WO1999036592A1 - Anodes metalliques exemptes de carbone a activite electrocatalytique pour des cellules electrolytiques de production d'aluminium - Google Patents

Anodes metalliques exemptes de carbone a activite electrocatalytique pour des cellules electrolytiques de production d'aluminium Download PDF

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Publication number
WO1999036592A1
WO1999036592A1 PCT/IB1999/000080 IB9900080W WO9936592A1 WO 1999036592 A1 WO1999036592 A1 WO 1999036592A1 IB 9900080 W IB9900080 W IB 9900080W WO 9936592 A1 WO9936592 A1 WO 9936592A1
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WO
WIPO (PCT)
Prior art keywords
anode
electrochemically active
oxygen
cell
metal
Prior art date
Application number
PCT/IB1999/000080
Other languages
English (en)
Inventor
Vittorio De Nora
Original Assignee
Moltech Invent S.A.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US09/126,114 external-priority patent/US6103090A/en
Priority claimed from US09/126,206 external-priority patent/US6077415A/en
Application filed by Moltech Invent S.A. filed Critical Moltech Invent S.A.
Priority to EP99900108A priority Critical patent/EP1049816A1/fr
Priority to CA002317596A priority patent/CA2317596A1/fr
Priority to AU17796/99A priority patent/AU739732B2/en
Publication of WO1999036592A1 publication Critical patent/WO1999036592A1/fr
Priority to US09/616,334 priority patent/US6413406B1/en
Priority to NO20003703A priority patent/NO20003703D0/no

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Classifications

    • 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
    • C25C7/02—Electrodes; Connections thereof
    • C25C7/025—Electrodes; Connections thereof used in cells for the 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
    • C25C3/06—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 having an electrocatalytically active surface for use in cells for the electrowinning of aluminium by the electrolysis of alumina dissolved in a molten fluoride- containing electrolyte, 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.
  • the operating temperature is still not less than 950°C in order to have a sufficiently high solubility and rate of dissolution of alumina and high electrical conductivity of the bath.
  • the carbon anodes have a very short life because during electrolysis the oxygen which should evolve on the anode surface combines with the carbon to form polluting C0 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.
  • US Patent 4,614,569 (Duruz/Derivaz/Debely/ Adorian) describes 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 by the addition of cerium compounds to the molten cryolite electrolyte. This made it possible to have a protection of the surface only from the electrolyte attack and to a certain extent from the gaseous oxygen but not from the 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 Patent 4,039,401 discloses anodes for the production of aluminium which are made of a metallic substrate coated with various electronic conductive oxide ceramics. However, protection of the substrate against corrosion is not addressed.
  • 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 of their poor performance .
  • An object of the invention is to reduce substantially the consumption of the electrochemically active anode surface of a non-carbon metal-based anode for aluminium electrowinning cells which is attacked by the nascent oxygen by enhancing the reaction of nascent oxygen to gaseous biatomic molecular gaseous oxygen.
  • Another object of the invention is to provide a coating for a non-carbon metal-based anode for aluminium electrowinning cells which has a high electrochemical activity and also a long life and which can easily be applied onto an anode substrate.
  • a further object of the invention is to provide a coating for a non-carbon metal-based anode for aluminium electrowinning cells which lowers the cell voltage compared to the voltage of cells having metal-based anodes which are not provided with this coating.
  • a major object of the invention is to provide an anode for the electrowinning of aluminium which has no carbon so as to eliminate carbon-generated pollution and reduce high cell operating costs.
  • the invention relates to a non-carbon, metal- based high temperature resistant anode of a cell for the production of aluminium by the electrolysis of alumina dissolved in a fluoride-containing electrolyte.
  • the anode has a highly conductive metal-based substrate coated with one or more electrically conductive adherent intermediate protective layers and an outer layer which is electrically conductive and electrochemically active.
  • the outer electrochemically active layer contains one or more electrocatalysts fostering the oxidation of oxygen ions as well as fostering the formation of biatomic molecular gaseous oxygen from the monoatomic nascent oxygen obtained by the oxidation of the oxygen ions present at the surface of the anode in order to inhibit ionic and/or monoatomic oxygen penetration.
  • the intermediate layer (s) constitute (s) a substantially impermeable barrier to ionic, monoatomic and/or biatomic gaseous oxygen to prevent attack of the metal-based substrate.
  • metal-based substrate means that the anode substrate contains at least one metal as such or as alloys, intermetallics and/or cermets.
  • the electrocatalyst (s) may be selected from iridium, palladium, platinum, rhodium, ruthenium, silicon, tin or zinc metals, Mischmetal and their oxides and metals of the Lanthanide series and their oxides as well as mixtures and compounds thereof.
  • the electrochemically active layer usually comprises mainly electrochemically active constituents selected from the group consisting of oxides, such as iron oxides, oxyfluorides , for instance cerium oxyfluoride, phosphides, carbides and combinations thereof.
  • oxides such as iron oxides, oxyfluorides , for instance cerium oxyfluoride, phosphides, carbides and combinations thereof.
  • An oxide may be present in the electrochemically active layer as such, or in a multi-compound mixed oxide and/or in a solid solution of oxides.
  • the oxide may be in the form of a simple, double and/or multiple oxide, and/or in the form of a stoichiometric or non- stoichiometric oxide.
  • the electrochemically active layer may in particular comprise spinels and/or perovskites, such as ferrite which may be selected from cobalt, manganese, molybdenum, nickel, magnesium and zinc ferrite, and mixtures thereof.
  • ferrite which may be selected from cobalt, manganese, molybdenum, nickel, magnesium and zinc ferrite, and mixtures thereof.
  • Nickel ferrite may be partially substituted with Fe 2+ .
  • ferrites may doped with at least one oxide selected from the group consisting of chromium, titanium, tantalum, tin and zirconium oxide.
  • the electrochemically active layer may comprise a chromite, such as iron, cobalt, copper, manganese, beryllium, calcium, strontium, barium, magnesium, nickel and zinc chromite.
  • the electrochemically active layer may be applied in the form of powder or slurry onto metal-based substrate, dried as necessary and heat-treated.
  • the electrochemically active layer may advantageously be applied in the form a slurry or suspension containing colloidal material and then dried and/or heat treated.
  • slurry or a suspension usually comprises at least one colloid selected from colloidal alumina, ceria, lithia, magnesia, silica, thoria, yttria, zirconia and colloids containing active constituents of the active filling.
  • Ferrites and/or chromites may advantageously be applied with a catalyst onto the metal- based substrate in a slurry or suspension.
  • electrochemically active layer such as dipping, spraying, painting, brushing, calendar rolling, electroplating, plasma spraying, physical vapour deposition or chemical vapour deposition.
  • the metal-based substrate comprises a metal, an alloy, an intermetallic compound or a cermet.
  • the metal-based substrate may comprise at least one metal selected from nickel, copper, cobalt, chromium, molybdenum, tantalum or iron.
  • the core structure may be made of an alloy consisting of 10 to 30 weight% of chromium, 55 to 90% of at least one of nickel, cobalt or iron, and 0 to 15% of aluminium, titanium, zirconium, yttrium, hafnium or niobium.
  • metal-based substrate may comprise an alloy or intermetallic compound containing at least two metals selected from nickel, iron and aluminium.
  • the metal-based substrate can comprise a cermet containing copper and/or nickel as a metal.
  • the metal-based substrate may, in particular, comprise a cermet containing a metal and at least one stable oxide selected from nickel cuprate, nickel ferrite or nickel oxide.
  • the anode substrate may be of the following composition and structure:
  • a metal-based core layer of low electrical resistance for connecting the anode to a positive current supply such as a metal, an alloy, an intermetallic compound and/or a cermet, for instance nickel-plated copper;
  • At least one intermediate layer on the metal-based core layer forming a barrier substantially impervious to monoatomic and molecular oxygen, such as chromium oxide and/or black non-stoichiometric nickel oxide, chromium or nickel-chromium alloys; and
  • one or more intermediate protective layers on the oxygen barrier to protect the oxygen barrier and which remain inactive in the reactions for the evolution of oxygen gas but inhibits the dissolution of the oxygen barrier, such as nickel and/or copper as metals and/or oxides; the intermediate protective layer (s) being coated with the electrically conductive, electrochemically active adherent applied layer comprising the electrocatalyst according to the invention.
  • the invention also relates to a cell for the production of aluminium by the electrolysis of alumina dissolved in a molten electrolyte comprising at least one anode as described above.
  • the cell may comprise at least one aluminium-wettable cathode which can be a drained cathode on which aluminium is produced and from which it continuously drains.
  • the cell is in a monopolar, multi- monopolar or in a bipolar configuration.
  • Bipolar cells may comprise the anodes as described above as the anodic side of at least one bipolar electrode and/or as a 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 PCT/IB98/00161 (de Nora/Duruz) or by periodically moving the anodes as described in co- pending application PCT/IB98/00162 (Duruz/Bell ⁇ ) .
  • the cell may be operated with the electrolyte at conventional temperatures, such as 950 to 970°C, or at reduced temperatures as low as 750°C.
  • Another aspect of the invention is a method of producing aluminium in such a cell, wherein alumina is dissolved in the electrolyte and then electrolysed to produce aluminium.
  • the anodes are protected with a protective coating of cerium oxyfluoride on the electrochemically active layer.
  • the protective coating is formed in-situ in the cell or pre-applied, and maintained by the addition of small amounts of cerium compounds to the electrolyte as described in US Patent 4,614,569 (Duruz/Derivaz/Debely/ Adorian) .
  • one or more constituents of the electrochemically active layer may be added to the electrolyte in an amount to slow down dissolution of the electrochemically active layer.
  • a test anode was made by applying on a copper substrate an electrochemically active coating containing an electrocatalyst in the form of iridium oxide for the rapid conversion of the monoatomic oxygen formed into biatomic molecular gaseous oxygen.
  • a 100 micron thick intermediate layer of a nickel-chromium alloy was directly applied on the copper substrate by arc spraying.
  • a slurry was prepared by mixing an amount of 1 g of commercially available nickel ferrite powder with 0.75 ml of an inorganic polymer containing 0.25 g nickel- ferrite per 1 ml of water. An amount corresponding to 5 weight% of Ir0 2 in the form of IrCl 4 was then added to the slurry.
  • the slurry was then brush-coated onto the nickel substrate by applying 3 successive layers of the slurry each layer being approximately 50 micron thick. Each slurry-applied layer was dried by heat-treating at 500°C for 15 minutes between each layer application.
  • the anode was then tested in molten cryolite containing approximately 6 weight% alumina at 970°C at a current density of about 0.8 A/cm 2 .
  • the anode was extracted from the cryolite after 100 hours and showed no sign of significant internal corrosion after microscopic examination of a cross-section of the anode specimen. Furthermore, during electrolysis the cell voltage was about 110 mV lower than the measured cell voltage of similarly prepared anodes having no electrocatalyst.
  • a test anode was made by coating by electro- deposition a core structure in the shape of a copper rod having a diameter of 12 mm a chromium-iron-nickel intermediate layer about 200 micron thick by arc spraying .
  • the coated structure was heat treated at 1000°C in argon for 5 hours. This heat treatment provides for the interdiffusion of nickel and copper to form an intermediate layer.
  • the structure was then heat treated for 24 hours at 1000° in air to form a chromium oxide (Cr 2 0 3 ) barrier layer on the core structure and oxidising at least partly the interdiffused nickel-copper layer thereby forming the intermediate layer .
  • Cr 2 0 3 chromium oxide
  • a slurry was prepared by mixing an amount of 1 g of commercially available nickel ferrite powder with 0.75 ml of an inorganic polymer containing 0.25 g nickel- ferrite per 1 ml of water. An amount corresponding to 5 weight% of Ir0 2 acting as an electrocatalyst for the rapid conversion of oxygen ions into monoatomic oxygen and subsequently gaseous oxygen, was then added to the slurry as IrCl 4 .
  • the slurry was then brush-coated onto the interdiffused nickel copper layer by applying 3 successive 50 micron thick layers of the slurry, each slurry-applied layer having been allowed to dry by heat- treating the anode at 500°C for 15 minutes between each layer application.
  • the anode was then tested in molten cryolite at 970°C containing approximately 6 weight% alumina, by passing a current at a current density of about 0.8 A/cm 2 .
  • the anode was extracted from the cryolite after 100 hours and showed no sign of significant internal corrosion after microscopic examination of a cross- section of the anode specimen.
  • the cell voltage was about 120 mV lower than the measured cell voltage of similarly prepared anodes having no electrocatalyst .

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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)

Abstract

Anode métallique exempte de carbone résistant à des températures élevées, pour une cellule électrolytique de production d'aluminium. Ladite anode possède un substrat métallique hautement conducteur couvert d'une ou plusieurs couches protectrices intermédiaires adhérentes électriquement conductrices, ainsi que d'une couche externe qui est électriquement conductrice et électrochimiquement active. La couche électrochimiquement active contient un ou plusieurs électrocatalyseurs favorisant l'oxydation des ions d'oxygène ainsi que la formation d'oxygène gazeux moléculaire biatomique à partir de l'oxygène naissant monoatomique obtenu par l'oxydation des ions d'oxygène présents à la surface de l'anode afin d'inhiber la pénétration d'oxygène ionique et/ou monoatomique. Les couches intermédiaires constituent une barrière pratiquement imperméable à l'oxygène gazeux ionique, monoatomique et/ou biatomique pour empêcher l'attaque du substrat métallique. L'électrocatalyseur peut être de l'iridium, du palladium, du platine, du rhodium, du ruthénium, du silicium, de l'étain, du zinc, du mischmétal et leurs oxydes et des métaux du groupe des lanthanides. La couche appliquée comporte des constituants électrochimiquement actifs, choisis parmi des oxydes, oxyfluorures, phosphures, carbures, en particulier des spinelles tels que la ferrite.
PCT/IB1999/000080 1998-01-20 1999-01-19 Anodes metalliques exemptes de carbone a activite electrocatalytique pour des cellules electrolytiques de production d'aluminium WO1999036592A1 (fr)

Priority Applications (5)

Application Number Priority Date Filing Date Title
EP99900108A EP1049816A1 (fr) 1998-01-20 1999-01-19 Anodes metalliques exemptes de carbone a activite electrocatalytique pour des cellules electrolytiques de production d'aluminium
CA002317596A CA2317596A1 (fr) 1998-01-20 1999-01-19 Anodes metalliques exemptes de carbone a activite electrocatalytique pour des cellules electrolytiques de production d'aluminium
AU17796/99A AU739732B2 (en) 1998-01-20 1999-01-19 Electrocatalytically active non-carbon metal-based anodes for aluminium production cells
US09/616,334 US6413406B1 (en) 1998-01-20 2000-07-15 Electrocatalytically active non-carbon metal-based anodes for aluminium production cells
NO20003703A NO20003703D0 (no) 1998-01-20 2000-07-19 Elektrokatalytisk aktive ikke-karbon metallbaserte anoder for aluminiumproduksjonsceller

Applications Claiming Priority (8)

Application Number Priority Date Filing Date Title
IB9800080 1998-01-20
IBPCT/IB98/00081 1998-01-20
IB9800081 1998-01-20
IBPCT/IB98/00080 1998-01-20
US09/126,206 1998-07-30
US09/126,114 US6103090A (en) 1998-07-30 1998-07-30 Electrocatalytically active non-carbon metal-based anodes for aluminium production cells
US09/126,114 1998-07-30
US09/126,206 US6077415A (en) 1998-07-30 1998-07-30 Multi-layer non-carbon metal-based anodes for aluminum production cells and method

Related Child Applications (1)

Application Number Title Priority Date Filing Date
US09/616,334 Continuation US6413406B1 (en) 1998-01-20 2000-07-15 Electrocatalytically active non-carbon metal-based anodes for aluminium production cells

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WO1999036592A1 true WO1999036592A1 (fr) 1999-07-22

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WO (1) WO1999036592A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000006800A1 (fr) * 1998-07-30 2000-02-10 Moltech Invent S.A. Anodes multicouches non carbonees a base de metal pour cellules de production d'aluminium

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0306101A1 (fr) * 1987-09-02 1989-03-08 MOLTECH Invent S.A. Anode inconsumable pour l'électrolyse du sel fondu

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0306101A1 (fr) * 1987-09-02 1989-03-08 MOLTECH Invent S.A. Anode inconsumable pour l'électrolyse du sel fondu

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000006800A1 (fr) * 1998-07-30 2000-02-10 Moltech Invent S.A. Anodes multicouches non carbonees a base de metal pour cellules de production d'aluminium

Also Published As

Publication number Publication date
EP1049816A1 (fr) 2000-11-08

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