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

Abstract

The application discloses a method for preparing ferrophosphorus by using steel slag and phosphorus tailings as raw materials, a product and application, and relates to the technical field of resource utilization, and comprises the following steps: S1, mixing steel slag, phosphorus tailings and a reducing agent according to a molar ratio of Fe:P:C of 1:(0.8-2):(3.5-5) to obtain a mixture; S2, performing calcination on the mixture after being pressed into a shape under an inert gas atmosphere, wherein the calcination temperature is 1200-1300 DEG C, and the calcination time is 4-6 hours; and S3, cooling the product obtained in S2 to room temperature, and obtaining ferrophosphorus after crushing and magnetic separation. According to the technical scheme, the ferrophosphorus is directly prepared by one-time carbon thermal reduction method by using the steel slag and the phosphorus tailings as raw materials, the process flow is short, the energy consumption is low, the environmental problems caused by the accumulation of the steel slag and the phosphorus tailings are solved, and the high-value utilization of the steel slag and the phosphorus tailings is realized.

Description

Technical Field

[0001] This invention belongs to the field of resource utilization technology, specifically a method, product, and application for preparing ferrous phosphide using steel slag and phosphate tailings as raw materials. Background Technology

[0002] The comprehensive utilization of steel slag is one of the important indicators of technological progress in the modern steel industry. The utilization of steel slag in sintering, ironmaking, blast furnaces, and as a chemical raw material is relatively low. Due to the high P and Si content in steel slag, a large amount of steel slag is returned to sintering feedstock, increasing raw material and energy consumption, leading to a gradual decrease in its use through this route and hindering large-scale recycling. Currently, steel slag is mainly used in engineering backfill, cement production, and building materials. Steel slag that has not undergone hot pulverization contains large amounts of f-CaO and f-MgO, which expand in volume by 96% and 148% respectively upon contact with water, resulting in poor stability. This makes it difficult to guarantee the quality of slag used for road paving and backfilling, and its use is also affected by factors such as transportation distance. In recent years, its use has been limited to steel slag cement, bricks, and wall materials; currently, no effective way to utilize steel slag resources on a large scale has been discovered.

[0003] Phosphate tailings are extremely fine byproducts of phosphate rock flotation. Compared to other phosphorus-containing wastes, phosphate tailings are considered a potential phosphorus resource due to their high phosphorus content. However, phosphate tailings resources are vast, yet their utilization efficiency is extremely low. Large-scale storage of phosphate tailings not only occupies significant amounts of land but also causes environmental problems such as ground dust and water pollution. Therefore, large-scale resource utilization of phosphate tailings in the phosphate industry is imperative. Compared to the aforementioned phosphorus-containing wastes, phosphate tailings have a higher P2O5 content (approximately 5-12 wt%), making them a more valuable secondary resource for phosphorus recovery. Therefore, phosphate tailings are a high-value secondary resource in terms of both phosphorus content and yield. 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 phosphorus (P) in the tailings significantly hinders cement setting, leading to a reduction in the mechanical strength of the cement. Summary of the Invention

[0004] To address the problems existing in the prior art, the main objective of this invention is to propose a method, product, and application for preparing ferrous phosphide using steel slag and phosphate tailings as raw materials. This method involves controlling the mixing ratio, adjusting the calcination time and temperature, and directly preparing ferrous phosphide using a single carbothermal reduction method combined with multi-stage wet magnetic separation. This process is short, has low energy consumption, solves the environmental problems caused by the accumulation of steel slag and phosphate tailings, and simultaneously achieves high-value utilization of these materials.

[0005] To solve the above-mentioned technical problems, according to a first aspect of the technical solution of the present invention, the present invention provides a method for preparing ferrous phosphide using steel slag and phosphate tailings as raw materials, wherein the method includes the following steps:

[0006] S1. Steel slag, phosphorus tailings, and reducing agent are mixed to obtain a mixture;

[0007] S2. After the mixture is pressed into shape, it is calcined in an inert gas atmosphere at a temperature of 1200~1300℃ for 4~6h.

[0008] S3. The product obtained from S2 is cooled to room temperature, and then crushed and magnetically separated to obtain ferrous phosphide.

[0009] As a preferred embodiment of the method for preparing ferrous phosphide from steel slag and phosphate tailings as raw materials according to the present invention, wherein: in step S1, the chemical composition of the steel slag is: 40~50 wt% CaO, 20~35 wt% TFe, 10~15 wt% SiO2, 5~13 wt% MgO, 1~5 wt% P2O5, 2~4 wt% Al2O3, 1~4 wt% MnO, and 0.5~3 wt% other.

[0010] Preferably, 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% other.

[0011] As a preferred embodiment of the method for preparing ferrous phosphide from steel slag and phosphate tailings as raw materials according to the present invention, wherein: in step S1, the chemical composition of the phosphate tailings is: 32~45 wt% CaO, 1~5 wt% TFe, 28~38 wt% SiO2, 10~20 wt% MgO, 6~16 wt% P2O5, 1~5 wt% Al2O3, and 2~8 wt% other.

[0012] Preferably, the chemical composition of the phosphate 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% other.

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

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

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

[0016] As a preferred embodiment of the method for preparing ferrous phosphide from steel slag and phosphate tailings according to the present invention, in 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 phosphate tailings as raw materials according to the present invention, in step S1, the carbonaceous reducing agent is powdered graphite or activated carbon with a particle size of 10~74μm.

[0018] As a preferred embodiment of the method for preparing ferrous phosphide from steel slag and phosphate tailings as raw materials according to the present invention, in step S2, the block after the mixture is pressed and formed is cylindrical, blocky or spherical.

[0019] As a preferred embodiment of the method for preparing ferrous phosphide from steel slag and phosphate tailings as raw materials according to the present invention, in step S2, the cross-sectional diameter of the cylindrical block is 6~10mm, the maximum diameter of the spherical block is 6~10mm, and the maximum side length of the block is 6~10mm.

[0020] As a preferred embodiment of the method for preparing ferrous phosphide from steel slag and phosphate tailings as raw materials according to the present invention, in step S2, the inert gas is argon.

[0021] As a preferred embodiment of the method for preparing ferrous phosphide from steel slag and phosphate tailings as raw materials according to the present invention, in step S2, the calcination temperature is 1300℃ and the calcination time is 5h.

[0022] As a preferred embodiment of the method for preparing ferrous phosphide from steel slag and phosphate tailings as raw materials according to the present invention, 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.

[0023] To solve the above-mentioned 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 means of the method described in any of the above aspects.

[0024] To address the aforementioned technical problems, according to a third aspect of the present invention, the present invention provides an application for preparing lithium iron phosphate using ferrous phosphide as a raw material, as described above. Due to its characteristics of large-scale production, high safety, low cost, and long lifespan, it has become one of the mainstream cathode materials and is widely used in the field of lithium-ion batteries.

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

[0026] This invention proposes a method for preparing ferrous phosphide using steel slag and phosphate tailings as raw materials. By controlling the proportion of the mixture and adjusting the calcination time and temperature, ferrous phosphide with a purity of over 85% is directly prepared using a single carbothermal reduction method combined with multi-stage wet magnetic separation. This process has a short flow rate and low energy consumption, solving the environmental problems caused by the accumulation of steel slag and phosphate tailings while achieving high-value utilization of steel slag and phosphate tailings. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0028] Figure 1 This is a schematic flowchart of the method for preparing ferrous phosphide using steel slag and phosphate tailings as raw materials according to the present invention.

[0029] Figure 2 The image shows the XRD pattern of ferrous phosphide prepared in Example 1 of this invention.

[0030] Figure 3 The image shows the XRD pattern of ferrous phosphide prepared in Example 2 of this invention.

[0031] Figure 4 This is the XRD pattern of the product prepared in Comparative Example 1 of this invention.

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

[0033] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0034] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

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

[0036] S1. Steel slag, phosphorus tailings, and reducing agent are mixed to obtain a mixture.

[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% SiO2, 5-13 wt% MgO, 1-5 wt% P2O5, 2-4 wt% Al2O3, 1-4 wt% MnO, and 0.5-3 wt% other components. In another preferred embodiment, the chemical composition of the steel slag is: 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% other components.

[0038] In a preferred embodiment, in step S1, the chemical composition of the phosphate tailings is: 32-45 wt% CaO, 1-5 wt% TFe, 28-38 wt% SiO2, 10-20 wt% MgO, 6-16 wt% P2O5, 1-5 wt% Al2O3, and 2-8 wt% other components. In another preferred embodiment, the chemical composition of the phosphate 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% other components.

[0039] In a preferred embodiment, in step S1, the steel slag and phosphorus tailings are crushed to below 0.074 mm before being mixed.

[0040] Here, in step S1, the high iron content in the steel slag is conducive to its capture of phosphorus in the environment, and reacts with the reduced phosphorus to generate ferrous phosphide, reducing phosphorus loss caused by phosphorus volatilization during the reaction, thereby improving the phosphorus recovery rate of steel slag and phosphorus tailings.

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

[0042] Here, excessively low carbon (C) content will prevent the sufficient reduction of Fe and P in steel slag and phosphate tailings, thus affecting the preparation of Fe₂P. The dissolution of C and P in elemental iron is competitive; excessively high C content will inhibit the dissolution of phosphorus in iron, leading to insufficient phosphorus recovery. Since P partially volatilizes or reacts with CaO in the slag phase during the reaction, an excess of P is required to ensure the formation of ferrous phosphide. Through research and analysis, the technical solution of this application determines that the optimal mixing ratio of steel slag, phosphate tailings, and reducing agent is 1:(0.8~2):(3.5~5) molar ratio of Fe:P:C.

[0043] In a preferred embodiment, in 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 with a particle size of 10~74μm.

[0045] S2. After pressing the mixture into shape, it is calcined at a temperature of 1200~1300℃ for 4~6 hours.

[0046] The reason for setting the calcination temperature at 1200~1300℃ and the calcination time at 4~6 h is as follows: a lower calcination temperature results in a slower reaction rate and cannot ensure a complete reaction; 1200~1300℃ ensures the reaction is fully completed; excessively high temperatures lead to excessive energy consumption and the risk of phosphorus volatilization; 4~6 h ensures the reaction is fully completed; a reaction time of less than 4 h results in an incomplete reaction, meaning the phosphorus oxides are not completely reduced and thus cannot be fully recovered; while an excessively long reaction time reduces process efficiency and increases energy consumption.

[0047] In a preferred embodiment, in step S2, the block formed by pressing the mixture is cylindrical, blocky, 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 side length of the block is 6-10 mm.

[0049] In a preferred embodiment, the inert gas in step S2 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 from S2 is cooled to room temperature, and then crushed and magnetically separated to obtain ferrous phosphide.

[0052] In a preferred embodiment, 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.

[0053] The reason for adopting the multi-stage wet magnetic separation method here is that the technical solution of this application adopts a single carbothermal reduction method. The combination of the two makes the process flow shorter, the Fe and P recovery rate higher, and achieves the purpose of reducing costs and improving production efficiency.

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

[0055] This invention provides a method for preparing lithium iron phosphate using the aforementioned ferrous phosphide as a raw material. Due to its characteristics of large-scale production, high safety, low cost, and long lifespan, 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 with reference to specific embodiments.

[0057] Example 1

[0058] A method for preparing ferrous phosphide from steel slag and phosphate tailings includes the following steps:

[0059] S1. Steel slag, phosphorus tailings, and graphite are mixed to obtain a mixture. The chemical composition of the steel slag is: 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% other. 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% other. Before mixing, the steel slag and phosphate tailings are crushed, and the size of the crushed material is ≤0.074mm. The powdered steel slag, phosphate tailings, and graphite with a particle size of 10μm are mixed in a Fe:P:C molar ratio of 1:1:4.

[0060] S2. After the mixture is pressed into shape, it is calcined under an argon atmosphere. The block after pressing is cylindrical with a cross-sectional diameter of 8 mm. The calcination temperature is 1300℃ and the calcination time is 5 h. After cooling to room temperature, it is crushed and magnetically separated to obtain ferrous phosphide.

[0061] The XRD pattern of the ferrous phosphide prepared in this embodiment is shown in the figure below. Figure 2 As shown, the diffraction peaks corresponding to Fe2P can all be indexed to the hexagonal Fe2P crystal structure (JCPDS No. 85-1727), indicating that the prepared product has the Fe2P structural framework.

[0062] Example 2

[0063] A method for preparing ferrous phosphide from steel slag and phosphate tailings includes the following steps:

[0064] S1. Steel slag, phosphate tailings, and activated carbon are mixed to obtain a mixture. The chemical composition of the steel slag is: 43.14 wt% CaO, 29.05 wt% TFe, 9.81 wt% SiO2, 7.91 wt% MgO, 2.21 wt% P2O5, 2.57 wt% Al2O3, 3.09 wt% MnO, 0.76 wt% TiO2, and 0.94 wt% other. The chemical composition of the phosphate 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% other. Before mixing, steel slag and phosphorus tailings are crushed separately, and the size of the crushed material is ≤0.074mm. Steel slag, phosphorus tailings and activated carbon with a particle size of 74μm are mixed in a Fe:P:C molar ratio of 1:1:4.

[0065] S2. After the mixture is pressed into shape, it is calcined under an argon atmosphere. The block after the mixture is pressed into shape is spherical with a maximum diameter of 8 mm. The calcination temperature is 1300℃ and the calcination time is 5 h. After cooling to room temperature, it is crushed and magnetically separated to obtain ferrous phosphide.

[0066] The XRD pattern of the ferrous phosphide prepared in this embodiment is shown in the figure below. Figure 3 As shown, the diffraction peaks corresponding to Fe2P can all be indexed to the hexagonal Fe2P crystal structure (JCPDS No. 85-1727), indicating that the prepared product has the Fe2P structural framework.

[0067] Comparative Example 1

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

[0069] The XRD pattern of the product prepared in this embodiment is shown in the figure. Figure 4 As shown, the main phases of the product are Ca2SiO4, Ca3SiO5, and Fe, which indicates that the prepared product is not Fe2P.

[0070] Comparative Example 2

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

[0072] The XRD pattern of the product prepared in this embodiment is shown in the figure. Figure 5 As shown, the main phases of the product are Ca2SiO4 and Ca7P2Si2O. 16This indicates that the prepared product is not Fe2P.

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

[0074] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preparing ferrous phosphide using steel slag and phosphorous tailings as raw materials, characterized by, The method comprises the following steps: S1, mixing the steel slag and the phosphorous tailings, and a reducing agent according to 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% other; and the chemical composition of the phosphorous tailings is: 32-45wt% CaO, 1-5wt% TFe, 28-38wt% SiO2, 10-20wt% MgO, 6-16wt% P2O5, 1-5wt% Al2O3, and 2-8wt% other; S2, calcining the shaped mixture in an inert gas atmosphere at a calcining temperature of 1200-1300℃ for 4-6h; S3, cooling the product obtained in S2 to room temperature, crushing, and magnetically selecting to obtain ferrous phosphide.

2. The method of claim 1, wherein, 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% other.

3. The method of claim 1, wherein, The chemical composition of the phosphorous 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% other.

4. The method of claim 1, wherein, In the step S1, the steel slag and the phosphorous tailings are respectively crushed to 0.074mm before mixing. The steel slag and the phosphorous tailings, and the reducing agent are mixed according to a molar ratio of Fe:P:C of 1:1:

4.

5. The method of claim 1, wherein, In the step S1, the reducing agent is a carbonaceous reducing agent. The carbonaceous reducing agent is powdered graphite or activated carbon with a particle size of 10-74μm.

6. The method of claim 1, wherein, In the step S2, the shaped mixture is in the shape of a cylinder, a block, or a sphere. The cross-sectional diameter of the cylindrical block is 6-10mm, the maximum diameter of the spherical block is 6-10mm, and the maximum dimension of the edge length of the block-shaped block is 6-10mm.

7. The method of claim 1, wherein, In the step S2, the calcining temperature is 1300℃, and the calcining time is 5h. In the step S2, the inert gas is argon.

8. The method of claim 1, wherein, In the step S3, the magnetic selection method is a multi-stage wet magnetic selection method, the magnetic selection strength is 100mT, the single magnetic selection time is 1min, and the magnetic selection times is 5.

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

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

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