US3386908A - Cell for refining aluminum by fusion electrolysis - Google Patents

Description

June 4, 1968 A. DAURAT 3,386,908

CELL FOR REFINING ALUMINUM BY FUSION ELECTROLYSIS Filed Nov. 27, 1964 Fjg.1 PRIOR ART INVENTOR. Anne: 4. 0400/47 79014 M feat A77]!- United States Patent 3,3863% CELL FOR REFINING ALUMINUM BY FUSION ELECTROLYSIS Andr Daurat, Auzat, Ariege, France, assignor to Pechiney, Compagnie de Produits Chimiques et Eicctrometallurgiques, Paris, France Filed Nov. 27,1964, Ser. No. 414,140

Claims priority, application France, Dec. 3, 1963, 95 ,021 7 Claims. (Cl. 204-243) ABSTRACT OF THE DISCLOSURE A cell for the electrolytic refining of aluminum which comprises an enclosure of refractory material having an access opening at the top and a cover dimensioned to span the access opening formed of a first stationary portion which is fixed to the housing and a movable portion which is adapted to be received in fitting relationship in an opening defined by the fixed stationary portion, an anodic sole plate at the bottom of the enclosure having an electrical connection, an anode layer of aluminum alloy to be refined overlying the anodic sole plate layer, a layer of electrolytic liquor overlying the anode layer, a cathode layer of refined metal substantially of frusto-conical shape having the base portion of larger cross-sectional dimension at the bottom in contact with the electrolytic liquor and an upper exposed portion of lesser dimension, and a cathode in contact with the cathode layer having an electrical lead extending through the housing into contact with the cathode layer.

This invention relates to the production of aluminum and more particularly to a new and improved novel cell for the refining of aluminum by fusion electrolysisf It is well known that cells for fusion electrolysis used for refining aluminum electrolytically generally comprise a conductive soleplate incontact with a soluble anode layer of a metal in the form of an 'alloy of themetal to be refined underlying a layer of electrolytic liquor which is disposed between the anode and a cathode in the form of another metallic layer consisting of the refined aluminum.

Since the final result of the electrolytic operation is selective transference of aluminum from the alloy of the anode to the metal of the cathode which, as stated above, is composed of the refined metal, the polarization voltage is only a very small fraction of the total voltage at the terminals of the cell. When the cell is in operation, the electric power absorbed is substantially equal to the heat losses. It is, therefore, desirable to seek to reduce these losses to a minimum so as to decrease the energy consumption per ton of refined metal. Some reduction may be achieved by thermal insulation of the cell about its bottom and side walls and by providing a hood to cover the upper surface but such usage results in the elimination of conventional suspended electrodes.

The French Patent No. 970,508, granted on June 21, 1956, describes an electrolytic cell for refining aluminum by the process which makes use of three superimposed layers including two conductive soleplates which are arranged at different levels and electrically insulated one from the other and separated by impervious brickwork made of appropriate materials and in contact with an end portion of one of the metallic layers with the soleplates acting as current carriers.

This type of cell has a number of disadvantages. One

Patented June 4, 1968 of the main objections is that the brickwork separating the soleplates tends to deteriorate rapidly because of the seepage therethrough of electrolytic liquor thereby shortening the life of the cell. Another serious objection is that the useful section of the cell is small for equivalent production and therefore calls for an increase in the cost of the cell and the space required to be made available.

It is an object of this invention to produce a cell for fusion electrolysis in the refining of aluminum in which the cell is characterize-d by high yield and it is a related object to produce a cell of the type described for the electrolytic refining of aluminum in which the cell is characterized by a long useful life and a working area of large dimension for greater efficiency.

' These and other objects and advantages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, embodiments of the invention are shown in the accompanying drawing, in which:

FIG. 1 is a schematic sectional elevational view of a cell embodying the construction heretofore employed for fusion electrolysis;

FIG. 2 is a schematic sectional elevational view of a cell embodying the features of this invention for fusion electrolysis in the refining of aluminum; and

FIG. 3 is a schematic sectional elevational view similar to that of FIG. 2 showing a modification in the fusion electrolysis cell.

Briefly, described, a cell embodying the features of this invention for high yield fusion electrolysis in the refining of aluminum and which is characterized by a long useful life and maximum working area comprises a cell having a cover which at least partially extends over a bath of refractory material; an anode formed of the alloy tobe refined in contact with an anodic soleplate in the bottom of the bath and having at least one current input lead which passes upwardly through the bath; and a cathode formed of the metal which is refined in contact with at least one cathodic electrode having at least one current input lead which passes downwardly through the bath and which is suspended from the upper portion of the masonry.

In a special embodiment of the invention, the electrolytic cell further comprises at least one of the additional features, namelythe bath is partially closed at its upper portion by a cover which is integral with the masonry of the bath and which contains an aperture sealed by a movable portion of the cover from which the cathodic electrode is suspended and in which the bath is closed in its upper portion by a cover comprising a stationary part integral with the masonry of the bath and from which the cathodic electrode is suspended and a movable portion through which access can be gained to the interior.

With reference now to the drawing, illustration is made of a bath 10 (5%) in FIG. 2) in FIG. 3) of insulating brick separated from the liquor by a lining in the form of a brickwork 11 (51 in FIG. 2) (71 in FIG. 3) of anticorrosive material. At the lower end of the space defined by the brickwork 11 is the anodic conductive soleplate 12 (52 in FIG. 2) (72 in FIG. 3) underlying the layer 15 (55 in FIG. 2) (75 in FIG. 3) of the alloy to be refined which in turn underlies the layer 16 (56 in FIG. 2) (76 in FIG. 3) of the electrolytic liquor. The latter is in turn covered by a layer 17 ('57 in FIG. 2) (77 in FIG. 3) of refined metal which functions as the cathode. The current reaches the :anodic soleplate through lead 18 (58 in FIG. 2) (78 in FIG. 3). In the standard cell of FIG. 1, the cathodic layer 17 of refined meal communicates at one end with a soleplate 13 which rests on the insulating brickwork 10 and is confined between the anti-corrosive linings 11. The lead 19 extends upwardly through the brickwork 10 into electrical contact with the soleplate 13.

The removable cover 14 extends across the upper portion of the cell to minimize heat loss from the bath in the upward direction.

The anodic alloy to be refined is supplied to the layer 15 (55 in FIG. 2) (75 in FIG. 3) through insulated pits 20 (60 in FIG. 2) (80 in FIG. 3) arranged in laterally spaced apart relation in the brickwork for good heat insulation, with each pit being provided with a removable lid 21 (61 in FIG. 2) ('81 in FIG. 3) over the inlet.

In FIG. 1, the refined aluminum is removed from the layer 17 by a suction tube operating through the top of the cell, either through an opening provided in the cover 14, which may or may not be provided with a sealing lid, or through the wide opening, when the cover is removed.

This arrangement has a number of disadvantages:

(1) The liquor 16 seeps into the anti-corrosive brickwork 11 and often operates to bring the liquor 16 into direct contact with the cathodic soleplate 13 and its lead 19 with the result that a large amount of energy is lost and the cell rapidly becomes inoperative;

(2) The alloy 15 may also seep into the brickwork 11 to cause a short-circuit between the anodic alloy 15 and the cathodic soleplate 13 with its lead 19;

(3) The working section of the bath, defined by the electrolytic liquor 16, is of small cross-section as compared to the total cross-section of the cell thereby to increase the cost of the bath and the amount of space required per unit volume of production;

(4) Consumption of electrolytic liquor 16 increases in proportion to the area of contact between the refined metal 17 and the atmosphere and, as will be seen, this area is far greater than the useful section thereby to introduce undesirable inefiiciencies;

The area of the cover is very large in relation to the useful section of the bath thereby to expose a substantial area to heat loss and the cover of larger dimension is more expensive and clifficult to operate.

In accordance with the practice of this invention, the cells shown in FIGS. 2 and 3 differ essentially from that of FIG. 1 in that instead of making use of a cathodic soleplate 13, use is made of a suspended electrode 53 in FIG. 2 and 73 in FIG. 3 with the leads 59 and 79 extending through the upper portion of the housing and fixed to some portions thereof to permit complete hooding.

In the cell of FIG. 2, use is made of a two-part cover in which one part 54 is fixed to form an integral part of the masonry 50 of the bath and which is formed with an access opening at the top of specific dimension. The other part 63 is a movable member in the form of a lid having a lower portion which is dimensioned to be received in fitting relationship within the opening and an upper portion of larger dimension than the opening to extend beyond the edge portions of the fixed portion so as to rest upon the portions of the stationary cover adjacent the opening when the portion of smaller dimension is received within the opening to seal the opening. The cathode electrode 53 is suspended from the stationary portion 54 of the cover and the lead 59, for current input, passes through said cover portion.

In the cell shown in FIG. 3, the cover again comprises a stationary portion 74 fixed to form an integral part of the masonry 70 of the bath and it is also formed with an opening therethrough for gaining access to the interior of the bath. The other portion 83 comprises a movable member similar to that described with reference to the lid 63 of FIG. 2. The cathode electrode 73 is suspended from the movable portion of the cover with the lead 79 extending therethrough.

With this construction, it is possible to arrange the cell with the cathode layer 57 dimensioned to span the entire bath for maximum area of contact with underlying layer 56 of electrolytic liquor and with the upper end portion of the cathode layer of lesser dimension to accommodate the cathode 53 alongside thereof without increasin the dimension of the bath. For this purpose, as shown in FIGS. 2 and 3, the cathode layer 57 and 77 is formed of a base portion of maximum crossseotion with a portion of frusto-conical shape in an intermediate portion, as shown in FIG. 2, or in an upper end portion, as shown in FIG. 3, to form the upper portion of lesser dimension than the base portion to accommodate the cathode 53 alongside the upper portion of the cathode layer of smaller dimension, as shown in FIG. 2, or for contact with the central portion of the cathode layer, when suspended from the movable lid, as shown in FIG. 3.

This novel arrangement obviates many of the disadvantages of the present cell as outlined above and as hereinafter briefly outlined:

(1) Attack on the brickwork 51 or 71 no longer remains as a problem since the brickwork has no point of weakness on the level of the liquor;

(2) Short-circuiting between the anodic alloy 52 or '72 and the cathodic electrode 53 or 73 will no longer occur since the electrodes and their corresponding leads are not at a level corresponding to that of the alloy;

(3) The useful section of the cell is markedly increased by comparison with thearrangement of FIG. 1 thereby to provide for a considerable reduction in the cost of insulation and in the amount of space required for the cell;

(4) The area of contact between the refined metal 57 or 77 and the air is less than that of the useful section thereby correspondingly to reduce the consumption of electrolytic liquor;

(5) The area of the access opening through the cover is markedly reduced;

(6) In the event of need for replacement of a graphite electrode for reasons of combustion, repair or exchange, access to the electrode can be had more easily and at less expense with cells of the type illustrated in FIGS. 2 and 3.

It will be apparent from the foregoing that the cell of this invention obviates the disadvantages experienced with cells of the type presently employed and at the same time permits integral hooding which is important to the achievement of high yields.

It will be understood that changes may be made in the details of construction, arrangement and operation, without departing from the spirit of the invention, especially as defined in the following claims.

I claim:

1. A cell for the electrolytic refining of aluminum comprising an enclosure of refractory material having an access opening at the top and a cover dimensioned to span the access opening formed of a first stationary portion fixed to the housing and having an access opening therethrough and a second movable portion adapted to be received in fitting relationship within said opening, an anodic soleplate at the bottom of the enclosure and an electrical lead extending upwardly through the enclosure into contact with the soleplate, an anode layer of aluminum alloy to be refined on the upper surface of the anodic soleplate, a cathode layer formed of the refined metal of greater cross-sectional dimension at the bottom portion and lesser dimension at its upper portion, a cathode in contact with the cathode layer and an electrical lead extending downwardly through the housing into contact with the anode, and a layer of electrolytic liquor in communication between the cathode layer and the anode layer, the cathode being suspended from the upper portion of the enclosure.

2. A cell as claimed in claim 1 in which the cathode is suspended from the movable lid.

3. A cell as claimed in claim 1 in which the cathode is suspended from the fixed portion of the cover.

4. A cell as claimed in claim 1 in which the cathode layer and the layer of electrolytic liquor are each of maximum dimension at their interface.

8,386, 908 5 6 5. A cell as claimed in claim 1 in which the cathode v References Cited is positioned alongside a portion of the cathode layer. P A NT 6. A cell as claimed in claim 5 in which the cathode UNITED STATES TE S is positioned alongside the upper portion of the cathode 2 g g g layer offset inwardly from the enclosure to maximize 5 22455O5 6/1941 2o4 67 the cross-section of the layer below the cathode. 16 en op 7. fi cell as claimed in claim 1 in which the cathode JOHN H. M ACK Primary Examiner. 1s positloned alongside the upper portion of lesser di- I mension and in an area which does not extend beyond the HOWARD WILLIAMS Examine base portion of larger dimension. 10 D. R. VALENTINE, Assistant Examiner.

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