WO2024021237A1 - Recovery method for lithium iron phosphate - Google Patents

Abstract

A recovery method for lithium iron phosphate. The method specifically comprises: mixing lithium iron phosphate and an acidic solution to prepare a slurry, mixing and leaching the resulting slurry and an oxidizing agent, and collecting a leachate and leaching residues; precipitating lithium from the leachate; subjecting the leaching residues to acid reduction leaching, so as to obtain a liquid-phase component; extracting the liquid-phase component, so as to obtain a water phase and an organic phase, wherein an extraction system used for extraction comprises TBP; separating an iron compound from the water phase; and back-extracting the organic phase, and separating a phosphorus compound from the resulting back-extracted phase. The recovery method provided can separately recover iron, phosphorus and lithium in lithium iron phosphate, thereby realizing high-selectivity comprehensive recovery.

Description

A kind of recycling method of lithium iron phosphate Technical field

The present invention relates to the technical field of recycling waste power batteries, and in particular, to a method for recycling lithium iron phosphate.

Background technique

With the vigorous development of the new energy automobile industry, power batteries represented by lithium-ion batteries have been widely used. Classified according to the cathode material, power batteries include lithium iron phosphate batteries (LFP), lithium cobalt oxide batteries (LCO), lithium manganate batteries (LMO) and ternary batteries (NCM). Among them, LFP has gradually penetrated into the global energy storage market with its advantages such as low cost, good stability, and long cycle life.

With the substantial growth in the use of lithium iron phosphate batteries, the amount of scrapped lithium iron phosphate batteries has also increased year by year. Data shows that there will be approximately 440,000 tons of scrapped lithium iron phosphate batteries in 2022. Lithium in lithium iron phosphate materials is an important resource, and iron and phosphorus also have certain recycling value. Recycling of lithium iron phosphate cathode materials not only has economic benefits, but also reduces environmental pollution.

At present, the recycling methods for waste lithium iron phosphate batteries mainly include high-temperature solid-phase fire recovery, high-temperature solid-phase repair, liquid-phase wet recovery, bioactive leaching recovery, and high-energy mechanochemical activation recovery. Among them, high-temperature solid-phase fire recycling and high-temperature solid-phase repair have the advantages of simple process and easy industrialization. However, due to their strict requirements for pre-treatment of waste materials, the process energy consumption is high, and toxic gases are easily released under the high temperature conditions of the regeneration and repair process. , and the recycled products have shortcomings such as high impurities and imperfect structural repairs, which make their recycling economic benefits low; while bioleaching and mechanochemical activation recycling are not mature technologies, and also have shortcomings such as long cycles and harsh leaching conditions, so they are temporarily Industrial application cannot be achieved. Therefore, so far, although liquid phase wet recovery has the disadvantages of higher process costs and more complex processes, it is currently the most widely used method due to its obvious advantages in mature technology, high metal recovery rate, and high purity of the resulting materials. .

However, wet recycling usually only recovers part of the components. For example, the recycling technology for scrapped lithium iron phosphate mainly focuses on selectively extracting and recovering lithium from scrap electrode pieces or active materials, and then adding precipitants to recover lithium salt products. The remaining Solid waste contains high levels of iron and phosphorus, but is usually not treated, resulting in a waste of resources and harm to the environment. In addition, the traditional method of extracting lithium from lithium iron phosphate usually involves acid leaching, followed by adjusting the pH with alkali to recover the iron phosphate, and then precipitating the lithium in the filtrate with sodium carbonate to obtain lithium carbonate. Although this method can convert elements such as lithium, iron, and phosphorus into All are recycled, but a large amount of additional acid and alkali need to be added, and because impurities such as copper and aluminum are high in the recycled lithium iron phosphate waste, the extracted iron phosphate has a high impurity content, making it difficult to meet battery-grade iron phosphate standards.

In summary, although the wet recycling process is relatively mature, there are problems such as the inability to fully recover materials and poor selectivity.

Contents of the invention

The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a recovery method for lithium iron phosphate, which can separately recover iron, phosphorus and lithium in lithium iron phosphate, achieving highly selective and comprehensive recovery.

According to the first embodiment of the present invention, a method for recycling lithium iron phosphate is provided, and the method includes the following steps:

Mix the lithium iron phosphate and the acid solution to make a slurry, mix the resulting slurry and the oxidizing agent for leaching, and collect the leaching liquid and leaching residue;

Precipitate lithium from the leachate;

Perform acidic reduction leaching on the leaching residue to obtain liquid phase components;

Extract the liquid phase component to obtain an aqueous phase and an organic phase, and the extraction system used for the extraction includes TBP;

isolating iron compounds from the aqueous phase;

The organic phase is stripped, and the phosphorus compound is separated from the resulting stripped phase.

The mechanism of the recovery method is as follows:

During the mixed leaching process, under the action of oxidant and acid, the oxidant oxidizes the divalent iron in lithium iron phosphate into trivalent iron, combines with phosphate to form iron phosphate precipitate, forces the lithium ions to escape, and realizes the synthesis of lithium and iron-phosphorus. Separation, that is, lithium is dissolved in the leach solution, and the main component of the leach residue includes iron phosphate;

In the process of acidic reduction leaching, the reducing agent can not only improve the dissolution rate of iron phosphate slag, but also reduce the ferric iron in the solution to divalent iron, which is beneficial to the next step of recovering the iron element in the dissolved solution. The liquid phase components include ferrous iron and phosphate (and may also include hydrogen phosphate and dihydrogen phosphate).

An extraction system including TBP (tributyl phosphate) can extract the phosphorus in the liquid phase component into the organic phase while leaving the iron in the aqueous phase.

Subsequently, iron compounds and phosphorus compounds can be obtained from the aqueous phase and organic phase respectively, and finally the recovery of phosphorus, iron and lithium can be achieved respectively.

According to some embodiments of the present invention, the recycling method has at least the following beneficial effects:

(1) When recycling lithium iron phosphate, the lithium iron phosphate used usually contains graphite and other powders. These impurity powders have good hydrophobicity. Therefore, in traditional technology, they are directly added to the acid and oxidant or water is added first to make a pulp and then the acid is added. The feeding method of oxidant and oxidant will cause the powder to float on the liquid surface for a long time, the stirring will not work, the early pulping time will be long, the overall reaction time will be prolonged or the reaction will be insufficient. When applied to industrial production, it will not only be inefficient, but also easily lead to The liquid pipe and liquid outlet pipe will be blocked by materials; in addition, directly mixing acid, oxidant and lithium iron phosphate will easily produce a large number of bubbles overflowing the reaction vessel, which is not conducive to safe reaction; the foam generated will in turn further increase the difficulty and consumption of pulping. time.

The present invention adopts a feeding method of first mixing lithium iron phosphate and acid solution for pulping, and then mixing the obtained slurry and oxidant. During the pulping process, almost no bubbles are generated, which reduces the difficulty of pulping and effectively shortens the time required for pulping. time, and effectively improves the operational safety of the recycling method.

(2) The present invention realizes the separate recovery of iron, phosphorus and lithium by rationally designing the steps of the recovery method, and the lithium salts, iron compounds, phosphorus compounds and other products that can be prepared respectively can be returned to lithium iron phosphate and its precursors It can be used in the synthesis of solids or other pharmaceutical, fertilizer or water treatment fields to realize the material circulation of the lithium iron phosphate battery industry chain, improve the economic benefits of the recycling method, and also alleviate the pressure of used lithium iron phosphate on the environment.

According to some embodiments of the present invention, the source of lithium iron phosphate includes at least one of lithium iron phosphate batteries, defective lithium iron phosphate powder products, and defective lithium iron phosphate cathode slurry products.

According to some embodiments of the present invention, the addition of the oxidant continues throughout the mixed leaching process. This ensures that during the entire process of mixed leaching, the system is oxidizing, and the oxidant content is moderate, so that a large number of bubbles will not be generated and cause safety issues.

Further, the oxidizing agent is added at a constant rate.

As a result, the oxidant is added to the liquid surface of the mixed leaching system, and the generated bubbles can quickly escape the system, which improves the safety of the mixed leaching; at the same time, the oxidant is added according to the above method, and the amount of bubbles generated per unit time is small. , further improving the safety and stability of mixed leaching; finally, the above-mentioned addition method can improve the utilization rate of the oxidant, save costs, and improve the economy of the recovery method.

According to some embodiments of the present invention, the acid in the acid solution includes at least one of sulfuric acid, nitric acid and hydrochloric acid.

According to some embodiments of the present invention, the molar ratio of the acid in the acid solution to the lithium in the lithium iron phosphate is (0.5-3):1.

According to some preferred embodiments of the present invention, the molar ratio of the acid in the acid solution to the lithium in the lithium iron phosphate is (0.6-1):1.

Research has found that if the molar ratio is higher than the above range, as the amount of acidic substances increases, the leaching rate of iron and phosphorus also increases. When it is lower than the above range, as the amount of acidic substances increases, the leaching rate of lithium increases, and the leaching rate of iron and phosphorus increases. There was little change in the leaching rate of phosphorus. Therefore, in the above molar ratio, on the one hand, the amount of acidic substances is low enough to fully avoid the leaching of iron, phosphorus and other elements, thereby improving the purity of the lithium salt obtained by depositing lithium; on the other hand, the amount of acidic substances The amount is high enough to fully leach lithium from lithium iron phosphate, improving the leaching rate of lithium without increasing impurities; finally, the amount of the above-mentioned acid substance can also balance the cost of the preparation method.

According to some embodiments of the present invention, the liquid-to-solid ratio of the pulping is (3-6):1.

Preferably, the liquid-to-solid ratio refers to the ratio of the volume of the liquid (in mL) to the mass of the solid (in g).

According to some preferred embodiments of the present invention, the liquid-to-solid ratio of the pulping is (3.5-4.5):1.

Within the above liquid-to-solid ratio range, the viscosity of the obtained slurry is moderate, which can provide a good viscosity environment for the leaching and migration of lithium ions, as well as the transfer and diffusion of acid in the acid solution, and improve the lithium leaching rate.

At the same time, on the premise of maintaining the molar ratio of the acid in the acid solution and the lithium in the lithium iron phosphate, the above solid-liquid ratio can also maintain the concentration of the acid solution, so that it can quickly and fully absorb the lithium in the lithium iron phosphate. leaching;

In summary, within the above liquid-to-solid ratio range, the leaching rate of lithium in lithium iron phosphate can be increased, and the concentration of lithium in the leachate can also be increased. Thus, the lithium precipitation process can be simplified, and no further evaporation and concentration is required before the lithium precipitation.

According to some embodiments of the present invention, the oxidizing agent includes at least one of hydrogen peroxide, sodium chlorate, and potassium chlorate.

According to some embodiments of the present invention, the molar ratio of the oxidant to the lithium in the lithium iron phosphate is (1-4):1.

According to some embodiments of the present invention, the molar ratio of the oxidant to the lithium in the lithium iron phosphate is (1.1-1.6):1.

The oxidant can convert iron from divalent to trivalent, which is beneficial to the formation of iron phosphate precipitates, thereby making the structure of lithium iron phosphate easier to decompose in acid solution. Therefore, the oxidant has a significant promotion effect on the leaching of lithium. Controlling the redox potential through oxidants can minimize the leaching of iron, and there will be decomposition of the oxidants during the reaction. Therefore, the amount of oxidants should be used in excess. However, considering that the larger the amount of oxidants added, the intense reaction in the later stage will easily produce a large amount of foam overflow. To reduce hazards and save production costs, it is optimal to control the dosage of oxidant within the above proportion range.

According to some embodiments of the present invention, the temperature of the mixed leaching is 30-90°C.

According to some embodiments of the present invention, the temperature of the mixed leaching is 30-45°C.

According to some embodiments of the present invention, the duration of the mixed leaching is 2 to 6 hours.

According to some embodiments of the present invention, the duration of the mixed leaching is 4 to 5 hours.

This can not only control the leaching rate of iron and phosphorus to the lowest possible level, but also ensure the leaching of lithium.

When the acid in the acid solution includes the sulfuric acid and the oxidizing agent includes the hydrogen peroxide, the reactions that occur in the mixed leaching include:

2LiFePO ₄ +H ₂ SO ₄ +H ₂ O ₂ =2FePO ₄ ↓+Li ₂ SO ₄ +2H ₂ O.

According to some embodiments of the present invention, the precipitating agent used to precipitate lithium includes at least one of soluble phosphate and soluble carbonate.

According to some embodiments of the present invention, the soluble phosphate includes at least one of sodium phosphate and potassium phosphate.

According to some embodiments of the present invention, the soluble carbonate includes at least one of sodium carbonate and potassium carbonate.

According to some embodiments of the present invention, in the lithium precipitation, the molar ratio of the lithium ions in the precipitating agent and the leachate is (1-5):1.

According to some preferred embodiments of the present invention, in the lithium precipitation, the molar ratio of the lithium ions in the precipitant and the leachate is (1.5-1.6):1.

According to some embodiments of the present invention, the operating temperature of the lithium precipitation is 70°C to 95°C.

According to some preferred embodiments of the present invention, the operating temperature of the lithium precipitation is 85°C to 90°C.

According to some embodiments of the present invention, the operation duration of the lithium precipitation is 1 to 6 hours.

According to some embodiments of the present invention, the operation time of the lithium precipitation is about 4 hours.

According to some embodiments of the present invention, the acidic reduction leaching includes adding a reducing agent after acid-dissolving the leaching residue.

According to some embodiments of the present invention, the acid dissolution time is 2 to 3 hours, so that the leaching residue and acid fully react; within the acid dissolution time range, the leaching rates of phosphorus and iron are relatively high.

According to some embodiments of the present invention, the reducing agent can be added in n times, where n≥2 and is a positive integer, such as 2, 3, 4, 5 and 6. Thus, it is possible to avoid a violent reaction that causes the reaction mixture to overflow the reaction vessel when an excessive amount of reducing agent is added at one time; and this addition form and addition time are the best for further improving the dissolution of the leaching slag, and the phosphorus and iron in the final leaching slag are The dissolution rate can reach 99%. The higher the dissolution rate, the more conducive it is to the subsequent separation and recovery of phosphorus and iron elements to ensure their concentration and recovery rate.

According to some embodiments of the present invention, the molar ratio of hydrogen ions in the acid used for acid reduction leaching and iron in the leaching residue is (1-4):1.

According to some embodiments of the present invention, the molar ratio of hydrogen ions in the acid used for acid reduction leaching and iron in the leaching residue is (1.5-2):1.

According to some embodiments of the present invention, the concentration of hydrogen ions in the acid used for acidic reduction leaching is 1 to 10 mol/L.

According to some preferred embodiments of the present invention, the concentration of hydrogen ions in the acid used for acidic reduction leaching is 4 to 5 mol/L.

According to some embodiments of the present invention, the acid used in the acid reduction leaching is sulfuric acid.

According to some embodiments of the present invention, the reducing agent used in the acid reduction leaching includes at least one of iron powder, oxalic acid and sodium metabisulfite.

According to some preferred embodiments of the present invention, the reducing agent used in the acidic reduction leaching is selected from iron powder; thus, no new impurities will be introduced into the liquid phase components, and the properties of the iron compounds and phosphorus compounds are improved. purity.

When the reducing agent is selected from the iron powder and the acid used in the acidic reduction leaching is sulfuric acid, the reactions that occur in the acidic reduction leaching include:

2FePO ₄ +3H ₂ SO ₄ +Fe=3FeSO ₄ +2H ₃ PO ₄ .

According to some embodiments of the present invention, the molar ratio of the reducing agent to the iron in the leaching slag is (1-4):1.

According to some embodiments of the present invention, the temperature of the acidic reduction leaching is 35-85°C.

According to some embodiments of the present invention, the duration of the acidic reduction leaching is 3 to 6 hours. Including the acid dissolution time, the adding time of the reducing agent, and the reaction time after adding the reducing agent.

According to some embodiments of the present invention, the liquid phase component includes ferrous ions, phosphate, hydrogen phosphate and dihydrogen phosphate. Preferably, the acid ions of the acid used in the acidic reduction leaching are also included.

According to some embodiments of the invention, the extraction system further includes kerosene.

According to some embodiments of the present invention, the volume ratio of the kerosene in the extraction system is 20% to 40%.

Therefore, a higher concentration of TBP can maximize the extraction rate of phosphorus and reduce the extraction loss of iron. In this way, phosphorus and iron can be fully separated.

According to some embodiments of the present invention, the proportion of the kerosene in the extraction system is 25% to 40%.

According to some embodiments of the present invention, the volume ratio of the extraction system and the liquid phase component is (1-3):1.

According to some embodiments of the present invention, the volume ratio of the extraction system and the liquid phase component is (2-3):1.

According to some embodiments of the present invention, the extraction includes mixing, standing and liquid separation in sequence.

Further, the mixing time for extraction is 10 to 120 minutes; preferably, the mixing time for extraction is 50 to 70 minutes;

Further, the standing time for extraction is 30 to 120 minutes; preferably, the standing time for extraction is 30 to 40 minutes.

According to some embodiments of the present invention, the recovery method further includes removing impurities from the aqueous phase before separating the iron compound.

According to some embodiments of the present invention, the impurity removal method includes at least one of copper removal and aluminum removal.

According to some embodiments of the present invention, the method for removing copper includes adding iron powder.

Further, in the copper removal, the molar ratio of iron powder to copper in the water phase is (1.0-2.0):1.

Further, in the copper removal, the molar ratio of iron powder to copper in the water phase is (1.0-1.1):1.

According to some embodiments of the present invention, the method for removing aluminum includes adjusting the pH of the aqueous phase to 4.5-5.0.

If the water phase contains both copper impurities and aluminum impurities, the impurity removal includes copper and aluminum removal in sequence.

According to some embodiments of the present invention, the method of isolating the iron compound includes evaporative crystallization.

According to some embodiments of the present invention, the iron compound includes a ferrous salt formed by combining acid ions and ferrous iron of the acid used for acidic reduction leaching.

Further, when the acid used for acidic reduction leaching is sulfuric acid, the iron compound includes ferrous sulfate.

According to some embodiments of the present invention, the stripping agent used for stripping includes water. Preferably, the conductivity of the water is between 0.2 and 20 μS/cm, that is, commonly referred to as pure water, ultrapure water and deionized water are all applicable.

According to some embodiments of the present invention, in the stripping, the volume ratio of the organic phase and the stripping agent is (4.5-5.5):1.

According to some embodiments of the present invention, in the stripping, the volume ratio of the organic phase and the stripping agent is about 5:1.

According to some embodiments of the present invention, the stripping phase contains phosphoric acid.

According to some embodiments of the invention, the phosphorus compound includes phosphoric acid.

According to some embodiments of the present invention, the separation method of the phosphorus compound includes evaporation concentration.

Furthermore, the organic liquid remaining after the back-extraction can be reused as the extraction system.

According to some embodiments of the present invention, the stripping includes shaking, standing and liquid separation in sequence.

Further, the duration of the stripping and shaking is 10 to 60 minutes.

Further, the standing time for stripping is 60 to 120 minutes.

Additional features and advantages of the 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 invention.

Description of drawings

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

Figure 1 is a schematic flow chart of a recycling method in an embodiment of the present invention.

Detailed ways

Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the drawings are exemplary and are only used to explain the present invention and cannot be understood as limiting the present invention.

If there is no special explanation, the main components of lithium iron phosphate in the specific embodiment are as follows (in mass percentage): Fe: 32.18%, P: 18.64%, Li: 4.2%, Cu: 0.4%, Al: 0.3%, C :3.42%, the balance is oxygen and untested impurities.

Example 1

This embodiment implements a method for recovering lithium iron phosphate. The specific flow chart is shown in Figure 1. The specific steps are:

S1. Lithium extraction: Mix lithium iron phosphate and sulfuric acid aqueous solution to make a pulp, where the solid-liquid ratio during the pulping process is 4:1, and the molar ratio of sulfuric acid in the sulfuric acid aqueous solution to lithium in the lithium iron phosphate is 0.6:1; The time required for slurry is 0.5h (mix until homogeneous);

After pulping, maintain the temperature at 50°C and continue to add hydrogen peroxide dropwise within 4 hours of reaction time; the molar ratio of hydrogen peroxide to lithium in lithium iron phosphate is 1.1:1;

After the addition of hydrogen peroxide is completed, filter (press filter) to obtain the leachate and leach residue.

S2. Lithium precipitation: Add sodium carbonate solution at a molar ratio of 1.5 times the lithium content in the leach solution, react at 85°C for 4 hours, and filter to obtain lithium carbonate solid.

S3. Acid reduction leaching: Mix the leaching residue obtained in step S1 with a sulfuric acid solution with an H ⁺ concentration of 5 mol/L, in which the amount of hydrogen ions in the sulfuric acid solution is 1.5 times the amount of iron in the leaching residue; then, Stir the reaction for 2 hours at 50°C (the speed is 300 to 500 rpm, the function of stirring is mixing, and the results will not be significantly affected within this range of stirring speed);

After that, add reduced iron powder in multiple batches (the molar ratio of iron powder and iron in the leaching slag is 1.2:1, add one batch in 30 minutes, and add in 4 batches in total), continue to stir and react for 3 hours, then filter, and obtain ferrous iron ions, sulfate ions and phosphate, hydrogen phosphate and dihydrogen phosphate ions.

S4. Separate phosphorus and iron: use TPB (60%) + kerosene (40%) (volume ratio) as the extraction agent and mix it with the liquid phase components obtained in step S3 according to the ratio of 2:1 (volume ratio), and stir for 60 minutes. Let it stand for 30 minutes, and then separate the liquid to obtain an organic phase and an aqueous phase.

S5. Separate iron compounds: Test the content of copper impurities in the water phase, add reduced iron powder equal to the amount of copper substances in the water phase, and adjust the pH value to 4.5~5.0 to remove impurities, stir for 2 hours and then filter. The filtrate is evaporated and crystallized to obtain ferrous sulfate.

S6. Separate phosphorus compounds: Add deionized water to the organic phase obtained in step S4 for stripping (the volume ratio of organic phase to stripping agent is 5:1), stir for 60 minutes and let stand for 60 minutes, then separate the water phase. It is dilute phosphoric acid, which is then concentrated by evaporation to obtain concentrated phosphoric acid. The obtained organic phase can be returned to be used as an extraction agent.

Example 2

This embodiment implements a method for recovering lithium iron phosphate. The specific flow chart is shown in Figure 1. The specific steps are:

S1. Lithium extraction: Mix lithium iron phosphate and hydrochloric acid aqueous solution to make a pulp, where the solid-liquid ratio during the pulping process is 3.5:1, and the molar ratio of sulfuric acid in the sulfuric acid aqueous solution to lithium in the lithium iron phosphate is 0.75:1;

After pulping, maintain the temperature at 40°C and continue to add hydrogen peroxide dropwise within a 4.5-h reaction time; the molar ratio of hydrogen peroxide to lithium in lithium iron phosphate is 1.2:1;

After the hydrogen peroxide is added, filter it to obtain the leachate and leach residue.

S2. Lithium precipitation: Add sodium carbonate solution at a molar ratio of 1.6 times the lithium content in the leach solution, react at 90°C for 4 hours, and filter to obtain lithium carbonate solid.

S3. Acidic reduction leaching: Mix the leaching residue obtained in step S1 with a sulfuric acid solution with an H ⁺ concentration of 4 mol/L. The amount of hydrogen ions in the sulfuric acid solution is twice the amount of iron in the leaching residue; then Stir the reaction for 3 hours at 55°C (speed 300-500rpm, the function of stirring is mixing, and the result will not be significantly affected within this range of stirring speed);

After that, add reduced iron powder in multiple batches (the molar ratio of iron powder and iron in the leaching slag is 1.1:1, add one batch in 30 minutes, and add in 6 batches in total), continue to stir and react for 3 hours, then filter, and obtain ferrous iron Liquid phase components of ions, sulfate ions and phosphate, hydrogenphosphate and dihydrogenphosphate ions.

S4. Separate phosphorus and iron: use TPB (70%) + kerosene (30%) (volume ratio) as the extraction agent and mix it with the liquid phase components obtained in step S3 according to the ratio of 3:1 (volume ratio), and stir for 60 minutes. Let it stand for 30 minutes, and then separate the liquid to obtain an organic phase and an aqueous phase.

S5. Separate iron compounds: Test the content of copper impurities in the water phase, add reduced iron powder 1.1 times the amount of copper substances to the water phase, and adjust the pH value to 4.5~5.0 to remove impurities, stir for 2 hours and then filter. The filtrate is evaporated and crystallized to obtain ferrous sulfate.

S6. Separate phosphorus compounds: Add deionized water to the organic phase obtained in step S4 for stripping (the volume ratio of organic phase to stripping agent is 5:1), stir for 60 minutes and let stand for 60 minutes, then separate the water phase. It is dilute phosphoric acid, which is then concentrated by evaporation to obtain concentrated phosphoric acid. The obtained organic phase can be returned to be used as an extraction agent.

Example 3

This embodiment implements a method for recovering lithium iron phosphate. The specific flow chart is shown in Figure 1. The specific steps are:

S1. Lithium extraction: Mix lithium iron phosphate and sulfuric acid aqueous solution to make a pulp, where the solid-liquid ratio during the pulping process is 5:1, and the molar ratio of sulfuric acid in the sulfuric acid aqueous solution to lithium in the lithium iron phosphate is 1:1;

After pulping, maintain the temperature at 55°C and continue to add hydrogen peroxide dropwise within the 5-hour reaction time; the molar ratio of hydrogen peroxide to lithium in lithium iron phosphate is 1.6:1;

After the hydrogen peroxide is added, filter it to obtain the leachate and leach residue.

S2. Lithium precipitation: Add sodium carbonate solution at a molar ratio of 1.5 times the lithium content in the leach solution, react at 85°C for 4 hours, and filter to obtain lithium carbonate solid.

S3. Acidic reduction leaching: Mix the leaching residue obtained in step S1 with a sulfuric acid solution with an H ⁺ concentration of 4 mol/L. The amount of hydrogen ions in the sulfuric acid solution is twice the amount of iron in the leaching residue; then Stir the reaction for 2 hours at 55°C (speed 300-500rpm, the function of stirring is mixing, and the result will not be significantly affected within this range of stirring speed);

After that, add reduced iron powder in multiple batches (the molar ratio of iron powder and iron in the leaching slag is 1.1:1, add one batch in 45 minutes, and add in 4 batches in total), continue to stir and react for 3 hours, then filter, and obtain ferrous iron Liquid phase components of ions, sulfate ions and phosphate, hydrogenphosphate and dihydrogenphosphate ions.

S4. Separate phosphorus and iron: Use TPB (75%) + kerosene (25%) (volume ratio) as the extraction agent and mix it with the liquid phase components obtained in step S3 according to the ratio of 2.5:1 (volume ratio), and stir for 60 minutes. Then let it stand for 30 minutes and then perform liquid separation to obtain an organic phase and an aqueous phase.

S5. Separate iron compounds: Test the content of copper impurities in the water phase, add reduced iron powder 1.1 times the amount of copper substances to the water phase, and adjust the pH value to 4.5~5.0 to remove impurities, stir for 2 hours and then filter. The filtrate is evaporated and crystallized to obtain ferrous sulfate.

S6. Separate phosphorus compounds: Add deionized water to the organic phase obtained in step S4 for stripping (the volume ratio of organic phase to stripping agent is 5:1), stir for 60 minutes and let stand for 60 minutes, then separate the water phase. It is dilute phosphoric acid, which is then concentrated by evaporation to obtain concentrated phosphoric acid. The obtained organic phase can be returned to be used as an extraction agent.

Comparative example 1

This comparative example illustrates a method for recovering lithium iron phosphate. The difference between the specific steps and Example 1 is:

In step S1, lithium iron phosphate and water are first mixed and pulped at a liquid-to-solid ratio of about 4:1. In this comparative example, the time required for pulping is 1 hour; then the temperature is controlled to 50°C (set temperature), and then Add sulfuric acid aqueous solution (commercially available 98% concentrated sulfuric acid, the required concentrated sulfuric acid at this time is 0.395m ³ as mentioned above) and the same amount of hydrogen peroxide as in Example 1, the addition time of the sulfuric acid aqueous solution and hydrogen peroxide (i.e., the leaching reaction time ) is 6h, and the solid-liquid separation occurs after the reaction is completed.

test case

The first aspect of this test example tested the time required for the process of Example 1 and Comparative Example 1 and the leaching rate; the leaching rate is the ratio of lithium, phosphorus and iron in the leachate obtained in step S1 to the corresponding components in lithium iron phosphate. Proportion; the testing method for the content of each component is ICP-OES. The test results are shown in Table 1. The filtration time in Table 1 is the filtration time required for solid-liquid separation in step S1.

Table 1 Process parameters and results of Example 1 and Comparative Example 1

According to the results in Table 1, although the difference between Comparative Example 1 and Example 1 is only the difference in liquid phase components used in the pulping process and the timing of adding the acid solution; but compared with Example 1, Comparative Example 1 The pulping method provided not only increases the operation time, but also increases the leaching rate of iron and phosphorus during the lithium extraction process. Most importantly, it also reduces the lithium leaching rate.

At the same time, it was also noticed during the reaction process that in Comparative Example 1, due to the simultaneous addition of sulfuric acid and hydrogen peroxide, the dilution heat of sulfuric acid and the heat of reaction with hydrogen peroxide and materials caused the temperature to rise sharply, so the decomposition rate of hydrogen peroxide was accelerated in the later stage, which would lead to Foaming in the reaction tank poses the risk of leaching, so the flow rate has to be reduced for control, which leads to an extension of the reaction time. Each tank can only complete less than three leaches per day.

In addition, the higher temperature in Comparative Example 1 will cause the decomposition of hydrogen peroxide to fail, requiring the addition of additional hydrogen peroxide or reducing the lithium leaching rate.

In summary, it can be seen that the recovery method provided by the present invention can significantly improve the operability, economy, lithium leaching rate and final lithium leaching rate of the corresponding recovery method by adjusting the pulping method, specifically the order of adding materials during the pulping process. The purity of the resulting lithium salt.

In the second aspect of this test example, the leachate, liquid phase components, lithium carbonate and ferrous sulfate obtained in Examples 1 to 3 were tested for component analysis (the method used was ICP-OES), and the product (lithium carbonate and sulfuric acid) was calculated. The impurity content, main content and comprehensive recovery rate in ferrous iron); the comprehensive recovery rate is the ratio of the corresponding elements between the product and lithium iron phosphate. The test results are shown in Table 2.

Table 2 Results of Examples 1 to 3

In Table 2, ND indicates that no detection was detected and the content is lower than the detection limit; "/" indicates that no detection was performed.

According to the data in Table 2, the recycling method provided by the present invention not only has high selectivity for recycling the main elements such as iron, phosphorus and lithium in the lithium iron phosphate waste, but also has a high recovery rate. In addition, the recovered products have high purity and low impurity content and can be returned to the synthesis of lithium iron phosphate and its precursors or used in other pharmaceutical, waste or water treatment fields, realizing the material cycle of the lithium iron phosphate battery industry chain and having good environmental protection and economic benefits.

The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various modifications can be made without departing from the purpose of the present invention. Variety.

Claims (10)

A method for recycling lithium iron phosphate, characterized in that the method includes the following steps: Mix the lithium iron phosphate and the acid solution to make a slurry, mix the resulting slurry and the oxidizing agent for leaching, and collect the leaching liquid and leaching residue; Precipitate lithium from the leachate; Perform acidic reduction leaching on the leaching residue to obtain liquid phase components; Extract the liquid phase component to obtain an aqueous phase and an organic phase, and the extraction system used for the extraction includes TBP; isolating iron compounds from the aqueous phase; The organic phase is stripped, and the phosphorus compound is separated from the resulting stripped phase. The recovery method according to claim 1, characterized in that the molar ratio of the acid in the acid solution to the lithium in the lithium iron phosphate is (0.5-3):1. The recovery method according to claim 1, characterized in that the liquid-to-solid ratio of the pulping is (3-6):1. The recovery method according to claim 1, characterized in that the molar ratio of the oxidant to the lithium in the lithium iron phosphate is (1-4):1. The recovery method according to claim 1, characterized in that the temperature of the mixed leaching is 30-90°C; preferably, the duration of the mixed leaching is 2-6 hours. The recovery method according to any one of claims 1 to 5, wherein the acidic reduction leaching includes adding a reducing agent after acid-dissolving the leaching residue. The recovery method according to claim 6, characterized in that the molar ratio of the reducing agent to the iron in the leaching slag is (1-4):1. The recovery method according to any one of claims 1 to 5, characterized in that the extraction system further includes kerosene. The recovery method according to any one of claims 1 to 5, characterized in that the recovery method further includes removing impurities from the aqueous phase before separating the iron compound. The recovery method according to any one of claims 1 to 5, characterized in that the stripping agent used for stripping includes water.

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