EP0157683A1 - Process for the bituminization of radioactive wastes constituted by cation-exchange resins and/or anion-exchange resins - Google Patents

Abstract

The invention relates to a process for bituminizing radioactive waste constituted by cation exchange resins and / or by anion exchange resins. This process comprises a step of pretreatment of the resins carried out so as to replace the H <+> ions of the cation exchange resins with ions chosen from the group comprising Ca <+> <+>, Sr <+> <+> and Ba <+> <+> and / or to replace the OH <->, and / or CI <-> ions of anion exchange resins with an anion chosen from the group comprising NO3 <->, HCO2 <-> and CH3CO2 <->. This pretreatment makes it possible to increase the capacity of the coating installation and to limit the swelling in water of the bituminous mixes obtained.

Description

The present invention relates to a conditioning process by coating in bitumen radioactive waste consisting of ion exchange resins.

The coating of radioactive waste in bitumen is generally carried out by mixing an aqueous suspension of radioactive waste with bitumen in the fluidized state, then carrying out an evaporation of the water from the suspension and pouring the mixture thus obtained into a container to solidify it.

French patent 1,315,162 filed on December 6, 1961 by the French Atomic Energy Commission describes a bituminization process of this type, according to LequeL. The suspension of waste is mixed with fluidized bitumen in the presence of a surfactant. which facilitates the separation of the water contained in the suspension, most of this water is then separated either by decantation or by means of a mechanical device, and the product obtained after separation of the water is then kneaded to a temperature such that it is sufficiently fluid, and finally poured so as to obtain by cooling solid blocks of suitable plasticity.

French patent 2,052,093 of the Atomic Energy Commission filed on July 15, 1969 describes an installation for coating a suspension of radioactive products with bitumen using a thin-film evaporator and a gear pump to extract the products. mixes obtained at the base of the evaporator.

In French patent FR-A-2,356,246, it is described an improvement to the processes for coating radioactive waste in bitumen, which consists in subjecting the waste to a pretreatment with salts such as calcium and barium chlorides, in order to improve the resistance to leaching of solidified products obtained.

In this case, the treated waste is evaporation concentrates and / or precipitation sludge which contain salts such as sodium carbonates and sulphates.

There are also known installations for continuously coating suspensions of radioactive waste using a twin or quadruple screw extruder, in which the mixing of the waste with the bitumen and the drying of the suspension takes place.

Generally, before proceeding with the coating of the suspension of waste, it is subjected to a neutralization treatment with sodium hydroxide. Indeed, iL is not recommended to coat with bitumen acid suspensions, in particular with free nitric acid, to avoid any risk of degradation of the bitumen at the end of the operation when, after evaporation of the water, the bitumen found in the presence of concentrated acid. In addition, prior neutralization before asphalting limits the corrosion of installations.

When the radioactive waste consists of organic ion-exchange resins, in particular of the anionic type in OH ^- and / or CL form, the implementation of these conditioning processes by coating in bitumen does not make it possible to obtain a capacity for sufficient treatment of the asphalt plant. In addition, the bituminous mixes obtained have the major drawback of swelling when they are then immersed in water. In this In this case, the increase in volume of the coated materials can reach 20%, and exceed 100% in certain extreme cases, which leads to disaggregation of the coated waste.

There are also known methods of packaging ion exchange materials in thermosetting resins or in cement, as described in French patent FR-A 2361724 and in Japanese patent 48-28899. According to these methods, to obtain packaged products free of cracks, it is necessary to carry out a pretreatment of the ion exchange resins to replace the H ⁺ ions with other cations, in order to avoid that the resins cannot fix some of the reagents necessary to obtain the hardening of the thermosetting resin or the setting of the cement.

German patent DE-A-3 102 473 also describes a process for the pretreatment of a mixture of cation exchange resins and anion exchange resins which then makes it possible to condition the resins separately by incorporation in bitumen or cement. According to this patent, in order to separate the cation exchange resins from the anion exchange resins, the mixture of resins is brought into contact with an aqueous solution of a salt, such as a sulfate, a chloride, a nitrate or an acetate. of alkali metal, to replace the H and / or Na ⁺ ions of cationic resins by sodium and the OH ions of anionic resins by other anions. The resins can then be separated by means of a liquid which has a density between that of the grains of one kind of resin and that of the grains of the other kind of resin. Thus, this patent does not deal with the problem of swelling in water of bituminous mixes.

The present invention has precisely for subject a method of conditioning by bituminization of radioactive waste constituted by ion exchange resins, which comprises a pretreatment step making it possible to solve the problems mentioned above.

• a) - à soumettre La ou Lesdites résines à un prétraitement au moyen d'un seL pour remplacer Les ions H⁺ et/ou Na des résines échangeuses de. cations par des ions choisis dans Le groupe comprenant Ca⁺⁺, Sr⁺⁺ et Ba , et/ou pour remplacer Les ions OH et/ou Cl^- des résines échangeuses d'anions par un anion choisi dans Le groupe comprenant NO₃, HCO₂ et CH₃CO^- ₂,
• b) - à mettre en suspension dans L'eau La ou Les résines ainsi prétraitées, et
• c) - à soumettre Ladite suspension à l'opération de bitumage.

According to the invention, the process for conditioning by bituminization of radioactive waste constituted by cation exchange resins and / or by anion exchange resins is characterized in that it consists:

• a) - subjecting the said resin (s) to a pretreatment using a seL to replace the H ⁺ and / or Na ions of the exchange resins. cations by ions chosen from the group comprising Ca ⁺⁺ , Sr ⁺⁺ and Ba, and / or to replace the OH and / or Cl ions ^- anion exchange resins by an anion chosen from the group comprising NO ₃ , HCO ₂ and CH ₃ CO ^- ₂ ,
• b) - to be suspended in the water or the resins thus pretreated, and
• c) - to subject the said suspension to the asphalting operation.

According to a characteristic of the invention, the pretreatment is carried out by bringing said resins into contact, preferably with stirring, with an aqueous solution of a calcium, strontium or barium salt, said salt being chosen from the group comprising nitrates, acetates and formates.

This embodiment of the pretreatment is in particular suitable for the treatment of a mixture of cation exchange resins and anion exchange resins because it allows the simultaneous replacement of OH or Cl ions ^- anionic resins by nitrate anions , acetates or formates and also to replace the H ⁺ ions of cationic resins with calcium, strontium or barium.

In this case, an aqueous solution of barium nitrate or acetate is generally used to carry out the pretreatment. In fact, the use of barium nitrate is preferable because the NO ^- ₃ anion is generally present in effluents, in particular in effluents from reprocessing centers and nuclear study centers.

Thanks to the pretreatment of the invention, the structure of the three-dimensional network of ion exchange resins is modified by introducing ions such as Ba ⁺⁺ and / or NO ^- ₃ or CH ₃ COO ^- into the molecular chain, which occupy a place more important than the H ⁺ , OH and Cl ^- ions initially present. This makes it possible to prevent the penetration of water into the denser macromolecular network of the pretreated resin and thus to decrease the degree of hydration of the resin.

Indeed, ion exchange resins, anionic and cationic have the particularity of swelling in water significantly. Their increase in volume is generally of the order of 20% for anionic resins in OH and / or CL form and greater than 50% for cationic resins in Na ⁺ form. This swelling is due to the penetration of water into the three-dimensional skeleton of the resins, particularly hydrophilic in the case of anionic resins which contain quaternary ammonium or amine groups and in the case of cationic resins which include grafted sodium sulfonate groups. for The two types of resins on a polystyrene radical. As a result, the processing capacity of bituminization plants is lower when dealing with resins of these types. Of moreover, the bituminous mixes obtained as a result of the bituminization treatment have the disadvantage of swelling in water.

On the other hand, when a pretreatment of the ion exchange resins is carried out according to the invention, the hydration capacity of the macromolecular network of the resins is reduced, and therefore the treatment capacity of the bituminization plants can be increased and Limit The swelling of the asphalt mixes obtained in contact with water.

Thus, in the method of the invention, the step of pretreatment of ion exchange resins with a salt such as barium nitrate, does not have the same object as the step of pretreatment of prior methods (FR- A-2361724 and Japanese Patent 48/28899), since it is not intended to prevent the ion-exchange resins from consuming some of the reagents necessary for the reaction to form the coating matrix.

Likewise, the pretreatment step of the invention does not have the same object as the pretreatment step of French patent FR-A-2 356 246. Indeed, in this patent The waste consists of concentrates of evaporation and / or sludge of radioactive material such as chemical precipitation sludge containing salts, and The problem to be solved is to transform salts such as sulphate and sodium carbonate into salts having a less tendency to capture molecules of water.

On the other hand, in the invention the waste is ion exchange resins, which do not contain salts, and the problem to be solved is to reduce the hydration capacity of the macromolecular network of ion exchange resins.

For the asphalting operation, we operate from in a conventional way using, for example, the techniques described in French patents 1,315,162 and 2,052,093 or American patent 3,298,961. The devices used are also of a conventional type and can be constituted by thin-film evaporators, double or quadruple screw extruders, etc ...

The process of the invention applies in particular to the treatment of cationic and / or anionic resins with a polystyrene skeleton in beads and / or ground.

Examples of such resins include resins in the form of beads such as the resins sold under the trademark DUOLITE by DIAPROSIM or resins sold under the trademark AMBERLITE by ROHM and HAAS. By way of example of ground resins, mention may be made of MICROIONEX resins sold by DIAPROSIM.

When, according to the invention, anionic and cationic resins are treated as a mixture, any proportion of anionic resins in the range between 0 and 100% can be used.

For the implementation of the process of the invention, the pretreatment step is preferably carried out by introducing into a tank a certain amount of an aqueous solution of a Ba, Ca ⁺⁺ or Sr ²⁺ salt containing NO ^- ₃ , NCO ^- ₂ or CH ₃ CO ^- ₂ ions. The resins to be pretreated are suspended in the solution and the whole is stirred for a sufficient time which is chosen, depending on the salt concentration of the solution, so as to obtain the desired saturation rate of the exchange resins. ions.

Preferably, the salt concentration and the duration of treatment are chosen so as to obtain a saturation rate in anions: N03, HCO ₂ or CH ₃ CO ₂ of anion exchange resins close to 100%.

• 1) - augmentant La capacité de traitement de l'installation de bitumage de 50% puisqu'on réduit Le volume des résines mises en suspension dans L'eau et qu'on augmente La capacité d'évaporation du dispositif de bitumage,
• 2) - supprimant dans Les distillats Les produits de dégradation des résines anioniques, en particuLier NH₃ et CH₃NH₂, grâce à une stabilisation chimique des groupes fonctionnels ammonium quaternaire ou amine tertiaire, ce qui permet de récupérer des condensats neutres et non plus basiques, et
• 3) - Limitant le processus de gonflement des enrobés bitumineux dans l'eau, Leur augmentation de volume ne dépassant pas 5% comme on Le verra ci-après.

Thanks to the pretreatment of ion exchange resins according to the process of the invention, the bituminization process can be improved by:

• 1) - increasing the treatment capacity of the asphalt installation by 50% since the volume of resins suspended in water is reduced and the evaporation capacity of the asphalt device is increased,
• 2) - eliminating in the distillates the degradation products of anionic resins, in particular NH ₃ and CH ₃ NH ₂ , thanks to a chemical stabilization of the functional groups quaternary ammonium or tertiary amine, which makes it possible to recover neutral condensates and no longer basic, and
• 3) - Limiting the swelling process of bituminous mixes in water, Their increase in volume not exceeding 5% as will be seen below.

Other characteristics and advantages of the invention will appear better on reading the following examples given of course by way of illustration and not limitation with reference to the appended drawing in which FIGS. 1 and 2 are diagrams representing the percentage increase in volume bituminous mixtures of cation exchange resins, obtained either by the method of the prior art, or by the method of the invention, depending on the time of immersion in water.

EXAMPLE 1

This example illustrates the treatment of AMBERLITE IR 120 H cation exchange resins.

The resins are transferred by means of a hy- drojector using demineralized water, in a treatment tank fitted with a mechanical stirrer and a device for ultrasonic detection of the level of the solid-liquid interface.

After decanting the mixture of resins for a period which can range from 24 to 48 h depending on whether the resins are in the form of beads or in the ground state, the supernatant water is eliminated, either by pumping or by vacuum siphoning. . Additional quantities of resins are again transferred and the decantation, pumping and siphoning operations are repeated under vacuum until the volume V of decanted resins reaches 50% of the volume of the tank.

In an auxiliary tank, a 0.37 mol.l ^-1 barium nitrate solution is prepared and a volume V of this solution is introduced into the treatment tank, that is to say a volume identical to that which occupy the decanted resins. The whole is stirred for two hours. It is then left to settle for 1 h and the supernatant solution is removed by means of a pump or a steam ejector or by vacuum siphoning. In this case, the volume of the solution eliminated corresponds to 1.22 V, which shows that not only was the pretreatment solution eliminated but also a certain amount of the water absorbed by the resins, this amount represents 14 % of the initial volume of decanted wet resins.

This operation is repeated three times to obtain a saturation rate in Ba ⁺⁺ of the resins close to 100% due to the Ba concentration (NO ₃ ) ₂ of the solution (0.37 mole.l ^-1 ) and of La duration of contact.

The saturation pretreatment causes a release of 10 to 15% of the initial activity of the resi nes. Also, the supernatant radioactive solution is returned to the head of the liquid effluent treatment station, either upstream of an evaporator, or upstream of a chemical coprecipitation chain.

After decantation and elimination of the supernatant solution, the pretreated resins are washed with demineralized water using a volume of washing water equal to 0.65 V, ie identical to that of the pretreated and decanted resins. The pH of the suspension of resins is adjusted to 7.5 ^± 0.2 using a baryte milk at 300 gl ^-1 of Ba (OH) ₂ . This washing operation is repeated four times, checking the NO ^- ₃ concentration of the washing water after each operation, until a NO ^- ₃ concentration of the washing water is obtained of less than 2 g ^-1. .

In fact, it is necessary to wash the pretreated resins before packaging them in bitumen, because if barium nitrate in excess was added to the dry extract of the resins, this would have the disadvantage of increasing, not only the volume of the final residue, but to further promote the leaching of this solubilized salt in water.

The transfer and washing waters are very weakly radioactive and they are sent to the effluent treatment station where their degree of radioactivity is checked.

The pretreated and washed resins are then resuspended in demineralized water using 0.4 to 0.45 V of water in a proportion of 0.6 to 0.55 V of the resin mixture. The suspension of pretreated organic resins is then sent to the bituminization plant, which is of the quadruple screw drying extruder type.

The properties of the mixes leaving the asphalt plant are then checked.

In Table 1, the results obtained are reported with regard to the hourly evaporation capacity of the extruder and the composition of the mix obtained during a bituminization operation carried out with bead resins.

The swelling properties in water of the coated materials obtained which have been poured and solidified in the form of cylindrical test pieces 48 mm in diameter and 90 mm in height are then evaluated.

To determine the swelling in water, the mixes are immersed in ordinary non-renewed water or non-renewed demineralized water, and the volume increase (in%) of the mixes is periodically measured as a function of the duration immersion (in days).

The volume ratio between the water and the coated materials is 4.5 and the surface / volume ratio of the coated materials is 10.5 cm ^-1 .

The results obtained are given on curves 1 of FIGS. 1 and 2 which represent the percentage increase in the volume of the coated materials as a function of time (in days). Figure 1 illustrates the results obtained with plain water and Figure 2 illustrates the results obtained with demineralized water.

In view of these results, it can be seen that the swelling of the coated materials after 365 days of immersion in ordinary water is 4.2% by volume, or 4.45% by weight, and that it is 5, 0% by volume, or 5.1% by weight, after 365 days of immersion in demineralized water.

EXAMPLE 2

As in Example 1, cation exchange resins AMBERLITE IR 120 H are treated, but using an aqueous solution of 1.5 mol.l ^-1 of acetate barium instead of 0.37 mol.l ^-1 aqueous solution of barium nitrate.

In an auxiliary tank, a 1.5 mole.l ^-1 barium acetate solution is prepared and a volume V of this solution is introduced into the treatment tank, that is to say a volume identical to that occupied by decanted resins. The whole is subjected to stirring for two hours, which allows a saturation rate of Ba ²⁺ of the resins greater than 90 × to be obtained due to the concentration of Ba (NO ₃ ) ₂ in the solution (1.5 moles. l ^-1 ) and the duration of contact.

It is then left to settle for one hour and the supernatant solution is eliminated by means of a pump or a steam ejector or by vacuum siphoning.

In this case, the volume of the solution removed corresponds to 1.34 V, which shows that not only was the pretreatment solution eliminated, but also a certain amount of the water absorbed by the resins, this amount represents 21X of the volume of decanted wet resins.

After decantation and elimination of the supernatant solution, the pretreated resins are washed with demineralized water using a volume of washing water equal to 0.83 V, ie identical to that of the pretreated and decanted resins.

The pH of the suspension of resins is adjusted to 7.5 ± 0.2 using a baryte milk at 300 gl ^-1 of Ba (OH) ₂ .

This washing operation is repeated three times, checking the CH ₃ CO ₂ concentration ^- of the washing water after each operation until a CH ₃ CO ₂ ^- washing water concentration of less than 2 g is obtained. ^-1 . We are following the operation as in example 1 and the asphalting operation is carried out under the same conditions using blown bitumen MR 90/40.

The properties of the asphalt leaving the asphalt plant are then checked.

The results obtained are given on curves 2 of FIGS. 1 and 2 which represent the percentage increase in volume of the mixes as a function of the time (in days) during which they were immersed in ordinary non-renewed water (FIG. 1 ) or in non-renewed demineralized water (Figure 2).

In view of these figures, it can be seen that the swelling of the coated materials after 120 days of immersion in ordinary water is 2.45% by volume, ie 3.4% by weight, and that the swelling after 120 days d immersion in demineralized water is 4.9% by volume, ie 5.0% by weight.

EXAMPLE 3

In this example, as in Example 1, AMBERLITE IR 120 H resin beads are treated, but using a 1.5 mol.l ^-1 sodium hydroxide solution instead of using the barium nitrate solution, which has the effect of bringing the resins in Na ⁺ form. The resins pretreated are coated in MR 90/40 bitumen under the same conditions as those of Example 1, and the properties of the mixes obtained are then determined as in Example 1.

The results obtained are given in Table 1 and on Curves 3 of Figures 1 and 2, which represent the percentage increase in volume of the mixes as a function of the time (in days) during which they were immersed in water. regular (Figure 1) or in renewed demineralized water (Figure 2).

In view of these results, it is found that the swelling of the coated materials after 15 days of immersion in demineralized water or in plain water is very significant. Indeed, the swelling is 38.7X by volume, or 25.1% by weight, in the case of demineralized water, and 50.1% by volume, or 45.6% by weight, in the case of plain water.

Thus, it can be seen that, in the process of the invention, the choice of the seL used for the pretreatment has a very significant effect on the results obtained.

EXAMPLE 4

This example illustrates the treatment of anion exchange resins AMBERLITE IRN-78 L.

In this example, the procedure of the previous examples is treated with AMBERLITE IRN-78 L resin beads using a 1.5 mol.l ^-1 sodium nitrate solution and washing with demineralized water. resins saturated with NO ₃ ^- until a supernatant whose salinity is less than 2 gl ^{-1 is} obtained. The coating of the pretreated resins is carried out in blown bitumen MR 90/40 under the same conditions as those of the preceding examples, and the properties of the prepared mixes are then determined. The results obtained are given in Table 1 and on Curves 4 of Figures 1 and 2, which represent the percentage increase in volume of the mixes as a function of time (in days) during which they were immersed in water. ordinary non-renewed (figure 1) or in non-renewed demineralized water (figure 2).

In view of these results, it can be seen that the swelling of the coated materials after 365 days of immersion is 9.5% by volume, ie 6.1% by weight in the case of ordinary water, and 7.2% in volume, i.e. 7.1% in weight in the case of demineralized water.

EXAMPLE 5

Anber exchange resins AMBERLITE IRN-78 L are treated as in Example 4, but using an aqueous solution containing 1.5 mol.l ^-1 of barium acetate. The operating mode is identical to that of Example 4.

The results obtained with the mixes emerging from the asphalting installation are given in Table 1 and on Curves 5 of Figures 1 and 2.

In view of these figures, it can be seen that the swelling of the coated materials after 55 days of immersion in demineralized water is 1.7% by volume, ie 4.9% by weight, and that the swelling after 55 days in ordinary water is 1.2% by volume, or 4.6% by weight.

Claims (5)

1. A method of conditioning by bituminization of radioactive waste constituted by cation exchange resins and / or by anion exchange resins, characterized in that it consists: a) - subjecting the said resin (s) to a pretreatment using a salt to replace the H ⁺ and / or Na ions of the cation exchange resins with ions chosen from the group comprising Ca ⁺⁺ , Sr ⁺⁺ and Ba and / or to replace OH ions and / or Cl ^- anion exchange resins with an anion chosen from the group comprising NO ^- ₃ , HCO ^- ₂ and CH ₃ CO ₂ , b) - to be suspended in the water or the resins thus pretreated, and c) - to subject the said suspension to the asphalting operation. 2. Method according to claim 1, characterized in that the pretreatment is carried out by bringing said resins into contact with an aqueous solution of a calcium, strontium or barium salt, said salt being chosen from the group comprising: nitrates, acetates and formates. 3. Method according to claim 1, characterized in that the pretreatment is carried out by bringing said resins into contact with an aqueous barium nitrate solution. * 4. Method according to claim 1, characterized in that the pretreatment is carried out by bringing said resins into contact with an aqueous barium acetate solution. 5. Method according to any one of claims 1 to 3, characterized in that the pretreatment is carried out so as to obtain a saturation rate of NO ^- ₃ , HCO ^- ₂ or CH ₃ CO ^- ₂ of the exchange resins d 'anions close to 100%.

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