Method for roasting and activating high alumina material

Abstract

This invention relates to the field of high-alumina solid waste resource utilization technology, specifically a method for calcining and activating high-alumina materials. The method includes the following steps: S1, grinding the high-alumina material to a particle size of -100 mesh or higher (70% or more); wherein the high-alumina material is the product obtained after secondary aluminum ash is treated with a wet process to remove metallic aluminum, aluminum nitride, fluoride salts, and nitride salts; S2, mixing the ground high-alumina material with an alkali, wherein the alkali consists of sodium peroxide and sodium oxide; S3, calcining the high-alumina material after mixing with the alkali. This invention addresses the problem of the difficulty in recovering inert alumina from high-alumina materials by innovatively proposing a sodium peroxide + sodium oxide calcination process, which can completely destroy the crystal structure of the high-alumina material through high-temperature calcination, achieving efficient aluminum recovery.

Description

Technical Field

[0001] This invention relates to the field of resource utilization technology for high-alumina solid waste, specifically a method for roasting and activating high-alumina materials. Background Technology

[0002] Aluminum ash, a hazardous solid waste, is generated during the production and smelting of primary aluminum, aluminum alloys, and recycled aluminum. Aluminum ash contains 35%–60% aluminum and has an aluminum-to-silicon ratio of 7–30, making it a high-quality secondary aluminum resource. However, it also contains soluble fluoride and chloride salts, which can lead to soil salinization and water pollution. Accumulation of aluminum ash can release ammonia and small amounts of hydrogen, forming explosive mixtures with air and reacting violently with open flames or fluorine and chlorine. Therefore, aluminum ash is classified as hazardous solid waste. Developing green and efficient aluminum ash resource utilization technologies can avoid environmental and health hazards, partially replace bauxite, and achieve aluminum recycling.

[0003] The composition of aluminum ash varies significantly depending on its source, and it is divided into primary aluminum ash and secondary aluminum ash. Primary aluminum ash has a high aluminum content (white color), and the processes for recovering aluminum (such as ash roasting, electric heating pressing, ball milling and screening) are mature. The residue after recovering aluminum is secondary aluminum ash (black ash), which has a low aluminum content, only 10%~20%, and mainly contains Al2O3, AlN, NaCl, CaF2, aluminum magnesium spinel, cryolite, etc.

[0004] Existing wet processing technology can remove toxic substances such as AlN and fluoride salts from secondary aluminum ash, while simultaneously producing products such as ammonia, hydrogen, and ammonium sulfate. Theoretically, the treated high-alumina material can replace bauxite in alumina extraction. It is worth noting that although the high-alumina material after wet denitrification and desalination is rich in alumina, its phase composition is fundamentally different from that of gibbsite or boehmite. Due to the primary aluminum smelting or high-temperature melting process, compared with secondary aluminum ash, aluminum in secondary aluminum ash mainly exists in five forms: elemental aluminum, aluminum nitride (content 15%–30%, generated by the reaction of molten aluminum with N2 in the air during high-temperature aluminum melting, and hydrolyzed in water to generate NH3, which is the core source of reactive hazardous waste in aluminum ash), activated alumina, corundum-type alumina, and magnesium aluminum spinel. Among them, aluminum nitride is an easily hydrolyzed hazardous phase, while α-Al2O3 and magnesium aluminum spinel have stable structures and are the most difficult inert aluminum-containing components to leach. The phases are tightly embedded and the particles are fine. Alumina (Al2O3) is mainly composed of γ-Al2O3 and α-Al2O3 (corundum), accounting for 20% to 35% of the total. The γ phase has high activity and is easily leached by acids and alkalis. The dense crystal structure of aluminum spinel (MgAl2O4) results in extremely high lattice energy. Under the conventional Bayer process alkaline dissolution conditions, its reactivity is extremely low, and even acid leaching at room temperature is difficult to destroy its Al-O bonds.

[0005] While high-alumina materials represent a significant potential secondary aluminum resource, the persistent nature of their corundum and spinel phases severely limits the efficiency of direct wet extraction. Conventional thermal activation methods also face industrial barriers of high energy consumption and high cost. Therefore, without altering their phase structure, high-alumina materials can only be used as low-end refractory fillers and cannot achieve metallurgical-grade aluminum recovery. A new, energy-efficient, environmentally friendly, and highly effective approach is urgently needed for the high-value utilization of high-alumina materials. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for calcining and activating high-alumina materials.

[0007] The objective of this invention is achieved through the following technical solution: a method for calcining and activating high-alumina materials, comprising the following steps: S1. Grind the high-alumina material to a density of over 70% (-100 mesh, 0.15 mm); wherein the high-alumina material is the product obtained by removing metallic aluminum, aluminum nitride, fluoride salts, and nitride salts from secondary aluminum ash using a wet process. S2. Mix the ground high-alumina material with the alkali evenly, wherein the alkali is composed of sodium peroxide and sodium oxide; S3. Roast the high-alumina material after mixing with alkali.

[0008] Furthermore, in step S1, the grinding method used is dry grinding, and the moisture content of the ground material needs to be controlled to be no higher than 3%. Preferably, Raymond milling is used for dry grinding.

[0009] Furthermore, in step S2, the molar ratio of sodium peroxide to sodium oxide is 5~20:1, preferably 9:1.

[0010] Furthermore, in step S2, the alkali ratio of the high-alumina material to sodium peroxide and sodium oxide is 1.1~1.25:1. Preferably, it is 1.2:1.

[0011] Furthermore, in step S3, the calcination temperature is 800℃~950℃, and the time is 80~120min. Preferably, the calcination temperature is 900℃, and the time is 100min.

[0012] Furthermore, in step S3, the equipment used for roasting is an internally heated rotary kiln.

[0013] The present invention also provides a method for calcining and leaching high-alumina materials, including the above steps, and further including the following steps: S4. After cooling the calcined high-alumina material to below 80°C, grind it to a particle size of <200 mesh (0.074 mm) accounting for 80%. Mix it with water at a solid-liquid ratio of 15~50 mL / g, heat to 70~90°C, and immerse in water for 15min~50min. Separate the solid and liquid to obtain an aluminum-rich leachate and a leaching residue. Preferably, the cooling method is air cooling, and the grinding method is Raymond mill dry grinding.

[0014] The principle of this invention is as follows: XRD and SEM analyses show that, under optimal calcination conditions, the inert alumina in the high-alumina material is successfully converted into water-soluble sodium aluminate through the synergistic effect of sodium peroxide and sodium oxide. This improves the leaching rate of sodium aluminate. Simultaneously, most heavy metal oxides and aluminosilicates are enriched in the leaching residue, simplifying the subsequent purification process. The leaching residue mainly consists of MgO and NaSiAlO4, exhibiting a honeycomb structure.

[0015] This invention not only provides a new energy-saving and environmentally friendly approach for the resource-based recycling of high-alumina hazardous waste, but also offers important technical reference for the efficient recycling of aluminum resources. This process is characterized by high efficiency and environmental friendliness, providing a more sustainable path for the comprehensive utilization of high-alumina materials.

[0016] The beneficial effects of this invention are as follows: Addressing the problem of the difficulty in directly leaching and recovering inert alumina from high-alumina materials, this invention innovatively proposes a combined sodium peroxide + sodium oxide roasting-water leaching process. This process completely destroys the crystal structure of high-alumina materials through high-temperature roasting, converting inert alumina into water-soluble sodium aluminate, thereby achieving efficient aluminum recovery and reducing subsequent impurity removal costs. This process not only effectively solves the aluminum recovery problem but also reduces the generation of highly acidic wastewater in traditional processes, resulting in significant environmental benefits. Attached Figure Description

[0017] Figure 1 XRD pattern of high-alumina material; Figure 2 SEM image of high-alumina material; Figure 3 This outlines the basic experimental procedure and reaction mechanism. Figure 4 XRD patterns of clinker roasted with different alkali-to-feed ratios; Figure 5 The effect of alkali ratio on aluminum leaching rate; Figure 6 The following are schematic diagrams of the scanning electron microscope (SEM) results of clinker under conditions of low alkali-to-material ratio and optimal roasting conditions: (a) SEM image of clinker roasted under an alkali-to-material ratio of 0.6; (b) SEM image of clinker roasted under an alkali-to-material ratio of 0.8; (c) SEM image of clinker roasted under an alkali-to-material ratio of 1.2. Figure 7XRD patterns of clinker roasted at different roasting temperatures; Figure 8 The effect of calcination temperature on aluminum leaching rate; Figure 9 SEM images and EDS elemental spectra of clinker roasted at the optimal roasting temperature; Figure 10 XRD patterns of clinker roasted for different roasting times; Figure 11 The effect of calcination time on aluminum leaching rate; Figure 12 Schematic diagram of the scanning electron microscope (SEM) results of clinker under over-roasting and optimal roasting conditions; (a) SEM image of clinker roasted at a roasting temperature of 1100℃; (b) SEM image of clinker roasted at a roasting time of 140 min; (c) SEM image of clinker roasted under optimal roasting conditions. Figure 13 The influence of various factors on aluminum leaching rate; Figure 14 XRD pattern of the leaching residue; Figure 15 SEM images and EDS elemental maps of the leaching residue; Figure 16 The Gibbs free energy at different temperatures during the calcination process; Figure 17 This is a schematic diagram of the leaching process; Figure 18 The variation of aluminum leaching rate at different temperatures; Figure 19 The fitting results of three kinetic equations with time are shown; (a) linear fitting of the chemical reaction-controlled kinetic equation with time, (b) linear fitting of the external diffusion-controlled kinetic equation with time, and (c) linear fitting of the internal diffusion-controlled kinetic equation with time. Figure 20 This is the intrinsic mechanism by which aluminum transforms from an inert phase into soluble sodium aluminate. Detailed Implementation

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to the following description.

[0019] Example 1: Physicochemical characteristics of high-alumina material The sample used in this invention comes from high-alumina material from Haineng Environmental Technology Co., Ltd. in Guangyuan City, Sichuan Province. It is a product obtained by wet treatment to remove toxic components such as aluminum nitride, fluoride salts, and nitrogen salts from aluminum ash. The sample is in the form of fine powder. After dry sieving, the material with a particle size greater than 100 mesh is dry ground. Finally, the particle size of the material is controlled to be more than 70% <100 mesh, with no adhesion or agglomeration. The color is grayish-black. The chemical composition and phase composition of the high-alumina material are analyzed by XRF and XRD, and the results are shown below.

[0020] Table 1 Chemical composition of high-alumina materials (mass fraction, %)

[0021] High-alumina materials are mainly composed of alumina, with a content as high as 76%, as shown in Table 1. The main aluminum-containing phases in high-alumina materials are alumina, aluminum hydroxide, magnesium aluminum spinel, and Diaoyu Island stone. Figure 1 Iron, silicon, and magnesium can be found mainly in the mineral phases of hematite, quartz, and aluminum-magnesium spinel.

[0022] To more intuitively and clearly observe the morphological characteristics and elemental distribution of the high-alumina material, this invention further performs scanning electron microscopy analysis on the high-alumina material, such as... Figure 2 As shown, the analysis results show that most of the magnesium aluminum spinel is embedded in the alumina particles, the oxides are closely connected, most elements are relatively uniformly distributed, and most impurities are associated with the surface of the alumina particles.

[0023] Example 2: High-alumina material roasting activation and water leaching method The method of this invention consists of two core steps: alkaline roasting activation and water leaching. First, inert aluminum-containing mineral phases are destroyed by high-temperature roasting with sodium peroxide and sodium oxide. Then, selective extraction of aluminum is achieved through water leaching. Specific operational steps are as follows: Figure 3 : (1) The high-alumina material was dry-milled to obtain 100-mesh fine powder as a test sample to ensure a full reaction.

[0024] (2) Weigh 30g of sample using a balance, add sodium peroxide + sodium oxide (9:1) according to a specific alkali-material ratio, grind thoroughly in a mortar to ensure uniform mixing of the material, and transfer the mixed material to a 100mL crucible.

[0025] (3) Set the muffle furnace to reach the specified temperature at a heating rate of 10℃ / min, then move the crucible containing the mixture into the muffle furnace that has been heated, and remove it after a certain period of calcination to room temperature.

[0026] (4) Dry grind the roasted clinker into powder to increase the specific surface area for dissolution. Add a certain amount of deionized water to a beaker according to a specific solid-liquid ratio, then place the beaker containing deionized water into a constant temperature water bath and heat it to the set temperature. Add the fully ground roasted clinker and stir for a certain time. After dissolution, vacuum filter to obtain leachate and red mud (leach residue).

[0027] Example 3: Selection of alkaline activator for calcination activation of high-alumina materials To investigate the effect of different alkaline activators on aluminum leaching rate, calcination experiments were conducted by adding equal amounts of NaOH, Na2O2, Na2CO3, Na2O, and Na2O + Na2O2 (molar ratio 1:9) to equal amounts of high-alumina material. The results showed that below 1100 °C, Na2CO3 had poor activation effect on the high-alumina material, failing to meet process requirements, with an aluminum leaching rate of approximately 75%. The optimal calcination temperature for NaOH was 950 °C, with an aluminum leaching rate of approximately 80%, but excessive volatiles caused significant corrosion to the exhaust gas treatment equipment. The optimal calcination temperature for Na2O2 was 1000 °C, with an aluminum leaching rate of approximately 85%. The optimal calcination temperature for Na2O was 1050 °C, with an aluminum leaching rate of approximately 80%, but severe side reactions occurred, including the reaction with silica in the material to form a sodium silicate coating. The optimal calcination temperature for Na₂O + Na₂O₂ (molar ratio 1:9) is 900℃, with an aluminum leaching rate exceeding 95%. This is significantly better and less costly than using NaOH, Na₂O₂, Na₂CO₃, Na₂O, Na₂O, or Na₂O₂ alone, resulting in a marked increase in aluminum leaching rate. Therefore, this invention selects Na₂O + Na₂O₂ as a calcination aid, achieving superior calcination results under the same dosage conditions.

[0028] Example 4: Screening of Activation Conditions for High-Alumina Material Calcination (1) Effect of alkali-to-material ratio on roasting effect An appropriate alkali-to-material ratio ensures the complete conversion of Al2O3 into soluble NaAlO2 while avoiding side reactions. To investigate the effect of the alkali-to-material ratio on aluminum leaching rate and the phase composition of the calcined clinker, five groups of 30g high-alumina materials were mixed with Na2O + Na2O2 at alkali-to-material ratios of 0.6, 0.8, 1.0, 1.2, and 1.4, respectively. The calcination time was 90 min, the calcination temperature was 800℃, the leaching temperature of the calcined clinker was 60℃, the leaching time was 15 min, and the solid-liquid ratio was 15 mL / g. The experimental results are as follows: Figure 4 , Figure 5 and 6 As shown.

[0029] As the alkali-to-material ratio increases, the diffraction peak intensities of Al(OH)3 and Al2O3 gradually decrease, while the diffraction peak intensities of NaAlO2 gradually increase. However, when the alkali-to-material ratio exceeds 1.2, the intensity of the diffraction peaks begins to decrease slightly. Figure 4 As shown. From Figure 5 It can be seen that when the alkali-to-material ratio increases from 0.6 to 1.2, the aluminum leaching rate increases from 62.32% to 93.64%. When the alkali-to-material ratio exceeds 1.2, the aluminum leaching rate decreases slightly to 88.26%. With the increase of Na2O+Na2O2 content, the contact between Na2O+Na2O2 and high-alumina material becomes more sufficient. However, when the Na2O+Na2O2 content is too high, a eutectic liquid phase will be formed under high-temperature calcination. Excessive liquid phase will lead to severe sintering and agglomeration of the material, forming a dense glassy shell, during which the internal NaAlO2 cannot dissolve.

[0030] Calcined clinker with high aluminum leaching rate appears as a matrix with uniform and continuous contrast under scanning electron microscopy. Figure 6 (c) The large, uniform, medium-contrast region is the generated NaAlO2 matrix. Conversely, the appearance of the calcined clinker under scanning electron microscopy when the alkali-to-material ratio is insufficient is as follows: Figure 6 (a) and (b) show mixed contrast and clear boundaries, with no obvious reaction halo or continuous area, indicating that the reaction is not thorough. Most of the aluminum still exists in the form of raw ore and has not been effectively converted into the target product, which is consistent with the XRD analysis results.

[0031] (2) Effect of temperature on roasting effect Calcination temperature is a key process parameter determining the phase transformation efficiency. A suitable temperature can effectively disrupt the inert Al₂O₃ crystal structure and promote the formation of NaAlO₂. To investigate the effect of temperature on aluminum leaching rate and the phase composition of the calcined clinker, five groups of 30g high-alumina materials were mixed with Na₂O + Na₂O₂ at an alkali-to-material ratio of 1.2. Calcination temperatures were 700, 800, 900, 1000, and 1100℃, with a calcination time of 90 min. The leaching temperature of the calcined clinker was 60℃, the leaching time was 15 min, and the solid-liquid ratio was 15 mL / g. The experimental results are as follows: Figure 7 , Figure 8 and Figure 9 As shown.

[0032] from Figure 7 It can be seen that as the calcination temperature increases, the intensity of the diffraction peak of NaAlO2 gradually increases, reaches its peak at 900℃, and then gradually weakens. A significant Na2CO3 diffraction peak appears at 1000℃, and the intensity of this peak increases further at 1100℃. At excessively high temperatures, more Na2O decomposed from Na2O2 diffuses to the material surface, preferentially reacting with CO2 in the air to form Na2CO3, causing unnecessary alkali loss and reducing the efficiency of the reaction between Na2O2 and the high-alumina material. Figure 8 It can be seen that the aluminum leaching rate gradually increased from an initial 87.14% to 94.12%, reaching a peak before gradually decreasing to 88.63%. From... Figure 9It can be seen that the main phase is light gray NaAlO2, with a small amount of MgO particles and nepheline phase (NaAlSiO4) particles attached to the surface of NaAlO2 particles. Most of the NaAlO2 particles are irregularly shaped lumps with a large specific surface area and are loose and porous, which is beneficial to the subsequent leaching process.

[0033] (3) Effect of roasting time on roasting effect Appropriately extending the calcination time is beneficial to the phase transformation, but excessive time leads to side reactions or increased energy consumption. To investigate the effect of calcination time on aluminum leaching rate and the phase composition of the calcined clinker, five groups of 30g high-alumina materials were mixed with Na₂O + Na₂O₂ at an alkali-to-material ratio of 1.2. The calcination temperature was 900℃, and the calcination times were 60 min, 80 min, 100 min, 120 min, and 140 min. The leaching temperature of the calcined clinker was 60℃, the leaching time was 15 min, and the solid-liquid ratio was 15 mL / g. The experimental results are as follows: Figure 10 , Figure 11 and Figure 12 As shown.

[0034] from Figure 10 It can be seen that as the calcination time increases, the intensity of the NaAlO2 diffraction peak gradually increases, reaches its peak at 100 min, and then gradually weakens. A significant Na2CO3 diffraction peak appears at 140 min. This is because in the first 120 min, the reaction is mainly between Na2O + Na2O2 and the high-alumina material. As the high-alumina material is gradually consumed, Na2O + Na2O2 begins to overflow and react with CO2 in the air. The leaching rate of aluminum also gradually increases from 90.45% initially to 95.68%, reaches its peak, and then gradually decreases to 89.14%. Figure 11 As shown.

[0035] Over-roasting manifests as severe caking in the experiment. Excessive roasting time or high roasting temperature will cause sintering necks to gradually form between particles, and small particles will merge into large particles with smooth edges. In order to reduce the total energy of the system, the Na2CO3 generated by the side reaction will precipitate on the particle surface, forming a "thin film" that coats the particle surface. Figure 12 The microstructures under different over-calcination conditions are compared and shown: Figure 12 (a) Morphology at excessively high temperatures (1100℃), Figure 12 (b) shows the morphology when the calcination time is too long (140 min). Both show obvious encapsulation, with large areas of uniform and continuous regions encapsulating other particles, indicating that the Na2CO3 melt produced by the side reaction causes the pores between clinker particles to close and the boundaries to become blurred.

[0036] In summary, the experimental results show that the aluminum leaching rate is significantly affected by the calcination temperature, calcination time, and alkali-to-material ratio. A low alkali-to-material ratio leads to incomplete alumina conversion, while excessively long calcination time or excessively high calcination temperature results in the formation of a sodium carbonate coating, inhibiting aluminum leaching. Through optimization, the optimal calcination conditions were determined to be: an alkali-to-material ratio of 1.2, a calcination temperature of 900℃, and a calcination time of 100 min.

[0037] Example 5: Determination of parameters for the water immersion process The roasted clinker was leached with deionized water under suitable conditions. NaAlO2 in the roasted clinker was fully introduced into the water, while other impurities were transferred to the precipitate. To ensure the accuracy of the experiment, the materials used for leaching in each group were roasted clinker under the same roasting conditions (alkali-to-material ratio 1.2, roasting temperature 900℃, roasting time 100min).

[0038] An appropriate solid-liquid ratio ensures sufficient dissolution and diffusion. A ratio that is too low can lead to excessively high viscosity and hindered mass transfer in the leaching system, while a ratio that is too high will increase the burden on subsequent concentration treatment. Under the conditions of 60℃ and a leaching time of 15 min, this paper investigates in detail the effects of solid-liquid ratios of 5, 10, 15, 20, and 25 mL / g on the aluminum leaching rate. The results are as follows: Figure 13 As shown in (a), increasing the solid-liquid ratio enhances the fluidity of the reaction system, and the leaching rate of aluminum increases with the increase of the solid-liquid ratio. When the solid-liquid ratio reaches 15 mL / g, the leaching rate of aluminum reaches its maximum value of 91.18%. When the solid-liquid ratio continues to increase, the change in the leaching rate of aluminum tends to be gradual. Therefore, the optimal solid-liquid ratio is determined to be 15 mL / g.

[0039] A suitable leaching time can ensure efficient aluminum recovery while avoiding increased energy consumption due to excessive leaching time. Under conditions of 60℃ and a solid-liquid ratio of 15 mL / g, the effects of leaching times of 5, 10, 15, 20, and 25 min on the aluminum leaching rate were investigated. The results are as follows: Figure 13 As shown in (b), because the concentration gradient of NaAlO2 between the calcined clinker and the solution is large in the initial stage of leaching, this phenomenon can promote the dissolution of NaAlO2. The leaching rate of aluminum has reached 72.13% at 5 min. As the leaching time increases, most of the NaAlO2 in the calcined clinker has entered the liquid phase. The leaching rate of aluminum reaches equilibrium after 15 min, which is 91.13%. The subsequent changes tend to be gradual. Finally, 15 min was determined to be the optimal leaching time.

[0040] Increasing temperature can enhance molecular thermal motion, reduce solution viscosity, and promote solute diffusion; however, excessively high temperatures can lead to solvent evaporation and hinder solute crystallization. Under the conditions of a solid-liquid ratio of 15 mL / g and a leaching time of 15 min, the effects of leaching temperatures of 20, 40, 60, 80, and 100 °C on the aluminum leaching rate were investigated. The results are as follows: Figure 13 As shown in (c), the leaching rate of aluminum increases with increasing leaching temperature, reaching a maximum of 95.33% at 80℃. However, when the temperature reaches 100℃, the liquid phase begins to boil, leading to more intense evaporation and a significant reduction in solution volume within a short period. This results in the precipitation of some NaAlO2 crystals, which has a negative impact on the leaching effect, causing a slight decrease in the leaching rate. Based on the aluminum leaching rate and energy consumption, 80℃ was selected as the optimal leaching temperature.

[0041] XRD of the leaching residue as follows Figure 14 As shown in the figure, the main phase in the leaching residue is MgO. Compared with the roasted clinker, the intensity of the MgO diffraction peak in the leaching residue is significantly enhanced, while the NaAlO2 diffraction peak disappears. This indicates that under optimal roasting conditions, the aluminum-containing phase in the high-alumina material is fully activated, transforming it into water-soluble NaAlO2.

[0042] The microstructure of the leaching residue was observed using scanning electron microscopy, and elemental analysis of the samples was performed using energy dispersive spectroscopy. The results are as follows: Figure 15 As shown, the roasted clinker exhibits a honeycomb structure after leaching due to the dissolution of NaAlO2. This honeycomb structure is mainly composed of MgO and NaSiAlO4 particles.

[0043] In summary, during the water leaching process, the aluminum leaching rate increases with the increase of solid-liquid ratio, leaching time, and leaching temperature, eventually stabilizing. Based on leaching kinetics analysis, the optimal conditions for leaching roasted clinker were determined to be: solid-liquid ratio of 15 mL / g, leaching time of 15 min, and leaching temperature of 80℃.

[0044] Under the optimized roasting-leaching conditions described above, the aluminum leaching rate can reach 95.33%, verifying the feasibility and efficiency of the sodium peroxide + sodium oxide roasting-water leaching combined process in the resource utilization of high-alumina materials.

[0045] Example 6: Calcination Mechanism Analysis Calcination is a key step in activating aluminum in high-alumina materials. To theoretically clarify the chemical reactions that occur during calcination and their spontaneous tendency at high temperatures, this section further speculates on the calcination process based on the raw material composition of high-alumina materials using thermodynamic analysis methods. The relevant reaction equations (1)-(7) are shown below. The Gibbs free energy change of the reaction is calculated using the thermodynamic software HSC Chemistry 6.0, and the results are as follows. Figure 16 As shown.

[0046]

[0047] The curve of reaction (1) shows that when the temperature is greater than 400℃, Na2O2 begins to decompose into Na2O and O2, and subsequent reactions can proceed smoothly. The curve of reaction (2) shows that when the temperature is higher than 100℃, Al(OH)3 begins to decompose into Al2O3 and water vapor. The curves of reactions (3), (4), (5), and (6) show that the Gibbs free energy of the reaction between Al2O3, MgAl2O4, Fe2O3, SiO2 and Na2O in the high-alumina material is negative at room temperature, that is, the thermodynamic reaction conditions are sufficient. The curve of reaction (6) is negative at 1000℃, which shows that under high temperature conditions, excess Na2O will react with CO2 to generate Na2CO3.

[0048] Example 7 Leaching Kinetics Analysis Thermodynamic analysis confirmed the feasibility of generating soluble NaAlO2 during roasting, providing a theoretical basis for subsequent water leaching. In practice, the leaching rate of NaAlO2 from roasted clinker directly determines the process efficiency. Studying the leaching kinetics of NaAlO2 can provide a more comprehensive understanding of its behavior and rate-controlling steps, thereby enabling the development of optimal leaching conditions to achieve higher leaching rates. The leaching of NaAlO2 from roasted clinker is a non-catalytic chemical reaction involving multiple stages, typically occurring at the solid-liquid boundary layer. Existing research indicates that the overall leaching rate largely depends on the slowest stage in the leaching process, which is referred to as the rate-controlling step. Figure 17 The following are the main reaction stages in the leaching process: (I) solvent diffusion into the material at the liquid boundary layer; (II) solvent diffusion into the material at the product layer; (III) solvent adsorption on the material surface; (IV) chemical reaction between the solvent and the material (surface reaction); (V) desorption of the product on the material surface; (VI) diffusion of the product into the solvent at the product layer; and (VII) diffusion of the product into the solvent at the liquid boundary layer.

[0049] Currently, there are three most commonly used leaching kinetic models: chemical reaction-controlled kinetic equations, external diffusion-controlled kinetic equations, and internal diffusion-controlled kinetic equations. These leaching kinetic equations are as follows:

[0050] After clarifying the kinetic model of the leaching process, a solid-liquid ratio of 15 mL / g was selected, and a series of leaching experiments were conducted at 40, 60, and 80 °C and at 3, 6, 9, 12, 15, 18, and 21 min. The leaching rate of aluminum changed with temperature and time as follows: Figure 18As shown, with the extension of leaching time, the leaching rate of aluminum increases rapidly in the first 15 minutes, while the leaching rate of aluminum begins to level off between 15 and 25 minutes. This indicates that NaAlO2 in the calcined clinker can dissolve rapidly in water. Furthermore, it can be found that temperature has a significant effect on the leaching rate of aluminum. Therefore, the aluminum leaching rates at 40, 60, and 80℃ and at 3, 6, 9, 12, and 15 minutes were used to perform linear fitting on the three models, and the fitting equations are (8), (9), and (10), respectively.

[0051] Table 4-1 Reaction rate constant K3 of the internal diffusion control kinetic equation

[0052] The fitting results of the three dynamic equations with time are as follows: Figure 19 As shown in Figure 1, Figure (a) shows that the R2 of the chemical reaction is greater than 0.93 at 40℃, while the R2 is greater than 0.95 at 60℃ and 80℃, indicating a large dispersion. Figure (b) shows that the R2 of the chemical reaction is less than 0.94 at 40℃, 60℃, and 80℃, indicating that external diffusion does not play a decisive role in the clinker leaching process. Figure (c) shows that the R2 of the chemical reaction is greater than 0.98 at 40℃, 60℃, and 80℃, indicating that the leaching reaction kinetics are highly consistent with the internal diffusion model. Furthermore, Table 1 shows that the reaction rate K3 increases with increasing temperature, further proving that increasing temperature can promote the leaching process of NaAlO2.

[0053] Based on the above experimental optimization and thermodynamic-kinetic analysis, this study further summarizes the intrinsic mechanism by which aluminum transforms from an inert phase to soluble sodium aluminate during the sodium peroxide + sodium oxide activation roasting-water leaching process. For example... Figure 20 As shown, during the roasting stage, sodium peroxide and sodium oxide decompose upon heating to generate strongly alkaline Na₂O and O₂, disrupting the stable lattice structure of α-Al₂O₃ and MgAl₂O₄ in the high-alumina raw material and generating water-soluble NaAlO₂. Simultaneously, impurities such as SiO₂ in the raw material form nepheline (NaAlSiO₄) or accumulate in the slag. During the water leaching stage, sodium aluminate rapidly dissolves into the solution, while MgO and insoluble silicates remain in the leaching residue, forming a honeycomb structure. This schematic diagram clearly illustrates the complete process path from "inert phase" to "soluble phase" and then to "efficient separation," intuitively demonstrating the decisive role of process parameter control in phase reconstruction.

[0054] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for calcining and activating high-alumina materials, characterized in that, Includes the following steps: S1. Grind the high-alumina material to a density of over 70% -100 mesh; wherein the high-alumina material is the product obtained by removing metallic aluminum, aluminum nitride, fluoride salts, and nitride salts from secondary aluminum ash using a wet process. S2. Mix the ground high-alumina material with the alkali evenly, wherein the alkali is composed of sodium peroxide and sodium oxide; S3. Roast the high-alumina material after mixing with alkali.

2. The method for calcining and activating high-alumina material according to claim 1, characterized in that, In step S1, the grinding method used is dry grinding, and the moisture content of the ground material needs to be controlled to be no higher than 3%.

3. The method for calcining and activating high-alumina material according to claim 1, characterized in that, In step S2, the molar ratio of sodium peroxide to sodium oxide is 5~20:

1.

4. The method for calcining and activating high-alumina material according to claim 1, characterized in that, In step S2, the ratio of the high-alumina material to the alkali material of sodium peroxide and sodium oxide is 1.1~1.25:

1.

5. The method for calcining and activating high-alumina material according to claim 1, characterized in that, In step S3, the roasting temperature is 800℃~950℃ and the time is 80~120min.

6. The method for calcining and activating high-alumina material according to claim 1, characterized in that, In step S3, the equipment used for roasting is an internally heated rotary kiln.

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