EP0026700B1 - Process for removing heavy metallic elements in suspension in a liquid - Google Patents

Process for removing heavy metallic elements in suspension in a liquid Download PDF

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Publication number
EP0026700B1
EP0026700B1 EP19800401343 EP80401343A EP0026700B1 EP 0026700 B1 EP0026700 B1 EP 0026700B1 EP 19800401343 EP19800401343 EP 19800401343 EP 80401343 A EP80401343 A EP 80401343A EP 0026700 B1 EP0026700 B1 EP 0026700B1
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EP
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Prior art keywords
particles
liquid
magnetite
ruthenium
suspension
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EP19800401343
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German (de)
French (fr)
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EP0026700A1 (en
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Lucien Dolle
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Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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Commissariat a lEnergie Atomique CEA
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Priority to DE8484200419T priority Critical patent/DE3072136D1/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C1/00—Magnetic separation
    • B03C1/02—Magnetic separation acting directly on the substance being separated
    • B03C1/28—Magnetic plugs and dipsticks
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C1/00—Magnetic separation
    • B03C1/005—Pretreatment specially adapted for magnetic separation
    • B03C1/01—Pretreatment specially adapted for magnetic separation by addition of magnetic adjuvants
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C1/00—Magnetic separation
    • B03C1/02—Magnetic separation acting directly on the substance being separated
    • B03C1/025—High gradient magnetic separators
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C2201/00—Details of magnetic or electrostatic separation
    • B03C2201/18—Magnetic separation whereby the particles are suspended in a liquid

Definitions

  • irradiated fuels from the electro-nuclear industry are reprocessed in order, in particular, to recover the fissile materials contained in the irradiated elements by separating them from the fission products.
  • these fuels are dissolved in a nitric medium.
  • the solution is subjected to several solvent extractions in order, firstly, to rid the uranium and the plutonium of the fission products associated with them, then to separate them from each other.
  • fission products present in irradiated fuels such as ruthenium for example, are not very soluble in the nitric medium from the dissolver in the reprocessing chain.
  • ruthenium 106 is abundantly produced by the fission of uranium, deposits of ruthenium form and strongly contaminate the walls of the components of the reprocessing chain which contain the nitric solutions.
  • Particles up to a few microns in size can be separated from the. nitric solution by filtration or by centrifugation.
  • the ruthenium particles whose size is of the order of or less than one micron cannot be removed by these conventional methods.
  • Document US-A-3 351 203 discloses a process for extracting non-magnetic particles such as particles of glass, plastic or stainless steel suspended in a liquid, for example sewage. According to this method, ferromagnetic particles are distributed inside the liquid to be filtered and a filter 24 is produced by means of an electromagnet 16 disposed around the pipe 15 in which the liquid is circulated. When the majority of the particles have been retained, the filtering operation is carried out on the particles in suspension in the liquid.
  • This problem is solved according to the present invention. Indeed, it specifically relates to a process for the elimination of metal particles of this size suspended in a liquid.
  • This process is particularly applicable to the elimination of heavy metallic elements such as ruthenium in suspension in nitric solutions for reprocessing irradiated fuel elements in nuclear reactors. However, it also applies to the filtration of other liquids charged with insoluble metal particles, such as for example the water in pools for the storage of irradiated fuel elements.
  • the method according to the present invention is based on the use of a finely divided ferromagnetic filter aid, in order to separate, by means of a magnetic field, the insoluble heavy metal elements which could not be effectively extracted by other means.
  • heavy elements is meant particles whose mass is large relative to that of the particles of the ferromagnetic adjuvant used.
  • ruthenium particles and as an adjuvant of magnetite a large fraction of the ruthenium particles has a diameter of a few tenths of a micron, and the magnetite has a diameter distribution curve which has a maximum at around 0.2 pm; moreover, the density of ruthenium is close to 12, and due to the agglomeration of the particles of suspended magnetic adjuvant, these have an even more apparent density, in particular lower than the density of the homogeneous massive magnetite which is close to 5.
  • an apparent magnetite density of 3 an average diameter of magnetite particles equal to 0.2 p and a diameter of ruthenium particles equal to 0.6 p, we find that the ratio of the masses is 108.
  • the insoluble elements are found in the solution in metallic form.
  • they cannot be included in a crystal lattice, such as for example a crystalline ferrite network as can happen with other elements such as copper, manganese in a mixture of iron-based corrosion products in high temperature water.
  • these elements cannot be the subject of an electrostatic attraction such as that which would be created between a ferromagnetic adjuvant and dielectric elements such as fibers, textiles, etc. Under these conditions, the forces of attraction between the particles of the ferromagnetic adjuvant and the metallic particles, of the force type of VAN der WAALS, cannot be sufficient to retain the latter.
  • the process according to the invention is based on the fact that the particles of this adjuvant tend to spontaneously agglomerate into larger grains.
  • the agglomeration is also the fact of the attraction of the tiny magnetic dipoles that become the particles of adjuvant if they undergo the effect of a magnetic field.
  • the larger particles that result from these phenomena, the last of which is called magnetic coagulation, are very spongy in nature. They contain a large amount of occluded fluid.
  • One or more non-ferromagnetic particles trapped according to this process in such a magnetite agglomerate are then naturally transported with it under the effect of a magnetic field gradient.
  • the stirring of the liquid and the application of a magnetic field are carried out by means of a single device constituted by a rotating shaft carrying permanent magnets whose neighboring poles are of the same polarity.
  • the ferromagnetic adjuvant particles are attracted to the magnetic poles where they attach, carrying with them the heavy metal particles.
  • the yield of the process according to the invention For example, in the case where ruthenium particles contained in the nitric medium for dissolving irradiated fuel are extracted. To this end, the fine ruthenium powder is placed in a 4N solution of uranyl nitrate, which is stirred and slightly heated, for example around 50 ° C., to simulate a nitric solution of irradiated fuel which spontaneously heats up under the effect of the decaying radiation of the fission products.
  • the metal powder was previously irradiated in a reactor in order to mark it with radioactive ruthenium 103, a gamma emitter.
  • radioactive ruthenium 103 a gamma emitter.
  • finely divided magnetite which was prepared separately by alkaline precipitation in a solution of ferrous iron, and whose particles initially measure from 0.1 ⁇ m to a few ⁇ m, the stirring of the liquid is continued for a few minutes.
  • the material balance of ruthenium 103 which can easily be established by measuring the activity of this radionuclide in the aliquot of metallic ruthenium before the experiment, then in the magnetite sludges after the extraction, allows to control this yield.
  • the yield is between 65 and 85%.
  • the ferromagnetic adjuvant used is ferrite, or alternatively magnetite.
  • the process for removing heavy metallic elements according to the invention leads to the production of a dense sludge, constituted by a mixture of the ferromagnetic adjuvant and heavy metallic elements.
  • the sludge adheres to the poles of the magnets.
  • This dense sludge can be easily separated from the wash water by decantation.
  • the metal particles can then be separated from the magnetite, either to isolate them under a small volume of waste, or with a view to the profitability of the metals which are their main constituents.
  • the container 1 contains a nitric solution of irradiated fuel 2 inside which there is a residue of insoluble fission products, including in particular ruthenium in the finely divided state, which is eliminate to prevent its accumulation by deposition in the components of the dissolution and extraction workshop of the reprocessing plant.
  • an amount of magnetite is added to solution 2. The optimal amount of magnetite to add is determined by preliminary experiments.
  • the mass ratio of the quantities of ruthenium and magnetite is between 1/6 and 1/12.
  • the solution 2 is stirred for a certain time, in order to maintain in suspension and in intimate contact the insoluble particles and the particles of magnetite.
  • the duration of the contact in the nitric solution must however be limited so that the dissolution of the magnetite itself remains weak.
  • laboratory orientation experiments show that the agitation of the nitric solution can advantageously be limited to less than half an hour.
  • FIG. 1 by the general reference 3.
  • the latter comprises a rotating shaft 4 carrying permanent magnets 5 which may have the form of bars or horseshoes.
  • the number of magnets 5 is sufficient for them to be able to fix all the magnetite added to the solution 2.
  • These magnets 5 are arranged in such a way that their neighboring poles are of the same polarity, or, at least, if they are of polarity different, that they are far enough apart that they cannot exert one on the other an action capable of significantly reducing the gradient of the magnetic field near the neighboring poles.
  • the speed of rotation of the shaft 4 is limited so that the linear speed of the poles of the magnets 5 remains low enough so that the attraction force exerted by these poles on the magnetite particles is greater than the tearing force that exerts on them the liquid by friction at the level of the polar surfaces.
  • the linear speed at the end of the poles can reach between 10 and 20 centimeters per second, when the viscosity of the liquid is of the same order of magnitude as that of water.
  • the linear speed to be chosen is inversely proportional to it.
  • the magnetic extraction is stopped by removing the agitator 3.
  • the magnets 5 are then loaded with sludge at their polar ends. These sludges naturally also retain a little solution containing plutonium and uranium which can be washed by rotating the agitator 3 at low speed in a container identical to container 1 and containing water. This water is renewed to remove the charge of sludge on the magnets 5.
  • This sludge is detached from the polar ends by means of water whose linear speed is sufficiently high.
  • the agitator 3 can be rotated in a container containing water with a speed of rotation such that the linear speed at the ends of the magnets 5 is greater than 40 cm per second.
  • a high speed water jet can be directed at these same ends, the rinsing water being collected in an initially empty container.
  • the agitator 3 is immediately reusable.
  • the subsequent treatment of the rinsing water consists in separating the magnetite in small volume with all the particles which it has entrained by prior sedimentation.
  • the aqueous effluent is then decontaminated by treatment with ion exchange resins.
  • Magnetite sludge can be conditioned as solid waste by a known method. If the recovery of platinoid elements such as ruthenium is of interest, they are separated by appropriate prior treatment of the sludge. For example, magnetite can be transformed by oxidation to a much more soluble form of iron, which then simply dissolves to separate the insoluble platinoid elements such as ruthenium.
  • the process for removing heavy metal particles according to the invention leads to a dense sludge easily separated from the washing water by decantation and which contains the insoluble fission products.
  • the latter can then be separated from the ferromagnetic adjuvant, either to isolate them under a small volume of waste, or for the profitability of the platinoid metals which are the major constituents thereof.

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  • Solid-Sorbent Or Filter-Aiding Compositions (AREA)
  • Manufacture And Refinement Of Metals (AREA)
  • Filtering Materials (AREA)

Description

On sait que les combustibles irradiés issus de l'industrie électro-nucléaire sont retraités afin, en particulier, de récupérer les matériaux fissiles contenus dans les éléments irradiés en les séparant des produits de fission. A cette fin, ces combustibles sont mis en solution dans un milieu nitrique. Après complète dissolution et ajustage de l'acidité et de la concentration en uranium, la solution est soumise à plusieurs extractions par solvant afin, dans un premier temps, de débarrasser l'uranium et le plutonium des produits de fission qui leur sont associés, puis de les séparer l'un de l'autre.It is known that irradiated fuels from the electro-nuclear industry are reprocessed in order, in particular, to recover the fissile materials contained in the irradiated elements by separating them from the fission products. To this end, these fuels are dissolved in a nitric medium. After complete dissolution and adjustment of the acidity and of the uranium concentration, the solution is subjected to several solvent extractions in order, firstly, to rid the uranium and the plutonium of the fission products associated with them, then to separate them from each other.

Cependant, certains produits de fission présents dans les combustibles irradiés, comme par exemple le ruthénium, sont peu solubles dans le milieu nitrique issu du dissolveur dans la chaîne de retraitement. Comme le ruthénium 106 est abondamment produit par la fission de l'uranium, des dépôts de ruthénium se forment et contaminent fortement les parois des composants de la chaîne de retraitement qui contiennent les solutions nitriques.However, certain fission products present in irradiated fuels, such as ruthenium for example, are not very soluble in the nitric medium from the dissolver in the reprocessing chain. As ruthenium 106 is abundantly produced by the fission of uranium, deposits of ruthenium form and strongly contaminate the walls of the components of the reprocessing chain which contain the nitric solutions.

A titre d'exemple, on trouve dans un dissolveur contenant une solution nitrique de combustible avec 300 grammes d'uranium par litre, une proportion de produits solides résultant de la présence d'environ 3 kg d'éléments platinoïdes, d'environ 0,2 kg de colloïdes et de l'ordre de 2,8 kg de résidus de gaines par tonne de combustible. Dans le mélange d'éléments platinoïdes, le ruthénium est de loin l'élément le plus abondant. En raison de ces inconvénients, on a cherché à éliminer le ruthénium en suspension dans les solutions nitriques de retraitement des combustibles nucléaires.For example, in a dissolver containing a nitric fuel solution with 300 grams of uranium per liter, there is a proportion of solid products resulting from the presence of approximately 3 kg of platinoid elements, of approximately 0, 2 kg of colloids and around 2.8 kg of cladding residues per tonne of fuel. In the mixture of platinoid elements, ruthenium is by far the most abundant element. Because of these drawbacks, attempts have been made to eliminate ruthenium in suspension in nitric solutions for reprocessing nuclear fuels.

Les particules dont la taille atteint quelques microns peuvent être séparées de la. solution nitrique par filtration ou par centrifugation. En revanche, les particules de ruthénium dont la taille est de l'ordre de ou inférieure au micron ne peuvent être éliminées par ces procédés classiques.Particles up to a few microns in size can be separated from the. nitric solution by filtration or by centrifugation. On the other hand, the ruthenium particles whose size is of the order of or less than one micron cannot be removed by these conventional methods.

On connaît par le document US-A-3 351 203 un procédé d'extraction de particules non magnétiques telles que des particules de verre, de matière plastique ou d'acier inoxydable en suspension dans un liquide, par exemple des eaux d'égoût. Selon ce procédé, on distribue des particules ferromagnétiques à l'intérieur du liquide à filtrer et on réalise un filtre 24 au moyen d'un électro-aimant 16 disposé autour de la canalisation 15 dans laquelle on fait circuler le liquide. Lorsque la majorité des particules a été retenue, on procède à l'opération de filtrage des particules en suspension dans le liquide.Document US-A-3 351 203 discloses a process for extracting non-magnetic particles such as particles of glass, plastic or stainless steel suspended in a liquid, for example sewage. According to this method, ferromagnetic particles are distributed inside the liquid to be filtered and a filter 24 is produced by means of an electromagnet 16 disposed around the pipe 15 in which the liquid is circulated. When the majority of the particles have been retained, the filtering operation is carried out on the particles in suspension in the liquid.

Cependant, un tel procédé ne s'applique pas à la filtration de particules métalliques lourdes, comme par exemple le ruthénium.However, such a process does not apply to the filtration of heavy metal particles, such as for example ruthenium.

Le problème de la formation de dépôts radioactifs provenant notament du ruthénium dans les divers dispositifs constituant la chaîne de retraitement s'est donc posé dès la construction des premières usines de retraitement et n'a, jusqu'à présent, trouvé aucune solution.The problem of the formation of radioactive deposits originating in particular from ruthenium in the various devices constituting the reprocessing chain therefore arose from the construction of the first reprocessing plants and has so far found no solution.

Ce problème est résolu selon la présente invention. En effet, celle-ci a précisément pour objet un procédé permettant l'élimination de particules métalliques de cette taille en suspension dans un liquide.This problem is solved according to the present invention. Indeed, it specifically relates to a process for the elimination of metal particles of this size suspended in a liquid.

Ce procédé s'applique particulièrement à l'élimination des éléments métalliques lourds tels que le ruthénium en suspension dans les solutions nitriques de retraitement des éléments combustibles irradiés dans les réacteurs nucléaires. Mais il s'applique également à la filtration d'autres liquides chargés de particules métalliques insolubles, tels que par exemple l'eau des piscines de stockage d'éléments combustibles irradiés.This process is particularly applicable to the elimination of heavy metallic elements such as ruthenium in suspension in nitric solutions for reprocessing irradiated fuel elements in nuclear reactors. However, it also applies to the filtration of other liquids charged with insoluble metal particles, such as for example the water in pools for the storage of irradiated fuel elements.

Le procédé selon la présente invention repose sur l'utilisation d'un adjuvant ferromagnétique de filtration finement divisé, en vue de séparer, au moyen d'un champ magnétique, les éléments métalliques lourds insolubles qui n'ont pu être efficacement extraits par d'autres moyens. Par éléments lourds, on entend des particules dont la masse est grande relativement à celle des particules de l'adjuvant ferromagnétique utilisé. Ainsi, dans le cas des particules de ruthénium et en tant qu'adjuvant de la magnétite, une fraction importante des particules de ruthénium a un diamètre de quelques dizièmes de micron, et la magnétite a une courbe de répartition des diamètres qui présente un maximum aux environs de 0,2 pm; par ailleurs, le densité du ruthénium est voisine de 12, et du fait de l'agglomération des particules d'adjuvant magnétique en suspension, celles-ci ont une densité plus apparente encore, notamment plus faible que la densité de la magnétite massive homogène qui est voisine de 5. Par exemple, pour une densité apparente de la magnétite de 3, un diamètre moyen de particules de magnétite égal à 0,2 p et un diamètre de particules de ruthénium égal à 0,6 p, on trouve que le rapport des masses est égal à 108.The method according to the present invention is based on the use of a finely divided ferromagnetic filter aid, in order to separate, by means of a magnetic field, the insoluble heavy metal elements which could not be effectively extracted by other means. By heavy elements is meant particles whose mass is large relative to that of the particles of the ferromagnetic adjuvant used. Thus, in the case of ruthenium particles and as an adjuvant of magnetite, a large fraction of the ruthenium particles has a diameter of a few tenths of a micron, and the magnetite has a diameter distribution curve which has a maximum at around 0.2 pm; moreover, the density of ruthenium is close to 12, and due to the agglomeration of the particles of suspended magnetic adjuvant, these have an even more apparent density, in particular lower than the density of the homogeneous massive magnetite which is close to 5. For example, for an apparent magnetite density of 3, an average diameter of magnetite particles equal to 0.2 p and a diameter of ruthenium particles equal to 0.6 p, we find that the ratio of the masses is 108.

Les éléments insolubles se trouvent dans la solution sous forme métallique. Dans le cas notamment d'une solution nitrique de combustibles irradiés, ils ne peuvent pas être inclus dans un réseau cristallin, tel que par exemple un réseau cristallin de ferrite comme cela peut se produire avec d'autres éléments tels que le cuivre, le manganèse dans un mélange de produits de corrosion à base de fer dans l'eau à haute température. Par ailleurs, ces éléments ne peuvent être l'objet d'une attraction électrostatique telle que celle qui se créerait entre un adjuvant ferromagnétique et des éléments diélectriques tels que fibres, textiles, ... Dans ces conditions, les forces d'attraction entre les particules de l'adjuvant ferromagnétique et les particules métalliques, du type forces de VAN der WAALS, ne peuvent être suffisantes pour retenir ces dernières. Le procédé selon l'invention repose au contraire sur le fait que les particules de cet adjuvant ont tendance à s'agglomérer spontanément en grains plus gros. L'agglomération est également le fait de l'attraction des minuscules dipôles magnétiques que deviennent les particules d'adjuvant si elles subissent l'effet d'un champ magnétique. Les plus grosses particules qui résultent de ces phénomènes dont le dernier est appelé coagulation magnétique, sont de nature très spongieuse. Elles renferment une grande quantité de liquide occlus. Une ou plusieurs particules non ferromagnétiques piégées selon ce processus dans un tel agglomérat de magnétite, sont alors naturellement transportées avec lui sous l'effet d'un gradient de champ magnétique. Indépendamment du piégeage dans la structure spongieuse pendant la formation spontanée d'un agglomérat ou pendant la coagulation magnétique de particules d'adjuvant, il peut se produire, dans un champ magnétique non homogène, du fait des déplacements des particules d'adjuvant dans la direction positive du gradient de champ, un transfert d'énergie cinétique par les chocs des particules ferromagnétiques en grande quantité sur les particules métalliques lourdes qui se déplacent ainsi dans le sens des premières.The insoluble elements are found in the solution in metallic form. In the case in particular of a nitric solution of irradiated fuels, they cannot be included in a crystal lattice, such as for example a crystalline ferrite network as can happen with other elements such as copper, manganese in a mixture of iron-based corrosion products in high temperature water. Furthermore, these elements cannot be the subject of an electrostatic attraction such as that which would be created between a ferromagnetic adjuvant and dielectric elements such as fibers, textiles, etc. Under these conditions, the forces of attraction between the particles of the ferromagnetic adjuvant and the metallic particles, of the force type of VAN der WAALS, cannot be sufficient to retain the latter. On the contrary, the process according to the invention is based on the fact that the particles of this adjuvant tend to spontaneously agglomerate into larger grains. The agglomeration is also the fact of the attraction of the tiny magnetic dipoles that become the particles of adjuvant if they undergo the effect of a magnetic field. The larger particles that result from these phenomena, the last of which is called magnetic coagulation, are very spongy in nature. They contain a large amount of occluded fluid. One or more non-ferromagnetic particles trapped according to this process in such a magnetite agglomerate, are then naturally transported with it under the effect of a magnetic field gradient. Independently of the entanglement in the spongy structure during the spontaneous formation of an agglomerate or during the magnetic coagulation of particles of adjuvant, it can occur, in a nonhomogeneous magnetic field, due to displacements of the particles of adjuvant in the direction positive of the field gradient, a transfer of kinetic energy by the shocks of ferromagnetic particles in large quantities on the heavy metallic particles which thus move in the direction of the former.

De manière plus précise, le procédé de l'invention d'élimination de particules en suspension dans un liquide est défini par la revendication 1 et comporte les étapes suivantes:

  • - addition de particules d'un adjuvant ferromagnétique finement divisé dans le liquide contenant les particules à extaire;
  • -agitation de ce liquide afin de réaliser une suspension de l'adjuvant ferromagnétique et un mélange de celui-ci avec les particules à extraire;
  • - application d'un champ magnétique audit liquide.
More specifically, the method of the invention for removing particles in suspension in a liquid is defined by claim 1 and comprises the following steps:
  • - addition of particles of a finely divided ferromagnetic adjuvant in the liquid containing the particles to be extracted;
  • agitation of this liquid in order to produce a suspension of the ferromagnetic adjuvant and a mixture of the latter with the particles to be extracted;
  • - application of a magnetic field to said liquid.

L'agitation du liquide et l'application d'un champ magnétique sont réalisées au moyen d'un appareil unique constitué par un arbre tournant portant des aimants permanents dont les pôles voisins sont de même polarité. Les particules d'adjuvant ferromagnétique sont attirées vers les pôles magnétiques où elles se fixent, entraînant avec elles les particules métalliques lourdes.The stirring of the liquid and the application of a magnetic field are carried out by means of a single device constituted by a rotating shaft carrying permanent magnets whose neighboring poles are of the same polarity. The ferromagnetic adjuvant particles are attracted to the magnetic poles where they attach, carrying with them the heavy metal particles.

Il est possible de déterminer le rendement du procédé selon l'invention. Par exemple, dans le cas où l'on extrait des particules de ruthénium contenues dans le milieu nitrique de dissolution de combustible irradié. A cette fin, on place la poudre fine de ruthénium dans une solution 4N de nitrate d'uranyle, que l'on agite et que l'on chauffe légèrement, par exemple vers 50°C, pour simuler une solution nitrique de combustible irradié qui s'échauffe spontanément sous l'effet du rayonnement de décroissance des produits de fission.It is possible to determine the yield of the process according to the invention. For example, in the case where ruthenium particles contained in the nitric medium for dissolving irradiated fuel are extracted. To this end, the fine ruthenium powder is placed in a 4N solution of uranyl nitrate, which is stirred and slightly heated, for example around 50 ° C., to simulate a nitric solution of irradiated fuel which spontaneously heats up under the effect of the decaying radiation of the fission products.

Pour simplifier la mesure des quantités de ruthénium, la poudre métallique a été préalablement irradiée en réacteur afin de la marquer au ruthénium 103 radioactif, émetteur gamma. Après addition de magnétite finement divisée, qui a été préparée séparément par précipitation alcaline dans une solution de fer ferreux, et dont les particules mesure initialement de 0,1 pm à quelques pm, on poursuit l'agitation du liquide pendant quelques minutes. Par mesure de la radioactivité du ruthénium 103 dans le liquide avant et après l'extraction de la magnétite au moyen d'un ou de plusieurs aimants, le rendement de l'extraction du ruthénium peut facilement être apprécié. D'autre part, le bilan matière du ruthénium 103 qui peut facilement être établi par mesure de l'activité de ce radio- nucléide dans l'aliquote de ruthénium métallique avant l'expérience, puis dans les boues de magnétite après l'extraction, permet de contrôler ce rendement.To simplify the measurement of the amounts of ruthenium, the metal powder was previously irradiated in a reactor in order to mark it with radioactive ruthenium 103, a gamma emitter. After addition of finely divided magnetite, which was prepared separately by alkaline precipitation in a solution of ferrous iron, and whose particles initially measure from 0.1 μm to a few μm, the stirring of the liquid is continued for a few minutes. By measuring the radioactivity of ruthenium 103 in the liquid before and after the extraction of the magnetite by means of one or more magnets, the yield of the ruthenium extraction can easily be appreciated. On the other hand, the material balance of ruthenium 103 which can easily be established by measuring the activity of this radionuclide in the aliquot of metallic ruthenium before the experiment, then in the magnetite sludges after the extraction, allows to control this yield.

Le rendement est compris entre 65 et 85%.The yield is between 65 and 85%.

De préférence, l'adjuvant ferromagnétique utilisé est de la ferrite, ou encore de la magnétite.Preferably, the ferromagnetic adjuvant used is ferrite, or alternatively magnetite.

Le procédé d'élimination des éléments métalliques lourds selon l'invention conduit à l'obtention d'une boue dense, constituée par un mélange de l'adjuvant ferromagnétique et des éléments métalliques lourds.The process for removing heavy metallic elements according to the invention leads to the production of a dense sludge, constituted by a mixture of the ferromagnetic adjuvant and heavy metallic elements.

Les boues adhèrent aux pôles des aimants.The sludge adheres to the poles of the magnets.

Cette boue dense peut être facilement séparée des eaux de lavage par décantation. Les particules métalliques peuvent ensuite être séparées de la magnétite, soit pour les isoler sous un faible volume de déchets, soit en vue de la rentabilisation des métaux qui en sont les constituants principaux.This dense sludge can be easily separated from the wash water by decantation. The metal particles can then be separated from the magnetite, either to isolate them under a small volume of waste, or with a view to the profitability of the metals which are their main constituents.

De toute façon, les caractéristiques et avantages de l'invention apparaîtront mieux après la description qui suit d'un exemple de mise en oeuvre donné à titre explicatif et nullement limitatif, du procédé selon la présente invention, en référence à la figure unique qui représente un appareil comportant un arbre tournant portant des aimants permanents.In any case, the characteristics and advantages of the invention will appear better after the following description of an exemplary implementation given by way of explanation and in no way limiting, of the method according to the present invention, with reference to the single figure which represents a device comprising a rotating shaft carrying permanent magnets.

Sur cette figure, le récipient 1 contient une solution nitrique de combustible irradié 2 à l'intérieur de laquelle on trouve un résidu de produits de fission insolubles, dont notamment du ruthénium à l'état finement divisé, qu'il s'agit d'éliminer pour empêcher son accumulation par dépôt dans les composants de l'atelier de dissolution et d'extraction de l'usine de retraitement. A cette fin, et conformément au procédé de l'invention, on ajoute à la solution 2 une quantité de magnétite. La quantité optimale de magnétite à ajouter est déterminée par voie d'expériences préliminaires.In this figure, the container 1 contains a nitric solution of irradiated fuel 2 inside which there is a residue of insoluble fission products, including in particular ruthenium in the finely divided state, which is eliminate to prevent its accumulation by deposition in the components of the dissolution and extraction workshop of the reprocessing plant. To this end, and in accordance with the process of the invention, an amount of magnetite is added to solution 2. The optimal amount of magnetite to add is determined by preliminary experiments.

Avantageusement, le rapport en masse des quantités de ruthénium et de magnétite se situe entre 1/6 et 1/12. Après l'addition de la magnétite, la solution 2 est agitée pendant un certain temps, afin de maintenir en suspension et en contact intime les particules insolubles et les particules de magnétite. La durée du contact dans la solution nitrique doit cependant être limitée pour que la dissolution de la magnétite elle-même reste faible. A une température voisine de la température ambiante, il est possible de maintenir la magnétite en milieu nitrique 4N pendant une heure sans que la quantité de fer dissous dépasse quelques dizaines de milligrammes par litre. Cependant, des expériences d'orientation en laboratoire montrent qu'on peut avantageusement limiter l'agitation de la solution nitrique à moins d'une demi-heure. Après cette durée d'agitation, l'agitateur mécanique est remplacé rapidement par un autre agitateur désigné sur la figure 1 par la référence générale 3. Ce dernier comprend un arbre tournant 4 portant des aimants permanents 5 qui peuvent avoir la forme de barreaux ou de fers à cheval. Le nombre des aimants 5 est suffisant pour qu'ils puissent fixer toute la magnétite ajoutée à la solution 2. Ces aimants 5 sont disposés de telle manière que leurs pôles voisins soient de même polarité, ou, au moins, s'ils sont de polarité différente, qu'ils soient suffisamment éloignés pour qu'ils ne puissent exercer l'un sur l'autre une action capable de diminuer notablement le gradient du champ magnétique à proximité des pôles voisins. On limite la vitesse de rotation de l'arbre 4 afin que la vitesse linéaire des pôles des aimants 5 reste suffisamment faible pour que la force d'attraction exercée par ces pôles sur les particules de magnétite soit supérieure à la force d'arrachage qu'exerce sur elles le liquide par frottement au niveau des surfaces polaires. Pour des aimants en alliage moderne de forte coercivité, la vitesse linéaire à l'extrémité des pôles peut atteindre entre 10 et 20 centimètres par seconde, quand la viscosité du liquide est du même ordre de grandeur que celle de l'eau. Quand la viscosité du liquide est notablement différente de celle de l'eau, la vitesse linéaire à choisir lui est inversement proportionnelle.Advantageously, the mass ratio of the quantities of ruthenium and magnetite is between 1/6 and 1/12. After the addition of the magnetite, the solution 2 is stirred for a certain time, in order to maintain in suspension and in intimate contact the insoluble particles and the particles of magnetite. The duration of the contact in the nitric solution must however be limited so that the dissolution of the magnetite itself remains weak. At a temperature close to room temperature, it is possible to maintain the magnetite in 4N nitric medium for one hour without the quantity of dissolved iron exceeding a few tens of milligrams per liter. However, laboratory orientation experiments show that the agitation of the nitric solution can advantageously be limited to less than half an hour. After this duration of agitation, the mechanical agitator is quickly replaced by another agitator designated in FIG. 1 by the general reference 3. The latter comprises a rotating shaft 4 carrying permanent magnets 5 which may have the form of bars or horseshoes. The number of magnets 5 is sufficient for them to be able to fix all the magnetite added to the solution 2. These magnets 5 are arranged in such a way that their neighboring poles are of the same polarity, or, at least, if they are of polarity different, that they are far enough apart that they cannot exert one on the other an action capable of significantly reducing the gradient of the magnetic field near the neighboring poles. The speed of rotation of the shaft 4 is limited so that the linear speed of the poles of the magnets 5 remains low enough so that the attraction force exerted by these poles on the magnetite particles is greater than the tearing force that exerts on them the liquid by friction at the level of the polar surfaces. For modern alloy magnets with high coercivity, the linear speed at the end of the poles can reach between 10 and 20 centimeters per second, when the viscosity of the liquid is of the same order of magnitude as that of water. When the viscosity of the liquid is significantly different from that of water, the linear speed to be chosen is inversely proportional to it.

Quand la solution nitrique 2 est limpide, on arrête l'extraction magnétique en retirant l'agitateur 3. Les aimants 5 sont alors chargés de boues à leurs extrémités polaires. Ces boues retiennent naturellement aussi un peu de solution contenant du plutonium et de l'uranium dont on peut les laver en faisant tourner l'agitateur 3 à faible vitesse dans un récipient identique au récipient 1 et contenant de l'eau. Cette eau est renouvelée pour procéder à l'enlèvement de la charge de boues sur les aimants 5. Ces boues se détachent des extrémités polaires au moyen d'eau dont la vitesse linéaire est suffisamment grande. A cette fin, on peut faire tourner l'agitateur 3 dans un récipient contenant de l'eau avec une vitesse de rotation telle que la vitesse linéaire aux extrémités des aimants 5 soit supérieure à 40 cm par seconde. Ou encore, on peut diriger sur ces mêmes extrémités un jet d'eau animé d'une grande vitesse, l'eau de rinçage étant recueillie dans un récipient initialement vide.When the nitric solution 2 is clear, the magnetic extraction is stopped by removing the agitator 3. The magnets 5 are then loaded with sludge at their polar ends. These sludges naturally also retain a little solution containing plutonium and uranium which can be washed by rotating the agitator 3 at low speed in a container identical to container 1 and containing water. This water is renewed to remove the charge of sludge on the magnets 5. This sludge is detached from the polar ends by means of water whose linear speed is sufficiently high. To this end, the agitator 3 can be rotated in a container containing water with a speed of rotation such that the linear speed at the ends of the magnets 5 is greater than 40 cm per second. Alternatively, a high speed water jet can be directed at these same ends, the rinsing water being collected in an initially empty container.

Après un tel rinçage, l'agitateur 3 est réutilisable immédiatement.After such rinsing, the agitator 3 is immediately reusable.

Le traitement ultérieur des eaux de rinçage consiste à séparer la magnétite sous faible volume avec toutes les particules qu'elle a entraînées par une sédimentation préalable. L'effluent aqueux est ensuite décontaminé par traitement avec des résines échangeuses d'ions. Les boues de magnétite peuvent être conditionnées sous forme de déchets solides par une méthode connue. Si la récupération des éléments platinoïdes comme le ruthénium présente un intérêt, on les sépare par un traitement approprié préalable des boues. Par exemple, on peut transformer la magnétite par oxydation en une forme beaucoup plus soluble du fer, qui'il suffit alors de dissoudre pour séparer les éléments platinoïdes insolubles tels que le ruthénium.The subsequent treatment of the rinsing water consists in separating the magnetite in small volume with all the particles which it has entrained by prior sedimentation. The aqueous effluent is then decontaminated by treatment with ion exchange resins. Magnetite sludge can be conditioned as solid waste by a known method. If the recovery of platinoid elements such as ruthenium is of interest, they are separated by appropriate prior treatment of the sludge. For example, magnetite can be transformed by oxidation to a much more soluble form of iron, which then simply dissolves to separate the insoluble platinoid elements such as ruthenium.

Le procédé d'élimination des particules métalliques lourdes selon l'invention conduit à une boue dense facilement séparée des eaux de lavage par décantation et qui contient les produits de fission insolubles. Ces derniers peuvent être ensuite séparés de l'adjuvant ferromagnétique, soit pour les isoler sous un faible volume de déchets, soit en vue de la rentabilisation des métaux platinoïdes qui en sont les constituants majeurs.The process for removing heavy metal particles according to the invention leads to a dense sludge easily separated from the washing water by decantation and which contains the insoluble fission products. The latter can then be separated from the ferromagnetic adjuvant, either to isolate them under a small volume of waste, or for the profitability of the platinoid metals which are the major constituents thereof.

Claims (6)

1. Process for removing suspended particles from a liquid, comprising the following steps:
- addition of particles of a finely-divided ferromagnetic additive to the liquid containing the particles to be removed;
- agitation of the liquid, whereby to form a suspension of the ferromagnetic additive, and bring about mixing of the latter with the. particles to be extracted;
- application of a magnetic field to said liquid;

characterized in that said agitation of the liquid and the application of the magnetic field are provided by means of a single apparatus constituted by a rotatable shaft carrying permanent magnets whose adjacent poles have the same polarity.
2. Process according to Claim 1, characterized in that the particles to be extracted are heavy metal particles, the mass ratio of metal particles to be extracted to particles of ferromagnetic additive being greater than 100:1.
3. Process according to Claim 2, characterized in that the metal particles comprise ruthenium.
4. Process according to any one of Claims 1 to 3, characterized in that the ferromagnetic additive is selected from the group ferrite and magnetite.
5. Process according to any one of Claims 1 to 4, characterized in that the maximum time of agitation is half an hour.
6. Process according to any one of Claims 1 to 5, characterized in that the ferromagnetic additive is magnetite employed in a mass between 6 and 12 times that of the heavy metal particles in suspension within the liquid to be treated.
EP19800401343 1979-10-02 1980-09-19 Process for removing heavy metallic elements in suspension in a liquid Expired EP0026700B1 (en)

Priority Applications (1)

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DE8484200419T DE3072136D1 (en) 1979-10-02 1980-09-19 Process for removing heavy metallic elements suspended in a liquid

Applications Claiming Priority (2)

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FR7924496 1979-10-02
FR7924496A FR2466282A1 (en) 1979-10-02 1979-10-02 METHOD FOR REMOVING HEAVY METALLIC ELEMENTS SUSPENDED IN A LIQUID USING A FINALLY DIVIDED FERROMAGNETIC ADJUVANT

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EP19840200419 Division-Into EP0127906B1 (en) 1979-10-02 1980-09-19 Process for removing heavy metallic elements suspended in a liquid
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DE3684448D1 (en) * 1985-12-20 1992-04-23 Syntex Inc PARTICLE SEPARATION PROCEDURE.
US5076950A (en) * 1985-12-20 1991-12-31 Syntex (U.S.A.) Inc. Magnetic composition for particle separation
ATE172890T1 (en) * 1995-02-21 1998-11-15 Iqbal W Dr Siddiqi APPARATUS AND METHOD FOR MIXING AND SEPARATION USING MAGNETIC PARTICLES
FR2830204A1 (en) * 2001-10-02 2003-04-04 Centre Nat Rech Scient PROCESS AND DEVICE FOR SEPARATING MARKED PARTICLES SUSPENDED IN A VISCOUS MEDIUM AND ITS APPLICATION TO MICROBIOLOGICAL PROCESSES
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CN112138864B (en) * 2020-09-14 2023-03-14 东莞市江合磁业科技有限公司 High-precision intelligent magnetic separator based on self-adjustment of magnetic strength

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EP0127906A1 (en) 1984-12-12
EP0026700A1 (en) 1981-04-08
DE3070456D1 (en) 1985-05-15
EP0127906B1 (en) 1988-11-30
JPS5658935A (en) 1981-05-22
FR2466282A1 (en) 1981-04-10
FR2466282B1 (en) 1983-11-10

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