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US 2011/0031129 A1Published application
Aluminium electrowinning cells with metal-based anodes
OwnerVittorio de Norainventor
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OwnerVittorio de Norainventor
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A cell for the electrowinning of aluminium comprises a metal-based anode (10) containing at least one of nickel, cobalt and iron, for example an anode made from an alloy consisting of 50 to 60 weight % in total of nickel and/or cobalt; 25 to 40 weight % iron; 6 to 12 weight % copper; 0.5 to 2 weight % aluminium and/or niobium; and 0.5 to 1.5 weight % in total of further constituents. The anode (10) may have an applied hematite-based coating and optionally a cerium oxyfluoride-based outermost coating. The cell contains a fluoride-containing molten electrolyte (5) at a temperature below 940° C., in which the anode is immersed and which consists of: 5 to 14 weight % dissolved alumina; 35 to 45 weight % aluminium fluoride; 30 to 45 weight % sodium fluoride; 5 to 20 weight % potassium fluoride; 0 to 5 weight % calcium fluoride; and 0 to 5 weight % in total of one or more further constituents. A nickel-containing anode stem (14b) can be used to suspend the anode (10) in the electrolyte facing a cathode (21,21A,25) that has an aluminium-wettable surface (20), in particular a drained horizontal or inclined surface.
A cell for electrowinning aluminium from alumina, comprising:
The cell of any preceding claim, wherein the electrolyte contains 34 to 43 weight % sodium fluoride.
The cell of any preceding claim, wherein the electrolyte contains 8 to 15 weight % potassium fluoride.
The cell of any preceding claim, wherein the electrolyte contains 2 to 4 weight % calcium fluoride.
The cell of any preceding claim, wherein the electrolyte contains 0 to 3 weight % of said one or more further constituents.
The cell of any preceding claim, wherein said one or more further constituents comprise at least one fluoride selected from magnesium fluoride, lithium fluoride, cesium fluoride, rubidium fluoride, strontium fluoride, barium fluoride and cerium fluoride.
The cell of any preceding claim, comprising a cathode that has an aluminium-wettable surface, in particular a horizontal or inclined drained surface.
The cell of any preceding claim, wherein the anode has a metallic or cermet body and an oxide layer on the anode body.
The cell of any preceding claim, wherein the anode body is made from an iron alloy containing nickel and/or cobalt.
The cell of any preceding claim, wherein the anode comprises an applied iron oxide-based coating.
The cell of any preceding claim, wherein the anode comprises a cerium oxyfluoride-based outermost coating.
The cell of any preceding claim, wherein the anode is suspended in the electrolyte by a nickel-containing stem, in particular a stem having a nickel-containing core covered with an applied oxide coating.
The cell of any preceding claim, comprising at least one component that contains a sodium-active cathodic material, such as elemental carbon, said sodium-active cathodic material being shielded from the electrolyte by a sodium-inert layer to inhibit the presence in the molten electrolyte of soluble cathodically-produced sodium metal that constitutes an agent for dissolving the active oxide-based anode surface.
A method of electrowinning aluminium in a cell as defined in any preceding claim, comprising electrolysing the dissolved alumina to produce oxygen on the anode and aluminium cathodically, and supplying alumina to the electrolyte to maintain therein a concentration of dissolved alumina of 5 to 14 weight %, in particular 7 to 10 weight %.
Dependencies are inferred from the claim text.