Process for resource utilization of ammonia-process ferric phosphate production wastewater

Abstract

The patent discloses a device for recovering iron phosphate from ammonia-process iron phosphate production wastewater and a process and device for recycling wastewater resources, which comprises 1, an iron phosphate recovery system, 2, a wastewater pretreatment system, 3, a wastewater advanced treatment system, and 4, a salt recovery and water recovery system. First, a solid-liquid separation device is used to recover iron phosphate from wastewater, and the wastewater after recovering iron phosphate enters the pretreatment system, a two-stage reaction is used to strengthen the reaction process, and the wastewater after the reaction is separated from metal precipitates by a solid-liquid separation device, the metal precipitates are treated after being pressed and filtered; then, the wastewater is heat-exchanged, cooled and pH-adjusted, the washing water is concentrated by a first concentration device, mixed with mother liquor, enters an ion filter to deeply remove metal ions such as calcium, magnesium, iron and manganese, and the wastewater is concentrated by a second concentration device and enters an evaporation crystallization device. The iron phosphate in the wastewater is recovered, the ammonium sulfate salt in the wastewater is recovered, and the water is reused.

Description

TECHNICAL FIELD

[0001] The present application relates to a process for resource utilization of ammonia-process iron phosphate production wastewater, belonging to the field of water treatment. BACKGROUND

[0002] In recent years, with the rapid development of the new energy automobile industry, the demand for iron phosphate, which is the precursor of lithium iron phosphate as the positive electrode material of the battery, has increased sharply. According to statistics, as of July 2021, the total production capacity of iron phosphate in China reached 351,000 tons / year, and it is estimated that by the end of 2022, the expansion capacity of iron phosphate with a clear timetable will reach 585,000 tons / year. About 40 tons of wastewater is generated per ton of iron phosphate produced, and the expansion capacity generates about 23.4 million tons of wastewater, mainly ammonia-process iron phosphate production wastewater. Ammonia-process iron phosphate production wastewater is acidic, with high salt content, high ammonia nitrogen, high phosphorus content, and high content of metal ions such as calcium, magnesium, iron, and manganese. A small amount of silicon and fluorine is also contained in the wastewater. The traditional discharge standard approach is not suitable for this wastewater, so the zero-emission process for ammonia-process iron phosphate production wastewater is of great concern. SUMMARY

[0003] The purpose of the present application is to solve the problem that the existing ammonia-process iron phosphate production wastewater zero-emission process cannot recover the iron phosphate in the wastewater and the recovered salt has low quality. Through the integration of iron phosphate recovery device, solid-liquid separation device, adjustment and heat exchange device, ion filter, concentration device, and evaporation crystallization device, not only is the ammonia-process iron phosphate wastewater zero-emission achieved, but also the resource utilization of iron phosphate and ammonium sulfate salt in the wastewater is achieved. At the same time, the operation process of the solid-liquid separation device is optimized, which can make the solid-liquid separator have a good recovery rate under the condition of less cleaning cost.

[0004] A process for resource utilization of ammonia-process iron phosphate production wastewater, comprising the following steps:

[0005] Step 1: solid-liquid separation of ammonia-process iron phosphate production wastewater to recover iron phosphate particles; the wastewater is crystallization mother liquor or washing water;

[0006] Step 2: adding an oxidizing agent and a pH adjusting agent to the filtrate obtained in step 1 to perform oxidation and precipitation reactions, respectively;

[0007] Step 3: solid-liquid separation of the wastewater obtained in step 2 to remove the precipitate;

[0008] Step 4: removing manganese with a manganese sand filter and removing impurity metal ions with ion exchange resin after the filtrate obtained in step 3;

[0009] Step 5: concentrating the wastewater obtained in step 4 and performing step-by-step evaporation crystallization to obtain ammonium sulfate and ammonium phosphate in sequence.

[0010] In step 2, the oxidant is hydrogen peroxide; the amount added is 100-500 ppm.

[0011] The pH adjuster in step 2 is ammonia; the pH is adjusted to 8-11.

[0012] The concentration process in step 5 is to make the salt content in the wastewater greater than 15 wt%.

[0013] The solid-liquid separation in steps 1 and 3 uses microfiltration or ultrafiltration membranes.

[0014] After solid-liquid separation in step 3, the filter membrane is sequentially cleaned with alkaline and acidic cleaning solutions in a cross-flow manner to restore membrane flux. During the cross-flow process, the flow velocity at the membrane surface is 1-10 m / s. The alkaline cleaning solution is a 0.1-0.5 wt% NaOH solution, and the acidic cleaning solution is a 0.1-0.5 wt% HCl solution.

[0015] The cleaning process described above, specifically the cleaning time with the acidic cleaning solution, is calculated using the following steps:

[0016] Step S1: Obtain data on the change of membrane flux over time during the solid-liquid separation process, and perform interpolation processing to obtain the original dataset;

[0017] Step S2: Iterate through the data points in the original dataset in turn, fit all data points before the current data point according to Equation (1), and fit all data points after the current data point according to Equation (2).

[0018]

[0019]

[0020] In the formula J v It is flux, J0 is the initial flux of the membrane; K cake These are the fitting parameters; K standard These are the fitting parameters; t is time.

[0021] The average value R of the correlation coefficients of the fitting results of equations (1) and (2) were obtained respectively. ave = (R1+R2) / 2;

[0022] After iterating through all data points, select the one with the smallest R. ave The time corresponding to the data point of the value is taken as the time point when membrane pore blockage fouling transforms into filter cake fouling.

[0023] Step S3: Calculate the membrane pore fouling resistance R based on the flux at the time point of fouling transformation. p The filter cake fouling resistance R is calculated based on the flux after all filtration is completed.c The membrane material resistance R is calculated based on the initial flux of the membrane. m ;

[0024] Step S4: After cleaning the membrane with alkaline cleaning solution, different acid washing times t2 are selected for cleaning. Equation (3) is fitted according to the flux after cleaning:

[0025] R' p ==(R total -R m )×(1-a×t2 b (3)

[0026] R' p It is the resistance to fouling and blockage of membrane pores after cleaning, R total t1 is the total resistance of the membrane after cleaning, t2 is the cleaning time of the acidic cleaning solution, and a and b are parameters.

[0027] Step S5 involves further filtration, alkaline cleaning, and acidic cleaning of the wastewater. The membrane pore fouling resistance R is calculated based on the data showing the change in membrane flux over time. p , R' p =α×R' p The membrane pore fouling resistance after the cleaning target is achieved is substituted into equation (3) to calculate the optimal acid cleaning time; where α is the set coefficient.

[0028] The value of α is between 0.01 and 0.1.

[0029] The interpolation mentioned is spline interpolation.

[0030] An apparatus for the resource utilization of wastewater from ammonia-based ferric phosphate production, comprising:

[0031] The first solid-liquid separation device is used to separate iron phosphate particles from wastewater;

[0032] The reaction tank is connected to the first solid-liquid separation device and is used to perform oxidation and precipitation reactions on the filtrate obtained from the first solid-liquid separation device.

[0033] The second solid-liquid separation device is connected to the reaction tank and is used to separate the precipitate in the wastewater after the reaction.

[0034] A manganese sand filter, connected to the second solid-liquid separation device, is used to treat the filtrate obtained from the second solid-liquid separation device by removing manganese ions with manganese sand;

[0035] An ultrafiltration membrane, connected to a manganese sand filter, is used to filter wastewater after manganese ion removal treatment.

[0036] An ion exchange resin column is connected to an ultrafiltration membrane and is used to remove metal ions from the filtrate obtained from the ultrafiltration membrane.

[0037] An evaporator crystallizer, connected to an ion exchange resin column, is used to evaporate and crystallize wastewater to obtain ammonium phosphate and ammonium sulfate.

[0038] It also includes a hydrogen peroxide addition tank and an ammonia addition tank, which are connected to the reaction tank respectively and are used to add hydrogen peroxide and ammonia.

[0039] The first and second solid-liquid separation devices are microfiltration membranes or ultrafiltration membranes.

[0040] The average pore size range of the first solid-liquid separation device and / or the second solid-liquid separation device is 50-200 nm.

[0041] The second solid-liquid separation device is connected to the manganese sand filter via the first concentration device.

[0042] The ion exchange resin column is connected to the evaporator crystallizer via a second concentration device.

[0043] The dilute outlet of the second concentration unit is connected to the third concentration unit.

[0044] The first, second, or third concentration device is a reverse osmosis membrane.

[0045] The evaporator crystallizer is a multi-effect evaporator or an MVR evaporator.

[0046] The average pore size of ultrafiltration membranes ranges from 10 to 50 nm.

[0047] Beneficial effects

[0048] This invention achieves zero wastewater discharge and recovers ferric phosphate and ammonium sulfate from wastewater. Ferric phosphate is recovered through a solid-liquid separation membrane, while ammonium sulfate is recovered through precipitation reaction, solid-liquid separation membrane, ion filter, concentration device, and evaporation crystallization device. The ammonium phosphate can be sold as a product for use in fertilizer production. Attached Figure Description

[0049] Figure 1 This is a flowchart of the patent;

[0050] Figure 2 This is a diagram of the device in this patent;

[0051] Figure 3 This is a graph showing the operational flux variation of the separation membrane in this patent.

[0052] Figure 4 This is a schematic diagram of the membrane fouling mechanism;

[0053] Figure 5is the correlation coefficient graph in the pollution conversion node determination process;

[0054] Figure 6 is the membrane flux data graph under different cleaning times.

[0055] Wherein, 1, first solid-liquid separation device;2, reaction tank;3, second solid-liquid separation device;4, first concentration device;5, manganese sand filter;6, ultrafiltration membrane;7, ion exchange resin column;8, second concentration device;9, evaporative crystallizer;10, third concentration device;2-1, hydrogen peroxide addition tank;2-2, ammonia water addition tank. DETAILED DESCRIPTION

[0056] The patent discloses a device for recovering iron phosphate from ammonia method iron phosphate production wastewater and a process and device for wastewater resource utilization, which mainly comprises 1, an iron phosphate recovery system, 2, a wastewater pretreatment system, 3, a wastewater advanced treatment system, and 4, a salt recovery and water recovery system. First, the solid-liquid separation device is used to recover the iron phosphate in the wastewater, and after the recovery of the iron phosphate, the wastewater enters the pretreatment system, a two-stage reaction is used to strengthen the reaction process, and after the reaction, the metal precipitate is separated from the water through the solid-liquid separation device, and the metal precipitate is treated after being pressed into a cake. Then, the wastewater is subjected to heat exchange cooling and pH adjustment, the washing water is concentrated through the first concentration device, mixed with the mother liquor, and then enters the ion filter to remove metal ions such as calcium, magnesium, iron and manganese, the wastewater is concentrated through the second concentration device, and then enters the evaporative crystallization device, and the water produced by the first and second concentration devices is treated through the third concentration device, and then the produced water is reused. Not only the recovery of the iron phosphate in the wastewater is realized, but also the recovery of the ammonium sulfate salt in the wastewater is realized, and the water is reused.

[0057] The production process of the ammonia method iron phosphate mentioned in the application mainly comprises the following steps: firstly, ferrous sulfate and ammonium phosphate are mixed, then subjected to oxidation treatment, and then subjected to reaction in a reaction kettle, so that the reaction product is obtained, the filter cake is obtained through plate and frame filtration, and the synthetic mother liquor is obtained in the plate and frame.

[0058] The wastewater of the ammonia method iron phosphate suitable for the application mainly refers to the mother liquor obtained after centrifugal separation in the production process and the washing water of the product, and in an embodiment, the water quality of the two kinds of wastewater is as follows:

[0059] Table 1

[0060]

[0061]

[0062] The main pollution characteristics of the wastewater are that a large amount of sulfate ions, phosphate ions and ammonia nitrogen are contained, and in addition, some other metal ions are also contained, and the wastewater also contains certain organic pollutants.

[0063] The resource utilization process of the ammonia-process ferric phosphate production wastewater of the present application comprises the following steps:

[0064] First, the ferric phosphate production mother liquor and washing water are used to recover ferric phosphate by a solid-liquid separation membrane; the solid-liquid separation membrane is an ultrafiltration membrane or a microfiltration membrane, and the average pore size of the solid-liquid separation membrane ranges from 50 nm to 200 nm; in this step, the suspended particles of ferric phosphate in the wastewater can be recovered by precision filtration, and the cross-flow filtration method is mainly used in the filtration process, and the cross-flow membrane surface flow rate can be 1-10 m / s; the ultrafiltration membrane or the microfiltration membrane herein can be made of ceramic material or polymer material.

[0065] Next, hydrogen peroxide and ammonia are added to the mother liquor and washing water after the recovery of ferric phosphate, so that the metal ions such as calcium, magnesium, iron and manganese in the wastewater are precipitated, and the generated precipitates mainly include magnesium hydroxide, iron hydroxide, manganese hydroxide, ammonium magnesium phosphate and calcium phosphate; the main function of this step is to precipitate metal ions and remove organic matter; the necessity of adding hydrogen peroxide lies in that, on the one hand, it converts divalent iron into trivalent iron, accelerating the precipitation reaction of metal impurities, and on the other hand, it forms a Fenton system with iron ions under acidic conditions, degrading organic matter in the wastewater; the hydrogen peroxide addition amount is one ten-thousandth to five ten-thousandths, and the ammonia adjusts the pH range to 8-11; the reaction tank is provided with a baffle, which is used to mix the hydrogen peroxide, ammonia and wastewater better; the solid-liquid separation membrane is an ultrafiltration membrane or a microfiltration membrane, and the average pore size of the solid-liquid separation membrane ranges from 50 nm to 200 nm; the washing water after the precipitation reaction first enters the solid-liquid separation membrane, and the concentrated water of the solid-liquid separation membrane then enters the plate and frame dehydration; the mother liquor after the precipitation reaction first enters the plate and frame dehydration, and the plate and frame filtrate then enters the solid-liquid separation membrane; the purpose of this step is to completely separate the precipitate from water, and the turbidity of the produced water is 0.1-0.3 NTU, ensuring that the wastewater SDI is ≤3, and the Ca 2+ <5ppm, Mg 2+ <3ppm, Fe 2+ / 3+ <3ppm, Mn 2+<3ppm, COD<10ppm. Specifically, during operation, the washing water after the precipitation reaction removes metal precipitates through a 2# solid-liquid separation membrane, the concentrated water of the 2# solid-liquid separation membrane enters a 2# plate and frame system for dehydration of the precipitate, the 2# plate and frame filtrate returns to the front end of the 2# solid-liquid separation membrane, and the water produced by the 2# solid-liquid separation membrane enters the first reverse osmosis after adjustment and heat exchange for concentration. The main purpose of this step is to increase the salt concentration of the washing water to about 6% close to the mother liquor. The mother liquor after the precipitation reaction enters a 1# plate and frame system for dehydration of the precipitate, the 1# plate and frame filtrate enters a 1# solid-liquid separation membrane to remove metal precipitates, the concentrated water of the 1# solid-liquid separation membrane returns to the front end of the 1# plate and frame, and the water produced by the 1# solid-liquid separation membrane is mixed with the concentrated water of the first reverse osmosis after adjustment and heat exchange. In this step, the precipitate generated contains suspended particles, hydroxide colloids, and small molecules of organic matter generated by oxidation, which can cause membrane pore blockage and surface filter cake pollution of the solid-liquid separation membrane, and the filtration and membrane cleaning process needs to be optimized and improved. The wastewater after removing the precipitate by the solid-liquid separation membrane enters the adjustment heat exchanger, and the main function of this step is to heat exchange and cool the wastewater. During operation, the pH of the wastewater needs to be adjusted to neutral, the pH adjustment range of the washing water is 6-9, and the temperature adjustment range is 20-40℃. The first concentration device, the second concentration device, and the third concentration device are selected from reverse osmosis devices.

[0066] The membrane element used in the first concentration device is a reverse osmosis membrane element, and the form of the membrane includes but is not limited to a roll-type membrane and a disc-type reverse osmosis membrane element. The desalination rate of the membrane element is not less than 97%, the operating temperature of the first concentration device is not more than 45℃, and the operating pressure is 0.1-5Mpa.

[0067] The membrane element used in the second concentration device is a reverse osmosis membrane element, and the form of the membrane includes but is not limited to a roll-type membrane and a disc-type reverse osmosis membrane element. The desalination rate of the membrane element is not less than 97%, the filtration temperature of the second concentration device is not more than 45℃, the operating pressure is 0.1-10MPa, and the concentration of the concentrated brine obtained after concentration is 10-15%.

[0068] The membrane element used in the third concentration device is a reverse osmosis membrane element, and the form of the membrane includes but is not limited to a roll-type membrane and a disc-type reverse osmosis membrane element. The desalination rate of the membrane element is not less than 97%, the operating temperature of the third concentration device is not more than 45℃, and the operating pressure is 0.1-2Mpa.

[0069] Next, the mixed wastewater enters an ion filter to further remove metal ions such as calcium, magnesium, iron and manganese. The main purpose of this step is to further reduce the content of metal ions such as calcium, magnesium, iron and manganese in the wastewater, so that Ca 2+ <1ppm, Mg 2+ <1ppm, Fe 2+ / 3+ <0.5ppm, Mn 2+<0.5ppm, to avoid metal ion fouling in subsequent membrane concentration process, ion filter contains manganese sand, ultrafiltration and ion exchange resin, and the wastewater is sequentially subjected to manganese sand, ultrafiltration and ion exchange resin, the necessity of which is that the wastewater is first subjected to manganese sand to remove iron and manganese ions to effectively prevent ion exchange resin poisoning, the purpose of setting ultrafiltration after manganese sand is to prevent colloids and particles in the water produced by manganese sand from entering ion exchange resin, and finally the wastewater is subjected to ion exchange resin to remove calcium and magnesium ions; the filtration rate of manganese sand is 10-20 m / h, and the filtration rate of ion exchange resin is 10-30 BV / h. The water produced by the ion filter enters the second reverse osmosis device for concentration, and the main purpose of this step is to increase the salt concentration of the wastewater to about 15%. The concentrated water of the second reverse osmosis device enters the evaporation crystallization device to recover ammonium phosphate and ammonium sulfate, and the main function of this step is to obtain ammonium sulfate and ammonium phosphate through evaporation crystallization. The evaporation crystallizer is selected from a multiple-effect evaporator or an MVR evaporator. The water produced by the second reverse osmosis device is mixed with the water produced by the first reverse osmosis device and then enters the third reverse osmosis device for desalination. The water produced by the third reverse osmosis device is used for production, and the conductivity is less than 10 mu s / cm. The process described in the present application not only realizes the recovery of iron phosphate, but also realizes the recovery of ammonium sulfate in the wastewater on the basis of the reuse of iron phosphate production wastewater. Through the system, the ammonia method iron phosphate production wastewater realizes zero discharge and resource utilization.

[0070] When the material liquid after peroxidation and precipitation is subjected to cross-flow filtration by using a solid-liquid separation membrane, the general operation flux curve is as shown in Figure 3 In the initial stage of filtration, the flux rapidly decreases, and in this process, the main phenomenon is the in-pore blocking of the membrane. Since the hydroxide colloidal particles generated by precipitation are small in size, they are easy to drill into the membrane pores, as shown in the left half of Figure 4 When the membrane pore blocking occurs to a certain stage, the main phenomenon is the generation of filter cake on the surface of the membrane, which is filter cake layer pollution, as shown in the right half of Figure 4 In the process of membrane cleaning, the filter cake layer can be easily removed by cross-flow flushing, because it is on the surface of the membrane and is not easy to adhere to the surface of the membrane under the impact of water flow. However, the main membrane pore blocking pollution in the membrane pores, which is mainly metal oxide, is not easy to be removed by cross-flow, mainly because the acid cleaning solution seeps into the pores slowly, and a long time of cross-flow, entrainment, dissolution and other methods are needed to remove the blocking particles in the membrane pores. However, if the cleaning time is set too long, the energy consumption will increase, and if the cleaning time is too short, the membrane pore blocking cannot be removed. Therefore, how to predict the cleaning operation conditions according to the solid-liquid separation situation is conducive to accurately controlling the membrane cleaning in the implementation process of the method.

[0071] The technical concept of the prediction method of the present application is:

[0072] (a), as Figure 3As shown, the first step is to collect data on membrane flux decay in solid-liquid separation. After collection, interpolation is performed according to time nodes to make the collected data points more refined and uniform, ensuring that flux data exists at each time node.

[0073] (b) The data points on the flux decay curve are traversed sequentially and fitted, that is: on the time axis, all data points before the current traversal node are fitted according to Equation 1 (Hemia model for filter cake generation).

[0074]

[0075] In the formula J v It is flux, J0 is the initial flux of the membrane; K cake These are the fitting parameters; t is time.

[0076] Then, on the time axis, take all data points after the current traversed node and fit them according to Equation 2 (Particle Blockage Hemia Model);

[0077]

[0078] In the formula J v It is flux, J0 is the initial flux of the membrane; K standard These are the fitting parameters; t is time.

[0079] Then, the average correlation coefficient R of the two fitted curves is calculated. ave = (R1+R2) / 2;

[0080] The entire dataset is iterated through, and the minimum correlation coefficient is taken from the average of all obtained correlation coefficients. Since this correlation coefficient is the minimum, it can be assumed that a transition from membrane pore clogging to cake fouling occurred at this current iteration point. Therefore, all events occurring before this time point are considered membrane pore clogging fouling, while all flux declines occurring after this time point are due to cake formation. The membrane pore clogging fouling resistance R can then be calculated based on Darcy's law and the flux at the time of the fouling type transition. p The filter cake fouling resistance R is calculated based on the flux after all filtration is completed. c The membrane material resistance R is calculated based on the initial flux of the membrane. m .

[0081] (c) During membrane cleaning, the membrane surface must first be rinsed with alkaline water to remove the filter cake layer contaminants. Since the filter cake layer is relatively easy to wash away, a fixed rinsing time t1 is usually used, and a time limit R is set after the cleaning and rinsing process and after the filter cake is removed. c= 0; for the membrane hole blockage, it is necessary to use pickling depth cleaning to remove the blockage in the membrane hole, and the rinse time t2 of the process is proportional to the removal rate N, the patent finds that the removal efficiency is higher when the initial cleaning is carried out, because the particles close to the middle of the membrane hole are easily carried away by diffusion, and when the cleaning is carried out in the later period, the removal rate begins to decrease, then the flux recovery rate %N = a x t2 b ; wherein, a and b are parameters, and t2 is the pickling time. Then after a certain pickling time, the membrane hole blockage pollution resistance is as shown in formula 3:

[0082] R' p = R p ×(1-N)=R p ×(1-a×t2 b )=(R total -R m )×(1-a×t2 b ); (3)

[0083] R total is the total resistance of the membrane layer after cleaning;

[0084] In the experiment, different pickling times t2 can be selected to obtain R' p , and the parameters a and b are obtained by parameter fitting.

[0085] (d), the material is filtered again, R' p is calculated according to step (b), R' p = 0.05 x R' p is the membrane hole pollution after the completion of the cleaning setting target, which is substituted into formula 3 to obtain the optimal acid cleaning time in this case.

[0086] Based on the above process, the device structure used in the patent is as shown in Figure 2 , which comprises:

[0087] The first solid-liquid separation device 1 is used for separating the iron phosphate particles in the wastewater;

[0088] The reaction tank 2 is connected to the first solid-liquid separation device 1, and is used for oxidation and precipitation reaction of the filtrate obtained by the first solid-liquid separation device 1;

[0089] The second solid-liquid separation device 3 is connected to the reaction tank 2, and is used for separating the precipitate in the wastewater after reaction;

[0090] The manganese sand filter 5 is connected to the second solid-liquid separation device 3, and is used for removing manganese ions from the filtrate obtained by the second solid-liquid separation device 3 by using manganese sand;

[0091] A ultrafiltration membrane 6 connected to the manganese sand filter 5, for filtering the wastewater treated by removing manganese ions;

[0092] An ion exchange resin column 7 connected to the ultrafiltration membrane 6, for removing metal ions from the filtrate obtained from the ultrafiltration membrane 6;

[0093] An evaporative crystallizer 9 connected to the ion exchange resin column 7, for evaporative crystallization of the wastewater to obtain ammonium phosphate and ammonium sulfate;

[0094] Further comprising a hydrogen peroxide adding tank 2-1 and an ammonia water adding tank 2-2, respectively connected to the reaction tank 2, for adding hydrogen peroxide and ammonia water respectively.

[0095] The first solid-liquid separation device 1 and the second solid-liquid separation device 3 are microfiltration membranes or ultrafiltration membranes.

[0096] The average pore size of the first solid-liquid separation device 1 and / or the second solid-liquid separation device is in the range of 50-200 nm.

[0097] The second solid-liquid separation device 3 is connected to the manganese sand filter 5 through the first concentration device 4.

[0098] The ion exchange resin column 7 is connected to the evaporative crystallizer 9 through the second concentration device 8.

[0099] The dilute liquid outlet of the second concentration device 8 is connected to the third concentration device 10.

[0100] The first concentration device 4, the second concentration device 8 or the third concentration device 10 are reverse osmosis membranes.

[0101] The evaporative crystallizer 9 is a multiple-effect evaporator or an MVR evaporator.

[0102] The average pore size of the ultrafiltration membrane 6 is in the range of 10-50 nm.

[0103] Example 1

[0104] Zero-emission recovery process of wastewater from ammonia method of iron phosphate production:

[0105] The mother liquor and the washing water are recovered respectively, and the water quality is shown in Table 1 respectively.

[0106] (1) First, the washing water is filtered by a 200 nm ceramic microfiltration membrane to obtain the suspended iron phosphate particles therein (further concentrated and recovered by plate and frame filtration if necessary), and the flow rate is 3 m / s in cross flow; hydrogen peroxide is added to the permeate for oxidation treatment, the oxidation reaction time is 60 min, and ammonia is added to adjust the pH to about 9.0 after the reaction, so that the metal ions therein form a precipitate, which is filtered by a 50 nm ceramic ultrafiltration membrane to obtain the precipitate (further concentrated and recovered by plate and frame filtration if necessary); the COD of the filtrate of the ceramic ultrafiltration membrane obtained is 15 ppm, which is concentrated by a reverse osmosis membrane;

[0107] The mother liquor is filtered by a 200 nm ceramic microfiltration membrane to obtain the suspended iron phosphate particles therein (further concentrated and recovered by plate and frame filtration if necessary), and the flow rate is 4 m / s in cross flow; hydrogen peroxide is added to the permeate for oxidation treatment, the oxidation reaction time is 70 min, and ammonia is added to adjust the pH to about 9.5 after the reaction, so that the metal ions therein form a precipitate, which is filtered by a 50 nm ceramic ultrafiltration membrane to obtain the precipitate, and the COD of the filtrate of the ultrafiltration membrane is 76 ppm, and the concentrated solution of the ultrafiltration membrane is further concentrated and recovered by plate and frame filtration if necessary;

[0108] (2) The reverse osmosis membrane concentrated solution and the filtrate of the ultrafiltration membrane obtained in step (1) are mixed, and ion exchange treatment is performed by an ion filter composed of a manganese sand filter, an ultrafiltration membrane, and an ion exchange resin connected in sequence, and the ion exchange resin is used to further remove residual metal ions to improve the purity of the recovered ammonium sulfate, and the ion exchange resin used here can be 001 x 7 sodium ion exchange resin.

[0109] The main metal ion content of the ion exchange resin product water is as follows:

[0110] Ca 2+ ]] 0.82 mg / L Mg 2+ ]]> 0.33 mg / L Fe 2+ / 3+ ]] 0.58 mg / L Mn 2+ ]] 0.06 mg / L Zn 2+ ]] 0.4 mg / L

[0111] (3) After the ion exchange resin column, the reverse osmosis membrane is used for further concentration, so that the salt concentration is increased to more than 15%, and then evaporation crystallization is carried out. The evaporation crystallization system is used to treat the crystal by step crystallization. According to the content and solubility of ammonium sulfate and ammonium phosphate, the ammonium sulfate crystal is precipitated by evaporation and concentration to supersaturation. After the crystal is precipitated by the evaporation crystallization system, it is pumped to the thickener for crystal collection. After a certain amount of crystallization is collected, it is discharged to the centrifuge for solid-liquid separation to obtain ammonium sulfate wet salt. The ammonium sulfate crystal is sent to the boiling fluidized bed A for drying and then enters the packing machine to obtain the ammonium sulfate product. The mother liquor 1 is returned to the MVR for evaporation. When the ammonium phosphate concentration reaches the design value, the centrifugal mother liquor 1 is discharged to the refrigeration crystallization system for refrigeration crystallization to precipitate ammonium phosphate crystal. After centrifugal separation, ammonium phosphate wet salt is obtained, which is dried by the boiling fluidized bed B and then enters the packing machine to obtain the ammonium phosphate product. The centrifugal mother liquor 2 is returned to the single-effect MVR for evaporation and crystallization of ammonium sulfate crystal and refrigeration crystallization of ammonium phosphate crystal. A small part of the mother liquor 3 needs to be discharged to the drum drying system to remove impurities to ensure the purity of the crystal. Finally, 98.5% ammonium sulfate and 97.1% ammonium phosphate are obtained. The permeate of the reverse osmosis membrane is concentrated again, and the concentrated solution is returned to the evaporation crystallization treatment. The conductivity of the permeate is less than 7 μs / cm.

[0112] Example 2

[0113] Zero discharge recovery treatment process of ammonia method of iron phosphate production wastewater:

[0114] The mother liquor and the washing water are recovered respectively, and the water quality is shown in Table 1.

[0115] (1) First, the washing water is filtered by using a ceramic microfiltration membrane with a pore size of 100 nm to obtain the suspended particles of iron phosphate (which needs to be further concentrated and recovered by using a plate and frame filter). The cross-flow flow rate is 2 m / s. Hydrogen peroxide is added to the permeate for oxidation treatment. The oxidation reaction time is 45 min. After the reaction, ammonia water is added to adjust the pH to about 8.5, so that the metal ions in the solution form a precipitate. The precipitate is filtered by using a ceramic ultrafiltration membrane with a pore size of 50 nm to obtain the precipitate (which needs to be further concentrated and recovered by using a plate and frame filter). The COD of the filtrate obtained by the ceramic ultrafiltration membrane is 13 ppm, which is concentrated by using a reverse osmosis membrane;

[0116] The mother liquor is filtered by using a ceramic microfiltration membrane with a pore size of 200 nm to obtain the suspended iron phosphate particles therein (if necessary, further concentrated and recovered by plate-and-frame filtration), and the permeate is treated by adding hydrogen peroxide, and the oxidation reaction is performed for 90 min. After the reaction, ammonia is added to adjust the pH to about 9.0, so that the metal ions therein form a precipitate. The precipitate is filtered by using a ceramic ultrafiltration membrane with a pore size of 50 nm to obtain the precipitate, and the filtrate of the ultrafiltration membrane has a COD of 68 ppm. If necessary, the concentrated solution of the ultrafiltration membrane is further concentrated and recovered by plate-and-frame filtration.

[0117] (2) The reverse osmosis membrane concentrated solution and the filtrate of the ultrafiltration membrane obtained in step (1) are mixed, and ion exchange treatment is performed by using an ion filter composed of a manganese sand filter, an ultrafiltration membrane, and ion exchange resin connected in sequence. The ion exchange resin is used to further remove residual metal ions, so that the purity of the recovered ammonium sulfate is improved. The ion exchange resin used herein can be 001 x 7 sodium ion exchange resin.

[0118] The main metal ion content of the water produced by the ion exchange resin is as follows:

[0119] Ca 2+ ]]> 0.75 mg / L Mg 2+ ]] 0.43 mg / L Fe 2+ / 3+ ]]> 0.28 mg / L Mn 2+ ]] 0.19 mg / L Zn 2+ ]] 0.6 mg / L

[0120] (3) After the water produced by the ion exchange resin column is obtained, further concentration is performed by using a reverse osmosis membrane, so that the salt concentration is increased to more than 15%, and then evaporation crystallization is performed. The evaporation crystallization is treated by using a step crystallization method. First, ammonium sulfate is precipitated, and then ammonium phosphate is precipitated after further concentration and crystallization. Finally, ammonium sulfate with a purity of 98.1% and ammonium phosphate with a purity of 95.3% are obtained. The permeate of the reverse osmosis membrane is concentrated again, and the concentrated solution is returned to the evaporation crystallization treatment. The conductivity of the permeate is less than 6 μs / cm.

[0121] Example 3

[0122] Membrane cleaning process optimization:

[0123] The washing water is subjected to a precipitation reaction under different reaction conditions (pH 8.0-9.0, hydrogen peroxide addition amount 50-100 ppm), and after the precipitation reaction, cross-flow filtration is performed by using a 50 nm ultrafiltration membrane (the membrane surface flow rate is controlled at 2-4 m / s during filtration), and the precipitate is removed. The filtration time is 180 min.

[0124] According to the above method, the membrane pore blockage pollution resistance R p , the filter cake pollution resistance R c , and the membrane material resistance R m are calculated, respectively.

[0125] The different filtration times were fitted according to the formula (1) and formula (2), the time point with the minimum correlation coefficient was found, and the correlation coefficient R2 at different time points was as shown in Figure 5 It can be seen from the figure that under the current filtration conditions, there is a change in the type of pollution when t = 24 min.

[0126] The 0.2wt% NaOH solution was used to cross-flow at 5m / s for 15min, and then the 0.5wt% hydrochloric acid was used to cross-flow at 3m / s, the cleaning time was varied from 20min to 90min, and the membrane flux was measured after each acid cleaning, and the cake resistance R c =0 was set, and the residual blocking pollution resistance was calculated. Different membrane blocking resistance, flux recovery rate, and alkali cleaning time were substituted into formula (3) to fit and regress the parameters a and b, and in this example, a = 0.61 and b = 0.55 were obtained.

[0127] Verification of the prediction method:

[0128] The same precipitation and ultrafiltration filtration were performed, the flux curve data and the node when the membrane pore blocking / cake conversion occurred were obtained, and the acid cleaning time when the blocking resistance remained 5% was calculated according to the above formula, which was 64.5min.

[0129] The following steps were used for membrane cleaning:

[0130] First, 0.2wt% NaOH solution was used to cross-flow at 5m / s for 15min;

[0131] Then, 0.5wt% hydrochloric acid was used to cross-flow at 3m / s, and the membrane flux was measured every 5min, and the membrane flux data at different times was as shown in Figure 6 It can be seen from the figure that the flux can be obviously recovered at about 65min, and the extension of the cleaning time has little effect on the flux recovery rate, so it can be verified that the prediction method of the present method can effectively calculate the cleaning time of the acid.

Claims

1. A process for resource utilization of ammonia process ferric phosphate production wastewater, characterized in that, The method comprises the following steps: Step 1, solid-liquid separation of the wastewater from the production of iron phosphate by the ammonia method to recover iron phosphate particles; the wastewater is a crystallization mother liquor or washing water; Step 2, oxidation and precipitation of the filtrate obtained in step 1 by adding an oxidizing agent and a pH regulator, respectively; Step 3, solid-liquid separation of the wastewater obtained in step 2 to remove the precipitate; Step 4, removal of manganese by a manganese sand filter and removal of impurity metal ions by an ion exchange resin after the filtrate obtained in step 3 is filtered; Step 5, concentration of the wastewater obtained in step 4, followed by step-by-step evaporation crystallization to obtain ammonium sulfate and ammonium phosphate in sequence; The solid-liquid separation in steps 1 and 3 is performed by using a microfiltration membrane or an ultrafiltration membrane; After the solid-liquid separation in step 3, the filter membrane is cleaned by using an alkaline cleaning solution and an acidic cleaning solution in sequence to restore the membrane flux; The cross-flow process has a membrane surface flow rate of 1-10 m / s; The alkaline cleaning solution is a 0.1-0.5 wt% NaOH solution, and the acidic cleaning solution is a 0.1-0.5 wt% HCl solution; The cleaning process is calculated by the following steps: Step S1, obtaining the data of the change of the membrane flux with time during the solid-liquid separation process and performing interpolation processing as the original data set; Step S2, sequentially traversing the data points on the original data set, fitting all data points before the current traversed data point according to formula (1), and fitting all data points after the current traversed data point according to formula (2); ； ； where J is flux, J0is the initial flux of the membrane; K v is a fitting parameter; K cake is a fitting parameter; K standard is a fitting parameter; t is time; The average of the correlation coefficients R for the fit results of formula (1) and formula (2) is obtained as R ave = (R1+R2) / 2; After traversing all the data points, the corresponding time of the corresponding data point with the minimum R ave value is taken as the time point of the conversion from membrane pore blocking contamination to filter cake contamination. Step S3, calculate the membrane pore blocking pollution resistance R according to the flux at the time point of pollution conversion p , calculate the filter cake pollution resistance R according to the flux after the completion of the whole filtration c , calculate the membrane material resistance R according to the initial flux of the membrane m ; Step S4, after the membrane is cleaned by the alkaline cleaning solution, the membrane is cleaned by selecting different acid cleaning times t2, and formula (3) is fitted according to the flux after cleaning: R' p = (R total - R m ) x (1 - a x t2 b ); (3) R' p is the resistance of the membrane hole blockage pollution after cleaning, R total is the total resistance of the membrane layer after cleaning, t2 is the cleaning time of the acid cleaning solution, and a and b are parameters; Step S5, the wastewater is filtered again, washed by alkaline cleaning solution, washed by acidic cleaning solution, and the membrane pore blocking pollution resistance R is calculated according to the data of the change of the membrane flux with time p , R' p = α × R' p is the membrane pore pollution resistance after the completion of the cleaning setting target, which is substituted into formula (3) to calculate the optimal acid cleaning time; wherein, α is a setting coefficient; and the α is 0.01-0.

1.

2. The process for resource utilization of ammonia process ferric phosphate production wastewater according to claim 1, characterized in that, The oxidizing agent in step 2 is hydrogen peroxide; the amount added is 100-500 ppm.

3. The process for resource utilization of ammonia process ferric phosphate production wastewater according to claim 1, characterized in that, The pH regulator in step 2 is ammonia water; the pH is adjusted to 8-11.

4. The process for resource utilization of ammonia process ferric phosphate production wastewater according to claim 1, characterized in that, The concentration process in step 5 is to make the salt content in the wastewater greater than 15 wt%.

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