Method and system for recycling and regenerating mixed acid and selectively removing arsenic

Abstract

The invention discloses a mixed acid recycling and regenerating and selective arsenic removal method and system, and belongs to the field of wet process chemical recycling and regenerating treatment. The system sequentially comprises a diffusion dialysis module, an electrodialysis module, a membrane contactor removal and resorption module and a transmembrane oxidation-complexing arsenic removal module along the technological process, and is provided with a bypass reflux valve group, a release port, an online sensor, a controller, a human-computer interface and a safety interlock. The membrane contactor operates under the condition of relative vacuum degree or inert replacement, is circularly communicated with the resorption liquid and is used for removing and absorbing volatile acidic components; and the transmembrane oxidation-complexing arsenic removal module is used for converting and selectively trapping arsenic. The controller performs release judgment based on online calibration results of conductivity, density and temperature, releases and generates a record when the standard is reached, and switches bypass backflow and executes in-situ cleaning when the standard is not reached; safety interlocking is used for exception handling and process tracing.

Description

Technical Field

[0001] This invention relates to a membrane coupling process for the recovery and regeneration of mixed acids (HF, HNO3, and HCl), along with an online quality control and safety interlocking system. Background Technology

[0002] When processing fluorine- and nitrogen-containing inorganic acid solutions, wet processing and etching sections typically generate complex mixed acid wastewater containing inorganic acids such as HF, HNO3, and HCl, as well as polyvalent metal ions, particles, and dissolved gases. In engineering practice, the evaluation of reuse quality often considers multiple dimensions: first, the recyclability of free acid and the stability of acidity after recovery; second, the controllability of ionic composition and conductivity to meet subsequent process windows; third, the control of volatile acidic components and dissolved gases to reduce the impact on equipment and the environment; and fourth, the residual levels and fluctuations of trace amounts of harmful elements such as arsenic. In continuous or near-continuous operation scenarios, these evaluation criteria also need to be considered in conjunction with constraints such as safety, energy consumption, emissions, and traceability.

[0003] Existing public information and engineering experience show that diffusion dialysis, driven by concentration gradients, has low energy consumption and a certain degree of repulsion for various metal ions, and has been used in scenarios such as pickling, metal refining, and electronic chemical regeneration to recover free acid. To further refine the ionic composition and conductivity, electrodialysis is often used in conjunction with it as a fine-tuning or closed-loop stage. For volatile acidic components and dissolved gases, hollow fiber membrane contactors, by increasing the gas-liquid interface and controlling mass transfer, achieve removal and absorption under vacuum or inert gas scavenging conditions in conjunction with the absorbent. This technology has been systematically reviewed and applied in similar systems such as deoxygenation and acid gas capture. Regarding arsenic removal, the internationally accepted standard is typically 10 μg·L⁻¹. -1 As a limit for arsenic in drinking water, published reviews list oxidation-adsorption or co-precipitation, ion exchange and membrane separation as the mainstream technical routes. Different routes have different focuses in terms of applicable water chemistry, reagent compatibility and by-product treatment.

[0004] Among the publicly available representative routes, one is the coupled recovery of diffusion dialysis and electrodialysis, suitable for scenarios with high acidity and a need for metal ion repulsion. Diffusion dialysis undertakes the main functions of free acid recovery and metal ion separation, while electrodialysis performs fine-tuning of conductivity and ionic composition in subsequent stages, thus providing more controllable feed quality for reuse or downstream purification. This route places high demands on the stability of the front-end pretreatment and the maintenance of the membrane modules, and in engineering, it is often paired with centralized or modular regeneration units.

[0005] Secondly, gas-liquid mass transfer and absorption based on membrane contactors can be used to control volatile acidic components and dissolved gases: Interfacial mass transfer is driven by vacuum operation or inert gas scavenging, combined with acidic or neutral absorbents. This can form a bypass or loop coupling with acid recovery processes to suppress NO. x The discharge and accumulation of components such as HF. On the other hand, publicly available information also indicates that nanofiltration or reverse osmosis is used in the final stage of total arsenic reduction or polishing, typically for feed solutions with adequate pretreatment and low contamination load.

[0006] Although the aforementioned unit processes have a relatively mature engineering foundation for their respective sub-objectives, several objective problems still exist in the context of full-process recovery and quality release for mixed acid systems: First, the sequence and coupling relationship of multiple units are affected by the combined influence of feed fluctuations, interfacial mass transfer efficiency, and ion balance, lacking a systematic characterization and configuration method within the same framework; Second, the absorption and safe disposal of volatile acidic components are coupled with the pressure, flow rate, and displacement strategy of the main process, and the descriptions of related interlocking logic and abnormal handling paths in publicly available information are relatively scattered; Third, regarding the online assessment of reuse quality, most public information focuses on offline detection or single index thresholds, and there are relatively limited engineering methods and public examples for online calibration of multiple parameters, batch-to-batch consistency, and traceability; Fourth, terminal arsenic removal or polishing modules suitable for strong acids, high ionic strength, and complex matrices still need further verification in terms of long-term stability, concentrated residual liquid management, and compatibility with upstream units. Summary of the Invention

[0007] Technical problems to be solved For the recovery and reuse of mixed acids containing HF, HNO3, and HCl, it is necessary to achieve the recyclability of free acid, maintain its ionic composition and conductivity within a controllable window under continuous or near-continuous operating conditions, while simultaneously controlling the volatile acidic components and dissolved gases, and stabilizing the residual level of trace arsenic within a release range. In engineering operations, release decisions should also be coordinated with safety, energy consumption, anomaly handling, and traceability; however, existing disclosures are mostly at the unit level, lacking a unified sequential coupling, online calibration, and interlocking release framework, resulting in insufficient batch-to-batch consistency and controllability of abnormal states.

[0008] Technical solution This invention proposes a cascade system and its operation method for mixed acid systems. The system sequentially includes: a diffusion dialysis module for recovering free acid; an electrodialysis module for refining ionic composition and conductivity; a membrane contactor module for removing volatile acidic components and dissolved gases under relative vacuum conditions and connected in a closed loop with the acidic backflow liquid; and a transmembrane oxidation-complexation module for selectively removing arsenic. The system is equipped with bypass and reflux valve groups and safety instrument functions, and is configured with a controller and human-machine interface (HMI) to collect and control the pressure, flow rate, conductivity, density, and temperature of each section. The release conditions are determined based on an online calibration model of conductivity-density-temperature (EC-ρ-T). If the conditions are met, the system outputs through the release port; if the conditions are not met, the system switches to bypass reflux and performs on-site cleaning.

[0009] In one embodiment, the feed-to-dialysis liquid volume ratio in diffusion dialysis is 1:0.8–1.2 to achieve synergistic effects of free acid recovery and metal ion repulsion; in another embodiment, the current density in electrodialysis is 5–20 mA·cm⁻¹. -2 The energy efficiency objective function is used to balance energy consumption and deviation from the target conductivity. In one embodiment, the membrane contactor operates under a relative vacuum of 0.02–0.08 MPa, with a reabsorption liquid pH of 1.0–3.0. The three-parameter online calibration model maps conductivity, density, and temperature to acid concentration and impurity index, which are used for release criteria. The above parameter ranges are examples of implementation methods; specific values ​​can be set according to the composition of the incoming material, the scale of the equipment, and the reuse specifications.

[0010] In terms of control and interlocking, the controller is configured to: drive the valve group to the release port and generate a release record when the online calibration result meets the release threshold; drive the valve group to switch to bypass reflux and trigger the corresponding on-site cleaning process when any online indicator fails to meet the release threshold or an integrity abnormality occurs; and execute safety procedures in the order of "stop feeding—empty or inertial replacement—switch to bypass reflux" when the trigger conditions of the safety instrument function are met. Preferably, the three-parameter online calibration chamber and the release port are connected by a hard interlock. When the online calibration residual or calibration deviation δ continuously exceeds the preset threshold, the release port remains closed and switches to bypass reflux. The control logic is used to ensure physical isolation between abnormal batches and normal batches and to shorten the recovery time.

[0011] Beneficial effects By sequentially coupling diffusion dialysis, electrodialysis, membrane contactor removal and reabsorption, transmembrane oxidation-complexation arsenic removal, and online calibration and interlocked release within a unified framework, the impact of volatile acidic components on downstream products and the environment can be reduced while ensuring free acid recovery, and the residual concentration of trace arsenic can be controlled within a stable range. Online calibration transforms release judgment from single-point detection to multi-parameter process measurement, improving batch-to-batch consistency; the combination of safety instrumented functions and bypass reflux makes the handling path in abnormal situations clear and verifiable, facilitating traceability and compliance management.

[0012] Under representative operating conditions, diffusion dialysis is used to recover free acid and reduce metal ion load, electrodialysis is used to fine-tune ion composition and conductivity, membrane contactors stabilize the absorption of volatile acidic components such as NOx and HF under relative vacuum conditions in conjunction with acidic backflow solution, and transmembrane oxidation-complexation module is used to selectively capture arsenic. The above units form a closed loop operation with online calibration, valve group action and on-site cleaning under the unified scheduling of the controller, thereby improving the repeatability and traceability of release judgment, and are suitable for engineering deployment and scale-up. Attached Figure Description

[0013] The diagram is only for illustrative purposes and does not constitute a limitation on the material or filter element microstructure.

[0014] Figure 1 Schematic diagram of the overall process and instrument signals for mixed acid recovery; Figure 2 Schematic diagram of the coupling arrangement of diffusion dialysis and electrodialysis; Figure 3 Schematic diagram of the membrane contactor removal and re-suction structure; Figure 4 Schematic diagram of a transmembrane oxidation-complexing reactor; Figure 5 Schematic diagram of the three-parameter calibration and release logic. Detailed Implementation

[0015] Terminology definition Relative vacuum (MPa): The pressure difference based on ambient atmospheric pressure. A positive value indicates a relative negative pressure.

[0016] Impurity Index: A comprehensive index used to characterize the impurity level in mixed acid, which can be obtained by weighted combination of the mass concentrations of one or more impurities. In one embodiment, the impurity index I... imp It can be represented as: .

[0017] Among them, I imp C is the impurity index. NOxThe mass concentration of NOx (or the NOx proxy index concentration as specified in the process); C F For F - The total fluoride (or fluoride ion) mass concentration is calculated; C Metal The mass concentration of metal ions is used as a proxy indicator; w1, w2, and w3 are weighting coefficients set according to the reuse specifications. imp The dimensions are consistent with the concentration index used (e.g., mg·L). -1 ).

[0018] The above expression is only used to illustrate one implementation method. The composition and weighting of the impurity index can be adjusted according to the reuse specifications and testing system, and does not constitute a limitation on the index form or formula.

[0019] Energy efficiency objective function (J): A multi-objective weighted function used to balance energy consumption per unit of acid production with the target conductivity deviation and its fluctuation. In one implementation, J can be expressed as: .

[0020] Where E is the energy consumption per unit of acid production (kWh·t) -1 t is tons); σ is the online conductance (also denoted as EC); σ0 is the target conductance; Var N (σ) represents the variance of σ within the most recent N sampling windows, where N is a preset positive integer; α, β, and γ are weighting coefficients. It is preferable to normalize each term to make it weighted for comparison, or to set α to a coefficient that matches E to ensure the dimensionality and interpretability of the objective function.

[0021] Integrity anomaly: refers to an abnormal state directly related to the safe operation of the device, including at least the negative pressure system anomaly, an abnormal increase in transmembrane pressure difference relative to the baseline, temperature or liquid level exceeding the limit at critical points, and continuous exceedance of the threshold for online calibration residual.

[0022] Acid concentration: Using titration or density-conductivity curves as references, select no fewer than 30 standard samples (temperature range 15–35°C) and train the regression model using the least squares method. In one implementation, the acid concentration C can be expressed as: .

[0023] Where C is the acid concentration (unit determined according to reference method, e.g., g·L). -1 Or mass fraction); EC is conductivity (mS·cm) -1 ); ρ is the density (g·cm³) -3 ); T is the temperature (°C); a0~a4 are model parameters, where a4 is the coefficient of the interaction term EC·ρ.

[0024] The generalization performance of the model was evaluated using 10-fold cross-validation. The validation bias δ ​​was calculated using the following formula: .

[0025] Among them, C pred C represents the model's predicted value. ref The measured value is used as a reference. And C ref ≠0 (usually C) ref >0). The verification deviation δ is preferably no greater than 5%. During operation, the online model can be sampled and retested at preset intervals. If the verification deviation δ or the online calibration residual continuously exceeds the preset threshold, it can be used as one of the triggering conditions for release interlock or safety instrumented function (SIF).

[0026] NOx: Determined by ion chromatography (IC) or UV-Vis spectrophotometry. Total fluorine (as F) - Calculation: Determined by ion chromatography or fluoride ion-selective electrode, and expressed as mass concentration (mg·L⁻¹). -1 )express.

[0027] Total arsenic: determined by inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma optical emission spectrometry (ICP-OES), with a detection limit not exceeding 1 μg·L⁻¹. -1 .

[0028] Energy consumption: kWh·t -1 (Acid production), automatically accumulated by HMI. Where t is tons.

[0029] System structure and operating parameters example See Figure 1 The system, following the process flow, sequentially includes a diffusion dialysis module 301, an electrodialysis module 302, a membrane contactor 303, a selective arsenic removal module 305, and a release port 310. It also includes a backflow liquid circulation system 304, a bypass and reflux valve assembly 306, a three-parameter calibration chamber 308, a controller and human-machine interface 309, and safety instrumented functions 307. All modules are connected via acid-resistant pipelines. Sampling ports and online sensors are installed at key nodes to enable the acquisition of operating parameters, release determination, and handling of anomalies.

[0030] The diffusion dialysis module 301 can be a plate-and-frame or spiral-wound assembly with a feed chamber and a dialysate chamber separated by an ion exchange membrane. Mixed acid is introduced on the feed side and dialysate is introduced on the dialysate side. The concentration gradient drives the free acid to migrate to the dialysate side to form osmotic acid, while simultaneously repelling metal ions to a certain extent. The free acid recovery rate can be calculated as the ratio of the amount of recovered free acid to the amount of feed free acid.

[0031] The electrodialysis module 302 can be formed by an electrodialysis stack and electrode chambers with alternating arrangement of cation exchange membranes and anion exchange membranes. Ion migration is achieved by applying a DC electric field to adjust the ionic composition and conductivity of the treatment solution. The current density can be adjusted within a preset window by the controller and human-machine interface 309, and the energy consumption per unit of acid production is constrained by the energy efficiency objective function J.

[0032] See Figure 3 The membrane contactor 303 can be a hollow fiber membrane contactor, equipped with an inlet 303-1, an outlet 303-2, a vacuum or inert gas replacement port 303-3, and a backflow port 303-4. During operation, the treatment liquid enters through 303-1 and flows out through 303-2. The membrane side is provided with negative pressure or replacement conditions by a vacuum system or inert gas source via 303-3 to promote the mass transfer of volatile components. The backflow liquid circulation 304 is connected to the membrane side or the predetermined mass transfer side via 303-4, so that the volatile components are absorbed in the acidic backflow liquid and form a closed loop.

[0033] The backflow liquid circulation 304 may include a backflow tank, a metering pump, and a heat exchanger. The backflow tank is used to contain acidic backflow liquid, the metering pump is used to provide circulation flow rate, and the heat exchanger is used to regulate the temperature of the backflow liquid. The acidity and circulation flow rate of the backflow liquid can be recorded by the controller and human-machine interface 309 and used for release traceability.

[0034] See Figure 4 The arsenic removal module 305 can employ a diaphragm-partitioned structure, separating the oxidant supply chamber from the mainstream complexing chamber. The oxidant enters the oxidant supply chamber through the oxidant inlet and, under the controlled release of the diaphragm, provides an oxidizing environment to the mainstream side to promote arsenic valence state conversion. Complexation sites or adsorption media are provided within the mainstream complexing chamber to selectively capture arsenic. The oxidant can be hydrogen peroxide, hypochlorite, ozone, or other reagents that can provide oxidizing power under acidic conditions. The complexation sites or adsorption media can be iron-based adsorption media, metal oxide supported media, or resins or membrane materials with complexing functional groups. These are merely examples and do not constitute a limitation.

[0035] The bypass and reflux valve assembly 306 is used to switch the treatment liquid to the reflux path and connect it to the cleaning circuit when the release judgment fails to meet the standard or an abnormality is triggered; the on-site cleaning can adopt at least two-stage cleaning sequence, including acid washing and water washing or alkali washing and water washing, and the specific cleaning medium and time can be set according to the scale of the equipment and the pollution load.

[0036] Safety instrumented function 307 is used to interlock and handle integrity anomalies. When any of the following triggering conditions are met, such as negative pressure system anomaly, abnormal increase in transmembrane pressure difference, critical point temperature or liquid level exceeding the limit, or online calibration residual or calibration deviation δ continuously exceeding the threshold, material stop is executed first, followed by venting or inert gas replacement, and the valve group is driven to switch to bypass reflux; the event and timestamp are recorded by the controller and human-machine interface 309 for traceability.

[0037] See Figures 1 to 5 The examples provide acid ratios, diffusion dialysis flow rates and recovery rates, electrodialysis current densities and energy consumption, relative vacuum of the membrane contactor and acidity of the backflow solution, and pH and residence time of the arsenic removal unit. The abnormal interlock priorities and purging or inert gas replacement procedures are described.

[0038] Reference Table of Figure Labels 301: Diffusion dialysis module; 302: Electrodialysis module; 303: Membrane contactor; 303-1: Liquid inlet; 303-2: Liquid outlet; 303-3: Vacuum or inert gas displacement port; 303-4: Back suction port; 304: Recirculation of backflow liquid (recirculation tank, metering pump, heat exchanger); 305: Select the arsenic removal module; 306: Bypass and reflux valve assembly; 307: Safety Instrumented Function (SIF); 308: Three-parameter calibration cavity; 309: Controllers and Human Machine Interfaces (HMIs); 310: Release gate.

[0039] Example 1 Standard Operating Condition like Figures 1 to 5 The device includes a diffusion dialysis module 301, an electrodialysis module 302, a membrane contactor 303, a backflow liquid circulation system 304, a selective arsenic removal module 305, a bypass and reflux valve assembly 306, a safety instrument function 307, a three-parameter calibration chamber 308, a controller and human-machine interface 309, and a release port 310. The representative ratio (mass fraction) of the mixed acid is: HF 2%, HNO3 12%, HCl 4%. The diffusion dialysis feed-to-permeate ratio is 1:1.0, with a free acid recovery rate of approximately 65%; the electrodialysis process is performed at 10 mA·cm⁻¹. -2 The system adaptively adjusts based on the unit acid production energy consumption as the objective function; the membrane contactor 303 operates at a relative vacuum of 0.06 MPa and a backflow solution pH of 1.5–2.0; the arsenic removal module 305 performs transmembrane oxidation-complexation under acidic conditions (e.g., pH 0.5–3.0) with a residence time of approximately 30 min. Release is determined by a three-parameter model; example data is shown in Table 3.

[0040] During the kth batch cycle of continuous operation, the controller and human-machine interface 309 sequentially perform the following operations: (1) collect online or offline data such as conductivity, density, temperature, NOx, HF, and total arsenic; (2) call the three-parameter online calibration model to calculate acid concentration and impurity index; (3) compare the calculation results with the release threshold and form a release judgment; (4) when any indicator fails to meet the release threshold, the instruction valve group switches to bypass reflux and performs two-stage on-site cleaning; (5) when all indicators meet the release threshold, the instruction valve group points to the release port 310 and generates a release record. The above judgment and actions are consistent in each batch cycle of Example 1.

[0041] Example 2: Abnormalities and SIF Handling After 6 hours of continuous operation, the transmembrane pressure difference of the simulated membrane contactor 303 abnormally increased and the backflow liquid temperature exceeded the limit, meeting the SIF trigger condition. The controller and human-machine interface 309 sequentially executed the following steps: stopped feeding, completed system purging or purging with inert gas, then switched the valve group to bypass reflux, and recorded event information and timestamps. After the parameters were restored and passed the integrity retest, the system was reset and restarted in the order of Example 1.

[0042] Example 3 Industrial Validation, 50 L·h -1 class A processing capacity of 50 L·h -1 Continuous operation verification was conducted on the mixed acid recovery unit. The unit is designed according to... Figure 1 The process flow diagram shows the sequential connection of diffusion dialysis module 301, electrodialysis module 302, membrane contactor 303, arsenic removal module 305, and release port 310. It also includes a backflow liquid circulation system 304, a bypass and reflux valve assembly 306, a three-parameter calibration chamber 308, a controller and human-machine interface 309, and safety instrumented functions 307. During continuous operation, samples are collected at the diffusion dialysis outlet, membrane contactor outlet, arsenic removal outlet, and release batch according to a preset sampling cycle. Free acid recovery rate, NOx, HF, total arsenic, and online calibration deviation of the three parameters are measured. Examples of key node index changes are shown in Table 2, and representative statistical results are shown in Table 3.

[0043] Comparative Example C: Under the same equipment and feeding conditions, the backflow liquid circulation 304 is eliminated, and the three-parameter release judgment is not used; instead, manual verification and release are performed. Comparative Example C is used to compare and illustrate the effects of backflow circulation and release logic on process stability and traceability.

[0044] Table 2 Examples of Key Node Indicator Changes Key ports and connectivity See Figure 3The membrane contactor 303 is equipped with an inlet 303-1, an outlet 303-2, a vacuum or inert gas replacement port 303-3, and a back suction port 303-4. The inlet 303-1 is connected to the upstream pipeline to introduce the liquid to be treated, and the outlet 303-2 is connected to the downstream arsenic removal module 305. The vacuum or inert gas replacement port 303-3 is connected to a vacuum system or inert gas source to provide a negative pressure environment or for replacement. The back suction port 303-4 is connected to a back suction liquid circulation 304, which includes a back suction tank, a metering pump, and a heat exchanger, used to circulate and regulate the temperature of the absorbent liquid and return the back suction liquid to a predetermined position on the membrane contactor 303.

[0045] Judgment and threshold In one implementation, total arsenic, NOx, HF, and the online calibration deviation of these three parameters can be used as release criteria, and the controller can set the release threshold in conjunction with reuse specifications. For example, under a certain validation condition, the total arsenic level can be set to no higher than 10 μg·L⁻¹. -1 NOx not exceeding 50 mg·L -1 HF not exceeding 30 mg·L -1 Furthermore, the online calibration deviation of the three parameters must not exceed 5% as a release condition. When any indicator fails to meet the release condition, the controller instructs the valve group to switch to bypass reflux and perform on-site cleaning; when all indicators meet the release condition, a release record is output and the vehicle is released.

[0046] Table 3 Representative Data (S3) As shown in Table 3, under representative operating conditions, the diffusion dialysis section achieved a stable output of free acid recovery rate; the membrane contactor 303 section had a stable reduction effect on NOx and HF levels, keeping them within the set upper limit range; the total arsenic at the arsenic removal outlet could be stably controlled at a low level, and the online calibration deviation of the three parameters met the accuracy requirements for release judgment. These results are consistent with the sequential coupling of the modules, the backflow liquid circulation, and the release judgment logic described in this application, verifying the feasibility and stability of the method and system from a data perspective.

[0047] The sample size n in Table 3 represents the number of valid samples obtained under continuous operation conditions according to the preset sampling period. "Mean ± 1σ" in the table represents the sample mean and sample standard deviation of the corresponding indicator; the minimum and maximum values ​​are the statistical results within the same sampling window. The detection and calculation methods are performed as shown in the table, and the online calibration deviation of the three parameters is calculated as the percentage of relative error defined in the "Measurement and Calibration Methods" section.

[0048] The method and system described in this application can be implemented in industrial settings and can operate in continuous or quasi-continuous mode. Quasi-continuous operation can be defined as follows: within an overall continuous processing framework, the feeding, release, and cleaning processes are periodically switched or intermittently executed according to a preset strategy to maintain stable system recovery and regeneration.

[0049] In some implementations, each processing unit is integrated and arranged as an engineered complete set of equipment, and the control unit executes control logic based on online monitoring signals and preset thresholds / criteria. The control logic includes, but is not limited to: bypass backflow and flow path switching, release and isolation control, on-site cleaning triggering and execution, and release record and traceability data generation, thereby forming a closed loop of "monitoring-judgment-disposal-recording", enabling the system to have traceable release judgment and abnormal handling capabilities.

[0050] In terms of engineering deployment, the system can be installed as a skid-mounted or cabinet-type complete unit in the waste acid recovery station or centralized regeneration station of the semiconductor manufacturing production line, and can be connected and interfaced with the front-end collection / homogenization unit and the back-end reuse acid supply unit. The system's processing capacity can be scaled up or down according to the production line scale; for example, the system's processing capacity can be 10–2000 L·h. -1 (or equivalent mass flow rate), higher throughput can be achieved by connecting multiple devices in parallel. The above values ​​are engineering examples used to illustrate feasibility and do not constitute a limitation on the scope of protection.

[0051] To adapt to strong acid and fluorine-containing operating conditions, key wetted components can be made of fluoropolymer materials (such as PFA, PTFE, PVDF, ETFE) or equivalent corrosion-resistant materials; pressure-bearing and heat-exchange components can be made of corrosion-resistant alloy materials (such as Hastelloy, titanium) or equivalent materials; and seals can be made of acid-resistant sealing materials (such as FFKM, PTFE-coated seals) or equivalent solutions. The above material selections are only examples, and adjustments can be made in actual engineering projects based on operating conditions such as acid composition, operating temperature, impurity load, and pressure rating.

[0052] In terms of control and safety, the control unit can adopt a PLC and / or DCS, and can be connected to a human-machine interface and data recording system to generate release records and traceability reports from online monitoring data, actuator action logs, release judgment results, and abnormal handling processes. In some implementations, the system can be configured with a safety interlock function, the triggering conditions of which may include negative pressure / vacuum abnormality, transmembrane pressure difference abnormality, critical temperature / liquid level exceeding the limit, continuous exceedance of online calibration residual, gas absorption circuit abnormality, etc.; after triggering, it can perform handling actions such as material stoppage, isolation, bypass reflux, venting and / or inertial replacement to improve the certainty of abnormal condition handling and operational safety.

[0053] In terms of maintenance and byproduct management, the system can perform on-site cleaning according to preset cycles and / or abnormal triggers, and can periodically check and replace the membrane stack, membrane contactor, and arsenic removal medium. Arsenic removal medium replacement materials and concentrated residual liquid can be collected, labeled, and disposed of in compliance with applicable regulations; the removed volatile components can be captured through the backflow liquid and connected to the exhaust gas treatment facility to reduce emission risks.

Claims

1. A method for the recovery and selective removal of arsenic from mixed acid, characterized in that, include: S1, the mixed acid to be treated is fed into the diffusion dialysis unit to recover free acid and obtain osmotic acid and residual liquid; S2, the remaining liquid is introduced into the electrodialysis unit to adjust the ionic composition and conductivity; the controller outputs control commands based on online monitoring signals and preset thresholds / criteria to adjust the current density and / or voltage and / or circulation loop flow of the electrodialysis unit; S3, the treatment solution after being treated by the electrodialysis unit is introduced into the membrane contactor, and nitrogen oxides and hydrogen fluoride are removed under vacuum and / or inert gas replacement conditions, and the removed volatile components are absorbed into the backflow liquid to obtain the devolatilization treatment solution; S4, the devolatilization treatment liquid is introduced into the selective arsenic removal unit, so that the devolatilization treatment liquid comes into contact with the oxidant and the complexing / adsorption medium, so as to convert arsenic into a complexable and / or adsorbable form and be selectively captured, to obtain the arsenic removal treatment liquid. S5 calculates acid concentration and impurity index based on conductivity, density and temperature obtained from online sensors through a three-parameter online calibration model; Calculate the calibration deviation δ and compare it with the preset threshold δ0, and perform a release judgment based on the comparison result: when the release conditions are met, generate a release record and release the vehicle; when the release conditions are not met, switch to bypass reflux and perform and / or trigger on-site cleaning.

2. The method according to claim 1, characterized in that, The dialysate to feed volumetric flow rate ratio of the diffusion dialysis unit is 0.8–1.2:1, and the free acid recovery rate is 50%–80%; the current density of the electrodialysis unit is 5–20 mA·cm⁻¹. -2 .

3. The method according to claim 1, characterized in that, The membrane contactor operates under a relative vacuum of 0.02 to 0.08 MPa, and the pH of the backflow liquid is 1.0 to 3.

0.

4. The method according to claim 1, characterized in that, The selective arsenic removal unit includes an oxidant supply side, a separator membrane separated from the treatment liquid side, and a complexing / adsorption medium disposed on the treatment liquid side. The oxidant is transferred from the oxidant supply side across the separator membrane to the treatment liquid side to form an oxidizing environment on the treatment liquid side, and works in conjunction with the complexing / adsorption medium to achieve selective arsenic capture.

5. The method according to claim 1, characterized in that, A safety interlock function is set in the system implementing the method. The triggering conditions of the safety interlock function include at least one or a combination of the following: abnormal negative pressure system, abnormal increase in transmembrane pressure difference, critical point temperature exceeding the limit, critical point liquid level exceeding the limit, and online calibration residual and / or calibration deviation δ continuously exceeding a preset threshold. When the safety interlock function is triggered, interlock handling is performed. The interlock handling includes at least closing the release and switching to bypass reflux, and may further perform evacuation and / or inertial replacement.

6. The method according to claim 1, characterized in that, The online calibration of the three parameters involves inputting the online measurements of conductivity, density, and temperature into the calibration model to obtain the predicted acid concentration C. pred And the impurity index, and the predicted acid concentration C pred The impurity index is used as the release criterion; wherein the calibration deviation δ is calculated according to the following formula: ； Among them, C ref The reference acid concentration is obtained from sampling and detection at the corresponding time, and C ref >0; Compare δ with the preset threshold δ0, and determine release when δ≤δ0 and the impurity index meets the preset range.

7. A system for implementing the method of claim 1, characterized in that, include: The diffusion dialysis module, electrodialysis module, membrane contactor and selective arsenic removal module are connected sequentially along the process flow, and a release valve group is set downstream of the selective arsenic removal module. The membrane contactor is provided with an inlet, an outlet, a vacuum port and / or an inert displacement port, and is circulated with the backflow liquid through a backflow port, so as to remove volatile components under vacuum and / or inert displacement conditions and absorb volatile components in the backflow liquid. The system also includes a bypass and reflux valve assembly, used to switch the processing fluid to the reflux path when the release judgment fails to meet the standard and / or an abnormality is triggered; The system also includes a controller, a human-machine interface, and a data recording unit. The controller is electrically connected to at least online sensors including conductivity, density, and temperature, and is configured to drive the switching between the release valve group and the bypass and return valve group. The data recording unit is used to record online monitoring data and valve group action / operation parameters to generate traceability records. The human-machine interface is used to display and / or query the traceability records. The system is also equipped with a safety interlock function, which is used to perform interlocking actions on the release valve group and / or the bypass and return valve group when the triggering conditions are met.

8. The system according to claim 7, characterized in that, The backflow liquid circulation includes a backflow tank, a metering pump, and a heat exchanger to maintain absorption efficiency.

9. The system according to claim 7, characterized in that, The controller is configured to construct an energy efficiency target function J and output control commands based on the energy efficiency target function J to adjust at least one operating parameter of the diffusion dialysis module and / or the electrodialysis module; in, ; E represents the energy consumption per unit of acid production, σ represents the conductivity measured by the online sensor, σ0 represents the target conductivity, and Var N (σ) represents the variance of σ obtained from N samplings within a preset time window, where α, β, and γ are weighting coefficients. The data recording unit records the relevant data of the energy efficiency target function J and the operating parameters for traceability, and the human-machine interface is used to display the traceability information.

10. The system according to claim 7, characterized in that, The system is equipped with a three-parameter online calibration chamber and forms a hard interlock with the release valve group. When the online calibration residual and / or calibration deviation δ continuously exceed the preset threshold, the interlock closes the release valve group and drives the bypass and return valve group to switch to the return path.

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