Method for recycling lithium iron phosphate positive black powder of waste battery

Abstract

The invention discloses a waste battery lithium iron phosphate positive electrode black powder recovery method which comprises the following steps: S1, activating and roasting positive electrode black powder to obtain pretreated black powder, and mixing and ball-milling the pretreated black powder, an oxidizing agent and an activating solvent to obtain pre-oxidized black powder; s3, the pre-oxidized black powder and an inorganic solvent are mixed for a leaching reaction, and mother liquor A and iron phosphate slag are obtained; s4, adding a pH regulator into the mother liquor A to remove impurities so as to obtain mother liquor B; s5, mixing and purifying the iron phosphate slag and phosphoric acid to obtain crude iron phosphate, washing the crude iron phosphate with water, and adding a complexing agent for further purification to obtain high-purity iron phosphate; and S6, concentrating the mother liquor B to obtain concentrated mother liquor C, and introducing carbon dioxide into the concentrated mother liquor C to precipitate lithium to obtain the battery-grade lithium carbonate. According to the process, iron, lithium, phosphorus and other elements in the positive electrode black powder are efficiently separated and recycled, low-acid or acid-free green leaching of lithium is achieved, the lithium leaching rate is larger than or equal to 98.0%, and the purity of obtained iron phosphate is larger than or equal to 99.3%; the purity of lithium carbonate is greater than or equal to 99.0%.

Description

Technical Field

[0001] The invention relates to the field of green battery recycling, and in particular to a method for recycling black powder from lithium iron phosphate positive electrodes of waste batteries. Background Art

[0002] Lithium iron phosphate batteries are widely used in new energy electric vehicles and energy storage due to their unique advantages such as high safety, high cycle times and low manufacturing cost. Their market share is increasing year by year. The retirement period of lithium iron phosphate batteries is 5-8 years, and the number of waste batteries is also increasing. With the development of new energy and the country's increasingly stringent requirements on solid waste emissions, the recycling of new energy batteries is becoming increasingly important.

[0003] At present, there are three main methods for recycling waste lithium batteries: direct recycling, pyrometallurgy and hydrometallurgy. The direct recycling method is to directly repair the defects of the electrode material to restore its original electrical properties and reuse it in the battery. It is an efficient and green recycling method, but the direct recycling technology is difficult to restore the electrical properties 1:1. Pyrometallurgy mainly extracts various elements from the positive electrode materials of waste batteries after high-temperature roasting. Pyrometallurgy has problems such as high energy consumption and high cost. Hydrometallurgy uses acid to dissolve valuable metal elements, separate them from black powder, and effectively recover each element through precipitation. However, conventional acid leaching recovery has a series of problems such as high-salt wastewater discharge.

[0004] At present, the wet recycling of waste lithium iron phosphate batteries is more commonly done by oxidation leaching, and the commonly used oxidants are hydrogen peroxide, ammonium persulfate, nitric acid, potassium permanganate, etc. It is urgent to find an efficient and green oxidation process. Summary of the invention

[0005] The present invention provides a method for recovering black powder from lithium iron phosphate positive electrodes of waste batteries. The present invention improves the wet acid leaching process, adopts a high-efficiency oxidant to first oxidize iron in the lithium iron phosphate into trivalent iron, and then uses an acid-free or low-acid wet process to leach lithium ions, so that lithium elements are preferentially recovered in an efficient and green manner, and then iron and phosphorus elements are recovered through a conventional wet process, thereby achieving full quantitative recovery of elements, a high recovery rate of valuable elements, and effectively reducing acid consumption, which is green and efficient.

[0006] The technical solution of the present invention is as follows:

[0007] A method for recovering black powder from positive and negative electrodes of lithium iron phosphate waste batteries, comprising the following preparation process:

[0008] S1: activating and roasting the positive electrode black powder to obtain pre-treated black powder, and mixing the pre-treated black powder with an oxidant and an activation solvent and ball milling to obtain pre-oxidized black powder;

[0009] S2: pre-oxidized black powder is mixed with an inorganic solvent to undergo a leaching reaction to obtain a mother liquor A and iron phosphate slag;

[0010] S3: adding Ph regulator to mother solution A to remove impurities to obtain mother solution B;

[0011] S4: the ferric phosphate slag is mixed with phosphoric acid to obtain crude ferric phosphate, the crude ferric phosphate is washed with water and a complexing agent is added to further purify it to obtain high-purity ferric phosphate;

[0012] S5: The mother liquor B is concentrated to obtain a concentrated mother liquor C, and the concentrated mother liquor C is introduced into carbon dioxide to precipitate lithium to obtain battery-grade lithium carbonate.

[0013] Furthermore, the positive electrode black powder has a lithium content of 2.5-4.5wt%;

[0014] The activation calcination temperature is 500-600°C, and the calcination time is 0.5-2 hours;

[0015] The oxidant is one or more combinations of potassium ferrate, hydrogen peroxide, and ammonium persulfate, and the mass ratio of black powder to oxidant is 1:(0.5-2);

[0016] The activation solvent is one or more combinations of dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid, and dilute phosphoric acid, and the solid-liquid ratio of black powder to the activation solvent is 1:(3-5).

[0017] Furthermore, the ball milling time is 1-3 hours.

[0018] Furthermore, the inorganic solvent is one or more combinations of dilute sulfuric acid, dilute hydrochloric acid, dilute phosphoric acid, and water, and the solid-liquid ratio of black powder to inorganic solvent is 1:(5-10).

[0019] Furthermore, the inorganic solvent concentration is 0-1 mol / L, the leaching temperature is 40-80° C., and the leaching time is 1-4 hours.

[0020] Furthermore, the pH value of the impurity removal process is adjusted to 7-9;

[0021] The regulator used to adjust Ph is lithium hydroxide.

[0022] Furthermore, in the iron phosphate slag purification stage, the phosphoric acid concentration is 2-6 mol / L, the phosphoric acid solution Ph is 1.0-2.5, the mass ratio of the iron phosphate slag to the phosphoric acid is 1:(3-8), and the purified liquid can repeatedly wash the iron phosphate slag.

[0023] Furthermore, in the iron phosphate slag purification stage, the mass ratio of crude iron phosphate to water is 1:(5-10), the complexing agent is EDTA, and the added amount is 0.1-0.5wt% of the crude iron phosphate, and the purity of the obtained iron phosphate is ≥99.0%.

[0024] Furthermore, the purified mother liquor B is adjusted to a pH of 11-13, and evaporated and concentrated to a lithium concentration of 20 g-30 g / L.

[0025] Furthermore, the flow rate of the introduced carbon dioxide is 10-20 Nm3 / h, and the ventilation is stopped when the solution Ph is 9-11.

[0026] The beneficial effects of the present invention are embodied in:

[0027] (1) The mechanical ball milling process is beneficial to the full oxidation of the oxidant and the black powder, and accelerates the dissolution of lithium between the black powder layers, achieving efficient lithium leaching under acid-free or low-acid and low-temperature conditions, with a lithium leaching rate of ≥98.0%.

[0028] (2) The lithium extraction process is adopted to dissolve lithium and a small amount of impurities first. Compared with the dissolution of all components, the amount of acid used is reduced and the lithium recovery rate is increased to ≥ 98%.

[0029] (3) The lithium and iron phosphate are distributed and recovered to avoid the loss of lithium caused by impurities in the purification process, and at the same time, the iron phosphate is highly purified, with the purity of the iron phosphate being ≥99.3%.

[0030] (4) Using carbon dioxide to precipitate lithium to obtain lithium carbonate with a purity of ≥99.0%. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. In the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0032] Invention In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or schemes that A and B meet at the same time. In addition, "multiple" refers to more than two. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist.

[0033] The positive electrode black powder with a lithium content of 2.5-4.5wt% is activated and calcined at a temperature of 500-600°C for 0.5-2.0 hours. The pretreated black powder is then subjected to mechanical ball milling-assisted pre-oxidation with an oxidant and an active solvent to obtain pre-oxidized black powder. The ball milling is performed for 1-3 hours. The mass ratio of black powder to oxidant is 1:(0.5-2), and the solid-liquid ratio of black powder to activation solvent is 1:(3-5).

[0034] First, ball milling can refine the particles and promote the dissolution of lithium between the black powder particle layers; second, it is conducive to the full oxidation of the black powder. At the same time, ball milling provides a certain temperature to quickly achieve the dissolution of lithium under low-acid conditions.

[0035] The activation solvent is one or more combinations of dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid, and dilute phosphoric acid, which mainly provides weak acid conditions to enhance the oxidizing effect of the oxidant and efficiently leaches lithium.

[0036] The pre-oxidized black powder is mixed with inorganic solvents such as dilute sulfuric acid, dilute salt, and water for leaching reaction. The concentration of the inorganic solvent is 0-1 mol / L, the leaching temperature is 40-80° C., and the leaching time is 1-4 hours, and finally mother liquor A and iron phosphate slag are obtained.

[0037] Water leaching achieves an acid-free leaching environment, reduces the leaching of insoluble impurities in the black powder, and reduces the burden of brine in the later stage.

[0038] Mother liquor A is added with a pH regulator such as sodium hydroxide, potassium hydroxide, lithium hydroxide, etc., the pH is adjusted to 7-9, and impurities are removed to obtain mother liquor B.

[0039] Aluminum, iron, and copper are removed in the form of phosphates, and lithium hydroxide is used without introducing sodium and potassium ions. At the same time, the lithium can be recycled later.

[0040] The purified mother liquor B is then adjusted to a pH of 11-13, and evaporated and concentrated to a lithium concentration of 20 g-30 g / L to increase the lithium carbonate conversion rate.

[0041] Carbon dioxide is introduced into the lithium-containing mother liquor at a flow rate of 10-20 Nm3 / h. When the solution Ph is 9-11, aeration is stopped. The precipitate is filtered, washed and dried to obtain lithium carbonate. The use of carbon dioxide precipitation does not introduce other impurity ions, thereby improving the purity of lithium carbonate.

[0042] The iron phosphate slag is mixed with 2-6 mol / L phosphoric acid for purification, the phosphoric acid solution has a Ph of 1.0-2.5, and the mass ratio of iron phosphate slag to phosphoric acid is 1: (3-8). The purified solution can be used to repeatedly wash the iron phosphate slag, and after purification, it is filtered and washed to obtain crude iron phosphate. The iron phosphate slag is leached and purified with phosphoric acid to dissolve other soluble impurities such as iron and aluminum in the slag.

[0043] The crude ferric phosphate is purified for the second time, washed with water and further purified by adding a chelating agent to obtain high-purity ferric phosphate. The mass ratio of crude ferric phosphate to water is 1:(5-10), the chelating agent is EDTA, and the added amount is 0.1-0.5wt% of the crude ferric phosphate. The purity of the obtained high-purity ferric phosphate is ≥99.5%.

[0044] The inventive method can efficiently separate and recover elements such as iron, lithium, and phosphorus in positive electrode black powder, realize low-acid or acid-free green extraction of lithium, with a lithium leaching rate of ≥98.0%, and the purity of the obtained iron phosphate being ≥99.3%; and the purity of lithium carbonate being ≥99.0%.

[0045] Example 1

[0046] The positive electrode black powder with a lithium content of 2.5wt% was activated and calcined at a temperature of 500°C for 0.5 hours. The pretreated black powder was then subjected to mechanical ball milling-assisted pre-oxidation with an oxidant and an active solvent to obtain pre-oxidized black powder. The pre-oxidized black powder was ball milled for 1 hour. The mass ratio of black powder to oxidant was 1:0.5, and the solid-liquid ratio of black powder to activation solvent was 1:3.

[0047] The pre-oxidized black powder is mixed with water for leaching reaction, the leaching temperature is 40°C, the leaching time is 4 hours, and finally mother liquor A and iron phosphate slag are obtained. Lithium hydroxide is added to mother liquor A as a Ph regulator, the pH is adjusted to 7, and impurities are removed to obtain mother liquor B. The purified mother liquor B is then adjusted to a pH of 11, evaporated and concentrated to a lithium concentration of 20 g / L. Carbon dioxide is introduced into the lithium-containing mother liquor at a flow rate of 10 m3 / h. The solution is stopped when the pH is 9, and the precipitate is filtered, washed, and dried to obtain lithium carbonate.

[0048] The iron phosphate slag is mixed and stirred with 2 mol / L phosphoric acid for purification, the phosphoric acid solution has a Ph of 2.5, the mass ratio of the iron phosphate slag to the phosphoric acid is 1:3, the purified solution can be used to repeatedly wash the iron phosphate slag, and after purification, the crude iron phosphate is obtained by filtering and washing. The crude iron phosphate is purified for the second time, washed with water and further purified by adding a complexing agent to obtain high-purity iron phosphate, the mass ratio of the crude iron phosphate to water is 1:5, the complexing agent is EDTA, and the amount added is 0.1wt% of the crude iron phosphate, and the purity of the obtained high-purity iron phosphate is 99.5%.

[0049] The method can efficiently separate and recover elements such as iron, lithium, and phosphorus in positive electrode black powder, realize low-acid or acid-free green extraction of lithium, with lithium leaching of 98.0%, and the purity of the obtained iron phosphate is 99.3%; the purity of lithium carbonate is 99.0%.

[0050] Example 2

[0051] The positive electrode black powder with a lithium content of 3.0wt% was activated and calcined at a temperature of 550°C for 1.0 hour. The pretreated black powder was then subjected to mechanical ball milling-assisted pre-oxidation with an oxidant and an active solvent to obtain pre-oxidized black powder. The ball milling was performed for 1.5 hours. The mass ratio of black powder to oxidant was 1:1, and the solid-liquid ratio of black powder to activation solvent was 1:3.5.

[0052] The pre-oxidized black powder is mixed with inorganic solvents such as dilute hydrochloric acid for leaching reaction. The concentration of the inorganic solvent is 0.2 mol / L, the leaching temperature is 50°C, and the leaching time is 3 hours, and finally mother liquor A and iron phosphate slag are obtained. Lithium hydroxide Ph regulator is added to mother liquor A to adjust the pH to 7.5, and mother liquor B is obtained by removing impurities. The purified mother liquor B is then adjusted to pH 11.5, evaporated and concentrated to a lithium concentration of 23 g / L. Carbon dioxide is introduced into the lithium-containing mother liquor at a flow rate of 15 Nm3 / h. The solution is ventilated when the Ph is 9.5, and the precipitate is filtered, washed, and dried to obtain lithium carbonate.

[0053] The iron phosphate slag is mixed and stirred with 3 mol / L phosphoric acid for purification, the phosphoric acid solution has a Ph of 2.0, the mass ratio of the iron phosphate slag to the phosphoric acid is 1:4, the purified solution can be used to repeatedly wash the iron phosphate slag, and after purification, the crude iron phosphate is filtered and washed. The crude iron phosphate is purified for the second time, washed with water and further purified by adding a complexing agent to obtain high-purity iron phosphate, the mass ratio of the crude iron phosphate to water is 1:6, the complexing agent is EDTA, and the amount added is 0.2wt% of the crude iron phosphate, and the purity of the obtained high-purity iron phosphate is 99.6%.

[0054] The invented method can efficiently separate and recover elements such as iron, lithium, and phosphorus in positive electrode black powder, realize low-acid or acid-free green extraction of lithium, with a lithium leaching rate of 98.4%, and the purity of the obtained iron phosphate is 99.6%; the purity of lithium carbonate is 99.2%.

[0055] Example 3

[0056] The positive electrode black powder with a lithium content of 4.0wt% was activated and calcined at a temperature of 580°C for 1.5 hours. The pretreated black powder was then subjected to mechanical ball milling-assisted pre-oxidation with an oxidant and an active solvent to obtain pre-oxidized black powder. The pre-oxidized black powder was ball milled for 2 hours. The mass ratio of black powder to oxidant was 1:1.5, and the solid-liquid ratio of black powder to activation solvent was 1:4.

[0057] The pre-oxidized black powder is mixed with inorganic solvents such as dilute hydrochloric acid for leaching reaction. The concentration of the inorganic solvent is 0.5 mol / L, the leaching temperature is 60°C, and the leaching time is 2 hours, and finally mother liquor A and iron phosphate slag are obtained. Ph regulators such as lithium hydroxide are added to mother liquor A to adjust the pH to 8, and mother liquor B is obtained by removing impurities. The purified mother liquor B is then adjusted to pH 12, evaporated and concentrated to a lithium concentration of 25 g / L. Carbon dioxide is introduced into the lithium-containing mother liquor at a flow rate of 18 Nm3 / h. The solution is ventilated when the pH is 10, and the precipitate is filtered, washed, and dried to obtain lithium carbonate.

[0058] The iron phosphate slag is mixed and stirred with 4 mol / L phosphoric acid for purification, the phosphoric acid solution has a Ph of 2.0, the mass ratio of the iron phosphate slag to the phosphoric acid is 1:6, the purified solution can be used to repeatedly wash the iron phosphate slag, and after purification, the crude iron phosphate is obtained by filtering and washing. The crude iron phosphate is purified for the second time, washed with water and further purified by adding a complexing agent to obtain high-purity iron phosphate, the mass ratio of the crude iron phosphate to water is 1:8, the complexing agent is EDTA, and the amount added is 0.4wt% of the crude iron phosphate, and the purity of the obtained high-purity iron phosphate is 99.7%.

[0059] The invented method can efficiently separate and recover elements such as iron, lithium, and phosphorus in positive electrode black powder, realize low-acid or acid-free green extraction of lithium, with a lithium leaching rate of ≥99.0%, and the purity of the obtained iron phosphate is 99.5%; the purity of lithium carbonate is 99.3%.

[0060] Example 4

[0061] The positive electrode black powder with a lithium content of 4.5wt% was activated and calcined at a temperature of 600°C for 2.0 hours. The pretreated black powder was then subjected to mechanical ball milling-assisted pre-oxidation with an oxidant and an active solvent to obtain pre-oxidized black powder. The pre-oxidized black powder was ball milled for 3 hours. The mass ratio of black powder to oxidant was 1:2, and the solid-liquid ratio of black powder to activation solvent was 1:5.

[0062] The pre-oxidized black powder is mixed with inorganic solvents such as dilute hydrochloric acid for leaching reaction. The concentration of the inorganic solvent is 1 mol / L, the leaching temperature is 80°C, and the leaching time is 1 hour, and finally mother liquor A and iron phosphate slag are obtained. Ph regulators such as lithium hydroxide are added to mother liquor A to adjust the pH to 9, and mother liquor B is obtained by removing impurities. The purified mother liquor B is then adjusted to pH 13, evaporated and concentrated to a lithium concentration of 30 g / L. Carbon dioxide is introduced into the lithium-containing mother liquor at a flow rate of 20 Nm3 / h. The solution is 11 and ventilation is stopped. The precipitate is filtered, washed, and dried to obtain lithium carbonate.

[0063] The iron phosphate slag is mixed and stirred with 6 mol / L phosphoric acid for purification, the phosphoric acid solution has a Ph of 1.0, the mass ratio of the iron phosphate slag to the phosphoric acid is 1:8, the purified solution can be used to repeatedly wash the iron phosphate slag, and after purification, the crude iron phosphate is filtered and washed. The crude iron phosphate is purified for the second time, washed with water and further purified by adding a complexing agent to obtain high-purity iron phosphate, the mass ratio of the crude iron phosphate to water is 1:10, the complexing agent is EDTA, and the amount added is 0.5wt% of the crude iron phosphate, and the purity of the obtained high-purity iron phosphate is 99.8%.

[0064] The invented method can efficiently separate and recover elements such as iron, lithium, and phosphorus in positive electrode black powder, realize low-acid or acid-free green extraction of lithium, with a lithium leaching rate of ≥99.2%, and the purity of the obtained iron phosphate ≥99.6%; the purity of lithium carbonate ≥99.5%.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for recovering black powder from positive and negative electrodes of lithium iron phosphate waste batteries, characterized in that: The preparation process includes the following: S1: activating and roasting the positive electrode black powder to obtain pre-treated black powder, and mixing the pre-treated black powder with an oxidant and an activation solvent and ball milling to obtain pre-oxidized black powder; S2: pre-oxidized black powder is mixed with an inorganic solvent to undergo a leaching reaction to obtain a mother liquor A and iron phosphate slag; S3: adding Ph regulator to mother solution A to remove impurities to obtain mother solution B; S4: the ferric phosphate slag is mixed with phosphoric acid to obtain crude ferric phosphate, the crude ferric phosphate is washed with water and a complexing agent is added to further purify it to obtain high-purity ferric phosphate; S5: The mother liquor B is concentrated to obtain a concentrated mother liquor C, and the concentrated mother liquor C is introduced into carbon dioxide to precipitate lithium to obtain battery-grade lithium carbonate.

2. According to claim 1, a method for recovering black powder from lithium iron phosphate positive electrodes of waste batteries, characterized in that: The positive electrode black powder has a lithium content of 2.5-4.5wt%; The activation calcination temperature is 500-600°C, and the calcination time is 0.5-2 hours; The oxidant is one or more combinations of potassium ferrate, hydrogen peroxide, and ammonium persulfate, and the mass ratio of black powder to oxidant is 1: (0.5-2); The activation solvent is one or more combinations of dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid, and dilute phosphoric acid, and the solid-liquid ratio of black powder to the activation solvent is 1: (3-5).

3. A method for recovering black powder from lithium iron phosphate cathode of waste batteries according to claim 1, characterized in that: The ball milling time is 1-3 hours.

4. A method for recovering black powder from lithium iron phosphate cathode of waste batteries according to claim 1, characterized in that: The inorganic solvent is one or more combinations of dilute sulfuric acid, dilute hydrochloric acid, dilute phosphoric acid, and water, and the solid-liquid ratio of black powder to inorganic solvent is 1: (5-10).

5. A method for recovering black powder from lithium iron phosphate positive electrodes of waste batteries according to claim 4, characterized in that: The inorganic solvent concentration is 0-1 mol / L, the leaching temperature is 40-80° C., and the leaching time is 1-4 hours.

6. A method for recovering black powder from lithium iron phosphate cathode of waste batteries according to claim 1, characterized in that: The pH value of the impurity removal process is adjusted to 7-9; The regulator used to adjust Ph is lithium hydroxide.

7. A method for recovering black powder from lithium iron phosphate positive electrodes of waste batteries according to claim 1, characterized in that: In the iron phosphate slag purification stage, the phosphoric acid concentration is 2-6 mol / L, the Ph of the phosphoric acid solution is 1.0-2.5, the mass ratio of the iron phosphate slag to the phosphoric acid is 1:(3-8), and the purified solution can repeatedly wash the iron phosphate slag.

8. A method for recovering black powder from lithium iron phosphate positive electrodes of waste batteries according to claim 7, characterized in that: In the iron phosphate slag purification stage, the mass ratio of crude iron phosphate to water is 1: (5-10), the complexing agent is EDTA, and the added amount is 0.1-0.5wt% of the crude iron phosphate. The purity of the obtained iron phosphate is ≥99.0%.

9. A method for recovering black powder from lithium iron phosphate positive electrodes of waste batteries according to claim 1, characterized in that: The purified mother liquor B is adjusted to a pH of 11-13 and evaporated and concentrated to a lithium concentration of 20 g-30 g / L.

10. A method for recovering black powder from lithium iron phosphate positive electrodes of waste batteries according to claim 1, characterized in that: The flow rate of the introduced carbon dioxide is 10-20 Nm3 / h, and the ventilation is stopped when the solution Ph is 9-11.