EP0522931A1 - Block containing contaminated ion-exchange resins and process for its preparation - Google Patents

Abstract

Block containing contaminated ion exchange resins with a view to their storage, the invention being characterised in that the ion exchange resins are incorporated, after saturation with water, in a composite matrix consisting of a cured hydrophilic epoxy resin and a hardened cement chosen from clinker slag cements and cements containing clinker and ash, to which the water necessary for the hydration of the components of the cement has been added. By virtue of the presence of cement in the composite matrix the core temperature of such blocks can be limited to 55-63 DEG C during their preparation. <IMAGE>

Description

The present invention relates to a block containing ion exchange resins contaminated, for example by toxic or radioactive elements, as well as a process for preparing such a block. It is particularly applicable in the field of storage of ion exchange resins contaminated by radioactive elements of low and medium activity.

The ion exchange resins used to purify water in nuclear installations undergo degradation phenomena after a certain time and consequently lose their effectiveness. It is then a question of storing these used ion exchange resins which, during their use, have fixed various radioelements giving them a certain radioactivity.

Several methods are known for conditioning these contaminated resins for storage. Among these, the coating methods in thermosetting resins, such as those described in documents FR-A- 2 251 081, FR-A- 2 361 724 and EP-A- 0 127 490 are satisfactory because they allow to ensure good retention of radioactivity, but they nevertheless have certain drawbacks.

Thus, the process of document FR-A-2 251 081 is not suitable for incorporating into an epoxy resin cationic resins which are not completely used because in this case, the polymerization of the epoxy resin is partially inhibited by the cationic resin which consumes certain compounds necessary for curing the resin.

This phenomenon can be avoided by carrying out a pretreatment in basic aqueous solution of the ion exchange resins as described in the document FR-A-2 251 081, but carrying out this additional step constitutes a drawback, all the more so since 'it leads to the production of new effluents contaminated by radioactive elements.

The process described in EP-A-0 127 490 also makes it possible to incorporate cationic resins which still have active sites into an epoxy resin, but it has the disadvantage of requiring the use of particular amine hardeners which are relatively expensive products. .

In addition, the processes using these thermosetting resins are sensitive to the initial temperature which accelerates the polymerization and / or leads to a release of heat detrimental to the quality of the block formed.

Also known from EP-A-0 274 927 is a process for packaging waste in composite matrices based on cement and epoxy resin, but in this case, the radioactive waste consists of chemical co-precipitation sludge which may contain 20 to 40% of water, dry pulverulent waste such as the incineration ashes of combustible materials or technological, non-combustible waste such as glass and metals.

It has also been considered to include ion exchange resins in a cement matrix, but this process is of limited interest due to the low coating coefficient obtained and the need to also carry out a pretreatment of the resins. to avoid any interaction with cement, as described by J. Duquesne - Cogéma and C. Jaouen SGN - Concrete Encapsulation of Ion Exchange Resins-International Conference Recod 87 - August 23 - 27, 1987 - Paris.

The present invention specifically relates to a block containing ion exchange resins contaminated for storage, which overcomes the drawbacks mentioned above of the known methods.

According to the invention, the block containing ion exchange resins contaminated for storage is characterized in that the ion exchange resins are incorporated in a composite matrix consisting of a hardened hydrophilic epoxy resin and a cement. hardened chosen from Clinker's slag cements and slag and ash cements.

In the block of the invention, the choice of a hydrophilic epoxy resin and a cement with a low heat of hydration constitutes by a clinker slag cement (CLK) and / or a slag cement and with fly ash ( CLC) provides a matrix compatible with ion exchange resins, even when these are saturated with water and contain, for example, 50 to 55% by weight of water, and / or contain active sites usually requiring pretreatment.

Furthermore, the choice of this matrix makes it possible to obtain a high coating coefficient and a block having very interesting physical and mechanical properties, in particular better resistance to compression.

In Figure 1 attached, there is shown the triangular Rankin diagram illustrating the compositions various cements in the ternary silica-alumina-calcium oxide system.

In this diagram, it can be seen that CLC and CLK cements have very different compositions from those of Portland cements and aluminous cements.

In addition, CLK and CLC cements have lower hydration heats than those of Portland and aluminous cements and a slower hydration kinetics.

In Table 1 below, the hydration heats (in J / g) are reported at 12 h and 1 day for CLK, CLC and Portland cements, giving the average value, the minimum and the maximum.

From this table, it can be seen that Portland cement has a much higher heat of hydration than CLK and CLC cements.

As a result, larger masses of waste can be coated in CLK and CLC cements because the temperature increase remains limited (<100 ° C) during coating.

On the other hand, when coating ion-exchange resins in a barrel of 200 l or more of Portland cement, the temperature can reach 120 ° C at the core, which causes the distillation of the water included in the exchange resins d 'ions and a degradation of the properties of the barrel.

• libération du ¹³⁷Cs ralentie,
• faible perméabilité obtenue grâce au grain fin de matériau, et
• bonne stabilité en présence sels tels que les nitrates et les sulfates.

CLC and CLK cements also have the following advantages:

• release of ¹³⁷Cs slowed down,
• low permeability obtained thanks to the fine grain of material, and
• good stability in the presence of salts such as nitrates and sulfates.

According to the invention, the proportions by weight of hardened cement and epoxy resin used in the constitution of the matrix are chosen so as to obtain the desired characteristics of radioelement retention, resistance to leaching and mechanical resistance for storage. of the block with a high degree of safety.

• de 35 à 65% en poids de résine époxyde durcie, et
• de 35 à 65% en poids de ciment durci au laitier de Clinker et/ou de ciment durci au laitier et aux cendres volantes.

Generally, the composite matrix includes:

• from 35 to 65% by weight of hardened epoxy resin, and
• from 35 to 65% by weight of cement hardened with slag from Clinker and / or cement hardened with slag and fly ash.

With this matrix, relatively large amounts of ion exchange resins can be included in the block; it can thus contain up to 45% by weight of contaminated ion exchange resins, saturated with water, whereas in the in the case of CLK cement alone, only 15 to 20% by weight of ion exchange resins could be coated.

These ion exchange resins can be constituted by cationic exchange resins, anionic resins or mixtures of these resins, in the form of grains or particles obtained by grinding.

Generally, these are organic ion exchange resins such as polystyrene resins crosslinked with divinyl benzene which comprise, for example, sulfonic groups or hydroxyl groups.

In the block of the invention, a hydrophilic epoxy resin is used, compatible both with the cement used and with the ion exchange resin to be conditioned.

By way of example of such hydrophilic epoxy resins, mention may be made of the diglycidyl ether of bis-phenol-A and the diglycidyl ether of bis-phenol-F hardened by reaction with an amino hardener.

Le diglycidyl éther de bis-phénol F répond à la formule :

It is specified that the diglycidyl ether of bis phenol A corresponds to the formula:

The bis-phenol F diglycidyl ether corresponds to the formula:

In the invention, the use of a hydrophilic epoxy resin is advantageous because it facilitates obtaining a homogeneous mixture with the cement, in the presence of water.

The invention also relates to a process for the preparation of the block containing the contaminated ion exchange resins, described above.

• 1) saturation en eau des résines échangeuses d'ions contaminées,
• 2) addition sous agitation de l'eau nécessaire à l'hydratation du ciment aux résines échangeuses d'ions saturées en eau,
• 3) addition du ciment, sous agitation à la suspension obtenue en 2), et
• 4) addition au mélange obtenu en 3) de la résine époxyde et de son durcisseur.

This process includes the following successive steps:

• 1) water saturation of contaminated ion exchange resins,
• 2) addition with stirring of the water necessary for the hydration of the cement to the ion-exchange resins saturated with water,
• 3) addition of the cement, with stirring to the suspension obtained in 2), and
• 4) addition to the mixture obtained in 3) of the epoxy resin and its hardener.

In the first step of this process, the contaminated ion exchange resins are saturated with water, which is done by immersing these resins in water for a sufficient time, for example for 24 hours. After this operation, the ion exchange resins are drained until disappearance of the water flow in order to ensure that the ion exchange resins contain only their saturation water which generally represents approximately 50 to 55% by weight of the saturated ion exchange resins, but can go in certain case up to 65% by weight.

In the second step of the process, the water necessary for the hydration of the cement is then added to the resins by carrying out this operation with stirring. The amount of water of hydration needed for curing Clinker's slag cements or slag and fly ash cements depends on the amount of cement that will be introduced into the block. It is generally such that the hydration water / cement weight ratio is from 0.25 to 0.35.

After introduction of the water, the cement is added with stirring and this stirring is continued until a fluid paste is obtained, then the epoxy resin in the liquid state and its amine hardener are added, continuing the agitation.

Generally, the operations of adding water, cement and epoxy resin are carried out in a mixer.

After adding the epoxy resin and its hardener, the mixture can be emulsified by rotation at high speed, left to stand and poured into a mold having the dimensions of the block to be manufactured.

After this operation, the block is allowed to harden in the mold, which can be obtained relatively quickly, for example in 12 hours.

In this process, the choice of the amine hardener is also important, because by choosing an appropriate amine hardener, the epoxy resin is allowed to harden in the presence of large amounts of water.

For example, it is possible to use amine hardeners containing a combination of aromatic and aliphatic amines, and by varying the amounts of these different amines, an optimized hardener can be obtained, suitable for the preparation of an epoxy composite matrix. cement suitable for coating ion exchange resins saturated with water to be conditioned.

Generally, the proportion of amine hardener is such that the hardener / epoxy resin weight ratio is preferably from 0.5 to 0.6.

• diminution des risques d'incendie dans les stockages en raison du pouvoir calorifique plus faible de la matrice d'enrobage,
• coefficient de gonflement par l'eau faible, et
• prix de revient inférieur de la matrice d'enrobage par rapport à celui des résines époxydes seules.

The blocks obtained by the process of the invention have very interesting properties because they are extremely hard and not very reactive to attack. In addition, they have the following advantages over ion exchange resins coated in other matrices:

• reduction of fire risks in storage due to the lower calorific value of the coating matrix,
• low water swelling coefficient, and
• lower cost of the coating matrix compared to that of epoxy resins alone.

• la figure 1, déjà décrite, est un diagramme ternaire représentant diverses compositions de ciment.
• la figure 2 est un diagramme donnant en fonction du temps la température au coeur d'un bloc conforme à l'invention, contenant des résines échangeuses d'ions contaminées, lors de son durcissement , pour deux essais identiques.
• La figure 3 est un diagramme donnant en fonction du temps la température d'un bloc de l'art antérieur, pour deux essais identiques.
• La figure 4 est un diagramme regroupant les valeurs moyennes obtenues sur les figures 2 et 3.

Other characteristics and advantages of the invention will appear better on reading the following examples, of course given by way of illustration and not limitation, with reference to the accompanying drawing in which

• Figure 1, already described, is a ternary diagram representing various cement compositions.
• Figure 2 is a diagram giving as a function of time the temperature at the heart of a block according to the invention, containing resins contaminated ion exchangers, during its hardening, for two identical tests.
• FIG. 3 is a diagram giving as a function of time the temperature of a block of the prior art, for two identical tests.
• FIG. 4 is a diagram grouping together the average values obtained in FIGS. 2 and 3.

Example 1.

• eau (78g),
• ciment au laitier de Clinker CLK 45 (222g),
• résine époxyde liquide commercialisée par la société Spado Lassailly sous la référence SL MN201T (200g), et
• durcisseur aminé commercialisé par la société Spado Lassailly sous la référence SL D6M5.

In this example, 490 g of contaminated ion exchange resins, consisting of anionic resins of the brand Rohm and Haas IR-400, are incorporated into a matrix formed from the following constituents:

• water (78g),
• Clinker CLK 45 slag cement (222g),
• liquid epoxy resin sold by the company Spado Lassailly under the reference SL MN201T (200g), and
• amine hardener marketed by the company Spado Lassailly under the reference SL D6M5.

First, the contaminated water exchange resins are saturated with water by swelling them in water for 24 h and then subjected to a spin. 400 g of drained anionic resins are then weighed and the 78 g of water added to them, that is to say the amount sufficient to hydrate the 222 g of CLK 45 cement.

The resins are mixed with water, then the CLK 45 cement is added to the suspension and the mixture is kneaded so as to obtain a very fluid paste.

Then adding, while continuing the mixing, the epoxy resin SL MN 201 T and the hardener SL D6 M5. The mixture is then poured into a mold and allowed to harden for 36 hours.

We then unmold the block obtained. This one has a very nice surface appearance. Its Shore D hardness is measured using a Shore durometer for thermosetting polymers which determines the hardness by sinking a needle mounted on a gauge. This is very high since it corresponds to a value of 70 Shore units.

The block obtained is also subjected to a water absorption test by immersing it for one month in water. After this period, it can be seen that the mass coefficient of water absorption is of the order of 1 to 3%.

The block obtained therefore has very satisfactory characteristics for the storage of anion exchange resins.

Example 2.

The same contaminated anion exchange resins and the same matrix constituents are used as in Example 1, except the hardener which in this example is the product sold by Spado Lassailly under the reference SL D 2005.

The same procedure is followed as in Example 1, using the same proportions for coating 400 g of anion exchange resins in the composite matrix.

A solid block is thus obtained having properties practically identical to those of the block obtained in Example 1, except that its external appearance is more shiny.

Example 3.

The same procedure is followed and the same matrix is used as in Example 1 to coat 400 g of cationic ion exchange resins of the Rohm and Haas IR 120 type.

The same proportions of water, cement, resin and hardener are also used.

The block obtained also has very good properties.

Indeed, its Shore hardness is 66 units and its water absorption coefficient at one month is 3%.

Example 4.

In this example, 400 g of a mixture of ion exchange resins comprising 266 g of Rohm and Haas IR 120 cationic resins and 134 g of Rohm anionic ion exchange resins are coated in the same composite matrix as that of Example 1. and Haas IR A 400.

The same procedure is followed and the same proportions are used as in Example 1,

• dureté Shore : 67 unités,
• taux d'absorption d'eau à un mois : 1 à 3%.

A solid block is thus obtained having the following characteristics:

• Shore hardness: 67 units,
• water absorption rate at one month: 1 to 3%.

Comparative example 1.

In this example, the coating of contaminated ion exchange resins is carried out using only as coating component an epoxy resin and its hardener.

• dureté Shore D : 60,
• taux d'absorption d'eau à un mois : 1%.

In this case, 200 g of water-saturated and wrung ion exchange resins are mixed with liquid epoxy resin SL MN 201T and hardener SL D6 M5 to prepare a block of ion exchange resins conditioned only in an epoxy resin having a volume of 0.5l. After 8 to 10 hours, the block is hardened and has the following characteristics:

• Shore D hardness: 60,
• water absorption rate at one month: 1%.

In Table 2 which follows, the characteristics of the block obtained in this example have been grouped together with the characteristics of blocks of 0.5 l obtained in the same way as in Examples 1 to 3.

In view of this table, it is noted that the characteristics of the blocks of the invention are more interesting, as regards the hardness and the maximum temperature at the heart of the block.

Thus, the fact of using in the invention an epoxy-cement composite matrix makes it possible, during polymerization, to limit the core temperature of the block to a value lower than that which is obtained with an epoxy resin alone.

In the case of the invention, the core temperature is limited to 58-63 ° C, while in the case of an epoxy resin alone, it can reach 78 ° C for a block of 0.5 l. Also, for blocks of larger volume, the core temperature can become higher than 100 ° C with an epoxy resin alone. However, at this temperature, the water contained in the ion-exchange resins saturated with water is brought to the boil and the water vapor generated in the block is the cause of more or less significant damage.

The use according to the invention of a composite matrix based on epoxy resin and cement thus provides a significant reduction in the exotherm of the block hardening reaction which includes both the polymerization of the resin and the hardening hydraulic binder.

For the hydraulic binder part of the matrix, the enthalpy corresponding to the setting of the binder is very substantially lower than the enthalpy of polymerization of the epoxy part.

• ΔH polymérisation (résine époxyde) = 25kcal/mol,
• ΔH hydratation (CLK) = 4 à 5kcal/mol.

By way of example, the values of the heat of polymerization, of an epoxy system and of the heat of hydration of a cement are given below. CLK:

• ΔH polymerization (epoxy resin) = 25kcal / mol,
• ΔH hydration (CLK) = 4 to 5kcal / mol.

In Figure 2 attached, the core temperature (in ° C) of 2 blocks according to the invention is shown weighing 640g, as a function of time (in h) during their hardening.

• 256g de résines échangeuses d'ions en lit mélangé (anioniques 1/3 - cationiques 2/3),
• 46g d'eau,
• 146g de ciment CLK 45,
• 128g de résine époxyde SL MN201 T,
• 64g de durcisseur SL D6M5,
• rapport résine/durcisseur : 2.

In this figure, curves 1 and 2 refer to a block prepared in duplicate from the following constituents:

• 256g of ion-exchange resins in a mixed bed (anionic 1/3 - cationic 2/3),
• 46g of water,
• 146g of CLK 45 cement,
• 128g of epoxy resin SL MN201 T,
• 64g of hardener SL D6M5,
• resin / hardener ratio: 2.

• du pic de température de polymérisation T°C=60°C ± 2°C
• du temps correspondant à l'obtention de ce pic t = 12 à 15h.

From the two curves, obtained from samples of identical mass and nature, the average values are drawn

• of the polymerization temperature peak T ° C = 60 ° C ± 2 ° C
• of the time corresponding to the obtaining of this peak t = 12 to 15 h.

• pic de temperature de polymérisation 76°C ± 2°C
• temps correspondant : 8 à 10h.

By way of comparison with the previous epoxy process, the same type of measurement was established on ion exchange resins in a mixed bed in an epoxy matrix alone. The mass of the samples is identical to the previous ones. The values obtained on two tests are represented by the curves of FIG. 3. From these two curves, the average values are drawn:

• polymerization temperature peak 76 ° C ± 2 ° C
• corresponding time: 8 to 10h.

In FIG. 4, curve A corresponds to the average values of the two curves in FIG. 2, and curve B corresponds to the average values of the two curves of FIG. 3.

These results show a decrease in the maximum polymerization temperature of 16 ° C between the cement epoxy process and the epoxy process alone. Similarly, an increase in the polymerization time of about 5 hours is observed, at the exothermic peak.

Of these two properties, the reduction of the peak of the polymerization exotherm is particularly sought after, because it increases the intrinsic safety of the process, in particular in the event of acceleration of the polymerization rate observed in hot weather: in this case, in Indeed, the polymerization kinetics is increased, and the temperature obtained at the core of the coating must imperatively be below the vaporization temperature of the REI water.

The use of the epoxy-cement process solves this problem.

Furthermore, the lengthening of the hardening time is an interesting phenomenon at the industrial stage because it allows increased possibilities of intervention on the process.

Another important advantage of the process of the invention is that it allows the coating of anionic, cationic or mixed ion exchange resins without requiring pretreatment. Indeed, the use of a hydraulic binder which releases in the aqueous medium dissociated ions, avoids prior saturation of any active sites of cation exchange resins since the ions released by the cement are capable of achieving this saturation.

Claims (6)

Block containing ion exchange resins contaminated for storage, characterized in that the ion exchange resins are incorporated into a composite matrix consisting of a hardened hydrophilic epoxy resin and a hard cement chosen from cements with Clinker's slag, and slag and ash cements. Block according to claim 1, characterized in that the composite matrix comprises: - from 35 to 65% by weight of hardened epoxy resin, and - from 35 to 65% by weight of hardened cement with clinker slag and / or hardened cement with slag and fly ash. Block according to either of Claims 1 and 2, characterized in that it contains up to 45% by weight of contaminated ion exchange resins. Block according to any one of Claims 1 to 3, characterized in that the ion exchange resins are chosen from cationic resins, anionic resins and their mixtures. Block according to any one of Claims 1 to 4, characterized in that the epoxy resin is a diglycidyl ether of bis-phenol-A and / or a diglycidyl ether of bis-phenol F hardened by reaction with an amino hardener . Process for the preparation of a block according to any one of Claims 1 to 5, characterized in that it comprises the following successive steps: 1) water saturation of contaminated ion exchange resins, 2) addition, with stirring, of the water necessary for the hydration of the cement to the ion-exchange resins saturated with water, 3) addition of the cement, with stirring, to the suspension obtained in 2), and 4) addition to the mixture obtained in 3) of the epoxy resin and its hardener.

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