A lithium extraction process from lithium-adsorbed grayish-brown salt lake clay

Abstract

The present application relates to the technical field of metal extraction, and particularly relates to a lithium extraction process for brown salt lake clay containing lithium-adsorbed ash. The lithium extraction process for brown salt lake clay containing lithium-adsorbed ash comprises the following steps: crushing and sieving the brown salt lake clay containing lithium-adsorbed ash, then immersing fine particles in a leaching agent, and filtering to obtain a leaching solution containing lithium elements; wherein the leaching agent is configured by low-mineralization water and concentrated sulfuric acid, the volume of the concentrated sulfuric acid is 5% to 20% of the volume of the leaching agent, and the low-mineralization water is natural water in Mahai Basin. The present application configures a composite leaching system by compounding low-mineralization water in a mining area with sulfuric acid, and through the triple synergistic effect of H + , SO4 2‑ and cations in low-mineralization water dissociated by sulfuric acid, the lithium leaching rate of 86.88% is achieved while the cost of the leaching agent is significantly reduced.

Description

Technical Field

[0001] This invention relates to the field of metal extraction technology, and in particular to a lithium extraction process for grayish-brown salt lake clay containing adsorbed lithium. Background Technology

[0002] Lithium, as an important strategic metal, is widely used in lithium batteries, ceramics, glass, alloys, and the nuclear industry. With the rapid development of new energy vehicles and energy storage industries, global demand for lithium resources continues to grow rapidly. Natural lithium resources are mainly found in salt lake brines and lithium minerals (such as spodumene, petalite, and lepidolite). Among these, spodumene, due to its high lithium content and relatively concentrated distribution, has become the primary raw material for lithium extraction from ore. The main chemical component of spodumene is Li₂O·Al₂O₃·4SiO₂. Its natural form is usually a chemically inert α-phase structure, which is difficult to leach directly by conventional acids and alkalis. Therefore, pretreatment is necessary to convert it into a more reactive form to achieve efficient lithium extraction.

[0003] Currently, the main industrial methods for extracting lithium from spodumene include the sulfuric acid process, the sulfate process, and the limestone process, but these methods all have limitations to varying degrees. For example, while the auxiliary roasting-leaching process of the sulfuric acid process can destroy the crystal lattice of lithium-containing minerals to extract lithium, it requires high temperatures and the lithium concentration in the leachate is low. Although the direct acid leaching process can extract lithium products, it significantly increases acid consumption, and the acid causes certain damage to the environment and equipment, with subsequent impurity removal costs accounting for a relatively high proportion.

[0004] The applicant has discovered that the saline lake clay of the Mahai Basin is a special type of lithium resource, characterized by complex chemical composition, fine particle size, and large differences in thermal stability. Its composition includes clay minerals such as montmorillonite and illite, as well as detrital minerals such as quartz and feldspar, with small and uniform particle size distribution. Lithium ions exist in three main forms within the clay minerals, corresponding to different adsorption types: first, they are mostly present in the interlayer space of 2:1 layered clay minerals such as montmorillonite in an ion-exchange adsorption state, achieving enrichment by replacing the original cations in the interlayer, which belongs to ion-exchange adsorption; second, they are embedded in the crystal lattice of minerals such as illite and chlorite in an isomorphous substitution state, replacing Mg in the crystal lattice. 2+ Fe 2+ The first type exists stably as cations, essentially belonging to chemisorption; the second type is adsorbed onto the surface of clay mineral particles in a surface-adsorbed state, with adsorption mechanisms encompassing both physical adsorption and surface complexation—physical adsorption relies on electrostatic attraction or hydrogen bonding of hydroxyl functional groups, while surface complexation occurs through the interaction of active sites on the mineral surface with Li. + Interactions occur in two ways: inner-layer complexes, which are formed by direct coordination of ligands to form inner-sphere complexes, and outer-layer complexes, which are formed by indirect binding through water molecules or anions to form outer-sphere complexes. These two types of complexation together constitute important adsorption forms in the surface adsorption state besides physical adsorption.

[0005] There is an urgent need in this field to develop a method for lithium extraction from saline lake clay in the Mahai Basin that is simple in process flow, mild in reaction conditions, low in energy consumption, environmentally friendly, and can realize the resource utilization of saline lake clay, so as to overcome the shortcomings of existing technologies. Summary of the Invention

[0006] The purpose of this invention is to address the aforementioned shortcomings of the prior art by proposing a lithium extraction process using grayish-brown salt lake clay containing adsorbed lithium.

[0007] The purpose of this invention is to provide a lithium extraction process for grayish-brown salt lake clay containing adsorbed lithium, comprising the following steps: crushing and sieving the grayish-brown salt lake clay containing adsorbed lithium, then impregnating the fine particles in a leaching agent, and filtering to obtain a leachate containing lithium; wherein the leaching agent is prepared by using low-mineralized water and concentrated sulfuric acid, the volume of concentrated sulfuric acid being 5% to 20% of the volume of the leaching agent, and the low-mineralized water being natural water from the Mahai Basin.

[0008] Furthermore, the impregnation temperature is 25°C to 55°C.

[0009] Furthermore, the impregnation temperature is 35°C to 45°C.

[0010] Furthermore, the soaking time is 30 to 60 minutes.

[0011] Furthermore, the liquid-to-solid ratio of the extractant and the adsorbed lithium-brown salt lake clay is 3-6:1.

[0012] Furthermore, mechanical stirring is used to assist impregnation under constant temperature conditions.

[0013] Furthermore, the particle size of the fine particles is 80-200 mesh.

[0014] Furthermore, the volume of concentrated sulfuric acid is 20% of the volume of the extractant, the impregnation temperature is 35°C, and the liquid-solid ratio of the extractant and the grayish-brown salt lake clay containing adsorbed lithium is 6:1.

[0015] To address the technical challenges of lithium extraction from grayish-brown salt lake clay containing adsorbed lithium, this invention innovatively develops an environmentally friendly lithium extraction process. The lithium ions in this clay exist through physical adsorption. The core of the process involves using a composite leaching system formed by combining low-mineralized water from the mining area with low-concentration sulfuric acid. The process utilizes the H+ released from the dissociation of sulfuric acid... + SO4 2- A triple synergistic effect is achieved with cations in low-mineralized water to leach lithium ions: H + Through acidification, lithium ions are desorbed and released from clay adsorption sites; SO4 2- As a doubly charged anion, it forms complexes or precipitates with some impurity cations, avoiding the influence of competitive exchange of hydrogen ions in subsequent leaching experiments, which is beneficial to Li+ With H + Ion exchange; high concentrations of Ca in low-mineralized water 2 + Mg 2+ Metal cations such as Li can react with Li + Through interaction, under the action of ion exchange and permeation, the pore structure will transfer from micropores to macropores and then decompose back into micropores, changing the morphology of mineral particles and resulting in a loose internal structure of clay minerals, which is conducive to the leaching of lithium.

[0016] In summary, this invention constructs a composite leaching system by combining low-mineralized water from the mining area with sulfuric acid, and utilizes the H+ released from the dissociation of sulfuric acid... + SO4 2- The triple synergistic effect of lithium leaching with cations in low-mineralized water significantly reduces the cost of leaching agents while achieving a lithium leaching rate of 86.88%. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the process of the present invention; Figure 2 The effect of pH on simulated lithium-ion adsorption; Figure 3 The images show the analytical results of clay ore in freshwater column leaching and ion column leaching: a. Freshwater column leaching NMR T2 spectrum; b. Freshwater column leaching porosity distribution; c. Ion column leaching NMR T2 spectrum; d. Ion column leaching porosity distribution. Figure 4 Pore ​​size distribution at different times: a. Freshwater immersion column; b. Ion immersion column. Detailed Implementation

[0018] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0019] Technical solution (1) Clay sample preparation Clay samples were taken using random sampling. A random sampling table was used to select a certain number of bags for sampling. The collected samples were spread out, mixed, and packaged for later use. An electrically heated constant-temperature drying oven was set to 110 ℃, and the clay samples were placed inside to dry completely. After the moisture in the samples was completely removed, they were packaged for later use. The samples dried using a jaw crusher were then crushed and mixed. Based on the particle size distribution results, the samples were passed through a 16-mesh sieve and finally packaged for later use.

[0020] (2) Preparation of leaching agent A composite leaching agent was prepared using sulfuric acid and low-mineralized water. A 1:10 volume ratio of sulfuric acid and low-mineralized water was measured, and then sulfuric acid solution was slowly added to the low-mineralized water. After stabilization, the supernatant was collected as the composite leaching agent for lithium extraction. The composition of the leaching agent is shown in Table 1.

[0021] Table 1. Composition of different leaching agents

[0022] (3) Leaching experiment Accurately weigh 100.00 g of dry clay sample into a 1 L beaker. While stirring, add the leaching agent to the beaker at a liquid-to-solid ratio of 6:1. Place the beaker in a heated ultrasonic cleaner, set the temperature and time, and turn on the top-mounted stirrer for leaching. Once the reaction is complete, immediately remove the beaker and use a circulating water vacuum pump to filter the leached suspension, obtaining the leachate and leaching residue. For grayish-brown lithium-adsorbed salt lake clay, an orthogonal experiment was conducted, selecting four factors: leaching temperature, leaching time, sulfuric acid concentration, and solid-liquid ratio. Each factor was set with four levels, resulting in sixteen orthogonal experiments. The leaching products were tested, the leaching rate was calculated, and the optimal experimental ratio was selected. Experimental conditions are shown in Table 2.

[0023] Table 2 Orthogonal Experiment Conditions

[0024] Note: L represents low-mineralized water, HH represents grayish-brown salt lake clay, and S represents sulfuric acid. (4) Content detection 1) Immersion test method: Accurately pipette 2.5 mL of the leachate sample into a 30 mL polytetrafluoroethylene crucible, place it on a constant temperature hot plate for heating, extract with HCl, and dilute to 100 mL in a volumetric flask. Plot a standard curve in 10% HCl medium using a mixed standard solution, determine lithium by ICP-MS, and automatically correct for matrix and spectral interferences using a computer.

[0025] 2) Methods for testing leaching residue: Weigh 0.1000 g of sample into a 30 mL polytetrafluoroethylene crucible, moisten with water, add hydrofluoric acid, hydrochloric acid, nitric acid and perchloric acid, soak on a hot plate overnight, pre-dissolve by heating the next day, decompose by heating and remove fluoride, extract with hydrochloric acid, and make up to 10 mL. Prepare a working curve using mixed standards, and determine the Li element content in 1% HCl solution by ICP-MS.

[0026] (5) Process flow: such as Figure 1 As shown.

[0027] (6) Calculation of leaching rate ×100% Examples and Comparative Examples The clay in the salt lake exhibits significant differentiation during deposition: the upper part is an evaporite layer, which can be further divided into clay with high halite content (referred to as halite layer clay) and clay with high silt content (referred to as silt layer clay); the lower part contains grayish-brown clay (shallow strata, in an oxidizing environment, containing brown minerals such as hematite) and grayish-green clay (deeper strata, in a reducing environment, containing grayish-green minerals such as siderite), and the lower clay is generally enriched in illite and chlorite, and the overall mineral composition also includes montmorillonite, quartz, feldspar, etc., with uniform grain size distribution. The grayish-brown clay was formed in the relatively moist, low-salinity oxidizing environment of the early salt lake. The low salinity of the water provided ample conditions for the dispersion of clay minerals such as montmorillonite and illite. Montmorillonite, as a 2:1 type layered clay mineral, can fix lithium ions in the lake water within the interlayer space through ion exchange adsorption, achieving initial lithium adsorption by replacing the original cations in the interlayer. Simultaneously, the oxidizing environment preserved the hydroxyl functional groups on the surface of the clay minerals. These functional groups can further complex and adsorb free lithium ions through electrostatic attraction and hydrogen bonding, forming a secondary lithium adsorption and enrichment process. Furthermore, the grayish-brown clay contains low levels of salts such as halite and gypsum, effectively avoiding interference from salt dissolution in the adsorption process and ensuring that lithium ions are stably adsorbed within the clay minerals, preventing loss due to changes in the external environment.

[0028] For gray-brown salt lake clay, halite layer clay, silty sand layer clay, and gray-green clay containing adsorbed lithium, an orthogonal experiment was used to systematically investigate the leaching effects of four different leaching systems: fresh water, low-mineralized water, sulfuric acid plus fresh water, and sulfuric acid plus low-mineralized water.

[0029] Case 1: Using sulfuric acid and low-mineralized water as leaching agents, an orthogonal experiment was conducted on gray-brown clay. Four factors were selected: leaching temperature, leaching time, sulfuric acid concentration, and solid-liquid ratio. Four levels were set for each factor, and sixteen orthogonal experiments were conducted. The leaching products were tested, the leaching rate was calculated, and the optimal experimental ratio was selected. The results are shown in Table 3.

[0030] Table 3. Orthogonal experimental table of sulfuric acid + low-mineralization water leaching of grayish-brown clay

[0031] Note: L represents low-mineralized water, HH represents grayish-brown salt lake clay, and S represents sulfuric acid. The results of 16 orthogonal experiments show that the leaching rate of Li ranged from 34.43% to 86.88%, with group 15 showing the highest leaching rate at 86.88%, indicating the best leaching effect. The corresponding experimental conditions were L - HH - S15, i.e., temperature 55℃, time 45 min, acid concentration 10%, and liquid-to-solid ratio 6:1. The key factor lies in the H+ ions dissociated from sulfuric acid. + SO4 2- The triple synergistic effect with cations in low-mineralized water: H + Through acidification, lithium ions are dissociated; SO4 2- As a doubly charged anion, it forms complexes or precipitates with some impurity cations, which is beneficial to Li + With H + Ion exchange; high concentrations of Ca in low-mineralized water 2+ Mg 2 + Metal cations such as Li can react with Li + Through interaction, under the action of ion exchange and permeation, the pore structure will transfer from micropores to macropores and then decompose back into micropores, changing the morphology of mineral particles and resulting in a loose internal structure of clay minerals, which is conducive to the leaching of lithium.

[0032] Case 2: Using sulfuric acid and fresh water as leaching agents, an orthogonal experiment was conducted on gray-brown clay. Four factors were selected: leaching temperature, leaching time, sulfuric acid concentration, and solid-liquid ratio. Four levels were set for each factor, and sixteen orthogonal experiments were conducted. The leaching products were tested, the leaching rate was calculated, and the optimal experimental ratio was selected. The results are shown in Table 4.

[0033] Table 4. Orthogonal experimental table of sulfuric acid + fresh water leaching of gray-brown clay

[0034] Note: D represents freshwater, HH represents grayish-brown salt lake clay, and S represents sulfuric acid. Table 4 shows that sulfuric acid is used as a leaching solvent with fresh water. Besides the H+ produced during the dissociation of sulfuric acid... + In addition to promoting lithium-ion dissociation through acidification, it can also dissociate SO4. 2- It reacts with other impurity cations, such as calcium and magnesium, to form precipitates, removing impurity ions and avoiding their impact on the competitive exchange process of hydrogen ions in subsequent leaching experiments. This improves lithium leaching efficiency to some extent, but the overall effect is still not as good as the sulfuric acid plus low-mineralization water system. The reason is that although the freshwater system can achieve basic acid dissociation with sulfuric acid, it lacks the activation and loosening effect of low-mineralization water on clay minerals.

[0035] Case 3: Using hydrochloric acid and low-mineralized water as the leaching agent, an orthogonal experiment was conducted, selecting four factors: leaching temperature, leaching time, hydrochloric acid concentration, and solid-liquid ratio. Each factor was set with four levels, and sixteen orthogonal experiments were performed. The leaching products were tested and the leaching rate was calculated. The experimental results are shown in Table 5.

[0036] Table 5. Results of orthogonal experiments on hydrochloric acid-soluble clay with low mineralization.

[0037] Note: L represents low-mineralized water, HH represents grayish-brown salt lake clay, and C represents hydrochloric acid. Table 5 shows that the leaching effect of hydrochloric acid with low-mineralized water is worse than that of the sulfuric acid system, mainly due to the difference in Cl. - Unable to be like SO4² - That way, it forms a precipitate with impurity cations such as calcium and magnesium, and the impurity ions remain in the leaching system and react with Li. + Competitive adsorption sites and H + This severely interferes with ion exchange reactions, and at the same time, Cl... - It will increase the ionic strength of the solution, inhibit the activation effect of low-mineralized water on the active sites of minerals, and ultimately result in a lower leaching rate.

[0038] Case 4: Low-mineralized water was used as the leaching agent. An orthogonal experiment was conducted on gray-brown clay, taking into account three factors: leaching temperature, leaching time, and solid-liquid ratio. The leaching products were tested, and the leaching rate was calculated. The experimental results are shown in Table 6.

[0039] Table 6. Orthogonal experimental results of water-soluble grayish-brown clay with low mineralization.

[0040] Note: L represents low-mineralized water, and HH represents grayish-brown salt lake clay. As shown in Table 6, the leaching effect of low-mineralization water is poor, with the leaching rate of Li in clay not exceeding 27%. The poor effect of using low-mineralization water alone is mainly due to its lack of effective components that can destroy the clay mineral structure, making it difficult to break the adsorption between lithium ions and clay, thus making it difficult to release lithium ions.

[0041] Case 5: Using fresh water as the leaching agent, an orthogonal experiment was conducted on gray-brown clay, taking into account three factors: leaching temperature, leaching time, and solid-liquid ratio. The leaching products were then analyzed, and the leaching rate was calculated. The experimental results are shown in Table 7.

[0042] Table 7. Orthogonal experimental table of freshwater-leached gray-brown clay

[0043] Note: D represents freshwater, and HH represents grayish-brown salt lake clay. As shown in Table 7, the leaching effect of fresh water is poor, with the leaching rate of Li in clay not exceeding 16%. The poor effect of leaching with fresh water is mainly due to the extremely low ionic strength of fresh water. It cannot reduce the adsorption of lithium by clay through ion competition, nor can it change the double electric layer structure on the surface of clay particles, making it difficult for lithium ions to desorb and diffuse into the solution, ultimately resulting in poor leaching effect.

[0044] Based on the excellent leaching effect of sulfuric acid plus low-mineralization water composite leaching agent on gray-brown clay, comparative leaching experiments were conducted on halite layer clay, silt layer clay, and gray-green clay to explore the leaching effect of sulfuric acid plus low-mineralization water leaching agent on different clay layers, and to further determine the leaching effect of sulfuric acid plus low-mineralization water composite leaching agent on gray-brown lithium-adsorbed salt lake clay.

[0045] Case Six: Using sulfuric acid and low-mineralized water as leaching agents, an orthogonal experiment was conducted on halite clay layers. Four factors were selected: leaching temperature, leaching time, sulfuric acid concentration, and solid-liquid ratio. Four levels were set for each factor, and sixteen orthogonal experiments were conducted. The leaching products were tested, the leaching rate was calculated, and the optimal experimental ratio was selected. The results are shown in Table 8.

[0046] Table 8. Orthogonal Experiment Table of Leaching of Salt Layer Clay with Sulfuric Acid and Low-Mineralization Water

[0047] Note: L represents low-mineralized water, SY represents halite clay, and S represents sulfuric acid. As shown in Table 8, the leaching rate of halite clay using sulfuric acid and low-mineralized water as a solvent did not exceed 70%. The overall leaching effect of halite clay was poor, mainly because the clay mineral content in halite clay was low and the content of other salt minerals was high, which hindered the leaching of lithium during the leaching process.

[0048] Case Seven: Using sulfuric acid and low-mineralized water as leaching agents, an orthogonal experiment was conducted on silty clay layers. Four factors were selected: leaching temperature, leaching time, sulfuric acid concentration, and solid-liquid ratio. Four levels were set for each factor, and sixteen orthogonal experiments were conducted. The leaching products were tested, the leaching rate was calculated, and the optimal experimental ratio was selected. The results are shown in Table 9.

[0049] Table 9. Orthogonal experimental table of sulfuric acid and low-mineralization water leaching of silty sand and clay layers

[0050] Note: L represents low-mineralized water, FS represents silty clay layer, and S represents sulfuric acid. As shown in Table 9, the leaching effect of sulfuric acid with low-mineralized water as a solvent for silty clay is relatively poor. This is mainly because the gray-brown clay has a higher content of effective clay minerals and a relatively loose structure with good pore connectivity, which can fully adapt to the mechanism of low-mineralized water activating mineral active sites and promoting ion exchange. In contrast, the silty clay has a low proportion of clay minerals and a dense particle arrangement with low porosity, so lithium ions cannot fully contact and react with the solvent.

[0051] Case 8: Using sulfuric acid and low-mineralized water as leaching agents, an orthogonal experiment was conducted on gray-green clay. Four factors were selected: leaching temperature, leaching time, sulfuric acid concentration, and solid-liquid ratio. Four levels were set for each factor, and sixteen orthogonal experiments were conducted. The leaching products were tested, the leaching rate was calculated, and the optimal experimental ratio was selected. The results are shown in Table 10.

[0052] Table 10 Orthogonal Experiment Table of Low-Mineralization Water Solubilization of Gray-Green Clay with Sulfuric Acid

[0053] Note: L represents low-mineralized water, HL represents grayish-green clay, and S represents sulfuric acid. As shown in Table 10, the leaching effect of sulfuric acid and low-mineralization water on gray-green clay is relatively poor. The gray-green clay contains a large amount of salt minerals such as halite, gypsum, and carbonates, which affects the leaching of lithium during the leaching process.

[0054] Study on leaching mechanism To further explore the leaching mechanism of lithium ions in clay minerals and clarify the influence of adsorption characteristics, acid concentration control, and ion exchange on the leaching effect, this study conducted a series of targeted experiments: Four typical clay minerals—illite, chlorite, montmorillonite, and kaolinite—were selected. Ion adsorption experiments were conducted to analyze the regulatory effect of different acid concentrations on lithium ion adsorption, providing a basis for optimizing the acid concentration in the leaching system. Simultaneously, column leaching experiments were designed, using Ca²⁺... + Mg² + Using a solution and deionized water as the leaching medium, the system traced the evolution of clay pore structure during the leaching process, revealing the characteristics of Ca²⁺ pore structure. + Mg² + The study elucidated the core mechanism of lithium ion leaching in clay minerals by investigating the exchange mechanism between lithium ions and changes in pore morphology.

[0055] The regulatory effect of pH on lithium ion adsorption Based on the types and characteristics of clay minerals in the clay layer, mineral samples such as illite, chlorite, montmorillonite, and kaolinite were selected to conduct lithium ion adsorption experiments to explore the effect of pH on the simulated adsorption of lithium ions.

[0056] from Figure 2 It can be seen from this that clay minerals affect Li + The adsorption of these compounds is mainly concentrated in the weakly alkaline range of pH 7-8, where the overall adsorption capacity is relatively high. Montmorillonite reaches its maximum adsorption capacity of 11.8 μg / g at pH 8. When pH > 8, the adsorption capacity of illite and kaolinite decreases due to precipitation reducing ionic strength, while chlorite shows relatively stable fluctuations. Therefore, it can be concluded that the lower the pH, the weaker the adsorption capacity of lithium ions, and H+ competes with lithium ions for adsorption.

[0057] Ca 2+ Mg 2+ Effect on lithium-ion leaching efficiency Use the prepared Ca respectively 2+ Mg 2+ Leaching tests were conducted on clay ore using column leaching solution and deionized water.

[0058] As shown in Figure 3(a) and (b), clay ore reaches saturation within 0.5 h of freshwater column immersion. It can be observed that the T2 spectrum curve and the relaxation time envelope area increase rapidly. Due to the water absorption and expansion of clay, the pore structure of clay undergoes significant changes in the early stage of column immersion. However, no ion exchange reaction occurs during this process. The T2 spectrum curves at subsequent times show almost no shift. After the clay reaches saturation, a seepage steady state is formed, and a fixed microtubule structure is formed inside, with the pore structure hardly changing anymore.

[0059] As shown in Figures 3(c) and (d), during the initial 1.0 h of leaching, the clay ore gradually reached saturation under the influence of CaCl2 and MgCl2 leaching solutions. The buoyancy of the water altered the particle distribution of the ore, leading to a significant increase in the envelope area of ​​the T2 spectrum curve and a significant increase in the number of pores. As the leaching process progressed, in the last 3.0 h of the saturated period, the envelope area of ​​the T2 spectrum curve did not change significantly, indicating that the number of pores in the saturated soil sample remained almost unchanged. 2+ Mg 2+ Li in clay minerals + The exchange process alters the morphology of the mineral particles. The T2 spectrum curve of the ion column impregnation of clay gradually shifts to the right, and the transverse relaxation time span continuously decreases. This causes the pore structure inside the sample to change from large pores to medium and small pores, thereby altering the pore distribution over time.

[0060] The size of pore radius within clay minerals is primarily controlled by their microstructure; the better the continuity of the pore structure, the larger the pore radius. Based on the criteria for defining pore radius and the actual measured pore size range, pores are classified into five categories: 0–0.1 μm for micropores, >0.1–0.16 μm for small pores, >0.16–0.25 μm for mesopores, >0.25–1 μm for macropores, and >1 μm for ultramacropores. The pore size distribution during freshwater column leaching and ion column leaching is shown in the figure. Figure 4 As shown in (a) and (b), despite being in different column impregnation stages, the clay contains a large proportion of small and medium pores, with medium pores accounting for the largest proportion and large pores accounting for a smaller proportion.

[0061] Using Ca 2+ Mg 2+ During solution leaching, in the early stage of leaching, as the clay sample gradually reaches saturation, Mg... 2+ Li in clay minerals + Ion exchange reactions disrupt the van der Waals forces between large clay particles, transforming them into smaller particles. This leads to an increase in the number of small particles, as well as micropores and mesopores, while significantly reducing the number of macropores. In the later stages of leaching, as microparticles migrate through the seepage flow of water, they migrate into these micropores, resulting in a substantial reduction in pores larger than 1 μm. In Li + After the exchange is completed, under the action of a stable seepage field, the pore morphology and its distribution remain basically unchanged.

[0062] Column immersion experiments show that, under the bidirectional coupling of the seepage field and the chemical field, due to the larger ionic radius of Ca... 2+ Mg 2 + Li in clay minerals + Exchange occurs, altering the morphology of the clay particles and resulting in a looser internal structure of the clay minerals. (Indicating Li) + During the leaching process, due to ion exchange and permeation, the pore structure shifts from micropores to macropores and then back into micropores, resulting in a gradual increase in the permeability coefficient. This is because the addition of Ca... 2+ Mg 2+ This is beneficial for lithium leaching. This is consistent with our results showing that using low-salinity water improved the lithium leaching rate.

[0063] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium extraction process using grayish-brown salt lake clay containing adsorbed lithium, characterized in that, The process includes the following steps: crushing and sieving the grayish-brown salt lake clay containing adsorbed lithium, then impregnating the fine particles in a leaching agent, and filtering to obtain a leaching solution containing lithium; wherein the leaching agent is prepared by using low-mineralized water and concentrated sulfuric acid, the volume of concentrated sulfuric acid being 5% to 20% of the volume of the leaching agent, and the low-mineralized water being natural water from the Mahai Basin.

2. The lithium extraction process from grayish-brown salt lake clay containing adsorbed lithium as described in claim 1, characterized in that, The impregnation temperature is 25°C to 55°C.

3. The lithium extraction process from grayish-brown salt lake clay containing adsorbed lithium as described in claim 1, characterized in that, The impregnation temperature is 35°C to 45°C.

4. The lithium extraction process from grayish-brown salt lake clay containing adsorbed lithium as described in claim 1, characterized in that, Soaking time is 30 to 60 minutes.

5. The lithium extraction process from grayish-brown salt lake clay containing adsorbed lithium as described in claim 1, characterized in that, The liquid-solid ratio of the extractant to the adsorbed lithium-brown salt lake clay is 3-6:

1.

6. The lithium extraction process from grayish-brown salt lake clay containing adsorbed lithium as described in claim 1, characterized in that, Mechanical stirring was used to assist in impregnation under constant temperature conditions.

7. The lithium extraction process from grayish-brown salt lake clay containing adsorbed lithium as described in claim 1, characterized in that, The particle size of the fine particles is 80-200 mesh.

8. The lithium extraction process for grayish-brown salt lake clay containing adsorbed lithium as described in claim 1, characterized in that, The volume of concentrated sulfuric acid was 20% of the volume of the extractant, the impregnation temperature was 35℃, and the liquid-solid ratio of the extractant and the gray-brown salt lake clay containing adsorbed lithium was 6:1.

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