EP0156744B1 - Process for winning a metal by electrolysis of molten halogenides whereby a simultaneous and continuous double disposition is taking place, and apparatus therefor - Google Patents

Process for winning a metal by electrolysis of molten halogenides whereby a simultaneous and continuous double disposition is taking place, and apparatus therefor Download PDF

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Publication number
EP0156744B1
EP0156744B1 EP85420040A EP85420040A EP0156744B1 EP 0156744 B1 EP0156744 B1 EP 0156744B1 EP 85420040 A EP85420040 A EP 85420040A EP 85420040 A EP85420040 A EP 85420040A EP 0156744 B1 EP0156744 B1 EP 0156744B1
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Prior art keywords
basket
bath
cathode
metal
halides
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German (de)
French (fr)
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EP0156744A1 (en
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Joseph Cohen
Gérard Lorthioir
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Pechiney SA
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Pechiney SA
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/26—Electrolytic production, recovery or refining of metals by electrolysis of melts of titanium, zirconium, hafnium, tantalum or vanadium
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
    • C25C7/005—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells of cells for the electrolysis of melts

Definitions

  • the present invention relates to a process for obtaining a metal by electrolysis of halides in a bath of molten salts comprising a simultaneous and continuous double deposition and to devices for applying said process.
  • metals concerned there are all those which have a melting point above 1000 ° C. and, preferably, several valence states such as in particular titanium, zirconium, hafnium, thorium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, uranium, plutonium as well as rare earth metals.
  • a metal can be deposited by introducing one of its derivatives such as a halide, for example, into a bath of molten salts and by subjecting it in its simplest principle. by the action of two electrodes connected to the poles of a direct current source: at the anode the halogen is released and at the cathode the metal is deposited.
  • This diaphragm can be made of ceramic or by depositing a refractory metal on a suitably polarized metal mesh.
  • the present invention uses a basket-shaped metal cathode which, while being able to serve as a diaphragm, serves above all as the first receiver of the metal to be deposited.
  • the documents GB 781.311, EP-A-0053567 and US-A-3.282.822 describe methods which could be compared to our invention.
  • the first of them describes a cell of parallelepiped shape containing a bath of chlorides; it is divided by a vertical partition into two compartments which communicate with each other by a space located between the bottom of the partition and the bottom of the cell.
  • a metal log constituting the anode and in the other a cathode assembly, in perforated sheet, composed of a tubular cathode and a concentric cathode basket supplied with halide of the metal to be deposited.
  • This cell operates according to two chloride supply regimes. In a first stage, it is quickly fed so as to have a mole TiC1 4 for 10 to 20 Faradays. This results in the formation on the inner walls of the box of fine titanium crystals which develop to form a more or less spongy deposit. Then, the amount of TiC1 4 is increased so as to have one mole of TiC1 4 for 4.5 to 6.5 Faradays. Under these conditions, a concentration of TiC1 2 occurs and titanium metal is preferably deposited on the cathode bars in the form of branched crystals.
  • the supply of TiC1 4 is interrupted, the current extended for a few moments to exhaust the soluble titanium, then the cathode box is taken out of the bath and cooled away from the atmosphere. The metal is then separated from the box, then washed with a dilute acid solution and dried.
  • the product obtained contains between 50 and 80% of metal having a Brinell hardness of around 120.
  • the product obtained is heterogeneous since the initial deposit of metal on the walls of the box, at the moment when the quantity of current admitted is large, is spongy in nature, while the subsequent deposit on cathode bars, at reduced quantity of current, has larger crystals;
  • EP-A-0053567 relates to a cell for the preparation by discontinuous electrolysis of zirconium or hafnium from a molten mixture of chlorides and alkali or alkaline earth fluorides.
  • a simultaneous and continuous double deposition of metal is brought into play on the one hand on a basket-shaped diaphragm maintained cathode relative to a central anode and on the other hand on cathodes outside this diaphragm.
  • a direct current Il is circulated between the anode and the diaphragm and simultaneously a current 1-1 1 between the diaphragm and the external cathodes from which the metal is recovered.
  • the invention is inspired by the technique taught in EP-A-0053567 and consists in a process for obtaining a metal by electrolysis of halides in a bath of molten halides contained in a tank comprising a simultaneous double deposition and continuous, in which a direct electrical current 1 1 is first circulated from an anode assembly to a cathode in the shape of a double-walled basket, both being immersed in the bath, by supplying the basket with a metal halogen to deposit, until the quantity of electricity delivered corresponds to the filling of 1/3 to 2/3 of the volume of the basket with the metal, then introduced into the compartment delimited by the interior walls of the tank and the external walls of the basket, the halide of the metal so as to have in the bath contained in said compartment a content of combined metal comprised between 1 and 7% by weight, and then is circulated, simultaneously with current 1 1, a current 1 2 from the basket to at least one cathode com while continuing to supply the basket with halides, and periodically extracted said complementary ca
  • a current 1 1 and a current 1 2 are passed simultaneously while continuing to supply the basket with halide.
  • the cell thus acquires its cruising speed. It then only remains to regularly remove the cathode (s) from the bath to recover the metal and to replace them with blank cathodes.
  • n cathodes the procedure is as follows: a single cathode having been placed in the bath during start-up, the n-1 others are successively immersed at regularly spaced times so that at the time of immersion of the nth, the first is covered by the quantity of refined metal desired.
  • the process according to the invention allows the supply of halide in a form which is not only liquid but also solid, which is different from the process of USP 3,282,822 which only admitted in the case of titanium tetrachloride and preferably gas.
  • This enlargement to the three physical states of matter results from the production of a deposit in two stages which frees the process from the quality constraints of the metal present in the basket since the latter constitutes only a transitory phase of its obtaining.
  • the process is applicable to most halides of type M (halogen) ,, where M is a metal such as titanium, zirconium, hafnium, thorium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, uranium, plutonium, rare earth metals and X one of the valences of the metal considered. It can also be applied to metals which are difficult to obtain directly in a correct crystalline state.
  • Subchlorides have the advantage over TiC1 4 of being soluble in the bath of molten salts and therefore of giving a more homogeneous bath. They also allow better control of the quantity of homogenides introduced and therefore of being able to limit the content of combined titanium in the basket and thus reduce the diffusion of titanium ions towards the anode and, consequently, losses due to anodic reoxidation.
  • the molten salt bath used is chosen according to the metal to be deposited.
  • titanium a mixture of calcium, barium and sodium chlorides is preferably taken, in suitable proportions.
  • This bath has the advantage of having a composition similar to that of the bath used for the electrolytic production of sodium: it is thus possible to design a loop comprising the pre-reduction of TiC1 4 to TiCl x by sodium and the recirculation of the bath from the anode compartment to the sodium electrolysis cell.
  • the current intensities applied they mainly depend on the metals to be deposited, the type of halide and the speed of supply and are therefore subject to specific adaptations.
  • a first device comprising a cylindrical tank designed to contain said bath sheltered from the atmosphere, an anode assembly comprising at least one anode of cylindrical shape placed in the center of the cell immersed in the bath, a metal cathode surrounding completely and symmetrically the anode assembly, means for connecting the upper parts of the anode assembly and of the cathode respectively to the positive and negative poles of a direct current source, at least one complementary cathode placed outside the cathode connected to a source of potential current which is more strongly negative than that of the cathode and characterized in that the cathode has the shape of a lattice basket, suspended in the bath, constituted by two vertical coaxial cylinders integral with a perforated bottom extending up to the axis of the tank so as to share the volume of the bath in three compartments, that it comprises a halide supply system placed at the upper part of the cathode and between the two cylinders, means for suction
  • This device differs from that of EP-A-0053567 in particular by the presence of a double-walled basket-shaped cathode.
  • the anode assembly occupies a central position in the electrolysis cell and is symmetrically surrounded by the cathode basket, so that the whole of the inner side wall and the whole of the outer side wall of said basket are each equidistant from the anode.
  • Such an arrangement creates in the anolyte a regularly distributed electric field which avoids local diffusions of titanium ions towards the anode and promotes the channeling of the released halogen.
  • the basket consists of a nickel metal mesh preferably with mesh sizes that prevent too easy passage of the metal particles without being a cause of clogging.
  • the upper part of the basket emerges from the bath and can be opened to closed. In both cases, it is in relation, on the one hand with the halide supply system, on the other hand with the negative pole of a current source by means of sealed passages made in the cover of the cell.
  • the central anode assembly preferably consists of a cylindrical piece of graphite, sculpted longitudinally in order to promote the release of gas, connected to the positive pole of a current source and placed inside d 'A bell tightly attached to the cell cover and through which the halide is sent to an external capture.
  • cathodes preferably of iron, nickel, titanium or metal to be deposited, which serve to receive the final metal.
  • This arrangement allows a regular distribution of the second deposit current and obtaining a uniform deposit of metal. It also contributes to facilitating the recovery of the metal due to good accessibility of said cathodes. By using a sufficient number of cathodes, the cathode current density is reduced and the quality of the deposit is improved.
  • anode compartment where the titanium content of the bath is practically zero
  • a compartment constituted by the basket where the bath is very rich in titanium ions
  • a cathode compartment delimited by the inner walls of the cell and the outer walls of the basket, where the titanium content of the bath is relatively low and of the order of a few percent by weight.
  • a device comprising a cylindrical tank designed to contain the bath sheltered from the atmosphere, a cathode in the shape of a metal perforated basket with vertical side wall secured to a bottom suspended in the bath, a set anode comprising at least one cylindrical anode immersed in the bath placed outside the basket, means for connecting the upper parts of the anode assembly and the cathode respectively to the positive and negative poles of a direct current source , at least one additional cathode placed inside the basket in a symmetrical manner, a halide supply device through the upper part of the cathode, means for suctioning the released halogen, characterized in that the side wall of the basket is in lattice, in the form of a cylinder, that the basket is internally equipped with a second lateral wall in metallic trellis parallel and coaxial with the first and fixed on the bottom so as to share the volume of the bath in three compartments, that the complementary cathode is connected by its upper part and by a means of
  • This device makes it possible to group the cathodes in the center of the cell, which has the result, in particular, of reducing the number of devices for extracting said cathodes. It resembles in this the device of US-A-3 282 822, but is distinguished by a polarization of the basket and its supply between two walls forming a space separate from the complementary cathodes hence the possibility of obtaining on these last a homogeneous and non-spongy metal deposit.
  • the bottom of the cell is equipped with a nozzle for extracting the bath which opens into the anode compartment.
  • the bath is then continuously recycled to the basket after having been properly recharged with the metal halide to be deposited.
  • FIG. 1 a section along an axial plane of an example cell according to the invention and in FIG. 2 a section of the same cell according to a horizontal plane of layout XX 'in FIG. 1.
  • Hastelloy C cell with an internal diameter of 235 mm and a height of 700 mm, equipped with a heating system, and inside which is placed a cylindrical nickel tank with a diameter of 220 mm and a height of 300 mm, we have loaded with 13.7 kg of a BaCI 2 -CaCI 2 -NaCI eutectic (16.3 - 46.9 - 36.7% in moles).
  • the cell was evacuated at around 550 ° C. to eliminate the humidity, then treatment with HCl to remove the oxides, hydroxides, and other impurities contained in the bath, then electrolysis at a DC voltage of 2.2 V until the residual current stabilizes.
  • the cover was then removed and an annular cylindrical basket made by means of a 3 mm diameter nickel wire frame covered with a metallic fabric made with 0.28 mm diameter nickel wire braided according to the bath was introduced. 35 mesh. Then, the cover was replaced with a central anode and its bell, its complementary cathodes, the various gas inlet and outlet pipes and the halide supply system.
  • the atmosphere of the cell was purged under vacuum, then under argon, then warmed to 550 ° C.
  • the bath being liquid, the various electrodes were immersed in it.
  • the height of the bath in the cell was then 150 mm.
  • TiCl x was prepared in a bath of molten salts, where X was 2.3 by oxidation of titanium powder with titanium tetrachloride. This solution contained about 10% by weight of titanium in the form of halide.
  • This TiCl x was introduced at the rate of 6 g / hour into the cell and a voltage of 3.5 V was applied. Current 1, then had the value 2 A.
  • the compartment delimited by the interior walls of the cell and the exterior walls of the basket was then supplied with TiCl x until a composition of between 1.5 and 2% by weight of titanium was reached and a voltage of -0 was imposed. , 9 V between cathode and basket. A current 1 2 with an average value of 1.5 A has been established.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electrolytic Production Of Metals (AREA)
  • Manufacture And Refinement Of Metals (AREA)
  • Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
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Abstract

This invention relates to an electrolysis process and cell for producing a metal by electrolyzing halides in a molten salt bath. It consists of using one cathode in the form of a basket, simultaneously passing a current I1 between this cathode and the anode in such a manner as to carry out a first deposit of crude metal in the basket and a current I2 between the said basket and the complimentary cathodes for depositing the final metal thereon. The cell consists of a central anodic system, a tubular cathodic basket surrounding the anode and a series of cathodes surrounding this basket, a positioning which can be reversed in relation to the basket. The invention finds its application in the continuous production of good quality refractory metal with a suitable material and electric yield.

Description

La présente invention est relative à un procédé d'obtention d'un métal par électrolyse d'halogénures en bain de sels fondus comportant un double dépôt simultané et continu et à des dispositifs d'application dudit procédé.The present invention relates to a process for obtaining a metal by electrolysis of halides in a bath of molten salts comprising a simultaneous and continuous double deposition and to devices for applying said process.

Parmi les métaux concernés, figurent tous ceux qui présentent un point de fusion supérieur à 1000°C et, de préférence, plusieurs états de valence tels que notamment le titane, le zirconium, l'hafnium, le thorium, le vanadium, le niobium, le tantale, le chrome, le molybdène, le tungstène, l'uranium, le plutonium ainsi que les métaux des terres rares.Among the metals concerned, there are all those which have a melting point above 1000 ° C. and, preferably, several valence states such as in particular titanium, zirconium, hafnium, thorium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, uranium, plutonium as well as rare earth metals.

L'homme de l'art sait qu'on peut obtenir le dépôt d'un métal en introduisant un de ses dérivés tels qu'un halogénure, par exemple, dans un bain de sels fondus et en le soumettant dans son principe le plus simple à l'action de deux électrodes reliées aux pôles d'une source de courant continu: à l'anode se dégage l'halogène et à la cathode se dépose le métal. Cette technique dite d'électrolyse ignée a fait l'objet de nombreuses études qui ont abouti à la conception de divers procédés se distinguant entre eux par la composition du bain, l'état physique et chimique de l'halogénure, la modulation du régime de courant appliqué et à la réalisation de multiples dispositifs ou cellules qui présentent des différences quant à leur structure et à leur forme, notamment au niveau des électrodes, des systèmes d'injection d'halogénures et de récupération du métal déposé.Those skilled in the art know that a metal can be deposited by introducing one of its derivatives such as a halide, for example, into a bath of molten salts and by subjecting it in its simplest principle. by the action of two electrodes connected to the poles of a direct current source: at the anode the halogen is released and at the cathode the metal is deposited. This so-called igneous electrolysis technique has been the subject of numerous studies which have led to the design of various processes which are distinguished between them by the composition of the bath, the physical and chemical state of the halide, the modulation of the applied current and the production of multiple devices or cells which have differences in their structure and shape, in particular at the level of the electrodes, the halide injection systems and the recovery of the deposited metal.

Il est cependant un point commun à l'ensemble de ces cellules, c'est la présence d'un diaphragme poreux qui sépare l'anode de la cathode et partage le bain en deux volumes distincts: l'anolyte et le catholyte. Ce diaphragme a notamment pour effet d'éviter que l'halogène dégagé à l'anode ne réoxyde les halogénures réduits dissous dans l'électrolyte quand le métal comporte plusieurs valences.There is, however, one point common to all of these cells, it is the presence of a porous diaphragm which separates the anode from the cathode and divides the bath into two distinct volumes: the anolyte and the catholyte. This diaphragm has the particular effect of preventing the halogen released at the anode from reoxidizing the reduced halides dissolved in the electrolyte when the metal has several valences.

Ce diaphragme peut être réalisé en céramique ou par dépôt d'un métal réfractaire sur un treillis métallique polarisé convenablement.This diaphragm can be made of ceramic or by depositing a refractory metal on a suitably polarized metal mesh.

La présente invention met en oeuvre une cathode métallique en forme de panier qui, tout en pouvant servir de diaphragme, sert surtout de premier récepteur du métal à déposer. Les documents GB 781.311, EP-A-0053567 et US-A-3.282.822 décrivent des procédés qu'on pourrait rapprocher de notre invention.The present invention uses a basket-shaped metal cathode which, while being able to serve as a diaphragm, serves above all as the first receiver of the metal to be deposited. The documents GB 781.311, EP-A-0053567 and US-A-3.282.822 describe methods which could be compared to our invention.

Le premier d'entre eux décrit une cellule de forme parallélépipédique renfermant un bain de chlorures; elle est partagée par une cloison verticale en deux compartiments qui communiquent entre eux par un espace situé entre le bas de la cloison et le fond de la cellule. Dans l'un des compartiments plonge un rondin métallique constituant l'anode et dans l'autre un ensemble cathodique, en tôle perforée, composé d'une cathode tubulaire et d'un panier cathodique concentrique alimenté en halogénure du métal à déposer. Selon l'inventeur, lorsque cette cellule fonctionne avec du tétrachlorure de titane gazeux, la distribution de courant sur les surfaces cathodiques est telle qu'il se forme du dichlorure qui est réduit rapidement en métal, non seulement à proximité des parois périphériques du panier, mais aussi à proximité des parois périphériques du tube central, tandis qu'il se dépose du trichlorure entre ces deux région. Comme le trichlorure est réduit moins rapidement en métal que le dichlorure, il en résulte le maintien d'une grande différence de concentration en chlorures réduits au sein du bain, ce qui a pour effet de donner des cristaux métalliques de taille relativement grande sur les parois cathodiques du panier. Ces cristaux sont alors récupérés, après arrêt en la cellule, en sortant le panier du bain et en les décollant de la paroi. On immerge à nouveau le panier pour entreprendre une nouvelle opération d'électrolyse.The first of them describes a cell of parallelepiped shape containing a bath of chlorides; it is divided by a vertical partition into two compartments which communicate with each other by a space located between the bottom of the partition and the bottom of the cell. In one of the compartments plunges a metal log constituting the anode and in the other a cathode assembly, in perforated sheet, composed of a tubular cathode and a concentric cathode basket supplied with halide of the metal to be deposited. According to the inventor, when this cell operates with gaseous titanium tetrachloride, the distribution of current on the cathode surfaces is such that dichloride is formed which is rapidly reduced to metal, not only near the peripheral walls of the basket, but also near the peripheral walls of the central tube, while trichloride is deposited between these two regions. As the trichloride is reduced less quickly in metal than the dichloride, this results in the maintenance of a large difference in concentration of reduced chlorides within the bath, which has the effect of giving metallic crystals of relatively large size on the walls. basket cathodics. These crystals are then recovered, after stopping in the cell, by removing the basket from the bath and by peeling them from the wall. The basket is immersed again to undertake a new electrolysis operation.

L'US-A-3.282.822 rappelle d'abord les difficultés rancontrées avec les procédés tels que celui qui vient d'être décrit, notamment en ce qui concerne ·la formation à la fois de cristaux très fins et donc très oxydables et d'amas de cristaux plus gros, mais spongieux et emprisonnant entre eux des quantités importantes de bain. Pour y parer, il enseigne la nécessité d'un meilleur contrôle des densités de courant et d'une uniformité du courant à la surface des électrodes. Il préconise alors comme moyen une cathode en forme de boîte cubique ayant des parois latérales perforées, une paroi supérieure et un fond pleins. Au centre de la paroi supérieure de cette boîte débouche une tubulure d'alimentation en tétrachlorure de titane et à l'intérieur sont suspendues des barres cathodiques verticales. Autour de cette boîte sont réparties symétriquement dans le bain d'autres barres verticales faisant fonction d'anodes. Un évent placé sur le couvercle de la cellule permet l'évacuation vers l'extérieur du chlore produit par l'électrolyse.US-A-3,282,822 first recalls the difficulties encountered with processes such as that which has just been described, in particular with regard to · the formation of both very fine crystals and therefore very oxidizable and d heap of larger, but spongy crystals, trapping large amounts of bath between them. To counter this, it teaches the need for better control of current densities and uniformity of current on the surface of the electrodes. He then recommends as a means a cathode in the shape of a cubic box having perforated side walls, a top wall and a solid bottom. In the center of the upper wall of this box opens a tube for supplying titanium tetrachloride and inside are suspended vertical cathode bars. Around this box are symmetrically distributed in the bath other vertical bars acting as anodes. A vent placed on the cell cover allows the chlorine produced by electrolysis to be discharged to the outside.

Cette cellule fonctionne suivant deux régimes d'alimentation en chlorures. Dans un premier stade, on l'alimente rapidement de manière à avoir une mole TiC14 pour 10 à 20 Faradays. Il en résulte la formation sur les parois intérieures de la boîte de fins cristaux de titane qui se développent pour former un dépôt plus ou moins spongieux. Puis, la quantité de TiC14 est accrue de manière à avoir une mole de TiC14 pour 4,5 à 6,5 Faradays. Dans ces conditions, une concentration en TiC12 se produit et du titane métal se dépose de préférence sur les barres cathodiques sous une forme de cristaux à ramifications. Quand la boîte est pleine de métal, l'alimentation en TiC14 est interrompue, le courant prolongé pendant quelques instants pour épuiser le titane soluble, puis la boîte cathodique est sortie du bain et refroidie à l'abri de l'atmosphère. Le métal est alors séparé de la boîte, puis lavé avec une solution d'acide dilué et séché. Le produit obtenu renferme entre 50 et 80% de métal ayant une dureté Brinell de 120 environ.This cell operates according to two chloride supply regimes. In a first stage, it is quickly fed so as to have a mole TiC1 4 for 10 to 20 Faradays. This results in the formation on the inner walls of the box of fine titanium crystals which develop to form a more or less spongy deposit. Then, the amount of TiC1 4 is increased so as to have one mole of TiC1 4 for 4.5 to 6.5 Faradays. Under these conditions, a concentration of TiC1 2 occurs and titanium metal is preferably deposited on the cathode bars in the form of branched crystals. When the box is full of metal, the supply of TiC1 4 is interrupted, the current extended for a few moments to exhaust the soluble titanium, then the cathode box is taken out of the bath and cooled away from the atmosphere. The metal is then separated from the box, then washed with a dilute acid solution and dried. The product obtained contains between 50 and 80% of metal having a Brinell hardness of around 120.

Si cette cellule apporte un progrès par rapport à la précédente, comme le prétend l'inventeur, elle présente néanmoins les inconvénients suivants:

  • - son fonctionnement est discontinu du fait de la nécessité pour chaque opération de production de métal, d'utiliser successivement deux régimes de fonctionnement différents et de sortir le panier du bain pour récupérer le métal;
  • - lorsqu'on sort le bac cathodique du bain, il y a décrochage de fines particules de titane. Ces fines s'accumulent sous forme de boue au fond de la cellule et diminuent le rendement métal. De plus, du fait de leur bonne conductibilité électrique, elles provoquent la fuite d'une partie du courant destiné à l'électrolyse, réduisant ainsi le rendement électrique de la cellule. C'est pourquoi, il s'avère nécessaire de procéder prériodiquement à l'enlèvement de ces boues. Cet enlèvement se fait soit de façon mécanique, opération très insalubre, soit par introduction de chlore comme dans l'USP 3 607 011 (qui se réfère d'ailleurs à L'US-A-3.282.822 cité plus haut), de manière à transformer le métal en TiC14, halogénure qui s'échappe alors du bain par vaporisation et que l'on condense en vue d'un recyclage ultérieur;
If this cell brings progress compared to the previous one, as the inventor claims, it nevertheless has the following disadvantages:
  • - its operation is discontinuous due to the need for each production operation metal, successively use two different operating modes and take the basket out of the bath to recover the metal;
  • - when the cathode bin is removed from the bath, there is a drop of fine titanium particles. These fines accumulate in the form of mud at the bottom of the cell and reduce the metal yield. In addition, due to their good electrical conductivity, they cause the leakage of part of the current intended for electrolysis, thus reducing the electrical efficiency of the cell. This is why it is necessary to proceed periodically to the removal of this sludge. This removal is done either mechanically, a very unsanitary operation, or by the introduction of chlorine as in USP 3,607,011 (which moreover refers to US-A-3,282,822 cited above), so transforming the metal into TiC1 4 , a halide which then escapes from the bath by vaporization and which is condensed for subsequent recycling;

le produit obtenu est hétérogène puisque le dépôt initial de métal sur les parois de la boîte, au moment où la quantité de courant admise est grande, est de nature spongieuse, alors que le dépôt ultérieur su les barres cathodiques, à quantité de courant réduite, est à plus gros cristaux;the product obtained is heterogeneous since the initial deposit of metal on the walls of the box, at the moment when the quantity of current admitted is large, is spongy in nature, while the subsequent deposit on cathode bars, at reduced quantity of current, has larger crystals;

du fait de la présence de produits spongieux, le contenu du panier retient une quantité notable de bain dont il faut se débarrasser par un traitement en milieu acide;due to the presence of spongy products, the contents of the basket retain a significant amount of bath which must be disposed of by treatment in an acid medium;

il n'est pas facile de saisir le moment où le pouvoir d'assimilation de cette cellule diminue, de sorte que du TiC12 et du TiCI3 apparaissent dans l'anolyte et se recombient avec le chlore libéré à l'anode, ce qui diminue le rendement matière de l'opération.it is not easy to grasp the moment when the assimilation capacity of this cell decreases, so that TiC1 2 and TiCI 3 appear in the anolyte and recombine with the chlorine released at the anode, which decreases the material yield of the operation.

L'EP-A-0053567 concerne une cellule pour la préparation par électrolyse en discontinu de zirconium ou d'hafnium à partir d'un mélange fondu de chlorures et de fluorures alcalins ou alcalino terreux.EP-A-0053567 relates to a cell for the preparation by discontinuous electrolysis of zirconium or hafnium from a molten mixture of chlorides and alkali or alkaline earth fluorides.

Dans un de ces modes de réalisation, on met en jeu un double dépôt de métal simultané et continu d'une part sur un diaphragme en forme de panier maintenu cathodique par rapport à une anode centrale et d'autre part sur des cathodes extérieures à ce diaphragme.In one of these embodiments, a simultaneous and continuous double deposition of metal is brought into play on the one hand on a basket-shaped diaphragm maintained cathode relative to a central anode and on the other hand on cathodes outside this diaphragm.

Pour cela, on fait circuler un courant continu Il entre l'anode et le diaphragme et simultanément un courant 1-11 entre le diaphragme et les cathodes extérieures à partir desquelles le métal est récupéré.For this, a direct current Il is circulated between the anode and the diaphragm and simultaneously a current 1-1 1 between the diaphragm and the external cathodes from which the metal is recovered.

Une telle cellule a cependant l'inconvénient de nécessiter une stabilisation de la valence des métaux mis en oeuvre et qui est de quatre dans le cas présent. Cela est obtenu au moyen d'ajout de fluorures dans le bain d'électrolyse. Mais d'une part ces composés sont corrosifs et polluants, d'autre part, ils ne peuvent être utilisés pour d'autres métaux polyvalents.However, such a cell has the disadvantage of requiring stabilization of the valence of the metals used, which is four in the present case. This is achieved by adding fluorides to the electrolysis bath. But on the one hand these compounds are corrosive and polluting, on the other hand, they cannot be used for other polyvalent metals.

C'est pourquoi le but de l'invention est de proposer un procédé d'électrolyse en continu de métaux polyvalents dans lequel:

  • on évite l'utilisation de fluorures
  • on supprime la formation de boues
This is why the object of the invention is to propose a process for the continuous electrolysis of polyvalent metals in which:
  • avoiding the use of fluorides
  • we suppress the formation of sludge

on recueille de façon aisée un métal essentiellement cristallisé, homogène n'emprisonnant pas de bain, apte sans traitement intermédiaire à être aggloméré par fusion.an essentially crystallized, homogeneous metal which does not trap a bath is easily collected, capable of being agglomerated by fusion without intermediate treatment.

Autant d'éléments qui contribuent à améliorer à la fois la capacité de production, les rendements matière et électrique, les conditions de travail et la qualité des produits fabriqués.These elements all contribute to improving production capacity, material and electrical yields, working conditions and the quality of the products produced.

L'invention s'inspire de la technique enseignée l'EP-A-0053567 et consiste en un procédé d'obtention d'un métal par électrolyse d'halogènures dans un bain d'halogénures fondus contenu dans une cuve comportant un double dépôt simultané et continu, dans lequel on fait d'abord circuler un courant électrique continu 11 d'un ensemble anodique vers une cathode en forme de panier à double paroi, tous deux étant immergés dans le bain, en alimentant le panier avec un halogène du métal à déposer, jusqu'à ce que la quantité d'électricité débitée corresponde au remplissage de 1/3 à 2/3 du volume du panier par le métal, puis on introduit, dans le compartiment délimité par les parois intérieurs de la cuve et les parois extérieures du panier, l'halogénure du métal de manière à avoir dans le bain contenu dans ledit compartiment une teneur en métal combiné comprise entre 1 et 7% en poids, puis on fait alors circuler, simultanément au courant 11, un courant 12 du panier vers au moins une cathode complémentaire tout en continuant à alimenter le panier en halogénures, et ont extrait périodiquement ladite cathode complémentaire pour récupérer le métal obtenu et la remplace par une autre cathode.The invention is inspired by the technique taught in EP-A-0053567 and consists in a process for obtaining a metal by electrolysis of halides in a bath of molten halides contained in a tank comprising a simultaneous double deposition and continuous, in which a direct electrical current 1 1 is first circulated from an anode assembly to a cathode in the shape of a double-walled basket, both being immersed in the bath, by supplying the basket with a metal halogen to deposit, until the quantity of electricity delivered corresponds to the filling of 1/3 to 2/3 of the volume of the basket with the metal, then introduced into the compartment delimited by the interior walls of the tank and the external walls of the basket, the halide of the metal so as to have in the bath contained in said compartment a content of combined metal comprised between 1 and 7% by weight, and then is circulated, simultaneously with current 1 1, a current 1 2 from the basket to at least one cathode com while continuing to supply the basket with halides, and periodically extracted said complementary cathode to recover the metal obtained and replaces it with another cathode.

Les différences présentées par l'invention par rapport à l'art antérieur sont les suivantes:The differences presented by the invention compared to the prior art are as follows:

l'utilisation d'un panier à double paroi isolé à la fois de l'anode et de la cathode complémentaire sur laquelle s'effectue le dépôt de métal,the use of a double-walled basket isolated from both the anode and the complementary cathode on which the metal is deposited,

l'introduction d'halogénures dans le panier jusqu'à y former une quantité de métal déterminée,the introduction of halides into the basket until a certain quantity of metal is formed therein,

l'introduction d'halogénures en quantité déterminée dans le volume de bain situé à la périphérie du panier,the introduction of halides in a determined quantity into the volume of bath situated at the periphery of the basket,

l'alimentation en continu du panier en halogénures.continuous supply of halides to the basket.

On constate que dans ces conditions, on supprime les inconvénients évoqués plus haut.It can be seen that under these conditions, the drawbacks mentioned above are eliminated.

Dans ce procédé, on peut agir facilement et à tout moment sur le rapport entre les courants I1 et I2, c'est-à-dire accroître la quantité de métal déposé dans le panier en réduisant le transfert vers la cathode ou au contraire diminuer la quantité de métal déposé dans le panier en augmentant le transfert vers la cathode. Si, en régime, on arrive à un certain équilibre et donc à un volume constant dans le temps de métal déposé dans le panier, il peut arriver qu'en raison d'irrégularités dans le débit d'halogènures ou autres perturbations, un début de colmatage des parois du panier se produise; dans ce cas, il suffit d'augmenter 12 pour dissoudre les dépôts gênants et éventuellement les boues, et rétablir une marche correcte. A la limite, on peut pendant un temps donné interrompre soit Je courant soit le courant 12 de sorte que le rapport I1/I2 peut varier de 0 à l'infini et cela sans aucune répercussion sur la qualité du métal produit. Ceci constitue un avantage notable sur le procédé de l'art antérieur où en cas de colmatage, on n'avait d'autres ressources que d'arrêter l'électrolyse et de sortir le panier du bain pour ne récupérer qu'un métal fortement pollué par les halogénures n'ayant pu être réduits.In this process, one can easily and at any time act on the ratio between the currents I 1 and I 2 , that is to say increase the quantity of metal deposited in the basket by reducing the transfer to the cathode or on the contrary decrease the amount of metal deposited in the basket by increasing the transfer to the cathode. If, in regime, one arrives at a certain equilibrium and therefore at a constant volume in time of metal deposited in the basket, it can happen that due to irregularities in the flow of halides or other disturbances, a beginning of clogging of the basket walls occurs; in this case, it is enough to increase 1 2 to dissolve the annoying deposits and possibly the sludge, and restore correct operation. Ultimately, it is possible for a given time to interrupt either the current or the current 1 2 so that the ratio I 1 / I 2 can vary from 0 to infinity and this without any repercussions on the quality of the metal produced. This constitutes a notable advantage over the process of the prior art where in the event of clogging, there was no other resource than to stop the electrolysis and to remove the basket from the bath to recover only a highly polluted metal. by halides which could not be reduced.

Mais, il convient, lors du démarrage de l'opération, de suivre un processus particulier consistant d'abord à constituer une réserve de métal dans le panier. Pour cela, on fait circuler uniquement un courant 11 entre l'anode et le panier, tandis que l'on introduit plusieurs charges successives d'halogénures dans la cellule. Quand la quantité d'électricité débitée correspond au remplissage de 1/2 à 2/3 environ du volume du panier par du métal, on introduit dans le compartiment délimité par les parois intérieures de la cellule et les parois extérieures du panier l'halogénure du métal à déposer qui se réduit à la valence 0 à la cathode en une seule étape, de manière à avoir une teneur en métal combiné comprise entre 1 et 7% en poids; ceci afin d'éviter la formation de produits pulvérulents. A ce moment, on fait passer simultanément un courant 11 et un courant 12 tout en continuant à alimenter le panier en halogénure. La cellule acquiert ainsi son régime de croisière. Il ne reste plus alors qu'à sortir régulièrement la ou les cathodes du bain pour récupérer le métal et à les remplacer par des cathodes vierges. Dans le cas de n cathodes, on opère de la manière suivante: un seule cathode ayant été mise en place dans le bain lors du démarrage, on immerge successivement les n-1 autres à des moments régulièrement espacés afin qu'au moment de l'immersion de la nième, la première soit recouverte par la quantité de métal raffiné souhaitée.However, it is advisable, when starting the operation, to follow a particular process consisting first of all in building up a reserve of metal in the basket. For this, only a current 1 1 is circulated between the anode and the basket, while several successive charges of halides are introduced into the cell. When the quantity of electricity delivered corresponds to the filling of approximately 1/2 to 2/3 of the basket volume with metal, the halide of the basket is introduced into the compartment delimited by the interior walls of the cell and the exterior walls of the basket. metal to be deposited which is reduced to valence 0 at the cathode in a single step, so as to have a combined metal content of between 1 and 7% by weight; this is to avoid the formation of powdery products. At this time, a current 1 1 and a current 1 2 are passed simultaneously while continuing to supply the basket with halide. The cell thus acquires its cruising speed. It then only remains to regularly remove the cathode (s) from the bath to recover the metal and to replace them with blank cathodes. In the case of n cathodes, the procedure is as follows: a single cathode having been placed in the bath during start-up, the n-1 others are successively immersed at regularly spaced times so that at the time of immersion of the nth, the first is covered by the quantity of refined metal desired.

La description ci-dessus fait état d'une alimentation en halogénure seul. Mais, le procédé s'acco- mode aussi bien d'un mélange d'halogénure et de bain, ce dernier circulant entre les électrodes et étant soutiré en continu et recyclé après recharge en halogénure du métal que l'on veut déposer.The above description describes a halide only feed. However, the process is also accustomed to a mixture of halide and bath, the latter circulating between the electrodes and being continuously withdrawn and recycled after recharging the metal which one wishes to deposit with halide.

La procédé selon l'invention permet l'alimentation en halogénure sous une forme non seulement liquide mais également solide, ce qui est différent du procédé de l'USP 3 282 822 qui admettait seulement dans le cas du titane du tétrachlorure et de préférence gazeux. Cet élargissement aux trois états physiques de la matière résulte de la réalisation d'un dépôt en deux stades qui libère le procédé des contraintes de qualité du métal présent dans le panier puisque ce dernier ne constitue qu'une phase transitoire de son obtention.The process according to the invention allows the supply of halide in a form which is not only liquid but also solid, which is different from the process of USP 3,282,822 which only admitted in the case of titanium tetrachloride and preferably gas. This enlargement to the three physical states of matter results from the production of a deposit in two stages which frees the process from the quality constraints of the metal present in the basket since the latter constitutes only a transitory phase of its obtaining.

Le procédé et applicable à la plupart des halogénures du type M (halogène),,, où M est un métal tel que le titane, le zirconium, l'hafnium, le thorium, le vanadium, le niobium, le tantale, le chrome, le molybdène, le tungstène, l'uranium, le plutonium, le métaux des terres rares et X une des valences du métal considéré. Il peut également s'appliquer aux métaux qu'il est difficile d'obtenir directement dans un état cristallin correct.The process is applicable to most halides of type M (halogen) ,,, where M is a metal such as titanium, zirconium, hafnium, thorium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, uranium, plutonium, rare earth metals and X one of the valences of the metal considered. It can also be applied to metals which are difficult to obtain directly in a correct crystalline state.

C'est ainsi que dans le cas du titante, tous les halogénures de type TiClx dans lesquels X a une valeur égale ou comprise entre 2 et 4, peuvent être mis en oeuvre. Ainsi, à la différence de l'USP cité plus haut, on peut utiliser outre du TiC14, du TiCl3 ou du TiC12 ou un mélange de ces derniers ou encore un produit partiellement réduit dans lequel, par exemple, X est voisin de 2,3.Thus, in the case of the titrant, all the halides of the TiCl x type in which X has a value equal to or between 2 and 4, can be used. Thus, unlike the USP mentioned above, it is possible to use, in addition to TiC1 4 , TiCl 3 or TiC1 2 or a mixture of the latter or a partially reduced product in which, for example, X is close to 2.3.

Les sous-chlorures ont l'avantage sur le TiC14 d'être solubles dans le bain de sels fondus et donc de donner un bain plus homogène. Ils permettent, en outre, un meilleur contrôle de la quantité d'ho- logénures introduits et donc de pouvoir limiter la teneur en titane combiné dans le panier et de réduire ainsi la diffusion d'ions titane vers l'anode et, par suite, les pertes dues à le réoxydation anodique.Subchlorides have the advantage over TiC1 4 of being soluble in the bath of molten salts and therefore of giving a more homogeneous bath. They also allow better control of the quantity of homogenides introduced and therefore of being able to limit the content of combined titanium in the basket and thus reduce the diffusion of titanium ions towards the anode and, consequently, losses due to anodic reoxidation.

La possibilité d'utiliser des sous-chlorures apporte donc à la technique antérieure un progrès important, qui ne pouvait être envisagé que dans la mesure où on n'était pas contraint d'imposer au dépôt métallique du panier des caractéristiques métallurgiques particulières, ce qui est le cas du présent procédé et qui en fait tout l'intérêt.The possibility of using subchlorides therefore brings significant progress to the prior art, which could only be envisaged insofar as one was not forced to impose on the metallic deposit of the basket particular metallurgical characteristics, which is the case of the present process and which makes it all the interest.

Le bain de sels fondus utilisé est choisi en fonction du métal à déposer. C'est ainsi que pour le titane, on prend de préférence un mélange de chlorures de calcium, baryum et sodium, en proportions convenables. Ce bain a l'avantage d'avoir une composition semblable à celle du bain utilisé pour la production électrolytique du sodium: on peut ainsi concevoir une boucle comportant la préréduction de TiC14 en TiClx par le sodium et la recirculation du bain du compartiment anodique vers la cellule d'électrolyse du sodium.The molten salt bath used is chosen according to the metal to be deposited. Thus for titanium, a mixture of calcium, barium and sodium chlorides is preferably taken, in suitable proportions. This bath has the advantage of having a composition similar to that of the bath used for the electrolytic production of sodium: it is thus possible to design a loop comprising the pre-reduction of TiC1 4 to TiCl x by sodium and the recirculation of the bath from the anode compartment to the sodium electrolysis cell.

Quant aux intensités de courant appliquées, elles dépendent principalement des métaux à déposer, du type d'halogénure et de la vitesse d'alimentation et font donc l'object d'adaptations spécifiques.As for the current intensities applied, they mainly depend on the metals to be deposited, the type of halide and the speed of supply and are therefore subject to specific adaptations.

L'invention concerne également deux dispositifs d'obtention de métaux. Un premier dispositif comprenant une cuve cylindrique conçue pour contenir ledit bain à l'abri de l'atmosphère, un ensemble anodique comprenant au moins une anode de forme cylindrique placée au centre de la cellule plongeant dans le bain, une cathode métallique entourant complètement et symétriquement l'ensemble anodique, des moyens de liaison des parties hautes de l'ensemble anodique et de la cathode respectivement aux pôles positif et négatif d'une source de courant continu, au moins une cathode complémentaire placée à l'extérieur de la cathode reliée à une source de courant de potentiel plus fortement négatif que celui de la cathode et caractérisé en ce que la cathode a la forme d'un panier en treillis, suspendu dans le bain, constitué par deux cylindres coaxiaux verticaux solidaires d'un fond perforé s'étendant jusqu'à l'axe de la cuve de manière à partager le volume du bain en trois compartiments, qu'il comporte un système d'alimentation en halogènures placé à la partie haute de la cathode et entre les deux cylindres, des moyens d'aspiration de l'halogène dégagé et des moyens de sortie de Ja cathode complémentaire du bain à l'arbi de l'air.The invention also relates to two devices for obtaining metals. A first device comprising a cylindrical tank designed to contain said bath sheltered from the atmosphere, an anode assembly comprising at least one anode of cylindrical shape placed in the center of the cell immersed in the bath, a metal cathode surrounding completely and symmetrically the anode assembly, means for connecting the upper parts of the anode assembly and of the cathode respectively to the positive and negative poles of a direct current source, at least one complementary cathode placed outside the cathode connected to a source of potential current which is more strongly negative than that of the cathode and characterized in that the cathode has the shape of a lattice basket, suspended in the bath, constituted by two vertical coaxial cylinders integral with a perforated bottom extending up to the axis of the tank so as to share the volume of the bath in three compartments, that it comprises a halide supply system placed at the upper part of the cathode and between the two cylinders, means for suctioning the released halogen and means for leaving the cathode complementary to the bath in the air.

Ce dispositif diffère de celui de l'EP-A-0053567 notamment par la présence d'une cathode en forme de panier à double paroi.This device differs from that of EP-A-0053567 in particular by the presence of a double-walled basket-shaped cathode.

Par ailleurs, l'ensemble anodique occupe une position centrale dans la cellule d'électrolyse et elle est entourée de façon symétrique par le panier cathodique, de sorte que l'ensemble de la paroi latérale intérieure et l'ensemble de la paroi latérale extérieure dudit panier sont chacun équidistants de l'anode. Une telle disposition crée dans l'anolyte un champ électrique régulièrement réparti qui évite des diffusions locales d'ions titane vers l'anode et favorise la canalisation de l'halogène dégagé.Furthermore, the anode assembly occupies a central position in the electrolysis cell and is symmetrically surrounded by the cathode basket, so that the whole of the inner side wall and the whole of the outer side wall of said basket are each equidistant from the anode. Such an arrangement creates in the anolyte a regularly distributed electric field which avoids local diffusions of titanium ions towards the anode and promotes the channeling of the released halogen.

La présence d'un fond perforé ou non à la base du panier et qui se prolonge jusqu'à l'axe de la cellule, contribue à former un compartiment où l'anolyte se trouve séparé électriquement du reste du bain et renforce les avantages dûs à la symétrie panier-anode.The presence of a perforated bottom or not at the base of the basket and which extends to the axis of the cell, contributes to forming a compartment where the anolyte is electrically separated from the rest of the bath and reinforces the advantages due to basket-anode symmetry.

Mais on peut encore accentuer l'isolement de l'anolyte en réalisant un double fond dont l'intérieur communique ou non avec le panier lui- même.But we can further accentuate the isolation of the anolyte by creating a double bottom, the interior of which communicates or not with the basket itself.

Le panier est constitué d'un treillis métallique en nickel de préférence dont les mailles ont des dimensions telles qu'elles empêchent un passage trop facile des particules de métal sans pour autant être une cause de colmatage.The basket consists of a nickel metal mesh preferably with mesh sizes that prevent too easy passage of the metal particles without being a cause of clogging.

La partie supérieure du panier émerge du bain et peut être ouverte au fermée. Dans les deux cas, elle est en relation, d'une part avec le système d'alimentation en halogénures, d'autre part avec le pôle négatif d'une source de courant par l'intermédiaire de passages étanches pratiqués dans le couvercle de la cellule.The upper part of the basket emerges from the bath and can be opened to closed. In both cases, it is in relation, on the one hand with the halide supply system, on the other hand with the negative pole of a current source by means of sealed passages made in the cover of the cell.

Quant à l'ensemble anodique central, il est constitué de préférence par une pièce de forme cylindrique, en graphite, sculptée longitudinalement en vue de favoriser le dégagement gazeux, reliée au pôle positif d'une source de courant et placée à l'intérieur d'une cloche fixée de façon étanche au couvercle de la cellule et par l'intermédiaire de laquelle l'halogénure est envoyé vers une captation extérieure.As for the central anode assembly, it preferably consists of a cylindrical piece of graphite, sculpted longitudinally in order to promote the release of gas, connected to the positive pole of a current source and placed inside d 'A bell tightly attached to the cell cover and through which the halide is sent to an external capture.

Autour du panier se trouvent placées de façon symétrique une ou des cathodes de préférence en fer, nickel, titane ou en métal à déposer, qui servent à recevoir le métal final. Cette disposition permet une répartition régulière du courant de deuxième dépôt et l'obtention d'un dépôt uniforme de métal. Elle contribue également à faciliter la récupération du métal en raison d'une bonne accessibilité desdites cathodes. En utilisant un nombre suffisant de cathodes, on diminue la densité de courant cathodique et favorise la qualité du dépôt. Une telle disposition aboutit à un partage de la cellule en trois compartiments distincts: un compartiment anodique où la teneur du bain en titane est pratiquement nulle, un compartiment constitué par le panier où le bain est très riche en ions titane et un compartiment cathodique délimité par les parois intérieures de la cellule et les parois extérieures du panier, où la teneur en titane du bain est relativement faible et de l'ordre de quelques pour cent en poids. D'où une structure originale qui convient parfaitement à application du procédé selon l'invention.Around the basket are symmetrically placed one or more cathodes preferably of iron, nickel, titanium or metal to be deposited, which serve to receive the final metal. This arrangement allows a regular distribution of the second deposit current and obtaining a uniform deposit of metal. It also contributes to facilitating the recovery of the metal due to good accessibility of said cathodes. By using a sufficient number of cathodes, the cathode current density is reduced and the quality of the deposit is improved. Such an arrangement results in the cell being divided into three separate compartments: an anode compartment where the titanium content of the bath is practically zero, a compartment constituted by the basket where the bath is very rich in titanium ions and a cathode compartment delimited by the inner walls of the cell and the outer walls of the basket, where the titanium content of the bath is relatively low and of the order of a few percent by weight. Hence an original structure which is perfectly suitable for applying the method according to the invention.

Cependant, il ne s'agit là que d'un dispositif préférentiel non limitatif et toute autre variante telle que celle, par exemple, consitant à l'inverser la disposition de l'ensemble anodique et de l'ensemble cathodique par rapport au panier fait partie de l'invention.However, this is only a non-limiting preferential device and any other variant such as that, for example, involving inverting the arrangement of the anode assembly and the cathode assembly relative to the basket made. part of the invention.

Dans ce cas, on a un dispositif comprenant une cuve cylindrique conçue pour contenir le bain à l'abri de l'atmosphère, une cathode en forme de panier perforé métallique à paroi latérale verticale solidaire d'un fond suspendu dans le bain, un ensemble anodique comportant au moins une anode de forme cylindrique plongeant dans le bain placé à l'extérieur du panier, des moyens de liaison des parties hautes de l'ensemble anodique et de la cathode respectivement aux pôles positif et négatif d'une source de courant continu, au moins une cathode complémentaire placée à l'intérieur du panier de façon symétrique, un dispositif d'alimentation en halogénures par la partie haute de la cathode, des moyens d'aspiration de l'halogène dégagé, caractérisé en ce que la paroi latérale du panier est en treillis, a la forme d'un cylindre, que le panier est équipé intérieurement d'une deuxième paroi latérale en treillis métallique parallèle et coaxiale à la première et fixée sur le fond de manière à partager le volume du bain en trois compartiments, que la cathode complémentaire est reliée par sa partie haute et par un moyen de liaison à une source de courant de potentiel plus fortement négatif que celui du panier, que le dispositif d'alimentation en halogénures est en relation avec l'intérieur du compartiment délimité par les deux parois en treillis du panier. Ce dispositif permet de regrouper les cathodes au centre de la cellule, ce que a pour résultat, notamment, de diminuer le nombre de dispositifs d'extraction desdites cathodes. Il ressemble en cela au dispositif de l'US-A-3 282 822, mais s'en distingue par une polarisation du panier et son alimentation entre deux parois formant un espace séparé des cathodes complémentaires d'où la possibilité d'obtenir sur ces dernières un dépôt de métal homogène et non spongieux.In this case, there is a device comprising a cylindrical tank designed to contain the bath sheltered from the atmosphere, a cathode in the shape of a metal perforated basket with vertical side wall secured to a bottom suspended in the bath, a set anode comprising at least one cylindrical anode immersed in the bath placed outside the basket, means for connecting the upper parts of the anode assembly and the cathode respectively to the positive and negative poles of a direct current source , at least one additional cathode placed inside the basket in a symmetrical manner, a halide supply device through the upper part of the cathode, means for suctioning the released halogen, characterized in that the side wall of the basket is in lattice, in the form of a cylinder, that the basket is internally equipped with a second lateral wall in metallic trellis parallel and coaxial with the first and fixed on the bottom so as to share the volume of the bath in three compartments, that the complementary cathode is connected by its upper part and by a means of connection to a current source of potential more strongly negative than that of the basket, that the halide supply device is in relation with the interior of the compartment delimited by the two lattice walls of the basket. This device makes it possible to group the cathodes in the center of the cell, which has the result, in particular, of reducing the number of devices for extracting said cathodes. It resembles in this the device of US-A-3 282 822, but is distinguished by a polarization of the basket and its supply between two walls forming a space separate from the complementary cathodes hence the possibility of obtaining on these last a homogeneous and non-spongy metal deposit.

Dans le cas où l'on désire alimenter la cellule avec un mélange de bain et d'halogénure du métal à déposer, on équipe le fond de la cellule d'un piquage d'extraction du bain qui débouche dans le compartiment anodique. Le bain est alors recyclé en continu vers le panier après avoir été rechargé convenablement en halogénure du métal à déposer.In the case where it is desired to supply the cell with a mixture of bath and halide of the metal to be deposited, the bottom of the cell is equipped with a nozzle for extracting the bath which opens into the anode compartment. The bath is then continuously recycled to the basket after having been properly recharged with the metal halide to be deposited.

L'invention sera mieux comprise à l'aide des dessins ci-joints et qui représentent à la figure 1 une coupe suivant un plan axial d'un exemple de cellule selon l'invention et à la figure 2 une coupe de la même cellule suivant un plan horizontal de tracé XX' sur la figure 1.The invention will be better understood with the aid of the attached drawings, which represent in FIG. 1 a section along an axial plane of an example cell according to the invention and in FIG. 2 a section of the same cell according to a horizontal plane of layout XX 'in FIG. 1.

Sur la figure 1, on distingue un bac cylindrique (1) équipé extérieurement de circuits de chauffage (2), d'un calorifugeage (3) et garni intérieurement d'un bain (4) de sels fondus jusqu'au niveau (5) et muni sur sa paroi inférieure d'un orifice (6) de sortie de bain. Sur le couvercle (7) de la cellule débouche une tubulure (8) d'injection de gaz inerte. Traversant ledit couvercle et, plongeant dans le bain on voit:

  • une anode centrale (10) avec son prolongement extérieur (11) destiné à être raccordé au pôle positif d'une source de courant continu;
  • une cloche (12) entourant l'anode et son prolongement extérieur (11) par l'intermédiaire d'une tubulure (13) raccordée à la tubulure (8) d'injection de gaz inerte de manière à faciliter l'entraînement de l'halogène hors de la cellule par la tubulure (9);
  • un panier cylindrique tubulaire (14) en treillis métallique comportant une paroi extérieure (15) et une paroi intérieure (16), un fond (17) qui s'étend jusqu'à l'axe de la cellule, une voûte (18) de fermeture se trouvant au-dessus du niveau du bain et équipée d'une tuyauterie (19) d'alimentation en bain et halogénure et d'un prolongement extérieur (20) destiné à être raccordé au pôle négatif d'une source de courant continu;
  • le panier contient un certain volume de métal (21);
  • deux cathodes (22) et (23) placées dans le compartiment délimité par les parois intérieures de la cellule et par les parois extérieures de panier re- couvertes d'un dépôt de métal avec leur prolongement extérieur (24) et (25) destinés à être raccordées au pôle négatif d'une source de courant continu à un potentiel plus négatif que (20);
In FIG. 1, there is a cylindrical tank (1) externally equipped with heating circuits (2), with thermal insulation (3) and internally lined with a bath (4) of molten salts up to level (5) and provided on its lower wall with a bath outlet orifice (6). On the cover (7) of the cell opens an inert gas injection pipe (8). Crossing said cover and, plunging into the bath, we see:
  • a central anode (10) with its external extension (11) intended to be connected to the positive pole of a direct current source;
  • a bell (12) surrounding the anode and its external extension (11) by means of a tube (13) connected to the tube (8) for injecting inert gas so as to facilitate the entrainment of the halogen out of the cell through the tubing (9);
  • a cylindrical tubular wire mesh basket (14) comprising an outer wall (15) and an inner wall (16), a bottom (17) which extends to the axis of the cell, a vault (18) of closure located above the level of the bath and equipped with piping (19) for bath and halide supply and with an external extension (20) intended to be connected to the negative pole of a DC source;
  • the basket contains a certain volume of metal (21);
  • two cathodes (22) and (23) placed in the compartment delimited by the interior walls of the cell and by the exterior walls of basket covered with a metal deposit with their exterior extension (24) and (25) intended for be connected to the negative pole of a direct current source at a more negative potential than (20);

Sur la figure 2, on retrouve certains des éléments de la figure 1, à savoir: la cellule (1), le système de chauffage (2), le calorifugeage (3), l'anode centrale (10) et la cloche (12), le panier et ses parois extérieure (15) et intérieure (16) contenant le métal (21) et huit cathodes dont deux repérés (22) et (23), revêtues d'un dépôt de métal d'épaisseur décroissante quand on tourne dans le sens des aiguilles d'une montre à partir de (22), cathode qui a connu le temps de séjour le plus long dans le bain.In Figure 2, we find some of the elements of Figure 1, namely: the cell (1), the heating system (2), the insulation (3), the central anode (10) and the bell (12 ), the basket and its outer (15) and inner (16) walls containing the metal (21) and eight cathodes, two of which are marked (22) and (23), coated with a metal deposit of decreasing thickness when one turns clockwise from (22), cathode with the longest residence time in the bath.

L'invention peut être illustrée à l'aide de l'exemple d'application suivant:The invention can be illustrated using the following example of application:

Dans une cellule en Hastelloy C, de diamètre intérieur 235 mm et hauteur 700 mm, équipée d'un système de chauffage, et à l'intérieur de laquelle est placée un cuve cylindrique en nickel de diamètre 220 mm et hauteur 300 mm, on a chargé 13,7 kg d'un eutectique BaCI2-CaCI2-NaCI (16,3 - 46,9 - 36,7% en moles). Après mise en place d'un couvercle étanche muni d'une anode en graphite et d'une cathode en nickel et de différentes tubulures obturables, on a procédé à une mise sous vide de la cellule vers 550°C pour élmi- ner l'humidité, puis à un traitement par l'HCI pour éliminer les oxydes, hydroxydes, et autres impuretés contenues dans le bain, puis à une électrolyse sous une tension continue de 2,2 V jusqu'à stabilisation du courant résiduel.In a Hastelloy C cell, with an internal diameter of 235 mm and a height of 700 mm, equipped with a heating system, and inside which is placed a cylindrical nickel tank with a diameter of 220 mm and a height of 300 mm, we have loaded with 13.7 kg of a BaCI 2 -CaCI 2 -NaCI eutectic (16.3 - 46.9 - 36.7% in moles). After fitting a tight cover fitted with a graphite anode and a nickel cathode and various closable pipes, the cell was evacuated at around 550 ° C. to eliminate the humidity, then treatment with HCl to remove the oxides, hydroxides, and other impurities contained in the bath, then electrolysis at a DC voltage of 2.2 V until the residual current stabilizes.

On a alors enlevé le couvercle et introduit dans le bain un panier cylindrique annulaire réalisé au moyen d'une armature en fil de nickel de diamètre 3 mm revêtue d'une toile métallique réalisée avec du fil de nickel de diamètre 0,28 mm tressée suivant une maille de 35 mesh. Puis, on a replacé le couvercle équipé d'une anode centrale et de sa cloche, de ses cathodes complémentaires, des différentes tubulures d'entrée et de sortie de gaz et du système d'alimentation en halogénure.The cover was then removed and an annular cylindrical basket made by means of a 3 mm diameter nickel wire frame covered with a metallic fabric made with 0.28 mm diameter nickel wire braided according to the bath was introduced. 35 mesh. Then, the cover was replaced with a central anode and its bell, its complementary cathodes, the various gas inlet and outlet pipes and the halide supply system.

On a purgé l'atmosphère de la cellule sous vide, puis sous argon, puis on a réchauffé à 550°C. Le bain étant liquide, on y a plongé les différentes électrodes. La hauteur du bain dans la cellule était alors de 150 mm.The atmosphere of the cell was purged under vacuum, then under argon, then warmed to 550 ° C. The bath being liquid, the various electrodes were immersed in it. The height of the bath in the cell was then 150 mm.

Par ailleurs, on a préparé une solution de TiClx en bain de sels fondus, où X était à 2,3 par oxydation de poudre de titane par du tétrachlorure de titane. Cette solution renfermait environ 10% en poids de titane sous forme d'halogénure.Furthermore, a solution of TiCl x was prepared in a bath of molten salts, where X was 2.3 by oxidation of titanium powder with titanium tetrachloride. This solution contained about 10% by weight of titanium in the form of halide.

Ce TiClx a été introduit à raison de 6 g/heure dans la cellule et on a appliqué une tension de 3,5 V. Le courant 1, avait alors pour valeur 2 A.This TiCl x was introduced at the rate of 6 g / hour into the cell and a voltage of 3.5 V was applied. Current 1, then had the value 2 A.

Après introduction dans le panier de 1500 g de bain de sel contenant 10% de titane sous forme de TiClx, le métal déposé dans le panier occupait environ la moitié de son volume. Un prélèvement de bain effectué près de la cathode complémentaire montrait la présence d'un sel parfaitement blanc, c'est-à-dire ne contenant aucune trace de sous-chlorure, résultat d'ailleurs confirmé par l'analyse.After introduction into the basket of 1500 g of salt bath containing 10% of titanium in the form of TiCl x , the metal deposited in the basket occupied about half of its volume. A bath sample taken near the complementary cathode showed the presence of a perfectly white salt, that is to say containing no trace of subchloride, a result confirmed by analysis.

On a alors alimenté en TiClx le compartiment délimité par les parois intérieures de la cellule et les parois extérieures du panier jusqu'à atteindre une composition comprise entre 1,5 et 2% en poids de titane et on a imposé une tension de -0,9 V entre cathode et panier. Il s'est établi un courant 12 de valeur moyenne 1,5 A.The compartment delimited by the interior walls of the cell and the exterior walls of the basket was then supplied with TiCl x until a composition of between 1.5 and 2% by weight of titanium was reached and a voltage of -0 was imposed. , 9 V between cathode and basket. A current 1 2 with an average value of 1.5 A has been established.

Après huit heures de marche, il s'est formé sur la cathode un dépôt de métal bien cristallisé n'entraînant que 1 à 2% en poids de sels fondus. Le poids recueilli était de 2,3 g.After eight hours of walking, a deposit of well crystallized metal was formed on the cathode, resulting in only 1 to 2% by weight of molten salts. The weight collected was 2.3 g.

L'opération a été menée sur une durée de 66 heures. Les tensions, intensités et poids de métal obtenus figurent dans le tableau suivant:

Figure imgb0001
Figure imgb0002
 The operation was carried out over a period of 66 hours. The voltages, intensities and weight of metal obtained are shown in the following table:
Figure imgb0001
Figure imgb0002

Claims (14)

1. Process for obtaining a metal by electrolysis of halides in a bath of dissolved halides contained in a tank comprising a double simultaneous and continuous deposit, in which firstly a continuous electric current 11 is circulated from an anodic assembly towards a cathode in the form of a double-walled basket, both being immersed in the bath, by supplying the basket with a halide of the metal which is to be deposited, until the quantity of electricity which is delivered corresponds to a filling of 1/3 to 2/3 of the volume of the basket by the metal, then into the compartment delimited by the interior walls of the tank and the exterior walls of the basket, the halide of the metal is introduced so as to have in the bath contained in the said compartment a content of combined metal comprised between 1 and 7% by weight, then simultaneously to the current 11, a current 12 is circulated from the basket to at least one complementary cathode, whilst continuing to supply the basket with halides, and periodically the said complementary cathode is extracted to recover the obtained metal, and it is replaced by another cathode.
2. Process according to Claim 1, characterized in that the ratio 11 / 12 ist modified constantly.
3. Process according to Claim 1, characterized in that the supply with halide of the metal which is to be deposited is carried out in the form of a mixture with the bath, which is circulated between the electrodes, continuously drawn off and recycled after recharging with halides.
4. Process according to Claim 1, characterized in that the basket is supplied with halides in solid state.
5. Process according to Claim 1, characterized in that at the start of normal operation, if n cathodes are used, a single electrode is plunged into the bath, then the n-1 others successively and periodically such that when the nth is plunged in, the first is covered by a desired quantity of refined metal.
6. Process according to Claim 1, characterized in that a halide M (Halog)x is used, of a metal having a melting point greater than 1000°C and preferably several valency states, like titanium, zirconium, hafnium, thorium, vandium, niobium, tantalum, chromium, molybdenum, tungsten, uranium, plutonium and also the rare earth metals.
7. Prosess according to Claim 4, characterized in that in the case of titanium, the halide is of the type TiClx in which X is equal or comprised between 2 and 4.
8. Process according to Claim 7, characterized in that X is comprised between 2 and 3.
9. Process according to Claim 8, characterized in that X is close to 2.3.
10. Device for the electrolysis of halides of the metal to be deposited contained in a bath of dissolved halides comprising a cylindrical tank designed to contain the said bath protected from the atmosphere, and anodic assembly comprising at least one anode (10) of cylindrical shape, placed at the centre of the cell, plunging into the bath (4), a metallic cathode (14) surrounding the anodic assembly completely and symmetrically, connection means (11) and (20) of the upper parts of the anodic assembly and of the cathode respectively to the positive and negative poles of a source of continuous current, at least one complementary cathode (22) placed on the outside of the cathode (14) connected to a source of current with a potential more strongly negative than that of the cathode (14), characterized in that the cathode (14) has the form of a lattice-work basket suspended in the bath constituted by two coaxial vertical cylinders (15) and (16) integral with a perforated base (17) extending to the axis of the tank so as to divide the volume of the bath into three compartments, that it comprises a supply system (19) for halides, which is placed in the upper part of the cathode and between the two cylinders, means for suction (9) of the halogen which is given off, and outlet means of the complementary cathode of the bath protected from the air.
11. Device for the electrolysis of halides of the metal which is to be deposited contained in a bath (4) of dissolved halides comprising a cylindrical tank (1) designed to contain the said bath protected from the atmosphere, a cathode (14) in the form of a metallic perforated basket comprising a lateral vertical wall (15) integral with a base (17), suspended in the bath, an anodic assembly comprising at least one anode (10) of cylindrical shape plunging into the bath placed on the exterior of the basket, means for connection (11, 20) of the upper parts of the anodic assembly and of the cathode respectively to the positive and negative poles of a source of continuous current, at least one complementary cathode (22) placed in the interior of the basket in a symmetrical manner, a device (19) for the supply of halides by the upper part of the cathode, means (9) for the suction of the halogen which is given off, characterized in that the lateral wall (15) of the basket is of lattice-work, has a cylindrical shape, that the basket is equipped on the interior with a second lateral metallic wall (16) of lattice-work, which is parallel and coaxial to the first, and is fixed to the base so as to divide the volume of the bath into three compartments, that the complementary cathode is joined by its upper part and by a connection means (24) to a source of current of a potential more strongly negative than that of the basket, that the device for the supply of halides is in relation to the interior of the compartment delimited by the two lattice-work walls of the basket.
12. Device according to Claims 10 and 11, characterized in that the base of the basket is double-walled, which delimits a volume in communication with the volume comprised between the two lateral walls of the basket.
13. Device according to Claims 10 and 11, characterized in that it comprises at least two complementary cathodes placed in a symmetrical manner around the basket.
EP85420040A 1984-03-12 1985-03-11 Process for winning a metal by electrolysis of molten halogenides whereby a simultaneous and continuous double disposition is taking place, and apparatus therefor Expired EP0156744B1 (en)

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