Preparation method for phosphides of iron having mixed phases

Abstract

The present invention relates to the technical field of waste utilization, in particular to a preparation method for phosphides of iron having mixed phases. The technical solution is characterized in comprising the following steps: S1, mixing raw materials: fully mixing a reducing agent and an iron phosphate powder to obtain a first mixture; S2, heating same: putting the first mixture into a corundum crucible, heating same, and when being heated, the reducing agent and iron phosphate undergoing a reaction at a high temperature under the protection of a nitrogen atmosphere; and S3, cooling same: when the reaction of the reducing agent and iron phosphate is finished, stopping heating, and cooling same to room temperature to obtain a mixture of FeP and Fe2P. The present invention uses electrode materials of waste power batteries as a raw material, thereby achieving high-value and recycling utilization of solid wastes and reducing raw material cost.

Description

A method for preparing mixed-phase iron phosphide Technical Field

[0001] The present invention relates to the technical field of waste utilization, and more particularly to a method for preparing mixed-phase iron phosphide. Background Art

[0002] In the production of some special steel products, the appropriate addition of iron phosphide products (a mixture of FeP and Fe2P, etc.) can significantly improve the performance of steel in certain aspects. For example, in the manufacture of rolling mills, engine parts, automobile cylinder liners, etc., the addition of iron phosphide can increase the corrosion resistance and wear resistance of mechanical parts; adding a certain amount of iron phosphide to molten steel can play a role in rapid deoxidation, significantly saving the cost and time of the deoxidation step; at the same time, iron phosphide can also be used in the manufacture of shells of grenades, bombs, etc. to improve their lethality, and therefore has attracted widespread research interest.

[0003] The iron phosphide products currently used in the metallurgical industry (mixtures of FeP and Fe2P) are mainly obtained from phosphorus-making electric furnaces. They are symbiotic compounds containing 20-26% phosphorus and 0.1-6% silicon. At the same time, iron phosphide products can also be prepared in the laboratory using the following method:

[0004] (1) Prepared by mixing elemental phosphorus and elemental iron in a certain proportion and heating them in a tube furnace; (2) Prepared by heating iron oxide nanomaterials and sodium hypophosphite in a tube furnace filled with protective gas; (3) Prepared by reacting iron hydroxide with phosphorous acid and then subjecting the product to programmed thermal reduction; (4) Prepared by reacting iron salts with ammonium phosphate in a reducing atmosphere; (5) Prepared by reacting metallic iron or iron oxide with PH3 in a reducing atmosphere, etc. (Catalysis Letter, 2012, 142, 1413-1436).

[0005] However, the preparation method of the above-mentioned iron phosphide product still has certain defects. The mixed-phase iron phosphide produced by the phosphorus production electric furnace method is highly dependent on phosphate rock, and the production lines are mainly located in provinces in southwestern China that are rich in phosphate rock resources. The phosphorus and iron sources involved in the laboratory preparation of iron phosphide are relatively expensive, which will significantly increase production costs.

[0006] With the booming new energy vehicle industry, the use of power batteries has increased annually. Currently, commercially available power batteries include nickel-cobalt-manganese ternary batteries, lithium iron phosphate batteries, lithium titanate batteries, lithium cobalt oxide batteries, lithium manganese oxide batteries, and lead-acid batteries. Among them, lithium iron phosphate power batteries hold a relatively large market share. Generally speaking, lithium power batteries have a lifespan of around five years. Retirement has begun in phases in recent years, and the peak retirement period has not yet arrived. By the end of 2022, the cumulative retired power battery volume in my country reached 266,000 tons, and it is expected to reach 135,000 tons in 2023, with lithium iron phosphate batteries accounting for over 50%. Currently, the main method for extracting black powder from spent lithium iron phosphate batteries is selective lithium extraction, producing lithium carbonate, which is then used to synthesize electrode materials for lithium iron phosphate batteries. However, this also produces a large amount of ferrophosphorus slag. With the increasing number of retired power batteries, the comprehensive and efficient utilization of ferrophosphorus slag has become a pressing issue. Ferrophosphorus slag contains a large amount of iron phosphate (FePO4) and graphite, which can be used as a phosphorus source and iron source as well as a thermal reducing agent for synthesizing iron phosphide. Under certain reaction conditions, a mixed phase iron phosphide product is generated, which also solves the problem of resource utilization and high value utilization of ferrophosphorus slag solid waste.

[0007] Summary of the Invention

[0008] In view of the shortcomings of the prior art, the object of the present invention is to provide a method for preparing mixed-phase iron phosphide, which has the advantages of reducing production costs and improving waste resource utilization.

[0009] The above technical objectives of the present invention are achieved through the following technical solutions: A method for preparing a mixed-phase iron phosphide, characterized in that it comprises the following steps:

[0010] S1. Mixing raw materials: fully mixing the reducing agent and the iron phosphate powder to obtain a first mixture;

[0011] S2. Heating: placing the first mixture into a corundum crucible and heating it; the reducing agent and the ferric phosphate react at high temperature under the protection of a nitrogen atmosphere;

[0012] S3, cooling, after the reaction of the reducing agent and the ferric phosphate is completed, heating is stopped, and after cooling to room temperature, a mixture of FeP and Fe2P is obtained.

[0013] In one embodiment, the reducing agent includes one or more of coke, graphite, ascorbic acid, hydrogen, phosphorous acid and hypophosphorous acid.

[0014] In one embodiment, the mass ratio of the iron phosphate to the reducing agent is 10:1-10:15.

[0015] In one embodiment, the iron phosphate is made of waste power battery electrode material.

[0016] In one embodiment, the heating temperature in step S2 is 1000-1450°C.

[0017] In one embodiment, the high-temperature heating reaction time of the ferric phosphate and the reducing agent is 1.5-4 hours.

[0018] In one embodiment, the heating equipment used in step S2 is a tube furnace, a rotary kiln, or a muffle furnace.

[0019] In one embodiment, the cooling time in step S3 is 1.5-5 hours.

[0020] The above-mentioned method for preparing a mixed-phase iron phosphide has the following beneficial effects:

[0021] First, by using waste power battery electrode materials as raw materials, we can realize the high-value resource utilization of solid waste and reduce the cost of raw materials;

[0022] Secondly, by controlling the preparation parameters, the relative proportions of the two phases, FeP and Fe2P, can be adjusted, facilitating targeted production according to demand. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 shows the standard PDF cards and simulated powder XRD diffraction patterns of FeP and Fe2P;

[0024] FIG2 is a powder diffraction XRD pattern of the mixed phase iron phosphide product 1;

[0025] FIG3 is a powder diffraction XRD pattern of the mixed phase iron phosphide product 2;

[0026] FIG4 is a powder diffraction XRD pattern of the mixed phase iron phosphide product 3;

[0027] FIG5 is a powder diffraction XRD pattern of the mixed phase iron phosphide product 4;

[0028] FIG6 is a powder diffraction XRD pattern of the mixed phase iron phosphide product 5;

[0029] FIG7 is a powder diffraction XRD pattern of the mixed phase iron phosphide product 6;

[0030] FIG8 is a powder diffraction XRD pattern of compound 1;

[0031] FIG9 is a powder diffraction XRD pattern of compound 2. DETAILED DESCRIPTION

[0032] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0033] A method for preparing a mixed-phase iron phosphide comprises the following steps:

[0034] S1. Mixing raw materials: fully mixing the reducing agent and the iron phosphate powder to obtain a first mixture;

[0035] Specifically, the reducing agent includes one or more of coke, graphite, ascorbic acid, hydrogen, phosphorous acid and hypophosphorous acid, and the mass ratio of iron phosphate to reducing agent is 10:1-10:15.

[0036] Preferably, the iron phosphate is made from waste power battery electrode materials.

[0037] S2. Heating: placing the first mixture into a corundum crucible and heating it; the reducing agent and the ferric phosphate react at high temperature under the protection of a nitrogen atmosphere;

[0038] The heating temperature is 1000-1450°C, and the heating time and reaction time are 1.5-4h.

[0039] Specifically, the heating equipment is one of a tubular furnace, a rotary kiln, and a muffle furnace.

[0040] S3, cooling, after the reaction of the reducing agent and the ferric phosphate is complete, heating is stopped, and the mixture is cooled to room temperature to obtain a mixture of FeP and Fe2P;

[0041] The cooling time is 1.5-5h.

[0042] Example 1

[0043] Iron phosphate (about 8.50 g) and desulfurized coke (about 2.65 g) were placed in a mortar and ground for 0.5 hours until they were thoroughly mixed to form a first mixture, and the first mixture was placed in a corundum crucible;

[0044] The corundum crucible was moved to a muffle furnace, and a heating, constant temperature, and cooling program was set to heat the temperature in the muffle furnace to 1180°C. Under the protection of a nitrogen atmosphere, the temperature was kept constant for 2 hours to allow the iron phosphate to fully react with the desulfurized coke.

[0045] After the temperature in the muffle furnace dropped to room temperature, the corundum crucible was taken out. The corundum crucible contained the iron phosphide product (a mixture of FeP and Fe2P), named mixed-phase iron phosphide product 1. The particle size was controlled according to the customer's specific requirements. As shown in Figure 2, the phase purity was characterized by powder diffraction XRD, which showed that it was a mixture of two phases, Fe2P and FeP. The diffraction peak of FeP was relatively strong, and the diffraction peak of Fe2P was relatively weak.

[0046] Example 2

[0047] Iron phosphate (about 1700 g) and desulfurized coke (about 550 g) were placed in a mortar and ground for 2 hours until they were thoroughly mixed to form a first mixture, and the first mixture was placed in a corundum crucible;

[0048] The corundum crucible was moved into a muffle furnace, and a heating, constant temperature, and cooling program was set to heat the temperature in the muffle furnace to 1200°C. Under the protection of a nitrogen atmosphere, the temperature was kept constant for 4 hours to allow the iron phosphate to fully react with the desulfurized coke;

[0049] After the temperature in the muffle furnace dropped to room temperature, the corundum crucible was taken out. The corundum crucible contained the iron phosphide product (a mixture of FeP and Fe2P), which was named mixed-phase iron phosphide product 2. The particle size was controlled according to the customer's specific requirements. As shown in Figure 3, the phase purity was characterized by powder diffraction XRD, which showed that it was a mixture of two phases, Fe2P and FeP. The diffraction peak of FeP was relatively strong, and the diffraction peak of Fe2P was relatively weak.

[0050] Example 3

[0051] Iron phosphate (about 9.54 g) and graphite carbon (about 1.26 g) were placed in a mortar and ground for 1.5 hours until they were thoroughly mixed to form a first mixture, which was then placed in a corundum crucible;

[0052] The corundum crucible was moved to a muffle furnace, and a heating, constant temperature, and cooling program was set to heat the temperature in the muffle furnace to 1220°C. Under the protection of a nitrogen atmosphere, the temperature was kept constant for 1.5 hours to allow the iron phosphate and graphite carbon to fully react;

[0053] After the temperature in the muffle furnace dropped to room temperature, the corundum crucible was taken out. The corundum crucible contained the iron phosphide product (a mixture of FeP and Fe2P), named mixed-phase iron phosphide product 3. The particle size was controlled according to the customer's specific requirements. As shown in Figure 4, the phase purity was characterized by powder diffraction XRD, which showed that it was a mixture of Fe2P and FeP phases, where the diffraction peak intensities of FeP and Fe2P were comparable.

[0054] Example 4

[0055] Iron phosphate (about 190.80 g) and graphite carbon (about 25.20 g) were placed in a mortar and ground for 2.5 hours until they were thoroughly mixed to form a first mixture, and the first mixture was placed in a corundum crucible;

[0056] The corundum crucible was moved to a muffle furnace, and a heating, constant temperature, and cooling program was set to heat the temperature in the muffle furnace to 1260°C. Under the protection of a nitrogen atmosphere, the temperature was kept constant for 5 hours to allow the iron phosphate and graphite carbon to fully react;

[0057] After the temperature in the muffle furnace dropped to room temperature, the corundum crucible was removed. The ferrous phosphide product (a mixture of FeP and Fe2P) was found inside, designated as mixed-phase ferrous phosphide product 4. The product was crushed to control particle size according to customer specifications. As shown in Figure 5, its phase purity was characterized by powder diffraction XRD, revealing a mixture of Fe2P and FeP phases. The diffraction peak intensities of FeP and Fe2P were comparable.

[0058] Example 5

[0059] Iron phosphate (about 80 g) and Vc (about 50 g) were placed in a mortar and ground for 1 hour until they were fully mixed to form a first mixture, which was then placed in a corundum crucible;

[0060] Move the corundum crucible into a muffle furnace, set the heating, constant temperature, and cooling programs, and heat the temperature in the muffle furnace to 1140°C. Under the protection of a nitrogen atmosphere, keep the temperature constant for 3.5 hours to allow the iron phosphate and Vc to fully react;

[0061] After the temperature in the muffle furnace dropped to room temperature, the corundum crucible was taken out. The corundum crucible contained the iron phosphide product (a mixture of FeP and Fe2P), named mixed-phase iron phosphide product 5. The particle size was controlled according to the customer's specific requirements. As shown in Figure 6, the phase purity was characterized by powder diffraction XRD, which showed that it was a mixture of two phases, Fe2P and FeP, among which the diffraction peak of FeP was relatively strong, and the diffraction peak of Fe2P was relatively weak.

[0062] Example 6

[0063] Iron phosphate (about 1600 g) and Vc (about 1000 g) were placed in a mortar and ball-milled for 2.5 hours until they were thoroughly mixed to form a first mixture, which was then placed in a corundum crucible;

[0064] Move the corundum crucible into a muffle furnace, set the heating, constant temperature, and cooling programs, heat the temperature in the muffle furnace to 1150 ° C, and keep the temperature constant for 4.5 hours under the protection of a nitrogen atmosphere to allow the iron phosphate and Vc to fully react;

[0065] After the temperature in the muffle furnace dropped to room temperature, the corundum crucible was removed. Inside was the iron phosphide product (a mixture of FeP and Fe2P), designated as mixed-phase iron phosphide product 6. The product was crushed to control particle size according to customer specifications. As shown in Figure 7, the phase purity was characterized by powder diffraction XRD, revealing a mixture of Fe2P and FeP phases. The diffraction peak of FeP was relatively strong, while that of Fe2P was relatively weak.

[0066] Comparative Example 1

[0067] Iron phosphate (about 95.40 g) and graphite carbon (about 12.60 g) were placed in a mortar and ground for 2 hours until they were thoroughly mixed to form a first mixture, and the first mixture was placed in a corundum crucible;

[0068] Move the corundum crucible into the muffle furnace, set the heating, constant temperature, and cooling programs, heat the temperature in the muffle furnace to 850 ° C, and keep the temperature constant for 5 hours under the protection of nitrogen atmosphere;

[0069] After the temperature in the muffle furnace dropped to room temperature, the corundum crucible was taken out. The product in the corundum crucible was a black block, named Compound 1, as shown in Figure 8. The phase was characterized by powder diffraction XRD, and no Fe2P and FeP phases were generated. It can be seen that the reaction temperature is very important for the formation of iron phosphide.

[0070] Comparative Example 2

[0071] Iron phosphate (about 95.40 g) and graphite carbon (about 4.20 g) were placed in a mortar and ground for 2 hours until they were thoroughly mixed to form a first mixture, and the first mixture was placed in a corundum crucible;

[0072] Move the corundum crucible into the muffle furnace, set the heating, constant temperature, and cooling programs, heat the temperature in the muffle furnace to 1220 ° C, and keep the temperature constant for 4.5 hours under the protection of nitrogen atmosphere;

[0073] After the temperature in the muffle furnace dropped to room temperature, the corundum crucible was taken out. The product in the corundum crucible was named Compound 2, as shown in Figure 9. The phase was characterized by powder diffraction XRD. Compared with the diffraction peak formed by non-iron phosphide substances, the diffraction peaks of the product Fe2P and FeP phases were very weak. It can be seen that the amount of reducing agent has a great influence on the formation of iron phosphide products.

[0074] Test Case

[0075] The phase purity of the mixed phase iron phosphide product 4 was characterized by powder XRD, which contained two phases, Fe2P and FeP. The chemical composition analysis (mass fraction) was shown in Table 1. The mixed phase iron phosphide product 4 contained 64.32% Fe, 243% P, 0.25% Ti, 0.48% Mn, 0.17% Si, 0.66% C, and 0.025% S.

[0076] Table 1

[0077] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for preparing a mixed phase iron phosphide, characterized in that: The following steps are involved: S1, mixing raw materials, mixing the reducing agent and iron phosphate powder sufficiently and uniformly to obtain a first mixture; S2, heating, placing the first mixture in a corundum crucible and heating it, wherein the reducing agent and the iron phosphate react under high temperature under the protection of a nitrogen atmosphere; S3, cooling, after the reaction of the reducing agent and the ferric phosphate is completed, the heating is stopped, and after cooling to room temperature, a mixture of FeP and Fe2P is obtained.

2. The method for preparing a mixed phase iron phosphide according to claim 1, characterized in that: The reducing agent includes one or more of coke, graphite, ascorbic acid, hydrogen, phosphorous acid and hypophosphorous acid.

3. The method for preparing a mixed phase iron phosphide according to claim 1, characterized in that: The mass ratio of the iron phosphate to the reducing agent is 10:1-10:

15.

4. The method for preparing a mixed phase iron phosphide according to claim 1, characterized in that: The iron phosphate is made of waste power battery electrode material.

5. The method for preparing a mixed phase iron phosphide according to claim 1, characterized in that: The heating temperature in step S2 is 1000-1450°C.

6. The method for preparing a mixed phase iron phosphide according to claim 1, characterized in that: The high temperature heating reaction time of the iron phosphate and the reducing agent is 1.5-4h.

7. The method for preparing a mixed phase iron phosphide according to claim 1, characterized in that: The equipment used for heating in step S2 is one of a tubular furnace, a rotary kiln and a muffle furnace.

8. The method for preparing a mixed phase iron phosphide according to claim 1, characterized in that: The cooling time in step S3 is 1.5-5h.

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