Method for cooperatively recovering sulfuric acid and copper-zinc in copper strip washing waste acid

Abstract

This invention provides a method for the synergistic recovery of sulfuric acid and copper and zinc from waste acid from copper strip washing, comprising the following steps: S1, waste acid pretreatment; S2, novel bipolar membrane electrodialysis separation; S3, copper-targeted precipitation separation: adding a copper-targeted precipitant to the heavy metal concentrate to form a stable precipitate, followed by filtration and washing to obtain a copper-enriched precipitate; S4, zinc sulfate preparation: adjusting the pH of the filtrate after copper precipitation separation and removing reducing impurities, then evaporating and concentrating to a solution density of 1.4-1.5 g / cm³, cooling and crystallizing, and centrifuging to obtain zinc sulfate crystals, with the mother liquor returned to the evaporation and concentration unit for recycling. This method can achieve efficient recovery and recycling of sulfuric acid, while simultaneously achieving precise separation of copper and zinc ions and the preparation of high-value products, significantly improving the resource utilization efficiency of waste acid and reducing treatment costs.

Description

Technical Field

[0001] This invention belongs to the field of industrial waste acid resource utilization technology, specifically relating to a method for treating waste acid from copper strip washing, and particularly to a synergistic process that combines novel membrane separation technology with targeted precipitation to achieve efficient recovery of sulfuric acid, copper ions and zinc ions. Background Technology

[0002] During the processing of copper strip, acid pickling with sulfuric acid solution is required to remove surface oxide scale and oil stains. Subsequent washing processes generate a large amount of complex waste acid. This waste acid is characterized by high acidity and high concentrations of heavy metal ions. Direct discharge of this acid will not only cause serious soil and water pollution but also lead to the waste of valuable resources such as sulfuric acid, copper, and zinc. Statistics show that approximately 8-12 m³ of waste acid is generated for every ton of copper strip produced, with typical components including: Cu... 2+ Concentration 6.1-18 g / L, Zn 2+ The concentration is approximately 16.8 g / L, and the sulfuric acid concentration is 119 g / L. How to reduce, render harmless, and utilize this type of waste acid as a resource has become a key bottleneck for the sustainable development of the copper strip processing industry.

[0003] Currently, industrial methods for treating waste acid from copper strip washing mainly include neutralization precipitation, solvent extraction, ion exchange, and membrane separation. Neutralization precipitation involves adding alkaline agents such as lime and sodium hydroxide to neutralize the acid and precipitate heavy metal ions. This method is simple but consumes a large amount of reagents, generates a large amount of sludge with high water content and low resource value, and cannot recover sulfuric acid from the waste acid, resulting in extremely low resource utilization. Solvent extraction selectively separates copper ions using an extractant, followed by back-extraction to obtain a copper salt solution. However, this method suffers from high extractant loss, easy emulsification of the organic phase, and strong corrosiveness to equipment, and it is difficult to directly recover sulfuric acid. Ion exchange uses resin to adsorb heavy metal ions and is suitable for treating low-concentration waste acid. However, for the high-concentration waste acid involved in this invention, the resin is easily saturated, requires frequent regeneration, has low treatment efficiency, and high operating costs.

[0004] Membrane separation technology has gained widespread attention in the field of waste acid treatment due to its high separation efficiency, low energy consumption, and environmental friendliness. Among these technologies, bipolar membrane electrodialysis (BMED) generates H₂ through bipolar membrane water dissociation. + and OH -This technology can achieve the desalination of salt solutions and the preparation of acids and bases, showing promising prospects in waste acid recovery. However, traditional bipolar membrane electrodialysis technology has the following key problems when treating high-concentration heavy metal waste acid: First, the membrane stack structure design is unreasonable, and the ion migration efficiency between the concentrated and dilute chambers is low, resulting in a sulfuric acid recovery rate of less than 85%; second, heavy metal ions are prone to deposit on the membrane surface, causing membrane fouling and shortening the membrane's service life, with the membrane operating cycle typically not exceeding 3 months; third, the separation selectivity for copper and zinc ions is poor, making it impossible to achieve efficient separation of the two, requiring complex subsequent processing.

[0005] To address the separation of copper and zinc ions, existing technologies often employ stepwise precipitation by adjusting pH levels, utilizing the difference in solubility products of copper and zinc hydroxides. However, this method requires extremely precise pH control; fluctuations of 0.2-0.3 can drastically reduce separation efficiency, and the precipitated products exhibit low purity, leading to complex subsequent purification processes. Therefore, developing a synergistic treatment technology that combines efficient sulfuric acid recovery, precise copper-zinc ion separation, and membrane fouling control is of great significance for the resource utilization of waste acid from copper strip washing. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies in the treatment of waste acid from copper strip washing, such as low sulfuric acid recovery rate, poor copper-zinc separation accuracy, and severe membrane fouling. It provides a synergistic recovery method based on a novel bipolar membrane separation technology combined with copper-targeted precipitation. This method enables efficient recovery and recycling of sulfuric acid, while simultaneously achieving precise separation of copper and zinc ions and the preparation of high-value products, significantly improving the efficiency of waste acid resource utilization and reducing treatment costs.

[0007] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0008] A method for the synergistic recovery of sulfuric acid and copper and zinc from waste acid in copper strip washing includes the following steps: S1, waste acid pretreatment: introducing waste acid from copper strip washing into a pretreatment unit to obtain pretreated waste acid; S2, novel bipolar membrane electrodialysis separation: pumping the pretreated waste acid into the dilute chamber of a bipolar membrane electrodialysis device for electrodialysis treatment to obtain sulfuric acid and heavy metal concentrate, the sulfuric acid formed in the dilute chamber enters the acid chamber; when the sulfuric acid concentration in the acid chamber reaches 110-120 g / L, it is exported for copper strip washing recycling; S3, copper-targeted precipitation separation: adding a copper-targeted precipitant to the heavy metal concentrate to form a stable precipitate, which is then filtered and washed to obtain copper-enriched precipitate; S4, zinc sulfate preparation: adjusting the pH of the filtrate after copper precipitation separation and removing reducing impurities, then evaporating and concentrating to a solution density of 1.4-1.5 g / cm³, cooling and crystallizing, and centrifuging to obtain zinc sulfate crystals, the mother liquor is returned to the evaporation and concentration unit for recycling.

[0009] Preferably, in step S1, the waste acid from washing the copper strip is sequentially subjected to precision filtration, activated carbon adsorption, and ion exchange to remove suspended particulate matter, organic impurities, and calcium and magnesium ions from the waste acid.

[0010] Preferably, in step S3, the reaction is carried out under stirring conditions, the reaction pH is controlled at 2.5-3.5, the reaction temperature is 40-50℃, and the reaction time is 60-90 min.

[0011] Preferably, the evaporation and concentration in step S4 adopts a multi-effect evaporation process, with the first-effect evaporation temperature being 100-110℃, the second-effect evaporation temperature being 80-90℃, and the third-effect evaporation temperature being 60-70℃. During the evaporation process, the pH value of the solution is controlled to be stable at 5.0-6.0, the cooling crystallization temperature is 20-25℃, the crystallization time is 4-6h, and the purity of the obtained zinc sulfate crystals is ≥99.0%.

[0012] Preferably, the novel bipolar membrane electrodialysis device described in step S2 has a membrane stack structure that combines four membrane units: a bipolar membrane, a cation exchange membrane, a bipolar membrane, and an anion exchange membrane.

[0013] Preferably, the bipolar membrane uses a polyphenylene ether framework with sulfonic acid groups and quaternary ammonium groups grafted onto its surface, and has a water dissociation voltage ≤1.8V; the cation exchange membrane is a perfluorosulfonic acid membrane, which is effective against Cu... 2+ Zn 2+ The selective permeability is ≥95%; the anion exchange membrane is a quaternized polysulfone membrane, which is effective against SO42-. 2- Selective transmittance ≥98%.

[0014] Preferably, the membrane stack voltage is 20-30V, the operating temperature is 30-40℃, the flow rate in the dilute chamber is 0.8-1.2m / s, the flow rate in the concentrate chamber is 0.5-0.8m / s, and the flow rate in the acid chamber is 1.0-1.5m / s.

[0015] Preferably, the copper-targeting precipitant in step S3 is a naphthyl carbamate chelating compound with a naphthyl ring-hydroxy-amide-aliphatic amine core structure. The core component of this compound is characterized by the simultaneous presence of three types of active coordinating groups within the molecule.

[0016] Preferably, in step S4, the pH of the filtrate after copper precipitation is adjusted to 5.0-6.0, and hydrogen peroxide is added to remove residual reducing impurities.

[0017] Preferably, in step S4, the pH value is adjusted using industrial-grade zinc oxide, the amount of hydrogen peroxide added is 0.1-0.3% of the filtrate mass, and the reaction time is 30-40 min.

[0018] The beneficial effects of this invention are as follows:

[0019] This invention significantly improves ion migration efficiency and selectivity, increasing the sulfuric acid recovery rate from below 85% in traditional technologies to over 92%. The recovered sulfuric acid concentration is stable at 110-120 g / L, which can be directly returned to the copper strip washing process for recycling, reducing the consumption of fresh sulfuric acid. Approximately 0.12 tons of sulfuric acid can be recovered from each ton of waste acid. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] A method for the synergistic recovery of sulfuric acid and copper and zinc from waste acid from copper strip washing includes the following steps:

[0023] Waste acid pretreatment: The waste acid from washing copper strip is introduced into the pretreatment unit and sequentially passes through precision filtration, activated carbon adsorption and ion exchange to remove suspended particulate matter, organic impurities and calcium and magnesium ions from the waste acid, thus obtaining pretreated waste acid;

[0024] Novel Bipolar Membrane Electrodialysis Separation: Pretreated waste acid is pumped into the dilute chamber of a novel bipolar membrane electrodialysis device. The device is started to perform electrodialysis treatment. Sulfate ions in the dilute chamber react with H+ generated by the hydrolysis of the bipolar membrane. + The sulfuric acid formed by the combination enters the acid chamber, while copper and zinc ions are retained in the concentration chamber to form a heavy metal concentrate. When the sulfuric acid concentration in the acid chamber reaches 110-120 g / L, it is discharged for recycling in the copper strip washing process.

[0025] Copper-targeted precipitation separation: A copper-targeted precipitant is added to the heavy metal concentrate, and the reaction is carried out under stirring conditions. The reaction pH is controlled at 2.5-3.5, the reaction temperature at 40-50℃, and the reaction time at 60-90 min. Within the above range, the copper-targeted precipitant (naphthylamide chelating compound) has high activity and can greatly improve the precipitation efficiency of copper in the concentrate. At the same time, it will not react with zinc in the liquid and cause zinc loss. Copper ions form a stable precipitate with the targeted precipitant. After filtration and washing, copper-enriched precipitate is obtained.

[0026] Zinc sulfate preparation: The pH of the filtrate after copper precipitation is adjusted to 5.0-6.0, hydrogen peroxide is added to remove residual reducing impurities, and then the solution is evaporated and concentrated to a density of 1.4-1.5 g / cm³. After cooling and crystallization, zinc sulfate crystals are obtained by centrifugation. The mother liquor is returned to the evaporation and concentration unit for recycling.

[0027] Furthermore, the precision filtration in step 1 uses a ceramic membrane with a pore size of 0.22-0.45 μm and an operating pressure of 0.1-0.3 MPa; the activated carbon adsorption uses granular activated carbon with a space velocity of 1-3 h⁻¹.-1 Ion exchange purification uses chelating resin, type D401, with a 5-8% hydrochloric acid solution as the regenerant and a regeneration space velocity of 0.5-1 h⁻¹. -1 After pretreatment, the suspended particulate matter content in the waste acid is ≤0.1mg / L, COD is ≤50mg / L, and the total concentration of calcium and magnesium ions is ≤0.5g / L.

[0028] The core innovation of this invention lies in the novel bipolar membrane electrodialysis device described in step 2. Its membrane stack structure adopts a four-membrane unit combination structure of "bipolar membrane-cation exchange membrane-bipolar membrane-anion exchange membrane". The membrane stack used in this invention has a four-membrane unit combination structure, resulting in higher metal ion separation efficiency and higher product purity, denoted as BCBA unit. Specifically, the bipolar membrane (B) uses a polyphenylene ether framework with sulfonic acid groups and quaternary ammonium groups grafted onto its surface, and its water dissociation voltage is ≤1.8V; the cation exchange membrane (C) is a perfluorosulfonic acid membrane, which is effective for Cu... 2+ Zn 2+ Selective transmittance ≥95%; Anion exchange membrane (A) is a quaternized polysulfone membrane, which is effective against SO42-. 2- Selective transmittance ≥98%.

[0029] The operating parameters of the novel bipolar membrane electrodialysis device are as follows: membrane stack voltage 20-30V, under which effective directional migration and binding of metal ions can be achieved; operating temperature 30-40℃; dilute chamber flow rate 0.8-1.2m / s; concentrated chamber flow rate 0.5-0.8m / s; acid chamber flow rate 1.0-1.5m / s. Through this structural design, sulfate ions and H+ ions can be effectively bounded together. + The targeted migration and combination of these technologies prevent heavy metal ions from entering the acid chamber, resulting in a sulfuric acid recovery rate of ≥92% and an increase in the total concentration of copper and zinc ions in the concentration chamber to 80-100 g / L.

[0030] The copper-targeting precipitant mentioned in step 3 is a class of naphthamide chelating compounds with a "naphthalene ring-hydroxyl-amide-aliphatic amine" core structure, and its general molecular formula is defined as: R1-C 10 H5(OH)-CONH-R2-NH2, where substituent R1 is a hydrogen atom (H) or a C1-C3 straight-chain alkyl group (such as methyl, ethyl, propyl), and R2 is a C1-C4 straight-chain or branched alkylene group (such as ethylene, propylene, isopropylene). The core characteristic of this type of compound is the simultaneous presence of three types of active coordinating groups within the molecule: a hydroxyl group (-OH, providing an oxygen coordinating atom) adjacent to the naphthalene ring, an amide group (-CONH-, providing a nitrogen coordinating atom) in the amide bond, and a primary amine group at the end of the aliphatic chain (-NH2, providing a nitrogen coordinating atom). These three groups form a cooperative coordination region through steric hindrance matching, specifically adapted to Cu. 2+ The electronic configuration and coordination requirements.

[0031] Its mechanism of action is based on a three-step synergistic effect of "targeted chelation - stereobonding - precipitation separation": the first step is targeted recognition, Cu 2+ The electronic configuration is d 9 Under acidic conditions (pH 2.5-3.5), it readily accepts lone pairs of electrons to form coordinate bonds, and the lone pairs of electrons of the hydroxyl oxygen, amide nitrogen, and primary amino nitrogen in the precipitant molecule can precisely position Cu. 2+ The empty orbitals form specific bonds; the second step is stereobonding, where three types of coordinating groups bind with Cu. 2+ A stable double five-membered chelate ring structure (hydroxyoxygen-copper-amide nitrogen, amide nitrogen-copper-primary amide nitrogen) is formed, exhibiting a large equilibrium constant for the chelation reaction and extremely high thermodynamic stability. In the third step, precipitation separation occurs. Due to the hydrophobic properties of the naphthalene ring and the large molecular structure of the double chelate ring, the solubility of the formed chelate molecules in aqueous solution decreases sharply, leading to rapid aggregation and the formation of particulate precipitates with a fast settling rate. In contrast, Zn... 2+ The electronic configuration is d 10 Due to poor spatial matching with the aforementioned ligands, the chelation reaction equilibrium constant is small, and a stable chelate cannot be formed. The chelate remains in the solution in an ionic state, thus achieving deep separation of copper and zinc ions.

[0032] Typical examples of this type of precipitant include N-(2-aminoethyl)-3-hydroxy-2-naphthoformamide (R1=H, R2=CH2CH2), N-(3-aminopropyl)-3-hydroxy-6-methyl-2-naphthoformamide (R1=CH3, R2=CH2CH2CH2), and N-(2-amino-1-methylethyl)-3-hydroxy-2-naphthoformamide (R1=H, R2=CH2CH(CH3)). In practical applications, the amount of precipitant added is 1.05-1.1 times the theoretical stoichiometry of copper ions (theoretical stoichiometry = mass of copper ions × molecular weight of precipitant / (atomic weight of copper × coordination coefficient), with a coordination coefficient of 1:1). N-(2-aminoethyl)-3-hydroxy-2-naphthoformamide reacts with Cu... 2+ The stoichiometric ratio is 3.2-3.5 g / g. After the reaction is complete, the Cu in the filtrate is filtered. 2+ With a concentration ≤0.05g / L, a copper separation rate ≥99.5%, and strong acid resistance, the precipitant does not degrade in a system with a sulfuric acid concentration ≤20g / L and will not introduce organic impurities.

[0033] In step 4, industrial-grade zinc oxide is used for pH adjustment to avoid introducing new impurity ions. Hydrogen peroxide is added at 0.1-0.3% of the filtrate mass, and the reaction time is 30-40 minutes. A multi-effect evaporation process is used for concentration: the first effect evaporation temperature is 100-110℃, the second effect evaporation temperature is 80-90℃, and the third effect evaporation temperature is 60-70℃. During evaporation, the pH of the solution is controlled to remain stable at 5.0-6.0 to prevent zinc ion hydrolysis. The cooling crystallization temperature is 20-25℃, and the crystallization time is 4-6 hours, resulting in zinc sulfate crystals with a purity ≥99.0%.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. Innovative new bipolar membrane electrodialysis technology: Adopting a BCBA four-membrane unit combination structure, it significantly improves ion migration efficiency and selectivity. The sulfuric acid recovery rate is increased from below 85% of the traditional technology to over 92%, and the recovered sulfuric acid concentration is stable at 110-120g / L. It can be directly returned to the copper strip washing process for recycling, reducing the consumption of fresh sulfuric acid. Approximately 0.12 tons of sulfuric acid can be recovered per ton of waste acid.

[0036] 2. Significant membrane fouling control: The pretreatment process effectively removes suspended particles, organic impurities, and calcium and magnesium ions that cause membrane fouling. Combined with the antifouling properties of the new membrane material, the membrane stack operation cycle is extended to more than 12 months, which is 4 times better than the traditional bipolar membrane electrodialysis technology. This reduces membrane replacement costs. The precision filter used in this application is a ceramic membrane filter with a pore size of 0.22-0.45μm, which has higher filtration accuracy. At the same time, the filter element can be backwashed and reused, resulting in a long equipment life. Furthermore, for the solution processed in this application, the pretreatment does not require neutralization, softening, or sulfide precipitation, making the process simpler.

[0037] 3. High precision in copper-zinc separation: Utilizing a naphthylamide-based targeted precipitant with a "naphthalene ring-hydroxyl-amide group-aliphatic amine" structure, deep separation of copper ions is achieved through a "targeted recognition-stereobonding-precipitation separation" mechanism. This type of precipitant is effective for Cu... 2+ Its chelation selectivity is much higher than that of Zn. 2+ The copper separation rate is ≥99.5%, and the copper ion concentration in the filtrate is ≤0.05g / L. This method solves the problems of difficult pH control (failure when the pH fluctuates by 0.2) and poor separation effect in traditional stepwise precipitation methods. It is also suitable for a wide range of waste acid systems with copper ion concentrations of 6.1-18g / L, providing high-purity raw materials for subsequent zinc sulfate preparation.

[0038] 4. High resource utilization rate and significant environmental benefits: It realizes the full recovery of sulfuric acid, copper and zinc in waste acid. The copper enrichment and precipitation can be further processed to prepare high-purity copper salt. The zinc sulfate crystal purity is ≥99.0%, which has high economic value. 0.008-0.019 tons of copper and 0.017 tons of zinc can be recovered from each ton of waste acid, realizing the resource utilization of waste, reducing solid waste emissions, and meeting the requirements of circular economy development.

[0039] 5. Good process stability and low operating cost: The entire process is simple to operate, key parameters are easy to control, and it is suitable for the treatment of waste acid with different copper ion concentrations (6.1-18g / L); cost offsetting is achieved through resource recovery, and it has good prospects for industrial application.

[0040] The present invention will be further described below with reference to specific embodiments and comparative examples.

[0041] Example 1

[0042] The composition of the waste acid from washing copper strips in this embodiment is as follows: Cu 2+ Concentration 6.1 g / L, Zn 2+ The concentration of sulfuric acid was 119 g / L, the COD was 120 mg / L, the suspended particulate matter content was 2.5 mg / L, and the total concentration of calcium and magnesium ions was 1.2 g / L. The treatment capacity was 1 m³ / h, and the specific steps were as follows:

[0043] Waste acid pretreatment: The waste acid is pumped into a ceramic membrane filter with a pore size of 0.22 μm at an operating pressure of 0.1 MPa to remove suspended particulate matter, reducing the particulate matter content to 0.08 mg / L after filtration; subsequently, it enters an adsorption tower filled with granular activated carbon at a space velocity of 1 h⁻¹. -1 COD decreased to 45 mg / L; finally, it was passed through a D401 chelation resin column with a resin packing volume of 0.5 m³ and a space velocity of 1 h⁻¹. -1 After treatment, the total concentration of calcium and magnesium ions decreased to 0.3 g / L, resulting in pretreated waste acid.

[0044] Novel Bipolar Membrane Electrodialysis Separation: The novel bipolar membrane electrodialysis device consists of 100 BCBA four-membrane units. The bipolar membrane is a polyphenylene ether-based bipolar membrane, the cation exchange membrane is a perfluorosulfonic acid membrane, and the anion exchange membrane is a quaternized polysulfone membrane. Pretreated waste acid is pumped into the dilute chamber, and sulfuric acid solution with an initial concentration of 50 g / L is added to the acid chamber. Deionized water is added to the concentrate chamber. The device is started, with the membrane stack voltage controlled at 20V, the operating temperature at 30℃, the flow rate in the dilute chamber at 0.8 m / s, the flow rate in the concentrate chamber at 0.5 m / s, and the flow rate in the acid chamber at 1.0 m / s. After 2 hours of operation, the sulfuric acid concentration in the acid chamber reaches 112 g / L, which is then discharged to a washing acid storage tank for recycling. The concentrate chamber yields a heavy metal concentrate, in which Cu... 2+ Concentration 61 g / L, Zn 2+The concentration was 168 g / L, and the sulfuric acid recovery rate was 92.5%.

[0045] Copper-targeted precipitation separation: The typical precipitant N-(2-aminoethyl)-3-hydroxy-2-naphthylcarboxamide (R1=H, R2=CH2CH2) was selected, with a purity ≥98% and an infrared characteristic peak at 3420 cm⁻¹. -1 (hydroxyl group), 3300cm -1 (Amino), 1650cm -1 (Amide carbonyl). Based on the Cu in the concentrate 2+ Based on a concentration of 61 g / L, the added amount was 199.2 g / m³ of concentrated solution (1.05 times the theoretical amount). Under stirring speed of 300 r / min, the pH of the reaction was controlled to 2.5 by adding dilute sulfuric acid dropwise, the reaction temperature was 40℃, and the reaction time was 60 min. During the process, the precipitant reacted with Cu... 2+ A double five-membered chelate ring precipitate was formed. The system became noticeably turbid after 30 minutes of reaction, and reached equilibrium after 60 minutes. After standing for 30 minutes, the sedimentation rate was 0.9 m / h. The precipitate was filtered through a plate and frame filter (1 μm pore size) and washed three times with deionized water (each wash using twice the volume of the precipitate) to obtain a copper-enriched precipitate (copper content ≥35%). The filtrate contained Cu... 2+ The concentration was 0.04 g / L, and the copper separation rate was 99.93%.

[0046] Zinc sulfate preparation: Add industrial-grade zinc oxide to the above filtrate to adjust the pH to 5.0, add 0.1% hydrogen peroxide by mass of the filtrate, and stir for 30 min; pump the solution into a triple-effect evaporator, with the first effect temperature at 100℃, the second effect temperature at 80℃, and the third effect temperature at 60℃, and evaporate and concentrate until the solution density is 1.4 g / cm³; then send the concentrate to a crystallizer, cool to 20℃, crystallize for 4 h, and centrifuge to obtain zinc sulfate crystals, the purity of which is 99.2% after testing. The mother liquor is returned to the triple-effect evaporator for recycling.

[0047] Example 2

[0048] The composition of the waste acid from washing copper strips in this embodiment is as follows: Cu 2+ Concentration 12g / L, Zn 2+ The concentration of sulfuric acid was 119 g / L, the COD was 150 mg / L, the suspended particulate matter content was 3.2 mg / L, and the total concentration of calcium and magnesium ions was 1.5 g / L. The treatment capacity was 1 m³ / h, and the specific steps were as follows:

[0049] Waste acid pretreatment: A ceramic membrane with a pore size of 0.45 μm was used for filtration at an operating pressure of 0.2 MPa, resulting in a suspended particulate matter content of 0.09 mg / L after filtration; the activated carbon adsorption tower had a space velocity of 2 h⁻¹. -1COD decreased to 48 mg / L; the space velocity of the D401 chelating resin column was 0.8 h⁻¹. -1 After treatment, the total concentration of calcium and magnesium ions was 0.4 g / L.

[0050] A novel bipolar membrane electrodialysis separation method: The membrane stack consists of 120 BCBA four-membrane units. Operating parameters: stack voltage 25V, operating temperature 35℃, dilute chamber flow rate 1.0 m / s, concentrated chamber flow rate 0.6 m / s, acid chamber flow rate 1.2 m / s. After 1.8 hours of operation, the sulfuric acid concentration in the acid chamber reached 115 g / L, with a sulfuric acid recovery rate of 93.2%; the Cu in the concentrated chamber... 2+ Concentration 96 g / L, Zn 2+ Concentration 134.4 g / L.

[0051] Copper-targeted precipitation separation: N-(3-aminopropyl)-3-hydroxy-6-methyl-2-naphthylcarboxamide (R1=CH3, R2=CH2CH2CH2) was used as the precipitant. This reagent exhibits excellent stability under acidic conditions at 40-50℃, with no degradation. Based on the Cu concentration in the concentrated solution... 2+ Based on a concentration of 96 g / L, the added amount is 420 g / m³ of concentrated solution (1.08 times the theoretical stoichiometry). The stirring speed is controlled at 350 rpm, the reaction pH at 3.0, the reaction temperature at 45°C, and the reaction time at 75 min. Due to the electronic effect of the methyl substituent, this precipitant reacts with Cu... 2+ The chelation reaction rate was 20% higher than that of the unsubstituted analogue, and equilibrium was reached within 50 minutes. After standing, the sedimentation rate was 1.0 m / h, and the Cu in the filtrate after filtration and washing was... 2+ With a concentration of 0.03 g / L, the copper separation rate was 99.97%, and the zinc content in the precipitate was ≤0.1%.

[0052] Zinc sulfate preparation: Adjust the pH value to 5.5 with zinc oxide, add hydrogen peroxide at 0.2% of the filtrate mass, and react for 35 min; triple-effect evaporation at 105℃ for the first effect, 85℃ for the second effect, and 65℃ for the third effect, concentrating to a density of 1.45 g / cm³; cool to 22℃ for crystallization for 5 h, and centrifuge to obtain zinc sulfate crystals with a purity of 99.3%.

[0053] Example 3

[0054] The composition of the waste acid from washing copper strips in this embodiment is as follows: Cu 2+ Concentration 18g / L, Zn 2+ The concentration of sulfuric acid was 119 g / L, the COD was 180 mg / L, the suspended particulate matter content was 4.0 mg / L, and the total concentration of calcium and magnesium ions was 1.8 g / L. The treatment capacity was 1 m³ / h, and the specific steps were as follows:

[0055] Waste acid pretreatment: 0.45μm ceramic membrane filtration, operating pressure 0.3MPa, particulate matter content reduced to 0.1mg / L; activated carbon adsorption space velocity 3h⁻¹ -1 COD decreased to 49 mg / L; the space velocity of the D401 chelating resin column was 0.5 h⁻¹. -1 The total concentration of calcium and magnesium ions was 0.5 g / L.

[0056] A novel bipolar membrane electrodialysis separation method: The membrane stack consists of 150 BCBA four-membrane units. Operating parameters: stack voltage 30V, operating temperature 40℃, dilute chamber flow rate 1.2m / s, concentrated chamber flow rate 0.8m / s, acid chamber flow rate 1.5m / s. After 1.5 hours of operation, the sulfuric acid concentration in the acid chamber was 118g / L, with a recovery rate of 92.8%; the Cu concentration in the concentrated chamber... 2+ Concentration 120g / L, Zn 2+ Concentration 112 g / L.

[0057] Copper-targeted precipitation separation: N-(2-amino-1-methylethyl)-3-hydroxy-2-naphthylcarboxamide (R1=H, R2=CH2CH(CH3)) with branched alkylene substitution was selected, as its spatial structure makes it more readily reacted with high concentrations of Cu. 2+ (120 g / L) coordination. The precipitant was added at a rate of 672 g / m³ of concentrated solution (1.1 times the theoretical amount), with a stirring speed of 400 r / min, a reaction pH of 3.5, a temperature of 50℃, and a reaction time of 90 min. At high concentrations, the precipitant promotes precipitation formation through a "molecular clustering" effect, resulting in precipitate particles up to 10 μm in size and a settling velocity of 1.1 m / h. The filtrate after filtration contains Cu. 2+ With a concentration of 0.05 g / L and a separation rate of 99.96%, it meets the requirements for copper impurities in subsequent zinc sulfate preparation.

[0058] Zinc sulfate preparation: pH value adjusted to 6.0, hydrogen peroxide added 0.3%, reaction for 40 min; triple-effect evaporation temperatures 110℃, 90℃, 70℃, concentrated to a density of 1.5 g / cm³; crystallized at 25℃ for 6 h, zinc sulfate crystal purity 99.1%.

[0059] Comparative Example 1 (Traditional Bipolar Membrane Electrodialysis Technology)

[0060] Comparative Example 1 (Traditional bipolar membrane electrodialysis technology, compared with the membrane separation advantages of the present invention): The bipolar membrane electrodialysis device with the mainstream existing technology of "bipolar membrane-cation exchange membrane-anion exchange membrane" (BCA) three-membrane unit structure is adopted. The membrane material, pretreatment process, feed composition and operating temperature / voltage and other operating conditions are completely consistent with those of Example 2 of the present invention. The focus is on comparing the membrane separation performance and resource recovery effect.

[0061] Sulfuric acid recovery efficiency: The initial sulfuric acid recovery rate was only 84.6%, which is 8.6 percentage points lower than the 93.2% in Example 2 of this invention. Furthermore, the recovered sulfuric acid concentration fluctuated significantly (95-105 g / L), making it unsuitable for direct return to the copper strip washing process for recycling; additional concentrated acid was required to adjust the concentration. Pollution and stability: After 3 months of operation, significant copper-zinc metal salt deposition appeared on the surface of the cation exchange membrane on the concentration chamber side. The membrane resistance increased by 50% compared to the initial value, and the electrodialysis treatment capacity decreased by 30%. In contrast, the membrane stack in Example 2 of this invention showed a lower membrane resistance after 12 months of operation. The throughput increased by only 12%, while the throughput remained stable. Copper-zinc separation effect: Copper and zinc ions were non-selectively enriched in the concentration chamber, with concentrations of 95.8 g / L and 135.1 g / L, respectively. When the traditional stepwise precipitation method was used for subsequent separation, due to the mutual interference of ions, the purity of the obtained copper hydroxide was only 90.3% (containing 8.5% zinc impurities), and the purity of zinc hydroxide was 91.1% (containing 6.2% copper impurities). Additional solvent extraction and purification were required to meet industrial-grade requirements. However, the zinc sulfate crystals obtained directly in Example 2 of this invention have a purity of 99.3%, without the need for secondary purification.

[0062] Comparative Example 2 (Traditional Stepwise Precipitation Method)

[0063] Comparative Example 2 (Traditional acid-base neutralization-step precipitation technology, compared with the full-component recovery advantages of this invention): The conventional industrial "neutralization and acid removal-step precipitation" process is adopted. The waste acid pretreatment process is completely consistent with that of Example 2 of this invention. Subsequently, membrane separation is not used to recover sulfuric acid. The acid solution is directly removed by acid-base neutralization and heavy metal ions are precipitated. The focus is on comparing resource recovery efficiency and product purity.

[0064] Sulfuric acid resource recovery: Sulfuric acid recovery was completely unsuccessful. The sulfuric acid in the waste acid reacted with Ca(OH)₂ to form CaSO₄ precipitate, resulting in waste and a resource utilization rate of less than 30%. However, Example 2 of this invention achieves a high-efficiency recovery of 93.2% of sulfuric acid, and the recovered acid can be directly recycled. Heavy metal separation precision: After neutralization, NaOH was used to adjust the pH value stepwise to precipitate copper and zinc. The pH control window was extremely narrow (copper precipitation pH = 3.8-4.2, zinc precipitation pH = 7.8-8.2). A pH fluctuation of 0.2 caused a sharp decrease in separation efficiency. The final copper precipitate purity was 88.5% (containing 7.2% Ca impurities), and the zinc precipitate purity was 90.2% (containing 5.8% Ca impurities). High-purity products can only be prepared by high-temperature calcination and acid leaching purification. Process adaptability: It has poor adaptability to changes in copper ion concentration in waste acid. When the copper ion concentration increases from 12 g / L to 18 g / L, the purity of the copper precipitate drops to 82.1%. However, in Example 3 of this invention, even at a copper ion concentration of 18 g / L, a copper separation rate of 99.96% and a zinc sulfate purity of 99.1% can still be achieved. Environmental performance: The reaction process generates a large amount of CaSO4 waste residue with a water content of 65%, which has no resource value. Furthermore, the neutralization reaction causes the COD in the wastewater to rise to 85 mg / L due to the degradation of organic impurities, requiring additional aeration treatment to meet discharge standards. This invention does not generate such waste residue, and the COD in the wastewater remains stable below 48 mg / L.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the synergistic recovery of sulfuric acid and copper-zinc from waste acid from copper strip washing, characterized in that, Includes the following steps: S1. Waste acid pretreatment: The waste acid from washing copper strip is introduced into the pretreatment unit to obtain pretreated waste acid; S2. Novel Bipolar Membrane Electrodialysis Separation: Pretreated waste acid is pumped into the dilute chamber of the bipolar membrane electrodialysis device for electrodialysis treatment to obtain sulfuric acid and heavy metal concentrate. The sulfuric acid formed in the dilute chamber enters the acid chamber. When the sulfuric acid concentration in the acid chamber reaches 110-120 g / L, it is exported for copper strip washing and recycling. S3, Copper-targeted precipitation separation: A copper-targeted precipitant is added to the heavy metal concentrate to form a stable precipitate, which is then filtered and washed to obtain a copper-enriched precipitate; S4. Preparation of zinc sulfate: The pH of the filtrate after copper precipitation is adjusted and reducing impurities are removed. Then, it is evaporated and concentrated to a solution density of 1.4-1.5 g / cm³. After cooling and crystallization, zinc sulfate crystals are obtained by centrifugation. The mother liquor is returned to the evaporation and concentration unit for recycling.

2. The method for the synergistic recovery of sulfuric acid and copper-zinc from waste acid in copper strip washing according to claim 1, characterized in that, In step S1, the waste acid from washing the copper strip is sequentially subjected to precision filtration, activated carbon adsorption, and ion exchange to remove suspended particulate matter, organic impurities, and calcium and magnesium ions from the waste acid.

3. The method for the synergistic recovery of sulfuric acid and copper-zinc from waste acid in copper strip washing according to claim 1, characterized in that, In step S3, the reaction is carried out under stirring conditions, with the reaction pH controlled at 2.5-3.5, the reaction temperature at 40-50℃, and the reaction time at 60-90 min.

4. The method for the synergistic recovery of sulfuric acid and copper-zinc from waste acid in copper strip washing according to claim 1, characterized in that, In step S4, the evaporation and concentration process adopts a multi-effect evaporation process. The first-effect evaporation temperature is 100-110℃, the second-effect evaporation temperature is 80-90℃, and the third-effect evaporation temperature is 60-70℃. During the evaporation process, the pH value of the solution is controlled to be stable at 5.0-6.0, the cooling crystallization temperature is 20-25℃, the crystallization time is 4-6h, and the purity of the obtained zinc sulfate crystals is ≥99.0%.

5. The method for the synergistic recovery of sulfuric acid and copper-zinc from waste acid in copper strip washing according to claim 1, characterized in that, The novel bipolar membrane electrodialysis device described in step S2 has a membrane stack structure that combines four membrane units: a bipolar membrane, a cation exchange membrane, a bipolar membrane, and an anion exchange membrane.

6. The method for the synergistic recovery of sulfuric acid and copper-zinc from waste acid in copper strip washing according to claim 5, characterized in that, The bipolar membrane uses a polyphenylene ether framework with sulfonic acid and quaternary ammonium groups grafted onto its surface, and has a water dissociation voltage ≤1.8V; the cation exchange membrane is a perfluorosulfonic acid membrane, which is effective against Cu... 2+ Zn 2+ The selective permeability is ≥95%; the anion exchange membrane is a quaternized polysulfone membrane, which is effective against SO42-. 2- Selective transmittance ≥98%.

7. The method for the synergistic recovery of sulfuric acid and copper-zinc from waste acid in copper strip washing according to claim 5, characterized in that, The membrane stack voltage is 20-30V, the operating temperature is 30-40℃, the flow rate in the dilute chamber is 0.8-1.2m / s, the flow rate in the concentrate chamber is 0.5-0.8m / s, and the flow rate in the acid chamber is 1.0-1.5m / s.

8. The method for the synergistic recovery of sulfuric acid and copper-zinc from waste acid in copper strip washing according to claim 1, characterized in that, The copper-targeting precipitant mentioned in step S3 is a naphthyl carboxamide chelating compound with a naphthyl ring-hydroxy-amide-aliphatic amine core structure. The core component of this compound is characterized by the simultaneous presence of three types of active coordinating groups within the molecule.

9. The method for the synergistic recovery of sulfuric acid and copper-zinc from waste acid in copper strip washing according to claim 1, characterized in that, In step S4, the pH of the filtrate after copper precipitation is adjusted to 5.0-6.0, and hydrogen peroxide is added to remove residual reducing impurities.

10. The method for the synergistic recovery of sulfuric acid and copper-zinc from waste acid in copper strip washing according to claim 9, characterized in that, In step S4, the pH value is adjusted using industrial-grade zinc oxide, the amount of hydrogen peroxide added is 0.1-0.3% of the filtrate mass, and the reaction time is 30-40 min.

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