WO2002097167A2 - Fonctionnement de cellules a extraction electrolytique d'aluminium pourvues d'anodes a base de metal - Google Patents

Fonctionnement de cellules a extraction electrolytique d'aluminium pourvues d'anodes a base de metal Download PDF

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Publication number
WO2002097167A2
WO2002097167A2 PCT/IB2002/001952 IB0201952W WO02097167A2 WO 2002097167 A2 WO2002097167 A2 WO 2002097167A2 IB 0201952 W IB0201952 W IB 0201952W WO 02097167 A2 WO02097167 A2 WO 02097167A2
Authority
WO
WIPO (PCT)
Prior art keywords
nickel
electrolyte
fluoride
aluminium
iron
Prior art date
Application number
PCT/IB2002/001952
Other languages
English (en)
Other versions
WO2002097167A3 (fr
Inventor
Thinh T. Nguyen
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
Application filed by Moltech Invent S.A. filed Critical Moltech Invent S.A.
Priority to CA002451574A priority Critical patent/CA2451574A1/fr
Priority to NZ529850A priority patent/NZ529850A/en
Priority to EP02735691A priority patent/EP1392893A2/fr
Publication of WO2002097167A2 publication Critical patent/WO2002097167A2/fr
Publication of WO2002097167A3 publication Critical patent/WO2002097167A3/fr
Priority to NO20035305A priority patent/NO20035305D0/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
    • 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
    • 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
    • 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
    • C25C3/18—Electrolytes

Definitions

  • This invention relates to operation of aluminium electrowinning cells with anodes made of an alloy of iron with nickel and/or cobalt whereby anode passivation by fluorination or oxidation of nickel and/or cobalt or anode corrosion by fluorination and dissolution of iron is inhibited or prevented, as well as aluminium production cells permitting such operation.
  • the technology for the production of aluminium by the electrolysis of alumina, dissolved in molten cryolite, at temperatures around 950°C is more than one hundred years old and still uses carbon anodes and cathodes.
  • metal anodes in commercial aluminium electrowinning cells would be new and drastically improve the aluminium process by reducing pollution and the cost of aluminium production.
  • 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 oxygen barrier layer. However, full protection of the alloy substrate was difficult to achieve.
  • OOO/06805 discloses an aluminium electrowinning anode having a metallic anode body which can be made of various alloys, for example a nickel-iron- copper alloy.
  • the surface of the anode body is oxidised by anodically evolved oxygen to form an integral electrochemically active oxide-based surface layer.
  • the oxidation rate of the anode body is equal to the rate of dissolution of the surface layer into the electrolyte. This oxidation rate is controlled by the thickness and permeability of the surface layer which limits the diffusion of anodically evolved oxygen therethrough to the anode body.
  • WO00/06803 (Duruz/de Nora/Crottaz) and O00/06804
  • WO 01/31086 discloses a cell having oxidised ⁇ ickel-iron alloy anodes and operating with an aluminium fluoride-comprising electrolyte at reduced temperature, e.g. 730° to 910°C. It is mentioned that the electrolyte may contain MgF 2 and/or LiF in an amount of up to 5 weight% each.
  • 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 for commercial aluminium production because their lifetime was too short and needs to be increased.
  • the invention relates to a method of inhibiting fluorination, corrosion and passivation of a metal-based anode having a nickel-iron alloy outer portion covered with an integral oxide surface layer facing a cathode in an aluminium fluoride-comprising molten electrolyte.
  • This method comprises maintaining an amount of at least one basic fluoride in the electrolyte to reduce the acidic activity of aluminium fluoride thereby inhibiting fluorination, corrosion of iron and passivation of nickel of the nickel-iron alloy outer portion.
  • the nickel of the nickel-iron alloy outer portion of the anode is wholly or predominantly substituted by cobalt which behaves substantially like nickel under the cell operating conditions discussed hereafter.
  • This method is particularly appropriate when operating with an electrolyte at reduced temperature, in particular to reduce the solubility of metal oxides when using metal-based anodes as disclosed in WO00/06802 (Duruz/de Nora/Crottaz) .
  • aluminium fluoride is added to the electrolyte.
  • the addition of aluminium fluoride increases the acidity of the electrolyte and promotes fluorination, corrosion of iron and passivation of nickel of the nickel-iron alloy outer portion by exposure to fluorides and/or fluorine which are derived from the aluminium fluoride and which diffuse in the integral oxide surface layer.
  • the Lewis acidity of the electrolyte and thus the activity of fluorides is reduced.
  • corrosion of iron and passivation of nickel of the anode can be inhibited and even stopped by replacing at least part of the aluminium fluoride by a basic fluoride.
  • the acid aluminium fluoride (AlF 3 ) of a conventional electrolyte vaporises and corrodes the iron of the anode to form volatile FeAlF 5 and attacks the nickel of the anode to form in the presence of anodically evolved oxygen alumina (Al 2 0 3 ) and nickel fluoride (NiF) that passivates the surface of the anode.
  • the acidity of the aluminium fluoride is neutralised by combination therewith (AlF 3 + MF -> A1F 4 " + M + ) , which inhibits vaporisation of aluminium fluoride and the resulting corrosion and/or passivation of the anode.
  • MF basic fluoride
  • Suitable basic fluorides of the invention are fluorides of metals of group IA and IIA of the Periodic Tables, in particular fluorides of calcium, lithium and magnesium.
  • the electrolyte may comprise calcium fluoride, preferably in such an amount that the density of the electrolyte is below the density of molten aluminium, typically up to 7 weight%, preferably from 1 to 6%, in particular 3 to 5%, calcium fluoride.
  • the electrolyte can alternatively or additionally comprise up to 4 weight%, preferably 1 to 3 weight% in particular 1.5 to 2.5 weight%, of lithium fluoride.
  • each added weight percent of calcium fluoride reduces the temperature of the electrolyte by about 1°C.
  • each added weight percent of lithium fluoride reduces the electrolyte's melting point by about 5°C.
  • the electrolyte should not comprise more than 24 weight% aluminium fluoride, in addition to cryolite.
  • the aluminium fluoride-content is comprised in the range from 14 to 22 weight% .
  • an adjusted amount of basic fluorides must be added to reduce the melting point of the electrolyte and de-acidify the electrolyte.
  • the melting point of the electrolyte is lowered even more by adding aluminium fluoride.
  • Each additional weight percent of aluminium fluoride in the electrolyte corresponds to a reduction of about 10°C of the electrolyte's melting point.
  • Lowering the electrolyte's temperature increases the required amount of aluminium fluoride and thus increases the required amount of one or more basic fluorides to neutralise the electrolyte.
  • the method of the invention may be used with an electrolyte which is at a temperature in the range from 880° to 940°C, preferably from 890° to 930°C.
  • the electrolyte may consist essentially of sodium fluoride, aluminium fluoride and the basic fluoride(s), containing dissolved alumina.
  • the cumulated amount of basic fluorides should be of at least about 5 to 7 weight% to avoid corrosion (iron) and passivation (nickel) , whereas at about 930°-940°C the required cumulated amount of basic fluorides is much lower, typically from 3 to 5 weight% .
  • the dissolution of the integral surface layer of the anode can be inhibited by permanently and uniformly substantially saturating the electrolyte with alumina.
  • the anode is coated with a protective layer of one or more cerium compounds, in particular cerium oxyfluoride.
  • the method of the invention advantageously comprises maintaining an amount of cerium species in the electrolyte to maintain the protective layer, as disclosed in the above-mentioned
  • the nickel-iron alloy outer portion may comprise up to or even more than 50 weight% iron. Also, the nickel- iron alloy outer portion can have an iron/nickel weight ratio in the range of 1 to 3.
  • the nickel-iron alloy outer portion of the anode comprises inclusions at the grain boundaries of the nickel-iron alloy for providing a controlled diffusion of iron from the outer portion to the integral oxide surface layer.
  • the inclusions at the grain boundaries may comprise at least one oxide of a rare earth metal that is substantially insoluble with nickel and iron, in particular an oxide of an Actinide, such as scandium or yttrium, and/or of a Lanthanide, such as cerium or ytterbium.
  • the inclusions at the grain boundaries may also comprise at least one oxide of a transition metal that has an affinity for oxygen which is greater than the oxygen affinity of iron and nickel, such as an oxide of aluminium, titanium, tantalum and chromium.
  • the inclusions at the grain boundaries can comprise at least one metal oxide, in particular the above rare earth metal oxide or the above transition metal oxide, that is present as one or more mixed oxides with iron and/or nickel.
  • the nickel-iron alloy outer portion of the anode may further comprise copper which improves the adherence and coherence of the integral oxide surface layer.
  • the anode can have an electrically conductive inner core, in particular made of nickel, or a nickel-iron alloy body which is covered with the integral oxide layer.
  • the invention also relates to a method of producing aluminium using a metal-based anode having a nickel-iron alloy outer portion covered with an integral oxide surface layer facing a cathode, in particular a drained cathode, in an aluminium fluoride-comprising molten electrolyte.
  • This method comprises dissolving alumina in the electrolyte, passing an electrolysis current between the metal-based anode and the cathode to evolve oxygen on the anode and produce aluminium on the cathode, and inhibiting fluorination, corrosion of iron and passivation of nickel of the metal-based anode by the above described method.
  • a further aspect of the invention relates to the use in an aluminium fluoride-comprising electrolyte for the electrowinning of aluminium from alumina dissolved in the electrolyte, of at least one basic fluoride for inhibiting fluorination, corrosion of iron and passivation of nickel of a nickel-iron alloy outer portion of a metal- based anode used in the electrolyte.
  • the basic fluoride (s) may be selected from fluorides of calcium and lithium.
  • a further aspect of the invention relates to a cell for the electrowinning of aluminium from alumina dissolved in a molten electrolyte comprising aluminium fluoride and at least one basic fluoride.
  • This cell comprises a metal-based anode having a nickel-iron alloy outer portion covered with an integral oxide surface layer in the molten electrolyte, and means for monitoring the amount of basic fluoride (s) in the electrolyte and for adjusting this amount such that it reduces the acidic activity of aluminium fluoride and inhibits fluorination, corrosion of iron and passivation of nickel of the nickel- iron alloy outer portion.
  • these means comprise a device for measuring the composition of the electrolyte, in particular the aluminium fluoride and the basic fluoride content, and/or a system or feeder for supplying aluminium fluoride as well as the basic fluoride as required according to the measured electrolyte composition.
  • An anode was made from a nickel-iron alloy rod which consisted of 50 weight% nickel, 0.3 weight% manganese, 0.5 weight silicon and 1.7 weight% yttrium, the balance being iron, and which was pre-oxidised in air at a temperature of 1100°C for 3 hours.
  • the anode was immersed in an electrolytic bath at 930°C of a laboratory scale cell consisting of 18 weight% aluminium fluoride, 6 weight% calcium fluoride, 4 weight% alumina, the balance being cryolite (melting point at 906°C) .
  • the alumina concentration was maintained at a substantially constant level throughout the test by adding alumina at a rate adjusted to compensate the cathodic aluminium reduction.
  • the test was run at a current density of about 0.6 A/cm 2 , and the electrical potential of the anode remained substantially constant at 4.2 volts throughout the test.
  • the used anode was cut perpendicularly to the anode operative surface and the resulting section of the used anode was subjected to microscopic examination.
  • Example 1 An anode as in Example 1 was immersed in an electrolytic bath at 930°C of a laboratory scale cell consisting of 18 weight% aluminium fluoride, 6 weight% alumina, the balance being cryolite (melting point at
  • the outer portion of the nickel-iron alloy underlying the oxide surface layer had a corrosion- porosity produced by internal oxidation and reaction with AlF 3 forming volatile FeAlF 5 . This outer portion had a thickness of about 1000 micron.
  • the diameter of the overall metallic inner part underlying the oxide surface layer of the anode had been reduced by 400 micron. This corresponds to a wear rate by oxidation of about 50 micron per day.
  • Example 1 can be modified as shown in the following table, each line showing at a given temperature a suitable composition, the balance being cryolite (Na 3 AlF 6 ) and alumina (A1 2 0 3 ) :

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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

L'invention concerne un procédé permettant d'inhiber la fluoration et la passivation d'une anode à base de métal pourvue d'une partie extérieure en alliage constituée de fer et de nickel et/ou de cobalt et recouverte par une couche de surface en oxyde solidaire, disposée face à une cathode, dans un électrolyte fondu contenant du fluorure d'aluminium. Le procédé selon l'invention consiste à maintenir dans l'électrolyte une quantité d'au moins un fluorure basique, tel que du fluorure de calcium ou de lithium, de sorte à réduire l'activité acide du fluorure d'aluminium, ce qui inhibe la fluoration, la corrosion du fer et la passivation du nickel et/ou du cobalt sur la partie extérieure en alliage.
PCT/IB2002/001952 2001-05-30 2002-05-28 Fonctionnement de cellules a extraction electrolytique d'aluminium pourvues d'anodes a base de metal WO2002097167A2 (fr)

Priority Applications (4)

Application Number Priority Date Filing Date Title
CA002451574A CA2451574A1 (fr) 2001-05-30 2002-05-28 Fonctionnement de cellules a extraction electrolytique d'aluminium pourvues d'anodes a base de metal
NZ529850A NZ529850A (en) 2001-05-30 2002-05-28 Operation of aluminium electrowinning cells having metal-based anodes
EP02735691A EP1392893A2 (fr) 2001-05-30 2002-05-28 Fonctionnement de cellules a extraction electrolytique d'aluminium pourvues d'anodes a base de metal
NO20035305A NO20035305D0 (no) 2001-05-30 2003-11-28 Drift av aluminium elektroutvinningsceller med metallbaserte anoder

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IBPCT/IB01/00954 2001-05-30
IB0100954 2001-05-30

Publications (2)

Publication Number Publication Date
WO2002097167A2 true WO2002097167A2 (fr) 2002-12-05
WO2002097167A3 WO2002097167A3 (fr) 2003-03-13

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PCT/IB2002/001952 WO2002097167A2 (fr) 2001-05-30 2002-05-28 Fonctionnement de cellules a extraction electrolytique d'aluminium pourvues d'anodes a base de metal

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Country Link
EP (1) EP1392893A2 (fr)
CA (1) CA2451574A1 (fr)
NO (1) NO20035305D0 (fr)
NZ (1) NZ529850A (fr)
WO (1) WO2002097167A2 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005017234A1 (fr) 2003-08-14 2005-02-24 Moltech Invent S.A. Cellule d'extraction electrolytique d'un metal comprenant un purificateur electrolytique
CN115073190A (zh) * 2022-06-23 2022-09-20 登封市宏源耐火材料有限公司 一种阳极炉出铜溜槽用铝镁锆质浇注料及其制备方法

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4455211A (en) * 1983-04-11 1984-06-19 Aluminum Company Of America Composition suitable for inert electrode
WO1999041431A1 (fr) * 1998-02-11 1999-08-19 Northwest Aluminum Technology Dissolution catalytique d'oxyde d'aluminium au cours d'une reduction electrolytique de l'alumine
WO2000006804A1 (fr) * 1998-07-30 2000-02-10 Moltech Invent S.A. Anodes a base d'un alliage nickel-fer, destinees a des cellules d'extraction electrolytique d'aluminium
US6030518A (en) * 1997-06-26 2000-02-29 Aluminum Company Of America Reduced temperature aluminum production in an electrolytic cell having an inert anode
WO2001031086A1 (fr) * 1999-10-26 2001-05-03 Moltech Invent S.A. Cellule fonctionnant a faible temperature pour extraction electrolytique d'aluminium
WO2001042535A1 (fr) * 1999-12-09 2001-06-14 Moltech Invent S.A. Extraction electrolytique d'aluminium a l'aide d'anodes metalliques

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4455211A (en) * 1983-04-11 1984-06-19 Aluminum Company Of America Composition suitable for inert electrode
US6030518A (en) * 1997-06-26 2000-02-29 Aluminum Company Of America Reduced temperature aluminum production in an electrolytic cell having an inert anode
WO1999041431A1 (fr) * 1998-02-11 1999-08-19 Northwest Aluminum Technology Dissolution catalytique d'oxyde d'aluminium au cours d'une reduction electrolytique de l'alumine
WO2000006804A1 (fr) * 1998-07-30 2000-02-10 Moltech Invent S.A. Anodes a base d'un alliage nickel-fer, destinees a des cellules d'extraction electrolytique d'aluminium
WO2001031086A1 (fr) * 1999-10-26 2001-05-03 Moltech Invent S.A. Cellule fonctionnant a faible temperature pour extraction electrolytique d'aluminium
WO2001042535A1 (fr) * 1999-12-09 2001-06-14 Moltech Invent S.A. Extraction electrolytique d'aluminium a l'aide d'anodes metalliques

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005017234A1 (fr) 2003-08-14 2005-02-24 Moltech Invent S.A. Cellule d'extraction electrolytique d'un metal comprenant un purificateur electrolytique
CN115073190A (zh) * 2022-06-23 2022-09-20 登封市宏源耐火材料有限公司 一种阳极炉出铜溜槽用铝镁锆质浇注料及其制备方法
CN115073190B (zh) * 2022-06-23 2023-04-21 登封市宏源耐火材料有限公司 一种阳极炉出铜溜槽用铝镁锆质浇注料及其制备方法

Also Published As

Publication number Publication date
EP1392893A2 (fr) 2004-03-03
NZ529850A (en) 2005-11-25
WO2002097167A3 (fr) 2003-03-13
NO20035305L (no) 2003-11-28
NO20035305D0 (no) 2003-11-28
CA2451574A1 (fr) 2002-12-05

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