EP0422142B1 - Substrat d'anode revetu d'oxycomposes de terres rares - Google Patents

Substrat d'anode revetu d'oxycomposes de terres rares Download PDF

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Publication number
EP0422142B1
EP0422142B1 EP90904311A EP90904311A EP0422142B1 EP 0422142 B1 EP0422142 B1 EP 0422142B1 EP 90904311 A EP90904311 A EP 90904311A EP 90904311 A EP90904311 A EP 90904311A EP 0422142 B1 EP0422142 B1 EP 0422142B1
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EP
European Patent Office
Prior art keywords
anode
oxide
mol
substrate
nickel
Prior art date
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Expired - Lifetime
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EP90904311A
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German (de)
English (en)
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EP0422142A1 (fr
Inventor
Jean-Louis Jorda
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Moltech Invent SA
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Moltech Invent SA
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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
    • 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
    • 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

Definitions

  • the invention relates to anodes for electrowinning metals such as aluminum from molten salt electrolytes, of the type comprising a substrate made of an electroconductive oxycompound which in use is coated with a surface coating comprising at least one rare earth oxycompound, typically including cerium oxyfluoride.
  • the invention also relates to electrowinning processes using such anodes.
  • US Patent 4 614 569 describes a method of electrowinning metals by electrolysis of a melt containing a dissolved species of the metal to be won using an anode immersed in the melt wherein the anode has a metal, alloy or cermet substrate and an operative anode surface which is a protective surface coating containing a compound of a metal less noble than the metal to be electrowon, the protective coating being preserved by maintaining in the melt a suitable concentration of a species of this less noble metal.
  • the protective anode coating comprises a fluorine-containing oxycompound of cerium (referred to as "cerium oxyfluoride”) alone or in combination with additives such as compounds of tantalum, niobium, yttrium, lanthanum, praesodymium and other rare earth elements, this coating being maintained by the addition of cerium and possibly other elements to the electrolyte.
  • the electrolyte can be molten cryolite containing dissolved alumina, i.e. for the production of aluminum.
  • This electrowinning method potentially has very significant advantages. To date, however, there remain problems with the anode substrate. When the substrate is a metal, alloy or cermet, it may be subject to oxidation leading to a reduced life of the anode, despite the excellent protective effect of the cerium oxyfluoride coating which protects the substrate from direct attack by corrosive electrolyte. When the substrate is a ceramic oxycompound, conductivity and corrosion are major problems.
  • a promising solution to these problems has been the use of a ceramic/metal composite material of at least one ceramic phase and at least one metallic phase, comprising mixed oxides of cerium with aluminum, nickel, iron and/or copper in the form of a skeleton interwoven with a continuous metallic network of an alloy or intermetallic compound of cerium with aluminum, nickel, iron and/or copper, as described in EP-A-0 257 708.
  • these materials When used as electrode substrates, these materials have promise, particularly those based on cerium and aluminum because even if they corrode, this does not lead to corrosion products that contaminate the electrowon aluminum. Nevertheless corrosion of the substrate remains a problem.
  • US Patent 4 374 050 discloses inert electrodes for aluminum production fabricated from at least two metals or metal compounds to provide a combination metal compound.
  • an alloy of two or more metals can be surface oxidised to form an oxycompound of the metals at the surface on an unoxidised alloy substrate.
  • US Patent 4 374 761 discloses similar compositions further comprising a dispersed metal powder in compositions which may be applied as a preformed oxide composition on a metal substrate by cladding or plasma spraying. Such application techniques, however, are known to involve many drawbacks and the adhesion is particularly poor.
  • US Patent 4 620 905 describes an oxidised alloy electrode based on tin or copper with nickel, iron silver, zinc, magnesium, aluminum and yttrium, either as a cermet or partially oxidised at its surface.
  • Such partially oxidised alloys suffer serious disadvantages in that the oxide layers formed are far too porous to oxygen, and not sufficiently stable in corrosive environments.
  • the partially oxidised structures continue to oxidize and this uncontrolled oxidation causes subsequent segregation of the metal and/or oxide layer. Adherence at the ceramic-metal interfaces is particularly difficult to achieve and this very problem has hampered use of such simple composites.
  • none of these materials has proven satisfactory as substrate for cerium oxyfluoride coatings of the type discussed.
  • Improved metal-based substrates are described in European Patent Applications 88201957.3, 88201851.8, 88201852.6, 88201853.4 and 88201854.2 all as yet unpublished. These typically include a substrate made of an alloy of chromium with nickel, cobalt and/or iron. On the surface of the substrate is a chromium oxide film on top of which is a layer of copper oxide in solid solution with nickel or manganese, obtained by oxidising a layer of nickel/copper or manganese/copper which is applied eg by electroplating. It was also mentioned that the nickel oxide in the surface layer may have its electrical conductivity improved by doping with lithium.
  • Ceramic intermediate layers which in use serve as anchorage for the in-situ maintained protective coating of cerium oxyfluoride to the metal substrate, these intermediate layers including: nickel ferrite; copper oxide and nickel ferrite; doped, non-stoichiometric and partially substituted ceramic oxide spinels containing combinations of divalent nickel, cobalt, magnesium, manganese, copper and zinc with divalent/trivalent nickel, cobalt, manganese and/or iron, and optionally dopants selected from Ti4+, Zr4+, Sn4+, Fe4+, Hf4+, Mn4+, Fe3+, Ni3+, Co3+, Mn3+, Al3+, Cr3+, Fe2+, Ni2+, Co2+, Mg2+, Mn2+, Cu2+, Zn2+ and Li2+ (see US patent No. 4 552 630); as well as coatings based on rare earth oxides and oxyfluorides
  • An object of the invention is to provide electrode substrates based on electroconductive oxycompounds which can be produced easily, have excellent conductivity and perform well as anode substrates when coated with an oxyfluoride-type coating.
  • the invention is based on the realization that sintered copper-nickel oxide suitably doped with lithium oxide to enhance conductivity fulfills the sought-after requirements of a material for the anode substrate.
  • an anode for electrowinning a metal from a molten salt electrolyte comprising an electroconductive oxycompound substrate which in use carries a surface coating comprising at least one rare earth oxycompound, is characterized in that the substrate comprises a sintered body composed of a nickel-copper-lithium oxide solid solution.
  • the nickel oxide is present in the solid solution in an amount of at least 70 mol%
  • the copper oxide is present in an amount of at most 29 mol%
  • the lithium oxide is present in an amount of at most 10mol%.
  • the solid solution contains 70-90 mol% nickel oxide, 5-29 mol% copper oxide and 1-10 mol% lithium oxide.
  • the concentration the lithium dopant preferably ranges from 1 to 10 atom % with an optimum value at about 5 atom %, this usually in combination with about 70-80 mol% nickel oxide and about 20-25 mol% copper oxide.
  • a method of preparing an anode substrate according to the invention comprises mixing powders of nickel oxide, copper oxide and a compound of lithium, firing at 900-1100°C, cooling, grinding, cold pressing and sintering at 1000-1300°C for 30-40 hours.
  • Shapes of lithium doped (Ni-Cu)O solid solution can thus conveniently be prepared by mixing powders of Li(NO3), Li2CO3 or LiOH; CuO; and NiO in the right proportions and firing for example at 900-1050°C in air for about 24 hours at a heating rate of about 100°C/hour. After cooling, the material is ground, cold pressed (eg at 10 tons/cm2) and sintered at 1000-1300°C e.g. 1100-1150°C for 30-40 hours.
  • the resulting sintered material shows a density of at least 70% theoretical density, typically 80%, and an electrical conductivity of about 150 (ohm cm) ⁇ 1 at 980°C compared to 1 (ohm cm) ⁇ 1 for the undoped (Ni-Cu)O.
  • a sintered specimen of such composition was tested as an anode substrate in a neutral cryolite containing 1.5% CeF3 and 1.5 Ta2O5.
  • a very dense tantalum-doped cerium oxyfluoride coating was obtained. No noticeable change in the substrate composition near the interface was observed.
  • the process may be optimized to improve densification by hot pressing and/or the addition of sintering aids.
  • the anode substrate according to the invention can be used as a massive body supporting the rare earth oxycompound coating. But it can, if desired, incorporate a metal or other current collector to assist the supply of electric current and facilitate connection to the power supply.
  • the rare earth oxide coating may be cerium oxyfluoride alone or preferably may be cerium oxyfluoride together with at least one compound of tantalum, niobium, yttrium, lanthanum, praesodymium and other rare earth elements.
  • the invention also provides a method of electrowinning aluminum from molten cryolite containing alumina wherein an anode is immersed, the anode having an electroconductive oxycompound substrate as set out above, carrying a surface coating comprising at least one rare earth oxycompound, the surface coating being maintained by the presence of cerium species in the molten cryolite, the method comprising passing electrolysis current between the anode and a cathode to evolve oxygen and to maintain the surface coating at the anode and to produce aluminum at the cathode.
  • a Li.05Ni.70Cu.25O sample was prepared using powder metallurgy techniques: Li(NO3), CuO and NiO powders were mixed in the right proportions and fired at 1000°C in air for 24 hours. The heating rate was 100°C/hour. After cooling the specimen was powdered, cold pressed at 10 tons/cm2 and sintered for 35 hours at 1150°C. The microstructure of the resulting sample showed a porosity of nearly 20% and CuO precipitates at the grain boundaries due to the slow cooling rate.
  • a typical SEM-EDX analysis over a window of about 0.25 mm2 gave nickel 71.0 atom% and copper 28.6 atom%, whereas for individual grains the composition was: nickel 76.6 atom% and copper 23.2 atom%. This analytical method is not suitable for detecting the lithium.
  • An ingot with a surface area of 7.5 cm2 was prepared from this sample and exposed for 5 hours in a neutral cryolitic bath of 900g containing 1.5% of Ta2O5 and 6g (i.e. about 0.7%) CeF3.
  • a current density of 200 mA/cm2 a dense tantalum-doped cerium oxyfluoride coating was formed on the substrate at a rate ranging from 0.15 to 0.16 g/cm2 per hour.
  • EDX analysis revealed that the concentration of nickel and copper did not significantly change during the cerium oxyfluoride deposition: 70 and 30 atom% for nickel and copper respectively for a window analysis; 76 atom% nickel and 23 atom% copper for a grain analysis.
  • This stability of the composition of the sample is an indication of the protective role of the deposit for the cryolite in the previously mentioned conditions.
  • the relative stability of the potential during the deposition may be related to the conductivity of the substrate which is strongly dependant on the lithium concentration.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Engineering & Computer Science (AREA)
  • Electrolytic Production Of Metals (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Solid Thermionic Cathode (AREA)
  • Secondary Cells (AREA)
  • Manufacture And Refinement Of Metals (AREA)
  • Inorganic Compounds Of Heavy Metals (AREA)
  • Superconductors And Manufacturing Methods Therefor (AREA)

Claims (10)

  1. Une anode pour la récupération électrolytique d'un métal à partir d'une électrolyte de sel fondu, comprenant un substrat oxycomposé électroconducteur qui pendant son utilisation est revêtu d'un revêtement de surface comprenant au moins un oxycomposé de terre rare, caractérisé en ce que le substrat comprend un corps fritté composé d'oxyde de nickel-cuivre-lithium en solution solide.
  2. L'anode de la revendication 1, dans laquelle l'oxyde de nickel est présent en solution solide dans une quantité d'au moins 70mol%, l'oxyde de cuivre est présent dans une quantité d'au plus 29mol% et l'oxyde de lithium est présent dans une quantité d'au plus 10mol%.
  3. L'anode de la revendication 2, dans laquelle la solution solide contient 70-90 mol% d'oxyde de nickel, 5-29 mol% d'oxyde de cuivre et 1-10 mol% de lithium.
  4. L'anode de la revendication 3, dans laquelle la solution solide contient environ 70-80 mol% d'oxyde de nickel, environ 20-25 mol% d'oxyde de cuivre et environ 5 mol% de lithium.
  5. L'anode de n'importe laquelle des revendications précédentes, dans laquelle le substrat est revêtu d'un revêtement de surface comprenant de l'oxyfluorure de cérium.
  6. L'anode de la revendication 5, dans laquelle le revêtement de surface comprend au moins un composé de tantale, niobium, yttrium, lanthane, praséodyme et d'autres éléments des terres rares.
  7. Méthode de préparation du substrat d'anode d'une anode selon n'importe laquelle des revendications précédentes, comprenant le mélange de poudres d'oxyde de nickel, oxyde de cuivre et un composé de lithium, le chauffage à 900-1100°C, le refroidissement, le broyage, le pressage à froid et le frittage à 1000-1300°C pendant 30-40 heures.
  8. Méthode de récupération électrolytique de l'aluminium à partir de cryolithe fondue contenant de l'alumine, caractérisée par l'utilisation d'une anode telle que revendiquée dans n'importe laquelle des revendications de 1 à 7.
  9. La méthode de la revendication 8, dans laquelle le revêtement de surface est maintenu sur l'anode par la présence d'espèces de cérium dans la cryolithe fondue.
  10. Méthode de récupération électrolytique de l'aluminium à partir de cryolithe fondue contenant de l'alumine dans laquelle une anode telle que revendiquée dans n'importe laquelle des revendications de 1 à 7 est immergée, et dans laquelle le revêtement de la surface de l'anode comportant au moins un oxycomposé de terre rare est maintenu par la présence d'espèces de cérium dans la cryolithe fondue, la méthode comprenant le passage d'un courant d'électrolyse entre l'anode et la cathode pour dégager de l'oxygène et pour maintenir le revêtement de surface à l'anode et pour produire de l'aluminium à la cathode.
EP90904311A 1989-03-07 1990-03-06 Substrat d'anode revetu d'oxycomposes de terres rares Expired - Lifetime EP0422142B1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP90904311A EP0422142B1 (fr) 1989-03-07 1990-03-06 Substrat d'anode revetu d'oxycomposes de terres rares

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
EP89810175 1989-03-07
EP89810175 1989-03-07
EP90904311A EP0422142B1 (fr) 1989-03-07 1990-03-06 Substrat d'anode revetu d'oxycomposes de terres rares
PCT/EP1990/000364 WO1990010735A1 (fr) 1989-03-07 1990-03-06 Substrat d'anode revetu d'oxycomposes de terres rares

Publications (2)

Publication Number Publication Date
EP0422142A1 EP0422142A1 (fr) 1991-04-17
EP0422142B1 true EP0422142B1 (fr) 1995-05-24

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EP90904311A Expired - Lifetime EP0422142B1 (fr) 1989-03-07 1990-03-06 Substrat d'anode revetu d'oxycomposes de terres rares

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EP (1) EP0422142B1 (fr)
AT (1) ATE123079T1 (fr)
AU (1) AU622000B2 (fr)
CA (1) CA2030788A1 (fr)
DE (1) DE69019664T2 (fr)
ES (1) ES2072427T3 (fr)
NO (1) NO910306L (fr)
WO (1) WO1990010735A1 (fr)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1994024321A1 (fr) * 1993-04-19 1994-10-27 Moltech Invent S.A. Composants, produits par reaction micropyritique, de cellules de production d'aluminium
JPH10158017A (ja) * 1996-11-29 1998-06-16 Sharp Corp リチウムニッケル銅複合酸化物とその製造法及びその用途
CN101915073B (zh) * 2010-08-03 2012-08-15 江西稀有金属钨业控股集团有限公司 原地浸取注液工艺
CN109811368B (zh) * 2019-03-20 2021-03-16 武汉大学 用于熔盐电解体系的锂离子强化型惰性阳极及其制备方法

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB8301001D0 (en) * 1983-01-14 1983-02-16 Eltech Syst Ltd Molten salt electrowinning method
EP0192603B1 (fr) * 1985-02-18 1992-06-24 MOLTECH Invent S.A. Procédé et production d'aluminium, cellule de production d'aluminium et anode pour l'électrolyse de l'aluminium
DE3667305D1 (de) * 1985-05-17 1990-01-11 Moltech Invent Sa Formstabile anode fuer die schmelzflusselektrolyse und elektrolyseverfahren.
JPS62284095A (ja) * 1986-06-02 1987-12-09 Permelec Electrode Ltd 耐久性を有する電解用電極及びその製造方法
DE3879819T2 (de) * 1987-09-02 1993-07-08 Moltech Invent Sa Schmelzflusselektrolyse mit sich nicht aufbrauchender anode.

Also Published As

Publication number Publication date
AU5180390A (en) 1990-10-09
NO910306D0 (no) 1991-01-25
EP0422142A1 (fr) 1991-04-17
NO910306L (no) 1991-01-25
DE69019664T2 (de) 1995-09-21
DE69019664D1 (de) 1995-06-29
AU622000B2 (en) 1992-03-26
ATE123079T1 (de) 1995-06-15
ES2072427T3 (es) 1995-07-16
CA2030788A1 (fr) 1990-09-08
WO1990010735A1 (fr) 1990-09-20

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