A method for preventing aluminum pollution from nanofiltration membranes used in lithium extraction from salt lakes

Abstract

The present application relates to water treatment agent and environmental pollution treatment material field, disclose a kind of salt lake lithium extraction nanofiltration membrane aluminum pollution prevention method, comprising: obtaining the real-time flow of salt lake lithium extraction concentrated water, aluminum ion concentration and initial pH value;Acid liquor is injected into water carrying liquid to produce dilution premix, by adjusting the ionic strength of the dilution premix to be lower than the ionic strength of concentrated water, using osmotic pressure gradient to drive hydrogen ion to penetrate steric barrier layer;The dilution premix is injected into inlet pipeline, so that hydrogen ion completes homogenization diffusion before entering nanofiltration membrane module entrance and contacting membrane active layer surface;Using proportional-integral-derivative algorithm to correct dosing flow, adjust injection pump frequency, maintain membrane entrance pH value between 0.5 and 2.5, the present application uses osmotic pressure surplus to assist proton penetration, solves mass transfer resistance under the environment of high concentration magnesium ion, by regulating aluminum ion to dissolve state and change membrane surface potential, realize in-situ active inhibition of aluminum pollution.

Description

Technical Field

[0001] This invention relates to a method for preventing aluminum pollution in nanofiltration membranes used for lithium extraction from salt lakes, belonging to the technical field of water treatment agents and environmental pollution treatment materials. Background Technology

[0002] Currently, nanofiltration membrane technology is the mainstream route for magnesium-lithium separation and lithium-ion enrichment. Its operational stability directly affects the recovery efficiency of lithium resources. However, in the front-end adsorption process, due to the dissolution of aluminum-based adsorbents, the output concentrate contains not only a high concentration of magnesium ions ranging from 7000ppm to 9000ppm, but also trace amounts of aluminum ions.

[0003] To maintain the continuous operation of a nanofiltration system, the aluminum ion concentration in the feed water must be controlled below 0.05 ppm. Existing technologies typically adjust the pH by adding acid to the main pipeline to inhibit aluminum adsorption and scaling on the membrane surface. However, in strong electrolyte systems with high magnesium ion backgrounds, intense hydration competition and steric hindrance exist between ions. When adjusting the acid is injected into this main phase fluid, protons face severe mass transfer resistance when crossing the interfacial charge layer, making it difficult for them to complete global homogeneous diffusion before contacting the nanofiltration membrane surface. While improvements in physical aspects such as pipeline mixing or static mixers enhance overall fluid uniformity, the control logic and surface mass transfer mechanism adjustment methods are insufficiently targeted. For example, Chinese invention patent application CN119351778A discloses a method for extracting lithium from salt lakes. The proposed method and extraction apparatus achieve deep lithium extraction through aluminum adsorption, multi-stage nanofiltration, reverse osmosis, and resin refining processes. The scheme involves alkali softening or multi-stage membrane separation to regulate ionic composition, which is based on the overall dosage adjustment of equilibrium theory. Simply increasing the dosage of reagents or setting up a static mixer often leads to uneven acidity distribution on the surface of the fluid cross-section. Locally high acidity accelerates the degradation of the polyamide membrane, while mononuclear hydroxyl complex adsorption of aluminum ions still occurs in proton-deficient areas. This heterogeneous reaction mechanism at the surface level makes it difficult for existing regulation methods to simultaneously maintain membrane flux and material durability under high-salt and complex operating conditions. Achieving precise proton mass transfer to the membrane interface under extremely high magnesium backgrounds and completing global aluminum contamination prevention without damaging the membrane structure is a core issue that urgently needs to be addressed in the field of lithium extraction water treatment in salt lakes.

[0004] Therefore, the technical problem to be solved by this invention is to precisely hedge against the risk of aluminum ion-induced scaling in complex electrolyte systems by controlling the mass transfer path of protons in high-salinity fluids. Summary of the Invention

[0005] To address the problems mentioned in the background art, the technical solution of the present invention is as follows: A method for preventing aluminum pollution from nanofiltration membranes used in lithium extraction from salt lakes, comprising: Step 101: Obtain real-time flow rate data, aluminum ion mass concentration data, and initial pH value of the lithium extraction concentrate from the salt lake at the inlet side of the nanofiltration system. The background mass concentration of magnesium ions in the lithium extraction concentrate from the salt lake is 7000 mg / L to 9000 mg / L. Step 102: Calculate the first acid dosage flow rate for suppressing the deposition of mononuclear aluminum hydroxide complexes based on real-time flow data and aluminum ion mass concentration data; Step 103: The acid solution is injected into the nanofiltration permeate carrier liquid to generate a diluted premixed solution. By adjusting the mass percentage concentration of the acid solution in the diluted premixed solution, the ionic strength of the diluted premixed solution is made lower than that of the lithium extraction concentrate from the salt lake. The osmotic pressure gradient is used to drive hydrogen ions to diffuse through the steric hindrance layer formed by high concentration of magnesium ions. Step 104: Inject the diluted premixed solution into the inlet pipe of the nanofiltration system so that hydrogen ions can complete radial homogenization diffusion before reaching the nanofiltration membrane surface, thereby eliminating local high acidity micro-regions and local low acidity micro-regions on the inlet flow channel cross section. Step 105: Real-time acquisition of the feedback pH value at the nanofiltration membrane inlet, calculation of the deviation between the feedback pH value and the preset target pH range, and correction of the first acid dosing flow rate based on the deviation using a proportional-integral-derivative algorithm to generate a control command to adjust the pump operating frequency. Step 106: In response to a control command, adjust the frequency of the acid injection pump to maintain the pH value at the nanofiltration membrane inlet between 0.5 and 2.5, thereby converting aluminum ions into a dissolved state. It also reduces the negative charge density on the surface of the nanofiltration membrane, thereby achieving in-situ suppression of aluminum contamination.

[0006] Preferably, step 103 specifically includes: step 1031: obtaining the permeate from the nanofiltration system as the carrier fluid for nanofiltration permeate; step 1032: adjusting the mass percentage concentration of the acid in the diluted premix to keep the ionic strength difference between the diluted premix and the lithium extraction concentrate from the salt lake within a preset threshold range; wherein, the pressure difference between the diluted premix at the injection point and the pressure difference between the fluid inside the inlet pipe is maintained between 0.1 MPa and 0.3 MPa, and the diffusion of hydrogen ions is assisted by the pressure difference.

[0007] Preferably, in step 101, the aluminum ion concentration in the lithium extraction concentrate from the salt lake is 0.5 mg / L to 2.5 mg / L; in step 102, calculating the first acid addition flow rate includes establishing a mapping relationship model between the aluminum ion mass concentration and the hydrogen ion equilibrium concentration, and determining the volume of hydrochloric acid required per unit time to reach the hydrogen ion equilibrium concentration based on real-time flow data.

[0008] Preferably, the method also includes step 107: real-time acquisition of operating pressure data and inter-segment pressure difference data of the nanofiltration system; when the fluctuation of the operating pressure within 24 hours exceeds 5%, the sampling frequency of the feedback pH value is increased; and the frequency adjustment accuracy of the acid injection pump is increased to compensate for the change in hydrogen ion diffusion rate caused by the flow rate variation.

[0009] Preferably, the membrane material of the nanofiltration membrane is modified polyamide or polypiperazine amide; by maintaining a pH value of 0.5 to 2.5, the interfacial potential of the nanofiltration membrane surface is regulated to weaken the electrostatic attraction of the nanofiltration membrane surface to aluminum ions and generate charge repulsion, thereby extending the continuous cleaning cycle of the nanofiltration system to more than 30 days.

[0010] Preferably, in step 104, the injection point of the diluted premix is ​​located in the turbulent zone near the inlet of the membrane module in the water inlet pipeline; by adjusting the flow rate of the nanofiltration permeate carrier fluid, the Reynolds number of the fluid in the water inlet pipeline is made higher than 4000 to eliminate radial concentration polarization.

[0011] Preferably, in step 105, the sampling frequency for real-time acquisition of the multi-parameter raw electrical signals generated by the online sensing terminal on the water inlet side is 100Hz to 500Hz to match the calculation cycle of the proportional-integral-differential algorithm, and the calculation cycle of the proportional-integral-differential algorithm is 5ms to 10ms, so as to ensure that the proton concentration on the surface of the nanofiltration membrane is above the aluminum ion hydrolysis equilibrium point in real time.

[0012] Preferably, the acid injection pump is a variable frequency metering pump; the control command includes a pulse width modulation signal for adjusting the stroke frequency of the variable frequency metering pump, so as to control the real-time dilution ratio of high-concentration hydrochloric acid in the nanofiltration permeate carrier liquid.

[0013] Preferably, the method further includes step 108: calibrating the pH sensor in step 101 and correcting the bias parameters in the mapping relationship model based on the zero-point drift of the sensor readings in order to maintain the chemical environment stability under the high-concentration saline system.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. In the prevention and control of aluminum fouling in nanofiltration membranes for lithium extraction from salt lakes, this invention achieves a technological evolution from overall acidity regulation to surface interface proton environment regulation through the synergistic effect of the acid addition control system and the acid-resistant nanofiltration membrane system. Since the concentrated lithium extract from salt lakes contains a high concentration of magnesium ions, these ions form a dense electrolyte hydration layer at the membrane interface, generating a steric hindrance effect and hindering the homogeneous diffusion of conventional protons. This invention calculates the hydrochloric acid dosing flow rate by collecting real-time aluminum ion mass concentration and combining it with the increase in hydrogen ion molar mass, enabling the injected protons to effectively penetrate the high-concentration magnesium ion blocking network. This regulation method avoids insufficient acidity in local areas of the membrane surface due to mass transfer obstruction, ensuring that aluminum ions are always in a highly soluble ionic state, thus eliminating the kinetic conditions for aluminum fouling layer accumulation on the membrane surface from a physicochemical perspective.

[0015] 2. By establishing a compensation coefficient based on aluminum ions The precise dosing logic constructs a dynamic repulsion mechanism targeting the charge properties of the membrane surface. Under specific acidic conditions, the aluminum ion's form changes from an easily adsorbed mononuclear hydroxyl complex to a more soluble form. Meanwhile, the negative charge density on the surface of the nanofiltration membrane made of modified polyamide or piperazine material decreases. This interfacial potential change caused by the acid addition control system weakens the electrostatic attraction between the membrane surface and aluminum ions. Through this charge repulsion, the present invention changes the prevention and control strategy from traditional post-deposition cleaning to in-situ active inhibition during operation, maintaining the long-term unobstructed flow of the nanofiltration membrane channel without adding an additional aluminum removal process.

[0016] 3. The combined feedforward control and feedback calibration adjustment mode resolves the balance between chemical environment stability and membrane material durability in complex high-salt systems. When handling extreme conditions with magnesium ion concentrations as high as 7000ppm to 9000ppm, the system calculates the hydrochloric acid dosing rate in real time and uses a proportional-integral-derivative algorithm to correct pH deviations, achieving millisecond-level response to influent acidity. This precise control ensures that the inlet pH of the membrane module is stably maintained within the target range of 0.5 to 2.5, avoiding the risk of magnesium hydroxide scaling caused by alkaline microenvironment and preventing chemical degradation of the membrane layer due to acidity fluctuations. This multi-mechanism synergistic stability regulation ensures that the nanofiltration system can maintain high operating pressure stability and a continuous operating cycle of more than 30 days even in extreme high-salt environments. Attached Figure Description

[0017] Figure 1 This is a flowchart of the closed-loop control system for aluminum pollution prevention and control of nanofiltration membranes used in lithium extraction from salt lakes, as described in this invention. Figure 2 This is a diagram of the core measurement and control logic and the homologous proton-mediated execution environment architecture of this invention.

[0018] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0020] A method for preventing aluminum pollution from nanofiltration membranes used in lithium extraction from salt lakes includes: Step 101: Obtain real-time flow rate data, aluminum ion mass concentration data, and initial pH value of the lithium extraction concentrate from the salt lake at the inlet side of the nanofiltration system. The background mass concentration of magnesium ions in the lithium extraction concentrate from the salt lake is 7000 mg / L to 9000 mg / L. Step 102: Calculate the first acid dosage flow rate for suppressing the deposition of mononuclear aluminum hydroxide complexes based on real-time flow data and aluminum ion mass concentration data; Step 103: The acid solution is injected into the nanofiltration permeate carrier liquid to generate a diluted premixed solution. By adjusting the mass percentage concentration of the acid solution in the diluted premixed solution, the ionic strength of the diluted premixed solution is made lower than that of the lithium extraction concentrate from the salt lake. The osmotic pressure gradient is used to drive hydrogen ions to diffuse through the steric hindrance layer formed by high concentration of magnesium ions. Step 104: Inject the diluted premixed solution into the inlet pipe of the nanofiltration system so that hydrogen ions can complete radial homogenization diffusion before reaching the nanofiltration membrane surface, thereby eliminating local high acidity micro-regions and local low acidity micro-regions on the inlet flow channel cross section. Step 105: Real-time acquisition of the feedback pH value at the nanofiltration membrane inlet, calculation of the deviation between the feedback pH value and the preset target pH range, and correction of the first acid dosing flow rate based on the deviation using a proportional-integral-derivative algorithm to generate a control command to adjust the pump operating frequency. Step 106: In response to a control command, adjust the frequency of the acid injection pump to maintain the pH value at the nanofiltration membrane inlet between 0.5 and 2.5, thereby converting aluminum ions into a dissolved state. It also reduces the negative charge density on the surface of the nanofiltration membrane, thereby achieving in-situ suppression of aluminum contamination.

[0021] Preferably, step 103 specifically includes: step 1031: obtaining the permeate from the nanofiltration system as the carrier fluid for nanofiltration permeate; step 1032: adjusting the mass percentage concentration of the acid in the diluted premix to keep the ionic strength difference between the diluted premix and the lithium extraction concentrate from the salt lake within a preset threshold range; wherein, the pressure difference between the diluted premix at the injection point and the pressure difference between the fluid inside the inlet pipe is maintained between 0.1 MPa and 0.3 MPa, and the diffusion of hydrogen ions is assisted by the pressure difference.

[0022] Preferably, in step 101, the aluminum ion concentration in the lithium extraction concentrate from the salt lake is 0.5 mg / L to 2.5 mg / L; in step 102, calculating the first acid addition flow rate includes establishing a mapping relationship model between the aluminum ion mass concentration and the hydrogen ion equilibrium concentration, and determining the volume of hydrochloric acid required per unit time to reach the hydrogen ion equilibrium concentration based on real-time flow data.

[0023] Preferably, the method also includes step 107: real-time acquisition of operating pressure data and inter-segment pressure difference data of the nanofiltration system; when the fluctuation of the operating pressure within 24 hours exceeds 5%, the sampling frequency of the feedback pH value is increased; and the frequency adjustment accuracy of the acid injection pump is increased to compensate for the change in hydrogen ion diffusion rate caused by the flow rate variation.

[0024] Preferably, the membrane material of the nanofiltration membrane is modified polyamide or polypiperazine amide; by maintaining a pH value of 0.5 to 2.5, the interfacial potential of the nanofiltration membrane surface is regulated to weaken the electrostatic attraction of the nanofiltration membrane surface to aluminum ions and generate charge repulsion, thereby extending the continuous cleaning cycle of the nanofiltration system to more than 30 days.

[0025] Preferably, in step 104, the injection point of the diluted premix is ​​located in the turbulent zone near the inlet of the membrane module in the water inlet pipeline; by adjusting the flow rate of the nanofiltration permeate carrier fluid, the Reynolds number of the fluid in the water inlet pipeline is made higher than 4000 to eliminate radial concentration polarization.

[0026] Preferably, in step 105, the sampling frequency for real-time acquisition of the multi-parameter raw electrical signals generated by the online sensing terminal on the water inlet side is 100Hz to 500Hz to match the calculation cycle of the proportional-integral-differential algorithm, and the calculation cycle of the proportional-integral-differential algorithm is 5ms to 10ms, so as to ensure that the proton concentration on the surface of the nanofiltration membrane is above the aluminum ion hydrolysis equilibrium point in real time.

[0027] Preferably, the acid injection pump is a variable frequency metering pump; the control command includes a pulse width modulation signal for adjusting the stroke frequency of the variable frequency metering pump, so as to control the real-time dilution ratio of high-concentration hydrochloric acid in the nanofiltration permeate carrier liquid.

[0028] Preferably, the method further includes step 108: calibrating the pH sensor in step 101 and correcting the bias parameters in the mapping relationship model based on the zero-point drift of the sensor readings in order to maintain the chemical environment stability under the high-concentration saline system.

[0029] Example 1: In an industrial lithium extraction line from a salt lake, concentrated wastewater is discharged during the adsorption and desorption process using aluminum-based adsorbents. The initial concentration of this wastewater... The value was 4.8, with a background magnesium ion concentration of 8500 mg / L, a lithium ion concentration of 42 mg / L, and an aluminum ion concentration of... The concentration was 2.2 mg / L. Because aluminum ions in the feed solution existed as mononuclear hydroxyl complexes, they were adsorbed and accumulated on the surface of the modified polyamide membrane in the acid-resistant nanofiltration membrane module due to the attraction of negative charges, leading to a 30% increase in operating pressure within 48 hours. To address the mass transfer hindrance caused by hydration competition and steric hindrance effects resulting from high-concentration magnesium ions, the acid control system adopted a homogeneous proton homogenization injection procedure. A reflux branch was drawn from the permeate side of the acid-resistant nanofiltration membrane system, and a portion of the nanofiltration permeate was intercepted as a mediator according to a preset reflux ratio. The magnesium ion rejection rate of the permeate was greater than or equal to 98%, and the permeate was a weakly acidic water with low ionic strength. A diluted premix is ​​generated by mixing the acid solution injected into the nanofiltration permeate carrier fluid. The mass percentage concentration of the acid solution in the diluted premix is ​​adjusted so that the ionic strength of the diluted premix is ​​lower than that of the lithium concentrate from the salt lake. In the premix chamber with a static mixing structure, the acid solution is mixed in a closed gas-liquid environment with the intercepted mediator. This allows the acid solution to undergo primary dissociation in the low-salt mediator, forming a homologous proton carrier fluid with density and dynamic viscosity parameters close to the main phase of the concentrate to be treated. Then, this homologous proton carrier fluid is injected in parallel at multiple points through multiple microporous injection heads distributed on the cross-section of the main pipe into the connection pipe between the concentrate tank and the acid-resistant nanofiltration membrane system.

[0030] The auxiliary design module configured within the control unit synchronously generates an acid addition timing blueprint based on a multi-level manifold grid projection. This blueprint maps the physical flow channel geometry parameters of the acid-resistant nanofiltration membrane module into a two-dimensional topological grid matrix composed of M×N data nodes. Real-time influent flow rate data, influent aluminum ion mass concentration data, and magnesium ion mass concentration data are injected as inlet boundary vectors into the outermost nodes of the two-dimensional topological grid matrix. Based on a pre-set decoupling logic for convective electromigration characteristics, the module calculates the local proton consumption rate and corresponding active electrostatic attraction potential of each node within the grid layer by layer. The local active electrostatic attraction potential value The calculation logic uses formulas ,in, This represents the local active electrostatic attraction potential. and The magnesium and aluminum concentration characteristic components projected onto the current grid node are respectively represented in mg / L. and Based on the pre-defined mapping weights of the hydrated ion radius, To determine the concentration polarization attenuation operator based on the topological position of the grid depth, the physical geometry of the acid-resistant nanofiltration membrane module needs to be discretized and mapped before generating the acid addition time-series blueprint. Within this computational architecture, the system calculates the local proton consumption rate for a specific grid node based on the joint construction of the lateral shear velocity of the boundary layer solution at that node and the real-time aluminum precursor concentration gradient. By extracting the reaction source term of the surface advection diffusion equation at the corresponding node and multiplying it by the three-dimensional micro-element volume under the jurisdiction of that node, the actual net proton consumption mass rate within the current micro-range is obtained through real-time numerical integration. The number of horizontal nodes M in the two-dimensional topological grid matrix is ​​taken as the membrane unfolding length divided by the span of a single strand of the influent baffle mesh, and the number of vertical nodes N is taken as the effective width of the flow channel divided by the spacing between the cross points of the baffle mesh flow channel. For the calculation formula of the local active electrostatic attraction potential, the system's internal logic presets the reference concentration as the denominator to construct a dimensionless calculation, set to 1 mg / L. The specific calculation formula of the local active electrostatic attraction potential is transformed into Specifically, concentration polarization attenuation operator The spatial attenuation coefficient is related by an exponential function. =1+α·exp(β·x) is determined, where x is the dimensionless depth coordinate of the grid node along the longitudinal direction of the flow channel, and α and β are empirical constants pre-calibrated based on the current surface hydraulic roughness of the nanofiltration membrane. The system accurately maps the two-dimensional topological position to the amplification factor of the mass transfer resistance of the interface micro-region through the analytical equation determined above.

[0031] Based on the generated barrier feature surface, the extreme regions of potential heavily polluted accumulation zones within the surface are identified. A nonlinear acid addition flow rate regulation sequence blueprint is generated in reverse along the time axis. When the barrier feature of the deep grid nodes in the flow channel is determined to cross the critical adsorption threshold, the corresponding flow rate peak command is pre-configured in the regulation sequence blueprint to drive the acid addition device to implement discrete frequency conversion dosing. This utilizes nonlinear time phase shift to counteract the charge repulsion microenvironment evolving within the membrane channel. Simultaneously, the control unit adjusts the flow rate based on the real-time aluminum ion mass concentration. Adjusting hydrochloric acid dosing flow rate based on data feedback Hydrochloric acid dosing flow rate The calculation is based on the formula. ,in, The flow rate for hydrochloric acid dosing. This refers to the concentrate influent flow rate. To divert a unit volume of concentrated water from the initial... The increase in the molar amount of hydrogen ions required to reduce to the target value This is the aluminum ion compensation coefficient. The mass concentration of aluminum ions in the influent. The molar concentration of hydrochloric acid is ultimately determined by the inlet of the acid-resistant nanofiltration membrane. The value remains stable between 0.5 and 2.5, causing aluminum ions to convert into a dissolved state. It also reduces the negative charge density on the surface of the acid-resistant nanofiltration membrane, inhibiting aluminum contamination. The acid-resistant nanofiltration membrane system remained stable during continuous operation and monitoring for 720 hours. The rejection rate of magnesium ions by the acid-resistant nanofiltration membrane module remained stable at 98.5%, and the rejection rate of lithium ions remained at 12.4%. The inlet and outlet pressure difference remained stable, and the continuous operation cycle of the nanofiltration membrane module reached 30 days. The specific calculation logic of the nonlinear time phase shift is as follows: the control unit extracts the hydraulic geometric pipe length of the target heavily contaminated grid node from the acid injection point in real time, divides it by the turbulent translation rate of the pipe section obtained by dynamic calculation through Reynolds number, obtains the basic fluid transmission delay time, and then subtracts the system valve opening and closing response time and the circuit conduction fixed hysteresis constant from this delay time. The finally obtained phase shift is used to trigger the peak dosing command of the reagent in advance on the time axis, thereby ensuring that the physical proton wave peak spatially coincides with the local charge peak within the time window when it arrives at the deep grid node.

[0032] In the specific operation of this invention, the preferred acid solution is commercially available industrial-grade hydrochloric acid with a mass percentage concentration of 31%. It is clearly stated that the nanofiltration permeate carrier fluid is directly taken from the permeate side reflux of the acid-resistant nanofiltration membrane system. This co-source mediated design is one of the core technical solutions of this invention. Regarding the innovative necessity of the premixing process, in a strong electrolyte system with a high concentration of magnesium ions (7000 mg / L to 9000 mg / L), magnesium ions have extremely strong hydration energy and will form a dense electrolyte hydration layer at the membrane interface. If, according to conventional engineering practices, the 31% high-concentration hydrochloric acid stock solution is directly added to the pipeline mixer, due to the huge chemical potential gradient and interfacial tension between the acid solution and the high-salt concentrated water, protons are easily locked in local areas by the high concentration of hydrated magnesium ions at the microscopic level, resulting in extremely uneven acidity distribution in the radial cross-section of the fluid. This invention… The premixing step is not because hydrogen ions are difficult to pass through the membrane pores (hydrogen ions themselves have extremely high membrane permeability), but rather to optimize the kinetic distribution of protons before they enter the membrane module. By first mixing the acid solution with nanofiltration permeate with low ionic strength to produce a diluted premix, the ionic strength of which is significantly lower than that of the concentrate phase, when this premix is ​​injected into the feed water pipeline, the artificially constructed osmotic pressure gradient serves as an auxiliary driving force to break through the steric hindrance layer and hydration resistance constructed by high-concentration magnesium ions. Essentially, it utilizes the permeation and diffusion characteristics of the low-salt carrier to achieve millisecond-level radial homogenization distribution with hydrogen ions, thereby eliminating micro-regions of local high acidity that could damage the membrane or local low acidity that could prevent aluminum ion scaling. This shift from overall dosage adjustment to precise interfacial mass transfer control is precisely the technological advancement of this solution compared to directly adding the active ingredient through the pipeline.

[0033] Example 2: This example establishes a pilot-scale acid-resistant nanofiltration verification platform for lithium extraction from salt lakes, including a spiral-wound polyamide nanofiltration membrane module with an effective membrane area of ​​7.9 square meters and equipped with an online... The test water supply for the main inlet pipeline of the high-frequency electromagnetic flowmeter was taken from the actual discharge of the lithium extraction adsorption and desorption process in a salt lake on the Qinghai-Tibet Plateau. Initially, the magnesium ion concentration was maintained between 8420 mg / L and 8580 mg / L. The coefficient of performance was set at 4.8. To address the mass transfer hindrance caused by hydration competition and steric hindrance due to high magnesium ion concentrations, a periodic sinusoidal flow rate fluctuation with a frequency of 0.1 Hz and an amplitude of 15% of the nominal flow rate was introduced at the water supply end. Simultaneously, a sudden change in aluminum ion concentration with a peak value of 3.8 mg / L was introduced every 12 hours to construct a dynamic testing environment. The aluminum ion compensation coefficient was set at 4.8. The value of this coefficient is determined based on the nonlinear mapping relationship between the coordination thermodynamic state of aluminum ions and the steric hindrance of magnesium ions. This coefficient is used to balance the acid consumption and the solubility of mononuclear hydroxyl complexes on the membrane surface. The system obtains the real-time magnesium-aluminum mass concentration ratio. When this ratio is detected to be lower than the baseline critical point of 3000, a compensation coefficient is set. The lower limit for this value is 1.5 mol / mg; when this ratio is higher than the reference critical point, the compensation coefficient increases linearly. When executing this incremental action, the system calculates in real time the difference between the current ratio and the critical point of 3000, and directly multiplies this difference by a pre-built proportional evolution slope. This evolution slope is calibrated to a constant of 0.0019 mol / mg in a real high-magnesium brine titration experiment. The product of the two is accumulated and added to the lower limit parameter of 1.5 mol / mg to generate a transient dynamic compensation function with continuous derivatives to output the real-time k value. Under the conditions set in this experiment, with a magnesium background mass concentration of 8500 mg / L and a normal aluminum ion mass concentration of 2.2 mg / L, the aluminum ion compensation coefficient is calculated. The value is 3.2 mol / mg. It's important to note that this compensation coefficient significantly exceeds the theoretical stoichiometric ratio for surface stoichiometry in conventional aluminic acid-base neutralization. The objective physical basis for this is that the extremely high magnesium background environment of the salt lake system possesses enormous proton competition and consumption potential energy. This, coupled with over 99% advection scouring and escape effects within the high-speed flow channel of the membrane module, leads to a geometrical decrease in the effective proton flux at the injection interface. Essentially, this coefficient is a comprehensive system dynamics compensation multiplier factor encompassing the overall advection shear dissipation rate and the surface hydration competition quenching rate. The reserved excess proton base is specifically used for parasitic consumption before physical landfilling, ensuring that the number of residual protons that ultimately leak into the bottom of the boundary layer is just enough to maintain the phase transition equilibrium point of aluminum ions. Based on the above settings, a multi-dimensional control system was constructed, with the first control group using conventional acid direct injection into the main pipeline. The target was set... The second control group consisted of 0.3 and 2.8, respectively; the sample group of the present invention was set up using the homology-mediated proton homogenization injection procedure, and a problem intensity gradient system was established for the sample group of the present invention, with three gradient levels of aluminum ion background mass concentrations of 1.2 mg / L, 2.3 mg / L and 3.4 mg / L.

[0034] The control unit receives real-time flow fluctuation disturbance data and concentration mutation signals, and injects the corresponding aluminum ion mass concentration and magnesium ion mass concentration data into the outer nodes of a two-dimensional topological mesh matrix composed of M×N data nodes, according to the formula... Calculate the active electrostatic attraction potential Under the perturbation condition of introducing a step abrupt change in aluminum ion concentration to 3.8 mg / L, the active electrostatic attraction potential of the deep mesh nodes in the flow channel is... Within 2.4 seconds, the potential value increased from the normal 14.2 to 28.7, exceeding the adsorption threshold of 25.0. The control unit extracted this potential value data and substituted it into the formula. The system generates an acid dosing command, and the acid dosing device responds to the control command by outputting the corresponding flow rate. This allows the acid to mix with the nanofiltration permeate with a preset reflux ratio of 5% in a static premixing chamber with cross-flow baffles, generating a homologous proton carrier fluid with an ionic strength lower than that of the concentrated water. This homologous proton carrier fluid is then injected into the main inlet pipe in parallel through a multi-point microporous injection head.

[0035] After 168 hours of continuous system operation, status parameters were collected. In the first control group, an irregular aluminum hydroxyl deposit appeared on the nanofiltration membrane surface, and the operating pressure increased from the initial 4.1 MPa to 4.4 MPa. This verified that direct injection of acid into the main pipeline without a homologous carrier would cause interfacial tension and proton diffusion lag, resulting in insufficient acidity in local micro-regions of the fluid cross-section. The second control group exhibited a nonlinear performance inflection point, when the target... When the value is set to 0.3, the nanofiltration membrane desalination layer undergoes chemical degradation, and the magnesium ion rejection rate decreases from 98.2% to 81.4%; when the target... When the pH was set to 2.8, the operating pressure rose to 4.53 MPa within 48 hours, verifying that 0.5 to 2.5 was the working window for maintaining the dissolution state of mononuclear hydroxyl complexes and the stability of the membrane structure. Under three aluminum ion gradient levels of 1.2 mg / L, 2.3 mg / L, and 3.4 mg / L, the operating pressure of the sample group of this invention was stable at 4.21 MPa, 4.22 MPa, and 4.23 MPa, respectively, and the magnesium ion rejection rate was maintained at 98.4%, 98.3%, and 98.1%. The gradient data confirmed that the acid addition timing control based on multi-level manifold grid projection and the homologous mediated mixing mechanism produced synergistic effects. The diluted premixed solution used the osmotic pressure gradient to drive hydrogen ions to penetrate the spatial steric hindrance layer constructed by high-concentration magnesium ions and complete radial diffusion before contacting the nanofiltration membrane surface. The dynamic flow rate adjustment action offset the dual disturbances of flow rate and concentration, confining the microenvironment at the nanofiltration membrane inlet within the acidity window, relieving the mass transfer hindrance caused by the deposition of mononuclear hydroxyl complexes, and maintaining the hydraulic stability of the membrane module.

[0036] Example 3: This example combines Figures 1 to 2 This document describes a method for preventing aluminum pollution from nanofiltration membranes used in lithium extraction from salt lakes. Figure 1 As shown, the aluminum fouling prevention system for lithium extraction from salt lakes using nanofiltration membranes includes a concentrate tank for supplying the feed solution to be treated. An acid addition node is installed on the inlet pipe between the concentrate tank and the acid-resistant nanofiltration membrane system to add hydrochloric acid to adjust the pH value. The fluid treated by the membrane module enters the acid addition control system for real-time monitoring. The system generates control signals based on the feedback chemical parameters and sends them back to the acid addition node to achieve closed-loop precision control of the acid addition amount.

[0037] like Figure 2As shown, the inlet-side online sensing terminal captures operating parameters in real time through a built-in online pH meter, high-frequency electromagnetic flow meter, and temperature sensor, generating a data stream with a sampling frequency of 100Hz to 500Hz. This data stream is transmitted to the core measurement and control unit cluster, which uses two-dimensional topological grid matrix logic to spatially model the membrane flow channel. Combining proportional-integral-derivative control algorithms and mapping relationship models, it calculates the precise acid replenishment value and outputs a pulse width modulation signal command. In the same proton-mediated execution environment, the variable frequency metering pump responds to the above command by injecting high-concentration acid solution into the nanofiltration permeate carrier liquid return branch, which then enters a three-stage system equipped with a static premixing chamber. The proton carrier fluid is fully premixed within the cross-flow baffle device, and the resulting homogeneous proton carrier fluid is injected in parallel into the nanofiltration lithium production environment. Protons are evenly distributed through multi-point microporous injection heads arranged in the turbulent region, eliminating radial concentration polarization on the polyamide surface of the acid-resistant nanofiltration membrane module. This suppresses aluminum ion adsorption and fouling at the surface interface. To ensure that the discrete pulse signal injected at the front end is not smoothed out by the overall transport of the main fluid, the multi-point microporous injection head array is physically positioned extremely close to the membrane module inlet using an ultra-short-pitch surface-fitting method. Simultaneously, by adjusting the pump frequency, the physical oscillation frequency of the microporous nozzle jet is directly locked and coupled into the membrane mesh. The inherent Karman vortex street shedding frequency ensures that the injected high-concentration acid is intact, cut and encapsulated within independent, non-dispersed turbulent micro-vortices. These proton clusters, resembling miniature physical capsules, directly penetrate the overall liquid phase, rushing downstream to specific grid nodes before colliding and rupturing to release peak acidity. This cross-scale signal transmission link between the dosing and reaction ends is established. For data acquisition and control command issuance in the acid addition control system, the core measurement and control unit cluster employs a cascaded dual-loop control architecture to perform proportional-integral-differential operations. The inner loop is configured as a flow field feedforward control loop, using a high-frequency electromagnetic flowmeter sampling at a frequency from 100Hz to 500Hz. The system continuously captures fluid dynamic fluctuations within the inlet pipeline and outputs a reference pulse stroke signal to the variable frequency metering pump. The outer loop is configured as a chemical parameter feedback compensation loop. The online sensing terminal on the inlet side includes an online pH meter equipped with a solid-state microfluidic ion-sensitive probe. The front end is fixedly inserted into the turbulent core area of ​​the main inlet pipeline section. The outer loop collects the feedback pH value from the nanofiltration membrane inlet at a sampling frequency of 1Hz to 5Hz. The main control module generates a threshold bias parameter based on the deviation between the feedback pH value and the preset target pH range. It periodically superimposes and corrects the reference pulse stroke signal of the inner loop flow field feedforward control loop, thus completing the decoupling of fluid dynamic transient compensation and chemical interface steady-state response physical control.

[0038] In the interface control process of this invention, by maintaining the inlet pH value of the nanofiltration membrane between 0.5 and 2.5, precise intervention in the charge state of the membrane surface is achieved. Since the modified polyamide or piperazine amide membrane is negatively charged under normal operating conditions, it easily attracts positively charged aluminum components electrostatically, leading to fouling deposition. This solution reduces the negative charge density on the membrane surface through protonation, firstly weakening the electrostatic attraction between the membrane surface and aluminum ions; as the interface potential shifts to the positive direction, the electrostatic attraction between the membrane surface and aluminum ions is reduced. An electrostatic repulsion effect is formed between them. This dynamic potential transition mechanism, which first weakens attraction and then establishes repulsion, blocks the adsorption path of aluminum contaminants on the membrane surface from a dynamic perspective, thereby significantly extending the continuous cleaning cycle of the system to more than 30 days.

[0039] Example 4: In the continuous operation of lithium extraction nanofiltration membranes in salt lakes, high concentrations of magnesium ions induce local concentration polarization in the flow channel. Objectively, it is necessary to adjust the acid solution to reach a preset ion strength attenuation state before injection into the main pipeline, while simultaneously suppressing the dynamic response of the acid pump. The water pollution control agent dosing system includes a premixing chamber, which is equipped with three levels of staggered cross-flow baffles. Nanofiltration permeate and conditioning acid are mixed in the premixing chamber. The measurement and control unit calculates the fluid Reynolds number in real time based on the equivalent pipe diameter and mixing velocity. When the fluid Reynolds number When the concentration is greater than or equal to 4000, the control unit determines that the mixed fluid is in a turbulent state. In engineering fluid mechanics, when the main channel crosses this turbulence threshold, the cross-sectional shear force excites dense, high-frequency turbulent micro-vortices. According to the fluid phase interface renewal theory, these active normal micro-vortices can continuously and uninterruptedly invade the membrane surface, like a physical scraper, continuously peeling away and disintegrating the surface static water retention layer attached to the membrane, compressing the mass transfer resistance layer thickness to the ultimate physical boundary. Thus, by relying on high-intensity forced hydraulic tumbling, the static water accumulation microenvironment required for concentration polarization is destroyed at its source. An online conductivity meter measures the conductivity of the diluted premix in real time to characterize its ionic strength. The main control module adjusts the reflux ratio of the nanofiltration permeate based on this conductivity value, thus reducing the concentration of the diluted premix... The conductivity is maintained between 15% and 20% of that of the lithium concentrate from the brine lake. The set conductivity difference creates an osmotic pressure gradient that diffuses towards the concentrate side, driving hydrogen ions in the diluted premix to penetrate the steric hindrance layer constructed by magnesium ions and reach the surface of the modified polyamide membrane within 0.5 seconds after injection into the main pipeline. When the diluted premix is ​​injected into the nanofiltration system's inlet pipeline, the microporous injection heads are evenly distributed in an array on the radial section of the main pipeline. The mixture is sprayed out in parallel from multiple points through the microporous injection heads. The hydrogen ions carried rely on the turbulent shear state of the fluid in the inlet pipeline with a Reynolds number greater than 4000, and penetrate the hydrated steric hindrance layer constructed by the high concentration of magnesium ions along the direction of the set osmotic pressure potential energy difference, reaching the surface of the modified polyamide membrane to participate in the aluminum ion state transformation. The online detector at the nanofiltration membrane inlet collects feedback at a sampling frequency of 1Hz. The main control unit calculates the feedback value. The acidity deviation between the value and the preset target value of 1.5 .

[0040] The main control unit executes the proportional-integral-derivative (PID) control algorithm and uses the critical proportional gain method to calibrate the various control parameters of the algorithm offline. Under closed-loop control, the system gradually increases the proportional gain until the control command output produces a continuous oscillation with constant amplitude. The main control unit records the critical proportional gain at this point. With equal amplitude oscillation period The main control unit sets the target control parameters based on the calibration record, specifically setting the proportional gain. Critical proportional gain The product of this and the constant 0.6 is used to set the integration time constant. The period of constant amplitude oscillation The product of this and the constant 0.5 is used to define the differential time constant. The period of constant amplitude oscillation The product of the constant 0.12, where, For the target proportional gain, The integral time constant is... As the differential time constant, the main control unit will collect the acidity deviation in real time. After input parameter calibration, the proportional-integral-derivative (PID) control algorithm calculates and obtains the correction parameter, and outputs a frequency duty cycle control signal corresponding to the correction parameter to the acid injection pump. Under the objective disturbance of a step change in the mass concentration of aluminum ions in the influent, the water pollution control agent dosing system limits the pH fluctuation of the nanofiltration membrane inlet to a value range of 0.1, and maintains the physical deposition rate of mononuclear aluminum hydroxyl complexes below the adhesion critical value on the nanofiltration membrane surface, ensuring the physical permeability of the membrane channel cross section. When the water pollution control agent dosing system is in the initial commissioning stage, the control unit executes the critical adsorption characteristic extraction procedure. The test base creates a step-decreasing pH gradient environment at the nanofiltration membrane inlet. The detector arranged on the permeate side of the acid-resistant nanofiltration membrane module monitors the breakthrough mass concentration curve of aluminum ions, and the calibration module records the instantaneous local active electrostatic attraction potential value when the aluminum ion mass concentration crosses 0.05 mg / L. The control unit stores the instantaneous potential value as the benchmark critical adsorption threshold in the static lookup table of the memory, thus establishing a physical basis for determining the charge properties of a specific membrane material.

[0041] Further clarification reveals that in highly turbulent pipes with Re>4000, fluid dynamic fluctuations are often accompanied by nonlinear noise with frequencies between 50Hz and 150Hz. To ensure that the proportional-integral-derivative (PID) algorithm can output stable pulse width modulation (PWM) signal commands within microsecond periods of 5ms to 10ms, the system must oversample the original analog signal from the sensor front end at frequencies between 100Hz and 500Hz. This high-frequency sampling, combined with the built-in digital filtering operator, can effectively eliminate electromagnetic interference caused by high-concentration magnesium ion background and instantaneous reading jumps caused by fluid cavitation. This logic chain of high-frequency acquisition, fast computation, and real-time correction ensures that when aluminum ion concentration undergoes a step change, the proton concentration on the nanofiltration membrane surface can always respond in milliseconds and remain above the hydrolysis equilibrium point, thereby eliminating the kinetic cause of aluminum contamination deposition.

[0042] Example 5: In a working condition where the physical flow channel of the acid-resistant nanofiltration membrane module has deviations in length and inner diameter and fluctuating influent characteristics, the control unit measures offline parameters before formally injecting the diluted premixed solution. A 1.0L sample of lithium-extracted concentrate from a salt lake is extracted from the test base and injected into the electrophoretic migration observation chamber. An electric field of 100V / m is applied to both ends of the electrophoretic migration observation chamber. A high-frequency electromagnetic flowmeter and a laser Doppler velocimeter are used to collect the directional migration rate of magnesium ions and mononuclear aluminum hydroxyl complexes under the influence of the electric field. The control unit receives the directional migration rate data, calculates the effective charge density of the corresponding ions based on the fluid resistance balance relationship, extracts the ratio of the effective charge density of magnesium ions to that of aluminum ions, and inputs it into the weight allocation matrix. The mapping weight of the corresponding magnesium ions is obtained through normalization calculation. Mapping weights with corresponding aluminum ions The control unit will acquire the mapping weights and Loading local active electrostatic attraction potential The calculation formula reduces the calculation error of polarization potential feature separation.

[0043] The control unit establishes an initial two-dimensional topological grid matrix based on the acquired physical dimensional parameters of the acid-resistant nanofiltration membrane module. The water pollution control agent dosing system injects test fluid containing a tracer concentration of 10 mg / L into the flow channel. A conductivity probe array arranged along the flow channel collects tracer concentration signals at the nodes. The control unit analyzes this tracer concentration signal to obtain the actual spatial concentration distribution curve, calculates the topological position deviation between the actual spatial concentration distribution curve and the theoretical value of the corresponding node in the initial two-dimensional topological grid matrix, and corrects the concentration polarization attenuation operator based on the topological position deviation. The spatial attenuation coefficient, the control unit will use the corrected concentration polarization attenuation operator Updated to the corresponding nodes of the two-dimensional topological mesh matrix, the system uses the corrected two-dimensional topological mesh matrix to calculate the acid addition timing blueprint, outputs control signals to adjust the discrete addition action of the acid addition device, and adjusts the acid inlet of the acid-resistant nanofiltration membrane. The value was controlled within the range of 0.5 to 2.5, maintaining the match between the dynamic control parameters and the physical channel structure.

[0044] When faced with the operating condition of fluctuating dynamic viscosity of influent concentrate due to diurnal temperature variations on the Qinghai-Tibet Plateau, the control unit introduces a temperature compensation operator to correct the aluminum ion compensation coefficient. The system uses temperature sensors installed in the main inlet pipeline to collect real-time temperature data. The calibration module generates a first-order linear compensation function based on the measured data of hydrogen ion diffusion rate at different temperatures. When the inlet water temperature is detected to be below 10 degrees Celsius, the main control unit calculates the coefficient increment based on the first-order linear compensation function and applies it to the aluminum ion compensation coefficient. The acid injection pump response was adjusted to increase the acid injection flow rate by adjusting the control signal after correction. The increased proton chemical potential gradient was used to offset the increase in diffusion resistance caused by low temperature, thus ensuring the timeliness of hydrogen ion penetration through the steric hindrance layer under extreme cold conditions.

[0045] Example 6: In a lithium extraction production line from a salt lake containing a high concentration of magnesium ions, the water pollution control agent dosing system completes the sensor reference calibration procedure before initiating the acid addition operation. The standard buffer solutions with values ​​of 4.01 and 7.00, respectively, were used for online inlet water treatment. Two-point linear calibration was carried out. The control unit recorded the response potential of the sensor and calculated the slope of the calibration curve to ensure that the measurement error was within the range of 0.02. The system set the sampling frequency of the online detector to 2Hz to match the data acquisition cycle with the time step of the fluid in the inlet pipe, thus establishing a stable data input source for the proportional-integral-derivative control algorithm.

[0046] When the system encounters a new batch of acid-resistant nanofiltration membrane modules, a mixing efficiency calibration process for the premixing chamber is initiated. The system injects deionized water and hydrochloric acid with a mass percentage concentration of 31% at both the minimum and maximum rated flow rates. The pressure drop across the premixing chamber is measured using a differential pressure transmitter with an accuracy of 0.5 kPa. The main control unit, based on the measured pressure drop Calculate the mixing intensity factor By controlling the mixing energy dissipation rate within the range of 0.5 W / kg to 1.2 W / kg, this procedure achieves the matching of the physical structure parameters of the premixing cavity with the spatial coordinates of the flow field nodes in the two-dimensional topological grid matrix, and suppresses the generation of local high acidity micro-regions induced by insufficient mixing intensity.

[0047] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preventing aluminum pollution from nanofiltration membranes used in lithium extraction from salt lakes, characterized in that, include: Step 101: Obtain real-time flow rate data, aluminum ion mass concentration data, and initial pH value of the lithium extraction concentrate from the salt lake at the inlet side of the nanofiltration system. The background mass concentration of magnesium ions in the lithium extraction concentrate from the salt lake is 7000 mg / L to 9000 mg / L. Step 102: Calculate the first acid dosage flow rate for suppressing the deposition of mononuclear aluminum hydroxide complexes based on real-time flow data and aluminum ion mass concentration data; Step 103: The acid solution is injected into the nanofiltration permeate carrier liquid to generate a diluted premixed solution. By adjusting the mass percentage concentration of the acid solution in the diluted premixed solution, the ionic strength of the diluted premixed solution is made lower than that of the lithium extraction concentrate from the salt lake. The osmotic pressure gradient is used to drive hydrogen ions to diffuse through the steric hindrance layer formed by high concentration of magnesium ions. Step 104: Inject the diluted premixed solution into the inlet pipe of the nanofiltration system so that hydrogen ions can complete radial homogenization diffusion before reaching the nanofiltration membrane surface, thereby eliminating local high acidity micro-regions and local low acidity micro-regions on the inlet flow channel cross section. Step 105: Real-time acquisition of the feedback pH value at the nanofiltration membrane inlet, calculation of the deviation between the feedback pH value and the preset target pH range, and correction of the first acid dosing flow rate based on the deviation using a proportional-integral-derivative algorithm to generate a control command to adjust the pump operating frequency. Step 106: In response to a control command, adjust the frequency of the acid injection pump to maintain the pH value at the nanofiltration membrane inlet between 0.5 and 2.5, thereby converting aluminum ions into a dissolved state. It also reduces the negative charge density on the surface of the nanofiltration membrane, thereby achieving in-situ suppression of aluminum contamination.

2. The method for preventing aluminum pollution from nanofiltration membranes used in lithium extraction from salt lakes according to claim 1, characterized in that, Step 103 specifically includes: Step 1031: Obtain the permeate from the nanofiltration system as the carrier fluid for nanofiltration permeate; Step 1032: Adjust the mass percentage concentration of acid in the diluted premix to keep the ionic strength difference between the diluted premix and the lithium extraction concentrate from the salt lake within a preset threshold range; wherein, the pressure difference between the diluted premix at the injection point and the pressure difference between the fluid inside the inlet pipe is maintained between 0.1 MPa and 0.3 MPa, and the diffusion of hydrogen ions is assisted by the pressure difference.

3. The method for preventing aluminum pollution from nanofiltration membranes used in lithium extraction from salt lakes according to claim 1, characterized in that, In step 101, the aluminum ion concentration in the lithium extraction concentrate from the salt lake is 0.5 mg / L to 2.5 mg / L; in step 102, the calculation of the first acid addition flow rate includes establishing a mapping relationship model between the aluminum ion mass concentration and the hydrogen ion equilibrium concentration, and determining the volume of hydrochloric acid required per unit time to reach the hydrogen ion equilibrium concentration based on real-time flow data.

4. The method for preventing aluminum pollution from nanofiltration membranes used in lithium extraction from salt lakes according to claim 1, characterized in that, It also includes step 107: real-time acquisition of operating pressure data and inter-segment pressure difference data of the nanofiltration system. When the fluctuation of the operating pressure within 24 hours exceeds 5%, the sampling frequency of the feedback pH value is increased, and the frequency adjustment accuracy of the acid injection pump is increased to compensate for the change in hydrogen ion diffusion rate caused by the flow rate variation.

5. The method for preventing aluminum pollution from nanofiltration membranes used in lithium extraction from salt lakes according to claim 1, characterized in that, The membrane material of the nanofiltration membrane is modified polyamide or polypiperazine amide; by maintaining a pH value of 0.5 to 2.5, the interfacial potential of the nanofiltration membrane surface is regulated to weaken the electrostatic attraction of the nanofiltration membrane surface to aluminum ions and generate charge repulsion, thereby extending the continuous cleaning cycle of the nanofiltration system to more than 30 days.

6. The method for preventing aluminum pollution from nanofiltration membranes used in lithium extraction from salt lakes according to claim 2, characterized in that, In step 104, the injection point of the diluted premixed solution is set in the turbulent zone near the inlet of the membrane module in the water inlet pipeline; by adjusting the flow rate of the nanofiltration permeate carrier liquid, the Reynolds number of the fluid in the water inlet pipeline is made higher than 4000 to eliminate radial concentration polarization.

7. The method for preventing aluminum pollution from nanofiltration membranes used in lithium extraction from salt lakes according to claim 1, characterized in that, In step 105, the sampling frequency for real-time acquisition of the multi-parameter raw electrical signals generated by the online sensing terminal on the water inlet side is 100Hz to 500Hz to match the calculation cycle of the proportional-integral-differential algorithm, and the calculation cycle of the proportional-integral-differential algorithm is 5ms to 10ms, so as to ensure that the proton concentration on the nanofiltration membrane surface is above the aluminum ion hydrolysis equilibrium point in real time.

8. The method for preventing aluminum pollution from nanofiltration membranes used in lithium extraction from salt lakes according to claim 1, characterized in that, The acid injection pump is a variable frequency metering pump; the control commands include a pulse width modulation signal for adjusting the stroke frequency of the variable frequency metering pump, which is used to control the real-time dilution ratio of high-concentration hydrochloric acid in the nanofiltration permeate carrier fluid.

9. A method for preventing aluminum pollution from nanofiltration membranes used in lithium extraction from salt lakes according to claim 1, characterized in that, It also includes step 108: calibrating the pH sensor from step 101 and correcting the bias parameters in the mapping relationship model based on the zero-point drift of the sensor readings in order to maintain the chemical environment stability under the high-concentration brine system.

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