US3729398A - Process and cell for the electrolytic recovery of aluminum - Google Patents

Process and cell for the electrolytic recovery of aluminum Download PDF

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Publication number
US3729398A
US3729398A US00113960A US3729398DA US3729398A US 3729398 A US3729398 A US 3729398A US 00113960 A US00113960 A US 00113960A US 3729398D A US3729398D A US 3729398DA US 3729398 A US3729398 A US 3729398A
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US
United States
Prior art keywords
melt
alumina
aluminum
cell
electrolyte
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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 - Lifetime
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US00113960A
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English (en)
Inventor
Hatting W Schmidt
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.)
Alcan Holdings Switzerland AG
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Alusuisse Holdings AG
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Filing date
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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
    • C25C3/20—Automatic control or regulation of cells
    • 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 fluoride melt itself is covered by a crust which forms by solidification of the electrolyte and a layer of aluminum oxide covers this crust.
  • This aluminum oxide is introduced into the fluoride melt by periodic breaking of the crust. If the concentration of aluminum oxide, which normally lies between 2 and and advantageously between 5 and 7%, drops below about 2% in the electrolyte, the so-called anode effect occurs.
  • the cell potential which is normally from 3.7 to 4.5 volts, rises suddenly to a value between 20 and 50 volts.
  • the crust on the electrolyte must be broken and new alumina introduced into the fluoride melt at this moment at the very latest.
  • the anode effect shows the operators that the concentration of alumina has dropped to a low value approximately between 1 and 2%.
  • the concentration of alumina in the electrolyte cannot be directly measured. It is indeed possible to take specimens of the melt and analyse these in a laboratory, but the time required is too long to allow corrections to the operation to be effected in good time.
  • alumina When adding alumina to the fluoride melt, care is taken to supply approximately that amount which will bridge the time interval until the next breaking of the crust, and in this period to maintain the concentration of alumina at about 5% or more.
  • the amount of alumina which is added to the melt during the servicing of the cell can not however be accurately controlled, but rather depends upon what happens when the crust is broken.
  • the current yield is the ratio of the amount of metal actually produced to that which could theoretically be separated according to Faradays law.
  • the difference in the two amounts of metals is essentially the result of re-oxidation of the aluminum dissolved in the melt by the anode gases.
  • the limit of solubility of the alumina in the melt may be locally exceeded. Then some of the alumina sinks through the electrolyte without going into solution, enters the metal lying on the bottom of the cell, and passes through this to the bottom. There it forms a sludge which in the course of time can lead to encrustation of the bottom. Such encrustation in turn brings about increase in the electric resistance of the bottom of the cell and thus increase in the specific consumption of electrical energy (kw. h./ kg. Al). Moreover because of non-uniform distribution of the current in the bottom the bath may be disturbed by movement and arching of the metal with resultant reduction in the current yield.
  • My object in this invention is to eliminate the difliculties described.
  • the electrolyte is kept during operation in direct contact with a melt which consists of electrolyte with high concentration of aluminum oxide and separated from the liquid cathodic aluminum. Because of the direct contact of the two melts and of the movement of the main melt in the cell, there is continuous interchange of melt highly concentrated or saturated in alumina with the electrolyte impoverished in alumina by the electrolysis.
  • the highly concentrated melt rests on a lower layer of undissolved alumina so that as it loses alumina by interchange with the main melt it takes fresh alumina into solution from this lower layer.
  • My invention includes apparatus for carrying out this process and comprising one or more troughs resting on the bottom of the cell for the reception of the highly concentrated or saturated melt, the upper edges of the trough or each trough being at such a height as to lie in operation in the layer of the electrolyte without reaching its surface and as the liquid cathodic aluminum in the main part of the cell cannot enter the trough.
  • a trough should of course be made of a material resistant to the electrolyte.
  • FIG. 1 is a longitudinal section
  • FIG. 2 is a cross-section on the line A-A inFIG. l;
  • FIG. 3 is a plan in which the anode supports and the current-conducting beam are omitted.
  • the cell shown comprises a steel pot 10 lined by heatresistant insulation 11, which in turn receives a carbon lining 12 in which iron cathode rods 13 are embedded.
  • the layer of aluminum electrolytically separated during the operation is shown at 14, and on top of it there is the fluoride melt 15 containing alumina in solution.
  • the melt is covered by a crust 16 and a layer of alumina 17 on top of it.
  • Anodes 18 dip into the melt from above and are suspended by rods 19 from a beam 20 which carries the current.
  • a trough 21 is let into the carbon bottom of the cell, and its sides 22, which are made of carbon, project upwards into the melt 15, so that the aluminum 14 cannot enter the trough.
  • This trough is filled with a melt 23 highly concentrated or saturated in alumina, which rests on a layer 24 of undissolved alumina.
  • alumina is supplied to the trough from above, and partly enters into solution and partly sinks to the bottom.
  • the aluminum separated from the melt forms a single layer, that is to say the trough 21 does not divide the cell into two parts, and therefore the level of the liquid aluminum 14 is the same throughout the cell.
  • the trough 21 shown in unitary with the bottom of the cell it can be separately made, and indeed from some other material than carbon, and inset in the bottom of the cell.
  • the application of the process according to the invention is not restricted to cells of conventional construction, but rather the process can be employed in any aluminum electrolytic cell in which a melt of fluoride electrolyte containing alumina in solution is electrolysed.
  • the electrolysis of aluminum value is often attached to the production of the anode effect at least occasionally, for example every 24 hours, because it gives an indication of the content of the dissolved alumina and it results in dissolving of the bottom sludge, which consists mainly of undissolved alumina and may lead to an encrustation of the cell bottom.
  • the invention allows on the one hand the alumina content of the melt never to fall to so low a value that the anode effect can arise, and on the other hand to ensure that the melt outside the trough is never saturated in alumina, so that no sludge requiring the anode eflect to remove it is ever formed.
  • An electrolytic cell for use in the recovery of aluminum from alumina dissolved in a main fluoride melt which is kept in direct contact with a feeding melt consisting of fluoride electrolyte highly concentrated or saturated in aluminum oxide and separated from the liquid cathodic aluminum,
  • a receptacle for receiving the main fluoride melt, said receptacle having a carbon bottom portion forming the cathode electrode upon which a layer of liquid aluminum is collected,

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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)
US00113960A 1970-02-17 1971-02-09 Process and cell for the electrolytic recovery of aluminum Expired - Lifetime US3729398A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CH229570A CH533686A (de) 1970-02-17 1970-02-17 Verfahren und Vorrichtung zum Regulieren der Al2O3-Konzentration im Fluoridelektrolyten bei der Aluminiumelektrolyse

Publications (1)

Publication Number Publication Date
US3729398A true US3729398A (en) 1973-04-24

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ID=4230430

Family Applications (1)

Application Number Title Priority Date Filing Date
US00113960A Expired - Lifetime US3729398A (en) 1970-02-17 1971-02-09 Process and cell for the electrolytic recovery of aluminum

Country Status (12)

Country Link
US (1) US3729398A (de)
JP (1) JPS5212129B1 (de)
AT (1) AT302676B (de)
BE (1) BE762968A (de)
CA (1) CA954474A (de)
CH (1) CH533686A (de)
DE (1) DE2107675C3 (de)
FR (1) FR2080571B1 (de)
GB (1) GB1321943A (de)
NL (1) NL150859B (de)
NO (1) NO125894B (de)
ZA (1) ZA71756B (de)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3787310A (en) * 1972-09-13 1974-01-22 A Johnson Reduction of aluminum with improved reduction cell and anodes
US3839167A (en) * 1973-06-28 1974-10-01 Aluminum Co Of America Novel alumina feed for aluminum cell
US4396481A (en) * 1980-04-03 1983-08-02 Swiss Aluminium Ltd. Electrolytic cell for the production of aluminum by fused salt electrolysis
US6093304A (en) * 1994-09-08 2000-07-25 Moltech Invent S.A. Cell for aluminium electrowinning
WO2010065989A1 (en) * 2008-12-08 2010-06-17 University Of South Australia Formation of nanoporous materials

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS61132224U (de) * 1985-02-04 1986-08-18

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3787310A (en) * 1972-09-13 1974-01-22 A Johnson Reduction of aluminum with improved reduction cell and anodes
US3839167A (en) * 1973-06-28 1974-10-01 Aluminum Co Of America Novel alumina feed for aluminum cell
US4396481A (en) * 1980-04-03 1983-08-02 Swiss Aluminium Ltd. Electrolytic cell for the production of aluminum by fused salt electrolysis
US6093304A (en) * 1994-09-08 2000-07-25 Moltech Invent S.A. Cell for aluminium electrowinning
WO2010065989A1 (en) * 2008-12-08 2010-06-17 University Of South Australia Formation of nanoporous materials

Also Published As

Publication number Publication date
JPS5212129B1 (de) 1977-04-05
CA954474A (en) 1974-09-10
CH533686A (de) 1973-02-15
DE2107675C3 (de) 1974-12-05
ZA71756B (en) 1971-10-27
DE2107675A1 (de) 1971-08-26
AT302676B (de) 1972-10-25
NL150859B (nl) 1976-09-15
GB1321943A (en) 1973-07-04
NO125894B (de) 1972-11-20
DE2107675B2 (de) 1974-05-02
NL7100879A (de) 1971-08-19
FR2080571A1 (de) 1971-11-19
FR2080571B1 (de) 1974-09-06
BE762968A (fr) 1971-07-16

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