A separation system and process suitable for lithium battery wastewater

Abstract

This invention provides a separation system and process suitable for lithium battery wastewater, employing a three-stage gradient negative pressure separation process to achieve purification of lithium battery wastewater and efficient recovery of lithium resources step by step. First, negative pressure ultrafiltration removes suspended particles and other physical impurities from the lithium battery wastewater. Then, negative pressure nanofiltration selectively retains high-valence metal ions, resulting in low-concentration Li... + After initial concentration, the third-stage negative pressure adsorption process utilizes Li + Crown ether-grafted polymer membranes with specific recognition capabilities are used for Li-containing solutions with coexisting monovalent ions. + Precise capture is achieved. This system, through gradient negative pressure drive and the combined action of functional membrane modules, effectively overcomes the challenges of capturing low-concentration Li. + The problems of low mass transfer efficiency and weak separation selectivity were finally solved, achieving efficient separation of lithium resources from complex lithium battery wastewater, providing key technical support for lithium resource recovery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery wastewater recycling, and further relates to a separation system and process suitable for lithium battery wastewater. BACKGROUND

[0002] Currently, several recovery and treatment methods for metals in lithium battery wastewater have significant limitations, making it difficult to meet the efficient, environmentally friendly and economic treatment needs.

[0003] Specifically, the chemical precipitation method has the problems of low lithium recovery rate (especially ineffective for low concentration lithium) and a large amount of heavy metal-containing sludge, and the subsequent treatment cost is high;

[0004] Although the solvent extraction method can selectively enrich lithium ions, it has the problems of COD exceeding standard due to residual organic phase, complex process flow (requiring multi-stage stripping), and sensitivity to pH;

[0005] Although the electrodialysis method selectively separates charged substances by driving ion migration through a direct current field, it still has the problems of poor selectivity for multivalent metal ions (Al 3+ , Fe 3+ ), inability to recover non-ionized components (such as organic solvents), and easy polarization and scaling, resulting in a decrease in current efficiency.

[0006] The mainstream positive pressure membrane separation technology (including reverse osmosis and nanofiltration) has the problems of serious membrane fouling caused by colloids or organic matter, resulting in short membrane life, and high energy consumption caused by high-pressure pumps;

[0007] Even the negative pressure separation technology, which is theoretically more energy-efficient, has the problems of insufficient vacuum degree to drive nanoscale membrane separation, lack of gradient pressure regulation leading to low multi-component separation efficiency, and aggravated membrane fouling under negative pressure conditions, making it impossible to achieve efficient and selective recovery of high-value metal resources in lithium battery wastewater. SUMMARY

[0008] To achieve the above-mentioned purposes, the present application provides the following technical solutions:

[0009] The application discloses a separation system suitable for lithium battery wastewater, which comprises a pretreatment unit for adjusting the pH value of the lithium battery wastewater and carrying out flocculation, and a gradient negative pressure separation unit in communication with the pretreatment unit and used for grading and separating metal ions in the pretreatment lithium battery wastewater; the gradient negative pressure separation unit comprises a negative pressure ultrafiltration tank, a negative pressure nanofiltration tank and a negative pressure adsorption tank arranged in sequence along a flow path, and is provided with a negative pressure vacuum pump for providing negative pressure for each tank body; the working negative pressure interval of the gradient negative pressure separation unit is -0.05 to -0.095 MPa, and the internal working pressures of the negative pressure ultrafiltration tank, the negative pressure nanofiltration tank and the negative pressure adsorption tank are sequentially and gradually decreased; the internal working pressures of the negative pressure ultrafiltration tank, the negative pressure nanofiltration tank and the negative pressure adsorption tank are respectively -0.05 to -0.07 MPa, -0.08 to -0.09 MPa and -0.09 to -0.095 MPa; each of the negative pressure ultrafiltration tank, the negative pressure nanofiltration tank and the negative pressure adsorption tank is provided with a membrane assembly, the membrane assembly in the negative pressure ultrafiltration tank is an ultrafiltration membrane assembly for intercepting particles in the lithium battery wastewater, the membrane assembly in the negative pressure nanofiltration tank is a nanofiltration membrane assembly for intercepting high-valence ions, and the membrane assembly in the negative pressure adsorption tank is a lithium ion selective permeation membrane assembly for capturing lithium ions, wherein the lithium ion selective permeation membrane assembly is a high polymer membrane grafted with 12-crown-4 ether.

[0010] In some embodiments, the ultrafiltration membrane assembly is a polyether sulfone hollow fiber membrane, and the nanofiltration membrane assembly is an inorganic ceramic membrane.

[0011] In some embodiments, the pretreatment unit comprises a pH adjusting tank and a flocculation tank in sequence, the pH adjusting tank is provided with a pH adjusting agent feeding port for receiving a pH adjusting agent, and the flocculation tank is provided with a flocculant feeding port for receiving a flocculant.

[0012] In some embodiments, a first buffer tank is connected in series between the flocculation tank and the negative pressure ultrafiltration tank, the inlet of the first buffer tank is in communication with the water phase outlet of the flocculation tank to receive and temporarily store the supernatant discharged from the flocculation tank, and the outlet of the first buffer tank is in communication with the inlet of the negative pressure ultrafiltration tank to supply the negative pressure ultrafiltration tank with a feed liquid.

[0013] In some embodiments, a second buffer tank is arranged between the water phase outlet of the negative pressure adsorption tank, the negative pressure ultrafiltration tank and the negative pressure nanofiltration tank, and the negative pressure nanofiltration tank and the negative pressure adsorption tank, and the negative pressure vacuum pump is in communication with the second buffer tank to suck the gas in the second buffer tank and provide the negative pressure driving force for the corresponding negative pressure ultrafiltration tank, negative pressure nanofiltration tank and negative pressure adsorption tank upstream of the second buffer tank.

[0014] In some embodiments, the surface of the membrane module is provided with fractal-distributed microgrooves, the shape of which is one of a tree-like branching shape, a wave-like vortex shape, or a mesh-like interconnection shape; the depth of the microgrooves is 50 micrometers, and the cross-section of the microgrooves is one of a V-shape, a U-shape, or a trapezoid.

[0015] In some embodiments, the separation system further includes a backwashing device connected to the negative pressure ultrafiltration tank, the negative pressure nanofiltration tank, and the negative pressure adsorption tank, respectively, to flush the membrane modules inside the tanks.

[0016] In some embodiments, the separation system further includes an intelligent control unit, which includes a controller and a plurality of detection devices and a plurality of actuators respectively connected to the controller; the detection devices include a pH detector for detecting the pH value of the feed solution, a turbidity detector for detecting the turbidity of the feed solution, a conductivity detector for detecting the conductivity of the feed solution, an inductively coupled plasma mass spectrometer for detecting the lithium ion concentration, and a transmembrane pressure difference monitoring device for detecting the transmembrane pressure difference of at least one of the membrane modules; the actuators include a pH adjuster dosing device, a flocculant dosing device, and the backwashing device; the controller is configured to control the operation of the negative pressure vacuum pump and the actuators according to the signals from the detection devices.

[0017] This invention also provides a separation process suitable for lithium battery wastewater, employing the above-mentioned separation system for lithium battery wastewater, the steps of which include:

[0018] Step 1, Pretreatment: Adjust the pH value of the lithium battery wastewater and perform flocculation and sedimentation on the pH-adjusted wastewater to obtain the supernatant;

[0019] Step 2, First-stage negative pressure ultrafiltration: The supernatant is subjected to negative pressure ultrafiltration at a pressure of -0.05 to -0.07 MPa, and particulate pollutants are retained by the ultrafiltration membrane module;

[0020] Step 3, Second-stage negative pressure nanofiltration: The feed solution obtained from the first-stage negative pressure ultrafiltration step is subjected to negative pressure nanofiltration. Under a pressure of -0.08 to -0.09 MPa, the nanofiltration membrane module is used to retain divalent and higher valence metal ions to obtain a feed solution rich in monovalent ions.

[0021] Step 4, Third-stage negative pressure adsorption: The feed solution rich in monovalent ions is subjected to negative pressure adsorption. Under a pressure of -0.09 to -0.095 MPa, lithium ions are selectively permeable using a lithium ion selective permeation membrane module while other monovalent ions are retained, ultimately obtaining a lithium ion enriched solution.

[0022] Compared with the prior art, the separation system and process for lithium battery wastewater provided by the present invention have the following beneficial effects:

[0023] 1. The separation system provided by this invention first removes suspended particles from lithium battery wastewater using a negative pressure ultrafiltration unit, and then uses a negative pressure nanofiltration unit to retain Co. 2+ Ni 2+ High-valence metal ions. These two stages of treatment effectively remove most interfering impurities, reduce the risk of competitive adsorption by subsequent membrane modules, and also enable the adsorption of low-concentration Li... + The initial pre-enrichment increases the relative concentration of lithium ions in the feed solution, creating favorable conditions for the efficient recovery of low-concentration lithium ions. In the final third-stage negative pressure adsorption process, a polymer membrane modified with crown ether is used, utilizing its vacuolar structure and... Specific matching, from monovalent ions with similar properties (such as...) , ) Capture and enrichment are achieved. This separation system utilizes gradient negative pressure to provide external mass transfer motive force in conjunction with a specific membrane module, solving the problems of insufficient mass transfer motive force and poor separation selectivity in low-concentration Li⁺, and ultimately achieving the goal of efficiently recovering metal resources from complex lithium battery wastewater;

[0024] To address the low mass transfer efficiency in membrane module flow channels during miniaturized system design, this invention provides a separation system that improves the membrane module flow channel by incorporating fractal-distributed microgrooves on the membrane module surface. Even at low flow rates, the feed liquid flowing over the microgroove surface generates eddies, transforming the originally stable laminar flow into turbulent flow. This enhances the turbulence intensity and shear force near the membrane module surface, thereby significantly improving mass transfer efficiency. Simultaneously, the turbulence also acts as a scouring agent on the membrane module surface, effectively inhibiting contaminant deposition and achieving self-cleaning.

[0025] 3. The separation system provided by this invention is also equipped with an intelligent control unit. The controller is linked with multiple detection and execution devices to precisely regulate the dosage of reagents, tank negative pressure, and backwashing process, thereby improving the efficiency of the separation process. Furthermore, a digital twin platform is introduced, which can map the equipment status in real time, providing transparent monitoring of the equipment status. It can also predict the remaining lifespan of the membrane modules, allowing maintenance personnel to promptly replace and flush the membrane modules based on the prompts, thus improving system reliability. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the separation system provided by the present invention;

[0027] Figure 2 This is a schematic diagram of the microgroove structure provided by the present invention.

[0028] Brief Description of Drawings

[0029] 10 - pretreatment unit; 101 - pH adjustment tank; 10101 - wastewater outlet; 10102 - pH adjuster feeding port; 102 - flocculation tank; 10201 - flocculant feeding port;

[0030] 20 - gradient negative pressure separation unit; 201 - negative pressure vacuum pump; 202 - collection pipeline; 203 - vacuum buffer tank; 204 - negative pressure ultrafiltration tank; 2041 - ultrafiltration membrane assembly; 205 - negative pressure nanofiltration tank; 2051 - nanofiltration membrane assembly; 2052 - steam delivery pipeline; 206 - negative pressure adsorption tank; 2061 - lithium ion selective permeation membrane assembly; 207 - first buffer tank; 208 - second buffer tank;

[0031] 30 - nitrogen pipeline:

[0032] 40 - microgroove. DETAILED DESCRIPTION

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, specific embodiments of the present application will be described below with reference to the drawings. Obviously, the drawings in the following description only represent some embodiments of the present application, and for those skilled in the art, other drawings can be obtained from these drawings without creative labor, and other embodiments can also be obtained.

[0034] In order to make the drawing simple, only the parts related to the application are shown in each drawing, which does not represent the actual structure of the product. In addition, in order to make the drawing simple and easy to understand, in some drawings, only one of the components with the same structure or function is shown schematically, or only one of them is marked. In this paper, "one" not only means "only one", but also means "more than one".

[0035] It should be further understood that the term "and / or" used in the specification and claims of the present application means any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0036] In this paper, it should be noted that unless otherwise specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integral connection; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0037] In addition, in the description of the present application, the terms "first", "second", etc. are only used for differentiation and cannot be understood as indicating or implying relative importance.

[0038] The embodiment provides a separation system suitable for lithium battery wastewater, which comprises a pretreatment unit 10 and a gradient negative pressure separation unit 20, and specifically comprises:

[0039] As shown in the figure, the pretreatment unit 10 is used for removing most of the heavy metals and suspended solids in the lithium battery wastewater, and comprises a pH adjusting tank 101 and a flocculation tank. Figure 1 The pH adjusting tank 101 is provided with a lithium battery wastewater inlet, a wastewater outlet 10101 and a pH adjusting agent feeding port 10102, a pH adjusting agent feeding device is in communication with the pH adjusting agent feeding port 10102, and an acidic adjusting agent and an alkaline adjusting agent are fed into the pH adjusting tank 101, so that the pH value of the lithium battery wastewater is adjusted to 6-8, and the metal ions can generate precipitates insoluble in water.

[0040] The flocculation tank is provided with a water phase inlet, a water phase outlet and a flocculant feeding port 10201, the water phase inlet is in communication with the wastewater outlet 10101 of the pH adjusting tank 101, and the lithium battery wastewater after pH adjustment is sent into the flocculation tank through the water phase inlet of the flocculation tank. A flocculant feeding device is in communication with the flocculant feeding port 10201, and a flocculant is fed into the flocculation tank.

[0041] Because the precipitate particles generated by the lithium battery wastewater are very small and in colloidal state, it is difficult to settle naturally. A flocculant (such as polyaluminum chloride PAC and polyacrylamide PAM) needs to be added to destroy the stability of the colloid by electric neutralization, so that it is destabilized and gradually forms larger and denser flocs. The formed flocs can quickly settle to the bottom of the reaction tank under the action of gravity, so as to realize solid-liquid separation, and the relatively clear wastewater supernatant is discharged into the gradient negative pressure separation unit 20 through the water phase outlet.

[0042] The gradient negative pressure separation unit 20 provided by the application comprises a negative pressure vacuum pump 201, a plurality of collection pipelines 202, and a negative pressure ultrafiltration tank 204, a negative pressure nanofiltration tank 205 and a negative pressure adsorption tank 206 which are sequentially communicated, wherein the negative pressure ultrafiltration tank 204, the negative pressure nanofiltration tank 205 and the negative pressure adsorption tank 206 are all provided with a negative pressure interface, the negative pressure vacuum pump 201 can be provided with three, and is in one-to-one correspondence with the negative pressure interfaces of the three tank bodies and is communicated, the gas in the tank is continuously extracted to establish a negative pressure environment, each negative pressure vacuum pump 201 is communicated with one collection pipeline 202, and the end of the collection pipeline 202 is communicated with a vacuum buffer tank 203 to store the gas or a small amount of liquid extracted from each tank body. It should be noted that the number of negative pressure vacuum pumps 201 is not limited to three, the negative pressure interface of the negative pressure ultrafiltration tank 204 can be connected with a plurality of negative pressure vacuum pumps 201 at the same time, and the negative pressure interfaces of the negative pressure nanofiltration tank 205 and the negative pressure adsorption tank 206 also adopt the same multi-pump parallel connection design.

[0043] Specifically, the inlet of the negative pressure ultrafiltration tank 204 is communicated with the water phase outlet of the flocculation tank, the negative pressure ultrafiltration tank 204 is provided with an ultrafiltration membrane assembly 2041 for intercepting particles in the supernatant of wastewater, the ultrafiltration membrane assembly 2041 can intercept particles with a particle size of >50 nm, such as polyvinylidene fluoride (PVDF) binder, SBR binder, graphite and small-molecule organic substance esters and the like, and the system directly guides the concentrated liquid of the intercepted pollutants to a special hazardous waste treatment unit for centralized disposal, so as to ensure the environmental safety of the whole process. The negative pressure working pressure of the negative pressure ultrafiltration tank 204 is set to -0.05~-0.07 MPa, in the embodiment, the ultrafiltration membrane assembly 2041 can be made of polysulfone materials (such as polysulfone, sulfonated polysulfone) and polyolefin materials (such as polypropylene). The ultrafiltration membrane assembly 2041 is preferably a polyether sulfone (PES) hollow fiber membrane, which can be in contact or work in a solution environment with a pH value of 1 to 12 for a long time, and its chemical structure, physical properties and separation performance will not be significantly degraded or damaged.

[0044] The inlet of the negative pressure nanofiltration tank 205 is communicated with the water phase outlet of the negative pressure ultrafiltration tank 204, the wastewater discharged from the negative pressure ultrafiltration tank 204 after removing the pollutant impurities enters the negative pressure nanofiltration tank 205, and the negative pressure nanofiltration tank 205 is provided with a nanofiltration membrane assembly 2051 for intercepting high-valence ions. The lithium battery wastewater contains a large amount of Li + , Na + , Co 2+ , Ni 2+ and other ions, the nanofiltration membrane assembly 2051 is selected from inorganic ceramic membranes, such as aluminum oxide (Al2O3) membranes, zirconium oxide (ZrO2) membranes and titanium oxide (TiO2) membranes. Co 2+ , Ni 2+High valence ions have stronger electrostatic attraction with the negatively charged groups on the surface of the nanofiltration membrane assembly 2051, and are more easily retained on one side of the membrane, while Li + , Na + have weaker charges and are more likely to pass through the membrane under negative pressure driving, so that after the feed liquid passes through the nanofiltration membrane assembly 2051, the Li + in the feed liquid is preliminarily enriched, and the concentration of Li + is increased by 5-10 times. The concentrated solution retained by the nanofiltration membrane assembly 2051, which is enriched in Co 2+ , Ni 2+ and other high-value metal ions, can be returned to a specific process node of the lithium ion battery production line through a special pipeline to realize recycling of resources.

[0045] In the present application, the nanofiltration membrane assembly 2051 is preferably a ZrO2 modified titanium dioxide ceramic membrane with a pore size of 2 nm, and the ZrO2 modified titanium dioxide ceramic membrane has a retention rate of >99% for high valence ions. The negative pressure working pressure of the negative pressure nanofiltration tank 205 is set to -0.08 to -0.09 MPa.

[0046] Further, the negative pressure nanofiltration tank 205 is also provided with a steam inlet in communication with a steam delivery pipeline 2052, and steam at a controllable temperature is injected into the negative pressure nanofiltration tank 205 to heat the feed liquid. The viscosity of the feed liquid decreases with increasing temperature, improving the flowability of the feed liquid and improving the separation efficiency.

[0047] The negative pressure working pressure of the negative pressure adsorption tank 206 is set to -0.09 to -0.095 MPa, and the negative pressure adsorption tank 206 is provided with a lithium ion selective permeation membrane assembly 2061. The lithium ion selective permeation membrane assembly 2061 is a high molecular film grafted with 12-crown-4 ether, and the high molecular film can be one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) and polypropylene (PP). In the present application, the lithium ion selective permeation membrane assembly 2061 is preferably a polyvinylidene fluoride (PVDF) film grafted with 12-crown-4 ether. The PVDF film grafted with 12-crown-4 ether can selectively permeate Li + and retain Na + , achieving the final enrichment of Li + in the wastewater. The principle is specific recognition based on molecular size matching: the cavity size of 12-crown-4 ether is 0.122-0.153 nm, the diameter of Li + is 0.118 nm, the diameter of Na + is 0.204 nm, and the diameter of Li + is close to the cavity size of 12-crown-4 ether and can perfectly embed in the crown ether cavity; while the diameter of Na + is much larger than the cavity size and cannot effectively enter. +The ether bond oxygen atoms in the 12-crown-4 ether cavity can form coordination, forming a stable complex structure. The complex is driven by negative pressure to pass through the membrane pore, and is desorbed and released on one side of the membrane. Na + The Li+ that cannot be effectively captured by the crown ether stays in the wastewater on the other side of the membrane. In this embodiment, the Li+ of the PVDF membrane grafted with 12-crown-4 ether + The flux is 120 L / (m 2 ·h). The high-concentration Li + The concentrated solution is accurately returned to the batching or synthesis section of the lithium battery production line, such as the preparation of positive electrode materials, thereby improving the resource recycling efficiency.

[0048] One of the methods for grafting 12-crown-4 ether on the polymer membrane is to generate free radicals on the surface of the polymer membrane by initiators or high-energy radiation. The double bond of the crown ether undergoes addition polymerization with the free radicals on the surface of the membrane to form covalent grafting chains. The second method is to add crown ethers containing crosslinkable groups and crosslinking agents to the casting solution. After membrane formation, thermal initiation or ultraviolet initiation is used to induce crosslinking reaction between the crown ether and the molecular chain of the membrane material, forming a network structure. The third method is to modify the polymer membrane to generate active functional groups (such as hydroxyl and carboxyl) on the surface of the membrane, and then react with crown ether molecules with complementary groups (such as esterification of hydroxyl and crown ether carboxyl) to achieve grafting.

[0049] In some embodiments, in order to ensure the stable operation of the gradient negative pressure separation unit 20, protect the membrane assembly, and improve the treatment effect, the gradient negative pressure separation unit 20 is further provided with a first buffer tank 207 and a plurality of second buffer tanks 208. The first buffer tank 207 is arranged between the flocculation tank and the negative pressure ultrafiltration tank 204. The inlet of the first buffer tank 207 is connected with the water phase outlet of the flocculation tank. The relatively clear wastewater discharged from the flocculation tank is first stored in the first buffer tank 207. The outlet of the first buffer tank 207 is in communication with the inlet of the negative pressure ultrafiltration tank 204. The feed liquid is introduced into the negative pressure ultrafiltration tank 204 from the first buffer tank 207.

[0050] A second buffer tank 208 is connected in series between the negative pressure ultrafiltration tank 204 and the negative pressure nanofiltration tank 205. The inlet of the second buffer tank 208 is connected to the water phase outlet of the negative pressure ultrafiltration tank 204. In this embodiment, the negative pressure vacuum pump 201 originally arranged in the negative pressure ultrafiltration tank 204 is replaced by the second buffer tank 208. By continuously pumping the gas in the second buffer tank 208, a negative pressure environment is formed between the second buffer tank 208 and the negative pressure ultrafiltration tank 204, thereby driving the negative pressure ultrafiltration tank 204 upstream of the second buffer tank 208 to generate a stable negative pressure. The pumped gas is directed to the vacuum buffer tank 203 through the collection pipeline 202 connected to the negative pressure vacuum pump 201 for centralized treatment. This design avoids the problems of liquid retention and accumulation caused by complex pipeline layout and winding direction when the negative pressure vacuum pump 201 is directly arranged in the negative pressure ultrafiltration tank 204, thereby ensuring smooth transmission of the liquid.

[0051] A second buffer tank 208 is also connected in series between the negative pressure nanofiltration tank 205 and the negative pressure adsorption tank 206. The inlet of the second buffer tank 208 is connected to the water phase outlet of the negative pressure nanofiltration tank 205. The negative pressure vacuum pump 201 originally arranged in the negative pressure nanofiltration tank 205 is replaced by the second buffer tank 208. By continuously pumping the gas in the second buffer tank 208, a negative pressure environment is formed between the second buffer tank 208 and the negative pressure nanofiltration tank 205. In addition, the second buffer tank 208 between the negative pressure nanofiltration tank 205 and the negative pressure adsorption tank 206 can also be directly used as a container for storing liquid. In this case, the negative pressure vacuum pump 201 is arranged in the negative pressure nanofiltration tank 205 to provide a negative pressure environment for the negative pressure nanofiltration tank 205. The liquid after separation of high-valence ions is first stored in the second buffer tank 208 between the negative pressure nanofiltration tank 205 and the negative pressure adsorption tank 206. The outlet of the second buffer tank 208 is connected to the inlet of the negative pressure adsorption tank 206 to send the liquid into the negative pressure adsorption tank 206.

[0052] A second buffer tank 208 is arranged downstream of the negative pressure adsorption tank 206. The water phase outlet of the negative pressure adsorption tank 206 is connected to the inlet of the second buffer tank 208. The negative pressure vacuum pump 201 originally arranged in the negative pressure adsorption tank 206 is replaced by the second buffer tank 208 downstream of the negative pressure adsorption tank 206. By continuously pumping the gas in the second buffer tank 208, a negative pressure environment is formed between the second buffer tank 208 and the negative pressure ultrafiltration tank 204 upstream of the second buffer tank 208, thereby avoiding liquid accumulation and flow dead zones caused by complex pipelines.

[0053] In some embodiments, the separation system further comprises a nitrogen pipeline 30 respectively communicating with the pH adjusting tank 101, the flocculation tank, the first buffer tank 207 and the second buffer tank 208. When the liquid in each tank completes the current process and needs to be transported to the next process tank, nitrogen is introduced into the tank to push the residual liquid to the subsequent tank by the positive pressure generated by the nitrogen, so as to ensure that the liquid is not retained and all enters the next processing link.

[0054] In addition, the lithium battery wastewater contains electrolyte decomposition products, especially lithium hexafluorophosphate (LiPF6), which is extremely sensitive to water. Once it comes into contact with water, even trace amounts of water vapor in the air, it will immediately undergo a violent hydrolysis reaction to generate highly corrosive hydrofluoric acid (HF), which is easy to corrode the tank body, pipeline, pump valve. The nitrogen pipeline 30 fills nitrogen into the tank, which can displace oxygen and water vapor in the air, effectively isolate moisture, and prevent LiPF6 from hydrolyzing. Moreover, the lithium battery wastewater contains valuable metals such as cobalt, nickel, and manganese. In the presence of oxygen, low-valence metal ions are easily oxidized to high-valence ions. The nitrogen pipeline 30 fills nitrogen into the tank to displace oxygen, which can also ensure that these valuable metal ions exist in a stable and easily recoverable valence state.

[0055] In summary of the above embodiments, the separation system provided by the present application operates according to the process of "pretreatment-three-stage separation", and the specific process is as follows:

[0056] Step one, pretreatment: the lithium battery wastewater first enters the pH adjusting tank 101, and after the pH value of the wastewater is adjusted to 6-8 by adding a pH adjusting agent, it is sent to the flocculation tank, and a flocculant is added for flocculation and sedimentation. The supernatant in the flocculation tank is sent to the first buffer tank 207 for temporary storage and subsequent processing.

[0057] Step two, first-stage negative pressure ultrafiltration: the supernatant temporarily stored in the first buffer tank 207 is introduced into the negative pressure ultrafiltration tank 204, and the negative pressure vacuum pump 201 matched with the negative pressure ultrafiltration tank 204 is started to adjust the pressure in the negative pressure ultrafiltration tank 204 to -0.05~-0.07MPa. The particle pollutants in the liquid are intercepted by the ultrafiltration membrane assembly 2041, and the permeate produced by the ultrafiltration membrane assembly 2041 enters the second buffer tank 208 downstream of the negative pressure ultrafiltration tank 204 for temporary storage.

[0058] Step three, second-stage negative pressure nanofiltration: the liquid in the second buffer tank 208 downstream of the negative pressure ultrafiltration tank 204 is transported to the negative pressure nanofiltration tank 205, and the matched negative pressure vacuum pump 201 is started to adjust the pressure in the negative pressure nanofiltration tank 205 to -0.08~-0.09MPa. The nanofiltration membrane assembly 2051 intercepts high-valence ions (such as Co 2+ , Ni 2+ ) in the liquid on the concentrated side of the membrane assembly, while Li + , Na +The low-valence ions pass through the membrane assembly along with the feed liquid and flow into the second buffer tank 208 downstream of the negative pressure nanofiltration tank 205 from the water phase outlet of the negative pressure nanofiltration tank 205 for storage.

[0059] Step four, third-stage negative pressure absorption: the feed liquid enters the negative pressure adsorption tank 206 from the second buffer tank 208 downstream of the negative pressure nanofiltration tank 205, and the matched negative pressure vacuum pump 201 is turned on to adjust the pressure in the negative pressure adsorption tank 206 to a high vacuum state of -0.09~-0.095 MPa, Li + pass through the membrane assembly through the specific separation effect of the lithium ion selective permeation membrane assembly 2061, Na + are intercepted, and the finally formed lithium ion-rich liquid is discharged from the water phase outlet of the negative pressure adsorption tank 206 into the second buffer tank 208 downstream of the negative pressure adsorption tank 206 for centralized storage, ready for subsequent recycling.

[0060] The Co 2+ , Ni 2+ concentrate produced in step three and the high-concentration Li + concentrate produced in step four are respectively transported through pipelines and directly recycled for use in the lithium ion battery production process.

[0061] In some embodiments, although there are many conventional lithium battery wastewater treatment methods, they generally rely on large coagulation tanks, sedimentation tanks and other facilities for treatment. Such large treatment facilities can only be used in specific areas, and a large amount of reagents are added, resulting in a large amount of hazardous waste and solid waste, high treatment cost, and unsuitability for small and micro enterprises to treat small amounts of lithium battery wastewater. Moreover, with the explosive growth of the new energy vehicle industry, the production of lithium batteries is increasing, and the treatment demand for lithium battery wastewater and solid waste is increasing sharply, and the limitations of the traditional wastewater treatment mode are increasingly prominent.

[0062] Under this background, if the lithium battery wastewater separation system is designed to be miniaturized, for example, a mobile or containerized treatment unit is created, it can flexibly adapt to the dispersed treatment scene of small and micro enterprises, effectively making up for the shortcomings of traditional large facilities in flexibility and applicability. Moreover, for some marginal salt lakes with small reserves and not worth building large factories, such miniaturized lithium battery wastewater separation systems can provide an economically feasible development plan.

[0063] However, when the system size is simply reduced, the flow channel of the membrane assembly in the separation unit is also shortened. In the shorter flow channel, the feed liquid is more likely to form laminar flow and have uneven flow velocity distribution and flow dead zones. In this way, the metal ions in the feed liquid cannot effectively contact the membrane surface for separation, and there is an insufficient mass transfer problem. Secondly, in the slow flow area, pollutants are easy to accumulate and form filter cake layers, blocking the membrane assembly.

[0064] In view of the technical defects of the separation system of the miniaturized design, the separation system provided by the application improves the flow channel structure on the surface of the membrane module, and specifically, the surface of the membrane module is provided with fractal distributed microgrooves 40, and the cross section of the microgrooves 40 is one of V-shaped, U-shaped or trapezoidal-shaped. The depth of the microgrooves 40 is 50 microns, when the liquid droplets of the feed liquid stay on the surface of the membrane module, the included angle (i.e. the contact angle) formed between the droplet edge and the surface of the microgrooves 40 is greater than 150°, at this time, the surface of the membrane module forms a "super-hydrophobic surface", at this time, the liquid droplets will be approximately spherical, and will easily roll off and will not wet the surface. Secondly, the fractal distributed shape of the microgrooves 40 can be one of a tree branch shape, a wave vortex shape or a net-like interconnected shape, Figure 2 An embodiment in which the microgrooves adopt a net-like interconnected shape is shown, and these fractal distributed shapes all have complex, non-periodic self-similarity, when the feed liquid flows through this "uneven" surface, the liquid will be constantly disturbed, divided and mixed, even at a very low flow rate, multi-scale vortexes and eddies are forced to be generated, the laminar flow is converted into turbulent flow, the turbulent intensity and shear force near the surface of the membrane module are enhanced, the membrane surface is continuously "brushed", the deposition conditions of the pollutants are destroyed, and the pollutants cannot be stably deposited in the local area to form a liquid or filter cake layer.

[0065] In some embodiments, the separation system provided by the application further comprises a backwashing device, the backwashing device is in communication with the backwashing water inlets of the negative pressure ultrafiltration tank 204, the negative pressure nanofiltration tank 205 and the negative pressure adsorption tank 206 respectively, and the backwashing device delivers flushing water to the tanks to flush the membrane modules in the tanks, prevent the membrane modules from being blocked, and prolong the service life of the membrane modules.

[0066] Further, an ultraviolet light emitting diode (UV-LED) is arranged in the negative pressure nanofiltration tank 205, the ultraviolet light emitting diode irradiates the surface of the nanofiltration membrane module 2051, excites the photocatalytic reaction of TiO2, generates free radicals with strong oxidizing ability, and degrades the organic matter attached to the surface of the nanofiltration membrane module 2051. In addition, ultraviolet light emitting diodes can also be arranged in the negative pressure ultrafiltration tank 204 and the negative pressure adsorption tank 206, and regularly irradiate the membrane modules in the tanks to disinfect and sterilize, inhibit the growth of microorganisms, reduce the risk of membrane pollution, and prolong the service life of the membrane modules.

[0067] In some embodiments, the separation system further comprises an intelligent control unit, which mainly comprises a controller, a plurality of detection devices and a plurality of actuators. The detection devices include a pH detector arranged on the pH adjusting tank 101 to detect the pH value of the feed liquid, a turbidity detector arranged on the flocculation tank to detect the turbidity of the feed liquid, an oxidation-reduction potential online analyzer arranged on the pH adjusting tank 101 and / or the flocculation tank to measure the oxidation-reduction potential of the feed liquid, a conductivity detector arranged on the negative pressure nanofiltration tank 205 and / or the negative pressure adsorption tank 206 to measure the conductivity of the feed liquid, an inductively coupled plasma mass spectrometer arranged on the negative pressure adsorption tank 206 to measure the lithium ion concentration of the feed liquid, and a transmembrane pressure difference (TMP) monitoring device for detecting the pressure difference of the membrane module. The actuators include a pH adjusting agent feeding device, a flocculating agent feeding device, and a backwashing device.

[0068] The controller is in control connection with the pH detector and the pH adjusting agent feeding device, respectively. The controller controls the amount of pH adjusting agent fed into the pH adjusting tank 101 according to the pH value detected by the pH detector.

[0069] The controller is in control connection with the turbidity detector and the flocculating agent feeding device, respectively. The controller controls the amount of flocculating agent fed into the flocculation tank according to the turbidity of the lithium battery wastewater detected by the turbidity detector.

[0070] The controller is in control connection with the pH adjusting agent feeding device and / or the flocculating agent feeding device and the oxidation-reduction potential online analyzer, respectively. The controller adjusts the amount of pH adjusting agent and flocculating agent based on the data collected by the oxidation-reduction potential online analyzer and the data collected by the pH detector and / or the turbidity detector.

[0071] The controller is in control connection with the conductivity detector and the negative pressure vacuum pump 201 matched with the negative pressure nanofiltration tank 205 and the negative pressure adsorption tank 206, respectively. The controller precisely controls the operating state of the negative pressure vacuum pump 201 based on the conductivity data collected by the conductivity detector, and dynamically adjusts the negative pressure value in each tank.

[0072] The controller is in control connection with the inductively coupled plasma mass spectrometer and the negative pressure vacuum pump 201 matched with the negative pressure adsorption tank 206. The controller dynamically adjusts the operating state of the negative pressure vacuum pump 201 matched with the negative pressure adsorption tank 206 based on the data collected by the inductively coupled plasma mass spectrometer and the conductivity detector arranged on the negative pressure adsorption tank 206.

[0073] The controller is in control connection with the transmembrane pressure difference monitoring device and the backwashing device. The controller controls the start or stop of the backwashing process of the membrane module according to the transmembrane pressure difference detected by the transmembrane pressure difference monitoring device.

[0074] In this embodiment, based on the above intelligent control unit, the application also constructs a digital twin platform suitable for the separation system to realize the visualization monitoring and precise regulation of the whole operation process of the system. Specifically:

[0075] A high-precision 3D model of the device is created using tools such as SolidWorks / UG, including the tank body, membrane assembly, pipeline, valve, pump, and all other components.

[0076] Device state sensors are set up to collect real-time operating parameters such as the rotational speed of the negative pressure vacuum pump 201, tank pressure / liquid level, valve switch state, pump body temperature / vibration, etc. The instantaneous and cumulative flow rates of the incoming water, produced water, concentrated water, and backwash water are also monitored. The real-time data collected are dynamically bound to the 3D model to map the device state in real time and obtain the lithium battery wastewater treatment progress at any time. For example, the lithium battery wastewater flow rate animation in the pipeline is displayed on the display according to the real-time monitoring data changes. For example, the color of the membrane assembly gradually changes from green to yellow and red according to its degree of pollution (detected by the TMP detection device). For example, the operator can click on any pump or valve on the real screen to pop up its real-time operating parameters.

[0077] Meanwhile, the digital twin platform establishes a time series prediction model based on LSTM (Long Short-Term Memory Network) to predict the service life of the membrane assembly. The time series prediction model takes the separation system operation process data as the input basis, specifically covering three types of core parameters:

[0078] Real-time operating parameters: vacuum degree of each tank body output by the negative pressure vacuum pump 201 (-0.05 ~ -0.09 MPa gradient range), TMP, produced water flux, backwash frequency / pressure / duration.

[0079] Dynamic incoming water quality parameters: pH value (1-12 adaptive range), water temperature, turbidity, COD value, conductivity, and concentration of target recovery component lithium ions of pretreated wastewater.

[0080] Historical maintenance parameters: membrane assembly cleaning records, and historical pollution treatment records (such as the TMP change curve corresponding to the pollution of the membrane assembly).

[0081] The time series prediction model dynamically selects the time series features in the historical data that significantly affect the membrane life through the gating mechanism of the LSTM network, combines the current parameter trend, and fits the quantitative relationship of the membrane pollution rate, life consumption, etc. Finally, it outputs prediction results such as "time to reach cleaning threshold" and "remaining life".

[0082] At the same time, the time series prediction model has an error correction mechanism, and through real-time collection of actual operation data of the membrane module (such as the flux recovery after cleaning, actual replacement time), continuous iteration optimization is carried out, so that the life prediction error is controlled within ±5%.

[0083] The above is only the preferred embodiment of the present application, it should be pointed out that, for those skilled in the technical field, without departing from the principles of the present application, can make a number of improvements and refinements, these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A separation system suitable for lithium battery wastewater, characterized in that, The system comprises: a pretreatment unit for adjusting the pH value of the lithium battery wastewater and flocculating; and a gradient negative pressure separation unit in communication with the pretreatment unit for grading and separating metal ions in the pretreated lithium battery wastewater; The gradient negative pressure separation unit comprises a negative pressure ultrafiltration tank, a negative pressure nanofiltration tank and a negative pressure adsorption tank arranged in sequence along the flow path, and is configured to provide negative pressure for each tank by a negative pressure vacuum pump; The working pressure range of the gradient negative pressure separation unit is -0.05~-0.095MPa, and the internal working pressures of the negative pressure ultrafiltration tank, the negative pressure nanofiltration tank and the negative pressure adsorption tank are gradiently decreased in sequence, which are -0.05~-0.07MPa, -0.08~-0.09MPa and -0.09~-0.095MPa respectively; Each of the negative pressure ultrafiltration tank, the negative pressure nanofiltration tank and the negative pressure adsorption tank is provided with a membrane assembly, the membrane assembly in the negative pressure ultrafiltration tank is an ultrafiltration membrane assembly for intercepting particles in the lithium battery wastewater, the membrane assembly in the negative pressure nanofiltration tank is a nanofiltration membrane assembly for intercepting high-valence ions, and the membrane assembly in the negative pressure adsorption tank is a lithium ion selective permeation membrane assembly for capturing lithium ions, and the lithium ion selective permeation membrane assembly is a high polymer membrane grafted with 12-crown-4 ether.

2. The separation system for lithium battery wastewater according to claim 1, wherein the ultrafiltration membrane assembly is a polyether sulfone hollow fiber membrane; the nanofiltration membrane assembly is an inorganic ceramic membrane.

3. The separation system for lithium battery wastewater according to claim 1, wherein the pretreatment unit comprises a pH adjusting tank and a flocculation tank connected in sequence, and the pH adjusting tank is provided with a pH adjusting agent feeding port for receiving a pH adjusting agent; the flocculation tank is provided with a flocculant feeding port for receiving a flocculant.

4. The separation system for lithium battery wastewater according to claim 3, wherein a first buffer tank is connected in series between the flocculation tank and the negative pressure ultrafiltration tank, the inlet of the first buffer tank is communicated with the water phase outlet of the flocculation tank to receive and temporarily store the supernatant discharged from the flocculation tank, and the outlet of the first buffer tank is communicated with the inlet of the negative pressure ultrafiltration tank to supply the negative pressure ultrafiltration tank with a feed liquid.

5. The separation system for lithium battery wastewater according to claim 1, wherein a second buffer tank is arranged between the water phase outlet of the negative pressure adsorption tank, the negative pressure ultrafiltration tank and the negative pressure nanofiltration tank, and between the negative pressure nanofiltration tank and the negative pressure adsorption tank; the negative pressure vacuum pump is communicated with the second buffer tank to suck the gas in the second buffer tank and provide negative pressure driving for the corresponding negative pressure ultrafiltration tank, negative pressure nanofiltration tank and negative pressure adsorption tank upstream of the second buffer tank.

6. The separation system for lithium battery wastewater according to claim 1 or 2, wherein the surface of the membrane assembly is provided with fractal distributed microgrooves, and the fractal distribution shape of the microgrooves is one of a tree branch shape, a wave vortex shape or a net-like interconnected shape. The micro-groove has a depth of 50 microns, and a cross-section in one of a V-shape, a U-shape or a trapezoidal shape.

7. The separation system suitable for lithium battery wastewater according to claim 1, wherein, The separation system further comprises a backwashing device in communication with the negative pressure ultrafiltration tank, the negative pressure nanofiltration tank and the negative pressure adsorption tank respectively, to flush the membrane assembly in the tank.

8. The separation system suitable for lithium battery wastewater according to claim 7, wherein, The separation system further comprises an intelligent control unit, which comprises a controller, and a plurality of detection devices and a plurality of execution mechanisms connected to the controller respectively; The detection devices comprise a pH detector for detecting the pH value of the feed liquid, a turbidity detector for detecting the turbidity of the feed liquid, a conductivity detector for detecting the conductivity of the feed liquid, an inductively coupled plasma mass spectrometer for detecting the lithium ion concentration, and a transmembrane pressure difference monitoring device for detecting the transmembrane pressure difference of at least one of the membrane assemblies; The execution mechanisms comprise a pH adjuster input device, a flocculant input device and the backwashing device; The controller is configured to control the operation of the negative pressure vacuum pump and the execution mechanisms according to the signals of the detection devices.

9. A separation process for lithium battery wastewater using the separation system for lithium battery wastewater according to any one of claims 1 to 8, characterized by the steps of Comprising: Step one, pretreatment: adjusting the pH value of the lithium battery wastewater and flocculating and settling the wastewater after adjusting the pH value to obtain a supernatant; Step two, first-stage negative pressure ultrafiltration: negative pressure ultrafiltration of the supernatant under a pressure of -0.05 to -0.07 MPa using an ultrafiltration membrane assembly to retain particulate pollutants; Step three, second-stage negative pressure nanofiltration: negative pressure nanofiltration of the feed liquid obtained in the first-stage negative pressure ultrafiltration step under a pressure of -0.08 to -0.09 MPa using a nanofiltration membrane assembly to retain high-valence metal ions of two or more valences, to obtain a feed liquid rich in monovalent ions; Step four, third-stage negative pressure adsorption: negative pressure adsorption of the feed liquid rich in monovalent ions under a pressure of -0.09 to -0.095 MPa using a lithium ion-selective permeation membrane assembly to selectively permeate lithium ions and retain other monovalent ions, to finally obtain a lithium ion-rich liquid.

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