The aluminum smelting from alumina in the Hall-Heroult cells can be dramatically improved by using one or a combination of the following features together or in alternative to the Bayer alumina as feedstock: Al.sup.+++ alumina, sawtooth shaped electrodes, and lower temperatures. Laboratory experiments have shown that higher rates of dissolution of the Al.sup.+++ alumina in molten fluoride baths combined with lower voltage drops and improved design of electrodes can allow the operation of the cells at even higher current density, thus increasing overall productivity and efficiency of the cells.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates generally to the aluminum smelting metal from
 alumina, and more specifically to improvements of the conventional
 Hall-Heroult aluminum smelting process that include an anode electrode
 with a sawtooth cross-section which allows oxygen bubbles to be rapidly
 carried away from the top and liquid aluminum to be drained away from
 below.
 2. Description of the Prior Art
 The principle commercial method used for the electrolytic reduction of
 alumina to aluminum metal is the so-called Hall-Heroult process. This
 traditional process uses a molten bath of sodium cryolite (Na.sub.3
 AlF.sub.6) contained in a carbon-lined cell. Molten aluminum puddles at
 the bottom of the cell and serves as the cell's cathode. Consumable carbon
 anodes with flat bottoms are dipped down into the electrolyte bath.
 Alumina feedstock is introduced to the bath. The alumina dissolves into
 the electrolyte and is reduced into liquid aluminum droplets when an
 intense electrical current is passed between the electrodes through the
 electrolyte.
 Typical pot-cell operating temperatures range from 950.degree. C.
 (1,742.degree. F.) to 1,000.degree. C. (1,832.degree. F.). Oxygen is
 liberated from the alumina and combines with the carbon in the anodes to
 produce carbon dioxide gas. Thus the carbon anodes will be consumed and
 must be periodically adjusted and/or replaced. Large amounts of
 electricity are also required, which makes aluminum recycling a
 competitive source of aluminum metal.
 On Jun. 3, 1986, U.S. Pat. No. 4,592,812, was issued to Theodore R. Beck,
 et al., which describes the electrolytic reduction of alumina. A cell used
 in the reduction has an electrolyte bath of halide salts. A non-consumable
 anode is positioned at the bottom of the bath, and a dimensionally-stable
 cathode coated with titanium diboride is spaced above in the bath.
 Particles of alumina are introduced to the bath and form ions of aluminum
 and oxygen. The oxygen ions are converted to gaseous oxygen at the anode
 when electricity is applied. The gaseous oxygen bubbles at the anode and
 agitates the bath. The aluminum ions are converted to metallic aluminum at
 the cathode. The cell temperature is just high enough to keep the metallic
 aluminum molten, and the liquid aluminum accumulates as a pool on top of
 sludge at the bottom the bath and the secondary cathode.
 Theodore R. Beck, et al., were issued U.S. Pat. No. 4,865,701, on Sep. 12,
 1989, which describes another electrolytic cell with a bath of halide
 salts. The anodes and cathodes are vertical plates that are interdigitated
 and dipped from above into the bath. Bubbling of oxygen at the anodes
 agitates the bath and resists the settling of alumina particles at the
 bottom of the bath. Molten aluminum droplets form at the cathodes and flow
 down to accumulate at the bottom of the bath in a sump.
 The use of finely-divided alumina particles in the electrolytic reduction
 of alumina to aluminum is described by Theodore R. Beck, et al., in U.S.
 Pat. No. 5,006,209, issued Apr. 9, 1991. Alternating, vertically-disposed
 cathodes and anodes are used with a horizontally-disposed gas-bubble
 generator in a molten electrolyte bath of balanced amounts of
 NaF+AlF.sub.3 eutectic, KF+AlF.sub.3 eutectic and LiF. The gas-bubble
 generator keeps the alumina particles in suspension. The bath eutectics
 allow the cell to be operated at a substantially lower temperature, e.g.,
 660.degree. C. (1220.degree. F.) to 800.degree. C. (1472.degree. F.). The
 cathodes are made of titanium diboride (TiB.sub.2), a refractory hard
 metal. The anodes are composed of nickel-iron-copper (Ni--Fe--Cu) cermet.
 The mean size of the alumina particles introduced to the bath ranges
 between one micron and one hundred microns, preferably within a range of
 two to ten microns. The smaller alumina particle sizes are described as
 being easier to maintain in suspension. But such fine particles are said
 to have a tendency to agglomerate into clumps which settle out of the bath
 rapidly. So bottom-located gas generators in the bath are included to deal
 with this problem.
 Theodore R. Beck, et al., describe a non-consumable anode and lining for an
 aluminum electrolytic reduction cell in U.S. Pat. No. 5,284,562, issued
 Feb. 8, 1994. The electrolyte used has a eutectic of AlF.sub.3 and either
 NaF, or primarily NaF with KF and LiF. The anodes used are made of copper,
 nickel and iron.
 A cell for the "production of aluminum with low-temperature fluoride melts"
 is described, by Theodore R. Beck, in Proceedings of the TMS Light Metals
 Committee, from the 123.sup.rd TMS Annual Meeting in San Francisco,
 Calif., Feb. 2, 1994 to Mar. 3, 1994, pp. 417-423, as published by The
 Minerals, Metals & Materials Society (TMS) 1994. The proposed commercial
 cell design uses a eutectic electrolyte with a freezing point below
 695.degree. C. of either NaF with AlF.sub.3 or a mixture of NaF/AlF.sub.3,
 KF/AlF.sub.3 and LiF/AlF.sub.3, eutectics operating about 750.degree. C. A
 five to ten percent slurry, by weight, of Al.sub.2 O.sub.3 with a particle
 size less than ten microns is required. Close-spaced vertical monopolar
 anodes and TiB.sub.2 cathodes are used, which makes a pot-room to house a
 pot-line of such cells dramatically reduced in size over the conventional
 horizontal-cell pot-rooms.
 A horizontal bottom auxiliary anode is used in the cell to agitate the
 electrolyte to keep sludge from forming from alumina that falls out of
 suspension, as occurs when the alumina particles agglomerate or are
 individually larger than ten microns. A device to continuously transport
 out aluminum produced by the cell is identified as a necessity, but no
 suitable mechanism is described. Also, feedstocks of alumina with particle
 sizes less than forty-four microns are generally not available, e.g.,
 because of the severe dust problem such powders can produce. Alumina is
 injected into the bath from above and contributes to a dust problem due to
 oxygen capturing alumina dust as it leaves the molten electrolyte surface.
 In addition, it is difficult in such tall cells to insure that the alumina
 reaches all the areas of electrolysis. This and the separation of the
 aluminum from the bottom sludge are problems for the commercial operation
 with unspecified solutions. Therefore, the description here by Beck of a
 practical commercial cell is incomplete.
 The typical consumable carbon anode used in the Hall-Heroult process
 operates with a gross cell cathode-anode voltage of about four to five
 volts. The typical ohmic resistance of the electrolyte is about 0.4
 ohms/cm, and a typical current density of 0.75 amps/cm.sup.2 produces a
 voltage drop of about 0.3 volts/cm. The ohmic drop is thus about 1.2-1.5
 volts, the reversible electromotive force (EMF) is about 1.2 volts, the
 kinetic overpotential is about 0.5 volts, and the gas-bubble layer
 interface resistance under the anode drops about 0.15 volts. This gives a
 total of about 3.2 volts that is dropped in the inter-electrode gap. About
 another volt is lost within the anode and cathode electrodes and their
 busbar connections. Typically, over thirteen kilowatt hours of electrical
 energy per kilogram of aluminum metal is needed, and this will result in
 about 0.45 kilograms of carbon being consumed from the carbon anode.
 A typical modern smelting cell will draw about 200,000 amperes and the
 electrical energy consumed in the pot cells contributes to both the Gibbs
 energy needed by the chemistry and the ohmic heating that keeps the
 electrolyte hot. The overall reaction approximates to,
 2Al.sub.2 O.sub.3 +3C+energy=4Al+3CO.sub.2.
 Alumina has been used as the primary feed material in the electrolytic
 aluminum smelting metal for over a hundred years. Bauxite, in particular,
 is the raw material that is universally used. Worldwide, over forty
 million tons per year of smelting alumina is produced and this, in turn,
 yields twenty million tons of aluminum metal. The so-called Bayer process
 is now the principle method used to convert bauxite to alumina, and such
 process depends on a caustic (e.g., NaOH) to leach the bauxite. Such use
 of a caustic yields negatively charged alumina. The present inventor, John
 S. Rendall, has determined that such negatively charged alumina feedstock
 produced from basic solutions results in a lower solubility and/or rate of
 dissolution of alumina in the pot cell electrolyte. The negatively charged
 alumina feedstock slows down the production rate, and causes more
 electrical power to be needed to drive the electrolysis than would be
 required if such charges were more positive.
 Alumina that is good enough to be used for the electrolytic aluminum
 smelting is typically referred to as "cell-grade alumina". One of the
 principle characteristics important to cell-grade alumina is its relative
 solubility in molten fluoride salt electrolyte. This is the reason that
 molten fluoride salt electrolytes are heated to 950.degree. C. Higher
 temperatures will raise the solubility. But even at these higher
 temperatures, the best solubility obtained is only about four percent by
 weight. An alumina that is inherently more soluble would allow better
 percentages at lower temperatures.
 The optimal alumina reactivity and the optimum electric voltage needed to
 produce a useful electrolytic dissociation of the alumina has been the
 subject of a great deal of scientific study. Just about all electrolytic
 cells are engineered to use alumina that has been precipitated as a
 hydroxide from caustic solutions, e.g., with nine pH.
 About four percent alumina, Al.sub.2 O.sub.3, by weight, is considered the
 upper limit of solubility at 950.degree. C. The usual way that alumina is
 fed into pot cells produces a lot of dust. Such alumina feed is also used
 in fluid beds to capture fluoride emissions. The voltage drop of four to
 six volts across a conventional electrolytic cell includes the bath
 resistance, the electrode resistance of two electrodes, and the energy of
 electrolysis ameliorated by the electrolytic formation of CO.sub.2.
 The solubility of the alumina in the molten bath is so low, it requires
 careful and sophisticated replenishment. Over-feeding the alumina can
 create a bottom sludge that can cover and electrically isolate the molten
 aluminum cathode surface. This will cause a reduction in the electrical
 current that can be induced due to the increased voltage required, and
 thereby cause the cell to freeze up because it cannot produce enough
 electrical heating.
 When the alumina in solution drops under one percent, by weight, an
 increase in the voltage drop occurs in the carbon anode. This, in turn,
 reduces the power input and heat generated, again causing the cell to
 freeze. Any localized heating can adversely affect the solid crust that
 forms at the top of the pot cell, and carbon fluoride gases can be
 released.
 SUMMARY OF THE PRESENT INVENTION
 An object of the present invention is to use Al.sup.+++ alumina feedstock
 to improve the otherwise conventional process of aluminum smelting by
 electrolysis.
 Another object of the present invention is to provide a method for reducing
 the voltage drop necessary in a Hall-Heroult pot cell.
 A further object of the present invention is to provide improved anode
 electrodes for existing Hall-Heroult cells.
 Another object of the present invention is to provide self-draining
 sawtooth-shaped electrodes for use in an Hall-Heroult cells fed with Bayer
 alumina.
 Briefly, a method embodiment of the present invention improves on
 Hall-Heroult aluminum smelting metal from alumina by shaping the anode
 electrode to have a sawtooth cross-section which allows oxygen bubbles to
 be rapidly carried away from the top and liquid aluminum to be drained
 away from below. Alternatively, the alumina feedstock is also changed from
 a negatively charged type to a positively charged type, e.g., Bayer
 alumina is substituted with a positively charged Al.sup.+++ acid-based
 alumina.
 An advantage of the present invention is that a method of aluminum smelting
 is provided that allows lower than normal smelting temperatures to be
 maintained without sacrificing the amount of metal that can be smelted.
 An advantage of the present invention is that an electrode is provided that
 can be used to improve a conventional Hall-Heroult cell for increased
 productivity.
 Another advantage of the present invention is that a process is provided
 for producing aluminum with reduced environmental concerns from
 carbon-monoxide, carbon-dioxide, and fluorides emission.
 An advantage of the present invention is that a method is provided that
 uses dimensionally stable anodes for improved system control and increased
 electrode surface area within an existing Hall-Heroult cell.
 Another advantage of the present invention is that a pot-cell anode
 electrode is provided with active electrode surfaces that are self
 draining and thus allows better control of the minimum operating
 separation between electrode surfaces.
 A further advantage of the present invention is that a method is provided
 that reduces the electrical power required to support the actual
 electrolysis chemistry.
 A still further advantage of the present invention is that a method is
 provided in which the amount of aluminum that is re-oxidized to alumina is
 reduced in a Hall-Heroult pot cell.
 These and other objects and advantages of the present invention will no
 doubt become obvious to those of ordinary skill in the art after having
 read the following detailed description of the preferred embodiments that
 are illustrated in the various drawing figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 FIG. 1 illustrates an aluminum-smelting pot cell embodiment of the present
 invention, and is referred to herein by the general reference numeral 100.
 In general, pot cell 100 is a Hall-Heroult type in which a cathode
 electrode and an anode electrode are immersed in an electrolyte bath 101
 of cryolite. A feedstock of alumina is dissolved in the electrolyte bath
 101 and a strong electrical current is forced to flow between the
 electrodes. The energy of the electricity breaks the oxygen free of the
 aluminum in the alumina feed. When such alumina is negatively charged, for
 whatever reason, the energy needed to reduce the alumina will be greater
 than if the alumina in the feed is more positively charged. For that
 reason, preferred embodiments of the present invention use feeds of
 Al.sup.+++ alumina rather than Bayer alumina.
 Conventional alumina-smelting pot cells have anode and cathode electrodes
 with flat faces that face one another along a horizontal plane inside the
 electrolyte bath. The anode is usually made of carbon that is intended to
 be consumed in the process. The anode electrode is therefore usually
 suspended above on a rod that can be lowered to maintain a near constant
 inter-electrode separation gap.
 The pot cell 100 differs most significantly from the conventional type in
 that an anode electrode 102 does not have a flat face. Rather, it has a
 sawtooth cross-section in at least one vertical plane, and alternatively
 in two vertical planes orthogonal to one another. When the sawtooth
 cross-section runs in only one vertical plane, the surface appears to
 consist of parallel ridges, e.g., like corduroy. When the sawtooth
 cross-section runs in two orthogonal vertical planes, the surface appears
 to consist of a cross-hatch of square-base pyramids, roughly resembling a
 paper egg crate. At present, the optimal geometry of the ridges and
 pyramids appears to be that of an equilateral triangle where the base and
 both sides have the same dimensions.
 A cathode electrode 104 has a corresponding and matching sawtooth
 cross-section that creates a constant separation distance at all points in
 an anode-cathode inter-electrode gap 106. A support rod 108 allows the
 inter-electrode gap 106 to be adjusted and set. The support rod 108 is
 provided with adjustments to keep the proper alignment with a uniform
 inter-electrode gap 106. The anode electrode 102 is a non-consumable type,
 i.e., it does not include sacrificial carbon. The direct current (DC)
 positive connection from the electrical power supply is connected to the
 support rod 108.
 The positively charged alumina feedstock in the electrolytic bath will be
 electrostatically propelled toward the negatively charged cathode
 electrode 104, e.g., at 2.98 coulombs per gram of alumina.
 The corrugated anode-cathode inter-electrode gap 106 by its nature will
 have high spots and low spots with inclined ramp areas in between. The
 bulk of the electrolysis will occur in gaps in the inclined ramp areas.
 The differences in the specific gravity of the liberated oxygen gas and
 liquid droplets of aluminum metal will cause the oxygen to immediately
 head for the high spots and the aluminum to immediately head for the low
 spots.
 A series of gas ports 110 are located at all such high spots. A tube 112
 connects to each gas port 110 and allows the oxygen gas to escape and a
 feedstock of alumina powder to be fed in. The escaping oxygen tends to
 fluff up the alumina powder and prevent caking and lumping as it enters
 the electrolyte.
 A series of drains 114 are correspondingly located at all the low spots.
 These allow the liquid aluminum metal to drain down into a pool 116. A
 carbon crucible 117 supports and contains the liquid aluminum metal pool
 116.
 The pot cell 100 further includes a stainless steel current-collector plate
 118 that supports the carbon crucible 117 and sends in an electrical
 cathode current. The DC-negative connection from the electrical power
 supply is connected to the steel current-collector plate 118. Cathode
 current is then conducted in through the carbon crucible 117 and the
 liquid aluminum metal pool 116. A heat insulator 120 is placed underneath
 in a sheet to prevent excess heatsinking and thereby help the pot cell
 maintain its proper operating temperature without excessive electrical
 power demands. A steel shell 122 supports the whole of the pot cell 100
 and is covered by a roof 124 with access doors.
 The electrolyte preferably comprises a pool of molten eutectic fluoride
 salts that include cryolite (Na.sub.3 AlF.sub.6), and the whole is
 maintained at a temperature of approximately 750.degree. C. Such heat is
 provided by the large electrical current that passes between the anode and
 cathode. A crust of frozen cryolite 126 will form at the top outside edges
 due to unavoidable heat losses at those points.
 The successful use of sawtooth shaped electrodes is described for the
 electro-winning of lead in an electrolysis cell by J. E. Murphy and M. F.
 Chambers, "Production Of Lead Metal By Molten-Salt Electrolysis With
 Energy-Efficient Electrodes," United States Department of Interior, Bureau
 of Mines, Report RI-9335, 1991. Such Report is incorporated herein by
 reference.
 In alternative embodiments of the present invention, hot anode gases
 escaping from the ports 110 and traveling up the tubes 112 are used to
 convert an incoming feedstock of aluminum hydroxide to Al.sup.+++ alumina.
 Such acid-based alumina conversion is facilitated by hydrogen flouride gas
 that is typically included in the hot anode gases.
 In still other alternative embodiments of the present invention, otherwise
 wasted heat is recovered from the hot anode gases escaping from the ports
 110 that travels up the feedstock tubes 112. Such recovered heat is used
 to conserve the electrical energy consumed in the smelting process. The
 total heat required in conventional smelters can often amount to five
 kilowatts per kilogram of aluminum produced. As much as forty to sixty
 percent of the input energy can escape as heat from the tops of even
 well-designed conventional pot cells. The heat required to convert
 aluminum hydroxide to alumina is theoretically about 2.5.times.10.sup.6
 BTU's per ton of alumina. Embodiments of the present invention therefore
 use such otherwise wasted heat to do the job of aluminum hydroxide to
 alumina conversion. As the powdered aluminum hydroxide feedstock drops
 down the feedstock tubes 112, each particle quickly picks up the heat from
 the escaping hot anode gases because the contact surface area is so great
 compared to the particle mass.
 In preferred embodiments of the present invention, any remaining flouride
 gas and/or dust particles in the gases to be released to the atmosphere
 can be water scrubbed out by bubbling them through liquid water.
 FIG. 2 illustrates a second pot cell embodiment of the present invention,
 and is referred to herein by the general reference numeral 200. The pot
 cell 200 differs from pot cell 100 in that several mechanically
 independent anodes are used. An anode electrode 202 is mechanically free
 of an anode electrode 203, but the two are tied to the same positive-DC
 electrical supply potential. A single cathode electrode 204 has a
 corresponding and matching sawtooth cross-section for all the anode
 electrodes 202 and 203 in their nominal zenith positions. A constant
 separation distance is preferred at all points in an anode-cathode
 inter-electrode gap 206. A pair of support rods 208 and 209 respectively
 allow the corresponding points in the inter-electrode gap 206 to be
 adjusted and set. The support rods 208 and 209 are each provided with
 adjustments to keep the proper alignment. The anode electrodes 202 and 203
 are a non-consumable type, i.e., they do not include sacrificial carbon.
 The direct current (DC) positive connection from the electrical power
 supply is connected to the support rods 208 and 209.
 As in the pot cell 100 (FIG. 1), the corrugated anode-cathode
 inter-electrode gap 206 has high spots and low spots with inclined ramp
 areas in between. The bulk of the electrolysis will occur in the gaps of
 the inclined ramp areas. The differences in the specific gravity of the
 liberated oxygen gas and liquid droplets of aluminum metal will cause the
 oxygen to immediately head for the high spots and the aluminum to
 immediately head for the low spots.
 A series of gas ports 210 are located at all such high spots. A tube 212
 connects to each gas port 210 and allows the oxygen gas to escape and a
 feedstock of alumina powder to be fed in. The escaping oxygen tends to
 fluff up the alumina powder and prevent caking and lumping as it enters
 the electrolyte.
 A series of drains 214 are correspondingly located at all the low spots.
 These allow the liquid aluminum metal to drain down into a pool 216. A
 carbon crucible 217 supports and contains the liquid aluminum metal pool
 216.
 The pot cell 200 further includes a steel current-collector plate 218 that
 supports the carbon crucible 217 and sends in an electrical cathode
 current. The DC-negative connection from the electrical power supply is
 connected to the steel current-collector plate 218. Cathode current is
 then conducted in through the carbon crucible 217 and the liquid aluminum
 metal pool 216. A heat insulator 220 is placed underneath in a sheet to
 prevent excess heatsinking and thereby help the pot cell maintain its
 proper operating temperature without excessive electrical power demands. A
 steel shell 222 supports the whole of the pot cell 200 and is covered by a
 roof 224 with access doors.
 The electrolyte preferably comprises a pool 226 of molten eutectic fluoride
 salts that include cryolite (Na.sub.3 AlF.sub.6), and the whole is
 maintained at a temperature of approximately 750.degree. C. Such heat is
 provided by the large electrical current that passes between the anode and
 cathode. A crust of frozen cryolite 228 will form at the top outside edges
 due to unavoidable heat losses at those points.
 FIG. 3 represents a feeding-scrubbing system embodiment of the present
 invention, and is referred to by the general reference numeral 300. The
 feeding-scrubbing system 300 includes one or more non-consumable anode
 electrodes 301 and 302, and a wettable-surface cathode electrode 304. A
 wetting agent, such as TiB.sub.2, is coated on the surface of the cathode
 electrode and will wet liquid metal aluminum to help draw it from the
 electrolyte and drain it away. The anode electrodes 301 and 302, and
 cathode electrode 304 have opposing matching faces that are triangularly
 facetted, e.g., at 60.degree. inclination. A uniform separation distance
 in an inter-electrode gap 306 is preferred and is filled with a eutectic
 electrolyte 307. A pool of liquid metal aluminum 308 collects at the
 bottom as it precipitates from the electrolyte during operation. The
 liquid metal aluminum 308 is drawn off through a siphon collector 310. A
 set of covers 311 is used to thermally insulate the hot electrolyte 307
 and keep in hot pot-cell gases.
 The electrolyte 307 includes molten eutectic fluoride salts including
 cryolite (Na.sub.3 AlF.sub.6) which is heated to 750.degree.
 C.-850.degree. C. by the large electrical current that is passed between
 the anode and cathode during operation.
 An alumina feeder assembly 312 drops positively charged acid-based alumina
 into the electrolyte 307, and includes an alumina-feed submersible pipe
 314, a bin 316, a hot-gas gas vent 318, a helix-coil conveyor 320, and a
 mixer motor 322. A feedstock is added to the system 300 via the pipe 314,
 and will comprise Bayer alumina, aluminum hydroxide, or acid-based
 alumina.
 The level of the feedstock in the bin 316 is controlled to maintain a gas
 seal within. The discharge end of pipe 314 is preferably set lower than
 the entry elevation of the hot-gas vent pipe 318. The helix-coil conveyor
 320 is a vertical or inclined spiral screw with at least two complete
 turns and is rotated by the mixer motor 322. A bearing 324 on the shaft of
 the helix-coil conveyor 320 permits the conveyor gap at the bottom to the
 electrolyte 307 to be adjusted.
 The helix-coil conveyor 320 is preferably made of a fine mesh material able
 to hold the feedstock and yet still allow escaping pot-cell gases to pass
 through. It may be advantageous to plate such mesh with a catalytic
 material that can initiate or speed the conversion to acid-based alumina.
 Hydrofluoric acid can also be added initially to the aluminum hydroxide
 feedstock to assist in the conversion to acid-based alumina. The addition
 of the hydrofluoric acid to the aluminum hydroxide produces a
 AlF.sub.3.multidot.3H.sub.2 O intermediate which on calcination around
 700.degree. C. in the hot pot-cell gases hydrolyzes into alumina. The
 calcination also produces hydrofluoric acid that can be used in a recycle.
 Various tests were conducted to see what effect the inclined area between
 the electrodes had over more conventional designs. A laboratory cell, with
 a conventional horizontal flat carbon anode and a molten aluminum cathode
 was operated at twelve amps with a current density of about 0.7
 amps/sq.cm. An overall voltage drop of 4.6 volts was observed over a few
 hours operation. The same cell, but with improvements comprising an
 inclined carbon anode surface and efficient anode gas removal operated
 under the same conditions. The gas removal and inclination of the anode
 surfaces was similar to that shown in FIG. 3. The improved laboratory cell
 demonstrated an overall voltage drop of 3.6 volts over a few hours of
 operation. In other words, the amount of energy saved by the improvements
 alone was (4.6V-3.6V)*12.0A, or twelve watt-hours per hour. The
 conventional cell used about 55.2 watt-hours per hour, so the energy saved
 amounted to better than seventy-eight percent.
 Another laboratory cell was used to test the bath circulation of positively
 charged acid-based alumina. Such acid-based alumina was produced from
 Al(OH).sub.3 using hot pot-cell gases for a conversion from aluminum
 hydroxide. The experiments were run at temperatures of 950.degree. C. to
 980.degree. C., and the voltage drops across the cell were calculated and
 measured for aluminum smelting. Cell currents of twelve amperes were the
 equivalent of anode current densities of 0.5 amps/cm.sup.2.
 The only significant voltage drops that were observed were across the
 cathode, the anode, and the electrolyte bath. In one six-hour test, in
 particular, no voltage drop at all could be attributed to the actual
 production of aluminum. In other words, the conversion of,
EQU Al.sub.2 O.sub.3 +energy=2Al+3/2O.sub.2,
 appeared to use only heat and not electricity to fuel the "energy" part of
 the chemical equation.
 The positive charge of the Al.sup.+++ alumina of the present invention
 appears to have supplied some or all of the electrical energy that is
 conventionally needed when using negatively charged alumina, such as Bayer
 alumina. The acid-based Al.sup.+++ alumina is believed to be completely
 ionized or disassociated in the bath.
 The laboratory test cell included a graphite crucible that was in the form
 of a round cylindrical cup about one hundred and ten millimeters tall and
 about eighty millimeters in diameter. Inside there was placed a sintered
 alumina side lining that contained a cryolite electrolyte bath. A pool of
 smelted aluminum formed just above a stainless steel current collection
 plate cathode. An alumina support and an alumina cement were used to
 enclose the bottom. An anode was specially designed to circulate the
 electrolyte bath up through a bottom hole and out through a series of side
 ports. The diameter of the anode was about 50.86 millimeters and the
 bottom hole and side ports were ten to fifteen millimeters in diameter. A
 steel tube was used to support the anode and to feed-in the positively
 charged acid-based alumina. A cathode collection rod was connected along
 with the anode to an electrical power source of four to five volts. The
 gap between the anode and the top of the aluminum was about twenty
 millimeters.
 From such experimental data, it is presently speculated that up to a three
 volt gain over conventional pot cell voltage requirements can be realized
 simply using Al.sup.+++ acid-based alumina. The voltage gain can be
 1.5-3.0 volts when feeding aluminum hydroxide counter current to pot gases
 into the molten fluoride bath with a sloped anode surface (for prevention
 of gas bubbles). It has also been shown that the cell's voltage-drops were
 the same if the anode surfaces were sloped from the horizontal. Carbon and
 carbon-free anodes both produced similar results.
 Therefore the economic benefits to be gained from production of the
 Al.sup.+++ acid-based alumina will be in the range of 1.5 volts and 3
 volts multiplied by 3.24 amps per gram of aluminum produced, according to
 Coulombs Law with a ninety-five percent efficiency. The passage of
 pot-cell gases at 950.degree. C. counter current to the aluminum hydroxide
 feed converts by acidification with hydrogen fluoride and fluorine, and
 calcination that removes the water so that one and one half tons of feed
 aluminum hydroxide produces one ton alumina (Al.sub.2 O.sub.3) equivalent.
 In yet another laboratory experiment, a small pot-cell was placed in a
 stainless steel container, and the whole was placed in a furnace. An
 insulation cover was placed over the furnace. Openings were included for
 an argon feed, and connections for an anode and a cathode from a rectified
 power source. A helix-coil conveyer inside a feeder dropped in the
 feedstock, A suction was applied from a vacuum pump and a gas vent on the
 feeder such that any off-gases from the pot-cell would enter the feeder
 and proceed through the feedstock material and then through a water bath.
 The temperature of the electrolytic bath was maintained between
 950.degree. C. and 970.degree. C., with the furnace controlling the heat
 losses.
 At a power input of over twelve amps, steady electrolysis was maintained in
 the molten fluoride bath which consisted of cryolite with about seven
 percent of AlF.sub.3, CaF.sub.2, and LiF.sub.2. The voltage drop for the
 cell remained steady over seven hours of operation and was, in the main,
 accounted for by the anode, cathode, its connections and the bath
 resistance. The alumina feed into the bath was replenished at intervals by
 additions of aluminum hydroxide at the top of the feeder and turns of the
 screw in the feeder column. The argon was maintained at around four
 hundred cc/min and the off-gases measured were about the same rate, which
 indicated leaks in the cover.
 The temperature of the off-gas exiting from the feeder was around
 70.degree. C., while the scrubbing water temperature remained around
 30.degree. C. The water remained clear and essentially free of fluoride.
 The contents of the feeder tube were analyzed as collected. A dark gray
 alumina was being fed into the bath with a color gradation to white with
 specks of gray at the top where the aluminum hydroxide feed was
 introduced.
 FIG. 4 illustrates an aluminum smelter embodiment of the present invention,
 and is referred to by the general reference numeral 400. The aluminum
 smelter 400 uses a pair of anodes 402 and 404. These may be either
 consumable carbon or non-consumable inert carbon-free metal. The anodes
 are suspended on a pair of support rods 406 and 408 that allow them to be
 lowered to maintain a particular inter-electrode gap. A steel current
 collector bar 410 underlies under a carbon crucible cathode 412. A metal
 cathode 414 includes a pool of liquid metal aluminum. A bath of molten
 fluoride salts 416 is heated to 750.degree. C.-950.degree. C. by a large
 electrical current that passes between the anodes 402, 404, and the
 collector bar 410. Ordinary cryolite must be mixed with a eutectic partner
 to lower the melting point low enough to be able to operate as low as the
 melting point of aluminum, i.e., 660.degree. C. Aluminum is smelted from
 the alumina-electrolyte solution in the inter-electrode gap and is drawn
 off from pools that form at the bottom.
 The very large electrical currents present in the cell 400 induce
 correspondingly strong magnetic fields that can slosh the smelted liquid
 aluminum around in the cathode 414. Such waves can affect the separation
 distances in the inter-electrode gap. A waffle structure of titanium
 diboride is preferably included within to control and limit such waves.
 The crests of waves of liquid aluminum can temporarily short out the cell
 if their amplitudes become too great.
 In preferred embodiments of the present invention, an alumina feed 418
 includes only positively charged alumina. A volumetric feeder 420 mixes
 the alumina feed into the pool of molten fluoride salts 416. A rim crust
 of frozen cryolite 422 usually forms at the outside edges and protects the
 carbon crucible lining 412 from erosion and burning if exposed to the air.
 A steel shell 424 supports the weight of the whole assembly. An insulative
 liner 426 wraps under and all around the crucible 412 to conserve the heat
 generated. A pair of doors provide access to the cell interior through a
 cover 428.
 No doubt those skilled in the art, could retrofit the cell described to
 insulate the molten bath and anodes in such a way as to minimize any
 ingress of air.
 In preferred embodiments of the present invention, the hot gases that exit
 from the system are jetted in and down at the delivery end of the
 volumetric feeders 420 (FIG. 4). This ensures that acid-based alumina will
 enter to the molten electrolyte bath 416. A heating element may be needed
 around volumetric feeder 420 for both start-up and steady operation. The
 hot pot cell gases which are jetted downward are used to convert an
 aluminum hydroxide feed to an Al.sup.+++ acid-based alumina feedstock. A
 water vapor and CO.sub.2 are discharged.
 About two barrels of oil are used in such conversion today, thus energy,
 operating and maintenance costs of for this process step will be saved.
 The heat is provided in embodiments of the present invention for this
 purpose by the pot cell gases which bubble out at about 750.degree. C. to
 950.degree. C., and leave the overall system between 70.degree. C. to
 100.degree. C. All the particulate and fluoride emissions are absorbed
 into the aluminum hydroxide feed. This accounts for around twenty
 kilograms of alumina per ton of aluminum and fifteen kilograms per ton
 aluminum of aluminum fluoride bath.
 Although the present invention has been described in terms of the presently
 preferred embodiments, it is to be understood that the disclosure is not
 to be interpreted as limiting. Various alterations and modifications will
 no doubt become apparent to those skilled in the art after having read the
 above disclosure. Accordingly, it is intended that the appended claims be
 interpreted as covering all alterations and modifications as fall within
 the true spirit and scope of the invention.