A method for extracting valuable metal elements from fly ash

Abstract

This invention discloses a method for extracting valuable metal elements from fly ash, belonging to the field of fly ash resource utilization technology. The method includes the following preparation steps: first, mechanically activating and desilicate the fly ash with alkali to obtain a leachate and a first precipitate; then, mixing and reacting the first precipitate with iron powder and sodium hydroxide solution, followed by magnetic separation to obtain an iron-containing substance and a second precipitate; next, acid-dissolving the second precipitate to obtain a supernatant and a third precipitate; calcining the third precipitate with bluestone powder, then mixing it with the supernatant for ripening and polymerization to obtain an aluminum-containing substance; then, mixing and reacting the aluminum-containing substance with the leachate, followed by centrifugation to obtain a fourth precipitate; finally, washing the fourth precipitate with an acidic aqueous solution, removing water, centrifuging with anhydrous ethanol, and separating to obtain a lithium-containing supernatant and a fifth precipitate. This method has dual significance for both solid waste resource utilization and environmental protection.

Description

Technical Field

[0001] This invention relates to the field of fly ash resource utilization technology, specifically a method for extracting valuable metal elements from fly ash. Background Technology

[0002] Fly ash is a major industrial solid waste produced by burning coal in boilers of coal-fired power plants. Its main components are oxides of silicon, aluminum, iron, calcium, and other minerals. With thermal power generation continuing to dominate my country's energy structure, the annual emissions of fly ash are enormous, with accumulated stockpiles exceeding billions of tons. The large-scale stockpiling of fly ash not only occupies land resources but also poses serious environmental risks by polluting surrounding soil, water bodies, and the atmosphere through dust generation and leaching. Meanwhile, fly ash from some regions, especially high-alumina fly ash, has an alumina content exceeding 30% and is accompanied by valuable metals such as iron, lithium, gallium, and scandium, making it highly valuable for resource utilization.

[0003] In recent years, with the increasing scarcity of bauxite resources and the growing dependence on imports, extracting valuable components such as alumina from high-alumina fly ash has become an important way to alleviate aluminum resource shortages and realize the resource utilization of solid waste. Traditional fly ash aluminum extraction processes mainly include acid methods, alkali methods, and combined acid-alkali methods. Among them, although the alkali method has been applied in industry, it generally suffers from problems such as high energy consumption, long process, large alkali consumption, and difficulty in separating silicon and calcium impurities. Although the acid method can achieve efficient leaching of metals such as aluminum and iron, it faces technical bottlenecks such as severe equipment corrosion, high acid recovery costs, and difficulty in purifying the leachate. In addition, most existing processes focus on the single extraction of aluminum or iron, failing to achieve the co-recovery of rare metals such as lithium and gallium co-occurring in fly ash, resulting in resource waste.

[0004] It is worth noting that with the rapid development of the new energy industry, lithium, as a key raw material for lithium batteries, is increasingly highlighting its strategic importance. Although the lithium content in high-alumina fly ash is relatively low, its total resource volume cannot be ignored due to its huge emission base. If lithium can be efficiently recovered while extracting aluminum and iron, the economic value and strategic significance of comprehensive utilization of fly ash will be significantly enhanced.

[0005] Therefore, developing an efficient, low-consumption, and environmentally friendly extraction method to achieve the synergistic extraction and separation of multiple valuable metals such as aluminum, iron, and lithium from high-alumina fly ash is of great significance for promoting the resource utilization of fly ash, alleviating pressure on mineral resources, and promoting circular economy and sustainable development. Summary of the Invention

[0006] The purpose of this invention is to provide a method for extracting valuable metal elements from fly ash, so as to solve the technical problems mentioned in the background section.

[0007] The technical solution to achieve the objective of this invention is:

[0008] This invention provides a method for extracting valuable metal elements from fly ash, comprising the following preparation steps:

[0009] (1) Mechanical activation of fly ash;

[0010] (2) The activated fly ash in step (1) is subjected to alkaline dissolution and desiliconization to obtain leachate and first precipitate respectively;

[0011] (3) The first precipitate is mixed with iron powder and sodium hydroxide solution and then subjected to magnetic separation to obtain iron-containing substances and the second precipitate.

[0012] (4) After acid dissolving the second precipitate, a supernatant and a third precipitate are obtained. The third precipitate is mixed with bluestone powder, calcined, and then mixed with the supernatant for aging and polymerization to obtain a substance containing aluminum.

[0013] (5) After mixing and reacting the aluminum-containing substance with the leachate from step (2), centrifuge to obtain the fourth precipitate;

[0014] (6) The fourth precipitate was shaken and washed in an acidic aqueous solution, and then the water was removed. The precipitate was then centrifuged in anhydrous ethanol to separate it, and a lithium-containing supernatant and a fifth precipitate were obtained.

[0015] This invention first mechanically activates fly ash to improve the leaching efficiency of its various elements. Then, an alkaline desilication process removes the glassy phase from the fly ash and releases valuable metals such as lithium, while retaining the mullite phase in the first precipitate, thus obtaining a high-value-added first precipitate rich in aluminum and iron. Next, this aluminum- and iron-rich first precipitate is mixed with iron powder and reacted, causing ferric oxide to react with the iron powder to generate magnetic magnetite. Magnetic separation is then used to separate the iron-containing substances, yielding an aluminum-rich magnetically separated first precipitate. Subsequently, this aluminum-rich material is acid-dissolved with hydrochloric acid. During acid dissolution, some aluminum elements exist in a more reactive form and readily react with the acid, dissociating and entering the solution, thus achieving separation from other components. The aluminum elements in the third precipitate, due to their stable structure... In a mineral phase with stable and strong acid resistance, the aluminum element is difficult to dissolve by acid and remains in the precipitate. This part of the insoluble aluminum element is then uniformly mixed with bluestone powder. Under high temperature calcination conditions, the calcium source in the bluestone powder reacts with aluminum to generate calcium aluminate mineral with high stability. The calcium aluminate is added to the supernatant after acid dissolution for polymerization and ripening, which can efficiently utilize the aluminum source to prepare polyaluminum chloride material in a short time. The obtained polyaluminum chloride material is then mixed and reacted with the leachate from step (2) to achieve selective adsorption of lithium element in the leachate. Subsequently, the lithium element is fully desorbed from the polyaluminum chloride material by shaking and washing in an acidic aqueous solution. Finally, under anhydrous ethanol conditions, the difference in solubility is used to achieve efficient separation of lithium element from polyaluminum chloride material. The obtained lithium product and the regenerated polyaluminum chloride material both have high purity and good recovery efficiency.

[0016] The reaction mechanism of step (3) is as follows:

[0017] Fe+2Fe2O3+4NaOH→Fe3O4+2Na2FeO2+2H2O.

[0018] The reaction mechanism of step (4) is as follows:

[0019] Al₂O₃ + 6HCl = 2AlCl₃ + 3H₂O;

[0020] CaCO3→CaO+CO2↑;

[0021] CaO + Al₂O₃ → Ca(AlO₂)₂;

[0022] (16-2n)AlCl3+4nH2O+nCa(AlO2)2→8Al2(OH) n Cl 6-n +nCaCl2.

[0023] This invention, through the coupling of multiple processes such as "mechanical activation—alkali dissolution desilication—magnetic conversion—acid dissolution to produce aluminum—adsorption desorption," not only achieves the tiered separation and high-value utilization of valuable metals such as aluminum, iron, and lithium in high-alumina fly ash, but more importantly, it utilizes the residue of fly ash itself to prepare functional material polyaluminum chloride, which is then used in reverse for lithium recovery. This forms an innovative path of "treating waste with waste and internal resource recycling," significantly improving the comprehensive utilization rate of resources while reducing overall energy consumption and reaction process complexity, and has significant environmental benefits and economic prospects.

[0024] Furthermore, the ball-to-material ratio for mechanical activation is 1:3-4 g / g; the ball milling time for mechanical activation is 1-2 h.

[0025] Furthermore, the concentration of the sodium hydroxide solution used for alkaline desilication is 150–250 g / L, the solid-liquid ratio is 15–25:1 mL / g, the alkaline desilication temperature is 85–95 °C, and the alkaline desilication time is 1.5–2.5 h.

[0026] Furthermore, the mass ratio of the iron powder to the iron element in the first precipitate is 15:85-86.

[0027] Furthermore, the sodium hydroxide concentration in step (3) is 40-45%.

[0028] Furthermore, the reaction temperature in step (3) is 150–170°C, and the reaction time is 1.5–2.5 h.

[0029] Further, the mass ratio of the second precipitate, hydrochloric acid, and water in the acid dissolution process is 40:100 to 140:160; the acid dissolution temperature is 75 to 95°C, and the reaction time is 1.5 to 2.5 hours; the mass ratio of the third precipitate to bluestone powder is 6:4, and the water content of the third precipitate is 45 to 55%; the calcination temperature is 1250 to 1350°C, and the calcination time is 1.5 to 2.5 hours.

[0030] Furthermore, the ripening polymerization temperature is 50–90°C, and the ripening time is 2–2.5 h.

[0031] Furthermore, the reaction temperature in step (5) is 24–26°C, and the reaction time is 1.5–2.5 h.

[0032] Furthermore, in step (6), the pH of the acidic aqueous solution is 3 to 3.5, and the shaking time is 12 to 24 hours.

[0033] By adopting the above technical solution, the present invention has the following beneficial effects:

[0034] Based on the differences in chemical activity and reaction behavior of different phases in fly ash, this invention achieves efficient separation and high-value recovery of valuable elements such as aluminum, iron, and lithium through a multi-step synergistic conversion and recycling mechanism.

[0035] First, the fly ash is mechanically activated by high-intensity grinding to disrupt its dense surface structure, increase specific surface area, and induce lattice distortion, significantly enhancing the reactivity and leaching kinetics of elements such as silicon, aluminum, iron, and lithium in subsequent reactions. Then, an alkaline desilication process is employed, dissolving the amorphous glass phase containing the main active silica and some lithium elements within the glassy phase under alkaline conditions. This preferentially removes silicon while releasing encapsulated lithium and other valuable metal ions into the leachate. The structurally stable mullite phase remains relatively inert under these conditions, thus yielding a first precipitate significantly enriched in aluminum and iron, laying the foundation for subsequent aluminum-iron co-extraction.

[0036] Furthermore, the first precipitate of aluminum-rich iron is mixed with iron powder and subjected to a reduction reaction. The ferric oxide in the mixture undergoes a solid-phase reduction reaction with the iron powder under heating conditions to generate magnetite, which has strong magnetic properties. This transformation converts the iron element originally dispersed in the mineral phase into a magnetic phase that is easily separated by magnetic separation. The iron-containing product can be efficiently separated by magnetic separation, and a purer aluminum-rich first precipitate after magnetic separation is obtained. Subsequently, the aluminum-rich material is subjected to hydrochloric acid acid dissolution treatment, which selectively dissolves the aluminum in the form of aluminum ions to form an aluminum-containing leachate.

[0037] To achieve high-value conversion of aluminum resources, the third precipitate is mixed with bluestone powder and calcined to generate reactive calcium aluminate. This calcium aluminate is then added to the aluminum-containing supernatant after acid dissolution for aging and polymerization, rapidly generating polyaluminum chloride material. This process cleverly utilizes the calcium and aluminum sources in the fly ash residue, achieving efficient recycling and functional conversion of aluminum elements within the system, avoiding the need for additional aluminum sources, significantly reducing raw material costs and energy consumption, and improving resource utilization.

[0038] Furthermore, taking advantage of the rich hydroxyl groups and positive charge on the surface of the prepared polyaluminum chloride material, it is mixed with the lithium-containing leachate obtained from the alkaline desilication in step (2). The polyaluminum chloride can achieve efficient adsorption and enrichment of lithium ions. After adsorption, the lithium-loaded polyaluminum chloride is shaken and washed with an acidic aqueous solution. Through hydrogen ion replacement, lithium ions are desorbed from the material surface and enter the liquid phase, achieving efficient release of lithium. Finally, in an anhydrous ethanol system, the good solubility of lithium salts (such as lithium chloride) in ethanol and the insolubility of polyaluminum chloride in organic solvents are used to separate the two. The resulting lithium product and the regenerated polyaluminum chloride material both have high purity and excellent separation efficiency.

[0039] This invention, through the coupling of multiple processes such as "mechanical activation—alkali dissolution desilication—magnetic conversion—acid dissolution to produce aluminum—adsorption desorption," not only achieves the tiered separation and high-value utilization of valuable metals such as aluminum, iron, and lithium in high-alumina fly ash, but more importantly, it utilizes the residue of fly ash itself to prepare functional material polyaluminum chloride, which is then used in reverse for lithium recovery. This forms an innovative path of "treating waste with waste and internal resource recycling," significantly improving the comprehensive utilization rate of resources while reducing overall energy consumption and reaction process complexity, and has significant environmental benefits and economic prospects. Attached Figure Description

[0040] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein...

[0041] Figure 1 This is a process flow diagram of the method for extracting valuable metal elements from fly ash according to the present invention. Detailed Implementation

[0042] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0044] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0045] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0046] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0047] The fly ash used in this embodiment of the invention is high-alumina fly ash, whose main components include 44.70 wt% alumina, 43.42 wt% silicon dioxide, 0.57 wt% calcium oxide, 2.68 wt% ferric oxide, 1.37 wt% titanium dioxide, 0.63 wt% magnesium oxide, and 324.45 μg / g lithium.

[0048] Example

[0049] See Figure 1 A method for extracting valuable metal elements from fly ash, comprising the following preparation steps:

[0050] (1) Mechanical activation of fly ash;

[0051] (2) The activated fly ash in step (1) is subjected to alkaline dissolution and desiliconization to obtain leachate and first precipitate respectively;

[0052] (3) The first precipitate is mixed with iron powder and sodium hydroxide solution and then subjected to magnetic separation to obtain iron-containing substances and the second precipitate.

[0053] (4) After acid dissolving the second precipitate, a supernatant and a third precipitate are obtained. The third precipitate is mixed with bluestone powder, calcined, and then mixed with the supernatant for aging and polymerization to obtain a substance containing aluminum.

[0054] (5) After mixing and reacting the aluminum-containing substance with the leachate from step (2), centrifuge to obtain the fourth precipitate;

[0055] (6) The fourth precipitate was shaken and washed in an acidic aqueous solution, and then the water was removed. The precipitate was then centrifuged in anhydrous ethanol to separate it, and a lithium-containing supernatant and a fifth precipitate were obtained.

[0056] The ball-to-material ratio for mechanical activation is 1:3-4 g / g; the ball milling time for mechanical activation is 1-2 h.

[0057] The concentration of the sodium hydroxide solution used for alkaline desilication is 150–250 g / L, the solid-liquid ratio is 15–25:1 mL / g, the alkaline desilication temperature is 85–95 °C, and the alkaline desilication time is 1.5–2.5 h.

[0058] The mass ratio of the iron powder to the iron element in the first precipitate is 15:85-86.

[0059] The sodium hydroxide concentration in step (3) is 40-45%.

[0060] The reaction temperature in step (3) is 150-170℃ and the reaction time is 1.5-2.5h.

[0061] The mass ratio of the second precipitate, hydrochloric acid, and water in the acid dissolution process is 40:100 to 140:160; the acid dissolution temperature is 75 to 95°C, and the reaction time is 1.5 to 2.5 hours; the mass ratio of the third precipitate to bluestone powder is 6:4, and the water content of the third precipitate is 45 to 55%; the calcination temperature is 1250 to 1350°C, and the calcination time is 1.5 to 2.5 hours.

[0062] The curing polymerization temperature is 50–90°C, and the curing time is 2–2.5 h.

[0063] The reaction temperature in step (5) is 24-26℃, and the reaction time is 1.5-2.5h.

[0064] In step (6), the pH of the acidic aqueous solution is 3 to 3.5, and the shaking time is 12 to 24 hours.

[0065] Example 1

[0066] A method for extracting valuable metal elements from fly ash includes the following preparation steps:

[0067] (1) Add 100g of fly ash to a zirconia ball mill jar and ball mill at 500rpm for 1h under the condition that the material-to-ball ratio is 1:3g / g;

[0068] (2) The activated fly ash from step (1) was mixed with 150 g / L sodium hydroxide solution at a solid-liquid ratio of 15:1 mL / g, heated in a water bath at 85°C for 1.5 h, and then filtered to separate the leachate and the first precipitate. The first precipitate was washed with deionized water and the washing liquid was combined into the leachate.

[0069] (3) The first precipitate was heated to 150°C and reacted with 0.1 MPa for 2 hours under sealed conditions with 0.28 g iron powder and 20 g 40% sodium hydroxide solution. After filtration, washing with water, secondary filtration, drying, and magnetic separation, 2.27 g of iron-containing substance and the second precipitate were obtained. The main component of the iron-containing substance was iron(III) oxide with a purity of 99.4%.

[0070] (4) The second precipitate was mixed with 6M hydrochloric acid and water at a mass ratio of 40:100:160 and reacted at 75°C for 1.5 hours. After the reaction was complete, the mixture was cooled and filtered using a vacuum filter to obtain the supernatant and the third precipitate. The water content of the third precipitate was adjusted to 45%, and then mixed with bluestone powder at a mass ratio of 6:4 and calcined at 1250°C for 1.5 hours. Then it was mixed with the supernatant and matured and polymerized at 50°C for 2 hours to obtain a substance containing aluminum.

[0071] (5) Mix the aluminum-containing substance with the leachate from step (2), stir and react at 25°C for 2 hours, then centrifuge and separate, then wash and dry to obtain a solid containing lithium and aluminum, and obtain the fourth precipitate.

[0072] (6) Adjust the pH of the deionized water solution to 3 with 0.1 mol / L hydrochloric acid to obtain an acidic water solution; wash the fourth precipitate with shaking at 60°C for 12 h in the acidic water solution with pH 3, then remove the water and centrifuge with anhydrous ethanol to separate the lithium-containing supernatant and the aluminum-containing fifth precipitate; then remove the anhydrous ethanol from the lithium-containing supernatant to obtain 178 mg of lithium chloride with a purity of 98.7%; the fifth precipitate containing aluminum has a mass of 82.67 g, of which the polyaluminum chloride content is 98.9%.

[0073] Example 2

[0074] A method for extracting valuable metal elements from fly ash includes the following preparation steps:

[0075] (1) Add 100g of fly ash to a zirconia ball mill jar and ball mill at 500rpm for 1.5h under the condition that the material-to-ball ratio is 1:3.5g / g;

[0076] (2) The activated fly ash from step (1) was mixed with 200 g / L sodium hydroxide solution at a solid-liquid ratio of 20:1 mL / g, heated in a water bath at 90°C for 2 h, and then filtered to separate the leachate and the first precipitate. The first precipitate was washed with deionized water and the washing liquid was combined into the leachate.

[0077] (3) The first precipitate was heated to 160°C and reacted with 0.28g iron powder and 20.5g 40% sodium hydroxide solution under sealed conditions for 2 hours at 0.1MPa. After filtration, washing with water, secondary filtration, drying, and magnetic separation, the iron-containing substance and the second precipitate were obtained. The mass of the iron-containing substance was 2.48g, and the main component of the iron-containing substance was iron(III) oxide with a purity of 99.7%.

[0078] (4) The second precipitate was mixed with 6M hydrochloric acid and water at a mass ratio of 40:120:160 and reacted at 85°C for 2 hours. After the reaction was complete, the mixture was cooled and filtered using a vacuum filter to obtain the supernatant and the third precipitate. The water content of the third precipitate was adjusted to 50%, and then mixed with bluestone powder at a mass ratio of 6:4 and calcined at 1300°C for 2 hours. Then it was mixed with the supernatant and matured and polymerized at 90°C for 2.5 hours to obtain a substance containing aluminum.

[0079] (5) Mix the aluminum-containing substance with the leachate from step (2), stir and react at 25°C for 2 hours, then centrifuge and separate, then wash and dry to obtain a solid containing lithium and aluminum, and obtain the fourth precipitate.

[0080] (6) Adjust the pH of the deionized water solution to 3.12 with 0.1 mol / L hydrochloric acid to obtain an acidic water solution; wash the fourth precipitate with shaking at 60°C for 18 h in the acidic water solution with pH 3.42, then remove the water and centrifuge with anhydrous ethanol to separate the lithium-containing supernatant and the aluminum-containing fifth precipitate; then remove the anhydrous ethanol from the lithium-containing supernatant to obtain 186 mg of lithium chloride with a purity of 99.0%; the fifth precipitate containing aluminum has a mass of 86.26 g, of which the main component, polyaluminum chloride, has a content of 99.2%.

[0081] Example 3

[0082] A method for extracting valuable metal elements from fly ash includes the following preparation steps:

[0083] (1) Add 100g of fly ash to a zirconia ball mill jar and ball mill at 500rpm for 2h under the condition that the material-to-ball ratio is 1:4g / g;

[0084] (2) The activated fly ash from step (1) was mixed with 250 g / L sodium hydroxide solution at a solid-liquid ratio of 25:1 mL / g, heated in a water bath at 95°C for 2.5 h, and then filtered to separate the leachate and the first precipitate. The first precipitate was washed with deionized water and the washing liquid was combined into the leachate.

[0085] (3) The first precipitate was heated to 170°C and reacted at 3MPa for 2 hours under sealed conditions with 0.28g iron powder and 21g 45% sodium hydroxide solution. After filtration, washing with water, secondary filtration, drying, and magnetic separation, the iron-containing substance and the second precipitate were obtained. The mass of the iron-containing substance was 2.39g, and the main component of the iron-containing substance was iron(III) oxide with a purity of 99.5%.

[0086] (4) The second precipitate was mixed with 6M hydrochloric acid and water at a mass ratio of 40:140:160 and reacted at 95°C for 2.5 hours. After the reaction was complete, the mixture was cooled and filtered using a vacuum filter to obtain the supernatant and the third precipitate. The water content of the third precipitate was adjusted to 55%, and then mixed with bluestone powder at a mass ratio of 6:4 and calcined at 1350°C for 2.5 hours. Then it was mixed with the supernatant and matured and polymerized at 90°C for 2.5 hours to obtain a substance containing aluminum.

[0087] (5) Mix the aluminum-containing substance with the leachate from step (2), stir and react at 25°C for 2 hours, then centrifuge and separate, then wash and dry to obtain a solid containing lithium and aluminum, and obtain the fourth precipitate.

[0088] (6) The pH of the deionized water solution was adjusted to 3.5 with 0.1 mol / L hydrochloric acid to obtain an acidic water solution; the fourth precipitate was washed by shaking at 60°C for 24 h in the acidic water solution with pH 3.5, and then the water was removed. After centrifugation with anhydrous ethanol, the lithium-containing supernatant and the fifth precipitate were obtained; then the lithium-containing supernatant was removed with anhydrous ethanol to obtain 182 mg of lithium chloride with a purity of 98.9%; the fifth precipitate containing aluminum had a mass of 84.32 g, of which the main component, polyaluminum chloride, had a content of 98.9%.

[0089] In summary, the methods used in Examples 1 to 3 for extracting valuable metal elements from fly ash all achieved good extraction results, with high recovery rates for iron, lithium, and aluminum, and excellent product purity. In Example 1, 2.27g of ferric oxide with a purity of 99.4%, 178mg of lithium chloride with a purity of 98.7%, and 82.67g of aluminum-containing polyaluminum chloride with a content of 98.9% were obtained. In Example 2, 2.48g of ferric oxide with a purity of 99.7% and 186mg of lithium chloride with a purity of 99.9% were obtained. Example 1 yielded 9.0% lithium chloride and 86.26g of aluminum-based material with a polyaluminum chloride content of 99.2%; Example 2 produced 2.39g of iron(III) oxide with a purity of 99.5%, 182mg of lithium chloride with a purity of 98.9%, and 84.32g of high-purity aluminum product with a polyaluminum chloride content of 98.9%. The results show that this method can stably achieve efficient separation and high-value conversion of aluminum, iron, and lithium in fly ash within different process parameter ranges. The extraction yield of each element is considerable, the product purity is high, the process repeatability is good, and it has good feasibility and application prospects.

[0090] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of extracting valuable metal elements from fly ash, characterized by, The preparation steps include the following: (1) Mechanical activation of fly ash; (2) The activated fly ash from step (1) is subjected to alkaline dissolution and desiliconization to obtain leachate and first precipitate, respectively; (3) The first precipitate is mixed with iron powder and sodium hydroxide solution and then subjected to magnetic separation to obtain iron-containing substances and a second precipitate; the reaction temperature is 150~170℃ and the reaction time is 1.5~2.5h; (4) After acid dissolving the second precipitate, a supernatant and a third precipitate are obtained. The third precipitate is mixed with bluestone powder, calcined, and then mixed with the supernatant for ripening and polymerization to obtain a substance containing aluminum. The mass ratio of the second precipitate, hydrochloric acid, and water in the acid dissolution is 40:100~140:160; the acid dissolution temperature is 75~95℃, and the reaction time is 1.5~2.5h; the mass ratio of the third precipitate to bluestone powder is 6:4, and the water content of the third precipitate is 45~55%; the calcination temperature is 1250~1350℃, and the calcination time is 1.5~2.5h; the ripening and polymerization temperature is 50~90℃, and the ripening time is 2~2.5h. (5) After mixing and reacting the aluminum-containing substance with the leachate from step (2), centrifuge to obtain the fourth precipitate; (6) The fourth precipitate was shaken and washed in an acidic aqueous solution, and then the water was removed. The precipitate was centrifuged in anhydrous ethanol to separate the lithium-containing supernatant and the fifth precipitate.

2. The method for extracting valuable metal elements from fly ash according to claim 1, characterized in that, The ball-to-material ratio for mechanical activation is 1:3~4 g / g; the ball milling time for mechanical activation is 1~2 h.

3. The method of claim 1, wherein the method further comprises, The concentration of the sodium hydroxide solution used for alkaline desilication is 150~250g / L, the solid-liquid ratio is 15~25:1mL / g, the alkaline desilication temperature is 85~95℃, and the alkaline desilication time is 1.5~2.5h.

4. The method for extracting valuable metal elements from fly ash according to claim 1, characterized in that, The mass ratio of the iron powder to the iron element in the first precipitate is 15:85~86.

5. The method of claim 1, wherein the method further comprises: The sodium hydroxide concentration in step (3) is 40-45%.

6. The method for extracting valuable metal elements from fly ash according to claim 1, characterized in that, The reaction temperature in step (5) is 24~26℃ and the reaction time is 1.5~2.5h.

7. The method of claim 1, wherein the method further comprises, In step (6), the pH of the acidic aqueous solution is 3 to 3.5, and the shaking time is 12 to 24 hours.

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