Method for low-acid selective separation and recovery of lithium and iron in retired lithium iron phosphate battery electrode

Abstract

The invention relates to a method for selectively separating and recycling lithium and iron in a retired lithium iron phosphate battery electrode with low acid, and belongs to the field of new energy material recycling. The method comprises the following steps: adding the retired lithium iron phosphate battery electrode into a low-acid solution system (a sulfuric acid solution with the concentration of 0.2-1.2 mol / L), and uniformly stirring and mixing to obtain a leaching system; ultrasonic waves are introduced into the leaching system, an oxidizing agent (the mass ratio of H2O2 to (NH4) 2S2O8 is 1: 0.5-1: 1.5) is added into the leaching system for selective leaching of ultrasonic synergistic oxidation for 10-30 min, and a lithium-rich solution and iron phosphate leaching residues are obtained through solid-liquid separation. LiFePO4 in the raw materials is efficiently stripped through ultrasound, the effective contact area is increased, and attached Li < + > is desorbed while organic carbon is promoted to float upwards; meanwhile, a large number of hydroxyl (. OH) free radicals and sulfate (SO4 < 2->.) free radicals with strong oxidizing property are generated under a synergistic system of hydrogen peroxide and ammonium persulfate to oxidize and degrade organic matters in the system, so that the solution impurity removal process is simplified, lithium dissolution is accelerated, Fe < 2 + > in LiFePO4 is fully oxidized into Fe < 3 + >, FePO4 precipitates are formed, and selective separation and recovery of Li2SO4 and FePO4 are realized.

Description

Technical Field

[0001] The present invention relates to a method for selectively separating and recovering lithium and iron from the electrodes of retired lithium iron phosphate batteries with low acid, and belongs to the field of new energy material recycling. Background Art

[0002] LiFePO4 (LFP) batteries are widely used in new energy vehicles, communication base stations, large-scale energy storage and other industries due to their advantages such as good theoretical safety, low energy density, and long service life. However, the service life of LiFePO4 batteries is only 8 - 10 years. Therefore, with a large number of LFP batteries being retired, how to efficiently recycle retired LFP batteries has become an urgent problem. The current methods for recycling failed LiFePO4 mainly include direct regeneration method and wet dissolution extraction. The direct regeneration methods mainly include wet regeneration repair, high-temperature direct repair, and lithium supplementation roasting repair. Although the regeneration repair technology does not damage the structure of LiFePO4, impurities such as copper and aluminum will have a negative impact on the electrochemical performance of the repaired material, and this method has extremely high requirements for material purity and recycling cost, so it has not been widely applied; wet dissolution extraction is a common recycling technology at present. Among them, the full dissolution extraction technology completely destroys the crystal structure of LiFePO4 through acid leaching reaction, so that Fe 2+ , Li + completely enter the solution, and then stepwise purification and impurity removal and lithium precipitation are carried out. However, this method still has problems such as poor lithium leaching effect and low recovery rate of iron phosphate (FePO4), and it is difficult to achieve the purpose of selective separation and recovery of lithium / iron. Therefore, it is of practical significance to develop a short-process, high-efficiency and industrially applicable recycling process for failed LiFePO4. Summary of the Invention

[0003] Aiming at the problems of high energy consumption, low recovery rate, complex process and large amount of waste liquid existing in the existing roasting - acid leaching - purification - lithium precipitation process, the present invention proposes a method for selectively separating and recovering lithium and iron from the electrodes of retired lithium iron phosphate batteries with low acid. Using ultrasonic external field in cooperation with oxidants (the mass ratio of H2O2 to (NH4)2S2O8 is 1:0.5 - 1:1.5) can not only efficiently strip LiFePO4 from the raw materials, increase the effective reaction contact area, promote the floating of organic carbon and desorb the attached Li + at the same time; it can also prevent the influence of the wrapping and adsorption behaviors of conductive carbon, binder, organic electrolyte, etc. on the lithium recovery rate; under the synergistic system of hydrogen peroxide and ammonium persulfate, a large number of highly oxidizing hydroxyl (·OH) radicals and sulfate (SO4 2- ·) radicals can be generated. On the one hand, they can oxidize and degrade the organic substances in the system to simplify the solution impurity removal process. On the other hand, while accelerating the lithium dissolution, Fe in LiFePO4 2+ is fully oxidized to Fe 3+And FePO4 precipitation is formed, thus realizing the selective separation and recovery of Li2SO4 and FePO4. The low-acid, high-efficiency and selective separation and recovery of Fe / Li from spent lithium iron phosphate under the control of external field and oxidant ratio can realize the high-value utilization of secondary resources and reduce environmental pressure.

[0004] A method for selectively separating and recovering lithium and iron from retired lithium iron phosphate battery electrodes using low-acid, the specific steps are as follows:

[0005] (1) adding retired lithium iron phosphate battery electrodes into a low-acid solution system and stirring to obtain a leaching system; the low-acid solution system is a sulfuric acid solution with a concentration of 0.2 to 1.2 mol / L;

[0006] (2) Introducing ultrasound into the leaching system, adding an oxidant into the leaching system for ultrasonic synergistic oxidation selective leaching for 10 to 30 minutes, and separating the solid and liquid to obtain a lithium-rich solution and iron phosphate leaching residue; the oxidant is a H2O2 / (NH4)2S2O8 composite oxidant, and the mass ratio of H2O2 to (NH4)2S2O8 in the oxidant is 1:0.5 to 1:1.5; the leaching reaction formula is as follows:

[0007] 2LiFePO4+H2SO4+H2O2→Li2SO4+2FePO4↓+2H2O;

[0008] 2LiFePO4+(NH4)2S2O8→Li2SO4+2FePO4↓+2(NH4)2SO4;

[0009] The lithium leaching rate can be as high as 99%, and the FePO4 recovery rate can reach 90%.

[0010] In terms of mass percentage, the retired lithium iron phosphate battery electrode in step (1) contains 4-5% Li and 32-33% Fe.

[0011] Preferably, the liquid-to-solid ratio mL:g of the low-acid solution system in step (1) to the retired lithium iron phosphate battery electrode is 8 to 12:1.

[0012] Preferably, the ultrasonic power in step (2) is 100-600W.

[0013] Preferably, the amount of the oxidant added in step (2) is 40 to 80 g / L.

[0014] Preferably, the temperature of the selective leaching in step (2) is 30-60°C.

[0015] The beneficial effects of the present invention are:

[0016] (1) The present invention can realize the high-value utilization of spent lithium iron phosphate (LiFePO4), and can efficiently strip LiFePO4 from the raw material through ultrasound, increase the effective contact area, promote the floating of organic carbon, and desorb the attached Li + ; The Li leaching rate can reach 99%, achieving the purpose of efficient lithium leaching;

[0017] (2) The oxidant ratio of the present invention is adjusted to provide a large number of strong oxidizing hydroxyl (·OH) free radicals and sulfate (SO4 2- ·) free radicals, on the one hand, can oxidize and degrade organic matter in the system to simplify the solution removal process, on the other hand, while accelerating the dissolution of lithium, Fe 2+ Fully oxidized to Fe 3+ The FePO4 precipitate is formed to achieve the selective separation and recovery of Li2SO4 and FePO4; after ultrasonic assisted oxidant leaching, the solid-liquid separation is carried out to obtain recoverable iron phosphate (FePO4) and lithium-rich solution (Li2SO4);

[0018] (3) The present invention can leach and separate the failed LiFePO4 in only 20 minutes under deep oxidation. The ultrasonic effect can open the package of the conductive carbon, binder, organic electrolyte, etc. on the failed lithium iron phosphate (LiFePO4), and there is no need to pre-treat the LiFePO4 by calcination, which greatly shortens the process flow;

[0019] (4) Compared with the conventional complex process with high temperature, high acid and low daily processing volume, the present invention utilizes ultrasonic external field to selectively leach retired LiFePO4 battery electrodes under the control of oxidant ratio, which has the advantages of short process, low energy consumption, strong selectivity, high efficiency and small amount of waste liquid. The lithium leaching rate can reach 99% and the FePO4 recovery rate can reach 90% by leaching at 30°C for 20 minutes. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below in conjunction with specific implementation modes, but the protection scope of the present invention is not limited to the described contents.

[0021] Example 1: The main components of the retired lithium iron phosphate battery electrode in this example are shown in Table 1;

[0022] Table 1 Main components of retired lithium iron phosphate battery electrodes (mass percentage)

[0023]

[0024] A method for selectively separating and recovering lithium and iron from retired lithium iron phosphate battery electrodes using low-acid, the specific steps are as follows:

[0025] (1) Add the spent lithium iron phosphate battery electrodes to a low-acid solution system (sulfuric acid solution with a concentration of 0.7 mol / L), and stir and mix evenly to obtain a leaching system; the liquid-solid ratio mL:g of the low-acid solution system to the spent lithium iron phosphate battery electrodes is 8:1;

[0026] (2) Introduce ultrasonic waves (power 200 W) into the leaching system, add an oxidant (H2O2 / (NH4)2S2O8 composite oxidant) to the leaching system, and perform selective leaching with ultrasonic synergistic oxidation at a temperature of 30 °C for 20 min, and perform solid-liquid separation to obtain a lithium-rich solution and iron phosphate leaching residue; the addition amount of the oxidant is 60 g / L, and the mass ratio of H2O2 to (NH4)2S2O8 in the oxidant is 1:1; the oxidant can provide a large number of strongly oxidizing hydroxyl (·OH) free radicals and sulfate (SO4 2- ·) free radicals in the reaction system. On the one hand, it can oxidize and degrade the organic matter in the system to simplify the solution purification process. On the other hand, while accelerating the dissolution of lithium, it fully oxidizes Fe in LiFePO4 2+ into Fe 3+ and forms FePO4 precipitation, thereby realizing the selective separation and recovery of Li2SO4 and FePO4;

[0027] The leaching reaction formula is as follows:

[0028] 2LiFePO4 + H2SO4 + H2O2 → Li2SO4 + 2FePO4↓ + 2H2O;

[0029] 2LiFePO4 + (NH4)2S2O8 → Li2SO4 + 2FePO4↓ + 2(NH4)2SO4;

[0030] After detection, the lithium leaching rate in this example is 99%, and the FePO4 recovery rate is 90%.

[0031] Example 2: The main components of the spent lithium iron phosphate battery electrodes in this example are shown in Table 2;

[0032] Table 2 Main components of spent lithium iron phosphate battery electrodes (mass percentage)

[0033]

[0034] A method for selectively separating and recovering lithium and iron from spent lithium iron phosphate battery electrodes with low acid is as follows:

[0035] (1) Add the spent lithium iron phosphate battery electrodes to a low-acid solution system (sulfuric acid solution with a concentration of 1.2 mol / L), and stir and mix evenly to obtain a leaching system; the liquid-solid ratio mL:g of the low-acid solution system to the spent lithium iron phosphate battery electrodes is 10:1;

[0036] (2) Introduce ultrasonic waves (power 500 W) into the leaching system, add an oxidant (H2O2 / (NH4)2S2O8 composite oxidant) to the leaching system, and carry out selective leaching with ultrasonic synergistic oxidation at a temperature of 40 °C for 10 min. After solid-liquid separation, a lithium-rich solution and iron phosphate leaching residue are obtained; the addition amount of the oxidant is 80 g / L, and the mass ratio of H2O2 to (NH4)2S2O8 in the oxidant is 1:0.5; the oxidant can provide a large number of strongly oxidizing hydroxyl (·OH) radicals and sulfate (SO4 2- ·) radicals in the reaction system. On the one hand, it can oxidize and degrade the organic matter in the system to simplify the solution purification process. On the other hand, while accelerating the dissolution of lithium, it fully oxidizes Fe in LiFePO4 2+ into Fe 3+ and forms FePO4 precipitation, thus realizing the selective separation and recovery of Li2SO4 and FePO4;

[0037] After detection, the lithium leaching rate in this example is 96%, and the FePO4 recovery rate is 80%.

[0038] Example 3: The main components of the retired lithium iron phosphate battery electrode in this example are shown in Table 3;

[0039] Table 3 Main components of the retired lithium iron phosphate battery electrode (mass percentage)

[0040]

[0041] A method for selectively separating and recovering lithium and iron from the electrodes of retired lithium iron phosphate batteries with low acid, the specific steps are as follows:

[0042] (1) Add the retired lithium iron phosphate battery electrode to a low-acid solution system (sulfuric acid solution with a concentration of 0.5 mol / L) and stir evenly to obtain a leaching system; the liquid-solid ratio mL:g of the low-acid solution system to the retired lithium iron phosphate battery electrode is 12:1;

[0043] (2) Introduce ultrasonic waves (power 100 W) into the leaching system, add an oxidant (H2O2 / (NH4)2S2O8 composite oxidant) to the leaching system, and carry out selective leaching with ultrasonic synergistic oxidation at a temperature of 60 °C for 30 min. After solid-liquid separation, a lithium-rich solution and iron phosphate leaching residue are obtained; the addition amount of the oxidant is 50 g / L, and the mass ratio of H2O2 to (NH4)2S2O8 in the oxidant is 1:1.5; the oxidant can provide a large number of strongly oxidizing hydroxyl (·OH) radicals and sulfate (SO4 2- ·) radicals in the reaction system. On the one hand, it can oxidize and degrade the organic matter in the system to simplify the solution purification process. On the other hand, while accelerating the dissolution of lithium, it fully oxidizes Fe in LiFePO4 2+ into Fe 3+And form FePO4 precipitate to achieve the selective separation and recovery of Li2SO4 and FePO4;

[0044] After detection, the lithium leaching rate in this example is 97%, and the recovery rate of FePO4 is 82%.

[0045] The above has described the specific embodiments of the present invention in detail. However, the present invention is not limited to the above embodiments, and various changes can be made without departing from the gist of the present invention within the scope of knowledge possessed by those of ordinary skill in the art.

Claims

1. A method for selectively separating and recovering lithium and iron from the electrodes of retired lithium iron phosphate batteries with low acid, characterized in that, The specific steps are as follows: (1) Add the electrodes of retired lithium iron phosphate batteries into a low-acid solution system and stir to mix evenly to obtain a leaching system; the low-acid solution system is a sulfuric acid solution with a concentration of 0.2 - 1.2 mol / L; (2) Introduce ultrasonic waves into the leaching system, add an oxidant into the leaching system for selective leaching with ultrasonic synergistic oxidation for 10 - 30 min, and perform solid-liquid separation to obtain a lithium-rich solution and iron phosphate leaching residue; the oxidant is a H2O2 / (NH4)2S2O8 composite oxidant, and the mass ratio of H2O2 to (NH4)2S2O8 in the oxidant is 1:0.5 - 1:1.

5.

2. The method for selectively separating and recovering lithium and iron from the electrodes of retired lithium iron phosphate batteries according to claim 1, characterized in that: Calculated by mass percentage, the retired lithium iron phosphate battery electrodes in step (1) contain 4 - 5% Li and 32 - 33% Fe.

3. The method for selectively separating and recovering lithium and iron in the electrodes of retired lithium iron phosphate batteries according to claim 1 or 2, characterized in that: In step (1), the liquid-solid ratio of the low-acid solution system to the retired lithium iron phosphate battery electrodes is 8 - 12 mL:g.

4. The method for selectively separating and recovering lithium and iron in the electrodes of retired lithium iron phosphate batteries according to claim 1, characterized in that: In step (2), the ultrasonic power is 100 - 600 W.

5. The method for selectively separating and recovering lithium and iron in the electrodes of retired lithium iron phosphate batteries according to claim 1, characterized in that: In step (2), the addition amount of the oxidant is 40 - 80 g / L.

6. The method for selectively separating and recovering lithium and iron in the electrodes of retired lithium iron phosphate batteries according to claim 1, characterized in that: In step (2), the temperature of the selective leaching is 30 - 60 °C.

Images