US1782616A - Electrolytic apparatus for refining aluminum and for like processes - Google Patents

Description

P. L. HULEN ELECTROLYTIC APPARATUS FOR REFINING ALUMINUM AND FOR LIKE FROGESSES Nov. 25, 1930.

Filed June 19, 1928 Patented Nov. 25, 1930 UNITED, STATES PATENT OFFICE I AUL LEON H'ULIN, OF GRENOBLE, FRANCE, ASSIGNOR T0 SOCIETE ANONYME COM- PAGNIE DE PRODUI'IS CHIMIQUES E'I. ELECTROMETALLUBGIQUES ALAIS, FROGES ET CAMARQUE, OF PARIS, FRANCE ELECTROLYTIC APPARATUS FOR REFINING ALUMINUM AND FOR LIKE PROCESSES Application filed June 19, 1928, Serial No. 286,588, and in France July 4, 1927.

This invention relates to the electrolytic refining of aluminum and like processes, and has for its primary object improvements in apparatus wherein refined aluminum is produced on the surface of an electrolytic bath, upon which it collects and'floats in the liquid condition, said aluminum being extracted from a denser molten alloy or metallic layer at the bottom of the apparatus. The invention is applicable also to any similar operation relating to the extraction of one or more metals of the same kind.

The apparatus operates in accordance with the classic process of the electrolytic extraction of light metals, in which the metal to be refined or extracted constitutes the anode and occupies the bottom of the apparatus in the condition of an alloy or metallic la er, in a state of-fusion'and denser than the e ectrolyte, whilst the light metal liberated by the electrolysis forms a liquid layer which floats on the electrolyte and there plays the part of the cathode.

The cathode. metal is removed periodically, whilst the anode is reconstituted, suitably, either by admixture of impure light metal, or'by partial or complete replacement of the mass.

Referring to the drawings:

Figure 1 is a sectional elevation of an apparatus embodying the present invention;

Figure 2 is a View similar to Figure 1 showing an insulating crust;

Figure 3 illustrates a sectional elevation showing the successive inner walls;

Figure 4 is a sectional elevation of an aluminum refining apparatus according'to my invention;

Figure 5 is a sectional elevation of. another embodiment of the invention.

This known process is carried out in an apparatus such as thatrepresented diagrammatically, as a sectional elevation, in Figure 1 of the accompanying drawings,.Figure 2 being a similar view showing an insulating crust instead of a complete lining of refractor material.

is an electrolytic tank (of iron, steel or the like). B is an interior lining of refractory material. C is the layer of light metal acting as the cathode. D is the denser alloy,

containing the metal and acting as the anode.

It will be understood that the apparatus is completed by the usual accessory devices (electric leads, pouring tap, etc.).

Usually the anode alloy D is arranged on a conductive sole, or better, contained in a carbon crucible F, the edges of which have hitherto been lower than the level of the anode alloy.

The lateral lining B should insulate completely the metal tank A and prevent any electrical connection between the electrodes C and D; moreover, it should offer adequate resistance to the solvent or liquefying action of the molten electrolyte. These conditions are most diflicult to secure conjointly, especially in the case of refining aluminum.

Since no insulating material capable of suitably resisting molten fluorides has been discovered, it has long been the practiceespecially in the case of the fluoride baths from which aluminum is extractedto form a lining for the electrolyzing tank by solidifyby externally applied cooling means, first with air, then by spraying, and finally by a cirqulation of water on the water-jacket princ1p e.

Figure 2 represents diagrammatically, at B, an insulating crust formed by the preliminary solidification of the electrolyte on the suitably cooled metal wall A. a

The layer C of light metal bears laterally against this lining, which, of course, should extend above the level of the metal.

The lining thus formedis highly unstable, tending to increase and diminish in thickness successively, according to variations in the working conditions of the electrolysis. The inner surface of this crust is necessarily pasty and lacking in consistency, so that it gives way or slips toa greater or less extent on contact with the metal. This gives rise to'diffusion of the liquid or pasty bath, the formation of magmas, excrescences, dispersions'of the hardened bath, and so on, which invade mg a layer of electrolyte on the metal walls lining presents a large superficial area, and

it is therefore impossible to raise the tem* perature of the bath to any notable extent above its fusing point, without lowering the insulation so far as to destroy it, and without affecting adversely the constitution of the apparatus itself.

The present invention provides electrolytic apparatus suitable for refining aluminum or for similar operations and intended to remedy the aforesaid inconveniences. It is characterized essentially by an arrangement of practically stable walls disposed in the zone of the electrolyte and that of the floating metal, ensuring the separation and insulation of the superimposed liquid layers, obviating the harmful penetration of hardened bath material into the refined metal, facilitating the accession and collection of the latter and the cathodic connection of the current in said layer of met-a1, greatly reducing the possibilities of oxidation, and so on.

With this object the lateral walls of the apparatus are divided into three distinct stages,

which are independent electrically the anode stage, the wall of which is formed by the edges of the bottom crucible; the electrolyte stage, the wall of which is formed by a frame of insulating material; and the cathode stage, the wall of which is a carbon frame electrically insulated from the exterior metal shell.

In the accompanying drawings, Figure 3 represents, as a sectional elevation, the essential composition of this system of apparatus with inner walls arranged in stages. The wall F, which contains the anode, is preferably of agglomerated carbon or graphite. The wall H, which surrounds the electrolyteis composed of suitable insulating material, or formed of the solidified electrolyte. The wall G, which encloses the cathode, is of agglomerated carbon or graphite. BB denote insulating substance inserted between the shell A and the walls G and F.

By reason of this arrangement, the refined metal accumulated as a liquid layer over the electrolyte is not surrounded by an electrically neutral wall with a asty and varying surface, formed by the so idified electrolyte, but rests against firm and solid walls which, at the same time, are conductors of current and electrically active.

The insulating wall H, reduced in height and situated lower than the crust B shown in Figure 2 is no longer exposed to the pressure and deforming influence of the bath of cathode metal; and bein protected, both above and below, by two ot er solid and fixed (except for wear{) walls, it acquires a satisfactory ing the aluminum to be refined, disposed in the carbon crucible F; E the electrolyte, forming a liquid layer of intermediate density and separating the electrodes C and D.

On the other hand, unlike the existing arrangement, the layer C of pure aluminum forming the active cathode, instead of being surrounded by an insulating material with a pasty and fugitive surface, is contained laterally b -a carbon frame G, forming a wall of de nite and invariable shape, which is independent of the shell A and, moreover, exhibits the characteristic of being an electric conductor. Between this carbon frame C and the upper edge of the crucible F also of carbon, a peripheral recess h is formed for housing a hollow metal frame H traversed by a current of water admitted and remove by pipe connections such as e.

The molten electrolyte with which the apparatus has been charged penetrates into the space it surrounding the frame H. There it is solidified by the cooling effect produced by the circulation of the water in the frame H, and forms an insulating ring or belt, which, in the example shown is of recumbent channel cross-section, separating the two carbon linings G and F.

This insulating ring, formed in the said manner and held between fixed solid members, may be kept out of contact with the liquid cathode, thus preventing the disturbances occurrin round this latter when entirely surroun ed by solidified electrolyte according to the principle set forth above with reference to Figure 2.

In the present arrangement, the height of the zone of solidified electrolyte is reduced to a minimum, thereby minimizing, and even rendering negligible, the consequence of the changes in thickness to which walls of this kind are, necessarily, liable.

This reduction of the area of solidified bath in contact with the molten electrolyte effects a saving in the energy required to keep the electrolyte in a state of fusion. The same reduction of the solidified zone enables the temperature of the electrolyte easily and quickly to be raised when necessary, Withoutand this is a very important point thelrieby causing any change in the cathode wa fyerted bowl G; with a. large central open mg.

Another characteristic feature of the invention is that the peripheral carbon lining G, which is in contact with the cathode of aluminum, serves to bring the current to the latter, with the advantage of affording readier access to' the up er part of the apparatus and the layer of re ned aluminum.

This lining G, which is covered convenratus to be shut o from the outer air when desired. I

Another embodiment of the invention, specially characterized by the arrangement of the cathode system, is shown in sectional elevation in Figure 5 of the accompanying drawings.

In this arrangement, the carbon lining G is extended towards the centre of the apparatus, in the form of a flattened hood or in- The refined aluminum collects under this hood or cupola, and is there protected efficiently. In this manner, the same active cathode surface is provided, as in the previous case, but the up er face, which is exposed to the air, is re uced considerably. in

this way a kind of pit J is formed, in which the refined metal collects to a greater thickness and whence it can be removed easily. 1

Other openings could, of course, be formed in the hood G according to requirements. Similarly, the pit J might, if desired, be disposedout of centre towards one side of the apparatus, in order to render it more accessible in an apparatus of large dimensions.

The inner rim of the pit J, which is in contact with the air, is preferably composed of a ring K of suitable refractory material, such as alundum, that is, very compact alumina,- or of corundum, both being agglomerated.

The hood G is preferably of graphite and a may be composed of several ,parts assembled together in various ways The same applies also to the frame C, Figure 4. The ring K,

Figure 5, might extend further towards the lining G' or be more or less merged into the insulating material m.

The cover plate I, is of course, adapted to the shape of the hood G to which it may convey the current in the manner already indicated with reference to Figure 4:. A thick layer m of heat-insulating material may be inserted between the hood G and the cover plate I.

The apparatus thus constituted is particularly suitable for being fitted with a detachable cover L, so that it can operate with exclusion of air and extraneous substances.

The other part of the apparatus according to Figure?) are similar to those ofthe apparatus according to Figure 4.

Any of the usual known other auxiliary accessories or devices may of course be adapted to the unit,'or employed in the service of the present system of apparatus, without any illustration or description being-necessary.

The apparatus forming the object of the invention, the essential arrangements and principles of which have just been described, is set in operation by any known means,

Being charged, in succession, with anode alloy, electrolyte and pure aluminum, all three in a good state of fusion, it may then be set in operation, the amount of current varying according to the dimensions of the apparatus, but about 8000 to 10000 amperes per sq. metre of electrode unit.

It may be started on cold materials by inportions do not represent limits. Other ele-.

ments, less electropositive than aluminum, may be added to the anode alloy in order to increase its density or fusibility.

When the anode alloy no longer contains sufficient aluminum, it receives a fresh charge thereof by means of a graphite dipping tube, or is itself drawn oil through a lower tap hole 0 and replaced by a fresh charge of molten alloy, introduced in the same manner through a graphite tube passed through the layer of refined metal.

The electrolyte has a cryolite basis, and contains a small proportion of alumina, and

a certain addition of aluminum fluoride and (above all) barium fluoride, so as to mcrease the density of thebath E to above that of the refined aluminum C.

These various compositions for obtaining suitable relative densities for the anode alloy and the bath, being variable and already known, per se, form no part of the invention; and the same applies to the composition and method of replenishing the anode alloy.

The described system of apparatus, which is more particularly intended for refining aluminum, may be applied to the extraction orrefining of other light metals.

Claims 1. An electrolytic apparatus for refining aluminum, extracting other metals, and similar operations, comprising a shell containing three superimposed layers in a state of fusion consisting of an anode of a dense alloy of the metal to be extracted, a halogenated bath forming the electrolyte, and a light metal forming the floating cathode, and an inner lining composed of a horizontal frame, of refractory material or carbon, surrounding the anode, a horizontal frame of insulating material containing the electrolyte, and a frame composed substantially of carbon, surrounding the cathode and insulated fromthe metal shell.

2. An electrolytic apparatus for refining aluminum, extracting other metals, and similar operations, comprising a shell containing three superimposed layers in a state of fusion consisting of an anode of a dense alloy of the metal to be extracted; a halogenated bath forming the electrolyte, and a light metal forming the floating cathode, and an inner lining composed of a horizontal frame, of refractory material or carbon, containing the anode, a horizontal frame of insulating material surrounding the electrolyte, and a frame composed substantially of carbon, surrounding the cathode and insulated from the metal shell, the insulating frame separating the car- 'bon cathode lining from the lower anode lining, and being composed of solidified electrolyte.

3. An electrolytic apparatus for refining aluminum, extracting other metals, and similar operations, comprising three superimposed layers in a state of fusion consisting of an anode of a dense alloy of the metal to be extracted, a halogenated bath forming the electrolyte, and a light metal forming the floating cathode, and an inner lining composed of a horizontal frame, of refractory material or carbon, containing the anode, a horizontal frame of insulating material containing the electrolyte, and a frame composed substantially of carbon, surrounding the cathode and insulated from the metal shell, the carbon frame enclosing the floating cathode being electrically active and being employed to lead the current into said metallic layer.

4. An apparatus for refining aluminum by electrolysis with fused fluorides, having a lateral lining comprising three superimposed members. consisting of a bottom member of carbon, a ring of solidified electrolyte and an upper member of carbon.

5. An electrolytic apparatus for refining aluminum, extracting other metals, and similar operations, comprising three superimposed layers in a state of fusion consisting of an anode of a dense alloy of the metal to be extracted, a halogenated bath forming the electrolyte, and a light metal forming the floating cathode, and an inner lining composed of a horizontal frame, of refractory material or carbon, containing. the anode, a horizontal frame of insulating material containing the electrolyte, and a frame composed substantially of carbon, surrounding the cathode and insulated from the metal shell, the upper member of the lining being extended above the bath, forming a hooded cover protecting the metallic layer and forming a pit in which the resulting metal collects readily.

6. An electrolytic apparatus for refining aluminum, extracting other metals, and similar operations, comprising a shell containing three superimposed layers in a state of fusion consisting of an anode of a dense alloy of the metal to be extracted, a halogenated bath forming the electrolyte, and a light metal forming the floating cathode, and an inner lining composed of a horizontal frame,- of refractory material or carbon, containing the anode, a horizontal frame of insulatinv material containing the electrolyte, and a rame composed substantially of carbon, surrounding the cathode and insulated from the metal shell, the upper member of the lining being extended above the bath, forming a hooded cover protecting the metallic layer and forming a. pit in which the resulting metal collects readily, the opening in the carbon hood being lined with a ring of refractory material.

7. An electrolytic apparatus for refining aluminum, extracting other metals, and sim ilar operations, comprising a metal shell containing three superimposed layers in a state of fusion consist-ing of an anode of a dense alloy of the metal to be' extracted, a halogenated bath forming the electrolyte, and a light metal forming the floating cathode, and an inner lining composed of a horizontal frame, of refractory material or carbon, containing the anode, a horizontal frame of insulating material containing the electrolyte, and a frame composed substantially of carbon, surrounding the cathode and insulated from the metal shell, the upper member of the lining being extended above the bath, forming a hooded cover protecting the metallic layer and forming a pit in which the resulting metal collects readily, a movable cover completing the cathode top, to protect the floating molten metal against oxidation and contamination from outside.

PAUL LEON HULIN.

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