A method for efficient leaching of lithium and aluminum from aluminum electrolysis solid waste and preparation of high-grade CaF2

Abstract

The application discloses a method for efficiently leaching lithium and aluminum in aluminum electrolysis solid waste and preparing high-grade CaF2, and belongs to the technical field of solid waste resource recovery, and solves the problems of low aluminum and lithium leaching rate in the alkali process, HF pollution and fluorine resource loss in the acid process, long process flow and high cost in the prior art. The method comprises the following steps: crushing, grinding and screening aluminum electrolysis solid waste blocks to obtain aluminum electrolysis solid waste powder A; uniformly mixing the aluminum electrolysis solid waste powder A with reaction accessories to obtain material B; preparing an alkali solution, adding the material B into the alkali solution, uniformly stirring, and adding into an alkali-resistant reaction device for reaction; after the reaction is completed, filtering the material to obtain filter residue and filtrate, and the filtrate can be used for aluminum and lithium recovery; using a low-concentration inorganic acid solution to perform pickling and impurity removal on the filter residue obtained in step 4, filtering, drying the filter cake, and obtaining high-grade CaF2. The method has high aluminum and lithium leaching rate and high calcium fluoride purity.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource recycling technology, and in particular to a method for efficient leaching of lithium aluminum from aluminum electrolysis solid waste and preparation of high-grade CaF2. Background Technology

[0002] Lithium has important applications in modern industry and technology, especially as an electrode material for high-energy-density batteries, with increasing use in portable electronic devices, electric vehicles, and grid energy storage systems. China is the world's largest lithium consumer, accounting for over 70% of global consumption in 2022. China is also the world's largest lithium battery producer, accounting for over 80% of global production. Despite abundant lithium reserves, China's supply and demand situation remains tight. China's self-sufficiency rate for lithium resources is relatively low, relying heavily on imports, which to some extent restricts the stable supply of lithium resources.

[0003] Fluorite is a scarce, non-renewable resource with a wide range of applications. Besides traditional sectors like steel, electrolytic aluminum, and cement, fluorite consumption accounts for as much as 52% of the total in the fluorochemical industry. Since 2018, global fluorite production has been on the rise. Demand for acid-grade fluorite concentrate and high-grade fluorite is particularly strong, with supply falling short of demand. In March 2022, six departments, including the Ministry of Industry and Information Technology, jointly issued the "Guiding Opinions on Promoting High-Quality Development of the Petrochemical Industry during the 14th Five-Year Plan Period," encouraging the development and utilization of associated fluorine resources.

[0004] Lithium-containing alumina is used as a raw material in the electrolytic aluminum production process. Lithium accumulates continuously in the electrolyte, causing significant changes in its composition and physicochemical properties. When the lithium content exceeds the standard, a portion of the electrolyte needs to be replaced, resulting in a certain amount of waste aluminum electrolyte containing more than 2% lithium. This waste aluminum electrolyte has a simple phase composition and high fluorine content, making it an important secondary fluorine resource.

[0005] Currently, the main treatment processes for waste aluminum electrolytes include alkaline / acid leaching and leaching after roasting. CN112919507B provides a method for extracting lithium salts from electrolytes, utilizing multiple alkaline leaching, acid leaching, and lithium carbonate precipitation to obtain high-grade cryolite and lithium carbonate; CN117430144A provides a green acid leaching method for the resource utilization of waste aluminum electrolytes, achieving lithium extraction and recovery by adding sodium salt to a medium-concentration acid solution; CN114890447B provides a method for directly preparing aluminum fluoride without roasting using aluminum electrolytes as raw materials, obtaining aluminum fluoride by adding aluminum salts for high-energy ball milling, followed by water washing and filtration. Existing technologies primarily employ alkaline leaching, acid leaching (or acid leaching with the addition of aluminum or sodium salts), and acid leaching after roasting. However, most of these methods focus on lithium extraction. Fluorine recovery during acid leaching often results in the release of harmful and highly corrosive HF gases, causing environmental pollution and wasting fluorine resources. In alkaline extraction, due to the dissolution of cryolite and the slight solubility of LiF, the leaching rate of aluminum and lithium is generally low, and the leaching residue contains both cryolite and aluminum fluoride phases, making recycling difficult. Furthermore, existing processes are often characterized by long workflows and high costs. Summary of the Invention

[0006] In view of the above, the present invention aims to provide a method for efficient leaching of lithium and aluminum from aluminum electrolysis solid waste and preparation of high-grade CaF2, in order to solve one of the following technical problems: low aluminum and lithium leaching rate in alkaline process, HF pollution and fluorine resource loss in acid process, long process flow and high cost.

[0007] The objective of this invention is mainly achieved through the following technical solutions:

[0008] This invention provides a method for efficient leaching of lithium aluminum from aluminum electrolysis solid waste and preparation of high-grade CaF2, comprising the following steps:

[0009] Step 1: Crush, grind, and screen the aluminum electrolysis solid waste blocks to obtain aluminum electrolysis solid waste powder A;

[0010] Step 2: Mix aluminum electrolysis solid waste powder A with reaction auxiliary materials evenly to obtain material B;

[0011] Step 3: Prepare the alkaline solution. Add material B to the alkaline solution, stir evenly, and then add it to the alkali-resistant reaction device for reaction.

[0012] Step 4: After the reaction is complete, the material is filtered to obtain filter residue and filtrate. The filtrate can be used for aluminum-lithium recovery.

[0013] Step 5: Use a low-concentration inorganic acid solution to acid wash and remove impurities from the filter residue obtained in step 4, filter, and dry the filter cake to obtain high-grade CaF2.

[0014] Furthermore, in step 1, the aluminum electrolysis solid waste is the solid waste generated during the aluminum electrolysis process, and its main component is cryolite.

[0015] Furthermore, solid waste from aluminum electrolysis includes at least one of the solid wastes generated during the aluminum electrolysis process, such as waste aluminum electrolyte, aluminum electrolysis overhaul slag, and carbon powder.

[0016] Furthermore, in step 2, the reaction excipient is one that can provide Ca. 2+ Calcium-containing substances.

[0017] Furthermore, in step 2, the reaction excipient is at least one of CaO, CaCl2, CaF2, Ca(OH)2, Ca(NO3)2 and their hydrates.

[0018] Furthermore, in step 2, the mass ratio of the reaction auxiliary material to aluminum electrolysis solid waste powder A is 0.7 to 0.9:1.

[0019] Furthermore, in step 3, the concentration of the alkaline solution is 20–160 g / L.

[0020] Furthermore, in step 3, the liquid-to-solid ratio of the alkaline solution to material B is in the range of (4-15 mL): 1 g.

[0021] Furthermore, in step 3, the reaction temperature of material B reacting with the alkaline solution is 120–200°C.

[0022] Furthermore, in step 3, the stirring speed is 200–500 rpm.

[0023] Furthermore, in step 5, the pH range of the solution during the acid washing process is 3 to 6.

[0024] This invention also provides a method for efficient and comprehensive recycling of solid waste from aluminum electrolysis, the method comprising steps 1 to 5 of the above method, and further comprising:

[0025] Step 5b: Extract the filtrate obtained in step 4 using an organic solvent extractant to obtain a loaded organic phase and raffinate;

[0026] Step 6a: Back-extract the supported organic phase obtained in step 5b to obtain a lithium-containing solution;

[0027] Step 6b: Add reaction excipients to the raffinate obtained in step 5b, stir evenly and react, let stand for a period of time, filter and separate to obtain calcium aluminate precipitate.

[0028] Step 7: Add more reaction excipients to the filtrate obtained in step 6b, stir evenly, let stand, and then filter to separate.

[0029] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0030] a) In the method for efficient leaching of lithium and aluminum from aluminum electrolysis solid waste and preparation of high-grade CaF2 of the present invention, under the action of reaction additives, the main cryolite phase in the aluminum electrolysis solid waste is rapidly decomposed in an alkaline solution. The strong coordination precipitation between calcium ions in the reaction additives and cryolite, resulting in fluoride ions, promotes the rapid conversion of fluoride ions entering the solution through alkaline leaching into CaF2 and their precipitation, avoiding coordination precipitation of fluoride ions with aluminum and lithium, thereby achieving efficient leaching of aluminum and lithium. Compared with existing alkaline leaching processes, the present invention achieves efficient leaching of aluminum and lithium through the addition of additives. While electrolytic solid waste dissolves in an alkaline solution, the fluoride ions generated after dissolution react directly with calcium ions to precipitate and remove the waste, avoiding the loss of valuable components such as Li / Al due to the complexation and precipitation of fluoride ions. Compared with existing alkaline roasting or calcium-added alkaline roasting-leaching processes, the method of this invention achieves the reaction process of cryolite dissolution and CaF2 formation in aluminum electrolytic solid waste in one step, avoiding problems such as low lithium-aluminum leaching rates caused by incomplete reactions, poorly dissolved LiF, and the encapsulation of Li / Al components by CaF2 formed during roasting. The method of this invention has a short process flow, low energy consumption, high aluminum-lithium leaching rate, and high calcium fluoride purity; the content of impurities such as fluoride / calcium in the solution is low, and the subsequent recovery of aluminum-lithium from the aluminum-lithium leaching solution is simple and easy to implement.

[0031] (b) In the method of the present invention for efficient leaching of lithium aluminum from aluminum electrolysis solid waste and preparation of high-grade CaF2, the leaching under alkaline system and the calcification transformation of fluoride ions avoid the overflow loss and dispersion of fluoride as HF gas compared with the acid roasting / leaching system. The fluoride in the aluminum electrolysis solid waste is basically converted into calcium fluoride, and the fluoride recovery rate is high. Compared with the existing alkaline leaching and alkaline roasting-leaching process technologies, by controlling the alkaline leaching process, the efficient dissolution of aluminum electrolysis solid waste can be achieved, and the control of the calcium fluoride precipitation process can make the produced calcium fluoride slag high in grade and low in impurities. After acid washing and impurity removal, it can reach a grade of 98 wt.%, which has higher value.

[0032] c) In the method for efficient and comprehensive recycling of aluminum electrolytic solid waste of the present invention, the main process is carried out in an alkaline system. The obtained alkaline lithium-containing solution is compatible with the lithium solution extraction system. Compared with acidic leaching and the extraction of the leachate after adjusting it to alkalinity, the method of the present invention does not require a large range of changes in the solution pH. The extraction process is easy to implement and the lithium extraction recovery rate is high. After adding reaction auxiliary materials to the raffinate, on the one hand, the aluminum can be efficiently removed and recovered through the coordination precipitation of calcium ions and aluminate ions, and high-purity calcium aluminate products can be prepared. On the other hand, it is also beneficial to improve the alkalinity of the raffinate. After the aluminum precipitation liquid is treated with reaction auxiliary materials, the alkaline solution can be concentrated in a non-evaporation manner to obtain a qualified alkaline solution. The energy consumption is low and the operation is easy. The obtained Ca(OH)2 can be used as a reaction auxiliary material in step 2.

[0033] d) The method for efficient and comprehensive recycling of aluminum electrolysis solid waste of the present invention has a short process flow and low energy consumption. Through the method of the present invention, multiple components such as fluorine, lithium, aluminum, and sodium in aluminum electrolysis solid waste are recovered in a stepwise and efficient manner, with a high comprehensive utilization rate.

[0034] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of what is particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0035] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0036] Figure 1 This is a process flow diagram for Example 1.

[0037] Figure 2 The image shows the XRD pattern of the filter residue from the alkaline leaching process in Example 1.

[0038] Figure 3 The aluminum-lithium leaching rate in Example 1;

[0039] Figure 4 The image shows the XRD pattern of the filter residue from the alkaline leaching process in Comparative Example 2. Detailed Implementation

[0040] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of the present invention and, together with the embodiments of the present invention, serve to illustrate the principles of the present invention.

[0041] This invention provides a method for efficient leaching of lithium aluminum from aluminum electrolysis solid waste and preparation of high-grade CaF2, comprising the following steps:

[0042] Step 1: Crush, grind, and screen the aluminum electrolysis solid waste blocks to obtain aluminum electrolysis solid waste powder A;

[0043] Step 2: Mix aluminum electrolysis solid waste powder A with reaction auxiliary materials evenly to obtain material B;

[0044] Step 3: Prepare the alkaline solution. Add material B to the alkaline solution, stir evenly, and then add it to the alkali-resistant reaction device for reaction.

[0045] Step 4: After the reaction is complete, the material is filtered to obtain filter residue and filtrate. The filtrate can be used for aluminum-lithium recovery.

[0046] Step 5: Use a low-concentration inorganic acid solution to acid wash and remove impurities from the filter residue obtained in step 4, filter, and dry the filter cake to obtain high-grade CaF2.

[0047] In one specific implementation, in step 1, the aluminum electrolysis solid waste is solid waste generated during the aluminum electrolysis process, and its main component is cryolite.

[0048] For example, solid waste from aluminum electrolysis includes at least one of the solid wastes generated during the aluminum electrolysis process, such as waste aluminum electrolyte, aluminum electrolysis overhaul slag, and carbon powder.

[0049] For example, the lithium content in aluminum electrolysis solid waste is 0.5–7 wt.%.

[0050] In one specific implementation, in step 1, considering that if the particle size of aluminum electrolysis solid waste powder A is too large, the leaching process will be inefficient and will result in low lithium aluminum leaching; if the particle size is too small, the material will easily clump together during the leaching process; therefore, the aluminum electrolysis solid waste block is crushed, ground and screened to obtain aluminum electrolysis solid waste powder A with a particle size ≤74μm.

[0051] In one specific implementation, in step 2, the reaction excipient is a substance that can provide Ca. 2+ The calcium-containing substances, such as reaction excipients, are at least one of CaO, CaCl2, CaF2, Ca(OH)2, Ca(NO3)2 and their hydrates. For example, the reaction excipients are one of CaO, Ca(OH)2, CaCl2, CaF2, or CaO+Ca(OH)2, CaO+CaCl2, CaO+CaF2, or CaO+CaCl2+CaF2.

[0052] It should be noted that the main purpose of the added reaction excipients is to provide CaO that combines with fluoride ions during the alkaline leaching process. 2+ This allows fluoride ions dissolved in the solution to be rapidly converted into calcium fluoride precipitate, reducing the concentration of fluoride ions in the solution and further promoting the alkaline leaching and dissolution of waste aluminum electrolytes. Calcium salts that can achieve this purpose are all within this protection range.

[0053] Compared with the prior art, the method of the present invention promotes the conversion of fluoride ions generated from the dissolution of aluminum electrolysis solid waste into CaF2 by adding reaction excipients. On the one hand, it further promotes the dissolution of aluminum electrolysis solid waste, and on the other hand, it can effectively avoid the formation of coordination precipitates between fluoride ions and dissolved aluminum, lithium and other materials, which would affect the leaching rate of aluminum and lithium. Using the method of the present invention, the efficient recovery of fluoride resources can be effectively achieved, avoiding problems such as fluoride dispersion and insufficient purity of the precipitate products.

[0054] In one specific implementation, in step 2, the mass ratio of the reaction auxiliary material to aluminum electrolysis solid waste powder A is 0.7 to 0.9:1, for example, the mass ratio is 0.7:1, 0.8:1, or 0.9:1.

[0055] It should be noted that when the mass ratio of the reaction auxiliary material to the aluminum electrolysis solid waste powder is low, not all the fluorine in the aluminum electrolysis solid waste can be converted into CaF2, which will reduce the lithium aluminum leaching rate and the fluorine recovery rate. When the mass ratio is high, the reaction auxiliary material will not react completely and will enter the calcium fluoride slag, affecting its grade. Therefore, the mass ratio of the reaction auxiliary material to the aluminum electrolysis solid waste powder A should be controlled at 0.7 to 0.9:1.

[0056] In one specific embodiment, in step 3, the alkaline solution is prepared using at least one of NaOH and KOH, preferably using NaOH, and the concentration of the alkaline solution is 20-160 g / L. For example, the concentrations of the alkaline solution are 30 g / L, 40 g / L, 60 g / L, 80 g / L, 100 g / L, 120 g / L, and 140 g / L.

[0057] It should be noted that when the concentration of the alkaline solution is too low, the solid waste from aluminum electrolysis will not dissolve completely; when the concentration of the alkaline solution is too high, the added calcium salt may have difficulty entering the solution; both of these will result in a low lithium-aluminum leaching rate. Therefore, the concentration of the alkaline solution should be controlled between 20 and 160 g / L. Preferably, the concentration of the alkaline solution is 40 to 100 g / L.

[0058] In one specific embodiment, in step 3, the liquid-to-solid ratio of the alkaline solution to material B ranges from (4 to 15 mL): 1 g; for example, the liquid-to-solid ratios are 5 mL: 1 g, 10 mL: 1 g, and 13 mL: 1 g.

[0059] It should be noted that if the liquid-to-solid ratio is too high, the single-batch processing capacity of the same volume reaction vessel will be reduced; if the liquid-to-solid ratio is too low, it will result in a high density of mixed slurry, slow solid-liquid reaction, and insufficient reactants in the alkaline solution. Therefore, the liquid-to-solid ratio of the alkaline solution to material B should be controlled within the range of (4-15 mL):1 g.

[0060] In one specific embodiment, in step 3, material B reacts with an alkaline solution at a reaction temperature of 120–200°C, a reaction time of 0.5–2 hours, and a stirring speed of 200–500 rpm; for example, the reaction temperatures are 130°C, 150°C, 170°C, and 190°C; the reaction times are 0.6 hours, 1.0 hours, 1.5 hours, and 1.8 hours; and the stirring speeds are 250 rpm, 300 rpm, 350 rpm, 400 rpm, and 450 rpm.

[0061] It should be noted that if the reaction temperature is below this range, the aluminum electrolysis solid waste is difficult to dissolve in the alkaline solution, and the reaction kinetics are limited. If the temperature is too high, energy consumption and reaction vessel pressure will be high. If the stirring speed is below this range, the solution will cause CaF2 precipitation, which will coat the unreacted aluminum electrolysis solid waste, thus hindering the leaching reaction. If the stirring speed is too high, vortices will easily form, which will not achieve the desired mixing effect. If the reaction time is below this range, the reaction will be incomplete. If it is above this range, the reaction efficiency will be limited. Therefore, the reaction temperature should be controlled at 120–200℃, the reaction time at 0.5–2 hours, and the stirring speed at 200–500 rpm.

[0062] In one specific embodiment, in step 5, the filter residue obtained in step 4 is acid-washed with an inorganic acid solution. The inorganic acid solution is prepared from at least one of hydrochloric acid and nitric acid, preferably hydrochloric acid. The pH range of the solution during acid washing is 3 to 6. For example, the pH of the solution is 3, 4, 4.5, 5, or 5.5.

[0063] It should be noted that, considering economic costs, concentrated hydrochloric acid is preferred for preparing the acid solution. The acid washing process mainly uses the acid solution to remove unreacted auxiliary materials such as CaO / Ca(OH)2 from the filter residue. If the solution pH is too low, it may cause CaF2 dissolution loss. If the solution pH is too high, it will cause incomplete removal of CaO / Ca(OH)2, affecting the purity of CaF2. Therefore, the pH range of the solution during the acid washing process should be controlled between 3 and 6.

[0064] This invention also provides a method for efficient and comprehensive recycling of solid waste from aluminum electrolysis, the method comprising steps 1 to 5 of the above method, and further comprising:

[0065] Step 5b: Extract the filtrate obtained in step 4 using an organic solvent extractant to obtain a loaded organic phase and raffinate;

[0066] Step 6a: Back-extract the supported organic phase obtained in step 5b to obtain a lithium-containing solution;

[0067] Step 6b: Add reaction excipients to the raffinate obtained in step 5b, stir evenly and react, let stand for a period of time, filter and separate to obtain calcium aluminate precipitate.

[0068] Step 7: Add more reaction excipients to the filtrate obtained in step 6b, stir evenly, let stand, and then filter to separate.

[0069] In one specific embodiment, in step 5b, the organic solvent extractant is mainly a mixed solvent composed of phosphate ester organic reagents, ketone organic reagents and sulfonated kerosene.

[0070] In a specific embodiment, in step 5b, the organophosphate organic reagent includes at least one of tributyl phosphate, trioctyl phosphate, trialkyl phosphonate, trioctylphosphine oxide and the like; the ketone organic reagent includes at least one of β-diketone, trifluorodimethylhexanedione and the like, and the molar concentration ratio of the organophosphate organic reagent to the ketone organic reagent is 0.5:0.1 to 0.1:0.5.

[0071] In a specific embodiment, in step 5b, the pH value of the filtrate from step 4 is controlled to be 12.5<pH<14, the volume ratio of the organic solvent extractant to the filtrate is 1:20 to 1:1, the oscillation time is 5 to 30 min, and the temperature is 10 to 40°C. Exemplarily, the pH is 12.5, 13, 13.5, 14, the volume ratio of the organic solvent extractant to the filtrate is 1:15, 1:10, 1:5, 1:2, the oscillation time is 10 min, 15 min, 20 min, 25 min, and the temperature is 15°C, 20°C, 25°C, 30°C, 35°C.

[0072] It should be noted that the ketone organic reagent has a selective chelating effect on lithium in the solution, while the neutral phosphorus-based organic reagent as a strong electron donor can enhance the selective stability of the extraction complex. Meanwhile, the extraction process is also affected by the organic phase concentration, solution pH value, organic phase / aqueous phase volume ratio O / A, oscillation time and temperature. In order to ensure complete extraction of lithium in the solution and avoid waste of organic reagents, the molar ratio of the organophosphate to the ketone organic phase is controlled to be 0.5:0.1 to 0.1:0.5.

[0073] In a specific embodiment, in step 6a, the stripping reagent is one of inorganic acids such as nitric acid, hydrochloric acid, sulfuric acid, carbonic acid, and the hydrogen ion concentration in the stripping reagent is controlled to be 1 to 6 mol / L.

[0074] In a specific embodiment, in step 6a, during stripping, the volume ratio of the loaded organic phase to the stripping reagent is 2:1 to 15:1, preferably 5:1 to 10:1.

[0075] It should be noted that, considering the comprehensive utilization efficiency and cost of the acid for stripping, as well as subsequent problems such as organic phase regeneration, hydrochloric acid is preferably used as the stripping reagent, and the hydrogen ion concentration is controlled to be 1 to 6 mol / L. Preferably, the hydrogen ion concentration of the hydrochloric acid solution is 4 mol / L. In addition, to ensure normal phase separation and operation during the stripping process, the volume ratio of the organic phase to the aqueous phase in stripping is 2:1 to 15:1, and preferably, the volume ratio of the organic phase to the aqueous phase in stripping is 10:1.

[0076] In a specific embodiment, in step 6a, after the lithium-containing solution is concentrated, the lithium ion concentration reaches 20 g / L or more, and sodium carbonate is added for lithium precipitation to obtain lithium carbonate.

[0077] In one specific embodiment, in step 6b, the reaction excipient is at least one of CaO and Ca(OH)2, preferably Ca(OH)2.

[0078] In one specific implementation, in step 6b, the theoretical amount is the mass of reaction excipients calculated based on the aluminum concentration in the solution and the molecular formula of calcium aluminate precipitate.

[0079] In one specific embodiment, in step 6b, the amount added is 1 to 1.5 times the theoretical amount, for example, 1, 1.3, or 1.5 times. It should be noted that although CaO can precipitate the aluminum component in the raffinate, the addition of CaO will increase the alkalinity of the solution, which is not conducive to the reaction process. Therefore, Ca(OH)2 is preferred as the reaction excipient. The reaction temperature is 20 to 80°C, the stirring speed is 200 to 500 rpm, the reaction time is 0.5 to 2 hours, and the standing time is 0.5 to 1 hour. For example, the reaction temperature is 20°C, 40°C, 60°C, or 80°C; the reaction time is 1 hour or 1.5 hours; and the stirring speed is 250 rpm, 300 rpm, 350 rpm, 400 rpm, or 450 rpm.

[0080] In one specific embodiment, in step 6b, the pickling uses HCl and HNO3 solutions with a pH of 2-5; preferably, HCl solution is used. It should be noted that, considering economic costs, concentrated hydrochloric acid is preferred for the acid solution. The pickling process mainly uses the acid solution to remove the unreacted Ca(OH)2 auxiliary material from the filter residue. If the solution pH is too low, it may cause the dissolution loss of calcium aluminate; if the solution pH is too high, it will cause incomplete removal of Ca(OH)2, affecting the purity of calcium aluminate. Therefore, the pH range of the solution during the pickling process is controlled to be 2-5.

[0081] In one specific implementation, in step 7, the reaction excipient is CaO.

[0082] Example 1

[0083] This embodiment provides a method for efficient leaching of lithium aluminum from aluminum electrolysis solid waste and preparation of high-grade CaF2. The aluminum electrolysis solid waste in this embodiment is waste aluminum electrolyte. The process flow diagram of this embodiment is shown below. Figure 1 As shown, it includes the following steps:

[0084] Waste aluminum electrolyte blocks were crushed, ground, and sieved to obtain waste aluminum electrolyte powder with a particle size ≤74μm. CaO, a reaction auxiliary material, was mixed with the waste aluminum electrolyte powder at a mass ratio of 0.8:1. NaOH solutions of 20g / L, 40g / L, 60g / L, 80g / L, 100g / L, and 160g / L were prepared. The mixed material was stirred with the NaOH solution at a liquid-to-solid ratio of 10mL:1g and placed in an alkali-resistant reactor. The reaction was carried out at 180℃ and 300rpm for 1.0 hour. After the reaction, the material was filtered to obtain filter residue and filtrate. The filter residue was acid-washed with low-concentration hydrochloric acid to remove impurities, maintaining the solution pH at 4.5. After filtration, the filter cake was dried to obtain high-grade calcium fluoride. The results of lithium-aluminum leaching rate, final fluorine recovery rate, and calcium fluoride content during the leaching process are shown in Table 1. Figure 2 The image shows the XRD pattern of the filter residue from the alkaline leaching process in Example 1. Figure 3 The figure represents the leaching rate of aluminum and lithium in Example 1. It should be noted that the alkali concentration not only significantly affects the leaching rate of aluminum and lithium, but also has a relatively significant impact on the fluorine recovery rate and the purity of calcium fluoride in the calcium fluoride product. As the alkali concentration increases, the leaching rate of aluminum and lithium first increases and then decreases, and the fluorine recovery rate and calcium fluoride content also show this trend. This is because the alkali concentration affects the solubility of the reaction excipients in water, thereby affecting the dissolution of cryolite in the waste aluminum electrolyte, thus having a corresponding impact on the above indicators.

[0085] In this embodiment, the aluminum-lithium leaching rate is high, and the obtained calcium fluoride product has high purity. For example, the lithium leaching rate is above 74% (e.g., 74.3% to 95.2%), the aluminum leaching rate is above 76% (e.g., 76.4% to 96.2%), the fluorine recovery rate is above 78% (e.g., 78.3% to 98.4%), and the purity of the calcium fluoride product is above 85% (e.g., 85.4% to 98.8%). When the purity of calcium fluoride reaches above 80%, it has high economic value. When it reaches above 98%, it can be used as a raw material for the production of electronic-grade HF, belonging to high-quality CaF2 products.

[0086] Table 1 Results of each process under different alkali concentrations

[0087] 20 74.3 86.1 92.1 87.2 40 93.3 95.4 98.4 95.1 60 95.2 96.2 98.3 98.8 80 94.6 95.6 96.2 96.7 100 94.5 93.2 91.3 91.5 160 86.5 76.4 78.3 85.4

[0088] Example 2

[0089] This embodiment provides a method for efficient leaching of lithium aluminum from aluminum electrolysis solid waste and preparation of high-grade CaF2. The aluminum electrolysis solid waste in this embodiment is waste aluminum electrolyte, and the method includes the following steps:

[0090] Waste aluminum electrolyte blocks were crushed, ground, and sieved to obtain waste aluminum electrolyte powder with a particle size ≤74μm. The reaction auxiliary materials CaO, Ca(OH)₂, CaCl₂, CaO+Ca(OH)₂, CaO+CaCl₂, CaO+CaF₂, and CaO+CaCl₂+CaF₂ were mixed with the waste aluminum electrolyte powder at a mass ratio of 0.8:1. A 60g / L NaOH solution was prepared, and the mixed material was stirred with the NaOH solution at a liquid-to-solid ratio of 10mL:1g. The mixture was then placed in an alkali-resistant reactor and reacted at 200℃ with stirring at 500rpm for 2.0 hours. After the reaction, the material was filtered to obtain filter residue and filtrate. The filter residue was acid-washed with low-concentration hydrochloric acid to remove impurities, maintaining the solution pH at 6.0. After filtration, the filter cake was dried to obtain high-grade calcium fluoride. The results of lithium-aluminum leaching rate, final fluorine recovery rate, and calcium fluoride content during the leaching process are shown in Table 2. It should be noted that different reaction excipients can all provide Ca in the alkaline leaching system. 2+ This process promotes the leaching of lithium aluminum and achieves the conversion of fluoride ions into CaF2. Therefore, various types of reaction excipients can achieve good reaction results. In this embodiment, the lithium aluminum leaching rate is high, and the obtained calcium fluoride product has high purity, for example, the purity of calcium fluoride reaches over 97%, which is a high-quality CaF2 product.

[0091] In this embodiment, the lithium leaching rate is above 93% (e.g., 93.1% to 95.3%), the aluminum leaching rate is above 94% (e.g., 94.7% to 96.7%), the fluorine recovery rate is above 97% (e.g., 97.8% to 98.5%), and the purity of the calcium fluoride product is above 97% (e.g., 97.6% to 98.8%).

[0092] Table 2 Results of each process under different reaction excipient conditions

[0093] CaO 95.2 96.2 98.3 98.8 <![CDATA[Ca(OH)2]]> 94.2 96.0 98.1 98.5 <![CDATA[CaCl2]]> 93.1 94.7 99.2 97.8 <![CDATA[CaO+Ca(OH)2]]> 95.1 96.4 98.5 98.6 <![CDATA[CaO+CaCl2]]> 95.0 95.7 97.8 98.5 <![CDATA[CaO+CaF2]]> 95.3 96.7 98.4 97.9 <![CDATA[CaO+CaCl2+CaF2]]> 94.8 96.1 98.4 97.6

[0094] Example 3

[0095] This embodiment provides a method for efficient leaching of lithium aluminum from aluminum electrolysis solid waste and preparation of high-grade CaF2. The aluminum electrolysis solid waste in this embodiment is waste aluminum electrolyte, and the method includes the following steps:

[0096] Waste aluminum electrolyte blocks were crushed, ground, and sieved to obtain waste aluminum electrolyte powder with a particle size ≤74μm. The reaction auxiliary material CaO+Ca(OH)2+CaF2 was mixed with the waste aluminum electrolyte powder at mass ratios of 0.7:1, 0.8:1, and 0.9:1. A 60g / L KOH solution was prepared, and the mixed material was stirred with the KOH solution at a liquid-to-solid ratio of 15mL:1g. The mixture was then placed in an alkali-resistant reactor and reacted at 180℃ with stirring at 200rpm for 0.5 hours. After the reaction, the material was filtered to obtain filter residue and filtrate. The filter residue was acid-washed with low-concentration hydrochloric acid to remove impurities, maintaining the solution pH at 3.0. After filtration, the filter cake was dried to obtain high-grade calcium fluoride. The results of lithium-aluminum leaching rate, final fluorine recovery rate, and calcium fluoride content during the leaching process are shown in Table 3. It should be noted that when the mass ratio is 0.7:1, the calcium ions provided by the reaction excipients are slightly lower than the theoretical requirement, resulting in a slightly lower aluminum-lithium leaching rate. Some fluoride ions enter the solution, leading to a slightly lower recovery rate. Additionally, some cryolite remains undissolved during the alkaline leaching process, resulting in a slightly lower CaF2 content. When the reaction excipient ratio reaches 0.8:1, the aluminum-lithium leaching rate is consistently higher. In this embodiment, the aluminum-lithium leaching rate is high, and the obtained calcium fluoride product has a high purity, for example, 92.1%–98.8%, which is considered a high-quality CaF2 product.

[0097] In this embodiment, the lithium leaching rate is above 89% (e.g., 89.3% to 96.2%), the aluminum leaching rate is above 91% (e.g., 91.4% to 97.9%), and the fluorine recovery rate is above 94% (e.g., 94.3% to 99.0%).

[0098] Table 3 Results of each process under different mass ratios of reaction additives and waste aluminum electrolyte powder.

[0099] 0.7:1 89.3 91.4 94.3 92.1 0.8:1 95.7 95.9 98.6 98.6 0.9:1 96.9 90.4 98.5 98.2

[0100] Example 4

[0101] This embodiment provides a method for efficient leaching of lithium aluminum from aluminum electrolysis solid waste and preparation of high-grade CaF2. The aluminum electrolysis solid waste in this embodiment is waste aluminum electrolyte, and the method includes the following steps:

[0102] Waste aluminum electrolyte blocks were crushed, ground, and sieved to obtain waste aluminum electrolyte powder with a particle size ≤74μm. The reaction auxiliary material CaO+Ca(OH)2 was mixed evenly with the waste aluminum electrolyte powder at a mass ratio of 0.8:1. A 60g / L NaOH+KOH mixed solution was prepared. The evenly mixed material was stirred with the alkaline solution at a liquid-to-solid ratio of 4mL:1g and placed in an alkali-resistant reactor. The reaction was carried out at 180℃ and 300rpm for 1.0 hour. After the reaction, the material was filtered to obtain filter residue and filtrate. The filter residue was acid-washed with low-concentration hydrochloric acid to remove impurities, maintaining the solution pH at 4.5. After filtration, the filter cake was dried to obtain high-grade calcium fluoride. The lithium and aluminum leaching rates were 84.1% and 86.7%, respectively, the fluorine recovery rate was 90.2%, and the CaF2 content was 84.6%. It should be noted that when the liquid-to-solid ratio is low, the amount of alkaline reactants is insufficient, resulting in incomplete dissolution of cryolite, which will affect the leaching rate of aluminum and lithium and the fluorine recovery rate, and the calcium fluoride product content will reach more than 80%.

[0103] Example 5

[0104] This embodiment provides a method for efficient leaching of lithium aluminum from aluminum electrolysis solid waste and preparation of high-grade CaF2. The aluminum electrolysis solid waste in this embodiment is waste aluminum electrolyte, and the method includes the following steps:

[0105] Waste aluminum electrolyte blocks were crushed, ground, and sieved to obtain waste aluminum electrolyte powder with a particle size ≤74μm. The reaction auxiliary material CaO+Ca(OH)2+CaF2 was mixed evenly with the waste aluminum electrolyte powder at a mass ratio of 0.8:1. A 60g / L NaOH solution was prepared, and the evenly mixed material was stirred with the NaOH solution at a liquid-to-solid ratio of 10mL:1g. The mixture was then placed in an alkali-resistant reactor and reacted for 1.0 hour at 120℃, 150℃, 180℃, and 200℃ with stirring at 200rpm. After the reaction, the material was filtered to obtain filter residue and filtrate. The filter residue was acid-washed with low-concentration hydrochloric acid to remove impurities, maintaining the solution pH at 4.5. After filtration, the filter cake was dried to obtain high-grade calcium fluoride. The results of lithium-aluminum leaching rate, final fluorine recovery rate, and calcium fluoride content during the leaching process are shown in Table 4. It should be noted that within the range of 120 to 200°C, the reaction temperature has little impact on the results of each process. When the temperature is above 150°C, efficient leaching of lithium aluminum can be achieved and high-quality CaF2 can be produced.

[0106] In this embodiment, the lithium leaching rate is above 89% (e.g., 89.5% to 96.2%), the aluminum leaching rate is above 91% (e.g., 91.7% to 97.8%), the fluorine recovery rate is above 94% (e.g., 94.8% to 99.0%), and the purity of the calcium fluoride product is above 93% (e.g., 93.1% to 98.8%).

[0107] Table 4 Results of each process under different reaction temperatures

[0108]

[0109]

[0110] Example 6

[0111] This embodiment provides a method for efficient leaching of lithium aluminum from aluminum electrolysis solid waste and preparation of high-grade CaF2. The aluminum electrolysis solid waste in this embodiment is aluminum electrolysis overhaul slag. The method includes the following steps: crushing, grinding, and sieving the aluminum electrolysis overhaul slag blocks to obtain overhaul slag powder with a particle size ≤74μm; mixing the reaction auxiliary material CaO+Ca(OH)2+CaF2 with the overhaul slag powder at a mass ratio of 0.8:1; preparing a 100g / L NaOH solution; mixing the uniformly mixed material with the NaOH solution at a liquid-solid ratio of 10mL:1g; placing the mixture in an alkali-resistant reactor; and reacting at 180℃ and 200rpm for 1.0 hour; after the reaction, filtering the material to obtain filter residue and filtrate; acid washing the filter residue with low-concentration hydrochloric acid to remove impurities, maintaining the solution pH at 3.5; filtering; and drying the filter cake to obtain high-grade calcium fluoride. During the leaching process, the leaching rates of aluminum and lithium were 93.8% and 95.1%, respectively, the fluorine recovery rate was 98.4%, and the calcium fluoride grade reached 81.2%. It should be noted that impurities other than cryolite and sodium fluoride in the overhaul slag during the leaching process do not affect the leaching rate of aluminum and lithium. These impurities enter the leaching slag during the leaching process, and after acid washing, the obtained calcium fluoride product has a high grade, which can meet the requirements of steel smelting enterprises for the CaF2 grade in slag-forming agents.

[0112] Example 7

[0113] This embodiment provides a method for efficient leaching of lithium aluminum from aluminum electrolysis solid waste and preparation of high-grade CaF2. The aluminum electrolysis solid waste in this embodiment is carbon powder, and the method includes the following steps: crushing, grinding, and sieving the cathode carbon block to obtain carbon powder with a particle size ≤74μm; mixing the reaction auxiliary material CaO+Ca(OH)2+CaF2 with the carbon powder at a mass ratio of 0.8:1; preparing a 100g / L NaOH solution; stirring the uniformly mixed material with the NaOH solution at a liquid-solid ratio of 10mL:1g; placing the mixture in an alkali-resistant reactor; and reacting at 180℃ and stirring at 200rpm for 1.0 hour; after the reaction, filtering the material to obtain filter residue and filtrate; acid washing the filter residue with low-concentration hydrochloric acid to remove impurities, maintaining the solution pH at 3.5; filtering; and drying the filter cake to obtain high-grade calcium fluoride. During the leaching process, the leaching rates of aluminum and lithium were 94.2% and 95.7%, respectively, the fluorine recovery rate was 98.8%, and the calcium fluoride grade reached 82.5%. It should be noted that impurities other than cryolite in the carbon powder did not affect the leaching rate of aluminum and lithium. These impurities entered the leaching residue during the leaching process and, after acid washing, yielded a high-grade calcium fluoride product that meets the requirements of steel smelting enterprises for the CaF2 grade in slag-forming agents.

[0114] Example 8

[0115] This embodiment provides a method for efficient and comprehensive recycling of solid waste from aluminum electrolysis, including the following steps:

[0116] Step 1: Crush, grind, and screen the waste aluminum electrolyte blocks to obtain waste aluminum electrolyte powder with a particle size ≤74μm;

[0117] Step 2: Mix the reaction excipients CaO+Ca(OH)2+CaF2 with the waste aluminum electrolyte powder at a mass ratio of 0.8:1 until homogeneous;

[0118] Step 3: Prepare a 100g / L NaOH solution. Mix the well-mixed material with the NaOH solution at a liquid-solid ratio of 10mL:1g, stir well, and put it into an alkali-resistant reaction vessel. React at 150℃ and 300rpm for 1.5 hours.

[0119] Step 4: After the reaction is complete, the material is filtered to obtain filter residue (leaching residue) and filtrate (leaching liquid);

[0120] Step 5a: Use low-concentration hydrochloric acid to acid wash the filter residue to remove impurities, keep the solution pH at 4, filter, and dry the filter cake to obtain high-grade calcium fluoride.

[0121] In step 4, the leaching rates of aluminum and lithium were 95.34% and 94.27%, respectively, the fluorine recovery rate was 99.87%, and the calcium fluoride grade reached 98.31%.

[0122] Step 5b: The leachate from Step 4 (pH = 13.1) and the organic solvent extractant (a mixture of tributyl phosphate and β-diketone organic reagents in a molar ratio of 0.3:0.4, prepared with sulfonated kerosene) were mixed in a separatory funnel at a volume ratio of 40 mL: 4 mL and subjected to three-stage countercurrent extraction. Subsequently, the obtained balanced loaded organic phase was mixed with 4 mol / L hydrochloric acid back-extraction reagent at a volume ratio of O / A = 20 mL: 2 mL and subjected to two-stage countercurrent back-extraction. The entire extraction-back-extraction process was carried out with a shaking time of 10 min and a temperature of 25 °C. The final back-extraction solution had a lithium concentration of 20.6 g / L and a lithium recovery rate of 98.6%.

[0123] The raffinate was treated with Ca(OH)2 at amounts of 1, 1.3, and 1.5 times the theoretical amount, respectively. The reaction was carried out at 60°C and a stirring speed of 300 rpm for 1 hour. After standing for 1 hour, the raffinate was separated by filtration, and the aluminum precipitation rates were 86.7%, 96.7%, and 97.9%, respectively.

[0124] The filter residue was acid-washed with hydrochloric acid solution at pH 4 to obtain calcium aluminate product with a purity of 98.6%; the filtrate was concentrated by adding CaO to obtain 30% alkali solution, and the overall sodium recovery rate reached 98.5%.

[0125] Example 9

[0126] This embodiment provides a method for efficient and comprehensive recycling of solid waste from aluminum electrolysis, including the following steps:

[0127] Step 1: Crush, grind, and screen the waste aluminum electrolyte blocks to obtain waste aluminum electrolyte powder with a particle size ≤74μm;

[0128] Step 2: Mix the reaction excipients CaO+Ca(OH)2+CaF2 with the waste aluminum electrolyte powder at a mass ratio of 0.8:1 until homogeneous;

[0129] Step 3: Prepare a 100g / L NaOH solution. Mix the well-mixed material with the NaOH solution at a liquid-solid ratio of 10mL:1g, stir well, and put it into an alkali-resistant reaction vessel. React at 150℃ and 300rpm for 1.5 hours.

[0130] Step 4: After the reaction is complete, the material is filtered to obtain filter residue (leaching residue) and filtrate (leaching liquid);

[0131] Step 5a: Use low-concentration hydrochloric acid to acid wash the filter residue to remove impurities, keep the solution pH at 4, filter, and dry the filter cake to obtain high-grade calcium fluoride.

[0132] In step 4, the leaching rates of aluminum and lithium were 95.34% and 94.27%, respectively, the fluorine recovery rate was 99.87%, and the calcium fluoride grade reached 98.31%.

[0133] Step 5b: The leachate from Step 4 (pH = 13.6) and the organic solvent extractant (a mixture of tributyl phosphate and β-diketone organic reagents in a molar ratio of 0.1:0.4, prepared with sulfonated kerosene) were mixed in a separatory funnel at a volume ratio of 40 mL: 2 mL and subjected to two-stage countercurrent back-extraction. The entire extraction-back-extraction process was carried out with shaking for 10 min at a temperature of 25 °C. The final back-extraction solution had a lithium concentration of 25.1 g / L and a lithium recovery rate of 98.7%.

[0134] The raffinate was treated with Ca(OH)2 at 1.3 times the theoretical amount. The reaction was carried out at 20℃, 40℃, 60℃, and 80℃ with a stirring speed of 300 rpm for 1 hour. After standing for 1 hour, the raffinate was separated by filtration. The aluminum precipitation rates were 67.2%, 93.9%, 96.7%, and 96.9%, respectively.

[0135] The filter residue was acid-washed with hydrochloric acid solution at pH 4 to obtain calcium aluminate product with a purity of over 96%; the filtrate was concentrated by adding CaO to obtain 30% alkali solution, and the overall sodium recovery rate reached over 98%.

[0136] Comparative Example 1

[0137] This comparative example provides a method for leaching lithium aluminum from aluminum electrolysis solid waste and preparing CaF2, including the following steps:

[0138] Waste aluminum electrolyte blocks were crushed, ground, and sieved to obtain waste aluminum electrolyte powder with a particle size ≤74μm. NaOH solutions of 20g / L, 40g / L, 60g / L, 80g / L, and 100g / L were prepared. The waste aluminum electrolyte powder was mixed with the NaOH solution at a liquid-to-solid ratio of 10mL:1g without the addition of reaction additives, and then placed in an alkali-resistant reactor. The reaction was carried out at 180℃ and 300rpm for 2.0 hours. After the reaction, the material was filtered to obtain filter residue and filtrate. The filter residue was acid-washed with low-concentration hydrochloric acid to remove impurities, maintaining the solution pH at 4.5. After filtration, the filter cake was dried to obtain the final filter residue. The results of lithium-aluminum leaching rate and final fluorine recovery rate during the leaching process are shown in Table 5.

[0139] Table 5 Results of each process under different alkali concentrations without the addition of reaction excipients.

[0140] 20 16.2 60.9 41.0 40 16.5 73.6 46.7 60 16.6 78.4 36.6 80 23.5 92.3 41.9 100 24.7 84.2 42.8 160 25.8 85.7 33.7

[0141] Comparing Example 1 and Comparative Example 1, it can be seen that without the addition of reaction excipients, the leaching rate of aluminum and lithium and the fluorine recovery rate are low, especially the leaching rate of lithium. Since the cryolite in the waste aluminum electrolyte is not completely dissolved, the filter residue obtained in step 4 is mainly cryolite phase. Since no reaction excipients are added during the leaching process, fluorine cannot be converted into calcium fluoride and enter the filter residue, resulting in low fluorine recovery rate and no CaF2 product.

[0142] Comparative Example 2

[0143] This comparative example provides a method for leaching lithium aluminum from aluminum electrolysis solid waste and preparing CaF2, including the following steps:

[0144] Waste aluminum electrolyte blocks were crushed, ground, and sieved to obtain waste aluminum electrolyte powder with a particle size ≤74μm. The waste aluminum electrolyte powder was mixed evenly with CaO, a reaction auxiliary material, at a mass ratio of 0.8:1. A 200g / L NaOH solution was prepared, and the evenly mixed material was stirred evenly with the NaOH solution at a liquid-to-solid ratio of 10mL:1g. The mixture was then placed in an alkali-resistant reactor and reacted at 180℃ and 300rpm for 1.0 hour. After the reaction, the material was filtered to obtain filter residue and filtrate. The filter residue was acid-washed with low-concentration hydrochloric acid to remove impurities, with the solution pH maintained at 4.5. After filtration, the filter cake was dried to obtain high-grade calcium fluoride. The lithium-aluminum leaching rate, final fluorine recovery rate, and calcium fluoride content during the leaching process were 73.3%, 35.3%, 56.8%, and 60.7wt.%, respectively.

[0145] Figure 4 The XRD pattern of the filter residue from the alkaline leaching process in Comparative Example 2 shows that, compared with Example 1, when the alkali concentration is too high, in a strongly alkaline solution system, the Ca(OH)2 converted from the added CaO auxiliary material is more difficult to release Ca. 2+ The filter residue from the alkaline leaching process clearly shows diffraction characteristic peaks of unreacted Ca(OH)2, which affects the cryolite dissolution process and the fluorine conversion process, thus affecting the aluminum-lithium leaching rate and the purity of CaF2 in the final product.

[0146] Comparative Example 3

[0147] This comparative example provides a method for leaching lithium aluminum from aluminum electrolysis solid waste and preparing CaF2, including the following steps:

[0148] Waste aluminum electrolyte blocks were crushed, ground, and sieved to obtain waste aluminum electrolyte powder with a particle size ≤74μm. This powder was then uniformly mixed with CaO and sodium carbonate, with CaO and sodium carbonate accounting for 80% of the waste aluminum electrolyte powder's mass. Water and a small amount of binder were added to form pellets, which were then heated in a high-temperature furnace at 1000℃ for 1 hour. After the reaction was complete, the pellets were removed, cooled to room temperature, and crushed to obtain powder B. Powder B was added to a 5% (w / w) NaOH solution and leached with stirring for 1 hour at a liquid-to-solid ratio of 5:1. After filtration, filter residue and a leachate containing aluminum and lithium were obtained. The obtained filter residue contained 67% CaF2, and the lithium and aluminum leaching rates during the leaching process were 72% and 69%, respectively. The obtained CaF2 residue contained a large amount of unreacted waste aluminum electrolyte (cryolite). The reason is that during the roasting process, the decomposition of cryolite in the waste aluminum electrolyte and the reaction with CaO are affected by the reaction product CaF2. Incomplete decomposition of cryolite inevitably leads to problems such as low aluminum-lithium leaching rate and low CaF2 content in the filter residue.

[0149] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for efficient leaching of lithium aluminum from aluminum electrolysis solid waste and preparation of high-grade CaF2, characterized in that, The method comprises the following steps: Step 1: Crushing, grinding and sieving the aluminum electrolysis solid waste blocks to obtain aluminum electrolysis solid waste powder A; Step 2: Uniformly mixing the aluminum electrolysis solid waste powder A with a reaction auxiliary material to obtain material B; Step 3: Preparing an alkali solution, adding the material B into the alkali solution, stirring uniformly, and transferring the mixture to an alkali-resistant reaction device for reaction; Step 4: After the reaction is completed, filtering the material to obtain filter residue and filtrate respectively, wherein the filtrate can be used for aluminum and lithium recovery; Step 5: Subjecting the filter residue obtained in step 4 to pickling for impurity removal using a low-concentration inorganic acid solution, filtering, and drying the filter cake to obtain high-grade CaF₂; Step 5b: Subjecting the filtrate obtained in step 4 to extraction using an organic solvent extractant to obtain a loaded organic phase and a raffinate; Step 6a: Subjecting the loaded organic phase obtained in step 5b to back extraction to obtain a lithium-containing solution; Step 6b: Adding a reaction auxiliary material to the raffinate obtained in step 5b, stirring uniformly for reaction, allowing the mixture to stand for a period of time, then filtering and separating to obtain calcium aluminate precipitate; the reaction auxiliary material is at least one of CaO and Ca(OH)₂; Step 7: Supplementing the reaction auxiliary material to the filtrate obtained in step 6b, stirring uniformly, then allowing the mixture to stand, filtering and separating; the reaction auxiliary material is CaO; In step 1, the aluminum electrolysis solid waste is the solid waste generated in the aluminum electrolysis process, with the main component being cryolite; In step 2, the reaction excipient is a substance that can provide Ca. 2+ The calcium-containing substances; the added reaction excipients are mainly used to provide calcium that combines with fluoride ions during the alkaline leaching process. 2+ The reaction excipients are at least one of CaO, CaCl2, CaF2, Ca(OH)2, Ca(NO3)2 and their hydrates. In step 2, the mass ratio of the reaction auxiliary material to the aluminum electrolysis solid waste powder A is 0.7~0.9:1; In step 3, the alkali solution is prepared using NaOH; the concentration of the alkali solution is 20~160g / L; the liquid-solid ratio range of the alkali solution to material B is 4~15 mL:1g; the reaction temperature for the reaction between material B and the alkali solution is 120~200℃; the stirring speed is 200~500rpm; In step 5, the pH range of the solution during the pickling process is 3~6; In step 5b, the pH value of the filtrate from step 4 is controlled to be 12.5<pH<14, the volume ratio of the organic solvent extractant to the filtrate is 1:20~1:1, the oscillation time is 5~30min, and the temperature is 10~40℃; In step 6a, the hydrogen ion concentration in the back extraction reagent is controlled to be 1~6mol / L.

2. The method according to claim 1, characterized in that, In step 2, the mass ratio of the reaction auxiliary material to the aluminum electrolysis solid waste powder A is 0.8~0.9:

1.

3. The method according to claim 1, characterized in that, In step 3, the concentration of the alkali solution is 20~100g / L.

4. The method according to claim 1, characterized in that, In step 3, the liquid-solid ratio range of the alkali solution to material B is 5~15 mL:1g.

5. The method according to claim 1, characterized in that, In step 3, the reaction temperature for the reaction between material B and the alkali solution is 150~200℃.

6. The method according to any one of claims 1 to 5, characterized in that, In step 5, the pH range of the solution during the pickling process is 3~5.5.

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