Method for preparing aluminum oxide from high-alumina fly ash

Abstract

The invention discloses a method for preparing aluminum oxide from high-alumina fly ash, and belongs to the technical field of preparation of aluminum oxide from fly ash. The method comprises the following steps: preparing the high-alumina fly ash, the soda and the quick lime into a raw material; performing high-temperature sintering to obtain sintered clinker and tail gas; the sintered clinker is subjected to alkali dissolution, and clinker dissolution liquid and calcium-silicon slag are obtained; a desiliconization agent is added into the clinker dissolution liquid for second-stage desiliconization treatment, pressure desiliconization is conducted in the first stage, desiliconization is conducted by adding the desiliconization agent in the second stage, then filtering treatment is conducted, and purified liquid is obtained; al (OH) 3 seed crystals are added into the purified liquid for carbonation (carbonation decomposition) treatment, and Al (OH) 3 precipitates are prepared; and finally, washing and calcining to obtain aluminum oxide. The invention provides an efficient, environment-friendly, economical and feasible method, the high-alumina fly ash is converted into a high-purity alumina product, and the method has wide application prospect and market value.

Description

Technical Field

[0001] The invention belongs to the technical field of preparing alumina from fly ash, and in particular relates to a method for preparing alumina from high-alumina fly ash. Background Art

[0002] Fly ash, the fine dust collected from the flue gases after coal combustion, is a major solid waste emitted by coal-fired power plants. The main oxide components of fly ash from thermal power plants are SiO2, Al2O3, FeO, Fe2O3, CaO, and TiO2. With the development of the power industry, fly ash emissions from coal-fired power plants have increased annually, becoming one of the largest industrial waste streams. Untreated large amounts of fly ash generate dust, polluting the atmosphere. Discharge into waterways can cause siltation, and the toxic chemicals contained in it can pose a threat to humans and organisms. Extracting alumina from fly ash represents a high-value-added utilization of fly ash as a secondary resource. Compared to research on fly ash applications in construction, building, and agriculture, the extraction of useful resources such as alumina from fly ash remains at the theoretical and experimental stage, with very limited technical pathways for industrial production.

[0003] Most of the research results on extracting useful resources such as Al2O3 from fly ash at home and abroad have strong theoretical significance. The main reasons limiting the industrialization of these research results are:

[0004] (1) Alumina in fly ash needs to be selectively dissolved, but other components (such as SiO2, Fe2O3, etc.) may also dissolve at the same time, making subsequent separation and purification more difficult; that is, the technical route obtained has certain defects in terms of extraction rate, energy consumption, material consumption, environmental protection and operability, thus limiting its industrial promotion;

[0005] (2) The research on the extraction of useful resources from fly ash is not systematic. The extraction of resources is not interconnected and integrated to form a feasible overall plan, which makes the extraction cost high and difficult to promote industrialization;

[0006] (3) Theoretical research and applied research are not organically unified, and applied research lacks systematic and in-depth support from basic theoretical research, which makes it difficult to produce technical solutions suitable for industrial production.

[0007] Therefore, there is an urgent need to provide a systematic, complete, efficient, environmentally friendly and economically feasible method to convert high-aluminum fly ash into metallurgical grade high-purity alumina. Summary of the Invention

[0008] In response to the above technical problems, the present invention proposes a method for preparing alumina using high-alumina fly ash.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] A method for preparing aluminum oxide using high-aluminum fly ash comprises the following steps:

[0011] High-alumina fly ash is mixed with soda and quicklime to form a raw meal, which is then sintered at high temperature in a rotary kiln to produce sintered clinker and tail gas. The tail gas obtained after sintering is concentrated using a dust removal and purification agent, using a special silica gel pressure swing adsorbent, to increase the carbon dioxide content in the tail gas from approximately 10% to 60-70%, and the gas is then used in the carbon fractionation process.

[0012] Alkaline dissolving the sintered clinker to obtain clinker dissolution solution and calcium silicon slag;

[0013] A desiliconizing agent is added to the clinker dissolution liquid to carry out a two-stage desiliconization treatment, wherein the first stage is pressure desiliconization, and the second stage is desiliconization by adding a desiliconizing agent, followed by filtration to obtain a purified liquid; wherein the pressure desiliconization is carried out at medium temperature and medium pressure (150-170°C, 0.5 MPa);

[0014] Al(OH)3 seed crystals are added to the purified liquid for carbonization (carbonation decomposition) treatment to obtain Al(OH)3 precipitate; finally, aluminum oxide is obtained after washing and calcination.

[0015] Optionally, the aluminum-silicon ratio (A / S) in the high-aluminum fly ash is 2-3.5; preferably 2.27.

[0016] Optionally, the alkali ratio of the soda and high-aluminum fly ash is 1.2, and the calcium ratio of the quicklime and high-aluminum fly ash is 2.2;

[0017] Among them, the alkali ratio is the ratio of the molar number of soda to the total molar number of SiO2 and Al2O3 in high-aluminum fly ash; the calcium ratio is the ratio of the molar number of calcium oxide to the molar number of SiO2 in high-aluminum fly ash.

[0018] Optionally, the high-aluminum fly ash has a fineness ratio of 60-100%, preferably 60%, 70%, 80%, 90%, 100%, and more preferably 70%, wherein the fineness ratio is the percentage of the mass of particles below 74 microns in the total mass of the high-aluminum fly ash.

[0019] Optionally, the conditions during the sintering process are:

[0020] The temperature is raised uniformly from room temperature to 1200-1300°C for 180-200 minutes, and then kept at this temperature for 1-2.5 hours, preferably raised to 1200°C for 2.5 hours.

[0021] Beneficial effects: In the clinker production process, the selection of sintering temperature is crucial. If the sintering temperature is too low, it will lead to under-burned clinker, which is manifested as a significant decrease in the extraction rate of alumina, and will cause the calcium silicon slag to expand, affecting the product quality; while if the sintering temperature is too high, over-burned clinker will be produced, which is manifested as: the solid solution content increases, resulting in a decrease in the dissolution rate of alumina and sodium oxide; the clinker hardness increases, the grindability deteriorates, and the subsequent processing difficulty increases; the production capacity of the rotary kiln is reduced, the kiln lining is easily damaged, and the operation cycle of the rotary kiln is shortened; energy consumption increases significantly, while increasing the equipment maintenance cost. Therefore, precise control of the sintering temperature is a key factor in ensuring clinker quality and production efficiency. Within the above-mentioned sintering temperature range defined by the present invention, not only can the extraction rate of alumina and sodium be improved, but also the production process can be optimized, energy consumption can be reduced and the service life of the equipment can be extended.

[0022] Alternatively, the preparation process of the special silica gel pressure swing adsorbent for dust removal and purification is as follows:

[0023] The method comprises the following steps: using a dilute sodium silicate solution as a raw material at room temperature, wherein the dilute sodium silicate solution has a mass concentration of 15%, adding a dilute hydrochloric acid solution, wherein the mass concentration of the dilute hydrochloric acid solution is 15%, and the volume ratio of the dilute sodium silicate solution to the dilute hydrochloric acid solution is 1:(2-3), and adding silica gel seed crystals with a size of less than 1 μm (the mass of the silica gel seed crystals is 0.5-1.0 wt.% of the total mass of the dilute sodium silicate solution and the dilute hydrochloric acid solution). The reaction is carried out for 15-30 minutes to prepare a silica gel suspension, and then filtering out the silica gel. The silica gel is then added to anhydrous ethanol at a liquid-to-solid ratio of 3, ultrasonically treated for 30-50 minutes, filtered, dried (85°C for 60-90 minutes), and finally microwave-roasted to 600°C for 30 minutes, and naturally cooled to obtain a silica gel pressure swing adsorbent for dust removal and purification.

[0024] Furthermore, the method for using the dust removal-purification-special silica gel pressure swing adsorbent is:

[0025] The special silica gel pressure swing adsorbent is placed in an adsorption tower for adsorption, which is specifically divided into the following steps:

[0026] Adsorption process: After the tail gas is purified, it is pressurized and cooled by the Roots blower and then enters the adsorption tower in 7 ways. The outlet of the adsorption tower obtains a nitrogen mixed gas with a CO2 content of about 10%. When the adsorption front is about to penetrate the adsorbent, the process switches to the next step.

[0027] Pressure drop process: After the adsorption process is completed, it enters the first pressure drop process;

[0028] Venting process: After the equalization pressure drop process is completed, the pressure in the adsorption tower is about 0.01MPa. In order to ensure that the vacuumed carbon dioxide concentration reaches 60%-70%, the residual gas in the adsorption tower is vented;

[0029] Vacuuming process: After the venting process is completed, the vacuuming process begins. This process is used to obtain the product carbon dioxide gas while desorbing the adsorbent, allowing the adsorbent to be regenerated and recycled. Once the vacuum pump's pumping capacity is determined, the longer the vacuuming time, the more complete the adsorbent regeneration.

[0030] Pressure equalization process: After the vacuum is completed, the pressure equalization process corresponding to the pressure drop is entered to prepare for the next adsorption;

[0031] Final pressurization process: In order to adsorb again, the pressure in the adsorption tower must be close to the raw gas pressure. To this end, in this step, the finished gas at the outlet of the adsorption tower is reversely charged into the adsorption tower after the pressure equalization is completed, completing the preparation work for the adsorption tower to adsorb again. The adsorption tower will enter the next adsorption process, and this cycle will repeat;

[0032] Dust removal and purification are routine operations and will not be described in detail here. The purpose of using dust removal-purification-special silica gel pressure swing adsorbent is to concentrate the carbon dioxide concentration in the exhaust gas to 60-70%.

[0033] Beneficial effects: The concentration of carbon dioxide used in ordinary carbon separation is about 30-40%, while the concentration of carbon dioxide in the tail gas generated by the rotary kiln is about 10%, and the carbon separation efficiency is low. The present invention adopts the method of dust removal-purification-special silica gel pressure swing adsorption to increase the concentration of carbon dioxide generated by the rotary kiln tail gas to 60-70%, significantly improving the decomposition rate of sodium aluminate solution and the yield of aluminum hydroxide, achieving the effect of enhanced carbon separation, and rationally utilizing the carbon dioxide generated by the rotary kiln tail gas, reducing carbon emissions and shortening the carbon separation time, thereby improving production efficiency.

[0034] Optionally, the alkali dissolution process is:

[0035] Alkali dissolution is carried out at a liquid-to-solid ratio of 5-6 and a temperature of 65-80°C, and the dissolution time is 20-40 minutes.

[0036] Further, the alkali dissolution process is:

[0037] Alkali dissolution was carried out at a liquid-to-solid ratio of 5 and a temperature of 80°C, and the dissolution time was 20 minutes.

[0038] Furthermore, the alkali solution used in the alkali dissolution process is a NaOH aqueous solution with a concentration of 0.5-2.0 mol / L.

[0039] Optionally, the desiliconizing agent is prepared by dissolving barium aluminate, hydrated calcium aluminate and quicklime in water.

[0040] Beneficial Effects: This invention combines barium aluminate, hydrated calcium aluminate, and lime milk in a specific ratio to produce a highly effective desiliconizing agent. This significantly improves the desiliconization efficiency compared to traditional lime milk, providing a solid foundation for producing qualified sand-like alumina. Specifically, when using a traditional lime milk (solids content of 100g / L) desiliconizer, the silicon content index in the sodium aluminate solution is only 200-300, resulting in an excessive silica content in the resulting alumina product. However, using the desiliconizing agent of this invention increases the silicon content index in the sodium aluminate solution to over 3000, ensuring the quality of the alumina produced.

[0041] Furthermore, the usage ratio of the barium aluminate, hydrated calcium aluminate, quicklime and water is: 8g:5g:10g:100mL.

[0042] Furthermore, the volume ratio of the clinker dissolution liquid to the desiliconizing agent is 1000:5.

[0043] Optionally, in the filtrate after filtration, the silicon content index A / S is ≥3000.

[0044] Optionally, the usage ratio of the Al(OH)3 seed crystals to the purification liquid is: 5-10:1 (g / L); preferably 5:1 (g / L).

[0045] Furthermore, the conditions for the carbon treatment are:

[0046] The carbon separation treatment is carried out at a carbon separation temperature of 70-85°C and a CO2 flow rate (exhaust gas) of 0.6 L / min until the end pH value is 11-12.5; wherein the CO2 is the 60-70% carbon dioxide gas obtained by concentrating the exhaust gas.

[0047] Optionally, the conditions during the calcination process are:

[0048] Calcinate at 1000℃ for 1-2h.

[0049] Compared with the prior art, the present invention has the following advantages and technical effects:

[0050] 1. High efficiency: Through the sintering and alkali dissolution conditions disclosed in the present invention, an Al2O3 dissolution rate of over 90% is achieved, and the dissolution of SiO2 is effectively suppressed, ensuring the purity of subsequent processes;

[0051] 2. Low impurities: The present invention discloses a highly efficient desiliconizing agent. The desiliconization process effectively removes silicon impurities in the solution, with the silicon content index A / S reaching over 3000, ensuring the high purity of the final product;

[0052] 3. High-quality products: Through the carbon content and calcination conditions disclosed in this invention, a metallurgical-grade alumina product is finally obtained, with an Al2O3 content of up to 98.74% and extremely low levels of other impurities (such as SiO2, Na2O, and Fe2O3), meeting the requirements of industrial applications;

[0053] 4. Comprehensive utilization of resources: The present invention not only solves the problem of handling high-aluminum fly ash, but also realizes the effective recovery and reuse of resources through reasonable process design, with significant economic and environmental benefits.

[0054] In summary, the present invention provides an efficient, environmentally friendly and economically feasible method for converting high-aluminum fly ash into metallurgical-grade high-purity alumina products, which has broad application prospects and market value. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0056] Figure 1 This is a process flow chart for preparing alumina according to Example 1 of the present invention;

[0057] Figure 2 This is a picture of the high-alumina fly ash used in Example 1 of the present invention;

[0058] Figure 3 This is the leaching rate curve of aluminum oxide in clinker 1# along with the subdivision ratio of high-aluminum fly ash;

[0059] Figure 4 This is the leaching rate curve of aluminum oxide in clinker 2# with alkali ratio;

[0060] Figure 5 This is the curve of the leaching rate of aluminum oxide in clinker 3# as a function of calcium ratio;

[0061] Figure 6 This is the curve of the leaching rate of aluminum oxide in clinker 4# as a function of temperature;

[0062] Figure 7 This is the curve of the leaching rate of aluminum oxide in clinker 5# as the holding time changes;

[0063] Figure 8 The aluminum hydroxide intermediate prepared from the high-aluminum fly ash in Example 1 of the present invention;

[0064] Figure 9 This is the alumina product prepared from the high-alumina fly ash in Example 1 of the present invention. DETAILED DESCRIPTION

[0065] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0066] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0067] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0068] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0069] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0070] Unless otherwise specified, the "room temperature" in the present invention refers to 20-30°C.

[0071] The raw materials used in the present invention are all purchased from the market. The high-aluminum fly ash in the present invention is a high-aluminum fly ash sample from Inner Mongolia Autonomous Region, which is powdery and gray. Figure 2 Its main chemical components are shown in Table 1.

[0072] Table 1 Analysis of main chemical components of high-alumina fly ash (%)

[0073] element <![CDATA[Al2O3]]> <![CDATA[SiO2]]> <![CDATA[Fe2O3]]> CaO <![CDATA[TiO2]]> content(%) 56.94 25.05 2.83 3.74 0.85

[0074] As can be seen from Table 1, high-aluminum fly ash contains 56.94% Al2O3, 25.05% SiO2, and an aluminum-silicon ratio A / S of 2.27, which is a typical high-aluminum fly ash.

[0075] The preparation process of the silica gel pressure swing adsorbent for dust removal and purification in the following examples is as follows:

[0076] A dilute sodium silicate solution is used as a raw material at room temperature, wherein the mass concentration of the dilute sodium silicate solution is 15%. A dilute hydrochloric acid solution is added to the solution, wherein the mass concentration of the dilute hydrochloric acid solution is 15% and the volume ratio of the dilute sodium silicate solution to the dilute hydrochloric acid solution is 1:2.5. Silica gel seed crystals with a size of less than 1 μm are added (the mass of the silica gel seed crystals is 0.7 wt.% of the total mass of the dilute sodium silicate solution and the dilute hydrochloric acid solution). The solution is reacted for 20 minutes to prepare a silica gel suspension. The silica gel is then filtered out. The silica gel is then added to anhydrous ethanol at a liquid-to-solid ratio of 3. The solution is ultrasonicated for 40 minutes, filtered, dried (85°C for 80 minutes), and finally calcined in a microwave oven to 600°C for 30 minutes. The solution is then naturally cooled to obtain a silica gel pressure swing adsorbent for dust removal and purification.

[0077] The method of using the above-mentioned dust removal and purification-specific silica gel pressure swing adsorbent is as follows:

[0078] The special silica gel pressure swing adsorbent is placed in an adsorption tower for adsorption, which is specifically divided into the following steps:

[0079] Adsorption process: After the tail gas is purified, it is pressurized and cooled by the Roots blower and then enters the adsorption tower in 7 ways. The outlet of the adsorption tower obtains a nitrogen mixed gas with a CO2 content of about 10%. When the adsorption front is about to penetrate the adsorbent, the process switches to the next step.

[0080] Pressure drop process: After the adsorption process is completed, it enters the first pressure drop process;

[0081] Venting process: After the equalization pressure drop process is completed, the pressure in the adsorption tower is about 0.01MPa. In order to ensure that the vacuumed carbon dioxide concentration reaches 60%-70%, the residual gas in the adsorption tower is vented;

[0082] Vacuuming process: After the venting process is completed, the vacuuming process begins. This process is used to obtain the product carbon dioxide gas while desorbing the adsorbent, allowing the adsorbent to be regenerated and recycled. Once the vacuum pump's pumping capacity is determined, the longer the vacuuming time, the more complete the adsorbent regeneration.

[0083] Pressure equalization process: After the vacuum is completed, the pressure equalization process corresponding to the pressure drop is entered to prepare for the next adsorption;

[0084] Final pressurization process: In order to adsorb again, the pressure in the adsorption tower must be close to the raw gas pressure. To this end, in this step, the finished gas at the outlet of the adsorption tower is reversely charged into the adsorption tower after the pressure equalization is completed, completing the preparation work for the adsorption tower to adsorb again. The adsorption tower will enter the next adsorption process, and this cycle will repeat;

[0085] Dust removal and purification are routine operations and will not be described in detail here. The purpose of using dust removal-purification-special silica gel pressure swing adsorbent is to concentrate the carbon dioxide in the exhaust gas to 60-70%.

[0086] The technical solution of the present invention is further illustrated by the following examples.

[0087] Example 1

[0088] like Figure 1 As shown, a method for preparing alumina using high-aluminum fly ash comprises the following steps:

[0089] Mixing high-aluminum fly ash, CaO and Na2CO3 in a certain proportion to obtain raw meal;

[0090] The raw material is sintered to obtain sintered clinker; the sintered clinker is then alkali-dissolved to obtain clinker dissolution liquid and calcium-silicon slag;

[0091] A desiliconizing agent is added to the clinker dissolution liquid to carry out a two-stage desiliconization treatment, wherein the first stage is pressure desiliconization, and the second stage is desiliconization by adding a desiliconizing agent, followed by filtration to obtain a purified liquid; wherein the pressure desiliconization is carried out at medium temperature and medium pressure (150-170°C, 0.5 MPa);

[0092] Al(OH)3 seed crystals are added to the purified liquid, and the concentrated gas (with a carbon dioxide volume content of 60-70%) obtained by treating the tail gas obtained after sintering through dust removal, purification, and special silica gel pressure swing adsorbent is subjected to carbon separation (carbonation decomposition) treatment to produce Al(OH)3 precipitate; finally, metallurgical grade alumina is obtained through washing and calcination.

[0093] By controlling a single variable, the following experiment on the preparation of alumina using high-aluminum fly ash was conducted:

[0094] 1.1 High-temperature sintering and dissolution test results of high-alumina fly ash + soda ash + quicklime

[0095] Clinker 1# test: 20g of high-alumina fly ash (tested according to the fine ratio of 60%, 70%, 80%, 90% and 100% respectively, where the coarseness is distinguished by 74 microns, such as fine: coarse 60:40 means the ratio of the mass of particles below 74 microns to the mass of particles above 74 microns) and prepared soda and quicklime (Na2CO3: 12.22g, CaO: 16.07g) are sintered at 1200℃ for 2h, and the heating time is 180min.

[0096] The sintered powder is ground to a size of at least 75% 230 mesh (63 microns). A 1 mol / L sodium hydroxide solution is added at a liquid-to-solid ratio of 5:1 and stirred at 80°C for 30 minutes. Dissolution is achieved by stirring and filtering. The residue is then washed three times with water at 90°C at a liquid-to-solid ratio of 3:1. The aluminum content of the residue (dried at 80°C for 720 minutes) is then calculated by chemical analysis of the aluminum content in the solution, thereby determining the aluminum leaching rate.

[0097] Figure 3 The following graph shows the leaching rate of alumina in clinker 1# as a function of the fines content of high-alumina fly ash. As can be seen from the graph, the alumina leaching rate generally increases with increasing fines content in clinker 1#, meaning that higher fines content leads to higher alumina leaching rates. Above 70% fines content, the leaching rate plateaus or even decreases slightly, indicating that further increasing the fines content has limited effect on improving the leaching rate after reaching a certain particle size ratio. At around 70% fines content, the leaching rate reaches a maximum of 74.07%.

[0098] Clinker 2# test: 20g of high-alumina fly ash was mixed with prepared soda and quicklime (the amount of Na2CO3 was added according to the alkali ratio of 1, 1.2, 1.4, 1.6, 1.8, and 2.0 respectively; CaO: 16.07g), and sintered at 1200℃ for 2h, with a heating time of 180min.

[0099] The sintered powder is ground to a size of at least 75% 230 mesh (63 microns). A 1 mol / L sodium hydroxide solution is added at a liquid-to-solid ratio of 5:1 and stirred at 80°C for 30 minutes. Dissolution is achieved by stirring and filtering. The residue is then washed three times with water at 90°C at a liquid-to-solid ratio of 3:1. The aluminum content of the residue (dried at 80°C for 720 minutes) is then calculated by chemical analysis of the aluminum content in the solution, thereby determining the aluminum leaching rate.

[0100] Figure 4 The following graph shows the leaching rate of alumina in clinker 2 as a function of alkali ratio. As can be seen from the figure, the relationship between alkali ratio and leaching rate shows an initial upward and then downward trend. This indicates that within a certain range, increasing the alkali ratio can effectively improve the leaching rate. However, beyond a certain threshold, further increases in the alkali ratio may lead to a decrease in the leaching rate. By analyzing the relationship between alkali ratio and alumina leaching rate, the optimal alkali ratio range was determined to be 1.2, with a maximum leaching rate of 76.33%.

[0101] Clinker Test 3: 20g of fly ash was mixed with prepared soda and quicklime (Na2CO3: 12.22g; quicklime was added in calcium ratios of 1, 1.2, 1.4, 1.6, 1.8, and 2, respectively). Sintering was performed at 1200°C for 2h, with a heating time of 180min.

[0102] The sintered powder is ground to a size of at least 75% 230 mesh (63 microns). A 1 mol / L sodium hydroxide solution is added at a liquid-to-solid ratio of 5:1 and stirred at 80°C for 30 minutes. Dissolution is achieved by stirring and filtering. The residue is then washed three times with water at 90°C at a liquid-to-solid ratio of 3:1. The aluminum content of the residue (dried at 80°C for 720 minutes) is then calculated by chemical analysis of the aluminum content in the solution, thereby determining the aluminum leaching rate.

[0103] Figure 5 The following is a curve of the leaching rate of alumina in clinker 3# as a function of calcium ratio. As can be seen from the figure, the relationship between calcium ratio and leaching rate shows a trend of first increasing and then decreasing, which indicates that within a certain range, increasing the calcium ratio can effectively increase the leaching rate. However, after exceeding a certain threshold, further increasing the calcium ratio may lead to a decrease in the leaching rate. Therefore, the optimal alkali ratio range can be determined to be 2.2, at which time the highest leaching rate of alumina is 77.83%.

[0104] Clinker Test 4: 20g of high-alumina fly ash was mixed with a mixture of soda and lime (12.22g of Na2CO3 and 16.07g of CaO). Sintering was performed at a constant temperature (5 gradients from 1100°C to 1300°C) for 2 hours, with a heating time of 180 minutes.

[0105] The sintered powder is ground to a size of at least 75% 230 mesh (63 microns). A 1 mol / L sodium hydroxide solution is added at a liquid-to-solid ratio of 5:1 and stirred at 80°C for 30 minutes. Dissolution is achieved by stirring and filtering. The residue is then washed three times with water at 90°C at a liquid-to-solid ratio of 3:1. The aluminum content of the residue (dried at 80°C for 720 minutes) is then calculated by chemical analysis of the aluminum content in the solution, thereby determining the aluminum leaching rate.

[0106] Figure 6 The following graph shows the leaching rate of aluminum oxide in clinker #4 as a function of temperature. As can be seen from the figure, the leaching rate of clinker #4 generally increases with increasing temperature, particularly between 1100°C and 1200°C, where the leaching rate increases significantly. However, after temperatures exceed 1200°C, the leaching rate growth levels off and even decreases slightly, indicating that further increases in temperature have limited effect on improving the leaching rate. The leaching rate reaches a maximum of 82.21% at around 1200°C.

[0107] Clinker #5 test: 20g fly ash and prepared soda lime (Na2CO3: 12.22g CaO: 16.07g) were sintered at 1200°C for a certain time (six gradients of 0.5, 1, 1.5, 2, 2.5, and 3 hours) with a heating time of 180 minutes.

[0108] The sintered powder is ground to a size of at least 75% 230 mesh (63 microns). A 1 mol / L sodium hydroxide solution is added at a liquid-to-solid ratio of 5:1 and stirred at 80°C for 30 minutes. Dissolution is achieved by stirring and filtering. The residue is then washed three times with water at 90°C at a liquid-to-solid ratio of 3:1. The aluminum content of the residue (dried at 80°C for 720 minutes) is then calculated by chemical analysis of the aluminum content in the solution, thereby determining the aluminum leaching rate.

[0109] Figure 7 The following graph shows the leaching rate of alumina in clinker 5# as a function of holding time. As can be seen from the figure, the leaching rate generally increases with increasing holding time, particularly between 1.5 and 2.5 hours, where the leaching rate significantly increases, indicating that holding time is a significant factor influencing the leaching rate. After holding time exceeds 2.5 hours, the growth in leaching rate slows, indicating that further increases in holding time have limited effect on improving the leaching rate. The figure shows that the optimal holding time is 2.5 hours, at which the highest alumina leaching rate of 90.82% is achieved.

[0110] From the above experimental results, it can be seen that the optimal experimental conditions can be achieved when the particle size ratio of fine:coarse is 70:30, the sintering temperature is 1200℃, the alkali ratio is 1.2, the calcium ratio is 2.1, and the holding time is 2.5h. At this time, the Al2O3 leaching rate is 90.82%.

[0111] 1.2 Test results of purification, desiliconization and carbon content of high-alumina fly ash clinker leachate

[0112] The sintered clinker obtained under the above optimal conditions is dissolved in alkali solution to obtain a crude sodium aluminate solution, which contains about 120g / L of Al2O3 and 3.0-6.0g / L of SiO2. The mass ratio of Al2O3 to SiO2 (silicon index A / S) is about 20-30. If carbon separation is carried out directly, a large amount of SiO2 will precipitate together with aluminum hydroxide, resulting in substandard product quality. Therefore, before the carbonation decomposition of the sodium aluminate solution, the crude solution must be specially desiliconized to produce a fine solution. The deeper the desiliconization, the higher the carbonation decomposition rate and yield of the sodium aluminate solution.

[0113] The present invention adopts a two-stage desiliconization process: a first stage of desiliconization at medium temperature and medium pressure, and a second stage of deep desiliconization using a high-efficiency desiliconizing agent. Specifically, the crude sodium aluminate solution is first desiliconized in an autoclave at 150-170°C and 0.5 MPa for 2 hours to raise the silicon content index of the solution to approximately 400. A second stage of desiliconization is then performed at atmospheric pressure, with the addition of a high-efficiency desiliconizing agent to raise the silicon content index to above 3000 and reduce the SiO2 concentration to below 15 mg / L, thereby ensuring the quality of the alumina product, particularly the silicon content.

[0114] The high-efficiency desiliconizing agent is barium aluminate, hydrated calcium aluminate, quicklime and water in a dosage ratio of 8g:5g:10g:100mL, and the volume ratio of the clinker dissolution liquid to the desiliconizing agent is 1000:5.

[0115] The carbon content test conditions are as follows: at 70°C, 35g / L of seed Al(OH) is added to the purified liquid, and the calcined tail gas that has been concentrated by dust removal, purification, and special silica gel pressure swing adsorbent is introduced to increase the carbon dioxide content in the calcined tail gas from about 10% to 60-70%. The tail gas flow rate is 1.2L / min. When the pH value of the solution is 11, the aeration is stopped, and the solution is slowly stirred for 1 hour and then filtered. The precipitate is filtered and the precipitate is washed with three-stage countercurrent to remove impurities and alkali. The last stage of washing uses distilled water, and the washing liquid-to-solid ratio is 0.5:1 (g / mL). After drying, an aluminum hydroxide intermediate is obtained, such as Figure 8 shown.

[0116] 1.3 Calcination test results of precipitated Al(OH)3

[0117] The washed and filtered precipitate -Al(OH)3 was calcined at 1000℃ for 1h to obtain metallurgical grade alumina. The quality of alumina is shown in Table 2 and Figure 9 As shown in Table 3, the quality standards of metallurgical grade alumina are shown.

[0118] Table 2 Quality of alumina prepared by the process of the present invention

[0119] serial number Calcination mass / g Calcination theoretical amount / g <![CDATA[Al2O3 / %]]> <![CDATA[SiO2 / %]]> <![CDATA[Na2O / %]]> <![CDATA[Fe2O3 / %]]> <![CDATA[Al2O3]]> 9.84 9.81 98.74 0.056 0.42 0.0096

[0120] Table 3 Metallurgical grade alumina quality standards

[0121]

[0122] The Al2O3 product quality analysis adopts the titration method, which shows that the Al2O3 content in the product is 98.74%, which is higher than the metallurgical grade I standard, and the SiO2, Na2O, and Fe2O3 impurity contents are lower than the metallurgical grade I standard. Therefore, the alumina product produced by the present invention meets the metallurgical grade I alumina standard.

[0123] Comparative Example 1

[0124] The only difference from Example 1 (optimal conditions) is that the conventional two-stage desiliconization process (one stage medium temperature and medium pressure + two stages lime milk desiliconization process) is adopted, specifically:

[0125] In the second stage desiliconization process, the high-efficiency desiliconizing agent was replaced with lime milk in the second stage desiliconization, wherein the volume ratio of the clinker dissolution liquid to the lime milk was 1000:5, wherein the solid content of the lime milk was 10%. The other preparation conditions were the same as those in Example 1.

[0126] The silicon content index of the solution obtained after desiliconization in Comparative Example 1 is only 1120. The quality of the alumina product is reduced after carbon separation, and the SiO2 content far exceeds the requirements of metallurgical-grade alumina. There is a risk of unqualified alumina products. The component contents of the final product obtained by Comparative Example 1 after carbon separation, washing, and calcination under the same conditions as in Example are shown in Table 4.

[0127] Table 4 Comparative Example 1 Alumina quality prepared by two-stage desiliconization process

[0128] serial number Calcination mass / g Calcination theoretical amount / g <![CDATA[Al2O3 / %]]> <![CDATA[SiO2 / %]]> <![CDATA[Na2O / %]]> <![CDATA[Fe2O3 / %]]> <![CDATA[Al2O3]]> 9.90 9.81 96.31 1.01 0.41 0.021

[0129] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing alumina using high-alumina fly ash, characterized in that: The following steps are involved: Mix high-aluminum fly ash with soda and quicklime to form raw meal, and sinter at high temperature to obtain sintered clinker and tail gas; Alkaline dissolving the sintered clinker to obtain clinker dissolution solution and calcium silicon slag; The clinker dissolution liquid is subjected to a two-stage desiliconization treatment, wherein the first stage is pressure desiliconization and the second stage is desiliconization by adding a desiliconizing agent, followed by filtration to obtain a purified liquid; The tail gas is introduced into the purified liquid and Al(OH)3 seed crystals are added for carbon treatment to obtain Al(OH)3 precipitate, which is finally washed and calcined to obtain aluminum oxide.

2. The method for preparing alumina using high-alumina fly ash according to claim 1, characterized in that: The aluminum-silicon ratio in the high-aluminum fly ash is 2-3.5; The molar ratio of the soda to the sum of SiO2 and Al2O3 in the high-alumina fly ash is 1.2; The molar ratio of the quicklime to SiO2 in the high-alumina fly ash is 2.

2.

3. The method for preparing alumina using high-alumina fly ash according to claim 1, characterized in that: The fine division ratio of the high-alumina fly ash is 70%.

4. The method for preparing alumina using high-alumina fly ash according to claim 1, characterized in that: The conditions during the high temperature sintering process are: Raise the temperature uniformly to 1200-1300℃ for 180-200min, and then keep at this temperature for 1-2.5h.

5. The method for preparing alumina using high-alumina fly ash according to claim 1, characterized in that: The alkali dissolution process is: Alkaline dissolution is carried out at a liquid-solid ratio of 4-6 mL:1 g and a temperature of 65-80°C, and the dissolution time is 20-40 min.

6. The method for preparing alumina using high-alumina fly ash according to claim 1, characterized in that: The desiliconizing agent is prepared by dissolving barium aluminate, hydrated calcium aluminate and quicklime in water; The usage ratio of the barium aluminate, hydrated calcium aluminate, quicklime and water is 8g:5g:10g:100mL.

7. The method for preparing alumina using high-alumina fly ash according to claim 1, characterized in that: The volume ratio of the clinker dissolution liquid to the desiliconizing agent is 1000:

5.

8. The method for preparing alumina using high-alumina fly ash according to claim 1, characterized in that: The usage ratio of the Al(OH)3 seed crystals to the purification liquid is 5-10 g:1 L.

9. The method for preparing alumina using high-alumina fly ash according to claim 1, characterized in that: The conditions for the carbon treatment are: The carbonization treatment was carried out at a carbonization temperature of 70-85°C and a CO2 flow rate of 0.6 L / min until the end point pH value was 11-12.

5.

10. The method for preparing alumina using high-alumina fly ash according to claim 1, characterized in that: The conditions during the calcination process are: calcination at 1000° C. for 1-2 hours.

Images