Resource utilization method for preparing calcium aluminate through aluminum ash denitrification and aluminum extraction-calcification roasting
By combining dry grinding, wet denitrification and high-temperature calcination and roasting, the problems of incomplete aluminum ash treatment and low resource utilization were solved, the harmless and high-value utilization of aluminum ash was achieved, and highly active calcium aluminate refining slag was prepared.
Patent Information
- Application Number
- CN202510879825.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-27
- Publication Date
- 2025-09-19
AI Technical Summary
The existing aluminum ash treatment technology has problems such as incomplete treatment, serious secondary pollution, and low resource utilization, making it difficult to achieve harmless and high-value utilization of aluminum ash.
A method combining dry grinding, wet denitrification and high-temperature calcination roasting is adopted to achieve efficient recovery of metallic aluminum and removal of harmful elements through physical separation and chemical reaction, and to prepare high-quality calcium aluminate steelmaking refining slag.
It achieves efficient denitrification and defluorination of aluminum ash, high recovery rate of metallic aluminum, and preparation of highly active calcium aluminate refined slag that meets national standards and has no secondary pollution.
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Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of solid waste resource utilization, and specifically relates to a method for harmless treatment and high-value utilization of hazardous waste aluminum ash, in particular a method through a process combining hydrometallurgy and pyrometallurgy. Background Art
[0002] Secondary aluminum ash is the residue obtained after extracting metallic aluminum from aluminum ash slag. Its output has also increased dramatically, with annual output reaching more than 2 million tons. However, the development of its resource utilization technology is slightly lagging behind, with a comprehensive utilization rate of less than 30% and a cumulative stockpile of tens of millions of tons.
[0003] Secondary aluminum ash is mainly composed of metallic aluminum, aluminum oxides and nitrides, molten salts and other substances, with a total aluminum content of 30% to 75%. Secondary aluminum ash has the dual characteristics of causing environmental damage and wasting resources: first, the presence of a large number of aluminum compounds makes it highly valuable for industrial recycling and reuse; second, the nitrides, heavy metal elements such as Cr, Cd, Pb and F - 、Cl - 、CN - Large-scale storage of aluminum ash and other hazardous ions can easily react with water in the air to form irritating and flammable gases such as NH3 and CH4. Large-scale landfilling can also pollute soil and groundwater. Therefore, the "National List of Hazardous Wastes (2021 Edition)" clearly lists secondary aluminum ash as hazardous solid waste.
[0004] Currently, aluminum ash treatment technologies are primarily categorized into pyrometallurgical, wet, and dry physical separation methods. Pyrometallurgical processes, such as the traditional rotary kiln "ash roasting" method, separate aluminum from slag by high-temperature melting and the addition of fluxes (such as mixed salts like NaCl and KCl). While this method can recover some metallic aluminum, it is energy-intensive and, at high temperatures, produces large amounts of chlorine- and fluorine-containing fumes and secondary pollutants such as dioxins. The resulting "salt slag" remains a hazardous waste and requires incomplete treatment. Wet processes typically employ acid or alkaline leaching. Acid methods (such as sulfuric acid and hydrochloric acid) can dissolve almost all aluminum-containing phases in aluminum ash, but they are subject to severe equipment corrosion, and subsequent solution purification and product preparation processes are complex and costly. Alkaline methods primarily utilize a strong base (NaOH) solution to dissolve aluminum oxide and metallic aluminum to produce a sodium aluminate solution. This method requires high equipment requirements, consumes significant energy, and is ineffective for treating the large amounts of aluminum nitride and fluoride in the aluminum ash. Furthermore, some wet processes generate ammonia when processing AlN, which can cause secondary pollution if not collected and utilized. Dry physical separation, such as through crushing, grinding, and screening, leverages the differences in physical properties (such as density, particle size, and ductility) of the aluminum ash components to separate them. This method is simple and chemically pollution-free, but it can only recover a portion of coarse aluminum metal particles. It cannot effectively separate and utilize fine-grained aluminum metal and non-metallic components (Al2O3, AlN), resulting in a low resource recovery rate and failing to address the issue of AlN detoxification.
[0005] In summary, existing aluminum ash treatment technologies generally suffer from issues such as incomplete treatment, severe secondary pollution, low resource utilization, and high process costs. This makes it difficult to achieve the coordinated goals of "denitrification and defluorination," "efficient recovery of aluminum metal," and "high-value utilization of residues." Therefore, developing a new aluminum ash resource recovery technology with a short process flow, environmental friendliness, and the ability to synergistically treat harmful components and fully utilize all components is of practical significance and economic value. Summary of the Invention
[0006] In response to the problems of environmental pollution and the inability to effectively separate and recover non-metallic components in existing aluminum ash treatment technologies, the purpose of the present invention is to provide a resource utilization method for aluminum ash denitrification and aluminum extraction-calcification roasting to prepare calcium aluminate. This method combines physical sorting, wet chemical reaction and pyrocalcination for synergistic treatment, which can efficiently remove harmful elements such as nitrogen and fluorine and recover the aluminum ash containing metallic aluminum, thereby achieving harmless treatment of aluminum ash, zero waste and high-value utilization of all components.
[0007] To achieve the above-mentioned object, the present invention provides a method for dry-grinding raw aluminum ash to achieve monomer dissociation to the micron level and then screening, wet-grinding the obtained aluminum ash fine powder in an aqueous medium for denitrification, screening and recovering metallic aluminum to obtain an aluminum-rich slag slurry; subjecting the aluminum-rich slag slurry to solid-liquid separation and leaching of soluble salts to obtain purified aluminum-rich slag; and subjecting the purified aluminum-rich slag to high-temperature calcification and roasting to obtain a calcium aluminate steelmaking refined slag with 12CaO·7Al2O3 as the main crystal phase.
[0008] The key to the present invention's technical solution lies in the wet denitrification and leaching steps, which create favorable conditions for subsequent high-temperature calcination and roasting. Specifically, this method utilizes wet denitrification and leaching to pre-remove the vast majority of aluminum nitride (AlN) and fluorine and chloride salts. This effectively prevents the negative impacts of these impurities during high-temperature sintering. First, excessive AlN residue decomposes at high temperatures to produce N2 gas, leading to numerous pores within the final product, a loose structure, and reduced strength. Second, residual fluorine and chloride salts have low melting points and are highly volatile. At high temperatures, they form a molten phase or volatilize, corroding equipment and interfering with the normal solid-phase reaction between CaO and Al2O3, hindering the formation of the target phase C12A7. They can also dissolve harmful elements into the product, resulting in substandard quality. Therefore, the high-purity aluminum-rich slag obtained through wet purification in this invention is a prerequisite and guarantee for the subsequent successful production of high-quality calcium aluminate refining slag.
[0009] The present invention first dry-grinds the raw aluminum ash, breaking up and finely grinding the bulk or irregular aluminum ash, breaking down the encapsulation structure of the various phases in the aluminum ash and achieving monomer dissociation, creating conditions for subsequent separation and reaction. The initial screening process also recovers metallic aluminum. It also increases the specific surface area of the material, providing a kinetic basis for the rapid hydrolysis of AlN in the subsequent wet process. The present invention creatively utilizes this "wet grinding" step to achieve three synergistic effects:
[0010] 1) Physical Separation of Aluminum Metal: The aluminum metal in aluminum ash has excellent ductility. Under the impact and abrasive action of the grinding media, it is not easily ground down, but rather rolled into flakes or spheres. Other brittle phases, such as Al2O3 and AlN, are further ground into powder. By controlling the grinding time, a significant size difference is created between the aluminum metal particles and the other material powders, allowing for efficient separation of relatively pure aluminum metal through simple screening.
[0011] 2) Chemically Promoted AlN Hydrolysis: During wet milling, the fresh AlN surface is continuously exposed, undergoing a vigorous hydrolysis reaction with water (AlN + 3H2O → Al(OH)3 + NH3↑), thereby removing nitrogen from the solid phase as ammonia gas, achieving efficient denitrification. The mechanical energy and reaction heat provided by wet milling, as well as the continuous exfoliation of the reaction product, the Al(OH)3 layer, greatly accelerate the reaction, allowing it to complete in a relatively short time.
[0012] 3) Initial leaching and dissolution of soluble salts: Chloride salts, fluoride salts, etc. in aluminum ash are fully dissolved into the water phase during the wet grinding process.
[0013] After wet grinding, the aluminum-rich slag slurry, from which metallic aluminum is separated, undergoes subsequent processing and conversion. This slurry primarily consists of Al2O3 and Al(OH)3 generated by hydrolysis. First, solid-liquid separation (such as vacuum filtration) is performed to produce an aluminum-rich slag filter cake and a filtrate containing soluble salts. To further improve product purity, the filter cake is subjected to agitation-enhanced leaching to remove residual soluble salts such as fluoride and chloride, ensuring that the nitrogen content of the sintered product is less than 0.5% and the fluorine content is less than 1.5%. This step simultaneously removes harmful elements such as nitrogen, fluorine, and chlorine. The purified aluminum-rich slag (primarily composed of Al2O3 and an ideal aluminum source for calcium aluminate synthesis) is then subjected to high-temperature calcification sintering with a calcium source to produce high-quality calcium aluminate steelmaking refining slag.
[0014] As a preferred embodiment, the dry grinding process utilizes a conical ball mill to grind the aluminum ash to a particle size of 150 μm or less for 10 to 60 minutes. The raw aluminum ash is secondary aluminum ash. The dry grinding particle size selected in the present invention fully achieves the encapsulation structure of the various phases in the aluminum ash, achieving monomer dissociation and further facilitating nitrogen removal during wet grinding.
[0015] As a preferred embodiment, the aqueous medium is pure water or an alkaline aqueous solution. The present invention primarily utilizes the hydrolysis reaction between AlN in aluminum ash and water in an aqueous medium to achieve denitrification. Experiments have shown that using a weakly alkaline solution as the medium can more effectively neutralize the local pH drop that may be caused by the dissolution of other acidic impurities during the AlN hydrolysis process, maintaining an alkaline environment conducive to hydrolysis and thus improving denitrification efficiency. Furthermore, the alkaline environment helps remove the oxide film on the surface of the aluminum metal, making it more ductile and increasing the recovery rate.
[0016] As a preferred solution, the wet grinding denitrification conditions are: a slurry liquid-to-solid mass ratio of (1.5-10):1, a temperature of 40-90°C, and a grinding time of 30-120 minutes. A low liquid-to-solid ratio enables efficient grinding and mass transfer. Furthermore, since the wet grinding process is accompanied by the production of water-soluble NH3, the limited amount of water can maintain the slurry pH at a high level, providing an alkaline environment for the wet grinding process. The applied temperature can achieve a higher denitrification rate in a shorter time. Since the hydrolysis of AlN (AlN + 3H2O → Al(OH)3 + NH3↑) is an endothermic chemical reaction, appropriately increasing the temperature within the scope of the present invention can significantly increase its reaction kinetics. Sufficient grinding time ensures that the AlN hydrolysis reaction is nearly complete, the metallic aluminum particles are sufficiently ductile and deformed to facilitate screening and recovery, and the soluble salts reach dissolution equilibrium, while reducing unnecessary energy consumption. By synergistically optimizing the liquid-to-solid ratio, temperature, and time, the residual harmful impurities in the aluminum-rich slag are reduced, and the formation of a large amount of low-melting-point phases or pores during subsequent high-temperature sintering is avoided, which seriously deteriorates the phase composition and macroscopic properties of the final calcium aluminate refined slag.
[0017] As a preferred solution, the pH of the alkaline aqueous solution is 8-12.
[0018] As a preferred solution, the soluble salt leaching treatment uses pure water and / or alkaline aqueous solution as a medium for stirring leaching.
[0019] As a preferred solution, the soluble salt leaching treatment temperature is 50-100°C, and the leaching time is 30-120 minutes. Leaching temperatures or times that are too short cannot ensure that the nitrogen and fluorine contents in the sintered product meet the relevant national standards (YB / T 4265-2011).
[0020] As a preferred solution, the soluble salt in the soluble salt leaching treatment includes at least one of fluoride and chloride.
[0021] As a preferred embodiment, the high-temperature calcination conditions are: using quicklime and / or limestone as the calcium source, a sintering temperature of 800-1400°C, and a holding time of 0.5-4 hours. The calcination temperature directly affects the content of the C12A7 phase in the final product. If the calcination temperature is too low, the reaction is incomplete, and the main phases remain CaO and Al2O3, with only a small amount of diffraction peaks of the calcium aluminate phase (such as CaO·Al2O3) appearing. If the sintering temperature is too high, the sintered product will experience partial melting, and the C12A7 phase will decompose or transform into other phases. The sintering temperature is further preferably between 1300-1400°C. Furthermore, the sintering temperature is between 1300-1350°C.
[0022] As a preferred solution, the mass ratio of the aluminum-rich slag and the calcium source is calculated based on the Al2O3 content in the aluminum-rich slag and the CaO content in the calcium source to control the molar ratio of CaO to Al2O3 in the sintered product to be (11.8~12):(7~7.2).
[0023] As a preferred solution, the mass fraction of the 12CaO·7Al2O3 phase in the calcium aluminate steelmaking refining slag is greater than or equal to 50%, the mass content of SiO2 is less than 4.0%, the mass content of S is less than 0.05%, the mass content of P is less than 0.05%, the mass content of N is less than 0.5%, and the mass content of F is less than 1.5%.
[0024] The present invention precisely blends the mixture to a molar ratio of CaO to Al2O3 close to 12:7, followed by sintering at a high temperature (e.g., 800-1400°C). At this temperature, the CaO and Al2O3 undergo a solid-phase reaction, producing a steelmaking refined slag dominated by the highly active dodecacalcium heptaaluminate (12CaO·7Al2O3, abbreviated as C12A7). This refined slag offers advantages such as a low melting point, strong desulfurization and deoxidation capabilities, and excellent inclusion adsorption, making it a highly sought-after, high-quality, off-furnace refining auxiliary material for the steel industry. As a preferred option, the aluminum-rich slag is mixed with a calcium source, briquetting, and then sintering, which can improve both processing efficiency and the C12A7 content in the final product while reducing impurity levels.
[0025] As a preferred solution, the ammonia gas generated during the wet grinding denitrification process can be collected and used to prepare ammonia water, ammonium sulfate or flue gas denitrification.
[0026] Compared with the prior art, the present invention has the following beneficial effects:
[0027] (1) This invention couples physical separation and chemical reaction in a single wet grinding process. It simultaneously utilizes the ductility of aluminum to separate the flaky or spherical particles formed during wet grinding from the particle size difference of other brittle materials. This separation is achieved by also utilizing wet grinding to promote AlN hydrolysis and denitrification, significantly shortening the process flow and improving processing efficiency. The denitrification rate can reach over 98%, and the aluminum recovery rate can reach over 80%.
[0028] (2) The present invention converts nitrogen into collectable ammonia through a wet process, and transfers fluorine and chlorine into a liquid phase for centralized treatment, fundamentally eliminating the harmfulness of aluminum ash. No secondary solid waste is generated throughout the process.
[0029] (3) The present invention utilizes wet denitrification and leaching to pre-remove most of the aluminum nitride (AlN) and fluorine and chloride salts, and can effectively avoid the negative impact of these impurities during the high-temperature sintering process, creating favorable conditions for the subsequent high-temperature calcification roasting. The main crystal phase of the prepared calcium aluminate refined slag is clear and is highly active C12A7. All physical and chemical indicators can meet the relevant national standards (YB / T 4265-2011). BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Figure 1 The following are scanning electron microscope (SEM) photos and energy spectrum (EDS) analysis of secondary aluminum ash used as raw material in the examples of the present invention.
[0031] Figure 2 This is the X-ray diffraction (XRD) pattern of the sample of aluminum-rich slag after enhanced leaching and drying in Example 4 of the present invention.
[0032] Figure 3 This is the X-ray diffraction (XRD) pattern of the calcium aluminate steelmaking refined slag product finally prepared in Example 4 of the present invention. DETAILED DESCRIPTION
[0033] The present invention will be further described in detail below with reference to specific examples. These examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.
[0034] Unless otherwise specified, the aluminum ash raw materials used in the following examples and comparative examples are all secondary aluminum ash from an aluminum plant, and their main chemical components (mass fraction) are: metallic aluminum (Al) 17.53%, aluminum oxide (Al2O3) 50.77%, aluminum nitride (AlN) 23.38%, silicon dioxide (SiO2) 0.94%, fluoride (as F - 1.68% chloride (as Cl - The rest are small amounts of other oxides.
[0035] Example 1
[0036] This embodiment provides a basic solution for aluminum ash treatment.
[0037] (1) Pretreatment: 100 g of the aluminum ash raw material was dry-ground in a laboratory conical ball mill. The grinding balls were steel balls and the rotation speed was 112 r / min. After dry grinding for 30 minutes, the raw material was sieved with a 100-mesh sieve. The aluminum metal particles and flakes on the sieve were recovered, and the aluminum ash fine powder with a size of -150 μm below the sieve was used as the raw material for wet grinding.
[0038] (2) Wet grinding for aluminum extraction and denitrification: 50 g of the -150 μm aluminum ash fine powder after dry grinding was taken and continued to be put into the conical ball mill, 75 g of deionized water (liquid-solid mass ratio 1.5:1) was added, nitrogen was introduced, and grinding was started. At the same time, the slurry temperature was heated and maintained at 80 ° C. During the reaction, obvious ammonia gas escaped. After 60 minutes of wet grinding, the grinding was stopped. The slurry was sieved through a standard sieve with a pore size of 75 μm, and the sieve material was collected, which was the flaky and spherical metallic aluminum. The sieve material was washed with ethanol, dried and weighed to obtain 10 g of metallic aluminum. After filtering and drying the slurry, the nitrogen content was detected by the Kjeldahl method, and the AlN removal rate was measured to reach 67.83%.
[0039] (3) Preparation of refined slag: The sieve slurry obtained in step (2) was vacuum filtered to obtain an aluminum-rich slag filter cake and a filtrate. 25 g of the dried and ground filter cake was placed back in a beaker, 37.5 g of pure water was added, and the mixture was stirred and washed at 80°C for 45 minutes. The mixture was filtered again to obtain a purified aluminum-rich slag filter cake. The filter cake was dried at 105°C to obtain a dry aluminum-rich slag powder. Samples were taken and analyzed for its composition, which was mainly Al2O3 and Al(OH)3, with a total Al2O3 content of approximately 85.3 wt%. According to the Al2O3 content in the slag, the ingredients were prepared according to a CaO / Al2O3 molar ratio of 12:7. Analytical pure CaO powder was weighed and thoroughly mixed with the aluminum-rich slag powder in a mortar. The mixture was placed in a corundum crucible, placed in a muffle furnace, and sintered at 1300°C for 2 hours. After natural cooling, it was taken out to obtain a grayish-white block sintered product, which was the calcium aluminate refined slag.
[0040] After testing, the refined slag has a C12A7 phase content of 75.8wt%, an Al2O3 content of 48.8wt%, a CaO content of 37.4wt%, a N content of 0.37%wt, a F content of 1.39wt%, and a SiO2 content of 0.8wt%, which meets the YB / T 4265-2011 standard.
[0041] Example 2
[0042] This example aims to investigate the effect of wet grinding media on the treatment effect.
[0043] The process was essentially the same as Example 1, with the only difference being that in step (2) wet grinding for aluminum extraction and denitrification, 75 g of deionized water was replaced with 75 g of a pH 10 NaOH aqueous solution. All other steps and conditions (liquid-to-solid ratio, temperature, and time) remained unchanged.
[0044] The AlN removal rate reached 89.27%. The final calcium aluminate refined slag had a C12A7 phase content of 78.2 wt%, with performance slightly better than that of Example 1.
[0045] The results show that using a weakly alkaline solution as a medium can more effectively neutralize the local pH drop that may be caused by the dissolution of other acidic impurities during the AlN hydrolysis process, maintaining an alkaline environment that is conducive to hydrolysis, thereby improving denitrification efficiency. At the same time, the alkaline environment helps remove the oxide film on the surface of the aluminum metal, making it more ductile and improving the recovery rate.
[0046] Example 3
[0047] This example aims to investigate the effect of sintering temperature on the physical phase of the final product.
[0048] Step (1) and step (2) are exactly the same as those in Example 1. In step (3) of preparing refined slag, the high-temperature sintering temperatures are set to 800°C, 1100°C, and 1400°C, respectively, and the holding time is still 2 hours.
[0049] Group A (800℃): The sintered product was a grayish-white agglomerate mixed with gray impurities. XRD analysis showed that the main phases were still CaO and Al2O3, with only a small amount of diffraction peaks of calcium aluminate phase (such as CaO·Al2O3) appearing. The content of the target phase C12A7 phase was less than 5wt%, indicating that the calcination temperature was too low and the reaction was incomplete.
[0050] Group B (1100℃): The sintered product is a white, fine-porous block. XRD analysis shows that the C12A7 phase has become the main crystalline phase with a content of about 45wt%, but there is still a small amount of unreacted raw material.
[0051] Group C (1400°C): The sintered product exhibited localized melting. XRD analysis revealed that, in addition to the C12A7 phase, numerous other calcium aluminate phases (e.g., CA and C3A) were present, while the C12A7 phase content decreased. This suggests that excessively high temperatures may have caused the C12A7 phase to decompose or transform into other phases.
[0052] This example shows that sintering temperature is a key factor in controlling the quality of the final product. In the system of the present invention, 1300-1400°C is the appropriate temperature range for generating a high content of C12A7 phase.
[0053] Example 4
[0054] This example demonstrates the optimized combination of the method of the present invention.
[0055] (1) Pretreatment: Same as Example 1.
[0056] (2) Wet grinding for aluminum extraction and denitrification: The conditions of Example 2 were adopted, i.e., a NaOH aqueous solution with a pH of 10 was used as the medium, and wet grinding was carried out at 80°C for 60 minutes.
[0057] (3) Preparation of refined slag: The conditions of Example 1 were adopted, but after mixing with CaO, it was first pressed into blocks at a pressure of 20 MPa, and then placed in a muffle furnace and sintered at 1300°C for 2 hours.
[0058] The aluminum metal recovery rate reached 80%, and the denitrification rate reached 95%. The resulting calcium aluminate refined slag had a dense and uniform appearance. XRD analysis revealed a C12A7 phase content of 82.5wt%, an Al2O3 content of 46.6wt%, a CaO content of 41.8wt%, a N content of 0.09wt%, a F content of 0.87wt%, a SiO2 content of 0.7wt%, and S and P contents of less than 0.05wt%. All indicators fully met the requirements of the YB / T 4265-2011 standard.
[0059] This example illustrates that by optimizing the wet grinding media, briquetting the powder before sintering, and appropriately increasing the sintering temperature, the process efficiency and final product quality can be synergistically improved.
[0060] Comparative Example 1
[0061] This comparative example is used to illustrate the necessity of the "pretreatment step" in the present invention.
[0062] Compared with Example 1, the dry grinding pretreatment in step (1) was omitted. Instead, 50 g of the untreated aluminum ash raw material, a mixture of lumps and powders, was directly subjected to wet ball milling and the operation in step (2) was carried out. After 60 minutes of wet milling, the product was sieved to obtain 4 g of metallic aluminum. Analysis of the final slurry showed an AlN removal rate of 46.8%.
[0063] The results showed that the unpretreated raw material had severe internal phase encapsulation and a small specific surface area, resulting in insufficient dissociation of metallic aluminum and incomplete AlN hydrolysis within the same wet milling time, resulting in a treatment efficiency far lower than that of Example 1, which underwent pretreatment. This comparative example demonstrates the importance of the pretreatment step in achieving sufficient dissociation of the components and improving the efficiency of subsequent treatments.
[0064] Comparative Example 2
[0065] This comparative example is intended to illustrate the necessity of the "wet grinding" step in the present invention.
[0066] The step (2) "wet grinding" in Example 1 was changed to "water washing and leaching". That is, 50 g of dry-ground aluminum ash fine powder was added to 75 g of deionized water at 80°C and magnetically stirred in a beaker for 60 minutes without applying grinding action.
[0067] After stirring, the slurry was a uniform gray suspension, and the aluminum particles could not be effectively separated by screening. Sampling analysis showed that the AlN removal rate was only 38.7%, far lower than the 67.83% in Example 1.
[0068] This comparative example demonstrates that water washing and leaching cannot effectively separate metallic aluminum, nor can it provide sufficient mechanical energy to accelerate AlN hydrolysis. The "wet grinding" process proposed in this invention, with its intense impact and grinding action, is key to achieving efficient synergy between physical separation and chemical reaction, and is the core of the technical effectiveness of this invention.
[0069] Comparative Example 3
[0070] This comparative example aims to illustrate as a whole the necessity of the three-step coordinated pre-treatment process of "dry grinding-wet grinding-water washing and leaching" proposed in the present invention for ultimately obtaining an improved calcium aluminate refined slag roasting product.
[0071] Compared to Example 1, the process flow of this comparative example completely omits the three-step pretreatment process of "dry grinding-wet grinding-water washing and leaching" included in the present invention. Instead, the raw aluminum ash and calcium source are directly mixed and briquette-pressed before undergoing a single high-temperature sintering step. The sintering schedule used in Example 1 is identical: sintering at 1300°C for 2 hours.
[0072] When the temperature rises above 700°C, a strong ammonia gas and pungent odor emanate from the furnace, indicating that the AlN and fluorine- and chloride-containing salts in the raw materials decompose and volatilize at high temperatures, causing some chemical corrosion to the furnace. The sintered product is non-uniform, contains a large number of impurities, has a loose structure, and some areas are in a molten glass state, failing to meet the specified physical and chemical specifications for calcium aluminate refining slag.
[0073] Comparative Example 4
[0074] This comparative example aims to illustrate the overall necessity of the systematic pre-treatment (dry grinding, wet grinding, water washing and leaching) and the addition of a calcium source proposed in the present invention for preparing qualified calcium aluminate refined slag.
[0075] Compared with Example 1, the process flow of this comparative example directly places the original, loose block and powder mixture into a corundum crucible, and then places the crucible into a muffle furnace, using the same sintering system as Example 1, that is, sintering at 1300°C for 2 hours.
[0076] During the heating process, especially above 700°C, ammonia and a pungent odor are emitted from the furnace, indicating that the AlN and fluorine- and chloride-containing salts in the raw materials are decomposing and volatilizing at high temperatures. Simultaneously, the metallic aluminum in the raw materials melts and oxidizes at high temperatures. The resulting product, after sintering, is not a refined slag of any kind, but rather a sintered mass with a mottled color (black, gray, and white), a loose structure, some areas with a metallic luster (incompletely oxidized aluminum), and others with a charred appearance. Its primary phases are metallic aluminum and corundum (α-Al2O3) formed by the oxidation of some aluminum nitride, as well as spinel and other impurities inherent in the raw materials. The target phase, dodecacalcium heptaaluminate (C12A7), is absent.
Claims
1. A resource utilization method for preparing calcium aluminate by denitrification and aluminum extraction of aluminum ash and calcification roasting, characterized by: The raw aluminum ash is dry-ground to achieve monomer dissociation to the micron level and then sieved. The obtained aluminum ash fine powder is wet-ground in an aqueous medium for denitrification, and the metallic aluminum is sieved to recover and obtain aluminum-rich slag slurry. The aluminum-rich slag slurry is subjected to solid-liquid separation and soluble salt leaching to obtain purified aluminum-rich slag. The purified aluminum-rich slag is subjected to high-temperature calcification and roasting to obtain calcium aluminate steelmaking refined slag with 12CaO·7Al2O3 as the main crystal phase.
2. The resource utilization method of aluminum ash denitrification and aluminum extraction-calcification roasting to prepare calcium aluminate according to claim 1, characterized in that: The dry grinding adopts a conical ball mill to grind to a particle size of less than or equal to 150 μm, and the grinding time is 10 to 60 minutes; the raw aluminum ash is secondary aluminum ash.
3. The resource utilization method of preparing calcium aluminate by denitrification and aluminum extraction of aluminum ash and calcification roasting according to claim 2, characterized in that: The aqueous medium is pure water or alkaline aqueous solution; and / or; The conditions for wet grinding denitrification are: a liquid-to-solid mass ratio of the slurry is (1.5-10):1, a temperature is 40-90°C, and a time is 30-120 minutes.
4. The resource utilization method of preparing calcium aluminate by denitrification and aluminum extraction of aluminum ash and calcification roasting according to claim 3, characterized in that: The pH of the alkaline aqueous solution is 8-12.
5. The resource utilization method of preparing calcium aluminate by denitrification and aluminum extraction of aluminum ash and calcification and roasting according to any one of claims 1 to 4, characterized in that: The soluble salt leaching treatment adopts pure water and / or alkaline aqueous solution as the medium for stirring leaching; and / or; The temperature for leaching the soluble salt is 50-100° C., and the leaching time is 30-120 minutes.
6. The resource utilization method of aluminum ash denitrification and aluminum extraction-calcification roasting to prepare calcium aluminate according to claim 5, characterized in that: The soluble salt in the leaching soluble salt treatment includes at least one of fluoride and chloride.
7. The resource utilization method of aluminum ash denitrification and aluminum extraction-calcification roasting to prepare calcium aluminate according to claim 1 or 5, characterized in that: The conditions for high-temperature calcification roasting are: using quicklime and / or limestone as a calcium source, a sintering temperature of 800-1400° C., and a holding time of 0.5-4 hours.
8. The resource utilization method of aluminum ash denitrification and aluminum extraction-calcification and roasting to prepare calcium aluminate according to claim 7, characterized in that: The mass ratio of the aluminum-rich slag to the calcium source is calculated based on the Al2O3 content in the aluminum-rich slag and the CaO content in the calcium source to control the molar ratio of CaO to Al2O3 in the sintered product to be (11.8~12):(7~7.2).
9. The resource utilization method of aluminum ash denitrification and aluminum extraction-calcification and roasting to prepare calcium aluminate according to claim 8, characterized in that: The calcium aluminate steelmaking refining slag has a mass fraction of 12CaO·7Al2O3 phase greater than or equal to 50%, a mass content of SiO2 less than 4.0%, a mass content of S less than 0.05%, a mass content of P less than 0.05%, a mass content of N less than 0.5%, and a mass content of F less than 1.5%.
10. The resource utilization method of aluminum ash denitrification and aluminum extraction-calcification and roasting to prepare calcium aluminate according to claim 1, 8 or 9, characterized in that: The ammonia generated during the wet grinding denitrification process can be collected and used to prepare ammonia water, ammonium sulfate or flue gas denitrification.