RECYCLING METHOD AND USE OF LITHIUM IRON PHOSPHATE (LFP) WASTE

Abstract

The present disclosure belongs to the technical field of battery recycling, and discloses a recycling method and use of lithium iron phosphate (LFP) waste. The method includes the following steps: mixing the LFP waste with water to prepare a slurry; adjusting a pH of the slurry to higher than 7.0 with an alkali, and heating to react; filtering a resulting mixture to obtain a filter residue; dissolving the filter residue in an acid, and filtering to obtain a filtrate; adding an oxalate-containing solution to react, and aging and filtering a resulting mixture to obtain a filter cake and a precipitation mother liquor; and subjecting the filter cake to slurrying, washing, and free water removal to obtain ferrous oxalate.

Claims

1. A recycling method of lithium iron phosphate (LFP) waste, comprising the following steps: (1) mixing the LFP waste with water to prepare a slurry; adjusting a pH of the slurry to higher than 7.0 with an alkali, and heating to react; and filtering a resulting mixture to obtain a filter residue; (2) dissolving the filter residue in an acid, and filtering to obtain a filtrate; and adding an oxalate-containing solution to allow a reaction to take place, and aging and filtering a resulting mixture to obtain a filter cake and a precipitation mother liquor; and (3) subjecting the filter cake to slurrying, washing, and free water removal to obtain ferrous oxalate; wherein step (2) further comprises adding a precipitating agent to the precipitation mother liquor for precipitation to obtain lithium dihydrogen phosphate; and the precipitating agent is a lithium dihydrogen phosphate seed crystal; in step (2), the acid is an inorganic acid; and the inorganic acid is at least one from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid; in step (2), the oxalate-containing solution is prepared as follows: dissolving an oxalate-containing substance in water, adding a surfactant, and stirring, the oxalate-containing substance is oxalic acid; the surfactant is one or two from the group consisting of ethanol and 1-methyl-2-pyrrolidinone (NMP).

2. The recycling method according to claim 1, wherein in step (1), main components of the LFP waste are LiFePO.sub.4 and C.

3. The recycling method according to claim 1, wherein in step (1), the alkali is one or two from the group consisting of sodium hydroxide, ammonia water; and the pH is adjusted to 8.0 to 12.5.

4. The recycling method according to claim 1, wherein in step (2), the reaction is conducted at 20 C. to 150 C. for 10 min to 360 min; and the aging is conducted for 0.5 h to 24 h.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0037] FIG. 1 is a scanning electron microscopy (SEM) image of ferrous oxalate prepared in Example 1 of the present disclosure, with a magnification of 5,000;

[0038] FIG. 2 is an SEM image of ferrous oxalate prepared in Example 1 of the present disclosure, with a magnification of 50,000;

[0039] FIG. 3 is an SEM image of lithium dihydrogen phosphate prepared in Example 1 of the present disclosure, with a magnification of 1,000;

[0040] FIG. 4 is an SEM image of lithium dihydrogen phosphate prepared in Example 1 of the present disclosure, with a magnification of 5,000;

[0041] FIG. 5 is an X-ray diffractometry (XRD) pattern of ferrous oxalate prepared in Example 1 of the present disclosure; and

[0042] FIG. 6 is an XRD pattern of lithium dihydrogen phosphate prepared in Example 1 of the present disclosure.

DETAILED DESCRIPTION

[0043] The concepts and technical effects of the present disclosure are clearly and completely described below in conjunction with examples, so as to allow the objectives, features and effects of the present disclosure to be fully understood. Apparently, the described examples are merely some rather than all of the examples of the present disclosure. All other examples obtained by those skilled in the art based on the examples of the present disclosure without creative efforts should fall within the protection scope of the present disclosure.

Example 1

[0044] A recycling method of LFP waste was provided in this example, including the following steps: [0045] (1) the LFP waste and water were mixed at a solid-to-liquid ratio of 5:1 and slurried, a sodium hydroxide liquid with a mass fraction of 30% was added to adjust a pH to 8.2, and a resulting slurry was heated at 60 C. for 120 min to react; and after the reaction was completed, a resulting mixture was filtered to obtain a filter residue; [0046] (2) the filter residue was washed, dried, and then added to a 2 mol/L sulfuric acid solution; and a resulting mixture was stirred and reacted at 80 C. for 3 h and then subjected to liquid-solid separation, and a resulting filtrate (iron solution) was retained; [0047] (3) oxalic acid was added to deionized water to prepare a 10% oxalic acid solution, and 10% of ethanol was added as a surfactant to dissolve oxalic acid; [0048] (4) according to a Fe.sup.2+:C.sub.2O.sub.4.sup.2 molar ratio of 1:1.3, the oxalic acid solution was continuously added to the iron solution for 2 h at 70 C. under stirring; after the oxalic acid solution was completely added, stirring was stopped and aging was conducted at 70 C. for 5 h; and a resulting mixture was subjected to liquid-solid separation to obtain a filter cake and a precipitation mother liquor; [0049] (5) the obtained filter cake was washed with deionized water to neutrality, and then subjected to free water removal to obtain yellow ferrous oxalate; and [0050] (6) a lithium dihydrogen phosphate seed crystal was added to the obtained precipitation mother liquor for precipitation to obtain lithium dihydrogen phosphate.

Example 2

[0051] A recycling method of LFP waste was provided in this example, including the following steps: [0052] (1) the LFP waste and water were mixed at a solid-to-liquid ratio of 3:1 and slurried, a sodium hydroxide liquid with a mass fraction of 30% was added to adjust a pH to 8.5, and a resulting slurry was heated at 55 C. for 150 min to react; and after the reaction was completed, a resulting mixture was filtered to obtain a filter residue; [0053] (2) the filter residue was washed, dried, and then added to a 2 mol/L sulfuric acid solution; and a resulting mixture was stirred and reacted at 80 C. for 3 h and then subjected to liquid-solid separation, and a resulting filtrate (iron solution) was retained; [0054] (3) oxalic acid was added to deionized water to prepare a 10% oxalic acid solution, and 10% of ethanol was added as a surfactant to dissolve oxalic acid; [0055] (4) according to a Fe.sup.2+:C.sub.2O.sub.4.sup.2 molar ratio of 1:1.3, the oxalic acid solution was continuously added to the iron solution for 2 h at 80 C. under stirring; after the oxalic acid solution was completely added, stirring was stopped and aging was conducted at 80 C. for 6 h; and a resulting mixture was subjected to liquid-solid separation to obtain a filter cake and a precipitation mother liquor; [0056] (5) the obtained filter cake was washed with deionized water to neutrality, and then subjected to free water removal to obtain yellow ferrous oxalate; and [0057] (6) a lithium dihydrogen phosphate seed crystal was added to the obtained precipitation mother liquor for precipitation to obtain lithium dihydrogen phosphate.

Example 3

[0058] A recycling method of LFP waste was provided in this example, including the following steps: [0059] (1) the LFP waste and water were mixed at a solid-to-liquid ratio of 5:1 and slurried, a sodium hydroxide liquid with a mass fraction of 20% was added to adjust a pH to 8.4, and a resulting slurry was heated at 65 C. for 150 min to react; and after the reaction was completed, a resulting mixture was filtered to obtain a filter residue; [0060] (2) the filter residue was washed, dried, and then added to a 2 mol/L sulfuric acid solution; and a resulting mixture was stirred and reacted at 80 C. for 3 h and then subjected to liquid-solid separation, and a resulting filtrate (iron solution) was retained; [0061] (3) oxalic acid was added to deionized water to prepare a 20% oxalic acid solution, and 10% of ethanol was added as a surfactant to dissolve oxalic acid; [0062] (4) according to a Fe.sup.2+:C.sub.2O.sub.4.sup.2 molar ratio of 1:1.2, the oxalic acid solution was continuously added to the iron solution for 2 h at 75 C. under stirring; after the oxalic acid solution was completely added, stirring was stopped and aging was conducted at 75 C. for 5 h; and a resulting mixture was subjected to liquid-solid separation to obtain a filter cake and a precipitation mother liquor; [0063] (5) the obtained filter cake was washed with deionized water to neutrality, and then subjected to free water removal to obtain yellow ferrous oxalate; and [0064] (6) a lithium dihydrogen phosphate seed crystal was added to the obtained precipitation mother liquor for precipitation to obtain lithium dihydrogen phosphate.

Example 4

[0065] A recycling method of LFP waste was provided in this example, including the following steps: [0066] (1) the LFP waste and water were mixed at a solid-to-liquid ratio of 5:1 and slurried, a sodium hydroxide liquid with a mass fraction of 10% was added to adjust a pH to 9.0, and a resulting slurry was heated at 70 C. for 180 min to react; and after the reaction was completed, a resulting mixture was filtered to obtain a filter residue; [0067] (2) the filter residue was washed, dried, and then added to a 2 mol/L sulfuric acid solution; and a resulting mixture was stirred and reacted at 80 C. for 3 h and then subjected to liquid-solid separation, and a resulting filtrate (iron solution) was retained; [0068] (3) oxalic acid was added to deionized water to prepare a 10% oxalic acid solution, and 10% of ethanol was added as a surfactant to dissolve oxalic acid; [0069] (4) according to a Fe.sup.2+:C.sub.2O.sub.4.sup.2 molar ratio of 1:1.3, the oxalic acid solution was continuously added to the iron solution for 1 h at 60 C. under stirring; after the oxalic acid solution was completely added, stirring was stopped and aging was conducted at 60 C. for 7 h; and a resulting mixture was subjected to liquid-solid separation to obtain a filter cake and a precipitation mother liquor; [0070] (5) the obtained filter cake was washed with deionized water to neutrality, and then subjected to free water removal to obtain yellow ferrous oxalate; and [0071] (6) a lithium dihydrogen phosphate seed crystal was added to the obtained precipitation mother liquor for precipitation to obtain lithium dihydrogen phosphate.

Comparative Example 1

[0072] A recycling method of LFP waste was provided in this comparative example, including the following steps: [0073] (1) the LFP waste and water were mixed at a solid-to-liquid ratio of 5:1 and slurried, a sodium hydroxide liquid with a mass fraction of 30% was added to adjust a pH, and a resulting slurry was heated and reacted for a specified time; and after the reaction was completed, a resulting mixture was filtered to obtain a filter residue; [0074] (2) the filter residue was washed, dried, and then added to a 2 mol/L mixed acid solution of sulfuric acid and hydrochloric acid; and a resulting mixture was stirred and reacted at 80 C. for 3 h and then subjected to liquid-solid separation to obtain iron phosphate and a filtrate; and [0075] (3) a 95 C. saturated sodium carbonate was added to the obtained filtrate, such that lithium was precipitated in the form of a lithium carbonate solid; and the filter residue was added to hydrochloric acid (iron was dissolved into the solution in the form of ions, thereby achieving the separation of iron from solid impurities), a resulting mixture was stirred at 50 C. for 6 h and then filtered to obtain a filtrate, and a pH of the filtrate was adjusted with NaOH+ammonia water to obtain iron hydroxide.

[0076] Result Comparison: [0077] (1) The recovery rates of iron from LFP waste in Examples 1 to 2 were compared with that in Comparative Example 1, separately.

TABLE-US-00001 TABLE 1 Iron recovery rate Example 1 Example 2 Comparative Example 1 Iron recovery rate (%) 99.02 99.10 98.30

[0078] It can be seen from Table 1 that, compared with the process of using LFP waste to synthesize iron phosphate, the process of using LFP waste to synthesize ferrous oxalate is easier to control and has a higher iron recovery rate.

TABLE-US-00002 TABLE 2 Lithium dihydrogen phosphate Example 1 Example 2 Example 3 Phosphorus recovery rate (%) 96.73 97.56 96.98 Lithium recovery rate (%) 96.92 97.79 97.12

[0079] It can be seen from the data in Table 2 that, during the process of adding a precipitating agent to the precipitation mother liquor obtained after iron is precipitated for precipitation to obtain lithium dihydrogen phosphate in the present disclosure, the recovery rates of phosphorus and lithium are both greater than 95%, indicating prominent recovery effect.

[0080] FIG. 1 and FIG. 2 show SEM images of ferrous oxalate prepared in Example 1 of the present disclosure. It can be seen from FIG. 1 and FIG. 2 that the synthesized ferrous oxalate has a block structure with a smooth surface, a uniform particle distribution, and a particle size of 8 m to 10 m. FIG. 3 and FIG. 4 show SEM images of lithium dihydrogen phosphate prepared from the precipitation mother liquor in Example 1 of the present disclosure. It can be seen from FIG. 3 that the lithium dihydrogen phosphate has needle-like and rod-like structures, and it can be seen from FIG. 4 that the needle-like and rod-like structures in the lithium dihydrogen phosphate are interleaved with each other and have a smooth surface.

[0081] FIG. 5 shows an XRD pattern of ferrous oxalate prepared in Example 1 of the present disclosure. It can be seen from FIG. 5 that the characteristic peaks in the XRD pattern of the prepared ferrous oxalate are corresponding to that in the spectrum of standard card (23-0293), respectively; and the diffraction peaks are sharp, characteristic peaks are obvious, and there are no impurity peaks, indicating that ferrous oxalate with high crystallinity is obtained. FIG. 6 shows an XRD pattern of lithium dihydrogen phosphate prepared in Example 1 of the present disclosure. Through comparative analysis and literature review, it can be known that the crystal phase of the material is formed, the characteristic peaks are obvious, and the space group is Pna21, indicating that the prepared lithium dihydrogen phosphate has prominent crystallinity and high purity.

[0082] The examples of present disclosure are described in detail with reference to the accompanying drawings, but the present disclosure is not limited to the above examples. Within the scope of knowledge possessed by those of ordinary skill in the technical field, various changes can also be made without departing from the purpose of the present disclosure. In addition, the examples in the present disclosure and features in the examples may be combined with each other in a non-conflicting situation.