SK123796A3 - Method and device for disposing of a solution containing an organic acid - Google Patents

Abstract

The invention concerns a method and device for disposing of a solution containing an organic acid and an iron complex, particularly the type of solution arising from the decontamination of the surfaces of radioactively contaminated equipment. The invention calls for the iron complex in the solution to be reduced by irradiation with UV light, thus forming a dissolved iron salt and carbon dioxide which is given off. An oxidizing agent is then added to the solution containing the dissolved iron salt and the organic acid. Water is formed and the iron complex is produced again. Part of the dissolved iron salt is removed from the solution in a cationic ion-exchanger. The solution containing the iron complex is again irradiated with UV light and the process repeated until all the organic acid has been consumed. Disclosed is also device form performing of this method.

Description

A method and apparatus for disposing of a solution comprising an organic acid

Technique

The present invention relates to a process for the disposal of an aqueous solution comprising an organic acid and an iron complex and which is produced as waste, in particular in the decontamination of radioactive contaminated surfaces of building components. The invention also relates to a device for disposing of an aqueous solution with a solution tank which contains organic acid and an iron complex and is produced as waste, in particular in the decontamination of the radioactive contaminated surfaces of the components.

BACKGROUND OF THE INVENTION

A method and an apparatus for the disposal of an organic substance are known from DE-A-41 26 971. By means of this method and the corresponding apparatus, the organic acids used for decontamination of the surface of radioactive contaminated components are treated.

After such decontamination, there remains a solution which, in addition to the proportion of acids which has not been chemically altered, contains chemicals formed during decontamination as well as radioactive substances which have been removed from the surface of the components. Such a solution must be solidified and finally stored in drums.

In order to accommodate as little final storage as possible, there is an attempt to reduce the volume of the solution before hardening.

It is known that hydrogen peroxide is introduced into the solution while it is in contact with the catalyst. Carbon dioxide and video are then formed as essential decomposition products. The concentration of the solution is thereby reduced, so that after one evaporation stage only a relatively small volume remains, which must be solidified and fed to the final depot.

The known method and the corresponding apparatus need a catalyst for the disposal of the organic substance. Such a catalyst must be brought into contact with the substance. Thereafter, the fixed catalyst substance must be kept floating in the liquidated solution. A variant requires costly maintenance of the catalyst.

During decontamination, metals in the form of anions and cations are produced as waste. Usually anion exchangers and cation exchangers are used to remove these metal ions. The anion exchanger removes the anionic metal complexes and also the decontamination chemicals. For this, a complete anion exchanger is needed. This results in a large amount of ion exchange resin which must be removed.

As a rule, the remaining solution is evaporated and the concentrate thus obtained is finally stored. The decontaminated system is finally rinsed and the rinsing water is evaporated. Thus, very large amounts of solutions or water must be treated.

The object of the invention was to provide a process for the disposal of an aqueous solution containing an organic acid which does not require the use of a costly catalyst. Appropriate equipment for the disposal of such an aqueous solution should also be provided.

After decontamination, little ion is produced, especially as waste

- 3 x resin and do not give rise to large amounts of solution which would have to be disposed of.

SUMMARY OF THE INVENTION

The first object is achieved by irradiating the solution with ultraviolet radiation, thereby reducing the iron complex and forming a dissolved iron salt and carbon dioxide, removing part of the dissolved iron salt from the solution by cation exchange, removing the other part of the dissolved salt iron, part of the acid and added oxidant form water and re-form the iron complex and that remain; the solution containing the iron complex and still unassociated organic acid is irradiated again with ultraviolet radiation and the cycle is continued until the organic acid is completely removed.

The iron complex present in the aqueous solution to be disposed of has entered this solution, for example, during decontamination. Such a solution may also contain chromium-nickel complexes which, instead of the iron complex, may contribute to the disposal of the aqueous solution containing the organic acid.

The process according to the invention achieves the advantage that the organic acid present in the solution is completely converted into carbon dioxide and water without the need for a catalyst. The process for the disposal of the organic acid can already be started during decontamination. No load equipment required. The process can be carried out, for example, directly in a tank which is decontaminated. Carbon dioxide can be removed as it does not contain radioactive substances.

The re-formed iron complex is advantageously reused in the process according to the invention. This creates a circular storyline.

The cycle provides that the complex iron anions are preferably converted to iron cations. Therefore, only cation exchangers have to be used, and no anion exchanger need be used.

The amount of ion exchange resin to be removed is preferably oriented only to the actual removal of the cations of the decontaminated system. This amount of resin is about a factor of 20 less than the amount of resin produced as waste in known decontamination processes. This is the case when the method of the invention is used to dispose of a saturated decontamination solution. A small amount of resin requires only a small final storage.

By means of the process according to the invention, the solution can advantageously be purified to such an extent that it can be reused, for example as a cooling medium, for later operation of the decontaminated system.

The costly disposal of the solution with the degree of evaporation falls out. The decontaminated system does not even need to be rinsed, leaving large amounts of water as waste, which should later evaporate.

Disposable dye solution; already contains an iron complex. This is formed from a portion of the organic acid to be removed and iron ions still present in the solution to be removed. These iron ions may enter the tank to be decontaminated, for example during the contamination process or previously.

However, if no iron ions are present in the solution, for example, ionized iron (iron ions) may be admixed to the solution to convert part of the acid into an iron complex. Thereafter, for example, an iron salt can be introduced into the solution, which ionizes there, thereby forming, inter alia, iron ions. The addition of iron ions provides the advantage that even if the iron ions should be absent in solution, the iron ions are sufficiently provided to convert part of the acid into an iron complex.

Ionized iron, for example, has a certain valency and forms an iron complex with a portion of the acid in which the iron has the same valence (an iron complex with the same valency).

For example, the ionized iron is trivalent formed with a portion of the organic ferric acid complex.

By irradiation with ultraviolet radiation, this complex is converted to form soluble carbon monoxide to form carbon dioxide, in which the iron valence is, for example, 1 smaller than the iron valence in the complex. . Iron Sol, whose valency is 1 less than that of the iron complex. This dissolved iron salt, acid residue and oxidizer to be added re-form the iron complex. In addition, water is produced.

The ferric complex is converted, for example, to a dissolved ferrous salt (divalent iron salt). This dissolved ferrous salt, organic acid residue and oxidizer that is added, the chemical reacts to form water and iron again—

- 6 th complex. This ferric complex corresponds to the previous ferric complex. Thus, the ferric complex is regenerated.

In the event that the entire organic acid residue has not reacted chemically with the iron salt and the oxidant because, for example, the amount of iron salt was not sufficient, the regenerated iron complex can be re-formed by irradiation with ultraviolet radiation to carbon dioxide and the dissolved iron salt. The iron salt is then reacted with the added oxidant and the remaining organic acid to re-form the iron-water complex. Preferably, a cycle occurs until the entire amount of organic acid is converted into a relatively small amount of iron salt which is removed by kgtex and into carbon dioxide and water. The carbon dioxide and water are removed.

The corresponding cycle is also possible using another ionized metal.

For example, if the organic acid is oxalic acid, reactions occur according to the following chemical equations:

(1) 3H ₂ C ₂ O ₄ + Fe IU - ^ FeUI (C ₂ O ₄ ) ₃ J ₃ Stannic acid + ferric ferric complex (2) ^ FeUI + UV — Fe (c ₂ O ₄ ) 2 + 2 C0 ₂ ferric complex + UV -> ferrous Sol + C0 «(3)

FelI (C ₂ O ₄ ) ₂ · + H ₂ C ₂ O ₄ + H ₂ O ₂ ferrous salt + 'oxalic acid + hydrogen peroxide' ^ FeIII (C ₂ O ₄ ) 3J ³ + 2 H ₂ 0> ferric complex. + h ₂ 0

The ferric complex formed by the reaction of chemical equation (3) is reused in the reaction of chemical equation (2). The two chemical reactions (2) and (3) alternate until the entire amount of oxalic acid is consumed. Only a small amount of ferrous salt remains in addition to CO2 and 40.

An appropriate cycle is also possible with any other metal complex that may be formed initially by the ionized metal.

No separate tank is required to run the cycle. It can even be carried out in a previously decontaminated tank.

The organic acid, which is not converted to the ferrous salt, is converted, by means of a cycle, completely completely into water and carbon dioxide, which do not need any expensive removal. Carbon dioxide may be removed.

The oxidant may be, for example, hydrogen peroxide or ozone, which are particularly suitable.

The concentration of the oxidant is, for example, 0.002 mol / l to 0.02 mol / l, in particular 0.005 to 0.007 mol / l. At a significantly higher concentration of hydrogen peroxide, less organic acid would be converted due to the UY-absorption of hydrogen peroxide.

A particularly suitable wavelength of the ultraviolet radiation used lies between 250 nm and 350 nm.

The second task, providing appropriate equipment

- 8 for the disposal of an aqueous solution with a tank for this solution containing organic acid and an iron complex and produced as waste, in particular during decontamination.Radioactive contaminated surfaces of building components, according to the invention is solved by leaving the tank and discharging into a negative circulation pipe. that the circulation line comprises a UV-irradiation portion and that it is associated with the circulation line. an associated supply line, an oxidant comprising a metering device, and a cation exchanger.

In the UV-irradiation section, the iron complex present in the solution is caused to be reduced so as to form a dissolved iron salt and carbon dioxide. Carbon dioxide is removed as a gas through the outlet. An appropriate amount of oxidant is then fed via the metering device through the supply line. The supply line may be connected via a tank or directly to the UV-irradiation section or elsewhere may flow into the circulation line. This ensures that the oxidant reaches where there is a solution at this point that contains the dissolved iron salt and the organic acid.

After the oxidant is filled, the iron complex is formed in addition to water. This iron complex corresponds to an iron complex that had previously occurred. This ensures that a cyclic process can take place. Again, the iron complex is irradiated with ultraviolet radiation and thereby reduced. In turn, dissolved iron salt and carbon dioxide are formed and the iron salt together with the remaining acid and oxidant re-form the iron complex as well as the water. This ring process can be continued until all the acid is consumed.

It may be connected to the tank or the circulation pipe

- 9 a supply line for a solution containing iron ions through a metering device. At the beginning of the process, a solution containing iron ions is filled through this inlet pipe if there are no iron ions in the solution present in the tank, but the iron ions are mostly present. If there were no iron ions in solution, no iron complex formed from the iron ions and the part of the acid to be removed could be present.

Since preferably no interfering anions are present, the remaining solution can be purified by Vatex to such an extent that it can be reused, for example, as a cooling medium. Therefore, no evaporators are required and therefore no evaporation residues need to be removed.

The chemical cyclic process is carried out in the circulation apparatus until the partial amount of organic acid which eventually remains after the reaction has been converted. This is possible because the iron complex S8 does not retain in the cation exchange. When the entire amount of acid is consumed, no iron complex is formed. Eventually a small amount of iron salt remains in the solution. However, the cationic portion of this iron salt is removed from the solution by cation exchange. Likewise, radioactive cations which may be in solution from the decontamination process are removed by means of a cation exchanger. The remaining solution no longer has to be processed further and can be reused as a cooling medium.

In particular, the method and apparatus of the present invention provide the advantage that, in the chemical cycle, the organic acid can be completely converted to carbon dioxide and water without the use of expensive catalyst technology. In addition, after the de-ontamination is carried out, neither an anion exchanger nor an evaporator is required to remove residuals.

An apparatus for disposing of an aqueous solution containing an organic acid is explained in more detail on the basis of the drawing.

DETAILED DESCRIPTION OF THE INVENTION

In the drawing there is shown a tank which may be a deconteminated tank and which is part of the circulation pipe 11. After decontamination has been carried out, the organic acid remains in the solution tank 1 and must be removed. However, the tank 1 may also be a separate tank into which an aqueous disposal solution containing organic acid is filled. The tank 1 has a filling opening 11 through which the disposal solution is then filled. In the case where the decontamination is carried out in the tank 1, the decontamination chemicals enter the tank before decontamination. In the event that the solution to be disposed of contains no iron complex, it is proposed to supply line 3 for iron ions which can be supplied in the form of dissolved salt of the iron. This supply line 3 comprises a metering device 4 and flows into the circulation line 2. It can also flow directly into the tank 1. Iron ions convert the portion of the organic acid present in the solution into an iron complex.

A UV-irradiation section 5 is connected to the outlet 3 of the tank 1, which is part of the circulation pipe 2. By means of irradiation with ultraviolet radiation, the iron complex in solution is reduced there, so that a dissolved iron salt and carbon dioxide are formed.

The carbon dioxide exits the UV-irradiation section 5 via an outlet 18 connected thereto. Carbon dioxide can be evacuated as it does not contain any contaminants.

The oxidant feed line 7 then enters the oxidant into the circulation line 2, in which the dissolved iron salt and the balance of the organic acid are present. The addition of the oxidant takes place via the metering device 8, which is located in the supply duct 7. The inlet ducts and / or 7 can also exit at a not shown location downstream of the UV-irradiation section 5 or directly to the UV-irradiation section 5. From the dissolved iron salt, part of the acid and oxidant, water is formed and again an iron complex corresponding to the aforementioned iron complex. From this point on, the cycle may be repeated: The iron complex is again reduced by ultraviolet radiation to form the dissolved iron salt and carbon dioxide. The oxidant is then reacted again to form the iron-water complex from the iron salt and the other part of the acid. Finally, after a number of such cycles, the entire amount of carbon dioxide, water and a small amount of iron salt are converted.

If the solution to be disposed of was a decontamination solution, the remaining solution still contains radioactive substances removed by decontamination. These substances and the cationic portion of the iron salt are removed from the solution by means of a cation exchanger 10, which can additionally be attached to the UV-irradiation portion. Nevertheless, the remaining liquid is so pure that it can be reused as a cooling medium, for example in a power plant. The cation exchanger 10 is arranged in the circulation pipe 2. It can be bridged by bypass 12 so that part of the solution can be passed around the kgtex 10 and thus not be released from the iron salt while iron salt is still required to re-form the iron complex. Typically, however, only one portion of the iron salt is removed from the solution with a cation exchanger 10 per flow.

No evaporator is necessary to remove residual liquid. Little waste of ion exchange resin is produced as waste and does not produce any evaporation residue which would have to be removed.

The emptying opening 13 serves for emptying the shown arrangement. In the circulation pipe 2 a pump 14 can be installed.

Claims (12)

A process for the disposal of an aqueous solution comprising an organic acid and an iron complex and which is produced in particular as waste in the decontamination of radioactive contaminated building surfaces, characterized in that the solution is irradiated with ultraviolet radiation, thereby reducing the iron complex and forming dissolved sol iron and carbon dioxide, that part of the dissolved iron salt is removed from the solution by cation exchange, that the other part of the dissolved iron salt, part of the acid and the added oxidant form water and again the iron complex, and that the remaining iron-containing solution and the decomposed organic acid is irradiated again with ultraviolet radiation and the cycle is continued until the organic acid is completely removed. Method according to claim 1, characterized in that ionized iron is admixed with the solution to convert part of the acid into an iron complex. Method according to claim 2, characterized in that part of the acid is converted by means of ionized iron of a certain valency into an iron complex of equal valency. 4. A process according to claim 3, wherein a portion of the acid is converted to the ferric complex by means of ionized trivalent iron. 14 Method according to one of Claims 1 to 4, characterized in that the iron complex is dissolved in solution to form a dissolved iron salt, whose valency is 1 less than the valency of the iron in the complex. 6. A process according to claim 5, wherein the ferric complex is dissolved in the solution to form a dissolved ferrous salt, part of the dissolved ferrous salt is removed from the solution by kstex, and the other portion of the dissolved iron salt is re-formed as a ferric complex. 7. A method according to one of the nations 1 to 6, characterized in that the oxidant is hydrogen peroxide or ozone. Method according to one of Claims 1 to 7, characterized in that the concentration of the oxidant is 0.002 mol / l to 0.02 mol / l. The method of claim 8, wherein the oxidant concentration is 0.005 mol / L to 0.007 mol / L. Method according to one of Claims 1 to 9, characterized in that the ultraviolet radiation has a wavelength of 250 nm to 350 nm. 1 1. Apparatus for the disposal of an aqueous solution by a method according to one of claims 1 to 10 with a solution tank (1) containing organic acid and an iron complex and which is produced as waste, in particular in decontamination of radioactive contaminated surfaces of building components, that a circulation pipe (2) emerges from the tank (1) and flows into it, that the circulation pipe (2) comprises an ultraviolet irradiation component (5) and that it is circulating; a conduit (7) for the oxidant, which comprises a metering device (8) and a cation exchanger (10), is assigned to the conduit (2). Apparatus according to claim 11, characterized in that an inlet pipe (3) for a solution containing iron ions is assigned to the circulation pipe (2), which comprises a metering device (4).