EP0424287B1 - Process and device for introducing at least one liquid or gaseous halide into the bath of a molten salt electrolysis cell - Google Patents
Process and device for introducing at least one liquid or gaseous halide into the bath of a molten salt electrolysis cell Download PDFInfo
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- EP0424287B1 EP0424287B1 EP90420443A EP90420443A EP0424287B1 EP 0424287 B1 EP0424287 B1 EP 0424287B1 EP 90420443 A EP90420443 A EP 90420443A EP 90420443 A EP90420443 A EP 90420443A EP 0424287 B1 EP0424287 B1 EP 0424287B1
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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
- C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
- C25C7/06—Operating or servicing
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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
- C25C3/26—Electrolytic production, recovery or refining of metals by electrolysis of melts of titanium, zirconium, hafnium, tantalum or vanadium
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- the invention relates to a method and a device for introducing at least one halide in the liquid or gaseous state into the bath of an igneous electrolysis cell.
- 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 submitting it in the simplest way. 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 and has led to the design of various methods and devices which differ from each other, in particular from the point of view of the introduction of the halide into the bath.
- USP 4113584 relating in particular to obtaining titanium by igneous electrolysis, where the introduction is carried out using a partially submerged feed cathode 28 in the bath and inside which there is a pipe 11a through which TiCl4 optionally arrives, possibly accompanied by argon to ensure the mixing of the chloride or of a solid metallic compound with the bath; this cathode is closed at its lower part and at the end 12a of the pipe 11a by a basket 14a whose porosities are carefully calculated.
- This basket which reduces TiCl4 to a lower valence must be kept in a narrow range of electric voltage values otherwise the basket pores become blocked, or on the contrary the basket deteriorates due to electrochemical corrosion.
- an electrolytic pre-reduction of TiCl4 is also carried out, using a cathode 3 in the shape of a bell which plunges into the bath and inside from which there is a pipe 4 through which esr introduces the halide possibly accompanied by argon; this piping is also provided with fins which by their rotation make it possible to stir the bath 2.
- the reduced material 15 is deposited inside the cathode 3 and is moved by the fins to be dispersed in the bath and to saturate it. This process therefore requires mechanical agitation; moreover, the search for saturation inevitably causes the presence of sludge and requires working at predetermined concentrations and valence states, hence a lack of flexibility in the operation of this process.
- This method of introducing at least one halide in the liquid or gaseous state into the bath of an igneous electrolysis cell in which are at least partially immersed an anode assembly and a cathode between which a continuous electric voltage is created and in which said halide is introduced at the same time as an inert gas is characterized in that a portion of said bath is confined in an annular volume elongated along a substantially vertical axis and in communication with said bath by its ends and prints on said volume using gas and halide introduced an upward movement inside the volume and downward outside.
- the invention consists in continuously or discontinuously introducing an inert gas into the bath simultaneously with the halide and in confining the volume of bath with which it comes into contact initially.
- the gas having a density much lower than that of the bath and being sparingly soluble in the latter, forms bubbles which rise to the surface.
- the rise of the bubbles induces in the confined volume a movement of the bath in the same direction.
- This produces a regular dissolution of the halide, resulting in relatively small variations in concentration compared to the average bath concentration as well as slight variations in valence in the case where the vein is polarized negatively so as to cause a reduction of the halide introduced.
- the movement of the bath is such that more than two renewals are provided per hour, but the best results are obtained in the range of renewals of between five and twenty.
- the upward movement of the gas is preferably carried out with a ratio of the volume of the gas to the volume of halide in the gaseous state between 0 and 5 under the conditions of bath working temperature.
- the invention also relates to a device for applying the method described above.
- This device is constituted by two concentric tubes plunging at least partially into the bath and separated from each other by said bath: an inner tube open at its ends and in which the halide and the inert gas flow from top to bottom , an outer tube with a solid wall closed at its upper end and open at its lower end and is characterized in that the wall of the inner tube has orifices located in its lower part and at a level higher than the end of the outer tube and that the wall of the outer tube has openings located at a level higher than that of the orifices.
- the device according to the invention which comprises an outer tube with a solid wall and openings differs from the devices described in US 4113584 and 4588485 where said tube has a porous wall and in GB 1579955 where the tube does not have any openings at the top.
- the particular configuration produced in the invention ensures the confinement of a portion of bath and allows the gas in combination with the orifices of the inner tube to cause the circulation of the bath and its permanent renewal in contact with the halide.
- the total area of the openings is greater than that of the annular space which separates the tubes in order to allow the bath to move easily.
- the length of the confined zone is large enough with respect to its width, hence a minimum distance ratio of the openings to the orifices to be the distance between the tubes between 1 and 20 and preferably between 2 and 10
- the height of the confined bath volume is related to the height of the bath in the cell, hence preferably a plunging depth of the tubes between 1/3 and 2/3 of the height of the bath.
- a feature of the invention consists in equipping the lower end of the inner tube with slots which can complete the role played by the orifices and increase the speed of circulation of the bath, if necessary for special operations.
- the outer tube is negatively polarized in order to ensure in the volume of the confined bath an electrochemical reduction of the halide, this reduction being moreover accelerated by the movement of the bath and promoting the obtaining of small variations of said valence at the time of introduction.
- the effect of this polarization is ideal when the reduction of the halide does not produce suspended metallic sludge or deposited metal, which is avoided by keeping the polarization current density below a limit value.
- this limit is generally situated around 0.05 A / cm2.
- the outer tube or the entire device will therefore be sized in order to respect this limit under the planned operating conditions.
- FIG. 1 represents a view in half-section in the long direction of the device in place in a bath.
- an outer tube 1 immersed in the bath shown diagrammatically by 2 which is closed at the top and open at the bottom and the wall of which is provided with three openings 3 situated a little below the level of the bath .
- an inner tube 4 concentric whose lower end is located at the same level as that of the other tube but whose upper end extends beyond.
- the two tubes determine between them a space 5 filled by the bath and the inner tube is provided downwards with two rows of four holes 6 and at its end with slots 7.
- the tubes 1 and 4 can be electrically insulated to allow polarization negative of the outer tube and the partial reduction of the halide introduced but this isolation does not appear in the figure.
- the mixture of liquid or gaseous halide and inert gas is introduced at the top of the inner tube according to arrow 8.
- the halide vaporizes and forms with the gas a mixture which escapes through the holes 6 according to arrow 9 in space 5 causing a movement of ascent of the bath by the lower part of the outer tube according to arrow 10.
- the halide dissolved in the bath and is possibly reduced to a lower valence state if the device is connected to a negative current source.
- the halide-recharged bath escapes from the outer tube through the openings 3 along arrow 11 while the gas bubbles burst on the surface of the bath. There is thus obtained a circulation of the bath from bottom to top in the device and from top to bottom outside which ensures a homogeneous distribution of the halide both in concentration and in valence.
- the method and the device according to the invention were applied to the introduction of niobium chloride NbCl5 into an igneous electrolysis cell of parallelepipedal shape delimiting a surface interior base 700 mm long and 500 mm wide which contained, over a height of 500 mm, around 270 kg of a molten salt bath maintained at 725 ° C and composed of an equimolecular mixture NaCl-KCl and 5% by weight of NaF.
- a molten salt bath maintained at 725 ° C and composed of an equimolecular mixture NaCl-KCl and 5% by weight of NaF.
- In this bath were immersed two surface cathodes 300x300 mm supplied with a current density of 0.18 A / cm2. Parallel to these cathodes and between them was placed a diaphragm surrounding an anode of length 150 mm in which a current of density 0.6 A / cm2 was flowing.
- the bath contained 0.5% by weight of Nb having an average valence of 3.2. 140 g / h of niobium in the form of gaseous NbCl5 were then introduced into a stream of argon of 40 l / h at normal temperature (i.e.
- the current density on the cathodes was 0.144 A / cm2 and on the anode 0.48 A / cm2.
- the tubes of the devices were polarized under a current density of 0.035 A / cm2, the total current corresponding to 1.9 Faraday per mole of TiCl4 introduced.
- the bath contained 2% by weight of titanium having an average valence of 2.1.
- the injection device according to the invention has been replaced by a device of the type described by US Pat. No. 4,113,584, namely an introduction cathode, the porous submerged part of which was made of a nickel fabric of 100 mesh coated with electrolytic Nickel until the electrical coefficient and flux values are obtained: 0.34 ⁇ Cd ⁇ 0.35 0.18 ⁇ Cf ⁇ 0.185 determined according to the precise procedures described in the above patent.
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Abstract
Description
L'invention est relative à un procédé et à un dispositif d'introduction d'au moins un halogénure à l'état liquide ou gazeux dans le bain d'une cellule d'électrolyse ignée.The invention relates to a method and a device for introducing at least one halide in the liquid or gaseous state into the bath of an igneous electrolysis cell.
L'homme de l'art sait qu'on peut obtenir le dépôt d'un métal en introduisant un de ses dérivés, tel qu 'un halogénure par exemple, dans un bain de sels fondus et en le soumettant de la manière la 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 et a abouti à la conception de divers procédés et dispositifs qui diffèrent entre eux, en particulier du point de vue de l'introduction de l'halogénure dans le bain.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 submitting it in the simplest way. 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 and has led to the design of various methods and devices which differ from each other, in particular from the point of view of the introduction of the halide into the bath.
En effet, cette opération est particulièrement délicate, notamment quand il s'agit d'halogénures de métaux multivalents et elle nécessite certaines précautions si on veut obtenir une dissolution régulière et homogène dudit halogénure et éviter les variations brusques de concentration et de valence qui sont la cause de formation de boues, de bouchages ou de perçage du diaphragme séparant l'anolyte du catholyte, ce qui conduit à une mauvaise qualité du métal déposé et, si le phénomène persiste ou se répète, à l'arrêt de l'installation par destruction du diaphragme ou accumulation de boues.Indeed, this operation is particularly delicate, in particular when it is a question of halides of multivalent metals and it requires certain precautions if one wants to obtain a regular and homogeneous dissolution of said halide and to avoid the abrupt variations of concentration and valence which are the cause of sludge formation, blockages or piercing of the diaphragm separating the anolyte from the catholyte, which leads to poor quality of the deposited metal and, if the phenomenon persists or repeats, the installation is stopped by destruction diaphragm or accumulation of sludge.
Ainsi, parmi les techniques de l'art antérieur, on peut citer l'USP 4113584 relatif notamment à l'obtention de titane par électrolyse ignée, où l'introduction est réalisée à l'aide d'une cathode d'alimentation 28 partiellement immergée dans le bain et à l'intérieur de laquelle se trouve une tuyauterie 11a par laquelle arrive du TiCl₄ éventuellement accompagné d'argon pour assurer le mélange du chlorure ou d'un composé métallique solide avec le bain; cette cathode est fermée à sa partie inférieure et au niveau de l'extrémité 12a de la tuyauterie 11a par un panier 14a dont les porosités sont soigneusement calculées. Ce panier qui réduit le TiCl₄ à une valence inférieure doit être maintenu dans une gamme étroite de valeurs de tension électrique sinon soit les pores du panier se bouchent, soit au contraire le panier se détériore par effet de corrosion électrochimique. Dans ces conditions, la dissolution du chlorure réduit dans le bain s'effectue de façon irrégulière et peut même provoquer la formation de boues. Il en résulte alors une variation de l'halogénure dans le bain à la fois en concentration et en valence, qui, au travers des variations de comportement du diaphragme, conduit à un dépôt métallique hétérogène et à un mauvais rendement Faraday.Thus, among the techniques of the prior art, there may be mentioned USP 4113584 relating in particular to obtaining titanium by igneous electrolysis, where the introduction is carried out using a partially submerged feed cathode 28 in the bath and inside which there is a pipe 11a through which TiCl₄ optionally arrives, possibly accompanied by argon to ensure the mixing of the chloride or of a solid metallic compound with the bath; this cathode is closed at its lower part and at the end 12a of the pipe 11a by a basket 14a whose porosities are carefully calculated. This basket which reduces TiCl₄ to a lower valence must be kept in a narrow range of electric voltage values otherwise the basket pores become blocked, or on the contrary the basket deteriorates due to electrochemical corrosion. Under these conditions, the reduced chloride dissolves in the bath irregularly and can even cause sludge to form. This then results in a variation of the halide in the bath both in concentration and in valence, which, through variations in the behavior of the diaphragm, leads to a heterogeneous metallic deposit and poor Faraday yield.
Dans le GB 1579955, également relatif à l'obtention de titane par électrolyse ignée, on procède aussi à une préréduction électrolytique du TiCl₄, à l'aide d'une cathode 3 en forme de cloche qui plonge dans le bain et à l'intérieur de laquelle se trouve une tuyauterie 4 par laquelle esr introduit l'halogénure accompagné éventuellement d'argon; cette tuyauterie est également munie d'ailettes qui par leur rotation permettent d'agiter le bain 2. Le matériau réduit 15 se dépose à l'intérieur de la cathode 3 et est déplacé par les ailettes pour être dispersé dans le bain et le saturer. Ce procédé nécessite donc une agitation mécanique; par ailleurs, la recherche de la saturation provoque inévitablement la présence de boues et impose de travailler à des concentrations et à des états de valence prédéterminés d'où un manque de souplesse dans l'exploitation de ce procédé.In GB 1579955, also relating to obtaining titanium by igneous electrolysis, an electrolytic pre-reduction of TiCl₄ is also carried out, using a
Dans le brevet US 4588485 qui décrit un procédé d'obtention de métal par électrolyse d'halogénures, on trouve également une cathode 14 en forme de panier en treillis métallique suspendue dans le bain, constituée par deux cylindres coaxiaux et surmontée d' un système 19 d'alimentation en halogénures. Dans ce panier circule un courant I₂ qu'il faut contrôler soigneusement pour éviter tout colmatage ou perçage du panier. Dans le cas de l'apparition d'un tel ennui, il faut modifier I₂ et il en résulte forcément une variation à la fois en concentration et en valence de l'halogénure dans le bain. En outre, si on désire procéder à des ajustements progressifs de concentration et/ou de valence, on ne peut le faire que dans les limites de fonctionnement du panier.In patent US 4588485 which describes a process for obtaining metal by electrolysis of halides, there is also a cathode 14 in the form of a wire mesh basket suspended in the bath, constituted by two coaxial cylinders and surmounted by a system 19 halide supply. In this basket there is a current I₂ which must be carefully checked to avoid any blockage or piercing of the basket. In the case of the appearance of such boredom, it is necessary to modify I₂ and this inevitably results in a variation both in concentration and in valence of the halide in the bath. In addition, if you wish to make progressive adjustments to the concentration and / or valence, you can only do so within the operating limits of the basket.
C'est dans le but de remédier à ces inconvénients que la demanderesse a cherché et trouvé un moyen par lequel elle puisse, d'une part maîtriser les valeurs de la concentration et de la valence de l'halogénure introduit et minimiser ainsi tout déséquilibre dans le bain consécutif à cette introduction, d'autre part pouvoir procéder à des ajustements progressifs et maîtrisés de concentration et/ou de valence. .It is in order to remedy these drawbacks that the plaintiff has sought and found a means by which it can, on the one hand control the values of the concentration and the valence of the halide introduced and thus minimize any imbalance in the bath consecutive to this introduction, on the other hand being able to make gradual and controlled adjustments of concentration and / or valence. .
Ce procédé d'introduction d'au moins un halogénure à l'état liquide ou gazeux dans le bain d'une cellule d'électrolyse ignée où sont au moins partiellement immergés un ensemble anodique et une cathode entre lesquels on crée une tension électrique continue et dans lequel on introduit ledit halogénure en même temps qu'un gaz inerte est caractérisé en ce que l'on confine une portion dudit bain dans un volume annulaire allongé suivant un axe sensiblement vertical et en communication avec ledit bain par ses extrémités et imprime audit volume à l'aide du gaz er de l'halogénure introduits un mouvement ascendant à l'intérieur du volume et descendant à l'extérieur.This method of introducing at least one halide in the liquid or gaseous state into the bath of an igneous electrolysis cell in which are at least partially immersed an anode assembly and a cathode between which a continuous electric voltage is created and in which said halide is introduced at the same time as an inert gas is characterized in that a portion of said bath is confined in an annular volume elongated along a substantially vertical axis and in communication with said bath by its ends and prints on said volume using gas and halide introduced an upward movement inside the volume and downward outside.
Ainsi, l'invention consiste à introduire en continu ou en discontinu un gaz inerte dans le bain simultanément avec l'halogénure et à confiner le volume de bain avec lequel il entre en contact initialement. Cela produit les phénomènes suivants : le gaz, ayant une masse volumique beaucoup plus faible que celle du bain et étant peu soluble dans ce dernier, forme des bulles qui montent à la surface. Du fait que la portion de bain initialement en contact avec le gaz est confinée sous forme d'une veine mais qu'elle a la possibilité de se déplacer dans une direction sensiblement verticale, l'ascension des bulles induit dans le volume confiné un mouvement du bain dans le même sens. Il en résulte une poussée de haut en bas sur le bain placé en dehors dudit volume et par suite une circulation en continu et un renouvellement permanent du bain au contact du gaz et de l'halogénure. On réalise ainsi une dissolution régulière de l'halogénure, d'où des variations relativement faibles de concentration par rapport à la concentration moyenne du bain de même que des variations faibles de valence dans le cas où la veine est polarisée négativement de manière à provoquer une réduction de l'halogénure introduit.Thus, the invention consists in continuously or discontinuously introducing an inert gas into the bath simultaneously with the halide and in confining the volume of bath with which it comes into contact initially. This produces the following phenomena: the gas, having a density much lower than that of the bath and being sparingly soluble in the latter, forms bubbles which rise to the surface. Because the bath portion initially in contact with the gas is confined in the form of a vein but that it has the possibility of moving in a substantially vertical direction, the rise of the bubbles induces in the confined volume a movement of the bath in the same direction. This results in a thrust from top to bottom on the bath placed outside said volume and consequently a continuous circulation and a permanent renewal of the bath in contact with the gas and the halide. This produces a regular dissolution of the halide, resulting in relatively small variations in concentration compared to the average bath concentration as well as slight variations in valence in the case where the vein is polarized negatively so as to cause a reduction of the halide introduced.
Il est préférable d'utiliser l'introduction en continu de façon à limiter au minimum les variations en concentration et en valence.It is preferable to use the continuous introduction so as to minimize variations in concentration and valence.
De préférence, le mouvement du bain est tel qu'on assure plus de deux renouvellements à l'heure, mais les meilleurs résultats sont obtenus dans la fourchette de renouvellements comprise entre cinq et vingt.Preferably, the movement of the bath is such that more than two renewals are provided per hour, but the best results are obtained in the range of renewals of between five and twenty.
D'autre part, au-delà de 50 renouvellements du bain par heure, la quantité de gaz inerte nécessaire provoque une volatilisation du bain trop importante.On the other hand, beyond 50 renewals of the bath per hour, the amount of inert gas required causes excessive volatilization of the bath.
Le mouvement ascendant du gaz est réalisé de préférence avec un rapport du volume du gaz au volume d'halogénure à l'état gazeux compris entre 0 et 5 dans les conditions de température de travail du bain.The upward movement of the gas is preferably carried out with a ratio of the volume of the gas to the volume of halide in the gaseous state between 0 and 5 under the conditions of bath working temperature.
L'invention concerne également un dispositif d'application du procédé décrit ci-dessus. Ce dispositif est constitué par deux tubes concentriques plongeant au moins partiellement dans le bain et séparés l'un de l'autre par ledit bain : un tube intérieur ouvert à ses extrémités et dans lequel circulent de haut en bas l'halogénure et le gaz inerte, un tube extérieur à paroi pleine fermé à son extrémité supérieure et ouvert à son extrémité inférieure et est caractérisé en ce que la paroi du tube intérieur présente des orifices situés dans sa partie inférieure et à un niveau supérieur à l'extrémité du tube extérieur et que la paroi du tube extérieur présente des ouvertures situées à un niveau supérieur à celui des orifices.The invention also relates to a device for applying the method described above. This device is constituted by two concentric tubes plunging at least partially into the bath and separated from each other by said bath: an inner tube open at its ends and in which the halide and the inert gas flow from top to bottom , an outer tube with a solid wall closed at its upper end and open at its lower end and is characterized in that the wall of the inner tube has orifices located in its lower part and at a level higher than the end of the outer tube and that the wall of the outer tube has openings located at a level higher than that of the orifices.
Ainsi, le dispositif selon l'invention qui comporte un tube extérieur à paroi pleine et des ouvertures se distingue des dispositifs décrits dans les US 4113584 et 4588485 où ledit tube présente une paroi poreuse et dans le GB 1579955 où le tube ne possède pas d'ouvertures à sa partie supérieure.Thus, the device according to the invention which comprises an outer tube with a solid wall and openings differs from the devices described in US 4113584 and 4588485 where said tube has a porous wall and in GB 1579955 where the tube does not have any openings at the top.
La configuration particulière réalisée dans l'invention assure le confinement d'une portion de bain et permet au gaz en combinaison avec les orifices du tube intérieur de provoquer la circulation du bain et son renouvellement permanent au contact de l'halogénure.
De préférence, l'aire totale des ouvertures est supérieure à celle de l'espace annulaire qui sépare les tubes afin de permettre au bain de se déplacer facilement.The particular configuration produced in the invention ensures the confinement of a portion of bath and allows the gas in combination with the orifices of the inner tube to cause the circulation of the bath and its permanent renewal in contact with the halide.
Preferably, the total area of the openings is greater than that of the annular space which separates the tubes in order to allow the bath to move easily.
Par ailleurs, pour avoir une durée de dissolution de l'halogénure dans le bain suffisamment grande, il est préférable que la longueur de la zone confinée soit assez importante par rapport à sa largeur, d'où un rapport distance minimum des ouvertures aux orifices à la distance qui sépare les tubes compris entre 1 et 20 et de préférence entre 2 et 10Furthermore, to have a sufficiently long duration of dissolution of the halide in the bath, it is preferable that the length of the confined zone is large enough with respect to its width, hence a minimum distance ratio of the openings to the orifices to be the distance between the tubes between 1 and 20 and preferably between 2 and 10
De même, on choisit un compromis entre le nombre d'orifices et leurs diamètres qui favorise à la fois la formation de petites bulles de gaz et leur passage vers le volume confiné.
La hauteur du volume de bain confiné est liée à la hauteur du bain dans la cellule d'où de préférence une profondeur de plongée des tubes comprise entre le 1/3 et les 2/3 de la hauteur du bain.Similarly, a compromise is chosen between the number of orifices and their diameters which promotes both the formation of small gas bubbles and their passage to the confined volume.
The height of the confined bath volume is related to the height of the bath in the cell, hence preferably a plunging depth of the tubes between 1/3 and 2/3 of the height of the bath.
Une particularité de l'invention consiste à équiper l'extrémité inférieure du tube intérieur de fentes qui peuvent compléter le rôle joué par les orifices et augmenter la vitesse de circulation du bain, si nécessaire pour des opérations spéciales.A feature of the invention consists in equipping the lower end of the inner tube with slots which can complete the role played by the orifices and increase the speed of circulation of the bath, if necessary for special operations.
Pour certains halogénures de métaux multivalents, il est préférable de les introduire à un état de valence inférieur à celui de l'halogénure d'alimentation et qui correspond généralement à l'état de valence global du bain. Dans ce cas, on polarise négativement le tube extérieur afin d 'assurer dans le volume du bain confiné une réduction électrochimique de l'halogénure, cette réduction étant d'ailleurs accélérée par le mouvement du bain et favorisant l'obtention de faibles variations de ladite valence au moment de l'introduction. L'effet de cette polarisation est idéal quand la réduction de l'halogénure ne produit pas de boues métalliques en suspension ou de métal déposé, ce qui est évité par le maintien de la densité de courant de polarisation en dessous d'une valeur limite. Dans le cas des métaux multivalents exemplifiés ici, cette limite est généralement située autour de 0,05A/cm². On dimensionnera donc le tube extérieur ou l'ensemble du dispositif afin de respecter cette limite dans les conditions prévues de fonctionnement.For certain multivalent metal halides, it is preferable to introduce them at a lower valence state than that of the feed halide and which generally corresponds to the overall valence state of the bath. In this case, the outer tube is negatively polarized in order to ensure in the volume of the confined bath an electrochemical reduction of the halide, this reduction being moreover accelerated by the movement of the bath and promoting the obtaining of small variations of said valence at the time of introduction. The effect of this polarization is ideal when the reduction of the halide does not produce suspended metallic sludge or deposited metal, which is avoided by keeping the polarization current density below a limit value. In the case of the multivalent metals exemplified here, this limit is generally situated around 0.05 A / cm². The outer tube or the entire device will therefore be sized in order to respect this limit under the planned operating conditions.
L'invention sera mieux comprise à l'aide de la figure 1 ci-jointe qui représente une vue en demi-coupe dans le sens long du dispositif en place dans un bain.
Sur cette figure, on distingue plus particulièrement un tube extérieur 1 immergé dans le bain schématisé par 2 qui est fermé vers le haut et ouvert vers le bas et dont la paroi est munie de trois ouvertures 3 situées un peu en-dessous du niveau du bain.
A ce tube est associé un tube intérieur 4 concentrique dont l'extrémité inférieure se situe au même niveau que celui de l'autre tube mais dont l'extrémité supérieure se prolonge au-delà. Les deux tubes déterminent entre eux un espace 5 rempli par le bain et le tube intérieur est muni vers le bas de deux rangées de quatre trous 6 et à son extrémité de fentes 7. Les tubes 1 et 4 peuvent être isolés électriquement pour permettre la polarisation négative du tube extérieur et la réduction partielle de l'halogénure introduit mais cet isolement n'apparaît pas sur la figure.
En fonctionnement, on introduit le mélange d'halogénure liquide ou gazeux et de gaz inerte en haut du tube intérieur suivant la flèche 8. Sous l'effet de la température du tube chauffé par le bain, l'halogénure sa vaporise et forme avec le gaz un mélange qui s'échappe par les trous 6 suivant la flèche 9 dans l'espace 5 provoquant un mouvement d'ascension du bain par la partie inférieure du tube extérieur suivant la flèche 10. Au cours de sa remontée, l' halogénure se dissout dans le bain et est éventuellement réduit à un état de valence inférieur si le dispositif est relié à une source de courant négatif. Le bain rechargé en halogénure s'échappe du tube extérieur par les ouvertures 3 suivant la flèche 11 tandis que les bulles de gaz éclatent à la surface du bain. On obtient ainsi une circulation du bain de bas en haut dans le dispositif et de haut en bas à l'extérieur ce qui assure une répartition homogène de l'halogénure à la fois en concentration et en valence.The invention will be better understood using the attached Figure 1 which represents a view in half-section in the long direction of the device in place in a bath.
In this figure, there is more particularly an
With this tube is associated an
In operation, the mixture of liquid or gaseous halide and inert gas is introduced at the top of the inner tube according to
L'invention peut être illustrée à l'aide des exemples d'application suivants :The invention can be illustrated with the aid of the following application examples:
Le procédé et le dispositif selon l'invention ont été appliqués à l'introduction du chlorure de niobium NbCl₅ dans une cellule d'électrolyse ignée de forme parallélipipédique délimitant une surface de base intérieure de longueur 700 mm et de largeur 500 mm qui contenait sur une hauteur de 500 mm environ 270 kg d'un bain de sels fondus maintenu à 725°C et composé d'un mélange équimoléculaire NaCl-KCl et de 5% en poids de NaF.
Dans ce bain étaient immergées deux cathodes de surface 300x300 mm alimentées sous une densité de courant de 0,18 A/cm². Parallèlement à ces cathodes et entre elles était placé un diaphragme entourant une anode de longueur 150 mm dans laquelle circulait un courant de densité 0,6 A/cm².The method and the device according to the invention were applied to the introduction of niobium chloride NbCl₅ into an igneous electrolysis cell of parallelepipedal shape delimiting a surface interior base 700 mm long and 500 mm wide which contained, over a height of 500 mm, around 270 kg of a molten salt bath maintained at 725 ° C and composed of an equimolecular mixture NaCl-KCl and 5% by weight of NaF.
In this bath were immersed two surface cathodes 300x300 mm supplied with a current density of 0.18 A / cm². Parallel to these cathodes and between them was placed a diaphragm surrounding an anode of length 150 mm in which a current of density 0.6 A / cm² was flowing.
Au moment du démarrage de l'électrolyse, le bain contenait 0,5% en poids de Nb ayant une valence moyenne de 3,2.
On a alors introduit 140 g/h de niobium sous forme de NbCl₅ gazeux dans un courant d'argon de 40 l/h à température normale (soit respectivement des volumes de 123 l/h et 146 l/h à 725°C) au moyen de deux dispositifs selon l'invention situés dans le plan de l'anode à une distance de 50 mm de cette dernière et à 50 mm de la paroi de la cellule et formés d'un tube intérieur de diamètre extérieur 26 mm percé à environ 80 mm du bas de 2 rangées de 4 trous de diamètre 1,2 mm et d'un tube extérieur de diamètre intérieur 80 mm. Ces tubes étaient constitués de graphite et plongeaient dans le bain jusqu'à une profondeur de 380 mm. Le tube extérieur était polarisé négativement de manière à faire passer un courant de densité 0,042A/cm² et correspondant à 1,8 Faraday par mole de NbCl₅ introduite.At the time of the start of electrolysis, the bath contained 0.5% by weight of Nb having an average valence of 3.2.
140 g / h of niobium in the form of gaseous NbCl₅ were then introduced into a stream of argon of 40 l / h at normal temperature (i.e. volumes of 123 l / h and 146 l / h at 725 ° C respectively) at by means of two devices according to the invention located in the plane of the anode at a distance of 50 mm from the latter and 50 mm from the wall of the cell and formed by an inner tube with an outside diameter of 26 mm drilled at approximately 80 mm from the bottom of 2 rows of 4 holes with a diameter of 1.2 mm and an outer tube with an inner diameter of 80 mm. These tubes were made of graphite and plunged into the bath to a depth of 380 mm. The outer tube was negatively polarized so as to pass a current with a density of 0.042 A / cm² and corresponding to 1.8 Faraday per mole of NbCl₅ introduced.
Or, a ainsi obtenu une circulation de bain induite suivant un débit voisin de 1 m³/h qui correspond à environ 7 renouvellements de bain par heure et la variation consécutive de concentration en poids de Nb entre l'entrée et la sortie du dispositif était de 0,9% relatif, la variation de valence de 0,6% relatif. Les variations de concentration et de valence du bain étaient non mesurables en fonctionnement à l'équilibre sur 1 h, soit :
- en valence : variation < 0,05 (limite de détection)
- en concentration : variation < 0,02% poids (limite de détection).
- en concentration entre ± 0,05 et 0,1% en poids
- en valence entre 0,1 et 0,3
- in valence: variation <0.05 (detection limit)
- in concentration: variation <0.02% by weight (detection limit).
- in concentration between ± 0.05 and 0.1% by weight
- in valence between 0.1 and 0.3
Dans une cellule identique à celle de l'exemple précédent contenant un bain de NaCl, KCl équimolaire maintenu à 725°C, les mêmes anodes et cathodes et les mêmes injecteurs, on a procédé à la fabrication de titane.In a cell identical to that of the previous example containing a bath of NaCl, equimolar KCl maintained at 725 ° C., the same anodes and cathodes and the same injectors, titanium was produced.
La densité de courant sur les cathodes était de 0,144 A/cm² et sur l'anode de 0,48 A/cm². Les tubes des dispositifs étaient polarisés sous une densité de courant de 0,035 A/cm², le courant total correspondant à 1,9 Faraday par mole de TiCl₄ introduit.The current density on the cathodes was 0.144 A / cm² and on the anode 0.48 A / cm². The tubes of the devices were polarized under a current density of 0.035 A / cm², the total current corresponding to 1.9 Faraday per mole of TiCl₄ introduced.
Initialement, le bain contenait 2% en poids de titane ayant une valence moyenne 2,1.Initially, the bath contained 2% by weight of titanium having an average valence of 2.1.
On a alors introduit 143 g/h de TiCl₄ à l'état liquide, qui se vaporisait au cours de son trajet sous argon dans le dispositif. Les variations relatives obtenues entre l'entrée et la sortie de dispositif étaient de 0,23% en poids pour la concentration et de 0,91% pour la valence.
Les variations de concentrations et de valence du bain en régime établi étaient non détectables sur 1h.Then introduced 143 g / h of TiCl₄ in the liquid state, which vaporized during its journey under argon in the device. The relative variations obtained between device entry and exit were 0.23% by weight for the concentration and 0.91% for the valence.
The variations in concentration and valence of the bath under steady state conditions were not detectable over 1 hour.
A titre de comparaison, on a remplacé le dispositif d' injection selon l'invention par un dispositif du type décrit par le brevet US 4113584, à savoir une cathode d'introduction dont la partie immergée poreuse était constituée d'un tissu de nickel de 100 mesh recouvert de Nickel électrolytique jusqu'à obtention des valeurs de coefficient électrique et de flux :
0,34 < Cd < 0,35
0,18 < Cf < 0,185
déterminés selon les procédures précises décrites dans le susdit brevet.By way of comparison, the injection device according to the invention has been replaced by a device of the type described by US Pat. No. 4,113,584, namely an introduction cathode, the porous submerged part of which was made of a nickel fabric of 100 mesh coated with electrolytic Nickel until the electrical coefficient and flux values are obtained:
0.34 <Cd <0.35
0.18 <Cf <0.185
determined according to the precise procedures described in the above patent.
Après stabilisation du fonctionnement de cette cathode, on a obtenu les résultats suivants :
- densité de courant nécessaire pour éviter la colmatation ou le perçage : variable entre 0 et 0,12 A/cm²
- variations relatives de concentration et de valeur entre intérieur et extérieur de la cathode :
- en concentration 265 %
- en valence 52 %.
et une valence comprise
- current density necessary to avoid clogging or drilling: variable between 0 and 0.12 A / cm²
- relative variations in concentration and value between inside and outside the cathode:
- in concentration 265%
- in valencia 52%.
and a valence between 1.9 and 3.2.
Claims (12)
- A method of introducing at least one liquid or gaseous halide into the bath of an igneous electrolysis cell in which there are at least partially immersed an anodic assembly and a cathode between which a continuous electrical voltage is established and into which said halide is introduced at the same time as an inert gas, characterised in that a portion of said bath disposed between the anode and the cathode is confined in an annular volume disposed in the immediate vicinity of the cathode along an axis which is substantially vertical and in communication with said bath through its ends, and an ascending motion on the inside of the volume and a descending motion on the outside are imparted to said volume by means of the gas and halide introduced.
- A method according to Claim 1, characterised in that the movement corresponds to more than two bath renewals per hour.
- A method according to Claim 2, characterised in that the movement corresponds to a number of bath renewals between five and twenty.
- A method according to Claim 1, characterised in that the ratio of the volume of gas to the volume of gaseous halide under the temperature conditions of the bath is between 0 and 5.
- A method according to Claim 1, characterised in that the halide is reduced electrochemically when it is introduced into the bath.
- An apparatus for carrying out the method according to Claim 1 which consists of two concentric tubes which plunge at least partially into the bath and which are separated from each other by said bath: an inner tube (4) open at its ends and in which the halide and the inert gas circulate from the top downwardly, an outer tube (1) having a solid wall closed at its top end and open at its bottom end, characterised in that the wall of the inner tube comprises orifices (6) situated in its lower part and at a level higher than the end of the outer tube and in that the wall of the outer tube comprises apertures (3) situated at a level higher than that of the orifices.
- An apparatus according to Claim 6, characterised in that the total area of the apertures is greater than that of the annular space which separates the tubes.
- An apparatus according to Claim 6, characterised in that the ratio of the minimum distance separating the orifices from the apertures to the distance which separates the tubes is between 1 and 20.
- An apparatus according to Claim 8, characterised in that the ratio is between 2 and 20.
- An apparatus according to Claim 6, characterised in that the tubes plunge to a depth of between
- An apparatus according to Claim 6, characterised in that the inner tube is provided at its bottom end with slots (7).
- An apparatus according to Claim 6, characterised in that the outer tube is negatively polarised.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8913878A FR2653139B1 (en) | 1989-10-17 | 1989-10-17 | METHOD AND DEVICE FOR INTRODUCING AT LEAST ONE LIQUID OR GASEOUS HALIDE IN THE BATH OF AN IGNIED ELECTROLYSIS CELL. |
| FR8913878 | 1989-10-17 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0424287A1 EP0424287A1 (en) | 1991-04-24 |
| EP0424287B1 true EP0424287B1 (en) | 1995-07-12 |
Family
ID=9386684
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP90420443A Expired - Lifetime EP0424287B1 (en) | 1989-10-17 | 1990-10-15 | Process and device for introducing at least one liquid or gaseous halide into the bath of a molten salt electrolysis cell |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US5110426A (en) |
| EP (1) | EP0424287B1 (en) |
| JP (1) | JPH0663109B2 (en) |
| AT (1) | ATE125000T1 (en) |
| BR (1) | BR9005169A (en) |
| DE (1) | DE69020851T2 (en) |
| FR (1) | FR2653139B1 (en) |
| NO (1) | NO180207C (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2691169B1 (en) * | 1992-05-12 | 1994-07-01 | Cezus Co Europ Zirconium | REFRACTORY METAL ALLOYS SUITABLE FOR TRANSFORMATION INTO HOMOGENEOUS AND PURE INGOTS AND METHODS FOR OBTAINING SAID ALLOYS. |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2830940A (en) * | 1952-03-28 | 1958-04-15 | Monsanto Chemicals | Production of metals |
| US2913378A (en) * | 1956-12-18 | 1959-11-17 | Chicago Dev Corp | Two-step electrorefining of titanium alloys |
| US2975111A (en) * | 1958-03-19 | 1961-03-14 | New Jersey Zinc Co | Production of titanium |
| US2908619A (en) * | 1958-08-01 | 1959-10-13 | New Jersey Zinc Co | Production of titanium |
| FR1374037A (en) * | 1962-11-15 | 1964-10-02 | Ciba Geigy | Advanced cell for the electrolysis of molten products |
-
1989
- 1989-10-17 FR FR8913878A patent/FR2653139B1/en not_active Expired - Fee Related
-
1990
- 1990-09-14 US US07/582,089 patent/US5110426A/en not_active Expired - Fee Related
- 1990-10-15 DE DE69020851T patent/DE69020851T2/en not_active Expired - Fee Related
- 1990-10-15 BR BR909005169A patent/BR9005169A/en not_active Application Discontinuation
- 1990-10-15 EP EP90420443A patent/EP0424287B1/en not_active Expired - Lifetime
- 1990-10-15 AT AT90420443T patent/ATE125000T1/en not_active IP Right Cessation
- 1990-10-16 NO NO904475A patent/NO180207C/en unknown
- 1990-10-16 JP JP2277606A patent/JPH0663109B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| DE69020851D1 (en) | 1995-08-17 |
| JPH0663109B2 (en) | 1994-08-17 |
| ATE125000T1 (en) | 1995-07-15 |
| US5110426A (en) | 1992-05-05 |
| NO904475D0 (en) | 1990-10-16 |
| FR2653139A1 (en) | 1991-04-19 |
| DE69020851T2 (en) | 1995-12-07 |
| NO180207B (en) | 1996-11-25 |
| NO904475L (en) | 1991-04-18 |
| FR2653139B1 (en) | 1991-12-13 |
| NO180207C (en) | 1997-03-05 |
| BR9005169A (en) | 1991-09-17 |
| JPH03207881A (en) | 1991-09-11 |
| EP0424287A1 (en) | 1991-04-24 |
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