Method for preparing ferrous phosphide by taking steel slag and phosphate tailings as raw materials, product and application

Abstract

The invention discloses a method for preparing ferrous phosphide by taking steel slag and phosphate tailings as raw materials, a product and application, and relates to the technical field of resource utilization, the method comprises the following steps: S1, mixing the steel slag, the phosphate tailings and a reducing agent according to the molar ratio of Fe: P: C being 1: (0.8-2): (3.5-5) to obtain a mixture; s2, the mixture is subjected to compression molding and then calcined in an inert gas atmosphere, the calcination temperature ranges from 1200 DEG C to 1300 DEG C, and the calcination time ranges from 4 h to 6 h; and S3, cooling the product obtained in the step S2 to room temperature, and performing crushing and magnetic separation to obtain ferrous phosphide. According to the technical scheme, the steel slag and the phosphate tailings serve as raw materials, ferrous phosphide is directly prepared through the one-time carbon thermal reduction method, the technological process is short, energy consumption is low, the environmental problem caused by accumulation of the existing steel slag and phosphate tailings is solved, and meanwhile high-added-value utilization of the steel slag and the phosphate tailings is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of resource utilization, and particularly relates to a method, a product and an application for preparing ferrous phosphide by using steel slag and phosphorus tailings as raw materials. Background Art

[0002] The comprehensive utilization of steel slag is one of the important symbols of the technological progress of the modern iron and steel industry. In China, the annual discharge of steel slag exceeds 150 million tons, but the comprehensive utilization rate is not high, and it is the bulk solid waste with the lowest utilization rate in the current iron and steel industry. Although there are numerous studies on the comprehensive utilization of steel slag in China, the output of steel slag increases year by year, and the development of steel slag comprehensive utilization technology is unbalanced, resulting in a decreasing comprehensive utilization rate of steel slag year by year and a lack of high-value utilization methods. The utilization amount of steel slag in sintering, ironmaking, cupola, and as chemical raw materials is relatively low. Due to the high content of P and Si in steel slag, the amount of steel slag returned to sintering batching is large, resulting in an increase in raw material consumption and energy consumption, so the amount used in this way gradually decreases, and large-scale recycling of steel slag cannot be achieved. At present, steel slag is mainly applied in fields such as engineering backfill materials, cement production, and building materials. The steel slag without thermal steaming and pulverization treatment contains a large amount of f-CaO and f-MgO. These two substances can cause the volume to expand by 96% and 148% respectively after contacting with water, resulting in poor stability of the steel slag. It is difficult to guarantee the quality when used for paving and backfilling, and affected by factors such as transportation distance, it has only been used for steel slag cement, bricks, wall materials, etc. in recent years. At present, no effective way to utilize steel slag resources on a large scale has been discovered.

[0003] Phosphorus tailings are extremely fine by-products in the process of phosphorus ore flotation. Compared with other phosphorus-containing wastes, phosphorus tailings are considered a potential phosphorus resource because of their large phosphorus content. The amount of phosphate tailings resources is huge, and the utilization efficiency is extremely low. A large amount of stored phosphate tailings not only occupy a large amount of land, but also cause environmental problems such as ground dust and water pollution. Therefore, it is imperative to realize the large-scale resource utilization of phosphate tailings in the phosphate industry. Compared with the above-mentioned phosphorus-containing wastes, the P 2 O 5 content of phosphate tailings is relatively high (about 5-12 wt%), and it is a more valuable secondary resource for phosphorus recovery. Therefore, whether from the perspective of phosphorus content or yield, phosphorus tailings are a secondary resource with relatively high value. The large-scale resource utilization of phosphate tailings is a key issue. When these phosphate tailings are directly used as building materials and backfill materials, the presence of P in the phosphate tailings brings great obstacles to the setting of cement, resulting in a reduction in the mechanical strength of the cement. Summary of the Invention

[0004] To solve the problems existing in the prior art, the main object of the present invention is to propose a method, product and application for preparing ferrous phosphide from steel slag and phosphorus tailings. Using steel slag and phosphorus tailings as raw materials, by controlling the proportion of the mixture, adjusting the calcination time and temperature, and directly preparing ferrous phosphide by the primary carbothermal reduction method combined with the multi-stage wet magnetic separation method, the process flow is short and the energy consumption is low. While solving the environmental problems caused by the accumulation of existing steel slag and phosphorus tailings, the high-value utilization of steel slag and phosphorus tailings is realized.

[0005] To solve the above technical problems, according to the first aspect of the technical solution of the present invention, the present invention provides a method for preparing ferrous phosphide from steel slag and phosphorus tailings, wherein the method comprises the following steps:

[0006] S1. Mix steel slag, phosphorus tailings and a reducing agent to obtain a mixture;

[0007] S2. Press the mixture into a mold and calcine it in an inert gas atmosphere, the calcination temperature is 1200-1300 °C, and the calcination time is 4-6 h;

[0008] S3. Cool the product obtained in S2 to room temperature, and obtain ferrous phosphide after crushing and magnetic separation.

[0009] 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 chemical composition of the steel slag is: 40-50 wt% CaO, 20-35 wt% TFe, 10-15 wt% SiO 2 , 5-13 wt% MgO, 1-5 wt% P 2 O 5 , 2-4 wt% Al 2 O 3 , 1-4 wt% MnO, 0.5-3 wt% others.

[0010] Preferably, the chemical composition of the steel slag is: 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.

[0011] As a preferred embodiment of the method for preparing ferrous phosphide from steel slag and phosphorus tailings according to the present invention, in the step S1, the chemical composition of the phosphorus tailings is as follows: 32-45 wt% CaO, 1-5 wt% TFe, 28-38 wt% SiO 2 , 10-20 wt% MgO, 6-16 wt% P 2 O 5 , 1-5 wt% Al 2 O 3 , 2-8 wt% others.

[0012] Preferably, 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.

[0013] As a preferred embodiment of the method for preparing ferrous phosphide from steel slag and phosphorus tailings according to the present invention, in the step S1, the steel slag and the phosphorus tailings are respectively crushed to less than 0.074 mm before mixing.

[0014] As a preferred embodiment of the method for preparing ferrous phosphide from steel slag and phosphorus tailings according to the present invention, in the step S1, the steel slag, the phosphorus tailings and the reducing agent are mixed in a molar ratio of Fe:P:C of 1:(0.8-2):(3.5-5).

[0015] Preferably, in the step S1, the steel slag, the phosphorus tailings and the reducing agent are mixed in a molar ratio of Fe:P:C of 1:1:4.

[0016] As a preferred embodiment of the method for preparing ferrous phosphide from steel slag and phosphorus tailings according to the present invention, in the step S1, the reducing agent is a carbonaceous reducing agent.

[0017] As a preferred embodiment of the method for preparing ferrous phosphide from steel slag and phosphorus tailings according to the present invention, in the step S1, the carbonaceous reducing agent is powdered graphite or activated carbon with a particle size of 10-74 μm.

[0018] As a preferred embodiment of the method for preparing ferrous phosphide from steel slag and phosphorus tailings according to the present invention, in the step S2, the block formed by pressing the mixture is cylindrical, block-shaped or spherical.

[0019] 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 S2, 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.

[0020] 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 step S2, the inert gas is argon.

[0021] 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 S2, the calcination temperature is 1300°C and the calcination time is 5 hours.

[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 S3, 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.

[0023] In order to solve the above technical problems, according to a second aspect of the technical solution of the present invention, the present invention provides ferrous phosphide, which is prepared by the method described in any one of the above aspects.

[0024] To solve the above technical problems, according to the third aspect of the technical solution of the present invention, the present invention provides an application of ferrous phosphide as a raw material for preparing lithium iron phosphate according to the above aspects. Due to its large-scale, high safety, low cost and long life, it has become one of the mainstream positive electrode materials and is widely used in the field of lithium-ion batteries.

[0025] The beneficial effects of the present invention are as follows:

[0026] The invention provides a method for preparing ferrous phosphide by using steel slag and phosphate tailings as raw materials. The method uses steel slag and phosphate tailings as raw materials, controls the proportion of the mixed materials, adjusts the calcination time and temperature, and directly prepares ferrous phosphide with a purity exceeding 85% by using a single carbon thermal reduction method combined with a multi-stage wet magnetic separation method. The process is short and has low energy consumption, solves the environmental problems caused by the accumulation of existing steel slag and phosphate tailings, and realizes the high added value utilization of steel slag and phosphate tailings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on the structures shown in these drawings.

[0028] Figure 1 It is a schematic flow chart of the method for preparing ferrous phosphide from steel slag and phosphorus tailings as raw materials according to the present invention.

[0029] Figure 2 It is an XRD analysis diagram of the ferrous phosphide prepared in Example 1 of the present invention.

[0030] Figure 3 It is an XRD analysis diagram of the ferrous phosphide prepared in Example 2 of the present invention.

[0031] Figure 4 It is an XRD analysis diagram of the product prepared in Comparative Example 1 of the present invention.

[0032] Figure 5 It is an XRD analysis diagram of the product prepared in Comparative Example 2 of the present invention.

[0033] The realization, functional characteristics and advantages of the object of the present invention will be further described in conjunction with the embodiments with reference to the accompanying drawings. Detailed Embodiments

[0034] 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.

[0035] The technical solution of the present invention first provides a method for preparing ferrous phosphide from steel slag and phosphorus tailings as raw materials. As Figure 1 shown, the method includes the following steps:

[0036] S1. Mix the steel slag, phosphorus tailings and a reducing agent to obtain a mixed material.

[0037] In a preferred embodiment, in step S1, the chemical composition of the steel slag is: 40 - 50 wt% CaO, 20 - 35 wt% TFe, 10 - 15 wt% SiO 2 , 5 - 13 wt% MgO, 1 - 5 wt% P 2 O 5 , 2 - 4 wt% Al 2 O 3, 1-4 wt% MnO, 0.5-3 wt% others. In a preferred embodiment, the chemical composition of the steel slag is: 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.

[0038] In a preferred embodiment, in the step S1, the chemical composition of the phosphorus tailings is: 32-45 wt% CaO, 1-5 wt% TFe, 28-38 wt% SiO 2 , 10-20 wt% MgO, 6-16 wt% P 2 O 5 , 1-5 wt% Al 2 O 3 , 2-8 wt% others. In a preferred embodiment, 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.

[0039] In a preferred embodiment, in the step S1, the steel slag and the phosphorus tailings are respectively crushed to less than 0.074 mm before mixing.

[0040] Here, in the step S1, the higher iron content in the steel slag is beneficial for capturing phosphorus in the environment, reacting with the reduced phosphorus to form iron phosphide, reducing the phosphorus loss caused by phosphorus volatilization during the reaction, and thus improving the phosphorus recovery rate of the steel slag and the phosphorus tailings.

[0041] In a preferred embodiment, in the step S1, the steel slag, the phosphorus tailings and the reducing agent are mixed in a molar ratio of Fe:P:C of 1:(0.8-2):(3.5-5). In a preferred embodiment, in the step S1, the steel slag, the phosphorus tailings and the reducing agent are mixed in a molar ratio of Fe:P:C of 1:1:4.

[0042] Here, too low C content will lead to insufficient reduction of Fe and P in slag and phosphate tailings, thus affecting Fe 2 In the preparation of P, 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, which will lead to the inability to fully recover phosphorus. Since P will partially volatilize or react with CaO in the slag phase during the reaction, an excess of P is required to ensure the formation of ferrous phosphide. After research and analysis, the technical solution of this application determines that the mixing of steel slag, phosphate tailings, and reducing agents in a molar ratio of Fe:P:C of 1:(0.8~2):(3.5~5) is the optimal ratio range.

[0043] In a preferred embodiment, in the step S1, the reducing agent is a carbonaceous reducing agent.

[0044] In a preferred embodiment, in step S1, the carbonaceous reducing agent is powdered graphite or activated carbon, and its particle size is 10 to 74 μm.

[0045] S2. After pressing the mixed material into a shape, calcining is performed at a temperature of 1200 to 1300° C. and a calcining time of 4 to 6 hours.

[0046] Here, the calcination temperature is set at 1200-1300°C and the calcination time is set at 4-6h. The reason is that: the reaction rate is slow when the calcination temperature is low and the reaction cannot be ensured to be complete. 1200-1300°C can ensure that the reaction is completed. Too high a temperature will lead to excessive energy consumption and bring the risk of phosphorus volatilization; 4-6h can ensure that the reaction is fully completed. If the reaction time is less than 4h, the incomplete reaction will result in the phosphorus oxides not being completely reduced and thus cannot be fully recovered. If the reaction time is too long, the process efficiency will be reduced and the energy consumption will increase.

[0047] In a preferred embodiment, in step S2, the blocks formed by pressing the mixture are cylindrical, block-shaped or spherical.

[0048] In a preferred embodiment, in step S2, 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 dimension of the side length of the block is 6-10 mm.

[0049] In a preferred embodiment, in step S2, the inert gas is argon.

[0050] In a preferred embodiment, in step S2, the calcination temperature is 1300° C. and the calcination time is 5 hours.

[0051] S3. The product obtained in S2 is cooled to room temperature, and ferrous phosphide is obtained after crushing and magnetic separation.

[0052] In a preferred embodiment, in step S3, 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.

[0053] Here, the reason for adopting the multi-stage wet magnetic separation method is that the technical solution of this application adopts a one-step carbothermal reduction method. The combination of the two makes the process flow shorter, and the recovery rates of Fe and P are high, achieving the purpose of reducing costs and improving production efficiency.

[0054] The technical solution of the present invention also provides a ferrous phosphide, which is prepared by the method described above.

[0055] The present invention provides a method for preparing lithium iron phosphate using the above-mentioned ferrous phosphide as a raw material. Due to its characteristics of large scale, high safety, low cost, and long life, it has become one of the mainstream cathode materials and is widely used in the field of lithium-ion batteries.

[0056] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0057] Example 1

[0058] A method for preparing ferrous phosphide using steel slag and phosphorus tailings as raw materials includes the following steps:

[0059] S1. Mix the steel slag, phosphorus tailings, and graphite to obtain a mixture; 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. The steel slag and phosphorus tailings are crushed before mixing, and the size after crushing is ≤ 0.074 mm; the powdered steel slag, phosphorus tailings, and graphite with a particle size of 10 μm are mixed in a molar ratio of Fe:P:C of 1:1:4;

[0060] S2. After pressing the mixture into shape, calcine it in an argon atmosphere. The block after pressing the mixture into shape is cylindrical, with a cross-sectional diameter of 8 mm, a calcination temperature of 1300 °C, a calcination time of 5 h, then cool it to room temperature, and obtain ferrous phosphide after crushing and magnetic separation.

[0061] The XRD analysis pattern of the ferrous phosphide prepared in this example is as Figure 2 shown, and the diffraction peaks corresponding to its Fe 2 P can all be indexed to the Fe 2 P (JCPDS No. 85-1727) with a hexagonal crystal system structure, which indicates that the prepared product has the structural framework of Fe 2 P.

[0062] Example 2

[0063] A method for preparing ferrous phosphide using steel slag and phosphorus tailings as raw materials, comprising the following steps:

[0064] S1. Mix steel slag, phosphorus tailings, and activated carbon to obtain a mixture; the chemical composition of the steel slag is: 43.14 wt% CaO, 29.05 wt% TFe, 9.81 wt% SiO 2 , 7.91 wt% MgO, 2.21 wt% P 2 O 5 , 2.57 wt% Al 2 O 3 , 3.09 wt% MnO, 0.76 wt% TiO 2 and 0.94 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. Crush the steel slag and phosphorus tailings respectively before mixing, and the size after crushing is ≤ 0.074 mm; mix the steel slag, phosphorus tailings, and activated carbon with a particle size of 74 μm according to the molar ratio of Fe:P:C of 1:1:4;

[0065] S2. After pressing the mixture into shape, calcine it in an argon atmosphere. The block after pressing the mixture into shape is spherical, with a maximum diameter of 8 mm, a calcination temperature of 1300 °C, a calcination time of 5 h, then cool it to room temperature, and obtain ferrous phosphide after crushing and magnetic separation.

[0066] The XRD analysis pattern of the iron phosphide prepared in this example is as follows Figure 3 shown, and the diffraction peaks corresponding to its Fe 2 P can all be indexed to the Fe 2 P (JCPDS No. 85-1727) with a hexagonal crystal structure, indicating that the prepared product has the structural framework of Fe 2 P.

[0067] Comparative Example 1

[0068] The difference from Example 1 is that the steel slag, phosphorus tailings, and graphite powder are mixed in a molar ratio of Fe:P:C of 4:1:4.

[0069] The XRD analysis pattern of the product prepared in this example is as follows Figure 4 shown, and the main phases of the product are Ca 2 SiO 4 , Ca 3 SiO 5 , Fe, indicating that the prepared product is not Fe 2 P.

[0070] Comparative Example 2

[0071] The difference from Example 1 is that the calcination time is 1 hour.

[0072] The XRD analysis pattern of the product prepared in this example is as follows Figure 5 shown, and the main phases of the product are Ca 2 SiO 4 , Ca 7 P 2 Si 2 O 16 , indicating that the prepared product is not Fe 2 P.

[0073] It can be seen from the above examples and comparative examples that the present invention uses steel slag and phosphorus tailings as raw materials, directly prepares iron phosphide with a purity exceeding 85% by controlling the mixture ratio, adjusting the calcination time and temperature, and using a one-step carbothermal reduction method combined with a multi-stage wet magnetic separation method. This process can achieve the efficient recovery of phosphorus elements in steel slag and phosphorus tailings, and has a short process and low energy consumption. The prepared iron phosphide can be further used as a raw material for the production of lithium iron phosphate, realizing the high-value utilization of steel slag and phosphorus tailings while solving the environmental problems caused by the accumulation of existing steel slag and phosphorus tailings.

[0074] 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 ferrous phosphide using steel slag and phosphate tailings as raw materials, characterized in that: The method comprises the following steps: S1. Mix steel slag, phosphate tailings and a reducing agent in a molar ratio of Fe:P:C of 1:(0.8-2):(3.5-5) to obtain a mixture; wherein the chemical composition of the steel slag is: 40-50wt% CaO, 20-35wt% TFe, 10-15wt% SiO2, 5-13wt% MgO, 1-5wt% P2O5, 2-4wt% Al2O3, 1-4wt% MnO, and 0.5-3wt% others; the chemical composition of the phosphate tailings is: 32-45wt% CaO, 1-5wt% TFe, 28-38wt% SiO2, 10-20wt% MgO, 6-16wt% P2O5, 1-5wt% Al2O3, and 2-8wt% others; S2, pressing the mixed material into a shape and then calcining it in an inert gas atmosphere, the calcination temperature is 1200-1300° C., and the calcination time is 4-6 hours; S3. The product obtained in S2 is cooled to room temperature, and ferrous phosphide is obtained after crushing and magnetic separation.

2. The method according to claim 1, characterized in that The chemical composition of the steel slag is: 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.

3. The method according to claim 1, characterized in that 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 1, characterized in that: In the step S1, the steel slag and the phosphate tailings are crushed to 0.074 mm before mixing; 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 1, characterized in that: In the step S1, 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 1, characterized in that In step S2, the mixture is pressed into a block having a cylindrical, block-like or spherical shape; 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.

7. The method according to claim 1, characterized in that In step S2, the calcination temperature is 1300° C. and the calcination time is 5 h; Wherein, in step S2, the inert gas is argon.

8. The method according to claim 1, characterized in that In step S3, 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.

9. A ferrous phosphide, characterized in that: The ferrous phosphide is prepared by the method according to any one of claims 1 to 8.

10. Use of the ferrous phosphide according to claim 9 as a raw material for preparing lithium iron phosphate.

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