Iron phosphate wastewater treatment process based on magnesium recycling

Abstract

The invention discloses an iron phosphate wastewater treatment process based on magnesium recycling, which comprises the following steps: precipitating an iron phosphate synthesis mother solution and an iron phosphate rinsing water concentrated solution by adopting an excessive magnesium compound, and removing heavy metal ions, hydrogen ions, fluorine ions, phosphate ions and ammonium ions at one time; then adjusting the pH value to 7-9 with dilute sulfuric acid, then carrying out evaporative crystallization to obtain a magnesium sulfate solid, and calcining the magnesium sulfate solid to obtain solid magnesium oxide and sulfur dioxide gas. The magnesium oxide prepared by the method can be continuously used for treating iron phosphate wastewater, the obtained sulfur dioxide gas can be used for preparing sulfuric acid, the recycling of magnesium is really realized, and the problem of secondary pollution is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of iron phosphate wastewater treatment, and in particular relates to an iron phosphate wastewater treatment process based on magnesium recycling. Background Art

[0002] Iron phosphate is the precursor of the positive electrode material of lithium iron phosphate batteries. As the market size of lithium iron phosphate batteries continues to expand, the production scale of iron phosphate has also grown rapidly. In order to reduce costs, the current iron phosphate production process mainly uses ferrous sulfate, a byproduct of titanium dioxide, as an iron source, and synthesizes iron phosphate through a "two-step" process. During the production process, iron phosphate will go through synthesis, rinsing and other processes, during which a large amount of synthesis mother liquor and rinsing wastewater will be generated. After long-term follow-up research, the pH of iron phosphate wastewater is 2~2.5, F - 30~50mg / L, total P2200~3000mg / L, Fe 2+ 30~50mg / L, Mg 2+ 500~700mg / L, NH3-N 6000~7000mg / L, SO4 2- 50000~60000mg / L. Therefore, the wastewater is high in ammonia nitrogen, phosphorus, salt and acid, which is very difficult to treat and will seriously damage the environment if discharged directly.

[0003] At present, the treatment of iron phosphate wastewater mainly includes "calcium method" and "ammonia method", but many problems are exposed during operation, such as serious scaling and blockage of the "calcium method" treatment device and incomplete removal of pollutants, and the "ammonia method" has a very large amount of ammonia water and incomplete salt separation. This makes the treatment of iron phosphate wastewater a global problem, and it is urgent to find a better solution. Summary of the invention

[0004] In order to overcome the problems in the prior art, the present invention provides a ferric phosphate wastewater treatment process based on the recycling of magnesium, which avoids the problems of scaling and clogging of the treatment device and the large amount of ammonia water added. The treated ferric phosphate wastewater will not cause secondary pollution. A single magnesium sulfate solid is obtained by treatment without the need for salt separation. The magnesium oxide produced after calcining the magnesium sulfate solid can be used again for the treatment of ferric phosphate wastewater, thereby realizing the recycling of magnesium.

[0005] In order to solve the above technical problems, the technical solutions proposed by the present invention are as follows: The first aspect of the present invention provides a ferric phosphate wastewater treatment process based on magnesium recycling, comprising the following steps: S1. Adding an excess amount of magnesium compound to the iron phosphate wastewater for precipitation reaction, and obtaining solid slag and precipitate after solid-liquid separation; S2, adjusting the pH of the precipitate obtained in step S1 to 7-9 with dilute sulfuric acid and then performing evaporation and crystallization to obtain magnesium sulfate solid; S3. Calcining the magnesium sulfate solid to obtain solid magnesium oxide and sulfur dioxide gas.

[0006] In order to solve the problem of secondary pollution and the generation of impure salts in the process of treating ferric phosphate wastewater, the present invention takes sulfate ions with the highest content in ferric phosphate wastewater as the main recovery product, adds an excess of magnesium compounds into the ferric phosphate wastewater, and mainly produces the following reaction, wherein M n+ Indicates heavy metal ions: MgO+M n+ +H + =M(OH) n +H2O+Mg 2+ ; Mg(OH)2+M n+ +H + =M(OH) n +H2O+Mg 2+ ; Mg 2+ +2F - =MgF2; NH4 + +OH - =NH3·H2O; HPO4 3- +Mg 2+ +NH3·H2O=NH4MgPO4+H2O.

[0007] After the above reaction, the heavy metal ions, hydrogen ions, fluoride ions, phosphate ions, and ammonium ions in the iron phosphate wastewater are effectively removed, and no new impurities are introduced. The purpose of removing precipitation is achieved at one time, avoiding the use of coagulation and precipitation procedures, shortening the process time, and the main component of the obtained solid slag is ammonium magnesium phosphate, which is commonly known as "struvite". It is a multi-element compound fertilizer containing N, P, and Mg and can be used directly as a fertilizer. The pH value of the obtained precipitate is greater than 9, and dilute sulfuric acid is added for neutralization. The pH value is controlled within the range of 7 to 9, so that the precipitate is mainly a magnesium sulfate solution, and then the magnesium sulfate is evaporated and crystallized to obtain a solid, and then calcined to obtain magnesium oxide and sulfur dioxide, wherein the magnesium oxide can be used again for the treatment of other iron phosphate wastewaters, and sulfur dioxide can be used for the preparation of sulfuric acid, which truly realizes the thorough treatment of iron phosphate wastewater without secondary pollution, and realizes the recycling of magnesium, solving the problems existing in the "calcium method" and "ammonia method" in the prior art.

[0008] The mass concentration of salt in the mother liquor of ferric phosphate synthesis is generally around 6%, and does not require concentration treatment. The mass concentration of salt in the ferric phosphate rinse water is generally around 1%, and concentration treatment can play a good role in reducing the amount of wastewater treatment in the subsequent process, thereby reducing both investment costs and operating costs.

[0009] As an optional embodiment, in the treatment process provided by the present invention, in step S1, the magnesium compound is selected from one or more of magnesium oxide, magnesium hydroxide, magnesium phosphate and magnesium hydrogen phosphate.

[0010] As an optional embodiment, in the treatment process provided by the present invention, in step S1, the ferric phosphate wastewater includes ferric phosphate synthesis mother liquor and ferric phosphate rinsing water concentrate; the ferric phosphate wastewater has a pH of 2-2.5, a fluoride ion concentration of 30-50 mg / L, a total phosphorus of 2200-3000 mg / L, and Fe 2+ The concentration is 30~50mg / L, Mg 2+ The concentration is 500~700mg / L, NH3-N is 6000~7000mg / L, SO4 2- The concentration is 50000~60000mg / L.

[0011] As an optional embodiment, in the treatment process provided by the present invention, the concentrated ferric phosphate rinse water is obtained by concentrating the ferric phosphate rinse water 4 to 6 times, and the concentrated fresh water is recovered.

[0012] In the present invention, the fresh water obtained after the ferric phosphate rinsing water is concentrated can be directly recycled and reused without causing secondary pollution.

[0013] As an optional embodiment, in the treatment process provided by the present invention, the amount of the magnesium compound added is determined by a beaker test.

[0014] In the present invention, the amount of magnesium added is determined according to the actual concentration of ions in the wastewater. The specific operation is a beaker test method. First, a 100 ml beaker is used to take the solution after the iron phosphate synthesis mother liquor and the iron phosphate rinse water concentrate are combined, and a magnesium compound is added. The ion concentration in the wastewater is stirred and tested, and the dosage is calculated.

[0015] As an optional embodiment, in the treatment process provided by the present invention, the amount of magnesium compound added is 10-20% excess of the theoretical mass.

[0016] As an optional embodiment, in the treatment process provided by the present invention, in step S1, the solid residue is used as fertilizer for the growth of crops.

[0017] In the present invention, the main component of the solid residue obtained after precipitation is ammonium magnesium phosphate, commonly known as struvite, which can be used as a fertilizer. The impurity content of other solid residues is relatively small and does not affect soil performance when used as fertilizer.

[0018] As an optional embodiment, in the treatment process provided by the present invention, in step S1, the ferric phosphate rinsing water is cooled to less than 40°C and then concentrated, and the ferric phosphate synthesis mother liquor is cooled to less than 40°C and then precipitated.

[0019] In the present invention, considering that the temperature of the iron phosphate rinse water is about 80 degrees Celsius, while the operating temperature of the RO membrane currently used for concentration is below 40°C, the iron phosphate rinse water must be cooled before entering the pure water membrane system.

[0020] As an optional embodiment, in the treatment process provided by the present invention, in step S2, the precipitate is treated with a plate and frame filter and a precision filter and then the pH value is adjusted with dilute sulfuric acid.

[0021] After the solid-liquid separation in step S1, the obtained precipitate still contains fine precipitates that are not removed during the solid-liquid separation process. Therefore, after being processed by a plate and frame filter and a precision filter to further remove the precipitates, it is beneficial to obtain a single magnesium sulfate product later.

[0022] As an optional embodiment, in the treatment process provided by the present invention, in step S2, the evaporation crystallization adopts an MVR evaporation system, and the MVR evaporation system produces condensed water and concentrated liquid. After the condensed water is cooled, it passes through a pure water membrane system to obtain pure water with a conductivity of less than 10us / cm, and the concentrated liquid enters the MVR evaporation system again to produce magnesium sulfate.

[0023] In the present invention, an MVR evaporation system is used to evaporate the filtered precipitate. The temperature of the condensed water obtained by evaporation is about 80-90°C, and it needs to be cooled first. The conductivity of the evaporated condensed water is still about 100us / cm, which does not meet the reuse index requirement (less than 10us / cm). Therefore, it needs to be treated by a pure water membrane system to reduce the conductivity. The obtained concentrated liquid enters the MVR evaporation system again to produce magnesium sulfate, and the generated condensed water is fresh water that can be directly recycled to meet the standards.

[0024] As an optional embodiment, in the treatment process provided by the present invention, in step S2, the solid magnesium oxide enters the iron phosphate wastewater treatment process again, and the sulfur dioxide gas enters the sulfuric acid production process.

[0025] After treating the iron phosphate wastewater in the present invention, solid magnesium oxide and gaseous sulfur dioxide are obtained, wherein the magnesium oxide can be further used in the treatment of the iron phosphate wastewater, thus realizing the recycling of magnesium, and the prepared sulfur dioxide gas can be used for the preparation of sulfuric acid.

[0026] As an optional embodiment, in the treatment process provided by the present invention, in step S2, in the solution after the pH value is adjusted with dilute sulfuric acid, the fluoride ion concentration is less than 5 mg / L, the iron ion concentration is less than 1 mg / L, the ammonia nitrogen concentration is less than 10 mg / L, and the total phosphorus concentration is less than 0.5 mg / L.

[0027] As an optional embodiment, in the treatment process provided by the present invention, an adjustment tank is used for precipitation in step S1, and the material of the adjustment tank is selected from one of PPH (propylene homopolymer), fiberglass, steel lining rubber, steel lining fiberglass or concrete lining anti-corrosion coating.

[0028] As an optional embodiment, in the treatment process provided by the present invention, the precision filter is selected from a microfiltration-level filter with or without an automatic backwashing device.

[0029] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses an excess of magnesium compounds to precipitate the iron phosphate synthesis mother liquor and the iron phosphate rinse water concentrate. After treatment, the fluoride ion concentration is less than 5 mg / L, the iron ion concentration is less than 1 mg / L, the ammonia nitrogen concentration is less than 10 mg / L, and the total phosphorus concentration is less than 0.5 mg / L. The heavy metal ions, hydrogen ions, fluoride ions, phosphate ions and ammonium ions are removed at one time, which can ensure the removal effect while retaining the sulfate ions in the solution without introducing new impurity ions. It is very important to improve the purity and grade of the magnesium sulfate product, and effectively avoid the problem of incomplete salt separation by the "ammonia method". The magnesium oxide obtained after calcining the magnesium sulfate product can continue to be used for the treatment of iron phosphate wastewater, and the obtained sulfur dioxide gas can be used for the preparation of sulfuric acid, which truly realizes the recycling of magnesium and has no secondary pollution problems.

[0030] (2) The defluorination of iron phosphate wastewater in the present invention can effectively reduce the corrosion of fluoride ions on the evaporation system and reduce the material requirements of the evaporation system: from 2205 duplex steel to 316L, thereby effectively reducing the investment cost.

[0031] (3) The present invention removes the divalent iron ions and other heavy metal ions in the iron phosphate wastewater. The divalent iron ions are colored. If they are not removed, they will enter the crystalline salt, seriously affecting the quality of the salt. In addition, iron ions will oxidize the reverse osmosis membrane, causing irreversible damage, and the content must be strictly controlled to ensure its stable operation. At the same time, iron ions will cause scaling and corrosion in the system. The present invention can effectively remove iron ions and other heavy metal ions, thereby improving the purity and grade of the magnesium sulfate by-product, protecting the reverse osmosis membrane, and making it run stably. At the same time, it can also effectively reduce the corrosion, scaling and clogging of the evaporation system, making it run more stably.

[0032] (4) The system of the present invention has a short process flow, removes pollutants efficiently and thoroughly, and has extremely low investment and operating costs. Compared with other technologies, it has incomparable advantages in cost and is more meaningful for promotion and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0034] Figure 1 This is a process flow chart for treating iron phosphate wastewater in Example 1 of the present application. DETAILED DESCRIPTION

[0035] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0036] Unless otherwise defined, all the professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0037] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0038] Example 1 A 50,000-ton iron phosphate project produced 84m3 of iron phosphate synthesis mother liquor 3 / h, temperature about 90℃, pH 2-2.5, F - 30-50mg / L, total P 2200-3000mg / L, Fe 2+ 30-50mg / L, Mg 2+ 500-700mg / L, NH3-N6000-7000mg / L, SO4 2- 50000-60000mg / L. Produces about 450m3 of iron phosphate rinse water 3 / h, temperature about 90℃, pH 2.2-2.5, F - ≤20mg / L, total P200-400mg / L, Fe 2+ ≤30mg / L, Mg 2+ 30-50mg / L, NH3-N1500-2000mg / L, SO4 2-3000-4000mg / L.

[0039] Treatment methods such as Figure 1 As shown: (1) The iron phosphate rinse water is first cooled to below 40°C by a plate heat exchanger before entering the membrane concentration system. The membrane concentration system has a water production rate of about 80%, and produces about 100m3 of concentrated water for iron phosphate rinse water. 3 / h enters the pH adjustment tank.

[0040] (2) The mother liquor of ferric phosphate synthesis is first cooled to below 35°C by a plate heat exchanger and then enters the regulating tank to be mixed with the concentrated water of ferric phosphate rinse water for homogenization.

[0041] (3) The volume of mixed wastewater is about 180m 3 / h, temperature about 30℃, pH 2-2.5, F - 50mg / L, total P 2500mg / L, Fe 2+ ≤1mg / L, Mg 2+ 500mg / L, NH3-N 7500mg / L, SO4 2- 50000mg / L.

[0042] (4) Add magnesium phosphate and magnesium hydroxide to the regulating tank. Before adding, use the beaker method to determine the amount to be added. The specific process is: first use a beaker to take 100mL of wastewater, add magnesium phosphate and magnesium hydroxide, stir and test the ammonia nitrogen concentration in the water. When the ammonia nitrogen concentration drops below 10mg / L, calculate the dosage. The test calculation shows that when the water volume of the mixed wastewater is 180m 3 / h, the dosage of reagents is: magnesium phosphate dosage is about 10kg / h, magnesium hydroxide dosage is 50kg / h. In actual production, the reagents are added in excess of 10%, that is, the actual dosage of magnesium phosphate is about 11kg / h, and the actual dosage of magnesium hydroxide is about 55kg / h, for precipitation reaction.

[0043] (5) After sufficient sedimentation, the effluent first passes through a vacuum belt dehydrator to separate the slag from the water, then passes through a two-stage filtration process of plate and frame filtration and a regenerable precision filter to remove fine suspended matter, and then enters the pH adjustment tank.

[0044] (6) Add 30% dilute sulfuric acid to the pH adjustment tank to adjust the pH of the solution to 7. The water quality of the pH adjustment tank outlet is: pH = 7, F - ≤6mg / L, total P≤0.5mg / L, Fe 2+ ≤1mg / L, NH3-N≤10mg / L, SO4 2- 50000mg / L, and the contents of other heavy metals fully meet the direct emission index requirements in the "Inorganic Chemical Industry Pollutant Emission Standard" (GB31573-2015).

[0045] (7) The effluent from the pH adjustment pool enters the MVR evaporation system. The condensed water produced by the MVR evaporation system has a temperature of 80°C. It is cooled to below 35°C by the heat exchanger and then enters the pure water membrane system. The pure water membrane system includes a security filter, ultrafiltration and reverse osmosis process to obtain pure water with a conductivity of less than 10us / cm. The pure water is returned to production. The concentrated water returns to the MVR evaporation system for evaporation and crystallization. The fresh water obtained here meets the standards for recycling, and the magnesium sulfate crystals obtained are used for standby. The magnesium sulfate output is about 12t / h.

[0046] In this embodiment, the MVR evaporation system, the heat exchanger and the pure water membrane system are all existing technologies and will not be described in detail here.

[0047] (8) The obtained magnesium sulfate crystals and charcoal powder are used as raw materials and calcined in a high-temperature calcining furnace. The calcination temperature is controlled to be 800°C, the calcination time is controlled to be 2 hours, and the ratio of magnesium sulfate to charcoal powder is controlled to be 8:1, thereby obtaining solid magnesium oxide and sulfur dioxide gas. The magnesium oxide can continue to be used for the treatment of iron phosphate wastewater, and the sulfur dioxide gas can be used to prepare sulfuric acid after being collected.

[0048] Example 2 The difference from Example 1 is that in step (4), magnesium phosphate, magnesium oxide and magnesium hydroxide are added to the regulating tank, and the amount to be added is determined by the beaker method before adding. The specific process is: first use a beaker to take 100mL of wastewater, add magnesium phosphate, magnesium oxide and magnesium hydroxide, stir and test the ammonia nitrogen concentration in the water, and when the ammonia nitrogen concentration drops below 10mg / L, the dosage can be calculated. It was calculated through testing that when the water volume of the mixed wastewater is 180m 3 / h, the dosage of reagents is: magnesium phosphate dosage is about 10kg / h, magnesium oxide dosage is about 17.5kg / h, and magnesium hydroxide dosage is about 25kg / h. In actual production, the reagents are added in excess of 20%, that is, magnesium phosphate dosage is about 12kg / h, magnesium oxide dosage is about 21kg / h, and magnesium hydroxide dosage is about 30kg / h, and precipitation reaction is carried out. In step (6), 30% dilute sulfuric acid is added to the pH adjustment tank to adjust the pH of the solution to 8. The water quality of the pH adjustment tank effluent is: pH=7, F - ≤2.7mg / L, total P≤0.2mg / L, Fe 2+ ≤0.6mg / L, NH3-N≤5mg / L, SO4 2- 50000mg / L, and the contents of other heavy metals fully meet the direct emission index requirements in the "Inorganic Chemical Industry Pollutant Emission Standard" (GB31573-2015). The output of magnesium sulfate obtained in step (7) is about 12t / h.

[0049] The remaining steps are the same as in Example 1.

[0050] Example 3 The difference from Example 1 is that in step (4), magnesium phosphate and magnesium oxide are added to the regulating tank, and the amount to be added is determined by the beaker method before adding. The specific process is: first use a beaker to take 100mL of wastewater, add magnesium phosphate and magnesium oxide, stir and test the ammonia nitrogen concentration in the water, and when the ammonia nitrogen concentration drops below 10mg / L, the dosage is calculated. The test calculation shows that when the water volume of the mixed wastewater is 180m 3 / h, the dosage of reagents is: magnesium phosphate dosage is about 10kg / h, magnesium oxide dosage is about 35kg / h. In actual production, the reagents are added in excess of 15%, that is, magnesium phosphate dosage is about 11.5kg / h, magnesium oxide dosage is about 38.5kg / h, and precipitation reaction is carried out. In step (6), 30% dilute sulfuric acid is added to the pH adjustment tank to adjust the pH of the solution to 9. The water quality of the pH adjustment tank outlet is: pH = 7, F - ≤1.8mg / L, total P≤0.3mg / L, Fe 2+ ≤0.5mg / L, NH3-N≤3mg / L, SO4 2- 50000mg / L, and the contents of other heavy metals fully meet the direct emission index requirements in the "Inorganic Chemical Industry Pollutant Emission Standard" (GB31573-2015). The output of magnesium sulfate obtained in step (7) is about 12t / h.

[0051] The remaining steps are the same as in Example 1.

[0052] Comparative Example 1 The difference from Example 1 is that in step (4), magnesium phosphate and magnesium hydroxide are added in equal amounts to the regulating tank, and the amount to be added is determined by the beaker method before adding. The specific process is: first use a beaker to take 100mL of wastewater, add magnesium phosphate and magnesium hydroxide, stir and test the ammonia nitrogen concentration in the water, and when the ammonia nitrogen concentration drops below 10mg / L, the dosage is calculated. It is calculated by testing that when the water volume of the mixed wastewater is 180m 3 / h, the dosage of the reagents is: magnesium phosphate dosage is about 10kg / h, magnesium hydroxide dosage is 50kg / h. Add in equal amounts.

[0053] (5) After sufficient sedimentation, the effluent first passes through a vacuum belt dehydrator to separate the slag from the water, then passes through a two-stage filtration process of plate and frame filtration and a regenerable precision filter to remove fine suspended matter, and then enters the pH adjustment tank.

[0054] (6) Add 30% dilute sulfuric acid to the pH adjustment tank to adjust the pH of the solution to 7. The water quality of the pH adjustment tank outlet is: pH = 7, F - 10mg / L, total P0.8mg / L, Fe 2+ 5mg / L, NH3-N 25mg / L, SO4 2- 50000mg / L.

[0055] (7) The effluent from the pH adjustment pool enters the MVR evaporation system. The condensed water produced by the MVR evaporation system has a temperature of 80°C. After being cooled to below 35°C by the heat exchanger, it enters the pure water membrane system. The pure water membrane system includes a security filter, ultrafiltration and reverse osmosis process to obtain pure water with a conductivity of less than 10us / cm. The pure water is returned to the production. The concentrated water returns to the MVR evaporation system for evaporation and crystallization. The fresh water obtained here contains a small amount of ammonia nitrogen. The magnesium sulfate crystals obtained contain a small amount of fluoride ions, phosphates and iron impurities and are slightly yellow. The magnesium sulfate output is about 12t / h.

[0056] The remaining processing steps are the same as in Example 1.

[0057] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the scope of protection of the present invention.

Claims

1. A ferric phosphate wastewater treatment process based on magnesium recycling, characterized in that: The following steps are involved: S1. Adding an excess amount of magnesium compound to the iron phosphate wastewater for precipitation reaction, and obtaining solid slag and precipitate after solid-liquid separation; S2, adjusting the pH of the precipitate obtained in step S1 to 7-9 with dilute sulfuric acid and then performing evaporation and crystallization to obtain magnesium sulfate solid; S3. Calcining the magnesium sulfate solid to obtain solid magnesium oxide and sulfur dioxide gas.

2. The ferric phosphate wastewater treatment process based on magnesium recycling according to claim 1 is characterized in that: In step S1, the magnesium compound is selected from one or more of magnesium oxide, magnesium hydroxide, magnesium phosphate and magnesium hydrogen phosphate.

3. The ferric phosphate wastewater treatment process based on magnesium recycling according to claim 1 is characterized in that: The ferric phosphate wastewater includes ferric phosphate synthesis mother liquor and ferric phosphate rinsing water concentrate; the ferric phosphate wastewater has a pH of 2-2.5, a fluoride ion concentration of 30-50 mg / L, a total phosphorus of 2200-3000 mg / L, and Fe 2+ The concentration is 30~50mg / L, Mg 2+ The concentration is 500~700mg / L, NH3-N is 6000~7000mg / L, SO4 2- The concentration is 50000~60000mg / L.

4. The ferric phosphate wastewater treatment process based on magnesium recycling according to claim 3 is characterized in that: The concentrated ferric phosphate rinse water is obtained by concentrating the ferric phosphate rinse water 4 to 6 times, and the concentrated fresh water is recovered for treatment.

5. The ferric phosphate wastewater treatment process based on magnesium recycling according to claim 1 is characterized in that: In step S1, the amount of magnesium compound added is 10-20% excess of the theoretical mass.

6. The ferric phosphate wastewater treatment process based on magnesium recycling according to claim 1 is characterized in that: In step S1, the solid residue is used as fertilizer for crops.

7. The ferric phosphate wastewater treatment process based on magnesium recycling according to claim 1 is characterized in that: In step S2, the precipitate is treated by a plate and frame filter and a precision filter and then the pH value is adjusted with dilute sulfuric acid.

8. The ferric phosphate wastewater treatment process based on magnesium recycling according to claim 1 is characterized in that: In step S3, the solid magnesium oxide enters the iron phosphate wastewater treatment process again, and the sulfur dioxide gas enters the sulfuric acid production process.

9. The ferric phosphate wastewater treatment process based on magnesium recycling according to claim 1, characterized in that: In step S2, in the solution after the pH value is adjusted with dilute sulfuric acid, the fluoride ion concentration is less than 5 mg / L, the iron ion concentration is less than 1 mg / L, the ammonia nitrogen concentration is less than 10 mg / L, and the total phosphorus concentration is less than 0.5 mg / L.

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