A lithium-magnesium-lithium separation and concentration system and method for salt lake

Abstract

This invention relates to the field of extraction and separation technology, and particularly to a lithium extraction system and method for magnesium-lithium separation and concentration in salt lakes. The system includes: a pretreatment module, a multi-stage nanofiltration module, a silicon removal module, a reverse osmosis module, a detection module, and a lithium extraction control module. The pretreatment module filters the initial brine to obtain impurity-free brine. The multi-stage nanofiltration module separates divalent ions such as calcium and magnesium through several stages of nanofiltration. The silicon removal module removes silicon from the impurity-free brine. The reverse osmosis module concentrates the nanofiltration permeate. The detection module detects the magnesium-lithium ratio in the impurity-free brine, obtains the silicon content in the initial brine, and detects the magnesium and lithium ion concentrations at each stage of nanofiltration to determine the permeability stability characterization parameters of the corresponding nanofiltration stages. The lithium extraction control module determines the working position and silicon removal mode of the silicon removal module, and determines whether there are any abnormalities in each stage of nanofiltration for adjustment. This invention combines magnesium-lithium separation and lithium concentration in lithium extraction from salt lakes, reducing membrane fouling.

Description

Technical Field

[0001] This invention relates to the field of extraction and separation technology, and in particular to a lithium-magnesium-lithium separation and concentration system and method for extracting lithium from salt lakes. Background Technology

[0002] Existing technologies for lithium extraction from salt lake brine face numerous challenges. Firstly, salt lake brine typically exhibits a high magnesium-to-lithium ratio, posing a significant challenge to lithium extraction. Traditional precipitation and extraction methods suffer from extremely low separation efficiency when dealing with such a high ratio, often requiring large quantities of chemical reagents and complex operational procedures to achieve even initial separation of lithium and magnesium. This not only increases production costs but also generates substantial waste, putting pressure on the environment. Furthermore, the cumbersome and inefficient lithium extraction process fails to meet the demands of large-scale industrial production. Secondly, single nanofiltration or reverse osmosis processes also have significant drawbacks. While these processes are widely used in water treatment and other fields, in salt lake lithium extraction, due to the similar properties of magnesium and lithium ions, using nanofiltration or reverse osmosis alone is insufficient to effectively separate magnesium and lithium while ensuring lithium recovery rates and achieving efficient lithium concentration. Moreover, single membrane separation processes are prone to membrane fouling, and frequent membrane cleaning and replacement increase operating costs and maintenance workload, severely restricting their long-term stable application in salt lake lithium extraction.

[0003] Meanwhile, the concentration process of salt lake brine faces numerous challenges. Impurities such as silicon, calcium, and magnesium easily precipitate during concentration. These precipitated impurities adhere to the membrane surface or clog the membrane pores, leading to a decrease in membrane flux. This not only increases energy consumption but also affects the stability of the entire system, making it difficult to conduct lithium extraction continuously and efficiently. Furthermore, the application of dialysis technology in existing technologies is insufficient. The selective permeation and recovery of lithium ions during dialysis are limited, resulting in a low lithium recovery rate. This fails to fully realize the potential of salt lake brine as a resource, leading to a waste of lithium resources and making it difficult to meet the growing market demand for lithium products and the large demand for high-quality lithium raw materials from new energy and other industries. Summary of the Invention

[0004] Therefore, the present invention provides a lithium extraction system and method for magnesium-lithium separation and concentration in salt lakes, which overcomes the problem that existing single nanofiltration or reverse osmosis processes cannot simultaneously achieve magnesium-lithium separation and lithium concentration, and that membrane fouling is severe.

[0005] To achieve the above objectives, on the one hand, the present invention provides a lithium-magnesium-lithium separation and concentration system for extracting lithium from salt lakes, comprising: a pretreatment module, which is used to filter the initial brine through several types of pretreatment equipment to obtain impurity-free brine;

[0006] A multi-stage nanofiltration module, which is connected to the pretreatment module, is used to separate calcium ions and magnesium ions step by step through several stages of nanofiltration to obtain several stages of nanofiltration permeate and final nanofiltration permeate.

[0007] The silicon removal module is connected to the multi-stage nanofiltration module and the pretreatment module respectively, and is used to remove silicon from the impurity-free brine by chemical precipitation or by adjusting the pH with alkali, combined with ultrafiltration membrane and / or ion exchange.

[0008] A reverse osmosis module, which is connected to the multi-stage nanofiltration module, is used to concentrate the first-stage nanofiltration permeate and to concentrate the permeate from the remaining stages of nanofiltration using reverse osmosis, and to desalinate each stage of reverse osmosis permeate.

[0009] The detection module is connected to the multi-stage nanofiltration module and the silicon removal module respectively, and is used to detect the magnesium-lithium ratio in the impurity-free brine, obtain the silicon content in the initial brine, and detect the magnesium ion concentration and lithium ion concentration of the nanofiltration permeate at each stage, so as to determine the permeability stability characterization parameters of the corresponding nanofiltration stage.

[0010] The lithium extraction control module is connected to the pretreatment module, the multi-stage nanofiltration module, and the detection module, respectively. It is used to determine the working position and silicon removal mode of the silicon removal module, and to determine whether there is any abnormality in the corresponding level of nanofiltration based on the permeability stability characterization parameters of each level of nanofiltration, and to determine the corresponding adjustment method.

[0011] As a preferred technical solution for the lithium extraction, magnesium, and lithium separation and concentration system in salt lakes, the pretreatment module includes:

[0012] The filtration unit includes several filtration devices to remove suspended solids from the initial brine to obtain the initial brine.

[0013] An adsorption unit, which is connected to the filtration unit, is used to selectively adsorb lithium ions in the first initial state brine to obtain a desorption solution and an adsorption-desorption solution.

[0014] An ultrafiltration unit, connected to the adsorption unit, is used to perform secondary filtration of the adsorption-desorption solution through an ultrafiltration membrane to obtain the impurity-free brine.

[0015] Lithium ions are present in the adsorption and desorption solution.

[0016] As a preferred technical solution for the lithium extraction, magnesium, and lithium separation and concentration system in salt lakes, the multi-stage nanofiltration module includes:

[0017] A primary nanofiltration system, comprising an initial primary nanofiltration stage and several secondary primary nanofiltration stages, is used to separate the calcium ions, the magnesium ions, and other divalent ions to obtain primary nanofiltration permeate.

[0018] The n-stage nanofiltration system is located after the outlet of the first-stage nanofiltration system. It is used to separate residual calcium and magnesium ions step by step to obtain n-stage nanofiltration permeate, and the concentrate from each stage of nanofiltration is returned to the previous two stages of nanofiltration for further treatment.

[0019] As a preferred technical solution for a lithium extraction and magnesium-lithium separation and concentration system in salt lakes, the reverse osmosis module includes:

[0020] The first-stage reverse osmosis unit, located downstream of the first-stage nanofiltration assembly outlet, is used to initially concentrate the first-stage nanofiltration permeate to increase the lithium-ion concentration.

[0021] The high-pressure reverse osmosis unit, located after the outlet of the third-stage nanofiltration, is used for secondary concentration of the third-stage nanofiltration permeate to increase the lithium ion concentration to Li+≥7g / L;

[0022] The secondary reverse osmosis unit is connected to the primary reverse osmosis unit, the high-pressure reverse osmosis unit, and the tertiary nanofiltration unit, respectively, and is used to desalinate the permeate from the primary reverse osmosis unit and the high-pressure reverse osmosis unit to obtain desalinated water. The resulting second reverse osmosis concentrate is then transported to the inlet of the tertiary nanofiltration unit.

[0023] As a preferred technical solution for the lithium extraction and magnesium-lithium separation and concentration system in salt lakes, the detection module is equipped with an ion detection device group on the outflow side of the initial stage nanofiltration and n-stage nanofiltration membranes in the multi-stage nanofiltration module, which is used to detect the concentration of magnesium ions and lithium ions at different positions of the nanofiltration membrane.

[0024] As a preferred technical solution for the lithium-magnesium-lithium separation and concentration system in salt lakes, the detection module determines the permeability stability characterization parameters based on the lithium ion concentration flowing through the nanofiltration membrane within a single detection time period and the lithium ion concentration of the impurity-free brine.

[0025] The detection module determines the difference in lithium-ion concentration before and after passing through the nanofiltration membrane for each level of nanofiltration, and calculates the average value of the lithium-ion concentration difference and the average deviation of the lithium-ion concentration difference.

[0026] The detection module determines the permeability stability characterization parameters of the current level of nanofiltration based on the ratio of the average deviation of the lithium ion concentration difference to the average value of the lithium ion concentration difference.

[0027] As a preferred technical solution for a lithium extraction and magnesium-lithium separation and concentration system in salt lakes, the lithium extraction control module determines whether there are any abnormalities in the corresponding level of nanofiltration based on the permeability stability characterization parameters of each level of nanofiltration, including:

[0028] If the permeation stability characterization parameter is greater than the standard stability characterization parameter of the corresponding level, the lithium extraction control module determines that there is an anomaly in the corresponding level of nanofiltration.

[0029] If the permeation stability characterization parameter is less than or equal to the standard stability characterization parameter of the corresponding level, the lithium extraction control module determines that there is no abnormality in the corresponding level of nanofiltration.

[0030] As a preferred technical solution for a lithium extraction and magnesium-lithium separation and concentration system in salt lakes, the lithium extraction control module is configured to determine the adjustment method of the nanofiltration membrane in response to the judgment result of an anomaly at the current level of nanofiltration, combined with permeability stability characterization parameters, including:

[0031] If the permeation stability characterization parameter exceeds the non-destructive permeation threshold, the lithium extraction control module determines that the nanofiltration membrane needs to be replaced.

[0032] If the permeation stability characterization parameter does not exceed the non-destructive permeation threshold, the lithium extraction control module determines that the corresponding level of nanofiltration pressure needs to be reduced.

[0033] As a preferred technical solution for a lithium extraction and magnesium-lithium separation and concentration system in salt lakes, the lithium extraction control module determines the working position and silicon removal method of the silicon removal module based on the silicon content in the initial brine, including:

[0034] If the silicon content in the initial brine is greater than the normal exchange content threshold, the silicon removal module is located after the ultrafiltration unit and operates by chemical precipitation or by adjusting the pH with alkali.

[0035] If the silicon content in the initial brine is less than or equal to the normal exchange content threshold and greater than the membrane removal threshold, the silicon removal module is located after the ultrafiltration unit and operates by removing silicon through the ultrafiltration membrane.

[0036] If the silicon content in the initial brine is less than or equal to the membrane removal threshold, the silicon removal module is located behind the first-stage nanofiltration assembly and operates by removing silicon through an ultrafiltration membrane.

[0037] On the other hand, the present invention also provides a method for lithium extraction from salt lakes, including magnesium-lithium separation and concentration, comprising:

[0038] The initial brine is filtered, adsorbed, and ultrafiltered to obtain impurity-free brine;

[0039] The pure brine is desiliconized by chemical precipitation or by adjusting pH with alkali combined with ultrafiltration membrane and / or ion exchange.

[0040] The silica-free brine was subjected to a first-stage nanofiltration process to separate calcium and magnesium ions, resulting in first-stage nanofiltration permeate.

[0041] After pure water nanofiltration dialysis of the first-stage nanofiltration concentrate, the first-stage nanofiltration permeate is subjected to several stages of nanofiltration to separate calcium and magnesium ions step by step, resulting in several stages of nanofiltration permeate.

[0042] The permeate from the three-stage nanofiltration enters the high-pressure nanofiltration to increase the lithium ion concentration and obtain high-lithium ion water. The permeate from the first-stage reverse osmosis and high-pressure reverse osmosis enters the second-stage reverse osmosis for further desalination to obtain desalinated water.

[0043] The high-lithium-ion water enters a four-stage nanofiltration process to obtain the final nanofiltration product water.

[0044] Compared with existing technologies, the beneficial effects of this invention are as follows: the lithium-magnesium-lithium separation and concentration system and method for salt lake extraction achieves efficient and stable lithium extraction through the synergistic effect of multi-stage nanofiltration, dialysis, detection, and control modules. The multi-stage nanofiltration module significantly improves the recovery rate and purity of lithium ions by separating calcium and magnesium ions step by step. The reverse osmosis module concentrates the nanofiltration permeate, effectively recovering lithium ions from the permeate and reducing water waste. The detection module monitors the lithium ion concentration of each stage of nanofiltration in real time and evaluates the membrane's operating status through osmotic stability characterization parameters, ensuring the efficient and stable operation of the system. The lithium extraction control module dynamically adjusts the nanofiltration pressure or replaces the membrane based on the detection results, further optimizing system performance. In addition, the system automatically switches the silicon removal mode according to the silicon content in the initial brine, effectively preventing membrane fouling and clogging, extending the membrane's service life, and reducing operating costs. This invention not only improves the lithium recovery rate and product purity but also enhances the system's stability and economy, providing strong support for the intelligent and efficient development of lithium extraction processes in salt lakes.

[0045] Furthermore, in this invention, the series structure of the initial first-stage nanofiltration and several second-stage first-stage nanofiltration not only enhances the separation effect but also effectively reduces the magnesium ion concentration in the permeate through step-by-step treatment. The permeate from each nanofiltration stage can be flexibly returned to the previous two stages, improving system flexibility and resource utilization. In addition, the n-stage nanofiltration further ensures deep removal of residual calcium and magnesium ions. Through at least four stages of nanofiltration, a stepwise separation of divalent ions is achieved, significantly improving the recovery rate and purity of lithium ions. The introduction of the reverse osmosis module, especially the at least three-stage pure water nanofiltration dialysis of the first-stage nanofiltration concentrate, effectively recovers lithium ions from the concentrate, improving the lithium recovery rate. Simultaneously, the recycling of dialysis water reduces water waste. The synergistic effect of the first-stage reverse osmosis unit and the high-pressure reverse osmosis unit further increases the lithium ion concentration, ensuring the production of high-quality lithium products. The secondary reverse osmosis unit desalinates the permeate from each stage, which not only improves water quality but also enables efficient recycling of water resources by returning the concentrate to the tertiary nanofiltration stage. This reduces the overall energy consumption and operating costs of the system, improves lithium recovery rate and product purity, and enhances the stability and economy of the system.

[0046] Furthermore, in this invention, by calculating the average value and average deviation of the lithium ion concentration difference and further determining the permeation stability characterization parameters, the operating status of each stage of nanofiltration membranes can be quantitatively evaluated. This effectively reflects the antifouling ability and separation performance stability of the membrane system, overcoming the limitations of traditional methods that rely solely on the detection of magnesium ion concentration at a single inlet. It avoids misjudgments caused by detection lag and the inability to individually assess the status of each nanofiltration membrane stage, thereby improving the overall system's operating efficiency and stability. In addition, by comparing the permeation stability characterization parameters with the standard stability characterization parameters, it accurately determines whether there are any abnormalities in each stage of nanofiltration, providing a scientific basis for timely maintenance measures. This invention can not only dynamically assess the overall health status of multi-stage membrane systems but also provide a quantitative basis for process parameter optimization and maintenance decisions, thereby ensuring the long-term stability of magnesium-lithium separation efficiency and lithium resource recovery rate during the lithium extraction process from salt lakes, significantly improving the intelligence and efficiency of the lithium extraction process from salt lakes.

[0047] Furthermore, in this invention, when the silicon content in the initial brine is too high, the silicon removal module is placed after the ultrafiltration unit, and silicon removal is carried out by chemical precipitation or by adjusting the pH with alkali. This effectively avoids damage to the subsequent ion exchange resin caused by high silicon content. When the silicon content is at a medium level, the system switches to ultrafiltration membrane silicon removal mode, which not only meets the silicon content requirements of nanofiltration and reverse osmosis membranes for the influent, but also reduces the secondary pollution that may be caused by chemical precipitation or adjusting the pH with alkali. For brine with low silicon content, the system is further optimized by placing the silicon removal module after the first-stage nanofiltration assembly and using ultrafiltration membrane for secondary silicon removal. This ensures that the silicon content of the brine entering the subsequent treatment unit meets the strict standards. This not only reduces manual intervention and improves the convenience and accuracy of operation, but also effectively prevents membrane fouling and clogging by precisely controlling the silicon removal process, extending the membrane's service life, reducing operating costs, and ensuring the stable operation of the entire salt lake lithium extraction system and the efficient recovery of lithium resources. Attached Figure Description

[0048] Figure 1 This is a structural block diagram of the lithium-magnesium-lithium separation and concentration system for salt lake extraction according to an embodiment of the present invention;

[0049] Figure 2 This is a schematic diagram of the preprocessing module in an embodiment of the present invention;

[0050] Figure 3 This is a schematic diagram of the structure of the multi-stage nanofiltration module and the reverse osmosis module according to an embodiment of the present invention;

[0051] Figure 4 This is a schematic flowchart of the lithium extraction, magnesium-lithium separation and concentration method from salt lakes according to an embodiment of the present invention;

[0052] Figure 5 This is a flowchart illustrating the separation and concentration of lithium, magnesium, and lithium in salt lakes, as described in an embodiment of the present invention. Detailed Implementation

[0053] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0054] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0055] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0056] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0057] Please see Figure 1 The diagram shown is a structural block diagram of a lithium-magnesium-lithium separation and concentration system for lithium extraction from salt lakes according to an embodiment of the present invention. The present invention provides a lithium-magnesium-lithium separation and concentration system for lithium extraction from salt lakes, comprising:

[0058] The pretreatment module is used to filter the initial brine through several types of pretreatment equipment to obtain impurity-free brine;

[0059] A multi-stage nanofiltration module, which is connected to the pretreatment module, is used to separate calcium ions and magnesium ions step by step through several stages of nanofiltration to obtain several stages of nanofiltration permeate and final nanofiltration permeate.

[0060] The silicon removal module is connected to the multi-stage nanofiltration module and the pretreatment module respectively, and is used to remove silicon from the impurity-free brine by chemical precipitation or by adjusting the pH with alkali, combined with ultrafiltration membrane and / or ion exchange.

[0061] A reverse osmosis module, which is connected to the multi-stage nanofiltration module, is used to concentrate the first-stage nanofiltration permeate and to concentrate the permeate from the remaining stages of nanofiltration using reverse osmosis, and to desalinate each stage of reverse osmosis permeate.

[0062] The detection module is connected to the multi-stage nanofiltration module and the silicon removal module respectively, and is used to detect the magnesium-lithium ratio in the impurity-free brine, obtain the silicon content in the initial brine, and detect the magnesium ion concentration and lithium ion concentration of the nanofiltration permeate at each stage, so as to determine the permeability stability characterization parameters of the corresponding nanofiltration stage.

[0063] The lithium extraction control module is connected to the pretreatment module, the multi-stage nanofiltration module, and the detection module, respectively. It is used to determine the working position and silicon removal mode of the silicon removal module, and to determine whether there is any abnormality in the corresponding level of nanofiltration based on the permeability stability characterization parameters of each level of nanofiltration, and to determine the corresponding adjustment method.

[0064] In practice, a nanofiltration system is installed after the pretreatment module to reduce the content of divalent ions, such as SO42-. 2- CO3 2- wait.

[0065] The final nanofiltration product is a pure lithium chloride solution, achieving a total lithium recovery rate of over 95%, a lithium chloride solution Li+ ≥ 7 g / L, and a total water recovery rate of over 75%.

[0066] The lithium-magnesium-lithium separation and concentration system and method for salt lake extraction of this invention achieves efficient and stable lithium extraction through the synergistic effect of multi-stage nanofiltration, dialysis, detection, and control modules. The multi-stage nanofiltration module significantly improves the recovery rate and purity of lithium ions by separating calcium and magnesium ions step by step. The reverse osmosis module concentrates the nanofiltration permeate, effectively recovering lithium ions from the permeate and reducing water waste. The detection module monitors the lithium ion concentration of each stage of nanofiltration in real time and evaluates the membrane's operating status through osmotic stability characterization parameters, ensuring the efficient and stable operation of the system. The lithium extraction control module dynamically adjusts the nanofiltration pressure or replaces the membrane based on the detection results, further optimizing system performance. In addition, the system automatically switches the silicon removal mode according to the silicon content in the initial brine, effectively preventing membrane fouling and clogging, extending membrane life, and reducing operating costs. This invention not only improves the lithium recovery rate and product purity but also enhances the system's stability and economy, providing strong support for the intelligent and efficient development of lithium extraction processes in salt lakes.

[0067] Please see Figure 2 As shown, this is a schematic diagram of the preprocessing module according to an embodiment of the present invention. The preprocessing module includes:

[0068] The filtration unit includes several filtration devices to remove suspended solids from the initial brine to obtain the initial brine.

[0069] An adsorption unit, which is connected to the filtration unit, is used to selectively adsorb lithium ions in the first initial state brine to obtain a desorption solution and an adsorption-desorption solution.

[0070] An ultrafiltration unit, connected to the adsorption unit, is used to perform secondary filtration of the adsorption-desorption solution through an ultrafiltration membrane to obtain the impurity-free brine.

[0071] Lithium ions are present in the adsorption and desorption solution.

[0072] In practice, the filtration equipment includes precision filters, self-cleaning filters, coagulation sedimentation tanks, V-type filters, sand filters, multi-media filters, or ultrafiltration. The filtration unit uses one or more combinations to filter the initial brine.

[0073] The adsorption unit selectively adsorbs lithium. The adsorbent is one of aluminum-based, manganese-based, or titanium-based adsorbents. The adsorption desorption solution is processed in the ultrafiltration system, and the desorbed solution enters the ultrafiltration unit for subsequent membrane treatment.

[0074] The ultrafiltration unit uses hollow fiber membranes or ceramic membranes for ultrafiltration. The ultrafiltration unit retains suspended solids, macromolecular organic matter and colloids in the adsorption and desorption solution.

[0075] Please see Figure 3 As shown, this is a structural schematic diagram of a multi-stage nanofiltration module and a reverse osmosis module according to an embodiment of the present invention. The multi-stage nanofiltration module includes:

[0076] A primary nanofiltration system, comprising an initial primary nanofiltration stage and several secondary primary nanofiltration stages, is used to separate the calcium ions, the magnesium ions, and other divalent ions to obtain primary nanofiltration permeate.

[0077] The n-stage nanofiltration system, located after the outlet of the first-stage nanofiltration system, is used to separate residual calcium and magnesium ions in stages, and the concentrate from each stage of nanofiltration is returned to the previous two stages for further treatment.

[0078] In practice, the pH of the brine without impurities is adjusted to 3.5-5 by adding acid before entering the first-stage nanofiltration assembly. This implementation does not specify the structure of each stage of nanofiltration, as long as the nanofiltration membrane can separate calcium ions, magnesium ions and other divalent ions. This is existing technology and will not be elaborated further.

[0079] The total number of secondary-stage nanofiltration stages is not less than 3, preferably 3, and can be increased according to actual conditions; the 3-stage secondary-stage nanofiltration stage consists of primary secondary-stage nanofiltration, secondary secondary-stage nanofiltration, and tertiary secondary-stage nanofiltration. The inlet of the primary secondary-stage nanofiltration stage is connected to the product water outlet of the primary primary-stage nanofiltration stage, the inlet of the secondary secondary-stage nanofiltration stage is connected to the product water outlet of the primary secondary-stage nanofiltration stage, and the inlet of the tertiary secondary-stage nanofiltration stage is connected to the product water outlet of the secondary secondary-stage nanofiltration stage. The product water from the primary primary-stage nanofiltration stage and the secondary secondary-stage nanofiltration stages enters the desiliconization module or the reverse osmosis module.

[0080] When the permeate from each nanofiltration stage meets the corresponding feed water standard for the next nanofiltration stage, it flows to the next nanofiltration stage. The nanofiltration concentrate from the second and third nanofiltration stages flows back to the feed water of the first nanofiltration stage, and the nanofiltration concentrate from the fourth nanofiltration stage flows back to the feed water of the second nanofiltration stage.

[0081] The standards for nanofiltration feed water are as follows: magnesium ion concentration in primary nanofiltration feed water ≤3000mg / l; magnesium ion concentration in dialysis nanofiltration feed water ≤13000mg / l; magnesium ion concentration in secondary nanofiltration feed water ≤600mg / l; magnesium ion concentration in tertiary nanofiltration feed water ≤120mg / l; and magnesium ion concentration in quaternary nanofiltration feed water ≤30mg / l.

[0082] The number of n is greater than 2, preferably 4.

[0083] In this implementation, the multi-stage nanofiltration module includes several primary nanofiltration combinations and several n-stage nanofiltrations. The specific number is determined according to the concentration rate required for time separation, and the number of each nanofiltration stage and the number of primary nanofiltration combinations are not less than 3.

[0084] Specifically, the reverse osmosis module includes:

[0085] The first-stage reverse osmosis unit, located downstream of the first-stage nanofiltration assembly outlet, is used to initially concentrate the first-stage nanofiltration permeate to increase the lithium-ion concentration.

[0086] The high-pressure reverse osmosis unit, located downstream of the third-stage nanofiltration outlet, is used for secondary concentration of the third-stage nanofiltration permeate, increasing the lithium-ion concentration to Li. + ≥7g / L;

[0087] The secondary reverse osmosis unit is connected to the primary reverse osmosis unit, the high-pressure reverse osmosis unit, and the tertiary nanofiltration unit, respectively, and is used to desalinate the permeate from the primary reverse osmosis unit and the high-pressure reverse osmosis unit to obtain desalinated water. The resulting second reverse osmosis concentrate is then transported to the inlet of the tertiary nanofiltration unit.

[0088] In practice, the first-stage nanofiltration concentrate undergoes at least three or more stages of pure water nanofiltration dialysis. Pure water dialysis is performed in all two-stage nanofiltration processes. The number of stages is determined based on the magnesium ion concentration in the last stage nanofiltration permeate matching the magnesium ion concentration in the second-stage nanofiltration feed water. The amount of pure water added for each dialysis (dialysis water) is one times the amount of the first-stage nanofiltration concentrate. The permeate from each stage of dialysis nanofiltration is combined with the permeate from the first-stage nanofiltration and enters the first-stage reverse osmosis unit. This embodiment does not specifically limit the structure of the osmosis equipment in the first-stage, second-stage, and high-pressure reverse osmosis units. Their operating parameters are determined based on the actual application scenario.

[0089] In this embodiment, the high-pressure reverse osmosis unit can be located behind any one of the outlets of the second-stage nanofiltration unit, the third-stage nanofiltration unit, the fourth-stage nanofiltration unit, and the first-stage reverse osmosis unit, preferably behind the third-stage nanofiltration unit outlet.

[0090] Specifically, the detection module is equipped with an ion detection device group on the outflow side of the initial stage nanofiltration and n-stage nanofiltration membranes in the multi-stage nanofiltration module, which is used to detect the concentration of magnesium ions and lithium ions at different positions of the nanofiltration membrane.

[0091] In practice, the ion detection equipment is located in the sample stream drawn from the high-pressure pipeline through a pressure reducing valve and a microporous filter (0.45μm). This bypass sampling design ensures detection accuracy while avoiding direct exposure of the sensor to the high-pressure environment, thus extending the equipment's lifespan.

[0092] The detection module can also detect the concentration of calcium ions and silicon at different locations along the nanofiltration membrane, which is existing technology and will not be described further.

[0093] Magnesium ion-selective electrodes (such as membrane electrodes based on the ETH 129 neutral carrier) exhibit specific responses to magnesium ions. The potential signal is converted into a concentration value using the Nernst equation, with a detection range of 0.1 mg / L to 1000 mg / L (covering the magnesium ion concentration in nanofiltration permeate). 2+ It can detect concentrations of less than 1 g / L and has a response time of less than 30 seconds, enabling continuous online monitoring.

[0094] The lithium-ion selective electrode (such as the electrode based on ETH 2120 or Corning 476107 membrane) has high selectivity for lithium ions. The response mechanism is based on the specific binding of the neutral support to lithium ions. Its detection range is 0.1 mg / L to 10000 mg / L (i.e., 0.1 mg / L to 10 g / L, covering the concentration range of the entire lithium extraction process in salt lakes), and the response time is less than 20 seconds, which can realize continuous monitoring.

[0095] In this invention, the series structure of an initial nanofiltration stage followed by several secondary nanofiltration stages not only enhances the separation effect but also effectively reduces the magnesium ion concentration in the permeate through stepwise treatment. The permeate from each nanofiltration stage can be flexibly returned to the previous two stages, improving system flexibility and resource utilization. Furthermore, the n-stage nanofiltration further ensures deep removal of residual calcium and magnesium ions. Through at least four stages of nanofiltration, a stepwise separation of divalent ions is achieved, significantly improving the recovery rate and purity of lithium ions. The introduction of the reverse osmosis module, particularly the at least three-stage pure water nanofiltration dialysis of the primary nanofiltration concentrate, effectively recovers lithium ions from the concentrate, increasing the lithium recovery rate. Simultaneously, the recycling of dialysis water reduces water waste. The synergistic effect of the primary reverse osmosis unit and the high-pressure reverse osmosis unit further increases the lithium ion concentration, ensuring the production of high-quality lithium products. The secondary reverse osmosis unit desalinates the permeate from each stage, which not only improves water quality but also enables efficient recycling of water resources by returning the concentrate to the tertiary nanofiltration stage. This reduces the overall energy consumption and operating costs of the system, improves lithium recovery rate and product purity, and enhances the stability and economy of the system.

[0096] Specifically, the detection module determines the permeability stability characterization parameters based on the lithium ion concentration flowing through the nanofiltration membrane during a single detection time period and the lithium ion concentration of the impurity-free brine.

[0097] The detection module determines the difference in lithium-ion concentration before and after passing through the nanofiltration membrane for each level of nanofiltration, and calculates the average value of the lithium-ion concentration difference and the average deviation of the lithium-ion concentration difference.

[0098] The detection module determines the permeability stability characterization parameters of the current level of nanofiltration based on the ratio of the average deviation of the lithium ion concentration difference to the average value of the lithium ion concentration difference.

[0099] In practice, the number of permeability stability characterization parameters is the same as that of n.

[0100] It is understandable that each stage of nanofiltration consists of multiple nanofiltration membranes, and the permeability stability parameter characterizes the stability and consistency of lithium-ion separation efficiency of each stage of nanofiltration membranes during operation. Specifically, this parameter quantifies the fluctuation of lithium-ion concentration differences among multiple nanofiltration membranes within the same stage, reflecting the membrane system's antifouling ability and the trend of separation performance degradation. When the ratio of the average deviation to the average value of the lithium-ion concentration difference is low, i.e., the permeability stability parameter is small, it indicates that the operating status of that stage of nanofiltration membrane is stable and the separation efficiency fluctuates little; conversely, an increase in the parameter value indicates that membrane fouling is aggravated or performance degradation, requiring backwashing or chemical cleaning procedures. By monitoring the permeability stability parameter of each stage of nanofiltration in real time, the overall health status of the multi-stage membrane system can be dynamically assessed, providing a quantitative basis for process parameter optimization (such as pressure regulation and concentrate reuse ratio) and maintenance decisions, thereby ensuring the long-term stability of magnesium-lithium separation efficiency and lithium resource recovery rate during lithium extraction from salt lakes.

[0101] In practice, different nanofiltration membranes have different clogging conditions. Therefore, directly detecting the magnesium ion concentration at the inlet of the next stage cannot effectively determine the clogging status of each nanofiltration membrane at the current stage. If only the magnesium ion concentration at the inlet of the next stage is used as the basis for judgment, there will be a lag in detection time and the working status of each stage of nanofiltration membrane cannot be evaluated individually. This may lead to misjudgment of the overall system operation and further affect the efficiency and stability of the lithium extraction process in salt lakes.

[0102] Furthermore, single-membrane detection requires contaminants to accumulate to a perceptible level before triggering an alarm. In contrast, permeability stability characterization parameters summarize the lithium-ion concentration difference fluctuations of all membranes at the same level in real time, enabling early detection of overall performance degradation trends and avoiding post-event remediation. In addition, the composition of salt lake brine is complex, and the fouling rates of each membrane are different. By amplifying single-membrane anomalies into overall level fluctuations through permeability stability characterization parameters, the system avoids frequent shutdowns due to temporary anomalies in a single membrane, while also preventing the omission of systemic risks of simultaneous deterioration of multiple membranes. For example, when only one or two membranes are slightly abnormal, the deviation has a limited impact on the average value, and the ratio remains within the safe range, allowing the system to continue operating normally. Conversely, when multiple membranes decline in performance simultaneously, even if the decline in a single membrane is not significant, the deviation will rapidly amplify, and the ratio will immediately exceed the threshold, indicating overall fouling and triggering cleaning or load reduction.

[0103] Specifically, the lithium extraction control module determines whether there are any abnormalities in the corresponding level of nanofiltration based on the permeability stability characterization parameters of each level of nanofiltration, including:

[0104] If the permeation stability characterization parameter is greater than the standard stability characterization parameter of the corresponding level, the lithium extraction control module determines that there is an anomaly in the corresponding level of nanofiltration.

[0105] If the permeation stability characterization parameter is less than or equal to the standard stability characterization parameter of the corresponding level, the lithium extraction control module determines that there is no abnormality in the corresponding level of nanofiltration.

[0106] In implementation, the stability characterization parameters of each standard are selected within the corresponding stability threshold range;

[0107] The stability threshold range is determined by combining the average value and standard deviation of the permeability stability characterization parameters corresponding to the lowest filtration amount of magnesium ions in the nanofiltration permeate of each stage in historical separation records.

[0108] In this invention, by calculating the average value and average deviation of the lithium ion concentration difference and further determining the permeation stability characterization parameters, the operating status of each stage of nanofiltration membranes can be quantitatively evaluated. This effectively reflects the antifouling ability and separation performance stability of the membrane system, overcoming the limitations of traditional methods that rely solely on the detection of magnesium ion concentration at a single inlet. It avoids misjudgments caused by detection lag and the inability to individually assess the status of each nanofiltration membrane stage, thereby improving the overall system's operating efficiency and stability. Furthermore, by comparing the permeation stability characterization parameters with the standard stability characterization parameters, it accurately determines whether there are any abnormalities in each stage of nanofiltration, providing a scientific basis for timely maintenance measures. This invention can not only dynamically assess the overall health status of multi-stage membrane systems but also provide a quantitative basis for process parameter optimization and maintenance decisions, thus ensuring the long-term stability of magnesium-lithium separation efficiency and lithium resource recovery rate during the lithium extraction process from salt lakes, significantly improving the intelligence and efficiency of the lithium extraction process from salt lakes.

[0109] Specifically, the lithium extraction control module is configured to determine the adjustment method of the nanofiltration membrane in response to the determination result of an anomaly in the current level of nanofiltration, combined with the permeation stability characterization parameters, including:

[0110] If the permeation stability characterization parameter exceeds the non-destructive permeation threshold, the lithium extraction control module determines that the nanofiltration membrane needs to be replaced.

[0111] If the permeation stability characterization parameter does not exceed the non-destructive permeation threshold, the lithium extraction control module determines that the corresponding level of nanofiltration pressure needs to be reduced.

[0112] In practice, the non-destructive permeation threshold is determined based on the minimum value of the permeation stability characterization parameter when there is a single nanofiltration membrane failure or blockage requiring replacement in historical records.

[0113] It is understandable that increasing the operating pressure will increase the solvent flux (the amount of solvent passing through the membrane per unit time), thereby accelerating the separation process. However, when the pressure is too high, the solute accumulates rapidly on the membrane surface (concentration polarization), forming a high-concentration boundary layer, which may reduce the effective rejection rate and lead to an increase in the solute concentration after the membrane.

[0114] In this invention, when the permeation stability characterization parameter exceeds the non-destructive permeation threshold, it indicates that the nanofiltration membrane has been damaged or clogged and needs to be replaced. This helps to promptly avoid the decrease in separation efficiency and waste of lithium resources caused by membrane damage. When the permeation stability characterization parameter does not exceed the non-destructive permeation threshold, reducing the corresponding level of nanofiltration pressure can effectively mitigate concentration polarization and prevent an increase in post-membrane solute concentration due to excessive pressure, thereby maintaining the efficient and stable operation of the nanofiltration system. This invention can dynamically adjust according to the actual operating status of the nanofiltration system, which not only extends the service life of the nanofiltration membrane but also improves the efficiency and stability of the lithium extraction process from salt lakes, providing strong support for the optimization and intelligent upgrading of the lithium extraction process from salt lakes.

[0115] Specifically, the lithium extraction control module determines the working position and silicon removal method of the silicon removal module based on the silicon content in the initial brine, including:

[0116] If the silicon content in the initial brine is greater than the normal exchange content threshold, the silicon removal module is located after the ultrafiltration unit and operates by chemical precipitation or by adjusting the pH with alkali.

[0117] If the silicon content in the initial brine is less than or equal to the normal exchange content threshold and greater than the membrane removal threshold, the silicon removal module is located after the ultrafiltration unit and operates by removing silicon through the ultrafiltration membrane.

[0118] If the silicon content in the initial brine is less than or equal to the membrane removal threshold, the silicon removal module is located behind the first-stage nanofiltration assembly and operates by removing silicon through an ultrafiltration membrane.

[0119] During implementation, the pH of the initial brine is adjusted to 9.5–11.5 by adding alkali before it enters the desiliconization module.

[0120] The normal exchange content threshold is 100 mg / L, and the membrane removal threshold is selected within the range of [20 mg / L, 50 mg / L]. If the silicon content is greater than the allowable content after silicon removal by the ultrafiltration unit, secondary silicon removal can be performed after the first-stage nanofiltration assembly.

[0121] Understandably, excessive silicon content can lead to membrane fouling and clogging. Nanofiltration and reverse osmosis membranes typically have strict requirements regarding the silicon content of the feed water, generally recommending a concentration not exceeding 20–50 mg / L. Exceeding this range significantly degrades membrane performance, requiring more frequent cleaning and maintenance. While ion exchange resins have relatively high tolerance to silicon, excessively high silicon content reduces their exchange efficiency and lifespan. It is generally recommended that the feed water silicon content not exceed 100 mg / L. When the silicon content exceeds this value, the resin regeneration cost increases significantly, and more frequent replacement may be necessary.

[0122] During implementation, the lithium extraction control module automatically switches between chemical precipitation or pH adjustment via alkali or ion exchange modes based on changes in the silicon content of the brine, reducing manual intervention.

[0123] In this invention, when the silicon content in the initial brine is too high, the silicon removal module is placed after the ultrafiltration unit, and silicon removal is carried out by chemical precipitation or pH adjustment with alkali. This effectively avoids damage to the subsequent ion exchange resin caused by high silicon content. When the silicon content is at a medium level, the system switches to ultrafiltration membrane silicon removal mode, which not only meets the silicon content requirements of nanofiltration and reverse osmosis membranes for the feed water, but also reduces the secondary pollution that may be caused by chemical precipitation or pH adjustment with alkali. For brine with low silicon content, the system is further optimized by placing the silicon removal module after the first-stage nanofiltration assembly and using ultrafiltration membrane for secondary silicon removal. This ensures that the silicon content of the brine entering the subsequent treatment unit meets the strict standards. This not only reduces manual intervention and improves the convenience and accuracy of operation, but also effectively prevents membrane fouling and clogging by precisely controlling the silicon removal process, extending the membrane's service life, reducing operating costs, and ensuring the stable operation of the entire salt lake lithium extraction system and the efficient recovery of lithium resources.

[0124] Please see Figure 4 The diagram shown is a schematic flow chart of the lithium extraction, magnesium-lithium separation and concentration method from salt lakes according to an embodiment of the present invention. The present invention also provides a lithium extraction, magnesium-lithium separation and concentration method from salt lakes, comprising:

[0125] Step S1: The initial brine is filtered, adsorbed, and ultrafiltered to obtain impurity-free brine;

[0126] Step S2: Remove silicon from the impurity-free brine by chemical precipitation or by adjusting pH with alkali combined with ultrafiltration membrane and / or ion exchange.

[0127] Step S3: The silica-free brine is subjected to primary nanofiltration to separate calcium and magnesium ions step by step to obtain primary nanofiltration permeate.

[0128] Step S4: After performing pure water nanofiltration dialysis on the first-stage nanofiltration concentrate, the first-stage nanofiltration permeate is subjected to several stages of nanofiltration to separate calcium and magnesium ions step by step, resulting in several stages of nanofiltration permeate.

[0129] Step S5: The permeate from the three-stage nanofiltration enters the high-pressure nanofiltration to increase the lithium ion concentration and obtain high-lithium ion water; the permeate from the first-stage reverse osmosis and the high-pressure reverse osmosis enters the second-stage reverse osmosis for further desalination to obtain desalinated water.

[0130] In step S6, the high-lithium-ion water enters a four-stage nanofiltration system to obtain the final nanofiltration product water.

[0131] Please see Figure 5The diagram shows a flowchart of lithium extraction, magnesium, and lithium separation and concentration in a salt lake according to an embodiment of the present invention. Initial brine is first filtered by a self-cleaning filter and then enters an adsorption and desorption system. This system adsorbs lithium ions and generates tail brine for discharge. The desorbed liquid enters a qualified eluent tank and then an ultrafiltration system, including primary and secondary ultrafiltration. The filtered permeate enters an ultrafiltration permeate tank, and the backwash water is returned to the backwash water tank. Simultaneously, a plate and frame filter press system processes the concentrate to obtain filter cake, which is then reused. The water in the permeate tank is reduced and pH adjusted by adding a reducing agent and acid before entering a silicon removal unit to remove silicon impurities. The desiliconized water enters a primary nanofiltration system, and the separated permeate sequentially enters a secondary nanofiltration system for further treatment. The final concentrate is discharged, and the dialysis water is reused. The permeate from the primary nanofiltration system enters a primary reverse osmosis system, and the reverse osmosis permeate enters a secondary reverse osmosis system for further treatment to obtain desalinated water. Simultaneously, a high-pressure reverse osmosis system processes the concentrate from the tertiary nanofiltration system, producing high-pressure reverse osmosis permeate, which enters a quaternary nanofiltration system to obtain the final nanofiltration permeate.

[0132] In practice, the above results and the selection of various additives are not specifically limited, as they are existing technologies in this field and will not be elaborated further.

[0133] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

[0134] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A lithium-magnesium-lithium separation and concentration system for lithium extraction from salt lakes, comprising: The pretreatment equipment group and several nanofiltration devices are characterized in that they include: A pretreatment module, used to filter the initial brine through several types of pretreatment equipment to obtain impurity-free brine, including: The filtration unit includes several filtration devices to remove suspended solids from the initial brine to obtain the initial brine. An adsorption unit, which is connected to the filtration unit, is used to selectively adsorb lithium ions in the initial brine to obtain a desorption solution and an adsorption-desorption solution. An ultrafiltration unit, connected to the adsorption unit, is used to perform secondary filtration of the adsorption-desorption solution through an ultrafiltration membrane to obtain the impurity-free brine. Lithium ions are present in the adsorption and desorption solution; A multi-stage nanofiltration module, connected to the pretreatment module, is used to separate calcium and magnesium ions through several stages of nanofiltration to obtain several levels of nanofiltration permeate and final nanofiltration permeate, including: A primary nanofiltration system, comprising an initial primary nanofiltration stage and several secondary primary nanofiltration stages, is used to separate the calcium ions, the magnesium ions, and other divalent ions to obtain primary nanofiltration permeate. The n-stage nanofiltration system is located after the outlet of the first-stage nanofiltration system. It is used to separate residual calcium and magnesium ions step by step to obtain n-stage nanofiltration permeate, and return the concentrate from each stage of nanofiltration to the previous two stages for further treatment. A silicon removal module, which is connected to the multi-stage nanofiltration module and the pretreatment module respectively, is used to remove silicon from the impurity-free brine by chemical precipitation combined with ultrafiltration membrane silicon removal; A reverse osmosis module, which is connected to the multi-stage nanofiltration module, is used to concentrate the first-stage nanofiltration permeate and to concentrate the permeate from the remaining stages of nanofiltration using reverse osmosis, and to desalinate each stage of reverse osmosis permeate. The detection module, which is connected to the multi-stage nanofiltration module and the silicon removal module respectively, is used to detect the magnesium-lithium ratio in the impurity-free brine, obtain the silicon content in the initial brine, and detect the magnesium ion concentration and lithium ion concentration of the permeate from each stage of nanofiltration to determine the permeability stability characterization parameters of the corresponding stage of nanofiltration; the permeability stability characterization parameters are determined based on the lithium ion concentration flowing through the nanofiltration membrane in a single detection time period and the lithium ion concentration of the impurity-free brine. The detection module determines the difference in lithium-ion concentration before and after passing through the nanofiltration membrane for each level of nanofiltration, and calculates the average value of the lithium-ion concentration difference and the average deviation of the lithium-ion concentration difference. The detection module determines the permeability stability characterization parameter of the current level of nanofiltration based on the ratio of the average deviation of the lithium ion concentration difference to the average value of the lithium ion concentration difference. A lithium extraction control module, connected to the pretreatment module, the multi-stage nanofiltration module, and the detection module, is used to determine the working position and silicon removal method of the silicon removal module based on the silicon content in the initial brine, including: If the silicon content in the initial brine is greater than the normal exchange content threshold, the silicon removal module is located after the ultrafiltration unit and operates through chemical precipitation. If the silicon content in the initial brine is less than or equal to the normal exchange content threshold and greater than the membrane removal threshold, the silicon removal module is located after the ultrafiltration unit and operates by removing silicon through the ultrafiltration membrane. If the silicon content in the initial brine is less than or equal to the membrane removal threshold, the silicon removal module is located after the first-stage nanofiltration assembly and operates by removing silicon through an ultrafiltration membrane. Furthermore, based on the permeability stability characterization parameters of each nanofiltration level, it is determined whether there are any anomalies in the corresponding nanofiltration level. In response to the determination that an anomaly exists in the current level of nanofiltration, the adjustment method for the nanofiltration membrane is determined in conjunction with the permeability stability characterization parameters, including: If the permeation stability characterization parameter exceeds the non-destructive permeation threshold, the lithium extraction control module determines that the nanofiltration membrane needs to be replaced. If the permeation stability characterization parameter does not exceed the non-destructive permeation threshold, the lithium extraction control module determines that the corresponding level of nanofiltration pressure needs to be reduced.

2. The lithium-magnesium-lithium separation and concentration system for salt lake extraction according to claim 1, characterized in that, The reverse osmosis module includes: The first-stage reverse osmosis unit, located downstream of the first-stage nanofiltration assembly outlet, is used to initially concentrate the first-stage nanofiltration permeate to increase the lithium-ion concentration. The high-pressure reverse osmosis unit, located downstream of the third-stage nanofiltration outlet, is used for secondary concentration of the third-stage nanofiltration permeate, increasing the lithium-ion concentration to Li. + ≥7g / L; The secondary reverse osmosis unit is connected to the primary reverse osmosis unit, the high-pressure reverse osmosis unit, and the tertiary nanofiltration unit, respectively, and is used to desalinate the permeate from the primary reverse osmosis unit and the high-pressure reverse osmosis unit to obtain desalinated water. The resulting second reverse osmosis concentrate is then transported to the inlet of the tertiary nanofiltration unit.

3. The lithium-magnesium-lithium separation and concentration system for salt lake extraction according to claim 2, characterized in that, The detection module is equipped with an ion detection device group on the outflow side of the initial stage nanofiltration and n-stage nanofiltration membranes in the multi-stage nanofiltration module, which is used to detect the concentration of magnesium ions and lithium ions at different positions along the nanofiltration membrane.

4. The lithium-magnesium-lithium separation and concentration system for salt lake extraction according to claim 3, characterized in that, The lithium extraction control module determines whether there are any abnormalities in the corresponding level of nanofiltration based on the permeability stability characterization parameters of each level of nanofiltration, including: If the permeation stability characterization parameter is greater than the standard stability characterization parameter of the corresponding level, the lithium extraction control module determines that there is an anomaly in the corresponding level of nanofiltration. If the permeation stability characterization parameter is less than or equal to the standard stability characterization parameter of the corresponding level, the lithium extraction control module determines that there is no abnormality in the corresponding level of nanofiltration.

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