Low temperature alumina electrolysis
AssigneeEltech Systems Corporation
InventorJean-Jacques Duruz
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Abstract
A method of producing aluminum by electrolysis of alumina dissolved in molten cryolite at temperature between 680.degree.-690.degree. C. is disclosed. The method comprises the employment of permanent anodes the total surface of which is increased up to 5 times compared to the total surface of anodes in a classical Hall-Heroult cell of comparable production rate. By this means the anodic current density is lowered to a degree which permits the discharge of oxide ions preferentially to fluoride ions at an acceptable rate. Additionally, the electrolyte is circulated by suitable means whereby it passes from an enrichment zone where it is saturated with alumina to an electrolysis zone and back.
Claims20
A method of producing aluminum by electrolysis of alumina dissolved in a molten fluoride electrolyte in an aluminum reduction cell using a low temperature melt, at a temperature up to 860.degree. C., characterized by effecting a continuing steady-state electrolysis using an oxygen-evolving, non-consumable anode having an electrochemically active surface area at least 1.5 times larger than the projected area of the anode onto a horizontal plane, said electrolysis being effected at an anodic current density which is at or below a threshold value corresponding to the maximum transport rate of oxide ions in the electrolyte and at which oxide ions are discharged preferentially to fluoride ions, the electrolyte circulating between an electrolysis zone wherein the electrolyte is depleted of alumina and an enrichment zone wherein the electrolyte is enriched with alumina.
An electrolytic alumina reduction cell containing a molten fluoride electrolyte with dissolved alumina in a low temperature melt at a temperature up to 860.degree. C., with the cell having an anode and a cathode, characterized by having a non-consumable, oxygen evolving anode comprising a total electrochemical surface which is at least 1.5 times larger than the projected area of the anode onto a horizontal plane, and with there being a circulation path for cell electrolyte including an electrolysis zone wherein the electrolyte is depleted of alumina and an enrichment zone where the electrolyte is enriched with alumina.
The method for the electrolytic reduction of alumina contained in a molten fluoride electrolyte, which method comprises;
- establishing an electrolyte containing at least approximately one weight percent dissolved alumina;
- maintaining said electrolyte as a low temperature melt at a temperature up to 860.degree. C.;
- providing a non-consumable, oxygen-evolving anode for the electrolysis;
- establishing an anodic current density at or below a threshold value corresponding to the maximum transport rate of oxide ions in said electrolyte, and at which oxide ions are discharged preferentially to fluoride ions, while maintaining a ratio of the anodic to cathodic current density of between 1:1.2 and 1:11, and
- providing means for alumina enrichment of said cell electrolyte.
An electrolytic alumina reduction cell containing a molten fluoride electrolyte containing at least one weight percent dissolved alumina in a low temperature melt at a temperature up to 860.degree. C., the cell having at least one cathode as well as a non-consumable, oxygen-evolving anode, said cell having an anodic current density at or below a threshold value corresponding to the maximum transport rate of oxide ions in said electrolyte and at which oxide ions are discharged preferentially to fluoride ions, and with the electrochemically active surface area of the anode being 1.5-5 times larger than the projected area of the anode onto a horizontal plane.
Dependencies are inferred from the claim text.