EP0096001B1 - Dimensionally stable drained aluminum electrowinning cathode method and apparatus - Google Patents

Dimensionally stable drained aluminum electrowinning cathode method and apparatus Download PDF

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Publication number
EP0096001B1
EP0096001B1 EP83810196A EP83810196A EP0096001B1 EP 0096001 B1 EP0096001 B1 EP 0096001B1 EP 83810196 A EP83810196 A EP 83810196A EP 83810196 A EP83810196 A EP 83810196A EP 0096001 B1 EP0096001 B1 EP 0096001B1
Authority
EP
European Patent Office
Prior art keywords
aluminum
sheath
cathode
cell
electrowinning
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.)
Expired
Application number
EP83810196A
Other languages
German (de)
English (en)
French (fr)
Other versions
EP0096001A1 (en
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
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 filed Critical Eltech Systems Corp
Priority to AT83810196T priority Critical patent/ATE24937T1/de
Publication of EP0096001A1 publication Critical patent/EP0096001A1/en
Application granted granted Critical
Publication of EP0096001B1 publication Critical patent/EP0096001B1/en
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

  • the present invention relates to an electrode for electrowinning aluminum in an electrolysis cell, presenting a drained electrically conductive electrowinning surface to contents of the cell.
  • the invention also relates to an electrolysis cell for electrowinning aluminum and to a method of electrowinning aluminum.
  • Aluminum is commonly produced by the electrolysis of AI 2 0 3 at about 900°C to 1000°C.
  • Aluminum oxide being electrolyzed is generally dissolved in molten Na3AIF, (cryolite) that generally contains additives helpful to the electrolytic process such as CaF 2 , AIF 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 nonperpendicular 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.
  • 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.
  • the cathode or vulnerable cathodic current feeder often is in generally continuous contact with molten cryolite.
  • This 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.
  • EP-A-0 069 502 discloses an electrolytic cell for the production of aluminum wherein one or several layers of shapes, such as spheres are arranged on the cathode floor.
  • CH-A-362531 discloses cathode structures for electrowinning of aluminum, wherein the surface of the cathodes comprises either a carbon sponge to receive aluminum in its pores, or a saw-like surface forming recesses in which aluminum may collect.
  • the surface of the cathodes comprises either a carbon sponge to receive aluminum in its pores, or a saw-like surface forming recesses in which aluminum may collect.
  • no indication is given in this Patent as to how the aluminum in the pores of the sponge may be retained or in the case of saw-like surface how the portions between the recesses may be protected.
  • the pores of the sheath which extend through the thickness of the latter provide fluid pathways for the aluminum which enters and fills the sheath.
  • 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, AION, SiAION, AIN and AIB 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 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.
  • 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.
  • 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, SiAION, AIB 12' AIN, TiB 2 , and combinations thereof.
  • 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 34.9x12.4x2.3 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 175 micrometer (7 mils) or less in thickness in which grain boundary corrosion was observed, whereas the tile from the unprotected cathode is found to have suffered grain boundary type corrosion losses of between 25 and 30 micrometer 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.

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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 Dimensionally stable drained aluminum electrowinning cathode method and apparatus Expired EP0096001B1 (en)

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)

Publication Number Publication Date
EP0096001A1 EP0096001A1 (en) 1983-12-07
EP0096001B1 true EP0096001B1 (en) 1987-01-14

Family

ID=23485801

Family Applications (1)

Application Number Title Priority Date Filing Date
EP83810196A Expired EP0096001B1 (en) 1982-05-10 1983-05-09 Dimensionally stable drained aluminum electrowinning cathode method and apparatus

Country Status (7)

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

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1994013861A1 (en) * 1992-12-17 1994-06-23 Comalco Aluminium Limited Electrolysis cell for metal production
US5472578A (en) * 1994-09-16 1995-12-05 Moltech Invent S.A. Aluminium production cell and assembly
CA2448313A1 (en) * 2001-05-30 2002-12-05 Moltech Invent S.A. Aluminium electrowinning cells having a drained cathode bottom and an aluminium collection reservoir

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BE549859A (no) * 1955-07-28
GB1068801A (en) * 1964-04-09 1967-05-17 Reynolds Metals Co Alumina reduction cell
US4231853A (en) * 1979-04-27 1980-11-04 Ppg Industries, Inc. Cathodic current conducting elements for use in aluminum reduction cells
ZA824255B (en) * 1981-06-25 1983-05-25 Alcan Int Ltd Electrolytic reduction cells
CH648870A5 (de) * 1981-10-23 1985-04-15 Alusuisse Kathode fuer eine schmelzflusselektrolysezelle zur herstellung von aluminium.
JPS5948969A (ja) * 1982-09-14 1984-03-21 Toshiba Corp 超音波探触子用酸化物圧電材料

Also Published As

Publication number Publication date
NO159808B (no) 1988-10-31
AU1438983A (en) 1983-12-08
JPS58207386A (ja) 1983-12-02
CA1218958A (en) 1987-03-10
EP0096001A1 (en) 1983-12-07
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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