NL8002381A - ELECTROLYTIC CELL. - Google Patents

Description

N / 29552-Kp / vdM * * - 1 -

Electrolytic cell.

The invention relates to a unique system for the electrolytic preparation of aluminum from a variety of raw materials R containing aluminum in a low temperature electrolytic bath B. The basis for the invention is a unique anode A, which is the sole source of the aluminum deposited on cathode H. The anode A comprises an aluminum source, usually aluminum oxide, Al 2 O 3, and a reducing agent such as carbon. In the anode A, conductors D can be included to improve the conductivity of the anode and a membrane M can be used which contains the raw materials R.

An electrolytic cell C, containing the anode A and cathode H, may have various shapes and electrodes with sloping walls or vertical walls.

In the preferred embodiment of the invention, electrodes with sloping walls are more economical and practical when used at low temperatures with the unique anode.

The electrolytic bath B may be composed of chlorides or fluorides or mixtures thereof, the initial addition of an aluminum salt to the bath being unnecessary. In an embodiment of the invention, the aluminum chloride cycle, aluminum chloride is present in the bath and is kept at a constant concentration by the reaction of the composite anode A in the bath, forming aluminum ions for reduction at the cathode. In another embodiment of the invention using a total fluoride bath, aluminum is also ionized at the anode A for deposition at the cathode H.

In the electrolytic system according to the invention, an electrolytic cell C, which is described with reference to the figures, is used for the unique continuous preparation of aluminum.

In Figures 1-6, a shape of the electrolytic cell structure is generally shown at IQ, composed of a steel outer shell with a difficult-to-melt 800 23 81-2 coating 14, which can either serve alone as a thermal insulator or both as an insulator and as an electrode. The hard-to-melt coating can be of any material that can withstand the action of the molten electrolytic bath 16. The hard-to-melt coating, which has conventional vertical sides 15 and bottom 17, is designed to provide the desired thermal balance in cell operation. and therefore can be very thin in cross-section to obtain a small thermal gradient, leading to a thin layer of congealed salt on the surface of the coating and a warm outer wall on the surface of the steel casing 12. The hard-to-melt coating also be quite thick to obtain a "freeze-out" salt layer within the difficult-to-melt coating, which leads to a cool surface on the steel casing, although this is not necessarily in the vertically arranged cell of Figures 1-6.

In contrast, in the oblique-wall electrode cell of FIG. 7, cathode 19 is a conductive coating formed on both sides of the anode. If desired, a thermal and electrical insulating coating can be placed between the cathode 19 and 20 the sheath 12. An anti-solidification coating must be present within the limits of this conductive coating or cathode 19 to prevent a solid salt layer from accumulating on the bath side of the electrodes. Such a salt layer would act as electrical insulation and prevent an effective electrical current.

The cell is provided at the top with a cover 18, which can close it airtight. This lid is only needed in a bath containing chloride. Thus, this lid prevents air and moisture from entering the cell or 30 vapors of the salt composition 16 from leaking out to react with the environment. The cover 18 may be coated with the hard-to-melt material 20, which may be the same material as the hard-to-melt coating 14 or any other hard-to-melt material, compatible with maintaining a temperature balance in the cell, as well as chemically inert is for the salt composition 16. The cover 18 rests on the seals 22. These seals are also attached to the electrodes 24, 25 and 26 to prevent moisture and 800 2 3 81 6% - 3 - air from entering the atmosphere in the cell penetrate or vapor from the cell to the environment. The seal at the lid 18 and around the electrodes may be of any materials that prevent vapor leaks and may be of standard or conventional packing material that is resistant to both operating temperature and electrolytic vapors. Acceptable materials for such gaskets include asbestos, fibrous ceramic, Teflon, Vitron, silicone, liquid metal gaskets, such as mercury, liquid solder, tin, lead, etc.

The electrodes 24, 25 and 26 can be anodes, cathodes or bipolar electrodes. They can include solid or coated conductors to carry the electrical current for the cell operation. These conductors can be made of any material that can withstand the temperature inside the cell, which is on the order of 150-1060 ° C, is stable to the halide composition 16 and offers good electrical conductivity. Materials useful for that purpose are carbon, graphite and titanium carbides, nitrides or borides and aluminum metal, which has been suitably shaped by heat transfer. The preferred materials for these conductors are graphite and titanium diboride when working in the form of a bipolar.

The aluminum cycle cell also includes a pipe 25 or output tube 28, which has a valve 30 to control the flow of gaseous elements from the tube and adjust the pressure build-up in the cell for continuous operation. The vapors rising from the cell are from the oxidized reducing agent, and in particular no chlorine gas at all is detected from a salt containing aluminum chloride. If chlorine were to be formed, it would react at anode 26 and be recycled as aluminum chloride. The molten aluminum 32 is drained by the conventional tap 34 or otherwise conveyed under vacuum 35 using standard siphon techniques, which are well known.

Figure 4 shows a modification of the cell design of Figure 1, again with vertically placed electrodes 19. The cell structure with the sheath 12 and 800 2 3 81 - 4 - the coating 14 is similar to that described above and the electrode 44 serving as an anode may be one of the anodes shown in Figures 2, 2A or 2B, but preferably that in Figure 3. The anode 44 is immersed in the electrolyte containing fluoride or chloride salts or mixtures thereof which has been heated to a temperature generally between 670 and 810 ° C. At the bottom of the cell, resting on cathode rod 45, which is placed over the hard-to-melt insulation 14, is a block 46, which is preferably slightly larger than the anode 44 and serves as a cathode in that it is suitably electrical connected to the cathode rod 45.

Block 46 can be made from any of the electrode materials described above. Block 46 must be close to base 50 of anode 44, which is the only surface for erode erode. A smaller anode-cathode space for such a form of electrodes is possible if the block 46 also rises above the level of the molten aluminum 32. Since the aluminum is deposited on the cathode block 46, its surface is wetted and the aluminum of the block flows into "the" pole 32 at the bottom of the cell, to be drained at 34 if desired.

Figure 4 also shows a clamp 47 for the power connection, schematically shown, which clamp is in contact with the anode 44 above, but preferably below the level of the bath and adjacent the bottom of the anode, to keep the current loss due to the resistance of the anode as small as possible. For example, the anode 44 may be formed as shown in Figures 3, 12 and 13. The clamp does not act as an anode because the composite anode preferably dissolves in the bath. The clamp 47 can completely or partially surround the anode 44 so that it can continuously feed the anode to the bath. The clamp is made of a suitable inert material that is electrically conductive. Suitable materials are, inter alia, graphite, carbon, T1B2 or mixtures thereof. The electrical contact between the clamp and the anode can take place through protruding contact points or bumps 48. The power supply of clamp 47 is effected by attachment of suitable split cylindrical conductors 49, which are above the top of stick out the cell.

Instead of periodically changing the anodes to supply fresh aluminum material, the present invention can be adapted to a continuous operation power supply mechanism, as shown in Figure 5, or the electrode power supply, as shown in Figure 4 of the pre-baked or Soderberg type.

Protruding through cell C of FIG. 5, an anode 10 electrode 44 penetrates deeply into the melt 16, but remains above the molten aluminum bath of aluminum 32 or the cathode block 46. Surrounding the anode 52 are the raw anode materials, generally designated R, which contain the aluminum material and the reducing agent. This anodic mixture can be formed of small particles with a size of about 2.5 mm to 2.5 cm or larger and can be prepared by extrusion, melting, etc. and introduced into the cell through the funnel 54. The crude material particles of the aluminum material and reducing agent are specifically indicated at 58 and 20 are in close contact with the anode 52 to provide the necessary aluminum source and reducing agent.

These anodic raw materials are held in close contact with each other and with the anode 52 by a porous membrane holder 60 surrounding the anode 52. If the anode materials 58 are consumed and their level falls below the level of molten bath 16, additional anodic material 58 is added to the porous membrane container 60 by means of the feed 54.

In the embodiment according to figure 6, a bipolar cell is indicated. Again the same figures have been used for the indications.

In the operation of the bipolar cell, the same basic principle is followed, except that a pair of electrodes are present at each end of the cell, which are connected to a suitable electrical supply. One of the electrodes 64 is a cathode and at the other end is an anode 66.

Between the electrodes 64 and 66 there is a group of electrodes 68 with spacing, which are not connected to each other or to any 800 electrical supply. A porous membrane holder 60 of the same type as described at 60 in Figure 5 is attached to each of these electrodes 68 and anode 66. However, the porous membrane 60 in the bipolar cell has as one side one of the electrodes 66 or 68, which provide the enclosure for the anodic raw material 58.

In the bipolar cell, the side of the electrode 68 closest to the anode 66 is negatively charged, and the side of the electrode 68, which is on the side of the cathode 64, is positively charged. This side 72 of the electrode 68 will act as an anode and is the side in contact with the anodic raw material 58. The electrolysis then supplies aluminum on the negative side of the electrode 68 and CO2 on the positive or anodic side of the same. -15 the electrodes. The aluminum falls down to the pole 32 on the bottom and is collected in the usual way.

Figures 7-11 show the electrolytic cell with sloping electrodes, which in combination with the anode composition of the present invention leads to a considerable economy in the process of depositing aluminum by electrical means.

In the typical Hall cell methods, aluminum reduction cells have an anode-cathode gap, taking into account the action of the magnetic field and the "return reaction", due to the undulation of the pool with aluminum. Therefore, the space between the bottom surface of the anode where all erosion takes place and the top of the pool with aluminum or the cathode electrode could not be less than about 4-5 cm. Another and equally important reason to increase the space between the cathode and anode, whether it be the vertical-wall Hall cell construction or an attempt to use oblique-wall electrodes, is the serious difficulty of dimensional stability. by the high temperatures required and the aggressive salts, which must necessarily be added to maintain a high temperature for the dissolution of the alumina. Due to the combination of the cells with sloping electrodes and the anode, which uses aluminum oxide and 800 23 81 # * - 7 - a reducing agent as the sole source for the aluminum, using temperatures just above the melting temperature of aluminum, the problems with minimized dimensional instability, allowing the cells of the present invention to be provided with a smaller anode-cathode gap, which has not been achieved in the past. Thus, it is the particular combination of the anode and the sloping walls for the construction of the cell that produces a lower IR current drop in the salt 10 due to the small gap between sloping walls and the decrease in the current density of the anode.

The cells of Figures 7-11 are essentially the same as those described above, except for the inclined surfaces forming the electrodes. In this cell structure, the anode 74 is provided with sloping walls 76, which, as shown, are exterior and downward and inward, although the direction of the angle is not critical at all. The slope of the walls can be in any direction or any angle from the level 20 of the bath B. The angle can even vary from 10 to 80 ° or more from the bath level. The use of the sloping walls of the anode bottom of the electrode and that part of the side of the sloping anode immersed in the bath 16 will cause the anode to erode over a larger part of the surface and as much as possible deposit aluminum on the cathode.

The cathode 78 has surfaces 79, which are formed in the same manner (complementary) as the sloping walls 76 of the anode, so that an electrode is created with a spacing on the sides, as indicated at the spacing Y. This spacing can be approx. 6 to 6 cm.

Larger gaps result in greater energy consumption. The space between the bottom 80 and the anode 74 in Figure 7 and the surface of the aluminum layer 82, which is part of the aluminum pool 84, is indicated at X and may be approx.

0.6-6 cm. Preferably, the interspaces X and Y are between about 0.6 and 2.5 cm.

The spacing between the anode and the cathode 800 23 81-8 above the solidified bath layer 86 is not significant for the practice of the invention. However, the spaces X and Y between the anode and the cathode may be the same or different depending on the desired current density and anode erosion, but if the above values are kept close, this will lead to significant savings in energy consumption.

The coating 78, which forms the cathode of the cell, may be of material typical of use with electrolytic cells, such as carbon, titanium diboride, or the like, and is formed as described above in accordance with the external shape of the anode 74 In addition, the base of the cladding has an inclined floor 90 for the aluminum pool, leading to a collection well 92 for the aluminum. As can be seen, the inclined floor 90 is made to retain only a limited depth of the aluminum layer, which layer can be controlled by draining means (not shown) of the aluminum from the sump. The purpose of the thin aluminum layer below the base 80 of the anode is mainly to eliminate the wrinkles or waves of the molten aluminum layer caused by the magnetic effects in the cell.

In other respects, the cell of Figure 7 is similar to that of Figure 1, i.e. that it is provided with a cover 18 with an outlet port 28, which is part of casing 12.

The cell can also be provided with hard-to-melt insulation of any suitable shape, as shown in Figure 14.

The combination of the use of the anode according to the present invention with tapered sides in accordance with the tapered cathodes allows for different shapes of the cell and anode, as indicated, for example, in Figures 8-11.

In Figures 8 and 9, the shape of the anode 74 is varied and has centrally located, outwardly tapering sides 94, which form a tip 96 in the anode. The carbon coating or other coating material, such as Ti2 / etc, which serves as the cathode, protrudes in accordance with the 800 2 3 81 - 9 - internal shape of the anode, as best shown in Figure 8. The operation of a cell, as shown in Figures 8 and 9, is essentially the same as that described in Figure 7, particularly with regard to the increased erosion surfaces 94.

In Figures 10 and 11, 2 anodes, 100 and 102, with oppositely shaped sloping sides 104 and 106, are placed in a cell with cathode 98, which is identical to that described in Figure 8.

When using electrolytic cells with a sloped-side cathode, as shown in Figures 7-11, it has been found that no solidified salt layer should be on the surfaces of the sloping cathode wall immersed and placed in the bath opposite a part of the anode surface, otherwise the desired space between the cathode and anode cannot be maintained. Furthermore, the solidified salt that would adhere to the wall of the cathode is a good electrical insulator which would inhibit the current flowing from the anode to the sloping cathode wall. The use of such sloping wall electrodes in the past has not made extensive use of such cells due to the problem of the salts solidifying on the sides and the dimensional instability of the coating. With the anode composition of the present invention and the lower temperatures of the bath, a variety of low melting salt compositions, which will not freeze on the sides, can be easily used. Ideally, the melting point of the salt and the thermal balance of the cell are controlled so that the freezing line of the salt is within the coating or steel casing rather than the coating or cathode bath interface. It is not important where the freezing line is located as long as it is within the coating and the salt is kept in a liquid state on the surface of the cathode coating immersed in the bath. In such a case, the correct cathode anode gap is maintained without difficulty.

The method a. Chloride-containing bath.

800 23 81 - 10 -

The electrolytic method of the present invention for the unique continuous production of aluminum ions at the anode utilizes the closed top electrolytic cell as depicted in Figure 1, or 5 of any of the other cells described above if the top is sealed or an appropriate device is made to prevent: (a) moisture from contacting the chloride electrolyte, or (b) the aluminum chloride from being oxidized while the bath contains the vaporous bath salts.

The advantages of the present invention when using the chloride-containing bath lie not only in the continuous in situ production of aluminum ions at the anode, but also in the use of considerably less energy to prepare high quality aluminum, without that any chlorine gas escapes from the cell.

The continuous production of aluminum ions at the anode is brought about by the formation of the anode from an aluminum-containing material containing aluminum oxide and a reducing agent. This anode is immersed in a molten bath containing alkali metal and / or alkaline earth metal halide salts of any composition, provided that aluminum chloride is present in the bath. In electrolysis, ionized aluminum is deposited in the bath as aluminum metal on the cathode, while in the reaction at the anode, in addition to aluminum ions, CO2 is also formed. The aluminum is collected as molten aluminum and tapped, but it is the anode reaction to reform aluminum ions that is an important part of the present invention.

It is possible that the halogen chlorine, be it the chloride ion, chlorine atom or chlorine gas, is part of the chloride reaction with the alumina of the aluminum-containing material and the reducing agent of the anode to form 35 aluminum ions plus the reducing agent oxide. . The anode aluminum is ionized in the molten bath to continue the cycle and the anions, which may be chlorides, oxides or others, maintain charge 800 2 3 81-11 balance with the aluminum ions.

The aluminum produced at the cathode is generally as pure as the aluminum-containing material forming the anode. According to the invention it is possible to prepare very pure aluminum by using a very pure alumina source or to prepare slightly impure aluminum by directly using aluminum-containing ores, such as bauxite or aluminum-containing clay such as kaolin or mixtures of these ores. It is generally possible to obtain an aluminum purity of at least 99.5%.

It is known in the Hall-Heroult cell reaction that the carbon of the anode contributes to the overall aluminum recovery reaction by lowering the decomposition voltage of ΑΙ, Ο Ο ^ 15. For example, the decomposition voltage of A ^ O ^ in cryolite on a platinum anode is about 2.2 volts, but on a carbon electrode, the decomposition voltage is about 1.2 volts, taking into account that about 50 vol.% CO and 50% CO2 is prepared. The same decomposition stress is obtained at Al 2 O 3 approximately when methane is injected under the platinum anode, producing mainly CO2.

The use of the composite anode in the present invention results in a lower decomposition voltage than would have been obtained if AlCl2 were to decompose with the formation of chlorine gas at the anode. In each electrochemical reaction, if the current voltage curve is extrapolated to current 0, a number approaches the decomposition voltage. In an electrolysis process of aluminum chloride, using a graphite anode, a decomposition of 1.3-2.0 volts can be obtained, which is in accordance with values described in the literature and with the theoretical value, which is is calculated using thermodynamics.

It has been found that the decomposition voltage of the present invention varies slightly with the composition of the electrolyte. With pure NaAlCl 2, the decomposition voltage is lowest, but if the AlCl 2 component of the electrolyte is reduced, the decomposition voltage increases slightly. The 800 2 3 81-12 - lowest decomposition voltage obtained was 0.5 volts and the highest 1.5 volts. The average value was 1.2 volts. Starting from the most common average decomposition voltage of 1.2 volts, it can be noted that in the present invention the decomposition voltage is 0.6 volts lower than that for AlCl 2, discharging chlorine and approaching the currently obtained value to that of Al2 O3 and carbon, indicating that the same overall reaction mechanism takes place in both the Hall-Heroult cell and in the present invention. This lower decomposition voltage leads to significant energy savings for the electrolytic production of aluminum, not only in comparison to the classic aluminum chloride systems, in which chlorine is discharged at the anode, but also when looking at the extra energy required to AlCl ^ to be prepared from 15 Al 2 O 3, carbon and chlorine.

The process conditions for the electrolytic preparation of aluminum are not critical with regard to the applied voltage or the current density. The temperature of the bath can vary considerably and should simply be such that the bath remains melted, which, depending on the composition of the halide salts present, can be achieved in the temperature range of 150-1000 ° C, but generally between melting point of aluminum and the boiling point of the cellular components, preferably 10-400 ° C and especially 10-150 ° C to less than 250 ° C above the melting point of aluminum. The pressure conditions in the closed cell are not critical, especially since no chlorine gas escapes, as is the case with the known salt processes with aluminum chloride. Although CO or CO2 or 30 can be formed in the present process, these gases are not as corrosive as chlorine. The pressure, which is not important, can range from atmospheric pressure to 10 or more psi.

b. Fluoride-containing bath only.

The Hall cell operates chemically based on the fact that aluminum oxide will dissolve in the cryolite fluoride salt bath at a temperature of 950-1000 ° C. Bayer alumina is soluble in the cryolite-containing bath at a minimum temperature of at least 900 ° C or above. A fluoride 800 2 3 81 »4> - 13 - containing bath at a temperature lower than approx. 900 ° C will not easily dissolve the normally prepared Bayer alumina, so that the alumina as source of the aluminum cannot enter the reduction reaction and it is also not possible for aluminum to be deposited on the cathode. Without this general solubility of aluminum oxide in the fluoride salt bath, it is not feasible to recover aluminum electrochemically.

In accordance with the invention, it has been found that in all 10 baths containing fluoride, the temperature may range from the melting point of aluminum to the boiling point of the cell components, preferably 10-400 ° C and especially 10-150 ° C to less than 250 ° C above the melting point of aluminum. In order to recover aluminum from the corresponding oxide or other oxygen-containing compound in the manner described herein, the temperature of the bath will generally be about 670-800 ° C and preferably 700-750 ° C. .

One important aspect of the invention, which makes it different from the conventional Hall-Heroult cell methods, is that the composite anode containing the mixture of alumina and reducing agent effects alumina production and produces aluminum ions in the fluoride bath at low temperature. However, it is believed that the overall reaction is essentially equal to the Hall cell reaction, as stated above. The aluminum is prepared in liquid form in the liquid metal pool that serves as the cathode. It is believed that a reaction takes place at the anode surface in a unique manner, which leads to the reaction of alumina, producing aluminum ions, similar to the mechanism that takes place in the Hall cell, although the temperature is only slightly above melting point of aluminum.

The importance of using the composite anode in the present invention will be apparent, because under the same conditions as those of the invention, but with a carbon anode or other anode not consumed, the addition of alumina to the bath will not lead to the dissolution of the aluminum oxide, or the deposition of the aluminum by electrochemical means. A notable feature of the invention is that when using the composite anode in an electrolytic bath containing only fluoride at a low temperature of 670-800 ° C, the Hall cell can operate in a manner as shown in Figure 4 indicated, without the closed top, required by the chloride bath, as shown in Figure 1. The composition of the bath, flow densities and other process variables are not critical to the operation of the chloride bath or fluoride bath containing cell.

The anode.

The main pillar for achieving the favorable results according to the invention is the use of a unique composite anode, which is composed of an oxygen-containing aluminum-containing compound, usually aluminum oxide and a reducing agent.

The anode provides the sole source of aluminum ions for the electrolytic reduction to aluminum at the cathode and, with a carbon reducer, the means to conduct electric current through the dielectric alumina to the reaction site for the alumina which is in contact with and immersed in the electrolyte. The anode also provides, at least in part, a necessary source of a reducing agent that allows the alumina to react in the anodic environment to produce aluminum for deposition as aluminum metal at the cathode.

The reducing agent is preferably, at least in part, mixed with the alumina to provide good contact between the reducing agent and the alumina. If properly selected, the reducing agent can also function as a conductor of the electric current to the reaction site for the alumina after it has been mixed with the alumina. Following the reaction of each alumina particle in contact with the electrolyte at a given location and having an electric current at hand, another particle at the same site is now uncovered and can react. This pattern occurs over the entire surface of the anode and continues until there is no more 800 23 81-15 aluminum oxide to react. If the reducing agent is non-conductive and is not mixed with the aluminum oxide, the electrical conduction function must be otherwise accomplished by conducting bars to keep the aluminum oxide anodic at the reaction site.

In an aluminum chloride salt bath, the anode has the function of providing a reducing agent, which aids in the theoretical reaction of the aluminum-containing source with the chloride or oxygen, or both, to maintain a constant concentration of aluminum chloride. Maintaining a constant concentration of aluminum chloride is an important part of the chloride cycle of the invention, because it eliminates the need for an external replenishment of the aluminum chloride which is electrically decomposed or whose chlorine is discharged on the anode.

In the total fluoride bath process, the anode of the invention, as in the chloride cycle, provides the aluminum oxide which reacts in the fluoride bath to aluminum ions at a uniquely low temperature, of the order of 670-800 ° C. The cell can also be open, as shown in Figures 4, 5 or 7.

The aluminum source is aluminum oxide, Al2C> 3, but it can also be any other alumina-containing material, such as bauxite or a clay, such as kaolin, or other material which reacts at the anode to aluminum ions, which are reduced at the cathode to the molten metal. , such as in the fluoride or chloride cycles.

If the anode is formed by the mixture, the ratio of at least 1.5 to an acceptable upper limit of 7.5, 20.0 or even 50.0 or more parts by weight of alumina in the aluminum-containing material per part by weight of the reducing agent. Preferably, in the present invention, the amount of alumina in the mixture of alumina material is 2.0-6.5, and especially 2.5-6.0, by weight. alumina per part reducing agent.

The reducing agent that can be used in the invention is not limited to any particular material, but can be any material that is active in reaction with the 800 2 3 81-16 alumina. The reaction in the fluoride and chloride baths has not been clearly determined, but it may be that the reducing agent reacts with it to form aluminum ions which eventually settle on the cathode to form CC 2 at the anode. The reaction mixture can be the same in all chloride, all fluoride, or mixed chloride / fluoride salt electrolytes.

Reducing agents which are particularly suitable for alumina and other oxides include carbon or a reducing carbon compound for use in the mixture. Sulfur, phosphorus or arsenic can also be used independently or in combination with carbon. Carbon is particularly preferred because it is capable of both feeding the current to the reaction site of the alumina, but also exerting a reducing action and giving a gaseous product to the anode.

The carbon source in the mixture can be any organic material, especially of fossil origin, such as tar, pitch, coal and coal products, reducing gases, e.g.

Carbon monoxide and may also include natural and synthetic resinous materials, such as wax, gum, phenols, epoxies, vinyls, etc., which can be converted to carbon if desired, even in the presence of the aluminum-containing material. The conversion to carbon of the carbon source mixed with the alumina compound can be performed by known techniques, such as those used with pre-baked anodes used in the Hall-Heroult cell.

This is done by casting, molding, extruding, etc., of a composite anode, such as A 2 O 3 pitch in the desired ratio of, for example, 6.5 parts. alumina to 1 part carbon in the proper state for conversion to carbon and slowly heating the formed anode in a non-oxidizing atmosphere to a temperature of 700-12Q0 ° C. After the composition has been converted to coal (coking), the composite anode is ready for use.

Within the scope of the present invention, it is also contemplated to prepare, for example, carbon as a reducing agent in the mixture with alumina by the carbon source in 800 23 81-17 - converting the molten electrolytic bath to carbon both before and during electrolysis. Favorable temperatures for the bath are on the order of 670-850 ° C. The time required for this reaction is not critical, but can be from several minutes to several hours, depending on the temperature of the molten bath and the weight of the mixture of aluminum-containing and reducing carbon material.

Continuous conversion is possible with the aid of the connecting clamp according to figure 4 by inserting an anode at the top of the clamp; since the anode is consumed it continually shrinks until it is completely consumed and the next one takes its place, etc. The anode can be continuously supplied to the cell in the green state, as is the case with the traditional Soderberg electrode . In this case, steel pins have traditionally been used to make contact, but the contacts can also be made with graphite, carbon, Ti, aluminum, or compositions thereof. The green composite anode material 20 is gradually converted by the heat of the cell in such a way that the end of the anode in the salt is always fully converted to the operating temperature of the cell. Soderberg conversion into the cell at 670-850 ° C gives a lower conductivity anode compared to composite anodes which are pre-baked at much higher temperatures.

As stated above, if desired, the entire source of the reducing agent need not be mixed with the alumina source to form the anode. For example, it has been found that the only requirements to be placed on the reducing agent is that it must be in contact with the anodic alumina and be present in sufficient amount to form aluminum metal on the cathode. It is clear, however, that electric current must be fed to the reaction site 35 for the reaction to proceed.

If the reducing agent, such as carbon, is not mixed to carry the current, it is conceivable that another conductor compatible with the cell and its contents 800 2 3 81-18 can be used. For example, combinations of aluminum or precious metals and high-melting conductive oxides, such as silver-tin oxide or TiB2 / alone or in compositions with carbon or graphite, can be mixed with aluminum-oxide in amounts that are merely sufficient to generate the electri current to the reaction site. Such an amount is not critical provided the alumina has been made anodic at the reaction site. Amounts from about 0.001 to at least about 0.75 parts. conductive material per part of aluminum-10 oxide can be used. Larger amounts increase the conductivity at the expense of the availability of the reactive material, but are possible without a certain upper limit. It goes without saying that a reducing agent still has to be present to effect the necessary reaction.

If aluminum oxide is used as the aluminum-containing material, hydrated or calcined aluminum oxide can be used. Anodes formed from hydrated alumina may exhibit better conductivity than calcined alumina, but hydrated alumina, Α ^ Ο ^ .β ^ Ο or Al (OH) ^ tends to break during pre-firing and when placed in the hot bath which is due to the water expelled during the conversion. In an aluminum chloride-containing salt, using hydrated alumina which is converted in the bath, the expelled water can undesirably hydrolyze the AlCl 2.

Cracking or breaking of the anode by expelled moisture does not cause problems, provided the anode is surrounded by a membrane, as shown in Figure 5. The parts of the anode that fall down are retained in the membrane for continuous reaction. The anode can also consist of hydrated and calcined oxide in any ratio to minimize the chance of breakage. The maximum amount of hydrated oxide that can be used affects the energy savings in calcination.

The size and surface area of the particles constituting the anode containing the aluminum oxide have not shown 800 2 3 81-19 sensitivity with respect to the reaction rate of the anode. This feature of the present invention is in contrast to known experience in the reaction of A12C> 3 and carbon with chlorine as a gas-solid reaction in an oven. It has been found in the past that the reaction temperature and the reaction speed are very sensitive to the particle size and the surface areas.

In the known methods, it is generally desirable to use aluminum oxide with a surface in the order of 10-125 m / g in the AlCl3 reaction. However, in the present invention, no sensitivity was observed with respect to the reaction speed of the anode, based on particle size or surface area, ie Al2C> 3 with a surface area of 0.5 m / g or less apparently reacts equally easily. as Al2 O3 with a surface area of 100 m / g. These results are based on experiments conducted with anodes containing aluminum oxide with particles of different surfaces and sizes. Anode current densities of 12 2 to 250 amps / cm were passed through the cells, the line of exhaustion being connected to an iodine starch indicator for the detection of chlorine. No chlorine gas was detected regardless of the current density or the surface area of the alumina. This indicates that if any chlorine is formed at the anode, it will either react completely to reform aluminum chloride or only aluminum ions at the anode will be formed from Al2O3, while the oxygen from Al2O3 will combine with carbon to CO2. It is believed that in order to produce chlorine at the anode it is necessary to raise the potential so high that it exceeds the decomposition potential of the A1C13, but even then the chlorine produced is likely to react with the A12C> 3 and carbon to produce more A1Cl3 than developing chlorine at the anode.

For use in electrolysis cells, anodes can be produced in a variety of shapes and with a variety of manufacturing processes. The anode can be formed in any suitable manner by a mixture of alumina material and the reducing agent. For example, a mixture 800 2 3 81-20 - can be attached to a typical electrode to form a coating surrounding the electrode all or one side, as shown in Figure 2 of the drawings. The anode may also be formed by anode material which has been melted or formed into a suitable model, to which an electrode rod or pin is attached in the manner shown in Figure 3 of the drawings. It is also possible according to the invention to form the anode in a manner other than a direct connection to the electrode. However, it is desirable that the aluminum-containing material be in intimate physical contact with the carbonaceous material or other reducing agent. The latter may be the case, for example, if the mixtures of the aluminum-containing material and the reducing agent are in the form of a homogeneous mixture of powders, small balls of the mixed powders, or larger composite briquettes or like mixed materials, which can be formed. by melting or extrusion in various sizes from 2.5 mm to 2.5 cm or more. Uniformity in the distribution of carbon and alumina has been found to be desirable to achieve maximum anode effectiveness during dissolution or reaction during electrolysis.

In order to hold in place the aluminum-containing material and the reducing agent which form the anodic materials in the region of the electrode and thus form the anode in combination, a container in the form of a porous membrane can be used.

The anode must be as conductive as possible for successful commercial application. Since the anode of the present invention is not a solid or pure carbon, as traditionally used in the Hall cell, it will be less conductive due to the presence of the aluminum-containing compound. If the anode were to have the same resistance as the salt electrolyte, the heat balance could be affected by overheating, which could occur by passing the same current through the anode with greater resistance. For example, if one uses a solid composite anode in the cell of Figure 1, as shown in Figure 3, it is necessary for the electric current to pass through the anode from the top 800 23 81 - 21 side to the bottom, with energy losses, which are accompanied by heating the bath. It is therefore desirable to construct an anode with the greatest possible conductivity. It is clear that the more conductive the anode material is, the lower the energy consumption for recovering metal, but in any case, for optimum operation, the conductivity of the anode must be greater than the conductivity of the salt. Especially if it is desired to obtain a maximum aluminum production with a minimum energy consumption, the resistance of the anode becomes significant.

It has been found that the conductivity of the anode varies considerably depending on how it is manufactured. The parameters that appear to affect conductivity are the ratio of the binding carbon material, such as pitch, carbon or coke particles included in the composite anode as the source of the reducing agent and the alumina type. The greater the carbon content of the anode, with the aforementioned ratio of alumina to reducing agent, the greater the conductivity. For example, it is possible, if a ratio of the order of 4: 1 to 6: 1 alumina to carbon is used, to construct a solid composite anode, which has at least one tenth of the conductivity of a standard Hall-Heroul anode.

To counteract the current loss through the composite anode, several alternatives are also shown in Figures 2, 2A, 2B and 4A.

In order to achieve higher conductivity and counteract current loss through the composite pre-baked anode, according to another embodiment of the invention, one or more conductive cores 36 or 37 are placed in the anode, as shown in Figures 2, 2A and 2B, or a number of vertically disposed conductive pins 39, as shown in Figure 4A.

The composite anode 26A, shown in Figure 2, has a conductive central core 36, which may be carbon or graphite, which is formed in the composite anode or composite anode material 38 formed or coated in a 800 2 3 81 - 22 - preformed model of a conductive core. The central core 36 can also be a metal, such as the same metal that is deposited, e.g., aluminum. The outside of the conductor 36 is coated on one side for bipolar application or surrounded on both sides for monopolar application by a sheath 38 of composite anode material containing the above-described mixture of aluminum oxides and reducing agent. If the conductor is coated on one side, bipolar action is expected. The term "oxides" also refers to silicates, which are often a combination of the metal oxide and silicon oxide or other oxygen-containing compound of the aluminum being deposited.

For large anodes, another embodiment is shown in Figures 2A and 2B. To improve conductivity, aluminum bars 36 and 37 of a first degree purity are preferred to be used as electrical conductors in a sheath of the composite anode material 38, which may be of the pre-baked or Soderberg type. Since first grade aluminum is used as guide bars, it will melt as the anode is consumed and join the metal at the cathode for a continuous cycle. The bars are spaced such that the voltage drop is reduced relative to the conductivity of the composite anode. In Figure 2B 25, the guide bars 36 are shown, which are connected to a plate 40, which is carried by a central guide 41.

The number and size of conductors 36 and 37 are selected according to the size of the anode, the current density of the anode, cell size, operating temperature and heat transfer, such that the aluminum conductors 36 and 37 melt at the same rate as the sheath 38 of the anode is consumed. The unique advantage of the anode embodiments, shown in Figures 2A and 2B, is the avoidance of a large voltage drop in the anode, which has a relatively high resistance, so that the process can take place with a considerably lower current consumption. The aluminum bars usually have a diameter of about 0.15-7.5 cm, preferably 0.3-5.0 cm, in particular 0.6-2.5 cm.

800 2 3 81 - 23 -

To achieve a desired conductivity in the anode, the space between the outer surface of the composite anode 38 and the surface of any aluminum rod, as shown in Figure 2, 2A or 2B, and the spacing 5 between the outer surfaces of these aluminum rods in Figure 2A and 2B, not critical and may range from 0.3-60 cm, preferably 2.5-15 cm and especially 3.7-10 cm. For example, if the conductivity of the composite anode is about 0.1 of a standard pre-baked Hall cell anode, a spacing between the aluminum bars of about 7.5 cm will result in an acceptable voltage drop.

Since the working temperature of the cell is usually in the range of 700-750 ° C, the aluminum bars may be sized to melt at approximately the same rate as the anode is consumed and thus will flow to the bottom of the anode. If the diameter of the aluminum rod is too large, it will not melt and a salt will deposit on the surface, leaving an aluminum stump in the anode being consumed, which will cause a short circuit with the cathode if the anode consumption is advanced. If the cross section of the rod is too small, it will melt too far into the anode, resulting in too great a voltage drop due to the longer conduction path. It is desirable that the aluminum bars melt slightly into the anode instead of remaining "flush" with the bottom surface of the anode, as this will reduce the anodic oxidation of the aluminum bars. The desired "melt-back distance" depends on the minimum voltage drop coupled with the minimum anodic oxidation of the aluminum bars. If the rods were to remain flush with the bottom surface of the anode, the aluminum ions could enter the bath both from the rods (as in a purification operation) and from the composite anode material, thereby increasing the Faraday activity of the cell The heat can be controlled so that the conductivity of the bath through the anode and the current generated by the conductors is balanced to effect the desired amount of melting of the conductive aluminum rods.

Figure 3 depicts another embodiment of the composition of an anode electrode, as shown at 26B. In this embodiment, electrode 26B consists of a composition 38, which may be the same as the coating 38 in Figure 2, but is formed in a suitable model for use as an electrode. This model of the electrode may be formed around a blunt or pen electrode 42 projecting above the top of the body of the electrode 26B so that it can be connected to the conventional electrical circuit. Electrode 26B can also be formed, after which stub 42 is introduced according to known techniques, such as are used in pre-baked Hall cell anodes.

Another embodiment is that shown in Figure 15A, illustrating an anode 26B having the same composition as described above, but including a plurality of pairs of vertically arranged conductive pins 39, with the lowest pair pins a bush 39A is directly attached, as in the Soderberg type joints 20. The placement of the pins 39 is not critical and they can be perpendicular to the anode axis or at an angle as shown. As the composite anode material is consumed, the bus terminals 39A are moved to the next higher pair of pins. The pens composed of first quality aluminum are also consumed and as mentioned above they are added to the pool of deposited aluminum. The pins can also be made of iron, as is often used in the Soderberg joint, and the pins are removed when the anode is used up.

The embodiments in Figures 12 and 13 indicate a variation in the conduction of electrical energy to the working surface of the anode. As indicated, block 94 of the composite anode A is covered with strips of aluminum metal 108. These strips operate in the same manner as the aluminum bars in Figures 2A and 2B. The shape and the number of bars (pictures) is not critical. The blocks can be in a continuous form and can be fed into the cell by clamp 47, 800 23 81 - 25 - as in Figure 4, making the electrical connection along the aluminum bars 108.

The number, spacing and thickness of the aluminum bars (plates) 108 are determined by the same factors as described with respect to conductors 36 and 37. Generally, the thickness will be in the order of 2.5mm to 1.2 cm, preferably 0.25-0.9 cm and in particular 0.25-0.6 cm. The aluminum plates must be of sufficient thickness to conduct the necessary current to avoid a large voltage drop and also melt in the cathode wafer when the anode is consumed. The space between the aluminum plates 108 is such that an excessive stress drop through the composite block is avoided, as noted with respect to conductors 36 and 37. Generally, the spacing will be on the order of 0.3-60 cm, preferably 2.5-15 cm and in particular 3.75-10 cm.

The membrane.

The membrane shown in Figure 5 of the drawings is designed for a three-fold function.

First, the membrane acts as a separator or quiescent barrier between the molten cathodic metal phase and the source of anode material, which is electrolyzed. With the use of the membrane according to the invention, the spacing can be significantly reduced, achieving a significant increase in conductivity and efficiency without turbulent effects, which would otherwise decrease the efficiency or the quality of the aluminum product could trigger.

Second, the membrane of the present invention also actually retains materials of the composite anode, such as, for example, the aluminum-containing raw material and the reducing agent. Because of this retention, these materials are held close to the electrode, whereby an anode is formed in the most efficient manner for the production of aluminum ions. The membrane also prevents the mixing of raw materials with the molten aluminum at the bottom of the cell. If a hydrated metal oxide, such as hydrated alumina, were used as any of the 800 2 3 81 - 26 - the anodic materials, the membrane retains all parts of the anode that would break down from the aluminum oxide due to moisture development during the conversion in the bath, solid. These pieces remain an aluminum source for the reduction reaction 5 as long as they are within the anode circuit in the membrane.

Third, the membrane allows the free passage of ions and dissolved solids in the electrolyte, but will inhibit the molten aluminum and undissolved solids, which form the usual impurities in the aluminum-containing source, and prevent the contamination of prevent cathodic deposition.

The shape of the outside of the membrane is not important and may be a cylindrical, prism, etc. shape or part thereof. The membrane can have a three- or four-sided shape with a bottom and thus form an enclosed container. This container is shaped to contain anodic raw materials for the reaction in the salt bath.

Due to the corrosive nature of the molten salt bath, the choice of the materials forming the membrane is important for the life of the cell and the success of the process. If the electrolyte used is a total chloride bath, the choice of membrane is slightly greater due to the less corrosive nature of such a bath compared to a bath containing fluorides. However, baths containing certain fluorides are preferred because of their lower volatility. The total fluoride bath has other advantages, as explained above. Materials suitable for use in a fluoride bath are of course also suitable for the less corrosive chloride bath.

Materials that have been found to be useful include vitreous carbon foam, carbon or graphite as a porous solid or porous solids of hard-to-melt carbides, such as: the nitrides of boron, aluminum, silicon (including the oxynitride), titanium, hafnium, zirconium and 35 tantalum; the silicides of molybdenum, tantalum and tungsten; the carbides of hafnium, tantalum, columbium, zircon, titanium, silicon, boron and tungsten? and the borides of hafnium, tantalum, zircon, columbium, titanium and silicon. Other difficult meltable carbides known for this purpose can also be used for the membrane, provided that they are resistant to the molten salt bath.

The hard-meltable carbide forming the membrane 5 according to the invention can be made in the form of a cloth, mat, felt, foam, porous sintered solid base or simply a coating on such a base, all of which are known in the literature for other purposes. The membrane must also meet certain standards in terms of passage porosity and connected pore size.

These two features can be defined as follows: passage porosity - the percentage of the total volume of the membrane made up of the passages 15 from one side of the membrane to the other side; connected pore size - the smallest cross section of a passage through the membrane.

The passage porosity varies with the nature of the membrane material, the temperature of the molten bath and the salt composition, but the common feature of useful membranes is that the porosity must be sufficient to pass all metal ions, such as aluminum, and all electrolyte salts, without that the unresolved impurities pass. It has been found that the greater the porosity, the greater the current flow and therefore the greater the electrical efficiency of the cell. The porosity can range from 1% to 97% or more, but is generally on the order of 30-70%. The preferred porosity to achieve the greatest efficiency is of the order of 90-97%. For example, a glassy carbon-30 foam is capable of giving such high porosity and retaining sufficient mechanical force.

The connected pore size should be small enough to retain the solid impurities that are not dissolved, but large enough to allow the ions and dissolved particles to pass through. In general, the acceptable pore size is between 1 µm and 1 cm.

The thickness of the membrane material is a function of the porosity, pore size and ability to retain undissolved impure solids and molten metal. It is clear that the thicker the membrane, the greater the electrical resistance will be. It is therefore desirable to use a membrane that is as thin as practically in accordance with the standards of porosity and pore size and with the mechanical strength of the membrane in the cell. The preferred thickness is 0.3-1.25 cm, but may also be 5 cm or more.

Typical membrane materials which have been found to be useful include glassy carbon foam, carbon or graphite in the form of a porous solid, felt or cloth, aluminum nitride, silicon nitride, silicon carbide, silicon oxynitride, boron nitride, and titanium nitride as a porous solid. a cloth or as a coating on the surface of a glassy carbon foam or porous graphite. Aluminum nitride appears to be the most desirable material. It has been found that aluminum nitride can be suitably obtained in a porous structure by first making a porous alumina structure, then impregnating it with carbon, followed by heating to 1750 ° C in a nitrogen atmosphere, converting the alumina to aluminum nitride. Such a process results in a highly porous structure, which is chemically compatible with the environment of corrosive salt and molten aluminum.

25 Molten bath composition.

The electrolytic bath of the present invention can vary considerably compared to the typical Hall cell salt composition. In the invention, the bath composition can comprise any halide salt, with chloride and fluoride being especially preferred. Any alkali or alkaline earth metal, such as in particular sodium, potassium, lithium, calcium, magnesium, barium and the like, can be used to form the halide salts. No critical composition or ratio is desired or necessary. It has been found that no aluminum salt need initially be present in the electrolyte to prepare aluminum by electrolysis with the composite anode. A salt electrolyte containing, for example, only alkali metal and / or alkaline earth metal halides will give aluminum metal at the cathode using the composite anode without "anode effect".

While not necessary for the practice of the invention, it is generally expedient that the salt bath initially contain an aluminum halide. For baths containing AlClg, which can only contain chloride anions or chloride and fluoride anions, the aluminum chloride concentration can be 2-60%, but also in the range 1-95% by weight AlCl2. The total fluoride bath may contain the same fluoride salts as indicated above and may also contain aluminum fluoride in any desired ratio.

Among the advantages and disadvantages of the different electrolyte types it can be mentioned that a total chloride bath has a very low tolerance for oxide contamination, but a very high conductivity and is the least corrosive for the heat-resistant substances and cell components.

In fluoride-containing electrolytes, the aluminum settles as droplets that readily fuse to form a puddle, but the electrolyte's corrosivity to the heat-resistant substances and cellular components increases significantly.

A lithium component will increase the conductivity in any electrolyte, but is expensive and increases the cost of the electrolyte. With each operation, the cost of the electrolyte, the conductivity of the electrolyte, and the resulting power consumption for producing aluminum must be weighed against each other.

The preferred electrolyte is an economical tradeoff of the salt components, conductivity, corrosivity to the coatings and cell components, tolerance to the oxide contamination and fusion of the deposited aluminum in a puddle for easy recovery.

The following examples further illustrate the invention.

EXAMPLE I '

In Figure 1, the anodes are formed by graphite plates and the cathode electrode is a titanium diboride plate.

800 2 3 81 - 30 -

The anodes were made with a coating 38, as shown in Figure 2, which consisted of purified from Bayer, calcined to 1000 ° C and mixed in a weight ratio of 5 din. A ^ O ^ to 1 part carbon at the conversion step. The carbon was obtained by mixing the A 2 O 4 with a phenolic resin and gradually heating this mixture to 1000 ° C in an inert atmosphere to convert the phenolic resin to carbon. The electrode coating was prepared by mixing it and the phenol component, plastering the electrode with the mixture, or otherwise applying the mixture to the electrode and heating to the conversion temperature.

The electrolyte consisted of an equimolar mixture of sodium chloride and aluminum chloride, which formed the double salt NaAlCl 2 at about 150 ° C. The temperature of the cell was raised to 700 ° C and the electrolysis of Al 2 O 3 was carried out for several hours, forming a layer of molten aluminum on the bottom of the cell. Examination of the anode showed that the coating had dissolved and the aluminum 20 was deposited on the cathode. This aluminum deposit was equivalent to the aluminum content of the A 2 O 2 dissolved at the anode. The total reaction is believed to be formed by the ionization of the A 2 O 2 in the anode, the oxygen reacting with the carbon to form primarily CO 2. During the electrolysis it was not found that any chlorine gas was released at the anodes and in the output tube. The released gas was analyzed to show that it was mainly CO2.

EXAMPLE II

The electrolyte salt composition consisted of 63% NaCl, 17% LiCl, 10% LiF, 10% AlCl 2 and the electrode coating of Figure 2 was prepared from standard bauxite Al 2 O 2 and a petroleum tar pitch which was reacted to yield A 2 O Carbon and carbon were formed in a ratio of 5.7: 1. The electrolysis was carried out in the cell of Figure 1 at a temperature of 750 ° C. The space between anode and cathode was 1.25 cm, which gave an electrode current density of approximately 94 2 amperes per cm at an applied voltage of 2.5 volts. No chlorine gas, which could originate from the anode, was detected. Aluminum was deposited. The recovered aluminum was produced with a Faraday efficiency of 92% at an energy consumption of 8.09 kwh / kg.

EXAMPLE III

The electrolyte salt composition consisted of 10% NaCl, 50% CaCl 2, 20% CaF 2 and 20% AlCl 2. The electrode coating of Figure 2 was prepared in the same manner as in Example II, but only on one side of the electrode. The electrical connections were made such that the anode adjacent to the output tube was connected to the positive end and the negative end to the electrode most distant from the output tube. The coated sides of electrodes 25 and 26 were both facing away from the output tube and facing the cathode. The electrode 24, the cathode, was uncoated. This results in the electrode 25 not being connected to the direct current supply. This electrode then becomes bipolar. The lace coated with the A ^ O ^ ”carbon mixture is thus positively charged. The side of the bipolar electrode 25 closest to the output tube is negatively charged, upon which the aluminum deposits and falls into the molten pool. The aluminum also deposits on the negatively charged electrode 24 and falls into the molten pool. The temperature of the cell operation was 800 ° C and the applied voltage was 3 volts with respect to each electrode or a total of 6 volts across the ends. This imposed voltage at an electrode spacing of 1.87 cm resulted in a 2 electrode current density of 1.92 amp / cm.

EXAMPLE IV

The anode electrodes were composed of titanium diboride rods and the cathode electrode was also titanium diboride. The anodes were coated with bauxite, as in Figure 2, which was calcined at 600 ° C, mixed with phenolic resin and reacted at 800 ° C. The ratio of aluminum-35 oxide in the bauxite to carbon after the conversion was 6: 1.

The electrolyte salt composition was 20% NaCl, 30% CaCl 2, 10% CaF 2, 4% NaF, and 36% AlCl 2. The electrolysis took place at 750 ° C at an electrode current density of 2.4amp / ^ 2- 80 0 2 3 81 - 32 -

This led to 4 volts at an electrode gap of approx.

1.87 cm. No chlorine gas was observed. The composition of the aluminum deposited in the molten pool was 97% pure and contained 0.5% Si, 1.5% Fe and 0.9% Ti and very small amounts of other ingredients.

EXAMPLE V

In the cell of Figure 5, a porous membrane of aluminum nitride material with a thickness of 0.48 cm and a porosity of 50%, with a pore size of the order of 12-24 µx is used. The aluminum nitride was obtained by impregnating a porous alumina body with carbon and then heating it to 1750 ° C in a nitrogen atmosphere. The anode conductor was a graphite rod and the aluminum-containing material of the anode was a mixed powder of Al303 (Bayer) and carbon, in a ratio of 6: 1. The electrolyte salt composition was 20% NaCl, 25% LiCl, 30 % LiF, 25% AlCl 2 and the electrolysis was carried out at 720 ° C. The gap between the membrane and the aluminum pool was about 1.25 cm and the electrolysis was carried out at an anode current density of 1.6 amp / cm. This resulted in a voltage of 2.8 volts. The aluminum was produced with an efficiency of 92% and a purity of 99.5%.

EXAMPLE VI

A salt composition consisting of 12% Naf, 25% Lif, 28% NaCl, 15% LiCl, 10% A1F3 and 10% A1Cl3 was melted in a straight-sided cell. A 5 cm thick aluminum block was melted on the bottom of the cell and the working temperature was set at 700 ° C. Using an anode, as shown in Figure 2A, a gap between the bottom of the anode and the aluminum block was set at 4.4 cm.

2

At an anode current density of 0.96 amp / cm, the cell potential was 3.5 volts.

After 8 hours of electrolysis, the anode was removed from the cell and placed in a cell with 45 ° sides, as shown in Figure 7. After several hours of electrolysis, the anode was eroded such that the sides were parallel to those of the cathode. The anode was immersed 7.5 cm in the salt 800 23 81-33. With the same current as in the right-sided cell, the potential was 2.45 volts. This reduced potential, caused by side anode erosion at 90% efficiency and at a constant production rate, reduces power consumption from 11.6 kwh / kg to 8.1 kwh / kg, means a reduction of 3.5 kwh / kg.

EXAMPLE VII

A salt composition consisting of 20% NaCl, 10 25% LiCl, 25% LiF, 10% NaF, 10% A1F3 and 10% A1Cl3 was melted in a straight-sided cell. An aluminum block with a thickness of 5 cm was melted on the bottom of the cell and the operating temperature was set at 700 ° C. With a composite anode 30 cm long, with a copper rod attached to one end in the usual manner, the anode-cathode gap was set at 4.4 cm. At an anode current density of 0.96 amp / cm, the cell potential was 5.75 V after equilibrium was reached.

An identical anode, which however had a 45 ° slope on the side opposite to which the tube was attached, was placed in a cell with 45 ° sides, as shown in Figure 7. The depth of immersion of the anode in the salt was 7.5 cm. After a few hours of electrolysis, the angle of the anode was the same as that of the sides of the cell. The potential required to obtain the same total current as used in the straight-sided cell was 4.4 V. This decreased potential caused by the erode side of the anode at a current efficiency of 90% and at a constant production rate between the two cell types, the energy consumption decreases from 19.0 kwh / kg to 14.5 kwh / kg, which means a reduction of 4.5 kwh / kg.

This example clearly demonstrates the reduction of constant current energy consumption in a 35-slope cathode cell, as compared to a traditional cell, where the bottom of the anode is only eroded.

EXAMPLE VIII

An anode was prepared with Alcoa A-1 A ^ O. ^ 800 23 81-34 - mixed with coal tar pitch and phenolic resin and formed in a closed mold, using heat to cure the phenolic component. The ratio of the components was such that the composite anode after conversion contained 17% carbon and 83% Al2 O3. The electrolyte consisted of 20% NaCl, 25% LiCl, 30% LiF and 25% Naf and the operating temperature was 700 * 3. A cell, as shown in Figure 7, was used, but no aluminum block was added. After several hours of electrolysis at about 700 ° C, aluminum was collected in the well, demonstrating that the composite anode will produce aluminum on electrolysis, without an aluminum salt initially present in the electrolyte.

EXAMPLE IX

A straight-walled cell, as shown in Figure 5, was used, but without the membrane 68 and anode rod 52. Instead, a carbon cylinder was placed just above the salt electrolyte layer, in which a short anode portion was provided, as shown in Figure 2A. A mixture of Al 2 O 3, petroleum coke powder and a mixture of tar and pitch was applied to the top of the pre-baked short anode and around the conductive bars 37. When converted to the salt electrolyte at a temperature of 740 ° C, the ratio was 18% carbon and 82% Al2 O3 · A salt electrolyte consisting of 10% NaF, 25% LiF, 20% NaCl, 15% LiCl, 20% A1F3 and 10 AlCl 3 was used. The electrical connection was made to the conductor bars 37 with clamps in the cooling section above the level of the anode composition of the

Soderberg type in the carbon cylinder. The electrolysis was carried out at an anode current density of 22 amp / cm with a gap of 3.1 cm between the aluminum pool and the anode.

Electrolysis was continued with additions of A12C> 3-carbon tar / pitch in the carbon cylinder and continuous feeding of the anode, which hardened and reacted upon contact with the salt electrolyte. The aluminum conductive rods melted with consumption of the anode and were added to the aluminum kethode 32.

In the same manner, electrolysis was carried out with 800 23 81 - 35 - a rectangle of carbon, rectangular pre-baked blocks and aluminum plates, as shown in figure 13. The aluminum plates were 0.15 cm thick and the pre-baked blocks had a thickness of 5 cm . The electrical connection was made with 5 rollers around each aluminum plate. During the consumption of the anode, additional pre-baked blocks were placed between the aluminum plates.

THE DRAWINGS

Figure 1 shows a schematic cross-section 10 of the electrolytic cell according to the invention, which contains a chloride bath, and the closed top of the cell is indicated by the placement of the electrodes.

Figure 2 schematically shows a partially cut-away electrode, which is used as a node and is coated with a mixture of aluminum-containing material and a reducing agent.

Figure 2A provides a schematic perspective view of another embodiment of the electrode of Figure 2, showing a number of conductive cores in a mold 20 of aluminum-containing material and reducing agent.

Figure 2B provides a schematic perspective view of a variation of the electrode shown in Figure 2A.

Figure 3 shows a schematic, partially cut away, illustration of another alternative electrode.

Figure 4 is a schematic cross-sectional illustration of an open-top electrolytic cell containing a total fluoride bath and an anode clamp providing the electrical current to a continuously fed anode.

Figure 4A is a schematic drawing of another alternative electrode, which is the same as the electrode of Figure 3.

Figure 5 is a schematic view of an embodiment of the present invention, showing the use of a porous membrane containing the various anodic materials, including an aluminum-containing 800 23 81-36 material and a reducing agent.

Figure 6 is a schematic cross-sectional view of another embodiment of an electrolytic cell, illustrating the use of bipolar electrodes.

Figure 7 is a schematic cross-sectional view of a combination of electrolytic cells with electrodes with sloping sides and the composite anode of complementary shape.

Figure 8 is a schematic cross section of a modification of the unique combination of the electrolytic cell and the composite anode.

Figure 9 provides a perspective view of the anode of Figure 8.

Figure 10 is a schematic cross section of another embodiment of the combination of Figure 8.

Figure 11 is a perspective drawing of the anode of Figure 10.

Figure 12 is a schematic perspective view of another embodiment of the composite anode of the present invention, showing a layered construction.

Figure 13 is also a schematic perspective view of the anode of Figure 12 and the anode clamp of Figure 4.

30 800 23 81

Claims (109)

1. An electrode suitable for use in an electrolytic cell for depositing aluminum from a molten electrolyte, an electric power source and a cathode for depositing aluminum, characterized in that the anode contains an oxygen-containing aluminum compound in an amount sufficient to provide aluminum during the electrolysis and a reducing agent which is in contact with the oxygen-containing aluminum compound and is present in an amount sufficient to react at the anode and then aluminum metal at the cathode wherein the weight ratio of the oxygen-containing compound, which is expressed as Al 2 O 3, to the reducing agent is at least about 1.5 parts by weight. An electrolytic cell for the deposition of aluminum, characterized in that it contains the electrode according to claim 1 and that the electrolyte contains chloride or fluoride ions or mixtures thereof and that the compound is capable of being attached to the anode react that aluminum ions are formed for the reduction at the cathode to aluminum metal. Electrolytic cell according to claim 2, characterized in that the temperature of the electrolyte is between the melting point of aluminum and the boiling point of the liquids in the cell. An electrolytic cell according to claim 1, characterized in that the temperature of the electrolyte is between about 10 ° C and 150 ° C above the melting point of the metal. Electrode or electrolytic cell according to one or more of claims 1 to 4, characterized in that the reducing agent consists of a carbonaceous compound or carbonaceous element, sulfur, phosphorus and arsenic. Electrode or electrolytic cell according to one or more of claims 1 to 4, characterized in that the reducing agent prior to conversion consists of an organic material which produces carbon by conversion. Electrode or electrolytic cell according to one or more of Claims 1 to 8 - 38 - more claims 1 to 4, characterized in that the oxygen-containing aluminum compound is mixed with the reducing agent in an amount of at least 1.5 parts by weight per part of reducing agent. . Electrode or electrolytic cell according to one or more of claims 1, 3 or 4, characterized in that the electrolyte is mainly formed from fluoride salts and that the compound is able to react at the anode to produce aluminum ions 10 for reduction at the cathode to aluminum metal. Electrode or electrolytic cell according to one or more of claims 1, 3 or 4, characterized in that the electrolyte is essentially a total fluoride salt, the compound contains aluminum and is capable of reacting at the anode to aluminum ions for the reduction at the cathode to aluminum metal and that the temperature of the electrolyte is between about 700 and 800 ° C. Electrode or electrolytic cell according to claim 9, characterized in that the reducing agent consists of carbon or a carbonaceous compound and that the oxygen-containing metal compound is aluminum oxide, bauxite, clay or a metal-containing oxide. 11. An electrolytic cell for the deposition of aluminum, characterized in that it comprises the electrode according to claim 1 and a membrane, which is placed in contact with the compound to substantially facilitate the passage of the undissolved solids. by preventing the membrane. Electrolytic cell according to Claim 11, 30, characterized in that the membrane contains the oxygen-containing aluminum compound to form an anode thereof. Electrolytic cell according to claim 11 or 12, characterized in that the membrane is formed from glassy carbon foam, graphite or solid carbon, the nitrides of boron, aluminum, silicon (including the oxynitride), titanium, hafnium, zirconium and tantalum ; the silicides of molybdenum, tantalum and tungsten; the carbides of hafnium, 800 2 3 81 - 39 - tantalum, columbium, zircon, titanium, silicon, boron and tungsten; and the borides of hafnium, tantalum, zircon, columbium, titanium and silicon, the material having a passage porosity sufficient to pass all materials in the liquid form into the electrolytic bath, but with molten aluminum, but with including ionic compounds, and dissolved solids and undissolved solids, which form impurities, substantially retain an electric current to flow and wherein the material has an interconnected pore size with a cross section sufficiently small to shield undissolved particles. Electrolytic cell according to claim 13, characterized in that the passage porosity is between about 1 to 97% and the connected pore size is between 1 and 1 cm. Electrolytic cell according to claim 11, characterized in that it contains a porous membrane placed in the electrolyte such that it contains as anode the compound and the reducing agent for the reaction. 16. Electrolytic cell according to claim 15, characterized in that it contains feed means, which are placed in the cell such that they continuously replenish the compound and the reducing agent in the membrane. The invention according to claim 7, characterized in that it comprises an anode formed from a central conductive core with a coating of the aluminum compound around it. The invention according to claim 1 or 3, characterized in that the anode has a number of pairs of vertically arranged conductive pins for connection to electric buses. Electrolytic cell according to one or more of claims 13 to 16, characterized in that it contains the electrolyte mainly formed from fluoride salts and the compound capable of reacting at the anode, whereby aluminum ions are formed for reduction at the cathode to aluminum. 800 2 3 81 - 40 - 20. An electrolytic cell according to any one of claims 2 to 4, characterized in that the cell contains a lid to close the top of the cell to prevent the escape of gases and hydrolysis of the electrolyte. Electrolytic cell according to one or more of claims 2 to 4, characterized in that the space between the anode and the cathode is less than about 2.5 cm. Electrolytic cell according to claim 21, 10, characterized in that the space between the anode and the cathode is less than about 1.25 cm. 23. The invention according to one or more of claims 1-4, characterized in that the anode is composed of at least one internally placed conductive material, which is surrounded by anodic material containing the aluminum compound. Electrolytic cell according to one or more of claims 2 to 4, characterized in that it comprises the anode, which is composed of at least one internally placed conductive material, surrounded by anodic material containing the aluminum compound, a membrane placed in contact with this aluminum compound to prevent the passage of undissolved solids through the membrane, and the electrolyte consisting essentially of fluoride salts and the aluminum-containing compound capable of reacting at the anode to aluminum ions which cathode are reduced to aluminum metal, the temperature of the electrolyte being between about 700 and 800 ° C. Electrolytic cell according to claim 24, 30, characterized in that the membrane contains a mixture of the aluminum compound and the reducing agent to form the anode thereof. An electrolytic cell according to claim 25, characterized in that it comprises: the membrane 35 formed from a material of glassy carbon foam, graphite or solid carbon, the nitrides of boron, aluminum, silicon (including the oxynitride), titanium, hafnium, zircon and tantalum; the silicides of molybdenum, tantalum and tungsten; 800 23 81 - 41 - The carbides of hafnium, tantalum, columbium, zircon, titanium, silicon, boron and tungsten; and the borides of hafnium, tantalum, zircon, columium, titanium and silicon, the material having a passage porosity sufficient to pass all materials in liquid form in the electrolytic bath except molten aluminum, but including ionic compounds and substantially retains dissolved solids and undissolved impurities which form an electric current to flow and the material has a connected pore size with a cross section sufficiently small to retain undissolved particles. 27. An electrolytic cell according to claim 26, characterized in that the passage porosity is between about 1 and 97% and the connected pore size is between about 1 and 1 cm. 28. An electrolytic cell according to one or more of claims 2, 3 or 4, characterized in that it contains a porous membrane placed in the electrolyte so that it contains a mixture of the aluminum compound and the reducing agent for reaction. at the anode. 29. The invention according to claim 9, characterized in that the anode is composed of at least one internally placed conductive material surrounded by anodic material containing the aluminum compound. The invention according to claim 24, characterized in that the membrane forms a compartment containing a mixture of the aluminum compound and the reducing agent and forming a bipolar electrode. The invention according to claim 30, characterized in that it comprises a cell incorporating a metal collection compartment, said cell located below the membrane and the cathode. 32. The invention according to claim 30 or 31, 35. characterized in that the membrane compartment contains the retained impurities and forms the bipolar electrode. The invention according to claim 30 or 31, 800 2 3 81 - 42 - characterized in that it contains: the electrolyte with chloride or fluoride ions or mixtures thereof, and the compound capable of being bonded to the anode react to metal ions for reduction at the cathode to metal. The invention according to claim 30 or 31, characterized in that the temperature of the electrolyte is between the melting point of the aluminum metal and the boiling point of the liquids in the cell. The invention according to claim 30 or 31, characterized in that the temperature of the electrolyte is between 10 ° C and 150 ° C above the melting point of the metal, as well as the electrolyte, which is formed from mainly fluoride salts and the metal which is directly reduced to molten metal at the anode. 36. A method for the electrochemical deposition of aluminum, using an electrolytic cell, which contains an electric current source, a molten electrolyte for conducting the electric current and a cathode for depositing the aluminum, characterized in that as anode is used a combination of an oxygen-containing aluminum compound in an amount sufficient to provide aluminum during the electrolysis and a reducing agent which is in contact with this compound and is sufficiently present to react on the anode 25, the cathode aluminum metal is formed, the weight ratio of the aluminum compound expressed as to the reducing agent is at least about 1.5: 1, the compound reacts at the anode, aluminum metal is formed at the cathode, and the aluminum at the cathode is then collected. A method according to claim 36, characterized in that the electrolyte contains chloride or fluoride ions or mixtures thereof and the compound is able to react at the anode to aluminum ions, which are reduced to aluminum at the cathode. A method according to claim 36, characterized in that the compound consists of aluminum oxide, bauxite, clay or an aluminum-containing oxide. 800 2 3 81 - 43 - A method according to claim 36, characterized in that the temperature of the electrolyte is between the melting point of aluminum and the boiling point of the liquids in the cell. 40. A method according to any one of claims 36-39, characterized in that the temperature of the electrolyte is between 10 ° C and 250 ° C above the melting point of the metal and that the electrolyte contains only fluorides. 41. A process according to any one of claims 36-39, characterized in that the reducing agent prior to conversion consists of an organic material which produces carbon upon conversion. 42. A process according to any one of claims 15, 36, 37 or 39, characterized in that the oxygen-containing aluminum compound is mixed with the reducing agent in an amount of 1.5-50.0 parts by weight per part of reducing agent. 43. A method according to claim 36, characterized in that the compound and the reducing agent are intimately and substantially mixed in mutual contact. 44. Method according to claim 36 or 39, characterized in that the reducing agent consists of a carbon-containing compound or element, sulfur, phosphorus or arsenic and in that the compound consists of aluminum oxide, bauxite or clay. 45. A method according to claim 36, characterized in that the reducing agent is immersed in the electrolyte at a temperature and for a time sufficient to cause the reducing agent to convert. A method according to claim 45, characterized in that the reducing agent prior to conversion consists of an organic material which gives carbon by conversion. A method according to claim 46, characterized in that the organic material consists of tar, pitch, coal, carbon products and natural or synthetic resinous materials. 800 23 81 - 44 - 48. A method according to claim 36, characterized in that the electrolyte is mainly formed of fluoride salts and that the compound is able to react at the anode to aluminum ions, which are reduced to aluminum at the cathode and that the temperature of the electrolyte is between 10 ° C and 150 ° C above the melting point of aluminum. 49. A method according to claim 42, characterized in that the temperature of the electrolyte is between 10 ° C and 150 ° C above the melting point of the metal and that the electrolyte is mainly formed from fluoride salts and that the compound is capable of to react at the anode to aluminum ions, which are reduced to aluminum at the cathode. A method according to claim 36, characterized in that a porous membrane is provided which is placed in the electrolyte to contain the compound and the reducing agent for reaction at the anode. 51. A method according to claim 36, characterized in that a total fluoride-containing electrolyte is provided and that the reducing agent is able to react at the anode to metal ions, which are reduced to metal at the cathode. 52. A method according to claim 48, characterized in that the temperature is in the range of 700-800 ° C and that the source of the metal is aluminum oxide. 53. A method for the electrochemical deposition of aluminum from aluminum chloride, using an electrolytic cell containing an electric power source, an electrolyte containing aluminum chloride for conducting the electric current, and a cathode for depositing aluminum, characterized in that as an anode a combination of an oxygen-containing aluminum compound in an amount sufficient to provide aluminum during the electrolysis and a reducing agent in contact with the compound is formed, that the weight ratio of the aluminum compound, expressed as A ^ Up to 800 2 3 81 - 45 - the reducing agent is at least about 1.5: 1, that aluminum ions are electrolyzed from the electrolyte, aluminum is deposited at the cathode and the aluminum ions are electrolyzed by the aluminum compound to react to the cathode with the reducing agent, be replenished continuously. 54. A process according to claim 53, characterized in that the aluminum compound is an oxygen-containing aluminum compound capable of reacting with the reducing agent to aluminum ions at the anode. 55. A method according to claim 53, characterized in that the aluminum compound consists of aluminum oxide, bauxite or clay. 56. Process according to one or more of claims 53-55, characterized in that the weight ratio to reducing agent is between 1.5 and 50.0 parts of A 2 O 2 per part of reducing agent. 57. Process according to one or more of claims 53-56, characterized in that the conversion reducing agent consists of an organic material, which gives carbon on conversion. 58. A method according to claim 57, characterized in that the organic material consists of tar, pitch, coal, carbon products and natural or synthetic resinous materials. 59. A process according to any one of claims 53-56, characterized in that the aluminum compound and the reducing agent are intimately and substantially mixed in mutual contact. 60. A method according to claim 53, characterized in that the reducing agent consists of a carbonaceous compound or element, sulfur, phosphorus or arsenic, the aluminum compound consists of aluminum oxide, bauxite or clay and the aluminum compound and the reducing agent are intimate and substantially are mixed in mutual contact. A method according to claim 53, characterized in that the reducing agent is immersed in the electrolyte at a temperature and for a time which is 800 23 81 - 46 - sufficient to convert the reducing agent. 62. A process according to claim 61, characterized in that the reducing agent before conversion consists of an organic material, which gives carbon 5 upon conversion. A method according to claim 62, characterized in that the organic material consists of tar, pitch, coal, carbon products and natural or synthetic resinous materials. 64. A method according to any one of claims 25-27, characterized in that the aluminum compound and the reducing agent are intimately and substantially mixed in mutual contact. 65. A method according to any one of claims 25-28, characterized in that a membrane is used which is placed in contact with the aluminum compound mainly to prevent the passage of undissolved ions through the membrane. 66. A method according to any one of claims 20, 26, 27 or 29, characterized in that the membrane contains the aluminum compound to form an anode thereof. 67. A method according to claim 16, characterized in that the voltage of the cell is reduced by maintaining aluminum chloride in the electrolytic bath. 68. A method according to claim 31, characterized in that the electrolytic bath contains a mixture consisting essentially of NaAlCl4 · 69. An electrode suitable for use as an aluminum source in the electrochemical deposition of aluminum, characterized in that it contains a mixture of aluminum-containing material containing aluminum oxide and a reducing agent in contact with the aluminum oxide from the aluminum-containing material and at least one metal conductor which is in contact with the electrode to conduct the electric current through the mixture, which conductor is placed in the electrode and protrudes at least on the side of the 800 23 81 - 47 end of the electrode to into the electrolyte. 70. An electrode according to claim 69, characterized in that the metal conductor is a longitudinally positioned central core of the electrode. An electrode according to claim 69, characterized in that the metal conductor has a number of pairs of pins arranged transversely of the electrode. 72. The electrode of claim 69, wherein the Lkenraerk is that the mixture is in the form of at least two adjacent layers and that the metal conductor is in the form of a plate interposed between the layers and thereby forms a unit. The electrode according to one or more of claims 69-72, characterized in that the ratio of the alumina in the aluminum-containing material to the reducing agent is between 1.5 and 50.0. 74. The electrode according to claim 73, characterized in that the ratio of the aluminum oxide in the aluminum-containing material to the reducing agent is between 2.5 and 6.0. 75. An electrolytic cell according to any one or more of claims 2-4, characterized in that an electrode is placed between the anode and cathode, which electrode is in electrical contact with the aluminum compound and the reducing agent for bipolar electrolysis. 76. An electrolytic cell according to claim 75, characterized in that the oxygen-containing aluminum compound is mixed with the reducing agent in an amount of 1.5-50.0 parts by weight per part reducing agent. 77. An electrolytic cell according to claim 75, characterized in that the reducing agent consists of carbon or a carbonaceous compound or element, sulfur, phosphorus or arsenic. An electrolytic cell according to one or more of claims 75-77, characterized in that the electrolyte mainly consists of fluoride salt, the compound contains aluminum and the temperature of the electrolyte is between 9 700 and 48 - between about 700 and 800 ° C. 79. An electrolytic cell according to claim 75, characterized in that the reducing agent consists of carbon or a carbonaceous compound or element, sulfur, phosphorus or arsenic, the oxygen-containing aluminum compound is mixed with the reducing agent in an amount of 1, 5-20.0 parts by weight Α120 ^ per part of reducing agent, the electrolyte mainly consists of fluoride salt, the compound contains aluminum and is able to react at the anode to aluminum ions, which are reduced to aluminum metal at the cathode and the temperature of the electrolyte is between approx. 700 and 800 ° C. 80. An electrolytic cell according to claim 75, characterized in that the electrode is coated on one side only with the compound and the reducing agent. An electrolytic cell according to claim 75, characterized in that the electrode is placed within a membrane containing the compound and the reducing agent in contact with the compound. 20 82 ^. Electrolytic cell according to claim 81, characterized in that the membrane substantially prevents the passage of undissolved solids. 83. A method according to claim 36, characterized in that an electrode is placed between the anode and cathode, the electrode is in contact with the aluminum compound and the reducing agent and the electrode are bipolar during the electrochemical deposition. 84. A method according to claim 83, characterized in that the oxygen-containing aluminum compound 30 is mixed with the reducing agent in an amount of 1.5-50.0 parts by weight per reducing agent. 85. A method according to claim 83, characterized in that the reducing agent consists of a carbonaceous compound or element, sulfur, phosphorus or arsenic. 86. Process according to one or more of claims 83-85, characterized in that the electrolyte consists wholly or almost entirely of fluoride salt, the compound contains aluminum and is capable of reacting at the anode 800 23 81 - 49 - aluminum ions which are reduced to aluminum metal at the cathode and that the temperature of the electrolyte is between about 700 and 800 ° C. 87. Process according to claim 84, characterized in that the reducing agent consists of a carbonaceous compound or element, sulfur, phosphorus or arsenic, the oxygen-containing aluminum compound is mixed with the reducing agent in a ratio of 1.5-50.0 parts by weight per part of reducing agent, the electrolyte consists wholly or substantially entirely of fluoride salt, the compound contains aluminum and is able to react at the anode to aluminum ions, which are reduced to aluminum metal at the cathode and that the temperature of the electrolyte is between approx. 700 and 800 ° C. 88. A method according to claim 84, characterized in that the electrode is coated on only one side with the compound and the reducing agent. 89. A method according to claim 83, characterized in that the electrode is placed in a membrane containing the compound and the reducing agent in contact with the compound. 90. Method according to one or more of claims 36, 39 and 48, characterized in that the anode has a sloping surface and the cathode has a complementary shaped surface and that the distance between the anodic and cathodic surface is chosen in advance. A method according to claim 90, characterized in that the space between the two complementary shaped surfaces is less than about 3.75 cm. 92. A method according to claim 90, characterized in that the distance is 0.6-2.5 cm. A method according to claim 90, characterized in that the angle between the inclined surface and the surface of the bath is approximately 10-80 °. A method according to claim 90, characterized in that the temperature of the cathode surface immersed in the electrolyte is kept high enough to prevent the electrolyte from solidifying on the cathode 800 23 81 - 50 surface and that the spacing is thereby maintained. 95. An electrolytic cell for the electrochemical deposition of aluminum / characterized in that it comprises the electrode according to claim 1, immersed in an electrolytic bath, the cell comprising the electrode as an anode to provide the aluminum for deposition , the anode having at least one sloping surface immersed in the electrolyte to increase the anodic surface subject to erosion, the cathode, at least a portion of the surface of which is complementary to the sloping anodic surface, the complementarily formed cathodic and anodic surfaces have a preselected short distance to each other to reduce the energy consumption of the deposit. 96. An electrolytic cell according to claim 95, characterized in that the spacing between the two complementary shaped surfaces is less than 3.75 cm2. An electrolytic cell according to claim 96, characterized in that the spacing is between 0.6 and 2.5 cm. 98. An electrolytic cell according to claim 95, characterized in that the sloping surface has an angle to the surface of the bath of about 10-80 °. 99. An electrolytic cell according to claim 95, characterized in that the sloping surface has an angle downwards and inwards. 100. An electrolytic cell according to claim 95, characterized in that the bottom surface of the anode has an angle with respect to the surface of the bath and the bottom surface of the cathode, which is opposite the anode, is at least partly complementary. at the bottom of the anode surface. 101. An electrolytic cell according to any one of claims 95-100, characterized in that the temperature of the electrolyte lies between the melting point of aluminum and the boiling point of the liquids in the cell. 102. An electrolytic cell according to one or more of claims 95-100, characterized in that the anode is composed of at least one internally placed conductive material surrounded by anodic material containing the aluminum compound. 103. An electrolytic cell according to one or more of claims 95-99, characterized in that it contains an aluminum source placed under the anode, which source has an inclined bottom under the anode, so as to increase the depth of an aluminum pool. as small as possible. 104. An electrolytic cell according to one or more of claims 95-100, characterized in that it comprises a liner which forms part of the cathode surface which is in contact with the electrolytic bath, which cathode surface has a temperature which not lower than the solidification temperature of the bath, maintaining the preselected small distance. 105. Membrane suitable for use in the electrochemical deposition of aluminum, which is resistant to the corrosivity of an electrolytic bath containing halide salts, characterized in that it comprises a material of glassy carbon foam, graphite or solid carbon, the nitrides of boron, aluminum, silicon (including the oxynitride), titanium, hafnium, zircon and tantalum; the silicides of molybdenum, tantalum or tungsten; the carbides of hafnium, tantalum, columbium, zircon, titanium, silicon, boron or tungsten? and the borides of hafnium, tantalum, zirconium, columbium, titanium and silicon, which material has a passage porosity sufficient to pass all materials in liquid form into the electrolytic bath, including ionic compounds and dissolved solids dissolves dissolved solids, which form impurities, through which an electric current can pass, and which material has a connected pore size with a cross section sufficiently small to retain undissolved particles. 800 2 3 81 - 52 - 106. The membrane according to claim 105, characterized in that the passage porosity is between about 1 and 97% and the connected pore size is between about 1 µm and 1 cm. Membrane according to claim 105, characterized in that it has a thickness of 0.3-5 cm. 108. Membrane according to claim 105, characterized in that it has a thickness of 0.3-1.25 cm. Membrane according to claim 105, characterized in that the passage porosity is between about 30 and 70%. 110. Membrane according to one or more of claims 105, 107 or 109, characterized in that the connected pore size is between about 1 and 1 cm. 20 800 23 81