Method for preparing high-purity alpha-Al2O3 by bauxite ammonium alum salting-out method

Abstract

The invention belongs to the technical field of bauxite utilization, and particularly relates to a method for preparing high-purity alpha-Al2O3 by a bauxite ammonium alum salting-out method. Research finds that within the range of 10-40 DEG C, the yield of aluminum chloride hexahydrate crystals is almost unchanged, but the precipitation speed of the aluminum chloride hexahydrate crystals is in direct proportion to the speed that a solution is saturated by HCl, impurities in aluminum chloride are removed by utilizing the property, and the aluminum chloride hexahydrate with very high purity is obtained by repeatedly dissolving and precipitating the impurities. According to the method, the high-purity alpha-Al2O3 is prepared through sulfuric acid leaching, ammonium alum crystallization and hydrochloride precipitation, the purity is 99.96% or above, the technological process is short, the steps are simple, operation is convenient, recycling of all materials is achieved, the production cost is low, desilicication is achieved through multiple times of filtration, and the added value of products is high.

Description

Technical Field

[0001] The invention belongs to the technical field of bauxite utilization, and specifically relates to a method for preparing high-purity alpha-Al2O3 by a bauxite ammonium alum salting-out method. Background Art

[0002] Bauxite, as the main raw material for aluminum products such as alumina, is divided into diaspore type, gibbsite type and diaspore type. Among them, diaspore type bauxite has complete crystallization, dense structure and large lattice energy. It is the main type of bauxite in my country. However, it is extremely difficult to dissolve and extract aluminum from this bauxite, which has hindered the development of my country's aluminum industry.

[0003] At present, most of my country's alumina industry adopts the Bayer process in the alkaline process, but the Bayer process requires a higher grade of bauxite, which means that for nearly 80% of my country's low-grade bauxite (aluminum-silicon ratio between 3 and 6), the dissolution conditions and costs are high. In addition, the alumina produced by the Bayer process is also accompanied by a large amount of industrial solid waste - red mud, and the resource utilization and recovery rate are low.

[0004] Chinese patent CN 107128959A discloses a method for preparing alumina by hydrochloric acid leaching of bauxite and its comprehensive utilization. The method adopts hydrochloric acid reaction dissolution to avoid the problems caused by the alkaline method, but the purity of the produced alumina cannot be guaranteed. Summary of the invention

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

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

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

[0008] (1) mixing bauxite with concentrated sulfuric acid for leaching reaction and then separating the solid and liquid to obtain circulating sulfuric acid and leaching material; the circulating sulfuric acid is directly used for the next leaching reaction;

[0009] (2) heating and mixing the leached material and water, and then separating the solid and liquid while hot to obtain a dissolved liquid and silicon slag;

[0010] (3) heating and mixing the dissolved solution and ammonium sulfate to obtain ammonium alum crystals;

[0011] (4) mixing the ammonium alum crystals with hydrochloric acid to obtain an ammonium alum solution;

[0012] (5) introducing hydrogen chloride gas into the ammonium alum solution to separate the solid and liquid after precipitation, thereby obtaining aluminum chloride crystals and a primary salting-out mother liquor;

[0013] (6) washing the aluminum chloride crystals with acid and then dissolving them to obtain an aluminum chloride solution, and then introducing hydrogen chloride gas into the aluminum chloride solution to separate the solid and liquid after precipitation to obtain purified aluminum chloride crystals and a secondary salting-out mother liquor; the acid washing is washing with concentrated hydrochloric acid;

[0014] (7) Repeating step (6) for more than 3 times to obtain final aluminum chloride crystals, pyrolyzing the final aluminum chloride crystals to obtain high-purity Al2O3, wherein the purity of the high-purity Al2O3 is 99.95% to 99.99%;

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

[0016] Preferably, the particle size of the bauxite is not greater than 74 microns.

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

[0018] Preferably, the primary salting-out mother liquor further comprises evaporation and distillation in sequence to obtain hydrogen chloride gas, azeotropic liquid, dilute sulfuric acid and impure aluminum chloride; the hydrogen chloride gas is used for the precipitation in step (3), (5), (6) or (7); the azeotropic liquid is used for dissolving aluminum chloride crystals or purifying aluminum chloride crystals to obtain aluminum chloride solution; the dilute sulfuric acid is used for the leaching reaction after being concentrated.

[0019] Preferably, the secondary salting-out mother liquor further comprises evaporation and distillation in sequence to obtain hydrogen chloride gas, azeotropic liquid, dilute sulfuric acid and impure aluminum chloride; the hydrogen chloride gas is used for the precipitation in step (3), (5), (6) or (7); the azeotropic liquid is used for dissolving aluminum chloride crystals or purifying aluminum chloride crystals to obtain aluminum chloride solution; the dilute sulfuric acid is used for the leaching reaction after being concentrated.

[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 1 g: (0.8-1.2) mL.

[0021] Preferably, the solvent used for the 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 1g:(1.8 to 2)mL; and the temperature of the redissolution is 20 to 30°C.

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

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

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

[0025] The present invention provides a method for preparing high-purity α-Al2O3 by a bauxite ammonium alum salting-out method. The present invention has found that within the range of 10 to 40°C, the yield of aluminum chloride hexahydrate crystals is almost unchanged, but its precipitation rate is proportional to the speed at which the solution is saturated with HCl. The present invention utilizes this property to remove impurities in aluminum chloride, and obtains aluminum chloride hexahydrate with high purity by repeatedly dissolving and precipitating the impurities.

[0026] The invention prepares high-purity alpha-Al2O3 by sulfuric acid leaching, ammonium alum crystallization and hydrochloric acid precipitation, the purity is above 99.96%, the process flow is short, the steps are simple, the operation is convenient, all materials can be recycled, the production cost is low, the desiliconization is performed multiple times, and the product has high added value. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 The process flow chart of the present invention is to prepare high-purity α-Al2O3 by the high-silicon bauxite ammonium alum salting-out method;

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

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

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

[0032] (1) mixing bauxite with concentrated sulfuric acid for leaching reaction and then separating the solid and liquid to obtain circulating sulfuric acid and leaching material; the circulating sulfuric acid is directly used for the next leaching reaction;

[0033] (2) heating and mixing the leached material and water, and then separating the solid and liquid while hot to obtain a dissolved liquid and silicon slag;

[0034] (3) heating and mixing the dissolved solution and ammonium sulfate to obtain ammonium alum crystals;

[0035] (4) mixing the ammonium alum crystals with hydrochloric acid to obtain an ammonium alum solution;

[0036] (5) introducing hydrogen chloride gas into the ammonium alum solution to separate the solid and liquid after precipitation, thereby obtaining aluminum chloride crystals and a primary salting-out mother liquor;

[0037] (6) washing the aluminum chloride crystals with acid and then dissolving them to obtain an aluminum chloride solution, and then introducing hydrogen chloride gas into the aluminum chloride solution to separate the solid and liquid after precipitation to obtain purified aluminum chloride crystals and a secondary salting-out mother liquor; the acid washing is washing with concentrated hydrochloric acid;

[0038] (7) Repeating step (6) for more than 3 times to obtain final aluminum chloride crystals, pyrolyzing the final aluminum chloride crystals to obtain high-purity Al2O3, wherein the purity of the high-purity Al2O3 is 99.95% to 99.99%;

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

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

[0041] The present invention mixes bauxite with concentrated sulfuric acid for leaching reaction and then separates the solid and liquid (referred to as the first solid-liquid separation) to obtain circulating sulfuric acid and leached material. In the present invention, the circulating sulfuric acid is preferably circulated for the leaching reaction.

[0042] In the present invention, the particle size of the bauxite is preferably not greater than 74 microns, more preferably not greater than 50 microns, and further preferably not greater than 25 microns.

[0043] In the present invention, the bauxite is preferably ground to a target particle size before use; the grinding speed is preferably 200-300 rpm, more preferably 220-270 rpm, and more preferably 240-260 rpm; the grinding time is preferably 60-300 min, more preferably 90-180 min, and more preferably 100-150 min; the grinding is preferably ball milling; the ball-to-material ratio of the ball milling is preferably 3-5:1, more preferably 4-5:1, and more preferably 4:1. The present invention can activate the bauxite by grinding, which is conducive to the subsequent reaction.

[0044] In the present invention, the mass concentration of the concentrated sulfuric acid is preferably 85% or more, more preferably 90% or more, and further preferably 90 to 95%.

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

[0046] In the present invention, the leaching reaction temperature is preferably 220-260°C, more preferably 230-250°C, and further preferably 240°C, and the holding time is preferably 3-6h, and more preferably 4-5h. The present invention obtains a dissolution slurry through a leaching reaction.

[0047] In the present 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 further preferably 110-120°C.

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

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

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

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

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

[0053] After obtaining the dissolved solution, the present invention heats and mixes the dissolved solution with ammonium sulfate (recorded as the second heating and mixing) and then precipitates (recorded as the first precipitation) to obtain 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 further preferably 1:1.2. The present invention adds excess ammonium sulfate, so that the aluminum element in the dissolved solution can completely react with the ammonium sulfate to generate ammonium alum.

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

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

[0056] In the present invention, the first precipitation is preferably performed by standing and cooling; the terminal temperature of the first precipitation is preferably 20 to 30°C, more preferably 24 to 27°C.

[0057] In the present invention, after the first precipitation, the process preferably further comprises sequentially subjecting the obtained product to solid-liquid separation A, neutralization of the separated mother liquor, solid-liquid separation B and distillation.

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

[0059] In the present invention, the neutralization of the separated mother liquor is preferably performed by: mixing the separated mother liquor with ammonium carbonate; the pH value of the neutralization of the separated mother liquor is preferably 6.8 to 7.5, more preferably 7.5.

[0060] In the present invention, the solid-liquid separation B is preferably filtration. In the present invention, impurities are filtered out by solid-liquid separation B.

[0061] In the present invention, the distillation temperature is preferably 80-120° C., more preferably 100° C., until ammonium sulfate is precipitated. In the present invention, ammonium sulfate is obtained by distillation.

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

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

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

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

[0066] In the present invention, the third mixing preferably further comprises filtering the obtained mixture. The present invention removes impurities in the mixture by filtering.

[0067] After obtaining the ammonium alum solution, the present invention introduces hydrogen chloride gas into the ammonium alum solution for precipitation (referred to as the second precipitation) and then performs 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 the H in the ammonium alum solution is + The concentration is 12~12.5mol / L.

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

[0069] In the present invention, after obtaining the primary salting-out mother liquor, the process preferably further comprises evaporating and distilling the primary salting-out mother liquor in sequence to obtain hydrogen chloride gas, azeotropic liquid, dilute sulfuric acid and impure aluminum chloride; the hydrogen chloride gas is preferably used for the precipitation in step (3), (5), (6) or (7); the azeotropic liquid is preferably used for dissolving the aluminum chloride crystals or purifying the aluminum chloride crystals to obtain an aluminum chloride solution; the dilute sulfuric acid is preferably used for the leaching reaction after being concentrated; the impure aluminum chloride is preferably purified to prepare industrial-grade aluminum chloride.

[0070] In the present invention, when the hydrogen chloride gas obtained from the primary salting-out mother liquor is insufficient, acid supplementation is preferably performed; the acid supplementation is preferably performed by mixing concentrated hydrochloric acid and concentrated sulfuric acid and evaporating them 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 leaching reaction or acid supplementation; the mixing of concentrated hydrochloric acid and concentrated sulfuric acid is preferably performed by dripping concentrated sulfuric acid into concentrated hydrochloric acid; the evaporation temperature is preferably 115-125° C., more preferably 120° C.

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

[0072] In the present invention, the acid washing is preferably: compacting the aluminum chloride crystals in a funnel, pouring concentrated hydrochloric acid into the funnel for filtering and washing; the mass concentration of the concentrated hydrochloric acid is preferably 32-38%, more preferably 36%; the mass volume ratio of the bauxite to the 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 further preferably 2 g: 1 mL. The present invention uses concentrated hydrochloric acid to wash the aluminum chloride crystals, which can better remove impurities.

[0073] In the present invention, the solvent used for the 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 the azeotropic solution obtained by evaporating the secondary salting-out mother liquor (the salting-out mother liquor remaining in the previous time); the temperature of the redissolution is preferably 20-30°C, more preferably 22-28°C, and further preferably 24-26°C.

[0074] In the present invention, after the redissolution, the product obtained is preferably also subjected to precision filtration; the pore size of the precision filtration is preferably 3-15 μm, more preferably 4.5-9 μm; the precision filtration is preferably compacted vacuum filtration; the compacted vacuum filtration is manual compaction, and the vacuum degree is preferably 0.075-0.095 MPa, more preferably 0.08-0.09 MPa.

[0075] In the present invention, the endpoint of the third precipitation is preferably H + The concentration is 11 to 12 mol / L, more preferably 11.5 mol / L.

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

[0077] In the present invention, after obtaining the secondary salting-out mother liquor, the process preferably further comprises evaporating and distilling the secondary salting-out mother liquor in sequence to obtain hydrogen chloride gas, azeotropic liquid, dilute sulfuric acid and impure aluminum chloride; the hydrogen chloride gas is preferably used for the precipitation in step (3), (5), (6) or (7); the azeotropic liquid is preferably used for dissolving the aluminum chloride crystals or purifying the aluminum chloride crystals to obtain an aluminum chloride solution; the dilute sulfuric acid is preferably used for the leaching reaction after being concentrated; and the impure aluminum chloride is preferably purified to prepare industrial-grade aluminum chloride.

[0078] In the present invention, when the hydrogen chloride gas obtained from the secondary salting-out mother liquor is insufficient, acid supplementation is preferably performed; the acid supplementation is preferably performed by mixing concentrated hydrochloric acid and concentrated sulfuric acid and evaporating them 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 supplementation; the mixing of concentrated hydrochloric acid and concentrated sulfuric acid is preferably performed by dripping concentrated sulfuric acid into concentrated hydrochloric acid; the evaporation temperature is preferably 115-125°C, more preferably 120°C.

[0079] After obtaining the purified aluminum chloride crystals, the present invention repeats step (6) for more than 3 times to obtain final aluminum chloride crystals, and pyrolyzes the final aluminum chloride crystals 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 the step (6) is repeated is preferably 3 to 5 times, and more preferably 4 to 5 times.

[0080] In the present invention, the last aluminum chloride crystal and the last salting-out mother liquor are obtained after repeating step (6) for more than 3 times, and the last salting-out mother liquor is preferably used for the ammonium alum crystal to prepare the ammonium alum solution; the treatment method of the salting-out mother liquor generated during the repeating step (6) is preferably the same as the treatment method of the secondary salting-out mother liquor in step (6), which will not be repeated here. The present invention further purifies the aluminum chloride crystals by repeating step (6).

[0081] In the present invention, the pyrolysis temperature is preferably 400-500°C, more preferably 420-480°C, further preferably 440-460°C, and the insulation time is preferably 1-3h, more preferably 1.5-2.5h, further preferably 2h.

[0082] In the present invention, the pyrolysis obtains high-purity Al2O3 and hydrogen chloride gas; the hydrogen chloride gas is preferably used for the next precipitation (the next precipitation of any step in the present invention) or the next redissolution (the next redissolution of any step in the present invention); when the hydrogen chloride gas is used for the next redissolution, it is preferably used after being absorbed by water.

[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, and the purity of the high-purity α-Al2O3 is more than 99.96%. In the present invention, the mass ratio of the seed crystals to the high-purity Al2O3 is preferably 4 to 6:100, more preferably 4.5 to 5.5:100, and further preferably 5:100.

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

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

[0086] In order to further illustrate the present invention, the scheme of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments, but they should not be understood as limiting the protection scope of the present invention.

[0087] Example 1

[0088] (1) Fine grinding: grinding and sieving the bauxite to obtain activated bauxite with a particle size not greater than 74 μm;

[0089] (2) Acid leaching: 120 g of activated bauxite was mixed with 600 mL of concentrated sulfuric acid and leached at 240 °C for 4 h to obtain a dissolution slurry;

[0090] (3) Filtration: The temperature of the dissolved slurry is cooled to 140° C. and filtered to obtain circulating sulfuric acid and leaching material;

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

[0092] (5) Alum preparation: 120 g of ammonium sulfate was added to the solution, heated to dissolve, filtered, and allowed to stand for cooling to obtain 462 g of ammonium alum; ammonium carbonate was added to the mother liquor separated after filtering out the ammonium alum crystals to neutralize it, impurities were filtered out, and then distilled and filtered to obtain ammonium sulfate, which was returned to step (5) for recycling;

[0093] (6) Acid dissolution: dissolve the 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: Add 500 mL of concentrated hydrochloric acid heated to 108°C into the solution at 70°C to obtain the resulting hydrogen chloride gas. Measure the H + The concentration reached 12.5 mol / L; filtered and washed to obtain 224.1 g of aluminum chloride crystals and a primary salting-out mother liquor;

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

[0096] ① At room temperature, dissolve aluminum chloride crystals in 450 mL of hydrochloric acid azeotropic solution, evaporate the primary salting-out mother liquor to 108°C to obtain hydrogen chloride gas and primary distilled liquid, pass hydrogen chloride gas into aluminum chloride solution, add acid, and then H + The concentration reaches 11.5 mol / L, and after filtering, 223.1 g of secondary aluminum chloride crystals and secondary salting-out mother liquor are obtained; the primary distilled liquid is further evaporated to obtain hydrochloric acid azeotropic solution, dilute sulfuric acid and aluminum chloride containing impurities, and the dilute sulfuric acid is further concentrated for acid leaching in step (2);

[0097] ② At room temperature, dissolve the secondary aluminum chloride crystals in 450mL of hydrochloric acid azeotropic solution, evaporate the secondary salting-out mother liquor to 108℃ to obtain hydrogen chloride gas and secondary distilled liquid, pass hydrogen chloride gas into aluminum chloride solution, add acid and H + The concentration reaches 10.0 mol / L, and after filtration, 201.2 g of three-stage aluminum chloride crystals and three-stage salting-out mother liquor are obtained; after the second distillation liquid is further evaporated, a hydrochloric acid azeotropic liquid and aluminum chloride containing impurities are obtained;

[0098] ③ At room temperature, dissolve the three aluminum chloride crystals in 405mL hydrochloric acid azeotropic solution, evaporate the three salting-out mother liquor to 108℃ to obtain hydrogen chloride gas and three distilled liquid, pass hydrogen chloride gas into aluminum chloride solution, add acid and H + The concentration reaches 10.6 mol / L, and after filtration, 194.6 g of aluminum chloride crystals and four salting-out mother liquors are obtained; the three distilled liquids are used as hydrochloric acid dissolution in step (6);

[0099] ④ At room temperature, dissolve the aluminum chloride crystals in 390 mL of hydrochloric acid azeotropic solution, evaporate the mother liquor of the fourth salting out to 108 ° C to obtain hydrogen chloride gas and fourth distilled liquid, pass hydrogen chloride gas into aluminum chloride solution, add acid, and then H + The concentration reaches 11.8 mol / L, and after filtering, 192.9 g of five-time aluminum chloride crystals (final aluminum chloride crystals) and five-time salting-out mother liquor are obtained; the four-time evaporation liquid is used as a hydrochloric acid azeotropic liquid; the five-time mother liquor is used as a hydrochloric acid azeotropic liquid after evaporation;

[0100] (9) Pyrolysis: Pyrolyze the quintic aluminum chloride crystals (final aluminum chloride crystals) at 400°C for 120 min to obtain 44.9 g of high-purity Al2O3 (purity: 99.96%) and hydrogen chloride gas. The obtained hydrogen chloride gas is absorbed by water and used as a hydrochloric acid azeotrope.

[0101] (10) Calcination: Add 5% seed crystals to the high-purity Al2O3 prepared in step (9), grind the mixture, and calcine the mixture at 1250°C 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, XRD and TEM tests. The test methods were based on GB / T 37248-2018. The results are shown in Tables 1 and Figures 2-3 shown.

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

[0104]

[0105] It can be seen from Table 1 that 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 the present invention is mainly α phase.

[0107] according to Figure 3 It can be seen that the microscopic appearance of the Al2O3 product prepared by the present invention is mainly worm-shaped, accompanied by ellipsoidal shape, and the surface is smooth.

[0108] Example 2

[0109] (1) Fine grinding: grinding and sieving the bauxite to obtain activated bauxite with a particle size not greater than 74 μm;

[0110] (2) Acid leaching: 120 g of activated bauxite was mixed with 600 mL of concentrated sulfuric acid and leached at 220 °C for 4 h to obtain a dissolution slurry;

[0111] (3) Filtration: The temperature of the dissolved slurry is cooled to 130° C. and filtered to obtain circulating sulfuric acid and leaching material;

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

[0113] (5) Alum preparation: 120 g of ammonium sulfate was added to the solution, heated to dissolve, filtered, and allowed to stand for cooling to obtain 405 g of ammonium alum; ammonium carbonate was added to the mother liquor separated after filtering out the ammonium alum crystals to neutralize it, impurities were filtered out, and then distilled and filtered to obtain ammonium sulfate, which was returned to step (5) for recycling;

[0114] (6) Acid dissolution: dissolve the 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: The hydrogen chloride gas obtained by evaporating the mother liquor four times at 70°C was passed into the solution, and the H +The concentration reached 12.5 mol / L; filtered and washed to obtain 187.1 g of aluminum chloride crystals and a primary salting-out mother liquor;

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

[0117] ① At room temperature, dissolve aluminum chloride crystals in 375 mL of hydrochloric acid azeotropic solution, evaporate the primary salting-out mother liquor to 108 °C to obtain hydrogen chloride gas and primary distilled liquid, pass hydrogen chloride gas into aluminum chloride solution, add acid, and then H + The concentration reaches 11.3 mol / L, and after filtration, 185.9 g of secondary aluminum chloride crystals and secondary salting-out mother liquor are obtained; the primary evaporation liquid is further evaporated to obtain hydrochloric acid azeotropic solution, dilute sulfuric acid and aluminum chloride containing impurities, and the dilute sulfuric acid is further concentrated and can be used for acid leaching in step (2);

[0118] ② At room temperature, dissolve the 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 secondary distilled liquid, pass hydrogen chloride gas into the aluminum chloride solution, add acid, and then H + The concentration reached 11.4 mol / L, and after filtration, 172.2 g of three-stage aluminum chloride crystals and three-stage salting-out mother liquor were obtained; after further evaporation of the secondary distilled liquid, hydrochloric acid azeotropic liquid and aluminum chloride containing impurities were obtained;

[0119] ③ At room temperature, dissolve the three aluminum chloride crystals in 344 mL of hydrochloric acid azeotropic solution, evaporate the three salting-out mother liquor to 108 ° C to obtain hydrogen chloride gas and three distilled liquid, pass hydrogen chloride gas into aluminum chloride solution, add acid, and then H + The concentration reaches 11.1 mol / L, and after filtration, 171.4 g of tetrachloroaluminum crystals (final tetrachloroaluminum crystals) and tetrachloroaluminum mother liquor are obtained; the tertiary distilled liquid can be used for hydrochloric acid dissolution in step (6);

[0120] (9) Pyrolysis: Pyrolyze the quaternary aluminum chloride crystals (final aluminum chloride crystals) at 500°C for 120 min to obtain 33.8 g of high-purity Al2O3 (purity: 99.96%) and hydrogen chloride gas. The obtained hydrogen chloride gas is absorbed by water and used as a hydrochloric acid azeotrope.

[0121] (10) Calcination: The high-purity Al2O3 prepared in step (9) was added with 5% seed crystals and ground, and then calcined at 1250°C for 240 min to obtain 30.2 g of high-purity α-Al2O3. The purity was 99.96% as determined by ICP-OES.

[0122] Example 3

[0123] (1) Fine grinding: grinding and sieving the bauxite to obtain activated bauxite with a particle size not greater than 74 μm;

[0124] (2) Acid leaching: 100 g of activated bauxite was mixed with 500 mL of concentrated sulfuric acid and leached at 230 °C for 4 h to obtain a dissolution slurry;

[0125] (3) Filtration: The temperature of the dissolved slurry is cooled to 90° C. and filtered to obtain circulating sulfuric acid and leached material;

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

[0127] (5) Preparation of alum: 95 g of ammonium sulfate was added to the solution, heated to dissolve, filtered, and allowed to stand for cooling to obtain 383 g of ammonium alum; ammonium carbonate was added to the mother liquor separated after filtering out the ammonium alum crystals for neutralization, impurities were filtered out, and then distilled and filtered to obtain ammonium sulfate, which was returned to step (5) for recycling.

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

[0129] (7) Aluminum chloride crystallization: The hydrogen chloride gas obtained by evaporating the salting-out mother liquor five times was passed into the solution at 70°C, and the H + The concentration reached 12.5 mol / L; filtered and washed to obtain 152.8 g of aluminum chloride crystals and a primary salting-out mother liquor;

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

[0131] ① At room temperature, dissolve aluminum chloride crystals in 306 mL of hydrochloric acid azeotropic solution, evaporate the primary salting-out mother liquor to 108 °C to obtain hydrogen chloride gas and primary distilled liquid, pass hydrogen chloride gas into aluminum chloride solution, add acid, and then H + The concentration reaches 11.1 mol / L, and after filtration, 151.7 g of secondary aluminum chloride crystals and secondary salting-out mother liquor are obtained; the primary evaporation liquid is further evaporated to obtain hydrochloric acid azeotropic solution, dilute sulfuric acid and aluminum chloride containing impurities, and the dilute sulfuric acid is further concentrated and can be used for acid leaching in step (2);

[0132] ② At room temperature, dissolve the 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 secondary distilled liquid, pass hydrogen chloride gas into the aluminum chloride solution, add acid, and then H + The concentration reached 10.8 mol / L, and after filtration, 143.4 g of three-stage aluminum chloride crystals and three-stage salting-out mother liquor were obtained; after further evaporation of the secondary distilled liquid, hydrochloric acid azeotropic liquid and aluminum chloride containing impurities were obtained;

[0133] ③ At room temperature, dissolve the three aluminum chloride crystals in 288mL hydrochloric acid azeotropic solution, evaporate the three salting-out mother liquor to 108℃ to obtain hydrogen chloride gas and three distilled liquid, pass hydrogen chloride gas into aluminum chloride solution, add acid and H + The concentration reaches 11.6 mol / L, and after filtration, 141.6 g of tetrachloroaluminum crystals (final tetrachloroaluminum crystals) and tetrachloroaluminum mother liquor are obtained; the tertiary distilled liquid can be used for hydrochloric acid dissolution in step (6);

[0134] (9) Pyrolysis: Pyrolyze the quaternary aluminum chloride crystals (final aluminum chloride crystals) at 400°C for 120 min to obtain 27.5 g of high-purity Al2O3 (purity: 99.96%) and hydrogen chloride gas. The obtained hydrogen chloride gas is absorbed by water and used as a hydrochloric acid azeotrope.

[0135] (10) Calcination: The high-purity Al2O3 prepared in step (9) was added with 5% seed crystals and ground, and then calcined at 1250°C for 240 min to obtain 26.8 g of high-purity α-Al2O3. The purity was 99.96% as determined by ICP-OES.

[0136] It can be seen from the above embodiments that the method provided by the present invention can prepare high-purity α-Al2O3 with a purity of more than 99.96%, with a short process flow, simple steps, convenient operation, and the recycling of all materials, with low production cost.

[0137] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, 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 in that: The following steps are involved: (1) mixing bauxite with concentrated sulfuric acid for leaching reaction and then separating the solid and liquid to obtain circulating sulfuric acid and leaching material; the circulating sulfuric acid is directly used for the next leaching reaction; (2) heating and mixing the leached material and water, and then separating the solid and liquid while hot to obtain a dissolved liquid and silicon slag; (3) heating and mixing the dissolved solution and ammonium sulfate to obtain ammonium alum crystals; (4) mixing the ammonium alum crystals with hydrochloric acid to obtain an ammonium alum solution; (5) introducing hydrogen chloride gas into the ammonium alum solution to separate the solid and liquid after precipitation, thereby obtaining aluminum chloride crystals and a primary salting-out mother liquor; (6) washing the aluminum chloride crystals with acid and then dissolving them to obtain an aluminum chloride solution, and then introducing hydrogen chloride gas into the aluminum chloride solution to separate the solid and liquid after precipitation to obtain purified aluminum chloride crystals and a secondary salting-out mother liquor; the acid washing is washing with concentrated hydrochloric acid; (7) Repeating step (6) for more than 3 times to obtain final aluminum chloride crystals, pyrolyzing the final aluminum chloride crystals to obtain high-purity Al2O3, wherein the purity of the high-purity Al2O3 is 99.95% to 99.99%; (8) The high-purity Al2O3 and seed crystals are mixed, ground, and then calcined to obtain high-purity α-Al2O3, wherein the purity of the high-purity α-Al2O3 is greater than 99.96%.

2. The method according to claim 1, characterized in that: The particle size of the bauxite is no greater than 74 microns.

3. The method according to claim 1 or 2, characterized in that: The leaching reaction temperature is 220-260° C., and the insulation time is 3-6 hours.

4. The method according to claim 1, characterized in that: The primary salting out of the mother liquor further comprises evaporating and distilling in sequence to obtain hydrogen chloride gas, azeotropic liquid, dilute sulfuric acid and impurity-containing aluminum chloride; The hydrogen chloride gas is used for the precipitation in step (3), (5), (6) or (7); The azeotropic liquid is used to dissolve aluminum chloride crystals or purify aluminum chloride crystals to obtain an aluminum chloride solution; The dilute sulfuric acid is concentrated and used for the leaching reaction.

5. The method according to claim 1 or 4, characterized in that: The secondary salting-out mother liquor further comprises evaporating and distilling in sequence to obtain hydrogen chloride gas, azeotropic liquid, dilute sulfuric acid and impurity-containing aluminum chloride; The hydrogen chloride gas is used for the precipitation in step (3), (5), (6) or (7); The azeotropic liquid is used to dissolve aluminum chloride crystals or purify aluminum chloride crystals to obtain an aluminum chloride solution; The dilute sulfuric acid is concentrated and used for the leaching reaction.

6. The method according to claim 1, characterized in that In step (4), the mass concentration of the hydrochloric acid is 18-20%; The mass volume ratio of the ammonium alum crystals to hydrochloric acid is 1 g: (0.8-1.2) mL.

7. The method according to claim 1, characterized in that The solvent used for the 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: (1.8-2) mL; The re-dissolving temperature is 20-30°C.

8. The method according to claim 1 or 7, characterized in that: The step (6) is repeated 3 to 5 times.

9. The method according to claim 1, characterized in that: The pyrolysis temperature is 400-500° C., and the insulation time is 1-3 hours.

10. The method according to claim 1 or 9, characterized in that: The calcination temperature is 1200-1250° C., and the heat preservation time is 2-4 hours.

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