Patent Publication Number: US-6221233-B1

Title: Aluminum production utilizing positively charged alumina

Description:
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 2 O 3 , which is dissolved in an electrolyte of molten cryolite, Na 3 AlF 6 , at temperatures of 945° C. to 975° 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 2  produces a voltage drop of about 0.3 volts/cm −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 2 O 3 +3C+energy=4Al+3CO 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° 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 2 O 3 , by weight, is considered the upper limit at 950° 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 2 . 
     The dissolution of the alumina in the molten bath is so low, it requires careful and sophisticated replenishment. At 750° 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° 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) 4   − . Such precipitation is usually done at a pH of about nine, and a temperature of about 80° 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° 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) 4   −  particles, at about pH of nine, to positively charged particles containing Al +++  with a pH of less than two, by using acid solutions. The alumina thus produced is referred to as Al +++  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 2 O 3 4SO 3 9H 2 O, which is in turn dehydrated and calcined to produce the Al +++  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 +++  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° C., which reduces heat losses in comparison to operation at 950° C. and allows for the use of “carbon free” (inert) anodes. In contrast, Bayer alumina is relatively insoluble at 750° C. in molten flouride, while Al +++  alumina appears to be soluble at a concentration in excess of four percent at 750° C. 
     Another apparent advantage of the present invention is that the use of Al +++  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 +++  alumina is soluble in the electrolyte at these lower temperatures and alumina produced with caustics is not. 
    
    
     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 embodiment that is illustrated in the drawing figures. 
     IN THE DRAWINGS 
     FIG. 1 is a cross sectional diagram of a first cell embodiment of the present invention that includes two consumable carbon anodes and uses a main feed of positively charged alumina; 
     FIG. 2 is a cross sectional diagram of a second cell embodiment of the present invention that includes two inert anodes and a main feed of positively charged alumina; 
     FIG. 3 is a process flow diagram illustrating a first process embodiment for the production of positively charged alumina from aluminum hydroxide; 
     FIG. 4 is a process flow diagram illustrating a second process embodiment for the production of positively charged alumina from aluminum hydroxide; and 
     FIG. 5 is a cross section of a laboratory cell taken along a central vertical plane that was used in an experiment which measured the various voltage drops that occur during aluminum smelting. 
    
    
     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 3 AlF 6 )  120  is heated to approximately 750° 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° 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° 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° 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° C. and not more than 210° 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° C. to the atmospheric boiling point, e.g., 100° 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° 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° 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° C. to 230° C., and preferably over 180° 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° 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° 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° 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 2  and SO 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 3  are removed in a drying step. The gases are then passed through a conventional SO 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° C. to 980° 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 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 +++  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 +++  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 +++  alumina can be electrolyzed in molten fluoride baths at all temperatures above the melting point of aluminum (660° C.). 
     Prior art processes that use the Hall-Heroult electrolytic process depend upon maintaining a molten cryolite, Na 3  AlF 6 , salt at about 950° 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 4 ) − . 
     The carbo-electrolysis in a molten bath of three percent, by weight, Al(OH 4 ) −  alumina, at about 950° C., will accumulate aluminum metal at the cathode. Oxygen at a carbon anode will produce carbon dioxide (CO 2 ) and some carbon monoxide (CO). This can be represented in a carbo-electrolytic reaction, where,                    
     The oxygen ions O −−  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 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 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° C. In the present invention, however, a stoichiometric amount of sulfuric acid and water are added to produce a basic aluminum sulfate (3Al 2 O 3 . 4SO 3 . 9H 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° C. to precipitate a family of basic aluminum sulfates, e. g., 6Al(OH) 3 +4H 2 SO 4 →3Al 2 O 3 . 4SO 3 . 9H 2 O+4H 2 O. 
     The basic aluminum sulfate is then separated from the mother liquor and washed to provide a feedstock of Al +++  charged alumina for aluminum production. The feedstock is calcined at about 950° 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&#39;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° 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 2 (SO 4 ) 3 . 14H 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° C. and a pH of approximately one. The temperature is raised under pressure to 170° C. to 230° C., preferably above 180° 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° 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° 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° 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&#39;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.