A method for extracting alumina from solid waste fly ash

Abstract

This application relates to the technical field of comprehensive utilization of fly ash, and specifically discloses a method for extracting alumina from solid waste fly ash. The extraction of the alumina successively undergoes raw material calcination and digestion, desilication treatment of the digested slurry, refining and crystallization of the mother liquor, and roasting and decomposition; among them, the desilication treatment of the digested slurry includes the following steps: adding a desilication agent to the digested slurry, heating for treatment, and filtering to obtain the carbonation mother liquor; the desilication agent is prepared by mixing raw materials in the following mass parts: 65-75 parts of deionized water, 30-40 parts of active desilication powder, 0.5-0.8 parts of dispersant, and 0.2-0.3 parts of stabilizer, and the active desilication powder is obtained by intercalating and compounding modified nano-sodalite and modified kaolin; by using the desilication agent of this application to treat the fly ash mixed raw meal, the removal rate of silicon dioxide in the digested slurry can reach ≥90.37%, and the purity of alumina in the product can reach more than 97.7%.

Description

Technical Field

[0001] This application relates to the technical field of comprehensive utilization of fly ash. More specifically, it relates to a method for extracting alumina from solid waste fly ash. Background Art

[0002] The main solid waste fly ash generated by coal-fired power plants has become an important potential resource for replacing bauxite to extract alumina due to its high aluminum content. However, alumina and silica in fly ash often coexist in amorphous or composite mineral forms, and the aluminum-silicon ratio is generally low, making it difficult to meet the raw material requirements for refining alumina by the industrial Bayer process. In order to optimize the separation and extraction efficiency of alumina, sodium carbonate or lime milk is usually added to the clinker after raw material calcination to dissolve the insoluble calcium silicate components. However, even after this step of treatment, a large amount of free silicate ions still remain in the slurry, and these ions will participate in the refining process of alumina, ultimately resulting in a decrease in the separation and extraction efficiency of alumina. Therefore, the difficulty of desilication has become the core technical bottleneck restricting the large-scale extraction of alumina from fly ash.

[0003] The Chinese patent application document with the publication number CN108622920A discloses a method for extracting alumina from high-aluminum fly ash. In the solution, the high-aluminum fly ash is sequentially subjected to activation treatment and pre-desilication treatment to obtain desilicated fly ash. Among them, acid solutions such as sulfuric acid and hydrochloric acid are used in the activation treatment, and in combination with the sodium hydroxide alkali solution used in the pre-desilication treatment, the initial desilication efficiency of the raw material can reach 45% - 53%. Only through the activation treatment step, the aluminum-silicon ratio of the fly ash can be increased to more than 2.6, greatly improving the purity of the obtained alumina product.

[0004] In the above solution, through the staged treatment of acid solution and alkali solution, the silicon-aluminum ratio of the raw material can be reduced, but the amount of acid and alkali treatment liquids used is large, making it difficult to meet the requirements of industrial production. Moreover, due to the continuous treatment steps of acid solution activation treatment and alkali solution pre-desilication in the treatment process, the residual acid in the previous step is easily neutralized by the alkali solution in the next step, reducing the use effect of the alkali solution and causing waste of the treatment liquid. Therefore, it is necessary to find a solution to reduce production costs while improving the desilication efficiency of the raw material fly ash. Summary of the Invention

[0005] In order to further reduce the cost of alumina extraction and improve the desilication rate of the raw material fly ash, this application provides a method for extracting alumina from solid waste fly ash.

[0006] A method for extracting alumina from solid waste fly ash adopts the following technical solution:

[0007] The extraction of alumina successively undergoes raw material calcination and digestion, desilication treatment of the digested slurry, refining and crystallization of the mother liquor, and roasting and decomposition; among them, the desilication treatment of the digested slurry includes the following steps: adding a desilication agent to the digested slurry, performing a temperature-raising treatment, and filtering to obtain the carbonation mother liquor;

[0008] The desilication agent is prepared by mixing raw materials including the following parts by mass: 65-75 parts of deionized water, 30-40 parts of active desilication powder, 0.5-0.8 part of dispersant, and 0.2-0.3 part of stabilizer. The active desilication powder is obtained by intercalation compounding of modified nano-sodalite and modified kaolin;

[0009] The preparation steps of the modified nano-sodalite include the following:

[0010] (1) Take aluminum chloride, dropwise add sodium hydroxide, perform an ice-water bath, then add tetraethyl orthosilicate, stir, add a crystal growth promoter, continue stirring, then adjust the pH, raise the temperature and keep warm, disperse and then raise the temperature again for treatment, filter to obtain the precipitate and wash it with alcohol, readjust the pH, and then dry and grind to obtain nano-sodalite;

[0011] (2) Take nano-sodalite, disperse it in a mixed solution, add an organic acid for treatment, raise the temperature and then add a silane coupling agent, continue the treatment, then supplement the silane coupling agent, react, then perform an ice-water bath and let it stand, centrifuge to obtain the precipitate, wash it with alcohol and then dry and grind to obtain the modified nano-sodalite;

[0012] The steps of the intercalation compounding include the following: take modified kaolin, mix it with modified nano-sodalite, disperse it, then perform low-speed centrifugation, then raise the temperature for treatment, and then obtain the product after suction filtration, alcohol washing, drying, and pulverization.

[0013] By adopting the above technical solution, after the calcined raw material is digested and then undergoes desilication treatment, effective desilication can be achieved. The desilication agent used is a dispersion liquid with a desilication active component. The modified nano-sodalite in the active component can provide crystal nuclei for the free silicate ions in the digested slurry. In the hot environment of the digested slurry, the free silicate ions participate in crystallization and continuously precipitate, so as to achieve the desilication effect. The kaolin is organically modified to inhibit its sedimentation behavior in the digested slurry, and through intercalation combination, it forms a composite structure with the modified nano-sodalite. When in use, the modified kaolin serves as a crystal bed for the crystallization of the modified nano-sodalite, effectively filtering large particle impurities through the interlayer gaps to avoid the incorporation of impurities affecting the growth of the crystal clusters of the modified nano-sodalite; at the same time, due to the isolation effect of the intercalation, the merger and flocculation of adjacent crystal clusters are inhibited. Through the combined action of the modified nano-sodalite and the modified kaolin, the desilication effect on the digested slurry can be improved.

[0014] Preferably, the preparation steps of the modified kaolin are as follows: Take kaolin, mix and grind it with ammonium carbamate, then place it in a closed reactor for heat treatment, collect the powder material, disperse it, then add a premixed solution, process it, add styrene monomer and initiator, adjust the temperature and reaction time, and finally filter to obtain the collected product, wash it with alcohol, and dry it to obtain the modified kaolin;

[0015] Preferably, the mixing mass ratio of the kaolin to ammonium carbamate is (8.5 - 9):(1.2 - 1.5);

[0016] Preferably, the heat treatment conditions are as follows: adjust the temperature to 72 - 85 °C and treat for 10 - 12 h.

[0017] By adopting the above technical solution, small molecules of ammonium carbamate can be intercalated into the interlayers of kaolin with a layered structure through grinding. Under the heat treatment environment, ammonium carbamate undergoes thermal decomposition to generate ammonia and carbon dioxide gases, which opens the interlayers of kaolin, and then exfoliated kaolin is obtained.

[0018] Preferably, the premixed solution is obtained by mixing vinyltriethoxysilane, deionized water, and acetic acid according to a mass - volume ratio of (1 - 1.5) g:1 ml:(0.2 - 0.3) ml.

[0019] By adopting the above technical solution, in the premixed solution, vinyltriethoxysilane is activated by acetic acid, hydrolyzes in deionized water to expose silanol groups, and undergoes dehydration condensation with the silanol groups on the exfoliated kaolin to obtain a grafted composite structure. At the same time, the presence of vinyl groups in the composite structure can provide a polymerization initiation point for the subsequent polymerization of styrene monomer, and then organically modified kaolin is obtained.

[0020] Preferably, the initiator is azobisisobutyronitrile, adjust the temperature to 35 - 40 °C, and react for 20 - 30 min.

[0021] By adopting the above technical solution, using the above initiator and initiation conditions, the best effect of low - molecular - weight polystyrene is obtained.

[0022] Preferably, in the step (1), the molar ratio of aluminum chloride, sodium hydroxide, and tetraethyl orthosilicate added is 1:(4 - 4.6):(0.85 - 1); the crystal growth promoter is prepared by mixing sodium pyrophosphate and aluminum isopropoxide according to a mass ratio of 0.3:(1 - 2).

[0023] By adopting the above technical solution, adjusting the raw material ratio can obtain a sodalite pre - polymer. Aluminum chloride, as an aluminum source, can react with excessive sodium hydroxide to obtain aluminate ions, and then continue to react with tetraethyl orthosilicate under ice - bath conditions to form a sodalite pre - polymer with a gel structure. The addition of the crystal growth promoter helps to improve the crystallization quality. After subsequent treatment of heating and pH adjustment, nano - sodalite can be obtained.

[0024] Preferably, in the step (2), the mixed solution is prepared by mixing deionized water, ethylene glycol, and polyvinyl alcohol in a volume ratio of 1:(1 - 1.5):(0.2 - 0.3); the organic acid is one of tartaric acid, citric acid, and acetic acid.

[0025] In the step (2), the silane coupling agent is one of 1,2 - bis(triethoxysilyl)ethane, vinyltrimethoxysilane, γ - aminopropyltriethoxysilane, and vinyltriethoxysilane.

[0026] By adopting the above technical solution, the mixed solution can uniformly disperse nano - sodalite, and the organic acid can activate the surface aluminum hydroxyl and silicon hydroxyl structures of nano - sodalite, promote the introduction of the silane coupling agent in the subsequent steps, play a role in modifying nano - sodalite, and improve the effect of the subsequent intercalation combination.

[0027] Preferably, in the step (2), the mass ratio of the silane coupling agent added for the first time to the supplementary silane coupling agent is (0.2 - 0.5):(1 - 1.5).

[0028] By adopting the above technical solution, adding the silane coupling agent twice can achieve the effect of regularizing the silane chain segments. First, under the activation of the organic acid, the aluminum / silicon hydroxyl groups on the nano - sodalite react with a small amount of the silane coupling agent added for the first time to complete grafting and form active grafting sites. The subsequent supplementary silane coupling agent can continue to react at the grafting sites, and finally, multi - cluster silane chain segments with nano - sodalite as the core are obtained. These silane chain segments serve as fixed anchors for nano - sodalite in the subsequent intercalation reaction, improving the firmness of the intercalation structure.

[0029] Preferably, in the intercalation composite step, the mass ratio of the modified kaolin to the modified nano - sodalite is (25 - 30):(7 - 8).

[0030] In summary, the present application has the following beneficial effects:

[0031] 1. The present application uses modified nano - sodalite and modified kaolin for treatment, and a desiliconizing agent is obtained after dispersion. In the active components of the desiliconizing agent, the modified nano - sodalite can provide crystal nuclei for the free silicate ions in the leaching slurry, and continuous crystallization behavior occurs in the hot leaching slurry environment to achieve the desiliconization effect. The kaolin is organically modified to inhibit its sedimentation behavior in the leaching slurry, and through intercalation combination, a composite structure is formed with the modified nano - sodalite.

[0032] 2. In this application, the method of intercalation combination is preferably used to obtain the active desiliconized powder. In the constructed intercalated composite structure, the modified kaolin serves as the crystal bed for the crystallization of the modified nano-sodalite. Through the interlayer insertion voids, large particle impurities are effectively filtered to avoid the influence of impurity incorporation on the growth of the modified nano-sodalite crystals. At the same time, due to the interlayer insertion isolation effect, the merger of adjacent crystal clusters and the occurrence of crystal cluster flocculation are inhibited. Through the combined action of the modified nano-sodalite and the modified kaolin, the desiliconization effect on the leaching slurry can be improved.

[0033] 3. Using the desiliconizing agent of this application to treat the fly ash mixed raw materials, the removal rate of silicon dioxide in the leaching slurry is ≥90.37%, and the purity of alumina in the product can reach more than 97.7%. Description of the Drawings

[0034] Figure 1 It is the percentage content of alumina in the products treated with the desiliconizing agents of Examples 1-5 and Comparative Examples 1-4 of this application.

[0035] Figure 2 It is the removal rate of silicon dioxide in the leaching slurry treated with the desiliconizing agents of Examples 1-5 and Comparative Examples 1-4 of this application. Detailed Description of the Invention

[0036] Preparation Example 1

[0037] Take 0.28 g of aluminum chloride, and gradually dropwise add 16 mL of 0.5 mol / L sodium hydroxide solution. Then, under ice bath conditions, add 0.36 g of tetraethyl orthosilicate to the system, adjust the magnetic stirring speed to 50 rpm, stir for 15 min, then add 0.2 g of crystal growth promoter, continue to treat for 10 min, then add ammonia water to adjust the pH to 8.5, adjust the temperature to 80 °C, keep warm for 20 min, then add 30 ml of n-butanol, adjust the magnetic stirring speed to 100 rpm, keep the temperature at 85 °C for 8 h, filter to obtain the precipitate, then wash the precipitate ultrasonically with anhydrous ethanol twice, adjust the pH to 7.5, then place it in an oven at 45 °C for drying, and finally grind for 1 min to obtain nano-sodalite.

[0038] Take 4.2 g of nano-sodalite, add it to 30 ml of the mixed solution, adjust the magnetic stirring speed to 75 rpm, disperse for 5 min, then add 0.2 g of tartaric acid, continue to treat for 20 min, then raise the temperature to 60 °C, add 0.2 g of 1,2-bis(triethoxysilyl)ethane, treat for 10 min, then add an additional 1 g of 1,2-bis(triethoxysilyl)ethane, reduce the magnetic stirring speed to 30 rpm, react for 1 h, and then treat the reaction solution for 10 min under ice bath conditions. Immediately centrifuge at 3000 rpm to obtain the bottom precipitate, wash the precipitate twice with hot anhydrous ethanol, dry it, and then grind for 3 min to obtain the modified nano-sodalite.

[0039] Take 8.5 g of kaolin, mix it with 1.2 g of ammonium carbamate, grind for 10 min, then place it in a closed reactor, treat it at 72 °C for 10 h, then slowly release the pressure to atmospheric pressure, collect the powder material, place it in 30 ml of acetone, ultrasonically treat it at 30 °C for 10 min, then add 1.7 ml of the premixed solution, treat for 20 min, then add 0.4 g of styrene monomer and 0.1 g of azobisisobutyronitrile to the system, adjust the temperature to 35 °C, react for 20 min, then filter to obtain the filtrate, wash it twice with alcohol, and dry it to obtain modified kaolin.

[0040] Take 25 g of modified kaolin, mix it with 7 g of modified nano-sodalite, add it to 100 ml of n-butanol and ultrasonically disperse it. Then place the dispersion in a centrifuge, adjust the rotation speed to 2500 rpm and centrifuge at low speed for 30 min. Subsequently, transfer it to a constant temperature water bath and treat it at 70 °C for 2.5 h. Then filter to obtain the filter cake, wash it twice with hot absolute ethanol and dry it. Finally, crush it and pass it through a 150-mesh sieve to obtain the active desiliconized powder.

[0041] Take 65 g of deionized water, 0.5 g of dispersant polyethylene glycol, 0.2 g of stabilizer sodium carboxymethyl cellulose, and 30 g of active desiliconized powder, adjust the magnetic stirring speed to 100 rpm, and treat for 20 min to obtain the desiliconizing agent.

[0042] Among them, the crystal growth promoter is prepared by mixing sodium pyrophosphate and aluminum isopropoxide in a mass ratio of 0.3:1. The mixed solution is prepared by mixing deionized water, ethylene glycol, and polyvinyl alcohol in a volume ratio of 1:1:0.2. The kaolin (model BR-5, average particle size 4.2 microns) is provided by Shanghai Kayin Chemical Co., Ltd. The premixed solution is obtained by mixing vinyltriethoxysilane, deionized water, and acetic acid in a mass-volume ratio of 1 g:1 ml:0.2 ml.

[0043] Preparation Example 2

[0044] Take 0.28 g of aluminum chloride, dropwise add 18.1 mL of 0.5 mol / L sodium hydroxide solution, then under ice bath conditions, add 0.4 g of tetraethyl orthosilicate to the system, adjust the magnetic stirring speed to 50 rpm, stir for 15 min, then add 0.25 g of the crystal growth promoter, continue to treat for 15 min, then add ammonia water to adjust the pH to 8.9, adjust the temperature to 82 °C, keep warm for 20 min, then add 30 ml of n-butanol, adjust the magnetic stirring speed to 100 rpm, keep the temperature constant at 87 °C for 8.5 h, then ultrasonically wash twice with absolute ethanol, adjust the pH to 7.8, then place it in an oven and dry at 45 °C, and finally grind for 2 min to obtain nano-sodalite.

[0045] Take 4.5 g of nano sodalite, add it to 30 ml of the mixed solution, adjust the magnetic stirring speed to 75 rpm. After dispersing for 8 min, add 0.3 g of citric acid and continue to process for 20 min. Then raise the temperature to 65 °C, add 0.25 g of 1,2-bis(triethoxysilyl)ethane, and process for 12 min. Then add an additional 1.1 g of 1,2-bis(triethoxysilyl)ethane, reduce the magnetic stirring speed to 35 rpm, react for 1.5 h, and then process the reaction solution for 15 min under ice bath conditions. Immediately centrifuge at 3000 rpm to obtain the bottom precipitate, wash the precipitate 3 times with hot absolute ethanol, dry it, and then grind it for 3 min to obtain modified nano sodalite.

[0046] Take 8.7 g of kaolin and mix it with 1.3 g of ammonium carbamate, grind for 12 min, then place it in a closed reaction kettle and treat it at 74 °C for 10 h. After that, slowly release the pressure to atmospheric pressure, collect the powder material, place it in 32 ml of acetone, and ultrasonically treat it at 30 °C for 11 min. Then add 1.8 ml of the premixed solution and process for 20 min. Then add 0.4 g of styrene monomer and 0.15 g of azobisisobutyronitrile to the system, adjust the temperature to 35 °C, and react for 20 min. Then filter to obtain the filtrate, wash it twice with alcohol, and dry it to obtain modified kaolin.

[0047] Take 27 g of modified kaolin and mix it with 7.2 g of modified nano sodalite, add it to 100 ml of n-butanol and ultrasonically disperse it. Then place the dispersion in a centrifuge, adjust the rotation speed to 2500 rpm and centrifuge at low speed for 30 min. Then transfer it to a constant temperature water bath and treat it at 72 °C for 2.5 h. Then filter to obtain the filter cake, wash it twice with hot absolute ethanol and then dry it. Finally, crush it and pass it through a 150-mesh sieve to obtain the active desiliconized powder.

[0048] Take 68 g of deionized water, 0.7 g of dispersant polyethylene glycol, 0.2 g of stabilizer sodium carboxymethyl cellulose, and 30 g of active desiliconized powder, adjust the magnetic stirring speed to 100 rpm, and process for 25 min to obtain the desiliconizing agent.

[0049] Among them, the crystal growth promoter is prepared by mixing sodium pyrophosphate and aluminum isopropoxide in a mass ratio of 0.3:1.2. The mixed solution is prepared by mixing deionized water, ethylene glycol, and polyvinyl alcohol in a volume ratio of 1:1.2:0.2. The kaolin (model BR-5, average particle size 4.2 microns) is provided by Shanghai Kayin Chemical Co., Ltd. The premixed solution is obtained by mixing vinyltriethoxysilane, deionized water, and acetic acid in a mass-volume ratio of 1.2 g:1 ml:0.25 ml.

[0050] Preparation Example 3

[0051] Take 0.28 g of aluminum chloride and gradually add 18.5 mL of 0.5 mol / L sodium hydroxide solution drop by drop. Then, under ice bath conditions, add 0.43 g of tetraethyl orthosilicate to the system, adjust the magnetic stirring speed to 50 rpm, stir for 15 min, then add 0.3 g of crystal growth promoter, continue to treat for 12 min, then add ammonia water to adjust the pH to 8.7, adjust the temperature to 83 °C, keep warm for 24 min, then add 30 ml of n-butanol, adjust the magnetic stirring speed to 100 rpm, keep the temperature constant at 87 °C for 9 h, then use absolute ethanol to wash ultrasonically for 2 times, adjust the pH to 7.6, then place it in an oven and dry at 50 °C, and finally grind for 2 min to obtain nano-sodalite.

[0052] Take 4.2 g of nano-sodalite, add it to 35 ml of the mixed solution, adjust the magnetic stirring speed to 85 rpm, disperse for 10 min, then add 0.5 g of acetic acid, continue to treat for 25 min, then raise the temperature to 70 °C, add 0.3 g of vinyltriethoxysilane, treat for 15 min, then add an additional 1.4 g of vinyltriethoxysilane, reduce the magnetic stirring speed to 35 rpm, react for 1.5 h, treat the reaction solution for another 15 min under ice bath conditions, immediately centrifuge at 3000 rpm to obtain the bottom precipitate, wash the precipitate 3 times with hot absolute ethanol, dry and then grind for 3 min to obtain modified nano-sodalite.

[0053] Take 9 g of kaolin and mix it with 1.4 g of ammonium carbamate, grind for 10 min, then place it in a closed reaction kettle and treat at 75 °C for 12 h. Then slowly release the pressure to atmospheric pressure, collect the powder material, place it in 30 ml of acetone, ultrasonically treat at 35 °C for 15 min, then add 2.1 ml of the premixed solution, treat for 25 min, then add 0.5 g of styrene monomer and 0.2 g of azobisisobutyronitrile to the system, adjust the temperature to 40 °C, react for 30 min, then filter to obtain the filtrate, wash with alcohol 3 times, and dry to obtain modified kaolin.

[0054] Take 28 g of modified kaolin and mix it with 7.8 g of modified nano-sodalite, add it to 120 ml of n-butanol for ultrasonic dispersion. Then place the dispersion in a centrifuge, adjust the rotation speed to 3000 rpm and centrifuge at low speed for 45 min. Subsequently, transfer it to a constant temperature water bath and treat at 75 °C for 3 h. Then filter to obtain the filter cake, wash it 3 times with hot absolute ethanol and then dry. Finally, pulverize it and pass through a 150-mesh sieve to obtain the active desiliconized powder.

[0055] Take 72 g of deionized water, 0.55 g of dispersant polyethylene glycol, 0.25 g of stabilizer sodium carboxymethyl cellulose, and 32 g of active desiliconized powder, adjust the magnetic stirring speed to 150 rpm, and treat for 20 min to obtain the desiliconizing agent.

[0056] Among them, the crystallization promoter is prepared by mixing sodium pyrophosphate and aluminum isopropoxide in a mass ratio of 0.3:1. The mixed solution is prepared by mixing deionized water, ethylene glycol, and polyvinyl alcohol in a volume ratio of 1:1.4:0.25. Kaolin (model BR-5, average particle size 4.2 microns) is provided by Shanghai Kayin Chemical Co., Ltd. The premixed solution is obtained by mixing vinyltriethoxysilane, deionized water, and acetic acid in a mass-volume ratio of 1 g:1 ml:0.3 ml.

[0057] Preparation Example 4

[0058] Take 0.28 g of aluminum chloride, and gradually add dropwise 18.7 mL of 0.5 mol / L sodium hydroxide solution. Then, under ice bath conditions, add 0.43 g of tetraethyl orthosilicate to the system, adjust the magnetic stirring speed to 75 rpm, stir for 20 min, then add 0.3 g of the crystallization promoter, and continue to process for 30 min. Then add ammonia water to adjust the pH to 8.7, adjust the temperature to 85 °C, and keep warm for 25 min. Then add 30 ml of n-butanol, adjust the magnetic stirring speed to 100 rpm, keep the temperature constant at 95 °C for 10 h, then wash ultrasonically with absolute ethanol 3 times, adjust the pH to 7.8, then place it in an oven at 50 °C to dry, and finally grind for 2 min to obtain nano-sodalite.

[0059] Take 5.5 g of nano-sodalite, add it to 35 ml of the mixed solution, adjust the magnetic stirring speed to 75 rpm, after dispersing for 10 min, add 0.45 g of acetic acid, and continue to process for 30 min. Then raise the temperature to 70 °C, add 0.5 g of vinyltrimethoxysilane, and process for 12 min. Then add an additional 1.5 g of vinyltrimethoxysilane, reduce the magnetic stirring speed to 35 rpm, react for 2 h, and then process the reaction solution for 20 min under ice bath conditions. Immediately centrifuge at 3500 rpm to take the bottom precipitate, wash the precipitate 3 times with hot absolute ethanol, dry and then grind for 4 min to obtain modified nano-sodalite.

[0060] Take 8.9 g of kaolin, mix it with 1.5 g of ammonium carbamate, grind for 12 min, then place it in a closed reaction kettle and treat it at 85 °C for 12 h. Then slowly release the pressure to atmospheric pressure, collect the powdered material, place it in 40 ml of acetone, ultrasonically treat it at 32 °C for 15 min, then add 2.3 ml of the premixed solution and process for 25 min. Then add 0.5 g of styrene monomer and 0.2 g of azobisisobutyronitrile to the system, adjust the temperature to 40 °C, and react for 30 min. Then filter to collect the filtrate, wash it 3 times with alcohol, and dry to obtain modified kaolin.

[0061] Take 28 g of modified kaolin, mix it with 8 g of modified nano sodalite, add it to 120 ml of n-butanol and disperse it by ultrasonic wave. Then place the dispersion liquid in a centrifuge, adjust the rotation speed to 3000 rpm and centrifuge at low speed for 45 min. Subsequently, transfer it to a constant temperature water bath and treat it at 75 °C for 2.5 h. Then filter it to obtain the filter cake, wash it 3 times with hot absolute ethanol and dry it. Finally, crush it and sieve it through a 150-mesh sieve to obtain the active desiliconized powder.

[0062] Take 75 g of deionized water, 0.75 g of dispersant polyethylene glycol, 0.3 g of stabilizer sodium carboxymethyl cellulose, and 37 g of active desiliconized powder, adjust the magnetic stirring speed to 200 rpm, and treat it for 30 min to obtain the desiliconizing agent.

[0063] Among them, the crystal growth promoter is prepared by mixing sodium pyrophosphate and aluminum isopropoxide in a mass ratio of 0.3:1. The mixed solution is prepared by mixing deionized water, ethylene glycol, and polyvinyl alcohol in a volume ratio of 1:1.2:0.3. The kaolin (model BR-5, average particle size 4.2 microns) is provided by Shanghai Kayin Chemical Co., Ltd. The premixed solution is obtained by mixing vinyltriethoxysilane, deionized water, and acetic acid in a mass-volume ratio of 1 g:1 ml:0.3 ml.

[0064] Preparation Example 5

[0065] Take 0.28 g of aluminum chloride, dropwise add 19.2 mL of 0.5 mol / L sodium hydroxide solution. Then, under ice bath conditions, add 0.43 g of tetraethyl orthosilicate to the system, adjust the magnetic stirring speed to 75 rpm, and stir for 20 min. Then add 0.4 g of the crystal growth promoter and continue to treat for 30 min. Then add ammonia water to adjust the pH to 8.9, adjust the temperature to 85 °C, and keep it warm for 25 min. Then add 30 ml of n-butanol, adjust the magnetic stirring speed to 100 rpm, keep it at a constant temperature of 95 °C for 10 h. Then wash it 3 times by ultrasonic wave with absolute ethanol, adjust the pH to 7.8, and then place it in an oven at 50 °C to dry. Finally, grind it for 2 min to obtain nano sodalite.

[0066] Take 5.5 g of nano sodalite, add it to 35 ml of the mixed solution, adjust the magnetic stirring speed to 100 rpm, disperse it for 10 min, then add 0.5 g of acetic acid and continue to treat for 30 min. Subsequently, raise the temperature to 70 °C, add 0.45 g of γ-aminopropyltriethoxysilane and treat for 10 min. Then add an additional 1.5 g of γ-aminopropyltriethoxysilane, reduce the magnetic stirring speed to 50 rpm, and react for 2 h. Then treat the reaction solution for 20 min under ice bath conditions. Immediately centrifuge at a high speed of 3500 rpm to obtain the bottom precipitate, wash the precipitate 3 times with hot absolute ethanol, dry it, and grind it for 5 min to obtain the modified nano sodalite.

[0067] Take 9 g of kaolin, mix it with 1.5 g of ammonium carbamate, grind for 20 min, then place it in a closed reaction kettle, treat it at 85 °C for 12 h, then slowly release the pressure to atmospheric pressure, collect the powder material, place it in 40 ml of acetone, ultrasonically treat it at 35 °C for 15 min, then add 2.3 ml of the premixed solution, treat for 25 min, then add 0.5 g of styrene monomer and 0.2 g of azobisisobutyronitrile to the system, adjust the temperature to 40 °C, react for 30 min, then filter to obtain the filtrate, wash it with alcohol 3 times, and dry it to obtain modified kaolin.

[0068] Take 30 g of modified kaolin, mix it with 8 g of modified nano-sodalite, add it to 120 ml of n-butanol and ultrasonically disperse it. Then place the dispersion in a centrifuge, adjust the rotation speed to 3000 rpm and centrifuge at low speed for 45 min. Subsequently, transfer it to a constant temperature water bath and treat it at 75 °C for 3 h. Then filter to obtain the filter cake, wash it 3 times with hot absolute ethanol and dry it. Finally, pulverize it and pass it through a 150-mesh sieve to obtain the active desiliconized powder.

[0069] Take 75 g of deionized water, 0.8 g of dispersant polyethylene glycol, 0.3 g of stabilizer sodium carboxymethyl cellulose, and 40 g of active desiliconized powder, adjust the magnetic stirring speed to 200 rpm, and treat for 30 min to obtain the desiliconizing agent.

[0070] Among them, the crystal growth promoter is prepared by mixing sodium pyrophosphate and aluminum isopropoxide in a mass ratio of 0.3:2. The mixed solution is prepared by mixing deionized water, ethylene glycol, and polyvinyl alcohol in a volume ratio of 1:1.5:0.3. The kaolin (model BR-5, average particle size 4.2 microns) is provided by Shanghai Kayin Chemical Co., Ltd. The premixed solution is obtained by mixing vinyltriethoxysilane, deionized water, and acetic acid in a mass-volume ratio of 1.5 g:1 ml:0.3 ml.

[0071] Example 1

[0072] Take 1000 g of fly ash, mix it with 45 g of fluorite and 1500 g of limestone, grind it and pass it through a 200-mesh sieve, bake it at 50 °C for 6 h, then calcine and ripen it at 1325 °C. Pulp the ripened material with a 15% sodium carbonate solution by mass, and treat the pulp liquid at 100 °C for 3 h, then filter to obtain the leaching slurry; add the desiliconizing agent to the leaching slurry at an addition amount of 35 g / L of the effective active desiliconized powder content, adjust the temperature to 65 °C, treat for 8 h and then filter again to obtain the carbonation stock solution; continuously introduce carbon dioxide into the carbonation stock solution, treat for 3 h, filter and then repulp it, keep it warm at 145 °C for 5 h. Then, according to the addition amount of 630 g / L of pure aluminum hydroxide, add aluminum hydroxide crystal seeds to the secondary pulp liquid, treat at 65 °C for 12 h, and then obtain the aluminum hydroxide raw residue after flash evaporation and filtration; take the raw residue and roast it in a high-temperature gas stream at 1075 °C for 3 h, naturally cool it and then pulverize it and pass it through a 100-mesh sieve to obtain the alumina product.

[0073] The above-mentioned desiliconizing agent was prepared according to Preparation Example 1.

[0074] Among them, the fly ash (industrial grade, Al2O3 wt%: 23.5%) was provided by Hunan Baolong Technology Development Co., Ltd.

[0075] Example 2

[0076] Take 1000 g of fly ash, mix 45 g of fluorite with 1500 g of limestone, grind them, pass through a 200-mesh sieve, bake at 50 °C for 6 h, then calcine and cure at 1350 °C. Pulp the cured material with a sodium carbonate solution with a mass fraction of 15%, treat the pulp liquid at 135 °C for 4 h, and then filter to obtain the leached slurry; add the desiliconizing agent to the leached slurry at an addition amount of 40 g / L of the effective active desiliconized powder content, adjust the temperature to 67 °C, filter again after treating for 8 h to obtain the carbonation stock solution; continuously introduce carbon dioxide into the carbonation stock solution, treat for 4 h, filter and then repulp, keep warm at 145 °C for 5 h, then add aluminum hydroxide seed crystals to the secondary pulp liquid according to the addition amount of 630 g / L of pure aluminum hydroxide, treat at 65 °C for 12 h, and then obtain the aluminum hydroxide crude residue after flash evaporation and filtration; take the crude residue and roast it in a high-temperature gas stream at 1075 °C for 5 h, naturally cool it, and then crush it through a 100-mesh sieve to obtain the alumina product.

[0077] The above-mentioned desiliconizing agent was prepared according to Preparation Example 2.

[0078] Among them, the fly ash (industrial grade, Al2O3 wt%: 23.5%) was provided by Hunan Baolong Technology Development Co., Ltd.

[0079] Example 3

[0080] Take 1000 g of fly ash, mix 45 g of fluorite with 1500 g of limestone, grind them, pass through a 200-mesh sieve, bake at 50 °C for 6 h, then calcine and cure at 1375 °C. Pulp the cured material with a sodium carbonate solution with a mass fraction of 15%, treat the pulp liquid at 135 °C for 4 h, and then filter to obtain the leached slurry; add the desiliconizing agent to the leached slurry at an addition amount of 30 g / L of the effective active desiliconized powder content, adjust the temperature to 65 °C, filter again after treating for 10 h to obtain the carbonation stock solution; continuously introduce carbon dioxide into the carbonation stock solution, treat for 4 h, filter and then repulp, keep warm at 150 °C for 6 h, then add aluminum hydroxide seed crystals to the secondary pulp liquid according to the addition amount of 630 g / L of pure aluminum hydroxide, treat at 70 °C for 14 h, and then obtain the aluminum hydroxide crude residue after flash evaporation and filtration; take the crude residue and roast it in a high-temperature gas stream at 1075 °C for 4 h, naturally cool it, and then crush it through a 100-mesh sieve to obtain the alumina product.

[0081] The above-mentioned desiliconizing agent was prepared according to Preparation Example 3.

[0082] Among them, the fly ash (industrial grade, Al2O3 wt%: 23.5%) was provided by Hunan Baolong Technology Development Co., Ltd.

[0083] Example 4

[0084] Take 1000 g of fly ash, mix it with 45 g of fluorite and 1500 g of limestone, grind it and then pass through a 200-mesh sieve, bake it at 50 °C for 6 h, then calcine and cure it at 1375 °C. Pulp the cured material with a sodium carbonate solution with a mass fraction of 15%, treat the pulp at 120 °C for 3.5 h, and then filter to obtain the leaching slurry; add a desilication agent to the leaching slurry according to the addition amount of 25 g / L of the effective active desiliconized powder content, adjust the temperature to 72 °C, filter again after 10 h of treatment to obtain the carbonation stock solution; continuously pass carbon dioxide into the carbonation stock solution, treat for 3 h, filter and then repulp, keep it warm at 150 °C for 6 h, then add aluminum hydroxide seed crystals to the secondary pulp according to the addition amount of 630 g / L of pure aluminum hydroxide, treat at 70 °C for 15 h, and then obtain the aluminum hydroxide crude residue after flash evaporation and filtration; take the crude residue and roast it in a high-temperature gas stream at 1075 °C for 3 h, naturally cool it and then crush it through a 100-mesh sieve to obtain the alumina product.

[0085] The above desilication agent was prepared from Preparation Example 4.

[0086] Among them, the fly ash (industrial grade, Al2O3 wt%: 23.5%) was provided by Hunan Baolong Technology Development Co., Ltd.

[0087] Example 5

[0088] Take 1000 g of fly ash, mix it with 45 g of fluorite and 1500 g of limestone, grind it and then pass through a 200-mesh sieve, bake it at 50 °C for 6 h, then calcine and cure it at 1375 °C. Pulp the cured material with a sodium carbonate solution with a mass fraction of 15%, treat the pulp at 135 °C for 4 h, and then filter to obtain the leaching slurry; add a desilication agent to the leaching slurry according to the addition amount of 24 g / L of the effective active desiliconized powder content, adjust the temperature to 72 °C, filter again after 10 h of treatment to obtain the carbonation stock solution; continuously pass carbon dioxide into the carbonation stock solution, treat for 4 h, filter and then repulp, keep it warm at 150 °C for 6 h, then add aluminum hydroxide seed crystals to the secondary pulp according to the addition amount of 630 g / L of pure aluminum hydroxide, treat at 65 °C for 15 h, and then obtain the aluminum hydroxide crude residue after flash evaporation and filtration; take the crude residue and roast it in a high-temperature gas stream at 1075 °C for 5 h, naturally cool it and then crush it through a 100-mesh sieve to obtain the alumina product.

[0089] The above desilication agent was prepared from Preparation Example 5.

[0090] Among them, the fly ash (industrial grade, Al2O3 wt%: 23.5%) was provided by Hunan Baolong Technology Development Co., Ltd.

[0091] Comparative Example 1

[0092] The difference between this comparative example and Example 1 is only that the preparation steps of the desilication agent are as follows:

[0093] Take 25 g of modified kaolin, mix it with 15 g of modified nano sodalite, add it to 100 ml of n-butanol and disperse it by ultrasonic wave. Then place the dispersion liquid in a centrifuge, adjust the rotation speed to 2500 rpm and centrifuge at low speed for 30 min. Subsequently, transfer it to a constant temperature water bath and treat it at 70 °C for 2.5 h. Then filter to obtain the filter cake, wash it twice with hot absolute ethanol and dry it. Finally, crush it and pass it through a 150-mesh sieve to obtain the active desilication powder.

[0094] Take 65 g of deionized water, 0.5 g of dispersant polyethylene glycol, 0.2 g of stabilizer sodium carboxymethyl cellulose, and 20 g of active desilication powder, adjust the magnetic stirring speed to 100 rpm, and treat it for 20 min to obtain the desilication agent.

[0095] All other steps are the same as those in Example 1.

[0096] Comparative Example 2

[0097] The difference between this comparative example and Example 1 is only that the desilication agent is lime milk with a calcium oxide content of 180 g / L.

[0098] All other steps are the same as those in Example 1.

[0099] Comparative Example 3

[0100] The difference between this comparative example and Example 1 is only that in the preparation steps of the modified kaolin in the desilication agent components: take 8.5 g of kaolin, mix it with 1.2 g of ammonium carbamate, grind it for 10 min, then place it in a closed reaction kettle and treat it at 75 °C for 10 h. Then slowly release the pressure to atmospheric pressure, collect the powder material, place it in 40 ml of acetone, ultrasonically treat it at 35 °C for 15 min, then add 2.3 ml of the premixed solution and treat it for 25 min. Then filter to obtain the collected material, wash it three times with alcohol, and dry it to obtain the modified kaolin.

[0101] All other steps are the same as those in Example 1.

[0102] Comparative Example 4

[0103] The difference between this comparative example and Example 1 is only that in the desilication agent components, the active desilication powder is directly obtained by mixing modified nano sodalite and untreated kaolin.

[0104] All other steps are the same as those in Example 1.

[0105] Performance detection test

[0106] Detection of alumina content

[0107] Referring to the national standards GB / T39201-2020 and GB / T6609.3-2004, take 2 g of the alumina products obtained from Examples 1-5 and Comparative Examples 1-4 as test samples. Respectively add them into 500 mL Erlenmeyer flasks containing EDTA standard solution, add 15 ml of hydrochloric acid standard solution, add hot water to a volume of about 80 ml, then heat and boil for 2 min, add 8 drops of phenolphthalein indicator, titrate with sodium hydroxide standard solution until it turns slightly red, then add 10 ml of acetic acid-sodium acetate buffer solution and 0.03 g of xylenol orange indicator, and titrate with zinc acetate standard solution until it turns purple-red, which is the end point. Finally, calculate the percentage content of alumina in the test sample according to the volume of zinc acetate standard solution used. Take three groups as the average value, and the test results are as Figure 1 shown.

[0108] Detection of silicon dioxide removal rate

[0109] Referring to the national standards GB / T39201-2020 and GB / T6609.3-2004, respectively take 10 ml of the digestion slurries and carbonization mother liquors obtained from Examples 1-5 and Comparative Examples 1-2, make up the volume to 100 ml with water, then add 5 ml of ammonium molybdate solution with a mass fraction of 5% respectively, shake well, and let it stand for color development. Then add 20 ml of sulfuric acid-oxalic acid-ferrous ammonium sulfate mixed solution respectively, dilute with water, shake well, and let it stand for 5 min. At a wavelength of 700 nm in a spectrophotometer, use a 1-cm colorimetric cell, zero with air as the reference, measure the absorbance, and obtain the content of silicon dioxide x1 in the digestion slurry and the content of silicon dioxide x2 in the carbonization mother liquor from the standard curve. According to the formula:

[0110] Silicon dioxide removal rate = [(x1 - x2) / x1] × 100%

[0111] Calculate the silicon dioxide removal rate, and the test results are as Figure 2 shown.

[0112] Among them, the steps for drawing the standard curve are as follows: Respectively transfer 0.00 ml, 1.00 ml, 2.00 ml, 3.00 ml, 4.00 ml, 5.00 ml, 6.00 ml of silicon dioxide standard solution (0.10 mg / mL) into 100 ml volumetric flasks, accurately add water to a volume of 60 ml, and carry out the determination according to the above steps to establish the standard curve.

[0113] Analyze Examples 1-5 and Comparative Examples 1-4 and combine with Figure 1-2 It can be seen that the extraction rate of alumina and the removal rate of silicon dioxide in the example solutions are both higher than those in the comparative example solutions. Among them, the product obtained from the solution of Example 2 has the highest purity of alumina and the highest removal rate of silicon dioxide, while the two data of the solution of Comparative Example 2 are at the lowest level among the example and comparative example groups.

[0114] Analyze Example 2 and Comparative Examples 1-4 and combine with Figure 1-2 It can be seen that in the solution of Comparative Example 3, the kaolin is not subjected to styrene grafting treatment, resulting in a decrease in the use effect of the desilication agent. This may be because, in the desilication agent solution, as the desilication process proceeds, the growth of sodalite crystal nuclei causes the kaolin to settle faster. The too-fast settlement causes the active components of the desilication agent to be separated from the dissolution slurry before being completely saturated, and finally leads to a decrease in the desilication effect of the solution. At the same time, it can be seen that the conventional lime milk used in the solution of Comparative Example 2 has a worse effect than the combination of modified nano-sodalite and modified kaolin.

[0115] This specific embodiment is only an interpretation of the present application and is not a limitation to the present application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions according to needs, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A method for extracting aluminum oxide from solid waste fly ash, characterized in that: The extraction of alumina is carried out in sequence through the steps of raw material burning and dissolution, dissolution slurry desiliconization, stock solution refining and crystallization, and roasting and decomposition; wherein the dissolution slurry desiliconization includes the following steps: adding a desiliconizing agent to the dissolution slurry, heating treatment, and filtering to obtain a carbon stock solution; The desiliconizing agent is prepared by mixing the following raw materials in parts by mass: 65-75 parts of deionized water, 30-40 parts of active desiliconizing powder, 0.5-0.8 parts of dispersant, and 0.2-0.3 parts of stabilizer, wherein the active desiliconizing powder is obtained by compounding modified nano-sodalite and modified kaolin through intercalation; The preparation steps of the modified nano-sodalite include the following: (1) Take aluminum chloride, add sodium hydroxide dropwise, put in an ice water bath, then add ethyl orthosilicate, stir, add a crystal promoter, continue stirring, then adjust the pH, heat up and then keep warm, heat up again after dispersion, filter and take the precipitate, wash with alcohol, readjust the pH, then dry and grind to obtain nano sodalite; (2) taking nano-sodalite, dispersing the mixture, adding an organic acid for treatment, adding a silane coupling agent after heating, continuing the treatment, then adding more silane coupling agent, reacting, then standing in an ice water bath, centrifuging to obtain a precipitate, washing with alcohol, drying and grinding, and obtaining modified nano-sodalite; The intercalation compounding step comprises the following steps: taking modified kaolin, mixing with modified nano-sodalite, dispersing, then centrifuging at a low speed, heating, filtering, washing with alcohol, drying, and crushing to obtain; The preparation steps of the modified kaolin include the following: taking kaolin, mixing and grinding with ammonium carbamate, then placing in a closed reactor for heat treatment, collecting powder material, dispersing, then adding premixed liquid, treating, adding styrene monomer and initiator, adjusting temperature and reaction time, and finally filtering the filtrate, washing with alcohol, and drying to obtain the modified kaolin.

2. The method for extracting alumina from solid waste fly ash according to claim 1, characterized in that: The mixing mass ratio of kaolin and ammonium carbamate is (8.5-9): (1.2-1.5); the heat treatment conditions are to adjust the temperature to 72-85° C. and treat for 10-12 hours.

3. The method for extracting aluminum oxide from solid waste fly ash according to claim 1, characterized in that: The premixed liquid is obtained by mixing vinyl triethoxysilane, deionized water and acetic acid in a mass volume ratio of (1-1.5) g:1 ml:(0.2-0.3) ml; the initiator is azobisisobutyronitrile, the temperature is adjusted to 35-40° C., and the reaction time is 20-30 min.

4. The method for extracting aluminum oxide from solid waste fly ash according to claim 1, characterized in that: In the step (1), the molar ratio of aluminum chloride, sodium hydroxide and tetraethyl orthosilicate added is 1:(4-4.6):(0.85-1).

5. The method for extracting alumina from solid waste fly ash according to claim 1, characterized in that: In the step (1), the crystal-growing agent is prepared by mixing sodium pyrophosphate and aluminum isopropoxide in a mass ratio of 0.3:(1-2).

6. The method for extracting aluminum oxide from solid waste fly ash according to claim 1, characterized in that: In the step (2), the mixed liquid is prepared by mixing deionized water, ethylene glycol and polyvinyl alcohol in a volume ratio of 1:(1-1.5):(0.2-0.3); the organic acid is one of tartaric acid, citric acid and acetic acid.

7. The method for extracting aluminum oxide from solid waste fly ash according to claim 1, characterized in that: In the step (2), the silane coupling agent is one of 1,2-bis(triethoxysilyl)ethane, vinyltrimethoxysilane, γ-aminopropyltriethoxysilane and vinyltriethoxysilane.

8. The method for extracting aluminum oxide from solid waste fly ash according to claim 1, characterized in that: In the step (2), the mass ratio of the first added silane coupling agent to the additional added silane coupling agent is (0.2-0.5): (1-1.5).

9. The method for extracting aluminum oxide from solid waste fly ash according to claim 1, characterized in that: In the intercalation composite step, the mass ratio of modified kaolin to modified nano-sodalite is (25-30): (7-8).

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