A method for recycling lithium iron phosphate extraction waste to prepare battery-grade iron phosphate

Abstract

This invention discloses a method for recovering lithium iron phosphate (LFP) extraction waste to prepare battery-grade iron phosphate, comprising the following steps: Leaching and filtering the LFP waste to obtain an acid leaching solution; adding an iron source to the acid leaching solution and adjusting the pH to 1.0-2.0, reacting, and filtering to obtain a titanium-removed filtrate; increasing the pH of the titanium-removed filtrate, reacting, and filtering to obtain an aluminum-removed filtrate; adding a phosphorus source to the aluminum-removed filtrate, then adding hydrogen peroxide and adjusting the pH, followed by a hydrothermal reaction and aging to obtain iron phosphate dihydrate; and sintering the iron phosphate dihydrate at high temperature to obtain anhydrous iron phosphate. This invention replaces inorganic acids with oxalic acid, ensuring that the entire iron phosphate recovery process does not produce polluting gases, has low corrosiveness to equipment, and requires a small amount of alkali for neutralization. This invention effectively removes titanium from the product while removing other impurity metal elements by forming titanium phosphate precipitate, resulting in higher purity recovered iron phosphate and solving the problem of titanium removal difficulties in existing technologies.

Description

Technical Field

[0001] This invention relates to a method for recycling and preparing battery-grade iron phosphate, and more particularly to a method for recycling lithium iron phosphate extraction waste to prepare battery-grade iron phosphate. Background Technology

[0002] Currently, wet recycling is the main method for recovering valuable metals and reprocessing iron phosphate. However, due to the high impurity content in waste batteries, the prepared iron phosphate precursor will also contain high levels of impurities.

[0003] In traditional hydrometallurgical processes, the black residue from spent lithium-ion batteries (after unloading, dismantling, crushing, and sorting) dissolves in inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, typically with the addition of reducing agents such as hydrogen peroxide. The filtered metal is then selectively recovered and purified using various techniques such as solvent extraction, precipitation, or crystallization. The use of these inorganic acids leads to various emissions (gas releases such as SO2, Cl2, or NO). x The specific method of recovery depends on the type of acid used and the formation of waste streams and wastewater. Different recovery methods produce phosphorus-iron slag with varying amounts and concentrations of inorganic acid required for acid leaching. To ensure recovery rates, high-concentration inorganic acids are often needed, resulting in very low pH levels. This necessitates the subsequent use of large amounts of alkali to adjust the pH, increasing subsequent alkali input. Furthermore, inorganic acids corrode equipment, increasing maintenance costs. Organic acids, on the other hand, are more environmentally friendly than traditional inorganic acids, producing less waste gas and exhibiting weaker acidity, significantly reducing their corrosive effect on equipment and demonstrating promising application prospects.

[0004] In addition, existing technologies can specifically remove metallic impurities such as copper, cobalt, manganese, magnesium and nickel to recover iron phosphate by wet process. However, titanium, as a metallic impurity, also exists in lithium extraction waste. Existing recycling methods are difficult to effectively remove titanium from iron phosphate, and titanium doping also affects the purity of the recovered iron phosphate. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a method for recycling lithium iron phosphate waste to prepare battery-grade iron phosphate, which solves the problems of existing recycling methods that are difficult to remove titanium and cause high pollution and maintenance costs due to the use of inorganic acids.

[0006] Technical solution: The present invention discloses a method for preparing battery-grade iron phosphate from lithium iron phosphate extraction waste, comprising the following steps:

[0007] (1) The lithium iron phosphate lithium extraction waste is acid-leached and filtered to obtain acid leaching solution;

[0008] (2) Add an iron source to the acid leaching solution and adjust the pH to 1.0-2.0. After the reaction, filter to obtain titanium-free filtrate.

[0009] (3) Increase the pH value of the titanium removal filtrate, filter after reaction to obtain aluminum removal filtrate;

[0010] (4) Add phosphorus source to aluminum removal filtrate, then add hydrogen peroxide and adjust pH, then carry out hydrothermal reaction and age to obtain ferric phosphate dihydrate.

[0011] (5) Anhydrous ferric phosphate is prepared by high-temperature sintering of ferric phosphate dihydrate.

[0012] This invention uses oxalic acid for acid leaching. Oxalic acid, as the strongest organic acid, is an excellent leaching and reducing agent. Furthermore, the mechanism by which oxalic acid dissolves metals is an acid / complex reaction; lithium reacts with oxalate ions to form simple oxalates, while copper, cobalt, manganese, magnesium, and nickel can form oxalate precipitates. This reduces the corrosion of equipment by inorganic acids and lowers maintenance costs. Because of its high dissolution efficiency, oxalic acid produces a higher pH value after dissolution, further reducing the need for large amounts of subsequent alkali input.

[0013] In step (2), the iron source is added. On the one hand, the copper ions in the system can be removed for a second time. On the other hand, the divalent iron in the acid leaching solution is not easily oxidized and an imbalance state of more iron and less phosphorus is formed in the reaction system. The pH value is adjusted to about 1.5 to generate titanium phosphate precipitate, and then titanium element is removed by filtration of the precipitate.

[0014] Preferably, in step (1), the acid leaching and filtration method is as follows: the lithium iron phosphate extraction waste is immersed in an oxalic acid solution for reaction, filtered after reaction, and the filtrate is taken to obtain an acid leaching solution; the molar ratio of oxalic acid to iron in the lithium iron phosphate extraction waste is 2-5. The mechanism of oxalic acid dissolving metals is an acid / complex. Lithium reacts with oxalate ions to form simple oxalates. Copper, cobalt, manganese, magnesium, and nickel can form oxalate precipitates. Aluminum only forms complex oxalate compounds that are soluble in aqueous media, which will then dissolve. Therefore, oxalic acid dissolution can remove most of the metal impurities, except for aluminum, which has a high content. At the same time, titanium cannot be removed. Subsequently, by adding an iron source to maintain the system in a ferrous environment, the risk of ferrous oxidation to form iron phosphate precipitate is reduced, the yield is increased, and copper is deeply removed while increasing the iron content in the system. Titanium phosphate precipitate is formed by adjusting the pH. Aluminum is removed by adjusting the pH value in subsequent step (3) to form a precipitate.

[0015] In some embodiments, the concentration of the oxalic acid solution is 0.5-2 mol / L, the solid-liquid ratio of lithium iron phosphate extraction waste to oxalic acid solution is 30-80 g / L, and the reaction conditions are 20-70°C for 0.5-2 h.

[0016] Preferably, in step (2), the iron source is one or more of iron powder, ferrous disulfide, and iron sulfide.

[0017] Preferably, in step (2), after adding an iron source to the acid leaching solution, the molar ratio of iron to phosphorus is 1.1-1.4:1.0, and the reaction conditions are 0.1-1h at 20-55℃. An iron-phosphorus ratio of 1.1-1.4:1 can cause an imbalance in the iron-phosphorus ratio in the acid leaching solution, thereby causing titanium to precipitate in the form of titanium phosphate.

[0018] Preferably, in step (3), the method for increasing the pH value of the titanium removal filtrate is to add ammonia water to the titanium removal filtrate to increase the pH value until the pH value is 2.0-4.0.

[0019] Preferably, in step (3), the reaction conditions are 0.5-2h at 25-80℃.

[0020] Preferably, in step (4), the phosphorus source is at least one of phosphoric acid, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0021] Preferably, in step (4), after adding a phosphorus source to the aluminum-removing filtrate, the molar ratio of iron to phosphorus is 1.0:1.0-1.1; the method of adding hydrogen peroxide and adjusting the pH before hydrothermal reaction is as follows: add hydrogen peroxide to the aluminum-removing filtrate, wherein the molar ratio of hydrogen peroxide to iron is 0.55-0.60:1, adjust the pH value to 1.0-2.5, and perform hydrothermal reaction at 70-100℃ for 0.5-3 hours; the aging time is 1-3 hours.

[0022] Preferably, in step (5), the high-temperature sintering conditions are sintering at 500-700℃ for 2-6 hours.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0024] (1) This invention replaces inorganic acid with oxalic acid, so that the entire iron phosphate recovery process does not produce polluting gases, has little corrosiveness to equipment, and requires a small amount of alkali for neutralization, effectively solving the problems of high pollution and high maintenance costs caused by the use of inorganic acid in existing recovery methods.

[0025] (2) By forming titanium phosphate precipitate, the present invention effectively removes titanium elements in the product while removing other impurity metal elements, resulting in higher purity of iron phosphate recovery and solving the problem of titanium element removal that is difficult to achieve in the prior art. Attached Figure Description

[0026] Figure 1 This is a microscopic morphology diagram of the iron phosphate obtained in this invention. Detailed Implementation

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0028] Example 1: A method for the efficient and green recycling of lithium iron phosphate extraction waste to prepare iron phosphate, the steps of which are as follows:

[0029] (1) 40g of the phosphorus-iron slag black powder after lithium iron phosphate extraction was immersed in a 0.6M oxalic acid solution at a solid-liquid ratio of 50g / L. The mixture was reacted and dissolved at 60℃ for 1 hour, then filtered to obtain an acid leaching solution rich in iron and phosphorus, and a filter residue containing graphite, oxalate, nickel, cobalt, manganese, and copper. The composition of the phosphorus-iron slag after lithium iron phosphate extraction is as follows:

[0030]

[0031] (2) Add iron powder to the acid leaching solution obtained in step (1). At this time, the molar ratio of iron to phosphorus in the acid leaching solution is 1.2:1. After adjusting the pH value to 1.5 with ammonia water, react at 35°C for 0.5 h. Filter to obtain titanium-free filtrate containing ferrous ions and copper-containing titanium filter residue. Titanium in the filter residue exists as titanium phosphate precipitate.

[0032] (3) Ammonia water was slowly added to the titanium removal filtrate to raise the pH value to 2.8. The reaction was carried out at 60°C for 1 hour to produce a precipitate. The filtrate was then filtered to obtain the aluminum removal filtrate. The aluminum element exists in the filter residue in the form of a precipitate.

[0033] (4) Add phosphoric acid to the aluminum removal filtrate, controlling the molar ratio of iron to phosphorus to be 1.0:1.05, adjust the pH of the solution to 1.8, add hydrogen peroxide to the aluminum removal filtrate, with a molar ratio of hydrogen peroxide to iron of 0.55:1, react hydrothermally at 90℃ for 2 hours, and age for 2 hours to obtain ferric phosphate dihydrate. Filter, wash, and dry to obtain ferric phosphate dihydrate. Sinter the ferric phosphate dihydrate at 600℃ for 4 hours to obtain anhydrous ferric phosphate. Figure 1 As shown.

[0034] Example 2: A method for the efficient and green recycling of lithium iron phosphate extraction waste to prepare iron phosphate, the steps of which are as follows:

[0035] (1) Immerse 40g of phosphorus-iron slag black powder after lithium extraction from lithium iron phosphate in a 0.5M oxalic acid solution at a solid-liquid ratio of 30g / L. React and dissolve at 20℃ for 2h. Filter to obtain an acid leaching solution rich in iron and phosphorus and filter residue containing graphite, oxalate, nickel, cobalt, manganese, copper, etc. The phosphorus-iron slag after lithium extraction from lithium iron phosphate is the same as in Example 1.

[0036] (2) Add iron powder to the acid leaching solution obtained in step (1). At this time, the molar ratio of iron to phosphorus in the acid leaching solution is 1.1:1. After adjusting the pH value to 1.4, react at 20°C for 1 hour. Filter to obtain titanium-removed filtrate containing ferrous ions and copper-titanium filter residue. Titanium in the filter residue exists as titanium phosphate precipitate.

[0037] (3) Slowly add ammonia to the titanium removal filtrate to raise the pH value to 2.0, react at 25°C for 2 hours to produce a precipitate, and filter to obtain the aluminum removal filtrate.

[0038] (4) Add phosphoric acid to the aluminum removal filtrate, control the molar ratio of iron to phosphorus to be 1.0:1.0, adjust the pH of the solution to 1.6, add hydrogen peroxide to the aluminum removal filtrate, the molar ratio of hydrogen peroxide to iron to be 0.60:1, react hydrothermally at 70℃ for 3h, age for 3h to obtain ferric phosphate dihydrate, filter, wash and dry to obtain ferric phosphate dihydrate, sinter ferric phosphate dihydrate at 500℃ for 6h to obtain anhydrous ferric phosphate.

[0039] Example 3: A method for the efficient and green recycling of lithium iron phosphate extraction waste to prepare iron phosphate, the steps of which are as follows:

[0040] (1) 40g of phosphorus-iron slag black powder after lithium extraction from lithium iron phosphate was immersed in a 2M oxalic acid solution at a solid-liquid ratio of 80g / L. The mixture was reacted and dissolved at 70℃ for 0.5h, and then filtered to obtain an acid leaching solution rich in iron and phosphorus and a filter residue containing graphite, oxalate, nickel, cobalt, manganese, and copper. The pH value was measured to be 1.0. The phosphorus-iron slag after lithium extraction from lithium iron phosphate was the same as in Example 1.

[0041] (2) Add ferrous disulfide to the acid leaching solution obtained in step (1). At this time, the molar ratio of iron to phosphorus in the acid leaching solution is 1.1:1. After adjusting the pH value to 1.6, react at 55℃ for 0.1h. Filter to obtain titanium-removed filtrate containing ferrous ions and copper-titanium filter residue. Titanium in the filter residue exists as titanium phosphate precipitate.

[0042] (3) Slowly add ammonia to the titanium removal filtrate to raise the pH value to 4.0, react at 80℃ for 0.5h to produce a precipitate, and filter to obtain the aluminum removal filtrate.

[0043] (4) Add ammonium hydrogen phosphate to the aluminum removal filtrate, control the molar ratio of iron to phosphorus to be 1.0:1.1, adjust the pH of the solution to 2.0 with sulfuric acid, add hydrogen peroxide to the aluminum removal filtrate, the molar ratio of hydrogen peroxide to iron to be 0.55:1, react hydrothermally at 100℃ for 0.5h, age for 1h to obtain ferric phosphate dihydrate, filter, wash and dry to obtain ferric phosphate dihydrate, sinter ferric phosphate dihydrate at 700℃ for 2h to obtain anhydrous ferric phosphate.

[0044] Example 4: A method for the efficient and green recycling of lithium iron phosphate extraction waste to prepare iron phosphate, the steps of which are as follows:

[0045] (1) Immerse 40g of phosphorus iron slag black powder after lithium extraction from lithium iron phosphate in a 1M oxalic acid solution at a solid-liquid ratio of 65g / L. React and dissolve at 45℃ for 1.5h. Filter to obtain an acid leaching solution rich in iron and phosphorus and a filter residue containing graphite, oxalate, nickel, cobalt, manganese, copper, etc. The phosphorus iron slag after lithium extraction from lithium iron phosphate is the same as in Example 1.

[0046] (2) Add iron sulfide to the acid leaching solution obtained in step (1). At this time, the molar ratio of iron to phosphorus in the acid leaching solution is 1.15:1. After adjusting the pH value to 1.8, react at 25°C for 0.3h. Filter to obtain titanium-removed filtrate containing ferrous ions and copper-titanium filter residue. Titanium in the filter residue exists as titanium phosphate precipitate.

[0047] (3) Slowly add ammonia to the titanium removal filtrate to raise the pH value to 3.5, react at 70℃ for 1.5h to produce a precipitate, and filter to obtain the aluminum removal filtrate.

[0048] (4) Add ammonium dihydrogen phosphate to the aluminum removal filtrate, control the molar ratio of iron to phosphorus to be 1.0:1.05, adjust the pH of the solution to 1.5 with sulfuric acid, add hydrogen peroxide to the aluminum removal filtrate, the molar ratio of hydrogen peroxide to iron to be 0.55:1, react hydrothermally at 80℃ for 2h, and age for 1.5h to obtain ferric phosphate dihydrate. Filter, wash and dry to obtain ferric phosphate dihydrate, and sinter the ferric phosphate dihydrate at 650℃ for 5h to obtain anhydrous ferric phosphate.

[0049] Example 5: A method for the efficient and green recycling of lithium iron phosphate extraction waste to prepare iron phosphate, the steps of which are as follows:

[0050] (1) Immerse 40g of phosphorus iron slag black powder after lithium extraction from lithium iron phosphate in a 1.5M oxalic acid solution at a solid-liquid ratio of 45g / L. React and dissolve at 50℃ for 1h, then filter to obtain an acid leaching solution rich in iron and phosphorus and a filter residue containing graphite, oxalate, nickel, cobalt, manganese, copper, etc. The phosphorus iron slag after lithium extraction from lithium iron phosphate is the same as in Example 1.

[0051] (2) Add a 1:1 mixture of iron powder and ferrous disulfide to the acid leaching solution obtained in step (1). At this time, the molar ratio of iron to phosphorus in the acid leaching solution is 1.1:1. After adjusting the pH value to 1.2, react at 25°C for 45 min. Filter to obtain titanium-free filtrate containing ferrous ions and copper-titanium filter residue. Titanium in the filter residue exists as titanium phosphate precipitate.

[0052] (3) Slowly add ammonia to the titanium removal filtrate to raise the pH value to 3.0, react at 75°C for 2 hours to produce a precipitate, and filter to obtain the aluminum removal filtrate.

[0053] (4) Add an equal mixture of ammonium dihydrogen phosphate and diammonium hydrogen phosphate to the aluminum removal filtrate, control the molar ratio of iron to phosphorus to be 1.0:1.05, adjust the pH of the solution to 1.6 with sulfuric acid, add hydrogen peroxide to the aluminum removal filtrate, the molar ratio of hydrogen peroxide to iron to be 0.55:1, react hydrothermally at 90℃ for 1 h, age for 1 h to obtain ferric phosphate dihydrate, filter, wash and dry to obtain ferric phosphate dihydrate, sinter ferric phosphate dihydrate at 550℃ for 3 h to obtain anhydrous ferric phosphate.

[0054] Comparative Example 1: Everything else is the same as in Example 1, except that:

[0055] In step (2), no iron powder is added. The pH is adjusted to 1.5 and the reaction is carried out directly, followed by filtration.

[0056] Comparative Example 2: Everything else is the same as in Example 1, except that:

[0057] The content of impurity elements in the iron phosphate product was investigated using the pH adjustment value after adding iron powder in step (2) as a variable (pH values ​​include 0.5, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, and 3.0).

[0058] Comparative Example 3: Everything else is the same as in Example 1, except that:

[0059] Using the molar ratio of iron to phosphorus in the acid leaching solution after adding iron powder in step (2) as a variable, the content of impurity elements in the iron phosphate product was investigated.

[0060] Table 1. Effects of different recovery methods on the recovery rate of ferric phosphate and the content of impurity elements in the product.

[0061]

[0062]

[0063] As shown in Table 1, in Comparative Example 1, due to the absence of an iron source, the reaction system did not achieve an imbalance of high iron and low phosphorus, making it difficult for titanium to form titanium phosphate precipitate. Consequently, titanium could not be effectively removed, resulting in a high titanium content in the product. Comparative Example 2 showed that even with an iron source to adjust the iron-phosphorus ratio, titanium could only be efficiently removed at a pH of 1.2-2.0. Excessively high or low pH levels would lead to a high titanium content in the product. Comparative Example 3 indicated that a ratio exceeding 1.1:1 was necessary to effectively remove titanium from the lithium extraction slag. Furthermore, the change in the iron-phosphorus ratio did not significantly affect the copper removal rate, indicating that the addition of an iron source was sufficient for further copper removal. Even at a ratio of 0.95-1.0:1, copper removal was still possible, but this ratio range was insufficient for effective titanium removal. These results demonstrate that in step (2), adding an iron source to adjust the iron-phosphorus ratio and adjusting the pH value both significantly impacted the titanium removal rate. These two factors complemented each other, working synergistically to remove titanium.

Claims

1. A method for recovering lithium iron phosphate waste to prepare battery-grade iron phosphate, characterized in that, Includes the following steps: (1) The lithium iron phosphate extraction waste was leached with oxalic acid solution and filtered to obtain an acid leaching solution; (2) Add an iron source to the acid leaching solution and adjust the pH to 1.2-2.

0. After the reaction, filter to obtain titanium-free filtrate. After adding an iron source to the acid leaching solution, the molar ratio of iron to phosphorus is 1.1-1.4:1.

0. The reaction conditions are 0.1-1h at 20-55℃. (3) Add ammonia to the titanium removal filtrate to raise the pH value until the pH value is 2.0-4.

0. After the reaction, filter to obtain aluminum removal filtrate. (4) Add phosphorus source to aluminum removal filtrate, then add hydrogen peroxide and adjust pH, then carry out hydrothermal reaction and age to obtain ferric phosphate dihydrate. (5) Anhydrous ferric phosphate is prepared by high-temperature sintering of ferric phosphate dihydrate.

2. The method for preparing battery-grade iron phosphate from lithium iron phosphate extraction waste according to claim 1, characterized in that, In step (1), the acid leaching and filtration methods are as follows: the lithium iron phosphate extraction waste is immersed in oxalic acid solution for reaction, filtered after reaction, and the filtrate is taken to obtain acid leaching solution; the molar ratio of oxalic acid to iron in lithium iron phosphate extraction waste is 2-5.

3. The method for preparing battery-grade iron phosphate from lithium iron phosphate extraction waste according to claim 2, characterized in that, The concentration of the oxalic acid solution is 0.5-2 mol / L, the solid-liquid ratio of lithium iron phosphate extraction waste to oxalic acid solution is 30-80 g / L, and the reaction conditions are 20-70℃ for 0.5-2 h.

4. The method for preparing battery-grade iron phosphate from lithium iron phosphate extraction waste according to claim 1, characterized in that, In step (2), the iron source is one or more of iron powder, ferrous disulfide, and iron sulfide.

5. The method for preparing battery-grade iron phosphate from lithium iron phosphate extraction waste according to claim 1, characterized in that, In step (3), the reaction conditions are 25-80℃ for 0.5-2h.

6. The method for preparing battery-grade iron phosphate from lithium iron phosphate extraction waste according to claim 1, characterized in that, In step (4), the phosphorus source is at least one of phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

7. The method for preparing battery-grade iron phosphate from lithium iron phosphate extraction waste according to claim 1, characterized in that, In step (4), after adding a phosphorus source to the aluminum-removing filtrate, the molar ratio of iron to phosphorus is 1.0:1.0-1.1; the method of adding hydrogen peroxide and adjusting the pH before hydrothermal reaction is as follows: add hydrogen peroxide to the aluminum-removing filtrate, the molar ratio of hydrogen peroxide to iron is 0.55-0.60:1, adjust the pH value to 1.0-2.5, and perform hydrothermal reaction at 70-100℃ for 0.5-3h; the aging time is 1-3h.

8. The method for preparing battery-grade iron phosphate from lithium iron phosphate extraction waste according to claim 1, characterized in that, In step (5), the high-temperature sintering conditions are sintering at 500-700℃ for 2-6 hours.

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