Aluminum oxide purification process and method thereof

Abstract

The invention relates to the technical field of aluminum oxide production, in particular to an aluminum oxide purification process and a method thereof. The method comprises the following steps: S1, raw material pretreatment: selecting industrial-grade aluminum sulfate as a raw material, and pretreating the industrial-grade aluminum sulfate to obtain a solution base material; s2, acid leaching activation: carrying out acid leaching activation treatment on the solution base material to obtain a first coarse material; s3, purification treatment: carrying out purification treatment on the first coarse material to obtain a second coarse material; s4, low-temperature crystallization: performing low-temperature crystallization treatment on the second coarse material to obtain powder; s5, calcining and converting, namely putting the powder into an atmosphere furnace, heating to 600-650 DEG C at the speed of 5 DEG C / min, preserving heat for 1 hour, heating to 1100-1200 DEG C at the speed of 3 DEG C / min, and preserving heat for 2-3 hours to obtain aluminum oxide; according to the method, low-temperature phase change induction is realized through an additive system, and the procedures of multiple times of acid leaching, filtering, crushing and the like are removed, so that the problems of high energy consumption and low productivity of high-purity aluminum oxide are solved.

Description

Technical Field

[0001] This invention relates to the field of alumina production technology, specifically to an alumina purification process and method. Background Technology

[0002] Alumina purification is an industrial technology that uses physical or chemical methods to remove impurities such as silicon, iron, and titanium from aluminum raw materials (such as bauxite, metallic aluminum, and aluminum salts) to produce high-purity alumina. The core objective is to improve the purity of alumina from industrial grade to electronic grade to meet the needs of different fields such as electrolytic aluminum production, electronic ceramics, and sapphire substrates.

[0003] Existing alumina purification processes rely excessively on high-temperature calcination to drive the transformation of alumina from the γ and θ phases to the target α phase. Due to the lack of precise guidance for the phase transformation process, the nucleation energy barrier of the α phase remains at a high level. This requires not only a continuous input of large amounts of heat energy to maintain the high-temperature environment but also extended calcination time to ensure sufficient phase transformation. Furthermore, the entire process involves multiple acid leaching, filtration, and subsequent crushing processes, resulting in high energy consumption and low production capacity for high-purity alumina. Therefore, this invention provides an alumina purification process and method. Summary of the Invention

[0004] The purpose of this invention is to provide an alumina purification process and method to solve the problems raised in the background art.

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

[0006] An alumina purification process and method, comprising the following steps:

[0007] S1: Raw material pretreatment. Industrial grade aluminum sulfate is selected as the raw material. The industrial grade aluminum sulfate is pretreated to obtain the solution base material.

[0008] S2: Acid leaching activation, the solution base material is subjected to acid leaching activation treatment to obtain the first coarse material;

[0009] S3: Purification treatment, the first coarse material is purified to obtain the second coarse material;

[0010] S4: Low-temperature crystallization, the second coarse material is subjected to low-temperature crystallization treatment to obtain powder;

[0011] S5: Calcination conversion: Place the powder in an atmosphere furnace, heat it to 600-650℃ at 5℃ / min and hold for 1 hour, then heat it to 1100-1200℃ at 3℃ / min and hold for 2-3 hours to obtain alumina;

[0012] The industrial-grade aluminum sulfate pretreatment method is as follows: industrial-grade aluminum sulfate is added to deionized water and heated to 75-85℃ and stirred to dissolve. The resulting product is filtered through a 5μm microporous membrane, and the filtrate is taken to obtain a solution base. The mass ratio of industrial-grade aluminum sulfate to deionized water is 1:(4.5-5.5).

[0013] Preferably, the acid leaching activation method is as follows: add the solution base material to an enamel-lined reactor, then add 15-25% (by mass) of acid leaching solution to the solution base material, heat to 55-65°C, and treat with a stirring rate of 180-220 rpm for 2-3 hours. Transfer the obtained product to a centrifuge, set to 4800-5200 rpm for 10-15 minutes, and take the solids to obtain the first coarse material.

[0014] Preferably, the raw materials of the acid leaching solution include 18-22 wt% hydrochloric acid solution, 14-16 wt% sulfuric acid solution, and 4-6 wt% citric acid solution.

[0015] Preferably, the method for preparing the acid leaching solution is as follows: hydrochloric acid solution, sulfuric acid solution, and citric acid solution are added to a stirred tank and treated at 30-50 rpm for 15-20 min to obtain an acid solution. Then, 0.08-0.1% sodium dodecylbenzenesulfonate by mass of the acid solution is added, the stirring speed is adjusted to 250-300 rpm, the temperature is raised to 55-65℃, and the mixture is stirred for 30-50 min. The resulting product is allowed to stand and mature at 35-45℃ under sealed conditions for 20-30 h to obtain the acid leaching solution. The mass ratio of hydrochloric acid solution, sulfuric acid solution, and citric acid solution is (5-6):(2-3):1.

[0016] Preferably, the purification process is as follows: First coarse material and deionized water are added to a disperser at a mass ratio of 1:(3-4), and the mixture is processed at a speed of 1800-2200 rpm for 10-15 minutes to obtain a diluted solution. The diluted solution is then transferred to an ultrasonic reactor, where a treatment solution is added. The power is set to 750-850 W, and the frequency to 38-42 kHz. After processing for 40-50 minutes, the mixture is transferred to a vacuum filter and filtered at -0.08 MPa to obtain a filter cake. The filter cake is washed with deionized water until the conductivity of the filtrate is ≤50 μS / cm to obtain the second coarse material. The mass of the treatment solution is 8-10% of the mass of the diluted solution.

[0017] Preferably, the raw materials of the treatment solution include 8-12 wt% ammonia buffer solution with a pH of 8-9, disodium ethylenediaminetetraacetate, chitosan, and sodium polyacrylate.

[0018] Preferably, the preparation method of the treatment solution is as follows: add ammonia buffer solution to a water bath, then add disodium ethylenediaminetetraacetate, heat to 55-65℃ and stir until dissolved to obtain a base solution. Transfer the base solution to an ultrasonic disperser, then add chitosan and sodium polyacrylate, set the power to 800W and treat for 20-30 minutes. The obtained product is then subjected to vacuum degassing treatment at -0.08MPa for 30-40 minutes to obtain the treatment solution. The mass ratio of ammonia buffer solution, disodium ethylenediaminetetraacetate, chitosan and sodium polyacrylate is (45-50):(4-6):2:1.

[0019] Preferably, the low-temperature crystallization method is as follows: the second coarse material is diluted with deionized water to a solid content of 15-20%, then added to a magnetically stirred tank, and the temperature is set to 75-85℃ and the stirring speed to 250-350 rpm for 30-45 min to obtain a preliminary mixture. Additives are added to the preliminary mixture and stirring is continued for 30-40 min. The resulting product is transferred to a crystallization tank and cooled to 25-30℃ at a rate of 1.8-2.2℃ / min, and allowed to stand for 10-20 min. The resulting product is then transferred to a high-speed centrifuge and processed at 2800-3200 rpm for 15-20 min. The solids are washed with anhydrous ethanol until neutral. The resulting product is then sent to an oven and vacuum dried at 60℃ and -0.09 MPa for 2 h to obtain a powder, wherein the mass of the additive is 0.7-0.9% of the mass of the second coarse material.

[0020] Preferably, the additive raw materials include nano-titanium dioxide, 4-6 wt% ammonium fluoride solution, and lanthanum oxide.

[0021] Preferably, the preparation method of the additive is as follows: nano-titanium dioxide and ammonium fluoride solution are added to a reaction vessel, and the reaction is carried out at 55-60°C and 180-250 rpm for 60-90 min. The resulting product is transferred to a planetary ball mill, and lanthanum oxide is added. The mixture is then ball-milled at 150-200 rpm for 4-5 h. The resulting product is then added to a spray dryer, and the inlet temperature is set at 160-180°C, the outlet temperature at 70-85°C, and the feed rate at 10 ml / min to obtain the additive. The mass ratio of nano-titanium dioxide, ammonium fluoride solution, and lanthanum oxide is (80-100):(350-400):0.1. Zirconia beads are selected as the ball milling media, and the ball-to-material ratio is 10:1.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. In this invention, a low-temperature phase transition induction is achieved through an additive system. Ammonium fluoride etches defects on the surface of the second coarse material, exposing active sites. Lanthanum oxide lowers the nucleation barrier of the α phase through lattice doping, reducing the phase transition initiation temperature from low to high. Nano-titanium dioxide serves as a seed template to guide epitaxial growth. The synergistic effect of the three components can significantly shorten the calcination time. Combined with the enhancing effect of sodium dodecylbenzenesulfonate on micropore permeability in the acid leaching solution system and the improvement of purification efficiency in the treatment solution system, the yield per unit time is effectively increased. This eliminates multiple acid leaching, filtration, and crushing processes, thereby solving the problem of high energy consumption and low production capacity of high-purity alumina.

[0024] 2. In this invention, during the purification of alumina from industrial-grade aluminum sulfate, hydrochloric acid in the leaching solution dissolves free metal ions, sulfuric acid destroys the silicon-aluminum coating, and citric acid chelates and locks in fine impurities. When using the treatment solution during the purification process, disodium ethylenediaminetetraacetate chelates transition metals, chitosan adsorbs anions, and sodium polyacrylate inhibits the aggregation of colloidal silica. With the synergistic effect of the leaching solution and the treatment solution, impurities in the raw materials can be deeply removed, thereby significantly improving the purity of alumina and solving the problem of purifying industrial aluminum sulfate to the electronic grade. Attached Figure Description

[0025] Figure 1 The present invention provides a flowchart of an alumina purification process and method. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1:

[0028] An alumina purification process and method, comprising the following steps:

[0029] S1: Raw material pretreatment. Industrial grade aluminum sulfate is selected as the raw material. The industrial grade aluminum sulfate is pretreated to obtain the solution base material.

[0030] S2: Acid leaching activation, the solution base material is subjected to acid leaching activation treatment to obtain the first coarse material;

[0031] S3: Purification treatment, the first coarse material is purified to obtain the second coarse material;

[0032] S4: Low-temperature crystallization, the second coarse material is subjected to low-temperature crystallization treatment to obtain powder;

[0033] S5: Calcination conversion: The powder is placed in an atmosphere furnace and heated to 600℃ at 5℃ / min and held for 1 hour, then heated to 1100℃ at 3℃ / min and held for 2 hours to obtain alumina;

[0034] The pretreatment method for industrial-grade aluminum sulfate is as follows: add industrial-grade aluminum sulfate to deionized water, heat to 75°C and stir to dissolve. Filter the resulting product through a 5μm microporous membrane, take the filtrate, and obtain the solution base material. The mass ratio of industrial-grade aluminum sulfate to deionized water is 1:4.5.

[0035] The acid leaching activation method is as follows: add the solution base material to the enamel reactor, then add 15% of the solution base material's mass of acid leaching solution, heat to 55℃, and treat with a stirring rate of 180 rpm for 2 hours. The resulting product is transferred to a centrifuge, set to 4800 rpm for 10 minutes, and the solids are taken to obtain the first coarse material.

[0036] The raw materials for the acid leaching solution include 18 wt% hydrochloric acid solution, 14 wt% sulfuric acid solution, and 4 wt% citric acid solution.

[0037] The method for preparing the acid leaching solution is as follows: hydrochloric acid solution, sulfuric acid solution, and citric acid solution are added to a stirred tank and treated at 30 rpm for 15 min to obtain an acid solution. Then, 0.08% sodium dodecylbenzenesulfonate by mass of the acid solution is added, the stirring speed is adjusted to 250 rpm, the temperature is raised to 55℃ and stirred for 30 min. The resulting product is allowed to stand and mature at 35℃ under sealed conditions for 20 h to obtain the acid leaching solution. The mass ratio of hydrochloric acid solution, sulfuric acid solution, and citric acid solution is 5:2:1.

[0038] The purification process is as follows: The first coarse material and deionized water are added to a disperser at a mass ratio of 1:3. The disperser is set to 1800 rpm and processed for 10 minutes to obtain a diluted solution. The diluted solution is then transferred to an ultrasonic reactor, where the treatment solution is added. The power is set to 750 W and the frequency to 38 kHz. After processing for 40 minutes, the solution is transferred to a vacuum filter and filtered at -0.08 MPa to obtain a filter cake. The filter cake is washed with deionized water until the conductivity of the filtrate is ≤50 μS / cm to obtain the second coarse material. The mass of the treatment solution is 8% of the mass of the diluted solution.

[0039] The raw materials for the treatment solution include 8 wt% ammonia buffer solution with pH 8, disodium ethylenediaminetetraacetate, chitosan, and sodium polyacrylate.

[0040] The preparation method of the treatment solution is as follows: Ammonia buffer solution is added to a water bath, followed by disodium ethylenediaminetetraacetate. The mixture is heated to 55°C and stirred until dissolved to obtain a base solution. The base solution is then transferred to an ultrasonic disperser, where chitosan and sodium polyacrylate are added. The mixture is treated at 800W for 20 minutes. The resulting product is then subjected to vacuum degassing at -0.08MPa for 30 minutes to obtain the treatment solution. The mass ratio of ammonia buffer solution, disodium ethylenediaminetetraacetate, chitosan, and sodium polyacrylate is 45:4:2:1.

[0041] The low-temperature crystallization method is as follows: the second coarse material is diluted with deionized water to a solid content of 15%, then added to a magnetically stirred tank, the temperature is set at 75℃ and the stirring speed at 250 rpm, and the mixture is treated for 30 min to obtain a preliminary mixture. Additives are added to the preliminary mixture and the mixture is stirred for another 30 min. The resulting product is transferred to a crystallization tank and cooled to 25℃ at a rate of 1.8℃ / min, then allowed to stand for 10 min. The resulting product is then transferred to a high-speed centrifuge and treated at 2800 rpm for 15 min. The solids are washed with anhydrous ethanol until neutral. The resulting product is then sent to an oven and vacuum dried at 60℃ and -0.09 MPa for 2 h to obtain a powder. The mass of the additives is 0.7% of the mass of the second coarse material.

[0042] The additives include nano-titanium dioxide, 4wt% ammonium fluoride solution, and lanthanum oxide.

[0043] The additive is prepared as follows: nano-titanium dioxide and ammonium fluoride solution are added to a reaction vessel, and the reaction is carried out at 55°C and 180 rpm for 60 min. The resulting product is then transferred to a planetary ball mill, and lanthanum oxide is added. The mixture is then ball-milled at 150 rpm for 4 h. The resulting product is then added to a spray dryer, with the inlet temperature set at 160°C, the outlet temperature at 70°C, and the feed rate at 10 ml / min. The additive is thus prepared. The mass ratio of nano-titanium dioxide, ammonium fluoride solution, and lanthanum oxide is 80:350:0.1. Zirconia beads are selected as the grinding media in the planetary ball mill, and the ball-to-material ratio is 10:1.

[0044] Example 2:

[0045] An alumina purification process and method, comprising the following steps:

[0046] S1: Raw material pretreatment. Industrial grade aluminum sulfate is selected as the raw material. The industrial grade aluminum sulfate is pretreated to obtain the solution base material.

[0047] S2: Acid leaching activation, the solution base material is subjected to acid leaching activation treatment to obtain the first coarse material;

[0048] S3: Purification treatment, the first coarse material is purified to obtain the second coarse material;

[0049] S4: Low-temperature crystallization, the second coarse material is subjected to low-temperature crystallization treatment to obtain powder;

[0050] S5: Calcination conversion: The powder is placed in an atmosphere furnace, heated to 620℃ at 5℃ / min and held for 1 hour, and then heated to 1150℃ at 3℃ / min and held for 2.5 hours to obtain alumina;

[0051] The pretreatment method for industrial-grade aluminum sulfate is as follows: add industrial-grade aluminum sulfate to deionized water, heat to 80°C and stir to dissolve. Filter the resulting product through a 5μm microporous membrane, take the filtrate, and obtain the solution base material. The mass ratio of industrial-grade aluminum sulfate to deionized water is 1:5.

[0052] The acid leaching activation method is as follows: add the solution base material to the enamel reactor, then add acid leaching solution of 20% of the mass of the solution base material, heat to 60℃, and treat with a stirring rate of 200 rpm for 2.5 h. The resulting product is transferred to a centrifuge, and treated at 5000 rpm for 12 min. The solids are then collected to obtain the first coarse material.

[0053] The raw materials for the acid leaching solution include 20 wt% hydrochloric acid solution, 15 wt% sulfuric acid solution, and 5 wt% citric acid solution.

[0054] The preparation method of the acid leaching solution is as follows: hydrochloric acid solution, sulfuric acid solution, and citric acid solution are added to a stirred tank and treated at 40 rpm for 18 min to obtain an acid solution. Then, 0.09% sodium dodecylbenzenesulfonate by mass of the acid solution is added, the stirring speed is adjusted to 280 rpm, the temperature is raised to 60℃ and stirred for 40 min. The resulting product is allowed to stand and mature at 40℃ under sealed conditions for 25 h to obtain the acid leaching solution. The mass ratio of hydrochloric acid solution, sulfuric acid solution, and citric acid solution is 5.5:2.5:1.

[0055] The purification process is as follows: The first coarse material and deionized water are added to a disperser at a mass ratio of 1:3.5. The disperser is set to a speed of 2000 rpm and processed for 12 minutes to obtain a diluted solution. The diluted solution is then transferred to an ultrasonic reactor, where the treatment solution is added. The power is set to 800 W and the frequency to 40 kHz. After processing for 45 minutes, the solution is transferred to a vacuum filter and filtered at -0.08 MPa to obtain a filter cake. The filter cake is washed with deionized water until the conductivity of the filtrate is ≤50 μS / cm to obtain the second coarse material. The mass of the treatment solution is 9% of the mass of the diluted solution.

[0056] The raw materials for the treatment solution include 10wt% ammonia buffer solution with a pH of 8.5, disodium ethylenediaminetetraacetate, chitosan, and sodium polyacrylate.

[0057] The preparation method of the treatment solution is as follows: Ammonia buffer solution is added to a water bath, followed by disodium ethylenediaminetetraacetate. The mixture is heated to 60°C and stirred until dissolved to obtain a base solution. The base solution is then transferred to an ultrasonic disperser, where chitosan and sodium polyacrylate are added. The mixture is treated at a power of 800W for 25 minutes. The resulting product is then subjected to vacuum degassing at -0.08MPa for 35 minutes to obtain the treatment solution. The mass ratio of ammonia buffer solution, disodium ethylenediaminetetraacetate, chitosan, and sodium polyacrylate is 48:5:2:1.

[0058] The low-temperature crystallization method is as follows: the second coarse material is diluted with deionized water to a solid content of 18%, then added to a magnetically stirred tank, the temperature is set to 80℃ and the stirring speed to 300 rpm, and the mixture is treated for 38 min to obtain a preliminary mixture. Additives are added to the preliminary mixture and the mixture is stirred for another 35 min. The resulting product is transferred to a crystallization tank and cooled to 28℃ at a rate of 2℃ / min, then allowed to stand for 15 min. The resulting product is then transferred to a high-speed centrifuge and treated at 3000 rpm for 18 min. The solids are washed with anhydrous ethanol until neutral. The resulting product is then sent to an oven and vacuum dried at 60℃ and -0.09 MPa for 2 h to obtain a powder. The mass of the additives is 0.8% of the mass of the second coarse material.

[0059] The additives include nano-titanium dioxide, 5wt% ammonium fluoride solution, and lanthanum oxide.

[0060] The additive is prepared as follows: nano-titanium dioxide and ammonium fluoride solution are added to a reaction vessel, and the reaction is carried out at 58°C and 210 rpm for 75 min. The resulting product is then transferred to a planetary ball mill, and lanthanum oxide is added. The mixture is then ball-milled at 180 rpm for 4.5 h. The resulting product is then added to a spray dryer, with an inlet temperature of 170°C, an outlet temperature of 78°C, and a feed rate of 10 ml / min. The additive is thus prepared. The mass ratio of nano-titanium dioxide, ammonium fluoride solution, and lanthanum oxide is 90:380:0.1. Zirconia beads are selected as the grinding media in the planetary ball mill, and the ball-to-material ratio is 10:1.

[0061] Example 3:

[0062] An alumina purification process and method, comprising the following steps:

[0063] S1: Raw material pretreatment. Industrial grade aluminum sulfate is selected as the raw material. The industrial grade aluminum sulfate is pretreated to obtain the solution base material.

[0064] S2: Acid leaching activation, the solution base material is subjected to acid leaching activation treatment to obtain the first coarse material;

[0065] S3: Purification treatment, the first coarse material is purified to obtain the second coarse material;

[0066] S4: Low-temperature crystallization, the second coarse material is subjected to low-temperature crystallization treatment to obtain powder;

[0067] S5: Calcination conversion: The powder is placed in an atmosphere furnace and heated to 650℃ at 5℃ / min and held for 1 hour, then heated to 1200℃ at 3℃ / min and held for 3 hours to obtain alumina;

[0068] The pretreatment method for industrial-grade aluminum sulfate is as follows: add industrial-grade aluminum sulfate to deionized water, heat to 85°C and stir to dissolve. Filter the resulting product through a 5μm microporous membrane, take the filtrate, and obtain the solution base material. The mass ratio of industrial-grade aluminum sulfate to deionized water is 1:5.5.

[0069] The acid leaching activation method is as follows: add the solution base material to the enamel reactor, then add 25% of the solution base material's mass of acid leaching solution, heat to 65℃, and treat with a stirring rate of 220 rpm for 3 hours. The resulting product is transferred to a centrifuge, set to 5200 rpm for 15 minutes, and the solids are taken to obtain the first coarse material.

[0070] The raw materials for the acid leaching solution include 22 wt% hydrochloric acid solution, 16 wt% sulfuric acid solution, and 6 wt% citric acid solution.

[0071] The method for preparing the acid leaching solution is as follows: hydrochloric acid solution, sulfuric acid solution, and citric acid solution are added to a stirred tank and treated at 50 rpm for 20 min to obtain an acid solution. Then, 0.1% sodium dodecylbenzenesulfonate by mass of the acid solution is added, the stirring speed is adjusted to 300 rpm, the temperature is raised to 65℃ and stirred for 50 min. The resulting product is allowed to stand and mature at 45℃ under sealed conditions for 30 h to obtain the acid leaching solution. The mass ratio of hydrochloric acid solution, sulfuric acid solution, and citric acid solution is 6:3:1.

[0072] The purification process is as follows: The first coarse material and deionized water are added to a disperser at a mass ratio of 1:4. The disperser is set to a speed of 2200 rpm and processed for 15 minutes to obtain a diluted solution. The diluted solution is then transferred to an ultrasonic reactor, where the treatment solution is added. The power is set to 850 W and the frequency to 42 kHz. After processing for 50 minutes, the solution is transferred to a vacuum filter and filtered at -0.08 MPa to obtain a filter cake. The filter cake is washed with deionized water until the conductivity of the filtrate is ≤50 μS / cm to obtain the second coarse material. The mass of the treatment solution is 10% of the mass of the diluted solution.

[0073] The raw materials for the treatment solution include 12wt% ammonia buffer solution with pH 9, disodium ethylenediaminetetraacetate, chitosan, and sodium polyacrylate.

[0074] The preparation method of the treatment solution is as follows: Ammonia buffer solution is added to a water bath, followed by disodium ethylenediaminetetraacetate. The mixture is heated to 65°C and stirred until dissolved to obtain a base solution. The base solution is then transferred to an ultrasonic disperser, where chitosan and sodium polyacrylate are added. The mixture is treated at a power of 800W for 30 minutes. The resulting product is then subjected to vacuum degassing at -0.08MPa for 40 minutes to obtain the treatment solution. The mass ratio of ammonia buffer solution, disodium ethylenediaminetetraacetate, chitosan, and sodium polyacrylate is 50:6:2:1.

[0075] The low-temperature crystallization method is as follows: the second coarse material is diluted with deionized water to a solid content of 20%, then added to a magnetically stirred tank, the temperature is set to 85℃ and the stirring speed to 350 rpm, and the mixture is treated for 45 min to obtain a preliminary mixture. Additives are added to the preliminary mixture and the mixture is stirred for another 40 min. The resulting product is transferred to a crystallization tank and cooled to 30℃ at a rate of 2.2℃ / min, then allowed to stand for 20 min. The resulting product is then transferred to a high-speed centrifuge and treated at 3200 rpm for 20 min. The solids are washed with anhydrous ethanol until neutral. The resulting product is then sent to an oven and vacuum dried at 60℃ and -0.09 MPa for 2 h to obtain a powder. The mass of the additives is 0.9% of the mass of the second coarse material.

[0076] The additives include nano-titanium dioxide, 6wt% ammonium fluoride solution, and lanthanum oxide.

[0077] The additive is prepared as follows: nano-titanium dioxide and ammonium fluoride solution are added to a reaction vessel, and the reaction is carried out at 60℃ and 250 rpm for 90 min. The resulting product is then transferred to a planetary ball mill, and lanthanum oxide is added. The mixture is then ball-milled at 200 rpm for 5 h. The resulting product is then added to a spray dryer, with the inlet temperature set at 180℃, the outlet temperature at 85℃, and the feed rate at 10 ml / min. The additive is thus prepared. The mass ratio of nano-titanium dioxide, ammonium fluoride solution, and lanthanum oxide is 100:400:0.1. Zirconia beads are selected as the grinding media in the planetary ball mill, and the ball-to-material ratio is 10:1.

[0078] Comparative Example 1: The difference between this comparative example and Example 1 is that the acid leaching solution in this comparative example is not subjected to a static aging treatment.

[0079] Comparative Example 2 differs from Example 1 in that citric acid solution is not added during the preparation of the acid leaching solution in this comparative example.

[0080] Comparative Example 3 differs from Example 1 in that chitosan is not added during the preparation of the treatment solution in this comparative example.

[0081] Comparative Example 4: The difference between this comparative example and Example 1 is that no additives are used in the low-temperature crystallization process in this comparative example.

[0082] Performance testing: The alumina prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to performance testing, and the test data are recorded in the table below:

[0083] Table 1

[0084] Testing items Alumina yield (%) Alumina purity (%) Example 1 88.3 99.92 Example 2 87.4 99.92 Example 3 88.1 99.93 Comparative Example 1 72.5 99.12 Comparative Example 2 73.1 99.23 Comparative Example 3 80.5 99.32 Comparative Example 4 65.9 99.38

[0085] In performance testing, the formula for calculating alumina yield is: alumina obtained from calcination conversion ÷ industrial grade aluminum sulfate × 100%; alumina purity testing is conducted in accordance with the standards GB / T6609.3-2004 + GB / T6609.4-2004.

[0086] It is evident that the alumina yield and purity prepared in Comparative Examples 1-4 are lower than those in Examples 1-3. This indicates that the process achieves low-temperature phase transformation induction through an additive system. Ammonium fluoride etches surface defects in the second coarse material, exposing active sites. Lanthanum oxide lowers the nucleation barrier of the α phase through lattice doping, reducing the phase transformation initiation temperature from low to high. Nano-titanium dioxide acts as a seed template to guide epitaxial growth. The synergistic effect of the three components can significantly shorten the calcination time. Combined with the enhancing effect of sodium dodecylbenzenesulfonate on micropore permeability in the acid leaching solution system and the improvement of purification efficiency in the treatment solution system, the yield per unit time is effectively increased. This process eliminates multiple acid leaching, filtration, and crushing processes, thereby solving the problem of high energy consumption and low production capacity of high-purity alumina.

[0087] In the process of purifying alumina using industrial-grade aluminum sulfate, hydrochloric acid in the leaching solution dissolves free metal ions, sulfuric acid destroys the silicon-aluminum coating, and citric acid chelates and locks in fine impurities. When a treatment solution is used in the purification process, disodium ethylenediaminetetraacetate chelates transition metals, chitosan adsorbs anions, and sodium polyacrylate inhibits the aggregation of colloidal silica. With the synergistic effect of the leaching solution and the treatment solution, impurities in the raw materials can be deeply removed, thereby significantly improving the purity of alumina and solving the problem of purifying industrial aluminum sulfate to the electronic grade.

[0088] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0089] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A process for purifying alumina and a method thereof, characterized by: The method comprises the following steps: S1: raw material pretreatment, industrial grade aluminum sulfate is selected, the industrial grade aluminum sulfate is pretreated to obtain a solution base; S2: acid leaching activation, the solution base is subjected to acid leaching activation treatment to obtain a first crude material; S3: purification treatment, the first crude material is subjected to purification treatment to obtain a second crude material; S4: low-temperature crystallization, the second crude material is subjected to low-temperature crystallization treatment to obtain a powder material; S5: calcination conversion, the powder material is placed in an atmosphere furnace, heated to 600-650 DEG C at a rate of 5 DEG C / min, kept for 1 h, then heated to 1100-1200 DEG C at a rate of 3 DEG C / min, kept for 2-3 h, and aluminum oxide is obtained. The industrial grade aluminum sulfate is added to deionized water, heated to 75-85 DEG C, stirred and dissolved, the obtained product is filtered through a 5-micron microporous filter membrane, the filtrate is taken, and a solution base is obtained, wherein the mass ratio of industrial grade aluminum sulfate to deionized water is 1:(4.5-5.5).

2. The purification process of alumina and method thereof according to claim 1, characterized by, The method of acid leaching activation is as follows: the solution base is added to a porcelain reaction kettle, an acid leaching solution with a mass fraction of 15-25% of the solution base is added, heated to 55-65 DEG C, and treated at a stirring rate of 180-220 rpm for 2-3 h, the obtained product is transferred to a centrifuge, set at 4800-5200 rpm for 10-15 min, and the solid is taken to obtain a first crude material.

3. The purification process of alumina and method thereof according to claim 2, characterized by, The raw material of the acid leaching solution comprises 18-22 wt% hydrochloric acid solution, 14-16 wt% sulfuric acid solution and 4-6 wt% citric acid solution.

4. The purification process of alumina and method thereof according to claim 3, characterized by, The preparation method of the acid leaching solution is as follows: the hydrochloric acid solution, the sulfuric acid solution and the citric acid solution are added to a stirring kettle, set at 30-50 rpm for 15-20 min to obtain an acid solution, 0.08-0.1% sodium dodecyl benzene sulfonate of the acid solution is added, the stirring speed is adjusted to 250-300 rpm, heated to 55-65 DEG C and stirred for 30-50 min, and the obtained product is placed at 35-45 DEG C under airtight conditions for 20-30 h to prepare the acid leaching solution, wherein the mass ratio of the hydrochloric acid solution, the sulfuric acid solution and the citric acid solution is (5-6):(2-3):

1.

5. The purification process of alumina and its method according to claim 1, characterized by the fact that, The method of the purification treatment is as follows: the first crude material and deionized water are added to a disperser at a mass ratio of 1:(3-4), set at a rotation speed of 1800-2200 rpm for 10-15 min to obtain a dilution liquid, the dilution liquid is transferred to an ultrasonic reactor, a treatment liquid is added, set at a power of 750-850 w and a frequency of 38-42 kHz, treated for 40-50 min, and then transferred to a vacuum filter under a vacuum of-0.08 MPa to obtain a filter cake, the filter cake is washed with deionized water until the conductivity of the filtrate is less than or equal to 50 mu S / cm to obtain a second crude material, wherein the mass of the treatment liquid is 8-10% of the mass of the dilution liquid.

6. The purification process of alumina and its method according to claim 5, characterized by the fact that, The raw material of the treatment liquid comprises 8-12 wt% ammonia water buffer with a pH value of 8-9, ethylenediaminetetraacetic acid disodium salt, chitosan and polyacrylic acid sodium.

7. The purification process of alumina and method thereof according to claim 6, characterized by, The preparation method of the treatment liquid is as follows: the ammonia water buffer is added into a water bath, then the disodium ethylenediaminetetraacetate is added, the temperature is increased to 55-65 DEG C, and constant temperature stirring is carried out until the disodium ethylenediaminetetraacetate is dissolved, so that a base liquid is obtained; the base liquid is transferred into an ultrasonic dispersing instrument, then the chitosan and the sodium polyacrylate are added, the power is set to 800 W, and the obtained product is treated for 20-30 min; the obtained product is subjected to vacuum defoaming treatment under the condition of -0.08 MPa for 30-40 min, so that the treatment liquid is prepared; wherein, the mass ratio of the ammonia water buffer, the disodium ethylenediaminetetraacetate, the chitosan and the sodium polyacrylate is (45-50):(4-6):2:

1.

8. The purification process of alumina and its method according to claim 1, characterized by the fact that, The low-temperature crystallization method is as follows: the second crude material is diluted to a solid content of 15-20% by deionized water, then the second crude material is added into a magnetic stirring tank, the temperature is set to 75-85 DEG C, the stirring speed is set to 250-350 rpm, and the obtained product is treated for 30-45 min, so that a preliminary mixture is obtained; the additive is added into the preliminary mixture, and the obtained product is continuously stirred and treated for 30-40 min; the obtained product is transferred into a crystallization tank, the temperature is decreased to 25-30 DEG C at a rate of 1.8-2.2 DEG C / min, and the obtained product is statically placed for 10-20 min; the obtained product is transferred into a high-speed centrifuge, and the obtained product is treated at 2800-3200 rpm for 15-20 min; the solid is washed to be neutral by anhydrous ethanol; the obtained product is sent into an oven, and the obtained product is vacuum dried at 60 DEG C and under the condition of -0.09 MPa for 2 h, so that a powder is obtained; wherein, the mass of the additive is 0.7-0.9% of the mass of the second crude material.

9. The purification process of alumina and method thereof according to claim 8, characterized by, The additive raw material comprises nanometer titanium dioxide, 4-6 wt% ammonium fluoride solution and lanthanum oxide.

10. The purification process of alumina and method thereof according to claim 9, characterized in that, The preparation method of the additive is as follows: the nanometer titanium dioxide and the ammonium fluoride solution are added into a reaction kettle, the temperature is set to 55-60 DEG C, and the stirring speed is set to 180-250 rpm, so that the obtained product is treated for 60-90 min; the obtained product is transferred into a planetary ball mill, the lanthanum oxide is added, the ball milling speed is set to 150-200 rpm, and the obtained product is treated for 4-5 h; the obtained product is added into a spray dryer, the inlet temperature is set to 160-180 DEG C, the outlet temperature is set to 70-85 DEG C, and the feeding rate is set to 10 ml / min, so that the additive is prepared; wherein, the mass ratio of the nanometer titanium dioxide, the ammonium fluoride solution and the lanthanum oxide is (80-100):(350-400):0.1; the ball milling medium of the planetary ball mill is zirconia beads, and the ball-to-material ratio is 10:1.

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