Method for recovering lithium, aluminum and iron from fly ash acid leachate
Through the membrane separation and concentration process of fly ash acid leaching liquid, combined with pH adjustment and evaporation concentration, the problems of high extraction costs and low recovery rates in the prior art are solved, and high efficiency and low energy consumption metals are achieved Recycling effect.
Patent Information
- Application Number
- CN202411364079.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-28
- Publication Date
- 2024-12-24
AI Technical Summary
When the prior art extracts lithium, aluminum, and iron from fly ash, the calcination and roasting processes lead to large energy consumption, high cost, and low lithium ion recovery rate, making it difficult to promote on a large scale.
The fly ash acidic leaching liquid is filtered and concentrated by microfiltration membrane, nanofiltration membrane and reverse osmosis membrane. By adjusting the flow rate and temperature, combined with pH adjustment and evaporation concentration, efficient enrichment and recovery of lithium, aluminum and iron are achieved.
The total recovery rate of lithium has reached more than 78%, the process is simple, the energy consumption is small, and the economic cost is low, which is suitable for industrial promotion.
Smart Images
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Abstract
Description
Technical Field
[0001] The present application relates to the technical field of waste resource recovery, and in particular to a method for recovering lithium, aluminum and iron from fly ash acid leaching solution. Background Art
[0002] Fly ash is mainly composed of oxides of silicon, aluminum, iron, calcium and other elements, and is one of the main solid wastes discharged by coal-fired power plants. With the development of my country's coal-fired power industry, the output of fly ash has increased year by year. Fly ash is rich in a variety of valuable metal elements, such as lithium, aluminum, iron, calcium, magnesium, etc. Therefore, the extraction of valuable metal elements in fly ash is of great significance for the recycling of fly ash waste resources.
[0003] At present, the main methods for extracting valuable metal elements from fly ash are acid leaching or alkaline leaching. For example, a related patent reported a method for separating and recovering lithium and aluminum by acid leaching. The method effectively extracts lithium and aluminum from fly ash through the steps of pretreatment-crushing-acid leaching-circulating acid leaching-mother liquor purification-aluminum-lithium in-situ co-precipitation-calcination separation-concentrated lithium precipitation, etc. However, the method adopts a calcination separation process, which leads to high energy consumption and high separation cost, and is difficult to promote and use on a large scale. There are also documents reporting a method for extracting lithium from lithium-rich fly ash alkaline mother liquor. The method includes the steps of desiliconization-pH control-aluminum-lithium co-precipitation separation-roasting-water washing-carbonation recovery of lithium carbonate, etc. Among them, in the aluminum-lithium co-precipitation separation process, the lithium ion recovery rate is low due to the large loss of lithium ions carried by the precipitate; in addition, the above method also adopts a roasting process, which has high energy consumption and high cost.
[0004] Therefore, it is necessary to provide a fly ash extraction process with low energy consumption, low cost and high metal element recovery rate to comprehensively recover the valuable metal elements such as lithium, aluminum and iron in fly ash and realize the resource recycling of fly ash. Summary of the invention
[0005] In order to extract lithium, aluminum and iron metal elements from fly ash at low cost and high efficiency, the present application provides a method for recovering lithium, aluminum and iron from fly ash acidic leaching solution.
[0006] The present application provides a method for recovering lithium, aluminum and iron from fly ash acidic leaching solution, which adopts the following technical scheme: A method for recovering lithium, aluminum and iron from fly ash acidic leaching solution, comprising the following steps: (1) first preparing fly ash acidic leachate; filtering the fly ash acidic leachate using a microfiltration membrane to obtain a permeate 1; the flow rate of the acidic leachate is 200-300 mL / min, and the temperature is 5-50° C.; (2) filtering the permeate 1 with a nanofiltration membrane to obtain a permeate 2 and a concentrated solution 3; the permeate 1 has a flow rate of 140-200 mL / min and a temperature of 20-50° C.; (3) using a reverse osmosis membrane to concentrate the permeate 2 to obtain a concentrated solution 4 and a permeate 5; the permeate 2 has a flow rate of 350-500 mL / min and a temperature of 0-50° C.; (4) adjusting the pH of the concentrated solution 4 and filtering to obtain a solution 6; (5) The solution 6 is evaporated and concentrated, a saturated sodium carbonate solution is added, and the solution is filtered, precipitated, washed, and dried to obtain lithium carbonate.
[0007] The present application provides a method for recovering lithium, aluminum, and iron from fly ash acid leachate. The method achieves lithium enrichment in fly ash acid leachate by filtering the fly ash acid leachate in sequence through a microfiltration membrane, a nanofiltration membrane, and a reverse osmosis membrane, and removing impurities through precipitation. The fly ash acid leachate is extracted using the method for recovering lithium, aluminum, and iron from fly ash acid leachate provided by the present application, and the total recovery rate of lithium can reach more than 78%. In addition, the method for recovering lithium, aluminum, and iron from fly ash acid leachate provided by the present application has the advantages of simple process, low energy consumption, low economic cost, high metal recovery rate, etc. It is easy to realize industrialization and has a good prospect for use.
[0008] In the present application, step (1) is filtered through a microfiltration membrane to effectively remove colloids and fine particles in the fly ash acid leachate; step (2) controls the temperature at 20-50°C, which can increase the solubility of salts in the fly ash acid leachate and prevent crystallization from clogging the filter holes. The permeate 2 is mainly a monovalent ion solution, such as Li, and the concentrated solution 3 is mainly a high-valent ion solution, such as Al and Fe.
[0009] Optionally, the microfiltration membrane, nanofiltration membrane or reverse osmosis membrane is each selected from an organic filter membrane or an inorganic filter membrane, the organic filter membrane is a polyamide filter membrane, a polyester filter membrane, a polypropylene filter membrane, a polycarbonate filter membrane or a polysulfide filter membrane, and the inorganic filter membrane is a ceramic filter membrane.
[0010] Optionally, when the microfiltration membrane, nanofiltration membrane or reverse osmosis membrane is an organic membrane, it is necessary to adjust the pH of the solution to 2-11 with ammonia water in advance; when the microfiltration membrane is an inorganic membrane, it is not necessary to adjust the pH.
[0011] Optionally, the step (4) is specifically as follows: sequentially adjusting the pH of the concentrated solution 4 to 2.8-3.2, pH=3.8-4.2, pH=4.8-5.2, pH=7.9-8.2, and pH=12.8-13.2, filtering at the above pH values respectively, combining the filtrate, and obtaining a solution 6.
[0012] In the present application, the pH value of the concentrated solution 4 is adjusted successively so that the Fe 3+ 、Al 3+ , Fe 2+ , Ca 2+ Mg 3+ Dissolution; Among them, when pH = 2.8-3.2, most of the Fe 3+ Dissolution; when pH = 3.8-4.2, most of the Al 3+ Dissolution; when pH = 4.8-5.2, residual Fe 3+ 、Al 3+ Dissolution; when pH = 7.9-8.2, Fe 2+ Dissolution; pH = 12.8-13.2, Ca 2+ Mg 3+ Dissolution.
[0013] Optionally, when adjusting the pH in step (4), the temperature of the concentrated solution 4 is always maintained at 80-90°C.
[0014] In the present application, the temperature of the concentrated solution 4 when the pH is adjusted in step (4) will affect the recovery rate of Li. When the temperature is too low, the Li in the concentrated solution 4 will be dissolved, resulting in a reduction in the Li content in the solution 6, thereby reducing the recovery rate of Li. When the temperature is too high, the recovery rate of Li will not change much, but the energy consumption will increase greatly. Therefore, the present application controls the temperature of the concentrated solution 4 when the pH is adjusted in step (4) within the above range, which can ensure that a higher total recovery rate of Li is obtained under low energy consumption.
[0015] Optionally, the concentration of the solution 6 after evaporation and concentration is ≥4 g / L.
[0016] Optionally, the method further comprises: (6) adding aqueous ammonia to the concentrated solution 3 obtained in step (2), adjusting the pH to 4-4.1, filtering the iron hydroxide precipitate, and drying to obtain iron hydroxide.
[0017] Optionally, the method further comprises: (7) continuing to add ammonia water to the filtrate after filtering the precipitate in step (6), adjusting the pH to 5-5.36, filtering the aluminum hydroxide precipitate, and drying to obtain aluminum hydroxide.
[0018] Optionally, the permeate 5 flows back to the permeate 1 for recycling.
[0019] Optionally, the fly ash acid leachate is prepared by taking fly ash, adding 80wt% concentrated sulfuric acid, mixing well, and then roasting at 400±50°C, soaking the roasted product in 80°C water to obtain a fly ash acid leachate with a pH value of less than 2.
[0020] In summary, this application has the following beneficial effects: 1. The present application provides a method for recovering lithium, aluminum and iron from fly ash acid leachate. The method adopts membrane separation method for the first time to achieve the enrichment of metal elements such as lithium in fly ash acid leachate. The method has the advantages of simple operation process, low energy consumption and low economic cost. The lithium recovery rate can reach a level comparable to that of the prior art, and has a good prospect for industrial promotion.
[0021] 2. This application uses fly ash acidic leachate as raw material, and sequentially uses microfiltration membrane, nanofiltration membrane and reverse osmosis membrane for membrane separation, and adjusts the flow rate and temperature of the permeate in each membrane separation step to achieve efficient extraction of lithium, aluminum and iron in fly ash acidic leachate. DETAILED DESCRIPTION The present application provides a method for recovering lithium, aluminum and iron from fly ash acidic leaching solution, comprising the following steps: (1) First, 80 wt% concentrated sulfuric acid is added to fly ash, mixed evenly, and then roasted at 400±50° C. The roasted product is immersed in 80° C. water to obtain an acidic leaching solution of fly ash with a pH value less than 2; then the acidic leaching solution is filtered using a microfiltration membrane to obtain a permeate 1; During the filtration process, the flow rate of the acidic leachate is 200-300 mL / min and the temperature is 5-50°C; (2) filtering the permeate 1 using a nanofiltration membrane to obtain a permeate 2 and a concentrated solution 3; During the filtration process, the flow rate of the permeate 1 is 140-200 mL / min and the temperature is 20-50°C; (3) using a reverse osmosis membrane to concentrate the permeate 2 to obtain a concentrated liquid 4 and a permeate 5; the permeate 5 is refluxed to the permeate 1 for recycling; During the filtration process, the flow rate of the permeate 2 is 350-500 mL / min and the temperature is 0-50°C; (4) using sodium hydroxide to adjust the pH of the concentrated solution 4 to 2.8-3.2, pH=3.8-4.2, pH=4.8-5.2, pH=7.9-8.2, and pH=12.8-13.2, respectively, filtering at the above pH values, combining the filtrates, and obtaining a solution 6; During the above process, the temperature of the solution was always maintained at 80-90°C.
[0023] (5) Evaporate and concentrate solution 6 to a concentration of ≥4 g / L, maintain the temperature ≥90° C., add a saturated sodium carbonate solution, filter the precipitate, wash it with pure water above 90° C., and dry it to obtain lithium carbonate.
[0024] (6) Adding aqueous ammonia to the concentrated solution 3 obtained in step (2), adjusting the pH to 4-4.1, filtering the iron hydroxide precipitate, and drying to obtain iron hydroxide.
[0025] (7) Adding ammonia water to the filtrate after filtering the precipitate in step (6), adjusting the pH to 5-5.36, filtering the aluminum hydroxide precipitate, and drying to obtain aluminum hydroxide.
[0026] Wherein, the microfiltration membrane, nanofiltration membrane or reverse osmosis membrane are independently selected from organic membranes or inorganic membranes, the organic membranes are polyamide membranes, polyester membranes, polypropylene membranes, polycarbonate membranes or polysulfide membranes, and the inorganic membranes are ceramic membranes. When the microfiltration membrane, nanofiltration membrane or reverse osmosis membrane is an organic membrane, it is necessary to use ammonia water to adjust the pH of the solution to 2-11 in advance; when the microfiltration membrane is an inorganic membrane, it is not necessary to adjust the pH.
[0027] In the present application, fly ash is commercially available; each filter membrane is purchased from Shandong Bona Biotechnology Co., Ltd.; and the remaining raw materials, reagents, solvents, etc. can be obtained commercially.
[0028] The present application is further described in detail below in conjunction with embodiments and performance testing experiments.
[0029] Examples 1-8 Examples 1-8 respectively provide a method for recovering lithium, aluminum and iron from fly ash acidic leaching solution.
[0030] The differences between the above embodiments are: pH of the fly ash acidic leachate and the types of each filter membrane, as shown in Table 1 below.
[0031] The method for recovering lithium, aluminum and iron from fly ash acidic leachate provided in Examples 1-8 comprises the following steps: (1) First, 80 wt% concentrated sulfuric acid is added to fly ash, mixed evenly, and then roasted at 400°C. The roasted product is immersed in 80°C water to obtain fly ash acidic leaching solution; then, the acidic leaching solution is filtered using a microfiltration membrane to obtain a permeate 1; during the filtration process, the flow rate of the acidic leaching solution is 230 mL / min and the temperature is 20°C; (2) filtering the permeate 1 using a nanofiltration membrane to obtain a permeate 2 and a concentrated solution 3; During the filtration process, the flow rate of permeate 1 was 160 mL / min and the temperature was 30 °C; (3) using a reverse osmosis membrane to concentrate the permeate 2 to obtain a concentrated liquid 4 and a permeate 5; the permeate 5 is refluxed to the permeate 1 for recycling; During the filtration process, the flow rate of permeate 2 was 450 mL / min and the temperature was 20 °C; (4) using 40 wt % sodium hydroxide, adjusting the pH of the concentrated solution 4 to 3, pH = 4, pH = 5, pH = 8, and pH = 13 in sequence, filtering at the above pH values, combining the filtrates, and obtaining a solution 6; During the above process, the temperature of the solution was always maintained at 85°C.
[0032] (5) Evaporate and concentrate solution 6 to a concentration of ≥4 g / L, maintain the temperature ≥90° C., add a saturated sodium carbonate solution, filter the precipitate, wash it with pure water above 90° C., and dry it to obtain lithium carbonate.
[0033] (6) Adding aqueous ammonia to the concentrated solution 3 obtained in step (2), adjusting the pH to 4-4.1, filtering the iron hydroxide precipitate, and drying to obtain iron hydroxide.
[0034] (7) Adding ammonia water to the filtrate after filtering the precipitate in step (6), adjusting the pH to 5-5.36, filtering the aluminum hydroxide precipitate, and drying to obtain aluminum hydroxide.
[0035] In the above process, when the microfiltration membrane, nanofiltration membrane or reverse osmosis membrane is an organic membrane, it is necessary to adjust the pH of the solution to 2-11 with ammonia water in advance; when the microfiltration membrane is an inorganic membrane, there is no need to adjust the pH.
[0036] Table 1 pH of fly ash acidic leachate and materials of each filter membrane in Examples 1-8 Examples 9-15 Examples 9-15 respectively provide a method for recovering lithium, aluminum and iron from fly ash acid leachate.
[0037] The difference between the above embodiment and embodiment 2 is that the flow rate and temperature in step (1-3) are specifically shown in Table 2 below.
[0038] Comparative Examples 1-3 Comparative Examples 1-3 respectively provide a method for recovering lithium, aluminum and iron from fly ash acidic leaching solution.
[0039] The difference between the above embodiment and embodiment 2 is that the flow rate and temperature in step (1-3) are specifically shown in Table 2 below.
[0040] Table 2 Flow rate and temperature in step (1-3) of Example 3, Examples 9-15, and Comparative Examples 1-3 Examples 18-21 Examples 18-21 respectively provide a method for recovering lithium, aluminum and iron from fly ash acid leachate.
[0041] The difference between the above embodiment and embodiment 2 is that the temperature of the concentrated liquid 4 is specifically shown in Table 3 below.
[0042] Table 3 Temperature of concentrated solution 4 in step (4) of Example 2 and Examples 18-21 Example Temperature of concentrate 4 2 85 18 75 19 80 20 90 21 95 Performance test The lithium, aluminum and iron in the fly ash acid leaching solution were recovered according to the methods provided in Examples 1-21 and Comparative Examples 1-3, and the total recovery rates of lithium, aluminum and iron were calculated. The results are shown in Table 3 below.
[0043] The contents of lithium, aluminum and iron in the fly ash acid leaching solution and the obtained lithium carbonate, aluminum hydroxide and iron hydroxide were all detected by inductively coupled plasma emission mass spectrometry. The total recovery rate of lithium, aluminum and iron was calculated as follows: The total recovery rate of lithium is calculated as follows: lithium content in lithium carbonate / lithium content in fly ash acid leaching solution × 100%; The total recovery rate of aluminum is calculated as follows: aluminum content in aluminum hydroxide / aluminum content in fly ash acid leaching solution × 100%; The total recovery rate of iron is calculated as follows: iron content in ferric hydroxide / iron content in fly ash acid leaching solution × 100%.
[0044] Table 3 Total recovery rates of lithium, aluminum and iron in Examples 1-15 and Comparative Examples 1-3 According to the test results in Table 3, the total recovery rate of lithium is 77.8-80.3%, the total recovery rate of aluminum is 95.4-96.5%, and the total recovery rate of iron is 96.4-97.3% when the fly ash acid leachate is treated by the method for recovering lithium, aluminum, and iron from fly ash acid leachate provided by Examples 1-21. Therefore, it is shown that the method for recovering lithium, aluminum, and iron from fly ash acid leachate provided by the present application has the advantages of simple process, low energy consumption, and low economic cost, and the total recovery rate of lithium, aluminum, and iron can reach the equivalent level of the prior art.
[0045] The test results of Examples 1-8 show that the present application uses microfiltration membrane, nanofiltration membrane and reverse osmosis membrane to filter the fly ash acid leachate in sequence, and adjusts the material of each filter membrane, which can achieve efficient extraction of lithium, aluminum and iron in the fly ash acid leachate. Further comparison shows that the three filtrations in Examples 2-4 are all filtered using organic filter membranes, and the total recovery rate of lithium can reach 79.2-79.5%, the total recovery rate of aluminum reaches 96.1-96.5%, and the total recovery rate of iron reaches 97.0-97.2%, and the extraction efficiency of lithium, aluminum and iron in the fly ash acid leachate is higher.
[0046] The test results of Example 2, Examples 9-11, and Comparative Example 1 show that the total recovery rate of lithium, aluminum, and iron from fly ash acidic leachate treated by the method for recovering lithium, aluminum, and iron from fly ash acidic leachate provided by Example 2 and Examples 9-11 is 79.1-79.5%, 95.4-96.3%, and 96.7-97.2% for aluminum. However, the total recovery rate of lithium, aluminum, and iron from fly ash acidic leachate treated by the method for recovering lithium, aluminum, and iron from fly ash acidic leachate provided by Comparative Example 1 is only 72.5%, 94.7%, and 94.8% for iron. Therefore, it is shown that the present application adjusts the flow rate of fly ash acidic leachate in step (1) to 200-300 mL / min and the temperature to 5-50° C., which can achieve efficient extraction of lithium, aluminum, and iron from fly ash acidic leachate.
[0047] The test results of Example 2, Examples 12-14, and Comparative Example 2 show that the total recovery rate of lithium is 78.6-79.5%, the total recovery rate of aluminum is 95.9-96.3%, and the total recovery rate of iron is 96.8-97.2% when the fly ash acid leachate is treated by the method for recovering lithium, aluminum, and iron from fly ash acid leachate provided by Example 2 and Examples 12-14. However, the total recovery rate of lithium is only 70.7% when the fly ash acid leachate is treated by the method for recovering lithium, aluminum, and iron from fly ash acid leachate provided by Comparative Example 2. Therefore, it is shown that the present application adjusts the flow rate of the permeate 1 in step (2) to 140-200 mL / min and the temperature to 20-50° C., which can achieve efficient extraction of lithium, aluminum, and iron from fly ash acid leachate.
[0048] The test results of Example 2, Examples 15-17, and Comparative Example 3 show that the total recovery rate of lithium is 79.0-79.5%, the total recovery rate of aluminum is 96.2-96.3%, and the total recovery rate of iron is 97.1-97.2% when the fly ash acid leachate is treated by the method for recovering lithium, aluminum, and iron from fly ash acid leachate provided by Example 2 and Examples 15-17. However, the total recovery rate of lithium is only 73.8% when the fly ash acid leachate is treated by the method for recovering lithium, aluminum, and iron from fly ash acid leachate provided by Comparative Example 3. Therefore, it is shown that the present application adjusts the flow rate of the permeate 2 in step (3) to 350-500 mL / min and the temperature to 0-50° C., which can achieve efficient extraction of lithium, aluminum, and iron from fly ash acid leachate.
[0049] The test results of Example 2 and Examples 18-21 show that as the temperature of the concentrated solution 4 in step (4) increases, the total recovery rates of aluminum and iron remain basically unchanged, while the recovery rate of lithium shows a trend of remaining basically unchanged. Among them, the total recovery rate of lithium obtained in Examples and Examples 19-21 is 78.2-80.3% (≥78%). Therefore, considering the comprehensive economic cost, the present application controls the temperature of the concentrated solution 4 in step (4) between 80-90°C, which can achieve efficient extraction of lithium, aluminum and iron in the fly ash acidic leachate.
[0050] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.
Claims
1. A method for recovering lithium, aluminum and iron from fly ash acidic leaching solution, characterized in that: The following steps are involved: (1) First, prepare fly ash acidic leachate; filter the fly ash acidic leachate using a microfiltration membrane to obtain a permeate 1; the flow rate of the acidic leachate is 200-300 mL / min, and the temperature is 5-50° C.; (2) filtering the permeate 1 with a nanofiltration membrane to obtain a permeate 2 and a concentrated solution 3; the permeate 1 has a flow rate of 140-200 mL / min and a temperature of 20-50° C.; (3) using a reverse osmosis membrane to concentrate the permeate 2 to obtain a concentrated solution 4 and a permeate 5; the permeate 2 has a flow rate of 350-500 mL / min and a temperature of 0-50° C.; (4) adjusting the pH of the concentrated solution 4, filtering, and obtaining a solution 6; (5) Solution 6 is evaporated and concentrated, and a saturated sodium carbonate solution is added. The solution is filtered, precipitated, washed, and dried to obtain lithium carbonate.
2. The method for recovering lithium, aluminum and iron from fly ash acidic leaching solution according to claim 1, characterized in that: The microfiltration membrane, nanofiltration membrane or reverse osmosis membrane are each independently selected from an organic filter membrane or an inorganic filter membrane, the organic filter membrane is a polyamide filter membrane, a polyester filter membrane, a polypropylene filter membrane, a polycarbonate filter membrane or a polysulfide filter membrane, and the inorganic filter membrane is a ceramic filter membrane.
3. The method for recovering lithium, aluminum and iron from fly ash acidic leaching solution according to claim 2, characterized in that: When the microfiltration membrane, nanofiltration membrane or reverse osmosis membrane is an organic membrane, it is necessary to use ammonia water to adjust the pH of the solution to 2-11 in advance; when the microfiltration membrane is an inorganic membrane, there is no need to adjust the pH.
4. The method for recovering lithium, aluminum and iron from fly ash acidic leaching solution according to claim 1, characterized in that: The step (4) specifically comprises: adjusting the pH of the concentrated solution 4 to 2.8-3.2, pH=3.8-4.2, pH=4.8-5.2, pH=7.9-8.2, and pH=12.8-13.2 in sequence, filtering at the above pH values respectively, combining the filtrate, and obtaining a solution 6.
5. The method for recovering lithium, aluminum and iron from fly ash acidic leaching solution according to claim 4, characterized in that: When adjusting the pH in step (4), the temperature of the concentrated solution 4 is always maintained at 80-90°C.
6. The method for recovering lithium, aluminum and iron from fly ash acidic leaching solution according to claim 1, characterized in that: The concentration of the solution 6 after evaporation and concentration is ≥4 g / L.
7. The method for recovering lithium, aluminum and iron from fly ash acidic leaching solution according to claim 1, characterized in that: The method further comprises: (6) Adding aqueous ammonia to the concentrated solution 3 obtained in step (2), adjusting the pH to 4-4.1, filtering the iron hydroxide precipitate, and drying to obtain iron hydroxide.
8. The method for recovering lithium, aluminum and iron from fly ash acidic leaching solution according to claim 7, characterized in that: The method further comprises: (7) Adding ammonia water to the filtrate after filtering the precipitate in step (6) to adjust the pH to 5-5.36, filtering the aluminum hydroxide precipitate, and drying to obtain aluminum hydroxide.
9. The method for recovering lithium, aluminum and iron from fly ash acidic leaching solution according to claim 1, characterized in that: The permeate 5 flows back to the permeate 1 for recycling.
10. The method for recovering lithium, aluminum and iron from fly ash acidic leaching solution according to claim 1, characterized in that: The preparation method of the fly ash acidic leaching solution is as follows: take fly ash, add 80wt% concentrated sulfuric acid, mix well, roast at 400±50℃, soak the roasted product in 80℃ water, and obtain the fly ash acidic leaching solution with pH<2.