Method for recycling and utilizing elements in waste lithium iron phosphate with assistance of ferric oxide

Abstract

The invention belongs to the field of electrode material recycling, and particularly relates to a method for recycling elements in waste lithium iron phosphate with the assistance of ferric oxide, which comprises the following steps: mixing a waste lithium iron phosphate material and ferric oxide, then carrying out heat treatment in a protective atmosphere, and then carrying out leaching treatment and solid-liquid separation on a heat treatment product, a lithium extracting solution and leaching residues containing iron phosphate and ferrous oxide are obtained; the temperature of the heat treatment is 400 to 700 DEG C; a leaching agent in the leaching stage is water or acid liquor with the concentration being 0.1 M or below. According to the method, ferric oxide is creatively adopted to assist in participating in heat treatment of lithium iron phosphate, so that the crystal structure of lithium iron phosphate can be cracked based on a brand new mechanism, and lithium can be effectively extracted and recycled based on water leaching and ultralow-concentration acid leaching.

Description

Technical Field

[0001] The present invention belongs to the field of battery waste recycling, and in particular relates to the field of waste lithium battery material recycling. Background Art

[0002] Improper disposal of waste lithium-ion batteries (landfill, incineration, etc.) can cause great harm to the environment and human health. In response to the requirements of low-carbon development, the call for an evolution of the energy structure is growing louder. The implementation of strategies such as increasing the installed capacity of renewable energy, electrifying vehicles, and promoting the integrated cascade utilization of energy are closely related to the development of lithium-ion batteries. However, the resource and environmental problems brought about by the large-scale production and utilization of lithium-ion batteries cannot be ignored. On the one hand, the reserves of several metal resources mainly involved in lithium-ion batteries are limited, and the distribution of key elements on the earth varies greatly. Continuing to develop new resources on the earth will not lead to the sustainable development of lithium-ion batteries. On the other hand, a large number of retired batteries need to be properly stored and handled. Otherwise, harmful substances such as heavy metals, lithium salts and organic solvents in the waste batteries will pollute the soil and water, threatening human health. As an important strategic metal, the recycling and utilization of lithium has become more urgent.

[0003] The prior art also provides some methods for recovering elements from waste lithium iron phosphate, for example, A Chinese patent document discloses a method for preparing porous FeS2@C nanoparticles using retired lithium iron phosphate battery positive electrode materials, FeS2@C nanoparticles and their applications. The document specifically describes the steps of first immersing the retired lithium iron phosphate batteries in salt water for discharge, then disassembling them, sorting out the positive electrode sheets and calcining them, separating the lithium iron phosphate positive electrode powder, then immersing the lithium iron phosphate positive electrode powder in an acidic solution and stirring until it is completely dissolved, centrifuging and filtering to obtain an acid leaching solution, adding an alkaline solution while stirring to a pH value of 4 to 6 to obtain a suspension, and then centrifuging, washing and drying them in sequence to obtain pure iron hydroxide powder.

[0004] For another example, Chinese patent document CN117650302A discloses a method and system for resource recovery of battery recyclables. The resource recovery method includes the following steps: subjecting a second battery recyclable to a primary calcination for a period of time and a secondary calcination for a period of time in an oxygen-containing atmosphere to obtain a calcined product; wherein the calcination temperatures of the primary calcination and the secondary calcination are within the range of 1060-1380°C, and the calcination temperature of the primary calcination is lower than the calcination temperature of the secondary calcination.

[0005] In summary, the existing roasting process requires a relatively high temperature, mostly around 1000°C, and subsequent acid leaching at a relatively high acidity is still required. Even a conversion agent needs to be added to promote the leaching of lithium ions. The process is complicated, resulting in a large loss of lithium in the process. Summary of the Invention

[0006] In response to the problems faced by existing sLFP recycling, the purpose of the present invention is to provide a method for recovering elements from waste lithium iron phosphate with the assistance of ferric oxide, aiming to improve the recovery rate of lithium ions and achieve efficient and selective recovery of lithium ions.

[0007] The present invention also provides a method for utilizing elements in waste lithium iron phosphate with the assistance of ferric oxide.

[0008] A method for recovering elements from waste lithium iron phosphate using ferric oxide as an aid, comprising mixing waste lithium iron phosphate material and ferric oxide, heat-treating the mixture in a protective atmosphere, and then leaching the heat-treated product and performing solid-liquid separation to obtain a lithium extract and a leached residue containing ferric phosphate and ferrous oxide;

[0009] The heat treatment temperature is 400-700°C;

[0010] The leaching agent in the leaching stage is water or an acid solution with a concentration below 0.1M.

[0011] The present invention innovatively uses ferric oxide to assist in the heat treatment of lithium iron phosphate. This can crack the crystal structure of lithium iron phosphate based on a new mechanism, thereby achieving effective extraction and recovery of lithium based on water leaching and ultra-low concentration acid leaching. In addition, it can also achieve effective utilization of leached residue.

[0012] The waste lithium iron phosphate material is a positive electrode material obtained by stripping the positive electrode of a waste lithium iron phosphate battery.

[0013] Preferably, the waste lithium iron phosphate material is also allowed to contain at least one of a conductive agent, a binder, and an electrolyte.

[0014] Preferably, the content of lithium iron phosphate in the waste lithium iron phosphate material is above 50 wt.%, more preferably above 80 wt.%, and further preferably 80-95 wt.%.

[0015] The molar ratio of lithium iron phosphate to ferric oxide in the waste lithium iron phosphate is 1:0.4~0.5.

[0016] The protective atmosphere is nitrogen or an inert gas.

[0017] The heat treatment time is 1~3 h.

[0018] Preferably, the heat treatment process described in the present invention includes two holding stages, wherein the temperature of the first holding stage is 350-450°C, and the temperature of the second holding stage is 550-700°C. Under this preferred process, the holding times of the first and second stages are 0.5-2 hours, respectively. Studies conducted in the present invention have shown that under this preferred two-stage treatment process, the enhanced heat treatment effect of ferric oxide can be further enhanced, and the extraction effect of lithium can be further enhanced, and good extraction performance can be obtained even under water extraction.

[0019] Furthermore, the two-stage heat preservation process is preferably performed under microwave assistance. Furthermore, there are no specific requirements for the microwave power, and for example, it can be 300-800W. In the present invention, performing the two-stage heat preservation process under microwave assistance can enhance the enhanced heat treatment effect of ferric oxide and further enhance the low-temperature, low-solvent extraction effect of lithium.

[0020] When the leaching agent in the leaching stage is a phosphoric acid solution (its concentration can be 0.01~0.05M), a better lithium extraction effect can be obtained. However, the research of the present invention also shows that through further optimization of the heat treatment process, its water extraction effect can be further enhanced, and a comparable leaching effect can be obtained by water extraction.

[0021] In the present invention, by adopting the leaching with low phosphoric acid concentration, a more ideal lithium recovery effect can be obtained.

[0022] The leaching temperature of the present invention is relatively mild, for example, the temperature in the leaching stage is 15-35°C.

[0023] The liquid-to-solid ratio in the leaching stage is 10~30ml / g.

[0024] The leaching stage lasts for 0.5 h or longer, preferably 0.5 h to 1.5 h.

[0025] As the same inventive concept, the present invention also provides a method for assisted recovery and utilization of elements in waste lithium iron phosphate using ferric oxide, wherein the method described in the present invention is used to obtain a lithium extract and a leaching residue containing ferric phosphate and ferrous oxide; the leaching residue is heat-treated in an oxygen-containing atmosphere, and then magnetically separated to obtain ferric phosphate and magnetically separated material, and the magnetically separated material is further used as an iron catalyst for the synthesis of ammonia.

[0026] The research of the present invention shows that the treatment method can unexpectedly improve the application effect of slag in the iron catalyst catalytic synthesis of ammonia, especially under the two-stage insulation and microwave-assisted insulation, the ammonia production performance of the iron catalyst after the leaching slag treatment can be further improved.

[0027] In the present invention, the oxygen-containing atmosphere is, for example, air or other oxygen-containing atmospheres.

[0028] The holding temperature in the oxygen-containing atmosphere is, for example, 350-550° C. The holding time is, for example, 1-5 hours.

[0029] Beneficial effects

[0030] The present invention innovatively uses ferric oxide to participate in the calcination of waste lithium iron phosphate, which can achieve the transformation of the lithium iron phosphate lattice based on the following mechanism (3LiFePO4 + Fe2O3 = Li3PO4 + 2FePO4 + 3FeO), thereby effectively destroying the lattice structure of lithium iron phosphate, thereby achieving efficient recovery of lithium therein.

[0031] In addition, in addition to being able to effectively extract lithium, the method of the present invention can also make high-value use of the leached residue for reasonable transformation and utilization. For example, the slag can be kept warm in an oxygen-containing atmosphere and subjected to magnetic separation treatment to obtain a high-performance iron catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is the XRD pattern of the calcined product of Example 1; DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below with reference to specific examples, but the present invention is not limited to the following examples.

[0034] In the present invention, the waste lithium iron phosphate positive electrode material can be obtained by stripping from the positive electrode of waste lithium iron phosphate batteries. There is no special requirement for the content of active material (LFP) therein. Considering the economic efficiency of the process, its content is preferably above 50wt.%. In the following cases, unless otherwise stated, its active content is 85~90wt.%.

[0035] Example 1:

[0036] Step 1: Mix the waste lithium iron phosphate material and Fe2O3 in a ratio of (LFP:Fe2O3) 1:0.5, place the mixture in a tube furnace, and introduce argon gas. The calcination temperature is 600℃ and the time is 2 hours;

[0037] Step 2: Leaching: The roasted slag was placed in a 0.01 M phosphoric acid solution and stirred for leaching, with a liquid-to-solid ratio of 20 mL / g, a leaching time of 1 h, and a leaching temperature of 30±2°C.

[0038] The leaching rate of lithium in the leachate was 99.3%, and the purity of the obtained Li3PO4 was 98.7%. The leached residue was calcined in air at 400°C for 1 hour, followed by magnetic separation to obtain FePO4 and magnetic separation material, respectively. The ferric phosphate can be used in the synthesis of LFP, while the magnetic separation material can be used as a raw material for iron catalyst. The volume fraction of NH3 in the equilibrium mixture for synthetic ammonia was determined by GC-9280 gas chromatography to be 49%, far exceeding the performance of traditional iron catalysts.

[0039] Example 2

[0040] Compared with Example 1, the only difference is that the waste lithium iron phosphate material and Fe2O3 are evenly mixed in a molar ratio of (LFP:Fe2O3) 1:0.4. Other operations and parameters are the same as those in Example 1.

[0041] The leaching rate of Li in the leachate is 99.5%, and the purity of the obtained Li3PO4 is 99.1%.

[0042] Example 3

[0043] Compared with Example 1, the only difference is that the roasting temperature is changed to 700° C., and the other operations and parameters are the same as Example 1.

[0044] The leaching rate of Li in the leachate was 99.6%, and the purity of the obtained Li3PO4 was 99.3%.

[0045] Example 4

[0046] Compared with Example 1, the only difference is that the roasted slag is immersed in water in an ice bath pot, and other operations and parameters are the same as Example 1.

[0047] The leaching rate of Li in the leachate is 99.1%, the purity of the obtained Li3PO4 is 98.2%, and under the action of iron catalyst, the volume fraction of NH3 in the equilibrium mixture of synthetic ammonia is 48%.

[0048] Example 5

[0049] Compared with Example 1, the only difference is that in step 1, the mixture is pre-heated at 400°C for 0.5h in the first stage, then heated to 600°C and kept warm for 1.5h, and then immersed in water, wherein the conditions of the water immersion are the same as those in Example 4.

[0050] The leaching rate of Li in the leachate is 99.9%, the purity of the obtained Li3PO4 is 99.9%, and under the action of iron catalyst, the volume fraction of NH3 in the synthetic ammonia equilibrium mixture is 53%.

[0051] Example 6

[0052] Compared with Example 5, the only difference is that in step 1, the two insulation stages are carried out under microwave assistance, wherein the power of the microwave is 500~550W. In addition, the liquid-to-solid ratio of the water immersion stage is 10ml / g, and the water immersion temperature is 20±2℃. Other operations and parameters are the same as those in Example 5.

[0053] The leaching rate of Li in the leachate is 99.8%, the purity of the obtained Li3PO4 is 99.9%, and under the action of iron catalyst, the volume fraction of NH3 in the synthetic ammonia equilibrium mixture is 59%.

[0054] Comparative Example 1

[0055] Compared with Example 1, the only difference is that Fe2O3 is not added. Other operations and parameters are the same as those in Example 1.

[0056] The leaching rate of Li in the leachate was 48.6%.

[0057] Comparative Example 2

[0058] Compared with Example 1, the only difference is that Fe2O3 is replaced by FeO, and other operations and parameters are the same as Example 1.

[0059] The leaching rate of Li in the leachate was 49.6%.

[0060] Comparative Example 3

[0061] Compared with Example 1, the only difference is that Fe2O3 is replaced by Fe3O4, and other operations and parameters are the same as Example 1.

[0062] The leaching rate of Li in the leachate is 80.3%, the purity of the obtained Li3PO4 is 82.7%, and under the action of iron catalyst, the volume fraction of NH3 in the equilibrium mixture of synthetic ammonia is 36%.

[0063] Comparative Example 4

[0064] Compared with Example 4, the only difference is that in step 1, Fe2O3 is not added, the argon gas in the system is replaced by air, and the calcination temperature is 600°C and the time is 2 h; then water immersion is performed, and other operations and parameters are the same as in Example 1.

[0065] The leaching rate of Li in the leachate was 95.8%. The water-leached residue was dried and magnetically separated, and the magnetic separation material was collected and used for iron catalyst application research. The results showed that the volume fraction of NH3 in the equilibrium mixture for synthetic ammonia was 34%.

Claims

1. A method for recovering elements from waste lithium iron phosphate using ferric oxide, characterized in that: The waste lithium iron phosphate material and ferric oxide are mixed and then heat-treated in a protective atmosphere, and then the heat-treated product is leached and solid-liquid separated to obtain a lithium extract and a leached residue containing iron phosphate and ferrous oxide; The temperature of the heat treatment is 400-700°C; The leaching agent in the leaching stage is water or an acid solution with a concentration below 0.1M.

2. The method according to claim 1, characterized in that The waste lithium iron phosphate material is a positive electrode material obtained by stripping the positive electrode of a waste lithium iron phosphate battery; Preferably, the waste lithium iron phosphate material is also allowed to contain at least one of a conductive agent, a binder, and an electrolyte; Preferably, the content of lithium iron phosphate in the waste lithium iron phosphate material is above 50 wt.%, more preferably above 80 wt.%, and further preferably 80-95 wt.%.

3. The method according to claim 1, characterized in that The molar ratio of lithium iron phosphate to ferric oxide in waste lithium iron phosphate is 1:0.4~0.

5.

4. The method according to claim 1, characterized in that The protective atmosphere is nitrogen or an inert gas.

5. The method according to claim 1, characterized in that The heat treatment time is 1~3 h.

6. The method according to claim 1, characterized in that The leaching agent in the leaching stage is phosphoric acid solution.

7. The method according to claim 6, characterized in that The concentration of the acid solution is 0.01~0.05M.

8. The method according to claim 1, characterized in that The temperature during the leaching stage is 15~35℃.

9. The method according to claim 1, characterized in that The liquid-to-solid ratio in the leaching stage is 10-30 ml / g; Preferably, the leaching stage lasts for more than 0.5 h, preferably 0.5 h to 1.5 h.

10. A method for recovering and utilizing elements in waste lithium iron phosphate by using ferric oxide, characterized in that: The method according to any one of claims 1 to 9 is used to obtain a lithium extraction solution and a leaching residue containing iron phosphate and ferrous oxide; the leaching residue is subjected to a heat preservation treatment in an oxygen-containing atmosphere, followed by magnetic separation to obtain iron phosphate and magnetic separation material, and the magnetic separation material is further used as an iron catalyst for the synthesis of ammonia.

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