A method for preparing high-purity alpha-Al2O3 by supercritical boiler fly ash aluminum sulfate salting-out method

Abstract

The present application belongs to the technical field of coal-based solid waste high-value resource, and particularly relates to a method for preparing high-purity alpha-Al2O3 by supercritical boiler fly ash aluminum sulfate salting-out method. ‑ The present application finds that, in the process of salting-out reaction, the crystallization yield of aluminum chloride hexahydrate is proportional to the concentration of Cl in the reaction solution. The present application uses the above-mentioned property of aluminum chloride hexahydrate to remove impurities in aluminum chloride, and through repeated salting-out purification, high-purity alpha-Al2O3 is obtained. The present application combines sulfuric acid method and hydrochloric acid method to extract high-purity alpha-Al2O3 from fly ash, and has low cost, low energy consumption, simple operation, good safety and high product added value.

Description

Technical Field

[0001] This invention belongs to the field of high-value resource utilization technology of coal-based solid waste, specifically involving a method for preparing high-purity α-Al2O3 by aluminum sulfate salting-out of supercritical boiler fly ash. Background Technology

[0002] Coal combustion produces a large amount of solid waste—fly ash. This fly ash has low activity and is difficult to utilize effectively; therefore, most of it is discarded, with only a small portion used in construction and engineering as filler and other low-value products. This not only results in low utilization of coal-based solid waste but also low added value, leading to resource waste. Later, researchers attempted to extract residual metallic minerals from fly ash, which not only enables the resource utilization of fly ash but also has significant economic and ecological benefits. Currently, methods for extracting alumina from fly ash mainly include activated sintering, alkaline methods, acid leaching, and combined acid-alkali methods.

[0003] Acid leaching mainly involves leaching with hydrochloric acid or sulfuric acid. This method has advantages such as simple process and mild conditions. However, during acid leaching, metal components such as sodium, magnesium and calcium are dissolved at the same time. It is necessary to remove these impurities. However, acidic conditions make leaching difficult and leave a large amount of residue, resulting in poor product purity and high cost. This seriously limits the market application of acid leaching. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing high-purity α-Al2O3 from supercritical boiler fly ash by aluminum sulfate salting-out. The method provided by this invention can extract high-purity α-Al2O3 from fly ash at low cost.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing high-purity α-Al₂O₃ by aluminum sulfate salting-out from supercritical boiler fly ash, comprising the following steps:

[0007] (1) Mix the ball-milled fly ash with sulfuric acid and leach it to obtain a dissolution slurry;

[0008] (2) The leaching slurry is separated into solid and liquid components to obtain circulating sulfuric acid and leaching material, wherein the circulating sulfuric acid is used in step (1);

[0009] (3) The leaching material and the dissolving agent are heated and mixed, and then the solid and liquid are separated while hot to obtain a solution and silicon slag;

[0010] (4) After passing hydrogen chloride gas into the solution to carry out the precipitation reaction, solid-liquid separation is performed to obtain primary aluminum chloride crystals and primary mother liquor;

[0011] (5) The primary aluminum chloride crystals are washed with hydrochloric acid to obtain acid-washed primary aluminum chloride crystals;

[0012] (6) The acid-washed aluminum chloride crystals are first mixed with an acid solution to obtain a first aluminum chloride solution, wherein the acid solution is hydrochloric acid or hydrochloric acid azeotropic solution, and the temperature of the first mixing is 20-30°C; the first mother liquor is evaporated to obtain hydrogen chloride gas and a first evaporator; the obtained hydrogen chloride gas is introduced into the first aluminum chloride solution to carry out a precipitation reaction and then the solid and liquid are separated to obtain secondary aluminum chloride crystals and a secondary mother liquor; the first evaporator is evaporated to obtain a hydrochloric acid azeotropic solution and dilute sulfuric acid, wherein the hydrochloric acid azeotropic solution is used as the acid solution, and the dilute sulfuric acid is concentrated to obtain sulfuric acid for use in step (1);

[0013] (7) After purifying the secondary aluminum chloride crystals by repeating step (6) more than 3 times, the obtained aluminum chloride crystals are pyrolyzed to obtain basic aluminum chloride.

[0014] (8) The basic aluminum chloride and seed crystals are mixed, ground and then calcined to obtain high-purity α-Al2O3 with a purity of 99.98% or higher.

[0015] Preferably, in step (1), the ball milling speed is 200-300 rpm, the ball-to-material ratio is 3-5:1, and the ball milling time is 1-3 hours.

[0016] Preferably, in step (1), the acid leaching temperature is 230-250°C and the leaching time is 180-300 min.

[0017] Preferably, in step (2), the temperature of the solid-liquid separation is 120-160°C.

[0018] Preferably, in step (3), the temperature of the heating mixture is 70-90°C and the holding time is 0.5-1.5h.

[0019] Preferably, in step (4), the temperature of the precipitation reaction is greater than or equal to 60°C, until H in the reaction solution... + Concentration greater than 11 mol / L.

[0020] Preferably, in step (6), the temperature of the precipitation reaction is 50–70°C, until H in the reaction solution... + Concentration greater than 11 mol / L.

[0021] Preferably, in step (6), when the hydrogen chloride gas is insufficient, it is prepared using an acidifying liquid; the acidifying liquid is sulfuric acid and hydrochloric acid; the concentration of the sulfuric acid is 85% or higher; and the concentration of the hydrochloric acid is 30-36%.

[0022] Preferably, in step (7), the pyrolysis temperature is 400-650°C and the holding time is 60-120 min.

[0023] Preferably, in step (8), the calcination temperature is 1200-1250℃ and the holding time is 120-240 min; the mass ratio of basic aluminum chloride to seed crystals is 100:4-7.

[0024] This invention provides a method for preparing high-purity α-Al₂O₃ by aluminum sulfate salting-out from supercritical boiler fly ash. The invention's research found that during the precipitation reaction, the yield of aluminum chloride hexahydrate crystals is related to the Cl₂ concentration in the reaction solution. - The concentration is directly proportional to the purity of α-Al₂O₃. This invention utilizes the aforementioned properties of AlCl₃·6H₂O to remove impurities from aluminum chloride. Through repeated precipitation purification, high-purity α-Al₂O₃ is obtained. This invention combines the sulfuric acid method and the hydrochloric acid method to extract high-purity α-Al₂O₃ from fly ash. The method is low-cost, low-energy-consumption, simple to operate, safe, and produces high-value-added products. Furthermore, throughout the entire process, all processed materials can be recycled, reducing production costs and overcoming the technical problems of difficult fly ash leaching and large residue volumes in existing technologies. Attached Figure Description

[0025] 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.

[0026] Figure 1 This is a process flow diagram of the present invention for preparing high-purity α-Al2O3 using fly ash;

[0027] Figure 2 The XRD pattern of the high-purity α-Al₂O₃ prepared in Example 1;

[0028] Figure 3 The image shows a TEM image of the high-purity α-Al2O3 prepared in Example 1. Detailed Implementation

[0029] This invention provides a method for preparing high-purity α-Al₂O₃ by aluminum sulfate salting-out from supercritical boiler fly ash, comprising the following steps:

[0030] (1) Mix the ball-milled fly ash with sulfuric acid and leach it to obtain a dissolution slurry;

[0031] (2) The leaching slurry is separated into solid and liquid components to obtain circulating sulfuric acid and leaching material, wherein the circulating sulfuric acid is used in step (1);

[0032] (3) The leaching material and the dissolving agent are heated and mixed, and then the solid and liquid are separated while hot to obtain a solution and silicon slag;

[0033] (4) After passing hydrogen chloride gas into the solution to carry out the precipitation reaction, solid-liquid separation is performed to obtain primary aluminum chloride crystals and primary mother liquor;

[0034] (5) The primary aluminum chloride crystals are washed with hydrochloric acid to obtain acid-washed primary aluminum chloride crystals;

[0035] (6) The acid-washed aluminum chloride crystals are first mixed with an acid solution to obtain a first aluminum chloride solution, wherein the acid solution is hydrochloric acid or hydrochloric acid azeotropic solution, and the temperature of the first mixing is 20-30°C; the first mother liquor is evaporated to obtain hydrogen chloride gas and a first evaporator; the obtained hydrogen chloride gas is introduced into the first aluminum chloride solution to carry out a precipitation reaction and then the solid and liquid are separated to obtain secondary aluminum chloride crystals and a secondary mother liquor; the first evaporator is evaporated to obtain a hydrochloric acid azeotropic solution and dilute sulfuric acid, wherein the hydrochloric acid azeotropic solution is used as the acid solution, and the dilute sulfuric acid is concentrated to obtain sulfuric acid for use in step (1);

[0036] (7) After purifying the secondary aluminum chloride crystals by repeating step (6) more than 3 times, the obtained aluminum chloride crystals are pyrolyzed to obtain basic aluminum chloride.

[0037] (8) The basic aluminum chloride and seed crystals are mixed, ground and then calcined to obtain high-purity α-Al2O3 with a purity of 99.98% or higher.

[0038] This invention involves mixing ball-milled fly ash with sulfuric acid for acid leaching to obtain a leaching slurry. In this invention, the ball milling speed is preferably 200–300 rpm, more preferably 240–260 rpm; the ball-to-material ratio is preferably 3–5:1, more preferably 4:1; and the ball milling time is preferably 1–3 hours, more preferably 2 hours. This invention obtains activated fly ash through ball milling.

[0039] In this invention, the particle size of the ball-milled fly ash is preferably below 74 micrometers, more preferably 0.01 to 50 micrometers, even more preferably 1 to 30 micrometers, and even more preferably 5 to 15 micrometers. Using fly ash within the above particle size range in this invention is beneficial for improving the leaching effect.

[0040] In this invention, the concentration of sulfuric acid is preferably 85 wt% or more, more preferably 85-95 wt%, even more preferably 88-93 wt%, and even more preferably 90 wt%.

[0041] In this invention, the mass ratio of the ball-milled fly ash to the volume of sulfuric acid is preferably 1g:(3-5)mL, more preferably 1g:(3.3-4.6)mL, even more preferably 1g:(3.7-4.3)mL, and even more preferably 1g:4mL.

[0042] In this invention, the acid leaching temperature is preferably 230-250°C, more preferably 235-245°C, and the leaching time is preferably 180-300 min, more preferably 210-250 min.

[0043] After obtaining the leaching slurry, the present invention performs solid-liquid separation of the leaching slurry to obtain circulating sulfuric acid and leaching material, wherein the circulating sulfuric acid is used in step (1). In the present invention, the solid-liquid separation is preferably filtration; the pore size of the filter is preferably 3-15 μm, more preferably 4.5-9 μm; the filtration is preferably pressure filtration; the temperature of the solid-liquid separation is preferably 120-160℃, more preferably 130-150℃. The circulating sulfuric acid obtained by the present invention can be directly used for acid leaching in the next step (1).

[0044] After obtaining recycled sulfuric acid and the leaching material, the present invention heats and mixes the leaching material with a dissolving agent, then performs solid-liquid separation while hot to obtain a dissolved solution and silicon slag. In the present invention, the dissolving agent is preferably dilute hydrochloric acid or water; the mass concentration of the dilute hydrochloric acid is preferably 15-24%, more preferably 18-20%; the water is preferably deionized water. The present invention uses dilute hydrochloric acid or water to dissolve the leaching material, thereby extracting as many rare metals as possible from the leaching material while separating the silicon slag, and also reducing the amount of hydrogen chloride used in subsequent precipitation reactions.

[0045] In this invention, the mass ratio of the ball-milled fly ash to the volume ratio of the dissolving agent is preferably 1g:(3-4)mL, more preferably 1g:(3.2-3.8)mL, and even more preferably 1g:(3.4-3.6)mL.

[0046] In this invention, the heating and mixing temperature is preferably 70–90°C, more preferably 75–85°C, and the holding time is preferably 0.5–1.5 h, more preferably 0.8–1.2 h; the heating and mixing is preferably stirring; the stirring speed is preferably 200–500 rpm, more preferably 350–400 rpm. This invention converts aluminum sulfate in the leaching material into aluminum chloride through heating and mixing, thereby separating the silica slag.

[0047] In this invention, the hot solid-liquid separation is preferably hot filtration; the pore size of the hot filtration is preferably 3-15 μm, more preferably 4.5-9 μm; the temperature of the hot solid-liquid separation is preferably 70-90℃, more preferably 75-85℃.

[0048] After obtaining the solution and silicon slag, the present invention introduces hydrogen chloride gas into the solution to carry out a precipitation reaction and then separates the solid and liquid to obtain primary aluminum chloride crystals and primary mother liquor. In the present invention, the hydrogen chloride gas is preferably introduced for 2 to 5 hours, more preferably 4 hours; the hydrogen chloride gas is preferably prepared by evaporating the mother liquor (including primary mother liquor, secondary mother liquor, up to the last mother liquor) or by evaporating the acidification liquid (i.e., acidification).

[0049] In this invention, the acidifying solution is preferably sulfuric acid and hydrochloric acid; the concentration of the sulfuric acid is preferably 85% or more, more preferably 85-90%; the concentration of the hydrochloric acid is preferably 30-36%, more preferably 32-34%; the volume ratio of hydrochloric acid to sulfuric acid is preferably 2:1; the preferred method for preparing the hydrogen chloride gas is to add sulfuric acid dropwise to hydrochloric acid and then heat it to obtain hydrogen chloride gas and dilute sulfuric acid.

[0050] In this invention, the temperature of the precipitation reaction (denoted as precipitation reaction Z) is preferably greater than or equal to 60°C, more preferably 60-70°C, and preferably until H2 is present in the reaction solution. + The concentration is greater than 11 mol / L, more preferably 12 to 12.5 mol / L.

[0051] In this invention, the solid-liquid separation is preferably filtration; the pore size of the filter is preferably 3-15 μm, more preferably 4.5-9 μm.

[0052] After obtaining primary aluminum chloride crystals and a primary mother liquor, the present invention washes the primary aluminum chloride crystals with hydrochloric acid to obtain acid-washed primary aluminum chloride crystals. In the present invention, the concentration of hydrochloric acid used for washing is preferably 32-38%, more preferably 34-38%, further preferably 34-36%, and even more preferably 36%.

[0053] In this invention, the preferred mass ratio of the ball-milled fly ash to the volume of hydrochloric acid is (1-2) g:(1-2) mL, more preferably (1-2) g:1 mL, and even more preferably 2 g:1 mL. During washing, the primary aluminum chloride crystals are compacted in a funnel, poured into hydrochloric acid, and filtered for washing.

[0054] In this invention, the hydrochloric acid washing is preferably performed until the aluminum chloride crystals dissolve in hydrochloric acid and turn colorless or pale yellow. This invention uses hydrochloric acid washing after the first precipitation reaction to remove a large amount of surface-adhered impurities, thereby reducing the number of subsequent precipitation reactions.

[0055] After obtaining acid-washed aluminum chloride crystals, the present invention mixes the acid-washed aluminum chloride crystals with an acid solution to obtain a first aluminum chloride solution, wherein the acid solution is hydrochloric acid or a hydrochloric acid azeotropic solution. In the present invention, the concentration of the acid solution is preferably 16-24 wt%, more preferably 18-20 wt%, and even more preferably 20 wt%; the hydrochloric acid azeotropic solution is obtained by evaporation and distillation of the primary mother liquor and / or the secondary mother liquor.

[0056] In this invention, the ratio of the mass of the primary aluminum chloride crystals to the volume of the acid solution is preferably 1g:(1.8-2.0)mL, more preferably 1g:(1.85-1.95)mL, and even more preferably 1g:1.9mL.

[0057] In this invention, the temperature of the first mixing is preferably 22-30°C, more preferably 22-28°C, and even more preferably 24-26°C.

[0058] This invention involves evaporating the mother liquor to obtain hydrogen chloride gas and a primary distillate. In this invention, the evaporation temperature is preferably 105–110°C, more preferably 108–110°C, and the holding time is preferably 2–5 hours, more preferably 4 hours. The hydrogen chloride gas obtained from the primary mother liquor evaporation is used in a subsequent precipitation reaction.

[0059] After obtaining hydrogen chloride gas and primary distillate, the present invention introduces the obtained hydrogen chloride gas into the first aluminum chloride solution to carry out a precipitation reaction, followed by solid-liquid separation to obtain secondary aluminum chloride crystals and secondary mother liquor. In the present invention, the temperature of the precipitation reaction (denoted as precipitation reaction A) is preferably 50-70°C, more preferably 55-65°C, and preferably until H+ is present in the reaction solution. + The concentration is greater than 11 mol / L, more preferably 11 to 12 mol / L, and even more preferably 11.5 mol / L.

[0060] In this invention, the introduction time of the obtained hydrogen chloride gas is preferably 2 to 5 hours, more preferably 4 hours.

[0061] In this invention, when the hydrogen chloride gas is insufficient, it is preferable to prepare it using an acidification solution (i.e., acidification); the acidification solution is preferably sulfuric acid and hydrochloric acid; the concentration of the sulfuric acid is preferably 85% or more, more preferably 85-90%; the concentration of the hydrochloric acid is preferably 30-36%, more preferably 32-34%; the volume ratio of hydrochloric acid to sulfuric acid is preferably 2:1; the preferred method for preparing the hydrogen chloride gas is: adding sulfuric acid dropwise to hydrochloric acid and heating to obtain hydrogen chloride gas and dilute sulfuric acid, using the hydrogen chloride gas for a precipitation reaction, and concentrating the dilute sulfuric acid to obtain sulfuric acid for use in the preparation of the acidification solution or in step (1) acid leaching; the heating temperature is preferably 120°C. This invention provides hydrogen chloride gas and dilute sulfuric acid by adding sulfuric acid dropwise to hydrochloric acid to expel the hydrogen chloride gas from the hydrochloric acid. The dilute sulfuric acid is concentrated into sulfuric acid, which can be used for the recycling of sulfuric acid in the acidification solution used in this step or in step (1) acid leaching.

[0062] In this invention, the solid-liquid separation is preferably filtration; the pore size of the filter is preferably 3-15 μm, more preferably 4.5-9 μm.

[0063] In this invention, the primary evaporator is evaporated to obtain a hydrochloric acid azeotropic solution and dilute sulfuric acid. The hydrochloric acid azeotropic solution is used as an acid solution, and the dilute sulfuric acid is concentrated to obtain sulfuric acid for use in step (1). In this invention, the evaporation temperature is preferably 120-130°C, more preferably 125-130°C, and the holding time is preferably 2-5 hours, more preferably 4 hours.

[0064] In this invention, the concentration is preferably evaporation concentration; the evaporation temperature of the evaporation concentration is preferably 230-260°C, more preferably 240-250°C.

[0065] In this invention, after purifying the secondary aluminum chloride crystals by repeating step (6) more than three times, the obtained aluminum chloride crystals are pyrolyzed to obtain basic aluminum chloride. In this invention, the repetition of step (6) more than three times is preferred to be four to six times, and more preferably five times. During the repetition of step (6), if the hydrogen chloride gas is insufficient, it is preferable to use an acidification solution (i.e., acidification); the acidification solution is preferably the same as the acidification solution in precipitation reaction A, and will not be described again here.

[0066] In this invention, repeating step (6) three times preferably includes: sequentially subjecting the first aluminum chloride solution to precipitation reaction A, precipitation reaction B, and precipitation reaction C; separating the products obtained from precipitation reaction A, precipitation reaction B, or precipitation reaction C into solid and liquid components to obtain secondary mother liquor, tertiary mother liquor, or quaternary mother liquor; evaporating the secondary or tertiary mother liquor to obtain hydrochloric acid azeotropic solution A or tertiary distillate; recycling hydrochloric acid azeotropic solution A as the acid solution in step (6), and recycling the tertiary distillate as the hydrochloric acid azeotropic solution or the dissolving agent in step (3); evaporating the quaternary mother liquor to obtain hydrogen chloride gas, which is used for the precipitation reaction in step (4) or step (6).

[0067] In this invention, repeating step (6) four times preferably includes: sequentially subjecting the first aluminum chloride solution to precipitation reaction A, precipitation reaction B, precipitation reaction C, and precipitation reaction D; separating the products obtained from precipitation reaction A, precipitation reaction B, precipitation reaction C, or precipitation reaction D into solid and liquid components to obtain secondary mother liquor, tertiary mother liquor, quaternary mother liquor, or quinary mother liquor; evaporating the secondary, tertiary, or quaternary mother liquor to obtain hydrochloric acid azeotropic solution A, hydrochloric acid azeotropic solution B, or tertiary evaporator; recycling hydrochloric acid azeotropic solution A, hydrochloric acid azeotropic solution B, and quinary mother liquor as acid in step (6), and recycling the tertiary evaporator as hydrochloric acid azeotropic solution or dissolving agent in step (3).

[0068] In this invention, repeating step (6) 5 times preferably includes: sequentially subjecting the first aluminum chloride solution to precipitation reaction A, precipitation reaction B, precipitation reaction C, precipitation reaction D, and precipitation reaction E; separating the products obtained from precipitation reaction A, precipitation reaction B, precipitation reaction C, precipitation reaction D, or precipitation reaction E into solid and liquid phases to obtain secondary mother liquor, tertiary mother liquor, quaternary mother liquor, quinary mother liquor, or sixth mother liquor; and separating the secondary mother liquor, tertiary mother liquor, quaternary mother liquor, or quinary mother liquor... The mother liquor is evaporated to obtain hydrochloric acid azeotropic solution A, hydrochloric acid azeotropic solution B, and tertiary or quaternary distillate, respectively. Hydrochloric acid azeotropic solution A, hydrochloric acid azeotropic solution B and quaternary distillate are recycled as acid in step (6) (quaternary distillate can also be recycled as a dissolving agent in step (3)). The tertiary distillate is recycled as hydrochloric acid azeotropic solution or dissolving agent in step (3). The mother liquor is evaporated to obtain hydrogen chloride gas, which is used for the precipitation reaction in step (4) or step (6).

[0069] In this invention, the pyrolysis temperature is preferably 400–650°C, more preferably 500–600°C, and the holding time is preferably 60–120 min, more preferably 80–100 min. This invention yields basic aluminum chloride with a purity of 4N through pyrolysis.

[0070] In this invention, the pyrolysis yields basic aluminum chloride and hydrogen chloride gas simultaneously; the hydrogen chloride gas is preferably absorbed by water and then used as an acid solution in step (6) for recycling.

[0071] After obtaining basic aluminum chloride, the present invention mixes the basic aluminum chloride and seed crystals, grinds them, and then calcines them to obtain high-purity α-Al₂O₃ with a purity of 99.98% or higher. In the present invention, the mass ratio of basic aluminum chloride to seed crystals is preferably 100:4 to 7, more preferably 100:4.5 to 6.5, and even more preferably 100:5 to 6.

[0072] In this invention, the grinding is preferably ball milling; the ball milling ratio is preferably 4:1, and the ball milling time is preferably 2 hours.

[0073] In this invention, the calcination temperature is preferably 1200–1250℃, more preferably 1210–1240℃, and even more preferably 1220–1230℃; the holding time is preferably 120–240 min, more preferably 150–210 min, and even more preferably 180–200 min. The process flow for preparing high-purity α-Al₂O₃ using fly ash in this invention is as follows: Figure 1 As shown.

[0074] 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.

[0075] Example 1

[0076] (1) Ball milling: The fly ash is ball milled to obtain activated fly ash with a particle size of less than 200 mesh;

[0077] (2) Acid leaching: Take 120g of activated fly ash from step (1), mix it with 600mL of sulfuric acid (mass fraction of 85%), and leach at 240℃ for 3h to obtain a leaching slurry;

[0078] (3) Filtration: The leaching slurry from step (2) is filtered and separated to obtain circulating sulfuric acid and leaching material;

[0079] (4) Dissolution: Add 480 mL of hydrochloric acid (20% by mass) to the leachate from step (3) to dissolve the leachate, react at 80°C for 30 min, filter while hot to obtain solution V1 and silica slag;

[0080] (5) Aluminum chloride crystallization: At a temperature of 70°C, 500 mL of hydrochloric acid (mass fraction 32%) is passed into the solution obtained in step (4) and heated to 108°C to obtain hydrogen chloride gas. The H2O is then measured. + After reaching a certain concentration, acidification is performed, and the final solution contains H... +The concentration reached 13 mol / L; after filtration and washing, 180.4 g of primary aluminum chloride crystals and primary mother liquor were obtained.

[0081] (6) Aluminum chloride purification: Repeat the crystallization process 4 times:

[0082] ① At room temperature, the primary aluminum chloride crystals from step (5) are washed with 32% hydrochloric acid and then dissolved in 360 mL of hydrochloric acid azeotropic solution (the hydrochloric acid azeotropic solution remaining from the previous implementation of the method of this invention) to obtain the first aluminum chloride solution. The primary mother liquor from step (5) is evaporated to 108°C to obtain hydrogen chloride gas and primary distillate. The obtained hydrogen chloride gas is passed into the first aluminum chloride solution to precipitate. After acidification, H + The concentration reached 11 mol / L, and after filtration, 102.7 g of secondary aluminum chloride crystals and secondary mother liquor were obtained; the primary distillate was further evaporated to obtain hydrochloric acid azeotropic solution, dilute sulfuric acid and aluminum chloride containing impurities, and the obtained dilute sulfuric acid was further concentrated for acid leaching in step (2);

[0083] ② At room temperature, dissolve the secondary aluminum chloride crystals from step ① in 205 mL of hydrochloric acid azeotropic solution to obtain a second aluminum chloride solution. Evaporate the secondary mother liquor from step ① to 108℃ to obtain hydrogen chloride gas and a secondary distillate. Pass the obtained hydrogen chloride gas into the second aluminum chloride solution to precipitate it. After acidification, H... + The concentration reached 11.2 mol / L, and after filtration, 91.6 g of aluminum chloride crystals and the mother liquor were obtained. The secondary distillate was further evaporated to obtain hydrochloric acid azeotrope and aluminum chloride containing impurities.

[0084] ③ At room temperature, dissolve the aluminum chloride crystals from step ② in 185 mL of hydrochloric acid azeotropic solution to obtain aluminum chloride solution. Evaporate the mother liquor from step ② to 108 °C to obtain hydrogen chloride gas and the evaporated liquid. Pass the obtained hydrogen chloride gas into the aluminum chloride solution to precipitate it. After acidification, H... + The concentration reached 11.3 mol / L, and after filtration, 89.4 g of tetrahydrate crystals and the mother liquor from the fourth distillation were obtained; the three distillates were used as hydrochloric acid for dissolution in step (4);

[0085] ④ At room temperature, dissolve the tetrahydrate crystals from step ③ in 180 mL of hydrochloric acid azeotropic solution to obtain the fourth aluminum chloride solution. Evaporate the fourth mother liquor from step ③ to 108℃ to obtain hydrogen chloride gas and the fourth distillate. Pass the obtained hydrogen chloride gas into the fourth aluminum chloride solution to precipitate it. After acidification, H... + The concentration reached 11.8 mol / L. After filtration, 89 g of five-stage aluminum chloride crystals and five-stage 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.

[0086] (7) Pyrolysis: The five-times aluminum chloride crystals from step ④ were pyrolyzed at 600℃ for 120 min to obtain 21.2 g of basic aluminum chloride and hydrogen chloride gas. The obtained hydrogen chloride gas was absorbed by water and used as a hydrochloric acid azeotropic solution.

[0087] (8) Calcination: After grinding the basic aluminum chloride from step (7) with 5% seed crystals, calcine it at 1250℃ for 240 min to obtain 16.5 g of high-purity α-Al2O3 with a purity of 99.98%.

[0088] Example 2

[0089] (1) Ball milling: The fly ash is ball milled to obtain activated fly ash with a particle size of less than 200 mesh;

[0090] (2) Acid leaching: Take 120g of activated fly ash from step (1), mix it with 600mL of sulfuric acid (mass fraction of 85%), and leach at 240℃ for 4h to obtain a leaching slurry;

[0091] (3) Filtration: The leaching slurry from step (2) is filtered and separated to obtain circulating sulfuric acid and leaching material;

[0092] (4) Dissolution: Add 450 mL of hydrochloric acid (20% by mass) to the leachate from step (3) to dissolve the leachate, react at 90°C for 30 min, filter while hot to obtain the solution and silicon slag;

[0093] (5) Aluminum chloride crystallization: At a temperature of 70°C, hydrogen chloride gas obtained from the evaporation of the mother liquor (the mother liquor obtained in the previous implementation of the method of this invention) obtained five times is passed into the solution from step (4), and the H is measured. + After concentration, acidification is performed, and the final solution contains H... + The concentration reached 13 mol / L; after filtration and washing, 127.8 g of primary aluminum chloride crystals and primary mother liquor were obtained.

[0094] (6) Aluminum chloride purification: Repeat the crystallization process 3 times:

[0095] ① At room temperature, the primary aluminum chloride crystals from step (5) are dissolved in 255 mL of hydrochloric acid azeotropic solution (the hydrochloric acid azeotropic solution remaining from the previous implementation of the method of this invention) to obtain the first aluminum chloride solution. The primary mother liquor from step (5) is evaporated to 108°C to obtain hydrogen chloride gas and primary distillate. The obtained hydrogen chloride gas is passed into the first aluminum chloride solution to precipitate. After acidification, H + The concentration reached 11.4 mol / L. After filtration, 127 g of secondary aluminum chloride crystals and secondary mother liquor were obtained. The primary distillate was further evaporated to obtain hydrochloric acid azeotropic solution, dilute sulfuric acid and aluminum chloride containing impurities. The obtained dilute sulfuric acid was further concentrated for acid leaching in step (2).

[0096] ② At room temperature, dissolve the secondary aluminum chloride crystals from step ① in 255 mL of hydrochloric acid azeotropic solution (the hydrochloric acid azeotropic solution obtained in step ①) to obtain a second aluminum chloride solution. Evaporate the secondary mother liquor from step ① to 108℃ to obtain hydrogen chloride gas and a secondary distillate. Pass the obtained hydrogen chloride gas into the second aluminum chloride solution to precipitate it. After acidification, H... + The concentration reached 11.2 mol / L, and after filtration, 121.3 g of aluminum chloride crystals and the mother liquor from the third distillation were obtained. The secondary distillate was further evaporated to obtain hydrochloric acid azeotrope and aluminum chloride containing impurities.

[0097] ③ At room temperature, dissolve the aluminum chloride crystals from step ② in 242 mL of hydrochloric acid azeotropic solution to obtain aluminum chloride solution ③. Evaporate the mother liquor from step ② to 108℃ to obtain hydrogen chloride gas and the tertiary distillate. Pass the obtained hydrogen chloride gas into the aluminum chloride solution ③ to precipitate it. After acidification, H + The concentration reached 11.3 mol / L, and after filtration, 119.7 g of tetrahydrate crystals and the mother liquor from the tetrahydrate were obtained; the three distillates were used as hydrochloric acid for dissolution in step (4);

[0098] (7) Pyrolysis: The tetrahydrate crystals obtained in step ③ are pyrolyzed at 650℃ for 60 min to obtain 23.8 g of basic aluminum chloride and hydrogen chloride gas. The obtained hydrogen chloride gas is absorbed by water and used as a hydrochloric acid azeotropic solution.

[0099] (8) Calcination: After grinding the basic aluminum chloride from step (7) with 5% seed crystals, calcine it at 1250℃ for 240 min to obtain 18.6 g of high-purity α-Al2O3 with a purity of 99.98%.

[0100] Example 3

[0101] (1) Ball milling: The fly ash is ball milled to obtain activated fly ash with a particle size of less than 200 mesh;

[0102] (2) Acid leaching: Take 150g of activated fly ash from step (1), mix it with 600mL of sulfuric acid (mass fraction of 85%), and leach at 250℃ for 4h to obtain a leaching slurry;

[0103] (3) Filtration: The leaching slurry from step (2) is filtered and separated to obtain circulating sulfuric acid and leaching material;

[0104] (4) Dissolution: Add 600 mL of hydrochloric acid (20% by mass) to the leachate from step (3) to dissolve the leachate, react at 80°C for 30 min, filter while hot to obtain the solution and silicon slag;

[0105] (5) Aluminum chloride crystallization: At a temperature of 70°C, hydrogen chloride gas obtained from the evaporation of the mother liquor (the remaining four mother liquors from the previous implementation of the method of this invention) obtained from the solution in step (4) is passed through the solution, and the H is measured.+ After reaching a certain concentration, acidification is performed, and the final solution contains H... + The concentration reached 13 mol / L; after filtration and washing, 161.3 g of primary aluminum chloride crystals and primary mother liquor were obtained.

[0106] (6) Aluminum chloride purification: Repeat the crystallization process 4 times:

[0107] ① At room temperature, the primary aluminum chloride crystals from step (5) are dissolved in 325 mL of hydrochloric acid azeotropic solution (the hydrochloric acid azeotropic solution remaining from the previous implementation of the method of this invention) to obtain the first aluminum chloride solution. The primary mother liquor is evaporated to 108°C to obtain hydrogen chloride gas and primary distillate. The obtained hydrogen chloride gas is passed into the first aluminum chloride solution to precipitate. After acidification, H + The concentration reached 11.2 mol / L. After filtration, 124.7 g of secondary aluminum chloride crystals and secondary mother liquor were obtained. The primary distillate was further evaporated to obtain hydrochloric acid azeotropic solution, dilute sulfuric acid and aluminum chloride containing impurities. The obtained dilute sulfuric acid was further concentrated for acid leaching in step (2).

[0108] ② At room temperature, dissolve the secondary aluminum chloride crystals from step ① in 250 mL of hydrochloric acid azeotropic solution to obtain a second aluminum chloride solution. Evaporate the secondary mother liquor from step ① to 108℃ to obtain hydrogen chloride gas and a secondary distillate. Pass the obtained hydrogen chloride gas into the second aluminum chloride solution to precipitate it. After acidification, H... + The concentration reached 11.2 mol / L, and after filtration, 111.3 g of aluminum chloride crystals and the mother liquor were obtained. The secondary distillate was further evaporated to obtain hydrochloric acid azeotrope and aluminum chloride containing impurities.

[0109] ③ At room temperature, dissolve the aluminum chloride crystals from step ② in 223 mL of hydrochloric acid azeotropic solution to obtain aluminum chloride solution ③. Evaporate the mother liquor from step ② to 108℃ to obtain hydrogen chloride gas and the tertiary distillate. Pass the obtained hydrogen chloride gas into the aluminum chloride solution ③ to precipitate it. After acidification, H + The concentration reached 11.3 mol / L, and after filtration, 108.7 g of tetrahydrate crystals and tetrahydrate mother liquor were obtained; the three distillates were used as hydrochloric acid for dissolution in step (4);

[0110] ④ At room temperature, dissolve the tetrahydrate crystals from step ③ in 217 mL of hydrochloric acid azeotropic solution to obtain the fourth aluminum chloride solution. Evaporate the fourth mother liquor from step ③ to 108℃ to obtain hydrogen chloride gas and the fourth distillate. Pass the obtained hydrogen chloride gas into the fourth aluminum chloride solution to precipitate it. After acidification, H... + The concentration reached 11.5 mol / L. After filtration, 108 g of five-stage aluminum chloride crystals and five-stage mother liquor were obtained. The fourth distillate was used as a hydrochloric acid azeotropic solution. The fifth mother liquor was evaporated and then used as a hydrochloric acid azeotropic solution.

[0111] (7) Pyrolysis: The five-times aluminum chloride crystals from step ④ were pyrolyzed at 600℃ for 120 min to obtain 22.6 g of basic aluminum chloride and hydrogen chloride gas. The obtained hydrogen chloride gas was absorbed by water and used as a hydrochloric acid azeotropic solution.

[0112] (8) Calcination: After grinding the basic aluminum chloride from step (7) with 5% seed crystals, calcine it at 1250℃ for 240 min to obtain 16.8 g of high-purity α-Al2O3 with a purity of 99.98%.

[0113] The high-purity α-Al2O3 prepared in Example 1 was subjected to ICP-OES testing, and the testing method was in accordance with GB / T37248-2018. The results are shown in Table 1.

[0114] Table 1. ICP-OES test results of Example 1

[0115]

[0116]

[0117] As can be seen from Table 1, the high-purity α-Al2O3 prepared by this invention has low impurity content and high purity.

[0118] The high-purity α-Al₂O₃ prepared in Example 1 was analyzed by XRD, and the results are as follows: Figure 2 As shown. According to Figure 2 It can be seen that the Al2O3 prepared by this invention is mainly composed of the α phase.

[0119] The high-purity α-Al₂O₃ prepared in Example 1 was analyzed by TEM, and the results are as follows: Figure 3 As shown. According to Figure 3 It can be seen that the microscopic morphology of Al2O3 products is mainly worm-shaped, with some ellipsoidal shapes, and the surface is smooth.

[0120] As can be seen from the above embodiments, the method provided by the present invention can extract high-purity α-Al2O3 from fly ash, which is low in cost, simple to operate, realizes the high-value resource utilization of fly ash, and has broad market prospects.

[0121] 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 from supercritical boiler fly ash by aluminum sulfate salting-out, characterized in that, The steps are: (1) mixing the ball-milled fly ash and sulfuric acid for acid leaching to obtain a leaching slurry; (2) solid-liquid separation of the leaching slurry to obtain recycled sulfuric acid and leaching material, wherein the recycled sulfuric acid is used in step (1); (3) mixing the leaching material with a leaching agent and then hot solid-liquid separation to obtain a dissolution liquid and a silicon residue, wherein the leaching agent is dilute hydrochloric acid, and the mass concentration of the dilute hydrochloric acid is 15-24%; (4) solid-liquid separation after passing hydrogen chloride gas into the dissolution liquid for precipitation reaction to obtain primary aluminum chloride crystals and a primary mother liquor; (5) hydrochloric acid washing of the primary aluminum chloride crystals to obtain acid-washed primary aluminum chloride crystals; (6) first mixing of the acid-washed primary aluminum chloride crystals with an acid liquid to obtain a first aluminum chloride dissolution liquid, wherein the acid liquid is hydrochloric acid or a hydrochloric acid azeotrope, the temperature of the first mixing is 20-30°C; evaporation of the primary mother liquor to obtain hydrogen chloride gas and a primary distillate; solid-liquid separation after passing the obtained hydrogen chloride gas into the first aluminum chloride dissolution liquid for precipitation reaction to obtain secondary aluminum chloride crystals and a secondary mother liquor; evaporation of the hydrochloric acid azeotrope and dilute sulfuric acid obtained from the primary distillate to obtain a hydrochloric acid azeotrope which is used as the acid liquid and concentrated dilute sulfuric acid which is used in step (1); (7) purification of the secondary aluminum chloride crystals by repeating step (6) for more than 3 times, and then pyrolysis of the obtained aluminum chloride crystals to obtain basic aluminum chloride; the temperature of the pyrolysis is 400-650°C, and the holding time is 60-120 min; (8) mixing and grinding of the basic aluminum chloride and seed crystals, and then calcination to obtain high-purity α-Al2O3 with a purity of more than 99.98%; the mass ratio of the basic aluminum chloride to the seed crystals is 100:4-7.

2. The method of claim 1, wherein, In step (1), the rotation speed of the ball milling is 200-300 rpm, the ball-to-material ratio is 3-5:1, and the ball milling time is 1-3 h.

3. The method according to claim 1 or 2, characterized in that, In step (1), the temperature of the acid leaching is 230-250°C, and the leaching time is 180-300 min.

4. The method of claim 1, wherein, In step (2), the temperature of the solid-liquid separation is 120-160°C.

5. The method according to claim 1 or 2, characterized in that, In step (3), the temperature of the heating and mixing is 70-90°C, and the holding time is 0.5-1.5 h.

6. The method of claim 1, wherein, In step (4), the temperature of the precipitation reaction is greater than or equal to 60°C until the concentration of H + greater than 11 mol / L.

7. The method according to claim 1 or 6, characterized in that, In step (6), the temperature of the precipitation reaction is 50-70°C until the concentration of H + greater than 11 mol / L.

8. The method of claim 1 or 6, wherein, In step (6), the hydrogen chloride gas is prepared by using an acidifying liquid when the hydrogen chloride gas is insufficient; the acidifying liquid is sulfuric acid and hydrochloric acid; the concentration of the sulfuric acid is more than 85%; and the concentration of the hydrochloric acid is 30-36%.

9. The method of claim 1, wherein, In step (8), the temperature of the calcination is 1200-1250°C, and the holding time is 120-240 min.

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