RU2553266C1 - Method for heterogenic catalytic decomposition of oxalate ions, complexing agents and surfactants in process mediums of radiochemical plants - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: what is provided is heterogenic catalytic decomposition of process media containing oxalate ions having the concentration of 16-18 g/l (complexing agents (up to 2 g/l), surfactant (up to 50 mg/l)) and nitric acid (up to 60 g/l) on a platinum catalyst applied on anion exchange resin VP-1AP (0.05-2 wt % of platinum). The effect is achieving a degree of decomposition of oxalate ions, complexing agents, surfactants up to 99.9%, in the residual concentrations - less than 10 mg/l in oxalate ions and less than 1 mg/l in complexing agent (EDTA, Trilon B) and surfactant (sulphonol).

EFFECT: improving the characteristics.

3 cl, 1 dwg

Description

The invention relates to radiochemical technology and can be used in the technology of processing liquid radioactive waste (LRW) of radiochemical plants and nuclear power plants.

An important task in ensuring radiation safety during the operation of nuclear power plants and radiochemical plants is to solve the problem of cleaning and processing LRW generated during various technological operations with solutions containing radionuclides, as well as decontamination of equipment and operation of power plants.

One of the main components of technological solutions of radiochemical production is complexing substances, which form strong soluble complexes with radionuclides ¹³⁴ Cs, ¹³⁷ Cs, ⁶⁰ Co, etc. Polyphosphates, aminopolycarboxylic acids, citric, tartaric, hydrofluoric acids and their salts are used. - citrates and fluorides. Separately, it is worth noting oxalate compounds, whose role has increased recently in connection with an increase in the production of nuclear fuel and the processing of spent nuclear fuel (SNF). Of the organic complexing agents such as aminopolycarboxylic acids, commonly called complexones and used in nuclear power plants and nuclear radiochemical plants, ethylene diamine tetraacetic acid (EDTA) and its disodium salt (trilon B) are of the greatest importance.

It follows that the processing of LRW is significantly simplified after the removal or destruction of the organic anions (oxalates, complexones) and surfactants contained in them, which bind the radionuclides and make it difficult to isolate them by traditional physicochemical methods, and also affect the extraction and sorption behavior of uranium, neptunium, plutonium during further processing.

From the existing level of technology is known oxidative [Lagunova Yu.O., Seliverstov AF, Ershov B.G.,. Basiev A.G. // Oxidative decomposition of oxalate ions in aqueous solutions by concentrated ozone. Atomic energy, 2012. V.111, No. 5. P.31-35] and the photooxidative method for the decomposition of oxalate ions and complexones [Lagunova Yu.O., Seliverstov AF, Ershov BG, Morozov PA, Kamrukov AS, Anguladze Sh .. // Photo-oxidative degradation of Trilon B in alkaline solutions. Materials of the 5th international scientific and technical conference: “Radioactive waste management”. M .: VNIIAES, 2006, S.39-40], among the shortcomings of which, first of all, it is worth highlighting the duration of the decomposition process (up to 100-150 min.), The increased consumption of oxidizing agent (ozone) to achieve a decomposition of 99% and more in terms of oxalate ion (complexon), a narrow working pH range (~ 10) during decomposition, as well as the extreme nature of the influence of process temperature on the efficiency of decomposition of oxalate ion, complexon.

A known method of oxidative and electrochemical destruction of surfactants with ozone, in particular sulfonol [Grinevich V.I., Gushchin A.A., Plastinina N.A. Destruction of phenol and synthetic surfactants dissolved in water during electrochemical exposure together with ozonation // News of Universities. Chemistry and chemical technology. 2009.- T.52. - Issue 2. - S.130-134]. Also known is the method of decomposition of synthetic surfactants by plasma-catalytic destruction [Grinevich V.I., Plastinina N.A. Plasma-catalytic wastewater treatment from organic compounds // Proceedings of the V International Symposium on Theoretical and Applied Plasma Chemistry, Ivanovo, 2008. - T.1. - S. 95-98]. The main disadvantages of these methods are the duration of the decomposition process, the complexity of the hardware design of the process, as well as the significant influence of the initial concentration of surfactants and the nature of the catalysts on the efficiency of decomposition.

Closest to the claimed method is a method for the decomposition of complexones in nitric acid solutions when heated to 50-90 ° C. The process is carried out in the presence of a catalyst — activated carbon or platinum supported on silica gel (0.86 wt.% Platinum) in a 9 ml temperature-controlled chromatographic column. The decomposition of complexone to 99.9% at a contact time of 20 minutes is shown. [Patent SU 1214607A, C02F 1/72, 02.28.86] (prototype). The disadvantage of this method is the long contact time of the solution with the catalyst - up to 20 minutes. The contact time of the proposed method is 50-55 seconds. The advantage of the claimed invention in the hardware design is the ability to quickly change the volume of the catalyst, the height of its layer in the column, i.e. easier maintenance of the installation, in contrast to the chromatographic column of the prototype. Moreover, as the platinum carrier in the present invention (method), the VP-1AP anion exchange resin is used, in contrast to silica gel (prototype), which significantly increases the stability of the catalyst in both alkaline and acidic media. Differences in favor of the invention exist in the amount of platinum deposited on the carrier — the minimum amount is 0.05 wt.%. platinum in the developed method against 0.86 wt.% in the prototype. Also, unlike the prototype, according to the developed method, heterogeneous catalytic decomposition of complexones is possible at lower temperatures (37-52 ° C) when hydrogen peroxide is introduced into the solution.

The problem to which the invention is directed, is the decomposition of organic anions, such as oxalate ions, complexones, surfactants, in technological solutions and liquid radioactive waste from radiochemical plants and nuclear power plants to discharge concentrations, in which these substances do not complicate further processing solutions containing them or LRW.

The problem is solved by the developed method of heterogeneous catalytic decomposition of oxalate ions, complexones and surfactants in technological solutions of radiochemical plants on a platinum catalyst deposited on an anion-exchange resin VP-1AP (0.05-2 wt.% Platinum).

The technical result of the invention is to achieve a degree of decomposition of more than 99% and residual concentrations of less than 10 mg / L for oxalate ion and less than 1 mg / L for complexon (EDTA, Trilon B) and surfactant (sulfonol).

The possibility of implementing the proposed method is confirmed by studies in the laboratory installation shown in figure 1, which includes: a catalytic column with a jacket (1), a thermostat (2), a peristaltic pump (3), a container with an initial solution (4), a receiving tank (5) graduated cylinder (6); V-01, V-02, V-03 - needle valves for flow control.

The proposed method is implemented in the following sequence: the catalyst is prepared by impregnating the VP-1AP resin with an alkaline solution of platinum, the prepared catalyst is placed in a column, and the thermostat is connected. By means of a peristaltic pump, the initial solution is supplied to the catalytic column, and the decomposition process is carried out. The solution after the catalytic column is collected in portions and analyzed for the content of H ₂ C ₂ O ₄ (complexone, surfactant) and HNO ₃ (pH). The total acidity of the solution and the concentration of HNO _{3 are} determined by potentiometric titration using an automatic titrator.

Example 1

A platinum catalyst and an initial solution of the following composition were prepared: oxalate ion - 16-18 g / l, nitric acid - 60 g / l.

The contact time of the initial solution with the catalyst is 55-75 s. The temperature of the process is 70-80 ° C. The flow rate of the initial solution is 7 colon.ob./h The experiment was carried out in the above sequence.

The residual concentration of oxalate ion was less than 10 mg / l, the degree of decomposition of 99.88-99.90%.

Example 2

The process of heterogeneous catalytic decomposition of Trilon B complexone was carried out analogously to example 1. The composition of the initial solution: Trilon B - 1.1-1.5 g / l, nitric acid - 12-25 g / l.

The temperature of the process is 75-80 ° C. The contact time of the initial solution with the catalyst is 55-75 s. The flow rate of the initial solution is 7 colon.ob./h

The residual concentration of Trilon B complexone was less than 1 mg / l, the degree of decomposition of 99.91%.

Example 3

The process was carried out analogously to example 2, however, the introduction of hydrogen peroxide (9 g / l) can increase the efficiency of decomposition of complexon (Trilon B) at a lower temperature, as well as reduce the content of nitric acid in the initial solution. The composition of the initial solution: Trilon B - 1.1-1.5 g / l, nitric acid - 0.2-0.3 g / l, hydrogen peroxide - 9 g / l.

The temperature of the process is 65-70 ° C. The contact time of the initial solution with the catalyst is 55-75 s. The flow rate of the initial solution is 7 colon.ob./h

The residual concentration of Trilon B complexone was less than 1 mg / l, the degree of decomposition of 99.91%.

Example 4

The process was carried out analogously to example 2, however, instead of complexon, the sulfonol surfactant was decomposed. The composition of the initial solution: sulfonol - up to 50 mg / l, nitric acid - 0.2 g / l, hydrogen peroxide - 9 g / l.

The temperature of the process is 65-70 ° C. The contact time of the initial solution with the catalyst is 55-75 s. The flow rate of the initial solution is 7 colon.ob./h

The residual concentration of sulfonol (surfactant) was less than 1 mg / l, the degree of decomposition of 99.9%.

Example 5

The process was carried out analogously to example 3, however, conducted a joint decomposition of the complexon of Trilon B and the surfactant sulfonol. The composition of the initial solution: Trilon B - 1.1-1.5 g / l, sulfonol - up to 50 mg / l, nitric acid - 0.2 g / l, hydrogen peroxide - 9 g / l.

The temperature of the process is 65-70 ° C. The contact time of the initial solution with the catalyst is 55-75 s. The flow rate of the initial solution is 7 colon.ob./h

The residual concentration of trilon B (complex) and sulfonol (surfactant) was less than 1 mg / l, the degree of decomposition of 99.9%.

Example 6

The experiment was carried out as in example 1. The composition of the initial solution: carbonate ion - 2 g / l, nitric acid - 60 g / l.

The temperature of the process is 70-80 ° C. The contact time of the initial solution with the catalyst is 55-75 s. The flow rate of the initial solution is 7 colon.ob./h

The residual concentration of the carbonate ion was less than 1 mg / l, the degree of decomposition of 99.9%.

The technical result of the invention, namely the achievement of a degree of decomposition of less than 10 mg / L in oxalate ion and less than 1 mg / L in complexon (EDTA, Trilon B) and surfactant (sulfonol), allows us to judge the potential implementation of this invention (method) in technology processing of liquid radioactive waste, in particular decontamination solutions (containing oxalate ions, complexones, surfactants) of radiochemical plants and nuclear power plants. Moreover, heterogeneous catalytic decomposition of oxalate ion can be introduced when designing a site for the catalytic decomposition of oxalate ions in mother liquors after plutonium oxalate precipitation in plutonium dioxide purification technology.

Claims (3)

1. The method of heterogeneous catalytic decomposition of oxalate ions, complexones and surfactants in technological solutions of radiochemical industries, characterized in that the catalyst used is platinum supported on anion exchange resin VP-1AP with a weight content of platinum of 0.05-2%. 2. The method according to claim 1, characterized in that hydrogen peroxide is added to the process solution to increase the efficiency of heterogeneous catalytic decomposition and lower the process temperature. 3. The method according to claim 1, characterized in that the technological solution contains carbonate ion up to 2 g / L.

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