Method for recovering lithium from NMP (N-Methyl Pyrrolidone) cleaning waste liquid in lithium battery industry

Abstract

The invention discloses a method for recovering lithium from NMP (N-Methyl Pyrrolidone) cleaning waste liquid in the lithium battery industry, which comprises the following steps: (1) taking the NMP cleaning waste liquid in the lithium battery industry, filtering to obtain a first filtrate and a first filter cake, and roasting the first filter cake to obtain lithium-containing carbon powder; (2) adding lithium-containing carbon powder into an oxalic acid solution, heating and stirring, and filtering to obtain a second filtrate and a second filter cake; (3) adding a calcium hydroxide solution into the second filtrate, stirring, and filtering to obtain a third filtrate and a third filter cake; and (4) carrying out vacuum concentration and drying treatment on the third filtrate to obtain a lithium hydroxide product. The purpose of recycling the positive electrode material in the NMP cleaning waste liquid is achieved, lithium hydroxide meeting the national standard is obtained, and the process is simple, easy to operate and convenient for industrial application.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery material recovery, and in particular to a method for recovering lithium from NMP cleaning waste liquid in the lithium battery industry. Background Art

[0002] With the development of the new energy industry, the demand for lithium-ion batteries is increasing. Lithium mainly comes from non-renewable lithium mines. As natural resources are depleted, the price of lithium will also rise. Therefore, recovering lithium from lithium-ion battery production waste or waste lithium-ion batteries has become a hot research direction.

[0003] In the production process of lithium-ion battery positive electrode sheets, NMP (N-methyl-2-pyrrolidone) is often used as a solvent for positive electrode slurry because of its strong polarity, good chemical stability and strong dissolving ability. It is also used as a cleaning agent for equipment. In the production process of lithium batteries, NMP is required for cleaning when switching materials or cleaning equipment regularly. This cleaning waste liquid mainly contains high-value positive electrode materials such as lithium iron phosphate or ternary lithium, as well as impurities such as conductive agents and binders.

[0004] For the recovery of positive electrode materials, conventional methods are pyrometallurgical recovery and wet recovery. The pyrometallurgical recovery process is simple, but it is highly polluting and energy-intensive. Wet recovery often uses inorganic acids and organic acids for recovery. Inorganic acids produce toxic and harmful gases during acid leaching, and produce a large amount of acid leaching wastewater, which endangers environmental safety. Organic acid leaching is relatively mild and has become the mainstream acid leaching process. Patent application CN110643816A discloses a method for recovering lithium from waste ternary lithium batteries. After the lithium battery is discharged, the positive electrode material is separated and leached with oxalic acid to obtain lithium carbonate. However, there is a small amount of slightly soluble iron oxalate and manganese oxalate in the oxalic acid leachate, which causes the recovered lithium carbonate to be impure. Moreover, this method is mainly applicable to waste ternary lithium batteries, and is less applicable to NMP cleaning waste liquid in the lithium battery industry. Summary of the invention

[0005] The main purpose of the present invention is to provide a method for recovering a relatively pure lithium hydroxide product from NMP cleaning waste liquid in the lithium battery industry, which has a simple process and is convenient for industrial application.

[0006] To achieve the above object, the present invention provides a method for recovering lithium from NMP cleaning waste liquid in the lithium battery industry, comprising the following steps: (1) taking NMP cleaning waste liquid from the lithium battery industry, filtering it to obtain a first filtrate and a first filter cake, and calcining the first filter cake to obtain lithium-containing carbon powder; (2) adding lithium-containing carbon powder to the oxalic acid solution, first heating and stirring, and then filtering to obtain a second filtrate and a second filter cake; (3) adding calcium hydroxide solution to the second filtrate, stirring the mixture, and filtering the mixture to obtain a third filtrate and a third filter cake; (4) The third filtrate is concentrated and dried under reduced pressure to obtain a lithium hydroxide product.

[0007] Furthermore, the NMP cleaning waste liquid in the lithium battery industry contains lithium iron phosphate or ternary lithium, as well as graphite, PVDF (polyvinylidene fluoride), NMP and water.

[0008] Furthermore, the content of each component in the NMP cleaning waste liquid of the lithium battery industry is 12wt% of lithium iron phosphate, 15wt% of graphite, 5wt% of PVDF, and 30wt% of NMP.

[0009] Furthermore, in step (1), the calcination temperature is 450-550° C. and the calcination time is 1-2 h.

[0010] Furthermore, in step (2), the concentration of the oxalic acid solution is 0.4-0.8 mol / L, and the solid-liquid ratio of the lithium-containing carbon powder to the oxalic acid solution is 1:30-1:50 g / mL.

[0011] Furthermore, in step (2), the temperature of the heating and stirring treatment is 60 to 80° C., the stirring speed is 300 to 400 rpm, and the time is 1 to 2 hours.

[0012] Furthermore, in step (3), the concentration of the calcium hydroxide solution is 10-20 wt%, and the amount of calcium hydroxide solution added is to adjust the pH to 11-13. The chemical reaction in this step is as follows: Soluble: Li2C2O4+Ca(OH)2--CaC2O4↓+2LiOH H2C2O4+Ca(OH)2--CaC2O4↓+2H2O Slightly soluble: Fe2(C2O4)3+3Ca(OH)2--2Fe(OH)3↓+3CaC2O4↓ MnC2O4+Ca(OH)2--Mn(OH)2↓+CaC2O4↓ Furthermore, in step (3), the stirring speed of the stirring treatment is 300 to 400 rpm, and the time is 1 to 2 hours.

[0013] Furthermore, in step (4), the temperature of the reduced pressure concentration and drying treatment is 60 to 80° C., the pressure is -0.05 to -0.1 MPa, and the time is 1 to 3 hours.

[0014] The beneficial effects of the present invention are embodied in: The present invention firstly separates the solution part of the cleaning waste liquid and the lithium-containing solid slag by filtering, removes the NMP remaining in the solid slag by roasting, thereby preventing organic matter from entering the subsequent steps and causing the prepared lithium hydroxide to have a high organic matter content, and roasts graphite and PVDF into carbon at the same time, and then leaches the lithium-containing carbon powder with oxalic acid to form a lithium oxalate solution, while most of the iron, manganese, nickel, cobalt and the like in the solid form oxalate precipitation, and only a small amount of slightly soluble components enter the filtrate, thereby achieving the purpose of primary impurity removal, and then uses calcium hydroxide to perform secondary impurity removal, calcium ions and oxalate radicals form calcium oxalate precipitation, and hydroxide radicals and slightly soluble iron ions, manganese ions, nickel ions and cobalt ions in the solution form hydroxide precipitation, thereby achieving the purpose of secondary impurity removal, and finally the remaining filtrate containing relatively pure lithium hydroxide is concentrated and dried under reduced pressure to obtain a lithium hydroxide product.

[0015] The invention achieves the purpose of recovering positive electrode materials in NMP cleaning waste liquid, obtains lithium hydroxide that meets national standards, and has simple process, easy operation and convenient industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The present invention is a process flow chart of a method for recovering lithium from NMP cleaning waste liquid in the lithium battery industry. DETAILED DESCRIPTION

[0017] The present invention is further described in detail below in conjunction with specific embodiments. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are generally only embodiments of a part of the present invention, rather than all embodiments. Therefore, based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work should fall within the scope of protection of the present invention.

[0018] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or can be obtained by existing known methods; unless otherwise specified, the methods used in the embodiments of the present invention are methods known to those skilled in the art. Among them, the main components of NMP cleaning wastewater in the lithium battery industry, except water, are shown in Table 1 below: Table 1 Main components of NMP cleaning waste liquid in lithium battery industry Example 1 Recovering lithium from NMP cleaning wastewater in the lithium battery industry See also Figure 1 , the steps are as follows: (1) 100 mL of NMP cleaning waste liquid from the lithium battery industry was taken and filtered to obtain a first filtrate and a first filter cake, the first filtrate was collected and recovered, and the first filter cake was calcined at 550° C. for 1 h to obtain lithium-containing carbon powder; (2) Take 2.5 g of lithium-containing carbon powder, add 125 mL of 0.4 mol / L oxalic acid solution, stir for 2 h at 60 ° C and 300 rpm, and then filter to obtain a second filtrate and a second filter cake; (3) adding 10 wt % calcium hydroxide solution to the second filtrate until the pH value reaches 11, stirring at a stirring speed of 400 rpm for 1 hour, and filtering to obtain a third filtrate and a third filter cake; (4) The third filtrate was concentrated and dried under reduced pressure at 60°C and -0.1 MPa for 1 h to obtain a lithium hydroxide product, which was recorded as LiOH-1.

[0019] Example 2 Recovering lithium from NMP cleaning wastewater in the lithium battery industry See also Figure 1 , the steps are as follows: (1) Taking 150 mL of NMP cleaning waste liquid from the lithium battery industry, filtering and treating it to obtain a first filtrate and a first filter cake, collecting and recovering the first filtrate, and calcining the first filter cake at 500° C. for 1.5 h to obtain lithium-containing carbon powder; (2) Take 2.5 g of lithium-containing carbon powder, add 100 mL of 0.6 mol / L oxalic acid solution, stir for 1.5 h at 70 ° C and 350 rpm, and then filter to obtain a second filtrate and a second filter cake; (3) adding 15 wt % calcium hydroxide solution to the second filtrate until the pH value reaches 12, then stirring at a stirring speed of 350 rpm for 1.5 h, and then filtering to obtain a third filtrate and a third filter cake; (4) The third filtrate was concentrated and dried under reduced pressure at 70°C and -0.07 MPa for 2 h to obtain a lithium hydroxide product, which was recorded as LiOH-2.

[0020] Example 3 Recovering lithium from NMP cleaning wastewater in the lithium battery industry See also Figure 1 , the steps are as follows: (1) Taking 200 mL of NMP cleaning waste liquid from the lithium battery industry, filtering and treating it to obtain a first filtrate and a first filter cake, collecting and recovering the first filtrate, and calcining the first filter cake at 450° C. for 2 h to obtain lithium-containing carbon powder; (2) Take 2.5 g of lithium-containing carbon powder, add 75 mL of 0.8 mol / L oxalic acid solution, stir for 1 h at 80 ° C and 400 rpm, and then filter to obtain a second filtrate and a second filter cake; (3) adding 20 wt % calcium hydroxide solution to the second filtrate until the pH value reaches 13, then stirring at a stirring speed of 300 rpm for 2 h, and then filtering to obtain a third filtrate and a third filter cake; (4) The third filtrate was concentrated and dried under reduced pressure at 80°C and -0.05 MPa for 3 h to obtain a lithium hydroxide product, which was recorded as LiOH-3.

[0021] Comparative Example 1 In this comparative example, lithium is recovered from NMP cleaning waste liquid in the lithium battery industry according to the same method as in Example 2, except that the calcination temperature of the first filter cake is reduced to 420° C. The lithium hydroxide product finally obtained is recorded as Comparative Product 1.

[0022] Comparative Example 2 In this comparative example, lithium was recovered from NMP cleaning waste liquid in the lithium battery industry according to the same method as in Example 2, except that the amount of calcium hydroxide solution added was adjusted until the pH reached 10, and the lithium hydroxide product finally obtained was recorded as Comparative Product 2.

[0023] Composition testing of lithium hydroxide products The components of the lithium hydroxide products prepared in the above examples and comparative examples were analyzed and compared with the national standards. The results are shown in Table 2 below: Table 2 Lithium hydroxide product indicators From the above, it can be seen that when the calcination temperature is lowered in Comparative Example 1, the organic components contained in the filter cake cannot be completely removed by high-temperature calcination, resulting in a lower purity of the subsequently prepared lithium hydroxide. In Comparative Example 2, when the pH is low during neutralization with calcium hydroxide, the prepared lithium hydroxide contains a small amount of lithium oxalate components that are not completely converted into lithium hydroxide, resulting in a lower purity of the product.

[0024] 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 lithium from NMP cleaning waste liquid in the lithium battery industry, characterized in that: The following steps are involved: (1) taking NMP cleaning waste liquid from the lithium battery industry, filtering it to obtain a first filtrate and a first filter cake, and calcining the first filter cake to obtain lithium-containing carbon powder; (2) adding lithium-containing carbon powder to the oxalic acid solution, first heating and stirring, and then filtering to obtain a second filtrate and a second filter cake; (3) adding calcium hydroxide solution to the second filtrate, stirring the mixture, and filtering the mixture to obtain a third filtrate and a third filter cake; (4) The third filtrate is concentrated and dried under reduced pressure to obtain a lithium hydroxide product.

2. The method for recovering lithium from NMP cleaning waste liquid in the lithium battery industry as claimed in claim 1, characterized in that, The NMP cleaning waste liquid in the lithium battery industry contains lithium iron phosphate or ternary lithium, as well as graphite, PVDF, NMP and water.

3. The method for recovering lithium in the NMP cleaning waste liquid of the lithium battery industry as claimed in claim 2, characterized in that, The NMP cleaning waste liquid from the lithium battery industry contains 12wt% of lithium iron phosphate, 15wt% of graphite, 5wt% of PVDF and 30wt% of NMP.

4. A method for recovering lithium in the NMP cleaning waste liquid of the lithium battery industry as claimed in claim 1, 2 or 3, characterized in that, Step (1), the calcination temperature is 450-550°C and the time is 1-2 hours.

5. A method for recovering lithium from NMP cleaning waste liquid in the lithium battery industry as claimed in claim 1, 2 or 3, characterized in that, In step (2), the concentration of the oxalic acid solution is 0.4-0.8 mol / L, and the solid-liquid ratio of the lithium-containing carbon powder to the oxalic acid solution is 1:30-1:50 g / mL.

6. A method for recovering lithium from NMP cleaning waste liquid in the lithium battery industry as claimed in claim 1, 2 or 3, characterized in that, In step (2), the temperature of the heating and stirring treatment is 60 to 80° C., the stirring speed is 300 to 400 rpm, and the time is 1 to 2 hours.

7. A method for recovering lithium from NMP cleaning waste liquid in the lithium battery industry as claimed in claim 1, 2 or 3, characterized in that, In step (3), the concentration of the calcium hydroxide solution is 10-20 wt %, and the amount of calcium hydroxide solution added is to adjust the pH to 11-13.

8. A method for recovering lithium from NMP cleaning waste liquid in the lithium battery industry as claimed in claim 1, 2 or 3, characterized in that, In step (3), the stirring speed of the stirring treatment is 300 to 400 rpm, and the time is 1 to 2 hours.

9. A method for recovering lithium from NMP cleaning waste liquid in the lithium battery industry as claimed in claim 1, 2 or 3, characterized in that, In step (4), the temperature of the reduced pressure concentration and drying treatment is 60 to 80° C., the pressure is -0.05 to -0.1 MPa, and the time is 1 to 3 hours.

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