EP1149188B1 - Anoden aus hochfestem, niedriglegiertem stahl für zellen zur aluminium-schmelzelektrolyse - Google Patents

Anoden aus hochfestem, niedriglegiertem stahl für zellen zur aluminium-schmelzelektrolyse Download PDF

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EP1149188B1
EP1149188B1 EP00900036A EP00900036A EP1149188B1 EP 1149188 B1 EP1149188 B1 EP 1149188B1 EP 00900036 A EP00900036 A EP 00900036A EP 00900036 A EP00900036 A EP 00900036A EP 1149188 B1 EP1149188 B1 EP 1149188B1
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anode
layer
electrolyte
iron
aluminium
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EP1149188A1 (de
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Vittorio De Nora
Jean-Jacques Duruz
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Moltech Invent SA
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Moltech Invent 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
    • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
    • C25C3/08—Cell construction, e.g. bottoms, walls, cathodes
    • C25C3/12—Anodes

Definitions

  • This invention relates to non-carbon, metal-based, anodes for use in cells for the electrowinning of aluminium from alumina dissolved in a fluoride-containing molten electrolyte such as cryolite, and to methods for their fabrication, as well as to electrowinning cells containing such anodes and their use to produce aluminium.
  • the anodes are still made of carbonaceous material and must be replaced every few weeks. During electrolysis the oxygen which should evolve on the anode surface combines with the carbon to form polluting CO 2 and small amounts of CO and fluorine-containing dangerous gases.
  • the actual consumption of the anode is as much as 450 Kg/Ton of aluminium produced which is more than 1/3 higher than the theoretical amount of 333 Kg/Ton.
  • metal anodes in aluminium electrowinning cells would drastically improve the aluminium process by reducing pollution and the cost of aluminium production.
  • US Patent 4,999,097 (Sadoway) describes anodes for conventional aluminium electrowinning cells provided with an oxide coating containing at least one oxide of zirconium, hafnium, thorium and uranium. To prevent consumption of the anode, the bath is saturated with the materials that form the coating. However, these coatings are poorly conductive and have not been used.
  • US Patent 4,504,369 discloses a method of producing aluminium in a conventional cell using anodes whose dissolution into the electrolytic bath is reduced by adding anode constituent materials into the electrolyte, allowing slow dissolution of the anode.
  • this method is impractical because it would lead to a contamination of the product aluminium by the anode constituent materials which is considerably above the acceptable level in industrial production.
  • US Patent 4,614,569 (Duruz/Derivaz/Debely/Adorian) describes metal anodes for aluminium electrowinning coated with a protective coating of cerium oxyfluoride, formed in-situ in the cell or pre-applied, this coating being maintained during electrolysis by the addition of small amounts of a cerium compound to the molten cryolite electrolyte. This made it possible to have a protection of the surface from the electrolyte attack and to a certain extent from gaseous oxygen but not from nascent monoatomic oxygen.
  • EP Patent application 0 306 100 (Nyguen/Lazouni/Doan) describes anodes composed of a chromium, nickel, cobalt and/or iron based substrate covered with an oxygen barrier layer and a ceramic coating of nickel, copper and/or manganese oxide which may be further covered with an in-situ formed protective cerium oxyfluoride layer.
  • US Patents 5,069,771, 4,960,494 and 4,956,068 disclose aluminium production anodes with an oxidised copper-nickel surface on an alloy substrate with a protective barrier layer. However, full protection of the alloy substrate was difficult to achieve.
  • Metal or metal-based anodes are highly desirable in aluminium electrowinning cells instead of carbon-based anodes. Many attempts were made to use metallic anodes for aluminium production, however they were never adopted by the aluminium industry because they had a short life and contaminated the aluminium produced.
  • a major object of the invention is to provide an anode for aluminium electrowinning which has no carbon so as to eliminate carbon-generated pollution and increase the anode life.
  • a further object of the invention is to provide an aluminium electrowinning anode material with a surface having a high electrochemical activity and a low solubility in the electrolyte.
  • Another object of the invention is to provide an anode for the electrowinning of aluminium which is covered with an electrochemically active layer with limited ionic conductivity for oxygen ions.
  • Yet another object of the invention is to provide an anode for the electrowinning of aluminium which is made of readily available material(s).
  • An important object of the invention is to substantially reduce the solubility of the surface layer of an aluminium electrowinning anode, thereby maintaining the anode dimensionally stable.
  • Yet another object of the invention is to provide operating conditions for an aluminium electrowinning cell under which the contamination of the product aluminium is limited.
  • This invention is based on the observation that low-carbon high-strength low-alloy (HSLA) steels such as Cor-TenTM even at high temperature form under oxidising conditions an iron oxide-based surface layer which is dense, electrically conductive, electrochemically active for oxygen evolution and, as opposed to oxide layers formed on standard steels or other iron alloys, is highly adherent and less exposed to delamination and limits diffusion of ionic, monoatomic and molecular oxygen.
  • HSLA low-carbon high-strength low-alloy
  • HSLA steels are used for their strength and resistance to atmospheric corrosion especially at lower temperatures (below 0°C) in different areas of technology such as civil engineering (bridges, dock walls, sea walls, piping), architecture (buildings, frames) and mechanical engineering (welded/bolted/riveted structures, car and railway industry, high pressure vessels).
  • civil engineering bridges, dock walls, sea walls, piping
  • architecture buildings, frames
  • mechanical engineering welded/bolted/riveted structures, car and railway industry, high pressure vessels.
  • these HSLA steels have never been proposed for applications at high temperature, especially under oxidising or corrosive conditions, in particular in cells for the electrowinning of aluminium.
  • the iron oxide-based surface layer grows until its thickness constitutes a sufficient barrier to oxygen and then remains dimensionally stable. If the HSLA steel is exposed to an environment promoting dissolution or delamination of the surface layer, the rate of formation of the iron oxide-based surface layer (by oxidation of the surface of the HSLA steel) reaches the rate of dissolution or delamination of the surface layer after a transitional period during which the surface layer grows or decreases to reach an equilibrium thickness in the specific environment.
  • the invention relates in particular to an anode of a cell for the electrowinning of aluminium from alumina dissolved in a fluoride-containing molten electrolyte.
  • This anode comprises a low-carbon high-strength low-alloy (HSLA) steel body or layer whose surface is oxidised to form a coherent and adherent outer iron oxide-based layer the surface of which is electrochemically active for the evolution of oxygen.
  • the iron oxide-based layer has a low solubility in the molten electrolyte.
  • the thickness of the iron oxide-based layer is such as to reduce or prevent diffusion of oxygen from the electrochemically active surface into the steel body or layer during use.
  • the reduced rate of diffusion through the oxide-based layer can be such that oxygen only diffuses into the steel body or layer in a controlled manner without significant increase of the thickness of the oxide-based layer.
  • High-strength low-alloy (HSLA) steel designates a group of low-carbon steels (typically up to 0.5 weight% carbon of the total) that contain small amounts of alloying elements. These steels have better mechanical properties and sometimes better corrosion resistance than carbon steels.
  • the surface of the high-strength low-alloy steel body or layer may be oxidised in an electrolytic cell or in an oxidising atmosphere, in particular a relatively pure oxygen atmosphere.
  • the surface of the high-strength low-alloy steel body or layer may be oxidised in a first electrolytic cell and then transferred to an aluminium production cell.
  • oxidation would typically last 5 to 15 hours at 800 to 1000°C. Oxidation may also take place in air or in oxygen for 5 to 25 hours at 750 to 1150°C before electrolysis.
  • a high-strength low-alloy steel body or layer may be tempered or annealed after pre-oxidation.
  • the high-strength low-alloy steel body or layer may be maintained at elevated temperature after pre-oxidation until immersion into the molten electrolyte of an aluminium production cell.
  • the high-strength low-alloy steel body or layer may comprise 94 to 98 weight% iron and carbon, the remaining constituents being one or more further metals selected from chromium, copper, nickel, silicon, titanium, tantalum, tungsten, vanadium, zirconium, aluminium, molybdenum, manganese and niobium, and possibly small amounts of at least one additive selected from boron, sulfur, phosphorus and nitrogen.
  • the anode comprises a layer of high-strength low-alloy steel on an oxidation resistant metallic core.
  • the layer of high-strength low-alloy steel may be applied on the metallic core before or after formation of the outer iron oxide-based layer.
  • the metallic core is preferably electrically highly conductive and may be made of copper or a copper alloy.
  • the metallic core may contain minor amounts of at least one oxide, such as alumina, hafnia, yttria and/or zirconia.
  • the metallic core may be coated with at least one metal selected from nickel, chromium, cobalt, iron, aluminium, hafnium, manganese, molybdenum, niobium, silicon, tantalum, titanium, tungsten, vanadium, yttrium and zirconium, and alloys, intermetallic compounds and combinations thereof.
  • the metallic core may be coated with an oxygen barrier layer of chromium and/or niobium.
  • the layer of high-strength low-alloy steel may be plasma sprayed, arc sprayed, slurry-applied or electrodeposited onto the metallic core.
  • the high-strength low-alloy steel layer may be bonded to the metallic core through at least one intermediate layer, in particular a film of silver, typically 0.1 to 10 micron thick, which is in intimate and continuous contact with the metallic core and with the steel layer, and/or at least one layer of nickel and/or copper.
  • the invention also relates to a bipolar electrode of a cell for the electrowinning of aluminium from alumina dissolved in a fluoride-containing electrolyte, comprising on its anodic side an anode as described above.
  • the high strength low allow (HSLA) steel body can also be bonded or connected to an electrically conductive anode structure of special design as disclosed in WO-A-00/40781 and WO-A-00/40782 (both in the name of de Nora).
  • One aspect of the invention is an anode precursor comprising a low-carbon high-strength low-alloy (HSLA) steel body or layer and which can be converted into a fully manufactured anode as described above by oxidising the surface of the steel body or layer to form the coherent and adherent outer iron oxide-based layer.
  • HSLA high-strength low-alloy
  • Another aspect of the invention is a method of manufacturing an anode as described above comprising:
  • a further aspect of the invention is a cell for the electrowinning of aluminium from alumina dissolved in a fluoride-containing molten electrolyte comprising at least one anode having a low-carbon high-strength low-alloy (HSLA) steel body or layer and an electrochemically active outer iron oxide-based layer whose surface is electrochemically active, as described above.
  • HSLA low-carbon high-strength low-alloy
  • the electrochemically active layer of the or each anode may be progressively further formed by surface oxidation of the steel body or layer by controlled oxygen diffusion through the electrochemically active layer, and progressively dissolved into the electrolyte at the electrolyte/anode interface, the rate of formation of the outer iron oxide-based layer being substantially equal to its rate of dissolution into the electrolyte.
  • the concentration of nickel (a frequent component of proposed metal-based anodes) found in aluminium produced in small scale tests at conventional cell operating temperatures is typically comprised between 800 and 2000 ppm, i.e. 4 to 10 times the maximum acceptable level which is 200 ppm.
  • Iron oxides and in particular hematite have a higher solubility than nickel in molten electrolyte.
  • the contamination tolerance of the product aluminium by iron is also much higher (up to 2000 ppm) than for other metal impurities.
  • Solubility is an intrinsic property of anode materials and cannot be changed otherwise than by modifying the electrolyte composition and/or the operating temperature of a cell.
  • an anode covered with an outer layer of iron oxide can be made dimensionally stable by maintaining a concentration of iron species and alumina in the molten electrolyte sufficient to reduce or suppress the dissolution of the iron-oxide layer, the concentration of iron species being low enough not to exceed the commercial acceptable level of iron in the product aluminium.
  • the presence of dissolved alumina in the electrolyte at the anode surface has a limiting effect on the dissolution of iron from the anode into the electrolyte, which reduces the concentration of iron species necessary to substantially stop dissolution of iron from the anode.
  • anodes according to the invention may be kept dimensionally stable by maintaining a sufficient amount of dissolved alumina and iron species in the electrolyte to reduce or prevent dissolution of the outer oxide layer.
  • the cell should be operated at a sufficiently low temperature to limit the solubility of iron species in the electrolyte, thereby limiting contamination of the product aluminium by constituents of the outer iron oxide-based layer of the anode(s) to a commercially acceptable level.
  • the operating temperature of the electrolyte should be below 910°C, usually from 730 to 870°C.
  • the amount of iron species and alumina dissolved in the electrolyte preventing dissolution of the iron oxide-based outside surface layer of the or each anode should be such that the product aluminium is contaminated by no more than 2000 ppm iron, preferably by no more than 1000 ppm iron, and even more preferably by no more than 500 ppm iron.
  • the iron species are intermittently fed into the electrolyte, for instance together with alumina, to maintain the amount of iron species in the electrolyte constant which, at the operating temperature, prevents the dissolution of the iron oxide-based outside surface layer of the anodes.
  • the iron species can also be continuously fed, for instance by dissolving a sacrificial electrode which continuously feeds the iron species into the electrolyte.
  • the iron species may be fed in the form of iron metal and/or an iron compound, in particular iron oxide, iron fluoride, iron oxyfluoride and/or an iron-aluminium alloy.
  • the cell may comprise an aluminium-wettable cathode which can be a drained cathode on which aluminium is produced and from which it continuously drains, as described in US Patent 5,651,874 (de Nora/Sekhar) and 5,683,559 (de Nora).
  • the cell is in a monopolar, multi-monopolar or in a bipolar configuration.
  • the bipolar cell comprises a terminal cathode facing a terminal anode and thereinbetween at least one bipolar electrode, the anode(s) described above forming the anodic side of the or each bipolar electrode and/or of the terminal anode.
  • the cell comprises means to improve the circulation of the electrolyte between the anodes and facing cathodes and/or means to facilitate dissolution of alumina in the electrolyte.
  • means to improve the circulation of the electrolyte between the anodes and facing cathodes can for instance be provided by the geometry of the cell as described in co-pending application WO 99/41429 (de Nora/Duruz) or by periodically moving the anodes as described in co-pending application WO 99/41430 (Duruz/Bell ⁇ ).
  • Yet another aspect of the invention is a method of producing aluminium in a cell as described above.
  • the method comprises dissolving alumina in the electrolyte and passing an ionic electric current between the electrochemically active surface of the anode(s) and the surface of the cathode(s), thereby producing aluminium on the cathode surface(s) and oxygen on the anode surface(s).
  • Yet a further aspect of the invention is a method of manufacturing an anode and producing aluminium in an electrolytic cell comprising inserting an anode precursor as described above into the electrolyte of an electrolytic cell and forming the iron oxide-based layer to produce a fully manufactured anode, and producing oxygen on the surface of the iron oxide-based layer and aluminium on a facing cathode in the same (or nearly the same) or in a different electrolyte.
  • the thus-produced anode may then be transferred from the electrolytic cell in which it was produced to an aluminium electrowinning cell.
  • the composition of the electrolyte in which the anode was produced can be suitably modified, for instance by dissolving alumina and optionally iron species, and electrolysis continued in the same cell to produce aluminium.
  • Electrolysis was carried out in a laboratory scale cell equipped with an anode according to the invention.
  • the anode was made with a Cor-TenTM type low-carbon high-strength (HSLA) steel containing niobium, titanium, chromium and copper in a total amount of less than 4 weight%.
  • the anode was pre-oxidised in air at about 1050°C for 15 hours for the formation of a dense hematite-based outer layer.
  • the anode was then tested in a fluoride-containing molten electrolyte at 850°C and at a current density of about 0.7 A/cm 2 .
  • the electrolyte contained cryolite and 15 weight% excess of AlF 3 , approximately 3 weight% alumina and approximately 200 ppm iron species obtained from the dissolution of iron oxide thereby surely saturating the electrolyte with iron species and inhibiting dissolution of the hematite-based anode surface layer.
  • the alumina feed contained sufficient iron oxide so as to replace the iron which had been deposited into the product aluminium, thereby maintaining the concentration of iron in the electrolyte at the limit of solubility and preventing dissolution of the hematite-based anode surface layer.
  • the produced aluminium was also analysed and showed an iron contamination of about 700 ppm which is below the tolerated iron contamination in commercial aluminium production.
  • the anode was made with a low-carbon high-strength (HSLA) steel containing manganese 0.4 weight%, niobium 0.02 weight%, molybdenum 0.02 weight%, copper 0.3 weight%, nickel 0.45 weight% and chromium 0.8 weight%.
  • the anode was pre-oxidised in air at about 850°C for 12 hours to form a dense hematite-based outer layer.
  • the anode was then tested under similar conditions as in Example 1 and the test results were similar.
  • the anode was made with a low-carbon high-strength (HSLA) steel containing nickel, copper and silicon in a total amount of less than 1.5 weight%.
  • HSLA low-carbon high-strength
  • the anode was pre-oxidised in air at about 850°C for 12 hours to form a dense hematite-based outer layer.
  • the anode was then tested under similar conditions as in Example 1 and the test results were similar.

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Claims (38)

  1. Anode von einer Zelle für die elektrolytische Gewinnung von Aluminium aus Aluminiumoxid, das in einem fluoridhaltigen, geschmolzenen Elektrolyten gelöst ist, wobei die Anode einen Körper oder eine Schicht aus einem kohlenstoffarmen, hochfesten, niedriglegierten (HSLA)-Stahl aufweist, deren Oberfläche oxidiert ist, um eine kohärente und haftende äußere, auf Eisenoxid basierende Schicht zu bilden, deren Oberfläche für die Sauerstoffentwicklung elektrochemisch aktiv ist, wobei die auf Eisenoxid basierende Schicht eine geringe Löslichkeit in dem geschmolzenen Elektrolyten besitzt und die Dicke der auf Eisenoxid basierenden Schicht so ist, dass die Diffusion von Sauerstoff von der elektrochemisch aktiven Oberfläche in den Stahlkörper oder die Stahlschicht vermindert oder verhindert wird.
  2. Anode nach Anspruch 1, bei der der Körper oder die Schicht aus hochfestem, niedriglegierten Stahl 94-98 Gew.-% Eisen und Kohlenstoff enthält, wobei die übrigen Bestandteile ein oder mehrere weitere Metalle, die aus Chrom, Kupfer, Nickel, Silizium, Titan, Tantal, Wolfram, Vanadium, Zirkonium, Aluminium, Molybdän, Mangan und Niob ausgewählt sind, sowie gegebenenfalls geringe Mengen von mindestens einem Additiv sind, das aus Bor, Schwefel, Phosphor und Stickstoff ausgewählt ist.
  3. Anode nach Anspruch 1, mit einer Schicht aus hochfestem, niedriglegierten Stahl auf einem oxidationsbeständigen metallischen Kern.
  4. Anode nach Anspruch 3, bei der der metallische Kern aus Kupfer oder einer Kupferlegierung hergestellt ist und gegebenenfalls geringe Mengen von mindestens einem Oxid enthält, wodurch die mechanischen Eigenschaften des metallischen Kerns verstärkt werden.
  5. Anode nach Anspruch 4, bei der das mindestens eine verstärkende Oxid aus Aluminiumoxid, Hafniumoxid, Yttriumoxid und Zirkonoxid ausgewählt ist.
  6. Anode nach Anspruch 3, bei der der metallische Kern mit mindestens einem Metall beschichtet ist, das ausgewählt ist aus Nickel, Chrom, Kobalt, Eisen, Aluminium, Hafnium, Mangan, Molybdän, Niob, Silizium, Tantal, Titan, Wolfram, Vanadium, Yttrium und Zirkonium, sowie Legierungen, intermetallischen Verbindungen und Kombinationen derselben.
  7. Anode nach Anspruch 6, bei der der metallische Kern mit einer Sauerstoffsperrschicht aus Chrom und/oder Niob beschichtet ist.
  8. Anode nach Anspruch 3, bei der die Schicht aus hochfestem, niedriglegierten Stahl auf dem metallischen Kern durch mindestens eine Zwischenschicht gebunden ist.
  9. Anode nach Anspruch 8, bei der die Schicht aus hochfestem, niedriglegierten Stahl auf dem metallischen Kern durch einen Film aus Silber und/oder mindestens eine Schicht aus Nickel und/oder Kupfer gebunden ist.
  10. Bipolare Elektrode von einer Zelle für die elektrolytische Gewinnung von Aluminium aus Aluminiumoxid, das in einem fluoridhaltigen Elektrolyten gelöst ist, mit einer Anode gemäß Anspruch 1 an ihrer anodischen Seite.
  11. Verfahren zur Herstellung einer Anode gemäß Anspruch 1, mit:
    Bereitstellen eines Körpers oder einer Schicht aus einem kohlenstoffarmen, hochfesten, niedriglegierten (HSLA)-Stahl; und
    Oxidieren der Oberfläche des Körpers oder der Schicht aus hochfestem, niedriglegierten Stahl, um die kohärente und haftende äußere, auf Eisenoxid basierende Schicht zu bilden, deren Oberfläche für de Sauerstoffentwicklung elektrochemisch aktiv ist.
  12. Verfahren nach Anspruch 11, mit dem Aufbringen einer Schicht aus hochfestem, niedriglegierten Stahl auf einen oxidationsbeständigen, metallischen vor oder nach Bildung der äußeren, auf Eisenoxid basierenden Schicht.
  13. Verfahren nach Anspruch 12, bei dem die Schicht aus hochfestem, niedriglegierten Stahl auf den metallischen Kern plasmagesprüht, im Lichtbogen gesprüht oder elektrolytisch abgeschieden wird.
  14. Verfahren nach Anspruch 12, bei dem die Schicht aus hochfestem, niedriglegierten Stahl durch mindestens eine Zwischenbindungsschicht auf den metallischen Kern gebunden wird.
  15. Verfahren nach Anspruch 11, bei dem die Oberfläche des Körpers oder der Schicht aus hochfestem, niedriglegierten Stahl in einem geschmolzenen Elektrolyten 5 bis 15 Stunden lang bei 800°C bis 1000°C oxidiert wird.
  16. Verfahren nach Anspruch 15, bei dem die Oberfläche des Körpers oder der Schicht aus hochfestem, niedriglegierten Stahl vor der Elektrolyse 5 bis 25 Stunden lang bei 750°C bis 1150°C in einer oxidierenden Atmosphäre, wie Luft oder Sauerstoff, oxidiert wird.
  17. Zelle für die elektrolytische Gewinnung von Aluminium aus Aluminiumoxid, das in einem fluoridhaltigen, geschmolzenen Elektrolyten gelöst ist, mit mindestens einer Anode mit einem Körper oder einer Schicht aus einem kohlenstoffarmen, hochfesten, niedriglegierten (HSLA)-Stahl und einer elektrochemisch aktiven, äußeren, auf Eisenoxid basierenden Schicht gemäß Anspruch 1.
  18. Zelle nach Anspruch 17, bei der beim normalem Betrieb die elektrochemisch aktive Schicht der oder jeder Anode durch Oberflächenoxidation des Stahlkörpers oder der Stahlschicht durch kontrollierte Sauerstoffdiffusion durch die elektrochemisch aktive Schicht fortschreitend weiter gebildet wird und an der Elektrolyt/Anoden-Grenzfläche fortschreitend in den Elektrolyten aufgelöst wird, wobei die Bildungsgeschwindigkeit der äußeren, auf Eisenoxid basierenden Schicht im wesentlichen gleich ihrer Auflösungsgeschwindigkeit in den Elektrolyten ist.
  19. Zelle nach Anspruch 17, bei der die oder jede Anode dimensionsstabil gehalten wird, indem eine ausreichende Menge von gelöstem Aluminiumoxid und Eisenspezies in dem Elektrolyten aufrechterhalten wird, um eine Auflösung der äußeren Oxidschicht der oder jeder Anode zu verhindern.
  20. Zelle nach Anspruch 19, die bei einer ausreichend niedrigen Temperatur betrieben wird, um die Löslichkeit der äußeren, auf Eisenoxid basierenden Schicht der Anode(n) zu begrenzen, wodurch die Verunreinigung des Produkt-Aluminiums durch Bestandteile der äußeren, auf Eisenoxid basierenden Schicht der Anode(n) begrenzt wird.
  21. Zelle nach Anspruch 17, die in einer bipolaren Anordnung geschaltet ist, mit einer Anschluß-Kathode, die einer Anschluß-Anode gegenüberliegt, und dazwischen mit mindestens einer bipolaren Elektrode, wobei die Anode(n) die anodische Seite der oder jeder bipolaren Elektrode und/oder der Anschluß-Anode bildet (bilden).
  22. Verfahren zur Herstellung von Aluminium in einer Zelle gemäß Anspruch 17, wobei das Verfahren umfasst: Lösen von Aluminiumoxid in dem Elektrolyten und Leiten von einem ionischen, elektrischen Strom zwischen der elektrochemisch aktiven Oberfläche der Anode(n) und der Oberfläche der Kathode(n), wodurch Aluminium an der Kathodenoberfläche(n) und Sauerstoff an der Anodenoberfläche(n) hergestellt wird.
  23. Verfahren nach Anspruch 22, bei dem die elektrochemisch aktive Schicht der oder jeder Anode durch Oberflächenoxidation des Stahlkörpers oder der Stahlschicht durch kontrollierte Sauerstoffdiffusion durch die elektrochemisch aktive Schicht fortschreitend weiter gebildet wird und an der Elektrolyt/Anoden-Grenzfläche fortschreitend in den Elektrolyten aufgelöst wird, wobei die Bildungsgeschwindigkeit der äußeren, auf Eisenoxid basierenden Schicht im wesentlichen gleich ihrer Auflösungsgeschwindigkeit in den Elektrolyten ist.
  24. Verfahren nach Anspruch 22, bei dem die oder jede Anode dimensionsstabil gehalten wird, indem eine ausreichende Menge von gelöstem Aluminiumoxid und Eisenspezies in dem Elektrolyten aufrechterhalten wird, um eine Auflösung der äußeren Oxidschicht der oder jeder Anode zu verhindern.
  25. Verfahren nach Anspruch 22, bei dem die Zelle bei einer ausreichend niedrigen Temperatur betrieben wird, um die Löslichkeit der äußeren, auf Eisenoxid basierenden Schicht der Anode(n) zu begrenzen, wodurch die Verunreinigung des Produkt-Aluminiums durch Bestandteile der äußeren, auf Eisenoxid basierenden Schicht der Anode(n) begrenzt wird.
  26. Verfahren nach Anspruch 25, bei dem die Zelle mit einer Betriebstemperatur des Elektrolyten unter 910°C betrieben wird.
  27. Verfahren nach Anspruch 26, bei dem die Zelle bei einer Elektrolyt-Temperatur von 730°C bis 870°C betrieben wird.
  28. Verfahren nach Anspruch 25, bei dem die Menge von Eisenspezies und Aluminiumoxid, die in dem Elektrolyten aufgelöst sind, wodurch die Auflösung der auf Eisenoxid basierenden, äußeren Oberflächenschicht der oder jeder Anode verhindert wird, so ist, dass das Produkt-Aluminium mit nicht mehr als 2000 ppm Eisen, vorzugsweise nicht mehr als 1000 ppm Eisen und insbesondere nicht mehr als 500 ppm Eisen, verunreinigt ist.
  29. Verfahren nach Anspruch 24, bei dem Eisenspezies diskontinuierlich oder kontinuierlich in den Elektrolyten eingebracht werden, um die Menge von Eisenspezies in dem Elektrolyten aufrechtzuerhalten, die bei der Betriebstemperatur die Auflösung der auf Eisenoxid basierenden, äußeren Oberflächenschicht der oder jeder Anode verhindert.
  30. Verfahren nach Anspruch 29, bei dem die Eisenspezies in Form von metallischem Eisen und/oder Eisenverbindung eingebracht werden.
  31. Verfahren nach Anspruch 30, bei dem die Eisenspezies in den Elektrolyten in Form von Eisenoxid, Eisenfluorid, Eisenoxyfluorid und/oder Eisen-Aluminium-Legierung eingebracht werden.
  32. Verfahren nach Anspruch 29, bei dem die Eisenspezies periodisch zusammen mit Aluminiumoxid in den Elektrolyten eingebracht werden.
  33. Verfahren nach Anspruch 29, bei dem eine Opferelektrode die Eisenspezies kontinuierlich in den Elektrolyten einbringt.
  34. Verfahren nach Anspruch 22 zur Herstellung von Aluminium auf einer mit Aluminium benetzbaren Kathode.
  35. Verfahren nach Anspruch 34, bei dem das hergestellte Aluminium kontinuierlich von der Kathode abläuft.
  36. Verfahren nach Anspruch 22, bei dem der Elektrolyt zwischen den Anoden und gegenüberliegenden Kathoden zirkuliert wird, wodurch die Auflösung von Aluminiumoxid in den Elektrolyten verbessert und/oder die Zufuhr von gelöstem Aluminiumoxid unter die aktiven Oberflächen der Anoden verbessert wird.
  37. Verwendung eines Körpers oder einer Schicht aus kohlenstoffarmem, hochfesten, niedriglegierten (HSLA)-Stahl als Anoden-Vorläufer, der durch Oxidieren der Oberfläche des Stahlkörpers oder der Stahlschicht in eine Anode für die elektrolytischen Gewinnung von Aluminium gemäß Anspruch 1 umgewandelt werden kann, um die kohärente und haftende, äußere, auf Eisenoxid basierende Schicht zu bilden.
  38. Verfahren zur Herstellung einer Anode und zur Produktion von Aluminium in einer Elektrolysezelle, mit dem Einsetzen eines Körper oder einer Schicht aus einem kohlenstoffarmen, hochfesten, niedriglegierten (HSLA)-Stahl als ein Anoden-Vorläufer in einen fluoridhaltigen, geschmolzenen Elektrolyten von einer Elektrolysezelle, Oxidieren der Oberfläche des Anoden-Vorläufers in-situ, um eine elektrochemisch aktive, auf Eisenoxid basierende Schicht herzustellen, wodurch den Anoden-Vorläufer in eine Anode nach Anspruch 1 umgewandelt wird, und Erzeugen von Sauerstoff an der Oberfläche der auf Eisenoxid basierenden Schicht und Aluminium an einer gegenüberliegenden Kathode in dem gleichen oder in einem unterschiedlichen Elektrolyten.
EP00900036A 1999-01-08 2000-01-10 Anoden aus hochfestem, niedriglegiertem stahl für zellen zur aluminium-schmelzelektrolyse Expired - Lifetime EP1149188B1 (de)

Applications Claiming Priority (3)

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IB9900015 1999-01-08
WOPCT/IB99/00015 1999-01-08
PCT/IB2000/000028 WO2000040783A1 (en) 1999-01-08 2000-01-10 High-strength low-alloy steel anodes for aluminium electrowinning cells

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EP1149188B1 true EP1149188B1 (de) 2002-09-11

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AU2002236142B2 (en) * 2001-03-07 2007-04-05 Moltech Invent S.A. Metal-based anodes for aluminium production cells
US10711359B2 (en) 2013-08-19 2020-07-14 United Company RUSAL Engineering and Technology Centre LLC Iron-based anode for obtaining aluminum by the electrolysis of melts
CN108588567B (zh) * 2018-07-04 2023-05-05 百色皓海碳素有限公司 消失模铸造阳极钢爪头的方法及阳极钢爪头消失模组

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US5510008A (en) * 1994-10-21 1996-04-23 Sekhar; Jainagesh A. Stable anodes for aluminium production cells

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AU1793200A (en) 2000-07-24
DE60000436T2 (de) 2003-05-15
ES2180506T3 (es) 2003-02-16
DE60000436D1 (de) 2002-10-17
WO2000040783A1 (en) 2000-07-13
CA2360094C (en) 2005-11-29
CA2360094A1 (en) 2000-07-13

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