A recycling method of aluminum electrolysis spent cathode

Abstract

The present application relates to a kind of recycling methods of aluminum electrolysis spent cathode, comprising the following steps: S1, spent cathode is crushed to obtain first powder;S2, first powder is added with prefabricated reagent, so that first powder and prefabricated reagent are mixed to obtain powder mixture.S3, powder mixture is calcined to obtain calcined product.S4, calcined product is crushed to obtain second powder;S5, second powder is added with water to leach and filter, obtain first filtrate and first residue;S6, first residue is separated from carbon powder in first residue using ultrasonic flotation device.By high-temperature calcination, the prefabricated reagent in molten state can more fully react with the powder of spent electrolyte, so that the purity of recycled carbon is higher.Moreover, the gas generated is ammonia, achieving truly green recycling of spent cathode.It can be better applied in industrialization.

Description

Technical Field

[0001] This invention relates to the field of aluminum electrolysis resource utilization technology, and in particular to a method for recycling and processing waste cathodes from aluminum electrolysis. Background Technology

[0002] Currently, in the aluminum electrolysis production process, to reduce the energy consumption of aluminum electrolytic cells and extend their service life, a lining structure is typically formed during the start-up and roasting of the electrolytic cell. This structure typically includes high-graphite cathode carbon blocks, fully graphite cathode carbon blocks, graphitized cathode carbon blocks with side carbon blocks, cathode paste, refractory materials, and insulation materials. When the cathode lining is damaged, waste cathode carbon blocks rich in graphite resources (50%–70%) will inevitably be released, also known as waste cathodes. Typically, about 10 kg of waste cathode carbon blocks are generated for every ton of electrolytic aluminum produced. In 2018, global electrolytic aluminum production reached 64.34 million tons, generating over 600,000 tons of waste cathodes—a massive quantity. Because waste cathodes contain various elements such as fluorine, lithium, sodium, potassium, and carbon, as well as soluble fluorides and cyanides, current disposal methods only allow for on-site storage or landfilling. However, both methods risk the diffusion of soluble fluorides and cyanides into the soil or seep into groundwater, posing a risk of contamination to human and animal food supplies and causing severe ecological damage. Therefore, the treatment of waste cathodes is currently a hot research topic in industrial production.

[0003] In existing technologies, the recycling and treatment of waste cathodes generally takes the following forms:

[0004] The first method involves crushing the waste cathode, then mixing the crushed carbon blocks from the electrolytic aluminum waste cathode with ammonium sulfate and roasting it. This is followed by water leaching, introducing new soluble fluorides to utilize fluorine's complexing ability to remove calcium and magnesium from the leachate. Next, aluminum salts are introduced, and the pH needs to be adjusted to remove aluminum and fluorine from the leachate. Finally, lithium precipitation is performed. This process generates large amounts of highly toxic gases such as hydrogen fluoride during ammonium sulfate roasting, and the process is complex. The introduction of fluorine, requiring the removal of calcium, magnesium, aluminum, and fluorine simultaneously, produces a large amount of secondary waste residue. Furthermore, since the lithium content in waste cathodes is generally low, the lithium precipitation process requires significant energy consumption through evaporation. This method treats aluminum and fluorine as impurities, meaning that only lithium and carbon are recovered. Other valuable elements, such as aluminum, remain in the waste cathode, and these are not recovered, resulting in a relatively low overall recovery rate compared to the waste cathode itself.

[0005] The second method: Chinese patent CN114572981A discloses a method for treating waste cathodes using microwave heating in a steam atmosphere. This method utilizes high-temperature steam to dissolve fluoride salts in the waste cathodes, thereby separating the carbon. However, microwave heating in a steam atmosphere generates a large amount of hydrofluoric acid, which is highly corrosive and can severely damage the equipment, posing a significant safety hazard to the operator. Furthermore, the reduction of carbon by steam during the reaction produces a large amount of toxic carbon monoxide gas, and the extremely high roasting temperature results in substantial carbon loss, affecting the overall recovery efficiency.

[0006] In summary, although there are currently many comprehensive recycling processes for carbon blocks from waste aluminum electrolysis cathodes, both the first and second methods generate toxic gases. Furthermore, the first method introduces other impurities, and the second method consumes a large amount of carbon, resulting in a low carbon recovery rate from the waste cathodes. Additionally, the lithium content itself is not high, and the introduction of other impurities further reduces the overall recovery rate of the waste cathodes. In other words, existing technologies generate other impurities during the processing of waste cathodes, making it difficult to efficiently separate carbon from other valuable elements. This leads to a low overall recovery rate of the waste cathodes, relatively low purity of the separation products, and the generation of toxic gases or highly corrosive substances. Consequently, the recycling and processing of waste cathodes has not been industrialized. Summary of the Invention

[0007] (a) Technical problems to be solved

[0008] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a method for recycling and processing waste cathodes from aluminum electrolysis. This method solves the technical problem that when processing waste cathodes, other impurities are generated, making it difficult to efficiently separate carbon from other valuable elements, resulting in a low overall recovery rate of waste cathodes and relatively low purity of the separated products. In addition, toxic gases or highly corrosive substances are also generated, which prevents the recycling and processing of waste cathodes from being industrialized.

[0009] (II) Technical Solution

[0010] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0011] A method for recycling and processing waste cathodes from aluminum electrolysis, characterized in that the method includes the following steps:

[0012] S1. The waste cathode is crushed to obtain the first powder;

[0013] S2. A pre-prepared reactant is added to the first powder in S1 to mix the first powder and the pre-prepared reactant to obtain a powder mixture, wherein the pre-prepared reactant is a mixed solvent of ammonium salt and calcium salt;

[0014] S3. The powder mixture in S2 is calcined at a certain temperature to obtain the calcined product;

[0015] S4. The roasted product in S3 is crushed to obtain the second powder.

[0016] S5. Add the second powder from S4 to water for leaching and filtration to obtain the first filtrate and the first filter residue.

[0017] S6. Separate the carbon powder in the first filter residue from S5 using an ultrasonic flotation device.

[0018] This invention proposes a method for recycling and processing waste cathodes from aluminum electrolysis. The waste cathode is mixed with a pre-prepared reactant to form a powder mixture, which is then calcined. Utilizing the strong binding effect of calcium and fluorine, the electrolyte contained in the waste cathode is dissociated. Furthermore, the high-temperature calcination allows the molten pre-prepared reactant to penetrate the graphite coating within the waste cathode more easily, thus improving contact with the internally encapsulated waste electrolyte. This results in a more thorough reaction between the calcium in the pre-prepared reactant and the fluorine in the waste cathode, further enhancing the separation of the electrolyte from the graphite and producing a product with higher purity. The calcined product is then leached, and high-purity carbon is separated by ultrasonic flotation. The first filter residue and the first filtrate are then processed separately to produce aluminum salts and high-purity calcium fluoride, respectively.

[0019] In addition, during the entire process, due to the reaction between calcium and fluorine, ammonium salt directly generates ammonia gas. Ammonia gas is non-toxic. Compared with the dangerous gases produced in the prior art, the present invention can avoid the generation of dangerous gases through the combination reaction of calcium and fluorine under high temperature calcination. Furthermore, the first filter residue and the first filtrate produced after calcination leaching can be effectively recovered and utilized.

[0020] Optionally, based on the concentrations of calcium and lithium ions in the first filtrate in S5, soluble carbonates are added to the first filtrate to remove calcium and extract lithium, yielding calcium carbonate and lithium carbonate respectively. The remaining filtrate can be evaporated and dried to obtain salt.

[0021] Optionally, the following steps are also included:

[0022] S7. After flotation in S6, the mixture is filtered to obtain the second filtrate, the second filter residue, and the flotation residue.

[0023] S8. Add an acid solution to the second filter residue in S7 for acid leaching, and filter after the reaction to obtain a third filtrate and a third filter residue, wherein the third filter residue is calcium fluoride.

[0024] Optionally, the following steps are also included:

[0025] S9. Based on the calcium ion concentration of the third filtrate described in S8, calcium is removed, and then the remaining filtrate is evaporated to obtain aluminum salt.

[0026] Optionally, the ammonium salt is one or more of ammonium chloride, ammonium nitrate, ammonium carbonate, and ammonium bicarbonate;

[0027] The calcium salt is one or more of calcium carbonate, calcium oxide, calcium hydroxide, calcium formate, and calcium propionate.

[0028] Optionally, the mass mixing ratio of the first powder in S2 to the pre-prepared reactant in S2 should be 1:(1-10);

[0029] In S2, the mass mixing ratio of the ammonium salt to the calcium salt of the pre-prepared reactant is 1:(1-10).

[0030] Optionally, in S3, the calcination temperature should be 200℃-650℃ and the calcination time should be 0.5h-6h.

[0031] Optionally, during the S5 leaching process, the liquid-to-solid ratio should be between 5 and 80, the leaching temperature should be between 30℃ and 120℃, and the leaching time should be between 0.5h and 10h.

[0032] (III) Beneficial Effects

[0033] The beneficial effects of this invention are as follows: This invention provides a method for recycling and processing waste cathodes from aluminum electrolysis. The waste cathode is mixed with a pre-prepared reactant to form a powder mixture, which is then calcined. Utilizing the strong binding effect of calcium and fluorine, the electrolyte contained in the waste cathode is dissociated. Furthermore, the high-temperature calcination allows the molten pre-prepared reactant to more easily penetrate the graphite coating within the waste cathode, thus improving contact with the internally encapsulated waste electrolyte. This results in a more thorough reaction between the calcium in the pre-prepared reactant and the fluorine in the waste cathode, further enhancing the separation effect between the electrolyte and graphite and producing a product with higher purity. The calcined product is then leached, and high-purity carbon is separated by ultrasonic flotation. The first filter residue and the first filtrate are then processed separately. The first filter residue can be used to produce aluminum salts and high-purity calcium fluoride, respectively.

[0034] In addition, during the entire process, due to the reaction between calcium and fluorine, ammonium salt directly generates ammonia gas. Ammonia gas is non-toxic. Compared with the dangerous gases produced in the prior art, the present invention can avoid the generation of dangerous gases through the combination reaction of calcium and fluorine under high temperature calcination. Furthermore, the first filter residue and the first filtrate produced after calcination leaching can be effectively recovered and utilized.

[0035] This invention enables the pre-prepared reactant, calcined at high temperatures to react more fully with the waste electrolyte powder, resulting in higher purity recycled carbon. Furthermore, the generated gas is ammonia, achieving truly green recycling of waste cathodes. This allows for better industrial application. Attached Figure Description

[0036] Figure 1 This is a flowchart of a method for recycling and processing waste cathodes from aluminum electrolysis, as disclosed in this invention.

[0037] Figure 2 This is the XRD of the third filter residue in Example 1 of this invention. Detailed Implementation

[0038] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] This invention provides a method for recycling and processing waste cathodes from aluminum electrolysis, comprising the following steps:

[0040] S1. The waste cathode is crushed to obtain the first powder.

[0041] S2. Add a pre-prepared reactant to the first powder in S1 to mix the first powder and the pre-prepared reactant to obtain a powder mixture, wherein the pre-prepared reactant is a mixed solvent of ammonium salt and calcium salt;

[0042] S3. The powder mixture in S2 is calcined at a certain temperature to obtain the calcined product;

[0043] S4. The roasted product in S3 is crushed to obtain the second powder.

[0044] S5. Add the second powder from S4 to water for leaching and filtration to obtain the first filtrate and the first filter residue.

[0045] S6. Separate the carbon powder in the first filter residue from S5 using an ultrasonic flotation device.

[0046] Furthermore, based on the concentrations of calcium and lithium ions in the first filtrate in S5, soluble carbonates are added to the first filtrate to remove calcium and extract lithium, yielding calcium carbonate and lithium carbonate respectively. The remaining filtrate can be evaporated and dried to obtain salt.

[0047] The present invention provides a method for recycling and processing waste cathodes from aluminum electrolysis. This method involves mixing the waste cathode with a pre-prepared reactant to form a powder mixture, which is then calcined. Utilizing the strong binding effect of calcium and fluorine, the electrolyte contained in the waste cathode is dissociated. Furthermore, the high-temperature calcination allows the molten pre-prepared reactant to penetrate the graphite coating within the waste cathode more easily, thus improving contact with the internally encapsulated waste electrolyte. This results in a more thorough reaction between the calcium in the pre-prepared reactant and the fluorine in the waste cathode, further enhancing the separation of the electrolyte from the graphite and producing a product with higher purity. The calcined product is then leached, and high-purity carbon is separated by ultrasonic flotation. The first filter residue and the first filtrate are then processed separately. The first filter residue can be used to produce aluminum salts and high-purity calcium fluoride, respectively.

[0048] Furthermore, it also includes the following steps:

[0049] S7. After flotation in S6, the mixture is filtered to obtain the second filtrate, the second filter residue, and the flotation residue.

[0050] S8. Add acid solution to the second filter residue in S7 for acid leaching. After the reaction, filter to obtain a third filtrate and a third filter residue, wherein the third filter residue is calcium fluoride. After flotation filtration, obtain a second filtrate, a second filter residue, and flotation residue. Recycle the second filtrate into the first filter residue for continued flotation.

[0051] Furthermore, it also includes the following steps:

[0052] S9. Based on the calcium ion concentration of the third filtrate in S8, calcium is removed, and then the remaining filtrate is evaporated to obtain aluminum salt.

[0053] Here, the flotation residue is discharged as waste. Further acid leaching of the second filter residue yields a third filter residue (calcium fluoride) and a third filtrate containing calcium ions. The third filtrate undergoes conventional impurity and calcium removal treatments, followed by evaporation and drying to obtain aluminum salts with higher purity. In other words, compared to other methods, this invention not only effectively recovers carbon from waste cathodes but also effectively recovers and fully utilizes other valuable elements such as aluminum, significantly improving the overall recovery rate of waste cathodes. It solves the technical problem that the processing of waste cathodes generates other impurities, making it difficult to efficiently separate carbon from other valuable elements, resulting in a low overall recovery rate and relatively low purity of the separation products. Furthermore, it generates toxic gases or highly corrosive substances, hindering the industrial application of waste cathode recycling.

[0054] Furthermore, the ammonium salt is one or more of ammonium chloride, ammonium nitrate, ammonium carbonate, and ammonium bicarbonate. These ammonium salts are easy to prepare and have low cost.

[0055] Calcium salts are one or more of calcium carbonate, calcium oxide, calcium hydroxide, calcium formate, and calcium propionate. The above ammonium salts are easy to prepare and have low cost.

[0056] Furthermore, the mass mixing ratio of the first powder in S2 to the pre-prepared reactant in S2 should be 1:(1-10). Preferably, it is 1:3.

[0057] In S2, the mass mixing ratio of the ammonium salt and calcium salt of the pre-prepared reactant is 1:(1-10), preferably 1:2.

[0058] Furthermore, in S3, the calcination temperature should be 200℃-650℃, and the calcination time should be 0.5h-6h. Preferably, the calcination time is 2h, and the calcination temperature is 550℃.

[0059] Furthermore, during the S5 leaching process, the liquid-to-solid ratio should be between 5 and 80, the leaching temperature should be between 30℃ and 120℃, and the leaching time should be between 0.5h and 10h.

[0060] Furthermore, the soluble carbonates in S5 include one or more of ammonium carbonate, ammonium bicarbonate, sodium carbonate, and potassium carbonate.

[0061] Furthermore, in the acid leaching process of S8, the acid used is an organic or inorganic acid with an acid concentration of 0.5-10 mol / L, a leaching liquid-to-solid ratio of 5-30, a leaching temperature of 30-100℃, and a leaching time of 0.5-10 h.

[0062] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present invention can be understood more clearly and thoroughly, and that the scope of the present invention can be fully conveyed to those skilled in the art.

[0063] It should be noted that the drying process described in the examples below was performed at 90°C for 12 hours. Evaporation was carried out at 100°C until a solid precipitated, which will not be elaborated upon further.

[0064] Example 1:

[0065] A method for recycling and processing waste cathodes from aluminum electrolysis, comprising the following steps:

[0066] S1. Take waste cathodes from an aluminum plant. The waste cathodes contain Na: 13.8wt%, Al: 6.6wt%, F: 16.3wt%, O: 9.6wt%, Si: 1.5wt%, Ca: 2.2wt%, C: 46.2wt%, and other components: 3.8wt%. Crush the waste cathodes and sieve out the particles with a particle size ≤200 mesh to make the first powder.

[0067] It should be noted that the purpose of crushing the waste cathode is to ensure a more complete reaction. Screening for particles with a size of 200 mesh or less facilitates subsequent reactions; the finer the particles, the more complete the reaction. Powder with a particle size greater than 200 mesh is returned to the powder processing unit for further processing.

[0068] S2. Take 10g of the first powder from S1, and add 30g of the pre-prepared reactant to the first powder to mix the first powder and the pre-prepared reactant to obtain a powder mixture. The pre-prepared reactant is a mixed solvent of 20g ammonium chloride and 10g calcium oxide, with 20g ammonium chloride serving as the first reactant and 10g calcium oxide serving as the second reactant. The two are mixed uniformly, with a mass ratio of the first reactant to the second reactant of 2:1.

[0069] S3. The powder mixture from S2 is calcined at a certain temperature to obtain the calcined product. Specifically, 10g of the first powder and 30g of the pre-prepared reactant are weighed and mixed evenly, with a mass ratio of the pre-prepared reactant to the first powder of 3:1. The mixture is then calcined at 550℃ for 2 hours. During the calcination process, the generated flue gas (ammonia) is passed into dilute hydrochloric acid to recover and form ammonium salt, which can be recycled as raw material for waste cathodes.

[0070] S4. The calcined product from S3 is crushed to produce a second powder. Then, in S5, the second powder from S4 is leached with water and filtered to obtain a first filtrate and a first filter residue. Specifically, the second powder is leached with water at a liquid-to-solid ratio of 10:1 at 50°C for 4 hours to obtain the first filter residue and the first filtrate. The first filter residue is treated with ultrasonic flotation to promote carbon separation, and the upper layer of foam is collected during flotation. S6. The carbon powder in the first filter residue from S5 is separated using an ultrasonic flotation device.

[0071] It should be noted that ultrasonic flotation uses an ultrasonic flotation device. The ultrasonic flotation time should be between 0.5h and 10h, and the power of the ultrasonic flotation device should be between 100W and 500W.

[0072] S7. After flotation in S6, the mixture is filtered. The remaining filtrate is filtered again to obtain a second filtrate, a second filter residue, and flotation residue. The collected foam is dried to obtain high-purity carbon powder. At this point, the carbon powder has been completely separated from the waste cathode.

[0073] Furthermore, the first filtrate, the second filtrate, and the second filter residue are each further processed and can all be utilized in a reasonable and sufficient manner.

[0074] In this embodiment, based on the concentrations of calcium and lithium ions in the first filtrate in step S5, a soluble carbonate is added to the first filtrate. Specifically, a 1 mol / L sodium carbonate solution is added at a calcium to carbonate molar ratio of 1:1. After the reaction, the solution is filtered to obtain calcium carbonate as the filter residue. The remaining filtrate is evaporated and dried to obtain salt for calcium removal and lithium extraction, yielding calcium carbonate and lithium carbonate, respectively. The remaining filtrate can be evaporated and dried to obtain salt.

[0075] Next, in step S8, 0.2 mol / L hydrochloric acid was added to the second filter residue after filtration in step S7 at a liquid-to-solid ratio of 5:1, and the mixture was acid-leached at 50°C for 1 hour. After filtration, the third filtrate and the third filter residue were obtained, wherein the third filter residue was calcium fluoride.

[0076] S9. Based on the calcium ion concentration of the third filtrate in S8, calcium is removed, and then the remaining filtrate is evaporated to obtain crystalline aluminum chloride.

[0077] In Example 1, the recovery rate of C was 99.34% and the toner purity was 99.07%.

[0078] Example 2:

[0079] The implementation method is the same as in Example 1, except that:

[0080] The first reactant used in S2 is ammonium carbonate, and the second reactant is calcium hydroxide. The mass ratio of the first reactant to the second reactant is 5:1, that is, the pre-prepared reactant is a mixed solvent of 20g of ammonium carbonate and 10g of calcium hydroxide.

[0081] In S2, the mass ratio of the pre-prepared reactant to the first powder is 5:1, and the calcination temperature is 200℃, with a calcination time of 6h.

[0082] The liquid-to-solid ratio in the S5 leaching process is 80, the leaching time is 5 hours, and the leaching temperature is 90℃.

[0083] In this embodiment, based on the concentrations of calcium and lithium ions in the first filtrate in step S5, a soluble carbonate is added to the first filtrate. Specifically, a 3 mol / L ammonium carbonate solution is added at a calcium to carbonate molar ratio of 1:1. After the reaction, the mixture is filtered to obtain calcium carbonate as the filter residue. The remaining filtrate is evaporated and dried to obtain salt for calcium removal and lithium extraction, yielding calcium carbonate and lithium carbonate, respectively. The remaining filtrate can be evaporated and dried to obtain salt.

[0084] The acid leaching process in S8 is as follows: add 0.2 mol / L nitric acid with a liquid-to-solid ratio of 1 at a temperature of 90℃ and leach for 4 hours.

[0085] In Example 2, the recovery rate of C was 99.15% and the toner purity was 99.13%.

[0086] Example 3:

[0087] The implementation method is the same as in Example 1, except that:

[0088] The first reactant used in S2 is ammonium bicarbonate, and the second reactant is calcium carbonate. The mass ratio of the first reactant to the second reactant is 5:1, that is, the pre-prepared reactant is a mixed solvent of 20g ammonium bicarbonate and 10g calcium carbonate.

[0089] The mass ratio of the mixture to the first powder in S2 is 5:1, and the calcination temperature is 600℃, with a calcination time of 3h.

[0090] The liquid-to-solid ratio in the S5 leaching process is 40, the leaching time is 3 hours, and the leaching temperature is 45℃.

[0091] In this embodiment, based on the concentrations of calcium and lithium ions in the first filtrate in step S5, a soluble carbonate is added to the first filtrate. Specifically, a 3 mol / L ammonium bicarbonate solution is added at a calcium to carbonate molar ratio of 1:1. After the reaction, the mixture is filtered to obtain calcium carbonate as the filter residue. The remaining filtrate is evaporated and dried to obtain salt for calcium removal and lithium extraction, yielding calcium carbonate and lithium carbonate, respectively. The remaining filtrate can be evaporated and dried to obtain salt.

[0092] The acid leaching process in S8 is as follows: add 0.2 mol / L nitric acid with a liquid-to-solid ratio of 1 at a temperature of 90℃ and leach for 4 hours;

[0093] In Example 3, the recovery rate of C was 98.95% and the toner purity was 98.72%.

[0094] Example 4:

[0095] The implementation method is the same as in Example 1, except that:

[0096] The second reactant used in S2 is calcium nitrate. That is, the mass of the second reactant in S2 is 60g, the mass of the first powder is 20g, and the mass ratio of the second reactant to the first powder is 3:1.

[0097] In S5, the liquid-to-solid ratio during the leaching process is 40, the leaching time is 1 hour, and the leaching temperature is 90℃.

[0098] In this embodiment, based on the concentrations of calcium and lithium ions in the first filtrate in step S5, a soluble carbonate is added to the first filtrate. Specifically, a 3 mol / L potassium carbonate solution is added at a calcium to carbonate molar ratio of 1:1, and the reaction is carried out at 40°C for 1 hour. After the reaction, the mixture is filtered to obtain calcium carbonate as the filter residue. The remaining filtrate is evaporated and dried to obtain salt for calcium removal and lithium extraction, yielding calcium carbonate and lithium carbonate, respectively. The remaining filtrate can be evaporated and dried to obtain salt.

[0099] In Example 4, the recovery rate of C was 98.77% and the toner purity was 98.97%.

[0100] Example 5:

[0101] The implementation method is the same as in Example 1, except that:

[0102] The second reactant used in S2 is calcium hydroxide; that is, the mass of the second reactant in S2 is 140g, the mass of the first powder is 20g, and the mass ratio of the second reactant to the first powder is 7:1.

[0103] The liquid-to-solid ratio in the S5 leaching process is 5, the leaching time is 2 hours, and the leaching temperature is 110℃.

[0104] In this embodiment, based on the concentrations of calcium and lithium ions in the first filtrate in step S5, a soluble carbonate is added to the first filtrate. Specifically, 4 mol / L ammonium carbonate is added at a calcium to carbonate molar ratio of 1:1, and the reaction is carried out at 50°C for 1 hour. After the reaction, the mixture is filtered to obtain calcium carbonate as the filter residue. The remaining filtrate is evaporated and dried to obtain salt for calcium removal and lithium extraction, yielding calcium carbonate and lithium carbonate, respectively. The remaining filtrate can be evaporated and dried to obtain salt.

[0105] The liquid-to-solid ratio of the acid leaching process in S8 is 10, the reaction temperature is 55℃, and the time is 2.5h.

[0106] In Example 5, the recovery rate of C was 99.01% and the toner purity was 98.96%.

[0107] Example 6:

[0108] The implementation method is the same as in Example 1, except that:

[0109] S2, wherein the second reactant of the pre-prepared reactant is calcium oxide, which is 120g of mixed solvent, and the mass ratio of the second reactant to the first powder is 6:1;

[0110] In S5, the liquid-to-solid ratio during the leaching process is 60, the leaching time is 2 hours, and the leaching temperature is 60℃.

[0111] In this embodiment, based on the calcium and lithium ion concentrations in the first filtrate in step S5, a soluble carbonate is added to the first filtrate. Specifically, 8 mol / L ammonium bicarbonate is added at a calcium to carbonate molar ratio of 1:1, and the reaction is carried out at 40°C for 2 hours. After the reaction, the mixture is filtered to obtain calcium carbonate as the filter residue. The remaining filtrate is evaporated and dried to obtain salt for calcium removal and lithium extraction, yielding calcium carbonate and lithium carbonate, respectively. The remaining filtrate can be evaporated and dried to obtain salt.

[0112] The liquid-to-solid ratio of the acid leaching process in S8 is 14, the reaction temperature is 55℃, and the time is 2.5h.

[0113] In Example 6, the recovery rate of C was 99.33% and the toner purity was 99.06%.

[0114] Example 7:

[0115] The implementation method is the same as in Example 1, except that:

[0116] In S2, the mass of the second reactant calcium oxide in the pre-prepared reactant is 40g, the mass of the first powder is 20g, and the mass ratio of the second reactant to the first powder is 2:1.

[0117] The liquid-to-solid ratio in the S5 leaching process is 50, the leaching time is 3 hours, and the leaching temperature is 20℃.

[0118] In this embodiment, based on the calcium and lithium ion concentrations in the first filtrate in step S5, a soluble carbonate is added to the first filtrate. Specifically, 4 mol / L sodium carbonate is added at a calcium to carbonate molar ratio of 1:1, and the reaction is carried out at 20°C for 1 hour. After the reaction, the mixture is filtered to obtain calcium carbonate as the filter residue. The remaining filtrate is evaporated and dried to obtain salt for calcium removal and lithium extraction, yielding calcium carbonate and lithium carbonate, respectively. The remaining filtrate can be evaporated and dried to obtain salt.

[0119] The acid leaching process in S8 is as follows: add 0.2 mol / L hydrochloric acid with a liquid-to-solid ratio of 1:5 at 20℃ and leach for 4 hours.

[0120] In Example 7, the recovery rate of C was 99.02% and the toner purity was 98.88%.

[0121] Example 8:

[0122] The implementation method is the same as in Example 1, except that:

[0123] In S5, the liquid-to-solid ratio during the leaching process is 50, the leaching time is 8 hours, and the leaching temperature is 90℃.

[0124] In this embodiment, based on the calcium and lithium ion concentrations in the first filtrate in step S5, a soluble carbonate is added to the first filtrate. Specifically, 2 mol / L ammonium carbonate is added at a calcium to carbonate molar ratio of 1:1, and the reaction is carried out at 30°C for 3 hours. After the reaction, the mixture is filtered to obtain calcium carbonate as the filter residue. The remaining filtrate is evaporated and dried to obtain salt for calcium removal and lithium extraction, yielding calcium carbonate and lithium carbonate, respectively. The remaining filtrate can be evaporated and dried to obtain salt.

[0125] The acid leaching process in S8 is as follows: add 0.2 mol / L hydrochloric acid with a liquid-to-solid ratio of 1:10 at 30℃ and leach for 5 hours.

[0126] In Example 8, the recovery rate of C was 98.85% and the toner purity was 98.76%.

[0127] Example 9:

[0128] A method for recycling and processing waste cathodes from aluminum electrolysis, comprising the following steps:

[0129] S1. Take waste cathodes from an aluminum plant. The waste cathodes contain Na: 13.8wt%, Al: 6.6wt%, F: 16.3wt%, O: 9.6wt%, Si: 1.5wt%, Ca: 2.2wt%, C: 46.2wt%, and other components: 3.8wt%. Crush the waste cathodes and sieve out the particles with a particle size ≤200 mesh to make the first powder.

[0130] It should be noted that the purpose of crushing the waste cathode is to ensure a more complete reaction. Screening for particles with a size of 200 mesh or less facilitates subsequent reactions; the finer the particles, the more complete the reaction. Powder with a particle size greater than 200 mesh is returned to the powder processing unit for further processing.

[0131] S2. Take 10g of the first powder from S1, and add 30g of the pre-prepared reactant to the first powder to mix the first powder and the pre-prepared reactant to obtain a powder mixture. The pre-prepared reactant is a mixed solvent of 20g ammonium chloride and 10g calcium oxide, with 20g ammonium chloride serving as the first reactant and 10g calcium oxide serving as the second reactant. The two are mixed uniformly, with a mass ratio of the first reactant to the second reactant of 2:1.

[0132] S3. The powder mixture from S2 is calcined at a certain temperature to obtain the calcined product. Specifically, 10g of the first powder and 30g of the pre-prepared reactant are weighed and mixed evenly, with a mass ratio of the pre-prepared reactant to the first powder of 3:1. The mixture is then calcined at 650℃ for 2 hours. During the calcination process, the generated flue gas (ammonia) is passed into dilute hydrochloric acid to recover and form ammonium salt, which can be recycled as raw material for waste cathodes.

[0133] S4. The calcined product from S3 is crushed to produce a second powder. Then, in S5, the second powder from S4 is leached with water and filtered to obtain a first filtrate and a first filter residue. Specifically, the second powder is leached with water at a liquid-to-solid ratio of 10:1 at 50°C for 4 hours to obtain the first filter residue and the first filtrate. The first filter residue is treated with ultrasonic flotation to promote carbon separation, and the upper layer of foam is collected during flotation. S6. The carbon powder in the first filter residue from S5 is separated using an ultrasonic flotation device.

[0134] It should be noted that ultrasonic flotation uses an ultrasonic flotation device. The ultrasonic flotation time should be between 0.5h and 10h, and the power of the ultrasonic flotation device should be between 100W and 500W.

[0135] S7. After flotation in S6, the mixture is filtered. The remaining filtrate is filtered again to obtain a second filtrate, a second filter residue, and flotation residue. The collected foam is dried to obtain high-purity carbon powder. At this point, the carbon powder has been completely separated from the waste cathode.

[0136] Furthermore, the first filtrate, the second filtrate, and the second filter residue are each further processed and can all be utilized in a reasonable and sufficient manner.

[0137] In this embodiment, based on the concentrations of calcium and lithium ions in the first filtrate in step S5, a soluble carbonate is added to the first filtrate. Specifically, a 1 mol / L sodium carbonate solution is added at a calcium to carbonate molar ratio of 1:1. After the reaction, the solution is filtered to obtain calcium carbonate as the filter residue. The remaining filtrate is evaporated and dried to obtain salt for calcium removal and lithium extraction, yielding calcium carbonate and lithium carbonate, respectively. The remaining filtrate can be evaporated and dried to obtain salt.

[0138] Next, in step S8, 0.2 mol / L hydrochloric acid was added to the second filter residue after filtration in step S7 at a liquid-to-solid ratio of 5:1, and the mixture was acid-leached at 50°C for 1 hour. After filtration, the third filtrate and the third filter residue were obtained, wherein the third filter residue was calcium fluoride.

[0139] S9. Based on the calcium ion concentration of the third filtrate in S8, calcium is removed, and then the remaining filtrate is evaporated to obtain crystalline aluminum chloride.

[0140] In Example 9, the recovery rate of C was 97.68% and the toner purity was 97.09%.

[0141] Comparative Example 1:

[0142] A method for recycling and processing waste cathodes from aluminum electrolysis, comprising the following steps:

[0143] S1. Take waste cathodes from an aluminum plant. The waste cathodes contain Na: 13.8wt%, Al: 6.6wt%, F: 16.3wt%, O: 9.6wt%, Si: 1.5wt%, Ca: 2.2wt%, C: 46.2wt%, and other components: 3.8wt%. Crush the waste cathodes and sieve out the particles with a particle size ≤200 mesh to make the first powder.

[0144] It should be noted that the purpose of crushing the waste cathode is to ensure a more complete reaction. Screening for particles with a size of 200 mesh or less facilitates subsequent reactions; the finer the particles, the more complete the reaction. Powder with a particle size greater than 200 mesh is returned to the powder processing unit for further processing.

[0145] S2. Take 10g of the first powder from S1, and add 30g of the pre-prepared reactant to the first powder to mix the first powder and the pre-prepared reactant to obtain a powder mixture. The pre-prepared reactant is a mixed solvent of 20g ammonium chloride and 10g calcium oxide, with 20g ammonium chloride serving as the first reactant and 10g calcium oxide serving as the second reactant. The two are mixed uniformly, with a mass ratio of the first reactant to the second reactant of 2:1.

[0146] S3. The powder mixture from S2 is calcined at a certain temperature to obtain the calcined product. Specifically, 10g of the first powder and 30g of the pre-prepared reactant are weighed and mixed evenly, with a mass ratio of the pre-prepared reactant to the first powder of 3:1. The mixture is then calcined at 850℃ for 2 hours. During the calcination process, the generated flue gas (ammonia) is passed into dilute hydrochloric acid to recover and form ammonium salt, which can be recycled as raw material for waste cathodes.

[0147] S4. The calcined product from S3 is crushed to produce a second powder. Then, in S5, the second powder from S4 is leached with water and filtered to obtain a first filtrate and a first filter residue. Specifically, the second powder is leached with water at a liquid-to-solid ratio of 10:1 at 50°C for 4 hours to obtain the first filter residue and the first filtrate. The first filter residue is treated with ultrasonic flotation to promote carbon separation, and the upper layer of foam is collected during flotation. S6. The carbon powder in the first filter residue from S5 is separated using an ultrasonic flotation device.

[0148] It should be noted that ultrasonic flotation uses an ultrasonic flotation device. The ultrasonic flotation time should be between 0.5h and 10h, and the power of the ultrasonic flotation device should be between 100W and 500W.

[0149] S7. After flotation in S6, the mixture is filtered. The remaining filtrate is filtered again to obtain a second filtrate, a second filter residue, and flotation residue. The collected foam is dried to obtain high-purity carbon powder. At this point, the carbon powder has been completely separated from the waste cathode.

[0150] Furthermore, the first filtrate, the second filtrate, and the second filter residue are each further processed and can all be utilized in a reasonable and sufficient manner.

[0151] In this embodiment, based on the concentrations of calcium and lithium ions in the first filtrate in step S5, a soluble carbonate is added to the first filtrate. Specifically, a 1 mol / L sodium carbonate solution is added at a calcium to carbonate molar ratio of 1:1. After the reaction, the solution is filtered to obtain calcium carbonate as the filter residue. The remaining filtrate is evaporated and dried to obtain salt for calcium removal and lithium extraction, yielding calcium carbonate and lithium carbonate, respectively. The remaining filtrate can be evaporated and dried to obtain salt.

[0152] Next, in step S8, 0.2 mol / L hydrochloric acid was added to the second filter residue after filtration in step S7 at a liquid-to-solid ratio of 5:1, and the mixture was acid-leached at 50°C for 1 hour. After filtration, the third filtrate and the third filter residue were obtained, wherein the third filter residue was calcium fluoride.

[0153] S9. Based on the calcium ion concentration of the third filtrate in S8, calcium is removed, and then the remaining filtrate is evaporated to obtain crystalline aluminum chloride.

[0154] In Comparative Example 1, the recovery rate of C for the entire process was 90.68%, and the toner purity was 91.02%.

[0155] Comparative Example 2:

[0156] A method for recycling and processing waste cathodes from aluminum electrolysis, comprising the following steps:

[0157] S1. Take waste cathodes from an aluminum plant. The waste cathodes contain Na: 13.8wt%, Al: 6.6wt%, F: 16.3wt%, O: 9.6wt%, Si: 1.5wt%, Ca: 2.2wt%, C: 46.2wt%, and other components: 3.8wt%. Crush the waste cathodes and sieve out the particles with a particle size ≤200 mesh to make the first powder.

[0158] It should be noted that the purpose of crushing the waste cathode is to ensure a more complete reaction. Screening for particles with a size of 200 mesh or less facilitates subsequent reactions; the finer the particles, the more complete the reaction. Powder with a particle size greater than 200 mesh is returned to the powder processing unit for further processing.

[0159] S2. Take 10g of the first powder from S1, and add 30g of the pre-prepared reactant to the first powder to mix the first powder and the pre-prepared reactant to obtain a powder mixture. The pre-prepared reactant is a mixed solvent of 20g ammonium chloride and 10g calcium oxide, with 20g ammonium chloride serving as the first reactant and 10g calcium oxide serving as the second reactant. The two are mixed uniformly, with a mass ratio of the first reactant to the second reactant of 2:1.

[0160] S3. The powder mixture from S2 is calcined at a certain temperature to obtain the calcined product. Specifically, 10g of the first powder and 30g of the pre-prepared reactant are weighed and mixed evenly, with a mass ratio of the pre-prepared reactant to the first powder of 3:1. The mixture is then calcined at 900℃ for 3 hours. During the calcination process, the generated flue gas (ammonia) is passed into dilute hydrochloric acid to recover and form ammonium salt, which can be recycled as raw material for waste cathodes.

[0161] S4. The calcined product from S3 is crushed to produce a second powder. Then, in S5, the second powder from S4 is leached with water and filtered to obtain a first filtrate and a first filter residue. Specifically, the second powder is leached with water at a liquid-to-solid ratio of 10:1 at 50°C for 4 hours to obtain the first filter residue and the first filtrate. The first filter residue is treated with ultrasonic flotation to promote carbon separation, and the upper layer of foam is collected during flotation. S6. The carbon powder in the first filter residue from S5 is separated using an ultrasonic flotation device.

[0162] It should be noted that ultrasonic flotation uses an ultrasonic flotation device. The ultrasonic flotation time should be between 0.5h and 10h, and the power of the ultrasonic flotation device should be between 100W and 500W.

[0163] S7. After flotation in S6, the mixture is filtered. The remaining filtrate is filtered again to obtain a second filtrate, a second filter residue, and flotation residue. The collected foam is dried to obtain high-purity carbon powder. At this point, the carbon powder has been completely separated from the waste cathode.

[0164] Furthermore, the first filtrate, the second filtrate, and the second filter residue are each further processed and can all be utilized in a reasonable and sufficient manner.

[0165] In this embodiment, based on the concentrations of calcium and lithium ions in the first filtrate in step S5, a soluble carbonate is added to the first filtrate. Specifically, a 1 mol / L sodium carbonate solution is added at a calcium to carbonate molar ratio of 1:1. After the reaction, the solution is filtered to obtain calcium carbonate as the filter residue. The remaining filtrate is evaporated and dried to obtain salt for calcium removal and lithium extraction, yielding calcium carbonate and lithium carbonate, respectively. The remaining filtrate can be evaporated and dried to obtain salt.

[0166] Next, in step S8, 0.2 mol / L hydrochloric acid was added to the second filter residue after filtration in step S7 at a liquid-to-solid ratio of 5:1, and the mixture was acid-leached at 50°C for 1 hour. After filtration, the third filtrate and the third filter residue were obtained, wherein the third filter residue was calcium fluoride.

[0167] S9. Based on the calcium ion concentration of the third filtrate in S8, calcium is removed, and then the remaining filtrate is evaporated to obtain crystalline aluminum chloride.

[0168] In Example 1, the recovery rate of C was 93.25% and the toner purity was 92.87%.

[0169] As can be seen from the above embodiments, the recovery rate of C obtained in the process of Example 1 is relatively high. This indicates that when the calcination temperature is 550℃, the calcination time is 2 hours, the leaching solid-liquid ratio is 50, the leaching temperature is 20℃, and the leaching time is 3 hours, and during acid leaching, the leaching time is 4 hours and the leaching temperature is 20℃, C in the waste cathode can be efficiently recovered, and other elements can also be recovered. In other words, compared with the prior art, the carbon powder prepared by the method in this application has a significantly improved purity. Moreover, the recovery rate of C in the waste cathode is also relatively high.

[0170] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for recycling spent aluminum electrolysis cathodes, characterized in that: The method comprises the following steps: S1, crushing the waste cathode to obtain a first powder; S2, adding a pre-prepared reagent to the first powder in S1 to mix the first powder and the pre-prepared reagent to obtain a powder mixture, wherein the pre-prepared reagent is a mixed solvent of ammonium salt and calcium salt; S3, roasting the powder mixture in S2 at a certain temperature to obtain a roasting product; S4, crushing the roasting product in S3 to obtain a second powder; S5, adding the second powder in S4 to water for leaching and filtering to obtain a first filtrate and a first residue; S6, separating carbon powder in the first residue in S5 by using an ultrasonic flotation device; The ammonium salt is one or more of ammonium chloride, ammonium nitrate, ammonium carbonate, and ammonium bicarbonate; The calcium salt is one or more of calcium carbonate, calcium oxide, calcium hydroxide, calcium formate, and calcium propionate; In S3, the roasting temperature should be 200-650°C, and the roasting time should be 0.5-6h.

2. The recycling method of aluminum electrolysis spent cathode according to claim 1, characterized in that: According to the concentration of calcium ions and lithium ions in the first filtrate in S5, soluble carbonate is added to the first filtrate to remove calcium and extract lithium, respectively obtaining calcium carbonate and lithium carbonate, and the remaining filtrate can be evaporated and dried to obtain a salt.

3. The recycling method of aluminum electrolytic spent cathode according to claim 1, characterized in that: Further comprising the following steps: S7, filtering after flotation in S6 to obtain a second filtrate, a second residue, and a flotation residue; S8, adding an acid solution to the second residue in S7 for acid leaching, filtering after reaction to obtain a third filtrate and a third residue, wherein the third residue is calcium fluoride.

4. The recycling method of aluminum electrolytic spent cathode according to claim 3, characterized in that: Further comprising the following steps: S9, removing calcium according to the concentration of calcium ions in the third filtrate in S8, and then evaporating the remaining filtrate to obtain an aluminum salt.

5. The recycling method of aluminum electrolysis spent cathode according to claim 1, characterized in that: The mass mixing ratio of the first powder in S2 to the pre-prepared reagent in S2 should be 1:(1-10); The mass mixing ratio of the ammonium salt to the calcium salt of the pre-prepared reagent in S2 is 1:(1-10).

6. The recycling method of aluminum electrolytic spent cathode according to claim 1, characterized in that: In the leaching process in S5, the liquid-solid ratio should be between 5 and 80, the leaching temperature is 30-120°C, and the leaching time should be 0.5-10h.

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