Method and device for improving diffusion dialysis recovery aluminum part chemical polishing waste acid

Abstract

The invention relates to a method and a device for improving diffusion dialysis recovery of aluminum part chemical polishing waste acid. The method comprises the following steps: pretreating waste acid to obtain filtrate; evaporating the filtrate, discharging the evaporated concentrated liquor into a second or third transfer barrel, and controlling the temperature of the concentrated liquor; adjusting the concentrated liquor to an operation temperature, and pumping the concentrated liquor into a separation chamber from an acid inlet; heating pure water to the temperature consistent with the temperature of the concentrated liquid, conveying the pure water to the separation chamber from the water inlet at the same flow speed, enabling the concentrated liquid and the pure water to pass through a diffusion dialysis membrane of the separation chamber in a countercurrent form, enabling phosphoric acid in the concentrated liquid to penetrate through the diffusion dialysis membrane, be absorbed by the pure water and flow out from the top to obtain membrane produced acid, and enabling residual liquid as membrane produced waste to flow out from the bottom; carrying out vapor concentration on the membrane production waste, carrying out heating diffusion dialysis membrane separation again, and repeating the step 3 to obtain secondary membrane production waste; performing evaporation concentration on the secondary membrane production waste to obtain a tertiary production waste concentrated solution; cooling, crystallizing and separating the third-time produced waste concentrated liquid to obtain mother liquor and crystal salt, and returning the mother liquor to perform heating diffusion dialysis membrane separation again.

Description

Technical Field

[0001] The present invention relates to the technical field of waste acid recovery, and in particular to a method and a device for improving diffusion dialysis recovery of waste acid from aluminum castings. Background Art

[0002] Currently, phosphoric acid recovery rates are around 50%, lower than the 80-90% recovery rates of sulfuric acid, hydrochloric acid, and nitric acid, but aluminum retention rates exceed 90%. Acid retardation, a method for recovering chemically discarded acid, achieves phosphoric acid recovery rates of around 60-80%, aluminum retention rates of only 50-70%, and a low acid production rate, resulting in high evaporation energy consumption. Resin-based aluminum absorption technology can achieve phosphorus recovery rates of around 90% and aluminum removal rates of around 90%, but produces an even lower acid production rate than acid retardation, consumes more evaporation energy, and consumes significant amounts of sulfuric acid for resin elution.

[0003] Compared with the above two technologies, diffusion dialysis membrane separation technology has the advantages of low energy consumption and operating costs, safety and environmental protection, high aluminum retention rate, high acid production rate, and simple operation. It has been successfully applied to the separation and recovery of waste acids such as sulfuric acid, hydrochloric acid, and nitric acid. The only drawback is the low acid recovery rate, and the higher the aluminum ion concentration, the lower the acid recovery rate. The driving force of diffusion dialysis membrane separation is the concentration difference. High concentration is conducive to the permeation of phosphoric acid through the membrane, but the higher the phosphoric acid concentration, the greater the viscosity, which is not conducive to diffusion, and the higher the aluminum ion concentration, the more unfavorable it is for separation. The purification and separation of phosphoric acid is limited by the low phosphoric acid recovery rate caused by the low permeability coefficient on traditional ion exchange membranes. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention provides a method and device for improving the recovery of waste acid from aluminum casting by diffusion dialysis, aiming to solve the problem of low phosphoric acid recovery rate in the existing diffusion dialysis membrane separation technology.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention discloses a method for improving the recovery of waste acid from aluminum castings by diffusion dialysis, comprising the following steps:

[0007] Step 1 is pretreatment: the waste acid passes through the waste acid collection tank, the first bag filter, the aeration mixing tank, the second bag filter, the first transfer tank, the automatic fine filter, and the filtrate tank in sequence to remove organic matter and suspended matter;

[0008] Step 2 is evaporation and concentration: the pretreated filtrate is passed from the filtrate barrel into a low-temperature evaporator for evaporation, and the evaporated concentrate is discharged into the second transfer barrel or the third transfer barrel, and the concentrate temperature is controlled;

[0009] Step 3 is the separation of the heated diffusion dialysis membrane: the concentrated solution in the second or third intermediate tank is adjusted to the operating temperature, and the concentrated solution is pumped into the separation chamber from the bottom inlet;

[0010] Meanwhile, the pure water in the pure water tank is heated to the same temperature as the concentrated solution in the second or third intermediate tank, and is transported to the separation chamber from the top water inlet at the same flow rate, so that the concentrated solution and the pure water pass through the diffusion dialysis membrane of the separation chamber in countercurrent form, and the phosphoric acid in the concentrated solution is absorbed by the pure water on the other side after passing through the diffusion dialysis membrane, and flows out from the top, obtaining the membrane product acid and the residual solution, which flows out from the bottom;

[0011] Step 4 is the secondary evaporation and concentration of the membrane waste: the membrane waste is pumped into the low-temperature evaporator for evaporation and concentration;

[0012] Step 5 is the secondary membrane separation: the evaporated and concentrated membrane waste is separated again by the heated diffusion dialysis membrane, and step 3 is repeated to obtain the secondary membrane waste;

[0013] Step 6 is the third evaporation and concentration of the membrane waste: the secondary membrane waste obtained in step 5 is pumped into the low-temperature evaporator for evaporation and concentration, obtaining the third waste concentrated solution;

[0014] Step 7 is cooling and crystallization: the third waste concentrated solution in step 6 is pumped into the crystallization device, and after cooling and crystallization separation, the mother liquor and the crystalline salt are obtained, and the mother liquor is returned to the third intermediate tank for heating and diffusion dialysis membrane separation again.

[0015] Further, in step 2, the temperature of the concentrated solution is controlled to be <40℃, the specific gravity of the evaporated concentrated solution is 1.40-1.50g / mL, and the filtrate is discharged into the second intermediate tank for the first evaporation and concentration.

[0016] Further, in step 3, the operating temperature is 30-40℃, and the treatment capacity of the diffusion dialysis membrane is 0.2-1L / (h·m2).

[0017] Further, in steps 4 and 6, the evaporation temperature is <40℃, and the specific gravity of the evaporated concentrated solution is 1.40-1.50g / mL; the evaporated concentrated solution in step 4 is discharged into the third intermediate tank; and the evaporated concentrated solution in step 6 is directly discharged into the cooling and crystallization device.

[0018] Further, in step 7, the cooling and crystallization temperature is 5-10℃, and the cooling time is 8-12 hours.

[0019] In a second aspect, the application discloses a device for improving the recovery of aluminum part polishing waste acid by diffusion dialysis, comprising: a pretreatment device, a low-temperature evaporation and concentration device, a heated diffusion dialysis device, and a crystallization device.

[0020] The pretreatment device is connected with the low-temperature evaporation and concentration device, and the low-temperature evaporation and concentration device is connected with the heated diffusion dialysis device and the crystallization device.

[0021] Furthermore, the low-temperature evaporation and concentration device includes: a low-temperature evaporator, a first transfer barrel, a second transfer barrel, a third transfer barrel, a fourth transfer barrel and a fifth transfer barrel; the fourth transfer barrel and the fifth transfer barrel are both connected to the feed port of the low-temperature evaporator; the second transfer barrel and the third transfer barrel are both connected to the discharge port of the low-temperature evaporator, and the connecting pipes are provided with insulation jackets; the second transfer barrel and the third transfer barrel are externally equipped with insulation devices, and internally equipped with heating devices, temperature controllers and stirring devices.

[0022] Furthermore, the heated diffusion dialysis device includes: a diffusion dialysis device, an acid production barrel, a pure water barrel, an alkali washing barrel, and a water washing barrel connected; the second transfer barrel and the third transfer barrel are both connected to the acid inlet of the diffusion dialysis device, and the pure water barrel is connected to the water inlet of the heated diffusion dialysis device; the alkali washing barrel and the water washing barrel are simultaneously connected to the acid production port and the waste outlet of the heated diffusion dialysis device; the pure water barrel is externally provided with an insulation device, and internally provided with a heating device and a temperature controller; the feed inlet and the water inlet of the diffusion dialysis device are simultaneously connected to the drain pipe discharged into the wastewater station; the second transfer barrel, the third transfer barrel, the pure water barrel and the diffusion dialysis device connecting pipes are all provided with insulation devices; and the diffusion dialysis device is externally provided with an insulation cover.

[0023] Furthermore, the crystallization device includes: a crystallization tank, which is equipped with a condenser, an agitator, a crystal discharge port, a solution overflow port, and a feed port; the crystallization tank has a conical bottom shape; the condenser is vertical and is 60-90° to the tank wall of the crystallization tank, and the inlet and outlet of the condenser are respectively connected to the freezing device; the distance between the solution overflow port and the bottom of the crystallization tank is 1 / 5-1 / 2 of the height of the crystallization tank, and the overflow port is connected to the fourth transfer barrel; the feed port is connected to the discharge port of the low-temperature evaporator.

[0024] Furthermore, the pretreatment device includes: a waste acid collection barrel, a first bag filter, an aeration and stirring barrel, a second bag filter, a first transfer barrel, an automatic fine filter, and a filtrate barrel; the filtration precisions of the first bag filter and the second bag filter are 10-40 μm and 200-301 μm, respectively; the aeration and stirring barrel is provided with an aeration pipe and a liquid level gauge, a liquid inlet and a solid inlet are provided on the top, and a discharge port is provided on the bottom; the filtration precision of the automatic fine filter is 100-500 nm, and it is composed of four groups of membrane components, and the filtrate outlet is connected to the filtrate barrel; the filtrate barrel is connected to the feed port of the low-temperature evaporator.

[0025] The present invention discloses a method and device for improving the recovery of waste acid from aluminum castings by diffusion dialysis, which has the following beneficial effects:

[0026] In the pretreatment stage, multi-stage filtration is used to remove organic matter and suspended solids, preventing impurities from clogging subsequent membrane components or evaporators, ensuring long-term stable operation of the system. Low-temperature evaporation increases the concentration of waste acid from aluminum castings, while increasing the temperature to reduce the viscosity of high-density acid, significantly improving the recovery rate of phosphoric acid while reducing the processing load of a single membrane separation. With the cyclic design of multi-stage distillation and concentration (steps 2, 4, and 6) and membrane separation (steps 3 and 5), membrane waste is separated at multiple levels. The lower the phosphoric acid concentration in the membrane waste, the lower the P / Al ratio (the mass ratio of phosphoric acid to aluminum ions) and the higher the pH. When the conditions for aluminum phosphate precipitation are met, a large amount of precipitate will precipitate, reducing the aluminum content in the residual liquid and increasing the P / Al ratio, which is conducive to further membrane separation. Cooling crystallization separates salts from the waste acid, and the mother liquor is returned for recycling, reducing resource waste and wastewater discharge, meeting the requirements of green chemical industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a flow chart of the method for improving diffusion dialysis to recover waste acid from aluminum parts of the present invention;

[0028] Figure 2 It is a structural schematic diagram of the device for recovering waste acid from aluminum parts by improving diffusion dialysis according to the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0030] like Figure 1 As shown, the present invention discloses a method for improving the recovery of aluminum casting waste acid by diffusion dialysis, comprising the following steps:

[0031] Step 1 is pretreatment: the waste acid passes through the waste acid collection tank, the first bag filter, the aeration mixing tank, the second bag filter, the first transfer tank, the automatic fine filter, and the filtrate tank in sequence to remove organic matter and suspended matter;

[0032] Step 2 is evaporation and concentration: the pretreated filtrate is passed from the filtrate barrel into a low-temperature evaporator for evaporation, and the evaporated concentrate is discharged into the second transfer barrel or the third transfer barrel, and the concentrate temperature is controlled;

[0033] Step 3 is heated diffusion dialysis membrane separation: the concentrate in the second transfer barrel or the third transfer barrel is adjusted to the operating temperature, and the concentrate is pumped into the separation chamber from the acid inlet at the bottom of the separation chamber;

[0034] At the same time, the pure water in the pure water tank is heated to the same temperature as the concentrate in the second or third transfer tank, and then transported to the separation chamber from the top water inlet at the same flow rate. The concentrate and pure water are countercurrently passed through the diffusion dialysis membrane in the separation chamber. The phosphoric acid in the concentrate passes through the diffusion dialysis membrane and is absorbed by the pure water on the other side, flowing out from the top to obtain membrane acid. The residual liquid is membrane waste and flows out from the bottom.

[0035] Step 4 is the secondary concentration of membrane waste: the membrane waste is pumped into the low-temperature evaporator for concentration;

[0036] Step 5 is secondary membrane separation: the concentrated membrane waste is separated again by heated diffusion dialysis membrane, and step 3 is repeated to obtain secondary membrane waste;

[0037] Step 6 is the tertiary concentration of membrane waste: the secondary membrane waste obtained in step 5 is pumped into a low-temperature evaporator for concentration to obtain a tertiary waste concentrate;

[0038] Step 7 is cooling crystallization: the tertiary waste concentrate of step 6 is pumped into the crystallization device, and mother liquor and crystal salt are obtained after cooling crystallization separation. The mother liquor is returned to the third transfer barrel for heating diffusion dialysis membrane separation again.

[0039] In the pretreatment stage, multi-stage filtration is used to remove organic matter and suspended solids, preventing impurities from clogging subsequent membrane components or evaporators, ensuring long-term stable operation of the system. Low-temperature evaporation increases the concentration of waste acid from aluminum castings, while increasing the temperature to reduce the viscosity of high-density acid, significantly improving the recovery rate of phosphoric acid while reducing the processing load of a single membrane separation. With the cyclic design of multi-stage distillation and concentration (steps 2, 4, and 6) and membrane separation (steps 3 and 5), membrane waste is separated at multiple levels. The lower the phosphoric acid concentration in the membrane waste, the lower the P / Al ratio (the mass ratio of phosphoric acid to aluminum ions) and the higher the pH. When the conditions for aluminum phosphate precipitation are met, a large amount of precipitate will precipitate, reducing the aluminum content in the residual liquid and increasing the P / Al ratio, which is conducive to further membrane separation. Cooling crystallization separates salts from the waste acid, and the mother liquor is returned for recycling, reducing resource waste and wastewater discharge, meeting the requirements of green chemical industry.

[0040] Furthermore, in step 2, the concentrated solution temperature is controlled to be less than 40° C., the evaporated concentrated solution specific gravity is 1.40-1.50 g / mL, and the filtrate is discharged into the second transfer barrel after the first evaporation.

[0041] Low-temperature evaporation (<40°C) avoids phosphoric acid decomposition or equipment corrosion caused by high temperatures, extending the service life of the evaporator. The concentrate concentration of 1.40-1.50 g / mL ensures the osmotic driving force (concentration difference) of phosphoric acid during subsequent membrane separation while avoiding the increased risk of membrane fouling due to excessive concentration. The first concentrated solution is discharged into the second transfer drum, providing a stable feed concentration for subsequent membrane separation, preventing concentration fluctuations from affecting separation efficiency.

[0042] Furthermore, in step 3, the operating temperature is 30-40° C., and the processing capacity of the diffusion dialysis membrane is 0.2-1 L / (h·m 2 ).

[0043] 30-40°C is the optimal operating temperature for diffusion dialysis membranes (below this temperature, the membrane flux decreases, and above this temperature, the membrane is prone to aging), which can maximize the permeation rate of phosphoric acid.

[0044] Processing capacity 0.2-1L / (h·m 2 ) balances the treatment efficiency and separation accuracy: if the flux is too high, the contact time between the concentrate and pure water is insufficient, and the phosphoric acid penetration is insufficient; if the flux is too low, the treatment efficiency is low and the energy consumption cost increases.

[0045] Furthermore, in steps 4 and 6, the evaporation temperature is both less than 40° C., and the specific gravity of the evaporated concentrate is both 1.40-1.50 g / mL; the evaporated concentrate of step 4 is discharged into the third transfer barrel; and the evaporated concentrate of step 6 is directly discharged into the cooling crystallization device.

[0046] Low-temperature evaporation maintains process consistency with the initial concentration, avoiding changes in membrane performance due to temperature fluctuations;

[0047] The concentrated solution in step 4 is discharged into the third transfer barrel, forming a double barrel alternating feeding with the second transfer barrel in step 2, thus ensuring the continuous operation of the membrane separation process;

[0048] In step 6, the concentrated solution is directly discharged into the crystallization device, which reduces the heat loss in the intermediate transfer link and improves the crystallization efficiency.

[0049] Furthermore, in step 7, the cooling crystallization temperature is 5-10° C., and the cooling time is 8-12 hours.

[0050] A low temperature environment of 5-10°C promotes the full crystallization and precipitation of salts (such as aluminum salts), avoiding the increase in solubility and incomplete crystallization caused by excessively high temperatures;

[0051] The cooling time of 8-12 hours provides sufficient time for crystal growth, and large crystal particles can be obtained (facilitating subsequent solid-liquid separation), while avoiding the increase in energy consumption caused by too long a time.

[0052] like Figure 2 As shown, the present invention discloses a device for improving diffusion dialysis to recover waste acid from aluminum casting, comprising: a pretreatment device, a low-temperature evaporation and concentration device, a heated diffusion dialysis device, and a crystallization device;

[0053] The pretreatment device is connected with the low-temperature evaporation and concentration device, and the low-temperature evaporation and concentration device is respectively connected with the heating diffusion dialysis device and the crystallization device.

[0054] The pretreatment unit removes organic matter and suspended solids through multi-stage filtration, preventing impurities from clogging the subsequent low-temperature evaporation and concentration unit or heated diffusion dialysis unit, ensuring long-term stable operation of the system. The low-temperature evaporation and concentration unit increases the concentration of the waste acid from aluminum castings, while the heated diffusion dialysis unit heats up and reduces the viscosity of the high-density acid, significantly improving the recovery rate of phosphoric acid while reducing the processing load of a single membrane separation. As the waste liquid passes through the low-temperature evaporation and concentration unit and the heated diffusion dialysis unit multiple times in a cyclic design, the membrane waste achieves multi-stage separation. The lower the phosphoric acid concentration in the membrane waste, the lower the P / Al ratio (the mass ratio of phosphoric acid to aluminum ions) and the higher the pH. When the conditions for aluminum phosphate precipitation are met, a large amount of precipitate will precipitate, reducing the aluminum content in the residual liquid and increasing the P / Al ratio, which is conducive to further membrane separation. The cooling crystallization in the crystallization unit separates the salts from the waste acid, and the mother liquor is returned for recycling, reducing resource waste and wastewater discharge, meeting the requirements of green chemical industry. Each device is connected by pipelines to form a continuous production line, which reduces manual intervention and reduces operational errors; the functional modules have clear division of labor, including pretreatment for impurity removal, evaporation and concentration, membrane separation for acid recovery, and crystallization for salt separation, which improves the reliability and maintainability of the system.

[0055] Furthermore, the low-temperature evaporation and concentration device includes: a low-temperature evaporator, a first transfer barrel, a second transfer barrel, a third transfer barrel, a fourth transfer barrel and a fifth transfer barrel; the fourth transfer barrel and the fifth transfer barrel are both connected to the feed port of the low-temperature evaporator; the second transfer barrel and the third transfer barrel are both connected to the discharge port of the low-temperature evaporator, and the connecting pipes are provided with insulation jackets; the second transfer barrel and the third transfer barrel are externally equipped with insulation devices, and internally equipped with heating devices, temperature controllers and stirring devices.

[0056] The insulation jacket and the heating device inside the barrel maintain the concentrated liquid temperature (<40°C), avoiding concentrated liquid crystallization or concentration fluctuations caused by ambient temperature changes;

[0057] The stirring device prevents salt precipitation in the concentrated solution and ensures uniform feeding of the evaporator;

[0058] The arrangement of multiple transfer barrels (the second and third transfer barrels) can alternately store concentrated solutions at different stages, thus ensuring continuous feeding of the membrane separation process.

[0059] Furthermore, the heated diffusion dialysis device includes: a diffusion dialysis device, an acid production barrel, a pure water barrel, an alkali washing barrel, and a water washing barrel are connected; the second transfer barrel and the third transfer barrel are both connected to the acid inlet of the diffusion dialysis device, and the pure water barrel is connected to the water inlet of the heated diffusion dialysis device; the alkali washing barrel and the water washing barrel are simultaneously connected to the acid production port and the waste outlet of the heated diffusion dialysis device; the pure water barrel is externally provided with an insulation device, and internally provided with a heating device and a temperature controller; the feed inlet and the water inlet of the diffusion dialysis device are simultaneously connected to the drainage pipe discharged into the wastewater station; the second transfer barrel, the third transfer barrel, the pure water barrel and the diffusion dialysis device connecting pipes are all provided with insulation devices; and the diffusion dialysis device is provided with an insulation cover outside.

[0060] The insulation jacket and pipe insulation maintain the operating temperature of the concentrate and pure water (30-40°C), avoiding heat loss and resulting in a decrease in separation efficiency;

[0061] The heating / temperature control device of the pure water tank ensures that the pure water and the concentrate are at the same temperature, reducing the pressure fluctuation on both sides of the membrane caused by temperature difference and extending the service life of the membrane;

[0062] Alkali washing tanks and water washing tanks can be used to clean the membrane components regularly (to remove organic matter or salt pollution on the membrane surface), restore membrane flux, and extend the membrane replacement cycle.

[0063] Furthermore, the crystallization device includes: a crystallization tank, which is equipped with a condenser, an agitator, a crystal discharge port, a solution overflow port, and a feed port; the crystallization tank has a conical bottom shape; the condenser is vertical and is 60-90° to the tank wall of the crystallization tank, and the inlet and outlet of the condenser are respectively connected to the freezing device; the distance between the solution overflow port and the bottom of the crystallization tank is 1 / 5-1 / 2 of the height of the crystallization tank, and the overflow port is connected to the fourth transfer barrel; the feed port is connected to the discharge port of the low-temperature evaporator.

[0064] The conical bottom structure facilitates crystal sedimentation and discharge (crystals are concentrated at the bottom of the cone and discharged through the discharge port);

[0065] The vertical condenser tube (60-90° to the tank wall) increases the cooling area, improves the cooling efficiency, and avoids interference between the condenser tube and the agitator;

[0066] The overflow port is 1 / 5-1 / 2 height from the bottom, so that the uncrystallized mother liquor (containing a small amount of dissolved salt) can be returned to the fourth transfer barrel through overflow for circulation, thereby reducing salt loss.

[0067] Furthermore, the pretreatment device includes: a waste acid collection barrel, a first bag filter, an aeration and stirring barrel, a second bag filter, a first transfer barrel, an automatic fine filter, and a filtrate barrel; the filtration precisions of the first bag filter and the second bag filter are 10-40 μm and 200-301 μm, respectively; an aeration pipe and a liquid level gauge are provided in the aeration and stirring barrel, a liquid inlet and a solid inlet are provided on the top, and a discharge port is provided at the bottom; the filtration precision of the automatic fine filter is 100-500 nm, and it is composed of four groups of membrane components, and the filtrate outlet is connected to the filtrate barrel; the filtrate barrel is connected to the feed port of the low-temperature evaporator.

[0068] The 10-40μm first bag filter removes large suspended particles (such as aluminum chips), the 200-301μm second bag filter intercepts medium-sized impurities, and the 100-500nm automatic fine filter removes tiny particles (such as colloids). Gradual filtration avoids the rapid clogging of a single high-precision filter;

[0069] The aeration pipe of the aeration mixing tank uses air to oxidize and decompose some organic matter (such as oil stains). The liquid level meter can monitor the amount of waste acid in real time to avoid overflow.

[0070] The automatic fine filter of the four groups of membrane components can operate alternately (one group is cleaned while the other groups are working) to ensure continuous feeding of the pretreatment process.

[0071] The above are merely preferred embodiments of the present invention and do not limit the technical scope of the present invention. Therefore, any minor modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for improving the recovery of waste acid from aluminum castings by diffusion dialysis, characterized in that: The following steps are involved: Step 1 is pretreatment: the waste acid passes through the waste acid collection tank, the first bag filter, the aeration mixing tank, the second bag filter, the first transfer tank, the automatic fine filter, and the filtrate tank in sequence to remove organic matter and suspended matter; Step 2 is evaporation and concentration: the pretreated filtrate is passed from the filtrate barrel into a low-temperature evaporator for evaporation, and the evaporated concentrate is discharged into the second transfer barrel or the third transfer barrel, and the concentrate temperature is controlled; Step 3 is heated diffusion dialysis membrane separation: the concentrate in the second transfer barrel or the third transfer barrel is adjusted to the operating temperature, and the concentrate is pumped into the separation chamber from the acid inlet at the bottom of the separation chamber; At the same time, the pure water in the pure water tank is heated to the same temperature as the concentrate in the second or third transfer tank, and then transported to the separation chamber from the top water inlet at the same flow rate. The concentrate and pure water are countercurrently passed through the diffusion dialysis membrane in the separation chamber. The phosphoric acid in the concentrate passes through the diffusion dialysis membrane and is absorbed by the pure water on the other side, flowing out from the top to obtain membrane acid. The residual liquid is membrane waste and flows out from the bottom. Step 4 is the secondary concentration of membrane waste: the membrane waste is pumped into the low-temperature evaporator for concentration; Step 5 is secondary membrane separation: the concentrated membrane waste is separated again by heated diffusion dialysis membrane, and step 3 is repeated to obtain secondary membrane waste; Step 6 is the tertiary concentration of membrane waste: the secondary membrane waste obtained in step 5 is pumped into a low-temperature evaporator for concentration to obtain a tertiary waste concentrate; Step 7 is cooling Crystallization: The tertiary waste concentrate from step 6 is pumped into the crystallization device, and after cooling and crystallization separation, mother liquor and crystal salt are obtained. The mother liquor is returned to the third transfer barrel for heating and diffusion dialysis membrane separation again.

2. The method for improving the recovery of aluminum waste acid by diffusion dialysis according to claim 1, characterized in that: In step 2, the concentrated solution temperature is controlled to be less than 40° C., the evaporated concentrated solution specific gravity is 1.40-1.50 g / mL, and the filtrate is discharged into the second transfer barrel after the first evaporation.

3. The method for improving the recovery of aluminum waste acid by diffusion dialysis according to claim 1, characterized in that: In step 3, the operating temperature is 30-40°C, and the processing capacity of the diffusion dialysis membrane is 0.2-1 L / (h·m2).

4. The method for improving the recovery of aluminum waste acid by diffusion dialysis according to claim 1, characterized in that: In steps 4 and 6, the evaporation temperature is both less than 40° C., and the specific gravity of the evaporated concentrate is both 1.40-1.50 g / mL; the evaporated concentrate in step 4 is discharged into the third transfer barrel; and the evaporated concentrate in step 6 is directly discharged into the cooling crystallization device.

5. The method for improving the recovery of aluminum waste acid by diffusion dialysis according to claim 1, characterized in that: In step 7, the cooling crystallization temperature is 5-10° C. and the cooling time is 8-12 hours.

6. A device for improving the recovery of waste acid from aluminum castings by diffusion dialysis, characterized in that: include: Pretreatment device, low-temperature evaporation and concentration device, heating diffusion dialysis device, crystallization device; The pretreatment device is connected to the low-temperature evaporation and concentration device, and the low-temperature evaporation and concentration device is respectively connected to the heating diffusion dialysis device and the crystallization device.

7. The device for improving the recovery of waste acid from aluminum castings by diffusion dialysis according to claim 6 is characterized in that: The low-temperature evaporation and concentration device includes: a low-temperature evaporator, a first transfer barrel, a second transfer barrel, a third transfer barrel, a fourth transfer barrel and a fifth transfer barrel; the fourth transfer barrel and the fifth transfer barrel are both connected to the feed port of the low-temperature evaporator; the second transfer barrel and the third transfer barrel are both connected to the discharge port of the low-temperature evaporator, and the connecting pipes are provided with insulation jackets; the second transfer barrel and the third transfer barrel are externally equipped with insulation devices, and internally equipped with heating devices, temperature controllers and stirring devices.

8. The device for improving the recovery of waste acid from aluminum castings by diffusion dialysis according to claim 7 is characterized in that: The heated diffusion dialysis device includes: a diffusion dialysis device, an acid production barrel, a pure water barrel, an alkali washing barrel, and a water washing barrel connected; the second transfer barrel and the third transfer barrel are both connected to the acid inlet of the diffusion dialysis device, and the pure water barrel is connected to the water inlet of the heated diffusion dialysis device; the alkali washing barrel and the water washing barrel are simultaneously connected to the acid production port and the waste outlet of the heated diffusion dialysis device; the pure water barrel is externally provided with an insulation device, and internally provided with a heating device and a temperature controller; the feed inlet and the water inlet of the diffusion dialysis device are simultaneously connected to the drainage pipe discharged into the wastewater station; the second transfer barrel, the third transfer barrel, the pure water barrel and the diffusion dialysis device connecting pipes are all provided with insulation devices; and the diffusion dialysis device is externally provided with an insulation sleeve.

9. The device for improving the recovery of waste acid from aluminum castings by diffusion dialysis according to claim 7, characterized in that: The crystallization device includes: a crystallization tank, which is equipped with a condenser, an agitator, a crystal discharge port, a solution overflow port, and a feed port; the crystallization tank has a conical bottom shape; the condenser is vertical and is 60-90 degrees to the tank wall of the crystallization tank, and the inlet and outlet of the condenser are respectively connected to a freezing device; the distance between the solution overflow port and the bottom of the crystallization tank is 1 / 5-1 / 2 of the height of the crystallization tank, and the overflow port is connected to the fourth transfer barrel; the feed port is connected to the discharge port of the low-temperature evaporator.

10. The device for improving the recovery of waste acid from aluminum castings by diffusion dialysis according to claim 6, characterized in that: The pretreatment device includes: a waste acid collection barrel, a first bag filter, an aeration and stirring barrel, a second bag filter, a first transfer barrel, an automatic fine filter, and a filtrate barrel; the filtration precisions of the first bag filter and the second bag filter are 10-40 μm and 200-301 μm, respectively; the aeration and stirring barrel is provided with an aeration pipe and a liquid level gauge, a liquid inlet and a solid inlet are provided on the top, and a discharge port is provided on the bottom; the automatic fine filter has a filtration precision of 100-500 nm, is composed of four groups of membrane components, and the filtrate outlet is connected to the filtrate barrel; the filtrate barrel is connected to the feed port of the low-temperature evaporator.

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