Method for recycling waste lithium iron phosphate positive electrode material

Abstract

The invention belongs to the technical field of lithium battery material recovery, and particularly relates to a method for recovering a waste lithium iron phosphate positive electrode material. The method comprises the following steps: (1) grinding and sieving the positive electrode material of the waste lithium iron phosphate battery, mixing with an alkaline solution, stirring and leaching, and carrying out solid-liquid separation to obtain a lithium-rich solution and leaching residues; (2) introducing a saturated sodium carbonate solution into the obtained lithium-rich solution, carrying out heating reaction, filtering, taking a solid phase, and drying to obtain lithium carbonate; and the obtained leaching residues are dried, and ferroferric oxide is obtained. According to the method, the waste lithium iron phosphate battery positive electrode material is leached through the alkaline liquid phase, it can be guaranteed that lithium and iron in waste lithium iron phosphate are separated through a one-step leaching method, and therefore selective lithium extraction is achieved. The whole technological process is convenient to operate, mild in reaction condition and low in energy consumption, does not need to use any acid or oxidant, avoids generation of a large amount of waste liquid and harmful gas, and is high in selective lithium extraction efficiency.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium battery material recycling, and particularly relates to a method for recycling waste lithium iron phosphate positive electrode material. BACKGROUND

[0002] Lithium iron phosphate (LFP) batteries have a large market share in power batteries, which also means that lithium iron phosphate batteries are an important part of future scrapped power batteries. Therefore, safe and effective resource recycling of waste lithium iron phosphate power batteries has gradually attracted people's attention.

[0003] In the process of recycling valuable metals from waste lithium ion battery positive electrode materials, the process is mainly divided into wet process and pyrometallurgical process according to the process characteristics. The wet process is to add acid and oxidizing agent to lithium iron phosphate, so that the lithium iron phosphate is converted into insoluble iron phosphate and soluble lithium salt, and then iron and lithium are separated by precipitation and filtration. However, the use of a large amount of strong acid and oxidizing agent in the lithium extraction process will cause difficulties in subsequent acid wastewater treatment, and will cause environmental pollution and cost waste. Although iron and lithium can be leached out, the process of precipitating iron will cause entrainment of lithium, resulting in loss of lithium, and the introduction of new impurities in the lithium liquid will require further impurity removal and purification, increasing the recovery cost and complicating the process flow, resulting in a decrease in the recovery effect of valuable metals. The pyrometallurgical process is to selectively extract lithium by high-temperature roasting, but the pyrometallurgical process has high energy consumption and poor safety, and will produce a large amount of harmful gas, causing environmental pollution.

[0004] Therefore, it is urgent to seek a recycling method for waste lithium iron phosphate positive electrode material with high safety, small environmental pollution, simple process flow and low processing cost. SUMMARY

[0005] In view of the shortcomings and deficiencies of the prior art, the purpose of the present application is to provide a method for recycling waste lithium iron phosphate positive electrode material. The method of the present application uses alkaline liquid leaching of waste lithium iron phosphate battery positive electrode material, which can ensure that lithium and iron in waste lithium iron phosphate are separated by one-step leaching method, thereby realizing selective lithium extraction. The whole process is easy to operate, the reaction conditions are mild, the energy consumption is low, no acid or oxidizing agent is needed, and a large amount of waste liquid and harmful gas is avoided, so the selective lithium extraction efficiency is high.

[0006] The purpose of the present application is achieved by the following technical scheme:

[0007] A method for recycling waste lithium iron phosphate positive electrode material, comprising the following steps:

[0008] (1) The waste lithium iron phosphate battery positive electrode material is ground and sieved, then mixed with an alkaline solution, stirred and leached, and then solid-liquid separated to obtain a lithium-rich solution and a leaching residue;

[0009] (2) in the obtained lithium-rich solution, saturated sodium carbonate solution is introduced, heated to react, and the solid phase is obtained by filtration and drying to obtain lithium carbonate; the obtained leaching residue is dried to obtain magnetite.

[0010] Further, the oxidation potential of the waste lithium iron phosphate battery positive electrode material in step (1) is -0.3-0V.

[0011] When the oxidation potential of the waste lithium iron phosphate battery positive electrode material is in the range of -0.3-0V, the hydroxyl radical double synergistic mechanism generated by the alkali metal hydroxide can ensure that the iron ions are generated in the form of Fe3O4 precipitate in the leaching residue after leaching, so as to realize the separation of lithium and iron.

[0012] Further, the grinding and sieving in step (1) refers to sieving after ball milling through 100-300 mesh.

[0013] Further, the alkaline solution in step (1) refers to a potassium hydroxide solution or a sodium hydroxide solution with a concentration of 0.5-3.5mol / L.

[0014] Further, the liquid-solid ratio of the alkaline solution mixed in step (1) is 20-70ml / g.

[0015] Further, the stirring leaching in step (1) refers to stirring leaching under the conditions of a temperature of 25-70℃ and a stirring rate of 200-400r / min for 30-120min.

[0016] Further preferably, the temperature of the stirring leaching in step (1) is 45-55℃.

[0017] Further, the temperature of the heating reaction in step (2) is 90-100℃, and the time is 2-4h.

[0018] The method for recycling waste lithium iron phosphate positive electrode material of the application relates to the following reaction (potassium hydroxide solution is used as the alkaline solution):

[0019] 3LiFePO4+6KOH→3Li + +6K + +3PO4 3- +Fe3O4+2H2O+H2.

[0020] The above reaction involves the following principles:

[0021] The key to this invention lies in converting waste LFP into lithium phosphate and iron(III) oxide through oxidative leaching in an alkaline solution, thereby achieving selective lithium extraction. To achieve selective lithium extraction, the waste LFP must be converted into Fe(+3) precipitate. Under acidic conditions, waste LFP is oxidized to ferric phosphate dihydrate when the potential exceeds 0V, while under alkaline conditions, it can only be oxidized to iron(III) oxide when the potential exceeds -0.3V. Potassium hydroxide itself has weak oxidizing power, but because the oxidation potential of waste LFP is low under alkaline conditions, it is directly oxidized to iron(III) oxide by potassium hydroxide, thus avoiding the need for additional oxidants and generating a certain amount of hydroxyl radicals, providing a suitable oxidizing environment.

[0022] Furthermore, waste LFP possesses an olivine structure, composed of LiO6 hexahedrons, FeO6 hexahedrons, and phosphate tetrahedra. The phosphate tetrahedra can confine Li... + The movement of Fe and the attachment of Fe(+2) to it make Fe oxidation crucial for the selective extraction of Li. In a low-potential environment, driven by the alkaline environment and the synergistic effect of hydroxyl radical oxidation, some Fe(+2) is oxidized by potassium hydroxide to FePO4, subsequently forming a Fe3O4 structure. The O(-2) in potassium hydroxide can fill oxygen vacancies generated during the reaction, thus promoting the disintegration of waste LFP. Furthermore, K+ ionized by potassium hydroxide... + The presence of Li in depleted LFP, coupled with certain stress effects, can promote the disintegration of LiFePO4. During this process, some FeO6 octahedra collapse into FeO4 tetrahedra, forming a Fe3O4 structure. Simultaneously, Li is separated from the framework of waste LFP and converted into water-soluble Li. + This allows for selective lithium extraction.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] (1) This invention provides an alkaline liquid phase leaching method for waste lithium iron phosphate battery cathode materials. By mixing alkaline substances with water to provide an alkaline liquid phase environment, lithium in the waste lithium iron phosphate is present in the solution in the form of soluble lithium salt, and iron is present in the leaching residue in the form of iron(III) oxide, thereby achieving the separation of lithium and iron in the waste lithium iron phosphate cathode material. This achieves the selective extraction of lithium from the waste lithium iron phosphate battery cathode material in a high-efficiency and low-energy manner.

[0025] (2) The method of the present invention avoids the problem of iron entering the leachate from the source, avoids the problem of impurity removal, reduces impurity removal costs, does not pollute the environment, and has high lithium extraction efficiency and good separation effect with other non-lithium metals. More importantly, the process does not require the addition of acid and oxidant, which simplifies the recycling process and avoids the problem of subsequent acidic wastewater treatment difficulties caused by the addition of large amounts of strong acid and oxidant, thus saving costs.

[0026] (3) The method of the present invention can achieve clean and efficient extraction of lithium resources from waste lithium-ion battery cathode materials in one step, avoid the generation of low-concentration lithium-containing leaching residue and reduce the loss of lithium in the subsequent impurity removal process of acid leaching, and achieve a high lithium recovery rate. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0028] The extraction rate formula is shown in the following examples:

[0029] Among them, E i C represents the leaching rate of the metal element to be measured. i The content of the target metal element in the lithium-rich solution was measured by inductively coupled plasma optical emission spectrometry (ICP-OES), V. i M is the volume of the lithium-rich solution, M is the mass of the waste lithium iron phosphate cathode material to be extracted, and W is the volume of the lithium-rich solution. i The content of the metal element to be tested in the waste lithium iron phosphate cathode material to be extracted, as determined by ICP-OES.

[0030] Example 1

[0031] (1) Take 100 parts by weight of waste lithium iron phosphate battery positive electrode powder (oxidation potential of -0.13V) and ball mill for 30 min. Then, sieve the ball-milled material through a 100-mesh sieve. Mix the ball-milled and sieved material with 0.5 mol / L potassium hydroxide solution at a liquid-to-solid ratio of 20 ml / g and stir for leaching. The leaching time is 30 min, the leaching temperature is 25℃, and the stirring rate is 200 r / min. Perform solid-liquid separation on the leachate to obtain a lithium-rich solution and iron(III) oxide leaching residue. The lithium extraction rate in the lithium-rich solution is determined to be 52.15%, and the iron extraction rate is 0.35%.

[0032] (2) A saturated sodium carbonate solution was passed into the obtained lithium-rich solution, and the mixture was heated to 95°C and reacted for 3 hours. The solid phase was filtered and dried to obtain lithium carbonate (purity 99.9%). The obtained leaching residue was dried to obtain iron(III) oxide.

[0033] Example 2

[0034] (1) Take 100 parts by weight of waste lithium iron phosphate battery positive electrode powder (oxidation potential of -0.02V) and ball mill for 30 min. Then, sieve the ball-milled material through a 100-mesh sieve. Mix the ball-milled and sieved material with 1.0 mol / L potassium hydroxide solution at a liquid-to-solid ratio of 30 ml / g and stir for leaching. The leaching time is 30 min, the leaching temperature is 35℃, and the stirring rate is 200 r / min. Perform solid-liquid separation on the leachate to obtain a lithium-rich solution and iron(III) oxide leaching residue. The lithium extraction rate in the lithium-rich solution is determined to be 78.36%, and the iron extraction rate is 0.11%.

[0035] (2) A saturated sodium carbonate solution was passed into the obtained lithium-rich solution, and the mixture was heated to 90°C and reacted for 4 hours. The solid phase was filtered and dried to obtain lithium carbonate (purity 99.9%). The obtained leaching residue was dried to obtain iron(III) oxide.

[0036] Example 3

[0037] (1) Take 100 parts by weight of waste lithium iron phosphate battery positive electrode powder (oxidation potential of -0.18V) and ball mill for 30 min. Then, sieve the ball-milled material through a 200-mesh sieve. Mix the ball-milled and sieved material with 1.0 mol / L potassium hydroxide solution at a liquid-to-solid ratio of 40 ml / g and stir for leaching. The leaching time is 60 min, the leaching temperature is 35℃, and the stirring rate is 300 r / min. Perform solid-liquid separation on the leachate to obtain a lithium-rich solution and iron(III) oxide leaching residue. The lithium extraction rate in the lithium-rich solution is determined to be 82.36%, and the iron extraction rate is 0.13%.

[0038] (2) A saturated sodium carbonate solution was passed into the obtained lithium-rich solution, heated to 100°C and reacted for 2 hours. The solid phase was filtered and dried to obtain lithium carbonate (purity 99.9%). The obtained leaching residue was dried to obtain iron(III) oxide.

[0039] Example 4

[0040] (1) Take 100 parts by weight of waste lithium iron phosphate battery positive electrode powder (oxidation potential of -0.30V) and ball mill for 30 min. Then, sieve the ball-milled material through a 200-mesh sieve. Mix the ball-milled and sieved material with 2.0 mol / L potassium hydroxide solution at a liquid-to-solid ratio of 70 ml / g and stir for leaching. The leaching time is 120 min, the leaching temperature is 45℃, and the stirring rate is 300 r / min. Perform solid-liquid separation on the leachate to obtain a lithium-rich solution and iron(III) oxide leaching residue. The lithium extraction rate in the lithium-rich solution is determined to be 88.73%, and the iron extraction rate is 0.08%.

[0041] (2) A saturated sodium carbonate solution was passed into the obtained lithium-rich solution, and the mixture was heated to 95°C and reacted for 3 hours. The solid phase was filtered and dried to obtain lithium carbonate (purity 99.9%). The obtained leaching residue was dried to obtain iron(III) oxide.

[0042] Example 5

[0043] (1) Take 100 parts by weight of waste lithium iron phosphate battery positive electrode powder (oxidation potential of -0.21V) and ball mill for 30 min. Then, sieve the ball-milled material through a 300-mesh sieve. Mix the ball-milled and sieved material with 2.5 mol / L potassium hydroxide solution at a liquid-to-solid ratio of 50 ml / g and stir for leaching. The leaching time is 90 min, the leaching temperature is 55℃, and the stirring rate is 400 r / min. Perform solid-liquid separation on the leachate to obtain a lithium-rich solution and iron(III) oxide leaching residue. The lithium extraction rate in the lithium-rich solution is determined to be 99.38%, and the iron extraction rate is 0.02%.

[0044] (2) A saturated sodium carbonate solution was passed into the obtained lithium-rich solution, and the mixture was heated to 95°C and reacted for 3 hours. The solid phase was filtered and dried to obtain lithium carbonate (purity 99.9%). The obtained leaching residue was dried to obtain iron(III) oxide.

[0045] The leaching temperature in step (1) of this embodiment was adjusted respectively, and the extraction rates of lithium and iron in the lithium-rich solution were measured. The results are shown in Table 1 below.

[0046] Table 1

[0047] Leaching temperature / °C Lithium extraction / % Iron extraction / % 20 36.56 0.03 25 52.15 0.05 35 78.36 0.08 45 90.68 0.04 55 99.38 0.02 65 78.59 0.03 70 69.38 0.02 75 41.39 0.03

[0048] As shown in Table 1, increasing leaching temperature significantly affects lithium extraction rate, while having no significant impact on iron extraction rate. This is because higher leaching temperatures activate some lower-energy molecules, increasing the number of activated molecules in the reactants and thus improving leaching efficiency. However, when the leaching temperature is too high, the ionic binding of some additional precipitates is activated, increasing the probability of collisions between them. This results in the formation of a large amount of precipitate and colloid, which then carries a large amount of lithium into the residue, causing a rapid decrease in lithium extraction rate. When the leaching temperature is between 25 and 70°C, the lithium extraction rate can reach over 50%; when the leaching temperature is between 45 and 55°C, the lithium extraction rate can reach over 90%.

[0049] The concentration of potassium hydroxide solution in step (1) of this embodiment was adjusted respectively, and the extraction rates of lithium and iron in the lithium-rich solution were measured. The results are shown in Table 2 below.

[0050] Table 2

[0051] Leaching concentration / mol / L Lithium extraction / % Iron extraction / % 0.3 29.34 0.06 0.5 52.15 0.35 1 78.36 0.11 1.5 86.19 0.09 2 95.38 0.05 2.5 99.38 0.02 3 98.12 0.03 3.5 98.05 0.02

[0052] As shown in Table 2, the concentration of the alkaline solution has a significant impact on the lithium extraction rate, while the iron extraction rate remains at a low level. With increasing leaching concentration, the lithium extraction rate initially increases and then decreases. This is because increasing the alkaline solution concentration increases the likelihood of collisions between reactants, thereby improving leaching efficiency. Excess hydroxide ions in the solution promote the precipitation of byproducts, which can carry away lithium, resulting in lithium loss. This leads to a slow decrease in lithium extraction efficiency at leaching concentrations above 2.5 mol / L. When the concentration of the alkaline leaching solution is in the range of 0.5–3.5 mol / L, the lithium extraction rate can reach over 50%.

[0053] Example 6

[0054] This embodiment describes a method for recycling waste lithium iron phosphate cathode materials. Compared with Example 5, the method uses a 2.5 mol / L sodium hydroxide solution instead of a potassium hydroxide solution, while the rest remains the same.

[0055] In this embodiment, the lithium extraction rate of the lithium-rich solution was 99.26%, and the iron extraction rate was 0.09%.

[0056] Comparative Example 1

[0057] The difference between this comparative example and Example 5 is that in step (1), the potassium hydroxide solution was replaced with sulfuric acid of the same concentration; otherwise, they are the same. The lithium extraction rate in the lithium-rich solution of this comparative example was 98.12%, and the iron leaching rate was 98.28%.

[0058] The results of this comparative example show that simple acid leaching cannot effectively separate lithium and iron.

[0059] Comparative Example 2

[0060] The difference between this comparative example and Example 5 is that the oxidation potential of the waste lithium iron phosphate battery cathode powder is -0.36V, while the rest are the same.

[0061] The lithium extraction rate in the lithium-rich solution of this comparative example was 51.19%, and the iron leaching rate was 0.03%.

[0062] The results of this comparative example show that a low oxidation potential in the cathode powder of spent lithium iron phosphate batteries leads to a significant decrease in lithium extraction rate. This is because when the oxidation potential is below -0.3V, iron is mainly formed in the form of ferric hydroxide colloid, resulting in excessive lithium adsorption and excessive lithium loss.

[0063] Comparative Example 3

[0064] The difference between this comparative example and Example 5 is that the oxidation potential of the waste lithium iron phosphate battery cathode powder is 0.15V, while the rest are the same.

[0065] The lithium extraction rate in the lithium-rich solution of this comparative example was 49.23%, and the iron leaching rate was 0.03%.

[0066] The results of this comparative example show that an excessively high oxidation potential in the cathode powder of spent lithium iron phosphate batteries leads to a significant decrease in lithium extraction rate. This is because an oxidation potential above 0V increases the activity of lithium and phosphorus ions, enhancing their precipitation mechanism and resulting in excessive lithium loss.

[0067] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for recycling a spent lithium iron phosphate cathode material, characterized in that, The method comprises the following steps: (1) mixing the ground and sieved positive electrode material of waste lithium iron phosphate battery with an alkaline solution, stirring and leaching, and then separating the solid and liquid phases to obtain a lithium-rich solution and a leaching residue; (2) passing saturated sodium carbonate solution into the obtained lithium-rich solution, heating and reacting, filtering and drying the solid phase to obtain lithium carbonate, and drying the obtained leaching residue to obtain magnetite.

2. The method for recycling waste lithium iron phosphate positive electrode material according to claim 1, characterized in that, The oxidation potential of the positive electrode material of waste lithium iron phosphate battery in step (1) is -0.3-0 V.

3. The method for recycling waste lithium iron phosphate positive electrode material according to claim 1, characterized in that, The grinding and sieving in step (1) refers to grinding and then sieving through a 100-300 mesh sieve.

4. The method for recycling waste lithium iron phosphate positive electrode material according to claim 1, characterized in that, The alkaline solution in step (1) refers to a potassium hydroxide solution or a sodium hydroxide solution with a concentration of 0.5-3.5 mol / L.

5. The method for recycling waste lithium iron phosphate positive electrode material according to claim 1, characterized in that, The liquid-solid ratio of the alkaline solution mixing in step (1) is 20-70 ml / g.

6. The method for recycling waste lithium iron phosphate positive electrode material according to claim 1, characterized in that, The stirring and leaching in step (1) is performed at a temperature of 25-70 ℃ and a stirring rate of 200-400 r / min for 30-120 min.

7. The method for recycling waste lithium iron phosphate cathode material according to claim 6, characterized in that, The temperature of the stirring and leaching in step (1) is 45-55 ℃. 8.The method of recycling waste lithium iron phosphate cathode material of claim 1, wherein, The temperature of the heating and reacting in step (2) is 90-100 ℃, and the time is 2-4 h.