EP0096001A1 - Cathode dimensionellement stable à drainage pour l'obtention électrolytique d'aluminium, méthode et appareil pour sa fabrication - Google Patents

Cathode dimensionellement stable à drainage pour l'obtention électrolytique d'aluminium, méthode et appareil pour sa fabrication Download PDF

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Publication number
EP0096001A1
EP0096001A1 EP83810196A EP83810196A EP0096001A1 EP 0096001 A1 EP0096001 A1 EP 0096001A1 EP 83810196 A EP83810196 A EP 83810196A EP 83810196 A EP83810196 A EP 83810196A EP 0096001 A1 EP0096001 A1 EP 0096001A1
Authority
EP
European Patent Office
Prior art keywords
aluminum
electrowinning
cathode
sheath
cell
Prior art date
Legal status (The legal status 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 status listed.)
Granted
Application number
EP83810196A
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German (de)
English (en)
Other versions
EP0096001B1 (fr
Inventor
Ajit Y. Sane
Douglas J. Wheeler
Charles S. Kuivila
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Moltech Invent SA
Original Assignee
Eltech Systems Corp
Diamond Shamrock Corp
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 Eltech Systems Corp, Diamond Shamrock Corp filed Critical Eltech Systems Corp
Priority to AT83810196T priority Critical patent/ATE24937T1/de
Publication of EP0096001A1 publication Critical patent/EP0096001A1/fr
Application granted granted Critical
Publication of EP0096001B1 publication Critical patent/EP0096001B1/fr
Expired legal-status Critical Current

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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

Definitions

  • This invention relates to electrowinning of aluminum, particularly from cryolite and specifically to dimensionally stable electrodes for electrowinning aluminum and methods for their making.
  • Aluminum is commonly produced by the electrolysis of Al 2 O 3 at about 900°C to 1000°C.
  • Aluminum oxide being electrolyzed is generally dissolved in molten Na 3 AlF 6 (cryolite) that generally contains additives helpful to the electrolytic process such as CaF 2 , AlF 3 and LiF.
  • the cathode is comprised of a material relatively resistant to corrosive effects of contents of the cell.such as cryolite. This cathode often covers substantially the entire.floor of the cell which typically can be 6 feet wide by 18 or more feet in length.
  • Molten aluminum is a substance relatively resistant to corrosive and solvating effects in an aluminum electrowinning cell.
  • the cathode is an assembly including a cathodic current feeder covered by a pool of aluminum ranging in depth, depending upon the cell, from a few inches to in excess of a foot.
  • the aluminum pool functions effectively as a cathode and also serves to.protect current feeders made from materials less than fully resistant to cell contents. For example, unprotected graphite used' as a cathode can generate aluminum carbide an undesirable contaminant, while when used as a covered current feeder, no such contamination results.
  • These pool type cell cathode assemblies contain. conductive current collectors. Where these conductive current collectors are utilized in some cell configurations, these collectors contribute to an electrical current flow within the cell that is not perpendicular to the cell bottom. These nonperpendicula- electrical currents can interact with strong electromagnetic fields established around cells by current flow through busses and the like contributing to strong electromagnetic fluxes within the cell.
  • cryolite In cells employing a pool of aluminum covering the cathode floor of the cell, the cryolite, containing the A1 2 0 3 to be electrolyzed, floats atop this aluminum pool. The cell anodes are immersed in this cryolite layer.
  • cell anodes are positioned within the cryolite to be substantially above the normal or expected level of the interface between cryolite and aluminum within the cell.
  • a packing or filler material is introduced into the cell, generally to a depth normally occupied by the aluminum pool.
  • the packing tends to break up wave motion within the cell making prediction of the position of the interface between the aluminum pool and the cryolite more predictable. Where the interface position is more reliable, the anodes can be positioned somewhat closer to the interface, promoting incrementally reduced power consumption.
  • Another proposed solution has been to employ so-called drained cathodes in constructing aluminum electrolysis cells.
  • no pool of aluminum is maintained upon a cathode current feeder to function as a cathode; aluminum drains from the cathode as it forms to be recovered from a collection area.
  • the anode and the cathode may be quite closely arranged, realizing significant electrical power savings.
  • the cathode or vulnerable cathodic current feeder often is in generally continuous contact with molten cryolite.
  • aggressive material in contact with a graphite or carbon cathode, contributes to material losses from the cathode as well as the formation of aluminum . carbides, a dysfunctional impurity.
  • Carbon or graphite for use as a drained cathode material of construction is therefore of quite limited utility due to service life constraints.
  • the improved cathode of the present invention presents an electrically conductive surface to aluminum being electrowon thereon from molten cryolite contained within the cell.
  • the improvement comprises a sheath or membrane conforming closely to the presented electrowinning surface.
  • the sheath or membrane at least covers those portions of the electrowinning surface upon which aluminum is being electrowon.
  • the sheath or membrane is porous or apertured. This porosity is open, that is the apertures extend from one sheath or membrane surface through a thickness of the sheath to the other so as to form continuous fluid pathways between the surfaces.
  • These pores or apertures are of a size and configuration whereby aluminum is retained therein during electrolysis, in contact with the cathode presented surface but substantially stagnant within the pores or apertures.
  • the sheath or membrane is formed from a material substantially resistant to corrosion by contents of the aluminum electrolysis cell. It is preferred that the sheath or membrane be relatively nonelectrically conductive. It is desirable but not essential that the sheath or membrane be somewhat wettable by the molten aluminum being retained within the pores and thereby substantially coating the cathode with a film of aluminum.
  • a drained cathode used for aluminum electrowinning is therefore rendered relatively dimensionally stable by providing a substantially stagnant coating of molten aluminum upon the surface of such a cathode presented for the electrowinning process.
  • this coating or film retained upon the cathode electrowinning surface is not less than about 0.5 millimeter and not greater than about 10.0 millimeters.
  • Aluminum depositing upon the cathode in a depth greater than the sheath thickness continues to drain from the cathode surface to be recovered.
  • a drained cathode structure results from the practice of the instant invention.
  • Aluminum being electrolyzed fills the porous sheath thereby protecting the cathode substantially from contact with cryolite contained within the cell by providing a substantially stagnant aluminum coating upon the cathode.
  • the cathode is rendered less subject to corrosion and therefore substantially dimensionally stable. Yet a narrow separation between anode and cathode within the cell can be maintained since substantial wave motion within the relatively thin aluminum coating provided upon the cathode by the sheath is unlikely.
  • the drained electrowinning surface of a refractory hard metal boride, nitride, carbide or mixtures or combinations thereof has molten aluminum retained in substantially stagnant contact therewith by at least one piece of a substantially non-electrically conductive material selected from Si 3 N 4 , BN, AlON, SiAION, AIN and AlB 12 .
  • This material can either be an apertured sheath, as described previously, or could be made up of several discrete pieces of any suitable shape which are so arranged as to leave spaces in which the molten aluminum is retained in stagnant contact with the electrowinning surface.
  • the present invention provides a drained cathode structure for use in an aluminum electrolysis cell.
  • the drained cathode is substantially dimensionally stable.
  • an aluminum electrolysis cell 10 is shown generally in Figure 1.
  • the cell 10 includes an anode 12 and a cathode 14 contained within a housing 16 that includes a liner assembly 18.
  • the housing 16 includes a shell 25 usually made from a suitable or conventional substance like steel. Contained within the housing 16 is a liner assembly 18 that includes a layer 27 that generally resists aggressive attack upon the shell 25 by contents of the cell such as cryolite. In this best embodiment, the layer 27 functions also as a current conductor for supplying electrical current to the cathode 14. In equally preferred embodiments, this layer 27 can include embedded current conductors (not shown) for supplying electrical current to the cathode 14. Refractory materials and graphite are suitable for fabricating this layer 27, as are other suitable or conventional materials.
  • An insulating layer 29 is provided to resist heat flow from the cell 10. While a variety of well-known structures are available for making this insulating structure, commonly the insulating layer 29 is crystallized contents of the electrolytic cell.
  • the anode 12 is fabricated from any suitable or conventional material and immersed in a cryolite phase 30 contained in the cell. Since oxygen ions react at the anode, the material must be either resistant to attack by oxygen or should be made of a material that can be agreeably consumed by the oxygen. Typically carbon or graphite is utilized.
  • the anode-12 should be arranged for vertical movement within the cell so that a desired spacing can be maintained between the anode and cathode notwithstanding the anode being consumed by evolved . oxygen.
  • the cathode 14 is mounted in the cell in electrical contact with the conductive liner 27 or with conductors contained within the liner.
  • the cathode has a surface 31 for electrolyzing aluminum. This surface is covered by a sheath 33 or membrane having apertures 35 or being openly porous. The porosity should communicate through the thickness of the sheath 33 so that aluminum being formed by electrolysis fills the apertures 35 or pores. Once filled, the aluminum in the pores remains substantially stagnant with further electrolysis occurring not on the presented surface 31 but upon a surface 37 defined by the filled porous sheath 33. Aluminum forming at this surface drains away to recovery areas 40,41 from which it is removed. Aluminum is maintained in the recovery areas .40,41 to a depth necessary to insure immersion of edge portions 45 of the sheath 33.
  • the substance of the cathode is shielded from contact with cryolite.
  • cryolite Once shielded from the cryolite, a variety of materials can be used in making the cathode that would otherwise be undesirable due to elevated material losses in the aggressive cell environment.
  • refractory metal borides, carbides and nitrides are thereby rendered suitable for use in fabricating drained cathodes.
  • borides, carbides and nitrides of: titanium; zirconium; niobium; tungsten; tantalum; molybdenum; silicon; as well as mixtures thereof.
  • Titanium boride of at least 97.5 percent purity and TiB2, composited with other of the refractory metal boride carbides and nitrides are most preferred. While these materials can be prohibitively expensive where consumed or corroded at a significant rate in an aluminum cell, once under a thin protective aluminum coating, they may be employed for electrolyzing for extended periods with little material losses.
  • Any cathode surface selected should be both electrically conductive and at least significantly aluminum wettable.
  • the cathode includes a refractory metal boride, nitride, or carbide layer 47 applied to a suitable or conventional electrically conductive substrate 49 such as graphite.
  • a refractory metal boride, nitride, or carbide layer 47 applied to a suitable or conventional electrically conductive substrate 49 such as graphite.
  • the refractory layer 47 is TiB 2 and is protected by maintaining an aluminum film or coating on the TiB 2 surface using the sheath 33 or membrane, a particularly advantageous, substantially dimensionally stable cathode structure results.
  • the anode and cathode can be positioned closely opposing each other. This close positioning permits cell operation at a reduced cell voltage, the anode being positioned in molten cryolite only a short distance from the sheathed cathode upon which molten aluminum is being electrolytically generated.
  • the sheath 33 or membrane can be of any suitable or conventional construction having a plurality of pores or apertures traversing its thickness.
  • the precise configuration can be an openly porous rigid foam 51, a single layer honeycomb structure, an interconnected cellular structure, or a bar and grid arrangement 53 to name a few, depending upon the material of construction.
  • the pores or apertures form interstices in the sheath that fill with molten aluminum during electrolysis to coat the cathode surface 31.
  • the sheath 33 or membrane may be formed from any suitable or conventional material substantially inert to aggressive chemical attack in the cell environment. Electrical conductivity is not requisite.
  • the material used for the sheath will be at least slightly wettable by aluminum to assist in filling interstices in the sheath with molten aluminum.
  • Particularly useful for making the sheath or membrane are: Si 3 N 4 , BN, AION, SiAlON, AlB 12 , AlN, TiB 2 , and combinations thereof.
  • Tne sheath or membrane should substantially infiltrate with molten aluminum so that the molten aluminum forms a continuous electrical current pathway between the surface 31 of the. cathode and cryolite phase 30 surrounding the sheath. Yet aluminum filling the sheath or membrane interstices should remain substantially stagnant avoiding circulation leading to significant contact between the molten cryolite phase 30 and the cathode surface 31. Since areas of the cathode 14, below the aluminum liquid and in the recovery areas 40, 41 do not contribute substantially to aluminum electrowinning, they are not sheathed.
  • the thickness of the sheath should preferably be such as to hold a thickness of between about 0.5 millimeter to about 10.0 millimeters of molten aluminum substantially stagnant upon the cathode surface 31. Most preferably, this thickness is between 1.0 and 2.5 millimeters.
  • Desirable cross-sectional dimensions of individual pores or apertures by necessity vary widely as a function of aluminum, cryolite and sheath material interfacial tensions. Generally the more aluminum wettable the sheath material, the smaller the pores may be made, and the less wettable by aluminum the sheath material, the larger the pores may be in cross-section. The wide variance in these traits from one sheath material to another requires individual determination of acceptable pore sizes for each sheath material of construction and cryolite phase formulation. Generally a suitable pore cross-sectional area will be found between about 25 microns and 5000 microns. It is to be expected that the thickness of the sheath 33 will impact upon the desirable pore or aperture 35 cross-sectional dimension.
  • a TiB 2 tile of 99 + percent purity is used to form the refractory layer 47, adhered to a graphite substrate 49, thereby forming the cell cathode 14.
  • a sheath of grid configuration as shown in Figure 4 is placed upon the electrolyzing surface 31 of the cathode in one of the cells.
  • the sheath is a plate 34.9 x 12.4 x 2.3 millimeters drilled to include a plurality of 2.6 millimeter diameter apertures.
  • the sheath or grid is formed from BN.
  • the cells are filled with cryolite having the composition (percent by weight) and electrolysis is commenced using a cell voltage of between about 2.98-3.27 volts D.C. at a current density of 0.5 amperes per square centimeter of cathode surface.
  • Anode-cathode spacing is about 2.5 centimeters.
  • the cells are shut down and the TiB 2 tiles checked for material losses.
  • the tile from the cell having sheath protection providing a layer of aluminum on the refractory layer 47 surface 31 is found to have a layer of 7 mils or less in thickness in which grain boundry corrosion was observed, whereas the tile from the unprotected cathode is found to have suffered grain boundry type corrosion losses of between 25 and 30 microns in thickness.
  • current efficiency during aluminum electrolysis was found to be 66.8 percent, this efficiency customarily being substantially greater when applied to commercial scale cells.
  • the aluminum produced in the cell was found to be contaminated with 65 parts per million titanium.
  • Example 1 Cells identical to those of Example 1 are assembled and operated for 100 hours before being shut down for evaluation of tile corrosion.
  • the protected cathode is found to have suffered between 5 and 11 microns corrosion of the TiB 2 refractory layer 27, the unprotected cathode between 26 and 40 microns.

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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)
  • Secondary Cells (AREA)
EP83810196A 1982-05-10 1983-05-09 Cathode dimensionellement stable à drainage pour l'obtention électrolytique d'aluminium, méthode et appareil pour sa fabrication Expired EP0096001B1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT83810196T ATE24937T1 (de) 1982-05-10 1983-05-09 Masshaltende drainierfaehige kathode zur aluminiumgewinnung, verfahren und vorrichtung zu ihrer herstellung.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US37662882A 1982-05-10 1982-05-10
US376628 1982-05-10

Publications (2)

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EP0096001A1 true EP0096001A1 (fr) 1983-12-07
EP0096001B1 EP0096001B1 (fr) 1987-01-14

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EP83810196A Expired EP0096001B1 (fr) 1982-05-10 1983-05-09 Cathode dimensionellement stable à drainage pour l'obtention électrolytique d'aluminium, méthode et appareil pour sa fabrication

Country Status (7)

Country Link
EP (1) EP0096001B1 (fr)
JP (1) JPS58207386A (fr)
AT (1) ATE24937T1 (fr)
AU (1) AU571833B2 (fr)
CA (1) CA1218958A (fr)
DE (1) DE3369162D1 (fr)
NO (1) NO159808C (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1996008590A1 (fr) * 1994-09-16 1996-03-21 Moltech Invent S.A. Ensemble immerge dans un bain d'aluminium pour cellules de production d'aluminium
US5658447A (en) * 1992-12-17 1997-08-19 Comalco Aluminium Limited Electrolysis cell and method for metal production
WO2002097169A1 (fr) * 2001-05-30 2002-12-05 Moltech Invent S.A. Enceintes d'electro-extraction d'aluminium comprenant un fond de cathode draine et un reservoir de collecte d'aluminium

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH362531A (de) * 1955-07-28 1962-06-15 Montedison Spa Schmelzflusselektrolyseverfahren zur Herstellung von Aluminium und Ofen zur Durchführung des Verfahrens
GB1068801A (en) * 1964-04-09 1967-05-17 Reynolds Metals Co Alumina reduction cell
EP0069502A2 (fr) * 1981-06-25 1983-01-12 Alcan International Limited Améliorations dans les cellules de réduction électrolytique
WO1983001465A1 (fr) * 1981-10-23 1983-04-28 Alusuisse Cathode de cellule d'electrolyse de masse en fusion pour la preparation d'aluminium

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4231853A (en) * 1979-04-27 1980-11-04 Ppg Industries, Inc. Cathodic current conducting elements for use in aluminum reduction cells
JPS5948969A (ja) * 1982-09-14 1984-03-21 Toshiba Corp 超音波探触子用酸化物圧電材料

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH362531A (de) * 1955-07-28 1962-06-15 Montedison Spa Schmelzflusselektrolyseverfahren zur Herstellung von Aluminium und Ofen zur Durchführung des Verfahrens
GB1068801A (en) * 1964-04-09 1967-05-17 Reynolds Metals Co Alumina reduction cell
EP0069502A2 (fr) * 1981-06-25 1983-01-12 Alcan International Limited Améliorations dans les cellules de réduction électrolytique
WO1983001465A1 (fr) * 1981-10-23 1983-04-28 Alusuisse Cathode de cellule d'electrolyse de masse en fusion pour la preparation d'aluminium

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
CHEMICAL ABSTRACTS, vol. 79, no. 16, 22nd October 1973, page 549, no. 99896n, Columbus, Ohio, USA & SU - A - 378 521 (IRKUTSK ALUMINUM PLANT) 18-04-1973 *

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5658447A (en) * 1992-12-17 1997-08-19 Comalco Aluminium Limited Electrolysis cell and method for metal production
WO1996008590A1 (fr) * 1994-09-16 1996-03-21 Moltech Invent S.A. Ensemble immerge dans un bain d'aluminium pour cellules de production d'aluminium
WO2002097169A1 (fr) * 2001-05-30 2002-12-05 Moltech Invent S.A. Enceintes d'electro-extraction d'aluminium comprenant un fond de cathode draine et un reservoir de collecte d'aluminium

Also Published As

Publication number Publication date
NO159808B (no) 1988-10-31
AU1438983A (en) 1983-12-08
EP0096001B1 (fr) 1987-01-14
JPS58207386A (ja) 1983-12-02
CA1218958A (fr) 1987-03-10
AU571833B2 (en) 1988-04-28
DE3369162D1 (en) 1987-02-19
NO831650L (no) 1983-11-11
NO159808C (no) 1989-02-08
ATE24937T1 (de) 1987-01-15

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