Method for preparing high-quality cryolite from waste electrolyte

Abstract

The invention relates to a method for extracting lithium from waste electrolyte and preparing cryolite in a linkage manner, and belongs to the technical field of resource recovery and inorganic material preparation. According to the method, through the steps of pretreatment, selective leaching, impurity removal and purification, lithium salt preparation, fluorine and aluminum synergistic reaction and the like, efficient recovery of lithium resources in the waste electrolyte is achieved, meanwhile, high-purity cryolite is prepared in a linkage mode, and the problems that in the traditional waste electrolyte treatment process, the resource utilization rate is low, secondary pollution is serious, and the added value of products is low are solved. The method is short in process route, low in energy consumption and good in environmental protection property, achieves the purposes of treating waste with waste and recycling resources, and has remarkable economic and environmental benefits.

Description

1. Technical Field

[0001] This invention relates to the fields of comprehensive resource utilization and inorganic chemical material preparation technology, specifically to a method for efficiently extracting lithium from waste electrolytes (carbon slag, overhaul slag, etc.) generated during aluminum electrolysis production and simultaneously preparing cryolite (Na3AlF6). 2. Background Technology

[0002] This technology is mainly used in the aluminum electrolysis industry. Cryolite, used as an electrolyte, becomes ineffective after long-term use due to the accumulation of impurities (such as lithium, potassium, calcium, and magnesium), forming waste electrolyte (often contained in carbon slag and overhaul slag). Statistics show that 5-10 kg of waste electrolyte is generated for every ton of primary aluminum produced, with global annual waste electrolyte emissions exceeding one million tons. These waste residues are classified as hazardous solid waste; improper storage or disposal can cause serious environmental pollution due to the soluble fluorides within them. However, the waste electrolyte contains valuable elements such as fluorine, lithium, and aluminum, with lithium content typically ranging from 1% to 5%, exhibiting extremely high recycling value. Furthermore, the fluorine and aluminum elements in the waste electrolyte are core raw materials for the preparation of cryolite.

[0003] Traditional waste electrolyte treatment methods mainly have the following problems:

[0004] (1) Low resource utilization: Existing lithium extraction processes focus on lithium element recovery and neglect the comprehensive utilization of elements such as fluorine and aluminum, resulting in a large amount of fluorine resources being discharged in the form of hydrogen fluoride or fluoride wastewater, which not only wastes resources but also causes serious environmental pollution.

[0005] (2) Serious secondary pollution: Some processes use strong acid leaching or high-temperature roasting, which will produce fluorine-containing waste gas and acidic wastewater, resulting in high treatment costs and easy pollution of soil and water bodies.

[0006] (3) Low added value of products: Traditional processes mostly produce crude lithium carbonate, which needs to be further purified to meet industrial demand. Moreover, they do not produce high-value-added products in conjunction with the production of these products, resulting in poor overall economic benefits.

[0007] (4) Poor process synergy: The lithium extraction process is independent of other product preparation processes, and a closed loop of resource recycling has not been formed, resulting in high energy and material consumption.

[0008] Therefore, developing a technology that can synergistically recover lithium and valuable elements (Al, F, Na) to achieve high-value, full-scale, and harmless utilization of waste electrolytes has significant environmental and economic implications. 3. Summary of the Invention

[0009] 3.1 Purpose of the Invention: The purpose of this invention is to overcome the shortcomings of existing waste electrolyte treatment technologies and provide a method with a short process, low cost, high lithium recovery rate, and no secondary pollution, realizing an integrated process of "lithium extraction - fluorine-aluminum utilization - cryolite preparation", improving resource utilization and product added value, and reducing environmental pollution.

[0010] 3.2 Technical Solution: To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A method for extracting lithium from waste electrolyte and simultaneously preparing cryolite, the method comprising the following steps:

[0012] 3.2.1 Waste Electrolyte Pretreatment

[0013] The waste electrolyte is crushed to a particle size of ≤0.5mm to facilitate subsequent acid dissolution treatment.

[0014] 3.2.2 Acid dissolution of aluminum hydroxide to prepare aluminum chloride solution

[0015] Industrial aluminum hydroxide was added to industrial hydrochloric acid diluted with water at a volume ratio of 1:2. The reaction temperature was set at 100-105℃, and the reaction time was 60-90 minutes. After the aluminum hydroxide was completely dissolved, the solution was filtered to obtain an aluminum chloride acid solution of a certain concentration, which was used as a leaching agent to leach the electrolyte.

[0016] 3.2.3 Acid dissolution treatment to dissolve valuable elements in the electrolyte.

[0017] The crushed waste electrolyte and leaching agent are mixed at a liquid-to-solid ratio of (8-10):1, and leached at 95-105℃ for 60-90 minutes with stirring to achieve selective dissolution of lithium. The leaching agent is a sodium carbonate solution with a mass fraction of 5%-10%, and the molar ratio of sodium carbonate to LiF in the waste electrolyte is (1.2-1.5):1. After leaching, solid-liquid separation is performed to obtain lithium-containing leachate and leachate residue (mainly composed of NaF, AlF3, CaF2, etc.).

[0018] Reaction principle: 3LiF + AlCl3 → 3LiCl + AlF3

[0019] LiNa2AlF6+AlCl3→LiCl+2NaCl+3AlF2Cl

[0020] Na3AlF6 + AlCl3 → 3NaCl + 2AlF3

[0021] 3.2.4 Preparation of cryolite from leachate

[0022] Add 7%-10% by volume of one or a mixture of sodium fluoride, ammonium fluoride, and ammonium bifluoride to the lithium-containing leachate, and stir the reaction at 80-100℃ for 1-1.5 hours to obtain cryolite precipitate. Filter to obtain cryolite filter cake and lithium-containing filtrate.

[0023] 3.2.5 Neutralization, concentration, and lithium precipitation of lithium-containing filtrate

[0024] The lithium-containing solution was neutralized to 6.5-7.5 with a sodium carbonate solution at a liquid-to-solid ratio of 3.5:1, filtered, and the filtrate was evaporated and concentrated to a concentration of 8-12 g / L (calculated as Li+). Then, an excess of sodium carbonate solution (molar ratio of sodium carbonate to Li+ was 1.2-1.5:1) was added, and the mixture was stirred at 60-80℃ for 1-2 h to form lithium carbonate precipitate. The precipitate was filtered, washed (washed 3-4 times with deionized water), and dried (dried at 105-110℃ for 2-3 h) to obtain a high-purity lithium carbonate product (purity ≥99.5%).

[0025] Reaction principle: 2LiCl + Na₂CO₃ → Li₂CO₃↓ + 2NaCl

[0026] 3.3 Beneficial Effects: Compared with the prior art, the present invention has the following significant advantages:

[0027] 3.3.1 Synergistic Resource Utilization: The two main valuable components (lithium and aluminum / fluorine) in the waste electrolyte are efficiently recovered to produce two high-value products, lithium carbonate and cryolite, realizing the full-scale and high-value utilization of waste.

[0028] 3.3.2 Low cost and good economic efficiency: The process flow is short, and the main reagents (hydrochloric acid, sodium carbonate, fluoride salts) are inexpensive and readily available; the fluorine, aluminum and sodium sources required for cryolite synthesis are all from the waste materials themselves and process by-products, which greatly reduces production costs.

[0029] 3.3.3 High product value: The main product, lithium carbonate, is a core material for new energy, with strong market demand; the by-product, cryolite, can be returned to aluminum electrolysis cells for reuse, forming a true circular economy model. 4. Detailed Implementation

[0030] The present invention will be further described in detail below through specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0031] Example 1:

[0032] This embodiment relates to a method for the combined lithium extraction and cryolite preparation from waste electrolytes, including the following steps:

[0033] (1) Dissolve 100g of industrial aluminum hydroxide in 650ml of industrial hydrochloric acid diluted with water at a volume ratio of 1:2 (the content of industrial hydrochloric acid is 34%, and the content after dilution is 20-21%), heat to 100-105℃, and react for 60 minutes with stirring at 80-100r / min. Filter to obtain a clear aluminum chloride solution, which is used as a leaching agent to leach the electrolyte. The concentration of the aluminum chloride solution is 50-55g / L.

[0034] (2) Dilute the aluminum chloride solution obtained in step 1 with water at a ratio of 1:1, take 800 ml, heat to above 90°C, add waste electrolyte crushed to a particle size ≤0.5 mm under stirring at a speed of 80-100 r / min, heat to 100-105°C, and continue stirring at the same speed for 90 minutes; after the reaction is completed, filter, collect the filtrate, and obtain a second mixed solution of leaching filtrate containing sodium, aluminum, fluorine and lithium and impurity filter cake;

[0035] (3) Under stirring conditions of 80-100 r / min, sodium fluoride with a mass-volume ratio of (14-15):100 was added to 1000 ml of the filtrate from step 2 at 80℃. The temperature was raised to 80-100℃ and the reaction was continued to be stirred at the same speed for 90 minutes. After the reaction was completed, the solution was filtered and the filtrate and filter cake were collected to obtain the third mixed solution and cryolite filter cake.

[0036] (4) Under stirring conditions of 80-100 r / min, add sodium carbonate solution to the third mixed solution, adjust the pH to 6.5-7.5, and continue stirring the reaction at 60-80℃ for 30 minutes; filter, evaporate and concentrate the solution to a lithium concentration of 10-12 g / L, add sodium carbonate to adjust the pH to 11-13, obtain precipitate, filter, and dry the filter cake at 200℃ for 2 hours to obtain lithium carbonate product.

[0037] Example 2:

[0038] This embodiment relates to a method for the combined lithium extraction and cryolite preparation from waste electrolytes, including the following steps:

[0039] (1) Dissolve 100g of industrial aluminum hydroxide in 650ml of industrial hydrochloric acid diluted with water at a volume ratio of 1:2 (the content of industrial hydrochloric acid is 34%, and the content after dilution is 20-21%), heat to 100-105℃, and react for 90 minutes with stirring at 80-100r / min. Filter to obtain a clear aluminum chloride solution, which is used as a leaching agent to leach the electrolyte. The concentration of the aluminum chloride solution is 50-55g / L.

[0040] (2) Dilute the aluminum chloride solution obtained in step 1 with water at a ratio of 1:1, take 1200ml, heat to above 90℃, add waste electrolyte crushed to a particle size ≤0.5mm under stirring at a speed of 80-100r / min, heat to 100-105℃, and continue stirring at the same speed for 150 minutes; after the reaction is completed, filter, collect the filtrate, and obtain the second mixed solution of leaching filtrate containing sodium, aluminum, fluorine and lithium and impurity filter cake;

[0041] (3) Under stirring conditions of 80-100 r / min, sodium fluoride was added to the filtrate of step 2 at 80℃, and the temperature was raised to 80-100℃. The reaction was continued to be stirred at the same speed for 120 minutes. After the reaction was completed, the filtrate and filter cake were collected to obtain the third mixed solution and cryolite filter cake.

[0042] (4) Under stirring conditions of 80-100 r / min, add sodium carbonate solution to the third mixed solution, adjust the pH to 6.5-7.5, and continue stirring the reaction at 60-80℃ for 30 minutes; filter, evaporate and concentrate the solution to a lithium concentration of 10-12 g / L, add sodium carbonate to adjust the pH to 11-13, obtain precipitate, filter, and dry the filter cake to obtain lithium carbonate product.

[0043] Example 3:

[0044] This embodiment relates to a method for the combined lithium extraction and cryolite preparation from waste electrolytes, including the following steps:

[0045] (1) Dissolve 100g of industrial aluminum hydroxide in 650ml of industrial hydrochloric acid diluted with water at a volume ratio of 1:2 (the content of industrial hydrochloric acid is 34%, and the content after dilution is 20-21%), heat to 100-105℃, and react for 60 minutes with stirring at 80-100r / min. Filter to obtain a clear aluminum chloride solution, which is used as a leaching agent to leach the electrolyte. The concentration of the aluminum chloride solution is 50-55g / L.

[0046] (2) Dilute the aluminum chloride solution obtained in step 1 with water at a ratio of 1:1, take 1200ml, heat to above 90℃, add waste electrolyte crushed to a particle size ≤0.5mm under stirring at a speed of 80-100r / min, heat to 100-105℃, and continue stirring at the same speed for 90 minutes; after the reaction is completed, filter, collect the filtrate, and obtain the second mixed solution of leaching filtrate containing sodium, aluminum, fluorine and lithium and impurity filter cake;

[0047] (3) Under stirring conditions of 80-100 r / min, add ammonium fluoride to the filtrate of step 2 at 80℃, raise the temperature to 80-100℃, and continue stirring the reaction at the same speed for 90 minutes; after the reaction is completed, filter, collect the filtrate and filter cake to obtain the third mixed solution and cryolite filter cake.

[0048] (4) Under stirring conditions of 80-100 r / min, add sodium carbonate solution to the third mixed solution, adjust the pH to 6.5-7.5, and continue stirring the reaction at 60-80℃ for 30 minutes; filter, evaporate and concentrate the solution to a lithium concentration of 10-12 g / L, add sodium carbonate to adjust the pH to 11-13, obtain precipitate, filter, and dry the filter cake to obtain lithium carbonate product.

[0049] Example 4:

[0050] This embodiment relates to a method for the combined lithium extraction and cryolite preparation from waste electrolytes, including the following steps:

[0051] (1) Dissolve 100g of industrial aluminum hydroxide in 650ml of industrial hydrochloric acid diluted with water at a volume ratio of 1:2 (the content of industrial hydrochloric acid is 34%, and the content after dilution is 20-21%), heat to 100-105℃, and react for 60 minutes with stirring at 80-100r / min. Filter to obtain a clear aluminum chloride solution, which is used as a leaching agent to leach the electrolyte. The concentration of the aluminum chloride solution is 50-55g / L.

[0052] (2) Dilute the aluminum chloride solution obtained in step 1 with water at a ratio of 1:1, take 1200ml, heat to above 90℃, add waste electrolyte crushed to a particle size ≤0.5mm under stirring at a speed of 80-100r / min, heat to 100-105℃, and continue stirring at the same speed for 90 minutes; after the reaction is completed, filter, collect the filtrate, and obtain the second mixed solution of leaching filtrate containing sodium, aluminum, fluorine and lithium and impurity filter cake;

[0053] (3) Under stirring conditions of 80-100 r / min, add ammonium bifluoride to the filtrate of step 2 at 80℃, raise the temperature to 80-100℃, and continue stirring the reaction at the same speed for 90 minutes; after the reaction is completed, filter, collect the filtrate and filter cake to obtain the third mixed solution and cryolite filter cake.

[0054] (4) Under stirring conditions of 80-100 r / min, add sodium carbonate solution to the third mixed solution, adjust the pH to 6.5-7.5, and continue stirring the reaction at 60-80℃ for 30 minutes; filter, evaporate and concentrate the solution to a lithium concentration of 10-12 g / L, add sodium carbonate to adjust the pH to 11-13, obtain precipitate, filter, and dry the filter cake to obtain lithium carbonate product.

[0055] Comparative Example 1

[0056] This comparative example relates to a method for purifying crude lithium fluoride. The difference between this comparative example and Example 1 is that the volume of the leaching agent added in step (2) is different. In this comparative example, 100g of electrolyte is added to 900mL of aluminum sulfate leaching agent solution. Other steps and parameters are the same as in Example 1.

[0057] Comparative Example 2

[0058] This comparative example relates to a method for purifying crude lithium fluoride. The difference from Example 1 is that the reaction time in step (2) is 60 minutes. That is, in this comparative example, 100g of electrolyte is added to 1200mL of aluminum sulfate solution as a leaching agent and reacted at 100-105℃ for 60 minutes. Other steps and parameters are the same as in Example 1.

[0059] Performance Measurement and Analysis

[0060] ICP analysis was performed on the second mixed solutions obtained in step (2) of Examples 1, 2, 3, 4 and Comparative Examples 1, 2, and 4. The results are shown in Table 1 below. Based on the ICP concentration results of each element and the volume of the first mixed solution, the amount of lithium ions dissolved can be calculated.

[0061]

[0062] ICP and fluorine content tests were performed on cryolite products and lithium carbonate products from Examples 1, 2, 3, and 4. The results are shown in Tables 1 and 2 below.

[0063] Table 1: Cryolite Product Quality

[0064]

[0065] Table 2: Lithium Carbonate Product Quality

[0066]

[0067] According to the ICP elemental analysis results of the second mixed solutions in Examples 1-4 and Comparative Examples 1-2, the lithium ion dissolution rate in the second mixed solution is most suitable when the liquid-solid ratio is 10-12:1. If the solution is too small, the lithium ions will not dissolve completely; if the solution is too large, the acid solution will be wasted. Low leaching temperature also leads to incomplete lithium ion dissolution.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for the combined lithium extraction and cryolite preparation from waste electrolyte, characterized in that, Includes the following steps: (1) Crush the waste electrolyte to a particle size ≤0.5mm to facilitate subsequent acid dissolution treatment and keep it for later use; (2) Under stirring conditions of 80-100 r / min, aluminum hydroxide is added to diluted industrial hydrochloric acid, the reaction temperature is set to 100-105℃, the reaction time is T0, and after the aluminum hydroxide is completely dissolved, it is filtered to obtain the first mixed solution, aluminum chloride solution. (3) Under stirring conditions of 80-100 r / min, add water and waste electrolyte crushed to particle size ≤0.5 mm to the first mixed solution aluminum chloride solution according to a certain liquid-solid ratio, adjust the pH of the solution to 0-1, raise the temperature to 100-105℃, and continue stirring at the same speed for reaction time T2; after the reaction is completed, filter, collect the filtrate, and obtain the second mixed solution. (4) Under stirring conditions of 80-100 r / min, add fluorine-containing material to the second mixed solution, heat the material to 80-100℃, and continue stirring at the same speed for reaction time T3; after the reaction is completed, filter, collect the filtrate and filter cake to obtain the third mixed solution and cryolite filter cake. (5) Under stirring conditions of 80-100 r / min, add sodium carbonate solution to the third mixed solution, adjust the pH to 6.5-7.5, and continue stirring at 60-80℃ for reaction time T4. After filtration, the solution is evaporated and concentrated. Sodium carbonate is added to adjust the pH to 11-13 to obtain a precipitate. The precipitate is then filtered and the filter cake is dried.

2. The preparation method according to claim 1, characterized in that, The content of the industrial hydrochloric acid solution is 31-34%; the aluminum hydroxide is industrial aluminum hydroxide with a purity of ≥98%; the main components of the waste electrolyte are lithium, potassium, calcium, magnesium, sodium, aluminum, and fluorine.

3. The preparation method according to claim 1, characterized in that, In step (2), the reaction temperature of hydrochloric acid solution with aluminum hydroxide is 100-105℃, the reaction time T0 is 60-90 minutes, and the concentration of aluminum chloride solution is 45-55g / L.

4. The preparation method according to claim 1, characterized in that, In step (3), the mass-to-volume ratio of electrolyte to aluminum chloride solution is 1:(10-12), the reaction temperature is controlled at 100-105℃, and the reaction time is controlled at 90-150 minutes.

5. The preparation method according to claim 1, characterized in that, In step (4), the mass-volume ratio of the fluorine-containing material to the second mixed solution is (14-15):100, the reaction temperature is controlled at 80-100℃, and the reaction time is 90-120 minutes.

6. The preparation method according to claim 1, characterized in that, In step (5), the volume ratio of sodium carbonate solution to the third mixed solution is 1-3:10; the pH of the solution is controlled at 6.5-7.

5.

7. The preparation method according to claim 1, characterized in that, In step (5), sodium carbonate is dissolved in water at a liquid-to-solid ratio of 3.5:1 and then added to the evaporation concentrate at a volume ratio of (1-2):10, with the pH controlled at 11-13.

8. The preparation method according to claim 1, characterized in that, In step (4), the fluorine-containing materials include, but are not limited to, one or a mixture of sodium fluoride, ammonium fluoride, and ammonium bifluoride.

9. The preparation method according to claim 1, characterized in that, In step (4), the cryolite filter cake obtained by filtration is dried at 120-150℃ for 2-3 hours to obtain a product that meets the national standard requirements.

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