Aluminum production utilizing positively charged alumina

The smelting of aluminum from alumina in the Hall-Heroult process can be dramatically improved by lowering power consumption and in the use of carbon free anodes by using a feed of positively charged alumina. Laboratory experiments have shown that the apparent solubility and reactivity of alumina in molten fluoride baths is surprisingly increased by altering the negatively charged aluminum hydroxide Al(OH).sub.4.sup.- particles, at about pH of nine, to positively charged particles containing Al.sup.+++ with a pH of less than two, by using acid solutions. The alumina thus produced is referred to as Al.sup.+++ alumina, or positively charged alumina. In particular, sulfuric acid is used to convert aluminum hydroxide using the Bayer process to a family of basic aluminum sulfates, 3Al.sub.2 O.sub.3.4SO.sub.3.9H.sub.2 O, which are dehydrated and calcined to produce Al.sup.+++ alumina.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates generally to the smelting of aluminum metal
 from alumina, and more specifically to using acid to convert aluminum
 hydroxide starting materials into positively charged alumina for increased
 solubility in a Hall-Heroult electrolyte.
 2. Description of the Prior Art
 Practically all the aluminum metal smelted from raw materials is made by
 the Hall-Heroult process invented in the nineteenth century. See, Ernest
 W. Dewing, "The Thermochemistry of Aluminum Smelting", pp. 341-350, Proc.
 of the Savard/Lee Intl. Symp. on Bath Smelting, The Materials and Metals
 Society (Canada), 1992. Such process uses very high electrical currents to
 electrolyze alumina, Al.sub.2 O.sub.3, which is dissolved in an
 electrolyte of molten cryolite, Na.sub.3 AlF.sub.6, at temperatures of
 945.degree. C. to 975.degree. C. But such high temperatures can cause the
 carbon in the anodes to burn with the air rather than contribute to the
 removal of oxygen from the alumina.
 A consumable carbon anode is used in the Hall-Heroult process with a gross
 cell cathode-anode voltage of about 4-5 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.sup.-1. The ohmic drop is thus about 1.2-1.5 volts, the
 reversible EMF is about 1.2 volts, the kinetic overpotential is about 0.5
 volts, and the gas-bubble layer 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
 kilowatts of electrical power 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 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
 smelting of aluminum 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 Bayer process is
 the principle method now 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 negative charges impair the
 dissolution of alumina (and the rate thereof) in the cell electrolyte, and
 require more electrical power to drive the electrolysis than would be
 required if such charges were positive or neutral.
 Alumina that is good enough to be used for the electrolytic smelting of
 aluminum 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. Universally, such molten
 fluoride salt electrolytes are heated to 950.degree. C. just to raise the
 solubility to a approximately four percent by weight.
 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 use engineered alumina precipitated as a hydroxide from caustic
 solutions of approximately nine pH. The low degree of alumina dissolution
 and the rate thereof in the molten bath electrolyte is an on-going
 problem. About four percent alumina, Al.sub.2 O.sub.3, by weight, is
 considered the upper limit at 950.degree. C. The usual way that alumina is
 fed into 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, as well as the
 energy of electrolysis ameliorated by the electrolytic formation of
 CO.sub.2.
 The dissolution of the alumina in the molten bath is so low, it requires
 careful and sophisticated replenishment. At 750.degree. C. the dissolution
 and rate thereof of the alumina is less than one percent and cannot be
 used at this temperature. Only six percent, by weight, is usually possibly
 at 950.degree. C. Over-feeding of alumina will 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. At under
 one percent, by weight, alumina in the bath causes an increase in the
 voltage drop that occurs in the carbon anode and reduces the power input
 (amps) causing the cell to freeze. This localizes heat generation there
 and adversely affects the crust seal at the top of the cell. This
 localized heating at the carbon anode can also be responsible for the
 production of carbon fluoride gases.
 In the preparation of alumina for use in cells, any alumina that
 precipitates as aluminum hydroxide from a sodium aluminate solution is
 usually considered to comprise negatively charged ions,
 Al(OH).sub.4.sup.-. Such precipitation is usually done at a pH of about
 nine, and a temperature of about 80.degree. C. The negatively charged ions
 are produced by caustic leaching of bauxite, and contribute to a
 clustering of crystals into larger particles. The bonding mechanisms in
 these clusters consumes most of the negative ionic charges, and the
 overall negative charge is almost completely neutralized. See, Karl Wefers
 Chanakya, "Oxides and Hydroxides of Aluminum", Alcoa Laboratories, 1987.
 In any event, an intermediate aluminum hydroxide must be aged 24-hours to
 get the type of alumina that will work well in smelters. The day-old
 aluminum hydroxide is then dried and calcined at about 1000.degree. C. to
 produce the desired cell-grade alumina.
 SUMMARY OF THE PRESENT INVENTION
 An object of the present invention is to provide a method for the
 production of alumina that is suitable in the low-temperature smelting of
 aluminum by electrolysis.
 Another object of the present invention is to provide a method for more
 efficient smelting of aluminum in a Hall-Heroult cell.
 Briefly, a method embodiment of the present invention includes the smelting
 of aluminum from alumina in the Hall-Heroult process by using a feed of
 "positively charged" alumina. Laboratory experiments have shown that the
 apparent solubility and reactivity of alumina in molten fluoride baths is
 significantly increased by altering the negatively charged aluminum
 hydroxide Al(OH).sub.4.sup.- particles, at about pH of nine, to positively
 charged particles containing Al.sup.+++ with a pH of less than two, by
 using acid solutions. The alumina thus produced is referred to as
 Al.sup.+++ alumina, or positively charged alumina. In particular, sulfuric
 acid is used to convert aluminum hydroxide using the Bayer process to a
 family of basic aluminum sulfates--3Al.sub.2 O.sub.3 4SO.sub.3 9H.sub.2 O,
 which is in turn dehydrated and calcined to produce the Al.sup.+++
 alumina.
 An advantage of the present invention is that an environmentally friendly
 process is provided for producing aluminum.
 Another advantage of the present invention is that a relatively inexpensive
 process is provided for the production of positively charged Al.sup.+++
 alumina.
 A further advantage of the present invention is that the positively charged
 alumina reduces or eliminates the power required to achieve actual
 electrolysis except for the power required for transmission of current
 through the system.
 A still further advantage of the present invention is the ability to
 operate an electrolytic reduction cell at temperatures around 750.degree.
 C., which reduces heat losses in comparison to operation at 950.degree. C.
 and allows for the use of "carbon free" (inert) anodes. In contrast, Bayer
 alumina is relatively insoluble at 750.degree. C. in molten flouride,
 while Al.sup.+++ alumina appears to be soluble at a concentration in
 excess of four percent at 750.degree. C.
 Another apparent advantage of the present invention is that the use of
 Al.sup.+++ alumina as the only feedstock in aluminum smelting reduces or
 eliminates the power needed by a cell to actually break the oxygen free of
 the aluminum in each alumina molecule.
 An advantage of the present invention is that a cell is provided that may
 be operated at lower temperatures because the Al.sup.+++ alumina is
 soluble in the electrolyte at these lower temperatures and alumina
 produced with caustics is not.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 FIG. 1 illustrates a first cell embodiment of the present invention, and is
 referred to by the general reference numeral 100. The cell 100 uses two
 carbon anodes so that aluminum smelting can proceed continuously even
 though one carbon anode has been consumed and may be electrically turned
 off for on-line replacement. FIG. 1 shows this as a new carbon anode 102
 that was recently replaced and a near expired carbon anode 104. A support
 106 and a clamp 108 allow the carbon anode 102 to be lowered to maintain a
 particular inter-electrode gap as the carbon in the anode is consumed by
 the smelting process. Similarly, a anode rod 110 and a clamp 112 allow the
 other carbon anode 104 to also be lowered to maintain its particular
 inter-electrode gap as its carbon is consumed by the smelting process. A
 steel current collector bar 114 lies under a cathode 116. A pool of liquid
 metal aluminum 118 forms in an inter-electrode gap and is drawn off as it
 is smelted. A pool of molten eutectic fluoride salts including cryolite
 (Na.sub.3 AlF.sub.6) 120 is heated to approximately 750.degree. C. by a
 large electrical current that passes between the anodes and cathode. An
 alumina feed 122 drops positively charged alumina into the pool of molted
 cryolite 120. A crust of frozen cryolite 124 usually forms at the outside
 edges due to heat losses. A steel shell 126 supports the weight of the
 whole assembly. An insulative liner 128 helps keep the heat generated
 inside to reduce the amount of electrical energy needed. A pair of doors
 130 and 132 provide access to the cell interior.
 FIG. 2 illustrates a second cell emodiment of the present invention, and is
 referred to by the general reference numeral 200. The cell 200 uses a pair
 of non-consumable inert carbon-free anodes 202 and 204. A support 206 and
 a clamp 208, and another anode rod 210 and a clamp 212, allow the anodes
 202 and 204, respectively, to be lowered to maintain a particular
 inter-electrode gap. A steel current collector bar 214 lies under a carbon
 crucible cathode 216. A metal cathode 218 includes a waffle structure of
 titanium diboride which is wetted by a pool of liquid metal aluminum. A
 pool of molten fluoride salts 220 is heated to approximately 750.degree.
 C. by a large electrical current that passes between the anodes 202 and
 204 and the collector bar 214. The aluminum smelted from the
 alumina-electrolyte solution forms in an inter-electrode gap of the
 anode-cathode and is drawn off as it is smelted.
 Very large electrical currents are present in the cell 200 and these induce
 very strong magnetic fields that can slosh the aluminum around in the
 cathode 218. The purpose in building the cathode 218 with a waffle
 structure of titanium diboride is to control such waves. If left out of
 control, the crests of the waves of liquid aluminum could temporarily
 short out the cell. Bus bar design ameliorates the problem.
 Ordinary cryolite must be mixed with a eutectic partner to lower the
 melting point low enough to operate as low as 660.degree. C., the melting
 point of aluminum.
 It is critical to the present invention that an alumina feed 222 drop only
 positively charged alumina into the pool of molten fluoride salts 220. A
 crust-breaking bar 223 helps to get the alumina feed mixed into the pool
 of molten cryolite. A rim crust of frozen cryolite 224 usually forms at
 the outside edges due to heat losses which also protects the lining from
 air burn and erosion. A steel shell 226 supports the weight of the whole
 assembly. An insulative liner 228 wraps under and around the crucible to
 conserve the heat generated inside better than that shown in FIG. 1. A
 pair of doors 230 and 232 provide access to the cell interior and for
 maintenance of the anodes.
 FIG. 3 represents a process embodiment of the present invention for making
 the positively charged alumina required in cells 100 and 200 (FIGS. 1 and
 2), and is referred to herein by the general reference number 300. The
 process 300 converts an aluminum hydroxide feed 302 into a positively
 charged alumina 304 for use in electrolytic smelting of aluminum. The
 process is, in essence, a "zero-discharge" facility excepting a small
 purge stream 306 which removes impurities that may have been introduced
 with the feed stock 302.
 The process 300 begins with a reaction step 308 wherein the aluminum
 hydroxide is fed, either as a wet cake or as a dry powder, with a slurry
 water 310 and an acid 312 into a pressure cooker. The acid 312 can be
 sulfuric acid. The temperature is raised to approximately 150.degree. C.
 to produce an aluminum sulfate in a molten hydrate form. The pressure is
 held high enough to maintain a liquid state, e.g., 1100 kilo-Pascals. The
 residence time is between one to ten minutes, and preferably about two
 minutes.
 The molten aluminum sulfate is fed as a slurry 314 to a process step 316
 under pressure. A second aluminum hydroxide feed 318 and water feed 320
 are added as required to maximize the final product basic aluminum
 sulfate. The slurry 314 uses a recycle stream 322. In step 316, the
 temperature is increased to at least 180.degree. C. and not more than
 210.degree. C. under the vapor pressure of the reacting mixture, about
 1900 kilo-Pascals. The residence time one to five minutes, and usually
 less than two minutes. A product slurry 324 is transferred to a
 pressure-letdown process step 326 wherein the pressure is reduced to
 atmospheric and thus flashes any water. This lowers the temperature from
 about 200.degree. C. to the atmospheric boiling point, e.g., 100.degree.
 C. A flashed water flow 328 is condensed in process step 330. A basic
 aluminum sulfate slurry 332 has a slurry concentration that ranges
 twenty-five to thirty-five percent and is nominally thirty percent. The
 slurry 332 is transferred to a solids separation process step 334. Widely
 available commercial filtration and centrifuge separators may be used to
 implement the solids separation process step 334. A separated mother
 liquor 336 is recycled to step 316. The purge 306 comes from the same
 separator and is used to rid the process of any accumulated impurities. A
 solid product basic aluminum sulfate flow 338 is transferred to step 340.
 The solids are washed out with a condensate provided from a solids drying
 step 342 and the condensing step 330. Such washing may be by any of the
 usual solids washing equipment in as many stages as necessary for
 efficient use of water.
 A final basic aluminum sulfate moist cake flow 344 has its free moisture
 removed in step 342 by drying at about 450.degree. C. This also drives off
 all or part of the waters of hydration associated with the basic aluminum
 sulfate product. The water vapor 346 produced in the solids drying step
 342 is condensed and recycled to step 308 via the washing step 340.
 Alternatively, the water vapor may be vented to the atmosphere.
 A solid product flow 348 is calcined in a step 350 by heating it to
 approximately 950.degree. C. Conventional calciners may be used, such as
 rotary drums or fluid flash calciners. A sulfur dioxide and sulfur
 trioxide flow 352 is produced by the calcination step 350 and forwarded to
 an acid plant 354 for recycling in a flow 356.
 The positively charged alumina flow 304 is discharged through coolers as is
 conventional for cell-grade alumina. Such positively charged alumina flow
 304 is directly useful as the alumina feeds 122 and 222 in FIGS. 1 and 2.
 The particle size distribution of the positively charged alumina flow 304
 preferably duplicates that produced in the conventional Bayer process. The
 particle size distribution is typically about fifty percent of so-called
 Bayer alumina, and the bulk density is about twenty to thirty percent less
 than that of Bayer alumina. The particle size distribution of the
 positively charged alumina flow 304 may be optimized by varying the pH of
 the slurry in step 316 with different amounts of sulfuric acid, higher or
 lower temperatures, and longer or shorter residence times.
 In the step 354, the off-gases from step 350 are processed through a
 conventional acid plant by: a) lowering the temperature for water vapor
 and sulfur trioxide adsorption with concentrated sulfuric acid, b)
 conversion of sulfur dioxide to the trioxide, and c) absorbing such sulfur
 trioxide in a concentrated sulfuric acid. The resulting sulfuric acid
 product is recycled in flow 356 to the beginning process step 308. Minor
 miscellaneous losses of sulfur dioxide can be made up either by burning
 sulfur provided at an input 358 as part of a fuel input 360 to calcination
 step 350, or by direct burning as part of the acid plant 354.
 FIG. 4 represents a process embodiment of the present invention, referred
 to herein by the general reference numeral 400, that optimizes the
 particle size distribution for a maximum positive charge on the produced
 alumina. Process 400 comprises a reaction step 402 for a main feed 404 and
 an acid input 406. The mixture is cooked in a reactor at a temperature of
 170.degree. C. to 230.degree. C., and preferably over 180.degree. C. while
 maintaining a reaction vapor pressure that generally exceeds 1400
 kilo-Pascals. The reactants are maintained in step 402 at a pH of two or
 less by varying the sulfuric acid feed 406 to the reactor. The main feed
 404 comprises aluminum hydroxide in cake or dried form, and is slurried
 with a recycle liquor 408. The residence time in the reactor of step 402
 is generally about two minutes. The residence time may need to be
 increased considerably when lower sulfuric acid concentrations are
 associated with higher pH, or when larger particle sizes of aluminum
 hydroxide feed are needed. The resulting yields of a flow 410 may vary
 according to the temperature, pH, and residence time elected.
 The pressure of flow 410 is let down in a step 412 in single or multiple
 stages to atmospheric pressure. The temperature generally drops to about
 100.degree. C. as a result. The vapor from the pressure letdown flash step
 412 is condensed for use as a washing fluid 414. A product slurry 416 is
 separated into product and mother liquor in a step 418, e.g., by vacuum
 filtration, pressure filtration, centrifugation, etc. A solid product 420
 is then washed in step 422 to remove the last of the mother liquor. Any of
 the ordinary separation practices currently used in the alumina industry
 can be used provided the equipment materials of construction are suitable
 for the acidic environment.
 In alternative embodiments of the present invention, the pressure available
 in step 402 is used to operate a pressurized solid-liquid separation. In
 such case, the pressure letdown of step 412 may be split to both precede
 and follow the solid liquid separation of step 418 and the washing of step
 422.
 A moist solids flow 424 is transferred to a step 426 for drying and
 dehydration at approximately 450.degree. C. A natural gas input 428
 provides the fuel needed for heating. Water vapor may be condensed for use
 in the washing step 422 or simply vented from the process. A dehydrated
 product flow 430 is transferred to a step 432 for calcination at
 approximately 950.degree. C. Alternatively, steps 426 and 432 may be
 combined. Depending upon the choice of equipment, e.g., rotary drums or
 fluid flash equipment, the feed 430 may be taken from either step 426, as
 shown, or step 422.
 A product flow 434 following calcination is cooled and made ready for
 aluminum production in commercial installations. Any off-gas flow 436 from
 calcination, that includes SO.sub.2 and SO.sub.3, is transferred to an
 acid plant step 438 where they are cooled and dried with concentrated
 sulfuric acid. In step 438, any moisture and SO.sub.3 are removed in a
 drying step. The gases are then passed through a conventional SO.sub.2
 converter.
 The water content of the calciner off-gases to the drying step must be
 critically controlled in the acid plant 438. Such is essential so as to
 not exceed the drying capacity of the concentrated sulfuric acid while
 maintaining acid quality for an acid recycle flow 440. The waste heat of
 the acid plant step 438, or simple evaporation, may be used to maintain a
 correct water balance.
 FIG. 5 represents a laboratory cell 500 that was used to test a bath
 circulation of positively charged alumina, e.g., aluminas 122, 222, 304,
 and 434. Such 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 the smelting of aluminum. For cell currents of ten to
 twenty-eight amperes, equal to anode current densities of 0.5 to 1.4
 amps/cm.sup.2, the only voltage drops that were observed were across the
 cathode, the anode, and the bath. In one test in particular that lasted
 for a period of over four hours, no voltage drop at all could be
 attributed to the actual production of aluminum. The positive charge of
 the Al.sup.+++ alumina of the present invention appears to have supplied
 the energy that is conventionally needed to be electrically applied from
 an external power source. The "acid-based" alumina of the present
 invention is now believed to be completely ionized or disassociated in the
 bath. The Al.sup.+++ alumina is propelled towards the cathode according to
 Coulombs Law, at 2.98 coulombs per gram of aluminum.
 The laboratory test cell 500 included a graphite crucible 502 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 504 that contained a cryolite electrolyte
 bath 506. A pool of smelted aluminum 508 formed just above a stainless
 steel current collection plate (cathode) 510. An alumina support 512 and
 an alumina cement 514 were used to enclose the bottom. An anode 516 was
 specially designed to circulate the electrolyte bath 506 up through a
 bottom hole 518 and out through a series of side ports 520. This is
 represented by arrows on dashed lines in FIG. 5. The diameter of the anode
 was about 50.86 millimeters and the bottom hole and side ports were about
 ten to fifteen millimeters in diameter. A steel tube 522 was used to
 support the anode and feed in positively charged alumina. A cathode
 collection rod 524 was connected along with the anode to an electrical
 power source of four to five volts. The gap between the anode 516 and the
 top of the aluminum 508 was about twenty millimeters. Surprisingly the
 voltage drop across the cell at five to fifteen amps was only that
 required to energize the cathode and anode. No voltage drop was associated
 with the disassociation of the alumina (electrolysis).
 Experimental work has shown that Al.sup.+++ alumina can be electrolyzed in
 molten fluoride baths at all temperatures above the melting point of
 aluminum (660.degree. C.).
 Prior art processes that use the Hall-Heroult electrolytic process depend
 upon maintaining a molten cryolite, Na.sub.3 AlF.sub.6, salt at about
 950.degree. C. The raw material is alumina produced from bauxite using the
 Bayer process. The usual chemical used to extract the aluminum values from
 bauxite is caustic (NaOH), and thus chemically creates a negatively
 charged product, Al(OH.sub.4).sup.-.
 The carbo-electrolysis in a molten bath of three percent, by weight,
 Al(OH.sub.4).sup.- alumina, at about 950.degree. C., will accumulate
 aluminum metal at the cathode. Oxygen at a carbon anode will produce
 carbon dioxide (CO.sub.2) and some carbon monoxide (CO). This can be
 represented in a carbo-electrolytic reaction, where,
 ##STR1##
 The oxygen ions O.sup.-- combine with carbon from the anode to produce a
 negative voltage drop. Some of the oxygen is also used in a thermal
 combustion or burning of the carbon anode. In both cases, the carbon from
 the anode is consumed.
 The theoretical voltage drop for equation (1) to produce the energy
 necessary to separate the aluminum and oxygen in the alumina is calculated
 from the energy of formation which is about 1600 kilojoule per gm mole of
 alumina. The voltage drop is about 2.2 volt. The energy liberated by the
 electrolytic production of CO.sub.2, according to equation (2), is about
 1.0 volt for one hundred percent conversion. It is generally accepted that
 fifty percent efficiency is achieved providing about 0.5 volt of the 2.2
 volt necessary for the electrolysis in equation (1). The net voltage drop
 needed in equations (1) and (2) combined is believed to be approximately
 1.7 volt.
 If "carbon free" anodes are used, the energy of equation (2) is not
 produced, and oxygen is liberated at the anode without the formation of
 CO.sub.2. The voltage drop is then about 2.2 volt. An overall voltage drop
 of five volts is required.
 Generally, embodiments of the present invention adapt the usual Bayer
 process which starts as aluminum hydroxide in a wet cake. Pressure is
 applied and the temperature is raised to about 140.degree. C. In the
 present invention, however, a stoichiometric amount of sulfuric acid and
 water are added to produce a basic aluminum sulfate (3Al.sub.2 O.sub.3.
 4SO.sub.3. 9H.sub.2 O) in solution. Sulfuric, nitric, carbolyic, and other
 such acids can be used, and the examples herein show the use of sulfuric
 acid. The pressure is increased and the temperature is raised to above
 180.degree. C. to precipitate a family of basic aluminum sulfates, e. g.,
 6Al(OH).sub.3 +4H.sub.2 SO.sub.4.fwdarw.3Al.sub.2 O.sub.3. 4SO.sub.3.
 9H.sub.2 O+4H.sub.2 O.
 The basic aluminum sulfate is then separated from the mother liquor and
 washed to provide a feedstock of Al.sup.+++ charged alumina for aluminum
 production. The feedstock is calcined at about 950.degree. C. and produces
 cell-grade alumina. Such alumina from acidic solutions can be prepared
 from aluminum bearing raw materials such as bauxites, clays, and various
 other ores. See, D. J. O'Conner, Alumina Extraction from Non-Bauxitic
 Materials. Aluminum hydroxide is commercially produced for later
 calcination into cell grade alumina.
 Solubilization of the aluminum hydroxide is carried out in two steps.
 Initially the sulfuric acid required to produce the basic aluminum sulfate
 is added at approximately 140.degree. C. to some of the aluminum hydroxide
 producing an aluminum sulfate solution. The quantity of water included in
 the solution is adjusted to assure dissolution of the aluminum sulfate.
 Laboratory experience has shown this quantity to be roughly equivalent to
 that in the hydrate, Al.sub.2 (SO.sub.4).sub.3. 14H.sub.2 O. The remainder
 of the aluminum hydrate slurried with the required dilution water, is
 added to produce the required basic aluminum sulfate component mix at
 approximately 140.degree. C. and a pH of approximately one. The
 temperature is raised under pressure to 170.degree. C. to 230.degree. C.,
 preferably above 180.degree. C., where a yield of approximately eighty
 percent precipitated basic aluminum sulfate is produced as a thirty
 percent slurry. After separation of the basic aluminum sulfate product
 from the mother liquor the latter is recycled to the beginning of the
 process. Basic aluminum sulfate thus produced is dried, dehydrated, and
 calcined at approximately 950.degree. C. The product thus produced has a
 surface area (BET) of approximately eighty and has flowability
 characteristics suitable for feeding an aluminum smelter system.
 The recycle liquor contains the unreacted components and water not removed
 with the basic aluminum sulfate product. This water is in excess of that
 required in the first solution step.
 Therefore, the product slurry produced at approximately 1400 kilo-Pascals
 is reduced to atmospheric in a pressure let down step thus approximately
 balancing the water involved in basic aluminum sulfate production by
 removing approximately ten percent of the water as flashed vapor. The net
 excess water is then limited to that produced in the combustion of natural
 gas in the calcination of basic aluminum sulfate to produce alumina.
 The addition of excess sulfuric acid, beyond the stoichiometric
 requirement, to the reactant mix can be used to influence the particle
 size distribution of the final positively charged alumina product. Any
 free acid remaining, up to ten percent of stoichiometric, is recycled.
 Extra acid is required to maintain a pH of one, and helps produce a
 particle size distribution that averages twenty microns. Such particle
 size gives good flowability and increased bulk density, which is an
 important advantage.
 Process embodiments of the present invention convert aluminum hydroxide
 into a reactive alumina that is highly soluble in molten electrolytes
 above the melting point of aluminum, 660.degree. C. Such alumina is
 suitable for use as catalyst as well as cell grade alumina for
 electrolysis of aluminum at temperatures greater than the melting point of
 aluminum, e.g., above 660.degree. C.
 Other processes using acids to extract the aluminum values from ores can be
 used including but not limited to bauxite, ores wherein "cell grade"
 positively charged alumina is produced with or without the need for
 caustic or the Bayer process. See, D. J. O'Conner, Alumina Extraction from
 Non-Bauxitic Materials.
 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.