Cyclic regeneration treatment method of stainless steel pickling waste liquid

Abstract

The invention discloses a cyclic regeneration treatment method of stainless steel pickling waste liquid, which realizes full-flow recycling of the pickling waste liquid by constructing a closed-loop system of pretreatment, adsorption, desorption, recovery, regeneration and circulation. A molecularly imprinted polymer adsorption technology is adopted, targeted capture of Cr < 3 + >, Ni < 2 + > and Fe < 2 + > / 3 < + > is achieved through specific recognition sites, and the bottleneck that a traditional adsorbent is poor in selectivity is broken through; the supercritical CO fluid extraction technology utilizes the characteristics of high diffusivity and low surface tension, efficient desorption of metal ions is achieved under mild conditions, and secondary pollution caused by a traditional organic solvent is avoided. A technical closed loop is formed among the steps through parameter synergy and substance circulation, and finally the dual purposes of full-amount regeneration of the pickling waste liquid and efficient recovery of metal resources are achieved.

Description

Technical Field

[0001] This application relates to the field of stainless steel pickling waste liquid treatment technology, and more specifically, to a method for recycling and regenerating stainless steel pickling waste liquid. Background Technology

[0002] The waste liquid generated during stainless steel pickling contains various heavy metal ions and acidic components, and traditional treatment methods have many technical shortcomings. The currently mainstream evaporation crystallization method frequently encounters pipe blockage due to crystallization, leading to high equipment maintenance costs. The lime neutralization method produces large amounts of fluorine-containing heavy metal sludge, which is classified as hazardous waste. Subsequent disposal not only incurs high costs but also poses a risk of secondary pollution.

[0003] Existing technologies show significant limitations in handling systems with coexisting multi-metal ions. Conventional ion exchange resins are ineffective against Cr... 3+ Ni 2+ Fe 2+ / 3+ The selectivity of metal ions is poor, making effective separation difficult. While a two-step neutralization process can partially improve treatment efficiency, it still cannot avoid the generation of large amounts of neutralized sludge. More importantly, these methods fail to achieve effective recovery of metal resources, resulting in a waste of valuable resources.

[0004] In acid recovery, traditional methods often require large amounts of fresh acid for replenishment, which not only increases operating costs but also makes it difficult for wastewater treatment systems to achieve true closed-loop operation. Furthermore, existing technologies generally suffer from high energy consumption and organic solvent residues during the treatment process, failing to meet green environmental protection requirements and increasing environmental compliance costs for enterprises.

[0005] To address the aforementioned issues, existing technologies urgently need improvement. Summary of the Invention

[0006] The purpose of this application is to provide a method for recycling and regenerating stainless steel pickling waste liquid, which has the advantages of improving treatment efficiency, avoiding pipeline blockage, reducing hazardous waste, recovering metal resources, and reducing operating costs.

[0007] This application provides a method for recycling and regenerating stainless steel pickling waste liquid, the technical solution of which is as follows:

[0008] include:

[0009] Step 1, Waste liquid pretreatment: Filter the stainless steel pickling waste liquid to remove suspended particles and dilute it;

[0010] Step 2, MIPs Adsorption: Adsorption of metal ions (Cr) in the waste liquid by molecularly imprinted polymers (MIPs). 3+ Ni2+ Fe 2 + / 3+ Adsorption occurs;

[0011] Step 3, SC-CO desorption: Supercritical CO fluid extraction (SC-CO) is used to desorb metal ions (Cr) from the molecularly imprinted polymer. 3+ Ni 2+ Fe 2+ / 3+ Desorption occurs;

[0012] Step 4, Metal Recovery: Electrodeposition is performed on the desorbed solution to obtain the elemental metal;

[0013] Step 5, Acid Regeneration: The waste acid from which metal has been removed is concentrated by vacuum distillation, and after adding new acid, it is returned to the pickling tank;

[0014] Step 6, CO recycling: The desorbed CO is dehydrated by molecular sieve and then liquefied and stored.

[0015] Furthermore, this application also proposes that step 1 includes:

[0016] Step 101: Filter the stainless steel pickling waste liquid to remove suspended particles, and adjust the pH value to 2.5-3.0 with dilute hydrochloric acid;

[0017] Step 102: Determine the concentration of total metal ions in the filtered waste liquid;

[0018] Step 103: Dilute the waste liquid to a target metal ion concentration of 100-500 mg / L, based on the total metal ion concentration.

[0019] Furthermore, this application also proposes that step 2 includes:

[0020] Step 201: Pass the pretreated waste liquid into a fixed-bed reactor filled with molecularly imprinted polymers (MIPs);

[0021] Step 202: Control the space velocity of the fixed-bed reactor to 1-5 / hour;

[0022] Step 203: Measure the adsorption capacity of molecularly imprinted polymers (MIPs). If the adsorption capacity is lower than the preset value, return to step 201 to continue adsorption. If the preset value is reached, proceed to step 3.

[0023] Furthermore, this application also proposes that step 3 includes:

[0024] Step 301: Place the MIPs adsorbed with metal ions into a supercritical fluid extraction device;

[0025] Step 302, proceed with Cr sequentially 3+Ni 2+ Fe 2+ / 3+ Stepwise extraction:

[0026] Step 302-1: Extract Cr at 15 MPa / 35℃ 3+ 30 minutes;

[0027] Step 302-2: Extract Ni at 10 MPa / 45℃ 2+ 20 minutes;

[0028] Step 302-3, Fe extraction at 7MPa / 60℃ 2+ / Fe 3+ 40 minutes;

[0029] Step 303: During the extraction process, the composition of the eluent is monitored in real time using ICP-MS, based on Cr... 3+ Ni 2+ Fe 2+ / Fe 3+ The extraction temperature and pressure are dynamically adjusted based on the concentration changes.

[0030] Furthermore, this application also proposes that step 4 includes:

[0031] Step 401: The desorption solution is introduced into the electrodeposition unit;

[0032] Step 402: Perform electrodeposition in the electrodeposition unit, controlling the current density to be 150-300 A / m. 2 ;

[0033] Step 403: Determine the purity and recovery rate of the deposited metal. If the requirements are not met, return to step 3 for re-extraction. If the requirements are met, proceed to step 5.

[0034] Furthermore, this application also proposes that step 5 includes:

[0035] Step 501: The demetallized waste acid is concentrated by vacuum distillation at -0.08 to -0.1 MPa;

[0036] Step 502: Mix the concentrated waste acid with the new acid at a mass ratio of 1:3 to 1:4;

[0037] Step 503: Measure the acid concentration after mixing and adjust it to HF 4-6% and HNO 8-10%.

[0038] Furthermore, this application also proposes that step 6 includes:

[0039] Step 601: Reduce the pressure of CO gas to 4 MPa / 25℃;

[0040] Step 602: Dehydrate and liquefy the product using a molecular sieve for storage;

[0041] Step 603: Use part of the CO to drive the compressor, and recycle the rest of the CO.

[0042] Furthermore, this application also proposes that, in step 2, the molecularly imprinted polymers (MIPs) are composed of a mixture of three resins: 70% sulfonic acid groups, 20% hydroxime groups, and 10% dithiocarboxylic acid groups, with the macroporous crosslinked styrene resin having a crosslinking degree of 10%; or, the molecularly imprinted polymers (MIPs) are composed of a mixture of three resins: 75% sulfonic acid groups, 15% hydroxime groups, and 10% dithiocarboxylic acid groups, with the macroporous crosslinked styrene resin having a crosslinking degree of 12%.

[0043] Furthermore, this application also proposes that, in step 3, 5-10% vol of ethanol or acetylacetone is added as an entrainer during supercritical CO fluid extraction (SC-CO) to enhance the solubility of polar metal complexes.

[0044] Furthermore, this application also proposes that step 3 includes the following steps: the desorbed CO is vaporized by a pressure reducing valve, the entrained agent is recovered by a condenser, and after purification, it is compressed into a liquid storage tank for recycling.

[0045] Compared with the prior art, the present invention provides a method for recycling and regenerating stainless steel pickling waste liquid, which has the following beneficial effects:

[0046] 1. This invention employs a combination of molecular imprinting (MIT) and supercritical fluid extraction (SCFE) techniques to achieve the extraction of Cr... 3+ Ni 2+ Fe 2+ / 3+ Highly selective separation and recovery of various metal ions. By optimizing the synthesis and functional design of molecularly imprinted polymers (MIPs) and the desorption mechanism of supercritical CO2 fluid extraction (SC-CO), the partition coefficient (K_d) of the target metal ions was significantly improved to 10. 3 L / kg, far exceeding that of ion exchange resins (K_d=10). 2 L / kg), which solves the problem of low metal ion separation efficiency in existing technologies;

[0047] 2. This invention employs SC-CO desorption technology, which, compared to traditional solvent extraction methods, offers advantages such as low energy consumption and good environmental friendliness. The energy consumption of SC-CO desorption is only 0.8 kWh / m³. 3 Waste liquid, only for solvent extraction (4kWh / m³) 3 It consumes 1 / 5 of the energy, leaves no organic solvent residue throughout the entire process, and reduces CO emissions by 90%, effectively solving the problems of high energy consumption and high pollution in existing technologies.

[0048] 3. This invention achieves efficient separation and recovery of metal ions through optimized MIPs design and SC-CO desorption parameters. Cr 3+ Ni 2+ Fe 2+ / 3+ The recovery rates of the metal ions reached 98%, 99.8%, and 97%, respectively, solving the problem of low metal resource utilization in existing technologies.

[0049] 4. This invention adopts a closed-loop design, achieving full recycling of waste liquid through CO circulation and regenerated acid reuse. After vacuum distillation and concentration, the waste acid is replenished with fresh acid and returned to the pickling tank, avoiding sludge generated during neutralization and precipitation, reducing treatment costs, and solving the sludge treatment problem in traditional methods.

[0050] 5. This invention grafts MIPs layers onto a silica substrate using a surface imprinting method, avoiding the deep burial problem caused by the embedding method and improving mass transfer efficiency. Simultaneously, by controlling the pore size (2-5 nm) and functional group density, it effectively suppresses Ca2+ degradation. 2+ / Mg 2+ The competitive adsorption of interfering ions improves the selectivity coefficient to over 100. Attached Figure Description

[0051] Figure 1 This is a flowchart of the steps in the recycling and regeneration treatment method for stainless steel pickling waste liquid according to the present invention.

[0052] Figure 2 This is a flowchart of step 1 of a method for recycling and regenerating stainless steel pickling waste liquid according to the present invention.

[0053] Figure 3 This is a flowchart of step 2 of the recycling and regeneration treatment method for stainless steel pickling waste liquid according to the present invention;

[0054] Figure 4 This is a flowchart of step 3 of a method for recycling and regenerating stainless steel pickling waste liquid according to the present invention.

[0055] Figure 5 This is a flowchart of step 4 of the recycling and regeneration treatment method for stainless steel pickling waste liquid according to the present invention.

[0056] Figure 6 This is a flowchart of step 5 of the recycling and regeneration treatment method for stainless steel pickling waste liquid according to the present invention.

[0057] Figure 7 This is a flowchart of step 6 of a method for recycling and regenerating stainless steel pickling waste liquid according to the present invention. Detailed Implementation

[0058] The technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. The components of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application. It should be noted that similar reference numerals and letters in the following drawings indicate similar items; therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. Furthermore, in the description of this application, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0059] In the treatment of stainless steel pickling waste liquid, traditional methods such as evaporation crystallization or lime method have significant technical limitations. Evaporation crystallization, due to the high concentration of fluorides and nitrates in the waste liquid, easily leads to the formation of complex salt precipitates during crystallization, causing scale buildup in heat exchangers and pipe blockage, reducing system heat transfer efficiency and shortening equipment lifespan. The lime method generates calcium fluoride sludge containing heavy metals through neutralization reactions, but chromium and nickel ions in the sludge form stable complexes with fluorine, making metal resource recovery difficult. Simultaneously, the neutralization process generates a large amount of acid mist, increasing the load on exhaust gas treatment. Existing processes lack the selective separation capability for multivalent metal ions, resulting in metal purity being affected by impurity ions during electrodeposition, impacting the quality of the recovered product. Furthermore, traditional desorption technologies rely on organic solvents, requiring additional solvent residue removal after extraction, increasing process complexity and the risk of secondary pollution.

[0060] For example, in the two-step neutralization method for treating Cr-containing substances 3+ 1200mg / L, Ni 2+ 800mg / L, Fe 3+ When dealing with 5000 mg / L pickling waste liquid, after adjusting the pH to 4.5-5.0 by adding lime slurry during the pre-neutralization stage, Fe... 3+ Fe(OH)₂ precipitate is formed preferentially, but the precipitate encapsulates unreacted Cr. 3+ and Ni 2+This causes a sharp drop in adsorption capacity in subsequent ion exchange processes. During the main neutralization stage, sodium hydroxide needs to be added to raise the pH to above 8.5 to precipitate residual metals. However, this process causes fluoride ions to combine with calcium ions to form CaF precipitate, resulting in fluoride-containing heavy metal sludge. The treated wastewater still contains residual metal ions that do not meet standards, requiring the addition of a deep treatment unit, thus increasing the system's footprint. When sulfuric acid is used for backwashing and regenerating the resin in the desorption process, acidic regeneration wastewater containing heavy metals is generated, requiring the construction of an additional neutralization tank for treatment, increasing operating costs.

[0061] If the above problems are not resolved, the system will face multiple technical obstacles: low metal ion separation efficiency leads to a decrease in current efficiency in the electrodeposition process, increasing energy consumption; the stable binding forms of heavy metals and fluorine in neutralized sludge hinder resource utilization and increase hazardous waste disposal costs; residual organic solvents contaminate the regenerated acid solution, affecting the quality of reused pickling; and the inability to recycle the desorption medium increases CO emissions, violating clean production requirements. These problems will severely restrict the sustainable operation of the pickling wastewater treatment system, reduce overall resource recovery efficiency, and bring potential environmental compliance risks.

[0062] Faced with the aforementioned problems, this application first considered how to overcome the limitations of traditional treatment processes. Addressing the scaling and clogging issues inherent in evaporation crystallization, this application attempted to replace the static crystallization process with a fluid-medium circulation method, maintaining stable system operation through dynamic filtration. For fluorine-containing heavy metal sludge generated by the lime process, it explored adsorption technologies for selectively separating metal ions to avoid neutralization reactions. To address the risk of residual organic solvents, the feasibility of environmentally friendly desorption media was investigated. Analysis of the possibilities of different process combinations revealed that while improving the adsorption material alone could increase metal recovery rates, it could not solve the pollution problem in the subsequent desorption stage; optimizing only the desorption process could not guarantee the selectivity of the initial adsorption. Ultimately, an adsorption-desorption synergistic system was chosen, achieving full-process optimization through the coupling of molecular recognition and supercritical fluid extraction technologies. The introduction of molecular imprinting technology solved the multi-metal separation problem, while the application of supercritical fluids overcame the environmental bottleneck of desorption media; the combination of the two forms a closed-loop treatment chain.

[0063] In this regard, such as Figure 1-7 As shown, this application proposes a method for the recycling and regeneration of stainless steel pickling waste liquid, comprising: Step 1, waste liquid pretreatment: filtering and removing suspended particles and diluting the stainless steel pickling waste liquid; Step 2, MIPs adsorption: using molecularly imprinted polymers (MIPs) to adsorb metal ions Cr in the waste liquid. 3+ Ni 2+ Fe 2+ / 3+ Adsorption occurs; Step 3, SC-CO desorption: Supercritical CO fluid extraction (SC-CO) is used to remove Cr metal ions from the molecularly imprinted polymer. 3+ Ni2+ Fe 2+ / 3+ Desorption is performed; Step 4, Metal recovery: The desorbed solution is electrodeposited to obtain elemental metal; Step 5, Acid regeneration: The waste acid from which metal has been removed is concentrated by vacuum distillation, replenished with fresh acid, and returned to the pickling tank; Step 6, CO recycling: The desorbed CO is dehydrated by molecular sieve and then liquefied and stored.

[0064] Filtration and dilution of stainless steel pickling waste liquid for suspended particle removal refers to removing solid impurities from the waste liquid through physical filtration and adjusting the waste liquid concentration to suit subsequent treatment processes. Specifically, dilute hydrochloric acid can be used to adjust the pH to an acidic range, and then deionized water can be added to dilute the metal ion concentration to a specific range. This operation can reduce the mass transfer resistance in the subsequent adsorption stage and avoid adsorbent poisoning caused by high concentrations of metal ions. Molecularly imprinted polymers for Cr 3+ Ni 2+ Fe 2+ / 3+ Adsorption refers to the selective capture of target metal ions using synthetic polymers with specific recognition sites. Specifically, resin systems combining sulfonic acid, hydroxyoxime, and dithiocarbamate functional groups can be used. Pre-assembly of template molecules forms adsorption sites that match the stereostructure of the target metal ions, effectively distinguishing the coordination characteristics of different metal ions. Supercritical CO2 fluid extraction and desorption of metal ions utilizes the high diffusivity and low surface tension of carbon dioxide in a supercritical state to achieve efficient desorption of metal ions. A gradient pressure and temperature control mode can be used, adjusting the type and proportion of entrainer to change the fluid polarity. This method achieves selective desorption of metal ions without damaging the adsorbent structure. Electrodeposition to produce elemental metals involves converting metal ions in the desorbate into solid metals through electrochemical reduction reactions. A segmented current density control method can be used, optimizing electrode materials and electrolyte composition to improve metal deposition purity. This step achieves high-value recovery of metal resources. Vacuum distillation concentration of demetallized waste acid involves lowering the boiling point of waste acid under negative pressure to achieve water evaporation and acid regeneration. Specifically, a multi-stage vacuum distillation apparatus can be used. By precisely controlling the vacuum level and heating temperature, acid mist can be prevented from escaping. This process can restore the acid concentration and reduce the consumption of new acid. CO dehydration and liquefaction storage via molecular sieves refers to drying the carbon dioxide medium after supercritical extraction and converting it into a liquid state for storage. Specifically, a dehydration system composed of activated alumina and silica gel can be used. Phase conversion of the medium is achieved through cyclic compression and cooling. This measure ensures that the recycling rate of the extractant reaches over 95%.

[0065] The core innovation of this application lies in constructing a closed-loop system for the full-process resource utilization of pickling waste liquid. It achieves highly selective adsorption of multi-metal ions through molecular imprinting technology, overcomes the efficiency bottleneck of traditional desorption processes by combining it with supercritical fluid extraction technology, and integrates an acid regeneration and media circulation system to form a clean production model with no secondary pollution emissions. This system organically integrates multiple technical elements such as specific identification of adsorption materials, supercritical phase transition control, and electrochemical reduction, achieving efficient recovery of metal resources while simultaneously regenerating the waste acid medium in situ. This effectively solves the technical problems of low separation efficiency, high energy consumption and pollution, and low resource utilization in traditional treatment methods.

[0066] The working process and principle of this application are as follows: This technical solution achieves the full-process resource utilization of pickling waste liquid by constructing a closed-loop system of pretreatment-adsorption-desorption-recovery-regeneration-circulation. In the waste liquid pretreatment stage, suspended particles are removed through filtration and dilution, creating a suitable concentration environment for subsequent selective adsorption. Molecularly imprinted polymer adsorption technology is employed, using specific recognition sites to achieve Cr… 3+ Ni 2+ Fe 2+ / 3+ Targeted capture overcomes the bottleneck of poor selectivity in traditional adsorbents. Supercritical CO2 fluid extraction technology utilizes its high diffusivity and low surface tension to achieve efficient desorption of metal ions under mild conditions, avoiding secondary pollution caused by traditional organic solvents. Electrodeposition converts metal ions in the desorbate into elemental forms, achieving high-value resource recovery. Vacuum distillation concentration combined with fresh acid replenishment restores the concentration of the pickling solution while avoiding the generation of neutralization sludge. The CO2 recycling system ensures the reuse of the extraction medium through molecular sieve dehydration and liquefaction storage, forming a complete material recycling chain. Through parameter coordination and material recycling, a technical closed loop is formed between each step, ultimately achieving the dual goals of full regeneration of pickling wastewater and efficient recovery of metal resources.

[0067] As a preferred embodiment, the solution of this application is specifically implemented as follows:

[0068] First, the waste liquid undergoes pretreatment. The stainless steel pickling waste liquid is filtered through a filter press to remove suspended particulate matter. The filtered waste liquid is then diluted to a suitable concentration using a dilution device.

[0069] Next, MIPs adsorption was performed. The pretreated waste liquid was pumped into a fixed-bed reactor filled with molecularly imprinted polymers. The molecularly imprinted polymers consist of three functional groups: sulfonic acid groups, hydroxyoxime groups, and dithiocarboxylic acid groups, which are effective for adsorbing Cr. 3+ Ni 2+ Fe 2+ / 3+ It has specific recognition capabilities. By controlling the flow rate of the waste liquid in the fixed bed, the metal ions can be fully contacted and adsorbed by the MIPs.

[0070] Further, SC-CO desorption is performed. The adsorbed MIPs are transferred to a supercritical fluid extraction device. Supercritical CO fluid is introduced, and the temperature and pressure parameters are adjusted. CO in the supercritical state has liquid-like dissolving ability and gas-like diffusion ability, which can penetrate the pore structure of MIPs, form complexes with metal ions, and extract them.

[0071] Subsequently, metal recovery is performed. The metal ion-containing solution obtained from desorption is introduced into an electrolytic cell. By adjusting the current density, elemental metals are deposited on the cathode. Different metals can be selectively deposited by controlling the potential.

[0072] Next, acid regeneration is performed. The waste acid after metal removal is sent to a vacuum distillation tower. It is concentrated under reduced pressure to remove some of the water. The concentrated waste acid is mixed with freshly prepared acid solution in a certain proportion, adjusted to a suitable concentration, and then returned to the pickling tank for recycling.

[0073] Finally, the CO is recycled. The desorbed CO gas is pressurized by a compressor and then passed through a molecular sieve adsorption tower to remove moisture. The dried CO gas is then cooled and liquefied, and stored in a liquid CO storage tank for future use.

[0074] Through the above-described scheme, this application achieves efficient recycling and regeneration of stainless steel pickling waste liquid. The combination of molecular imprinting technology and supercritical fluid extraction improves the separation efficiency of metal ions, solving the problem of poor selectivity in traditional methods. Supercritical CO, as a green solvent, replaces organic solvents for desorption, reducing energy consumption and avoiding secondary pollution. Electrodeposition directly recovers elemental metals, improving resource utilization. Waste acid regeneration and CO recycling form a closed-loop treatment system, reducing waste emissions. The overall scheme overcomes the problems of low metal separation efficiency, high energy consumption, and high pollution in existing technologies, achieving full recycling of pickling waste liquid and efficient recovery of metal resources.

[0075] In some of the solutions described above in this application, waste liquid pretreatment is proposed to remove suspended particles and dilute the waste liquid. However, in this process, there may be a problem that the subsequent molecularly imprinted polymer adsorption efficiency will be reduced due to the failure to control the pH of the waste liquid. At the same time, if the dilution ratio is not adjusted according to the actual metal ion concentration, the waste liquid may be insufficiently or excessively diluted, thereby affecting the mass transfer efficiency of the adsorption reaction and the selective separation of the target metal ions.

[0076] In this regard, this application further proposes that step 1 includes: filtering the stainless steel pickling waste liquid to remove suspended particles, adjusting the pH value to 2.5-3.0 with dilute hydrochloric acid; measuring the concentration of total metal ions in the filtered waste liquid; and diluting the waste liquid to a target metal ion concentration of 100-500 mg / L based on the total metal ion concentration.

[0077] The pH adjustment involves using dilute hydrochloric acid to shift the initial pickling waste liquid from a strongly acidic range to a weakly acidic range. This can be achieved by adding 0.1-1 mol / L dilute hydrochloric acid dropwise while monitoring the pH count in real time. The total metal ion concentration can be quantitatively analyzed using atomic absorption spectrometry or inductively coupled plasma mass spectrometry, for example, by converting absorbance data into concentration values ​​using a standard curve method. The dilution ratio is calculated based on the ratio of the target metal ion concentration to the measured total concentration. Dilution is required when the total concentration exceeds 500 mg / L, while concentration is required when the total concentration is below 100 mg / L, or the solution can be directly proceeded to subsequent processing.

[0078] Specifically, after filtering out suspended particles larger than 50 μm, the pH is adjusted to 2.5-3.0 to ensure that the metal ions in the waste liquid are in a suitable charge state for complexation and adsorption, while preventing the functional groups on the surface of the molecularly imprinted polymer from becoming deactivated due to excessive protonation. The determination of the total metal ion concentration provides a precise basis for the dilution operation. For example, when the measured total concentration is 2000 mg / L, the waste liquid needs to be diluted four times to reduce it to 500 mg / L. Controlling the metal ion concentration after dilution within the range of 100-500 mg / L ensures that the adsorption reaction occurs within the optimal mass transfer rate range of the molecularly imprinted polymer. For example, the adsorption rate constant measured at 300 mg / L is 0.15 min⁻¹, significantly higher than the 0.08 min⁻¹ at 1000 mg / L. This concentration range also reduces the viscosity of the waste liquid, increasing the diffusion coefficient to 1.2 × 10⁻¹. -5 cm 2 / s, which is 30% higher than that of undiluted waste liquid, thereby optimizing the kinetic conditions of the adsorption reaction.

[0079] As a preferred embodiment, the solution of this application is specifically implemented as follows:

[0080] In the wastewater pretreatment step, the stainless steel pickling wastewater was first filtered through a 0.45 μm pore size filter membrane to remove suspended particles. Then, 0.1 mol / L dilute hydrochloric acid solution was added dropwise to the wastewater while the pH was monitored in real time using a pH meter until the pH reached 2.8. Next, the concentration of total metal ions in the filtered wastewater was determined using inductively coupled plasma mass spectrometry (ICP-MS). Based on the measured total metal ion concentration, the wastewater was diluted with deionized water to a target metal ion concentration of 300 mg / L. The entire pretreatment process was carried out at room temperature with a stirring speed maintained at 200 rpm.

[0081] Through the above technical solution, this application achieves effective pretreatment of stainless steel pickling waste liquid. By adjusting the pH value to a suitable range, the protonation deactivation of functional groups of molecularly imprinted polymers by a strongly acidic environment is avoided, while a suitable charge environment is provided for the complexation and adsorption of metal ions. By measuring the total metal ion concentration and performing appropriate dilution, the high efficiency and stability of the subsequent adsorption process are ensured. This pretreatment method not only improves the adsorption efficiency of molecularly imprinted polymers but also enhances the mass transfer efficiency of the waste liquid, laying the foundation for subsequent selective separation of metal ions.

[0082] In some of the schemes described above in this application, due to the differences in the physicochemical properties of different metal ions, it is difficult to achieve efficient gradient desorption of multiple metal ions under a single extraction condition. At the same time, the lack of dynamic monitoring and parameter adjustment mechanism for the desorption process leads to large fluctuations in desorption efficiency and insufficient selectivity for target metals.

[0083] To this end, this application further proposes placing MIPs adsorbed with metal ions in a supercritical fluid extraction device, and sequentially performing Cr extraction. 3+ Ni 2+ Fe 2+ / 3+ Stepwise extraction: Extraction of Cr at 15MPa / 35℃ 3+ Ni was extracted at 10 MPa / 45℃ for 30 minutes. 2+ Fe was extracted for 20 minutes at 7 MPa / 60℃. 2+ / Fe 3+ For 40 minutes, the composition of the eluent was monitored in real time using ICP-MS during the extraction process, based on Cr... 3+ Ni 2+ Fe 2+ / Fe 3+ The extraction temperature and pressure are dynamically adjusted based on the concentration changes.

[0084] The stepwise extraction parameters can be set based on the differences in the stability of metal complexes. For example, Cr 3+ The extraction stage pressure can be controlled within the range of 14.5-15.5 MPa, and the temperature can be set to 34-36℃; Ni 2+ The stage pressure can be adjusted to 9.5-10.5 MPa, and the temperature is in the range of 44-46℃; Fe 2+ / 3+ The stage pressure can be reduced to 6.8-7.2 MPa, while the temperature is maintained at 58-62℃. The extraction time can be adaptively adjusted according to the metal desorption kinetics, for example, Cr. 3+ The phase can last for 28-32 minutes, Ni 2+ The phase can last 18-22 minutes, Fe 2+ / 3+ The phase can last 38-42 minutes.

[0085] Specifically, the desorption process achieves metal separation through the coordinated control of pressure-temperature gradients and real-time monitoring. In Cr... 3+ During the desorption stage, high pressure and low temperature conditions can maintain the high solubility of supercritical CO. For example, when the pressure is maintained at 15 MPa, the CO density can reach 0.85 g / cm³. 3 Above, at this time Cr 3+ The solubility of the complex is increased to 3-5 times under normal conditions. Temperature control at 35℃ can suppress Ni... 2+ and Fe 2+ / 3+ Premature desorption was prevented, and the desorption rates were limited to below 5% and 2%, respectively. When ICP-MS detected Cr... 3+ When the desorption rate drops to 20% of the initial rate, the system automatically switches to Ni. 2+ Desorption stage. In Ni 2+ During this stage, raising the temperature to 45℃ can reduce the dissociation activation energy of the nickel complex by 30-40 kJ / mol. Combined with a pressure of 10 MPa to maintain appropriate solubility, Ni... 2+ The desorption rate can reach 98.5% while Fe 2+ / 3+ The desorption rate is still below 8%. When Ni 2+ When the concentration change rate is less than 0.5 mg / (L·min), it enters Fe 2+ / 3+ During the desorption stage, low-pressure conditions reduce the solvation effect, while a high temperature of 60℃ increases the desorption equilibrium constant of the iron complex to 2.5 × 10⁻³. Parameters are dynamically adjusted by real-time monitoring data; for example, when Fe… 3+ If the desorption rate is higher than expected, the pressure can be finely adjusted to 7.2 MPa to reduce the desorption process and ensure that the desorption selectivity of the target metal at each stage is maintained above 95%.

[0086] As a preferred embodiment, the solution of this application is specifically implemented as follows:

[0087] The metal ions adsorbed by micro-injections (MIPs) are placed in a supercritical fluid extraction apparatus. The apparatus includes an extraction vessel, a CO storage tank, a pressure pump, a heater, and an ICP-MS online monitoring system.

[0088] First, Cr 3+ Extraction was performed. The extraction vessel temperature was set to 35℃ and the pressure to 15MPa. The CO storage tank valve was opened, and CO was pressurized to a supercritical state using a pressure pump and delivered to the extraction vessel. The extraction time was set to 30 minutes.

[0089] Next, proceed with Ni 2+Extraction was performed. The temperature of the extraction vessel was adjusted to 45°C, and the pressure was reduced to 10 MPa. Supercritical CO was continued to be introduced for extraction, and the time was set to 20 minutes.

[0090] Finally, Fe... 2+ / Fe 3+ Extraction was then carried out. The temperature of the extraction vessel was increased to 60°C, and the pressure was further reduced to 7 MPa. Supercritical CO was continued to be introduced for extraction, and the time was set to 40 minutes.

[0091] Throughout the extraction process, Cr in the desorption solution was monitored in real time using ICP-MS. 3+ Ni 2+ Fe 2+ / Fe 3+ The concentration of Cr can be dynamically adjusted based on monitoring results. For example, when Cr is detected... 3+ When the concentration begins to decrease, the extraction time can be extended or the pressure can be fine-tuned to improve the desorption efficiency.

[0092] Through the above technical solution, this application achieves the control of Cr 3+ Ni 2+ Fe 2+ / Fe 3+ Highly efficient gradient desorption of three metal ions was achieved. By setting stepwise extraction parameters from high pressure and low temperature to low pressure and high temperature, the differences in the stability of different metal ion complexes were fully utilized, improving the selective separation of the target metal. Simultaneously, ICP-MS was used to monitor the composition of the desorption solution in real time and dynamically adjust the extraction parameters, effectively solving the problem of large fluctuations in desorption efficiency. This method significantly improves the separation efficiency and selectivity of multi-metal ions, providing technical support for the efficient recovery of metal resources from stainless steel pickling wastewater.

[0093] In some of the above-mentioned schemes of this application, metal ions in molecularly imprinted polymers are desorbed by supercritical CO fluid extraction. However, during the desorption process, due to the differences in solubility and desorption kinetics of different metal ions in supercritical CO, directly using a single desorption condition will lead to problems such as low desorption efficiency, disordered desorption sequence and insufficient purity of metal ions. At the same time, there is no dynamic adjustment mechanism for desorption parameters during the desorption process, making it difficult to adapt to the influence of fluctuations in the concentration of metal ions in the waste liquid.

[0094] To this end, this application further proposes the following scheme in step 3: placing the MIPs adsorbed with metal ions in a supercritical fluid extraction device; sequentially performing Cr... 3+ Ni 2+ Fe 2+ / 3+ The stepwise extraction specifically includes the extraction of Cr at 15 MPa / 35 °C.3+ Ni was extracted for 30 minutes at 10 MPa / 45 °C. 2+ Fe was extracted for 20 minutes at 7 MPa / 60 °C. 2+ / Fe 3+ 40 minutes; during the extraction process, the composition of the eluent was monitored in real time using ICP-MS, based on Cr... 3+ Ni 2+ Fe 2+ / Fe 3+ The extraction temperature and pressure are dynamically adjusted based on the concentration changes.

[0095] The step-by-step extraction conditions are set based on the differences in the physicochemical properties of different metal ions. For example, Cr 3+ Ni preferentially desorbs under high pressure and low temperature conditions, utilizing its high polarity to form a stable complex with supercritical CO; 2+ Desorption occurs under moderate pressure and temperature; the desorption kinetics are accelerated by decreasing the pressure and increasing the temperature; Fe 2+ / Fe 3+ Desorption occurs under low-pressure, high-temperature conditions, with increased temperature promoting greater solubility. Pressure parameters can be set to 7-15 MPa, and temperature parameters can be adjusted to 35-60°C, with each stage lasting 20-40 minutes. Dynamic adjustment of extraction parameters is achieved through real-time monitoring of the metal ion concentration in the desorption solution using ICP-MS; for example, when Cr... 3+ When the desorption efficiency is lower than the preset threshold, the duration of the 15MPa stage is extended to more than 35 minutes, or the Fe... 3+ When the concentration is abnormally high, its desorption temperature is increased to 65℃.

[0096] Specifically, in the supercritical fluid extraction device, the adsorbed MIPs are first subjected to Cr extraction at a pressure of 15 MPa and a temperature of 35 °C. 3+ Desorption. Under these conditions, supercritical CO has a higher density and reacts with Cr. 3+ Stable carbonate complexes are formed, thereby achieving selective desorption. This completes the process of Cr... 3+ After desorption, the pressure was gradually reduced to 10 MPa and the temperature was raised to 45 °C. At this point, the solubility of supercritical CO decreased, but the diffusion coefficient increased, which was beneficial to Ni. 2+ Rapid desorption occurs. Finally, the pressure drops to 7 MPa and the temperature rises to 60°C, which, by reducing the solvent strength and increasing the thermal energy, promotes Fe... 2+ / Fe 3+ It detaches from MIPs. During desorption, ICP-MS is used to continuously sample and analyze the eluent. When Cr is detected... 3+ When the desorption rate decreases, the system automatically extends the processing time of the 15MPa stage; when Fe 3+When the concentration exceeds the preset range, the temperature regulation module is triggered to raise the desorption temperature to 62-65℃ to maintain desorption efficiency. By combining staged parameter control with a real-time feedback mechanism, the orderly desorption and purity control of multi-metal ions are achieved, while adapting to fluctuations in the concentration of metal ions in the waste liquid.

[0097] As a preferred embodiment, the solution of this application is specifically implemented as follows:

[0098] MIPs adsorbed with metal ions were placed in a supercritical fluid extraction apparatus. Cr was then extracted sequentially. 3+ Ni 2+ Fe 2+ / 3+ Stepwise extraction. First, Cr was extracted under a pressure of 15 MPa and a temperature of 35 °C. 3+ 30 minutes. Then, the pressure was reduced to 10 MPa, and the temperature was increased to 45°C to extract Ni. 2+ 20 minutes. Finally, the pressure was further reduced to 7 MPa and the temperature increased to 60°C to extract Fe. 2+ / Fe 3 + 40 minutes. During the extraction process, the composition of the eluent was monitored in real time using ICP-MS, based on Cr... 3+ Ni 2+ Fe 2+ / Fe 3+ The extraction temperature and pressure are dynamically adjusted based on changes in Cr concentration. For example, when Cr is detected... 3+ When the concentration is lower than the expected value, the extraction time of the high-pressure stage can be appropriately extended or the temperature can be fine-tuned; when Fe 3+ When the concentration is abnormal, the temperature can be adjusted appropriately to promote desorption.

[0099] Through the above technical solution, this application achieves efficient separation and recovery of various metal ions. The step-desorption method sets specific pressure and temperature conditions based on the physicochemical properties of different metal ions, effectively improving the desorption efficiency of each metal ion. Under high pressure and low temperature conditions, Cr is preferentially desorbed. 3+ Ni utilizes its high polarity to form stable complexes at lower temperatures. Subsequently, the pressure is reduced and the temperature increased to enhance Ni's ability to form stable complexes. 2+ The desorption kinetics were analyzed to shorten the desorption time. Finally, the pressure was further reduced and the temperature increased to desorb Fe. 2+ / Fe 3+ This method utilizes high temperatures to enhance the solubility of iron ions. The phased control of pressure and temperature parameters enables the orderly desorption of different metal ions, avoiding cross-contamination. Simultaneously, real-time monitoring of the desorption solution composition using ICP-MS and dynamic parameter adjustment allows the desorption process to adapt to fluctuations in metal ion concentration in the waste liquid, ensuring the stability and efficiency of the desorption process.

[0100] In some of the solutions described above in this application, waste acid that has been demetallized by vacuum distillation is concentrated and new acid is added to regenerate the acid solution. However, if the pressure is not properly controlled during the waste acid concentration process, it may lead to acid loss due to volatilization or insufficient concentration efficiency. If the acid replenishment ratio is not accurate, the concentration of regenerated acid may deviate from the process requirements, resulting in a decrease in pickling efficiency or waste of resources.

[0101] In response, this application further proposes a scheme including the following steps: the waste acid after demetallization is concentrated by vacuum distillation at -0.08-0.1 MPa; the concentrated waste acid is mixed with new acid at a mass ratio of 1:3-1:4; the concentration of the mixed acid is measured and adjusted to HF 4-6% and HNO 8-10%.

[0102] The pressure range for vacuum distillation is set to -0.08 to -0.1 MPa. This range can be achieved by adjusting the vacuum pump power, for example, by using a rotary vane vacuum pump in conjunction with a pressure sensor for dynamic adjustment. The mixing ratio of waste acid and fresh acid can be metered and controlled using a mass flow meter. The selection of the mixing ratio needs to be calculated based on the residual acidity after waste acid concentration and the concentration of fresh acid. In the acid concentration adjustment step, the concentration ranges of HF and HNO can be monitored online based on conductivity methods or acid-base titration methods, and adjusted by adding deionized water or high-concentration acid solution.

[0103] The pressure parameters in the vacuum distillation step must be set in conjunction with the metal removal effect of the preceding process. When the residual metal ion concentration in the waste acid is below 50 mg / L, this pressure range ensures that the boiling point of the acid solution is reduced to 40-60℃, thereby achieving rapid water evaporation while suppressing HF volatilization. The mixing ratio design in the acid replenishment step considers the concentration gradient between concentrated waste acid and fresh acid. For example, when the HF concentration of the concentrated waste acid is 12%, a 1:3 mixing ratio can dilute it to the target range. The acid concentration adjustment step needs to be combined with the real-time requirements of the acid washing process. When the HNO3 concentration is detected to be below 8%, it can be adjusted by adding 65% concentrated nitric acid.

[0104] Specifically, during implementation, the demetallized waste acid first enters a vacuum evaporator. The pressure control system dynamically adjusts the vacuum level according to the evaporation rate. When the pressure deviates from the set range by more than 5%, an alarm is triggered and automatic compensation is initiated. The concentrated waste acid is then transported via pipeline to a mixing tank, where it is mass-produced with new acid using a proportioning valve. The mixing process employs a spiral stirrer to achieve uniform dispersion. The acid concentration detection module collects samples every ten minutes. When the detected HF concentration is below 4%, the system automatically starts an acid replenishment pump to inject a 40% hydrofluoric acid solution until the preset threshold is reached. The operating parameters of the entire system are controlled by a PLC to ensure that the concentration fluctuation of the regenerated acid is controlled within ±0.2%.

[0105] This scheme utilizes a coordinated mechanism of pressure control, optimized mixing ratios, and concentration feedback adjustment to stabilize the HF and HNO concentrations of the regenerated acid within the process window. The water removal rate during vacuum distillation reaches 85%, while acid loss is controlled below 3%. Precise control of the mixing ratio reduces fresh acid consumption by 40%, and the automated concentration adjustment system reduces the concentration fluctuation frequency in the pickling tank from 5 times per hour to 0.5 times per hour. Through the implementation of this scheme, the standard deviation of pickling efficiency has been reduced from 15% using traditional methods to 3%, achieving highly efficient and stable operation of the waste acid regeneration process.

[0106] As a preferred embodiment, the solution of this application is specifically implemented as follows:

[0107] The demetallized waste acid is placed in a vacuum distillation apparatus, with the vacuum level controlled at -0.09 MPa. Distillation concentration is carried out under this vacuum condition, with the distillation temperature set to 80℃ and the distillation time set to 2 hours. The concentrated waste acid is then mixed with freshly prepared acid solution at a mass ratio of 1:3.5. For example, 100 kg of concentrated waste acid can be mixed with 350 kg of freshly prepared acid solution. After mixing, the acid concentration of the mixture is measured using a pH meter. Based on the measurement results, the acid concentration is adjusted by adding concentrated HF and concentrated HNO3 to achieve a final regenerated acid concentration of 5% HF and 9% HNO3. The adjusted regenerated acid can then be directly returned to the pickling tank for use.

[0108] Through the above technical solution, this application achieves efficient concentration and precise regeneration of waste acid. By controlling the pressure range of vacuum distillation, acid evaporation loss is suppressed while water evaporation is accelerated, improving concentration efficiency. Precise control of the acid replenishment ratio ensures the acidity balance of the regenerated acid, avoiding resource waste caused by excessive acid replenishment. Real-time monitoring and control of acid concentration ensures that the regenerated acid meets the concentration requirements of the stainless steel pickling process, maintaining consistent pickling results. This method not only improves the recycling rate of waste acid but also reduces the consumption of new acid, lowers waste acid treatment costs, and ensures the stability of the pickling process.

[0109] In some of the schemes described above in this application, CO is recycled by dehydration and liquefaction storage using molecular sieves. However, in the gas treatment process after supercritical CO desorption, the specific operating parameters and diversion methods for CO recycling are not clearly defined, resulting in low CO recovery efficiency, high energy consumption, and insufficient system self-circulation capacity.

[0110] In response, this application further proposes to reduce the pressure of CO gas to 4 MPa / 25℃; to dehydrate it through a molecular sieve and then liquefy and store it; to use part of the CO to drive the compressor and to recycle the rest of the CO.

[0111] The CO gas depressurization to 4 MPa / 25℃ is achieved through pressure and temperature balance optimization. The pressure parameter is controlled near the critical liquefaction pressure; for example, a pressure of 4 MPa is chosen to meet the phase change requirements of liquefaction storage while avoiding excessive pressure that could increase compressor power consumption. The temperature parameter is limited to 25℃ to prevent equipment frosting or blockage due to excessive temperature differences during liquefaction. For the molecular sieve dehydration process, 3A type molecular sieves with a pore size of 0.3-0.5 nm are preferentially used to effectively remove residual moisture from the CO gas, ensuring that the dew point of the dehydrated CO is below -40℃, preventing equipment corrosion caused by residual moisture during subsequent liquefaction storage. In the diversion and reuse process, CO is divided into two parts: a power source to drive the compressor and a raw material for recycling. The proportion of CO driving the compressor is set to 15-20% of the total flow, with the remainder entering the recycling path. The diversion ratio is dynamically adjusted through a flow control valve, for example, by adjusting the diversion ratio according to the real-time power demand of the compressor to maximize energy utilization efficiency.

[0112] Specifically, the desorbed CO gas first enters the depressurization unit, where the pressure is gradually reduced from the supercritical state to 4 MPa, and the temperature is maintained at 25°C by the cooling system. Under these conditions, CO reaches a gas-liquid two-phase equilibrium, providing phase change conditions for subsequent liquefaction and storage. Subsequently, the gas enters the molecular sieve adsorption tower, where it undergoes staged dehydration through multiple adsorption layers, reducing the moisture content to below 50 ppm. The dehydrated CO then enters the liquefaction storage tank for storage in liquid form. In the splitting stage, liquid CO is pumped to the compressor drive unit, where its own pressure potential energy drives the compressor. Simultaneously, another portion of liquid CO returns to the supercritical fluid extraction unit for reuse via a circulation pipeline. During this process, the CO flow rate required for compressor operation is controlled in a closed loop using a proportional-integral-derivative controller, for example, by adjusting the splitting valve opening in real time based on compressor speed feedback signals to ensure the stability of the system's self-circulation. Through this technical solution, the energy consumption of the CO circulation process is reduced to less than 30% of that of traditional methods, the system's self-circulation rate is increased to over 85%, and equipment corrosion problems caused by residual moisture are avoided.

[0113] As a preferred embodiment, the solution of this application is specifically implemented as follows:

[0114] CO gas is reduced to 4 MPa / 25℃ by a pressure reducing valve. The reduced CO gas then enters a molecular sieve dehydration unit, where it undergoes dehydration using 3A molecular sieves. The dehydrated CO gas then enters a liquefaction storage unit, where it is liquefied and stored at -20℃. The liquefied CO is divided into two parts: one part is used to drive the compressor, and the other part is recycled back for the supercritical CO desorption process. The CO gas driving the compressor is heated to 35℃ via a heat exchanger before entering the turbo compressor, with an outlet pressure of 15 MPa. The recycled CO is heated to 35℃ via a heat exchanger before entering the supercritical CO desorption unit.

[0115] Through the above technical solution, this application achieves efficient recycling of CO gas. By reducing the pressure of the CO gas to 4 MPa / 25℃, both the requirements for liquefaction storage are met, while avoiding increased energy consumption due to excessive pressure. Molecular sieve dehydration treatment ensures the purity of CO during liquefaction storage, preventing equipment corrosion and process interference. CO is diverted for driving the compressor and for recycling, utilizing the CO's own pressure potential energy to reduce external energy consumption, while simultaneously achieving a closed-loop CO cycle and reducing resource waste. This solution improves CO recovery efficiency, reduces energy consumption, and enhances the system's self-circulation capability.

[0116] In some of the solutions described above in this application, the acid regeneration method, which involves concentrating the demetallized waste acid through vacuum distillation and then adding new acid to return it to the pickling tank, may lead to a decrease in the waste acid concentration efficiency if the pressure parameters of the vacuum distillation are not properly controlled during implementation. This could affect the accuracy of the subsequent acid replenishment ratio. If the mixing ratio of the concentrated waste acid and the new acid is not optimized, it may cause fluctuations in the concentration of the regenerated acid, which may fail to meet the requirements of the pickling process. In some cases, the concentration imbalance may even trigger a neutralization reaction that produces secondary sludge.

[0117] In response, this application further proposes a technical solution to concentrate the demetallized waste acid under vacuum distillation at -0.08-0.1 MPa, mix the concentrated waste acid with new acid at a mass ratio of 1:3-1:4, measure the acid concentration of the mixture, and adjust it to HF 4-6% and HNO 8-10%.

[0118] The vacuum distillation pressure range is selected as -0.08 to -0.1 MPa, which can be achieved by adjusting the operating frequency of the vacuum pump during implementation. For example, in a 1000L distillation vessel, when the pressure reaches -0.09 MPa, the boiling point of the waste acid drops to 60-65℃, which is about 50℃ lower than that of atmospheric distillation, significantly improving the evaporation rate. The mixing ratio of concentrated waste acid to fresh acid can be dynamically adjusted based on the concentration factor. When the waste acid is concentrated to 1 / 3 of its original volume by distillation, a 1:3 mixing ratio can restore the HF concentration to more than 90% of the initial level. The concentration of the mixed acid solution is adjusted using an online conductivity meter coupled with ion chromatography. When the HF concentration is detected to deviate from the range of 4-6%, the flow rate of the fresh acid replenishment pump is automatically adjusted.

[0119] Specifically, the vacuum distillation stage achieves a balance between equipment energy consumption and evaporation efficiency by precisely controlling the negative pressure range. When the pressure is above -0.08 MPa, the evaporation temperature increases, leading to an increase in acid mist emission; when the pressure is below -0.1 MPa, the energy consumption of the vacuum system increases exponentially. In the mixing and proportioning stage, the ratio range of 1:3 to 1:4 is determined based on mathematical modeling of the residual acid concentration in the concentrated waste acid and the initial concentration of the new acid. For example, when the concentrated waste acid contains 18% HF, mixing it with the new acid at a ratio of 1:3.5 will result in an HF concentration of 5.2%. The concentration adjustment stage employs a dual-component independent adjustment mechanism, achieving precise control of the target concentration window by adding concentrated HF or HNO3 in stages. Throughout the process, the concentration efficiency of vacuum distillation directly affects the selection of mixing and proportioning parameters, while real-time concentration monitoring ensures that the final acid solution meets the dual control requirements of the pickling process for oxidation capacity and corrosion rate, avoiding intergranular corrosion or passivation on the surface of the pickled steel plate due to concentration fluctuations.

[0120] As a preferred embodiment, the solution of this application is specifically implemented as follows:

[0121] The demetallized waste acid was concentrated by vacuum distillation at -0.09 MPa. The concentrated waste acid was then mixed with fresh acid at a mass ratio of 1:3.5. After mixing, the acid concentration was measured and adjusted to 5% HF and 9% HNO₃. Specifically, the demetallized waste acid was first fed into a vacuum distillation apparatus. The vacuum pump was started, and the system pressure was reduced to -0.09 MPa. The heating device was turned on, and the waste acid temperature was controlled to rise to 80°C. Distillation and concentration were carried out under these conditions, and the concentrated waste acid was collected. Next, the concentrated waste acid was mixed with freshly prepared acid solution at a mass ratio of 1:3.5. For example, 100 kg of concentrated waste acid was added to 350 kg of freshly prepared acid solution, and the mixture was stirred thoroughly. Finally, the concentration of the mixed acid solution was measured using a pH meter. If the HF concentration was below 5%, hydrofluoric acid was added; if the HNO₃ concentration was below 9%, nitric acid was added. Through repeated measurements and adjustments, the final mixed acid solution was adjusted to have an HF concentration of 5% and an HNO₃ concentration of 9%.

[0122] Through the above technical solutions, this application achieves efficient concentration and precise proportioning of waste acid. This improves waste acid concentration efficiency and ensures the accuracy of acid replenishment ratios. Furthermore, the optimized mixing ratio avoids fluctuations in the concentration of regenerated acid, meeting the requirements of the pickling process. Specifically, a vacuum of -0.09 MPa ensures distillation efficiency while avoiding excessive equipment energy consumption. A 1:3.5 mixing ratio achieves a reasonable proportion of waste acid and new acid, preventing problems of excessive or insufficient acid replenishment. Finally, the controlled concentrations of 5% HF and 9% HNO3 ensure that the regenerated acid has appropriate pickling activity while suppressing the risk of excessive corrosion on metal surfaces.

[0123] In some of the above-mentioned solutions in this application, the adsorption of metal ions in waste liquid by molecularly imprinted polymers is proposed. However, if the composition ratio and cross-linking degree of the molecularly imprinted polymer are not properly designed, it may lead to insufficient adsorption capacity of metal ions, reduced selectivity or poor material structure stability, thereby affecting the separation efficiency of target metal ions and the cycle life of the adsorbent.

[0124] In response, this application further proposes a scheme in which the molecularly imprinted polymer is composed of a mixture of three resins: 70% sulfonic acid group, 20% hydroxime group, and 10% dithiocarbamate group, and the crosslinking degree of the macroporous crosslinked styrene resin is 10%, or a scheme in which the three resins are mixed with 75% sulfonic acid group, 15% hydroxime group, and 10% dithiocarbamate group, and the crosslinking degree is 12%.

[0125] The proportion of sulfonic acid groups is controlled within the range of 70% or 75%, as the strongly acidic sites of this component preferentially bind to highly charged metal ions. The proportion of hydroxyoxime groups is adjusted to 20% or 15%, and the coordination between the hydroxyl and oxime groups enhances the selective adsorption of specific metal ions. The fixed proportion of dithiocarbamate groups improves adsorption stability through the strong complexation ability of sulfur atoms with metal ions. Both formulation schemes balance the adsorption priority of different metal ions by adjusting the ratio of sulfonic acid groups to hydroxyoxime groups. When the degree of crosslinking of the macroporous crosslinked styrene resin is selected as 10% or 12%, the former increases pore size by reducing the degree of crosslinking to promote mass transfer efficiency, while the latter enhances the mechanical strength of the material by increasing the degree of crosslinking.

[0126] Specifically, when the pretreated wastewater enters a fixed-bed reactor filled with this molecularly imprinted polymer, 70% of the sulfonic acid groups are used to react with Cr. 3+ Fe 3+ The adsorption capacity can reach 3.2 mmol / g, while the hydroxyoxime group has a high adsorption capacity for Ni. 2+ The selectivity coefficient reached 180. The resin with a crosslinking degree of 10% maintained a porosity of 65% at a flow rate of 5 / h, and the structural recovery rate after desorption reached 98%. When using a 75% sulfonic acid group ratio, it could still maintain Cr at pH 2.5. 3+ The adsorption efficiency reaches over 95%, and the compressive strength of the resin with a crosslinking degree of 12% decreases by only 7% after 20 adsorption-desorption cycles. This technical solution achieves high adsorption capacity while ensuring the structural stability of the material through the synergistic effect of each component, enabling the adsorbent to operate stably in the waste liquid treatment system for a long time.

[0127] As a preferred embodiment, the specific implementation of this application is as follows: Styrene monomer and divinylbenzene are subjected to suspension polymerization in toluene solvent, with the reaction temperature controlled at 85°C and maintained for 8 hours to form a macroporous cross-linked styrene resin matrix. Sulfonic acid resin, hydroxyoxime resin, and dithiocarbamate resin are mixed in a mass ratio of 70:20:10 and uniformly dispersed using a mechanical stirrer at 1200 rpm. The mixed resin and matrix material are grafted under ultrasonic assistance, maintaining a reaction pressure of 0.3 MPa, with the cross-linking agent accounting for 10% of the total resin amount, ultimately obtaining an adsorbent material with a pore size distribution in the range of 50-200 μm. After cleaning with acetone, the prepared molecularly imprinted polymer is dried in a vacuum drying oven at a constant temperature of 60°C for 12 hours, and then loaded into a fixed-bed reactor for wastewater treatment.

[0128] Through the above technical solutions, the distribution density of metal ion binding sites in the adsorption material is effectively optimized, the electrostatic interaction between sulfonic acid groups and high-charge metal ions is strengthened, the coordination selectivity of hydroxyoxime groups for specific divalent metals is significantly improved, and the dithiocarboxylic acid groups stabilize the metal complex structure through sulfur bonds. The pore size control of the macroporous cross-linked structure reduces the diffusion resistance of metal ions within the material while ensuring the mechanical integrity of the support during recycling. Different cross-linking degrees of design schemes achieve a dynamic balance between mass transfer efficiency and structural strength, providing a suitable solution for the selective adsorption of multiple metal ions in complex wastewater systems.

[0129] In some of the schemes described above in this application, due to the non-polar nature of supercritical CO fluid, its ability to dissolve polar metal complexes is limited, resulting in insufficient desorption efficiency and difficulty in achieving sufficient desorption and separation of metal ions.

[0130] In this regard, this application further proposes to add ethanol or acetylacetone with a volume concentration of 5-10% as an entrainer during the supercritical CO fluid extraction process, while desorbing the CO through a pressure reducing valve, recovering the entrainer using a condenser, purifying it, and then compressing it into a liquid storage tank for recycling.

[0131] The addition ratio of ethanol or acetylacetone is limited to a volume concentration of 5-10%. This concentration range enhances the solubility of the metal ions in supercritical CO by forming polar complexes with them, while avoiding excessive addition that would increase the load on subsequent separation processes. The flow rate of the entrainer can be precisely controlled using a high-pressure metering pump, for example, by ensuring sufficient contact between 6% volume concentration ethanol and CO in a mixer. During the stepwise extraction process, the polarity-enhancing effect of the entrainer synergistically interacts with different pressure and temperature conditions. Specifically, under conditions of 15 MPa / 35℃, the reaction between ethanol and Cr... 3+The solubility of the formed complex is increased to 3 times that of conventional SC-CO. After the desorbed CO is reduced to atmospheric pressure, the entrainer is separated and recovered in liquid phase in the condenser, with a recovery rate of over 95%. The purified entrainer, after testing and finding that its metal residue is less than 1 ppm, can be reinjected into the system.

[0132] Specifically, in a supercritical fluid extraction apparatus, the entrainer is mixed with CO through a separate injection channel and then enters the extraction vessel containing an adsorbed saturated molecularly imprinted polymer. Adjusting the polarity of the mixed fluid increases the partition coefficient of the metal complex in the supercritical phase to 2.5 times that without the addition of CO. For example, when using 8% acetylacetone, Ni... 2+ The mass transfer rate is from 0.15 g / (min·m 2 Increased to 0.38 g / (min·m 2 During dynamic desorption, the real-time monitoring system automatically adjusts the entrainer injection amount based on changes in metal concentration. When Fe is detected... 2+ / 3+ When the desorption rate decreases, the entrainer concentration can be instantaneously increased to 10% to maintain desorption efficiency. After the desorbed CO-entrainer mixture enters the separation unit, the pressure is gradually reduced to below 4 MPa. At this point, the phase separation efficiency between the entrainer and CO reaches 98%. The recovered ethanol, after dehydration by molecular sieves, has a purity restored to over 99.2% and can be directly returned to the entrainer storage tank for closed-loop utilization. This process stabilizes the metal desorption rate in the 97-99.8% range while controlling the entrainer replenishment amount to within 5% of the initial addition.

[0133] As a preferred embodiment, the specific implementation of this application is as follows: In a supercritical fluid extraction device, a molecularly imprinted polymer adsorbed with metal ions is placed in a high-pressure container, and acetylacetone with a volume concentration of 8% is continuously injected into a circulating carbon dioxide system as an entrainer. After the extraction process, the carbon dioxide fluid carrying the metal complex flows through a pressure reducing valve to reduce its pressure below the critical point, achieving phase separation between the gaseous carbon dioxide and the liquid entrainer. The gaseous carbon dioxide enters a condensation system, where the residual entrainer vapor is liquefied and recovered through a condenser controlled at -5°C. After purification by activated carbon adsorption, it is reinjected into a storage tank for later use. The liquid metal complex then enters an electrodeposition unit for metal recovery, and the residual carbon dioxide gas is dehydrated by a molecular sieve, compressed, liquefied, and returned to the storage tank for recycling.

[0134] Through the above technical solution, this application effectively improves the solubility of polar metal complexes in supercritical carbon dioxide, enabling metal ions to exist stably in the fluid phase in a complexed state, thereby improving the mass transfer efficiency of the metal desorption process. The entrainer recycling mechanism avoids the residue of organic solvents in the desorption solution, ensuring the purity of the product in subsequent metal electrodeposition processes, while reducing the replenishment cost of the entrainer.

[0135] In some of the schemes described above in this application, due to the non-polar nature of supercritical CO fluid, its ability to dissolve polar metal complexes is limited, resulting in insufficient desorption efficiency and difficulty in achieving sufficient desorption and separation of metal ions.

[0136] In this regard, this application further proposes to add ethanol or acetylacetone with a volume concentration of 5-10% as an entrainer during the supercritical CO fluid extraction process, while desorbing the CO through a pressure reducing valve, recovering the entrainer using a condenser, purifying it, and then compressing it into a liquid storage tank for recycling.

[0137] The addition ratio of ethanol or acetylacetone is limited to a volume concentration of 5-10%. This concentration range enhances the solubility of the metal ions in supercritical CO by forming polar complexes with them, while avoiding excessive addition that would increase the load on subsequent separation processes. The flow rate of the entrainer can be precisely controlled using a high-pressure metering pump, for example, by ensuring sufficient contact between 6% volume concentration ethanol and CO in a mixer. During the stepwise extraction process, the polarity-enhancing effect of the entrainer synergistically interacts with different pressure and temperature conditions. Specifically, under conditions of 15 MPa / 35℃, the reaction between ethanol and Cr... 3+ The solubility of the formed complex is increased to 3 times that of conventional SC-CO. After the desorbed CO is reduced to atmospheric pressure, the entrainer is separated and recovered in liquid phase in the condenser, with a recovery rate of over 95%. The purified entrainer, after testing and finding that its metal residue is less than 1 ppm, can be reinjected into the system.

[0138] Specifically, in a supercritical fluid extraction apparatus, the entrainer is mixed with CO through a separate injection channel and then enters the extraction vessel containing an adsorbed saturated molecularly imprinted polymer. Adjusting the polarity of the mixed fluid increases the partition coefficient of the metal complex in the supercritical phase to 2.5 times that without the addition of CO. For example, when using 8% acetylacetone, Ni... 2+ The mass transfer rate is from 0.15 g / (min·m 2 Increased to 0.38 g / (min·m 2 During dynamic desorption, the real-time monitoring system automatically adjusts the entrainer injection amount based on changes in metal concentration. When Fe is detected... 2+ / 3+When the desorption rate decreases, the entrainer concentration can be instantaneously increased to 10% to maintain desorption efficiency. After the desorbed CO-entrainer mixture enters the separation unit, the pressure is gradually reduced to below 4 MPa. At this point, the phase separation efficiency between the entrainer and CO reaches 98%. The recovered ethanol, after dehydration by molecular sieves, has a purity restored to over 99.2% and can be directly returned to the entrainer storage tank for closed-loop utilization. This process stabilizes the metal desorption rate in the 97-99.8% range while controlling the entrainer replenishment amount to within 5% of the initial addition.

[0139] As a preferred embodiment, the specific implementation of this application is as follows: In a supercritical fluid extraction device, a molecularly imprinted polymer adsorbed with metal ions is placed in a high-pressure container, and acetylacetone with a volume concentration of 8% is continuously injected into a circulating carbon dioxide system as an entrainer. After the extraction process, the carbon dioxide fluid carrying the metal complex flows through a pressure reducing valve to reduce its pressure below the critical point, achieving phase separation between the gaseous carbon dioxide and the liquid entrainer. The gaseous carbon dioxide enters a condensation system, where the residual entrainer vapor is liquefied and recovered through a condenser controlled at -5°C. After purification by activated carbon adsorption, it is reinjected into a storage tank for later use. The liquid metal complex then enters an electrodeposition unit for metal recovery, and the residual carbon dioxide gas is dehydrated by a molecular sieve, compressed, liquefied, and returned to the storage tank for recycling.

[0140] Through the above technical solution, this application effectively improves the solubility of polar metal complexes in supercritical carbon dioxide, enabling metal ions to exist stably in the fluid phase in a complexed state, thereby improving the mass transfer efficiency of the metal desorption process. The entrainer recycling mechanism avoids the residue of organic solvents in the desorption solution, ensuring the purity of the product in subsequent metal electrodeposition processes, while reducing the replenishment cost of the entrainer.

[0141] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of 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 scope of protection of this application.

Claims

1. A method for recycling and regenerating stainless steel pickling waste liquid, characterized in that, include: Step 1, Waste liquid pretreatment: Filter the stainless steel pickling waste liquid to remove suspended particles and dilute it; Step 2, MIPs Adsorption: Adsorption of metal ions (Cr) in the waste liquid by molecularly imprinted polymers (MIPs). 3+ Ni 2+ Fe 2+ / 3+ Adsorption occurs; Step 3, SC-CO desorption: Supercritical CO fluid extraction (SC-CO) is used to desorb metal ions (Cr) from the molecularly imprinted polymer. 3 + Ni 2+ Fe 2+ / 3+ Desorption occurs; Step 4, Metal Recovery: Electrodeposition is performed on the desorbed solution to obtain the elemental metal; Step 5, Acid Regeneration: The waste acid from which metal has been removed is concentrated by vacuum distillation, and after adding new acid, it is returned to the pickling tank; Step 6, CO recycling: The desorbed CO is dehydrated by molecular sieve and then liquefied and stored.

2. The method for recycling and regenerating stainless steel pickling waste liquid according to claim 1, characterized in that, Step 1 includes: Step 101: Filter the stainless steel pickling waste liquid to remove suspended particles, and adjust the pH value to 2.5-3.0 with dilute hydrochloric acid; Step 102: Determine the concentration of total metal ions in the filtered waste liquid; Step 103: Dilute the waste liquid to a target metal ion concentration of 100-500 mg / L, based on the total metal ion concentration.

3. The method for recycling and regenerating stainless steel pickling waste liquid according to claim 1, characterized in that, Step 2 includes: Step 201: Pass the pretreated waste liquid into a fixed-bed reactor filled with molecularly imprinted polymers (MIPs); Step 202: Control the space velocity of the fixed-bed reactor to 1-5 / hour; Step 203: Measure the adsorption capacity of molecularly imprinted polymers (MIPs). If the adsorption capacity is lower than the preset value, return to step 201 to continue adsorption. If the preset value is reached, proceed to step 3.

4. The method for recycling and regenerating stainless steel pickling waste liquid according to claim 1, characterized in that, Step 3 includes: Step 301: Place the MIPs adsorbed with metal ions into a supercritical fluid extraction device; Step 302, proceed with Cr sequentially 3+ Ni 2+ Fe 2+ / 3+ Stepwise extraction: Step 302-1: Extract Cr at 15 MPa / 35℃ 3+ 30 minutes; Step 302-2: Extract Ni at 10 MPa / 45℃ 2+ 20 minutes; Step 302-3, Fe extraction at 7MPa / 60℃ 2+ / Fe 3+ 40 minutes; Step 303: During the extraction process, the composition of the eluent is monitored in real time using ICP-MS, based on Cr... 3+ Ni 2+ Fe 2+ / Fe 3+ The extraction temperature and pressure are dynamically adjusted based on the concentration changes.

5. The method for recycling and regenerating stainless steel pickling waste liquid according to claim 1, characterized in that, Step 4 includes: Step 401: The desorption solution is introduced into the electrodeposition unit; Step 402: Perform electrodeposition in the electrodeposition unit, controlling the current density to be 150-300 A / m. 2 ; Step 403: Determine the purity and recovery rate of the deposited metal. If the requirements are not met, return to step 3 for re-extraction. If the requirements are met, proceed to step 5.

6. The method for recycling and regenerating stainless steel pickling waste liquid according to claim 1, characterized in that, Step 5 includes: Step 501: The demetallized waste acid is concentrated by vacuum distillation at -0.08 to -0.1 MPa; Step 502: Mix the concentrated waste acid with the new acid at a mass ratio of 1:3 to 1:4; Step 503: Measure the acid concentration after mixing and adjust it to HF 4-6% and HNO 8-10%.

7. The method for recycling and regenerating stainless steel pickling waste liquid according to claim 1, characterized in that, Step 6 includes: Step 601: Reduce the pressure of CO gas to 4 MPa / 25℃; Step 602: Dehydrate and liquefy the product using a molecular sieve for storage; Step 603: Use part of the CO to drive the compressor, and recycle the rest of the CO.

8. The method for recycling and regenerating stainless steel pickling waste liquid according to claim 1, characterized in that, In step 2, the molecularly imprinted polymers (MIPs) are composed of a mixture of three resins: 70% sulfonic acid groups, 20% hydroxime groups, and 10% dithiocarboxylic acid groups, with a crosslinking degree of 10% for the macroporous crosslinked styrene resin. Alternatively, the molecularly imprinted polymers (MIPs) are composed of a mixture of three resins: 75% sulfonic acid groups, 15% hydroxime groups, and 10% dithiocarboxylic acid groups, with a crosslinking degree of 12% for the macroporous crosslinked styrene resin.

9. The method for recycling and regenerating stainless steel pickling waste liquid according to claim 1, characterized in that, In step 3, the supercritical CO fluid extraction (SC-CO) process involves adding 5-10% vol of ethanol or acetylacetone as an entrainer to enhance the solubility of the polar metal complex.

10. A method for recycling and regenerating stainless steel pickling waste liquid according to claim 9, characterized in that, Step 3 includes the following steps: the desorbed CO is vaporized by a pressure reducing valve, the entrained agent is recovered by a condenser, and after purification, it is compressed into a liquid storage tank for recycling.

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