Method for passivating arsenic pollution of tailings by modified biochar loaded nano zero-valent iron

Abstract

This application discloses a method for passivating arsenic contamination in tailings using modified biochar-supported nano-zero-valent iron. The method includes: real-time acquisition of broadband electrochemical impedance spectroscopy data and passivation layer thickness data through an integrated micro three-electrode system to establish an initial passivation layer resistance value benchmark, and real-time extraction of the current passivation layer resistance and capacitance values ​​to calculate the characteristic resonant frequency and minimum breakdown voltage; when the current passivation layer resistance exceeds a preset multiple of the benchmark value, the fluctuation amplitude of the characteristic resonant frequency is less than a preset fluctuation threshold, and the passivation layer thickness is within a preset range, a sinusoidal AC voltage is applied at the characteristic resonant frequency to form a conductive channel in the passivation layer through dielectric breakdown, and then the channel is stabilized by a DC reduction pulse to achieve in-situ activation of the passivation layer and periodic recovery of material activity.

Description

Technical Field

[0001] This application relates to the field of environmental pollution control technology, specifically to a method for passivating arsenic pollution in tailings by loading modified biochar with nano-zero valent iron. Background Technology

[0002] Nano-zero-valent iron (nZVI) is widely used for passivation remediation of arsenic contamination in tailings due to its strong reducing properties and high specific surface area. Loading nZVI onto modified biochar can effectively improve its dispersibility and stability. However, after nZVI is added to the tailings environment, a dense iron oxide passivation layer (Fe2O3 / FeOOH) rapidly forms on its surface. The thickness of this passivation layer increases from 1-2 nm to 10-20 nm within hours to days, hindering electron transport and covering reactive sites, ultimately reducing the effective activity window of the material to only 3-7 days. Arsenic release from tailings is a long-term process that lasts for several years, and current technologies cannot effectively resolve this fundamental contradiction of "mismatch between the active window and the pollution release cycle."

[0003] To slow down the passivation process, existing technologies mainly employ the following strategies: First, surface coating, such as coating the surface of nano-zero valent iron with polymer or silica layers, which delays oxidation through physical isolation. However, the coating layer also hinders arsenic mass transfer, sacrificing initial activity. Second, doping modification, such as incorporating noble metals like palladium and nickel to form a galvanic cell and accelerate electron transfer. However, this does not solve the problem of passivation layer formation and significantly increases costs. Third, multiple additions or increased addition amounts are used to compensate for activity loss with more materials. However, costs increase linearly, and the risk of secondary pollution rises.

[0004] Therefore, there is an urgent need for a method that can accurately sense the state of the passivation layer, achieve controllable activation of the passivation layer with the lowest energy at the optimal time, and at the same time preserve the structural integrity of the material. Summary of the Invention

[0005] This application aims to at least partially address one of the technical problems in the related art.

[0006] Therefore, one objective of this application is to overcome the shortcomings of existing technologies where the rapid growth of the surface passivation layer of nano-zero-valent iron results in a short active window period that cannot match the long-term arsenic release cycle in tailings. This application provides a method for passivating arsenic contamination in tailings using modified biochar-supported nano-zero-valent iron. This method involves real-time monitoring of the electrochemical impedance spectroscopy characteristics of the passivation layer, calculating the characteristic resonant frequency and minimum breakdown voltage, applying a sinusoidal AC voltage matching the characteristic resonant frequency when the passivation layer grows to a specific thickness, constructing a conductive channel in the passivation layer using dielectric breakdown, and stabilizing the channel through a DC reduction pulse. This achieves "in-situ activation" of the passivation layer and periodic recovery of material activity, extending the active window period to match the arsenic release cycle.

[0007] To achieve the above objectives, the first aspect of this application proposes a method for passivating arsenic contamination in tailings by loading modified biochar with nano-zero valent iron, comprising the following steps:

[0008] Step S10: Acquire broadband electrochemical impedance spectroscopy data at a preset frequency. The broadband electrochemical impedance spectroscopy data includes the impedance modulus and phase angle corresponding to each frequency point within the preset frequency range, and simultaneously acquire passivation layer thickness data. Based on the broadband electrochemical impedance spectroscopy data acquired for the first time, use a preset circuit model to fit and obtain the initial passivation layer resistance value and store it as a reference value.

[0009] Step S20: Based on the real-time acquired broadband electrochemical impedance spectroscopy data, a preset circuit model is used for fitting to extract the current passivation layer resistance value and the current passivation layer capacitance value. The characteristic resonant frequency is calculated based on the current passivation layer resistance value and the current passivation layer capacitance value. At the same time, the minimum breakdown voltage is calculated based on the passivation layer thickness data.

[0010] Step S30: Determine whether the following conditions are met simultaneously: the current passivation layer resistance value exceeds a preset multiple of the reference value, the fluctuation amplitude of the characteristic resonant frequency is less than a preset fluctuation threshold, and the passivation layer thickness is within a preset range. When the above three conditions are met simultaneously, it is determined to enter the activation intervention window.

[0011] Step S40: Apply a sinusoidal AC voltage at the characteristic resonant frequency. The amplitude of the sinusoidal AC voltage starts from a preset percentage of the minimum breakdown voltage and increases at a preset incremental rate while monitoring the impedance modulus in real time.

[0012] Step S50: When the impedance modulus suddenly drops, it is determined that the passivation layer has undergone dielectric breakdown and formed a conductive channel. Switch to DC reduction pulse to reduce the iron ions at the edge of the channel to zero-valent iron in order to stabilize the conductive channel.

[0013] Furthermore, the synchronous acquisition of passivation layer thickness data specifically includes: acquiring the passivation layer thickness data at preset time intervals, and aligning the passivation layer thickness data as verification data with the broadband electrochemical impedance spectroscopy data in time sequence.

[0014] Furthermore, the preset circuit model is the following equivalent circuit model: solution resistance The first parallel branch and the second parallel branch are connected in series, and the first parallel branch is a charge transfer resistor. With double-layer capacitance The components are connected in parallel, with the second parallel branch being the passivation layer resistor. With passivation layer capacitance Composed of parallel connections.

[0015] Furthermore, the formula for calculating the characteristic resonant frequency is:

[0016]

[0017] in, The characteristic resonant frequency, This represents the resistance value of the passivation layer. This represents the capacitance value of the passivation layer.

[0018] Furthermore, the formula for calculating the minimum breakdown voltage is as follows:

[0019]

[0020] in, The minimum breakdown voltage value, For the pre-calibrated dielectric strength, This refers to the passivation layer thickness data; the pre-calibrated dielectric strength is preset to 6 × 10⁻⁶ based on the ratio of Fe₂O₃ to FeOOH in the passivation layer. 6 V / cm to 1×10 7 Values ​​within the range of V / cm.

[0021] Furthermore, the preset multiple is 3 times, the preset fluctuation threshold is 5%, and the preset range of the passivation layer thickness is 3nm~8nm.

[0022] Furthermore, the preset percentage is 50%, and the preset increment rate is 0.1 V / s; during the application of the sinusoidal AC voltage, the ratio of the current applied voltage value to the minimum breakdown voltage value is continuously calculated, and the increment stops when the ratio reaches a preset upper limit threshold.

[0023] Furthermore, the determination of the sudden drop in impedance magnitude specifically includes: calculating the difference value of the impedance magnitude at continuous sampling time, and determining that the impedance magnitude has suddenly dropped when the absolute value of the difference value exceeds a preset change threshold.

[0024] Further, the DC reduction pulse is specifically a negative DC pulse with an amplitude of -0.8 V and a duration of 0.5 seconds; the cycle of steps S40 to S50 is repeated 2 to 3 times until an interconnected conductive channel network is formed in the passivation layer.

[0025] Furthermore, the method also includes step S60: after completing the DC reduction pulse, re-execute steps S10 and S20 to obtain the activated passivation layer resistance value, and determine whether the activated passivation layer resistance value is less than or equal to twice the initial resistance value. If so, the activation is successful; otherwise, repeat steps S40 to S50.

[0026] The beneficial effects of this application are as follows:

[0027] This application addresses the problems of unstable treatment effects, low remediation efficiency, and high energy consumption in traditional arsenic pollution remediation technologies by combining modified biochar-supported nano-zero-valent iron with electrochemical impedance spectroscopy (EIS). Through dynamic monitoring and precise control of the passivation layer resistance, characteristic resonant frequency, and passivation layer thickness, this application can assess the stability of the passivation layer in real time and determine the optimal intervention time during the pollution remediation process. Compared to traditional remediation methods relying on static physical adsorption, this application effectively improves the flexibility and efficiency of the remediation process through electrochemical monitoring.

[0028] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0029] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0030] Figure 1 This is a flowchart of the method for passivating arsenic contamination in tailings using modified biochar supported on nano-zero valent iron, as described in this application.

[0031] Figure 2 This is a schematic diagram of the equivalent circuit model in this application;

[0032] Figure 3 This is a graph showing the change of impedance modulus during the activation process in this application;

[0033] Figure 4 This is a schematic diagram comparing the passivation layer structure before and after activation in this application. Detailed Implementation

[0034] Specific embodiments of this application will be described in detail below. Although this application is described in conjunction with these specific embodiments, it should be understood that it is not intended to limit this application to these specific embodiments. Rather, these embodiments are intended to cover alternative, modified, or equivalent embodiments that may be included within the spirit and scope of the invention as defined by the claims. In the following description, numerous specific details are set forth in order to provide a complete understanding of this application. This application may be practiced without some or all of these specific details.

[0035] When used in conjunction with the terms "comprising," "method comprising," or similar language in this specification and appended claims, the singular forms "a," "some," and "the" include plural references unless the context clearly indicates otherwise. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0036] The following is in conjunction with the appendix Figure 1-4 The preferred embodiments of this application will be described in detail so that those skilled in the art can implement this application accordingly.

[0037] This embodiment provides a method for passivating arsenic contamination in tailings by loading modified biochar with nano-zero valent iron. This method is applied to a material activation system comprising a micro-three-electrode system and a processor unit, and includes the following steps:

[0038] Step S10: Initial data acquisition and baseline value establishment.

[0039] Specifically, a micro-tri-electrode system was first integrated into modified biochar-supported nano-zero-valent iron material and connected to a processor unit. The processor unit controlled the micro-tri-electrode system to acquire broadband electrochemical impedance spectroscopy data at a sampling frequency of 100 Hz. The frequency scan range was set to 10 mHz to 100 kHz, and a total of 50 frequency points were scanned, recording the impedance modulus corresponding to each frequency point. With phase angle Simultaneously, passivation layer thickness data were acquired hourly using an in-situ elliptic polarization spectrometer. The spectrometer uses a He-Ne laser source with a wavelength of 632.8 nm and an incident angle of 70°. The film thickness is calculated by measuring the change in the polarization state of the reflected light. The processor unit aligns the passivation layer thickness data with the broadband electrochemical impedance spectroscopy data according to the acquisition time, specifically using a linear interpolation method: for the impedance spectroscopy data acquisition time... Find the thickness data acquisition time closest to that time. ,like If the time is less than the preset time tolerance (30 seconds in this embodiment), then direct matching is performed; if it is greater than the tolerance, then two adjacent thickness data points are taken. and Through linear interpolation formula Calculate the thickness data at that moment, establish a timestamp correspondence, so that the impedance spectrum data at each moment has corresponding thickness data as a verification benchmark.

[0040] Based on the initially acquired broadband electrochemical impedance spectroscopy data, the processor unit performs nonlinear least-squares fitting using a pre-defined circuit model. The objective function of the fitting is to minimize the root mean square error between the measured impedance value and the model-calculated value. The initial passivation layer resistance value is obtained through this fitting process. This value represents the electron transport resistance during the initial stage of material application, before the passivation layer has grown significantly. The processor unit stores this initial passivation layer resistance value in non-volatile memory as a reference value for subsequent judgments.

[0041] Step S20: Real-time monitoring and characteristic parameter calculation.

[0042] Specifically, the processor unit acquires broadband electrochemical impedance spectroscopy data in real time at a frequency of once per minute, and uses the same equivalent circuit model as in step S10 to fit the data and extract the current passivation layer resistance value. With the current passivation layer capacitance value The equivalent circuit model In the middle, the resistance of the solution The ohmic resistance of the tailings leachate itself typically ranges from 10 to 100 Ω·cm. 2 Within range; charge transfer resistance With double-layer capacitance The parallel structure represents the electrochemical reaction process at the interface between nano-zero valent iron and solution; passivation layer resistance With passivation layer capacitance The parallel structure directly reflects the electrical properties of the iron oxide passivation layer, in which It increases with the thickness of the passivation layer. It decreases as the passivation layer thickens.

[0043] The processor unit calculates the characteristic resonant frequency based on the current passivation layer resistance and capacitance values. In the equivalent circuit model, the solution resistance... The first parallel branch and the second parallel branch are connected in series. The first parallel branch is a charge transfer resistor. With double-layer capacitance The circuit is composed of parallel components, with the second parallel branch being the passivation layer resistor. With passivation layer capacitance Composed of parallel connections. The specific formula is: The passivation layer is partially composed of resistors. With capacitor This is a parallel connection. According to circuit theory, the impedance expression for this parallel branch is: ,in Let ω be the angular frequency. When the frequency of the applied AC voltage changes, the distribution ratio of the voltage drop between the passivation layer branch and other branches changes accordingly. To maximize the concentration of activation energy in the passivation layer rather than its consumption in solution resistance or charge transfer processes, the impedance magnitude of the passivation layer branch must be minimized, i.e., its capacitive reactance and resistance must be matched. In a parallel circuit, the impedance magnitude of the branch is minimized when the capacitive reactance equals the resistance; its mathematical condition is... ,in For capacitive reactance. Substitute , can be obtained After simplification, the expression for the characteristic resonant frequency is obtained. The physical meaning of this formula is that when a frequency is applied... When the AC voltage is applied, the capacitive reactance and resistance of the passivation layer are equal, and the voltage drop is maximized on the passivation layer, thus making the breakdown energy most effectively concentrated in the target area.

[0044] According to circuit theory, this parallel branch ,in Let be the angular frequency. To maximize the concentration of activation energy in the passivation layer, the impedance modulus of the passivation layer branch must be minimized, i.e., its capacitive reactance and resistance must be matched. The mathematical condition is: Substitute The characteristic resonant frequency can be derived. The calculation formula is:

[0045]

[0046] Alternatively, to further improve calculation accuracy, the actual passivation layer can be considered to have constant phase angle element characteristics, and its impedance behavior can be expressed by the parameter Q (constant phase angle coefficient, unit F·cm). -2 ·s n-1 )and (Described by the diffusion index, dimensionless, 0.5 ≤ n ≤ 1). Under this model, the calculation of the characteristic resonant frequency can be optimized to the following formula:

[0047]

[0048] Among them, when When this happens, the optimized formula degenerates into the formula described above. Those skilled in the art will understand that the formula and All of these can be used to implement this application, formula It can provide more accurate results when the passivation layer is significantly non-ideal.

[0049] The processor unit uses the current passivation layer thickness data Calculate the minimum breakdown voltage According to the basic principle of dielectric breakdown, the breakdown voltage is directly proportional to the dielectric thickness, and the proportionality constant is the dielectric strength. Therefore, the formula for calculating the minimum breakdown voltage is:

[0050]

[0051] in, This represents the pre-calibrated equivalent dielectric strength of the passivation layer.

[0052] In a more precise implementation, the passivation layer is typically composed of a mixture of Fe2O3 and FeOOH, with an equivalent dielectric strength of This is related to the composition ratio. At this point, the composition can be inverted using electrochemical impedance spectroscopy data, and the above formula can be refined. Specifically, firstly, based on the characteristic resonant frequency... Phase angle at Through pre-calibrated relational expressions Calculate the mass fraction of FeOOH .in, and These are the characteristic phase angles of the pure material. Next, the equivalent dielectric strength is calculated using linear interpolation: Finally, consider the interface barrier. Due to the influence of [the factors], the optimized formula for calculating the minimum breakdown voltage is obtained:

[0053]

[0054] Those skilled in the art will understand that the formula An estimate based on average dielectric strength is provided, and the formula... It provides more precise values ​​that take into account composition and interface effects. In practical applications, the appropriate value can be selected based on the required accuracy.

[0055] It should be noted that, Characteristic frequency points The corresponding phase angle is directly extracted from broadband electrochemical impedance spectroscopy data; The characteristic phase angle of the Fe2O3 passivation layer at the characteristic frequency point was obtained through previous experimental calibration. The characteristic phase angle of the FeOOH passivation layer at the characteristic frequency point was obtained through previous experimental calibration; The interface barrier, in eV, was obtained through previous experimental calibration. The elementary charge has a value of 1.602 × 10⁻⁶. -19 C.

[0056] Step S30: Determine the activation intervention window.

[0057] The processor unit extracts the current passivation layer resistance value in step S20. Characteristic resonant frequency Its fluctuation range and passivation layer thickness A comprehensive judgment is made. The fluctuation amplitude of the characteristic resonant frequency is obtained by calculating the relative standard deviation of the most recent 10 measurements. .

[0058] The processor unit determines whether the following three conditions are met simultaneously: First, the current passivation layer resistance value. Does it exceed the initial passivation layer resistance value stored in step S10? Three times; second, characteristic resonant frequency Third, the passivation layer thickness. Is it within the 3nm to 8nm range? The processor unit determines that the current moment is an activation intervention window and triggers subsequent activation operations only if all three conditions above are met.

[0059] It should be noted that the above three conditions have clear physical meanings: First, a resistance value exceeding three times the reference value indicates that the passivation layer has grown to a point where electron transport is severely impeded, making activation necessary. Second, a resonant frequency fluctuation of less than 5% indicates that the passivation layer has formed a uniform and dense structure rather than a loose and porous state; at this point, dielectric breakdown can form regular conductive channels rather than disordered fractures. Third, a thickness between 3 and 8 nanometers indicates that the passivation layer thickness is moderate, the energy required for breakdown is moderate, and the channels formed after breakdown can exist stably. The combination of these three conditions ensures precise triggering of the activation operation, avoiding premature or delayed intervention.

[0060] In this embodiment, when the material has been running for 5 days, (Exceeding the benchmark value by 100 Ω·cm) 2 3 times) The fluctuation range was 3.2% (less than 5%). (In the 3-8 nm range), if all three conditions are met simultaneously, the processor unit will determine whether to enter the activation intervention window.

[0061] Step S40: Apply adaptive AC voltage.

[0062] Specifically, the processor unit controls the miniature three-electrode system, and the characteristic resonant frequency calculated in step S20... A sinusoidal alternating voltage is applied at the point. The voltage amplitude starts from the minimum breakdown voltage. Starting at 50%, the voltage increases linearly at a rate of 0.1 V / s. During this voltage increase, the processor unit continuously monitors the impedance magnitude. The change, and calculate the current applied voltage value in real time. With minimum breakdown voltage value ratio When this ratio reaches the preset upper limit threshold of 1.2, if no breakdown event is detected, the voltage increase will stop to avoid irreversible damage to the material caused by excessive voltage application.

[0063] This step employs a voltage ramp-up strategy, from... The voltage ratio is increased starting at 50% to avoid damage to the material from voltage overshoot and to accommodate slight differences in the dielectric strength of the passivation layer between different batches of material. Applying voltage at the characteristic resonant frequency is because the voltage drop is mainly concentrated in the passivation layer at this frequency, resulting in the highest energy utilization efficiency and enabling passivation layer breakdown with minimal energy input. Continuously monitoring the voltage ratio and setting an upper limit threshold prevents material damage caused by unlimited voltage increase when the passivation layer cannot break down due to local defects. In this embodiment, the processor unit... A sinusoidal AC voltage is applied at the point, starting from 2 V and increasing in increments of 0.1 V / s, while the impedance magnitude is monitored in real time.

[0064] Step S50: Dielectric breakdown and stabilization of conductive channels.

[0065] Specifically, the processor unit continuously acquires the impedance magnitude at a sampling frequency of 100 Hz during the application of a sinusoidal AC voltage. And calculate the difference between adjacent sampling times. .when When the absolute value exceeds the preset change threshold, it is determined that the impedance modulus has suddenly dropped, that is, the passivation layer has undergone dielectric breakdown and a nanoscale conductive channel has been formed.

[0066] The selection of the preset threshold value directly affects the accuracy and sensitivity of the breakdown determination. If the threshold is set too low, misjudgment may occur due to measurement noise; if the threshold is set too high, breakdown events may be missed. In this embodiment, an adaptive threshold calculation method based on real-time background noise is adopted, so that the threshold is dynamically adjusted according to the ambient noise level. Before applying a sinusoidal AC voltage, the processor unit first collects impedance modulus data under undisturbed conditions, with a duration of 1 second and a total of 100 sampling points, and calculates the standard deviation of this data segment. Based on the principles of mathematical statistics, a change in impedance magnitude exceeding three standard deviations is considered significant. Considering that the impedance magnitude change caused by a breakdown event is typically much larger than the background noise, to balance sensitivity and reliability, the preset change threshold is set to five standard deviations. The formula for calculating the adaptive preset change threshold is then derived:

[0067]

[0068] in, The number of sampling points. For the first Impedance magnitude at each sampling point This represents the average value of the data in that segment.

[0069] Upon breakdown, the processor unit immediately switches the miniature three-electrode system to a DC reduction pulse. This DC reduction pulse has an amplitude of -0.8 V and a duration of 0.5 seconds. The negative pulse's function is to neutralize the Fe generated at the edge of the breakdown channel due to high-temperature oxidation. 3+ The iron is reduced to zero valence iron, thereby stabilizing the channel and preventing it from closing due to re-oxidation. The number of conductive channels formed by a single breakdown is limited. The processor unit repeats the cycle of steps S40 to S50 2 to 3 times. In each cycle, the characteristic resonant frequency is recalculated and AC breakdown and DC reduction are performed until an interconnected conductive channel network is formed in the passivation layer.

[0070] Step S60: Verification of activation effect.

[0071] In the specific implementation of this step, after the processor unit completes the DC reduction pulse in step S50, it re-executes steps S10 and S20, that is, it re-acquires broadband electrochemical impedance spectroscopy data and performs equivalent circuit fitting to obtain the resistance value of the activated passivation layer. Then, the processor unit compares this value with the initial passivation layer resistance value stored in step S10. Compare them.

[0072] Processor unit judgment Is it less than or equal to? If yes, the activation operation is considered successful, and the material's electron transport capability has been restored to an acceptable level; if no, it indicates that the conductive channel network is not yet perfect, and the processor unit repeats steps S40 to S50 for supplementary activation. In this embodiment, the measured value after activation is... Approximately 90 Ω·cm 2 The initial resistance value was 100 Ω·cm. 2 Since 90 is less than 200, the activation was deemed successful.

[0073] The purpose of this step is to form a closed-loop control, verify the activation effect, and ensure the effectiveness of each activation operation, avoiding ineffective activation that would cause the material to remain in a low-activity state. By periodically executing steps S10 to S60, nano-zero-valent iron can maintain high activity over operating cycles lasting months or even years, achieving a match with the long-term arsenic release cycle in tailings.

[0074] The following provides a complete application scenario embodiment to further illustrate the application of the method of this application in actual engineering.

[0075] Taking a copper mine tailings pond as an example, the leachate from this pond has a pH of approximately 6.5, a dissolved oxygen concentration of 5 mg / L, and an arsenic concentration of 10 mg / L. The method described in this application, which uses modified biochar loaded with nano-zero-valent iron to passivate arsenic contamination in tailings, was employed for treatment.

[0076] Before implementation, a micro-tri-electrode system was first integrated into a modified biochar-supported nano-zero-valent iron material. This material used biochar with a particle size of 50 to 100 micrometers as a carrier and supported nano-zero-valent iron particles with a particle size of approximately 20 nanometers. The integrated tri-electrode system was added to the tailings dam leachate treatment area at a rate of 1 kg of material per cubic meter of leachate. After material addition, the processor unit automatically executed step S10, acquiring broadband electrochemical impedance spectroscopy data at a sampling frequency of 100 Hz, with a frequency range of 10 mHz to 100 kHz, and simultaneously acquiring passivation layer thickness data using an in-situ elliptic polarization spectrometer. The initial data acquisition showed that the initial passivation layer resistance was 100 Ω·cm. 2 The passivation layer thickness is approximately 1.2 nm, and the processor unit stores this value as a reference value.

[0077] During material processing, the processor unit executes step S20 once per minute to monitor the passivation layer status in real time. By day 5, data showed that the current passivation layer resistance had risen to 320 Ω·cm. 2 The passivation layer capacitance is 1.2 × 10⁻⁶. -5 F / cm 2 The passivation layer thickness is 5 nm. The processor unit calculates the characteristic resonant frequency to be approximately 41 Hz based on the characteristic resonant frequency formula modified by the dispersion index, and calculates the minimum breakdown voltage to be 4V based on the minimum breakdown voltage formula considering the composition ratio and interface barrier. At this point, all three conditions in step S30 are simultaneously satisfied, and the processor unit determines that it is entering the activation intervention window.

[0078] Subsequently, the processor unit executes step S40, applying a sinusoidal AC voltage at a frequency of 41 Hz, starting at 2 V and increasing at a rate of 0.1 V / s. When the voltage increases to approximately 3.8 V, step S50 detects a sudden drop in the impedance modulus from 800 Ω to 400 Ω, determining that dielectric breakdown has occurred. It immediately switches to a -0.8 V DC reduction pulse lasting 0.5 seconds to reduce the iron ions at the edge of the breakdown channel to zero-valent iron. After repeating this cycle three times, the impedance modulus drops to 120 Ω, indicating that an interconnected conductive channel network has been formed.

[0079] Finally, in step S60, the resistance of the passivation layer after activation was remeasured and found to be 90 Ω·cm. 2 The resistance value was less than twice the initial resistance value, indicating successful activation. By periodically performing the above activation operation, the material maintained high efficiency in arsenic removal over an operating cycle of up to 6 months, with the removal rate consistently above 85%. Compared with traditional materials that do not use the method described in this application, its active window period is significantly extended, iron utilization is greatly improved, and the amount of material added is significantly reduced, thereby lowering remediation costs and the risk of secondary pollution.

[0080] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

[0081] In the description of this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0082] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0083] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for passivation of arsenic-contaminated tailings by modified biochar supported nano zero-valent iron, characterized in that, Includes the following steps: Step S10: Acquire broadband electrochemical impedance spectroscopy data at a preset frequency. The broadband electrochemical impedance spectroscopy data includes the impedance modulus and phase angle corresponding to each frequency point within the preset frequency range, and simultaneously acquire passivation layer thickness data. Based on the first collection of broadband electrochemical impedance spectroscopy data, the initial passivation layer resistance value was obtained by fitting the data using a preset circuit model and stored as a reference value. Step S20: Based on the real-time acquired broadband electrochemical impedance spectroscopy data, a preset circuit model is used for fitting to extract the current passivation layer resistance value and the current passivation layer capacitance value. The characteristic resonant frequency is calculated based on the current passivation layer resistance value and the current passivation layer capacitance value. At the same time, the minimum breakdown voltage is calculated based on the passivation layer thickness data. Step S30: Determine whether the following conditions are met simultaneously: the current passivation layer resistance value exceeds a preset multiple of the reference value, the fluctuation amplitude of the characteristic resonant frequency is less than a preset fluctuation threshold, and the passivation layer thickness is within a preset range. When all three conditions are met, determine to enter the activation intervention window. Step S40: Apply a sinusoidal AC voltage at the characteristic resonant frequency. The amplitude of the sinusoidal AC voltage starts from a preset percentage of the minimum breakdown voltage and increases at a preset incremental rate while monitoring the impedance modulus in real time. Step S50: When the impedance modulus suddenly drops, it is determined that the passivation layer has undergone dielectric breakdown and formed a conductive channel. Switch to DC reduction pulse to reduce the iron ions at the edge of the channel to zero-valent iron in order to stabilize the conductive channel. The preset circuit model is an equivalent circuit model as follows: solution resistance , the first parallel branch and the second parallel branch are connected in series, the first parallel branch is composed of charge transfer resistance and double-layer capacitance in parallel, and the second parallel branch is composed of passivation layer resistance and passivation layer capacitance in parallel. The determination of a sudden drop in impedance magnitude specifically includes: calculating the difference in impedance magnitude at continuous sampling times, and determining that a sudden drop in impedance magnitude has occurred when the absolute value of the difference exceeds a preset change threshold. The method further includes step S60: after completing the DC reduction pulse, re-execute steps S10 and S20 to obtain the activated passivation layer resistance value, and determine whether the activated passivation layer resistance value is less than or equal to twice the initial resistance value. If so, the activation is successful; otherwise, repeat steps S40 to S50.

2. The method of claim 1, wherein, The synchronous acquisition of passivation layer thickness data specifically includes: acquiring the passivation layer thickness data at preset time intervals, and aligning the passivation layer thickness data as verification data with the broadband electrochemical impedance spectroscopy data in time sequence.

3. The method of claim 1, wherein, The formula for calculating the characteristic resonant frequency is: wherein, is the characteristic resonance frequency, is the passivation layer resistance value, is the passivation layer capacitance value.

4. The method of claim 1, wherein, The formula for calculating the minimum breakdown voltage is as follows: in, The minimum breakdown voltage value, For the pre-calibrated dielectric strength, This refers to the passivation layer thickness data; the pre-calibrated dielectric strength is preset to 6 × 10⁻⁶ based on the ratio of Fe₂O₃ to FeOOH in the passivation layer. 6 V / cm to 1×10 7 Values ​​within the range of V / cm.

5. The method of claim 1, wherein, The preset multiple is 3 times, the preset fluctuation threshold is 5%, and the preset range of the passivation layer thickness is 3nm~8nm.

6. The method of claim 1, wherein, The preset percentage is 50%, and the preset increment rate is 0.1 V / s; during the application of the sinusoidal AC voltage, the ratio of the current applied voltage value to the minimum breakdown voltage value is continuously calculated, and the increment stops when the ratio reaches the preset upper limit threshold.

7. The method of claim 1, wherein, The DC reduction pulse is specifically a negative DC pulse with an amplitude of -0.8 V and a duration of 0.5 seconds; the cycle of steps S40 to S50 is repeated 2 to 3 times until an interconnected conductive channel network is formed in the passivation layer.

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