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WO1983000170A1 - Procede ameliore de reduction electrolytique de metaux et electrode amelioree en carbone particulaire utilisee avec ce procede - Google Patents

Procede ameliore de reduction electrolytique de metaux et electrode amelioree en carbone particulaire utilisee avec ce procede Download PDF

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Publication number
WO1983000170A1
WO1983000170A1 PCT/US1981/000919 US8100919W WO8300170A1 WO 1983000170 A1 WO1983000170 A1 WO 1983000170A1 US 8100919 W US8100919 W US 8100919W WO 8300170 A1 WO8300170 A1 WO 8300170A1
Authority
WO
WIPO (PCT)
Prior art keywords
metal
metal compound
electrolytic
electrolytic reduction
bath
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.)
Ceased
Application number
PCT/US1981/000919
Other languages
English (en)
Inventor
Graphite Co. Superior
William M. Goldberger
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.)
Superior Graphite Co
Original Assignee
Superior Graphite Co
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 Superior Graphite Co filed Critical Superior Graphite Co
Priority to BR8109035A priority Critical patent/BR8109035A/pt
Priority to PCT/US1981/000919 priority patent/WO1983000170A1/fr
Priority to EP19810902118 priority patent/EP0082839A4/fr
Publication of WO1983000170A1 publication Critical patent/WO1983000170A1/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
    • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
    • C25C7/005—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells of cells for the electrolysis of melts
    • 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
    • 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

Definitions

  • the present invention relates generally to methods and apparatus for electrolytic reduction of metal and more particularly to improved methods and apparatus for the continuous provision of a high purity and highly conductive, particulate, free-flowing carbon material to serve as the anode of the reduction cell.
  • metals are reduced from metallic compounds by means of the fused salt electroly ⁇ sis cell.
  • This technique is particularly applicable to the reduction of aluminum wherein alumina (Al- O ⁇ ) is reduced to aluminum metal with the utilization of a carbon anode.
  • The,electro-chemical reaction which re ⁇ sults in the formation of metallic aluminum yields oxy ⁇ gen at the anode. Oxygen in turn reacts with the anode carbon to form carbon dioxide.
  • the overall electrolysis of alumina can be summarized by the simplified equation:
  • anode carbon is an expensive reagent for a chemical process .
  • Anode carbon is in itself a product of manufacture that must meet close speci ications .
  • the carbon anodes which are typically used for this pro ⁇ cess must have suitable density, low sulfur content and grindability.
  • One method of producing carbon anodes is by pre-baking of ground carbon.
  • the manufacture of pre- baked bulk carbon anodes is a complex series of oper ⁇ ations involving mixing of calcined petroleum coke or anthracite with pitch materials and binders, extruding the mix into the desired shape, and then slow baking in a furnace at temperatures in excess of 1000°C.
  • calcined petroleum coke or calcined anthracite can be mixed as a paste and baked in place as it is used in the electrolytic cell.
  • This continuously formed electrode is known as the Soderberg-type electrode.
  • the present trend because of emission control and process control considerations, is to use the pre- baked carbon shapes.
  • Anodes made of graphite can be used in the Hall-Heroult cell in place of the pre-baked or Soder- berg-type carbon electrodes.
  • Graphite is less reactive and, therefore, consumption of graphite anodes would be substantially lower than that of carbon.
  • This potential advantage of graphite is offset by the fact that graph- ite is more costly to produce.
  • Substantially higher furnace temperatures and longer baking times are required to manufacture graphite than to make carbon electrodes.
  • the lower electrical resistance and higher thermal conductivity of graphite electrodes results in higher heat loss through the electrode column, which leads to a higher rate of oxidation of the electrode at the top.
  • partic ⁇ ulate graphite as part of the carbon mix going into the manufacture of such anodes. It is found, however, that it is difficult to form the desired electrode shape using particulate graphite, and other economic factors have pre cluded the use of particulate graphite for this purpose.
  • an improved process for the electrolytic reduction of a metal from a metal compound comprises the steps of providing a preferably saucer-shaped car- bon cathode within a container, dissolving the metal compound in a molten salt electrolyte solvent bath dis ⁇ posed within the container, the molten electrolyte bath having a higher decomposition potential than the metal compound and having a lesser density than the reduced molten metal, and continuously providing a particulate, free-flowing, high purity and highly conductive carbon anode material to the molten bath, with the particulate carbon material having a lesser density than the molten bath, placing an electrical connection in contact with the particulate carbon material and applying an elec ⁇ tric current thereto, and collecting a reduced metal at - 5 - the preferably saucer-shaped cathode.
  • a high purity and highly conductive, free-flowing particu late carbon material having a density lower than that o an electrolytic bath and floating thereon is provided t form the cell anode, and in preferred embodiments is co tinuously provided to the cell as the particulate carbo anode material is consumed.
  • FIG. 1 is a longitudinal cross-sectional view of an electrolytic cell for the production of reduced metal, such as aluminum, and includes a carbon cathode in contact with an insulated electrical, terminal, a molten salt electrolyte solvent bath having the metallic compound to be reduced dissolved therein, particulate carbon anode material floating on the electrolytic bath, electrical connection means in contact with the particu ⁇ late carbon anode material, means for the continuous in- troduction of such particulate carbon anode material, means for trapping and collecting gas generated at the cell anode, and reduced metal collected at the cathode.
  • reduced metal such as aluminum
  • the improved process for the electrolytic re ⁇ duction of a metal from a metallic compound comprises in preferred embodiments the first step of providing a ca.r- bon cathode within a container.
  • the carbon cathode is preferably saucer-shaped for collection of the reduced metal and is disposed in preferred embodiments near the bottom of the container.
  • a metallic compound is dis ⁇ solved in a molten salt electrolyte solvent bath which is disposed within the container and in contact with the cathode.
  • the molten electrolyte has a higher decomposi ⁇ tion potential than the metallic compound to be reduced and also has a lesser density than the reduced molten metal.
  • a particulate, free-flowing, high purity and highly conductive carbon material is preferably continu ⁇ ously provided and preferably near or at the surface of the molten electrolyte bath and has a lesser density than the bath to float thereon.
  • An electrical connec ⁇ tion is placed in contact with the particulate carbon anode material and electrical current is supplied there ⁇ to, whereby reduced metal is formed and collected at the cathode.
  • the reduced metal may be aluminum and the metallic compound may be alumina.
  • the molten electrolyte preferably comprises cryolite (Na., AlF g ) .
  • the metallic compound may comprise an aluminum halide, in which case the molten electrolyte is selected from the group consisting of alkali metal hal- ides and alkaline earth halides.
  • the gas which is produced at the anode may be collected and vented.
  • the particulate carbon material may be preferably formed from desulfurized petroleum coke which may be partially graphitized.
  • Another aspect of the present invention is di ⁇ rected to an improved anode apparatus for use in an electrolytic cell for the electrolytic reduction of a metal from a metal compound.
  • a cell preferably includes a carbon cathode disposed in contact with a molten salt electrolytic bath in which the metal compound to be reduced is dissolved.
  • the improved anode apparatus of the present invention comprises a high purity and highly conductive, free-flowing, particulate carbon material having a density lower than the electrolytic bath and floating thereon to comprise the cell anode.
  • Electrical connector means are disposed in contact with the free-flowing particulate carbon material to provide electrical current thereto.
  • means are included for continuously providing the free-flowing particulate carbon anode material to the cell.
  • These means may preferably comprise a tubular electrode hous ⁇ ing having a central aperture therein for containing a head of the free-flowing particulate carbon anode mater ⁇ ial for gravity feeding the same to float on the molten salt electrolytic bath as the particulate carbon anode material is consumed.
  • Gas collecting means may be further provided for collecting and evacuating gases formed at the par ⁇ ticulate carbon anode.
  • Such gas collecting means may preferably comprise a truncated conical skirt having a bottom edge and a top edge, with the top edge sealingly disposed on the electrode housing for preventing leakage of the gas therebetween. The bottom edge is disposed downwardly and into the particulate carbon anode elec ⁇ trode material for collecting the gas generated thereby.
  • the carbon cathode may preferably comprise a saucer-shaped plate disposed be ⁇ neath the molten salt electrolyte bath, and such carbon cathode plate preferably rests on a cathode collector bar and is insulated at the bottom thereof.
  • the particulate carbon anode material utilized may in preferred embodiments be a partially graphitized carbon which is preferably prepared from petroleum coke. Also in preferred embodiments, there may be provided solid electrolyte bath material which is seal- ingly disposed between the conical skirt bottom edge and the cathode for funneling the generated gases upwardly to be confined by the skirt. Additionally, a portion of the metal compound may be disposed over and substantially covering the solid electrolyte material.
  • cell 10 for the electrolytic re-duction of a metal, such as aluminum metal from a metal compound such as alumina or aluminum halides, is shown, cell 10 comprises a container 12 having a cathode col ⁇ lector bar 14 disposed at the bottom thereof.
  • the cath ⁇ ode collector bar 14 is insulated at the bottom surface thereof with insulation 16.
  • Floating on top of the molten aluminum 20 is a lower density electrolyte bath 22 and floating on bath 22 are carbon anode particles 24.
  • the electrolyte bath 22 is in a frozen condition, as shown at 26, and may be covered with a covering 28 of the frozen material 26 of the aluminum compound which has also been dissolved in the molten electrolyte bath 22.
  • Means for continuously supplying particulate carbon anode material, such as an electrode housing 30, are provided, with electrode hous- ing 30 having a central aperture 32 therein for supply ⁇ ing a head 33 of the carbon anode particulate material.
  • the electrode housing 30 is provided with an electrical terminal 34 for supplying electrical current thereto.
  • Central aperture 32 may be supplied through a particu- late carbon feeder tube 36.
  • electrode housing 30 may be supplied with a gas collecting skirt 38 which is preferably a truncated cone in shape and is sealingly connected to the electrode housin ⁇ 30.
  • the lower Deri- pheral edges 40 of skirt 38 are embedded in and covered by the metallic compound covering 28 disposed over the frozen electrolyte 26, whereby gases generated by carbon particulate anode material 24 are trapped beneath skirt 38 for collection and venting.
  • the apparatus and methods of the present invention use particles of carbon, rather than bulk-fabricated shapes of carbon as the anode of material.
  • the particular carbon particles which are usable in the method of the present invention must have suitable chemical and physical characteristics to pro ⁇ vide the needed operating requirements of this fused salt electrolysis process.
  • the par ⁇ ticulate carbon must be of high purtiy and essentially free of volatile hydrocarbons, sulfur and metallic impurities such as iron, silicon, titanium, vanadium, and nickel.
  • the particles of carbon must flow freely in the dry state. This free-flowing particulate carbon can be introduced into the electrolysis cell as needed to maintain a steady state electro-chemical reaction condi ⁇ tion.
  • Carbon block is used as the material for cath- ode 18.
  • Carbon or preferably graphite is used as the material for electrode housing 30, through which partic ⁇ ulate carbon 24 is feed into cell 10.
  • the housing may preferably be partially encased in a steel covering 31.
  • the particulate carbon 24 is fed through electrode housing 30 on demand.
  • the elevation of head 33 of par ⁇ ticulate carbon 24 maintained within electrode housing 30 can be monitored by various known automatic measur ⁇ ing devices (not shown) and used to automatically con ⁇ trol the feed of particulate carbon 24 through electrode housing 30.
  • particulate carbon 24 to be used by the method described are extremely impor ⁇ tant to the successful performance of the electrolysis cell.
  • the particulate material should have low electric ⁇ al resistivity to minimize the internal energy losses within the current carrying circuit.
  • the particulate material should also have a relatively low thermal con- ductivity to minimize heat losses through the column of particulate and the electrode housing.
  • Of critical importance also is the density of particulate carbon 24.
  • the density of aluminum metal varies between 2.25 and 2.28 within the range of electrolysis cell operating temperatures.
  • particulate carbon material be lower in density than the cryolite bath 22 to maintain suf icient buoyancy to float thereon and to effectively surround and shield the bottom surfaces of electrode housing 30 as indicated in the drawing of Fig. 1. It is important also that the particulate carbon be relatively non-reactive with oxygen within the operating conditions of the cell.
  • the "DESULCO” material is thermally purified and contains generally less than about 0.02% sulfur, no volatile hydrocarbons and only trace amounts of metallic elements. It is substantially more electrically conductive than petroleum coke. Of key importance, the "DESULCO” material oxidizes only very slowly in comparison with petroleum coke or baked carbon.
  • the particle density of "DESULCO” carbon is generally about 1.5 grams/cc. This provides adequate difference in density to maintain a buoyant layer of "DESULCO” on the upper surface of molten cryolite.
  • This particulate carbonaceous material may be preferably made according to the methods of U.S. Patent Ko. 4,160,813.

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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

Procédé amélioré de réduction électrolytique d'un métal (20) à partir d'un composé métallique et consistant à utiliser une cathode en carbone (18) dans un conteneur (12), à dissoudre le composé métallique dans un bain de solvant d'un électrolyte de sel en fusion (22) qui est disposé dans le conteneur (12), le bain d'électrolyte en fusion ayant un potentiel de décomposition supérieur au composé métallique et ayant une densité inférieure à celle du métal en fusion réduit (20), et à amener en continu un matériau de carbone particulaire, coulant, de haute pureté et hautement conducteur (24) au bain en fusion (22) pour servir d'anode, le matériau de carbone particulaire (24) ayant une densité inférieure au bain en fusion (22), à placer une connexion électrique (30, 34) en contact avec le matériau d'anode de carbone particulaire (24) et à y appliquer un courant électrique, et à récupérer le métal réduit (20) sur la cathode (18). Dans un autre aspect de la présent invention, un matériau de carbone particulaire coulant, de haute pureté et hautement conducteur (24) ayant une densité inférieure à celle d'un bain électrolytique (22) et flottant sur celui-ci forme l'anode de l'élément et dans des modes préférentiels de réalisation ce matériau (24) est alimenté en continu vers la cellule ou élément (10) au fur et à mesure que le matériau de carbone particulaire d'anode (24) est consumé.
PCT/US1981/000919 1981-07-06 1981-07-06 Procede ameliore de reduction electrolytique de metaux et electrode amelioree en carbone particulaire utilisee avec ce procede Ceased WO1983000170A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
BR8109035A BR8109035A (pt) 1981-07-06 1981-07-06 Processo aperfeicoado para reducao eletrolitica de um metal e celula eletrolitica para reducao eletrolitica de um metal
PCT/US1981/000919 WO1983000170A1 (fr) 1981-07-06 1981-07-06 Procede ameliore de reduction electrolytique de metaux et electrode amelioree en carbone particulaire utilisee avec ce procede
EP19810902118 EP0082839A4 (fr) 1981-07-06 1981-07-06 Procede ameliore de reduction electrolytique de metaux et electrode amelioree en carbone particulaire utilisee avec ce procede.

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/US1981/000919 WO1983000170A1 (fr) 1981-07-06 1981-07-06 Procede ameliore de reduction electrolytique de metaux et electrode amelioree en carbone particulaire utilisee avec ce procede

Publications (1)

Publication Number Publication Date
WO1983000170A1 true WO1983000170A1 (fr) 1983-01-20

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Country Status (2)

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EP (1) EP0082839A4 (fr)
WO (1) WO1983000170A1 (fr)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB309605A (en) * 1928-04-14 1930-07-14 Ig Farbenindustrie Ag Process and apparatus for the electrolysis of molten substances
GB483068A (en) * 1935-09-27 1938-04-07 Magall Ag Improvements in or relating to the production of magnesium and other alkali earth metals by electrolysis of fused electrolytes
US3582483A (en) * 1962-06-29 1971-06-01 Elektrokemisk As Process for electrolytically producing aluminum
US4257855A (en) * 1978-07-14 1981-03-24 Solomon Zaromb Apparatus and methods for the electrolytic production of aluminum metal

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB309605A (en) * 1928-04-14 1930-07-14 Ig Farbenindustrie Ag Process and apparatus for the electrolysis of molten substances
GB483068A (en) * 1935-09-27 1938-04-07 Magall Ag Improvements in or relating to the production of magnesium and other alkali earth metals by electrolysis of fused electrolytes
US3582483A (en) * 1962-06-29 1971-06-01 Elektrokemisk As Process for electrolytically producing aluminum
US4257855A (en) * 1978-07-14 1981-03-24 Solomon Zaromb Apparatus and methods for the electrolytic production of aluminum metal

Also Published As

Publication number Publication date
EP0082839A1 (fr) 1983-07-06
EP0082839A4 (fr) 1983-11-11

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