Multi-stage electrodialysis method for high-selectivity recovery and concentration of sulfuric acid in heavy metal waste acid solution

Abstract

The application discloses a multi-stage electrodialysis method for highly selective recovery and concentration of sulfuric acid in heavy metal waste acid liquid, and comprises the following steps: introducing the heavy metal waste acid liquid into a first MCS-ED system, and performing ion migration and pre-concentration under the action of a direct current electric field to obtain first MCS-ED recovery acid liquid; if the terminal acid concentration and the recovery rate are to be improved, the first MCS-ED recovery acid liquid is introduced into a gradient chamber of an L-MCS-ED electrodialysis system, the heavy metal waste acid liquid is introduced into a dilute chamber of the L-MCS-ED electrodialysis system, and the first MCS-ED recovery acid liquid or deionized water is introduced into a concentrated chamber of the L-MCS-ED electrodialysis system to obtain a recovered sulfuric acid product liquid; if the energy consumption is to be reduced, the first MCS-ED recovery acid liquid is introduced into a dilute chamber and a concentrated chamber of a second MCS-ED system respectively to obtain the recovered sulfuric acid product liquid. The process is clear, the recovery rate of sulfuric acid is up to 80.79%, the purity is up to 99.32%, and the application has the advantages of high efficiency, low consumption and engineering applicability.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation and resource recovery technology, specifically relating to a multi-stage electrodialysis method for highly selective recovery and concentration of sulfuric acid from heavy metal waste acid. Background Technology

[0002] With rapid industrialization, industries such as electroplating, steel processing, chemical manufacturing, and electronics generate large quantities of waste acid containing heavy metals during production. This type of waste liquid is characterized by extremely low pH values ​​(typically less than 2) and the coexistence of high concentrations of toxic heavy metals (such as chromium, nickel, copper, lead, cadmium, and zinc), exhibiting a complex pollution effect of "acidity and toxicity superimposed." If improperly disposed of or leaked, hydrogen ions in the waste acid can severely disrupt the buffering capacity of the soil and the acid-base balance of water bodies, leading to environmental acidification. Simultaneously, the heavy metal ions dissolved and activated by the acid are non-degradable and bioaccumulative, migrating in water bodies, accumulating in soil, and entering the food chain through crops or groundwater. This synergistic effect of "acidification accelerating heavy metal leaching and heavy metals inhibiting acid neutralization" makes pollution remediation extremely difficult, posing a long-term and irreversible threat to the ecosystem. Therefore, the efficient recovery of sulfuric acid from this type of waste acid is of great significance for achieving resource recycling and reducing wastewater treatment costs.

[0003] Currently, conventional methods for recovering sulfuric acid in industry mainly include evaporation concentration, chemical precipitation, ion exchange, and membrane separation. However, these methods all have significant limitations in application. For example, evaporation concentration consumes extremely high energy and has stringent requirements for equipment materials, making it prone to corrosion; chemical methods usually require the addition of other chemicals, which may introduce new impurities and complicate subsequent processing; traditional ion exchange methods suffer from problems such as frequent resin regeneration and the generation of secondary waste liquid.

[0004] Electrodialysis, as a highly efficient membrane separation technology, relies on an electric field to drive the selective migration of ions through an ion exchange membrane. It offers advantages such as continuous processing, no need for chemical reagents, and environmental friendliness, demonstrating promising application potential in acid recovery. However, conventional single-stage electrodialysis processes still face limiting technical bottlenecks when treating high-concentration nickel-containing waste acid. As the concentration process progresses, the acid concentration in the concentration chamber increases, the system resistance rises sharply, leading to a surge in operating voltage and a significant increase in energy consumption. Simultaneously, concentration polarization and membrane fouling intensify, causing a substantial decrease in current efficiency during the deep concentration stage. These factors collectively limit the final acid concentration achievable with single-stage electrodialysis, making it difficult to achieve high-rate, high-selectivity concentration and recovery of sulfuric acid.

[0005] Therefore, developing a novel electrodialysis process that can overcome the above-mentioned shortcomings and is efficient, low-energy, and capable of producing high-concentration recovered acid has become a key problem that urgently needs to be solved in this technical field. Summary of the Invention

[0006] To address the above problems, the present invention aims to provide a multi-stage electrodialysis method for highly selective recovery and concentration of sulfuric acid from heavy metal waste acid.

[0007] The specific technical solution is as follows:

[0008] A multi-stage electrodialysis method for highly selective recovery and concentration of sulfuric acid from heavy metal waste acid includes the following steps:

[0009] 1) The heavy metal waste acid solution is introduced into the primary MCS-ED system, where ion migration and pre-concentration are carried out under the action of a DC electric field to obtain the primary MCS-ED recovered acid solution.

[0010] 2) To increase the final acid concentration and improve the recovery rate, the primary MCS-ED recovered acid solution is introduced into the gradient chamber of the L-MCS-ED electrodialysis system, while the heavy metal waste acid solution is introduced into the dilute chamber of the L-MCS-ED electrodialysis system, and the primary MCS-ED recovered acid solution or deionized water is introduced into the concentrated chamber of the L-MCS-ED electrodialysis system to obtain the recovered sulfuric acid product solution.

[0011] 3) To reduce energy consumption, the acid solution recovered from the primary MCS-ED system is introduced into the dilute and concentrated chambers of the secondary MCS-ED system to obtain the recovered sulfuric acid product solution.

[0012] The MCS-ED system is a monovalent and divalent selective electrodialysis cation exchange membrane + ordinary anion exchange membrane system, while the L-MCS-ED system is an electrodialysis gradient system for electrodialysis concentration processes.

[0013] Furthermore, the heavy metal waste acid solution is preferably a nickel-containing heavy metal waste acid solution, with the following ion concentrations: nickel ions 60-70 g / L, boric acid 1-3 g / L, hydrogen ions 1-2 g / L, sulfate ions 160-170 g / L, pH value 2.0-4.0, and conductivity 136.0-142.0 mS / cm.

[0014] Furthermore, the primary MCS-ED system includes cation exchange membranes, anion exchange membranes, electrodes, and separators. The cation exchange membranes and anion exchange membranes are alternately arranged to form at least 5 sets of repeating unit electrodialysis cells. The membranes are separated into a dilute chamber and a concentrated chamber by separators. Nickel-containing heavy metal waste acid solution is introduced into the dilute chamber, and deionized water is introduced into the concentrated chamber. The space between the electrodes and the ion exchange membranes is the electrode liquid chamber, into which sulfuric acid solution is introduced.

[0015] Furthermore, the cation exchange membrane is a CIMS membrane, the operating current density of the first-stage MCS-ED system is 20 mA / cm², and the initial feed volume ratio of the dilute chamber to the concentrate chamber of the first-stage MCS-ED system is 1:1.

[0016] Furthermore, the secondary MCS-ED system includes cation exchange membranes, anion exchange membranes, electrodes, and separators. The cation exchange membranes and anion exchange membranes are alternately arranged to form at least 5 sets of repeatable unit electrodialysis cells. The membranes are separated into a dilute chamber and a concentrated chamber by separators. The acid recovered from the primary MCS-ED is introduced into the dilute chamber and concentrated chamber of the secondary MCS-ED system at a volume ratio of 1-3:1. The space between the electrodes and the ion exchange membranes is the electrode liquid chamber, which is circulated with sulfuric acid solution.

[0017] Furthermore, the runtime of the secondary MCS-ED system is 60-80 minutes.

[0018] Furthermore, the L-MCS-ED electrodialysis system is a three-compartment electrodialysis system, including electrode plates and at least 5 sets of repeating unit electrodialysis cells. Each set of unit electrodialysis cells includes a dilute chamber, a gradient chamber, and a concentrate chamber. The gradient chamber is composed of anion exchange membranes, and the concentrate and dilute chambers are composed of anion exchange membranes and cation exchange membranes, respectively. The space between the electrode plates and the ion exchange membranes is the electrode liquid chamber, which is circulated with sulfuric acid solution. The initial feed volume ratio of the dilute chamber, concentrate chamber, and gradient chamber is 1:1:1.

[0019] Furthermore, the L-MCS-ED electrodialysis system is a four-compartment electrodialysis system, including electrodes and at least 5 sets of repeatable unit electrodialysis cells. Each set of unit electrodialysis cells includes a dilute chamber, a first gradient chamber L1, a second gradient chamber L2, and a concentrate chamber. The first gradient chamber L1 and the second gradient chamber L2 are respectively composed of anion exchange membranes, and the concentrate chamber and the dilute chamber are respectively composed of anion exchange membranes and cation exchange membranes. The space between the electrodes and the ion exchange membranes is the electrode liquid chamber, which is circulated with sulfuric acid solution. The initial feed volume ratio of the dilute chamber, the first gradient chamber L1, the second gradient chamber L2, and the concentrate chamber is 1-2:1-3:1-2:1-2.

[0020] Furthermore, the L-MCS-ED electrodialysis system has an operating time of 110~130 min.

[0021] Furthermore, the final sulfuric acid concentration of the primary MCS-ED acid recovery solution is 0.50~0.60 mol / L, the sulfuric acid concentration of the recovered sulfuric acid product solution obtained after the secondary MCS-ED system is 0.74~0.88 mol / L, and the sulfuric acid concentration of the recovered sulfuric acid product solution obtained after the L-MCS-ED electrodialysis system is 0.80~1.05 mol / L.

[0022] The beneficial effects of this invention are as follows:

[0023] The multi-stage electrodialysis coupled recovery and concentration method described in this invention can effectively separate, enrich, and recover sulfuric acid from heavy metal waste acid systems while maintaining high purity of the recovered solution. By combining primary MCS-ED pre-concentration with subsequent secondary MCS-ED or L-MCS-ED electrodialysis for deep concentration, the endpoint acid concentration, sulfuric acid recovery rate, recovered solution purity, and energy consumption can be adjusted and matched according to different application requirements. Among them, the secondary MCS-ED scheme has better overall energy consumption advantages, and the four-compartment dual-gradient chamber L-MCS-ED electrodialysis scheme is more effective in improving the endpoint acid concentration, indicating that this invention has good process flexibility and promising industrial application prospects. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the process of the present invention;

[0025] Figure 2 A schematic diagram illustrating the working mechanism of a primary MCS-ED system for concentrating nickel-containing acidic solutions;

[0026] Figure 3 A schematic diagram illustrating the working mechanism of a two-stage MCS-ED system for concentrating nickel-containing acidic solutions;

[0027] Figure 4 This is a schematic diagram illustrating the working mechanism of the three-compartment L-MCS-ED electrodialysis system;

[0028] Figure 5 This is a schematic diagram of the working mechanism of a four-compartment L-MCS-ED electrodialysis system. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited thereto.

[0030] Unless otherwise stated, the concentrations of each ion in the raw material solution in the embodiments of the present invention were determined using conventional analytical methods, pH was measured using a pH meter, and conductivity was measured using a conductivity meter. Unless otherwise specified, the test temperature in all embodiments was 30±2℃. The sulfuric acid recovery rate, sulfuric acid purity, energy consumption, and current efficiency mentioned in the embodiments were calculated according to the following formulas:

[0031] 1) The sulfuric acid recovery rate W is calculated as the total amount of sulfuric acid in the recovered solution after migration / the total amount of free sulfuric acid in the original solution, using the following formula:

[0032]

[0033] in:

[0034] W represents the sulfuric acid recovery rate, which has no unit; C 游离酸In this embodiment, the estimated free sulfuric acid content in the original solution is approximately 0.5–0.6 mol / L.

[0035] C 酸 The concentration of sulfuric acid recovered from the recovered solution is expressed in mol / L; C Ni Ni in the recovery liquid 2+ The concentration is expressed in mol / L.

[0036] V 酸 The volume of the recovered liquid is in liters (L).

[0037] V 游离酸 The volume of the original solution is expressed in liters (L).

[0038] 2) The sulfuric acid purity P is calculated based on the relative content of sulfuric acid and total impurities in the recovered solution; in this embodiment of the invention, it is characterized by the mass ratio of sulfuric acid to nickel salt impurities in the recovered solution, and the calculation formula is as follows:

[0039] in:

[0040] P indicates the purity of sulfuric acid, which has no unit; C 酸 The concentration of sulfuric acid recovered from the recovered solution is expressed in mol / L; C Ni Ni in the recovery liquid 2+ The concentration is expressed in mol / L.

[0041] 3) The energy consumption per unit of acid production, E, is calculated as the ratio of the electrical energy consumed during electrodialysis operation to the mass of recovered sulfuric acid, using the following formula:

[0042]

[0043] in:

[0044] E represents energy consumption, measured in kWh / kg;

[0045] U is the operating voltage, in V; I is the operating current, in A; t is the energizing time, in min; C t This represents the final sulfuric acid concentration in the concentration chamber, expressed in mol / L.

[0046] V t The volume of sulfuric acid in the (concentrated chamber) of the recovered solution is expressed in liters (L).

[0047] M is the molar mass of sulfuric acid, which is 98, and the unit is g / mol.

[0048] Note: Unit: Wh / g = kWh / kg.

[0049] 4) The current efficiency η is calculated as the ratio of the actual migration equivalent (based on sulfuric acid) to the theoretical current-carrying equivalent, using the following formula:

[0050]

[0051] in:

[0052] η represents current efficiency, which has no unit.

[0053] C t This represents the final sulfuric acid concentration in the concentration chamber, expressed in mol / L.

[0054] C0 represents the initial sulfuric acid concentration in the concentration chamber, in mol / L.

[0055] (C t -C0)Vt represents the net amount of sulfuric acid that migrates, in mol.

[0056] V t The volume of sulfuric acid in the (concentrated chamber) of the recovered solution is in L; F is the Faraday constant, taken as 96485 C / mol; N is the effective repeating unit of the membrane stack; I is the operating current in A; t is the energizing time in min, where 60 in the denominator is used to convert min to s.

[0057] like Figure 1 As shown, a multi-stage electrodialysis method for highly selective recovery and concentration of sulfuric acid from heavy metal waste acid includes the following steps:

[0058] 1) The heavy metal waste acid solution is introduced into the primary MCS-ED system, where ion migration and pre-concentration are carried out under the action of a DC electric field to obtain the primary MCS-ED recovered acid solution.

[0059] 2) To increase the final acid concentration and improve the recovery rate, the primary MCS-ED recovered acid solution is introduced into the gradient chamber of the L-MCS-ED electrodialysis system, while the heavy metal waste acid solution is introduced into the dilute chamber of the L-MCS-ED electrodialysis system, and the primary MCS-ED recovered acid solution or deionized water is introduced into the concentrated chamber of the L-MCS-ED electrodialysis system to obtain the recovered sulfuric acid product solution.

[0060] 3) To reduce energy consumption, the acid solution recovered from the primary MCS-ED system is introduced into the dilute and concentrated chambers of the secondary MCS-ED system to obtain the recovered sulfuric acid product solution.

[0061] Example 1

[0062] pH and conductivity tests were conducted on the nickel-containing acidic wastewater from Xiamen Jiarong Technology Co., Ltd. The concentrations of each ion in the nickel-containing acidic wastewater were 65 g / L for nickel ions, 3 g / L for boric acid, 1 g / L for hydrogen ions, and 166 g / L for sulfate ions. The pH value was 2.0-4.0, and the conductivity was 136.0-142.0 mS / cm.

[0063] Adopting such Figure 2 The primary MCS-ED system shown performs initial treatment. The primary MCS-ED system includes cation exchange membranes, anion exchange membranes, electrodes, and separators. Cation and anion exchange membranes are alternately arranged to form five sets of repeatable electrodialysis cells. The membranes are separated into two compartments, a dilute compartment and a concentrated compartment, by separators. Nickel-containing heavy metal waste acid is introduced into the dilute compartment, and deionized water is introduced into the concentrated compartment. The space between the electrodes and the ion exchange membranes is the electrode liquid compartment, which is circulated with sulfuric acid solution. The cation exchange membranes are Aston CIMS, and the anion exchange membranes are AMT from Zhejiang Baichen Low Carbon Technology Co., Ltd. Each membrane has an effective membrane area of ​​189 cm². Each compartment is connected to an external storage tank via a magnetic pump, and the water then returns to the external storage tank through the effluent outlet on the membrane stack, forming a closed loop.

[0064] In this embodiment, 500 mL of deionized water was added to each concentration chamber of the primary MCS-ED system, 500 mL of nickel-containing acidic waste liquid was added to each dilute chamber, and 500 mL of 0.1 M sulfuric acid solution was added to each electrode chamber. The pump was started, and once the flow rate stabilized at 30 L / h, the power was turned on, and the system operated at a constant current of 3.78 A. The power was disconnected when the conductivity of the dilute chamber was below 40 mS / cm, and the system was stopped when the test temperature reached 30 ± 2 °C. The dilute chamber liquid (corresponding to…) was collected. Figure 2 Low concentration nickel sulfate) and concentrated solution (corresponding to Figure 2 (Low concentration of nickel-containing H2SO4). Under these conditions, the final acid concentration of the concentrate after the first-stage MCS-ED was approximately 0.55 mol / L. Sulfuric acid recovery was 53.06%, with a purity of 98.75%.

[0065] Example 2

[0066] The concentrated solution obtained in Example 1 was prepared using the following method: Figure 3 The secondary MCS-ED system shown is further condensed through the following steps:

[0067] The concentrated solution obtained from the primary MCS-ED system has a pH of 2.0–2.5 and a conductivity of 180.0–190.0 mS / cm. The secondary MCS-ED system includes cation exchange membranes, anion exchange membranes, electrodes, and separators. The cation and anion exchange membranes are alternately arranged, forming five sets of repeatable electrodialysis cells. The membranes are separated into dilute and concentrated compartments by separators. The acid recovered from the primary MCS-ED system is introduced into the dilute and concentrated compartments of the secondary MCS-ED system at a volume ratio of 1-3:1. The electrode compartment is located between the electrodes and the ion exchange membranes, and is circulated with sulfuric acid solution. The electrodes are made of two titanium-plated ruthenium materials. The cation exchange membrane uses Aston CIMS, and the anion exchange membrane uses AMT from Zhejiang Baichen Low Carbon Technology Co., Ltd. Each membrane has an effective membrane area of ​​189 cm². Each compartment is connected to an external storage tank via a magnetic pump, and the solution then returns to the external storage tank through the outlet on the membrane stack, forming a closed loop.

[0068] In this embodiment, 500 mL of the recovered acid solution from the first-stage MCS-ED was added to each concentration chamber of the two-stage MCS-ED system, and 500 mL of the recovered acid solution from the first-stage MCS-ED was added to each dilute chamber, i.e., the volume ratio of the concentration chamber to the dilute chamber was 1:1. 500 mL of 0.1 M sulfuric acid solution was added to the electrode chamber. The pump was started, and once the flow rate stabilized at 30 L / h, the power was turned on, and the system operated at a constant current of 3.78 A. The system continued until the conductivity of the dilute chamber was below 30 mS / cm, at which point the power was disconnected, and the system was stopped when the test temperature reached 30 ± 2 °C. The dilute chamber liquid (corresponding to…) was collected. Figure 3 (lower concentrations of nickel sulfate) and concentrated solution (corresponding to) Figure 3 The high concentration of H2SO4 in the solution was used. The secondary MCS-ED running time was set to 60 min. After electrodialysis, when the volume ratio of the concentrated chamber to the dilute chamber was 1:1, the final acid concentration (high concentration of H2SO4) was approximately 0.755 mol / L; the sulfuric acid recovery rate was 56.64%, and the purity was 96.79%.

[0069] Example 3

[0070] Adopting such Figure 3 The secondary MCS-ED system shown is used for further concentration. The operation process is the same as in Example 2, except that 400 mL of the recovered acid from the primary MCS-ED is added to each concentration chamber, and 800 mL of the recovered acid from the primary MCS-ED is added to each dilute chamber, i.e., the volume ratio of the concentration chamber to the dilute chamber is 1:2. The pump is started, and once the flow rate stabilizes at 30 L / h, the power is turned on and it runs at a constant current of 3.78 A. The power is disconnected when the conductivity of the dilute chamber is below 30 mS / cm, and the operation is stopped when the test temperature is 30 ± 2℃. The dilute chamber liquid (corresponding to...) is collected. Figure 3 (lower concentrations of nickel sulfate) and concentrated solution (corresponding to) Figure 3The high concentration of H2SO4 in the solution was used. The secondary MCS-ED running time was set to 60 min. After electrodialysis, when the volume ratio of the concentrated chamber to the dilute chamber was 1:2, the final acid concentration (high concentration of H2SO4) was approximately 0.875 mol / L; the sulfuric acid recovery rate was 74.30%, and the purity was 99.32%.

[0071] Example 4

[0072] Adopting such Figure 3 The secondary MCS-ED system shown was further concentrated, and its operation was the same as in Example 2, except that 300 mL of the recovered acid from the primary MCS-ED was added to each concentration chamber, and 900 mL of the recovered acid from the primary MCS-ED was added to each dilute chamber, i.e., the volume ratio of the concentration chamber to the dilute chamber was 1:3. The pump was started, and after the flow rate stabilized at 30 L / h, the power was turned on and it was run at a constant current of 3.78 A. The power was turned off when the conductivity of the dilute chamber was lower than 30 mS / cm, and the operation was stopped when the test temperature was 30±2℃. The dilute chamber liquid (corresponding to...) was collected. Figure 3 (lower concentrations of nickel sulfate) and concentrated solution (corresponding to) Figure 3 The high concentration of H2SO4 in the solution was used. The secondary MCS-ED cycle time was set to 60 min. After electrodialysis, when the volume ratio of the concentrated to dilute chamber was 1:3, the final acid concentration (high concentration of H2SO4) was approximately 0.748 mol / L. The sulfuric acid recovery rate was 59.75%, and the purity was 96.62%.

[0073] For Examples 5-10, the subsequent deep concentration system uses an L-MCS-ED electrodialysis system. The recovered acid solution from the first-stage MCS-ED is introduced into the L-MCS-ED electrodialysis system as the gradient chamber solution to establish an acid concentration gradient. The original nickel-containing acidic solution is introduced into the dilute chamber, and deionized water or the receiving solution (the recovered acid solution from the first-stage MCS-ED) is introduced into the concentrate chamber. Under the action of a DC electric field, sulfuric acid is further migrated and enriched from the dilute chamber to the concentrate chamber. Except for the volume configuration of each chamber, the other operating conditions are basically the same.

[0074] Example 5

[0075] The concentrated solution obtained in Example 1 was prepared using the following method: Figure 4 The three-compartment L-MCS-ED electrodialysis shown herein is used for deep concentration. The specific steps include:

[0076] The concentrated solution obtained from the first-stage MCS-ED has a pH of 2.0–2.5 and a conductivity of 180.0–190.0 mS / cm. The L-MCS-ED electrodialysis system is a three-compartment system, comprising electrodes and five sets of repeating unit electrodialysis cells. Each unit electrodialysis cell includes a dilute chamber, a gradient chamber, and a concentrated chamber. The gradient chamber is composed of anion exchange membranes, while the concentrated and dilute chambers are composed of anion exchange membranes and cation exchange membranes, respectively. The electrode chamber, between the electrodes and the ion exchange membranes, is purged with sulfuric acid solution. The electrodes are two titanium-plated ruthenium materials. The cation exchange membrane is an Aston CIMS, and the anion exchange membrane is an AMT from Zhejiang Baichen Low Carbon Technology Co., Ltd. Each membrane has an effective membrane area of ​​189 cm². Each chamber is connected to an external storage tank via a magnetic pump, and the solution then returns to the external storage tank through the outlet on the membrane stack, forming a closed loop.

[0077] In this embodiment, 500 mL of deionized water was added to each concentration chamber of the three-compartment L-MCS-ED electrodialysis system, 500 mL of nickel-containing acidic solution was added to each dilute chamber, 500 mL of the recovered acid solution from the first-stage MCS-ED was added to each gradient chamber, and 500 mL of 0.1M sulfuric acid solution was added to each electrode chamber. The pump was started, and after the flow rate stabilized at 30 L / h, the power was turned on and the system was run at a constant current of 3.78 A. The power was disconnected when the conductivity of the dilute chamber was lower than 30 mS / cm, and the system was stopped when the test temperature reached 30±2℃. The dilute chamber solution (corresponding to...) was collected. Figure 4 (lower concentrations of nickel sulfate) and concentrated solution (corresponding to) Figure 4 The L-MCS-ED electrodialysis system had a high concentration of H2SO4. The operating time was 120 min. After electrodialysis, when the feed volume ratio of the concentrated to dilute chambers was 1:1 and the gradient chamber volume was 500 mL (i.e., a single-gradient chamber L-MCS-ED electrodialysis system), the endpoint acid (high concentration of H2SO4) concentration was approximately 0.843 mol / L. The sulfuric acid recovery rate was 67.62%, and the purity was 97.46%.

[0078] Example 6

[0079] The concentrated solution obtained in Example 1 was prepared using the following method: Figure 5 The four-compartment L-MCS-ED electrodialysis shown in the figure involves deep concentration, and the specific steps include:

[0080] The concentrated solution obtained from the first-stage MCS-ED has a pH of 2.0–2.5 and a conductivity of 180.0–190.0 mS / cm. The L-MCS-ED electrodialysis system is a four-compartment system, comprising electrodes and five sets of repeating unit electrodialysis cells. Each unit includes a dilute cell, a first gradient cell (L1), a second gradient cell (L2), and a concentrated cell. The first and second gradient cells (L1 and L2) are constructed from anion exchange membranes, while the concentrated and dilute cells are constructed from anion and cation exchange membranes, respectively. The electrode chamber is located between the electrodes and the ion exchange membranes, and is circulated with sulfuric acid solution. The electrodes are two titanium-plated ruthenium materials. The cation exchange membrane is an Aston CIMS, and the anion exchange membrane is an AMT from Zhejiang Baichen Low Carbon Technology Co., Ltd. Each membrane has an effective membrane area of ​​189 cm². Each compartment is connected to an external storage tank via a magnetic pump, and the solution then returns to the external storage tank through the outlet on the membrane stack, forming a closed loop.

[0081] In this embodiment, 500 mL of deionized water was added to each concentration chamber of the four-compartment L-MCS-ED electrodialysis system, 500 mL of nickel-containing acidic solution was added to the dilute chamber, 500 mL of the recovered acid solution from the first-stage MCS-ED was added to each of the gradient chambers L1 and L2, and 500 mL of 0.1M sulfuric acid solution was added to the electrode chamber. The pump was started, and after the flow rate stabilized at 30 L / h, the power was turned on and the system was run at a constant current of 3.78A. The system was run until the conductivity of the dilute chamber was below 30 mS / cm, at which point the power was turned off and the system was stopped at a test temperature of 30±2℃. The dilute chamber solution (corresponding to...) was collected. Figure 5 (lower concentrations of nickel sulfate) and concentrated solution (corresponding to) Figure 5 The high concentration of H2SO4 was measured. The L-MCS-ED electrodialysis run time was 120 min. After electrodialysis, when the feed volume ratio of the concentrated chamber to the dilute chamber was 1:1, and the volume ratio of gradient chamber L1 to gradient chamber L2 was 1:1, the endpoint acid concentration (high concentration of H2SO4) of the dual-gradient chamber L-MCS-ED electrodialysis system was approximately 0.918 mol / L. The sulfuric acid recovery rate was 70.79%, and the purity was 97.98%.

[0082] Example 7

[0083] Adopting such Figure 5The four-compartment L-MCS-ED system shown was further concentrated, and its operation was the same as in Example 6, except that 500 mL of deionized water was added to each concentration compartment, 1000 mL of nickel-containing acidic solution was added to the dilute compartment, 500 mL of the recovered acid solution from the first-stage MCS-ED was added to each of the gradient compartments L1 and L2, and 500 mL of 0.1M sulfuric acid solution was added to the electrode compartment. The pump was started, and after the flow rate stabilized at 30 L / h, the power was turned on and the system was run at a constant current of 3.78 A. The power was turned off when the conductivity of the dilute compartment was lower than 30 mS / cm, and the system was stopped when the test temperature was 30±2℃. The dilute compartment liquid (corresponding to...) was collected. Figure 5 (lower concentrations of nickel sulfate) and concentrated solution (corresponding to) Figure 5 The high concentration of H2SO4 was detected. The L-MCS-ED electrodialysis run time was 120 min. After electrodialysis treatment, when the volume ratio of the concentrated to dilute chambers was 1:2 and the volume ratio of gradient chamber L1 to gradient chamber L2 was 1:1, the final acid concentration (high concentration of H2SO4) was approximately 0.903 mol / L. The sulfuric acid recovery rate was 80.79%, and the purity was 98.68%.

[0084] Example 8

[0085] Adopting such Figure 5 The four-compartment L-MCS-ED system shown was further concentrated, and its operation was the same as in Example 6, except that 300 mL of deionized water was added to each concentration compartment, 900 mL of nickel-containing acidic solution was added to the dilute compartment, 500 mL of the recovered acid solution from the first-stage MCS-ED was added to each of the gradient compartments L1 and L2, and 500 mL of 0.1M sulfuric acid solution was added to the electrode compartment. The pump was started, and after the flow rate stabilized at 30 L / h, the power was turned on and the system was run at a constant current of 3.78 A. The power was turned off when the conductivity of the dilute compartment was lower than 30 mS / cm, and the system was stopped when the test temperature was 30±2℃. The dilute compartment liquid (corresponding to...) was collected. Figure 5 (lower concentrations of nickel sulfate) and concentrated solution (corresponding to) Figure 5 The high concentration of H2SO4 was detected. The L-MCS-ED electrodialysis run time was 120 min. After electrodialysis treatment, when the feed volume ratio of the concentrated chamber to the dilute chamber was 1:3 and the gradient chamber volume ratio of gradient chamber L1 to gradient chamber L2 was 1:1, the final acid concentration (high concentration of H2SO4) was approximately 0.918 mol / L. The sulfuric acid recovery rate was 76.29%, and the purity was 97.18%.

[0086] Example 9

[0087] Adopting such Figure 5The four-compartment L-MCS-ED system shown is further concentrated using the same procedure as in Example 6, except that in the electrodialysis process, 500 mL of deionized water is added to the concentration chamber, 1000 mL of nickel-containing acidic solution is added to the dilute chamber, 500 mL of the recovered acid solution from the first-stage MCS-ED is added to the gradient chamber L1, 1000 mL of the recovered acid solution from the first-stage MCS-ED is added to the gradient chamber L2, and 500 mL of 0.1M sulfuric acid solution is added to the electrode chamber. The pump is started, and once the flow rate stabilizes at 30 L / h, the power is connected and the system operates at a constant current of 3.78 A. The power is disconnected when the conductivity of the dilute chamber drops below 30 mS / cm, and the system is stopped when the test temperature reaches 30 ± 2℃. The dilute chamber solution (corresponding to…) is collected. Figure 5 (lower concentrations of nickel sulfate) and concentrated solution (corresponding to) Figure 5 (High concentration of H2SO4 in the solution). The L-MCS-ED electrodialysis run time was 120 min. After electrodialysis treatment, when the feed volume ratio of the concentrated chamber to the dilute chamber was 1:2, and the gradient chamber volume ratio of gradient chamber L1 to gradient chamber L2 was 1:2, the endpoint acid concentration was approximately 0.820 mol / L. The sulfuric acid recovery rate was 61.12%, and the purity was 99.10%.

[0088] Example 10

[0089] Adopting such Figure 5 The four-compartment L-MCS-ED system shown was further concentrated, and its operation was the same as in Example 6, except that 500 mL of deionized water was added to each concentration chamber, 1000 mL of nickel-containing acidic solution was added to the dilute chamber, 1000 mL of the recovered acid solution from the first-stage MCS-ED was added to gradient chamber L1, and 500 mL of the recovered acid solution from the first-stage MCS-ED was added to gradient chamber L2. When the volume ratio of concentration chamber to dilute chamber was 1:2 and the volume ratio of gradient chamber L1 to gradient chamber L2 was 2:1, 500 mL of 0.1M sulfuric acid solution was added to the electrode chamber. The pump was started, and after the flow rate stabilized at 30 L / h, the power was turned on and the system was run at a constant current of 3.78 A. The power was turned off when the conductivity of the dilute chamber was lower than 30 mS / cm, and the system was stopped when the test temperature was 30±2℃. The dilute chamber liquid (corresponding to...) was collected. Figure 5 (lower concentrations of nickel sulfate) and concentrated solution (corresponding to) Figure 5 The high concentration of H2SO4 was detected. The L-MCS-ED electrodialysis run time was 120 min. After electrodialysis, with a feed volume ratio of 1:2 between the concentrated and dilute chambers and 2:1 between the gradient chambers, the final acid (high concentration H2SO4) concentration was approximately 1.008 mol / L. The sulfuric acid recovery rate was 80.04%, and the purity was 99.17%.

[0090] Table 1 shows a comparison of the products in each embodiment:

[0091] Table 1 Comparison of Products in Each Embodiment

[0092] Example 1 0.55 mol / L 53.06% 98.75% 5.667 kWh / kg 37.45% Example 2 0.755 mol / L 56.64% 96.79% 1.484 kWh / kg 74.45% Example 3 0.875 mol / L 74.30% 99.32% 2.02 kWh / kg 79.26% Example 4 0.748 mol / L 59.75% 96.62% 2.655 kWh / kg 71.91% Example 5 0.843 mol / L 67.62% 97.46% 6.92 kWh / kg 41.80% Example 6 0.918 mol / L 70.79% 97.98% 7.149 kWh / kg 46.50% Example 7 0.903 mol / L 80.79% 98.68% 3.441 kWh / kg 32.60% Example 8 0.918 mol / L 76.29% 97.18% 4.293 kWh / kg 22.90% Example 9 0.820 mol / L 61.12% 99.10% 5.149 kWh / kg 37.20% Example 10 1.008 mol / L 80.04% 99.17% 2.959 kWh / kg 70.9%

[0093] This invention addresses nickel-containing acidic wastewater by constructing an acid recovery process based on multi-stage selective electrodialysis concentration. The main components of the feed solution include nickel ions, boric acid, hydrogen ions, and sulfate ions. Specifically, the nickel-containing acidic wastewater has a nickel ion concentration of 65 g / L, a boric acid concentration of 3 g / L, a hydrogen ion concentration of 1 g / L, a sulfate concentration of 166 g / L, a pH of 2.0–4.0, and a conductivity of 136.0–142.0 mS / cm.

[0094] This invention first employs a two-compartment MCS-ED membrane stack for primary pre-concentration. The stack consists of titanium-plated ruthenium electrodes and five repeating electrodialysis cells. Each cell, from anode to cathode, comprises a cation exchange membrane, an anion exchange membrane, and a dilute and concentrate chamber formed by a separator. Each membrane has an effective area of ​​189 cm². During operation, 500 mL of nickel-containing acidic waste liquid is added to the dilute chamber, 500 mL of deionized water to the concentrate chamber, and 500 mL of 0.1 mol / L sulfuric acid solution to the electrode chamber. The flow rate is controlled at 30 L / h, and the system operates under a constant current of 3.78 A until the conductivity of the dilute chamber drops below 40 mS / cm. After primary MCS-ED treatment, the acid concentration of the concentrated recovery solution is approximately 0.55 mol / L, the sulfuric acid recovery rate is 53.06%, and the purity is 98.75%.

[0095] Based on the primary MCS-ED product, this invention further incorporates a secondary MCS-ED concentration process. The secondary MCS-ED also employs a membrane stack structure with two compartments and five repeating units. The membrane material and effective area are the same as in the primary MCS-ED. Operating conditions are maintained at a flow rate of 30 L / h and a constant current of 3.78 A. The termination condition is when the conductivity of the dilute compartment is below 30 mS / cm, and the operating time is set to 60 min. The secondary MCS-ED achieves different degrees of acid concentration by adjusting the feed volume ratio between the dilute and concentrated compartments.

[0096] When the volume ratio of the concentrate to dilute solution in the two-stage MCS-ED process is 1:1, the endpoint acid concentration is approximately 0.755 mol / L, the sulfuric acid recovery rate is 56.64%, and the purity is 96.79%. When the volume ratio is adjusted to 1:2, the endpoint acid concentration increases to 0.875 mol / L, the sulfuric acid recovery rate increases to 74.30%, and the purity reaches 99.32%. When the volume ratio is further adjusted to 1:3, the endpoint acid concentration is approximately 0.748 mol / L, the sulfuric acid recovery rate is 59.75%, and the purity is 96.62%. These results indicate that in the two-stage MCS-ED process, appropriately increasing the volume ratio of the concentrate to dilute chambers is beneficial for increasing the endpoint acid concentration, but the recovery rate and purity do not change monotonically with the volume ratio. The 1:2 ratio shows the best overall effect.

[0097] In addition to employing a series-connected two-stage MCS-ED, this invention also proposes a deep concentration process coupled with a single-stage MCS-ED and L-MCS-ED electrodialysis. For the three-compartment L-MCS-ED structure, the membrane stack consists of a dilute chamber, a gradient chamber L, and a concentrate chamber; for the four-compartment L-MCS-ED structure, the membrane stack consists of a dilute chamber, gradient chambers L1 and L2, and a concentrate chamber. Both types of membrane stacks consist of titanium-plated ruthenium electrodes and five repeating units, with each membrane having an effective area of ​​189 cm². Each chamber forms a closed-loop circulation system via an external storage tank and a magnetic pump, operating at a flow rate of 30 L / h, a constant current of 3.78 A, and termination when the dilute chamber conductivity is below 30 mS / cm. The L-MCS-ED operating time is 120 min. Examples 5-10 mainly investigate the effects of the number of gradient chambers and the volume configuration of each chamber on acid recovery performance.

[0098] When a three-compartment L-MCS-ED electrodialysis is coupled after a first-stage MCS-ED, and the volume ratio of the dilute to the concentrated compartment is 1:1, the final acid concentration obtained from the recovered acid solution from the first-stage MCS-ED is approximately 0.843 mol / L, the sulfuric acid recovery rate is 67.62%, and the purity is 97.46%.

[0099] When a four-compartment L-MCS-ED electrodialysis is coupled after a primary MCS-ED, the acid concentration results can be significantly affected by further adjusting the volume configuration of the dilute, concentrated, and dual-gradient chambers. When the volume ratio of the concentrated chamber to the dilute chamber is 1:1, and the volume ratio of gradient chamber L1 to gradient chamber L2 is 1:1, the endpoint acid concentration is approximately 0.918 mol / L, the sulfuric acid recovery rate is 70.79%, and the purity is 97.98%. When the volume ratio of the concentrated chamber to the dilute chamber is 1:2, and the volume ratio of gradient chamber L1 to gradient chamber L2 is 1:1, the endpoint acid concentration is approximately 0.903 mol / L, the sulfuric acid recovery rate reaches 80.79%, and the purity is 98.68%. When the volume ratio of the concentrated chamber to the dilute chamber is 1:3, and the volume ratio of gradient chamber L1 to gradient chamber L2 is 1:1, the endpoint acid concentration is approximately 0.918 mol / L, the sulfuric acid recovery rate is 76.29%, and the purity is 97.18%. When the volume ratio of the concentrated chamber to the dilute chamber is 1:2, and the volume ratio of gradient chamber L1 to gradient chamber L2 is 1:2, the endpoint acid concentration decreases to 0.820 mol / L. The sulfuric acid recovery rate was 61.12% and the purity was 99.10% when the volume ratio of the concentrated chamber to the dilute chamber was 1:2 and the volume ratio of gradient chamber L1 to gradient chamber L2 was 2:1. The final acid concentration could reach 1.008 mol / L, the sulfuric acid recovery rate was 80.04%, and the purity was 99.17%.

[0100] Based on the results of the various embodiments, it can be seen that the multi-stage electrodialysis acid recovery process proposed in this invention can effectively achieve the selective migration, enrichment, and recovery of sulfuric acid in nickel-containing acidic wastewater. Compared with single-stage MCS-ED, multi-stage MCS-ED or the coupling process of MCS-ED and L-MCS-ED can further increase the sulfuric acid concentration in the recovered liquid; among them, the four-compartment L-MCS-ED coupling scheme shows better deep concentration capability. In the listed embodiments, Example 10 obtained the highest sulfuric acid concentration in the recovered liquid, which was 1.008 mol / L, while maintaining a sulfuric acid recovery rate of 80.04% and a sulfuric acid purity of 99.17%; Example 7 obtained the highest sulfuric acid recovery rate, which was 80.79%, corresponding to a sulfuric acid concentration of 0.903 mol / L and a purity of 98.68%. Example 3 showed better overall performance under two-stage MCS-ED conditions, with a sulfuric acid concentration of 0.875 mol / L in the recovered liquid, a sulfuric acid recovery rate of 74.30%, a purity of 99.32%, and relatively low energy consumption.

[0101] This invention addresses nickel-containing acidic wastewater by constructing a process system comprising primary MCS-ED pre-concentration, secondary MCS-ED further concentration, and deep concentration via a coupling of MCS-ED and L-MCS-ED electrodialysis. Experimental results demonstrate that this process effectively achieves selective recovery and enrichment of sulfuric acid in the wastewater. The four-compartment L-MCS-ED coupling process is particularly effective in increasing the final acid concentration, while the secondary MCS-ED process exhibits good overall separation performance with low energy consumption. This indicates that this invention has high practicality and promising industrial application prospects for acid resource recovery from nickel-containing acidic wastewater.

Claims

1. A multi-stage electrodialysis method for highly selective recovery and concentration of sulfuric acid from heavy metal waste acid, characterized in that, Includes the following steps: 1) The heavy metal waste acid solution is introduced into the primary MCS-ED system, where ion migration and pre-concentration are carried out under the action of a DC electric field to obtain the primary MCS-ED recovered acid solution. 2) To increase the final acid concentration and improve the recovery rate, the primary MCS-ED recovered acid solution is introduced into the gradient chamber of the L-MCS-ED electrodialysis system, while the heavy metal waste acid solution is introduced into the dilute chamber of the L-MCS-ED electrodialysis system, and the primary MCS-ED recovered acid solution or deionized water is introduced into the concentrated chamber of the L-MCS-ED electrodialysis system to obtain the recovered sulfuric acid product solution. 3) To reduce energy consumption, the acid solution recovered from the primary MCS-ED system is introduced into the dilute and concentrated chambers of the secondary MCS-ED system to obtain the recovered sulfuric acid product solution.

2. The multi-stage electrodialysis method for highly selective recovery and concentration of sulfuric acid from heavy metal waste acid as described in claim 1, characterized in that, The primary MCS-ED system includes cation exchange membranes, anion exchange membranes, electrodes, and separators. The cation exchange membranes and anion exchange membranes are alternately arranged to form at least 5 sets of repeating unit electrodialysis cells. The membranes are separated into a dilute chamber and a concentrated chamber by separators. Heavy metal waste acid solution is introduced into the dilute chamber, and deionized water is introduced into the concentrated chamber. The space between the electrodes and the ion exchange membranes is the electrode liquid chamber, which is circulated with sulfuric acid solution.

3. The multi-stage electrodialysis method for highly selective recovery and concentration of sulfuric acid from heavy metal waste acid as described in claim 2, characterized in that, The cation exchange membrane is a CIMS membrane, the operating current density of the first-stage MCS-ED system is 20 mA / cm², and the initial feed volume ratio of the dilute chamber to the concentrate chamber of the first-stage MCS-ED system is 1:

1.

4. The multi-stage electrodialysis method for highly selective recovery and concentration of sulfuric acid from heavy metal waste acid as described in claim 1, characterized in that, The secondary MCS-ED system includes cation exchange membranes, anion exchange membranes, electrodes, and separators. The cation exchange membranes and anion exchange membranes are alternately arranged to form at least 5 sets of repeating unit electrodialysis cells. The membranes are separated into two compartments, a dilute compartment and a concentrated compartment, by separators. The acid recovered from the primary MCS-ED is introduced into the dilute compartment and the concentrated compartment of the secondary MCS-ED system at a volume ratio of 1-3:

1. The space between the electrodes and the ion exchange membranes is the electrode liquid compartment, which is circulated with sulfuric acid solution.

5. The multi-stage electrodialysis method for highly selective recovery and concentration of sulfuric acid from heavy metal waste acid as described in claim 4, characterized in that, The runtime of the Level 2 MCS-ED system is 60-80 minutes.

6. The multi-stage electrodialysis method for highly selective recovery and concentration of sulfuric acid from heavy metal waste acid as described in claim 1, characterized in that, The L-MCS-ED electrodialysis system is a three-compartment electrodialysis system, including electrodes and at least 5 sets of repeating unit electrodialysis cells. Each set of unit electrodialysis cells includes a dilute chamber, a gradient chamber, and a concentrate chamber. The gradient chamber is composed of anion exchange membranes, while the concentrate and dilute chambers are composed of anion exchange membranes and cation exchange membranes, respectively. The space between the electrodes and the ion exchange membranes is the electrode liquid chamber, which is circulated with sulfuric acid solution. The initial feed volume ratio of the dilute chamber, concentrate chamber, and gradient chamber is 1:1:

1.

7. The multi-stage electrodialysis method for highly selective recovery and concentration of sulfuric acid from heavy metal waste acid as described in claim 1, characterized in that, The L-MCS-ED electrodialysis system is a four-compartment electrodialysis system, including electrodes and at least five sets of repeating unit electrodialysis cells. Each set of unit electrodialysis cells includes a dilute chamber, a first gradient chamber L1, a second gradient chamber L2, and a concentrate chamber. The first gradient chamber L1 and the second gradient chamber L2 are respectively composed of anion exchange membranes, and the concentrate chamber and the dilute chamber are respectively composed of anion exchange membranes and cation exchange membranes. The space between the electrodes and the ion exchange membranes is the electrode liquid chamber, which is circulated with sulfuric acid solution. The initial feed volume ratio of the dilute chamber, the first gradient chamber L1, the second gradient chamber L2, and the concentrate chamber is 1-2:1-3:1-2:1-2.

8. The multi-stage electrodialysis method for highly selective recovery and concentration of sulfuric acid from heavy metal waste acid as described in claim 1, characterized in that, The L-MCS-ED electrodialysis system has an operating time of 110-130 minutes.

9. The multi-stage electrodialysis method for highly selective recovery and concentration of sulfuric acid from heavy metal waste acid as described in claim 1, characterized in that, The final sulfuric acid concentration of the primary MCS-ED acid recovery solution is 0.50-0.60 mol / L. The sulfuric acid concentration of the recovered sulfuric acid product solution obtained after the secondary MCS-ED system is 0.74-0.88 mol / L. The sulfuric acid concentration of the recovered sulfuric acid product solution obtained after the L-MCS-ED electrodialysis system is 0.80-1.05 mol / L.

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