Circulating concentration device and application thereof

Abstract

The invention provides a circulating concentration device which comprises a stirring tank, a circulating concentration tank and a cross-flow filtering membrane mechanism, a feeding port of the circulating concentration tank is connected with a discharging port of the stirring tank, and a discharging port of the circulating concentration tank is connected with a feeding port of the cross-flow filtering membrane mechanism and a feeding port of the stirring tank. And a discharge port of the cross-flow filtering membrane mechanism is connected with a circulating feed port of the circulating concentration tank. The method can be used for pretreating the iron phosphate mother liquor, shortens the technological process, reduces the occupied area and lowers the equipment failure rate. The device can also be used for cleaning iron phosphate products, washing water is completely mixed and fully contacted with the iron phosphate products or intermediate products, cleaning is thorough, iron phosphate slurry with impurity ions meeting requirements is obtained, water consumption can be saved, full-automatic operation is achieved, labor is saved, and operation is easy. According to the invention, one set of equipment has two purposes, and the production cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of battery production, and in particular to a circulation concentration device and application thereof. Background Art

[0002] Lithium iron phosphate is an important positive electrode material for batteries. With the rapid development of the electric vehicle industry, the market demand for lithium iron phosphate has gradually increased. As one of the precursors for the synthesis of lithium iron phosphate, the quality of iron phosphate has an important impact on the performance of lithium iron phosphate.

[0003] The typical production process of iron phosphate is as follows: ferrous sulfate solution, hydrogen peroxide, and monoammonium phosphate solution react in a reactor to obtain a precipitate, the precipitate is washed and impurities are removed to obtain iron phosphate precipitate; the washed iron phosphate is re-pulped and aged, then washed again, and the product iron phosphate is obtained after drying.

[0004] In this process, the iron phosphate reaction slurry needs to be squeezed, the reaction mother liquor needs to be discharged, and the formed filter cake needs to be washed twice. Therefore, a large amount of mother liquor and rinse water will be discharged during the iron phosphate production process. The mother liquor and rinse water contain phosphate, hydrogen ions, and metal ions such as manganese, magnesium, calcium, iron, and aluminum.

[0005] After these mother liquors and rinse water are discharged into the wastewater treatment section, they are pretreated with a process of dosing + neutralization stirring tank reaction + high-density clarification tank + filter + ultrafiltration. The ultrafiltration water then enters the reverse osmosis process. After deep treatment, the reverse osmosis water returns to the iron phosphate production process to rinse the product.

[0006] The pretreatment process route of dosing + neutralization stirring tank reaction + high-density clarification tank + filter tank + ultrafiltration, which is commonly used for pretreatment of mother liquor and wash water in iron phosphate production, has the following disadvantages: 1. The mixing efficiency of the stirred tank reaction is low, requiring a larger reaction volume and a higher ammonia dosage; 2. The mother liquor, washing water and ammonia water react directly. There is no condensation nucleus in the reaction system, resulting in small particles of manganese phosphate, magnesium ammonium phosphate, iron phosphate and calcium phosphate, poor precipitation effect, and poor fluidity of the slurry formed by precipitation, which can easily lead to blockage of the high-density clarification tank; 3. High-density clarifiers and filter tanks have a small water treatment load, resulting in a large area occupied by water treatment structures.

[0007] At the same time, during the production process of iron phosphate, iron phosphate needs to be washed twice. The washing effect has an important impact on the purity and quality of iron phosphate products. At present, the filtration and washing of iron phosphate are usually carried out using a plate and frame filter press. The iron phosphate slurry is filtered using a plate and frame filter press, and then pure water is injected into the filter plate to wash the filter cake. The main problems with the current washing method are: 1. When using a plate and frame filter press to wash the filter cake, the iron product may not be washed thoroughly due to problems such as short flow in the middle or uneven washing water flow. After washing, the existing iron phosphate filter cake still contains a small amount of impurities, which affects the quality of the iron phosphate; 2. The washing operation using a plate and frame filter press is complicated, and there are problems such as intermittent operation and high labor intensity.

[0008] 3. When using a plate and frame filter press for washing, there are problems such as iron phosphate particles penetrating through the filter, resulting in product loss and increased turbidity of the rinsing wastewater.

[0009] 4. The particle size of iron phosphate product particles is generally distributed between several hundred nanometers and several microns. These particles are in a compacted state in the plate and frame filter press, which is difficult to clean. In order to meet the cleaning standards, a large amount of high-temperature pure water must be used. The corresponding amount of washing water required to be processed is also very high, which increases the production cost of iron phosphate.

[0010] 5. The manual operation is complicated, and re-slurry filtration and manual plate unloading are required during the two washing processes.

[0011] At present, the pretreatment of the mother liquor and wash water in the production of ferric phosphate and the cleaning of the ferric phosphate product require two different sets of equipment, which increases the production cost. Summary of the invention

[0012] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the present invention provides a circulating concentration device and its application, which can be used for pretreatment of mother liquor and wash water in iron phosphate production, and can also be used for cleaning iron phosphate products to reduce production costs. The first aspect of the present invention proposes a circulating concentrating device, comprising: a stirring tank, a circulating concentrating tank and a cross-flow filtration membrane mechanism, wherein the stirring tank has a first feed port, a second feed port and a discharge port, and a first stirring device is arranged in the stirring tank; the circulating concentrating tank has a feed port, a circulating feed port and a discharge port, the first feed port of the circulating concentrating tank is connected to the discharge port of the stirring tank, and a second stirring device is arranged in the circulating concentrating tank; the cross-flow filtration membrane mechanism has a feed port, a water outlet and a discharge port, the discharge port of the circulating concentrating tank is respectively connected to the feed port of the cross-flow filtration membrane mechanism and the feed port of the stirring tank, the circulating concentrating tank is connected to a concentrated liquid discharge valve, and the discharge port of the cross-flow filtration membrane mechanism is connected to the circulating feed port of the circulating concentrating tank.

[0013] In some embodiments, the cross-flow filtration membrane mechanism comprises a microfiltration membrane.

[0014] In some embodiments, the feed port of the stirring tank is connected to a lift pump through a pipeline, and the lift pump has an impeller for mixing inside.

[0015] In some embodiments, the discharge port of the circulating concentration tank is connected to a concentrated liquid circulation pump.

[0016] In some embodiments, the discharge port of the circulating concentrating tank is connected to the feed port of the stirring tank through a first pipeline, the discharge port of the circulating concentrating tank is connected to the feed port of the cross-flow filtration membrane mechanism through a second pipeline, a first regulating valve is connected to the first pipeline, a second regulating valve is connected to the second pipeline, and a concentrated liquid discharge valve is connected to the circulating concentrating tank.

[0017] In some embodiments, an aeration device is provided in the circulating concentration tank.

[0018] In some embodiments, the circulating concentration device further comprises a backwashing device, which backwashes the filter membrane in the cross-flow filter membrane mechanism.

[0019] In some embodiments, the circulating concentration device further comprises a chemical cleaning device, which performs chemical cleaning on the filter membrane in the cross-flow filter membrane mechanism.

[0020] The second aspect of the present invention provides an application of the above-mentioned circulating concentration device in the pretreatment of iron phosphate mother liquor, comprising the following steps: The ferric phosphate mother liquor and ammonia water are mixed by the lifting pump and then introduced into a stirring tank for reaction to generate a reaction liquid; the reaction liquid is introduced into a circulation concentration tank and mixed with the concentrated liquid filtered by a cross-flow filtration membrane mechanism to form a reaction liquid circulating concentrated liquid; a part of the reaction liquid circulating concentrated liquid is returned to the lifting pump, mixed with the ferric phosphate mother liquor and ammonia water, and then introduced into the stirring tank together, and the remaining part of the reaction liquid circulating concentrated liquid is introduced into a cross-flow filtration membrane mechanism for circulation concentration, the fresh water in the reaction liquid circulating concentrated liquid is discharged and introduced into a reverse osmosis system, and the reverse osmosis produced water is further deeply treated and reused in the ferric phosphate production system for flushing the ferric phosphate product; the reaction liquid circulating concentrated liquid after filtering and removing part of the water is returned to the circulation concentration tank again, mixed with the feed liquid, and circulated back and forth, and the concentration of the reaction liquid circulating concentrated liquid of the ferric phosphate mother liquor is gradually increased, and when it is increased to a certain concentration, part of it is discharged from the circulation concentration tank.

[0021] The third aspect of the present invention provides an application of the above-mentioned circulating concentration device in the cleaning of iron phosphate products, comprising the following steps: The iron phosphate product or intermediate product to be cleaned and the washing water are passed into a circulating concentration tank for stirring washing and aeration washing to form a circulating water-washed slurry; the circulating water-washed slurry is passed into a cross-flow filtration membrane mechanism for circulating filtration to discharge part of the washing water and soluble impurities in the circulating water-washed slurry; the circulating water-washed slurry from which part of the washing water and soluble impurities have been filtered out is returned to the circulating concentration tank again, mixed with the washing water newly added to the circulating concentration tank, and circulated back and forth until the conductivity of the discharged washing water is lower than the set value, and the cleaning is completed, and the cleaned iron phosphate product or intermediate product is discharged to the subsequent section. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings. in: Figure 1 It is a structural schematic diagram of a circulating concentration device according to an embodiment of the present invention; Reference numerals: 1. Lifting pump; 2. Stirring tank; 3. Circulating concentration tank; 4. Concentrate circulation pump; 5. Cross-flow filtration membrane mechanism; 6. First regulating valve; 7. Second regulating valve; 8. Concentrate discharge valve. DETAILED DESCRIPTION

[0023] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0024] The following describes the circulating concentration device and its application according to the embodiment of the present invention with reference to the accompanying drawings.

[0025] like Figure 1 As shown, the first embodiment of the present invention proposes a circulation concentrating device, comprising: a stirring tank 2, a circulation concentrating tank 3 and a cross-flow filtration membrane mechanism 5, the stirring tank 2 having a feed port and a discharge port, and a first stirring device is arranged in the stirring tank 2; the circulation concentrating tank 3 having a first feed port, a second feed port, a circulation feed port and a discharge port, the first feed port of the circulation concentrating tank 3 is connected to the discharge port of the stirring tank 2, the second feed port of the circulation concentrating tank 3 is used to introduce the ferric phosphate product or intermediate product to be cleaned and washing water, and a second stirring device is arranged in the circulation concentrating tank 3; the cross-flow filtration membrane mechanism 5 has a feed port, a water outlet and a discharge port, the discharge port of the circulation concentrating tank 3 is respectively connected to the feed port of the cross-flow filtration membrane mechanism 5 and the feed port of the stirring tank 2, the circulation concentrating tank is connected to a concentrated liquid discharge valve 8, and the discharge port of the cross-flow filtration membrane mechanism 5 is connected to the circulation feed port of the circulation concentrating tank 3.

[0026] The circulating concentration device of the embodiment of the present invention can be used for pretreatment of iron phosphate mother liquor and cleaning of iron phosphate slurry to obtain iron phosphate slurry with impurity ions meeting the requirements, thereby achieving dual uses of one set of equipment and reducing production costs.

[0027] The circulating concentration device of the embodiment of the present invention is not limited to the above two uses, but can also be widely used in the chemical industry, biomedicine and the like.

[0028] The concentrated liquid discharge valve 8 is used to discharge the iron phosphate product or intermediate product after washing and the iron phosphate mother liquor (or washing water) after pretreatment to the subsequent process. When the slurry in the circulating concentration tank 3 is concentrated to a certain extent, the concentrated liquid discharge valve 8 is opened to discharge part of the slurry. The concentrated liquid discharge valve 8 can also adjust the opening according to the operating conditions to achieve continuous discharge of the concentrated slurry in the circulating concentration tank 3 at a certain ratio.

[0029] Furthermore, the stirring tank 2 and the circulating concentration tank 3 are combined to allow the material after reaction or cleaning in the stirring tank 2 to quickly enter the circulating concentration tank 3 for circulating concentration treatment, thereby improving efficiency.

[0030] Furthermore, the stirring tank 2 is separated from the circulating concentrating tank 3 by a partition, and an overflow port is provided on the partition for sending the slurry in the stirring tank 2 into the circulating concentrating tank 3 by overflow.

[0031] Furthermore, a temperature regulating device is provided in the stirring tank 2 to regulate the reaction temperature and the cleaning temperature.

[0032] Furthermore, the water discharged from the water outlet of the cross-flow filtration membrane mechanism 5 is qualified produced water of the system and enters the subsequent reverse osmosis section.

[0033] In some embodiments, the cross-flow filtration membrane means 5 comprises a microfiltration membrane.

[0034] Furthermore, the microfiltration membrane can be a high temperature resistant microfiltration membrane, which can withstand the relatively high temperature of the material to be filtered.

[0035] Furthermore, the microfiltration membrane can be a tubular microfiltration membrane. The cross-flow filtration membrane mechanism 5 with a tubular membrane is used to replace the plate and frame filter press system to clean the iron phosphate slurry. The washing water and the slurry are completely mixed and fully contacted, which not only has a good cleaning effect, but also can save water.

[0036] In some embodiments, the feed port of the stirring tank 2 is connected to the lifting pump 1 through a pipeline, and the internal impeller of the lifting pump 1 can be used for mixing.

[0037] Furthermore, the feed port of the stirring tank 2 is connected to the liquid inlet pipe, the mother liquor (or washing water) enters the stirring tank 2 through the liquid inlet pipe, the lifting pump 1 is connected to the liquid inlet pipe, and the liquid inlet pipe is provided with a concentrated liquid reflux port and a dosing port for adding the reaction liquid circulating concentrated liquid and ammonia water, and the concentrated liquid reflux port and the dosing port are both arranged at the upstream position of the lifting pump 1.

[0038] Furthermore, the other end of the liquid inlet pipe is connected to a storage tank for storing mother liquor or wash water.

[0039] In some embodiments, the discharge port of the circulating concentration tank 3 is connected to the concentrated liquid circulating pump 4. By providing the concentrated liquid circulating pump 4, the circulating concentrated liquid of the reaction liquid in the circulating concentration tank 3 can be quickly sent to the cross-flow filtration membrane mechanism 5 and the stirring tank 2.

[0040] When the circulating concentration device of the embodiment of the present invention is used for pretreatment of iron phosphate mother liquor, the concentrated liquid circulation pump 4 first sends a portion of the concentrated liquid to the lifting pump 1, where it is efficiently mixed with the iron phosphate mother liquor (or washing water) and ammonia water, and then enters the stirring tank 2.

[0041] In some embodiments, the discharge port of the circulating concentration tank 3 is connected to the feed port of the stirring tank 2 through a first pipeline, and the discharge port of the circulating concentration tank 3 is connected to the feed port of the cross-flow filtration membrane mechanism 5 through a second pipeline, and the first pipeline is connected to a first regulating valve 6, and the second pipeline is connected to a second regulating valve 7. The flow rate of the circulating concentrated liquid of the reaction liquid entering the cross-flow filtration membrane mechanism 5 and the stirring tank 2 can be adjusted.

[0042] The first regulating valve 6 and the second regulating valve 7 can be selectively opened and closed or flow-regulated according to actual conditions. When the circulating concentrating device of the embodiment of the present invention is used for cleaning iron phosphate slurry, since the circulating water-washed slurry discharged from the circulating concentrating tank 3 does not need to flow back to the stirring tank 2, the first regulating valve 6 can be closed.

[0043] Furthermore, a drain pipe is connected to the second pipeline through a tee near the concentrate circulation pump 4, and a concentrate discharge valve 8 is connected to the drain pipe. When the iron phosphate product or intermediate product after cleaning needs to be discharged, the first regulating valve 6 and the second regulating valve 7 are closed, and the concentrate discharge valve 8 is opened.

[0044] In some embodiments, an aeration device is provided in the circulating concentration tank 3. During the ferric phosphate slurry cleaning operation, the hydraulic shearing effect between the washing water and the ferric phosphate product can be increased without consuming the washing water, thereby improving the flushing effect. The aeration device can be used optionally.

[0045] Furthermore, an aeration device is provided at the bottom of the circulation concentrating tank 3. Aeration from the bottom of the circulation concentrating tank 3 can improve the flushing effect.

[0046] In some embodiments, the circulating concentration device further includes a backwashing device, which backwashes the filter membrane in the cross-flow filter membrane mechanism 5 .

[0047] Furthermore, the backwashing device includes a backwashing water tank and a backwashing water pump. The backwashing water tank is connected to the cross-flow filtration membrane mechanism 5 through a pipeline, and the backwashing water pump is arranged on the pipeline, which can backwash the filtration membrane regularly to relieve the fouling of the membrane system.

[0048] In some embodiments, the circulating concentration device further comprises a chemical cleaning device, which performs chemical cleaning on the filter membrane in the cross-flow filter membrane mechanism 5. When the filter membrane is fouled, the chemical cleaning device can be activated to perform chemical cleaning on the filter membrane.

[0049] Furthermore, the chemical cleaning device comprises a reagent barrel and a circulation pump. The reagent barrel is connected to the cross-flow filter membrane mechanism 5 through a circulation pipeline, and the circulation pump is arranged on the pipeline to chemically clean the filter membrane through the circulation flow of the reagent.

[0050] The second aspect of the present invention provides an application of the above-mentioned circulating concentration device in the pretreatment of iron phosphate mother liquor, comprising the following steps: After the ferric phosphate mother liquor and ammonia water are mixed by the lifting pump 1, they are passed into the stirring tank 2 for reaction to generate a reaction liquid containing suspended solids; the liquid is passed into the circulation concentration tank 3 and mixed with the concentrated liquid filtered by the cross-flow filtration membrane mechanism 5 to form a reaction liquid circulating concentrated liquid; a part of the reaction liquid circulating concentrated liquid is returned to the lifting pump 1, mixed with the ferric phosphate mother liquor and ammonia water, and then passed into the stirring tank 2 together, and the remaining part of the reaction liquid circulating concentrated liquid is passed into the cross-flow filtration membrane mechanism 5 for circulation and concentration, and the fresh water in the reaction liquid circulating concentrated liquid is discharged and passed into the reverse osmosis system. After the reverse osmosis produced water is deeply treated, the fresh water is passed into the ferric phosphate production system for flushing the ferric phosphate product; the reaction liquid circulating concentrated liquid after filtering and removing part of the water is returned to the circulation concentration tank 3 again, mixed with the newly entered reaction liquid, and circulated back and forth, and the concentration of the reaction liquid circulating concentrated liquid of the ferric phosphate mother liquor is gradually increased. When it is increased to a certain concentration, part of it is discharged from the circulation concentration tank 3.

[0051] The ferric phosphate mother liquor (or wash water) to be treated is mixed with ammonia water in the lifting pump 1, and is fully mixed with the refluxed concentrated liquid through the stirring action of the impeller, which can improve the mixing efficiency of the materials, make the reaction more complete, and reduce the dosage of ammonia water reagent. At the same time, manganese phosphate, magnesium ammonium phosphate, iron phosphate, calcium phosphate, etc. generated by the reaction of ferric phosphate mother liquor (or wash water) with ammonia water can be fully combined with the high-concentration, high-specific surface area solid suspended matter in the circulating concentrated liquid of the reaction liquid, attached and grown on the existing solid particles to form larger solid particles, which can improve the solid-liquid separation efficiency.

[0052] By using a circulating concentration device in the pretreatment method of iron phosphate mother liquor, it can replace the traditional iron phosphate wastewater pretreatment method, shorten the process flow, reduce land occupation, and reduce equipment failure rate.

[0053] Furthermore, the cross-flow filtration membrane mechanism 5 includes a microfiltration membrane, and part of the water in the reaction liquid circulating concentrate passes through the microfiltration membrane to form produced water, while the solid suspended matter cannot pass through the microfiltration membrane and is retained in the reaction liquid circulating concentrate and returned to the circulating concentration tank 3. By using the microfiltration membrane for solid-liquid separation, the separation efficiency can be improved, the water quality of the produced water can be improved, the produced water can be used in the reverse osmosis process, and the water resources can be recycled. By using the microfiltration membrane for cross-flow filtration, there is no need to add PAM agents, which reduces the adverse effects of PAM agents on the subsequent reverse osmosis membrane.

[0054] The third aspect of the present invention provides an application of the above-mentioned circulating concentration device in the cleaning of iron phosphate products, comprising the following steps: (1) The iron phosphate product or intermediate product to be cleaned and washing water are introduced into the circulating concentration tank 3 for stirring washing and aeration washing. The iron phosphate slurry in a loose state is repeatedly in contact with the washing water, and the surface impurities are taken away by the washing water.

[0055] (2) The circulating water-washed slurry is passed through the cross-flow filtration membrane mechanism 5 for circulating filtration, and part of the washing water and soluble impurities in the circulating water-washed slurry are discharged.

[0056] (3) The circulating water-washed slurry from which part of the washing water and soluble impurities have been filtered out is returned to the circulating concentrating tank 3 again, mixed with the washing water newly added to the circulating concentrating tank 3, and circulated back and forth until the conductivity of the discharged washing water is lower than the set value. The cleaning is completed, and the concentrated liquid discharge valve 8 is opened to discharge the cleaned iron phosphate product or intermediate product through the concentrated liquid circulation pump 4 to the subsequent process section.

[0057] The circulating concentrator is used in the cleaning of iron phosphate slurry, so that the washing water and slurry are completely mixed and fully contacted, and the cleaning is thorough, saving water. The slurry after cleaning is in a mixed liquid state, not a filter cake. For the entire process of iron phosphate production, the re-slurry process can be omitted, saving equipment investment. There is no need for manual plate unloading, and full automatic operation is achieved, saving labor and simple operation.

[0058] Furthermore, the washing water is deionized water.

[0059] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features.

[0060] In the present invention, unless otherwise clearly specified and limited, the terms "connected", "connection" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0061] In the present invention, the term "some embodiments" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments and features of the different embodiments described in this specification without contradiction.

[0062] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A circulating concentration device, characterized in that: include: A stirring tank, wherein the stirring tank has a feed inlet and a discharge outlet, and a first stirring device is arranged in the stirring tank; A circulating concentrating tank, wherein the circulating concentrating tank has a first feed inlet, a second feed inlet, a circulating feed inlet and a discharge inlet, wherein the first feed inlet of the circulating concentrating tank is connected to the discharge inlet of the stirring tank, and a second stirring device is provided in the circulating concentrating tank; A cross-flow filtration membrane mechanism, wherein the cross-flow filtration membrane mechanism has a feed inlet, a water outlet and a discharge port, the discharge port of the circulating concentration tank is respectively connected to the feed inlet of the cross-flow filtration membrane mechanism and the feed inlet of the stirring tank, the circulating concentration tank is connected to a concentrated liquid discharge valve, and the discharge port of the cross-flow filtration membrane mechanism is connected to the circulating feed inlet of the circulating concentration tank.

2. The circulating concentration device according to claim 1, characterized in that: The cross-flow filtration membrane mechanism comprises a microfiltration membrane.

3. The circulating concentration device according to claim 1, characterized in that: The feed inlet of the stirring tank is connected to a lifting pump through a pipeline, and an impeller for mixing is provided inside the lifting pump.

4. The circulating concentration device according to claim 1, characterized in that: The discharge port of the circulating concentration tank is connected to a concentrated liquid circulating pump.

5. The circulating concentration device according to claim 1, characterized in that: The discharge port of the circulating concentrating tank is connected to the feed port of the stirring tank through a first pipeline, and the discharge port of the circulating concentrating tank is connected to the feed port of the cross-flow filtration membrane mechanism through a second pipeline. The first pipeline is connected to a first regulating valve, and the second pipeline is connected to a second regulating valve.

6. The circulating concentration device according to claim 1, characterized in that: An aeration device is arranged in the circulating concentration tank.

7. The circulating concentration device according to claim 1, characterized in that: It also includes a backwashing device, which backwashes the filter membrane in the cross-flow filter membrane mechanism.

8. The circulating concentration device according to claim 1, characterized in that: It also includes a chemical cleaning device, which chemically cleans the filter membrane in the cross-flow filter membrane mechanism.

9. Use of the circulating concentration device according to any one of claims 1 to 8 in pretreatment of iron phosphate mother liquor, characterized in that: The steps include: After being mixed by a lifting pump, the iron phosphate mother liquor and ammonia water are introduced into a stirring tank for reaction to generate a reaction liquid; The reaction liquid is passed into a circulating concentration tank and mixed with the concentrated liquid filtered by the cross-flow filtration membrane mechanism to form a circulating concentrated liquid of the reaction liquid; A portion of the reaction liquid circulating concentrate is returned to the lift pump, mixed with the iron phosphate mother liquor and ammonia water, and then introduced into the stirring tank together; the remaining portion of the reaction liquid circulating concentrate is introduced into the cross-flow filtration membrane mechanism for circulating concentration; the fresh water in the reaction liquid circulating concentrate is discharged and introduced into the reverse osmosis system; after the reverse osmosis produced water is deeply treated, the fresh water is introduced into the iron phosphate production system for flushing the iron phosphate product; After filtering and removing part of the water, the circulating concentrated liquid of the reaction liquid returns to the circulating concentrating tank again, mixes with the newly entered reaction liquid, and circulates back and forth. The concentration of the circulating concentrated liquid of the reaction liquid of the iron phosphate mother liquor is gradually increased. When it reaches a certain concentration, part of it is discharged from the circulating concentrating tank.

10. Use of the circulating concentration device according to any one of claims 1 to 8 in the cleaning of iron phosphate products, characterized in that: The steps include: The iron phosphate product or intermediate product to be cleaned and the washing water are passed into a circulating concentration tank for stirring washing and aeration washing to form a circulating water washing slurry; The circulating water-washed slurry is passed through a cross-flow filtration membrane mechanism for circulating filtration, and part of the washing water and soluble impurities in the circulating water-washed slurry are discharged; The circulating water-washed slurry from which part of the washing water and soluble impurities are filtered out returns to the circulating concentrating tank again, is mixed with the washing water newly added to the circulating concentrating tank, and circulates back and forth until the conductivity of the discharged washing water is lower than the set value, then the cleaning is completed, and the cleaned ferric phosphate product or intermediate product is discharged to the subsequent process section.

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