CA1211075A - Electrolytic cell with conductor through anodic body of metal compound and reducing agent - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

There is described an apparatus for the electrolytic production of aluminum. The apparatus includes an anode body comprising a mixture of an oxygen-containing compound of aluminum and an electrically conductive reducing agent. The anode body includes at least a portion adapted to be immersed in an appropriate electrolyte, with at least one active surface of the portion adapted to be positioned in opposed relationship to but spaced from the surface of a cathode for providing an active anode surface at which the metal oxide may be converted to metal ions recoverable as molten metal at the opposing surface of the cathode. The apparatus further includes a conductor of higher electrical conductivity than the anodic mixture in physical contact with the anode body, the conductor being adapted to conduct substantially the entire anodic current to the immersible portion of the anode body when connected to a source of electrical power.
The conductor extends through the anode body mixture and has an end positioned at least approximately adjacent the active surface of the anode body for transmitting anodic current directly from the conductor to at least the mixture adjacent the end of the conductor and to the active surface thereby providing a short, low resistance current path through the mixture to the surface. The conductor itself comprises at least one member adapted during the electrolytic production of aluminum to leave the end position of the conductor relative to the active surface substantially unchanged as the anodic mixture at the surface is consumed in the electrolytic process.

Description

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This is a division of Canadian Application Serial No.
347,289 filed March 7, 1980.
This invention relates to the electrolytic production ¦ of aluminum from aloneness materiels using an electrolyte path containing holidays, more particularly, the present invention relates to the electro,~eposition of aluminum using an anode as the sole source of aluminum in an electrolytic cell maintaining dimensionally stable spacing between cathode and anode at low path temperatures to effect great energy savings.

Lo BACI~GI~OUND Ox TIRE INVENTION

The co~ercial production of the aluminum in the world has been by the Hall-~leroult process. In this well known . process a purified source of alumina is dissolved in a molten primarily fluoride salt solvent, consisting essentially .
ox cruelty and theft reduced electrolytically with a carbon anode according to the reactions ., 1/2 Aye 3j4 C + ye ~________~_ Al + 3j4 C02 and 1/2 ~1203 + 3/2 C ye Al 3/2 CO.

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75i Three characteristics of this system which are inherent in the ¦ Hall-}leroult process include: first, carbon dioxide is produced ¦ and the carbon anode is consumed at the rate of .33 to 1 pound of carbon per pound of aluminum produced which results in a required continual movement of the carbon anode downwardly toward the cathode aluminum pool at the bottom of the cell to maintain constant spacing for uniform aluminum production and -thermal balance in the jell; second, the need to feed intermittently and evenly the solid alumina in a limited concentration range to the "open type" cell to maintain peak efficiency of operation in order to avoid "anode effects";
third severe corrosion of jell materials due to the high temperatures of 950-1000C and the fluoride salts resulting in relatively low cell life and increased labor.

A fourth characteristic,- not inherent in the system but . present nonetheless is that the cell power efficiency is limited to less than about 50% due to the practical requirement of main-twining a carbon anode to liquid aluminum distance greater than one inch to reduce the magnetic fields' undulation of the I aluminum layer causing intermittent shorting with resultant Foredeck losses due to the back reaction of aluminum droplets with carbon dioxide, 1 3/2 C02 _ --I 3- 1/2 Aye + 3/2 CO.

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Jo The first three inherent limitations of the conventional ~lall-Heroult process can potentially be overcome either by use of an aluminum chloride electrolysis process which in the prior art would directly produce aluminum and chlorine gas or through the use of all fluoride bath at temperatures of 670-750C for the direct reduction of aluminum oxide.

The potential advantages of. an aluminum chloride salt electrolysis process include: (1) the use of chloride salts which are generally more economical than the fluorides of the ¦ Hall-~leroult salts, have a lower operating temperature of 670-800C are much less corrosive to cell construction materials and have in general a lower specific gravity which can permit closer anode-cathode spacing; (2) the aluminum chloride electrolysis process requires a closed system reducing air pollution problems; (3) the chloride electrolytes, even at the lower operating temperature of 670-800C, have higher conductivities than that of the Hall-Heroult fluoride salts at 950-1000C. This results in the production of aluminum at lower energy consumption and at higher power and current I efficiencies; (4) the use ox the aluminum chloride electrolysis process has a very broad operating range of aluminum concentra lion which results in no anode effect"; (5) it is possible to design the aluminum chloride electrolytic process cell with bipolar electrodes which result in a much more compact cell with increased production potential per unit volume.

lZ1~075 There are, however, poterltial advantages to the use of an all fluoride bath if it is possible to use the Hall-~leroult reaction mechanism system and yet continue to deposit metal, The all fluoride bath potenticllly: (l) avoids substantial structural changes in the cell if the aluminum oxide can be directly reacted thereby making unnecessary the requirement of the chloride system to close the top of the cell and (2) does not evolve any corrosive, noxious anode gas, merely COY. To '- ¦ achieve these advantages the all fluoride bath must be used at .0 1 low temperatures of 670~-800C' but such is not possible in accordance with prior art techniques because alumina, unlike alwninum chloride, will not readily dissolve at such low temperatures.

In the comparison of the con only used Hall-Heroult alumina-fluoride process and the much less familiar aluminum chloride process, there appear to be significant benefits in the use of the aluminum chloride process, but a fair comparison should not overlook the significant disadvantage of the aluminum chloride electrolytic process in producing large quantities of 0 the corrosive gas chlorine liberated at the anode. The chlorine entrains the chloride electrolyte to clog the exit ports and deplete the bath. This entrained electrolyte must be collected and returned to the cell and the liberated chlorine must be recycled to produce further aluminum chloride.

although the potential advantages of utilizing an alumiJ1um chloride electrolysis process for the electrolytic production of aluminum have been recognized for well over a century, commercial realization of such a process has not ox-cuffed. The lack of a sufficiently simple and economical process l l 75 to produce large, commercial quantities of high purity an hydrous aluminum chloride has been one of the reasons that an aluminum chloride electrolysis process has never reached commercial prominence.

In general, the usual process known to the prior art for producing aluminum chloride has been the conversion of an alumina-containing material with chlorine in the presence of carbon to yield aluminum chloride and a mixture of the gases carbon dioxide and carbon monoxide. This reaction, .
AYE C + ~12 Alec + COY and CO

has been carried out under a wide range of conditions, each variation having some alleged advantage. All of these procedures for producing aluminum chloride have a common thread however. Each involves the use of a source of carbon, a source of chlorine, and an aluminum chloride reactor separate from the electrolytic cell in which the metallic aluminum is electrolytically produced.

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I The normal reaction temperature for the production of ¦ aluminum chloride is generally in the Lange ox 400C to 1000C

l depending upon the form of the reacting agents. Unless a high purity a umlna source is used, other elements that are generally .

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¦ present such as iron, silicon, and titanium, are also chlorinated and must undergo difficult separation from the aluminum chloride. This contributes to the size and cost of the aluminum chloride producing plants.
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The aluminum chloride electrolytic process would have an unusual advantage beyond those advantages heretofore cited if it were possible -Jo avoid both the chlorine collection and the independent production of aluminum chloride in a plant separate from the electrolysis plant.

The electrode position of aluminum by the direct reduction ¦ of alumina in an all fluoride bath is an attractive alternative to the aluminum chloride system provided that the alumina would dissolve at the low temperatures of 670-800C rather than the 950-1000C considered to be required for dissolution in molten cruelty. Existing Hall-Heroult cells could be used without substantial capital expenditures and great energy savings would be possible With such an all fluoride bath but no such process for the electrode position of aluminum is available to those skilled in the art.

¦ The fourth disadvantage of the Hall-Heroult cell, cell ¦ vower efficiency, has been considered by those skilled in the art but it appears that: the practical limit to energy saving and eye edgy in present l{all-lleroult cells has been reached lo 7 I

¦¦ through careful design and operation of 150 to 225 Kemp cells at anode current densities between 4.0 and 5.5 amps/in2. The lower energy limit appears to be about 5.6 to 6.0 Kwh/lb utilizing the most advanced currently known designs, computer controls, bath modification and other improvements.

It is known that larger cells capable of operating at lower anode current density consume considerably less ¦ energy. Lower anode current density, however, decreases the production of aluminum per unit cell volume. The net result is that larger cells produce aluminum more economically but at a lower production ratio If the anode current density could be lowered but at the same time not reduce the I production rate of the cell, a substantial economy in the production of aluminum would result.

The prior art suggests that increasing the surface area of the anode that is electrolytically active would lower the current density. US. patent 3,067,124 for instance discloses a type of electrolytic cell in which the electrodes are inclined towards the center in the shape of a pyramid or frustum of a pyramid. It would normally be expected that the inherent advantages of utilizing the lower current density would he achieved with such structure. However, when such inclined electrode system is embodied in the Hall cell system requiring a high temperature bath at about 950C, the critical spacing between cathode and anode is often lost. This desired spacing cannot be maintained due to the I

inherent dimensional instability of the cell structure due both to such high temperatures of cell operation and the inherent aggressive nature of the salts required for high temperature use.

Lower temperatures are not possible in the Hall cell due to the lack of volubility of aluminum oxide in the cruelty at temperatures below about 940~C and the fact that cruelty base salts have a freezing point in the range of 925-950C.
The lack of dissolved AYE present in the bath would result in an anode effect which would at least increase the required voltage by 10-20 fold and cease aluminum deposition. If a low temperature operation of such a cell would have been possible, non-cryoli~e salt; would permit both the use of non aggressive salt compositions and reduced temperature gradients that would result in little or no dimensional change in the cell walls end bottoms and consequently minimize the spacing changes between the anode and cathode.

A composition for use as an anode in the low temperature electrode position of aluminum comprises an luminous source such as Aye and a reducing agent such as carbon in compound or element for.

According to the present invention then, there is provided apparatus for the electrolytic production of aluminum comprising an anodic body comprising a mixture of an oxygen-containing come pound of aluminum and an electrically conductive reducing agent, the anodic body including at least a portion thereof adapted to be immersed in an appropriate electrolyte, with at least one g _ -~Z~75 active surface of the portion adapted to be positioned in opt posed relationship to but spaced from the surface of a cathode for providing an active anode surface at which the metal oxide may be converted to metal isles recoverable as molten metal at the opposing surface of the cathode, conductor means of higher electrical conductivity than the anodic mixture in physical con-tact with the anodic body, the conductor means being adapted to conduct substantially the entire anodic current to the portion when connected to a source owe electrical power, the conductor means extending to the portion of the anodic mixture and having an end thereof positioned at least approximately adjacent the one active surface for transmitting anodic current directly from the conductor means to at least the mixture adjacent the end of the conductor jeans and to the active surface thereby providing a short, low resistant current path through the mixture to the surface, the conductor means comprising at least one member adapted during the electrolytic production of aluminum to pro-sent the end of the conductor means relative to the active sun-face substantially unchanged as the anodic mixture at the sun-I face is consumed in the electrolytic process.
inductor rods may be incorporated within the anode tininess conductivity of the anode.

- pa -if I 75 I The electrolytic production of aluminum in a single cell from a molten halide salt bath containing aluminum and ¦ chloride ions which is depleted during electrolysis and wherein aluminum ions are reproduced in situ from the anode within the electrolytic cell. Aluminum ions are produced at the anode by the reaction of an luminous source and a reducing ¦¦ agent serving as the anode. The aluminum ions era then deposited as aluminum metal at the cathode. A unique porous men~rane passes electrolyte or other dissolved material while withholding undissolved impurities.

Aluminum also may be deposited by the direct electrolytic l reduction of a dissociated and/or dissolved aluminum oxide to produce molten metal at a temperature as low as 670-810C with ¦¦ the use of an all fluoride containing bath and an anode containing aluminum oxide and reducing agent.

I, Dimensionally stable cells for the electrode position of ¦ aluminum may have sloped walls forming electrodes which reduce anode current density and permit the maintenance of a reduced l anode-cathode spacing when using the low temperature non-aggressive baths permissible with the particular anode composition.

i2~10'75 ¦ ~nbodiments of the invention will now be described with ¦ reference to the accompanying drawings in which:

Figure 1 is a schematic showing in cross section of the electrolytic cell of the present invention eontainirlg a chloride bath and illustrating the closed top of the cell along with the relative positioning of the electrodes.

Figure 2 is a schematic showing partly broken away of an electrode being used as an anode and having coated thereon the mixture of luminous materiel and reducing agent.

l Figure PA is a schematic: vie in perspective of an alternate embodiment of the electrode of Figure 2 showing a plurality of conductor cores within a matrix of the luminous material and reducing agent ¦ Figure 2B is a schematic perspective view of a variation of the electrode illustrated in Figure PA.

Figure 3 is a schematic illustration partly broken away of another alternative electrode.

Figure 4 is a schematic illustration in cross section of , an open top electrolytic eel having an all fluoride bath and an anode clamp providing a source of electric current to a contilluously introduced anode Faker I is a schcmatil drywall of another alternative electrode similar to the electrode of Figure 3.

- aye -sly inure 5 is a schematic view of an embodiment of the present invention which illustrates the use of a porous membrane to contain the various anodic materials including an aluminum containing material and a reducing agent j Figure 6 is a schematic view in cross section of another Al alternate embodiment of an electrolytic cell illustrating the use ¦¦ of bipolar electrodes.

Figure 7 which is on the same page as Figures 12 and 13) is a schematic cross sectional view of a combination of electron lyric cells with sloped sided electrodes and the composite anode of complementary shape.

Figure 8 is a schematic cross sectional view of a modification of the unique combination electrolytic cell and composite anode.
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¦ Figure 9 is a perspective illustration of the anode of Figure 8.

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

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

Figure 12 is a schematic perspective view of a further embodiment of the keenest anode of the present invention illustrating a laming construction.
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Figure 13 is also a schematic perspective view of the anode of Figure 12 and the anode clamp of Figure 4 - 10~)-¦ GIRL DESCRIPTION OF THY INVENTION

The present invention is a unique system for ¦ electrolytically producing aluminum from a variety of raw materials R containing aluminum in a low temperature electrolyte bath B. The basis for -the invention is a unique anode A which is the sole source of the aluminum being deposited on the cathode H. The anode A includes a combination of an luminous source usually alumina, Aye and a reducing agent such a, carbon. Conductors D may be incorporated with the anode A to enhance conductivity of the anode and a membrane M may be used to contain the Few materials An electrolytic cell C containing the anode A and cathode H may take a variety of structural forms having sloped wall electrodes or vertical wall electrodes. In the preferred embodiment sloped wall electrodes are more economical and practical when used at low temperatures with the unique anode.

The electrolytic bath B may be composed of chlorides or fluorides or mixtures thereof and does not require the initial addition of an aluminum salt to the bath. In one form of the invention, the aluminum chloride cycle, aluminum chloride is present in the bath and is maintained at a constant concentration due to the reaction of the composite anode A in the bath to form the aluminum ions for reduction at the cathode. In another form of the invention, using an all fluoride bath, aluminum is also ionized at the anode A for deposition at the cathode H.

l ~Z~75 lo SCHOLL N OF Till INVENTION

The Electrolytic Cells The electrolytic system of the present invention utilizes an electrolytic cell C depicted in any one of the Figures for the unique continuous production of aluminum.

In Figures 1-6 one form of the electrolytic cell structure is shown generally at 10 as composed of an outer steel shell having a refractory lining I that may serve solely as a thermal insulator or as both insulator and electrode. The refractory lining may be of any material resistant to the action of the molten electrolytic bath 16. The refractory lining having conventional vertical sides 15 and bottom 17 is designed to maintain the desired thermal balance in the cell operation and therefore may be very thin in cross section in order to achieve a small thermal gradient resulting in both a thin layer of frozen salt on the surface of the refractory and a hot outer wall on the surface of the steel shell 12. The refractory lining may also be quite thick to achieve a fruit layer of salt within the refractory lining resulting in a cool surface on the steel shell although this is not necessary in the vertical sided cell of Figures 1-6. In contrast, in the slope sided electrode cell of Figure 7 cathode 19 is a conductive lining formed on both sides of the anode. A
thermal and electrical insulation lining may be positioned between the cathode 19 and the shell 12 if desired. The freeze line should be within the boundaries ox this conductive lining or cathode 19 in order to prevent a solid layer of salt collecting on the bath side of the electrodes. Such a salt Lowry would act as an electrical insulator and prevent effective ¦¦ current wow. - 12 -Al 3LZ~ I .

The lid 18 is provided on the top of the cell to produce an air-tight closure and is only necessary in a chloride containing bath. This lid thus prevents air and moisture from seeping inside the cell or any vapors of the salt composition 16 from leaking out to react with the environment.
The lid 18 may be lined with the refractory material 20 which may be the same as the refractory lining 14 or any other refractory material consistent with maintaining a temperature balance in the cell as well as being chemically inert to the salt composition 16. Seals 22 are supported on the lid 18 and are secured against the electrodes 24, 25 and 26 to prevent atmospheric air and moisture from seeping into the cell or the vapors from the cell exiting to the environment.
The sealing at the lid 18 and around the electrodes may be by any means which prevents vapor leaks and may be standard or conventional packing and gasket material capable of withstanding the temperature of the operation while being resistant to the electrolyte vapors. Acceptable materials for such packing gasket use include asbestos, fibrous ceramics Tao, Vitro* silicones liquid metal seals such as mercury, liquid solder, tin, lead, etc.

Electrodes 24, 25 and 26 may be anodes, cathodes or bipolar electrodes. They may include solid or coated conductors to carry electric current for the cell operation. These conductors may be any material that may withstand the temperature within the cell which is the range of 150 to 1060C, stable to the halide composition 16 and is a good electrical conductor. Materials that are useful for this purpose are carbon, graphite, and titanium carbides, nitrides * Trademark .

~21~1)75 or brides and aluminum metal as appropriately sized for heat transfer balance. The preferred materials for these conductors have been found Jo be graphite and titanium debarred when operating in the bipolar mode The aluminum chloride cycle cell also includes a stack or exit tube 28 having a valve 30 to control the flow of any gaseous elements from the stack and establish the pressure buildup in the cell for continuous operation. Gaseous vapors emanating from the cell are those of the oxidized lo reducing agent and notably where is no chlorine gas detected at all with an aluminum chloride containing salt. If any chlorine is produced it would react at the anode 26 and be recycled a aluminum chloride. The molten aluminum 32 is tapped out my conventional tap 34 or otherwise drawn out by vacuum through standllrd siphoning techniques well known in the art Figure 4 illustrates a modification of the cell design of Figure l again illustrating vertical sided electrodes lo.
The cell structures including the shell lo and refractory 14, are the same as that previously described, the electrode 44 serving as the anode may be either one of the anodes shown in Figures 2, PA or 2l3 but preferably Figure 3. The anode 44 is immersed in the electrolyte containing fluoride or chloride salts or mixtures thereof and heated to a temperature generally between ~70 and ~10C. it the bottom of the cell, and resting upon cathode bar 45 positioned over the refractory insulation 14 is a lock 46 which preferably is slightly wider than the anode 44 and serves as the cathode through suitable electrical connection to cathode bar 45.
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~21~L[175 file lock Go may I made front any ox ho previously described electrode materials. The lock 46 should extend close to the base 50 of thy anode I which is the only surface for erosion of the anode. Closer anode-cathode spacing for such electrode configuration is possible when the block 46 also rises above the level of the molten aluminum 32. As the aluminum is deposited on the cathode block 46, its surface is wetted and the aluminum runs off the block into the pool 32 at the bottom of the cell to be tapped of as desired at 34.

Figure 4 also illustrate, a power attachment clamp 47, shown schematically, in contact with the anode 44 either above but preferably below bath level and adjacent to the bottom of the anode to minimize the power loss due to the resistance of the anode. Anode 44 may be structured for instance as shown in Figures 3, 12 and 13. The clump does not act as an anode. Rather, the composite anode 44 dissolves in the bath in the anode reaction. The clamp 47 may partially or completely surround the anode 44 so that the anode 44 may I be fed continuously into the bath while maintaining electrical contact with clamp 47. The clamp is composed of any suitable inert material that is electrically conductive. Among these materials are graphite, carbon Tub or mixtures of these.
The electrical contact between the clamp and the anode may ye through protruding contact pollinate or nub 48. The power attach-mint to the clamp 47 is through suitable split cylindrical conductors 49 that extend Ahab the cell top.

~.1075 In lieu ch~nyillg the anodes periodically to supply fresh luminous material, the present invention is adaptable to a feed mechanism for continuous operation as shown in Figure 5 or the continuous feed of an electrode as shown in Figure 4 of the prebaked or Soderberg typo Protruding up through the cell C of Figure 5 is an anode electrode 52 which penetrates deeply into the melt 16 but remains above thy molten aluminum pool of aluminum 32 or the cathode block 46. Surrounding the anode 52 are the anode jaw materials, shown generally at R, comprising to luminous material and the reducing agent. this anodic mixture may be formed into small particle size from a .001 inch approximately to 1.0 inch or more and may have been formed by extrusion, molding or the like and fed into the cell by the hopper I The raw material particles of luminous material and reducing agent are identified specifically at 58 and are in close contact with the anode 52 to provide the necessary source of aluminum and the reducing agent.
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¦ These anodic raw materials are hold in close contcLct with each other and with they'll anode 52 by being contained in lo porous membrane container 60 which surrounds the anode 52.
WAS the anode materials 58 are used up and their level drops substantially below the level of the molten bath 16, feed 54 is operated to add additional anodic materials 58 into the porous membrane container Al In the embodiment of Figure G there is illustrated a bipolar cell. Again, like structure has been designated with the same identifying numerals.

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11, ¦ - The same basic principle in operation of the bipolar cell exists except that there is a pair of electrodes at either end of the cell which are connected to a suitable electric source. One of the electrodes 64 is a cathode and at the opposite end is an anode 66. Between the electrodes 64 ¦ and 66 is a group of spaced electrodes 68 which are unconnected to each other or to any electrical source. Secured to each of the electrodes 68 and the anode 66 is a porous membrane l container 60 of the same type as that described at 60 in Figure 5. The porous membrane 60, however, in the bipolar cell has as one side, one of the electrodes 66 or 68 that form the enclosure for the anodic raw materials 58.
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In the bipolar cell the side of the electrode 68 nearest I the anode 66 becomes negatively charged and the side of the ¦¦ electrode 68 facing the cathode 64 becomes positively charted.

I This side 72 of the electrode 68 will act as the anode and ¦¦ is the side -that is in contact with the,anodic raw materials 58. The electrolysis then produces aluminum on the negative side of the electrode 68 and COY on the positive or anodic ~20 ¦ side of the same electrodes. The aluminum falls to the pool ¦ 32 at the bottom to be collected in the usual manner.

In Figures 7 through 11 there is illustrated the sloping sided elec~rode-electrolytic cell which in combination with -the anode composition of the present invention results in substantial economies in the electrocleposition of aluminum.

In typical Hall cell procedures aluminum reduction cells have an anode-cathode spacing which must take into consider-lion the magnetic yield effect and the "back reaction" due to the undulations of the aluminum pool. Such considerations prevent any closer spacing than about 1.5 and 2.0 inches between the bottom surface of the anode where all erosion occurs and the top of the aluminum pool or the cathode electrode. A further and equally significant reason for the requirement of greater spacing between -the cathode and anode whether in the Hall cell construction using vertical sides or any attempt to use a sloping side electrode is the serious difficulty of maintaining dimensional stability due to the high temperatures required and the aggressive salts that necessarily were included to retain a high temperature for the dissolution of the alumina. In the combination of the slope sided electrode cells and the anode utilizing aluminum oxide and a reducing agent to provide the sole source of aluminum, the use of temperatures as low as just above the melting temperature of aluminum minimizes any of the problems regarding dimensional instability and therefore enables the cells of the present invention to be structured with a closer anode-cathode spacing unattainable in the past.
Thus it is the particular combination of the anode and the sloped walls for the construction of the cell that achieves a lower IT power drop in the salt due -Jo the close spacing permissible between the sloped walls and the reduction in the anode current density.

, , Al slightly the cells of Forks 7 through 11 are similar to those previously described except for the sloping surfaces forming the electrodes. With this cell structure Thea anode 74 is provided with sloping sides 76 which as i shown are external and directed downwardly and inwardly although the direction of the angle is not at all critical.
The slope of the sides may be in any direction or any angle from the level of the bath B. The angle may even vary from l 10 to 80 or more from the bath level. Through the use of the sloping sided electrode's anode bottom and that portion of the sloping anode side that is i~nersed in the bath 16, the anode will erode over a greater surface area and supply the aluminum for ultimate deposit on the cathode.
If Jo The cathode 78 has surfaces 79 of complementary shape to the sloping sides 76 of the anode to provide for an electrode spacing on the sides as shown by the spacing Y.
this spacing may be between 0.25 and 2.5 inches. Greater Spacing produces greater energy consumption. The spacing l between the bottom 80 of the anode 74 in Figure 7 and the ¦ surface of the alumina layer 82 forming a part of the aluminum pool 84 is shown at X and may be 0~25 to OWE inches.
Preferably the spacings X and Y should be between about 0.25 to 1.0 inches.

The spacing between the anode and the cathode above the solidi~icd bath layer 86 is not significant to the utility ox tic invention. Ilowever the spacings X and Y between the anode and the cathode may be equal or do f fervent depending upon the desired current density and anode erosion but when set as close as specified above will result in substantial energy ¦ consumption Savings he linillcJ I for no Lowe Cole of the cell may be of typical material used for electrolytic cells such as carbon, titanium debarred, or the Lowe and is shaped as previously stated to conform to the external shaping of the anode 74.
Additionally, the base of the lining has an inclined floor 90 for the aluminum pool leading into a catch well I for the aluminum. us can be seen the sloping floor 90 is such as to retain only a limited depth of aluminum layer which can be regulated through draw-off means (not shown). of the aluminum from the catch well,. The purpose of the thin aluminum layer below the base 80 of the anode is substantially to eliminate the ripple or wave like undulations of the molten aluminum layer due to the magnetic effects within the cell.
l l In other respects the cell of Figure 7 is like that of Figure l in that a lid 18 is provided with an exhaust port I being part of shell 12. Refractory insulation of any suitable form as Shinto 14 may also be included.

The combination of the use of the anode of the present on invention with sloped sides to conform to the sloped cathodes enables the configurations owe the cell and anode to vary substantially as shown in Figures 8 through if.

In Figures 8 and 9 the shape of the anode 74 is varied and has centrally located divergently sloped sides 94 which form an apex 96 in the anode. The carbon or other lining material such as 'isle, ate serving as the cathode projects upwardly to complement the internal shaping of the anode as best shown in Figure 8. The operation of such a cell as shown in Figures 8 and 9 is essentially the same as that described in Figure 7 particularly with regard to the increased erosion surfaces 94.

In Figures 10 and 11 dual anodes 100 and 102 with oppositely shaped sloped sides 104 and 106 respectively are positioned in a cell with cathode 98 shaped essentially identically to that described in Figure 8.

The use of the sloped cathode concept of electrolytic cells shown in Figures 7 through 11 has been found to require that no frozen salt layer be permitted on the surfaces of the sloped cathode wall immersed in the bath and confronted with a portion of the anode surface. Otherwise the desired spacing between cathode and anode cannot be maintained.
Additionally, the frozen salt that would adhere to the wall of the cathode is a good electric insulator and thus would inhibit current flow from the anode to the sloped cathode It side wall. In prior use of such sloped wall electrodes the problem of salts freezing on the sides as well as dime-signal instability of the lining prevented any extensive use of such cells. However with the anode composition of the present invention and the lower bath temperatures a variety of low melting salt compositions which will not freeze out on the side wall can readily be utilized. Ideally the melting point of the salt and the cell thermal balance is adjusted such that the freeze line of the salt is within the lining or at the steel shell rather than at the lining or cathode-bath interface. It is not important where the freeze line is located so long as the freeze line is within the lining and that the salt is maintained in a liquid state on the surface of the cathode lining immersed in the path.
on such instance the proper cathode-anode spacing is maintain-Ed without difficulty.

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a. Chloride Containing Bath I The electrolytic process of the present invention for the unique continuous production of aluminum ions at thinned utilizes the closed top electrolytic cell depicted yin Figure 1 or any of the other cells disclosed herein, if the .¦ top is closed or adequate provision is made to prevent:
(a) moisture from contacting the chloride electrolyte, or l (h) oxidation of the aluminum chloride, while containing the l vaporized bath salts. The benefits of the present invention in using the chloride containing bath are derived not only from the continuous in situ production of aluminum ions ¦ at the anode but also from the use of a substantially lower energy requirement to produce a high quality aluminum with the total absence of chlorine gas exiling from the cell.

The continuous production of aluminum ion at the anode is brought about through the formation of the anode from an luminous material containing aluminum oxide and a reducing agent. This anode is immersed in a molten bath containing alkali metal and/or alkaline earth metal halide salts of any composition provided that aluminum chloride is present in the bath. Upon electrolysis, ionized aluminum in the bath is deposited as aluminum metal on the cathode while the reaction at the allude also forms COY in addition to the aluminum ion.
The aluminum is collected as molten aluminum and drawn off but it is the reaction at the anode to reform aluminum ions that constitutes an important part of the present invention.

It is possible the Helen chlorine, whether it is the chloride ion, atomic chlorine or chlorine gas, may take part in the chloride reaction with the aluminum oxide of the luminous material and the reducing event of the anode to produce aluminum ions plus the reducing agent oxide. Aluminum from the anode is ionized in the Mouton bath for continuation of the cycle and the anions while may be chloride, oxide or other ¦
maintain the charge balance with the aluminum ions.

The aluminum produced at the cathode generally is as pure as the luminous material forming the anode. It is possible to produce ultrapure aluminum in accordance with the present invention by utilizing a very pure alumina source or to produce a slightly impure aluminum by the direct use of luminous ore materials such as bauxite or aluminum bearing clays such as kaolin or mixtures of these ores. In general it is possible to obtain purity of aluminum of at least 99.5%.

It is known in the Hall-Heroult cell reaction that the carbon of the anode contributes to the overall reaction of winning aluminum by decreasing the decomposition voltage of AYE. For example the decomposition of AYE in cruelty on a platinum anode is about 2.2 volts but on a carbon electrode considering about vowel% CO produced and 50~ COY, the decomposition voltage is about 1.2. Approximately, the same decomposition voltage is obtained from AYE if methane is injected under the platinum anode to produce mainly COY.
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In thy instant inventioJl, the use of the composite anode results in a lower decomposition voltage than would be obtained if Alec were decomposed with the discharge of Clue gas on the anode. In any electrochemical reaction if the current voltage curve is extrapolated to 0 current, a number approximating the decomposition voltage is obtained. In an aluminum chloride electrolysis process when a graphite anode is used, a decomposition of 1~8 to 2.0V can be obtained which is consistent with values reported in the literature and the theoretical value calculated from thermodynamics.

It was found that the decomposition voltage of the instant invention varies slightly with electrolyte composition. With pure NaAlC14 the decomposition voltage is the lowest but as the : ~lC13 component of the electrolyte decreased, the decomposition voltage tended to increase slightly. The lowest decomposition voltage obtained was 0.5 volts and the highest 1.5 volts.
The average value was 1.2 volts. Utilizing the most prevalent average value of 1.2 decomposition voltage, it can be observed that in the present invention the decomposition voltage is less by 0.6 volts than that for ~lC13 when chlorine is discharged and the presently obtained value approximates that of Aye and carbon which suggests that the same overall reaction mechanism occurs both in the Hall-Heroult cell and in the present invention.
This lower decomposition voltage results in a considerable energy saving for the electrolytic production of aluminum not only ; compared to classical aluminum chloride systems where chlorine is discharged at the anode but also when considering the : additional energy necessary to produce ~lC13 from Aye, carbon . and chlorine.

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The process conditions or the electrolytic production of aluminum have not been found to be critical with respect to the voltage applied or the current density. The temperature of the bath may vary considerably and is simply that necessary to maintain the bath molten which, depending upon the composition of thy halide salts present may be achieved within the temperature range of 150 to 1000C but generally may be in the range of between the melting point of aluminum and the boiling point of the cell components, preferably 10 to 400C
and most preferably 10 to 150C up to less than 250C above the melting point of the aluminum. The pressure conditions within the enclosed cell are not critical particularly inasmuch as there is no chlorine gas escaping as in prior art aluminum chloride salt processes. Isle CO or C02 or both may be generated from the present process, these gases are no as corrosive as chlorine. The pressure conditions, no-t being important, may range from atmospheric to 10 or more prig.

b. All Fluoride Containing Bath The Lyle cell operates chemically based upon the fact that alumina will dissolve in the cryolite-fluoride salt bath at a temperature of 950-1000C. Bayer alumina is soluble in the cruelty containing bath at a minimum temperature of at least 900C or above. Any fluoride containing bath at a temperature below about 900C Jill not readily syllables ordinary processed awry alumina and, therefore, alumina, as the sour of aluminum, cannot enter the reduction reaction .
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nor is it possible for alulllinum to be deposited at the cathode.
Without this general volubility of alumina in the fluoride salt bath, it is not feasible to electron aluminum.

It has been discovered, as one aspect of the present invention, that in all fluoride containing baths the temperatures may be in the range of between the melting point of aluminum and the boiling point of the cell components, preferably 10-400C and most preferably 10 to 150C up to less than 250~C
above the melting point of the aluminum. To electron aluminum from its corresponding oxide or other oxygen containing compound the range of bath temperatures generally would be about 670-800C and preferably 700-750C.

The important aspect of this discovery which differentiates it from the conventional procedures of the Hall-Heroult cell is that the composite anode containing the mixture of aluminum oxide and reducing agent effects a transformation of the aluminum oxide and produces ionic aluminum in the low temperature fluoride bath. The overall reaction, however, is believed to be essentially the same as the Hall cell reaction as previously stated. The aluminum is produced in liquid form on the liquid metal pool serving as the cathode. It is _ presumed that a reaction occurs at the anode surface in a unique manner that results in the reaction of aluminum oxide to I produce aluminum ions similar to the mechanism that occurs in the flail cell even though the temperature is only slightly above the melting point of aluminum.

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The importance of utilizing -the composite anode in the present invention should be quite clear because under the same conditions as that of the present invention but using a carbon or other non-consumable anode, the addition of aluminum oxide to the bath will not result in either the dissolution of the aluminum oxide or the electrode position of the aluminum.
A notable feature of the present invention is that, utilizing the composite anode in a low temperature from 670-800 with an all fluoride electrolytic bath, the Hall cell can be operated in a manner such as Figure 4 without the closed top required in the operation of the chloride bath as shown in Figure 1. The bath composition, current densities and other process parameters are not critical to the operation of the chloride bath or fluoride bath containing cell.

The principal support for the achievement of the bone-fits of the present invention lies in the use of a unique composite anode composed of an oxygen containing luminous 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 as well as with a carbon reducing agent, the means to conduct electrical current through the dielectric aluminum oxide to the reaction site for the aluminum oxide in contact with and immersed in the electrolyte. The anode also preferably provides at least in part a necessary source of a reducing agent that enables the aluminum oxide to react in the anodic environment to produce the aluminum for deposition at the cathode as aluminum metal.

The reducing agent is preferably, at least in part, intermixed with the aluminum oxide to provide intimate contact between the reducing agent and the aluminum oxide.
The reducing agent, if properly selected to be conductive may when intermixed with the aluminum oxide also fulfill the function of a conductor of electrical current to the reaction site for the aluminum oxide. Following the reaction of a particle of aluminum oxide at a particular site in contact I with the electrolyte and having present an electrical cur-rant, another particle at the same site now is uncovered and can react. This pattern occurs throughout the surface of the anode and continues until there is no more aluminum oxide to react. I the reducing agent is not conductive and is not intermixed with the aluminum oxide, the electrical conductor function must be otherwise achieved by conductor rods to maintain the aluminum oxide anodic at the reaction site.

In an aluminum chloride salt bath, the anode functions to provide a reducing agent thaw aids in the theorized reaction of the luminous source with the chloride or oxygen or both to main-lain a constant concentration of aluminum chloride. That is, the reaction which results from the dissolving of the AWOKE
mixture releases CO or COY gas rather than chlorine gas, so that the chlorine of the aluminum chloride is not dissipated, as occurs in former processes using aluminum chloride electrolyte.
The maintenance of a constant concentration of aluminum chloride is an important part of the chloride cycle of the present invent lion because it eliminates the necessity for any external no-plenishment of the aluminum chloride being electroly~ed or the discharge of chlorine on the anode.
In the all fluoride bath process, the anode of this invent lion as in the case of the chloride cycle provides the aluminum oxide that reacts in the flickered bath to form aluminum ions at a uniquely low temperature in the 670-800C range. The cell may also be open as in Figures 4, 5 or 7.
The source of the aluminum is alumina, AYE, but also it could be any aluminum oxide bearing material such as bauxite or a clay such as kaolin or other material which would react at the anode to produce aluminum tolls to be reduced to the molten metal at the cathode as in the fluoride or chloride cycle processes.
When the intermixture forms the anode, the ratio is in an amount that ranges from at least lo up, with acceptable upper limits of 7.5, 20.0 or even 50.0 or more parts by weight of aluminum oxide in the luminous material per part of the weight of the reducing agent. Preferably, for the purposes of the pro-sent invention, the amount of aluminum oxide in the luminous material intermixture will be 2.0 to 6.5 and most preferably 2.5 6.0 parts by weight aluminum oxide per part reducing agent.

i The reducing agent that may be used in accordance with the present invention is not limited to any particular material, but could be any of those materials known to be effective to rocket with the aluminum oxide. The reaction in the fluoride and chloride baths is not clearly defined but it may be that the reducing agent reacts with the Allah to produce aluminum ions that eventually deposit on the cathode and C02 at the anode.
The reaction mechanism may be the same in all chloride, all fluoride or mixed chloride/f:Luoride salt electrolytes.

Among the reducing agents that are particularly useful for alumina and other oxides are carbon or a reducing carbon compound used in the intermixture. Sulfur, phosphorus ¦¦ or arsenic may also be used independently or in combination with carbon. Carbon is particularly preferred because it characteristically has the dual capability of carrying current to the reaction site of the aluminum oxide as well as main-twining a reducing function and giving off a gaseous product at the anode.

The source ox carbon in the intermixture can be any ¦ organic material particularly those having a fossil origin such as tar, pitch, coal and coal products, reducing gases, for example carbon monoxide, and may also include natural and synthetic resinous materials such as the waxes, gums, phenolics, epoxies, vinyls, etc. and the like which may if desired be coked even while in the presence of the luminous material.

Coking of the carbon source intermixed with the aluminum oxide compound can be accomplished by known art techniques such as those used in prebaked anodes that are utilized in the Hall-Harlot cell. This is accomplished by casting, molding, extruding, etc., a composite anode such as Alopecia in the s I

Desired ratio of, for example 6.5 parts aluminum oxide to zone part carbon in the coked condition, and slowly heating the foxed anode in a nonoxidizillg atmosphere to a coking temperature of 700 to 1200C~ After callusing, the composite anode is then ready for use.

It is also, for instance, contemplated within the scope of the present invention to produce carbon as a reducing agent join the intermixture with aluminum oxide by coking the carbon source in the molten electrolytic bath both prior to and during electrolysis. Bath temperatllres typically in the range of G70 to 850C are adequate to coke the carbon source to produce the carbon necessary. The time to achieve such coking is not critical but it may require several minutes to several hours depending upon the temperature of the molten bath and the mass ¦ of the mixture of luminous source and the reducing carbon l source.
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Continuous coking is possible using the attachment clamp of Figure 4 by introducing one anode on top of the last and as consumption occurs the anode is continuously lowered until I one is completely consumed and the next takes its place, and so on. The anode may be fed continuously to the cell in the green state as in the case of a traditional Soderberg electrode. In this case, steel pins are traditionally used to make contact but the contacts could also be graphite, carbon, Tao, aluminum or composites of these. The green composite anode material is gradually coked from the heat of the cell such that the end of the anode in the salt is always fully coked to the operating temperature of thy cell. Coking in the Soderberg fashion in the ceil at 670 - 850 produces a lower conductivity anode compared to composite anodes prebaked at much higher temperatures.
The source of the entire reducing agent, as previously stated, need not be intermixed with the aluminum oxide source to form the anode. It has been found, for instance, that the only requirements for the reducing agent are that it be in contact with the anodic aluminum oxide and present in sufficient amounts to produce aluminum metal at the cathode. It is manifest however that electric current must be transmitted to the reaction site to enable the reaction to proceed.
If the reducing agent such as carbon is not intermixed with aluminum oxide to carry the current, it is conceivable that another conductor, compatible with the cell and its contents, could be used. For instance, aluminum or noble metals or high melting conductive oxides such as silver-tin oxide or Tub, either alone or as composites with carbon or graphite, may be intermixed with the aluminum oxide in amounts merely sufficient to carry electric current to the reaction site. Such amount is not critical provided the aluminum oxide is made anodic at that reaction site. Amounts as low as about 0~001 up to at least about 0.75 parts conductive material per part aluminum oxide may be used.
Greater amounts increase the conductivity at the expense of the availability ox the reactive material but are possible without any actual upper limit. Of course, there still must be present a reducing agent to achieve the necessary reaction.

lZilV75 e case Or alumina a; tic luminous material, the use of hydrate or calcined alumilla may be used. Anodes formed from hydrate alumina can show improved conductivity compared to calcined alumina but hydrated alumina, Aye x 3H20 or Al (0ll)3 alas the ~en~lency to crack during prebaked type coking and when placed in the hot bath, due to the water driven off during the coking operation With an aluminum chloride containing salt utilizing an in bath coking of the hydrated alumina, the water driven off could undesirably hydrolyze the Alec.
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Any cracking or breaking of the anode due to the expelled moisture causes no difficulty provided the membrane as shown in Figure 5 surrounds the anode. Any particles of the anode that drop off will be contained in the membrane for continual reaction. The anode may also contain any proportion of hydrated and calcined oxide to minimize the cracking.
The maximum amount of hydrated oxide that can be used affects an energy saving in calcining.
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The size and surface area of the particles making up the anode containing the alw~inum oxide have not shown any sensitivity regarding anode reaction rate. This characteristic of the present invention is in contrast to prior art experience in the reaction of Aye and carbon with chlorine as a gas-solid reaction in a furnace. In the past it has been found that tile reaction temperature and rate are highly sensitive to the particle size and particle surface areas.
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It is generally desired in the prior art to utilize alumina with a surface area in the range of 10 to 125 mug in the Alec reaction. However, in the present invention, ~2~Q~5 no sensitivity was dejected with regard to reaction rate of the anode based upon particle size or surface area. That issue, Aye with a surface area of .5m2/g or less apparently reacted as readily as AYE with a surface area of loo m go These results are based upon experiments run with anodes containing alumina having particles with differing surface area and sizes. node current densities ranging from 12 to 40 amps/in2 were run in cells with the exhaust line I connected to a starch-iodine indicator for chlorine detection.
NO chlorine gas was detected regardless of the current density or the surface area of the alumina. This suggests that if any chlorine is produced at the anode it all reacts to reform aluminum chloride or that only aluminum ions form at the anode from the AYE while the oxygen from the AYE
combines with the carbon producing COY. It is believed that to produce chlorine at the anode it would be necessary to raise the potential so high as to overcome the decomposition potential of the Alec but even then the produced chlorine would l probably react with the AYE and carton to produce moxie Alec rather than evolve chlorine at the anode.

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Anode for use in electrolysis cell may be produced ¦ in a variety of forms and by a variety of fabrication processes.
mixture of aluminum oxide material and the reducing agent may form -the anode in any convenient manner. For instance, a mixture may be bonded to a typical electrode to form a ¦ coating surrounding all or one side of the electrode as shown ¦ in Figure 2 of the drawings It is also contemplated that the Al node material may form the anode on being mounded or otherwise l formed into a suitable shape to which is attached one end of the electrode rod or pin in the manner shown in Figure 3 of the drawings. It is also possible to meet the requirements of the present invention to form the anode in the manner other than having any physical bonding directly to the electrode. It is desirable, however, that the luminous material be in intimate physical contact with the carbonaceous material or other reducer. The latter concept may be brought into being if the i mixtures of the luminous material and reducer are in the form of a homogeneous mixture of powders, small pellets of the mixed powders, or larger composite briquettes of such mixed materials I that may have been wormed by molding or extrusion into various sizes from .001 inch to 1 inch or more. Uniformity of the distribution of the carbon and aluminum oxide has been found to be desirable to attain maximum anode efficiency during its dissolution or reaction under electrolysis.

row hold the aloneness material and the reducing agent forming the Andy materials in the region of the electrode and thus in combination forming the anode, a container in the form of a porous membrane may be utilized.

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For successful commercial use, the anode should be as conductive as possible. Since the anode of the present invention is not solid or pure carbon as is traditionally used l in the Hall cell, it will be less conductive because of the I presence of the luminous compound. If the anode were permitted I to become as resistive as one salt electrolyte then the heat balance can be affected due to overheating that can occur as a ¦ result of passing thy same current through the more resistive I anode. For instance, when using a solid composite anode such I as shown in Figure 3 in the cell of Figure 1, it is necessary for the electric current -to travel through the anode from top I to bottom, with power losses translated to heating of the bath.
If It is therefore desirable to construct an anode to have as high Al a conductivity as possible. Obviously, the more conductive the anode material, the lower the power consumption for winning metal but in any event the conductivity of the anode should be greater than the conductivity of the salt for optimum operation.
¦ Particularly when it is desired to achieve the goal of maximum I production of aluminum with minimum power usage, the resistance ¦ of the anode becomes significant.
It has been found that the conductivity of the anode I varies considerably depending on the manufacturing process.
The parameters which have been found to affect conductivity are the ratio of binder carbon material such as pitch, carbon or I coke particles included in the composite anode as the source ¦ of the reducing agent and the -type of aluminum oxide. The ¦ critter the carbon content of the anode, within the previously ¦ specified ratio of aluminum oxide to reducing agent, the greater If .

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If .

the conductivity. It is possible, for example, when using ¦ a ratio in the range of 4/1 to 6/1 aluminum oxide to carbon to construct a solid composite anode that has at least a tenth the conductivity of a standard Hall-Heroul~ anode In order to reduce the power loss through the composite anode, several alternatives are also shown in Figures 2, PA, 2B and PA.

To achieve higher conductivity and reduce power loss l through the composite preba:ked anode another embodiment utilizes ¦ one or more conductive cores 36 or 37 positioned in the anode ¦ as shown in Figures 2, PA and 2B or a plurality of vertically ¦ arranged conductor pins 39 as shown in Figure PA.

The composite anode 26.~ shown in Figure 2 has a conductive central core 36 that can be carbon or graphite molded into the composite anode with the composite anode material 38 molded or coated into an annuls thereabout.
The central core 36 may also be a metal such as the same metal being deposited, for example, aluminum. The exterior Jo of the conductor 36 is coated on one side for bipolar us or surrounded on both sides for monopolar use by a matrix 38 of composite anode material comprising the mixture of aluminum oxides and reducing agent as previously described. When coated on a single side a bipolar operation is anticipated.
The term "oxides" should be interpreted to include the silicates ¦ which often are a combination ox the metal oxide and silicon ¦ oxide or any other oxygen containing compound of the aluminum ¦ to be deposited.

LQ~5 For lyric size anodes another altcrnat~ embodiment is shown in Figure I end 2B. To improve conductivity, primary grade purity aluminum rods 36 and 37 are preferred to be used as electrical conduction buses in a matrix of the composite anode composition 38 that may be of the prebaked or Soderberg type. Since primary grade aluminum is used to form the conductor rods, it will molt: as the anode is consumed and join the cathode metal for a continuous cycle. The sods ware spaced such that the voltage drop is minimized relative to the conductivity of the composite anode. In Figure 2B
the conductor rods 36 are shown to be connected to a plate 40 supported by a central conductor 41.

The number and size of the conductors 36 and 37 are selected based on anode size, current density of the anode, cell size, operating temperature and heat transfer such that the aluminum conductors 36 and 37 melt at the same rate that the matrix 38 of the anode LO consumed. The unique advantage of the anode embodiments shown in Figures PA and 2B is the avoidance of large voltage drops in the relatively highly resistive anode so as to permit the process to be operated at substantially reduced power consumption. The size of the aluminum rods may fall within the diameter range of 0.0625 to 3.
` inches preferably 0.125 to 2.0 inches most preferably 0~25 to lo inch.

¦ For achieving desirable conductivity in the anode, Thea spacing between the outer surface of the composite anode material 38 and the surface of any aluminum rod as in Figure 2, I or 2B and spacing between the outer surfaces of these ~2~75 al~ninum rods in Figure PA and 2B is not critical and may range from 0.125 to 24 inches, preferably 1~0 to 6.0 inches and most preferably 1.5 to 4.0 inches. As an example, if the conductivity of -the composite anode is approximately 0.1 off standard prebaked Hall cell anode then aluminum rod spacing of approximately 3.0 inches will result in an acceptable voltage drop.

Since Lowe operating temperature of the cell is usually in the 700 - 750C range the aluminum rods can be sized such that they will melt approximately a-t the same rate as the anode is consumed and will thus conduct power to the bottom of the anode. If the diameter of the aluminum rod is too large, it will not melt and salt will freeze over its surface which results in the anode being consumed leaving an aluminum stub that will short to the cathode as the anode is advanced. If the rod diameter is too small it will melt back too far into the anode which results in too large a voltage drop due to the longer conductivity path. It is desirable that the aluminum rods melt back in-to the anode to a slight degree rather than remaining flush with the bottom surface of the anode. This is so that anodic oxidation of the aluminum rods will be minimized. Desirable melt back distance is based upon that which provides the minimum voltage drop coupled with -the minimum anodic oxidation of the aluminum rods. Should the rods remain flush with the bottom surface of the anode, there would be a tendency for aluminum ions to sass into the bath from the rods (as in a refining operatioll) as well as from the composite anode material, thus lowering the cell's ~aradaic efficiency float can be b~lancecl such that the conductance from the bath up through the anode and power generated through the conductors is balanced to achieve the desired amount of melting of the conductor aluminum rods.

Figure 3 discloses another alternative embodiment of the composition of an anode electrode as shown at 26B. In the embodiment electrode EYE is composed of a composite 38 which is the same material as the coating 38 in Figure 2 and is formed into a suitable shape for use as an electrode. This form of the electrode may be molded about a stub or pin electrode 42 which extends out from the upper end of top body of the electrode 26B for connection of the usual electrical circuit. Alternatively electrode 26B is molded and then stub 42 is inserted by known art techniques such as utilized with prebaked Hall cell anodes.

Another alternative embodiment is that shown in Figure PA wherein an anode 26B is illustrated having the same composition as previously described but being provided with a plurality of pairs of vertically arranged conductor pins I US to which fewer pair of pins, a bus AYE is attached directly as in the Soderberg type corlnections The positioning of . the pins 39 is not critical and they may be perpendicular to the anode axis or angled as shown. As the composite anode material is consumed the bus connections AYE are moved upwardly to the next higher pair of pins. The pins being composed of primary trade aluminum are also consumed and as previous mentioned ore added to the pool of deposited . lZl~L075 ` I

alumillum. Alternatively ill Lens may be of iron as typically used in the Soderberg connection and the pins are removed as the anode is consumed.

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The embodiments of Figures 12 and 13 illustrate a variation of conducting electrical energy -to the working surface of the anode. As shown blocks off the composite anode A are laminated with sheets of aluminum metal 108. These sheets act precisely as the aluminum rods in Figures I and 2B. The shape and number of laminate are not critical. The blocks may lie in continuous form and fed into the cell through clamp 47 as in Figure 4 to which along Wit to the aluminum sheets 108, the electrical connection is made.

The number, spacing end thickness of the aluminum sheets 108 are determined by the same factors as described with respect to the conductors 36 and 37~ Generally the aluminum sheet thickness will range from .001 to .5 inches thick and preferably .010 to .375 uncles and most preferably .010 to .25 inches thick. The aluminum sheets must be of sufficient thickness to conduct the necessary current to avoid major voltage drop and also melt into the cathode pool as the anode is consumed. The spacing between the aluminum sheets 108 is such as to avoid excessive voltage drop through the composite block as set forth with respect to conductors 36 and 37.
Generally the spacing Jill range from .125 to 24.0 inches preferably from 1.0 to 6.0 Lynches and most preferably 1.5 - 4.0 inches.

s i.

The Membrane _ I

The men~rane as shown in Figure 5 of the drawings is designed to have a tripartite function or capability.

First, the membrane acts as a separator or quiescent barrier between the molten cathodic metal phase and the source of anode material to be electrolyzed. With the use of the membrane of this invention, the spacing can be reduced sub-staunchly to achieve significant increases in conductibility and efficiency without any turbulent effects that could otherwise produce a reduction in the efficiency or quality of the aluminum product.

Second, in the present invention, the membrane physically restrains materials of the composite anode that, for instance, may include the luminous raw material and the reducing agent.
This restraint maintains these materials close to the electrode to form an anode for production of aluminum ions in the most efficient manner. The membrane also prevents mixing of the raw materials with the molten aluminum at the cell bottom. Should a hydrated metal oxide, such as the hydrated alumina, be used as on of the anodic materials, the membrane holds any of the pieces of the anode that may crack off due to the evolution of moisture from the alumina during bath coking. These pieces continue to be a source of aluminum through the reduction reaction as long as they are within the anode circuit within the membrane.

if US
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Third, the membrane permits the free passage of ionic substances and dissolved solids in the electrolyte but will not pass and will substantially reject molten aluminum and undissolved solid materials that constitute the usual impurities present in the alumnus source and prevent the contamination of the cathodic deposition.

The external shape of the membrane is not important and may be in the form of a cylinder, prism, etc., or portion thereof For instance, the membrane may have a three or four-lo sided shape with a bottom end thus form an enclosed container.
This container is so designed to hold the anodic raw materials for reaction in the salt bath.

Due to the corrosive nature of the molten salt bath the selection of the materiels to form the membrane is important to the life of the cell and the success of the process. If the electrolyte to be used is an all chloride bath, the choices for the membrane are somewhat greater due to the reduced corrosive character of such a bath as compared to a bath containing fluorides. Baths containing some fluorides are preferred, however, because of their lower volatility.

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¦ The all fluoride bath possesses other advantages as set forth above. Materials suitable for use in a fluoride bath would of course be useful in the less corrosive chloride bath.

Among the materials that have been found to be useful include vitreous carbon foam, carbon or graphite as a porous solid or porous solids of refractory hard metals such as:
the nitrides of boron, aluminum silicon (including the oxynitride), titanium, hafn.ium, zirconium and tantalum; the silicides of molybdenum, tantalum and tungsten; the carbides off hafnium, tantalum, columbium zirconium, titanium, silicon, boron and tungsten; and the brides of hafnium, tantalum, zirconium, columbium, titanium and silicon. Other refractory hard metals as known in the art may be found useful to form the membrane provided that they are resistant to the molten salt bath.

The refractory hard metals forming the membrane of the present invention may be lade into the Norm of a cloth, melt felt, foam, porous Sinatra. solid base or simply a coating on such a base, all of which are known in the art for other ~20 purposes. The membrane must also meet particular standards of through passage porosity and connected pore size.

These two characteristics may be defined as follows:
..
through passacJe porosity - the percentage of the total volume of the membrane that is made up of passages that pass through from one side of the membrane to the other;

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¦ connected pore size - the smallest diameter ox a passage through the membrane.
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The through passage porosity varies with the nature of the membrane material, the temperature of the molten bath and the salt composition but the common characteristic of useful membranes is that the porosity must be sufficient to pass all the metal ions such as aluminum and all the electrolyte salts without passing the undissolved impurities. It has been found that the greater -the porosity, the greater is the current flow and, therefore, the greater the electrical efficiency of the cell. The porosity may vary from I to 97% or more, but generally is in the range of 30~ to 70%. The preferred porosity to achieve the greatest efficiency is in the 90% to 97% range. A vitreous carbon foam, for instance, is capable of yielding such a high pearliest and retain sufficient mechanical strength.

The connected pore size must be small enough to reject the solid impurities that have not been dissolved but large enough to pass the ionic and dissolved particles. Generally, the acceptable pore size is between on micron and one 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 Melbourne, tile greater the electrical resistance. It is 12110~5 therefore desirable to use as thin a membrane as is practical consistent with the porosity end pore size standards as well as the mechanical strength of the membrane in position in the cell. The preferable -thickness is .125 to .5 inch but may be as thick as 2.0 inches or more.

Typical membrane materials that have been found useful include but are not limited to vitreous carbon foam, carbon or graphite in the form of a porous solid, felt or cloth, aluminum nitride, silicon nitride, silicon carbide, silicon oxynitride, boron nitride and titanium nitride as a porous solid, as a cloth or as a coating on the surface of a vitreous carbon foam or porous graphite. aluminum nitride appears to be the most desirable material. It has been found that aluminum nitride can conveniently be formed in a porous structure by first making a porous alumina structure then impregnating with carbon followed by heating to 1750C in a nitrogen atmosphere to convert the alumina to aluminum nitride. Such a procedure results in a strong porous structure that is chemically compatible with the corrosive salt environment and the molten aluminum.

The Molten Bath Composition The electrolytic bath ox the present invention can vary considerably in comparison to the typical Hall cell salt composition. In -toe present invention the bath composition may include any halide salt, particularly, chloride and fluoride are favored. any alkali or alkaline earth metal such as particularly sodium, potassium, lithium, calcium, magnesillm, barium and the like may be used to form the halide salts.
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Lowry is no critical composition or range of proportions desired or necessary. It has been observed that no aluminum salt need initially be present in the electrolyte to produce aluminum under electrolysis utilizing the composite anode For example, a salt electrolyte containing only alkali and/or alkaline earth halides will produce aluminum metal at the cathode utilizing the composite anode and with no Lund effect."

It is generally preferred for the salt bath to initially contain an aluminum halide, although this is not necessary to practice the invention. In the case of the Alec containing baths which may contain only chloride anions or both chloride and fluoride anions, the aluminum chloride concentration may be 2 to GO% but may also be in the range of I to 95~ by wright Alec. The all fluoride bath may include the same fluoride salts as set forth above and may as well contain aluminum fluoride in any proportion desired.

Among the advantages and disadvantages of the various electrolyte types are that the all chloride bath has very low tolerance to oxide contamination, but has very high conductivity I and is the least corrosive to refractories and cell components.

In fluoride containing electrolytes the ¦¦ aluminum deposits as droplets which agglomerate and pool I, readily, but the corrosivity of the electrolyte to refractories and cell components is greatly increased.

¦ A lithium component of any electrolyte will increase the conductivity but is expensive and increases the cost of the electrolyte. This has to be balanced in any operation as to the electrolyte cost, conductivity of the electrolyte and the resultant power consumption of producing the aluminum.

The preferred electrolyte is a balance of economics of the salt components, conductivity, corrosiveness to refractories and cell components, tolerance to oxide contamination and l agglomeration of the deposited aluminum into a pool for easy I harvesting.
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If 47 --OX ISLES

Example 1 inn Figure 1, the anodes are graphite plates and the ¦ cathode electrode is a titanium dioxide plate. The anodes were prepared with a coating 38 as shown in Figure 2 which consisted of Bayer Process purified AYE calcined to 1000C
and mixed in a weight proportion of five parts AYE to one part carbon in the coked stage. The carbon was obtained by mixing the Aye with a finlike rosin and gradually heating to 1000C in an inert atmosphere for coking the finlike resin to carbon. The electrode coating was prepared by mixing the AYE and finlike resin, troweling or otherwise applying the mixture on the electrode, and heating to coking temperature.
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¦ The electrolyte consisted of an equimolar mixture of sodium chloride and aluminum chloride forming the double salt NaAlC14 at about 150C. The temperature of the cell was raised to 700C and electrolysis of the AYE conducted for several hours which produced a layer of molten aluminum on the bottom of the cell. Examination of the anode revealed that the coating had dissolved and aluminum was deposited at the cathode. This deposition of aluminum was equivalent to the aluminum content of the AYE dissolved at the anode.

Lowe overall controlling reaction is believed to be the ionization of the OWE in the anode with the carbon reacting to form primarily COY. During the electrolysis there was no evidence of any chlorine gas being liberated at the anodes and in the exit tube The exit gas was analyzed and determined to be primarily COY.

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lZ1~075 example 2 If I The electrolyte salt composition consisted of 63% Nail, 17% Lick, 10~ Lift 10~ Alec and the electrode coating of Figure 2 was prepared from standard bauxite OWE and a petroleum tar pitch which was coked to produce an AYE to carbon (as coked) ratio of 5.7 to 1. The electrolysis was conducted in the Figure 1 cell at a temperature of 750C.
The spacing between anode and cathode was 1/2 inch which produced an electrode current density of 15 amps/in2 at an imposed voltage of 2.5 volts. There was no chlorine gas detected as being released from the anode which is indicative ox the AYE in the bauxite reacting so as to prevent any free chlorine from being formed in the anodic cycle. Aluminum was deposited which settled to the bottom of the cell. The harvested aluminum was produced at a Foredeck efficiency of 92~ with an energy consumption of 3.67 Kwh/lb.

zanily 3 The electrolyte salt composition consisted of 10% Nail, ~50% Cook, 20~ Cafe, 20% Alec. The electrode coating of '20 Figure 2 was prepared as in Example 2 but only on one side of the electrode. The electrical connections were made such that the anode adjacent to the exit tube was connected to the positive terminal and the negative terminal to the electrode most remote to the exit tube. The coated sides of the electrodes 25 and 26 cad, laced away from the exit tube and toward the cathode. Electrode 24, the cathode, was not coaled. This results in electrode 25 not being physically connected to the direct current power supply. That electrode then becomes bipolar. The side coated with the AWOKE

slakes mixture is thus positively charged. The side of bipolar electrode 25 nearest the exit tube becomes negatively charged upon which aluminum is deposited and sinks into the molten pool. Aluminum also deposits on the negatively charged electrode 24 and sinks into the molten pool. The temperature of the cell operation was 800C and the imposed voltage was

3 volts with respect to each electrode or a total of 6 volts across the -terminals. This imposed voltage with an electrode spacing of 3/4 inch resulted in an electrode current density of 12 amps/in2.

example 4 The anode electrodes were composed of titanium debarred rods and the cathode electrode was also titanium debarred.
The anodes were coated with bauxite as in Figure 2 which has been calcined at 600C, mixed with finlike resin, and coked at 800C. The ratio of aluminum oxide in the bauxite to carbon after coking was 6 to 1. The electrolyte salt composition was 20~ Nail, 30~ Cook, 10% Cafe, 4% Nay, 36~ Alec and was operated at 750C at an electrode density of 15 amps/in2~
This resulted in 4 volts at an electrode spacing approximately 3/4 inch. No chlorine gas was observed in the discharge exit port which shows that if any chlorine was generated at the anode it reacted with the bauxite to reform metal chlorides Lucia were then deposited as metal at the cathode. The composition of the-aluminum deposited in the molten pool was 97~ sure COntainincJ .5% Six 1.5~ Fe and I To with minor other constituents.

s Example S

The electrolyte salt composition consisted of 65~
Cook, 20~ Cafe, I Nay, end 10% ~lC13. The anode electrodes wore as shown in Figure 3 made an aluminum oxide to carbon ratio of 5.5 to 1 using a copper bus pin. The aluminum oxide was commercial grade Alcoa* I and the carbon was obtained from a mixture of finlike and pitch which was coked to 1100C. Electrolysis in a cell as shown in Figure 1 produced aluminum metal that settled into the pool at the bottom of the cell. No chlorine gas was detected in the exit tube. The aluminum produced had a purity of 99.9%.
I
Example 6 The electrolyte salt composition consisted of 30% Nikolai I Lick, 27% Cook, 20% Cafe, 10~ Lit and I Alec. The anode electrodes were graphite coated with a clay mineral kaolin and carbon as in Pig~lre 2 to yield a ratio of 5~6 Aye in the clay to 1 carbon after coking. Electrolysis yielded aluminum without any chlorine gas being detected in the exit tube while the anode coating dissolved as a result 2Q of electrolysis.

* Trademark::

1~11075 Employ 7 The electrolyte of Example 4 was used and the anode electrode of Figure 2 was prepared by mixing bauxite and a finlike resin in a consistency to approximate that of a viscous gel and which would yield a ratio of contained aluminum oxide to carbon of 5.5 to 1 upon coking. The ~auxite-phenolic was troweled onto the graphite or use as an anode and dried to 150C which produced a hard coating But not one fully cured. The electrode was then gradually lowered into the salt electrolyte which was at a temperature of 780C. After a five minute period to allow volatile From the finlike to escape and coking to occur, electrolysis was conducted which produced aluminum and anode dissolution without the evolution of any chlorine gas in the exit tube.

example 8 The cell in Figure utilized a porous membrane of aluminum nitride material 3/16 inch thick having 50% porosity with a pore size in the range of 12 to 24 microns. The aluminum nitride was obtained by impregnating an alumina porous body with carbon and then heating to 1750C in a nitrogen atmosphere. The anode conductor was a graphite rod and the anode luminous material was a Bayer AYE and carbon mixed powder in a ratio of 6 to 1. The electrolyte salt composition was 20% Nail, 25% Lick, 30% Lift 25% Alec and electrolysis was conducted at 720C. 'Lowe spacing between the membrane and the aluminum pool was approximately 1/2 inch and electrolysis was run at an anode current density of 1.

10 amps/in2. Lucy resulted in a voltage of 2.8. The aluminum was produced at an efficiency of 92~ and had a purity of 99.5~.

example 9 A salt composition consisting of 12~ Nay, 25~ Lift 28 Nail, 15~ Lick, 10% Alpha and 10~ Alec was melted into a cell with straight side walls. A 2" thick aluminum pad was melted on the bottom of the cell and the operation temperature was adjusted to 700C. Utilizing an anode as shown in Figure PA a spacing between the bottom of the anode and the aluminum pad of 1-3/4 inches was set. At an anode current density of 6 amps/in2 the cell potential was 3.5 volts.

After 8 hours electrolysis, the anode was removed from Thea cell and placed in a cell with 45 side walls such as shown in Figure 7. After a few hours electrolysis the anode had eroded such that its sides were parallel to the cathode side walls. The anode immersion depth in the salt was three inches Utilizing the same total current as in the straight sided cell, the potential was 2.45 volts. This lowered potential due to side anode erosion at 90~ current efficiency and at a constant production rate reduces the power cons~nption from 5.25 kwh/lb to 3.68 kwh~lb which is a reduction of 1.57 quill. _ . Jo lZ11075 A salt composition consisting of 20~ Nikko, 25% Lick, 25~ Lift lost Nay, 10~ ~lF3, 10% Alec was melted in a cell with straight side walls. 2" thick aluminum pad was melted on the bottom of the cell and the operation temperature adjusted to 700C. Utilizing a composite anode 12 inches long with a copper bus bar fitted into one end in the traditional manner, the anode-cathode spacing was adjusted to 1-3/4 inches. it an anode current density of 6 amps/in2 the cell potential was 5.75 v. after equilibrium had been reached.

An identical anode but with a 45 slope on the end opposite the bus bar was inserted into a cell with 45~ side ; walls such as shown in Figure 7. Immersion depth of the anode in the salt was three inches. After a few hours electrolysis to assure the angle on the anode was the same as the side walls of the cell the potential required to achieve the same total current Acadia been used in the straight sided cell was 4.4 v. This lowered potential due to side anode erosion at 90~ current efficiency and at constant production rate between the two cell types, reduces the power consumption from 8..63 kwh/lb to 6.6 kwh/lb which is a reduction of 2.03 kwh/lb.

The reduction in power consumption at a constant current between thought used in the tr2,diti.0nal cell where the bottom of the anode only is eroded and that in a sloped cathode cell is obvious from this example.

lo Exhume An anode was made utilizing Alcoa* I Allah mixed with cold tar pitch and finlike and molded in a closed die with heat applied to harden the finlike component The ratio of components was such that after coking the composite anode contained 17% carbon and 83~ Al o . The electrolyte consisted of 20~ Nail, 25% Lick, 30~ Lit and owe Nay and was operated at 700C. A cell as shown in Figure 7 was used but no aluminum pad was added. After several hours electrolysis at about 700C aluminum collected in the well showing the composite anode will produce aluminum under electrolysis without the initial use of an aluminum salt in the electrolyte.
These results suggest the reaction mechanism of the composite anode is to release aluminum ions into the salt electrolyte which are reduced at the cathode and the carton in the anode reacts to produce COY, Example 12 A straight sided cell such as shown in Figure 5 was utilized, but without the membrane 68 and anode rod 52. Instead a carbon cylinder was mounted just above the salt electrolyte layer into which was inserted a short anode section such as shown in Figure PA. On top of the prebaked short anode and around the conductor rods 37 a mixture of Aye, petroleum coke powder and a mixture of tar' and pitches were added. The mixtures of OWE coke peculiar and tars/pitches were such as to yield 18% carbon and 82% Alrlo3 when coked to the salt electrolyte temperature of ,'40C. salt electrolyte consisting * Trademark I I

of 10% Nay, 25~ Lift 20% Nail, 15% Lick, 20~ Alpha and 10 Alkali was utilized. Electrical connection was made to conductor rods 37 with clips in the cool area above the level I Soderberg type anode composition in the carbon cylinder.
Electrolysis was conducted at 10 amps/in2 anode current density with a spacing of 1-1/4 inches between the aluminum pool and anode. Electrolysis was continued with additions of arson tar/pitch in the carbon cylinder and continuous feed of the anode which hearkened and coked as it entered the salt electrolyte. The aluminum conductor rods melted as the anode was consumed and joined the cathode pool 32 of aluminum.

similar run was made utilizing a carbon rectangle, rectangular prebaked blocks and aluminum sheet as shown in Figure 13. The aluminum sheets were .060 thick and the prebaked blocks were 2.0 inches thick. Electrical connection was made utilizing rollers on each aluminum sheet. As the anode was advanced additional prebaked blocks were inserted between the aluminum sheets.

.

Claims (43)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In an apparatus for the electrolytic production of metal such as aluminum from metal oxides the improvement comprising:
an anodic body comprising a mixture of an oxygen-containing compound of the metal and an electrically conductive reducing agent, said anodic body including at least a portion thereof having an active surface and adapted to be immersed in an appropriate electrolyte with said active surface of said portion adapted to be positioned in opposed relationship to but spaced from the surface of a cathode for providing an active anode surface at which the metal oxide may be converted to metal ions recoverable as molten metal at the opposing surface of the cathode, conductor means of higher electrical conductivity than said anodic body in physical contact with said anodic body, said conductor means being adapted to conduct substantially the entire anodic current to said portion when connected to a source of electrical power, said conductor means extending to said portion of said anodic body and having an end thereof positioned at least approximately adjacent said one active surface for transmitting anodic current directly from said conductor means to at least the body adjacent the end of said conductor means and to said active surface thereby providing a short, low resistance current path through the body to said surface, said conductor means comprising at least one member adapted during the electrolytic production of the metal to present the end of said conductor means relative to said active surface in substantially unchanged electrical conductivity as said anodic body at the surface is consumed in the electrolytic process.

2. The apparatus as defined in Claim 1 wherein said conductor means is bonded to the anodic body.

3. The apparatus of Claim 1 wherein said metal is aluminum and said conductor means comprises a plurality of spaced apart aluminum members having axes extending through said anodic body.

4. The apparatus of Claim 3 wherein said conductor means comprises a plurality of spaced apart aluminum members with a spacing between adjacent aluminum members in the range of 1 to 6 inches.

5. The apparatus of Claim 4 wherein said spaced apart aluminum members have a cross-section such that each said member will melt at substantially the same rate as said mixture is consumed.

6. The apparatus of Claim 3 wherein the plane of said active surface is inclined relative to the axes of said conductor means.

7. The apparatus of Claim 1 wherein said end of said conductor means is recessed from said surface.

8. Apparatus as defined in Claim 1 wherein the conductor means comprises a conductor clamp member in external contact with said anodic body for contacting the conductive member at a position near the termination of the anode in the electrolyte.

9. Apparatus as defined in Claim 1 wherein the anodic body mixture is in the form of small particles and confined in a membrane porous to liquid electrolyte constituents, said particles being held in electrical anodic connection with said conductor means for releasing metal ions from the metal compound solely by the anodic chemical reaction as the sole source of metal produced.

10. The apparatus of Claim 9 wherein said membrane is formed from a material selected from the group consisting of a vitreous carbon foam, graphite or carbon solid, the nitrides of boron, aluminum, silicon (including the oxynitride), titanium, hafnium, zirconium and tantalum; the silicides of molybdenum, tantalum, and tungsten; the carbides of hafnium, tantalum, columbium, zirconium, titanium, silicon, boron and tungsten; and the borides of hafnium, tantalum zirconium, columbium, titanium and silicon, and said material having a connected pore size of a diameter sufficiently small to screen out said mixture and sufficiently large to pass said aluminum ions.

11. The apparatus of Claim 9 wherein the reducing agent comprises carbon and the anodic body mixture comprises a plurality of bodies having the carbon and an aluminum compound bonded together.

12. The apparatus of Claim 9 further including a bipolar electrode of higher electrical conductivity than the particles and, in contact with said particles.

13. The apparatus of Claim 12 wherein bipolar electrode faces are presented respectively by said conductor means and said anode body.

14. The apparatus of Claim 13 wherein said conductor means cooperates with said membrane to form a compartment containing said anode body.

15. The apparatus of Claim 14 wherein said conductor means is composed of graphite.

16. The apparatus of Claim 14 further including a plurality of spaced apart compartments with each compartment containing said particles.

17. Apparatus as defined in Claim 1 wherein said anodic body comprises at least two adjacent members, conductor means extends substantially through the anodic body and is recessed from the face of the anodic body making contact with the electrolyte and comprises a metallic sheet positioned between the two adjacent members to form a laminated structure therewith.

18. The apparatus of Claim 17 wherein the reducing agent is a carbonaceous material of a character and quantity which upon coking provides a reducing agent in a ratio by weight of 1 part carbon to at least 1.5 parts of metal oxide.

19. The apparatus of Claim 17 wherein said metallic sheet is sized such that it will melt substantially at the same rate as said mixture is consumed.

20. Apparatus as defined in Claim 1 wherein said conductor comprises a bipolar electrode structure presenting anode and cathode faces for operation in electrical contact with said electrolyte, the anode face of said electrode structure comprising said mixture of metal oxide and said reducing agent with said conductor means being covered on one face only with said metal oxide and reducing agent.

21. Apparatus as defined in Claim 1 wherein the conductor means is axially disposed through the anodic body, wherein cathode and anode surfaces are positioned in a parallel relationship, means for feeding the anodic mixture along a vertical feed axis as the metal compound is consumed to maintain a substantially constant voltage drop while maintaining a substantially constant anode-cathode spacing through the electrolyte, and wherein the conductor means comprises at least one metallic member of a cross-section that will melt and sink into the electrolyte along the axis of the anodic body during the electrolytic production of said metal at substantially the same rate at which the mixture is consumed.

22. The anode improvement as defined in Claim 21 wherein said conductor means has a substantially constant cross-section along the feed axis to establish said \

current flow path through the mixture as the anode mixture is consumed.

23. An electrolytic cell for the production of aluminum comprising, in combination:
an electrolyte disposed at a predetermined level in the cell, said electrolyte including ions selected from the group consisting of chlorides, fluorides or mixtures thereof, a cathode immersed in the electrolyte presenting a surface for electrolytic winning of molten aluminum, an anode comprising a body of said anodic mixture of an oxygen containing compound of aluminum and an electrically conductive reducing agent held together in anodic contact which serves as the sole source of aluminum ore and is consumable in the electrolytic production of aluminum, said anode including at least said portion thereof immersed in the electrolyte with at least said active surface of said portion positioned in opposed relationship to but spaced from the surface of said cathode for providing an active anode surface at which the aluminum oxide may be converted to aluminum ions recoverable as said molten aluminum at the opposing surface of said cathode, said conductor means extending to the said portion of said anodic body below the level of said electrolyte and having an end thereof positioned at least approximately adjacent said one active surface for providing short, low resistance current paths from said end of said conductor means through the body to said active surface, and means for connecting a source of electrical power to said conductor means and said cathode, said conductor means being of a material and cross-section for conducting substantially the entire anodic current directly from said power source to at least the mixture adjacent the end of said conductor means and to said active surface and comprising means maintaining the position of the end of said conductor means relative to said active anode surface substantially unchanged as said anodic mixture at said active surface is consumed in the electrolytic process.

24. The apparatus of Claim 23 wherein the material of said conductor means comprises aluminum of a cross-section proportioned to prevent said aluminum from melting into the electrolyte during the electrolytic production of said molten aluminum at a rate substantially in excess of the rate at which said anodic mixture is consumed.

25. The apparatus of Claim 24 wherein said conductor means comprises a plurality of conductors extending through said anodic body and spaced from each other a distance in the range of 1 to 6 inches.

26. The apparatus of Claim 23 wherein said anodic body is formed as a plurality of small particles of aluminum oxide and said reducing agent, and a membrane containing said particles with said membrane having a pore structure of a size to prevent passage of said particles through the membrane but to permit free passage of ionic aluminum and electrolyte for reaction of the particles within said electrolyte at said active surface.

27. The apparatus of Claim 26 wherein said membrane is formed from a material selected from the group consisting of a vitreous carbon foam, graphite or carbon solid, the nitrides of boron, aluminum, silicon (including the oxynitride), titanium, hafnium, zirconium and tantalum; the silicides of molybdenum tantalum and tungsten; the carbides of hafnium, tantalum, columbium, zirconium, titanium, silicon, boron and tungsten; and the borides of hafnium, tantalum, zirconium, columbium, titanium, and silicon.

28. The apparatus of Claim 23 further including means for replenishing the portion of said anodic body immersed in the electrolyte as it is consumed.

29. The apparatus of Claim 28 wherein said replenishing means comprises means for advancing said anodic body toward said cathode surface.

30. The apparatus of Claim 28 wherein said anodic mixture comprises loose particles, and compartment means for containing said particles and holding them in anodic contact with said conductor means, said replenishing means comprising means for feeding additional particles of said mixture into said compartment means as said mixture at said active surface is consumed.

31. The apparatus of Claim 29 wherein said conductor means is bonded to said body and advances with said body.

32. The apparatus of Claim 23 wherein said active anode surface is spaced from said cathode surface a distance on the order of 1 inch or less.

33. Apparatus as defined in Claim 23 having a bipolar electrode positioned in the electrolyte between said anode and said cathode, said bipolar electrode being covered on one side only with said compound and said reducing agent and being in electrical contact with said compound of aluminum and said reducing agent for bipolar electrolysis.

34. The apparatus of Claim 23 including, said oxygen compound of aluminum being Al2O3 and being intermixed with said reducing agent in the amount of 1.5 to 50.0 parts by weight of Al2O3 per part reducing agent.

35. The apparatus of Claim 34 said reducing agent being carbon.

36. The apparatus of Claim 23 wherein said electrolyte comprises substantially all fluoride salt, and means for establishing the temperature of the electrolyte between about 700 to 800°C during electrolysis.

37. The apparatus of Claim 23 wherein said reducing agent is carbon, said oxygen compound of aluminum is Al2O3 intermixed with said reducing agent in the amount of 1.5 to 20.0 parts by weight of Al2O3 per part reducing agent, said electrolyte is substantially all fluoride salt, and means for establishing the temperature of the electrolyte between about 700°C and 800°C during electrolysis.

38. An electrolytic cell for the production of a metal comprising in combination, an electrolyte disposed in the cell, said electrolyte including ions selected from the group consisting of chlorides, fluorides or mixtures thereof, a cathode immersed in the electrolyte presenting a surface for electrolytic winning of molten metal, an anode body comprising a mixture of an oxygen containing compound of the metal and an electrically conductive reducing agent which mixture serves as a sole source of the metallic ore and is consumable in the electrolytic process, said body having at least one active surface positioned in opposed relationship to but at all positions equally spaced from the surface of said cathode for providing an active anode surface at which the metallic oxide may be converted to metal ions recoverable as said molten metal at the opposing surface of said cathode, longitudinally extending conductor means of higher electrically conductivity than said anodic mixture and being covered on at least one face thereof with said mixture, said conductor means including at least one laterally extending branch thereof extending through said anodic body and having an end thereof positioned at least approximately adjacent said one active surface for providing short low resistant current paths from said one end through the mixture to said active surface, and means for connecting a source of electrical power to said conductor means and said cathode whereby substantially the entire anodic current flows directly from said power source through said conductor means and at least the mixture adjacent the end of said conductor means and therefrom through the electrolyte to said active surface.

39. The cell of Claim 38 wherein said conductor means is of graphite.

40. The cell of Claim 38 and further including a membrane porous to electrolyte, said membrane cooperating with said conductor means to form a compartment for said mixture.

41. The cell of Claim 38 and further including a membrane porous to electrolyte and providing a compartment for said anodic mixture.

42. A cell as defined in Claim 38 having means disposed therein for recovering the molten metal from the electrolyte in a segregated zone positioned to prevent the metal from electrically shorting the electrodes.

43. An electrolytic cell for the production of magnesium comprising in combination, a housing having sidewalls and a bottom surface, an electrolyte in the cell, said electrolyte including ions selected from the group consisting of chlorides, fluorides or mixtures thereof, a cathode immersed in the electrolyte presenting a surface for electrolytic winning of molten magnesium, an anode comprising a particulate mixture of an oxygen containing compound of magnesium and an electrically conductive reducing agent, which mixture serves as a sole source of magnesium ore and is consumable in the electrolytic production of magnesium, said anode being immersed in the electrolyte beneath said cathode surface with the upper surface of said anode providing an active anode surface, a plurality of conductor means of higher electrically conductivity than said anode projecting upwardly from the bottom surface of said cell, said conductor means extending internally through said anode with each conductor means having an end thereof positioned at least approximately adjacent said upper surface of said anode, and means for connecting a source of electrical power to said conductor means and said cathode.