In-situ quality-divided resource recycling method and system for chemical polishing waste acid solution

Abstract

The invention relates to the technical field of waste liquid resourceful treatment, and discloses an in-situ quality-divided resourceful recycling method and system for chemical polishing waste acid liquid, the system adopts a nanofiltration and diffusion dialysis targeted coupling process, a nanofiltration unit firstly separates waste acid into low-aluminum first recycled acid and aluminum-rich nanofiltration concentrated liquid; when the diffusion dialysis unit treats the nanofiltration concentrated solution, the synergistic effect that high-concentration aluminum ions inhibit transmembrane migration is utilized, the one-way separation efficiency and the recovery rate of acid and aluminum are both larger than 90%, the system mixes and concentrates two streams of recovered acid through the acid evaporation concentration unit, clean condensate water is reused for diffusion dialysis, water balance and near-zero emission of the system are achieved, and the energy consumption of the system is reduced. The aluminum-rich residual liquid can be used for preparing industrial-grade aluminum sulfate through impurity removal and crystallization, aluminum phosphate is obtained under precipitation operation, intelligent integrated control of flow and load is combined, the fluctuation problem of multi-unit series connection is solved, and efficient waste acid recycling and optimal operation energy efficiency are achieved.

Description

Technical Field

[0001] This invention relates to the field of waste liquid resource utilization technology, and in particular to a method and system for in-situ fractional recycling of chemical waste acid. Background Technology

[0002] Surface treatments for aluminum alloys include: mechanical treatment (mechanical polishing, etc.); chemical treatment (chemical polishing, chemical conversion treatment, etc.); electrochemical treatment (electrochemical polishing, electroplating, anodizing, etc.); and physical treatment (electrostatic spraying, metal spraying, and other physical surface treatments). Among these, chemical polishing, as an advanced finishing method, can remove minor mold marks and scratches from the surface of aluminum products, as well as friction streaks, heat-deformation layers, and oxide films that may form during mechanical polishing. This smooths rough surfaces, achieving a near-mirror-like finish and enhancing the decorative effect and commercial value of aluminum products. Chemical polishing is an indispensable surface treatment technology in the preparation of highly finished and bright aluminum products.

[0003] Phosphate-based baths are widely used in the chemical polishing of aluminum alloys to achieve a mirror-like finish. However, the accumulation of aluminum ions (>25 g / L) during processing leads to bath inactivation, generating large amounts of highly acidic and corrosive hazardous waste (HW34), with an actual acid utilization rate of only 10%–15%. Existing treatment methods include neutralization, which consumes large amounts of reagents and produces difficult-to-treat sludge; diffusion dialysis, resin adsorption, and solvent extraction methods suffer from high investment costs, low treatment efficiency, low acid recovery concentrations, or regeneration difficulties, making it difficult to achieve economical and efficient comprehensive resource recovery and resulting in significant resource waste and environmental burden.

[0004] Aluminum products are continuously dissolved in the polishing solution. Eventually, the high aluminum ion concentration in the solution leads to a deterioration in polishing results, necessitating replacement and replenishment. This process generates a large amount of high-concentration aluminum-containing chemical polishing wastewater. Furthermore, aluminum alloy products are transferred from the chemical polishing tank to a washing tank, introducing a significant amount of the chemical polishing solution and resulting in substantial amounts of acidic and aluminum-containing rinsing wastewater. Industrially, the treatment of these chemical polishing wastewater and rinsing wastewater typically involves alkali neutralization and flocculation sedimentation. This method consumes large quantities of chemicals and generates substantial amounts of industrial sludge (hazardous waste), requiring external deep treatment of the sludge and significantly increasing operating costs. Additionally, the 85%–90% unused chemical polishing solution represents a huge waste of resources. Therefore, there is an urgent need for recyclable equipment to remove impurities from waste acid and recycle it, directly reducing pollutant emissions, lowering operating costs, and conserving non-renewable resources.

[0005] Therefore, existing technologies lack an in-situ resource recovery technology that can completely separate acid and aluminum and achieve high-quality reuse of both, thus realizing a closed-loop process and regeneration. Summary of the Invention

[0006] In view of the lack of a continuous, stable, efficient and near-zero emission in-situ resource recovery technology that can completely separate acid and aluminum and achieve high-quality reuse of both, this invention overcomes the bottleneck of the existing technology and provides a method and system for in-situ fractional resource recovery and reuse of chemical waste acid, ensuring the continuity, stability, efficiency and near-zero emission of the entire chemical waste acid resource recovery process.

[0007] In some aspects of the invention, an in-situ fractional recycling system for chemical waste acid is proposed, comprising the following functional modules: The pretreatment and preparation module removes solid suspended impurities from the chemical waste acid solution before conveying it to the membrane separation core module. The membrane separation core module includes a nanofiltration unit and a dialysis unit. The nanofiltration unit separates the chemical waste acid solution into a nanofiltration concentrate and a first recovered acid solution. The dialysis unit receives the nanofiltration concentrate from the nanofiltration unit and separates it into a second recovered acid solution and an output residue solution under the action of an anion exchange membrane. The output residual liquid is processed by the residual liquid treatment module to obtain aluminum salt solid.

[0008] In some specific embodiments of the in-situ fractionation and resource recovery system for chemical waste acid liquid described in the first aspect, the nanofiltration unit includes a nanofiltration membrane group composed of several parallel spiral wound nanofiltration membranes and / or tubular nanofiltration membranes, and a multi-stage centrifugal high-pressure pump. The multi-stage centrifugal high-pressure pump is configured to pump chemical waste acid liquid to the nanofiltration membrane group. The chemical waste acid liquid is separated by the acid-resistant nanofiltration membrane group to obtain nanofiltration concentrate and first recovered acid liquid. The nanofiltration unit is equipped with a level gauge, which is connected to the system integration and intelligent control module. The system integration and intelligent control module adjusts the frequency of the first pump of the dialysis unit according to the output of the nanofiltration concentrate. The chemical polishing waste acid solution has a phosphate concentration of 100 g / L to 300 g / L and an aluminum ion concentration of 1 g / L to 15 g / L. The nanofiltration concentrate has an aluminum ion concentration of 20 to 30 g / L.

[0009] This invention innovatively uses a nanofiltration concentrate with a specific composition as a diffusion dialysis feed, and the extremely high aluminum ion concentration unexpectedly inhibits Al 3+ Transmembrane migration, driven by concentration gradients, and H2 + The efficient permeation of acid radicals and ions enables high-purity separation of acid and aluminum, solving the bottleneck in the disposal of nanofiltration concentrate.

[0010] In some specific embodiments of the in-situ fractional recycling system for chemical waste acid liquid described in the first aspect, the dialysis unit includes a plate diffusion dialysis unit, a first pump and a second pump; The plate-type diffusion dialysis unit is composed of several anion exchange membranes and flow channel plates stacked alternately. It has a nanofiltration concentrate inlet and a condensate inlet. The first pump is configured to deliver nanofiltration concentrate to the nanofiltration concentrate inlet, and the second pump is configured to deliver condensate to the condensate inlet. H in nanofiltration concentrate + The acid radical ions move towards the condensate through the anion exchange membrane to obtain the output residue and the second recovered acid.

[0011] In some specific embodiments of the in-situ fractionation and resource recovery system for chemical waste acid liquid described in the first aspect, the pretreatment and blending module includes a homogenization tank. The homogenization tank is equipped with a level gauge. The level gauge signal is connected to the system integration and intelligent control module. The system integration and intelligent control module controls the pumping of chemical waste acid liquid in the homogenization tank to the nanofiltration unit according to the level signal of the homogenization tank, and controls the start and stop of the multi-stage centrifugal high-pressure pump.

[0012] In some specific embodiments of the in-situ fractionation and resource recovery system for chemical waste acid liquid described in the first aspect, an acid evaporation and concentration unit is also included; The second recovered acid and the first recovered acid are mixed in an acid evaporation and concentration unit, and then heated and evaporated to obtain condensate and concentrated acid; The condensate is pumped by a second pump, and the condensate produced by evaporation is recycled as the receiving liquid of the dialysis unit. The concentrated acid is conveyed to the chemical polishing tank; The concentrated acid outlet is equipped with a discharge valve and a density meter that are electrically connected to the system integration and intelligent control module. The system integration and intelligent control module adjusts the opening of the discharge valve and / or the evaporation intensity of the acid evaporation and concentration unit based on the feedback signal from the densitometer.

[0013] In some specific embodiments of the in-situ fractionation and resource recovery system for chemical waste acid liquid described in the first aspect, a filtration unit is further provided between the homogenization tank and the nanofiltration unit for filtering the chemical waste liquid transported from the homogenization tank to the nanofiltration unit. The filtration unit includes a bag filter and a precision cartridge filter connected in series. In some specific embodiments of the in-situ fractionation and resource recovery system for chemical waste acid liquid described in the first aspect, the residual liquid treatment module processes the received output residual liquid, adjusts the pH to 3.2~3.8, obtains aluminum phosphate precipitate, filters, and crystallizes the filtrate to obtain aluminum sulfate.

[0014] The second aspect of this invention proposes an in-situ fractional recycling method for chemical waste acid, comprising the following steps: S1: After pretreatment of the chemical polishing waste acid, the nanofiltration membrane separates the chemical polishing waste acid into nanofiltration concentrate and first recovered acid under pressure. S2: The nanofiltration concentrate is used as the feed liquid, and pure water or dilute acid is used as the receiving liquid. The solution is introduced into a diffusion dialysis device equipped with an anion exchange membrane for separation to obtain the second recovered acid and the output residue. S3: The second recovered acid and the first recovered acid solution are evaporated to obtain condensate and concentrated acid. The condensate is used as the receiving liquid in step S2, and the concentrated acid is introduced into the chemical polishing tank for reuse. S4: The output residual liquid is subjected to pH adjustment, precipitation, and crystallization treatment to obtain an aluminum-containing solid.

[0015] In some specific embodiments of the in-situ fractionation and resource recovery method for chemical waste acid liquid described in the second aspect, in step S1, the phosphate concentration of the chemical waste acid liquid is 100g / L to 300g / L, the aluminum ion concentration is 1g / L to 15g / L, and the aluminum ion concentration of the nanofiltration concentrate is 20g / L to 30g / L. In some specific embodiments of the in-situ fractionation and resource recovery method for chemical polishing waste acid liquid described in the second aspect, in step S1, the pretreatment of chemical polishing waste acid liquid involves removing suspended impurities from the waste acid liquid by passing the waste acid liquid through a 0.5~2.0μm precision filter to remove solid suspended matter.

[0016] In some specific embodiments of the in-situ fractionation and resource recovery method for chemical waste acid liquid described in the second aspect, the driving pressure value in step S1 is 3.0~5.0MPa.

[0017] In some specific embodiments of the in-situ fractionation and resource recovery method for chemical waste acid liquid described in the second aspect, in step S1, the volume ratio of the first recovered acid liquid to the nanofiltration concentrate is (3~5):1.

[0018] In some specific embodiments of the in-situ fractionation and resource recovery method for chemical waste acid liquid described in the second aspect, the volume ratio of the output residual liquid in step S2 to the chemical waste acid liquid in step S1 is 1:(4~6).

[0019] In some specific embodiments of the in-situ fractionation and resource recovery method for chemical waste acid liquid described in the second aspect, the nanofiltration membrane in step S1 is selected from any one of polysulfonamide, triazine ring, sulfonated polymer, or polyelectrolyte.

[0020] In some specific embodiments of the in-situ fractionation and resource recovery method for chemical waste acid liquid described in the second aspect, the molecular weight cutoff of the nanofiltration membrane in step S1 is 200 Da to 400 Da.

[0021] In some specific embodiments of the in-situ fractionation and resource recovery method for chemical waste acid liquid described in the second aspect, the nanofiltration membrane in step S1 has a pressure resistance of ≤60 bar.

[0022] In some specific embodiments of the in-situ fractionation and resource recovery method for chemical waste acid liquid described in the second aspect, the nanofiltration membrane in step S1 has a membrane area of ​​20-30 m². 2 Membrane flux is 6~10 LMH.

[0023] In some specific embodiments of the in-situ fractionation and resource recovery method for chemical waste acid liquid described in the second aspect, the nanofiltration membrane rejection rate in step S1 is ≥80%.

[0024] In some specific embodiments of the in-situ fractionation and resource recovery method for chemical waste acid liquid described in the second aspect, in step S2, the anion exchange membrane is selected from polyphenylene ether and / or polysulfone.

[0025] In some specific embodiments of the in-situ fractionation and resource recovery method for chemical waste acid liquid described in the second aspect, in step S2, the flow rate ratio of the feed liquid to the receiving liquid is 1:1 to 1:2.

[0026] In some specific embodiments of the in-situ fractional recycling method for chemical waste acid liquid described in the second aspect, in step S3, the evaporation process is carried out under a vacuum of 0.08~0.095MPa, and the evaporation temperature is controlled at 60~80℃.

[0027] In some specific embodiments of the in-situ fractionation and resource recovery method for chemical waste acid liquid described in the second aspect, the pH adjustment and crystallization treatment of the output residual liquid in step S4 specifically involves using aluminum hydroxide slurry to adjust the pH of the output residual liquid to 3.2~3.8, and the metal ion precipitation in the output residual liquid. Preferably, the metal ion precipitation is aluminum phosphate precipitation, and more preferably, the metal precipitation also includes iron ion precipitation.

[0028] Advantages of the present invention The first aspect of this invention achieves targeted coupling of nanofiltration and diffusion dialysis, significantly improving the separation efficiency. This invention utilizes a nanofiltration unit for "coarse separation" with a high aluminum ion rejection rate, converting waste acid from chemical polishing into a low-aluminum first-stage recovered acid and an aluminum-rich nanofiltration concentrate. Subsequently, a diffusion dialysis unit performs secondary separation on the nanofiltration concentrate, leveraging the effect of high-concentration metal ions inhibiting transmembrane migration; that is, the extremely high aluminum ion concentration unexpectedly inhibits Al during diffusion dialysis. 3+ Passing through the anion exchange membrane, the concentration gradient drives H+. + Highly efficient permeability. This synergistic effect has enabled a qualitative leap in both the single-pass separation efficiency and total recovery rate of acid and aluminum (both greater than 90%), effectively solving the technical bottlenecks of low acid recovery rate of nanofiltration alone and large throughput of diffusion dialysis alone.

[0029] The second aspect of this invention constructs a multi-dimensional material closed-loop system, achieving near-zero emissions and resource maximization. By mixing and concentrating the first recovered acid from the nanofiltration process and the second recovered acid from the diffusion dialysis process through an acid evaporation and concentration unit, it not only ensures that the concentration of the reused acid meets the requirements of the chemical polishing process and avoids the risk of phosphoric acid polymerization, but also directly reuses the clean condensate generated by evaporation as the receiving liquid in the diffusion dialysis unit, realizing water balance and closed-loop circulation within the system. There is no waste liquid discharge at the end of the entire process, truly achieving the environmentally friendly near-zero emission goal.

[0030] Thirdly, through system integration and intelligent control modules, flow and load matching between units is achieved. For example, by using the feedback of nanofiltration concentrate and evaporator output to adjust the pump frequency of diffusion dialysis, the problem of flow fluctuation in multi-unit series systems is solved, resulting in excellent operational stability and cost-effectiveness. Attached Figure Description

[0031] Figure 1 Flowchart of the waste acid recycling system; Figure 2 Diagram of a waste acid recycling system; Figure 3 This invention provides a flow path diagram for plate-and-frame diffusion dialysis. 1. Homogenizing tank 1; 2. Feed pump; 3. Bag filter; 4. Precision filter; 5. Nanofiltration feed pump; 6. Nanofiltration unit; 7. Nanofiltration concentrate tank; 8. Diffusion dialysis feed pump; 9. Plate diffusion dialysis unit; 10. Diffusion dialysis residual liquid tank; 11. Acid mixing first recovery tank; 12. Acid evaporation feed pump; 13. Acid evaporation and concentration unit; 14. Acid recovery tank B; 15. Condensate storage tank; 16. Second pump; 17. Residual liquid feed pump; 18. Aluminum precipitation reaction tank; 19. Plate and frame feed pump; 20. Plate and frame filter press; 21. Sulfate solution tank. Detailed Implementation

[0032] The following examples further illustrate the above-described content of the present invention, but it should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention.

[0033] This invention proposes an in-situ fractionation and resource recovery system for chemical waste acid, comprising the following functional modules: The pretreatment and preparation module removes solid suspended impurities from the chemical waste acid solution before conveying it to the membrane separation core module. The membrane separation core module includes a nanofiltration unit 6 and a dialysis unit. The nanofiltration unit 6 separates the chemical waste acid solution into a nanofiltration concentrate and a first recovered acid solution. The dialysis unit receives the nanofiltration concentrate from the nanofiltration unit 6 and separates it into a second recovered acid solution and an output residue. The output residual liquid is processed by the residual liquid treatment module to obtain aluminum salt solid.

[0034] like Figure 2 As shown, in some specific embodiments of the in-situ separation and resource recovery system for chemical waste acid, the nanofiltration unit 6 includes a nanofiltration concentrate tank 7, a nanofiltration membrane group composed of parallel spiral wound nanofiltration membranes and / or tubular nanofiltration membranes, and a multi-stage centrifugal high-pressure pump. The multi-stage centrifugal high-pressure pump is configured to pump chemical waste acid to the nanofiltration membrane group at a pumping pressure of 3.0~5.0MPa to drive the chemical waste acid to be separated through the acid-resistant nanofiltration membrane group to obtain nanofiltration concentrate and first recovered acid. The nanofiltration concentrate is stored in the nanofiltration concentrate tank 7, and the volume ratio of the first recovered acid to the nanofiltration concentrate is (3~5):1, preferably 4:1. Preferably, the nanofiltration membrane material is selected from any one of polysulfonamides, triazine rings, sulfonated polymers, and polyelectrolytes; In some embodiments, the multi-stage centrifugal high-pressure pump is equipped with a pressure regulating valve and a pressure sensor to precisely control the nanofiltration operating pressure.

[0035] In some embodiments, the nanofiltration membrane in step S1 has a molecular weight cutoff of 200–400 Da, a pressure resistance of ≤60 bar, and a membrane area of ​​20–30 m². 2 Membrane flux 6~10 LMH, nanofiltration membrane rejection ≥80%.

[0036] The nanofiltration concentrate tank 7 is equipped with a level gauge, which is connected to the system integration and intelligent control module. The system integration and intelligent control module adjusts the frequency of the first pump 8 of the plate diffusion dialyzer 9 according to the output of the nanofiltration concentrate. The phosphate concentration of the waste acid solution is 100-300 g / L, the aluminum ion concentration is 1.0-15 g / L, and the aluminum ion concentration of the concentrate is 25 g / L-30 g / L. In some specific embodiments of the in-situ fractionation and resource recovery system for chemical waste acid, the dialysis unit includes a plate diffusion dialysis unit 9, a first pump 8 and a second pump 16. The plate-type diffusion dialysis unit 9 is composed of several anion exchange membranes and flow channel plates stacked alternately. It has a nanofiltration concentrate inlet and a condensate inlet. The first pump 8 is configured to deliver nanofiltration concentrate to the nanofiltration concentrate inlet, which serves as the feed liquid. The second pump 16 is configured to deliver condensate to the condensate inlet, which serves as the receiving liquid.

[0037] H in nanofiltration concentrate +The acid radical ions move towards the condensate through the anion exchange membrane to obtain the output residue and the second recovered acid. After the output residue enters the diffusion dialysis residue tank 10 for collection, it is transported by the residue feed pump 17 to the aluminum precipitation reaction tank 18 for aluminum ion precipitation and crystallization in the residue treatment module.

[0038] In some embodiments, the flow rate ratio of the feed liquid to the receiving liquid is 1:1 to 1:2, and the feed liquid and the receiving liquid flow through adjacent flow channel plates respectively. In some preferred embodiments, the feed liquid and the receiving liquid flowing through adjacent flow channel plates flow in opposite directions, and the anion exchange membrane is selected from polyphenylene ether and / or polysulfone.

[0039] This invention innovatively uses a nanofiltration concentrate with a specific composition as a diffusion dialysis feed, and the aluminum ion concentration of approximately 24 g / L unexpectedly inhibits Al 3+ Transmembrane migration, driven by concentration gradients, and H2 + The efficient permeation of acid radicals enables high-purity separation of acid and aluminum, solving the bottleneck in the disposal of nanofiltration concentrate. However, for the use of exchange membrane technology alone, the process of this invention can handle aluminum ions at concentrations of 5 g / L or even lower.

[0040] The residual liquid treatment module includes an aluminum precipitation reaction tank 18. The pH of the aluminum precipitation reaction tank 18 is adjusted to 3.2~3.8 by aluminum hydroxide slurry. A precipitate mainly composed of aluminum phosphate is generated in the output residual liquid. The precipitate is transported to a plate and frame filter press 20 by a plate and frame feed pump 19 for filtration to obtain aluminum phosphate product. The filtrate is collected in a sulfate solution tank 21 and crystallized to obtain aluminum sulfate.

[0041] In some specific embodiments of the in-situ fractionation and resource recovery system for chemical waste acid, the pretreatment and blending module includes a homogenization tank 1. The homogenization tank 1 is equipped with a level gauge. The level gauge signal is connected to the system integration and intelligent control module. The system integration and intelligent control module controls the nanofiltration feed pump 5 to pump the chemical waste acid to the nanofiltration unit 6 according to the level signal of the homogenization tank 1, and controls the start and stop of the multi-stage centrifugal high-pressure pump.

[0042] In some specific embodiments of the in-situ fractionation and resource recovery system for chemical waste acid, an acid evaporation and concentration unit 13 is also included. The second recovered acid and the first recovered acid are mixed in the acid mixing first recovery tank 11, and then pumped to the acid evaporation and concentration unit 13 by the acid evaporation feed pump 12. After heating and evaporation, and condensation, condensate and concentrated acid are obtained. The evaporation process is carried out under a vacuum of 0.08~0.095MPa and the evaporation temperature is controlled at 60~80℃. The condensate is pumped by the second pump 16, and the condensate produced by evaporation is recycled as the receiving liquid for diffusion dialysis. Preferably, the condensate generated by the acid evaporation system is input into the condensate storage tank 15. The condensate storage tank 15 is equipped with a level gauge. The level of the condensate storage tank 15 is interlocked with the receiving liquid replenishment valve of the second pump 16 and the plate diffusion dialyzer 9. According to the level, an opening signal is sent to the receiving liquid replenishment valve to pump condensate into the plate diffusion dialyzer 9 as the receiving liquid, thereby realizing the self-balancing of water resources in the system and zero external discharge.

[0043] Preferably, the acid evaporation and concentration unit 13 adopts a falling film evaporator or a mechanical vapor recompression evaporator. The acid evaporation and concentration unit 13 is equipped with an online density meter for real-time monitoring of the concentration of concentrated acid and interlocking control of the discharge valve. The concentrated acid is collected and homogenized in the second acid recovery tank 14. Under the control of the discharge valve, the concentrated acid is transported to the chemical slurry tank. The discharge valve and online density meter are both integrated with the system and electrically connected to the intelligent control module; The system integration and intelligent control module is configured to adjust the opening of the discharge valve and / or adjust the evaporation intensity of the acid evaporation and concentration unit 13 according to the feedback signal of the online density meter; optionally, the acid evaporation and concentration unit 13 adopts a falling film evaporator or a mechanical vapor recompression evaporator. The in-situ fractionation and resource recovery system for chemical waste acid liquid includes a pretreatment and blending module that further comprises a filtration unit. This filtration unit is located between the homogenization tank and the nanofiltration unit 6 and is used to filter the chemical waste liquid transported from the homogenization tank to the nanofiltration unit 6. The filtration unit includes bag filters 3 and / or precision cartridge filters 4 connected in series. Preferably, the bag filter and / or precision cartridge filter are equipped with differential pressure sensors at the inlet and outlet to provide early warning of cartridge blockage.

[0044] The pretreatment of chemical polishing waste acid is as follows: after removing suspended impurities from the chemical polishing waste acid in the homogenization tank 1, the feed pump 2 provides pressure, and the chemical polishing waste acid is filtered through a bag filter and / or a precision cartridge filter with a specification of 0.5~2.0μm to remove suspended solids.

[0045] The system integration and intelligent control module can optionally be a PLC+SCADA unit, which provides centralized control and status monitoring for all system equipment.

[0046] A second aspect of this invention also proposes an in-situ fractional recycling method for chemical waste acid, comprising the following steps: S1: After pretreatment of the chemical polishing waste acid, the nanofiltration membrane separates the chemical polishing waste acid into nanofiltration concentrate and first recovered acid under pressure. S2: The nanofiltration concentrate is used as the feed liquid, and pure water or dilute acid is used as the receiving liquid. The solution is introduced into a diffusion dialysis device equipped with an anion exchange membrane for separation to obtain the second recovered acid and the output residue. S3: The second recovered acid and the first recovered acid solution are evaporated to obtain condensate and concentrated acid. The condensate is used as the receiving liquid in step S2, and the concentrated acid is introduced into the chemical polishing tank for reuse. S4: The output residual liquid is subjected to pH adjustment, precipitation, and crystallization treatment to obtain an aluminum-containing solid.

[0047] In some specific embodiments of the in-situ fractionation and resource recovery method for chemical waste acid liquid described in the second aspect, in step S1, the phosphate concentration of the chemical waste acid liquid is 100-300 g / L, the aluminum ion concentration is 1.0-15 g / L, and the aluminum ion concentration of the nanofiltration concentrate is 20-30 g / L. A waste acid solution from an aluminum processing plant, containing sulfuric acid and phosphoric acid, has the following composition:

[0048] Pretreatment: The chemical waste acid solution containing phosphoric acid, sulfuric acid and aluminum ions is first passed through a 1μm precision filter to remove suspended solids.

[0049] Nanofiltration separation: The pretreated waste acid solution is passed through an acid-resistant nanofiltration membrane system at a pressure of 3.8~4.2 MPa. The result is: Nanofiltration permeate (first recovered acid): accounts for approximately 78-82% of the total flow rate, with aluminum ions <0.35 g / L; Nanofiltration concentrate: accounts for approximately 18-22% of the total flow rate, with aluminum ions approximately 24 g / L.

[0050]

[0051] Diffusion dialysis purification: The above nanofiltration concentrate is pumped into the feed chamber of the diffusion dialysis unit (equipped with anion exchange membrane) at a certain flow rate (0.15 LMH) as the feed liquid, and condensate is pumped into the receiving liquid chamber as the receiving liquid. The unit is operated at room temperature to obtain the output residue and the second recovered acid.

[0052] The first recovered acid from nanofiltration percolate is mixed with the second recovered acid from diffusion dialysis to obtain a mixed acid solution with a specific gravity of 1.1 (approximately 18% phosphoric acid and 4% sulfuric acid). This solution is pumped into an evaporator and concentrated to a specific gravity of 1.7 at -0.09 MPa and 75°C. The evaporated condensate is reused as the diffusion dialysis receiving solution. After removing iron ions and most of the aluminum ions, the mixed acid solution is reused in the chemical polishing production line, and the product gloss meets the standards.

[0053] The output residue is subjected to pH adjustment and crystallization treatment. Specifically, aluminum hydroxide slurry is used to adjust the pH of the output residue to 3.2~3.8, and the metal ions in the output residue precipitate to obtain aluminum phosphate solid. The metal precipitation also includes iron ion precipitation.

[0054] After removing the precipitate, the liquid is crystallized to obtain high-purity aluminum sulfate crystals.

[0055] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A system for in-situ resource utilization of spent acid liquid by quality separation, characterized in that, The application relates to a phosphoric acid recovery system. The system comprises the following functional modules: A pretreatment and adjustment module which removes solid suspended impurities in the chemical polishing waste acid solution and then delivers the solution to a membrane separation core module; The membrane separation core module comprises a nanofiltration unit and a dialysis unit, the nanofiltration unit separates the chemical polishing waste acid solution into nanofiltration concentrated solution and first recovered acid solution, and the dialysis unit receives the nanofiltration concentrated solution from the nanofiltration unit and separates the solution into second recovered acid and output residual liquid under the action of an anion exchange membrane; 2. The system for in-situ resource utilization of spent acid liquid according to claim 1, characterized in that, The output residual liquid is treated by a residual liquid treatment module to obtain an aluminum salt. The nanofiltration unit comprises a nanofiltration membrane group composed of a plurality of parallel combined rolling nanofiltration membranes and / or tubular nanofiltration membranes, and a multistage centrifugal high-pressure pump configured to pump the chemical polishing waste acid solution to the nanofiltration membrane group, the chemical polishing waste acid solution is separated by the acid-resistant nanofiltration membrane group to obtain nanofiltration concentrated solution and first recovered acid solution; The nanofiltration unit is provided with a liquid level meter connected with a system integration and intelligent control module signal, the system integration and intelligent control module adjusts the first pump frequency of the dialysis unit according to the yield of the nanofiltration concentrated solution; 3. The system for in-situ resource utilization of spent acid liquid according to claim 1, characterized in that, The chemical polishing waste acid solution has a phosphate concentration of 100g / L-300g / L and an aluminum ion concentration of 1g / L-15g / L, and the nanofiltration concentrated solution has an aluminum ion concentration of 20-30g / L. The dialysis unit comprises a plate-type diffusion dialyzer, a first pump and a second pump; H + and the acid ions move through the anion exchange membrane to the condensed water to obtain an output raffinate and a second recovered acid.

4. The system for in-situ resource utilization of spent pickling acid according to any one of claims 1 to 3, characterized in that, The plate-type diffusion dialyzer is composed of a plurality of anion exchange membranes and flow channel plates which are alternately stacked, and has a nanofiltration concentrated solution inlet and a condensate water inlet, the first pump is configured to deliver the nanofiltration concentrated solution to the nanofiltration concentrated solution inlet, and the second pump is configured to deliver condensate water to the condensate water inlet; 5. The system for in-situ resource utilization of spent acid liquid according to claim 2, characterized in that, The pretreatment and adjustment module comprises a homogenizing tank provided with a liquid level meter, the liquid level meter signal is connected to a system integration and intelligent control module, the system integration and intelligent control module controls the pumping of the chemical polishing waste acid solution in the homogenizing tank to the nanofiltration unit and controls the start and stop of the multistage centrifugal high-pressure pump according to the liquid level signal of the homogenizing tank. An acid evaporation and concentration unit is further included; The second recovered acid and the first recovered acid are mixed in the acid evaporation and concentration unit, heated and evaporated to obtain condensate water and concentrated acid; The condensate water is delivered by the second pump, and the condensate water generated by evaporation is recycled as the receiving liquid of the dialysis unit; The concentrated acid is delivered to a chemical polishing tank; The concentrated acid outlet is provided with a discharge valve and a densimeter which are electrically connected with the system integration and intelligent control module; 6. The system for in-situ resource utilization of spent pickling acid according to any one of claims 1 to 5, characterized in that, The system integration and intelligent control module adjusts the opening degree of the discharge valve and / or the evaporation intensity of the acid evaporation and concentration unit according to the feedback signal of the densimeter.

7. The system for in-situ resource utilization of spent pickling acid according to any one of claims 1 to 6, characterized in that, A filter unit is further arranged between the homogenizing tank and the nanofiltration unit, and is used for filtering the chemical polishing liquid delivered from the homogenizing tank to the nanofiltration unit, the filter unit comprises a bag filter and a precision core filter connected in series.

8. An in-situ multi-quality resource recycling method of chemical polishing waste acid solution, characterized in that, The residual liquid treatment module receives the output residual liquid, adjusts the pH to 3.2-3.8, obtains aluminum phosphate precipitate, filters the precipitate, crystallizes the filtrate, and obtains aluminum sulfate. The application further discloses a phosphoric acid recovery method comprising the following steps: S1: after the chemical polishing waste acid solution is pretreated, the nanofiltration membrane separates the chemical polishing waste acid solution into nanofiltration concentrated solution and first recovered acid solution under pressure driving; S2: introducing the nanofiltration concentrated liquid as a feed liquid and pure water or dilute acid as an accept liquid into a diffusion dialysis device equipped with an anion exchange membrane to separate and obtain second recovered acid and output residual liquid; S3: evaporating the second recovered acid and the first recovered acid liquid to obtain condensed water and concentrated acid, wherein the condensed water is used as the accept liquid in S2, and the concentrated acid is introduced into a chemical polishing tank for reuse; S4: adjusting the pH of the output residual liquid, precipitating, and crystallizing to obtain an aluminum-containing solid.

9. The method according to claim 8, wherein the spent acid solution is in-situ resource utilization by fractionation. In S1, the phosphorus concentration of the chemical polishing waste acid liquid is 100-300 g / L, the aluminum ion concentration is 1-15 g / L, and the aluminum ion concentration of the nanofiltration concentrated liquid is 20-30 g / L; And / or, in the S1 step, the pretreatment of the spent pickling acid is removing suspended impurities from the spent pickling acid, and the spent pickling acid is filtered through a 0.5-2.0 μm precision filter to remove solid suspended matter; and / or, in the S1 step, the driving pressure value is 3.0-5.0 MPa; and / or, in the S1 step, the volume ratio of the first recovered acid to the nanofiltration concentrated liquid is (3-5):1; and / or, in the S2 step, the volume ratio of the output residual liquid to the spent pickling acid in the S1 step is 1:(4-6); and / or, in the S1 step, the nanofiltration membrane is selected from any one of polysulfonamide, triazine ring, sulfonated polymer, and polyelectrolyte; and / or, in the S1 step, the nanofiltration membrane has a molecular weight cut-off of 200-400 Da; and / or, in the S1 step, the nanofiltration membrane has a pressure resistance of ≤60 bar; and / or, in the S1 step, the nanofiltration membrane has a membrane area of 20-30 m 2 ; a membrane flux of 6-10 LMH; and / or, in the S1 step, the nanofiltration membrane has a rejection rate of ≥80%.

10. The method according to any one of claims 8 or 9, characterized in that, In S2, the anion exchange membrane is selected from polyphenylene ether and / or polysulfone; and / or, in S2, the flow rate ratio of the feed liquid to the accept liquid is 1:1 to 1:2; and / or, in S3, the evaporation process is carried out under a vacuum degree of 0.08-0.095 MPa, and the evaporation temperature is controlled at 60-80°C; and / or, in S4, the output residual liquid is adjusted in pH and crystallized, specifically, the pH of the output residual liquid is adjusted to 3.2-3.8 using aluminum hydroxide slurry, the metal ions in the output residual liquid are precipitated, preferably, the metal ion precipitation is aluminum phosphate precipitation, and further preferably, the metal precipitation also includes iron ion precipitation.

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