Method for preparing iron phosphate by reducing and roasting crude iron phosphate and application thereof

Abstract

The invention discloses a method for preparing iron phosphate through reduction roasting of crude iron phosphate and application of the method, and the method comprises the following steps: S1, crushing the crude iron phosphate, mixing the crushed crude iron phosphate with a reducing substance, and carrying out reduction roasting to obtain clinker; s2, the clinker is subjected to all-component leaching with low-concentration acid at the normal temperature, and a leached liquid phase part I is collected; s3, taking the liquid phase part I, adjusting the pH value, removing aluminum, and collecting a liquid phase part II after aluminum removal; s4, adding a precipitator into the liquid phase part II to remove impurities, and collecting a liquid phase part III after impurity removal; s5, adding an oxidizing agent into the liquid phase part III, controlling the pH value of the system to be 0.8-2.0, and after the reaction is completed, carrying out solid-liquid separation, washing, drying, calcining and crushing to obtain iron phosphate; the precipitant comprises at least one of amorphous magnesium phosphate and hydroxyl magnesium phosphate. The method solves a plurality of technical problems in the field of iron phosphate dissolution and purification, and has a good application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field related to new energy, and in particular to a method for preparing ferric phosphate by reduction roasting of crude ferric phosphate and application thereof. Background Art

[0002] As the world explores the new energy field more and more deeply, the environmentally friendly and low-carbon power battery industry has ushered in unprecedented development opportunities. Among them, lithium iron phosphate positive electrode materials have been widely used in many key fields such as consumer electronics, medical health, electric vehicles, aerospace, national defense security and large-scale energy storage due to their excellent charge and discharge stability, excellent safety, low self-discharge rate, significant cost-effectiveness and environmental friendliness. However, this wide application has also given rise to the urgent need for the recycling and treatment of waste lithium iron phosphate batteries, which has become an important challenge facing the current industry.

[0003] At present, lithium iron phosphate recovery technology mainly focuses on the selective extraction of lithium elements through oxidative acid leaching processes, while the remaining iron, phosphorus and possible mixed metal impurities such as nickel, manganese, cobalt, copper, zinc, etc. remain in the leached residue. However, due to the insufficient standardization of the recycling market, lithium manganese oxide batteries and lithium iron phosphate batteries are often mixed and broken during the recycling process. In addition, the introduction of new battery technologies such as the use of nickel composite current collectors such as nickel foam makes crude iron phosphate usually contain higher concentrations of impurity elements such as nickel and manganese, which not only affects the purity of iron phosphate, but may also have an adverse effect on subsequent applications. Therefore, how to achieve green and efficient utilization of ferrophosphorus slag, especially to convert it into high-quality iron phosphate that meets market demand, has become a key issue that needs to be solved urgently.

[0004] In response to this situation, a number of patent technologies are dedicated to optimizing the processing flow of iron phosphate slag. For example, patent application document CN115231537A proposes an innovative recovery method, which effectively separates aluminum, phosphorus, iron and other elements through acid-base step-by-step treatment, and finally synthesizes iron phosphate. Patent application document CN115784187A further explores the preparation path of anhydrous iron phosphate, and improves the purity and performance of the product through fine alkali leaching, purification and subsequent treatment steps. However, although these technologies have their own characteristics, they are still limited in the treatment of multi-metal impurities, especially nickel and manganese, and some processes have high costs and complex operations that are not conducive to industrial promotion. Although patent application document CN107902637A has achieved the production of high-purity iron phosphate through multiple impurity removal and the use of special additives, its complex process flow, high energy consumption and high cost limit its application in large-scale production.

[0005] Therefore, developing an iron phosphate re-preparation process that is widely applicable to a variety of impurity systems and has the characteristics of simple operation, economical and efficient is of great significance for promoting the recycling of waste battery resources and promoting the sustainable development of the new energy industry. Summary of the invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a method for preparing ferric phosphate by reducing and roasting crude ferric phosphate, which can be used for a crude ferric phosphate system with many impurities, and the recovery rate of the prepared ferric phosphate is high.

[0007] The present invention also proposes the application of the above method.

[0008] According to one aspect of the present invention, a method for preparing ferric phosphate by reduction roasting of crude ferric phosphate is provided, comprising the following steps:

[0009] S1, crushing the crude ferric phosphate and mixing it with a reducing substance, and reducing roasting it to obtain clinker;

[0010] S2, leaching all components of the clinker at room temperature and with low-concentration acid, and collecting the liquid phase I after leaching;

[0011] S3, adding an antioxidant to the liquid phase part I, mixing it with the pH regulator in parallel, removing aluminum, and collecting the liquid phase part II after aluminum removal;

[0012] S4, adding a precipitant to the liquid phase II to remove impurities, and collecting the liquid phase III after impurities removal;

[0013] S5, adding an oxidant to the liquid phase part III and controlling the pH of the system to be between 0.8 and 2.0, and after the reaction is completed, solid-liquid separation, washing, and drying are performed to obtain ferric phosphate dihydrate;

[0014] S6, calcining and crushing the ferric phosphate dihydrate (preferably, crushing to a particle size of ferric phosphate Dv50 = 1 to 5 μm) to obtain the ferric phosphate;

[0015] Wherein, the precipitant includes at least one of amorphous magnesium phosphate and hydroxy magnesium phosphate, and the pH regulator is a buffer salt.

[0016] According to a preferred embodiment of the present invention, at least the following beneficial effects are achieved: the present invention converts iron phosphate into a more easily handled clinker form by reducing and roasting iron phosphate, which can be completely dissolved at room temperature with only a low-concentration acid solution, greatly simplifies the operation steps, and significantly reduces energy consumption and production costs; the strategy effectively avoids the byproducts and environmental pollution problems that may be generated under high temperature and high pressure environments; the present invention creatively introduces a specific precipitant containing amorphous magnesium phosphate and / or hydroxy magnesium phosphate, which has high selectivity and activity, and can preferentially combine with impurity ions such as nickel, cobalt, and manganese to form a stable precipitate, thereby achieving efficient removal of these impurities. This innovation not only solves the problem of incomplete removal of impurities such as nickel, cobalt, and manganese in traditional methods, which affects the quality of the final product, but also significantly improves the purity of iron phosphate, and the phosphorus iron yield is extremely high, providing solid technical support for the production of high-purity iron phosphate products. In addition, the very small amount of magnesium remaining in the precipitant is doped into the iron phosphate during the precipitation process, so that the lithium iron phosphate prepared using the iron phosphate can directly improve the discharge performance, and at the same time, it can also improve the particle morphology and further optimize its electrochemical performance by indirect means. The scheme of the present invention has extremely high adaptability and flexibility, and can be widely used in the processing of crude iron phosphate raw materials in various complex systems. Whether it is iron phosphate derived from different ore extraction, waste battery recycling or other industrial by-products, it can be effectively converted into high-purity iron phosphate products through the process path of the present invention, which provides strong technical support for the upgrading of related industrial chains and the development of circular economy. In summary, the present invention not only solves multiple technical problems in the field of iron phosphate dissolution and purification, but also demonstrates good economic benefits and social value through its simple, efficient, energy-saving and environmentally friendly characteristics, and has good application prospects.

[0017] Crude iron phosphate is an important intermediate product in the lithium iron phosphate recovery process. It is usually obtained through a series of chemical reactions and physical separation processes after disassembling, crushing, leaching and other treatment steps of waste lithium iron phosphate batteries. In the lithium iron phosphate recovery process, the preparation of crude iron phosphate usually involves the following steps: 1) Waste battery treatment: First, the waste lithium iron phosphate batteries are discharged, disassembled and separated to obtain key materials such as lithium iron phosphate positive electrode sheets. 2) Crushing and screening: The lithium iron phosphate positive electrode sheets are crushed, and the positive electrode materials are separated from impurities such as aluminum foil by physical methods such as screening. 3) Leaching and reaction: Add a leaching agent (such as an acid solution) to the treated lithium iron phosphate waste powder, dissolve the iron phosphate through a chemical reaction, and form a lithium iron leaching solution. Subsequently, by adding a precipitant, adjusting the pH value and other steps, the iron phosphate is precipitated from the solution to form crude iron phosphate.

[0018] In some embodiments of the present invention, the crude ferric phosphate satisfies at least one of the following indicators:

[0019] 1) The mass content of P is above 28%;

[0020] 2) The mass content of Fe is above 22%;

[0021] 3) The moisture content is below 10%;

[0022] 4) Acidity is below 5%;

[0023] 5) The particle size is between 1 and 5 mm.

[0024] In some embodiments of the present invention, the crude ferric phosphate further has at least one of the following indicators:

[0025] The content of Ni is above 0.03%, the content of Co is above 0.0015%, and the content of Mn is above 0.085%. The scheme of the present invention is particularly suitable for crude iron phosphate containing relatively high Ni, Co, and Mn.

[0026] In some embodiments of the present invention, the reduction roasting conditions in step S1 include at least one of the following conditions:

[0027] 1) The calcination temperature is 300°C to 750°C, preferably 400°C to 750°C, more preferably 550°C to 750°C; further preferably 650°C to 750°C;

[0028] 2) The heating rate is 2°C / min to 10°C / min, preferably 5°C / min, 8°C / min or 10°C / min;

[0029] 3) The reducing agent is at least one of glucose, fructose and maltose;

[0030] 4) The mass ratio of the reducing agent to the iron phosphate is 0.2 to 1.2, preferably 0.2, 0.5, 0.8, 1.0 or 1.2.

[0031] In some embodiments of the present invention, the leaching conditions in step S2 include at least one of the following conditions:

[0032] 1) The liquid-to-solid ratio is 3 mL / g to 20 mL / g, preferably 3 mL / g to 10 mL / g, and more preferably 3 mL / g to 5 mL / g;

[0033] 2) The acid is at least one of sulfuric acid, hydrochloric acid and nitric acid;

[0034] 3) The concentration of the acid is 0.1 mol / L to 5 mol / L, preferably 0.1 mol / L to 2 mol / L, more preferably 0.5 mol / L to 2 mol / L, further preferably 0.5 mol / L to 1 mol / L, and further preferably 0.8 mol / L to 1 mol / L;

[0035] 4) the leaching temperature is 25°C to 95°C, preferably 45°C to 95°C, more preferably 75°C to 95°C;

[0036] 5) The leaching time is 0.5h to 10h, preferably 0.5h to 8h, more preferably 3h to 8h, and further preferably 5h to 8h;

[0037] 6) The leaching stirring frequency is 200 r / min to 600 r / min, preferably 300 r / min to 600 r / min.

[0038] In some embodiments of the present invention, the aluminum removal step in step S3 includes at least one of the following conditions:

[0039] 1) The pH is 2.0 to 3.5; preferably 2.5, 2.8, 3.0, 3.2 or 3.5;

[0040] 2) The pH adjuster is at least one of sodium carbonate, ammonium carbonate, potassium carbonate, sodium bicarbonate, ammonium bicarbonate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, trisodium phosphate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, and triammonium phosphate; preferably, the concentration of the pH adjuster is 15-25 g / L; more preferably, the concentration of the pH adjuster is at least one of 15 g / L, 18 g / L, 20 g / L, or 25 g / L;

[0041] 3) The concentration of the antioxidant is 2 g / L to 20 g / L; preferably 2 g / L, 5 g / L, 10 g / L, 15 g / L or 20 g / L;

[0042] 4) The dealuminization reaction temperature is 25°C to 75°C, preferably 25°C, 45°C, 60°C or 75°C;

[0043] 5) The reaction time is 10 min to 150 min, preferably 10 min, 25 min, 30 min, 60 min, 90 min, 120 min or 150 min.

[0044] In some embodiments of the present invention, the antioxidant is at least one of ascorbic acid, citric acid, tartaric acid, vitamin C and its derivatives.

[0045] In some embodiments of the present invention, a pipeline mixer is used for feeding in the aluminum removal process; preferably, the management mixer is a static mixer; more preferably, the management mixer includes at least one of a nozzle type, a vortex type, and a plate type.

[0046] The present invention preferably uses a mild pH buffer system and adopts a multi-channel pipeline mixer for parallel feeding, which can greatly reduce the change of pH concentration gradient in the reaction system, and then can accurately control the window range of pH value of the reaction system, which is beneficial to achieve deep removal of impurities. At the same time, this invention deeply solves the problem that the local pH of the feed liquid is too high due to simple mixed feeding using a strong alkaline system in the industry, resulting in a significant reduction in the yield of the target components iron, phosphorus and lithium.

[0047] In some embodiments of the present invention, the feed flow rate is 2 mL / min to 20 mL / min, preferably 2 mL / min, 5 mL / min, 10 mL / min, 15 mL / min or 20 mL / min.

[0048] In some embodiments of the present invention, the impurity removal condition in step S4 includes at least one of the following conditions:

[0049] 1) The amount of the precipitant added is 0.8 to 1.2 times the theoretical molar amount, preferably 0.8, 0.9, 1.0 or 1.2 times;

[0050] 2) The reaction temperature is 25°C to 75°C, preferably 25°C, 45°C, 60°C or 75°C;

[0051] 3) The pH value is adjusted to 2.0 to 3.2, preferably 2.5, 2.8, 3.0, 3.2 or 3.2;

[0052] 4) The reaction time is 10 min to 150 min, preferably 10 min, 25 min, 30 min, 60 min, 90 min, 120 min or 150 min.

[0053] The introduction of trace amounts of precipitants can preferentially precipitate impurities such as nickel, cobalt, and manganese while ensuring a high yield of iron phosphate.

[0054] In some embodiments of the present invention, the reaction conditions in step S5 include at least one of the following conditions:

[0055] 1) The oxidant is at least one of hydrogen peroxide, ozone, sodium persulfate, and ammonium persulfate;

[0056] 2) The amount of the oxidant added is 1.0 to 2.0 times the theoretical chemical amount;

[0057] 3) The regulator used to control the pH of the system is at least one of sodium hydroxide, ammonia water, phosphoric acid and sulfuric acid;

[0058] 4) The reaction temperature is 25°C to 95°C;

[0059] 5) The reaction time is 1h to 6h.

[0060] In some embodiments of the present invention, the calcination temperature is 500° C. to 650° C.; and / or the calcination time is 2 h to 10 h.

[0061] According to another aspect of the present invention, application of the above method in preparing lithium iron phosphate material or lithium ion battery is proposed.

[0062] According to the application of a preferred embodiment of the present invention, at least the following beneficial effects are achieved: the scheme of the present invention is easy to operate and has high economic value. At the same time, efficient recovery of phosphorus and iron resources can be achieved. At the same time, when the iron phosphate is used to prepare lithium iron phosphate and lithium batteries, they have excellent electrical properties and have good industrial application prospects.

[0063] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0065] Figure 1 This is a process flow chart of preparing ferric phosphate by reduction roasting of crude ferric phosphate in an embodiment of the present invention.

[0066] Figure 2 This is a SEM image of the crude iron phosphate before reduction roasting in Example 1 of the present invention.

[0067] Figure 3 This is a SEM image of the iron phosphate after reduction roasting in Example 1 of the present invention.

[0068] Figure 4 This is the XRD diagram of the iron phosphate prepared in Example 1 of the present invention.

[0069] Figure 5 This is a SEM image of the iron phosphate prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0070] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, other embodiments obtained by technicians in this field without creative work are all within the scope of protection of the present invention. The test methods used in the embodiments are conventional methods unless otherwise specified; the materials, reagents, etc. used, unless otherwise specified, can be reagents and materials obtained from commercial channels. Unless otherwise specified, the same parameter in each embodiment has the same value. The embodiments described below are exemplary and are only used to explain the present invention, and cannot be understood as limitations on the present invention.

[0071] In the description of the present invention, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0072] The "normal temperature" referred to in the present invention refers to 20±10°C, and specifically 25°C in the embodiments.

[0073] The composition information of the crude lithium iron phosphate used in the following examples and comparative examples is shown in Table 1 below:

[0074] Table 1

[0075] element Fe P Al Cu Ca Mg Zn Na Ni Co Mn Wt% 28.95 16.30 0.082 0.006 0.003 0.001 0.001 0.004 0.035 0.002 0.089

[0076] In addition to the above elements, the remaining elements are carbon and oxygen.

[0077] Example 1

[0078] This example provides a method for preparing ferric phosphate by reducing and roasting crude ferric phosphate, such as Figure 1 As shown, the specific process is:

[0079] (1) 100 g of crude iron phosphate (the SEM characterization results are as follows) Figure 2 The mixture was mixed with 40 g glucose, ground into 200 mesh, spread into a magnetic boat, and then heated to 750°C for 5 h, with the heating rate controlled at 5°C / min. After roasting, the mixture was ground again to obtain roasted clinker.

[0080] (2) 36.75 g of sulfuric acid (98.3 wt% H2SO4) was added to 500 mL of pure water to prepare a dilute sulfuric acid solution, and then 50 g of the roasted clinker powder was added to the sulfuric acid solution. The mixture was stirred at room temperature for 3 hours and filtered to obtain a first filtrate.

[0081] After testing, the concentrations of Fe, P, Al, Cu, Ni and Mn in the first filtrate were 28.95 g / L, 16.3 g / L, 0.082 g / L, 0.005 g / L, 0.035 g / L and 0.089 g / L, respectively.

[0082] (3) Take an appropriate amount of sodium carbonate to prepare a pH buffer solution, wherein the sodium carbonate concentration is controlled at 18 g / L; add 5 g / L of ascorbic acid to the first filtrate, and then feed the pH buffer solution (6 mL / min) and the first filtrate (12 mL / min) in parallel (the pH buffer solution has a small volume and a slow flow rate. To ensure that the feeding starts and ends at the same time, in this embodiment, the first filtrate sulfuric acid is 12 ml / min and the buffer flow rate is 6 ml / min. The specific flow rate can be determined according to the volume of the two.) into a pipeline mixer together. The filtrate and the pH buffer are evenly mixed in the nozzle pipeline mixer. By adjusting the concentration of the pH buffer solution, the pH of the solution at the outlet of the pipeline mixer is ensured to be 3.5. The reaction is carried out at room temperature for 10 min, and the second filtrate is obtained by filtration.

[0083] After testing, the aluminum ion concentration in the second filtrate was 0.008 g / L;

[0084] (4) Then, 0.11 g of amorphous magnesium phosphate was added to the second filtrate, the pH value was adjusted to 3.2 at a flow rate of 0.5 mL / min of ammonia water, the reaction was carried out at 65° C. for 60 min for precipitation conversion, and the third filtrate was obtained by filtration.

[0085] After testing, the concentrations of Fe, P, Cu, Ni and Mn in the third filtrate were 28.92 g / L, 16.22 g / L, 0.0002 g / L, 0.0010 g / L and 0.0045 g / L, respectively.

[0086] (5) 120 g of 30% by mass hydrogen peroxide was added dropwise to the third filtrate at room temperature at a flow rate of 3 mL / min, and the mixture was stirred for reaction for 30 min. Sodium hydroxide solution was added at a flow rate of 2 mL / min to adjust the pH to 1.0. The mixture was kept at 92° C. for 2 h, and then the solid-liquid separation was performed. The mixture was washed and dried at 110° C. for 10 h to obtain ferric phosphate dihydrate. The total yield of the entire process was 98.6%.

[0087] ICP testing was performed on the prepared ferric phosphate dihydrate. After testing, the content of impurity magnesium in the prepared ferric phosphate dihydrate was 220 ppm, and the contents of other impurities such as aluminum, copper, sodium, calcium, cobalt, nickel, manganese, and fluorine were all less than 20 ppm.

[0088] The prepared ferric phosphate dihydrate was subjected to SEM characterization test. Figure 3 It can be seen that the iron phosphate prepared in this embodiment has a uniform particle size, good dispersibility, and a "flower-like" morphology.

[0089] (6) The prepared ferric phosphate dihydrate was calcined at 550° C. for 3 h, crushed, ground and sieved, and then analyzed for particle size, specific surface, compaction, and composition.

[0090] After testing, the target product Dv50 is 2.39μm and BET is 10.50m 2 / g, TD is 0.75g / cm 3 , Fe is 31.56%, P is 18.15%, and Fe / P is 0.964. The XRD and SEM characterization test results of the iron phosphate prepared above are as follows: Figure 4 and 5 As shown by Figure 4 It is known that the characteristic peaks of the ferric phosphate product prepared in this embodiment are consistent with those of the standard card; Figure 5 It can be seen that the iron phosphate prepared in this embodiment has a uniform particle size and good dispersibility.

[0091] Example 2

[0092] This example provides a method for preparing ferric phosphate by reducing and roasting crude ferric phosphate, such as Figure 1 As shown, the specific process is:

[0093] (1) 100 g of crude ferric phosphate and 40 g of glucose were mixed evenly, ground into 200 mesh, spread into a magnetic boat, and then heated to 750 ° C and kept for 5 h, with the heating rate controlled at 5 ° C / min. After roasting, the mixture was ground again to obtain roasted clinker.

[0094] (2) 36.75 g of sulfuric acid (98.3 wt% H2SO4) was added to 250 mL of pure water to prepare a dilute sulfuric acid solution, and then 50 g of the roasted clinker powder was added to the sulfuric acid solution. The mixture was stirred at room temperature for 3 hours and filtered to obtain a first filtrate.

[0095] After testing, the concentrations of Fe, P, Al, Cu, Ni and Mn in the first filtrate were 27.80 g / L, 15.46 g / L, 0.06 g / L, 0.0046 g / L, 0.029 g / L and 0.082 g / L, respectively.

[0096] (3) taking an appropriate amount of sodium carbonate to prepare a pH buffer solution, wherein the sodium carbonate concentration is controlled at 20 g / L; adding 7.5 g / L of ascorbic acid to the first filtrate, and then feeding the pH buffer solution and the first filtrate into a pipeline mixer in parallel, wherein the feed liquid and the pH buffer solution are uniformly mixed in the pipeline mixer, and the pH of the solution at the outlet of the pipeline mixer is ensured to be 3.6 by adjusting the concentration of the pH buffer solution, reacting at room temperature for 10 minutes, and filtering to obtain a second filtrate.

[0097] After testing, the aluminum ion concentration in the second filtrate was 0.005 g / L;

[0098] (4) Then, 0.12 g of amorphous magnesium phosphate was added to the second filtrate, the pH value was adjusted to 3.2 at a flow rate of 0.5 mL / min of ammonia water, the reaction was carried out at 65° C. for 60 min for precipitation conversion, and the third filtrate was obtained by filtration.

[0099] After testing, the concentrations of Fe, P, Cu, Ni and Mn in the third filtrate were 27.41 g / L, 15.39 g / L, 0.0002 g / L, 0.0010 g / L and 0.0036 g / L, respectively.

[0100] (5) 120 g of 30% by mass hydrogen peroxide was added dropwise to the third filtrate at room temperature at a flow rate of 3 mL / min, and the mixture was stirred for reaction for 30 min. Sodium hydroxide solution was added at a flow rate of 2 mL / min to adjust the pH to 1.0. The mixture was kept at 92° C. for 2 h, and then the solid-liquid separation was performed. The mixture was washed and dried at 110° C. for 10 h to obtain ferric phosphate dihydrate with a total yield of 97.2%.

[0101] ICP detection was performed on the prepared ferric phosphate dihydrate. After testing, the content of impurity magnesium in the prepared ferric phosphate dihydrate was 240 ppm, and the contents of other impurities such as aluminum, copper, sodium, calcium, cobalt, nickel, manganese, and fluorine were all less than 30 ppm.

[0102] (6) The prepared ferric phosphate dihydrate was calcined at 550°C for 3h, crushed, ground and sieved, and then analyzed for particle size, specific surface, vibration, and composition. The target product Dv50 was 2.57μm and BET was 9.85m 2 / g, TD is 0.69g / cm 3 , Fe is 29.05%, P is 16.61%, and Fe / P is 0.969.

[0103] The prepared ferric phosphate dihydrate and ferric phosphate were subjected to XRD and SEM characterization tests, and the characterization results were basically the same as those in Example 1, which will not be repeated here.

[0104] Example 3

[0105] This example provides a method for preparing ferric phosphate by reducing and roasting crude ferric phosphate, such as Figure 1 As shown, the specific process is:

[0106] (1) 100 g of crude ferric phosphate and 100 g of glucose were mixed evenly, ground into 200 mesh, spread into a magnetic boat, and then heated to 750 ° C and kept for 5 h, with the heating rate controlled at 5 ° C / min. After roasting, they were ground again to obtain roasted clinker.

[0107] (2) 50 g of sulfuric acid (98.3 wt% H2SO4) was added to 500 mL of pure water to prepare a dilute sulfuric acid solution, and then 50 g of the roasted clinker solid powder was added to the sulfuric acid solution. The mixture was stirred at room temperature for 3 hours and filtered to obtain a first filtrate.

[0108] After testing, the concentrations of Fe, P, Al, Cu, Ni and Mn in the first filtrate were 28.95 g / L, 16.30 g / L, 0.080 g / L, 0.005 g / L, 0.032 g / L and 0.086 g / L, respectively.

[0109] (3) taking an appropriate amount of sodium carbonate to prepare a pH buffer solution, wherein the sodium carbonate concentration is controlled at 25 g / L; adding 10 g / L of ascorbic acid to the first filtrate, and then feeding the pH buffer solution and the first filtrate into a pipeline mixer in parallel, wherein the feed liquid and the pH buffer solution are uniformly mixed in the pipeline mixer, and the pH of the solution at the outlet of the pipeline mixer is ensured to be 3.45 by adjusting the concentration of the pH buffer solution, reacting at room temperature for 10 minutes, and filtering to obtain a second filtrate.

[0110] After testing, the aluminum ion concentration in the second filtrate was 0.002 g / L;

[0111] (4) Then, 0.10 g of amorphous magnesium phosphate was added to the second filtrate, the pH value was adjusted to 3.2 at a flow rate of 0.5 mL / min of ammonia water, the reaction was carried out at 65° C. for 60 min for precipitation conversion, and the third filtrate was obtained by filtration.

[0112] After testing, the concentrations of Fe, P, Cu, Ni and Mn in the third filtrate were 28.86 g / L, 15.95 g / L, 0.0001 g / L, 0.0010 g / L and 0.0040 g / L, respectively.

[0113] (5) 120 g of 30% by mass hydrogen peroxide was added dropwise to the third filtrate at room temperature at a flow rate of 3 mL / min, and the mixture was stirred for reaction for 30 min. Sodium hydroxide solution was added at a flow rate of 2 mL / min to adjust the pH to 1.0. The mixture was kept at 92° C. for 2 h, and then the solid-liquid separation was performed. The mixture was washed and dried at 110° C. for 10 h to obtain ferric phosphate dihydrate with a yield of 98.4%.

[0114] ICP testing was performed on the prepared ferric phosphate dihydrate. After testing, the content of impurity magnesium in the prepared ferric phosphate dihydrate was 200 ppm, and the contents of other impurities such as aluminum, copper, sodium, calcium, cobalt, nickel, manganese, and fluorine were all less than 20 ppm.

[0115] (6) The prepared ferric phosphate dihydrate was calcined at 550°C for 3h, crushed, ground and sieved, and then analyzed for particle size, specific surface, vibration, and composition. The target product Dv50 was 2.37μm and BET was 9.63m 2 / g, TD is 0.65g / cm 3 , Fe is 29.12%, P is 16.63%, and Fe / P is 0.971.

[0116] The prepared ferric phosphate dihydrate was subjected to XRD and SEM characterization tests, and the characterization results were basically the same as those in Example 1, which will not be repeated here.

[0117] Comparative Example 1

[0118] This example provides a method for preparing ferric phosphate from crude ferric phosphate, which differs from Example 1 in that no reduction roasting is performed.

[0119] Reaction results: Under the same experimental conditions, it was found that iron phosphate was basically insoluble. The leaching results further proved the advantages of reduction roasting. It can be seen from the electron microscope that the pore size of iron phosphate increased after reduction roasting, the structure "collapsed" seriously, and the reaction kinetics of the leaching agent and iron phosphate was increased, so that after reduction roasting of iron phosphate, only extremely low concentration of sulfuric acid can be used to dissolve iron phosphate.

[0120] Comparative Example 2

[0121] This example provides a method for preparing ferric phosphate from crude ferric phosphate, which differs from Example 1 in that the operation is basically the same as the first filtrate preparation step in Example 1, without reducing roasting, the sulfuric acid concentration is 5 mol / L, and the stirring reaction time is 12 h.

[0122] Reaction results: There is still a small amount of iron phosphate that has not dissolved. After the reaction is completed, the remaining leaching residue is 76.72g (water content 45.32%), equivalent to 41.95g on a dry basis, indicating that it is difficult to dissolve all the iron phosphate in concentrated acid for a long time without reducing roasting.

[0123] Comparative Example 3

[0124] This example provides a method for preparing ferric phosphate from crude ferric phosphate, which differs from Example 1 in that the operation is basically the same as the first filtrate preparation step in Example 1, without reduction roasting, and the leaching temperature is 92°C, and the stirring reaction time is 12 hours.

[0125] Reaction results: most of the iron phosphate is still undissolved. After the reaction is completed, the leaching residue remains 82.51g (water content 51.82%), equivalent to 39.75g on a dry basis, indicating that it is still difficult to dissolve all the iron phosphate by increasing the leaching temperature under low acid conditions without reducing roasting.

[0126] Comparative Example 4

[0127] This example provides a method for preparing ferric phosphate from crude ferric phosphate, which differs from Example 1 in that the operation is basically the same as the first filtrate preparation step in Example 1, without reduction roasting, and the leaching time is 12 hours.

[0128] Reaction results: Most of the iron phosphate was still undissolved. After the reaction was completed, 91.77 g (48.95% water content) of leached residue remained, equivalent to 46.85 g on a dry basis, indicating that it was still difficult to dissolve all the crude iron phosphate by increasing the leaching time under low-acid conditions without reducing roasting.

[0129] Comparative Example 5

[0130] This example provides a method for preparing ferric phosphate from crude ferric phosphate, which differs from Example 1 in that the operation is basically the same as the first filtrate preparation step in Example 1, without reduction roasting, the leaching temperature is 92°C, the time is 6h, and the sulfuric acid concentration is 7.5mol / L.

[0131] Reaction results: only a small part of the iron phosphate was not dissolved. After the reaction was completed, 4.99g of leached residue remained (water content 46.27%), equivalent to 2.68g on a dry basis, indicating that crude iron phosphate can be almost completely dissolved only by combining high temperature, high concentration acid, and long time leaching without reducing roasting.

[0132] Comparative Example 6

[0133] This example provides a method for preparing ferric phosphate by reduction roasting of crude ferric phosphate, which differs from Example 1 in that the pH regulating solution is replaced by a sodium hydroxide solution.

[0134] Reaction phenomenon: During the parallel flow feeding process, "blocking" occurs when the parallel flows converge, that is, the two mix violently and precipitation occurs immediately, which is not conducive to the experiment.

[0135] Test results: When sodium hydroxide was used to adjust the pH, the loss rate of the target elements iron and phosphorus reached 25.62%.

[0136] Comparative Example 7

[0137] This example provides a method for preparing ferric phosphate by reduction roasting of crude ferric phosphate, which differs from Example 1 in that no pipeline mixer is used for co-flow feeding, and the two are directly mixed.

[0138] Reaction phenomenon: The precipitation rate is fast. Compared with pipeline mixing and co-flow feeding, this implementation method will also cause the pH to be locally too alkaline and the precipitation reaction to be violent.

[0139] Test results: The loss rate of target elements iron and phosphorus is 20.85%.

[0140] Comparative Example 8

[0141] This comparative example provides a method for preparing ferric phosphate by reduction roasting of crude ferric phosphate. The operation is basically the same as the second filtrate preparation process in Example 1, with the only difference being that no antioxidant is added to the first filtrate.

[0142] Reaction phenomenon: The precipitation rate is fast and the precipitation reaction is violent.

[0143] Test results: The loss rate of target elements iron and phosphorus is 12.51%.

[0144] Comparative Example 9

[0145] This comparative example provides a method for preparing ferric phosphate by reduction roasting of crude ferric phosphate, which differs from Example 1 in that amorphous magnesium phosphate is replaced by an equal amount of calcium phosphate.

[0146] The final test found that the content of metal ions such as sodium, aluminum, copper, calcium, cobalt, nickel, and manganese in the obtained ferric phosphate dihydrate was between 100 and 350 ppm, the content of magnesium was 87 ppm, and the content of fluorine was below 20 ppm. The loss rate of the target elements iron and phosphorus was about 8.47%.

[0147] The present invention relates to a method for preparing ferric phosphate by reduction roasting of crude ferric phosphate. In the reduction roasting and leaching stages, according to the test results in Examples 1 to 3 and Comparative Examples 1 to 5, the clinker after reduction roasting can completely dissolve the ferric phosphate with only low concentration of dilute sulfuric acid (0.75 mol / L) at room temperature, while the ferric phosphate that has not been reduced roasted can be completely dissolved under high temperature, high concentration and long time conditions. According to the SEM characterization results, it can be seen that the morphology of the crude ferric phosphate before and after reduction roasting has changed significantly, that is, the surface of the ferric phosphate after reduction roasting is relatively rough, and the pores increase, which is conducive to the infiltration and diffusion reaction of sulfuric acid with its structure, increases the kinetic reaction, and makes the reaction faster and more thorough.

[0148] In the aluminum removal process stage, the present invention abandons the methods such as aluminum removal by complexation of sodium fluoride and other complexing agents, wherein the aluminum removal by sodium fluoride will cause a substantial loss of lithium, and the amount of sodium fluoride should not be controlled at the same time, and the addition of too much sodium fluoride will cause economic waste, and the fluorine in the aluminum removal liquid exceeds the standard, which will increase the difficulty of subsequent treatment of fluorine-containing wastewater; other complexing methods for aluminum removal will cause impurity ions to form complex macromolecules with complexing agents and exist in the solution, which is not easy to separate from the target component. The present invention selects a mild sodium carbonate solution as a pH buffer solution, and selects a pipeline mixer for feeding, so that the feed liquid and the pH buffer solution are divided into small units and then fully mixed, and the change of pH is more balanced than the direct mixing method of a strong base, so that the pH value can be more accurately regulated to reduce the loss of the target component to a minimum value, while promoting the removal of the impurity component to a maximum.

[0149] In the process of removing impurities such as nickel, cobalt, and manganese, due to the chaotic management of the waste battery market and the upgrading of other technical means, metal components such as nickel and manganese will be introduced into lithium iron phosphate batteries, making the removal of nickel, cobalt, and manganese one of the biggest challenges for the full-component recovery of lithium iron phosphate battery waste. The present invention introduces a trace amount of magnesium phosphate precipitant and cleverly utilizes the precipitation conversion principle of the same type of precipitant. Under suitable pH and other conditions, by controlling the amount of magnesium phosphate added, impurities such as nickel and manganese in the solution are precipitated preferentially with iron phosphate.

[0150] Finally, in the stage of synthesizing iron phosphate, a one-step method is used to directly synthesize dihydrate iron phosphate, and the concentrations of other impurity elements in the system except magnesium are within the standard range of impurity content of battery-grade iron phosphate. In the present invention, the iron phosphate prepared is characterized by ICP, SEM, XRD, TD, BET, etc., and it is known that the quality of the iron phosphate prepared by the present invention has reached the requirements of iron phosphate, and the economic efficiency is very considerable.

[0151] In the scheme of the present invention, the impurity magnesium can significantly improve the electrical performance of lithium iron phosphate after being doped with iron phosphate. To verify this effect, the above iron phosphate is prepared into lithium iron phosphate, and its discharge capacity at 0.1C is tested. The specific operation process is as follows:

[0152] The iron phosphate prepared in the above Examples 1 to 3 and Comparative Example 9 was sand-milled and spray-granulated with lithium carbonate and glucose in a molar ratio of 1:1:0.012 to obtain a mixture; wherein the solid content of the sand-milling was 30wt%, the rotation speed of the sand-milling was 1500r / min, and the sand-milling time was 3h.

[0153] The lithium iron phosphate mixture was sintered at 700° C. for 6 h in a muffle furnace under nitrogen protection to obtain lithium iron phosphate. The lithium iron phosphate material was made into a button battery, and its first discharge performance at 0.1C was tested as shown in Table 2 below.

[0154] Table 2

[0155] First discharge capacity Example 1 Example 2 Example 3 Comparative Example 9 Sample (mAh / g) 167.8 168.9 166.2 135.3

[0156] As can be seen from the above table, the magnesium-containing precipitant used in the scheme of the present invention not only ideally removes impurities other than magnesium in iron phosphate, but also significantly improves the electrochemical performance of lithium iron phosphate due to the presence of magnesium. The discharge capacity at 0.1C increases with the increase of the residual amount of magnesium. When a precipitant without magnesium is used, although the impurity removal effect can also be achieved, the impurity removal effect is far weaker than that of the precipitant of the embodiment of the present invention, and the electrochemical performance of the lithium iron phosphate obtained is significantly lower than that of the embodiment of the present invention.

[0157] It is speculated that the reason for the above phenomenon is that lithium iron phosphate containing a small amount of magnesium is conducive to lithium insertion during the discharge process, thereby improving its discharge performance. The magnesium-doped lithium iron phosphate sample shows a higher discharge capacity under 0.1C discharge conditions, indicating that magnesium doping promotes the use of sample capacity; at the same time, magnesium doping may also change the internal structure of the material, improve electronic ion conductivity, etc., indirectly improving the electrochemical properties of lithium iron phosphate.

[0158] The embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A method for preparing ferric phosphate by reducing and roasting crude ferric phosphate, characterized in that: The steps include: S1, crushing the crude ferric phosphate and mixing it with a reducing substance, and reducing roasting it to obtain clinker; S2, leaching all components of the clinker at room temperature and with low-concentration acid, and collecting the liquid phase I after leaching; S3, adding an antioxidant to the liquid phase part I, mixing it with the pH regulator in parallel, removing aluminum, and collecting the liquid phase part II after aluminum removal; S4, adding a precipitant to the liquid phase II to remove impurities, and collecting the liquid phase III after impurities removal; S5, adding an oxidant to the liquid phase part III and controlling the pH of the system to be between 0.8 and 2.0, and after the reaction is completed, solid-liquid separation, washing, and drying are performed to obtain ferric phosphate dihydrate; S6, calcining and crushing the ferric phosphate dihydrate to obtain the ferric phosphate; Wherein, the precipitant includes at least one of amorphous magnesium phosphate and hydroxy magnesium phosphate, and the pH regulator is a buffer salt.

2. The method for preparing ferric phosphate by reduction roasting of crude ferric phosphate according to claim 1, characterized in that: The reduction roasting conditions in step S1 include at least one of the following conditions: 1) The calcination temperature is 300°C to 750°C; 2) The heating rate is 2℃ / min~10℃ / min; 3) The reducing agent is at least one of glucose, fructose and maltose; 4) The mass ratio of the reducing agent to the iron phosphate is 0.2 to 1.

2.

3. The method for preparing ferric phosphate by reduction roasting of crude ferric phosphate according to claim 1, characterized in that: The leaching conditions in step S2 include at least one of the following conditions: 1) Liquid-to-solid ratio is 3mL / g~20mL / g; 2) The acid is at least one of sulfuric acid, hydrochloric acid and nitric acid; 3) The concentration of the acid is 0.1 mol / L to 5 mol / L; 4) The leaching temperature is 25°C to 95°C; 5) Leaching time is 0.5h~10h; 6) The leaching stirring frequency is 200r / min~600r / min.

4. The method for preparing ferric phosphate by reduction roasting of crude ferric phosphate according to claim 1, characterized in that: The aluminum removal step in step S3 includes at least one of the following conditions: 1) the pH value is 2.0 to 3.5; 2) The pH regulator is at least one of sodium carbonate, ammonium carbonate, potassium carbonate, sodium bicarbonate, ammonium bicarbonate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, trisodium phosphate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, and triammonium phosphate; preferably, the concentration of the pH regulator is 15-25 g / L; 3) The concentration of the antioxidant is 2 g / L to 20 g / L; 4) The dealuminization reaction temperature is 25°C to 75°C; 5) The reaction time is 10 min to 150 min.

5. The method for preparing ferric phosphate by reduction roasting of crude ferric phosphate according to claim 1 or 5, characterized in that: The parallel flow feeding adopts a pipeline mixer for feeding; preferably, the management mixer is a static mixer; more preferably, during the parallel flow feeding, the flow rate of each flow path is 2mL / min to 20mL / min.

6. The method for preparing ferric phosphate by reduction roasting of crude ferric phosphate according to claim 1, characterized in that: The impurity removal conditions in step S4 include at least one of the following conditions: 1) The amount of precipitant added is 0.8 to 1.2 times the theoretical molar amount; 2) The reaction temperature is 25°C to 75°C; 3) The pH value is adjusted to 2.0-3.2; 4) The reaction time is 10 min to 150 min.

7. The method for preparing ferric phosphate by reduction roasting of crude ferric phosphate according to claim 1, characterized in that: The reaction conditions in step S5 include at least one of the following conditions: 1) The oxidant is at least one of hydrogen peroxide, ozone, sodium persulfate, and ammonium persulfate; 2) The amount of the oxidant added is 1.0 to 2.0 times the theoretical chemical amount; 3) The regulator used to control the pH of the system is at least one of sodium hydroxide, ammonia water, phosphoric acid and sulfuric acid; 4) The reaction temperature is 25°C to 95°C; 5) The reaction time is 1h to 6h.

8. The method for preparing ferric phosphate by reduction roasting of crude ferric phosphate according to claim 1, characterized in that: The reaction conditions in step S5 include at least one of the following conditions: 1) The washing standard is that the conductivity of the washing liquid is 300μS / cm; 2) The drying temperature is 100℃~150℃, and the drying time is 8h~12h.

9. The method for preparing ferric phosphate by reduction roasting of crude ferric phosphate according to any one of claims 1 or 6-8, characterized in that: The calcination temperature is 500° C. to 650° C.; and / or the calcination time is 2 h to 10 h.

10. Use of the method according to any one of claims 1 to 9 in preparing lithium iron phosphate materials or lithium ion batteries.

Images