Chemistry: electrical and wave energy – Processes and products
Patent
1989-02-15
1991-05-28
Niebling, John F.
Chemistry: electrical and wave energy
Processes and products
304 64R, 304243R, 304290R, 304291, 204292, 204293, C25C 306, C25C 308
Patent
active
050192256
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to an electrode for electrowinning a metal by electrolysis of a compound of the metal dissolved in a molten salt electrolyte, the electrode having a body at least a section of which is cathodically polarized. The invention further relates to a cell for molten salt electrowinning comprising at least one electrode according to this invention, and finally the invention relates to a method of electrowinning a metal by molten salt electrolysis using at least one electrode according to the present invention.
BACKGROUND ART
In the art of electrowinning aluminum by electrolysis of alumina dissolved in molten cryolite, considerable efforts have been made to provide dimensionally stable materials for cell components which are in contact with the liquid contents of the cell. Such components include the electrodes as well as lining materials and elements which are immersed in the liquid aluminum to restrict hath movements.
Among the materials proposed for use under the severe corrosion conditions in a molten salt electrolysis cell are primarily the refractory oxides; the Refractory Hard Metal (RHM) borides and cermets containing either of them together with an intimately mixed metallic phase for applications where high electrical conductivity is essential.
Refractory ceramic and cermet materials are known from numerous publications. These materials are used in a wide variety of applications, and their specific composition, structure and other physical and chemical properties may be adapted to the specific intended use.
Materials which were proposed for their use as anodes in molten salt aluminum electrowinning cells are mainly based on oxides of e.g. iron, cobalt, nickel, tin and other metals, which oxides may be provided with enhanced electronic conductivity by doping, non-stoichiometry and so forth. Cathodic materials are mainly based on titanium diboride and similar RHM boride compounds. For example, EP-A-0 115 689 discloses reaction sintered oxide-boride ceramic bodies and EP-A-0 116 809 discloses a porous oxide-boride cermet which is infiltrated with molten aluminum. Oxide-boride ceramics have however not proven to be commercially acceptable as cathode materials in molten salt electrolysis.
FR-A-2 375 349 has described bipolar electrodes with an anode made of a boride/silicide/carbon composite and a cathodic section of various borides including titanium diboride and yttrium boride.
A completely new concept for a dimensionally stable inert anode for an aluminum cell and its manufacture was described in EP-A-0 114 085 wherein such anodes are produced by depositing in-situ a fluorine-containing oxycompound of cerium (referred to as "cerium oxyfluoride") on an anode substrate during electrolysis, with a cerium compound dissolved in the melt and maintained at a suitable concentration. This anode coating is maintained dimensionally stable as long as a sufficient concentration of the cerium-containing compounds is maintained in the melt.
In EP-A-0 094 353 it has also been proposed to use materials in a molten salt aluminum electrowinning cell which are composed of a refractory ceramic coated with TiB.sub.2 and wherein the TiB.sub.2 coating is maintained by addition of titanium and boron to the liquid aluminum.
A co-pending patent application Ser. No. 322,850, which was simultaneously filed with the present application discloses a new substrate material for the above described cerium oxyfluoride anode coating, this new substrate material being a cermet having a ceramic phase basically comprising a mixture of cerium oxide(s) and alumina and a metallic phase comprising an alloy of cerium and aluminum.
OBJECTS OF THE INVENTION
It is one of the objects of the present invention to provide a new electrode for aluminum electrowinning by electrolysis of a molten salt electrolyte comprising alumina, which electrode has a cathodic section which may be kept dimensionally stable during operation.
It is another object of the present invention to provide an electrode with a catho
REFERENCES:
patent: 3930967 (1976-01-01), Alder
patent: 4111765 (1978-09-01), DeNora et al.
patent: 4309467 (1982-01-01), Kovach et al.
patent: 4529494 (1985-07-01), Joo' et al.
Darracq Dominique
Durmelat Claude
Duruz Jean-Jacques
Freer John J.
Gorgos Kathryn
Moltech Invent S.A.
Niebling John F.
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