Prevention of dissolution of metal-based aluminium production anodes

Abstract

A method of inhibiting dissolution of a transition metal alloy anode (40) of an aluminium electrowinning cell comprises providing a barrier layer (11,20,50,50′) on a non-anodic structural cell material (15), such as carbon, and electrolysing alumina dissolved in a molten electrolyte (30). The non-anodic structural material is able to supply an oxidisable by-product to the electrolyte and / or is active for reducing electrolyte species exposed to the structural material into an oxidisable by-product, such as sodium metal or carbon dust. However, the barrier layer inhibits the presence in the molten electrolyte (30) of the oxidisable by-product that constitutes an agent for chemically reducing the anode's transition metal oxides and anodically evolved oxygen. This inhibits reduction of the anode's transition metal oxides by the oxidisable by-product and maintains the anodically evolved oxygen 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 barrier layer may comprise molten aluminium (20) and / or a layer of refractory hard material (11,50,50′).

Description

FIELD OF THE INVENTION

[0001] This invention relates to inhibiting dissolution of an oxygen-evolving anode of a cell for the production of aluminium from alumina dissolved in an sodium ion-containing molten electrolyte. BACKGROUND ART

[0002] The technology for the production of aluminium by the electrolysis of alumina, dissolved in molten cryolite, at temperatures around 950° C. is more than one hundred years old. This process, conceived almost simultaneously by Hall and Héroult, has not evolved as many other electrochemical processes.

[0003] Industrial anodes are still made of carbonaceous material and must be replaced every few weeks. During electrolysis the oxygen which should evolve on the anode surface combines with the carbon to form polluting CO2 and small amounts of CO and fluorine-containing dangerous gases. The actual consumption of the anode is as much as 450 Kg / Ton of aluminium produced which is more than ⅓ higher than the theoretical amount of 333 Kg / Ton.

[0004] Using m...

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