Moltech Invent S.a.

Eltech Systems Corporation

Other

Moltech Invent S.a. Luxembourg

Diamond Shamrock Corporation

Heraeus Elektrochemie Gmbh

Jean-Jacques R Duruz

Vittorio De Nora

Jainagesh A Sekhar

James Jenq Liu

Olivier Crottaz

Georges Berclaz

Jean-Pierre Derivaz

Vittorio Bello

James Jeng Liu

Dominique Darracq

Brian Cronin

Douglas J Wheeler

Thinh Trong Nguyen

Jurgen F Gauger

Ajit Y Sane

Ulrich Stroder

Iudita L Adorian

Jean-Marie Fresnel

Jean-Louis Jorda

Fausto Manganiello

Claude Durmelat

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.

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 layer , an oxygen barrier layer ( ), one or more intermediate layers ( A, B) and an iron layer ( ). The anode substrate is covered with an electrochemically active iron oxide-based outside layer ( ), in particular a hematite-based layer, which remains dimensionally stable during operation in a cell by maintaining in the electrolyte a sufficient concentration of iron species. 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.

A cell for the electrowinning of aluminum using anodes ( ) made from a alloy of iron with nickel and/or cobalt is arranged to produce aluminum of low contamination and of commercial high grade quality. The cell comprises a cathode ( ) of drained configuration and operates at reduced temperature without formation of a crust or ledge of solidified electrolyte. The cell is thermally insulated using an insulating cover ( ) and an insulating sidewall lining ( ). The molten electrolyte ( ) is substantially saturated with alumina, particularly on the electrochemically active anode surface, and with species of at least one major metal present at the surface of the nickel-iron alloy based anodes ( ). The cell is preferably operated at reduced temperature from 730&deg; to 910&deg; C. to limit the solubility of these metal species and consequently the contamination of the product aluminum.

Low temperature operating cell for the electrowinning of aluminium

A refractory boride body or coating made of a boride of titanium, chromium, vanadium, ziconium, hafnium, niobium, tantalum, molybednum and cerium is produced from a slurry of the refractory boride or a precursor in a collidal carrier preferably composed of two more different grades of the same colloidal carrier selected from colloidal alumina, yttria, ceria, thoria, zirconia, magnesia, lithia, monoaluminum phosphate and cerium acetate. The slurry can also comprise an organic additive selected from polyvinyl alcohol; polyacrylic acid; hydroxyy propyl methyl cellulose; polythylene glycol; ethylene glycol, butyl benzyl phthalate; ammonium polymethacrylate and mixtures thereof. The retractory boride body or coated body is useful as a component of aluminum electrowinning cells.

Slurry and method for producing refractory boride bodies and coatings for use in aluminium electrowinning cells

A drained cathode cell for the electrowinning of aluminium comprises a cell bottom ( ) arranged to collect product aluminium and thermic insulating sidewalls ( &prime;) lined with a molten electrolyte resistant sidewall lining ( ) which is made of material liable to react with molten aluminium, in particular containing silicon carbide, silicon nitride or boron nitride. The thermic insulating sidewalls ( &prime;) inhibit formation of an electrolyte crust on the lining ( ), whereby the lining ( ) is exposed to molten electrolyte. The cell bottom ( ) has a peripheral surface from which the insulating sidewalls ( &prime;) extend generally vertically to form, with the cell bottom, a trough for containing molten electrolyte and aluminium produced on at least one drained cathode ( ). The peripheral surface of the cell bottom ( ) is arranged to keep the product aluminium from contacting and reacting with the molten electrolyte resistant sidewall lining ( ) above and around the entire peripheral surface.

Aluminium electrowinning cell with sidewalls resistant to molten electrolyte

A method of inhibiting dissolution of a transition metal alloy anode ( ) of an aluminium electrowinning cell comprises providing a sodium-inert layer ( &prime;) on a sodium-active cathodic cell material ( ), such as carbon, and electrolysing alumina dissolved in a sodium ion-containing molten electrolyte ( ). Aluminium ions rather than sodium ions are cathodically reduced on the sodium-inert layer to inhibit the presence in the molten electrolyte ( ) of soluble cathodically-produced sodium metal that constitutes an agent for chemically reducing the anode's transition metal oxides and anodically evolved oxygen, thereby inhibiting reduction of the anode's transition metal oxides by sodium metal and maintaining the evolved oxygen at the anode at a concentration such as to produce at the alloy/oxide layer interface stable and coherent transition metal oxides having a high level of oxidation. The sodium-inert layer may comprise molten aluminium ( ) and/or a layer of refractory hard material ( &prime;).

Prevention of dissolution of metal-based aluminium production anodes

A method of manufacturing an anode for use in a cell for the electrowinning of aluminium comprises oxidising before cell operation an iron-nickel alloy substrate in an oxygen-containing atmosphere, such as air, at a temperature which is at least 50&deg; C., preferably 100&deg; C., above the operating temperature of the cell to form on the surface of the iron-nickel substrate a coherent and adherent iron oxide-containing outer layer, in particular a hematite-containing layer having a limited ionic conductivity for oxygen ions and acting as a partial barrier to monoatomic oxygen. The outer layer is electrochemically active for the oxidation of oxygen ions and reduces also diffusion of oxygen to the iron-nickel alloy substrate when the anode is in use.

Nickel-iron alloy-based anodes for aluminium electrowinning cells

A bipolar cell for the electrowinning of aluminium has bipolar electrodes each comprising a carbon cathode body having on one side an active surface on which aluminium is produced and connected on the other side through an oxygen impermeable barrier layer to an electrochemically active anode layer having an oxygen evolving iron oxide-based outer surface. The anode layer may comprise a metal-based anode substrate and a transition metal oxide-based outside layer, in particular an iron oxide-based outside layer, which either is an applied layer or is obtainable by oxidising the surface of the anode substrate which contains iron. During operation, the anode layer can be kept dimensionally stable by maintaining in the electrolyte a concentration of transition metal species which are present as one or more corresponding transition metal oxides in the electrochemically-active layer. The cell operating temperature is sufficiently low so that the required concentration The cell operating temperature is sufficiently low so that the required concentration of transition metal species in the electrolyte is limited by the reduced solubility thereof in the electrolyte at the operating temperature. This limits the contamination of the product aluminium by the transition metal species to an acceptable level.

Bipolar cell for the production of aluminium with carbon cathodes

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 layer , an 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 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.

An anode of a cell for the electrowinning of aluminium comprises an iron-nickel alloy body or layer whose surface is oxidised to form a coherent and adherent outer iron oxide-based layer, in particular hematite, the surface of which is electrochemically active for the oxidation of oxygen ions and which reduces diffusion of oxygen from the electrochemically active surface into the iron-nickel alloy body or layer. The anode may be kept dimensionally stable during cell operation by maintaining a sufficient amount of dissolved alumina and iron species in the electrolyte to prevent dissolution of the outer oxide layer of the or each anode and by reducing the electrolyte operating temperature to limit dissolution of iron and by reducing the electrolyte operating temperature to limit dissolution of iron species in the electrolyte.

An electrolytic cell for the electrowinning of aluminium comprises a cathode cell bottom provided with a series of sloped active cathode surfaces ( ) down which produced aluminium ( ) is drained, and a series of recessed grooves or channels ( ), below the bottom of the cathode active surfaces ( ) and extending therealong which collect and evacuate the drained produced aluminum ( ). Preferably the active surfaces ( ) are V-shaped and the recessed grooves or channels ( ) are provided with a sloping bottom and a constant cross-sectional area. Alumina is so fed into the cell as to supply alumina-rich electrolyte ( ) into the recessed grooves or channels ( ) which contain the alumina-rich electrolyte along substantially their entire length above the drained layer of aluminium ( ). The recessed grooves or channels ( ) supply the alumina-rich electrolyte ( ) to the bottom part of the active cathode surfaces ( ) under the effect of the electrolyte circulation produced by propelling gas ( ) released under the anodes.

Drained cathode aluminium electrowinning cell with alumina distribution

A non-carbon, metal-based slow-consumable anode of a cell for the electrowinning of aluminium self-forms during normal electrolysis an electrochemically-active oxide-based surface layer ( ). The rate of formation ( ) of the layer ( ) is substantially equal to its rate of dissolution ( ) at the surface layer/electrolyte interface ( ) thereby maintaining its thickness substantially constant, forming a limited barrier controlling the oxidation rate ( ). The anode ( ) usually comprises an alloy of iron with at least one of nickel, copper, cobalt or zinc which during use forms an oxide surface layer ( ) mainly containing ferrite.

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Geneva, Switzerland

Jean-Jacques R Duruz