Method for recycling aluminum electrolysis waste alkaline fluorine extraction dissolution liquid

Abstract

The invention relates to a method for recycling aluminum electrolysis waste alkaline fluorine extraction dissolution liquid, and belongs to the technical field of recycling of fluorine-containing dissolution liquid in the fluorine extraction process of aluminum electrolysis waste. The method comprises the following steps: adding an aluminum electrolysis waste alkaline fluorine extraction dissolution solution into an acidic aluminum salt solution until the acidic aluminum salt solution has a first preset pH value and no precipitate is generated, so as to obtain a first solution; adding alkali into the first solution until the first solution has a second preset pH value and precipitates are generated, so as to obtain a second solution; performing solid-liquid separation on the second solution to obtain a first precipitate and a third solution; adding a fluorinating agent into the first precipitate to obtain a mixed material; and calcining the mixed material to obtain the aluminum fluoride. Adding alkali into the third solution until the third solution has a third preset pH value to obtain a fourth solution; and carrying out solid-liquid separation on the fourth solution to obtain cryolite. In the aluminum fluoride obtained by the embodiment of the invention, the fluorine content is more than 61%, the aluminum content is more than 31.5%, and the utilization rate of fluorine in the alkaline fluorine extraction dissolution liquid is more than 99.9%.

Description

Technical Field

[0001] The present application relates to the technical field of recovery of fluorine-containing dissolution solution in the process of fluorine extraction from aluminum electrolysis waste, and in particular to a method for recovery and utilization of alkaline fluorine extraction dissolution solution from aluminum electrolysis waste. Background Art

[0002] Aluminum electrolysis waste is waste generated during the production process of aluminum electrolysis, mainly including overhaul slag, waste electrolyte, etc., among which the overhaul slag includes waste cathode, waste refractory, waste castable, waste anti-seepage material and mixed material, etc. According to calculations, for an electrolytic cell with a cell life of 6 to 8 years, about 15 to 20 kg of overhaul slag is produced for every ton of aluminum produced. During the long-term operation of the electrolytic cell, a large amount of fluoride salt will infiltrate the overhaul slag, and fluoride salt needs to be added every day for the stable operation of the electrolytic cell. Therefore, extracting fluoride salt from aluminum electrolysis waste to prepare aluminum fluoride products for recycling in the electrolytic cell has a good market prospect.

[0003] At present, the utilization of fluoride in aluminum electrolysis waste is mostly done by acid leaching or alkali leaching, and the leaching solution is repeatedly adjusted. The precipitation reaction process generally requires heating and a long reaction time. A large amount of byproduct salt is produced during the reaction, and the recovered product is mostly sodium hexafluoroaluminate, with less aluminum fluoride or more sodium hexafluoroaluminate doped with aluminum fluoride, and the purity is low. Fluoride salts in aluminum electrolysis waste are the main toxic substances and are also valuable resources with high content. The recovery of fluoride salts is the focus of aluminum electrolysis waste, but the existing recovery of fluoride salts generally has problems such as low product purity, low recovery rate, and long overall process. Summary of the invention

[0004] The present application provides a method for recycling alkaline fluorine extraction solution from aluminum electrolysis waste to solve the following technical problem: how to improve the purity of aluminum fluoride prepared from alkaline fluorine extraction solution from aluminum electrolysis waste.

[0005] In a first aspect, an embodiment of the present application provides a method for recycling an alkaline fluorine extraction solution of aluminum electrolysis waste, the method comprising:

[0006] Adding an alkaline fluorine extraction solution of aluminum electrolysis waste to an acidic aluminum salt solution until the acidic aluminum salt solution has a first preset pH value and no precipitation is generated, thereby obtaining a first solution;

[0007] adding a base to the first solution until the first solution has a second preset pH value and a precipitate is generated, thereby obtaining a second solution;

[0008] performing solid-liquid separation on the second solution to obtain a first precipitate and a third solution;

[0009] adding a fluorinating agent to the first precipitate to obtain a mixed material;

[0010] The mixed material is calcined to obtain aluminum fluoride.

[0011] Optionally, the first preset pH value is 3.5-4.2.

[0012] Optionally, the acidic aluminum salt includes at least one of the following: aluminum sulfate, aluminum nitrate, and aluminum chloride.

[0013] Optionally, the pH value of the acidic aluminum salt solution is 1.8 to 3.0.

[0014] Optionally, the second preset pH value is 4.5-5.5.

[0015] Optionally, the fluorinating agent comprises at least one of the following: hydrofluoric acid, ammonium bifluoride; and / or,

[0016] The amount of the fluorinating agent added is 1.1 to 1.5 times the theoretical amount of the fluorinating agent added, and the theoretical amount of the fluorinating agent added is the mass of the fluorinating agent required for the first precipitate and the fluorinating agent to completely react to generate aluminum fluoride during the calcination process.

[0017] Optionally, the calcination includes a first calcination and a second calcination in sequence, wherein:

[0018] The temperature of the first calcination is 200°C to 300°C, and the temperature of the second calcination is 450°C to 600°C.

[0019] Optionally, the second solution is subjected to solid-liquid separation to obtain a first precipitate and a third solution, and then the process further comprises:

[0020] adding the base to the third solution until the third solution has a third preset pH value to obtain a fourth solution;

[0021] The fourth solution is subjected to solid-liquid separation to obtain a second precipitate and a fifth solution.

[0022] Optionally, the alkali includes at least one of the following: aqueous ammonia and sodium hydroxide.

[0023] Optionally, the third preset pH value is >6.

[0024] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0025] The method for recycling the alkaline fluorine extraction solution of aluminum electrolysis waste provided in the embodiment of the present application comprises:

[0026] Adding an alkaline fluorine extraction solution of aluminum electrolysis waste to an acidic aluminum salt solution until the acidic aluminum salt solution has a first preset pH value and no precipitation is generated, thereby obtaining a first solution; adding an alkali to the first solution until the first solution has a second preset pH value and a precipitation is generated, thereby obtaining a second solution; performing solid-liquid separation on the second solution to obtain a first precipitation and a third solution; adding a fluoridating agent to the first precipitation to obtain a mixed material; and calcining the mixed material to obtain aluminum fluoride. Adding an alkaline fluorine extraction solution of aluminum electrolysis waste to an acidic aluminum salt solution until the acidic aluminum salt solution has a first preset pH value and no precipitation is generated can ensure that there is sufficient aluminum in the acidic aluminum salt solution and that the solution remains acidic, and avoid the formation of sodium hexafluoroaluminate; adding an alkali to the first solution until the first solution has a second preset pH value and a precipitation is generated, thereby ensuring that the precipitate is all hydroxyaluminum fluoride (Al[F 0.5 (OH) 0.5 ]3·0.5H2O); adding a fluorinating agent to the precipitate to supplement the fluorine content, and then calcining to obtain high-purity aluminum fluoride, in which the fluorine content is greater than 61%, the aluminum content is greater than 31.5%, and other indicators are better than the AF-0 standard of GB / T 4292-2017. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0028] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0029] Figure 1 A schematic flow chart of a method for recycling alkaline fluorine extraction solution from aluminum electrolysis waste provided in an embodiment of the present application. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0031] Various embodiments of the present application may be presented 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 understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have 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., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0032] In the present application, in the absence of any contrary description, the directional words used, such as "upper" and "lower", are specifically the directions of the drawings in the accompanying drawings. In addition, in the description of the present specification, the terms "including", "comprising", etc. refer to "including but not limited to". In this article, 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 that there is any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of the associated objects, indicating that there may be three relationships, for example, A and / or B, which can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A, B can be singular or plural. In this article, "at least one" refers to one or more, and "plural" refers to 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 singular or plural items. For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e. a and b), ac, bc or abc, where a, b, c can be single or plural, respectively.

[0033] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0034] In a first aspect, the present application provides a method for recycling alkaline fluorine extraction solution from aluminum electrolysis waste. Figure 1 A schematic diagram of a method for recycling an alkaline fluorine extraction solution from aluminum electrolysis waste provided in an embodiment of the present application; see Figure 1 , the method comprising:

[0035] S1. Adding an alkaline fluorine extraction solution of aluminum electrolysis waste to an acidic aluminum salt solution until the acidic aluminum salt solution has a first preset pH value and no precipitation is generated, thereby obtaining a first solution;

[0036] The alkaline fluorine extraction solution of aluminum electrolysis waste is added to the acidic aluminum salt solution, and the addition is continued until the pH value of the acidic aluminum salt solution reaches a preset first pH value, and it is ensured that no precipitation is generated during the process. The purpose of this step is to ensure that the acidic aluminum salt solution contains sufficient aluminum ions while avoiding the formation of sodium hexafluoroaluminate.

[0037] In some embodiments, the first preset pH value is 3.5-4.2.

[0038] Aluminum electrolysis waste mainly refers to various solid wastes generated in the aluminum electrolysis production process. Aluminum electrolysis is the process of producing aluminum by electrolyzing molten alumina (Al2O3). In this process, waste materials such as waste cathode carbon blocks, waste anode paste, and electrolyte waste slag are produced. The alkaline fluorine extraction solution of aluminum electrolysis waste is an alkaline fluorine-containing filtrate obtained by fluorine extraction from aluminum electrolysis waste. The alkaline fluorine extraction solution of aluminum electrolysis waste mainly includes fluoride ions, sodium ions and a small amount of aluminum ions, among which fluoride ions mainly come from the aluminum electrolysis waste itself. Depending on the different waste raw materials, the fluorine content in the fluorine extraction solution is 5g / L~20g / L; the sodium content mainly comes from the aluminum electrolysis waste itself (6g / L~26g / L) and the added fluorine extraction agent (if the fluorine extraction agent is sodium hydroxide). The aluminum content is mainly dissolved when sodium hydroxide and other alkalis are used as fluorine extraction agents, and the content is 1.5g / L~6.0g / L.

[0039] In the embodiment of the present application, an alkaline fluorine extraction solution of aluminum electrolysis waste is added to an acidic aluminum salt solution until the acidic aluminum salt solution has a first preset pH value and no precipitation is generated, which can ensure that there is sufficient aluminum in the acidic aluminum salt solution and the solution remains acidic, and avoid the formation of sodium hexafluoroaluminate. The aluminum-fluorine molar ratio of sodium hexafluoroaluminate is 1:6, and the aluminum-fluorine molar ratio of aluminum fluoride is 1:3. The aluminum required for the formation of sodium hexafluoroaluminate is less than the fluorine and requires a pH greater than 6. Therefore, an alkaline fluorine extraction solution of aluminum electrolysis waste is added to the acidic aluminum salt solution and cannot be added in reverse. The first preset pH value can be 3.5-4.2 and no precipitation is generated, which can avoid excessive addition of alkaline fluorine extraction solution, which leads to an increase in the fluorine content and pH in the acidic aluminum salt solution, directly generating sodium hexafluoroaluminate, and then subsequently reducing the purity and yield of the aluminum fluoride product. Exemplarily, the first preset pH value may be 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, etc.

[0040] In some embodiments, the acidic aluminum salt includes at least one of the following: aluminum sulfate, aluminum nitrate, and aluminum chloride.

[0041] In some embodiments, the pH value of the acidic aluminum salt solution is 1.8-3.0.

[0042] In the embodiment of the present application, the acidic aluminum salt can be a combination of one or more of aluminum sulfate, aluminum nitrate, and aluminum chloride, and the pH value of the acidic aluminum salt solution can be 1.8 to 3.0, so that when the alkaline fluorine extraction solution of aluminum electrolysis waste is added to the acidic aluminum salt solution, the acidic aluminum salt solution always remains acidic and no precipitation is generated, so that no sodium hexafluoroaluminate is generated in the acidic solution with sufficient aluminum ions. Exemplarily, the pH value of the acidic aluminum salt solution can be 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, etc.

[0043] S2, adding alkali to the first solution until the first solution has a second preset pH value and a precipitate is generated, to obtain a second solution;

[0044] Add alkali to the first solution obtained in the previous step until the pH value of the solution reaches a preset second pH value, at which time a precipitate will be generated. This step ensures that the generated precipitate is all aluminum hydroxyfluoride (Al[F 0.5 (OH) 0.5 ]3·0.5H2O).

[0045] In some embodiments, the second preset pH value is 4.5-5.5.

[0046] In some embodiments, the base comprises at least one of the following: aqueous ammonia, sodium hydroxide.

[0047] In the embodiment of the present application, an alkali is added to the first solution until the first solution has a second preset pH value and a precipitate is generated. The added alkali does not contain fluorine, which can avoid the increase of fluorine content and pH value in the first solution, thereby preventing the formation of sodium hexafluoroaluminate, and the reaction is sufficient to make the precipitate (white) all hydroxyaluminum fluoride (Al[F 0.5 (OH) 0.5 ]3·0.5H2O). The second preset pH value can be 4.5-5.5 to ensure a thorough reaction and avoid the second preset pH value being higher than 5.5, resulting in the formation of sodium hexafluoroaluminate. Exemplarily, the second preset pH value can be 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, etc. The alkali can be one or both of ammonia water and sodium hydroxide, and the selection of ammonia water will not introduce a fluorine source, which can be converted into ammonia gas during the later calcination process, further ensuring the purity of the subsequent aluminum fluoride.

[0048] S3, performing solid-liquid separation on the second solution to obtain a first precipitate and a third solution;

[0049] The second solution containing the precipitate is subjected to solid-liquid separation to obtain a first precipitate (i.e., hydroxyaluminum fluoride precipitate) and a third solution. In the embodiment of the present application, the second solution is subjected to solid-liquid separation, and the first precipitate is hydroxyaluminum fluoride (Al[F 0.5 (OH) 0.5 ]3·0.5H2O), the third solution is a solution composed of a small amount of fluorine, aluminum and sodium, which can be mixed into the aluminum salt solution for recycling.

[0050] S4, adding a fluorinating agent to the first precipitate to obtain a mixed material;

[0051] A fluorinating agent is added to the first precipitate to supplement the fluorine content. This step is to ensure the purity of aluminum fluoride in the final product.

[0052] S5. calcining the mixture to obtain aluminum fluoride.

[0053] The mixed material is calcined to finally obtain aluminum fluoride. The aluminum fluoride obtained in this way has high purity, with a fluorine content of more than 61% and an aluminum content of more than 31.5%. Other indicators are better than the AF-0 level in the GB / T 4292-2017 standard.

[0054] In some embodiments, the fluorinating agent comprises at least one of: hydrofluoric acid, ammonium bifluoride; and / or,

[0055] The amount of the fluorinating agent added is 1.1 to 1.5 times the theoretical amount of the fluorinating agent added, and the theoretical amount of the fluorinating agent added is the mass of the fluorinating agent required for the first precipitate and the fluorinating agent to completely react to generate aluminum fluoride during the calcination process.

[0056] In the present embodiment, the first precipitate is added with a fluorinating agent, which is hydroxyaluminum fluoride (Al[F 0.5 (OH) 0.5 ]3·0.5H2O) provides a fluorine source, the aluminum-fluorine ratio in hydroxyaluminum fluoride is 1:1.5, and the aluminum-fluorine ratio of aluminum fluoride is 1:3, and 1.5 moles of fluorine need to be added to generate aluminum fluoride. The fluorinating agent can be one or both of hydrofluoric acid (HF) and ammonium bifluoride (NH4HF2), which can supplement the fluorine source for hydroxyaluminum fluoride on the one hand, and on the other hand, it does not introduce impurities into the mixed material to affect the quality of the aluminum fluoride product.

[0057] The amount of the fluorinating agent added can be 1.1 to 1.5 times the theoretical amount of the fluorinating agent added, which can ensure that a sufficient amount of fluorine source is provided to fully generate aluminum fluoride. Exemplarily, the amount of the fluorinating agent added can be 1.1, 1.2, 1.3, 1.4, 1.5, etc. of the theoretical amount of aluminum fluoride generated by the first precipitate reaction.

[0058] In some embodiments, the calcination includes a first calcination and a second calcination in sequence, wherein:

[0059] The temperature of the first calcination is 200°C to 300°C, and the temperature of the second calcination is 450°C to 600°C.

[0060] In the embodiment of the present application, calcination includes first calcination and second calcination in sequence, and the temperature of the first calcination can be 200℃~300℃, which can remove the crystal water of the first precipitate in the mixed material. The temperature of the second calcination can be 450℃~600℃, which can fully make the first precipitate react with the fluorinating agent to generate aluminum fluoride. The time of the first calcination and the second calcination can be 90min~150min respectively. The ammonia gas in the calcination process is absorbed and recycled, and the ammonia gas is mainly brought in by wet hydroxyaluminum fluoride and the fluorinating agent. Exemplarily, the temperature of the first calcination can be 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, etc.; the temperature of the second calcination can be 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, 520℃, 540℃, 560℃, 580℃, 600℃, etc.

[0061] In some embodiments, the second solution is subjected to solid-liquid separation to obtain a first precipitate and a third solution, and then further comprises:

[0062] S6, adding the base to the third solution until the third solution has a third preset pH value, to obtain a fourth solution;

[0063] S7. Performing solid-liquid separation on the fourth solution to obtain a second precipitate and a fifth solution.

[0064] The third solution is continuously added with alkali until the third solution reaches a preset third pH value, which can combine the remaining fluorine and aluminum in the third solution to form cryolite products, thereby increasing the utilization rate of fluorine to more than 99.9%. The fourth solution is subjected to solid-liquid separation to obtain a second precipitate and a fifth solution. The second precipitate is dried to obtain cryolite (the main component of cryolite is sodium hexafluoroaluminate), and the fifth solution can be recycled.

[0065] In some embodiments, the third preset pH value is >6.

[0066] In an embodiment of the present application, alkali is continuously added to the third solution until the third solution has a third preset pH value, and the third preset pH value may be >6, which can fully combine the remaining fluorine and aluminum in the third solution to form cryolite products, and the utilization rate of fluorine is increased to more than 99.9%. Exemplarily, the third preset pH value may be 6.2, 6.4, 6.6, 6.8, 7.0, etc. Therefore, the embodiment of the present application obtains hydroxyaluminum fluoride and cryolite in steps by adjusting the pH value, thereby avoiding the problem of low product purity caused by mutual doping.

[0067] The method for recycling the alkaline fluorine extraction solution of aluminum electrolysis waste provided in the embodiment of the present application has the following advantages:

[0068] 1. The overall technical solution extracts and prepares aluminum fluoride and cryolite in steps by controlling aluminum first and then supplementing fluorine. The product indicators meet the standard requirements. The fluorine content in aluminum fluoride is greater than 61%, and the aluminum content is greater than 31.5%. Other indicators are better than the AF-0 level in the GB / T4292-2017 standard. The utilization rate of fluorine in the alkaline fluorine extraction solution can reach more than 99.9%.

[0069] 2. The entire process is mainly controlled by the simple and easy-to-measure pH value. The preset pH values ​​at different stages determine the direction of the reaction and the type of products. Accurate pH adjustment, especially the control of the addition direction of the acidic aluminum salt solution and the alkaline fluoride extraction solution of aluminum electrolysis waste, can prevent the precipitation of unnecessary impurities (such as avoiding the formation of sodium hexafluoroaluminate) and guide the formation of the target compound hydroxyaluminum fluoride;

[0070] 3. Add fluorinating agent to supplement fluorine in the precipitation of hydroxyaluminum fluoride, calcine to make the material undergo a series of reactions such as crystal phase transformation, and finally produce high-purity aluminum fluoride;

[0071] 4. The fluorine content of the final aluminum fluoride is greater than 61%, and the aluminum content is greater than 31.5%. Other indicators are better than the AF-0 level in the GB / T4292-2017 standard, which means that the product has fewer impurities and better quality. The alkali is used to adjust the pH value of the third solution, and the remaining ions in the solution that have not been precipitated into hydroxyaluminum fluoride are converted into cryolite. The utilization rate of fluorine in the alkaline fluoride extraction solution is more than 99.9%, which greatly reduces resource waste and is in line with the concept of green circular economy.

[0072] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for the unrecorded specific conditions in the following examples are usually measured according to national standards. If there is no corresponding national standard, then carry out according to general international standards, normal conditions or according to the conditions recommended by the manufacturer.

[0073] Example 1

[0074] A method for recycling an alkaline fluorine extraction solution of aluminum electrolysis waste, wherein the alkaline fluorine extraction solution has a fluorine content of 8.24 g / L, a sodium content of 9.97 g / L, and an aluminum content of 0.065 mg / L, comprising:

[0075] S11, adding an alkaline fluorine extraction solution of aluminum electrolysis waste to an acidic aluminum salt solution until the acidic aluminum salt solution has a first preset pH value and no precipitation is generated, to obtain a first solution; wherein the acidic aluminum salt solution is an aluminum sulfate solution with a pH value of 1.8; and the first preset pH value is 3.8;

[0076] S21, adding alkali to the first solution until the first solution has a second preset pH value and a precipitate is generated, thereby obtaining a second solution; wherein the second preset pH value is 4.5;

[0077] S31, performing solid-liquid separation on the second solution to obtain a first precipitate and a third solution;

[0078] S41, adding a fluorinating agent to the first precipitate to obtain a mixed material; wherein the fluorinating agent is HF, and the amount of HF added is 1.1 times the theoretical amount of HF added;

[0079] S51, calcining the mixture to obtain aluminum fluoride; wherein the calcinations sequentially include: a first calcination: calcination at 200° C. for 90 min, a second calcination: calcination at 450° C. for 150 min;

[0080] S61, adding the base to the third solution until the third solution has a third preset pH value, to obtain a fourth solution; wherein the third preset pH value is 7.5;

[0081] S71. Perform solid-liquid separation on the fourth solution to obtain a second precipitate and a fifth solution; the second precipitate is dried to obtain cryolite; and the fluorine content in the fifth solution is 2.3 mg / L.

[0082] The aluminum fluoride product prepared in Example 1 has a fluorine content of 62.9%, an aluminum content of 33.1%, and other indicators meet the AF-0 standard of "Aluminum Fluoride" (GB / T 4292-2017). The cryolite product meets the standard of "Cryolite" (GB / T 4291-2017), and the fluorine recovery rate is 99.97%.

[0083] Example 2

[0084] A method for recycling an alkaline fluorine extraction solution of aluminum electrolysis waste, wherein the alkaline fluorine extraction solution has a fluorine content of 16.23 g / L, a sodium content of 14 g / L, and an aluminum content of 0.079 mg / L, comprising:

[0085] S12, adding an alkaline fluorine extraction solution of aluminum electrolysis waste to an acidic aluminum salt solution until the acidic aluminum salt solution has a first preset pH value and no precipitation is generated, to obtain a first solution; wherein the acidic aluminum salt solution is an aluminum sulfate solution with a pH value of 2.0; and the first preset pH value is 4.0;

[0086] S22, adding alkali to the first solution until the first solution has a second preset pH value and a precipitate is generated, thereby obtaining a second solution; wherein the second preset pH value is 4.8;

[0087] S31, performing solid-liquid separation on the second solution to obtain a first precipitate and a third solution;

[0088] S42, adding a fluorinating agent to the first precipitate to obtain a mixed material; wherein the fluorinating agent is HF, and the amount of HF added is 1.2 times the theoretical amount of HF added;

[0089] S52, calcining the mixture to obtain aluminum fluoride; wherein the calcinations sequentially include: a first calcination: calcination at 250° C. for 110 min, and a second calcination: calcination at 550° C. for 135 min.

[0090] S62, adding the base to the third solution until the third solution has a third preset pH value, to obtain a fourth solution; wherein the third preset pH value is 6.2;

[0091] S72, separating the fourth solution into solid and liquid to obtain a second precipitate and a fifth solution; the second precipitate is dried to obtain cryolite; and the fluorine content in the fifth solution is 9.6 mg / L.

[0092] The aluminum fluoride product prepared in Example 2 has a fluorine content of 62.8%, an aluminum content of 32.6%, and other indicators meet the AF-0 standard of "Aluminum Fluoride" (GB / T 4292-2017). The cryolite product meets the standard of "Cryolite" (GB / T 4291-2017), and the fluorine recovery rate is 99.9%.

[0093] Example 3

[0094] A method for recycling an alkaline fluorine extraction solution of aluminum electrolysis waste, wherein the alkaline fluorine extraction solution has a fluorine content of 18.02 g / L, a sodium content of 23.09 g / L, and an aluminum content of 4.85 g / L, comprising:

[0095] S13, adding an alkaline fluorine extraction solution of aluminum electrolysis waste to an acidic aluminum salt solution until the acidic aluminum salt solution has a first preset pH value and no precipitation is generated, to obtain a first solution; wherein the acidic aluminum salt solution is an aluminum sulfate solution with a pH value of 2.2; and the first preset pH value is 3.5;

[0096] S23, adding alkali to the first solution until the first solution has a second preset pH value and a precipitate is generated, thereby obtaining a second solution; wherein the second preset pH value is 5.2,

[0097] S33, performing solid-liquid separation on the second solution to obtain a first precipitate and a third solution;

[0098] S43, adding a fluorinating agent to the first precipitate to obtain a mixed material; wherein the fluorinating agent is NH4HF2, and the amount of NH4HF2 added is 1.3 times the theoretical amount of NH4HF2 added;

[0099] S53, calcining the mixture to obtain aluminum fluoride; wherein the calcinations sequentially include: a first calcination: calcination at 300° C. for 130 min, and a second calcination: calcination at 600° C. for 115 min.

[0100] S63, adding the base to the third solution until the third solution has a third preset pH value, to obtain a fourth solution; wherein the third preset pH value is 8.2;

[0101] S73, separating the fourth solution into solid and liquid to obtain a second precipitate and a fifth solution; the second precipitate is dried to obtain cryolite; the fluorine content in the fifth solution is 12.91 mg / L.

[0102] The aluminum fluoride product prepared in Example 3 has a fluorine content of 62.4%, an aluminum content of 32.9%, and other indicators meet the AF-0 standard of "Aluminum Fluoride" (GB / T 4292-2017). The cryolite product meets the standard of "Cryolite" (GB / T 4291-2017), and the fluorine recovery rate is 99.93%.

[0103] Example 4

[0104] A method for recycling an alkaline fluorine extraction solution of aluminum electrolysis waste, wherein the alkaline fluorine extraction solution has a fluorine content of 12.05 g / L, a sodium content of 17.42 g / L, and an aluminum content of 3.02 g / L, comprising:

[0105] S14, adding an alkaline fluorine extraction solution of aluminum electrolysis waste to an acidic aluminum salt solution until the acidic aluminum salt solution has a first preset pH value and no precipitation is generated, to obtain a first solution; wherein the acidic aluminum salt solution is an aluminum sulfate solution with a pH value of 3.0; and the first preset pH value is 4.2;

[0106] S24, adding alkali to the first solution until the first solution has a second preset pH value and a precipitate is generated, thereby obtaining a second solution; wherein the second preset pH value is 5.5;

[0107] S34, performing solid-liquid separation on the second solution to obtain a first precipitate and a third solution;

[0108] S44, adding a fluorinating agent to the first precipitate to obtain a mixed material; wherein the fluorinating agent is NH4HF2, and the amount of NH4HF2 added is 1.5 times the theoretical amount of NH4HF2 added;

[0109] S54, calcining the mixture to obtain aluminum fluoride; wherein the calcinations sequentially include: a first calcination: calcination at 250° C. for 150 min, and a second calcination: calcination at 500° C. for 90 min.

[0110] S64, adding the base to the third solution until the third solution has a third preset pH value, to obtain a fourth solution; wherein the third preset pH value is 6.7;

[0111] S74, separating the fourth solution into solid and liquid to obtain a second precipitate and a fifth solution; the second precipitate is dried to obtain cryolite; and the fluorine content in the third solution is 9.2 mg / L.

[0112] The aluminum fluoride product prepared in Example 4 has a fluorine content of 62.2%, an aluminum content of 32.1%, and other indicators meet the AF-0 standard of "Aluminum Fluoride" (GB / T 4292-2017). The cryolite product meets the standard of "Cryolite" (GB / T 4291-2017), and the fluorine recovery rate is 99.93%.

[0113] Comparative Example 1

[0114] Based on the disclosure of Example 1, the difference between Comparative Example 1 and Example 1 is that:

[0115] Acidic aluminum salt solution is added to the alkaline fluorine extraction solution of aluminum electrolysis waste.

[0116] Result: Precipitation occurs immediately in the solution. Even if the pH value of the solution is finally adjusted to the first preset pH value range, the solid phase obtained after solid-liquid separation is a cryolite phase mixture without hydroxyaluminum fluoride or aluminum fluoride phase.

[0117] Comparative Example 2

[0118] Adding an alkaline fluorine extraction solution of aluminum electrolysis waste to an acidic aluminum salt solution until the acidic aluminum salt solution has a first preset pH value but a precipitate is generated, thereby obtaining a first solution; wherein the first preset pH value is 4.2;

[0119] Adding alkali to the first solution until the first solution has a second preset pH value to obtain a second solution; wherein the second preset pH value is 5.0;

[0120] Performing solid-liquid separation on the second solution to obtain a first precipitate and a third solution;

[0121] Results: The first precipitate obtained was a cryolite phase mixture without hydroxyaluminum fluoride or aluminum fluoride phase.

[0122] Therefore, through Examples 1 to 4 of the present application, the fluorine content in aluminum fluoride can be greater than 61%, the aluminum content can be greater than 31.5%, and other indicators are better than the AF-0 level in the GB / T 4292-2017 standard, and the utilization rate of fluorine in the alkaline fluorine extraction solution is more than 99.9%, thereby realizing the effective recycling of the alkaline fluorine extraction solution. However, the addition direction of the alkaline fluorine extraction solution and the acidic aluminum salt solution of the aluminum electrolysis waste in Comparative Example 1 is opposite to that of the present application embodiment; in Comparative Example 2, although the acidic aluminum salt solution has the first preset pH value, precipitation is generated, so that Comparative Examples 1 to 2 do not obtain high-purity aluminum fluoride, and only obtain a cryolite phase mixture, that is, the two products of aluminum fluoride and cryolite are not obtained, resulting in the failure to achieve effective high-quality recycling of the alkaline fluorine extraction solution.

[0123] One or more technical solutions in the embodiments of the present application also have at least the following technical effects or advantages:

[0124] (1) In the present embodiment, aluminum fluoride of AF-0 grade in accordance with the GB / T 4292-2017 standard is obtained by first controlling aluminum and then supplementing fluorine. Aluminum fluoride and cryolite are extracted and prepared step by step. The product indicators all meet the standard requirements, and the utilization rate of fluorine in the alkaline fluorine extraction solution can reach more than 99.9%;

[0125] (2) The embodiments of the present application solve the technical problems existing in the prior art, such as low purity, low fluorine recovery rate and low efficiency of aluminum fluoride-doped sodium hexafluoroaluminate prepared from alkaline fluorine extraction solution of aluminum electrolysis waste.

[0126] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and 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 the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for recycling alkaline fluorine extraction solution from aluminum electrolysis waste, the method comprising: Adding an alkaline fluorine extraction solution of aluminum electrolysis waste to an acidic aluminum salt solution until the acidic aluminum salt solution has a first preset pH value and no precipitation is generated, thereby obtaining a first solution; adding a base to the first solution until the first solution has a second preset pH value and a precipitate is generated, thereby obtaining a second solution; performing solid-liquid separation on the second solution to obtain a first precipitate and a third solution; adding a fluorinating agent to the first precipitate to obtain a mixed material; The mixed material is calcined to obtain aluminum fluoride.

2. The method according to claim 1, characterized in that The first preset pH value is 3.5-4.

2.

3. The method according to claim 1, characterized in that The acidic aluminum salt includes at least one of the following: aluminum sulfate, aluminum nitrate, and aluminum chloride.

4. The method according to claim 1 or 3, characterized in that: The pH value of the acidic aluminum salt solution is 1.8-3.

0.

5. The method according to claim 1, characterized in that The second preset pH value is 4.5-5.

5.

6. The method according to claim 1, characterized in that The fluorinating agent comprises at least one of the following: hydrofluoric acid, ammonium bifluoride; and / or, The amount of the fluorinating agent added is 1.1 to 1.5 times the theoretical amount of the fluorinating agent added, and the theoretical amount of the fluorinating agent added is the mass of the fluorinating agent required for the first precipitate and the fluorinating agent to completely react to generate aluminum fluoride during the calcination process.

7. The method according to claim 1, characterized in that The calcination includes a first calcination and a second calcination in sequence, wherein: The temperature of the first calcination is 200°C to 300°C, and the temperature of the second calcination is 450°C to 600°C.

8. The method according to claim 1, characterized in that The second solution is subjected to solid-liquid separation to obtain a first precipitate and a third solution, and then further comprises: adding the base to the third solution until the third solution has a third preset pH value to obtain a fourth solution; The fourth solution is subjected to solid-liquid separation to obtain a second precipitate and a fifth solution.

9. The method according to claim 1 or 8, characterized in that: The alkali includes at least one of the following: aqueous ammonia and sodium hydroxide.

10. The method according to claim 8, characterized in that The third preset pH value is >6.

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