Method for preparing cryolite through aluminum electrolysis fluorine-containing waste

Abstract

The invention provides a method for preparing cryolite from aluminum electrolysis fluorine-containing waste, and relates to the technical field of harmless treatment and resource utilization of aluminum electrolysis dangerous waste residues. The method comprises the following steps: S1, carrying out wet ball milling on the fluorine-containing waste, and then adding into a reaction system to form slurry of which the upper layer is a floating object and the lower layer is a solution; taking the solution, pressurizing and carrying out alkaline leaching to obtain a fluorine-aluminum precursor, carrying out size mixing on the fluorine-aluminum precursor, and adding a reaction accelerator to obtain fluorine-aluminum precursor slurry; s2, the fluorine-aluminum precursor slurry enters from the upper end of an absorption tower and flows from top to bottom, hydrogen fluoride gas enters from the lower end of the absorption tower and flows from bottom to top, and the fluorine-aluminum precursor slurry and hydrogen fluoride gas flow reversely for mass transfer reaction to obtain regenerated cryolite slurry; and S3, carrying out heat preservation crystallization and calcination on the regenerated cryolite slurry to obtain the regenerated cryolite. According to the method, the fluorine-aluminum precursor can be converted into the high-purity cryolite, the high-valued process of the overhaul slag and the carbon slag in the harmless treatment and comprehensive utilization process is achieved, and remarkable economic benefits are generated.

Description

Technical Field

[0001] The present invention relates to the technical field of harmless disposal and resource utilization of hazardous waste residues from aluminum electrolysis, and in particular to a method for preparing cryolite from fluorine-containing waste materials from aluminum electrolysis. Background Art

[0002] In November 2020, the National Hazardous Waste List (2021 Edition) was officially released by the Ministry of Ecology and Environment Order No. 15. Hazardous waste slags involved in the electrolytic aluminum industry include overhaul slag (321-023-48) and carbon slag (321-025-48). Their main hazardous characteristics include toxicity (T) and reactivity (R), as shown in the table below:

[0003]

[0004] Among them, overhaul slag is the waste slag produced by the maintenance and replacement of the cathode lining of the electrolytic cell in the electrolytic aluminum production process; carbon slag is the uneven combustion and selective oxidation of the carbon anode that causes the carbon particles to fall off. The main components of aluminum electrolysis carbon slag are carbon and electrolyte, generally containing 20-30% carbon and 60-70% electrolyte. The main components of the electrolyte are Na3AlF6, Al2O3, CaF2, etc. Domestic university scholars have done a lot of research on the disposal and comprehensive utilization of resources of hazardous waste slag from aluminum electrolysis. At present, there are technologies at home and abroad. The harmless disposal and comprehensive utilization of resources of hazardous waste slag from aluminum electrolysis can be divided into two categories: wet treatment and pyrolysis. The wet treatment process mainly includes water leaching, alkali leaching, acid leaching, acid-base combined leaching, or using the waste cathode as a carbonaceous material with a usable calorific value resource, or high-temperature recovery of electrolytes. However, such treatment will cause the loss of valuable F and Al valuable elements in the overhaul slag and carbon slag, resulting in waste of resources and failure to achieve high-value utilization.

[0005] CN115448345A discloses a method for harmlessly producing cryolite from overhaul slag, comprising the following steps: (1) grinding the overhaul slag, mixing it with water, heating it for dissolution, filtering and washing it to obtain filter residue A and filtrate A; (2) adding an aluminum salt solution to the filter residue A, heating it for dissolution, filtering and washing it to obtain filter residue B and filtrate B; (3) heating the filtrate A and the filtrate B for reaction, filtering and washing it to obtain synthetic cryolite slag C and filtrate C; (4) adding a fluorine-fixing agent to the filter residue B, mixing it for reaction, filtering and washing it to obtain harmless overhaul slag D and filtrate D; at the same time, before dissolution or reaction in one or more steps of steps (1) to (4), a cyanide removal agent is added.

[0006] CN115676866A discloses a method for producing cryolite regenerated from electrolytic aluminum overhaul slag resources, the method comprising: (1) crushing and ball-milling the electrolytic aluminum overhaul slag to obtain powder; (2) mixing the powder obtained in step (1) with alkali solution to obtain slurry; (3) subjecting the slurry obtained in step (2) to pressurized alkali leaching, and cooling and reducing the pressure after the pressurized alkali leaching is completed; (4) mixing the slurry obtained in step (3) with a cyanide removal agent for cyanide removal treatment, and obtaining leached slag and leaching liquid by liquid-solid separation; (5) mixing the leaching liquid obtained in step (4) with an acidic aluminum salt solution, and performing liquid-solid separation after the reaction to obtain solid-phase regenerated cryolite and filtrate.

[0007] CN113072089A discloses a method for recovering cryolite by combined treatment of aluminum electrolysis overhaul slag and aluminum ash, and relates to aluminum electrolysis solid waste treatment technology. The method comprises the following steps: (1) water leaching and acid leaching of overhaul slag; (2) water leaching of aluminum ash; (3) alkali leaching of aluminum ash water leaching slag: reacting the saline-alkali mixed solution obtained in step (1) with the water leaching slag to obtain a mixed solution of sodium aluminate and salt; (4) detecting the aluminum content and salt content of the mixed solution in step (3), compounding the mixed solution of sodium aluminate and salt to obtain a mixed compound solution for standby use; (5) mixing the mixed compound solution obtained in step (4) with the hydrofluoric acid obtained in step (1) to carry out a cryolite synthesis reaction.

[0008] Although the above method can extract the valuable fluorine and aluminum elements in the aluminum electrolysis overhaul slag and convert them into cryolite, it has technical problems such as high production cost and difficulty in controlling the quality of the product cryolite.

[0009] In addition, for the treatment of hazardous waste residues from aluminum electrolysis and comprehensive resource utilization, CN113426807A discloses a method for the combined treatment of hazardous waste residues from aluminum electrolysis and comprehensive resource utilization, which achieves harmless treatment of carbon residues and produces fluorinated aluminum precursors. The phase components of the produced fluorinated aluminum precursors are mainly AlF3+Al2O3, Na3AlF6, Na2SO4, etc. The phase components of the AlF3+Al2O3 product are mainly AlF 1.5 (OH) 1.5 (H2O) 0.375 , Al(OH)3, Na3AlF6, Na5Al3F 14 After calcination and drying, AlF3+Al2O3 products are produced, but AlF3+Al2O3 products have technical problems such as high content of sulfate, sodium ions, and iron elements, and fine particle size, which cannot meet the requirements of aluminum electrolysis production process. Therefore, it is necessary to study the key technology of preparing aluminum fluoride from fluorine aluminum precursors and explore new technologies for preparing cryolite from fluorine aluminum precursors to improve the purity of cryolite, reduce the impurity content, and meet the requirements of aluminum electrolysis production process. Summary of the invention

[0010] The purpose of the present invention is to provide a method for preparing cryolite from fluorine-containing waste materials from aluminum electrolysis, which can convert fluorine-aluminum precursors into high-purity cryolite, realize the high-value process of overhaul slag and carbon slag in the process of harmless disposal and comprehensive utilization, and produce significant economic benefits.

[0011] The present invention is achieved through the following technical solutions:

[0012] The present invention provides a method for preparing cryolite from fluorine-containing waste by aluminum electrolysis, comprising the following steps:

[0013] S1, wet ball-milling the fluorine-containing waste material and adding it to the reaction system to form a slurry with a floating material on the upper layer and a solution on the lower layer, wherein the reaction system includes kerosene and aluminum sulfate solution;

[0014] Taking the solution and leaching it under pressure to obtain a fluorine aluminum precursor, and adding a reaction accelerator after slurrying the fluorine aluminum precursor to obtain a fluorine aluminum precursor slurry;

[0015] S2, the fluorine aluminum precursor slurry enters from the upper end of the absorption tower and flows from top to bottom, and the hydrogen fluoride gas enters from the lower end of the absorption tower and flows from bottom to top, and the two react in countercurrent to obtain the regenerated cryolite slurry;

[0016] S3, heat-insulating and crystallizing the regenerated cryolite slurry, and calcining to obtain the regenerated cryolite.

[0017] The technical solution of the present invention has at least the following advantages and beneficial effects:

[0018] In the present invention, the fluoroaluminum precursor slurry and hydrogen fluoride gas are subjected to countercurrent mass transfer in a reaction tower. The hydrogen fluoride gas has a strong diffusion capacity and can fully contact and react with the fluoroaluminum precursor slurry to prepare cryolite, eliminating the process of preparing hydrofluoric acid, reducing production costs, and shortening the production process. Hydrogen fluoride gas has a higher purity than hydrofluoric acid. Directly reacting with hydrogen fluoride gas can improve the purity of cryolite products and effectively avoid the introduction of impurities. During the reaction, sulfate ions and iron elements in the fluoroaluminum precursor combine under acidic conditions to form ferric sulfate. Ferric sulfate is easily soluble in water and is removed by washing with water. Aluminum hydroxide and aluminum oxide react with hydrogen fluoride to form aluminum fluoride, respectively. Sodium ions and aluminum fluoride combine to form cryolite.

[0019] Then, the particle size of cryolite is controlled by heat preservation crystallization to meet the requirements of aluminum electrolysis production process for cryolite particle size. Then, the water in the regenerated cryolite is removed by calcination to prevent it from affecting the production process after being added to the aluminum electrolysis cell. The four-stage calcination can effectively remove the crystal water in the cryolite and obtain high-purity regenerated cryolite.

[0020] Ball milling of fluorine-containing waste can increase the specific surface area of ​​fluorine-containing waste, increase the diffusion and leaching path of fluorine element, and significantly improve the leaching rate of fluorine element in fluorine-containing waste, thereby reducing the fluoride content in the leached residue, achieving the purpose of harmlessness, and ensuring that as much fluorine element as possible enters the leaching solution, so that fluorine-containing waste can be more fully utilized as a resource. At the same time, it can break the tight embedding state between carbon powder and fluoride in fluorine-containing waste residue, and promote the full dissociation between carbon powder and fluoride.

[0021] Fluorine-containing waste contains a large amount of inorganic mineral fine mud. During the flotation process, these fine particles will cover the surface of carbon powder, thereby further reducing the hydrophobicity of the carbon powder surface. Therefore, adding kerosene and aluminum sulfate solution to the slurry together can, on the one hand, utilize aluminum sulfate to react with fine particles on the surface of carbon powder to release carbon powder, thereby improving the capture effect of kerosene on carbon powder and improving the recovery rate of carbon powder. On the other hand, utilizing aluminum sulfate to react with fluoride can prevent fluoride from being attached to kerosene and entering the flotation product with bubbles.

[0022] The mixed solution of the lower layer is taken for pressurized alkaline leaching to increase the leaching rate of fluorine in the fluorine-containing waste and reduce the fluoride content in the leached residue. The role of slurry adjustment of the fluoroaluminum precursor is to facilitate the leaching of aluminum fluoride, aluminum oxide and sodium fluoride in water to ensure contact and reaction with hydrogen fluoride gas in the subsequent mass transfer process. The addition of the reaction accelerator makes it easier to generate hydroxyaluminum fluoride that is closer to the AlF3 structure, and can form a hydrophobic protective layer on the surface of hydroxyaluminum fluoride to reduce the content of crystal water. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0024] Since the main components of fluorine-containing waste materials include carbon slag and electrolytes, the carbon slag in the fluorine-containing waste materials needs to be removed before preparing regenerated cryolite using fluorine-containing waste materials. The prior art uses aluminum salt to leach fluorine elements and filter out the carbon slag. However, since fluorides adhere to the surface of the carbon slag, part of the fluorides will still remain on the surface of the carbon slag during the process of removing the carbon slag, causing fluorine element loss, affecting the resource utilization rate of the fluorine element, and affecting the output of regenerated cryolite. Alternatively, a collector is used to float the carbon slag. However, since inorganic minerals exist on the surface of some carbon slag, the carbon slag cannot be fully floated, and carbon slag still exists in the product after flotation, affecting the purity of the regenerated cryolite. Therefore, the inventor proposes the following technical solutions:

[0025] A method for preparing cryolite from fluorine-containing waste materials by aluminum electrolysis, comprising the following steps:

[0026] S1, wet ball-milling the fluorine-containing waste material and adding it to the reaction system to form a slurry with a floating material on the upper layer and a solution on the lower layer, wherein the reaction system includes kerosene and aluminum sulfate solution;

[0027] Taking the solution and leaching it under pressure to obtain a fluorine aluminum precursor, and adding a reaction accelerator after slurrying the fluorine aluminum precursor to obtain a fluorine aluminum precursor slurry;

[0028] S2, the fluorine aluminum precursor slurry enters from the upper end of the absorption tower and flows from top to bottom, and the hydrogen fluoride gas enters from the lower end of the absorption tower and flows from bottom to top, and the two react in countercurrent to obtain the regenerated cryolite slurry;

[0029] S3, heat-insulating and crystallizing the regenerated cryolite slurry, and calcining to obtain the regenerated cryolite.

[0030] Ball milling of fluorine-containing waste can increase the specific surface area of ​​fluorine-containing waste, increase the diffusion and leaching path of fluorine element, and significantly improve the leaching rate of fluorine element in fluorine-containing waste, thereby reducing the fluoride content in the leached residue, achieving the purpose of harmlessness, and ensuring that as many fluorine elements as possible enter the leachate, so that fluorine-containing waste can be more fully utilized as a resource. At the same time, the tightly embedded state between carbon powder and fluoride in fluorine-containing waste residue can be broken, and the full dissociation between carbon powder and fluoride can be promoted. Preferably, a sodium hydroxide solution with a volume concentration of 60-80g / L is used, and the solid-liquid mass ratio is controlled at 1:0.8-1. Ball milling by sodium hydroxide solution can not only allow carbon powder and fluoride to be fully dissociated, but also allow fluoride to react with sodium hydroxide to achieve the initial leaching of fluorine element.

[0031] Fluorine-containing waste contains a large amount of inorganic mineral fine mud. During the flotation process, these fine particles will cover the surface of the carbon powder, thereby further reducing the hydrophobicity of the carbon powder surface. Therefore, by adding kerosene and aluminum sulfate solution to the slurry together, on the one hand, aluminum sulfate can be used to react with fine particles on the surface of the carbon powder to release the carbon powder, thereby improving the capture effect of kerosene on the carbon powder and improving the recovery rate of the carbon powder. On the other hand, by using aluminum sulfate to react with fluoride, fluoride can be prevented from being attached to kerosene and entering the flotation product with bubbles, thereby achieving secondary leaching of fluorine element, reducing the fluoride content in the leached residue, and allowing fluorine-containing waste to be more fully utilized as a resource.

[0032] The mixed solution of the lower layer is taken for pressurized alkaline leaching to further improve the leaching rate of fluorine in the fluorine-containing waste and reduce the fluoride content in the leached residue. The role of slurry adjustment of fluoroaluminum precursor is to facilitate the leaching of aluminum fluoride, aluminum oxide and sodium fluoride in water to ensure contact and reaction with hydrogen fluoride gas in the subsequent mass transfer process. The addition of reaction accelerator makes it easier to generate hydroxyaluminum fluoride that is closer to the AlF3 structure, and can form a hydrophobic protective layer on the surface of hydroxyaluminum fluoride to reduce the content of crystal water.

[0033] The fluoroaluminum precursor slurry and hydrogen fluoride gas are subjected to countercurrent mass transfer in a reaction tower. Hydrogen fluoride gas has a strong diffusion capacity and can fully contact and react with the fluoroaluminum precursor slurry to prepare cryolite, eliminating the process of preparing hydrofluoric acid, which can reduce production costs and shorten the production process. Hydrogen fluoride gas has a higher purity than hydrofluoric acid. Direct reaction with hydrogen fluoride gas can improve the purity of cryolite products and effectively avoid the introduction of impurities. During the reaction, sulfate ions and iron elements in the fluoroaluminum precursor combine under acidic conditions to form ferric sulfate. Ferric sulfate is easily soluble in water and is removed by washing with water. Aluminum hydroxide and aluminum oxide react with hydrogen fluoride to form aluminum fluoride, respectively. Sodium ions and aluminum fluoride combine to form cryolite.

[0034] Then, the particle size of cryolite is controlled by heat preservation crystallization to meet the requirements of aluminum electrolysis production process for cryolite particle size. Then, the water in the regenerated cryolite is removed by calcination to prevent it from affecting the production process after being added to the aluminum electrolysis cell. The four-stage calcination can effectively remove the crystal water in the cryolite and obtain high-purity regenerated cryolite.

[0035] In this embodiment, the reaction accelerator includes one or more of sodium fluoride, ammonium fluoride and ammonium bifluoride. Sodium fluoride is preferred, which can not only generate hydroxyaluminum fluoride, but also provide sodium ions, so that the fluorine element in the fluorine-containing waste material can be fully converted into cryolite, thereby improving the utilization rate of the fluorine element.

[0036] In this embodiment, when the fluoroaluminum precursor is slurried, the temperature is 90° C., the time is 60-90 min, and the stirring speed is maintained at 1000-2000 r / min.

[0037] In this embodiment, the liquid-to-solid ratio of the fluorine aluminum precursor slurry is 3-4:1 mL / g, and the fluorine ion concentration is 150-180 g / L. Under this condition, the fluorine element can react better with the hydrogen fluoride gas.

[0038] In this embodiment, the mass transfer reaction temperature is 90°C, the time is 60-120min, and the pH value of the mass transfer reaction system is 1-1.5. During the mass transfer reaction, the amount of hydrogen fluoride gas introduced is 1.5-2 times the theoretical value of combining with aluminum ions and fluoride ions in the fluoroaluminum precursor to form aluminum fluoride. The hydrogen fluoride gas can be a gas produced during the preparation of fluorine-containing materials discarded from aluminum electrolysis. By controlling the pH value of the mass transfer reaction, the sulfate ions and iron elements in the fluoroaluminum precursor slurry can be fully combined under acidic conditions to form ferric sulfate. Ferric sulfate is easily soluble in water and is removed by washing to improve the purity of the regenerated cryolite.

[0039] In this embodiment, the heat preservation crystallization process is as follows: water is added to the regenerated cryolite slurry for slurry preparation, the stirring speed is 1000-2000r / min, the liquid-solid ratio of the slurry is controlled to be 3:1mL / g, the heat preservation temperature is 80-90°C, and the heat preservation time is 60-120min. Under the heat preservation crystallization conditions, the particle size of the regenerated cryolite can be better adjusted for subsequent use.

[0040] In this embodiment, the calcination process is as follows: the product after heat preservation and crystallization is placed in a rotary furnace for four-stage drying and calcination, the first stage is 150-250° C., the second stage is 250-300° C., the third stage is 300-350° C., and the fourth stage is 500-600° C. Through multi-stage calcination, and the temperature is gradually increased, it is possible to avoid excessive temperature changes that damage the structure of the regenerated cryolite, while ensuring that the moisture content in the regenerated cryolite is minimized.

[0041] Example 1

[0042] A method for preparing cryolite from fluorine-containing waste materials by aluminum electrolysis, comprising the following steps:

[0043] S1. Preparation of fluorine-containing waste into fluorine-aluminum precursor slurry:

[0044] S11, adding the fluorine-containing waste material to a sodium hydroxide solution with a volume concentration of 60 g / L for wet ball milling, wherein the solid-liquid mass ratio is controlled at 1:0.8, and adding the wet ball milled waste material to the reaction system to form a slurry with a floating material on the upper layer and a solution on the lower layer, wherein the reaction system includes kerosene and an aluminum sulfate solution;

[0045] S12, taking the solution and leaching it under pressure to obtain a fluorine aluminum precursor;

[0046] S13. Send the fluoroaluminum precursor into a slurry mixing tank, add water for slurry mixing, control the liquid-solid ratio to 3:1 mL / g, the fluoride ion concentration to 150 g / L, the slurry mixing temperature to 90°C, the time to 60 min, and maintain a stirring speed of 1000 r / min; then add a reaction accelerator (sodium fluoride) to obtain a fluoroaluminum precursor slurry.

[0047] S2. Fluoroaluminum precursor slurry enters from the upper end of the absorption tower and flows from top to bottom. Hydrogen fluoride gas enters from the lower end of the absorption tower and flows from bottom to top. The two are countercurrently reacted to obtain regenerated cryolite slurry. The mass transfer reaction temperature is 90°C, the time is 60 minutes, and the pH value of the mass transfer reaction system is 1.

[0048] S3, preparing regenerated cryolite:

[0049] S31, returning the regenerated cryolite slurry to the slurry mixing tank for slurry mixing, with a stirring speed of 1000r / min, controlling the slurry liquid-solid ratio to 3:1mL / g, the insulation temperature to 80°C, and the insulation time to 60min;

[0050] S32, placing the product after heat preservation and crystallization in a rotary kiln for drying and calcining, using a rotary kiln to dry and calcine the product in four stages, the first stage at 150°C, the second stage at 250°C, the third stage at 300°C, and the fourth stage at 500°C, to obtain regenerated cryolite.

[0051] Example 2

[0052] A method for preparing cryolite from fluorine-containing waste materials by aluminum electrolysis, comprising the following steps:

[0053] S1. Preparation of fluorine-containing waste into fluorine-aluminum precursor slurry:

[0054] S11, adding the fluorine-containing waste material to a sodium hydroxide solution with a volume concentration of 70 g / L for wet ball milling, wherein the solid-liquid mass ratio is controlled at 1:0.9, and adding the wet ball milled waste material to the reaction system to form a slurry with a floating material on the upper layer and a solution on the lower layer, wherein the reaction system includes kerosene and aluminum sulfate solution;

[0055] S12, taking the solution and leaching it under pressure to obtain a fluorine aluminum precursor;

[0056] S13. Send the fluoroaluminum precursor into a slurry mixing tank, add water for slurry mixing, control the liquid-solid ratio to 3.5:1 mL / g, the fluoride ion concentration to 160 g / L, the slurry mixing temperature to 90°C, the time to 80 min, and maintain a stirring speed of 1500 r / min; then add a reaction accelerator (ammonium fluoride) to obtain a fluoroaluminum precursor slurry.

[0057] S2. Fluoroaluminum precursor slurry enters from the upper end of the absorption tower and flows from top to bottom. Hydrogen fluoride gas enters from the lower end of the absorption tower and flows from bottom to top. The two react in countercurrent to obtain regenerated cryolite slurry. The mass transfer reaction temperature is 90°C, the time is 100 minutes, and the pH value of the mass transfer reaction system is 1.2.

[0058] S3, preparing regenerated cryolite:

[0059] S31, returning the regenerated cryolite slurry to the slurry mixing tank for slurry mixing, with a stirring speed of 1500r / min, controlling the slurry liquid-solid ratio to 3:1mL / g, the insulation temperature to 85°C, and the insulation time to 100min;

[0060] S32, placing the product after heat preservation and crystallization in a rotary kiln for drying and calcining, using a rotary kiln to dry and calcine the product in four stages, the first stage at 200°C, the second stage at 280°C, the third stage at 320°C, and the fourth stage at 550°C, to obtain regenerated cryolite.

[0061] Example 3

[0062] A method for preparing cryolite from fluorine-containing waste materials by aluminum electrolysis, comprising the following steps:

[0063] S1. Preparation of fluorine-containing waste into fluorine-aluminum precursor slurry:

[0064] S11, adding the fluorine-containing waste material to a sodium hydroxide solution with a volume concentration of 80 g / L for wet ball milling, controlling the solid-liquid mass ratio at 1:1, and adding the wet ball milled material to the reaction system to form a slurry with a floating material on the upper layer and a solution on the lower layer, wherein the reaction system includes kerosene and aluminum sulfate solution;

[0065] S12, taking the solution and leaching it under pressure to obtain a fluorine aluminum precursor;

[0066] S13. Send the fluoroaluminum precursor into a slurry mixing tank, add water for slurry mixing, control the liquid-solid ratio to 4:1 mL / g, the fluoride ion concentration to 180 g / L, the slurry mixing temperature to 90°C, the time to 90 min, and maintain a stirring speed of 2000 r / min; then add a reaction accelerator (ammonium bifluoride) to obtain a fluoroaluminum precursor slurry.

[0067] S2. Fluoroaluminum precursor slurry enters from the upper end of the absorption tower and flows from top to bottom. Hydrogen fluoride gas enters from the lower end of the absorption tower and flows from bottom to top. The two are countercurrently reacted to obtain regenerated cryolite slurry. The mass transfer reaction temperature is 90°C, the time is 120 minutes, and the pH value of the mass transfer reaction system is 1.5.

[0068] S3, preparing regenerated cryolite:

[0069] S31, returning the regenerated cryolite slurry to the slurry mixing tank for slurry mixing, with a stirring speed of 2000r / min, controlling the slurry liquid-solid ratio to 3:1mL / g, the insulation temperature to 90°C, and the insulation time to 120min;

[0070] S32, placing the product after heat preservation and crystallization in a rotary kiln for drying and calcining, using a rotary kiln to dry and calcine the product in four stages, the first stage at 250°C, the second stage at 300°C, the third stage at 350°C, and the fourth stage at 600°C, to obtain regenerated cryolite.

[0071] Comparative Example 1

[0072] In this comparative example, the fluorine-containing waste material was not ball-milled.

[0073] Comparative Example 2

[0074] In this comparative example, kerosene is first added for flotation, and then aluminum sulfate solution is added for leaching after flotation separation.

[0075] Comparative Example 3

[0076] In this comparative example, aluminum sulfate solution was first added for leaching, and then kerosene was added for flotation.

[0077] Comparative Example 4

[0078] No reaction accelerator was added in this comparative example.

[0079] Comparative Example 5

[0080] In this comparative example, the fluoroaluminum precursor slurry is directly mixed with hydrofluoric acid to prepare the regenerated cryolite.

[0081] Comparative Example 6

[0082] In this comparative example, the pH value of the mass transfer reaction system is 4.

[0083] Test Case

[0084] The contents of various elements in the regenerated cryolite obtained in the above examples and comparative examples were tested, and the results were as follows:

[0085] Table 1

[0086] index fluorine / % aluminum / % sodium / % Silicon dioxide / % Iron oxide / % Calcium oxide / % Example 1 52 13 33 0.21 0.03 0.08 Example 2 51 13 32 0.20 0.03 0.08 Example 3 52 12 31 0.22 0.04 0.07 Comparative Example 1 41 10 27 0.25 0.06 0.11 Comparative Example 2 39 9 28 0.24 0.07 0.12 Comparative Example 3 40 9 27 0.26 0.06 0.10 Comparative Example 4 36 7 25 0.28 0.08 0.15 Comparative Example 5 45 11 30 0.22 0.03 0.09 Comparative Example 6 51 13 32 0.20 0.11 0.08

[0087] It can be seen from Table 1 that the regenerated cryolite prepared in the example has higher purity.

[0088] In summary, the method for preparing cryolite from fluorine-containing waste materials from aluminum electrolysis provided by the present invention can prepare high-purity regenerated cryolite.

[0089] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing cryolite from fluorine-containing waste materials by aluminum electrolysis, characterized in that: The following steps are involved: S1, wet ball-milling the fluorine-containing waste material and adding it to the reaction system to form a slurry with a floating material on the upper layer and a solution on the lower layer, wherein the reaction system includes kerosene and aluminum sulfate solution; Taking the solution and leaching it under pressure to obtain a fluorine aluminum precursor, and adding a reaction accelerator after slurrying the fluorine aluminum precursor to obtain a fluorine aluminum precursor slurry; S2, the fluorine aluminum precursor slurry enters from the upper end of the absorption tower and flows from top to bottom, and the hydrogen fluoride gas enters from the lower end of the absorption tower and flows from bottom to top, and the two react in countercurrent to obtain the regenerated cryolite slurry; S3, heat-insulating and crystallizing the regenerated cryolite slurry, and calcining to obtain the regenerated cryolite.

2. The method for preparing cryolite from fluorine-containing waste from aluminum electrolysis according to claim 1, characterized in that: The reaction accelerator includes one or more of sodium fluoride, ammonium fluoride and ammonium bifluoride.

3. The method for preparing cryolite from fluorine-containing waste from aluminum electrolysis according to claim 1, characterized in that: When the fluoroaluminum precursor is slurried, the temperature is 90°C, the time is 60-90 minutes, and the stirring speed is maintained at 1000-2000 r / min.

4. The method for preparing cryolite from fluorine-containing waste from aluminum electrolysis according to claim 3, characterized in that: The liquid-to-solid ratio of the fluorine-aluminum precursor slurry is 3-4:1 mL / g, and the fluoride ion concentration is 150-180 g / L.

5. The method for preparing cryolite from fluorine-containing waste from aluminum electrolysis according to claim 1, characterized in that: The mass transfer reaction temperature is 90°C, the time is 60-120 minutes, and the pH value of the mass transfer reaction system is 1-1.

5.

6. The method for preparing cryolite from fluorine-containing waste from aluminum electrolysis according to any one of claims 1 to 5, characterized in that: The heat preservation crystallization process is as follows: add water to the regenerated cryolite slurry for slurry preparation, the stirring speed is 1000-2000r / min, the liquid-solid ratio of the slurry is controlled to be 3:1mL / g, the heat preservation temperature is 80-90℃, and the heat preservation time is 60-120min.

7. The method for preparing cryolite from fluorine-containing waste from aluminum electrolysis according to claim 6, characterized in that: The calcination process is as follows: placing the product after heat preservation and crystallization into a rotary furnace for four-stage drying and calcination, the first stage is 150-250°C, the second stage is 250-300°C, the third stage is 300-350°C, and the fourth stage is 500-600°C.

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