Impurity removal method for ferrophosphorus slag, ferromanganese phosphate precursor and iron phosphate

Abstract

According to the impurity removal method for the ferrophosphorus slag, impurities such as Al, Cu, Ti, carbon and organic electrolyte in the ferrophosphorus slag can be effectively removed through the method. The method comprises the following steps: (1) carrying out high-temperature calcination on ferrophosphorus slag A and chloride under a reduction condition to obtain ferrophosphorus slag B; (2) leaching the ferrophosphorus slag B to obtain ferrophosphorus liquid A and filter slag A; (3) adding sodium fluoride into the ferrophosphorus liquid A to obtain ferrophosphorus liquid B and filter residues B; and (4) adding iron powder into the ferrophosphorus liquid B, and carrying out solid-liquid separation to obtain the high-purity ferrophosphorus liquid. Meanwhile, the invention provides a method for preparing a ferromanganese phosphate precursor and an iron phosphate precursor by adopting the high-purity ferrophosphorus liquid obtained by the method.

Description

Technical Field

[0001] The invention belongs to the technical field of battery recycling, and particularly relates to a method for removing impurities from ferrophosphorus slag and a method for preparing ferromanganese phosphate precursor and ferric phosphate by using the method. Background Art

[0002] In recent years, the new energy vehicle industry has developed rapidly, and the production, sales and installation volume of lithium iron phosphate batteries have continued to increase. It can be foreseen that a large number of waste lithium iron phosphate batteries will enter the market in the future and face recycling problems, which will in turn promote the rapid development of the lithium iron phosphate battery recycling industry.

[0003] At present, hydrometallurgy is LiFePO 4 The mainstream recycling process of positive electrode materials is usually to convert LiFePO 4 The positive electrode material is selectively leached and converted into lithium salt and ferrophosphorus slag. Lithium salt can be directly used to prepare battery-grade lithium carbonate, but ferrophosphorus slag contains a large amount of impurities such as Al, Cu, Ti, carbon and organic electrolytes. At present, there is no process in the market that can efficiently utilize ferrophosphorus slag and generate greater economic value.

[0004] The invention patent with publication number CN117623256A discloses a method for efficiently removing impurities from waste lithium iron phosphate to synthesize battery-grade lithium carbonate and iron phosphate. The invention first burns the waste lithium iron phosphate in an oxidizing atmosphere, then immerses the obtained powder in a solvent, mixes it evenly and then filters it to obtain a lithium filtrate containing copper and aluminum impurities and a lithium extraction slag; the lithium filtrate containing copper and aluminum impurities is removed from the lithium filtrate, concentrated and carbonized to obtain lithium carbonate, and the iron phosphate slag is acid-leached, the phosphorus-iron ratio is adjusted, and then aged and calcined at high temperature to obtain iron phosphate. The method obtains chlorides or bromides of aluminum and copper by calcining in a high-temperature chlorine or bromine atmosphere. First, it is difficult to control chlorine or bromine at high temperatures, and leakage can cause great harm to the human body. The process uses chlorine or bromine throughout, which is very costly. The invention does not explain the Ti removal process. Since most of the lithium iron phosphate products currently on the market are doped with 1000 to 8000 ppm of Ti to improve the stability and compaction density of lithium iron phosphate, it is difficult to remove Ti from the recovered lithium iron phosphate material during acid leaching.

[0005] The invention patent with the publication number CN117480116A discloses a method for recycling waste battery lithium-extracting phosphorus iron slag in a full chain integration. The invention performs an acid leaching on the phosphorus iron slag after lithium extraction, and adds an iron ion precipitant to react to obtain impurity-free phosphorus iron slag; the impurity-free phosphorus iron slag is subjected to a secondary acid leaching to obtain a phosphorus iron solution; the phosphorus iron solution and a buffer solution are mixed to perform a precipitation reaction, and after the reaction, the obtained precipitate is heat-treated to obtain iron phosphate. This process does not perform a Ti removal process, and does not explain the Cu removal process. In addition, due to the two acid leachings, the process consumes a large amount of acid and alkali, and generates a large amount of wastewater. Summary of the invention

[0006] In order to solve the above technical problems, the present invention proposes a new method for removing impurities from ferrophosphorus slag. By adopting this method, impurities such as Al, Cu, Ti, carbon and organic electrolyte in the ferrophosphorus slag can be effectively removed.

[0007] On the one hand, the present invention provides a method for removing impurities from ferrophosphorus slag, comprising the following steps:

[0008] (1) calcining ferrophosphorus slag A and chloride at high temperature under reducing conditions to obtain ferrophosphorus slag B;

[0009] (2) leaching the ferrophosphorus slag B to obtain ferrophosphorus liquid A and filter residue A;

[0010] (3) adding fluoride to the above ferrophosphorus liquid A to obtain ferrophosphorus liquid B and filter residue B;

[0011] (4) Add iron powder to the above ferrophosphorus liquid B, and separate the solid and liquid to obtain high-purity ferrophosphorus liquid.

[0012] In a specific embodiment of the present invention, the reducing conditions in step (1) include adding carbon material.

[0013] In a specific embodiment of the present invention, the carbon material is one or more of sucrose, glucose, PVA, PEG, carbon nanotubes, and graphene.

[0014] In a specific embodiment of the present invention, the amount of the carbon material added is 0.01-10% of the mass of the ferrophosphorus slag A.

[0015] Preferably, the amount of the carbon material added is 0.4-2% of the mass of the ferrophosphorus slag A.

[0016] In the present invention, the purpose of adding carbon material is to reduce Fe in ferrophosphorus slag by carbon thermal reduction in high temperature reaction. 3+ Reduction to Fe 2+ , which is convenient for subsequent synthesis.

[0017] In a specific embodiment of the present invention, the high-temperature calcination in step (1) is carried out under vacuum conditions.

[0018] In a specific embodiment of the present invention, the high-temperature calcination in step (1) is carried out in a high-temperature fluidized bed;

[0019] Preferably, the vacuum degree in the high-temperature fluidized bed is not less than 50 torr.

[0020] In a specific embodiment of the present invention, the high temperature calcination temperature in step (1) is 400-800° C. and the time is 2-10 hours; preferably, the high temperature calcination time is 4-5 hours.

[0021] In a specific embodiment of the present invention, the high temperature calcination temperature in step (1) is 400°C, 500°C, 600°C, 700°C, 800°C, etc.

[0022] In a specific embodiment of the present invention, the high-temperature calcination in step (1) is carried out under an inert atmosphere.

[0023] In a specific embodiment of the present invention, the chloride is one or more of sodium chloride, potassium chloride and ferric chloride.

[0024] In a specific embodiment of the present invention, the amount of chloride added is 0.01-1% of the mass of the ferrophosphorus slag A.

[0025] Preferably, the amount of chloride added is 0.4-1% of the mass of the ferrophosphorus slag A.

[0026] In the present invention, the chloride is added to generate molten salt chlorination and Ti to form TiCl 4 .

[0027] In a specific embodiment of the present invention, the ferrophosphorus slag A is the ferrophosphorus slag obtained after lithium extraction from scrapped lithium iron phosphate or lithium iron manganese phosphate positive electrode materials.

[0028] Specifically, the ferrophosphorus slag A is obtained by disassembling, crushing, screening and other pretreatment of scrapped lithium iron phosphate or lithium iron manganese phosphate positive electrode materials to obtain black powder, and then acid leaching lithium from the black powder to obtain ferrophosphorus slag. The ferrophosphorus slag A contains a large amount of impurities such as Al, Cu, Ti, carbon and organic electrolyte.

[0029] After the operation of step (1), the impurity titanium in the ferrophosphorus slag A is converted into TiCl 4 At the same time, the iron in the ferrophosphorus slag A becomes +2 valent.

[0030] In a specific embodiment of the present invention, the leaching in step (2) is sulfuric acid leaching.

[0031] Furthermore, the sulfuric acid leaching has at least one of the following technical features:

[0032] (1) The solid content of the leaching system is 10-30%;

[0033] (2) sulfuric acid concentration is 10 to 50 wt%;

[0034] (3) Leach at 60-95°C for 1-5 hours.

[0035] In a specific embodiment of the present invention, the step (2) further comprises calcining the filter residue A at high temperature in an air atmosphere to obtain titanium carbide. After the operation of step (2), the Fe and P elements in the ferrophosphorus slag are transferred to the ferrophosphorus liquid A. The filter residue A is mainly carbon and other impurities that cannot be leached. After high-temperature calcination, titanium tetrachloride is converted into titanium carbide.

[0036] In a specific embodiment of the present invention, in step (3), the fluoride is one or more of sodium fluoride, ammonium fluoride and potassium fluoride.

[0037] In a specific embodiment of the present invention, in step (3), the amount of fluoride added is 0.05-2% of the mass of ferrophosphide liquid A.

[0038] Preferably, the amount of fluoride added is 0.05-0.6% of the mass of the ferrophosphide liquid A.

[0039] In the present invention, the purpose of adding sodium fluoride is to remove the Al impurities in the ferrophosphorus liquid A, and the reaction occurs: 6NaF+Al 3+ →Na 3 AlF 6 +3Na + , where the main component of residue B is cryolite Na 3 AlF 6 .

[0040] In a specific embodiment of the present invention, in step (4), the amount of iron powder added is 0.05-5% of the mass of ferrophosphorus liquid B.

[0041] Preferably, in step (4), the amount of iron powder added is 0.05-0.3% of the mass of ferrophosphorus liquid B.

[0042] In the present invention, the purpose of adding iron powder is to remove Cu impurities in ferrophosphorus liquid B. Iron powder can replace copper, and if other active metal elements are added, impurities will be introduced.

[0043] In a second aspect, the present invention provides a method for preparing a ferromanganese phosphate precursor, using the high-purity ferrophosphorus liquid obtained by the above preparation method as a raw material, comprising the following steps:

[0044] S1. Optionally add an iron source, a phosphorus source and a manganese source to the high-purity ferrophosphorus liquid to obtain a feed liquid A;

[0045] S2. Add a precipitant to the above-mentioned liquid A to carry out a coprecipitation reaction, separate the solid and the liquid, and then vacuum dry to obtain the ferromanganese phosphate precursor.

[0046] In a specific embodiment of the present invention, the phosphorus source is one or more of phosphoric acid, monoammonium phosphate, diammonium phosphate, and trisodium phosphate.

[0047] In a specific embodiment of the present invention, the iron source is one or more of ferrous sulfate, ferric sulfate, ferric nitrate and ferric oxalate.

[0048] In a specific embodiment of the present invention, the manganese source is one or more of manganese sulfate, manganese chloride, manganese nitrate and manganese oxalate.

[0049] In the present invention, the amount of iron source, phosphorus source and manganese source added is based on the target manganese ferrophosphate precursor Mn x Fe 1-x PO 4 The stoichiometric ratio of and the ferrophosphorus content in the high-purity ferrophosphorus liquid are determined, wherein 0<x<1; preferably, 0.3≤x≤0.7.

[0050] In a specific embodiment of the present invention, the ferromanganese phosphate precursor is Mn 0.3 Fe 0.7 PO 4 , Mn 0.4 Fe 0.6 PO 4 , Mn 0.5 Fe 0.5 PO 4 , Mn 0.6 Fe 0.4 PO 4 or Mn 0.7 Fe 0.3 PO 4 .

[0051] In a specific embodiment of the present invention, the specific operation process of S2 includes:

[0052] S2-1, preparing a mixed solution of a precipitant and an oxidant as feed solution B;

[0053] S2-2, using pure water as the base liquid and nitrogen as the protective atmosphere, adding feed liquid A and feed liquid B at the same time to carry out a coprecipitation reaction;

[0054] S2-3. Wash and filter the slurry after the coprecipitation reaction, and obtain the ferromanganese phosphate precursor by vacuum drying the obtained filter cake.

[0055] In a specific embodiment of the present invention, the precipitant is one or more of ammonia water, diammonium phosphate, and monoammonium phosphate.

[0056] In a specific embodiment of the present invention, the amount of the precipitant added is determined according to a stoichiometric ratio of N:P of 1.5 to 3.0.

[0057] In a specific embodiment of the present invention, the oxidant is one or more of hydrogen peroxide and ammonium persulfate.

[0058] In a specific embodiment of the present invention, the addition amount of the oxidant is determined according to 1.0 to 3.0 times the theoretical amount of the oxidant required for oxidizing Fe 2+ and Mn 2+ .

[0059] In a specific embodiment of the present invention, the pH value of the coprecipitation reaction is 5 to 6, and the temperature is 30 to 60 °C.

[0060] In a specific embodiment of the present invention, the drying temperature of the filter cake by vacuum drying is 60 to 80 °C, and the time is 20 to 30 h.

[0061] In the present invention, the manganese iron phosphate precursor Mn x Fe 1-x PO 4 (0 < x < 1) is mixed with a lithium salt and calcined to prepare lithium manganese iron phosphate.

[0062] Thirdly, the present invention provides a method for preparing battery-grade anhydrous iron phosphate, using the high-purity phosphorus iron liquid obtained by the above preparation method as a raw material, wherein the phosphorus iron slag A is the phosphorus iron slag obtained after lithium extraction from the scrapped lithium manganese iron phosphate cathode material, and the method comprises the following steps:

[0063] S3. Optionally supplement an iron source and a phosphorus source to the above high-purity phosphorus iron liquid to obtain a feed liquid C;

[0064] S4. Add a precipitant to the above feed liquid C for coprecipitation reaction, perform solid-liquid separation, and then obtain the iron phosphate after high-temperature calcination.

[0065] In step S3, the addition amounts of the iron source and the phosphorus source are determined according to the stoichiometric ratio of the target product iron phosphate FePO 4 and the phosphorus and iron contents in the high-purity phosphorus iron liquid.

[0066] In a specific embodiment of the present invention, the specific operation process of S4 includes:

[0067] S4-1. Prepare a mixed solution of a precipitant and an oxidant as a feed liquid D;

[0068] S4-2. Use pure water as the bottom liquid and nitrogen as the protective atmosphere, and simultaneously add the feed liquid C and the feed liquid D for coprecipitation reaction;

[0069] S4-3. Wash and filter the slurry after the coprecipitation reaction, and the obtained filter cake is dried by blowing and then calcined at high temperature to obtain battery-grade anhydrous iron phosphate.

[0070] Among them, the addition amount of the precipitant is determined according to the stoichiometric ratio of N:P being 1.5 to 3.0.

[0071] Among them, the addition amount of the oxidant is determined according to oxidizing Fe2+ The required amount of oxidant is 1.0 to 2.0 times the theoretical amount of oxidant required.

[0072] Wherein, the iron source, phosphorus source, precipitant and oxidant have the definitions as mentioned above.

[0073] Wherein, the pH value of the coprecipitation reaction is 1.5-2.5, and the temperature is 40-60°C.

[0074] The filter cake is dried at a temperature of 60 to 80° C. and for 20 to 30 hours by air drying.

[0075] Wherein, the temperature of the high temperature calcination is 500-700°C, and the time is 2-10 hours; preferably, the temperature of the high temperature calcination is 500-600°C, and the time is 3-5 hours.

[0076] Beneficial effects:

[0077] (1) The impurity removal method provided by the present invention can accurately remove impurity elements Al, Ti, Cu, carbon, and organic electrolytes in mainstream lithium iron phosphate waste batteries (including lithium iron manganese phosphate), so that the iron manganese phosphate precursor or iron phosphate product can meet battery-grade indicators;

[0078] (2) The main raw material used in the preparation of ferromanganese phosphate precursor or ferrophosphate in the present invention is lithium slag extracted from waste batteries, which has extremely low cost and is available in large quantities in the market. The remaining auxiliary materials are also bulk commodities and are very easy to obtain, which lays a foundation for the technology to be able to scale up production and generate economic benefits;

[0079] (3) The present invention uses a sulfuric acid system to leach waste lithium iron phosphate battery slag with high impurity content and low quality requirements once after carbon reduction to remove titanium, to obtain ferrophosphorus liquid, to add the target element after removing impurities such as Al and Cu, and to co-precipitate in a reactor, and to obtain a battery-grade ferromanganese phosphate precursor or ferrophosphate after vacuum drying or calcination. The method of the present invention has low raw material cost, strong applicability, and makes full use of waste resources to prepare a battery-grade ferromanganese phosphate precursor or ferrophosphate product with high added value and large market demand. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Figure 1 A schematic diagram of a process flow for preparing a ferromanganese phosphate precursor provided in Example 1 of the present invention;

[0081] Figure 2 This is a SEM image of the ferromanganese phosphate precursor prepared in Example 1 of the present invention;

[0082] Figure 3 This is the XRD pattern of the ferromanganese phosphate precursor prepared in Example 1 of the present invention;

[0083] Figure 4 This is a charge and discharge curve diagram of the battery prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0084] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0085] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0086] In the description of the present invention, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0087] The present invention is further described in detail below through specific embodiments.

[0088] In the specific embodiment, the ferrophosphorus slag A used is obtained by extracting lithium from black powder of waste lithium iron phosphate batteries on the market. The ferrophosphorus slag is obtained by flash drying and passing through a 150-mesh sieve.

[0089] The components of ferrophosphorus slag A were analyzed, and the results are shown in Table 1 below:

[0090] Table 1

[0091]

[0092] Example 1

[0093] This embodiment provides a manganese ferrophosphate precursor (Mn 0.6 Fe 0.4 )PO 4 The preparation method comprises the following specific steps:

[0094] Take 500g of ferrophosphorus slag A, 5g of sodium chloride and 10g of glucose, mix them evenly, place them in a fluidized bed, under the protection of a high-purity nitrogen atmosphere and keep the vacuum degree below 50torr, heat them to 800℃ and keep them warm for 5h. After the reaction is completed, cool them down naturally to obtain ferrophosphorus slag B.

[0095] The ferrophosphorus slag B was leached in 1500g sulfuric acid solution (40%) at 80°C for 4h (solid content 25%), and 1900g ferrophosphorus liquid A was obtained by filtration; 10g sodium fluoride was added and stirred for 10min, and filtered to obtain 1887g ferrophosphorus liquid B; 5g iron powder was added and stirred for 5min and filtered to obtain high-purity ferrophosphorus liquid.

[0096] According to calculation, 407g of wet-process phosphoric acid (85%) and 555.8g of manganese sulfate were added to the above-mentioned high-purity ferrophosphorus liquid to obtain feed liquid A; 380g of ammonia water with a content of 22% and 247g of a mixed solution of hydrogen peroxide with a content of 27.5% were prepared as feed liquid B; in a reactor, 200g of pure water was used as the base liquid and nitrogen was used as the protective atmosphere, and feed liquid A and feed liquid B were added at the same time, the pH value of the system was controlled to be 6.0±0.2, and the temperature was maintained at 60℃±5℃, and coprecipitation was carried out to obtain a slurry.

[0097] The slurry was washed and filtered with 3 L of pure water, and the obtained filter cake was dried in a vacuum oven at 80 ° C for 24 h to obtain a manganese iron phosphate precursor (Mn 0.6 Fe 0.4 )PO 4 .

[0098] The ferromanganese phosphate precursor obtained above was subjected to SEM and XRD analysis. The XRD spectrum is as follows: Figure 3 As shown, the product is confirmed to be the target product, ferromanganese phosphate precursor; SEM picture is as follows Figure 2 As shown in the figure, it can be seen that the grain distribution of the ferromanganese phosphate precursor is uniform, the primary particles are olivine-like type with a size of about 80nm, the primary particles are relatively large (monoclinic system), and they form honeycomb-shaped secondary particles with a combination of large and small particles.

[0099] The manganese iron phosphate precursor is prepared into the positive electrode material lithium manganese iron phosphate, and then assembled into a battery. The specific process is:

[0100] The precursor is mixed with lithium carbonate and glucose and sintered to obtain LiFe with uniform carbon coating. 0.4 Mn 0.6 PO 4 Materials, prepared by weight ratio of LiFe 0.4 Mn 0.6 PO 4A mixed slurry of carbon black: polyvinylidene fluoride (PVDF) = 8:1:1 was then evenly coated on a current collector aluminum foil to obtain an electrode sheet, and a CR2032 battery was prepared in a glove box protected by an argon atmosphere.

[0101] The assembled battery's buckle performance is as follows: Figure 4 As shown, the 0.1C discharge specific capacity reaches 158.65mAh / g.

[0102] Example 2

[0103] This embodiment provides a manganese ferrophosphate precursor (Mn 0.5 Fe 0.5 )PO 4 The preparation method comprises the following specific steps:

[0104] Take 500g of ferrophosphorus slag A, 2g of sodium chloride and 2g of glucose, mix them evenly, place them in a fluidized bed, under the protection of a high-purity nitrogen atmosphere and keep the vacuum degree below 50torr, heat them to 800℃ and keep them warm for 5h. After the reaction is completed, cool them down naturally to obtain ferrophosphorus slag B.

[0105] The ferrophosphorus slag B was leached in 1500g sulfuric acid solution (40%) at 80°C for 4h, and 1900g ferrophosphorus liquid A was obtained by filtration; 10g sodium fluoride was added and stirred for 10min, and filtered to obtain 1887g ferrophosphorus liquid B; 5g iron powder was added and stirred for 5min and filtered to obtain high-purity ferrophosphorus liquid.

[0106] According to calculation, 271g of wet-process phosphoric acid (85%) and 369g of manganese sulfate were added to the above-mentioned high-purity ferrophosphorus liquid to obtain feed liquid A; 380g of ammonia water with a content of 22% and 247g of a mixed solution of hydrogen peroxide with a content of 27.5% were prepared as feed liquid B; in a reactor, 200g of pure water was used as the base liquid and nitrogen was used as the protective atmosphere, and feed liquid A and feed liquid B were added at the same time, the pH value of the system was controlled to be 6.0±0.2, and the temperature was maintained at 60℃±5℃, and coprecipitation was carried out to obtain a slurry.

[0107] The slurry was washed and filtered with 3 L of pure water, and the obtained filter cake was dried in a vacuum oven at 80 ° C for 24 h to obtain a manganese iron phosphate precursor (Mn 0.5 Fe 0.5 )PO 4 .

[0108] Example 3

[0109] This embodiment provides a manganese ferrophosphate precursor (Mn 0.6 Fe 0.4 )PO 4 The preparation method comprises the following specific steps:

[0110] Take 500g of ferrophosphorus slag A, 5g of potassium chloride and 10g of sucrose and mix them evenly. Then place them in a fluidized bed. Under the protection of a high-purity nitrogen atmosphere and keeping the vacuum degree below 50torr, heat them to 400℃ and keep them warm for 5h. After the reaction is completed, cool them down naturally to obtain ferrophosphorus slag B.

[0111] The ferrophosphorus slag B was leached in 1500g sulfuric acid solution (40%) at 80°C for 4h, and 1900g ferrophosphorus liquid A was obtained by filtration; 1g sodium fluoride was added and stirred for 10min, and filtered to obtain 1893g ferrophosphorus liquid B; 1g iron powder was added and stirred for 5min and filtered to obtain high-purity ferrophosphorus liquid.

[0112] According to calculation, 407g of wet-process phosphoric acid (85%) and 555.8g of manganese sulfate were added to the above-mentioned high-purity ferrophosphorus liquid to obtain feed liquid A; 380g of ammonia water with a content of 22% and 247g of a mixed solution of hydrogen peroxide with a content of 27.5% were prepared as feed liquid B; in a reactor, 200g of pure water was used as the base liquid and nitrogen was used as the protective atmosphere, and feed liquid A and feed liquid B were added at the same time, the pH value of the system was controlled to be 6.0±0.2, and the temperature was maintained at 60℃±5℃, and coprecipitation was carried out to obtain a slurry.

[0113] The slurry was washed and filtered with 3 L of pure water, and the obtained filter cake was dried in a vacuum oven at 80 ° C for 24 h to obtain a manganese iron phosphate precursor (Mn 0.6 Fe 0.4 )PO 4 .

[0114] Example 4

[0115] This embodiment provides a manganese ferrophosphate precursor (Mn 0.6 Fe 0.4 )PO 4 The preparation method comprises the following specific steps:

[0116] Take 500g of ferrophosphorus slag A, 5g of sodium chloride and 10g of glucose, mix them evenly, place them in a fluidized bed, under the protection of a high-purity nitrogen atmosphere, and keep the vacuum degree below 50torr. Heat it to 400℃ and keep it for 4h. After the reaction is completed, cool it down naturally to obtain ferrophosphorus slag B.

[0117] The ferrophosphorus slag B was leached in 1500g sulfuric acid solution (40%) at 80°C for 4h, and 1900g ferrophosphorus liquid A was obtained by filtration; 10g sodium fluoride was added and stirred for 10min, and filtered to obtain 1887g ferrophosphorus liquid B; 5g iron powder was added and stirred for 5min and filtered to obtain high-purity ferrophosphorus liquid.

[0118] According to calculation, 407g of wet-process phosphoric acid (85%) and 555.08g of manganese sulfate were added to the above-mentioned high-purity ferrophosphorus liquid to obtain feed liquid A; 380g of ammonia water with a content of 22% and 247g of a hydrogen peroxide mixed solution with a content of 27.5% were prepared as feed liquid B; in a reactor, 200g of pure water was used as the base liquid and nitrogen was used as the protective atmosphere, and feed liquid A and feed liquid B were added at the same time, the pH value of the system was controlled to be 6.0±0.2, and the temperature was maintained at 60℃±5℃, and coprecipitation was carried out to obtain a slurry.

[0119] The slurry was washed and filtered with 3 L of pure water, and the filter cake was dried in a vacuum oven at 80 ° C for 24 h to obtain a manganese ferrophosphate precursor (Mn 0.6 Fe 0.4 )PO 4 .

[0120] Example 5

[0121] This embodiment provides an iron phosphate FePO 4 The preparation method comprises the following specific steps:

[0122] Take 500g of ferrophosphorus slag A, 5g of sodium chloride and 10g of glucose, mix them evenly, place them in a fluidized bed, under the protection of a high-purity nitrogen atmosphere, and keep the vacuum degree below 50torr. Heat it to 400℃ and keep it for 4h. After the reaction is completed, cool it down naturally to obtain ferrophosphorus slag B.

[0123] The ferrophosphorus slag B was leached in 1500g sulfuric acid solution (40%) at 80°C for 4h, and 1900g ferrophosphorus liquid A was obtained by filtration; 10g sodium fluoride was added and stirred for 10min, and filtered to obtain 1887g ferrophosphorus liquid B; 5g iron powder was added and stirred for 5min and filtered to obtain high-purity ferrophosphorus liquid.

[0124] According to calculation, 2.5 g of wet-process phosphoric acid (85%) was added to the above-mentioned high-purity ferrophosphorus liquid to obtain liquid A; 150 g of ammonia water with a content of 22% and 180 g of a hydrogen peroxide mixed solution with a content of 27.5% were prepared as liquid B; in a reactor, 200 g of pure water was used as the base liquid, and liquid A and liquid B were added at the same time, the pH value of the system was controlled to 2.0±0.2, the temperature was maintained at 50°C±5°C, and co-precipitation was carried out to obtain a slurry.

[0125] The slurry was washed and filtered with 3L of pure water. The filter cake was dried in an oven at 80°C for 24h and then calcined in a muffle furnace at 560°C for 4h to obtain the iron phosphate precursor FePO 4 .

[0126] Comparative Example 1

[0127] The difference between this comparative example and Example 1 is that no sodium chloride is added, and the other operations are the same.

[0128] Comparative Example 2

[0129] The difference between this comparative example and Example 1 is that sodium fluoride is not added, and the other operations are the same.

[0130] Comparative Example 3

[0131] The difference between this comparative example and Example 1 is that no iron powder is added, and the other operations are the same.

[0132] The element content of the products obtained in the above embodiments and comparative examples was detected by the following detection methods: "Lithium manganese iron phosphate positive electrode material for lithium ion batteries" -J / CIAPS-20220010 and "Anhydrous iron phosphate" T_ATCRR18-2020. The test results are shown in Table 2.

[0133] Table 2:

[0134]

[0135] It can be seen from the data in the table that the ferromanganese phosphate precursors prepared in Examples 1 to 5 and the ferrophosphate prepared in Example 6 all use high-impurity-content and low-cost lithium extraction slag as ferrophosphorus raw materials. Since the processes all contain impurity removal processes, the impurity content in the products is relatively low. Figure 2 It can be seen that the ferromanganese phosphate precursor product prepared by the co-precipitation method has high consistency and a good combination of large and small particles, and the prepared lithium ferromanganese phosphate positive electrode material has good electrochemical properties.

[0136] In Comparative Example 1, no sodium chloride raw material was added. Under high temperature inert gas, Ti in the ferrophosphorus slag could not form TiCl 4 , and thus cannot react with the carbon source to form titanium carbide. The Ti impurities in the system eventually flow into the product, making the Ti content in the ferromanganese phosphate precursor 502.55ppm. No Ti removal process was added to the system, and the Ti content in the product is related to the Ti content in the raw materials. Since the raw materials are by-products of lithium extraction, it is impossible to ensure that the Ti content in each batch of raw materials remains consistent, and thus the Ti content in the product cannot be stabilized, which is not conducive to the stability of the downstream ferromanganese ferrophosphate lithium preparation process.

[0137] In Comparative Example 2, no sodium fluoride raw material was added, and no sodium aluminum fluoride precipitation could be produced in the process. Al impurities in the system could not be removed and directly entered the product, resulting in an Al content of 2570.4ppm in the ferromanganese phosphate precursor, which could not meet the market requirements for ferromanganese phosphate precursors. A large number of literatures show that Al impurities can reduce the discharge capacity and cycle life of positive electrode materials.

[0138] In Comparative Example 3, no iron powder raw material was added, and the iron powder replacement and copper removal could not be completed in the process. The Cu impurities in the system could enter the product, and the Cu content in the ferromanganese phosphate precursor was 80.8ppm, which could not meet the market requirements for ferromanganese phosphate precursors. The copper metal impurities in the positive electrode material will dissolve in the electrolyte during the charging process, and pass through the diaphragm and deposit on the surface of the lithium metal, causing an internal short circuit and thus causing the battery to fail.

[0139] The specific embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0140] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0141] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for removing impurities from ferrophosphorus slag, characterized in that: The following steps are involved: (1) calcining ferrophosphorus slag A and chloride at high temperature under reducing conditions to obtain ferrophosphorus slag B; (2) leaching the ferrophosphorus slag B to obtain ferrophosphorus liquid A and filter residue A; (3) adding fluoride to the above ferrophosphorus liquid A to obtain ferrophosphorus liquid B and filter residue B; (4) Add iron powder to the above ferrophosphorus liquid B, and separate the solid and liquid to obtain high-purity ferrophosphorus liquid.

2. The preparation method according to claim 1, characterized in that: In step (1), the reducing conditions include adding a carbon material; Preferably, the carbon material is one or more of sucrose, glucose, PVA, PEG, carbon nanotubes, and graphene; Preferably, the amount of the carbon material added is 0.01-10% of the mass of the ferrophosphorus slag A.

3. The preparation method according to claim 1, characterized in that: In step (1), the high-temperature calcination is carried out in a high-temperature fluidized bed; Preferably, the high-temperature calcination is performed under an inert atmosphere.

4. The preparation method according to claim 3, characterized in that: In step (1), the high temperature calcination temperature is 400 to 800° C. and the time is 2 to 10 hours; Preferably, the vacuum degree in the high-temperature fluidized bed is not less than 50 torr.

5. The preparation method according to claim 1, characterized in that: In step (1), the chloride is one or more of sodium chloride, potassium chloride, and ferric chloride; Preferably, the amount of chloride added is 0.01-1% of the mass of the ferrophosphorus slag A.

6. The preparation method according to claim 1, characterized in that: In step (3), the fluoride is one or more of sodium fluoride, ammonium fluoride, and potassium fluoride; Preferably, the amount of fluoride added is 0.05-2% of the mass of the ferrophosphide liquid A.

7. The preparation method according to claim 1, characterized in that: In step (4), the amount of iron powder added is 0.05-5% of the mass of ferrophosphorus liquid B.

8. The preparation method according to claim 1, characterized in that: The ferrophosphorus slag A is the ferrophosphorus slag obtained after lithium extraction from scrapped lithium iron phosphate or lithium iron manganese phosphate positive electrode materials.

9. A method for preparing a ferromanganese phosphate precursor from a high-purity ferrophosphorus liquid obtained by the method according to any one of claims 1 to 8, characterized in that: include: Optionally adding an iron source, a phosphorus source, and a manganese source to the high-purity ferrophosphorus liquid to obtain a feed liquid A; A precipitant is added to the above-mentioned liquid A to carry out a co-precipitation reaction, and the solid-liquid is separated and vacuum dried to obtain the manganese ferrophosphate precursor.

10. A method for preparing battery-grade anhydrous ferric phosphate from the high-purity ferrophosphorus liquid obtained by the method according to any one of claims 1 to 8, characterized in that: include: Optionally adding an iron source and a phosphorus source to the high-purity ferrophosphorus liquid to obtain a feed liquid C; Adding a precipitant to the above-mentioned liquid C to carry out a coprecipitation reaction, separating the solid and the liquid, and calcining at a high temperature to obtain the iron phosphate; The ferrophosphorus slag A is the ferrophosphorus slag obtained after lithium extraction from scrapped lithium iron phosphate positive electrode materials.

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