Method for selectively extracting lithium and removing aluminum from waste lithium iron phosphate positive electrode powder

Abstract

The invention relates to the technical field of waste lithium iron phosphate electrode material recovery, and particularly discloses a method for selectively extracting lithium and removing aluminum from waste lithium iron phosphate positive electrode powder. The method comprises the following steps: S1, adding pure water into waste lithium iron phosphate positive electrode powder for size mixing, and carrying out ball milling on the size; s2, heating the ball-milled slurry, and then adding nitric acid for acid leaching for 1-1.5 h; s3, an oxidizing agent is added into the acid leaching slurry to react for 2-3 h; s4, adding pure water into the slurry, and continuously reacting for 1-2 hours; s5, slurry obtained after the reaction is completed is filtered, obtained filter residues are filtered after being washed with water, washing filtrate is returned to the front end for acid leaching use, and the filter residues are low-aluminum lithium extraction residues; according to the method, the lithium iron phosphate positive electrode powder is mechanically activated, the nitric acid and the oxidizing agent are accurately proportioned according to the content of the impurity lithium and the impurity aluminum in the raw materials, and the high-efficiency selective lithium extraction and aluminum removal effects are realized by adding water in batches for reaction.

Description

Technical Field

[0001] This invention relates to the field of waste lithium iron phosphate electrode material recycling technology, and in particular to a method for selectively extracting lithium and removing aluminum from waste lithium iron phosphate cathode powder. Background Technology

[0002] Currently, the main method for recovering lithium from waste lithium iron phosphate batteries / cathode materials is to selectively extract lithium using sulfuric acid and hydrogen peroxide. This process is relatively mature, but it only considers the recovery of the precious metal lithium and does not address the removal of impurities such as aluminum. As a result, the lithium iron phosphate slag after lithium extraction has a high content of impurities such as aluminum.

[0003] Many experts and scholars have conducted research on the recovery of elemental iron and phosphorus from phosphorus slag after lithium extraction, including acid washing / alkali washing to remove aluminum, and stepwise aluminum removal by adjusting pH after reduction acid leaching. However, these methods have limited aluminum removal rates and inevitably result in iron and phosphorus loss during the impurity removal process, leading to low iron and phosphorus recovery rates.

[0004] CN119979903A discloses a method for preferential lithium extraction from waste lithium iron phosphate battery cathode materials via salt leaching. This method uses a mixed solution of soluble chloride and metal sulfate to leach the waste lithium iron phosphate battery cathode materials, obtaining a lithium-containing leachate and iron phosphate slag. The salt leaching process achieves high leaching rates of both lithium and aluminum, resulting in good lithium extraction and aluminum removal. However, the lithium extraction solution introduces chloride and sulfate ions, requiring high-quality equipment. Furthermore, the lithium ions exist as a mixed salt of lithium sulfate and lithium chloride, necessitating complete conversion to lithium sulfate before lithium carbonate preparation. The mixed salts generated during lithium carbonate preparation can only be treated as solid waste. Secondly, this selective lithium extraction method has a high liquid-to-solid ratio, resulting in a low lithium ion concentration in the prepared lithium solution, requiring multiple leaching and concentration operations, making the process complex. Therefore, there is an urgent need to develop a simple, environmentally friendly, and efficient method for lithium extraction and aluminum removal. Summary of the Invention

[0005] To address the problems mentioned in the background art, the present invention aims to provide a method for selectively extracting lithium and removing aluminum from waste lithium iron phosphate cathode powder.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A method for selectively extracting lithium and removing aluminum from waste lithium iron phosphate cathode powder includes the following steps: S1: Add pure water to the waste lithium iron phosphate cathode powder to make a slurry, and then ball mill the slurry; S2: Heat the ball-milled slurry, then add nitric acid for acid leaching for 1-1.5 hours; S3: Add oxidant to the acid slurry and react for 2-3 hours; S4: Add pure water to the slurry and continue the reaction for 1-2 hours; S5: Filter the slurry after the reaction is complete; S6: The filter residue obtained from S5 is washed with water and then filtered. The washing filtrate is returned to the front end for acid leaching. The filter residue is a low-aluminum lithium extraction residue.

[0007] First, the lithium iron phosphate cathode powder is pretreated by wet ball milling. The lithium iron phosphate cathode powder is subjected to mechanical forces such as shearing, impact and extrusion, which impacts the crystal structure, reduces the particle size, increases the active surface of the lithium iron phosphate crystal, exposes more active sites, and makes the subsequent acid leaching reaction more thorough.

[0008] After adding nitric acid, the waste lithium iron phosphate powder reacts with an appropriate amount of nitric acid. Due to insufficient acid, an activation energy is needed for the redox reaction. Therefore, before adding nitric acid, the slurry is heated to overcome the activation energy barrier, allowing the waste lithium iron phosphate powder and nitric acid to undergo a redox reaction. Furthermore, water is added in two batches, indirectly increasing the nitric acid concentration during acid leaching, further promoting the redox reaction. Lithium ions are extracted from the lithium iron phosphate lattice and exist in the leachate as lithium nitrate. Phosphorus exists as phosphate, and iron exists as a mixture of ferrous and ferric ions. Because the amount of nitric acid added is insufficient to oxidize all the ferrous iron to ferric ions, an oxidant is subsequently added to oxidize all the ferrous iron in the leachate to ferric ions. Then, by adding pure water to the system, the pH of the slurry is raised to 1.4-1.6. At this point, the ferric ions in the leachate combine with the free phosphate ions to form ferric phosphate, which is then precipitated back into the leaching residue. The aluminum impurities react with the excess nitric acid in the system to form aluminum nitrate. Since the pH at the end of the reaction does not reach the precipitation value of aluminum ions, the aluminum impurities exist in the leachate in ionic form. After filtration, both elemental lithium and aluminum exist in the leachate in ionic form, and the leaching residue is phosphorus-iron slag after lithium extraction and impurity removal.

[0009] The entire reaction principle is as follows:

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[0012]

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[0015] Furthermore, in step S1, the amount of water added is 50%-55% of 2.8-3.3 times the mass of the lithium iron phosphate cathode powder, the ball-to-material ratio is 10:1, the ball milling speed is 600 r / min, and the ball milling time is 30-45 min.

[0016] Furthermore, in step S2, the slurry heating temperature is 70-80℃, and the amount of nitric acid added is 1.35-1.40 times the total molar amount of lithium and impurity aluminum in the lithium iron phosphate cathode powder.

[0017] Furthermore, in step S3, the oxidant is hydrogen peroxide, and the amount of hydrogen peroxide added is 5%-10% of the mass of the lithium iron phosphate cathode powder.

[0018] Furthermore, in step S4, the amount of water added is 45%-50% of 2.8-3.3 times the mass of the lithium iron phosphate cathode powder.

[0019] Furthermore, in step S6, the liquid-to-solid ratio of the pure water added to the filter residue during washing is 1.5-2:1, the washing temperature is room temperature, the washing time is 1-2 hours, and the washing filtrate is returned to the front end for acid leaching as pure water.

[0020] The beneficial effects of the present invention are as follows: (1) The present invention achieves efficient selective lithium extraction and aluminum removal by means of the synergistic effect of nitric acid and oxidant, and by precisely proportioning the content of impurity lithium and impurity aluminum in the raw materials and adding the corresponding amount of acid and oxidant. In the end, the lithium recovery rate is >98%, the aluminum removal rate is >94%, and the iron and phosphorus loss rate is <3%; (2) The lithium extraction process uses nitric acid, which has oxidizing properties, which reduces the consumption of oxidants in the lithium extraction process and lowers the cost of auxiliary materials; (3) The lithium extraction from waste lithium iron phosphate powder and the aluminum removal from iron phosphate slag are combined into one step, which simplifies the process flow. (4) The lithium concentration in the lithium solution produced during the lithium extraction process can reach 13g / L~17g / L, which is beneficial for subsequent lithium recovery. Attached Figure Description

[0021] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art are within the protection scope of the present invention.

[0023] Example 1: The raw material used, waste lithium iron phosphate cathode powder, contains Li: 4.1%, Fe: 32.4%, P: 18.6%, and Al: 0.5%. (1) Take 100g of waste lithium iron phosphate cathode powder and put it in a beaker. Add 150g of pure water to make a slurry. Then add the slurry to a planetary ball mill for ball milling. The ball-to-material ratio is 10:1, the ball milling speed is 600r / min, and the ball milling time is 40min. (2) Heat the slurry to a temperature of 80°C, and add 65% nitric acid to the heated slurry. The amount of nitric acid is 1.38 times the total molar amount of lithium and aluminum impurities in the waste lithium iron phosphate cathode powder. (3) After reacting for 1 hour, add 6% hydrogen peroxide (based on the mass of the raw material cathode powder) to the acid leaching slurry and react for 2.5 hours. (4) Add another 150g of pure water to the slurry and continue the reaction for 1 hour; (5) After the reaction is completed, the slurry is filtered, and the filter residue is washed with 1.7 times the wet basis weight of water and then filtered. The filtrate is returned to the front end for acid leaching. The filter residue is a low-lithium and low-aluminum lithium extraction residue. The lithium solution obtained contained 16.2 g / L of lithium, 0.19% of iron, and 0.11% of phosphorus. The lithium extraction residue (dry residue) contained 0.048% of lithium and 0.026% of aluminum. The lithium extraction rate was 98.91%, the aluminum removal rate was 95.33%, the iron loss rate was 1.51%, and the phosphorus loss rate was 1.50%.

[0024] Example 2: The raw material used, waste lithium iron phosphate cathode powder, contains Li: 4.0%, Fe: 31.8%, P: 17.6%, and Al: 0.7%. (1) Take 100g of waste lithium iron phosphate cathode powder and put it in a beaker. Add 166g of pure water to make a slurry. Then add the slurry to a planetary ball mill for ball milling. The ball-to-material ratio is 10:1, the ball milling speed is 600r / min, and the ball milling time is 40min. (2) Heat the slurry to a temperature of 75°C, and add 65% nitric acid to the heated slurry. The amount of nitric acid is 1.4 times the total molar amount of lithium and aluminum impurities in the raw material waste lithium iron phosphate cathode powder. (3) After reacting for 1.5 hours, add 10% hydrogen peroxide (based on the mass of the raw material cathode powder) to the acid leaching slurry and react for 3 hours. (4) Add 154g of pure water to the slurry and continue the reaction for 1.5h; (5) After the reaction is completed, the slurry is filtered, and the filter residue is washed with water at twice the wet basis weight and then filtered. The filtrate is returned to the front end for acid leaching. The filter residue is a low-lithium and low-aluminum lithium extraction residue. The lithium solution obtained contained 14.9 g / L of lithium, 0.31% of iron, and 0.17% of phosphorus. The lithium extraction residue (dry residue) contained 0.061% of lithium and 0.039% of aluminum. The lithium extraction rate was 98.62%, the aluminum removal rate was 94.83%, the iron loss rate was 2.62%, and the phosphorus loss rate was 2.61%.

[0025] The raw materials used in the following comparative examples are the same as those in Example 1. Comparative Example 1: Without ball milling, add pure water all at once: Place 100g of waste lithium iron phosphate cathode powder in a beaker, add 300g of pure water to make a slurry, and heat the slurry to a temperature of 80℃; add 65% nitric acid to the heated slurry, the amount of nitric acid being 1.38 times the total molar amount of lithium and aluminum impurities in the raw waste lithium iron phosphate cathode powder; after reacting for 1 hour, add 6% hydrogen peroxide (by weight of the raw cathode powder) to the acid leaching slurry, and react for 3.5 hours; filter the slurry after the reaction, wash the filter residue with 1.7 times the wet basis weight of water, and filter again, returning the filtrate to the front end for acid leaching.

[0026] The lithium solution obtained contained 12.1 g / L of lithium, 2.96% of iron, 1.49% of phosphorus, and 0.014% of aluminum. The lithium extraction rate was 73.78%, the iron loss rate was 22.84%, the phosphorus loss rate was 20.03%, and the aluminum removal rate was 7.01%.

[0027] Comparative Example 2: No ball milling, no heating after mixing water and materials: Take 100g of waste lithium iron phosphate cathode powder and place it in a beaker, add 150g of pure water to mix the slurry; add 65% nitric acid to the slurry, the amount of nitric acid being 1.38 times the total molar amount of lithium and aluminum impurities in the raw waste lithium iron phosphate cathode powder; after reacting for 1 hour, add 6% hydrogen peroxide (by weight of the raw cathode powder) to the acid leaching slurry and react for 2.5 hours; add another 150g of pure water to the slurry and continue reacting for 1 hour; filter the slurry after the reaction is complete, wash the filter residue with 1.7 times the wet basis weight of water and filter again, return the filtrate to the front end for acid leaching.

[0028] The lithium solution obtained contained 10.2 g / L of lithium, 4.47% of iron, 2.43% of phosphorus, and 0.038% of aluminum. The lithium extraction rate was 62.19%, the iron loss rate was 34.49%, the phosphorus loss rate was 32.66%, and the aluminum removal rate was 19.01%.

[0029] Comparative Example 3: Adding hydrogen peroxide directly after adding acid without reaction: Take 100g of waste lithium iron phosphate cathode powder and place it in a beaker. Add 150g of pure water to make a slurry. Then add the slurry to a planetary ball mill for ball milling. The ball-to-powder ratio is 10:1, the ball milling speed is 600r / min, and the ball milling time is 40min. Heat the slurry to a material temperature of 80℃. Add 65% nitric acid to the heated slurry. The amount of nitric acid is 1.38 times the total molar amount of lithium and aluminum impurities in the raw material waste lithium iron phosphate cathode powder. Then add 6% hydrogen peroxide (by weight of the raw material cathode powder) to the acid leaching slurry and react for 2.5h. Add another 150g of pure water to the slurry and continue the reaction for 1h. Filter the slurry after the reaction is complete. Wash the filter residue with water (1.7 times the wet basis weight) and filter again. Return the filtrate to the front end for acid leaching.

[0030] The lithium solution obtained contained 15.2 g / L of lithium, 1.05% of iron, 0.26% of phosphorus, and 0.002% of aluminum. The lithium extraction rate was 93.42%, the iron loss rate was 8.17%, the phosphorus loss rate was 3.52%, and the aluminum removal rate was 1.01%.

[0031] Comparative Example 4: The amount of nitric acid added is lower than the range required by the invention: Take 100g of waste lithium iron phosphate cathode powder and place it in a beaker. Add 150g of pure water to make a slurry. Then add the slurry to a planetary ball mill for ball milling. The ball-to-powder ratio is 10:1, the ball milling speed is 600r / min, and the ball milling time is 40min. Heat the slurry to a material temperature of 80℃. Add 65% nitric acid to the heated slurry. The amount of nitric acid is 1.3 times the total molar amount of lithium and aluminum impurities in the raw material waste lithium iron phosphate cathode powder. After reacting for 1h, add 6% hydrogen peroxide (based on the mass of the raw material cathode powder) to the acid leaching slurry and react for 2.5h. Add another 150g of pure water to the slurry and continue reacting for 1h. Filter the slurry after the reaction is completed. Wash the filter residue with water (1.7 times the mass of the wet basis) and filter again. Return the filtrate to the front end for acid leaching.

[0032] The lithium solution obtained contained 16.5 g / L of lithium, 0.23% of iron, 0.10% of phosphorus, and 0.15% of aluminum. The lithium extraction rate was 97.79%, the iron loss rate was 1.73%, the phosphorus loss rate was 1.31%, and the aluminum removal rate was 72.90%.

[0033] Table 1 is a comparison chart of the embodiments and comparative examples.

[0034] Table 1

[0035] As shown in Table 1, the removal rates of lithium and aluminum were significantly improved by using wet milling to pretreat the lithium iron phosphate cathode powder and adding water in batches for reaction.

[0036] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for selectively extracting lithium and removing aluminum from waste lithium iron phosphate cathode powder, characterized in that, Includes the following steps: S1: Add pure water to the waste lithium iron phosphate cathode powder to make a slurry, and then ball mill the slurry; S2: Heat the ball-milled slurry, then add nitric acid for acid leaching for 1-1.5 hours; S3: Add oxidant to the acid slurry and react for 2-3 hours; S4: Add pure water to the slurry and continue the reaction for 1-2 hours; S5: After the reaction is completed, the slurry is filtered, the resulting filter residue is washed with water and then filtered again. The washing filtrate is returned to the front end for acid leaching. The filter residue is a low-aluminum lithium extraction residue.

2. The method for selectively extracting lithium and removing aluminum from waste lithium iron phosphate cathode powder according to claim 1, characterized in that, In step S1, the amount of water added is 50%-55% of 2.8-3.3 times the mass of the lithium iron phosphate cathode powder, the ball-to-material ratio is 10:1, the ball milling speed is 600 r / min, and the ball milling time is 30-45 min.

3. The method for selectively extracting lithium and removing aluminum from waste lithium iron phosphate cathode powder according to claim 1, characterized in that, In step S2, the slurry is heated to 70-80℃, and the amount of nitric acid added is 1.35-1.40 times the total molar amount of lithium and aluminum impurities in the lithium iron phosphate cathode powder.

4. The method for selectively extracting lithium and removing aluminum from waste lithium iron phosphate cathode powder according to claim 1, characterized in that, In step S3, the oxidant is hydrogen peroxide, and the amount of hydrogen peroxide added is 5%-10% of the mass of lithium iron phosphate cathode powder.

5. The method for selectively extracting lithium and removing aluminum from waste lithium iron phosphate cathode powder according to claim 1, characterized in that, In step S4, the amount of water added is 45%-50% of the mass of lithium iron phosphate cathode powder, which is 2.8-3.3 times the mass of the lithium iron phosphate cathode powder.

6. The method for selectively extracting lithium and removing aluminum from waste lithium iron phosphate cathode powder according to claim 1, characterized in that, In step S5, the liquid-to-solid ratio of the pure water added to the filter residue during washing is 1.5-2:1, the washing temperature is room temperature, the washing time is 1-2 hours, and the washing filtrate is returned to the front end for acid leaching as pure water.

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