A method for producing lithium iron phosphate by recycling water resources

Abstract

The present invention discloses a method for producing lithium iron phosphate by recycling water resources, which belongs to the field of new energy material technology, including: using filtered wash water to dissolve ferrous sulfate and monoammonium phosphate, which undergo synthesis and aging reactions to obtain an iron phosphate reaction liquid, which undergoes solid-liquid separation, washing, etc. to obtain dihydrated iron phosphate; the dihydrated iron phosphate reacts with a lithium source and a carbon source, and is then dried and calcined to obtain lithium iron phosphate. During the entire process, the production wastewater is recycled after simple treatment, achieving zero discharge of wastewater and effective recovery of lithium ions, greatly reducing production costs. According to statistics, the present invention actually saves 0.15-0.58 kg of lithium and 24.3-29.3 m3 of pure water per ton of lithium iron phosphate. 3 , reduce the amount of washing water and iron-lithium wastewater treatment to 28.6~29.8m 3 and 1.6~2.2m 3 .

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy materials, and specifically relates to a method for producing lithium iron phosphate by recycling water resources. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] In recent years, with the transformation of industry and equipment electrification, electric vehicles and energy storage equipment technologies have developed rapidly, resulting in a sharp increase in demand for lithium iron phosphate positive electrode materials. At present, the lithium iron phosphate material manufacturers in the market have developed explosively, and their products are very competitive. Exploring environmentally friendly, economical and green process routes to reduce production costs is an important issue that needs to be urgently addressed.

[0004] The conventional route for lithium iron phosphate synthesis is generally divided into two steps. First, an oxidation precipitation process is used to synthesize ferrous salts, phosphate salts and hydrogen peroxide, age them, and wash the filter cake to obtain dihydrated iron phosphate. The dihydrated iron phosphate is then flashed, calcined and ground to obtain anhydrous iron phosphate. Then, a solid-phase carbon thermal reduction process is used to disperse anhydrous iron phosphate, lithium carbonate and glucose in phosphoric acid and pure water solution. After grinding, drying, calcining, crushing and demagnetization, battery-grade lithium iron phosphate is obtained. This method has easy-to-obtain raw materials, a simple process route, and the produced iron lithium has stable crystal form, uniform particle size, large specific surface area and excellent performance. However, from the perspective of energy saving, cost reduction and green recyclability, the following problems exist:

[0005] 1. The flash drying process of anhydrous ferric phosphate involves high equipment investment costs, high labor costs, high energy consumption, and severe dust hazards in the workshop. Improving the process route, reducing the manufacturing cost of lithium iron phosphate, and improving the working environment of employees are the current research focuses in the industry.

[0006] 2. At present, the dissolution of ferrous salts / phosphorus salts, filter cake cleaning, and material grinding and dispersion in the solid-phase carbon thermal reduction process in the lithium iron phosphate production process all require about 42 to 45 tons of pure water, generating about 40.5 to 43.5 tons of mother liquor, wash water, and lithium iron wastewater. The pH value of the wastewater generated is low, and it contains COD, phosphate, sulfate, iron ions, and lithium ions, which causes great environmental pressure and high processing costs. The waste of phosphate, iron ions, and lithium ions invisibly increases the production cost of lithium iron phosphate.

[0007] Therefore, there is an urgent need for an energy-saving, green and environmentally friendly production method of lithium iron phosphate. Summary of the Invention

[0008] In order to address the deficiencies of the prior art, the present invention aims to provide a method for recycling water resources to produce lithium iron phosphate. The method provided by the present invention enables production wastewater to be recycled, greatly reducing production costs and simplifying the production process of lithium iron phosphate.

[0009] In order to achieve the above object, the technical solution of the present invention is:

[0010] A first aspect of the present invention provides a method for producing lithium iron phosphate by recycling water resources, comprising the following steps:

[0011] (1) using the filtered washing water to dissolve ferrous sulfate, and obtaining a ferrous sulfate clear solution through a purification process; using the filtered washing water to dissolve monoammonium phosphate, adding hydrogen peroxide to obtain a prepared solution; mixing the prepared solution and the ferrous sulfate clear solution, and performing a synthesis reaction and an aging reaction to obtain a ferric phosphate reaction solution;

[0012] (2) The ferric phosphate reaction liquid in step (1) is subjected to solid-liquid separation to obtain filter cake 1 and mother liquor 1, respectively, and the filter cake 1 is washed with a wash water to obtain wash water;

[0013] (3) adding a precipitant to the mother liquor 1 of step (2) to remove sulfate ions, obtaining a clear liquid and a turbid liquid after filtration, wherein the turbid liquid is sent to a membrane treatment system, and the clear liquid is used to dissolve the filter cake 1 washed in step (2);

[0014] (4) using the clear liquid in step (3) to dissolve the filter cake 1 washed in step (2), and fully dissolve and pulp to obtain a suspension; the suspension is separated into solid and liquid to obtain filter cake 2 and mother liquor 2, respectively, and the mother liquor 2 and the turbid liquid in step (3) are sent to the membrane treatment system together;

[0015] (5) washing the filter cake 2 obtained in step (4) with pure water to obtain a wash water, and then squeezing and purging the filter cake 2 to obtain ferric phosphate dihydrate;

[0016] (6) The ferric phosphate dihydrate obtained in step (5) and the lithium source and the carbon source are dispersed and ground in pure water to obtain a slurry and iron-lithium wastewater; the slurry is spray-dried and calcined to obtain lithium iron phosphate; the iron-lithium wastewater and the washing water in step (2) of adding ferrous sulfate heptahydrate are mixed, reacted and settled, and the mixed solution is adjusted to be acidic. During the process, hydrogen peroxide is added to obtain a suspension. After the suspension is filtered, the filter residue is sent out as solid waste treatment, and the washing water after filtration is circulated into the system for dissolving raw materials, thereby achieving the purpose of water recycling in the entire production system.

[0017] In the present invention, pure water is used to perform countercurrent washing on filter cakes 1 and 2 in two steps, which can effectively remove impurity ions in the filter cakes and fully recycle water resources, thereby reducing the amount of pure water used for washing the filter cakes by about 9.6 to 11.8 m3. 3, and simultaneously reduce the amount of wash water to be treated by 9.6~11.8m 3 .

[0018] At the same time, the present invention grinds and mixes the ferric phosphate dihydrate directly with the lithium source and the carbon source without drying and calcining, which saves the energy consumed in the drying and calcining process of the ferric phosphate dihydrate and also saves the amount of pure water used in the dispersion and grinding process, which is about 0.7 to 1.1 m 3 .

[0019] In some embodiments of the present invention, in step (1), a ferrous sulfate clear solution is obtained by a purification process using an ammonia method to remove impurities.

[0020] In some embodiments of the present invention, in step (1), the mass percentage of ferrous sulfate in the ferrous sulfate clear solution is 13.6% to 17.3%.

[0021] In some embodiments of the present invention, in step (1), after dissolving the monoammonium phosphate using the post-filtration wash water, the mass percentage of the monoammonium phosphate in the obtained monoammonium phosphate solution is 24.3% to 26.7%.

[0022] In some embodiments of the present invention, in step (1), the mass percentage of hydrogen peroxide in the prepared solution is 2.8% to 4.1%.

[0023] In some embodiments of the present invention, in step (1), the synthesis reaction temperature is 20-70° C., the reaction time is 1.5-4.5 h, and the stirring frequency is 20-45 Hz.

[0024] In some embodiments of the present invention, in step (1), the synthesis reaction temperature is 10-50° C., and the aging time is 3-8 h.

[0025] The present invention uses the filtered washing water to dissolve ferrous sulfate heptahydrate and monoammonium phosphate, and saves about 6.7 to 10.2 m3 of pure water for each ton of lithium iron phosphate produced. 3 .

[0026] In some embodiments of the present invention, in step (3), an online sulfate content detector is installed in the mother liquor 1 pipeline, and an interlocking relationship is established between the detector and the precise flow meter of the precipitant pipeline to ensure that sulfate can be effectively removed without introducing new impurities; the precipitant is barium hydroxide.

[0027] The present invention installs an online sulfate content detector, accurately adds a precipitant to the mother liquor 1 according to the interlocking relationship, precipitates to remove sulfate, and then filters out the precipitate through a bag filter, so that the clear liquid after the mother liquor 1 is treated can be used for filter cake pulping, saving the pure water required for the pulping process, which is about 5.8 to 9.2 m 3 , and simultaneously reduce the wastewater generated that should be treated as washing water, 6.2 to 9.7 m 3 .

[0028] In some embodiments of the present invention, in step (6), the mass ratio of the lithium source, carbon source, and ferric phosphate dihydrate is: 10.8% to 13.2%: 5.7% to 7.1%: 1. The lithium source includes, but is not limited to, lithium dihydrogen phosphate, lithium carbonate, or lithium hydroxide. The carbon source includes, but is not limited to, glucose, sucrose, and fructose.

[0029] In some embodiments of the present invention, in step (6), the amount of ferrous sulfate heptahydrate added is 0.3% to 1.1% of the mass of the washing water.

[0030] In some embodiments of the present invention, in step (6), adjusting the mixed solution to be acidic means adjusting the pH of the mixed solution to 2.8-4.1.

[0031] In some embodiments of the present invention, in step (6), the amount of hydrogen peroxide added is 7.8% to 13.4% of the COD content in the iron-lithium wastewater.

[0032] The present invention mixes alkaline wastewater (i.e., iron-lithium wastewater) generated in a dispersion and grinding process with washing water added with ferrous sulfate heptahydrate, and adds hydrogen peroxide, so that the COD contained in the iron-lithium wastewater is decomposed and precipitated to form a turbid liquid. The filtered washing water is obtained by plate and frame filter pressing and is recycled back into the system. This method uses acidic washing water to neutralize the alkalinity in the iron-lithium wastewater, simultaneously removes the COD in the iron-lithium wastewater, and also allows the lithium in the iron-lithium wastewater to be recycled, thereby reducing the iron-lithium wastewater to be treated by about 1.6 to 2.2 m 3 , Wash water to be treated 9.9~11.8m 3 , recycling lithium resources and saving the pure water required for dissolving iron salts / phosphate salts, which can be said to achieve four goals at one stroke.

[0033] In some embodiments of the present invention, in step (1), 5.2 to 6.7 m 3 After filtration, wash water is used to dissolve ferrous sulfate, using 1.5 to 3.5 ml 3 Dissolve monoammonium phosphate in the filtered wash water;

[0034] Or, in step (2), the output of mother liquor 1 is 6.2 to 9.7 m 3 ;

[0035] Or, in step (2), use 9.9 to 11.8 m 3 Washing the filter cake 1 with washing water;

[0036] Or, in step (3), the output of the clear liquid is 5.8 to 9.2 m 3 The output of turbid liquid is 0.3~0.5m 3 ;

[0037] Or, in step (4), the output of mother liquor 2 is 6.5 to 8.2 m 3;

[0038] Or, in step (5), use 10.8 to 12.3 m 3 The filter cake 2 obtained in step (4) is washed with pure water to obtain 9.9-11.8 m 3 ;

[0039] Or, in step (6), ferric phosphate dihydrate, lithium source and carbon source are mixed at 1.8 to 2.5 m 3 Disperse and grind in pure water to obtain slurry and 1.6~2.2m 3 Iron-lithium wastewater;

[0040] Or, in step (6), 1.6 to 2.2 m 3 Iron-lithium wastewater and 9.9-11.8m 3 The washing water is mixed, reacted and settled, and finally filtered washing water of 8.4 to 9.7 m 3 ;

[0041] The amounts of the post-filtration wash water, mother liquor 1, first wash water, clear liquid, turbid liquid, mother liquor 2, pure water and lithium iron phosphate wastewater are all the consumption or output required for the production of one ton of lithium iron phosphate.

[0042] The beneficial effects of the present invention are:

[0043] The present invention discloses a method for recycling water resources to produce lithium iron phosphate. In particular, the production wastewater can be completely recycled after simple treatment, achieving zero wastewater discharge. At the same time, lithium ions are effectively recovered to reduce the amount of lithium source used. Compared with the existing technology, the method for producing lithium iron phosphate of the present invention is simple, efficient and greatly reduces production costs. According to statistics, the present invention actually saves 0.15-0.58kg of lithium and 24.3-29.3m3 of pure water per ton of lithium iron phosphate. 3 , reduce the amount of washing water and iron-lithium wastewater treatment to 28.6~29.8m 3 and 1.6~2.2m 3 .

[0044] In addition, the method provided by the present invention requires little equipment investment and low operating cost, and is suitable for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0046] Figure 1 This is a flow chart of the method for producing lithium iron phosphate by recycling water resources according to the present invention. DETAILED DESCRIPTION

[0047] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0048] The present invention adopts the following technical solution (the pure water, wash water, mother liquor, and iron-lithium wastewater in the solution are the consumption and output required per ton of lithium iron phosphate)

[0049] Example 1

[0050] A method for producing lithium iron phosphate by recycling water resources comprises the following steps:

[0051] (1) Use filtered washing water (6.7m 3 ) dissolving ferrous sulfate heptahydrate, and obtaining a ferrous sulfate clear solution (13.6% by mass of ferrous sulfate) through a purification process.

[0052] (2) Use filtered washing water (3.5m 3 ) to dissolve monoammonium phosphate to produce a monoammonium phosphate solution (24.3% by mass of monoammonium phosphate), and an appropriate proportion of hydrogen peroxide is added to obtain a prepared solution (2.8% by mass of hydrogen peroxide).

[0053] (3) The monoammonium phosphate prepared liquid and the ferrous sulfate clear liquid are injected into the synthesis reactor in proportion, and the ferric phosphate reaction liquid is obtained through synthesis reaction and aging reaction.

[0054] (4) The ferric phosphate reaction solution in step (3) was subjected to a plate-and-frame filter press to achieve solid-liquid separation, and filter cake 1 and mother liquor 1 (9.7 m 3 ), use a wash water (9.9m 3 ) The filter cake is thoroughly washed to obtain wash water.

[0055] (5) The main impurity in the mother liquor 1 is sulfate. An online sulfate content detector is installed in the mother liquor 1 pipeline. The detector and the precipitant (barium hydroxide) pipeline precision flow meter are interlocked to ensure that sulfate can be effectively removed without introducing new impurities. The mother liquor 1 and the precipitant are fully mixed in the pipeline mixer and then filtered through a bag filter to obtain a clear liquid (9.2m 3 ) and turbid liquid (0.5m 3 ), the turbid liquid goes to the membrane treatment system, and the clear liquid is used to dissolve the filter cake 1 after washing in step (4).

[0056] (6) Using the clear liquid in step (5) to dissolve the filter cake washed in step (4), the mixture is fully dissolved and beaten with a stirrer to obtain a suspension.

[0057] (7) The suspension in step (6) was subjected to a membrane filter press to achieve solid-liquid separation, and filter cake 2 and mother liquor 2 (8.5 m 3), the mother liquor 2 and the turbid liquid in step (5) are sent to the membrane treatment system together.

[0058] (8) Use pure water (10.8m 3 ) Wash the filter cake 2 obtained in step (7) to obtain a wash water (9.9m 3 ), and then the filter cake 2 is squeezed and purged to obtain ferric phosphate dihydrate.

[0059] (9) The ferric phosphate dihydrate, lithium dihydrogen phosphate and sucrose obtained in step (8) were mixed in pure water (1.8 m 3 ) were dispersed and ground to obtain slurry and iron-lithium wastewater (1.6m 3 ), the mass ratio of lithium dihydrogen phosphate, sucrose and ferric phosphate dihydrate is: 10.8%:5.7%:1.

[0060] (10) The slurry is spray-dried and calcined to obtain lithium iron phosphate;

[0061] (11) Iron-lithium wastewater (1.6m 3 ) and the washing water (9.9m 3 ) for mixed reaction and sedimentation, and the pH was adjusted to 2.8. During the process, hydrogen peroxide (7.8% of the COD content in the iron-lithium wastewater) was added to obtain a suspension. After the suspension was filtered through a plate and frame filter press, the filter residue was sent out as solid waste treatment, and the post-filtration washing water (9.7m 3 ) circulates into the system for raw material dissolution, achieving the purpose of water recycling in the entire production system.

[0062] Table 1: A list of actual production cost savings per ton of lithium iron phosphate in Example 1

[0063]

[0064] Example 2

[0065] A method for producing lithium iron phosphate by recycling water resources comprises the following steps:

[0066] (1) Use filtered washing water (6m 3 ) dissolving ferrous sulfate heptahydrate, and obtaining a ferrous sulfate clear solution (15.6% by mass of ferrous sulfate) through a purification process.

[0067] (2) Use filtered washing water (2.5m 3 ) to dissolve monoammonium phosphate to produce a monoammonium phosphate solution (25.2% by mass of monoammonium phosphate), and an appropriate proportion of hydrogen peroxide is added to obtain a prepared solution (3.4% by mass of hydrogen peroxide).

[0068] (3) The monoammonium phosphate prepared liquid and the ferrous sulfate clear liquid are injected into the synthesis reactor in proportion, and the ferric phosphate reaction liquid is obtained through synthesis reaction and aging reaction.

[0069] (4) The ferric phosphate reaction solution in step (3) was subjected to a plate-and-frame filter press to achieve solid-liquid separation, and filter cake 1 and mother liquor 1 (7.9 m 3 ), use a wash water (10.5m 3 ) The filter cake is thoroughly washed to obtain wash water.

[0070] (5) The main impurity in the mother liquor 1 is sulfate. An online sulfate content detector is installed in the mother liquor 1 pipeline. The detector and the precipitant (barium hydroxide) pipeline precision flow meter are interlocked to ensure that sulfate can be effectively removed without introducing new impurities. The mother liquor 1 and the precipitant are fully mixed in the pipeline mixer and then filtered through a bag filter to obtain a clear liquid (7.6m 3 ) and turbid liquid (0.3m 3 ), the turbid liquid goes to the membrane treatment system, and the clear liquid is used to dissolve the filter cake 1 after washing in step (4).

[0071] (6) Using the clear liquid in step (5) to dissolve the filter cake washed in step (4), the mixture is fully dissolved and beaten with a stirrer to obtain a suspension.

[0072] (7) The suspension in step (6) was subjected to a membrane filter press to achieve solid-liquid separation, and filter cake 2 and mother liquor 2 (7.3 m 3 ), the mother liquor 2 and the turbid liquid in step (5) are sent to the membrane treatment system together.

[0073] (8) Use pure water (11.3m 3 ) Wash the filter cake 2 obtained in step (7) to obtain a wash water (10.5m 3 ), and then the filter cake 2 is squeezed and purged to obtain ferric phosphate dihydrate.

[0074] (9) The ferric phosphate dihydrate, lithium hydroxide and glucose obtained in step (8) were mixed in pure water (2.2 m 3 ) were dispersed and ground to obtain slurry and iron-lithium wastewater (1.8m 3 ), the mass ratio of lithium source, carbon source and ferric phosphate dihydrate is: 11.7%:6.2%:1.

[0075] (10) The slurry is spray-dried and calcined to obtain lithium iron phosphate;

[0076] (11) Iron-lithium wastewater (1.8m 3 ) and the washing water (10.5m 3) for mixed reaction and sedimentation, and the pH was adjusted to 3.3. During the process, hydrogen peroxide (9.5% of the COD content in the iron-lithium wastewater) was added to obtain a suspension. After the suspension was filtered through a plate and frame filter press, the filter residue was sent out as solid waste treatment, and the post-filtration washing water (9.2m 3 ) circulates into the system for raw material dissolution, achieving the purpose of water recycling in the entire production system.

[0077] Table 2 A list of actual production cost savings per ton of lithium iron phosphate in Example 2

[0078]

[0079] Example 3

[0080] A method for producing lithium iron phosphate by recycling water resources comprises the following steps:

[0081] (1) Use filtered washing water (5.2m 3 ) dissolving ferrous sulfate heptahydrate, and obtaining a ferrous sulfate clear solution (17.3% by mass of ferrous sulfate) through a purification process.

[0082] (2) Use filtered washing water (1.5m 3 ) was dissolved in monoammonium phosphate to produce a monoammonium phosphate solution (26.7% by mass of monoammonium phosphate), and an appropriate proportion of hydrogen peroxide was added to obtain a prepared solution (4.1% by mass of hydrogen peroxide).

[0083] (3) The monoammonium phosphate prepared liquid and the ferrous sulfate clear liquid are injected into the synthesis reactor in proportion, and the ferric phosphate reaction liquid is obtained through synthesis reaction and aging reaction.

[0084] (4) The ferric phosphate reaction solution in step (3) was subjected to a plate-and-frame filter press to achieve solid-liquid separation, and filter cake 1 and mother liquor 1 (6.2 m 3 ), use a wash water (11.8m 3 ) The filter cake is thoroughly washed to obtain wash water.

[0085] (5) The main impurity in the mother liquor 1 is sulfate. An online sulfate content detector is installed in the mother liquor 1 pipeline. The detector and the precipitant (barium hydroxide) pipeline precision flow meter are interlocked to ensure that sulfate can be effectively removed without introducing new impurities. The mother liquor 1 and the precipitant are fully mixed in the pipeline mixer and then filtered through a bag filter to obtain a clear liquid (5.8m 3 ) and turbid liquid (0.4m 3 ), the turbid liquid goes to the membrane treatment system, and the clear liquid is used to dissolve the filter cake 1 after washing in step (4).

[0086] (6) Using the clear liquid in step (5) to dissolve the filter cake washed in step (4), the mixture is fully dissolved and beaten with a stirrer to obtain a suspension.

[0087] (7) The suspension in step (6) was subjected to a membrane filter press to achieve solid-liquid separation, and filter cake 2 and mother liquor 2 (5.6 m 3 ), the mother liquor 2 and the turbid liquid in step (5) are sent to the membrane treatment system together.

[0088] (8) Use pure water (12.3m 3 ) Wash the filter cake 2 obtained in step (7) to obtain a wash water (11.8m 3 ), and then the filter cake 2 is squeezed and purged to obtain ferric phosphate dihydrate.

[0089] (9) The ferric phosphate dihydrate, lithium carbonate and glucose obtained in step (8) were mixed in pure water (2.5 m 3 ) were dispersed and ground to obtain slurry and iron-lithium wastewater (2.2m 3 ), the mass ratio of lithium source, carbon source and ferric phosphate dihydrate is: 13.2%:7.1%:1.

[0090] (10) The slurry is spray-dried and calcined to obtain lithium iron phosphate;

[0091] (11) Iron-lithium wastewater (2.2m 3 ) and the washing water (11.8m 3 ) for mixed reaction and sedimentation, and the pH was adjusted to 4.1. During the process, hydrogen peroxide (13.4% of the COD content in the iron-lithium wastewater) was added to obtain a suspension. After the suspension was filtered through a plate and frame filter press, the filter residue was sent out as solid waste treatment, and the post-filtration washing water (11.6m 3 ) circulates into the system for raw material dissolution, achieving the purpose of water recycling in the entire production system.

[0092] Table 3 A summary of actual production cost savings per ton of lithium iron phosphate in Example 3

[0093]

[0094] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for producing lithium iron phosphate by recycling water resources, characterized in that: The steps include: (1) using the filtered washing water to dissolve ferrous sulfate, and obtaining a ferrous sulfate clear solution through a purification process; using the filtered washing water to dissolve monoammonium phosphate, adding hydrogen peroxide to obtain a prepared solution; mixing the prepared solution and the ferrous sulfate clear solution, and performing a synthesis reaction and an aging reaction to obtain a ferric phosphate reaction solution; (2) The ferric phosphate reaction liquid in step (1) is subjected to solid-liquid separation to obtain filter cake 1 and mother liquor 1, respectively, and the filter cake 1 is washed with a wash water to obtain wash water; (3) adding a precipitant to the mother liquor 1 of step (2) to remove sulfate ions, obtaining a clear liquid and a turbid liquid after filtration, wherein the turbid liquid is sent to a membrane treatment system, and the clear liquid is used to dissolve the filter cake 1 washed in step (2); (4) using the clear liquid in step (3) to dissolve the filter cake 1 washed in step (2), and fully dissolve and pulp to obtain a suspension; the suspension is separated into solid and liquid to obtain filter cake 2 and mother liquor 2, respectively, and the mother liquor 2 and the turbid liquid in step (3) are sent to the membrane treatment system together; (5) washing the filter cake 2 obtained in step (4) with pure water to obtain a wash water, and then squeezing and purging the filter cake 2 to obtain ferric phosphate dihydrate; (6) The ferric phosphate dihydrate obtained in step (5) and the lithium source and the carbon source are dispersed and ground in pure water to obtain a slurry and iron-lithium wastewater; the slurry is spray-dried and calcined to obtain lithium iron phosphate; the iron-lithium wastewater and the washing water in step (2) of adding ferrous sulfate heptahydrate are mixed, reacted and settled, and the mixed solution is adjusted to be acidic. During the process, hydrogen peroxide is added to obtain a suspension. After the suspension is filtered, the filter residue is sent out as solid waste treatment, and the washing water after filtration is circulated into the system for dissolving raw materials, thereby achieving the purpose of water recycling in the entire production system.

2. The method for producing lithium iron phosphate by recycling water resources according to claim 1, characterized in that: In step (1), the mass percentage of ferrous sulfate in the ferrous sulfate clear solution is 13.6% to 17.3%.

3. The method for producing lithium iron phosphate by recycling water resources according to claim 1, characterized in that: In step (1), after dissolving the monoammonium phosphate using the post-filtration washing water, the mass percentage of the monoammonium phosphate in the obtained monoammonium phosphate solution is 24.3% to 26.7%.

4. The method for producing lithium iron phosphate by recycling water resources according to claim 1, characterized in that: In step (1), the mass percentage of hydrogen peroxide in the prepared solution is 2.8% to 4.1%.

5. The method for producing lithium iron phosphate by recycling water resources according to claim 1, characterized in that: In step (3), an online sulfate content detector is installed in the mother liquor 1 pipeline, and an interlocking relationship is established between the detector and the precipitant pipeline precision flow meter to ensure that sulfate can be effectively removed without introducing new impurities; The precipitant is barium hydroxide.

6. The method for producing lithium iron phosphate by recycling water resources according to claim 1, characterized in that: In step (6), the mass ratio of the lithium source, the carbon source and ferric phosphate dihydrate is: 10.8% to 13.2%: 5.7% to 7.1%:

1.

7. The method for producing lithium iron phosphate by recycling water resources according to claim 1, characterized in that: In step (6), the amount of ferrous sulfate heptahydrate added is 0.3% to 1.1% of the mass of the washing water.

8. The method for producing lithium iron phosphate by recycling water resources according to claim 1, characterized in that: In step (6), adjusting the mixed solution to be acidic means adjusting the pH of the mixed solution to 2.8 to 4.

1.

9. The method for producing lithium iron phosphate by recycling water resources according to claim 1, characterized in that: In step (6), the amount of hydrogen peroxide added is 7.8% to 13.4% of the COD content in the iron-lithium wastewater.

10. The method for producing lithium iron phosphate by recycling water resources according to any one of claims 1 to 9, characterized in that: In step (1), use 5.2 to 6.7 m 3 After filtration, wash water is used to dissolve ferrous sulfate, using 1.5 to 3.5 ml 3 Dissolve monoammonium phosphate in the filtered wash water; Or, in step (2), the output of mother liquor 1 is 6.2 to 9.7 m 3 ; Or, in step (2), use 9.9 to 11.8 m 3 Washing the filter cake 1 with washing water; Or, in step (3), the output of the clear liquid is 5.8 to 9.2 m 3 The output of turbid liquid is 0.3~0.5m 3 ; Or, in step (4), the output of mother liquor 2 is 5.6 to 8.2 m 3 ; Or, in step (5), use 10.8 to 12.3 m 3 The filter cake 2 obtained in step (4) is washed with pure water to obtain 9.9-11.8 m 3 ; Or, in step (6), ferric phosphate dihydrate, lithium source and carbon source are mixed at 1.8 to 3.2 m 3 Disperse and grind in pure water to obtain slurry and 1.6~2.2m 3 Iron-lithium wastewater; Or, in step (6), 1.6 to 2.2 m 3 Iron-lithium wastewater and 9.9-11.8m 3 The washing water is mixed, reacted and settled, and finally filtered washing water of 8.4 to 9.7 m 3 ; The amounts of the post-filtration wash water, mother liquor 1, first wash water, clear liquid, turbid liquid, mother liquor 2, pure water and lithium iron phosphate wastewater are all the consumption or output required for the production of one ton of lithium iron phosphate.

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