A method for recovering iron phosphate from lithium iron phosphate extraction slag and its application

Abstract

The present invention relates to a method for recovering iron phosphate in lithium iron phosphate extraction slag and its application, and relates to the field of waste battery recycling. The recovery method comprises the following steps: using a high potential acid system to perform high potential leaching on the lithium iron phosphate extraction slag, filtering to obtain a high potential filtrate and a high potential filter residue; using a low potential acid system to perform low potential leaching on the high potential filter residue, filtering to obtain a low potential filtrate and a low potential filter residue; removing impurities from the low potential filtrate, precipitating to obtain an iron phosphate precursor, filtering, taking the filter residue, and drying. The recovery method can greatly reduce material loss, increase the yield of iron phosphate, and the obtained iron phosphate is battery-grade iron phosphate.

Description

Technical Field

[0001] The invention relates to the field of waste battery recycling, and in particular to a method for recycling iron phosphate in lithium iron phosphate extraction slag and application thereof. Background Art

[0002] Currently, there are two main recovery methods for lithium iron phosphate slag: pyrometallurgy and wet method. The pyrometallurgy uses carbon thermal reduction to convert ferrophosphorus slag into iron and phosphate compounds to obtain iron and phosphate products. This type of method has the disadvantages of high energy consumption, low product economic value and difficulty in market promotion. The wet method uses high-concentration sulfuric acid, nitric acid and other inorganic acids to dissolve iron phosphate, and then adjusts the pH of the leaching solution by adding alkali to form iron phosphate precipitation. However, during the strong acid leaching process, impurities such as aluminum and copper in the lithium phosphate slag are also dissolved, resulting in the purity of the newly prepared iron phosphate unable to meet the battery-grade iron phosphate standard. In addition, a large amount of concentrated acid and alkali is used, the reagent cost is high, and it is highly corrosive to the equipment.

[0003] In summary, the currently publicly reported technology for recovering iron phosphate from lithium iron phosphate slag has disadvantages such as high product impurity content, high energy consumption, and poor economy. It is of great significance to develop a new process with high economy. Summary of the invention

[0004] In view of the above problems, the present invention provides a method for recovering iron phosphate from lithium iron phosphate extraction slag, which can greatly reduce material loss and increase iron phosphate yield, and the obtained iron phosphate is battery-grade iron phosphate.

[0005] In order to achieve the above-mentioned purpose, the present invention provides a method for recovering iron phosphate in lithium iron phosphate extraction slag, comprising the following steps: subjecting the lithium iron phosphate extraction slag to high-potential leaching with a high-potential acid system, filtering to obtain a high-potential filtrate and a high-potential filter residue; subjecting the high-potential filter residue to low-potential leaching with a low-potential acid system, filtering to obtain a low-potential filtrate and a low-potential filter residue; removing impurities from the low-potential filtrate, precipitating to obtain an iron phosphate precursor, filtering, taking the filter residue, and drying.

[0006] In the previous research, some people proposed to mix ferrophosphorus slag with water, and then use sulfide and sulfuric acid for reduction leaching to obtain a leachate containing ferrous ions, and then add an oxidant to oxidize the ferrous ions into trivalent and form iron phosphate precipitation. This method can effectively reduce the content of copper ions, but it does not treat the aluminum ions in the waste slag. Therefore, the content of aluminum phosphate in the prepared iron phosphate is relatively high, which reduces the electrochemical performance of the battery positive electrode material prepared with iron phosphate as the raw material. Some people also carry out two acid leaching to remove impurities and one organic solvent separation and purification, and then high-temperature roast the ferrophosphorus slag after three treatments to remove organic matter and graphite to obtain battery-grade iron phosphate. This method is not effective in removing aluminum, and the organic solvent benzene used has a large burden on water and the atmosphere, increasing the environmental pressure of the factory. Some people also use concentrated acid to leach ferrophosphorus slag to obtain a ferrous ion leachate, and then dealuminate the leachate with ion exchange resin, but this method has high investment costs. Based on this, the inventors propose the above-mentioned recovery method, which can not only recover iron phosphate from lithium iron phosphate extraction slag, but also significantly reduce impurities such as copper and aluminum therein. The recovery method first performs acid leaching and impurity removal on the lithium extraction slag in a high-potential acid system, significantly reducing the content of impurities in the lithium extraction slag and reducing the loss of iron phosphate slag, and then performs acid leaching through a low-potential acid system to leach iron phosphate, greatly reducing material loss, obtaining a higher iron phosphate yield, and reducing the impurity content in the reduction leaching solution. After simple oxidation and impurity removal and precipitation operations, battery-grade iron phosphate can be obtained.

[0007] In one embodiment, the leaching solution of the high potential acid system includes sulfuric acid, and the oxidant of the high potential acid system includes at least one of hydrogen peroxide, ozone, peracetic acid, and oxygen.

[0008] In one of the embodiments, the concentration of sulfuric acid in the leaching solution of the high potential acid system is 0.01-3 mol / L.

[0009] In one embodiment, the volume ratio of the oxidant to the leaching solution of the high potential acid system is (0.1-5):100; the mass volume ratio of the lithium iron phosphate lithium extraction slag to the leaching solution of the high potential acid system is 1:(3-10).

[0010] In one embodiment, the high potential leaching temperature is 50-95° C., and the high potential leaching time is 30-120 min.

[0011] In one embodiment, the leaching solution of the low-potential acid system includes sulfuric acid and phosphoric acid, and the reducing agent of the low-potential acid system includes iron powder.

[0012] The above raw materials are selected as the reducing agent and the leaching solution of the low-potential acid system. On the one hand, iron powder is used as the reducing agent to reduce the mixing of other metal ions. On the other hand, the acid leaching system adopts a phosphoric acid + sulfuric acid mixed system to reduce the use of concentrated acid. The phosphate and iron powder added in proportion can generate iron phosphate, which greatly reduces material loss and increases the output of iron phosphate.

[0013] In one embodiment, the concentration of sulfuric acid and phosphoric acid in the leaching solution of the low potential acid system is 0.5-2.5 mol / L.

[0014] In one embodiment, the molar ratio of the reducing agent to the iron phosphate in the high potential filter residue is (0.8-1.6):1, and the molar ratio of the phosphate radical of the phosphoric acid to the reducing agent is (0.8-1.5):1;

[0015] The mass volume ratio of the high potential filter residue to the leaching solution of the low potential acid system is 1:(3-10).

[0016] In one embodiment, the temperature of the low-potential leaching is 50-90° C., and the time of the low-potential leaching is 10-60 min.

[0017] In one embodiment, the pH of the impurity removal is 1.5-2.5, and the impurity removal includes: adding an aluminum removal agent, performing an aluminum removal reaction under a protective atmosphere to obtain an impurity removal filtrate; the molar ratio of the aluminum removal agent to the aluminum ions in the low-potential filtrate is (4-8):1.

[0018] In one embodiment, the aluminum removal agent includes sodium fluoride, the temperature of the aluminum removal reaction is 40-70° C., the time of the aluminum removal reaction is 30-180 min, and the protective atmosphere includes nitrogen and / or argon.

[0019] In one embodiment, the precipitation includes: adjusting the pH of the impurity removal filtrate to 1.5-2.5, adding an oxidant, water bathing, heat preservation and aging to obtain an iron phosphate precursor.

[0020] In one embodiment, the oxidant includes hydrogen peroxide, and the amount of the oxidant is Fe 2+ ions, the temperature of the water bath is 75-90°C, and the insulation aging time is 85-100min.

[0021] The invention also provides the ferric phosphate obtained by the recovery method.

[0022] The present invention also provides application of the recycling method in recycling lithium iron phosphate batteries.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The invention discloses a method for recovering iron phosphate from lithium iron phosphate extraction slag and application thereof. The recovery method can greatly reduce material loss and increase the output of iron phosphate, and the obtained iron phosphate is battery-grade iron phosphate. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the process flow of Example 1. DETAILED DESCRIPTION

[0026] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0028] source:

[0029] Unless otherwise specified, the reagents, materials, and equipment used in this example are all commercially available; the experimental methods are all conventional experimental methods in the art unless otherwise specified.

[0030] Example 1

[0031] A method for recovering iron phosphate from lithium iron phosphate extraction slag.

[0032] The process flow of this embodiment is as follows Figure 1 shown.

[0033] 1. Leaching is carried out using a high potential acid system.

[0034] Weigh 100g of lithium iron phosphate lithium extraction slag, add a 0.5mol / L sulfuric acid solution (i.e., add 500mL sulfuric acid solution) at a liquid-solid ratio of 5:1, add 5ml of hydrogen peroxide, stir at 300r / min, set the water bath temperature to 70°C, and react for 120min. Then filter to separate the solid and liquid to obtain a high-potential filter residue and a high-potential filtrate. The aluminum content in the high-potential filter residue is reduced by 80% compared with that in the lithium extraction slag.

[0035] 2. Leaching is carried out using a low potential acid system.

[0036] A high potential filter residue was obtained, sulfuric acid and phosphoric acid were added at a liquid-solid ratio of 5:1, the concentration of sulfuric acid and phosphoric acid in the mixed acid was 1.5 mol / L, and iron powder was added in an amount of 1.0 times the molar amount of iron phosphate in the high potential filter residue; the stirring speed was 300 r / min, the water bath temperature was 60°C, the reaction time was 30 min, and then filtration was performed to separate the solid and liquid to obtain a low potential filter residue and a Fe-containing 2+ and PO4 3- of the low potential filtrate.

[0037] 3. Remove impurities.

[0038] The low potential filtrate was transferred to a reactor and nitrogen was introduced for protection. Ammonia water was added dropwise to adjust the pH to 2.0. Sodium fluoride was added at a molar amount of 6 times that of the aluminum ion in the low potential filtrate. The water bath temperature was 30°C and the reaction time was 60 min. The filtrate was then filtered to obtain a decontaminated filtrate. The content of impurity aluminum in the filtrate was less than 15 ppm.

[0039] 4. Sedimentation.

[0040] The pH of the impurity removal filtrate was adjusted to about 2.0 by using ammonia water, sodium hydroxide, diammonium hydrogen phosphate, etc., and hydrogen peroxide with a mass concentration of 15% was slowly added dropwise. The amount of Fe 2+ The concentration of ferric phosphate was 1.2 times of the theoretical value, the water bath temperature was 80°C, and the aging was carried out for 90 minutes to obtain iron phosphate slurry.

[0041] 5. Filter.

[0042] The iron phosphate slurry is filtered to obtain iron phosphate dihydrate, which is washed with pure water for multiple times and then dried to obtain an iron phosphate product. The quality of the iron phosphate product is better than the requirements of battery-grade iron phosphate products, and the mass content of the key impurity metal aluminum is less than 0.04%.

[0043] Example 2

[0044] A method for recovering iron phosphate from lithium iron phosphate extraction slag.

[0045] 1. Leaching is carried out using a high potential acid system.

[0046] Weigh 100g of lithium iron phosphate lithium extraction slag, add a 1.5mol / L sulfuric acid solution (i.e., add 500mL sulfuric acid solution) at a liquid-solid ratio of 5:1, add 5ml of hydrogen peroxide, stir at 300r / min, water bath temperature at 80°C, reaction time for 80min, then filter to separate the solid and liquid to obtain a high-potential filter residue and a high-potential filtrate; the aluminum content in the high-potential filter residue is reduced by 85% compared with the lithium extraction slag;

[0047] 2. Leaching is carried out using a low potential acid system.

[0048] A high potential filter residue was obtained, sulfuric acid and phosphoric acid were added at a liquid-solid ratio of 5:1, the concentration of sulfuric acid and phosphoric acid in the mixed acid was 0.5 mol / L, and iron powder was added in an amount of 1.2 times the molar amount of iron phosphate in the high potential filter residue; the stirring speed was 300 r / min, the water bath temperature was 60°C, the reaction time was 30 min, and then filtration was performed to separate the solid and liquid to obtain a low potential filter residue and a Fe-containing 2+ and PO4 3- The low potential filtrate;

[0049] 3. Remove impurities.

[0050] The low potential filtrate was transferred to a reactor and nitrogen was introduced for protection. Ammonia water was added dropwise to adjust the pH to 2.0. Sodium fluoride was added at a molar amount of 6 times that of the aluminum ion in the low potential filtrate. The water bath temperature was 40°C and the reaction time was 180 min. The reaction was then filtered to obtain a decontaminated filtrate. The content of impure aluminum in the filtrate was less than 11 ppm.

[0051] 4. Sedimentation.

[0052] The pH of the impurity-removing filtrate was adjusted to 2.0 by diammonium hydrogen phosphate, and 15% hydrogen peroxide was slowly added dropwise. 2+ 1.2 times of the theoretical value, water bath temperature 80°C, insulation aging for 90 min, to obtain iron phosphate slurry;

[0053] 5. Filter.

[0054] The iron phosphate slurry is filtered to obtain iron phosphate dihydrate, which is washed with pure water for multiple times and then dried to obtain an iron phosphate product. The quality of the iron phosphate product is better than the requirements of battery-grade iron phosphate products, and the mass content of the key impurity metal aluminum is less than 0.035%.

[0055] Example 3

[0056] A method for recovering iron phosphate from lithium iron phosphate extraction slag.

[0057] 1. Leaching is carried out using a high potential acid system.

[0058] Weigh 100g of lithium iron phosphate lithium extraction slag, add a 0.5mol / L sulfuric acid solution (i.e., add 500mL sulfuric acid solution) at a liquid-solid ratio of 5:1, add 8ml of hydrogen peroxide, stir at 300r / min, water bath temperature at 80°C, reaction time for 120min, then filter to separate the solid and liquid to obtain a high-potential filter residue and a high-potential filtrate; the aluminum content in the high-potential filter residue is reduced by 91% compared with the lithium extraction slag;

[0059] 2. Leaching is carried out using a low potential acid system.

[0060] A high potential filter residue was obtained, sulfuric acid and phosphoric acid were added at a liquid-solid ratio of 5:1, the concentration of sulfuric acid and phosphoric acid in the mixed acid was 1.0 mol / L, and iron powder was added in an amount of 1.1 times the molar amount of iron phosphate in the high potential filter residue; the stirring speed was 300 r / min, the water bath temperature was 60°C, the reaction time was 30 min, and then filtration was performed to separate the solid and liquid to obtain a low potential filter residue and a Fe-containing 2+ and PO4 3- of the low potential filtrate.

[0061] 3. Remove impurities.

[0062] The low potential filtrate was transferred to a reactor and nitrogen was introduced for protection. Ammonia water was added dropwise to adjust the pH to 2.0. Sodium fluoride was added at a molar amount of 6 times that of the aluminum ion in the low potential filtrate. The water bath temperature was 40°C and the reaction time was 180 min. The reaction was then filtered to obtain a decontaminated filtrate. The content of impure aluminum in the filtrate was less than 18 ppm.

[0063] 4. Sedimentation.

[0064] The pH of the impurity-removing filtrate was adjusted to 2.0 by diammonium hydrogen phosphate, and 15% hydrogen peroxide was slowly added dropwise. 2+ 1.2 times of the theoretical value, water bath temperature 80°C, insulation aging for 90 min, to obtain iron phosphate slurry;

[0065] 5. Filter.

[0066] The iron phosphate slurry is filtered to obtain iron phosphate dihydrate, which is washed with pure water for multiple times and then dried to obtain an iron phosphate product. The quality of the iron phosphate product is better than the requirements of battery-grade iron phosphate products, and the mass content of the key impurity metal aluminum is less than 0.05%.

[0067] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0068] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for recovering iron phosphate from lithium iron phosphate extraction slag, characterized in that: The following steps are involved: The lithium iron phosphate extraction residue is subjected to high-potential leaching using a high-potential acid system, filtered to obtain a high-potential filtrate and a high-potential filter residue; the high-potential filter residue is subjected to low-potential leaching using a low-potential acid system, filtered to obtain a low-potential filtrate and a low-potential filter residue; the low-potential filtrate is impurity-removed, precipitated, and an iron phosphate precursor is obtained, filtered, and the filter residue is taken and dried; The leaching solution of the high potential acid system includes sulfuric acid, and the oxidant of the high potential acid system includes at least one of hydrogen peroxide, ozone, peracetic acid, and oxygen; the volume ratio of the oxidant to the leaching solution of the high potential acid system is (0.1-5):100; the mass volume ratio of the lithium iron phosphate lithium extraction slag to the leaching solution of the high potential acid system is 1:(3-10); The leaching solution of the low potential acid system includes sulfuric acid and phosphoric acid, and the reducing agent of the low potential acid system includes iron powder; The molar ratio of the reducing agent to the iron phosphate in the high potential filter residue is (0.8-1.6):1, and the molar ratio of the phosphate radical of the phosphoric acid to the reducing agent is (0.8-1.5):1; The mass volume ratio of the high potential filter residue to the leaching solution of the low potential acid system is 1:(3-10).

2. The recycling method according to claim 1, characterized in that: The temperature of the high potential leaching is 50-95° C., and the time of the high potential leaching is 30-120 min.

3. The recycling method according to claim 1, characterized in that: The temperature of the low potential leaching is 50-90° C., and the time of the low potential leaching is 10-60 min.

4. The recycling method according to claim 1, characterized in that: The pH of the impurity removal is 1.5-2.5, and the impurity removal includes: adding an aluminum removal agent, performing an aluminum removal reaction under a protective atmosphere, and obtaining an impurity removal filtrate; the molar ratio of the aluminum removal agent to the aluminum ions in the low-potential filtrate is (4-8):

1.

5. Application of the recovery method according to any one of claims 1 to 4 in recovering lithium iron phosphate batteries.

Images