Moltech Invent S.a.

Olivier Crottaz

Jean-Jacques R Duruz

Vittorio De Nora

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

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 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.

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Petit-Lancy, Switzerland

Olivier Crottaz