Resource utilization method of iron-process iron phosphate waste acid water

Abstract

The invention discloses a resource utilization method of iron-process iron phosphate waste acid water, which comprises the following steps: firstly, evaporating and concentrating the waste acid water generated by an iron-process iron phosphate production process to obtain a strong phosphoric acid solution, and then treating the strong phosphoric acid solution by an ultrafiltration membrane to obtain an ultrafiltration concentrated solution and an ultrafiltration clear solution; treating the ultrafiltration clear liquid through a nanofiltration membrane to obtain nanofiltration concentrated liquid and nanofiltration clear liquid; carrying out a neutralization reaction on the ultrafiltration concentrated liquid and the nanofiltration concentrated liquid to obtain neutralized slurry; filtering to remove filter residues to obtain filtrate; and evaporating and concentrating the filtrate to obtain a concentrated solution, cooling and crystallizing to obtain crystal slurry, and centrifuging to obtain a disodium hydrogen phosphate product and secondary filtrate. According to the resource utilization method of the iron-process iron phosphate waste acid water, the technologies of ultrafiltration, nanofiltration, evaporative crystallization, filter pressing and centrifugation are adopted, harmful substances in the waste acid water are effectively removed, disodium hydrogen phosphate is produced in combination with an accurate online pH linkage control method, disodium hydrogen phosphate with the purity of 97% or above is produced as a byproduct, and the conversion rate of the generated disodium hydrogen phosphate is larger than 95%.

Description

Technical Field

[0001] The present invention relates to the technical field of iron phosphate preparation, and particularly relates to a method for resource utilization of waste acid water from iron-process iron phosphate. Background Art

[0002] Iron phosphate is the main precursor for producing lithium iron phosphate, the cathode material of batteries. There are three main production methods for iron phosphate: the iron process, the ammonium process, and the sodium process. Currently, the sodium process has been gradually phased out by the market due to the difficult treatment of by-product sodium sulfate. Among them, the iron process has attracted more and more attention from enterprises due to its advantages such as simple process, low energy consumption, and good product consistency. The production process of the iron-process iron phosphate uses pure iron as the iron source and refined phosphoric acid as the phosphorus source. After the iron and phosphoric acid undergo a ferric dissolution reaction to form a ferrous dihydrogen phosphate solution, hydrogen peroxide is added to oxidize the divalent iron in the ferrous dihydrogen phosphate solution to form iron phosphate dihydrate. Finally, anhydrous iron phosphate is obtained after filtration, washing, drying, and calcination. During the production process of the iron-process iron phosphate, there are phosphorus-containing waste acid waters such as the waste water from the spray of the ferric dissolution exhaust gas, the waste water from the filtration of iron slag, the process filtrate generated during the pressure leaching process, and the waste water from the washing of the filter cake. If these waste acid waters are only recycled to the iron phosphate device through MVR without undergoing deep treatment, it will cause the increase of metal ions such as Fe 3+ , Ca 2+ , Mg 2+ , Mn 2+ , Ti 2+ , etc., and non-metal ions such as SO4 2- , etc., as well as the increase of COD and SS concentrations. If directly discharged, it will cause serious pollution to the environment.

[0003] Existing waste acid water treatment technologies mainly include physicochemical methods, biological methods, membrane separation technologies, and ion exchange technologies, etc. Physicochemical methods mainly precipitate harmful substances in waste acid water by adding chemicals; biological methods use the metabolic functions of microorganisms to convert harmful substances in waste acid water into harmless substances; membrane separation technologies separate harmful substances in waste acid water through the selective permeation of membranes; ion exchange technologies use ion exchange resins to adsorb harmful substances in waste acid water onto the resins. Although existing waste acid water treatment technologies can effectively remove harmful substances in waste acid water, these technologies have some problems and disadvantages. Physicochemical methods and biological methods require the addition of a large amount of chemicals, which not only increases the treatment cost but also may cause secondary pollution; although membrane separation technologies and ion exchange technologies can effectively remove harmful substances in waste acid water, these technologies require a large amount of energy and resources, and there are also problems such as membrane fouling and resin regeneration. In addition, most existing waste acid water treatment technologies can only achieve partial resource recovery and reuse, and resource waste still exists. For example, the Chinese patent application with the publication number CN114835325A discloses a resource utilization process for phosphoric acid iron mother liquor and rinsing water, which adopts a microporous + ultrafiltration + pressure filtration + three-stage reverse osmosis process. This method has a large initial investment, high operating costs, high membrane prices, and large membrane losses due to the high content of metal ions in the mother liquor and washing water.

[0004] In summary, in the field of iron-process phosphoric acid iron, there is no good process that can achieve the full reuse of waste phosphoric acid and produce high-quality by-products, and the waste acid water of iron-process phosphoric acid iron has not been resourcefully utilized. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to reduce the treatment cost of waste acid water generated in the iron-process phosphoric acid iron production process, and at the same time fully reuse the waste acid water and improve the purity of the by-product disodium hydrogen phosphate product. The present invention provides a method for resourcefully utilizing waste acid water of iron-process phosphoric acid iron.

[0006] The technical solution adopted by the present invention to solve its technical problems is: a method for resourcefully utilizing waste acid water of iron-process phosphoric acid iron, comprising the following steps:

[0007] S1. Pretreatment: Send the waste acid water generated in the iron-process phosphoric acid iron production process to an evaporation and concentration device for evaporation and concentration to obtain a concentrated phosphoric acid solution; the concentrated phosphoric acid solution is pumped into a raw water tank for storage and cooled to 38°C through a plate heat exchanger in a cycle;

[0008] S2. Ultrafiltration: The concentrated phosphoric acid solution is treated by an ultrafiltration membrane to obtain an ultrafiltration concentrate and an ultrafiltration permeate;

[0009] S3. Nanofiltration: The ultrafiltration permeate is treated by a nanofiltration membrane to obtain a nanofiltration concentrate and a nanofiltration permeate;

[0010] S4, Neutralization: Carry out a neutralization reaction on the ultrafiltration concentrate and nanofiltration concentrate to obtain a neutralized slurry;

[0011] S5, Filtration: Filter the neutralized slurry to remove the filter residue to obtain a filtrate;

[0012] S6, Evaporation and crystallization: Evaporate and concentrate the filtrate to obtain a concentrated solution, and then cool the concentrated solution to crystallize to obtain a crystal slurry;

[0013] S7, Centrifugation: Centrifuge the crystal slurry to obtain disodium hydrogen phosphate products and a secondary filtrate;

[0014] S8, Return the secondary filtrate obtained in S7 to step S6 for evaporation and crystallization; Send the nanofiltration filtrate obtained in step S3 to the iron dissolution process of the iron process for producing iron phosphate as a production raw material for the iron process for producing iron phosphate.

[0015] Further, in step S4, a 20 - 32% NaOH solution is added to the ultrafiltration concentrate and nanofiltration concentrate for neutralization reaction, and the pH of the reaction system is controlled to be 9.2 - 9.5, and the reaction temperature is 35 - 45°C.

[0016] Further, stirring is carried out during the neutralization reaction, and the stirring rate is 35 - 65 r / min.

[0017] Further, in step S6, an evaporation kettle with a jacket steam heating method is used for evaporation to obtain a concentrated solution with a water content of 60% - 70%, the evaporation temperature is 95 - 125°C, the vacuum degree is 50%, and the pH is 9.7 - 10.2; then circulating water is introduced into the jacket to cool the temperature of the concentrated solution below 35°C to obtain a crystal slurry with a concentration of 20% - 50%.

[0018] Further, the secondary steam generated after the jacket steam heating of the evaporation kettle in step S6 enters the condenser, and the condensed water is recycled for use in the iron phosphate device.

[0019] Further, in step S1, MVR evaporation and concentration is adopted to obtain a concentrated phosphoric acid solution with a mass concentration of 20% - 30%.

[0020] Further, before ultrafiltration in step S2, the concentrated phosphoric acid solution is cooled to below 40°C.

[0021] Further, the water content of the disodium hydrogen phosphate product obtained by centrifugal separation in step S7 is 10% - 15%.

[0022] Further, the pore size of the ultrafiltration membrane filtration element in step S2 is 50 - 100 nm, and the retention molecular weight is 20 KD - 200 KD; the operating pressure of the ultrafiltration membrane is 0.15 - 0.35 MPa, and the operating temperature is 25 - 45°C.

[0023] Further, the pore size of the nanofiltration membrane filtration element in step S3 is 4-6 nm, and the molecular weight cut-off is 1 KD-20 KD; the operating pressure of the nanofiltration membrane is 5.6-6.0 MPa, and the operating temperature is 25-45 °C.

[0024] The beneficial effects of the present invention are as follows: The resource utilization method of Tiefa iron phosphate waste acid water of the present invention adopts ultrafiltration, nanofiltration, evaporation crystallization, pressure filtration, and centrifugation processes, effectively removing harmful substances in the waste acid water, solving the problem that the quality is affected by the accumulation of impurities in the long-term reuse of waste phosphoric acid in the iron phosphate device, and at the same time realizing the full reuse and zero discharge of the waste acid water; combining with the precise on-line pH interlock control method to produce disodium hydrogen phosphate, by-product disodium hydrogen phosphate with a purity of more than 97%, and the conversion rate of disodium hydrogen phosphate production is greater than 95%. It not only improves the purity of the product but also increases the added value of the product;

[0025] The treatment process of the present invention is simple, easy to operate, and easy to realize industrial production; a large amount of chemicals are not added in the treatment process of the present invention, which not only reduces the treatment cost but also avoids secondary pollution. Specific embodiments

[0026] The present invention will be further described below in conjunction with embodiments.

[0027] A resource utilization method of Tiefa iron phosphate waste acid water includes the following steps:

[0028] S1. Source and pretreatment of waste acid water: The waste acid water generated by the Tiefa iron phosphate production process is sent to an evaporation and concentration device for evaporation and concentration to obtain a concentrated phosphoric acid solution; MVR evaporation and concentration can be used, and the mass concentration of the obtained concentrated phosphoric acid solution is 20-30%;

[0029] S2. Ultrafiltration: The concentrated phosphoric acid solution obtained in step S1 is cooled to below 40 °C, and then treated by an ultrafiltration membrane to obtain an ultrafiltration concentrate and an ultrafiltration filtrate; the pore size of the ultrafiltration membrane filtration element is 50-100 nm, and the molecular weight cut-off is 20 KD-200 KD; the operating pressure of the ultrafiltration membrane is 0.15-0.35 MPa, and the operating temperature is 25-45 °C; SS can be treated to below 0.1 ppm;

[0030] S3. Nanofiltration: The ultrafiltration filtrate is treated by a nanofiltration membrane to obtain a nanofiltration concentrate and a nanofiltration filtrate; the pore size of the nanofiltration membrane filtration element is 4-6 nm, and the molecular weight cut-off is 1 KD-20 KD; the operating pressure of the nanofiltration membrane is 5.6-6.0 MPa, and the operating temperature is 25-45 °C; metal ions such as Fe 3+ 、Ca 2+ 、Mg 2+ 、Mn 2+ 、Ti 2+etc., and non-metallic ion SO4 2- etc., and the COD removal rate reaches over 92%;

[0031] S4, Neutralization: Neutralize the ultrafiltration concentrate and nanofiltration concentrate to obtain a neutralized slurry; that is, add a 20 - 32% NaOH solution to the ultrafiltration concentrate and nanofiltration concentrate for neutralization reaction, control the pH of the reaction system to be 9.2 - 9.5, the reaction temperature to be 35 - 45°C, stir during the neutralization reaction, and the stirring rate to be 35 - 65 r / min;

[0032] S5, Filtration: Filter the neutralized slurry to remove the filter residue to obtain a filtrate; plate and frame filtration can be used. The filter residue is mainly Mg(OH)2, Fe(OH)3, Ca(OH)2, etc., which can be sold externally;

[0033] S6, Evaporation and Crystallization: Evaporate the filtrate using an evaporation kettle with a steam heating method for the kettle jacket to obtain a concentrated liquid with a water content of 60% - 70%. The evaporation temperature is 95 - 125°C, the time is 2 - 4 h, the vacuum degree is 50%, and the pH is 9.7 - 10.2; then circulate water in the jacket to lower the temperature of the concentrated liquid below 35°C to obtain a crystal slurry with a concentration of 20% - 50%; the secondary steam generated after the steam heating of the kettle jacket of the evaporation kettle enters the condenser, and the condensed water is recycled for use in the iron phosphate device; during the evaporation and concentration process, the pH of the system gradually increases. When the pH is in the range of 9.7 - 10.2, sodium dihydrogen phosphate is converted into disodium hydrogen phosphate;

[0034] S7, Centrifugation: Centrifuge the crystal slurry to obtain a disodium hydrogen phosphate product with a water content of 10% - 15% and a secondary filtrate;

[0035] S8, Return the secondary filtrate obtained in S7 to step S6 for evaporation and crystallization; send the nanofiltration filtrate obtained in step S3 to the iron dissolution process of the iron process for iron phosphate production as a production raw material for the iron process for iron phosphate production. The nanofiltration filtrate is a phosphoric acid solution with a mass concentration of 17 - 25%.

[0036] Example 1:

[0037] Collect the phosphorus-containing waste acid water such as the iron dissolution waste gas spray wastewater, iron slag filtration wastewater, process filtrate generated during the pressure spray process, and filter cake washing wastewater during the production process of the iron process for iron phosphate as waste acid water for standby. The main components of the waste acid water are shown in Table 1;

[0038] Treat the waste acid water of the iron process for iron phosphate according to the following method, including the following steps:

[0039] S1. Source and pretreatment of waste acid water: The waste acid water generated from the iron process for producing iron phosphate is sent to MVR for evaporation and concentration to obtain a concentrated phosphoric acid solution with a mass concentration of 25%; the concentrated phosphoric acid solution is sent to the raw water tank for storage and cooling, and the storage time is 2 hours; then the concentrated phosphoric acid solution is pumped into a plate heat exchanger to be cooled to 38 °C;

[0040] S2. Ultrafiltration: The concentrated phosphoric acid solution obtained after cooling in step S1 is sent to the ultrafiltration circulation water tank, and then pumped through a right-angle filter into the ultrafiltration device. After being treated by the ultrafiltration membrane, ultrafiltration concentrated liquid and ultrafiltration permeate are obtained; the pore size of the ultrafiltration membrane is 50 nm, and the molecular weight cut-off is 20 KD - 200 KD; the operating pressure of the ultrafiltration membrane is 0.15 MPa, and the operating temperature is 25 °C; the SS is treated to below 0.1 ppm; ultrafiltration adopts a circulating feed treatment method to remove macromolecular substances in the waste acid water;

[0041] S3. Nanofiltration: The ultrafiltration permeate obtained in step S2 passes through the nanofiltration membrane to obtain nanofiltration concentrated liquid and nanofiltration permeate; the pore size of the nanofiltration membrane is 4 nm, and the molecular weight cut-off is 1 KD - 20 KD; the operating pressure of the nanofiltration membrane is 5.8 MPa, the operating temperature is 27 °C, and the nanofiltration time is 8 h; metal ions such as Fe 3+ , Ca 2+ , Mg 2+ , Mn 2+ , Ti 2+ etc., and non-metal ions such as SO4 2- etc., and the COD removal rate reaches over 92%;

[0042] S4. Neutralization: The ultrafiltration concentrated liquid and the nanofiltration concentrated liquid are subjected to a neutralization reaction to obtain a neutralization slurry; that is, 30% NaOH solution is added to the ultrafiltration concentrated liquid and the nanofiltration concentrated liquid for neutralization reaction, controlling the pH of the reaction system to be 9.2 - 9.5, the reaction temperature to be 35 °C, stirring is carried out during the neutralization reaction, the stirring rate is 40 r / min, and the reaction time is 60 min;

[0043] S5. Filtration: The neutralization slurry is filtered by a plate and frame filter press to remove the filter residue to obtain a filtrate; the filter residue is mainly Mg(OH)2, Fe(OH)3, Ca(OH)2, etc., which can be sold externally;

[0044] S6. Evaporation and crystallization: The filtrate obtained in step S5 is evaporated in an evaporation kettle with a steam heating method for the kettle jacket, the evaporation temperature is 95 - 110 °C, the vacuum degree is 50%, to obtain a concentrated liquid with a water content of 60 - 65%, controlling the pH to be 9.7 - 10.2; then circulating water is introduced into the jacket to cool the temperature of the concentrated liquid below 35 °C to obtain a crystal slurry with a concentration of 25 - 28%; the secondary steam generated after the steam heating of the kettle jacket of the evaporation kettle enters the condenser, and the condensed water is recycled for use in the iron phosphate device;

[0045] S7, Centrifugation: Pump the crystal slurry into a centrifuge for centrifugal separation to obtain disodium hydrogen phosphate products with a water content of 12% and secondary filtrate.

[0046] S8. Return the secondary filtrate obtained in S7 to step S6 for evaporation and crystallization; send the nanofiltration filtrate obtained in step S3 to the iron dissolution process of the iron process for producing iron phosphate as a production raw material for the iron process for producing iron phosphate. The nanofiltration filtrate is a phosphoric acid solution with a mass concentration of 17.9%.

[0047] The nanofiltration filtrate and disodium hydrogen phosphate products obtained in S3 are respectively detected, and the results are shown in Table 2 and Table 3.

[0048] Example 2:

[0049] Collect the phosphorus-containing waste acid water such as the iron dissolution waste gas spray wastewater, iron slag filtration wastewater, process filtrate generated during the pressure spray process, and filter cake washing wastewater in the production process of the iron process for producing iron phosphate as spare waste acid water. The main components of the waste acid water are shown in Table 1.

[0050] Treat the waste acid water of the iron process for producing iron phosphate according to the following method, including the following steps:

[0051] S1. Source and pretreatment of waste acid water: Send the waste acid water generated in the iron process for producing iron phosphate to MVR for evaporation and concentration to obtain a concentrated phosphoric acid solution with a mass concentration of 23%; send the concentrated phosphoric acid solution to the raw water tank for storage and cooling, and the storage time is 2 hours; then use a pump to pump the concentrated phosphoric acid solution into a plate heat exchanger to cool it to 35°C.

[0052] S2. Ultrafiltration: Send the concentrated phosphoric acid solution obtained after cooling in step S1 to the ultrafiltration circulation water tank, and then use a pump to send it through a right-angle filter into the ultrafiltration device. After being treated by the ultrafiltration membrane, ultrafiltration concentrated liquid and ultrafiltration filtrate are obtained; the pore size of the ultrafiltration membrane is 70nm, and the molecular weight cut-off is 20KD - 200KD; the operating pressure of the ultrafiltration membrane is 0.20MPa, and the operating temperature is 30°C; treat the SS to below 0.1ppm; ultrafiltration adopts a circulating feed treatment method to remove macromolecular substances in the waste acid water.

[0053] S3. Nanofiltration: Pass the ultrafiltration filtrate obtained in step S2 through the nanofiltration membrane to obtain nanofiltration concentrated liquid and nanofiltration filtrate; the pore size of the nanofiltration membrane is 5nm, and the molecular weight cut-off is 1KD - 20KD; the operating pressure of the nanofiltration membrane is 5.6MPa, the operating temperature is 32°C, and the nanofiltration time is 8h; remove metal ions such as Fe 3+ , Ca 2+ , Mg 2+ , Mn 2+ , Ti 2+ etc., and non-metal ions such as SO4 2- etc., and the COD removal rate reaches more than 92%.

[0054] S4, Neutralization: Carry out a neutralization reaction on the ultrafiltration concentrate and the nanofiltration concentrate to obtain a neutralized slurry; that is, add a 30% NaOH solution to the ultrafiltration concentrate and the nanofiltration concentrate for neutralization reaction, control the pH of the reaction system to be 9.2 - 9.5, the reaction temperature to be 35 °C, stir during the neutralization reaction, the stirring rate is 40 r / min, and the reaction time is 60 min;

[0055] S5, Filtration: Filter the neutralized slurry with a plate and frame filter press to remove the filter residue, obtaining a filtrate; the filter residue is mainly Mg(OH)2, Fe(OH)3, Ca(OH)2, etc., which can be sold externally;

[0056] S6, Evaporation and crystallization: Evaporate the filtrate obtained in step S5 using an evaporation kettle with a steam heating method for the kettle jacket, the evaporation temperature is 95 - 110 °C, the vacuum degree is 50%, obtaining a concentrated solution with a water content of 60 - 65%, control the pH to be 9.7 - 10.2; then pass circulating water into the jacket to cool the temperature of the concentrated solution below 35 °C, obtaining a crystal slurry with a concentration of 26 - 29%; the secondary steam generated after the steam in the kettle jacket of the evaporation kettle is heated is condensed in the condenser, and the condensed water is recycled for use in the iron phosphate device;

[0057] S7, Centrifugation: Pump the crystal slurry into a centrifuge for centrifugal separation to obtain a disodium hydrogen phosphate product with a water content of 12% and a secondary filtrate;

[0058] S8, Return the secondary filtrate obtained in S7 to step S6 for evaporation and crystallization; send the nanofiltration filtrate obtained in step S3 to the iron dissolution process of the iron process iron phosphate production process for use as a production raw material in the iron process iron phosphate production process, and the nanofiltration filtrate is a phosphoric acid solution with a mass concentration of 17.6%.

[0059] Detect the nanofiltration filtrate and the disodium hydrogen phosphate product obtained in S3 respectively, and the results are shown in Table 2 and Table 3.

[0060] Example 3:

[0061] Treat the waste acid water of the iron process iron phosphate according to the following method, including the following steps:

[0062] S1, Source and pretreatment of waste acid water: Send the waste acid water generated in the iron process iron phosphate production process to MVR for evaporation and concentration to obtain a concentrated phosphoric acid solution with a mass concentration of 26%; send the concentrated phosphoric acid solution to the raw water tank for storage and cooling, and the storage time is 2 hours; then pump the concentrated phosphoric acid solution into a plate heat exchanger to cool it to 35 °C;

[0063] S2. Ultrafiltration: Feed the concentrated phosphoric acid solution obtained after cooling in step S1 into the ultrafiltration circulating water tank, and then use a pump to send it through a right-angle filter into the ultrafiltration device. After treatment by the ultrafiltration membrane, an ultrafiltration concentrate and an ultrafiltrate are obtained; the pore size of the ultrafiltration membrane is 60 nm, and the molecular weight cut-off is 20 KD - 200 KD; the operating pressure of the ultrafiltration membrane is 0.30 MPa, and the operating temperature is 40 °C; reduce SS to below 0.1 ppm; the ultrafiltration adopts a circulating feed treatment method to remove macromolecular substances in the waste acid water;

[0064] S3. Nanofiltration: Pass the ultrafiltrate obtained in step S2 through the nanofiltration membrane to obtain a nanofiltration concentrate and a nanofiltrate; the pore size of the nanofiltration membrane is 6 nm, and the molecular weight cut-off is 1 KD - 20 KD; the operating pressure of the nanofiltration membrane is 5.9 MPa, the operating temperature is 35 °C, and the nanofiltration time is 8 h; remove metal ions such as Fe 3+ , Ca 2+ , Mg 2+ , Mn 2+ , Ti 2+ etc., and non-metal ions such as SO4 2- etc., and the COD removal rate reaches over 92%;

[0065] S4. Neutralization: Carry out a neutralization reaction on the ultrafiltration concentrate and the nanofiltration concentrate to obtain a neutralization slurry; that is, add a 30% NaOH solution to the ultrafiltration concentrate and the nanofiltration concentrate for neutralization reaction, control the pH of the reaction system to be 9.2 - 9.5, the reaction temperature to be 40 °C, stir during the neutralization reaction, the stirring rate is 50 r / min, and the reaction time is 60 min;

[0066] S5. Filtration: Use a plate and frame filter press to remove the filter residue from the neutralization slurry to obtain a filtrate; the filter residue is mainly Mg(OH)2, Fe(OH)3, Ca(OH)2, etc., which can be sold externally;

[0067] S6. Evaporation and crystallization: Evaporate the filtrate obtained in step S5 using an evaporation kettle with a steam heating method for the kettle jacket, the evaporation temperature is 95 - 110 °C, the vacuum degree is 50%, to obtain a concentrated solution with a water content of 60 - 65%, and control the pH to be 9.9 - 10.2; then pass circulating water into the jacket to cool the temperature of the concentrated solution to 30 °C to obtain a crystal slurry with a concentration of 28 - 31%; the secondary steam generated after the steam heating of the kettle jacket of the evaporation kettle enters the condenser, and the condensed water is recycled for use in the iron phosphate device;

[0068] S7. Centrifugation: Pump the crystal slurry into a centrifuge for centrifugal separation to obtain a disodium hydrogen phosphate product with a water content of 15% and a secondary filtrate;

[0069] S8. Return the secondary filtrate obtained in S7 to step S6 for evaporation crystallization; send the nanofiltration filtrate obtained in step S3 to the iron dissolution process of the iron process for producing iron phosphate as a production raw material for the iron process for producing iron phosphate. The nanofiltration filtrate is a phosphoric acid solution with a mass concentration of 18.3%.

[0070] The nanofiltration filtrate and disodium hydrogen phosphate product obtained in S3 were respectively tested, and the results are shown in Table 2 and Table 3.

[0071] Comparative Example 1: (The pH of neutralization is different, and others are the same as Example 1)

[0072] Collect the waste acid water containing phosphorus such as the iron dissolution waste gas spray wastewater, iron slag filtration wastewater, process filtrate generated during the pressure spray process, and filter cake washing wastewater in the production process of the iron process for producing iron phosphate as waste acid water for standby. The main components of the waste acid water are shown in Table 1;

[0073] Treat the waste acid water of the iron process for producing iron phosphate according to the following method, including the following steps:

[0074] S1. Source and pretreatment of waste acid water: Send the waste acid water generated in the iron process for producing iron phosphate to MVR for evaporation and concentration to obtain a concentrated phosphoric acid solution with a mass concentration of 25%; send the concentrated phosphoric acid solution to the raw water tank for storage and cooling, and the storage time is 2 hours; then use a pump to send the concentrated phosphoric acid solution into a plate heat exchanger to cool it to 38°C;

[0075] S2. Ultrafiltration: Send the concentrated phosphoric acid solution obtained after cooling in step S1 into the ultrafiltration circulation water tank, and then use a pump to send it through a right-angle filter into the ultrafiltration device. After being treated by the ultrafiltration membrane, an ultrafiltration concentrate and an ultrafiltration filtrate are obtained; the pore size of the ultrafiltration membrane is 50 nm, and the molecular weight cut-off is 20 KD - 200 KD; the operating pressure of the ultrafiltration membrane is 0.15 MPa, and the operating temperature is 25°C; treat the SS to below 0.1 ppm; the ultrafiltration adopts a circulating feed treatment method to remove macromolecular substances in the waste acid water;

[0076] S3. Nanofiltration: Pass the ultrafiltration filtrate obtained in step S2 through the nanofiltration membrane to obtain a nanofiltration concentrate and a nanofiltration filtrate; the pore size of the nanofiltration membrane is 4 nm, and the molecular weight cut-off is 1 KD - 20 KD; the operating pressure of the nanofiltration membrane is 5.8 MPa, the operating temperature is 27°C, and the nanofiltration time is 8 h; remove metal ions such as Fe 3+ 、Ca 2+ 、Mg 2+ 、Mn 2+ 、Ti 2+ etc., and non-metal ions such as SO4 2- etc., and the COD removal rate reaches over 92%;

[0077] S4, Neutralization: Carry out a neutralization reaction on the ultrafiltration concentrate and the nanofiltration concentrate to obtain a neutralized slurry; that is, add a 30% NaOH solution to the ultrafiltration concentrate and the nanofiltration concentrate for neutralization reaction, control the pH of the reaction system to be 9.6 - 9.8, the reaction temperature to be 30°C, stir during the neutralization reaction, the stirring rate is 40 r / min, and the reaction time is 60 min;

[0078] S5, Filtration: Filter the neutralized slurry with a plate and frame filter press to remove the filter residue, obtaining a filtrate; the filter residue is mainly Mg(OH)2, Fe(OH)3, Ca(OH)2, etc., which can be sold externally;

[0079] S6, Evaporation and Crystallization: Evaporate the filtrate obtained in step S5 using an evaporation kettle with a jacket steam heating method, the evaporation temperature is 95 - 110°C, the vacuum degree is 50%, obtaining a concentrated solution with a water content of 60 - 65%, control the pH to be 9.7 - 10.2; then pass circulating water into the jacket to cool the temperature of the concentrated solution below 35°C, obtaining a crystal slurry with a concentration of 25 - 28%; the secondary steam generated after the jacket steam of the evaporation kettle is heated is condensed in a condenser, and the condensed water is recycled for use in the iron phosphate device;

[0080] S7, Centrifugation: Pump the crystal slurry into a centrifuge for centrifugal separation to obtain a disodium hydrogen phosphate product with a water content of 12% and a secondary filtrate;

[0081] S8, Return the secondary filtrate obtained in S7 to step S6 for evaporation and crystallization; Send the nanofiltration filtrate obtained in step S3 to the iron dissolution process of the iron process for iron phosphate production as a production raw material for the iron process for iron phosphate production, and the nanofiltration filtrate is a phosphoric acid solution with a mass concentration of 18.7%.

[0082] Detect the nanofiltration filtrate and the disodium hydrogen phosphate product obtained in S3 respectively, and the results are shown in Table 2 and Table 3.

[0083] Comparative Example 2: (The pH of neutralization and the pH of evaporation and crystallization are different, and the others are the same as Example 1)

[0084] Collect the phosphorus-containing waste acid water such as the iron dissolution waste gas spray wastewater, iron slag filtration wastewater, process filtrate generated during the pressure spray process, and filter cake washing wastewater in the production process of the iron process for iron phosphate as waste acid water for standby, and the main components of the waste acid water are shown in Table 1;

[0085] Treat the waste acid water of the iron process for iron phosphate according to the following method, including the following steps:

[0086] S1. Source and pretreatment of waste acid water: The waste acid water generated from the iron process for producing iron phosphate is sent to MVR for evaporation and concentration to obtain a concentrated phosphoric acid solution with a mass concentration of 25%; the concentrated phosphoric acid solution is sent to the raw water tank for storage and cooling, and the storage time is 2 hours; then the concentrated phosphoric acid solution is pumped into a plate heat exchanger to be cooled to 38°C;

[0087] S2. Ultrafiltration: The concentrated phosphoric acid solution obtained after cooling in step S1 is sent to the ultrafiltration circulation water tank, and then pumped through a right-angle filter into the ultrafiltration device. After being treated by the ultrafiltration membrane, ultrafiltration concentrated liquid and ultrafiltration filtrate are obtained; the pore size of the ultrafiltration membrane is 50 nm, and the molecular weight cut-off is 20 KD - 200 KD; the operating pressure of the ultrafiltration membrane is 0.15 MPa, and the operating temperature is 25°C; the SS is treated to below 0.1 ppm; ultrafiltration adopts a circulating feed treatment method to remove macromolecular substances in the waste acid water;

[0088] S3. Nanofiltration: The ultrafiltration filtrate obtained in step S2 passes through the nanofiltration membrane to obtain nanofiltration concentrated liquid and nanofiltration filtrate; the pore size of the nanofiltration membrane is 4 nm, and the molecular weight cut-off is 1 KD - 20 KD; the operating pressure of the nanofiltration membrane is 5.8 MPa, the operating temperature is 27°C, and the nanofiltration time is 8 h; metal ions such as Fe 3+ 、Ca 2+ 、Mg 2+ 、Mn 2+ 、Ti 2+ etc., and non-metal ions such as SO4 2- etc., and the COD removal rate reaches more than 92%;

[0089] S4. Neutralization: The ultrafiltration concentrated liquid and the nanofiltration concentrated liquid are subjected to a neutralization reaction to obtain a neutralization slurry; that is, a 30% NaOH solution is added to the ultrafiltration concentrated liquid and the nanofiltration concentrated liquid for neutralization reaction, and the pH of the reaction system is controlled to be 9.1 - 9.4, the reaction temperature is 36°C, stirring is carried out during the neutralization reaction, the stirring rate is 40 r / min, and the reaction time is 60 min;

[0090] S5. Filtration: The neutralization slurry is filtered by a plate and frame filter press to remove the filter residue to obtain a filtrate; the filter residue is mainly Mg(OH)2, Fe(OH)3, Ca(OH)2, etc., which can be sold externally;

[0091] S6. Evaporation and crystallization: The filtrate obtained in step S5 is evaporated in an evaporation kettle using the steam heating method of the kettle jacket, the evaporation temperature is 95 - 110°C, the vacuum degree is 50%, and a concentrated liquid with a water content of 60 - 65% is obtained, and the pH is controlled to be 9.2 - 9.5; then circulating water is introduced into the jacket to cool the temperature of the concentrated liquid below 35°C to obtain a crystal slurry with a concentration of 24 - 27%; the secondary steam generated after the steam in the jacket of the evaporation kettle is heated is condensed in the condenser, and the condensed water is recycled for use in the iron phosphate device;

[0092] S7. Centrifugation: Pump the crystal slurry into a centrifuge for centrifugal separation to obtain disodium hydrogen phosphate products with a water content of 12% and secondary filtrate.

[0093] S8. Return the secondary filtrate obtained in S7 to step S6 for evaporation crystallization; send the nanofiltration filtrate obtained in step S3 to the iron dissolution process of the iron phosphate production process as a production raw material for the iron phosphate production process. The nanofiltration filtrate is a phosphoric acid solution with a mass concentration of 18.5%.

[0094] Detect the nanofiltration filtrate and disodium hydrogen phosphate products obtained in S3 respectively, and the results are shown in Table 2 and Table 3.

[0095] Table 1 Metal ion and non-metal ion contents in waste acid water of examples and comparative examples

[0096]

[0097] Table 2 Detection of nanofiltration filtrate of examples and comparative examples

[0098]

[0099]

[0100] Table 3 Detection of disodium hydrogen phosphate products of examples and comparative examples

[0101] Conversion rate / % Disodium hydrogen phosphate / % Sodium dihydrogen phosphate / % Sodium phosphate / % Others / % Example 1 99.3 98.2 0.3 0.4 0.9 Example 2 99.2 97.9 0.4 0.4 1.3 Example 3 99.5 98.4 0.2 0.3 1.1 Comparative Example 1 99.3 97.6 0.3 0.4 1.7 Comparative Example 2 97.2 94.3 2.7 0.1 2.9

[0102] Conversion rate calculation: Concentration of hydrogen phosphate / (Concentration of hydrogen phosphate + Concentration of phosphate + Concentration of dihydrogen phosphate); Note: Other types of hydrogen phosphate salts are not included in the conversion rate statistics.

Claims

1. A method for resource utilization of iron process phosphoric acid iron waste acid water, characterized in that, It includes the following steps: S1. Pretreatment: Send the waste acid water generated by the Tiefa ferric phosphate production process to an evaporation and concentration device for evaporation and concentration to obtain a concentrated phosphoric acid solution; S2. Ultrafiltration: After treating the concentrated phosphoric acid solution through an ultrafiltration membrane, an ultrafiltration concentrate and an ultrafiltration filtrate are obtained; S3. Nanofiltration: After treating the ultrafiltration filtrate through a nanofiltration membrane, a nanofiltration concentrate and a nanofiltration filtrate are obtained; S4. Neutralization: Carry out a neutralization reaction on the ultrafiltration concentrate and the nanofiltration concentrate to obtain a neutralization slurry; S5. Filtration: Filter the neutralization slurry to remove the filter residue to obtain a filtrate; S6. Evaporation and crystallization: Evaporate and concentrate the filtrate to obtain a concentrated solution, and then cool the concentrated solution to crystallize to obtain a crystal slurry; S7. Centrifugation: Centrifugally separate the crystal slurry to obtain a disodium hydrogen phosphate product and a secondary filtrate; S8. Return the secondary filtrate obtained in S7 to step S6 for evaporation and crystallization; Send the nanofiltration filtrate obtained in step S3 to the iron dissolution process of the Tiefa ferric phosphate production process for use as a production raw material for the Tiefa ferric phosphate production process.

2. The resource utilization method of Tiefa iron phosphate waste acid water according to claim 1, characterized in that: In step S4, a 20-32% NaOH solution is added to the ultrafiltration concentrate and the nanofiltration concentrate for neutralization reaction, and the pH of the reaction system is controlled to be 9.2-9.5 and the reaction temperature is 35-45°C.

3. The resource utilization method of Tiefa iron phosphate waste acid water according to claim 2, characterized in that: Stirring is carried out during the neutralization reaction, and the stirring rate is 35-65 r / min.

4. A method for resource utilization of Tiefa iron phosphate waste acid water according to claim 1, characterized in that: In step S6, an evaporation kettle using a steam heating method with a jacket is used for evaporation to obtain a concentrated solution with a water content of 60%-70%, the evaporation temperature is 95-125°C, the vacuum degree is 50%, and the pH is 9.7-10.2; Then, circulating water is introduced into the jacket to cool the temperature of the concentrated solution below 35°C to obtain a crystal slurry with a concentration of 20%-50%.

5. The resource utilization method of Tiefa iron phosphate waste acid water according to claim 4, characterized in that: The secondary steam generated after the steam in the jacket of the evaporation kettle is heated in step S6 enters the condenser, and the condensed water is recycled for use in the ferric phosphate device.

6. A method for resource utilization of Tiefa iron phosphate waste acid water according to claim 1, characterized in that: In step S1, MVR evaporation and concentration is adopted, and the mass concentration of the obtained concentrated phosphoric acid solution is 20-30%.

7. A method for resource utilization of Tiefa iron phosphate waste acid water according to claim 1, characterized in that: Before ultrafiltration in step S2, the concentrated phosphoric acid solution is cooled to below 40°C.

8. The resource utilization method of Tiefa phosphoric acid iron waste acid water according to claim 1, characterized in that: The water content of the disodium hydrogen phosphate product obtained by centrifugal separation in step S7 is 10%-15%.

9. The resource utilization method of Tiefa phosphoric acid iron waste acid water according to claim 1 is characterized in that: The pore diameter of the ultrafiltration membrane filtration element in step S2 is 50-100 nm, and the molecular weight cut-off is 20 KD-200 KD; The operating pressure of the ultrafiltration membrane is 0.15-0.35 MPa, and the operating temperature is 25-45°C.

10. A method for resource utilization of Tiefa iron phosphate waste acid water according to claim 1, characterized in that: The pore diameter of the nanofiltration membrane filtration element in step S3 is 4-6 nm, and the molecular weight cut-off is 1 KD-20 KD; The operating pressure of the nanofiltration membrane is 5.6-6.0 MPa, and the operating temperature is 25-45°C.

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