A process and system for treating iron phosphate wastewater

Abstract

The present application relates to the technical field of wastewater treatment, and specifically discloses a ferric phosphate wastewater treatment process and treatment system, wherein the treatment process comprises the following steps: S1, adding ferrous sulfate and hydrogen peroxide; adding alkali, adjusting the pH value to 3-5; adding flocculant, precipitating and separating, and obtaining a first-level effluent; S2, adding alkali, adjusting the pH value to 6-9; adding flocculant, precipitating and separating, and obtaining a second-level effluent; S3, adding aluminum-based defluoridation agent; adding flocculant and micro-sand, precipitating and separating, and obtaining a third-level effluent; S4, reverse osmosis concentration; S5, adding aluminum-based defluoridation agent; adding flocculant and micro-sand, precipitating and separating, and obtaining a fourth-level effluent; S6, evaporation and crystallization. The treatment process not only has a high removal effect on magnesium, iron, manganese, fluorine, and phosphorus in wastewater, but also realizes the recovery of ferric phosphate and ammonium sulfate, has the advantages of simple process and low cost, and meets market demand.

Description

Technical Field

[0001] The present application relates to the technical field of wastewater treatment, and more specifically, to a process and system for treating iron phosphate wastewater. Background Art

[0002] Iron phosphate is a white or off-white monoclinic crystal powder, which is mainly used in lithium battery materials, catalysts, ceramics, etc. For lithium batteries, compared with lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide, the positive electrode material of lithium iron phosphate batteries uses iron phosphate. In terms of energy density, cycle life, production cost, safety, etc., it is the most ideal power battery invented so far. Although there are some technical and price defects, it has already embarked on the road of commercialization. And as the technology matures, the price will also be greatly reduced with the expansion of production capacity, and it will even become the cheapest power battery in the future. Therefore, lithium iron phosphate batteries have broad application prospects and represent the future development direction of lithium batteries.

[0003] The iron phosphate in lithium iron phosphate batteries is an ideal precursor material for positive electrode materials of automotive lithium-ion power batteries, grid energy storage batteries, and power tool batteries. With the rapid development of electric vehicles, the demand for power batteries continues to rise, and the demand for iron phosphate is also increasing. However, in the production process of iron phosphate, wastewater containing high concentrations of ammonia nitrogen, phosphorus, manganese, fluoride and other inorganic salts will inevitably be produced. It mainly comes from iron phosphate synthesis mother liquor, iron phosphate rinse water, etc. According to the differences in the manufacturer's process, some manufacturers may also come from conversion mother liquor, etc. This type of wastewater not only has a large amount of wastewater, but also has certain difficulties in treatment, which obviously restricts the development of manufacturers.

[0004] At present, for the treatment of iron phosphate wastewater, most manufacturers mainly use the lime method. Although it can remove phosphorus from the wastewater, the total salt content of the effluent exceeds the standard, and the effluent discharge causes great pollution to the surrounding water environment. Some manufacturers also use high-concentration ammonia nitrogen stripping and magnesium ammonium phosphate precipitation, but a large amount of alkali is required to adjust the pH value, and it needs to be adjusted after the reaction, which has high treatment costs. A small number of manufacturers also use a combination of membrane and multi-effect evaporation processes, which can produce sulfur-ammonia and phosphorus-ammonia fertilizers, and the distilled water can also be recycled, but the process is complicated and the investment cost is high. Summary of the invention

[0005] In order to reduce the iron phosphate wastewater treatment process and cost, the present application provides an iron phosphate wastewater treatment process and treatment system.

[0006] In the first aspect, the present application provides a process for treating iron phosphate wastewater, which adopts the following technical solution:

[0007] A process for treating iron phosphate wastewater comprises the following steps:

[0008] S1. Primary phosphorus removal: Add ferrous sulfate and hydrogen peroxide to the wastewater and mix them for aeration treatment; then add alkali to adjust the pH value to 3-5; then add flocculant and mix, precipitate and separate to obtain primary effluent and sludge a;

[0009] Among them, the wastewater is iron phosphate wastewater;

[0010] S2, secondary iron, manganese and magnesium removal: add alkali to the primary effluent to adjust the pH value to 6-9; then add flocculant, mix, precipitate and separate to obtain secondary effluent and sludge b;

[0011] S3, tertiary defluorination: add aluminum-based defluorination agent to the secondary effluent and mix; then add flocculant and micro sand to mix, precipitate and separate, and obtain tertiary effluent and sludge c;

[0012] S4, reverse osmosis concentration: the tertiary effluent is subjected to reverse osmosis concentration to obtain reverse osmosis concentrate and clean water;

[0013] S5, 4th stage defluorination: add aluminum series defluorination agent to the reverse osmosis concentrate and mix; then add flocculant and micro sand to mix, precipitate and separate, and obtain 4th stage effluent and sludge d;

[0014] S6, evaporation crystallization: evaporate and crystallize the water from the fourth stage.

[0015] By adopting the above technical scheme, ferrous sulfate and hydrogen peroxide are added to the wastewater, trivalent iron ions are introduced, and then the pH value is adjusted to 3-5. At this time, iron phosphate precipitation is mainly formed, and the iron phosphate is recycled. Moreover, the iron phosphate precipitation can adsorb fluoride and reduce the three-stage defluorination load. At the same time, there is no need to use a coagulant to reduce costs. Then the pH value is further adjusted to 6-9, so that the trivalent iron ions, manganese ions, magnesium ions, and residual phosphate ions in the wastewater form precipitation. Not only the trivalent iron ions, manganese ions, and magnesium ions in the wastewater are removed, but also the phosphate ions are further removed. Moreover, fluoride can also be adsorbed to reduce the three-stage defluorination load. At the same time, there is no need to use a coagulant to reduce costs. Afterwards, aluminum-based defluorination agents are used to further form aluminum phosphate and aluminum hydroxide precipitations, which can further adsorb fluoride in the wastewater and improve the fluoride removal effect of wastewater. In the present application, through the cooperation between the primary phosphorus removal, the secondary iron, manganese and magnesium removal, and the tertiary fluoride removal, the magnesium ion removal rate is >97%, the trivalent iron ion removal rate is >99%, the manganese ion removal rate is >98%, the fluoride ion removal rate is >98%, and the phosphate ion removal rate is >94%.

[0016] The applicant found in actual research that if the tertiary effluent is directly subjected to evaporation and crystallization, the evaporation and crystallization cost is greatly increased based on the large processing volume of the tertiary effluent. On this basis, in this application, the tertiary effluent is subjected to reverse osmosis concentration to form a reverse osmosis concentrated liquid, which greatly reduces the evaporation and crystallization processing volume. Further, the applicant also found that the reverse osmosis concentrated liquid formed by the concentration of the tertiary effluent contains a large amount of fluoride ions. If the reverse osmosis concentrated liquid is directly subjected to evaporation and crystallization, the fluoride ions have serious corrosion on the evaporation crystallizer used. On this basis, in this application, the reverse osmosis concentrated liquid is subjected to defluorination treatment to reduce the fluoride ion concentration in the reverse osmosis concentrated liquid, that is, to reduce the corrosive effect of the quaternary effluent on the evaporation crystallizer. At the same time, the applicant also found in actual research that the quaternary effluent contains a large amount of ammonium ions and sulfate ions. If the reverse osmosis concentrated liquid is refluxed to the tertiary defluorination, although the purpose of defluorination can be achieved, the ammonium ions and sulfate ions cannot be recovered. On this basis, in the present application, after the fourth-stage effluent is treated by evaporation and crystallization, ammonium sulfate can be obtained, and the ammonium sulfate can be recycled and utilized, for example, in sulfur-ammonia fertilizer.

[0017] The iron phosphate wastewater treatment process of the present application, through the mutual coordination among primary phosphorus removal, secondary iron, manganese and magnesium removal, tertiary fluorine removal, reverse osmosis concentration, quaternary fluorine removal and evaporation crystallization, not only achieves the removal of magnesium, iron, manganese, fluorine and phosphorus in the wastewater, but also realizes the recycling of iron phosphate and ammonium sulfate, has the advantages of simple process and low cost, and meets market demand.

[0018] Step S1, in one embodiment, the pH value is adjusted to 4.1, and the pH value can also be adjusted to 3, 3.5, 4, 4.5, 5, etc. as needed.

[0019] In step S2, in one embodiment, the pH value is adjusted to 7.4, and the pH value can also be adjusted to 6, 6.5, 7, 7.5, 8, 8.5, 9, etc. as needed.

[0020] Optionally, the pH value of the wastewater is 1-3, the temperature of the wastewater is 50-80°C, the ammonium ion concentration in the wastewater is ≤15000ppm, the magnesium ion concentration is ≤250ppm, the trivalent iron ion concentration is ≤300ppm, the manganese ion concentration is ≤300ppm, the sulfate ion concentration is ≤80000ppm, the fluoride ion concentration is ≤450ppm, and the phosphate ion concentration is ≤15000ppm.

[0021] By adopting the above technical scheme, the concentrations of ammonium ions, magnesium ions, trivalent iron ions, manganese ions, sulfate ions, fluoride ions and phosphate ions in the wastewater are optimized to maintain the stability of the iron phosphate wastewater treatment process.

[0022] Optionally, the amount of hydrogen peroxide used is 90-110 mg / L, and / or,

[0023] In step S1, the amount of ferrous sulfate used is 1.2-1.5 times the molar concentration of phosphate ions in the wastewater, and / or, in step S1 and step S2, the alkali is ammonia water, and the mass concentration of the ammonia water is 15-25%.

[0024] By adopting the above technical solution, the usage of hydrogen peroxide and ferrous sulfate is optimized, and the alkali is optimized to maintain the stability of the iron phosphate wastewater treatment process.

[0025] Furthermore, the hydrogen peroxide is a hydrogen peroxide solution, and the mass concentration of hydrogen peroxide in the hydrogen peroxide solution is 20-50%. In one embodiment, the mass concentration of hydrogen peroxide in the hydrogen peroxide solution is 27.5%, and the mass concentration can also be adjusted to 20%, 25%, 30%, 35%, 40%, 50%, etc. as needed.

[0026] Ferrous sulfate adopts ferrous sulfate solution, and the mass concentration of ferrous sulfate solution is 20-40%. In one embodiment, the mass concentration of ferrous sulfate solution is 30%, and the mass concentration can also be adjusted to 20%, 25%, 35%, 40% and the like as needed. In the preparation of ferric phosphate, ferrous salt and phosphate are often reacted under the action of an oxidant, and ferrous salt generally adopts ferrous sulfate. At this time, ferrous sulfate solution can adopt the ferrous phosphate solution produced in the preparation process of ferrous phosphate, and no additional reagent is required, which reduces cost.

[0027] Optionally, the flocculant used in step S1, step S2, step S3, and step S5 is flocculant PAM, and the amount of flocculant used is 1-2 mg / L, and / or, in step S3 and step S5, the average particle size of the micro sand is 80-130 μm, and the concentration of the micro sand in the wastewater is 5-10 g / L, and / or,

[0028] In step S3 and step S5, the amount of aluminum-based defluoridation agent used is such that the molar concentration of aluminum in the aluminum-based defluoridation agent is 3-5 times the molar concentration of fluoride ions in the wastewater.

[0029] By adopting the above technical solution, the usage of flocculants, micro-sand, and aluminum-based defluorination agents is optimized to maintain the stability of the iron phosphate wastewater treatment process.

[0030] Optionally, the fluoride ion concentration in the reverse osmosis concentrate is ≤30 ppm, and / or,

[0031] The fluoride ion concentration in the fourth-stage effluent is ≤5ppm.

[0032] For reverse osmosis concentrate, as the concentration multiple of the tertiary effluent increases, the concentration of fluoride ions, ammonium ions, and sulfate ions in the reverse osmosis concentrate increases, that is, the inorganic salt content in the reverse osmosis concentrate increases, reducing the service life of the reverse osmosis device. The fluoride ion concentration in the reverse osmosis concentrate is optimized to optimize the concentration multiple of the tertiary effluent, reduce the impact of excessive concentration multiples on the service life of the reverse osmosis device, and also reduce the increase in the fourth-stage defluorination load caused by excessive concentration multiples.

[0033] In one embodiment, the fluoride ion concentration in the reverse osmosis concentrated liquid is 14 ppm. The fluoride ion concentration in the reverse osmosis concentrated liquid may also be 30 ppm, 20 ppm, 10 ppm, etc. according to the concentration multiple.

[0034] For the fourth-stage effluent, the fluoride ion concentration in the fourth-stage effluent is optimized to avoid the fluoride ion concentration in the fourth-stage effluent being too high and affecting the service life of the evaporation crystallizer, thereby ensuring the normal operation and service life of the evaporation crystallizer.

[0035] In one embodiment, the fluoride ion concentration in the quaternary effluent is 2.9 ppm. The fluoride ion concentration in the quaternary effluent can also be set to 5 ppm, 4 ppm, 3 ppm, 2 ppm, 1 ppm, 0.5 ppm, etc. as needed.

[0036] Optionally, in step S1 and step S2, the sedimentation load is 3-6m 3 / (m 2 h), and / or,

[0037] In step S3 and step S5, the sedimentation load is 6-10m 3 / (m 2 h).

[0038] Preferably, in step S1, the sedimentation load is 4m 3 / (m 2 h). In step S2, the sedimentation load is 4 m 3 / (m 2 h). In step S3, the sedimentation load is 10 m 3 / (m 2 h). In step S5, the sedimentation load is 7.5 m 3 / (m 2 h).

[0039] Optionally, in step S2, part of the sludge b is returned to the primary effluent and used together with the flocculant, and 10-40wt% of the total amount of the sludge b is returned.

[0040] In step S2, after the flocculant is added, since there are fewer flocs, part of the sludge b is returned for treatment, which can effectively increase the sludge concentration, not only facilitate the growth and precipitation of flocs, but also reduce the amount of flocculant used and reduce costs.

[0041] In one embodiment, 27wt% of the total amount of sludge b is refluxed, which can also be adjusted to 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt% and the like of the total amount of sludge b as needed.

[0042] Optionally, in step S3, sludge c is separated to obtain recovered micro-sand and sludge c2, and the recovered micro-sand is returned to the secondary effluent and used together with flocculant, and the amount of new micro-sand used is 3-5 mg / L;

[0043] In step S5, the sludge d is separated to obtain recovered micro-sand and sludge d2. The recovered micro-sand is returned to the fourth-stage effluent and used together with the flocculant. The amount of new micro-sand used is 3-5 mg / L.

[0044] In step S3 and step S5, the recovered micro-sand is refluxed for treatment, and the flocs use the micro-sand as the crystal nucleus to increase the sedimentation of the flocs. Based on the fact that most of the micro-sand is refluxed, the amount of new micro-sand used is 3-5 mg / L, which greatly reduces the amount of new micro-sand used and reduces costs.

[0045] Optionally, the sludge a is concentrated by filter pressing and dried to obtain iron phosphate, which is then recycled, and / or the sludge b, sludge c2, and sludge d2 are concentrated by filter pressing and dried to obtain solids, which are then recycled.

[0046] In a second aspect, the present application provides an iron phosphate wastewater treatment system as described above, which adopts the following technical scheme: an iron phosphate wastewater treatment system as described above, comprising a primary phosphorus removal unit, a secondary iron, manganese and magnesium removal unit, a tertiary fluorine removal unit, a reverse osmosis device, a quaternary fluorine removal unit, and an evaporation crystallizer;

[0047] The primary phosphorus removal unit comprises a primary reaction tank a, a secondary reaction tank b, a primary flocculation tank, a primary sedimentation tank, and a sludge tank a which are connected in sequence;

[0048] The secondary iron, manganese and magnesium removal unit comprises a secondary reaction tank, a secondary flocculation tank, a secondary sedimentation tank and a sludge tank b which are connected in sequence, and the secondary reaction tank is connected to the primary sedimentation tank;

[0049] The three-stage defluorination unit comprises a three-stage reaction tank, a three-stage flocculation tank, a three-stage sedimentation tank, and a micro-sand separator a which are connected in sequence. The three-stage reaction tank is connected to the secondary sedimentation tank, the micro-sand separator a is connected to the three-stage flocculation tank and the sludge tank b respectively, and the three-stage sedimentation tank is connected to the reverse osmosis device;

[0050] The four-stage defluorination unit includes a four-stage reaction tank, a four-stage flocculation tank, a four-stage sedimentation tank, and a micro-sand separator b which are connected in sequence. The four-stage reaction tank is connected to a reverse osmosis device, the micro-sand separator b is connected to the four-stage flocculation tank and the sludge tank b respectively, and the four-stage sedimentation tank is connected to an evaporation crystallizer.

[0051] In summary, this application has at least the following beneficial effects:

[0052] 1. The iron phosphate wastewater treatment process of the present application, through the mutual coordination between primary phosphorus removal, secondary iron, manganese and magnesium removal, tertiary fluorine removal, reverse osmosis concentration, quaternary fluorine removal and evaporation crystallization, not only realizes the removal of magnesium, iron, manganese, fluorine and phosphorus in the wastewater, but also realizes the recycling of iron phosphate and ammonium sulfate, has the advantages of simple process and low cost, and meets market demand.

[0053] 2. This application also limits the fluoride ion concentration in the fourth-stage effluent to avoid the fluoride ion concentration in the fourth-stage effluent being too high and affecting the service life of the evaporation crystallizer, thereby ensuring the normal operation and service life of the evaporation crystallizer.

[0054] 3. In step S2, the sludge b is refluxed, which not only increases the sedimentation effect, but also reduces the amount of flocculant used and reduces costs. In steps S3 and S5, the recovered micro sand is refluxed, which reduces the amount of micro sand used and reduces costs, and increases the sludge settling speed, greatly reducing the sedimentation area. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a flow chart of the iron phosphate wastewater treatment process of this application. DETAILED DESCRIPTION

[0056] In order to make the present application easier to understand, the present application will be further described in detail below in conjunction with the examples, which are merely illustrative and are not intended to limit the scope of application of the present application. The raw materials or components used in the present application can be obtained through commercial routes or conventional methods unless otherwise specified.

[0057] Example

[0058] Example 1

[0059] A treatment process for iron phosphate wastewater, which is used to treat iron phosphate wastewater, wherein the pH value of the iron phosphate wastewater is 1.2 and the temperature is 60°C. Figure 1 , specifically including the following steps:

[0060] S1, primary phosphorus removal

[0061] S11. Introduce wastewater into the primary reaction tank a. The wastewater is iron phosphate wastewater. The water volume of the iron phosphate wastewater is 120m 3 / h. Then add ferrous sulfate and hydrogen peroxide to mix. Ferrous sulfate uses the ferrous sulfate solution produced in the preparation process of ferric phosphate. The mass concentration of ferrous sulfate solution is 30%. The amount of ferrous sulfate used is 1.2 times the molar concentration of phosphate ions in the wastewater. Hydrogen peroxide uses hydrogen peroxide, and the mass concentration of hydrogen peroxide is 27.5%. The amount of hydrogen peroxide used is 370.4 mg / L, and then aeration is performed to supplement oxygen. At this time, the following reactions are carried out in the wastewater:

[0062] 4Fe 2+ +O2+4H + →4Fe 3+ +2H2O

[0063] 2Fe 2+ +H2O2+2H + →2Fe 3+ +2H2O

[0064] In this process, the ferrous iron ions in the wastewater and the input ferrous iron ions are all converted into ferric iron ions. Moreover, the addition of hydrogen peroxide, as a catalyst, can effectively accelerate the oxidation rate of the ferrous iron ions and facilitate the reaction.

[0065] S12, introducing the wastewater treated in step S11 into the primary reaction tank b, and then adding ammonia water, the mass concentration of which is 20%, and adjusting the pH value to 4.1. At this time, the following reactions are carried out in the wastewater:

[0066] Fe 3+ +PO4 3- →FePO4↓

[0067] Fe 3+ +3OH - →2Fe(OH)3↓

[0068] In this process, since trivalent iron ions are supplemented in step S11 and the content of trivalent iron ions is relatively high, the trivalent iron ions convert phosphate into iron phosphate precipitate, and at the same time, a small amount of iron hydroxide precipitate is also produced.

[0069] S13, introduce the wastewater treated in step S12 into the primary flocculation tank, then add flocculant and mix, the flocculant is PAM, the molecular weight of PAM is 10 million, and the amount of PAM used is 1.5 mg / L. Then introduce it into the primary sedimentation tank for sedimentation and separation, the load of the primary sedimentation tank is 4m 3 / (m 2 h), and obtain primary effluent and sludge a.

[0070] The sludge a is deposited at the bottom and further discharged and enters the sludge pool a. The sludge a is filtered, concentrated, and dried to obtain iron phosphate, which is then recycled.

[0071] In this process, since the wastewater contains a large amount of iron phosphate and a small amount of iron hydroxide, there is no need to add coagulants. The generated iron phosphate and iron hydroxide can be directly used as coagulants, and flocculants are added to make the flocs grow rapidly and become dense, forming dense and mature alum flowers, which are convenient for subsequent precipitation and separation. At the same time, iron phosphate and iron hydroxide can also absorb part of the fluoride, reducing the subsequent three-stage defluorination load.

[0072] S2, secondary iron, manganese and magnesium removal

[0073] S21, introduce the primary effluent into the secondary reaction tank, then add ammonia water, the mass concentration of ammonia water is 20%, and the pH value is adjusted to 7.4. At this time, the following reactions are carried out in the wastewater:

[0074] Fe 3+ +PO4 3- →FePO4↓

[0075] Fe 3+ +3OH - →2Fe(OH)3↓

[0076] Mn 2+ +2OH - →2Mn(OH)2↓

[0077] Mg 2+ +2OH - →2Mg(OH)2↓

[0078] During this process, the trivalent iron ions in the wastewater further convert phosphate into iron phosphate precipitates, and at the same time convert manganese ions, magnesium ions, and trivalent iron ions into precipitates, forming manganese hydroxide, magnesium hydroxide, and iron hydroxide.

[0079] S22, introduce the wastewater treated in step S21 into the secondary flocculation tank, then add flocculant and mix, the flocculant is PAM, the molecular weight of PAM is 10 million, and the amount of PAM used is 1.5 mg / L. Then introduce it into the secondary sedimentation tank for sedimentation and separation, the load of the secondary sedimentation tank is 4m 3 / (m 2 h), and obtain secondary effluent and sludge b.

[0080] Sludge b is deposited at the bottom, 73wt% of the total amount of sludge b is discharged and enters sludge pool b, and is filtered, concentrated and dried. 27wt% of the total amount of sludge b is returned to the secondary flocculation pool to increase the concentration in the secondary flocculation pool.

[0081] In this process, since the wastewater contains iron phosphate, manganese hydroxide, magnesium hydroxide, and iron hydroxide, there is no need to add coagulants, and the generated iron phosphate and iron hydroxide can be directly used as coagulants. However, due to the small number of flocs, the sludge b produced in the secondary sedimentation tank is returned to the secondary flocculation tank to increase the concentration in the secondary flocculation tank and reduce the amount of flocculants used. At the same time, the flocculant PAM is added to make the flocs grow instantly and become dense, forming dense and mature alum flowers, which are convenient for subsequent precipitation and separation. At the same time, iron phosphate, manganese hydroxide, magnesium hydroxide, and iron hydroxide can also absorb part of the fluoride, reducing the subsequent tertiary defluorination load.

[0082] S3, three-stage defluorination

[0083] S31, introducing the secondary effluent into the tertiary reaction tank, and then adding an aluminum-based defluoridation agent, the aluminum-based defluoridation agent is selected from PAC, and the amount of the aluminum-based defluoridation agent used is such that the molar concentration of aluminum in the aluminum-based defluoridation agent is 3 times the molar concentration of fluoride ions in the wastewater. At this time, the following reaction is carried out in the wastewater:

[0084] Al 3+ +PO4 3- →AlPO4↓

[0085] Al 3+ +3OH - →Al(OH)3↓

[0086] In this process, aluminum ions in the wastewater convert phosphate into aluminum phosphate precipitate, and at the same time, aluminum hydroxide precipitate is also produced. Aluminum phosphate precipitate and aluminum hydroxide precipitate quickly adsorb fluoride in the wastewater, thereby removing fluoride in the wastewater.

[0087] S32, introduce the wastewater treated in step S31 into the third-stage flocculation tank, then add flocculant and micro sand to mix, the flocculant uses flocculant PAM, the molecular weight of flocculant PAM is 10 million, and the amount of flocculant PAM used is 1.5 mg / L. The average particle size of micro sand is 100 μm, and the concentration of micro sand in the wastewater is 15 g / L. Then introduce it into the third-stage sedimentation tank for sedimentation and separation. The load of the third-stage sedimentation tank is 10m 3 / (m 2 h), and obtain tertiary effluent and sludge c.

[0088] Sludge c is introduced into micro-sand separator a, and after separation, recovered micro-sand and sludge c2 are obtained. The recovered micro-sand is returned to the third-level flocculation tank to facilitate the growth and precipitation of floc nuclei. Based on the recycled micro-sand, the amount of new micro-sand used is 5 mg / L, which greatly reduces the amount of new micro-sand input. Sludge c2 is discharged and enters sludge tank b, and is filtered, concentrated, and dried.

[0089] In this process, since the wastewater contains aluminum phosphate, aluminum hydroxide and micro sand, there is no need to add coagulant, and the generated aluminum phosphate and aluminum hydroxide can be directly used as coagulants. In addition, the micro sand is used as the crystal nucleus, which greatly increases the sedimentation of the flocs, and under the flocculant, the flocs grow up instantly and become dense, forming dense and mature alum flowers, which is convenient for subsequent precipitation and separation. At the same time, the micro sand in the sludge c is separated, and the micro sand is refluxed to reduce the use of micro sand.

[0090] S4, reverse osmosis concentration

[0091] The tertiary effluent is introduced into the reverse osmosis device for reverse osmosis concentration to obtain reverse osmosis concentrate and clean water. The clean water is recycled.

[0092] S5, four-stage defluorination

[0093] S51, introducing the reverse osmosis concentrate into the four-stage reaction tank, and then adding an aluminum-based defluoridation agent, the aluminum-based defluoridation agent is selected from PAC, and the amount of the aluminum-based defluoridation agent used is such that the molar concentration of aluminum in the aluminum-based defluoridation agent is 5 times the molar concentration of fluoride ions in the wastewater. At this time, the following reaction is carried out in the wastewater:

[0094] Al 3+ +PO4 3- →AlPO4↓

[0095] Al 3+ +3OH - →Al(OH)3↓

[0096] In this process, aluminum ions in the wastewater convert phosphate into aluminum phosphate precipitate, and at the same time, aluminum hydroxide precipitate is also produced. Aluminum phosphate precipitate and aluminum hydroxide precipitate quickly adsorb fluoride in the wastewater, thereby removing fluoride in the wastewater.

[0097] S52, introduce the wastewater treated in step S51 into the fourth-stage flocculation tank, then add flocculant and micro sand to mix, the flocculant uses flocculant PAM, the molecular weight of flocculant PAM is 10 million, and the amount of flocculant PAM used is 1.5 mg / L. The average particle size of micro sand is 100 μm, and the concentration of micro sand in the wastewater is 5 g / L. Then introduce it into the fourth-stage sedimentation tank for sedimentation and separation. The load of the fourth-stage sedimentation tank is 7.5 m 3 / (m 2 h), and obtain the fourth-level effluent and sludge d.

[0098] Sludge d is introduced into micro-sand separator b, and after separation, recovered micro-sand and sludge d2 are obtained. The recovered micro-sand is returned to the third-stage flocculation tank to facilitate the growth and precipitation of floc nuclei. Most of the micro-sand is returned. At this time, the amount of new micro-sand used is 3 mg / L, which greatly reduces the amount of new micro-sand input. Sludge d2 is discharged and enters sludge tank b, and is filtered, concentrated, and dried.

[0099] S6, evaporation crystallization

[0100] The tertiary effluent is introduced into an evaporation crystallizer for evaporation and crystallization to obtain ammonium sulfate for recycling.

[0101] Performance Testing

[0102] The wastewater, the effluent from the first-stage phosphorus removal, the effluent from the second-stage iron, manganese and magnesium removal, the effluent from the third-stage fluoride removal, the effluent from the reverse osmosis concentration, and the effluent from the fourth-stage fluoride removal were tested respectively, and the test results are shown in Table 1.

[0103] Table 1 Iron phosphate wastewater and treatment effect of Example 1

[0104]

[0105] Note: “ / ” means not detected.

[0106] As can be seen from Table 1, the iron phosphate wastewater treatment process of the present application, after primary phosphorus removal, secondary iron, manganese and magnesium removal, and tertiary fluoride removal, the magnesium ion concentration in the tertiary effluent is 4.1ppm, the trivalent iron ion concentration is 0.3ppm, the manganese ion concentration is 2.8ppm, the fluoride ion concentration is 3.5ppm, and the phosphate ion is 530ppm. At this time, the magnesium ion removal rate reaches 97.27%, the trivalent iron ion removal rate reaches 99.85%, the manganese ion removal rate reaches 98.53%, the fluoride ion removal rate reaches 98.83%, and the phosphate ion removal rate reaches 94.11%. Further, after reverse osmosis concentration, four-stage defluoridation, evaporation and crystallization, ammonium sulfate is obtained. In the present application, through the coordination between primary phosphorus removal, secondary iron, manganese and magnesium removal, tertiary fluorine removal, reverse osmosis concentration, quaternary fluorine removal and evaporation crystallization, not only the magnesium, iron, manganese, fluorine and phosphorus in the wastewater are highly removed, but also the recycling of iron phosphate and ammonium sulfate is realized, which has the advantages of simple process and low cost, and meets market demand.

[0107] Example 2

[0108] A treatment process for ferric phosphate wastewater, which differs from Example 1 in that the ferric phosphate wastewater is different. The ferric phosphate wastewater and the treatment effect are shown in Table 2.

[0109] Table 2 Iron phosphate wastewater and treatment effect of Example 2

[0110]

[0111] Note: “ / ” means not detected.

[0112] As can be seen from Table 2, the iron phosphate wastewater treatment process of the present application, after the first-level phosphorus removal, the second-level iron, manganese and magnesium removal, and the third-level fluoride removal, the magnesium ion concentration in the tertiary effluent is 6.5ppm, the trivalent iron ion concentration is 0.4ppm, the manganese ion concentration is 4.2ppm, the fluoride ion concentration is 5.1ppm, and the phosphate ion is 750ppm. At this time, the magnesium ion removal rate reaches 97.40%, the trivalent iron ion removal rate reaches 99.87%, the manganese ion removal rate reaches 98.60%, the fluoride ion removal rate reaches 98.87%, and the phosphate ion removal rate reaches 95.00%.

[0113] Example 3

[0114] A treatment process for ferric phosphate wastewater, which differs from Example 1 in that the ferric phosphate wastewater is different. The ferric phosphate wastewater and the treatment effect are shown in Table 3.

[0115] Table 3 Iron phosphate wastewater and treatment effect of Example 3

[0116]

[0117] Note: “ / ” means not detected.

[0118] As can be seen from Table 3, the iron phosphate wastewater treatment process of the present application, after the first-level phosphorus removal, the second-level iron, manganese and magnesium removal, and the third-level fluoride removal, the magnesium ion concentration in the tertiary effluent is 5.1ppm, the trivalent iron ion concentration is 0.3ppm, the manganese ion concentration is 3.3ppm, the fluoride ion concentration is 4.4ppm, and the phosphate ion is 650ppm. At this time, the magnesium ion removal rate reaches 97.45%, the trivalent iron ion removal rate reaches 99.88%, the manganese ion removal rate reaches 98.68%, the fluoride ion removal rate reaches 98.95%, and the phosphate ion removal rate reaches 94.58%.

[0119] Example 4

[0120] A ferric phosphate wastewater treatment system, referring to Figure 1 , including a primary phosphorus removal unit, a secondary iron, manganese and magnesium removal unit, a tertiary fluorine removal unit, a reverse osmosis device, a quaternary fluorine removal unit, and an evaporation crystallizer.

[0121] The primary phosphorus removal unit comprises a primary reaction tank a, a secondary reaction tank b, a primary flocculation tank, and a primary sedimentation tank which are connected in sequence. The downstream of the primary sedimentation tank is connected in sequence with a sludge tank a and a filter press a.

[0122] The wastewater passes through the primary reaction tank a, the secondary reaction tank b, the primary flocculation tank, and the primary sedimentation tank to form primary effluent and sludge a. The primary effluent enters the secondary iron, manganese and magnesium removal unit. Sludge a enters the sludge tank a, passes through the filter press and is dried to form iron phosphate, which is then recycled.

[0123] The secondary iron, manganese and magnesium removal unit includes a secondary reaction tank, a secondary flocculation tank and a secondary sedimentation tank which are connected in sequence. The secondary reaction tank is connected to the primary sedimentation tank. The downstream of the secondary sedimentation tank is connected in sequence with a sludge tank b and a filter press b. The secondary sedimentation tank is also connected to the secondary flocculation tank for reflowing part of the sludge b.

[0124] The primary effluent passes through the secondary reaction tank, the secondary flocculation tank, and the secondary sedimentation tank to form the secondary effluent and sludge b. The secondary effluent enters the tertiary defluorination unit. Part of the sludge b flows back to the secondary flocculation tank, and part of the sludge b enters the sludge tank b, passes through the filter press b, and is dried to form solids.

[0125] The three-stage defluorination unit includes a three-stage reaction tank, a three-stage flocculation tank, and a three-stage sedimentation tank which are connected in sequence. The three-stage reaction tank is connected to the two-stage sedimentation tank. The downstream of the three-stage sedimentation tank is connected to a micro-sand separator a, which is connected to the three-stage flocculation tank and the sludge tank b respectively.

[0126] The secondary effluent passes through the tertiary reaction tank, the tertiary flocculation tank, and the tertiary sedimentation tank to form the tertiary effluent and sludge c. The tertiary effluent enters the reverse osmosis device. The sludge c enters the micro-sand separator a to form the recovered micro-sand and sludge c2. The sludge c2 enters the sludge tank b, passes through the filter press b, and is dried to form solids.

[0127] The reverse osmosis device is connected to the third-stage sedimentation tank. The third-stage effluent passes through the reverse osmosis device to form reverse osmosis concentrate and clean water. The clean water is recycled. The reverse osmosis concentrate enters the fourth-stage defluorination unit.

[0128] The four-stage defluorination unit includes a four-stage reaction tank, a four-stage flocculation tank, and a four-stage sedimentation tank which are connected in sequence. The four-stage reaction tank is connected to a reverse osmosis device. The downstream of the four-stage sedimentation tank is connected to a micro-sand separator b, which is respectively connected to the four-stage flocculation tank and the sludge tank b.

[0129] The reverse osmosis concentrate passes through the fourth-stage reaction tank, the fourth-stage flocculation tank, and the fourth-stage sedimentation tank to form the fourth-stage effluent and sludge d. The fourth-stage effluent enters the evaporation crystallizer. The sludge d enters the micro-sand separator b to form the recovered micro-sand and sludge d2. The sludge d2 enters the sludge tank b, passes through the filter press b, and is dried to form solid matter.

[0130] The evaporation crystallizer is connected to the fourth-stage sedimentation tank. The fourth-stage effluent passes through the evaporation crystallizer to form solid matter.

[0131] In this application, sludge a is introduced into sludge pool a to further recover iron phosphate. Sludge b, sludge c2, and sludge d2 are introduced into sludge pool b for further processing to form solids, which can effectively reduce the number of sludge pools, simplify the process, and reduce costs.

[0132] It should be noted that the embodiments described above are only used to explain the present application and do not constitute any limitation to the present application. The present application is described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present application may be modified as specified within the scope of the claims of the present application, and the present invention may be revised without departing from the scope and spirit of the present application. Although the present application described therein relates to specific methods, materials and embodiments, it does not mean that the present application is limited to the specific examples disclosed therein. On the contrary, the present application can be extended to all other methods and applications with the same functions.

Claims

1. A process for treating iron phosphate wastewater, characterized in that: The steps include: S1, primary phosphorus removal: add ferrous sulfate and hydrogen peroxide to the wastewater, mix, and aerate; then add alkali to adjust the pH value to 3-5; then add flocculant, mix, precipitate, separate, and obtain primary effluent and sludge a; Among them, the wastewater is iron phosphate wastewater; S2, secondary iron, manganese and magnesium removal: add alkali to the primary effluent to adjust the pH value to 6-9; then add flocculant, mix, precipitate and separate to obtain secondary effluent and sludge b; S3, tertiary defluorination: add aluminum-based defluorination agent to the secondary effluent and mix; then add flocculant and micro sand to mix, precipitate and separate, and obtain tertiary effluent and sludge c; S4, reverse osmosis concentration: the tertiary effluent is subjected to reverse osmosis concentration to obtain reverse osmosis concentrate and clean water; S5, 4th stage defluorination: add aluminum series defluorination agent to the reverse osmosis concentrate and mix; then add flocculant and micro sand to mix, precipitate and separate, and obtain 4th stage effluent and sludge d; S6, evaporation crystallization: evaporate and crystallize the water from the fourth stage.

2. A process for treating iron phosphate wastewater according to claim 1, characterized in that: The pH value of the wastewater is 1-3, the temperature of the wastewater is 50-80°C, the ammonium ion concentration in the wastewater is ≤15000ppm, the magnesium ion concentration is ≤250ppm, the trivalent iron ion concentration is ≤300ppm, the manganese ion concentration is ≤300ppm, the sulfate ion concentration is ≤80000ppm, the fluoride ion concentration is ≤450ppm, and the phosphate ion concentration is ≤15000ppm.

3. A process for treating iron phosphate wastewater according to claim 1, characterized in that: In step S1, the amount of hydrogen peroxide used is 90-110 mg / L, and / or, In step S1, the amount of ferrous sulfate used is 1.2-1.5 times the molar concentration of phosphate ions in the wastewater, and / or, In step S1 and step S2, the alkali is aqueous ammonia, and the mass concentration of the aqueous ammonia is 15-25%.

4. A process for treating iron phosphate wastewater according to claim 1, characterized in that: The flocculant used in step S1, step S2, step S3, and step S5 is flocculant PAM, and the amount of the flocculant used is 1-2 mg / L, and / or, In step S3 and step S5, the average particle size of the micro sand is 80-130 μm, and the concentration of the micro sand in the wastewater is 5-10 g / L, and / or, In step S3 and step S5, the amount of aluminum-based defluoridation agent used is such that the molar concentration of aluminum in the aluminum-based defluoridation agent is 3-5 times the molar concentration of fluoride ions in the wastewater.

5. A process for treating iron phosphate wastewater according to claim 1, characterized in that: The fluoride ion concentration in the reverse osmosis concentrate is ≤30ppm, and / or The fluoride ion concentration in the fourth-stage effluent is ≤5ppm.

6. The iron phosphate wastewater treatment process according to claim 1 is characterized in that: In step S1 and step S2, the sedimentation load is 3-6m 3 / (m 2 h), and / or, In step S3 and step S5, the sedimentation load is 6-10m 3 / (m 2 h).

7. A process for treating iron phosphate wastewater according to claim 1, characterized in that: In step S2, part of the sludge b is returned to the primary effluent and used together with the flocculant, and 10-40wt% of the total amount of the sludge b is returned.

8. A process for treating iron phosphate wastewater according to claim 1, characterized in that: In step S3, sludge c is separated to obtain recovered micro-sand and sludge c2, and the recovered micro-sand is returned to the secondary effluent and used together with flocculant, and the amount of new micro-sand used is 3-5 mg / L; In step S5, the sludge d is separated to obtain recovered micro-sand and sludge d2. The recovered micro-sand is returned to the fourth-stage effluent and used together with the flocculant. The amount of new micro-sand used is 3-5 mg / L.

9. A process for treating iron phosphate wastewater according to claim 8, characterized in that: The sludge a is concentrated by filtration and dried to obtain iron phosphate, which is recycled and / or, The sludge b, sludge c2 and sludge d2 are concentrated by filter pressing and dried to obtain solid matter, which is then recycled.

10. A process for treating iron phosphate wastewater according to claim 1, characterized in that: It includes a primary phosphorus removal unit, a secondary iron, manganese and magnesium removal unit, a tertiary fluorine removal unit, a reverse osmosis device, a quaternary fluorine removal unit and an evaporation crystallizer; The primary phosphorus removal unit comprises a primary reaction tank a, a secondary reaction tank b, a primary flocculation tank, a primary sedimentation tank, and a sludge tank a which are connected in sequence; The secondary iron, manganese and magnesium removal unit comprises a secondary reaction tank, a secondary flocculation tank, a secondary sedimentation tank and a sludge tank b which are connected in sequence, and the secondary reaction tank is connected to the primary sedimentation tank; The three-stage defluorination unit comprises a three-stage reaction tank, a three-stage flocculation tank, a three-stage sedimentation tank, and a micro-sand separator a which are connected in sequence. The three-stage reaction tank is connected to the secondary sedimentation tank, the micro-sand separator a is connected to the three-stage flocculation tank and the sludge tank b respectively, and the three-stage sedimentation tank is connected to the reverse osmosis device; The four-stage defluorination unit includes a four-stage reaction tank, a four-stage flocculation tank, a four-stage sedimentation tank, and a micro-sand separator b which are connected in sequence. The four-stage reaction tank is connected to a reverse osmosis device, the micro-sand separator b is connected to the four-stage flocculation tank and the sludge tank b respectively, and the four-stage sedimentation tank is connected to an evaporation crystallizer.

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