Short-process recovery method for lithium, cobalt and nickel in solid-phase reduction leaching lithium battery positive electrode waste

Abstract

The invention provides a short-process recovery method for lithium, cobalt and nickel in a solid-phase reduction leaching lithium battery positive electrode waste material. The method comprises the following steps: S1, mixing the positive electrode waste material containing lithium, cobalt and nickel oxides with a reducing agent according to a mass ratio to obtain a mixture; s2, roasting the mixture in an inert atmosphere to obtain a roasted product, wherein the roasting enables the high-valence metal oxide to be reduced into soluble salt; s3, mixing the roasted product with water according to a solid-to-liquid ratio, and leaching to obtain a leaching solution, wherein the leaching solution contains lithium-cobalt-nickel soluble salt; and S4, further treating the leachate to separate and recover metal elements such as lithium, cobalt and nickel. The process is remarkably shortened, the environmental load is reduced, efficient and green recovery is achieved, the recovery rate is high, the energy consumption is low, the purity is excellent, and a short-process, efficient and environment-friendly technical path is provided for resource utilization of the waste lithium batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium battery recycling technology, and in particular to a short-process method for the recovery of lithium, cobalt, and nickel from lithium battery cathode waste by solid-phase reduction leaching. Background Technology

[0002] Waste lithium-ion battery cathode materials contain large amounts of high-value metals such as lithium, cobalt, and nickel, which are crucial for the sustainable development of the new energy industry. With the rapid increase in the amount of discarded batteries, efficiently recovering these metals from cathode waste has become one of the most urgent tasks in resource recycling. Traditional recycling mainly relies on hydrometallurgical processes, which use strong acids to dissolve the metals in the waste and then extract the target metals through multi-step separation. While this method is widely used, it has revealed a series of unavoidable difficulties in actual operation.

[0003] When processing cathode waste, wet processes must address the fact that metals in the material exist in the form of high-valence oxides. For example, cobalt exists in a trivalent form, and nickel in a trivalent or divalent form, stably bound in the crystal lattice. These high-valence oxides are chemically extremely stable, hardly reacting with water or weak acids. They can only be barely dissolved by using high-concentration sulfuric acid with the addition of strong reducing agents. This directly leads to huge acid consumption and generates large amounts of wastewater containing heavy metals and sulfate that are difficult to treat. Even more challenging is that even after consuming large amounts of acid to dissolve the material, subsequent processes such as extraction, precipitation, and impurity removal are still required to separate lithium, cobalt, and nickel one by one. The entire process is lengthy, and even slight fluctuations in conditions can cause metal mixing or loss.

[0004] Of all the difficulties, the most critical bottleneck lies in the sharp conflict between the chemical stability of high-priced metal oxides and the subsequent requirement for efficient separation: without destroying this high stability, the metal cannot enter the solution; however, forcibly destroying it with strong acid inevitably leads to a chain reaction of high acid consumption, high pollution, and a long process. This conflict makes it difficult to reconcile the two opposing requirements of "complete dissolution" and "minimizing acid use and waste generation" in the recycling process.

[0005] Therefore, how to convert highly chemically stable high-valence lithium cobalt nickel oxides in cathode waste into water-soluble salts without using strong acids, so as to enable the metal to quickly enter the solution and be efficiently separated thereafter, has become a key issue restricting the short-process and green recycling of waste lithium battery cathode materials. Summary of the Invention

[0006] To address the technical problems mentioned in the background section, this invention provides a short-process method for the solid-phase reduction leaching of lithium-cobalt-nickel recovery from lithium-ion battery cathode waste, comprising: S1, mixing cathode waste containing lithium-cobalt-nickel oxides with a reducing agent at a mass ratio to obtain a mixture; S2, calcining the mixture under an inert atmosphere to obtain a calcined product, wherein the calcination reduces the high-valence metal oxides to soluble salts; S3, mixing the calcined product with water at a solid-liquid ratio for leaching to obtain a leachate, wherein the leachate contains soluble lithium-cobalt-nickel salts;

[0007] S4, the leachate is further processed to separate and recover lithium, cobalt and nickel metal elements.

[0008] Furthermore, step S1 also includes: performing preliminary cleaning of the positive electrode waste to remove any impurities that may exist on the surface.

[0009] Furthermore, step S1 further includes: step S11, crushing the positive electrode waste to a preset particle size and then mixing it with a reducing agent; step S12, determining the amount of reducing agent according to a mass ratio, wherein the mass ratio is the mass ratio of the reducing agent to the positive electrode waste; and step S13, the reducing agent in the mixture is uniformly distributed on the surface of the positive electrode waste particles.

[0010] Further, step S11 includes: step S111, the reducing agent is a carbon-based reducing agent or an organic reducing agent; step S112, the carbon-based reducing agent and the organic reducing agent provide reducing capacity at a mass ratio; step S113, the type of reducing agent is adjusted according to the metal oxide content in the cathode waste.

[0011] Furthermore, step S113 includes:

[0012] The adjustment process includes first sampling and analyzing the cathode waste, using inductively coupled plasma atomic emission spectrometry to determine the content of lithium, cobalt, and nickel. Based on the analysis results, if the proportion of cobalt and nickel is high, a strong reducing carbon-based reducing agent is selected; if the proportion of lithium is high, a mild organic reducing agent is selected.

[0013] Further, step S2 includes: step S21, placing the mixture in a calcination device and introducing an inert gas to form an inert atmosphere; step S22, heating the mixture to the calcination temperature under the inert atmosphere for calcination; step S23, during the calcination process, the high-valence metal oxide is gradually reduced to a soluble salt to obtain the calcined product.

[0014] Further, step S22 includes: step S221, the inert gas is nitrogen or argon; step S222, the roasting conditions are determined by the combination of roasting temperature and roasting time; step S223, the roasting conditions selectively reduce the metal oxides in the mixture; step S224, the inert atmosphere is adjusted by monitoring the gas composition during the roasting process.

[0015] Furthermore, step S3 includes: step S31, adding the roasted product to water to form a slurry; step S32, adjusting the pH value of the slurry and then stirring to leach; step S33, separating the slurry to obtain a leachate, wherein the lithium cobalt nickel soluble salts in the leachate are dissolved.

[0016] Furthermore, step S32 includes: step S321, adjusting the pH value of the slurry to an acidic range by adding a pH adjuster; step S322, keeping the soluble salts dissolved at the pH value; step S323, stirring to ensure that the calcined product is fully in contact with water; and step S324, using the filtrate obtained by solid-liquid separation as the final leachate.

[0017] Furthermore, step S4 includes:

[0018] Step S41: Filter and purify the leachate to improve the clarity of the solution;

[0019] Step S42: Add a precipitant to the purified leachate to separate cobalt and nickel;

[0020] Step S43: Wash and dry the separated cobalt-nickel precipitate;

[0021] Step S44: Add carbonate to the remaining solution to precipitate lithium ions;

[0022] Step S45: Separate and purify the lithium carbonate precipitate.

[0023] The technical solution provided by this invention has the following beneficial effects:

[0024] This invention discloses a short-process recovery method for lithium, cobalt, and nickel from lithium-ion battery cathode waste through solid-phase reduction leaching. Addressing the challenges of traditional wet recycling processes, such as high acid consumption, severe wastewater pollution, long processes, and difficulties in directly leaching high-valent metal oxides, the core step involves thoroughly mixing cathode waste with a reducing agent at a specific mass ratio, followed by reduction roasting under an inert atmosphere. This selectively converts chemically stable high-valent lithium, cobalt, and nickel oxides into water-soluble salts such as lithium carbonate and cobalt oxalate. Subsequent direct water leaching yields a soluble salt leachate containing the target metals, which is then further separated and recovered as lithium, cobalt, and nickel. This invention cleverly integrates premixing uniformity control, inert atmosphere-protected roasting, optimized conditions for selective reduction, and gentle water leaching separation. It avoids the use of strong acids and complex pretreatment, significantly shortening the process and reducing environmental impact. This achieves efficient and green recycling with high recovery rates, low energy consumption, and excellent purity, providing a short-process, efficient, and environmentally friendly technical path for the resource utilization of spent lithium-ion batteries. Attached Figure Description

[0025] Figure 1This is a flowchart of the short-process recovery method for lithium, cobalt, and nickel from lithium battery cathode waste by solid-phase reduction leaching according to the present invention. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] like Figure 1 As shown, this invention provides a short-process recovery method for lithium, cobalt, and nickel from lithium-ion battery cathode waste via solid-phase reduction leaching. The aim is to achieve efficient recycling of cathode waste containing lithium, cobalt, and nickel oxides, extracting valuable metal elements and forming soluble salts for subsequent separation and reuse. The technical solution of this invention is described in detail below with reference to specific embodiments to make the objectives, technical solutions, and advantages of this invention clearer. In one embodiment, the lithium-ion battery cathode waste recovery method provided by this invention includes multiple steps, covering a complete process from waste pretreatment to metal element leaching. The overall method is based on reduction roasting, converting high-valence metal oxides into soluble salts through chemical reactions, and combining this with a leaching process to achieve effective separation of metal elements. The specific implementation process unfolds in a logical order, ensuring that the technical features of each step are supported in detail.

[0028] Specifically, the method includes: S1, mixing cathode waste containing lithium cobalt nickel oxide with a reducing agent in a mass ratio to obtain a mixture.

[0029] This step is the starting point of the entire recycling process, aiming to ensure sufficient contact between the reducing agent and the waste through physical mixing, laying the foundation for subsequent chemical reactions. Cathode waste containing lithium, cobalt, and nickel oxides typically originates from the dismantling of spent lithium batteries, such as cathode materials from electric vehicle batteries or portable electronic device batteries. These wastes mainly contain metallic elements such as lithium, cobalt, and nickel, existing in oxide form, exhibiting high chemical stability and being difficult to dissolve directly. Therefore, mixing with a reducing agent is necessary to create conditions for the subsequent roasting and reduction reaction. Specifically, in step S1, the cathode waste is first preliminarily cleaned to remove any impurities that may be present on the surface, such as residual electrolyte or adhered non-metallic materials. The cleaned waste is then mixed with the reducing agent according to a preset mass ratio. The mass ratio is determined based on the content of metal oxides in the waste and the reducing capacity of the reducing agent, usually requiring experimental data or theoretical calculations to determine the appropriate proportion. The mixing process can be completed in a stirring device, such as a planetary ball mill or a high-speed mixer, ensuring sufficient contact between the reducing agent particles and the waste particles. In one possible implementation, step S1 further includes controlling the homogeneity of the mixture. Homogeneity directly affects the efficiency of the subsequent calcination reaction; uneven distribution of the reducing agent may result in some waste materials not being fully reduced. Therefore, the mixing effect can be improved by extending the stirring time or adjusting the speed of the stirring equipment. For example, on a laboratory scale, a stirrer with a speed of 300 rpm can be used, and the stirring time can be controlled to be more than 30 minutes to ensure that the components in the mixture are evenly distributed.

[0030] Optionally, this step also includes:

[0031] Step S11: Crush the positive electrode waste to a preset particle size and then mix it with the reducing agent. Step S12: Determine the amount of the reducing agent according to the mass ratio, where the mass ratio is the mass ratio of the reducing agent to the positive electrode waste. Step S13: The reducing agent in the mixture is uniformly distributed on the surface of the positive electrode waste particles.

[0032] Specifically, the mixing process can be further optimized to address the differences in the source and composition of cathode waste. Cathode waste from different sources may have different particle morphologies and chemical compositions. For example, some waste may contain a higher proportion of nickel oxide, while others may contain a higher proportion of lithium oxide. To address this, the waste can be analyzed for composition before mixing, using equipment such as X-ray fluorescence spectrometry to analyze the proportion of metal elements, thereby adjusting the amount and type of reducing agent to match the reduction requirements of the waste.

[0033] The choice of mixing equipment also significantly impacts the mixing effect. In industrial production, large horizontal mixers or drum mixers can be used to handle larger batches of waste and reducing agents. Compared to laboratory equipment, industrial equipment offers higher mixing efficiency, enabling the uniform mixing of large quantities of materials in a shorter time. For example, when processing 1 ton of cathode waste per batch, a drum mixer can be used, set at 50 revolutions per minute, for 1 hour to ensure thorough mixing. In one embodiment, the mixing process can also be combined with wet mixing. Wet mixing involves adding a small amount of liquid medium, such as water or ethanol, to improve the flowability between particles, thereby enhancing mixing uniformity. After wet mixing, the mixture needs to be dried to remove the liquid medium and prevent moisture from interfering with the reaction during subsequent calcination. For example, in wet mixing, water can be added at 5% of the waste mass as a medium. After mixing with a mixer for 30 minutes, the mixture is placed in an 80°C oven to dry for 2 hours, resulting in a dried mixture.

[0034] Furthermore, step S11 also includes:

[0035] Step S111, the reducing agent is a carbon-based reducing agent or an organic reducing agent.

[0036] This sub-step provides a specific selection of the reducing agent. Carbon-based reducing agents, such as activated carbon or graphite, are characterized by low cost and strong reducing power, while organic reducing agents, such as starch or glucose, can generate more gaseous products during the roasting process, promoting the reaction. Specifically, in step S111, the selection of the reducing agent needs to be determined based on the composition of the cathode waste and the roasting equipment conditions. For example, for waste with a high cobalt content, activated carbon can be selected as the reducing agent to provide a stable solid-phase reduction environment. For waste with a high lithium content, starch can be selected as the reducing agent to reduce lithium volatilization loss. In one possible implementation, step S111 includes pre-treating the reducing agent before mixing, for example, grinding the activated carbon to below 200 mesh to increase its specific surface area and improve the contact efficiency with waste particles. Mixing the pre-treated reducing agent with the waste can significantly improve the uniformity of the roasting reaction. In step S112, the carbon-based reducing agent and the organic reducing agent provide reducing power at a mass ratio.

[0037] This sub-step illustrates the synergistic effect of different types of reducing agents, which, at a specific mass ratio, can provide sufficient reduction potential to ensure the complete conversion of high-valence metal oxides. In one embodiment, step S112 can employ a composite reducing agent, such as mixing activated carbon and glucose in a certain proportion as a reducing agent. This composite approach allows for rapid reduction by organic matter in the initial stage of roasting, followed by long-term reduction maintained by carbon-based materials, thus improving overall reaction efficiency. Step S113 involves adjusting the type of reducing agent according to the metal oxide content in the cathode waste.

[0038] This sub-step demonstrates the flexibility in reducing agent selection, dynamically adjusting the type of reducing agent through component analysis to match the reduction requirements of the waste and avoid excessive or insufficient reducing agent. Specifically, in this step, the adjustment process includes first sampling and analyzing the cathode waste, using inductively coupled plasma atomic emission spectrometry to determine the content of lithium, cobalt, and nickel. Based on the analysis results, if the proportion of cobalt and nickel is high, a strong reducing carbon-based reducing agent is preferred; if the proportion of lithium is high, a mild organic reducing agent is selected to protect the lithium element. In one possible implementation, the adjustment in step S113 can establish an empirical database, for example, recording the optimal type and amount of reducing agent corresponding to different waste components. In actual production, the reducing agent scheme can be quickly determined by querying the database based on real-time detection results, improving production efficiency. S2, the mixture is calcined under an inert atmosphere to obtain a calcined product, wherein the calcination reduces the high-valence metal oxide to a soluble salt.

[0039] This step is the core of the entire recycling method. Through high-temperature roasting and reduction reactions, high-valence metal oxides in the waste are converted into easily soluble low-valence compounds, providing conditions for subsequent leaching separation. Roasting needs to be carried out in an inert atmosphere to avoid side reactions between oxygen in the air and the reducing agent or metal elements, which would affect the reduction effect. Specifically, in step S2, the mixture obtained in step S1 is placed in roasting equipment, such as a tube furnace or rotary kiln, and an inert gas is introduced to form a protective atmosphere. The inert gas can effectively isolate oxygen and prevent the metal elements from re-oxidizing at high temperatures. During roasting, the mixture undergoes a chemical reaction at high temperatures. The reducing agent reacts with the metal oxides, reducing the high-valence metal ions to low-valence states, forming soluble salt compounds. These soluble salts can be separated by water leaching in subsequent steps. In one possible implementation, the roasting conditions in step S2 need to be adjusted according to the composition of the waste and the type of reducing agent. Calcination temperature and time are key parameters affecting the reaction effect. Too low a temperature may lead to incomplete reduction, while too high a temperature may cause the formation of byproducts or equipment damage. For example, when processing waste containing lithium cobalt nickel oxides, the calcination temperature can be controlled between 600 and 800 degrees Celsius, and the calcination time can be 2 to 4 hours to ensure that the metal oxides are fully converted into soluble salts.

[0040] Optionally, this step further includes: step S21, placing the mixture in a calcining apparatus and introducing an inert gas to form an inert atmosphere.

[0041] This sub-step aims to provide an oxygen-free environment for the calcination reaction, ensuring the smooth progress of the reduction reaction. The choice of inert gas is usually based on cost and safety considerations; commonly used gases include nitrogen and argon. Nitrogen is less expensive and suitable for large-scale industrial production, while argon has higher chemical stability and is suitable for scenarios with high requirements for reaction conditions. In one embodiment, step S21 specifically involves loading the mixture into the reaction chamber of the calcination equipment, followed by introducing an inert gas at a certain flow rate to purge the original air from the chamber. For example, on a laboratory scale, a tube furnace can be used as the calcination equipment, introducing nitrogen at a flow rate of 500 ml per minute for 10 minutes to ensure that the oxygen content in the chamber is reduced to a minimum. Subsequently, the nitrogen flow rate is maintained at 100 ml per minute as a protective atmosphere to sustain the calcination process. Step S22 involves heating the mixture to the calcination temperature under the inert atmosphere for calcination.

[0042] This sub-step is the core of the roasting reaction. Heating the mixture brings it to the required temperature for the reaction, prompting a chemical change between the reducing agent and the metal oxide. The heating process needs to be gradual to avoid sudden temperature changes that could stress the equipment or cause the reaction to runaway. For example, a programmed temperature rise method can be used, increasing the temperature from room temperature to the target temperature at a rate of 5 degrees Celsius per minute and maintaining that temperature for a period of time. In one possible implementation, the combination of roasting temperature and time in step S22 needs to be optimized based on the specific composition of the waste. For waste with a high lithium content, the roasting temperature can be appropriately reduced to around 600 degrees Celsius to avoid lithium volatilization loss; while for waste with a high cobalt and nickel content, the temperature can be increased to 750 degrees Celsius to accelerate the reduction reaction. The roasting time is adjusted according to the amount of reactants and the characteristics of the equipment, typically between 2 and 5 hours. For example, when processing 500 grams of the mixture, roasting at 700 degrees Celsius for 3 hours can ensure a complete reaction.

[0043] Optionally, this step also includes:

[0044] In step S221, the inert gas is nitrogen or argon.

[0045] This sub-step further clarifies the specific composition of the inert atmosphere. Nitrogen and argon, as commonly used protective gases, can effectively isolate oxygen and ensure the smooth progress of the roasting reaction. Nitrogen is widely available and has a low cost, making it suitable for industrial-scale production; although argon is more expensive, it has stronger chemical inertness and is suitable for scenarios requiring high reaction purity. In one possible implementation, the specific implementation of step S221 can select a suitable inert gas based on the production scale and cost budget. For example, in small-scale laboratory research, high-purity argon can be used as a protective atmosphere to ensure a highly pure reaction environment and reduce the occurrence of side reactions. In industrial production, industrial-grade nitrogen is usually selected, and an oxygen-free environment is maintained by introducing it at a high flow rate. For example, in the roasting process of processing 2 tons of mixture per batch, nitrogen can be introduced at a flow rate of 1 cubic meter per hour, continuing throughout the entire roasting cycle. Step S222, the combination of roasting temperature and roasting time determines the roasting conditions.

[0046] This sub-step emphasizes the importance of roasting conditions for the reaction effect. A proper combination of temperature and time ensures the full reduction of metal oxides while avoiding energy waste or equipment damage. Determining the roasting conditions requires comprehensive consideration of the waste composition, the type of reducing agent, and equipment performance. In one embodiment, step S222 specifically involves designing different roasting conditions based on the chemical composition of the waste. For example, for waste with a relatively balanced lithium-cobalt-nickel ratio, a roasting temperature of 700 degrees Celsius combined with a roasting time of 3 hours can be used to achieve complete reduction of the metal oxides. For waste with a high nickel content, the temperature can be increased to 800 degrees Celsius and the time shortened to 2.5 hours to accelerate the reduction reaction of nickel oxides while avoiding the volatilization loss of lithium. Step S223, the roasting conditions selectively reduce the metal oxides in the mixture.

[0047] This sub-step further illustrates the optimization goal of the roasting conditions, namely, to achieve selective reduction of different metal oxides by controlling temperature and time. Selective reduction can improve the conversion rate of the target metal element, reduce the generation of by-products, and create favorable conditions for subsequent leaching and separation. Specifically, in step S223, the achievement of selective reduction depends on the ease of reduction of different metal oxides. For example, the reduction temperature of cobalt oxide is usually lower than that of nickel oxide, so a staged heating method can be used to first reduce cobalt oxide at a lower temperature, and then gradually increase the temperature to reduce nickel oxide. This staged roasting method can effectively improve the conversion efficiency of each metal element. For example, when processing waste with a high proportion of cobalt and nickel, it is possible to first roast at 600 degrees Celsius for 1 hour to complete the initial reduction of cobalt oxide, and then raise the temperature to 750 degrees Celsius for 2 hours to complete the reduction of nickel oxide. In step S224, the gas composition is monitored during the roasting process to adjust the inert atmosphere.

[0048] This sub-step aims to maintain the stability of the reaction environment by monitoring the gas composition generated during the roasting process in real time, judging the reaction progress, and dynamically adjusting the inert atmosphere flow rate. Changes in gas composition can reflect the extent of the reduction reaction; for example, an increase in carbon monoxide concentration usually indicates that the reduction reaction is proceeding vigorously. In one possible implementation, step S224 includes installing a gas detection device at the tail gas outlet of the roasting equipment to collect real-time concentration data of carbon monoxide and carbon dioxide in the tail gas. When a significant increase in carbon monoxide concentration is detected, the flow rate of inert gas can be appropriately increased to dilute the gas generated by the reaction and prevent excessive pressure inside the equipment. For example, if the carbon monoxide concentration exceeds a preset threshold during roasting, the nitrogen flow rate can be increased from 100 ml / min to 200 ml / min for 10 minutes, and then the gas composition can be reassessed and adjusted to a suitable flow rate. In step S23, the high-valence metal oxide is gradually reduced to a soluble salt during roasting to obtain the roasted product.

[0049] This sub-step describes the chemical nature of the roasting reaction, namely, the conversion of high-valence metal oxides in the waste into low-valence soluble salt compounds through the action of a reducing agent. These soluble salts are water-soluble in the subsequent leaching step, thereby achieving the separation of metal elements. Specifically, in step S23, the reducing agent reacts with the metal oxides during roasting. For example, a carbon-based reducing agent decomposes at high temperature to produce carbon monoxide or elemental carbon, which reacts with the high-valence metal oxides to generate low-valence compounds and gaseous byproducts. The generated low-valence compounds usually exist in the form of salts and have good water solubility. After roasting, the mixture is cooled to room temperature to obtain a solid roasted product, awaiting further processing. In one embodiment, the reaction progress in step S23 can be indirectly judged by monitoring the composition of the exhaust gas from the equipment. For example, a gas analyzer can be installed at the outlet of the roasting equipment to detect changes in the concentration of carbon monoxide or carbon dioxide in real time. When the carbon monoxide concentration gradually decreases and tends to stabilize, the reduction reaction can be considered to be near completion. At this point, heating can be stopped, and the roasted product can be allowed to cool naturally to avoid secondary oxidation of the metal elements at high temperatures.

[0050] Optionally, this step also includes:

[0051] Step S231, the calcination product contains soluble salts such as Li2CO3 and CoC2O4.

[0052] This sub-step further clarifies the typical composition of the roasted products. These soluble salts are direct products of the reduction roasting reaction and are effectively soluble in water during the leaching step, forming a leachate containing the target metal. Specifically, in step S231, the lithium carbonate in the roasted products originates from the reaction of lithium oxide with carbon dioxide generated during the reduction process, while cobalt oxalate originates from the reaction products of cobalt oxide with organic or carbon-based reducing agents. The formation of these compounds depends on the precise control of roasting conditions, such as the stability of temperature and atmosphere. In one possible implementation, the product composition of step S231 can be verified through chemical analysis. For example, X-ray diffraction analysis of a roasted product sample confirms that the main phases are lithium carbonate and cobalt oxalate, while containing a small amount of unreacted oxides. This analysis helps optimize roasting parameters and improve the yield of the target soluble salt. In step S232, the soluble salt is dissolved in the leachate to separate insoluble residues.

[0053] This sub-step emphasizes the selective dissolution characteristic of the leaching process, where soluble salts enter the liquid phase while insoluble residues are separated as the solid phase. Insoluble residues mainly include unreacted reducing agent residues or impurity compounds. In one embodiment, the separation process in step S232 can improve dissolution efficiency through multiple leaching operations. For example, the calcined product is added to water in batches for a second leaching; after the first leaching, the residue is separated, and then a second leaching is performed on the residue to maximize the extraction of soluble salts. The two leaching solutions are combined as the final leaching solution. In step S3, the calcined product is mixed with water at a solid-liquid ratio and leached to obtain a leaching solution containing lithium-cobalt-nickel soluble salts.

[0054] This step is crucial for the separation of metal elements after roasting. Soluble salts in the roasted product are dissolved through water leaching to form a leachate containing the target metal element, providing a foundation for subsequent metal recovery. The leaching process needs to be carried out at a suitable solid-liquid ratio to ensure sufficient dissolution of the soluble salts while avoiding excessively high solution concentrations that would reduce dissolution efficiency. Specifically, in step S3, the roasted product obtained in step S2 is mixed with water at a preset solid-liquid ratio to form a slurry, which is then stirred to promote the dissolution of the soluble salts. The solid-liquid ratio is determined by comprehensively considering the solubility characteristics of the roasted product and the volume of the leaching equipment, typically controlled between 1:5 and 1:10. During the leaching process, the soluble salts in the roasted product gradually dissolve in water, forming a solution containing metal ions such as lithium, cobalt, and nickel, while insoluble impurities remain in solid form in the slurry. In one embodiment, the leaching process in step S3 can be carried out at room temperature to reduce energy consumption. For example, 100 grams of the calcined product is mixed with 500 ml of deionized water to form a slurry with a solid-liquid ratio of 1:5. This slurry is then stirred in a mixer at 200 rpm for 1 hour to ensure complete dissolution of the soluble salts. After stirring, the slurry is separated by filtration to obtain a clear leachate for subsequent metal element extraction.

[0055] Optionally, this step may further include: step S31, adding the roasted product to water to form a slurry.

[0056] This sub-step is the starting point of the leaching process. By mixing the solid calcined product with water to form a homogeneous slurry, conditions are prepared for the subsequent dissolution of soluble salts. The formation of the slurry requires control of the solid-liquid ratio to avoid excessive solid content, which could lead to difficulty in stirring or incomplete dissolution. In one possible implementation, step S31 involves slowly adding the calcined product to pre-prepared water while simultaneously starting a stirring device to ensure uniform dispersion of solid particles. For example, on a laboratory scale, 50 grams of calcined product can be added in batches of 10 grams to 300 ml of deionized water, stirring thoroughly until all solids are added and a stable slurry is formed. During stirring, the rotation speed can be controlled at 150 rpm to prevent solid sedimentation in the slurry. Step S32 involves adjusting the pH value of the slurry and then stirring for leaching.

[0057] This sub-step aims to optimize the dissolution environment of soluble salts and improve leaching efficiency by adjusting the pH of the slurry. Some soluble salts have higher solubility within a specific pH range, therefore, the pH of the slurry needs to be controlled by adding a regulator, followed by stirring to promote dissolution. Specifically, in step S32, pH adjustment is typically achieved by adding acidic or alkaline substances, such as dilute sulfuric acid or sodium hydroxide solution, to adjust the slurry pH to a suitable range. Stirring leaching is then performed using mechanical stirring equipment to ensure sufficient contact between the solid particles in the slurry and the water. For example, when processing calcined products containing lithium, cobalt, and nickel soluble salts, the slurry pH can be adjusted to between 5.5 and 6.5, followed by stirring at 200 rpm for 2 hours to promote the dissolution of the soluble salts.

[0058] Optionally, this step also includes:

[0059] Step S321: Adjust the pH value of the slurry to the acidic range by adding a pH adjuster.

[0060] This sub-step further clarifies the specific direction of pH adjustment. An acidic environment generally favors the dissolution of certain metal salts; for example, soluble salts of cobalt and nickel have high solubility under weakly acidic conditions. The selection of the pH adjuster needs to consider its potential impact on the metal element and avoid introducing impurity ions. In one possible implementation, step S321 involves using a dilute acid solution as the pH adjuster, such as a 1 mol / L sulfuric acid solution, added dropwise to the slurry while simultaneously monitoring the slurry's pH in real time using a pH meter. For example, when processing 200 mL of slurry, 5 mL of dilute sulfuric acid solution can be slowly added to adjust the pH from the initial 7.0 to 5.8, followed by thorough stirring to ensure a stable acidic environment. Step S322 ensures that the soluble salt remains dissolved at the specified pH value.

[0061] This sub-step explains the purpose of pH control: to ensure that soluble salts in the roasted product do not precipitate or decompose due to environmental changes by maintaining a suitable pH. The solubility of soluble salts directly affects the concentration and recovery rate of metal elements in the leachate. Specifically, in step S322, a pH within the acidic range can effectively prevent certain metal salts from precipitating. For example, soluble salts of lithium, cobalt, and nickel can remain stable in solution at a pH of 5.5 to 6.0. If the pH is too high, some metal ions may precipitate as hydroxides, reducing leaching efficiency. Therefore, during the leaching process, the pH of the slurry needs to be monitored periodically to ensure it remains within the target range. In step S323, stirring ensures that the roasted product is fully in contact with water.

[0062] This sub-step emphasizes the crucial role of stirring in the leaching process. Mechanical stirring increases the contact area and time between solid particles and water, promoting the dissolution of soluble salts. Optimizing stirring conditions can significantly improve leaching efficiency. In one embodiment, step S323 specifically involves selecting suitable stirring equipment and parameters. For example, on a laboratory scale, a magnetic stirrer can be used to stir the slurry at 300 rpm for 1.5 hours to ensure complete dissolution of soluble salts in the calcined product. In industrial production, large stirring tanks equipped with multiple layers of impellers can be used to stir at 200 rpm for 2 hours to process larger volumes of slurry. In step S324, the filtrate obtained after solid-liquid separation is used as the final leachate.

[0063] This sub-step further clarifies the method of obtaining the leachate. Insoluble residues are removed through solid-liquid separation, resulting in a clear filtrate as the final leachate. The effectiveness of solid-liquid separation directly affects the purity of the leachate and is crucial for subsequent metal element extraction. In one possible implementation, step S324 involves using various separation devices to improve separation efficiency. For example, after initial filtration, the filtrate can be filtered a second time using a filter membrane with smaller pore sizes to remove fine particles and ensure the clarity of the leachate. For instance, when processing 500 ml of slurry, it can be initially filtered through ordinary filter paper, followed by fine filtration using a filter membrane with a pore size of 0.45 micrometers to obtain a high-purity leachate for subsequent processes. In one embodiment, the leachate obtained from the aforementioned steps contains lithium, cobalt, and nickel soluble salts, which can be further recovered and utilized through subsequent separation processes. The soluble salts in the leachate mainly originate from the dissolution of the roasting products in water. These salt compounds can exist stably under suitable conditions, providing a high-quality feedstock for subsequent metal extraction. The entire recycling method, through the close connection of the aforementioned steps, ensures continuous processing from waste to leachate, avoiding the loss of metal elements. Step S33: Separate the slurry to obtain leachate, in which lithium, cobalt, and nickel soluble salts dissolve.

[0064] This sub-step is the final stage of the leaching process, separating the liquid containing dissolved metal salts from the insoluble solid residue through solid-liquid separation to obtain the target leachate. The separation process must ensure the clarity of the leachate to prevent solid impurities from affecting subsequent processing. In one embodiment, step S33 specifically involves separating the slurry using a filtration or centrifuge. For example, in a laboratory setting, a vacuum filtration device can be used to pour the slurry onto filter paper, separating the liquid and solids through negative pressure filtration to obtain a clear leachate. In industrial production, a horizontal centrifuge can be used to centrifuge the slurry at 3000 rpm, collecting the liquid portion as the leachate and treating the solid residue separately. Step S4 further processes the leachate to separate and recover metal elements such as lithium, cobalt, and nickel.

[0065] This process is based on the different chemical properties of metal ions in the leachate, achieving selective separation through methods such as chemical precipitation or extraction. As a direct product of the aforementioned leaching step, the composition and concentration of the leachate directly determine the efficiency of subsequent separation, thus requiring precise control based on pretreatment. Specifically, in step S4, the leachate is first treated to remove impurities, removing any trace amounts of insoluble matter or organic residues that may have been mixed in. Subsequently, according to the separation order of the target metals, precipitants are added stepwise or solution conditions are adjusted to cause specific metal ions to precipitate, while other ions remain in solution. For example, cobalt and nickel are separated first, followed by lithium, to achieve stepwise recovery of metal elements. In one possible implementation, the separation process in step S4 can be divided into multiple stages. The first stage targets the recovery of cobalt and nickel by adding precipitants such as oxalic acid or sulfides to form insoluble salt precipitates. The second stage targets the recovery of lithium by adding carbonates to the remaining solution to form lithium carbonate precipitates. This staged separation effectively improves the recovery purity and yield of each metal.

[0066] Optionally, this step may also include: step S41, filtering and purifying the leachate to improve the clarity of the solution.

[0067] This sub-step aims to remove residual fine solid particles from the leachate, ensuring that subsequent separation processes are not interfered with by impurities. The filtered and purified leachate has higher transparency, which is beneficial for the uniform precipitation reaction. In one embodiment, step S41 specifically involves using a multi-stage filtration device, for example, first removing larger particles through coarse filtration, and then removing micron-sized impurities through a fine filtration membrane. For example, when processing 1 liter of leachate, primary filtration can be performed using filter paper, followed by secondary filtration through a filter membrane with a pore size of 0.22 microns, resulting in a highly clear leachate. Step S42 involves adding a precipitant to the purified leachate to separate cobalt and nickel.

[0068] This sub-step utilizes the reaction properties of cobalt and nickel ions with specific reagents to form insoluble precipitates, thereby achieving preliminary separation from lithium ions. The selection of the precipitant needs to consider the reaction selectivity and the purity of the precipitate. Specifically, in step S42, commonly used precipitants include ammonium oxalate or sodium oxalate, which can form cobalt oxalate and nickel oxalate precipitates with cobalt and nickel ions, while lithium ions do not participate in the reaction and remain in the solution. The precipitation process needs to be carried out under controlled temperature and pH conditions to ensure complete precipitation and easy filtration. In one possible implementation, the precipitation operation in step S42 includes heating the leachate to about 50 degrees Celsius, followed by the slow addition of a saturated oxalic acid solution while continuously stirring. During the addition, the pH of the solution is monitored and maintained between 4.0 and 5.0 to promote complete precipitation of cobalt and nickel. After the reaction is complete, the precipitate is allowed to settle for a period of time, and then collected by filtration. In step S43, the separated cobalt and nickel precipitate is washed and dried.

[0069] This sub-step aims to remove impurity ions adsorbed on the surface of the precipitate, improving the purity of the cobalt and nickel compounds. The washing process typically involves multiple rinses with deionized water, while drying is performed at a suitable temperature to prevent compound decomposition. In one embodiment, step S43 specifically involves washing the filtered cobalt-nickel oxalate precipitate 3 to 5 times with deionized water, filtering again after each wash until the washing solution is neutral. Subsequently, the precipitate is dried in an oven at 80 degrees Celsius for 4 hours to obtain a dried cobalt-nickel mixed salt, which can be used for further separation or direct utilization. In step S44, carbonate is added to the remaining solution to precipitate lithium ions.

[0070] This sub-step focuses on lithium recovery by adding sodium carbonate or potassium carbonate to the solution after removing cobalt and nickel, causing lithium ions to precipitate as lithium carbonate. Lithium carbonate, a common lithium salt, has low solubility, making it easy to separate and collect. Specifically, in step S44, the precipitation process requires heating the solution to above 90 degrees Celsius to reduce the solubility of lithium carbonate and promote precipitation. The addition rate of the carbonate needs to be controlled to avoid excessively high local concentrations that could lead to overly fine precipitate particles affecting filtration. In one possible implementation, step S44 involves heating the remaining solution to 95 degrees Celsius, followed by slowly adding a sodium carbonate solution with a concentration of 2 mol / L until the solution pH reaches above 10. Stirring is continuous during the addition process, and after reacting for 30 minutes, the solution is cooled to room temperature and allowed to stand to allow complete precipitation of the lithium carbonate. Step S45 involves separating and purifying the lithium carbonate precipitate.

[0071] This sub-step yields a high-purity lithium carbonate product through filtration and washing, while the mother liquor can be recycled or further processed. The purification process effectively removes impurities such as sodium ions. In one embodiment, step S45 specifically involves separating the lithium carbonate precipitate using a vacuum filtration device, followed by washing the precipitate 2 to 3 times with hot water to dissolve residual soluble salts. After washing, the precipitate is dried at 110 degrees Celsius to obtain battery-grade lithium carbonate. It should be noted that the entire recovery method, through the organic combination of the above steps, achieves efficient extraction of precious metals from lithium battery cathode waste. Soluble salts in the roasting product are effectively separated in the leachate, and subsequent processing further improves the purity and yield of metal recovery. This method avoids the environmental pollution problems caused by traditional acid leaching processes while reducing energy and reagent consumption. In one embodiment, the insoluble residue can also be subjected to secondary treatment to recover residual metal elements. For example, the leached residue can be mixed again with a small amount of reducing agent for secondary roasting and leaching to further improve the overall recovery rate. This recycling method maximizes the utilization of waste resources. Specifically, the secondary treatment process can simplify roasting conditions, such as lowering the temperature to 500 degrees Celsius and shortening the time to 1 hour, to supplement and reduce any remaining unreacted substances in the residue. The solution obtained after the secondary leaching is combined with the first leaching solution for further treatment, avoiding resource waste. In one possible implementation, the entire method can also be integrated with existing lithium battery recycling production lines for industrial-scale implementation. For example, when processing tons of cathode waste, a continuous rotary kiln can be used for roasting, and a large stirred tank can be used for leaching, achieving automated continuous production, improving processing capacity and economic efficiency. The control and monitoring of the inert atmosphere in steps S221 to S224 is particularly important in actual production. By adjusting the gas flow rate and composition in real time, the stability of the roasting process can be ensured, reducing the occurrence of side reactions. This refined control ensures high conversion rates. Furthermore, in the subsequent separation process of the leaching solution, an extraction process can be introduced as a supplement to the precipitation method. For example, an organic extractant can be used for liquid-liquid extraction of cobalt and nickel to achieve separation with higher purity. This combined process can adapt to the needs of leachates of varying qualities. In one embodiment, the extraction process involves acidifying the leachate and then contacting it with an extractant, allowing cobalt and nickel to enter the organic phase while lithium remains in the aqueous phase. Subsequently, a cobalt- and nickel-rich solution is obtained through back-extraction. This approach is advantageous when processing high-concentration leachates, reducing precipitant consumption. It is important to note that pH control of the leachate plays a crucial role throughout the separation process, requiring different acidic and alkaline environments at different stages. For example, a weakly acidic environment is maintained during the cobalt-nickel precipitation stage, while the environment is adjusted to alkaline during the lithium precipitation stage to achieve selective separation. Specifically, stepwise pH control can be achieved through an automated acid / alkali addition system. An online pH meter is installed in the production line to monitor and automatically add adjusting agents in real time, ensuring precise and stable solution conditions at each stage.In one possible implementation, the separated metal salts can be further converted, for example, by heating cobalt oxalate to decompose it into cobalt powder, or by using lithium carbonate to synthesize new cathode materials, achieving closed-loop recycling. This subsequent utilization improves the economic value of the entire process. Through the detailed description above, this method forms a complete recycling chain from cathode waste pretreatment, reduction roasting, water leaching to metal separation. Each step has multiple implementation options to adapt to different production scales and conditions. The soluble salts in the roasting products are fully dissolved and separated, ensuring efficient recovery of lithium, cobalt, and nickel.

[0072] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that implementing all or part of the above embodiments and making equivalent changes in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A short-process method for recovering lithium, cobalt, and nickel from lithium-ion battery cathode waste via solid-phase reduction leaching, characterized in that, include: S1, mixing cathode waste containing lithium cobalt nickel oxide with a reducing agent in a certain mass ratio to obtain a mixture; S2, calcining the mixture under an inert atmosphere to obtain a calcined product, wherein the calcination reduces the high-valence metal oxide to a soluble salt; S3, leaching the calcined product with water in a certain solid-liquid ratio to obtain a leachate, wherein the leachate contains soluble lithium cobalt nickel salt. S4, the leachate is further processed to separate and recover lithium, cobalt and nickel metal elements.

2. The method as described in claim 1, characterized in that, Step S1 further includes: performing preliminary cleaning of the positive electrode waste to remove any impurities that may exist on the surface.

3. The method as described in claim 2, characterized in that, Step S1 further includes: Step S11, crushing the positive electrode waste to a preset particle size and then mixing it with a reducing agent; Step S12, determining the amount of reducing agent according to the mass ratio, wherein the mass ratio is the mass ratio of the reducing agent to the positive electrode waste; Step S13, the reducing agent in the mixture is uniformly distributed on the surface of the positive electrode waste particles.

4. The method as described in claim 3, characterized in that, Step S11 includes: Step S111, the reducing agent is a carbon-based reducing agent or an organic reducing agent; Step S112, the carbon-based reducing agent and the organic reducing agent provide reducing power at a mass ratio; Step S113, the type of reducing agent is adjusted according to the metal oxide content in the cathode waste.

5. The method as described in claim 4, characterized in that, Step S113 includes: The adjustment process includes first sampling and analyzing the cathode waste, using inductively coupled plasma atomic emission spectrometry to determine the content of lithium, cobalt, and nickel. Based on the analysis results, if the proportion of cobalt and nickel is high, a strong reducing carbon-based reducing agent is selected; if the proportion of lithium is high, a mild organic reducing agent is selected.

6. The method as described in claim 1, characterized in that, Step S2 includes: Step S21, placing the mixture in a calcining device and introducing an inert gas to form an inert atmosphere; Step S22, heating the mixture to the calcining temperature under the inert atmosphere for calcination; Step S23, during the calcination process, the high-valence metal oxide is gradually reduced to a soluble salt to obtain the calcined product.

7. The method as described in claim 6, characterized in that, Step S22 includes: step S221, the inert gas is nitrogen or argon; step S222, the roasting conditions are determined by the combination of roasting temperature and roasting time; step S223, the roasting conditions selectively reduce the metal oxides in the mixture; step S224, the inert atmosphere is adjusted by monitoring the gas composition during the roasting process.

8. The method as described in claim 1, characterized in that, Step S3 includes: step S31, adding the roasted product to water to form a slurry; step S32, adjusting the pH value of the slurry and then stirring to leach; step S33, separating the slurry to obtain a leachate, wherein the lithium cobalt nickel soluble salts in the leachate are dissolved.

9. The method as described in claim 8, characterized in that, Step S32 includes: step S321, adjusting the pH value of the slurry to an acidic range by adding a pH adjuster; step S322, keeping the soluble salts dissolved at the pH value; step S323, stirring to ensure that the calcined product is fully in contact with water; and step S324, using the filtrate obtained by solid-liquid separation as the final leachate.

10. The method as described in claim 1, characterized in that, Step S4 includes: Step S41: Filter and purify the leachate to improve the clarity of the solution; Step S42: Add a precipitant to the purified leachate to separate cobalt and nickel; Step S43: Wash and dry the separated cobalt-nickel precipitate; Step S44: Add carbonate to the remaining solution to precipitate lithium ions; Step S45: Separate and purify the lithium carbonate precipitate.

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