Impurity removal method of waste lithium iron phosphate black powder pickle liquor

Abstract

The invention discloses an impurity removal method for waste lithium iron phosphate black powder pickle liquor, and belongs to the field of waste lithium iron phosphate battery recycling. The method comprises the steps that waste lithium iron phosphate black powder is selectively leached with acid and an oxidizing agent, and leaching liquor containing iron and copper impurities is obtained; according to the method disclosed by the invention, a selective leaching process is firstly adopted, so that the concentration of an impurity iron element in the leachate is reduced while the lithium is efficiently extracted. Then a precipitation method is adopted, the concentration of a precipitator and precipitation conditions are regulated and controlled, iron and copper ions can be removed through one-step precipitation, step-by-step impurity removal is not needed, meanwhile, the high lithium retention rate is achieved, the obtained high-purity lithium-rich solution can be used for preparing lithium carbonate and other high-added-value lithium salt products, the process technology is simple, and the potential of large-scale utilization is achieved.

Description

Technical Field

[0001] The invention relates to a method for removing impurities from waste lithium iron phosphate black powder acid leaching liquid, and belongs to the field of waste lithium iron phosphate battery recycling. Background Art

[0002] With the rapid development of new energy vehicles, the amount of scrapped power batteries has also increased year by year. According to the 4-6 year lifespan of power batteries, my country's power batteries have entered the peak period of scrapping, and the market scale is rapidly expanding. It is estimated that by 2030, the scale of lithium-ion battery recycling will reach 108.9 billion yuan, of which the scale of scrapped lithium iron phosphate batteries is expected to reach 44 billion yuan.

[0003] Previously, the recycling of power batteries was mainly carried out around ternary batteries and lithium cobalt oxide batteries, while there was little enthusiasm for lithium iron phosphate batteries. With the increase in lithium demand and the high external dependence on lithium resources, researchers began to pay attention to the recycling of lithium iron phosphate batteries.

[0004] In recent years, many institutions at home and abroad have proposed different acid leaching processes to treat waste lithium iron phosphate and maximize the leaching rate of lithium. Among them, the selective leaching process can effectively extract lithium and retain iron and phosphorus in the leaching residue, which can be used to prepare iron phosphate. The lithium-containing liquid obtained by selective leaching needs further impurity removal before it can be used to prepare high-purity lithium salt products (lithium carbonate, etc.). The most common methods for impurity removal of leachate include precipitation, adsorption and extraction. The precipitation method is to add a precipitant to the lithium-containing leachate. The impurity ions in the solution will react with it and form a precipitate that is difficult to dissolve in water. However, in order to avoid the loss of lithium during the precipitation process, it is necessary to improve the selectivity of the precipitation process. Usually, step-by-step precipitation is used to remove impurities. The adsorption process is simple, but the stability and recyclability of the adsorbent material in an acidic environment must be considered. The extraction method has the advantages of simple operation, continuous operation, and environmental friendliness. The main disadvantages are that the solvent used for extraction may have certain volatility and toxicity. Therefore, the waste liquid generated during the extraction process must be specially treated before it can be discharged. Summary of the invention

[0005] In view of this, the present invention provides a method for removing impurities from waste lithium iron phosphate black powder acid leaching solution. The impurity ions iron and copper in the waste lithium iron phosphate black powder acid leaching solution can be efficiently removed by selectively leaching the black powder and coupling it with a one-step precipitation. The method has the characteristics of simple operation, strong purification and impurity removal ability, and high lithium retention rate.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A method for removing impurities from waste lithium iron phosphate black powder acid leaching liquid, comprising the following steps:

[0008] (1) adding waste lithium iron phosphate black powder into acid, and adding an oxidant for selective leaching to obtain an acid leaching solution containing iron and copper impurities;

[0009] (2) adding a precipitant to the acid-base solution to a pH of 6-12 for reaction, and filtering after the reaction to obtain a lithium-rich solution and copper and iron precipitates.

[0010] On the basis of the above technical solution, the present invention further defines the solution as follows:

[0011] Furthermore, the acid in step (1) is at least one of hydrochloric acid, sulfuric acid, citric acid, and malic acid;

[0012] The oxidizing agent is hydrogen peroxide.

[0013] Preferably, the amount of acid added is 90-99 mL, and the concentration is 0.1-1.5 mol / L;

[0014] The amount of the oxidant added is 1-10 mL, and the concentration is 30% (mass fraction).

[0015] Furthermore, in step (2), the precipitant is at least one of sodium hydroxide, sodium bicarbonate, sodium sulfide, sodium phosphate, and calcium hydroxide.

[0016] Preferably, the concentration of the sodium type precipitant is 0.25-2.25 mol / L, and the mass ratio of the calcium type and sodium type precipitants is 1-4:10.

[0017] Furthermore, in step (2), the reaction temperature is 20-90° C. and the reaction time is 10-60 minutes.

[0018] Furthermore, the method also includes the operation of adding sodium carbonate solution after evaporating and concentrating the lithium-rich solution to precipitate and crystallize lithium carbonate.

[0019] The beneficial effects of the present invention are:

[0020] The present invention first adopts a selective leaching process to efficiently extract lithium while reducing the concentration of impurity iron in the leachate. Then, a precipitation method is adopted to achieve one-step precipitation removal of iron and copper ions by adjusting the concentration of the precipitant and the precipitation conditions, without the need for step-by-step impurity removal, and at the same time having a high lithium retention rate. The obtained high-purity lithium-rich solution can be used to prepare high-value-added lithium salt products such as lithium carbonate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the XRD spectrum of the lithium carbonate product in Example 5 of the present invention. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments 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.

[0023] Example 1

[0024] The method for removing impurities from waste lithium iron phosphate black powder acid leaching liquid is as follows:

[0025] (1) 30 g of crushed waste lithium iron phosphate black powder (passed through a 200-mesh sieve) was placed in a 250-mL beaker, 90 mL of a 1 mol / L sulfuric acid solution was added thereto, and 10 mL of a 30% hydrogen peroxide solution was added dropwise thereto in a 60° C. water bath. The mixture was reacted for 60 minutes. After the reaction was completed, the leaching solution was obtained by suction filtration.

[0026] (2) Take 30 mL of the leaching solution and put it into a 250 mL beaker. Heat it in a water bath and set the temperature to 60°C. Add 1 mol / L and 3.5 mol / L sodium hydroxide solutions to adjust the pH of the solution until the pH is 7. After standing for 30 min, filter and wash.

[0027] Under these conditions, the removal rates of iron and copper were 99.99% and 97.61% respectively, and the retention rate of lithium was 86.68%.

[0028] Example 2

[0029] The method for removing impurities from waste lithium iron phosphate black powder acid leaching liquid, step (1) is the same as in Example 1, and step (2) is as follows:

[0030] Take 30mL of the leaching solution and put it into a 250mL beaker, heat it in a water bath, set the temperature to 60°C, add 0.65mol / LNa2S solution until the pH is 7, let it stand for 30 minutes, then filter and wash.

[0031] Under these conditions, the removal rates of iron and copper were 99.85% and 99.92% respectively, and the retention rate of lithium was 92.24%.

[0032] Example 3

[0033] The method for removing impurities from waste lithium iron phosphate black powder acid leaching liquid, step (1) is the same as in Example 1, and step (2) is as follows:

[0034] Take 30 mL of the leachate in Example 1 and put it into a 250 mL beaker, heat it in a water bath, set the temperature to 60°C, add 0.35 mol / L Na3PO4·12H2O solution until the pH is 7, let it stand for 30 min, then filter and wash.

[0035] Under these conditions, the removal rates of iron and copper were 99.99% and 98.27% respectively, and the retention rate of lithium was 89.5%.

[0036] Example 4

[0037] The method for removing impurities from waste lithium iron phosphate black powder acid leaching liquid is as follows:

[0038] (1) Weigh 8.00 g of sieved (80 mesh) waste lithium iron phosphate black powder and put it into a 250 mL three-necked flask, add 97.0 mL of 0.1 mol / L citric acid solution, slowly dropwise add 3.0 mL of 30% hydrogen peroxide solution under stirring in a 25° C. water bath, and react for 60 minutes. After the reaction is completed, filter and collect the leaching liquid.

[0039] (2) Take 100 mL of the leaching solution, set the impurity removal temperature to 25° C., add a 20% calcium hydroxide emulsion dropwise until the pH value is 12, let it stand, and then perform suction filtration and washing.

[0040] Under these conditions, the removal rates of iron and copper were 99.40% and 99.21% respectively, and the retention rate of lithium was 83.4%.

[0041] Example 5

[0042] After the lithium-containing purified liquid obtained by suction filtration in step (2) of Example 1 is concentrated to about 15 g / L, it is subjected to a further deep impurity removal to remove the iron ions contained therein.

[0043] The obtained lithium-rich solution was added to a beaker, and the water bath temperature was adjusted to 90°C. The mixture was stirred continuously. After the preset temperature was reached, the sodium carbonate solution was added to the beaker. The reaction temperature and stirring speed were maintained. The reaction was continued for 1 hour. The molar mass ratio of sodium carbonate to lithium content was 1:1.2. The obtained precipitated crystals were lithium carbonate. The obtained lithium carbonate was tested. The results were as follows: Figure 1 shown.

Claims

1. A method for removing impurities from waste lithium iron phosphate black powder acid leaching solution, characterized in that: The following steps are involved: (1) adding waste lithium iron phosphate black powder into acid, and adding an oxidant for selective leaching to obtain an acid leaching solution containing iron and copper impurities; (2) adding a precipitant to the acid-base solution to a pH of 6-12 for reaction, and filtering after the reaction to obtain a lithium-rich solution and copper and iron precipitates.

2. The impurity removal method of waste lithium iron phosphate black powder acid leaching liquid according to claim 1, characterized in that: The acid in step (1) is at least one of hydrochloric acid, sulfuric acid, citric acid and malic acid; The oxidizing agent is hydrogen peroxide.

3. The impurity removal method of waste lithium iron phosphate black powder acid leaching liquid according to claim 1 or 2, characterized in that: In step (1), the amount of acid added is 90-99 mL, and the concentration is 0.1-1.5 mol / L.

4. The impurity removal method of waste lithium iron phosphate black powder acid leaching liquid according to claim 1 or 2, characterized in that: The amount of the oxidant added in step (1) is 1-10 mL, and the concentration is 30%.

5. The impurity removal method of waste lithium iron phosphate black powder acid leaching liquid according to claim 1, characterized in that: In step (2), the precipitant is at least one of sodium hydroxide, sodium bicarbonate, sodium sulfide, sodium phosphate and calcium hydroxide.

6. The method for removing impurities from waste lithium iron phosphate black powder acid leaching liquid according to claim 5, characterized in that: The concentration of the sodium type precipitant is 0.25-2.25 mol / L, and the mass concentration of the calcium hydroxide emulsion is 10-35%.

7. The impurity removal method of waste lithium iron phosphate black powder acid leaching liquid according to claim 1, characterized in that: In step (2), the reaction temperature is 20-90° C. and the reaction time is 10-60 minutes.

8. The method for removing impurities from waste lithium iron phosphate black powder acid leaching liquid according to claim 1, characterized in that: The process also includes the steps of evaporating and concentrating the lithium-rich solution, adding a sodium carbonate solution, and precipitating and crystallizing to obtain lithium carbonate.

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