CN115340237A

CN115340237A - Iron phosphate production wastewater treatment method and system

Info

Publication number: CN115340237A
Application number: CN202210912776.5A
Authority: CN
Inventors: 侯愉婷; 童秋桃
Original assignee: Zhejiang Huayou Cobalt Co Ltd
Current assignee: Zhejiang Huayou Cobalt Co Ltd
Priority date: 2022-07-31
Filing date: 2022-07-31
Publication date: 2022-11-15

Abstract

The application discloses a method and a system for treating wastewater generated in iron phosphate production. The method for treating the wastewater generated in the iron phosphate production comprises the following steps: mixing wastewater generated in iron phosphate production with a calcium-containing compound, carrying out precipitation reaction, collecting ammonia generated in the process, carrying out solid-liquid separation on a generated mixed solution containing calcium sulfate precipitate to obtain calcium sulfate precipitate and filtrate, further preparing calcium sulfate into concentrated sulfuric acid and calcium oxide, using the concentrated sulfuric acid for pH adjustment or selling, recycling the calcium oxide as the calcium-containing compound, concentrating the filtrate to obtain concentrated solution and water, and combining the concentrated solution into the wastewater for centralized treatment. The collected ammonia and water were used for iron phosphate production. The iron phosphate production wastewater treatment method and system can treat iron phosphate production wastewater, are high in wastewater treatment efficiency, low in economic cost, low in energy consumption and environment-friendly, and the recovered byproducts can be collected and recycled to realize comprehensive utilization of resources in a sulfur, ammonium, phosphorus and calcium recycling mode.

Description

Iron phosphate production wastewater treatment method and system

Technical Field

The application belongs to the technical field of wastewater treatment, and particularly relates to a method and a system for treating wastewater generated in iron phosphate production.

Background

The ferric phosphate is an important precursor material of the anode material of the lithium ion battery. Currently, iron phosphate is mainly prepared by a coprecipitation method. In the co-precipitation process, the iron phosphate product is obtained by mixed precipitation of an iron source and a phosphorus source (e.g., monoammonium phosphate), but also produces a large amount of sulfate-containing (SO) at a high concentration ₄ ^2- ) Phosphate radical (PO) ₄ ^3- ) And ammonia Nitrogen (NH) ₄ -N) acid waste water.

At present, pollutants such as ammonia nitrogen, phosphate radical, sulfate radical, acid and the like in the iron phosphate wastewater are mainly removed by a chemical precipitation method, but residues generated by precipitation contain calcium phosphate and calcium sulfate, so that the recycling is difficult, and the problems of high operation cost, phosphorus and sulfur resource waste and the like are caused. From the viewpoint of environmental protection and resource recycling, it is necessary to develop a method which can recover phosphate and sulfate from wastewater from iron phosphate production and has low running cost.

The waste water treatment link is an important cost source in the iron phosphate production, and at present, the treatment method aiming at the waste water generated in the iron phosphate production process mainly comprises the following steps: (1) direct treatment: removing phosphorus elements in the wastewater by a coprecipitation method, adjusting the pH value to 13-14, removing ammonia nitrogen in the wastewater by blowing, and then adjusting the pH value back to neutral and discharging to a sewage treatment plant for treatment; (2) ammonium sulfate recovery treatment: adjusting the pH value of the wastewater, removing metal ions in the wastewater in a precipitation mode, and then performing membrane concentration, evaporative crystallization and other steps to obtain a ammonium sulfate byproduct; (3) recycling treatment method: and (3) mixing the concentrated washing water with the mother liquor, removing sulfate radicals in the mixed liquor in a calcium salt precipitation mode, and recycling the mixed liquor to recycle ammonium radicals and phosphate radicals.

Although the existing treatment method for wastewater generated in the iron phosphate production process can effectively treat wastewater to a certain extent, some defects are found in actual generation, and the treatment method of the method (1) is simple, but the wastewater amount is large, phosphorus in the wastewater cannot be utilized, and the environmental protection cost is high; although the method (2) can increase the income of a certain amount of ammonium sulfate byproducts, at least 20 tons of water need to be evaporated to treat the wastewater generated by each ton of iron phosphate, the steam consumption is large, and the energy consumption cost is extremely high; the method (3) can reduce the amount of waste water, but on one hand, phosphate radical in the waste water can be combined with calcium ions to generate calcium phosphate, and a large amount of phosphogypsum is generated, so that partial phosphorus is lost; on the other hand, the phosphogypsum belongs to hazardous waste, the consumption of a rear-end industrial chain is less, the treatment is difficult, the environmental pollution is easy to cause, and the large-scale application is difficult.

Therefore, the existing method for treating wastewater generated in the iron phosphate production process has the problems of environmental pollution, waste of nitrogen and phosphorus resources or high energy consumption and the like, and along with the popularization of battery application, the wastewater treatment pressure of iron phosphate production is increased. How to improve the wastewater treatment efficiency of iron phosphate production, improve the utilization rate of nitrogen and phosphorus and reduce energy consumption and economic cost is a problem which is urgently expected to be overcome by the current efforts in the field.

Disclosure of Invention

The purpose of the embodiment of the application is to overcome the above defects of the prior art at least to a certain extent, and provide a method for treating wastewater from iron phosphate production and a system for treating wastewater from iron phosphate production for implementing the method, so as to solve the technical problems of environmental pollution, waste of nitrogen and phosphorus resources or high energy consumption and the like in the existing method for treating wastewater from iron phosphate production.

In order to achieve the purpose of the application, in a first aspect of the application, a method for treating wastewater generated in iron phosphate production is provided. The method for treating the wastewater generated in the iron phosphate production comprises the following steps:

mixing wastewater generated in iron phosphate production with a calcium-containing compound, and carrying out precipitation reaction treatment to generate calcium sulfate precipitate;

carrying out solid-liquid separation on the mixed solution containing the calcium sulfate precipitate to obtain calcium sulfate-containing filter residue and filtrate;

and concentrating the filtrate to obtain a concentrated solution and water.

In a second aspect of the application, a wastewater treatment system for iron phosphate production is provided. The iron phosphate production wastewater treatment system is used for realizing the iron phosphate production wastewater treatment method, and comprises the following steps:

the calcium sulfate precipitation reaction device is used for reacting the iron phosphate production wastewater with the calcium-containing compound to generate calcium sulfate precipitation;

the solid-liquid separation device is used for carrying out solid-liquid separation on the mixed solution containing the calcium sulfate precipitate generated in the calcium sulfate precipitation reaction device to obtain filter residue containing the calcium sulfate and filtrate;

and the solution concentration device is used for concentrating the filtrate separated by the solid-liquid separation device to obtain a concentrated solution and water.

Compared with the prior art, the method has the following technical effects:

the iron phosphate production wastewater treatment method adopts a calcium-containing compound to carry out precipitation reaction on iron phosphate production wastewater, sulfate ions in the wastewater can be separated and collected by calcium sulfate precipitation, the energy consumption is low, recovered byproducts such as calcium sulfate filter residues, concentrated solution and water can be collected and recycled, and equipment and wastewater treatment steps are not additionally added, so that the wastewater treatment efficiency of the iron phosphate production wastewater treatment method is effectively improved, the economic cost is obviously reduced, the method is environment-friendly, hazardous waste generation is effectively avoided simultaneously, and the harm to the environment is reduced or completely avoided.

This application iron phosphate waste water treatment system can effectively implement this application iron phosphate waste water treatment method to the realization is handled iron phosphate waste water, and reaches the energy consumption low, and the accessory substance of recovery all can be collected basically and recycled, realizes simultaneously that waste water treatment is efficient, and economic cost is low, and environment-friendly.

Drawings

In order to more clearly illustrate the detailed description of the present application or the technical solutions in the prior art, the drawings needed to be used in the detailed description of the present application or the prior art description will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is a schematic process flow diagram of a wastewater treatment method in iron phosphate production according to an embodiment of the present application;

FIG. 2 is a process flow diagram of a wastewater treatment method in iron phosphate production according to an embodiment of the present application;

fig. 3 is a Scanning Electron Microscope (SEM) of anhydrous iron phosphate prepared in step S2 of example 1 of the present application;

fig. 4 is a Scanning Electron Microscope (SEM) of anhydrous iron phosphate prepared in step S2 of example 2 of the present application;

fig. 5 is a Scanning Electron Microscope (SEM) of anhydrous iron phosphate prepared in step S2 of comparative example 1.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present application more clearly apparent, the present application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

In the present application, "at least one" means one or more, "a plurality" means two or more. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of the singular or plural items. For example, "at least one (one) of a, b, or c," or "at least one (one) of a, b, and c," may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, and c may be single or plural, respectively.

It should be understood that, in various embodiments of the present application, the sequence numbers of the foregoing processes do not imply an execution sequence, some or all of the steps may be executed in parallel or executed sequentially, and the execution sequence of each process should be determined by its function and inherent logic, and should not limit the implementation process of the embodiments of the present application.

The terminology used in the embodiments of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the examples of this application and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

The weight of the related components mentioned in the description of the embodiments of the present application may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, and therefore, the content of the related components is scaled up or down within the scope disclosed in the description of the embodiments of the present application as long as it is scaled up or down according to the description of the embodiments of the present application. Specifically, the mass described in the specification of the embodiments of the present application may be a mass unit known in the chemical industry field such as μ g, mg, g, kg, etc.

The terms "first" and "second" are used for descriptive purposes only and are used for distinguishing purposes such as substances from one another, and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. For example, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX, without departing from the scope of embodiments of the present application. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

In a first aspect, the embodiment of the application provides a method for treating wastewater generated in iron phosphate production. The process flow of the iron phosphate production wastewater treatment method in the embodiment of the application is shown in fig. 1 and fig. 2, and comprises the following steps:

s01: mixing wastewater generated in iron phosphate production with a calcium-containing compound, and carrying out precipitation reaction treatment to generate ammonia-containing gas and calcium sulfate precipitate;

s02: carrying out solid-liquid separation on the mixed solution containing the calcium sulfate precipitate to obtain calcium sulfate-containing filter residue and filtrate;

s03: and concentrating the filtrate to obtain a concentrated solution and water.

According to the iron phosphate production wastewater treatment method in the embodiment of the application, through the treatment steps, particularly, if a calcium-containing compound is adopted to perform precipitation reaction on iron phosphate production wastewater in the step S01, sulfate ions in the wastewater can be separated and collected in the step S02 through calcium sulfate precipitation, the energy consumption is low, recovered byproducts such as calcium sulfate filter residues can be collected and reused, and the generation of hazardous waste is avoided. The concentrated solution and water can be further collected by the concentration processing in step S03, and both can be collected and reused. Therefore, the iron phosphate production wastewater treatment method provided by the embodiment of the application does not additionally increase equipment and wastewater treatment steps, effectively improves the stability and efficiency of wastewater treatment, obviously reduces the economic cost, is environment-friendly, effectively avoids hazardous wastes, and reduces or completely avoids the harm to the environment.

Wherein, the ferric phosphate production in step S01 can be prepared according to the existing method. In the embodiment of the present application, the iron phosphate production may be prepared according to the method shown in fig. 2, which specifically includes the following steps:

s011: preparing a mixture solution containing ferrous salt, a phosphorus source, an oxidant and a pH regulator;

s012: reacting the mixed solution in the step S011 at a certain temperature to obtain iron phosphate slurry;

s013: performing solid-liquid separation treatment on the iron phosphate slurry in the step S012 to obtain an iron phosphate filter cake and a mother solution,

s014: washing the iron phosphate filter cake obtained in the step S013 to obtain washing water and iron phosphate;

s015: the mother liquor in step S013 and/or the wash water in step S013 is used as wastewater.

In the step S011, the mixture solution may be prepared by first preparing a ferrous salt solution and a phosphorus source solution, and then mixing the solutions in a certain ratio to form the mixture solution. Or ferrous salt, a phosphorus source, an oxidant and a pH regulator can be directly added into a solvent according to a certain proportion for dissolving to prepare a mixture solution; it is also possible to prepare a mixed solution of a ferrous salt and a phosphorus source first, and then add an oxidizing agent and a pH adjusting agent to form a mixed solution. When the ferrous salt solution and the phosphorus source solution are prepared first, in an embodiment, the molar concentration of the ferrous salt solution may be 1.0 to 2.0mol/L, and the molar concentration of the phosphorus source solution may be 1.0 to 3.0mol/L. In particular embodiments, the ferrous salt may include ferrous sulfate, and the source of phosphorus may include at least one of phosphoric acid, monoammonium phosphate, diammonium phosphate, triammonium phosphate. Additionally, the solvent may be water.

In an embodiment, the ferrous salt and the phosphorus source in step S011 can be mixed according to a ratio of a molar ratio of the phosphorus element to the iron element of 0.9 to 1.5.

In addition, the oxidizing agent in step S011 is such that ferrous ions are oxidized to generate ferric ions. The presence of a pH adjuster to increase the yield of iron phosphate. The addition amount of the oxidant can be excessive relative to the ferrous ions so as to ensure that the ferrous ions are fully oxidized to generate ferric ions, and for example, the addition amount of the oxidant can be controlled to be 0.5-0.65 times of the mole number of the ferrous ions. When the oxidizing agent is added in the form of a solution, the oxidizing agent has a concentration of 27-33% by weight. In a specific embodiment, the oxidant may include hydrogen peroxide, such as hydrogen peroxide solution with a concentration of 27-33% by weight. The addition amount of the pH adjuster may be a conventional addition amount according to the preparation of iron phosphate. In a specific embodiment, the pH adjuster may include at least one of ammonia water and caustic soda, wherein the ammonia water has a concentration of 17% to 28% and the caustic soda has a concentration of 25% to 33%.

In step S012, by this reaction treatment, ferrous iron is oxidized to generate ferric ions, and reacts with phosphate ions to generate iron phosphate precipitates. In an embodiment, the temperature of the reaction treatment in step S012 may be 25 to 90 ℃, and the reaction time should be sufficient, for example, 2 to 4 hours. So that the iron ions are fully precipitated and the yield of the iron phosphate is improved.

Since solid-liquid separation in step S013 is performed for the purpose of separating the iron phosphate precipitate from the solvent, any separation method that can separate the iron phosphate precipitate and the solvent is within the range disclosed in the description of the embodiments of the present application, and such separation method may be filtration, centrifugation, or other methods. Wherein the filtrate, i.e. the mother liquor, constitutes the waste liquid to be treated, and can be used as the waste water in step S01.

The washing process in step S014 is to purify the iron phosphate precipitate and improve the purity of the iron phosphate precipitate. After this washing treatment, washing water is obtained, which constitutes a waste liquid to be treated like the mother liquid in step S013, and which may also be used as the waste water in step S01.

The ferric phosphate precipitate after washing treatment can be dried, roasted and the like, crystal water is removed, and the purity of the ferric phosphate precipitate is improved. As shown in the embodiment, the drying temperature of the ferric phosphate precipitate (also called ferric phosphate filter cake) is 100-150 ℃, and the drying time is 0.5-6 h. The roasting treatment of the iron phosphate precipitate can be carried out as follows: firstly, heat preservation treatment is carried out for 0.5 to 2 hours at the temperature of between 150 and 300 ℃, and then the temperature is raised to between 500 and 800 ℃ for heat preservation for 2 to 5 hours.

In step S015, the mother liquor in step S013 and the washing water in step S014 are collected or the mother liquor and the washing water are mixed as wastewater in step S01.

After treatment based on the iron phosphate preparation method, phosphate radicals can be precipitated to the maximum extent, and sulfate is the main component in the wastewater, so that after the calcium-containing compound is mixed with the wastewater in step S01, the calcium ions can perform precipitation reaction with sulfate ions in the wastewater to generate calcium sulfate precipitates, and the sulfate ions are effectively removed. In the embodiment, the wastewater and the calcium-containing compound can be mixed according to the ratio of the molar ratio of the sulfur element to the calcium element contained in the wastewater being 0.9 to 1.5. In a particular embodiment, the calcium-containing compound comprises at least one of calcium oxide, calcium hydroxide, calcium carbonate. The calcium-containing compounds have good solubility, provide calcium ions, and do not generate other impurity ions, so that the filtrate in step S02 can be utilized or the environmental pressure of the subsequent treatment of the filtrate can be reduced. In the embodiment of the present application, calcium oxide is relatively preferable, so that when the calcium sulfate precipitate is subjected to a subsequent treatment such as a calcination treatment of the calcium sulfate precipitate, the generated calcium oxide can be directly used as the calcium-containing compound to be subjected to a mixing treatment and a precipitation reaction treatment with wastewater generated in the production of iron phosphate, so as to fully utilize by-products generated in the wastewater treatment.

In an embodiment, the temperature of the precipitation reaction treatment in step S01 may be 30 to 70 ℃; or further controlling the air pressure of the precipitation reaction processing environment to be 0.07-0.1 Mpa. Through controlling the precipitation reaction, can effectively improve sulfate ion's precipitation efficiency, improve sulfate ion's rate of recovery, when ammonia generates, also be favorable to the discharge and the collection of ammonia. In addition, the time of the precipitation reaction should be sufficient to ensure that the sulfate and calcium ions are sufficiently reacted. When the calcium-containing compound is calcium oxide, the temperature of the precipitation reaction treatment can be caused by heat generated by the reaction of the calcium oxide and the wastewater, and the precipitation reaction treatment is not required to be additionally heated, so that the energy consumption of wastewater treatment can be saved.

In the embodiment, when the wastewater contains ammonium ions in step S01, for example, the wastewater contains ammonium sulfate or ammonia, for example, when an ammonia pH adjuster is added during the iron phosphate process or/and the phosphorus source is ammonium phosphate, ammonia-containing gas is also generated during the precipitation reaction treatment in step S01. Based on the alkaline property of ammonia gas, the method for treating wastewater from iron phosphate production in the embodiment of the application further comprises the step of using the generated ammonia-containing gas as a pH regulator or using a solution after water absorption, namely ammonia water, as the pH regulator for preparing iron phosphate. Namely, as a pH adjuster in step S011 of the above iron phosphate production method or as shown in fig. 2, the ammonia-containing gas or the solution after absorption with water is returned to the mixture solution. Therefore, the reutilization rate of the by-products generated by the iron phosphate production wastewater treatment method in the embodiment of the application can be further improved.

The solid-liquid separation in step S02 is to separate the calcium sulfate precipitate from the solvent in step S01 to obtain a calcium sulfate filter residue and a filtrate, respectively. Therefore, any separation method that can separate the precipitated calcium sulfate from the solvent is within the scope of the disclosure in the present embodiment, and may be, for example, filtration, centrifugation, or other methods.

The collected calcium sulfate precipitate can be reused according to the application requirement. As in the embodiment, after the step of solid-liquid separation treatment in step S02, the method further includes a step of calcining the calcium sulfate-containing filter residue to generate sulfur dioxide. The calcining condition can be set according to the thermal decomposition characteristic of calcium sulfate, for example, the calcining temperature is 650-1300 ℃, so that the calcium sulfate filter residue is fully decomposed to generate sulfur dioxide. In addition, due to the content factor of the moisture in the calcium sulfate filter residue, the calcium sulfate filter residue may be dried before the calcination treatment, so as to remove the moisture contained in the calcium sulfate filter residue and improve the efficiency of the calcination treatment, for example, in the embodiment, the drying treatment of the calcium sulfate filter residue may be performed at 100 to 150 ℃ for 0.5 to 6 hours, so as to sufficiently dry the calcium sulfate filter residue.

In order to fully utilize the calcium sulfate filter residue, in a further embodiment, after the step of performing the above-mentioned calcination treatment on the calcium sulfate filter residue, a step of performing oxidation treatment on sulfur dioxide generated by the calcination treatment to generate sulfur trioxide, and preparing concentrated sulfuric acid by using the sulfur trioxide is further included. As the concentrated sulfuric acid is an important industrial production raw material, the concentrated sulfuric acid can offset the cost consumed by the iron phosphate production wastewater treatment method in the embodiment of the application, such as the energy consumption cost consumed by calcination treatment, so that the economic cost of the iron phosphate production wastewater treatment method is reduced. In the embodiment, the prepared concentrated sulfuric acid may be introduced into the filtrate obtained by solid-liquid separation in step S02 to adjust the pH in the filtrate.

In an embodiment, a calcium-containing product, that is, calcium oxide, generated by subjecting the calcium sulfate filter residue to the calcination treatment may be used as the calcium-containing compound in step S01, that is, the method for treating wastewater from iron phosphate production according to the embodiment of the present application further includes a step of mixing the calcium-containing product generated by subjecting the calcium sulfate filter residue to the calcination treatment with the wastewater in step S01, and performing a precipitation reaction treatment. Thus, the by-products generated by the iron phosphate production wastewater treatment method can be fully utilized. Of course, a small amount of phosphate ions still remain in the wastewater in step S01 during the actual generation process, and a small amount of calcium phosphate is also generated from the remaining small amount of phosphate ions during the precipitation reaction between the wastewater and the calcium-containing compound. When the calcium sulfate filter residue is decomposed into calcium oxide and sulfur dioxide in the calcination treatment, the calcium phosphate with low content is not decomposed. Which is enriched with the calcium oxide as a calcium-containing compound in step S01 during recycling. In order to realize the recycling of the enriched calcium phosphate, after the calcium phosphate is enriched to a certain content, sulfuric acid can be adopted to react with the calcium phosphate, so that the generated calcium sulfate can be collected and calcined for recycling as described above, and phosphorus elements cannot be wasted. Therefore, in the embodiment, the recycling step of mixing calcium oxide as a calcium-containing compound with wastewater and performing precipitation reaction treatment further comprises the following steps after the recycling is performed for at least one cycle:

s021: firstly, measuring the content of calcium phosphate in calcium sulfate precipitation generated by precipitation reaction, when the content of detected calcium phosphate reaches a preset content, firstly adding sulfuric acid and calcium phosphate into the calcium sulfate precipitation to carry out displacement reaction treatment, carrying out solid-liquid separation after the displacement reaction treatment is finished, and collecting phosphoric acid or ammonium phosphate solution and the calcium sulfate precipitation;

s022: calcining the calcium sulfate precipitate to generate calcium oxide and collecting sulfur dioxide, carrying out catalytic oxidation treatment on the sulfur dioxide to obtain sulfur trioxide, and preparing concentrated sulfuric acid by utilizing the sulfur trioxide; mixing the generated calcium oxide with wastewater for treatment and carrying out precipitation reaction treatment; using the collected phosphoric acid or ammonium phosphate salt solution as a phosphorus source for producing iron phosphate;

s023: concentrated sulfuric acid is then added to the filtrate to adjust the pH of the filtrate.

Wherein, the predetermined content of calcium phosphate in the calcium sulfate precipitation in step S021 can be set according to the actual production conditions or requirements. When the concentration of the enriched calcium phosphate reaches the preset content, namely the preset concentration, the replacement reaction treatment of the calcium sulfate sediment is started firstly, so that the enriched calcium phosphate in the calcium sulfate sediment is eliminated firstly. During the displacement reaction treatment, calcium phosphate reacts with sulfuric acid to produce soluble phosphoric acid or phosphate and calcium sulfate precipitate. Wherein the soluble phosphate may be monoammonium phosphate. After the replacement reaction treatment and the solid-liquid separation, the obtained calcium sulfate precipitate has high relative purity. And after the treatment of the step S016, the solid waste of the calcium phosphate is effectively eliminated.

In step S022, calcium sulfate is calcined to generate calcium oxide and sulfur dioxide. The calcium oxide is free of enriched calcium phosphate. The reuse of the calcium oxide and the further preparation of sulfuric acid from sulfur dioxide are as described above. And the phosphoric acid or ammonium phosphate salt solution collected in step S022 can be reused for the production of iron phosphate.

The adjustment of the pH of the filtrate by adding concentrated sulfuric acid to the filtrate in step S023 may be collection of ammonia remaining in the filtrate by sulfuric acid as described below for step S02.

Therefore, by the scheme of recycling in the embodiment, corresponding elements can be fully recycled, zero discharge of iron phosphate production wastewater treatment can be realized, the environmental friendliness is effectively improved, and the economic cost of iron phosphate production wastewater treatment can be remarkably reduced.

The filtrate obtained by the solid-liquid separation treatment in step S02 can be repeatedly subjected to a recovery treatment because it contains water and a small amount of ammonia, for example. In the embodiment, when the wastewater contains ammonium ions or ammonia, the filtrate obtained in step S02 further contains a small amount of residual ammonia after the treatment in steps S01 and S02, and if detected, the weight percentage concentration of ammonia in the filtrate is 0.02-3.0%, or further, the pH of the filtrate can reach 9-12. In this case, in the embodiment, a step of adjusting the pH of the filtrate with an acid is further included before the step of subjecting the filtrate to the concentration treatment in step S03. Adjusting the filtrate with acid to neutralize the content of residual ammonia in the filtrate, for example, adjusting the pH value of the filtrate to 6-8, so that ammonia generates ammonium sulfate, after the concentration treatment in step S03, the concentrated solution containing ammonium sulfate can be introduced into the wastewater in step S01 to be mixed for recycling, and simultaneously collecting the water obtained from the concentration treatment, such as pure water. In the examples, the acid used for adjusting the filtrate may be a commonly used acid as long as the filtrate can be adjusted to a neutral pH. However, according to the embodiment of the present application, after the filtrate is subjected to the concentration process of step S03, it is desirable to reuse the concentrated solution, so as to improve the recycling rate of the by-products, and reduce the waste discharge. And combining the characteristics of the wastewater in step S01, the acid used for pH adjustment of the filtrate is preferably sulfuric acid, so that the main ions in the concentrate are sulfate ions, which remain the same as the main sulfate ions in the wastewater. Therefore, in an embodiment, the sulfuric acid may be concentrated sulfuric acid prepared by the above-described sintering treatment of calcium sulfate, and is introduced into the filtrate obtained by solid-liquid separation in step S02 to adjust the pH of the filtrate.

In step S03, after the filtrate obtained in step S02 is concentrated, a concentrated solution can be obtained, and water can be collected, so that zero discharge of wastewater is realized. For the purpose of the concentration treatment, any method that can achieve the purpose of the concentration treatment is within the scope disclosed in the present specification, and for example, a membrane concentration treatment may be employed. As in the example, the concentration treatment in step S03 is a membrane filtration treatment in which the filtrate is passed through a nanofiltration membrane. The nanofiltration membrane is adopted for concentration treatment, so that the purpose of concentration treatment can be effectively achieved, and pure water and concentrated solution are obtained; on the other hand, the energy consumption is reduced, and the economic cost of the iron phosphate production wastewater treatment method in the embodiment of the application is reduced.

Since the water is collected by the concentration process, in the embodiment, the collected water can be directly returned to the ferric phosphate production, specifically, as the water for performing the washing process on the ferric phosphate filter cake as shown in fig. 2, so as to perform the washing process on the ferric phosphate filter cake, so as to reduce the water consumption in the ferric phosphate production. Of course, the water collected from the concentration process may also be used to prepare the feed solution. The concentrated solution generally contains residual ions such as sulfate ions and ammonia ions, so that the concentrated solution can be treated and utilized again, for example, in the embodiment, the concentrated solution is mixed with the wastewater in the step S01 for treatment, and the next treatment, such as the step S01 to the step S03, is carried out, so that the efficiency of wastewater treatment is improved, the yield of byproducts is improved, and zero waste discharge can be almost realized.

Therefore, in the iron phosphate production wastewater treatment method in each embodiment, calcium compounds are used to perform precipitation treatment on sulfate ions contained in iron phosphate production wastewater to obtain calcium sulfate precipitates, and the calcium sulfate can be further subjected to thermal decomposition treatment to finally prepare sulfuric acid and other byproducts, so that the economic value of the byproducts is improved. After the solution of the precipitation reaction is concentrated, the concentrated solution can be further subjected to secondary treatment or mixed with wastewater to be subjected to repeated calcium sulfate precipitation treatment, so that the treatment efficiency of the wastewater is improved. And by means of the repeated utilization of the byproducts collected during the wastewater treatment, the utilization rate of elements in the wastewater is effectively improved, zero waste discharge to the environment can be realized, the harm to the environment is avoided, and the environment friendliness is improved. And the water collected by the concentration treatment can be pure water and can be returned to the iron phosphate production for secondary application, so that the water consumption for the iron phosphate production is reduced, and the economic cost for the iron phosphate production is reduced. In addition, the iron phosphate production wastewater treatment method in each embodiment has the advantages of easily controlled process, and stable treatment efficiency and effect.

In a second aspect, the embodiment of the application provides a wastewater treatment system for iron phosphate production. The iron phosphate production wastewater treatment system can be used for realizing the above iron phosphate production wastewater treatment method. In combination with the above method for treating wastewater from iron phosphate production and the process flow shown in fig. 2, the system for treating wastewater from iron phosphate production according to the embodiment of the present application comprises:

the calcium sulfate precipitation reaction device is used for reacting the iron phosphate production wastewater with a calcium-containing substance to generate calcium sulfate precipitation;

and the solution concentrating device is used for concentrating the filtrate separated by the solid-liquid separation device to obtain concentrated solution and water.

In an embodiment, the calcium sulfate precipitation reaction device included in the iron phosphate production wastewater treatment system in the embodiment of the present application includes a reaction vessel for calcium sulfate precipitation reaction and a feed opening for adding a calcium-containing substance into the reaction vessel, where the feed opening is communicated with the reaction vessel, or the reaction vessel is directly provided with the feed opening for adding the calcium-containing substance. The reaction vessel is also provided with a calcium sulfate slurry outlet for discharging calcium sulfate precipitation.

Of course, the reaction vessel contained in the calcium sulfate precipitation reaction device also comprises a wastewater inlet for conveying the iron phosphate production wastewater into the reaction vessel to be purified and reused. In the embodiment, the waste water inlet of the reaction vessel is communicated with a mother liquid outlet and a washing water outlet which are contained in the iron phosphate production system. So as to flexibly control the mother liquor and/or the washing water to be conveyed to a calcium sulfate precipitation reaction device, particularly to a reaction container thereof, and carry out purification treatment.

Since waste water may generally contain ammonia, etc., gas such as ammonia-containing gas is generally generated and overflows during the operation of the reaction vessel included in the calcium sulfate precipitation reaction device, particularly during the calcium sulfate precipitation reaction. In a further embodiment, the reaction container of the calcium sulfate precipitation reaction device further comprises an exhaust gas outlet, and the exhaust gas outlet is communicated with a pH regulator adding device contained in the iron phosphate production system. Therefore, byproducts generated in the wastewater treatment can be fully utilized, the cost of wastewater treatment is reduced, the harm to the environment is reduced, and the environmental protection performance is improved.

In an embodiment, the solid-liquid separation device that iron phosphate production wastewater treatment system of this application embodiment contains is equipped with thick liquids feed inlet, filter residue discharge port and filtrating discharge port, and wherein, the thick liquids feed inlet communicates with the calcium sulfate precipitation discharge port that calcium sulfate precipitation reaction unit set up. Therefore, the calcium sulfate precipitate is introduced into the solid-liquid separation device through the slurry feeding port to be subjected to solid-liquid separation, so that the separation of calcium sulfate filter residue and filtrate can be realized. The solid-liquid separation device may be, but is not limited to, a centrifugal separation device or a filter press device, etc.

In an embodiment, the iron phosphate production wastewater treatment system further comprises a sulfuric acid preparation device, and the sulfuric acid preparation device utilizes the calcium sulfate-containing filter residue to prepare sulfuric acid. In a specific embodiment, the sulfuric acid preparation device is provided with a calcium sulfate feeding port and a decomposition container for decomposing calcium sulfate, the calcium sulfate feeding port is used for introducing the calcium sulfate-containing filter residue into the decomposition container arranged in the sulfuric acid preparation device to thermally decompose calcium sulfate, and the calcium sulfate is thermally decomposed to generate sulfur dioxide and calcium compounds as described in the above iron phosphate production wastewater treatment method. Therefore, a calcium sulfate feeding port of the sulfuric acid preparation device is communicated with a filter residue discharge port of the solid-liquid separation device. Of course, the sulfuric acid production plant also includes a reaction vessel for further catalyzing the sulfur dioxide to sulfur trioxide and reacting the sulfur trioxide with water to concentrated sulfuric acid. In a further embodiment, the discharge port of the concentrated sulfuric acid of the sulfuric acid preparation device may be communicated with a container for holding filtrate of the solid-liquid separation device, so as to introduce the concentrated sulfuric acid into the filtrate to adjust the pH of the filtrate.

In a further embodiment, the sulfuric acid preparation device is also provided with a calcium compound outlet, and the calcium compound outlet is communicated with a feed inlet which is arranged on the calcium sulfate precipitation reaction device and used for adding calcium-containing substances. Therefore, the calcium compound which is the product of thermal decomposition of the sulfuric acid preparation device can be added into the calcium sulfate precipitation reaction device as the calcium-containing compound to react with the wastewater to generate calcium sulfate precipitation, so that the utilization rate of by-products generated in wastewater treatment is further improved, the environmental protection performance of the wastewater treatment device is improved, and the wastewater treatment cost is reduced.

In the embodiment, the solution concentration device contained in the iron phosphate production wastewater treatment system in the embodiment of the application is provided with a solution feed inlet, a concentrated solution discharge port and a solvent discharge port, wherein the solution feed inlet is communicated with a filtrate discharge port arranged on the solid-liquid separation device. Thus, the solution concentration device can directly perform concentration treatment, such as separation into a concentrated solution and water (such as pure water), on the filtrate generated by the solid-liquid separation device.

In an embodiment, a solvent outlet of the solution concentration device is communicated with a washing device for iron phosphate filter cakes, which is contained in an iron phosphate production system. Thus, the solvent outlet discharges water, such as pure water, which can directly realize the washing treatment of the iron phosphate filter cake after being communicated with the washing device for the iron phosphate filter cake.

Therefore, based on the device that the iron phosphate production wastewater treatment system of the above-mentioned text application embodiment contains, this application embodiment iron phosphate production wastewater treatment system can effectively implement this application iron phosphate production wastewater treatment method to realize handling iron phosphate production wastewater, and reach the energy consumption low, the accessory substance of recovery basically all can be collected and recycled, can almost reuse all the accessory substances that generate in this application embodiment iron phosphate production wastewater treatment method technology, realize that the waste water treatment is efficient simultaneously, economic cost is low, and environment-friendly.

The method for treating wastewater from iron phosphate production according to the embodiment of the present application is illustrated by a plurality of specific examples.

Example 1

The embodiment provides a method for treating wastewater generated in iron phosphate production. In this embodiment 1, the iron source is ferrous sulfate, the phosphorus source is monoammonium phosphate, and a plurality of sets of different concentrations (ferrous sulfate concentration, monoammonium phosphate concentration) and different reaction conditions (different synthesis pH, reaction time, temperature, and the like) are explored.

The following reaction conditions are taken as examples: the concentration of ferrous sulfate is 1.5mol/L, the concentration of monoammonium phosphate is 2.0mol/L, the oxidant is hydrogen peroxide with the concentration of 30%, and the molar ratio of phosphorus element to iron element in the phosphorus source and the iron source is 1.1.

The method for treating the wastewater generated in the iron phosphate production comprises the following steps:

s1, preparation of a ferrous solution and a phosphate solution: dissolving ferrous sulfate and monoammonium phosphate with the pure water obtained in step S5 to obtain 10m ³ Ferrous solution with ferric salt concentration of 1.5mol/L and 8.2m ³ Phosphate solution with the phosphate concentration of 2 mol/L;

s2, preparing iron phosphate: mixing the ferrous solution obtained in the step S1 and a phosphoric acid solution, controlling the reaction temperature to be 40 ℃, slowly adding hydrogen peroxide to oxidize ferrous, heating to 85 ℃, keeping the temperature for 2 hours to obtain iron phosphate slurry, filtering, washing the iron phosphate filter cake with the pure water obtained in the step S5 to obtain an iron phosphate filter cake, and obtaining 14.5m ³ Mother liquor and 8m ³ Washing with water to obtain a mixture of mother liquor and washing water of 22.5m ³ Waste water; the ferric phosphate filter cake is subjected to flash evaporation drying and rotary kiln calcination to obtain 2265Kg of anhydrous ferric phosphate; through detection, the physical and chemical indexes of the wastewater in the step S2 are shown in the table 1;

s3, wastewater precipitation reaction treatment: adding 840Kg of calcium oxide into the wastewater, adjusting the pH value of the wastewater to 13, controlling the pressure in the reaction kettle to be 0.09MPa, continuously stirring at 60 ℃, allowing ammonia gas to escape from the solution with stirring, and introducing the overflowed ammonia gas into the reaction kettle to 2.5m ³ Obtaining dilute ammonia water with the ammonia gas content of 10% in pure water, escaping with ammonia gas, gradually reducing the pH value of the solution, stirring for 4 hours, reducing the pH value of the solution to be below 10, and filtering to obtain a calcium sulfate filter cake (calcium sulfate filter residue) and a filtrate with the pH value of 19.3m ³ Filtering the solution; through detection, the physical and chemical indexes of the filtrate in the step S3 are shown in the table 2;

s4, calcium sulfate treatment: the calcium sulfate filter cake is dried by flash evaporation, crushed and then placed in a pushed slab kiln to be calcined for 3 hours at 900 ℃ to obtain 840Kg of calcium oxide, calcined tail gas-sulfur dioxide is collected, the sulfur dioxide is catalyzed and oxidized by a catalyst to obtain sulfur trioxide, and the sulfur trioxide is introduced into pure water to obtain concentrated sulfuric acid;

s5, filtrate treatment: and adding sulfuric acid into the filtrate to finely adjust the pH value, performing precise filtration, introducing a nanofiltration membrane to obtain pure water and concentrated solution, and adding the concentrated solution into the wastewater for treatment together.

TABLE 1 physicochemical indices of wastewater in step S2 of this example 1

S-g/L	N-g/L	Fe-g/L	P-g/L	pH value	Volume-m ³
						21.8	12.7	0.0028	0.423	0.84	22.5

TABLE 2 physicochemical indices of the filtrate in step S3 of example 1

S-g/L	N-g/L	Fe-g/L	P-g/L	Ca-g/L	pH value	Volume-m ³
							0.0013	0.046	0.0007	0.00004	0.007	9.43	19.3

As can be seen from table 1, the wastewater generated in step S01 mainly contains ammonium sulfate and free sulfuric acid, and has high acidity, after calcium oxide is added, calcium oxide is dissolved in water to release a large amount of heat to form calcium hydroxide, the calcium hydroxide and sulfuric acid undergo a neutralization reaction, and a large amount of heat is also released, so that the temperature of the solution rises to above 60 ℃, and the excess calcium hydroxide and ammonium sulfate react to form calcium sulfate and ammonia water, so that the pH value rises.

As shown in Table 2, the filtrate obtained in step S03 was subjected to microfiltration, then a small amount of sulfuric acid was added to adjust the pH to 6.5, and the filtrate was concentrated by passing through a nanofiltration membrane to obtain a concentration of 0.3m ³ Concentrated solution of ammonium sulfate concentration of 1.2% and 19m ³ Desalting pure water to obtain filtrate of 0.3m ³ And (5) merging the concentrated solution into the wastewater in the step S03 for centralized treatment.

And (3) observing the microscopic morphology of the anhydrous iron phosphate prepared in the step (S2) by using a scanning electron microscope, wherein the result is shown in figure 3. The physical and chemical indexes of the anhydrous iron phosphate prepared in the step S2 are further detected by a conventional method, and the results are shown in the following table 3:

TABLE 3 physicochemical indices of anhydrous iron phosphate in step S2 of example 1

As can be seen from table 3, the iron phosphate finished product prepared in this example 1 has low impurities, and the test results of various physical and chemical indexes all meet the requirements of battery-grade iron phosphate.

Further, the cost calculation was performed on the iron phosphate production wastewater treatment method of example 1, and the results are shown in table 4:

TABLE 4 cost of the iron phosphate production wastewater treatment method of example 1

As can be seen from Table 4, the wastewater treatment cost is mainly the energy consumption of calcium sulfate calcination, and more natural gas is consumed due to the higher decomposition temperature of calcium sulfate, but the consumption of calcium sulfate calcination can be covered by the sale of the prepared sulfuric acid, and in addition, the byproduct ammonia water can also offset part of the wastewater treatment cost.

Example 2

The embodiment provides a method for treating wastewater generated in iron phosphate production. In the present embodiment, the iron source is ferrous sulfate, the phosphorus source is wet-process unpurified phosphoric acid (phosphoric acid content is 30 wt%), and a plurality of groups of different concentrations (ferrous sulfate concentration, phosphoric acid concentration) and different reaction conditions (different synthesis pH, reaction time, temperature, and the like) are explored.

The following reaction conditions are taken as examples: the concentration of ferrous sulfate is 1.5mol/L, the concentration of phosphate is 2.0mol/L, the concentration of oxidant is hydrogen peroxide with the concentration of 30wt%, the pH regulator is the filtrate obtained in the step S3, and the molar ratio of phosphorus source and phosphorus element in the iron source to iron element is 1.1.

s1, preparation of a ferrous solution and a phosphate solution: dissolving ferrous sulfate with the pure water obtained in step S5 to obtain 10m ³ Ferrous solution with ferric salt concentration of 1.5 mol/L; take 3.6m ³ Adding 5.4 tons of wet-process unpurified phosphoric acid into the filtrate obtained in the step S3, introducing the ammonia gas obtained in the step S3 into the filtrate, adjusting the pH value to 4.0, filtering, and preparing into 8.2m filtrate ³ Ammonium phosphate solution with ammonium phosphate concentration of 2 mol/L;

s2, preparing iron phosphate: mixing the ferrous solution obtained in the step S1 and the ammonium phosphate solution, controlling the reaction temperature to be 40 ℃, slowly adding hydrogen peroxide to oxidize ferrous, heating to 85 ℃, keeping the temperature for 2 hours to obtain iron phosphate slurry, and filtering and washing to obtain an iron phosphate filter cake of 14.5m ³ Mother liquor and 8m ³ Washing with water, mixing the mother liquor with the washing water to obtain a mixture with a particle size of 22.5m ³ Waste water; carrying out flash drying and rotary kiln calcination on the iron phosphate filter cake to obtain anhydrous iron phosphate; through detection, the physicochemical indexes of the wastewater in the step S2 are shown in Table 5;

s3, wastewater precipitation reaction treatment: adding 840Kg calcium oxide into the wastewater, raising pH to 13, controlling the air pressure in the reaction kettle to be micro negative pressure, stirring for 30min, reducing the pH of the solution to below 11, and filtering to obtain calcium sulfate filter cake and 19.3m ³ Filtering, and collecting escaped ammonia gas; through detection, the physical and chemical indexes of the filtrate in the step S3 are shown in the table 6;

s4, calcium sulfate treatment: the calcium sulfate filter cake is dried by flash evaporation, crushed and then placed in a pushed slab kiln, calcined for 2 hours at 930 ℃ to obtain 840Kg of calcium oxide, calcined tail gas-sulfur dioxide is collected, the sulfur dioxide is catalyzed and oxidized by a catalyst to obtain sulfur trioxide, and the sulfur trioxide is introduced into pure water to obtain concentrated sulfuric acid;

s5, filtrate treatment: adding sulfuric acid into the filtrate to adjust the pH value, performing microfiltration, introducing a reverse osmosis membrane to obtain pure water and a concentrated solution, and merging the concentrated solution into the wastewater for treatment.

The physical and chemical indexes of the wastewater 1 to be treated are detected, and the results are shown in the following table 5:

TABLE 5 physicochemical indexes of wastewater in step S2 of example 2

S-g/L	N-g/L	Fe-g/L	P-g/L	pH value	Volume-m 3
						22.4	12.3	0.0017	0.392	0.79	22.5

TABLE 6 physicochemical indexes of the filtrate in step S3 of example 2

S-g/L	N-g/L	Fe-g/L	P-g/L	Ca-g/L	pH value	Volume-m ³
							0.0023	0.146	0.0005	0.00004	0.006	10.3	19.3

As shown in table 5, the wastewater generated in step S01 mainly contains ammonium sulfate and free sulfuric acid, and has high acidity, after calcium oxide is added, calcium oxide is dissolved in water to release a large amount of heat to form calcium hydroxide, and calcium hydroxide and sulfuric acid undergo a neutralization reaction and also release a large amount of heat, so that the temperature of the solution rises to above 60 ℃, and the excess calcium hydroxide and ammonium sulfate react to form calcium sulfate and ammonia water, so that the pH rises.

As can be seen from Table 6, the filtrate obtained in step S03 was subjected to microfiltration, then a small amount of sulfuric acid was added to adjust the pH to 6.5, and then the filtrate was concentrated by passing through a nanofiltration membrane to obtain a concentration of 0.14m ³ Concentrated water with ammonium sulfate concentration of 6.2% and ammonium sulfate concentration of 15.6m ³ Desalting pure water to obtain filtrate with particle size of 0.14m ³ And (5) merging the concentrated solution into the wastewater of the step S03 for centralized treatment.

And (3) observing the anhydrous iron phosphate prepared in the step (S2) by using a scanning electron microscope to perform microscopic morphology characterization, wherein the result is shown in FIG. 4. The physical and chemical indexes of the anhydrous iron phosphate prepared in the step S2 are further detected by a conventional method, and the results are shown in the following table 7:

table 7 physicochemical indices of anhydrous iron phosphate in step S2 of example 2

As can be seen from table 7, the iron phosphate finished product prepared in this example 2 has low impurities, and the test results of various physical and chemical indexes all meet the requirements of battery-grade iron phosphate.

Further, the cost calculation of the iron phosphate production wastewater treatment method of this example 2 resulted in the following results shown in table 8:

TABLE 8 cost of iron phosphate production wastewater treatment method in this example 2

As can be seen from Table 8, the cost of wastewater treatment is still the energy consumption of calcium sulfate calcination, but the consumption of calcium sulfate calcination can be covered by the outsourcing of the produced sulfuric acid, and ammonia is not included in the byproduct profit due to the return to the raw material solution preparation stage and the neutralization reaction of wet-process unpurified phosphoric acid with lower grade.

Example 3

The embodiment provides a method for treating wastewater generated in iron phosphate production. In this embodiment 3, the iron source is polyferric sulfate, the iron concentration is 1.2mol/L, the phosphorus source is monoammonium phosphate, the concentration is 1.5mol/L, and the molar ratio of the phosphorus source to the phosphorus element in the iron source to the iron element is 1.1.

s1, preparing an iron salt solution and a phosphate solution: respectively dissolving polymeric ferric sulfate and monoammonium phosphate by using the pure water obtained in the step S5 to obtain 10m ³ Ferrous solution with iron salt concentration of 1.2mol/L and iron salt concentration of 8.8m ³ Phosphate solution with the phosphate concentration of 1.5 mol/L;

s2, preparing iron phosphate: controlling the reaction temperature to be 50 ℃, mixing the ferric salt solution and the phosphate solution obtained in the step S1, heating to 90 ℃, keeping the temperature for 2 hours to obtain ferric phosphate slurry, filtering, washing the ferric phosphate filter cake with the pure water obtained in the step S5 to obtain the ferric phosphate filter cake and 12.3m ³ Mother liquor and 8m ³ Washing with water, mixing the mother liquor with the washing water to obtain 20.3m ³ Waste water; the iron phosphate filter cake is subjected to flash drying and rotary kiln calcination to obtain 1812Kg of anhydrous iron phosphate; through detection, the physical and chemical indexes of the wastewater in the step S2 are shown in the table 1;

s3, wastewater precipitation reaction treatment: 880Kg of calcium hydroxide is added into the wastewater, the pH value of the wastewater is adjusted to be increased to 13, the pressure in the reaction kettle is controlled to be 0.09MPa, the stirring is continued at 60 ℃, ammonia escapes from the solution along with the stirring, and the overflowed ammonia is introduced into the reaction kettle for 2m ³ Obtaining dilute ammonia water with the ammonia gas content of 10% in pure water, escaping with ammonia gas, gradually reducing the pH value of the solution, stirring for 4 hours, reducing the pH value of the solution to be below 10, and filtering to obtain a calcium sulfate filter cake (calcium sulfate filter residue) and 17.2m ³ Filtering the solution; through detection, the physical and chemical indexes of the filtrate in the step S3 are shown in the table 2;

s4, calcium sulfate treatment: flash evaporation drying and crushing the calcium sulfate filter cake, then putting the calcium sulfate filter cake into a pushed slab kiln, and calcining the calcium sulfate filter cake for 3 hours at 1200 ℃ to obtain 666Kg of calcium oxide, wherein the obtained calcium oxide is used for removing sulfate radicals in wastewater of the next batch; collecting calcination tail gas-sulfur dioxide, carrying out catalytic oxidation on the sulfur dioxide by using a catalyst to obtain sulfur trioxide, and introducing the sulfur trioxide into pure water to obtain concentrated sulfuric acid;

s5, filtrate treatment: and adding sulfuric acid into the filtrate to finely adjust the pH, performing precise filtration, introducing a nanofiltration membrane to obtain pure water and concentrated solution, and merging the concentrated solution into the S03 wastewater for centralized treatment.

TABLE 9 physicochemical indexes of wastewater in step S2 of example 3

S-g/L	N-g/L	Fe-g/L	P-g/L	pH value	Volume-m ³
						18.9	10.03	0.0073	0.329	0.91	20.3

TABLE 10 physicochemical indexes of the filtrate in step S3 of example 3

S-g/L	N-g/L	Fe-g/L	P-g/L	Ca-g/L	pH value	Volume-m ³
							0.0009	0.064	0.0005	0.00006	0.006	9.72	17.2

As can be seen from table 9, the wastewater generated in step S01 mainly contains ammonium sulfate and free sulfuric acid, and has high acidity, after the calcium hydroxide is added, the calcium hydroxide is dissolved in water to release a large amount of heat, and the calcium hydroxide and the sulfuric acid undergo a neutralization reaction and also release a large amount of heat, so that the temperature of the solution rises to above 60 ℃, and the excess calcium hydroxide and the ammonium sulfate react to generate calcium sulfate and ammonia water, so that the pH rises. The indexes of the treated wastewater are shown in Table 10.

The filtrate obtained in the step S03 is subjected to precise filtration, a small amount of sulfuric acid is added to adjust the pH value to 6.5, and then the filtrate is introduced into a nanofiltration membrane to be concentrated to obtain the filtrate with the thickness of 0.27m ³ Concentrated solution with ammonia sulfate concentration of 1.53% and 16.9m ³ Desalting pure water to obtain filtrate of 0.27m ³ And (5) merging the concentrated solution into the wastewater in the step S03 for centralized treatment.

The physicochemical indexes of the anhydrous iron phosphate prepared in the step S2 were measured according to a conventional method, and the results are shown in the following table 11:

TABLE 11 physicochemical indices of anhydrous iron phosphate in step S2 of example 1

As can be seen from table 11, the iron phosphate finished product prepared in this example 3 has low impurities, and the test results of various physical and chemical indexes all meet the requirements of battery-grade iron phosphate.

Further, the cost calculation of the iron phosphate production wastewater treatment method of example 3 shows the results in table 12:

TABLE 12 cost of the iron phosphate production wastewater treatment method of this example 3

As can be seen from table 12, the wastewater treatment cost is mainly the energy consumption of calcium sulfate calcination, and more natural gas is consumed due to the higher decomposition temperature of calcium sulfate, but the consumption of calcium sulfate in calcination can be covered by the sale of the produced sulfuric acid, and in addition, the byproduct ammonia water can also offset a part of the wastewater treatment cost.

Example 4

The embodiment provides a method for treating wastewater generated in iron phosphate production. The method for treating the wastewater generated in the iron phosphate production is improved on the basis of the embodiment 1, and specifically comprises the following steps:

s1, preparation of a ferrous solution and a phosphate solution: refer to step S1 of example 1;

s2, preparing iron phosphate: step S2 of reference example 1;

s3, wastewater precipitation reaction treatment: step S3 of reference example 1; wherein, the calcium oxide in the step is calcium oxide generated by sintering calcium sulfate in the step S4;

s4, calcium sulfate treatment: step S4 of reference example 1; conveying the calcium oxide generated in the step S4, namely the calcium oxide generated in the sintering treatment of the calcium sulfate in the step S3, and mixing the calcium oxide with the wastewater to generate calcium sulfate precipitate; after the calcium oxide in the step is recycled for at least 5 times according to the recycling method, detecting the calcium phosphate contained in the calcium sulfate, when the content of the calcium phosphate is detected to reach the preset content, firstly adding sulfuric acid into the calcium sulfate until the pH value in the mixed solution reaches 3-4 to generate monoammonium phosphate solution and calcium sulfate precipitate with lower concentration, after the sulfuric acid and the calcium phosphate are reacted, carrying out solid-liquid separation to obtain the calcium sulfate precipitate and monoammonium phosphate, continuously calcining the calcium sulfate precipitate according to the step S4 in the reference example 1 to obtain calcium oxide, and conveying the calcium oxide to the step S3 to be mixed with the wastewater to generate the calcium sulfate precipitate; meanwhile, collecting calcination tail gas-sulfur dioxide, carrying out catalytic oxidation on the sulfur dioxide by using a catalyst to obtain sulfur trioxide, introducing the sulfur trioxide into pure water to obtain concentrated sulfuric acid, wherein the concentrated sulfuric acid is used as sulfuric acid in the step S5 and is used for adjusting the pH value of the filtrate; detecting the phosphorus content of the generated monoammonium phosphate solution, and adding a certain amount of ammonium phosphate to prepare a phosphorus source solution as the phosphate solution in the step S1 for producing the iron phosphate;

s5, filtrate treatment: reference is made to step S5 of example 1.

Comparative example 1

The comparative example provides a method for treating wastewater generated in iron phosphate production. Wherein, the iron source is ferrous sulfate, the phosphorus source is monoammonium phosphate, and the optimal reaction conditions are taken as examples: the concentration of ferrous sulfate is 1.5mol/L, the concentration of monoammonium phosphate is 2.0mol/L, the oxidant is hydrogen peroxide with the concentration of 30%, and the molar ratio of phosphorus element to iron element in the phosphorus source and the iron source is 1.1.

The method for treating wastewater generated in iron phosphate production of the comparative example comprises the following steps:

s1, preparation of a ferrous solution and a phosphate solution: dissolving ferrous sulfate and monoammonium phosphate with pure water respectively to obtain a solution with a particle size of 7.5m ³ Ferrous solution with ferric salt concentration of 1.5mol/L and 11m ³ Phosphate solution with the phosphate concentration of 2 mol/L;

s2, preparing iron phosphate: mixing the ferrous solution obtained in the step S1 and a phosphate solution material, controlling the reaction temperature to be 40 ℃, slowly adding hydrogen peroxide to oxidize the ferrous, and then adding hydrogen peroxide to oxidize the ferrousHeating to 85 ℃, keeping the temperature for 2 hours to obtain iron phosphate slurry, and filtering and washing to obtain an iron phosphate filter cake of 15.5m ³ Mother liquor and 6m ³ Washing with water to obtain 21.5m ³ Waste water; the ferric phosphate filter cake is subjected to flash evaporation drying and rotary kiln calcination to obtain 755Kg of anhydrous ferric phosphate;

s3, wastewater treatment: adjusting the pH value of the wastewater to 9.0 by using ammonia water, filtering, finely adjusting the pH value to 6.5 by using sulfuric acid, introducing the wastewater into an MVR evaporator, and evaporating to obtain solid ammonium sulfate.

And (3) observing the microscopic morphology of the anhydrous iron phosphate prepared in the step (S2) by using a scanning electron microscope, wherein the result is shown in figure 5. The physical and chemical indexes of the anhydrous iron phosphate prepared in the step S2 are further detected by a conventional method, and the results are shown in the following table 13:

TABLE 13 physicochemical indices of anhydrous iron phosphate in step S2 of comparative example 1

As can be seen from table 13, the iron phosphate finished product prepared in comparative example 1 has low impurities, and the test results of various physical and chemical indexes all meet the requirements of battery-grade iron phosphate.

Further, the cost of the method for treating the iron phosphate production wastewater of comparative example 1 was calculated, and the results are shown in table 14:

TABLE 14 cost of iron phosphate production wastewater treatment method of comparative example 1

As can be seen in Table 14, the wastewater treatment cost is mainly the energy and power consumption cost required for evaporating the ammonium sulfate solution by MVR.

Based on the above examples 1 to 4 and comparative example 1, it can be seen from comparison of fig. 3 and 5, and tables 3 and 13 that there is no significant difference in the manner of wastewater treatment between the anhydrous ferric phosphates prepared in example 1 and comparative example 1, and the main difference is. Wherein, the comparative example 1 adopts the conventional water treatment mode, adjust the pH value of the waste water to alkalescence with ammonia water and then filter, remove the metal impurity in the waste water, reuse sulfuric acid pH adjust pH value neutral, evaporate concentrate with mvr, get ammonium sulfate salt, this method is relatively power-consuming, with high costs. In the embodiment 1, sulfate radicals in the wastewater are removed in a coprecipitation mode by adopting a calcium-containing compound, calcium is a basic compound, the pH value of the solution is improved while the sulfate radicals are removed, the volatilization speed of ammonia water is increased, and a byproduct of dilute ammonia water is obtained; the obtained calcium sulfate liquid is calcined to obtain concentrated sulfuric acid and calcium oxide, and the calcium oxide is recycled without generating solid waste. And 615 yuan of cost can be saved in the aspect of wastewater treatment when one ton of ferric phosphate is produced. Example 3 is similar to example 1 in cost of wastewater treatment. Example 4 in addition to example 1, calcium oxide obtained by calcining a calcium sulfate solution can be mixed with wastewater to produce calcium sulfate, and therefore calcium oxide is further reused, and the wastewater treatment cost is lower in example 4 than in example 1, and almost no solid waste is generated.

As can be seen by comparing fig. 4 with fig. 5, and tables 7 and 13, there is no significant difference between the iron phosphates prepared in example 2 and comparative example 1, and the main difference between the two is still in the wastewater treatment mode. Wherein, the comparative example 1 is as above, and adopts the conventional water treatment mode, and the method is energy-consuming and high in cost. In the embodiment 2, after sulfate radicals in the wastewater are removed by adopting a calcium-containing compound, the phosphorus source is prepared by utilizing the residual diluted ammonia water in the solution and the wet-process unpurified phosphoric acid with cheaper price, so that on one hand, the ammonia element and water are recycled, the ammonia nitrogen pollution is avoided, and the element utilization rate is improved; on the other hand, because the wet-process phosphoric acid contains a large amount of impurities and can be used after impurity removal, the impurity removal process of the wet-process phosphoric acid is complex in an acidic environment, the cost is higher than that of wastewater treatment in example 1, but the cost is still remarkably reduced compared with that of conventional wastewater treatment in comparative example 1, and after the phosphate solution is prepared by mixing dilute ammonia water and phosphoric acid, metal impurities, hydroxide radicals and phosphate radicals form insoluble substances due to the fact that the pH value is increased, and the insoluble substances can be removed through filtration. Thus, example 2 not only reduces water treatment costs during the wastewater treatment stage, but also has greater compatibility with low grade, high impurity phosphorus sources.

The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. The method for treating wastewater generated in iron phosphate production is characterized by comprising the following steps:

carrying out solid-liquid separation on the mixed solution containing the calcium sulfate precipitate to obtain filter residue containing calcium sulfate and filtrate;

and concentrating the filtrate to obtain a concentrated solution and water.

2. The method for treating wastewater from iron phosphate production according to claim 1, wherein the mixing treatment and the precipitation reaction treatment satisfy at least one of the following conditions:

the waste water and the calcium-containing compound are mixed according to the molar ratio of the sulfur element to the calcium element contained in the waste water being 0.9 to 1.5;

the calcium-containing compound comprises at least one of calcium oxide, calcium hydroxide and calcium carbonate;

the temperature of the precipitation reaction treatment is 30-70 ℃;

the air pressure of the precipitation reaction treatment environment is 0.07-0.1 Mpa.

3. The method for treating wastewater from iron phosphate production according to claim 1 or 2, comprising at least one of the following steps:

generating ammonia-containing gas in the precipitation reaction treatment process, and using the generated ammonia-containing gas as a pH regulator or using a solution absorbed by water as a pH regulator for preparing the iron phosphate;

the method also comprises the step of calcining the calcium sulfate-containing filter residue to generate sulfur dioxide.

4. The method for treating wastewater from iron phosphate production according to claim 3, comprising at least one of the following steps:

the method also comprises the steps of carrying out oxidation treatment on the generated sulfur dioxide to generate sulfur trioxide, and preparing concentrated sulfuric acid by utilizing the sulfur trioxide;

the method also comprises the following steps of treating the calcium oxide generated by calcination treatment:

and mixing the calcium oxide serving as the calcium-containing compound with the wastewater for treatment and carrying out precipitation reaction treatment.

5. The method for treating wastewater from iron phosphate production according to claim 4, wherein the method further comprises, after performing at least one cycle of mixing the calcium oxide as the calcium-containing compound with the wastewater and performing precipitation reaction treatment, the steps of:

firstly, measuring the content of calcium phosphate in calcium sulfate sediment generated by a precipitation reaction, when the content of the detected calcium phosphate reaches a preset content, firstly adding sulfuric acid into the calcium sulfate sediment to carry out a displacement reaction treatment with the calcium phosphate, carrying out solid-liquid separation after the displacement reaction treatment is finished, and collecting phosphoric acid or ammonium phosphate solution and the calcium sulfate sediment;

calcining the calcium sulfate precipitate to generate calcium oxide and collecting sulfur dioxide, carrying out catalytic oxidation treatment on the sulfur dioxide to obtain sulfur trioxide, and preparing concentrated sulfuric acid by using the sulfur trioxide; mixing the generated calcium oxide with the wastewater for treatment and carrying out precipitation reaction treatment; using the collected phosphoric acid or ammonium phosphate salt solution as a phosphorus source for producing iron phosphate;

the concentrated sulfuric acid is then added to the filtrate to adjust the pH of the filtrate.

6. The method for treating wastewater from iron phosphate production according to claim 3, wherein at least one of the following conditions is adopted:

the temperature of the calcination treatment is 650-1300 ℃;

the filtrate contains ammonia, and the weight percentage concentration content of the ammonia in the filtrate is 0.02-3.0%;

the pH value of the filtrate is 9-12.

7. The method for treating iron phosphate production wastewater according to any one of claims 1, 2, 4 or 6, characterized by comprising one of the following steps:

the method also comprises a step of combining the concentrated solution and the wastewater for treatment;

before the step of concentrating the filtrate, the method also comprises the step of adjusting the pH value of the filtrate by using acid;

the concentration treatment is to introduce the filtrate into a nanofiltration membrane for membrane filtration treatment;

and returning the water obtained by the concentration treatment to the iron phosphate production process for washing the iron phosphate filter cake.

8. The method for treating wastewater from iron phosphate production according to claim 7, characterized in that: adjusting the pH value of the filtrate to 6-8 by using the acid; and/or

The acid comprises sulfuric acid.

9. The method for treating wastewater from iron phosphate production according to any one of claims 1, 2, 4, 6 or 8, wherein: the wastewater comprises mother liquor generated in the production process of the iron phosphate and washing water for washing the iron phosphate filter cake.

10. An iron phosphate production wastewater treatment system, characterized in that the iron phosphate production wastewater treatment system is used for realizing the iron phosphate production wastewater treatment method according to any one of claims 1 to 9, and comprises:

the solid-liquid separation device is used for carrying out solid-liquid separation on the mixed solution containing the calcium sulfate precipitate generated in the calcium sulfate precipitate reaction device to obtain filter residue containing calcium sulfate and filtrate;

11. The iron phosphate production wastewater treatment system according to claim 10, wherein: the calcium sulfate precipitation reaction device comprises a reaction vessel for calcium sulfate precipitation reaction, the reaction vessel is also provided with a feed inlet, and the reaction vessel is also provided with a calcium sulfate slurry discharge port for discharging the calcium sulfate precipitation;

the solid-liquid separation device is provided with a slurry feeding port, a filter residue discharging port and a filtrate discharging port, wherein the slurry feeding port is communicated with the calcium sulfate slurry discharging port;

the solution concentration device is provided with a solution feed port, a concentrated solution discharge port and a solvent discharge port, and the solution feed port is communicated with the filtrate discharge port.

12. The iron phosphate production wastewater treatment system according to claim 11, wherein:

the concentrated solution outlet is communicated with a wastewater inlet of the reaction container; and/or

The reaction container also comprises an exhaust gas outlet, and the exhaust gas outlet is communicated with a pH regulator adding device contained in the iron phosphate production system; and/or

A wastewater inlet of the reaction container is communicated with a mother liquid outlet and a washing water outlet which are contained in the iron phosphate production system; and/or

The solvent outlet of the solution concentration device is communicated with a washing device for a lithium iron phosphate filter cake contained in the iron phosphate production system; and/or

The iron phosphate production wastewater treatment system further comprises a sulfuric acid preparation device, and the sulfuric acid preparation device prepares sulfuric acid from the calcium sulfate filter residues.