A method for preparing high-purity α-Al₂O₃ by bauxite ammonium alum salting-out.

Abstract

This invention belongs to the field of bauxite utilization technology, specifically relating to a method for preparing high-purity α-Al₂O₃ from bauxite using ammonium alum salt precipitation. The invention discovered that within the temperature range of 10–40°C, the yield of aluminum chloride hexahydrate crystals remains almost constant, but its precipitation rate is directly proportional to the rate at which the solution becomes saturated with HCl. This invention utilizes this property to remove impurities from aluminum chloride, repeatedly dissolving and precipitating them to obtain high-purity aluminum chloride hexahydrate. This invention prepares high-purity α-Al₂O₃ with a purity of over 99.96% through sulfuric acid leaching, ammonium alum crystallization, and hydrochloric acid salt precipitation. The process is short, simple, and easy to operate, allowing for the recycling of all materials, resulting in low production costs. Multiple filtration and desilication processes also contribute to high product added value.

Description

Technical Field

[0001] This invention belongs to the field of bauxite utilization technology, specifically relating to a method for preparing high-purity α-Al2O3 by bauxite ammonium alum salting-out method. Background Technology

[0002] Bauxite, as the main raw material for aluminum products such as alumina, is classified into three types: gibbsite, trihydrate, and diaspore. Among them, diaspore bauxite has complete crystal structure, dense structure, and high lattice energy, and is the main type of bauxite in my country. However, it is extremely difficult to extract aluminum from this type of bauxite, which hinders the development of my country's aluminum industry.

[0003] Currently, the vast majority of my country's alumina industry uses the Bayer process within the alkaline process. However, the Bayer process requires high-grade bauxite, which presents higher leaching conditions and costs for my country's nearly 80% low-grade bauxite (with an aluminum-silicon ratio between 3 and 6). Furthermore, alumina produced via the Bayer process generates a large amount of industrial solid waste—red mud—resulting in low resource utilization and recovery rates.

[0004] Chinese patent CN 107128959A discloses a method for preparing alumina from bauxite by stepwise electrolysis with hydrochloric acid leaching and its comprehensive utilization. The method uses hydrochloric acid reaction leaching, which avoids the problems caused by the alkaline method. However, the purity of the produced alumina cannot be guaranteed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing high-purity α-Al2O3 by bauxite ammonium alum salting-out. The method provided by this invention has simple steps, all materials are recycled, the cost is low, and the Al2O3 obtained has high purity.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing high-purity α-Al₂O₃ by bauxite ammonium alum salting-out, comprising the following steps:

[0008] (1) After leaching bauxite with concentrated sulfuric acid, solid-liquid separation is performed to obtain recycled sulfuric acid and leaching material; the recycled sulfuric acid is directly used for the next leaching reaction.

[0009] (2) The leaching material and water are heated and mixed, and then the solid and liquid are separated while hot to obtain a solution and silicon slag;

[0010] (3) After heating and mixing the solution and ammonium sulfate, ammonium alum crystals are precipitated.

[0011] (4) The ammonium alum crystals are mixed with hydrochloric acid to obtain an ammonium alum solution;

[0012] (5) Hydrogen chloride gas is introduced into the ammonium alum solution to precipitate the solid-liquid separation, and aluminum chloride crystals and primary salting-out mother liquor are obtained.

[0013] (6) The aluminum chloride crystals are acid-washed and then dissolved to obtain an aluminum chloride solution. Then, hydrogen chloride gas is introduced into the aluminum chloride solution to precipitate the solid and liquid phases, resulting in purified aluminum chloride crystals and a secondary salting-out mother liquor. The acid washing is concentrated hydrochloric acid washing.

[0014] (7) Repeat step (6) more than 3 times to obtain the last aluminum chloride crystal. Pyrolyze the last aluminum chloride crystal to obtain high-purity Al2O3. The purity of the high-purity Al2O3 is 99.95% to 99.99%.

[0015] (8) The high-purity Al2O3 and the seed crystal are mixed, ground and then calcined to obtain high-purity α-Al2O3, wherein the purity of the high-purity α-Al2O3 is above 99.96%.

[0016] Preferably, the particle size of the bauxite is no greater than 74 micrometers.

[0017] Preferably, the leaching reaction temperature is 220–260°C, and the holding time is 3–6 hours.

[0018] Preferably, the primary salting-out mother liquor further includes sequential evaporation and distillation to obtain hydrogen chloride gas, azeotropic liquid, dilute sulfuric acid, and aluminum chloride containing impurities; the hydrogen chloride gas is used for precipitation in steps (3), (5), (6), or (7); the azeotropic liquid is used to dissolve aluminum chloride crystals or purify aluminum chloride crystals to obtain aluminum chloride solution; the dilute sulfuric acid is concentrated and used for the leaching reaction.

[0019] Preferably, the secondary salting-out mother liquor further includes sequential evaporation and distillation to obtain hydrogen chloride gas, azeotropic liquid, dilute sulfuric acid, and aluminum chloride containing impurities; the hydrogen chloride gas is used for precipitation in steps (3), (5), (6), or (7); the azeotropic liquid is used to dissolve aluminum chloride crystals or purify aluminum chloride crystals to obtain aluminum chloride solution; the dilute sulfuric acid is concentrated and used for the leaching reaction.

[0020] Preferably, in step (4), the mass concentration of the hydrochloric acid is 18-20%; the mass-volume ratio of the ammonium alum crystals to the hydrochloric acid is 1g:(0.8-1.2)mL.

[0021] Preferably, the solvent used for redissolution is hydrochloric acid; the mass concentration of the hydrochloric acid is 32% to 38%; the volume ratio of the aluminum chloride crystals to the hydrochloric acid is 1 g:(1.8 to 2) mL; and the redissolution temperature is 20 to 30°C.

[0022] Preferably, the number of times step (6) is repeated is 3 to 5.

[0023] Preferably, the pyrolysis temperature is 400–500°C, and the holding time is 1–3 hours.

[0024] Preferably, the calcination temperature is 1200–1250°C, and the holding time is 2–4 hours.

[0025] This invention provides a method for preparing high-purity α-Al₂O₃ by bauxite ammonium alum salting-out. The invention's research found that the yield of aluminum chloride hexahydrate crystals remains almost constant within the temperature range of 10–40°C, but its precipitation rate is directly proportional to the rate at which the solution becomes saturated with HCl. This invention utilizes this property to remove impurities from aluminum chloride, and by repeatedly dissolving and precipitating them, high-purity aluminum chloride hexahydrate is obtained.

[0026] This invention prepares high-purity α-Al2O3 with a purity of over 99.96% by means of sulfuric acid leaching, ammonium alum crystallization, and hydrochloric acid precipitation. The process is short, simple, and easy to operate, and all materials can be recycled, resulting in low production costs. Multiple filtrations and desiliconization processes result in high added value for the product. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a process flow diagram for preparing high-purity α-Al2O3 by the high-silica bauxite ammonium alum salting-out method of the present invention;

[0029] Figure 2 The XRD pattern of high-purity α-Al2O3 prepared in Example 1 of this invention;

[0030] Figure 3 This is a TEM image of the high-purity α-Al2O3 prepared in Example 1 of the present invention. Detailed Implementation

[0031] This invention provides a method for preparing high-purity α-Al₂O₃ by bauxite ammonium alum salting-out, comprising the following steps:

[0032] (1) After leaching bauxite with concentrated sulfuric acid, solid-liquid separation is performed to obtain recycled sulfuric acid and leaching material; the recycled sulfuric acid is directly used for the next leaching reaction.

[0033] (2) The leaching material and water are heated and mixed, and then the solid and liquid are separated while hot to obtain a solution and silicon slag;

[0034] (3) After heating and mixing the solution and ammonium sulfate, ammonium alum crystals are precipitated.

[0035] (4) The ammonium alum crystals are mixed with hydrochloric acid to obtain an ammonium alum solution;

[0036] (5) Hydrogen chloride gas is introduced into the ammonium alum solution to precipitate the solid-liquid separation, and aluminum chloride crystals and primary salting-out mother liquor are obtained.

[0037] (6) The aluminum chloride crystals are acid-washed and then dissolved to obtain an aluminum chloride solution. Then, hydrogen chloride gas is introduced into the aluminum chloride solution to precipitate the solid and liquid phases, resulting in purified aluminum chloride crystals and a secondary salting-out mother liquor. The acid washing is concentrated hydrochloric acid washing.

[0038] (7) Repeat step (6) more than 3 times to obtain the last aluminum chloride crystal. Pyrolyze the last aluminum chloride crystal to obtain high-purity Al2O3. The purity of the high-purity Al2O3 is 99.95% to 99.99%.

[0039] (8) The high-purity Al2O3 and the seed crystal are mixed, ground and then calcined to obtain high-purity α-Al2O3, wherein the purity of the high-purity α-Al2O3 is above 99.96%.

[0040] The method for preparing high-purity α-Al₂O₃ by salting out high-silica bauxite ammonium alum provided by this invention is as follows: Figure 1 As shown, the specific process is as follows:

[0041] This invention involves mixing bauxite with concentrated sulfuric acid for a leaching reaction, followed by solid-liquid separation (referred to as the first solid-liquid separation) to obtain recycled sulfuric acid and leaching material. In this invention, the recycled sulfuric acid is preferably recycled for the leaching reaction.

[0042] In this invention, the particle size of the bauxite is preferably no greater than 74 micrometers, more preferably no greater than 50 micrometers, and even more preferably no greater than 25 micrometers.

[0043] In this invention, the bauxite is preferably ground to the target particle size before use; the grinding speed is preferably 200-300 rpm, more preferably 220-270 rpm, and even more preferably 240-260 rpm; the grinding time is preferably 60-300 min, more preferably 90-180 min, and even more preferably 100-150 min; the grinding is preferably ball milling; the ball-to-material ratio is preferably 3-5:1, more preferably 4-5:1, and even more preferably 4:1. This invention, through grinding, can activate the bauxite, which is beneficial for subsequent reactions.

[0044] In this invention, the mass concentration of the concentrated sulfuric acid is preferably 85% or more, more preferably 90% or more, and even more preferably 90-95%.

[0045] In this invention, the mass-to-volume ratio of bauxite to concentrated sulfuric acid is preferably 1g:(3-5)mL, more preferably 1g:(3.5-4.5)mL, and even more preferably 1g:(3.8-4.2)mL.

[0046] In this invention, the leaching reaction temperature is preferably 220–260°C, more preferably 230–250°C, and even more preferably 240°C; the holding time is preferably 3–6 hours, more preferably 4–5 hours. This invention obtains a leaching slurry through a leaching reaction.

[0047] In this invention, the first solid-liquid separation is preferably pressure filtration or vacuum filtration; the temperature of the first solid-liquid separation is preferably 90-140°C, more preferably 100-130°C, and even more preferably 110-120°C.

[0048] After obtaining the leachate, the present invention heats and mixes the leachate with water (referred to as the first heating and mixing), and then separates the solid and liquid components while hot to obtain a solution and silicon slag. In the present invention, the water is preferably pure water.

[0049] In this invention, the mass ratio of bauxite to water is preferably 1:5 to 9, more preferably 1:5.5 to 7, and even more preferably 1:5.8 to 6.2.

[0050] In this invention, the temperature of the first heating and mixing is preferably 70-90°C, more preferably 75-85°C, and even more preferably 80°C, and the mixing time is preferably 0.5-1.5h, more preferably 0.8-1.2h, and even more preferably 1h.

[0051] In this invention, the hot solid-liquid separation is preferably hot filtration; the temperature of the hot solid-liquid separation is preferably 70-90°C, more preferably 75-85°C, and even more preferably 80°C.

[0052] In this invention, the silicon slag is preferably used to extract silicon, and the obtained silicon can be used to produce silicon-containing products such as water glass.

[0053] After obtaining the solution, the present invention heats and mixes the solution with ammonium sulfate (referred to as the second heating and mixing) to precipitate (referred to as the first precipitation), thus obtaining ammonium alum crystals. In the present invention, the molar ratio of Al2O3 to ammonium sulfate in the bauxite is preferably 1:1 to 1.4, more preferably 1:1.1 to 1.3, and even more preferably 1:1.2. The present invention adds excess ammonium sulfate, which enables the aluminum element in the solution to react completely with the ammonium sulfate to form ammonium alum.

[0054] In this invention, the temperature of the second heating and mixing is preferably 70-90°C, more preferably 75-85°C, and even more preferably 80°C, until the ammonium sulfate is completely dissolved in the solution.

[0055] In this invention, the second heating and mixing process preferably includes hot solid-liquid separation; the hot solid-liquid separation is preferably hot filtration; the temperature of the hot solid-liquid separation is preferably 70-90°C, more preferably 75-85°C. This invention performs hot solid-liquid separation to prevent ammonium alum from precipitating and hindering filtration after the solution cools.

[0056] In this invention, the first precipitation is preferably subjected to static cooling; the endpoint temperature of the first precipitation is preferably 20-30°C, more preferably 24-27°C.

[0057] In this invention, the first precipitation preferably further includes sequentially performing solid-liquid separation A, neutralization of the mother liquor, solid-liquid separation B, and distillation on the obtained product.

[0058] In this invention, the solid-liquid separation A is preferably filtration. This invention obtains ammonium alum crystals and a separation mother liquor through solid-liquid separation A.

[0059] In this invention, the neutralization of the separation mother liquor is preferably achieved by mixing the separation mother liquor with ammonium carbonate; the pH value of the neutralized separation mother liquor is preferably 6.8 to 7.5, more preferably 7.5.

[0060] In this invention, the solid-liquid separation B is preferably filtration. This invention uses solid-liquid separation B to filter out impurities.

[0061] In this invention, the distillation temperature is preferably 80–120°C, more preferably 100°C, until ammonium sulfate precipitates. This invention obtains ammonium sulfate through distillation.

[0062] In this invention, the ammonium sulfate is preferably used in the solution to prepare ammonium alum crystals.

[0063] After obtaining ammonium alum crystals, the present invention mixes the ammonium alum crystals with hydrochloric acid (referred to as the third mixture) to obtain an ammonium alum solution. In the present invention, the mass concentration of the hydrochloric acid is preferably 18-20%, more preferably 18.5-19.5%, and even more preferably 19%.

[0064] In this invention, the mass-to-volume ratio of the ammonium alum crystals to hydrochloric acid is preferably 1g:(0.8-1.2)mL, more preferably 1g:(0.9-1.1)mL, and even more preferably 1g:1mL.

[0065] In this invention, the temperature of the third mixing is preferably 20-30°C, more preferably 22-28°C, and even more preferably 25°C, until the ammonium alum crystals are completely dissolved in hydrochloric acid.

[0066] In this invention, the third mixing process preferably further includes filtering the resulting mixture. Filtration removes impurities from the mixture.

[0067] After obtaining the ammonium alum solution, the present invention introduces hydrogen chloride gas into the ammonium alum solution to precipitate (referred to as the second precipitation), followed by solid-liquid separation (referred to as the second solid-liquid separation) to obtain aluminum chloride crystals and a primary salting-out mother liquor. In the present invention, the temperature of the second precipitation is preferably greater than 60°C, more preferably greater than 80°C, until H+ in the ammonium alum solution... + The concentration is 12–12.5 mol / L.

[0068] In this invention, the second solid-liquid separation is preferably performed by filtration.

[0069] In this invention, after obtaining the primary salting-out mother liquor, it is preferable to further include evaporating and distilling the primary salting-out mother liquor sequentially to obtain hydrogen chloride gas, azeotropic liquid, dilute sulfuric acid, and aluminum chloride containing impurities; the hydrogen chloride gas is preferably used for precipitation in steps (3), (5), (6), or (7); the azeotropic liquid is preferably used to dissolve the aluminum chloride crystals or purify the aluminum chloride crystals to obtain an aluminum chloride solution; the dilute sulfuric acid is preferably concentrated and then used for the leaching reaction; the aluminum chloride containing impurities is preferably purified to prepare industrial-grade aluminum chloride.

[0070] In this invention, when the hydrogen chloride gas obtained from the primary salting-out mother liquor is insufficient, acid replenishment is preferably performed; the acid replenishment is preferably performed by mixing concentrated hydrochloric acid and concentrated sulfuric acid and evaporating the mixture to obtain hydrogen chloride gas and dilute sulfuric acid, then passing the hydrogen chloride gas into an ammonium alum solution, and concentrating the dilute sulfuric acid for use in the leaching reaction or for acid replenishment; the mixing of concentrated hydrochloric acid and concentrated sulfuric acid is preferably performed by adding concentrated sulfuric acid dropwise into concentrated hydrochloric acid; the evaporation temperature is preferably 115-125°C, more preferably 120°C.

[0071] After obtaining aluminum chloride crystals, the present invention acid-washes and then dissolves the aluminum chloride crystals to obtain an aluminum chloride solution. Then, hydrogen chloride gas is introduced into the aluminum chloride solution to precipitate (referred to as the third precipitation), followed by solid-liquid separation (referred to as the third solid-liquid separation) to obtain purified aluminum chloride crystals and secondary salting-out mother liquor.

[0072] In this invention, the acid washing is preferably performed by compacting aluminum chloride crystals in a funnel, pouring concentrated hydrochloric acid into the mixture, and then filtering and washing. The mass concentration of the concentrated hydrochloric acid is preferably 32-38%, more preferably 36%. The mass-to-volume ratio of bauxite to concentrated hydrochloric acid is preferably (1-3) g:(0.5-2) mL, more preferably (1.5-2.5) g:(0.8-1.5) mL, and even more preferably 2 g:1 mL. This invention utilizes concentrated hydrochloric acid to wash the aluminum chloride crystals, which can better remove impurities.

[0073] In this invention, the solvent used for redissolution is preferably hydrochloric acid; the mass concentration of the hydrochloric acid is preferably 18-22%, more preferably 20%; the volume ratio of the aluminum chloride crystals to the hydrochloric acid is preferably 1g:(1.8-2)mL, more preferably 1g:1.9mL; the hydrochloric acid is preferably an azeotropic solution obtained by evaporating the secondary salting-out mother liquor (the remaining salting-out mother liquor from the previous salting-out); the temperature of redissolution is preferably 20-30℃, more preferably 22-28℃, and even more preferably 24-26℃.

[0074] In this invention, the process of redissolving preferably further includes precision filtration of the resulting product; the pore size of the precision filter is preferably 3-15 μm, more preferably 4.5-9 μm; the precision filtration is preferably compacted vacuum filtration; the compacted vacuum filtration is manually compacted, and the vacuum degree is preferably 0.075-0.095 MPa, more preferably 0.08-0.09 MPa.

[0075] In this invention, the endpoint of the third precipitation is preferably H in the aluminum chloride solution. + The concentration is 11–12 mol / L, more preferably 11.5 mol / L.

[0076] In this invention, the third solid-liquid separation is preferably filtration; the filtration temperature is preferably room temperature.

[0077] In this invention, after obtaining the secondary salting-out mother liquor, it is preferable to further include evaporating and distilling the secondary salting-out mother liquor sequentially to obtain hydrogen chloride gas, azeotropic liquid, dilute sulfuric acid, and aluminum chloride containing impurities; the hydrogen chloride gas is preferably used for precipitation in steps (3), (5), (6), or (7); the azeotropic liquid is preferably used to dissolve the aluminum chloride crystals or purify the aluminum chloride crystals to obtain an aluminum chloride solution; the dilute sulfuric acid is preferably concentrated and then used for the leaching reaction; the aluminum chloride containing impurities is preferably purified to prepare industrial-grade aluminum chloride.

[0078] In this invention, when the hydrogen chloride gas obtained from the secondary salting-out mother liquor is insufficient, acid replenishment is preferably performed; the acid replenishment is preferably performed by mixing concentrated hydrochloric acid and concentrated sulfuric acid and evaporating the mixture to obtain hydrogen chloride gas and dilute sulfuric acid, then passing the hydrogen chloride gas into an aluminum chloride solution, and concentrating the dilute sulfuric acid for leaching reaction or acid replenishment; the mixing of concentrated hydrochloric acid and concentrated sulfuric acid is preferably performed by adding concentrated sulfuric acid dropwise to concentrated hydrochloric acid; the evaporation temperature is preferably 115-125°C, more preferably 120°C.

[0079] After obtaining purified aluminum chloride crystals, the present invention repeats step (6) more than 3 times to obtain final aluminum chloride crystals. The final aluminum chloride crystals are then pyrolyzed to obtain high-purity Al2O3, wherein the purity of the high-purity Al2O3 is 99.95% to 99.99%. In the present invention, the number of times step (6) is repeated is preferably 3 to 5 times, more preferably 4 to 5 times.

[0080] In this invention, after repeating step (6) three or more times, a final aluminum chloride crystal and a final salting-out mother liquor are obtained. The final salting-out mother liquor is preferably used to prepare an ammonium alum solution from the ammonium alum crystallization. The treatment method for the salting-out mother liquor generated during the repeated step (6) is preferably the same as the treatment method for the secondary salting-out mother liquor in step (6), and will not be repeated here. This invention further purifies the aluminum chloride crystals by repeating step (6).

[0081] In this invention, the pyrolysis temperature is preferably 400-500℃, more preferably 420-480℃, and even more preferably 440-460℃, and the heat preservation time is preferably 1-3h, more preferably 1.5-2.5h, and even more preferably 2h.

[0082] In this invention, the pyrolysis yields high-purity Al2O3 and hydrogen chloride gas; the hydrogen chloride gas is preferably used for the next precipitation (precipitation in the next implementation of any step in this invention) or the next redissolution (redissolution in the next implementation of any step in this invention); when the hydrogen chloride gas is used for the next redissolution, it is preferable to absorb the hydrogen chloride gas with water before use.

[0083] After obtaining high-purity Al2O3, the present invention mixes the high-purity Al2O3 and seed crystals, grinds them, and then calcines them to obtain high-purity α-Al2O3, wherein the purity of the high-purity α-Al2O3 is above 99.96%. In the present invention, the mass ratio of the seed crystals to high-purity Al2O3 is preferably 4-6:100, more preferably 4.5-5.5:100, and even more preferably 5:100.

[0084] In this invention, the grinding is preferably ball milling; the grinding speed is preferably 200-300 rpm, more preferably 220-270 rpm, and the grinding time is preferably 60-300 min, more preferably 90-300 min; the ball-to-material ratio of the ball milling is preferably 3-5:1, more preferably 4:1.

[0085] In this invention, the calcination temperature is preferably 1200-1250℃, more preferably 1210-1240℃, and even more preferably 1220-1230℃, and the holding time is preferably 2-4h, more preferably 2.5-3.5h, and even more preferably 3h.

[0086] To further illustrate the present invention, the following detailed description of the invention's solutions, in conjunction with the accompanying drawings and embodiments, is provided, but should not be construed as limiting the scope of protection of the present invention.

[0087] Example 1

[0088] (1) Fine grinding: The bauxite is ground and sieved to obtain activated bauxite with a particle size of no more than 74 micrometers;

[0089] (2) Acid leaching: Take 120g of activated bauxite, mix it with 600mL of concentrated sulfuric acid, and leach at 240℃ for 4h to obtain the leaching slurry;

[0090] (3) Filtration: The temperature of the leaching slurry is cooled to 140℃ and filtered to separate the slurry, obtaining circulating sulfuric acid and leaching material;

[0091] (4) Water dissolution: Add 720 mL of pure water to dissolve the leaching material, stir at 90°C for 30 min, filter while hot to obtain the solution and silicon slag;

[0092] (5) Alum making: Add 120g of ammonium sulfate to the solution, heat to dissolve, filter, and let stand to cool to obtain 462g of ammonium alum; add ammonium carbonate to the separation mother liquor after the ammonium alum crystallization is filtered out to neutralize, filter out the impurities, and then distill and filter to obtain ammonium sulfate, which is returned to step (5) for recycling;

[0093] (6) Acid dissolution: Dissolve ammonium alum crystals in 462 mL of 20% hydrochloric acid, filter, and obtain 762.3 mL of ammonium alum solution;

[0094] (7) Aluminum chloride crystallization: 500 mL of concentrated hydrochloric acid was passed into the solution at 70°C and heated to 108°C to obtain hydrogen chloride gas. The H2 content in the final solution was then measured. + The concentration reached 12.5 mol / L; after filtration and washing, 224.1 g of aluminum chloride crystals and the first salting-out mother liquor were obtained.

[0095] (8) Aluminum chloride purification: Repeat the crystallization process 4 times:

[0096] ① At room temperature, aluminum chloride crystals are dissolved in 450 mL of hydrochloric acid azeotropic solution. The mother liquor from the first salting-out process is distilled to 108 °C to obtain hydrogen chloride gas and the first distillate. The hydrogen chloride gas is then passed into the aluminum chloride solution, and after acid is added, H+ is added. + The concentration reached 11.5 mol / L. After filtration, 223.1 g of secondary aluminum chloride crystals and secondary salting-out mother liquor were obtained. After the primary distillate was further evaporated, hydrochloric acid azeotropic solution, dilute sulfuric acid and aluminum chloride containing impurities were obtained. The dilute sulfuric acid was further concentrated for acid leaching in step (2).

[0097] ② At room temperature, dissolve secondary aluminum chloride crystals in 450 mL of hydrochloric acid azeotropic solution. Evaporate the secondary salting-out mother liquor to 108 °C to obtain hydrogen chloride gas and a secondary distillate. Pass the hydrogen chloride gas into the aluminum chloride solution, and after adding acid, H₂... + The concentration reached 10.0 mol / L. After filtration, 201.2 g of aluminum chloride crystals and the mother liquor from the third salting out were obtained. The second distillate was further evaporated to obtain hydrochloric acid azeotrope and aluminum chloride containing impurities.

[0098] ③ At room temperature, dissolve aluminum chloride crystals in 405 mL of hydrochloric acid azeotropic solution. Evaporate the mother liquor from the third salting-out process to 108 °C to obtain hydrogen chloride gas and the third distillate. Pass the hydrogen chloride gas into the aluminum chloride solution, and after adding acid, H... + The concentration reached 10.6 mol / L, and after filtration, 194.6 g of tetrahydrate crystals and the mother liquor from the four salting-out processes were obtained; the three distillates were used for hydrochloric acid dissolution in step (6);

[0099] ④ At room temperature, dissolve aluminum chloride tetrahydrate crystals in 390 mL of hydrochloric acid azeotropic solution. Evaporate the mother liquor from the tetrahydrate salting-out process to 108 °C to obtain hydrogen chloride gas and the distillate. Pass the hydrogen chloride gas into the aluminum chloride solution, and after adding acid, H₂... + The concentration reached 11.8 mol / L. After filtration, 192.9 g of five-stage aluminum chloride crystals (final aluminum chloride crystals) and five-stage salting-out mother liquor were obtained. The fourth distillate was used as a hydrochloric acid azeotropic solution. The fifth mother liquor was evaporated and used as a hydrochloric acid azeotropic solution.

[0100] (9) Pyrolysis: Pyrolysis of five-times aluminum chloride crystals (last aluminum chloride crystals) at 400℃ for 120 min yields 44.9 g of high-purity Al2O3 (purity of 99.96%) and hydrogen chloride gas. The obtained hydrogen chloride gas is absorbed by water and used as a hydrochloric acid azeotropic solution.

[0101] (10) Calcination: The high-purity Al2O3 obtained in step (9) was added to 5% seed crystals and ground, and then calcined at 1250℃ for 240 min to obtain 37.0 g of high-purity α-Al2O3.

[0102] The high-purity α-Al₂O₃ prepared in Example 1 was subjected to ICP-OES detection, XRD testing, and TEM testing, following the methods specified in GB / T 37248-2018. The results are shown in Table 1 and... Figures 2-3 As shown.

[0103] Table 1. ICP-OES test results of high-purity α-Al₂O₃ in Example 1

[0104]

[0105] As can be seen from Table 1, the purity of the high-purity α-Al2O3 prepared in this embodiment is 99.96%.

[0106] according to Figure 2 It can be seen that the Al2O3 prepared by this invention is mainly composed of the α phase.

[0107] according to Figure 3 It can be seen that the microstructure of the Al2O3 product prepared by this invention is mainly worm-shaped, with some ellipsoidal shapes and a smooth surface.

[0108] Example 2

[0109] (1) Fine grinding: The bauxite is ground and sieved to obtain activated bauxite with a particle size of no more than 74 micrometers;

[0110] (2) Acid leaching: Take 120g of activated bauxite, mix it with 600mL of concentrated sulfuric acid, and leach at 220℃ for 4h to obtain a leaching slurry;

[0111] (3) Filtration: The temperature of the leaching slurry is cooled to 130°C and filtered to separate the slurry, yielding recycled sulfuric acid and leaching material;

[0112] (4) Water dissolution: Add 840 mL of pure water to dissolve the leaching material, stir at 90 °C for 30 min, filter while hot to obtain the solution and silicon slag;

[0113] (5) Alum making: Add 120g of ammonium sulfate to the solution, heat to dissolve, filter, and let stand to cool to obtain 405g of ammonium alum; add ammonium carbonate to the separation mother liquor after the ammonium alum crystallization is filtered out to neutralize, filter out the impurities, and then distill and filter to obtain ammonium sulfate, which is returned to step (5) for recycling.

[0114] (6) Acid dissolution: Dissolve ammonium alum crystals in 405 mL of 20% hydrochloric acid, filter, and obtain 681.1 mL of ammonium alum solution;

[0115] (7) Aluminum chloride crystallization: Hydrogen chloride gas obtained from the evaporation of the mother liquor after four salting-out processes is passed into the solution at 70℃, and the H+ content in the final solution is measured. +The concentration reached 12.5 mol / L; after filtration and washing, 187.1 g of aluminum chloride crystals and the first salting-out mother liquor were obtained.

[0116] (8) Aluminum chloride purification: Repeat the crystallization process 3 times:

[0117] ① At room temperature, aluminum chloride crystals are dissolved in 375 mL of hydrochloric acid azeotropic solution. The mother liquor from the first salting-out process is distilled to 108 °C to obtain hydrogen chloride gas and the first distillate. The hydrogen chloride gas is then passed into the aluminum chloride solution, and after acid is added, H+ is added. + The concentration reached 11.3 mol / L. After filtration, 185.9 g of secondary aluminum chloride crystals and secondary salting-out mother liquor were obtained. After further evaporation of the first distillate, hydrochloric acid azeotropic solution, dilute sulfuric acid and aluminum chloride containing impurities were obtained. The dilute sulfuric acid was further concentrated and could be used for acid leaching in step (2).

[0118] ② At room temperature, dissolve secondary aluminum chloride crystals in 372 mL of hydrochloric acid azeotropic solution. Evaporate the secondary salting-out mother liquor to 108 °C to obtain hydrogen chloride gas and a secondary distillate. Pass the hydrogen chloride gas into the aluminum chloride solution, and after adding acid, H₂... + The concentration reached 11.4 mol / L. After filtration, 172.2 g of aluminum chloride crystals and the mother liquor from the third salting out were obtained. The second distillate was further evaporated to obtain hydrochloric acid azeotrope and aluminum chloride containing impurities.

[0119] ③ At room temperature, dissolve aluminum chloride crystals in 344 mL of hydrochloric acid azeotropic solution. Evaporate the mother liquor from the third salting-out process to 108 °C to obtain hydrogen chloride gas and the third distillate. Pass the hydrogen chloride gas into the aluminum chloride solution, and after adding acid, H₂... + The concentration reached 11.1 mol / L. After filtration, 171.4 g of tetrahydrate crystals (final tetrahydrate crystals) and tetrahydrate mother liquor were obtained. The third distillate can be used for hydrochloric acid dissolution in step (6).

[0120] (9) Pyrolysis: The tetradecanoic aluminum chloride crystals (last aluminum chloride crystals) were pyrolyzed at 500℃ for 120 min to obtain 33.8 g of high-purity Al2O3 (purity of 99.96%) and hydrogen chloride gas. The obtained hydrogen chloride gas was absorbed by water and used as a hydrochloric acid azeotropic solution.

[0121] (10) Calcination: The high-purity Al2O3 obtained in step (9) was added to 5% seed crystals and ground, then calcined at 1250℃ for 240 min to obtain 30.2 g of high-purity α-Al2O3. After ICP-OES analysis, its purity was 99.96%.

[0122] Example 3

[0123] (1) Fine grinding: The bauxite is ground and sieved to obtain activated bauxite with a particle size of no more than 74 micrometers;

[0124] (2) Acid leaching: Take 100g of activated bauxite, mix it with 500mL of concentrated sulfuric acid, and leach at 230℃ for 4h to obtain a dissolution slurry;

[0125] (3) Filtration: Cool the leaching slurry to 90°C and filter to separate it, obtaining circulating sulfuric acid and leaching material;

[0126] (4) Water dissolution: Add 600 mL of pure water to dissolve the leaching material, stir at 90°C for 30 min, filter while hot to obtain the solution and silicon slag;

[0127] (5) Alum preparation: Add 95g of ammonium sulfate to the solution, heat to dissolve, filter, and let stand to cool to obtain 383g of ammonium alum; add ammonium carbonate to the separation mother liquor after the ammonium alum crystallization is filtered out to neutralize, filter out impurities, and then distill and filter to obtain ammonium sulfate, which is returned to step (5) for recycling.

[0128] (6) Acid dissolution: Dissolve ammonium alum crystals in 383 mL of 20% hydrochloric acid, filter, and obtain 632 mL of ammonium alum solution;

[0129] (7) Aluminum chloride crystallization: Hydrogen chloride gas obtained from the evaporation of the mother liquor after five salting-out processes is passed into the solution at 70℃, and the H+ content in the final solution is measured. + The concentration reached 12.5 mol / L; after filtration and washing, 152.8 g of aluminum chloride crystals and the first salting-out mother liquor were obtained.

[0130] (8) Aluminum chloride purification: Repeat the crystallization process 3 times:

[0131] ① At room temperature, aluminum chloride crystals are dissolved in 306 mL of hydrochloric acid azeotropic solution. The mother liquor from the first salting-out process is distilled to 108 °C to obtain hydrogen chloride gas and the first distillate. The hydrogen chloride gas is then passed into the aluminum chloride solution. After acid is added, H+ is added. + The concentration reached 11.1 mol / L. After filtration, 151.7 g of secondary aluminum chloride crystals and secondary salting-out mother liquor were obtained. After further evaporation of the first distillate, hydrochloric acid azeotropic solution, dilute sulfuric acid and aluminum chloride containing impurities were obtained. The dilute sulfuric acid was further concentrated and could be used for acid leaching in step (2).

[0132] ② At room temperature, dissolve secondary aluminum chloride crystals in 304 mL of hydrochloric acid azeotropic solution. Evaporate the secondary salting-out mother liquor to 108 °C to obtain hydrogen chloride gas and a secondary distillate. Pass the hydrogen chloride gas into the aluminum chloride solution, and after adding acid, H₂... + The concentration reached 10.8 mol / L. After filtration, 143.4 g of aluminum chloride crystals and the mother liquor from the third salting out were obtained. The second distillate was further evaporated to obtain hydrochloric acid azeotrope and aluminum chloride containing impurities.

[0133] ③ At room temperature, dissolve aluminum chloride crystals in 288 mL of hydrochloric acid azeotropic solution. Evaporate the mother liquor from the third salting-out process to 108 °C to obtain hydrogen chloride gas and the third distillate. Pass the hydrogen chloride gas into the aluminum chloride solution, and after adding acid, H₂... + The concentration reached 11.6 mol / L. After filtration, 141.6 g of tetrahydrate crystals (final tetrahydrate crystals) and tetrahydrate mother liquor were obtained. The third distillate can be used for hydrochloric acid dissolution in step (6).

[0134] (9) Pyrolysis: The tetradecanoic aluminum chloride crystals (final aluminum chloride crystals) were pyrolyzed at 400℃ for 120 min to obtain 27.5 g of high-purity Al2O3 (purity of 99.96%) and hydrogen chloride gas. The obtained hydrogen chloride gas was absorbed by water and used as a hydrochloric acid azeotropic solution.

[0135] (10) Calcination: The high-purity Al2O3 obtained in step (9) was added to 5% seed crystals and ground, then calcined at 1250℃ for 240 min to obtain 26.8 g of high-purity α-Al2O3. After ICP-OES analysis, its purity was 99.96%.

[0136] As can be seen from the above embodiments, the method provided by the present invention can prepare high-purity α-Al2O3 with a purity of over 99.96%, with a short process flow, simple steps, convenient operation, and the ability to recycle all materials, resulting in low production costs.

[0137] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing high purity α-Al2O3 by bauxite ammonium alum salting-out method, characterized by, The method comprises the following steps: (1) mixing bauxite with concentrated sulfuric acid to perform leaching reaction, and then performing solid-liquid separation to obtain circulating sulfuric acid and leaching material; the circulating sulfuric acid is directly used for next leaching reaction; the leaching reaction is performed at a temperature of 220-260 ℃, and the solid-liquid separation is performed at a temperature of 90-140 ℃; (2) mixing the leaching material with water and then performing hot solid-liquid separation to obtain a dissolving solution and a silicon residue; (3) mixing the dissolving solution with ammonium sulfate and then performing precipitation to obtain ammonium alum crystals; (4) mixing the ammonium alum crystals with hydrochloric acid to obtain an ammonium alum dissolving solution; (5) passing hydrogen chloride gas into the ammonium alum dissolved solution to precipitate aluminum chloride crystals and primary salting-out mother liquor after solid-liquid separation; the H + concentration of the ammonium alum dissolved solution after passing hydrogen chloride gas is 12-12.5 mol / L; (6) the aluminum chloride crystal is pickled and then dissolved to obtain an aluminum chloride solution, hydrogen chloride gas is then introduced into the aluminum chloride solution to precipitate, and then solid-liquid separation is performed to obtain purified aluminum chloride crystal and a secondary salting-out mother liquor; the pickling is concentrated hydrochloric acid washing; the H + concentration of the aluminum chloride solution after the introduction of the hydrogen chloride gas is 11-12 mol / L; (7) repeating step (6) for more than 3 times to obtain last aluminum chloride crystals, and pyrolyzing the last aluminum chloride crystals to obtain high-purity Al2O3, wherein the purity of the high-purity Al2O3 is 99.95%-99.99%; (8) mixing the high-purity Al2O3 with seed crystals, performing grinding, and then performing calcination to obtain high-purity α-Al2O3, wherein the purity of the high-purity α-Al2O3 is more than 99.96%; In step (4), the mass concentration of the hydrochloric acid is 18-20%, and the mixing temperature is 20-30 ℃; The primary salting-out mother liquor further comprises sequentially performing evaporation and distillation to obtain hydrogen chloride gas, azeotrope, dilute sulfuric acid and impurity-containing aluminum chloride; The hydrogen chloride gas is used for the precipitation in steps (3), (5), (6) or (7); The azeotrope is used for dissolving aluminum chloride crystals or purifying aluminum chloride crystals to obtain an aluminum chloride dissolving solution; The dilute sulfuric acid is used for the leaching reaction after being concentrated; The secondary salting-out mother liquor further comprises sequentially performing evaporation and distillation to obtain hydrogen chloride gas, azeotrope, dilute sulfuric acid and impurity-containing aluminum chloride; The hydrogen chloride gas is used for the precipitation in steps (3), (5), (6) or (7); The azeotrope is used for dissolving aluminum chloride crystals or purifying aluminum chloride crystals to obtain an aluminum chloride dissolving solution; The dilute sulfuric acid is used for the leaching reaction after being concentrated.

2. The method of claim 1, wherein, The particle size of the bauxite is not more than 74 microns.

3. The method according to claim 1 or 2, characterized in that, The holding time of the leaching reaction is 3-6 h.

4. The method of claim 1, wherein, In step (4), the mass-volume ratio of the ammonium alum crystals to the hydrochloric acid is 1 g:(0.8-1.2) mL.

5. The method of claim 1, wherein, The solvent used for the redissolution is hydrochloric acid; The mass concentration of the hydrochloric acid is 32%-38%; The volume ratio of the aluminum chloride crystals to the hydrochloric acid is 1 g:(1.8-2) mL; The temperature of the redissolution is 20-30 ℃.

6. The method according to claim 1 or 5, characterized in that, The number of times of repeating step (6) is 3-5 times.

7. The method of claim 1, wherein, The temperature of the pyrolysis is 400-500 ℃, and the holding time is 1-3 h.

8. The method according to claim 1 or 7, characterized in that, The temperature of the calcination is 1200-1250 ℃, and the holding time is 2-4 h.

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