Recycling treatment method of lithium iron phosphate waste

Abstract

The invention relates to a resourceful treatment method of lithium iron phosphate waste powder, which comprises the following steps: carrying out acid leaching on the lithium iron phosphate waste powder, and carrying out solid-liquid separation to obtain leaching residues and a leaching solution; reducing the leachate, and performing solid-liquid separation to obtain a reduced liquid and a slag phase; mixing the reduced solution with alkaline residues and an alkaline solution to obtain a mixed solution; aging the mixed solution, and carrying out solid-liquid separation to obtain alkali-regulated solution and alkali residues; and carrying out oxidation and iron precipitation treatment on the alkali-adjusted solution, and carrying out solid-liquid separation to obtain iron phosphate dihydrate and a lithium-rich solution. According to the resourceful treatment method, high-added-value recycling of core elements such as Li, Fe, P and C in the lithium iron phosphate waste powder can be achieved, and battery-grade lithium carbonate and battery-grade iron phosphate with high added values are obtained; moreover, the alkali residues generated in the midway can be used for alkali adjustment, the waste residue amount and the alkali consumption can be effectively reduced, expensive reagents, equipment investment and strict operation requirements are not needed, the comprehensive economic benefits are high, and the industrialization feasibility is high.

Description

Technical Field

[0001] The invention relates to a resource treatment method for lithium iron phosphate waste, in particular to a method for preparing battery-grade iron phosphate from waste lithium iron phosphate batteries, and belongs to the technical field of waste lithium iron phosphate battery recycling. Background Art

[0002] In the context of the explosive growth of the new energy vehicle industry, the rational utilization and recycling of waste lithium iron phosphate to achieve the recycling of lithium battery resources is a current hot research direction. Currently, many process technologies have been used to realize the extraction and leaching of lithium from waste lithium iron phosphate materials, but the industrialization of waste iron phosphate residue recycling is still blank. As a result, a large amount of solid iron-phosphorus slag waste has been accumulated after lithium extraction. How to recycle and utilize lithium resources based on the full wet process and wet equipment with mature industrial technology, low-cost, low-pollution, simple and easy process to achieve the recycling of iron-phosphorus elements and convert them into battery-grade lithium iron phosphate with higher added value is a technical difficulty that needs to be solved and broken through.

[0003] Chinese invention patent application CN202310579182.1 uses alkaline leaching to treat iron phosphate waste residue. Subsequently, multiple process steps and equipment such as resin impurity removal, sulfuric acid dissolution, and low-temperature freezing crystallization are required to achieve phosphorus recovery, while iron needs to be recovered in the form of iron powder after high-temperature roasting and magnetic separation; resin impurity removal will result in a high amount of wastewater, and the use of low-temperature freezing and pyro-roasting will result in high energy consumption of the process, and the process requires the use of wet reactors, ion exchange resin columns, freezing crystallization equipment, roasting furnaces, magnetic separators and other equipment, with lengthy steps, complex processes and low industrial feasibility.

[0004] In the Chinese invention patent application CN202310285978.6, the prepared β-cyclodextrin / NaOH inclusion compound is used as a selective precipitant to selectively remove the main impurity elements Al and Cu. The process flow of this method is relatively short, but the preparation of the β-cyclodextrin / NaOH inclusion compound requires spray drying facilities, and the impurity removal process requires nitrogen protection throughout the process. The reagent cost, preparation cost, equipment investment and operation requirements are high, and the final recovery of the prepared Li 2 CO 3 and FePO 4 The purities are 98.13% and 99.87% respectively, which cannot meet the relevant standards of battery-grade products and have low practical application value.

[0005] Chinese invention patent application CN202310159784.1 obtains high-purity lithium iron phosphate materials through pre-calcination and organic washing, then recovers lithium elements through vacuum reduction metallurgy, and then recovers the iron phosphate in combination with hydrometallurgical means to prepare battery-grade iron phosphate. This patent is prone to failure when faced with doped lithium iron phosphate waste due to the lack of effective impurity removal methods, and thus battery-grade iron phosphate products cannot be obtained. In addition, the cost of pyrometallurgical pretreatment and vacuum metallurgy is relatively high, and the use of organic systems results in poor overall environmental friendliness of the process.

[0006] Chinese invention patent application CN116177510A discloses a method for preparing cell-grade iron phosphate using waste lithium iron phosphate battery positive electrode powder, which selectively extracts lithium elements by weak acid oxidation acid leaching, and completely extracts iron and phosphorus elements by strong acid leaching. Subsequently, hydrazine hydrate, glucose, formaldehyde and other reducing agents are used to completely reduce the trivalent iron in the leachate, and then the pH is adjusted and a precipitant is added to remove impurities, and finally a clean iron-phosphorus solution is obtained to prepare iron phosphate. This method requires the use of an excess of oxidant in the lithium leaching step to achieve Fe 2+ Complete oxidation promotes the complete leaching of lithium, and accordingly, an excess of reducing agent is required in the impurity removal step to make Fe 3+ Complete reduction, the superposition of oxidants and reductants makes the cost of impurity removal high, and the introduction of organic reductants in the solution will affect the morphology and COD content of the synthesized iron phosphate, affecting product quality and increasing the difficulty of wastewater treatment. In the actual operation of impurity removal by adjusting the pH alone, due to the inevitable local concentration difference during pH adjustment, there will often be significant co-precipitation and a large amount of iron and phosphorus loss, while impurities cannot be fully removed. This is one of the reasons why the process needs to control the pH above 3.5 to achieve hydrolysis and impurity removal to finally obtain battery-grade iron phosphate.

[0007] Chinese invention patent application CN 116477591 A discloses a method for comprehensive utilization of waste lithium iron phosphate positive electrode materials. The process uses two-stage sulfuric acid leaching, and the leaching solution removes copper and aluminum before and after precipitation to obtain an iron phosphate product. After precipitation, the lithium solution is precipitated with sodium carbonate to prepare a lithium carbonate product. The process uses conventional methods to adjust pH to remove impurities, and aluminum is precipitated and removed in the form of aluminum phosphate. On the one hand, the pH adjustment process is difficult to control, which easily causes the entrainment loss of Fe, P, and Li elements. On the other hand, the aluminum slag in the form of aluminum phosphate cannot be recycled and a large amount of phosphorus is lost. A large amount of pH adjuster must be consumed to achieve neutralization precipitation and aluminum removal, and a high-purity iron phosphate product is not obtained, and the process added value is low. Summary of the invention

[0008] In view of the deficiencies of the prior art, the object of the present invention is to provide a resource treatment method for lithium iron phosphate waste, so as to better realize the recovery of Fe, P, Li and other elements in the lithium iron phosphate waste.

[0009] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0010] The resource treatment method of lithium iron phosphate waste comprises the following steps:

[0011] S1. After acid leaching the lithium iron phosphate waste to be treated, solid-liquid separation is performed to obtain leached residue and a leaching solution rich in iron, phosphorus and lithium; preferably, the lithium iron phosphate waste is in powder form;

[0012] S2, reducing the leaching solution obtained in S1, separating the solid and the liquid, and obtaining a reduced liquid and a slag phase;

[0013] S3, mixing the reduced liquid obtained in S2 with alkaline residue and alkaline solution to obtain a mixed liquid with a pH value of 2-4;

[0014] S4, aging the mixed solution obtained in S3, and then separating the solid and the liquid to obtain a alkali-adjusted liquid and alkali residue;

[0015] The alkali slag is partially or completely returned to step S3, and the mass ratio of aluminum to iron in the alkali slag returned to step S3 is less than 0.3, preferably less than 0.26, more preferably less than 0.22, and even more preferably less than 0.14; accordingly, the alkali slag that does not meet the requirements is discharged; generally speaking, the more times the alkali slag is recycled, the higher the mass ratio of aluminum to iron is. Preferably, the alkali slag is recycled 3-6 times before being discharged;

[0016] S5. After the alkali-adjusted liquid obtained in S4 is subjected to iron precipitation treatment, solid-liquid separation is performed to obtain ferric phosphate dihydrate and a lithium-rich solution.

[0017] In this way, through acidic leaching, the iron, phosphorus, and lithium in the lithium iron phosphate waste powder enter the leachate, and impurity ions such as aluminum and copper will inevitably enter the leachate; through reduction, not only can the copper ions in the leachate be reduced and precipitated, but also a small amount of trivalent iron in the system can be reduced to divalent iron, avoiding the loss of trivalent iron in the form of ferrous phosphate in the subsequent step. Premature precipitation and loss; then, by mixing the reduced liquid with the alkaline solution and the alkaline slag returned from step S4, the alkaline slag can be used to consume the acid remaining in the reduced liquid, thereby effectively reducing the consumption of the added alkaline solution, and allowing the divalent iron and the entrained phosphorus-containing substances in the alkaline slag to return to the solution, effectively reducing the loss of Fe and P elements in the aluminum removal process; at the same time, the alkaline slag is used to adjust the alkali, the reaction is relatively mild, and local pH imbalance can be avoided. By controlling the pH value and aging of the mixed solution, aluminum can be removed in the form of Al(OH) 3In the form of precipitation, aluminum can be removed by more than 99%, and a small part of divalent iron is precipitated as Fe(OH) 2 The alkali residue is co-precipitated in the form of , and the organic impurities in the adsorbed solution are entrained to form an alkaline residue with good filtering performance; by returning part or all of the alkaline residue with an aluminum-iron mass ratio of less than 0.3 to step S3, it can not only meet the need for alkali adjustment, but also ensure a good dealumination effect, and effectively reduce the loss of iron entrainment, and obtain a high-purity alkali-adjusted liquid. After subsequent iron precipitation treatment, solid-liquid separation can be performed to obtain dihydrated iron phosphate and lithium-rich solution, realizing the recovery and enrichment of valuable elements such as Fe, P and Li, and having significant industrial promotion and application value; by controlling the aluminum-iron mass ratio of the returned alkaline residue, it can not only meet the need for alkali adjustment, but also avoid the aluminum content of the returned alkaline residue being too high, resulting in an unsatisfactory aluminum removal effect. The dihydrated iron phosphate can be further treated by general washing, dehydration and the like to prepare high-purity iron phosphate; after the lithium-rich solution is purified, it can be further prepared into lithium salt products such as lithium carbonate by a general lithium precipitation method.

[0018] Generally, the leached residue obtained in S1 is crude graphite containing organic matter, which can be sold as a by-product; it can also be further purified to prepare high-purity graphite for sale.

[0019] Further, in S3, the reduced liquid obtained in S2 is mixed with the alkali residue, and an alkali solution is added, so that the pH value of the mixed liquid is increased to 2-4 at a rate of ≤0.4 / min, preferably, the pH value of the mixed liquid is increased to 2.8-3.2 at a rate of ≤0.4 / min, and more preferably, the pH value of the mixed liquid is increased to 2.9-3.1 at a rate of ≤0.4 / min. Preferably, the alkali solution is uniformly added to the reduced liquid, and the stirring rate of the system is controlled to be>300rpm, and further to be 350-450rpm.

[0020] Further, in S3, the concentration of the alkali in the alkali solution is ≤1 mol / L, preferably 0.2-0.8 mol / L; preferably, the alkali solution contains NH 3 ·H 2 O, NaOH, KOH or more; preferably, the alkaline solution is NH 3 ·H 2 O mixed alkaline solution with NaOH and / or KOH.

[0021] Furthermore, in S4, the aging temperature is 40-60°C, preferably 45-55°C; the aging time is 20-40 min, preferably 25-35 min.

[0022] Furthermore, in S1, when acid leaching is performed, the acid used is one or more of sulfuric acid, hydrochloric acid, and phosphoric acid.

[0023] Furthermore, in S1, when acid leaching is performed, the lithium iron phosphate waste powder is first mixed with water to obtain a slurry; and then the slurry is mixed with an acid solution for leaching.

[0024] Preferably, during mixing and slurrying, the mass ratio of lithium iron phosphate waste powder to water is 5:1-1:2, more preferably 3-4:1.

[0025] Preferably, the total molar amount of Li and Fe in the slurry is equal to the total molar amount of H + The molar ratio of is 1:1-1.5, more preferably 1:1.2-1.3.

[0026] Preferably, after the slurry is mixed with the acid solution, the initial liquid-to-solid ratio is 3-10:1, more preferably 4-8:1.

[0027] Preferably, the acid solution contains one or more of sulfuric acid, hydrochloric acid and phosphoric acid.

[0028] Preferably, the leaching is carried out with stirring at 20-70°C for 0.2-3h, more preferably, the leaching is carried out with stirring at 40-60°C for 20-40min.

[0029] Further, in S2, the leaching solution and the reducing agent are mixed for reduction, wherein the reducing agent comprises one or more of iron powder, zinc powder and magnesium powder; preferably, the amount of the reducing agent added is the amount of Fe 3+ and Cu 2+ 1-1.2 times the total molar amount of; preferably, the leachate and the reducing agent are mixed, stirred for 0.5-2h, and then the solid-liquid is separated.

[0030] Furthermore, the reducing agent is iron powder; after S2, the slag phase is subjected to magnetic separation to obtain iron powder and copper element, and preferably, the iron powder is returned to S2. Using iron powder as a reducing agent not only has a price advantage, but also facilitates the separation of the unreacted reducing agent and the solution, and the iron remaining in the slag phase and the copper element obtained by reduction can be separated by simple magnetic separation, and the separated iron powder can be returned to S2 as a reducing agent for repeated use.

[0031] Further, in S5, the alkali-adjusted solution and the oxidant are mixed or contacted for reaction, and a pH adjuster is added to maintain the pH of the system at 1.5-2.5. 2+ When the concentration is less than 0.01 g / L (preferably 0.001-0.008 g / L), solid-liquid separation is performed to obtain ferric phosphate dihydrate and a lithium-rich solution;

[0032] Among them, the amount of the oxidant is 1-1.2 times the theoretical equivalent, preferably 1.1 times; the oxidant includes at least one of hydrogen peroxide, thiosulfate, ozone, peroxyacid salt, oxygen, and air; the pH adjuster includes at least one of sodium hydroxide, potassium hydroxide, ammonia water, and ferrous hydroxide.

[0033] Further, after S5, the dihydrated iron phosphate obtained in S5 is washed with acidic washing water for more than 3 times (in this way, a purer dihydrated iron phosphate can be obtained), and then dehydrated to obtain iron phosphate;

[0034] Preferably, the pH value of the acidic wash water is 0.5-2, more preferably 0.8-1;

[0035] Preferably, the acidic washing water includes one or more of hydrochloric acid, phosphoric acid, and sulfuric acid;

[0036] Preferably, the temperature of the acidic washing water is ≥80°C, more preferably 85-99°C;

[0037] Preferably, during washing, the liquid-to-solid mass ratio is controlled to be 2-4:1;

[0038] Preferably, the number of washes is 5-8 times;

[0039] Preferably, dehydration is achieved by calcining at 550-650°C for 1-3 hours; more preferably, dehydration is achieved by calcining at 580-630°C for 1.5-2.5 hours.

[0040] Preferably, the calcination is carried out at 650° C. for 1 hour and then cooled to room temperature.

[0041] Preferably, the purity of the ferric phosphate is ≥99.9wt%, more preferably ≥99.95wt%.

[0042] Furthermore, after S5, the lithium-rich solution is purified and impurities are removed to obtain a lithium-rich purified solution, which is then subjected to lithium precipitation treatment and solid-liquid separation to obtain a lithium salt product.

[0043] Preferably, the lithium-rich purified liquid is mixed with a water-soluble carbonate or a solution thereof, and after lithium precipitation, the solid-liquid separation and drying are performed to obtain a lithium carbonate product. Optionally, the water-soluble carbonate is one or more of sodium carbonate, potassium carbonate and ammonium carbonate.

[0044] Furthermore, the lithium iron phosphate waste includes one or more of lithium iron phosphate powder scrapped by battery manufacturers, lithium iron phosphate powder obtained after battery disassembly and sorting, and lithium iron phosphate powder obtained by processing lithium iron phosphate pole pieces.

[0045] Furthermore, in the lithium iron phosphate waste powder, the aluminum content is ≤5wt%, the copper content is ≤5wt%, and the lithium content is ≤6wt%; further preferably, the aluminum content is ≤3wt%, the copper content is ≤3.5wt%, and the lithium content is ≤5%; more preferably, the aluminum content is ≤1wt%, the copper content is ≤0.5wt%, and the lithium content is ≤4.85%.

[0046] In view of the current situation that the existing waste lithium iron phosphate treatment technology can only selectively extract lithium but cannot effectively recycle iron and phosphorus elements, resulting in a large amount of accumulation of iron phosphate solid waste, the present invention proposes a resource treatment method for lithium iron phosphate waste, which can effectively extract and recycle lithium elements and prepare battery-grade iron phosphate in one step, and can effectively solve the problem that iron and phosphorus elements cannot be effectively recycled and utilized and the problem of iron and phosphorus solid waste treatment in the existing treatment technology.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] (1) After being treated by the resource recovery method of the present invention, the core elements Li, Fe, P, and C in the lithium iron phosphate waste powder can be recovered with high added value: the lithium element can be completely leached and can be used to prepare battery-grade lithium carbonate for recovery, and the iron and phosphorus elements can also be recovered to obtain battery-grade iron phosphate by removing impurities. XRD detection shows that the iron phosphate product has a good crystal form and accurately matches the standard iron phosphate card without impurity peaks. SEM detection shows that the surface of the iron phosphate product is uniform at the microscopic level, and the primary grains are nano-scale smooth particles with excellent morphology. The overall morphology and crystal shape are good. At the same time, the carbon element in the leached slag can be purified and regenerated to have a certain economic value, and can be sold as a process by-product.

[0049] (2) The present invention realizes full element leaching through the acid leaching step, and only a small amount of reducing agent, such as reduced iron powder, is required during reduction to reduce the small amount of oxidized Fe 3+ , impurities can be removed by maintaining the reducing atmosphere of the system, and the excess iron powder can be recycled. It is low-cost and does not introduce impurity elements, and has no significant effect on the morphology of iron phosphate and COD content.

[0050] (3) The present invention uses an alkaline solution in combination with alkaline slag to circulate and control the pH value, which can effectively save alkaline solution while gently adjusting the alkali to effectively avoid local pH imbalance. The loss rate of valuable elements such as Fe, P, and Li in the impurity removal step is effectively reduced from 40% to less than 10% through the circulating alkali adjustment process, and the Al concentration after impurity removal can be reduced to less than 0.02 g / L. The selective hydrolysis of impurities can be effectively achieved by controlling the hydrolysis pH within a certain range, while effectively and selectively removing impurities and reducing the loss of iron and phosphorus elements, further improving the recovery rate of iron phosphate, and with the subsequent slag washing and impurity removal, a battery-grade iron phosphate product with a purity of up to 99.9wt% can be obtained.

[0051] (4) The reagents and equipment used in the resource recovery treatment method of the present invention are common and easy to obtain, and the operation is simple. The alkaline slag produced in the middle can be returned for alkali adjustment, the amount of waste slag is low, and no expensive equipment investment and strict operating requirements are required. The products are high-value-added battery-grade iron phosphate and lithium carbonate products with high economic value, strong industrial feasibility, and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is the XRD diagram of the battery-grade iron phosphate product obtained in Example 3.

[0053] Figure 2 This is a SEM image of the battery-grade iron phosphate obtained in Example 3 (magnified 5000 times).

[0054] Figure 3 This is a SEM image of the battery-grade iron phosphate obtained in Example 3 (magnified 10,000 times). DETAILED DESCRIPTION

[0055] The present invention will be described in detail below in conjunction with the embodiments. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other. Unless otherwise specified, the relevant percentages refer to mass percentages.

[0056] Example 1

[0057] The resource treatment method of lithium iron phosphate waste powder in this embodiment includes the following steps:

[0058] S1. First, 50 kg of lithium iron phosphate waste powder to be treated (Al content of 0.59%, Cu content of 0.06%, Li content of 4.83%, Fe content of 32.25%) was mixed with water at a mass ratio of 1:1 to obtain a slurry; then the slurry was mixed with a sulfuric acid solution, stirred and leached at 60°C for 0.5h, and then the solid-liquid was separated to obtain a leaching residue and a leaching solution rich in iron, phosphorus and lithium; the total molar amount of Li and Fe in the slurry was equal to the total molar amount of H + The molar ratio of the slurry to the sulfuric acid solution is 1:1.25; after the slurry is mixed with the sulfuric acid solution, the initial liquid-to-solid ratio is 3:1;

[0059] S2, the leaching solution obtained in S1 and the reducing agent are mixed, stirred and reacted at room temperature for 2 hours, and then the solid and liquid are separated to obtain a reduced liquid and a slag phase; wherein the reducing agent is iron powder; the amount of the reducing agent added is the Fe content in the leaching solution. 3+ and Cu 2+ 1.1 times the total molar amount;

[0060] S3, mixing the reduced liquid obtained in S2 with the alkaline residue, and adding 0.8 mol / L ammonia water, so that the pH value of the mixed solution is increased to 3.10±0.05 at a rate of 0.1 / min, to obtain a mixed solution with a pH value of 3.10±0.05;

[0061] S4, aging the mixed solution obtained in S3 at 50° C. for 30 min, and then separating the solid and the liquid to obtain a alkali-adjusted liquid and alkali residue;

[0062] The alkali residue is returned to step S3. In this embodiment, the alkali residue is recycled 4 times and then discharged (at this time, the mass ratio of aluminum to iron in the alkali residue is 0.14), and the liquid aluminum removal rate after alkali adjustment is 99.6%;

[0063] S5, the alkali-adjusted solution and hydrogen peroxide were mixed and stirred, and a pH adjuster was added to control the pH value of the system to be maintained at 1.75±0.05, and the stirring rate was 300 rpm. 2+ When the concentration of is less than 0.01 g / L, solid-liquid separation is performed to obtain ferric phosphate dihydrate and lithium-rich solution; wherein, the amount of hydrogen peroxide used is the theoretical equivalent (i.e., the Fe 2+ All oxidized to Fe 3+ The concentration of the hydrogen peroxide is 30%, and the pH regulator is sodium hydroxide.

[0064] After S2, the slag phase is subjected to magnetic separation to obtain iron powder and copper element, and the iron powder is returned to S2 as a reducing agent.

[0065] After S5, the dihydrated iron phosphate obtained in S5 was washed 6 times with acidic washing water, roasted and dehydrated at 650°C for 1 hour, and then cooled to room temperature to obtain 36.07 kg of iron phosphate product;

[0066] The acidic washing water is prepared from hydrochloric acid and phosphoric acid, and the pH value of the acidic washing water is 0.5; the temperature of the acidic washing water is 80°C; during washing, the liquid-solid mass ratio is controlled to be 3:1.

[0067] After S5, the lithium-rich solution is purified and impurities are removed, and then mixed with sodium carbonate. After lithium precipitation, the solid and liquid are separated and dried to obtain 8.2 kg of battery-grade lithium carbonate product.

[0068] According to calculation, the recovery rates of Fe, P and Li are 87.2%, 86.4% and 99.5% respectively (the recovery rate of lithium is calculated based on the lithium-rich solution, the same below). The purity of lithium carbonate in the lithium carbonate product reaches 99.57%, which meets the relevant requirements of GB / T 6678-2003.

[0069] Example 2

[0070] The resource treatment method of lithium iron phosphate waste powder in this embodiment includes the following steps:

[0071] S1. First, 50 kg of lithium iron phosphate waste powder to be treated (Al content is 0.76%, Cu content is 0.15%, Li content is 4.22%, and Fe content is 32.75%) is mixed with water at a mass ratio of 2:1 to obtain a slurry; then the slurry is mixed with a hydrochloric acid solution, stirred and leached at 30°C for 2 hours, and then the solid and liquid are separated to obtain a leaching residue and a leaching solution rich in iron, phosphorus and lithium; the total molar amount of Li and Fe in the slurry is equal to the total molar amount of H in the hydrochloric acid solution. + The molar ratio of the slurry to the hydrochloric acid solution is 1:1.2; after the slurry is mixed with the hydrochloric acid solution, the initial liquid-to-solid ratio is 4:1;

[0072] S2, the leaching solution obtained in S1 and the iron powder are mixed, stirred and reacted at room temperature for 1 hour, and then the solid and liquid are separated to obtain the reduced liquid and slag phase; wherein the amount of reducing agent added is the amount of Fe in the leaching solution. 3+ and Cu 2+ 1.2 times the total molar amount;

[0073] S3, mixing the reduced liquid obtained in S2 with the alkaline residue, and adding an alkaline solution, so that the pH value of the mixed solution increases to 2.95±0.05 at a rate of 0.2 / min, to obtain a mixed solution with a pH value of 2.95±0.05; wherein the alkaline solution is a mixed solution of sodium hydroxide and ammonia water with a concentration of 1 mol / L, and the sodium hydroxide and NH 3 ·H 2 The molar ratio of O is 1:1;

[0074] S4, aging the mixed solution obtained in S3 at 45°C for 35 minutes, and then separating the solid and the liquid to obtain a alkali-adjusted liquid and alkali residue;

[0075] All the alkali residues are returned to S3. In this embodiment, the alkali residues are recycled for 5 times and then discharged (at this time, the mass ratio of aluminum to iron in the alkali residues is 0.22). After alkali adjustment, the removal rate of liquid aluminum is 99.5%;

[0076] S5, the alkali-adjusted solution and hydrogen peroxide were mixed and stirred, and a pH adjuster was added to control the pH value of the system to be maintained at 1.6±0.05, and the stirring rate was 350 rpm. 2+ When the concentration is less than 0.01 g / L, solid-liquid separation is performed to obtain ferric phosphate dihydrate and lithium-rich solution;

[0077] The amount of hydrogen peroxide used is the theoretical equivalent (i.e., the Fe 2+ All oxidized to Fe 3+ The concentration of hydrogen peroxide is 30%; the pH regulator is sodium hydroxide;

[0078] After S2, the slag phase is subjected to magnetic separation to obtain iron powder and copper element.

[0079] After S5, the dihydrated ferric phosphate obtained in S5 was washed 5 times with acidic washing water, and then calcined and dehydrated at 600°C for 3 hours and cooled to room temperature to obtain 38.76 kg of ferric phosphate product; wherein, the acidic washing water was prepared from hydrochloric acid and phosphoric acid, and the pH value of the acidic washing water was 0.6; the temperature of the acidic washing water was 90°C; during washing, the liquid-to-solid mass ratio was controlled to be 4:1.

[0080] After S5, the lithium-rich solution is purified and mixed with carbonate. After lithium precipitation, the solid and liquid are separated and dried to obtain 6.92 kg of battery-grade lithium carbonate product.

[0081] According to calculation, the recovery rates of Fe, P and Li are 89.7%, 90.1% and 99.7% respectively. The purity of lithium carbonate in the lithium carbonate product reaches 99.51%, which meets the relevant requirements of GB / T 6678-2003.

[0082] Example 3

[0083] The resource treatment method of lithium iron phosphate waste powder in this embodiment includes the following steps:

[0084] S1. First, 50 kg of lithium iron phosphate waste powder to be treated (Al content is 0.11%, Cu content is 0.02%, Li content is 4.17%, Fe content is 32.86%) is mixed with water at a mass ratio of 1:2 to obtain slurry; then the slurry is mixed with an acid solution, stirred and leached at 70°C for 1 hour, and then the solid and liquid are separated to obtain leached residue and a leachate rich in iron, phosphorus and lithium; wherein the total molar amount of Li and Fe in the slurry is equal to the total molar amount of H in the acid solution. + The molar ratio of the slurry to the acid solution is 1:1.1; after the slurry is mixed with the acid solution, the initial liquid-to-solid ratio is 3:1; the acid solution is a nitric acid solution;

[0085] S2, mixing the leaching solution obtained in S1 with iron powder, stirring and reacting at room temperature for 1.5 hours, and then separating the solid and liquid to obtain a reduced liquid and a slag phase;

[0086] Wherein, the reducing agent is iron powder; the amount of reducing agent added is Fe in the leaching solution. 3+ and Cu 2+ 1.15 times the total molar amount;

[0087] S3, mixing the reduced liquid obtained in S2 with the alkaline residue, and adding an alkaline solution, so that the pH value of the mixed solution increases to 3.05±0.05 at a rate of 0.3 / min, to obtain a mixed solution with a pH value of 3.05±0.05; wherein the alkaline solution is a potassium hydroxide solution with a concentration of 1 mol / L;

[0088] S4, aging the mixed solution obtained in S3 at 55°C for 25 minutes, and then separating the solid and the liquid to obtain a alkali-adjusted liquid and alkali residue;

[0089] Among them, all the alkali residues are returned to step S3. In this embodiment, the alkali residues are recycled for 6 times and then discharged. After alkali adjustment, the removal rate of liquid aluminum is 99.3%;

[0090] S5, the alkali-adjusted solution and sodium chlorate were mixed and stirred at a stirring rate of 400 rpm, and a pH adjuster (sodium hydroxide) was added to control the pH value of the system to be maintained at 2±0.05. 2+ When the concentration of is less than 0.01 g / L, solid-liquid separation is performed to obtain ferric phosphate dihydrate and lithium-rich solution; wherein, the amount of sodium chlorate used is the theoretical equivalent (i.e., the Fe 2+ All oxidized to Fe 3+ 1.05 times the theoretical amount of oxidant required);

[0091] After S2, the slag phase is subjected to magnetic separation to obtain iron powder and copper element.

[0092] After S5, the dihydrated iron phosphate obtained from S5 was washed three times with hydrochloric acid and phosphoric acid at 85°C, roasted and dehydrated at 650°C for 1 hour, and then cooled to room temperature to obtain 39.47 kg of iron phosphate product;

[0093] Among them, the pH value of the acidic washing water is 0.65; during washing, the liquid-to-solid mass ratio is controlled to be 5:1.

[0094] After S5, the lithium-rich solution is purified and mixed with sodium carbonate. After lithium precipitation, the solid and liquid are separated and dried to obtain 6.72 kg of battery-grade lithium carbonate product.

[0095] According to calculation, the recovery rates of Fe, P and Li are 91.2%, 92.6% and 99.8% respectively. The purity of lithium carbonate in the lithium carbonate product reaches 99.52%, which meets the relevant requirements of GB / T 6678-2003.

[0096] The test was carried out according to HG / T 4701-2021, and the composition analysis results of the iron phosphate obtained in each embodiment are shown in Table 1.

[0097] Table 1 Composition analysis results of iron phosphate obtained in each embodiment

[0098]

[0099] Among them, the industry standard refers to HG / T 4701-2021 iron phosphate for batteries.

[0100] Comparative Example 1

[0101] Example 1 was repeated, except that in S3, the pH value of the obtained mixed solution was 1.5±0.05.

[0102] After testing, the removal rate of liquid aluminum after alkali adjustment was 8.13%, the recovery rate of iron was 89.12%, and the recovery rate of phosphorus was 88.84%. However, the purity of the iron phosphate product was only 99.06%, the Fe content was 35.87%, the P content was 20.268%, the Fe:P ratio was 0.9797, and the Al content was 0.921%, which did not meet the industry standard requirements for battery-grade iron phosphate.

[0103] Comparative Example 2

[0104] Example 1 was repeated, except that in S3, the pH value of the obtained mixed solution was 4.5±0.05.

[0105] After testing, the removal rate of liquid aluminum after alkali adjustment was 99.5%; the recovery rate of iron was 16.79%, and the recovery rate of phosphorus was 12.41%.

[0106] Comparative Example 3

[0107] Example 1 was repeated, except that the alkali residue in S4 was not returned to S3, and the pH value in S3 was adjusted only by alkali solution. After testing, the removal rate of liquid aluminum after alkali adjustment was 99.2%, the recovery rate of iron was 55.72%, and the recovery rate of phosphorus was 48.718%.

[0108] The contents explained in the above embodiments should be understood as these embodiments are only used to more clearly illustrate the present invention, and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

Claims

1. A method for recycling lithium iron phosphate waste. It is characterized in that The steps include: S1. After acid leaching the lithium iron phosphate waste to be treated, solid-liquid separation is performed to obtain leached residue and a leaching solution rich in iron, phosphorus and lithium; S2, reducing the leaching solution obtained in S1, separating the solid and the liquid, and obtaining a reduced liquid and a slag phase; S3, mixing the reduced liquid obtained in S2 with alkaline residue and alkaline solution to obtain a mixed liquid with a pH value of 2-4; S4, aging the mixed solution obtained in S3, and then separating the solid and the liquid to obtain a alkali-adjusted liquid and alkali residue; The alkali slag is partially or completely returned to step S3, and the mass ratio of aluminum to iron in the alkali slag returned to step S3 is less than 0.3; S5. After the alkali-adjusted liquid obtained in S4 is subjected to iron precipitation treatment, solid-liquid separation is performed to obtain ferric phosphate dihydrate and a lithium-rich solution.

2. The resource recovery method according to claim 1, It is characterized in that In S3, the reduced liquid obtained in S2 is mixed with the alkaline residue, and an alkaline solution is added, so that the pH value of the mixed liquid is increased to 2-4 at a rate of ≤0.4 / min, preferably, the pH value of the mixed liquid is increased to 2.8-3.2 at a rate of ≤0.4 / min.

3. The resource recovery method according to any one of claims 1 to 2, It is characterized in that In S3, the concentration of the alkali in the alkali solution is ≤1 mol / L, preferably 0.2-0.8 mol / L; preferably, the alkali solution contains NH 3 ·H 2 O, NaOH, KOH or more; preferably, the alkaline solution is NH 3 ·H 2 O mixed alkaline solution with NaOH and / or KOH.

4. The resource recovery method according to any one of claims 1 to 2, It is characterized in that In S4, the aging temperature is 40-60°C, preferably 45-55°C; the aging time is 20-40 min, preferably 25-35 min.

5. The resource recovery method according to any one of claims 1 to 2, It is characterized in that In S1, when acid leaching is performed, the lithium iron phosphate waste powder is first mixed with water to obtain a slurry; then the slurry is mixed with an acid solution and leached; Preferably, during mixing and slurrying, the mass ratio of lithium iron phosphate waste powder to water is 5:1-1:2, more preferably 3-4:1; Preferably, the total molar amount of Li and Fe in the slurry is equal to the total molar amount of H + The molar ratio of is 1:1-1.5, more preferably 1:1.1-1.3; Preferably, after the slurry is mixed with the acid solution, the initial liquid-to-solid ratio is 3-10:1, more preferably 4-8:1; Preferably, the acid solution contains one or more of sulfuric acid, hydrochloric acid, and phosphoric acid; Preferably, the leaching is carried out with stirring at 20-70°C for 0.2-3h, more preferably, the leaching is carried out with stirring at 40-60°C for 20-40min.

6. The resource recovery method according to any one of claims 1 to 2, It is characterized in that In S2, the leaching solution and the reducing agent are mixed for reduction, wherein the reducing agent comprises one or more of iron powder, zinc powder and magnesium powder; preferably, the amount of the reducing agent added is the amount of Fe in the leaching solution. 3+ and Cu 2+ 1-1.2 times the total molar amount of; preferably, the leachate and the reducing agent are mixed, stirred for 0.5-2h, and then the solid-liquid is separated.

7. The resource recovery method according to claim 6, It is characterized in that The reducing agent is iron powder; after S2, the slag phase is subjected to magnetic separation to obtain iron powder and copper element, and preferably, the iron powder is returned to S2.

8. The resource recovery method according to any one of claims 1 to 2, It is characterized in that In S5, the alkali-adjusted solution and the oxidant are mixed or contacted for reaction, and a pH adjuster is added to maintain the pH of the system at 1.5-2.

5. 2+ When the concentration is less than 0.01 g / L, solid-liquid separation is performed to obtain ferric phosphate dihydrate and lithium-rich solution; Wherein, the amount of the oxidant is 1-1.2 times of the theoretical equivalent, preferably 1.1 times; the oxidant includes at least one of hydrogen peroxide, thiosulfate, ozone, peroxyacid salt, oxygen, and air; Preferably, the stirring speed is controlled to be above 300 rpm during the iron precipitation process.

9. The resource recovery method according to claim 8, It is characterized in that After S5, the dihydrated iron phosphate obtained in S5 is washed with acidic washing water for more than 3 times, and then dehydrated to obtain iron phosphate; Preferably, the pH value of the acidic wash water is 0.5-2, more preferably 0.8-1.5; Preferably, the acidic washing water includes one or more of hydrochloric acid, phosphoric acid, and sulfuric acid; Preferably, the temperature of the acidic washing water is ≥80°C, more preferably 85-99°C; Preferably, during washing, the liquid-to-solid mass ratio is controlled to be 2-4:1; Preferably, the number of washes is 5-8 times; Preferably, dehydration is achieved by calcining at 550-650°C for 1-3 hours; more preferably, dehydration is achieved by calcining at 580-630°C for 1.5-2.5 hours.

10. The resource recovery method according to claim 8, It is characterized in that After S5, the lithium-rich solution is purified and impurities removed to obtain a lithium-rich purified liquid, which is then subjected to lithium precipitation treatment, followed by solid-liquid separation to obtain a lithium salt product; preferably, the lithium-rich purified liquid is mixed with a water-soluble carbonate or a solution thereof, and after lithium precipitation, the solid-liquid separation and drying are performed to obtain a lithium carbonate product.

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