Method for separating, purifying and concentrating ammonium citrate waste liquid in low-voltage formed foil feed tank

Abstract

The invention discloses a method for separating, purifying and concentrating ammonium citrate in an ammonium citrate bath solution, which comprises the following steps: separating and purifying the ammonium citrate bath solution by using a nanofiltration membrane, and concentrating ammonium citrate by using a high-pressure reverse osmosis membrane at the same time; ammonium citrate is subjected to nanofiltration dialysis, a small amount of ammonium citrate thin liquid and purified ammonium citrate concentrated liquid are obtained at the same time, reverse osmosis membrane filtrate is recycled in the process, and the Cl <-> formed foil closed-loop clean production technology is formed. According to the invention, chlorine can be well removed and ammonium citrate can be concentrated by using a membrane technology. The scale of the membrane treatment system in the process is customized according to a production line, the membrane treatment system can be matched with industrial production to be continuously carried out, the system process is simple, the treatment efficiency is high, the utilization rate of water resources can be increased, the water resources are purified and recycled, zero emission of a project is achieved, and good economic benefits are comprehensively generated.

Description

Technical Field

[0001] The invention relates to the technical field of producing anode foil from chemically formed foil, and in particular to a method for separating and purifying ammonium citrate tank liquid and concentrating ammonium citrate. Background Art

[0002] In the aluminum electrolytic capacitor corrosion method, hydrochloric acid or nitric acid is often used to etch the aluminum foil. The aluminum foil is corroded and dissolved by hydrochloric acid or nitric acid to produce porous corrosion foil. After corrosion, the aluminum foil is washed with clean water to remove Cl - and surface aluminum powder, will produce Al 3+ The medium and low chemical formation process mainly forms a dense and voltage-resistant γ-Al2O3 oxide film dielectric layer on the surface of the etched aluminum foil, which is generally used as the anode of the capacitor.

[0003] The main chemical solutions used in the chemical process are ammonium citrate, citric acid, ammonium pentaborate and non-aqueous chemical solutions. - and Al 3+ The electrolyte accumulates continuously in the feed tank, and the feed tank liquid needs to be replaced with fresh one after a period of time. A large amount of waste liquid is generated in the production process of aluminum foil formation, and direct discharge not only pollutes the environment but also wastes resources. In addition, the price of ammonium citrate is also very expensive, so the cost of replacing the electrolyte is very high, which is a heavy burden for the aluminum electrolysis electrode foil industry. While increasing production costs, it also reduces economic competitiveness. In addition, the waste liquid not only contains ammonia nitrogen but also organic matter adipic acid, which increases the acidity of the solution. If the waste liquid can be reused, it will not only reduce production costs, but also reduce environmental pollution and reduce wastewater discharge from the source.

[0004] In view of the above shortcomings, a method that can effectively solve the problem of Cl in ammonium citrate is proposed. - The problem of high content, Cu and Fe enrichment and reduced aluminum foil concentration is solved while achieving Cl - A closed-loop clean production method for formed foil is urgently needed in the industry. Summary of the invention

[0005] Based on the above analysis, the object of the present invention is to provide a method for separating and purifying ammonium citrate and concentrating ammonium citrate, which solves the problem of Cl - The problem of high content, Cu and Fe enrichment and reduced aluminum foil concentration is solved while achieving Cl - The method uses nanofiltration membrane to separate and purify the ammonium citrate tank liquid, and uses high-pressure reverse osmosis membrane to concentrate the ammonium citrate; the ammonium citrate is dialyzed by nanofiltration, and a dilute liquid containing a small amount of ammonium citrate and a purified ammonium citrate concentrated liquid are obtained at the same time. In the process, the reverse osmosis membrane filtrate is recycled to form Cl - Closed-loop clean production process for formed foil.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for separating and purifying ammonium citrate and concentrating ammonium citrate, comprising the following steps:

[0008] S1, after the foil is formed, it contains Cl - The tank liquid is pretreated to make the filtrate clear, and the ammonium citrate filtrate that meets the conditions for entering the membrane system is obtained; the pretreatment is to use a precision filter, the filter element intercepts the solid impurities in the feed liquid, and plays a protective role on the membrane system. The precision filter selects a precision filter element with a filtration accuracy of 1um to 5um;

[0009] S2, the ammonium citrate filtrate and the concentrated and pure water liquid of the nanofiltration system 2 are mixed in a volume ratio of 5:1:1, and the inlet pressure and temperature are controlled so that the comprehensive inlet liquid of the nanofiltration system 1 enters the nanofiltration system 1 for purification, and the purified ammonium citrate concentrate and the dialyzate of the nanofiltration system 1 are obtained, and the ammonium citrate concentrate is returned to the production line to continue to be circulated and used as the formation foil tank liquid;

[0010] S3, using the dilute liquid of nanofiltration system 1 and the concentrated liquid of reverse osmosis as the comprehensive inlet of nanofiltration system 2, controlling the pressure and temperature of the inlet, so that the comprehensive inlet of nanofiltration system 1 enters nanofiltration system 2 for secondary treatment, obtaining the ammonium citrate concentrated liquid after secondary treatment and the dialysate of nanofiltration system 2, and the ammonium citrate concentrated liquid returns to the nanofiltration system 1 for recycling;

[0011] S4, according to the preset concentration concentration of the system, adjust the inlet pressure, temperature, and conductivity. The dialysate of the nanofiltration system 1 and the dilute ammonium citrate in S2 are passed through the high-pressure reverse osmosis concentration system to obtain reverse osmosis concentrate and reverse osmosis dialysis water. The effluent is controlled to meet the water use standard and returned to the nanofiltration system 1 dialysis process through the water storage tank for water replenishment. The excess water is returned to the enterprise for use as pure water replenishment;

[0012] S5. Adjust the inlet pressure, temperature and conductivity to allow the reverse osmosis concentrate to enter the nanofiltration system 2 for purification to obtain ammonium citrate concentrate and ammonium citrate dilute solution. The ammonium citrate concentrate returns to the comprehensive inlet liquid storage tank of the nanofiltration system 1 as the comprehensive inlet liquid of the nanofiltration system 1 to circulate and continue to recover ammonium citrate.

[0013] Furthermore, the concentrated solution of the nanofiltration system 2 is 0.5%-1% ammonium citrate and 0.1%-0.2% ammonium citrate dilute solution; the comprehensive inlet of the nanofiltration system 1 is Cl - , ammonium citrate, and a mixture of water; the dialysate of the nanofiltration system 1 is Cl - and ammonium citrate; the reverse osmosis concentrate is a mixture of trace amounts of Cl - and ammonium citrate-based solutions.

[0014] Furthermore, the membrane system includes a comprehensive liquid inlet storage tank, a nanofiltration system 1, a reverse osmosis concentration system, and a nanofiltration system 2; the comprehensive liquid inlet storage tank is connected to the nanofiltration system 1, and the nanofiltration system 1 includes a power pump b, a regulating valve b, a sensor b, a flow element b, a nanofiltration membrane of the nanofiltration system 1, an ammonium citrate concentrate storage tank, and a filtrate storage tank of the nanofiltration system 1 connected by a pipeline; the reverse osmosis concentration system is connected to the filtrate storage tank of the nanofiltration system 2, and the reverse osmosis concentration system includes a power pump, a regulating valve d, a sensor d, a flow element d, a reverse osmosis membrane, a reverse osmosis concentrate storage tank, and a water storage tank connected by a pipeline, and the water storage tank is also connected to the liquid inlet tank of the nanofiltration system 1; the dilute liquid of the nanofiltration system 2 is a reverse osmosis concentrate storage tank, and the nanofiltration system 2 includes a power pump, a regulating valve c, a sensor c, a flow element c, a nanofiltration membrane of the nanofiltration system 2, and an ammonium citrate semi-finished concentrated liquid storage tank connected by a pipeline, and the concentrated liquid of the nanofiltration system 2 is also connected to the comprehensive liquid inlet storage tank through a pipeline.

[0015] Further, the sensor a includes a temperature sensor a, a pressure sensor a, and a liquid level sensor a; the sensor b includes a temperature sensor b, a pressure sensor b, and a liquid level sensor b; the sensor c includes a temperature sensor c and a pressure sensor c; the sensor a, sensor b, sensor c, regulating valve b, regulating valve c, regulating valve d, flow element b, flow element c, and flow element d are electrically connected to the control system.

[0016] Furthermore, the reverse osmosis membrane used in the membrane system is an acid-resistant high-pressure reverse osmosis membrane, and the nanofiltration membrane of the nanofiltration system 1 and the nanofiltration membrane of the nanofiltration system 2 are acid-resistant high-pressure nanofiltration membranes.

[0017] Further, in the nanofiltration system 1, Cl - During solution separation and dialysis purification, the inlet pressure is 3.5-7Mpa and the temperature is 25-40℃.

[0018] Furthermore, when the ammonium citrate is concentrated using a reverse osmosis concentration system, the inlet pressure is 3-8 MPa and the temperature is 15-35°C.

[0019] Furthermore, when the nanofiltration system 2 is used for ammonium citrate purification, the inlet pressure is 3.5-4.5 MPa and the temperature is 20-35°C.

[0020] Furthermore, the ammonium citrate content in the ammonium citrate solution obtained in step S2 reaches more than 45 g / l.

[0021] Furthermore, the concentration of the ammonium citrate solution obtained in step S3 is above 15 g / l.

[0022] Furthermore, the concentration of the ammonium citrate solution obtained in step S4 is above 5 g / l.

[0023] The beneficial effects of the present invention are:

[0024] 1. The membrane technology can effectively remove chlorine and concentrate ammonium citrate. During the concentration process, chloride ions will be separated from the permeable side. The concentration of concentrated ammonium citrate increases, and the chloride ions continue to decrease. Then, the method of adding water for dialysis can be used to further separate chloride ions without reducing the content of ammonium citrate, so as to achieve the concentration of Cl - and the purpose of separating chloride ions;

[0025] 2. The scale of the membrane treatment system in the process of the present invention is tailored according to the production line, and can be matched with continuous industrial production. The system process is simple and the treatment efficiency is high. The system adopts integrated intelligent control; integrated control method: each system is an independent skid-mounted unit. By controlling the programming logic of the CPU and monitoring the feedback values ​​such as pressure, flow, temperature, concentration, pump frequency, valve opening, etc., the system program automatically controls and adjusts the real-time operation value according to the set target value to achieve the production target; the system has a high degree of control automation, precise automatic adjustment, and realizes paperless office and unattended operation in the workshop;

[0026] 3. The permeable water in the nanofiltration system 1 process uses a secondary nanofiltration system to concentrate ammonium citrate, thereby improving the recovery rate of ammonium citrate. The reverse osmosis system further improves the recovery rate of ammonium citrate for the dilute liquid of the secondary nanofiltration system. The concentrated permeable water can be directly reused in the nanofiltration dialysis process section, thereby improving the utilization rate of water resources, purifying water resources for reuse, achieving zero discharge of the project, and generating good economic benefits in an integrated manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a schematic diagram of a separation, purification and concentration device; in the figure: 1, raw liquid tank; sensor a; 9, power pump; 13, CMF filter; 2, integrated liquid inlet storage tank; 6, nanofiltration system 1 nanofiltration membrane; regulating valve b; sensor b; flow element b; 5, ammonium citrate concentrated solution storage tank; 3, nanofiltration system filtrate storage tank; 8, reverse osmosis membrane; regulating valve d; sensor d; flow element d; 12, power pump; 7, nanofiltration system 2 nanofiltration membrane; 4, secondary nanofiltration dilute liquid storage tank; regulating valve c; sensor c; flow element c; 11, power pump. DETAILED DESCRIPTION

[0028] like Figure 1As shown, the membrane system includes a raw liquid tank 1, which passes through the pressure sensor a, temperature sensor a, and flow element a on sensor a through the CMF filter to enter the comprehensive liquid inlet storage tank 2, the nanofiltration system 6, the reverse osmosis concentration system 8, and the nanofiltration system 7; after the comprehensive liquid in the nanofiltration system 6 passes through the comprehensive liquid inlet storage tank 2, the data reflected by the pressure sensor b, temperature sensor b, and flow element b on the sensor b are controlled by the control system to control the regulating valve b, so that the comprehensive liquid in the nanofiltration system reaches the condition of entering the nanofiltration system 6, and the purified Cl--removed concentrated solution and the dialysate of the nanofiltration system 6 are obtained, and the ammonium citrate concentrated solution enters the ammonium citrate concentrated solution storage tank 5; the dialysate of the nanofiltration system 6 enters the filtrate storage tank 3 of the nanofiltration system, and passes through the pressure sensor c, temperature sensor b, and flow element b on the sensor c. The data reflected by the sensor c and the flow element c are used to control the regulating valve c through the control system, so that the dialysate of the nanofiltration system 7 reaches the conditions for entering the reverse osmosis concentration system, and after purification, a Cl-containing dilute liquid and a low-concentration ammonium citrate are obtained. The low-concentration ammonium citrate liquid returns to the comprehensive liquid inlet storage tank 2 as the comprehensive liquid inlet of the nanofiltration system 6 for circulation, and the Cl-containing dilute liquid enters the secondary nanofiltration system dilute liquid storage tank 4; the secondary nanofiltration system dilute liquid storage tank 4 is used as the reverse osmosis liquid inlet storage tank, and the data reflected by the pressure sensor d, the temperature sensor d, and the flow element d on the sensor d are used to control the regulating valve d through the control system, so that the reverse osmosis concentrated liquid and the reverse osmosis dilute liquid are obtained, and the reverse osmosis dilute liquid is returned to the nanofiltration system 1 for use, and the reverse osmosis concentrated liquid enters the nanofiltration system filtrate storage tank 3.

[0029] The present invention provides a method for separating and purifying ammonium citrate and concentrating ammonium citrate, comprising the following steps:

[0030] S1. Pre-treating the Cl-containing tank liquid after the foil is formed to clarify the filtrate and obtain the ammonium citrate filtrate that meets the conditions for entering the membrane system; the pre-treatment is to use a precision filter, the filter element intercepts the solid impurities in the feed liquid, and protects the membrane system. The precision filter selects a precision filter element with a filtration accuracy of 1um to 5um;

[0031] S2, the ammonium citrate filtrate and the concentrated and pure water liquid of the nanofiltration system 2 are mixed in a volume ratio of 5:1:1, and the inlet pressure and temperature are controlled so that the comprehensive inlet liquid of the nanofiltration system 1 enters the nanofiltration system 1 for purification, and the purified ammonium citrate concentrate and the dialyzate of the nanofiltration system 1 are obtained, and the ammonium citrate concentrate is returned to the production line to continue to be circulated and used as the formation foil tank liquid;

[0032] S3, using the dilute liquid of nanofiltration system 1 and the concentrated liquid of reverse osmosis as the comprehensive inlet of nanofiltration system 2, controlling the pressure and temperature of the inlet, so that the comprehensive inlet of nanofiltration system 1 enters nanofiltration system 2 for secondary treatment, obtaining the ammonium citrate concentrated liquid after secondary treatment and the dialysate of nanofiltration system 2, and the ammonium citrate concentrated liquid returns to the nanofiltration system 1 for recycling;

[0033] S4, according to the preset concentration concentration of the system, adjust the inlet pressure, temperature, and conductivity. The dialysate of the nanofiltration system 1 and the dilute ammonium citrate in S2 are passed through the high-pressure reverse osmosis concentration system to obtain reverse osmosis concentrate and reverse osmosis dialysis water. The effluent is controlled to meet the water use standard and returned to the nanofiltration system 1 dialysis process through the water storage tank for water replenishment. The excess water is returned to the enterprise for use as pure water replenishment;

[0034] S5. Adjust the inlet pressure, temperature and conductivity to allow the reverse osmosis concentrate to enter the nanofiltration system 2 for purification to obtain ammonium citrate concentrate and ammonium citrate dilute solution. The ammonium citrate concentrate returns to the comprehensive inlet liquid storage tank of the nanofiltration system 1 as the comprehensive inlet liquid of the nanofiltration system 1 to circulate and continue to recover ammonium citrate.

[0035] This process involves membrane concentration and membrane purification systems using acid-resistant high-pressure nanofiltration membranes and reverse osmosis membrane elements (the membrane elements of this process are all provided by Chengdu Paiyilai).

[0036] Example 1

[0037] S1. Pre-treat ammonium citrate to obtain a formed ammonium citrate stock solution that meets the conditions for entering the membrane system, and the turbidity detection value of the clear solution is less than 0.1 NTU;

[0038] S2, mixing the pre-treated aluminum foil stock solution and the nanofiltration system 6 concentrate in a volume ratio of 5:1 to obtain a comprehensive inlet solution for the nanofiltration system 6, wherein the comprehensive inlet solution for the nanofiltration system 6 is an ammonium citrate solution containing a small amount of Cl-;

[0039] S3, controlling the inlet temperature to 25-30°C and the pressure level to 3.5MPa, allowing the comprehensive inlet liquid to enter the nanofiltration system 6 for purification, obtaining a purified Cl- less than 1PPM concentrated solution and a dialyzate from the nanofiltration system 6, and the Cl- content in the purified ammonium citrate concentrated solution is less than 1PPM;

[0040] S4, the dialysate of the nanofiltration system 6 enters the nanofiltration system 7 for purification, the inlet temperature is controlled at 25-30°C, the pressure level is 2.5MPa, and the semi-finished ammonium citrate concentrate with Cl- less than 1PPM and the chlorine-containing dilute liquid are separated, and the ammonium citrate content reaches 15g / l. The semi-finished ammonium citrate concentrate with Cl- less than 1PPM can be returned to the comprehensive inlet of the nanofiltration system 6 for further concentration;

[0041] S5. According to the preset concentration of the system, the dilute liquid of the nanofiltration system 7 is passed through the reverse osmosis concentration system, and the inlet temperature is controlled at 15-35°C and the pressure level is 3MPa to obtain concentrated ammonium citrate and reverse osmosis dilute liquid.

[0042] Table 1 Comparison of the data of ammonium citrate stock solution recovered by this process and the product data is as follows

[0043]

[0044] It can be seen from Table 1 that by controlling the inlet temperature and pressure level, the recycled waste liquid enters this process for purification, and the chloride ion of the waste liquid is reduced from 3.4PPM to 0.5PPM. The Cl- content in the product liquid is less than 1PPM after enterprise testing, meeting the enterprise reuse standard.

[0045] Table 2 Comparison of the data of ammonium citrate stock solution recovered by this process and the product data is as follows

[0046]

[0047]

[0048] From Table 2, we can know that the inlet temperature and pressure level are controlled to make the recycled waste liquid enter this process for purification.

[0049] The liquid chloride ion was reduced from 2.8PPM to 0.6PPM. The Cl- content in the product liquid was less than 1PPM after testing by the company, reaching the company's

[0050] Industry recycling standards.

[0051] Table 3 Comparison of the data of ammonium citrate stock solution recovered by this process and the product data is as follows

[0052]

[0053] Table 3 shows that the inlet temperature and pressure level are controlled to allow the recovered waste liquid to enter this process for purification.

[0054] The liquid chloride ion was reduced from 4.1PPM to 0.8PPM. The Cl- content in the product liquid was less than 1PPM after testing by the enterprise, reaching the enterprise standard.

[0055] Industry recycling standards.

[0056] Example 2

[0057] S1, pre-treat ammonium citrate to obtain the ammonium citrate stock solution that meets the conditions for entering the membrane system,

[0058] Liquid turbidity test value shows <0.1NTU;

[0059] S2, the pre-treated aluminum foil stock solution and the nanofiltration system 6 concentrate were mixed in a volume ratio of 4:1 to obtain

[0060] The integrated inlet liquid of the nanofiltration system 6 is an ammonium citrate solution containing a small amount of Cl-;

[0061] S3, control the inlet temperature to 25-30℃ and the pressure level to 4MPa, so that the comprehensive inlet liquid enters the nanofiltration system 6 for

[0062] Purification, to obtain a concentrated solution with a purified Cl- content of less than 1PPM and a dialyzate from a nanofiltration system 6, to purify the Cl- content in the ammonium citrate concentrated solution

[0063] Less than 1PPM;

[0064] S4, the dialysate from nanofiltration system 6 enters nanofiltration system 7 for purification, and the inlet temperature and pressure are controlled at 25-30°C.

[0065] At 3MPa, the semi-finished ammonium citrate concentrate with Cl- less than 1PPM and the chlorine-containing dilute liquid are separated, and the ammonium citrate content reaches

[0066] To 15g / l, Cl- is less than 1PPM semi-finished ammonium citrate concentrate can be returned to the nanofiltration system 6 comprehensive feed for further concentration

[0067] shrink;

[0068] S5, according to the system preset concentration, the dilute liquid of the nanofiltration system 7 passes through the reverse osmosis concentration system to control the liquid inlet

[0069] The temperature is 15-35°C and the pressure level is 3.5MPa, and concentrated ammonium citrate and reverse osmosis dilute liquid are obtained.

[0070] Table 4 Comparison of the data of ammonium citrate stock solution recovered by this process and the product data is as follows

[0071]

[0072]

[0073] It can be seen from Table 4 that by controlling the inlet temperature and pressure level, the recycled waste liquid can enter this process for purification. The chloride ion of the waste liquid is reduced from 2.9PPM to 0.8PPM. The Cl- content in the product liquid is less than 1PPM after enterprise testing, meeting the enterprise reuse standard.

[0074] Table 5 Comparison of the data of ammonium citrate stock solution recovered by this process and the product data is as follows

[0075]

[0076] It can be seen from Table 5 that by controlling the inlet temperature and pressure level, the recycled waste liquid enters this process for purification, and the chloride ion of the waste liquid is reduced from 3.6PPM to 0.6PPM. The Cl- content in the product liquid is less than 1PPM after enterprise testing, meeting the enterprise reuse standard.

[0077] Table 6 Comparison of the data of ammonium citrate stock solution recovered by this process and the product data is as follows

[0078]

[0079] It can be seen from Table 6 that by controlling the inlet temperature and pressure level, the recycled waste liquid can enter this process for purification. The chloride ion content of the waste liquid can be reduced from 5.1PPM, which is seriously exceeded, to 0.9PPM. The Cl- content in the product liquid is less than 1PPM after enterprise testing, meeting the enterprise reuse standard.

[0080] Through real data feedback from six groups of enterprises, our company can stably produce products that meet the enterprise's reuse standards through membrane technology by adjusting different temperatures and pressures to cope with the company's fluctuating chloride ion concentration.

[0081] It should be noted that this article focuses on the removal of chloride ions in ammonium citrate, while the removal of copper ions and iron ions is omitted in this discussion.

Claims

1. A method for separating and purifying ammonium citrate and concentrating ammonium citrate, comprising: S1, after the foil is formed, it contains Cl - The tank liquid is pre-treated by a precision filter element with a filtration accuracy of 1um to 5um to make the filtrate clear, and obtain the ammonium citrate filtrate that meets the conditions for entering the membrane system; S2, the ammonium citrate filtrate and the concentrated and pure water liquid of the nanofiltration system 2 are mixed in a volume ratio of 5:1:1, and the inlet pressure and temperature are controlled so that the comprehensive inlet liquid of the nanofiltration system 1 enters the nanofiltration system 1 for purification, and the purified ammonium citrate concentrate and the dialyzate of the nanofiltration system 1 are obtained, and the ammonium citrate concentrate is returned to the production line to continue to be circulated and used as the formation foil tank liquid; S3, using the dilute liquid of nanofiltration system 1 and the concentrated liquid of reverse osmosis as the comprehensive inlet of nanofiltration system 2, controlling the pressure and temperature of the inlet, so that the comprehensive inlet of nanofiltration system 1 enters nanofiltration system 2 for secondary treatment, obtaining the ammonium citrate concentrated liquid after secondary treatment and the dialysate of nanofiltration system 2, and the ammonium citrate concentrated liquid returns to the nanofiltration system 1 for recycling; S4, according to the preset concentration concentration of the system, adjust the inlet pressure, temperature, and conductivity. The dialysate of the nanofiltration system 1 and the dilute ammonium citrate in S2 are passed through the high-pressure reverse osmosis concentration system to obtain reverse osmosis concentrate and reverse osmosis dialysis water. The effluent is controlled to meet the water use standard and returned to the nanofiltration system 1 dialysis process through the water storage tank for water replenishment. The excess water is returned to the enterprise for use as pure water replenishment; S5. Adjust the inlet pressure, temperature and conductivity to allow the reverse osmosis concentrate to enter the nanofiltration system 2 for purification to obtain ammonium citrate concentrate and ammonium citrate dilute solution. The ammonium citrate concentrate returns to the comprehensive inlet liquid storage tank of the nanofiltration system 1 as the comprehensive inlet liquid of the nanofiltration system 1 to circulate and continue to recover ammonium citrate.

2. The method according to claim 1, wherein: The concentrated solution of the nanofiltration system 2 is 0.5%-1% ammonium citrate and 0.1%-0.2% ammonium citrate dilute solution; The comprehensive influent of the nanofiltration system 1 is Cl - , a mixture of ammonium citrate and water; The dialysate of the nanofiltration system 1 is Cl - and ammonium citrate mixture; The reverse osmosis concentrate comprises: - and ammonium citrate solution.

3. The method according to claim 1, wherein: The membrane system comprises a comprehensive liquid inlet storage tank, a nanofiltration system 1, a reverse osmosis concentration system, and a nanofiltration system 2; the comprehensive liquid inlet storage tank is connected to the nanofiltration system 1; The nanofiltration system 1 includes a power pump b, a regulating valve b, a sensor b, a flow element b, a nanofiltration membrane of the nanofiltration system 1, an ammonium citrate concentrate storage tank, and a filtrate storage tank of the nanofiltration system 1 connected by pipelines; The reverse osmosis concentration system is connected to the filtrate storage tank of the nanofiltration system 2; The reverse osmosis concentration system includes a power pump, a regulating valve d, a sensor d, a flow element d, a reverse osmosis membrane, a reverse osmosis concentrate storage tank, and a water storage tank connected by pipelines; The water storage tank is also connected to the liquid inlet tank of the nanofiltration system 1; The dilute liquid of the nanofiltration system 2 is a reverse osmosis concentrated liquid storage tank, and the nanofiltration system 2 includes a power pump, a regulating valve c, a sensor c, a flow element c, a nanofiltration membrane of the nanofiltration system 2, and an ammonium citrate semi-finished concentrated liquid storage tank connected by pipelines; the concentrated liquid of the nanofiltration system 2 is also connected to the comprehensive liquid inlet storage tank through a pipeline.

4. The method according to claim 3, wherein: The sensor a includes: a temperature sensor a, a pressure sensor a, and a liquid level sensor a; The sensor b includes: a temperature sensor b, a pressure sensor b, and a liquid level sensor b; The sensor c includes: a temperature sensor c and a pressure sensor c; The sensor a, sensor b, sensor c, regulating valve b, regulating valve c, regulating valve d, flow element b, flow element c, and flow element d are electrically connected to the control system.

5. The method according to claim 1, wherein: The reverse osmosis membrane used in the membrane system is an acid-resistant high-pressure reverse osmosis membrane, and the nanofiltration membrane of the nanofiltration system 1 and the nanofiltration membrane of the nanofiltration system 2 are acid-resistant high-pressure nanofiltration membranes.

6. The method according to claim 1, wherein: In the nanofiltration system 1, Cl - When the solution is separated and purified by dialysis, the inlet pressure is 3.5-7Mpa and the temperature is 25-40°C; when ammonium citrate is concentrated by reverse osmosis concentration system, the inlet pressure is 3-8Mpa and the temperature is 15-35°C; When the nanofiltration system 2 is used for ammonium citrate purification, the inlet pressure is 3.5-4.5 MPa and the temperature is 20-35°C.

7. The method according to claim 1, wherein: The ammonium citrate content in the ammonium citrate solution obtained in step S2 is greater than 45 g / l.

8. The method of claim 1, wherein: The concentration of the ammonium citrate solution obtained in step S3 is above 15 g / l.

9. The method according to claim 1, wherein: The concentration of the ammonium citrate solution obtained in step S4 is above 5 g / l.

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