Methods for recovering lithium from lithium batteries

Abstract

The present application discloses a method for recovering lithium from a lithium battery, and belongs to the field of lithium battery recovery. The method comprises: after decomposing the lithium battery, pyrolyzing it at 200-500°C to obtain a slag; placing the slag in a composite leaching agent, adjusting the pH to 1.5-2.5, leaching the lithium in the slag to obtain a leachate; the composite leaching agent comprises oxalic acid, amino acid ligands, persulfate and fluoride ions; adjusting the pH of the leachate to 5.5-6.2, adding an extractant to the leachate, extracting the lithium ions in the leachate, and separating to obtain a lithium-rich organic phase and a lithium-containing waste liquid; the extractant comprises crown ethers and organic phosphates; stripping the lithium-rich organic phase to release lithium ions from the organic phase to obtain a lithium-rich stripping solution, and adding a carbonate solution to the lithium-rich stripping solution to obtain a lithium carbonate precipitate. The method for recovering lithium from a lithium battery provided in the present application can achieve selective leaching of lithium and improve the comprehensive yield of lithium in a lithium battery.

Description

Technical Field

[0001] The present application belongs to the technical field of battery recycling, and specifically relates to a method for recycling lithium in a lithium battery. Background Art

[0002] With the widespread popularity of consumer electronic products such as electric vehicles and smart phones, the use of lithium batteries has increased significantly, resulting in a rapid increase in the number of retired lithium batteries. If the lithium resources in lithium batteries cannot be effectively recycled, it will not only waste precious resources, but also cause potential pollution to the environment. Therefore, lithium battery recycling has become a hot issue at present.

[0003] However, retired lithium batteries have complex components, including positive electrode materials, negative electrode materials, electrolytes and other additional materials. The chemical properties of these materials vary greatly, and elements such as lithium, cobalt, nickel, and titanium often exist in different chemical forms. During the recycling process, how to effectively extract lithium from these materials and ensure the selectivity and efficiency of the recycling process is a major challenge facing current recycling technology.

[0004] In the existing methods for recycling retired lithium batteries, the pretreatment process is usually complicated and time-consuming, and each step may cause lithium loss. For example, during the pyrolysis process, some lithium may volatilize due to high temperature or react with other elements, resulting in a reduced recovery rate. In addition, lithium loss is also relatively serious during the traditional leaching process, especially under the interference of other metal elements in the leachate, the lithium extraction effect is far from ideal.

[0005] Therefore, it is necessary to provide a new solution to the above technical problems. Summary of the invention

[0006] The purpose of the present application is to provide a method for recovering lithium in a lithium battery, which can achieve selective leaching of lithium and improve the comprehensive yield of lithium in the lithium battery.

[0007] To achieve the above objectives, the technical solutions provided by this application are as follows:

[0008] The present application provides a method for recovering lithium in a lithium battery, which comprises:

[0009] S101: After the lithium battery is decomposed, it is pyrolyzed at 200-500° C. to obtain slag;

[0010] S102: placing the slag in a composite leaching agent, adjusting the pH to 1.5-2.5, leaching lithium in the slag to obtain a leachate; the composite leaching agent includes oxalic acid, amino acid ligands, persulfate and fluoride ions;

[0011] S103: adjusting the pH of the leachate to 5.5-6.2, adding an extractant to the leachate, extracting lithium ions in the leachate, and separating to obtain a lithium-rich organic phase and a lithium-containing waste liquid; the extractant includes a crown ether and an organic phosphate;

[0012] S104: stripping the lithium-rich organic phase to release lithium ions from the organic phase to obtain a lithium-rich stripping solution, and adding a carbonate solution to the lithium-rich stripping solution to obtain a lithium carbonate precipitate.

[0013] In one or more embodiments, the pyrolysis treatment in step S101 includes: mixing the decomposed lithium battery material with lanthanum oxide to obtain a mixed material; wherein the mass of lanthanum oxide is 1-5% of the mass of the lithium battery material; placing the mixed material in a pyrolysis furnace and keeping it at 200-250°C for 20-30 minutes; then heating it to 340-360°C at a heating rate of 2-3°C / min, and keeping it for 1.5-3 hours; then heating it to 400-500°C at a heating rate of 0.5-1°C / min, and keeping it for 3-5 hours.

[0014] In one or more embodiments, the preparation method of the composite leaching agent in step S102 includes: adding oxalic acid, amino acid ligand, fluoride and persulfate to pure water, stirring evenly until completely dissolved, to obtain a composite leaching agent; wherein the molar ratio of oxalic acid, amino acid ligand, fluoride and persulfate is 10:(0.8~1.2):(0.3~0.5):(0.8~1.2).

[0015] In one or more embodiments, the amino acid ligand includes at least one of histidine and aspartic acid; and / or the fluoride includes at least one of potassium fluoride, sodium fluoride and hydrofluoric acid; and / or the persulfate includes at least one of potassium persulfate and sodium persulfate.

[0016] In one or more embodiments, the preparation method of the extractant in step S103 includes: mixing the crown ether and the organic phosphate in a volume ratio of 1:(0.4~0.6), adding kerosene to dilute to obtain a mixed solution; adding isooctyl alcohol to the mixed solution and mixing to obtain an extractant; wherein the volume ratio of the crown ether to the isooctyl alcohol is 1:(0.2~0.3).

[0017] In one or more embodiments, the crown ether includes at least one of 15-crown-5, 18-crown-6, and 12-crown-4; and / or the organic phosphate includes at least one of di(2-ethylhexyl)phosphate, tri(2-ethylhexyl)phosphate, and di(3-methyl-1-butyl)phosphate.

[0018] In one or more embodiments, the lithium ions in the leachate in step S103 are extracted by a multi-stage countercurrent extraction method, and the multi-stage countercurrent extraction method includes: mixing the leachate and the extractant in a volume ratio of 1:1, adding the mixture to the first stage of the extraction tank, stirring for 10 to 15 minutes at a constant temperature of 25°C, and standing for 10 to 15 minutes after stirring to separate the organic phase and the aqueous phase; after separation, collecting the aqueous phase and sending it to the next extraction tank, and temporarily storing the organic phase to prepare for the next round of countercurrent extraction; the number of stages of the multi-stage countercurrent extraction is 3 to 10.

[0019] In one or more embodiments, the stripping method in step S104 includes: adding a dilute hydrochloric acid solution with a concentration of 0.5 mol / L to the lithium-rich organic phase, and the volume ratio of the lithium-rich organic phase to the dilute hydrochloric acid solution is 1:1; stirring at 25°C for 20 to 40 minutes to release lithium ions from the organic phase and enter the aqueous phase; separating the lithium-rich aqueous phase to obtain a lithium-rich stripping solution.

[0020] In one or more embodiments, the waste gas generated during the pyrolysis process of step S101 is treated, and the waste gas treatment method includes: filtering the waste gas generated during the pyrolysis process and then burning it at a temperature of 800-950°C; rapidly cooling the waste gas after combustion to below 200°C within 30 seconds, and performing deacidification, adsorption and catalytic purification treatment on the rapidly cooled waste gas.

[0021] In one or more embodiments, the method further includes: adding a functionalized adsorbent to the lithium-containing waste liquid obtained in step S103, so that the functionalized adsorbent adsorbs lithium ions in the lithium-containing waste liquid; wherein the preparation method of the functionalized adsorbent includes: dispersing the MCM-41 molecular sieve in ethanol, adding aminopropyltriethoxysilane, and ball milling at room temperature for 1 to 1.5 hours; mixing 15-crown-5 and disulfide hydroxyethyltriethoxysilane in ethanol at a molar ratio of 1:1, adding the mixture to the ball-milled MCM-41 molecular sieve, continuing ball milling at room temperature for 2 to 3 hours, and drying at 50 to 70°C to obtain the functionalized adsorbent.

[0022] Compared with the prior art, the method for recovering lithium from a lithium battery provided in the present application can selectively leach lithium from lithium battery materials and reduce the leaching of transition metals through a leaching agent composed of oxalic acid, amino acid ligands, persulfate and fluoride ions; through an extractant comprising crown ethers and organic phosphates, lithium ions in the leachate can be efficiently extracted, and lithium recovery can be achieved in combination with a precipitation method; this method can achieve selective leaching of lithium and improve the comprehensive yield of lithium in lithium batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings required for use in the embodiments or the prior art description are briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 This is a flow chart of a method for recovering lithium from a lithium battery in one embodiment of the present application;

[0025] Figure 2 is an optical image of the slag obtained in Example 1 of the present application;

[0026] Figure 3 This is a scanning electron microscope image of the functionalized adsorbent prepared in Example 1 of the present application;

[0027] Figure 4 This is an optical image of the lithium carbonate recovered in Example 1 of the present application. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present application.

[0029] It should be noted that in the following description, the "%" indicating the amount is a weight basis unless otherwise specified. Unless otherwise specified, all numbers used in this specification and claims to indicate characteristic dimensions, quantities and physical properties should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise specified, the numerical parameters listed in the above specification and the attached claims are approximate values, and those skilled in the art can use the teachings disclosed herein to seek to obtain the desired properties and appropriately change these approximate values. The use of numerical ranges expressed as endpoints includes all numbers within the range and any range within the range, for example, 1 to 5 includes 1, 1.2, 1.4, 1.55, 2, 2.75, 3, 3.80, 4 and 5, etc.

[0030] With the widespread use of lithium batteries in various electronic devices and electric vehicles, the recycling and resource reuse of retired lithium batteries has become increasingly prominent. Traditional lithium recycling technology faces many challenges, including complex recycling processes, large lithium losses, and low recycling efficiency. Most existing recycling methods rely on harsh conditions such as high temperature, high pressure, and strong acid, which not only increases energy consumption and costs, but also increases the risk of environmental pollution. At the same time, in existing recycling technologies, the extraction of lithium is usually interfered with by other metals (such as nickel, cobalt, manganese, etc.), resulting in lithium recovery efficiency that is difficult to meet actual needs. Therefore, there is an urgent need for a technical solution that is efficient, environmentally friendly, and can significantly improve the lithium recovery rate.

[0031] The inventors of the present application recognize that although the existing lithium recovery technology can extract lithium, it has multiple bottlenecks in key links such as pretreatment, leaching, and extraction, especially the chemical similarity between lithium and other metal ions leads to difficulties in the recovery of lithium. In addition, traditional recovery processes often require a large amount of external resources, such as reducing agents, which not only increases costs, but also creates greater environmental pressure. Therefore, the present application proposes a new lithium recovery method that combines low-oxygen low-temperature pyrolysis and composite leaching technology.

[0032] The core idea of ​​this method is to reduce lithium loss and improve recovery rate through a series of simplified and efficient process steps. This method uses pyrolysis treatment to achieve the dissociation of positive and negative electrode materials of lithium batteries without the need for external reducing agents, and promotes the reduction reaction of metal elements such as nickel, cobalt, and manganese, creating favorable conditions for subsequent leaching and extraction steps. The efficient leaching of lithium is promoted by the composite leaching agent, while avoiding the interference of other metal ions, thereby achieving effective extraction of lithium. In the extraction stage, selective extractants are used to efficiently separate lithium ions to ensure the purity and recovery rate of lithium, and finally the lithium ions are converted into lithium carbonate that is easy to store and transport through back extraction.

[0033] Specifically, the technical implementation idea of ​​this application forms a simple and efficient lithium recovery process through the synergistic effect of low-temperature pyrolysis, composite leaching and selective extraction. This solution not only significantly improves the recovery rate of lithium and reduces lithium loss, but also reduces energy consumption and environmental pollution while improving recovery efficiency.

[0034] Please refer to Figure 1 As shown, a flow chart of a method for recovering lithium from a lithium battery in an embodiment of the present application. The method for recovering lithium from a lithium battery specifically comprises the following steps:

[0035] S101: After the lithium battery is decomposed, it is subjected to pyrolysis treatment at 200-500° C. to obtain slag.

[0036] The main purpose of step S101 is to decompose the organic matter (such as battery separators, conductive agents, etc.) in retired lithium batteries and promote the reduction reaction of metal elements in positive and negative electrode materials, thereby achieving effective decomposition and recycling of battery materials. Specifically, pyrolysis is to heat the lithium battery at a temperature range of 200~500℃, so that the organic components inside are decomposed into gas or low molecular weight compounds, and interact with the metal materials in the battery, thereby destroying the original structure of the battery and effectively separating the various components of the battery.

[0037] When implementing step S101, the lithium battery must first be pre-processed, such as mechanically crushing or cutting, to separate the battery shell and internal components to ensure that the chemical substances inside the battery can be fully exposed to the pyrolysis environment. Then, the treated battery material is placed in a pyrolysis furnace and pyrolyzed under controllable temperature conditions. During the pyrolysis process, the diaphragm and other organic matter in the battery will decompose into gases (such as CO, CO2, methane, etc.) or small molecule compounds. These gases and the graphite negative electrode can act as reducing agents. At the same time, the positive electrode material of the battery (such as nickel-cobalt-manganese ternary material) will undergo a reduction reaction during the pyrolysis process, and the oxidation state of some metal elements will be reduced to a lower oxidation state, thereby providing better chemical conditions for subsequent leaching and extraction processes.

[0038] Step S101 removes organic components from the battery through pyrolysis treatment to reduce interference with subsequent leaching and extraction steps. At the same time, pyrolysis can promote the reduction reaction of metal elements and create a favorable chemical environment for the extraction of lithium. For example, lithium batteries usually contain metals such as nickel, cobalt, and manganese. The high-valent states of these metals are usually not easy to react with lithium. Through the reduction effect of pyrolysis, the oxidation state of these metals can be reduced, making them easier to separate from the material. In this process, lithium itself will also be converted into forms such as lithium oxide or lithium carbonate, providing more stable and operable chemicals for subsequent lithium extraction.

[0039] Since step S101 is performed at a relatively low temperature (200-500°C), compared with the traditional high-temperature smelting method, it has lower energy consumption and safer operation. Moreover, this process does not require the addition of an external reducing agent, but uses the organic matter of the battery itself and the graphite in the negative electrode material as the reducing agent, which not only simplifies the process, but also reduces the introduction of external substances and reduces the environmental burden.

[0040] In an exemplary embodiment, the pyrolysis treatment in step S101 includes: mixing the decomposed lithium battery material with lanthanum oxide to obtain a mixed material; wherein the mass of lanthanum oxide is 1-5% of the mass of the lithium battery material; placing the mixed material in a pyrolysis furnace and keeping it at 200-250°C for 20-30 minutes; then heating it to 340-360°C at a heating rate of 2-3°C / min, and keeping it for 1.5-3 hours; then heating it to 400-500°C at a heating rate of 0.5-1°C / min, and keeping it for 3-5 hours.

[0041] The main function of lanthanum oxide (La2O3) as a phase transformation catalyst in the lithium battery recycling process is to promote the phase transformation reaction in the positive electrode material, thereby improving the lithium extraction efficiency. The catalyst accelerates and optimizes the chemical reaction by reducing the energy barrier of the reaction, increasing the reaction rate, and guiding the reaction path during the phase transformation process. Specifically in the phase transformation process in lithium battery recycling, the role of the catalyst is to promote the lattice destruction of the positive electrode material (such as lithium nickel cobalt manganese oxide, LiNiCoMnO2) and the migration of lithium ions, thereby transferring lithium from the solid phase to the liquid phase and improving the lithium extraction efficiency.

[0042] Lanthanum oxide is a rare earth metal oxide with high thermal stability, good oxidizability and excellent catalytic activity. Its crystal structure is usually hexagonal or cubic, which allows lanthanum oxide to remain stable at high temperatures and has a large surface area, which is conducive to contact with reactants. In addition, lanthanum oxide has a certain acidity, which helps to react with metal ions in the positive electrode material and promote the destruction of the lattice structure and phase transformation.

[0043] Lanthanum oxide interacts with the metal oxide surface in the positive electrode material through the active sites on its surface. These active sites can adsorb and activate reactant molecules, promoting the deintercalation and migration of lithium ions. For example, oxygen atoms on the surface of lanthanum oxide can form coordination bonds with lithium ions, helping lithium ions to dissociate from the lattice.

[0044] In addition, lanthanum oxide has good electron transfer ability, which can promote the flow of electrons during phase transformation and maintain the continuous reaction. During the pyrolysis of lithium battery positive electrode materials, the migration of lithium ions is usually accompanied by electron transfer reactions. Lanthanum oxide promotes these redox reactions by providing a medium for electron acceptance or release, thereby enhancing the efficiency of lithium ion deintercalation.

[0045] Keep the temperature at 200-250℃ for 20-30min; this initial heating stage aims to remove moisture and some volatile organic matter from the material. The pretreatment process helps to remove impurities that affect subsequent reactions and provide a good chemical environment for subsequent temperature-raising reactions. Then, slowly increase the temperature to 340-360℃ at a heating rate of 2-3℃ / min and keep it at this temperature for 1.5-3h; the pyrolysis temperature setting at this stage is to activate the reduction process of metal oxides in lithium batteries, so that the chemical reactions of metals such as lithium, nickel, cobalt, and manganese are more complete, and promote the release and extraction of lithium; slow heating helps to avoid uneven heating and thermal stress caused by rapid heating, and ensure the stability of the pyrolysis reaction and the integrity of the material.

[0046] Continue to heat up to 400~500℃, keep warm for 3~5h, and the heating rate is 0.5~1℃ / min. Slow heating is beneficial to the directional regulation of the phase; keeping warm for 3~5h is conducive to the full phase transformation, so that lithium can migrate out of the lattice to form lithium oxide or lithium carbonate.

[0047] In an exemplary embodiment, the waste gas generated during the pyrolysis process of step S101 is treated, and the waste gas treatment method includes: filtering the waste gas generated during the pyrolysis process, and then burning it at a temperature of 800~950℃; the waste gas after combustion treatment is rapidly cooled to below 200℃ within 30s, and the waste gas after rapid cooling is deacidified, adsorbed and catalytically purified.

[0048] The waste gas generated during the pyrolysis process usually contains various harmful gases, such as organic compounds, acidic gases (such as hydrogen chloride, hydrogen fluoride, etc.), and potentially toxic substances (such as dioxins). Therefore, in order to ensure that the treated waste gas meets environmental protection standards, the waste gas must first be filtered to remove particulate matter and impurities. Filtration is usually achieved by using high-efficiency gas filtration equipment (such as bag filters or activated carbon adsorption devices). These devices can effectively remove large particle impurities and dust in the waste gas, so that subsequent combustion and chemical treatment are more efficient.

[0049] After being filtered, the waste gas enters the combustion stage. The combustion treatment of the waste gas is carried out in the temperature range of 800~950℃. The high temperature combustion is to burn and decompose volatile organic compounds (VOCs). The formation of dioxins is usually related to the incomplete combustion of organic substances under low temperature conditions. The high temperature range of 800~950℃ can ensure the complete combustion of organic matter in the waste gas and avoid the formation of harmful substances such as dioxins. At this stage, harmful organic matter in the waste gas (such as organic solvents, chlorides, etc.) will be completely oxidized and decomposed into carbon dioxide and water.

[0050] The exhaust gas after combustion flows to the quenching device. The main purpose of quenching is to quickly reduce the temperature to avoid the re-synthesis of harmful gases such as dioxins. Through the heat exchange system in the quencher, the exhaust gas temperature is quickly reduced from 950°C to below 200°C in a short time. Dioxins are usually easily formed in the temperature range of 300°C to 500°C. This quenching step can effectively block the synthesis process of toxic substances such as dioxins. The quenching method includes cooling towers, spray cooling or high-efficiency heat exchangers to quickly cool the exhaust gas to a safe temperature.

[0051] Acidic gases, heavy metals and some organic pollutants may still remain in the exhaust gas after rapid cooling, so further deacidification, adsorption and catalytic purification treatment are required. Deacidification usually uses alkaline adsorbents (such as lime, sodium hydroxide, etc.) to remove acidic gases (such as hydrogen chloride, sulfide, etc.) in the exhaust gas. Adsorption treatment uses materials such as activated carbon or molecular sieves to remove volatile organic compounds (VOCs) and other harmful substances in the exhaust gas. Catalytic purification treatment uses catalysts (such as platinum or rhodium catalysts) to promote the oxidation reaction of harmful gases at low temperatures, further decompose residual toxic organic matter, such as volatile organic compounds (VOCs), and convert them into harmless gases (such as carbon dioxide and water).

[0052] After these treatment steps, the harmful substances in the exhaust gas are almost completely removed, and the concentration of harmful components in the exhaust gas finally discharged into the atmosphere is lower than the national emission standards.

[0053] S102: placing the slag in a composite leaching agent, adjusting the pH to 1.5-2.5, leaching lithium in the slag to obtain a leachate; the composite leaching agent includes oxalic acid, amino acid ligands, persulfate and fluoride ions.

[0054] The purpose of step S102 is to convert the lithium in the slag from a solid state to a dissolved state through a chemical reaction, and the leaching solution can be obtained after filtering the residue, thereby providing a basis for subsequent extraction and recovery. The composition of the composite leaching agent includes oxalic acid, amino acid ligands, persulfate and fluoride ions, each of which plays a specific role in this process and can effectively promote the leaching and separation of lithium.

[0055] The role of oxalic acid in the composite leaching agent is mainly to provide an acidic environment to promote the release of lithium ions in lithium ore. Oxalic acid is a weak organic acid that can dissolve lithium elements in lithium ore under acidic conditions to form soluble lithium ions. Oxalic acid can not only provide the necessary acidic conditions, but also promote the dissolution of lithium ions, thereby improving the recovery efficiency of lithium. For example, in lithium battery slag, the addition of oxalic acid can destroy the crystal structure of lithium and convert lithium ions from a solid state to an ionic form in the solution, thereby accelerating the leaching process of lithium.

[0056] The role of amino acid ligands in composite leaching agents is to form complexes with lithium ions, enhance the solubility of lithium, and reduce the affinity with other transition metal ions. The amino (-NH2) and carboxyl (-COOH) structures in amino acid ligands can form relatively stable complexes with lithium ions, which makes lithium ions more easily dissolved in the solution. At the same time, amino acid ligands have weak complexing ability for transition metal ions, thereby reducing their solubility and avoiding competitive dissolution of lithium with metals such as nickel and cobalt. By adding amino acid ligands, the composite leaching agent can selectively extract lithium and maintain a relatively high lithium extraction rate.

[0057] The role of fluoride ions is to inhibit the leaching of transition metals by regulating the fluoride ion concentration in the solution and adjusting the redox environment. Fluoride ions can form fluorides with some transition metals such as nickel and cobalt. These fluorides have low solubility in the solution and can inhibit the further dissolution of these metals. Therefore, fluoride ions effectively avoid the co-leaching of metals such as nickel and cobalt, making the lithium extraction process more selective. For example, in the recycling process of lithium batteries, fluoride ions can form fluorides with nickel and cobalt. These fluorides are difficult to dissolve in water, thereby effectively reducing the interference of these metals in the leaching process and ensuring the preferential dissolution of lithium.

[0058] Persulfate (such as potassium persulfate, K2S2O8) is a strong oxidant that helps maintain the oxidation state of transition metals by providing an oxidant, making them more stable and inhibiting their further dissolution. Specifically, potassium persulfate can maintain a high oxidation state of transition metals (such as nickel, cobalt, etc.), which reduces the activity of these metals in solution and inhibits their dissolution. For example, potassium persulfate can oxidize nickel (Ni 2+ ) is the high valence state of nickel (Ni 3+ ), and convert it into insoluble substances through oxidation, thereby reducing its concentration in the leaching solution and increasing the lithium leaching rate.

[0059] During the leaching process, the pH value is set between 1.5 and 2.5. When the pH value is lower than 1.5, the acidity is too strong. Although it can promote the dissolution of lithium, it will also cause other metal ions (such as nickel and cobalt) to be excessively dissolved, thus affecting the selective extraction of lithium; and the acidity is too strong to affect the activity of the amino acid ligand, reducing its selectivity for lithium ions. When the pH value is higher than 2.5, the acidity is too weak and may not effectively promote the dissociation of lithium ions, resulting in poor leaching effect.

[0060] In an exemplary embodiment, the preparation method of the composite leaching agent in step S102 includes: adding oxalic acid, amino acid ligand, fluoride and persulfate to pure water, stirring evenly until completely dissolved, to obtain a composite leaching agent; wherein the molar ratio of oxalic acid, amino acid ligand, fluoride and persulfate is 10:(0.8~1.2):(0.3~0.5):(0.8~1.2).

[0061] The molar ratio of amino acid is set to 0.8~1.2 to ensure that it can form a stable complex with lithium ions in an acidic environment, while avoiding excessive complexation or other negative reactions caused by too much amino acid ligand. Too much amino acid ligand will compete with lithium complexation and reduce lithium recovery, while too little amino acid ligand may not effectively enhance lithium solubility and selectivity.

[0062] The molar ratio of fluoride is set at 0.3-0.5, which is sufficient to form transition metal fluoride without causing excessive consumption of ligands by fluoride ions or instability of lithium complexes. This ratio effectively inhibits the dissolution of transition metals while not significantly affecting the complexation and dissolution of lithium ions.

[0063] The molar ratio of persulfate is set at 0.8-1.2 to ensure sufficient oxidizing capacity to maintain the transition metal ions in the solution in a low-solubility oxidation state. The appropriate molar ratio avoids ligand degradation or other side reactions caused by excessive persulfate, while effectively inhibiting the dissolution and migration of transition metals.

[0064] In an exemplary embodiment, the amino acid ligand includes at least one of histidine and aspartic acid; and / or the fluoride includes at least one of potassium fluoride, sodium fluoride and hydrofluoric acid; and / or the persulfate includes at least one of potassium persulfate and sodium persulfate.

[0065] Histidine is an amino acid with an imidazole group, which is relatively stable in an acidic environment. The imidazole group can form a stable coordination complex with lithium ions, which can effectively improve the solubility of lithium. At the same time, the molecular structure of histidine can reduce the affinity with transition metal ions. In the presence of oxalic acid, fluoride ions and potassium persulfate, the imidazole group of histidine is less likely to be destroyed, so it has strong acid resistance and oxidation resistance, and can maintain its complexation during the leaching process.

[0066] Aspartic acid, as an amino acid containing a carboxyl group, can form a stable complex with lithium ions. Although amino acid ligands usually have certain stability issues in a strong acidic environment, the carboxyl structure of aspartic acid has a high affinity with lithium ions, which helps to enhance the solubility of lithium; and aspartic acid has good resistance to fluoride ions and potassium persulfate, and can avoid strong complexation with transition metal ions, which is suitable for selective leaching of lithium.

[0067] S103: adjusting the pH of the leachate to 5.5-6.2, adding an extractant to the leachate, extracting lithium ions in the leachate, and separating to obtain a lithium-rich organic phase and a lithium-containing waste liquid; the extractant includes crown ethers and organic phosphates.

[0068] In the process of lithium battery recycling, lithium ions and other metal ions (such as nickel, cobalt, etc.) coexist in the leachate. Therefore, lithium needs to be separated from other metal ions through the extraction process. Crown ether is a class of organic compounds with strong affinity, which has the characteristics of coordination reaction with lithium ions. It can effectively form complexes with lithium ions, so that lithium ions are transferred from the aqueous phase to the organic phase. Since crown ether molecules contain multiple oxygen atoms, they have strong complexing ability and can selectively extract lithium ions from the leachate, but are not easy to react with other metal ions. Therefore, it has high selectivity for the extraction of lithium ions. Organic phosphates used in combination with crown ethers are another class of chemical substances with strong solubility, which can enhance the extraction efficiency of lithium ions in the liquid-liquid extraction process; through the synergistic effect with crown ethers, the extraction efficiency of lithium ions can be improved and the interference of other metal ions can be reduced.

[0069] Crown ethers are a class of cyclic polyether molecules whose oxygen atoms in the ring can form stable complexes with cations of specific sizes. Taking 15-crown-5 as an example, its ring diameter is about 5.1 Å, which just matches the hydration radius of lithium ions (about 0.76 Å). Therefore, it can effectively wrap lithium ions through spatial coordination to form a highly stable lithium-crown ether complex. This specific spatial matching makes crown ethers highly selective for lithium ions and reduces their affinity for other transition metal ions. However, the solubility of crown ethers themselves in organic phases is limited, and their coordination ability may not be sufficient to achieve efficient extraction at lower concentrations.

[0070] Organic phosphates (such as di(2-ethylhexyl) phosphate, D2EHPA) are a class of extractants with acidic functional groups that can form stable complexes with metal ions through acid-base neutralization reactions and coordination. In lithium ion extraction, organic phosphates form coordination bonds with lithium ions through their phosphate groups, enhancing the organic phase solubility of lithium ions. In addition, organic phosphates have good organic phase solubility and interfacial activity, and can effectively promote the migration of lithium ions from the aqueous phase to the organic phase. However, when organic phosphates are used alone, the extraction efficiency is not high due to the relatively weak complexing ability of lithium ions in an acidic environment, and the selectivity for lithium ions is insufficient, which easily leads to co-extraction problems.

[0071] The combination of crown ether and organic phosphate can give full play to the complementary advantages of the two, thereby significantly improving the extraction efficiency and selectivity of lithium ions. Crown ether forms a preliminary spatial coordination with lithium ions through its cyclic structure, stabilizes the existence of lithium ions, and provides a more effective coordination environment for organic phosphate. At this time, organic phosphate can further form a double coordination bond with lithium ions through its phosphate group, significantly improving the stability and solubility of the lithium-extractant complex.

[0072] Organic phosphates have good organic phase solubility and can effectively carry crown ether-lithium complexes into the organic phase. The introduction of crown ethers enhances the organic phase solubility of lithium ions, while organic phosphates promote the efficient migration of lithium ions through their interfacial activity. Under the synergistic effect of the two, the extraction selectivity of lithium ions is significantly improved, and the co-extraction of transition metal ions is effectively suppressed.

[0073] In the pH range of 5.5-6.2, crown ethers and organic phosphates are in the most suitable dissociation and coordination state. This pH range ensures that the acidic groups in the extractant molecules are partially dissociated, enhancing their coordination ability with lithium ions, while avoiding excessive dissociation that causes the extractant to be inactivated or non-selective coordination with other metal ions.

[0074] In the pH range of 5.5-6.2, lithium ions mainly exist in the form of hydrated ions (such as [Li(H2O)6] + ). At this time, lithium ions still maintain a high affinity to coordinate with crown ethers and organic phosphates to form stable complexes, which promote their transfer to the organic phase. In the pH range of 5.5-6.2, transition metal ions usually exist in the form of hydroxides, chlorides or sulfates. For example, nickel ions may partially exist in the form of Ni(OH) + or NiCl + The cobalt and manganese ions are similar.

[0075] These transition metal ions are not easy to form stable complexes with crown ethers due to their large ionic radius and multivalent characteristics. At the same time, the coordination ability of organophosphates to these transition metal ions is weak in this pH range, resulting in a decrease in their mobility in the organic phase.

[0076] Therefore, in the pH range of 5.5-6.2, the coordination priority between lithium ions and the extractant is higher than that between transition metal ions. Since the coordination between lithium ions and the extractant is more stable and favorable, it is difficult for transition metal ions to form competitive complexes with the extractant, thereby reducing their migration in the organic phase.

[0077] In an exemplary embodiment, the preparation method of the extractant in step S103 includes: mixing the crown ether and the organic phosphate in a volume ratio of 1:(0.4~0.6), adding kerosene to dilute to obtain a mixed solution; adding isooctyl alcohol to the mixed solution and mixing to obtain an extractant; wherein the volume ratio of the crown ether to isooctyl alcohol is 1:(0.2~0.3).

[0078] The extractant preparation method in step S103 is to prepare a liquid-liquid extractant with strong selectivity, good solubility and easy operation by combining crown ether, organic phosphate, kerosene and isooctyl alcohol, which is mainly used for selectively extracting lithium ions from aqueous phase leachate. Crown ether and organic phosphate are mixed in a volume ratio of 1: (0.4-0.6), diluted with kerosene, and finally isooctyl alcohol is added to form an extractant system with excellent performance.

[0079] Kerosene is used as a diluent in this formula to reduce the viscosity of the extractant, improve the operability of the extraction system, and ensure a good phase separation effect of the organic phase and the aqueous phase during the extraction process. Kerosene is used as an extraction solvent, and its low polarity and good chemical inertness ensure the stability of the chemical components during the extraction process. In addition, the addition of kerosene can also regulate the density of the organic phase, making it easier to separate from the aqueous phase, thereby improving the extraction efficiency. In the present embodiment, the volume of kerosene is preferably about 3 times the total volume of the crown ether and the organic phosphate.

[0080] As a phase modifier, isooctyl alcohol mainly functions to further optimize the interfacial properties and solubility of the extractant. The volume ratio of crown ether to isooctyl alcohol is preferably 1:(0.2-0.3), which can improve the dispersibility of crown ether in kerosene and improve the interfacial tension of the extractant. Isooctyl alcohol is a surfactant, and its addition can reduce the interfacial tension between the organic phase and the aqueous phase and promote the transfer of lithium ions from the aqueous phase to the organic phase. At the same time, the appropriate use of isooctyl alcohol can prevent the phase separation or emulsification problem of the extractant under high-load operating conditions, thereby enhancing the stability of the extractant.

[0081] In an exemplary embodiment, the crown ether includes at least one of 15-crown-5, 18-crown-6, and 12-crown-4; and / or the organic phosphate includes at least one of di(2-ethylhexyl)phosphate, tri(2-ethylhexyl)phosphate, and di(3-methyl-1-butyl)phosphate.

[0082] In an exemplary embodiment, the lithium ions in the leachate in step S103 are extracted by a multi-stage countercurrent extraction method, and the multi-stage countercurrent extraction method includes: mixing the leachate and the extractant in a volume ratio of 1:1, adding the mixture to the first stage of the extraction tank, stirring for 10 to 15 minutes at a constant temperature of 25°C, and standing for 10 to 15 minutes after stirring to separate the organic phase and the aqueous phase; after separation, collecting the aqueous phase and sending it to the next stage extraction tank, and temporarily storing the organic phase to prepare for the next round of countercurrent extraction; repeating the aforementioned extraction steps until the entire multi-stage countercurrent extraction process is completed, and the number of stages of the multi-stage countercurrent extraction is 3 to 10.

[0083] The multi-stage countercurrent extraction method aims to efficiently and selectively transfer lithium ions in the leachate from the aqueous phase to the organic phase through continuous extraction steps, and finally achieve lithium separation and purification. This method utilizes the interaction between the solvent and the aqueous phase, and through multiple repeated extraction steps at a constant temperature and appropriate time, the lithium ions are gradually transferred to the organic solvent, thereby improving the lithium recovery efficiency.

[0084] When performing multi-stage countercurrent extraction, the leachate and the extractant are mixed in a volume ratio of 1:1. This ratio is set to ensure that the contact area between the organic phase and the aqueous phase is maximized, thereby improving the transfer efficiency of lithium ions from the aqueous phase to the organic phase. After mixing, it is added to the first stage of the extraction tank and stirred for 10 to 15 minutes at a constant temperature of 25°C. This temperature range ensures the stability of the extraction reaction and will not affect the solubility and complexation efficiency of lithium ions due to excessively high or low temperatures. The purpose of stirring is to promote full contact between the aqueous phase and the organic phase, making it easier for lithium ions to transfer from the aqueous phase to the organic phase.

[0085] After the stirring is completed, keep it still for a certain period of time (10-15 minutes) to separate the organic phase and the aqueous phase. This stage of standing can ensure the effective separation of the two phases, and the lithium ions rich in the organic phase can be separated from the aqueous phase, avoiding the reduction of lithium recovery rate due to incomplete separation. The aqueous phase in the separation process continues to enter the next extraction tank for the next round of extraction, while the organic phase is temporarily stored to prepare for the next round of countercurrent extraction.

[0086] In the multi-stage countercurrent extraction process, the aqueous phase is sent to the next extraction tank after each stage of extraction, gradually reducing the lithium ion concentration therein. The organic phase continuously extracts more lithium ions through multiple cycles. Each round of extraction will increase the lithium concentration in the organic phase and reduce the lithium concentration in the aqueous phase, thereby achieving the separation and recovery of lithium ions. The multi-stage countercurrent design maximizes the mass transfer efficiency between the organic phase and the aqueous phase, and through repeated dissolution-separation processes, the lithium extraction process is made more thorough.

[0087] S104: stripping the lithium-rich organic phase to release lithium ions from the organic phase to obtain a lithium-rich stripping solution, and adding a carbonate solution to the lithium-rich stripping solution to obtain a lithium carbonate precipitate.

[0088] The purpose of the stripping in step S104 is to release the lithium ions in the lithium-rich organic phase, recover and convert them into lithium carbonate that can be used for industrial applications. Through stripping, the lithium ions are returned from the organic phase to the aqueous phase, and lithium carbonate precipitation is generated by adding a carbonate solution to achieve solid recovery of lithium.

[0089] Stripping is the reverse process of liquid-liquid extraction, and its purpose is to change the solvent environment to promote the transfer of extracted lithium ions from the organic phase to the aqueous phase. Usually, stripping is done by adding a solution with strong hydrophilicity to dissociate the lithium ions in the extractant from the complex, thereby completing the release of lithium ions. The stripping process is usually carried out in the aqueous phase by controlling the pH value or electrolyte concentration to allow lithium ions to enter the aqueous phase from the extractant, and finally obtain a lithium-rich aqueous solution.

[0090] The aqueous phase after stripping contains a large amount of lithium ions. A carbonate solution (usually sodium carbonate or potassium carbonate) is added to the aqueous phase to generate insoluble lithium carbonate precipitate through chemical reaction. The carbonate reacts with the lithium ions in the water to generate lithium carbonate precipitate. The chemical equation of this reaction can be expressed as:

[0091]

[0092] The resulting lithium carbonate precipitate can be separated by filtration, centrifugation or sedimentation, and the resulting lithium carbonate powder can be used in industrial applications such as battery production.

[0093] In an exemplary embodiment, the stripping method in step S104 includes: adding a dilute hydrochloric acid solution with a concentration of 0.5 mol / L to the lithium-rich organic phase, and the volume ratio of the lithium-rich organic phase to the dilute hydrochloric acid solution is 1:1; stirring at 25°C for 20 to 40 minutes to release lithium ions from the organic phase and enter the aqueous phase; separating the lithium-rich aqueous phase to obtain a lithium-rich stripping solution.

[0094] In this embodiment, dilute hydrochloric acid is selected as the stripping agent. Hydrochloric acid has a strong acidity. When it is added to the lithium-rich organic phase, it can effectively change the desorption environment of lithium ions in the lithium-rich organic phase. Specifically, the hydrogen ions (H + ) reacts with the lithium complex in the organic phase, weakening its binding force with the ligand in the organic phase, causing the lithium ions to dissociate from the complex and then transfer to the aqueous phase. This process is similar to the principle of acid hydrolysis, where hydrochloric acid releases lithium ions from the organic phase by lowering the pH value of the solution.

[0095] The lithium-rich organic phase is mixed with a dilute hydrochloric acid solution with a concentration of 0.5 mol / L in a volume ratio of 1:1. This ratio ensures that the concentration of the acidic solution is sufficient to effectively release lithium ions during the stripping process, while avoiding other unnecessary side reactions caused by excessive acidity of the solution. Stir the mixed solution at a constant temperature of 25°C for 20 to 40 minutes. This stirring time is set to ensure that the acidic solution is in full contact with the organic solvent so that the lithium ions can be completely released from the organic phase into the aqueous phase.

[0096] After stirring, the mixture is allowed to stand and the organic phase and aqueous phase in the mixture will separate into layers. Due to the density difference between the organic solvent and the aqueous phase, the lithium-rich aqueous phase will be distributed in the upper or lower layer, while the organic phase can be separated. By separating the aqueous phase and collecting it, a lithium-rich stripping solution can be obtained. The stripping solution contains the lithium ions that have been desorbed from the organic phase and provides a basis for the subsequent precipitation reaction.

[0097] In an exemplary embodiment, the method further includes: adding a functionalized adsorbent to the lithium-containing waste liquid obtained in step S103, so that the functionalized adsorbent adsorbs lithium ions in the lithium-containing waste liquid; wherein the preparation method of the functionalized adsorbent includes: dispersing the MCM-41 molecular sieve in ethanol, adding aminopropyltriethoxysilane, and ball milling at room temperature for 1 to 1.5 hours; mixing 15-crown-5 and disulfide hydroxyethyltriethoxysilane in ethanol at a molar ratio of 1:1, adding the mixture to the ball-milled MCM-41 molecular sieve, continuing ball milling at room temperature for 2 to 3 hours, and drying at 50 to 70°C to obtain the functionalized adsorbent.

[0098] The lithium ions in the lithium-containing waste liquid obtained in step S103 can be further recovered by an adsorbent to improve the recovery efficiency of lithium. To this end, this embodiment uses a functionalized adsorbent. Specifically, the functionalized adsorbent is modified by modifying the MCM-41 molecular sieve with specific chemical substances to enhance the ability to adsorb lithium ions.

[0099] MCM-41 molecular sieve is a mesoporous material with a high specific surface area and a relatively large pore structure, making it very suitable as an adsorbent carrier. In the step of preparing the functionalized adsorbent, the MCM-41 molecular sieve is first dispersed in ethanol, and then aminopropyltriethoxysilane (APTES) is added. Aminopropyltriethoxysilane is an organosilane reagent that can react with the siloxy groups on the surface of MCM-41 through its amino (-NH2) group to form a covalent bond, thereby introducing amino groups on the surface of the molecular sieve. This amino functionalization process can increase the affinity between the MCM-41 surface and lithium ions, because the amino group can interact with lithium ions through coordination, enhancing its adsorption performance.

[0100] Next, 15-crown-5 and disulfide hydroxyethyl triethoxysilane (TEOS-GA) were mixed and reacted in ethanol at a molar ratio of 1:1. Disulfide hydroxyethyl triethoxysilane, as an organic silicon compound, can form a stable silicon-oxygen bond with 15-crown-5 to form a stable silane bridge. The silane bridge solution was added to the amino-treated MCM-41 molecular sieve and continued to be ball-milled at room temperature for 2 to 3 hours, so that 15-crown-5 can be firmly connected to the surface of the MCM-41 molecular sieve through silicon-oxygen bonds. Then, it was dried at 50 to 70 ° C to obtain the final functionalized adsorbent.

[0101] After ball milling and drying, the functionalized adsorbent not only retains the original pore structure of the MCM-41 molecular sieve, but also adds functional groups such as amino and 15-crown-5 on the surface. These groups can form coordination complexes with lithium ions, thereby greatly improving the adsorption capacity of the adsorbent for lithium ions. The functionalized adsorbent can effectively remove lithium ions from lithium-containing waste liquid through efficient adsorption of lithium ions, thereby improving the recovery efficiency of lithium.

[0102] The present application is further described below in conjunction with specific embodiments.

[0103] Example 1: (1) Disassembly of lithium battery

[0104] The retired lithium-ion batteries are discharged and disassembled to obtain electrolyte, adhesive, separator, positive electrode material and graphite negative electrode.

[0105] (2) Pyrolysis treatment

[0106] The decomposed electrolyte, adhesive, diaphragm, positive electrode material and graphite negative electrode are mixed with lanthanum oxide at a mass ratio of 100:3 to obtain a mixed material; the mixed material is placed in a pyrolysis furnace, and high-purity nitrogen is introduced at a flow rate of 200 mL / min to replace the air in the furnace for 30 minutes to ensure that the furnace is in an inert atmosphere.

[0107] Carry out low-temperature pyrolysis, heating from room temperature to 200°C and keeping the temperature for 30 minutes at a heating rate of 5°C / min, in order to remove moisture and volatile substances in the material; continue to heat to 350°C at a heating rate of 2°C / min to start the initial reaction of phase transformation; keep at 350°C for 2 hours to promote lattice destruction and initial phase transformation of the positive electrode material; continue to heat to 450°C at a heating rate of 1°C / min, and slow heating is beneficial to the directional regulation of the phase; keep at 450°C for 4 hours to fully carry out the phase transformation and make lithium migrate from the lattice to form lithium oxide or lithium carbonate.

[0108] After the pyrolysis is completed, the heating system is turned off and the furnace is allowed to cool naturally to room temperature. At the same time, nitrogen is continuously introduced to prevent the material from being oxidized by contact with air at high temperature. After cooling, the material is crushed to micron level to obtain slag (black powder with a lithium content of 10.31%). Figure 2 This is an optical image of the slag obtained in Example 1.

[0109] (3) Leaching

[0110] 100g of slag is added to the composite leaching agent, and the solid-liquid ratio of slag to composite leaching agent is 1:10 (i.e., 100mL of composite leaching agent corresponds to every 10g of slag). The composite leaching agent consists of oxalic acid (concentration of 0.5mol / L), histidine (concentration of 0.05mol / L), potassium fluoride (concentration of 0.02mol / L), potassium persulfate (concentration of 0.05mol / L) and water (solvent). Adjust the pH to about 1.5, stir at 300 rpm for 4h at 40℃ to leach lithium ions in the slag.

[0111] During the leaching process, monitor the pH value of the solution. The initial pH value is about 1.5, due to the acidic effect of oxalic acid. As the reaction proceeds, lithium ions transfer from the solid phase to the liquid phase, and the pH value of the solution may rise slightly. In order to maintain the stability of the leaching conditions, add oxalic acid solution appropriately to ensure that the pH value is maintained between 1.5 and 2.0.

[0112] After leaching is completed, solid-liquid separation is performed. The slurry is filtered by vacuum filtration to obtain leaching solution and filter residue. The filter residue is washed three times with a small amount of deionized water, and the washing solution is combined with the main leaching solution to reduce lithium loss.

[0113] (4) Extraction

[0114] The pH of the leachate was adjusted to 5.5, and the leachate and the extractant were mixed in a volume ratio of 1:1, wherein the extractant consisted of 15-crown-5, di(2-ethylhexyl) phosphate, kerosene and isooctyl alcohol in a volume ratio of 1:0.5:4.5:0.3.

[0115] During the extraction process, a multi-stage countercurrent extraction method is used: the leachate and the extractant solution are added to the first-stage extraction tank in the same ratio (1:1, volume ratio). Stir at a constant temperature of 25°C for 15 minutes at a speed of 200rpm. After completion, let it stand for 10 minutes, and after the phases are completely separated, collect the aqueous phase and the organic phase. The aqueous phase enters the next stage of extraction, and the organic phase is temporarily stored. The entire extraction process has five stages, and the above operation is repeated at each stage. After the extraction is completed, all lithium-rich organic phases and lithium-containing waste liquid (aqueous phase) are collected.

[0116] (5) Stripping

[0117] The stripping agent is a 0.5 mol / L dilute hydrochloric acid solution. The lithium-rich organic phase is mixed with the stripping agent in a volume ratio of 1:1 and stirred at 25°C for 30 minutes. Due to the competition of hydrogen ions, lithium ions are released from the extractant and enter the aqueous phase. After stirring, the phases are allowed to stand and the aqueous phase is collected as the lithium-rich stripping solution.

[0118] (6) Adsorption

[0119] Functionalized adsorbents were added to the low-concentration lithium-containing waste liquid after extraction. The functionalized adsorbent was prepared by dispersing MCM-41 molecular sieves in ethanol, adding aminopropyltriethoxysilane (APTES), and ball milling at room temperature for 1 hour to aminize the MCM-41 molecular sieves. Then, 15-crown-5 and disulfide hydroxyethyltriethoxysilane (TEOS-GA) were reacted in ethanol at a molar ratio of 1:1 to form a silane bridge. The silane bridge solution was slowly added to the aminized MCM-41 molecular sieves, and ball milling was continued at room temperature for 2 hours to ensure that 15-crown-5 was firmly connected to the alumina surface through silicon-oxygen bonds. Finally, the final functionalized adsorbent was obtained by drying at 60°C for 12 hours. Figure 3 This is a scanning electron microscope image of the functionalized adsorbent prepared in Example 1.

[0120] Functionalized adsorbent was added to the lithium-containing waste liquid at a solid-liquid ratio of 1:200 (mass-to-volume ratio, i.e., 5 g of adsorbent was added per liter of lithium-containing waste liquid), and adsorption was carried out on a constant temperature shaker at 25°C and stirred at a speed of 150 rpm to ensure that the adsorbent was in full contact with the lithium-containing waste liquid. After the adsorption was completed, the adsorbent was separated from the waste liquid by vacuum filtration.

[0121] A 0.5 mol / L hydrochloric acid solution was used as a desorbent. The adsorbent after lithium adsorption was added to the desorbent at a mass volume ratio of 1:20. The mixture was stirred at 150 rpm for 3 h at 25 °C to desorb lithium ions from the adsorbent and enter the solution. After desorption was completed, the adsorbent and the desorption liquid were separated by filtration.

[0122] (7) Sedimentation

[0123] The lithium-rich stripping solution in step (5) and the desorption solution in step (6) are mixed to obtain a lithium solution. In order to further concentrate the lithium solution, an evaporation concentration method is adopted. The lithium solution is placed in a rotary evaporator, and the volume of the lithium solution is reduced to 1 / 3 of the original volume under the conditions of 60°C and reduced pressure (-0.08MPa), so that the lithium ion concentration is increased.

[0124] Add saturated sodium carbonate (Na2CO3) solution dropwise to the concentrated lithium solution, while keeping the solution temperature at 60°C and stirring at 300 rpm. Controlling the pH value to around 10 is conducive to the formation of lithium carbonate. With the addition of sodium carbonate, lithium ions combine with carbonate ions to form a white lithium carbonate precipitate. To ensure complete precipitation, continue stirring for 1 hour.

[0125] After the precipitation is formed, vacuum filtration is used for solid-liquid separation. The filter cake is the crude lithium carbonate product. In order to improve the purity, the filter cake is washed; it is washed three times with deionized water (about 60°C), and the volume of each washing liquid is twice the volume of the filter cake to remove soluble impurities. After washing, the filter cake is dried in an oven at 80°C for 12 hours to obtain lithium carbonate with higher purity. Figure 4 This is an optical image of the lithium carbonate recovered in Example 1.

[0126] Example 2: The difference compared with Example 1 is that lanthanum oxide is not added in the pyrolysis treatment step of Example 2; the remaining steps and conditions are consistent with Example 1.

[0127] Example 3: The difference compared with Example 1 is that the pyrolysis temperature in the pyrolysis treatment step of Example 3 is first increased from room temperature to 200°C and kept warm for 30 minutes at a heating rate of 5°C / min; then continued to be heated to 450°C at a heating rate of 2°C / min, and kept warm at 450°C for 6 hours; the remaining steps and conditions are consistent with Example 1.

[0128] Example 4: The difference compared with Example 1 is that the initial pH value in the leaching step of Example 4 is about 2.5, and the pH value is maintained between 2.5 and 2.7 during the leaching process; the remaining steps and conditions are consistent with Example 1.

[0129] Example 5: The difference compared with Example 1 is that in the leaching step of Example 5, the histidine in the composite leaching agent is replaced by tyrosine; the remaining steps and conditions are consistent with Example 1.

[0130] Example 6: The difference compared with Example 1 is that isooctyl alcohol is not added as the extractant in the extraction step of Example 6; the remaining steps and conditions are consistent with those of Example 1.

[0131] Example 7: The difference compared with Example 1 is that the pH of the leaching solution in the extraction step of Example 7 is adjusted to 6.2; the remaining steps and conditions are consistent with Example 1.

[0132] Example 8: The difference compared with Example 1 is that in the extraction step of Example 8, 15-crown-5 in the extractant is replaced by 18-crown-6; the remaining steps and conditions are consistent with Example 1.

[0133] Example 9: The difference compared with Example 1 is that in the extraction step of Example 9, di(2-ethylhexyl) phosphate in the extractant is replaced by di(3-methyl-1-butyl) phosphate; the remaining steps and conditions are consistent with Example 1.

[0134] Example 10: The difference compared with Example 1 is that the adsorbent in the adsorption step of Example 10 is untreated MCM-41 molecular sieve; the remaining steps and conditions are consistent with Example 1.

[0135] Comparative Example 1: The difference compared with Example 1 is that no amino acid ligand (histidine) is added to the composite leaching agent in the leaching step of Comparative Example 1; the remaining steps and conditions are consistent with Example 1.

[0136] Comparative Example 2: The difference compared with Example 1 is that no fluoride ion (potassium fluoride) is added to the composite leaching agent in the leaching step of Comparative Example 2; the remaining steps and conditions are consistent with those of Example 1.

[0137] Comparative Example 3: The difference compared with Example 1 is that no persulfate (potassium persulfate) is added to the composite leaching agent in the leaching step of Comparative Example 3; the remaining steps and conditions are consistent with those of Example 1.

[0138] Comparative Example 4: The difference compared with Example 1 is that the initial pH value in the leaching step of Comparative Example 4 is about 1, and the pH value is maintained between 1 and 1.3 during the leaching process; the remaining steps and conditions are consistent with Example 1.

[0139] Comparative Example 5: The difference compared with Example 1 is that the initial pH value in the leaching step of Comparative Example 5 is about 3, and the pH value is maintained between 3 and 3.3 during the leaching process; the remaining steps and conditions are consistent with Example 1.

[0140] Comparative Example 6: The difference compared with Example 1 is that the pH of the leaching solution in the extraction step of Comparative Example 6 is adjusted to 5; the remaining steps and conditions are consistent with Example 1.

[0141] Comparative Example 7: The difference compared with Example 1 is that the pH of the leaching solution in the extraction step of Comparative Example 7 is adjusted to 6.5; the remaining steps and conditions are consistent with Example 1.

[0142] Comparative Example 8: The difference compared with Example 1 is that crown ether (15-crown-5) is not added as the extractant in the extraction step of Comparative Example 8; the remaining steps and conditions are consistent with those of Example 1.

[0143] Comparative Example 9: The difference compared with Example 1 is that in the extraction step of Comparative Example 9, no organic phosphate (di(2-ethylhexyl) phosphate) is added as the extractant; the remaining steps and conditions are consistent with those of Example 1.

[0144] Recycling effect evaluation

[0145] The lithium carbonate recovered in Examples 1 to 10 and Comparative Examples 1 to 9 was tested for chemical composition, and the recovery effects of each Example and Comparative Example were analyzed. The results are shown in Table 1:

[0146] Table 1 - Recovery effect test results

[0147]

[0148] In summary, the method for recovering lithium from a lithium battery provided in the present application can selectively leach lithium from lithium battery materials and reduce the leaching of transition metals through a leaching agent composed of oxalic acid, amino acid ligands, persulfate and fluoride ions; through an extractant comprising crown ethers and organic phosphates, lithium ions in the leachate can be efficiently extracted, and lithium recovery can be achieved in combination with a precipitation method; this method can achieve selective leaching of lithium and improve the comprehensive yield of lithium in lithium batteries.

[0149] It is obvious to those skilled in the art that the present application is not limited to the details of the exemplary embodiments described above, and that the present application can be implemented in other specific forms without departing from the spirit or essential features of the present application. Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of the present application is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present application. Any reference numeral in a claim should not be regarded as limiting the claim to which it relates.

[0150] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for recovering lithium from a lithium battery, characterized in that: include: S101: After the lithium battery is decomposed, it is pyrolyzed at 200-500° C. to obtain slag; S102: placing the slag in a composite leaching agent, adjusting the pH to 1.5-2.5, leaching lithium in the slag to obtain a leachate; the composite leaching agent includes oxalic acid, amino acid ligands, persulfate and fluoride ions; S103: adjusting the pH of the leachate to 5.5-6.2, adding an extractant to the leachate, extracting lithium ions in the leachate, and separating to obtain a lithium-rich organic phase and a lithium-containing waste liquid; the extractant includes a crown ether and an organic phosphate; S104: stripping the lithium-rich organic phase to release lithium ions from the organic phase to obtain a lithium-rich stripping solution, and adding a carbonate solution to the lithium-rich stripping solution to obtain a lithium carbonate precipitate.

2. The method for recovering lithium from a lithium battery according to claim 1, characterized in that: The pyrolysis treatment in step S101 includes: The decomposed lithium battery material is mixed with lanthanum oxide to obtain a mixed material; wherein the mass of lanthanum oxide is 1-5% of the mass of the lithium battery material; The mixed material is placed in a pyrolysis furnace and kept at 200-250°C for 20-30 minutes; then the temperature is increased to 340-360°C at a heating rate of 2-3°C / min and kept for 1.5-3 hours; then the temperature is increased to 400-500°C at a heating rate of 0.5-1°C / min and kept for 3-5 hours.

3. The method for recovering lithium from a lithium battery according to claim 1, characterized in that: The preparation method of the composite leaching agent in step S102 includes: Add oxalic acid, amino acid ligand, fluoride and persulfate into pure water, stir evenly until completely dissolved, and obtain a composite leaching agent; wherein the molar ratio of oxalic acid, amino acid ligand, fluoride and persulfate is 10:(0.8~1.2):(0.3~0.5):(0.8~1.2).

4. The method for recovering lithium from a lithium battery according to claim 3, characterized in that: The amino acid ligand comprises at least one of histidine and aspartic acid; and / or The fluoride comprises at least one of potassium fluoride, sodium fluoride and hydrofluoric acid; and / or The persulfate includes at least one of potassium persulfate and sodium persulfate.

5. The method for recovering lithium from a lithium battery according to claim 1, characterized in that: The preparation method of the extractant in step S103 includes: The crown ether and the organic phosphate are mixed in a volume ratio of 1:(0.4-0.6), and kerosene is added for dilution to obtain a mixed solution; Add isooctyl alcohol to the mixed solution and mix well to obtain an extractant; wherein the volume ratio of the crown ether to the isooctyl alcohol is 1:(0.2-0.3).

6. The method for recovering lithium from a lithium battery according to claim 5, characterized in that: The crown ether includes at least one of 15-crown-5, 18-crown-6, and 12-crown-4; and / or The organic phosphate includes at least one of di(2-ethylhexyl)phosphate, tri(2-ethylhexyl)phosphate, and di(3-methyl-1-butyl)phosphate.

7. The method for recovering lithium from a lithium battery according to claim 1, characterized in that: In step S103, lithium ions in the leachate are extracted by a multi-stage countercurrent extraction method, and the multi-stage countercurrent extraction method includes: After mixing the leaching solution and the extractant in a volume ratio of 1:1, add them to the first stage of the extraction tank, stir them for 10-15 minutes at a constant temperature of 25°C, and let them stand for 10-15 minutes after stirring to separate the organic phase and the aqueous phase; After separation, the aqueous phase is collected and sent to the next extraction tank, while the organic phase is temporarily stored in preparation for the next round of countercurrent extraction; the number of stages of multi-stage countercurrent extraction is 3 to 10.

8. The method for recovering lithium from a lithium battery according to claim 1, characterized in that: The stripping method in step S104 includes: Adding a 0.5 mol / L dilute hydrochloric acid solution to the lithium-rich organic phase, wherein the volume ratio of the lithium-rich organic phase to the dilute hydrochloric acid solution is 1:1; Stir at 25°C for 20-40 minutes to release lithium ions from the organic phase into the aqueous phase; The lithium-rich aqueous phase is separated to obtain a lithium-rich stripping solution.

9. The method for recovering lithium from a lithium battery according to claim 1, characterized in that: The waste gas generated during the pyrolysis process of step S101 is treated, and the waste gas treatment method includes: After filtering the waste gas generated during the pyrolysis process, it is burned at a temperature of 800-950°C; The exhaust gas after combustion treatment is rapidly cooled to below 200°C within 30 seconds, and the rapidly cooled exhaust gas is subjected to deacidification, adsorption and catalytic purification treatment.

10. The method for recovering lithium from a lithium battery according to claim 1, characterized in that: The method further comprises: Adding a functionalized adsorbent to the lithium-containing waste liquid obtained in step S103, so that the functionalized adsorbent adsorbs lithium ions in the lithium-containing waste liquid; wherein the preparation method of the functionalized adsorbent comprises: Disperse MCM-41 molecular sieve in ethanol, add aminopropyltriethoxysilane, and ball-mill for 1-1.5 h at room temperature; 15-crown-5 and disulfide hydroxyethyltriethoxysilane were mixed in ethanol at a molar ratio of 1:1, added to the ball-milled MCM-41 molecular sieve, and continued to ball-mill for 2-3 hours at room temperature, and then dried at 50-70°C to obtain a functionalized adsorbent.

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