutions in optimal ranges. This is explained by the fact that organic acids with a higher rate of dissolution of oxides, after transferring the elements of oxides into the solution, “transfer” PM cations to complexing agents whose compounds with metals are stronger. The liberated (regenerated) organic acid maintains the pH of the solutions in the optimum acid region and re-enters the dissolution reaction of the oxides / T.X. Margulova. The use of complexones in the power system. - M .: Energoatomizdat, 1986, p. 147 /, N.M. Dyatlova, V.Ya. Temkina, K.I. Popov. Complexones and complexonates of metals. - M.: Chemistry, 1988, p. 461 /. Additionally, the introduction of organic acids provides “synergistic” effects, which are manifested in a non-stoichiometric increase in the concentration of PM in solutions. It has been established that for complex molecules formed in these solutions — associates — with the participation of metal cations and complex-forming and organic acid ligands, stoichiometric ratios cannot be determined by the additivity rule /Т.Х. Margulova. The use of complexones in the power system, - M .: Energoatoizdat, 1986, pp. 147-148 /. The effects are associated with changes in the stability of metal complexonates in solutions in the presence of other reagents / N.M. Dyatlova, V.Ya. Temkina, K.I. Popov. Complexones and complexonates of metals. - M.: “Chemistry”, 1988, pp. 100-101, 104 /.

Determination of the instability constants of PM complexonates, the relationship of the structure of complex compounds with the reactivity of complexing agents with PM cations is one of the most important problems in the chemistry of coordination compounds. It is difficult to calculate and determine the instability constants in solutions of complexones containing additional reagents. The pK values of compounds in the presence of competing ligands can both decrease and increase / M.I. Bulatov. Calculations of equilibria in analytical chemistry. - Leningrad .: "Chemistry", 1984, pp. 100-105 /. Despite the sharp increase in the accuracy of measuring equipment over the period from the mid 40s of the last century to the present, on the improvement of methods for processing experimental results, the pK values obtained by research teams for the same PM complexons and cations under the same experimental conditions are often significantly are different. An example is the instability constants obtained for ethylene diamine tetraacetate Cr ³⁺ , namely, 23.0 and 12.8, the difference between which is 10 orders of magnitude (10 ¹⁰ ). The reason, as a rule, is systematic errors, the identification of the source of which is far from always possible. The relevance of the problems of determining pK associated with systematic errors remains at present / N.M. Dyatlova, V.Ya. Temkina, K.I. Popov. Complexones and complexonates of metals. - M .: "Chemistry", 1988, pp. 99-105 /.

Considerable experience has been accumulated in washing and deactivating NPP circuits, a large number of compositions (formulations) of solutions for dissolving transition metal oxides have been developed, but their improvement continues. PM concentrations achieved in solutions of complexing agents, as well as the stability of complex compounds with metal cations, largely depend on the pH and chemical composition of the solutions, and the concentration ratios of the reagents. Evaluation of their influence, especially for solutions of complex chemical composition, including other agents along with complexones, is impossible without experiments on the dissolution of oxides in laboratory conditions. Until now, the advantages of certain formulations are confirmed by the results of experimental studies on the dissolution of PM oxides, including measurements of physicochemical parameters of solutions. Known work to determine the optimal parameters of the dissolution of iron oxides in solutions containing Trilon B and other reagents, namely, organic acids. The ratios of Trilon B and citric acid, Trilon B and maleic anhydride were determined at which the highest concentrations of the transition metal, iron, are achieved in solutions. Samples of oxides were dissolved in a number of solutions with given concentrations and ratios of reagents. The final concentrations of iron (C _Fe ) were measured. Based on the measurement results, graphical dependences of C _Fe on the ratio of reagents in solutions were constructed. It was determined that the maximum concentration of Fe ³⁺ in solutions is achieved when the ratio of reagents (complexon and organic acid) is 1: 1. At the same time, it was noted that in order to solve the need for introducing reducing agents into the given formulations, further studies are necessary, since the results of the work obtained using the above method for establishing the optimal parameters for the dissolution of PM oxides are not unique / T. Margulova. Chemical cleaning of heat power equipment, M., Energy, 1969, pp. 174-175).

The ambiguity in interpreting the results of experimental measurements of the above physicochemical parameters of solutions to determine the optimal conditions for the dissolution of PM oxides is confirmed by published data, from which the difference and inconsistency of the recommended parameters for the use of solutions containing the same complex for the same purposes follows. For example, to dissolve iron oxides in world practice, the following formulations are used, the main active agents of which are EDTA and Trilon B:

- with the content of reagents in% of their total concentration in solutions:

- 5 EDTA + 95 sulfamic acid (UK);

- 20 EDTA + 60 H ₃ Cit + 20 monoethanolamine (France);

- 40 EDTA + 30 H ₃ Cit + 30 H ₂ C ₂ O ₄ at pH = 2.5 ÷ 3.0, ∑С of _agents = 1 ÷ 2.5 g / l (Canada);

- with the content of reagents in solutions in% by weight:

- 0.3 Trilon B + 0.15 H ₃ Cit + 0.05 NH ₂ OH (hydroxylamine) (Russia);

- 0.3 EDTA + 0.1 H ₃ Cit at pH _beg. = 3.0 (Russia);

- 0.23 Trilon B + 0.11 H ₃ Cit at pH = 3.6 ÷ 4.7 (Russia);

- 0.72 EDTA + 0.52 H ₃ Cit + 0.002 N ₂ H ₄ at pH = 3.5 (Germany);

- 10 EDTA + NH ₄ OH (ammonia) to pH = 6.0 + 1 N ₂ H ₄ (USA)

/ T.X. Margulova. Chemical cleaning of heat power equipment, M., Energy, 1969, p. 165 /, / T.Kh. Margulova. The use of complexones in the power system, M., Energoatomizdat, 1986, p. 209 /, / A.F. Sedov, A.F. Nechaev, V.A. Doilnitsyn et al. Chemical Technology of Fluids of Nuclear Power Plants, Moscow: Energoatomizdat, 1985, pp. 262-263, Table 5.2 /, / T.Kh. Margulova, O.I. Martynova. Water regimes of thermal and nuclear power plants, - M.: Higher School, 1987, p. 297 /, N.I. Ampelogova, Yu.M. Simanovsky, A.A. Trapeznikov. Decontamination in nuclear energy, - M.: Energoizdat, 1982, p. 185, table 11.1 /, / M. Yovchev. Corrosion of thermal power and nuclear power equipment, Moscow: Energoatomizdat, 1988, p. 159 /.

Studies are known to determine the optimal parameters for the dissolution of iron oxides in solutions simultaneously containing hydroxyethylidene diphosphonic acid (OEDP) and Trilon B, including experimental measurements of the physicochemical parameters of solutions at different given concentrations of reagents. As indicators, we used the concentrations of iron (C _Fe ), the maximum achieved by dissolving the oxides, the initial and final values of the pH of the solutions (pH _beginning , pH _con. , Respectively). Graphical dependencies of indicators were built. Based on the graphical dependences of C _Fe on pH _beg. and pH _con. of solutions, it was found that the maximum iron - capacity in solutions of 2.5 g / l HEDP + 2.5 g / l of Trilon B is achieved in the range of initial pH values of solutions from 2.0 to 2.5 and final in the range from 3.0 to 3.5 / T.X. Margulova. The use of complexones in the power system, M., Energoatomizdat, 1986, p. 255 /.

This method of determining the optimal parameters of the dissolution of transition metal oxides in solutions containing a complexing agent is the closest to the claimed and adopted as a prototype.

The disadvantages of the prototype method are as follows.

1. The reliability of determining the optimal parameters of the processes of dissolution of PM oxides in solutions containing a complexing agent, based on the measurement of such indicators of solutions as C _Me , pH _beg. and pH _con. is not sufficient, since these parameters do not allow determining authentic pH values of solutions at which complex compounds with transition metal cations in solutions are most stable, compliance with which allows to achieve maximum concentrations of metal cations in solutions and which, accordingly, must be maintained directly during dissolution oxides.

2. When using the prototype method, it is necessary to conduct a large number of chemical analyzes to determine the weight concentrations of transition metal cations in solutions containing a complexing agent.

The determination of PM concentrations in solutions of complexing agents is a separate task in analytical chemistry. The stability of complex compounds leads to the "masking" of metal cations in solutions, complicates the use of traditional methods. This necessitates the development of original methods of analysis adapted to specific recipes, or the use of other methods, for example, the method of atomic absorption analysis / I. Khavezov, D. Tsalev. Atomic absorption analysis, - L .: Chemistry, 1983, pp. 86-105 / or optical emission spectroscopy with inductively coupled plasma / M. Thompson, D.N. Walsh. Inductively coupled plasma spectrometric analysis guide, M .: Nedra, 1988, pp. 9-11 /, which requires the use of expensive equipment and the involvement of highly qualified specialists.

The objective of the present invention is to provide a method for determining the optimal parameters of the dissolution of transition metal oxides in solutions containing a complexing agent, allowing:

- increase the reliability of determining the optimal parameters for the dissolution of transition metal oxides, namely, the pH of solutions, in which complex compounds with transition metal cations that quantitatively determine the elemental composition of oxides are most stable, maximum concentrations of metal cations are achieved in solutions, and which (parameters) are necessary support directly in the process of dissolution of PM oxides;

- completely eliminate or minimize chemical analyzes of solutions containing complexing agents, by definition of weight concentrations of transition metal cations.

To solve the problem and achieve the technical results in a method for determining the optimal parameters of the dissolution of transition metal oxides in solutions containing a complexing agent, including experimental measurements of physicochemical parameters of solutions, including pH values of solutions, the construction of graphical dependencies of indicators on pH values of solutions, according to the invention, it is proposed:

- use the volumetric distribution coefficients of the transition metal radioactive isotopes, which determine the composition of the oxides, between the strongly basic anion exchange resin in the form of a complexing agent and the solutions of this complexing agent and the equilibrium pH values of the solutions, for which radioactive transition metal isotopes are added to the studied solutions, then into fixed volumes solutions with predetermined concentrations of reagents, activities of transition metal isotopes and initial pH values to introduce fixed volumes of anion exchange resin in the form of a complexing agent, measure the radioactivity of transition metal isotopes in solutions before and after establishing ion-exchange equilibrium between solutions and anion exchange resin in the form of a complexing agent and equilibrium pH values of solutions, calculate the volume distribution coefficients of radioactive isotopes from the results of measurements of the activity of solutions transition metals between solutions and anion exchange resin in the form of a complexing agent, and the choice is optimal To determine the dissolution parameters of transition metal oxides from the graphical dependence of the changes in the volume distribution coefficients of the transition metal radioactive isotopes on the equilibrium pH values of solutions, to determine the pH equilibrium ranges corresponding to the maximum values of the volume distribution coefficients of the transition metal radioactive isotopes;

- the time to establish the ion-exchange equilibrium of the radioactive isotopes of transition metals between the anion exchange resin in the form of a complexing agent and solutions of this complexing agent is determined by the stabilization of the activity of solutions by transition metal isotopes.

It is known to use the volume distribution coefficients (K _p ) of metal cations between solutions and various sorbents, ion exchangers as indicators characterizing the selectivity (affinity) of sorption materials to metal cations in solutions of different compositions. The values of the distribution coefficients of metal cations between solutions and sorbents, the dependence of K _p on the parameters of solutions, namely, the concentrations and ratios of reagents in solutions, pH values, are used in substantiating and predicting the possibility of sorption processes involving the separation and concentration of metals, for example, in separation metal cations from solutions in analytical chemistry, in radiochemistry, in the purification of aqueous coolants of nuclear power plants, liquid radioactive waste, etc. / I.K. Tsitovich. Course of analytical chemistry. - M.: Higher School, 1994, p. 424-428 /, / О. Samuelson. Ion exchange separation in analytical chemistry. - M.: “Chemistry”, 1966, p. 288-299 /, / A.S. Nikiforov, V.V. Kulichenko, M.I. Zhikharev. Neutralization of liquid radioactive waste. - M .: Energoatomizdat, 1985, pp. 26-33 /.

The proposed use of volumetric distribution coefficients (K _p ) of metal radioactive isotopes that determine the elemental composition of PM oxides between complexon solutions and anion exchangers in the form of this complexon as indicators for determining the optimal parameters of oxide dissolution in complexon solutions, namely, optimal pH values at which complex compounds with metal cations are most stable; maximum concentrations of metal cations are achieved in solutions and which must be maintained eposredstvenno during dissolution of oxides, not previously considered or applied.

When conducting experimental studies to determine the optimal parameters for the dissolution of iron oxides in solutions containing hydroxyethylidene diphosphonic acid as a complexing agent, the authors of the proposed method encountered the phenomenon of the jelly-like precipitation of Fe ³⁺ cation compounds on the surfaces of pearlite class with complexon in mono-solutions of OEDP. It was also found that the formation of precipitation is eliminated by introducing reducing agents into the solutions, for example, hydrazine. The concentration of N ₂ H ₄ with which precipitation ceases was experimentally determined at ~ 160 mg / L at a concentration of HEDP in solution of 1 g / L, which corresponds to a ratio of molar concentrations of reactants of 1: 1. The optimal concentration of N ₂ H ₄ and the initial pH values of HEDP solutions obtained by measuring C _Me , pH _beg. solutions when dissolving weighed portions of magnetite oxides were determined by the ranges 0.25 ÷ 0.30 g / l and 3.5 ÷ 5.0, respectively.

As a result of the work, the authors found:

- as indicators for determining the optimal parameters of the dissolution of transition metal oxides in solutions containing a complexing agent, namely, the pH values of solutions at which the maximum concentration of metal cations is achieved in them and the complex compounds are most stable, volumetric distribution coefficients of radioactive cations can be used PM isotopes that determine the elemental composition of oxides between solutions and strongly basic anion exchangers in the form of this complexing agent and Significant pH values of solutions;

- the desired optimal pH values of solutions that must be directly supported during the dissolution of PM oxides can be determined from the dependences of the volume distribution coefficients (K _p ) of PM radioactive isotopes between complexon solutions and strongly basic anion exchangers in the form of this complexon on the equilibrium pH values of solutions;

- the optimal pH values of the solutions are the equilibrium pH values corresponding to the maximum values of the volume K _{p of} radioactive isotopes of transition metals.

In contrast to the prototype method, which includes dissolving weighed portions of PM oxides, experimental measurement of weight concentrations of metal cations, initial and final pH values of the studied solutions, determination of pH ranges at which PM concentrations are maximum, the proposed technical solution does not require the dissolution of oxides and chemical analyzes.

The inventive method for determining the optimal parameters of the dissolution of PM oxides in solutions containing a complexing agent is as follows.

Prepare the test solutions with different initial values of pH (pH _beg.) And the predetermined concentration of the complexing agent and the other reactants. If necessary, adjust the pH of the _beginning. from acidic to alkaline, it is carried out by adding alkali additives, for example, ammonia, to the solutions. A radioactive isotope of a transition metal, quantitatively determining the elemental composition of the oxide, for example, ⁵⁹ Fe radionuclide in the case of dissolution of iron oxides, is introduced into fixed volumes of solutions (V _solution ), and the initial radioactivity (N _ref ) of the solutions is measured.

Strongly basic anion exchange resin is transferred to the form of a complexing agent that determines the composition of the solution. As ion exchangers, for example, helium anion exchange resin of the AB-17-8chS or AMBERLIGHT-IRN78 brands in the OH ^- form can be used. The preparation of ion exchangers is carried out by known methods in dynamic or static conditions / GOST 20255.2-89. Ionites. Methods for determining the dynamic exchange capacity /, / GOST 20255.1-89. Ionites. Methods for determination of static exchange capacity. The result is anion exchange resin in the form of complexon - complexite.

Fixed volumes of complexite (V _resin ) are _introduced into fixed volumes of the studied solutions (V _solution ). The solutions are kept and complexite until the ion-exchange equilibrium between them is determined, which is determined by stabilizing the results of measurements of the activity of isotopes in solutions, after which the equilibrium activity of the solutions (N _equal ) and the equilibrium pH values of the solutions (pH _equal ) are measured.

Calculate the volume distribution coefficients (K _p ) of the radioactive metal isotope between solutions and complexite according to the formula:

$$K_p=[(N_{\mathrm{and}\mathrm{from}x.}-N_{R\mathrm{but}\mathrm{at}n.})/V_{\mathrm{from}m\mathrm{about}ls}]\cdot [V_{R\mathrm{but}\mathrm{from}t\mathrm{at}\mathrm{about}R\mathrm{but}}/N_{R\mathrm{but}\mathrm{at}n.}],(2)$$

where N _ref. , N _{equal to} - the initial and equilibrium radioactivity of the solution according to the corresponding isotope, imp./min · ml;

V _resin , V _solution - the volume of resin and solution, ml.

Take the logarithms of the volume distribution coefficients (logK _p ).

Graphical dependences of logK _p values on pH _{equal are built.} solutions.

Determine pH ranges _{equal to} where the values of logK _{p are} maximal.

These ranges correspond to the optimal parameters of the dissolution of PM oxide, the optimal pH values that must be maintained directly during the dissolution of the oxide and at which the maximum concentration of metals in solutions is achieved, which means that PM compounds with complexon are most stable.

An example implementation of the proposed method.

The results of the experiment are shown in table 1 and are illustrated by the attached figures, where:

Figure 1 - Dependence of the logarithm of the volume distribution coefficient (LgK _p ) of the cation of the radioactive isotope ⁵⁹ Fe ²⁺ on the anion exchange resin AB-17-8 hC in the HEDP form on the equilibrium pH of the solution composition, g / l: 1 ÷ 5 HEDP + 0.25 ÷ 1.5 N ₂ H ₄ + NH ₄ OH. Test conditions: static, T = 70 ± 2 ° C, V _solution = 100 ml, V _resin = 2 ml.

Figure 2 - Change in iron content in solutions containing HEDP with a concentration of 1 g / l and hydrazine, with the dissolution of magnetite (Fe ₃ O ₄ ) depending on the pH of the _beginning. solutions corresponding to predetermined concentrations of HEDP and N ₂ H ₄ .

The concentration of N ₂ H ₄ (C _hydr. ), Mg / l → pH _beg. solutions: C _hydr. = 0 → pH _nach. = 28; C _hydr. = 50 → pH _nach. = 2.40; C _hydr. = 100 → pH _nach. = 2.60; C _hydr. = 150 → pH _beginning = 2.85; C _hydr. = 200 → pH _nach. = 3.00; C _hydr. = 250 → pH _nach. = 3.50; C _hydr. = 300 → pH _nach. = 6.00; C _hydr. = 350 → pH _nach. = 6.95.

Test conditions: dissolution of Fe ₂ O ₃ when purging the solutions with argon; the ratio of the volume of the solution to the mass of the sample is 2: 1 (per 2 cm ³ - 1 mg of Fe ₃ O ₄ ); temperature - 70 ± 2 ° C; time - 2 hours. The iron content in the solutions was determined by the atomic absorption method on a Saturn spectrophotometer / Saturn spectrophotometer. Technical description and instruction manual. 5 G I.550.082. TO /.

An example of determining the optimal dissolution parameters of magnetite in solutions containing hydroxyethylidene diphosphonic acid (HEDP) and hydrazine (N ₂ H ₄ ).

Prepare solutions containing HEDP and N ₂ H ₄ with the given concentrations of reagents and initial pH values of the solutions. The pH adjustment is carried out by adding ammonia to the solutions. Measure the initial pH of the solutions (pH _nach. ).

Strongly basic AB-17-8 hC anion exchange resin is transferred to the HEDP form, for which purpose, the anion exchange resin is placed in the OH ^- form in a glass column and the complexone mono-solution is passed through the ion exchange resin. The pH is measured in the filtrate. The preparation of the anion exchange resin is completed when the pH of the filtrate is equal to the pH of the passed solution.

Fixed volumes (100 ml) of HEDP + N ₂ H ₄ solutions with known concentrations of agents and different pH values are placed _. into the flasks.

A radioactive isotope of a transition metal is introduced into the solution volumes, which quantitatively determines the elemental composition of Fe ₃ O ₄ , namely, the ⁵⁹ Fe radionuclide.

Aliquots of solutions (1 ml) were taken from the flasks and the initial activity of the solutions (N _ref. ) _Was measured using radiometric equipment, for example, a beta radiometer. The date and time of the measurement are noted.

Introduce a fixed volume of the anion exchanger in the HEDP-form (2 ml) solution volumes (100 ml) with different pH values _beginning. and note the time of bringing the solutions into contact with complexitis.

Maintain solutions with complexite until the ion-exchange equilibrium of the ⁵⁹ Fe radionuclide is established between them. To reduce the time to establish equilibrium, the flasks with the solutions are placed in a thermostat with a temperature of 70 ° C. The authors found that ion-exchange equilibrium at ~ 20 ° C under static conditions occurs after ~ 200 hours. At a temperature of 70 ° C, allowed for AB-17-8hS in terms of heat resistance, the time of equilibrium is reduced to ~ 10 hours.

Maintain complexite in solutions for at least 10 hours.

Samples of solutions are taken. The volume of the samples is increased taking into account the expected decrease in the activity of the radionuclide in the solutions during their exposure in contact with complexite and leave enough volumes to measure the pH of the solutions.

Measure the equilibrium (final) activity of the solutions and recalculate the measurement results on the date and time of determining the initial activity of the solutions, taking into account the half-life of the radionuclide, namely, ⁵⁹ Fe (N _equal ).

Measure the equilibrium pH of the solutions (pH _equ. ).

The volume distribution coefficients (K _p ) of the isotope cation ( ⁵⁹ Fe ²⁺ ) between complexite and solutions are calculated by formula 2.

Take the logarithms of the volume distribution coefficients (log K _p ).

Build a graph of the dependence of the values of lg To _p from pH values _{equal to} solutions.

From the graph determine the pH range _{equal to} solutions, which corresponds to the region of maximum values of log K _p .

The found pH range is _{equal to} is optimal for carrying out the dissolution of transition metal oxide - magnetite in these solutions containing specified concentrations of HEDP and hydrazine.

Table 1 shows the physicochemical parameters (K _p , pH _equal ) of solutions containing HEDP and hydrazine, after the onset of ion-exchange equilibrium in the distribution of ⁵⁹ Fe radionuclide between solutions and AB-17-8hC anion exchange resin in HEDP form, obtained from experimental results measurements of the activity of solutions and equilibrium pH values of solutions.

Based on the data in Table 1 (pH _equal , log K _p ), a graphical dependence of the logarithms of the volume distribution coefficients of the cation of the radioactive isotope ⁵⁹ Fe ²⁺ on the equilibrium pH values of the solutions was constructed (Fig. 1).

From the graph (figure 1) the range of equilibrium pH values of the solutions, which corresponds to the range of maximum values of K _p corresponds to the range of pH values from 2.5 to 4.8. The highest values of K _p correspond to the pH range of solutions from 3.0 to 3.5. Maintaining the pH of solutions in this range directly during the dissolution of iron oxides in HEDP + N ₂ H ₄ solutions is the most optimal, ensures maximum concentrations of iron cations and corresponds to the formation of the most stable complex compounds with Fe ²⁺ cation in solutions.

The validity of this conclusion is confirmed by the results of determining the weight concentrations of iron cations in HEDP + N ₂ H ₄ solutions with given concentrations of reagents and different initial pH values when dissolving a portion of magnetite. The results are experimentally obtained by the authors in a traditional way similar to the prototype method. From the graph (figure 2), which shows the dependence of the achieved concentrations of iron in solutions on pH _beginning. solutions, it follows that the maximum concentration of iron ions in the solutions corresponds to a range of initial pH values from 3.5 to 5.0, after which the iron-capacity of the solutions decreases.

The authors experimentally established:

1. There is a direct proportional relationship between the volume distribution coefficients of the transition metal isotopes between solutions containing a complexing agent and strongly basic anion exchangers in the form of this complexing agent and the stability of PM complexonates formed in these solutions.

2. As physicochemical parameters of solutions containing a complexing agent, for more reliable determination of the optimal parameters of dissolution of PM oxides, namely, the pH values of solutions that must be maintained directly during the dissolution of oxides, volumetric distribution coefficients of radioactive isotopes of metals between studied complexon solutions and strongly basic anion exchangers in the form of this complexon (complexites) and equilibrium pH values of solutions;

3. The dependence of the volume distribution coefficients of metal isotopes quantitatively determining the elemental composition of oxides, for example, the ⁵⁹ Fe isotope in the case of studying the dissolution parameters of Fe ₃ O ₄ , from the equilibrium pH values of solutions, allows us to determine the optimal parameters of the dissolution of oxides and characterizes the performance of solutions;

4. The optimal parameters for the dissolution of PM oxide deposits, namely, the optimal pH values, correspond to the ranges of equilibrium pH values of solutions that correspond to the maximum values of the volume distribution coefficients of metal cations;

5. In these optimal pH ranges at given concentrations of reagents in solutions, the maximum concentrations of metals that determine the composition of PM oxides are reached, and the complex complexes formed - associates - with the participation of metal cations and ligands of complexing agents are most stable.

The established patterns apply not only to the example of the specific implementation of the proposed method, but are also applicable for determining the optimal parameters for the dissolution of PM oxides in solutions containing other complexones and in solutions containing ligands of organic and mineral acids and other agents along with complexing agent ligands. This was experimentally confirmed by the authors when checking the optimal parameters of the dissolution of iron oxides in solutions of EDTA + H ₃ Cit + H ₂ C ₂ O ₄ , namely, the recommended initial pH of solutions equal to 2.5, with a ratio of agents in solutions of 4: 3: 3 and total concentration of reagents 1 ÷ 2.5 g / l. The recipe is used in the decontamination of the first circuits of industrial nuclear power plants with a heavy water coolant according to the "low concentration" chemical technology, which in world practice is designated by the abbreviation "CAN-DECON" / 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 12-13, 47-51 /. Obtained using the proposed method, the optimal pH of the solutions of EDTA + H ₃ Cit + H ₂ C ₂ O ₄ , which must be maintained directly in the process of dissolution of iron oxides, coincided with the area recommended by the developers of the formulation. At the same time, based on the dependence of K _{p of the} radioactive isotopes of ⁵⁹ Fe between the solutions of EDTA + H ₃ Cit + H ₂ C ₂ O ₄ and the anion exchange resin AB-17-8 hC in the EDTA form, the pH is _{equal to} It was shown in solutions that even slight deviations of pH values from the optimal values during the dissolution of iron oxides, for example, from 2.5 to 3.5, are critical for the processes of decontamination of the first NPP circuits using a formulation. It was found that these deviations lead to a significant, at least an order of magnitude, decrease in the stability of complex compounds with Fe ³⁺ cations, which determines for solutions containing EDTA the significant relevance of maintaining and maintaining optimal pH values directly in the process of deactivation of NPP loops.

The elemental composition of oxides depends on the CM contours, but in any case is determined by transition metals, which are distinguished from other elements based on the incompleteness of the internal electron shells of their atoms or ions. The incompleteness of the shells determines the ability of the PM to form coordination (complex) compounds, which is their common property. This suggests that the method is applicable to determine the optimal dissolution parameters of not only iron oxides, but also oxides of other PM, for example, oxides of chromium, manganese, cobalt, nickel, zinc, zirconium.

The presence of gamma-spectrometric equipment, which allows to identify and measure the activity of several gamma-emitting radioactive isotopes of PM in solutions at the same time, provides researchers with additional opportunities. Since the concentration of PM radioactive isotopes introduced into solutions is negligible, and their influence on the isotope distribution coefficients between solutions and complexites can be neglected, it is possible to simultaneously determine the optimal dissolution parameters of various transition metal oxides in solutions containing one or another complexing agent . For this, it is necessary to simultaneously introduce gamma-emitting isotopes of several transition metals at once into the investigated solutions with given concentrations and ratios of reagents, initial pH values, quantitatively determining the elemental composition of certain oxides, for example, isotopes ⁵⁹ Fe, ⁹⁵ Zr, ⁹⁵ Nb, ⁵⁴ Mn , ⁵¹ Cr, ⁶⁰ Co, ⁵⁸ Co.

The inventive method is easily feasible. For its implementation, radioactive isotopes of transition metals that are part of specific PM oxides and radiometric equipment are required, which makes it possible to measure the activity of solutions using introduced radionuclides.

Table 1. Experimental data on the measurement of physicochemical parameters (K _p , pH _equal ) of solutions containing specified concentrations of HEDP and hydrazine, according to the equilibrium distribution of the cation of the radioactive isotope ⁵⁹ Fe ²⁺ between solutions and AB-17-8hC anion exchange resin in the HEDP form, to determine optimal parameters of dissolution of magnetite. Test conditions: static, T = 70 ± 2 ° C, V _solution = 100 ml, V _resin = 2 ml. PH adjustment _beginning. solutions with specified concentrations of reagents was carried out by ammonia. No. p / p The composition of the solution, g / l pH _beginning N _ref. N _{equal to} pH _{equal to} lg K _p one 2 3 four 5 6 7 one 5 OEDP + 1.2 N ₂ H ₄ 3.23 4972 40 2.78 3.80 2 5 OEDP + 1.2 N ₂ H ₄ + NH ₄ OH 4.23 4972 29th 3.04 3.90 3 5 OEDP + 1.2 N ₂ H ₄ + NH ₄ OH 6.38 4972 61 3.43 3.60 four 5 OEDP + 1.2 N ₂ H ₄ + NH ₄ OH 6.78 4972 62 4.49 3.60 5 5 OEDP + 1.2 N ₂ H ₄ + NH ₄ OH 7.11 4972 150 5.73 3.20 6 5 OEDP + 1.2 N ₂ H ₄ + NH ₄ OH 7.50 4972 990 6.32 2,30 7 5 OEDP + 1.2 N ₂ H ₄ + NH ₄ OH 6.58 4972 60 3.73 3.60 8 5 OEDP + 1.2 N ₂ H ₄ + NH ₄ OH 6.16 4972 44 3.27 3.70 9 5 OEDP + 1.5 N ₂ H ₄ 6.12 4020 fifteen 3.47 4.10 10 5 OEDP + 1.1 N ₂ H ₄ 3.43 3310 23 2.97 3.85 eleven 5 OEDP + 0.17 N ₂ H ₄ 1.98 3246 58 1.96 3.40 12 5 OEDP + 0.18 N ₂ H ₄ 2.95 3853 52 2.77 3.60 13 5 OEDP + 1.4 N ₂ H ₄ 5.68 3881 27 3.27 3.85 fourteen 5 OEDP + 1.5 N ₂ H ₄ + NH ₄ OH 7.09 3975 114 6.03 3.20 fifteen 5 OEDP + 1.5 N ₂ H ₄ + NH ₄ OH 7.96 3958 2287 6.97 1,50 16 5 OEDP + 1.5 N ₂ H ₄ + NH ₄ OH 9.02 3938 3508 8.28 0.8 17 5 OEDP + 1.5 N ₂ H ₄ + NH ₄ OH 10.16 3611 3244 9.93 0.8 eighteen 2.5 OEDP + 0.6 N ₂ H ₄ 4.20 1855 17 3.02 3.70 19 2.5 OEDP + 0.75 N ₂ H ₄ 6.00 1955 eleven 3.15 3.95 twenty 1 OEDP + 0.28 N ₂ H ₄ 4.49 3825 27 3.21 3.85

Claims (2)

1. The method of determining the optimal parameters of the dissolution of transition metal oxides in solutions containing a complexing agent, including experimental measurements of physico-chemical parameters of solutions, including pH values of solutions, the construction of graphical dependencies of indicators on pH values, characterized in that volume indicators are used distribution coefficients of radioactive isotopes of transition metals that determine the composition of oxides between strongly basic anion exchange resin in the form of complexing of the agent and the solutions of this complexing agent and the equilibrium pH of the solutions, for which radioactive isotopes of transition metals are added to the studied solutions, then fixed volumes of anion exchange resin in the form of a complexing agent are introduced into the fixed volumes of solutions with the given concentrations of the reagents, the activity of the transition metal isotopes and the initial pH of the solutions agent, measure the radioactivity of the isotopes of transition metals in solutions before and after the establishment of ion-exchange equilibrium between solutions and anion exchange resin in the form of a complexing agent and the equilibrium pH values of solutions, according to the results of measurements of the activity of the solutions, the volume distribution coefficients of the radioactive isotopes of transition metals between the solutions and the anion exchange resin in the form of a complexing agent are calculated, and the optimal parameters for the dissolution of transition metal oxides are selected from the graphical dependence of volumetric distribution coefficients of radioactive isotopes of transition metals from equilibrium x solutions pH values, which define the ranges of values of the equilibrium pH, corresponding to the maximum values of the distribution coefficients of the volume of radioactive isotopes of transition metals. 2. The method according to claim 1, characterized in that the time of establishing the ion-exchange equilibrium of the radioactive transition metal isotopes between the anion exchange resin in the form of a complexing agent and the solutions of this complexing agent is determined by stabilizing the activity of the solutions according to the transition metal isotopes.

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