Method for preparing lithium iron phosphate by taking ferrous phosphide as raw material and product

Abstract

The invention discloses a method for preparing lithium iron phosphate by using ferrous phosphide as a raw material and a product, and relates to the technical field of green sustainable development technologies and new energy materials in the steel industry, and the method comprises the following steps: preparing ferrous phosphide by using steel slag and phosphate tailings as raw materials, leaching the ferrous phosphide by using nitric acid, and controlling the pH value to be 2.5-3 during leaching, the leaching time is 2-5 hours; adding phosphoric acid into the leachate, wherein the adding amount of the phosphoric acid is controlled to be that the molar ratio of Fe to P in the solution is 0.6-0.8 after the phosphoric acid is added; filtering the leachate, and roasting the filtered precipitate in an air atmosphere at the temperature of 700-900 DEG C for 10-12 hours; mixing the roasted product with lithium hydroxide and glucose according to a molar ratio of FePO4 to LiOH.H2O to C6H12O6 of 1: 1.06: (0.18-0.21), and mixing the mixture with the lithium hydroxide and the glucose; and pressing the mixed raw materials into blocks, and roasting at 700 DEG C for 10 hours in an inert atmosphere to obtain the lithium iron phosphate. The steel slag recovery product is used for preparing the lithium iron phosphate material, and bidirectional green development of the iron and steel industry and the new energy industry is achieved.

Description

Technical Field

[0001] The present invention relates to the technical fields of green and sustainable development technologies in the iron and steel industry and new energy material technologies, and specifically relates to a method for preparing lithium iron phosphate using ferrous phosphide produced from steel slag as a raw material and the product thereof. Background Art

[0002] In recent years, with the rapid development of industries such as new energy vehicles, lithium iron phosphate (LiFePO 4 ) has been widely used in new generation lithium ion batteries as a cathode material that does not use rare metals such as cobalt and nickel.

[0003] In addition, the traditional preparation of lithium iron phosphate uses high-grade phosphate rock as a raw material, with a long production process and high energy consumption. The depletion of high-grade phosphate rock has further increased the supply risk and ecological cost of lithium iron phosphate. Summary of the Invention

[0004] Aiming at the above deficiencies in the existing lithium iron phosphate production process, the purpose of the present invention is to provide a method for preparing lithium iron phosphate using ferrous phosphide as a raw material and the product thereof. First, using steel slag and phosphorus tailings as raw materials, by controlling the proportion of the mixed material, adjusting the calcination time and temperature, high-purity ferrous phosphide is directly prepared by the primary carbothermal reduction method combined with the multi-stage wet magnetic separation method. Then, using the prepared ferrous phosphide as a raw material, lithium iron phosphate is prepared by combining acid leaching and pyrometallurgical reduction methods. The process flow is short and the energy consumption is low. The preparation of lithium iron phosphate materials using the recycled product of steel slag realizes the two-way green development of the iron and steel industry and the new energy industry.

[0005] According to the first aspect of the technical solution of the present invention, a method for preparing lithium iron phosphate using ferrous phosphide as a raw material is provided, including the following steps:

[0006] S1: Prepare ferrous phosphide using steel slag and phosphorus tailings as raw materials, leach the ferrous phosphide using nitric acid, control the pH of the leaching to 2.5 - 3, and the leaching time to 2 - 5 h; add phosphoric acid to the leaching solution, and control the addition amount of phosphoric acid so that the Fe / P molar ratio in the solution after addition is 0.6 - 0.8;

[0007] S2: Filter the leaching solution obtained in S1, and calcine the filtered precipitate in an air atmosphere at 700 - 900 °C for 10 - 12 h;

[0008] S3: Mix the calcined product obtained in S2 with lithium hydroxide and glucose, and mix them according to the molar ratio of FePO 4 :LiOH·H 2 O:C 6 H 12 O 6 of 1:1.06:0.18 - 0.21;

[0009] S4: Press the raw materials mixed in S3 into blocks and calcine them at 700 °C for 10 hours under an inert atmosphere to obtain lithium iron phosphate.

[0010] As a preferred embodiment of the method for preparing ferrous phosphide from steel slag and phosphorus tailings according to the present invention, wherein: in the step S1, the method for preparing ferrous phosphide is as follows:

[0011] S11: Mix steel slag, phosphorus tailings and a reducing agent to obtain a mixture;

[0012] S12: Press the mixture into a mold and calcine it under an inert gas atmosphere at a calcination temperature of 1200-1300 °C for 4-6 h;

[0013] S13: Cool the product obtained in S12 to room temperature, and obtain ferrous phosphide after crushing and magnetic separation.

[0014] As a preferred embodiment of the method for preparing ferrous phosphide from steel slag and phosphorus tailings according to the present invention, wherein: in the step S11, the chemical composition of the steel slag is: 41.34 wt% CaO, 30.8 wt% TFe, 13.45 wt% SiO 2 , 4.88 wt% MgO, 2.23 wt% P 2 O 5 , 2.58 wt% Al 2 O 3 , 2.84 wt% MnO, 0.59 wt% TiO 2 and 0.78 wt% others.

[0015] As a preferred embodiment of the method for preparing ferrous phosphide from steel slag and phosphorus tailings according to the present invention, wherein: in the step S11, the chemical composition of the phosphorus tailings is: 35.45 wt% CaO, 1.01 wt% TFe, 30.67 wt% SiO 2 , 13.78 wt% MgO, 8.97 wt% P 2 O 5 , 1.36 wt% Al 2 O 3 , 4.89 wt% C, 0.51 wt% F, 1.52 wt% SO 3 and 1.84 wt% others.

[0016] As a preferred embodiment of the method for preparing ferrous phosphide from steel slag and phosphorus tailings according to the present invention, wherein: in the step S11, the steel slag and the phosphorus tailings are respectively crushed to less than 0.074 mm before mixing.

[0017] As a preferred embodiment of the method for preparing ferrous phosphide using steel slag and phosphate tailings as raw materials described in the present invention, wherein: in the step S11, the steel slag, phosphate tailings and reducing agent are mixed in a molar ratio of Fe:P:C of 1:1:4.

[0018] As a preferred embodiment of the method for preparing ferrous phosphide using steel slag and phosphorus tailings as raw materials of the present invention, wherein: in the step S11, the reducing agent is a carbonaceous reducing agent;

[0019] Wherein, the carbonaceous reducing agent is powdered graphite or activated carbon, and its particle size is 10 to 74 μm.

[0020] As a preferred embodiment of the method for preparing ferrous phosphide using steel slag and phosphorus tailings as raw materials of the present invention, wherein: in the step S12, the block formed by pressing the mixture is cylindrical, blocky or spherical;

[0021] Among them, the cross-sectional diameter of the cylindrical block is 6 to 10 mm, the maximum diameter of the spherical block is 6 to 10 mm, and the maximum dimension of the side length of the block is 6 to 10 mm.

[0022] As a preferred embodiment of the method for preparing ferrous phosphide using steel slag and phosphate tailings as raw materials described in the present invention, wherein: in the step S12, the inert gas is argon.

[0023] As a preferred embodiment of the method for preparing ferrous phosphide using steel slag and phosphate tailings as raw materials described in the present invention, wherein: in the step S12, the calcination temperature is 1300° C. and the calcination time is 5 hours.

[0024] As a preferred embodiment of the method for preparing ferrous phosphide using steel slag and phosphate tailings as raw materials described in the present invention, wherein: in the step S13, the magnetic separation method adopts a multi-stage wet magnetic separation method, the magnetic separation intensity is 100mT, the single magnetic separation time is 1min, and the number of magnetic separations is 5 times.

[0025] As a preferred embodiment of the method for preparing ferrous phosphide using steel slag and phosphate tailings as raw materials described in the present invention, wherein: in S1, the concentration of nitric acid is 1 mol / L, and the concentration of phosphoric acid is 1 mol / L.

[0026] As a preferred embodiment of the method for preparing ferrous phosphide using steel slag and phosphate tailings as raw materials described in the present invention, the roasting temperature in S2 is 700° C. and the roasting time is 10 hours.

[0027] As a preferred embodiment of the method for preparing ferrous phosphide using steel slag and phosphate tailings as raw materials described in the present invention, the roasting temperature in S4 is 700° C. and the roasting time is 10 hours.

[0028] According to the second aspect of the technical solution of the present invention, a lithium iron phosphate is provided, and the lithium iron phosphate is prepared by the method described in any of the above aspects.

[0029] The beneficial effects of the present invention are as follows:

[0030] (1) The present invention uses steel slag and phosphorus tailings as raw materials, controls the proportion of the mixture, adjusts the calcination time and temperature, and directly prepares ferrous phosphide with a purity exceeding 85% by the one-step carbothermal reduction method combined with the multi-stage wet magnetic separation method;

[0031] (2) Using the high-purity ferrous phosphide obtained by the above process as the raw material, the present invention combines acid leaching and pyrometallurgical reduction methods to prepare lithium iron phosphate. The crystal structure of the product has no defects and has the structural characteristics of an electrode material. Among them, iron phosphate is used as an intermediate product, and an iron phosphate material without impurity phases is obtained by acid leaching and coprecipitation methods, so that the prepared lithium iron phosphate can be used for the preparation of lithium ion batteries. Description of the Drawings

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on the structures shown in these drawings without creative efforts.

[0033] Figure 1 It is a schematic flow chart of the method for preparing lithium iron phosphate with ferrous phosphide as the raw material according to the present invention.

[0034] Figure 2 It is an XRD analysis chart of the lithium iron phosphate prepared in the embodiment of the present invention.

[0035] The realization, functional characteristics and advantages of the object of the present invention will be further described in conjunction with the embodiments and with reference to the drawings. Detailed Embodiments

[0036] The following will clearly and completely describe the technical solutions in the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0037] As a large amount of solid waste in the iron and steel industry, the annual output of steel slag gradually increases with the increase in steel production, and the resulting environmental pollution and potential safety hazards are becoming increasingly prominent. In addition, the development of the new energy vehicle industry has made the supply of phosphorus resources increasingly tense. The technical solution of the present invention uses ferrous phosphide as an alternative to traditional phosphorus resources for the production of lithium iron phosphate, which not only realizes the recovery of valuable elements in steel slag but also greatly alleviates the phosphorus resource supply crisis. Specifically, the technical solution of the present invention uses high-purity ferrous phosphide as a raw material to produce lithium iron phosphate, which can not only reduce the previous purification treatment process using phosphate rock as a raw material but also flexibly control the process to obtain high-purity lithium iron phosphate products. Combining the steel slag recovery product ferrous phosphide with the production technology of lithium iron phosphate is to develop a green and low-carbon new preparation process of lithium iron phosphate based on secondary resources, which is of great significance for ensuring the supply of lithium iron phosphate. Constructing an efficient value-added regeneration technology system for directly preparing industrial phosphorus products from the secondary phosphorus resources in steel slag can further improve the utilization efficiency of steel slag resources and promote green and sustainable development in the iron and steel production process.

[0038] The technical solution of the present invention first provides a method for preparing lithium iron phosphate using ferrous phosphide as a raw material, as Figure 1 shown, which includes the following steps:

[0039] S1: Leach ferrous phosphide with 1 mol / L nitric acid, control the pH of the leaching to 2.5 - 3, and the leaching time to 2 - 5 h; add 1 mol / L phosphoric acid to the leaching solution, and control the addition amount of phosphoric acid so that the Fe / P in the solution after addition is 0.6 - 0.8 (molar ratio).

[0040] Here, since nitric acid has oxidizing properties, it can ensure that Fe is oxidized to ferric ions during the leaching process.

[0041] In addition, during the leaching process, when pH < 2.5, Fe(OH) 3 precipitation will occur preferentially. An excessively high pH value will waste more chemical reagents during the pH adjustment control stage, and in an alkaline environment, it is more conducive to the precipitation of Fe(OH) 3 precipitation. Therefore, the leaching pH is controlled at 2.5 - 3.

[0042] In a preferred embodiment, the preparation method of the ferrous phosphide is as follows:

[0043] S11: Mix steel slag, phosphorus tailings, and a reducing agent to obtain a mixture;

[0044] S12: Press the mixture into a mold and calcine it in an inert gas atmosphere at a calcination temperature of 1200 - 1300 °C and a calcination time of 4 - 6 h;

[0045] S13. Cool the product obtained in S12 to room temperature, and obtain ferrous phosphide after crushing and magnetic separation.

[0046] In a preferred embodiment, in the step S11, the chemical composition of the steel slag is: 41.34 wt% CaO, 30.8 wt% TFe, 13.45 wt% SiO 2 , 4.88 wt% MgO, 2.23 wt% P 2 O 5 , 2.58 wt% Al 2 O 3 , 2.84 wt% MnO, 0.59 wt% TiO 2 and 0.78 wt% others; the chemical composition of the phosphorus tailings is: 35.45 wt% CaO, 1.01 wt% TFe, 30.67 wt% SiO 2 , 13.78 wt% MgO, 8.97 wt% P 2 O 5 , 1.36 wt% Al 2 O 3 , 4.89 wt% C, 0.51 wt% F, 1.52 wt% SO 3 and 1.84 wt% others.

[0047] Here, in the step S1, a higher iron content in the steel slag is beneficial for capturing phosphorus in the environment, reacting with the reduced phosphorus to form ferrous phosphide, reducing the phosphorus loss caused by phosphorus volatilization during the reaction, and thus improving the recovery rate of phosphorus from the steel slag and phosphorus tailings.

[0048] In a preferred embodiment, in the step S11, the steel slag and the phosphorus tailings are respectively crushed to less than 0.074 mm before mixing.

[0049] In a preferred embodiment, in the step S11, the steel slag, the phosphorus tailings, and the reducing agent are mixed in a molar ratio of Fe:P:C of 1:1:4.

[0050] Here, too low a C content will cause insufficient reduction of Fe and P in the steel slag and phosphorus tailings, thus affecting the preparation of Fe2P. There is a competitive relationship between the dissolution of C and P in elemental iron. Too high a C content will inhibit the dissolution of phosphorus in iron, and thus lead to insufficient phosphorus recovery. Since P will partially volatilize or react with CaO in the slag phase during the reaction, an excessive amount of P needs to be used to ensure the formation of ferrous phosphide. Through research and analysis, mixing the steel slag, the phosphorus tailings, and the reducing agent in a molar ratio of Fe:P:C of 1:1:4 is the best ratio range.

[0051] In a preferred embodiment, in the step S11, the reducing agent is a carbonaceous reducing agent. In a preferred embodiment, the carbonaceous reducing agent is powdered graphite or activated carbon, and its particle size is 10 - 74 μm.

[0052] Here, in the step S12, the calcination temperature is set to 1200 - 1300 °C and the calcination time is 4 - 6 h. The reason is that when the calcination temperature is too low, the reaction rate is slow and the reaction cannot be ensured to be complete. 1200 - 1300 °C can ensure the complete reaction. Too high a temperature will lead to excessive energy consumption and the risk of phosphorus volatilization. 4 - 6 h can ensure the complete reaction. If the reaction time is less than 4 h, the reaction is incomplete, resulting in incomplete reduction of phosphorus oxides and insufficient recovery. If the reaction time is too long, the process efficiency will be reduced and the energy consumption will increase.

[0053] In a preferred embodiment, in the step S12, the block formed after the mixture is pressed and formed is cylindrical, block-shaped or spherical. Among them, the cross-sectional diameter of the cylindrical block is 6 - 10 mm, the maximum diameter of the spherical block is 6 - 10 mm, and the maximum side length of the block-shaped block is 6 - 10 mm.

[0054] In a preferred embodiment, in the step S12, the inert gas is argon.

[0055] In a preferred embodiment, in the step S12, the calcination temperature is 1300 °C and the calcination time is 5 h.

[0056] In a preferred embodiment, in the step S13, the magnetic separation method uses a multi-stage wet magnetic separation method. The magnetic separation intensity is 100 mT, the single magnetic separation time is 1 min, and the number of magnetic separation times is 5 times.

[0057] Here, the combination of the multi-stage wet magnetic separation method and the one-step carbothermal reduction method makes the process flow shorter, with high Fe and P recovery rates, achieving the purpose of reducing costs and improving production efficiency.

[0058] S2: Filter the leaching solution in step 1, and calcine the precipitate removed by filtration in an air atmosphere at 700 - 900 °C for 10 - 12 h.

[0059] As a preferred scheme of the method for preparing ferrous phosphide from steel slag and phosphorus tailings according to the present invention, wherein: in the S2, the calcination temperature is 700 °C and the calcination time is 10 hours.

[0060] Here, the roasting temperature is 700 - 900 °C, which is the temperature for the formation and stable existence of iron phosphate crystals. At too low a temperature, the crystal structure of iron phosphate is unstable; while the roasting time is 10 - 12 h to ensure complete crystal growth and form a product with a defect-free crystal structure, ensuring that the crystal structure of the finally obtained lithium iron phosphate also contains no defects, thus having the structural characteristics as an electrode material.

[0061] S3: Mix the roasted product (iron phosphate, FePO 4 ) obtained in S2 with lithium hydroxide (LiOH·H 2 O) and glucose (C 6 H 12 O 6 ), and mix them in a molar ratio of FePO 4 :LiOH·H 2 O:C 6 H 12 O 6 of 1:1.06:0.18 - 0.21.

[0062] S4: Press the mixed raw materials in S3 into blocks and roast them at 700 °C for 10 hours in an inert atmosphere.

[0063] Here, the roasting temperature of 700 °C is the temperature for the formation and stable existence of iron phosphate crystals. At too low a temperature, the crystal growth is slow and the crystal structure of the generated product has defects. The roasting time of 10 hours can ensure complete crystal growth and form a product with a defect-free crystal structure, ensuring that the crystal structure of the finally obtained lithium iron phosphate also contains no defects, thus having the structural characteristics as an electrode material.

[0064] The technical solution of the present invention also provides a lithium iron phosphate, which is prepared by the method described in the above aspects.

[0065] Example

[0066] The preparation method of lithium iron phosphate in this example includes the following steps:

[0067] (1) Mix steel slag, phosphorus tailings, and graphite to obtain a mixture. The chemical composition of the steel slag is as follows: 41.34 wt% CaO, 30.8 wt% TFe, 13.45 wt% SiO2, 4.88 wt% MgO, 2.23 wt% P2O5, 2.58 wt% Al2O3, 2.84 wt% MnO, 0.59 wt% TiO2, and 0.78 wt% others. The chemical composition of the phosphorus tailings is: 35.45 wt% CaO, 1.01 wt% TFe, 30.67 wt% SiO2, 13.78 wt% MgO, 8.97 wt% P2O5, 1.36 wt% Al2O3, 4.89 wt% C, 0.51 wt% F, 1.52 wt% SO3, and 1.84 wt% others. The steel slag and phosphorus tailings are crushed before mixing, and the size after crushing is ≤ 0.074 mm. Mix the powdered steel slag, phosphorus tailings, and graphite with a particle size of 10 μm in a molar ratio of Fe:P:C of 1:1:4. After pressing the mixture into a mold, calcine it in an argon atmosphere. The block after pressing the mixture into a mold is cylindrical, with a cross-sectional diameter of 8 mm, a calcination temperature of 1300 °C, and a calcination time of 5 h. Then cool it to room temperature, and obtain ferrous phosphide after crushing and magnetic separation;

[0068] (2) Leach the obtained ferrous phosphide with 1 mol / L nitric acid. After leaching, add 1 mol / L H 3 PO 4 ,H 3 PO 4 . The addition amount is to ensure that Fe / P = 0.6 (mole ratio) in the solution. During the leaching process, control the pH = 3 with a pH titrator, and the leaching time is 3 h. Since Fe(OH) 3 is very easy to precipitate, so control Fe / P = 0.6 (mole ratio). Excessive P can ensure that all the precipitates are FePO 4 . At the same time, pH = 3 is also to avoid the precipitation of Fe(OH) 3 . At pH = 3, FePO 4 precipitates prior to Fe(OH) 3 ;

[0069] (3) Filter the leaching system in (1) using a suction filter, and calcine the filtrate in the air for 10 hours at a calcination temperature of 700 °C;

[0070] (4) Mix the calcined product in (3) (iron phosphate, FePO 4 , all ferrous phosphide is converted to iron phosphate) with lithium hydroxide (LiOH·H 2 O) and glucose (C 6 H 12 O 6 ). According to FePO4 :LiOH·H 2 O:C 6 H 12 O 6 were mixed in a ratio of 1:1.06:0.18;

[0071] (5) The mixed materials in (4) were pressed into blocks with a diameter of 1 cm;

[0072] (6) The block-shaped raw materials in (5) were calcined at 700 °C for 10 hours, and the calcination atmosphere was an inert atmosphere.

[0073] (7) After the reaction ended, it was cooled to room temperature to obtain a sample of lithium iron phosphate.

[0074] Figure 2 is the XRD analysis pattern of lithium iron phosphate prepared using steel slag and after thermal reduction in the examples. The corresponding diffraction peaks of lithium iron phosphate in the sample can all be indexed to the orthorhombic structure of LiFePO 4 (JCPDS No. 81-1173), which indicates that the prepared product has the structural framework of lithium iron phosphate.

[0075] Comparative Example 1

[0076] The preparation method of lithium iron phosphate in this comparative example includes the following steps:

[0077] (1) Ferrous phosphide was leached with 1 mol / L nitric acid, and the pH was controlled at pH = 3 during the leaching process, and the leaching time was 3 h;

[0078] (2) The leaching system in (1) was filtered using a suction filter, and the filtrate was calcined in air for 10 hours, and the calcination temperature was 700 °C;

[0079] (3) The detection result of the calcined product in (2) was Fe 3 PO 7 , and the peak corresponding to iron phosphate did not appear. When the pH was controlled at 3, since H 3 PO 4 was not added, the Fe / P in the solution was 3:1. Therefore, FePO 4 and Fe(OH) 3 precipitated simultaneously and reacted to form Fe 3 PO 7 at the high-temperature stage in (2). There was a precipitate of Fe(OH) 3 in the solution precipitate. Therefore, the preparation of lithium iron phosphate could not continue.

[0080] Comparative Example 2

[0081] The preparation method of lithium iron phosphate in this comparative example includes the following steps:

[0082] (1) Leach ferrous phosphide with 1 mol / L nitric acid. During the leaching process, use a pH titrator to control the pH = 3, and the leaching time is 3 h;

[0083] (2) Filter the leaching system in (1) using a suction filter, and calcine the filtrate in air for 10 hours at a calcination temperature of 700 °C;

[0084] (3) Detect the calcination product in (2), and the result is Fe 3 PO 7 , and the peak corresponding to iron phosphate does not appear. Control the pH at 2, and Fe(OH) 3 precipitate appears in the solution precipitate. Therefore, the preparation of lithium iron phosphate cannot be continued.

[0085] In summary, the present invention uses steel slag and phosphorus tailings as raw materials, controls the proportion of the mixture, adjusts the calcination time and temperature, directly prepares ferrous phosphide with a purity exceeding 85% by the one-step carbothermal reduction method combined with multi-stage wet magnetic separation method, and adopts acid leaching and pyrometallurgical reduction method, which can quickly produce high-purity lithium iron phosphate, and the preparation process is simple and realizes the high-value utilization of steel slag.

[0086] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent structural transformation made using the content of the specification of the present invention under the inventive concept of the present invention, or direct / indirect application in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A method for preparing lithium iron phosphate using ferrous phosphide as raw material, characterized in that: The steps include: S1: using steel slag and phosphorus tailings as raw materials to prepare ferrous phosphide, using nitric acid to leach the ferrous phosphide, the leaching pH is controlled to be 2.5-3, and the leaching time is 2-5 hours; adding phosphoric acid to the leachate, and the amount of phosphoric acid added is controlled to be Fe / P=0.6-0.8 molar ratio in the solution after addition; S2: filtering the leaching solution obtained in S1, and calcining the filtered precipitate at 700-900° C. for 10-12 h in an air atmosphere; S3: Mix the calcined product obtained in S2 with lithium hydroxide and glucose according to the formula of FePO4:LiOH·H2O:C6H 12 The molar ratio of O6 is 1:1.06:0.18-0.21; S4: The raw materials mixed in S3 are pressed into blocks, and calcined at 700° C. for 10 hours under an inert atmosphere, thereby obtaining lithium iron phosphate.

2. The method according to claim 1, characterized in that In the step S1, the preparation method of the ferrous phosphide is as follows: S11, mixing steel slag, phosphate tailings and a reducing agent to obtain a mixture; S12, pressing the mixed material into a shape and then calcining it in an inert gas atmosphere, the calcination temperature being 1200-1300° C. and the calcination time being 4-6 hours; S13. The product obtained in S12 is cooled to room temperature, and then crushed and magnetically separated to obtain ferrous phosphide.

3. The method according to claim 2, characterized in that In the step S11, the chemical composition of the steel slag is: 41.34wt% CaO, 30.8wt% TFe, 13.45wt% SiO2, 4.88wt% MgO, 2.23wt% P2O5, 2.58wt% Al2O3, 2.84wt% MnO, 0.59wt% TiO2 and 0.78wt% others; the chemical composition of the phosphate tailings is: 35.45wt% CaO, 1.01wt% TFe, 30.67wt% SiO2, 13.78wt% MgO, 8.97wt% P2O5, 1.36wt% Al2O3, 4.89wt% C, 0.51wt% F, 1.52wt% SO3 and 1.84wt% others.

4. The method according to claim 2, characterized in that: In the step S11, the steel slag, phosphate tailings and reducing agent are mixed in a molar ratio of Fe:P:C of 1:1:

4.

5. The method according to claim 2, characterized in that: In the step S11, the reducing agent is a carbonaceous reducing agent; Wherein, the carbonaceous reducing agent is powdered graphite or activated carbon, and its particle size is 10 to 74 μm.

6. The method according to claim 2, characterized in that In the step S12, the calcination temperature is 1300° C. and the calcination time is 5 hours.

7. The method according to claim 2, characterized in that In step S13, the magnetic separation method is a multi-stage wet magnetic separation method, the magnetic separation intensity is 100 mT, the single magnetic separation time is 1 min, and the number of magnetic separations is 5 times.

8. The method according to claim 1, characterized in that In S1, the concentration of nitric acid is 1 mol / L, and the concentration of phosphoric acid is 1 mol / L.

9. The method according to claim 1, characterized in that: The calcination temperature in S2 is 700° C. and the calcination time is 10 hours; the calcination temperature in S4 is 700° C. and the calcination time is 10 hours.

10. A lithium iron phosphate, wherein the lithium iron phosphate is prepared by the method according to any one of claims 1 to 9.

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