A salt lake lithium extraction system and method based on membrane separation coupled with adsorption

Abstract

The application discloses a salt lake lithium extraction system and method based on membrane separation coupling adsorption. The salt lake lithium extraction system comprises, in sequence, an ultrafiltration device, a nanofiltration device, an adsorption device, a sand filtration-ultrafiltration combined treatment device, a reverse osmosis device, a boron removal resin, a lithium chloride MVR device, a lithium precipitation device and a separation and recovery device. The membrane method treatment is carried out through the ultrafiltration, nanofiltration, sand filtration-ultrafiltration combined treatment device and reverse osmosis device, and the adsorption treatment is carried out through the adsorption device and the boron removal resin. That is, the application adopts a raw brine membrane method coupling adsorption lithium extraction process. The membrane method is used to separate calcium, magnesium, sulfate, carbonate and other ions from lithium and other monovalent and divalent ions. Then, adsorption, membrane method and evaporation concentration are used to reduce the evaporation scale, so that high-purity lithium resources can be extracted under the conditions of low energy consumption and low cost. In addition, the method combining the membrane method and adsorption can completely remove impurities, improve the purity of lithium, and has low adsorbent consumption and high adsorption and desorption efficiency.

Description

Technical Field

[0001] This application relates to the field of lithium-ion recovery technology, and in particular to a lithium extraction system and method for salt lakes based on membrane separation coupled adsorption. Background Technology

[0002] Salt lake brine refers to water bodies containing high concentrations of salts and minerals found in salt lakes. It is formed from natural groundwater through long-term accumulation and evaporation. Salt lake brine is a natural resource with a wide range of applications. It contains abundant lithium resources. Compared to lithium extraction from hard rock mines, the development of lithium resources from salt lake brine has advantages such as simpler processes, lower costs, higher product purity, and stronger market competitiveness, gradually becoming the main approach for lithium development and production both domestically and internationally.

[0003] Besides lithium, salt lake brines also contain large amounts of sodium, potassium, boron, magnesium, and other elements. Therefore, the lithium extraction process requires the separation and purification of impurity ions, with the separation of magnesium and lithium being the most difficult. Compared to other countries, most salt lakes in my country (such as Qinghai Salt Lake) have high magnesium-to-lithium and sodium-to-lithium ratios in their brines, making separation difficult. This results in high lithium loss rates, high development costs, and low comprehensive utilization rates during the lithium extraction process.

[0004] Due to differences in composition, magnesium-to-lithium ratio, sodium-to-lithium ratio, and other parameters, lithium extraction from salt lakes typically employs various processes such as precipitation, calcination, adsorption, extraction, and solar pond + carbonization. Furthermore, a unique process is usually used for each type of salt lake.

[0005] The principle of solvent extraction is to add a second liquid, which is immiscible with the solution but has a high solubility for the solute, to a solution containing the solute. Utilizing the difference in solubility between the two phases, some of the solute migrates through the interface into the second phase, achieving phase inversion and concentration. Solvent extraction is suitable for treating brine with a high magnesium-to-lithium ratio. However, its process is lengthy, the extractant is organic, and it poses significant environmental risks.

[0006] The precipitation method utilizes solar energy to naturally evaporate, concentrate, and produce salt from lithium-containing brine in an evaporation tank. Then, through processes such as boron removal and calcium and magnesium removal, lithium remains in the old brine. Once the lithium content reaches an appropriate concentration, carbonates are used as a precipitant to precipitate the lithium as lithium carbonate. The precipitation method is a mature and reliable process, but it is not suitable for brine containing large amounts of alkaline earth metals or brine with low lithium concentrations, and its efficiency is not high.

[0007] The calcination-leaching method involves evaporating the brine after boron extraction to obtain old brine. A precipitant is then added to the old brine, causing magnesium and lithium to precipitate out. Finally, the precipitate is calcined and decomposed, and through carbonation, lithium dissolves in the solution while magnesium remains in the precipitate, thus achieving magnesium-lithium separation. While the calcination-leaching method can comprehensively utilize magnesium and lithium resources, it has a complex process, causes severe environmental pollution, consumes high energy, has high costs, and requires significant investment.

[0008] Adsorption is a method that uses adsorbents that selectively adsorb lithium ions to separate them from other impurity ions. The key is to find adsorbents with good selectivity, high recyclability, and relatively low cost. For brine with low lithium content, adsorption is a good method. While the adsorption process is simple and particularly suitable for lithium separation in brine, it places high demands on the adsorbent, which is expensive. Aluminum-based adsorbents have high freshwater consumption, while titanium-based adsorbents have high acid and alkali consumption.

[0009] Selective semi-permeable membrane methods are divided into nanofiltration and electrodialysis. Nanofiltration is a pressure-driven membrane separation method between reverse osmosis and ultrafiltration, which can effectively separate monovalent and polyvalent ions. Electrodialysis uses one or more electrodialysis units to circulate and concentrate lithium using monovalent cation-selective ion exchange membranes and monovalent anion-selective ion exchange membranes, and then adds soda ash to precipitate lithium carbonate. This method is suitable for separating lithium from magnesium and other ions in relatively high-magnesium and high-lithium brine, but the lithium content must reach 2 g / L or higher, otherwise the power consumption will be too high.

[0010] Therefore, the aforementioned lithium extraction processes generally suffer from several drawbacks: extraction methods are lengthy, prone to equipment corrosion, and the extractants typically possess water-soluble, flammable, and volatile properties. Precipitation methods are lengthy, consume large amounts of materials, and are complex to operate, making them only suitable for low magnesium-to-lithium ratio salt lakes. Calcination methods are complex, prone to equipment corrosion, and consume high energy. Adsorption methods, due to the prevalence of powdered adsorbents, suffer from poor flowability and adsorption capacity, easily leading to a decline in adsorption performance. Selective semi-permeable membrane methods, as an emerging separation technology, incorporate multiple technologies including ultrafiltration, nanofiltration, and reverse osmosis, effectively separating monovalent and divalent cations and anions to achieve lithium ion recovery and purification. However, existing membrane-based lithium purification technologies still suffer from poor purification efficiency and low purity, and their costs are generally high. Therefore, a new technical solution is urgently needed to address the problems existing in current technologies. Summary of the Invention

[0011] This application provides a lithium extraction system and method based on membrane separation coupled adsorption in salt lakes, which solves the problems of high cost and low purity of lithium extraction in existing salt lake processes.

[0012] To achieve the above objectives, this application provides the following technical solution:

[0013] In the first aspect, this application provides a lithium extraction system for salt lakes based on membrane separation coupled adsorption, comprising an ultrafiltration device, a nanofiltration device, an adsorption device, a sand filtration and ultrafiltration combined treatment device, a qualified liquid reverse osmosis device, a boron removal resin, a lithium chloride MVR device, a lithium precipitation device, and a separation and recovery device connected in sequence.

[0014] The inlet of the ultrafiltration device is connected to the pipeline transporting brine from the salt lake. The product water end of the ultrafiltration device is connected to the nanofiltration device. The nanofiltration device is connected to the adsorption device. The qualified liquid outlet of the adsorption device is connected to the inlet of the sand filtration-ultrafiltration combined treatment device. The product water end of the sand filtration-ultrafiltration combined treatment device is connected to the inlet of the qualified liquid reverse osmosis device. The concentrate outlet of the qualified liquid reverse osmosis device is connected to the boron removal resin. The product water end of the boron removal resin is connected to the inlet of the lithium chloride MVR device. The outlet of the lithium chloride MVR device is connected to the inlet of the lithium precipitation device. The lithium precipitation device is equipped with a sodium carbonate inlet. The sodium carbonate in the lithium precipitation device reacts with the lithium chloride solution to generate lithium carbonate precipitate. The discharge port of the lithium precipitation device is connected to the separation and recovery device, which is used to achieve solid-liquid separation and recover the lithium carbonate precipitate.

[0015] In the above technical solution, optionally, the adsorption device is a titanium adsorption device, which has a water inlet, an acid water inlet, a qualified liquid outlet, and an unqualified liquid outlet.

[0016] Optionally, the nanofiltration device includes a primary nanofiltration module, the inlet of which is connected to the product water end of the ultrafiltration device, the concentrate outlet of which is connected to the inlet of the titanium adsorption device, and the qualified liquid outlet of the titanium adsorption device is connected to the inlet of the sand filtration and ultrafiltration combined treatment device.

[0017] Optionally, the titanium adsorption device further includes a lithium precipitation mother liquor inlet, which is connected to the mother liquor outlet of the lithium precipitation device, and the lithium precipitation mother liquor inlet is also connected to the regenerated liquid outlet of the boron removal resin.

[0018] In the above technical solution, optionally, the adsorption device is an aluminum adsorption device, which has a liquid inlet, a qualified liquid outlet, a water inlet, and a tail brine outlet.

[0019] Optionally, the nanofiltration device includes a multi-stage nanofiltration module, which includes at least a primary nanofiltration module and a secondary nanofiltration module. The inlet of the primary nanofiltration module is connected to the product water end of the ultrafiltration device, the product water end of the primary nanofiltration module is connected to the inlet of the secondary nanofiltration module, the product water end of the secondary nanofiltration module is connected to the liquid inlet of the aluminum adsorption device, and the qualified liquid outlet of the aluminum adsorption device is connected to the inlet of the sand filtration and ultrafiltration combined treatment device. An alkali addition port is provided on the pipe connecting the product water end of the primary nanofiltration module and the inlet of the secondary nanofiltration module.

[0020] Optionally, the secondary nanofiltration module is connected to the aluminum adsorption device via a carbon remover, the carbon remover having a first inlet, an exhaust port, and a liquid outlet; the water production end of the secondary nanofiltration module is connected to the first inlet, the liquid outlet is connected to the liquid inlet of the aluminum adsorption device, and the exhaust port is used to discharge carbon dioxide gas; an acid addition port is provided on the pipe connecting the water production end of the secondary nanofiltration module and the first inlet of the carbon remover.

[0021] Optionally, the decarbonator also has a second inlet, which is connected to a sodium carbonate nanofiltration device; the inlet of the sodium carbonate nanofiltration device is connected to the concentrate outlet of the secondary nanofiltration module via a connecting pipe, and a water inlet is provided on the connecting pipe; the product water outlet of the sodium carbonate nanofiltration device is connected to the second inlet, the concentrate outlet of the sodium carbonate nanofiltration device is connected to a sodium carbonate recovery device, and the outlet of the sodium carbonate recovery device is connected to the sodium carbonate inlet on the lithium precipitation device.

[0022] Optionally, the sodium carbonate recovery device includes a sodium carbonate MVR device and a boron removal device.

[0023] In the above technical solution, optionally, the product water end of the qualified liquid reverse osmosis device is connected to the inlet end of the product water reverse osmosis device, the concentrate outlet end of the product water reverse osmosis device is connected to the inlet end of the sand filter ultrafiltration combined treatment device, and the product water end of the product water reverse osmosis device is connected to the user's water supply end.

[0024] Optionally, in the above technical solution, the sand filtration and ultrafiltration combined treatment device includes a sand bed and an ultrafiltration membrane assembly connected to the effluent side of the sand bed.

[0025] Secondly, this application also provides a method for lithium extraction from salt lakes based on membrane separation coupled adsorption, which employs the aforementioned lithium extraction system based on membrane separation coupled adsorption from salt lakes. This method for lithium extraction from salt lakes includes the following steps:

[0026] S1: The brine from the salt lake is fed into an ultrafiltration device to remove suspended solids and colloids from the brine.

[0027] S2: The brine from the salt lake after being treated by the ultrafiltration device enters the first-stage nanofiltration module, which is used to remove sulfate and carbonate ions from the brine.

[0028] S3: The liquid discharged from the concentrate outlet of the first-stage nanofiltration module enters the titanium adsorption device, which is used to adsorb lithium in the liquid.

[0029] S4: The qualified adsorption liquid discharged from the titanium adsorption device enters the sand filtration and ultrafiltration combined treatment device, which is used to remove liquid suspended solids and colloids and reduce turbidity.

[0030] S5: The liquid treated by the sand filtration and ultrafiltration combined treatment device enters the qualified liquid reverse osmosis device, and the liquid discharged from the concentrate outlet of the qualified liquid reverse osmosis device enters the boron removal resin for boron removal.

[0031] S6: The liquid flowing out from the water production end of the boron removal resin enters the lithium chloride MVR device, and the lithium chloride MVR device concentrates the liquid entering it.

[0032] S7: The lithium chloride concentrate obtained by the lithium chloride MVR device enters the lithium precipitation device and reacts with the sodium carbonate solution to form lithium carbonate precipitate. The lithium carbonate precipitate is then separated and recovered from the solution by the separation and recovery device.

[0033] Thirdly, this application also provides another method for lithium extraction from salt lakes based on membrane separation coupled adsorption, which employs the aforementioned lithium extraction system based on membrane separation coupled adsorption from salt lakes. This method includes the following steps:

[0034] S1: The brine from the salt lake is fed into an ultrafiltration device to remove suspended solids and colloids from the brine.

[0035] S2: The brine from the salt lake after being treated by the ultrafiltration device enters the first-stage nanofiltration module, which is used to remove sulfate and carbonate ions from the brine.

[0036] S3: The liquid discharged from the product water end of the first-stage nanofiltration module enters the second-stage nanofiltration module to remove carbonate ions;

[0037] S4: The liquid discharged from the product water end of the secondary nanofiltration module enters the decarbonator to remove bicarbonate ions;

[0038] S5: The liquid discharged from the decarbonizer enters the aluminum adsorption device, which is used to adsorb lithium in the liquid;

[0039] S6: The qualified adsorption liquid discharged from the aluminum adsorption device enters the sand filtration and ultrafiltration combined treatment device, which is used to remove liquid suspended solids and colloids and reduce turbidity.

[0040] S7: The liquid treated by the sand filtration and ultrafiltration combined treatment device enters the qualified liquid reverse osmosis device, and the liquid discharged from the concentrate outlet of the qualified liquid reverse osmosis device enters the boron removal resin for boron removal.

[0041] S8: The liquid flowing out from the water production end of the boron removal resin enters the lithium chloride MVR device, and the lithium chloride MVR device concentrates the liquid entering it.

[0042] S9: The lithium chloride concentrate obtained by the lithium chloride MVR device enters the lithium precipitation device and reacts with the sodium carbonate solution to form lithium carbonate precipitate. The lithium carbonate precipitate is then separated and recovered from the solution by the separation and recovery device.

[0043] In step S3 above, alkali is added to the liquid discharged from the product water end of the first-stage nanofiltration module, and then it is discharged into the second-stage nanofiltration module.

[0044] In step S4 above, acid is added to the liquid discharged from the product water end of the secondary nanofiltration module, and then it is discharged into the decarbonator.

[0045] Compared with the prior art, this application has the following advantages:

[0046] 1. This application provides a lithium extraction system for salt lakes based on membrane separation coupled with adsorption, comprising an ultrafiltration unit, a nanofiltration unit, an adsorption unit, a sand filtration and ultrafiltration combined treatment unit, a qualified liquid reverse osmosis unit, a boron removal resin, a lithium chloride MVR unit, a lithium precipitation unit, and a separation and recovery unit connected in sequence. The system performs functional treatment on salt lake brine through the aforementioned devices. Membrane treatment is achieved through the ultrafiltration, nanofiltration, and sand filtration combined treatment unit and the reverse osmosis unit, while adsorption treatment is achieved through the adsorption unit and the boron removal resin. Specifically, this application employs a raw brine membrane coupled with adsorption lithium extraction process. It utilizes membrane technology to separate divalent ions such as calcium, magnesium, sulfate, and carbonate from monovalent ions such as lithium. Then, adsorption, membrane technology, and evaporation concentration are used to reduce the scale of evaporation, achieving the goal of extracting high-purity lithium resources under low energy consumption and low cost conditions. Furthermore, the combination of membrane technology and adsorption can thoroughly remove impurities, improve lithium purity, reduce adsorbent consumption, and achieve high adsorption-desorption efficiency.

[0047] 2. For raw brine with relatively low lithium content and mineralization, but high sodium sulfate and sodium chloride content, the traditional process directly uses solar energy to concentrate the lithium-containing brine. This has problems such as large water volume, low efficiency, and greater difficulty in treating concentrated magnesium carbonate, which is prone to scaling. The salt lake lithium extraction system provided in this application can extract high-purity lithium from raw brine with relatively low lithium content and mineralization, but high sodium sulfate and sodium chloride content. It uses membrane technology to remove calcium, magnesium, sulfate, carbonate and other factors that are prone to scaling, and then uses adsorption, membrane technology and evaporation concentration. This not only reduces the scale of evaporation and energy consumption, but also completely removes impurities to achieve high-purity lithium extraction.

[0048] 3. Traditional adsorption methods suffer from problems such as high acid and alkali consumption and high adsorbent cost of titanium-based adsorbents, and small capacity and high freshwater consumption of aluminum-based adsorbents. The lithium extraction system from salt lakes provided in this application combines titanium adsorption devices and aluminum adsorption devices with membrane separation technologies (such as ultrafiltration devices, nanofiltration devices, sand filtration and ultrafiltration combined treatment devices, and reverse osmosis devices) to achieve membrane separation coupled adsorption process, which specifically solves the above problems, reduces adsorbent consumption, reduces freshwater resource consumption, and reduces overall operating and investment costs.

[0049] 4. In the lithium extraction system from salt lakes provided in this application, there are more membrane separation devices and fewer evaporation and high-temperature devices, which reduces the probability of equipment failure and reduces the amount and difficulty of maintenance.

[0050] 5. The ultrafiltration device in the lithium extraction system from salt lakes provided in this application is preferably a submerged ultrafiltration device. Compared with the traditional multi-media + external pressure ultrafiltration, the submerged ultrafiltration device used in this application is resistant to extremely high suspended solids, resists high turbidity shocks from incoming water, has strong shock resistance, is easy to operate and manage, produces good effluent quality, has a recovery rate of up to 95%, low operating costs, and comparable investment costs.

[0051] 6. Based on the lithium extraction system from salt lakes provided in this application, this application also provides a corresponding lithium extraction method from salt lakes. The lithium extraction route is short and efficient. Compared with traditional lithium extraction methods, it can save about 20% of electricity and reduce the total operating cost by 10-15%. Under the condition of comparable investment costs, the lithium extraction method provided in this application can obtain a higher rate of return on investment. Attached Figure Description

[0052] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. It should be understood that the specific shapes and structures shown in the drawings should not generally be regarded as limiting conditions for implementing this application; for example, based on the technical concepts disclosed in this application and the exemplary drawings, those skilled in the art are able to easily make conventional adjustments or further optimizations to the addition / reduction / classification, specific shapes, positional relationships, connection methods, and size ratios of certain units (components).

[0053] Figure 1 This is a schematic diagram of the processing flow of a lithium extraction system from salt lakes based on membrane separation coupled adsorption provided in this application in one embodiment;

[0054] Figure 2 This is a schematic diagram of the first lithium extraction route using a titanium adsorption device in this application.

[0055] Figure 3 This is a partial process flow diagram of the second lithium extraction route using an aluminum adsorption device in this application, showing only the processing between the secondary nanofiltration module and sand filtration + ultrafiltration.

[0056] Figure 4 This is a schematic diagram of the sodium carbonate recovery route provided in this application, showing only the processing after the secondary nanofiltration module. Detailed Implementation

[0057] The present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0058] In the description of this application: unless otherwise stated, "a plurality of" means two or more. The terms "first," "second," "third," etc., in this application are intended to distinguish the objects referred to and do not have any special meaning in terms of technical connotation (e.g., they should not be construed as an emphasis on importance or order). Expressions such as "comprising," "including," and "having" also mean "not limited to" (certain units, components, materials, steps, etc.).

[0059] The terms used in this application, such as "upper," "lower," "left," "right," and "middle," are generally used to facilitate intuitive understanding by referring to the accompanying drawings, and are not absolute limitations on the positional relationships in the actual product. Changes in these relative positional relationships, without departing from the technical concept disclosed in this application, should also be considered within the scope of this application.

[0060] Example 1

[0061] To address the problems existing in the prior art, this application provides a lithium extraction system for salt lakes based on membrane separation coupled with adsorption. This system can process low-grade lithium ore with low lithium content and mineralization. The process route of the membrane separation coupled with adsorption system provided in this application considers the separation of monovalent and divalent ions, removing alkalinity and boron, while ensuring the resource recovery and utilization of sodium carbonate, sodium chloride, potassium chloride, and lithium carbonate. Overall, the membrane separation coupled with adsorption system provided in this application adopts a raw brine membrane coupled with adsorption lithium extraction process route, mainly including raw brine filtration, membrane separation, adsorption section, membrane purification and concentration section, bipolar membrane electrolysis section, lithium chloride evaporation and crystallization section, lithium precipitation section, and bipolar membrane acid and alkali production section.

[0062] This application provides a lithium extraction system from salt lakes based on membrane separation coupled with adsorption, which mainly includes, in sequence, an ultrafiltration unit, a nanofiltration unit, a titanium adsorption unit, a sand filtration-ultrafiltration combined treatment unit, a qualified liquid reverse osmosis unit, a boron removal resin, a lithium chloride MVR unit, a lithium precipitation unit, and a separation and recovery unit. These functional units cooperate with each other throughout the entire process, and are used sequentially according to process requirements to achieve the goal of lithium extraction from salt lakes.

[0063] The following provides a detailed description of the structural principle of the lithium extraction system from salt lakes provided in this application, as well as the functional structure of each device in the system architecture.

[0064] I. Ultrafiltration Device

[0065] In this application, the brine from the salt lake can be directly fed into the membrane tank of the ultrafiltration device, or the brine can be pre-filtered according to specific process conditions before being discharged into the membrane tank.

[0066] This application employs submerged flat-plate ultrafiltration to reduce the suspended solids content in salt lake brine, meeting the influent requirements of subsequent equipment. The ultrafiltration device in this application involves directly immersing the submerged flat-plate ultrafiltration unit into the membrane tank. A pump or siphon is used to create negative pressure, drawing water and dissolved small molecules out of the membrane to remove suspended solids, colloidal particles, and large organic molecules, thereby improving water clarity.

[0067] In this application, the ultrafiltration device may include a membrane tank, a submerged ultrafiltration unit immersed in the membrane tank, and suction pumps, cleaning pumps, and backwash fans disposed outside the membrane tank. The submerged ultrafiltration unit in the membrane tank may be a submerged flat-plate ultrafiltration unit, including one or more submerged ultrafiltration membrane modules.

[0068] Submerged ultrafiltration membrane modules consist of hollow fiber membranes fixed on a horizontal or vertical frame and permeate collection tubes located at the top and bottom of the frame. Each collection tube contains a layer of specialized resin sealing the membrane fibers, thereby connecting the membrane's inner cavity to the tubes to collect product water. Several or dozens of membrane modules are connected to form a complete membrane tank. Several membrane tanks are connected in parallel and submerged in a membrane pool to form a membrane row. Several membrane rows are connected in parallel to form membrane treatment systems of different treatment capacities. During operation, periodic backwashing and gentle air scrubbing can reduce the membrane fouling rate. Unlike traditional pressure membrane filtration, submerged ultrafiltration membranes operate under low negative pressure. The principle is to use siphon or pump suction to filter water from the outside to the inside under negative pressure, achieving stable operation with low transmembrane pressure differential and moderate membrane flux. The overall energy consumption cost of submerged ultrafiltration membrane modules is lower than that of pressure membrane filtration. Their main characteristics include: 1) Effective solid-liquid separation, with a separation effect far superior to traditional sedimentation tanks, resulting in excellent effluent quality with near-zero suspended solids and turbidity, allowing for direct reuse and realizing wastewater resource recovery; 2) Standardized and modular membrane module design, adaptable to different treatment volumes, and flexible water supply scale; 3) Facilitates the retention, growth, and reproduction of slowly proliferating nitrifying bacteria, improving system nitrification efficiency. The membrane bioreactor (MBR) process, combining submerged ultrafiltration membrane modules with biochemical processes, exhibits superior nitrogen and phosphorus removal capabilities compared to traditional biological treatment processes.

[0069] Compared to pressure ultrafiltration, the submerged flat-plate ultrafiltration device used in this application can withstand high suspended solids content. The feed water can directly enter the high-strength membrane without filtration, resulting in high-quality permeate. Traditional pressure ultrafiltration typically requires sand filtration before entering the ultrafiltration membrane. Therefore, using a submerged flat-plate ultrafiltration device eliminates the need for sand filters or multi-media filters, greatly simplifying the process. Furthermore, the use of negative pressure suction results in low operating pressure, saving energy and eliminating the risk of overpressure operation. In addition, the open membrane tank allows direct observation of the membrane fibers, facilitating operation and management.

[0070] In a specific installation application example, the submersible flat-plate ultrafiltration unit operates at a pressure of -0.02 MPa to -0.08 MPa, has a filtration cycle of 30 to 50 minutes, a total backwashing time of 90 seconds, and a design flux of no more than 20 L / m³. 2 .h, Water backwash intensity: 25~50L / m 2 .h, self-use rate ≤5%, product water turbidity <1NTU.

[0071] II. Nanofiltration Device

[0072] This application uses a nanofiltration device to remove sulfate and carbonate ions from salt lake brine. The nanofiltration device in this application includes multi-stage nanofiltration modules, with each stage connected in sequence.

[0073] In one specific embodiment, the multi-stage nanofiltration module includes a primary nanofiltration module and a secondary nanofiltration module; of course, a tertiary nanofiltration module can also be reserved as needed. The structures of each nanofiltration module are generally the same, including a corrosion-resistant housing, a nanofiltration membrane assembly housed within the housing, and an inlet, a concentrate outlet, and a product outlet formed on the housing. To achieve cleaning and stability monitoring, each nanofiltration module is equipped with a cleaning system and a control system. The cleaning system is used to periodically or as needed clean the nanofiltration membrane assembly to remove dirt and blockages from the membrane surface, ensuring the normal operation of the device and maintaining a long service life. The cleaning system can include physical cleaning (such as backwashing) and chemical cleaning (such as acid-alkali cleaning). The control system is used to monitor and regulate the operating status of the device. The control system can monitor parameters such as inlet and outlet water pressure and temperature, and automatically control the device according to the set parameters to ensure the stability of the nanofiltration unit.

[0074] The lithium extraction system for salt lakes provided in this application can be divided into three parallel processing routes at the primary and secondary nanofiltration modules: A) The concentrate from the primary nanofiltration module is used for subsequent lithium precipitation, which is the first lithium extraction route; B) The product water end of the primary nanofiltration module is connected to the secondary nanofiltration module, and the concentrate from the secondary nanofiltration module participates in subsequent sodium carbonate recovery, which is the sodium carbonate recovery route, or the lithium precipitation reactant preparation route; C) The product water from the secondary nanofiltration module is further adsorbed to obtain a qualified adsorption solution, which is used for subsequent lithium precipitation, which is the second lithium extraction route.

[0075] The system architecture of treatment route A is as follows: the inlet of the ultrafiltration unit is connected to the pipeline transporting brine from the salt lake; the product water of the ultrafiltration unit is connected to the inlet of the first-stage nanofiltration module; the concentrate outlet of the first-stage nanofiltration module is connected to the titanium adsorption unit; the qualified liquid outlet of the titanium adsorption unit is connected to the inlet of the sand filtration-ultrafiltration combined treatment unit; the product water of the sand filtration-ultrafiltration combined treatment unit is connected to the inlet of the qualified liquid reverse osmosis unit; the concentrate outlet of the qualified liquid reverse osmosis unit is connected to the boron removal resin; the product water of the boron removal resin is connected to the inlet of the lithium chloride MVR unit; the outlet of the lithium chloride MVR unit is connected to the inlet of the lithium precipitation unit; a sodium carbonate inlet is provided on the lithium precipitation unit; the sodium carbonate in the lithium precipitation unit reacts with the lithium chloride solution to generate lithium carbonate precipitate; the discharge port of the lithium precipitation unit is connected to the separation and recovery unit; the separation and recovery unit (lithium carbonate centrifuge) realizes solid-liquid separation and recovers the lithium carbonate precipitate.

[0076] The system architecture of processing route B is as follows: the product water end of the primary nanofiltration module is connected to the inlet end of the secondary nanofiltration module, the concentrate outlet end of the secondary nanofiltration module is connected to the inlet end of the sodium carbonate nanofiltration unit, the concentrate outlet end of the sodium carbonate nanofiltration unit is connected to the sodium carbonate recovery unit, and the outlet of the sodium carbonate recovery unit is connected to the sodium carbonate inlet of the lithium precipitation unit.

[0077] The sodium carbonate recovery device includes a sodium carbonate MVR device and a boron removal device; an alkali addition port is provided on the pipe connecting the product water end of the primary nanofiltration module and the inlet water end of the secondary nanofiltration module; and a water addition port is provided on the pipe connecting the concentrate outlet end of the secondary nanofiltration module and the inlet end of the sodium carbonate nanofiltration device.

[0078] The system architecture of treatment route C is as follows: the product water end of the secondary nanofiltration module is connected to the first inlet of the decarbonator, the product water outlet of the sodium carbonate nanofiltration unit is connected to the second inlet of the decarbonator, the discharge outlet of the decarbonator is connected to the inlet of the aluminum adsorption unit, and the qualified liquid outlet of the aluminum adsorption unit is connected to the inlet of the sand filtration and ultrafiltration combined treatment unit.

[0079] The pipe connecting the product water end of the secondary nanofiltration module to the first inlet of the decarbonator is equipped with an acid inlet to remove bicarbonate ions, which are then converted into CO2 and discharged in the decarbonator. The decarbonator is equipped with an exhaust port for discharging carbon dioxide gas. The aluminum adsorption device is equipped with a water inlet and a tail brine outlet.

[0080] In practical installations, nanofiltration devices use membranes with nanoscale pore sizes, typically between 0.001 and 0.01 micrometers. Compared to ultrafiltration membranes, nanofiltration membranes have smaller pore sizes, allowing for more effective removal of dissolved substances, most inorganic salts, and organic matter. Depending on the specific needs, different separation effects and permeability can be achieved by selecting different nanofiltration membrane materials, operating pressures, and operating conditions.

[0081] The working principle of a nanofiltration device is explained below:

[0082] Nanofiltration membranes exhibit ion selectivity, showing lower removal rates for monovalent ions but higher removal rates for polyvalent ions. This is due to the Donnan equilibrium effect, which exists for anions with different valence states, as most nanofiltration membranes are charged. Positively charged ions in water can permeate through the membrane under the influence of concentration gradients, but negatively charged ions are blocked by the negatively charged membrane and cannot (or very little) permeate to the freshwater side. Furthermore, the principle of electroneutrality restricts the diffusion of positively charged ions to the freshwater side, thus achieving desalination. The permeability of nanofiltration membranes to salts is mainly determined by the valence state of the ions. Monovalent ions can permeate through the membrane in large quantities (but not without obstruction), while polyvalent ions (such as sulfates and carbonates) have a higher removal rate. Therefore, this application employs a nanofiltration device to effectively separate monovalent and divalent salt concentrates.

[0083] Using a nanofiltration membrane with anti-contamination material, the retention rate of sulfate ions can reach over 98%. By efficiently retaining sulfate ions in concentrated brine, the concentrated brine is effectively separated into two parts after treatment by the nanofiltration system: nanofiltration permeate, which is almost entirely composed of NaCl, and nanofiltration concentrate, which is mainly composed of Na2SO4, thus achieving the initial salt separation target of concentrated brine.

[0084] Because inorganic salts can permeate nanofiltration membranes, their osmotic pressure is much lower than that of reverse osmosis membranes. Therefore, at a given flux, the external pressure required for nanofiltration is much lower than that for reverse osmosis; and at the same pressure, the flux of nanofiltration is much higher than that of reverse osmosis. Nanofiltration allows concentration and desalination to occur simultaneously. Therefore, when nanofiltration replaces reverse osmosis, the concentration process can be carried out effectively and rapidly, achieving a greater concentration factor.

[0085] By utilizing the salt separation advantages of special nanofiltration membranes and their efficient retention of organic matter with a molecular weight of over 200, it is possible to concentrate and reduce the volume of divalent brine, thereby reducing the amount of subsequent nanofiltration concentrate to be processed by crystallization. Sodium sulfate is obtained through evaporation crystallization and freeze crystallization. At the same time, due to the low content of TOC (Total Organic Carbon) and divalent ions in the permeate water, the pressure of organic matter contamination in the nanofiltration permeate water during subsequent reverse osmosis concentration treatment is reduced through nanofiltration separation. Furthermore, the residual TOC impurities in the product are effectively controlled during the subsequent sodium chloride evaporation crystallization process, resulting in a high-purity sodium chloride product.

[0086] III. Titanium Adsorption Device

[0087] Inorganic ion adsorbents exhibit strong selectivity for lithium ions and a specific memory effect, enabling effective selective extraction of lithium from dilute solutions. Inorganic ion exchange adsorbents can be classified into aluminum-based, manganese-based, and titanium-based adsorbents. This application selects aluminum-based and titanium-based adsorbents.

[0088] The liquid discharged from the concentrate outlet of the first-stage nanofiltration module is a neutral alkaline brine. In this application, a titanium adsorption device is selected to adsorb and treat the concentrate discharged from the first-stage nanofiltration module.

[0089] Specifically, titanium adsorbents in titanium adsorption devices are used to adsorb lithium, mainly through the selective adsorption function of the adsorbent to adsorb lithium ions from the brine of salt lakes. Titanium adsorbents are usually made of titanium fibers, titanium particles, or titanium nanomaterials as fillers, increasing their surface area and pore structure to improve adsorption performance. Lithium can be captured and stored by the adsorbent, and then desorbed from the adsorbent to collect the qualified liquid. For example, desorption can be carried out under the action of an eluent to obtain a lithium-rich solution, thus achieving the separation and purification of lithium; while the unqualified liquid (or tail brine) after adsorption is directly discharged into the salt lake.

[0090] The titanium adsorption device used in this application has the advantages of large adsorption capacity, wide applicability, high selectivity, and low solubility loss rate.

[0091] In this application, the titanium adsorption device has a water inlet, an acid water inlet, a lithium precipitation mother liquor inlet, a qualified liquid outlet, and a non-qualified liquid outlet. Since both the lithium precipitation mother liquor and the boron removal resin regeneration liquid contain a certain amount of lithium, they are recycled back to the titanium adsorption device for treatment, adhering to the principle of maximizing resource recovery. Therefore, the lithium precipitation mother liquor inlet is connected to the lithium precipitation mother liquor outlet, and the lithium precipitation mother liquor inlet is also connected to the boron removal resin regeneration liquid outlet.

[0092] IV. Sand Filtration and Ultrafiltration Combined Treatment Unit

[0093] The sand filtration and ultrafiltration combined treatment device in this application can be understood as "sand filtration + ultrafiltration". Sand filtration is a filtration technology that uses a multi-layer sand bed; when water passes through the sand bed, suspended solids, silt, and large particles are filtered out, resulting in clearer water. Sand filtration is often used in the primary filtration stage to remove larger solid particles and reduce turbidity and suspended solids content in the water. Ultrafiltration is a membrane filtration technology that uses microporous membranes for separation. The pore size of ultrafiltration membranes is typically between 0.01 and 0.1 micrometers, which can effectively remove suspended solids, colloids, bacteria, viruses, and most high-molecular-weight organic matter, achieving higher water quality requirements.

[0094] The sand filtration and ultrafiltration combined treatment device adopted in this application can achieve better water treatment effect. First, sand filtration can be used as a pretreatment step to remove larger particulate matter and suspended solids in the water, thereby reducing the burden on the ultrafiltration membrane and extending its service life. Second, ultrafiltration is set on the outlet side of the sand filter as a fine filtration step to remove smaller particles, colloids and other substances that cannot be completely removed by sand filtration.

[0095] V. Qualified liquid reverse osmosis unit

[0096] The qualified liquid reverse osmosis device in this application is a reverse osmosis device used to treat adsorbed qualified liquid. Its structural principle can be briefly described as follows: The reverse osmosis device mainly includes a water inlet system, a high-pressure pump, a reverse osmosis membrane module, a concentrate discharge pipe, a pure water collection pipe, and a corresponding control system. The water inlet system includes an inlet pipe, an inlet valve, and pretreatment equipment, used to introduce the water source to be treated. The pretreatment equipment generally includes particulate filters, activated carbon filters, etc., used to remove suspended particles, chlorine, and organic compounds from the water. The high-pressure pump is connected after the water inlet system to provide sufficient water pressure to overcome the osmotic resistance of the reverse osmosis membrane. The high-pressure pump increases the pressure of water flowing through the membrane, causing water molecules to pass through the membrane pores, while solutes and particulate matter are retained. The reverse osmosis membrane module is the core part of the entire device, composed of multiple thin films. The membrane layers are usually semi-permeable membranes with micropores or nano-sized pores, which can retain most ions, solutes, and particulate matter, allowing only water molecules to pass through. When water passes through the membrane, the solutes and particulate matter are retained on the membrane surface or discharged from the device. During reverse osmosis, some of the water that does not pass through the membrane (concentrate) is discharged from the concentrate discharge pipe to dilute the concentrated solute in the feed water. The purified water retained on the membrane module (clean water) flows out through the membrane pores and is collected in the pure water collection pipe. The control system monitors parameters such as inlet and outlet water pressure and membrane module status, and performs automatic control as needed to ensure the normal operation of the unit.

[0097] In this application, the product water end of the qualified liquid reverse osmosis device is connected to the inlet end of the product water reverse osmosis device. Since the concentrate outlet end of the product water reverse osmosis device still contains a certain amount of lithium, the concentrate outlet end of the product water reverse osmosis device is connected to the inlet end of the sand filtration and ultrafiltration combined treatment device to recover lithium in the concentrate discharged from the product water reverse osmosis device, thereby improving the lithium recovery rate. The water treated by the product water reverse osmosis device can be used as pure water for self-use, so the product water end of the product water reverse osmosis device can be connected to the user's water supply end. Therefore, the salt lake lithium extraction system provided in this application can not only realize the extraction of high-purity lithium resources, but also produce pure water for self-use, with an extremely high resource recovery and utilization rate.

[0098] VI. Boron Removal Resin

[0099] Boron removal resin is an adsorbent material used to remove boron from water, which can help purify water sources and reduce the boron content in water.

[0100] Boron removal resins typically use organic functionalized resins as the base material. After special treatment, their surface possesses specific adsorption properties, allowing them to selectively adsorb boron ions from water. These resin materials have a large surface area and pore size, providing ample contact opportunities and adsorption capacity to effectively remove boron from water.

[0101] The working principle of boron removal resin is mainly to capture and fix boron ions in water onto the resin surface through adsorption. When water passes through the boron removal resin device, boron ions undergo an adsorption reaction with the active sites on the resin surface, thereby removing the boron ions from the water. Once the resin is saturated, a regeneration operation is required to restore its adsorption performance. Typically, the regeneration methods for boron removal resin include acid washing, alkali washing, or other special regeneration processes.

[0102] VII. Lithium Chloride MVR Unit

[0103] A lithium chloride MVR (Mechanical Vapor Recompression) unit is a device that uses mechanical compression vapor regeneration technology to recover and purify lithium chloride solutions.

[0104] The lithium chloride MVR unit regenerates the lithium chloride solution through the following steps: heating the lithium chloride solution using an evaporator to evaporate the water and generate steam; compressing the steam using a compressor to increase its temperature and pressure; exchanging heat between the high-temperature, high-pressure steam and the lithium chloride solution using a heat exchanger to raise its temperature and evaporate some of the water; cooling the high-temperature, high-pressure steam using a condenser to condense it into steam with even higher heat; separating the condensed water and lithium chloride solution using a separator; and recirculating the lithium chloride solution in the separator back to the evaporator using a recirculation pump for the next cycle.

[0105] By continuously repeating the above steps, the lithium chloride MVR device achieves the removal of water and concentration of lithium chloride in the lithium chloride solution. Compared with traditional thermal evaporation methods, MVR technology utilizes the high temperature and high pressure of compressed steam to achieve energy recycling, reducing energy consumption and operating costs; it also improves the quality and stability of the lithium chloride solution, enables the recovery and reuse of lithium chloride, and reduces waste liquid discharge.

[0106] VIII. Lithium Deposition Unit

[0107] In this application, when lithium chloride and sodium carbonate enter the lithium precipitation unit, they react to form lithium carbonate precipitate. The discharged lithium precipitation mother liquor refers to a solution containing lithium ions, which mainly contains lithium chloride, sodium carbonate, and other impurities. In the lithium precipitation unit, lithium chloride and sodium carbonate react to form lithium carbonate precipitate and sodium chloride. The reaction equation is as follows:

[0108] 2LiCl + Na₂CO₃ → Li₂CO₃ + 2NaCl

[0109] After the reaction, the aqueous lithium carbonate precipitate enters a separation and recovery unit to remove water. The mother liquor discharged from the lithium precipitation unit may still contain unreacted lithium chloride, sodium carbonate, and other impurities, such as metal ions and impurity salts. If necessary, the mother liquor can be further processed to extract and purify the lithium carbonate for use in lithium compound preparation or other industrial applications. Common processing methods include filtrate extraction, leaching, crystallization, and ion exchange. Through these steps, lithium carbonate can be separated and purified from the mother liquor to obtain high-purity lithium compound products.

[0110] In this application, the lithium precipitation mother liquor is discharged into a titanium adsorption device for further processing and purification, thereby improving the purification rate and resource recovery rate.

[0111] IX. Separation and Recovery Device

[0112] The separation and recovery device in this application includes a lithium carbonate centrifuge, whose main structural principle includes a centrifuge body, a feeding system, a centrifugal separation system, a liquid phase discharge system, a solid phase collection system, and a corresponding control system. The centrifuge body includes a shell, a centrifuge rotor, a motor, etc., and is typically made of corrosion-resistant materials (such as stainless steel) to adapt to the special properties of lithium carbonate solutions.

[0113] The feeding system includes a feed pipe and a feed pump. The aqueous lithium carbonate precipitate discharged from the self-precipitating lithium unit is fed into the centrifuge through the feed pipe, and the feed pump provides pressure and flow velocity. The core component of the lithium carbonate centrifuge is the centrifugal separation system, which includes a centrifuge rotor and a centrifugal force field. The high-speed rotating centrifuge rotor generates a strong centrifugal force, separating the solid particles (lithium carbonate precipitate) from the aqueous lithium carbonate precipitate. The centrifuge rotor typically contains centrifuge plates or centrifuge baskets to collect the separated solid particles. After centrifugation, the liquid phase (lithium carbonate-rich solution) needs to be discharged. The centrifuge discharges the liquid phase from the centrifuge rotor through a liquid phase discharge system, which can be discharged to the titanium adsorption device described in this application for further processing. The solid phase (lithium carbonate solid particles containing impurities) needs to be collected and processed. It is generally collected through centrifuge plates or centrifuge baskets within the centrifuge rotor, and can be further processed through drying, filtration, and other steps. The control system monitors the centrifuge's operating status, speed, temperature, and other parameters, and automatically controls the system according to set conditions to ensure the safe and stable operation of the device.

[0114] Therefore, this application effectively separates solid particles from lithium carbonate solution by using the centrifugal separation principle of a lithium carbonate centrifuge, thereby achieving dehydration and solid-liquid separation.

[0115] 10. Carbon separator

[0116] The carbon remover in this application can achieve gas-liquid separation and carbon removal. Acid is added to the permeate of the secondary nanofiltration module and discharged into the carbon remover. The permeate of the sodium carbonate nanofiltration can also be discharged into the carbon remover. Bicarbonate ions in the liquid react with acid to generate gas and are discharged, thus achieving liquid decarbonization.

[0117] XI. Aluminum Adsorption Device

[0118] The aluminum adsorption device includes an aluminum-based adsorbent and is suitable for sulfate or chloride-type brine in neutral to slightly acidic environments. This application uses an aluminum-based adsorbent after the two-stage nanofiltration module because sulfuric acid is separated in the concentrate from the first-stage nanofiltration module, while the product water from the second-stage nanofiltration module mainly contains chlorides. The application uses a titanium-based adsorbent after the concentrate from the first-stage nanofiltration module primarily because of the high sulfate concentration. Furthermore, the volume of the concentrate is generally much smaller than that of the product water; therefore, the aluminum adsorption device is sufficient to meet the application requirements.

[0119] This application involves discharging the liquid discharged from the decarbonizer into an aluminum adsorption device to adsorb lithium ions using an aluminum-based adsorbent. The lithium is then desorbed from the adsorbent and collected as a qualified liquid. For example, desorption can be carried out under the action of an eluent to obtain a lithium-rich solution, thereby achieving lithium separation and purification. The unqualified liquid (or tail brine) after adsorption is discharged and further processed (for example, further processing to recover potassium and sodium resources depending on the actual situation), or the tail brine can be discharged into a salt lake.

[0120] The aluminum adsorption device in this application has a liquid inlet, a qualified liquid outlet, a water inlet, and a tail brine outlet. The liquid inlet is connected to a decarbonator, and the qualified liquid outlet is connected to a sand filtration and ultrafiltration combined treatment device.

[0121] The aluminum adsorption device used in this application has the advantages of being suitable for industrial production, having good selectivity, and being environmentally friendly.

[0122] 12. Sodium carbonate nanofiltration device

[0123] The main difference between sodium carbonate nanofiltration units and general nanofiltration units lies in the characteristics of the filter membrane and the treatment effect. Regarding membrane characteristics, sodium carbonate nanofiltration units use filter membranes with specific pore sizes, typically ranging from a few nanometers to tens of nanometers, capable of filtering out most fine particles, dissolved substances, and organic matter. General nanofiltration units, on the other hand, may use different types of filter membranes with a wider pore size range. In terms of treatment effect, due to the difference in membrane pore size, sodium carbonate nanofiltration units are more suitable for removing fine particles and organic matter from water, as well as for concentrating solutes. Therefore, the primary function of sodium carbonate nanofiltration units is to remove impurities and dissolved substances from water through nanofiltration technology, and to achieve water separation and concentration.

[0124] In summary, the brine lithium extraction system provided in this application achieves a lithium extraction process using a coupled adsorption process, consisting of an ultrafiltration unit, a nanofiltration unit, an adsorption unit, a sand filtration-ultrafiltration combined treatment unit, a qualified liquid reverse osmosis unit, a boron removal resin, a lithium chloride MVR unit, a lithium precipitation unit, and a separation and recovery unit connected in sequence. It utilizes membrane technology to separate divalent ions such as calcium, magnesium, sulfate, and carbonate from monovalent ions such as lithium, and then employs adsorption, membrane technology, and evaporation for concentration, reducing the scale of evaporation and achieving the goal of extracting high-purity lithium resources under low energy consumption and low cost conditions. Furthermore, the combined membrane and adsorption method can thoroughly remove impurities, improve lithium purity, reduce adsorbent consumption, and achieve high adsorption-desorption efficiency.

[0125] Example 2

[0126] Using the above-described membrane separation coupled adsorption-based lithium extraction system from salt lakes, this application provides a method for lithium extraction from salt lakes based on membrane separation coupled adsorption. This embodiment mainly illustrates the first lithium extraction route, and the process principle of this lithium extraction method is as follows:

[0127] The raw brine first enters an ultrafiltration unit (submerged ultrafiltration), where suspended solids, colloids, and other turbidity are removed to prevent clogging of subsequent membrane units. The permeate from the submerged ultrafiltration enters a first-stage nanofiltration module, where divalent ions such as sulfate and carbonate are separated from monovalent ions such as lithium and chloride. The concentrate from the first-stage nanofiltration module contains a large number of divalent ions, but the flow rate is small. This concentrate is then discharged into a titanium adsorption unit, where lithium is adsorbed. The qualified lithium-adsorbed solution enters a combined ultrafiltration and sand filtration treatment unit (ultrafiltration + sand filtration), while the remaining brine (unqualified solution) is returned to the salt lake. The qualified solution from the titanium adsorption unit enters an ultrafiltration + sand filtration unit to remove suspended solids and other turbidity from the brine. The effluent from the ultrafiltration + sand filtration unit enters a qualified solution reverse osmosis unit (qualified solution RO), where lithium is concentrated and enriched on the RO concentrate side. The qualified RO concentrate is then treated with boron removal resin to remove boron before entering a lithium chloride MVR unit for concentration, followed by a lithium precipitation unit. Lithium reacts with sodium carbonate to form lithium carbonate precipitate, which is then separated by a centrifuge to achieve solid lithium carbonate recovery.

[0128] In this embodiment, both the mother liquor from the lithium precipitation unit and the boron removal resin regeneration liquid contain a certain amount of lithium. In accordance with the principle of maximizing resource recovery rate, they are recycled to the titanium adsorption unit for treatment.

[0129] In this embodiment, the qualified liquid RO permeate is treated by the permeate reverse osmosis unit (permeate RO) and then the permeate (pure water) is reused in the production process. The permeate reverse osmosis concentrate is returned to the ultrafiltration + sand filtration unit for further lithium extraction.

[0130] Example 3

[0131] Using the above-described membrane separation coupled adsorption-based lithium extraction system from salt lakes, this application provides a method for lithium extraction from salt lakes based on membrane separation coupled adsorption. This embodiment mainly illustrates the second lithium extraction route, and the process principle of this lithium extraction method is as follows:

[0132] The raw brine first enters an ultrafiltration unit (submerged ultrafiltration), where suspended solids, colloids, and other turbidity are removed to prevent clogging of subsequent membrane units. The submerged ultrafiltration permeate then enters a first-stage nanofiltration module, where divalent ions such as sulfate and carbonate are separated from monovalent ions such as lithium and chloride. The first-stage nanofiltration permeate contains a large amount of HCO3- in addition to lithium. - Cl - Calcium is added to the brine product, and the bicarbonate alkalinity (HCO3) in the brine is increased. - ) is converted into carbonate (CO3) 2- After the permeate undergoes an alkali reaction, it enters a secondary nanofiltration module where carbonate ions are retained on the concentrate side. Acid is added to the permeate from the secondary nanofiltration module, resulting in a small amount of HCO3 in the permeate. - The lithium is converted into carbon dioxide and removed from the brine by a decarbonator. The effluent from the decarbonator is then filtered by an aluminum adsorbent device to remove lithium. The qualified aluminum-adsorbed solution enters an ultrafiltration and sand filtration system to remove suspended solids and other turbidity from the brine. The unqualified aluminum-adsorbed solution is discharged into the salt lake as tail brine or further treated. The effluent from the ultrafiltration and sand filtration system enters a qualified solution reverse osmosis (RO) system, where lithium is concentrated and enriched on the RO concentrate side. The qualified RO concentrate is then filtered by a boron removal resin to remove boron before entering a lithium chloride MVR system for concentration. It then enters a lithium precipitation unit, where lithium reacts with sodium carbonate to form lithium carbonate precipitate. Finally, the precipitate is separated into solid and liquid components by a centrifuge to achieve solid lithium carbonate recovery.

[0133] Example 4

[0134] Based on the above embodiment three, a method for lithium extraction from salt lakes based on membrane separation coupled adsorption is provided. This embodiment recovers sodium carbonate based on the lithium extraction method provided in embodiment three, which can be used as a source of sodium carbonate added to the lithium precipitation device.

[0135] Based on Example 3, the concentrate from the secondary nanofiltration module is discharged into the sodium carbonate nanofiltration device, where carbonate ions are retained and separated on the concentrate side. The permeate from the sodium carbonate nanofiltration device and the permeate from the secondary nanofiltration module are combined and then enter the decarbonator. After boron removal, the concentrate from the sodium carbonate nanofiltration device is used to recover sodium carbonate using a sodium carbonate MVR device.

[0136] Example 5

[0137] The lithium extraction methods provided in Examples 2 and 3 above can be combined; see the flowchart below. Figure 1 The merged lithium extraction method has two parallel lithium extraction routes, which not only achieves full lithium extraction, but also recovers sodium carbonate, which can be used as a source of sodium carbonate added to the lithium precipitation unit, thereby reducing operating investment costs.

[0138] The lithium extraction method for salt lakes based on membrane separation coupled adsorption provided in this embodiment is applicable to salt lakes with low lithium content and mineralization, but high sodium sulfate and sodium chloride content. In a specific example, this method can extract lithium from salt lake brine with the water quality shown in Table 1 below.

[0139] Table 1. Water Quality of Salt Lake Brine

[0140] Ion name unit numerical values <![CDATA[mg 2+ ]]> mg / L 3.7 <![CDATA[K + ]]> mg / L 16230 <![CDATA[Ca 2+ ]]> mg / L 3.3 <![CDATA[Na + ]]> mg / L 78000 <![CDATA[Li + ]]> mg / L 200 <![CDATA[B - ]]> mg / L 860 <![CDATA[SO4 2- ]]> mg / L 14200 <![CDATA[CL - ]]> mg / L 56700 <![CDATA[CO3 2- ]]> mg / L 13500 <![CDATA[HCO3 - ]]> mg / L 4500

[0141] The lithium extraction method from salt lakes provided in this application takes into account the separation of monovalent and divalent ions, removes alkalinity and boron, and at the same time ensures the resource recovery and utilization of sodium carbonate, sodium chloride, potassium chloride and lithium carbonate.

[0142] The lithium extraction method provided in this application is compared with traditional lithium extraction methods, as shown in Table 2 below.

[0143] Table 2. Comparison of the advantages of the lithium extraction method provided in this application with traditional lithium extraction methods in various aspects.

[0144]

[0145]

[0146] In summary, this application provides a lithium extraction system for salt lakes based on membrane separation coupled with adsorption. The system comprises, in sequence, an ultrafiltration unit, a nanofiltration unit, an adsorption unit, a sand filtration-ultrafiltration combined treatment unit, a qualified liquid reverse osmosis unit, a boron removal resin, a lithium chloride MVR unit, a lithium precipitation unit, and a separation and recovery unit. This system functionally treats the salt lake brine using these devices. Membrane treatment is achieved through the ultrafiltration, nanofiltration, and sand filtration-ultrafiltration combined treatment unit and the reverse osmosis unit, while adsorption treatment is achieved through the titanium adsorption unit and the boron removal resin. In other words, this application employs a raw brine membrane coupled with adsorption lithium extraction process. Membrane technology is used to separate calcium, magnesium, sulfate, carbonate, etc., from lithium and other monovalent and divalent ions. Adsorption, membrane technology, and evaporation concentration are then used to reduce the scale of evaporation, achieving high-purity lithium extraction under low energy consumption and low cost conditions. Furthermore, the combination of membrane technology and adsorption can thoroughly remove impurities, improve lithium purity (lithium product purity > 94%), and reduce adsorbent consumption, decrease the frequency of adsorbent backwashing, improve adsorbent efficiency, and reduce backwash freshwater consumption.

[0147] Furthermore, the lithium-potassium-sodium resource integrated recovery system provided in this application can also produce sodium carbonate as a source of lithium-precipitated sodium carbonate, reducing the investment cost of preparation; in addition, pure water will also be produced during the lithium extraction process for self-use, reducing the cost of water resource input, improving the recovery rate of salt lake brine resources, and improving the return on investment.

[0148] Example 6

[0149] Based on the lithium extraction method provided in Example 3, this example further processes the tail brine discharged from the aluminum adsorption device in Example 3 to recover potassium ions, sodium ions, and chloride ions from the salt lake brine.

[0150] Specifically, the tail brine of the aluminum adsorption unit contains a large number of monovalent ions, such as potassium ions, sodium ions, and chloride ions. A small portion of the tail brine is used to produce acid and alkali for reuse or export through nanofiltration and bipolar membrane electrodialysis. Most of the tail brine enters the chloride production unit. Taking advantage of the temperature difference between sodium chloride and potassium chloride precipitation, sodium chloride is first removed by primary / secondary solar low-temperature evaporation and solar thermal melting, and finally potassium chloride is precipitated by cold precipitation.

[0151] In this embodiment, the process of recovering potassium, sodium, and chloride ions from the tail brine of the aluminum adsorption device is parallel to the lithium extraction route provided in Examples 3 to 5 above. The construction and commissioning of the potassium, sodium, and chloride ion recovery system and the construction and commissioning of the lithium extraction system do not affect each other, and the construction and commissioning of the lithium extraction system can be carried out separately.

[0152] The technical features of the above embodiments can be combined in any way (as long as there is no contradiction in the combination of these technical features). For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described; these embodiments not explicitly written should also be considered to be within the scope of this specification.

[0153] The present application has been described in a relatively specific and detailed manner above through general descriptions and specific embodiments. It should be understood that, based on the technical concept of the present application, several conventional adjustments or further innovations can be made to these specific embodiments; however, as long as they do not depart from the technical concept of the present application, the technical solutions obtained by these conventional adjustments or further innovations also fall within the protection scope of the claims of the present application.

Claims

1. A salt lake lithium extraction system based on membrane separation coupled with adsorption, characterized in that, The device comprises, in sequence, an ultrafiltration device, a nanofiltration device, an adsorption device, a sand filtration-ultrafiltration combined treatment device, a qualified liquid reverse osmosis device, a boron removal resin, a lithium chloride MVR device, a lithium precipitation device, and a separation and recovery device. The water inlet end of the ultrafiltration device is connected with a pipeline for conveying salt lake brine, the water outlet end of the ultrafiltration device is connected with the nanofiltration device, the nanofiltration device is connected with the adsorption device, the qualified liquid outlet of the adsorption device is connected with the inlet end of the sand filtration-ultrafiltration combined treatment device, the water outlet end of the sand filtration-ultrafiltration combined treatment device is connected with the water inlet end of the qualified liquid reverse osmosis device, the concentrated water outlet end of the qualified liquid reverse osmosis device is connected with the boron removal resin, the water outlet end of the boron removal resin is connected with the water inlet end of the lithium chloride MVR device, the water outlet end of the lithium chloride MVR device is connected with the liquid inlet of the lithium precipitation device, a sodium carbonate adding port is arranged on the lithium precipitation device, the sodium carbonate in the lithium precipitation device reacts with the lithium chloride solution to generate lithium carbonate precipitate, the discharge port of the lithium precipitation device is connected with the separation and recovery device, and the separation and recovery device is used to realize solid-liquid separation and recover the lithium carbonate precipitate. The nanofiltration device comprises a plurality of nanofiltration modules, and the plurality of nanofiltration modules at least comprise a first nanofiltration module and a second nanofiltration module. The adsorption device comprises a titanium adsorption device and an aluminum adsorption device, the titanium adsorption device has a water inlet, an acid water adding port, a qualified liquid outlet, and an unqualified liquid outlet, and the aluminum adsorption device has a liquid inlet, a qualified liquid outlet, a water adding port, and a tail brine outlet. The water inlet end of the first nanofiltration module is connected with the water outlet end of the ultrafiltration device, the concentrated water outlet end of the first nanofiltration module is connected with the water inlet of the titanium adsorption device, and the qualified liquid outlet of the titanium adsorption device is connected with the inlet end of the sand filtration-ultrafiltration combined treatment device. The water outlet end of the first nanofiltration module is connected with the water inlet end of the second nanofiltration module, the water outlet end of the second nanofiltration module is connected with the liquid inlet of the aluminum adsorption device, and the qualified liquid outlet of the aluminum adsorption device is connected with the inlet end of the sand filtration-ultrafiltration combined treatment device, wherein the second nanofiltration module is connected with the aluminum adsorption device through a carbon remover, the carbon remover has a first inlet, an exhaust port, and a liquid outlet, the water outlet end of the second nanofiltration module is connected with the first inlet, the liquid outlet is connected with the liquid inlet of the aluminum adsorption device, and the exhaust port is used to exhaust carbon dioxide gas; an acid adding port is arranged on a pipeline connecting the water outlet end of the second nanofiltration module and the first inlet of the carbon remover.

2. The lithium extraction system from salt lake based on membrane separation coupled with adsorption according to claim 1, characterized in that, The titanium adsorption device further has a lithium precipitation mother liquor adding port, the lithium precipitation mother liquor adding port is connected with the mother liquor discharge port of the lithium precipitation device, and the lithium precipitation mother liquor adding port is connected with the regenerated liquid discharge port of the boron removal resin.

3. The lithium extraction system from salt lake based on membrane separation coupled with adsorption according to claim 1, characterized in that, An alkali adding port is arranged on a pipeline connecting the water outlet end of the first nanofiltration module and the water inlet end of the second nanofiltration module.

4. The lithium extraction system from salt lake based on membrane separation coupled with adsorption according to claim 3, characterized in that, The carbon remover further has a second inlet, and the second inlet is connected with a sodium carbonate nanofiltration device. The inlet end of the sodium carbonate nanofiltration device is connected with the concentrated water outlet end of the secondary nanofiltration module through a connecting pipeline, and a water inlet is arranged on the connecting pipeline; the water outlet of the sodium carbonate nanofiltration device is connected with the second inlet, and the concentrated water outlet end of the sodium carbonate nanofiltration device is connected with a sodium carbonate recovery device, and the outlet of the sodium carbonate recovery device is connected with the sodium carbonate adding port on the lithium precipitation device. The sodium carbonate recovery device comprises a sodium carbonate MVR device and a boron removal device.

5. The lithium extraction system from salt lakes based on membrane separation coupled with adsorption according to claim 1, characterized in that, The water outlet end of the qualified liquid reverse osmosis device is connected with the inlet end of a water production reverse osmosis device, the concentrated water outlet end of the water production reverse osmosis device is connected with the inlet end of the sand filtration-ultrafiltration combined treatment device, and the water outlet end of the water production reverse osmosis device is connected with the user water end. The sand filtration-ultrafiltration combined treatment device comprises a sand bed and an ultrafiltration membrane assembly connected on the water outlet side of the sand bed.

6. A method for extracting lithium from salt lake based on membrane separation coupled with adsorption, characterized in that, The lithium extraction system from salt lake based on membrane separation coupled with adsorption according to any one of claims 1-2 comprises the following steps: S1: inputting the salt lake brine into the ultrafiltration device to remove the suspended solids and colloids in the salt lake brine through the ultrafiltration device; S2: inputting the salt lake brine treated by the ultrafiltration device into the primary nanofiltration module, and the primary nanofiltration module is used to remove the sulfate and carbonate in the salt lake brine; S3: inputting the liquid discharged from the concentrated water outlet end of the primary nanofiltration module into the titanium adsorption device, and the titanium adsorption device is used to adsorb the lithium in the liquid; S4: inputting the adsorption qualified liquid discharged from the titanium adsorption device into the sand filtration-ultrafiltration combined treatment device, and the sand filtration-ultrafiltration combined treatment device is used to remove the suspended solids and colloids in the liquid and reduce the turbidity; S5: inputting the liquid treated by the sand filtration-ultrafiltration combined treatment device into the qualified liquid reverse osmosis device, and inputting the liquid discharged from the concentrated water outlet end of the qualified liquid reverse osmosis device into the boron removal resin for boron removal; S6: inputting the liquid flowed out from the water outlet end of the boron removal resin into the lithium chloride MVR device, and the lithium chloride MVR device concentrates the liquid inputted thereinto; S7: inputting the lithium chloride concentrated liquid obtained by the lithium chloride MVR device into the lithium precipitation device to react with the sodium carbonate solution, generating lithium carbonate precipitate in the solution, and separating and recovering the generated lithium carbonate precipitate from the solution by the separation and recovery device.

7. A method for extracting lithium from salt lake based on membrane separation coupled with adsorption, characterized in that, The lithium extraction system from salt lake based on membrane separation coupled with adsorption according to claim 3 comprises the following steps: S1: inputting the salt lake brine into the ultrafiltration device to remove the suspended solids and colloids in the salt lake brine through the ultrafiltration device; S2: inputting the salt lake brine treated by the ultrafiltration device into the primary nanofiltration module, and the primary nanofiltration module is used to remove the sulfate and carbonate in the salt lake brine; S3: inputting the liquid discharged from the water outlet end of the primary nanofiltration module into the secondary nanofiltration module to remove the carbonate; S4: inputting the liquid discharged from the water outlet end of the secondary nanofiltration module into the carbon removal device to remove the bicarbonate; S5: inputting the liquid discharged from the carbon removal device into the aluminum adsorption device, and the aluminum adsorption device is used to adsorb the lithium in the liquid; S6: The adsorption qualified liquid discharged from the aluminum adsorption device enters the sand filter-ultrafiltration combined treatment device, which is used to remove liquid suspended solids and colloids and reduce turbidity; S7: The liquid treated by the sand filter-ultrafiltration combined treatment device enters the qualified liquid reverse osmosis device, and the liquid discharged from the concentrated water outlet end of the qualified liquid reverse osmosis device enters the boron removal resin for boron removal; S8: The liquid flowing out from the water production end of the boron removal resin enters the lithium chloride MVR device, which concentrates the liquid entering it; S9: The lithium chloride concentrated liquid obtained by concentrating the lithium chloride MVR device enters the lithium precipitation device to react with a sodium carbonate solution, lithium carbonate precipitate is generated in the solution, and the generated lithium carbonate precipitate is separated and recovered from the solution by the separation and recovery device.

8. The method for extracting lithium from salt lake based on membrane separation coupled with adsorption according to claim 7, characterized in that, In step S3, alkali is added to the liquid discharged from the water production end of the primary nanofiltration module, and then it is discharged into the secondary nanofiltration module; In step S4, acid is added to the liquid discharged from the water production end of the secondary nanofiltration module, and then it is discharged into the carbon removal device.

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