Chemistry: electrical and wave energy – Processes and products
Patent
1990-03-15
1992-08-04
Valentine, Donald R.
Chemistry: electrical and wave energy
Processes and products
204243R, 204294, C25C 308
Patent
active
051356210
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to aluminum reduction cells of the type having a cell bottom comprising a carbon body through which current is supplied to a pool of molten aluminum resting on the cell bottom, as well as to methods of fabricating and assembling such cells and methods of producing aluminum by electrolysis of a molten salt containing a dissolved aluminum compound in particular molten cryolite containing alumina, using an improved cell of this type.
BACKGROUND ART
Conventional Hall-Heroult cells for the electrolytic production of aluminum employ a carbon cell bottom which serves to supply current to a deep pool of molten aluminum forming the cathode. The cathodic aluminum is necessarily thick (at least 80-100 mm) because carbon is non-wettable by molten aluminum and during operation would not completely cover the carbon if the aluminum layer were thinner. In the conventional arrangement, a horizontal steel conductor bar is embedded in the lower part of the carbon cell bottom for the supply of current from an external source. Thus, the entire cell bottom in contact with the molten aluminum cathode consists of carbon which, in operation, is impregnated with sodium species and other ingredients of the cryolite leading to the formation of toxic compounds including cyanides. Despite the many disadvantages associated with carbon as cathode current feeder material (non-wettability by aluminum, necessitating deep pool operation; the relatively high electrical resistance of carbon, leading to energy losses; reactions within the cell environment necessitating disposal of large quantities of contaminated carbon when the cell bottom is renewed; swelling, which must be compensated by supporting the cell sidewalls in cradles, etc), attempts to replace carbon with theoretically more advantageous materials and employing new cell designs have not so far met with success.
Thus, for example, an aluminum production cell having an electrically non-conductive refractory lining with a "bottom entry" current collector is described in U.S. Pat. No. 3,287,247. The inner end of the current collector has a cap of TiB.sub.2 projecting into a depression containing a deep pool of molten aluminum. U.S. Pat. No. 3,321,392 describes a similar arrangement in which the protruding ends of TiB.sub.2 conductor bars are rounded. U.S. Pat. Nos. 3,093,570 and 3,457,158 disclose similar designs in which bottom-entry cylindrical current collector bars or posts of TiB.sub.2 or graphite extend through a non-conductive refractory lining consisting throughout of powders of alumina and cryolite or aluminum fluoride.
U.S. Pat. No. 4,613,418 has proposed an aluminum production cell with an alumina potlining in which bottom-entry current collectors are embedded and extend to a recess in the potlining. To prevent the unwanted collection of sludge in these depressions, this patent proposes filling the depressions with balls of aluminum-wettable material. Related designs are proposed in U.S. Pat. No. 4,612,103.
These alternative cell designs, using a non-carbon cell bottom, have great promise. Replacement of the carbon cell bottom with, e.g., alumina leads to potential savings in materials and operating costs. However, such proposals heretofore have generally relied on the use of a family of materials known as Refractory Hard Metals ("RHM") encompassing the borides and carbides of metals of Group IVB (Ti, Zr, Hf) and VB (V, Nb, Ta) of the periodic table of the elements. TiB.sub.2 has been identified as the most promising RHM material. The use of these materials as part of the current supply arrangement has encountered a number of problems including cost and the difficulty of producing and machining large pieces of the materials. Such difficulties have led to the design expedients proposed in the aforementioned U.S. Pat. Nos. 4,613,418 and 4,612,103, where, for example, small pieces of TiB.sub.2 are assembled or packed together in an environment of molten aluminum as part of the current supply arrangement.
The problems experienced with RH
REFERENCES:
patent: 3093570 (1963-06-01), Dewey
patent: 3287247 (1966-11-01), Dewey
patent: 3370071 (1968-02-01), Patchett et al.
patent: 3390071 (1968-06-01), McMinn et al.
patent: 3457158 (1969-07-01), Bullough
patent: 3960696 (1976-06-01), Wittner
patent: 4392925 (1983-07-01), Alder et al.
patent: 4505796 (1985-03-01), Huni et al.
patent: 4540475 (1985-09-01), DeAngelis
patent: 4592820 (1986-06-01), McGeer
patent: 4612103 (1986-09-01), Dewing et al.
patent: 4613418 (1986-09-01), Dewing et al.
patent: 4619750 (1986-10-01), Bessard
patent: 4673481 (1987-06-01), Scharpey
patent: 4737254 (1988-04-01), Gesing et al.
patent: 4795540 (1989-01-01), Townsend
patent: 4877507 (1989-10-01), Hudson et al.
Cronin Brian
De Nora Vittorio
Duruz Jean-Jacques
Freer John J.
Moltech Invent S.A.
Valentine Donald R.
LandOfFree
Composite cell bottom for aluminum electrowinning does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Composite cell bottom for aluminum electrowinning, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Composite cell bottom for aluminum electrowinning will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-776122