Production of high-purity alumina and / or smelter-grade alumina

Abstract

A method for recovering high-grade alumina products (HPA and / or SGA) from aluminic raw materials such as kaolinite or halloysite is described. The process includes leaching the calcined material with recycled 18% hydrochloric acid, removing anionic impurities such as iron and zinc by ion exchange, a novel removal step for magnesium and calcium, thermal hydrolysis of the resulting solution, and calcining after washing the crude alumina solid. Optionally, a final purification step is introduced by caustic leaching of the washed solid, followed by hydrolysis to gibbsite.

Description

Technical Field

[0001] (Cross - reference to related applications) This application claims priority from Australian Provisional Patent Application No. 2023901781, filed on June 6, 2023, entitled "PRODUCTION OF HIGH PURITY ALUMINA AND / OR SMELTER - GRADE ALUMINA", the content of which is incorporated herein by reference in its entirety.

[0002] The present disclosure generally relates to a process for recovering alumina products such as smelter - grade (SGA) and high - purity (HPA) alumina from aluminous materials, particularly halloysite and kaolinite.

Background Art

[0003] Alumina (aluminum oxide: Al2O3) is an intermediate product in the production of aluminum. Alumina is typically produced from bauxite using the Bayer process, which involves leaching mineral bauxite with high - temperature and high - pressure caustic soda to produce a solution of sodium aluminate, followed by crystallizing gibbsite (Al(OH)3) and firing it to form Al2O3, a grade of alumina commonly known as metallurgical alumina or SGA, smelter - grade alumina. Despite many attempts to find alternative methods for producing SGA, the Bayer process has seen relatively little improvement since it was first used. In the subsequent Hall - Heroult electrolysis process, the alumina fed into the electrolytic cells is required to have both specific purity and physical properties, and the Bayer process, or more precisely, the crystallization of sodium aluminate produced by the Bayer process, is positioned as being almost the only one that gives products meeting these specifications.

[0004] The Bayer process requires a supply of materials with a relatively low silica content to be efficient and effective. Bauxite, an aluminum-based laterite material readily available in many parts of the world, has traditionally been the preferred raw material. A notable exception to this is the use of a similar mineral, nepheline, which is somewhat more difficult to process than bauxite, but is widely used in Russia, where there are no primeval bauxite deposits but vast quantities of nepheline are available. Processing nepheline requires an initial calcination step, but otherwise it is very similar to the Bayer process, except for a silica removal step that must be added to the process flow sheet due to nepheline's high silica content.

[0005] Both of the commercial processes described above employ a caustic soda leaching process, both of which produce large amounts of iron oxide residue, so-called red mud, which must be discarded and constitute a significant environmental liability. To overcome the problem of red mud, for many years there have been numerous attempts to develop acid-based chloride leaching processes and take advantage of the unique properties of aluminum chloride, AlCl3, or more specifically, aluminum chloride hexahydrate, AlCl3·6H2O(ACH). Despite considerable efforts made by the United States Bureau of Mines (USBM) over many years, achieving the required purity and alumina morphology with this technique proved extremely difficult, and the process was abandoned. The main problematic elements were iron and magnesium. There were also significant health and safety concerns associated with the high concentrations of HCl in the atmosphere associated with the crystallization and filtration unit operations.

[0006] More recent attempts to develop acid-based chloride leaching processes involve leaching alumina clay in regenerated hydrochloric acid and crystallizing aluminum chloride from the leaching solution by spraying nearly dry hydrogen chloride gas (Patent Document 1). The resulting crystals are then calcined to recover the chloride components for regeneration, forming alumina. Aside from the problem of various impurities, the cost of producing large quantities of dry hydrogen chloride gas is very high.

[0007] More recently, instead of SGA, efforts have focused on producing only small quantities of high-grade HPA (high-purity alumina), targeting the rapidly growing electronics and electric vehicle industries. Notable commercial operations have not yet been achieved.

[0008] As will be apparent from the foregoing, there is a need for a process that can produce SGA or HPA grade alumina from any alumina-containing raw material, especially relatively high-grade materials such as kaolinite, halloysite, or mixtures of kaolinite and halloysite, without relying on either the generation of red mud or crystallization processes requiring dried hydrogen chloride gas. Alternatively, there is a need for a process that can produce SGA or HPA grade alumina from any alumina-containing raw material and provide a useful alternative to known processes. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] U.S. Patent No. 9,382,600 [Overview of the project]

[0010] A process for recovering alumina of at least smelter-grade purity from alumina-containing raw materials is described in accordance with a broad aspect of this disclosure.

[0011] According to the first embodiment, a process for producing alumina from alumina material raw materials, i. To manufacture AlCl3 solution and ii. Reducing the impurity content in the AlCl3 solution by ion exchange or solvent extraction to produce a semi-purified AlCl3 solution, iii. To produce crude alumina solid by thermal hydrolysis of a semi-purified AlCl3 solution, iv. Washing the crude alumina solid to remove non-hydrolyzable chlorides and / or residual alkaline earth oxides and bicarbonates to produce a washed solid, v. Drying and calcining the washed solid to produce alumina. A process including this is provided.

[0012] In a particular embodiment of the first aspect, the process further includes redissolving the alumina obtained from step iv in a caustic soda solution, and subsequently hydrolyzing it to form gibbsite.

[0013] In certain embodiments of the first embodiment, the process further includes removing magnesium and calcium from the semi-purified AlCl3 solution produced in step ii. In these embodiments, magnesium and calcium can be removed from the semi-purified AlCl3 solution by adding fluoride ions to precipitate them. The source of the fluoride ions may be aluminum fluoride.

[0014] In certain embodiments of the first embodiment, the alumina material is a kaolinite material. For example, the kaolinite material may be the mineral kaolinite, halloysite, or a mixture of kaolinite and halloysite. In certain other embodiments of the first embodiment, the alumina material is an aluminum-containing process byproduct, such as red clay.

[0015] In a particular embodiment of the first aspect, step i is ia. The process of producing calcined products by calcining alumina material raw materials, ib. Leaching the calcination product in hydrochloric acid to produce a leaching slurry, ic. By solid-liquid separation, silicate residue is removed from the leachate slurry to produce AlCl3 solution. Includes.

[0016] In certain embodiments of the first aspect, the process further includes recovering hydrochloric acid from step iii and supplying the recovered hydrochloric acid to leaching step ib.

[0017] In certain embodiments of the first aspect, the firing temperature used in step ia is from about 600 °C to about 1000 °C, such as from about 800 °C to about 900 °C, for example about 850 °C.

[0018] In certain embodiments of the first aspect, the leaching temperature used in step ib is from ambient temperature to boiling temperature, such as from about 80 °C to about 100 °C, for example from about 90 °C to about 95 °C.

[0019] In certain embodiments of the first aspect, the acid strength of the hydrochloric acid used in step ib is from 5% to 35% HCl, such as about 18%.

[0020] In certain embodiments of the first aspect, step ii includes a first stage that reduces the amount of anionic impurities such as, but not limited to, iron, zinc, and chromium by contacting a quaternary or tertiary amine extractant with an AlCl3 solution.

[0021] In certain embodiments of the first aspect, step ii further includes a second stage that reduces the amount of complex cationic impurities such as, but not limited to, titanium by contacting a cation exchanger with an AlCl3 solution. The cation exchanger may be phosphinic acid or iminodiacetic acid.

[0022] In certain embodiments of the first aspect, step ii further includes a third stage that reduces the amount of silica by contacting an inorganic adsorbent with an AlCl3 solution. The inorganic adsorbent may be a calcined iron oxide hydrate.

[0023] In certain embodiments of the first aspect, step iii involves thermally hydrolyzing the AlCl3 solution in a spray or fluidized bed roaster at a temperature below about 900 °C, such as below about 800 °C. In some of these embodiments, the thermal hydrolysis is carried out using a gas phase containing a partial pressure of carbon dioxide (CO2) of 20 vol% or less, such as about 15 vol%. In these embodiments, carbon dioxide reacts with calcium and magnesium present in the semi-purified AlCl3 solution and converts them to their bicarbonates. The bicarbonates formed are highly water-soluble and thus calcium and magnesium are easily removed in the subsequent washing step. On the other hand, aluminum does not form carbonates and is thus converted to its own oxide.

[0024] In certain embodiments of the first aspect, step iv involves washing the crude alumina solid using deionized water or distilled water. The washing step is designed to remove non-hydrolyzable metal chlorides, particularly alkali and alkaline earth metal chlorides such as, but not limited to, sodium, potassium, and calcium.

[0025] Advantageously, the washing step will also remove the residual amounts of magnesium and calcium. Magnesium and calcium can be present as their oxides or oxychlorides, but particularly as their bicarbonates as mentioned above. The former compounds have a low but finite solubility and can be removed, while the bicarbonates are highly water-soluble and are thus much more easily removed from the alumina solid.

[0026] According to a second aspect, there is provided alumina produced by the process of the first aspect.

[0027] Embodiments of the present disclosure are discussed with reference to the accompanying figures.

Brief Description of the Drawings

[0028] [Figure 1] It is a process flow diagram showing an embodiment of the present disclosure. [Figure 2] This is a process flow diagram illustrating another embodiment of the present disclosure. [Figure 3] The graphs show the cumulative amount of HCl released over time during the thermal hydrolysis of AlCl3 solution at 500°C, 600°C, and 700°C. [Figure 4] This graph shows the cumulative amount of HCl released over time during the thermal hydrolysis of AlCl3 solution at 600°C under various CO2 partial pressures. [Modes for carrying out the invention]

[0029] In the following description, similar reference numerals indicate the same or corresponding parts throughout the figures.

[0030] Embodiments of this disclosure will be better understood by referring to the detailed description below.

[0031] Details of the terminology used herein are provided below for the purpose of guiding those skilled in the art to practice this disclosure. The technical terms used herein are intended to be useful for providing a better description of specific embodiments and should not be considered limiting.

[0032] Unless otherwise stated, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art of the field to which this disclosure pertains.

[0033] In the context of this disclosure, the terms “about” and “approximately” are used in conjunction with a quantity, number, or value, in which case the combination describes the stated quantity, number, or value alone, and the quantity, number, or value plus or minus 10% of that quantity, number, or value. For example, the phrases “about 40%” and “approximately 40%” disclose both “40%” and “36% to 44% including both ends.”

[0034] As used herein, % or wt.% means weight percent unless otherwise indicated. Where used herein, % refers to weight percent compared to the total weight percent of the phase or composition being discussed.

[0035] The singular terms "a," "an," and "the" refer to multiple objects unless explicitly indicated otherwise in the context. The term "comprises" means "includes." Therefore, "comprising A" or "B" means including A, including B, or including both A and B.

[0036] Methods and materials similar to or equivalent to those described herein may be used in the practice or testing of this disclosure, but preferred methods and materials are described herein. In case of any inconsistency, this specification shall prevail, including in the explanation of terms. Furthermore, materials, methods, and examples are illustrative only and are not intended to be limiting.

[0037] As previously discussed, prior art processes for producing alumina from bauxite and nepheline encompass the Bayer process, which is pressurized caustic leaching. Prior art processes for producing alumina from kaolinite or aluminic clay generally encompass either crystallization of ACH (aluminum chloride hexahydrate, AlCl3·6H2O) in either form, or precipitation with caustic agents. Precipitation with caustic agents produces a gel-like precipitate that requires the use of a centrifuge for solid / liquid separation, and the liquid retention is very high, leading to material balance problems.

[0038] In contrast to known prior art processes, the inventors have developed a process for producing alumina (either SGA or HPA) without an ACH crystallization step or a caustic precipitation step. Therefore, disclosed herein is a process for producing alumina from aluminic material raw materials. The process is as follows: i. To manufacture AlCl3 solution and ii. Reducing the impurity content in the AlCl3 solution by ion exchange or solvent extraction to produce a semi-purified AlCl3 solution, iii. To produce crude alumina solid by thermal hydrolysis of a semi-purified AlCl3 solution, iv. Washing the crude alumina solid to remove non-hydrolyzable chlorides and / or residual alkaline earth oxides and bicarbonates to produce a washed solid, v. Drying and calcining the washed solid to produce alumina. Includes.

[0039] Embodiments of this process are shown in Figures 1 and 2. Referring to Figure 1, a process for producing alumina 36 from an alumina material raw material 10 is shown. Broadly speaking, the alumina material raw material 10 may be any aluminum-containing material having an aluminum oxide mass fraction of 20% to 27% by weight relative to the total material weight. Preferably, the alumina material raw material 10 has an iron content of less than about 30%. The alumina material raw material 10 may also be an ore. Suitable ore materials include, but are not limited to, kaolinite, halloysite, and aluminum-containing ores such as muscovite, pyrophyllite, nacreous mica, or chlorite. Materials derived from bauxite with reduced iron content may also be used. The alumina material raw material 10 may also be aluminum alkoxides, such as those produced from aluminum metal and alcohol, or from furnace suspended matter, dross, or residues. The alumina material raw material 10 may also be aluminum-containing process by-products, such as red clay. In some preferred embodiments, the alumina material raw material 10 is alumina clay, or a kaolinite-type material such as halloysite (Al2Si2O5(OH)4) or kaolinite (Al2Si2O5(OH)4). The alumina material raw material 10 may also be any two or more combinations of the above materials.

[0040] AlCl3 solution 17 is produced from alumina material raw material 10. The content of impurities 19 such as iron (Fe), zinc (Zn), chromium (Cr), titanium (Ti), and silicon (Si) in AlCl3 solution 17 is reduced by ion exchange or solvent extraction to produce semi-purified AlCl3 solution 26. The semi-purified AlCl3 solution 26 is subjected to thermal hydrolysis (27) to produce crude alumina solid 28. The crude alumina solid 28 is washed with water 30 (29) to remove non-hydrolyzable chlorides and / or residual alkaline earth oxides and bicarbonates to produce a washed solid slurry 31, as well as additional residual magnesium and calcium oxides or oxychlorides or bicarbonates. In the solid-liquid separation step 32, liquid 33 containing impurities such as sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg) is separated from the washed solid 34. Next, the washed solid 34 is dried and calcined in calcination step 35 to produce alumina 36. Further details of each of these steps are described below.

[0041] Further embodiments are schematically shown with reference to Figure 2. AlCl3 liquid 17 is produced from alumina material raw materials 10, in this embodiment halloysite (Al2Si2O5(OH)4) and kaolinite (Al2Si2O5(OH)4) (either 1% halloysite and 87% kaolinite, or 32% halloysite and 58% kaolinite) by calcining 11 to ensure that the minerals are compatible with acid leaching 12 using recycled hydrochloric acid 13. The calcination (11) temperature may be from 600°C to 1000°C, preferably from 800°C to 900°C, and more preferably about 850°C. The calcination (11) may be carried out in any suitable equipment, but a rotary kiln is preferred.

[0042] Next, the calcined material is subjected to a leaching process 12. Leaching is carried out at temperatures ranging from ambient temperature to boiling point, but optimally at 80°C to 100°C, more preferably at about 90°C to 95°C. The solid content load (wt.%) is adjusted to an acid strength that yields the maximum aluminum extraction rate, typically about 95% to 98%. The hydrochloric acid strength may be between 5% and 35%, determined by downstream operations. In this embodiment, spray roasting is used to achieve an acid strength of about 18% HCl. Any suitable leaching mechanism, such as atmospheric pressure or a pressurized stirred tank reactor, may be used.

[0043] The main leaching reaction for the dissolution of aluminum is given by equation (1) [ka] It is shown here.

[0044] Optionally, by including an oxidizing agent, all of the iron can be present in its higher oxidation state. Furthermore, oxidation also brings phosphorus into its higher oxidation state as a phosphate, promoting the formation of iron phosphate. Because iron phosphate (FePO4) has very low solubility in water, iron and phosphorus mutually remove each other. Any suitable oxidizing agent may be used, but is not limited to these, such as hydrogen peroxide, chlorine, or ozone. The latter two are preferred because they avoid the addition of water.

[0045] The leaching slurry 14 produced in the leaching process 12 then proceeds to solid-liquid separation 15. Solid-liquid separation 15 may be carried out by any convenient means, but is not limited to, flocculation and thickening, backflow decantation, filter press, or vacuum belt filter. The solid 16 from the leaching slurry 14 is mostly silica and is therefore environmentally friendly, and may be disposed of, for example, as landfill waste or used as road aggregate. Alternatively, the solid 16 is pure enough to be used as a precursor for the production of high-purity silica.

[0046] The filtrate 17 is a solution of aluminum chloride containing small amounts of impurities 19, including, but not limited to, iron, chromium, silica, titanium, and zinc. The amount of these impurities 19 depends on the composition of the supply material 10, but is typically less than 5 g / L, and usually less than about 1 g / L.

[0047] The purification of these types of AlCl3 liquids 17 or solutions is carried out by multi-step salting-out crystallization performed with dry HCl gas, according to practice. In contrast, the primary purification in the process of this disclosure is carried out by a series of ion exchange resins 18. The nature of the impurities 19 will determine how many ion exchange (IX) 18 steps are required, but typically there are two or three. Solvent extraction (SX) may be used as an alternative, but IX 18 is preferred.

[0048] AlCl3 solution 17 first undergoes the removal of elements that form chloroanions in strong chloride solutions, such as iron, chromium, and zinc, but not limited to these. Resins having quaternary or tertiary amine functionality are preferred. Titanium, if present, tends to form oxycations rather than chloroanions and can be effectively removed secondarily by cationic resins. Resins having phosphinic acid functionality are preferred. Finally, silica, if present, may be removed in the third step of ion exchange 18 by a resin adsorbent having, for example, an amorphous iron oxide structure. Optionally, the silica removal step may be performed first in case residual iron dissolves from the silica adsorbent. In this way, all of iron, zinc, chromium, titanium, and silica 19 can be removed from AlCl3 solution 17 to produce a semi-purified AlCl3 solution 20. The filled resin can be effectively stripped using either water (anionic) or hydrochloric acid.

[0049] Next, if it becomes necessary to remove high concentrations (≧500 mg / L) of magnesium and calcium, the semi-purified AlCl3 solution 20 may optionally undergo a new magnesium and calcium removal step 21. In this step, the semi-purified AlCl3 solution 20 is mixed with solid aluminum fluoride 22, which is only very slightly soluble, at any suitable temperature from ambient temperature to boiling point. Ambient temperature is preferred. Solid aluminum fluoride 22 reacts with magnesium and calcium in a double decomposition reaction to form magnesium and calcium fluorides, respectively, and both fluorides have been found to be substantially insoluble. The amount of aluminum fluoride added depends on the concentrations of magnesium and calcium in the semi-purified AlCl3 solution 20. Approximately 5%, slightly in excess of the stoichiometric amount, is added. The small amount of soluble fluoride in the solution is recovered and regenerated with hydrochloric acid, so it does not pose a problem when proceeding to the next step. The reaction is shown in equations (2) and (3). [ka]

[0050] The slurry 23, after the removal of magnesium and calcium, proceeds to solid-liquid separation 24. Solid-liquid separation 24 may be carried out by any convenient means, but is not limited to, flocculation and thickening, backflow decantation, filter press, or vacuum belt filter. The solid 25 is a mixture of magnesium fluoride and calcium fluoride.

[0051] Next, the filtrate 26 undergoes thermal hydrolysis 27. This is a common and well-known process in the steel pickling and magnesia industries, but has never been commercially applied to aluminum chloride solutions. The aluminum chloride is converted to the reactive form of alumina 28, and the hydrochloric acid 13 is recovered for regeneration. Due to the nature of the thermal hydrolysis process 27, approximately 18% of the quasi-azeotropic acid 13 is also recovered.

[0052] The thermal hydrolysis of AlCl3 solution is carried out at temperatures below 900°C, such as below 800°C, in a spray or fluidized bed roasting furnace. In certain embodiments, the thermal hydrolysis is carried out at 600-700°C. The thermal hydrolysis can be carried out using a gas phase containing the partial pressure of carbon dioxide (CO2), which is approximately 15% by volume, but should be less than 20%. The purpose of the carbon dioxide is to react with calcium and magnesium present in the feed solution, resulting in the following reactions: [ka] The process involves converting them into their bicarbonates.

[0053] The formation of these bicarbonates is advantageous to the process because they are highly water-soluble, and therefore calcium and magnesium are easily removed in the subsequent washing step. On the other hand, aluminum does not form carbonates and is therefore converted into its own oxide.

[0054] Next, the alumina solid 28 is subjected to a washing step 29 using water 30. Firstly, the washing step 29 removes non-hydrolyzable metal chlorides. In particular, this step removes both metals (Na, K, Ca) and residual chlorides. Secondly, the washing step 29 removes the bicarbonates and residual oxides 33 of Mg and Ca that are formed during the thermal hydrolysis step. In particular, if an HPA-quality product is required, the washing step 29 should be carried out using deionized water 30. The washing step 29 can also remove all of the residual low concentrations of magnesium oxide or calcium oxide 33 because their water solubility is low.

[0055] The washing slurry 31 proceeds to solid-liquid separation 32. Solid-liquid separation 32 may be performed by any convenient means, but is not limited to, flocculation and thickening, backflow decantation, filter press, or vacuum belt filter. Solution 33 contains the aforementioned alkali metals having trace amounts of magnesium and calcium and is discarded or, preferably, used as a quenching solution to condense HCl resulting from the thermal hydrolysis process.

[0056] The resulting solid 34 is dried and calcined (35) to form the final alumina product 36. Under normal circumstances, especially when the supply material 10 is kaolinite and / or halloysite, the product should be of at least 4N HPA quality. However, optionally, if an even purer product is required, especially if silica and magnesium have not been completely and effectively removed, the wet and washed solid 34 may be dissolved in caustic soda (not shown) to form a sodium aluminate solution. In this case, magnesium and calcium do not dissolve, and subsequently, silica can be removed using lime, as is done in the Bayer process. The sodium aluminate solution can then be treated as in the existing Bayer process to hydrolyze aluminum and precipitate gibbsite (Al(OH)3), which can then be calcined to alumina. The resulting product is suitable for existing aluminum smelters but is also of 4N or 5N HPA quality.

[0057] The principles of the present invention are illustrated by the following embodiments, which are provided for illustrative purposes but should not be construed as limiting the scope of the invention.

[0058] [Example 1] Samples of kaolinite and halloysite mineral mixtures from South Australia were calcined at various temperatures to determine the optimal temperature for leaching. The calcined samples were then leached in HCl at 32% and 18% acid concentrations to determine whether the recovered acid originated from the calcination of ACH crystals or from thermal hydrolysis. Unless otherwise noted, leaching was performed under standard conditions of 10% solid input, 32% acid, 95°C, and a residence time of 2 hours. Table 1 shows the results of these tests.

[0059] [Table 1]

[0060] The results show that high aluminum extraction rates were achieved under all tested firing conditions except ambient temperature, and that the effect of temperature was relatively small in the 800°C to 900°C range. Mass loss was 16% to 17% for all firing tests. There was little effect within the 15 to 75 minute time frame. From this point onward, the standard condition of 850°C for 45 minutes was adopted for all subsequent leaching tests.

[0061] The calcined material was head-grade aluminum with 22% content and 1.08% iron, the main impurity. As mentioned above, leaching tests showed high aluminum extraction rates under most conditions, and an iron extraction rate of approximately 60%. In terms of solid input during leaching, 20% at 32% HCl appears to be the practical maximum value consistent with the aluminum recovery rate. The higher the proportion of solids, the lower the aluminum recovery rate. No reactions involving aluminum were observed during leaching at ambient temperature.

[0062] Leaching with a lower acid content of 18%, equivalent to that obtained from regeneration using a thermal hydrolysis apparatus, showed high aluminum recovery comparable to that achieved with 32% acid, at both 10% and 15% solid inputs. This example demonstrates that a combination of calcination and hydrochloric acid leaching is effective in recovering virtually all aluminum present in a mixture of kaolinite and halloysite.

[0063] [Example 2] Based on the above tests, the composite leaching solution, which was analyzed to contain 34.7 g / L of Al, 1.09 g / L of Fe, 67 mg / L of Cr, 19 mg / L of Ti, 7.8 mg / L of Zn, and 120 g / L of free HCl, was treated with various ion exchange resins in a shakeout test at a ratio of 10% resin solids.

[0064] [Table 2]

[0065] The results clearly demonstrate that ion exchange can effectively remove problematic impurities from aluminum chloride solutions, and that aluminum itself is not substantially adsorbed. Lewatit TP107 was not as effective at adsorbing iron, but it did suggest some removal of chromium. Chromium removal would be possible by reducing the free acid content, which was 50-100 g / L of HCl. The fact that the cationic resin removed titanium, while the anionic resin did not, indicates that titanium exists in these solutions as an oxycation rather than as an anionic species.

[0066] [Example 3] Based on the optimal results of the leaching test, a synthetic chloride leaching solution with the following analytical values ​​(mg / L) was prepared: Al 44,200, Ca 85, Cr 4, K 420, Mg 90, and Na 72. This solution was then supplied to an experimental thermal hydrolysis unit to investigate the effect of isothermal operating temperature. Thermal hydrolysis was performed at an isothermal temperature of 500°C to 700°C with a total gas flow rate of 200 ml / min and 15 v% vapor. Figure 3 shows the obtained results.

[0067] These data indicate that 600°C is more effective than 500°C, and that virtually all HCl is recovered.

[0068] [Example 4] The solid produced in the previous test under thermal hydrolysis conditions at 600°C was slurryed using deionized water at both 20°C and 90°C for 3 hours at a 1:100 S / L ratio. Table 3 shows the analysis of the solid, and Table 4 shows the analysis of the washing solution.

[0069] [Table 3]

[0070] [Table 4]

[0071] The results indicate that washing at 90°C is highly efficient and removes virtually all impurities. Adding a washing step effectively removes any remaining trace amounts of chlorine, which would otherwise be removed by calcination of the washed solid.

[0072] [Example 5] The same solution used in Example 3 was subjected to isothermal hydrolysis at 600°C while varying the partial pressure of carbon dioxide present in the gas phase. The total gas flow rate was 400 ml / min, and the vapor content was 15 v%. Figure 4 shows the obtained results.

[0073] The data indicates that thermal hydrolysis was more effective when CO2 was present in the gas phase and the ideal content was between 10% and 20%.

[0074] Those skilled in the art will recognize that this disclosure is not limited to use for one or more specific uses described herein. This disclosure is also not limited in respect to certain elements and / or features described or depicted herein in its preferred embodiments. While this disclosure is not limited to the embodiments disclosed, it will be recognized that many reconfigurations, modifications, and substitutions are possible without departing from the scope described and defined by the following claims.

[0075] Any reference to prior art in this specification shall not, and should not, be construed as an endorsement or suggestion in any way that such prior art forms part of the ordinary general knowledge.

[0076] The terms “comprise” and “include” as used herein and in the subsequent claims, and all their derivatives (e.g., “comprises,” “comprising,” “includes,” “including”), should be interpreted as including the features referred to by the terms, and it will be understood that they are not intended to exclude the presence of any additional features unless otherwise stated or implied.

[0077] In some cases, a single embodiment may combine multiple features for the sake of brevity and / or to aid in understanding the scope of the present disclosure. In such cases, it should be understood that these multiple features may be provided separately (in separate embodiments) or in any other preferred combination. Alternatively, if separate features are described in separate embodiments, these separate features may be combined into a single embodiment unless otherwise stated or implied. The same applies to the claims, which can be rearranged in any combination; that is, a claim may be amended to include features defined in any other claim. Furthermore, the phrase referring to “at least one (type) of” the enumeration of items refers to any combination of those items that include a single component. For example, “at least one (type) of a, b, or c” is intended to include a, b, c, a and b, a and c, b and c, and a, b and c.

Claims

1. A process for producing alumina from alumina material raw materials, i. AlCl ３ Manufacturing the liquid, ii. By ion exchange or solvent extraction, the AlCl ３ By reducing the amount of impurities in the liquid, semi-purified AlCl ３ Manufacturing the liquid, iii. The semi-purified AlCl ３ The process involves thermally hydrolyzing a liquid to produce a crude alumina solid, iv. Washing the crude alumina solid to remove non-hydrolyzable chlorides and / or residual alkaline earth oxides and bicarbonates to produce a washed solid, v. Drying and calcining the washed solid to produce alumina. A process that includes this.

2. The process according to claim 1, further comprising redissolving the alumina obtained from step iv in a caustic soda solution, and subsequently hydrolyzing it to form gibbsite.

3. Semi-purified AlCl produced in step ii ３ The process according to either claim 1 or claim 2, further comprising removing magnesium and calcium from the liquid.

4. By adding fluoride ions to precipitate magnesium and calcium, the magnesium and calcium are semi-purified AlCl ３ The process according to claim 3, comprising removing from the liquid.

5. The process according to claim 4, wherein the source of the fluoride ions is aluminum fluoride.

6. The process according to any one of claims 1 to 5, wherein the alumina material raw material is a kaolinite material.

7. The process according to claim 6, wherein the kaolinite material is kaolinite, halloysite, or a mixture thereof.

8. Process i. ia. Manufacture a calcined product by calcining the supplied raw materials, ib. Producing a leaching slurry by leaching the calcined material in hydrochloric acid, ic. By solid-liquid separation, silicate residue is removed from the leached slurry, and the AlCl ３ Manufacturing liquid and The process according to any one of claims 1 to 7, including the process described in any one of claims 1 to 7.

9. The process according to claim 8, wherein the firing temperature used in step ia is from about 600°C to about 1000°C, preferably from about 800°C to about 900°C, and more preferably from about 850°C.

10. The process according to claim 8 or claim 9, wherein the leaching temperature used in step ib is from ambient temperature to boiling point, preferably from about 80°C to about 100°C, more preferably from about 90°C to about 95°C.

11. The process according to any one of claims 8 to 10, wherein the acid strength of the hydrochloric acid used in step ib is from 5% to 35% HCl, preferably about 18%.

12. The process according to any one of claims 8 to 11, wherein the hydrochloric acid used in step ib is regenerated from step iii, which involves thermal hydrolysis.

13. Step ii. involves a quaternary or tertiary amine extractant and the AlCl ３ The process according to any one of claims 1 to 12, comprising a first step of reducing the amount of anionic impurities, such as, but not limited to, iron, zinc, and chromium, by contacting them with a liquid.

14. Step ii. further includes a second step including, but not limited to, a step of reducing the amount of complex cationic impurities such as titanium by contacting the cation exchanger with an AlCl ３ solution, the process according to claim 13.

15. The process according to claim 14, wherein the cation exchanger is phosphinic acid or iminodiacetic acid.

16. Step ii. involves the inorganic adsorbent and the AlCl ３ The process according to any one of claims 13 to 15, further comprising a third step of reducing the amount of silica by contacting it with a liquid.

17. The process according to claim 16, wherein the inorganic adsorbent is calcined iron oxide hydrate.

18. The process according to any one of claims 1 to 17, wherein step iv. comprises washing the crude alumina solid with deionized water or distilled water.

19. The process according to claim 18, wherein the washing step removes non-hydrolyzable metal chlorides and bicarbonates and residual oxides of Mg and Ca formed during the thermal hydrolysis step.

20. Alumina produced by the process described in any one of claims 1 to 18.

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