EP0318367A1 - Process for conditionning radioactive or toxic waste in thermosetting resins - Google Patents

Abstract

Process for packaging in a heat-curable resin wastes which are stored in water. …<??>According to the invention, a water-immiscible hardener whose density is higher than that of water is employed for producing the curing of the resin, this hardener is mixed with the wastes which are stored in water, the wastes are then allowed to settle in the hardener, the water present above the settled wastes which have been transferred into the liquid hardener is extracted, and the wastes transferred into the liquid hardener are mixed with the epoxy resin to obtain a solid block. …<??>The wastes may be, in particular, ion exchange resins. The addition of the hardener to the wastes which are stored in water makes it possible to limit the increase in temperature during the hardening and to obtain solid products which have an improved density.

Description

The present invention relates to a process for packaging radioactive or toxic waste in thermosetting resins.

More specifically, it relates to the packaging of radioactive or toxic waste stored in water, in particular radioactive waste comprising ion exchange resins and / or acidic compounds.

In nuclear installations, ion exchange resins are used in particular to purify contaminated water, in particular the effluents from these installations. After a certain time, these resins undergo degradation phenomena and consequently lose their effectiveness. Since these used resins have fixed a certain number of radioelements during their use, it is then necessary to condition them in an appropriate material to ensure good retention of their radioactivity.

There are also in nuclear installations waste consisting of acid-functional materials, for example acid compounds such as salts such as lead iodide, in the form of powder or grains in a humid environment, which is also necessary. condition after use to ensure good retention of the radioactivity attached to these materials.

Among the processes currently developed for treating this type of waste, there are in particular processes for conditioning in thermosetting resins such as epoxy resins. These processes are described in particular in French patents FR-A-2 251 081, FR-A-2 361 724, FR-A-2 544 909 and FR-A-2 577 709.

In the first three French patents which apply in particular to the treatment of exchange resins, ion, it is planned either to directly coat the ion exchange resins in the thermosetting resin (FR-A-2 251 081), or to subject the resins to a pretreatment to saturate their active sites with a basic compound and the then coat in the thermosetting resin (FR-A-2 361 724), or use appropriate amino hardeners with epoxy resins to directly carry out the coating in order to effect this saturation at the time of hardening and to avoid pretreatment with a basic compound. In all cases, the waste which is stored in the water is first of all subjected to a wringing before incorporating it in the mixture of thermosetting resin and hardener so as not to coat the water in which it was conveyed and stored.

The implementation of this preliminary spin step leads to certain drawbacks. Indeed, during the final mixing of the wrung waste with the resin and the hardener, it is difficult to avoid that air is included in the mixture due to the viscosity of the products used and the increase in temperature resulting from the exothermicity of the reactions. This presence of air is harmful because it lowers, on the one hand, the density of the solid block, and it increases, on the other hand, the porosity at the expense of the confining power.

It would therefore be desirable to improve the methods described above to avoid this inclusion of air in the final product.

The subject of the present invention is precisely a process for packaging waste stored in water in a thermosetting resin which makes it possible to avoid this drawback.

• a) addition et mélange du durcisseur liquide aux déchets stockés dans l'eau,
• b) décantation des déchets avec le durcisseur liquide,
• c) extraction de l'eau présente au-dessus des déchets décantés et transférés dans le durcisseur liquide, et
• d) mélange des déchets transférés dans le durcisseur liquide avec la résine thermodurcissable.

This process consists in mixing the waste with the thermosetting resin and a liquid hardener, characterized in that a liquid hardener is used, immiscible with water, having a density greater than that of water, and in that the process comprises the following successive steps:

• a) adding and mixing the liquid hardener to the waste stored in water,
• b) decanting the waste with the liquid hardener,
• c) extraction of the water present above the decanted waste and transferred to the liquid hardener, and
• d) mixing of the waste transferred into the liquid hardener with the thermosetting resin.

In the process of the invention, the resin hardener is thus used as the liquid phase for transferring the waste into the thermosetting resin. This makes it possible to avoid the introduction of air into the mixture and to facilitate the water extraction operation since it suffices to allow the solid waste to settle naturally for a few minutes in order to be able to easily extract the water located above it. above the waste transferred into the liquid phase of the hardener. This avoids the inclusion of air and the coating of waste storage water in the thermosetting resin.

In the process of the invention, thermosetting resins suitable for coating radioactive or toxic waste can be used, provided that these can be hardened by a liquid hardener having a density greater than that of water.

By way of example of such thermosetting resins, mention may be made of unsaturated polyester resins, vinyl resins, epoxy resins and phenoplast resins.

Preferably, in the invention, an epoxy resin is used which can be cured by active hydrogen hardeners such as amines, phenols, polyacids and polyalcohols.

Generally, an amino hardener is used which can be introduced in the pure state or in the form of a solution in a suitable diluent, or alternatively in the form of an adduct, that is to say the product of the reaction of a weak amount of the epoxy resin with an amino compound, to which a diluent can also be added if necessary to obtain a liquid phase having the desired viscosity.

As an example of diluents that may be used, mention may be made of benzyl alcohol.

The method of the invention can be used for the treatment of different types of radioactive or toxic waste stored in water.

By way of example, the radioactive waste can be used ion exchange resins, precipitation sludge originating for example from the chemical treatment of radioactive waste water, activated carbon originating from filtration and purification installations, precipitates forming. for example during storage of radioactive residual solutions and residual deposits forming for example in storage containers.

By way of example of toxic waste, mention may be made of cadmium and arsenic derivatives, cyanides, chromium derivatives, mercury and its salts, tin and antimony derivatives, thallium derivatives, solid residues containing plant protection agents, insecticides, fungicides, etc.

The method of the invention applies in particular to the treatment of radioactive waste comprising ion exchange resins and / or acidic compounds.

In this case, according to a preferred embodiment of the process of the invention, use is made of an epoxy resin and a liquid amine hardener capable of saturating the active sites of ion exchange resins and / or acid compounds, as it is described in French patent FR-A-2,544,909.

The amino hardener may comprise at least one amino compound chosen from the group consisting of cycloaliphatic and aromatic amines, aromatic and cycloaliphatic polyamines, propylene amine derivatives and polyaminoamides.

Preferably, the amino hardener consists of an adduct which is the product of the reaction of a small amount of the epoxy resin with one of the amino compounds mentioned above. You can also add a thinner to obtain a liquid phase with the desired viscosity.

When such amine hardeners are used with ion exchange resins, it is generally necessary to introduce them in excess of the amount required to cure the epoxy resin and also saturate the active sites of the epoxy resin.

Also, to avoid using such an excess, it is preferred to choose amino hardeners constituted by a mixture of an aromatic amine or polyamine and an aliphatic or cycloaliphatic amine or polyamine, as described in FR-A-2,544 909.

When such a mixture is used, the aromatic amine or polyamine can be present in the form of an adduct with a small amount of the epoxy resin. One can also add a non-reactive diluent such as benzyl alcohol.

In all cases, the liquid hardener may further comprise a hardening accelerator, consisting for example of the reaction product of acrylic acid, benzoic acid, salicylic acid, or phenol resorcinol with a amino compound, for example diaminodiphenylmethane. Other additives can also be added to the liquid hardener, for example compounds capable of preventing the decantation of radioactive or toxic waste in the resin during hardening, for example a thixotropic agent, or a product such as a solution pitch, as described in French patent FR-A-2,577,709.

In this preferred embodiment of the process of the invention, the fact of adding the liquid amine hardener before mixing the waste with the epoxy resin makes it possible to limit the exothermicity of the hardening reaction. In fact, during the conditioning of ion exchange resins, the amino hardener reacts with the active sites of the resins to neutralize these, and a temperature rise is generally obtained due to the exothermicity of the neutralization reaction which is added to the temperature increase due to neutralization which is added to the increase in temperature due to the curing reaction which is also exothermic. However, in order to obtain solidified products having satisfactory characteristics, it is necessary not to exceed 100 ° C., which poses certain problems.

In the process of the invention, this neutralization reaction is carried out in water, before the actual hardening reaction, and the heat produced during this neutralization reaction is diluted or eliminated by water. Therefore, the initial temperature of the polymerization reaction is no longer influenced by this neutralization reaction, and the maximum temperature reached during the curing of the epoxy resin is lower, by at least 10 ° C, than that reached when the dewatered waste is directly mixed with the resin and the hardener.

Furthermore, the fact of adding the liquid hardener to the waste stored in water makes it possible to simplify the operation of kneading the resin with the waste. In fact, the mixture of waste and hardener is more fluid than waste alone, and less energy is used for the mixing operation.

The following examples, of course given without limitation, illustrate the packaging of ion exchange resins in an epoxy resin by the process of the invention.

EXAMPLE 1

In this example, ion exchange resins in the form of beads are conditioned in an epoxy resin which consist of a mixture of 60% by weight of anion exchange resins in OH-IRA 400 form sold by ROHM and HAAS and of 40%. by weight of cationic resins in Na⁺ IR 120 form sold by ROHM and HAAS.

In this example, an epoxy resin constituted by a diglycidyl ether of bisphenol A having an epoxide equivalent of approximately 190 diluted with neopentyl diglycidyl ether and marketed by CDF Chimie under the reference MN 201T, and a hardener consisting of the product are used. sold under the reference D6M5 by CDF Chimie, which is composed of a cycloaliphatic polyamine having an amine equivalent of approximately 63 and a diaminodiphenylmethane adduct and epoxy resin MN 201 T having an amine equivalent of approximately 130.

The amounts of resin and hardener used are respectively 100 and 60 parts by weight with a weight ratio, ion exchange resins / (thermosetting resin + hardener), equal to 1.

For a final volume of 200 l, 110 kg of the mixture of ion exchange resins with their transfer water are first introduced into a 225 l container. 41.3 kg of the hardener D6M5 are added thereto, the whole is mixed for 3 minutes, then the mixture is allowed to settle for a few minutes so that the hardener D6M5 and the ion exchange resins are entrained at the bottom of the container. The supernatant water is then removed by pumping, then 68.7 kg of the MN 201 T epoxy resin are added and the mixture is mixed using a lost-blade agitator driven by an electric motor for about 5 minutes.

The mixture is then left to harden for 24 hours at room temperature, and the density of the product obtained is determined.

In the annexed table 1, the density obtained is indicated as well as the conditions used to carry out the packaging.

COMPARATIVE EXAMPLE 1

In this example, the same mixture of ion exchange resin is packaged in the same epoxy resin using the method of the prior art described in FR-A-2,544,909.

In this case and for a final volume of 200 l, the mixture of ion exchange resins is first wrung for 8 minutes to remove the storage water, then 100 kg of the mixture of wrought ion exchange resins are introduced. in the 225l container. Then added 62.5 kg of the epoxy resin MN 201T and 37.5 kg of hardener D6 M5 and the mixture is kneaded also using a stirring paddle driven by an electric motor and then the product is allowed to harden at room temperature. The density of the product obtained after hardening is then determined.

The results and the conditions used for conditioning are also indicated in table 1 appended.

In view of this table, it can be seen that the method of the invention makes it possible to obtain a density gain of 10%, a time saving of 160% over the pumping time of the water, a gain of 12% over the maximum temperature reached during hardening and a gain of 360% on the intensity necessary to achieve agitation of the mixture.

It is thus noted that the process of the invention is safer with regard to the maximum temperature reached, since the margin of safety with respect to the limit temperature of 100 ° C. is greatly increased. Likewise, the product obtained has improved safety characteristics since it is denser. Finally, an economic gain is obtained on the energy required to carry out the agitation as well as on the pumping time of the water.

EXAMPLE 2

In this example, in the same way as in Example 1, a mixture of ion exchange resins in the form of beads is conditioned, identical to that of Example 1, but using:
- an epoxy resin from Ciba Geigy referenced LMB 4203,
- a Ciba Geigy hardener referenced LMB 4278,
- a thixotropic agent also from Ciba Geigy referenced LMB 4212. In this case, the thixotropic agent is added to the hardener and the amounts of resin, hardener and thixotropic agent are respectively 90, 60 and 10 parts by weight. The weight ratio, ion exchange resins / (epoxy resin + hardener + thixotropic agent) is equal to 1.

We operate in the same way as in Example 1 but in using the amounts of ion exchange resin, epoxy resin, hardener and thixotropic agent given in the attached Table 2.

The density obtained and the conditions for carrying out the packaging are indicated in this table 2.

COMPARATIVE EXAMPLE 2

In this example, the same mixture of ion exchange resin and the same epoxy resin, the same hardener and the same thixotropic agent as in Example 2 are used, but the packaging is carried out using the process of the prior art as in Comparative Example 1.

The quantities used, the density of the product obtained and the reaction conditions are given in the attached Table 2.

In view of this table, it can be seen that the process of the invention makes it possible to obtain:
- a gain of 9% on the density of the finished product,
- a gain of 18% on the maximum temperature reached during polymerization,
- a gain of 320% on the intensity necessary to carry out the agitation, and
- a gain of 100% on the pumping time of the water.

The method of the invention thus allows many advantages to be obtained compared to the method of the prior art.

Claims (10)

1. A method of packaging waste stored in water in a thermosetting resin, consisting of mixing the waste with the resin and a liquid hardener, characterized in that a liquid hardener, immiscible with water, having a density greater than that of water, and in that the process comprises the following successive stages: a) adding and mixing the liquid hardener to the waste stored in water, b) decanting the waste with the liquid hardener, c) extraction of the water present above the decanted waste and transferred to the liquid hardener, and d) mixing of the waste transferred into the liquid hardener with the thermosetting resin. 2. Method according to claim 1, characterized in that the thermosetting resin is an epoxy resin. 3. Method according to any one of claims 1 and 2, characterized in that the waste comprises ion exchange resins and / or acidic compounds. 4. Method according to any one of claims 2 and 3, characterized in that the liquid hardener is an amine hardener. 5. Method according to claim 4, characterized in that the amino hardener comprises at least one amino compound chosen from the group consisting of cycloaliphatic and aromatic amines, cycloaliphatic and aromatic polyamines, derivatives of propylene amine and polyaminoamides. 6. Method according to claim 5, characterized in that the amino hardener consists of an adduct which is the product of the reaction of a small amount of the epoxy resin with the amino compound. 7. Method according to claims 2 and 3, characterized in that the liquid hardener consists of a mixture an aromatic amine or polyamine and an aliphatic or cycloaliphatic amine or polyamine. 8. Method according to claim 7, characterized in that the aromatic amine or polyamine is in the form of adduct with a small amount of the epoxy resin. 9. Method according to any one of claims 1 to 8, characterized in that the liquid hardener comprises a thixotropic agent. 10. Method according to any one of claims 1 to 9, characterized in that the liquid hardener comprises pitch.