Method and system for extracting lithium from salt lake and synchronously removing silicon and boron

Abstract

The invention relates to a method for extracting lithium from a salt lake and synchronously removing silicon and boron. The method comprises the following steps: pre-treating and filtering lithium-containing brine; carrying out reverse osmosis concentration treatment to concentrate lithium to be more than 2.5 g / L; carrying out nanofiltration treatment to remove magnesium, calcium and sulfate ions; treating by adopting an electrodialysis system to obtain a high-silicon and high-boron desalted solution and a low-silicon and low-boron lithium concentrated solution; the low-silicon and low-boron lithium concentrated solution is treated with chelating resin and boron removal resin, so that magnesium and calcium ions are smaller than or equal to 2 mg / L, boron is smaller than or equal to 20 mg / L, and the refined lithium concentrated solution is obtained; concentrating by an evaporation system, adding a precipitant, precipitating, filtering, washing, crushing and demagnetizing to obtain a low-silicon low-boron battery-grade lithium carbonate product. The invention further discloses a system for extracting lithium from the salt lake and synchronously removing silicon and boron, the complex and low-efficiency boron removal and silicon removal nanofiltration process is adopted, and concentration of lithium and efficient removal of silicon and boron are synchronously achieved; silicon scaling pollution caused by membrane separation and heat exchanger tube nests is avoided, and deep removal of silicon and boron is realized.

Description

Technical Field

[0001] The present invention belongs to the field of extracting lithium from lithium-containing brine resources or industrial tail liquids, and particularly relates to a method for simultaneously removing silicon and boron during lithium extraction from salt lakes. Background Art

[0002] Metallic lithium is a strategic energy metal for humanity in the 21st century. With the explosive growth of new energy electric vehicles in recent years, the demand for basic lithium salt products such as lithium carbonate and lithium hydroxide has increased sharply. Lithium mainly exists in nature in two forms: solid minerals and liquid minerals. Among them, the lithium resource amount in brines from salt lakes, geothermal areas, and oil fields accounts for about 70%. The cost of extracting lithium from brines is lower than that of solid raw materials such as spodumene and lepidolite. Therefore, lithium extraction from brines has become the main source in the global lithium market.

[0003] The production methods for separating and extracting lithium from salt lakes mainly include salt pond fractional concentration and precipitation method, calcination leaching method, solvent extraction method, adsorption method, nanofiltration membrane method, selective electrodialysis, electrochemical deintercalation, etc. The salt pond concentration and precipitation method is difficult to quickly adapt to the supply and demand changes in the lithium salt market under the new situation due to its long brine evaporation cycle, low overall recovery rate, and slow production capacity adjustment. The calcination leaching method uses old brine as raw material and faces elimination due to constraints such as high energy consumption, environmental pollution, and equipment corrosion. The lithium extraction by the extraction method uses old brine as raw material and is difficult to achieve large-scale application because the dissolution loss and residue in the extraction system will leave an impact on the salt lake and its surrounding environment. The selective electrodialysis method uses salt pond concentrated old brine as raw material. The lithium content in the lithium extraction tail liquid is still 100 - 800 mg / L, and the concentrated liquid still needs to be further refined by chemical precipitation method to remove magnesium and boron before it can be used to produce lithium carbonate. The overall efficiency is restricted by the salt pond step. Therefore, the prospect of further popularizing this method is limited. The adsorption method for lithium extraction has high selectivity, is green and environmentally friendly, and has a high lithium recovery rate. It can directly extract lithium from the original solution efficiently, is more stable and has higher efficiency than the electrochemical deintercalation method, and has become the preferred solution for directly extracting lithium from salt lakes, geothermal areas, and oil field waters or recovering lithium from industrial tail liquids. However, the qualified liquid after lithium enrichment by adsorption generally only has a lithium content of 300 - 1500 mg / L, and still needs to be treated by membrane separation technologies such as reverse osmosis and nanofiltration to concentrate lithium and recover fresh water therein to save precious fresh water resources. However, the membrane concentration technology has high requirements for the quality of the influent water. The content of its pollution elements such as iron, silicon, and aluminum has a great impact on the performance and service life of the membrane, significantly increasing the operating cost of membrane separation.

[0004] In natural water bodies such as salt lake brines, the impurity elements such as iron and aluminum are generally below 1 ppm, and can be effectively removed by pretreatment such as sand filtration, microfiltration, and ultrafiltration. However, silicon and boron do not exist in a single form in brines, and it is difficult to completely remove them by a single means. This is because the forms of silicon in aqueous solutions can be divided into reactive silicon and non-reactive silicon. Non-reactive silicon refers to silica existing in the form of polymers (particles) or colloids, which more often appears as a solid state. Particulate silica exists in nature or forms when reactive silicon reaches saturation, and its size is generally above 1 micron, while colloidal silica has a smaller size, which can be as low as 8 nanometers. Reactive silicon refers to dissolved silica, with a small part existing in the form of ions and not forming long-chain polymers. Most non-reactive silicon can be removed by methods such as conventional filtration, microfiltration, and ultrafiltration, while a small part of colloidal silicon and reactive silicon are difficult to remove by simple means. Although the solubility of silica changes with conditions such as temperature and pH, the overall solubility is low, and it is more likely to polymerize and precipitate in the presence of ions such as iron, magnesium, and calcium. In water at 20 °C, the solubility of SiO2 is only 120 mg / L. Therefore, during membrane concentration and evaporation processes, as its concentration gradually increases, it is extremely easy to reach saturation and precipitate, forming a fouling layer on the membrane surface, causing membrane fouling and blockage, and greatly shortening the service life; scaling on the surface of the heat exchange tubes in the evaporator seriously affects the heat exchange effect, reducing the evaporation intensity and the concentration of the product liquid. Currently, the main method to solve this problem is still to continuously or periodically discharge a stream of concentrated water from the end of the membrane at the back end to balance the silicon concentration in the system and control the silicon within the non-scaling range. However, discharging concentrated water regularly or continuously will, on the one hand, cause a large loss of lithium and reduce the lithium recovery rate of the entire system, and on the other hand, it cannot eliminate the pollution of the membrane system caused by the precipitation of silicon.

[0005] In addition, too high silicon content in products such as lithium carbonate and lithium hydroxide also has an adverse impact on the performance of lithium-ion batteries: high silicon content leads to unstable structure of the cathode material, resulting in a decline in the cycle stability of the battery; it reduces the electronic conductivity of the cathode material and the rate performance of the battery; it generates by-products, affects the output voltage, reduces the discharge capacity and energy density of the battery; it causes the thermal stability of the battery to decline under high temperature or overcharge conditions, increasing the risk of thermal runaway. Similarly, too high boron content will also have an adverse impact on aspects such as the capacity, rate, cycle performance, and safety of lithium-ion batteries. Therefore, during the preparation and application of lithium carbonate, it is necessary to strictly control the silicon and boron content to ensure the comprehensive performance and safety of the battery. For example, in the national standard "Lithium Carbonate from Brines" (GB / T 23853—2022), it is stipulated that for type I (battery-grade) lithium carbonate, the silicon content should be controlled below 20 ppm and the boron content should be controlled below 50 ppm.

[0006] To remove silicon from saline solutions, the current main treatment methods include: coagulation desilication method, reverse osmosis desilication method, ultrafiltration for removing colloidal silicon, air flotation for removing colloidal silicon, electrocoagulation desilication method, ion exchange desilication method, adsorption desilication method, etc. The coagulation desilication method is a non-depth desilication method. Generally, 90% of colloidal silicon can be removed through coagulation and clarification filtration. However, this method will introduce foreign substances and is mostly used for front-end solution treatment. The reverse osmosis desilication method can remove colloidal silicon and dissolved silicon, and the desilication rate of SiO2 can reach 80%. But it is necessary to remove calcium and magnesium ions in advance and carry out complex processes of adjusting alkali and acid. The overall system is relatively complex, with high costs, and it cannot separate silicon and lithium. The method of ultrafiltration for removing colloidal silicon has almost no desilication effect on dissolved silicon. The electrocoagulation desilication method uses the method of sacrificial anode to remove silicon, which not only greatly increases the consumption of aluminum and electric energy, introduces foreign substances such as aluminum and iron ions, but also is not suitable for lithium-rich solutions with high magnesium ion content, and its application range is limited. The ion exchange desilication method uses hydroxide ions to exchange with silicate ions. It is not only interfered by other anions and has no desilication ability for colloidal silicon, but also pretreatment and pre-desalination are required to remove suspended substances and colloidal substances to prevent them from polluting the resin and reducing the efficiency of the treatment system. The adsorption desilication method uses materials such as activated alumina as adsorbents, which are easily interfered by other ions and have high costs. Since these methods generally only consider removing silicon impurities and do not simultaneously consider removing boron impurities, their operating efficiency is low and the costs are high.

[0007] Chinese Patent 202410275778.7 discloses a method. For the qualified solution obtained by adsorption lithium extraction from salt lakes, first, filter the silicon- and boron-containing qualified solution through methods such as multi-media filter, ultrafiltration membrane, ceramic membrane or plate and frame filtration to remove suspended substances and most of the colloids in it. Then, use a hardening removal nanofiltration membrane to remove calcium and magnesium ions. Then, use reverse osmosis to concentrate the nanofiltration product water. Then, use a boron removal membrane to concentrate and remove boron in the reverse osmosis concentrated water, so that the silicon content in the boron removal concentrated water reaches more than 0.15 g / L. Adjust the alkali of the boron removal concentrated water, and then use a silicon removal nanofiltration membrane to remove silicon, so that the silicon content in the silicon removal concentrated water further increases. Then, use the methods of adjusting acid and filtration to remove silicon in the silicon removal concentrated water. In this method, boron removal and silicon removal are carried out separately. Before silicon removal, the qualified solution is concentrated layer by layer, resulting in a relatively high silicon content in the lithium-rich solution. There is a greater possibility of silicon saturation precipitation in the membrane process before alkali adjustment, which is likely to cause fouling of reverse osmosis and nanofiltration membranes and shorten their service life. In addition, due to the limited rejection rates of nanofiltration for silicon and boron removal, the boron rejection rate of the first-stage boron removal membrane is only about 60%. Although it can avoid the problem of scale formation in the evaporation heat exchanger, the boron and silicon contents in the boron and silicon removal product water are still relatively high, which is likely to cause silicon and boron impurities in the product to exceed the standard.

[0008] Chinese Patent Application 202311071045.3 discloses a silicon removal system and method for lithium extraction from salt lakes. For the qualified liquid obtained from lithium extraction by adsorption from salt lakes, it is first filtered to remove suspended solids and most of the colloids therein. Then, a hard removal nanofiltration membrane is used to refine the qualified liquid to remove calcium and magnesium ions. Then, reverse osmosis is used to concentrate the nanofiltration product water. Then, a boron removal membrane is used to remove boron from the reverse osmosis concentrate water. A part of the boron removal concentrate water is treated by electrodialysis to remove most of the silicon therein, and the silicon removal concentrate water is returned to the boron removal nanofiltration system for boron removal. The boron removal nanofiltration step adopted by this method must first adjust the pH of the reverse osmosis concentrate water to above 10, and at the same time, boron and silicon are concentrated and removed. Then, the pH of the boron removal concentrate water is adjusted to about 3.5, and then electrodialysis is carried out. Due to the complex forms of boron and silicon in the salt solution, which have a buffering effect on acid-base adjustment, a large amount of acid and base needs to be consumed. At the same time, due to the high silicon content in the reverse osmosis system and the electrodialysis feed water, silicon is likely to saturate and precipitate on the membrane surface and the spacer under neutral and slightly acidic conditions, blocking the fluid channels, causing fouling of the reverse osmosis membrane pores and an increase in the electrodialysis membrane resistance, resulting in a substantial increase in maintenance costs. At the same time, since only a part of the silicon is removed by electrodialysis in this method, the contents of silicon and boron depend on the rejection performance of the boron removal nanofiltration membrane, and the rejection rate of boron by the two-stage boron removal nanofiltration membrane can only reach about 80%. Although this method can avoid the problem of scale formation in the evaporation heat exchanger, the boron and silicon contents in the silicon removal and boron removal product water are still relatively high, which is also likely to cause the silicon and boron impurities in the product to exceed the standard.

[0009] Chinese Patent Application No. 202410472126.2 discloses a method for simultaneously separating impurity boron and silicon in lithium extraction from carbonate-type salt lakes. For carbonate-type salt lake brine, first, a suspension and colloid catcher are added for clarification and filtration, then nanofiltration treatment is carried out to remove about 95% of the carbonate ions therein. Then, an aluminum-based adsorbent is used to adsorb lithium ions in the nanofiltration permeate. Then, magnesium removal nanofiltration is used to remove magnesium ions in the qualified solution obtained by adsorption. The nanofiltration product water obtained after magnesium removal is concentrated by reverse osmosis, and then electrodialysis treatment is carried out to separate boron and silicon from lithium therein. During the process of using nanofiltration to filter the raw brine, due to the presence of magnesium ions, magnesium combines with carbonate ions therein to form basic magnesium carbonate on the nanofiltration concentrate side. The basic magnesium carbonate coagulates with other impurities in the brine, causing membrane pore blockage, and the cost of nanofiltration membrane loss is relatively high, and the actual lithium recovery rate is also difficult to guarantee; the nanofiltration permeate obtained from the raw brine nanofiltration still contains a relatively high content of carbonate ions. When directly using an aluminum-based adsorbent to treat lithium, the aluminum-based adsorbent is prone to poisoning and losing its activity; before electrodialysis, first carry out magnesium removal nanofiltration and then use reverse osmosis for concentration treatment. The water volume treated by the nanofiltration membrane is relatively large, and the loss is relatively high; the silicon element content in the reverse osmosis concentrate can reach about 100 mg / L, which is easy to co-precipitate with residual iron, aluminum, organic matter and other pollution components in the reverse osmosis concentrate and the electrodialysis desalination liquid, causing fouling of the reverse osmosis membrane and the electrodialysis membrane, and increasing the maintenance cost; during the electrodialysis process, due to the electro-osmosis of water molecules, the water volume in the obtained desalination liquid accounts for a very small proportion relative to the qualified solution, and there are more boron and silicon impurities, and the cost of fresh water recovery is extremely high, and the lithium therein is not effectively recovered. In addition, after the relatively high silicon content in the reverse osmosis concentrate passes through the first-stage electrodialysis, the silicon in the obtained lithium concentrate is still relatively high, which easily causes the silicon impurity in the lithium carbonate product to exceed the standard.

[0010] In summary, regarding the problem of removing silicon and boron in the lithium-enriched liquid obtained from lithium extraction from salt lakes, existing methods all have limitations. They do not comprehensively consider the membrane separation process from the front end to the back end, and cannot achieve deep removal of silicon and boron while avoiding the formation of silicon scale fouling in membrane separation and heat exchanger tubes, and controlling the impurities in the lithium carbonate product at a relatively low level. Summary of the Invention

[0011] The present invention provides a simple, efficient, economical and environmentally friendly method, which avoids consuming a large amount of acid-base reagents, avoids using a complex and inefficient boron and silicon removal nanofiltration process, and on the basis of comprehensively considering the membrane separation process from the front end to the back end, simultaneously realizes the concentration of lithium and the efficient removal of silicon and boron; while avoiding the formation of silicon scale fouling in membrane separation and heat exchanger tubes, it realizes the deep removal of silicon and boron, and controls the impurities in the lithium carbonate product at a relatively low level.

[0012] A method for simultaneously removing silicon and boron in lithium extraction from salt lakes specifically includes the following steps: (1) Pretreat the lithium-containing brine to obtain a qualified solution, and filter to obtain a filtered qualified solution; (2) Reverse osmosis preconcentration: Perform reverse osmosis concentration on the qualified liquid after filtration to concentrate lithium to more than 2.5 g / L and obtain a preconcentrate. (3) Hardness removal nanofiltration: Perform nanofiltration on the preconcentrate obtained in step (2) to remove magnesium, calcium, and sulfate ions therein and obtain a nanofiltration permeate; recycle the nanofiltration concentrate with high calcium and magnesium content to the front-end system for reuse. (4) Electrodialysis treatment: Treat the nanofiltration permeate with an electrodialysis system. Use cation membranes and anion membranes to enrich lithium ions and chloride ions in the concentrate respectively, and simultaneously remove impurities such as silicon and boron therein to obtain a desalted liquid with high silicon and high boron and a lithium concentrate with low silicon and low boron; recycle the desalted liquid with high silicon and high boron to the front-end system for reuse. (5) Resin refining: Treat the lithium concentrate with low silicon and low boron obtained in step (4) with chelating resin and boron removal resin to make the magnesium and calcium ions ≤ 2 mg / L and boron ≤ 20 mg / L, and obtain a refined lithium concentrate. (6) Evaporation concentration and lithium carbonate precipitation: Concentrate the refined lithium concentrate through an evaporation system, then add sodium carbonate solution as a precipitant, and obtain battery-grade lithium carbonate products with low silicon and low boron through hot precipitation, filtration, washing, pulverization, and demagnetization. During the reverse osmosis concentration treatment in step (2), control Si ≤ 70 mg / L; the reverse osmosis concentration multiple is 2.19 - 7.27.

[0013] Preferably, when the mass ratio of silicon to lithium in the preconcentrate in step (2) > 0.015 and the mass ratio of boron to lithium > 0.1, add a stage of electrodialysis unit before the hardness removal nanofiltration in step (3) to treat the preconcentrate; recycle the desalted water produced by the first-stage electrodialysis to the front-end system for reuse.

[0014] Preferably, when the weight ratio of magnesium to lithium in the preconcentrate in step (2) > 0.30, the first-stage electrodialysis unit uses a membrane stack equipped with a monovalent ion selective membrane; the electrodialysis treatment unit uses a membrane stack equipped with a monovalent ion selective membrane or a membrane stack equipped with a common membrane.

[0015] Preferably, the nanofiltration permeate fed into the electrodialysis treatment unit contains Si ≤ 70 mg / L.

[0016] Preferably, the lithium-containing brine is intercrystalline brine of magnesium sulfate subtype salt lake, sodium sulfate subtype salt lake brine, carbonate type salt lake brine, high magnesium and high boron brine, or slightly alkaline salt lake brine.

[0017] Preferably, in step (1), the pretreatment is an adsorption method, and the adsorbent is an aluminum-based or titanium-based adsorbent; the lithium concentration in the qualified liquid ≤ 2000 mg / L.

[0018] Preferably, the nanofiltration membrane used in the nanofiltration treatment in step (3) is a monovalent ion selective nanofiltration membrane; the concentrations of magnesium and calcium ions in the nanofiltration permeate are ≤ 20 mg / L.

[0019] A system for simultaneous lithium extraction and silicon and boron removal from salt lakes, the system comprising an adsorption system, a filtration pretreatment, a reverse osmosis preconcentration unit, a hard removal nanofiltration unit, an electrodialysis treatment unit, a resin refining unit, an evaporation concentration unit, and a lithium precipitation conversion unit connected in sequence; The hard removal nanofiltration unit includes a primary hard removal nanofiltration unit and a secondary hard removal nanofiltration unit connected in sequence.

[0020] Preferably, the fresh water outlet of the reverse osmosis preconcentration unit is connected to the adsorption system; the concentrated water outlet of the hard removal nanofiltration unit is connected to the inlet of the adsorption system; the desalted liquid outlet of the electrodialysis treatment unit is connected to the inlet of the adsorption system.

[0021] Preferably, the system further includes a primary electrodialysis treatment unit, which is placed between the reverse osmosis preconcentration unit and the hard removal nanofiltration unit. Specifically, it includes an adsorption system, a filtration pretreatment, a reverse osmosis preconcentration unit, a primary electrodialysis treatment unit, a hard removal nanofiltration unit, an electrodialysis treatment unit, a resin refining unit, an evaporation concentration unit, and a lithium precipitation conversion unit connected in sequence; the fresh water outlet of the reverse osmosis preconcentration unit is connected to the adsorption system; the desalted liquid of the primary electrodialysis treatment unit is connected to the inlet of the adsorption system; the concentrated water outlet of the hard removal nanofiltration unit is connected to the inlet of the primary electrodialysis treatment unit; the desalted liquid outlet of the electrodialysis treatment unit is connected to the inlet of the hard removal nanofiltration unit.

[0022] Advantages of the present invention: (1) By controlling the concentration multiple of the qualified liquid in the reverse osmosis preconcentration, the silicon content therein is made lower than the saturation precipitation concentration. During the entire process of membrane concentrating lithium, the silicon content always remains at a low level (<70 mg / L). The silicon content in the lithium concentrated liquid entering the evaporation system is extremely low, thus avoiding the fouling problems of the membrane surface, reverse osmosis spacer, and electrodialysis separator caused by the saturation precipitation of silicon in the membrane concentration system, and avoiding the formation of silicon scale on the surface of the heat exchanger tubes in the evaporation system, enabling the stable operation of the entire membrane separation and evaporation concentration process, and significantly reducing the system maintenance and membrane replacement costs. Compared with other methods, the method of the present invention truly solves the long-term stable operation problem of the membrane concentration system and the evaporation system restricted by the silicon content.

[0023] (2) By placing the nanofiltration hard removal unit after the reverse osmosis concentration unit, the amount of qualified liquid treated by the hard removal nanofiltration unit is smaller, significantly improving the lithium ion flux of the hard removal nanofiltration unit and saving the investment in nanofiltration.

[0024] (3) By returning the electrodialysis desalted liquid with high silicon and high boron to the adsorption step or the salt field system, on the one hand, the loss of lithium ions is avoided, and on the other hand, since the high silicon and high boron impurities are discharged from the system with the adsorption tail liquid, the enrichment in the membrane system is avoided, thus eliminating the costly lithium-loss treatment processes such as silicon removal by adsorption and boron removal by high-pressure reverse osmosis for the electrodialysis desalted liquid with high silicon and high boron.

[0025] (4) Through two-stage electrodialysis treatment and deep boron removal by resin, the Si / Li (weight ratio) in the refined lithium concentrate is reduced to 10 -4 Hereinafter, B / Li is reduced to 10 -3 Hereinafter, after evaporation concentration and lithium precipitation conversion, the silicon, boron and other impurity indexes of the obtained lithium carbonate product fully meet the requirements of type I (battery grade) lithium carbonate in the national standard "Lithium Carbonate from Brine" (GB / T 23853—2022), thus solving the problem that the boron and silicon impurity contents of the lithium carbonate products obtained by other silicon removal and boron removal methods do not meet the standards. Description of the Drawings

[0026] Figure 1 It is a process schematic diagram of the system for simultaneous silicon removal and boron removal from lithium in salt lakes in Example 1 of this application.

[0027] Figure 2 It is a process schematic diagram of the system for simultaneous silicon removal and boron removal from lithium in salt lakes in Example 4 of this application.

[0028] Reference Numerals: 1. Adsorption system; 2. Filtration pretreatment unit; 3. Reverse osmosis preconcentration unit; 4. Hardness removal nanofiltration unit; 41. First hardness removal nanofiltration unit; 42. Second hardness removal nanofiltration unit; 5. Electrodialysis treatment unit; 6. Resin refining unit; 7. Evaporation concentration unit; 8. Lithium precipitation conversion unit; 51. Primary electrodialysis treatment unit. Specific Embodiments

[0029] Example 1 A system for simultaneous silicon removal and boron removal from lithium in salt lakes mainly includes an adsorption system (1), a filtration pretreatment unit (2), a reverse osmosis preconcentration unit (3), a hardness removal nanofiltration unit (4), an electrodialysis treatment unit (5), a resin refining unit (6), an evaporation concentration unit (7) and a lithium precipitation conversion unit (8) connected in sequence; The hardness removal nanofiltration unit (4) includes a first hardness removal nanofiltration unit (41) and a second hardness removal nanofiltration unit (42) connected in sequence; The fresh water outlet of the reverse osmosis preconcentration unit (3) is connected to the adsorption system (1); the concentrated water outlets of the first hardness removal nanofiltration unit (41) and the second hardness removal nanofiltration unit (42) are connected to the adsorption system inlet; the desalted liquid outlet of the electrodialysis treatment unit (5) is connected to the adsorption system (1) inlet.

[0030] According to the above-mentioned system, the method for synchronous silicon and boron removal in lithium extraction from salt lakes specifically includes the following steps: (1) Using the intercrystalline brine of a magnesium sulfate subtype salt lake as the raw material, which contains 0.42 g / L of lithium, 15.6 g / L of magnesium, 0.56 g / L of boron. After being treated by the adsorption system (1) filled with an aluminum-based adsorbent, the qualified liquid obtained contains 0.77 g / L of lithium, 105 mg / L of magnesium, 4 mg / L of calcium, 80 mg / L of boron, and 5.2 mg / L of silicon. After being filtered by the filtration pretreatment unit (2), the filtered qualified liquid is obtained; (2) The filtered qualified liquid is subjected to reverse osmosis concentration treatment in the reverse osmosis pre-concentration unit (3), and the concentration multiple is 7.27 times to obtain the pre-concentrated liquid; the pre-concentrated liquid contains 5.5 g / L of lithium, 750 mg / L of magnesium, 29 mg / L of calcium, 375 mg / L of boron, and 37.1 mg / L of silicon; the reverse osmosis fresh water returns to the adsorption unit (1) as the desorption water; (3) The pre-concentrated liquid in step (2) is respectively subjected to two-stage nanofiltration treatment in the first-stage hard removal nanofiltration unit (41) and the second-stage hard removal nanofiltration unit (42) to remove the magnesium, calcium, and sulfate ions therein, and obtain 7.02 m 3 / h of nanofiltration permeate, which contains 6.8 g / L of lithium, 1.4 mg / L of magnesium, 0.7 mg / L of calcium, 436 mg / L of boron, and 42.1 mg / L of silicon; the lithium content in the nanofiltration concentrate only accounts for 2.0%, and it is recycled to the adsorption system (1) and mixed with the raw material brine for use as the adsorption raw material; the lithium flux of the first-stage hard removal nanofiltration unit (41) is 172 g / m 2 / h; (4) The nanofiltration permeate is treated by the electrodialysis treatment unit (5) equipped with a common membrane stack to obtain 2.59 m 3 / h of low-silicon and low-boron lithium concentrate, which contains 17.9 g / L of lithium, 3.8 mg / L of magnesium, 1.9 mg / L of calcium, 166 mg / L of boron, and 2.9 mg / L of silicon; the lithium recovery rate of electrodialysis is 97.1%, the silicon removal rate is 97.5%, and the boron removal rate is 86%; the lithium content in the high-silicon and high-boron desalted liquid is less than 3%, and it is returned to the adsorption system (1) and mixed with the raw material brine for use as the adsorption raw material; (5) The low-silicon and low-boron lithium concentrate obtained in step (4) is treated by chelating resin and boron removal resin in the resin refining unit (6) to obtain a lithium concentrate, which contains 17.7 g / L of lithium, 13.2 mg / L of boron, and 2.3 mg / L of silicon; (6) The refined lithium concentrate is processed through an evaporation concentration unit (7), and then sodium carbonate solution is added as a precipitant in a lithium precipitation and conversion unit (8). After heat precipitation, filtration, washing, pulverization, and demagnetization, a battery-grade lithium carbonate product with a purity of 99.7% and low silicon and boron content is obtained, containing 10 ppm of silicon, 17 ppm of boron, and the contents of other impurities also fully meet the requirements of Type I (battery-grade) lithium carbonate in the national standard "Lithium Carbonate from Brine".

[0031] Example 2 A method for synchronous silicon and boron removal in lithium extraction from salt lakes, specifically including the following steps: (1) Using sodium sulfate subtype salt lake brine as raw material, containing 0.63 g / L of lithium, 1.48 g / L of magnesium, 0.875 g / L of boron, 111 g / L of sodium. After being processed by an adsorption system (1) filled with an aluminum-based adsorbent, the qualified liquid obtained contains 0.83 g / L of lithium, 30 mg / L of magnesium, 8 mg / L of calcium, 102 mg / L of boron, 7 mg / L of silicon, and 0.34 g / L of sodium. After filtration pretreatment by a filtration pretreatment unit (2), a filtered qualified liquid is obtained; (2) The filtered qualified liquid is subjected to reverse osmosis concentration treatment in a reverse osmosis pre-concentration unit (3) with a concentration multiple of 7.39 times to obtain a pre-concentrated liquid; the pre-concentrated liquid contains 6.02 g / L of lithium, 218 mg / L of magnesium, 58 mg / L of calcium, 486 mg / L of boron, 50.7 mg / L of silicon, and 2.47 g / L of sodium; the reverse osmosis fresh water returns to the adsorption unit (1) as desorption water; (3) The pre-concentrated liquid in step (2) is subjected to two-stage nanofiltration treatment in a first-stage hard removal nanofiltration unit (41) and a second-stage hard removal nanofiltration unit (42) respectively to remove magnesium, calcium, and sulfate ions therein, and obtain a 6.35 m 3 / h nanofiltration permeate, containing 7.5 g / L of lithium, 10 mg / L of magnesium, 10 mg / L of calcium, 500 mg / L of boron, and 50 mg / L of silicon; the lithium content in the nanofiltration concentrate only accounts for 2.1%, and it is recycled to the adsorption system (1) and mixed with the raw brine as adsorption raw material; the lithium flux of the first-stage hard removal nanofiltration unit (41) is 190 g / m2 / h; (4) The nanofiltration permeate is processed by an electrodialysis treatment unit (5) equipped with a common membrane stack to obtain a 2.84 m 3 / h low-silicon and low-boron lithium concentrate, containing 16.3 g / L of lithium, 22.5 mg / L of magnesium, 22.3 mg / L of calcium, 159 mg / L of boron, and 2.8 mg / L of silicon; the electrodialysis lithium recovery rate is 97.2%, the silicon removal rate is 98%, and the boron removal rate is 86%; the lithium content in the high-silicon and high-boron desalinated liquid is less than 3%, and it is returned to the adsorption system (1) and mixed with the raw brine as adsorption raw material; (5) Treat the low-silicon and low-boron lithium concentrate obtained in step (4) with chelating resin and boron-removing resin in the resin refining unit (6) to obtain a lithium concentrate containing 16.2 g / L of lithium, 12.7 mg / L of boron, and 2.3 mg / L of silicon; (6) Treat the refined lithium concentrate through the evaporation concentration unit (7), and then add sodium carbonate solution as a precipitant in the lithium precipitation and conversion unit (8). After heat precipitation, filtration, washing, pulverization, and demagnetization, a battery-grade lithium carbonate product with a purity of 99.7% and low silicon and low boron is obtained, containing 10 ppm of silicon, 18 ppm of boron, and the contents of other impurities also fully meet the requirements of type I (battery-grade) lithium carbonate in the national standard "Lithium Carbonate from Brine"; Its lithium extraction system from salt lake is the same as that in Example 1.

[0032] Example 3 A method for synchronous silicon removal and boron removal in lithium extraction from salt lake specifically includes the following steps: (1) Using carbonate-type salt lake brine as raw material, which contains 0.846 g / L of lithium, 131 g / L of sodium, 40.5 g / L of potassium, 0.88 g / L of magnesium, 5.6 g / L of boron, 36.6 g / L of carbonate radical, 16.8 g / L of sulfate radical, and pH of 10.2. After treatment with the adsorption system (1) filled with titanium-based adsorbent, the obtained qualified liquid contains 1.30 g / L of lithium, 143 mg / L of magnesium, 1 mg / L of calcium, 195 mg / L of boron, and 13 mg / L of silicon. After filtration pretreatment by the filtration pretreatment unit (2), the filtered qualified liquid is obtained; (2) Perform reverse osmosis concentration treatment on the filtered qualified liquid in the reverse osmosis pre-concentration unit (3) with a concentration multiple of 4.7 times to obtain a pre-concentrated liquid; the pre-concentrated liquid contains 6.0 g / L of lithium, 660 mg / L of magnesium, 4 mg / L of calcium, 238 mg / L of boron, and 61 mg / L of silicon; the reverse osmosis fresh water returns to the adsorption unit (1) as desorption water; (3) Perform two-stage nanofiltration treatment on the pre-concentrated liquid in step (2) in the first-stage hardness removal nanofiltration unit (41) and the second-stage hardness removal nanofiltration unit (42) respectively to remove magnesium, calcium, and sulfate ions therein, and obtain 6.97 m 3 / h of nanofiltration permeate, which contains 7.1 g / L of lithium, 1.9 mg / L of magnesium, 0.1 mg / L of calcium, 286 mg / L of boron, and 67 mg / L of silicon; the lithium content in the nanofiltration concentrate only accounts for 2.0%. Recover it to the adsorption system (1) and mix it with the raw brine as adsorption raw material; the lithium flux of the first-stage hardness removal nanofiltration unit (41) is 180 g / m 2 / h; (4) Treat the nanofiltration permeate with the electrodialysis treatment unit (5) equipped with a common ion exchange membrane stack to obtain 2.54 m 3 / h low-silicon and low-boron lithium concentrate, containing 18.2 g / L of lithium, 5.0 mg / L of magnesium, 0.3 mg / L of calcium, 121 mg / L of boron, and 3.9 mg / L of silicon; the lithium recovery rate is 95.3%, the silicon removal rate is 98.0%, and the boron removal rate is 84%; the lithium content in the high-silicon and high-boron desalinated liquid is less than 5%, which is returned to the adsorption system (1) and mixed with the raw brine as the adsorption raw material; (5) Treat the low-silicon and low-boron lithium concentrate obtained in step (4) with chelating resin and boron-removing resin in the resin refining unit (6) to obtain a lithium concentrate, containing 17.4 g / L of lithium, 9.3 mg / L of boron, and 3.4 mg / L of silicon; (6) Treat the refined lithium concentrate through the evaporation concentration unit (7), and then add sodium carbonate solution as a precipitant in the lithium precipitation and conversion unit (8). After heat precipitation, filtration, washing, pulverization, and demagnetization, a battery-grade lithium carbonate product with low silicon and low boron and a purity of 99.6% is obtained, containing 15 ppm of silicon, 12 ppm of boron, and the contents of other impurities also fully meet the requirements of type I (battery-grade) lithium carbonate in the national standard "Lithium Carbonate from Brine"; Its lithium extraction system from salt lake is the same as that in Example 1.

[0033] Example 4 A system for synchronous silicon removal and boron removal in lithium extraction from salt lake, the system further includes a primary electrodialysis treatment unit (51), and the primary electrodialysis treatment unit (51) is placed between the reverse osmosis pre-concentration unit (3) and the hardness removal nanofiltration unit (4), specifically including an adsorption system (1), a filtration pretreatment unit (2), a reverse osmosis pre-concentration unit (3), a primary electrodialysis treatment unit (51), a hardness removal nanofiltration unit (4), an electrodialysis treatment unit (5), a resin refining unit (6), an evaporation concentration unit (7), and a lithium precipitation and conversion unit (8) connected in sequence. The fresh water outlet of the reverse osmosis pre-concentration unit (3) is connected to the adsorption system (1); the desalinated liquid of the primary electrodialysis treatment unit (51) is connected to the inlet of the adsorption system (1); the concentrated water outlet of the hardness removal nanofiltration unit (4) is connected to the inlet of the primary electrodialysis treatment unit (51); the desalinated liquid outlet of the electrodialysis treatment unit (5) is connected to the inlet of the hardness removal nanofiltration unit (4); The hardness removal nanofiltration unit (4) includes a primary hardness removal nanofiltration unit (41) and a secondary hardness removal nanofiltration unit (42) connected in sequence.

[0034] A method for synchronous silicon removal and boron removal in lithium extraction from salt lake, specifically including the following steps: (1) Using high-magnesium and high-boron brine as raw material, which contains 0.76 g / L of lithium, 46.3 g / L of magnesium, 3.30 g / L of boron. After being treated by the adsorption system (1) filled with aluminum-based adsorbent, the qualified liquid obtained contains 0.73 g / L of lithium, 563 mg / L of magnesium, 3.2 mg / L of calcium, 1210 mg / L of boron, and 9.0 mg / L of silicon. After being filtered by the filtration pretreatment unit (2), the filtered qualified liquid is obtained; (2) The filtered qualified liquid is subjected to reverse osmosis concentration treatment in the reverse osmosis pre-concentration unit (3), and the concentration multiple is 5.13 times to obtain the pre-concentrated liquid; the pre-concentrated liquid contains 3.7 g / L of lithium, 2832 mg / L of magnesium, 16 mg / L of calcium, 3907 mg / L of boron, and 45 mg / L of silicon; the reverse osmosis fresh water returns to the adsorption unit (1) as the desorption water; (3) The pre-concentrated liquid is treated by the first-stage electrodialysis unit (51) equipped with a monovalent ion selective membrane stack to obtain 5.03 m 3 / h of the first concentrated liquid, which contains 10.0 g / L of lithium, 3545 mg / L of magnesium, 39 mg / L of calcium, 1000 mg / L of boron, and 6.4 mg / L of silicon; the lithium recovery rate is 95.0%, the silicon removal rate is 95.0%, and the boron removal rate is 91%; the lithium content in the first desalted liquid only accounts for 5% of the feed, and it can be returned to the adsorption system (1) and mixed with the raw material brine as the adsorption raw material; (4) The first concentrated liquid obtained in step (3) is successively subjected to two-stage nanofiltration treatment in the first-stage hardness removal nanofiltration unit (41) and the second-stage hardness removal nanofiltration unit (42) to remove magnesium, calcium, and sulfate ions therein, and 5.08 m 3 / h of nanofiltration permeate is obtained, which contains 9.7 g / L of lithium, 19.1 mg / L of magnesium, 1.1 mg / L of calcium, 985 mg / L of boron, and 5.5 mg / L of silicon; the lithium content in the nanofiltration concentrate only accounts for 2%, and it is recovered to the adsorption system and mixed with the raw material brine as the adsorption raw material; the lithium flux of the first-stage hardness removal nanofiltration unit (41) is 245 g / m 2 / h; (4) The nanofiltration permeate is treated by the electrodialysis treatment unit (5) equipped with a monovalent ion selective membrane stack to obtain 2.56 m3 / h of low-silicon and low-boron lithium concentrate, which contains 18.5 g / L of lithium, 26.5 mg / L of magnesium, 1.6 mg / L of calcium, 468 mg / L of boron, and 1.1 mg / L of silicon; the electrodialysis lithium recovery rate is 96.3%, the silicon removal rate is 90.0%, and the boron removal rate is 76%; the lithium content in the high-silicon and high-boron desalted liquid accounts for 3.6% of the feed, and it is returned to the adsorption system (1) and mixed with the raw material brine as the adsorption raw material; (5) Treat the low-silicon and low-boron lithium concentrate obtained in step (4) in the resin refining unit (6) with chelating resin and boron-removing resin to obtain a lithium concentrate containing 18.2 g / L of lithium, 18.5 mg / L of boron, and 1.0 mg / L of silicon; (6) Treat the refined lithium concentrate through the evaporation concentration unit (7), and then add sodium carbonate solution as a precipitant in the lithium precipitation and conversion unit (8). After heat precipitation, filtration, washing, pulverization, and demagnetization, a battery-grade lithium carbonate product with a purity of 99.7% and low silicon and low boron is obtained, containing 4 ppm of silicon, 23 ppm of boron, and the contents of other impurities also fully meet the requirements of type I (battery-grade) lithium carbonate in the national standard "Lithium Carbonate from Brine".

[0035] Example 5 A method for simultaneously removing silicon and boron from lithium extracted from salt lakes, specifically including the following steps: (1) Using slightly alkaline salt lake brine as raw material, containing 0.28 g / L of lithium, 0.89 g / L of magnesium, 0.811 g / L of boron, and a pH of 9.5. After treatment with the adsorption system (1) filled with titanium-based adsorbent, the qualified liquid obtained contains 1.30 g / L of lithium, 300 mg / L of magnesium, 60 mg / L of calcium, 560 mg / L of boron, and 32 mg / L of silicon. After filtration, the filtered qualified liquid is obtained; (2) Perform reverse osmosis concentration treatment on the filtered qualified liquid in the reverse osmosis pre-concentration unit (3) with a concentration multiple of 2.19 times to obtain a pre-concentrate; the pre-concentrate contains 2.80 g / L of lithium, 646 mg / L of magnesium, 129 mg / L of calcium, 909 mg / L of boron, and 69 mg / L of silicon; the reverse osmosis fresh water returns to the adsorption unit (1) as desorption water; (3) Treat the pre-concentrate with the first-stage electrodialysis unit (51) equipped with a stack of ordinary ion exchange membranes to obtain a first concentrate of 6.23 m 3 / h, containing 8.0 g / L of lithium, 1940 mg / L of magnesium, 390 mg / L of calcium, 386 mg / L of boron, and 4.2 mg / L of silicon; the lithium recovery rate is 94.3%, the silicon removal rate is 98.0%, and the boron removal rate is 86%; the lithium content in the first desalted liquid only accounts for 5.6% of the feed and can be returned to the adsorption system to be mixed with the raw material brine as adsorption raw material; (4) Perform two-stage nanofiltration treatment on the first concentrate obtained in step (3) in the first-stage hard removal nanofiltration unit (41) and the second-stage hard removal nanofiltration unit (42) respectively to remove magnesium, calcium, and sulfate ions therein, and obtain 6.26 m 3 / h nanofiltration permeate, containing 7.8 g / L of lithium, 4.5 mg / L of magnesium, 7.6 mg / L of calcium, 382 mg / L of boron, and 3.7 mg / L of silicon; the lithium content in the nanofiltration concentrate only accounts for 2%, which is recycled to the adsorption system and mixed with the raw brine as the adsorption raw material; the lithium flux of the primary hard removal nanofiltration unit (41) is 197 g / m 2 / h; (4) Treat the nanofiltration permeate with an electrodialysis treatment unit (5) equipped with a common ion exchange membrane stack to obtain 2.49 m3 / h of low-silicon and low-boron lithium concentrate, containing 18.6 g / L of lithium, 11.3 mg / L of magnesium, 18.8 mg / L of calcium, 249 mg / L of boron, and 0.7 mg / L of silicon; the lithium recovery rate is 94.9%, the silicon removal rate is 93.0%, and the boron removal rate is 74%; the lithium content in the high-silicon and high-boron desalted liquid accounts for 5.0% of the feed, which is returned to the adsorption system and mixed with the raw brine as the adsorption raw material; (5) Treat the low-silicon and low-boron lithium concentrate obtained in step (4) with chelating resin and boron removal resin in the resin refining unit (6) to obtain a lithium concentrate, containing 17.9 g / L of lithium, 19.3 mg / L of boron, and 0.6 mg / L of silicon; (6) Treat the refined lithium concentrate through an evaporation concentration unit (7), and then add sodium carbonate solution as a precipitant in the lithium precipitation conversion unit (8). After thermal precipitation, filtration, washing, crushing, and demagnetization, a battery-grade lithium carbonate product with a purity of 99.7% and low silicon and low boron is obtained, containing 7 ppm of silicon, 24 ppm of boron, and the contents of other impurities also fully meet the requirements of type I (battery grade) lithium carbonate in the national standard "Lithium Carbonate from Brine".

[0036] Its lithium extraction system from salt lakes is the same as that in Example 4.

[0037] Comparative Example 1 To compare the treatment effect when extracting lithium from the same salt lake brine as in Example 2 by the method disclosed in Chinese Patent No. 202410275778.7.

[0038] A method for synchronous silicon removal and boron removal in lithium extraction from salt lakes specifically includes the following steps: Using the same salt lake brine as in Example 2 as the raw material, after treatment with a continuous ion exchange adsorption system filled with an aluminum-based adsorbent, filtering the obtained qualified liquid, and then treating it with a nanofiltration hard removal system, the obtained nanofiltration permeate is further concentrated by a reverse osmosis system to obtain a pre-concentrate, containing 6.86 g / L of lithium, 500 mg / L of boron, and 28 mg / L of silicon. By using a two-stage boron removal nanofiltration system and coupling it with a silicon removal nanofiltration system and a chemical silicon removal system, the obtained low-boron and low-silicon nanofiltration product water contains 6.9 g / L of lithium, 105 mg / L of boron, and 3.9 mg / L of silicon.

[0039] The low-boron and low-silicon nanofiltration product water is evaporated and concentrated by the MVR system, with a large amount of evaporated water and high energy consumption. Through steps such as conversion and lithium precipitation, lithium carbonate products with a purity of 99.6% are finally obtained, containing 43 ppm of silicon and 344 ppm of boron, both exceeding the indicators of type I (battery grade) lithium carbonate in the national standard "Lithium Carbonate from Brine".

[0040] Comparative Example 2 When extracting lithium from the same salt lake brine as in Example 2, the effect of the treatment method disclosed in Chinese Patent Application No. 202311071045.3.

[0041] A method for simultaneous silicon and boron removal in lithium extraction from salt lakes specifically includes the following steps: Using the same salt lake brine as in Example 2 as the raw material, after treatment with a continuous ion exchange adsorption system filled with an aluminum-based adsorbent, the qualified liquid obtained by filtration is treated with a nanofiltration hard removal system, and the nanofiltration permeate obtained is then concentrated by a reverse osmosis system. The pre-concentrated liquid obtained contains 7.50 g / L of lithium, 500 mg / L of boron, and 50 mg / L of silicon. A two-stage nanofiltration boron removal system is used for treatment, and part of the high-boron concentrated water enters the electrodialysis system for silicon removal to improve the lithium recovery rate. The high-boron concentrated water from boron removal by nanofiltration contains 2940 mg / L of boron and 289 mg / L of silicon. After adjusting the acid to pH 3.5, it enters the electrodialysis system. During operation, silicon saturation precipitation occurs, resulting in fouling in the electrodialysis membrane surface and spacer, an increase in fluid resistance, an increase in membrane surface resistance, frequent shutdowns for maintenance of the electrodialysis due to failures, serious losses in membrane cleaning, and a soaring cost. The low-boron and low-silicon nanofiltration product water obtained from the nanofiltration boron removal system contains approximately 7.9 g / L of lithium, 70 mg / L of boron, and 4.8 mg / L of silicon.

[0042] The low-boron and low-silicon nanofiltration product water is evaporated and concentrated by the MVR system, with a large amount of evaporated water and high energy consumption. Through steps such as conversion and lithium precipitation, lithium carbonate products with a purity of 99.6% are finally obtained, containing 45 ppm of silicon and 200 ppm of boron, both exceeding the indicators of type I (battery grade) lithium carbonate in the national standard "Lithium Carbonate from Brine".

[0043] Comparative Example 3 To compare the effect of the treatment method disclosed in Chinese Patent Application No. 202410472126.2 when extracting lithium from the same carbonate-type salt lake brine as in Example 3.

[0044] Using the same carbonate-type salt lake brine as in Example 3 as the raw material, the nanofiltration product water obtained after treatment with a carbonate-removing nanofiltration membrane contains 0.81 g / L of lithium, 0.30 g / L of magnesium, 2.01 g / L of carbonate, 23 mg / L of silicon, 2.15 g / L of boron, and the pH is 8.6. Due to the presence of magnesium ions, the nanofiltration membrane flux decreases rapidly, indicating that fouling is likely to occur.

[0045] The nanofiltration product water is treated by a continuous ion exchange adsorption system filled with an aluminum-based adsorbent. Initially, a qualified adsorption and desorption solution containing 1.2 g / L of lithium, 0.30 g / L of magnesium, 195 mg / L of boron, and 8 mg / L of silicon is obtained. The working capacity of the adsorbent is 2.5 g / L. However, after 4 days of operation, the working capacity of the adsorbent gradually decreases to less than 1.0 g / L, indicating that the aluminum-based adsorbent has been poisoned and inactivated.

[0046] The qualified solution is directly treated by magnesium-removing nanofiltration. The obtained nanofiltration lithium flux is only 30 g / m2 / h, indicating that the magnesium-removing efficiency of nanofiltration is low and the required equipment investment is high.

Claims

1. A method for extracting lithium from a salt lake and simultaneously removing silicon and boron, characterized in that: The specific steps include: (1) Pre-treating the lithium-containing brine to obtain a qualified solution, filtering it, and obtaining a filtered qualified solution; (2) Reverse osmosis pre-concentration: The qualified liquid after filtration is subjected to reverse osmosis concentration treatment to concentrate lithium to greater than 2.5 g / L to obtain a pre-concentrated liquid; (3) Hardness removal nanofiltration: The pre-concentrated liquid of step (2) is subjected to nanofiltration treatment to remove magnesium, calcium and sulfate ions therein to obtain nanofiltration permeate; and the high calcium and magnesium nanofiltration concentrated water is recycled to the front-end system for recycling; (4) Electrodialysis treatment: The nanofiltration permeate is treated with an electrodialysis system, using the cation membrane and anion membrane to enrich lithium ions and chloride ions in the concentrate, while removing impurities such as silicon and boron, to obtain high-silicon and high-boron desalted liquid and low-silicon and low-boron lithium concentrate; the high-silicon and high-boron desalted liquid is recycled to the front-end system for recycling; (5) Resin refining: treating the low-silicon and low-boron lithium concentrate obtained in step (4) with a chelating resin and a boron removal resin to make the magnesium and calcium ions ≤ 2 mg / L and the boron ≤ 20 mg / L, thereby obtaining a refined lithium concentrate; (6) Evaporation concentration and lithium carbonate precipitation: The refined lithium concentrate is concentrated by an evaporation system, and then sodium carbonate solution is added as a precipitant. After thermal precipitation, filtration, washing, crushing and demagnetization, a low-silicon and low-boron battery-grade lithium carbonate product is obtained; In the reverse osmosis concentration process in step (2), Si is controlled to be ≤70 mg / L; and the multiple of reverse osmosis concentration is 2.19-7.

27.

2. The method for extracting lithium from salt lakes and simultaneously removing silicon and boron according to claim 1, characterized in that: When the silicon-lithium mass ratio in the pre-concentrated liquid of step (2) is greater than 0.015 and the boron-lithium mass ratio is greater than 0.1, a first-stage electrodialysis unit is added before the hardness removal nanofiltration in step (3) to treat the pre-concentrated liquid; the first-stage electrodialysis desalination water is recovered to the front-end system for cyclic use.

3. The method for extracting lithium from salt lakes and simultaneously removing silicon and boron according to claim 2, characterized in that: When the weight ratio of magnesium to lithium in the pre-concentrated solution in step (2) is greater than 0.30, the primary electrodialysis unit adopts a membrane stack equipped with a monovalent ion selective membrane; the electrodialysis treatment unit adopts a membrane stack equipped with a monovalent ion selective membrane or a membrane stack equipped with a common membrane.

4. The method for extracting lithium from salt lakes and simultaneously removing silicon and boron according to claim 1, characterized in that: The nanofiltration permeate fed into the electrodialysis treatment unit contains Si≤70 mg / L.

5. The method for extracting lithium from salt lakes and simultaneously removing silicon and boron according to claim 2, characterized in that: The lithium-containing brine is magnesium sulfate subtype salt lake intercrystalline brine, sodium sulfate subtype salt lake brine, carbonate salt lake brine, high magnesium and high boron brine or alkaline salt lake brine.

6. The method for simultaneous silicon removal and boron removal from salt lakes for lithium extraction according to claim 2, characterized in that: The pretreatment in step (1) is an adsorption method, and the adsorbent is an aluminum or titanium adsorbent; the lithium concentration in the qualified solution is ≤2000 mg / L.

7. The method for extracting lithium from salt lakes and simultaneously removing silicon and boron according to claim 2, characterized in that: The nanofiltration membrane used in the nanofiltration treatment in step (3) is a monovalent ion selective nanofiltration membrane; the concentration of magnesium and calcium ions in the nanofiltration permeate is ≤20 mg / L.

8. A system for extracting lithium from a salt lake and simultaneously removing silicon and boron, characterized in that: The system comprises an adsorption system, a filtration pretreatment, a reverse osmosis preconcentration unit, a hardness removal nanofiltration unit, an electrodialysis treatment unit, a resin refining unit, an evaporation concentration unit and a lithium precipitation conversion unit which are connected in sequence; The hardness removal nanofiltration unit comprises a primary hardness removal nanofiltration unit and a secondary hardness removal nanofiltration unit which are connected in sequence.

9. The system for simultaneous silicon and boron removal during lithium extraction from salt lakes according to claim 8, characterized in that: The fresh water outlet of the reverse osmosis pre-concentration unit is connected to the adsorption system; the concentrated water outlet of the hardness removal nanofiltration unit is connected to the inlet of the adsorption system; and the desalted liquid outlet of the electrodialysis treatment unit is connected to the inlet of the adsorption system.

10. The system for extracting lithium from salt lakes and simultaneously removing silicon and boron according to claim 8, characterized in that: The system also includes a primary electrodialysis treatment unit, which is placed between the reverse osmosis pre-concentration unit and the hardness removal nanofiltration unit, and specifically includes an adsorption system, a filtration pretreatment, a reverse osmosis pre-concentration unit, a primary electrodialysis treatment unit, a hardness removal nanofiltration unit, an electrodialysis treatment unit, a resin refining unit, an evaporation concentration unit, and a lithium precipitation conversion unit connected in sequence; The fresh water outlet of the reverse osmosis pre-concentration unit is connected to the adsorption system; the desalted liquid of the primary electrodialysis treatment unit is connected to the inlet of the adsorption system; the concentrated water outlet of the hardness removal nanofiltration unit is connected to the inlet of the primary electrodialysis treatment unit; the desalted liquid outlet of the electrodialysis treatment unit is connected to the inlet of the hardness removal nanofiltration unit.

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