Moltech Invent S.a.

Rio Tinto Alcan International Limited

Eltech Systems Corporation

Other

Diamond Shamrock Chemicals Company

Detra Sa

Moitech Invent S.a.

Titalyse Sa

Thinh Trong Nguyen

Vittorio De Nora

Christopher J Vance

Kim S Doan

Jean-Jacques R Duruz

Michel Schwab

Henri B Beer

René Von Kaenel

Frank Schnyder

Jean-Pol Wiaux

Abdelkrim Lazouni

Mai Tu Xuan

Jean P Wia

Jean-Marie Fresnel

Siegfried Ernst

Adbelkrim Lazouni

Jean-Jacques Duruz

A metallic oxygen evolving anode for electrowinning aluminum by decomposition of alumina dissolved in a cryolite-based molten electrolyte, and operable at anode current densities of 1.1 to 1.3 A/cm2, comprises an alloy of nickel, iron, manganese, optionally copper, and silicon. Preferably, the alloy is composed of 64-66 w % Ni; Iron; 25-27 w % Fe; 7-9 w % Mn; 0-0.7 w % Cu; and 0.4-0.6 w % Si. The weight ratio Ni/Fe is in the range 2.1 to 2.89, preferably 2.3 to 2.6, the weight ratio Ni/(Ni+Cu) is greater than 0.98, the weight ratio Cu/Ni is less than 0.01, and the weight ratio Mn/Ni is from 0.09 to 0.15. The alloy surface can comprise nickel ferrite produced by pre-oxidation of the alloy. The alloy, optionally with a pre-oxidized surface, can be coated with an external coating comprising cobalt oxide CoO.

Metallic oxygen evolving anode operating at high current density for aluminum reduction cells

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 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 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 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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Onex, Switzerland

Thinh Trong Nguyen