RU2569374C1 - Method for heterogeneous catalytic decomposition of complexons and surface-active substances in technological solutions of radiochemical productions on nickel-ferricyanide catalyst - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to method for heterogeneous catalytic decomposition of complexons and surface-active substances in technological solutions of radiochemical productions on nickel-ferricyanide catalyst. Nickel ferricyanide, applied on anion-exchange resin, is applied as catalyst under impact of oxidative system, which consists of hydrogen peroxide and nitric acid, in dynamic mode in thermostatted apparatus of column type. Possibility of claimed method realisation is confirmed by researches on laboratory installation, shown on fig. 1, which includes: catalytic column with jacket (1), thermostat (2), peristaltic pump (3), reservoir with initial solution (4), receiving tank (5), measuring cylinder (6), V-01, V-02, V-03 are needle valves for consumption regulation.

EFFECT: method makes it possible to reach almost complete degree of decomposition and minimal residual concentrations by complexon and surface-active substance.

4 cl, 1 dwg, 2 tbl, 3 ex

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 and others. Polyphosphates, aminopolycarboxylic acids, citric, tartaric, hydrofluoric acids and their salts are used as such substances. citrates and fluorides. 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 (complexones) and surface-active substances (surfactants, synthetic surfactants (SAS)) contained in them, which bind the radionuclides and make it difficult to isolate them by traditional physicochemical methods, as well as 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. // Decomposition of ozone with EDTA and its complexes with cobalt in aqueous solutions. Sixth Russian Conference on Radiochemistry "RADIOCHEMISTRY - 2009", October 12-16, 2009 - Istra, p. 267] and the photooxidative decomposition method for complexones [Lagunova Yu.O., Seliverstov AF, Ershov BG, Morozov PA, Kamrukov AS, Anguladze Sh. // Photooxidative destruction of Trilon B in alkaline solutions . Materials of the 5th International Scientific and Technical Conference: "Radioactive Waste Management". - M.: “VNIIAES”, 2006, p. 39-40], among the disadvantages of which, first of all, it is worth highlighting the duration of the decomposition process (up to 100-150 min), the increased consumption of an oxidizing agent (ozone) to achieve decomposition of 99% or more of the complexone, a narrow working pH range (~ 10) at decomposition, as well as the extreme nature of the influence of process temperature on the efficiency of decomposition of complexon (EDTA, Trilon B).

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. - Vol. 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 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 complexon to 99.9% at a contact time of 20 minutes is shown [Patent SU 1214607 A, 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. Platinum is a rather expensive metal (unlike nickel and ferricyanide), and it is almost impossible to avoid the loss of platinum, and when using activated carbon, the destruction of the catalyst occurs. 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, the VP-1AP anion exchange resin, in contrast to silica gel (prototype), significantly increases the stability of the catalyst in both alkaline and acidic media, as the carrier of the nickel-ferricyanide catalyst in the present invention (method). Also, unlike the prototype according to the developed method, heterogeneous catalytic decomposition of complexones and surfactants 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 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 the further processing of solutions containing them or LRW.

The problem is solved by the developed method for the heterogeneous catalytic decomposition of complexones and surfactants in technological solutions of radiochemical production on a nickel-ferricyanide catalyst deposited on an anion exchange resin under the influence of an oxidizing system consisting of hydrogen peroxide and nitric acid, in a dynamic mode in a thermostatic column apparatus type. In the particular case, the VP-1AP resin with a weight content of nickel ferricyanide of 5-7% is used as the anion exchange resin. The process of catalytic decomposition of complexones and surfactants is carried out in the pH range from 1 to 5 at a temperature of 50-80 ° C.

, который сразу же распадается на анион OH^- и свободный гидроксильный радикал

. Образующиеся в результате свободные радикалы (в том числе и выделяющийся активный кислород) обладают высокими окислительными потенциалами (окислительный потенциал

составляет 2,8 В) и способны разрушить многие устойчивые соединения, в частности комплексоны (трилон Б) и поверхностно-активные вещества в разработанном способе их разложения.For the catalytic decomposition of complexones and surfactants according to the developed method, hydrogen peroxide is used as an oxidizing agent. The use of hydrogen peroxide is due to the possibility of its catalytic destruction with the formation of oxidizing radicals. The decomposition of hydrogen peroxide proceeds according to a radical chain mechanism, while the role of the catalyst is to initiate free radicals: in aqueous solutions in the presence of hexacyanoferrates, the electron transfer reaction to the H ₂ O ₂ molecule takes place with the formation of a very unstable anion radical

which immediately decomposes into an OH ^- anion and a free hydroxyl radical

. The resulting free radicals (including the liberated active oxygen) have high oxidative potentials (oxidative potential

is 2.8 V) and can destroy many stable compounds, in particular complexones (Trilon B) and surfactants in the developed method for their decomposition.

The essence of the proposed (developed) method is to carry out a process of heterogeneous catalytic oxidation of complexones and surfactants adsorbed on the surface of the granular layer of a nickel-ferricyanide catalyst, followed by desorption of the products of oxidation (decomposition). The catalytic initiation of the decomposition of hydrogen peroxide introduced into the solution makes it possible, as a result of its decomposition, to obtain compounds with a high oxidation potential, which determines the local oxidative activity of the system at the active centers of the ion exchange of the carrier (anion exchange resin).

The mechanism of the catalytic decomposition (oxidation) of Trilon B:

The mechanism proposed in the invention demonstrates the formation of hydroxyl radicals as a result of the decomposition of hydrogen peroxide on the surface of the catalyst locally at the sites of adsorption of decomposable compounds. In this case, in addition to direct oxidation by the hydroxyl radical of organic components adsorbed on the surface, oxidation of the surface of the insoluble compound of the modified support to Fe (III) (ferricyanide), subsequent oxidation of the adsorbed organic component on the catalyst surface with the reduction of iron (in the catalytic layer) to Fe (II ) (ferrocyanide), desorption of oxidation products from the surface of the catalyst (redox cycle). Thus, the implementation of the redox cycle due to the reversibility of the redox ferrocyanide-ferricyanide system allows it to be used as a catalyst for the production of oxidizing radicals resulting from the decomposition of hydrogen peroxide and leading to the destruction of organic components (complexones, surfactants), which is accompanied by the formation of reduced forms, providing, in turn, the regeneration of active centers on the surface of the catalyst. The completeness of the decomposition of organic components is achieved by the intensification of adsorption-desorption processes in a fixed granular catalyst bed as a result of the organization of a dynamic regime in a column type apparatus.

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

The possibility of implementing the inventive method is confirmed by studies in the laboratory setup shown in FIG. 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), a 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 a solution of potassium ferricyanide and then treating it with a solution of nickel nitrate to fix the resulting nickel-ferricyanide catalyst on the resin surface (5-7% R-Ni [Fe (CN) ₆ ], where R is VP-1AP anion exchange resin ), the prepared nickel-ferricyanide catalyst is placed in the column, 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 complexon content, surfactant and pH.

Example 1

A nickel-ferricyanide catalyst and an initial solution of the following composition were prepared: Trilon B - 1.1 g / l, nitric acid - 2 g / l, hydrogen peroxide - 6 g / l.

Hydrogen peroxide during its decomposition (contact with the surface of the nickel-ferricyanide catalyst) acted as a donor of active oxygen and free radicals during the catalytic destruction of Trilon B. complexon.

The contact time of the initial solution with the catalyst is 55-75 s. The temperature of the process is 50-60 ° C. The flow rate of the initial solution is 7 columns. r / h The experiment was carried out in the above sequence.

The residual concentration of Trilon B was less than 1 mg / l, the degree of decomposition of 99.9%. The degree of decomposition of hydrogen peroxide during the oxidative destruction of the complexone was ~ 100%.

Example 2

The process was carried out analogously to example 1, however, instead of the complexon Trilon B, decomposition of the surfactant sulfonol was carried out. The composition of the initial solution: sulfonol - 50 mg / l, nitric acid - 2 g / l, hydrogen peroxide - 6 g / l.

The process temperature 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 columns. r / h

The residual concentration of sulfonol (surfactant) was less than 1 mg / l, the degree of decomposition was more than 98%. The degree of decomposition of hydrogen peroxide during the oxidative destruction of the complexone was ~ 100%.

Example 3

The process was carried out analogously to example 1, however, the developed method was tested on real technological solutions: pulp decantates were used after sedimentation of the drainage-desorption solutions formed during deactivation of the technological equipment of the VVER-1000 spent nuclear fuel storage facility.

In a series of experiments after decomposition of complexones and surfactants (the degree of decomposition of complexones and surfactants was -99.9%) contained in LRW, according to the developed method using hydrogen peroxide and a nickel-ferricyanide catalyst, it was subsequently possible to purify ¹³⁷ Cs of radionuclides and ⁶⁰ Co to a level of less than 1 Bq / l (purification factors from cesium-137 and cobalt-60 were more than 51677 and 1133, respectively).

The catalytic effect of the prepared and used catalyst was confirmed in a series of experiments on the removal of radionuclides from LRW in a similar way, characterized in that the process of oxidation of organic components of LRW (Trilon B, surfactant) with hydrogen peroxide was carried out without the use of a nickel-ferricyanide catalyst. As a result of oxidative degradation, complexon and surfactants were not observed, and the efficiency of the subsequent removal of radionuclides from the solution decreased significantly: the cesium-137 and cobalt-60 purification coefficients were less than 25 and 3, respectively.

The use of a nickel-ferricyanide catalyst when testing the developed method on real technological solutions did not affect its stability and work efficiency. The probability of sorption of radionuclides on the catalyst, noted during the experiments, did not affect its catalytic properties and the technological mode of the process of decomposition of complexones and surfactants.

The technical result of the invention, namely the achievement of a degree of decomposition of less than 1 mg / l by complexone (EDTA, Trilon B) and surfactant (sulfonol), allows us to judge the potential implementation of this invention (method) in the processing technology of liquid radioactive waste, in particular decontamination solutions ( containing complexones, surfactants) radiochemical industries and nuclear power plants.

Claims (4)

1. The method of heterogeneous catalytic decomposition of complexones and surfactants in technological solutions of radiochemical plants on a nickel-ferricyanide catalyst, characterized in that nickel ferricyanide deposited on an anion exchange resin is used as a catalyst when exposed to an oxidizing system consisting of hydrogen peroxide and nitrogen acid, in a dynamic mode in a thermostatic apparatus of column type. 2. The method according to claim 1, characterized in that the VP-1AP resin is used as the anion exchange resin. 3. The method according to p. 1, characterized in that the weight content of nickel ferricyanide on the resin is 5-7%. 4. The method according to claim 1, characterized in that the process of catalytic decomposition of complexones and surfactants is carried out in the pH range from 1 to 5.