Method for recovering phosphorus, iron and lithium in lithium iron phosphate black powder

Abstract

The invention belongs to the field of waste lithium iron phosphate battery recycling, and particularly discloses a method for recycling phosphorus, iron and lithium in lithium iron phosphate black powder, which comprises the following steps: S1, leaching the lithium iron phosphate black powder by dilute acid, and carrying out filter pressing to obtain an acid leaching solution; s2, alkali liquor is added into the pickle liquor to adjust the pH value, ferric phosphate is precipitated, and ferric phosphate dihydrate and ferric phosphate precipitated liquor are obtained through filtering; s3, adding caustic soda liquid into the iron phosphate precipitation post-liquid to adjust the pH value, filtering to obtain lithium phosphate and a lithium phosphate precipitation post-liquid, returning the filtered lithium phosphate to S1 for acid leaching, and supplementing phosphorus and enriching lithium; and S4, carrying out MVR concentration on the lithium phosphate precipitation solution to enable the lithium to reach a certain concentration, adding the lithium phosphate precipitation solution into a sodium carbonate solution, and carrying out lithium precipitation and washing to finally obtain a lithium carbonate product. According to the method disclosed by the invention, the lithium phosphate is returned to the acid leaching section to be leached without additionally adding a phosphorus supplementing agent, so that phosphorus can be supplemented for precipitated iron phosphate, the lithium can be enriched, and iron, phosphorus and lithium resources in the lithium iron phosphate black powder can be effectively recovered.

Description

Technical Field

[0001] The invention belongs to the field of recycling waste lithium iron phosphate batteries, and specifically relates to a method for recycling lithium iron phosphate in lithium iron phosphate black powder. Background Art

[0002] In recent years, driven by new energy vehicles and energy storage lithium batteries, the demand for lithium iron phosphate batteries has increased significantly. However, due to the limited service life of lithium batteries, they will degrade after a certain period of use, resulting in a large number of waste lithium iron phosphate batteries. Nowadays, green travel and green life are advocated, and the recycling of waste lithium iron phosphate batteries is urgent.

[0003] At present, the recycling process of waste lithium iron phosphate batteries is mainly through acid leaching, preparing iron phosphate and lithium phosphate. However, in the process of preparing iron phosphate, phosphoric acid needs to be added as a phosphorus supplement, which increases the recycling cost. In this process, it is found that the iron phosphate mother liquor contains a small amount of iron and phosphorus. Therefore, in the subsequent preparation of lithium phosphate, the quality of lithium phosphate products is poor, which directly leads to a significant reduction in the value of lithium. In addition, due to the poor quality of lithium phosphate products, lithium is found in the filtered lithium phosphate mother liquor, resulting in a lower recovery rate of metallic lithium.

[0004] Therefore, there is an urgent need to find a simple and highly recyclable method for lithium iron phosphate in waste lithium iron phosphate batteries. Summary of the invention

[0005] The purpose of the present invention is to provide a method for recovering lithium iron phosphate in lithium iron phosphate black powder, which can effectively realize the efficient recovery of iron, phosphorus and lithium resources in the lithium iron phosphate black powder. The whole method is simple to operate. In the process of recovering iron, phosphorus and lithium, no additional phosphorus supplementing agent is needed. The prepared lithium phosphate is returned to the acid leaching stage for leaching, which can not only serve as phosphorus supplement for precipitated iron phosphate but also enrich lithium, thereby reducing the loss of valuable metals and improving the recovery rate of iron, phosphorus and lithium and the economic benefits of the enterprise.

[0006] In order to solve the above technical problems, the present invention provides a method for recovering lithium iron phosphate from lithium iron phosphate black powder, the method comprising the following steps:

[0007] S1, leaching the lithium iron phosphate black powder with dilute acid and filtering to obtain an acid leaching solution;

[0008] S2, adding alkali solution to the acid leaching solution to adjust the pH to precipitate iron phosphate, and filtering to obtain iron phosphate dihydrate and a post-precipitation iron phosphate solution containing lithium and a small amount of phosphorus and iron through chemical precipitation;

[0009] S3, adding liquid alkali to the post-precipitation iron phosphate solution containing lithium and a small amount of phosphorus and iron to adjust the pH to precipitate lithium phosphate, filtering to obtain lithium phosphate and the post-precipitation lithium phosphate solution through chemical precipitation, and returning the filtered lithium phosphate to S1 for acid leaching to supplement phosphorus and enrich lithium;

[0010] S4. The liquid after lithium phosphate precipitation is concentrated by MVR to make lithium reach a certain concentration, and the concentrated liquid after lithium phosphate precipitation is added to a sodium carbonate solution for lithium precipitation and washing to finally obtain a lithium carbonate product.

[0011] Furthermore, the lithium iron phosphate black powder in S1 comes from dismantling waste lithium iron phosphate batteries, discharging, crushing and sorting. 1.5-2.5 mol / L of sulfuric acid is added to the lithium iron phosphate black powder at a liquid-to-solid ratio of 2-10:1, the reaction temperature is controlled to 70-90°C, the reaction time is 1-4h, and the acid leaching solution is filtered.

[0012] Furthermore, the alkali solution in S2 is one or both of liquid alkali or sodium carbonate, the pH is adjusted to 1.5-2.0, the precipitation reaction temperature is controlled to 80-95°C, the reaction time is 4-6h, and the dihydrate ferric phosphate product is obtained after filtration, and washed with deionized water for 5-8 times, and the dihydrate ferric phosphate is calcined at 500-700°C for 4-6h to obtain an anhydrous ferric phosphate product.

[0013] Furthermore, the concentration of the liquid alkali or sodium carbonate in S2 is 1 to 4 mol / L.

[0014] Furthermore, in S3, the pH of the solution after precipitation of iron phosphate is adjusted to 8-11 by liquid alkali, the temperature is controlled to 70-90°C, the reaction time is 1-2h, and the prepared lithium phosphate is returned to S1 for acid leaching to supplement phosphorus and enrich lithium for precipitation of iron phosphate.

[0015] Furthermore, the solution after precipitation of lithium phosphate in S4 is concentrated by MVR until the lithium content in the solution is ≥20 g / L.

[0016] Furthermore, the concentration of sodium carbonate in S4 is 200 g / L to 300 g / L, and the addition time is 50 to 60 min.

[0017] Furthermore, the reaction time of lithium precipitation in S4 is 30 min to 90 min, and the reaction temperature is 90 to 95°C.

[0018] Furthermore, the lithium carbonate in S4 is washed twice, the drying temperature is 120-150° C., and the drying time is 1-2 hours.

[0019] Furthermore, the lithium carbonate in S4 is washed with deionized water at 80-100°C.

[0020] The beneficial effects of the present invention are:

[0021] 1. Through the method for recovering lithium iron phosphate in lithium iron phosphate black powder of the present invention, the recycling of waste batteries themselves is realized, and the problem of optimizing and improving the recovery rate of metallic lithium is solved. Among them, the recovery rates of iron, phosphorus and lithium in lithium iron phosphate black powder can reach 99.4%, 99.8% and 99.3% or more respectively, which greatly improves the recycling rate of resources and can effectively realize the efficient recovery of iron, phosphorus and lithium resources in lithium iron phosphate black powder. The whole method is simple to operate. In the process of recovering iron, phosphorus and lithium, no additional phosphorus supplementing agent is required. The prepared lithium phosphate is returned to the acid leaching stage for leaching, which can not only supplement phosphorus for the precipitated iron phosphate but also enrich lithium, thereby reducing the loss of valuable metals, improving the recovery rate of iron, phosphorus and lithium and the economic benefits of the enterprise. The present invention has a simple process and high economy. The prepared iron phosphate and lithium carbonate products are both higher than the battery grade standard.

[0022] 2. When preparing lithium carbonate products, the present invention adopts a reverse addition method, by adding the concentrated lithium phosphate precipitation liquid into the sodium carbonate solution for lithium precipitation, which can accelerate the precipitation of lithium carbonate, reduce the Na+ content in the lithium carbonate product, and improve the purity of the lithium carbonate product. At the same time, it also reduces the use of sodium carbonate solution and reduces the recovery cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 The present invention is a flow chart of a method for recovering lithium iron phosphate from lithium iron phosphate black powder. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the specification of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Example 1

[0027] like Figure 1 As shown, a method for recovering lithium iron phosphate from lithium iron phosphate black powder comprises the following steps:

[0028] S1, placing 1 ton of waste lithium iron phosphate black powder in a 2 mol / L sulfuric acid solution at a liquid-to-solid ratio of 4:1 for 4 hours at a reaction temperature of 85° C., and filtering to obtain an acid leaching solution;

[0029] S2, placing the acid leaching solution in a reactor, using 2 mol / L liquid alkali to adjust the pH of the solution to 1.6 to precipitate iron phosphate, controlling the reaction temperature to be below 95°C, reacting for 6 hours, obtaining a dihydrate iron phosphate product and a post-precipitation iron phosphate solution containing lithium and a small amount of phosphorus and iron, washing the dihydrate iron phosphate product with deionized water for 5 times, and then roasting the dihydrate iron phosphate at 600°C for 4 hours to obtain an anhydrous iron phosphate product, wherein the detection results of the anhydrous iron phosphate product are shown in Table 1;

[0030] S3, adding liquid alkali to the post-precipitation iron phosphate solution containing lithium and a small amount of phosphorus and iron to adjust the pH to 11 for lithium phosphate precipitation, controlling the temperature to 80° C., the reaction time to 1 hour, and filtering to obtain lithium phosphate and post-precipitation lithium phosphate solution through chemical precipitation, returning the filtered lithium phosphate to S1 for acid leaching to supplement phosphorus and enrich lithium for the precipitated iron phosphate;

[0031] S4. With the cyclic enrichment of lithium, the liquid after lithium phosphate precipitation is concentrated by MVR to make the lithium content reach 30g / L. The concentrated liquid after lithium phosphate precipitation is added into 250g / L sodium carbonate solution by reverse addition to precipitate lithium carbonate. The feeding time is controlled to be 60min, the reaction temperature is 90℃, the lithium precipitation reaction time is 30min, the lithium carbonate product is filtered, and then washed twice with deionized water at 100℃ and dried at 120℃ for 2h to obtain battery lithium carbonate. The test results are shown in Table 2.

[0032] Note: In Example 1, 1 ton of waste lithium iron phosphate black powder can obtain 0.695 tons of iron phosphate product and 0.155 tons of lithium carbonate product, wherein the recovery rates of iron, phosphorus and lithium reach 99.46%, 99.83% and 99.35% respectively.

[0033] Example 2

[0034] like Figure 1 As shown, a method for recovering lithium iron phosphate from lithium iron phosphate black powder comprises the following steps:

[0035] S1. Place 1 ton of waste lithium iron phosphate black powder in a 2 mol / L sulfuric acid solution at a liquid-to-solid ratio of 4:1 for 4 hours at a reaction temperature of 85° C. and filter to obtain an acid leaching solution;

[0036] S2, placing the acid leaching solution in a reactor, using 2 mol / L liquid alkali to adjust the solution pH to 1.7 to precipitate iron phosphate, controlling the temperature below 95°C to react for 6 hours, obtaining a dihydrate iron phosphate product and a solution after precipitation of iron phosphate, washing the dihydrate iron phosphate product with deionized water for 5 times, and roasting the washed dihydrate iron phosphate at 600°C for 4 hours to obtain an anhydrous iron phosphate product. The test results are shown in Table 1;

[0037] S3, adding liquid alkali to the post-precipitation iron phosphate solution containing lithium and a small amount of phosphorus and iron to adjust the pH to 10.5 for lithium phosphate precipitation, controlling the temperature to 80° C., the reaction time to 1 hour, and filtering to obtain lithium phosphate and post-precipitation lithium phosphate solution through chemical precipitation, returning the filtered lithium phosphate to S1 for acid leaching to supplement phosphorus and enrich lithium for the precipitated iron phosphate;

[0038] S4. With the cyclic enrichment of lithium, the liquid after lithium phosphate precipitation is concentrated by MVR to make the lithium content reach 25g / L. The concentrated liquid after lithium phosphate precipitation is added into 250g / L sodium carbonate solution by reverse addition to precipitate lithium carbonate. The feeding time is controlled to be 60min, the reaction temperature is 90°C, the lithium precipitation reaction time is 30min, the lithium carbonate product is filtered, and then washed twice with deionized water at 100°C and dried at 120°C for 2h to obtain battery lithium carbonate. The test results are shown in Table 2.

[0039] Note: In Example 2, 1 ton of waste lithium iron phosphate black powder can obtain 0.696 tons of iron phosphate products and 0.155 tons of lithium carbonate products, wherein the recovery rates of iron, phosphorus and lithium reach 99.45%, 99.82% and 99.36% respectively.

[0040]

[0041] Table 1

[0042]

[0043] Table 2

[0044] The lithium iron phosphate black powder in Examples 1 and 2 of the present invention is obtained by disassembling waste lithium iron phosphate batteries, discharging, crushing and sorting, which can realize the recycling of waste batteries themselves and optimize and improve the recovery rate of metallic lithium. Among them, the recovery rates of iron, phosphorus and lithium in the lithium iron phosphate black powder can reach 99.4%, 99.8% and 99.3% respectively, which greatly improves the recycling rate of resources.

[0045] The method for recovering lithium iron phosphate in lithium iron phosphate black powder of the present invention is simple to operate. In the process of recovering iron, phosphorus and lithium, no additional phosphorus supplementing agent is needed. The prepared lithium phosphate is returned to the acid leaching stage for leaching, which can not only supplement phosphorus for precipitated iron phosphate but also enrich lithium, thereby reducing the loss of valuable metals, improving the recovery rate of iron, phosphorus and lithium and the economic benefits of the enterprise. The method of the present invention is simple in process and highly economical. The prepared iron phosphate and lithium carbonate products are both higher than the battery grade standard.

[0046] The above disclosures are merely two preferred embodiments of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for recovering lithium iron phosphate from lithium iron phosphate black powder, characterized in that: The method comprises the following steps: S1, leaching the lithium iron phosphate black powder with dilute acid and filtering to obtain an acid leaching solution; S2, adding alkali solution to the acid leaching solution to adjust the pH to precipitate iron phosphate, and filtering to obtain iron phosphate dihydrate and the solution after precipitation of iron phosphate through chemical precipitation; S3, adding liquid alkali to the solution after precipitation of iron phosphate to adjust the pH to precipitate lithium phosphate, filtering to obtain lithium phosphate and the solution after precipitation of lithium phosphate by chemical precipitation, returning the filtered lithium phosphate to S1 for acid leaching to supplement phosphorus and enrich lithium; S4. The liquid after lithium phosphate precipitation is concentrated by MVR to make lithium reach a certain concentration, and the liquid after lithium phosphate precipitation is added into sodium carbonate solution to precipitate lithium and wash, and finally obtain lithium carbonate product.

2. The method for recovering lithium iron phosphate from lithium iron phosphate black powder according to claim 1, characterized in that: The lithium iron phosphate black powder in S1 comes from dismantling waste lithium iron phosphate batteries, discharging, crushing and sorting. 1.5-2.5 mol / L sulfuric acid is added to the lithium iron phosphate black powder at a liquid-to-solid ratio of 2-10:1, the reaction temperature is controlled to be 70-90°C, the reaction time is 1-4h, and the acid leaching solution is filtered.

3. The method for recovering lithium iron phosphate from lithium iron phosphate black powder according to claim 1, characterized in that: The alkali solution in S2 is one or both of liquid alkali or sodium carbonate, the pH is adjusted to 1.5-2.0, the precipitation reaction temperature is controlled to 80-95°C, the reaction time is 4-6h, and the dihydrate ferric phosphate product is obtained after filtration, and washed with deionized water for 5-8 times, and the dihydrate ferric phosphate is calcined at 500-700°C for 4-6h to obtain an anhydrous ferric phosphate product.

4. The method for recovering lithium iron phosphate from lithium iron phosphate black powder according to claim 3, characterized in that: The concentration of the liquid caustic soda or sodium carbonate in S2 is 1-4 mol / L.

5. The method for recovering lithium iron phosphate from lithium iron phosphate black powder according to claim 1, characterized in that: In S3, the pH of the solution after precipitation of iron phosphate is adjusted to 8-11 by liquid alkali, the temperature is controlled to 70-90°C, the reaction time is 1-2h, and after filtration, the prepared lithium phosphate is returned to S1 for acid leaching to supplement phosphorus and enrich lithium for precipitation of iron phosphate.

6. The method for recovering lithium iron phosphate from lithium iron phosphate black powder according to claim 1, characterized in that: The solution after precipitation of lithium phosphate in S4 is concentrated by MVR until the lithium content in the solution is ≥20 g / L.

7. The method for recovering lithium iron phosphate from lithium iron phosphate black powder according to claim 6, characterized in that: The concentration of sodium carbonate in the S4 is 200 g / L to 300 g / L, and the addition time is 50 to 60 min.

8. The method for recovering lithium iron phosphate from lithium iron phosphate black powder according to claim 1, characterized in that: The reaction time of lithium precipitation in S4 is 30min-90min, and the reaction temperature is 90-95°C.

9. The method for recovering lithium iron phosphate from lithium iron phosphate black powder according to claim 1, characterized in that: The lithium carbonate in S4 is washed twice, the drying temperature is 120-150° C., and the drying time is 1-2 hours.

10. The method for recovering lithium iron phosphate from lithium iron phosphate black powder according to claim 9, characterized in that: The lithium carbonate in S4 is washed with deionized water at 80-100°C.

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