High-purity aluminum oxide by electrodialysis

Abstract

The present invention describes a method for producing a high purity aluminum salt solution by electrodialysis and a method for ultimately converting the high purity aluminum salt into high purity aluminum oxide.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Non-Provisional Patent Application No. 16 / 850,261, filed April 16, 2020, entitled "HIGH PURITY ALUMINUM OXIDE VIA ELECTRODIALYSIS," and also claims the benefit of U.S. Provisional Patent Application No. 62 / 835,585, filed April 18, 2019, entitled "HIGH PURITY ALUMINUM OXIDE VIA ELECTRODIALYSIS," the entire contents of which are incorporated herein by reference.

[0002] The present invention relates generally to a method for producing high purity aluminum salt solutions by electrodialysis, and ultimately to a method for producing high purity aluminum oxide. [Background technology]

[0003] High-purity alumina preferably has a purity of more than 99.9% Al2O3. High-purity aluminum oxide has numerous applications. For example, high-purity alumina is used in ceramic processing, the production of translucent alumina, luminescent compositions for fluorescent lamps, bioceramics, LED lighting products, separators for lithium-ion batteries, and metal polishing. High-purity alumina is also a raw material for producing single crystals using the Verneuil crystallization technique.

[0004] Various processes can be used to obtain high-purity alumina. Some processes utilize aluminum as the starting material. In these cases, aluminum is converted to an organic acid salt or alcoholate, which is then hydrolyzed or pyrolyzed to finally obtain alumina. Although regeneration of the alcohol is possible in some cases, the cost of this alumina is quite high due to the need to use metallic aluminum.

[0005] Several other routes start from impure aluminum hydroxide products, many of which are obtained in the mineral-based aluminum industry. These routes involve passing through intermediate mineral salts, which can be crystallized to remove most of the impurities. The product thus obtained is then pyrolyzed to form pure alumina. Several other procedures based on this principle are based on the crystallization of ammonium alum, which is formed starting from aluminum hydroxide, sulfuric acid, and ammonia, but this method of operation with such salts has many drawbacks.

[0006] Other approaches include the production and purification of aluminum oxide through numerous steps, such as those in U.S. Patent Nos. 7,837,961 and 10,081,553, which require multiple washings of the material, isolation of intermediate product(s), leaching, concentration of each solution, redissolution of intermediate product(s), further isolation of each component, drying, grinding, and isolation of multiple components from various steps of the process.

[0007] The requirement for multi-step processing increases the operating and capital costs associated with the desired high purity aluminum oxide, as well as the potential for contamination with undesirable ions during processing.

[0008] Furthermore, materials used in current processes must include high-purity water and anion(s), high-purity HCl, high-purity aluminum metal, or high-purity 1-hexanol to avoid introducing impurities into the product. (See U.S. Pat. No. 10,081,553.) All requirements for using high-purity materials increase the cost of producing high-purity aluminum oxide.

[0009] Therefore, there is a need to overcome one or more of the current deficiencies discussed above. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent No. 7,837,961 [Patent Document 2] U.S. Patent No. 10,081,553 Summary of the Invention

[0011] The present invention surprisingly provides a very simple, concise, and cost-saving approach to making high purity alumina (HPA) without the need for expensive aluminum metal or complex processes. The present invention generally relates to a method for producing a high purity aluminum salt solution and ultimately a method for producing high purity aluminum oxide.

[0012] The method described herein involves providing an initial aluminum salt aqueous solution having an aluminum salt dissolved therein, and then subjecting the initial aluminum salt aqueous solution to an electrodialysis environment comprising a cation-permeable membrane and an anion-permeable membrane or a bipolar membrane to remove monovalent and / or polyvalent cations from the initial aluminum salt aqueous solution.

[0013] The purified aqueous aluminum salt solution is produced by reducing or completely removing unwanted monovalent and / or polyvalent non-aluminum cations from the initial aqueous aluminum salt solution.

[0014] The resulting purified aqueous aluminum salt solution contains lower levels of monovalent and polyvalent non-aluminum cations than the initial aluminum salt solution, e.g., less than 1000 ppm to about 1 ppm or less in total, e.g., 900 ppm, 800 ppm, 700 ppm, 600 ppm, 500 ppm, 400 ppm, 300 ppm, 200 ppm, 100 ppm, 50 ppm, 25 ppm, 10 ppm, 5 ppm, 1 ppm, 0.5 ppm, 0.2 ppm, 0.1 ppm, 0.05 ppm, 0.02 ppm, 0.01 ppm, 0.001 ppm, based on aluminum oxide, of Na, K, Li, Ca, Cr, Zn, Cu, Ti, Mg, Mn, Fe, Si, or other cations, or mixtures thereof, to provide a purified aluminum salt.

[0015] The resulting purified aluminum salt aqueous solution can be subjected to various processes to isolate the purified aluminum salt, which can then be subjected to various methods to convert the purified aluminum salt into high-purity aluminum oxide. The resulting high-purity aluminum oxide has a purity ranging from about 3N (99.9% purity, with impurity levels of only 0.1%, or 1000 ppm) to about 6N (99.9999% purity, with impurity levels of only 0.0001%, or 1 ppm).

[0016] This embodiment offers several advantages over current processes known in the art.

[0017] The use of electrodialysis to produce high purity aqueous aluminum salt solutions ultimately provides a low cost, efficient process for producing high purity aluminum oxide.

[0018] The direct removal of impurities from aqueous aluminum salt solutions provides a means of process control.

[0019] The embodiments described herein provide the ability to remove unwanted impurities from aqueous aluminum salt solutions in a single process step, for example, electrodialysis.

[0020] Impurities such as sodium and calcium removed from the aqueous aluminum salt solution by the electrodialysis process do not become concentrated in the mother liquor during the subsequent crystallization or evaporation process, thereby minimizing the mother liquor purification requirements and allowing for efficient regeneration of the mother liquor.

[0021] The embodiments described herein provide an opportunity to use lower purity, lower cost raw materials, including an aluminum source, an aluminum salt source, a water source, and an anion source.

[0022] Furthermore, the capital costs associated with the embodiments described herein are much lower due to the nature of the overall electrodialysis process and the expensive equipment required. Many current commercial processes require multiple processing steps to achieve adequate purity of aluminum oxide.

[0023] While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description. As will be apparent, the present invention is capable of modification in various obvious aspects, all without departing from the spirit and scope of the present invention. Accordingly, the detailed description is to be regarded as illustrative in nature and not restrictive. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 illustrates the basic components and operation of an electrodialysis process using a single layer membrane. [Figure 2] FIG. 1 illustrates the basic components and operation of an electrodialysis process using bipolar membranes in a two-compartment configuration. DETAILED DESCRIPTION OF THE INVENTION

[0025] As used in this specification and claims, the terms "comprise" and "comprising" are open-ended terms and should be interpreted to mean "including, but not limited to." These terms encompass the more restrictive terms "consisting essentially of" and "consisting of."

[0026] It should be noted that, as used in this specification and the appended claims, things include plural references unless the context dictates otherwise. Similarly, terms preceded by "one or more," "at least one," and the same terms without these prefixes can be used interchangeably herein. It should also be noted that the terms "comprising," "characterized by," and "having" can be used interchangeably.

[0027] As used herein, the term "high purity aluminum oxide" (AlO) refers to aluminum oxide having a purity of about 3N (99.9% purity, with impurity levels of as little as 0.1%, i.e., 1000 ppm) or greater. In some examples, the term "high purity aluminum oxide" refers to aluminum oxide having a purity ranging from about 3N to about 6N (99.9999% purity, with impurity levels of as little as 0.0001%, i.e., 1 ppm).

[0028] Electrodialysis (ED) is an electrochemical process in which ions are transported from one solution to another through an ion-permeable membrane under the influence of a potential gradient. The ions' charge drives them through the membrane, which is made of an ion-exchange polymer. Applying a voltage between two end electrodes creates the potential field necessary for ion transport across the membrane. Because the membranes used in electrodialysis selectively transport ions with a positive or negative charge and reject ions of the opposite charge, useful concentrations, removals, or separations of electrolytes can be achieved by electrodialysis. Commercial applications of electrodialysis include the removal of salt from brackish water to produce drinking water, the concentration of seawater to a 20% salt concentration as a first step toward salt production, the reduction of minerals from whey to produce infant formula, and the reduction of salt from soy sauce.

[0029] The equipment used in the electrodialysis process is commonly called an electrodialysis stack. The essential elements of an electrodialysis stack for electrodialysis are an anode, a cathode, a cation-permeable membrane, and an anion-permeable membrane. The essential elements of an electrodialysis stack for bipolar electrodialysis are an anode, a cathode, a cation-permeable or anion-permeable membrane, and a bipolar membrane, or in the case of a three-compartment bipolar electrodialysis stack, a cation-permeable and anion-permeable membrane, and a bipolar membrane.

[0030] Figure 1 illustrates the basic components and operation of an electrodialysis process using a single membrane. Thus, cation- and anion-permeable membranes are alternately positioned between the anode and cathode. Assembling the ion-permeable membranes in this manner creates two separate sets of compartments. The first set of compartments or cells consists of anion-permeable membranes on the anode side and cation-permeable membranes on the cathode side. This set of cells is oriented relative to the anode and cathode so that ions are removed from these cells when a voltage is applied. The solutions in this set of compartments are referred to as the feed, dilution, or depletion streams. The second set of compartments or cells consists of anion-permeable membranes on the cathode side and cation-permeable membranes on the anode side. This set of cells is oriented relative to the anode and cathode so that ions are accepted and concentrated in these cells when a voltage is applied to the electrodes. The solutions in this second set of compartments are referred to as the acceptor, concentrate, or enrichment streams. Thus, the net effect of the electrodialysis process is to transfer electrolytes from the feed solution to the acceptor solution and concentrate the electrolytes in the acceptor solution.

[0031] Figure 2 illustrates the basic components and operation of an electrodialysis process using bipolar membranes in a two-compartment configuration. Thus, bipolar and cation-permeable membranes are alternately positioned between the anode and cathode. Assembling the bipolar and cation-permeable membranes in this manner creates two separate sets of compartments. The first set of compartments or cells consists of a cation-permeable membrane on the cathode side and a bipolar membrane on the anode side. The solutions in this set of compartments are referred to as the feed, dilute, or depleted stream. When a voltage is applied, H +The bipolar membrane provides the aluminum salt feed stream with an ion-permeable membrane, and unwanted cations are depleted from these cells. A second set of compartments or cells consists of a cation-permeable membrane on the anode side and a bipolar membrane on the cathode side. This set of cells is oriented relative to the anode and cathode so that electrolyte is received and concentrated in these cells when a voltage is applied to the electrodes. The solution in this second set of compartments is called the receiving, concentrate, or enriched stream. Thus, the net effect of the bipolar electrodialysis process is to transfer electrolyte from the feed solution to the receiving solution and concentrate that electrolyte in the receiving solution. To prevent the precipitation of metal hydroxides such as Ca(OH)2 and Mg(OH)2, a suitable acid, such as hydrochloric acid, may be added to the receiving compartment to adjust the pH of the receiving solution.

[0032] 1 and 2 are examples showing the movement of cations Na+, Ca++, K+, and anion Cl- and are shown for illustrative purposes. As known to those skilled in the art, other materials such as aluminum ions, water, or other molecules may also be present.

[0033] It should be understood that other configurations, such as a three-compartment biopolar system, are possible and are within the scope of the embodiments described herein.

[0034] No specific current or voltage is required, and typical electrodialysis conditions are approximately 1.2 V / cell pair and 500 amperes / m 2 Current densities of up to approximately 1.8 V / cell pair and 600 amperes / m are suitable for conventional electrodialysis. 2 A current density of 0.15 m / s is suitable for bipolar electrodialysis.

[0035] By treating the Al salt solution with either electrodialysis or bipolar electrodialysis, cations are selectively and efficiently removed from the Al salt feed solution and transported to the receiving solution. An advantage of the process is that unwanted cations are separated from the Al salt solution and efficiently removed from the system.

[0036] Materials of construction for electrodialysis system components, such as electrodialysis stack components, tanks, pumps, valves, piping, and equipment, can include non-fouling materials, coatings, or liners that can withstand the chemical and operating environments of the electrodialysis process without contaminating the process with additional impurities. Examples include, but are not limited to, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), chlorinated polyvinyl chloride (CPVC), polyvinyl chloride (PVC), rubber, polypropylene, glass, vinyl ester resins, and chemically compatible thermoplastics.

[0037] Impurities contained in aluminum salts can be efficiently and selectively removed from aluminum salt solutions using electrodialysis to levels comparable to those of aluminum salts made from high-purity metals, high-purity acids, and high-purity water. Thus, the embodiments described herein offer the advantage that the water, acid, and aluminum sources do not necessarily need to be highly pure due to the unique characteristics of the electrodialysis process.

[0038] For example, the electrodialysis process includes:

[0039] That is, providing a conventional electrodialysis stack with cation and anion membranes, or providing a bipolar electrodialysis stack with bipolar and cation membranes. Exemplary membranes include cation membranes such as Astom's Neosepta CMB and anion membranes such as Astom's Neosepta AHA, as well as Astom's bipolar membranes. Cation, anion, and bipolar membranes from other manufacturers may also be used.

[0040] The aluminum salt is placed in a feed tank and circulated through the feed compartment of a stack consisting of a cation membrane on the cathode side of the compartment and an anion membrane on the anode side of the compartment, or a bipolar membrane on the anode side of the compartment and a cation membrane on the cathode side of the compartment.

[0041] The receiving solution can be water with added electrolytes such as hydrochloric acid, a solution of aluminum salts, or other solutions suitable for electrodialysis. The receiving solution is placed in a receiving tank and circulated through the receiving compartments of a stack consisting of an anionic membrane on the cathode side of the compartment and a cation membrane on the cathode side of the compartment, or a bipolar membrane on the anode side of the compartment and a cation membrane on the cathode side of the compartment.

[0042] Each solution is circulated through the electrodialysis stack as conventional in an electrodialysis process and by application of appropriate DC power. An electrode rinse solution is provided and circulated through the electrode compartments as conventional in an electrodialysis process.

[0043] Each solution can optionally be filtered before, during, or after the electrodialysis process.

[0044] The electrodialysis process can be carried out under any physical conditions, such as temperature and pressure, suitable for electrodialysis.

[0045] Cations, including but not limited to sodium, calcium, magnesium, lithium, and potassium, are selectively and efficiently removed from the aluminum salt feed solution and transported to the receiving solution.

[0046] The receiving solution can be disposed of, recycled, or further treated and purified by electrodialysis.

[0047] The aluminum contained in the aluminum salt product substantially remains in the product solution contained within the feed loop of the electrodialysis system.

[0048] Suitable aluminum salts include, but are not limited to, aluminum chloride, aluminum sulfate, aluminum ammonium sulfate, aluminum nitrate, aluminum citrate, 1-hexanol aluminum, polyaluminum chloride (PAC), aluminum chlorohydrate (ACH), aluminum acetate, aluminum choline solution, or mixtures thereof.

[0049] The ratio of [Al]:[ligand] can vary. For example, aluminum salts such as AlCl, polyaluminum chloride, or cations of the formula Al(OH) 6-x Cl x Al2(OH)5Cl (aluminum chlorohydrate), defined by the formula: where x is any integer or fraction, and the resulting molecular formula represents a soluble aluminum compound or any aluminum salt in solution with HCl, may be used.

[0050] Aluminum salts can be obtained from sources including, but not limited to, aluminum-containing clays such as kaolin or bauxite, aluminum hydroxide, aluminum trihydrate (ATH), aluminum metal, or mixtures thereof.

[0051] These aluminum sources contain impurities including monovalent and polyvalent cations such as Na, K, Li, Ca, Mg, Mn, Fe, Si, etc.

[0052] The electrodialysis processes described herein offer the advantage that the processes herein do not require high purity aluminum metal or other aluminum sources as a starting material for making the aluminum salts, which provides substantial cost savings and also provides the ability to use alternative based aluminum source materials other than high purity aluminum metal.

[0053] The electrodialysis process is effective in removing contaminants, such as monovalent and polyvalent cations, from aluminum salt solutions. Examples of monovalent and polyvalent cations that may be contaminants in the initial aluminum salt solution that ultimately results in the purified aluminum salt solution include, but are not limited to, Na, K, Li, Ca, Cr, Zn, Cu, Ti, Mg, Mn, Ba, Sr, V, Ni, Pb, Co, Sb, As, B, Sn, Be, Mo, Fe, Si, or mixtures thereof.

[0054] Typically, the aluminum salt solutions (receiving / enriched and depleted / feed streams) are aqueous. That is, the solutions used in the electrodialysis process include water, but can also include non-aqueous solvents such as 1-hexanol, or other aluminum alkoxides, and aqueous choline solutions (see, e.g., U.S. Pat. No. 5,225,229). Due in part to the nature of the electrodialysis process, the use of high-purity water in the process is not required. The elimination of the need for purified water in the processes described herein results in substantial cost savings and waste reduction.

[0055] The electrodialysis process described herein results in a purified aqueous aluminum salt solution that contains lower levels of monovalent and polyvalent non-aluminum cations than the initial aluminum salt solution, e.g., less than about 1000 ppm to about 1 ppm or even less total of one or more undesired monovalent and / or polyvalent cations based on aluminum oxide.

[0056] After obtaining the purified aluminum salt aqueous solution, the solution can be subjected to various treatments to ultimately produce high-purity aluminum oxide with a purity of about 3N (99.9%) to 6N (99.9999%) or higher.

[0057] In one embodiment, the purified aqueous aluminum salt solution is subjected to a separation process to recover the purified aluminum salt, which can be accomplished by methods known in the art, such as crystallization, evaporation of water from the solution, centrifugation, or the like.

[0058] In another embodiment, the purified aqueous aluminum salt solution is acidified with an acid such as hydrochloric acid, nitric acid, or sulfuric acid, and the resulting precipitate can then be recovered by methods known in the art.

[0059] The separation and isolation process can include, but is not limited to, settling, filtration, or centrifugation of the aluminum salt crystal and mother liquor mixture. Separation can be performed in one or more non-fouling separation vessels and handling devices, which can comprise one of the non-fouling materials described above for electrodialysis configurations.

[0060] The separated purified aluminum salt(s) can optionally be washed with a washing solution to remove impurities that may adhere to the aluminum salt crystals. In one example, the washing solution can include at least one of a high-purity acid such as HCl, concentrated hydrochloric acid, high-purity acetone or another high-purity solvent, or a high-purity solution of an aluminum salt (e.g., if the crystals are aluminum chloride crystals, an aluminum chloride solution can be used as the washing solution), and high-purity water. In one example, an acidic washing solution (e.g., high-purity HCl such as concentrated HCl) is used at a sufficiently high concentration so that a significant portion of the purified aluminum salt material does not dissolve back into solution. Washing of the purified aluminum salt material can also be performed sufficiently quickly so that a significant portion of the purified aluminum salt material does not dissolve. The washing solution is purified and can be reused in the process. The aluminum salt product can optionally be milled or tumbled so that the size of the resulting material can be smaller later in the process.

[0061] The purified aluminum salt can be further processed. In one example, the purified aluminum salt aqueous solution or crystals can be directly treated by multiple heat treatment methods to remove water and anions and provide highly purified aluminum oxide. In another method, the purified aluminum salt solution or crystals can be heated to convert it to highly purified aluminum oxide.

[0062] For example, an aqueous solution or crystals of a purified aluminum salt can be subjected to calcination to provide highly purified aluminum oxide. Alternatively, isolated purified aluminum salt crystals can be calcined directly. A fine mist of the aqueous solution of the purified aluminum salt is sprayed into a calcination furnace to remove water and anions, and the highly purified aluminum salt is converted to form highly purified aluminum oxide. The highly purified aluminum oxide can be collected in a non-contaminating container formed from one of the non-contaminating materials described above, such as Teflon.

[0063] In another embodiment, the purified aluminum salt solution can be subjected to spray roasting, a type of calcination, and then the high-purity aluminum salt solution can be converted to obtain high-purity aluminum oxide.

[0064] Typically, the calcination or spray roasting step is carried out over a temperature range of about 300° C. to about 1800° C., more specifically about 500° C. to about 1300° C., and more specifically about 800° C. to about 1200° C. Generally, a temperature range of about 1000° C. to about 1300° C. will convert the gamma, theta, kappa, or other phase of alumina to the desired alpha alumina.

[0065] Spray roasting or calcination decomposes the Al salt solution, separating HCl and water from the alumina to form intermediate alumina, e.g., gamma, theta, kappa, or other phases. If desired, the intermediate alumina can be further heated to form a desired crystalline phase, such as alpha alumina.

[0066] Alternatively, the HPA can be provided by spray drying an aluminum salt solution to form dry aluminum salt crystals, followed by calcining the dried aluminum salt.

[0067] In another embodiment, aluminum oxide can be made by subjecting a purified aqueous aluminum solution to an "oil drop" process, in which the solution is contacted with hot oil to remove water and HCl and convert the purified aluminum salt to aluminum oxide.

[0068] In all cases, the ligand or acid generated from the decomposition of the aluminum salt during calcination can be trapped and then reacted with an aluminum source, such as alumina trihydrate, kaolin, or aluminum metal, to produce the initial Al salt for use in the process. For example, the hydrochloric acid and water generated upon heating a solution or crystals of the aluminum salt condense to form a hydrochloric acid solution. This hydrochloric acid solution can be used to dissolve an aluminum source, such as aluminum trihydrate, kaolin, or aluminum metal, and then completely regenerated.

[0069] The resulting high purity aluminum oxide can optionally be washed, or crushed or tumbled so that the size of the resulting material can be smaller for further processing.

[0070] The high-purity aluminum oxide described herein has many applications. For example, high-purity aluminum oxide or alumina powder can be used to make translucent tubes for high-pressure sodium lamps, sapphire for watch covers, high-strength ceramic tools, abrasives for magnetic tape, light-emitting diodes as substrates for GaN, silicon microchip wafers for optoelectronics, aircraft windows and cowls, protective windows for vehicle headlamps, cell phones and other electronic devices, stop signals, surgical scalpels, micro-optical elements in medical fiber optic probes, optical scanners for barcodes, UV CD and DVD optical systems, prisms, lenses, optical plates, optical tuning forks and IR tuning forks, display windows for cell phones, mobile devices, and fiber optic systems, LED lighting, catalytic materials, insulating materials for electrical applications such as lithium-ion batteries, equipment for chemical manufacturing in corrosive and high-temperature environments (tubes, crucibles, funnels, chemical glassware), abrasives, battery components, bearings, and jewelry. Impurities such as monovalent and multivalent cations are harmful to these materials.

[0071] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All publications and patents specifically mentioned herein are incorporated by reference in their entirety for all purposes, including describing and disclosing the chemicals, instruments, statistical analyses, and methodologies described in those publications that may be used in connection with the present invention. All references cited herein should be construed as indicating the state of the art. Nothing herein should be construed as an admission that the present invention is not entitled to antedate its disclosure by virtue of prior invention.

[0072] The following paragraphs, listed consecutively from 1 to 50, define various aspects of the various embodiments described herein. In one embodiment, in the first paragraph (1), the present invention provides: 1. A method for producing a high-purity aqueous aluminum salt solution, comprising:

[0073] providing an initial aluminum salt solution having an aluminum salt dissolved therein;

[0074] and subjecting the initial aqueous aluminum salt solution to electrodialysis to remove monovalent and polyvalent cations from the initial aqueous aluminum salt solution, thereby reducing the amount of unwanted monovalent and / or polyvalent cations from the initial aqueous aluminum salt solution to produce a purified aqueous aluminum salt solution.

[0075] 2. The method of paragraph 1, wherein the unwanted monovalent and / or polyvalent cations are completely removed from the purified aqueous aluminum salt solution.

[0076] 3. The method of paragraph 1, wherein the unwanted monovalent and / or polyvalent cations of the initial aqueous aluminum salt solution comprise Na, K, Li, Ca, Cr, Zn, Cu, Ti, Mg, Mn, Ba, Sr, V, Ni, Pb, Co, Sb, As, B, Sn, Be, Mo, Fe, Si, or other cations, or mixtures thereof.

[0077] 4. The method of any of paragraphs 1 to 3, wherein the aluminum salt of the initial aqueous aluminum salt solution comprises aluminum chloride, aluminum sulfate, aluminum ammonium sulfate, aluminum nitrate, aluminum citrate, 1-hexanol aluminum, polyaluminum chloride (PAC), aluminum chloride hydrate (ACH), aluminum acetate, aluminum choline solution, or a mixture thereof.

[0078] 5. The method of paragraph 4, wherein the aluminum salt is derived from an aluminum-containing clay.

[0079] 6. The method of paragraph 5, wherein the aluminum clay is kaolin or bauxite, or other alumina clay.

[0080] 7. The method of paragraph 4, wherein the aluminum salt is derived from aluminum hydroxide, alumina trihydrate (ATH), or aluminum metal.

[0081] 8. The method of any of paragraphs 1 to 7, wherein the purified aqueous aluminum salt solution contains lower levels of monovalent and polyvalent non-aluminum cations, based on aluminum oxide and total unwanted monovalent and / or polyvalent cations, than the initial aluminum salt solution.

[0082] 9. The method of any of paragraphs 1 to 7, wherein the purified aqueous aluminum salt solution contains less than about 1000 ppm to about 1 ppm total of unwanted monovalent and / or polyvalent cations based on aluminum oxide.

[0083] 10. The method of any of paragraphs 1 to 7, wherein the purified aqueous aluminum salt solution contains less than about 100 ppm to about 1 ppm total of unwanted monovalent and / or polyvalent cations based on aluminum oxide.

[0084] 11. The method of paragraph 10, wherein the purified aqueous aluminum salt solution contains less than about 10 ppm or less than about 1 ppm or even less total undesired monovalent and / or multivalent cations based on aluminum oxide.

[0085] 12. The method of any of paragraphs 1 to 11, further comprising:

[0086] crystallizing a purified aluminum salt from said aqueous solution of purified aluminum salt.

[0087] 13. The method of paragraph 12, wherein the purified aluminum salt is separated from the aqueous purified aluminum salt solution.

[0088] 14. The method of any of paragraphs 1 to 11, further comprising:

[0089] evaporating the aqueous portion of said purified aluminum salt solution to obtain a purified aluminum salt.

[0090] 15. The method of any of paragraphs 1 to 11, further comprising:

[0091] treating said aqueous purified aluminum salt solution with an acid to obtain a precipitate of purified aluminum salt.

[0092] 16. The method of paragraph 15, wherein the acid is hydrochloric acid, nitric acid, sulfuric acid, or a mixture thereof.

[0093] 17. The method of any of paragraphs 12 to 16, wherein the purified aluminum salt is treated with a high purity aluminum salt solution or other solution such as concentrated hydrochloric acid.

[0094] 18. The method of any of paragraphs 12 to 16, wherein the purified aluminum salt is washed with a high purity aluminum salt solution.

[0095] 19. The method of either paragraph 17 or 18, wherein the purified aluminum salt is washed or treated with a high purity saturated aluminum salt solution.

[0096] 20. The method of any of paragraphs 12 to 19, further comprising:

[0097] subjecting the purified aluminum salt to heating, roasting, calcining, spray roasting, or oil drop treatment, or other heating process to provide purified aluminum oxide.

[0098] 21. The method of paragraph 20, wherein the purified aluminum oxide contains lower levels of monovalent and polyvalent non-aluminum cations, based on aluminum oxide and total unwanted monovalent and / or polyvalent cations, than the initial aluminum salt solution.

[0099] 22. The method of paragraph 20, wherein the purified aluminum oxide contains less than about 1000 ppm to about 1 ppm total of one or more undesired monovalent and / or multivalent cations based on the aluminum oxide.

[0100] 23. The method of paragraph 20, wherein the purified aluminum oxide contains less than about 100 ppm to about 1 ppm total of one or more undesired monovalent and / or multivalent cations based on the aluminum oxide.

[0101] 24. The method of paragraph 20, wherein the purified aluminum oxide contains less than about 10 ppm, or less than about 1 ppm, or even less, of one or more undesired monovalent and / or multivalent cations in total, based on the aluminum oxide.

[0102] 25. A method for removing monovalent and polyvalent metal cations from aqueous aluminum salt solutions, comprising:

[0103] providing an initial aluminum salt solution having an aluminum salt dissolved therein;

[0104] and subjecting the initial aqueous aluminum salt solution to electrodialysis to remove monovalent and polyvalent cations from the initial aqueous aluminum salt solution, thereby reducing the amount of unwanted monovalent and / or polyvalent cations from the initial aqueous aluminum salt solution to produce a purified aqueous aluminum salt solution.

[0105] 26. The method of paragraph 25, wherein the unwanted monovalent and / or polyvalent cations are completely removed from the purified aqueous aluminum salt solution.

[0106] 27. The method of paragraph 25, wherein the unwanted monovalent and / or polyvalent cations of the initial aqueous aluminum salt solution comprise Na, K, Li, Ca, Cr, Zn, Cu, Ti, Mg, Mn, Ba, Sr, V, Ni, Pb, Co, Sb, As, B, Sn, Be, Mo, Fe, Si, or other cations, or mixtures thereof.

[0107] 28. The method of any of paragraphs 25 to 27, wherein the aluminum salt of the initial aqueous aluminum salt solution comprises aluminum chloride, aluminum sulfate, aluminum ammonium sulfate, aluminum nitrate, aluminum citrate, 1-hexanol aluminum, polyaluminum chloride (PAC), aluminum chloride hydrate (ACH), aluminum acetate, aluminum choline solution, or a mixture thereof.

[0108] 29. The method of paragraph 27, wherein the aluminum salt is derived from an aluminum-containing clay.

[0109] 30. The method of paragraph 29, wherein the aluminum clay is kaolin or bauxite, or other aluminous clay.

[0110] 31. The method of paragraph 28, wherein the aluminum salt is derived from aluminum hydroxide, alumina trihydrate (ATH), or aluminum metal.

[0111] 32. The method of any of paragraphs 25 to 31, wherein the purified aqueous aluminum salt solution contains lower levels of monovalent and polyvalent non-aluminum cations, based on aluminum oxide and total unwanted monovalent and / or polyvalent cations, than the initial aluminum salt solution.

[0112] 33. The method of any of paragraphs 25 to 31, wherein the purified aqueous aluminum salt solution contains less than about 1000 ppm to about 1 ppm total of unwanted monovalent and / or polyvalent cations based on aluminum oxide.

[0113] 34. The method of any of paragraphs 25 to 31, wherein the purified aqueous aluminum salt solution contains less than about 100 ppm to about 1 ppm total of unwanted monovalent and / or polyvalent cations based on aluminum oxide.

[0114] 35. The method of paragraph 34, wherein the purified aqueous aluminum salt solution contains less than about 10 ppm or less than about 1 ppm or even less total undesired monovalent and / or multivalent cations based on aluminum oxide.

[0115] 36. The method of any of paragraphs 25 to 35, further comprising:

[0116] crystallizing a purified aluminum salt from said aqueous solution of purified aluminum salt.

[0117] 37. The method of paragraph 36, wherein the purified aluminum salt is separated from the aqueous purified aluminum salt solution.

[0118] 38. The method of any of paragraphs 25 to 35, further comprising:

[0119] evaporating the aqueous portion of said purified aluminum salt solution to obtain a purified aluminum salt.

[0120] 39. The method of any of paragraphs 25 to 35, further comprising:

[0121] treating said aqueous purified aluminum salt solution with an acid to obtain a precipitate of purified aluminum salt.

[0122] 40. The method of paragraph 39, wherein the acid is hydrochloric acid, nitric acid, sulfuric acid, or a mixture thereof.

[0123] 41. The method of any of paragraphs 36 to 40, wherein the purified aluminum salt is treated with a high purity aluminum salt solution or other solution such as concentrated hydrochloric acid.

[0124] 42. The method of any of paragraphs 36 to 40, wherein the high purity aluminum salt is washed with a high purity aluminum salt solution.

[0125] 43. The method of either paragraph 41 or 42, wherein the purified aluminum salt is treated or washed with a saturated high-purity aluminum salt solution.

[0126] 44. The method of any of paragraphs 36 to 43, further comprising:

[0127] subjecting the purified aluminum salt to heating, roasting, calcining, spray roasting, or oil drop treatment, or other heating process to provide purified aluminum oxide.

[0128] 45. The method of paragraph 44, wherein the purified aluminum oxide contains lower levels of monovalent and polyvalent non-aluminum cations, based on aluminum oxide and total unwanted monovalent and / or polyvalent cations, than the initial aluminum salt solution.

[0129] 46. ​​The method of paragraph 44, wherein the purified aluminum oxide contains less than about 1000 ppm to about 1 ppm total of one or more undesired monovalent and / or multivalent cations based on the aluminum oxide.

[0130] 47. The method of paragraph 44, wherein the purified aluminum oxide contains less than about 100 ppm to about 1 ppm total of one or more undesired monovalent and / or multivalent cations, based on the aluminum oxide.

[0131] 48. The method of paragraph 44, wherein the purified aluminum oxide contains less than about 10 ppm, or less than about 1 ppm, or even less, of one or more undesired monovalent and / or multivalent cations in total, based on the aluminum oxide.

[0132] 49. High purity alumina (HPA) provided by any of the processes in paragraphs up to and including 48.

[0133] 50. The high purity aluminum of paragraph 49, wherein the HPA is used in high pressure sodium lamps, sapphire for watch covers, high strength ceramic tools, abrasives for magnetic tapes, light emitting diodes as substrates for GaN, silicon microchip wafers for optoelectronics, windows and cowls for aircraft, protective windows for vehicle headlamps, mobile phones and other electronic devices, stop signals, surgical scalpels, micro-optical elements in medical fiber optic probes, optical scanners for bar codes, UV CD and DVD optical systems, prisms, lenses, optical plates, optical systems for optical and IR tuning forks, mobile phones, display windows for mobile phones, display windows for mobile devices and fiber optic systems, LED lighting, catalytic materials, insulating materials for electrical applications such as lithium ion batteries, equipment for chemical manufacturing in aggressive and high temperature environments (tubes, crucibles, funnels, chemical glassware), abrasives, battery components, bearings, and jewelry.

[0134] The present invention will be further described with reference to the following non-limiting examples. It will be apparent to those skilled in the art that many modifications can be made to the described embodiments without departing from the scope of the invention. Accordingly, the scope of the present invention is not limited to the embodiments described in this application, but only by the embodiments described by the language of the claims and equivalents of those embodiments. Unless otherwise specified, all percentages are by weight. [Example]

[0135] [Example 1] Production of high-purity aluminum chloride hexahydrate crystals by electrodialysis

[0136] Electrodialysis stack and system: A Euro 2 electrodialysis stack provided by Eurodia Industrie, comprising 10 cell pairs configured as described in Figure 1 herein, and equipped with Astom Neosepta CMB cation membranes and Astom Neosepta AHA anion membranes. The anolyte solution was dilute sulfuric acid, and the catholyte solution was dilute hydrochloric acid. These solutions were circulated through the compartments containing the electrodes and, in each example, separated by membranes from the active cells of the ED stack.

[0137] Feed Solution: 3000 grams of a polyaluminum chloride solution prepared from alumina trihydrate, hydrochloric acid, and water, the analysis of which is based on aluminum oxide and is listed in Table 1 below as Solution 1.

[0138] Receptor solution: 7900 grams of deionized water adjusted to pH 2.5 with HCl.

[0139] The above feed and receiver solutions were placed in the feed and receiver tanks of the Euro 2 system. The circulation pumps were started to circulate each solution through the Euro 2 ED stack and back to their respective tanks. The temperature of the feed and receiver solutions was maintained at 40°C. The DC power supply was started at 17V and a maximum current of 9 amps was applied. A total charge of 11.97 amp hours was applied.

[0140] The DC power was turned off, the circulation pumps were stopped, and each solution was removed from each tank.

[0141] The purified feed solution obtained from the above electrodialysis run was analyzed and the analytical results, based on aluminum oxide, are reported in Table 1 as Solution 2.

[0142] 15.5 grams of concentrated HCl was added to 54.5 grams of the purified diluted solution with stirring to form aluminum chloride hexahydrate (ACH) crystals in the mother liquor.

[0143] The ACH crystals were separated from the mother liquor by filtration through a Buchner funnel equipped with filter paper and then washed with 100 milliliters of concentrated HCl. 17.7 grams of ACH crystals were recovered and analyzed. The analytical results, based on aluminum oxide, are reported in Table 1 as Crystal 1.

[0144] The above process may be operated in batch mode, or in continuous mode where the Al salt feed solution is continuously added to the system and continuously removed, and the receiving solution is continuously added and continuously removed. The system may also be operated in semi-batch mode, or any combination of batch and continuous modes.

[0145] All analyses described herein were performed by inductively coupled plasma optical emission spectrometry (ICP-OES), also known as inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Other suitable methods for identifying impurities include, for example, glow discharge mass spectrometry (e.g., Thermo Scientific Element GD Plus BD-MS) and / or X-ray fluorescence spectroscopy.

[0146] Aluminum salt solutions, aluminum salt crystals, or HPA were analyzed for trace elements using a Spectro ARCOS EOP (Earth-on Plasma or Axial Photometry) ICP-OES. The ICP-OES utilized an OptiMist® VORTEX nebulizer and cyclonic spray chamber from Texas Scientific Products, and a D-Torch with a quartz outer tube and a 2.4 mm sapphire injector from Glass Expansion. HPA samples were digested with sulfuric acid, diluted with nitric acid, and subjected to elemental analysis. Calibration was performed using standard solutions of various monovalent or polyvalent cations of known concentrations prepared under similar conditions. The aluminum source for the HPA standard was a 20 mg / mL standard (#SM-1934-001-1L) from High Purity Standards.

[0147] Elements below the detection limit are excluded.

[0148] [Table 1]

[0149] [Example 2] Preparation of high-purity aluminum chloride solution

[0150] The electrodialysis process in Example 2 was carried out in a Eurodia EUR6B-20 electrodialysis stack. The stack consisted of dimensionally stable electrode (DSE) anodes and cathodes, and a combination of Neosepta AHA anion-permeable membranes and Neosepta CMB cation-permeable membranes. There were 20 pairs of electrodialysis membranes, each with a working surface area of ​​0.056 m. 2 Other cation and anion exchange membranes, including fluorinated membranes, can be used in the electrodialysis process.

[0151] The feed tank was a 75-liter polypropylene tank, and an Iwaki centrifugal pump was used to circulate the feed solution to the electrodialysis stack. The inlet pressure, flow rate, and temperature were monitored during operation. The receiver tank was a 75-liter polypropylene tank, and an Iwaki centrifugal pump was used to circulate the feed solution to the electrodialysis stack. The inlet pressure, flow rate, pH, and temperature of this solution were also monitored during operation. The electrode rinse system consisted of two 20-liter polypropylene tanks for the anode and cathode solutions, each equipped with an Iwaki centrifugal circulation pump. DC power was supplied to the stack by a Sorensen DCS40-25 power supply. Current and voltage data were collected during the process.

[0152] The system may be operated in batch mode, or in continuous mode where the Al salt feed solution is continuously added to the system and continuously removed, and the receiving solution is continuously added and continuously removed. The system may also be operated in semi-batch mode, or any combination of batch and continuous modes.

[0153] A feed solution tank was charged with 60,000 grams of a polyaluminum chloride salt solution prepared from the reaction of aluminum trihydrate, hydrochloric acid, and water, the analysis of which is shown in Table 2 as PAC solution. The conductivity was 150 mS / cm. 2 55,000 grams of hydrochloric acid solution with a conductivity of 150 ms / cm was placed in the receiving solution tank. 2 A hydrochloric acid solution of 150 ms / cm is placed in the cathode solution tank. 2 The sulfuric acid solution was placed in the anode solution tank. The four solutions were circulated through each compartment of the electrodialysis stack by a centrifugal pump and returned to their respective tanks. Each solution was heated to 40°C by an electric immersion heater, and the temperature was maintained at 40°C throughout the run. DC power of 25 amps and 20 V was applied. A total charge of 80 amp-hours was applied. The DC power and circulating pump were shut off, and the feed solutions were analyzed. The analytical results are reported in Table 2 as high purity (HP)-PAC solutions. All solutions and high purity alumina were analyzed using ICP-OES.

[0154] The Al salts described in this example are only examples. Formula Al(OH) x Cl6- x Other Al chloride salts can be used, including any of the Al salts described by

[0155] [Table 2]

[0156] [Example 3] Preparation of high-purity aluminum sulfate solution

[0157] Description of the electrodialysis stack used: Euro 2 electrodialysis stack system supplied by Eurodia Industries, equipped with 10 pairs of Astom Neosepta AHA and CMB active cells, with a dilute sulfuric acid electrode rinse solution.

[0158] 3000 grams of aluminum sulfate solution, the analytical results of which are shown in Table 3 below, were placed in a feed solution tank. 7900 grams of the same solution was placed in a receiver solution tank. Each solution was circulated through the ED stack and back to its respective tank. DC power was applied at 17 volts and 5 amps. A total of 10 amp hours was applied. The DC power and circulating pumps were turned off, and the feed solution was analyzed, with the analytical results reported in Table 3 as HP-Aluminum Sulfate Solution. Analysis of all solutions was performed using ICP-OES.

[0159] [Table 3]

[0160] [Example 4] Production of high-purity alumina from HP PAC solution

[0161] A sample of the HP PAC solution prepared by the method described in Example 2 was dried by heating in an oven. The dried polyaluminum chloride was then placed in a muffle furnace, which was heated to 1050°C. The sample was held at that temperature for 1 hour and then cooled. The analytical results of the high-purity alumina thus produced are shown in Table 2 as HPA from HP PAC.

[0162] [Example 5] Production of high-purity alumina from aluminum chloride hexahydrate crystallization

[0163] The HP-PAC solution prepared by the method described in Example 2 was converted to an aluminum chloride solution by adding hydrochloric acid. The analytical results of the resulting aluminum chloride solution, referred to as HP AlCl3 solution, are shown in Table 2. One hundred ninety pounds of HP AlCl3 solution was placed in a glass-lined, jacketed, stirred vessel. With the agitator running, steam was directed against the vessel jacket, heating the solution to boiling. Water was evaporated from the solution while HP AlCl3 solution was added to maintain a constant weight. The solution was concentrated in this manner until an AlCl3 solution concentration of approximately 31.5% was obtained. At this point, crystals began to form, and the process was continued until an AlCl3·6H2O crystal slurry with a mother liquor concentration of approximately 25% was obtained. Approximately 40 pounds of the slurry was removed from the vessel, and the crystals were separated from the mother liquor by centrifugation. The mother liquor was then returned to the vessel. HP AlCl3 solution was added to the vessel to maintain a 190 pound AlCl3·6H2O / mother liquor slurry in the vessel. The process was repeated in this manner, with the crystallizer operating in a semi-continuous mode. The crystals separated from the mother liquor were analyzed. The results are shown in Table 2 as HP AlCl3·6H2O.

[0164] A portion of the AlCl3·6H2O crystals was rinsed with a saturated HP-AlCl3 solution prepared by dissolving HP-AlCl3·6H2O crystals in deionized water to remove impurities from the mother liquor and the surface of the HP-AlCl3·6H2O. The weight ratio of the rinse solution to the crystals was 0.25:1. The rinse solution was separated from the HP-AlCl3·6H2O crystals by centrifugation. The rinsed HP-AlCl3·6H2O crystals were analyzed by ICP-OES, and the results are listed in Table 2 as HP-AlCl3·6H2O after rinsing.

[0165] A portion of the HP-AlCl3·6H2O crystals was calcined in a muffle furnace at 1050°C for 1 hour to decompose the HP-AlCl3·6H2O and produce high-purity alumina. The high-purity alumina thus produced was analyzed by ICP-OES. The analytical results of this high-purity alumina are listed in Table 2 as HPA.

[0166] After rinsing, a portion of the HPAlCl3·6H2O crystals was calcined in a muffle furnace at 1050°C for 1 hour to decompose the HPAlCl3·6H2O, followed by rinsing to produce high-purity alumina. The high-purity alumina produced in this manner was analyzed by ICP-OES. The analytical results of this high-purity alumina are listed in Table 2 as HPA after rinsing.

[0167] While the present invention has been described with reference to preferred embodiments, those skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. All references cited throughout this specification, including those in the Background Art, are incorporated herein in their entirety. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention specifically described herein. Such equivalents are intended to be encompassed by the following claims.

Claims

1. 1. A method for producing aluminum oxide, comprising: providing an initial aluminum salt aqueous solution having an aluminum salt dissolved therein; subjecting the initial aqueous aluminum salt solution to electrodialysis to remove non-aluminum monovalent and / or polyvalent cations from the initial aqueous aluminum salt solution, thereby reducing the amount of non-aluminum monovalent and / or polyvalent cations from the initial aqueous aluminum salt solution to produce a purified aqueous aluminum salt solution; heating the purified aluminum salt aqueous solution to obtain aluminum oxide; A method comprising:

2. 10. The method of claim 1, wherein the non-aluminum monovalent and / or polyvalent cations are removed from the purified aqueous aluminum salt solution.

3. 2. The method of claim 1, wherein the non-aluminum monovalent and / or polyvalent cations of the initial aqueous aluminum salt solution comprise Na, K, Li, Ca, Cr, Zn, Cu, Ti, Mg, Mn, Ba, Sr, V, Ni, Pb, Co, Sb, As, B, Sn, Be, Mo, Fe, Si, or mixtures thereof.

4. 10. The method of claim 1, wherein the aluminum salt of the initial aqueous aluminum salt solution comprises aluminum chloride, aluminum sulfate, aluminum ammonium sulfate, aluminum nitrate, aluminum citrate, 1-hexanol aluminum, polyaluminum chloride (PAC), aluminum chlorohydrate (ACH), aluminum acetate, aluminum chloride solution, or a mixture thereof.

5. 5. The method of claim 4, wherein the aluminum salt is derived from an aluminum-containing clay.

6. 6. The method of claim 5, wherein the aluminum-containing clay is kaolin or bauxite, or other aluminous clay.

7. 5. The method of claim 4, wherein the aluminum salt is derived from aluminum hydroxide, alumina trihydrate (ATH), or aluminum metal.

8. 2. The method of claim 1, wherein the refined aqueous aluminum salt solution contains, on an aluminum oxide basis, a lower level of monovalent and / or polyvalent non-aluminum cations, expressed as the sum of non-aluminum monovalent and / or polyvalent cations, than the initial aqueous aluminum salt solution.

9. 10. The method of claim 1, wherein the purified aqueous aluminum salt solution contains less than 1000 ppm total non-aluminum monovalent and / or polyvalent cations based on aluminum oxide.

10. 10. The method of claim 1 further comprising: prior to said heating, crystallizing a purified aluminum salt from said aqueous purified aluminum salt solution.

11. 11. The method of claim 10, wherein the purified aluminum salt is separated from the aqueous purified aluminum salt solution.

12. 10. The method of claim 1 further comprising: evaporating the aqueous portion of said purified aluminum salt solution to obtain a purified aluminum salt.

13. 10. The method of claim 1 further comprising: treating said aqueous purified aluminum salt solution with an acid to obtain a precipitate of purified aluminum salt.

14. 14. The method of claim 13, wherein the acid is hydrochloric acid, nitric acid, sulfuric acid, or a mixture thereof.

15. 11. The method of claim 10, wherein the purified aluminum salt is treated with an aluminum salt solution or other solution.

16. 16. The method of claim 15, wherein the purified aluminum salt is washed with an aluminum salt solution.

17. 17. The method of claim 16, wherein the purified aluminum salt is washed with a saturated aluminum salt solution.

18. 18. The method of any one of claims 10 to 17, further comprising: subjecting the purified aluminum salt to heating, roasting, calcining, spray roasting, or oil drop treatment, or other heating process to provide purified aluminum oxide.

19. 20. The method of claim 18, wherein the purified aluminum oxide contains a lower level of monovalent and / or polyvalent non-aluminum cations, based on aluminum oxide and total non-aluminum monovalent and / or polyvalent cations, than the initial aqueous aluminum salt solution.

20. 20. The method of claim 18, wherein the purified aluminum oxide comprises less than 1000 ppm total of one or more non-aluminum monovalent and / or polyvalent cations based on aluminum oxide.

21. 20. The method of claim 18, wherein the purified aluminum oxide comprises less than 100 ppm total of one or more non-aluminum monovalent and / or polyvalent cations based on aluminum oxide.

22. 1. A method for removing non-aluminum monovalent and / or polyvalent metal cations from an aqueous aluminum salt solution to obtain aluminum oxide, comprising the steps of: providing an initial aluminum salt aqueous solution having an aluminum salt dissolved therein; subjecting the initial aqueous aluminum salt solution to electrodialysis to remove non-aluminum monovalent and / or polyvalent cations from the initial aqueous aluminum salt solution, thereby reducing the amount of non-aluminum monovalent and / or polyvalent cations from the initial aqueous aluminum salt solution to produce a purified aqueous aluminum salt solution; heating the purified aluminum salt aqueous solution to obtain aluminum oxide; A method comprising:

23. 23. The method of claim 22, wherein the non-aluminum monovalent and / or multivalent cations are removed from the purified aqueous aluminum salt solution.

24. 23. The method of claim 22, wherein the non-aluminum monovalent and / or polyvalent cations of the initial aqueous aluminum salt solution comprise Na, K, Li, Ca, Cr, Zn, Cu, Ti, Mg, Mn, Ba, Sr, V, Ni, Pb, Co, Sb, As, B, Sn, Be, Mo, Fe, Si, or mixtures thereof.

25. 23. The method of claim 22, wherein the aluminum salt of the initial aqueous aluminum salt solution comprises aluminum chloride, aluminum sulfate, aluminum ammonium sulfate, aluminum nitrate, aluminum citrate, 1-hexanol aluminum, polyaluminum chloride (PAC), aluminum chloride hydrate (ACH), aluminum acetate, aluminum chloride solution, or a mixture thereof.

26. 25. The method of claim 24, wherein the aluminum salt is derived from an aluminum-containing clay.

27. 27. The method of claim 26, wherein the aluminum-containing clay is kaolin or bauxite, or other aluminous clay.

28. 26. The method of claim 25, wherein the aluminum salt is derived from aluminum hydroxide, alumina trihydrate (ATH), or aluminum metal.

29. 23. The method of claim 22, wherein the refined aqueous aluminum salt solution contains, on an aluminum oxide basis, a lower level of monovalent and polyvalent non-aluminum cations, expressed as the sum of non-aluminum monovalent and / or polyvalent cations, than the initial aqueous aluminum salt solution.

30. 23. The method of claim 22, wherein the purified aqueous aluminum salt solution contains less than 1000 ppm total non-aluminum monovalent and / or polyvalent cations based on aluminum oxide.

31. 23. The method of claim 22, further comprising: The method includes, prior to said heating, crystallizing a purified aluminum salt from said aqueous purified aluminum salt solution.

32. 32. The method of claim 31 , wherein the purified aluminum salt is separated from the aqueous purified aluminum salt solution.

33. 23. The method of claim 22, further comprising: evaporating the aqueous portion of said purified aluminum salt solution to obtain a purified aluminum salt.

34. 23. The method of claim 22, further comprising: treating said aqueous purified aluminum salt solution with an acid to obtain a precipitate of purified aluminum salt.

35. 35. The method of claim 34, wherein the acid is hydrochloric acid, nitric acid, sulfuric acid, or a mixture thereof.

36. 32. The method of claim 31, wherein the purified aluminum salt is treated with an aluminum salt solution or other solution.

37. 32. The method of claim 31 , wherein the purified aluminum salt is washed with an aluminum salt solution.

38. 32. The method of claim 31 , wherein the purified aluminum salt is washed or treated with a saturated aluminum salt solution.

39. 39. The method of any one of claims 22 to 38, comprising: The method wherein the step of heating to obtain aluminum oxide comprises subjecting the aluminum oxide to roasting, calcination, spray roasting, or oil drop treatment, or other heating process to provide purified aluminum oxide.

40. 40. The method of claim 39, wherein the purified aluminum oxide contains a lower level of monovalent and / or polyvalent non-aluminum cations, based on aluminum oxide and total non-aluminum monovalent and / or polyvalent cations, than the initial aqueous aluminum salt solution.

41. 40. The method of claim 39, wherein the purified aluminum oxide contains less than 1000 ppm total of one or more non-aluminum monovalent and / or polyvalent cations based on aluminum oxide.

42. 40. The method of claim 39, wherein the purified aluminum oxide comprises less than 100 ppm total of one or more non-aluminum monovalent and / or polyvalent cations based on aluminum oxide.

43. 40. The method of claim 39, wherein the heating is performed at a temperature between 500 degrees and 1300 degrees.

44. 22. The method of any one of claims 1 to 21, wherein the heating is performed at a temperature between 500 and 1300 degrees.

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