A gradient microwave activation-fluorosilicate synergistic selective lithium extraction method

Abstract

This invention relates to a method for lithium extraction using gradient microwave activation and fluorosilicate synergistic selection. The method comprises the following steps: adding fluorosilicate as an activator to lepidolite concentrate for pretreatment; performing gradient microwave activation to obtain activated lepidolite concentrate powder; mixing the lepidolite concentrate powder with a composite acid leaching agent, a configuration modifier, and a stabilizer for acid leaching to obtain a lithium-rich solution; wherein the composite acid leaching agent includes at least phosphoric acid. This invention solves the problems of high impurity content in existing lepidolite lithium extraction leaches, leading to low total lithium yield, complex subsequent purification processes, and high costs. It also solves the problem of difficult lithium-aluminum separation, reduces impurity content, improves lithium recovery rate and purity, and simultaneously reduces processing costs.

Description

Technical Field

[0001] This invention relates to the field of lithium extraction technology from ores, specifically to a method for gradient microwave activation-fluorosilicate synergistic selective lithium extraction. Background Technology

[0002] In the field of lithium extraction via acid processing from lepidolite, lithium-aluminum separation has always been one of the key bottlenecks restricting the development of this technology. Lepidolite, as an important lithium resource carrier, has a high aluminum content, typically around 28%. In traditional acid processing, aluminum enters the leachate in large quantities as soluble salts. This not only significantly increases the impurity content in the leachate but also increases the difficulty of subsequent purification, greatly increasing the complexity and cost of the entire lithium extraction process.

[0003] Aluminum and lithium share many chemical similarities, making them difficult to separate effectively using simple physical or chemical methods when they coexist in leachates. In practical industrial operations, various complex treatment methods are typically required to achieve effective separation of lithium and aluminum. For example, aluminum-removing agents (such as calcium carbonate, calcium hydroxide, and sodium hydroxide) are added to promote aluminum precipitation, forming insoluble compounds such as aluminum hydroxide or aluminum fluoride hydroxide, thereby achieving lithium-aluminum separation. However, these methods still face many technical challenges in practical applications. For instance, the aluminum hydroxide particles generated in the reaction are often small and dispersed, easily leading to difficulties in the solid-liquid separation process, which in turn affects the lithium recovery rate and purity.

[0004] Furthermore, the high impurity content in the leachate complicates the subsequent purification process. This not only increases processing costs but also results in a low overall lithium yield, failing to meet the levels required for industrial applications. Therefore, although the lepidolite acid process for lithium extraction is theoretically feasible, its practical application faces numerous challenges in large-scale industrial production due to the technical difficulties in the crucial lithium-aluminum separation step. Effectively solving the lithium-aluminum separation problem, reducing impurity content, improving lithium recovery rate and purity, and simultaneously lowering processing costs have become key technical bottlenecks that urgently need to be overcome in the lepidolite acid process for lithium extraction. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a gradient microwave activation-fluorosilicate synergistic selective lithium extraction method to solve the problems of high impurity content in the leaching solution of existing lithium mica lithium extraction, which leads to low total lithium yield, complex subsequent purification and high cost. It can also solve the problem of difficult lithium-aluminum separation, reduce impurity content, improve lithium recovery rate and purity, and reduce processing costs.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for gradient microwave activation-fluorosilicate synergistic selective lithium extraction includes the following steps:

[0008] S1. Add fluorosilicate as an activator to lepidolite concentrate, pretreat, and then perform gradient microwave activation treatment to obtain activated lepidolite concentrate powder.

[0009] S2. Mix lithium mica concentrate powder, composite acid leaching agent, configuration modifier and stabilizer and acid leaching to obtain lithium-rich solution;

[0010] The composite acid leaching agent includes at least phosphoric acid.

[0011] Based on the aforementioned technical methods, a preferential lithium migration channel was effectively formed through gradient microwave activation and synergistic activation treatment with fluorosilicates. This disrupted the Si-O-Al bond while retaining the Al-O-Al bond, increasing the binding energy difference between lithium and aluminum in the crystal lattice to 28%, thus enhancing the activity of lithium in lepidolite concentrate. Then, a stable complex (stability constant lgK = 5.88) was formed between the lithium and a composite acid leaching agent, while the phosphate ions in the composite acid formed a poorly soluble aluminum precipitate, achieving preferential lithium leaching while reducing aluminum dissolution. Furthermore, the synergistic effect of configuration modifiers and stabilizers further optimized the leaching process, effectively reducing the content of impurities such as aluminum in the leachate and improving lithium recovery and purity. The entire process reduces energy consumption by 30% compared to traditional processes, eliminates the need for high-temperature roasting, reduces equipment investment by 40%, and increases the Li / Al molar ratio in the leachate to over 8:1, significantly reducing the difficulty of subsequent separation. Overall, this process achieves efficient lithium extraction and effective impurity control, simplifies subsequent lithium purification steps, reduces purification costs, and improves economic efficiency. This method solves the problems of high impurity content in the leaching solution of lithium extraction from lepidolite, which leads to low total lithium yield, complex subsequent purification processes, and high costs. It also solves the problem of difficult separation of lithium and aluminum, reduces impurity content, improves lithium recovery rate and purity, and reduces processing costs.

[0012] Preferably, the fluorosilicate is selected from ammonium fluorosilicate.

[0013] Preferably, the composite acid leaching agent comprises an organic acid and an inorganic acid, wherein the organic acid is selected from one or both of fumaric acid and tartaric acid, and the inorganic acid is selected from phosphoric acid.

[0014] Among them, fumaric acid / tartaric acid forms a stable complex with lithium (stability constant lgK=5.88), while phosphate forms an insoluble aluminum phosphate precipitate with aluminum, achieving a lithium preferential leaching rate of >97%, while controlling the aluminum dissolution rate to <10%.

[0015] Preferably, the configuration modifier is selected from polyethylene glycol-4000.

[0016] Preferably, the stabilizer is selected from β-cyclodextrin. Specifically, β-cyclodextrin serves as a fumaric acid / tartaric acid-Li + Coordination stabilizer.

[0017] Preferably, the temperature of the gradient microwave activation treatment is 300~400 ℃, the microwave power is 300~800 W, and the microwave frequency is 2.45 GHz.

[0018] Preferably, during the gradient microwave activation process, the microwave power changes in a gradient, specifically including: 300 W for 0-5 min, 500 W for 5-10 min, and 800 W for 10-15 min.

[0019] Among them, 0~5 min, 5~10 min and 10~15 min all include the upper limit value, but do not include the lower limit value.

[0020] Preferably, the pretreatment involves adding lepidolite concentrate to a Raymond mill, adding fluorosilicate as an activator, controlling the Raymond mill spindle speed to 80-120 r / min, the material moisture content to 5-10%, and the Raymond mill pretreatment time to 40-50 min, in order to achieve pretreatment of the lepidolite concentrate.

[0021] Preferably, the mass ratio of lepidolite concentrate to fluorosilicate is 1:0.15~0.3.

[0022] Preferably, the composite acid leaching agent is phosphoric acid, fumaric acid and tartaric acid, and the molar ratio of phosphoric acid, fumaric acid and tartaric acid is 1:1~3:1~3.

[0023] Preferably, the pH value of the composite acid leaching agent is 4.0~4.5.

[0024] Preferably, the mass of the configuration modifier added is 0.8 to 1.0% of the lepidolite concentrate.

[0025] Preferably, the amount of stabilizer used is 0.1 mM to 0.3 mM.

[0026] During acid leaching, the composite acid leaching agent, configuration modifier, and stabilizer can be added together. Specifically, fumaric acid and tartaric acid are first dissolved in deionized water, phosphoric acid is slowly added dropwise while stirring, polyethylene glycol-4000 and β-cyclodextrin are then added and dissolved, and finally added together to a high-pressure reactor.

[0027] Preferably, the acid leaching is carried out in a high-pressure reactor at a temperature of 65-90°C, a pressure of 0.1-0.2 MPa, and a leaching time of 100-120 min. The ratio of the activated lepidolite concentrate powder to the mixture is 1:4-5 (g:mL). The mixture is a mixture of the activated lepidolite concentrate powder and the composite acid leaching agent.

[0028] Preferably, after acid leaching, the process includes: keeping the acid-leached mixture warm and filtering it with a quartz fiber filter membrane to separate the lithium-containing filtrate and aluminum slag; rinsing the aluminum slag with a dilute organic acid to obtain a rinsing solution to recover residual lithium; mixing the rinsing solution with the lithium-containing filtrate and adding activated carbon to adsorb organic impurities to obtain a lithium-rich solution.

[0029] Preferably, the insulation temperature is 65~90 ℃.

[0030] Preferably, the rare organic acid is selected from one or both of fumaric acid and tartaric acid.

[0031] Preferably, the pH value of the dilute organic acid is 4.0.

[0032] Preferably, the aluminum slag is rinsed with dilute organic acid 2 to 3 times.

[0033] Preferably, the activated carbon used is 0.02 to 0.04% of the lepidolite concentrate.

[0034] Preferably, the molar ratio of lithium to aluminum in the lithium-rich liquid is greater than 8:1.

[0035] Preferably, the lithium-rich solution contains Li + The concentration of Li is >20 g / L and the ratio of Li to Al is >8:1.

[0036] Preferably, the chemical composition and mass percentage of the lepidolite concentrate are as follows: LiO2 2.8 w / %, Al2O3 24.33 w / %, SiO2 54.12 w / %, Fe2O3 0.46 w / %, CaO 0.15 w / %, MgO 0.15 w / %, K2O 7.84 w / %, Na2O 2.83 w / %, TiO2 0.03 w / %, ZrO2 <0.01 w / %, P2O5 0.42 w / %, SO3 <0.05 w / %, F 4.69 w / %, ZnO 0.04 w / %, SrO <0.01 w / %, MnO 0.32 w / %, NiO 0.03 w / %, CoO <0.01 w / %, CuO <0.01 w / %, Rb2O 1.32 w / %, BaO <0.05 w / %, Cs2O 0.13 w / %, the remainder being other impurities.

[0037] Preferably, the lithium leaching rate in the lepidolite concentrate is greater than 97%, and the aluminum dissolution rate is less than 10%. The lithium leaching rate is calculated based on Li₂O.

[0038] The gradient microwave activation-fluorosilicate synergistic selective lithium extraction method of the present invention is based on the synergistic effect of mineral structure directional modification and selective coordination leaching, and achieves lithium-aluminum source separation through two-stage processing.

[0039] The first stage is the gradient microwave activation process: a mixture of lepidolite and ammonium fluorosilicate is treated with a microwave field to form preferential migration channels for lithium elements and expand the binding energy difference between lithium and aluminum in the crystal lattice.

[0040] The so-called "lithium preferential migration channel" is not a pre-existing physical channel, but rather a dynamic defect network dynamically constructed through chemical reactions under the specific spatiotemporal conditions of a gradient microwave field. Lithium ions preferentially occupy and pass through this network due to their superior kinetic properties. This process fully embodies the advanced metallurgical concept of utilizing the differences in the physicochemical properties of materials to achieve efficient separation of specific elements through precise energy control. Its core logic chain is as follows:

[0041] First, by using (NH4)2SiF6 as a microwave absorber, precise and efficient heating of the reaction initiation site was achieved, overcoming the weakness of poor microwave absorption capability of the lepidolite bulk. Microwave heating induces in-situ decomposition of (NH4)2SiF6, and the generated HF gas selectively attacks the Si-O-Al bonds in the lepidolite lattice, which have different chemical bond energies and steric hindrances, thus achieving lattice disruption. The high-temperature HF gas can efficiently break these bonds; the reaction can be simplified as follows:

[0042]

[0043] The resulting Si-F bonds are unstable and will further react with HF to eventually form volatile SiF4, thereby removing silicon from the crystal lattice and causing permanent structural damage and vacancies. As is well known, calcination processes can destroy Si-O bonds; in this system, high temperature and highly reactive HF play a similar or even stronger role.

[0044] In contrast, the Al-O-Al bonds within the octahedral layer are protected by other atomic layers, resulting in greater steric hindrance and better stability. When reaction conditions are precisely controlled (i.e., gradient power prevents over-reaction), HF attacks primarily target the more readily accessible and reactive Si-O-Al connections, while the octahedral framework remains relatively intact. This selective chemical attack effectively "removes" the "hinge" connecting the silicon-oxygen tetrahedral and aluminum-oxygen octahedral layers, but preserves the basic framework of the aluminum-oxygen octahedron. It is this disruption that creates the preconditions for lithium-ion migration. However, within the disrupted lattice, lithium ions (Li... + With its inherent advantages of "+1 valence and low charge" and "small ionic radius", it possesses a much lower charge than other cations (especially Al). 3+ Si 4+ The migration barrier of lithium ions was used to achieve selective preferential migration of lithium ions from a kinetic perspective. Throughout the process, the application of gradient power ensured that the above chemical reactions and physical processes could proceed gently, orderly, and deeply, avoiding runaway reactions and maximizing the efficiency of destroying the target structure and preserving the non-target structure (Al-O-Al framework). Among them, the Al-O-Al bonds inside the octahedral layer are protected by other atomic layers, which is mainly achieved by the following three levels: (1) Physical barrier: The upper and lower silicon-oxygen tetrahedral layers (T layer) provide direct spatial shielding, making it difficult for external reactants to directly contact the interior of the octahedral layer (O layer). (2) Structural support: The interlayer cation layer (mainly K + (3) Internal binder: The hydroxyl layer (OH-) is part of the O-layer structure. - This enhances the chemical bonding and stability within the O layer, allowing it to maintain a certain degree of skeletal integrity even after the T layer is peeled off.

[0045] The second stage is selective coordination leaching: a mixed solution of fumaric acid / tartaric acid-phosphoric acid is used. Fumaric acid / tartaric acid forms a stable complex with lithium, and phosphate ions form an insoluble aluminum phosphate precipitate with aluminum, thus achieving preferential leaching of lithium.

[0046] The chemical equilibrium of the entire leaching system hinges on the "attribution" of aluminum ions. Fumaric acid / tartaric acid can not only complex lithium but also form stable, soluble complexes with aluminum ions. Therefore, a direct competitive relationship exists within the system:

[0047]

[0048]

[0049] Under conditions of pH 4.0–4.5 and temperature 65–90 °C, the reaction leading to the formation of aluminum phosphate precipitate is thermodynamically more advantageous than the formation of soluble aluminum-fumaric acid / tartaric acid complexes. This is because aluminum phosphate is a poorly soluble substance with a very small solubility product (pKsp), approximately 19–20, and its free energy decrease is much greater than that of the aluminum-fumaric acid / tartaric acid complex. The 3:1 molar ratio of fumaric acid / tartaric acid to phosphate also ensures a sufficient amount of phosphate ions to "win" the competition for aluminum ions.

[0050] Polyethylene glycol-4000, as a configuration modifier, has a dual regulatory mechanism:

[0051] 1) Inhibition of aluminum-fumaric acid / tartaric acid complexation reaction (kinetic hindrance): Due to the high charge density of lithium ions, a stable hydration layer is more easily formed on their surface. The adsorption of PEG-4000 is affected by this hydration layer, resulting in weak adsorption capacity. Therefore, PEG-4000 molecular chains selectively adsorb onto the surface of aluminum-containing solid phases, forming a dense, hydrophilic molecular "isolation network." Fumaric acid / tartaric acid molecules have a relatively large volume, and the diffusion resistance to penetrate this network structure composed of PEG-4000 molecular chains and contact the aluminum active sites on the particle surface to undergo a complexation reaction is significantly increased. This physical hindrance kinetically slows down the aluminum dissolution rate.

[0052] 2) Promotes in-situ precipitation of aluminum phosphate (stabilizing effect): Unlike the larger fumaric acid / tartaric acid molecules, the relatively smaller phosphate ions (PO4) promote in-situ precipitation. 3- It is easier for aluminum ions to penetrate the PEG-4000 adsorption layer. More importantly, when a small amount of aluminum ions dissolve from the solid surface and enter the PEG adsorption layer region, this network rich in water and polar groups can serve as an ideal micro-reaction domain. Within this region, aluminum ions meet phosphate ions and rapidly form the core of aluminum phosphate precipitate. The network structure of the PEG molecular chains can stabilize the newly formed precipitate particles, preventing them from redissolving or agglomerating and growing, thus promoting the "in-situ" formation of aluminum phosphate on the surface of the solid particles in the form of a capping layer, further strengthening the "lock-in" effect on the internal aluminum.

[0053] The role of PEG-4000 can be understood as a selective permeation membrane: it kinetically hinders the attack of large fumaric acid / tartaric acid molecules on aluminum, while providing a stable reaction and precipitation site for phosphate ions and the small amount of dissolved aluminum ions, thus achieving efficient inhibition of aluminum dissolution through thermodynamic selectivity.

[0054] The beneficial effects of this invention are:

[0055] The gradient microwave activation-fluorosilicate synergistic selective lithium extraction method of this invention first employs a gradient microwave field to treat a mixture of lepidolite and the activator ammonium fluorosilicate. Through the synergistic effect of the gradient microwave treatment and the activator, a preferential migration channel for lithium is effectively formed, and the binding energy difference between lithium and aluminum in the crystal lattice is expanded. Then, utilizing the synergistic effect of a composite acid leaching agent, configuration modifier, and stabilizer, a stable complex is formed with lithium, while a sparingly soluble aluminum precipitate is formed with aluminum. This not only achieves preferential lithium leaching but also restricts aluminum dissolution, thereby effectively reducing the content of impurities such as aluminum in the leachate and improving the lithium recovery rate and purity. The entire process reduces energy consumption by 30% compared to traditional processes, eliminates the need for high-temperature roasting, reduces equipment investment by 40%, and increases the Li / Al molar ratio in the leachate to over 8:1, significantly reducing the difficulty of subsequent separation. This method has significant application value in the field of lithium extraction from ores. Detailed Implementation

[0056] The following description, with reference to preferred embodiments, illustrates the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are merely illustrative of the present invention and not intended to limit the scope of protection of the present invention.

[0057] Where specific techniques or conditions are not specified in the detailed embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0058] In the following examples and comparative examples, the chemical composition and mass percentage of the lepidolite concentrate used were as follows: LiO2 2.8 w / %, Al2O3 24.33 w / %, SiO2 54.12 w / %, Fe2O3 0.46 w / %, CaO 0.15 w / %, MgO 0.15 w / %, K2O 7.84 w / %, Na2O 2.83 w / %, TiO2 0.03 w / %, ZrO2 <0.01 w / %, P2O5 0.42 w / %, SO3 <0.05 w / %, F 4.69 w / %, ZnO 0.04 w / %, SrO <0.01 w / %, MnO 0.32 w / %, NiO 0.03 w / %, CoO <0.01 w / %, CuO <0.01 w / %, Rb2O 1.32 w / %, BaO <0.05 w / %, Cs2O 0.13 w / %, the remainder being other impurities.

[0059] Example 1

[0060] A method for gradient microwave activation-fluorosilicate synergistic selective lithium extraction includes the following steps:

[0061] S1. Lithium mica concentrate and activator ammonium fluorosilicate (NH4SiF6) are added to a Raymond mill at a mass ratio of 1:0.2 for dry grinding. The Raymond mill spindle speed is controlled at 90 r / min, the material moisture content is 6%, and the Raymond mill pretreatment time is 40 min to ensure uniform mixing of materials, thereby achieving pretreatment of lithium mica concentrate and obtaining a ground mixture. The amount of lithium mica concentrate used is 1000g.

[0062] S2. The mixture is placed in a quartz crucible, covered with quartz wool, and placed in the center of the microwave cavity of a multi-cavity microwave reactor. Under constant conditions of 300 ℃ and 2.45 GHz microwave frequency, the microwave power is varied as follows: 300 W for 0~5 min, 500 W for 5~10 min, and 800 W for 10~15 min. Gradient microwave activation treatment is carried out. After naturally cooling to room temperature, the product is taken out and passed through a 200-mesh sieve to obtain activated lepidolite concentrate powder.

[0063] S3. Add the activated lithium mica concentrate powder to a polytetrafluoroethylene-lined high-pressure reactor, then add phosphoric acid and fumaric acid at pH 4.2 and a molar ratio of 1:3 as a composite acid leaching agent, 0.8% polyethylene glycol-4000 as a configuration modifier, and 0.1 mM β-cyclodextrin as a fumaric acid-Li + The coordination stabilizer was then subjected to acid leaching for 100 min at a temperature of 65 ℃ and a pressure of 0.1 MPa, with the liquid-solid ratio of the activator to the leaching solution being 1:4, to obtain the acid-leached mixture.

[0064] S4. The mixture after acid leaching is kept at 65 ℃ and filtered while hot using a quartz fiber filter membrane to separate the lithium-containing filtrate and aluminum slag. The aluminum slag is washed twice with fumaric acid, a dilute organic acid with a pH of 4, to obtain a washing solution to recover residual lithium. The washing solution is mixed with the lithium-containing filtrate and 0.02% activated carbon is added to adsorb organic impurities to obtain a lithium-rich solution.

[0065] Example 2

[0066] A method for gradient microwave activation-fluorosilicate synergistic selective lithium extraction includes the following steps:

[0067] S1. Lithium mica concentrate and activator ammonium fluorosilicate (NH4SiF6) are added to a Raymond mill at a mass ratio of 1:0.25 for dry grinding. The Raymond mill spindle speed is controlled at 100 r / min, the material moisture content is 6%, and the Raymond mill pretreatment time is 45 min to ensure uniform mixing of materials, thereby achieving pretreatment of lithium mica concentrate and obtaining a ground mixture. The amount of lithium mica concentrate used is 1000g.

[0068] S2. The mixture is placed in a quartz crucible, covered with quartz wool, and placed in the center of the microwave cavity of a multi-cavity microwave reactor. Under the constant conditions of 400 ℃ and 2.45 GHz microwave frequency, the microwave power is varied as follows: 300 W for 0~5 min, 500 W for 5~10 min, and 800 W for 10~15 min. Gradient microwave activation treatment is carried out. After naturally cooling to room temperature, the product is taken out and passed through a 200-mesh sieve to obtain activated lepidolite concentrate powder.

[0069] S3. Add the activated lithium mica concentrate powder to a polytetrafluoroethylene-lined high-pressure reactor, then add phosphoric acid and tartaric acid (pH 4.3, molar ratio 1:3) as a composite acid leaching agent, 0.9% polyethylene glycol-4000 as a configuration modifier, and 0.2 mM β-cyclodextrin as a tartaric acid-Li... + The coordination stabilizer was then subjected to acid leaching for 110 min at a temperature of 75 ℃ and a pressure of 0.15 MPa, with the liquid-solid ratio of the activator to the leachate being 1:4, to obtain the acid-leached mixture.

[0070] S4. The mixture after acid leaching is kept at 75 ℃ and filtered while hot using a quartz fiber filter membrane to separate the lithium-containing filtrate and aluminum slag. The aluminum slag is washed twice with tartaric acid, a dilute organic acid with a pH of 4, to obtain a washing solution to recover residual lithium. The washing solution is mixed with the lithium-containing filtrate and 0.03% activated carbon is added to adsorb organic impurities to obtain a lithium-rich solution.

[0071] Example 3

[0072] A method for gradient microwave activation-fluorosilicate synergistic selective lithium extraction includes the following steps:

[0073] S1. Lithium mica concentrate and activator ammonium fluorosilicate (NH4SiF6) are added to Raymond mill at a mass ratio of 1:0.3 for dry grinding. The Raymond mill spindle speed is controlled at 110 r / min, the material moisture content is 7%, and the Raymond mill pretreatment time is 50 min to ensure uniform mixing of materials, so as to achieve pretreatment of lithium mica concentrate and obtain the ground mixture. The amount of lithium mica concentrate used is 1000g.

[0074] S2. The mixture is placed in a quartz crucible, covered with quartz wool, and placed in the center of the microwave cavity of a multi-cavity microwave reactor. Under the constant conditions of 450 ℃ and 2.45 GHz microwave frequency, the microwave power is varied as follows: 300 W for 0~5 min, 500 W for 5~10 min, and 800 W for 10~15 min. Gradient microwave activation treatment is carried out. After naturally cooling to room temperature, the product is taken out and passed through a 200-mesh sieve to obtain activated lithium mica concentrate powder.

[0075] S3. Add the activated lithium mica concentrate powder to a polytetrafluoroethylene-lined high-pressure reactor. Then add phosphoric acid, fumaric acid, and tartaric acid at pH 4.1 and a molar ratio of 1:2:1 as a composite acid leaching agent, 1.0% polyethylene glycol-4000 as a configuration modifier, and 0.3 mM β-cyclodextrin as a fumaric acid / tartaric acid-Li + The coordination stabilizer was then subjected to acid leaching for 120 min at a temperature of 90 ℃ and a pressure of 0.2 MPa, with the liquid-solid ratio of the activator to the leaching solution being 1:4, to obtain the acid-leached mixture.

[0076] S4. The mixture after acid leaching is kept at 90 ℃ and filtered while hot using a quartz fiber filter membrane to separate the lithium-containing filtrate and aluminum slag. The aluminum slag is washed three times with tartaric acid, a dilute organic acid with a pH of 4, to obtain a washing solution to recover residual lithium. The washing solution is mixed with the lithium-containing filtrate and 0.04% activated carbon is added to adsorb organic impurities to obtain a lithium-rich solution.

[0077] Comparative Example 1

[0078] A method for selective lithium extraction from fluorosilicates includes the following steps:

[0079] S1. Lithium mica concentrate and activator ammonium fluorosilicate (NH4SiF6) are added to Raymond mill at a mass ratio of 1:0.3 for dry grinding. The Raymond mill spindle speed is controlled at 110 r / min, the material moisture content is 7%, and the Raymond mill pretreatment time is 50 min to ensure uniform mixing of materials, so as to achieve pretreatment of lithium mica concentrate and obtain the ground mixture. The amount of lithium mica concentrate used is 1000g.

[0080] S2. The mixture is placed in a quartz crucible, covered with quartz wool, and kept in a muffle furnace at 450 ℃ for 15 min. After naturally cooling to room temperature, the product is taken out and passed through a 200-mesh sieve to obtain pre-activated lepidolite concentrate powder.

[0081] S3. Add the pre-activated lithium mica concentrate powder to a polytetrafluoroethylene-lined high-pressure reactor. Then add phosphoric acid, fumaric acid, and tartaric acid at pH 4.1 and a molar ratio of 1:2:1 as a composite acid leaching agent, 1.0% polyethylene glycol-4000 as a configuration modifier, and 0.3 mM β-cyclodextrin as a fumaric acid / tartaric acid-Li + The coordination stabilizer was then subjected to acid leaching for 120 min at a temperature of 90 ℃ and a pressure of 0.2 MPa, with the liquid-solid ratio of the activator to the leaching solution being 1:4, to obtain the acid-leached mixture.

[0082] S4. The mixture after acid leaching is kept at 90 ℃ and filtered while hot using a quartz fiber filter membrane to separate the lithium-containing filtrate and aluminum slag. The aluminum slag is washed three times with tartaric acid, a dilute organic acid with a pH of 4, to obtain a washing solution to recover residual lithium. The washing solution is mixed with the lithium-containing filtrate and 0.04% activated carbon is added to adsorb organic impurities to obtain a lithium-containing leachate.

[0083] Comparative Example 2

[0084] A method for gradient microwave activation-fluorosilicate synergistic selective lithium extraction includes the following steps:

[0085] S1. Lithium mica concentrate and activator ammonium fluorosilicate (NH4SiF6) are added to Raymond mill at a mass ratio of 1:0.3 for dry grinding. The Raymond mill spindle speed is controlled at 110 r / min, the material moisture content is 7%, and the Raymond mill pretreatment time is 50 min to ensure uniform mixing of materials, so as to achieve pretreatment of lithium mica concentrate and obtain the ground mixture. The amount of lithium mica concentrate used is 1000g.

[0086] S2. The mixture is placed in a quartz crucible, covered with quartz wool, and placed in the center of the microwave cavity of a multi-cavity microwave reactor. Under the constant conditions of 450 ℃ and 2.45 GHz microwave frequency, the microwave power is varied as follows: 300 W for 0~5 min, 500 W for 5~10 min, and 800 W for 10~15 min. Gradient microwave activation treatment is carried out. After naturally cooling to room temperature, the product is taken out and passed through a 200-mesh sieve to obtain activated lithium mica concentrate powder.

[0087] S3. The activated lithium mica concentrate powder was added to a polytetrafluoroethylene-lined high-pressure reactor, and then 98% sulfuric acid and 35% fluorosilicic acid were added as a composite acid leaching agent. The mass ratio of lithium mica concentrate powder, 98% sulfuric acid and 35% fluorosilicic acid was 1:1:2. Acid leaching was then carried out for 120 min at a temperature of 90 ℃ and a pressure of 0.2 MPa. The liquid-solid ratio of the activated material to the leaching solution was 1:4, and the acid-leached mixture was obtained.

[0088] S4. After filtering the mixture after acid leaching, add Ca(OH)2 to the filtrate to adjust the pH value to above 12, so as to remove aluminum / fluorine impurities with the precipitant and obtain lithium-containing leachate after impurity removal.

[0089] Comparative Example 3

[0090] The traditional lithium extraction process using lepidolite and sulfuric acid at high temperature includes the following steps:

[0091] S1. Mix 1000 g of lepidolite concentrate powder with 98% concentrated sulfuric acid, then place the mixture in a muffle furnace and acidify and roast it at 900 ℃ for 90 min to obtain the roasted product; wherein the mass ratio of lepidolite concentrate powder to 98% concentrated sulfuric acid is 1:1.

[0092] S2. The roasted product obtained in S1 is mixed with pure water at a mass ratio of 1:4, and then stirred and leached for 90 min under a water bath at a temperature of 95 ℃. After filtration, lithium-containing leachate and leaching residue are obtained.

[0093] S3. Add Ca(OH)2 to the lithium-containing leachate to adjust the pH value to above 12, so as to remove aluminum / fluorine impurities with the precipitant and obtain the lithium-containing leachate after impurity removal.

[0094] Detection and Analysis

[0095] 1) Determination of Li2O content, Al2O3 content, pH value of lithium-rich solution, pH value of lithium-containing leachate, leaching residue yield, and Li2O leaching rate and Al2O3 leaching rate in leachite concentrate.

[0096] The formula for calculating the Li2O leaching rate in lepidolite concentrate is as follows: Lithium leaching rate = [volume of lithium-rich liquid (L) * lithium oxide concentration in lithium-rich liquid (g / L)] / [lithium oxide content in lepidolite concentrate (%) * mass of lepidolite concentrate (g)] * 100%, or, Lithium leaching rate = [volume of lithium-containing leaching liquid (L) * lithium oxide concentration in lithium-containing leaching liquid (g / L)] / [lithium oxide content in lepidolite concentrate (%) * mass of lepidolite concentrate (g)] * 100%; Aluminum leaching rate = [volume of lithium-rich liquid (L) * lithium oxide concentration in lithium-containing leaching liquid (g / L)] / [lithium oxide content in lepidolite concentrate (%) * mass of lepidolite concentrate (g)] * 100%; [[Al2O3 concentration in lithium-rich solution (g / L)] / [Al2O3 content in lepidolite concentrate (%)*mass of lepidolite concentrate (g)]*100%, or, aluminum leaching rate = [volume of lithium-containing leaching solution (L)*Al2O3 concentration in lithium-containing leaching solution (g / L)] / [Al2O3 content in lepidolite concentrate (%)*mass of lepidolite concentrate (g)]*100%; yield of leaching residue (%) = [100%×dry weight of leaching residue (g)] / dry weight of lepidolite concentrate powder (g). The results are shown in Table 1.

[0097] Table 1 shows the test results for lithium-rich solution, lithium-containing leaching solution, and leaching residue.

[0098]

[0099] As can be seen from the analysis of Table 1, by activating the lithium mica concentrate with a gradient microwave field, and then selectively leaching lithium using one or two of the following: phosphoric acid and high molecular weight organic acids, such as malonic acid or tartaric acid, the leaching rate of Li2O can be above 97%, while the aluminum dissolution rate is <10%.

[0100] By comparing Example 3 and Comparative Example 1, it can be seen that, compared with the lithium extraction process of lepidolite concentrate without pre-activation by gradient microwave field, when the lepidolite concentrate is pre-activated by gradient microwave field, the leaching rate of Li2O in the leachate is increased by 10.48% and the leaching rate of Al2O3 is reduced by 6.37%.

[0101] Comparing Example 3 and Comparative Example 2, it can be seen that Comparative Example 2, using the traditional sulfuric acid and fluorosilicic acid leaching process, resulted in an aluminum leaching rate as high as 24.40%, which is very detrimental to subsequent impurity removal and ensuring product purity. When Example 3 used phosphoric acid and one or two of the polymeric organic fumaric acid or tartaric acid to selectively leach lithium, the leaching rate of Li2O in the leachate increased by 11.05% compared to the traditional acid leaching, while the leaching rate of Al2O3 decreased by 15.64%.

[0102] By comparing Example 3 and Comparative Example 3, it can be seen that when Example 3 uses a gradient microwave field to activate lithium mica concentrate, and then uses one or two of phosphoric acid and high molecular weight organic acids such as malonic acid or tartaric acid to selectively leach lithium, the leaching rate of Li2O in the leachate is increased by 16.80% compared with the traditional sulfuric acid 900 ℃ high-temperature roasting process in Comparative Example 3, and the leaching rate of Al2O3 is reduced by 29.99%.

[0103] In summary, this invention utilizes a gradient microwave field to activate lepidolite concentrate, followed by selective leaching of lithium using one or two of phosphoric acid and high-molecular-weight organic acids, such as malonic acid or tartaric acid. This synergistic effect significantly improves the leaching rate of Li₂O while effectively controlling the leaching rate of aluminum. The conversion of lithium in lepidolite can be achieved at relatively low temperatures, saving energy and reducing production costs for subsequent impurity removal.

[0104] 2) Determination of leachate composition

[0105] The lithium-rich solution obtained in S4 of Example 3 and the lithium-containing leachate obtained in S3 of Comparative Example 3 were analyzed by inductively coupled plasma atomic emission spectrometry (ICP), gas chromatography-mass spectrometry (GC-MS), atomic absorption spectrophotometry (AAS), and automatic potentiometric titration, respectively. The results are shown in Tables 2 and 3.

[0106] Table 2 shows the main components of the lithium-rich solution obtained in Example 3.

[0107]

[0108] Note: Organic acid radicals are fumarate (C4H3O4⁻) and tartrate (C4H4O6⁻). 2- .

[0109] Table 3 shows the main components of the lithium-containing leachate obtained in Comparative Example 3.

[0110]

[0111] As shown in Table 2, the lithium-rich solution obtained in S4 of Example 3 has a Li concentration of 1.59 g / L. The main impurities include Ca, Al, Fe, SiO2, and F, while other impurities include Mg and Mn. Compared to the traditional sulfuric acid method shown in Table 3, the impurity content is reduced by more than 50%. The content of the main impurity Al is reduced by 77.4%, and the content of SiO2 is reduced by 53.9%. The content of other impurity elements is all below 0.01 g / L. This result indicates that the mild reaction conditions of the organic acid effectively reduce the dissolution of impurities, thereby significantly improving the purity of the subsequent product. Furthermore, this process also shows significant advantages in lithium-aluminum separation, further ensuring the purity and quality of the product.

[0112] In summary, the gradient microwave activation-fluorosilicate synergistic selective lithium extraction method of this invention first employs a gradient microwave field to treat a mixture of lepidolite and the activator ammonium fluorosilicate. Through the synergistic effect of gradient microwave treatment and the activator, a preferential migration channel for lithium is effectively formed, and the binding energy difference between lithium and aluminum in the crystal lattice is expanded. Then, utilizing the synergistic effect of a composite acid leaching agent, configuration modifier, and stabilizer, a stable complex is formed with lithium, while a sparingly soluble aluminum precipitate is formed with aluminum. This not only achieves preferential leaching of lithium but also restricts the dissolution of aluminum, thereby effectively reducing the content of impurities such as aluminum in the leachate and improving the lithium recovery rate and purity. The entire process reduces energy consumption by 30% compared to traditional processes, eliminates the need for high-temperature roasting, reduces equipment investment by 40%, and increases the Li / Al molar ratio in the leachate to over 8:1, significantly reducing the difficulty of subsequent separation. It has significant economic benefits and environmental friendliness, providing a new technical approach for the efficient utilization of lepidolite resources, reducing environmental pollution, and is of great significance to the sustainable development of the lithium industry. It has promotional and application value in the field of ore lithium extraction technology.

[0113] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A method for gradient microwave activation-fluorosilicate synergistic selective lithium extraction, characterized in that, Includes the following steps: S1. Add fluorosilicate as an activator to lepidolite concentrate, pretreat, and then perform gradient microwave activation treatment to obtain activated lepidolite concentrate powder. S2. Mix lithium mica concentrate powder, composite acid leaching agent, configuration modifier and stabilizer and acid leaching to obtain lithium-rich solution; The composite acid leaching agent includes organic acid and inorganic acid, wherein the organic acid is selected from one or two of fumaric acid and tartaric acid, and the inorganic acid is selected from phosphoric acid; The configuration modifier is selected from polyethylene glycol-4000; The stabilizer is selected from β-cyclodextrin; The pH value of the composite acid leaching agent is 4.0~4.5, and the acid leaching temperature is 65~90℃.

2. The method for gradient microwave activation-fluorosilicate synergistic selective lithium extraction according to claim 1, characterized in that, The fluorosilicate is selected from ammonium fluorosilicate.

3. The method for gradient microwave activation-fluorosilicate synergistic selective lithium extraction according to claim 1, characterized in that, The gradient microwave activation treatment is performed at a temperature of 300-400 °C, a microwave power of 300-800 W, and a microwave frequency of 2.45 GHz.

4. The method for gradient microwave activation-fluorosilicate synergistic selective lithium extraction according to claim 3, characterized in that, During the gradient microwave activation process, the microwave power changes in a gradient, specifically: 300 W for 0-5 min, 500 W for 5-10 min, and 800 W for 10-15 min.

5. The method for gradient microwave activation-fluorosilicate synergistic selective lithium extraction according to claim 1, characterized in that, The pretreatment involves adding lepidolite concentrate to a Raymond mill, adding fluorosilicate as an activator, controlling the Raymond mill spindle speed to 80-120 r / min, the material moisture content to 5-10%, and the Raymond mill pretreatment time to 40-50 min, in order to achieve the pretreatment of lepidolite concentrate.

6. The method for gradient microwave activation-fluorosilicate synergistic selective lithium extraction according to claim 1, characterized in that, The mass ratio of lepidolite concentrate to fluorosilicate is 1:0.15~0.3; And / or, the composite acid leaching agent is phosphoric acid, fumaric acid and tartaric acid, wherein the molar ratio of phosphoric acid, fumaric acid and tartaric acid is 1:1~3:1~3; And / or, the mass of the configuration modifier added is 0.8~1.0% of the lepidolite concentrate; And / or, the amount of the stabilizer used is 0.1 mM to 0.3 mM.

7. The method for gradient microwave activation-fluorosilicate synergistic selective lithium extraction according to claim 1, characterized in that, The acid leaching is carried out in a high-pressure reactor at a pressure of 0.1-0.2 MPa for 100-120 min. The ratio of the activated lithium mica concentrate powder to the mixture is 1:4-5 (g:mL). The mixture is a mixture of activated lepidolite concentrate powder and a composite acid leaching agent.

8. The method for gradient microwave activation-fluorosilicate synergistic selective lithium extraction according to claim 1, characterized in that, After acid leaching, the process includes: keeping the acid-leached mixture warm and filtering it with a quartz fiber filter membrane to separate the lithium-containing filtrate and aluminum slag; rinsing the aluminum slag with a dilute organic acid to obtain a rinsing solution to recover residual lithium; mixing the rinsing solution with the lithium-containing filtrate and adding activated carbon to adsorb organic impurities to obtain a lithium-rich solution.

9. The method for gradient microwave activation-fluorosilicate synergistic selective lithium extraction according to claim 8, characterized in that, The insulation temperature is 65~90℃; And / or, the rare organic acid is selected from one or both of fumaric acid and tartaric acid; And / or, the activated carbon used is 0.02% to 0.04% of the mass of the lepidolite concentrate; And / or, the molar ratio of lithium to aluminum in the lithium-rich solution is greater than 8:

1.

10. The method for gradient microwave activation-fluorosilicate synergistic selective lithium extraction according to claim 1, characterized in that, The chemical composition and mass percentage of the lepidolite concentrate are as follows: LiO2 2.8 w / %, Al2O3 24.33 w / %, SiO2 54.12 w / %, Fe2O3 0.46 w / %, CaO 0.15 w / %, MgO 0.15 w / %, K2O 7.84 w / %, Na2O 2.83 w / %, TiO2 0.03 w / %, ZrO2 <0.01 w / %, P2O5 0.42 w / %, SO3 <0.05 w / %, F 4.69 w / %, ZnO 0.04 w / %, SrO <0.01 w / %, MnO 0.32 w / %, NiO 0.03 w / %, CoO <0.01 w / %, CuO <0.01 w / %, Rb2O 1.32 w / %, BaO <0.05 w / %, Cs2O 0.13 w / %, the remainder being other impurities; And / or, the lithium leaching rate in the lithium mica concentrate is greater than 97%, and the aluminum dissolution rate is less than 10%.

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