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WO2000040783A1 - Anodes en acier haute resistance faiblement allie pour cellules d'extraction electrolytique de l'aluminium - Google Patents

Anodes en acier haute resistance faiblement allie pour cellules d'extraction electrolytique de l'aluminium Download PDF

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Publication number
WO2000040783A1
WO2000040783A1 PCT/IB2000/000028 IB0000028W WO0040783A1 WO 2000040783 A1 WO2000040783 A1 WO 2000040783A1 IB 0000028 W IB0000028 W IB 0000028W WO 0040783 A1 WO0040783 A1 WO 0040783A1
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WO
WIPO (PCT)
Prior art keywords
anode
layer
electrolyte
aluminium
iron
Prior art date
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Ceased
Application number
PCT/IB2000/000028
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English (en)
Inventor
Vittorio De Nora
Jean-Jacques Duruz
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Moltech Invent SA
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Moltech Invent SA
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 SA filed Critical Moltech Invent SA
Priority to DE60000436T priority Critical patent/DE60000436T2/de
Priority to EP00900036A priority patent/EP1149188B1/fr
Priority to CA002360094A priority patent/CA2360094C/fr
Priority to AU17932/00A priority patent/AU1793200A/en
Publication of WO2000040783A1 publication Critical patent/WO2000040783A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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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

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 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.
  • 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.
  • 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. Objects of the Invention
  • 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
  • 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 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
  • PCT/IB99/00017 and PCT/IB99/00018 both in the name of de
  • 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.
  • this type of anode may be maintained dimensionally stable under specific cell operating conditions.
  • even the least soluble anode material releases excessive amounts of constituents into the bath, which leads to an excessive contamination of the product aluminium.
  • 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 PCT/IB98/00161 (de Nora/Duruz) or by periodically moving the anodes as described in co-pending application PCT/IB98/00162 (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 - In ⁇
  • 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 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.
  • aluminium was produced in a laboratory scale cell equipped with an anode according to the invention.
  • the anode was made with a low-carbon high-strength
  • HSLA HSLA steel containing nickel, copper and silicon in a total amount of less than 1.5 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.

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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 une anode de cellule d'extraction électrolytique de l'aluminium comprenant un corps ou une couche en acier haute résistance faiblement allié à faible teneur en carbone dont la surface est oxydée afin de former une couche extérieure cohérente et adhésive à base d'oxyde de fer. La surface de cette couche extérieure est électrochimiquement active de façon à permettre l'émission d'oxygène. La couche à base d'oxyde de fer présente une solubilité réduite dans l'électrolyte fondu. Lors de l'utilisation, l'épaisseur de la couche à base d'oxyde de fer est suffisante pour réduire ou empêcher la diffusion d'oxygène dans le corps ou la couche d'acier depuis la surface électrochimiquement active. Pendant le fonctionnement de la cellule, on peut conserver la stabilité des dimensions de l'anode en saturant l'électrolyte avec des constituants de l'anode.
PCT/IB2000/000028 1999-01-08 2000-01-10 Anodes en acier haute resistance faiblement allie pour cellules d'extraction electrolytique de l'aluminium Ceased WO2000040783A1 (fr)

Priority Applications (4)

Application Number Priority Date Filing Date Title
DE60000436T DE60000436T2 (de) 1999-01-08 2000-01-10 Anoden aus hochfestem, niedriglegiertem stahl für zellen zur aluminium-schmelzelektrolyse
EP00900036A EP1149188B1 (fr) 1999-01-08 2000-01-10 Anodes en acier haute resistance faiblement allie pour cellules d'extraction electrolytique de l'aluminium
CA002360094A CA2360094C (fr) 1999-01-08 2000-01-10 Anodes en acier haute resistance faiblement allie pour cellules d'extraction electrolytique de l'aluminium
AU17932/00A AU1793200A (en) 1999-01-08 2000-01-10 High-strength low-alloy steel anodes for aluminium electrowinning cells

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IB9900015 1999-01-08
IBPCT/IB99/00015 1999-01-08

Publications (1)

Publication Number Publication Date
WO2000040783A1 true WO2000040783A1 (fr) 2000-07-13

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PCT/IB2000/000028 Ceased WO2000040783A1 (fr) 1999-01-08 2000-01-10 Anodes en acier haute resistance faiblement allie pour cellules d'extraction electrolytique de l'aluminium

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EP (1) EP1149188B1 (fr)
AU (1) AU1793200A (fr)
CA (1) CA2360094C (fr)
DE (1) DE60000436T2 (fr)
ES (1) ES2180506T3 (fr)
WO (1) WO2000040783A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002070786A1 (fr) * 2001-03-07 2002-09-12 Moltech Invent S.A. Anodes a base de metal pour cellules de production d'aluminium
CN108588567A (zh) * 2018-07-04 2018-09-28 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
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

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5510008A (en) * 1994-10-21 1996-04-23 Sekhar; Jainagesh A. Stable anodes for aluminium production cells

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5510008A (en) * 1994-10-21 1996-04-23 Sekhar; Jainagesh A. Stable anodes for aluminium production cells

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002070786A1 (fr) * 2001-03-07 2002-09-12 Moltech Invent S.A. Anodes a base de metal pour cellules de production d'aluminium
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
CN108588567A (zh) * 2018-07-04 2018-09-28 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

Also Published As

Publication number Publication date
CA2360094A1 (fr) 2000-07-13
AU1793200A (en) 2000-07-24
EP1149188A1 (fr) 2001-10-31
CA2360094C (fr) 2005-11-29
DE60000436D1 (de) 2002-10-17
EP1149188B1 (fr) 2002-09-11
ES2180506T3 (es) 2003-02-16
DE60000436T2 (de) 2003-05-15

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