Method for recovering iron phosphate and lithium carbonate from positive electrode material of waste lithium battery

Abstract

This invention discloses a method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials. The preparation method includes the following steps: (1) sequentially heating and acidifying the waste lithium battery cathode material with microwave to obtain product a; the microwave heating temperature is 450-650℃; (2) ball milling product a in the presence of acid to obtain product b; during the ball milling process, the mass of the grinding balls is 30%-60% of the total mass of the ball-milled material; the ball milling time is 0.8-3h; (3) separating iron and lithium from product b to obtain iron phosphate and lithium carbonate respectively. The method of this invention is not only simple in process, short in time, and low in production cost, but also has a high leaching rate of iron and lithium elements.

Description

Technical Field

[0001] This invention relates to a method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials. Background Technology

[0002] Lithium-ion batteries possess numerous advantages, including high energy density and long lifespan, and have been widely used in electric vehicles, energy storage, and electronic products. Among various types of lithium-ion batteries, lithium iron phosphate (LFP) batteries have significant potential advantages in material cost and cycle life, and are generally considered the future direction for lithium battery cathode materials. With the development of the lithium battery industry and the large-scale application of LFP batteries, the number of waste LFP batteries is becoming increasingly substantial. Recycling and reusing waste LFP batteries, especially their cathode materials, offers both economic and environmental benefits.

[0003] Chinese invention patent document CN114249313A discloses a method for recovering battery-grade iron phosphate from waste lithium iron phosphate powder. The method involves separating lithium iron phosphate from the electrode by adding acid, oxidizing ferrous iron to ferric iron by adding hydrogen peroxide, adjusting the pH to precipitate iron phosphate, and finally purifying with nitric acid solution. While this method can yield battery-grade iron phosphate, it neglects the recovery of other elements such as lithium, resulting in resource waste.

[0004] Chinese invention patent document CN113120876A discloses a method for regenerating and preparing lithium iron phosphate (LFP) materials from waste LFP battery electrodes. The method involves alkali washing of waste battery electrodes to obtain LFP active material, followed by acid leaching and filtration. The pH of the leaching mother liquor is adjusted to precipitate iron phosphate and remove impurities. After filtration, carbonate is added to precipitate lithium. Finally, the obtained iron phosphate and lithium carbonate are co-calcined to regenerate LFP battery materials. Although this method achieves full recovery of lithium, iron, and phosphorus from waste LFP, the process uses pressurized acid leaching and oxidizing gas to completely dissolve the LFP active material. In practice, with a large number of electrodes, not only is acid dissolution time long and inefficient, but the use of oxidants also increases production costs.

[0005] Chinese invention patent CN106450547B discloses a method for recovering iron phosphate and lithium carbonate from lithium iron phosphate waste. This method involves a series of processes: oxidative roasting, electrode cleaning, phosphoric acid ball milling activation, acid washing to separate FePO4, and filtrate precipitation of lithium, enabling the separate recovery of iron phosphate and lithium carbonate. While this process boasts a high resource recovery rate, it involves ball milling the oxidized and roasted electrodes. Firstly, the initial oxidative roasting temperature is not high, making complete oxidation and uneven oxidation difficult when dealing with a large number of electrodes. Secondly, the subsequent steps involve adding concentrated phosphoric acid and dilute sulfuric acid, resulting in a relatively large amount of acid used. Summary of the Invention

[0006] The technical problem solved by this invention is to overcome the shortcomings of existing technologies in recycling waste lithium batteries, such as long processing time, high production costs, and low leaching rates of iron and lithium. This invention provides a method for recovering iron phosphate and lithium carbonate from the cathode material of waste lithium batteries. The method of this invention is not only simple in process, short in time, and low in production cost, but also achieves a high leaching rate of iron and lithium.

[0007] Existing methods for recycling spent lithium batteries typically involve adding acid and an oxidant to lithium iron phosphate (LFP) to convert it into insoluble iron phosphate and soluble lithium salts, followed by precipitation and filtration to separate the iron and lithium. However, simply adding the acid and oxidant mixture to the LFP slurry causes the LFP powder to tend to accumulate at the bottom, and even stirring cannot ensure sufficient contact between the materials for a complete reaction.

[0008] This invention employs microwave acidification to pre-activate the microwave-heated product with acid, shortening the subsequent reaction time while increasing the leaching rates of iron and lithium. Sufficient acid is added to the microwave-acidified iron-phosphorus material, and ball milling is used to ensure a thorough reaction. Although both Li3Fe2(PO4)3 and Fe2O3 are soluble in acid, in practice, their reaction rate with acid is found to be very slow. Therefore, this invention uses microwave acidification for pre-activation, ensuring thorough mixing and pre-reaction with the acid solution. Subsequent ball milling creates a localized high-temperature, high-pressure environment, allowing the active iron-phosphorus material to fully contact the acid solution. This two-step approach shortens the reaction time, improves reaction efficiency, and simultaneously increases the leaching rates of iron and lithium.

[0009] The present invention solves the above-mentioned technical problems through the following technical solutions:

[0010] This invention provides a method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials, comprising the following steps:

[0011] (1) Waste lithium battery cathode material is successively subjected to microwave heating and microwave acidification to obtain product a; the temperature of microwave heating is 450-650℃.

[0012] (2) In the presence of acid, the product a is ball-milled to obtain product b;

[0013] During the ball milling process, the mass of the grinding balls is 30%-60% of the total mass of the material being milled; the milling time is 0.8-3 hours.

[0014] (3) The product b is subjected to lithium iron phosphate separation to obtain iron phosphate and lithium carbonate respectively.

[0015] In step (1), the waste lithium battery cathode material can be conventional waste lithium iron phosphate battery cathode material in the art.

[0016] Preferably, the waste lithium iron phosphate battery cathode material comprises 4.4% Li, 28.5% Fe, 1.4% Al, 16.7% P, 0.9% Cu and 45.1% O, where % refers to the percentage of each element in the total mass of the waste lithium iron phosphate battery cathode material.

[0017] In step (1), the microwave heating temperature is preferably 500-620°C, for example 500°C, 550°C or 600°C.

[0018] In step (1), the microwave heating time can be 0.5-2h, preferably 0.5-1h, for example 0.5h or 1h.

[0019] In step (1), the gas atmosphere for microwave heating is generally air.

[0020] In the recycling process of waste lithium batteries, most of the current methods use traditional high-temperature sintering. When processing large quantities of lithium iron phosphate, this method suffers from uneven heating reaction. Although the external materials can reach high temperatures, the internal materials may not reach the set temperature. This invention uses microwave heating to fully convert the divalent iron in lithium iron phosphate into trivalent iron in a high-temperature oxygen-containing environment, avoiding the use of subsequent oxidants. At the same time, it removes the binder, making it easier to separate the active material of lithium iron phosphate from the aluminum electrode plate by crushing and alkaline leaching.

[0021] According to conventional practice in the art, after microwave heating and before microwave acidification, crushing, sieving, alkaline washing, and filtration are generally required. The mesh size of the sieve used in the crushing and sieving process can be conventional in the art, for example, 40 mesh. After crushing and sieving, the particle size of the product is generally below 0.355 mm. In the alkaline washing process, the alkali used can be conventional in the art, such as an aqueous solution of sodium hydroxide. The mass concentration of the aqueous solution of sodium hydroxide can be conventional in the art, for example, 10%. In the alkaline washing process, the solid-liquid ratio can be conventional in the art, for example, 5 mL / g. After filtration, the filter residue is generally dried before microwave acidification.

[0022] In step (1), microwave acidification generally refers to the operation of mixing the material to be treated with acid and then heating it with microwave.

[0023] In step (1), the type of acid used in the microwave acidification process can be conventional in the art, such as 98% concentrated sulfuric acid.

[0024] In step (1), during the microwave acidification process, the amount of acid used is preferably 4.5wt%-11wt%, more preferably 5wt%-10wt%, for example 5wt%, 6wt% or 10wt%, where wt% is the weight percentage of the acid to the substance to be acidified.

[0025] In step (1), the temperature of microwave acidification is preferably 140-260°C, more preferably 150-250°C, for example 150°C, 160°C, 200°C or 250°C.

[0026] In step (1), the microwave acidification time is preferably 0.5-1h, for example 0.5h or 1h.

[0027] In step (2), the mass of the grinding balls is preferably 30%-55% of the total mass of the grinding material, for example 30%, 40% or 50%.

[0028] In step (2), the diameter of the grinding ball is preferably 5-15 mm, for example 5 mm, 10 mm or 15 mm, and more preferably 8-12 mm.

[0029] In step (2), the frequency of the ball mill is preferably 10-30Hz, for example 10Hz, 20Hz or 30Hz, more preferably 15-25Hz.

[0030] In step (2), the ball milling time is preferably 0.8-2h, for example 1h, 1.5h or 2h.

[0031] In step (2), the type of acid can be conventional in the art, such as sulfuric acid.

[0032] In step (2), the concentration of the acid is preferably 1-3.5 mol / L, for example 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L, more preferably 2-3 mol / L. The concentration of the acid refers to the concentration of the acid in the ball-milled material.

[0033] In step (2), the product a is generally prepared as a slurry and then ball-milled.

[0034] The solvent for the slurry can be conventional in the art, such as water. The addition of water provides a wet milling environment, allowing product a to come into full contact with the acid, thus saving on the amount of acid used.

[0035] The solid-liquid ratio of the slurry can be 5-20 mL / g, for example, 10 mL / g.

[0036] In step (2), after ball milling, the waste residue is generally removed by filtration to obtain product b.

[0037] In step (3), the method for separating lithium iron phosphate can be conventional in the art, and preferably includes: adjusting the pH of the product b and then filtering it to obtain a lithium-containing filtrate and the iron phosphate;

[0038] After adjusting the pH of the lithium-containing filtrate, sodium carbonate is added to obtain the lithium carbonate.

[0039] In order to obtain the iron phosphate, the pH of the product b is generally adjusted to 2 < pH < 3, for example, 2.5.

[0040] In order to obtain the lithium carbonate, the pH of the lithium-containing filtrate can be adjusted in accordance with conventional practices in the art.

[0041] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0042] The reagents and raw materials used in this invention are all commercially available.

[0043] The positive and progressive effects of this invention are as follows:

[0044] (1) In the process of recycling waste lithium battery cathode materials, the present invention uses microwave heating to treat cathode materials, promotes high-temperature reaction process, shortens reaction time, and ensures uniform heating inside and outside the material, resulting in a more complete reaction. Microwave heating can not only remove the binder in lithium iron phosphate electrode and aluminum electrode plate, facilitating subsequent separation, but also oxidize the ferrous iron in lithium iron phosphate, so that the divalent ferrous iron is completely converted into trivalent iron, avoiding the use of oxidants in subsequent processes.

[0045] (2) In the process of recycling waste lithium battery cathode materials, the present invention uses a combination of microwave acidification and ball milling to ensure that the reactants are in full contact and promote the complete reaction.

[0046] (3) The method of the present invention is not only simple in process, short in time, and low in production cost, but also has a high leaching rate of iron and lithium elements. Attached Figure Description

[0047] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0048] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0049] In the following examples and comparative examples, the elemental contents of the waste lithium iron phosphate positive electrode sheets used, after being crushed and sieved, were determined by inductively coupled plasma (ICP) analysis, as shown in Table 1:

[0050] Table 1

[0051] element Content (wt%) lithium 4.4 iron 28.5 aluminum 1.4 phosphorus 16.7 copper 0.9 oxygen 45.1 Other impurities (graphite, calcium, magnesium, etc.) 3

[0052] Note: wt% refers to the percentage of each element in the total weight of waste lithium iron phosphate battery cathode material.

[0053] Figure 1 This is a process flow diagram of the present invention.

[0054] Example 1

[0055] Step (1), microwave heating: Weigh the waste lithium iron phosphate positive electrode sheet and microwave it in a microwave heating reactor. The temperature is controlled at 600℃ and the heating time is controlled at 0.5h.

[0056] The chemical reaction that occurs in this step is shown below:

[0057] 12LiFePO4(s)+3O2(g)==4Li3Fe2(PO4)3(s)+2Fe2O3(s)

[0058] Step (2), crushing and alkali leaching: the microwave-heated product is crushed and sieved (a 40-mesh sieve is used for sieving, and the particle size after sieving is below 0.355mm), and then washed and filtered with sodium hydroxide aqueous solution (the mass concentration of sodium hydroxide solution is 10%, and the solid-liquid ratio during the alkali washing process is 5mL / g). After filtration, filter residue and aluminum-containing solution are obtained. The filter residue is dried and recorded as product one.

[0059] Step (3), microwave acidification: Product 1 is subjected to microwave acidification reaction with 98% concentrated sulfuric acid, which is 5 wt% of the weight of Product 1. The microwave temperature is controlled at 150℃ and the reaction time is controlled at 0.5h. The product after microwave acidification is recorded as Product 2.

[0060] Step (4), high-energy ball milling: Deionized water was added to product two to prepare a slurry with a solid-liquid ratio of 10 mL / g. 98% concentrated sulfuric acid was added to the slurry and then placed in a ball mill jar for reaction in a high-energy vibrating ball mill. The ball-milled product was collected. During the collection process, a small amount of deionized water was used to rinse the ball mill jar and grinding balls, and this product was recorded as product three.

[0061] The mass of the grinding balls is 50% of the sum of the mass of the slurry and concentrated sulfuric acid. The diameter of a single grinding ball is 10 mm. The grinding frequency is 20 Hz. The grinding time is 1 h. The concentration of sulfuric acid after being diluted in the slurry is 2 mol / L.

[0062] The reactions of phosphorus iron with acid in steps (3) and (4) are as follows: Li3Fe2(PO4)3(s) + Fe2O3(s) + 6H +(aq)==3Li + (aq)+4Fe 3+ (aq) + 3PO4 3- (aq) + 3H₂O(l)

[0063] Step (5), lithium iron phosphate separation: filter the product three to remove the waste residue, add an appropriate amount of alkali solution to the filtrate to adjust the pH to 2.5, so that the ferric ions form ferric phosphate precipitate, filter, the filter residue is the ferric phosphate product, and the filtrate is recorded as product four.

[0064] Step (6), precipitation of lithium carbonate: Add alkaline solution to product four to adjust the pH, and add sodium carbonate to precipitate lithium.

[0065] In step (2), the purpose of the crushing and alkaline leaching step is to separate the lithium iron phosphate positive electrode active material from the aluminum substrate, so as to facilitate the further processing of the active material.

[0066] The phosphorus iron substances, especially Fe2O3, generated after microwave oxidation react very slowly with acid. This invention employs a combined microwave acidification and high-energy ball milling method. During microwave acidification, the oxidized phosphorus iron substances are pre-activated and their structure is partially disrupted, which is beneficial for the subsequent ball milling process. During high-energy ball milling, on the one hand, the high-speed, omnidirectional impact and disturbance of the grinding balls ensures sufficient contact between lithium iron phosphate and the acid solution, leading to a complete reaction. On the other hand, the interaction between the grinding balls, the lithium iron phosphate slurry, and the grinding jar generates localized high temperatures and pressures, accelerating the reaction.

[0067] Both Li3Fe2(PO4)3 and Fe2O3 are soluble in acids, but in practice, their reaction rate with acids is very slow. Therefore, this invention employs microwave acidification for pre-activation, thoroughly mixing them with the acid solution and generating a pre-reaction, transforming the product into a near-slurry state, which is beneficial for dispersion in the subsequent ball milling. Therefore, the amount of sulfuric acid added should not be excessive. High-energy ball milling is then used to create a localized high-temperature, high-pressure environment, allowing the phosphorus-iron active substances to fully contact the acid solution. This two-step approach effectively shortens the reaction time and improves reaction efficiency.

[0068] Example 2

[0069] Compared with Example 1, except that the microwave heating temperature in step (1) is adjusted to 500°C, all other operations and conditions are the same as in Example 1.

[0070] Compared to Example 1, the microwave heating temperature was reduced to 500°C, resulting in a slight decrease in the leaching rates of iron and lithium. At this temperature, the binder can be completely decomposed. Therefore, the microwave heating temperature mainly affects the degree of oxidation of divalent iron in lithium iron phosphate, which in turn affects the subsequent iron recovery.

[0071] Example 3

[0072] Compared with Example 1, except that the microwave heating time in step (1) is adjusted to 1 hour, all other operations and conditions are the same as in Example 1.

[0073] Compared to Example 1, the microwave heating time was increased to 1 hour, and the leaching rates of iron and lithium remained almost unchanged, demonstrating that the oxidation of ferrous iron and the decomposition of the binder can be completed within 0.5 hours of microwave heating. Compared to traditional calcination, which requires at least 1 hour, microwave heating significantly shortens the reaction time.

[0074] Example 4

[0075] Compared with Example 1, except that the microwave heating temperature in step (3) is adjusted to 250°C, all other operations and conditions are the same as in Example 1.

[0076] Compared with Example 1, increasing the reaction temperature of the microwave acidification process from 150°C to 250°C resulted in a decrease in the leaching rates of iron and lithium. The experiment also showed that increasing the microwave reaction temperature significantly increased the volatilization of sulfuric acid, leading to a reduction in the amount of sulfuric acid participating in the pre-activation reaction, thus weakening the pre-activation effect.

[0077] Example 5

[0078] Compared with Example 1, except that the microwave heating time in step (3) is adjusted to 1 hour, all other operations and conditions are the same as in Example 1.

[0079] Compared with Example 1, the reaction time of the microwave acidification process was increased from 0.5h to 1h. It was found that the leaching rate of iron and lithium remained almost unchanged, which proves that 0.5h of microwave acidification is sufficient to activate the phosphorus and iron substances after microwave heating, indicating that microwave is a highly efficient reaction aid.

[0080] Example 6

[0081] Compared with Example 1, except that the ball milling time in step (4) is adjusted to 2 hours, all other operations and conditions are the same as in Example 1.

[0082] Compared with Example 1, the ball milling time was increased to 2 hours. The results of iron and lithium recovery were not much different from those of ball milling for 1 hour. Therefore, ball milling for 1 hour is sufficient for the reaction to occur.

[0083] Example 7

[0084] Compared with Example 1, except that the amount of sulfuric acid added in step (4) was adjusted to 1 mol / L, all other operations and conditions were the same as in Example 1.

[0085] Compared with Example 1, the amount of sulfuric acid added during the high-energy ball milling process was reduced from 2 mol / L to 1 mol / L. Insufficient addition of sulfuric acid will lead to incomplete and incomplete reaction during the ball milling process, thus the leaching rate of iron and lithium will decrease significantly.

[0086] Example 8

[0087] Compared with Example 1, except that the amount of sulfuric acid added in step (4) was adjusted to 3 mol / L, all other operations and conditions were the same as in Example 1.

[0088] The amount of acid increased significantly, but the leaching rates of lithium and iron were not significantly different. Therefore, after reaching 2 mol / L, further increasing the amount of acid had very little effect on the leaching rates of iron and lithium.

[0089] Therefore, 2 mol / L is the preferred amount of sulfuric acid to be added.

[0090] Example 9

[0091] Compared with Example 1, except that the diameter of a single grinding ball in step (4) is adjusted to 5 mm, all other operations and conditions are the same as in Example 1.

[0092] Compared to Example 1, the size of the grinding balls in the high-energy ball milling process was changed, decreasing from a diameter of 10 mm to 5 mm. This resulted in a decrease in the leaching rates of lithium and iron. This is likely because the forces exerted by the grinding balls on the material during ball milling are primarily cutting and impact forces. With smaller grinding balls, cutting forces dominate, while with larger grinding balls, impact forces dominate. Since the reaction process mainly utilizes impact forces, using smaller grinding balls would have a certain negative impact on the reaction.

[0093] Example 10

[0094] Compared with Example 1, except that the diameter of a single grinding ball in step (4) is adjusted to 15 mm, all other operations and conditions are the same as in Example 1.

[0095] The leaching rates of lithium and iron also decreased, which may be because the grinding balls were too large, reducing the contact area with the materials and thus affecting the reaction effect.

[0096] Therefore, 10mm is the preferred grinding ball diameter.

[0097] Example 11

[0098] Compared with Example 1, except that the mass of the grinding balls in step (4) is adjusted to 30% of the sum of the mass of the slurry and sulfuric acid, all other operations and conditions are the same as in Example 1.

[0099] Compared to Example 1, the mass of grinding balls added during the high-energy ball milling process was reduced from 50% to 30% of the sum of the mass of slurry and sulfuric acid. The leaching rates of lithium and iron decreased, which may be because the interaction between the grinding balls and the materials was weakened when the amount of grinding balls added was less.

[0100] Example 12

[0101] Compared with Example 1, except that the frequency of high-energy ball milling in step (4) is adjusted to 10Hz, all other operations and conditions are the same as in Example 1.

[0102] Compared with Example 1, the frequency of high-energy ball milling was reduced from 20Hz to 10Hz, and the leaching rates of lithium and iron decreased. This indicates that the ball milling frequency was too low, which reduced the intensity of the reaction and had a negative effect on the reaction effect.

[0103] Example 13

[0104] Compared with Example 1, except that the frequency of high-energy ball milling in step (4) is adjusted to 30Hz, all other operations and conditions are the same as in Example 1.

[0105] Compared with Example 1, it can be seen that when the ball milling frequency is increased to 30Hz, the leaching rate of lithium and iron also decreases. On the one hand, if the ball milling frequency is too high, the material will undergo radial segregation; on the other hand, the ball milling frequency is high, the energy consumption is high, and the wear of the machine will also increase.

[0106] Therefore, 20Hz is the preferred ball milling frequency.

[0107] Example 14

[0108] Compared with Example 1, except that the amount of concentrated sulfuric acid added in step (3) was adjusted to 10 wt%, all other operations and conditions were the same as in Example 1.

[0109] Compared with Example 1, the amount of sulfuric acid added in microwave acidification was increased from 5 wt% to 10 wt%, and the leaching rates of lithium and iron changed very little. This indicates that increasing the amount of sulfuric acid in the microwave acidification step has little effect on the metal leaching rate of the entire process. This also shows that this step mainly plays the role of reaction activation, rather than the main process of the reaction.

[0110] Therefore, 5 wt% is the preferred amount of sulfuric acid added for microwave acidification.

[0111] Comparative Example 1

[0112] Step (1), microwave heating: Weigh a portion of the electrode sheet and microwave it in a microwave heating reactor. The temperature is controlled at 600℃ and the heating time is controlled at 0.5h.

[0113] Step (2), crushing and alkali leaching: the product heated by microwave is crushed and sieved, washed and filtered with sodium hydroxide alkali, and the filtered residue is dried and recorded as product one.

[0114] Step (3), sulfuric acid leaching: Deionized water was added to product one to adjust the slurry, with a solid-liquid ratio of 10 mL / g. The slurry was stirred and mixed, and sulfuric acid was added dropwise at a uniform rate. The reaction was carried out for 3 hours and recorded as product two. The amount of sulfuric acid added was 2 mol / L.

[0115] Step (4), lithium iron phosphate separation: filter product two to remove waste residue, add an appropriate amount of alkali solution to the filtrate to adjust the pH to 2.5, so that ferric ions form ferric phosphate precipitate, filter, the filter residue is ferric phosphate product, and the filtrate is recorded as product three.

[0116] Step (5), precipitation of lithium carbonate: Add alkaline solution to product three to adjust the pH, and add sodium carbonate to precipitate lithium.

[0117] Compared to the ball milling method in Example 1, Comparative Example 1 changed the reaction method of mixing sulfuric acid and lithium iron phosphate, performing a simple mixing and stirring. The experiment clearly showed that even after 3 hours of acid leaching, significant solid deposits remained at the bottom of the beaker, undissolved. This indicates that the solid iron phosphate reacted incompletely with the acid after microwave heating, and the unreacted solid iron phosphate was removed as waste, affecting the leaching rates of iron and lithium. From the perspective of iron and lithium recovery efficiency, the microwave acidification-high-energy ball milling method results in a shorter reaction time and a higher leaching rate of iron and lithium.

[0118] Comparative Example 2

[0119] Step (1), microwave heating: Weigh a portion of the electrode sheet and microwave it in a microwave heating reactor. The temperature is controlled at 500℃ and the heating time is controlled at 0.5h.

[0120] Step (2), crushing and alkali leaching: the product heated by microwave is crushed and sieved, washed and filtered with sodium hydroxide alkali, and the filtered residue is dried and recorded as product one.

[0121] Step (3), high-energy ball milling: Add deionized water to product one to adjust the slurry, with a solid-liquid ratio of 10 mL / g. Add sulfuric acid to the slurry and place it in a ball mill jar for reaction in a high-energy vibrating ball mill. Collect the ball-milled product, rinsing the ball mill jar and grinding balls with a small amount of deionized water during the collection process, and record it as product two.

[0122] The mass of the grinding balls was 50% of the sum of the masses of the slurry and sulfuric acid. The diameter of a single grinding ball was 10 mm. The grinding frequency was 20 Hz, and the grinding time was 1 hour. The amount of sulfuric acid added was 2 mol / L.

[0123] Step (4), lithium iron phosphate separation: filter product two to remove waste residue, add an appropriate amount of alkali solution to the filtrate to adjust the pH to 2.5, so that ferric ions form ferric phosphate precipitate, filter, the filter residue is ferric phosphate product, and the filtrate is recorded as product three.

[0124] Step (5), precipitation of lithium carbonate: Add alkaline solution to product three to adjust the pH, and add sodium carbonate to precipitate lithium.

[0125] Compared with the microwave acidification-high-energy ball milling method in Example 1, this comparative example did not perform microwave acidification, but only used high-energy ball milling to react the ferrophosphorus material with acid. It can be found that if the ferrophosphorus material is not pre-activated, there is still obvious undissolved solid material in the ball milling tank after ball milling. During the filtration step, some of the ferrophosphorus material enters the slag phase, resulting in a significant decrease in the ferrophosphorus leaching rate.

[0126] Comparative Example 3

[0127] Compared with Example 1, except that the microwave heating temperature in step (1) is adjusted to 700°C, all other operations and conditions are the same as in Example 1.

[0128] During the experiment, it was found that the aluminum foil and the active material of lithium iron phosphate were severely sintered, which affected the subsequent separation of the two and the purity of lithium iron phosphate.

[0129] Comparative Example 4

[0130] Compared with Example 1, except that the ball milling time in step (4) is adjusted to 0.5h, all other operations and conditions are the same as in Example 1.

[0131] If the ball milling time is too short, the reaction will not proceed fully, and some undissolved phosphorus and iron substances will enter the waste residue, resulting in a significant decrease in the leaching rate of lithium and iron.

[0132] Therefore, if the ball milling time is too short, the reaction cannot proceed fully, and if the ball milling time is too long, energy is wasted. 1-2 hours is the preferred ball milling time.

[0133] Effect Example

[0134] The formulas for calculating the leaching rates of iron and lithium in the positive electrode sheets of spent lithium iron phosphate batteries are as follows:

[0135] Let M (in grams) be the mass of the crushed electrode powder, and ω be the mass fraction of lithium in it. Li (%), the mass fraction of iron is ω Fe (%)

[0136] For Examples 1-14 and Comparative Examples 3-4, let V (L) be the volume of the solution obtained after ball milling and filtration in step (4), and let C be the concentration of iron in the solution. Fe (g / L), the lithium concentration is C Li(g / L);

[0137] For Comparative Example 1, let V (L) be the volume of the solution obtained after leaching with sulfuric acid in step (3) and C be the concentration of iron in the solution. Fe (g / L), the lithium concentration is C Li (g / L);

[0138] For Comparative Example 2, let V (L) be the volume of the solution obtained after ball milling and filtration in step (3), and C be the concentration of iron in the solution. Fe (g / L), the lithium concentration is C Li (g / L).

[0139] The lithium leaching rate

[0140] The iron leaching rate is

[0141] The relevant effects of Examples 1-14 and Comparative Examples 1-4 are described in Table 2:

[0142] Table 2

[0143]

[0144]

[0145] This invention combines microwave and ball milling. In this process, microwaves play three roles: microwave heating oxidizes ferrous iron to ferric iron, eliminating binders and organic solvents; and microwave acidification promotes the reaction of the oxidized ferric phosphate with acid. If microwave heating and acidification are not followed by high-energy ball milling, the generated ferric phosphate, especially Fe2O3, is difficult to dissolve completely in acid, resulting in a long reaction time and low efficiency. Conversely, if microwave heating and acidification are not used before high-energy ball milling, the electrode oxidation effect is poor, and an oxidant may be needed during ball milling, lengthening the process and reducing the ferric phosphate separation efficiency. Therefore, the two complement each other, and their combined use effectively improves the separation effect of the process.

Claims

1. A method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials, characterized in that, It includes the following steps: (1) Waste lithium battery cathode material is subjected to microwave heating and microwave acidification sequentially to obtain product a; the temperature of microwave heating is 450-650℃; the amount of acid used in the microwave acidification process is 4.5wt%-11wt%; (2) In the presence of acid, product a is ball-milled to obtain product b; In step (2), product a is prepared into a slurry and ball-milled; The solid-liquid ratio of the slurry is 5-20 mL / g; The concentration of the acid is 1.5-3.5 mol / L; During the ball milling process, the mass of the grinding balls is 40%-60% of the total mass of the material being milled; the milling time is 0.8-3 hours; and the milling frequency is 15-30 Hz. (3) The product b is subjected to lithium iron phosphate separation to obtain iron phosphate and lithium carbonate respectively.

2. The method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials as described in claim 1, characterized in that, In step (1), the waste lithium battery cathode material is the waste lithium iron phosphate battery cathode material.

3. The method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials as described in claim 1 or 2, characterized in that, In step (1), the temperature of microwave heating is 500-620℃; And / or, in step (1), the microwave heating time is 0.5-2h.

4. The method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials as described in claim 1 or 2, characterized in that, In step (1), the temperature of the microwave heating is 500℃, 550℃ or 600℃; And / or, in step (1), the microwave heating time is 0.5-1h.

5. The method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials as described in claim 1 or 2, characterized in that, In step (1), during the microwave acidification process, the amount of acid used is 5wt%-10wt%, where wt% is the weight percentage of the acid to the substance to be acidified.

6. The method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials as described in claim 1 or 2, characterized in that, In step (1), during the microwave acidification process, the amount of acid used is 5wt%, 6wt%, or 10wt%, where wt% is the weight percentage of the acid to the substance to be acidified.

7. The method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials as described in claim 1 or 2, characterized in that, In step (1), the temperature of microwave acidification is 140-260℃; And / or, in step (1), the microwave acidification time is 0.5-1h.

8. The method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials as described in claim 1 or 2, characterized in that, In step (1), the temperature of microwave acidification is 150-250℃; And / or, in step (1), the microwave acidification time is 0.5h or 1h.

9. The method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials as described in claim 1 or 2, characterized in that, In step (1), the temperature of microwave acidification is 150°C, 160°C, 200°C or 250°C.

10. The method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials as described in claim 1 or 2, characterized in that, In step (2), the mass of the grinding balls is 40%-55% of the total mass of the grinding material; And / or, in step (2), the diameter of the grinding ball is 5-15 mm.

11. The method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials as described in claim 1 or 2, characterized in that, In step (2), the mass of the grinding balls is 40% or 50% of the total mass of the grinding material; And / or, in step (2), the diameter of the grinding ball is 5 mm, 10 mm or 15 mm.

12. The method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials as described in claim 1 or 2, characterized in that, In step (2), the diameter of the grinding ball is 8-12 mm.

13. The method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials as described in claim 1 or 2, characterized in that, In step (2), the frequency of the ball mill is 20 Hz or 30 Hz; And / or, in step (2), the ball milling time is 0.8-2h.

14. The method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials as described in claim 1 or 2, characterized in that, In step (2), the frequency of the ball mill is 15-25Hz; And / or, in step (2), the ball milling time is 1h, 1.5h or 2h.

15. The method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials as described in claim 1 or 2, characterized in that, In step (2), the acid is sulfuric acid; And / or, the concentration of the acid is 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L.

16. The method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials as described in claim 1 or 2, characterized in that, The concentration of the acid is 2-3 mol / L.

17. The method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials as described in claim 1 or 2, characterized in that: The solvent for the slurry is water.

18. The method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials as described in claim 1 or 2, characterized in that: The solid-liquid ratio of the slurry is 10 mL / g.

19. The method for recovering iron phosphate and lithium carbonate from waste lithium battery cathode materials as described in claim 1 or 2, characterized in that, In step (3), the method for separating lithium iron phosphate includes: adjusting the pH of product b and then filtering it to obtain a lithium-containing filtrate and the iron phosphate. After adjusting the pH of the lithium-containing filtrate, sodium carbonate is added to obtain the lithium carbonate.

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