Moltech Invent S.a.

Diamond Shamrock Technologies S.a.

Oronzio Denora Impianti Elettrochimici S.p.a.

Rio Tinto Alcan International Limited

Eltech Systems Corporation

Other

Signetics

Parel Societe Anonyme

Electronor Corporation

Moltech Invent S.a. Luxembourg

Moitech Invent S.a.

Vittorio De Nora

Jean-Jacques R Duruz

Jainagesh A Sekhar

Antonio Nidola

Placido M Spaziante

Oronzio De Nora

Thinh Trong Nguyen

Giuseppe Bianchi

Georges Berclaz

Patrizio Gallone

Luigi Giuffre

Placido Spaziante

Olivier Crottaz

Brian Cronin

Henri B Beer

James J Stewart

James Jenq Liu

Jurgen F Gauger

Anthony J Vaccaro

Bohumil Polata

René Von Kaenel

Iudita L Adorian

Jean-Marie Fresnel

Rinaldo Santi

James Jeng Liu

Lawrence L Frank

Robert D Penny

Gaynor Johnston

Antonia Nidola

Georg Messner

Jaihagesh A Sekhar

A cell for the electrowinning of aluminium has a cavity for containing electrolyte () and one or more non emerging active anode bodies () that are suspended in the electrolyte. The electrolyte's surface (') has an expanse extending over the cavity and is substantially covered by a self-formed crust () of frozen electrolyte. The crust is mechanically reinforced by at least one preformed refractory body (&#x2033;). The electrolyte crust is formed against the preformed refractory body and bonded thereto so as to inhibit mechanical failure of the crust and collapse of the crust into the cavity.

Aluminium electrowinning cell with enhanced crust

A cell for the electrowinning of aluminium () from alumina dissolved in a molten electrolyte comprises a generally horizontal cell bottom (), preferably aluminium-wettable, on which a pool of product aluminium () is collected from at least one electrically conductive cathodic element () having aluminium-wettable cathode surfaces (). The cathodic element comprises an inclined cathodic wall () in the electrolyte () above the generally horizontal cell bottom (). The cathodic wall () has an upwardly-oriented inclined face () that forms a sloping upper aluminium-wettable drained active cathode surface on which aluminium is produced and drains into the aluminium pool (), and a downwardly-oriented inclined face () which is in contact with the molten electrolyte () and which overlies the aluminium pool (). The aluminium pool () covers substantially the entire cell bottom () including underneath the cathodic wall (). A return path for alumina-enriched electrolyte () towards a bottom end of the anode-cathode gap () may be provided behind the cathodic wall () along an inactive surface () thereof. The cell may be fitted with anodes () that are foraminate, e.g. an arrangement of spaced apart parallel rods, or solid plates.

Aluminium electrowinning cells with inclined cathodes

A cell for the electrowinning of aluminum () from alumina, comprises an inclined plate-like or grid-like open anode structure () which has a generally v-shaped configuration in cross-section. The anode structure () has a downwardly-oriented sloping electrochemically active surface that is generally v-shaped in cross-section and spaced above an upwardly-oriented corresponding sloping cathode surface () by an anode-cathode gap () in which alumina dissolved in a circulating electrolyte () is electrolysed. The anode structure () has a plurality of anode through-passages () distributed thereover for an up-flow of alumina-depleted electrolyte () from the anode-cathode gap (). One or more electrolyte guide members (&#x2033;) located above the open anode structure () is/are arranged to guide substantially all the up-flowing alumina-depleted electrolyte () to an alumina feeding area (), where it is enriched with alumina and then over and around an upper end () of the generally v-shaped plate-like or grid-like anode structure () into the anode-cathode gap (). Alumina-enriched electrolyte () can be fed into a lower end and/or into an upper end of the anode-cathode gap ().

Aluminium electrowinning cells with sloping foraminate oxygen-evolving anodes

A slurry comprises suspended aluminum particles in a colloid having dispersed colloidal particles of a metal oxide such as a hydroxide. The metal oxide is reducible by metallic aluminum. The slurry has such a basic pH that dissolution of the aluminum particles in the slurry is inhibited so that when the slurry is subjected to a heat treatment, the undissolved aluminum particles are reactable with the colloidal particles to form an aluminum-based mixture resistant to chemical attack made of aluminum oxide, metal aluminum and the metal of the colloidal particles. The slurry can be used to form an aluminum-based protective coating on a component, in particular of an aluminum electrowinning cell or an apparatus for treating molten aluminum.

Slurries for producing aluminium-based coatings

A cell for electrowinning a metal, in particular aluminium, from a compound thereof dissolved in an electrolyte () comprises an anode () and a cathode () that contact the electrolyte (), the cathode () being during use at a cathodic potential for reducing thereon species of the metal to be produced from the dissolved compound. The electrolyte () further contains species of at least one element that is liable to contaminate the product metal () and that has a cathodic reduction potential which is less negative than the cathodic potential of the metal to be produced. The cell further comprises a collector () for removing species of such element (s) from the electrolyte (). During use the collector () is at a potential that is: less negative than the cathodic potential of the produced metal () to inhibit reduction thereon of species of the metal to be produced; and at or more negative than the reduction potential of the species of said element(s) to allow reduction thereof on the collector (). The cell is so arranged that species of said element(s) are reduced on the collector () rather than on the cathode () so as to inhibit contamination of the product metal () by said element(s).

Metal electrowinning cell with electrolyte purifier

An anode for electrowinning of aluminium from alumina comprises a cobalt-containing metallic outer part that is covered with an integral oxide layer containing predominantly cobalt oxide CoO. The integral oxide layer can be formed by surface oxidation of cobalt from the metallic outer part before use.

Non-carbon anodes

An anode for electrowinning aluminium comprises an electrically conductive substrate that is covered with an applied electrochemically active coating comprising a layer that contains predominantly cobalt oxide CoO. The CoO layer can be connected to the substrate through an oxygen barrier layer, in particular containing copper, nickel, tungsten, molybdenum, tantalum and/or niobium.

Non-carbon anodes with active coatings

A cell for the electrowinning of aluminium by the electrolysis from an aluminium compound dissolved in a molten electrolyte (), comprises: (I) a plurality of non-carbon anodes (), each anode being suspended in operating in the molten electrolyte by an anode stem () that connects the anode () to a positive current source; and (II) a thermic insulating cover (') which covers the electrolyte () and through which each anode stem () extends from the positive current source to an anode (). The insulating cover (&#x2032;) comprises a plurality of movable sections () that together cover a substantial part of the electrolyte (). Each movable section () covers a corresponding portion of the electrolyte () that is located therebelow and that can be uncovered by moving the corresponding movable section (). The anode stem () of each anode () extends through the insulating cover (&#x2032;) between two movable sections () or between a movable section () and a fixed section (&#x2032;) of the insulating cover (&#x2032;) when the sections () are in a covering position over the electrolyte (). Each movable section () is movable to uncover the corresponding electrolyte portion without interrupting operation of any anode (), for example by tilting, in particular pivoting, or sliding and/or lifting the section ().

Aluminium electrowinning cell design with movable insulating cover sections

A cell for electrowinning aluminium from alumina, comprises: a metal-based anode having an electrochemically active outer part comprising a layer that contains predominantly cobalt oxide CoO; and a fluoride-containing molten electrolyte in which the active anode surface is immersed. The electrolyte is at a temperature below 950&#xb0; C., in particular in the range from 910&#xb0; to 940&#xb0; C. The electrolyte consists of: 6.5 to 11 weight. % dissolved alumina; 35 to 44 weight % aluminium fluoride; 38 to 46 weight % sodium fluoride; 2 to 15 weight % potassium fluoride; 0 to 5 weight % calcium fluoride; and 0 to 5 weight % in total of one or more further constituents.

An anode for the electrowinning of aluminium by the electrolysis of alumina in a molten fluoride electrolyte has an electrochemically active integral outside oxide layer obtainable by surface oxidation of a metal alloy which consists of 20 to 60 weight % nickel; 5 to 15 weight % copper; 1.5 to 5 weight % aluminium; 0 to 2 weight % in total of one or more rare earth metals, in particular yttrium; 0 to 2 weight % of further elements, in particular manganese, silicon and carbon; and the balance being iron. The metal alloy of the anode has a copper/nickel weight ratio in the range of 0.1 to 0.5, preferably 0.2 to 0.3.

Surface oxidised nickel-iron metal anodes for aluminium production

A method of manufacturing a component, in particular an aluminium electrowinning anode, for use at elevated temperature in an oxidising and/or corrosive environment comprises: applying onto a metal-based substrate layers of a particle mixture containing iron oxide particles and particles of a reactant-oxide selected from titanium, yttrium, ytterbium and tantalum oxides; and heat treating the applied layers to consolidate by reactive sintering of the iron oxide particles and the reactant-oxide particles to turn the applied layer into a protective coating made of a substantially continuous reacted oxide matrix of one or more multiple oxides of iron and the metal from the reactant-oxide. The metal-based substrate comprises at its surface during the heat treatment an integral anchorage-oxide of at least one metal of the substrate. The anchorage-oxide anchors the multiple oxide matrix to the substrate by reacting with the iron oxide and/or the reactant-oxide to form an integral multiple bonding oxide of the metal of the integral anchorage-oxide and iron from the iron oxide and/or the metal of the reactant-oxide. The particle mixture can be applied in a colloidal and/or polymeric slurry.

Non-carbon anodes for aluminium electrowinning and other oxidation resistant components with slurry-applied coatings

A method of forming a dense and crack-free hematite-containing protective layer on a metal-based substrate for use in a high temperature oxidising and/or corrosive environment comprises applying onto the substrate a particle mixture consisting of: 60 to 99 95 weight %, in particular 70 to 95 weight % such as 75 to 85 weight %, of hematite with or without iron metal and/or ferrous oxide; 1 to 25 weight %, in particular 5 8 to 20 weight % such as 8 to 15 weight %, of nitride and/or carbide particles, such as boron nitride, aluminium nitride or zirconium carbide particles; and 0 to 15 weight %, in particular 5 to 15 weight %, of one or more further constituents that consist of at least one metal or metal oxide or a heat-convertible precursor thereof. The hematite particles are then sintered by heat treating the particle mixture to form the protective layer that is made of a microporous sintered hematite matrix in which the nitride and/or carbide particles are embedded and which contains, when present, said one or more further constituents. The mechanical, electrical and electrochemical properties of the protective layer can be improved by using an oxide of titanium, zinc, zirconium or copper. Typically, the protected substrate can be used in a cell for the electrowinning of a metal such as aluminium.

Protection of non-carbon anodes and other oxidation resistant components with iron oxide-containing coatings

An anode of a cell for the electrowinning of aluminium comprises a nickel-iron alloy substrate having a nickel metal rich outer portion with an electrolyte pervious integral nickel-iron oxide containing surface layer which adheres to the nickel metal rich outer portion of the nickel-iron alloy and which in use is electrochemically active for the evolution of oxygen. The oxide surface layer has a thickness such that, during use, the voltage drop therethrough is below the potential of dissolution of nickel-iron oxide. The nickel metal rich outer portion may contain cavities some or all of which, after oxidation, are partly or completely filled with iron oxides to form iron oxide containing inclusions.

Metal-based anodes for aluminium electrowinning cells

A cell for the electrowinning of aluminium comprising one or more anodes (), each having a metal-based anode substrate, for instance comprising a metal core () covered with an metal layeran oxygen barrier layer (), one or more intermediate layers (A,B) and an iron layer (). The anode substrate is covered with an electrochemically active transition metal oxide layer, in particular an iron oxide-based outside layer () such as a hematite-based layer, which remains dimensionally stable during operation in a cell by maintaining in the electrolyte a sufficient concentration of iron species and dissolved alumina. The cell operating temperature is sufficiently low so that the required concentration of iron species in the electrolyte () is limited by the reduced solubility of iron species in the electrolyte at the operating temperature, which consequently limits the contamination of the product aluminium by iron to an acceptable level. The iron oxide-based layer () is usually an applied coating or an oxidised surface of a substrate (), the surface () of which contains iron.

Cells for the electrowinning of aluminium having dimensionally stable metal-based anodes

An anode of a cell for the electrowinning of aluminium comprises a nickel-iron alloy substrate having an openly porous nickel metal rich outer portion whose surface is electrochemically active. The outer portion is optionally covered with an external integral nickel-iron oxide containing surface layer which adheres to the nickel metal rich outer portion of the nickel-iron alloy and which in use is pervious to molten electrolyte. During use, the nickel metal rich outer portion contains cavities some or all of which are partly or completely filled with iron and nickel compounds, in particular oxides, fluorides and oxyfluorides.

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Nassau, Bahamas

Vittorio De Nora