Chemistry: electrical and wave energy – Processes and products
Patent
1988-06-13
1989-09-26
Niebling, John F.
Chemistry: electrical and wave energy
Processes and products
204 66, 204243R, 204247, C25C 300, C25C 700
Patent
active
048697907
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to the separation of metals from metal salts and more particularly relates to the separation of metals from fused salts by electrochemical or electrowinning processes.
It is known to separate certain metals from their salts by electrolysis of the molten electrolyte for example, the individual separation of aluminum may be achieved by the electrolysis of a molten solution of alumina in cryolite (the so-called Hall-Heroult process). An alternative process for the production of aluminium involves the electrolysis of molten aluminium chloride using a bipolar cell. Also magnesium may be produced by the electrolysis of molten magnesium chloride in a bipolar cell as disclosed in European patent numbers 0096990 and 0101243.
Requirements for the efficient production of metals by electrolysis of their molten salts include a cell having a low tendency for the products of the electrolysis to recombine and a low electrical internal resistance. The tendency for recombination may be overcome by the interposition of a diaphragm to separate the anode and cathode. However, the presence of the diaphram tends to internal resistance of the cell.
SUMMARY OF THE INVENTION
Thus, it is desirable to have a diaphragmless cell having high current efficiency by use of reduced anode-cathode gaps giving reduced internal resistance but without significant recombination of the products of the electrolysis. The present invention relates to an improved process for the separation of metals by electrolysis of a molten salt which uses rotating or movable electrodes to reduce the tendency for product recombination.
Thus according to the present invention there is provided an electrolytic cell for the electrolysis of molten salts comprising a container for a molten electrolyte, an anode electrode and a cathode electrode, one or both being adapted for rotation and being located within the container, the electrodes having means facilitating the removal of evolved gases from the surfaces of the electrodes and means for collecting metal liberated at the electrode.
The rotatable anode or cathode are suitably conical in shape, the apex of the cone oriented upwardly towards the top of the cell. The conical shape of the cell tends to enhance removal of the products of electrolysis by the effect of gravity and the effect of centrifugal forces. The cell is preferably a bipolar cell and most preferably has a plurality of conical shaped electrodes, the electrodes being arranged in a symmetrical stack. The angle of divergence of the come from the horizontal is preferably from 30.degree. to 50.degree..
BRIEF DESCRIPTION OF THE DRAWINGS
The means facilitating removal of evolved gases from the surfaces of the electrodes preferably comprises one or more vent holes preferably passing through the upper most electrode of the cell. The rotational speed of the electrodes is dependent on the flow conditions but is usually chosen to give a minimal degree of turbulence, turbulence tending to cause the undesirable recombination of the products of electrolysis.
Also according to a further aspect of the invention there is provided a process for producing metal from molten metal salts comprising the steps of (a) electrolysing the molten metal salt in a container having one or more anode and cathode electrodes, (b) the electrodes being adapted for relative rotation and having means facilitating the removal of evolved gases, and (c) collecting the metal liberated from the electrode. The process may be a batch process or a continuous process. The electrodes of the cell may be treated e.g. by coating with a suitable material, to enhance the flow of the metal produced off the surface of the electrodes. The electrodes are preferably fabricated from graphite and is preferably very hard so as to resist impact or mechanical damage. It is also envisaged that conducting borides such as titanium boride could be used as the cathode and inert conducting oxides as the anode. It is envisaged that the cell and process may be u
REFERENCES:
patent: 808095 (1905-12-01), Lang
patent: 3450524 (1969-06-01), Pascaud et al.
patent: 3691048 (1972-09-01), Yznaga
patent: 3909375 (1975-09-01), Holiday et al.
Bureau of Mines Report of Investigations, 6454, 1964, by F. X. McCawley et al., pp. 1-4.
Charles James A.
Copham Piers M.
Fray Derek J.
Curatolo Joseph G.
Evans Larry W.
Moxon II George W.
Niebling John F.
Ryser David G.
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