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

Abstract

The invention relates to a method for preparing aluminum fluoride from aluminum electrolysis fluorine-containing waste, and belongs to the technical field of aluminum electrolysis fluorine-containing waste recovery. The method comprises the steps that the aluminum electrolysis fluorine-containing waste is subjected to a leaching reaction, and slurry containing soluble fluoride salt is obtained; carrying out solid-liquid separation on the slurry containing the soluble fluoride salt to obtain a first liquid material; the aluminum-fluorine ratio and the pH value of the first liquid material are adjusted, and a second liquid material with the set aluminum-fluorine ratio and the set pH value is obtained; and mixing the second liquid material, an activated seed crystal and a crystal growth inducer, and carrying out a crystallization reaction to obtain aluminum fluoride. The purity of the aluminum fluoride prepared by the embodiment of the invention is greater than 95%, and D10 is greater than 62 microns.

Description

Technical Field

[0001] This application relates to the technical field of recycling of fluorine-containing waste in aluminum electrolysis, and particularly relates to a method for preparing aluminum fluoride from fluorine-containing waste in aluminum electrolysis. Background Art

[0002] During the aluminum electrolysis process, aluminum fluoride or feeding fluoride-bearing alumina needs to be continuously supplemented to balance the increase in the electrolyte molecular ratio caused by the sodium content in industrial alumina, resulting in an increase in the electrolyte in the electrolytic cell. For every ton of aluminum produced, about 17.5 kg of overhaul slag and 9.5 kg of carbon slag are generated. During the treatment of fluorine-containing waste such as carbon slag and overhaul slag in aluminum electrolysis, the regenerated electrolyte and the fished-out electrolyte generated are continuously accumulating due to the current national production capacity restrictions. For every ton of aluminum produced, about 10 kg of surplus electrolyte is generated. Based on this calculation, the annual output of surplus electrolyte in China is about 370,000 tons. The large amount of idle electrolyte not only causes waste of resources, but also occupies a large amount of storage space, which has become an important problem that cannot be ignored by aluminum electrolysis enterprises.

[0003] Currently, aluminum and fluorine in fluorine-containing waste in aluminum electrolysis are recovered in the form of aluminum hydroxyfluoride precipitate. However, the molar ratio of fluorine to aluminum in the molecular formula of aluminum hydroxyfluoride (AlF 1.5 (OH) 1.5 (H 2 O) 0.375 、Al 2 F 3.24 (OH) 2.76 ·H 2 O) is small, and it contains crystal water, resulting in strong side reactions during the dehydration and dehydroxylation processes, and a large amount of the generated aluminum fluoride decomposes into alumina, with low purity. Generally, for the preparation of aluminum fluoride involving wet methods, the generated aluminum fluoride has too fine particle size, low purity, large flying loss, which is not conducive to the automatic feeding and molecular ratio regulation in aluminum electrolysis production. Summary of the Invention

[0004] This application provides a method for preparing aluminum fluoride from fluorine-containing waste in aluminum electrolysis to solve the following technical problem: how to increase the particle size of the aluminum fluoride prepared from fluorine-containing waste in aluminum electrolysis.

[0005] In a first aspect, an embodiment of this application provides a method for preparing aluminum fluoride from fluorine-containing waste in aluminum electrolysis, and the method includes:

[0006] Performing a leaching reaction on the fluorine-containing waste in aluminum electrolysis to obtain a slurry containing soluble fluorinated salts;

[0007] Performing solid-liquid separation on the slurry containing soluble fluorinated salts to obtain a first liquid material;

[0008] Adjusting the aluminum-fluorine ratio and pH value of the first liquid material to obtain a second liquid material with a set aluminum-fluorine ratio and a set pH value;

[0009] Mix the second liquid material, the activated seed crystal, and the crystal growth inducer to carry out a crystallization reaction to obtain aluminum fluoride.

[0010] Optionally, the set aluminum-fluorine ratio is 1:(3 - 3.5).

[0011] Optionally, the set pH value is 2.5 - 6.0.

[0012] Optionally, the temperature of the mixing is 90°C - 110°C.

[0013] Optionally, the crystal growth inducer includes at least one of the following: zinc phytate, ammonium fluoride, lauryl alcohol, stearyl alcohol.

[0014] Optionally, the mass of the activated seed crystal is 3% - 20% of the mass of the second liquid material; and / or,

[0015] The mass of the crystal growth inducer is 0.002‰ - 0.05‰ of the mass of the second liquid material.

[0016] Optionally, the step of mixing the second liquid material, the activated seed crystal, and the crystal growth inducer to carry out a crystallization reaction to obtain aluminum fluoride includes:

[0017] Soak the aluminum fluoride precursor with the seed crystal activator to obtain an activated seed crystal;

[0018] Mix the second liquid material, the activated seed crystal, and the crystal growth inducer to carry out a crystallization reaction to obtain aluminum fluoride.

[0019] Optionally, the particle size of the aluminum fluoride precursor is 5μm - 20μm.

[0020] Optionally, the seed crystal activator includes at least one of the following: zirconium fluoride, titanium fluoride, citric acid, sulfuric acid, aluminum sulfate, aluminum chloride.

[0021] Optionally, the aluminum fluoride meets at least one of the following indicators: purity greater than 95%, D10 > 62μm.

[0022] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art:

[0023] The method for preparing aluminum fluoride from aluminum electrolysis fluorine-containing waste provided by the embodiments of the present application includes: performing a leaching reaction on the aluminum electrolysis fluorine-containing waste to obtain a slurry containing soluble fluorinated salts; performing solid-liquid separation on the slurry containing soluble fluorinated salts to obtain a first liquid material; adjusting the aluminum-fluorine ratio and pH value of the first liquid material to obtain a second liquid material with a set aluminum-fluorine ratio and a set pH value; mixing the second liquid material, activated seeds, and crystal growth inducer to perform a crystallization reaction to obtain aluminum fluoride. Performing a leaching reaction on the aluminum electrolysis fluorine-containing waste can cause corrosion or coordination reactions of cryolite and other fluorine-containing minerals in the aluminum electrolysis fluorine-containing waste to generate water-soluble fluorinated salts, thereby realizing the transformation of insoluble fluorinated salts into soluble fluorinated salts; adjusting the aluminum-fluorine ratio of the first liquid material can cause aluminum fluoride to be generated in the subsequent crystallization reaction of the second liquid material; adjusting the pH value of the first liquid material can give crystal growth power in the subsequent crystallization reaction; the characteristics of the activated seeds with many surface active sites and microelectric field reset are beneficial to the growth and enlargement of aluminum fluoride crystals, thereby facilitating the obtaining of large-grained aluminum fluoride crystals; the crystal growth inducer can change the microelectric field distribution of the mixed system, thereby facilitating the progress of the crystallization reaction, and can also change the activity of the surface of the aluminum fluoride crystal, thereby promoting the continuous growth and enlargement of the aluminum fluoride crystal; therefore, the second liquid material with a set aluminum-fluorine ratio and a set pH value can promote heterogeneous nucleation under the action of the activated seeds, induce the growth and enlargement of aluminum fluoride on the surface active sites of the seeds, and the further improvement of the solution microelectric field and crystal surface activity by the crystal growth inducer can maximize the realization of seed-induced crystallization to generate large-grained aluminum fluoride. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present application and, together with the specification, are used to explain the principles of the present application.

[0025] To more clearly illustrate the technical solutions in the embodiments of the present application or in the prior art, the following will briefly introduce the accompanying drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1 It is a schematic flow chart of a method for preparing aluminum fluoride from aluminum electrolysis fluorine-containing waste provided by the embodiments of the present application;

[0027] Figure 2 It is a phase diagram of aluminum fluoride prepared by a method for preparing aluminum fluoride from aluminum electrolysis fluorine-containing waste provided by the embodiments of the present application;

[0028] Figure 3The particle size distribution diagram of aluminum fluoride prepared by a method for preparing aluminum fluoride from aluminum electrolysis fluorine-containing waste provided by an embodiment of the present application. Detailed implementation manners

[0029] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the scope of protection of the present application.

[0030] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the description of the range has specifically disclosed all possible sub-ranges and the individual values within that range. For example, it should be considered that the description of the range 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 the individual numbers within that range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0031] In this application, unless otherwise specified, the orientation terms such as "upper" and "lower" specifically refer to the drawing direction in the attached drawings. Additionally, in the description of this application's specification, terms such as "include" and "comprise" mean "include but not limited to". In this text, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this text, "and / or" describes the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B can be singular or plural. In this text, "at least one" means one or more, and "a plurality" means two or more. "At least one kind", "at least one of the following items (pieces)" or similar expressions refer to any combination of these items, including any combination of single items (pieces) or plural items (pieces). 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, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively. In the proportional relationships involved in this text, the parameters that need to be described by proportion should be understood as the antecedents of the proportion formula in the order of description, and the proportional numbers should be understood as the consequents of the proportion formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the proportional numbers in the proportion formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0032] Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments, equipment, etc. used in this application can be obtained through market purchase or can be prepared by existing methods.

[0033] In a first aspect, an embodiment of this application provides a method for preparing aluminum fluoride from aluminum electrolysis fluorine-containing waste. Figure 1 It is a schematic flow chart of a method for preparing aluminum fluoride from aluminum electrolysis fluorine-containing waste provided by an embodiment of this application; please refer to Figure 1 , the method includes:

[0034] S1. Perform a leaching reaction on the aluminum electrolysis fluorine-containing waste to obtain a slurry containing soluble fluorinated salts;

[0035] Aluminum electrolysis fluorine-containing waste is the waste generated during the aluminum electrolysis production process. The aluminum electrolysis fluorine-containing waste includes at least one of the following: carbon slag, overhaul slag, electrolyte after carbon slag flotation, electrolyte after pyrometallurgical treatment of carbon slag, electrolyte fished out from the electrolytic cell, and regenerated electrolyte obtained after treatment of other aluminum electrolysis cell fluorine-containing waste. The aluminum electrolysis fluorine-containing waste undergoes a leaching reaction, which can cause corrosion or coordination reactions of cryolite and other fluorine-containing minerals in the aluminum electrolysis fluorine-containing waste to generate water-soluble fluorides, thereby realizing the transformation of insoluble fluorides into soluble fluorides. The initial aluminum electrolysis fluorine-containing waste is ground and sieved through a 200-mesh sieve, and the material under the sieve can be used as the aluminum electrolysis fluorine-containing waste for the above leaching reaction. In step S1, a leaching agent can be used to carry out the leaching reaction on the aluminum electrolysis fluorine-containing waste. The leaching agent can be an acidic reagent or a basic reagent; the acidic reagent can be sulfuric acid, hydrochloric acid, nitric acid, aluminum sulfate, aluminum chloride, etc.; the basic reagent can be sodium hydroxide, potassium hydroxide, etc. The dosage of the leaching agent can be 1.5 to 2.5 times the mass of the aluminum electrolysis fluorine-containing waste, and the liquid-solid ratio of the leaching reaction system can be (4 to 10):1.

[0036] S2. Solid-liquid separation is performed on the slurry containing soluble fluoride to obtain a first liquid material;

[0037] Performing solid-liquid separation on the slurry containing soluble fluoride to obtain a first liquid material effectively removes insoluble solid impurities in the system after the leaching reaction and separates the soluble fluoride, making the subsequent treatment of the first liquid material containing soluble fluoride purer and more efficient.

[0038] S3. Adjust the aluminum-fluorine ratio and pH value of the first liquid material to obtain a second liquid material with a set aluminum-fluorine ratio and a set pH value;

[0039] Adjusting the aluminum-fluorine ratio of the first liquid material lays a material composition foundation for the subsequent crystallization reaction to generate aluminum fluoride. Adjusting the pH value provides crystal growth driving force for the subsequent crystallization reaction. Therefore, the second liquid material provides a suitable element ratio and a suitable pH environment for the generation of aluminum fluoride.

[0040] In some embodiments, the set aluminum-fluorine ratio is 1:(3 to 3.5).

[0041] The set aluminum-fluorine ratio (molar ratio) can be 1:(3 - 3.5), so that the second liquid material has appropriate aluminum and fluorine contents, and high-purity large-grained aluminum fluoride can be fully produced. If the aluminum-fluorine ratio is greater than 1:3, there will be too much aluminum in the second liquid material, which may cause the fluorine content of the produced aluminum fluoride to be too low and the purity to be not high. If the aluminum-fluorine ratio is less than 1:3.5, there will be too much fluorine in the second liquid material, which may cause the fluorine content in the remaining liquid after crystallization to be too high, and direct discharge will cause secondary pollution. Exemplarily, the set aluminum-fluorine ratio can be 1:3, 1:3.1, 1:3.2, 1:3.3, 1:3.4, 1:3.5, etc.

[0042] In some embodiments, the set pH value is 2.5 - 6.0.

[0043] The set pH value can be 2.5 - 6.0, which can effectively avoid the generation of homogeneous nucleation in the crystallization reaction and ensure the crystallization of aluminum fluoride and the growth of crystals on the surface of the seed crystal at a low supersaturation. If the set pH value is higher than 6.0, impurities may be generated, affecting the purity of aluminum fluoride; if the set pH value is lower than 2.5, the driving force for the crystallization reaction and crystal growth may be insufficient. Exemplarily, the set pH value can be 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, etc.

[0044] S4. Mix the second liquid material, the activated seed crystal, and the crystal growth inducer to carry out a crystallization reaction to obtain aluminum fluoride.

[0045] The second liquid material has an appropriate aluminum-fluorine ratio and pH value, providing an appropriate element ratio and an appropriate pH environment for the production of aluminum fluoride. On this basis, the activated seed crystal can promote heterogeneous nucleation, induce the growth and enlargement of aluminum fluoride at the active sites on the surface of the seed crystal, and the crystal growth inducer can further improve the microelectric field of the solution and the surface activity of the crystal to maximize the realization of seed crystal-induced crystallization and produce large-grained aluminum fluoride. After the crystallization reaction, the product is subjected to solid-liquid separation and drying to obtain an aluminum fluoride product.

[0046] In some embodiments, the temperature of the mixing is 90°C - 110°C.

[0047] The temperature of the mixing can be 90°C - 110°C, which is beneficial to the crystallization reaction. If the temperature of the mixing is higher than 110°C, impurities may be generated, affecting the purity of aluminum fluoride; if the temperature of the mixing is lower than 90°C, the driving force for the crystallization reaction and crystal growth may be insufficient. Exemplarily, the temperature of the mixing can be 90°C, 92°C, 94°C, 96°C, 98°C, 100°C, 102, 104, 106°C, 108°C, 110°C, etc. The mixing time can be 3h - 8h. The mixing method can be stirring and mixing.

[0048] In some embodiments, the crystal growth inducer includes at least one of the following: zinc phytate, ammonium fluoride, lauryl alcohol, and stearyl alcohol.

[0049] The crystal growth inducer can be a combination of one or more of zinc phytate, ammonium fluoride, lauryl alcohol, and stearyl alcohol. These crystal growth inducers can change the microelectric field distribution of the mixed system, improve the surface activity of the crystal, and be more beneficial to the crystallization reaction and crystal growth.

[0050] In some embodiments, the mass of the activated seed crystal is 3% - 20% of the mass of the second liquid material; and / or,

[0051] The mass of the crystal growth inducer is 0.002‰ - 0.05‰ of the mass of the second liquid material.

[0052] The mass of the activated seed crystal can be 3% - 20% of the mass of the second liquid material, providing sufficient activated seed crystals to fully generate aluminum fluoride crystals. If the mass of the activated seed crystal is less than 3% of the mass of the second liquid material, it may cause insufficient heterogeneous nucleation sites due to insufficient seed crystal amount, resulting in too little aluminum fluoride crystal formation; if the mass of the activated seed crystal is higher than 20% of the mass of the second liquid material, the initial supersaturation will decrease too quickly due to excessive seed crystal amount, which is not conducive to the subsequent crystal growth. Exemplarily, the mass of the activated seed crystal is 3%, 5%, 7%, 9%, 11%, 13%, 15%, 17%, 19%, 20%, etc. of the mass of the second liquid material.

[0053] The mass of the crystal growth inducer can be 0.002‰ - 0.05‰ of the mass of the second liquid material, fully adjusting the surface activity of the seed crystal and the microelectric field distribution of the solution, promoting the subsequent crystal growth, and thus generating large particles of high-purity crystals. If the mass of the crystal growth inducer is higher than 0.05‰ of the mass of the second liquid material, the quality of the product aluminum fluoride will be affected due to excessive impurity introduction; if the mass of the crystal growth inducer is less than 0.002‰ of the mass of the second liquid material, the adjustment of the surface activity of the seed crystal and the microelectric field distribution of the solution is insufficient, which is not conducive to the subsequent crystal growth. Exemplarily, the mass of the crystal growth inducer can be 0.002‰, 0.003‰, 0.004‰, 0.005‰, 0.01‰, 0.02‰, 0.03‰, 0.04‰, 0.05‰, etc. of the mass of the second liquid material.

[0054] In some embodiments, mixing the second liquid material, the activated seed crystal, and the crystal growth inducer to perform a crystallization reaction to obtain aluminum fluoride includes:

[0055] Soaking the aluminum fluoride precursor with the seed crystal activator to obtain an activated seed crystal;

[0056] Mix the second liquid material, the activated seed crystal, and the crystal growth inducer to carry out a crystallization reaction to obtain aluminum fluoride.

[0057] Soak the aluminum fluoride precursor with a seed crystal activator to activate the aluminum fluoride precursor as a seed crystal, realize etching on the surface of the seed crystal and reset the microelectric field on the surface, increase the active sites on the surface of the seed crystal and change the microelectric field, which is more conducive to crystal growth and enlargement, thereby facilitating the obtaining of large-grained aluminum fluoride crystals.

[0058] In some embodiments, the particle size of the aluminum fluoride precursor is 5 μm to 20 μm.

[0059] The particle size of the aluminum fluoride precursor can be 5 μm to 20 μm, which fully realizes the induction of crystal growth, effectively avoids homogeneous nucleation, and promotes the formation of large-grained aluminum fluoride. If the particle size of the aluminum fluoride precursor is less than 5 μm, since the crystal nucleus size for inducing crystallization is not reached, it cannot be used as a crystal nucleus to induce crystal growth, resulting in a large amount of homogeneous nucleation; if the particle size of the aluminum fluoride precursor is greater than 20 μm, due to insufficient sites for seed crystal-induced crystallization, it cannot well induce crystal growth, resulting in more homogeneous nucleation, affecting the purity and particle size of the product aluminum fluoride. Exemplarily, the particle size of the aluminum fluoride precursor can be 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 20 μm, etc.

[0060] In some embodiments, the seed crystal activator includes at least one of the following: zirconium fluoride, titanium fluoride, citric acid, sulfuric acid, aluminum sulfate, aluminum chloride.

[0061] The seed crystal activator can be a combination of one or more of zirconium fluoride, titanium fluoride, citric acid, sulfuric acid, aluminum sulfate, and aluminum chloride. These seed crystal activators can realize etching on the surface of the seed crystal and reset the microelectric field on the surface, increase the active sites on the surface of the seed crystal and change the microelectric field, which is more conducive to subsequent crystal growth and enlargement, and is more conducive to obtaining large-grained aluminum fluoride crystals. In addition, the mass of the seed crystal activator can be 0.001‰ to 0.002‰ of the mass of the aluminum fluoride precursor.

[0062] In some embodiments, the aluminum fluoride meets at least one of the following indicators: purity greater than 95%, D10 > 62 μm.

[0063] The method for preparing aluminum fluoride from aluminum electrolysis fluorine-containing waste provided by the embodiments of the present application has the following advantages:

[0064] 1. By adjusting the aluminum-fluorine ratio and pH value of the first liquid material, the chemical composition and acidity of the reaction system can be precisely controlled, creating ideal conditions for subsequent crystallization reactions. A suitable aluminum-fluorine ratio ensures that the reaction can produce aluminum fluoride according to stoichiometric relationships, while an appropriate pH value provides the necessary driving force for crystal growth.

[0065] 2. During the crystallization reaction, the activated crystal seeds have more surface active sites and a reset microelectric field, which can promote heterogeneous nucleation and induce the growth of aluminum fluoride on the surface active sites of the crystal seeds. The crystal growth inducer can change the microelectric field distribution of the mixed system and the activity of the aluminum fluoride crystal surface, prompting the continuous growth and enlargement of the aluminum fluoride crystal. The synergistic effect of the two is conducive to obtaining large-grained aluminum fluoride crystals.

[0066] The following further elaborates on this application in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate this application and not to limit the scope of this application. For the experimental methods without specific conditions noted in the following embodiments, they are usually determined according to national standards. If there is no corresponding national standard, they are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0067] Example 1

[0068] Perform a leaching reaction on aluminum electrolysis fluorine-containing waste to obtain a slurry containing soluble fluorinated salts;

[0069] Specifically: After flotation of carbon slag, the electrolyte is crushed, passed through a 200-mesh sieve, and the undersize is taken. The undersize of the electrolyte after flotation of carbon slag is mixed with sulfuric acid to carry out the leaching reaction.

[0070] Perform solid-liquid separation on the slurry containing soluble fluorinated salts to obtain the first liquid material;

[0071] Adjust the aluminum-fluorine ratio and pH value of the first liquid material to obtain a second liquid material with a set aluminum-fluorine ratio and a set pH value; among them, the set aluminum-fluorine ratio is 1:3, and the set pH value is 5.0;

[0072] Soak the aluminum fluoride precursor with a crystal seed activator to obtain activated crystal seeds; among them, the crystal seed activator is fluotitanic acid and sulfuric acid, and the particle size of the aluminum fluoride precursor is 5 μm to 10 μm;

[0073] Mix the second liquid material, the activated crystal seeds, and the crystal growth inducer to carry out a crystallization reaction to obtain aluminum fluoride; among them, the crystal growth inducer is lauryl alcohol and ammonium fluoride, the mass of the activated crystal seeds is 10% of the mass of the second liquid material; the mass of the crystal growth inducer is 0.03‰ of the mass of the second liquid material; the mixing temperature is 95 °C, and the mixing time is 4 h.

[0074] Example 2

[0075] The fluorine-containing waste from aluminum electrolysis is subjected to a leaching reaction to obtain a slurry containing soluble fluorinated salts;

[0076] Specifically, after the carbon slag is treated by pyrometallurgy, the electrolyte is crushed, passed through a 200-mesh sieve, and the undersize is taken. The undersize of the electrolyte after the carbon slag is flotation is mixed with aluminum chloride for a leaching reaction.

[0077] The slurry containing soluble fluorinated salts is subjected to solid-liquid separation to obtain a first liquid material;

[0078] The aluminum-fluorine ratio and pH value of the first liquid material are adjusted to obtain a second liquid material with a set aluminum-fluorine ratio and a set pH value; wherein, the set aluminum-fluorine ratio is 1:3.2 and the set pH value is 2.5;

[0079] The aluminum fluoride precursor is soaked with a seed activator to obtain an activated seed; wherein, the seed activator is zirconium fluozirconate, and the particle size of the aluminum fluoride precursor is 10 μm to 20 μm;

[0080] The second liquid material, the activated seed, and a crystal growth inducer are mixed for a crystallization reaction to obtain aluminum fluoride; wherein, the crystal growth inducer is zinc phytate, the mass of the activated seed is 3% of the mass of the second liquid material; the mass of the crystal growth inducer is 0.002‰ of the mass of the second liquid material; the mixing temperature is 90 °C and the mixing time is 3 h.

[0081] Example 3

[0082] The fluorine-containing waste from aluminum electrolysis is subjected to a leaching reaction to obtain a slurry containing soluble fluorinated salts;

[0083] Specifically, the electrolyte fished out from the aluminum electrolysis cell is crushed, passed through a 200-mesh sieve, and the undersize is taken. The undersize of the electrolyte after the carbon slag is flotation is mixed with aluminum sulfate for a leaching reaction.

[0084] The slurry containing soluble fluorinated salts is subjected to solid-liquid separation to obtain a first liquid material;

[0085] The aluminum-fluorine ratio and pH value of the first liquid material are adjusted to obtain a second liquid material with a set aluminum-fluorine ratio and a set pH value; wherein, the set aluminum-fluorine ratio is 1:3.5 and the set pH value is 6.0;

[0086] The aluminum fluoride precursor is soaked with a seed activator to obtain an activated seed; wherein, the seed activator is citric acid and aluminum chloride, and the particle size of the aluminum fluoride precursor is 10 μm to 20 μm;

[0087] Mix a second liquid material, activated seeds, and a crystal growth inducer to carry out a crystallization reaction to obtain aluminum fluoride; wherein, the crystal growth inducer is octadecanol, and the mass of the activated seeds is 20% of the mass of the second liquid material; the mass of the crystal growth inducer is 0.05‰ of the mass of the second liquid material; the mixing temperature is 110°C, and the mixing time is 5 h.

[0088] Example 4

[0089] Carry out a leaching reaction on aluminum electrolysis fluorine-containing waste to obtain a slurry containing soluble fluorinated salts;

[0090] Specifically: After the carbon slag is flotation-selected, the electrolyte is crushed, passed through a 200-mesh sieve, and the material under the sieve is taken. The material under the sieve of the carbon slag flotation-selected electrolyte is mixed with sodium hydroxide to carry out a leaching reaction.

[0091] Carry out solid-liquid separation on the slurry containing soluble fluorinated salts to obtain a first liquid material;

[0092] Adjust the aluminum-fluorine ratio and pH value of the first liquid material to obtain a second liquid material with a set aluminum-fluorine ratio and a set pH value; wherein, the set aluminum-fluorine ratio is 1:3.3, and the set pH value is 4.0;

[0093] Soak the aluminum fluoride precursor with a seed activator to obtain activated seeds; wherein, the seed activator is zirconium fluoride acid and aluminum sulfate, and the particle size of the aluminum fluoride precursor is 5 μm to 10 μm;

[0094] Mix the second liquid material, activated seeds, and a crystal growth inducer to carry out a crystallization reaction to obtain aluminum fluoride; wherein, the crystal growth inducer is octadecanol and zinc phytate, and the mass of the activated seeds is 8% of the mass of the second liquid material; the mass of the crystal growth inducer is 0.01‰ of the mass of the second liquid material; the mixing temperature is 100°C, and the mixing time is 10 h.

[0095] Example 5

[0096] Carry out a leaching reaction on aluminum electrolysis fluorine-containing waste to obtain a slurry containing soluble fluorinated salts;

[0097] Specifically: After the carbon slag is flotation-selected, the electrolyte is crushed, passed through a 200-mesh sieve, and the material under the sieve is taken. The material under the sieve of the carbon slag flotation-selected electrolyte is mixed with sodium hydroxide to carry out a leaching reaction.

[0098] Carry out solid-liquid separation on the slurry containing soluble fluorinated salts to obtain a first liquid material;

[0099] Adjust the aluminum-fluorine ratio and pH value of the first liquid material to obtain a second liquid material with a set aluminum-fluorine ratio and a set pH value; wherein, the set aluminum-fluorine ratio is 1:3.4, and the set pH value is 3.0;

[0100] Soak the aluminum fluoride precursor with a seed activator to obtain activated seeds; wherein, the seed activator is zirconium fluoroacid and titanium fluoroacid, and the particle size of the aluminum fluoride precursor is 8 μm to 20 μm;

[0101] Mix the second liquid material, the activated seeds, and the crystal growth inducer to carry out a crystallization reaction to obtain aluminum fluoride; wherein, the crystal growth inducer is lauryl alcohol, the mass of the activated seeds is 15% of the mass of the second liquid material; the mass of the crystal growth promoter is 0.008‰ of the mass of the second liquid material; the mixing temperature is 105 °C, and the mixing time is 6 h.

[0102] Comparative Example 1

[0103] In Comparative Example 1, the aluminum-fluorine ratio is set to 1:2.5, and other steps are the same as those in Example 1;

[0104] Comparative Example 2

[0105] In Comparative Example 2, the aluminum-fluorine ratio is set to 1:4.0, and other steps are the same as those in Example 1;

[0106] Comparative Example 3

[0107] In Comparative Example 3, the pH value is set to 2.0, and other steps are the same as those in Example 1.

[0108] Comparative Example 4

[0109] In Comparative Example 4, the pH value is set to 6.5, and other steps are the same as those in Example 1.

[0110] Comparative Example 5

[0111] In Comparative Example 5, the activated seeds are 2% of the mass of the second liquid material, and other steps are the same as those in Example 1.

[0112] Comparative Example 6

[0113] In Comparative Example 6, the activated seeds are 25% of the mass of the second liquid material, and other steps are the same as those in Example 1.

[0114] Comparative Example 7

[0115] In Comparative Example 7, the crystal growth promoter is 0.001‰ of the mass of the second liquid material, and other steps are the same as those in Example 1.

[0116] Comparative Example 8

[0117] In Comparative Example 8, the crystal growth promoter is 0.06‰ of the mass of the second liquid material, and other steps are the same as those in Example 1.

[0118] Comparative Example 9

[0119] In Comparative Example 9, the particle size of the aluminum fluoride precursor is 1 μm to 4 μm, and other steps are the same as those in Example 1.

[0120] Comparative Example 10

[0121] In Comparative Example 10, the particle size of the aluminum fluoride precursor is 25 μm to 30 μm, and other steps are the same as those in Example 1.

[0122] The reaction conditions, purity, particle size of the final products, and fluoride ion concentration in the crystallization filtrate in Examples 1 to 5 and Comparative Examples 1 to 10 are statistically shown in Table 1.

[0123] Table 1

[0124]

[0125]

[0126] It can be seen from the data in Table 1 that: A method for preparing aluminum fluoride from fluorine-containing waste in aluminum electrolysis provided by the embodiments of the present application can achieve a purity of aluminum fluoride greater than 95% and D10 > 62 μm. Figure 2 This is the phase diagram of the aluminum fluoride prepared by the method for preparing aluminum fluoride from fluorine-containing waste in aluminum electrolysis provided by the embodiments of the present application; please refer to Figure 2 , and it can be seen that the main phase of the prepared aluminum fluoride is AlF 3 , with high purity; Figure 3 This is the particle size distribution diagram of the aluminum fluoride prepared by the method for preparing aluminum fluoride from fluorine-containing waste in aluminum electrolysis provided by the embodiments of the present application; please refer to Figure 3 , indicating that the prepared aluminum fluoride is large-particle aluminum fluoride, and the minimum particle size is close to 75 μm.

[0127] In Comparative Example 1, the aluminum-fluorine ratio is set to 1:2.5. Since the aluminum-fluorine ratio is greater than 1:3, there is too much aluminum in the solution, resulting in too low fluorine content in the generated aluminum fluoride and low purity.

[0128] In Comparative Example 2, the aluminum-fluorine ratio is set to 1:4.0. Since the aluminum-fluorine ratio is less than 1:3.5, there is too much fluorine in the solution, resulting in too high fluorine content in the remaining liquid after crystallization, and direct discharge will cause secondary pollution.

[0129] In Comparative Example 3, the pH value is set to 2.0. Since the pH is too low, too little aluminum fluoride is generated, resulting in a product purity of only 85.25%, too fine particle size, D10 is only 35.33 μm, and too high fluorine content in the crystallization filtrate, which is 45 mg / L.

[0130] In Comparative Example 4, the pH value is set to 6.5. Since the pH is too high, other impurities precipitate simultaneously, resulting in a product purity of only 91.05% and too fine particle size, D10 is only 57.26 μm.

[0131] In Comparative Example 5, the dosage of the activated seed crystal was 2%. Since the dosage of the activated seed crystal was too low, the amount of seed crystal was insufficient, resulting in insufficient heterogeneous nucleation sites, so that too few aluminum fluoride crystals were formed, the product purity was only 92.12%, the particle size was too fine, D10 was only 37.55 μm, and the fluorine content in the filtrate after crystallization was too high, reaching 32 mg / L.

[0132] In Comparative Example 6, the dosage of the activated seed crystal was 25%. Since the dosage of the activated seed crystal was too high, the initial supersaturation decreased too fast due to the excessive amount of seed crystal, which was not conducive to the subsequent crystal growth, so that the product purity was only 93.78%, the particle size was too fine, D10 was only 41.27 μm.

[0133] In Comparative Example 7, the dosage of the seed crystal growth promoter was 0.001‰. Since the dosage of the crystal induction growth agent was too low, the adjustment of the surface activity of the seed crystal and the distribution of the solution microelectric field was insufficient, which was not conducive to the subsequent crystal growth, so that the product purity was only 89.43%, the particle size was too fine, D10 was only 35.54 μm, and the fluorine content in the filtrate after crystallization was too high, reaching 34 mg / L.

[0134] In Comparative Example 8, the dosage of the seed crystal growth promoter was 0.06‰. Since the dosage of the crystal induction growth agent was too high, the quality of the product aluminum fluoride was affected due to excessive impurity introduction, so that the product purity was only 94.24%.

[0135] In Comparative Example 9, the particle size of the aluminum fluoride precursor was 1 μm - 4 μm. Since the seed crystal particle size was too fine and did not reach the crystal nucleus size for inducing crystallization, it could not be used as a crystal nucleus to induce crystal growth, resulting in a large amount of homogeneous nucleation, so that the product purity was only 86.75%, the particle size was too fine, D10 was only 31.254 μm, and the fluorine content in the filtrate after crystallization was too high, reaching 35 mg / L.

[0136] In Comparative Example 10, the particle size of the aluminum fluoride precursor was 25 μm - 30 μm. Since the seed crystal particle size was too large and the seed crystal-induced crystallization sites were insufficient, it could not induce crystal growth well, resulting in more homogeneous nucleation, so that the product purity was only 87.26%, the particle size was too fine, D10 was only 44.561 μm, and the fluorine content in the filtrate after crystallization was too high, reaching 41 mg / L.

[0137] One or more technical solutions in the embodiments of the present application at least further have the following technical effects or advantages:

[0138] (1) During the activation process of the aluminum fluoride seed crystal, the etching of the seed crystal surface and the reset of the surface microelectric field can be realized by adding the seed crystal activator, making the seed crystal more conducive to the continuous growth and enlargement of the crystal.

[0139] (2) The reasonable design of the control of the aluminum-fluorine molar ratio and pH value can effectively control the crystal growth and effectively avoid the generation of homogeneous nucleation;

[0140] (3) The addition of a growth promoter for aluminum fluoride crystals can effectively change the distribution of the micro-electric field in the solution and the surface activity of the crystal growth surface, making it more conducive to the continuous growth and enlargement of the crystals;

[0141] (4) Realize the resource utilization of fluorine-containing waste in aluminum electrolysis to prepare large-grained aluminum fluoride. The overall process flow is simple, the operation is convenient, and there is no secondary pollution.

[0142] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing aluminum fluoride from fluorine-containing waste by aluminum electrolysis, the method comprising: The aluminum electrolysis fluoride-containing waste is subjected to leaching reaction to obtain a slurry containing soluble fluoride salts; Performing solid-liquid separation on the slurry containing the soluble fluoride salt to obtain a first liquid material; Adjusting the aluminum-fluorine ratio and the pH value of the first liquid material to obtain a second liquid material having a set aluminum-fluorine ratio and a set pH value; The second liquid material, the activated seed crystal and the crystal growth inducing agent are mixed to carry out a crystallization reaction to obtain aluminum fluoride.

2. The method according to claim 1, characterized in that The aluminum-fluorine ratio is set to 1:(3-3.5).

3. The method according to claim 1, characterized in that The set pH value is 2.5-6.

0.

4. The method according to claim 1, characterized in that The mixing temperature is 90°C to 110°C.

5. The method according to claim 1, characterized in that The crystal growth inducing agent comprises at least one of the following: zinc phytate, ammonium fluoride, lauryl alcohol, and stearyl alcohol.

6. The method according to claim 1, characterized in that The mass of the activated seed crystals is 3% to 20% of the mass of the second liquid material; and / or, The mass of the crystal growth inducing agent is 0.002‰ to 0.05‰ of the mass of the second liquid material.

7. The method according to claim 1, characterized in that The second liquid material, the activated seed crystal and the crystal growth inducing agent are mixed to perform a crystallization reaction to obtain aluminum fluoride, comprising: Using the seed crystal activator to soak the aluminum fluoride precursor to obtain an activated seed crystal; The second liquid material, the activated seed crystal and the crystal growth inducing agent are mixed to carry out a crystallization reaction to obtain aluminum fluoride.

8. The method according to claim 7, characterized in that The particle size of the aluminum fluoride precursor is 5 μm to 20 μm.

9. The method according to claim 7, characterized in that: The seed activator includes at least one of the following: fluorozirconic acid, fluorotitanic acid, citric acid, sulfuric acid, aluminum sulfate, and aluminum chloride.

10. The method according to any one of claims 1 to 9, characterized in that: The aluminum fluoride meets at least one of the following indicators: purity greater than 95%, D10>62μm.

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