EP0092525A1 - Nichtbenetzbare Füllkörper für eine Elektrolysezelle zur Herstellung von Aluminium - Google Patents

Nichtbenetzbare Füllkörper für eine Elektrolysezelle zur Herstellung von Aluminium Download PDF

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Publication number
EP0092525A1
EP0092525A1 EP83810164A EP83810164A EP0092525A1 EP 0092525 A1 EP0092525 A1 EP 0092525A1 EP 83810164 A EP83810164 A EP 83810164A EP 83810164 A EP83810164 A EP 83810164A EP 0092525 A1 EP0092525 A1 EP 0092525A1
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EP
European Patent Office
Prior art keywords
aluminum
cathode
pool
cryolite
molten
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.)
Withdrawn
Application number
EP83810164A
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English (en)
French (fr)
Inventor
D.J. Wheeler
M.G. Konicek
R.K. Sen
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.)
Diamond Shamrock Corp
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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 Diamond Shamrock Corp filed Critical Diamond Shamrock Corp
Publication of EP0092525A1 publication Critical patent/EP0092525A1/de
Withdrawn legal-status Critical Current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 the metal electrowinning cells, and particularly to cells for the electrowinning of aluminum. More specifically, this invention relates to cathode arrangements for use in these aluminum electrowinning cells.
  • Aluminum is commonly produced by electrowinning aluminum from Al203 (alumina) at about 900°C to 1,000°C. Aluminum oxide being electrowon frequently is dissolved in molten Na 3 AlF 6 (cryolite) that generally contains other additives helpful to the electrowinning process such as CaF 2 , AlF 3 and LiF.
  • anode and cathode are arranged in vertical spaced configuration within the cell, the anode being uppermost. Reduction of aluminum oxide to aluminum occurs at the cathode which customarily is positioned at the bottom or floor of the cell. Oxygen is electrochemically disassociated from Al 2 O 3 , in most commercial cells combining with carbonacious material comprising the cell anode and being emitted from the cell as CO and C0 2 .
  • Cryolite is an aggressive chemical necessitating use of a cathode material substantially resistant to this aggressive cryolite.
  • a cathode material substantially resistant to this aggressive cryolite.
  • One popular choice is the use of molten aluminum as a cathode. While use of other cathodes such as bare graphite in contact with cryolite has been contemplated, formation of undesirable by-products such as aluminum carbides has discouraged use. In many commercial cells, 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.
  • the cathode In utilizing aluminum for cathode purposes in a cell, typically the cathode is included in an assembly of 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, but generally about 6 inches.
  • 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.
  • These aluminum pool type cell cathode assemblies contain conductive current collectors. Where these conductive current collectors are utilized in certain 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 magnetic fields established around cells by current flow through busses and the like to contribute 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 Al 2 0 3 to be electrolyzed, floats atop this aluminum pool. The cell anodes are immersed in this cryolite layer.
  • the cathode particularly where non wettable by molten aluminum is in generally continuous contact with molten cryolite.
  • This aggressive material in contact with a graphite or carbon cathode, can contribute to material loss from the cathode and can trigger formation of such undesirables as aluminum carbides.
  • carbon or graphite for use as a drained cathode material of construction is therefore of quite limited utility due to possible service life constraints and carbide contaminant formation.
  • the molten cryolite contributes to TiB 2 corrosion by fluxing reaction products of TiB 2 and aluminum generated near grain boundaries of the material. While it is known that in aluminum electrowinning cells essentially pure TiB 2 does not exhibit as substantial a corrosion susceptibility as does lower purity TiB 2 , cost and availability factors seriously limit the use of TiB 2 sufficiently pure to withstand the aggressive cell environment.
  • the present invention provides an improved cathode assembly for use in an aluminum electrowinning cell.
  • the improved cathode is intended for use in an aluminum electrowinning cell having an anode and cathode in vertical spaced relationship within the cell, the anode being immersed in a molten cryolite pool.
  • the improved cathode assembly includes a cathodic current feeder arranged in vertical spaced. relationship with the anode.
  • a pool of molten aluminum covers the cathodic current feeder with the molten cryolite in which the anode is immersed being atop the molten aluminum.
  • Immersed in the molten aluminum is a packed bed of loose packing elements.
  • the elements are of a refractory material non-wettable by aluminum, and are substantially resistant to attack by molten aluminum and cryolite while immersed in the aluminum.
  • the loose packed bed elements are disposed atop the current feeder relatively uniformly to a predetermined depth not greater than the depth of the aluminum pool atop the cathodic current feeder.
  • the packing elements should be each sufficiently large to permit continuous electrical current pathways of molten aluminum between the cathodic current feeder and the molten cryolite atop the molten aluminum, notwithstanding the packing elements being non-wettable by molten aluminum. That is, the packing should not be so densely arranged as to preclude the presence of molten aluminum from substantial void volume within the packed bed by virtue of surface tension.
  • the packing functions to suppress wave motion in the molten aluminum cathode resulting from magnetic flux from electrical currents flowing non-perpendicularly to the flow of the aluminum electrowinning cell.
  • the anode, immersed in the molten cryolite can be arranged to be in closer proximity to the molten aluminum cathode. Voltage required for aluminum electrowinning is reduced by this anode cathode arrangement in close proximity, and power requirements for cell operation are correspondingly reduced.
  • Fig. 1 is a cross sectional representation of an aluminum electrowinning cell embodying the loosely packed bed elements of the invention.
  • Fig. 1 shows in cross section a representation of an aluminum electrowinning cell 10.
  • the cell includes a base 14 and sidewalls 16, 18, generally of steel, surrounding the cell.
  • the cell includes a cathodic current feeder 20 and anodes 22, 24.
  • the base and sidewalls enclose the cathodic current feeder 20 which in this best embodiment functions also as a cell liner. Portions 26 of the liner define a floor of the cell. Well known refractory materials and graphite are suitable for fabricating this.current feeder 20, as are other suitable or conventional materials.
  • a current buss 28, embedded in the feeder 20 provides electrical current for distribution within the cell 10. The buss 28 is connected to an external source of electrical current (not shown).
  • the anodes 22, 24 are arranged in vertical spaced relationship with the current feeder portions 26 defining the floor of the cell.
  • the anodes 22,24 are separated from the cathodic current feeder by two pools 30, 32 of molten material.
  • One pool 30 comprises essentially molten aluminum. This molten aluminum pool functions as a cathode for electrowinning of aluminum within the cell. While the pool consists essentially of aluminum, impurities customarily associated with aluminum produced electrolytically may be present.
  • the remaining pool 32 is comprised of molten cryolite, Na 3 A1F 6 , containing dissolved A1 2 0 3 .
  • a number of cryolite formulations that include additives such as CaF 2 , LiF, and AlF 3 for enhancing electrolysis of the Al 2 O 3 to aluminum are possible and are contemplated as being utilized within the scope of the invention.
  • This cryolite layer being less dense than the molten aluminum, floats upon the aluminum.
  • An interface 36 separates the molten aluminum 30 from the molten cryolite 32.
  • An insulating layer 39 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 39 is crystallized contents of the electrolytic cell.
  • the anodes 22, 24 are fabricated from any suitable or conventional material and immersed in a cryolite phase 32 contained in the cell. Since oxygen is released in some form at the anode, the anode material must be either resistant to attack by oxygen or should be made of a material that can be agreeably reacted with the evolving oxygen, preferably producing a lower anode half cell voltage by virtue of reactive depolarization. Typically, carbon or graphite is utilized.
  • the anodes 22, 24 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.
  • a packed bed 41 of loose elements 42 is positioned in the cell, in the molten aluminum pool 30.
  • These elements are formed of a substance substantially non-wettable by aluminum.
  • the elements are maintained in the molten aluminum at a level at or below the interface between the molten aluminum and molten cryolite, the depth to which the elements are packed being substantially uniform across the cell.
  • the elements should be not further than 5 centimeters from the interface, but should not extend substantially above the interface, particularly where the elements 42 may be subject to aggressive attack by the cryolite.
  • the packed bed elements can be of any shape. It is preferred that the shapes provide, when packed, substantial interstices through the packed bed to assure that aluminum fills gaps in the packing to maintain uniform electrical conductivity through the packed pool of aluminum. Particularly, packing in the form of berl saddles, Intalox saddles, Raschig rings and equiaxed shapes such as cylinders and spheres are much preferred; however randomly shaped packing, blocks or bricks may also suffice.
  • the packing is fabricated from a material substantially non-wettable by molten aluminum, with alumina, Al 2 O 3 , being much preferred. Since alumina is soluble in the molten cryolite, and since aluminum is being electrolyzed from alumina dissolved in the cryolite layer 32, it is important that the alumina packing be maintained reliably beneath the interface. Immersion in the molten aluminum shields the packing elements from aggressive attack by the cryolite.
  • suitable materials for fabrication of the packing include AlN, A1 4 C 3 , AlB 12 , BN, SiAlON, AlB 2 , ZrO 2 , Hf0 2 , ThO 2 , mixtures of these refractory materials and mixtures with aluminum oxide. Particularly, preferred are Al 2 O 3 , Al 4 C 3 , SiAlON, ZrO 2 , HfO 2 and ThO 2 , mixtures thereof, and mixtures thereof with Al 2 O 3 .
  • Electrical conductivity of the packing elements is relatively unimportant. Conductivity pathways through the aluminum immersing the packing provide the substantial current routes between the cathodic current feeder and the interface 36 where active electrowinning occurs. Where the packing provides interstices too small to permit a substantial number of electrical pathways through the aluminum non-wettable packed bed from the current feeder to the interface, than an unacceptably elevated voltage in operating the cell results.
  • the packing elements 42 arranged in the cell and immersed in the molten aluminum function to suppress wave formation and propagation in the molten aluminum. Reduced wave action permits quite close anode spacing to the molten aluminum cathode interface 36. This close spacing reduces voltage requirements in operating the cell, thereby reducing power consumption. In order to dampen effectively wave formation in the molten aluminum, it is preferred that the packing be quite close to the-interface while remaining immersed in the molten aluminum. Spacings between the packing and the interface of greater than about 5 centimeters generally will provide less than satisfactory performance in dampening wave motion.
  • non-wettable materials such as alumina for packing materials can offer a substantial cost advantage over the use of expensive wettable materials such as titanium boride.
  • electrical conductivity in the packing material is not required.
  • suitable packing elements 42 range in size from about .1 centimeters to about 5 centimeters, with packing in a size range of from 1 centimeter to 3 centimeters being preferred.
  • Alumina tubes fabricated from McDanel Grade 998 alumina, some tubes 39 millimeter (mm) O.D. x 90 mm tall, having a 2 mm wall and some 12.7 mm O.D. x 90 mm tall and having a 2 mm wall were inserted vertically into a laboratory cell containing 600 grams of molten aluminum, interfacing with a thin layer of molten cryolite mix. The tubes protruded slightly through the interface. The cell was held at 1,000°C for one hour; then cooled to room temperature and the solid aluminum containing the alumina tubes was cross-sectioned. It was found that aluminum had completely encapsulated the alumina and filled the tubes.
  • alumina had fractured, it is believed, due to thermal shock and a small section of the 12.7 mm O.D. tubing was found laying horizontally at the bottom of the cell, completely filled by aluminum. Sections of the alumina tubes protruding through the aluminum into the cryolite had the typical appearance of poor wetting' by aluminum with an apparent contact angle greater than 90°.
  • Raschig rings of alumina, McDanel Grade 998, 29 mm O.D. x 7 mm with a wall thickness of 2 mm were placed in an alumina crucible 54 mm O.D. x 45 mm deep and covered with 150 grams of aluminum shot, Alfa 3.2 mm.
  • the crucible was fitted with an alumina covered graphite current feeder to form a cathode assembly.
  • the cathode assembly was inserted into a larger alumina crucible, 73 mm I.D. x 152 mm tall, with a 4 mm wall, and 500 grams of cryolite mix was added to cover the cathode assembly.
  • a carbon anode was attached to the larger crucible in contact with the cryolite, thereby forming an aluminum electrowinning cell which was then inserted into a ' crucible furnace.
  • electrowinning of aluminum was undertaken with an average cell voltage of 3.52 V and at a cathode current density of 0.5 A/cm 2 for 5.5 hours.
  • alumina aluminum-non-wettable elements in a commercial cell was evaluated by insertion of packing elements into a commercial cell for controlled periods of time.
  • Packing elements utilized were fused-cast alumina bricks, preheated, for four hours prior to insertion into a 60 kiloampere vertical stud Soderberg cell.
  • the fused-cast bricks, some measuring 95 x 110 x 148 mm and some 110 x 148 x 187 mm, were lowered into the cell at the edge of the anode shadow and placed on the bottom of the cell.
  • the bricks were exposed to the commercial cell environment for periods of 15 minutes, 1 week, and 41 ⁇ 2 months.

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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)
EP83810164A 1982-04-21 1983-04-19 Nichtbenetzbare Füllkörper für eine Elektrolysezelle zur Herstellung von Aluminium Withdrawn EP0092525A1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US37056582A 1982-04-21 1982-04-21
US370565 1982-04-21

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EP0092525A1 true EP0092525A1 (de) 1983-10-26

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EP (1) EP0092525A1 (de)
JP (1) JPS5913087A (de)
AU (1) AU1369583A (de)
NO (1) NO831398L (de)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4737254A (en) * 1985-09-06 1988-04-12 Alcan International Limited Linings for aluminium reduction cells
WO1994013861A1 (en) * 1992-12-17 1994-06-23 Comalco Aluminium Limited Electrolysis cell for metal production
WO2010146369A1 (en) * 2009-06-18 2010-12-23 Metalysis Limited Feedstock
CN106011942A (zh) * 2016-07-29 2016-10-12 四川华索自动化信息工程有限公司 一种基于信号电平调节电路的铝电解用自动加料控制系统

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3041680A1 (de) * 1979-12-05 1981-06-11 Schweizerische Aluminium AG, 3965 Chippis Kathodenanordnung fuer einen schmelzflusselektrolyseofen
EP0033630A1 (de) * 1980-01-28 1981-08-12 Diamond Shamrock Corporation Elektrolytische Zelle für die elektrolytische Gewinnung von Aluminium aus geschmolzenen Salzen
DE3110490A1 (de) * 1980-04-03 1981-12-24 Schweizerische Aluminium AG, 3965 Chippis Schmelzflusselektrolysezelle zur herstellung von aluminium
US4308115A (en) * 1980-08-15 1981-12-29 Aluminum Company Of America Method of producing aluminum using graphite cathode coated with refractory hard metal
DE3024172A1 (de) * 1980-06-27 1982-01-21 Schweizerische Aluminium AG, 3965 Chippis Kathode fuer eine schmelzflusselektrolysezelle
FR2508496A2 (fr) * 1981-02-24 1982-12-31 Pechiney Aluminium Elements cathodiques amovibles en refractaire electroconducteur pour la production d'aluminium par le procede hall-heroult

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3041680A1 (de) * 1979-12-05 1981-06-11 Schweizerische Aluminium AG, 3965 Chippis Kathodenanordnung fuer einen schmelzflusselektrolyseofen
EP0033630A1 (de) * 1980-01-28 1981-08-12 Diamond Shamrock Corporation Elektrolytische Zelle für die elektrolytische Gewinnung von Aluminium aus geschmolzenen Salzen
DE3110490A1 (de) * 1980-04-03 1981-12-24 Schweizerische Aluminium AG, 3965 Chippis Schmelzflusselektrolysezelle zur herstellung von aluminium
DE3024172A1 (de) * 1980-06-27 1982-01-21 Schweizerische Aluminium AG, 3965 Chippis Kathode fuer eine schmelzflusselektrolysezelle
US4308115A (en) * 1980-08-15 1981-12-29 Aluminum Company Of America Method of producing aluminum using graphite cathode coated with refractory hard metal
FR2508496A2 (fr) * 1981-02-24 1982-12-31 Pechiney Aluminium Elements cathodiques amovibles en refractaire electroconducteur pour la production d'aluminium par le procede hall-heroult

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4737254A (en) * 1985-09-06 1988-04-12 Alcan International Limited Linings for aluminium reduction cells
WO1994013861A1 (en) * 1992-12-17 1994-06-23 Comalco Aluminium Limited Electrolysis cell for metal production
US5658447A (en) * 1992-12-17 1997-08-19 Comalco Aluminium Limited Electrolysis cell and method for metal production
WO2010146369A1 (en) * 2009-06-18 2010-12-23 Metalysis Limited Feedstock
EA023858B1 (ru) * 2009-06-18 2016-07-29 Металисиз Лимитед Исходное сырье
CN106011942A (zh) * 2016-07-29 2016-10-12 四川华索自动化信息工程有限公司 一种基于信号电平调节电路的铝电解用自动加料控制系统

Also Published As

Publication number Publication date
NO831398L (no) 1983-10-24
AU1369583A (en) 1983-10-27
JPS5913087A (ja) 1984-01-23

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