A method for preparing a two-dimensional flaky Li4SiO4 adsorbent using attapulgite and discarded lithium batteries and its application

Abstract

The present invention belongs to the technical field of waste lithium battery resource utilization and CO2 adsorbent preparation, and specifically relates to a method for preparing a two-dimensional flaky Li4SiO4 adsorbent using attapulgite and waste lithium batteries and its application. The method comprises the following steps: (1) using attapulgite as a silicon source, performing acid treatment to remove most of the metal ions in its skeleton and retaining the unique Si-O tetrahedral structure inside to obtain SiO2; (2) using waste lithium battery positive electrode material as a lithium source, utilizing waste biomass carbon thermal reduction to recover Li2CO3 from the waste lithium battery; (3) utilizing microwave hydrothermal method to convert one-dimensional rod-shaped SiO2 and Li2CO3 into two-dimensional flaky lithium silicate. The present invention utilizes inexpensive precursors (Si source and Li source) to synthesize a highly efficient Li4SiO4 adsorbent having a large specific surface area, capable of stably and efficiently capturing CO2, and realizing the transformation of waste into treasure.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste lithium battery resource utilization and CO2 adsorbent preparation, and particularly relates to a method for preparing a two-dimensional flaky Li4SiO4 adsorbent using attapulgite and waste lithium batteries and its application. Background Art

[0002] The massive emission of CO2 is one of the main causes of global climate change and poses a serious threat to human survival. Countries around the world are developing corresponding technologies to meet this challenge. Carbon dioxide capture and storage (CCS) technology is considered one of the main measures to solve this crisis. Among the different CCS technology fields, post-combustion capture (PCC) of thermal storage solid adsorbents has been found to be suitable for carbon capture in high-temperature flue gases from large power plants. Among high-temperature CO2 adsorbents such as CaO-based, lithium-based ceramics and clay minerals (such as hydrotalcite-like materials), Li4SiO4 is considered to be one of the most promising options due to its moderate operating temperature and good cyclic stability.

[0003] Attapulgite (ATP) is a natural clay mineral with abundant reserves. Its crystal structure is composed of a double-chain layer of Si-O tetrahedrons, with the octahedron center surrounded by Mg 2+ Since transition metals can be incorporated into silicates at octahedral positions, metal silicates with octahedral structures may be developed as silicate-based catalysts. For example, patent CN111569879A provides a method of converting ATP into rod-shaped SiO2, and then adding Co. 3+ The preparation method of rod-shaped Co2SiO4 provides the possibility for synthesizing Li4SiO4 from clay minerals.

[0004] Lithium batteries are widely used as energy storage units and the most common power supply units for new energy vehicles, mobile phones and computers, and a large number of lithium batteries are wasted every year. In existing research, patent CN113549765A discloses a method for obtaining pyrolysis coke using cheap materials such as pyrolysis coal / biomass, and reducing discarded lithium batteries to metal elements and metal oxides through pyrolysis coke. Patent CN102664293A discloses a method for preparing CO2 adsorbent Li4SiO4 by calcining discarded lithium batteries with SiO2. The current improved methods for preparing Li4SiO4 adsorbent materials mainly include improving the microstructure of the adsorbent, optimizing the adsorbent precursor, doping metal ions and loading molten salts. However, how to construct an adsorbent material with high efficiency and stable CO2 adsorption capacity is a huge challenge facing the development of CCS technology. Summary of the Invention

[0005] The present invention provides a two-dimensional sheet-like Li4SiO4 adsorbent material with readily available raw materials, low price, high efficiency and stable CO2 adsorption capacity. The preparation method is simple and does not require complex and expensive equipment, which is conducive to large-scale promotion.

[0006] To achieve the purpose of the present invention, the technical solution adopted is:

[0007] A method for preparing a two-dimensional flaky Li4SiO4 adsorbent using attapulgite and discarded lithium batteries comprises the following steps:

[0008] (1) Discharging, peeling off and sieving the discarded lithium battery cathode material LiCoO2 (LCO, 98 wt%, 160 mesh), and then drying in an oven for later use; freeze-drying the discarded biomass, taking it out, grinding it, sieving it, and setting it aside;

[0009] (2) taking an appropriate amount of LiCoO2 treated in step (1) and biomass and mixing them thoroughly, then placing them in a tube furnace, first purging with nitrogen, then heating and calcining to obtain a solid sample after carbon thermal reduction treatment, then hydrothermally stirring the solid sample, filtering, recovering the filtrate, and evaporating it to obtain Li2CO3 powder;

[0010] (3) Ultrasonic dispersion of attapulgite (ATP) in an acid solution, stirring in a water bath at 80°C, washing the obtained product until neutral, filtering it, and drying it in an oven overnight to obtain SiO2;

[0011] (4) Weigh the SiO2 obtained in step (3) and ultrasonically disperse it in deionized water, then add NaOH, hydrothermally stir, then add an appropriate amount of Li2CO3 obtained in step (2), stir and react, then add NH4F, and then add ammonia water dropwise to adjust the pH of the solution, and then transfer the above solution into a microwave hydrothermal reactor for reaction. After the reaction is completed, the obtained product is centrifuged, washed, dried, and then placed in a muffle furnace for calcination to obtain Li4SiO4.

[0012] Furthermore, the waste lithium battery described in step (1) is any one of lithium cobalt oxide, nickel cobalt manganese or lithium iron phosphate, and the drying time is 4-8 hours.

[0013] Furthermore, the waste biomass in step (1) is any one of onion, garlic, celery, lotus leaf, chestnut shell, pomegranate peel or wheat straw, and the freeze-drying time is 6-12 hours.

[0014] Furthermore, in step (2), the mass ratio of LiCoO2 to biomass is 1:0.2-0.7.

[0015] Furthermore, the nitrogen purge time in step (2) is 10-20 minutes.

[0016] Furthermore, in step (2), the calcination temperature is 400-500° C., the calcination time is 20-40 min, and the heating rate is 2-15° C. / min.

[0017] Furthermore, in step (2), the temperature of the hydrothermal stirring is 60-80° C., and the time is 5-15 h.

[0018] Furthermore, the acid solution in step (3) is any one of hydrochloric acid, nitric acid or phosphoric acid.

[0019] Furthermore, in step (4), the molar ratio of SiO2 to NaOH is 1:2-2.4, and the hydrothermal stirring time is 1-2h.

[0020] Furthermore, in step (4), the molar ratio of SiO2 to Li2CO3 is 1:2.0-2.2, and the stirring reaction time is 0.5-1.5h.

[0021] Furthermore, in step (4), the molar ratio of SiO2 to NH4F is 1:4-8, and aqueous ammonia is used to adjust the pH of the solution to 9-13.

[0022] Furthermore, in step (4), the microwave hydrothermal reaction temperature is 140-180° C., and the reaction time is 60-120 min.

[0023] Furthermore, in step (4), the muffle furnace calcination temperature is 750-850° C., and the calcination time is 4 hours.

[0024] The two-dimensional sheet-like Li4SiO4 adsorbent prepared according to the above method was applied to CO2 adsorption.

[0025] The CO2 adsorption performance of the adsorbent was determined by thermogravimetric analysis. The specific method is as follows: 10 mg of sample was placed in a crucible and heated in 100 vol% nitrogen at 10 °C·min -1 The sample was heated to the adsorption temperature of 625°C at a heating rate of 1000 ℃ and maintained for 120 min. At the same time, the gas was switched to 15 vol% CO2 (nitrogen balance), and the sample began to adsorb CO2, with a CO2 or N2 gas flow rate of 50 mL·min -1 , the adsorption capacity of the adsorbent (Cn, gCO2 / gsorbent) is defined according to the following formula:

[0026] Cn=(m2-m1) / m1×100%

[0027] Where m1 and m2 represent the initial mass and maximum mass of the adsorbent during the adsorption process, respectively.

[0028] Compared with the existing technology, the present invention has the following beneficial effects: using waste biomass to carbon-thermally reduce waste lithium batteries, and then using microwave hydrothermal method to convert one-dimensional rod-shaped clay minerals into two-dimensional sheet silicates, that is, using inexpensive precursors to synthesize a highly efficient two-dimensional sheet-structured Li4SiO4 adsorbent, and promoting the recycling of waste lithium batteries and alleviating heavy metal pollution. In addition, the use of waste biomass to reduce waste lithium batteries is a process in which the waste biomass is pre-treated during carbon-thermal recovery of the lithium source. Some nitrogen and fluorine elements remain in the waste biomass, interfering with the adsorption and desorption process of CO2, lowering the equilibrium temperature and improving the adsorption performance of the adsorbent Li4SiO4. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 XRD patterns of original ATP, SiO2 and Li4SiO4 in Example 1;

[0030] Figure 2 IR spectra of original ATP and Li4SiO4 in Example 1;

[0031] Figure 3 Transmission electron micrographs of SiO2 (a) and Li4SiO4 (b) in Example 1;

[0032] Figure 4 This is a graph showing the CO2 adsorption performance of Li4SiO4 prepared in Example 1, Comparative Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0033] Example 1

[0034] (1) The discarded lithium battery positive electrode material LiCoO2 (LCO, 98 wt%, 160 mesh) was first subjected to pre-treatment operations such as discharge, aluminum foil peeling and screening, and then dried for use. Fresh onions were freeze-dried, taken out, ground, sieved and set aside for use.

[0035] (2) 3.00 g of LCO and 1.5 g of onion powder (mass ratio of 1:0.5) were thoroughly mixed and dried in an oven at 100 °C for 2 h. Then the mixture was placed in a tube furnace and purged with nitrogen for 15 min, and then heated at a rate of 10 °C min -1 The raw material was heated to 450°C and maintained for 30 minutes to obtain a solid sample after carbothermal reduction treatment. The solid sample was then hydrothermally stirred at 80°C for 6 hours, filtered, and the filtrate was recovered and evaporated to obtain Li2CO3 powder.

[0036] (3) Ultrasonic dispersion: Dissolve 1g of ATP in 50mL of 5mol / L hydrochloric acid solution and stir in a water bath at 80°C for 10h. The product is then washed until neutral, filtered, and dried in an oven overnight. The metal ion content of the modified ATP is very low, with SiO2 being the main component.

[0037] (4) Add 5 mmol of SiO2 obtained by ATP acid treatment and 10 mmol of NaOH to a beaker. After hydrothermal stirring for 1.5 h, add 10.5 mmol of Li2CO3 recovered from waste LCO. After 1 h, add 22 mmol of NH4F, and then add ammonia water dropwise to adjust the pH to 12. Finally, transfer the solution into a 100 mL microwave hydrothermal reactor and perform hydrothermal treatment at 160°C for 90 min. After the reaction, the sample is centrifuged, washed, dried overnight, and then calcined at 800°C in a muffle furnace for 4 h to obtain Li4SiO4.

[0038] The Li4SiO4 adsorbent material in Example 1 was tested by thermogravimetric analysis. 10 mg of the sample was placed in a crucible and heated in 100 vol% nitrogen at 10 °C·min -1 The temperature was raised to 625 °C and maintained for 120 min at a flow rate of 50 mL min -1 15vol% CO2 / N2 was used as a simulated industrial flue gas, and CO2 was adsorbed at 625℃ for 60min. The adsorption capacity Cn of the adsorbent was 0.307g / g.

[0039] The Li4SiO4 adsorbent prepared in this example was subjected to X-ray powder diffraction experiments and infrared spectroscopy analysis experiments, and its morphology and structure were observed under a transmission electron microscope.

[0040] Figure 1 Figure 3 shows the XRD patterns of pristine ATP, SiO2, and Li4SiO4. The peaks at 8.5°, 20.1°, 28.0°, and 35.8° correspond to the characteristic peaks of ATP. Compared with pristine ATP, the characteristic peaks of acid-treated ATP disappear, indicating that most of the metal ions in ATP are dissolved and correspond to the characteristic peaks of SiO2. The characteristic peaks at 24.0°, 29.2°, 34.8°, 38.8°, 51.7°, 55.5°, and 60.1° correspond to the (101), (020), (002), (102), (300), (013), and (231) crystal planes of Li4SiO4, respectively (PDF#37-1472), indicating that Li4SiO4 was successfully prepared using the Li source from waste LCO and the Si source from ATP as precursors.

[0041] Figure 2 The FT-IR spectra of original ATP and Li4SiO4 are shown below. In original ATP, 3561 cm -1 The characteristic peaks at 1385 and 1628 cm are the stretching vibrations of the -OH structure. -1This is caused by the bending vibration of -OH of water adsorbed in the sample. The peak of Li4SiO4 is sharper than that of ATP, indicating that it has more surface active sites. -1 The bending vibration of Si-O-Si bond proves that the Si-O tetrahedral structure of a-Li4SiO4 exists, and the 785cm -1 The peak at corresponds to the Li-O-Li absorption vibration peak.

[0042] Figure 3 (a) and (b) are TEM images of SiO2 and Li4SiO4 respectively. The microstructure of SiO2 produced by ATP acidification still maintains the one-dimensional nanofiber rod structure of ATP, but there are local rod-like fractures and tends to fold into sheets, such as Figure 3 (a) is shown. Figure 3 As shown in (b), the microstructure of Li4SiO4 and b-Li4SiO4 prepared with ATP as silicon source is a two-dimensional thin sheet. The reason is that after the acid destroys the ATP skeleton, the silicon-oxygen tetrahedron structure in the skeleton can be retained. Then, under alkaline hydrothermal conditions, the chain structure of lithium and silicon-oxygen tetrahedron can combine and grow directionally into a two-dimensional Li4SiO4 thin sheet.

[0043] Example 2

[0044] (1) The discarded lithium battery positive electrode material LiCoO2 (LCO, 98wt%, 160 mesh) was first subjected to pre-treatment operations such as discharge, aluminum foil peeling and screening, and then dried for use. Fresh onions were then freeze-dried, taken out, ground, sieved and set aside for use.

[0045] (2) 3.00 g of LCO and 0.6 g of onion powder (mass ratio of 1:0.2) were thoroughly mixed and dried in an oven at 100 °C for 2 h. The raw materials were placed in a tube furnace and purged with nitrogen for 20 min, then heated at a rate of 5 °C·min -1 The raw material is heated to 400°C and maintained for 40 minutes to obtain a solid sample after carbon thermal reduction treatment. The solid sample is then hydrothermally stirred at 80°C for 6 hours, filtered, and the filtrate is recovered and evaporated to obtain Li2CO3 powder.

[0046] (3) Modification of ATP is consistent with step (3) of Example 1.

[0047] (4) The microwave hydrothermal preparation of Li4SiO4 is consistent with step (4) of Example 1, but the pH value needs to be adjusted to 13.

[0048] The Li4SiO4 adsorbent material in Example 2 was tested by thermogravimetric analysis. 10 mg of the sample was placed in a crucible and heated in 100 vol% nitrogen at 10 °C·min -1The temperature was raised to 625 °C and maintained for 120 min at a flow rate of 50 mL min -1 15vol% CO2 / N2 was used as a simulated industrial flue gas, and CO2 was adsorbed at 625℃ for 60min. The adsorption capacity Cn of the adsorbent was 0.285g / g.

[0049] Example 3

[0050] (1) The discarded lithium battery positive electrode material LiCoO2 (LCO, 98wt%, 160 mesh) was first subjected to pre-treatment operations such as discharge, aluminum foil peeling and screening, and then dried for use. Fresh onions were then freeze-dried, taken out, ground, sieved and set aside for use.

[0051] (2) 3.00 g of LCO and 2.1 g of onion powder (mass ratio of 1:0.7) were thoroughly mixed and dried in an oven at 100 °C for 2 h. The raw materials were placed in a tube furnace and purged with nitrogen for 10 min, then heated at a rate of 10 °C min -1 The raw material is heated to 500°C and maintained for 20 minutes to obtain a solid sample after carbon thermal reduction treatment. The solid sample is then hydrothermally stirred at 80°C for 6 hours, filtered, and the filtrate is recovered and evaporated to obtain Li2CO3 powder.

[0052] (3) Modification of ATP is consistent with step (3) of Example 1.

[0053] (4) The microwave hydrothermal preparation of Li4SiO4 was consistent with step (4) of Example 1, but the pH value needed to be adjusted to 9.

[0054] The Li4SiO4 adsorbent material in Example 3 was tested by thermogravimetric analysis. 10 mg of the sample was placed in a crucible and heated in 100 vol% nitrogen at 10 °C·min -1 The temperature was raised to 625 °C and maintained for 120 min at a flow rate of 50 mL min -1 15vol% CO2 / N2 was used as a simulated industrial flue gas, and CO2 was adsorbed at 625℃ for 60min. The adsorption capacity Cn of the adsorbent was 0.298g / g.

[0055] Example 4

[0056] (1) The treatment of waste lithium batteries and waste biomass is consistent with step (1) of Example 1.

[0057] (2) The carbon thermal reduction of the waste lithium battery positive electrode material is consistent with step (2) of Example 1.

[0058] (3) Modification of ATP is consistent with step (3) of Example 1.

[0059] (4) Add 5 mmol of SiO2 obtained by ATP acid treatment and 12 mmol of NaOH to a beaker. After hydrothermal stirring for 1 hour, add 10 mmol of Li2CO3 recovered from waste LCO. After 1.5 hours, add 20 mmol of NH4F, and then add ammonia water dropwise to adjust the pH to 10. Finally, transfer the solution into a 100 mL microwave hydrothermal reactor and perform hydrothermal treatment at 160°C for 120 minutes. After the reaction, the sample is centrifuged, washed, dried overnight, and then calcined at 750°C in a muffle furnace for 4 hours to obtain Li4SiO4.

[0060] The Li4SiO4 adsorbent material in Example 4 was tested by thermogravimetric analysis. 10 mg of the sample was placed in a crucible and heated in 100 vol% nitrogen at 10 °C·min -1 The temperature was raised to 625 °C and maintained for 120 min at a flow rate of 50 mL min -1 15vol% CO2 / N2 was used as a simulated industrial flue gas, and CO2 was adsorbed at 625℃ for 60min. The adsorption capacity Cn of the adsorbent was 0.283g / g.

[0061] Example 5

[0062] (1) The treatment of waste lithium batteries and waste biomass is consistent with step (1) of Example 1.

[0063] (2) The carbon thermal reduction of the waste lithium battery positive electrode material is consistent with step (2) of Example 1.

[0064] (3) Modification of ATP is consistent with step (3) of Example 1.

[0065] (4) Add 5 mmol of SiO2 obtained by ATP acid treatment and 12 mmol of NaOH to a beaker. After hydrothermal stirring for 2 h, add 11 mmol of Li2CO3 recovered from waste LCO. After 0.5 h, add 40 mmol of NH4F, and then add ammonia water dropwise to adjust the pH to 12. Finally, transfer the solution into a 100 mL microwave hydrothermal reactor and perform hydrothermal treatment at 180°C for 60 min. After the reaction, the sample is centrifuged, washed, dried overnight, and then calcined at 850°C in a muffle furnace for 4 h to obtain Li4SiO4.

[0066] The Li4SiO4 adsorbent material in Example 5 was tested by thermogravimetric analysis. 10 mg of the sample was placed in a crucible and heated in 100 vol% nitrogen at 10 °C·min -1 The temperature was raised to 625 °C and maintained for 120 min at a flow rate of 50 mL min -115vol% CO2 / N2 was used as a simulated industrial flue gas, and CO2 was adsorbed at 625℃ for 60min. The adsorption capacity Cn of the adsorbent was 0.301g / g.

[0067] It can be seen from Examples 1, 2 and 3 that the ratio of waste lithium battery positive electrode material to biomass and the carbon thermal reduction temperature are key factors affecting the recovery of lithium sources. Therefore, the prepared Li4SiO4 has slightly different CO2 adsorption performance. When the temperature is too low (below 400°C), the carbon thermal reduction reaction is not complete, and the yield of Li2CO3 is lower than 450°C in Example 1. When the temperature is too high (above 500°C), onion powder is easily converted into biochar, which may lead to the transfer of gas-solid reaction to solid-solid carbon thermal reduction, and solid carbon thermal reduction may convert Co in LCO into biochar. 3+ Reduction to metallic Co, CoO and Co3O4 results in reduced lithium source recovery efficiency. In addition, high temperature not only increases energy consumption but also may lead to possible loss of Li and secondary pollution.

[0068] From Examples 1, 4 and 5, it can be seen that in the preparation of Li4SiO4, after ATP is treated with high concentration acid, its rod-like structure is destroyed and broken and tends to assemble into sheets. The formation of the Li4SiO4 sheet structure may be due to the retention of the silicon-oxygen tetrahedron structure in the skeleton after the ATP structure is destroyed. + After addition, under alkaline hydrothermal conditions, the chain structure of silicon-oxygen tetrahedrons regularly grows into Li4SiO4 nanosheets. It is worth noting that Li2CO3 needs to be added in excess because Li is easily volatilized under hydrothermal reaction conditions.

[0069] Comparative Example 1

[0070] The same as Example 1, but the lithium source recovered from the waste lithium battery positive electrode material in step (4) is replaced with analytical grade lithium carbonate.

[0071] The Li4SiO4 adsorbent material in Comparative Example 1 was tested by thermogravimetric analysis. 10 mg of the sample was placed in a crucible and heated in 100 vol% nitrogen at 10 °C·min -1 The temperature was raised to 625 °C and maintained for 120 min at a flow rate of 50 mL min -1 15vol% CO2 / N2 was used as a simulated industrial flue gas, and CO2 was adsorbed at 625℃ for 60min. The adsorption capacity Cn of the adsorbent was 0.266g / g.

[0072] Compared to Example 1, the adsorption capacity of the adsorbent in the comparative example is much lower than that in Example 1. This is likely due to the fact that the lithium source recovered from discarded lithium batteries via carbothermal reduction with onion powder contains small amounts of elements such as nitrogen and fluorine, which promote CO adsorption. Furthermore, the cost is much lower than that of analytically pure lithium carbonate. Furthermore, the trace amount of biochar remaining during the carbothermal reduction process may support the two-dimensional nanosheets, improving the stability of the flaky Li₄SiO₄. Therefore, the Li₄SiO₄ prepared in Example 1 exhibits superior adsorption stability.

[0073] Comparative Example 2

[0074] The same as Example 1, but the silicon source obtained from the modified attapulgite in step (3) is replaced by analytically pure silica sol.

[0075] The Li4SiO4 adsorbent material in Comparative Example 2 was tested by thermogravimetric analysis. 10 mg of the sample was placed in a crucible and heated in 100 vol% nitrogen at 10 °C·min -1 The temperature was raised to 625 °C and maintained for 120 min at a flow rate of 50 mL min -1 15vol% CO2 / N2 was used as a simulated industrial flue gas, and CO2 was adsorbed at 625℃ for 60min. The adsorption capacity Cn of the adsorbent was 0.212g / g.

[0076] Compared with Example 1, the adsorption capacity of the adsorbent in the above comparative example is much lower than that in Example 1. The reason may be that the Li4SiO4 prepared by SiO2 sol has the morphology of agglomerated spherical particles, while the microstructure of Li4SiO4 prepared by ATP as the silicon source is a two-dimensional thin sheet. This is due to the structural specificity of attapulgite, and the lamellar structure has a higher porosity and a larger adsorption specific surface area. Therefore, the Li4SiO4 prepared in Example 1 has stronger adsorption performance.

[0077] Comparative Example 3

[0078] The same as Example 1, but in step (4), NH4F was not added, and only NH3·H2O was added to adjust the pH to 12.

[0079] The Li4SiO4 adsorbent material in Comparative Example 3 was tested by thermogravimetric analysis. 10 mg of the sample was placed in a crucible and heated in 100 vol% nitrogen at 10 °C min -1 The temperature was raised to 625 °C and maintained for 120 min at a flow rate of 50 mL min -1 15vol% CO2 / N2 was used as a simulated industrial flue gas, and CO2 was adsorbed at 625℃ for 60min. The adsorption capacity Cn of the adsorbent was 0.207g / g.

[0080] Compared with Example 1, the adsorption capacity of the adsorbent in the comparative example is much lower than that in Example 1. The reason may be that NH4F is not added, which causes Li4SiO4 to agglomerate and cannot grow into a lamellar structure.

Claims

1. An application of a two-dimensional sheet-like Li4SiO4 adsorbent prepared from attapulgite and discarded lithium batteries in CO2 adsorption, characterized in that: The preparation method of the adsorbent comprises the following steps: (1) Discharge the discarded lithium battery positive electrode material LiCoO2, peel off the aluminum foil and screen it, then put it in an oven to dry for later use; freeze-dry the discarded biomass, take it out, grind it, screen it and set it aside; (2) Taking an appropriate amount of LiCoO2 treated in step (1) and waste biomass, mixing them thoroughly, then placing them in a tube furnace, purging them with nitrogen, and then heating and calcining them to obtain a solid sample after carbon thermal reduction treatment. The solid sample is then hydrothermally stirred, filtered, and the filtrate is recovered and evaporated to obtain Li2CO3 powder; (3) Ultrasonic dispersion of attapulgite in an acid solution, stirring in a water bath at 80°C, washing the obtained product until neutral, filtering it, and drying it in an oven overnight to obtain SiO2; (4) Weigh the SiO2 obtained in step (3) and ultrasonically disperse it in deionized water. Then add NaOH and stir hydrothermally. Then add an appropriate amount of Li2CO3 obtained in step (2) with a molar ratio of SiO2 to Li2CO3 of 1:2.0-2.

2. Stir and react. Then add NH4F and then add ammonia water dropwise to adjust the pH of the solution. Then transfer the above solution into a microwave hydrothermal reactor to react. After the reaction is completed, centrifuge the obtained product, wash, dry, and then calcine in a muffle furnace to obtain Li4SiO4.

2. The use of the two-dimensional sheet-like Li4SiO4 adsorbent prepared from attapulgite and waste lithium batteries in CO2 adsorption according to claim 1, characterized in that: The waste lithium battery described in step (1) is any one of lithium cobalt oxide and nickel cobalt manganese, and the drying time is 4-8 hours; And / or, the waste biomass is any one of onion, garlic, celery, lotus leaf, chestnut shell, pomegranate peel or wheat straw, and the freeze-drying time is 6-12 hours.

3. The use of the two-dimensional sheet-like Li4SiO4 adsorbent prepared from attapulgite and discarded lithium batteries in CO2 adsorption according to claim 1, characterized in that: In step (2), the mass ratio of LiCoO2 to waste biomass is 1:0.2-0.7; and / or, the nitrogen purge time is 10-20 min; And / or, the calcination temperature is 400-500° C., the calcination time is 20-40 min, and the heating rate is 2-15° C. / min.

4. The use of the two-dimensional flaky Li4SiO4 adsorbent prepared from attapulgite and discarded lithium batteries in CO2 adsorption according to claim 1, characterized in that: The temperature of the hydrothermal stirring in step (2) is 60-80°C and the time is 5-15h.

5. The use of the two-dimensional sheet-like Li4SiO4 adsorbent prepared from attapulgite and discarded lithium batteries in CO2 adsorption according to claim 1, characterized in that: The acid solution in step (3) is any one of hydrochloric acid, nitric acid or phosphoric acid.

6. The use of the two-dimensional flaky Li4SiO4 adsorbent prepared from attapulgite and discarded lithium batteries in CO2 adsorption according to claim 1, characterized in that: In step (4), the molar ratio of SiO2 to NaOH is 1:2-2.4, and the hydrothermal stirring time is 1-2h.

7. The use of the two-dimensional sheet-like Li4SiO4 adsorbent prepared from attapulgite and waste lithium batteries in CO2 adsorption according to claim 1, characterized in that: The stirring reaction time in step (4) is 0.5-1.5h.

8. The use of the two-dimensional sheet-like Li4SiO4 adsorbent prepared from attapulgite and waste lithium batteries in CO2 adsorption according to claim 1, characterized in that: In step (4), the molar ratio of SiO2 to NH4F is 1:4-8, and aqueous ammonia is used to adjust the pH of the solution to 9-13.

9. The use of the two-dimensional sheet-like Li4SiO4 adsorbent prepared from attapulgite and waste lithium batteries in CO2 adsorption according to claim 1, characterized in that: The temperature of the microwave hydrothermal reaction in step (4) is 140-180°C, and the reaction time is 60-120 min; And / or, the muffle furnace calcination temperature is 750-850° C., and the calcination time is 4 hours.

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