JPS6325077B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a unique system for electrolytically producing aluminum from various aluminum-containing raw materials (R) in a low temperature electrolytic bath (B). The basis of this invention is the cathode (H)
A unique anode (A) that is the only source of aluminum deposited on This anode (A) comprises a combination of an aluminum source, usually alumina Al ₂ O ₃ and a reducing agent such as carbon. A conductor (D) is combined with the anode (A) to increase the conductivity of the anode, and a membrane (M) is used to contain the raw material (R).

The electrolytic cell (C) containing the anode (A) and the cathode (H) can take various constructional forms with inclined wall electrodes or vertical wall electrodes. In a preferred embodiment, a sloped wall electrode is more economical and practical when used at low temperatures with the unique anode.

The electrolytic bath (B) can consist of chlorides or fluorides or mixtures thereof and does not require the initial addition of aluminum salts to the bath. In the aluminum chloride cycle, which is one form of the present invention, aluminum chloride is present in the bath, and the aluminum chloride is maintained at a constant concentration by the reaction of the composite anode (A) in the bath, and aluminum ions are used for reduction at the cathode. form. In another version of the invention using a total fluoride bath, the aluminum is also ionized at the anode (A) for deposition at the cathode (H).

Electrolytic Cell The electrolytic system of the present invention utilizes an electrolytic cell (C) shown in the accompanying drawings for the unique continuous production of aluminum.

In Figures 1-6, one form of electrolyzer construction is shown generally at 10 and consists of an outer steel shell with a refractory lining 14 that can serve solely as a thermal insulator or as both an insulator and an electrode. This refractory lining may be any material that withstands the action of the molten electrolytic bath 16. A refractory lining with conventional vertical sides 15 and a bottom 17 is designed to maintain the desired thermal balance in the operation of the vessel;
The cross section can therefore be made very thin in order to achieve a small temperature gradient created both in the thin layer of coagulation salt on the refractory surface and in the hot outer wall on the surface of the steel shell 12. The refractory lining can be made quite thick to achieve a solidified precipitation layer of salt within the refractory lining that occurs at the cooling surface on the steel shell, but this is unnecessary in the vertical sided vessels of Figures 1-6. . On the other hand, in the inclined side electrode tank of FIG. 7, the cathode 19
are conductive linings formed on both sides of the anode. A thermal and electrical insulating lining can be placed between cathode 19 and shell 12 if desired. To prevent a solid layer of salt from collecting on both sides of the electrode,
The coagulation line should be within the boundaries of this conductive lining or cathode 19. Such a salt layer acts as an electrical insulator and prevents useful electrical current flow.

A lid 18 is placed on the top of the tank to obtain an airtight closure.
, which is only necessary for chloride-containing baths.
This prevents air or moisture from escaping into the vessel or vapors of the salt composition 16 from escaping and reacting with the environment. The lid 18 can be lined with a refractory material 20, which can be the same as the refractory lining 14, or which maintains the temperature equilibrium of the vessel and contains the salt composition 1.
The refractory material may be any other refractory material that is chemically inert to 6. The seal 22 is the lid 18
and is secured to the electrodes 24, 25, 26 to prevent atmospheric air and moisture from leaking into the tank or vapor from the tank to the environment. The sealing around the lid 18 and electrodes can be any means to prevent vapor leakage and can be standard or conventional packing and gasketing materials that can withstand operating temperatures and withstand electrolyte vapors. Acceptable materials for such packing gaskets include asbestos, fibrous ceramics, Teflon, Vitron, silicone,
Liquid metal seals such as mercury, liquid solder, tin, lead, etc.

Electrodes 24, 25, 26 can be anodes, cathodes, or depolarized electrodes. These can include solid or coated conductors to carry current for cell operation. These conductors can be any material that can withstand bath temperatures ranging from 150 to 1060°C, is stable to the halogenated composition 16, and is a good electrical conductor. Materials useful for this purpose are carbon, suitably sized for heat transfer balance;
Graphite, titanium carbide, titanium nitride, or titanium boride, aluminum metal. Preferred materials for these conductors have been found to be graphite and titanium diboride when operated in a depolarized manner.

The aluminum chloride cycle tank also includes a chimney or outlet pipe 28 having a valve 30 to control the flow of gaseous elements from the chimney and to ensure pressure buildup within the tank for continuous operation. The gaseous vapor leaving the tank is that of the oxidized reducing agent, and in particular no chlorine gas is detected from the aluminum chloride-containing salt. Even if chlorine is produced, it reacts at the anode 26 and is recycled as aluminum chloride. The molten aluminum 32 is discharged by a conventional screw 34 or by vacuum standard siphoning techniques well known in the art.

FIG. 4 shows a variation of the cell design of FIG. 1, again showing vertical side electrodes 19. FIG. The tank structure including shell 12 and refractory 14 is the same as described above, and electrode 44 serving as an anode can be one of the anodes shown in FIG. 2, FIG. 2A or FIG. 2B, but is preferred. is the anode in Figure 3. The anode 44 is immersed in an electrolyte containing fluoride salts or chlorides or mixtures thereof and heated to a temperature typically between 670 and 810C. At the bottom of the vessel, on a cathode rod 45 placed on the refractory insulation 14, there is a block 46, which is preferably slightly wider than the anode 44, and which by means of a suitable electrical connection to the cathode rod 45 serves as a cathode. . Block 46 can be made from any of the electrode materials mentioned above. Block 46 should extend near the base 50 of anode 44, which is the only surface of anode erosion. Closer anode-cathode spacing for such electrode arrangements is also possible when block 46 rises above the level of molten aluminum 32. As the aluminum is deposited on the cathode block 46, its surface is wetted and the aluminum flows from the block into a pool 32 at the bottom of the bath and is removed at 34 when desired.

FIG. 4 also schematically shows an anode 4 adjacent to the bottom of the anode above but preferably below the bath level.
A power attachment clamp 47 is shown in contact with 4 to minimize power loss due to anode resistance.
The anode 44 can have the structure shown in FIGS. 3, 12, and 13, for example. Since the composite anode preferentially dissolves in the bath, the clamp does not act as an anode. Clamp 47 can partially or completely surround anode 44 for continuous feeding into the bath. The clamp is made of a suitable inert material that is electrically conductive. This material includes graphite, carbon,
There is TiB ₂ or a mixture thereof. The electrical connection between the clamp and the anode is by a raised contact or nub 48. Attachment of power to clamp 47 is by means of a suitable split cylindrical conductor 49 extending above the top of the tank.

Instead of periodically changing the anode to supply fresh aluminum material, the present invention uses a feed mechanism for continuous operation as shown in FIG. Can be adapted to continuous supply of electrodes.

Projecting upwardly through the tank (C) of FIG.
Or it remains above the cathode block 46.
Surrounding the anode 52 is an anode material, generally designated (R), consisting of an aluminum material and a reducing agent. This anode mixture ranges from 0.025 to about 25.4mm (0.001 to
The particles can be formed into small particle sizes (about 1.0 inch) or larger, and can be formed by extrusion, molding, etc., and are fed to the tank by a hopper 54. Raw particles of aluminum material and reducing agent are particularly identified at 58 and in intimate contact with the anode 52, providing the necessary source of aluminum and reducing agent.

These anode materials are kept in intimate contact with each other and the anode 52 by placing them in a porous membrane container 60 surrounding the anode 52. When the anode material 58 is used up and its level falls substantially below the level of the molten bath 16, the feed 54 is operated to add additional anode material 58 to the porous membrane vessel 60.

In the specific example of FIG. 6, a bipolar type battery case is shown. Also, similar structures are designated by the same numerals.

The same basic principles exist for the operation of depolarized cells, except that there is a pair of electrodes connected to a suitable power source at either end of the cell. One of the electrodes 6
4 is a cathode, and at the opposite end is an anode 66. Between electrodes 64 and 66 are spaced apart electrodes 68 that are not connected to each other or to a power source.
Each of the electrode 68 and the anode 66 has a
A porous membrane container 60 of the same type as that described in 0 is fixed. However, the porous membrane 60 of the depolarized cell has one of the electrodes 66 or 68 on one side to form an enclosure for the anode material 58.

In a depolarized battery case, the side of the electrode closest to the anode 66 is negatively charged, and the side of the electrode 6 facing the cathode 64 is negatively charged.
The side of 8 becomes positively charged. This side 72 of electrode 68 serves as an anode and is the side that contacts anode raw material 58 . Next, electrolysis is done at electrode 6.
8 produces aluminum on the negative side and CO ₂ on the positive or anode side of the same electrode. The aluminum falls into the bottom pool 32 and is collected in the conventional manner.

7-11, a sloped side electrode-electrolyzer is shown which, in combination with the anode composition of the present invention, yields substantial economies in the electrolytic deposition of aluminum.

In typical Hall cell operation,
The aluminum reduction tank has an anode-cathode spacing that must take into account magnetic field effects and "reverse reactions" due to the undulation of the aluminum pool. Such considerations preclude a spacing closer than about 1.5 and 2.0 inches between the bottom surface of the anode and the top of the aluminum pool or cathode, where all erosion occurs. A further equally important reason for the need for greater spacing between the cathode and anode in hole tank configurations using vertical sides or in attempts to use sloped side electrodes is the high temperature required and the maintenance of high temperatures due to the dissolution of the alumina. This makes it extremely difficult to maintain dimensional stability due to the corrosive salts that are necessarily present. In combination with a sloped-sided electrode bath and an anode that utilizes aluminum oxide and a reducing agent to provide the sole source of aluminum,
Low temperatures, just above the melting temperature of aluminum, are used to minimize problems with dimensional instability, so the cells of the present invention can be constructed with closer anode-to-cathode spacings not achievable in the past. Thus, it is the particular combination of sloped walls for the anode and cell configuration that achieves lower IR power drop in the salt due to the close spacing allowed between sloped walls and the reduction in anode current density.

Essentially, the vessels of Figures 7-11 are similar to those described above, except that the sloped surfaces form the electrodes. In this tank construction, the anode 74 is on the outer surface as shown with downwardly and inwardly facing slanted sides 7.
6, but the direction of the angle is not of any importance. The slope of this side can be in any direction or at any angle from the level of the bath (B). This angle can vary from 10 to 80 degrees or more from the bath level.
By using the anode bottom of the sloped side electrode and that portion of the sloped anode side immersed in bath 16, the anode erodes over a larger surface area, providing aluminum that is ultimately deposited at the cathode.

The cathode 78 has a complementary shaped surface 79 on the sloped side 76 of the anode to provide electrode spacing on the sides as indicated by spacing (Y). This spacing can be 6.35-63.5 mm (0.25-2.5 inches). Larger spacing results in greater energy consumption. The spacing between the bottom 80 of the anode 74 and the surface of the aluminum layer 82 forming a portion of the aluminum pool 84 in FIG. 7 is shown (X) and can be between 0.25 and 2.5 inches. . Preferably the spacing (X) and (Y) are
It should be 6.35-25.4mm (approximately 0.25-1.0 inch).

The spacing between the anode and cathode above solidified bath layer 86 is not critical to the usefulness of the present invention. However, the spacing (X) and (Y) between the anode and cathode can be equal or different depending on the desired current density and anodic erosion, but there is a substantial savings in energy consumption when set close as above. occurs.

The lining 78 forming the cathode of the cell can be comprised of typical materials used in electrolytic cells, such as carbon, titanium diboride, etc., and is shaped as described above to match the contour of the anode 74. In addition, the bottom of this lining has a sloped floor 90 for an aluminum pool leading to an aluminum collection well 92. As can be seen, the sloped bed 90 is such that it retains only a limited depth of aluminum layer, which depth can be adjusted by means (not shown) of removing aluminum from the collection wells. . The purpose of the thin aluminum layer under the bottom 80 of the anode is to substantially eliminate undulations in the molten aluminum layer due to magnetic effects within the bath.

Otherwise, the lid 18 is provided with an outlet 28 that is part of the shell 12.
The tank of FIG. 7 is similar to the tank of FIG. A suitably shaped refractory insulator such as that shown at 14 may also be included.

The combination of the use of the anode of the present invention and the sloped side surface adapted to the sloped anode allows the configuration of the tank and the anode to be
As shown in FIG.

In FIGS. 8 and 9, the shape of the anode 74 has been changed to include a centrally located, diverging sloped side surface 94 that forms an apex 96 on the anode. The carbon or other lining material, such as _TiB2 , which acts as the cathode, projects upwardly to complement the internal shape of the anode, as shown in FIG. The operation of a bath such as that shown in FIGS. 8 and 9 is essentially the same as that described in FIG. 7, particularly with respect to the increased eroded surface 94.

In FIGS. 10 and 11, two anodes 100 and 102, each having inverted sloped sides 104, 106, are placed in a bath with a cathode 98 having essentially the same shape as that shown in FIG. ing.

It has been found that the use of the sloped cathode concept of the electrolytic cell shown in Figures 7-11 requires not allowing a coagulated salt layer on the surface of the sloped cathode wall immersed in the bath and facing a portion of the anode surface. Ta. Otherwise, the desired spacing between the cathode and anode cannot be maintained. Furthermore, the coagulated salt that adheres to the walls of the cathode is a good electrical insulator, thus suppressing current flow from the anode to the sloped cathode sidewalls. In previous uses of the inclined wall electrodes, problems with salt congealing on the sides and dimensional instability of the lining prevented widespread use of such vessels. However, with the anode compositions of the present invention and lower bath temperatures, a variety of low melting point salt compositions that do not solidify and precipitate on the sidewalls are readily available.
Ideally, the melting point of the salt and the thermal balance of the bath are adjusted such that the line of solidification of the salt is within the lining or the steel shell rather than at the lining or cathode-bath interface. The location of the coagulation line is not critical as long as the coagulation line is within the lining and the salt remains liquid on the surface of the cathode lining immersed in the bath. In such cases, a suitable cathode-anode spacing is maintained without difficulty.

Method (a) Chloride-Containing Baths The electrolysis method of the present invention for the unique continuous production of aluminum ions at the anode utilizes a closed-top electrolytic cell as shown in FIG. by closing the top or by providing suitable equipment (a) to prevent moisture from coming into contact with the chloride electrolyte;
or (b) if the oxidation of aluminum chloride is prevented;
Use any of the other vessels shown here. The advantage of the present invention of using a chloride-containing bath is not only the continuous in situ production of aluminum ions at the anode, but also the complete absence of chlorine gas leaving the bath using substantially lower energy requirements. This means that high-grade aluminum can be manufactured using aluminum.

Continuous production of aluminum ions at the anode is provided by forming the anode from an aluminum material containing aluminum oxide and a reducing agent. When aluminum chloride is present in the bath, which composition of alkali metal and/or
The anode is also immersed in a molten bath containing an alkaline earth metal halide salt. Due to electrolysis, the ionized aluminum in the bath is deposited as aluminum metal at the cathode, while the reaction at the anode produces _CO2 as well as aluminum ions. This aluminum is collected and removed as molten aluminum, but an important part of the invention is a reaction at the anode that regenerates the aluminum ions.

Chloride ions, atomic chlorine, or halogen chlorine, which is chlorine gas, can be involved in a chloride reaction with aluminum oxide and a reducing agent in the aluminum feedstock of the anode to form aluminum ions and reducing agent oxides. It is. Aluminum from the anode is ionized in the melt bath as the cycles continue, and anions, which can be chlorides, oxides, etc., balance the charge with the aluminum ions.

The aluminum produced at the cathode is generally as pure as the aluminum material forming the anode. It is possible to produce ultra-pure aluminum according to the present invention by utilizing very pure alumina sources, or aluminum ores such as boxide or aluminum-containing clays such as kaolin, or mixtures of these ores. can be used directly to produce slightly impure aluminum.

It is known that in the Hall-Heroult cell reaction, carbon at the anode contributes to the overall reaction to extract aluminum by lowering the decomposition voltage of Al ₂ O ₃ . For example, the decomposition of Al ₂ O ₃ in cryolite on a platinum anode is about 2.2 volts,
The decomposition voltage is about 1.2 volts on a carbon electrode, where about 50% by volume CO and 50% by volume _CO2 are thought to be produced. Almost the same decomposition voltage is obtained from Al ₂ O ₃ when methane is injected under the platinum anode to produce primarily CO ₂ .

In the present invention, the use of the composite anode produces a decomposition voltage lower than that obtained by decomposing AlCl ₃ by discharging Cl ₂ gas at the anode. For any electrochemical reaction, if the current-voltage curve is extrapolated to the current O, a number approximating the decomposition voltage is obtained. The aluminum chloride electrolytic method when using graphite anodes yields decomposition voltages of 1.8 to 2.0 volts, which are in agreement with values reported in the literature and theoretical values calculated from mathematical mechanics.

It was found that the decomposition voltage of the present invention varies slightly with electrolyte composition. In pure _NaAlCl4 ,
Although the decomposition voltage is minimal, the decomposition voltage tends to increase slightly as the _AlCl3 content of the electrolyte decreases.
The lowest decomposition voltage obtained was 0.5 volts and the highest decomposition voltage was 1.5 volts. The average value was 1.2 volts. Using the most common decomposition voltage average value of 1.2 volts, the decomposition voltage in the present invention is 0.6 volts lower than the decomposition voltage of _AlCl3 when releasing chlorine, and _the currently obtained value _is is close to the value of , which implies that the same overall reaction mechanism occurs in both the Hall-Heroux tank and the present invention. Compared to the classical aluminum chloride system, which discharges chlorine at the anode, it also eliminates Al ₂ O ₃ , carbon,
When considering the additional energy required to produce AlCl ₃ from chlorine and chlorine, the lower decomposition voltage described above results in considerable energy savings for the electrolytic production of aluminum.

The process conditions for the electrolytic production of aluminum have not been found to be important in terms of applied voltage or current density. The bath temperature can vary considerably;
It is simply necessary to keep the bath in a molten state;
This depends on the composition of the halide salts present.
It can be achieved within the range of 150 to 1000°C, but generally can be in the range between the melting point of aluminum and the boiling point of the bath components, preferably 10 to 400°C above the melting point of aluminum, most preferably above the melting point of aluminum. From 10 to 150℃ to below 250℃. The pressure conditions within the closed vessel are not particularly important as long as chlorine gas does not escape as in prior art aluminum chloride salt processes. Although CO or _CO2 or both can be generated from this process, this gas is not as corrosive as chlorine. Pressure conditions are not important, but
It can range from normal pressure to 0.70 Kg/cm ² (gauge) or higher.

(b) Total fluoride-containing bath In the Hall bath, alumina is cryolite at 950-1000℃.
It works chemically based on the fact that it dissolves in fluoride salt baths. Bayer alumina is at least
Soluble in cryolite-containing baths at a minimum temperature of 900°C or above. Any fluoride-containing bath below about 900° C. will not readily solubilize normally processed Bayer alumina, so the alumina as an aluminum source cannot enter into the reduction reaction or the aluminum cannot be deposited on the cathode. Without this general solubility of alumina in fluoride salt baths, electrowinning of aluminum is not possible.

As an aspect of the invention, in a fully fluoride containing bath, the temperature is in a range between the melting point of aluminum and the boiling point of the bath components, preferably 10-400°C above the melting point of aluminum, most preferably 10°C above the melting point of aluminum. It was discovered that the temperature is ~150℃ and below 250℃. For electrowinning aluminum from the corresponding oxide or other oxygen-containing compound, the bath temperature range is generally about 670-800°C, preferably 700-750°C.

An important aspect of this discovery, which distinguishes it from the normal operation of a Hall-Heroux tank, is that a composite anode containing a mixture of aluminum oxide and a reducing agent acts to transform the aluminum oxide, producing ionic aluminum in a low-temperature fluoride bath. be. However, the overall reaction is believed to be essentially the same as the Hall tank reaction, as described above. Aluminum is produced in liquid form on a liquid metal pool that acts as a cathode. The reaction occurs in a unique manner at the surface of the anode, where the aluminum oxide reacts to produce aluminum ions, similar to the mechanism that occurs in Hall baths, although at temperatures only slightly above the melting point of aluminum.

The importance of utilizing the composite anode of the present invention is that under the same conditions as the present invention, but using carbon or other non-consumable anodes and adding aluminum oxide to the bath, no dissolution of aluminum oxide or electrolytic deposition of aluminum will occur. is obvious. Using the composite anode at low temperatures of 670 to 800°C with a total fluoride electrolytic bath, it can be used in the manner shown in Figure 4 without the closed top required for operation with chloride baths as shown in Figure 1. The ability to manipulate the hole tank is a significant feature of the present invention.
Bath composition, current density, and other process parameters are not critical to the operation of chloride or fluoride bath-containing vessels.

Anode The primary support for achieving the advantages of the present invention lies in the use of a unique composite anode consisting of an oxygen-containing aluminum compound, usually aluminum oxide, and a reducing agent.

The anode provides the sole source of aluminum ions for electrolytic reduction to aluminum at the cathode, and the carbon reducing agent allows current to pass through the dielectric aluminum oxide to the aluminum oxide immersed in the electrolyte and in contact with the electrolyte. It provides a means to reach the reaction point of Preferably, the anode also provides, at least in part, the necessary source of reducing agent that allows aluminum oxide to react in the anode environment to produce aluminum, which is precipitated at the cathode as aluminum metal.

The reducing agent is preferably at least partially mixed with the aluminum oxide to provide intimate contact between the reducing agent and the aluminum oxide. If suitably chosen, the electrically conductive reducing agent, when mixed with aluminum oxide, also serves as a conductor of electrical current to the reaction sites of the aluminum oxide. For each particle of aluminum oxide reacting at a particular point that is in contact with the electrolyte and has an electric current, another particle at the same point is uncovered and can react. This pattern occurs across the surface of the anode and continues until no more aluminum oxide reacts. When the reducing agent is not electrically conductive and is not mixed with aluminum oxide, it is necessary to perform the electrical conductor function by means of a conductor rod in order to keep the aluminum oxide anodic at the reaction site.

In an aluminum chloride salt bath, the anode functions to provide a reducing agent that aids in the stoichiometric reaction of the aluminum source with 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 present invention since it eliminates the need for external replenishment of electrolyzed aluminum chloride or the need for chlorine removal at the anode.

In the all-fluoride bath method, the anode of the present invention is reacted in a fluoride bath as in the chloride cycle and the 670
Provides aluminum oxide that forms aluminum ions at uniquely low temperatures ranging from ~800°C. The tank can also be open as in FIG. 4, FIG. 5, or FIG. 7.

The aluminum source is alumina, Al ₂ O ₃ , but also boxide, or clays such as kaolin, or aluminum ions that react at the anode and are reduced to molten metal at the cathode, as in fluoride or chloride cycle processes. Other materials produced can be aluminum oxide-containing materials.

Where the mixture forms the anode, the aluminum oxide in the aluminum material ranges from at least 1.5 parts by weight per part by weight of reducing agent, with permissible upper limits of 7.5, 20.0, or 50.0 parts by weight or more. It is a percentage. Preferably, for purposes of the present invention, the amount of aluminum oxide in the mixture of aluminum material is between 2.0 and 1 part by weight of reducing agent.
6.5 parts by weight, most preferably 2.5 to 6.0 parts by weight.

Reducing agents that can be used in accordance with the present invention are not limited to particular materials, but can be materials known to be effective in reacting with aluminum oxide. The reactions in the fluoride and chloride baths have not been clarified, but the reducing agent reacts with Al ₂ O ₃ and eventually forms CO ₂ at the anode with aluminum ions precipitated at the cathode.
It can be a reaction that produces The reaction mechanism can be the same for all chloride, all fluoride, or mixed chloride/fluoride salt electrolytes.

Particularly useful reducing agents for alumina and other oxides include carbon or reducing carbon compounds used in the mixture. Sulfur, phosphorus, or arsenic can also be used independently or in combination with carbon. Carbon is particularly preferred because of its two properties: the ability to carry current to the reaction sites of the aluminum oxide, and the ability to maintain a reducing function and provide a gaseous product at the anode.

The carbon source in the mixture can be any organic substance, in particular those with fossil sources, such as tar, pitch, coal, coal products, reducing gases such as carbon monoxide, and also natural and synthetic resinous substances such as wax, rubber,
Phenolic resins, epoxy resins, vinyl resins, etc. may also be included, which can be coked even in the presence of aluminum material if desired. Coking of the carbon source mixed with the aluminum oxide compound can be accomplished by methods known in the art, such as those used in pre-calcined anodes utilized in Hall-Heroux tanks. A composite anode such as an Al ₂ O ₃ pitch in the desired ratio, e.g. 6.5 parts aluminum oxide to 1 part carbon, is poured under coking conditions, molded and extruded, and the formed anode is heated to 700°C to 700°C in a non-oxidizing atmosphere.
The coking is accomplished by gradual heating to a coking temperature of 1200°C. After coking, the composite anode is ready for use.

It is also contemplated within the scope of this invention to produce carbon as a reducing agent in a mixture with aluminum oxide, for example, by coking the carbon source in a molten electrolytic bath before and during electrolysis.
Bath temperatures typically in the range of 670-850°C are suitable for coking the carbon source to the required carbon. The time to achieve this coking is not critical, but may require minutes to hours depending on the temperature of the melt bath and the mass of the mixture of aluminum source and reduced carbon source.

Using the mounting clamp shown in Figure 4, attach the
Continuous coking is possible by introducing several anodes, lowering the anode successively as depletion occurs until the anode is completely consumed, and placing the next anode in the same location. As in the case of traditional Soederberg electrodes, the anode can be delivered continuously to the bath in the green state. In this case, traditionally a steel pin is used to make the contact, but this contact can be made using graphite, carbon, _TiB2 ,
It can also be aluminum or a composite thereof. The raw composite anode material is gradually coked by the heat of the bath, such that the end of the anode in the salt is always fully coked for the operating temperature of the bath.
Soederberg coking in a bath at 627°C to 850°C produces an anode with lower conductivity than composite anodes prefired at higher temperatures.

As previously mentioned, the entire reducing agent source does not need to be mixed with the aluminum oxide to form the anode when desired. For example, it has been found that the only requirement for the reducing agent is that it be in contact with the anodized aluminum and present in a sufficient amount to produce aluminum metal at the cathode. However, it is clear that in order for the reaction to proceed, a current must be transmitted to the reaction point.

It is contemplated that when a reducing agent such as carbon is not mixed to carry the current, another conductor compatible with the vessel and its contents may be used. For example, a combination of aluminum or a noble metal and a refractory conductive oxide such as silver-tin oxide or _TiB2 , alone or in combination with carbon or graphite, in an amount sufficient to carry a current to the point of reaction. Can be mixed with aluminum oxide. The amount is not critical as long as the aluminum oxide is made anodic at the reaction site. from as little as about 0.001 part of conductive material per part of aluminum oxide to at least about
Amounts up to 0.75 parts may be used. Larger amounts increase conductivity at the expense of reactive material availability, but there can be no practical upper limit. Of course, it is still necessary to have a reducing agent present in order to achieve the necessary reaction.

In the case of alumina as the aluminum material, hydrated or calcined alumina can be used. Although anodes made from hydrated alumina can exhibit improved conductivity compared to calcined alumina, hydrated alumina
Al ₂ O ₃ ×3H ₂ O or Al(OH) ₃ tends to crack during precalcined coking and when placed in a hot bath by the water displaced during the coking operation. For aluminum chloride-containing salts that utilize bath coking of hydrated alumina, expelled water is undesirable.
Can hydrolyze AlCl ₃ .

When a membrane such as that shown in FIG. 5 surrounds the anode, cracking or fracturing of the anode due to expelled moisture is not difficult. Falling anode particles are contained within the membrane for subsequent reaction. To minimize cracking, the anode can also have a proportion of hydrated and calcined oxides. The maximum amount of hydrated oxide that can be used affects energy savings in calcination.

The size and surface area of the particles making up the aluminum oxide-containing anode were not sensitive to the anodic reaction rate. This feature of the present invention is in contrast to prior art experience with the reaction of Al ₂ O ₃ and carbon with chlorine as a gas-solid reaction in a furnace. In the past, reaction temperatures and rates were found to be extremely sensitive to particle size and particle surface area.

In the conventional technology, ₁₀ to 125
It is generally desirable to use alumina with a surface area in the range of m ² /g. However, in the present invention, no sensitivity was detected with respect to the reaction rate of the anode based on particle size or surface area. i.e. 0.5
Al ₂ O ₃ with a surface area of m ² /g or less
It reacted as easily as Al ₂ O ₃ with a surface area of 100 m ² /g. These results are based on experiments with alumina-containing anodes with particles with different surface areas and dimensions. A tank with an exhaust line connected to a starch-iodine indicator for chlorine detection.
Anodic current densities ranging from 2 to 40 amps per square inch (~6.20 amps per square inch) were used. No chlorine was detected regardless of current density or alumina surface area. This means that even though chlorine is produced at the anode, all of the chlorine reacts to regenerate aluminum chloride, or from Al ₂ O ₃ only aluminum ions are produced at the anode, while oxygen from Al ₂ O ₃ is converted to carbon It is implied that it combines with CO2 to produce _CO2 . In order to generate chlorine at the anode, it is thought that it is necessary to raise the potential high enough to overcome the decomposition potential of AlCl ₃ , but even then, the generated chlorine is probably more Al ₂ O than the chlorine generated at the anode. ₃ and will react with carbon to further produce _AlCl3 .

The anodes used in electrolytic cells can be manufactured in various forms and by various manufacturing methods. A mixture of aluminum oxide material and reducing agent is formed into an anode by conventional means. For example, as shown in FIG. 2, the mixture is bonded to a representative electrode to form a coating that surrounds all or one side of the electrode. It is also contemplated that the anode material may be formed into a suitable shape and one end of an electrode rod or pin may be coupled thereto in the manner shown in FIG. 3 to form the anode. Forming the anode in other ways with direct physical bonding to the electrode may also meet the requirements of the present invention. However, it is desirable that the aluminum material be in intimate physical contact with the carbonaceous material or other reducing agent. The latter concept is
If the mixture of aluminum material and reducing agent is in the form of a homogeneous mixture of powder, it may be
Small pellets of the mixed powder or large composite briquettes of the mixed material can be formed into various sizes of 0.025 to 25.4 mm (0.001 to 1 inch) or larger. It has been found that during reactions under dissolution or electrolysis, a uniform distribution of carbon and aluminum oxide is desirable for maximum anodic efficiency.

In order to keep the aluminum material forming the anode material and the reducing agent in the area of the electrode and thus the anode in combination, a porous membrane type container can be utilized.

For satisfactory commercial use, the anode must be as conductive as possible. Since the anode of the present invention is not solid or pure carbon as is commonly used in Hall tanks, it is less conductive due to the presence of the aluminum compound. If the anode is allowed to become as resistive as the salt electrolyte, the thermal balance can be affected by overheating that can occur as a result of passing the same current through a more resistive anode. For example, when using a solid composite anode such as that shown in Figure 3 in the bath of Figure 1, current is required to flow through the anode from top to bottom, and power losses translate into heating of the bath. .
It is therefore desirable to construct the anode to have as high a conductivity as possible. Obviously, the more conductive the anode material, the lower the power consumption for metal extraction, but in any case for optimal operation the conductivity of the anode should be greater than that of the salt. Anode resistance is important, especially when it is desired to achieve maximum aluminum production objectives using minimum power.

It has been found that the conductivity of the anode varies considerably depending on the manufacturing method. Parameters that have been found to influence conductivity are the ratio of binder carbon material, such as pitch, carbon, or coke particles, and the type of aluminum oxide included in the composite anode as the reducing agent source. Within the above defined ratio of aluminum oxide to reducing agent, the greater the carbon content of the anode, the greater the electrical conductivity. For example, from 4/1
Using an aluminum oxide to carbon ratio of 6/1, it is possible to create a solid composite anode having at least 1/10 the conductivity of a standard Hall-Hellou anode.

In order to reduce the power loss through the composite anode,
Some alternatives are also shown in Figures 2, 2A, 2B, and 4A.

In order to achieve higher conductivity and reduce power loss through the pre-fired composite anode, another embodiment may include one or more of the pre-fired composite anodes placed within the anode as shown in Figures 2, 2A and 2B. Either the conductive cores 36 or 37 described above may be used, or a number of vertically arranged conductor pins 39 may be used as shown in FIG. 4A.

The composite anode 26A shown in FIG. 2 is a composite anode formed or coated in the shape of a preformed conductive core or a conductive central core which can be carbon or graphite molded into a composite anode material composition 38. 3
6. This central core 36 can also be the same metal as that to be deposited, such as aluminum. The outside of the conductor 36 is provided with a matrix 38 of composite anode material consisting of a mixture of aluminum oxide and a reducing agent as described above.
For depolarization, one side is coated, or for unipolar use, both sides are coated. When coating one side, a depolarization operation is planned. It is to be understood that the term "oxide" includes silicates or other oxygen-containing compounds of precipitated aluminum, which are often a combination of the metal oxide and silicon oxide.

For large size anodes, alternative embodiments are shown in FIGS. 2A and 2B. To improve electrical conductivity, it is preferred to use first grade aluminum rods 36 and 37 as electrically conductive busbars and within a matrix 38 of a composite anode composition, which can be precalcined or of the Soederberg type. Since first grade aluminum is used to form the conductor bars, this aluminum melts as the anode is consumed and bonds with the cathode metal for continuous cycles. The bars are spaced such that the voltage drop is minimal relative to the conductivity of the composite anode. In FIG. 2B, the conductor bar 36 is connected to the center conductor 4.
It is shown connected to a plate 40 supported by 1.

The number of conductors 36 and 37 is determined based on the anode dimensions, anode current density, bath dimensions, operating temperature, and heat transfer so that the aluminum conductors 36 and 37 melt at the same rate as the anode matrix 38 is consumed. and choose the dimensions. A unique advantage of the anode embodiment shown in FIGS. 2A and 2B is that large voltage drops are avoided at the relatively high resistance anode, allowing the process to operate there with substantially reduced power consumption.
The dimensions of this aluminum rod are 1.59~76.2mm
(0.0625 to 3.0 inches), preferably 3.18 to 50.8 mm (0.125 to 2.0 inches), most preferably 6.35 to 25.4 mm (0.25 to 1.0 inches).

In order to achieve the desired electrical conductivity in the anode, the spacing between the outer surface of the composite anode 38 and the surface of the aluminum rods as in FIGS. 2, 2A, or 2B and the aluminum bars in FIGS. The mutual spacing between the outer surfaces of the bars is not critical and ranges from 3.18 to 609.6 mm (0.125 to 24 inches),
Preferably it can be 1.0 to 6.0 inches, most preferably 1.5 to 4.0 inches. As an example, when the conductivity of the composite anode is approximately 0.1 of a standard pre-fired Hall bath anode, an aluminum bar spacing of about 3.0 inches produces an acceptable voltage drop.

Since the operating temperature of the cell is typically in the range of 700-750°C, the size of the aluminum rod is such that it melts at approximately the same rate as the anode is consumed and thus transfers power to the bottom of the anode. You can decide. If the diameter of the aluminum rod is too large, the aluminum will not melt and salt will solidify on its surface, resulting in an anode that wears out leaving an aluminum stub that shorts to the cathode as the anode is advanced. If the diameter of the rod is too small, the aluminum rod will melt far inside the anode.
back), resulting in too large a pressure drop due to the long conductivity path. It is desirable that the aluminum rod melt back into the anode to a lesser extent than remain flush with the bottom surface of the anode. This will minimize anodization of the aluminum rod. The desired meltback distance is the distance that provides the minimum voltage drop combined with the minimum anodization of the aluminum bar. If the rod remains flush with the bottom surface of the anode, aluminum ions tend to pass from the rod (as in purification operations) and from the composite anode material into the bath, where they reduce the faradic efficiency of the bath. The conductance from the bath to the anode and the power generated through the conductor can be balanced to balance the heat to obtain the desired amount of melting of the conductive aluminum rod.

FIG. 3 shows another embodiment of the anode composition, designated 26B. In this specific example, electrode 26
B consists of a composite 38 which can be identical to the coating 38 of FIG. 2, but shaped into a suitable shape for use as an electrode. This electrode form is
It can be molded around a stub or pin electrode 42 that projects out from the top end of the body of electrode 26B for connection to a conventional electrical circuit. or electrode 26B
is formed and then the stub 42 is inserted by methods known in the art, such as those used in pre-fired Hall tank anodes.

Another embodiment is shown in FIG. 4A, in which an anode 26B is shown having the same composition as previously described, but with a plurality of pairs of vertically disposed conductor pins 39, Connect the bus bar 39A to a pair of pins.
are directly connected like a Soederberg type connection. The placement of pin 39 is not critical and can be perpendicular to the anode axis or at an angle as shown. Once the composite anode material is consumed, the busbar connection 39
A is moved up to the next higher pair of pins.
Pins made of primary grade aluminum are also consumed and added to the pool of deposited aluminum as described above. On the other hand, the pin can be made of iron, as typically used in Soederberg connections, and is removed when the anode is consumed.

The embodiments of FIGS. 12 and 13 illustrate modifications that transfer electrical energy to the working surface of the anode. As shown, the block 94 of the composite anode (A) is laminated with sheets 108 of aluminum metal. These sheets work in exactly the same way as the aluminum bars of Figures 2A and 2B. The shape and number of layers are not critical. This block is present in continuous form and can be fed into the tank by means of a clamp 47, as shown in FIG.
Electrical connections are also made.

The number, spacing, and thickness of aluminum sheets 108 are determined by the same factors described for conductors 36 and 37. Generally the thickness of aluminum sheet is 0.025-12.7mm (0.001-0.5 inch), preferably 0.25-9.53mm (0.010-0.375 inch), most preferably 0.25-6.35mm (0.010-0.25 inch)
inches). This aluminum sheet must be thick enough to carry the necessary current to avoid large voltage drops, and to melt into the cathode pool when the anode is consumed. The spacing between the aluminum sheets 108 is the same as that between the conductors 36 and 3.
7, the spacing is such as to avoid excessive voltage drops across the composite block. Generally, this spacing is 3.18 to 609.6 mm (0.125 to 24.0 inches),
Preferably it ranges from 1.0 to 6.0 inches, most preferably from 1.5 to 4.0 inches.

Membranes Membranes such as the one shown in Figure 5 are designed to have three functions.

First, the membrane acts as a separator or static barrier between the molten cathode metal phase and the source of the electrolyzed anode material. By using the membrane of the invention, the spacing can be substantially reduced and significant increases in conductivity and efficiency can be achieved without turbulence effects that can result in a reduction in efficiency or the quality of the aluminum product.

Second, in the present invention, the membrane physically constrains the material of the composite anode, which can include, for example, an aluminum raw material and a reducing agent. This restraint keeps the material close to the electrode to form an anode that produces aluminum ions in the most efficient manner. This membrane also prevents the feedstock from mixing with the molten aluminum at the bottom of the tank. When a hydrated metal oxide, such as hydrated alumina, is used as one of the anode materials, the membrane retains the anode pieces which may crack and fall off due to the evolution of moisture from the alumina during coking of the bath. As long as these pieces remain in the anode circuit within the membrane, they continue to serve as a source of aluminum through a reduction reaction.

Third, the membrane freely passes ionic substances and dissolved solids in the electrolyte, but substantially excludes undissolved solid substances that constitute the usual impurities present in molten aluminum and aluminum sources; Prevent contamination of cathodic deposition.

The external shape of the membrane is not critical; it can be cylindrical, prismatic, etc. in whole or in part. For example, the membrane can have a three- or four-sided shape with a bottom, where it can form a closed container. This vessel is designed to hold the anode raw material for reaction in the salt bath.

Due to the corrosive nature of molten salt baths, the selection of materials forming the membrane is critical to bath life and process success. When the electrolyte used is an all-chloride bath, the choice of membranes is somewhat wider due to the reduced corrosivity of the bath compared to baths containing fluoride. However, baths containing some fluoride are preferred due to their low volatility. Full fluoride baths have other advantages as mentioned above. Materials suitable for use in fluoride baths are of course also useful in less corrosive chloride baths.

Materials that have been found to be useful include vitreous carbon foam as a porous solid.
foam), carbon, or graphite, or porous solids of refractory hard metals such as boron, aluminum,
Silicon (including oxynitrides), titanium, hafnium, zirconium, tantalum nitrides, molybdenum, tantalum, tungsten silicides, hafnium, tantalum, niobium, zirconium, titanium, silicon, boron, tungsten carbides, hafnium, tantalum , zirconium, niobium, titanium, and silicon borides. Other refractory hard metals known in the art may also be useful in forming the film if they are resistant to the molten salt bath.

The refractory hard metal forming the membrane of the present invention can be made in the form of cloth, mat, felt, foam, porous sintered solid base, or simply a coating on said base, all of which serve other purposes. is known in the art for. The membrane must also pass certain standards for passage porosity and communicating pore size.

These two properties can be defined as follows.

Passage Porosity - The percentage of the total volume of a membrane that constitutes passageways from one side of the membrane to the other.

Connecting pore diameter - the smallest diameter of a passageway in a membrane.

Passage porosity varies with the nature of the membrane material, temperature of the melt bath, and salt composition, but the common properties of useful membranes are that they pass all of the metal ions, such as aluminum, and all of the electrolyte salts, without passing undissolved impurities. The porosity must be sufficient to allow the passage of.
It was found that the greater the porosity, the greater the current flow and therefore the electrical efficiency of the cell.
Porosity can vary from 1 to 97% or more, but generally ranges from 30 to 70%. The preferred porosity to achieve maximum efficiency is in the range of 90-97%. For example, vitreous carbon foam can produce such high porosity and retain sufficient mechanical strength.

The communicating pore size must be small enough to exclude undissolved solid impurities, but large enough to pass ionic and dissolved particles.
Generally, acceptable pore sizes are between 1 micron and 1 cm.

The thickness of the membrane material is a function of its porosity, pore size, and ability to retain undissolved impure solids and molten metal. Obviously, the thicker the film, the greater the electrical resistance. Therefore, it is desirable to use a membrane that is thin enough to practically meet standards for porosity and pore size and the mechanical strength of the membrane placed in the bath. Preferred thickness is 3.18
~12.7mm (0.125~0.5 inch) but 50.8mm
(2.0 inches) or thicker.

Typical membrane materials found to be useful are vitreous carbon foam, carbon, or graphite in the form of porous solids, felts, or cloths, or on the surface of vitreous carbon foams or porous graphite. including, but not limited to, aluminum nitride, silicon nitride, silicon carbide, silicon oxynitride, boron nitride, titanium nitride as a coating. Aluminum nitride appears to be the most desirable material. First, create a porous alumina structure,
It is then impregnated with carbon and then under a nitrogen atmosphere.
It was found that aluminum nitride can be conveniently formed into porous structures by heating to 1750°C to convert the alumina to aluminum nitride. Such operations create a corrosive salt environment and a porous structure that is chemically compatible with molten aluminum.

Molten Bath Composition The electrolytic baths of the present invention can vary considerably compared to typical Hall bath salt compositions. In the present invention, the bath composition can include any halide salt, with chlorides and fluorides being particularly preferred. Alkali metals or alkaline earth metals, such as sodium, potassium, lithium, calcium, magnesium, barium, among others, can be used for halide salt formation. There is no critical composition or desired or necessary range of proportions. It has been found that in order to produce aluminum electrolytically using the composite anode, there is no need for an aluminum salt to be present in the electrolyte at the outset. For example, a salt electrolyte containing only alkali and/or alkaline earth halides uses the composite anode to produce aluminum metal at the cathode without an "anodic effect."

Although not required for the practice of this invention, it is generally preferred that the salt bath initially contain aluminum halide. Can contain only chloride anions or both chloride and fluoride ions
In the case of _AlCl3- containing baths, the aluminum chloride concentration can be between 2 and 60% by weight _AlCl3 , but can also range from 1 to 95% by weight. The all-fluoride bath can contain the same fluoride salts described above, but can also contain aluminum fluoride in any desired proportions.

Among the advantages and disadvantages of the various electrolyte types, all chloride baths have very low tolerance to oxide contamination, but have significantly higher electrical conductivity and are the least corrosive to refractories and bath structures. In fluoride-containing electrolytes, aluminum precipitates as droplets that aggregate and easily accumulate, but the corrosivity of the electrolyte to refractories and bath components increases significantly.

The lithium component of the electrolyte increases conductivity, but is expensive and adds to the cost of the electrolyte. The cost of the electrolyte, the conductivity of the electrolyte, and the power consumption of the resulting aluminum production must be balanced in operation.

Preferred electrolytes balance economy of salt components, electrical conductivity, corrosiveness to refractories and bath components, tolerance to oxide contamination, and agglomeration of precipitated aluminum into a pool for easy harvesting.

Example 1 In FIG. 1, the anode is a graphite plate and the cathode is a titanium diboride plate. The anode was created with a coating 38 as shown in FIG. The coating consisted of Bayer-refined Al ₂ O ₃ calcined at 1000° C. mixed in a weight ratio of 5 parts Al ₂ O ₃ to 1 part carbon in the coking stage. This Al ₂ O ₃
The above carbon was obtained by mixing and gradually heating the phenolic resin to 1000° C. in an inert atmosphere to coke the phenolic resin into carbon. The electrode coating was created by mixing the Al ₂ O ₃ with the phenolic resin, troweling or otherwise applying the mixture to the electrode, and heating to coking temperature.

The electrolyte consisted of an equimolar mixture of aluminum and sodium chloride forming the double salt NaAlCl ₄ at about 150°C. The temperature of the tank was raised to 700°C, and Al ₂ O ₃ electrolysis was performed for several hours to obtain a molten aluminum layer at the bottom of the tank. Inspection of the anode revealed that the coating had dissolved and aluminum had deposited on the cathode. This aluminum precipitation was equal to the aluminum content of the Al ₂ O ₃ dissolved at the anode. The total activity-limited reaction is considered to be a reaction in which Al ₂ O ₃ is ionized at the anode and carbon reacts to mainly produce CO ₂ . There was no evidence of chlorine gas being liberated in the anode or outlet tube during electrolysis. Analysis of the exhaust gas revealed that it was mainly CO ₂ .

Example 2 Electrolyte composition is NaCl 63%, LiCl 17%, LiF 10%,
A second electrode coating is made from standard bauxite Al ₂ O ₃ consisting of 10% AlCl ₃ and coked to yield an Al ₂ O ₃ to carbon (when coked) ratio of 5.7:1 and petroleum tar pitch. Ivy. Electrolysis was carried out at 750°C in the first tank. The spacing between the anode and cathode is 12.7 mm (1/2 inch),
This is 2.32 amps/cm ² at an applied voltage of 2.5 volts.
(15 amps per square inch). No chlorine gas liberated from the anode was detected. Aluminum was precipitated. The extracted aluminum was produced with an energy consumption of 8.09 kwh/Kg (3.67 kwh/lb) and a faradaic efficiency of 92%.

Example 3 Electrolyte salt composition was NaCl 10%, CaCl ₂ 50%,
It consisted of 20% CaF ₂ and 20% AlCl ₃ .

The electrode coating of Figure 2 was made as in Example 2, but on only one side of the electrode.
Electrical connections were made such that the anode adjacent the outlet tube was connected to the positive terminal and the negative terminal was connected to the electrode furthest from the outlet tube. The coated sides of electrodes 25 and 26 each faced the cathode without facing the outlet tube. Cathode 24 was uncoated. This results in electrode 25 not being physically connected to the DC power supply. This electrode becomes depolarized. The side coated with the Al ₂ O ₃ --C mixture is then positively charged. The side of the depolarizing electrode 25 closest to the exit tube becomes negatively charged and aluminum is deposited on it and sinks into the molten pool. Aluminum is negatively charged electrode 2
4 also precipitates and sinks into the molten pool. The tank operating temperature is
At 800°C, the applied voltage was 3 volts to each electrode,
There was a total of 6 volts across the terminals. Electrode spacing 3/
At 4 inches, this applied voltage is 1.86 amperes/cm ² (12
This resulted in an electrode current density of amps per square inch).

Example 4 The anode consisted of a titanium diboride rod and the cathode was also titanium diboride. The anode was coated with bauxite calcined at 600°C, mixed with phenolic resin and coked at 800°C as shown in Figure 2. The ratio of aluminum oxide to carbon in the bauxite after coking was 6:1. The electrolyte salt composition is
20% NaCl, 30% CaCl ₂ , 10% CaF ₂ , 36% AlCl ₃ and operated at 750° C. and a current density of 15 amps/in 2 . This produced 4 volts with approximately 3/4 inch electrode spacing. No chlorine gas was detected. The composition of the aluminum deposited in the molten pool is 97% pure, with 0.5% Si, 1.5% Fe,
Contained 0.9% Ti, and small amounts of other components.

Example 5 The vessel of Figure 5 utilized a porous membrane of aluminum nitride material having a porosity of 50%, a pore size ranging from 12 to 24 microns, and a thickness of 4.76 mm (3/16 inch). An alumina porous body was impregnated with carbon and heated to 1750° C. in a nitrogen atmosphere to obtain the aluminum nitride. The anode conductor was a graphite rod and the anode aluminum material was a 6:1 Bayer Al ₂ O ₃ and carbon powder mix. Electrolyte salt composition is NaCl20%, LiCl25%,
LiF was 30%, AlCl ₃ was 25%, and electrolysis was carried out at 720°C. The distance between the membrane and the aluminum pool is approximately 12.7mm
(1/2 inch) and an anodic current density of 1.55 amps/cm ² (10 amps/in 2 ). This produced a voltage of 2.8 volts. Aluminum was produced with 92% efficiency and had a purity of 99.5%.

Example 6 NaF12%, LiF25%, NaCl28%, LiCl15%,
A salt composition consisting of 10% AlF ₃ and 10% AlCl ₃ was melted in a vessel with vertical side walls. A 50.8 mm (2 inch) thick aluminum pad was melted on the bottom of the vessel and the operating temperature was adjusted to 700°C. Using an anode as shown in Figure 2A, the spacing between the bottom of the anode and the aluminum pad was set to 44.5 mm (13/4 inch). At an anodic current density of 0.93 amps/cm ² (6 amps/in 2 ), the bath potential was 3.5 volts.

After 8 hours of electrolysis, the anode was removed from the cell and placed in a cell with 45 degree side walls as shown in FIG. After several hours of electrolysis, the anode side surface eroded to become parallel to the cathode side wall. The anode immersion depth in the salt was 76.2 mm (3 inches). The same total current was used as for the vertical sidewalls, and the potential was 2.45 volts. This reduced potential due to side anodic corrosion at 90% current efficiency and constant production rate reduces power consumption to 11.57kwh/Kg
(5.25kwh/lb) to 8.11kwh/Kg
(3.68kwh/lb), which is
This is a decrease of 3.46kwh/Kg (157kwh/lb).

Example 7 NaCl20%, LiCl25%, LiF25%, NaF10%,
A salt composition consisting of 10% AlF ₃ and 10% AlCl ₃ was melted in a vessel with vertical side walls. A 50.8 mm (2 inch) thick aluminum pad is melted on the bottom of the tank,
The operating temperature was adjusted to 700°C. Using a 12 inch long composite anode 12 with a copper busbar attached to one end in the customary manner, the anode-cathode spacing was
Adjusted to 44.5mm (13/4 inch). At an anodic current density of 0.93 amps/cm ² (6 amps/in 2 ), the bath potential after reaching equilibrium was 5.75 volts.

An identical anode, but with a 45 degree slope at the opposite end of the bus bar, was inserted into a vessel with 45 degree side walls as shown in FIG. The immersion depth of the anode in the salt is 76.2
mm (3 inches). After several hours of electrolysis to ensure that the angle of the anode was the same as the side wall of the cell, the potential required to achieve the same total current as used on the vertical side wall was 4.4 volts. At 90% current efficiency and a constant production rate between the two types of baths, this reduced potential due to side anode corrosion reduces power consumption from 19.03 kwh/Kg (8.63 kwh/lb)
reduced to 14.55kwh/Kg (6.6kwh/lb), which is a reduction of 4.48kwh/Kg (2.03kwh/lb).

The reduction in power consumption at constant current used in a tilted cathode cell compared to that used in a conventional cell which erodes only the bottom of the anode is evident from this example.

Example 8 An anode was made using Alcoa A-1 Al ₂ O ₃ which had been mixed with coal tar pitch and phenolic resin, molded in a closed die, and heated to harden the phenolic resin component. After coking, the composite anode contained 17% carbon and 83% Al ₂ O ₃ . Electrolyte is NaCl20%, LiCl25%, LiF30
%, NaF25%, and operated at 700°C. A bath such as that shown in Figure 7 was used, but no aluminum pads were added. After electrolysis at approximately 700℃ for several hours,
Aluminum collects in the wells, indicating that the composite anode can produce aluminum electrolytically without first using an aluminum salt in the electrolyte.

Example 9 A vertical side tank as shown in Fig. 5 was used.
Membrane 68 and anode rod 52 were missing. Instead, a carbon cylinder was placed just above the salt electrolyte layer and a short anode section, as shown in Figure 2A, was inserted into it. Al ₂ O ₃ , petroleum coke powder,
A mixture of tar and pitchch mixture was added. 740
Carbon 18% when coked at salt electrolyte temperature of °C
and Al ₂ O ₃ , coke powder, which yields 82% Al ₂ O ₃ .
It was a tar/pitch mixture. NaF10%,
LiF25%, NaCl20%, LiCl15%, _AlF3 20%,
A salt electrolyte consisting of 10% AlCl ₃ was used. Electrical connections were made by clips to conductor rods 37 in the cold area above the level of the Soederberg anode composition in the carbon cylinder. Spacing between aluminum pool and anode
1.55 amps/cm ² at 31.75 mm (11/4 inch)
Electrolysis was carried out at an anodic current density of (10 amps/in²). Al ₂ O ₃ -carbon-tar/pitch was added to the carbon cylinder, and an anode was continuously supplied to continue electrolysis. The anode hardened and coked when it entered the salt electrolyte. Once the anode is consumed, the aluminum conductor rod melts and forms an aluminum cathode pool 32.
combined with.

Using a rectangular prefired block of carbon and an aluminum sheet as shown in Figure 13,
A similar experiment was conducted. The aluminum sheet was 1.52 mm (0.060 inch) thick and the prefired block was 50.8 mm (2.0 inch) thick. Electrical connections were made to each aluminum sheet using a roller. As the anode progressed, additional prefire blocks were inserted between the aluminum sheets.

Next, embodiments of the present invention will be described.

(1) the anode is in contact with an oxygen-containing compound of aluminum in an amount sufficient to provide aluminum during electrolysis and to react at the anode and subsequently form aluminum metal at the cathode; a reducing agent present in a sufficient amount such that the weight ratio of the oxygen-containing compound to the reducing agent, expressed as Al ₂ O ₃ , is at least about 1.5; From the deposition cathode to the electrode used in the electrolytic bath for electrolytic deposition of aluminum.

(2) the electrolyte contains ions selected from the group consisting of chlorides, fluorides, or mixtures thereof, and the compound is capable of reacting at the anode to produce aluminum ions that are reduced to metal at the cathode;
An electrolytic cell for aluminum electrolytic deposition, comprising the electrode described in item (1) above.

(3) The electrolytic cell according to item (2) above, wherein the temperature of the electrolytic solution is between the melting point of aluminum and the boiling point of the liquid in the cell.

(4) The temperature of the electrolyte is about 10 to above the melting point of the metal.
The electrolytic cell according to item (1) above, which has a temperature of 150°C.

(5) The reducing agent is selected from the group consisting of carbon-containing compounds or elements, sulfur, phosphorus, and arsenic.
The invention described in paragraph (1), (2), (3) or (4).

(6) The invention according to the above item (1), (2), (3), or (4), wherein the reducing agent before coking is selected from the group consisting of organic substances that generate carbon upon coking.

(7) or (1), (2), or (3) above, wherein the aluminum oxygen compound is intermixed with the reducing agent in an amount of at least 1.5 parts by weight of Al ₂ O ₃ per 1 part by weight of the reducing agent.
The invention described in (4).

(8) Paragraph (1), (3) or (4) above, wherein said electrolyte is formed substantially entirely of fluoride salts, and said compound is capable of reacting at the anode to produce aluminum ions which are reduced to metal at the cathode. The invention described in Section 1.

(9) the electrolyte is substantially all fluoride salts, the compound contains aluminum and can react at the anode to produce aluminum ions that are reduced to aluminum metal at the cathode, and the temperature of the electrolyte is approximately
The invention according to item (1), (3) or (4) above, wherein the temperature is 700 to 800°C.

(10) The above item (9), wherein the reducing agent is selected from the group consisting of carbon and carbon-containing compounds, and the oxygen-containing compound of the metal is selected from the group consisting of alumina, bauxite, clay, and the metal-containing oxide. invention of.

(11) An electrolytic cell for electrolytic deposition of aluminum, comprising an electrode according to paragraph (1) above, wherein the membrane is placed in contact with the compound to substantially prevent insoluble solids from passing through the membrane.

(12) The electrolytic cell according to item (11) above, wherein the membrane contains the compound and forms an anode.

(13) The film may contain glassy carbon foam, graphite or carbon solids, boron, aluminum, silicon (including oxynitrides), titanium, hafnium,
nitrides of zirconium and tantalum; silicides of molybdenum, tantalum, and tungsten; carbides of hafnium, tantalum, niobium, zirconium, titanium, silicon, boron, and tungsten; carbides of hafnium, tantalum, zirconium, niobium, titanium, and silicon formed of a material selected from the group consisting of borides, which material passes all liquid substances other than molten aluminum in the electrolyte bath, including ionic substances and dissolved solids, and substantially frees undissolved solids constituting impurities. said (11) material having a through porosity sufficient to exclude the upper and lower parts thereof, thereby creating a current flow, and having communicating pores of sufficient small diameter to occlude undissolved particles. ) or the electrolytic cell described in (12).

(14) The above-mentioned item (13), wherein the passage porosity is about 1 to 97% and the communicating pore diameter is 1 micron to 1 cm.
Electrolytic cell described in section.

(15) The electrolytic cell according to the above item (11), wherein the membrane is porous and is arranged in the electrolytic solution so as to contain the compound for reacting as an anode and the reducing agent.

(16) The electrolytic cell according to the above item (15), which includes a supply device disposed on the tank for continuously replenishing the compound and the reducing agent into the membrane.

(17) The invention according to item (7) above, wherein the anode is formed from a central conductive core and has a coating of the aluminum compound on the core.

(18) The invention according to item (1) or (3) above, wherein the anode has a plurality of pairs of vertically arranged conductor pins for connection to an electric bus bar.

(19) Items (13), (14), and (15) above, wherein the electrolyte is formed substantially entirely of fluoride salts, and the compound is capable of reacting at the anode to produce aluminum ions that are reduced to aluminum at the cathode. Or the electrolytic cell described in (16).

(20) The electrolytic cell according to paragraph (2), (3) or (4) above, wherein the cell has a lid for sealing the top of the cell to prevent loss of gas and hydrolysis of the electrolyte.

(21) The distance between the anode and cathode is approximately 25.4 mm (1 inch)
The electrolytic cell according to the following item (2), (3) or (4) above.

(22) The distance between anode and cathode is approximately 12.7 mm (0.5 inch)
The electrolytic cell according to the above item (21), which is as follows.

(23) Item (1) above, wherein the anode is comprised of at least one internally disposed conductive material surrounded by an anode material containing an aluminum compound;
The invention described in paragraph (2), (3) or (4).

(24) the anode is surrounded by at least one internally disposed conductive material containing an aluminum compound and in contact with the aluminum compound to substantially prevent undissolved solids from passing through the membrane; Consists of arranged membranes,
The electrolyte is substantially all fluoride salts, the compound contains aluminum and can react at the anode to produce aluminum ions that are reduced to aluminum metal at the cathode, and the temperature of the electrolyte is approximately
The electrolytic cell according to item (2), (3) or (4) above, which has a temperature of 700 to 800°C.

(25) The electrolytic cell according to the above item (24), wherein the membrane contains a mixture of the aluminum compound and the reducing agent and forms an anode.

(26) The film may contain glassy carbon foam, graphite or carbon solids, boron, aluminum, silicon (including oxynitrides), titanium, hafnium,
nitrides of zirconium and tantalum; silicides of molybdenum, tantalum, and tungsten; carbides of hafnium, tantalum, niobium, zirconium, titanium, silicon, boron, and tungsten; carbides of hafnium, tantalum, zirconium, niobium, titanium, and silicon formed from a material selected from the group consisting of borides, which material contains ionic substances and dissolved solids, which pass through all liquid substances other than molten aluminum in the electrolyte bath and which constitute impurities; said material having a through-porosity sufficient to substantially exclude solids, thereby creating a current flow, and said material having communicating pore sizes of a sufficiently small diameter to occlude undissolved particles; The electrolytic cell described in paragraph (25).

(27) The electrolytic cell according to item (26), wherein the passage porosity is about 1 to 97% and the communicating pore diameter is about 1 micron to 1 cm.

(28) said first cell comprising a porous membrane disposed in said electrolyte to contain a mixture of said aluminum compound and said reducing agent to react as an anode;
Electrolytic cell described in paragraph (2), (3) or (4).

(29) The invention according to the above item (9), wherein the anode comprises at least one conductive material disposed inside the anode material surrounded by an anode material containing an aluminum compound.

(30) The invention according to the above item (24), wherein the film forms a partition containing a mixture of the aluminum compound and the reducing agent, and forms a depolarizing electrode.

(31) Said paragraph (30), wherein said tank includes a metal collection partition placed below said membrane and said cathode.
The invention described in Section 1.

(32) The above-mentioned (30) wherein the membrane partition contains retained impurities and also forms a depolarizing electrode.
Or the invention described in paragraph (31).

(33) Said electrolyte contains ions selected from the group consisting of chloride, fluoride, or a mixture thereof, and said compound can react at the anode to produce metal ions that are reduced to metal at the cathode. ) or the invention described in paragraph (31).

(34) The invention according to item (30) or (31) above, wherein the temperature of the electrolytic solution is between the melting point of aluminum metal and the boiling point of the liquid in the tank.

(35) The temperature of the electrolyte is about 10 to above the melting point of the metal.
150°C, the electrolyte is formed substantially entirely of fluoride salts, and the metal is directly reduced to molten metal at the cathode.

(36) Current source, molten electrolyte for transmitting current;
In the electrolytic deposition process of aluminum, which uses an electrolytic cell with a cathode for aluminum deposition, an oxygen-containing compound of aluminum is in contact with the compound in an amount sufficient to supply the aluminum during electrolysis, and the aluminum metal is deposited at the cathode. The combination with a reducing agent present in sufficient quantity to react at the anode to form an anode, but
The weight ratio of the aluminum compound to the reducing agent expressed as Al ₂ O ₃ is at least about 1.5 to 1.
an improvement consisting in reacting the compound at the anode, obtaining aluminum metal at the cathode, and then collecting this aluminum at the cathode.

(37) Said electrolyte contains ions selected from the group consisting of chloride, fluoride, or mixtures thereof, and said compound is capable of reacting at the anode to produce aluminum ions that are reduced to aluminum at the cathode. ) method described in section.

(38) The method according to item (36) above, wherein the compound is selected from the group consisting of alumina, bauxite, clay, and aluminum-containing oxides.

(39) The method according to item (36) above, wherein the temperature of the electrolyte is approximately between the melting point of aluminum and the boiling point of the liquid in the tank.

(40) The temperature of the electrolyte is about 10 to above the melting point of the metal.
The method according to item (36), (37), (38) or (39), wherein the temperature is 250°C and the electrolyte contains total fluoride.

(41) The method according to item (36), (37), (38), or (39) above, wherein the reducing agent before coking is selected from the group consisting of organic substances that generate carbon upon coking.

(42) the above-mentioned (36) and (37), wherein the aluminum oxygen-containing compound is intermixed with the reducing agent in an amount of 1.5 to 50.0 parts by weight of Al ₂ O ₃ per 1 part by weight of the reducing agent;
or the method described in paragraph (39).

(43) The method according to the above item (36), wherein the compound and the reducing agent are intimately mixed and brought into substantially contact with each other.

(44) The reducing agent is a carbon-containing compound or element,
The method according to item (36) or (39), wherein the compound is selected from the group consisting of sulfur, phosphorus, and arsenic, and the compound is selected from the group consisting of alumina, bauxite, and clay.

(45) The method according to the above item (36), wherein the reducing agent is immersed in the electrolytic solution at a temperature sufficient to coke the reducing agent for a sufficient time.

(46) The method according to the above item (45), in which the reducing agent before coking is selected from the group consisting of organic substances that generate carbon during coking.

(47) The method according to the above item (46), wherein the organic substance is selected from the group consisting of tar, pitch, coal, coal products, and natural or synthetic resinous substances.

(48) The electrolyte is formed substantially entirely of fluoride salts, the compounds react at the anode to produce aluminum ions that are reduced to aluminum at the cathode, and the electrolyte temperature is 10 to 150°C above the melting point of aluminum. The method according to item (36) above, wherein the temperature is °C.

(49) The temperature of the electrolyte is about 10 to above the melting point of the metal.
150° C., wherein the electrolyte is formed substantially entirely of fluoride salts, and wherein the compound is capable of reacting at the anode to produce aluminum ions that are reduced to aluminum at the cathode.

(50) The method according to item (36) above, comprising a porous membrane disposed in the electrolyte so as to contain the compound and the reducing agent for reaction at the anode.

(51) The method according to item (36) above, wherein a total fluoride-containing electrolytic solution is prepared, and the reducing agent reacts at the anode to generate metal ions that are reduced to metal at the cathode.

(52) No. (48) above, wherein the temperature is in the range of 700 to 800°C and the source of the metal compound is alumina.
The method described in section.

(53) To supply aluminum during electrolysis in the electrolytic deposition of aluminum from aluminum chloride using an electrolytic cell having a current source, an electrolyte containing aluminum chloride for transmitting current, and a cathode for depositing aluminum. A combination of a sufficient amount of an oxygen-containing compound of aluminum and a reducing agent in contact with the compound is formed as an anode, provided that the weight ratio of the aluminum compound to the reducing agent, expressed as Al ₂ O ₃ , is at least about 1.5. It consists of electrolyzing aluminum ions from an electrolytic solution to precipitate aluminum at the cathode, and continuously replenishing the electrolyzed aluminum ions by reacting the aluminum compound and a reducing agent at the anode. Improvement.

(54) No. (53) above, wherein the aluminum compound is an oxygen-containing compound of aluminum that can react with a reducing agent at the anode to generate aluminum ions.
The method described in section.

(55) The method according to item (53) above, wherein the aluminum compound is selected from the group consisting of alumina, bauxite, and clay.

(56) The method according to item (53), (54) or (55), wherein the ratio is 1.5 to 50.0 parts by weight per 1 part by weight of reducing agent.

(57) The method according to item (53), (54), (55), or (56), wherein the reducing agent before coking is selected from the group consisting of organic substances that generate carbon upon coking.

(58) The organic compound is tar, pitch, coal,
The method according to the above item (57), which is selected from the group consisting of coal products, natural or synthetic resinous substances.

(59) The method according to item (53), (54), (55), or (56), wherein the aluminum compound and the reducing agent are intimately mixed and brought into substantially contact with each other.

(60) The reducing agent is a carbon-containing compound or element,
the aluminum compound is selected from the group consisting of alumina, bauxite, and clay, and the aluminum compound and the reducing agent are intimately mixed to substantially contact each other; 53) Method described in section 53).

(61) The method according to the above item (53), wherein the reducing agent is immersed in the electrolytic solution at a temperature and for a sufficient time to coke the reducing agent.

(62) The method according to the above item (61), wherein the reducing agent before coking is selected from the group consisting of organic substances that generate carbon upon coking.

(63) The method according to the above item (62), wherein the organic substance is selected from the group consisting of tar, pitch, coal, coal products, and natural or synthetic resinous substances.

(64) The electrolytic cell according to item (25), (26), or (27), wherein the aluminum compound and the reducing agent are intimately mixed and brought into substantially contact with each other.

(65) Paragraphs (25), (26), and (27) above, comprising a membrane disposed in contact with the aluminum compound to substantially prevent undissolved solids from passing through the membrane;
Or the electrolytic cell described in paragraph (28).

(66) The above-mentioned No. (25), (26), and (27), wherein the film contains the aluminum compound and forms an anode.
Or the electrolytic cell described in (29).

(67) The electrolytic cell according to item (16), wherein the cell voltage is lowered by retaining aluminum chloride in the electrolyte bath.

(68) The electrolytic cell according to paragraph (31) above, wherein the electrolyte bath essentially comprises a mixture of NaAlCl ₄ .

(69) A mixture of an aluminum material, the electrode of which contains an aluminum oxide, a reducing agent in contact with the aluminum oxide of the aluminum material, and at least one metal conductor in contact with the electrode to conduct current through the mixture. the conductor is disposed within the electrode and extends to at least adjacent one end of the electrode inserted into the electrolyte;
An electrode used as an aluminum source in the electrolytic deposition of aluminum.

(70) The electrode according to the above item (69), wherein the metal conductor is the central core of the electrode arranged vertically.

(71) The electrode according to item (69), wherein the metal conductor is a plurality of pairs of pins inserted laterally along the electrode.

(72) The method according to paragraph (69) above, wherein the mixture is in the form of at least two adjacent laminates and the metal conductor is in the form of a sheet disposed between the laminates forming a single combination. electrode.

(73) The electrode according to item (69), (70), (71) or (72), wherein the weight ratio of aluminum oxide to reducing agent in the aluminum material is 1.5 to 50.0:1.

(74) The electrode according to item (73), wherein the weight ratio of aluminum oxide to the reducing agent in the aluminum material is 2.5 to 6.0.

(75) Said electrode is disposed between the anode and the cathode, and the electrode is electrically connected to the aluminum compound and the reducing agent for depolarization electrolysis.
Electrolytic cell described in (2), (3), or (4).

(76) The electrolytic cell according to the above item (75), wherein the aluminum oxygen compound is mixed with the reducing agent in an amount of 1.5 to 50.0 parts by weight of Al ₂ O ₃ per 1 part by weight of the reducing agent.

(77) The electrolytic cell according to the above item (75), wherein the reducing agent is selected from the group consisting of carbon and carbon-containing compounds or elements, sulfur, phosphorus, and arsenic.

(78) the electrolyte is substantially entirely fluoride salt;
(75), (76), wherein the compound contains aluminum and the temperature of the electrolyte is about 700 to 800°C;
Or the electrolytic cell described in paragraph (77).

(79) The reducing agent is selected from the group consisting of carbon and carbon-containing compounds or elements, sulfur, phosphorus, arsenic, and the aluminum oxygen compound is added in an amount of 1.5 to 20.0 parts by weight of Al ₂ O ₃ per part by weight of the reducing agent. is intermixed with the reducing agent, the electrolyte is substantially all fluoride salts, the compound contains aluminum and is capable of reacting at the anode to produce aluminum ions which are reduced to aluminum metal at the cathode; The electrolytic cell according to item (75) above, wherein the temperature of the liquid is about 700 to 800°C.

(80) The electrolytic cell according to the above item (75), wherein the anode is coated on only one side with the compound and the reducing agent.

(81) The electrolytic cell according to paragraph (75), wherein the electrode is disposed within a membrane containing the compound and the reducing agent in contact with the compound.

(82) The electrolytic cell according to paragraph (81) above, wherein the membrane substantially prevents the passage of undissolved solids.

(83) The method according to the above item (36), wherein an electrode is placed between the electrode and the cathode, the electrode is brought into contact with the aluminum compound and the reducing agent, and the electrode is depolarized during electrodeposition.

(84) The method according to the above item (83), wherein the aluminum oxygen compound is intermixed with the reducing agent in an amount of 1.5 to 50.0 parts by weight of Al ₂ O ₃ per 1 part by weight of the reducing agent.

(85) The reducing agent is a carbon-containing compound or element,
The method according to item (83) above, wherein the method is selected from the group consisting of sulfur, phosphorus, and arsenic.

(86) the electrolyte is substantially entirely fluoride salt;
(83) or (84) above, wherein the compound contains aluminum and can react at the anode to generate aluminum ions that are reduced to aluminum metal at the cathode, and the temperature of the electrolyte is about 700 to 800 ° C., or The method described in paragraph (85).

(87) The reducing agent is a carbon-containing compound or element,
The aluminum oxygen compound selected from the group consisting of sulfur, phosphorus, and arsenic is intermixed with the reducing agent in an amount of 1.5 to 50.0 parts by weight of Al ₂ O ₃ per 1 part by weight of the reducing agent, so that the electrolyte is substantially Said No. 84, which is a total fluoride salt, the compound contains aluminum and can react at the anode to produce aluminum ions that are reduced to aluminum metal at the cathode, and the temperature of the electrolyte is about 700 to 800 °C. ) method described in section.

(88) The method according to item (84) above, wherein only one side of the electrode is coated with the compound and the reducing agent.

(89) The method according to item (83) above, wherein the electrode is disposed within a membrane containing the compound and the reducing agent in contact with the compound.

(90) The above-mentioned (36), (39) wherein the anode surface is provided with an inclined surface and the cathode is provided with a surface of a mutually complementary shape, and the anode surface and the cathode surface are spaced apart by a preselected distance. ), the method described in paragraph (48).

(91) The method of paragraph (90), wherein the spacing between the surfaces of the mutually complementary shapes is about 63.5 mm (2.5 inches) or less.

(92) The method according to the above item (90), wherein the distance is 6.35 to 25.4 mm (0.25 to 25.4 inches).

(93) The inclined surface is approximately 10 to 80 degrees relative to the bath surface.
The method according to paragraph (90) above, having an angle of degrees.

(94) The method according to paragraph (90) above, wherein the temperature of the surface of the cathode immersed in the electrolyte is maintained high enough to prevent solidification of the electrolyte on the surface of the cathode, thereby maintaining the spacing. .

(95) The electrode according to paragraph (1) above is immersed in an electrolyte bath, and the bath contains the electrode as an anode for supplying aluminum for precipitation, and the anode is immersed in the electrolyte. the cathode has at least one sloped surface to increase the anode surface subject to erosion, the cathode having at least a portion of the cathode surface having a complementary shape to the sloped anode surface, the mutually complementary shape; An electrolytic cell for aluminum electrolytic deposition, wherein the cathode surface and the anode surface are spaced at a preselected close distance from each other to substantially reduce the energy consumption of the deposition.

(96) The electrolytic cell according to paragraph (95), wherein the spacing between the surfaces of the mutually complementary shapes is about 63.5 mm (2.5 inches) or less.

(97) The distance is 6.35~25.4mm (0.25~1.0 inch)
The electrolytic cell according to item (96) above.

(98) The sloped surface is about 10 to
The electrolytic cell according to item (95) above, which has an angle of 80 degrees.

(99) The electrolytic cell according to the above item (95), wherein the inclined surface has an angle downward and inward.

(100) The bottom surface of the anode is inclined at an angle with respect to the surface of the bath, and the bottom surface of the cathode facing the anode has a shape that is at least partially complementary to the bottom anode surface. Electrolytic cell described in paragraph (95).

(101) No. (95), (96), where the temperature of the electrolyte is between the melting point of aluminum and the boiling point of the liquid in the tank;
The electrolytic cell described in (97), (98), (99), or (100).

(102) The above-mentioned items (95), (96), (97), and (98), wherein the anode is comprised of at least one internally disposed conductive material surrounded by an anode material containing an aluminum compound. , (99), or the electrolytic cell described in (100).

(103) Paragraphs (95) and (96) above, including an aluminum collection well located below the anode, the collection well having a sloped floor below the anode to minimize the depth of the aluminum pool. ), (97), (98),
Or the electrolytic cell described in paragraph (99).

(104) The lining of the cell forms a portion of the cathode surface in contact with the electrolyte bath, and the cathode surface is at a temperature not below the freezing temperature of the bath, such that the preselected near distance The electrolytic cell according to item (95), (96), (97), (98), (99), or (100), which maintains the following.

(105) Glassy carbon foams, graphite or carbon solids, nitrides of boron, aluminum, silicon (including oxynitrides), titanium, hafnium, zirconium, and tantalum; silicides of molybdenum, tantalum, and tungsten; hafnium, consisting of a material selected from the group consisting of carbides of tantalum, niobium, zirconium, titanium, silicon, boron, and tungsten; borides of hafnium, tantalum, zirconium, niobium, titanium, and silicon;
The material has sufficient passage porosity to pass all liquid substances in the electrolyte bath, including ionic substances and dissolved solids, but substantially excludes undissolved solids that constitute impurities. Aluminum electrolytic materials that can withstand corrosion in electrolyte baths containing halide salts, where the material has interconnecting pores of small enough diameter to block undissolved particles. Membrane for use.

(106) The membrane according to item (105), wherein the passage porosity is about 1 to 97% and the communicating pore diameter is about 1 micron to 1 cm.

(107) The film according to item (105), wherein the film has a thickness of 3.18 to 50.8 mm (0.125 to 2.0 inches).

(108) The film according to item (105), wherein the film has a thickness of 3.18 to 12.7 mm (0.125 to 0.5 inch).

(109) The membrane according to item (105), wherein the passage porosity is about 30 to 70%.

(110) The membrane according to item (105), (107), or (109), wherein the communicating pore diameter is about 1 micron to 1 cm.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an electrolytic cell of the invention containing a chloride bath, showing the closed top of the cell as well as the relative positioning of the electrodes. FIG. 2 is a schematic cutaway of a portion of an electrode coated with a mixture of aluminum material and reducing agent, used as an anode. FIG. 2A is a schematic perspective view of another embodiment of the electrode of FIG. 2, showing a number of conductor cores within a matrix of aluminum material and reducing agent. FIG. 2B is a schematic perspective view of the modification of the electrode shown in FIG. 2A. FIG. 3 is a schematic cut-away diagram of another electrode. FIG. 4 is a cross-sectional schematic view of an open top electrolytic cell with an all-fluoride bath and an anode clamp providing a current source to the continuously introduced anode. FIG. 4A is a schematic diagram of another electrode similar to the electrode of FIG. FIG. 5 is a schematic diagram of an embodiment of the present invention, illustrating the use of a porous membrane to accommodate various anode materials, including an aluminum-containing material and a reducing agent. FIG. 6 is a cross-sectional schematic diagram of another embodiment of an electrolytic cell, illustrating the use of depolarizing electrodes. FIG. 7 is a cross-sectional schematic view of an electrolytic cell combination with sloped side electrodes and complementary shaped composite anodes. FIG. 8 is a cross-sectional schematic diagram of a unique combination of electrolyzer and composite anode variant. Figure 9 is the 8th
FIG. 3 is a perspective view of the anode shown in the figure. FIG. 10 is a schematic cross-sectional view of another specific example of the combination shown in FIG. 8. FIG. 11 is a perspective view of the anode of FIG. 10. FIG. 12 is a schematic perspective view of another embodiment of the composite anode of the present invention, showing a laminated structure. FIG. 13 is a schematic perspective view of the anode of FIG. 12 and the anode clamp of FIG. 4;

Claims (1)

Claims: 1. An anode mixture comprising an anode mixture of an oxygen-containing compound of aluminum and a conductive reducing agent, and conductor means having a higher electrical conductivity than said anode mixture in physical contact with said mixture, said anode mixture comprising: , adapted to be located in opposing relation to, but spaced from, the surface of the cathode to provide an active anode surface where metal oxides are converted to metal ions that can be recovered as molten metal at the opposing surface of the cathode. comprising at least a portion of the mixture adapted to be immersed in a suitable electrolyte together with at least one active surface of the portion, and the conductor means conducts a total anodic current to the portion of the mixture when connected to a power supply. the conductor means being adapted to conduct substantially a portion of the anodic mixture for conducting an anodic current directly from the conductor means to the mixture adjacent at least one end of the conductor means and to the surface; extending inwardly through the mixture and having one end thereof located at least substantially adjacent to said one active surface, thereby providing a short, low resistance current path through the mixture to said surface; The conductor means also comprises at least one aluminum member having a cross-sectional area adapted to melt and settle in the electrolyte along the axis at substantially the same rate as the mixture is consumed during aluminum electrolytic production. An anode for electrolytic manufacturing of aluminum, whereby one end of the conductor means associated with the surface remains substantially unchanged when the anode mixture is consumed at the surface in an electrolytic process.