A method for preparing high-purity alumina based on secondary aluminum ash activated by calcium peroxide.

Abstract

This invention discloses a method for preparing high-purity alumina from secondary aluminum ash activated by calcium peroxide. The method includes mixing secondary aluminum ash with an activation additive at a mass ratio of 100:3 to 100:10, and calcining at 1100 to 1300°C for 1 to 4 hours to obtain activated calcined ash. The activation additive contains calcium peroxide with a mass fraction of not less than 50%. During calcination, the active oxygen released from the decomposition of calcium peroxide oxidizes AlN in the secondary aluminum ash, and the generated CaO reacts with fluorides to form CaF2. CaO undergoes a solid-state reaction with MgAl2O4, destroying the spinel structure of MgAl2O4 and Ca... 2+ The embedding of Al2O3 in the crystal lattice causes Al2O3 lattice distortion. This invention adopts a coupled process route of "fire method followed by wet method", which eliminates the water washing / hydrolysis pretreatment unit with large water consumption in the prior art, reducing the amount of wastewater generated from the source (about 60% less than conventional processes), making the process flow simpler, and solving the problems of large water consumption and high salt wastewater generation in the hydrolysis / washing process in the existing process.

Description

Technical Field

[0001] This invention belongs to the field of solid waste treatment and resource utilization technology, and specifically relates to a method for preparing high-purity alumina from secondary aluminum ash activated by calcium peroxide. Background Technology

[0002] Secondary aluminum dross (SAD) is a hazardous waste (HW48) generated during aluminum profile processing and aluminum recycling. Its phase composition is complex, containing multiple components such as AlN, NaF, AlF3, and MgAl2O4, and is also enriched with heavy metals such as Ni, Pb, and As. It has both significant hazardous characteristics and resource recycling value.

[0003] In existing technologies for preparing alumina from secondary aluminum ash, a patent (such as CN201910733547.5) has reported a process route of "hydrothermal / alkali dissolution detoxification pretreatment → acid / alkali leaching selective aluminum dissolution → purification precipitation → calcination". This technology removes AlN and soluble salts through hydrothermal or alkali dissolution pretreatment, and then combines alkali leaching or acid leaching to achieve selective extraction of aluminum, finally producing high-purity alumina with a purity ≥99.5%. However, this process still has the following shortcomings: (1) The hydrothermal or alkali dissolution pretreatment process consumes a large amount of water and is prone to generating high-salt wastewater; (2) MgAl2O4 (magnesium aluminum spinel) has extremely stable chemical properties, and conventional acid leaching or alkali leaching is difficult to effectively dissolve it, which limits the overall aluminum recovery rate; (3) The pretreatment and leaching processes are independent of each other, the process flow is long, and the overall efficiency needs to be improved.

[0004] In recent years, Huang Kaihua et al. (publication number CN119430251A) proposed a method for efficient detoxification of secondary aluminum ash and simultaneous extraction of high-purity alumina, the technical route of which is "hydrolysis + alkaline roasting + leaching". In this method, modified calcium oxide and glucose are introduced during the hydrolysis process to inhibit the formation and coating of calcium aluminate on the surface of alumina during the hydrolysis of calcium oxide. The hydrolysis denitrification rate reaches more than 97%, and the alumina leaching rate reaches more than 94%. However, this technology still has the following shortcomings: (1) the hydrolysis process still consumes a lot of water resources, and the problem of high-salt wastewater has not been fundamentally solved; (2) the reaction time of the hydrolysis process is long, and the treatment efficiency is limited; (3) no efficient destruction scheme for the spinel structure of MgAl2O4 is involved; (4) the purity index of the final product is not clearly defined.

[0005] It is worth noting that MgAl2O4, as a phase with a stable spinel structure, is almost insoluble under conventional acid and alkaline conditions, posing a key bottleneck to the efficient recovery of aluminum resources from secondary aluminum ash. Currently, existing technologies have not proposed an effective solution to address the structural damage of MgAl2O4. Summary of the Invention

[0006] The purpose of this application is to overcome the above-mentioned deficiencies of the prior art and provide a method for preparing high-purity alumina based on secondary aluminum ash activated by calcium peroxide. By adding calcium peroxide (CaO2) or a mixture of CaO2 and Na2CO3 as an activating additive, the method achieves efficient destruction of the spinel structure of MgAl2O4 and lattice activation of the aluminum phase during high-temperature calcination, significantly improving the acid leaching rate of aluminum, and obtaining high-purity alumina products through deep purification.

[0007] To achieve the aforementioned objectives, this application provides a method for preparing high-purity alumina from secondary aluminum ash activated by calcium peroxide. The method includes mixing secondary aluminum ash with an activation additive at a mass ratio of 100:3 to 100:10, and calcining at 1100 to 1300°C for 1 to 4 hours to obtain activated calcined ash. The activation additive contains calcium peroxide with a mass fraction of not less than 50%. During calcination, the active oxygen released from the decomposition of calcium peroxide oxidizes AlN in the secondary aluminum ash, and the generated CaO reacts with fluorides to form CaF2, undergoes a solid-state reaction with MgAl2O4 to destroy the spinel structure of MgAl2O4, and reacts with Ca... 2+ The embedding of Al2O3 into the Al2O3 lattice causes Al2O3 lattice distortion.

[0008] This invention addresses the problems of existing secondary aluminum ash resource recovery technologies, such as difficulty in destroying the MgAl2O4 spinel structure, low aluminum recovery rate, and large wastewater generation. It proposes a coupled "fire-first, wet-second" process. First, secondary aluminum ash is mixed with the activating additive calcium peroxide (CaO2) or a mixture of CaO2 and Na2CO3, and calcined at 1100-1300℃. The active oxygen released from the decomposition of CaO2 enhances the oxidative decomposition of AlN (denitrification rate >99.5%). Simultaneously, CaO reacts with fluorides to generate CaF2, achieving in-situ solidification of fluorine (solidification rate >95%). CaO undergoes a solid-phase reaction with MgAl2O4, destroying the MgAl2O4 spinel structure. 2+ The embedding of Al2O3 into the lattice causes Al2O3 lattice distortion and defects, which significantly improves the acid reactivity of the aluminum phase.

[0009] Preferably, the method for preparing high-purity alumina based on secondary aluminum ash activated by calcium peroxide according to the present invention specifically includes the following steps: S1: Calcium peroxide activation calcination; secondary aluminum ash and activation additives are mixed at a mass ratio of 100:3~100:10 and calcined at 1100~1300℃ for 1~4h to obtain activated calcined ash; the activation additives contain calcium peroxide with a mass fraction of not less than 50%; S2: Acid leaching; The activated calcined ash obtained in S1 is leached with an acid solution, and the acid leaching solution is obtained by separation; S3: Iron removal; adjusting the pH of the acid leaching solution obtained in S2 to Fe...3+ Within the range of hydrolysis precipitation, ferric hydroxide precipitate is removed by filtration; S4: Precipitate aluminum; adjust the pH of the filtrate obtained from S3 to Al. 3+ Aluminum hydroxide filter cake was obtained by filtration within the range of aluminum hydroxide precipitation. S5: Alkali dissolution; The aluminum hydroxide filter cake obtained in S4 is dissolved in an alkaline solution to obtain an aluminate solution; S6: Carbon precipitation; Carbon dioxide is bubbled into the aluminate solution obtained in S5 to precipitate aluminum hydroxide precipitate; S7: Purification; The aluminum hydroxide precipitate obtained in S6 is washed and / or ion-exchanged to obtain the purified aluminum hydroxide precursor. S8: Calcination; The aluminum hydroxide precursor obtained in S7 is calcined to obtain high-purity aluminum oxide.

[0010] The specific preparation process described above involves activated calcined ash undergoing sulfuric acid leaching (Al leaching rate 98.5%), neutralization to remove iron, precipitation of Al(OH)3, alkaline dissolution to extract aluminum, and carbon precipitation. Following this, it undergoes deep purification (water washing-acid washing-ion exchange) and high-temperature calcination to obtain a high-purity alumina product. This invention eliminates the water-intensive pretreatment unit, reducing wastewater generation by approximately 60%. The overall aluminum recovery rate reaches over 85%, and the deep purification step effectively removes Na entrained in the Al(OH)3 precipitate. + Ca² + Mg² + Fe³ + The removal of impurity ions increases the purity of the final product, Al2O3, to over 99.5%, meeting the high-purity alumina standard (YS / T 89-2011). This allows for applications in high-end ceramics, sapphire substrates, and lithium-ion battery separator coatings. Simultaneously, the carbon mother liquor can be recycled, with an alkali recycling rate exceeding 85%, effectively reducing reagent consumption and operating costs. The resulting acid leaching residue can be used in building material production, realizing the full resource utilization of secondary aluminum ash.

[0011] The present invention generates low levels of pollutants during the treatment process, is environmentally friendly, and conforms to the concepts of green environmental protection and circular economy.

[0012] Preferably, the activating additive is calcium peroxide or a mixture of calcium peroxide and sodium carbonate. The activating additive is calcium peroxide (CaO2), and the amount added is 4% to 7% of the mass of the secondary aluminum ash, more preferably 5%. Even more preferably, the activating additive is a mixture of calcium peroxide and sodium carbonate, wherein the mass ratio of calcium peroxide to sodium carbonate is (1~3):1, and the total amount added is 5% to 10% of the mass of the secondary aluminum ash.

[0013] During the calcination process, the activating additives exert the following synergistic effects: ① Oxidative decomposition: CaO2 decomposes at high temperature to generate CaO and active oxygen (2CaO2→ 2CaO + O2↑). The released active oxygen enhances the oxidative decomposition of AlN (4AlN + 3O2→ 2Al2O3+ 2N2↑), thereby improving denitrification efficiency. ② Fluoride curing: The CaO generated from the decomposition reacts with the fluorides (NaF, AlF3) in the aluminum ash to form stable CaF2 (CaO + 2NaF → CaF2 + Na2O; 3CaO + 2AlF3 → 3CaF2 + Al2O3), thus achieving in-situ curing of the fluorides; ③ Spinel structure destruction: CaO reacts with MgAl2O4, destroying its stable spinel structure and releasing Al2O3 (CaO + MgAl2O4 → CaAl2O4 + MgO). ④ Lattice activation and defect engineering: Ca² + It enters the Al2O3 lattice, causing lattice distortion and defects, increasing surface active sites, and significantly improving the reactivity of the aluminum phase in the subsequent acid leaching process; ⑤ Synergistic effect of sodium carbonate: When Na2CO3 is added, Na2CO3 reacts with Al2O3 at high temperature to generate soluble sodium aluminate (NaAlO2), which further promotes the transformation and activation of the aluminum phase.

[0014] Preferably, the calcination temperature in S1 is 1150~1250℃, more preferably 1200℃. At this temperature, the decomposition rate of CaO2 and the activity of CaO are optimally balanced, ensuring sufficient decomposition while avoiding excessive growth of CaO particles that would lead to a decrease in activity, and avoiding energy waste and CaO sintering caused by excessively high temperatures.

[0015] Preferably, the acid solution in S2 is a sulfuric acid solution with a concentration of 3-5 mol / L; the alkali solution in S5 is a NaOH solution with a concentration of 3-5 mol / L. The sulfuric acid concentration is preferably 3.5-4.5 mol / L, more preferably 4 mol / L; the reaction temperature is preferably 90-100℃, more preferably 95℃; the reaction time is preferably 2-3 h, more preferably 2.5 h; and the liquid-to-solid ratio is preferably (4.5-5.5):1, more preferably 5:1. The NaOH concentration is preferably 3.5-4.5 mol / L, more preferably 4 mol / L; the reaction temperature is preferably 80-90℃, more preferably 85℃; the reaction time is preferably 1.2-1.8 h, more preferably 1.5 h; and the liquid-to-solid ratio is preferably (3.5-4.5):1, more preferably 4:1.

[0016] This invention achieves deep separation of aluminum and impurities through the dual selective dissolution of aluminum by acid leaching and alkali dissolution, laying the foundation for the final preparation of high-purity alumina with a purity of ≥99.5%.

[0017] Preferably, the CO2 flow rate in step S6 is 1.0~2.0 L / min, more preferably 1.5 L / min; the reaction temperature is 40~60℃, more preferably 50℃; and the endpoint pH is 7.3~7.8, more preferably 7.5. In step S6 (carbon precipitation), controlling the CO2 flow rate, reaction temperature, and endpoint pH within specific ranges aims to efficiently and purely precipitate Al(OH)3 from sodium aluminate solution NaAl(OH)4, while minimizing impurity entrainment and secondary contamination.

[0018] Preferably, the purification in S7 includes: washing the aluminum hydroxide precipitate obtained in S6 with deionized water until the conductivity of the washing solution is <10 μS / cm, then acid washing with dilute hydrochloric acid (0.1~0.5 mol / L) or dilute nitric acid (0.1~0.5 mol / L), and then washing with deionized water until neutral. The purification in S7 also includes: redissolving the acid-washed aluminum hydroxide in dilute hydrochloric acid or dilute nitric acid, adjusting the pH to 2~3, performing ion exchange to remove impurities using a cation exchange resin column, then adjusting the pH to 7.5~8.0 with alkali to redefine aluminum hydroxide, and obtaining a high-purity Al(OH)3 precursor after washing.

[0019] In step S7, the series of meticulous operations—"water washing-acid washing-redissolving-ion exchange-reprecipitation"—can remove trace impurities (especially Na) that are difficult to remove by conventional methods. + Fe³ + Ca² + (etc.) are reduced to the ppm level, thereby ensuring that the final alumina product meets the high purity standard.

[0020] Preferably, the pH range for aluminum precipitation in S4 is 7.5~8.0, and the final pH range for carbon precipitation in S6 is 7.0~8.0. Through precise pH control, S4 and S6 achieve efficient aluminum precipitation and deep separation of impurities at different process nodes.

[0021] Preferably, the calcination temperature in step S8 is 1100~1300℃, and the calcination time is 1~3h. Further, the calcination temperature is preferably 1150~1250℃, more preferably 1200℃; the calcination time is preferably 1.5~2.5h, more preferably 2h. Step S8 employs a calcination process of 1200℃+2h, achieving a complete and efficient conversion of high-purity Al(OH)3 precursor to high-purity α-Al2O3, ensuring that the final product meets the technical requirements of YS / T 89-2011 standard: Al2O3 purity ≥99.5%, α-phase crystal form, and excellent physical properties (particle size, specific surface area, whiteness).

[0022] The high-purity alumina prepared by this invention has high purity, with Al2O3 purity ≥ 99.5%, Na2O content ≤ 100 ppm, Fe2O3 content ≤ 50 ppm, SiO2 content ≤ 50 ppm, CaO content ≤ 50 ppm, and MgO content ≤ 50 ppm.

[0023] Compared with the prior art, this application has the following technical effects: 1. This invention is the first to propose calcium peroxide (CaO2) as an activation additive for secondary aluminum ash calcination. Utilizing the high-temperature decomposition of CaO2 to release active oxygen, it enhances the oxidative decomposition of AlN. The decomposed CaO solidifies fluorides (solidification rate >95%). CaO disrupts the spinel structure of MgAl2O4, solving the key technical problems of difficult dissolution of MgAl2O4 and limited aluminum recovery rate in existing technologies. + Ingress into the Al2O3 lattice causes distortion and defects, increasing the number of surface active sites; when Na2CO3 is added, soluble sodium aluminate can also be generated, further promoting the transformation of the aluminum phase.

[0024] 2. This invention adopts a coupled process route of "fire method followed by wet method", which eliminates the water washing / hydrolysis pretreatment unit with large water consumption in the prior art, reduces the amount of wastewater generated from the source (about 60% less than conventional process), and the process flow is simpler. It solves the problems of large water consumption and high salt wastewater generation in the hydrolysis / washing process in the existing process.

[0025] 3. This invention effectively removes Na entrained in Al(OH)3 precipitate by adding a deep purification step (washing with deionized water, acid washing, ion exchange, etc.). + Ca 2+ Mg 2+ Fe 3+ The presence of impurity ions increases the purity of the final product Al2O3 to over 99.5%, meeting the 99.5% requirement of the high-purity alumina standard (YS / T 89-2011). This allows it to be applied in high-end fields such as high-end ceramics, sapphire substrates, and lithium battery separator coatings. Attached Figure Description

[0026] Figure 1 This is a process flow diagram of the preparation of high-purity alumina based on secondary aluminum ash activated by calcium peroxide according to the present invention. Detailed Implementation

[0027] To enable those skilled in the art to better understand the present invention, the present invention will now be further described in conjunction with specific embodiments.

[0028] In the following description, the embodiments of this application are for illustrative purposes and not for limiting purposes, so as to provide a thorough understanding of the embodiments. However, those skilled in the art will understand that the embodiments of this application can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known preparation methods have been omitted so as not to obscure the description of the embodiments of this application with unnecessary details. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available.

[0029] It should also be understood that the terms "comprising," "including," "having," and their variations all mean "including but not limited to," unless otherwise specifically emphasized. Only content related to the inventive points is described here; other details can be obtained from related technologies and will not be elaborated further here. The following embodiments merely illustrate several implementations of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

[0030] The specific implementation method is as follows: like Figure 1 As shown, after secondary aluminum ash is mixed with calcium peroxide (CaO2) or a mixture of CaO2 and Na2CO3, it is subjected to calcium-based activation calcination (1100-1300℃) to achieve efficient decomposition of AlN (denitrification rate >99.5%), in-situ solidification of fluorides (solidification rate >95%), destruction of the spinel structure of MgAl2O4, and Ca²⁺. + Lattice doping activation; the activated calcined ash is sequentially subjected to acid leaching (H2SO4), neutralization to remove iron, precipitation of Al(OH)3, alkali dissolution to extract aluminum (NaOH), and carbon precipitation (CO2), followed by deep purification (deionized water washing-acid washing-ion exchange-reprecipitation) and high-temperature calcination (1100-1300℃) to obtain high-purity alumina product (Al2O3≥99.5%). The carbon mother liquor is returned to the alkali dissolution process for recycling, achieving an alkali recycling rate of over 85%.

[0031] Example 1: This embodiment provides a method for preparing high-purity alumina based on secondary aluminum ash activated by calcium peroxide, including the following steps: (1) Activated calcination of calcium peroxide: 1000g of secondary aluminum ash (aluminum content 32.0%) produced by an aluminum profile processing enterprise in Guangdong Province was mixed evenly with 50g of CaO2 and placed in a muffle furnace for calcination at 1200℃ for 2h to obtain activated calcined ash. The AlN removal rate was >99.5% and the fluoride curing rate was >95%.

[0032] (2) Acid leaching for impurity removal: The activated calcined ash obtained in step (1) was added to a 4 mol / L sulfuric acid solution and stirred at 95°C for 2.5 h with a liquid-to-solid ratio of 5:1. After the reaction was completed, the mixture was filtered to separate the acid leaching solution and the acid leaching residue. The Al leaching rate was found to be 98.5%.

[0033] (3) Neutralization and iron removal: Adjust the pH of the acid leaching solution obtained in step (2) to 4.5~5.0 to neutralize Fe³⁺. + The precipitate is obtained by hydrolysis and is then removed by filtration.

[0034] (4) Precipitate Al(OH)3: Adjust the pH of the filtrate obtained in step (3) to 7.5~8.0, so that Al³⁺ precipitates. + The precipitate is formed as Al(OH)3, and the filter cake is obtained by filtration.

[0035] (5) Alkali dissolution for aluminum extraction: The Al(OH)3 filter cake obtained in step (4) was added to a 4 mol / L NaOH solution and stirred at 85°C for 1.5 h with a liquid-to-solid ratio of 4:1 to generate a sodium aluminate solution. The Al dissolution rate was found to be 97.6%.

[0036] (6) Carbon precipitation: CO2 gas was introduced into the sodium aluminate solution obtained in step (5) at a flow rate of 1.5 L / min, and the reaction was carried out at 50 °C. The final pH was controlled to be 7.5, so that Al precipitated out as Al(OH)3. The Al(OH)3 precipitate was obtained by filtration. The Al precipitation rate was found to be 99.3%.

[0037] (7) Deep purification: The Al(OH)3 precipitate obtained in step (6) was repeatedly washed with deionized water until the conductivity of the washing solution was <10 μS / cm. Then, it was acid-washed with 0.2 mol / L dilute hydrochloric acid at 60℃ for 30 min with stirring. After acid washing, it was washed with deionized water until neutral. To further improve the purity, the acid-washed Al(OH)3 was redissolved in dilute hydrochloric acid (pH=2.5) and passed through an ion exchange column packed with cation exchange resin (flow rate 2~3 times resin volume / hour) to remove residual Na. + Ca² + Mg² + Fe³ +Impurity ions were removed. The effluent was collected, and the pH was adjusted to 7.5-8.0 with ammonia to cause Al(OH)3 to redefine and precipitate. The effluent was then washed with deionized water until neutral to obtain a high-purity Al(OH)3 precursor.

[0038] (8) High-temperature calcination: The high-purity Al(OH)3 precipitate obtained in step (7) is calcined at 1200℃ for 2 hours to obtain a high-purity alumina product.

[0039] The overall aluminum recovery rate for the entire process is 87.6%. The overall aluminum recovery rate for the entire process refers to the percentage of aluminum that is effectively recovered into the final product from the initial aluminum-containing raw materials to the final target product, relative to the total mass of aluminum in the raw materials.

[0040] The purity analysis results of the product, obtained by XRF and ICP-MS testing, are shown in Table 1 below: Table 1 Example 2: This embodiment provides a method for preparing high-purity alumina based on secondary aluminum ash activated by calcium peroxide, including the following steps: (1) Activated calcination of calcium peroxide: Take 1000g of secondary aluminum ash, mix it evenly with 40g of CaO2 and 20g of Na2CO3 (CaO2:Na2CO3=2:1), and calcine at 1200℃ for 2h to obtain activated calcined ash.

[0041] (2)~(6) Same as Example 1.

[0042] (7) Deep purification: The same deep purification steps as in Example 1 were used (washing with deionized water → acid washing → ion exchange → reprecipitation).

[0043] (8) High-temperature calcination: Same as in Example 1.

[0044] XRF and ICP-MS tests showed that the purity of Al2O3 was 99.58%, the Na2O content was 58 ppm, the Fe2O3 content was 25 ppm, the SiO2 content was 32 ppm, the CaO content was 20 ppm, and the MgO content was 16 ppm, all of which met the 99.5% requirement of the high-purity alumina standard (YS / T 89-2011).

[0045] The overall aluminum recovery rate for the entire process was 84.8%.

[0046] Example 3: This embodiment provides a relatively simplified deep purification scheme, suitable for scenarios where the purity requirement is slightly lower but still needs to reach 99.5%. (1)~(6) Same as Example 1.

[0047] (7) Deep purification: The Al(OH)3 precipitate obtained in step (6) is repeatedly washed with deionized water until the conductivity of the washing solution is <10μS / cm. Then, it is acid washed with 0.2mol / L dilute hydrochloric acid at 60℃ for 30min. After acid washing, it is washed with deionized water until neutral. The acid washing-water washing is repeated 2~3 times to obtain high-purity Al(OH)3 precursor.

[0048] (8) High-temperature calcination: Same as in Example 1.

[0049] XRF and ICP-MS analysis showed that the Al2O3 purity was 99.52%, Na2O content was 85 ppm, Fe2O3 content was 42 ppm, SiO2 content was 48 ppm, CaO content was 35 ppm, and MgO content was 28 ppm, meeting the 99.5% requirement of the high-purity alumina standard (YS / T 89-2011). The overall aluminum recovery rate for the entire process was 86.5%.

[0050] Example 4: This embodiment provides a technical solution at a relatively low calcination temperature (1150℃). It includes the following steps: (1) Activated calcination of calcium peroxide: Take 1000g of the same secondary aluminum ash as in Example 1, add 40g of CaO2 and 10g of Na2CO3 (total addition 5%, CaO2:Na2CO3=4:1), mix evenly, and calcine at 1150℃ for 3h to obtain activated calcined ash. The AlN removal rate was 96.5%, and the fluoride curing rate was 90%.

[0051] (2) Acid leaching: Same as in Example 1 (4 mol / L H2SO4, 95℃, 2.5h, liquid-solid ratio 5:1). The measured Al leaching rate was 95.2%.

[0052] (3) Neutralization and iron removal: Same as in Example 1 (adjust pH to 4.5~5.0, filter).

[0053] (4) Precipitate Al(OH)3: Same as in Example 1 (adjust pH to 7.5~8.0).

[0054] (5) Alkali dissolution: Same as in Example 1 (4 mol / L NaOH, 85℃, 1.5h, liquid-solid ratio 4:1). Al dissolution rate 95.8%.

[0055] (6) Carbon precipitation: Same as in Example 1 (CO2 1.5 L / min, 50℃, endpoint pH=7.5). Al precipitation rate 98.5%.

[0056] (7) Deep purification: The simplified scheme of Example 3 was adopted (water washing → acid washing 2~3 times).

[0057] (8) High-temperature calcination: Same as in Example 1 (1200℃, 2h).

[0058] XRF and ICP-MS analysis showed that the Al2O3 purity was 99.53%, Na2O content was 88 ppm, Fe2O3 content was 45 ppm, SiO2 content was 48 ppm, CaO content was 42 ppm, and MgO content was 29 ppm, meeting the 99.5% requirement of the high-purity alumina standard (YS / T 89-2011). The overall aluminum recovery rate for the entire process was 84.5%.

[0059] Example 5: This embodiment provides a technical solution with a high calcium peroxide ratio (CaO2:Na2CO3=5:1), including the following steps: (1) Activated calcination of calcium peroxide: 1000g of secondary aluminum ash was mixed with 50g of CaO2 and 10g of Na2CO3 (total addition amount 6%, CaO2:Na2CO3=5:1) and calcined at 1200℃ for 2h to obtain activated calcined ash. The AlN removal rate was >99.5% and the fluoride curing rate was 96.5%.

[0060] (2)~(6) Same as Example 1.

[0061] (7) Deep purification: The same complete purification steps as in Example 1 were used (washing with deionized water → acid washing → ion exchange → reprecipitation).

[0062] (8) High-temperature calcination: Same as in Example 1.

[0063] XRF and ICP-MS analysis showed that the Al2O3 purity was 99.68%, Na2O content was 55 ppm, Fe2O3 content was 22 ppm, SiO2 content was 28 ppm, CaO content was 18 ppm, and MgO content was 14 ppm, meeting the 99.5% requirement of the high-purity alumina standard (YS / T 89-2011). The overall aluminum recovery rate for the entire process was 86.2%.

[0064] Comparative Example 1: Without calcium peroxide activation and calcination, direct acid leaching is performed. The specific steps include: (1) Activation and calcination omitted: 1000g of secondary aluminum ash was directly reacted with 4 mol / L H2SO4 at 95℃ (liquid-solid ratio 5:1, 2.5h).

[0065] Phenomenon: The reaction is violent, producing a large amount of NH3 (with a pungent odor), and the solution foams severely.

[0066] Test results: Al leaching rate was only 62.3% (due to unconverted AlN and fluoride encapsulation hindering leaching).

[0067] (2) Neutralization and iron removal: Same as in Example 1, but with greater loss of Al in the filtrate.

[0068] (3) Precipitate Al(OH)3, dissolve in alkali, carbonize, purify (same as the simplified scheme in Example 3), and calcine in the same way as in Example 1.

[0069] XRF and ICP-MS analysis showed that the Al2O3 purity was 85.2%, far below the 99.5% standard. Major impurities included: Na2O 1.8%, Fe2O3 0.65%, SiO2 0.85%, CaO 0.42%, MgO 0.35%, and approximately 0.58% fluoride residue. The overall aluminum recovery rate for the entire process was 48.6%.

[0070] It is known that without activation by calcium oxide, AlN hydrolysis / acidification produces NH3 and reduces the leaching rate, fluorides do not solidify, impurities are difficult to remove, and the requirements for high-purity alumina cannot be met.

[0071] Comparative Example 2: The amount of calcium peroxide used was too low.

[0072] The specific steps are as follows: (1) Calcium peroxide calcination: 1000g of secondary aluminum ash + 10g of CaO2 (mass ratio 100:1, lower than 100:3), mixed and calcined at 1200℃ for 2h.

[0073] Test results: AlN removal rate 68.5%, fluoride curing rate 52%.

[0074] (2)~(8) Same as Example 1 (including complete deep purification process).

[0075] Problems encountered: The acid leaching still produced a noticeable NH3 odor, and the Al leaching rate was only 78.3%. Some fluoride entered the leachate, causing subsequent precipitation to carry CaF2, increasing the difficulty of purification.

[0076] Final product purity: Al2O3 90.5%, not meeting the 99.5% purity requirement; main impurities include: Na2O 1.2%, Fe2O3 0.48%, SiO2 0.52%, CaO 0.35%, MgO 0.28%, and fluoride residue approximately 0.32%. Overall aluminum recovery rate: 65.2%.

[0077] Insufficient calcium peroxide dosage fails to effectively destroy AlN and MgAl2O4, and also fails to fully solidify fluorides, resulting in substandard leaching rate and purity.

[0078] Comparative Example 3: Compared with Example 1, the activating additives were changed to 25% CaO2 and 75% Na2CO3 (i.e., the mass fraction of CaO2 was only 25%), and the total amount added was still 5% of the mass of the secondary aluminum ash (i.e., 1000g aluminum ash + 12.5g CaO2 + 37.5g Na2CO3).

[0079] The specific steps are as follows: (1) Activation and calcination: Same as above, calcined at 1200℃ for 2h. The AlN removal rate was measured to be 71.3%, and the fluoride curing rate was 48.6%.

[0080] (2) Acid leaching: Same as in Example 1. During acid leaching, obvious bubbles and ammonia were released. Unreacted AlN was hydrolyzed by acid to produce NH3. The Al leaching rate was 76.8%.

[0081] (3) Neutralization and iron removal: Same as Example 1. Because the leachate has a high fluoride content, some of the fluoride reacts with Ca during pH adjustment. 2+ (Calcium residue from acid leaching residue or solution) forms fine CaF2 suspensions that are difficult to filter.

[0082] (4) Precipitation of Al(OH)3: Same as Example 1. The aluminum hydroxide precipitate contained CaF2 and unwashed Na. + The filter cake is slightly grayish in color.

[0083] (5) Alkali dissolution for aluminum extraction: Same as Example 1. Al leaching rate 82.3%. The amount of alkali-soluble residue is significantly greater than in Example 1.

[0084] (6) Carbon precipitation: Same as Example 1. The Al precipitation rate was 96.5%, slightly lower than 99.3% in Example 1, due to interference from a small amount of residual impurities in the aluminate solution.

[0085] (7) Deep purification: The process is exactly the same as in Example 1.

[0086] (8) High-temperature calcination: Same as Example 1.

[0087] Final product purity: Al2O3 88.6%, not meeting the 99.5% purity requirement. Major impurities include: Na2O 2.1%, Fe2O3 0.55%, SiO2 0.62%, CaO 0.48%, MgO 0.35%, and approximately 0.45% fluoride residue. Overall aluminum recovery rate: 69.4%.

[0088] When the mass fraction of calcium peroxide in the activating additive is less than 50% (only 30% in this comparative example), even after a complex subsequent deep purification process (ion exchange + recrystallization), it is impossible to obtain a high-purity alumina product that meets the standards.

[0089] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A method for preparing high-purity alumina based on secondary aluminum ash activated by calcium peroxide, characterized in that, The process involves mixing secondary aluminum ash with an activating additive at a mass ratio of 100:3 to 100:10, and calcining the mixture at 1100 to 1300°C for 1 to 4 hours to obtain activated calcined ash. The activating additive contains calcium peroxide with a mass fraction of not less than 50%. During calcination, the active oxygen released from the decomposition of the calcium peroxide oxidizes AlN in the secondary aluminum ash, and the CaO generated from the decomposition reacts with fluorides to form CaF2, undergoes a solid-state reaction with MgAl2O4 to destroy the spinel structure of MgAl2O4, and... 2+ The embedding of Al2O3 into the Al2O3 lattice causes Al2O3 lattice distortion.

2. The method for preparing high-purity alumina based on secondary aluminum ash activated by calcium peroxide as described in claim 1, characterized in that, Includes the following steps: S1: Calcium peroxide activation calcination; secondary aluminum ash and activation additives are mixed at a mass ratio of 100:3~100:10 and calcined at 1100~1300℃ for 1~4h to obtain activated calcined ash; the activation additives contain calcium peroxide with a mass fraction of not less than 50%; S2: Acid leaching; The activated calcined ash obtained in S1 is leached with an acid solution, and the acid leaching solution is obtained by separation; S3: Iron removal; adjusting the pH of the acid leaching solution obtained in S2 to Fe... 3+ Within the range of hydrolysis precipitation, ferric hydroxide precipitate is removed by filtration; S4: Precipitate aluminum; adjust the pH of the filtrate obtained from S3 to Al. 3+ Aluminum hydroxide filter cake was obtained by filtration within the range of aluminum hydroxide precipitation. S5: Alkali dissolution; The aluminum hydroxide filter cake obtained in S4 is dissolved in an alkaline solution to obtain an aluminate solution; S6: Carbon precipitation; Carbon dioxide is bubbled into the aluminate solution obtained in S5 to precipitate aluminum hydroxide precipitate; S7: Purification; The aluminum hydroxide precipitate obtained from S6 was washed and / or ion-exchanged to obtain the purified aluminum hydroxide precursor. S8: Calcination; The aluminum hydroxide precursor obtained in S7 is calcined to obtain high-purity aluminum oxide.

3. The method for preparing high-purity alumina based on secondary aluminum ash activated by calcium peroxide as described in claim 1, characterized in that, The activating additive is calcium peroxide or a mixture of calcium peroxide and sodium carbonate.

4. The method for preparing high-purity alumina based on secondary aluminum ash activated by calcium peroxide as described in claim 2, characterized in that, The calcination temperature in S1 is 1150~1250℃, the activating additive is a mixture of calcium peroxide and sodium carbonate, wherein the mass ratio of calcium peroxide to sodium carbonate is (1~3):1, and the amount of activating additive added is 5%~10% of the mass of secondary aluminum ash.

5. The method for preparing high-purity alumina based on secondary aluminum ash activated by calcium peroxide as described in claim 2, characterized in that, The acid solution mentioned in S2 is a sulfuric acid solution with a concentration of 3~5 mol / L; the alkaline solution mentioned in S5 is a NaOH solution with a concentration of 3~5 mol / L.

6. The method for preparing high-purity alumina based on secondary aluminum ash activated by calcium peroxide as described in claim 2, characterized in that, The purification described in S7 includes: washing the aluminum hydroxide precipitate obtained in S6 with deionized water until the conductivity of the washing solution is <10μS / cm, then acid washing with dilute hydrochloric acid or dilute nitric acid, and then washing with deionized water until neutral.

7. The method for preparing high-purity alumina based on secondary aluminum ash activated by calcium peroxide as described in claim 6, characterized in that, The purification described in S7 also includes: redissolving the acid-washed aluminum hydroxide in dilute hydrochloric acid or dilute nitric acid, adjusting the pH to 2-3, removing impurities by ion exchange through a cation exchange resin column, and then adjusting the pH to 7.5-8.0 with alkali to reprecipitate aluminum hydroxide.

8. The method for preparing high-purity alumina based on secondary aluminum ash activated by calcium peroxide as described in claim 2, characterized in that, The pH range for the precipitated aluminum in S4 is 7.5~8.0, and the final pH range for the carbon precipitation in S6 is 7.0~8.

0.

9. The method for preparing high-purity alumina based on secondary aluminum ash activated by calcium peroxide as described in claim 2, characterized in that, The calcination temperature described in S8 is 1100~1300℃, and the calcination time is 1~3h.

10. The method for preparing high-purity alumina based on secondary aluminum ash activated by calcium peroxide as described in claim 2, characterized in that, The CO2 flow rate in S6 is 1.0~2.0 L / min, the reaction temperature is 40~60℃, and the endpoint pH is 7.3~7.8.

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