Separation and concentration system and method for extracting lithium, magnesium and lithium from salt lake

Abstract

The invention relates to the technical field of extraction and separation, in particular to a separation and concentration system and method for extracting lithium, magnesium and lithium from a salt lake, the system comprises 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 multi-stage nanofiltration module separates divalent ions such as calcium and magnesium step by step through multi-stage nanofiltration, the silicon removal module removes silicon from the impurity-free brine, the reverse osmosis module concentrates nanofiltration produced water, the detection module detects the ratio of magnesium to lithium in the impurity-free brine, and the silicon content in the initial brine is obtained. And the lithium extraction control module is used for detecting the magnesium ion concentration and the lithium ion concentration of each level of nanofiltration to determine the permeation stability characterization parameter of the corresponding level of nanofiltration, and the lithium extraction control module is used for determining the working position and the silicon removal mode of the silicon removal module and determining whether each level of nanofiltration is abnormal or not so as to carry out adjustment. The membrane pollution is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of extraction and separation, and particularly relates to a salt lake lithium extraction and magnesium-lithium separation and concentration system and method. BACKGROUND

[0002] In the prior art, there are many problems in the field of lithium extraction from salt lake brine. On the one hand, the salt lake brine usually has a high magnesium-lithium ratio, which brings great challenges to lithium extraction. The traditional precipitation method and extraction method have very low separation efficiency when facing such a high magnesium-lithium ratio, and a large amount of chemical reagents and complex operation steps are often needed to achieve the preliminary separation of lithium and magnesium, which not only increases the production cost, but also produces a large amount of waste, causing certain pressure on the environment. Moreover, the lithium extraction process is complicated, inefficient, and difficult to meet the needs of large-scale industrial production. On the other hand, single nanofiltration or reverse osmosis process also has obvious defects. Although these two processes have a wide range of applications in the field of water treatment, they are difficult to separate magnesium and lithium while ensuring lithium recovery rate and achieving efficient concentration of lithium in the process of lithium extraction from salt lake. In addition, single membrane separation process is prone to membrane pollution, and frequent membrane cleaning and replacement increase the operation cost and maintenance workload, which seriously restricts the long-term stable application of the process in the field of lithium extraction from salt lake.

[0003] At the same time, the salt lake brine also faces many problems in the concentration process. Impurities such as silicon, calcium and magnesium are easily precipitated during concentration. These precipitated impurities will adhere to the membrane surface or block the membrane pores, resulting in a decrease in membrane flux, which not only increases the energy consumption, but also affects the stability of the whole system, making it difficult to continuously and efficiently extract lithium. Moreover, the application of dialysis process in the prior art is not sufficient, and the selective permeation and recovery effect of lithium ions in the dialysis process is limited, resulting in a low lithium recovery rate, which cannot fully exploit the potential of salt lake brine resources, causing waste of lithium resources and difficulty in meeting the growing market demand for lithium products and the large demand for high-quality lithium raw materials in the new energy industry. SUMMARY

[0004] Therefore, the present application provides a salt lake lithium extraction and magnesium-lithium separation and concentration system and method to overcome the problem that single nanofiltration or reverse osmosis process in the prior art cannot simultaneously consider magnesium-lithium separation and lithium concentration, and the membrane is severely polluted.

[0005] To achieve the above-mentioned purpose, on the one hand, the present application provides a salt lake lithium extraction and magnesium-lithium separation and concentration system, comprising: a pretreatment module for filtering the initial brine through several types of pretreatment equipment to obtain a non-impurity brine;

[0006] a multi-stage nanofiltration module connected with the pretreatment module, for separating calcium ions and magnesium ions by several stages of nanofiltration to obtain several levels of nanofiltration product water and final nanofiltration product water;

[0007] a desilication module connected with the multi-stage nanofiltration module and the pretreatment module, for desilicating the halogen water by chemical precipitation or by adjusting pH with alkali, in combination with ultrafiltration membranes and / or ion exchange;

[0008] a reverse osmosis module connected with the multi-stage nanofiltration module, for concentrating the first-stage nanofiltration product water and reverse osmosis concentrating the remaining levels of nanofiltration product water, and desalting each reverse osmosis product water;

[0009] a detection module connected with the multi-stage nanofiltration module and the desilication module, for detecting the magnesium-lithium ratio in the halogen water, obtaining the silicon content in the initial halogen water, and detecting the magnesium ion concentration and lithium ion concentration of each level of nanofiltration product water to determine the osmotic stability characterization parameter of the corresponding level of nanofiltration;

[0010] a lithium extraction control module connected with the pretreatment module, the multi-stage nanofiltration module, and the detection module, for determining the working position and desilication method of the desilication module, and determining whether there is an anomaly in the corresponding level of nanofiltration according to the osmotic stability characterization parameter of each level of nanofiltration, and determining the corresponding adjustment method.

[0011] As a preferred technical solution of the salt lake lithium extraction and magnesium-lithium separation and concentration system, the pretreatment module comprises:

[0012] a filtration unit comprising several filtration devices for removing suspended solids in the initial halogen water to obtain initial-state halogen water;

[0013] an adsorption unit connected with the filtration unit for selectively adsorbing lithium ions in the first initial-state halogen water to obtain desorption liquid and adsorption desorption liquid;

[0014] an ultrafiltration unit connected with the adsorption unit for secondary filtration of the adsorption desorption liquid by ultrafiltration membranes to obtain the halogen water without impurities;

[0015] wherein the lithium ions are in the adsorption desorption liquid.

[0016] As a preferred technical solution of the salt lake lithium extraction and magnesium-lithium separation and concentration system, the multi-stage nanofiltration module comprises:

[0017] a first-stage nanofiltration combination comprising an initial first-stage nanofiltration and several secondary second-stage nanofiltrations for separating the calcium ions, the magnesium ions, and other divalent ions to obtain first-stage nanofiltration product water;

[0018] n-stage nanofiltration, which is located behind the outlet of the first-stage nanofiltration, is used to separate residual calcium ions and magnesium ions step by step, to obtain n-stage nanofiltration product water, and to return the concentrated water of each stage of nanofiltration to the upper two stages of nanofiltration for reprocessing.

[0019] As a preferred technical solution of the lithium-magnesium-lithium separation and concentration system for extracting lithium from salt lakes, the reverse osmosis module comprises:

[0020] A first-stage reverse osmosis unit, which is located behind the outlet of the first-stage nanofiltration group, is used to preliminarily concentrate the first-stage nanofiltration product water and increase the lithium ion concentration;

[0021] A high-pressure reverse osmosis unit, which is located behind the outlet of the third-stage nanofiltration, is used to secondarily concentrate the third-stage nanofiltration product water and increase the lithium ion concentration to Li+≥7g / L;

[0022] A second-stage reverse osmosis unit, which is connected to the first-stage reverse osmosis unit, the high-pressure reverse osmosis unit and the third-stage nanofiltration, is used to desalt the product water of the first-stage reverse osmosis unit and the high-pressure reverse osmosis unit to obtain desalted water, and to transport the obtained second-stage reverse osmosis concentrated water to the inlet of the third-stage nanofiltration.

[0023] As a preferred technical solution of the lithium-magnesium-lithium separation and concentration system for extracting lithium from salt lakes, the detection module is provided with a group of ion detection devices on the water flow outflow side of the initial first-stage nanofiltration and the n-stage nanofiltration in the multi-stage nanofiltration module, to detect the magnesium ion concentration and the lithium ion concentration flowing through different positions of the nanofiltration membrane.

[0024] As a preferred technical solution of the lithium-magnesium-lithium separation and concentration system for extracting lithium from salt lakes, the detection module determines a penetration stability characterization parameter according to the lithium ion concentration flowing through the nanofiltration membrane in a single detection time period and the lithium ion concentration of the halogen water.

[0025] The detection module determines the difference between the lithium ion concentrations before and after flowing through the nanofiltration membrane of each stage 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 penetration stability characterization parameter of the current stage of nanofiltration according to 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 of the lithium-magnesium-lithium separation and concentration system for extracting lithium from salt lakes, the extraction lithium control module determines whether there is an abnormality in the corresponding stage of nanofiltration according to the penetration stability characterization parameter of each stage of nanofiltration, comprising:

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

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

[0030] As a preferred technical solution of the lithium-magnesium-lithium separation and concentration system for extracting lithium from salt lakes, the lithium extraction control module is configured to determine the adjustment mode of the nanofiltration membrane in response to the determination result of the abnormality of the nanofiltration of the current level in combination with the permeation stability characteristic parameter, including:

[0031] If the permeation stability characteristic parameter exceeds the lossless permeation threshold, the lithium extraction control module determines that the nanofiltration membrane needs to be replaced;

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

[0033] As a preferred technical solution of the lithium-magnesium-lithium separation and concentration system for extracting lithium from salt lakes, the lithium extraction control module determines the working position and the silicon removal mode of the silicon removal module according to 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 working position of the silicon removal module is behind the ultrafiltration unit, and the working mode is chemical precipitation or adjusting pH by 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 working position of the silicon removal module is behind the ultrafiltration unit, and the working mode is to remove silicon by the ultrafiltration membrane;

[0036] If the silicon content in the initial brine is less than or equal to the membrane removal threshold, the working position of the silicon removal module is behind the first nanofiltration combination, and the working mode is to remove silicon by the ultrafiltration membrane.

[0037] In another aspect, the present application also provides a method for lithium-magnesium-lithium separation and concentration from salt lakes, including:

[0038] Filtering, adsorbing and ultrafiltrating the initial brine to obtain a clean brine;

[0039] Removing silicon from the clean brine by chemical precipitation or adjusting pH by alkali in combination with an ultrafiltration membrane and / or ion exchange;

[0040] Performing first-stage nanofiltration on the silicon-removed clean brine to separate calcium ions and magnesium ions step by step to obtain first-stage nanofiltration water;

[0041] After dialysis of the first-stage nanofiltration water by pure water nanofiltration, performing several-stage nanofiltration on the first-stage nanofiltration water to separate calcium ions and magnesium ions step by step to obtain several-stage nanofiltration water;

[0042] The water produced by the tertiary nanofiltration enters high-pressure nanofiltration to increase the lithium ion concentration to obtain high-lithium-ion water, and the water produced by the primary reverse osmosis and high-pressure reverse osmosis enters the secondary reverse osmosis for further desalination treatment to obtain desalted water.

[0043] The high-lithium-ion water enters the fourth nanofiltration to obtain the final nanofiltration water.

[0044] Compared with the prior art, the beneficial effects of the present application are that the salt lake lithium extraction and magnesium-lithium separation and concentration system and method realize efficient and stable lithium extraction through the synergistic effect of the multi-stage nanofiltration, dialysis, detection and control modules, the multi-stage nanofiltration module separates calcium ions and magnesium ions by stages, significantly improves the recovery rate and purity of lithium ions, the reverse osmosis module concentrates the nanofiltration water, effectively recovers lithium ions in the water, reduces water resource waste, the detection module monitors the lithium ion concentration of each stage of nanofiltration in real time, evaluates the running state of the membrane through the osmotic stability characteristic parameter, ensures the efficient and stable operation of the system, the lithium extraction control module dynamically adjusts the nanofiltration pressure or replaces the membrane according to the detection result, further optimizes the system performance, in addition, the system automatically switches the silicon removal mode according to the silicon content in the initial brine, effectively prevents membrane pollution and blockage, prolongs the service life of the membrane, and reduces the operation cost, the present application not only improves the recovery rate and purity of lithium, but also enhances the stability and economy of the system, and provides strong support for the intelligentization and high efficiency of the salt lake lithium extraction process.

[0045] Further, in the present application, the series structure of the initial primary nanofiltration and several secondary primary nanofiltrations not only enhances the separation effect, but also effectively reduces the magnesium ion concentration in the water through step-by-step processing, the nanofiltration water of each stage can be flexibly returned to the upper two stages of nanofiltration, improving the flexibility and resource utilization rate of the system. In addition, the setting of n-stage nanofiltration further ensures the deep removal of residual calcium and magnesium ions, through at least 4-stage nanofiltration processing, the step-by-step separation of divalent ions is realized, the recovery rate and purity of lithium ions are significantly improved. The introduction of the reverse osmosis module, especially at least three-stage nanofiltration dialysis of the concentrated water of the primary nanofiltration, effectively recovers the lithium ions in the concentrated water, improves the recovery rate of lithium, and the recycling of the dialysis water also reduces the waste of water resources. The synergistic effect of the primary reverse osmosis unit and the high-pressure reverse osmosis unit further improves the lithium ion concentration, ensuring the output of high-quality lithium products. The secondary reverse osmosis unit desalination treatment of the water produced by each stage not only improves the water quality, but also realizes efficient recycling of water resources by returning the concentrated water to the third nanofiltration, reducing the overall energy consumption and operation cost of the system, not only improving the recovery rate and purity of lithium, but also enhancing the stability and economy of the system.

[0046] Further, in the present application, by calculating the average value and average deviation of the lithium ion concentration difference, and further determining the permeation stability characterization parameter, the running state of each level of nanofiltration membrane can be quantitatively evaluated, the anti-pollution ability and the stability of the separation performance of the membrane system can be effectively reflected, the limitation of relying only on the detection of the magnesium ion concentration at the single inlet in the traditional method is overcome, the misjudgment caused by the detection lag and the inability to evaluate the state of each level of nanofiltration membrane alone is avoided, and thus the running efficiency and stability of the whole system are improved. In addition, according to the comparison between the permeation stability characterization parameter and the standard stability characterization parameter, it can be accurately judged whether there is an abnormality in each level of nanofiltration, and a scientific basis is provided for timely maintenance measures. The present application not only can dynamically evaluate the overall health state of the multi-stage membrane system, but also can provide quantitative basis for process parameter optimization and maintenance decision, so as to ensure the long-term stability of the magnesium-lithium separation efficiency and the lithium resource recovery rate in the salt lake lithium extraction process, and significantly improve the intelligence and efficiency of the salt lake lithium extraction process.

[0047] Further, in the present application, when the silicon content in the initial brine is too high, the silicon removal module is placed behind the ultrafiltration unit, and chemical precipitation or pH adjustment by alkali is used for silicon removal, effectively avoiding the damage of high silicon content to the subsequent ion exchange resin. When the silicon content is at a moderate level, the system switches to the ultrafiltration membrane silicon removal mode, which not only meets the requirements of nanofiltration and reverse osmosis membranes for the silicon content of the inlet water, but also reduces the secondary pollution that may be caused by chemical precipitation or pH adjustment by alkali. For low-silicon-content brine, the system is further optimized, the silicon removal module is placed behind the first nanofiltration combination, and the ultrafiltration membrane is used for secondary silicon removal, ensuring that the silicon content of the brine entering the subsequent processing unit meets the strict standards. Not only does this reduce manual intervention and improve the convenience and accuracy of operation, but it also effectively prevents membrane pollution and blockage by precisely controlling the silicon removal process, prolonging the service life of the membrane and reducing operating costs, while ensuring the stable operation of the entire salt lake lithium extraction system and the efficient recovery of lithium resources. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 The structure block diagram of the salt lake lithium extraction magnesium-lithium separation and concentration system of the embodiment of the present application is shown in the figure.

[0049] Figure 2 The structure schematic diagram of the pretreatment module of the embodiment of the present application is shown in the figure.

[0050] Figure 3 The structure schematic diagram of the multi-stage nanofiltration module and the reverse osmosis module of the embodiment of the present application is shown in the figure.

[0051] Figure 4 The flowchart of the salt lake lithium extraction magnesium-lithium separation and concentration method of the embodiment of the present application is shown in the figure.

[0052] Figure 5 The flowchart of the salt lake lithium extraction magnesium-lithium separation and concentration of the embodiment of the present application is shown in the figure. 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] a detection module connected with the multi-stage nanofiltration module and the desilication module, for detecting the magnesium-lithium ratio in the halogen water, obtaining the silicon content in the initial halogen water, and detecting the magnesium ion concentration and the lithium ion concentration of the nanofiltration water of each stage to determine the osmotic stability characteristic parameter of the corresponding stage nanofiltration;

[0063] an extraction lithium control module connected with the pretreatment module, the multi-stage nanofiltration module and the detection module, for determining the working position and the desilication mode of the desilication module, and determining whether there is an abnormality in the corresponding stage nanofiltration according to the osmotic stability characteristic parameter of the corresponding stage nanofiltration, and determining the corresponding adjustment mode.

[0064] In the implementation, the nanofiltration system is arranged behind the pretreatment module to reduce the content of divalent ions such as SO4 2- , CO3 2- , etc.

[0065] The final nanofiltration water is a pure lithium chloride solution, realizing that the total lithium recovery rate is greater than 95%, the lithium chloride solution Li+ is greater than or equal to 7g / L, and the total water recovery rate is greater than 75%.

[0066] The salt lake lithium extraction and magnesium-lithium separation and concentration system and method realize efficient and stable lithium extraction through the synergistic effect of the multi-stage nanofiltration, dialysis, detection and control modules, the multi-stage nanofiltration module separates calcium ions and magnesium ions through stage-by-stage separation, significantly improves the recovery rate and purity of lithium ions, the reverse osmosis module concentrates the nanofiltration water, effectively recovers the lithium ions in the water, reduces the waste of water resources, the detection module monitors the lithium ion concentration of each stage nanofiltration in real time, evaluates the running state of the membrane through the osmotic stability characteristic parameter, and ensures the efficient and stable operation of the system, the extraction lithium control module dynamically adjusts the nanofiltration pressure or replaces the membrane according to the detection result, further optimizes the system performance, in addition, the system automatically switches the desilication mode according to the silicon content in the initial halogen water, effectively prevents membrane pollution and blockage, prolongs the service life of the membrane, and reduces the operation cost, the present application not only improves the recovery rate and purity of lithium, but also enhances the stability and economy of the system, and provides strong support for the intelligentization and high efficiency of the salt lake lithium extraction process.

[0067] Please refer to Figure 2 Fig. 1, which is a structural schematic diagram of the pretreatment module of the embodiment of the present application, the pretreatment module comprises:

[0068] a filtration unit comprising a plurality of filtration devices, for removing suspended solids in the initial halogen water to obtain initial-state halogen water;

[0069] an adsorption unit connected with the filtration unit, for selectively adsorbing lithium ions in the first initial-state halogen water to obtain desorption liquid and adsorption desorption liquid;

[0070] a ultrafiltration unit connected with the adsorption unit, for performing secondary filtration on the adsorption elution liquid through a ultrafiltration membrane to obtain the halogen water without impurities;

[0071] wherein lithium ions are in the adsorption elution liquid.

[0072] In the implementation, the filtering device is a precision filter, a self-cleaning filter, a coagulation sedimentation tank, a V-shaped filter tank, a sand filter, a multi-medium filter, or a ultrafiltration, and the filtering unit adopts one or more combinations to filter the initial halogen water.

[0073] The adsorption unit selectively adsorbs lithium, and the adsorbent adopts one of an aluminum-based adsorbent, a manganese-based adsorbent, and a titanium-based adsorbent; the adsorption elution liquid enters the ultrafiltration system for treatment, and the desorption liquid enters the ultrafiltration unit for subsequent membrane treatment.

[0074] The ultrafiltration membrane in the ultrafiltration unit adopts a hollow fiber membrane or a ceramic membrane, and the ultrafiltration unit intercepts suspended solids, macromolecular organic matter, and colloids in the adsorption elution liquid.

[0075] Please refer to Figure 3 As shown in the figure, it is a structure schematic diagram of a multi-stage nanofiltration module and a reverse osmosis module according to an embodiment of the present application, and the multi-stage nanofiltration module comprises:

[0076] The primary nanofiltration combination comprises an initial primary nanofiltration and a plurality of secondary primary nanofiltrations, which are used to separate the calcium ions, the magnesium ions and other divalent ions to obtain primary nanofiltration product water.

[0077] The n-stage nanofiltration is located behind the outlet of the primary nanofiltration, and is used to separate the residual calcium ions and magnesium ions step by step, and return the concentrated water of each stage of nanofiltration to the upper two stages of nanofiltration for reprocessing.

[0078] In the implementation, the pH of the halogen water without impurities is adjusted to 3.5-5 before entering the primary nanofiltration combination; the structure of each stage of nanofiltration is not specifically limited in the implementation, wherein the nanofiltration membrane can separate the calcium ions, the magnesium ions and other divalent ions, which is prior art and will not be described in detail.

[0079] The total number of the plurality of secondary primary nanofiltrations is not less than 3, and is preferably three, which can be increased according to actual conditions; the three secondary primary nanofiltrations are a first secondary nanofiltration, a second secondary nanofiltration and a third secondary nanofiltration; the inlet of the first secondary nanofiltration is connected with the outlet of the initial primary nanofiltration; the inlet of the second secondary nanofiltration is connected with the outlet of the first secondary nanofiltration; the inlet of the third secondary nanofiltration is connected with the outlet of the second secondary nanofiltration; the product water of the initial primary nanofiltration and the plurality of secondary primary nanofiltrations enters a desiliconization module or a reverse osmosis module.

[0080] When the water produced by each stage of nanofiltration meets the corresponding nanofiltration inlet water standard of the next stage, it flows to the next stage of nanofiltration, and the nanofiltration concentrated water of the second and third stages of nanofiltration flows back to the inlet water of the first stage of nanofiltration combination, and the nanofiltration concentrated water of the fourth stage of nanofiltration flows back to the inlet water of the second stage of nanofiltration combination.

[0081] The nanofiltration inlet water standard is: the magnesium ion concentration of the first stage of nanofiltration inlet water is ≤3000 mg / l; the magnesium ion concentration of dialysis nanofiltration inlet water is ≤13000 mg / l; the magnesium ion concentration of the second stage of nanofiltration inlet water is ≤600 mg / l; the magnesium ion concentration of the third stage of nanofiltration inlet water is ≤120 mg / l; and the magnesium ion concentration of the fourth stage of nanofiltration inlet water is ≤30 mg / l.

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

[0083] In the embodiment, the multi-stage nanofiltration module comprises a plurality of first-stage nanofiltration combinations and a plurality of n-stage nanofiltrations, and the specific number is determined according to the rate of concentration required by time separation. The number of each stage of nanofiltration and the number of first-stage nanofiltration combinations are both not less than 3.

[0084] Specifically, the reverse osmosis module comprises:

[0085] A first-stage reverse osmosis unit located behind the outlet of the first-stage nanofiltration combination, used to preliminarily concentrate the first-stage nanofiltration produced water and increase the lithium ion concentration;

[0086] A high-pressure reverse osmosis unit located behind the outlet of the third-stage nanofiltration, used to secondarily concentrate the third-stage nanofiltration produced water and increase the lithium ion concentration to Li + ≥7 g / L.

[0087] A second-stage reverse osmosis unit connected with the first-stage reverse osmosis unit, the high-pressure reverse osmosis unit and the third-stage nanofiltration, respectively, used to desalt the produced water of the first-stage reverse osmosis unit and the high-pressure reverse osmosis unit to obtain desalted water, and used to transport the second-stage reverse osmosis concentrated water to the inlet of the third-stage nanofiltration.

[0088] In the embodiment, the first-stage nanofiltration concentrated water is subjected to at least three-stage or more pure water nanofiltration dialysis, and the pure water dialysis is realized in all second-stage nanofiltrations. The number is determined according to whether the magnesium ion concentration in the produced water of the last second-stage nanofiltration meets the magnesium ion concentration of the second-stage nanofiltration inlet water. The amount of pure water (dialysis water) added each time is 1 times the amount of water of the first-stage nanofiltration concentrated water. The produced water of each dialysis nanofiltration is combined with the first-stage nanofiltration produced water and then enters the first-stage reverse osmosis unit. The structure of the permeation device in the first-stage, second-stage and high-pressure reverse osmosis units is not specifically limited in the embodiment, and the working parameters are determined according to actual application scenarios.

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

[0090] Specifically, the detection module is provided with a group of ion detection devices on the water flow outflow side of the nanofiltration membranes of the initial-stage nanofiltration and the n-stage nanofiltration in the multi-stage nanofiltration module, to detect the concentrations of magnesium ions and lithium ions flowing through different positions of the nanofiltration membranes.

[0091] In implementation, the group of ion detection devices is located in the sample flow drawn from the high-pressure pipeline through a pressure-reducing valve and a microporous filter (0.45 μm), i.e., a bypass sampling design is adopted for detection, which ensures the accuracy of detection, avoids direct exposure of the sensor to a high-pressure environment, and prolongs the service life of the equipment.

[0092] The detection module can also detect the concentrations of calcium ions and silicon flowing through different positions of the nanofiltration membranes, which is prior art and will not be described in detail.

[0093] The magnesium ion-selective electrode (such as a membrane electrode based on ETH 129 neutral carrier) has a specific response to magnesium ions, and the potential signal is converted into a concentration value through the Nernst equation, with a detection range of 0.1 mg / L to 1000 mg / L (covering the Mg 2+ <1 g / L detection requirement) of the nanofiltration product water, and a response time of less than 30 seconds, which can realize continuous online monitoring.

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

[0095] In the present application, the series connection of the initial primary nanofiltration and several secondary primary nanofiltration not only enhances the separation effect, but also effectively reduces the magnesium ion concentration in the produced water through step-by-step processing. The nanofiltration produced water of each stage can be flexibly returned to the upper two stages of nanofiltration, improving the flexibility and resource utilization rate of the system. In addition, the setting of n-stage nanofiltration further ensures the deep removal of residual calcium and magnesium ions. Through at least 4-stage nanofiltration processing, gradient separation of divalent ions is realized, significantly improving the recovery rate and purity of lithium ions. The introduction of the reverse osmosis module, especially at least three-stage pure water nanofiltration dialysis of the primary nanofiltration concentrated water, effectively recovers lithium ions in the concentrated water, improves the recovery rate of lithium, and the recycling of dialysis water also reduces the waste of water resources. The synergistic effect of the primary reverse osmosis unit and the high-pressure reverse osmosis unit further improves the lithium ion concentration, ensuring the output of high-quality lithium products. The secondary reverse osmosis unit desalts the water produced by each stage, not only improving the water quality, but also recycling the water resources by returning the concentrated water to the third-stage nanofiltration, reducing the overall energy consumption and operating cost of the system, improving the recovery rate and product purity of lithium, and enhancing the stability and economy of the system.

[0096] Specifically, the detection module determines the permeation stability characterization parameter according to the lithium ion concentration flowing through the nanofiltration membrane in a single detection period and the lithium ion concentration of the halogen-free brine;

[0097] The detection module determines the difference between the lithium ion concentrations before and after flowing through the nanofiltration membrane of each stage 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 permeation stability characterization parameter of the current stage of nanofiltration according to the ratio of the average deviation of the lithium ion concentration difference to the average value of the lithium ion concentration difference.

[0099] In implementation, the permeation stability characterization parameter is the same as the number n.

[0100] It can be understood that each stage of nanofiltration is composed of multiple nanofiltration membranes, and the permeation stability characteristic parameter represents the stability and consistency of the lithium ion separation efficiency of each stage of nanofiltration membranes during operation. Specifically, by quantifying the fluctuation degree of the lithium ion concentration difference of multiple nanofiltration membranes in the same level, the anti-pollution ability and separation performance degradation trend of the membrane system are reflected. When the ratio of the average deviation of the lithium ion concentration difference to the average value is low, that is, the permeation stability characteristic parameter is small, it indicates that the operation state of the nanofiltration membrane of this level is stable, and the fluctuation of the separation efficiency is small; on the contrary, the increase of the parameter value indicates that the membrane pollution is intensified or the performance is degraded, and the backwashing or chemical cleaning program needs to be triggered. By monitoring the permeation stability characteristic parameter of each stage of nanofiltration in real time, the overall health status of the multi-stage membrane system can be dynamically evaluated, and quantitative basis for process parameter optimization (such as pressure adjustment, concentrated water reuse ratio) and maintenance decision-making can be provided, so as to ensure the long-term stability of the magnesium-lithium separation efficiency and the lithium resource recovery rate in the salt lake lithium extraction process.

[0101] In actual work, different nanofiltration membranes have different blockage conditions, so directly detecting the magnesium ion concentration at the inlet of the next level cannot effectively determine the blockage condition of each nanofiltration membrane in the current level. If only the magnesium ion concentration at the inlet of the next level is used as the basis for judgment, not only is there a lag in the detection time, but also the working state of each nanofiltration membrane cannot be evaluated individually, which may lead to misjudgment of the running state of the whole system, further affecting the efficiency and stability of the salt lake lithium extraction process.

[0102] In addition, single-membrane detection needs to wait for the accumulation of pollutants to a perceptible degree before alarming, while the permeation stability characteristic parameter real-time aggregates the lithium ion concentration difference fluctuation of all membranes in the same level, which can capture the overall performance degradation trend at an early stage and avoid after-the-fact remediation. In addition, the composition of salt lake brine is complex, and the pollution rate of each membrane is different. By magnifying the single-membrane abnormality to the overall fluctuation of the level through the permeation stability characteristic parameter, neither frequent shutdown due to temporary abnormality of a few membranes nor missing the systematic risk of simultaneous deterioration of most membranes can occur. For example, when only one or two membranes are slightly abnormal, the influence of the deviation on the average value is limited, and the ratio is still within the safe range, so the system continues to operate normally. On the contrary, when multiple membranes simultaneously experience performance degradation, even if the single-membrane decline is not large, the deviation will be quickly amplified, and the ratio will immediately exceed the threshold, prompting overall pollution and triggering cleaning or load reduction.

[0103] Specifically, the lithium extraction control module determines whether there is an abnormality in the corresponding level of nanofiltration according to the permeation stability characteristic parameter of each level of nanofiltration, including:

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

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

[0106] In implementation, the standard stability characteristic parameter of each level is selected within the corresponding stability threshold interval.

[0107] The stability threshold interval is determined according to the average value of the permeation stability characteristic parameter corresponding to the minimum filtration amount of the corresponding filtered magnesium ions in each level of nanofiltration water in the historical separation record combined with the standard deviation.

[0108] In the present application, by calculating the average value and average deviation of the lithium ion concentration difference, and further determining the permeation stability characteristic parameter, the running state of each level of nanofiltration membrane can be quantitatively evaluated, the stability of the anti-pollution ability and separation performance of the membrane system can be effectively reflected, the limitations of the traditional method which only relies on the detection of the magnesium ion concentration of the single inlet water are overcome, the misjudgment caused by the detection lag and the inability to evaluate the state of each level of nanofiltration membrane alone is avoided, and the running efficiency and stability of the whole system are improved. In addition, according to the comparison between the permeation stability characteristic parameter and the standard stability characteristic parameter, it is accurately judged whether there is an abnormality in each level of nanofiltration, which provides a scientific basis for timely maintenance measures. The present application not only can dynamically evaluate the overall health status of the multi-level membrane system, but also can provide quantitative basis for process parameter optimization and maintenance decision, so as to ensure the long-term stability of the magnesium-lithium separation efficiency and the lithium resource recovery rate in the salt lake lithium extraction process, and significantly improve the intelligence and efficiency of the salt lake lithium extraction process.

[0109] Specifically, the lithium extraction control module is configured to determine the adjustment mode of the nanofiltration membrane in response to the determination result that the current level of nanofiltration has an abnormality combined with the permeation stability characteristic parameter, including:

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

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

[0112] In implementation, the lossless permeation threshold is determined according to the minimum value of the permeation stability characteristic parameter when there is a single nanofiltration membrane damage or blockage degree requiring replacement in the historical record.

[0113] It can be understood that increasing the operating pressure will increase the flux of the solvent (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 will quickly accumulate on the membrane surface (concentration polarization), forming a high-concentration boundary layer, which may reduce the effective rejection rate and cause the solute concentration behind the membrane to rise.

[0114] In the present application, when the penetration stability characteristic parameter exceeds the non-damage penetration threshold value, it indicates that the nanofiltration membrane has been damaged or clogged and needs to be replaced, which helps to avoid the decrease of separation efficiency and the waste of lithium resources caused by membrane damage in time, when the penetration stability characteristic parameter does not exceed the non-damage penetration threshold value, by reducing the nanofiltration pressure of the corresponding level, the concentration polarization phenomenon can be effectively slowed down, and the increase of solute concentration after the membrane caused by excessive pressure can be avoided, thereby maintaining the efficient and stable operation of the nanofiltration system, the present application can dynamically adjust according to the actual operation state of the nanofiltration system, not only prolongs the service life of the nanofiltration membrane, but also improves the efficiency and stability of the salt lake lithium extraction process, and provides strong support for the optimization and intelligent upgrading of the salt lake lithium extraction process.

[0115] Specifically, the lithium extraction control module determines the working position and silicon removal mode of the silicon removal module according to 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 value, the working position of the silicon removal module is behind the ultrafiltration unit, and the working mode is chemical precipitation or adjusting pH by alkali;

[0117] If the silicon content in the initial brine is less than or equal to the normal exchange content threshold value and greater than the membrane removal threshold value, the working position of the silicon removal module is behind the ultrafiltration unit, and the working mode is to remove silicon by the ultrafiltration membrane;

[0118] If the silicon content in the initial brine is less than or equal to the membrane removal threshold value, the working position of the silicon removal module is behind the primary nanofiltration combination, and the working mode is to remove silicon by the ultrafiltration membrane.

[0119] In implementation, the pH of the initial brine is adjusted to 9.5-11.5 by adding alkali before entering the silicon removal module.

[0120] The normal exchange content threshold value is 100mg / L, the membrane removal threshold value is selected within the interval [20mg / L, 50mg / L], and if the silicon content is greater than the allowable content after the silicon removal module removes silicon after the ultrafiltration unit, secondary silicon removal can be performed after the primary nanofiltration combination.

[0121] It can be understood that if the silicon content is too high, it will cause membrane pollution and clogging. Generally, nanofiltration and reverse osmosis membranes have strict requirements for the silicon content of the influent, and it is generally recommended that the silicon content of the influent does not exceed 20-50mg / L. When the silicon content exceeds this range, the performance of the membrane will decrease significantly, and more frequent cleaning and maintenance are required. Ion exchange resins have relatively high tolerance to silicon, but too high silicon content will reduce the exchange efficiency and service life of the resin. It is generally recommended that the silicon content of the influent does not exceed 100mg / L. When the silicon content exceeds this value, the regeneration cost of the resin will increase significantly, and more frequent replacement may be required

[0122] In the implementation, the lithium extraction control module automatically switches the chemical precipitation or the pH adjustment by alkali or ion exchange mode according to the silicon content of the brine, reducing manual intervention.

[0123] In the present application, when the silicon content in the initial brine is too high, the silicon removal module is placed behind the ultrafiltration unit, and chemical precipitation or pH adjustment by alkali is used for silicon removal, effectively avoiding the damage of high silicon content to the subsequent ion exchange resin. When the silicon content is at a moderate level, the system switches to the ultrafiltration membrane silicon removal mode, which not only meets the requirements of nanofiltration and reverse osmosis membranes for the silicon content of the feed water, but also reduces the secondary pollution that may be caused by chemical precipitation or pH adjustment by alkali. For low-silicon-content brine, the system is further optimized, the silicon removal module is placed behind the first-stage nanofiltration combination, and the ultrafiltration membrane is used for secondary silicon removal, ensuring that the silicon content of the brine entering the subsequent treatment unit meets the strict standards. Not only does this reduce manual intervention, improve the convenience and accuracy of operation, but also effectively prevents membrane pollution and blockage through precise control of the silicon removal process, prolongs the service life of the membrane, reduces operating costs, and ensures the stable operation of the entire salt lake lithium extraction system and the efficient recovery of lithium resources.

[0124] Please refer to Figure 4 As shown in the figure, it is a flowchart of the method for extracting lithium from salt lake and separating and concentrating lithium and magnesium according to an embodiment of the present application. The present application also provides a method for extracting lithium from salt lake and separating and concentrating lithium and magnesium, comprising:

[0125] Step S1: filtering, adsorbing and ultrafiltering the initial brine to obtain a clean brine;

[0126] Step S2: removing silicon from the clean brine by chemical precipitation or pH adjustment by alkali in combination with ultrafiltration membrane and / or ion exchange;

[0127] Step S3: performing first-stage nanofiltration on the clean brine after silicon removal to separate calcium ions and magnesium ions step by step, obtaining first-stage nanofiltration water;

[0128] Step S4: performing pure water nanofiltration dialysis on the first-stage nanofiltration concentrated water, and performing nanofiltration on the first-stage nanofiltration water step by step to separate calcium ions and magnesium ions, obtaining nanofiltration water of several levels;

[0129] Step S5: the water produced by the third-stage nanofiltration enters high-pressure nanofiltration to increase the lithium ion concentration, obtaining high-lithium-ion water; the water produced by the first-stage reverse osmosis and the high-pressure reverse osmosis enters the second-stage reverse osmosis for further desalination, obtaining desalinated water;

[0130] Step S6: the high-lithium-ion water enters the fourth-stage nanofiltration to obtain final nanofiltration water.

[0131] Please refer to Figure 5As shown, it is the flow chart of the embodiment of the application for extracting lithium from salt lake, concentrating and separating magnesium and lithium. After the initial brine is preliminarily filtered by the self-cleaning filter, the brine enters the adsorption and desorption system, adsorbs lithium ions and produces tail brine discharge, the desorption liquid enters the qualified eluent tank, the desorption liquid enters the ultrafiltration system including the first-stage ultrafiltration and the second-stage ultrafiltration, the filtered water enters the ultrafiltration water tank, the backwash water returns to the backwash water tank, the concentrated water is treated by the plate and frame filter system to obtain filter residue and make the filtrate reusable, the water in the water tank is added with a reducing agent and an acid to perform reduction and pH adjustment, and then enters the silicon removal unit to remove silicon impurities. The water after the silicon removal enters the first-stage nanofiltration system, the separated water enters the second-stage nanofiltration in sequence to perform deep treatment, and finally the concentrated water is discharged, and the dialysis water is reused. The water after the first-stage nanofiltration enters the first-stage reverse osmosis system, the reverse osmosis water enters the second-stage reverse osmosis system to perform further treatment, and desalinated water is obtained. Meanwhile, the concentrated water of the third-stage nanofiltration system is treated by the high-pressure reverse osmosis system to obtain high-pressure reverse osmosis water, and the concentrated water thereof enters the fourth-stage nanofiltration system to obtain the final nanofiltration water.

[0132] In the implementation, the above results and the selection of various additives are not specifically limited, which are the existing technologies in the field, and will not be repeated here.

[0133] So far, the technical solutions of the application have been described in combination with the preferred embodiments shown in the drawings, but those skilled in the art can easily understand that the protection scope of the application is obviously not limited to these specific embodiments. Those skilled in the art can make equivalent changes or replacements to the related technical features without departing from the principles of the application, and the technical solutions after the changes or replacements will fall within the protection scope of the application.

[0134] The above description is only the preferred embodiments of the application and is not used to limit the application; for those skilled in the art, the application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application shall be included in the protection scope of the application.

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

2. The lithium-magnesium-lithium separation and concentration system for salt lake extraction according to claim 1, characterized in that, The preprocessing module includes: 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 first initial state 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.

3. The lithium-magnesium-lithium separation and concentration system for salt lake extraction according to claim 1, characterized in that, The multi-stage nanofiltration module includes: 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 the concentrate from each stage of nanofiltration is returned to the previous two stages of nanofiltration for further treatment.

4. The lithium-magnesium-lithium separation and concentration system for salt lake extraction according to claim 3, 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.

5. The lithium-magnesium-lithium separation and concentration system for salt lake extraction according to claim 3, 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.

6. The lithium-magnesium-lithium separation and concentration system for salt lake extraction according to claim 5, characterized in that, 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. 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 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.

7. The lithium-magnesium-lithium separation and concentration system for salt lake extraction according to claim 6, 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.

8. The lithium-magnesium-lithium separation and concentration system for salt lake extraction according to claim 7, characterized in that, 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 at the current level of nanofiltration, combined with 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.

9. The lithium-magnesium-lithium separation and concentration system for salt lake extraction according to claim 8, characterized in that, 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: 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. 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 behind the first-stage nanofiltration assembly and operates by removing silicon through an ultrafiltration membrane.

10. A method for lithium extraction, magnesium-lithium separation and concentration from salt lakes according to any one of claims 1-9, characterized in that, The initial brine is filtered, adsorbed, and ultrafiltered to obtain impurity-free brine; The pure brine is desiliconized by chemical precipitation or by adjusting pH with alkali combined with ultrafiltration membrane and / or ion exchange. The silica-free brine was subjected to a first-stage nanofiltration process to separate calcium and magnesium ions, resulting in first-stage nanofiltration permeate. 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. 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. The high-lithium-ion water enters a four-stage nanofiltration process to obtain the final nanofiltration product water.

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