CN111924817A - A method for comprehensive utilization of waste lithium iron phosphate cathode materials - Google Patents

Abstract

The invention discloses a method for comprehensive utilization of waste lithium iron phosphate positive electrode materials. The method comprises leaching the waste lithium iron phosphate positive electrode materials with acid solution. The reaction converts ferrous ions into iron ions, generates iron phosphate precipitation, and separates liquid-solid to obtain hydrated iron phosphate and lithium-containing solution; after removing heavy metal ions from the lithium-containing solution by precipitation, liquid-solid separation is obtained to obtain heavy metal precipitation slag and lithium-containing solution. Lithium purification solution; Lithium ion precipitant is added to the lithium-containing purification solution, and the pH value is adjusted to be weakly acidic or alkaline to carry out the lithium ion precipitation reaction, and then liquid-solid separation is performed to obtain a lithium salt product. The method can recover iron, phosphorus and lithium in the waste lithium iron phosphate cathode material with high recovery rate, and obtain iron phosphate and lithium salt products of high purity and high tap density at the same time, and the recovery process is simple, the conditions are mild, and the cost is low, which can meet the industrial production requirements. Require.

Description

A method for comprehensive utilization of waste lithium iron phosphate cathode materials

technical field

The invention relates to a method for recycling waste lithium iron phosphate positive electrode materials, in particular to a method for comprehensive utilization of waste lithium iron phosphate positive electrode materials, and belongs to the technical field of waste new energy material disposal and resource utilization.

Background technique

In recent years, my country's electric vehicle industry has developed rapidly, and in the future, the sales of electric vehicles will continue to grow rapidly. At present, lithium ion secondary batteries using lithium iron phosphate as the positive electrode material have been widely used in power batteries for electric vehicles due to their low cost and good safety performance. The rapid development of the electric vehicle industry promotes the rapid growth of power batteries, and the number of waste lithium-ion batteries will also increase rapidly year by year. Therefore, in order to recycle and reuse materials, save costs and protect the environment, when the era of large-scale scrapping of electric vehicles in my country comes, it becomes very urgent to recycle waste lithium iron phosphate cathode materials.

The recycling methods of waste lithium iron phosphate cathode materials can be roughly divided into two categories: the first type is pyroprocessing technology, that is, the regeneration of lithium iron phosphate by high temperature treatment. The specific process is to generate lithium iron phosphate by hydrothermal reaction or solvothermal reaction of lithium source and waste lithium iron phosphate cathode material, or calcining recovered waste lithium iron phosphate cathode material and lithium source by solid-phase ball milling, and calcining the waste lithium iron phosphate in a lithium-deficient state. Lithium iron phosphate is directly repaired with lithium in liquid or solid phase, and then covered with conductive agent or coated with conductive agent and doped with metal ions for targeted repair and regeneration. The main advantage of this method is that the process flow is very simple, but there are still problems such as entrainment of part of the binder, impurities in the electrolyte, and incomplete repair of the damaged lithium iron phosphate structure. The second type is the wet processing technology, that is, iron phosphate and lithium carbonate are produced by wet chemical process, and then lithium iron phosphate is regenerated by carbothermal reduction method. The process is to crush the waste lithium iron phosphate cathode material and dissolve it with acid, then add lye to adjust pH to precipitate iron and phosphorus, and obtain iron phosphate and lithium-containing solution after solid-liquid separation. Sodium carbonate or sodium bicarbonate is added to the lithium solution to obtain a lithium carbonate product, and then the obtained iron phosphate, lithium carbonate and a carbon source reducing agent are mixed and calcined to obtain a lithium iron phosphate positive electrode material. The method realizes the high value-added recovery and utilization of waste lithium iron phosphate cathode materials, but the disadvantage is that impurities such as aluminum and copper inevitably exist in waste lithium iron phosphate cathode materials. How to improve the quality of iron phosphate products has always been a restriction. The technical bottleneck of this method.

SUMMARY OF THE INVENTION

In view of the defects existing in the method for recycling waste and old lithium iron phosphate cathode material resources by wet method in the prior art, the purpose of the present invention is to provide a method for comprehensive utilization of waste and old lithium iron phosphate cathode material, which can be recovered with high recovery rate The iron, phosphorus and lithium in the waste lithium iron phosphate cathode material can be obtained at the same time with high purity and high tap density iron phosphate and high purity lithium salt, and the recovery process is simple, the conditions are mild, and the cost is low, which meets the requirements of industrial production.

In order to achieve the above-mentioned technical purpose, the present invention provides a method for comprehensive utilization of waste lithium iron phosphate positive electrode material, comprising the following steps:

1) Leaching the waste lithium iron phosphate cathode material with acid solution to obtain a leaching solution containing iron, phosphorus and lithium;

2) After adjusting the iron-to-phosphorus ratio and pH value of the leaching solution to 0.01-1.2, adding an oxidant to carry out an oxidation reaction to convert ferrous ions into iron ions, and then heating up to 80-120° C. for 8.0-48.0 hours, the reaction is completed Then, liquid-solid separation is performed to obtain a hydrated iron phosphate product and a lithium-containing solution;

3) adjusting the pH of the lithium-containing solution to 2.0 to 5.0 and adding a heavy metal precipitant to carry out a heavy metal ion precipitation reaction, and then liquid-solid separation to obtain a heavy metal precipitation residue and a lithium-containing purification solution;

4) Lithium precipitating agent is added to the lithium-containing purification solution, and the pH value of the lithium-containing purification solution is adjusted to be weakly acidic or basic to carry out lithium ion precipitation reaction, and liquid-solid separation is performed to obtain a lithium salt product.

The main reaction process of the technical solution for comprehensive utilization of waste lithium iron phosphate positive electrode materials of the present invention includes the reaction steps of leaching, generating iron phosphate, removing impurities, and precipitating lithium. The high-efficiency dissolution of ferric phosphate, phosphate and lithium is beneficial to the subsequent recovery process; the second step reaction is the synthesis of hydrated iron phosphate and the crystal growth process. It can not only effectively prevent the co-crystallization process of metal impurities such as Al ³⁺ and Cu ²⁺ , but also control them in the solution system so that they do not co-precipitate with iron ions to obtain high-purity hydrated iron phosphate. The growth process of hydrated iron phosphate crystals is regulated to obtain a hydrated iron phosphate product with high tap density, and the tap density reaches about 1.2g/cm ³ ; the third step reaction is the process of removing impurities of heavy metal ions, mainly by precipitation method to precipitate heavy metal ions Separation, the fourth step reaction is a lithium ion precipitation reaction process, and lithium is recovered in the form of lithium salt by using a lithium precipitation agent.

In the technical scheme of the present invention, the principle of controlling the formation and growth of hydrated iron phosphate crystals by controlling the acidity of the reaction system, reaction temperature and reaction time is as follows: using reaction conditions such as high acidity to ensure that the phosphorus source is mainly composed of phosphoric acid molecules or dihydrogen phosphate. The existence of radical ions, combined with the synergistic control of reaction temperature and reaction time, promotes the ionization of phosphoric acid molecules or hydrogen phosphate ions and their slow rates, releases low concentrations of phosphate ions, and greatly reduces the formation of iron phosphate precipitation. The nucleation rate can control the growth of iron phosphate grains into high-density hydrated iron phosphate with higher crystallinity. The solubility product constant Ksp (1.3×10 ^-22 ) of iron phosphate is extremely small. In the initial stage of the reaction, under the condition of high Fe ³⁺ concentration (≥1.5mol/L), even if it is a phosphoric acid molecule or phosphoric acid diphosphate The hydrogen ion ^ionizes a very small amount of phosphate ion, and it can also continuously form hydrated iron phosphate precipitate; In some cases, also because of the extremely low solubility product constant of iron phosphate, [Fe ³⁺ ]*[PO ₄ ^3- ] is also easily ≥1.3×10 ^-22 , thereby forming a hydrated iron phosphate precipitation, which ensures the complete precipitation reaction. It is precisely due to the extremely low solubility product constant of iron phosphate and the slow ionization of iron phosphate under high acidity conditions to release a very low concentration of phosphate, thus ensuring the continuous growth of hydrated iron phosphate grains, thereby obtaining high tap density hydrated iron phosphate products. . At the same concentration, the phosphate solubility product constant of metal ions such as copper is very large, and still exists in the solution system in the form of metal ions.

As a preferred technical solution, the leaching conditions are as follows: the leaching liquid-solid ratio is 2-8 mL:1 g, the temperature is 40-90° C., and the time is 1.0-5.0 h. Under the preferred leaching conditions, iron, lithium and phosphate radicals in the waste lithium iron phosphate positive electrode material can be leached to the greatest extent, so as to improve the recovery rate of useful elements. The amount of acid solution is 0.5 to 1.5 times the theoretical amount (preferably 0.8 to 1.2 times), and the theoretical amount refers to the theoretical molar amount of acid required to form the corresponding salts from Fe, Li, Al, etc. in the waste lithium iron phosphate positive electrode material. . The leachate-solid ratio is preferably 3-5mL:1g. The leaching temperature is preferably 50-80°C, and the time is preferably 1.5-3.0h. The acid solution is a sulfuric acid solution, a hydrochloric acid solution, or a mixed solution of sulfuric acid and hydrochloric acid.

As a preferred technical solution, the leaching solution adjusts the iron-phosphorus ratio to 1:1.1-1.5. The iron source or phosphorus source can be added to satisfy the ratio. Within the preferred ratio range, it is beneficial to the formation of iron phosphate precipitation and to improve the iron conversion rate. The iron-replenishing reagent is ferrous sulfate heptahydrate or ferrous sulfate solution obtained by dissolving iron flakes/iron filings in sulfuric acid, and the phosphorus-replenishing reagent is phosphoric acid, sodium or potassium or ammonium monohydrogen phosphate or dihydrogen phosphate or phosphate. One or more of these reagents are well known in the industry.

As a preferred technical solution, the oxidant is at least one of hydrogen peroxide, potassium peroxide, sodium peroxide, and persulfate. Persulfate is one or more of sodium, potassium or ammonium persulfate.

As a preferred technical solution, the amount of the oxidant is measured by 1 to 2 times the theoretical molar amount of the oxidant required to convert all the ferrous ions in the leachate into iron ions.

As a preferred technical solution, in the preparation process of converting phosphorus and iron into hydrated iron phosphate in step 2), the pH value of the leaching solution is preferably adjusted to 0.01-1.2 (more preferably 0.1-0.8). Process parameters for preparing hydrated iron phosphate by precipitating Fe and P: the precipitation reaction temperature is preferably 90-115°C, and the precipitation reaction time is preferably 10.0-36.0h. The reagent used to adjust the pH of the solution is one or more of sulfuric acid, ammonia water or lithium hydroxide solution with a concentration of 1:1.

As a preferred technical solution, the conditions of the oxidation reaction are as follows: the temperature is 30-80° C., and the time is 1.0-2.0 h. The oxidation reaction temperature is preferably 40-60° C., and the time is preferably 1.2-1.5 h.

As a preferred technical solution, the conditions of the precipitation reaction are as follows: the temperature is 30-80° C., the time is 1.5-5.0 h, and the amount of the heavy metal precipitant is to convert all the heavy metal ions in the lithium-containing solution into the required amount of precipitation. 0.8 to 2.5 times the theoretical molar amount of the heavy metal precipitant. The preferred pH during the heavy metal ion precipitation reaction is 3.0-4.0. The preferred reaction temperature is 40 to 60°C. The preferred reaction time is 2.0 to 3.0 h. The preferred amount of heavy metal precipitant is 1 to 2 times the theoretical amount. During the heavy metal ion precipitation reaction, the reagent for adjusting the pH of the solution is one or more of 1:1 dilute ammonia water or lithium hydroxide solution. Heavy metal precipitants are water-soluble hydroxides (such as common sodium hydroxide, potassium hydroxide, etc.), water-soluble sulfide salts (such as sodium sulfide, etc.), water-soluble hydrosulfides (such as sodium hydrosulfide, etc.), insoluble active two One or more of valence iron compounds (such as active ferrous sulfide), the theoretical dosage is calculated according to MS or M(OH) ₂ (M represents heavy metal ions such as Cu ²⁺ ).

As a preferred technical solution, the conditions of the lithium ion precipitation reaction are as follows: the temperature is 30-80° C., the time is 1.5-3.0 h, and the amount of the lithium precipitating agent is used to convert all the lithium ions in the lithium-containing purification solution into The corresponding precipitation needs 1 to 1.5 times the theoretical molar amount of the lithium precipitant. During the lithium ion precipitation reaction process: the preferred pH is 7.0-10.0, the preferred reaction temperature is 40-60°C, the preferred reaction time is 2-2.5h; the preferred dosage of lithium precipitant is 1.1-1.3 of the theoretical amount times. In the process of preparing lithium salt by lithium ion precipitation reaction, the reagent for adjusting the pH of the solution is one or more of 1:1 dilute ammonia water or lithium hydroxide solution. The precipitation reagents for precipitating lithium ions are water-soluble carbonate (such as sodium carbonate/ammonium, etc.), water-soluble bicarbonate (sodium bicarbonate/ammonium, etc.), water-soluble phosphate (sodium/ammonium phosphate), water-soluble hydrogen phosphate One or more of salts (sodium hydrogen phosphate/ammonium) and water-soluble dihydrogen phosphate (sodium dihydrogen phosphate/ammonium, etc.), the theoretical dosage of the precipitation reagent is calculated according to the lithium salt.

The waste lithium iron phosphate positive electrode material of the present invention is powder produced by the waste lithium iron phosphate battery after crushing and sorting, and mainly includes the lithium iron phosphate positive electrode active material.

A method for comprehensive utilization of waste lithium iron phosphate positive electrode materials provided by the invention comprises the following specific steps:

(1) Controllable leaching process of waste lithium iron phosphate cathode material: Mix waste lithium iron phosphate cathode material with a certain concentration and volume of acid solution leaching agent, and the amount of acid leaching agent is 0.5 to 1.5 times the theoretical amount. The solid ratio is 2～8:1, and the temperature is controlled at 40～90℃, and the reaction is carried out for 1.0～5.0h, and Fe, P and Li in the waste lithium iron phosphate cathode material are transferred into the solution, and the liquid-solid separation is obtained. Leachate and leaching residue, the leaching solution is used to prepare hydrated iron phosphate and lithium carbonate, and the leaching residue is used to recover Al and graphite powder.

(2) Preparation process of selective precipitation of Fe/P or hydrated ferric phosphate: including the oxidation of Fe ²⁺ to Fe ³⁺ and the preparation of hydrated ferric phosphate by precipitating Fe and P: analysis step (1) Fe and P content in the leaching solution , based on the Fe/P ratio of 1:1.1 to 1.5, add the missing iron source or phosphorus source, and adjust the pH value of the solution to 0.01 to 1.2 (more preferably 0.1 to 0.8), add an oxidant to remove the Fe in the solution ²⁺ is oxidized to Fe ³⁺ , the amount of oxidant is 1.1 to 2.0 times the theoretical amount of oxidized Fe ²⁺ , the oxidation reaction temperature is 30 to 80 ° C, the oxidation reaction time is 1.0 to 2.0 h, and then the temperature is raised to 80 to 120 ° C. Precipitation The reaction time is 6.0-48.0h, and hydrated iron phosphate is generated. After the reflux reaction is completed, the liquid-solid separation is performed to obtain Li ⁺ filtrate and crude hydrated iron phosphate; the Li ⁺ filtrate is used to prepare lithium carbonate products, and the crude hydrated iron phosphate is washed with water until chlorinated. After the barium solution or silver nitrate solution detects no sulfate ion or chloride ion, it is dried to obtain high-purity hydrated iron phosphate.

(3) Precipitation lithium ion or lithium carbonate preparation process: including two processes of removing heavy metal ions by precipitation and preparing lithium salt products: the process of removing heavy metal ions by precipitation is to add an alkali reagent to the Li filtrate containing step ( ² ), adjust The pH value of the solution is 2.0-5.0, and heavy metal precipitating agent is added to remove a small amount of heavy metal ions such as Cu ²⁺ in the Li ⁺ filtrate. The amount of heavy metal precipitating agent is 0.8-2.5 times the theoretical amount, the precipitation reaction temperature is 30-80 ℃, and the reaction time The process of preparing lithium salt by precipitation method is to add lithium precipitant to the Li ⁺ purification solution, adjust the pH value of the system to 6.0-12.0, ^and then adjust the pH value of the system to 6.0-12.0. Under the temperature condition of 30～80℃, the constant temperature reaction is performed for 1.5～3.0h, and the liquid-solid separation is carried out to obtain the precipitation lithium filtrate and the crude lithium salt product. After the barium chloride solution or silver nitrate solution detects no sulfate ion or chloride ion, it is dried to obtain a high-purity lithium salt product.

Relative to the prior art, the beneficial technical effects brought by the technical solution of the present invention:

1. The present invention not only comprehensively recovered the main components such as phosphorus, iron, and lithium elements in the waste lithium iron phosphate positive electrode material, but also recovered the entrained aluminum, copper, etc. and graphite powder negative electrode material, and the recovery rate of each component was higher, can reach more than 90%.

2. The controllable leaching process of leaching the waste lithium iron phosphate cathode material in the present invention divides aluminum, graphite powder, iron, lithium and phosphorus into two groups, which greatly reduces the purification of solutions containing Fe ²⁺ , Li ⁺ and PO ₄ ^3- The burden is to prepare the hydrated iron phosphate under the condition of high acidity, which avoids the entry of impurity components such as Al ³⁺ and Cu ²⁺ into the hydrated iron phosphate product, can obtain high-purity and high tap density iron phosphate, and simplifies the synthesis of hydrated iron phosphate. craft.

3. The present invention adopts ammonium salt or lithium salt or ammonia water or lithium hydroxide as solution pH adjusting reagent and precipitation reagent, which avoids the introduction of other cationic components in the solution, and obtains high-purity lithium salt after heavy metal ion precipitation and impurity removal. product.

Description of drawings

Fig. 1 is the technological process of comprehensive utilization of waste lithium iron phosphate cathode material;

Fig. 2 is the SEM photo of embodiment 1 hydrated iron phosphate;

Fig. 3 is embodiment 1 hydrated iron phosphate product XRD figure;

Fig. 4 is the SEM photo of embodiment 2 hydrated iron phosphate;

Fig. 5 is embodiment 2 hydrated iron phosphate product XRD figure;

Fig. 6 is the SEM photo of embodiment 3 hydrated iron phosphate;

Fig. 7 is embodiment 3 hydrated iron phosphate product XRD figure;

Fig. 8 is the SEM photo of embodiment 4 hydrated iron phosphate;

Fig. 9 is the XRD figure of the hydrated iron phosphate product of embodiment 4;

Fig. 10 is the SEM photo of embodiment 5 hydrated iron phosphate;

Figure 11 is the XRD pattern of the hydrated iron phosphate product of Example 5.

Detailed ways

The following examples are intended to further illustrate the content of the present invention, rather than limit the scope of protection of the claims.

Example 1

(1) Controllable leaching process of waste lithium iron phosphate positive electrode material: Weigh 100 g of waste lithium iron phosphate battery positive electrode material according to the stoichiometry of iron/phosphorus/lithium in the raw material, add 0.8 times the theoretical amount of sulfuric acid, and control the liquid-solid ratio 3:1, the leaching temperature is 50 °C, and the leaching time is 2.0 h to obtain a suspension, and vacuum filtration is performed for liquid-solid separation to obtain a leaching solution containing lithium/phosphorus/iron and a leaching slag containing aluminum/graphite powder. The contents of Fe, Li, P and Al in the leaching solution were analyzed and measured, and the leaching rate was calculated.

(2) Preparation process of selective precipitation Fe/P or hydrated ferric phosphate: according to the measured values of Fe and P in the leaching solution in step (1), the ratio of Fe:P according to the amount of substances is 1:1.15 and ferrous sulfate heptahydrate is added , stir until the ferrous sulfate solid is completely dissolved, use 1:1 dilute sulfuric acid to adjust the pH value of the solution to 0.20, add 30% hydrogen peroxide to oxidize the ferrous ions, the dosage is 1.2 times the theoretical dosage, and the oxidation temperature is 40 ℃. The oxidation reaction time was 1.0h, then the temperature of the reaction system was raised to 100°C, and the reaction was performed under constant temperature reflux for 18.0h. After the reaction reached the end point, the filtrate was separated from the liquid and solid by vacuum suction to obtain a filtrate containing lithium ions. The filter residue was washed with water until there was no sulfate ion. Dry to obtain a hydrated iron phosphate product. The content of Fe, P and Li in the filtrate was analyzed, and the precipitation rate was calculated. The hydrated iron phosphate product was sent for ICP full-component determination, and the Fe/P in the hydrated iron phosphate product was calculated. The hydrated iron phosphate product was sampled for tap density determination, SEM and XRD detection.

(3) Precipitation of lithium ions or lithium carbonate preparation process: analysis and determination of the content of Cu ²⁺ in the filtrate containing Li ⁺ in step (2), using a 1:1 LiOH solution to adjust the pH of the solution to 3.5, adding 1.2 times the theoretical amount of Ammonium sulfide solution, carry out sulfide precipitation to remove heavy metal ^ions , control the reaction temperature to be 40 °C, and the reaction time to be 2.0 h to reach the end of the reaction ^. times of ammonium bicarbonate to precipitate lithium ions, use 1:1 dilute ammonia water to adjust the pH of the solution to 8, the reaction temperature of the constant system is 60 °C, and the reaction time is 2.0 h. After the reaction is completed, vacuum filtration, washing and drying are used to obtain carbonic acid. Lithium products were sampled for ICP full component content determination.

The leaching rate of main elements in step (1) and the precipitation rate of main elements in step (2) are shown in Table 1, the hydrated iron phosphate ICP detection results and Fe/P and tap density are shown in Table 2, and the lithium carbonate ICP detection results are shown in Table 3, The SEM and XRD test results of the hydrated iron phosphate product are shown in Figures 1 and 2.

Example 2

(1) Controllable leaching process of waste lithium iron phosphate positive electrode material: Weigh 100g of waste lithium iron phosphate battery positive electrode material, calculate according to the stoichiometry of iron/phosphorus/lithium in the raw material, add 1.2 times the theoretical amount of hydrochloric acid to control the liquid-solid The ratio was 4:1, the leaching temperature was 80 °C, and the leaching time was 3.0 h to obtain a suspension, which was subjected to liquid-solid separation by vacuum filtration to obtain the leaching solution containing lithium/phosphorus/iron and the leaching slag containing aluminum/graphite powder. The contents of Fe, Li, P and Al in the leaching solution were analyzed, and the leaching rate was calculated.

(2) Selective precipitation Fe/P or hydrated ferric phosphate preparation process: according to the measured values of Fe and P in the leaching solution of step (1), add ammonium dihydrogen phosphate according to the ratio Fe:P of the amount of matter to 1:1.2, Stir until the solid ammonium dihydrogen phosphate is completely dissolved, use 1:1 dilute sulfuric acid to adjust the pH of the solution to 0.30, add 30% hydrogen peroxide to oxidize the ferrous ions, the dosage is 1.3 times the theoretical dosage, and the oxidation temperature is 60 ℃ , the oxidation reaction time is 1.5h, then the temperature of the reaction system is raised to 1005°C, and the constant temperature reflux reaction is performed for 24.0h. After the reaction reaches the end point, the filtrate is separated from the liquid and solid by vacuum suction to obtain a filtrate containing lithium ions, and the filter residue is washed with water until there is no chloride ion. , drying to obtain a hydrated iron phosphate product. The content of Fe, P and Li in the filtrate was analyzed, and the precipitation rate was calculated. The hydrated iron phosphate product was sent for ICP full-component determination, and the Fe/P in the hydrated iron phosphate product was calculated. The hydrated iron phosphate product was sampled for tap density determination and SEM and XRD detection.

(3) Precipitated lithium ion or lithium carbonate preparation process: analysis and determination step ( ² ) Cu content in Li ⁺ filtrate, using 1:1 LiOH solution to adjust the pH of the solution to 4.0, adding 1.15 times the theoretical amount of ammonium sulfide , carry out sulfide precipitation to remove heavy metal ions, control the reaction temperature to be 60 °C, and the reaction time to be 1.50 h. At the end of the reaction, vacuum filtration to obtain a purified solution containing Li ⁺ ; measure the concentration of Li ⁺ in the purified solution, and add 1.3 times the theoretical amount of hydrogen carbonate. Ammonium was used to precipitate lithium ions, and 1:1 diluted ammonia water was used to adjust the pH of the solution to 9. The reaction temperature of the constant system was 60 °C, and the reaction time was 1.5 h. After the reaction was completed, vacuum filtration, washing, and drying were performed to obtain lithium carbonate products, which were sampled. Perform ICP total component content determination.

The leaching rate of main elements in step (1) and the precipitation rate of main elements in step (2) are shown in Table 1, the hydrated iron phosphate ICP detection results and Fe/P and tap density are shown in Table 2, and the lithium carbonate ICP detection results are shown in Table 3, The SEM and XRD test results of the hydrated iron phosphate product are shown in Figures 3 and 4.

Example 3

(1) Controllable leaching process of waste lithium iron phosphate positive electrode material: Weigh 100g of waste lithium iron phosphate battery positive electrode material, calculate according to the stoichiometry of iron/phosphorus/lithium in the raw material, add 1.0 times the theoretical amount of sulfuric acid to control the liquid-solid The ratio is 5:1, the leaching temperature is 70 °C, and the leaching time is 3.0 h to obtain a suspension, which is subjected to liquid-solid separation by vacuum filtration to obtain a leaching solution containing lithium/phosphorus/iron and a leaching slag containing aluminum/graphite powder. The contents of Fe, Li, P and Al in the leaching solution were analyzed, and the leaching rate was calculated.

(2) The preparation process of selective precipitation of Fe/P or hydrated iron phosphate: according to the measured values of Fe and P in the leaching solution in step (1), the ratio of Fe:P according to the amount of matter is 1:1.2 to supplement the solid-phase dihydrogen phosphate ammonium, stir until the solid ammonium dihydrogen phosphate is completely dissolved, use 1:1 dilute sulfuric acid to adjust the pH value of the solution to 0.30, add 30% hydrogen peroxide to oxidize the ferrous ions, the dosage is 1.15 times the theoretical dosage, and the oxidation temperature is 50°C, the oxidation reaction time is 2.0h, then the temperature of the reaction system is raised to 95°C, and the reaction is carried out under constant temperature reflux for 30.0h. After the reaction reaches the end point, the filtrate is vacuum suctioned for liquid-solid separation to obtain a filtrate containing lithium ions, and the filter residue is washed with water until it is free of Sulfate ion, drying to obtain hydrated iron phosphate product. The content of Fe, P and Li in the filtrate was analyzed, and the precipitation rate was calculated. The hydrated iron phosphate product was sent for ICP full-component determination, and the Fe/P in the hydrated iron phosphate product was calculated. The hydrated iron phosphate product was sampled for tap density determination and SEM and XRD detection.

(3) Precipitation of lithium ions or lithium carbonate preparation process: analysis and determination of step (2) Cu ²⁺ content in Li ⁺ filtrate, using 1:1 NH ₃ ﹒ The pH value of the solution was adjusted to 4.0 with H ₂ O solution, 2.0 times the theoretical amount of ammonium hydrosulfide was added to carry out sulfide precipitation to remove heavy metal ions, the reaction temperature was controlled to 60 °C, and the reaction time was 2.0 h. ⁺ Purification solution; measure the Li ⁺ concentration in the purification solution, add 1.25 times the theoretical amount of ammonium bicarbonate to precipitate lithium ions, use 1:1 dilute ammonia water to adjust the pH of the solution to 10, the constant system temperature is 50 °C, and the reaction time is 3.0h , the reaction is completed, vacuum filtration, washing, drying to obtain lithium carbonate product, and sampling is carried out to determine the content of all components by ICP.

The leaching rate of main elements in step (1) and the precipitation rate of main elements in step (2) are shown in Table 1, the hydrated iron phosphate ICP detection results and Fe/P and tap density are shown in Table 2, and the lithium carbonate ICP detection results are shown in Table 3, The SEM and XRD test results of the hydrated iron phosphate product are shown in Figures 5 and 6.

Example 4

(1) Controllable leaching process of waste lithium iron phosphate cathode material: Weigh 100 g of waste lithium iron phosphate battery cathode material, calculate according to the stoichiometry of iron/phosphorus/lithium in the raw material, add 0.9 times the theoretical amount of sulfuric acid to control the liquid-solid The ratio was 4:1, the leaching temperature was 80 °C, and the leaching time was 2.5 h to obtain a suspension, which was subjected to liquid-solid separation by vacuum filtration to obtain a leaching solution containing lithium/phosphorus/iron and a leaching slag containing aluminum/graphite powder. The contents of Fe, Li, P and Al in the leaching solution were analyzed, and the leaching rate was calculated.

(2) Selective precipitation Fe/P or hydrated ferric phosphate preparation process: according to the measured values of Fe and P in the leaching solution in step (1), add the missing heptahydrate sulfuric acid according to the ratio Fe:P of the substance to 1:1.15 Ferrous iron, stir until the solid phase of ferrous sulfate is completely dissolved, use 1:1 dilute sulfuric acid to adjust the pH value of the solution to 0.50, add 30% hydrogen peroxide to oxidize the ferrous ions, the dosage is 1.2 times the theoretical dosage, and the oxidation temperature The temperature of the reaction system was raised to 115°C, and the reaction was carried out under constant temperature reflux for 18.0h. After the reaction reached the end point, the filtrate was separated from the solid by vacuum suction to obtain a filtrate containing lithium ions. The filtrate was washed with water until No sulfate ion, drying to obtain hydrated iron phosphate product. The content of Fe, P and Li in the filtrate was analyzed, and the precipitation rate was calculated. The hydrated iron phosphate product was sent for ICP full-component determination, and the Fe/P in the hydrated iron phosphate product was calculated. The hydrated iron phosphate product was sampled for tap density determination and SEM and XRD detection.

(3) Precipitation of lithium ions or lithium carbonate preparation process: analysis and determination of step (2) the content of Cu ²⁺ in the Li ⁺ -containing solution, using 1:1 LiOH solution to adjust the pH of the solution to 4.5, adding 1.20 times the theoretical amount of Ammonium sulfide, carry out sulfide precipitation to remove heavy metal ions, control the reaction temperature to 50°C, and the reaction time to 2.0h. At the end of the reaction, vacuum filtration to obtain a purified solution containing Li ⁺ ; measure the concentration of Li ⁺ in the purified solution, and add 2.0 times the theoretical amount. Ammonium phosphate was used to precipitate lithium ions, the pH value of the solution was adjusted to 9 with 1:1 dilute ammonia water, the reaction temperature of the constant system was 50°C, and the reaction time was 2.5h. Perform ICP total component content determination.

The leaching rate of main elements in step (1) and the precipitation rate of main elements in step (2) are shown in Table 1, the hydrated iron phosphate ICP detection results and Fe/P and tap density are shown in Table 2, and the lithium phosphate ICP detection results are shown in Table 3, The SEM and XRD test results of the hydrated iron phosphate product are shown in Figures 7 and 8.

Example 5

(1) Controllable leaching process of waste lithium iron phosphate cathode material: Weigh 100g of waste lithium iron phosphate battery cathode material, calculate according to the stoichiometry of iron/phosphorus/lithium in the raw material, add 1.2 times the theoretical amount of sulfuric acid to control the liquid-solid The ratio was 4:1, the leaching temperature was 80 °C, and the leaching time was 1.5 h to obtain a suspension, which was subjected to liquid-solid separation by vacuum filtration to obtain a leaching solution containing lithium/phosphorus/iron and a leaching slag containing aluminum/graphite powder. The contents of Fe, Li, P and Al in the leaching solution were analyzed, and the leaching rate was calculated.

(2) The preparation process of selective precipitation Fe/P or hydrated iron phosphate: according to the measured values of Fe and P in the leaching solution in step (1), the ratio of Fe:P is 1:1.2, and the missing dihydrogen phosphate is added Ammonium solid, stir until the solid phase of ammonium dihydrogen phosphate is completely dissolved, use 1:1 dilute sulfuric acid to adjust the pH value of the solution to 0.6, add 30% hydrogen peroxide to oxidize the ferrous ion, the dosage is 1.5 of the theoretical dosage, and the oxidation temperature The temperature of the reaction system was raised to 110 °C, and the constant temperature reflux reaction was 36.0 h. After the reaction reached the end point, the filtrate was separated from the solid by vacuum suction to obtain a filtrate containing lithium ions, and the filter residue was washed with water. To the absence of sulfate ions, drying to obtain a hydrated iron phosphate product. The content of Fe, P and Li in the filtrate was analyzed, and the precipitation rate was calculated. The hydrated iron phosphate product was sent for ICP full-component determination, and the Fe/P in the hydrated iron phosphate product was calculated. The hydrated iron phosphate product was sampled for tap density determination and SEM and XRD detection.

(3) Precipitation lithium ion or lithium carbonate preparation process: analysis and determination step (2) Cu ²⁺ content in Li ⁺ -containing solution, using 1:1 LiOH solution to adjust the pH value of the solution to 3.5, adding 1.5 times the theoretical amount of sulfide ammonium, carry out sulfide precipitation to remove heavy metal ions, control the reaction temperature to 60°C, and the reaction time to 1.5h. At the end of the reaction, vacuum filtration to obtain a purified solution containing Li ⁺ ; measure the concentration of Li ⁺ in the purified solution, and add 2.0 times the theoretical amount of phosphoric acid. Ammonium dihydrogen was used to precipitate lithium ions, and 1:1 dilute ammonia water was used to adjust the pH of the solution to 9. The reaction temperature of the constant system was 60 °C, and the reaction time was 3.0 h. After the reaction was completed, the lithium phosphate product was obtained by vacuum filtration, washing and drying. Samples were taken for ICP full-component content determination.

The leaching rate of main elements in step (1) and the precipitation rate of main elements in step (2) are shown in Table 1, the hydrated iron phosphate ICP detection results and Fe/P and tap density are shown in Table 2, and the lithium phosphate ICP detection results are shown in Table 3, The SEM and XRD test results of the hydrated iron phosphate product are shown in Figure 9 and Figure 10 .

Comparative Example 1

Step (2) adjust the pH value of the solution with 1:1 dilute sulfuric acid to be 2.0, and other processes are the same as in Example 1. The leaching rate of main elements in step (1) and the precipitation rate of main elements in step (2) are shown in Table 1. The tap density of hydrated iron phosphate was determined to be only 0.8702 g/cm ³ .

As can be seen from the results in Table 1, although the precipitation rates of Fe, P and Li in step (2) have increased, due to the high pH in the preparation process of hydrated iron phosphate, the nucleation rates of iron ions and phosphate ions are relatively large. The grain growth rate of hydrated ferric phosphate is reduced, resulting in a significantly lower tap density of hydrated ferric phosphate products.

Comparative Example 2

The reflux constant temperature reaction temperature of step (2) is 70 DEG C, and other processes are the same as in Example 1. After the liquid-solid separation of the synthetic hydrated iron phosphate product, the concentrations of the remaining iron ions and phosphate ions in the precipitated iron/phosphorus filtrate were measured, and the calculated precipitation rates of iron ions and phosphate ions were only 69.3% and 67.8%. Obviously, too low temperature is not conducive to the precipitation of iron ions and phosphate ions.

Table 1: The leaching rate of main elements in step (1) and the precipitation rate of main elements in step (2)

Table 2: ICP detection results of hydrated iron phosphate and Fe/P and tap density

Test items Example 1 Example 2 Example 3 Example 4 Example 5 Tap density (g/cm³) 1.2013 1.2562 1.1878 1.2137 1.1905 P(%) 16.08 15.98 16.67 16.70 16.36 Fe(%) 29.03 28.87 30.09 30.15 29.52 Fe/P 0.9994 1.0001 0.9986 0.9994 0.9989 Ca(ppm) 5.3 8.7 2.8 3.5 7.1 Mg(ppm) 1.1 3.9 2.5 1.9 4.2 Na(ppm) 5.1 6.7 3.6 2.3 1.9 Ni(ppm) 0.1 0.9 0.6 0.8 0.2 Zn(ppm) 0.8 0.4 0.2 0.6 0.3 Cu(ppm) 0.3 0.5 0.2 0.6 0.4 Mn(ppm) 4.1 3.9 7.2 5.7 6.3 Pb(ppm) 1.3 2.8 1.9 1.6 2.5 Cr(ppm) 0.9 0.4 0.6 0.2 0.7 K(ppm) 1.3 2.8 1.7 3.0 1.9 Co(ppm) 0.2 0.7 0.6 0.3 0.5 Al(ppm) 99 87 103 92 101 S(ppm) 110 108 127 93 105

Table 3: Lithium Carbonate or Lithium Phosphate ICP Test Results

Claims (9)

1. a method for utilizing the comprehensive utilization of waste and old lithium iron phosphate positive electrode material, is characterized in that: may further comprise the steps: 1) Leaching the waste lithium iron phosphate cathode material with acid solution to obtain a leaching solution containing iron, phosphorus and lithium; 2) After adjusting the iron-to-phosphorus ratio and pH value of the leaching solution to 0.01-1.2, adding an oxidant to carry out an oxidation reaction to convert ferrous ions into iron ions, and then heating up to 80-120° C. for 8.0-48.0 hours, the reaction is completed Then, liquid-solid separation is performed to obtain a hydrated iron phosphate product and a lithium-containing solution; 3) adjusting the pH of the lithium-containing solution to 2.0 to 5.0 and adding a heavy metal precipitant to carry out a heavy metal ion precipitation reaction, and then liquid-solid separation to obtain a heavy metal precipitation residue and a lithium-containing purification solution; 4) adding a lithium precipitant to the lithium-containing purification solution and adjusting the pH value of the lithium-containing purification solution to be weakly acidic or alkaline, and after lithium ion precipitation reaction, liquid-solid separation to obtain a lithium salt product. 2. a kind of method utilizing waste lithium iron phosphate cathode material comprehensive utilization according to claim 1, is characterized in that: the condition of described leaching is: leachate solid ratio is 2～8mL:1g, and temperature is 40～90 ℃ , the time is 1.0-5.0h, the amount of acid solution is 0.5-1.5 times the theoretical molar amount of acid required to convert Fe, Li, Al into corresponding salts, and the acid solution is sulfuric acid solution, hydrochloric acid solution, or sulfuric acid and hydrochloric acid. mixed solution. 3 . The method for comprehensive utilization of waste lithium iron phosphate positive electrode material according to claim 1 , wherein the leaching solution adjusts the iron-to-phosphorus ratio to 1:1.1-1.5. 4 . 4. a kind of method utilizing waste lithium iron phosphate cathode material comprehensive utilization according to claim 1, is characterized in that: The oxidant is at least one of hydrogen peroxide, potassium peroxide, sodium peroxide and persulfate; The amount of the oxidant is calculated by 1 to 2 times the theoretical molar amount of the oxidant required to convert all the ferrous ions in the leaching solution into iron ions. 5. A method for comprehensive utilization of waste lithium iron phosphate positive electrode material according to claim 1 or 4, characterized in that: the condition of the oxidation reaction is: the temperature is 30～80 ℃, and the time is 1.0～2.0h . 6. A method for comprehensive utilization of waste lithium iron phosphate positive electrode material according to claim 1, characterized in that: the conditions for the heavy metal ion precipitation reaction are: the temperature is 30～80 ℃, and the time is 1.5～5.0h The dosage of the heavy metal precipitant is calculated by 0.8 to 2.5 times the theoretical molar amount of the heavy metal precipitant required to convert all the heavy metal ions in the lithium-containing solution into precipitation. 7. a kind of method utilizing waste lithium iron phosphate cathode material comprehensive utilization according to claim 6, is characterized in that: described heavy metal ion precipitating agent is water-soluble hydroxide, water-soluble sulfide salt, water-soluble hydrosulfuric acid At least one of the salts, or an insoluble active divalent iron material (such as ferrous sulfide, etc.). 8. A method for comprehensive utilization of waste lithium iron phosphate positive electrode material according to claim 1, characterized in that: the conditions for the lithium ion precipitation reaction are: the temperature is 30～80°C, and the time is 1.5～3.0h , the amount of the lithium precipitant is calculated by 1 to 1.5 times the theoretical molar amount of the lithium precipitant required to convert all the lithium ions in the lithium-containing purification solution into precipitation. 9. a kind of method utilizing waste lithium iron phosphate cathode material comprehensive utilization according to claim 8, is characterized in that: described lithium precipitating agent is water-soluble carbonate, water-soluble bicarbonate, water-soluble phosphate, At least one of water-soluble hydrogen phosphate and water-soluble dihydrogen phosphate.

Images