Preparation method for producing aluminum oxide from fly ash, aluminum oxide and application of aluminum oxide

Abstract

The invention provides a preparation method for producing aluminum oxide from fly ash, aluminum oxide and application thereof. The preparation method comprises the following steps: S1, taking fly ash, and sequentially carrying out acid dissolution, crystallization and first roasting to obtain a coarse aluminum oxide solid; s2, carrying out hydrothermal reaction on the coarse aluminum oxide solid, and sequentially carrying out alkali dissolution, carbonation and secondary roasting to obtain aluminum oxide; the aluminum oxide can be continuously subjected to a sanding process and spray drying to obtain superfine aluminum oxide; wherein the pH (Potential of Hydrogen) value of the carbonated material subjected to carbonation treatment is 9.0 to 11.0. The invention effectively solves the problem of low alumina purity or low alpha-alumina content of alumina prepared from fly ash in the prior art.

Description

Technical Field

[0001] The invention relates to the technical field of comprehensive utilization of fly ash resources, and in particular to a method for preparing alumina from fly ash, alumina and applications thereof. Background Art

[0002] The industrial production of alumina from fly ash is mainly based on the traditional alkaline process. However, due to the low aluminum-silicon ratio in fly ash, a large amount of silicon dioxide will be dissolved under alkaline conditions, which makes it difficult to separate silicon and aluminum, and there are problems such as high production costs and large slag volume. With the advancement of modern material technology, the process of extracting alumina from fly ash using the acid method has gradually emerged, thus opening up a new path for extracting alumina from fly ash. At the same time, the diversified development of alumina products has also become a research focus of researchers.

[0003] For example, Chinese patent application number: CN111320461A (publication date 2020-06-23) discloses a method for preparing alumina for plate-shaped corundum. The patent discloses that industrial alumina is kept in a hot field at 400 to 1000°C for 30 to 240 minutes, so that the industrial alumina is in the transition phase γ-Al 2 O 3 The specific surface area in the state is reduced by 10 to 30%. The plate-shaped corundum prepared by the present invention has a large density and can meet the requirements of high-density plate-shaped corundum. However, the alumina is prepared by the industrial alkali method, which is different from the physical and chemical properties of alumina prepared by the acid method, the particle size is relatively large, and the properties of the prepared products are completely different. Chinese patent application number: CN101618961B discloses a lightweight thermal insulation refractory product of alumina and a preparation method thereof. The invention adopts a corundum material and a method prepared by waste active alumina. The raw materials in the present invention are composed of waste active alumina. The raw materials used in the invention are not only conducive to waste utilization and solve the serious pollution of waste active alumina to the environment, but also the products produced have high added value and pollution-free high-quality refractory materials, saving production costs. However, the alumina has the disadvantages of complex preparation process and high cost.

[0004] In summary, the use of fly ash in the prior art to prepare alumina has problems such as low purity of alumina, large particle size, or low content of α-alumina. The present invention provides a method for preparing alumina using fly ash to improve the above problems. Summary of the invention

[0005] The main purpose of the present invention is to provide a method for producing alumina from fly ash, alumina and its application, so as to solve the problem of low alumina purity or low α-alumina content in the prior art of preparing alumina from fly ash.

[0006] According to one aspect of the present invention, a method for producing alumina from fly ash is provided, comprising the following steps: step S1, taking fly ash and subjecting it to acid dissolution, crystallization and first calcination in sequence to obtain a crude alumina solid; step S2, taking the crude alumina solid and subjecting it to hydrothermal reaction, and subjecting it to alkali dissolution, carbonization and second calcination in sequence to obtain alumina; wherein the pH value of the carbonized material after the carbonization treatment is 9.0-11.0; the fly ash has the following components by weight percentage: 30-60wt% SiO 2 , 45-60wt% Al 2 O 3 , 2-8wt% CaO, 2-5wt% MgO, 2-6wt% Fe 2 O 3 , 1-2wt% TiO 2 and 1-5wt% LOI.

[0007] Furthermore, the hydrothermal reaction is carried out in a hydrothermal reactor; preferably, the solid-liquid ratio of the hydrothermal reaction is 1:(6-10), the reaction temperature is 80-180°C, and the reaction time is 1.5-4.0h; preferably, the acid in the acid dissolution treatment is an inorganic acid, and more preferably, the inorganic acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid or hydrofluoric acid; preferably, the concentration of the inorganic acid is 20-28%, the acid dissolution treatment temperature is 120-180°C, and the treatment time is 2-4h; preferably, the weight ratio of fly ash to acid is 1:(4-7).

[0008] Furthermore, after the acid dissolution treatment and before the crystallization treatment, the acid-dissolved material needs to be filtered. Further preferably, the filtration treatment is carried out in a plate and frame filter; preferably, the crystallization treatment is selected from one or more of salting out, evaporative crystallization, recrystallization or cooling crystallization, and salting out crystallization treatment is more preferred; preferably, the salting out agent used in the salting out crystallization is selected from hydrochloric acid; preferably, the flow rate of the salting out agent is 0.2 to 2.0 L / min, and the crystallization treatment temperature is 20 to 30°C.

[0009] Furthermore, after the crystallization treatment and before the first roasting treatment, the crystallized material needs to be separated; preferably, the temperature of the first roasting is 250-350°C, and the first roasting time is 2-3h; preferably, the fly ash needs to be ground before the acid dissolution treatment, and more preferably, the particle size of the ground particles is D50 of 20-40μm.

[0010] Furthermore, after the hydrothermal reaction and before the alkaline dissolution, the hydrothermal reaction product needs to be filtered and washed in sequence; preferably, the filtration treatment is carried out in a plate and frame filter; preferably, the alkali for the alkaline dissolution treatment is an inorganic alkali, and more preferably, the inorganic alkali is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate; preferably, the concentration of the inorganic alkali is 220-350 g / L; preferably, the temperature of the alkaline dissolution treatment is 200-300°C, and the treatment time is 2-4 h.

[0011] Furthermore, during the carbon treatment, CO 2 The flow rate of is 0.05L / min~0.2L / min, and the flow rate of air is 0.1L / min~0.4L / min; preferably, after the carbon treatment and before the second roasting treatment, the carbon fraction material needs to be filtered; preferably, the weight ratio of fly ash to inorganic alkali is 1:(1~2).

[0012] Furthermore, the temperature of the second calcination is 1200-1250°C, and the second calcination time is 2-4h; preferably, grinding treatment is required after the second calcination, and more preferably, the grinding is carried out in a sand mill; preferably, the sand milling time is 1.0-2.0h, and the particle size D50 of the ground particles is 60-90nm, and D90 is 120-150nm; preferably, after the grinding treatment, the ground material needs to be filtered, and preferably further spray dried, and the treatment temperature is 260-300°C.

[0013] According to another aspect of the present invention, there is also provided an aluminum oxide, which is the aluminum oxide obtained by the above preparation method.

[0014] Furthermore, the aluminum oxide is in a granular form. More preferably, the particle size D50 of the aluminum oxide particles is 60 to 90 nm, and D90 is 120 to 150 nm.

[0015] According to another aspect of the present invention, there is also provided application of the above-mentioned aluminum oxide in the fields of ceramics, wear-resistant materials, gemstone materials or laser instrument materials.

[0016] The invention effectively solves the problem of low purity of alumina or low content of α-alumina in the preparation of alumina from fly ash in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0018] Figure 1 A process flow chart of a method for preparing activated alumina in one embodiment of the present invention is shown. DETAILED DESCRIPTION

[0019] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0020] As described in the background of the present invention, the alumina prepared by using fly ash in the prior art has the problems of low purity, large particle size, or low content of α-alumina. The present invention provides a method for producing alumina from fly ash, such as Figure 1 As shown, the preparation method comprises: step S1, taking fly ash and carrying out acid dissolution, crystallization and first roasting in sequence to obtain a crude alumina solid; step S2, taking the crude alumina solid and carrying out hydrothermal reaction, and then carrying out alkali dissolution, carbonization and second roasting in sequence to obtain alumina. The pH value of the carbonized material after carbonization treatment is 9.0-11.0, and the composition of the fly ash is as follows by weight percentage: 30-60wt% SiO 2 , 45-60wt% Al 2 O 3 , 2-8wt% CaO, 2-5wt% MgO, 2-6wt% Fe 2 O 3 , 1-2wt% TiO 2 and 1-5wt% LOI (loss on ignition).

[0021] It should be noted that the fly ash raw material used in the present invention can also be selected from one or more of kaolin, coal gangue, low-grade bauxite and clay ore. Among them, the composition of kaolin is as follows, calculated by weight percentage: 30-50wt% SiO 2 , 30-40wt% Al 2 O 3 , 0.1-1.0wt% CaO, 0.1-1.0wt% MgO, 0.1-2.0wt% Fe 2 O 3 , 0.1~1.0wt% TiO 2 and 10-25wt% LOI, the composition of coal gangue is as follows: 20-40wt% SiO 2 20-40wt% Al 2 O 3 , 0.1-1.0wt% CaO, 0-1wt% MgO, 0-2wt% Fe 2 O 3 , 1-2wt% TiO 2 and 20-40wt% LOI. The composition of low-grade bauxite is as follows: 30-40wt% SiO 220-30wt% Al 2 O 3 , 2-5wt% CaO, 1-3wt% MgO, 5-20wt% Fe 2 O 3 , 1-5wt% TiO 2 and 1-5wt% LOI. The composition of clay ore is as follows: 40-60wt% SiO 2 20-30wt% Al 2 O 3 , 2-8wt% CaO, 2-5wt% MgO, 1-6wt% Fe 2 O 3 , 0.8-2wt% TiO 2 and 1-5wt% LOI.

[0022] The present invention uses fly ash containing the above-mentioned components as raw material to prepare alumina, especially the fly ash has a relatively high silicon-aluminum ratio, thereby overcoming the problem that when alumina is produced from fly ash by the traditional alkaline method in the prior art, a large amount of silicon dioxide components are dissolved in the alkaline solution due to the relatively low silicon-aluminum ratio, resulting in difficulty in separating silicon and aluminum. The specific preparation steps in the present invention are: first, fly ash is taken and acid-dissolved, crystallized and first calcined in sequence, wherein the silicon and aluminum in the fly ash are completely separated by acid-dissolving treatment, avoiding the doping of silicon oxide impurities in alumina, while also reducing the number of processes, improving efficiency, and further improving the purity of alumina and the content of α-alumina. The acid-dissolved material is further crystallized to improve the purity of the target product, and the crystallization step is simple and easy to operate, and the crystallized product is further subjected to a first calcination treatment to obtain a crude alumina solid. Then a series of treatments are carried out to purify the above crude alumina solid, specifically including: taking the above crude alumina solid for hydrothermal reaction, during the reaction process, the solubility of the crude alumina increases as the reaction proceeds, and a more stable phase of crude alumina is formed in the supersaturated crude alumina solution. Then alkali dissolution is carried out in sequence, and impurities (such as iron, calcium, magnesium, manganese, etc.) are removed during the alkali dissolution process to obtain a metaaluminate solution, and then carbon fractionation is carried out, and carbon dioxide gas is introduced into the solution until the pH value of the carbon fraction material is 9.0-11.0, thereby generating aluminum hydroxide precipitate, and further the above alumina is obtained by a second roasting. The alumina prepared by the present invention has high purity, low impurity content and small particle size, wherein the content of α-alumina is high, thereby providing a new idea for upgrading alumina products to make them high-end and refined, as well as the multi-purpose application of alumina products.

[0023] In a preferred embodiment, the hydrothermal reaction is carried out in a hydrothermal reactor, so that the solubility of the reaction materials in the hydrothermal reactor increases as the reaction proceeds, thereby making the crude alumina solution supersaturated, thereby precipitating crude alumina with a more stable phase. Further preferably, the solid-liquid ratio of the hydrothermal reaction is 1:(6-10), the reaction temperature is 80-180°C, and the reaction time is 1.5-4.0h, thereby increasing the reaction rate of the hydrothermal reaction, accelerating the reaction, and improving the reaction efficiency.

[0024] In order to further improve the purity of alumina prepared from fly ash and completely separate silicon and aluminum in fly ash, the acid in the acid dissolution treatment is preferably an inorganic acid, and more preferably the inorganic acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid or hydrofluoric acid. More preferably, the concentration of the inorganic acid is 20-28%, the acid dissolution treatment temperature is 120-180°C, and the treatment time is 2-4h, so that the inorganic acid can better dissolve the fly ash, and further preferably the weight ratio of fly ash to acid is 1:(4-7).

[0025] In a preferred embodiment, after the acid dissolution treatment and before the crystallization treatment, the acid dissolution material needs to be filtered, and it is further preferred that the filtering treatment is carried out in a plate-frame filter to obtain an aluminum chloride filtrate and a white mud filter cake. The crystallization treatment is selected from one or more of salting-out, evaporative crystallization, recrystallization or cooling crystallization, and the salting-out crystallization treatment is more preferred. The salting-out crystallization method can further improve the purity of the precipitated aluminum chloride crystals, and it also has a high precipitation rate, high yield, simple operation, and easy to achieve industrial production. In order to further improve the purity and yield of aluminum chloride, the salting-out agent used in the salting-out crystallization is selected from hydrochloric acid, more preferably hydrochloric acid, and the flow rate of the further preferred salting-out agent is 0.2 to 2.0 L / min, and the crystallization treatment temperature is room temperature.

[0026] In order to further improve the purity of aluminum chloride and the content of α-alumina, after the crystallization treatment and before the first calcination treatment, the crystallized material needs to be separated, preferably the temperature of the first calcination is 250-350°C, and the first calcination time is 2-3h. In order to further promote the complete dissolution of fly ash in inorganic acid, it is preferred that the fly ash needs to be ground before the acid dissolution treatment, and more preferably the grinding particle size D50 is 20-40μm, thereby promoting the separation of silicon dioxide and aluminum oxide in the fly ash.

[0027] In a preferred embodiment, aluminum chloride crystals are first calcined to generate aluminum oxide and hydrochloric acid, wherein the generated hydrochloric acid gas can be used as a salting-out agent for salting-out crystallization, and can be directly introduced into the salting-out crystallization process to play the role of a salting-out agent, which can not only save costs and improve resource utilization, but also has a simple process, is easy to operate, is suitable for large-scale production, and has broad industrial application value.

[0028] In a preferred embodiment, after the hydrothermal reaction and before the alkaline dissolution treatment, the hydrothermal reaction product needs to be filtered and washed in sequence. Preferably, the filtration treatment is carried out in a plate and frame filter. In order to further improve the purity of the aluminum oxide, it is preferred to use evaporated condensed water 3 to 5 times the mass of the filtered material to wash the filtered material, thereby removing impurities such as sodium chloride, calcium chloride, and magnesium chloride.

[0029] In order to further improve the purity of aluminum chloride and the content of α-alumina therein, the alkali for alkali dissolution treatment is preferably an inorganic alkali, and more preferably the inorganic alkali is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate. It is further preferred that the concentration of the inorganic alkali is 220-350 g / L, and the temperature of the alkali dissolution treatment is more preferably 200-300° C., and the treatment time is 2-4 h, so that the crude aluminum chloride solid is further alkali-dissolved into a metaaluminate solution, thereby removing impurities contained therein (such as iron, calcium, magnesium, manganese), thereby improving the purity of aluminum chloride.

[0030] In order to promote the formation of aluminum hydroxide, an intermediate product of aluminum oxide, it is preferred to introduce CO into the carbonization process. 2 The flow rate of the carbonization agent is 0.05L / min to 0.2L / min, and the flow rate of the air is 0.1L / min to 0.4L / min; the aluminate solution can be promoted to obtain an aluminum hydroxide intermediate product after carbonization treatment, and further promote the formation of high-purity aluminum oxide. Preferably, after carbonization treatment and before the second roasting treatment, the carbonization material needs to be filtered to prepare for the second roasting. In order to further promote complete alkali dissolution, the weight ratio of aluminum oxide to the inorganic base is preferably 1: (1 to 2).

[0031] In a preferred embodiment, the temperature of the second calcination is preferably 1200-1250°C, and the second calcination time is 2-4h, so as to further promote the production of alumina products from aluminum hydroxide under the second calcination conditions, and improve the purity of alumina and the content of α-alumina. In order to further reduce the particle size of alumina and make it have a more refined application value, it is preferred that grinding treatment (such as sand grinding) is required after the second calcination, and the grinding is more preferably carried out in a grinder. It is further preferred that the grinding time is 1.0-2.0h, and the particle size D50 of the grinding treatment is 60-90nm, and D90 is 120-150nm. In order to further improve the purity of alumina and remove impurities therein, the ground material needs to be spray-dried after the grinding treatment, and the treatment temperature is 260-300°C, so as to further improve the quality of the alumina product.

[0032] Another aspect of the present invention provides an aluminum oxide, which is aluminum oxide prepared by the above preparation method. The aluminum oxide has high purity, low impurity content and small particle size, wherein the content of α-alumina is high, thereby opening up ideas for upgrading aluminum oxide products to make them high-end and refined, and for the multi-purpose application of aluminum oxide products.

[0033] In order to further promote the refinement of alumina products and the multi-purpose application of alumina products, the alumina is preferably in granular form, and more preferably the particle size D50 of the alumina particles is 60-90nm, and D90 is 120-150nm, so that the alumina particle size is smaller and the application field is wider.

[0034] Another aspect of the present invention provides an application of aluminum oxide in the fields of ceramics, wear-resistant materials, gemstone materials or laser instrument materials.

[0035] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0036] Example 1

[0037] The fly ash composition is as follows: 39.76wt% SiO 2 、48.10wt%Al 2 O 3 , 2.24wt% CaO, 3.42wt% MgO, 1.98wt% Fe 2 O 3 , 1.2wt% TiO 2 and 3.3 wt% LOI.

[0038] Step S1, grinding fly ash to a particle size D50 of 20-40 μm; acid dissolving fly ash and 28% hydrochloric acid at a solid-liquid weight ratio of 1:4 at 150°C for 2 hours; after fly ash is dissolved, the slurry is filtered using a plate-frame filter to obtain an aluminum chloride filtrate. The aluminum chloride filtrate is used for salting out crystallization, the flow rate of the HCl gas is 0.5 L / min, the salting out crystallization treatment temperature is 25°C, and the HCl mass concentration in the aluminum chloride solution after salting out crystallization reaches 28%; the aluminum chloride crystals are centrifuged, and the moisture content of the filter cake after separation is 5%; the aluminum chloride crystals are first roasted at a temperature of 280°C and a roasting time of 2 hours to obtain a crude aluminum chloride solid.

[0039] Step S2, taking crude alumina for hydrothermal reaction, the solid-liquid ratio of the reaction is 1:8, the reaction temperature is 80°C, the hydrothermal time is 2h, the slurry after the hydrothermal reaction is filtered by a plate-frame filter, and sodium hydroxide with a concentration of 220g / L is added to the obtained filter cake for alkali dissolution, the weight ratio of alumina to inorganic alkali is 1:1, the alkali dissolution temperature is 200°C, and the alkali dissolution time is 2 hours; the sodium aluminate solution obtained by alkali dissolution is subjected to carbon separation, and CO is introduced 2 The gas flow rate is 50 mL / min, the air rate is 100 mL / min, the endpoint pH = 10.5, and an aluminum hydroxide intermediate is obtained after filtration. The aluminum hydroxide intermediate is then calcined at 1200°C for 2 hours, then ground in a sand mill for 120 minutes, and spray-dried at 300°C to obtain an alumina product.

[0040] Example 2

[0041] The only differences from Example 1 are: the acid dissolution temperature is 160° C. and the time is 3 h; the flow rate of the salting-out agent is 1 L / min; the temperature of the first calcination is 300° C. and the calcination time is 3 h.

[0042] Example 3

[0043] The only difference from Example 1 is that the solid-liquid ratio of the hydrothermal reaction is 1:10, the reaction temperature is 100° C., and the reaction time is 3 h.

[0044] Example 4

[0045] The only difference from Example 1 is that the grinding time of the aluminum hydroxide intermediate is 100 minutes, the second roasting temperature is 1250° C., and the roasting time is 3 hours.

[0046] Comparative Example 1

[0047] The only difference from Example 1 is that the acid dissolution temperature is 160°C, and the acid dissolution time is 3 hours; the flow rate of the hydrogen sulfide gas is 3L / min; the first roasting temperature is 200°C, and the roasting time is 1 hour; the grinding time of the aluminum hydroxide intermediate is 40 minutes, the second roasting temperature is 1100°C, and the second roasting time is 2.5 hours.

[0048] Comparative Example 2

[0049] The only difference from Example 1 is that the acid dissolution temperature is 160°C, and the acid dissolution time is 3 hours; the flow rate of the hydrogen sulfide gas is 4L / min; the first roasting temperature is 400°C, and the roasting time is 3 hours; the grinding time of the aluminum hydroxide intermediate is 25 minutes, the second roasting temperature is 1050°C, and the second roasting time is 3 hours.

[0050] Comparative Example 3

[0051] The only difference from Example 1 is that a conventional method for producing alumina from fly ash is adopted, and adsorption is used instead of the crystallization treatment in the present invention.

[0052] Comparative Example 4

[0053] The only difference from Example 1 is that no hydrothermal reaction treatment is performed.

[0054] Comparative Example 5

[0055] The only difference from Example 1 is that the solid-liquid ratio of the hydrothermal reaction is 1:3, the reaction temperature is 60° C., and the reaction time is 1 h.

[0056] Comparative Example 6

[0057] The only difference from Example 1 is that the solid-liquid ratio of the hydrothermal reaction is 1:12, the reaction temperature is 200° C., and the reaction time is 6 h.

[0058] Performance test: The alumina in the above embodiments and comparative examples were subjected to performance tests. The test results are shown in Table 1 below.

[0059] Table 1

[0060]

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for producing alumina from fly ash, characterized in that: The preparation method comprises the following steps: Step S1, taking fly ash and performing acid dissolution, crystallization and first roasting in sequence to obtain a crude alumina solid; Step S2, taking the crude alumina solid and subjecting it to hydrothermal reaction, and then sequentially subjecting it to alkali dissolution, carbon separation and second calcination to obtain the alumina; wherein, The pH value of the carbon fraction after the carbon fraction treatment is 9.0 to 11.0; The fly ash has the following components by weight percentage: 30-60wt% SiO2, 45-60wt% Al2O3, 2-8wt% CaO, 2-5wt% MgO, 2-6wt% Fe2O3, 1-2wt% TiO2 and 1-5wt% LOI.

2. The preparation method according to claim 1, characterized in that: The hydrothermal reaction is carried out in a hydrothermal reaction kettle; Preferably, the solid-liquid ratio of the hydrothermal reaction is 1:(6-10), the reaction temperature is 80-180°C, and the reaction time is 1.5-4.0h; Preferably, the acid in the acid dissolution treatment is an inorganic acid, more preferably, the inorganic acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid or hydrofluoric acid; Preferably, the concentration of the inorganic acid is 20-28%, the acid dissolving treatment temperature is 120-180°C, and the treatment time is 2-4h; Preferably, the weight ratio of the fly ash to the acid is 1:(4-7).

3. The preparation method according to claim 1 or 2, characterized in that: After the acid dissolution treatment and before the crystallization treatment, the acid-dissolved material needs to be filtered. More preferably, the filtering treatment is performed in a plate-and-frame filter; Preferably, the crystallization treatment is selected from one or more of salting-out, evaporative crystallization, recrystallization or cooling crystallization, more preferably salting-out crystallization; Preferably, the salting-out agent used in the salting-out crystallization is selected from hydrochloric acid; Preferably, the flow rate of the salting-out agent is 0.2-2.0 L / min, and the crystallization treatment temperature is 20-30°C.

4. The preparation method according to any one of claims 1 to 3, characterized in that After the crystallization treatment and before the first calcination treatment, the crystallized material needs to be separated; Preferably, the first calcination temperature is 250-350°C, and the first calcination time is 2-3h; Preferably, the fly ash needs to be ground before the acid dissolution treatment. More preferably, the particle size D50 of the ground particles is 20-40 μm.

5. The preparation method according to any one of claims 1 to 4, characterized in that: After the hydrothermal reaction and before the alkaline dissolution, the hydrothermal reaction product needs to be filtered and washed with water in sequence; Preferably, the filtration process is carried out in a plate and frame filter; Preferably, the alkali used in the alkali dissolution treatment is an inorganic alkali, and more preferably, the inorganic alkali is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate; Preferably, the concentration of the inorganic base is 220-350 g / L; Preferably, the temperature of the alkali dissolution treatment is 200-300° C., and the treatment time is 2-4 hours.

6. The preparation method according to any one of claims 1 to 5, characterized in that In the carbon treatment, the flow rate of CO2 is 0.05L / min to 0.2L / min, and the flow rate of air is 0.1L / min to 0.4L / min; Preferably, after the carbon fraction treatment and before the second roasting treatment, the carbon fraction material needs to be filtered; Preferably, the weight ratio of the fly ash to the inorganic alkali is 1:(1-2).

7. The preparation method according to any one of claims 1 to 6, characterized in that The second calcination temperature is 1200-1250°C, and the second calcination time is 2-4h; Preferably, a grinding process is required before the second roasting, and more preferably, the grinding is performed in a grinder; Preferably, the grinding time is 1.0 to 2.0 h, and the particle size D50 of the grinding-treated particles is 60 to 90 nm, and D90 is 120 to 150 nm; Preferably, after the grinding process, the ground material needs to be filtered.

8. Alumina, characterized in that: The aluminum oxide is aluminum oxide obtained by the preparation method according to any one of claims 1 to 7.

9. The aluminum oxide according to claim 8, characterized in that The aluminum oxide is in a granular form. More preferably, the particle size D50 of the aluminum oxide particles is 60 to 90 nm, and D90 is 120 to 150 nm.

10. Use of the aluminum oxide according to claim 9 in the fields of ceramics, wear-resistant materials, gem materials or laser instrument materials.

Images