Method for preparing graphite powder and ferrophosphorus manganese by using iron phosphate waste residue

Abstract

The application provides a method for preparing graphite powder and ferromanganese phosphate by using iron phosphate waste residue, and the method comprises the following steps: washing the iron phosphate waste residue with water, separating the iron phosphate waste residue, and performing solid-liquid separation on the iron phosphate waste residue after reacting with dilute nitric acid to obtain filter residue containing iron phosphate and carbon; mixing the filter residue with reduced manganese sand and inorganic acid, performing preliminary reduction reaction, adding reduced iron powder for further reduction, adjusting pH, and performing solid-liquid separation to obtain carbon residue and filter liquor containing ferromanganese phosphate; washing and drying the carbon residue to obtain crude graphite powder; removing heavy metal residues by reacting the filter liquor containing ferromanganese phosphate with a sodium sulfide solution, supplementing a divalent iron source or adding pure water to the filter liquor, adjusting the iron concentration in the mixed solution by adding an antioxidant, adjusting the molar ratio of Fe to Mn and P and the pH of the solution, and obtaining a ferromanganese phosphate product by using a coprecipitation method. The prepared ferromanganese phosphate product has high yield, few processes, high efficiency, and can effectively recycle and utilize the iron phosphate waste residue.

Description

Technical Field

[0001] This invention relates to the field of ferric phosphate waste application technology, specifically to a method for preparing graphite powder and ferrous manganese phosphate using ferric phosphate waste. Background Technology

[0002] Lithium iron phosphate is mainly used in various lithium-ion batteries. With the rapid development of new energy vehicles, the output of used lithium iron phosphate batteries is increasing year by year.

[0003] To reduce environmental pollution and resource waste, researchers have developed technologies for recycling lithium from spent lithium iron phosphate batteries. One such technology involves the oxidative leaching of lithium iron phosphate mixed powder (mainly composed of lithium iron phosphate and carbon powder, with a small amount of positive and negative electrode fragments mixed in during dismantling). This process generates a large amount of waste residue, referred to as "iron phosphate waste residue." How to recycle and utilize this waste residue is a pressing technical problem that needs to be solved. Summary of the Invention

[0004] Therefore, it is necessary to provide a method for preparing graphite powder and ferrous manganese phosphate using ferric phosphate waste residue.

[0005] The present invention adopts the following technical solution:

[0006] This invention provides a method for preparing graphite powder and ferrous manganese phosphate from ferric phosphate waste residue, comprising the following steps: washing and separating the ferric phosphate waste residue with water to obtain ferric phosphate residue and a lithium-containing solution (which can be used for lithium extraction); heating the ferric phosphate residue with dilute nitric acid to dissolve copper and aluminum impurities in the ferric phosphate waste residue, followed by solid-liquid separation to obtain filter residue containing ferric phosphate and carbon; mixing the filter residue containing ferric phosphate and carbon with reduced manganese sand and inorganic acid for a preliminary reduction reaction, then adding reduced iron powder for a further reduction reaction and adjusting the pH to 1.0–1.5, and finally... The solution is separated into carbon slag and filtrate containing ferrous manganese phosphorus. The carbon slag is washed with pure water and dried to obtain crude graphite powder. The filtrate containing ferrous manganese phosphorus is mixed with sodium sulfide solution and reacted. Solid-liquid separation is performed to remove heavy metal residues. A ferrous iron source or pure water is added to the filtrate, along with an antioxidant. The iron concentration in the mixed solution is adjusted, the molar ratio of Fe to Mn and P is adjusted, and the pH of the solution is adjusted to 6-8. The reaction yields ferrous manganese phosphate slurry. The ferrous manganese phosphate slurry is subjected to solid-liquid separation, and the filter cake is washed to obtain ferrous manganese phosphate product.

[0007] Furthermore, the method for preparing graphite powder and ferrous manganese phosphate from ferric phosphate waste also includes the step of drying and calcining the ferrous manganese phosphate product (preferably at a calcination temperature of 500–580°C, a calcination time of 4–6 h, and a calcination atmosphere of nitrogen) to obtain anhydrous ferrous manganese phosphate. Even further, the method for preparing graphite powder and ferrous manganese phosphate from ferric phosphate waste also includes the step of crushing, sieving, and removing iron from the anhydrous ferrous manganese phosphate to obtain a battery-grade anhydrous ferrous manganese phosphate precursor.

[0008] In some embodiments, the process parameters for the heating reaction of ferric phosphate slag with dilute nitric acid are as follows: the concentration of the dilute nitric acid solution is 0.1 mol / L, the solid-liquid mass ratio is 1:(1-3), and the reaction temperature is 35-50°C. More preferably, after the reaction of ferric phosphate slag with dilute nitric acid, the process further includes a step of washing the filter residue containing ferric phosphate and carbon with a dilute nitric acid solution with a pH of 1.5-2.5.

[0009] In some embodiments, during the multi-step reduction reaction, the molar amount of reduced manganese sand added is 70-95% of the stoichiometric amount for the chemical reaction; the inorganic acid is selected from at least one of sulfuric acid, phosphoric acid, and hydrochloric acid; the molar amount of acid added is 1.3-2.0 times the theoretical amount added for the reaction; the solid-liquid mass ratio is 1:(2-7); and the reaction temperature is 40-90°C. Preferably, the solid-liquid mass ratio is 1:(3-5); and the reaction temperature is 50-70°C.

[0010] In some embodiments, the iron concentration in the mixed solution is adjusted to 0.6–0.8 mol / L, the molar ratio of Fe to Mn is controlled to be a:(1-a) (satisfying 0.3≤a≤0.5), and the molar ratio of P to (Fe+Mn) is controlled to be 2:3.

[0011] In some embodiments, the added Mn source is selected from one or more of MnSO4, MnCl2, Mn(OH)2, and MnCO3. Preferably, the added Mn source is selected from one or more of insoluble Mn(OH)2 and MnCO3.

[0012] Compared with the prior art, the core advantage of this invention is:

[0013] 1) This invention can prepare high-value-added ferrous manganese phosphate products and crude graphite powder by performing multiple reaction processes on ferric phosphate waste residue.

[0014] 2) Existing technologies mainly employ a hydrothermal method to synthesize ferrous manganese phosphate. The iron sources used are primarily ferrous sulfate and iron powder, the phosphorus sources are phosphoric acid, MAP, and DAP, and the manganese sources are manganese(II) sulfate and manganese oxide. This method has high energy consumption in synthesizing ferrous manganese phosphate. 2+Easily oxidized, the resulting product is impure, and the final pH at the synthesis endpoint is low, leading to a low yield. In contrast, this method utilizes waste iron phosphate slag as both the phosphorus and iron sources, representing the recycling of waste resources. The co-precipitation method for preparing ferrous manganese phosphate yields high efficiency with fewer steps. The resulting ferrous manganese phosphate precursor can be used to prepare lithium manganese iron phosphate, a positive electrode active material for batteries, thus realizing the transformation of waste into a high-value-added product.

[0015] 3) In the method of preparing crude graphite powder and ferrous manganese phosphate from ferric phosphate waste in this invention, the reduced manganese sand is more reactive than iron, and the leaching reaction with inorganic acid is faster, which can reduce the leaching time. The manganese added later is preferably manganese hydroxide and manganese carbonate, which can not only supplement manganese, but also adjust the pH, thereby reducing the amount of pH adjuster and reducing production costs. Attached Figure Description

[0016] Figure 1 A schematic diagram of the process flow for preparing crude graphite powder and ferrous manganese phosphate using ferric phosphate waste residue. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to specific embodiments, so that those skilled in the art can more clearly understand the present invention. The following embodiments are only used to illustrate the present invention, and are not intended to limit the scope of the present invention. Based on the specific embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention. In the embodiments of the present invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art; in the embodiments of the present invention, unless specifically specified, the technical means used are conventional means well known to those skilled in the art.

[0018] Iron phosphate waste residue: The iron phosphate waste residue in this experiment comes from the leaching process of battery powder in a battery recycling and lithium extraction company. This waste residue is a gray-black waste residue obtained by solid-liquid separation after oxidation and acid leaching of lithium iron phosphate waste powder. Since its main component is iron phosphate, it is called "iron phosphate waste residue".

[0019] Based on extensive testing and research, the composition of ferric phosphate waste residue is shown in the table below:

[0020] Solid content 35-55 wt% Fe 7.7–12.1 wt% P 4.3–6.8 wt% C 6.7–10.4 wt% Li 0.32–0.48 wt% Cr <200ppm Ca <400ppm Cu <5000ppm K <100ppm Mg <1500ppm Na <300ppm Ni <800ppm Pb <20ppm Zn <700ppm Mn <1000ppm Co <150ppm Cd <10ppm Ti <1000ppm Al <5000ppm

[0021] Example 1

[0022] like Figure 1 As shown, this embodiment provides a method for preparing crude graphite powder and ferrous manganese phosphate using ferric phosphate waste residue, including the following steps:

[0023] S1. The iron phosphate residue is washed with water, and the solid-liquid mass ratio is 1:2. After stirring for 40 minutes, the solid and liquid are separated to obtain iron phosphate residue and lithium-containing solution (which can be used for lithium extraction).

[0024] S2, ferric phosphate slag is heated and reacted with dilute nitric acid. The process parameters are: concentration of dilute nitric acid solution is 0.1 mol / L, solid-liquid mass ratio is 1:2, reaction temperature is 45℃, and reaction time is 150 min. After solid-liquid separation, filter residue containing ferric phosphate and carbon is obtained. This step utilizes the reaction principle that ferric phosphate and carbon are not easily soluble in dilute nitric acid, while copper and aluminum are soluble in dilute nitric acid, to achieve the effect of removing copper and aluminum.

[0025] The filter residue containing ferric phosphate and carbon was further washed with dilute nitric acid (pH 2.0) for 3 minutes, followed by washing with pure water for 7 minutes. The relationship between the wash water flow rate and the filter press filtration area was: the ratio of the filter press filtration area to the wash water flow rate was 100 m² / 2. 2 8m 3 / h, the filter residue containing ferric phosphate and carbon is purified.

[0026] S3, the purified filter residue containing ferric phosphate and carbon is mixed with a small amount of 40-mesh reduced manganese sand and inorganic acid (phosphoric acid) for a preliminary reduction reaction. Stirring continues for 30 minutes, then 120-mesh reduced iron powder is added for further reduction, and the pH is adjusted to 1.5. Solid-liquid separation yields carbon slag and ferrous (Fe)-containing residue. 2+ Manganese (Mn) 2+ Filtrate containing phosphorus (P).

[0027] In this step, if the amount of manganese added is insufficient, Fe will be present in the system. 3+ , Mn and Fe 2+ The reaction that produces elemental iron will not occur. The amount of manganese sand added as a reducing agent is 80% of the stoichiometric amount of the chemical reaction. The amount of acid added is controlled to be 1.5 times the theoretical amount added for the reaction. The solid-liquid mass ratio of the reaction is 1:4, and the reaction temperature is 60℃.

[0028] The reaction principle is as follows:

[0029] 2FePO4 + 4H3PO4 + Mn = 2Fe(H2PO4)2 + Mn(H2PO4)2 (minimum amount of manganese)

[0030] 2FePO4+4H3PO4+Fe=3Fe(H2PO4)2

[0031] Fe + 2H + =Fe 2+ +H2↑ (adjust pH)

[0032] S4. The carbon slag is washed with pure water until the conductivity of the wash water is 650±150μS / cm. The washing is then stopped, and the slag is dried using a flash dryer to obtain crude graphite powder, which can be sold externally.

[0033] S5 involves mixing the filtrate containing ferrous manganese phosphorus with a sodium sulfide solution for reaction. The process parameters are as follows: the concentration of the sodium sulfide solution is 25 kg / m³. 3 The amount of sodium sulfide solution added was 0.5 g sodium sulfide / L solution. Solid-liquid separation was performed to remove heavy metal residues, and filtrate was obtained.

[0034] S6. Add ferrous nitrate (Fe2+) or pure water to the filtrate, along with an antioxidant (ascorbic acid, 0.5 g / L). Use MAP as the phosphorus source and MnCO3 as the manganese source. Adjust the iron concentration in the mixed solution to 0.7 mol / L, then adjust the molar ratio of Fe to Mn and P to control the Fe to Mn molar ratio at 0.5:0.5 and the P to (Fe+Mn) molar ratio at 2:3. Adjust the pH to 7.0 with ammonia water, stir for 2 hours, and the reaction yields a ferrous manganese phosphate slurry. Perform solid-liquid separation on the ferrous manganese phosphate slurry, wash the filter cake until the conductivity of the wash water is 500 ± 50 μS / cm, then stop washing to obtain pure ferrous manganese phosphate product.

[0035] S7. The ferrous manganese phosphate product was dried in an atmosphere furnace to obtain n-hydrate ferrous manganese phosphate powder. The n-hydrate ferrous manganese phosphate powder was then transferred to a box-type atmosphere furnace for calcination at a temperature of 550℃ for 5 hours in a nitrogen atmosphere to obtain anhydrous ferrous manganese phosphate.

[0036] S8 involves crushing, screening, and removing iron from anhydrous ferrous manganese phosphate to obtain a battery-grade anhydrous ferrous manganese phosphate precursor.

[0037] Example 2

[0038] This embodiment provides a method for preparing crude graphite powder and ferrous manganese phosphate using ferric phosphate waste residue, comprising the following steps:

[0039] S1. The iron phosphate residue is washed with water, and the solid-liquid mass ratio is 1:2. After stirring for 40 minutes, the solid and liquid are separated to obtain iron phosphate residue and lithium-containing solution (which can be used for lithium extraction).

[0040] S2, ferric phosphate slag is heated and reacted with dilute nitric acid. The process parameters are: the concentration of dilute nitric acid solution is 0.1 mol / L, the solid-liquid mass ratio is 1:1.5, the reaction temperature is 35℃, the reaction time is 180 min, the solid and liquid are separated, and filter residue containing ferric phosphate and carbon is obtained.

[0041] The filter residue containing ferric phosphate and carbon was further washed with dilute nitric acid (pH 1.5) for 3 minutes, followed by washing with pure water for 5 minutes. The relationship between the wash water flow rate and the filter press filtration area was: the ratio of the filter press filtration area to the wash water flow rate was 100 m² / 2. 2 5m 3 / h, the filter residue containing ferric phosphate and carbon is purified.

[0042] S3. The filter residue containing ferric phosphate and carbon is mixed with a small amount of 60-mesh reduced manganese sand and inorganic acid (sulfuric acid) for a preliminary reduction reaction. Stirring is continued for 30 minutes. Then, 100-mesh reduced iron powder is added for a further reduction reaction and the pH is adjusted to 1.2. Solid-liquid separation is performed to obtain carbon residue and filtrate containing ferrous manganese phosphorus.

[0043] In this step, if the amount of manganese added is insufficient, Fe will be present in the system. 3+ , Mn and Fe 2+ The reaction that produces elemental iron will not occur. The amount of manganese sand added as a reducing agent is 70% of the stoichiometric amount of the chemical reaction. The amount of acid added is controlled to be 1.8 times the theoretical amount added for the reaction. The solid-liquid mass ratio of the reaction is 1:3, and the reaction temperature is 50℃.

[0044] The reaction principle is as follows:

[0045] 2FePO4 + 2H2SO4 + Mn = Fe(H2PO4)2 + FeSO4 + MnSO4 (minimum amount of manganese)

[0046] 2FePO4+2H2SO4+Fe=Fe(H2PO4)2+2FeSO4

[0047] Fe + 2H + =Fe 2+ +H2↑

[0048] S4. The carbon slag is washed with pure water until the conductivity of the wash water is 650±150μS / cm. The washing is then stopped, and the slag is dried using a flash dryer to obtain crude graphite powder, which can be sold externally.

[0049] S5 involves mixing the filtrate containing ferrous manganese phosphorus with a sodium sulfide solution for reaction. The process parameters are as follows: the concentration of the sodium sulfide solution is 25 kg / m³. 3 The amount of sodium sulfide solution added was 0.5 g sodium sulfide / L solution. Solid-liquid separation was performed to remove heavy metal residues, and filtrate was obtained.

[0050] S6. Add a ferrous iron source (ferrous sulfate heptahydrate) or pure water to the filtrate, and add an antioxidant (ascorbic acid, 0.5 g / L).

[0051] Using MAP as the phosphorus source and Mn(OH)₂ as the manganese source, the iron concentration in the mixed solution was adjusted to 0.6 mol / L. The molar ratios of Fe, Mn, and P were then adjusted to control the Fe:Mn molar ratio at 0.4:0.6 and the P:(Fe+Mn) molar ratio at 2:3. The pH was adjusted to 6.0 using ammonia water, and the mixture was stirred for 2 hours to obtain a ferrous manganese phosphate slurry. The ferrous manganese phosphate slurry was subjected to solid-liquid separation, and the filter cake was washed until the conductivity of the wash water reached 500 μS / cm. Washing was then stopped, yielding pure ferrous manganese phosphate product.

[0052] S7. The ferrous manganese phosphate product was dried in an atmosphere furnace to obtain n-hydrate ferrous manganese phosphate powder. The n-hydrate ferrous manganese phosphate powder was then transferred to a box-type atmosphere furnace for calcination at a temperature of 530℃ for 6 hours in a nitrogen atmosphere to obtain anhydrous ferrous manganese phosphate.

[0053] S8 involves crushing, screening, and removing iron from anhydrous ferrous manganese phosphate to obtain a battery-grade anhydrous ferrous manganese phosphate precursor.

[0054] Example 3

[0055] This embodiment provides a method for preparing crude graphite powder and ferrous manganese phosphate using ferric phosphate waste residue, comprising the following steps:

[0056] S1. The iron phosphate residue is washed with water at a solid-liquid mass ratio of 1:2.5 and stirred for 40 minutes to separate the solid and liquid, yielding iron phosphate residue and a lithium-containing solution (which can be used for lithium extraction).

[0057] S2, ferric phosphate slag is reacted with dilute nitric acid under heating conditions: nitric acid solution concentration of 0.1 mol / L, solid-liquid mass ratio of 1:2.5, reaction temperature of 50℃, and reaction time of 120 min. Solid-liquid separation is then performed to obtain filter residue containing ferric phosphate and carbon. The filter residue containing ferric phosphate and carbon is further washed with a dilute nitric acid solution (pH 2.5) for 3 min, followed by washing with pure water for 10 min. The ratio of wash water flow rate to filter press area is: filter press area to wash water flow rate is 100 m² / min. 2 10m 3 / h, the filter residue containing ferric phosphate and carbon is purified.

[0058] S3. The purified filter residue containing ferric phosphate and carbon is mixed with a small amount of 20-mesh reduced manganese sand and inorganic acid (hydrochloric acid) for a preliminary reduction reaction. Stirring is continued for 30 minutes, and then 150-mesh reduced iron powder is added for a further reduction reaction. The pH is adjusted to 1.0, and the solid and liquid are separated to obtain carbon residue and filtrate containing ferrous manganese phosphorus.

[0059] In this step, if the amount of manganese added is insufficient, Fe will be present in the system. 3+ , Mn and Fe 2+The reaction that produces elemental iron will not occur. The amount of manganese sand added as a reducing agent is 95% of the stoichiometric amount of the chemical reaction. The amount of acid added is controlled to be 2.0 times the theoretical amount added for the reaction. The solid-liquid mass ratio of the reaction is 1:5, and the reaction temperature is 70℃.

[0060] The reaction principle is as follows:

[0061] 2FePO4 + 4HCl + Mn = Fe(H2PO4)2 + FeCl2 + MnCl2 (minimum amount of manganese)

[0062] 2FePO4+4HCl+Fe=Fe(H2PO4)2+2FeCl2

[0063] Fe + 2H + =Fe 2+ +H2↑

[0064] S4. The carbon slag is washed with pure water until the conductivity of the wash water is 650±150μS / cm. The washing is then stopped, and the slag is dried using a flash dryer to obtain crude graphite powder, which can be sold externally.

[0065] S5 involves mixing the filtrate containing ferrous manganese phosphorus with a sodium sulfide solution for reaction. The process parameters are as follows: the concentration of the sodium sulfide solution is 25 kg / m³. 3 The amount of sodium sulfide solution added was 0.5 g sodium sulfide / L solution. Solid-liquid separation was performed to remove heavy metal residues, and filtrate was obtained.

[0066] S6. Add ferrous chloride or pure water to the filtrate, and add an antioxidant (ascorbic acid, 0.5 g / L).

[0067] Using DAP as the phosphorus source and MnCl2 as the manganese source, the iron concentration in the mixed solution was adjusted to 0.8 mol / L. The molar ratios of Fe, Mn, and P were then adjusted to control the Fe:Mn molar ratio at 0.3:0.7 and the P:(Fe+Mn) molar ratio at 2:3. The pH was adjusted to 8.0 using sodium carbonate, and the mixture was stirred for 2 hours to obtain a ferrous manganese phosphate slurry. The ferrous manganese phosphate slurry was subjected to solid-liquid separation, and the filter cake was washed until the conductivity of the wash water reached 500 μS / cm. Washing was then stopped, yielding pure ferrous manganese phosphate product.

[0068] S7. The ferrous manganese phosphate product was dried in an atmosphere furnace to obtain n-hydrate ferrous manganese phosphate powder. The n-hydrate ferrous manganese phosphate powder was then transferred to a box-type atmosphere furnace for calcination at a temperature of 580℃ for 4 hours in a nitrogen atmosphere to obtain anhydrous ferrous manganese phosphate.

[0069] S8 involves crushing, screening, and removing iron from anhydrous ferrous manganese phosphate to obtain a battery-grade anhydrous ferrous manganese phosphate precursor.

[0070] Comparative Example 1

[0071] This comparative example provides a method for preparing crude graphite powder and ferrous manganese phosphate using ferric phosphate waste residue. The method steps are basically the same as those in Example 1, with the only difference being:

[0072] In step S2, the ferric phosphate slag and dilute nitric acid react at room temperature. The reaction process parameters are as follows: the concentration of the dilute nitric acid solution is 0.1 mol / L, the solid-liquid mass ratio is 1:3, the reaction temperature is 25℃, and the reaction time is 120 min.

[0073] Comparison Column 2

[0074] This comparative example provides a method for preparing crude graphite powder and ferrous manganese phosphate using ferric phosphate waste residue. The method steps are basically the same as those in Example 1, with the only difference being:

[0075] In step S3, the molar amount of acid added is controlled to be 1.0 times the theoretical amount added for the reaction.

[0076] The iron leaching rate in the ferric phosphate waste in this comparative example was 65.35%, which is lower than the iron leaching rate in the ferric phosphate waste in Example 1 (93.21%).

[0077] Comparative Example 3

[0078] This comparative example provides a method for preparing crude graphite powder and ferrous manganese phosphate using ferric phosphate waste residue. The method steps are basically the same as those in Example 1, with the only difference being:

[0079] In step S6, the pH is adjusted to 4.0 with ammonia water, and the mixture is stirred for 2 hours to obtain ferrous manganese phosphate slurry.

[0080] The residual iron content in the mother liquor was tested, and the yield of ferrous manganese phosphate synthesized under these conditions was 87.24%, which was lower than the yield of ferrous manganese phosphate in Example 1 (99.14%).

[0081] Comparative Example 4

[0082] This comparative example provides a method for preparing crude graphite powder and ferrous manganese phosphate using ferric phosphate waste residue. The method steps are basically the same as those in Example 1, with the only difference being:

[0083] In step S2, the reaction of ferric phosphate slag with nitric acid is replaced by the reaction of ferric phosphate slag with hydrochloric acid.

[0084] The filtrate was tested, and the iron loss rate under these conditions was 66.32%, while in Example 1, the iron loss rate was 1.08% under the same conditions when dilute nitric acid was used.

[0085] The elemental content of the ferrous manganese phosphate precursors prepared in the above experimental examples was tested, and the results are shown in the table below:

[0086] Statistical table of impurities and performance test results of ferrous manganese phosphate precursor

[0087]

[0088]

[0089] The crude graphite powder prepared in the above experimental examples was subjected to partial elemental analysis, and the results are shown in the table below:

[0090]

[0091] It should be noted that the above embodiments are only for further elaboration and explanation of the technical solution of the present invention, and are not intended to further limit the technical solution of the present invention. The method of the present invention is only a preferred embodiment and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing graphite powder and ferrous manganese phosphate from ferric phosphate waste residue, characterized in that, The steps include the following: The ferric phosphate residue is washed and separated to obtain ferric phosphate slag. The ferric phosphate slag is heated and reacted with dilute nitric acid to dissolve the copper and aluminum impurities in the ferric phosphate waste slag. The solid and liquid are separated to obtain filter residue containing ferric phosphate and carbon. The filter residue containing ferric phosphate and carbon is mixed with metallic manganese and inorganic acid for a preliminary reduction reaction. Then, reduced iron powder is added for a further reduction reaction and the pH is adjusted to 1.0~1.

5. The solid and liquid are separated to obtain carbon residue and filtrate containing ferrous manganese and phosphorus. The carbon slag is washed with pure water and dried to obtain crude graphite powder. The filtrate containing ferrous manganese phosphorus is mixed with sodium sulfide solution and reacted. Solid-liquid separation is performed to remove heavy metal residues. A ferrous iron source or pure water is added to the filtrate, and an antioxidant is added at the same time. The iron ion concentration in the mixed solution is adjusted, the molar ratio of Fe to Mn and P is adjusted, and the pH is adjusted to 6-8. The reaction yields ferrous manganese phosphate slurry. The ferrous manganese phosphate slurry was subjected to solid-liquid separation, and the filter cake was washed to obtain the ferrous manganese phosphate product.

2. The method for preparing graphite powder and ferrous manganese phosphate from ferric phosphate waste according to claim 1, characterized in that, It also includes the step of drying and calcining the ferrous manganese phosphate product to obtain anhydrous ferrous manganese phosphate.

3. The method for preparing graphite powder and ferrous manganese phosphate from ferric phosphate waste according to claim 2, characterized in that, It also includes the steps of crushing, screening, and removing iron from anhydrous ferrous manganese phosphate to obtain battery-grade anhydrous ferrous manganese phosphate precursor.

4. The method for preparing graphite powder and ferrous manganese phosphate from ferric phosphate waste according to any one of claims 1 to 3, characterized in that, The process parameters for the heating reaction of ferric phosphate slag with dilute nitric acid are as follows: the concentration of the dilute nitric acid solution is 0.1 mol / L, the solid-liquid mass ratio is 1:(1~3), and the reaction temperature is 35~50℃.

5. The method for preparing graphite powder and ferrous manganese phosphate from ferric phosphate waste according to claim 4, characterized in that, It also includes a step of washing the filter residue containing ferric phosphate and carbon with dilute nitric acid at a pH of 1.5 to 2.

5.

6. The method for preparing graphite powder and ferrous manganese phosphate from ferric phosphate waste according to any one of claims 1 to 3, characterized in that, In the initial reduction reaction step, the molar amount of metallic manganese added is 70-95% of the stoichiometric amount of the chemical reaction, the inorganic acid is selected from at least one of sulfuric acid, phosphoric acid, and hydrochloric acid, the molar amount of inorganic acid added is 1.3-2.0 times the theoretical amount added for the reaction, the solid-liquid mass ratio of the reaction is 1:(2-7), and the reaction temperature is 40-90℃.

7. The method for preparing graphite powder and ferrous manganese phosphate from ferric phosphate waste according to claim 6, characterized in that, The solid-liquid mass ratio of the reaction is 1:(3~5), and the reaction temperature is 50~70℃.

8. The method for preparing graphite powder and ferrous manganese phosphate from ferric phosphate waste according to any one of claims 1 to 3, characterized in that, Adjust the iron ion concentration in the mixed solution to 0.6~0.8 mol / L, control the molar ratio of Fe to Mn to be a:(1-a), where 0.3≤a≤0.5; control the molar ratio of P to (Fe +Mn) to be 2:

3.

9. The method for preparing graphite powder and ferrous manganese phosphate from ferric phosphate waste according to claim 8, characterized in that, When adjusting the molar ratio of Fe to Mn and P, Mn is selected from one or more of MnSO4, MnCl2, Mn(OH)2, and MnCO3.

10. The method for preparing graphite powder and ferrous manganese phosphate from ferric phosphate waste according to claim 9, characterized in that, Mn is selected from one or more of Mn(OH)2 and MnCO3.

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