Lepidolite treatment method for synergistically extracting lithium and solidifying thallium from metal-rich lepidolite and method for extracting lithium and / or rubidium, cesium and potassium

Abstract

The invention discloses a lepidolite treatment method for synergistically extracting lithium and solidifying thallium from metal-rich lepidolite and a method for extracting lithium and / or rubidium, cesium and potassium, and belongs to the field of hydrometallurgy. The method comprises the following steps: firstly, selectively crushing lepidolite by adopting a shear type mill, so that the lepidolite is longitudinally broken along an interlayer to expose metal ions; mixing the crushed fine powder with an activating agent, a calcium-based fluorine fixing agent and a pore forming agent for pelletizing; two-step roasting is conducted, firstly, pores are formed in the pellets through decomposition of a pore forming agent at the low temperature, then a replacement reaction and a thallium fixing reaction are conducted at the high temperature in the air atmosphere, and thallium is oxidized and fixed in a stable calcium ferrite / iron calcium silicate phase; and finally leaching, separating and recovering lithium, rubidium, cesium and potassium. According to the method, through multi-stage cooperation of physical exposure, pore-forming mass transfer and atmosphere regulation and control, the industrial problem that the leaching rate of the valuable metal and the thallium curing rate are difficult to consider at the same time is fundamentally solved, the process is clean and efficient, and remarkable economic and environmental benefits are achieved.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgical technology, specifically relating to a method for extracting valuable metals from lepidolite ore and simultaneously solidifying harmful elements, particularly a method for synergistically extracting lithium, rubidium, cesium, and potassium from metal-rich lepidolite and achieving stable solidification of thallium. Background Technology

[0002] Lithium mica is an important lithium resource, often associated with valuable metals such as rubidium, cesium, and potassium. However, lepidolite also often contains the toxic heavy metal thallium (Tl). During the extraction process, thallium easily enters the solution in the form of soluble monovalent ions (Tl⁺), causing serious environmental pollution and increasing the cost of subsequent wastewater treatment. Currently, the mainstream lithium extraction processes from lepidolite include the sulfuric acid method and the limestone method. These traditional methods have the following bottlenecks: (1) Low leaching rate of valuable metals: Conventional crushing methods such as ball milling and vertical milling easily cause lepidolite to undergo layer dissociation, resulting in an increased specific surface area. However, the metal ions between the layers are encapsulated, making it difficult for them to contact the reactants, resulting in unsatisfactory leaching rates of lithium, rubidium, and cesium. (2) Prominent risk of thallium pollution: During the roasting and leaching process, thallium is difficult to be effectively fixed, and after dissolution, it forms a potential environmental pollution hazard. (3) Low reaction efficiency: The roasting process is a solid-solid reaction with poor mass transfer efficiency, resulting in high energy consumption, long reaction time, and insufficient replacement. In the current lithium extraction process from lepidolite, the pollution control of the associated heavy metal thallium and the efficient extraction of the main metal have long been irreconcilable contradictions. Existing technologies mostly adopt the "end-of-pipe treatment" approach, such as high-temperature melting and solidification of thallium-containing waste residue (CN117534357A) or wet ion exchange removal (CN118321326A), which have bottlenecks such as high energy consumption, secondary pollution, or resource waste; there have also been attempts to add composite thallium-fixing agents in the roasting process (CN116891952A), but these are limited by the introduction of impurity ions, high costs, and failure to form a synergistic effect with the extraction of the main metal. All of the above methods regard thallium fixation as an additional cost link independent of lithium extraction, and fail to fundamentally solve the contradiction between environmental protection and economic benefits. Summary of the Invention

[0003] The primary objective of this invention is to overcome the shortcomings of existing technologies and provide a method for treating lepidolite that simultaneously achieves efficient leaching of lithium, rubidium, and cesium, and stable solidification of thallium from the source. Another objective of this invention is to provide a comprehensive recycling process that is highly efficient, energy-saving, and environmentally friendly. This invention achieves these technical objectives through the following technical means.

[0004] A method for synergistically extracting lithium and thallium from metal-rich lepidolite mica, characterized by comprising the following steps: S1. Selective crushing: The lepidolite ore is crushed using a shear mill, which has fixed outer ring teeth and rotating inner ring teeth, causing the lepidolite to fracture longitudinally along the interlayer cleavage plane to obtain fine lepidolite powder; S2. Functional mixing: The lithium mica fine powder is mixed evenly with an activator, a calcium-based fluorine fixative and a pore-forming agent. The activator is a sodium and / or potassium chloride or sulfate, and the pore-forming agent is an inorganic carbonate and / or a CH organic polymer that can decompose at 300-600℃. S3. Controlled Atmosphere Calcination: The mixed materials are pelletized and then calcined in two steps. First, calcination is carried out in a low-temperature section at 300-600℃ for pre-decomposition, which decomposes the pore-forming agent and forms microporous channels inside the pellets, while simultaneously hardening the pellets. Then, the temperature is raised to a high-temperature section at 800-950℃, and air is introduced into the calcination furnace. High-temperature calcination is carried out in a flowing air atmosphere, which oxidizes iron and thallium to the trivalent state and reacts with the calcium-based fluorine-fixing agent and the iron and silicon components in lepidolite to generate stable calcium ferrite and calcium iron silicate compounds, thereby realizing the iron replacement and thallium solidification reaction.

[0005] Furthermore, in step S1, the shear mill has a moving wheel and a fixed wheel that rotate relative to each other, and the shearing force between the moving wheel and the fixed wheel causes the lithium mica particles to fracture longitudinally along their (001) cleavage plane.

[0006] Further, in step S2, the mass ratio of the activator, calcium-based fluorine-fixing agent and lepidolite is (0.1-0.5):(0.2-0.8):1; the amount of pore-forming agent added is 1%-10% of the total mass of the mixture.

[0007] Further, in step S2, the activator is sodium sulfate, sodium chloride, sodium sulfate, potassium sodium sulfate double salt, or potassium sodium chloride double salt; the calcium-based fluoride fixative is at least one of calcium oxide, calcium hydroxide, or limestone; the pore-forming agent is at least one of ammonium carbonate, ammonium bicarbonate, or an organic polymer, and the particle size of the pore-forming agent is D50 = 20 to 50 μm.

[0008] Furthermore, in step S3, the calcination time of the low-temperature section is 0.5-2 hours; the calcination time of the high-temperature section is 0.5-2 hours.

[0009] Furthermore, in step S3, during the high-temperature roasting, the air flow rate is controlled at 0.1-5 L / min·kg, preferably 0.2-1 L / min·kg.

[0010] The lepidolite treated product obtained according to the lepidolite treatment method.

[0011] The method for extracting lithium using the lepidolite treated material is characterized by leaching the lepidolite treated material as raw material to obtain a leachate containing lithium, rubidium, cesium, and potassium, followed by extraction and evaporation crystallization processes to extract lithium.

[0012] Furthermore, it also includes steps such as recovering potassium-sodium double salts and extracting rubidium and cesium by evaporation and crystallization of the filtrate after lithium extraction.

[0013] A system for implementing the method described in any one of the above claims, characterized in that it comprises: Selective crushing unit: a shear mill with fixed outer ring teeth and rotating inner ring teeth; Mixing and pelletizing unit: used to mix and pelletize lepidolite fine powder, activator, fluorine fixative and pore-forming agent; Controlled atmosphere roasting furnace: The roasting furnace is connected to an air source and equipped with a flow meter, which has a gas flow rate regulation function and is used for roasting pelletizing materials; Leaching and separation unit: used to leach and separate valuable metals from roasted clinker.

[0014] The beneficial effects of this invention are as follows: Compared with existing technologies, the lepidolite processing method for synergistic lithium and thallium extraction from metal-rich lepidolite provided by this invention achieves a fundamental leap from "end-of-pipe treatment" to "source prevention" and "process control," demonstrating significant synergistic effects and comprehensive technical advantages. Specifically, this invention creatively integrates the solid thallium reaction with the lithium extraction process through a multi-level synergistic technology system of "selective crushing-pore-forming mass transfer-precise atmosphere control," rather than simply superimposing them. Its core advantages are: 1. It resolves the conflict between environmental protection and economic benefits. By constructing an internal porous reaction microenvironment and precisely controlling the oxidation atmosphere, it significantly improves the leaching rate of valuable metals such as lithium, rubidium, and cesium using inexpensive calcium-based components. For example, the lithium leaching rate is increased by about 10 percentage points. Harmful thallium elements are stably solidified in situ in the inert mineral lattice such as calcium ferrite and calcium iron silicate, with a thallium solidification rate of over 99.5%, thus achieving an organic unity of "quality improvement" and "emission reduction".

[0015] 2. Excellent technical and economic efficiency. This process eliminates expensive potassium ferrate and other special thallium-fixing agents, and avoids the high energy consumption of subsequent melting and solidification (>1200℃) or complex thallium-containing wastewater treatment process. It mainly relies on process control to achieve the goal, and the operating cost is significantly reduced.

[0016] 3. High resource utilization rate: It achieves synergistic and efficient extraction of multiple strategic metals such as lithium, rubidium, cesium, and potassium, and transforms the final waste residue into environmentally friendly and harmless products, truly realizing a green, efficient, and resource-based process. In summary, this invention provides an integrated solution for the clean extraction of lepidolite that is forward-looking, economical, and practical, offering a new solution to the dual challenges of environmental protection and cost faced by the industry. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the method for synergistic extraction of lithium and thallium from lithium mica according to the present invention, which involves processing lithium mica and extracting lithium, rubidium, cesium, and potassium.

[0018] Figure 2 This is a schematic diagram of the shear mill described in this invention.

[0019] Figure 3 This is a SEM image of lithium mica after being crushed by the shear mill described in this invention.

[0020] Explanation of reference numerals in the attached figures: 1. Fix the outer ring tooth, 2. Rotate the inner ring tooth. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0022] The lepidolite processing method for synergistic extraction of lithium and thallium from metal-rich lepidolite according to the present invention is characterized by comprising the following steps: S1. Selective crushing: The lepidolite ore is crushed using a shear mill, which has fixed outer ring teeth and rotating inner ring teeth, causing the lepidolite to fracture longitudinally along the interlayer cleavage plane to obtain fine lepidolite powder; S2. Functional mixing: The lithium mica fine powder is mixed evenly with an activator, a calcium-based fluorine fixative and a pore-forming agent. The activator is a sodium and / or potassium chloride or sulfate, and the pore-forming agent is an inorganic carbonate and / or a CH organic polymer that can decompose at 300-600℃. S3. Controlled Atmosphere Calcination: The mixed materials are pelletized and then calcined in two steps. First, calcination is carried out in a low-temperature section at 300-600℃ for pre-decomposition, which decomposes the pore-forming agent and forms microporous channels inside the pellets, while simultaneously hardening the pellets. Then, the temperature is raised to a high-temperature section at 800-950℃, and air is introduced into the calcination furnace. High-temperature calcination is carried out in a flowing air atmosphere, which oxidizes iron and thallium to the trivalent state and reacts with the calcium-based fluorine-fixing agent and the iron and silicon components in lepidolite to generate stable calcium ferrite and calcium iron silicate compounds, thereby realizing the iron replacement and thallium solidification reaction.

[0023] In step S1, the shear mill has a moving wheel and a fixed wheel that rotate relative to each other. The shearing force between the moving wheel and the fixed wheel causes the lithium mica particles to fracture longitudinally along their (001) cleavage plane, rather than dissociating, thinning or flattening.

[0024] In step S2, the mass ratio of the activator, calcium-based fluorine-fixing agent and lepidolite is (0.1-0.5):(0.2-0.8):1; the amount of pore-forming agent added is 1%-10% of the total mass of the mixture.

[0025] In step S2, the activator is sodium sulfate, sodium chloride, sodium sulfate, potassium sodium sulfate double salt, or potassium sodium chloride double salt; the calcium-based fluoride-fixing agent is at least one of calcium oxide, calcium hydroxide, or limestone; and the pore-forming agent is at least one of ammonium carbonate, ammonium bicarbonate, or an organic polymer. The particle size of the pore-forming agent is D50 = 20 to 50 μm. If the particle size of the pore-forming agent is too coarse, it cannot form a continuous airflow channel, resulting in insufficient reaction, low leaching rate, and reduced thallium fixation effect; if the particle size of the pore-forming agent is too fine, it creates excessively sufficient contact conditions, resulting in the formation of a dense and stable "coating layer" in the early stage of calcination, which hinders the replacement and dissolution of lithium in the main reaction.

[0026] In step S3, the roasting time of the low-temperature section is 0.5-2 hours; the roasting time of the high-temperature section is 0.5-2 hours.

[0027] In step S3, during high-temperature roasting, the air flow rate is controlled at 0.1-5 L / min·kg, preferably 0.2-1 L / min·kg.

[0028] The lepidolite treated using the aforementioned lepidolite treatment method is used as raw material for leaching. After solid-liquid separation, a leachate containing lithium, rubidium, cesium, and potassium is obtained. Lithium is then extracted through extraction and evaporation crystallization processes to obtain lithium carbonate. The thiosulfate (Tl) content in the leachate is lower than the national hazardous waste identification standard of 0.5 μg / L. The raffinate after lithium extraction is used to recover potassium-sodium double salts through evaporation crystallization, and to extract rubidium and cesium to obtain rubidium sulfate and cesium sulfate, respectively. Figure 1 As shown.

[0029] This invention also provides a system for performing the above-described lithium mica processing and extraction of lithium and / or rubidium, cesium, and potassium, comprising: Selective crushing unit: a shear mill with fixed outer ring teeth and rotating inner ring teeth, wherein the gap between the outer ring teeth and the inner ring teeth gradually decreases in the opposite direction of the rotation of the inner ring teeth; for example... Figure 2 As shown.

[0030] Mixing and pelletizing unit: used to mix and pelletize lepidolite fine powder, activator, fluorine fixative and pore-forming agent; Controlled atmosphere roasting furnace: The roasting furnace is connected to an air source and equipped with a flow meter, which has a gas flow rate regulation function and is used for roasting pelletizing materials; Leaching and separation unit: used to leach and separate valuable metals from roasted clinker. Example 1

[0031] To verify the comprehensive advantages of the "selective crushing-pore-forming mass transfer-atmosphere control" synergistic process of this invention in improving the leaching rate of valuable metals and solidifying thallium, Example 1 and Comparative Example 1 were designed using lepidolite from Linwu, Hunan Province, with the composition shown in Table 1, as raw material.

[0032] Table 1. Composition of lepidolite raw materials used in Example 1 and Comparative Example 1

[0033] S1: Using a type of lepidolite mica from Linwu, Hunan Province, with the composition shown in Table 1, as raw material. The lepidolite mica from Linwu, Hunan Province, with the composition shown in Table 1, is processed using a shear mill, such as... Figure 2 As shown, selective crushing is performed to a particle size of D50 = 34 μm, as... Figure 3 As shown, the crushed particles have rounded edges and no large lamellar structure.

[0034] S2: Mix the following materials by mass ratio: lepidolite: sodium sulfate: calcium hydroxide: ammonium carbonate = 1:0.3:0.5:0.05 and then pelletize them.

[0035] S3: After pelletizing, the spherical material is placed in a programmable temperature-controlled roasting furnace for two-step roasting. First stage: Low-temperature roasting, held at 450℃ for 1 hour, causing the pore-forming agent to decompose and form microporous channels inside the pellets, while simultaneously hardening the pellets. Second stage: High-temperature roasting, raising the furnace temperature to 900℃ and introducing air into the furnace at a flow rate of 0.5 L / min·kg (liters per kilogram of material per minute), holding for 1 hour. During the high-temperature roasting process, the reaction progress is controlled by adjusting the air flow rate, causing iron and thallium to be oxidized to their trivalent state and react with the calcium-based fluorine-fixing agent and the iron and silicon components in lepidolite to generate stable calcium ferrite and calcium iron silicate compounds, thereby achieving the replacement of iron and the solidification of thallium.

[0036] S4: Leach the clinker with water at a liquid-to-solid ratio of 5:1 for 30 minutes.

[0037] Comparative Example 1 uses a conventional process, in which lithium mica in the same proportion as in Example 1 is fed into a vertical mill for ultrafine grinding and mixing, and then the same calcination and leaching operations as in Example 1 are performed.

[0038] Table 2 Comparison of experimental results between Example 1 and Comparative Example 1

[0039] Results Analysis: Compared with the conventional vertical mill mixing process of Comparative Example 1, Example 1 of this invention significantly improved the leaching rate of valuable metals by approximately 15-20%. Simultaneously, the solidification rate of thallium increased from 85.3% to over 99.5%, and the thallium concentration in the leachate was far below the hazardous waste identification standard of 0.5 μg / L. This demonstrates the crucial importance of selectively breaking down and exposing the reaction interface and avoiding excessive mixing to prevent the formation of an encapsulation layer. Example 2

[0040] To investigate the key influence of airflow rate on the thallium solidification effect during high-temperature roasting, the airflow rate during high-temperature roasting in step S3 was changed separately, while other conditions remained the same as in Example 1. Lithium mica was treated with airflow rates of 0.1, 0.5, and 2.0 L / min·kg, respectively, and the experimental results are shown in Table 3.

[0041] Table 3. Experimental results using different air flow rates during high-temperature roasting.

[0042] Results analysis: When the air velocity was 0.1 L / min·kg, the air velocity was too low, resulting in insufficient oxygen and incomplete oxidation of thallium. When the air velocity was 2 L / min·kg, the velocity was too high, which may affect the stability of the temperature field inside the furnace and slightly reduce the reaction efficiency. The best results were achieved with a velocity of 0.5 L / min·kg, confirming the decisive role of precise control of the high-temperature roasting atmosphere in the formation of stable solid thallium minerals.

[0043] Example 3: Stability test of complex raw materials with high thallium content To verify the adaptability and stability of this process for lepidolite with high thallium content and complex composition, high-thallium lepidolite from Linwu, Hunan Province, with a Tl content as high as 420 ppm and a relatively high Fe2O3 content (~5%), was used as raw material. The process was the same as in Example 1, but the ammonium carbonate addition was increased to 7%, and the air flow rate in the high-temperature section was increased to 0.8 L / min·kg to cope with the higher thallium and iron content. The experimental results are shown in Table 4.

[0044] Table 4 Results of high thallium feedstock treatment in Example 3

[0045] Results Analysis: Even with complex raw materials containing significantly higher thallium content than usual, this process still achieves efficient leaching of valuable metals and near-complete solidification of thallium by finely adjusting the pore-forming agent content and airflow rate, demonstrating the process's strong adaptability and stability. The higher iron content actually promotes the formation of more calcium ferrite solid thallium phase.

[0046] Example 4: Stability test of complex raw materials with high thallium content To verify the adaptability and stability of this process for lepidolite with high thallium content and complex composition, high-thallium lepidolite from Linwu, Hunan Province, with a thallium content as high as 660 ppm and high Al2O3 (~7%) and Fe2O3 (~5%) content, was used as raw material. The process was the same as in Example 1, but the amount of ammonium carbonate added was increased to 10%, and the air flow rate in the high-temperature section was increased to 1 L / min·kg to cope with the higher thallium and iron content.

[0047] Table 5 Results of high thallium feedstock treatment in Example 4

[0048] Results Analysis: Even with complex raw materials containing significantly higher thallium content than usual, this process still achieves efficient leaching of valuable metals and near-complete solidification of thallium by finely adjusting the pore-forming agent content and airflow rate, demonstrating the process's strong adaptability and stability. The higher iron content actually promotes the formation of more calcium ferrite solid thallium phase.

[0049] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for the simultaneous extraction of lithium and immobilization of thallium from metal-lithium rich mica, characterized in that, Comprising the following steps: S1. Selective crushing: crushing the lepidolite ore with a shear mill having fixed outer ring teeth and rotating inner ring teeth to cause longitudinal fracture of the lepidolite along the interlayer cleavage plane, thereby obtaining lepidolite fine powder; S2. Functional mixing: uniformly mixing the lepidolite fine powder with an activating agent, a calcium-based fluorine-fixing agent, and a pore-forming agent, wherein the activating agent is a chloride salt or a sulfate salt of sodium and / or potassium, and the pore-forming agent is an inorganic carbonate or a C-H organic polymer that can be decomposed at 300-600°C; S3. Controllable atmosphere roasting: balling the mixed material and then performing two-step roasting; first, roasting at a low temperature of 300-600°C to perform pre-decomposition, decompose the pore-forming agent, and form micro-porous channels in the interior of the pellets, while hardening the pellets; then, increasing the temperature to a high temperature of 800-950°C, introducing air into the roasting furnace, and performing high-temperature roasting in a flowing air atmosphere to oxidize iron and thallium to trivalent states, and react with the calcium-based fluorine-fixing agent and iron and silicon components in the lepidolite to generate stable calcium ferrite and calcium ferrite silicate compounds, thereby achieving iron replacement and thallium solidification.

2. The method of processing lepidolite according to claim 1, wherein, In step S1, the shear mill has a dynamic wheel and a static wheel in relative rotation, and the shear force between the dynamic wheel and the static wheel causes the lepidolite particles to fracture longitudinally along the (001) cleavage plane.

3. The method of treating lepidolite according to claim 1, wherein, In step S2, the mass ratio of the activating agent, the calcium-based fluorine-fixing agent, and the lepidolite is (0.1-0.5):(0.2-0.8):1; and the addition amount of the pore-forming agent is 1%-10% of the total mass of the mixed material.

4. The processing method of lepidolite according to claim 1, characterized in that, In step S2, the activating agent is at least one of sodium sulfate, sodium chloride, sodium sulfate, sodium potassium sulfate complex salt, and potassium sodium chloride complex salt; the calcium-based fluorine-fixing agent is at least one of calcium oxide, calcium hydroxide, and limestone; and the pore-forming agent is at least one of ammonium carbonate, ammonium bicarbonate, and an organic polymer, and the particle size of the pore-forming agent is D50=20-50μm.

5. The processing method of lepidolite according to claim 1, characterized in that, In step S3, the roasting time at the low temperature is 0.5-2 hours; and the roasting time at the high temperature is 0.5-2 hours.

6. The processing method of lepidolite according to claim 1, characterized in that, In step S3, when roasting at the high temperature, the air flow rate is controlled at 0.1-5 L / min·kg, and preferably 0.2-1 L / min·kg.

7. A lepidolite treatment obtained by the lepidolite treatment method according to any one of claims 1-6.

8. A method for extracting lithium using the lithium mica treatment material according to claim 7, characterized by, The lepidolite treatment is used as a raw material for leaching to obtain a leaching solution containing lithium, rubidium, cesium, and potassium, and then lithium is extracted through extraction and evaporation crystallization processes.

9. The method of lithium extraction from lepidolite treatment according to claim 8, characterized by, The step of recovering potassium sodium complex salt and extracting rubidium and cesium from the raffinate after lithium extraction through evaporation crystallization is also included.

10. A system for implementing the method of any one of claims 1-6, 8-9, characterized in that, Comprising: a selective crushing unit: a shear mill having fixed outer ring teeth and rotating inner ring teeth, wherein the gap between the outer ring teeth and the inner ring teeth gradually decreases in the opposite direction of the rotation of the rotating inner ring teeth; a mixing and balling unit: for mixing and balling lepidolite fine powder, an activating agent, a fluorine-fixing agent, and a pore-forming agent; a controllable atmosphere roasting furnace: connected with an air source and equipped with a flow meter, having a gas flow rate regulation function, and used for roasting the balling material; a leaching and separation unit: for leaching and separating and recovering valuable metals from the roasted material.

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