Method for producing sandy alumina by treating aluminum ash through soda lime sintering method

Abstract

The invention discloses a method for producing sandy aluminum oxide by treating aluminum ash through a soda lime sintering method, and belongs to the technical field of aluminum industry environmental protection. According to the invention, the aluminum ash, sodium carbonate and limestone are mixed according to a certain proportion, high-temperature sintering is directly carried out, and the sandy alumina is obtained through the procedures of ball milling alkaline leaching, solid-liquid separation, deep desilicication, carbon component strengthening and the like, so that the risk that toxic combustible and explosive gases such as ammonia gas, methane, hydrogen and the like are generated when the traditional aluminum ash is washed with water is avoided; salt such as chlorine salt and villiaumite volatilized at high temperature is prepared into the aluminum smelting fluxing medium according to a proper proportion, so that high-value resource utilization of the aluminum ash is realized. The efficient desiliconizing agent is prepared from barium aluminate, hydrated calcium aluminate, hydrated calcium carboaluminate and lime milk according to a certain proportion, the desiliconizing effect is greatly improved compared with that of traditional lime milk, and a solid guarantee is provided for producing qualified sandy alumina. The concentration of carbon dioxide adopted for common carbon separation is 30-40%, the concentration of carbon dioxide in tail gas generated by the rotary kiln is about 10%, and the carbon separation efficiency is low, so that the concentration of carbon dioxide generated by the tail gas of the rotary kiln can be increased to 60-70% by adopting a purification-special silica gel pressure swing adsorption mode; the decomposition rate of the sodium aluminate solution and the yield of aluminum hydroxide are greatly improved, the effect of enhancing carbon content is achieved, carbon dioxide generated by the tail gas of the rotary kiln is reasonably utilized, and the carbon emission is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum industry environmental protection, and particularly relates to a method for producing sandy aluminum oxide by treating aluminum ash with a soda-lime sintering method. Background Art

[0002] Aluminum ash is produced in all aluminum melting processes such as aluminum electrolysis and aluminum (including recycled aluminum) processing. Its sources can be divided into aluminum electrolysis smelting process, aluminum casting process and recycled aluminum processing process. It is often divided into primary aluminum ash and secondary aluminum ash. Usually, the slag produced during the original aluminum casting, scrap aluminum smelting, melt transfer and purification and impurity removal process is classified as primary aluminum ash, in which the metallic aluminum content is relatively high, as high as 15-75%. The fine aluminum ash produced after the aluminum metal is separated and recovered by various methods is called secondary aluminum ash. The main treatment object of the present invention is secondary aluminum ash.

[0003] Currently, there are three main methods for disposing aluminum ash: wet processing, pyrolysis, and wet processing combined with pyrolysis. However, there is still a lack of a process technology that combines economic, environmental, and social benefits. For example, patent CN1673084A provides a method for producing aluminum oxide from waste aluminum ash, and patent CN104261445 provides a method for harmlessly treating aluminum ash and preparing sand-like aluminum oxide. Both methods use wet alkaline washing to remove reactive substances such as aluminum nitride, aluminum carbide, and metallic aluminum from the aluminum ash, generating toxic, flammable, and explosive gases such as ammonia, methane, and hydrogen, which increases the risk of safe disposal of the aluminum ash. In addition, the wet treatment processes such as water washing and alkaline washing dissolve a large amount of chloride and some fluoride in the aluminum ash, resulting in a large amount of waste brine such as chloride in the wet solution, causing secondary pollution. The treatment of aluminum ash is still in its early stages, and a considerable amount of aluminum ash is buried or discarded without treatment. Not only is the useful components in the aluminum ash not effectively and comprehensively utilized, but it also causes serious environmental pollution. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for producing sand-like alumina from aluminum ash using a soda-lime sintering process, in order to address the problems of the prior art described above. The present invention innovatively proposes key core technologies, such as "soda-lime sintering crystallization transformation - denitrification / chlorine-fluorine fixation - deep desiliconization - and enhanced carbonization," for the production of high-quality alumina. This process is a safe, green, and efficient new technology for the resource utilization of aluminum ash, solving the challenges of safe and harmless disposal and high-value resource utilization of aluminum ash, and achieving high-value utilization of all components of aluminum ash.

[0005] A method for producing sand-like alumina by treating aluminum ash with an alkali-lime sintering process comprises the following steps: uniformly mixing aluminum ash, soda ash, and limestone, and then sintering to obtain sintered clinker, and collecting tail gas; adding alkali liquor to the sintered clinker, and ball milling to obtain clinker slurry; diluting the clinker slurry, and further alkali leaching, and performing solid-liquid separation on the obtained leached slurry to obtain a filtrate and a leached residue; deeply desiliconizing the leached solution, strengthening carbon content, and performing solid-liquid separation to obtain an aluminum hydroxide precipitate and a sodium carbonate solution; and roasting the aluminum hydroxide precipitate to obtain the sand-like alumina.

[0006] The carbon enhancement process includes treating the tail gas collected during the alkali sintering process to obtain sintering tail gas with a carbon dioxide content of 60-70%; and then introducing the sintering tail gas into the desiliconized leaching solution to precipitate aluminum hydroxide.

[0007] The basic principle of the soda-lime sintering method: The soda-lime sintering method is a process that mixes aluminum ash, sodium carbonate, and limestone in a certain proportion and sinters them at high temperature. Its core principle is to use sodium carbonate to react with Al2O3 in the aluminum ash to produce soluble NaAlO2, while SiO2 in the aluminum ash reacts with lime to produce insoluble 2CaO·SiO2, thereby achieving the separation of aluminum and silicon. The fluoride in the aluminum ash reacts with lime to produce calcium fluoride, achieving the solidification of fluorine. During the sintering process, the oxides in the raw material (such as Al2O3, Fe2O3, SiO2, and TiO2) are converted into sodium aluminate, sodium ferrite, dicalcium silicate, and calcium titanate, respectively. After roasting, the sodium aluminate can be dissolved in an alkaline solution to extract aluminum oxide. The residue containing phases such as dicalcium silicate, hematite, and calcium titanate can be used as a raw material for Portland cement. The alkaline solution is evaporated and concentrated to precipitate soda ash, which is used as a raw material for sintering.

[0008] The mixed raw materials are placed in a rotary kiln or other high-temperature equipment and sintered at temperatures between 1100°C and 1300°C. During the sintering process, the mullite phase (3Al2O3·2SiO2) and quartz phase (SiO2) in the fly ash react with lime and sodium carbonate to form water-soluble sodium aluminate (NaAlO2) and insoluble dicalcium silicate (2CaO·SiO2).

[0009] The specific reaction equations involved in the soda lime sintering process are as follows:

[0010] CaCO3→CaO+CO2↑;

[0011] SiO2+2CaO→2CaO·SiO2;

[0012] Al2O3+Na2CO3→2NaAlO2+CO2↑;

[0013] Al6Si2O 13+4CaO+3NaCO3→2Ca2SiO4+6NaAlO2+3CO2↑;

[0014] Fe2O3+Na2CO3→Na2O·Fe2O3+CO2↑;

[0015] TiO2+CaO→CaTiO3.

[0016] After the clinker is crushed, aluminum and silicon are separated by alkaline solution. NaAlO2 dissolves in the solution, dicalcium silicate and calcium titanate enter the slag phase, and NaFeO2 is hydrolyzed and converted into Fe2O3·3H2O, which precipitates into the slag phase, realizing solid-liquid separation.

[0017]

[0018] Na2Fe2O4+4H2O→2NaOH+Fe2O3·3H2O↓;

[0019] Aluminum hydroxide is obtained through filtration separation, deep desiliconization, and enhanced carbon separation, and then the aluminum hydroxide is calcined to obtain the alumina product.

[0020] 2Al(OH)3→3Al2O3+3H2O;

[0021] The alkali sintering process solves the problem of converting inert alumina such as α-type and mullite-type into active sodium aluminate, realizes crystal transformation, improves the utilization rate of aluminum, and solves the problem of industrial rotary kiln scarring; adding an appropriate amount of limestone solidifies most of the fluoride, and the aluminum nitride in the aluminum ash is oxidized into nitrogen oxides, which are converted into nitrogen after denitrification, and the chloride salt evaporates into smoke. Chlorine and a small amount of fluoride salts can be used to produce slag removers for aluminum smelting according to a certain ratio; the carbon separation process has high requirements for the silicon content in the sodium aluminate solution. The present invention provides a new and efficient desiliconization method to ensure carbon separation. High-quality aluminum hydroxide precipitate is produced during the carbonization process, providing a solid guarantee for the production of qualified sand-like alumina products; the concentration of carbon dioxide used in ordinary carbonization is 30-40%, while the carbon dioxide concentration in the tail gas generated by the rotary kiln is about 10%, and the carbonization efficiency is relatively low. The present invention adopts a purification-special silica gel pressure swing adsorption method to increase the carbon dioxide concentration generated by the rotary kiln tail gas to 60-70%, greatly improving the decomposition rate and yield of the sodium aluminate solution, achieving the effect of strengthening carbonization, and rationally utilizing the carbon dioxide generated by the rotary kiln tail gas, thereby reducing carbon emissions.

[0022] Preferably, the mass ratio of the aluminum ash, soda ash and limestone is 1:(1-1.4):(0.1-0.2).

[0023] Preferably, the sintering temperature is 1100-1300° C., and the sintering time is 30-60 minutes.

[0024] Preferably, the solid-liquid ratio of the sintered clinker to the alkali solution is 1:(1-3) (g / mL).

[0025] Preferably, the alkali leaching is performed by adding alkali solution to the clinker slurry to dilute the solid-liquid ratio to 1:(3-5) (g / mL).

[0026] More preferably, the alkali leaching time is 1-3 hours.

[0027] Preferably, the deep desiliconization comprises the following steps: adding a complex of barium aluminate, hydrated calcium aluminate, hydrated calcium carbonoaluminate and lime milk to the leachate, and performing solid-liquid separation after the desiliconization reaction to obtain a purified leachate.

[0028] More preferably, the mass ratio of the barium aluminate, hydrated calcium aluminate and hydrated calcium carbonoaluminate is (3-5):(1-2):(2-3); the solid-liquid ratio of the mixture of the barium aluminate, hydrated calcium aluminate and hydrated calcium carbonoaluminate to the lime milk is 1:(20-40) (g / mL), and the solid content of the lime milk solution is 80-100 g / L.

[0029] Preferably, the flow rate of the sintering tail gas in the enhanced carbon fraction is 16-35 L / min, the temperature of the enhanced carbon fraction is 50-70° C., and the time is 90-240 min.

[0030] Preferably, the calcination temperature is 900-1000° C. and the calcination time is 10-30 minutes.

[0031] Compared with the prior art, the present invention has the following advantages and technical effects:

[0032] The present invention uses a direct soda-lime sintering method to convert inert aluminum oxides such as α-type and mullite-type aluminum oxides in aluminum ash into active sodium aluminate to the greatest extent possible, successfully resolving the problem of crystal transformation and thereby improving aluminum utilization. Simultaneously, by adding an appropriate amount of limestone, most of the fluorides are solidified. The aluminum nitride in the aluminum ash is oxidized to nitrogen oxides, which are then converted into nitrogen gas after denitrification treatment, while the chloride salts are volatilized into the smoke. Substances containing chlorine and a small amount of fluoride salts can be used in a certain proportion to produce a slag remover for aluminum smelting. This method completely solves the problem of reactive substances such as aluminum nitride, aluminum carbide, and metallic aluminum in the aluminum ash generating toxic, flammable, and explosive gases such as ammonia, methane, and hydrogen. Furthermore, the chlorides and fluorides in the aluminum ash are crystallized and precipitated after high-temperature evaporation. Appropriate salts such as chlorides and fluorides are added in a certain proportion to prepare a slag remover for aluminum smelting, achieving safe disposal of the aluminum ash and full utilization of its valuable components.

[0033] Conventional carbon separation uses carbon dioxide at a concentration of 30-40%, while the carbon dioxide concentration in the tail gas produced by the rotary kiln is about 10%, resulting in a low carbon separation efficiency. The present invention uses a purification-special silica gel pressure swing adsorption method to increase the carbon dioxide concentration produced by the rotary kiln tail gas to 60-70%, greatly improving the decomposition rate of the sodium aluminate solution and the yield of aluminum hydroxide, achieving the effect of enhanced carbon separation, and rationally utilizing the carbon dioxide produced by the rotary kiln tail gas, thereby reducing carbon emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 The present invention provides a process flow chart of a method for producing sand-like alumina by treating aluminum ash with a soda-lime sintering method. DETAILED DESCRIPTION

[0036] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0037] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0038] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0039] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0040] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0041] The present invention has done a lot of research and development work from laboratory to pilot scale to industrial application, and proposed the concept of "safe and high-value utilization of all components". It has developed key core technologies such as "soda lime burning crystallization transformation - denitrification / chlorine solidification - deep desiliconization - enhanced carbon separation" to produce high-quality alumina. This process technology is a safe, green and efficient new technology for the utilization of aluminum ash resources, which solves the problem of safe and harmless aluminum ash and high-value resource utilization. In order to further demonstrate the difference between the present invention and the existing technology, the three methods of wet method, pyrolysis and wet method + pyrolysis are now explained as follows:

[0042] 1) Wet treatment process

[0043] This method is based on the physical properties of aluminum nitride, metallic aluminum, and aluminum carbide in aluminum ash that readily react with water to form aluminum hydroxide, ammonia, hydrogen, and methane. It transforms harmful substances in the aluminum ash through a hydrolysis reaction. This method is primarily produced in workshops, concentrated in Guangdong, Henan, and other regions. The conversion process volatilizes the ammonia, hydrogen, and methane gases for collection and disposal, while simultaneously solidifying the soluble fluorides in the secondary aluminum ash. This completes the transformation of the aluminum ash from hazardous waste to general industrial waste, achieving harmless disposal of the secondary aluminum ash. However, the alumina in the aluminum ash is not utilized as a resource, resulting in a low added value product.

[0044] The combustible gases such as hydrogen and methane generated during this disposal process can be recycled and reused as fuel, and ammonia can be prepared into ammonia water for sale. The advantage of recycling ammonia water is that the process is relatively simple and the equipment investment is relatively small. However, combustible gases such as hydrogen and methane are flammable and explosive gases. The combustion and explosion prevention and control requirements of these gases are high, the decomposition of nitrogen compounds is incomplete, the ammonia recovery rate is low, and the concentration of the obtained ammonia water is low (1.5-7.5%). In addition, a large amount of high-salt solution wastewater is generated and urgently needs to be treated.

[0045] In addition, by adding acid or alkaline solution during the water washing process, products such as aluminum sulfate, aluminum chloride and aluminum hydroxide can be prepared. However, the alumina in the aluminum ash is mainly mullite phase and α type, which has problems such as low reaction efficiency, high product impurities, low product added value and weak market competitiveness.

[0046] 2) Pyrometallurgical treatment process

[0047] This process primarily involves roasting aluminum ash under high-temperature, oxygen-containing conditions. Appropriate chemical substances, such as alkaline substances like calcium carbonate and sodium carbonate, can be added during the roasting process to produce products such as steel desulfurizers and cement accelerators. Currently, industrialized applications have been achieved in steel desulfurizers, exemplified by the 30,000-ton / year aluminum ash treatment line in Zunyi. This process utilizes a high-temperature roasting reaction of aluminum ash and limestone to produce a calcium aluminate composite desulfurizer, which is used as a desulfurizer for steelmaking raw materials. This treatment process denitrifies nitrides, such as aluminum nitride, from the aluminum ash by converting them into nitrogen gas. Fluorine and chlorine primarily enter the dust, while aluminides are primarily converted into calcium aluminate products, achieving harmless and resourceful utilization of the aluminum ash. However, this product is significantly affected by steel market conditions, leading steelmakers to reduce their use of calcium aluminate, resulting in sluggish sales. Sodium carbonate can also be added during the roasting process to produce sodium aluminate, which is used in cement slow-release agents. However, the national policy favors alkali-free accelerators, and the chlorine content in the material does not meet the requirements for cement accelerators, forcing this process to adapt. In addition, researchers have also studied the addition of a certain proportion of aluminum ash as a sintering raw material for refractory materials or as an additive to cement. However, due to the high salt content and complex impurities in aluminum ash, these have adverse effects on refractory performance, especially the effects of fluorine and chlorine. Therefore, large-scale industrial application has not been achieved.

[0048] 3) Wet + pyrometallurgical treatment process

[0049] This process combines the advantages of both wet and pyrometallurgical processes. Based on proprietary technologies developed by the Kunming Metallurgical Research Institute and Central South University, Yunnan Wenshan Aluminum Co., Ltd. established a production line capable of processing 50,000 tons of aluminum ash annually. The wet process accelerates the decomposition of nitrides by adding a dilute alkaline solution. This solution is then absorbed in an absorption tower to produce dilute ammonia for desulfurization. The generated combustible gases, such as hydrogen and methane, are collected and used as roasting fuel, saving energy. The hydrolyzed aluminum ash is then injected at high pressure into a rotary kiln for roasting, producing sodium aluminate clinker. This is then milled and dissolved in a ball mill before entering the Bayer process alumina production system.

[0050] This process realizes the resource utilization of ammonia, hydrogen and methane; aluminum ash is fed in the form of high-pressure injection after hydrolysis, and the material reaction is more complete and rapid; the sintered clinker is incorporated into the 1.4 million tons / year alumina production system, which reduces the operating cost of the production line, and the leached slag enters the slag storage along with the red mud. However, the explosion-proofness of flammable gases such as hydrogen and methane in the wet reaction process and how to increase the concentration of ammonia water are still huge challenges. The generation of a large amount of wastewater containing fluorine and chloride salts has adverse effects on the entire alumina production system, such as a decrease in decomposition rate and scarring of the evaporator; the moisture content of aluminum ash after hydrolysis is relatively high (about 35%), resulting in energy consumption of sintering aluminum ash (about 100m 3 / t-aluminum ash) is higher, 30m higher than direct fire sintering 3As mentioned above, the alkali content of the leached residue after incorporation into Bayer process production is high, limiting its resource utilization. In addition, many companies do not have Bayer process alumina production lines, which also limits the promotion and application of this process technology.

[0051] The embodiment of the present invention provides a method for producing sand-like alumina by treating aluminum ash with a soda-lime sintering method, which mainly includes the steps of batching - sintering - ball milling - dissolution - solid-liquid separation - desiliconization - carbon separation - roasting. The specific steps are as follows:

[0052] Ingredients: Aluminum ash, industrial soda ash and limestone are mixed in a mass ratio of 1: (1-1.4): (0.1-0.2), and stirred evenly to obtain a mixed raw material;

[0053] Sintering: The mixed raw materials are roasted at 1100-1300℃ for 30-60min, and then cooled to room temperature to obtain sintered clinker; more than 98% of the chloride salt and more than 70% of the fluoride salt volatilize to smoke dust at high temperature. According to the formula of the slag agent, an appropriate amount of chloride salt and fluoride salt are added to prepare a slag agent for electrolytic aluminum and aluminum processing. The remaining 30% of the fluoride salt reacts with limestone at high temperature to generate calcium fluoride (fluorite), so that the fluoride is solidified; the tail gas generated in the sintering process is subjected to dust removal, denitrification, purification, and concentration by a special silica gel pressure swing adsorbent to obtain The sintering tail gas with a carbon dioxide content of 60-70% is used as the gas source for carbon content. The present invention uses soda lime to directly sinter aluminum ash, which can convert inert aluminum oxides such as α-type and mullite-type in the aluminum ash into active sodium aluminate, thereby realizing the crystal transformation of the inert aluminum oxide in the aluminum ash, improving the utilization rate of aluminum, and avoiding the hydrolysis of aluminum ash when it encounters moisture to generate toxic, flammable and explosive gases such as ammonia, methane and hydrogen, thereby improving the safety of aluminum ash utilization. The addition of appropriate limestone solidifies the non-volatile fluoride in the aluminum ash, so that the leached residue of the aluminum ash becomes general industrial solid waste after washing, thereby realizing the harmlessness of the aluminum ash.

[0054] Ball milling: adding alkali solution to the obtained sintered clinker and ball milling for 10-30 minutes. The particle size is required to be 63 μm or more, accounting for more than 75%. The concentration of sodium carbonate in the alkali solution is 100-150 g / L. The solid-liquid ratio of sintered clinker to alkali solution is 1: (1-3) (g / mL). After ball milling, clinker slurry is obtained.

[0055] Dissolution: The above clinker slurry is further diluted with alkali solution (sodium carbonate concentration is 100-150g / L) to a solid-liquid ratio of 1:(3-5) (g / mL), and the sodium aluminate not dissolved during the ball milling process is further dissolved. The dissolution residence time is 1-3h to obtain a leaching slurry. The dissolution rate of aluminum oxide in the aluminum ash reaches more than 90%;

[0056] Liquid-solid separation: The leachate slurry is subjected to liquid-solid separation using a plate and frame filter press to obtain a filtrate (sodium aluminate solution) and a leach residue. Hot water (90°C) is used as a washing liquid, and the solid-liquid ratio of the leach residue to the washing liquid is 1:3 (g / mL). Countercurrent washing is performed to obtain the washing liquid and a leach residue composed mainly of substances such as 2CaO SiO2, CaO, MgO, Fe2O3, Na3MgAlSi2O8, and NaAlSiO4. The leach residue is similar to the main components of cement and can be used as a cement additive. The washing liquid is added to the filtrate as a diluent to obtain a leachate.

[0057] Deep desiliconization: The leachate contains a small amount of impurities such as silicon and iron, which require further removal. The specific method includes adding a complex of barium aluminate, hydrated calcium aluminate, hydrated calcium carbonoaluminate, and lime milk to the leachate, performing a desiliconization reaction, and then performing solid-liquid separation to obtain a purified leachate. The mass ratio of barium aluminate, hydrated calcium aluminate, and hydrated calcium carbonoaluminate is (3-5):(1-2):(2-3); the solid-to-liquid ratio of the mixture of barium aluminate, hydrated calcium aluminate, and hydrated calcium carbonoaluminate to lime milk is 1:(20-40) (g / mL), and the solid content of the lime milk solution is 80-100 g / L.

[0058] Enhanced carbon separation: The calcined tail gas with a carbon dioxide content of 60-70% is introduced into the purified leachate, and the sodium aluminate is decomposed to separate aluminum hydroxide. The liquid and solid are separated to obtain aluminum hydroxide and sodium carbonate solution. The aluminum hydroxide is washed with three-stage countercurrent washing to remove impurities and alkali. The last stage of washing uses distilled water from evaporated crystallized sodium carbonate.

[0059] Conventional carbon separation uses a carbon dioxide concentration of about 30-40%, while the carbon dioxide concentration in the tail gas produced by the rotary kiln is about 10%, resulting in a low carbon separation efficiency. The present invention uses a dust removal-denitrification-purification-special silica gel pressure swing adsorbent concentration method to increase the carbon dioxide concentration produced by the rotary kiln tail gas to 60-70%, greatly improving the decomposition rate and yield of the sodium aluminate solution, achieving the effect of enhanced carbon separation, and rationally utilizing the carbon dioxide produced by the rotary kiln tail gas, thereby reducing carbon emissions.

[0060] Calcination: Calcinate the obtained aluminum hydroxide at 900-1000℃ for 10-30min to obtain high-quality alumina;

[0061] The sodium carbonate solution is evaporated and crystallized to obtain sodium carbonate crystals, which are dried and used as raw materials in the sintering process. The water obtained by evaporation is distilled water, which is used for countercurrent washing of aluminum hydroxide to achieve alkali balance and water balance in the entire system.

[0062] The present invention fundamentally solves the impact of toxic gases such as ammonia and flammable and explosive gases such as methane and hydrogen produced by the hydrolysis of elements such as nitrogen, carbon and metallic aluminum in aluminum ash, and adopts a high-temperature volatilization method to prepare fluoride salts and chloride salts recovered from aluminum ash into slag removers used in aluminum electrolysis and aluminum processing, and uses limestone to solidify some residual fluoride salts, thereby achieving harmlessness of aluminum ash. Figure 1 The present invention provides a process flow chart of a method for producing sand-like alumina by treating aluminum ash with a soda-lime sintering method.

[0063] The preparation process of the special silica gel pressure swing adsorbent in the embodiment of the present invention is as follows: using a dilute sodium silicate solution as a raw material at room temperature, wherein the dilute sodium silicate solution has a mass concentration of 15%, adding a dilute hydrochloric acid solution, wherein the mass concentration of the dilute hydrochloric acid solution is 15%, and the volume ratio of the dilute sodium silicate solution to the dilute hydrochloric acid solution is 1: (2-3), and adding silica gel seed crystals with a size of less than 1 mm (the mass of the silica gel seed crystals is 0.5-1.0 wt.% of the total mass of the dilute sodium silicate solution and the dilute hydrochloric acid solution), reacting for 15-30 minutes to prepare a silica gel suspension, then filtering out the silica gel, and then adding the silica gel to anhydrous ethanol at a solid-liquid ratio of silica gel to anhydrous ethanol of 1:3 (g / mL), ultrasonicating for 30-50 minutes, filtering, drying (85° C., 60-90 minutes), and finally calcining in a microwave to 600° C. for 30 minutes, and naturally cooling to obtain the special silica gel pressure swing adsorbent.

[0064] The special silica gel pressure swing adsorbent is placed in the adsorption tower for adsorption, which is specifically divided into the following steps:

[0065] Adsorption process: After the raw gas is purified, it is pressurized and cooled by a Roots blower and then enters the adsorption tower in 7 routes. A nitrogen mixed gas with a CO2 content of about 10% is obtained at the outlet of the adsorption tower. When the adsorption front is about to penetrate the adsorbent, it switches to the next sequence.

[0066] Pressure drop process: After the adsorption process is completed, it enters the first pressure drop process.

[0067] Venting process: After the equalization pressure drop process, the pressure in the adsorption tower is about 0.01MPa. In order to ensure that the vacuumed carbon dioxide concentration reaches 60%-70%, the residual gas in the adsorption tower is vented.

[0068] Vacuuming: After the venting process, the vacuuming process begins. This process simultaneously desorbs the adsorbent while producing the product carbon dioxide gas, allowing the adsorbent to be regenerated and recycled. Once the vacuum pump's pumping capacity is determined, the longer the evacuation time, the more complete the adsorbent regeneration.

[0069] Pressure equalization process: After the vacuum is completed, the pressure equalization process corresponding to the pressure drop is entered to prepare for the next adsorption.

[0070] Final pressurization process: In order to adsorb again, the pressure in the adsorption tower must be close to the raw gas pressure. To this end, in this step, the finished gas at the outlet of the adsorption tower is reversely charged into the adsorption tower after the pressure equalization is completed, completing the preparation work for the adsorption tower to adsorb again. The adsorption tower will enter the next adsorption process, and this cycle will repeat.

[0071] In the embodiment of the present invention, by adjusting the adsorption pressure and adding a special silica gel adsorbent, the carbon dioxide content of the combustion exhaust gas is 60%, 65% and 70%, respectively. The specific adjustment process of the adsorption pressure and the special silica gel adsorbent can be conventionally adjusted according to the carbon dioxide content in the combustion exhaust gas and will not be elaborated in detail.

[0072] The room temperature in the present invention refers to 25±2°C.

[0073] The aluminum ash in the embodiments of the present invention is all secondary aluminum ash, and the reagents required in the embodiments of the present invention are all purchased from the market.

[0074] Example 1

[0075] 1) Weigh 100 g of aluminum ash, 100 g of industrial soda ash, and 10 g of limestone, mix and stir uniformly to obtain a mixed raw material, calcine the mixed raw material at 1200° C. for 40 min, and then cool to room temperature to obtain a sintered clinker. The sintering exhaust gas is subjected to dust removal, denitrification, purification, and concentration using a special silica gel pressure swing adsorbent to obtain a sintering exhaust gas with a carbon dioxide content of 60%;

[0076] 2) The sintered clinker and alkali solution were mixed at a solid-liquid ratio of 1:2 (g / mL) to obtain a mixed slurry, which was ball-milled for 10 minutes. The particle size distribution of the ball-milled product in the obtained ball-milled clinker slurry was: 63 μm accounted for more than 75%, wherein the concentration of sodium carbonate in the alkali solution was 100 g / L; the ball-milled clinker slurry was further diluted to a solid-liquid ratio of 1:4 (g / mL) by adding alkali solution (the concentration of sodium carbonate was 100 g / L), and the dissolution residence time was 2 hours to obtain a leaching slurry, wherein the dissolution rate of aluminum oxide in the aluminum ash reached more than 90%;

[0077] 3) filtering the leached slurry for liquid-solid separation to obtain a filtrate (sodium aluminate solution) and a leached residue; washing the leached residue three times in a countercurrent manner at 85° C. with distilled water as a washing liquid at a solid-to-liquid ratio of 1:3 (g / mL), followed by a final washing step with distilled water to obtain a washed leached residue, which was then added to the filtrate as a diluent to obtain a leachate; adding a homemade desiliconizing agent to the leachate (3 g, 1 g, and 2 g of barium aluminate, hydrated calcium aluminate, and hydrated calcium carbonoaluminate, respectively, were mixed uniformly and added to a lime milk solution at a solid-to-liquid ratio of 1:20 (g / mL) to the lime milk solution, with the solid content of the lime milk solution being 80 g / L) for deep desiliconization (80° C., 60 min), followed by solid-liquid separation to obtain a purified leachate;

[0078] 4) The calcination tail gas with a carbon dioxide content of 60% obtained in step 1) is passed into the purified leachate (at a flow rate of 16 L / min, a temperature of 70°C, and a time of 90 minutes) to precipitate aluminum hydroxide. After filtration, an aluminum hydroxide precipitate and a carbon denominator liquid are obtained. The aluminum hydroxide precipitate is calcined at 900°C for 30 minutes to obtain 67.5 g of a sandy alumina product. The carbon denominator liquid (i.e., a sodium carbonate solution) is concentrated and evaporated to precipitate sodium carbonate crystals, which are then dried and returned to the sintering process for use, completing the recycling of the alkali. The evaporated distilled water is used to wash the aluminum hydroxide, completing the water circulation of the system.

[0079] Example 2

[0080] 1) Weighing 100 g of aluminum ash, 120 g of industrial soda ash, and 15 g of limestone, mixing and stirring uniformly to obtain a mixed raw material, calcining the mixed raw material at 1250° C. for 50 min, and then cooling to room temperature to obtain sintered clinker, and subjecting the sintering tail gas to dust removal, denitrification, purification, and concentration using a special silica gel pressure swing adsorbent to obtain a sintering tail gas having a carbon dioxide content of 65%;

[0081] 2) The sintered clinker and alkali solution were mixed at a solid-liquid ratio of 1:2.5 (g / mL) to obtain a mixed slurry, which was ball-milled for 10 minutes. The particle size distribution of the ball-milled product in the obtained ball-milled clinker slurry was: 63 μm accounted for more than 75%, wherein the concentration of sodium carbonate in the alkali solution was 120 g / L; the ball-milled clinker slurry was further diluted with alkali solution (sodium carbonate concentration was 120 g / L) to a solid-liquid ratio of 1:5 (g / mL), and the dissolution residence time was 2 hours to obtain a leaching slurry, wherein the dissolution rate of aluminum oxide in the aluminum ash reached more than 92%;

[0082] 3) filtering the leachate slurry for liquid-solid separation to obtain a filtrate (sodium aluminate solution) and a leach residue. The leach residue is washed three times in a countercurrent manner at 90° C. with a solid-to-liquid ratio of 1:2 (g / mL) using distilled water as a washing liquid, followed by a final washing with distilled water. The washed leach residue is then washed with water, and the washing liquid is added to the filtrate to obtain a leachate. A homemade desiliconizing agent is added to the leachate (4 g, 1 g, and 2 g of barium aluminate, hydrated calcium aluminate, and hydrated calcium carbonoaluminate, respectively, are weighed and uniformly mixed, and the mixture is added to a lime milk solution at a solid-to-liquid ratio of the mixture to the lime milk of 1:30 (g / mL), and the solid content of the lime milk solution is 100 g / L). Further impurities are removed (85° C., 90 min), and solid-liquid separation is performed to obtain a purified leachate.

[0083] 4) The calcination tail gas with a carbon dioxide content of 65% obtained in step 1) is passed into the purified leachate (at a flow rate of 18 L / min, a temperature of 60°C, and a time of 150 minutes) to precipitate aluminum hydroxide. After filtration, an aluminum hydroxide precipitate and a carbon denominator liquid are obtained. The obtained aluminum hydroxide precipitate is calcined at 950°C for 20 minutes to obtain 69 g of a sand-like alumina product; the carbon denominator liquid (sodium carbonate solution) is concentrated and evaporated to precipitate sodium carbonate crystals, which are then returned to the sintering process after drying, completing the recycling of the alkali. The evaporated distilled water is used to wash the aluminum hydroxide, completing the water circulation of the system.

[0084] Example 3

[0085] 1) Weigh 100 g of aluminum ash, 140 g of industrial soda ash, and 20 g of limestone, mix and stir uniformly to obtain a mixed raw material, calcine the mixed raw material at 1300° C. for 30 min, and then cool to room temperature to obtain a sintered clinker. The sintering exhaust gas is subjected to dust removal, denitrification, purification, and concentration using a special silica gel pressure swing adsorbent to obtain a sintering exhaust gas with a carbon dioxide content of 70%;

[0086] 2) The sintered clinker and alkali solution were mixed at a solid-liquid ratio of 1:3 (g / mL) to obtain a mixed slurry, which was ball-milled for 10 minutes. The particle size distribution of the ball-milled product in the obtained ball-milled clinker slurry was: 63 μm accounted for more than 75%, wherein the concentration of sodium carbonate in the alkali solution was 140 g / L; the ball-milled clinker slurry was further diluted with alkali solution (sodium carbonate concentration was 140 g / L) to a solid-liquid ratio of 1:5 (g / mL), and the dissolution residence time was 2 hours to obtain a leaching slurry, wherein the dissolution rate of aluminum oxide in the aluminum ash reached more than 95%;

[0087] 3) filtering the leachate slurry for liquid-solid separation to obtain a filtrate (sodium aluminate solution) and a leach residue. The leach residue is washed three times in a countercurrent step at a solid-to-liquid ratio of 1:3 (g / mL) using distilled water as a washing liquid, and the final step is washed with distilled water to obtain washed leach residue. The washing liquid is then added to the filtrate to obtain a leachate; a homemade desiliconizing agent is added to the leachate (5 g, 2 g, and 3 g of barium aluminate, hydrated calcium aluminate, and hydrated calcium carbonoaluminate, respectively, are weighed and uniformly mixed, and the mixture is added to a lime milk solution at a solid-to-liquid ratio of the mixture to the lime milk of 1:40 (g / mL), and the solid content of the lime milk solution is 100 g / L) to further remove impurities (90°C, 45 min), and solid-liquid separation is performed to obtain a purified leachate;

[0088] 4) The calcination tail gas with a carbon dioxide content of 70% obtained in step 1) is passed into the purified leachate (at a flow rate of 35 L / min, a temperature of 50°C, and a time of 240 minutes) to precipitate aluminum hydroxide. After filtration, an aluminum hydroxide precipitate and a carbon denominator liquid are obtained. The obtained aluminum hydroxide precipitate is roasted at 980°C for 8 minutes to obtain 71 g of a sand-like alumina product; the carbon denominator liquid (sodium carbonate solution) is concentrated and evaporated to precipitate sodium carbonate crystals, which are returned to the sintering process after drying, completing the recycling of the alkali. The evaporated distilled water is used to wash the aluminum hydroxide, completing the water circulation of the system.

[0089] Comparative Example 1

[0090] The same as Example 1, except that, in step 3), a conventional desiliconizing agent of lime milk (solid content of 100 g / L) is added, and the silicon content index in the sodium aluminate solution is only 560, so the silicon dioxide content in the obtained alumina product exceeds the standard; the present invention uses a homemade desiliconizing agent, and the silicon content index in the sodium aluminate solution exceeds 1000, thereby ensuring the quality of the prepared alumina.

[0091] Comparative Example 2

[0092] The same as Example 1, except that in step 4), the calcination exhaust gas with a carbon dioxide content of 35% is introduced, the carbon separation time is 180 minutes, the decomposition rate of sodium aluminate is 85%, and 60 g of sandy alumina product is obtained; Example 1 of the present invention adopts dust removal-denitrification-purification-special silica gel pressure swing adsorbent concentration to increase the carbon dioxide content in the calcination exhaust gas from about 10% to 60%, the carbon separation time is 90 minutes, the decomposition rate of sodium aluminate reaches more than 90%, and more than 67.5 g of sandy alumina product is obtained, which greatly shortens the carbon separation time and improves production efficiency.

[0093] Comparative Example 3

[0094] The same as Example 1, except that the calcination temperature in step 1) is 1000°C, and the inert alumina such as α-type and mullite-type in the aluminum ash is not completely converted into active sodium aluminate, resulting in a low dissolution of alumina in the aluminum ash, and only 53.4 g of sandy alumina product is obtained.

[0095] Determination of decomposition yield of sodium aluminate:

[0096] The initial concentration of sodium aluminate in the filtrate of Examples 1-3 and Comparative Example 1 was determined to be Ci (unit: g / L); after the carbon fraction was completed, the concentration of sodium aluminate in the solution was again determined to be C (unit: g / L); the calculation formula for the decomposition rate and decomposition yield of sodium aluminate was:

[0097] Decomposition rate = (Ci-C) / Ci×100%

[0098] Decomposition yield = Ci × decomposition rate × 100%

[0099] Table 1 shows the decomposition rate of sodium aluminate and the yield of aluminum oxide in the filtrate in Examples 1-3 and Comparative Examples 1-2.

[0100] Table 1

[0101] Leaching rate (%) Decomposition rate (%) Alumina yield (%) Example 1 95 94.7 90.0 Example 2 95 96.8 92 Example 3 95 98 93 Comparative Example 1 95 95 90.2 (Silicon content exceeds the standard) Comparative Example 2 95 85 81 Comparative Example 3 75 95 75

[0102] The first-level standard for the physical and chemical properties of metallurgical-grade alumina is that the SiO2 content is ≤0.02%. In Comparative Example 1, traditional lime milk desiliconization was used, and the silicon index in the sodium aluminate solution was only 560, and the silicon dioxide content in the obtained alumina exceeded the standard (SiO2 content was 0.024%). However, the present invention uses a homemade desiliconizing agent, and the silicon index in the sodium aluminate solution exceeds 1000. The silicon dioxide content in the obtained alumina product is 0.016%, which exceeds the first-level standard for the physical and chemical properties of metallurgical-grade alumina.

[0103] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for producing sand-like alumina by treating aluminum ash with a soda-lime sintering method, characterized in that: The following steps are involved: Aluminum ash, soda ash and limestone are mixed and then sintered to obtain sintered clinker, and the tail gas is collected; adding alkali solution to the sintered clinker and ball milling to obtain clinker slurry; The clinker slurry is diluted and further alkali leached, and the obtained leached slurry is separated into solid and liquid to obtain a filtrate and a leached residue; The leachate is subjected to deep desiliconization, enhanced carbon separation, and solid-liquid separation to obtain aluminum hydroxide precipitate and sodium carbonate solution; calcining the aluminum hydroxide precipitate to obtain the sandy aluminum oxide; The carbon enhancement process includes treating the tail gas collected during the alkali sintering process to obtain sintering tail gas with a carbon dioxide content of 60-70%; and then introducing the sintering tail gas into the leaching solution to precipitate aluminum hydroxide.

2. The method for producing sandy alumina by treating aluminum ash with soda lime sintering method according to claim 1, characterized in that: The mass ratio of the aluminum ash, soda ash and limestone is 1:(1-1.4):(0.1-0.2).

3. The method for producing sandy alumina by treating aluminum ash with soda lime sintering method according to claim 1, characterized in that: The sintering temperature is 1100-1300° C., and the sintering time is 30-60 minutes.

4. The method for producing sandy alumina by treating aluminum ash with soda lime sintering method according to claim 1, characterized in that: The solid-liquid ratio of the sintered clinker to the alkali solution is 1:(1-3) (g / mL).

5. The method for producing sandy alumina by treating aluminum ash with soda lime sintering method according to claim 1, characterized in that: The alkali leaching comprises the step of adding alkali solution into the clinker slurry to dilute the mixture to a solid-liquid ratio of 1:(3-5) (g / mL).

6. The method for producing sandy alumina by treating aluminum ash with soda lime sintering method according to claim 5, characterized in that: The alkali leaching time is 1-3 hours.

7. The method for producing sandy alumina by treating aluminum ash with soda lime sintering method according to claim 1, characterized in that: The deep desiliconization comprises the following steps: adding a complex of barium aluminate, hydrated calcium aluminate, hydrated calcium carbonoaluminate and lime milk to the leachate, performing solid-liquid separation after desiliconization reaction, and obtaining a purified leachate.

8. The method for producing sandy alumina by treating aluminum ash with soda lime sintering method according to claim 7, characterized in that: The mass ratio of the barium aluminate, hydrated calcium aluminate and hydrated calcium carbonoaluminate is (3-5):(1-2):(2-3); the solid-liquid ratio of the mixture of the barium aluminate, hydrated calcium aluminate and hydrated calcium carbonoaluminate to the lime milk is 1:(20-40) (g / mL), and the solid content of the lime milk solution is 80-100 g / L.

9. The method for producing sandy alumina by treating aluminum ash with soda lime sintering method according to claim 1, characterized in that: The flow rate of the calcined tail gas in the carbon strengthening process is 16-35 L / min, the temperature of the carbon strengthening process is 50-70° C., and the time is 90-240 min.

10. The method for producing sandy alumina by treating aluminum ash with soda lime sintering method according to claim 1, characterized in that: The calcination temperature is 900-1000° C. and the calcination time is 10-30 minutes.

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