Method for preparing aluminum fluoride using aluminum electrolysis fluorine-containing waste

Abstract

The application relates to a method for preparing aluminum fluoride from aluminum electrolysis fluorine-containing waste, which comprises the following steps: converting the fluorine-containing components in the waste into soluble salt, regulating the aluminum fluoride molar ratio and pH value of the obtained fluorine-containing solution, adding activated seed crystals prepared from aluminum fluoride precursors and carrying out reaction, so that aluminum fluoride products with relatively coarse particle size are successfully prepared; wherein the activated seed crystals are prepared by immersing the precursors in a saturated solution of seed crystal activator, so that high-density active sites are formed on the surface of the aluminum fluoride precursor seed crystals, and a surface microelectric field environment beneficial to the growth of aluminum fluoride product crystals is constructed; the method not only effectively meets the requirements of the particle size and physical properties of the automatic feeding system of the aluminum electrolysis cell, but also realizes efficient and large-scale resource utilization of aluminum electrolysis fluorine-containing waste such as carbon residue and overhaul residue. Meanwhile, the wastewater generated in the process can realize standard discharge of fluorine ions after treatment, so that environmental pollution is avoided.

Description

Technical Field

[0001] This application relates to the field of aluminum electrolysis technology, and in particular to a method for preparing aluminum fluoride using fluorine-containing waste from aluminum electrolysis. Background Technology

[0002] In the aluminum electrolysis production process, industrial alumina raw materials typically contain a certain amount of sodium impurities. This sodium enters the cryolite-based electrolyte system during electrolysis, leading to an increase in the NaF content in the electrolyte and a continuous rise in the molecular ratio (NaF / AlF3 molar ratio). To maintain the stability of the electrolysis process, aluminum fluoride (AlF3) or fluorinated alumina needs to be continuously added to balance the molecular ratio, resulting in a continuous accumulation of the total electrolyte in the electrolytic cell.

[0003] According to industry statistics, producing 1 ton of primary aluminum generates approximately 9.5 kg of carbon slag and 17.5 kg of overhaul slag. Additionally, due to national capacity control and material recycling restrictions, an extra 10 kg of electrolyte is generated. Based on my country's annual primary aluminum production of approximately 37 million tons, this translates to an annual surplus of approximately 370,000 tons of electrolyte. Long-term storage of this type of fluorine-containing solid waste not only occupies significant storage space but also results in a serious waste of valuable resources such as fluorine and aluminum, becoming a prominent issue hindering the green and sustainable development of aluminum electrolysis enterprises.

[0004] For the resource utilization of fluorine-containing waste from aluminum electrolysis (such as carbon slag, overhaul slag, salvaged electrolyte, and regenerated electrolyte), existing technologies mostly employ wet recovery methods—leaching the waste with acid and / or aluminum salts, then adjusting the pH to co-precipitate aluminum and fluorine into aluminum hydroxyfluoride. However, the resulting products are often aluminum hydroxyfluoride with specific compositions, such as AlF₂. 1.5 (OH) 1.5 (H2O) 0.375 or Al2F 3.24 (OH) 2.76 ·H2O. These compounds have a low molar ratio of aluminum fluoride and contain water of crystallization and hydroxyl groups. They are prone to violent side reactions during subsequent calcination and dehydration, causing some fluorine to escape in the form of HF, etc. The product contains a large amount of alumina impurities, and the purity of aluminum fluoride is difficult to meet the requirements of electrolysis.

[0005] Furthermore, the aluminum fluoride obtained by the aforementioned wet process generally suffers from problems such as excessively fine particle size, large specific surface area, and poor flowability. This type of aluminum fluoride is prone to severe dust loss during transportation and storage; simultaneously, the physical properties of this powder are difficult to adapt to the automatic feeding systems of modern aluminum electrolysis cells, leading to decreased feeding accuracy, affecting the stable control of the electrolyte molecular ratio, and consequently reducing current efficiency.

[0006] In view of this, it is necessary to design a method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis in order to solve the above problems. Summary of the Invention

[0007] This application provides a method for preparing aluminum fluoride from fluorine-containing waste generated during aluminum electrolysis, in order to solve the current problems of difficulty in efficiently and on a large scale utilizing fluorine-containing waste such as carbon slag and overhaul slag generated during aluminum electrolysis, and the fact that the prepared aluminum fluoride products generally have excessively fine particle size, insufficient purity, and poor flowability, which cannot meet the requirements of automatic feeding and process control in electrolytic cells.

[0008] In a first aspect, this application provides a method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis, comprising the following steps: The fluorine-containing substances in the aluminum electrolysis fluorine-containing waste are converted into soluble salts to obtain the first mixture; The first mixture is subjected to a first solid-liquid separation to obtain a first leachate; The aluminum-fluorine ratio and pH value of the first leachate are adjusted to obtain the second leachate; Activated seed crystals are added to the second leachate to obtain a second mixture; The second mixture is subjected to a crystallization reaction to obtain a third mixture; and, The third mixture is subjected to a second solid-liquid separation to obtain aluminum fluoride product; The particle size distribution of the aluminum fluoride product satisfies: D 10 The diameter is 39μm~46μm, D 50 68μm~77μm; D 90 The thickness ranges from 125μm to 133μm. The method for preparing the activated seed crystals includes the following steps: sequentially mixing the precursor and a saturated solution of the seed crystal activator, followed by a third solid-liquid separation, to obtain the activated seed crystals; The precursor includes aluminum fluoride.

[0009] In some embodiments, the seed activator saturated solution comprises any one or more of the following: ammonium trifluoroacetate saturated solution, tetrabutylammonium fluoride saturated solution, sodium perfluorooctanoate saturated solution, sodium 2,2,2-trifluoroethanol saturated solution, and cerium trifluoromethanesulfonate saturated solution; and / or, The precursor has a particle size of 20 μm to 30 μm; and / or, The first mixing time is 0.5h to 6h.

[0010] In some embodiments, the mass ratio of the second leachate to the activated seed crystals is 100:(1~9).

[0011] In some embodiments, the crystallization reaction comprises the following three stages: First crystallization stage: The second mixture is stirred at 80℃~90℃ for 10min~20min to obtain the first crystal; Second crystallization stage: Under continuous stirring at 80℃~90℃, the system pressure of the first crystal is reduced to -0.1MPa~-0.4MPa at a first depressurization rate to obtain the second crystal; Third crystallization stage: The second crystal is stirred for 4 to 5 hours at 80℃~90℃ and -0.1MPa~-0.4MPa to obtain the third mixture.

[0012] In some embodiments, the first pressure reduction rate is 10 kPa / min to 30 kPa / min.

[0013] In some embodiments, the molar ratio of aluminum to fluorine in the second leachate is 1:(3~3.5); The pH value of the second leachate is 2.5~6.0.

[0014] In some embodiments, adjusting the aluminum-fluorine ratio of the first leachate includes adding a first reagent; the first reagent includes a soluble aluminum salt and / or a soluble fluoride; the soluble aluminum salt includes any one or more of aluminum sulfate, aluminum nitrate, and aluminum chloride; the soluble fluoride includes any one or more of ammonium fluoride, sodium fluoride, potassium fluoride, and hydrofluoric acid.

[0015] In some embodiments, adjusting the pH of the first leachate includes adding a second reagent; the second reagent includes any one or more of sulfuric acid, hydrochloric acid, nitric acid, sodium hydroxide, ammonia, ammonium carbonate, and ammonium bicarbonate.

[0016] In some embodiments, the method for converting fluorine-containing substances in aluminum electrolysis fluorine-containing waste into soluble salts includes: mixing the aluminum electrolysis fluorine-containing waste with a solvent to obtain the first mixture; The solvent includes any one or more of the following: sulfuric acid with a concentration of 1% to 98%, hydrochloric acid with a concentration of 1% to 36%, nitric acid with a concentration of 1% to 65%, sodium hydroxide with a concentration of 1% to 20%, sodium carbonate with a concentration of 1% to 16%, aluminum sulfate with a concentration of 1% to 25%, aluminum nitrate with a concentration of 1% to 25%, and aluminum chloride with a concentration of 1% to 25%. The mass ratio of the aluminum electrolysis fluorine-containing waste to the solvent is 1:(1~10).

[0017] In some embodiments, the particle size of the aluminum electrolysis fluorine-containing waste is ≤74μm; and / or, The aluminum electrolysis fluorine-containing waste includes any one or more of the following: carbon slag, electrolytic cell overhaul slag, electrolyte obtained from carbon slag flotation, electrolyte obtained from carbon slag pyrochemical treatment, electrolyte obtained from electrolytic cell dredging, and regenerated electrolyte obtained from the treated aluminum electrolysis fluorine-containing waste.

[0018] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis. The method involves converting the fluorine-containing components in the waste into soluble salts, adjusting the aluminum-fluorine molar ratio and pH value of the resulting fluorine-containing solution, and then adding activated seed crystals prepared from an aluminum fluoride precursor and reacting to successfully produce a coarser-sized aluminum fluoride product. The activated seed crystals are prepared by immersing the precursor in a saturated solution of a seed activator. This process aims to form a higher density of active sites on the surface of the aluminum fluoride seed crystals and create a surface micro-electric field environment more conducive to the growth of the aluminum fluoride product crystals. This method not only effectively meets the particle size and physical properties requirements of the automatic feeding system in aluminum electrolysis cells but also achieves efficient and large-scale resource utilization of fluorine-containing waste from aluminum electrolysis, such as carbon slag and overhaul slag. Simultaneously, the wastewater generated during the process can be treated to achieve fluoride ion discharge standards, avoiding environmental pollution. Overall, the preparation method provided in this application has a simple process flow and is easy to operate. It does not require complicated equipment and obtains high-quality aluminum fluoride without generating secondary pollution, thus achieving both environmental and economic benefits. Attached Figure Description

[0019] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A flowchart of a method for preparing aluminum fluoride from fluorine-containing waste electrolyzed by aluminum, as provided in this application, is shown. Figure 2 The XRD pattern of the aluminum fluoride product prepared in Example 1 of this application is shown. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] Various embodiments of this application may exist in the form of a range. It should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of this application. Therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is indicated in this application, it means including any referenced number (fraction or integer) within the indicated range. Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this application can be purchased commercially or prepared by existing methods. In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. In addition, in this application, the terms "comprising," "including," etc., mean "including but not limited to." In this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, without necessarily requiring or implying any actual relationship or order between these entities or operations. In this application, "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this application, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c," or "at least one of a, b, and c," can both represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can each be single or multiple.

[0024] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0025] like Figure 1 As shown in the figure, this application provides a method for preparing aluminum fluoride using fluorine-containing waste from aluminum electrolysis, comprising the following steps: Step S1: Convert the fluorine-containing substances in the aluminum electrolysis fluorine-containing waste into soluble salts to obtain the first mixture; Step S2: Perform a first solid-liquid separation on the first mixture to obtain a first leachate; Step S3: Adjust the aluminum-fluorine ratio and pH value of the first leachate to obtain the second leachate; Step S4: Add activated seed crystals to the second leachate to obtain a second mixture; perform a crystallization reaction on the second mixture to obtain a third mixture; Step S5: Perform a second solid-liquid separation on the third mixture to obtain aluminum fluoride product; the particle size distribution of the aluminum fluoride product satisfies: D 10 The diameter is 39μm~46μm, D 50 68μm~77μm; D 90 The thickness ranges from 125μm to 133μm. The method for preparing the activated seed crystals includes the following steps: sequentially mixing the precursor and a saturated solution of the seed crystal activator, followed by a third solid-liquid separation, to obtain the activated seed crystals; The precursor includes aluminum fluoride.

[0026] The method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis provided in this application involves converting the fluorine-containing components in the waste into soluble salts, adjusting the aluminum-fluorine molar ratio and pH value of the resulting fluorine-containing solution, and then adding activated seed crystals prepared from aluminum fluoride precursors and reacting to successfully produce aluminum fluoride products with relatively coarse particle sizes. This method not only effectively meets the particle size and physical properties requirements of the automatic feeding system in aluminum electrolysis cells, but also achieves efficient and large-scale resource utilization of fluorine-containing waste from aluminum electrolysis such as carbon slag and overhaul slag. Simultaneously, the wastewater generated during the process can be treated to achieve fluoride ion discharge standards, avoiding environmental pollution. Overall, the preparation method provided in this application has a simple process flow and is easy to operate, requiring no complex equipment. It obtains high-quality aluminum fluoride without generating secondary pollution, thus achieving both environmental and economic benefits.

[0027] As an optional implementation, in this embodiment of the application, the saturated solution of the seed activator includes any one or more of the following: a saturated solution of ammonium trifluoroacetate (CAS registration number of the ammonium trifluoroacetate used is 3336-58-1), a saturated solution of tetrabutylammonium fluoride (CAS registration number of the tetrabutylammonium fluoride used is 429-41-4), a saturated solution of sodium perfluorooctanoate (CAS registration number of the sodium perfluorooctanoate used is 335-95-5), a saturated solution of sodium 2,2,2-trifluoroethanol (CAS registration number of the sodium 2,2,2-trifluoroethanol used is 75-89-8), and a saturated solution of cerium trifluoromethanesulfonate (CAS registration number of the cerium trifluoromethanesulfonate used is 76089-77-5).

[0028] Optionally, the seed activator saturated solution is prepared by mixing a saturated solution of ammonium trifluoroacetate and a saturated solution of sodium perfluorooctanoate; the mass ratio of the saturated solution of ammonium trifluoroacetate to the saturated solution of sodium perfluorooctanoate is 3:1.

[0029] Optionally, the seed activator saturated solution is prepared by mixing the tetrabutylammonium fluoride saturated solution and the 2,2,2-trifluoroethanol sodium saturated solution; the mass ratio of the tetrabutylammonium fluoride saturated solution to the 2,2,2-trifluoroethanol sodium saturated solution is 1:1.

[0030] Optionally, the seed activator saturated solution is prepared by mixing the 2,2,2-trifluoroethanol sodium saturated solution and the cerium trifluoromethanesulfonate saturated solution; the mass ratio of the 2,2,2-trifluoroethanol sodium saturated solution to the cerium trifluoromethanesulfonate saturated solution is 2:1.

[0031] Therefore, the use of a saturated solution of seed activator is to form a higher density of active sites on the surface of the precursor aluminum fluoride seed crystals and to construct a surface micro-electric field environment more conducive to the growth of aluminum fluoride product crystals. Furthermore, compared to other reagents (such as 5wt% sulfuric acid), the saturated solution of seed activator used in this application can more effectively achieve surface modification of the precursor aluminum fluoride seed crystals, increasing the number of active sites on the seed surface by more than 20%.

[0032] In this embodiment, the precursor particle size needs to be ground to 20μm~30μm; the activated seed crystal particle size is 20μm~30μm.

[0033] In the embodiments of this application, the first mixing time is 0.5h~6h (that is, the aluminum fluoride precursor is activated by soaking it in a saturated solution of seed activator for a certain period of time, and the saturated solution of seed activator can further etch the aluminum fluoride precursor).

[0034] Thus, after the precursor aluminum fluoride is successively ground and activated, wear and structural defects are generated on the surface of the precursor aluminum fluoride crystal. The activated seed crystals obtained in this way are more conducive to the etching of the surface by the saturated solution of the seed activator. At the same time, it can also provide more active sites for the growth of aluminum fluoride product crystals, which is conducive to the nucleation and growth of aluminum fluoride product crystals on the surface of the activated seed crystals, thereby promoting the directional formation of aluminum fluoride products.

[0035] In addition, if the particle size of the activated seed crystal is less than 20 μm, it will not reach the critical size required for effective crystallization and will be difficult to play a heterogeneous nucleation role, resulting in a large number of homogeneous nucleations in the system. If the particle size of the activated seed crystal is greater than 30 μm, the effective induction sites provided per unit mass will decrease, the crystal growth guidance ability of aluminum fluoride products will decrease, and more homogeneous nucleation will be triggered, which will affect the purity and particle size distribution of aluminum fluoride products.

[0036] As an optional implementation, in this embodiment of the application, the mass ratio of the second leachate to the activated seed crystal is 100:(1~9).

[0037] Therefore, if the mass ratio of the second leaching solution to the activated seed crystals is greater than 100:1 (i.e., the content of activated seed crystals is less than 1% of the mass of the second leaching solution), the insufficient number of activated seed crystals will result in too few heterogeneous nucleation sites, leading to a significant increase in homogeneous nucleation in the system. This will result in excessively fine particle size of the obtained aluminum fluoride product, and a high residual fluorine content in the waste liquid after crystallization. Conversely, if the mass ratio of the second leaching solution to the activated seed crystals is less than 100:9 (i.e., the content of activated seed crystals is greater than 9% of the mass of the second leaching solution), the excessive number of activated seed crystals will result in an excessively high density of heterogeneous nucleation sites. This will rapidly deplete the local concentration of fluorine and aluminum ions in the solution, resulting in insufficient driving force for crystal growth. Consequently, the crystal growth of the aluminum fluoride product will be limited, again resulting in excessively fine particle size of the obtained aluminum fluoride product. Therefore, controlling the mass ratio of the second leaching solution to the activated seed crystals within the range of 100:(1~9) can effectively balance the nucleation and growth processes, obtaining aluminum fluoride products with moderate particle size and uniform distribution.

[0038] As an optional implementation, in this embodiment of the application, the crystallization reaction includes the following three stages in sequence: First crystallization stage: The second mixture is stirred at 80℃~90℃ for 10min~20min to obtain the first crystal; Second crystallization stage: Under continuous stirring at 80℃~90℃, the system pressure of the first crystal is reduced to -0.1MPa~-0.4MPa at a first depressurization rate to obtain the second crystal; Third crystallization stage: The second crystal is stirred for 4 to 5 hours at 80℃~90℃ and -0.1MPa~-0.4MPa to obtain the third mixture.

[0039] Thus, by synergistically controlling the stirring intensity, system pressure, and temperature during the reaction process, coarser-sized aluminum fluoride products can be produced from fluorine-containing waste from aluminum electrolysis.

[0040] As an optional implementation, in this embodiment of the application, the first pressure reduction rate is 10 kPa / min to 30 kPa / min.

[0041] Thus, by gradually reducing the system pressure according to the set system during the reaction process, the mass transfer resistance of aluminum fluoride crystal growth can be reduced to a certain extent, which is conducive to the continuous growth of aluminum fluoride crystals. At the same time, the crystallization process under negative pressure can achieve effective crystallization at a lower temperature, which helps to reduce the overall energy consumption of the system.

[0042] Furthermore, if the first pressure reduction rate is less than 10 kPa / min, the pressure drop is too slow, insufficient to alleviate the resistance to crystal growth, thus limiting the crystal growth of the aluminum fluoride product and resulting in a smaller particle size. If the first pressure reduction rate is greater than 30 kPa / min, the system pressure drops sharply, and the environment around the aluminum fluoride crystal changes rapidly. Specific crystal faces on the active sites do not grow sufficiently before entering the next pressure stage, causing the aluminum fluoride crystal to grow excessively in a layered manner with loose interlayer bonding. This layered structure is prone to dissociation during subsequent solid-phase transport or processing, leading to pulverization and finer particle size of the aluminum fluoride product, failing to meet the requirements for particle strength and particle size stability in automatic feeding of aluminum electrolysis cells. Therefore, controlling the first pressure reduction rate within the range of 10 kPa / min to 30 kPa / min balances crystal growth kinetics and structural integrity, resulting in aluminum fluoride products with coarse particle size, dense structure, and good flowability.

[0043] As an optional implementation, in this embodiment of the application, the molar ratio of aluminum to fluorine in the second leachate is 1:(3~3.5); Therefore, if the molar ratio of aluminum to fluorine in the second leachate is greater than 1:3 (i.e., the aluminum content in the second leachate is too high), the resulting aluminum fluoride product will have insufficient fluorine content, leading to reduced purity. Conversely, if the molar ratio is less than 1:3.5 (i.e., the fluorine content in the second leachate is too high), the residual fluorine concentration in the mother liquor after the crystallization reaction will be too high. Direct discharge of this fluoride-containing wastewater could easily cause secondary environmental pollution. Therefore, controlling the molar ratio of aluminum to fluorine in the second leachate within the range of 1:(3~3.5) can effectively reduce the fluorine load in the waste liquor while ensuring high purity of the aluminum fluoride product, thus balancing product quality and environmental protection requirements.

[0044] In this embodiment of the application, the pH value of the second leachate is 2.5 to 6.0.

[0045] Therefore, if the pH value in the second leachate is greater than 6.0, other impurity elements will co-precipitate, reducing the purity of the aluminum fluoride product. If the pH value is less than 2.5, too little aluminum fluoride will be generated, resulting in a low product yield, and the residual fluoride concentration in the mother liquor after the crystallization reaction will be too high. Direct discharge of this solution could easily cause fluoride-containing wastewater pollution and trigger secondary environmental problems. Therefore, controlling the pH value of the second leachate within the range of 2.5 to 6.0 can effectively reduce the fluoride load in the waste liquid while ensuring the high purity of the aluminum fluoride product, thus balancing product quality and environmental protection requirements.

[0046] As an optional implementation, in this embodiment of the application, adjusting the aluminum-fluorine ratio of the first leachate includes adding a first reagent; the first reagent includes a soluble aluminum salt and a soluble fluoride; the soluble aluminum salt includes any one or more of aluminum sulfate, aluminum nitrate, and aluminum chloride; the soluble fluoride includes any one or more of ammonium fluoride, sodium fluoride, potassium fluoride, and hydrofluoric acid.

[0047] As an optional implementation, in this embodiment of the application, adjusting the pH value of the first leachate includes adding a second reagent; the second reagent includes any one or more of sulfuric acid, hydrochloric acid, nitric acid, sodium hydroxide, ammonia, ammonium carbonate, and ammonium bicarbonate.

[0048] As an optional implementation, in this embodiment of the application, the method for converting fluorine-containing substances in aluminum electrolysis fluorine-containing waste into soluble salts includes: mixing the aluminum electrolysis fluorine-containing waste with a solvent to obtain the first mixture; The solvent includes any one or more of the following: sulfuric acid with a mass concentration of 1% to 98%, hydrochloric acid with a mass concentration of 1% to 36%, nitric acid with a mass concentration of 1% to 65%, sodium hydroxide with a mass concentration of 1% to 20%, sodium carbonate with a mass concentration of 1% to 16%, aluminum sulfate with a mass concentration of 1% to 25%, aluminum nitrate with a mass concentration of 1% to 25%, and aluminum chloride with a mass concentration of 1% to 25%.

[0049] In this embodiment of the application, in order to fully convert the fluorine-containing substances in the aluminum electrolysis fluorine-containing waste into soluble salts, the mass ratio of the aluminum electrolysis fluorine-containing waste to the solvent is controlled to be 1:(1~10).

[0050] As an optional implementation, in this embodiment of the application, the particle size of the aluminum electrolysis fluorine-containing waste is controlled to ≤74μm by grinding and passing it through a 200-mesh sieve.

[0051] This allows the fluorides in the fluorine-containing waste from aluminum electrolysis to be fully exposed, thereby improving the efficiency of their conversion into soluble salts.

[0052] As an optional implementation, in this embodiment of the application, the aluminum electrolysis fluorine-containing waste includes any one or more of the following: carbon slag, electrolytic cell overhaul slag, electrolyte obtained from carbon slag flotation, electrolyte obtained from carbon slag pyrochemical treatment, electrolyte obtained from electrolytic cell dredging, and regenerated electrolyte obtained from the treated aluminum electrolysis fluorine-containing waste.

[0053] In this way, all the above-mentioned fluorine-containing wastes can be used as raw materials for efficient and large-scale resource utilization, which not only significantly reduces solid waste accumulation and environmental pollution, but also realizes the closed-loop recycling of valuable components such as fluorine and aluminum, providing a practical and feasible technical path for the green and low-carbon transformation of the aluminum electrolysis industry.

[0054] As an optional implementation, in this embodiment of the application, after performing a second solid-liquid separation on the third mixture, the method further includes: drying the solid phase collected after the second solid-liquid separation to obtain the aluminum fluoride.

[0055] The aluminum fluoride products prepared using this method can meet the requirements for automatic feeding and process control in electrolytic cells.

[0056] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If no corresponding national standard exists, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0057] Example 1 Example 1 provides a method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis, comprising the following steps: Step S1: Convert the fluorine-containing substances in aluminum electrolysis fluorine-containing waste with a particle size ≤74μm into soluble salts to obtain the first mixture; Fluorine-containing waste from aluminum electrolysis is the electrolyte obtained from the flotation of carbon slag; The method for converting fluorine-containing substances in aluminum electrolysis fluorine-containing waste into soluble salts includes: mixing aluminum electrolysis fluorine-containing waste with a solvent at a mass ratio of 1:1 to obtain a first mixture; the solvent is a mixture composed of sulfuric acid (mass concentration of 1%), aluminum sulfate (mass concentration of 25%), and aluminum nitrate (mass concentration of 1%) at a mass ratio of 1:2:1.

[0058] Step S2: Perform a first solid-liquid separation on the first mixture to obtain a first leachate; Step S3: Adjust the aluminum-fluorine ratio and pH value of the first leachate to obtain the second leachate; in the second leachate, the molar ratio of aluminum to fluorine is 1:3; the pH value of the second leachate is 4.5. The method of adjusting the aluminum-fluorine ratio of the first leachate includes adding a first reagent; the first reagent includes aluminum sulfate and sodium fluoride; The pH of the first leachate is adjusted by adding a second reagent; the second reagent includes sulfuric acid and sodium hydroxide.

[0059] Step S4: Add activated crystals to the second leachate at a mass ratio of 100:5 to obtain a second mixture; perform a crystallization reaction on the second mixture to obtain a third mixture. The method for preparing activated seed crystals includes the following steps: aluminum fluoride precursor with a particle size of 20μm~30μm and a saturated solution of seed crystal activator are sequentially subjected to a first mixing and a third solid-liquid separation to obtain activated seed crystals; the first mixing time is 0.5h; The seed activator saturated solution is prepared by mixing a saturated solution of ammonium trifluoroacetate and a saturated solution of sodium perfluorooctanoate (the mass ratio of the saturated solution of ammonium trifluoroacetate and the saturated solution of sodium perfluorooctanoate is 3:1). The crystallization reaction consists of the following three stages: First crystallization stage: The second mixture is stirred at 80°C for 10 minutes to obtain the first crystal; Second crystallization stage: Under continuous stirring at 80℃, the system pressure of the first crystal is reduced to -0.1MPa at a first depressurization rate of 10kPa / min to obtain the second crystal; Third crystallization stage: The second crystal was stirred for 4 hours at 80℃ and -0.1MPa to obtain the third mixture; The stirring rate throughout the entire stage was 20 r / min.

[0060] Step S5: Perform a second solid-liquid separation on the third mixture to obtain filtrate and solid phase; collect the solid phase and dry it to obtain aluminum fluoride product; The fluoride ion concentration in the filtrate was 8 mg / L, which meets the emission standards. By mass percentage, the aluminum fluoride product contains 61.3% sulfur (F) and 31.8% aluminum (Al); the particle size distribution of the aluminum fluoride product is: D 10 =42.715μm, D 50 =76.204μm, D 90 =128.925μm.

[0061] Furthermore, the aluminum fluoride product prepared in this embodiment was analyzed by X-ray diffraction (XRD), and the results are as follows: Figure 2 As shown, the product phase is pure phase AlF3, and no other impurities were detected.

[0062] Example 2 Example 2 provides a method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis, comprising the following steps: Step S1: Convert the fluorine-containing substances in aluminum electrolysis fluorine-containing waste with a particle size ≤74μm into soluble salts to obtain the first mixture; Fluorine-containing waste from aluminum electrolysis is the electrolyte obtained from the pyrometallurgical treatment of carbon slag; The method for converting fluorine-containing substances in aluminum electrolysis fluorine-containing waste into soluble salts includes: mixing aluminum electrolysis fluorine-containing waste with a solvent at a mass ratio of 1:10 to obtain a first mixture; the solvent is a mixture composed of hydrochloric acid (mass concentration of 36%), nitric acid (mass concentration of 1%), aluminum nitrate (mass concentration of 25%), and aluminum chloride (mass concentration of 1%) in a mass ratio of 2:2:1:1.

[0063] Step S2: Perform a first solid-liquid separation on the first mixture to obtain a first leachate; Step S3: Adjust the aluminum-fluorine ratio and pH value of the first leachate to obtain the second leachate; in the second leachate, the molar ratio of aluminum to fluorine is 1:3.2; the pH value of the second leachate is 5. The method of adjusting the aluminum-fluorine ratio of the first leachate includes adding a first reagent; the first reagent includes aluminum nitrate and ammonium fluoride; The pH of the first leachate is adjusted by adding a second reagent; the second reagent includes hydrochloric acid, nitric acid, and ammonia.

[0064] Step S4: Add activated crystals to the second leachate at a mass ratio of 100:1 to obtain a second mixture; perform a crystallization reaction on the second mixture to obtain a third mixture. The method for preparing activated seed crystals includes the following steps: aluminum fluoride precursor with a particle size of 20μm~30μm and a saturated solution of seed crystal activator are sequentially subjected to a first mixing and a third solid-liquid separation to obtain activated seed crystals; the first mixing time is 6h; The seed activator saturated solution is prepared by mixing a saturated solution of tetrabutylammonium fluoride and a saturated solution of sodium 2,2,2-trifluoroethanol (the mass ratio of the saturated solution of tetrabutylammonium fluoride and the saturated solution of sodium 2,2,2-trifluoroethanol is 1:1). The crystallization reaction consists of the following three stages: First crystallization stage: The second mixture is stirred at 85°C for 15 minutes to obtain the first crystal; Second crystallization stage: Under continuous stirring at 85℃, the system pressure of the first crystal is reduced to -0.4MPa at a first depressurization rate of 30kPa / min to obtain the second crystal; Third crystallization stage: The second crystal was stirred for 5 hours at 85℃ and -0.4MPa to obtain the third mixture; the stirring rate throughout the stage was 25r / min.

[0065] Step S5: Perform a second solid-liquid separation on the third mixture to obtain filtrate and solid phase; collect the solid phase and dry it to obtain aluminum fluoride product; The fluoride ion concentration in the filtrate was 5 mg / L, which meets the emission standards. By mass percentage, the aluminum fluoride product contains 61.3% sulfur (F) and 31.7% aluminum (Al). The particle size distribution of aluminum fluoride products is: D 10 =40.132μm, D 50 =71.216μm, D 90 =130.415μm.

[0066] Example 3 Example 3 provides a method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis, comprising the following steps: Step S1: Convert the fluorine-containing substances in aluminum electrolysis fluorine-containing waste with a particle size ≤74μm into soluble salts to obtain the first mixture; Fluorine-containing waste from aluminum electrolysis is the electrolyte obtained from the electrolytic cell. The method for converting fluorine-containing substances in aluminum electrolysis fluorine-containing waste into soluble salts includes: mixing aluminum electrolysis fluorine-containing waste with a solvent at a mass ratio of 1:5 to obtain a first mixture; the solvent is a mixture composed of sulfuric acid (mass concentration of 98%), hydrochloric acid (mass concentration of 1%), aluminum sulfate (mass concentration of 1%), nitric acid (mass concentration of 65%), and aluminum chloride (mass concentration of 25%) in a mass ratio of 1:1:1:1:1:1.

[0067] Step S2: Perform a first solid-liquid separation on the first mixture to obtain a first leachate; Step S3: Adjust the aluminum-fluorine ratio and pH value of the first leachate to obtain the second leachate; in the second leachate, the molar ratio of aluminum to fluorine is 1:3.5; the pH value of the second leachate is 6.0. The method of adjusting the aluminum-fluorine ratio of the first leachate includes adding a first reagent; the first reagent includes aluminum chloride, potassium fluoride, and hydrofluoric acid; The pH of the first leachate can be adjusted by adding a second reagent; the second reagent includes sulfuric acid, ammonium carbonate, and ammonium bicarbonate.

[0068] Step S4: Add activated crystals to the second leachate at a mass ratio of 100:9 to obtain a second mixture; perform a crystallization reaction on the second mixture to obtain a third mixture. The method for preparing activated seed crystals includes the following steps: aluminum fluoride precursor with a particle size of 20μm~30μm and a saturated solution of seed crystal activator are sequentially subjected to a first mixing and a third solid-liquid separation to obtain activated seed crystals; the first mixing time is 3h; The seed activator saturated solution is prepared by mixing a saturated solution of sodium 2,2,2-trifluoroethanol and a saturated solution of cerium trifluoromethanesulfonate (the mass ratio of the saturated solution of sodium 2,2,2-trifluoroethanol to the saturated solution of cerium trifluoromethanesulfonate is 2:1). The crystallization reaction consists of the following three stages: First crystallization stage: The second mixture is stirred at 90°C for 20 minutes to obtain the first crystal; Second crystallization stage: Under continuous stirring at 90℃, the system pressure of the first crystal is reduced to -0.3MPa at a first depressurization rate of 25kPa / min to obtain the second crystal; Third crystallization stage: The second crystal was stirred for 4.5 h at 90℃ and -0.3 MPa to obtain the third mixture; the stirring rate throughout the stage was 20 r / min.

[0069] Step S5: Perform a second solid-liquid separation on the third mixture to obtain filtrate and solid phase; collect the solid phase and dry it to obtain aluminum fluoride product; The fluoride ion concentration in the filtrate was 9 mg / L, which meets the emission standards. By mass percentage, the aluminum fluoride product contains 61.4% sulfur (F) and 31.9% aluminum (Al). The particle size distribution of aluminum fluoride products is: D 10 =45.516μm, D 50 =73.321μm, D 90 =132.067μm.

[0070] Example 4 Example 4 provides a method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis, comprising the following steps: Step S1: Convert the fluorine-containing substances in aluminum electrolysis fluorine-containing waste with a particle size ≤74μm into soluble salts to obtain the first mixture; Fluorine-containing waste from aluminum electrolysis is the electrolyte obtained from the flotation of carbon slag; The method for converting fluorine-containing substances in aluminum electrolysis fluorine-containing waste into soluble salts includes: mixing aluminum electrolysis fluorine-containing waste with a solvent at a mass ratio of 1:8 to obtain a first mixture; the solvent is a mixture composed of sodium hydroxide (mass concentration of 1%) and sodium carbonate (mass concentration of 16%) at a mass ratio of 1:2.

[0071] Step S2: Perform a first solid-liquid separation on the first mixture to obtain a first leachate; Step S3: Adjust the aluminum-fluorine ratio and pH value of the first leachate to obtain the second leachate; in the second leachate, the molar ratio of aluminum to fluorine is 1:3.5; the pH value of the second leachate is 2.5. The method of adjusting the aluminum-fluoride ratio of the first leachate includes adding a first reagent; the first reagent includes soluble aluminum salts and soluble fluorides; the soluble aluminum salts include any one or more of aluminum sulfate, aluminum nitrate, and aluminum chloride; the soluble fluorides include any one or more of ammonium fluoride, sodium fluoride, potassium fluoride, and hydrofluoric acid. The pH value of the first leachate can be adjusted by adding a second reagent; the second reagent includes any one or more of sulfuric acid, hydrochloric acid, nitric acid, sodium hydroxide, ammonia, ammonium carbonate, and ammonium bicarbonate.

[0072] Step S4: Add activated crystals to the second leachate at a mass ratio of 100:3 to obtain a second mixture; perform a crystallization reaction on the second mixture to obtain a third mixture. The method for preparing activated seed crystals includes the following steps: aluminum fluoride precursor with a particle size of 20μm~30μm and a saturated solution of seed crystal activator are sequentially subjected to a first mixing and a third solid-liquid separation to obtain activated seed crystals; the first mixing time is 2h; The seed activator saturated solution is a saturated solution of ammonium trifluoroacetate; The crystallization reaction consists of the following three stages: First crystallization stage: The second mixture is stirred at 82°C for 13 minutes to obtain the first crystal; Second crystallization stage: Under continuous stirring at 82℃, the system pressure of the first crystal is reduced to -0.2MPa at a first depressurization rate of 20kPa / min to obtain the second crystal; Third crystallization stage: The second crystal was stirred for 4.3 h at 82℃ and -0.2 MPa to obtain the third mixture; the stirring rate throughout the stage was 20 r / min.

[0073] Step S5: Perform a second solid-liquid separation on the third mixture to obtain filtrate and solid phase; collect the solid phase and dry it to obtain aluminum fluoride product; The fluoride ion concentration in the filtrate was 6 mg / L, which meets the emission standards. By mass percentage, aluminum fluoride products contain 61.6% sulfur (F) and 31.8% aluminum (Al). The particle size distribution of aluminum fluoride products is: D 10 =39.577μm, D 50 =68.132μm, D 90 =125.326μm.

[0074] Example 5 Example 5 provides a method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis, comprising the following steps: Step S1: Convert the fluorine-containing substances in aluminum electrolysis fluorine-containing waste with a particle size ≤74μm into soluble salts to obtain the first mixture; Fluorine-containing waste from aluminum electrolysis is the electrolyte obtained from the flotation of carbon slag; The method for converting fluorine-containing substances in aluminum electrolysis fluorine-containing waste into soluble salts includes: mixing aluminum electrolysis fluorine-containing waste with a solvent at a mass ratio of 1:3 to obtain a first mixture; the solvent is a mixture composed of sodium hydroxide (mass concentration of 20%) and sodium carbonate (mass concentration of 1%) at a mass ratio of 3:1.

[0075] Step S2: Perform a first solid-liquid separation on the first mixture to obtain a first leachate; Step S3: Adjust the aluminum-fluorine ratio and pH value of the first leachate to obtain the second leachate; in the second leachate, the molar ratio of aluminum to fluorine is 1:3.3; the pH value of the second leachate is 3.5. The method of adjusting the aluminum-fluorine ratio of the first leachate includes adding a first reagent; the first reagent includes aluminum sulfate and hydrofluoric acid; The pH of the first leachate can be adjusted by adding a second reagent; the second reagent includes hydrochloric acid, ammonia, and ammonium bicarbonate.

[0076] Step S4: Add activated crystals to the second leachate at a mass ratio of 100:7 to obtain a second mixture; perform a crystallization reaction on the second mixture to obtain a third mixture. The method for preparing activated seed crystals includes the following steps: aluminum fluoride precursor with a particle size of 20μm~30μm and a saturated solution of seed crystal activator are sequentially subjected to a first mixing and a third solid-liquid separation to obtain activated seed crystals; the first mixing time is 1h; The saturated solution of the seed activator is a saturated solution of sodium perfluorooctanoate; The crystallization reaction consists of the following three stages: First crystallization stage: The second mixture is stirred at 88°C for 16 minutes to obtain the first crystal; Second crystallization stage: Under continuous stirring at 88℃, the system pressure of the first crystal is reduced to -0.25MPa at a first depressurization rate of 15kPa / min to obtain the second crystal; Third crystallization stage: The second crystal was stirred for 4.8 h at 88℃ and -0.25 MPa to obtain the third mixture; The stirring rate throughout the entire stage was 20 r / min.

[0077] Step S5: Perform a second solid-liquid separation on the third mixture to obtain filtrate and solid phase; collect the solid phase and dry it to obtain aluminum fluoride product; The fluoride ion concentration in the filtrate was 4 mg / L, which meets the emission standards. By mass percentage, the aluminum fluoride product contains 61.8% sulfur (F) and 32.0% aluminum (Al). The particle size distribution of aluminum fluoride products is: D 10 =44.231μm, D 50 =72.458μm, D 90 =131.124μm.

[0078] Comparative Example 1 Comparative Example 1 provides a method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis, differing from Example 1 in the amount of activated seed crystals added. In Comparative Example 1, the mass ratio of the second leachate to the activated seed crystals is 100:0.5.

[0079] The other steps and parameters are the same as in Example 1, and will not be repeated here.

[0080] Comparative Example 2 Comparative Example 2 provides a method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis, which differs from Example 1 in that the content of the added activated seed crystals is different. In Comparative Example 2, the mass ratio of the second leachate to the activated seed crystals is 100:10.

[0081] The other steps and parameters are the same as in Example 1, and will not be repeated here.

[0082] Comparative Example 3 Comparative Example 3 provides a method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis, which differs from Example 1 in that the reaction temperature of the second mixture is different. In Comparative Example 3, the reaction temperature of the second mixture is 75°C.

[0083] The other steps and parameters are the same as in Example 1, and will not be repeated here.

[0084] Comparative Example 4 Comparative Example 4 provides a method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis, which differs from Example 1 in that the reaction temperature of the second mixture is different. In Comparative Example 4, the reaction temperature of the second mixture is 95°C.

[0085] The other steps and parameters are the same as in Example 1, and will not be repeated here.

[0086] Comparative Example 5 Comparative Example 5 provides a method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis, which differs from Example 1 in that the first pressure reduction rate is different. In Comparative Example 5, the first pressure reduction rate is 5 kPa / min.

[0087] The other steps and parameters are the same as in Example 1, and will not be repeated here.

[0088] Comparative Example 6 Comparative Example 6 provides a method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis, which differs from Example 1 in that the first pressure reduction rate is different. In Comparative Example 6, the first pressure reduction rate is 35 kPa / min.

[0089] The other steps and parameters are the same as in Example 1, and will not be repeated here.

[0090] Comparative Example 7 Comparative Example 7 provides a method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis. The difference from Example 1 lies in the pressure during the second stirring of the crystals. In Comparative Example 7, the pressure during the second stirring of the crystals is -0.05 MPa.

[0091] The other steps and parameters are the same as in Example 1, and will not be repeated here.

[0092] Comparative Example 8 Comparative Example 8 provides a method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis. The difference from Example 1 lies in the pressure during the second stirring of the crystals. In Comparative Example 8, the pressure during the second stirring of the crystals is -0.45 MPa.

[0093] The other steps and parameters are the same as in Example 1, and will not be repeated here.

[0094] Comparative Example 9 Comparative Example 9 provides a method for preparing aluminum fluoride using aluminum electrolysis fluorine-containing waste. The difference from Example 1 is that the seed crystals were not soaked in a saturated solution of seed activator.

[0095] The other steps and parameters are the same as in Example 1, and will not be repeated here.

[0096] The process parameters and performance characterization results of the aluminum fluoride products for each embodiment and comparative example are shown in Table 1.

[0097] Table 1. Process parameters and performance characterization results of aluminum fluoride products for each embodiment and comparative example.

[0098] Experimental results show that: Comparing Example 1 and Comparative Examples 1-2, it can be seen that when the mass ratio of the second leachate to the activated seed crystals is greater than 100:1 (i.e., the content of activated seed crystals is less than 1% of the second leachate), the insufficient content of activated seed crystals leads to insufficient heterogeneous nucleation sites, resulting in the formation of more homogeneous nucleation fine crystals, thus making the obtained aluminum fluoride product too fine in particle size; and the fluorine content in the filtrate is too high. Conversely, when the mass ratio of the second leachate to the activated seed crystals is less than 100:9 (i.e., the content of activated seed crystals is greater than 9% of the second leachate), the excessive content of activated seed crystals leads to too many heterogeneous nucleation sites, resulting in insufficient driving force for crystal growth, limiting crystal growth, and similarly making the aluminum fluoride product have a fine particle size.

[0099] Comparing Example 1 and Comparative Examples 3-4, it can be seen that when the reaction temperature of the second mixture is below 80°C, the crystallization temperature is too low during initial stirring, resulting in insufficient kinetic energy for crystal growth and an insignificant induced crystallization effect. Consequently, the amount of aluminum fluoride product generated is not only too small, but the particle size of the aluminum fluoride product is also fine; in addition, the fluorine content in the filtrate is also high. When the reaction temperature of the second mixture is above 90°C, the crystallization temperature is too high during initial stirring, resulting in excessively rapid crystal growth in the initial stage. The induction ability is less than the homogeneous nucleation ability, which generates more fine grains, affecting the particle size distribution of the aluminum fluoride product.

[0100] Comparing Example 1 and Comparative Examples 5-6, it can be seen that when the second mixture reacts, if the first depressurization rate is less than 10 kPa / min, the effect of reducing crystal growth resistance is too small, resulting in hindered crystal growth and excessively small particle size of the generated aluminum fluoride product. When the second mixture reacts, if the first depressurization rate is greater than 30 kPa / min, the pressure around the aluminum fluoride product crystals decreases too quickly due to the excessively rapid depressurization rate. Crystals in a certain direction at the active sites are forced to enter the next pressure atmosphere before they can grow properly. The growth of the aluminum fluoride product crystals is layered and the layers are not tightly bonded. In the later stage, the layered structure of the aluminum fluoride product is easily disintegrated during solid-phase transport, resulting in a finer aluminum fluoride product, which is not conducive to automatic feeding.

[0101] Comparing Example 1 and Comparative Examples 7-8, it can be seen that if the system pressure is below -0.1 MPa during the reaction and second stirring of the second mixture, the effect of reducing the resistance to crystal growth of aluminum fluoride is too small, resulting in hindered crystal growth and excessively small particle size of the generated aluminum fluoride product. If the system pressure is above -0.4 MPa during the reaction and second stirring of the second mixture, the aluminum fluoride crystal growth is too rapid in the initial stage, and the induction ability is less than the homogeneous nucleation ability, resulting in the formation of more fine grains and affecting the particle size distribution of the aluminum fluoride product.

[0102] Comparative Examples 1 and 9 show that, during the preparation of activated seed crystals, if the precursor is not treated with a saturated solution of seed activator, a higher density of active sites cannot be formed on the surface of the aluminum fluoride seed crystals, nor can a surface micro-electric field environment more conducive to the growth of aluminum fluoride product crystals be constructed. Therefore, the particle size of the obtained aluminum fluoride product is smaller than that of Example 1.

[0103] It is evident that the excellent results of the method for preparing aluminum fluoride from aluminum electrolysis fluorine-containing waste provided in this application are based on the combined effect of various parameters, none of which can be omitted.

[0104] In summary, this invention provides a method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis. This method involves converting the fluorine-containing components in the waste into soluble salts, adjusting the aluminum-fluorine molar ratio and pH value of the resulting fluorine-containing solution, and then adding activated seed crystals prepared from an aluminum fluoride precursor and reacting to successfully produce aluminum fluoride products with relatively coarse particle sizes. The activated seed crystals are prepared by immersing the precursor in a saturated solution of seed activator. This process aims to form a higher density of active sites on the surface of the aluminum fluoride seed crystals and create a surface micro-electric field environment more conducive to the growth of aluminum fluoride crystals. This method not only effectively meets the particle size and physical properties requirements of the automatic feeding system in aluminum electrolysis cells but also achieves efficient and large-scale resource utilization of fluorine-containing waste from aluminum electrolysis, such as carbon slag and overhaul slag. Furthermore, the wastewater generated during the process can be treated to achieve fluoride ion discharge standards, avoiding environmental pollution. Overall, the preparation method provided in this application has a simple process flow and is easy to operate. It does not require complicated equipment and obtains high-quality aluminum fluoride without generating secondary pollution, thus achieving both environmental and economic benefits.

[0105] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis, characterized in that, Includes the following steps: The fluorine-containing substances in the aluminum electrolysis fluorine-containing waste are converted into soluble salts to obtain the first mixture; The first mixture is subjected to a first solid-liquid separation to obtain a first leachate; The aluminum-fluorine ratio and pH value of the first leachate are adjusted to obtain the second leachate; Activated seed crystals are added to the second leachate to obtain a second mixture; The second mixture is subjected to a crystallization reaction to obtain a third mixture; and, The third mixture is subjected to a second solid-liquid separation to obtain aluminum fluoride product; The particle size distribution of the aluminum fluoride product satisfies: D 10 The diameter is 39μm~46μm, D 50 The thickness ranges from 68μm to 77μm. D 90 The thickness ranges from 125μm to 133μm. The method for preparing the activated seed crystals includes the following steps: sequentially mixing the precursor and a saturated solution of the seed crystal activator, followed by a third solid-liquid separation, to obtain the activated seed crystals; The precursor includes aluminum fluoride.

2. The method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis according to claim 1, characterized in that, The seed activator saturated solution comprises any one or more of the following: ammonium trifluoroacetate saturated solution, tetrabutylammonium fluoride saturated solution, sodium perfluorooctanoate saturated solution, sodium 2,2,2-trifluoroethanol saturated solution, and cerium trifluoromethanesulfonate saturated solution; and / or The precursor has a particle size of 20 μm to 30 μm; and / or, The first mixing time is 0.5h to 6h.

3. The method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis according to claim 2, characterized in that, The mass ratio of the second leachate to the activated seed crystals is 100:(1~9).

4. The method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis according to claim 2, characterized in that, The crystallization reaction includes the following three stages: First crystallization stage: The second mixture is stirred at 80℃~90℃ for 10min~20min to obtain the first crystal; Second crystallization stage: Under continuous stirring at 80℃~90℃, the system pressure of the first crystal is reduced to -0.1MPa~-0.4MPa at a first depressurization rate to obtain the second crystal; Third crystallization stage: The second crystal is stirred for 4 to 5 hours at 80℃~90℃ and -0.1MPa~-0.4MPa to obtain the third mixture.

5. The method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis according to claim 4, characterized in that, The first pressure reduction rate is 10 kPa / min to 30 kPa / min.

6. The method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis according to claim 2, characterized in that, In the second leachate, the molar ratio of aluminum to fluorine is 1:(3~3.5); The pH value of the second leachate is 2.5~6.

0.

7. The method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis according to claim 6, characterized in that, The method of adjusting the aluminum-fluorine ratio of the first leachate includes adding a first reagent; the first reagent includes a soluble aluminum salt and / or a soluble fluoride; the soluble aluminum salt includes any one or more of aluminum sulfate, aluminum nitrate, and aluminum chloride; the soluble fluoride includes any one or more of ammonium fluoride, sodium fluoride, potassium fluoride, and hydrofluoric acid.

8. The method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis according to claim 7, characterized in that, The pH value of the first leachate is adjusted by adding a second reagent; the second reagent includes any one or more of sulfuric acid, hydrochloric acid, nitric acid, sodium hydroxide, ammonia, ammonium carbonate, and ammonium bicarbonate.

9. The method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis according to claim 1, characterized in that, The method for converting fluorine-containing substances in aluminum electrolysis fluorine-containing waste into soluble salts includes: mixing the aluminum electrolysis fluorine-containing waste with a solvent to obtain the first mixture; The solvent includes any one or more of the following: sulfuric acid with a concentration of 1% to 98%, hydrochloric acid with a concentration of 1% to 36%, nitric acid with a concentration of 1% to 65%, sodium hydroxide with a concentration of 1% to 20%, sodium carbonate with a concentration of 1% to 16%, aluminum sulfate with a concentration of 1% to 25%, aluminum nitrate with a concentration of 1% to 25%, and aluminum chloride with a concentration of 1% to 25%. The mass ratio of the aluminum electrolysis fluorine-containing waste to the solvent is 1:(1~10).

10. The method for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis according to any one of claims 1 to 9, characterized in that, The particle size of the aluminum electrolysis fluorine-containing waste is ≤74μm; and / or, The aluminum electrolysis fluorine-containing waste includes any one or more of the following: carbon slag, electrolytic cell overhaul slag, electrolyte obtained from carbon slag flotation, electrolyte obtained from carbon slag pyrochemical treatment, electrolyte obtained from electrolytic cell dredging, and regenerated electrolyte obtained from the treated aluminum electrolysis fluorine-containing waste.

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