Electrolytic reduction of alumina
AssigneesElectrochemical Technology Corp., Brooks Rand Inc
InventorsTheodore R. Beck, Richard J. Brooks
Life of this patent
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Abstract
Finely divided particles of alumina are electrolytically reduced to aluminum in an electrolytic reduction vessel having a plurality of vertically disposed, non-consumable anodes and a plurality of vertically disposed, dimensionally stable cathodes in closely spaced, alternating arrangement with the anodes. A horizontally disposed, gas bubble generator is located at the vessel bottom, underlying the cathodes and the spaces between each pair of adjacent electrodes. The vessel contains a molten electrolyte bath composed of (1) NaF+Alf.sub.3 eutectic, (2) KF+AlF.sub.3 eutectic and (3) LiF. The alumina particles are maintained in suspension in the molten electrolyte bath by rising gas bubbles generated at the anodes and at the gas bubble generator during the reduction process.
Claims65
A method for the electrolytic reduction of alumina to aluminum in a vessel having a bottom and sidewalls, said method comprising the steps of:
- containing within said vessel a molten electrolyte bath consisting essentially of (1) NaF+AlF.sub.3 eutectic, (2) KF+AlF.sub.3 eutectic and (3) LiF;
- said molten electrolyte bath having a density less than the density of molten alumina and less than the density of alumina;
- maintaining said bath at a temperature substantially below 950.degree. C.;
- providing within said bath a plurality of vertically disposed, spaced apart, non-consumable anodes and a plurality of vertically disposed, spaced apart, dimensionally stable cathodes in close, alternating relation to said anodes, with a space defined between each pair of adjacent electrodes;
- introducing finely divided alumina particles into said bath;
- passing an electric current through said bath from said anodes to said cathodes;
- forming bubbles of gaseous oxygen at each of said anodes;
- allowing said bubbles to pass upwardly from said anodes;
- forming a slurry composed of said finely divided alumina particles suspended in said molten electrolyte bath;
- forming metallic aluminum at each cathode;
- allowing said metallic aluminum to flow downwardly as molten aluminum along each cathode at which aluminum is formed, toward the bottom of said vessel;
- and accumulating said molten aluminum at the bottom of said vessel.
A method for the electrolytic reduction of alumina to aluminum in a vessel having a bottom and sidewalls, said method comprising the steps of:
- containing within said vessel a molten electrolyte bath consisting essentially of (1) NaF+AlF.sub.3 eutectic, (2) KF+AlF.sub.3 eutectic and (3) LiF;
- maintaining said bath at a temperature substantially below 950.degree. C.;
- providing within said bath a plurality of vertically disposed, spaced apart, non-consumable, copper-containing anodes and a plurality of vertically disposed, spaced apart, dimensionally stable cathodes in close, alternating relation with said anodes;
- introducing finely divided alumina particles into said bath;
- passing an electric current through said bath from said anodes to said cathodes;
- forming metallic aluminum at each cathode;
- forming an oxide of copper at each anode during the passage of said electric current, at least during the beginning stages in the performance of said method;
- and incorporating Li.sup.+ ions into said oxide of copper during said beginning stages, to decrease anode resistance during the performance of said method.
A combination for use in the electrolytic reduction of alumina to aluminum, said combination comprising:
- a vessel having a bottom and sidewalls;
- a molten electrolyte bath contained within said vessel and consisting essentially of (1) NaF+AlF.sub.3 eutectic, (2) KF+AlF.sub.3 eutectic and (3) LiF;
- said molten electrolyte bath having a density less than that of molten aluminum and less than that of alumina;
- means for maintaining said bath at a temperature substantially below 950.degree. C.;
- a plurality of electrodes within said bath, said electrodes including a plurality of vertically disposed, spaced apart, non-consumable anodes and a plurality of vertically disposed, spaced apart dimensionally stable cathodes in close, alternating relation to said primary anodes, with a space defined between each pair of adjacent electrodes;
- means for introducing finely divided alumina particles into said bath;
- means for passing an electric current through said bath from said anodes to said cathodes;
- each of said anodes comprising means for forming, from said alumina, during passage of said electric current, bubbles of gaseous oxygen at said anode;
- said combination comprising means for allowing said bubbles to pass upwardly from said anodes;
- each of said cathodes comprising means for forming metallic aluminum at said cathode, during passage of said electric current;
- said combination comprising means for allowing said metallic aluminum, formed at said cathodes, to flow downwardly as molten aluminum along each cathode at which aluminum is formed, toward the bottom of said vessel;
- and means at the bottom of said vessel for accumulating and draining molten aluminum.
A slurry formed during a process for the electrolytic reduction of alumina to aluminum, said slurry consisting essentially of:
- finely divided alumina particles suspended in a molten electrolyte;
- said molten electrolyte consisting essentially of (1) NaF+AlF.sub.3 eutectic, (2) KF+AlF.sub.3 eutectic and (3) LiF.
A molten electrolyte for use in the electrolytic reduction of alumina to aluminum, said molten electrolyte consisting essentially of:
- (1) NaF+AlF.sub.3 eutectic, (2) KF+AlF.sub.3 eutectic and (3) LiF.
A composition for use as an electrolyte in the electrolytic reduction of alumina to aluminum, the ingredients in said composition consisting essentially of, in wt. % adjusted to exclude impurities:
- ______________________________________ NaF 6-26 KF 7-33 LiF 1-6 AlF.sub.3 60-65 ______________________________________
An apparatus for use in the electrolytic reduction of alumina to aluminum, said apparatus comprising:
- a vessel having a bottom and sidewalls;
- a plurality of electrodes extending into said vessel, said electrodes including a plurality of vertically disposed, spaced apart, non-consumable primary anodes and a plurality of vertically disposed, spaced apart dimensionally stable cathodes in close, alternating relation to said primary anodes, with a space defined between each pair of adjacent electrodes;
- said space being defined unfilled by solid material;
- and horizontally disposed gas bubble generating means at substantially the bottom of said vessel, at a location underlying at least said cathodes and the spaces between adjacent electrodes.
Dependencies are inferred from the claim text.