CN115340237A - Iron phosphate production wastewater treatment method and system - Google Patents

Abstract

The application discloses a method and system for treating waste water from ferric phosphate production. The wastewater treatment method of ferric phosphate production includes: mixing the wastewater generated by ferric phosphate production with calcium-containing compounds and carrying out precipitation reaction, collecting the ammonia generated during the process, and separating the mixed solution containing calcium sulfate precipitates for solid-liquid separation to obtain calcium sulfate precipitates And filtrate, calcium sulfate is further prepared into concentrated sulfuric acid and calcium oxide, concentrated sulfuric acid is used for pH adjustment or sale, calcium oxide is recycled as a calcium-containing compound, and the filtrate is concentrated to obtain concentrated liquid and water, and the concentrated liquid is combined into wastewater Centralized processing. The collected ammonia and water are used for ferric phosphate production. The iron phosphate production wastewater treatment method and system of the present application can treat the iron phosphate production wastewater, and the wastewater treatment efficiency is high, the economic cost is low, the energy consumption is low, the environment is friendly, and the recovered by-products can be collected and reused. Ammonium, phosphorus, and calcium are recycled to realize the comprehensive utilization of resources.

Description

Ferric phosphate production wastewater treatment method and system

technical field

The application belongs to the technical field of wastewater treatment, and in particular relates to a method and system for treating wastewater from ferric phosphate production.

Background technique

Iron phosphate is an important precursor material for lithium-ion battery cathode materials. At present, iron phosphate is mainly prepared by co-precipitation method. In the co-precipitation method, the iron phosphate product is obtained through the mixed precipitation of iron source and phosphorus source (such as monoammonium phosphate), but it will also produce a large number of high concentrations of sulfate (SO ₄ ^2- ), phosphate (PO ₄ ^{3 -} ) and ammonia nitrogen (NH ₄ -N) acid wastewater.

At present, ammonia nitrogen, phosphate, sulfate, acid and other pollutants in iron phosphate wastewater are mainly removed by chemical precipitation, but the slag produced by precipitation contains calcium phosphate and calcium sulfate, which is difficult to reuse, and at the same time leads to high operating costs. Waste of phosphorus and sulfur resources and other issues. From the perspective of environmental protection and resource recycling, it is necessary to develop a method that can recover phosphate and sulfate from ferric phosphate production wastewater with low operating costs.

Wastewater treatment is an important source of cost in the production of ferric phosphate. At present, the treatment methods for wastewater generated in the production of ferric phosphate mainly include: (1) Direct treatment: remove phosphorus in wastewater by co-precipitation, and then adjust the pH to 13-14 stripping to remove the ammonia nitrogen in the wastewater, and then adjust the pH value to neutral and discharge it to the sewage treatment plant for treatment; (2) Ammonium sulfate recovery treatment method: adjust the pH value of the wastewater, and remove the metal ions in the wastewater as Removal by precipitation, followed by film concentration, evaporation crystallization and other steps to obtain ammonium sulfate as a by-product; (3) recycling treatment method: after washing and concentrating, mix with mother liquor, and remove sulfate radicals in the mixed liquor by calcium salt precipitation, and reuse The mixed solution can recycle ammonium and phosphate.

Although the above-mentioned current treatment methods for producing wastewater in the iron phosphate production process can effectively treat wastewater to a certain extent, it is found that there are also some deficiencies in actual generation, such as the above-mentioned method (1). Although the treatment method is simple, the amount of wastewater is large, and the wastewater The phosphorus element in the medium cannot be utilized, and the environmental protection cost is high; although the above method (2) can increase a certain amount of ammonium sulfate by-product income, at least 20 tons of water need to be evaporated to treat the waste water produced by each ton of ferric phosphate, and the steam consumption is large, and the energy consumption cost is extremely high. High; the above method (3) can reduce the amount of wastewater, but on the one hand, the phosphate radicals in the wastewater will combine with calcium ions to form calcium phosphate, resulting in a large amount of phosphogypsum, resulting in the loss of some phosphorus; on the other hand, phosphogypsum is a hazardous waste, and the back-end The amount used in the industrial chain is small, it is difficult to handle, it is easy to cause environmental pollution, and it is difficult to apply it on a large scale.

Therefore, the existing wastewater treatment methods in the production process of iron phosphate have problems such as environmental pollution, waste of nitrogen and phosphorus resources, or high energy consumption. With the popularization of battery applications, the pressure of wastewater treatment in iron phosphate production has increased. How to improve the wastewater treatment efficiency of ferric phosphate production, improve the utilization rate of nitrogen and phosphorus, and reduce energy consumption and economic cost are current efforts in this field and are also eager to overcome problems.

Contents of the invention

The purpose of the embodiments of the present application is to overcome the above-mentioned deficiencies of the prior art at least to a certain extent, and provide a method for treating wastewater from ferric phosphate production and a system for treating wastewater from ferric phosphate production to solve the problem of treating wastewater from ferric phosphate production. The method has technical problems such as environmental pollution, waste of nitrogen and phosphorus resources, or high energy consumption.

In order to achieve the purpose of the above application, the first aspect of the present application provides a method for treating wastewater from ferric phosphate production. The iron phosphate production wastewater treatment method of the present application comprises the following steps:

The waste water produced by ferric phosphate production is mixed with calcium-containing compounds and subjected to precipitation reaction treatment to generate calcium sulfate precipitation;

Separating the mixed solution containing calcium sulfate precipitation from solid to liquid to obtain calcium sulfate-containing filter residue and filtrate;

The filtrate was concentrated to obtain a concentrate and water.

The second aspect of the present application provides a wastewater treatment system for ferric phosphate production. The iron phosphate production wastewater treatment system of this application is used to realize the iron phosphate production wastewater treatment method of this application, including:

Calcium sulfate precipitation reaction device, used to react ferric phosphate production wastewater with calcium-containing substances to generate calcium sulfate precipitation;

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

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

Compared with the prior art, the present application has the following technical effects:

The iron phosphate production wastewater treatment method of the present application uses calcium-containing compounds to carry out precipitation reaction on the iron phosphate production wastewater, which can separate and collect the sulfate ions in the wastewater with calcium sulfate precipitation, and the energy consumption is low, and the recovered by-products such as calcium sulfate The filter residue, concentrate and water can be collected and reused without adding additional equipment and wastewater treatment steps, thereby effectively improving the wastewater treatment efficiency of the wastewater treatment method for ferric phosphate production in this application, significantly reducing economic costs, and being environmentally friendly. At the same time, the generation of hazardous waste is effectively avoided, and the harm to the environment is reduced or completely avoided.

The ferric phosphate production wastewater treatment system of the present application can effectively implement the ferric phosphate production wastewater treatment method of the present application, so as to realize the treatment of the ferric phosphate production wastewater, and achieve low energy consumption, and the recovered by-products can basically be collected and reused, and at the same time realize The wastewater treatment efficiency is high, the economic cost is low, and the environment is friendly.

Description of drawings

In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the accompanying drawings that need to be used in the description of the specific embodiments or prior art. Obviously, the accompanying drawings in the following description The drawings are some implementations of the present application, and those skilled in the art can obtain other drawings based on these drawings without creative work.

Fig. 1 is the technological process schematic diagram of the iron phosphate production wastewater treatment method of the embodiment of the present application;

Fig. 2 is the block diagram of the technical process of the iron phosphate production wastewater treatment method of the embodiment of the present application;

Fig. 3 is the scanning electron microscope (SEM) of anhydrous ferric phosphate that step S2 makes in the embodiment 1 of the present application;

Fig. 4 is the scanning electron microscope (SEM) of anhydrous ferric phosphate that step S2 makes in the embodiment 2 of the present application;

5 is a scanning electron microscope (SEM) of anhydrous iron phosphate prepared in step S2 in Comparative Example 1.

Detailed ways

In order to make the technical problems, technical solutions and beneficial effects to be solved in the present application clearer, the present application will be further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described here are only used to explain the present application, and are not intended to limit the present application.

In this application, "at least one" means one or more, and "multiple" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one item (unit) of a, b, or c", or "at least one item (unit) of a, b, and c" can mean: a, b, c, a-b( That is, a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

It should be understood that in various embodiments of the present application, the sequence numbers of the above-mentioned processes do not mean the order of execution, and some or all steps may be executed in parallel or sequentially, and the execution order of each process shall be based on its functions and The internal logic is determined and should not constitute any limitation to the implementation process of the embodiment of the present application.

Terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of this application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

The weight of the relevant components mentioned in the description of the embodiments of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of the various components. The scaling up or down of the content of the fraction is within the scope disclosed in the description of the embodiments of the present application. Specifically, the mass described in the description of the embodiments of the present application may be μg, mg, g, kg and other well-known mass units in the chemical industry.

The terms "first" and "second" are only used for descriptive purposes to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX can also be called the second XX, and similarly, the second XX can also be called the first XX. Thus, a feature defined as "first" and "second" may explicitly or implicitly include one or more of these features.

In the first aspect, the embodiment of the present application provides a method for treating wastewater from ferric phosphate production. The technical process of the iron phosphate production wastewater treatment method in the embodiment of the present application is shown in Figure 1 and Figure 2, including the following steps:

S01: Mix the waste water produced by ferric phosphate production with calcium-containing compounds and carry out precipitation reaction treatment to generate ammonia-containing gas and calcium sulfate precipitation;

S02: Separating the mixed solution containing calcium sulfate precipitation into solid-liquid to obtain calcium sulfate-containing filter residue and filtrate;

S03: Concentrate the filtrate to obtain a concentrate and water.

The iron phosphate production wastewater treatment method in the embodiment of the present application is through the above-mentioned treatment steps, specifically, in step S01, a calcium-containing compound is used to carry out precipitation reaction on the iron phosphate production wastewater, so that the sulfate ions in the wastewater can be precipitated with calcium sulfate in the step S01. S02 is separated and collected, and the energy consumption is low, and the recovered by-products such as calcium sulfate filter residue can be collected and reused, avoiding the generation of hazardous waste. The concentrate and water can be further collected through the concentration treatment in step S03, and both can be collected and reused. Therefore, the iron phosphate production wastewater treatment method in the embodiment of the present application does not add additional equipment and wastewater treatment steps, effectively improves the stability and efficiency of wastewater treatment, significantly reduces economic costs, is environmentally friendly, and effectively avoids the generation of hazardous waste , reduce or completely avoid the harm to the environment.

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

S011: Prepare a mixture solution containing ferrous salt, phosphorus source, oxidizing agent and pH regulator;

S012: reacting the mixed solution in step S011 at a certain temperature to obtain iron phosphate slurry;

S013: subjecting the ferric phosphate slurry in step S012 to solid-liquid separation to obtain ferric phosphate filter cake and mother liquor,

S014: washing the iron phosphate filter cake in step S013 to obtain washing water and iron phosphate;

S015: use the mother liquor in step S013 and/or the washing water in step S013 as waste water.

Wherein, the preparation of the mixture solution in step S011 may be to first prepare the ferrous salt solution and the phosphorus source solution, and then mix the solutions in a certain proportion to form the mixture solution. It is also possible to directly add ferrous salt, phosphorus source, oxidant and pH regulator into the solvent to dissolve in a certain proportion to prepare a mixture solution; it is also possible to prepare a mixed solution of ferrous salt and phosphorus source first, and then add oxidant and pH adjustment agent to form a mixture solution. When preparing the ferrous salt solution and the phosphorus source solution first, in the embodiment, the molar concentration of the ferrous salt solution may be 1.0-2.0 mol/L, and the molar concentration of the phosphorus source solution may be 1.0-3.0 mol/L. In a specific embodiment, the ferrous salt may include ferrous sulfate, and the phosphorus source may include at least one of phosphoric acid, monoammonium phosphate, diammonium phosphate, and triammonium phosphate. Alternatively, the solvent may be water.

In an embodiment, the ferrous salt and phosphorus source in step S011 can be mixed according to the molar ratio of phosphorus to iron in a ratio of 0.9:1 to 1.5:1, that is, in the mixture solution in step S011, The molar ratio of phosphorus element to iron element is 0.9:1˜1.5:1.

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

In step S012, through the reaction treatment, ferrous iron is oxidized to generate ferric ions, and reacts with phosphate ions to generate ferric phosphate precipitates. In an embodiment, the temperature of the reaction treatment in the step S012 may be 25-90° C., and the reaction time should be sufficient, such as 2-4 hours. Make iron ions fully precipitated and increase the yield of iron phosphate.

The solid-liquid separation in step S013 is to achieve the purpose of ferric phosphate precipitation and solvent separation. Therefore, as long as the separation methods that can realize the separation of the two are within the scope disclosed in the description of the embodiments of this application, such as filtration, centrifugation or other and so on. Wherein, the filtrate, that is, the mother liquor, constitutes the waste liquid to be treated, which can be used as the waste water in step S01.

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

The ferric phosphate precipitate after washing treatment can be dried, roasted and other treatments to remove crystal water and improve its purity. As in the embodiment, the drying temperature of iron phosphate precipitation (also called iron phosphate filter cake) is 100-150° C., and the drying time is 0.5-6 hours. The roasting treatment of iron phosphate precipitation can be carried out according to the following method: first heat preservation treatment at 150-300°C for 0.5-2h, and then heat up to 500-800°C for 2-5h.

In step S015, collect the mother liquor in step S013 and the washing water in step S014, or mix the mother liquor and washing water as waste water in step S01.

After treatment based on the above iron phosphate preparation method, the phosphate radical can be precipitated to the greatest extent, and the main component in the wastewater is sulfate. Therefore, in step S01, after the calcium-containing compound is mixed with the wastewater, the calcium ion will be mixed with the wastewater Sulfate ions in the solution undergo a precipitation reaction to generate calcium sulfate precipitates, effectively removing sulfate ions. In the embodiment, it is possible to control the wastewater and the calcium-containing compound to be mixed according to the molar ratio of sulfur and calcium contained in the wastewater in a ratio of 0.9:1 to 1.5:1, so as to avoid the occurrence of sulfate ions on the basis of fully precipitating sulfate ions. In step S02, calcium ions remain in the filtrate or the residual calcium ion content in the filtrate in step S02 is reduced as much as possible. In a specific embodiment, the calcium-containing compound includes at least one of calcium oxide, calcium hydroxide, and calcium carbonate. These 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 here or reduce the environmental pressure of the subsequent treatment of the filtrate. In the embodiment of the present application, calcium oxide is relatively preferred, so that when the calcium sulfate precipitate is subjected to subsequent treatment such as calcium sulfate precipitate is calcined, the calcium oxide generated can be directly used as the calcium-containing compound and ferric phosphate production. The generated wastewater is mixed and treated with precipitation reaction to make full use of the by-products generated from wastewater treatment.

In an embodiment, the temperature of the precipitation reaction treatment in step S01 may be 30-70° C.; or the air pressure of the precipitation reaction treatment environment may be further controlled to be 0.07-0.1 Mpa. By controlling the precipitation reaction, the precipitation efficiency of sulfate ions can be effectively improved, and the recovery rate of sulfate ions can be improved. When ammonia is generated, it is also conducive to the discharge and collection of ammonia. In addition, the time of the precipitation reaction should be sufficient to ensure that the sulfate radical and the calcium ion fully carry out the precipitation reaction. When the calcium-containing compound is calcium oxide, the temperature of the precipitation reaction treatment can be caused by the heat generated by the reaction between calcium oxide and wastewater, and there is no need for additional heating treatment for the precipitation reaction treatment, which can save energy consumption for wastewater treatment.

In an embodiment, when the waste water in step S01 contains ammonium ions such as ammonium sulfate or ammonia in the waste water, when adding ammonia pH regulator or/and phosphorus source as ammonium phosphate in the ferric phosphate process, the precipitation in step S01 Ammonia-containing gas is also generated during the reaction process. Based on the alkaline characteristics of ammonia, the method for treating wastewater from ferric phosphate production in the embodiment of the present application also includes using the generated ammonia-containing gas as a pH regulator or the solution absorbed by water, that is, ammonia water, as a pH regulator for ferric phosphate preparation. That is, as the pH regulator in step S011 of the iron phosphate preparation method above, or as shown in FIG. 2 , the ammonia-containing gas or the solution absorbed by water is returned to the mixture solution. In this way, the reutilization rate of by-products produced by the method for treating wastewater from iron phosphate production in the embodiment of the present 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 calcium sulfate filter residue and filtrate respectively. Therefore, any separation method that can realize the separation of calcium sulfate precipitation and solvent is within the scope disclosed in the description of the embodiments of the present application, such as filtration, centrifugation or other methods.

The collected calcium sulfate precipitate can be used for secondary use according to the needs of the application. As in the embodiment, after the step of solid-liquid separation in step S02, a step of calcining the filter residue containing calcium sulfate to generate sulfur dioxide is also included. The conditions of the calcination treatment can be set according to the thermal decomposition characteristics of calcium sulfate, for example, the temperature of the calcination treatment is 650-1300° C., so that the calcium sulfate filter residue is fully decomposed to generate sulfur dioxide. In addition, due to the moisture content factor of the calcium sulfate filter residue, before the calcining process, the calcium sulfate filter residue can be dried to remove the moisture contained in it and improve the efficiency of the calcining process. As in the examples, the calcium sulfate filter residue can be dried. It is 100-150 ℃, and the time is 0.5-6 hours, so as to fully dry the calcium sulfate filter residue.

In order to make full use of the calcium sulfate filter residue, in a further embodiment, after the above-mentioned calcination treatment step on the calcium sulfate filter residue, it also includes oxidizing the sulfur dioxide generated by the calcination treatment to generate sulfur trioxide, and using sulfur trioxide to prepare Concentrated sulfuric acid step. Because concentrated sulfuric acid is an important industrial production raw material, like this, this concentrated sulfuric acid can hedge the cost that the application embodiment iron phosphate production wastewater treatment method consumes such as the energy consumption cost that calcining process consumes, thereby reduces the cost of iron phosphate production wastewater treatment method economic cost. In an embodiment, the prepared concentrated sulfuric acid may be drained into the filtrate obtained from the solid-liquid separation in step S02, so as to adjust the pH in the filtrate.

In the embodiment, the calcium-containing product generated by the calcination treatment of the calcium sulfate filter residue, that is, calcium oxide, can also be used as the calcium-containing compound in step S01, that is, the method for treating wastewater from ferric phosphate production in the embodiment of the present application also includes adding sulfuric acid The step of mixing the calcium-containing product generated by the calcium filter residue through the calcination treatment with the wastewater in S01 and performing precipitation reaction treatment. In this way, the by-products generated by the ferric phosphate production wastewater treatment method can be fully utilized. Certainly, during the actual generation process of the wastewater in step S01, a small amount of phosphate ions remains, and when the wastewater reacts with the calcium-containing compound, the residual phosphate ions will also generate a small amount of calcium phosphate. When the calcium sulfate filter residue is decomposed into calcium oxide and sulfur dioxide in the calcination process, the calcium phosphate with a small content will not be decomposed. It will be enriched during the process of reusing calcium oxide as the calcium-containing compound in step S01. In order to realize the reuse of the enriched calcium phosphate, sulfuric acid can be used to react with calcium phosphate after it has been enriched to a certain level. In this way, the generated calcium sulfate can be collected and calcined for reuse as described above, and the phosphorus element will not be wasted. Therefore, in the embodiment, calcium oxide is mixed with waste water as calcium-containing compound and treated in the recycling step of precipitation reaction treatment, when the recycling is performed at least once, the following steps are also included:

S021: First measure the calcium phosphate content of the calcium sulfate precipitate generated by the precipitation reaction. When the detected calcium phosphate content reaches the preset content, first add sulfuric acid and calcium phosphate to the calcium sulfate precipitate for replacement reaction treatment, and wait for the replacement reaction treatment After the end, solid-liquid separation is carried out to collect phosphoric acid or ammonium phosphate solution and calcium sulfate precipitate;

S022: Calcinate the calcium sulfate precipitate to generate calcium oxide and collect sulfur dioxide. The sulfur dioxide is catalyzed and oxidized to obtain sulfur trioxide, and sulfur trioxide is used to prepare concentrated sulfuric acid; the generated calcium oxide is mixed with waste water and subjected to precipitation reaction Treatment; use the collected phosphoric acid or ammonium phosphate solution as a phosphorus source for the production of iron phosphate;

S023: then adding concentrated sulfuric acid to the filtrate to adjust the pH of the filtrate.

Wherein, the preset content of calcium phosphate contained in the calcium sulfate precipitate in step S021 can be set according to actual production conditions or requirements. When the concentration of calcium phosphate enrichment reaches the preset content, that is, the preset concentration, the replacement reaction treatment on the calcium sulfate precipitate is first started to eliminate the calcium phosphate enriched in the calcium sulfate precipitate. During the displacement reaction treatment, calcium phosphate reacts with sulfuric acid to form soluble phosphoric acid or phosphate and calcium sulfate precipitates. Wherein, the soluble phosphate may be monoammonium phosphate. After the replacement reaction treatment and solid-liquid separation, the obtained calcium sulfate precipitate has relatively high purity. Moreover, after the treatment in step S016, the calcium phosphate solid waste is effectively eliminated.

In step S022, calcium sulfate is calcined to generate calcium oxide and sulfur dioxide. The calcium oxide has no enriched calcium phosphate. The reuse of the calcium oxide and the further preparation of sulfuric acid from sulfur dioxide are all 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.

Adding concentrated sulfuric acid to the filtrate to adjust the pH of the filtrate in step S023 may be as described in step S02 below, collecting residual ammonia in the filtrate through sulfuric acid.

Therefore, through the reuse scheme of the above-mentioned embodiment, the corresponding elements can be fully reused, zero discharge of ferric phosphate production wastewater treatment can be realized, environmental friendliness is effectively improved, and the cost of ferric phosphate production wastewater treatment can be significantly reduced. economic cost.

The filtrate obtained through the solid-liquid separation in step S02 contains water and a small amount such as ammonia, so it can be recycled repeatedly. In the embodiment, when the waste water contains ammonium ions or ammonia, after the treatment in the above steps S01 and S02, the filtrate obtained in the step S02 also contains a small amount of residual ammonia. As detected, the weight of ammonia in the filtrate is 100%. The sub-concentration content is 0.02-3.0%, or further, the pH value of the filtrate can reach 9-12. At this time, in the embodiment, before the step of concentrating the filtrate in step S03, a step of adjusting the pH value of the filtrate with an acid is also included. Regulate the filtrate treatment by acid to neutralize the residual ammonia content in the filtrate, such as adjusting the pH value of the filtrate to 6-8, so that ammonia generates ammonium sulfate, after the concentrated treatment in step S03, the concentrated solution containing ammonium sulfate can be It is passed into the waste water in step S01 to be mixed for recycling, and the water obtained from concentration treatment, such as pure water, is collected at the same time. In an embodiment, the acid used to adjust the filtrate may be a commonly used acid, as long as the pH of the filtrate can be adjusted to neutral. However, based on the embodiment of the present application, after the filtrate is concentrated in step S03, it is desired to reuse the concentrated liquid to increase the reuse rate of by-products and reduce waste discharge. In combination with the characteristics of the wastewater in step S01, the acid used to adjust the pH of the filtrate is ideally sulfuric acid, so that the main ions in the concentrated solution are sulfate ions, which remain the same as the main sulfate ions in the wastewater. Therefore, in an embodiment, the sulfuric acid may be the concentrated sulfuric acid prepared by the calcium sulfate sintering treatment described above to be diverted into the filtrate obtained from the solid-liquid separation in step S02 to adjust the pH of the filtrate.

In step S03, after the filtrate in step S02 is concentrated, a concentrated liquid can be obtained, and water can be collected to realize zero discharge of waste water. Based on the purpose of the concentration treatment, therefore, as long as the method that can achieve the purpose of the concentration treatment is within the scope of the disclosure of this application specification, for example, membrane concentration treatment can be used. As in the embodiment, the concentration treatment in step S03 is to pass the filtrate into a nanofiltration membrane for membrane filtration treatment. On the one hand, the use of nanofiltration membranes for concentration treatment can effectively achieve the purpose of concentration treatment and obtain pure water and concentrate; on the other hand, it reduces energy consumption and reduces the economic cost of the method for treating wastewater from ferric phosphate production in the embodiment of the present application.

Because the concentration process can collect water, therefore, in the embodiment, the collected water can be directly returned to the production of ferric phosphate, specifically as shown in Figure 2, as the water used for washing the ferric phosphate filter cake, for the treatment of phosphoric acid Iron filter cake washing treatment to reduce water consumption in iron phosphate production. Of course, the water collected in the concentration treatment can also be used to prepare the raw material liquid. The concentrated solution generally contains residual ions such as sulfate ions and ammonium ions. Therefore, the concentrated solution can be processed and utilized again. As in the embodiment, the concentrated solution is mixed with the wastewater in step S01 for the next round. Such as step S01 to step S03, so as to improve the efficiency of wastewater treatment, increase the yield of by-products, and almost realize zero waste discharge.

Therefore, the iron phosphate production wastewater treatment method in the above-mentioned each embodiment adopts calcium compound to carry out precipitation treatment to the sulfate radical ion contained in the iron phosphate production wastewater, so as to obtain calcium sulfate precipitation, and calcium sulfate can be further thermally decomposed and processed to finally prepare By-products such as sulfuric acid, thereby increasing the economic value of by-products. After the solution of the precipitation reaction is concentrated and treated, the concentrated solution can be further treated twice or mixed with waste water for repeated calcium sulfate precipitation treatment, which improves the treatment efficiency of waste water. Moreover, through the above-mentioned reuse of by-products collected from wastewater treatment, the utilization rate of elements in wastewater can be effectively improved, zero waste discharge to the environment can be realized, harm to the environment can be avoided, and the friendliness of the environment can be improved. Moreover, the water collected by the concentration treatment can be pure water, and can be returned to the secondary application of ferric phosphate production, thereby reducing the water consumption of ferric phosphate production, thereby reducing the economic cost of ferric phosphate production. In addition, the process of the iron phosphate production wastewater treatment method in the above-mentioned embodiments is easy to control, and the treatment efficiency and effect are stable.

In the second aspect, the embodiment of the present application provides a wastewater treatment system for ferric phosphate production. The iron phosphate production wastewater treatment system in the embodiment of the present application can be used to realize the above iron phosphate production wastewater treatment method. In conjunction with the above iron phosphate production wastewater treatment method and the process flow shown in Figure 2, the application embodiment iron phosphate production wastewater treatment system includes:

Calcium sulfate precipitation reaction device, used to react ferric phosphate production wastewater with calcium-containing substances to generate calcium sulfate precipitation;

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

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

In the embodiment, the calcium sulfate precipitation reaction device contained in the iron phosphate production wastewater treatment system in the embodiment of the present application includes a reaction vessel for the calcium sulfate precipitation reaction and a feed port for adding calcium-containing substances into the reaction vessel. The feed port It communicates with the reaction container, or the reaction container is directly provided with the feeding port for adding calcification. The reaction vessel is also provided with a calcium sulfate slurry discharge port for calcium sulfate precipitation discharge.

Certainly, the reaction vessel contained in the calcium sulfate precipitation reaction device also includes a waste water inlet for transporting ferric phosphate production waste water into the reaction vessel for purification and reuse. In an embodiment, the waste water inlet of the reaction vessel communicates with the mother liquor outlet and the washing water outlet contained in the ferric phosphate production system. In order to flexibly control the delivery of the mother liquor and/or washing water to the calcium sulfate precipitation reaction device, specifically to the reaction container thereof, and carry out purification treatment.

Since the waste water generally may contain ammonia, etc., during the working process of the reaction vessel contained in the calcium sulfate precipitation reaction device, specifically during the calcium sulfate precipitation reaction process, generally there will be gas such as ammonia-containing gas generated and overflowed. In a further embodiment, the reaction vessel of the calcium sulfate precipitation reaction device further includes a waste gas outlet, and the waste gas outlet is communicated with the pH regulator adding device contained in the ferric phosphate production system. In this way, the by-products produced in wastewater treatment can be fully utilized, the cost of wastewater treatment can be reduced, the harm to the environment can be reduced, and its environmental protection can be improved.

In the embodiment, the solid-liquid separation device contained in the iron phosphate production wastewater treatment system in the embodiment of the present application is provided with a slurry inlet, a filter residue outlet and a filtrate outlet, wherein the slurry inlet and the calcium sulfate precipitation reaction device The set calcium sulfate precipitate discharge port is connected. In this way, the calcium sulfate precipitate is passed through the slurry feed port into the solid-liquid separation device for solid-liquid separation, which can realize the separation of calcium sulfate filter residue and filtrate. The solid-liquid separation device may be, but not limited to, a centrifugal separation device or a filter press device.

In the embodiment, the ferric phosphate production wastewater treatment system further includes a sulfuric acid preparation device, and the sulfuric acid preparation device uses calcium sulfate-containing filter residue to prepare sulfuric acid. In a specific embodiment, the sulfuric acid preparation device is provided with a calcium sulfate feed port and a decomposition vessel for decomposing calcium sulfate, and the calcium sulfate feed port is used to pass calcium sulfate filter residue into the decomposition container provided by the sulfuric acid preparation device Calcium sulfate is thermally decomposed, as described above in the iron phosphate production wastewater treatment method, and calcium sulfate is thermally decomposed to generate sulfur dioxide and calcium compounds. Therefore, the calcium sulfate feed inlet of sulfuric acid preparation unit is communicated with the filter residue outlet of solid-liquid separation unit. Certainly, the sulfuric acid preparation device also includes a reaction vessel for further catalyzing sulfur dioxide to generate sulfur trioxide and reacting sulfur trioxide with water to generate concentrated sulfuric acid. In a further embodiment, the outlet of the concentrated sulfuric acid of the sulfuric acid preparation device can communicate with the container of the solid-liquid separation device for holding the filtrate, so as to pass 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 discharge port, and the calcium compound discharge port communicates with the feeding port provided by the calcium sulfate precipitation reaction device for adding calcium-containing compounds. In this way, the calcium compound produced by thermal decomposition of the sulfuric acid preparation device can be added to the calcium sulfate precipitation reaction device as a calcium-containing compound to react with wastewater to generate calcium sulfate precipitation, thereby further improving the utilization rate of by-products produced in wastewater treatment and improving It is environmentally friendly and reduces the cost of wastewater treatment.

In the embodiment, the solution concentration device contained in the iron phosphate production wastewater treatment system in the embodiment of the present application is provided with a solution feed port, a concentrated liquid discharge port and a solvent discharge port, wherein the solution feed port and the filtrate provided by the solid-liquid separation device The outlet is connected. In this way, the solution concentration device can directly concentrate the filtrate produced by the solid-liquid separation device, for example, separate it into concentrated liquid and water (such as pure water).

In an embodiment, the solvent outlet provided by the solution concentrating device communicates with the iron phosphate filter cake washing device contained in the iron phosphate production system. Like this, what this solvent outlet discharges is water, as pure water, and after it communicates with the device for iron phosphate filter cake washing so, this water, as pure water can directly realize that iron phosphate filter cake is washed.

Therefore, based on the device contained in the iron phosphate production wastewater treatment system of the above application embodiment, the iron phosphate production wastewater treatment system of the embodiment of the present application can effectively implement the iron phosphate production wastewater treatment method of the present application to realize the treatment of the iron phosphate production wastewater , and achieve low energy consumption, the recovered by-products can basically be collected and reused, and almost all of the generated by-products can be reused in the process of the wastewater treatment method for iron phosphate production in the embodiment of the present application, while achieving wastewater treatment efficiency High, low economic cost, and environmentally friendly.

A number of specific examples are used below to illustrate the method for treating wastewater from iron phosphate production in the embodiments of the present application.

Example 1

This embodiment provides a method for treating wastewater from ferric phosphate production. Wherein, the iron source in the present embodiment 1 is ferrous sulfate, and phosphorus source is monoammonium phosphate, explored many groups of different concentrations (ferrous sulfate concentration, monoammonium phosphate concentration), different reaction conditions (different synthetic pH, reaction time and temperature, etc.).

Take the following reaction conditions as an example: the concentration of ferrous sulfate is 1.5mol/L, the concentration of monoammonium phosphate is 2.0mol/L, the oxidant is hydrogen peroxide with a concentration of 30%, and the molar ratio of phosphorus to iron in the phosphorus source and iron source is 1.1:1.

The present embodiment ferric phosphate production wastewater treatment method comprises the following steps:

S1. Preparation of ferrous solution and phosphate solution: with the pure water obtained in step S5, ferrous sulfate and monoammonium phosphate are dissolved respectively to obtain 10 m of ferrous solution and 8.2 ^{m of} iron salt concentration of 1.5 mol/L Phosphate solution with a phosphate concentration of 2mol/L;

S2. Preparation of ferric phosphate: mix the ferrous solution and phosphoric acid solution obtained in step S1, control the reaction temperature to 40°C, slowly add hydrogen peroxide to oxidize the ferrous, and then heat up to 85°C for 2 hours to obtain ferric phosphate slurry. Filter, wash the iron phosphate filter cake with the pure water that step S5 obtains, obtain iron phosphate filter cake, 14.5m ³ mother liquor and 8m ³ washing water, obtain 22.5m ³ waste water after mother liquor and washing water are mixed; Obtain 2265Kg anhydrous ferric phosphate after steaming dry, rotary kiln calcining; After testing, each physical and chemical index of the waste water in this step S2 is as shown in Table 1;

S3. Wastewater precipitation reaction treatment: add 840Kg of calcium oxide to the wastewater, adjust the pH value of the wastewater to 13, control the pressure in the reactor to a negative pressure of 0.09MPa, keep stirring at 60°C, and ammonia gas escapes from the solution with stirring , pour the overflowing ammonia gas into 2.5m ³ pure water to obtain dilute ammonia water with an ammonia gas content of 10%. As the ammonia gas escapes, the pH value of the solution gradually decreases. After stirring for 4 hours, the pH value of the solution decreases to below 10 and then filtered. Obtain calcium sulfate filter cake (calcium sulfate filter residue) and ^19.3m filtrate; After testing, each physical and chemical index of filtrate in this step S3 is as shown in table 2;

S4. Calcium sulfate treatment: put the calcium sulfate filter cake into a pusher kiln after being flash-dried and crushed, and calcined at 900°C for 3 hours to obtain 840Kg of calcium oxide, collect the calcined tail gas-sulfur dioxide, and obtain three To oxidize sulfur, pass sulfur trioxide into pure water to obtain concentrated sulfuric acid;

S5. Filtrate treatment: add sulfuric acid to fine-tune the pH of the filtrate, and then pass it through a nanofiltration membrane to obtain pure water and concentrated liquid after precision filtration, and incorporate the concentrated liquid into waste water for treatment together.

Table 1 The physical and chemical indicators of waste water in Step S2 of Example 1

S-g/L N-g/L Fe-g/L P-g/L pH value volume-m³ 21.8 12.7 0.0028 0.423 0.84 22.5

Each physical and chemical index of filtrate in the step S3 of table 2 present embodiment 1

S-g/L N-g/L Fe-g/L P-g/L Ca-g/L pH value volume-m³ 0.0013 0.046 0.0007 0.00004 0.007 9.43 19.3

As can be seen in Table 1, the waste water produced in step S01 is mainly ammonium sulfate and free sulfuric acid, and the acidity is relatively high. After calcium oxide is added, calcium oxide dissolves in water and emits a large amount of heat to form calcium hydroxide, and calcium hydroxide and sulfuric acid are generated. And reaction, also release a lot of heat, cause the temperature of the solution to rise above 60 ℃, excess calcium hydroxide and ammonium sulfate react to generate calcium sulfate and ammonia water, resulting in an increase in pH value, due to the high pH value and temperature, ammonia gas is extremely It is easy to escape from the solution, and the pH decreases slowly with the release of ammonia gas.

As can be seen from Table 2, the filtrate in the step S03 is precision filtered and then added a small amount of sulfuric acid to adjust the pH value to 6.5, and then passed through the nanofiltration membrane to concentrate to obtain 0.3 ^m Ammonium sulfate concentration of 1.2% concentrated solution and 19 ^m desalination Pure water, the 0.3m ³ concentrate is incorporated into the waste water of step S03 for centralized treatment.

Using a scanning electron microscope to observe the anhydrous iron phosphate prepared in the above step S2 for microscopic morphology characterization, the results are shown in FIG. 3 . Further, the anhydrous ferric phosphate prepared in step S2 was tested for physical and chemical indicators according to conventional methods, and the results were shown in Table 3 below:

Table 3 Physical and chemical indicators of anhydrous ferric phosphate in step S2 of the present embodiment 1

It can be seen from Table 3 that the finished product of iron phosphate produced in Example 1 has relatively low impurities, and the test results of various physical and chemical indicators all meet the requirements of battery-grade iron phosphate.

Further, to present embodiment 1 iron phosphate production waste water treatment method cost calculation, the result is as shown in table 4:

Table 4 The cost link cost of iron phosphate production wastewater treatment method in Example 1

It can be seen from Table 4 that the cost of wastewater treatment is mainly the energy consumption of calcium sulfate calcination. Due to the high decomposition temperature of calcium sulfate, more natural gas is consumed, but the sulfuric acid produced can cover the consumption during calcium sulfate calcination. In addition, the by-product ammonia can also offset part of the cost of wastewater treatment.

Example 2

This embodiment provides a method for treating wastewater from ferric phosphate production. Wherein, the iron source in the present embodiment is ferrous sulfate, and the phosphorus source is the wet process unpurified phosphoric acid (phosphoric acid content 30wt%), has explored many groups of different concentrations (ferrous sulfate concentration, phosphoric acid concentration), different reaction conditions ( Different synthetic pH, reaction time and temperature, etc.).

Taking the following reaction conditions as an example: the concentration of ferrous sulfate is 1.5mol/L, the concentration of phosphate is 2.0mol/L, the oxidant is hydrogen peroxide with a concentration of 30wt%, the pH regulator is the filtrate obtained in step S3, the phosphorus source and iron The molar ratio of phosphorus to iron in the source is 1.1:1.

The present embodiment ferric phosphate production wastewater treatment method comprises the following steps:

S1. the preparation of ferrous solution, phosphate solution: with the pure water that obtains in step S5, ferrous sulfate is dissolved, obtains 10m Ferrous solution that iron salt concentration is ^1.5mol /L ^; Get 3.6m Obtained in step S3 Add 5.4 tons of wet-process unpurified phosphoric acid to the filtrate, pass the ammonia gas obtained in step S3 into the filtrate to adjust the pH value to 4.0, and then filter to prepare 8.2 ^m ammonium phosphate with an ammonium phosphate salt concentration of 2 mol/L saline solution;

S2. Preparation of ferric phosphate: mix the ferrous solution and ammonium phosphate salt solution obtained in step S1, control the reaction temperature to 40°C, slowly add hydrogen peroxide to oxidize the ferrous iron, then raise the temperature to 85°C and keep it for 2 hours to obtain ferric phosphate slurry After filtering and washing, ferric phosphate filter cake, 14.5m ³ mother liquor and 8m ³ washing water were obtained, and 22.5m ³ waste water was obtained after mixing the mother liquor and washing water; Ferric phosphate water; after testing, the physical and chemical indicators of the waste water in this step S2 are as shown in table 5;

S3. Wastewater precipitation reaction treatment: add 840Kg of calcium oxide to the wastewater, and the pH value rises to 13. Control the pressure in the reactor to a slight negative pressure. After stirring for 30 minutes, the pH value of the solution decreases to below 11 and then filters to obtain a calcium sulfate filter cake. And 19.3m ³ filtrate, collect and escape ammonia gas; After testing, each physical and chemical index of the filtrate in this step S3 is as shown in table 6;

S4. Calcium sulfate treatment: put the calcium sulfate filter cake into a pusher kiln after being flash-dried and crushed, and calcined at 930°C for 2 hours to obtain 840Kg of calcium oxide. To oxidize sulfur, pass sulfur trioxide into pure water to obtain concentrated sulfuric acid;

S5. Filtrate treatment: add sulfuric acid to the filtrate to fine-tune the pH, and then pass it through the reverse osmosis membrane after precision filtration to obtain pure water and concentrated solution, and incorporate the concentrated solution into wastewater for treatment together.

The waste water 1 to be treated was taken for physical and chemical index detection, and the results are shown in Table 5 below:

Table 5 The physical and chemical indicators of waste water in Step S2 of Example 2

S-g/L N-g/L Fe-g/L P-g/L pH value volume-m3 22.4 12.3 0.0017 0.392 0.79 22.5

Each physical and chemical index of filtrate in the step S3 of table 6 present embodiment 2

S-g/L N-g/L Fe-g/L P-g/L Ca-g/L pH value volume-m³ 0.0023 0.146 0.0005 0.00004 0.006 10.3 19.3

As can be seen in Table 5, the waste water produced in step S01 is mainly ammonium sulfate and free sulfuric acid, and the acidity is relatively high. After adding calcium oxide, calcium oxide dissolves in water and emits a large amount of heat to form calcium hydroxide, and calcium hydroxide and sulfuric acid are generated. And the reaction also releases a lot of heat, causing the temperature of the solution to rise above 60°C, and the excess calcium hydroxide and ammonium sulfate react to form calcium sulfate and ammonia water, resulting in an increase in the pH value. Due to the high pH value and temperature, the pH is high When the ammonia escapes faster, the pH drops faster.

As can be seen from Table 6, after the filtrate in step S03 is precision filtered, a small amount of sulfuric acid is added to adjust the pH value to 6.5, and then passed through the nanofiltration membrane to concentrate to obtain ^0.14m Ammonium sulfate concentration is 6.2% strong water and ^15.6m Desalinated pure water, the 0.14m ³ concentrated solution was incorporated into the waste water of step S03 for centralized treatment.

Using a scanning electron microscope to observe the anhydrous iron phosphate prepared in the above step S2 for microscopic morphology characterization, the results are shown in FIG. 4 . Further, the anhydrous ferric phosphate prepared in step S2 was tested for physical and chemical indicators according to conventional methods, and the results were shown in Table 7 below:

Table 7 Physical and chemical indicators of anhydrous ferric phosphate in step S2 of the present embodiment 2

It can be seen from Table 7 that the finished product of iron phosphate produced in Example 2 has relatively low impurities, and the test results of various physical and chemical indicators all meet the requirements of battery-grade iron phosphate.

Further, to present embodiment 2 iron phosphate production waste water treatment method cost calculation, the result is as shown in table 8:

Table 8 The cost link cost of iron phosphate production wastewater treatment method in the present embodiment 2

It can be seen from Table 8 that the waste water treatment cost is still the energy consumption of calcium sulfate calcination, but the consumption of calcium sulfate calcination can be covered by selling the prepared sulfuric acid, and the ammonia is returned to the raw material liquid preparation stage, and the lower grade The wet process unpurified phosphoric acid undergoes neutralization reaction, so it is not included in the income of by-products.

Example 3

This embodiment provides a method for treating wastewater from ferric phosphate production. Wherein, the iron source in the present embodiment 3 is polyferric sulfate, and the iron concentration is 1.2mol/L, and the phosphorus source is monoammonium phosphate, and the concentration is 1.5mol/L, and the molar ratio of phosphorus element to iron element in the phosphorus source and the iron source is The ratio is 1.1:1.

The present embodiment ferric phosphate production wastewater treatment method comprises the following steps:

S1. Preparation of iron salt solution and phosphate solution: with the pure water obtained in step S5, polyferric sulfate and monoammonium phosphate are dissolved respectively to obtain 10m ferrous solution and 8.8m ferrous solution with iron salt concentration of ^1.2mol / ^L Phosphate solution with a phosphate concentration of 1.5mol/L;

S2. Preparation of iron phosphate: control the reaction temperature at 50°C, mix the iron salt solution and phosphate solution obtained in step S1, then heat up to 90°C for 2 hours to obtain iron phosphate slurry, filter, and use step S5 to obtain Wash the iron phosphate filter cake with pure water to obtain iron phosphate filter cake, 12.3m ³ mother liquor and 8m ³ washing water, and mix the mother liquor and washing water to obtain 20.3m ³ waste water; after the iron phosphate filter cake is flash-dried and calcined in a rotary kiln Obtain 1812Kg anhydrous ferric phosphate; After testing, each physical and chemical index of the waste water in this step S2 is as shown in table 1;

S3. Wastewater precipitation reaction treatment: add 880Kg of calcium hydroxide to the wastewater, adjust the pH value of the wastewater to 13, control the pressure in the reactor to a negative pressure of 0.09MPa, and keep stirring at 60°C. The ammonia gas escapes from the solution with the stirring The overflow ammonia gas is passed into 2m ³ pure water to obtain dilute ammonia water with an ammonia gas content of 10%. As the ammonia gas escapes, the pH value of the solution gradually decreases. After stirring for 4 hours, the pH value of the solution decreases to below 10 and then filtered. Obtain calcium sulfate filter cake (calcium sulfate filter residue) and ^17.2m filtrate; After testing, each physical and chemical index of filtrate in this step S3 is as shown in table 2;

S4. Calcium sulfate treatment: put the calcium sulfate filter cake into a pusher kiln after flash drying, crushing, and calcining at 1200°C for 3 hours to obtain 666Kg of calcium oxide, which is used for the removal of sulfate radicals in the next batch of wastewater ;Collect the calcined tail gas-sulfur dioxide, the sulfur dioxide is catalyzed and oxidized by the catalyst to obtain sulfur trioxide, and the sulfur trioxide is passed into pure water to obtain concentrated sulfuric acid;

S5. Filtrate treatment: adding sulfuric acid to fine-tune the pH of the filtrate, and then passing it through a nanofiltration membrane to obtain pure water and a concentrated solution after precision filtration, and incorporating the concentrated solution into S03 wastewater for centralized treatment.

Table 9 The physical and chemical indicators of waste water in Step S2 of Example 3

S-g/L N-g/L Fe-g/L P-g/L pH value volume-m³ 18.9 10.03 0.0073 0.329 0.91 20.3

Each physical and chemical index of filtrate in the step S3 of table 10 present embodiment 3

S-g/L N-g/L Fe-g/L P-g/L Ca-g/L pH value volume-m³ 0.0009 0.064 0.0005 0.00006 0.006 9.72 17.2

As shown in Table 9, the waste water produced in step S01 is mainly ammonium sulfate and free sulfuric acid, and the acidity is relatively high. After adding calcium hydroxide, calcium hydroxide dissolves in water and emits a large amount of heat, and the neutralization reaction occurs between calcium hydroxide and sulfuric acid. It also releases a lot of heat, causing the temperature of the solution to rise above 60°C. The excess calcium hydroxide and ammonium sulfate react to form calcium sulfate and ammonia water, resulting in an increase in pH value. Due to the high pH value and temperature, ammonia gas is easily released from the solution. With the release of ammonia gas, the pH decreases slowly. The indicators of the treated wastewater are shown in Table 10.

After the filtrate in the step S03 is precision filtered, add a small amount of sulfuric acid to adjust the pH value to 6.5, and then pass through the nanofiltration membrane to concentrate to obtain 0.27m Ammonium sulfate concentration is a concentrated solution of 1.53% and ^{16.9m Desalted} pure water, the ^The 0.27m concentrated solution is incorporated into the waste water of step S03 for centralized treatment.

The anhydrous ferric phosphate prepared in step S2 is tested for physical and chemical indicators according to conventional methods, and the results are shown in Table 11 below:

Table 11 Physical and chemical indicators of anhydrous ferric phosphate in step S2 of Example 1

It can be seen from Table 11 that the finished product of iron phosphate produced in Example 3 has relatively low impurities, and the test results of various physical and chemical indicators all meet the requirements of battery-grade iron phosphate.

Further, the cost calculation of the wastewater treatment method for iron phosphate production in Example 3, the results are shown in Table 12:

Table 12 The cost link cost of iron phosphate production wastewater treatment method in the present embodiment 3

It can be seen from Table 12 that the cost of wastewater treatment is mainly the energy consumption of calcium sulfate calcination. Due to the high decomposition temperature of calcium sulfate, more natural gas is consumed, but the sulfuric acid produced can cover the consumption of calcium sulfate calcination. In addition, the by-product ammonia can also offset part of the cost of wastewater treatment.

Example 4

This embodiment provides a method for treating wastewater from ferric phosphate production. The iron phosphate production waste water treatment method of this embodiment is improved on the basis of embodiment 1, specifically comprises the following steps:

S1. the preparation of ferrous solution, phosphate solution: step S1 with reference to embodiment 1;

S2. Preparation of iron phosphate: refer to step S2 of Example 1;

S3. Wastewater precipitation reaction treatment: refer to step S3 of embodiment 1; wherein, the calcium oxide in this step is the calcium oxide generated by calcium sulfate sintering treatment in step S4;

S4. Calcium sulfate treatment: with reference to step S4 of embodiment 1; And the generation calcium oxide in this step is the calcium oxide that calcium sulfate sintering treatment generates in the step S4 is delivered to step S3 and mixed with waste water to generate calcium sulfate precipitation; After the calcium oxide in the step is recycled at least 5 times according to the reuse method, the calcium phosphate contained in the calcium sulfate is detected. When the calcium phosphate content reaches the preset content, sulfuric acid is first added to the calcium sulfate until When the pH value in the mixed solution reaches 3-4, a lower concentration of monoammonium phosphate solution and calcium sulfate precipitation is generated. After the reaction between the sulfuric acid and calcium phosphate is completed, solid-liquid separation is carried out to obtain calcium sulfate precipitation and monoammonium phosphate. The calcium sulfate precipitation continues to be calcined according to step S4 of Example 1 to obtain calcium oxide, which is transported to step S3 and mixed with waste water to generate calcium sulfate precipitation; while collecting the calcined tail gas-sulfur dioxide, after the sulfur dioxide is catalyzed and oxidized by the catalyst To obtain sulfur trioxide, pass sulfur trioxide into pure water to obtain concentrated sulfuric acid, which is used as sulfuric acid in step S5 to adjust the pH of the filtrate; the generated monoammonium phosphate solution is added with a certain amount of phosphoric acid after detecting the phosphorus content Ammonium salt is made into phosphorus source solution and is used for the production of ferric phosphate as the phosphate solution in step S1;

S5. Filtrate treatment: carry out with reference to step S5 of Example 1.

Comparative example 1

This comparative example provides a method for treating wastewater from ferric phosphate production. Among them, the iron source is ferrous sulfate, and the phosphorus source is monoammonium phosphate. Taking the optimal reaction conditions as an example: the concentration of ferrous sulfate is 1.5mol/L, the concentration of monoammonium phosphate is 2.0mol/L, and the concentration of oxidant is 30 % hydrogen peroxide, the molar ratio of phosphorus to iron in the phosphorus source and iron source is 1.1:1.

This comparative example ferric phosphate production wastewater treatment method comprises the following steps:

S1. Preparation of ferrous solution and phosphate solution: Dissolve ferrous sulfate and monoammonium phosphate respectively with pure water to obtain 7.5m ferrous solution with iron salt concentration of ^1.5mol /L and 11m ferrous solution with phosphate concentration ^of 2mol /L of phosphate solution;

S2. Preparation of ferric phosphate: mix the ferrous solution and phosphate solution obtained in step S1, control the reaction temperature to 40°C, slowly add hydrogen peroxide to oxidize the ferrous, then raise the temperature to 85°C for 2 hours to obtain ferric phosphate slurry After filtering and washing, iron phosphate filter cake, 15.5m ³ mother liquor and 6m ³ washing water were obtained, and 21.5m ³ waste water was obtained after mixing the mother liquor and washing water; the iron phosphate filter cake was flash-dried and calcined in a rotary kiln to obtain 755Kg free ferric phosphate;

S3. Wastewater treatment: adjust the pH value of the wastewater to 9.0 with ammonia water and then filter, then fine-tune the pH value to 6.5 with sulfuric acid, and then pass it into the MVR evaporator to evaporate to obtain solid ammonium sulfate.

Using a scanning electron microscope to observe the anhydrous iron phosphate prepared in the above step S2 for microscopic morphology characterization, the results are shown in FIG. 5 . Further, the anhydrous ferric phosphate prepared in step S2 was tested for physical and chemical indicators according to conventional methods, and the results were shown in Table 13 below:

Table 13 Physical and chemical indicators of anhydrous ferric phosphate in step S2 of this comparative example 1

It can be seen from Table 13 that the finished product of iron phosphate produced in Comparative Example 1 has relatively low impurities, and the test results of various physical and chemical indicators all meet the requirements of battery-grade iron phosphate.

Further, the cost calculation of the wastewater treatment method for iron phosphate production in Comparative Example 1, the results are shown in Table 14:

Table 14 The cost link cost of iron phosphate production wastewater treatment method in this comparative example 1

It can be seen from Table 14 that the cost of wastewater treatment is mainly the cost of energy and power consumption for evaporating ammonium sulfate solution with MVR.

Known based on above-mentioned embodiment 1 to embodiment 4 and comparative example 1, compare Fig. 3 and Fig. 5, table 3 and table 13 as can be seen, the anhydrous ferric phosphate that embodiment 1 and comparative example 1 make have no significant difference, mainly The difference lies in the way wastewater is treated. Among them, comparative example 1 adopts the conventional water treatment method, uses ammonia water to adjust the pH value of the wastewater to weak alkaline, and then filters to remove metal impurities in the wastewater, then uses sulfuric acid to neutralize the pH value, and then uses MVR to evaporate and concentrate to obtain sulfuric acid Ammonium salt, this method consumes more energy and has high cost. However, in Example 1, calcium-containing compounds are used to remove sulfate radicals in wastewater by co-precipitation. Calcium is an alkaline compound. When removing sulfate radicals, the pH value of the solution is also improved, and the volatilization rate of ammonia water is increased to obtain dilute by-products. Ammonia; the obtained calcium sulfate solution is calcined to obtain concentrated sulfuric acid and calcium oxide, and the calcium oxide is recycled without generating solid waste. For every ton of ferric phosphate produced, 615 yuan can be saved in waste water treatment. The cost of wastewater treatment in Example 3 is close to that in Example 1. Embodiment 4 Owing to being able on the basis of embodiment 1, calcium sulfate liquid is further obtained by calcining and mixed with waste water to generate calcium sulfate, therefore, calcium oxide has been further utilized again, relative to embodiment 1, embodiment 4 The cost of wastewater treatment is lower, and basically no solid waste is generated.

Comparing Figure 4 and Figure 5, Table 7 and Table 13, it can be seen that there is no significant difference between Example 2 and Comparative Example 1 and the ferric phosphate produced, and the main difference between the two is still in the way of wastewater treatment. Wherein, comparative example 1 is as above-mentioned, and it adopts conventional water treatment method, and this method consumes energy more, and cost is high. In Example 2, after the sulfuric acid radicals in the waste water were removed by calcium-containing compounds, the phosphorus source was prepared by using the remaining dilute ammonia in the solution and the cheaper wet-process unpurified phosphoric acid. On the one hand, the recycling of ammonia and water avoids Ammonia nitrogen pollution is eliminated and the utilization rate of elements is improved; on the other hand, because wet-process phosphoric acid contains a large amount of impurities, it needs to be removed before it can be used. The process of removing impurities in wet-process phosphoric acid is complicated in an acidic environment, although the cost is higher than that of wastewater treatment in Example 1. , but the cost of conventional wastewater treatment is still significantly reduced relative to Comparative Example 1, and after it is mixed with dilute ammonia and phosphoric acid to prepare a phosphate solution, due to the increase in pH, metal impurities and hydroxide, phosphate An insoluble material formed which was removed by filtration. Therefore, Example 2 not only reduces the cost of water treatment in the wastewater treatment stage, but also has higher compatibility with low-grade, high-impurity phosphorus sources.

The above descriptions are only preferred embodiments of the application, and are not intended to limit the application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the application should be included in the protection of the application. within range.

Claims (12)

1. The method for treating wastewater generated in iron phosphate production is characterized by comprising 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 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 calcium sulfate precipitation reaction device is used for reacting the iron phosphate production wastewater with a calcium-containing substance 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 precipitate reaction device to obtain filter residue containing 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.

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.

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