A method for producing lithium carbonate from battery recyclates

Abstract

The application specifically discloses a method for preparing lithium carbonate from battery recyclates, and the method comprises the following steps: mixing battery recyclates and first residue, wherein the battery recyclates comprise lithium-containing positive electrode materials and electrolyte, and the first residue comprises residual water, residual sulfuric acid and solid matters; then pyrolyzing at a temperature of 260-350 DEG C to obtain a pyrolysis mixture; reducing and roasting the pyrolysis mixture in the presence of a reducing agent to obtain a roasting product and a reduction tail gas; contacting the roasting product with an acid solution and carbon dioxide gas to obtain a lithium bicarbonate solution, and evaporating and decomposing the lithium bicarbonate solution to obtain lithium carbonate. The preparation method provided by the application has small pollution, low cost and good economy.

Description

Technical Field

[0001] This application belongs to the field of battery recycling technology, and in particular relates to a method for preparing lithium carbonate from battery recycling materials. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the demand for lithium resources is also increasing. Batteries contain abundant lithium resources, and recovering valuable elements from batteries has gradually become a hot research direction in the industry.

[0003] However, lithium resource recycling often faces dual constraints from environmental pollution and economic efficiency, making it difficult to achieve both simultaneously. How to reduce environmental pollution while improving the economics of battery recycling is a pressing technical challenge that needs to be addressed. Summary of the Invention

[0004] This application is made in view of the above-mentioned technical problems. The purpose is to provide a method for preparing lithium carbonate from battery recycling materials, which reduces pollution while improving the economics of battery recycling material processing.

[0005] To address the aforementioned technical problems, this application provides a method for preparing lithium carbonate from battery recycled materials, comprising:

[0006] Obtain and mix battery recyclables and a first residue, wherein the battery recyclables include lithium-containing cathode material and electrolyte, and the first residue includes residual water, residual sulfuric acid and solids;

[0007] The mixed battery recyclables and the first slag were pyrolyzed at a temperature of 260-350℃ to obtain a pyrolyzed mixture.

[0008] The pyrolysis mixture was reduced and roasted in the presence of a reducing agent to obtain roasting products and reduction tail gas.

[0009] The roasted product is contacted with an acidic solution and carbon dioxide gas for carbonation and impurity removal to obtain a lithium bicarbonate solution and a first filter residue. The lithium bicarbonate solution is then evaporated and decomposed to obtain lithium carbonate.

[0010] By co-processing battery recyclables with the first slag, utilizing the residual moisture in the first slag and controlling the pyrolysis temperature, it is beneficial to recover the electrolyte in the battery recyclables as much as possible. At the same time, it promotes the conversion of fluorine and phosphorus in the battery recyclables into hydrogen fluoride and phosphorus pentoxide, respectively, thereby reducing the amount of fluorides and phosphides entering the reduction tail gas during the reduction roasting process and reducing pollution.

[0011] In some embodiments, the reducing agent is hydrogen and carbon powder.

[0012] In some embodiments, the pyrolysis mixture is mixed with a second slag before reduction roasting, and the reduction reaction of the reducing agent carbon powder is catalyzed by the sulfuric acid in the second slag, which includes residual water, residual sulfuric acid and solids.

[0013] In some embodiments, the mass ratio of the battery recyclables to the total residue is 2-5.6:1, the mass of the total residue is the sum of the masses of the first residue and the second residue, and the mass of the second residue is 40-70% of the mass of the total residue.

[0014] In some embodiments, the reduction exhaust gas is treated, specifically including:

[0015] The reduction tail gas is subjected to dust removal, washing, cooling, and conversion in sequence; at least part of the carbon monoxide and water in the reduction tail gas is converted into hydrogen and carbon dioxide through conversion; and the converted hydrogen and carbon dioxide are separated and recovered, the separated and recovered carbon dioxide is returned to the carbonization and impurity removal, and the separated and recovered hydrogen is returned to the reduction roasting.

[0016] In some embodiments, the carbon dioxide obtained from the separation and recovery is mixed with the carbon dioxide emitted from the evaporation and decomposition of lithium bicarbonate solution and then recovered and concentrated. A portion of the recovered and concentrated carbon dioxide is returned to carbonization for impurity removal, and another portion of the recovered and concentrated carbon dioxide is returned to reduction roasting.

[0017] In some embodiments, the mass ratio of the recovered and concentrated carbon dioxide returned to carbonization for purification to the carbon dioxide returned to reduction roasting is 1.2-3.5:1.

[0018] In some embodiments, the separation and recovery are performed using pressure swing adsorption (PSA), with a temperature of 20-40°C and a pressure of 0.8-2.5 MPa.

[0019] In some embodiments, the reduction tail gas treatment further includes reforming methanol and water to obtain reformed gas, and mixing the reformed gas with the washed and cooled reduction tail gas for conversion; the reforming temperature is 150-350℃, and the reforming pressure is 1-2.6MPa; the reformed gas includes H2, CO, CO2 and H2O, wherein the H2 content is 50-75%.

[0020] In some embodiments, the first filter residue is further subjected to acid leaching to obtain a second filter residue, a second filtrate, and hydrogen.

[0021] In some embodiments, the pH of the acidic solution is 3-6.

[0022] In some embodiments, the acidic solution includes at least one of sulfuric acid and acidic circulating mother liquor, wherein the acidic circulating mother liquor is obtained by centrifugation of the filtrate obtained after evaporation and decomposition of lithium bicarbonate solution.

[0023] In some embodiments, the carbon dioxide volume concentration during the carbonization and impurity removal process is controlled at 80-99%, the temperature at 5-30°C, the pressure at 0.15-0.6 MPa, and the excess carbon dioxide coefficient at 1.7-3.5.

[0024] In some embodiments, the molar ratio of the reducing agent to the lithium salt in the pyrolysis mixture during the reduction roasting process is 2.1-2.3:1, the reduction roasting temperature is 500-800℃, and the reduction roasting time is 2.5-4.5h. Attached Figure Description

[0025] Figure 1 This is a flowchart of a method for preparing lithium carbonate from battery recycled materials according to this application. Detailed Implementation

[0026] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0027] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0028] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0029] Unless otherwise specified, the pressures mentioned in this application are gauge pressures, where gauge pressure = absolute pressure - standard atmospheric pressure. For example, an evaporation decomposition pressure of 0.2 MPa means that the gauge pressure of the evaporation decomposition pressure is 0.2 MPa, and the absolute pressure is (0.2 + 0.1013) MPa.

[0030] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0031] To better understand the above-mentioned objectives, features, and advantages of this application, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. Additional embodiments and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice. It should be noted that, unless otherwise specified, the embodiments of this application and the features thereof can be combined with each other.

[0032] In this application, battery recyclables can be recyclables containing positive electrode material and electrolyte obtained from lithium batteries. For example, battery recyclables can be positive electrode material obtained from disassembling batteries, wherein the positive electrode material contains a small amount of electrolyte components; or they can be recyclables obtained from battery crushing and sieving, wherein the recyclables contain positive electrode material and a certain amount of electrolyte components. The positive electrode material includes at least one of nickel, cobalt, manganese, lithium, iron, sodium, and potassium, and the electrolyte includes at least one of LiPF6, LiBF4, LiAsF6, ethylene carbonate, and dimethyl carbonate. The lithium content in the battery recyclables, measured as lithium oxide, is 7-13%.

[0033] In this application, both the first slag and the second slag contain residual water, residual sulfuric acid, and solids. For example, the slag includes lithium ore slag, wherein the lithium ore may be spodumene with a lithium oxide content of 2.5-6% or lepidolite with a lithium oxide content of 0.8-4.5%. The lithium ore slag may be lithium ore slag obtained after leaching and filtration of lithium ore, containing 0.05-0.5% lithium, 0.05-1% sulfuric acid, and 5-15% water.

[0034] like Figure 1 As shown, a method for preparing lithium carbonate from battery recycling materials includes the following steps:

[0035] Obtain and mix battery recyclables and a first residue, wherein the battery recyclables include lithium-containing cathode material and electrolyte, and the first residue includes residual water, residual sulfuric acid and solids;

[0036] The mixed battery recyclables and the first slag were pyrolyzed at a temperature of 260-350℃ to obtain a pyrolyzed mixture.

[0037] The pyrolysis mixture was reduced and roasted in the presence of a reducing agent to obtain roasting products and reduction tail gas.

[0038] The roasted product is contacted with an acidic solution and carbon dioxide gas for carbonation and impurity removal to obtain a lithium bicarbonate solution and a first filter residue. The lithium bicarbonate solution is then evaporated and decomposed to obtain lithium carbonate.

[0039] In this embodiment, by co-processing the battery recyclables with the first slag, utilizing the residual moisture in the first slag and controlling the pyrolysis temperature, it is beneficial to recover the electrolyte in the battery recyclables as much as possible. At the same time, it promotes the conversion of fluorine and phosphorus in the battery recyclables into hydrogen fluoride and phosphorus pentoxide, respectively, thereby reducing the amount of fluorides and phosphides entering the reduction tail gas during the reduction roasting process and reducing pollution.

[0040] The residual moisture in the first batch of residue helps hydrolyze the electrolyte in the battery recycling. When the pyrolysis temperature is above 350℃, the organic solvents in the electrolyte are easily decomposed, which is not conducive to electrolyte recovery. When the pyrolysis temperature is below 260℃, the recovery effect of the organic solvents in the electrolyte is poor. Therefore, the pyrolysis temperature is controlled between 260-350℃. Under this process condition, the by-products can be directly recovered after the electrolyte evaporates, thereby improving the economics of the production process.

[0041] During pyrolysis, the residual moisture in the first residue promotes the hydrolysis of lithium hexafluorophosphate in the electrolyte. By controlling the pyrolysis temperature, lithium hexafluorophosphate can be converted into hydrogen fluoride and phosphorus pentoxide while ensuring the evaporation of organic solvents in the recovered electrolyte. Specifically, this includes:

[0042] H₂O + LiPF₆ → PF₅ + HF + LiOH

[0043] H₂O + PF₅ → POF₃ + 2HF

[0044] 3H₂O + 2POF₃ → P₂O₅ + 6HF

[0045] Meanwhile, the hydrogen fluoride and some phosphorus pentoxide obtained can volatilize along with the electrolyte, thereby reducing the amount of fluoride entering the reduction tail gas and reducing pollution.

[0046] In some embodiments, the pyrolysis time is 3.2-6.3 hours to ensure a complete reaction during pyrolysis and full evaporation of the electrolyte.

[0047] In some embodiments, the reducing agent is hydrogen and carbon powder. Based on the added reducing agent hydrogen and carbon powder, nickel, cobalt, and manganese elements in the battery recycling mixture are converted into nickel, cobalt metals, and nickel, cobalt, and manganese oxides using both hydrogen reduction roasting and carbon reduction roasting methods. Simultaneously, lithium in the battery recycling mixture is converted into lithium hydroxide and lithium carbonate. Possible reactions include:

[0048] LiNi x Co y Mn 1-x-y O2+H2→LiOH+H2O+Ni+Co+MnO2+MnO

[0049] LiNi x Co y Mn 1-x-y O2+C→Lt2CO3+CO2+Ni+Co+MnO2+MnO

[0050] LiNi x Co y Mn 1-x-y O2+CO→Li2CO3+CO2+Ni+Co+MnO2+MnO.

[0051] In some embodiments, the pyrolysis mixture is mixed with a second slag before reduction roasting, and the reduction reaction of the reducing agent carbon powder is catalyzed by the residual sulfuric acid in the second slag, which includes residual water, residual sulfuric acid and solids.

[0052] In this embodiment, because the higher the temperature, the stronger the oxidizing power of sulfuric acid, the residual sulfuric acid in the second slag can promote the conversion of reducing agent carbon powder into gaseous carbon monoxide and carbon dioxide, and sulfuric acid into gaseous sulfur dioxide. The reduction effect of gaseous carbon monoxide and sulfur dioxide is better than that of carbon powder, and their utilization rate is higher. Therefore, the residual sulfuric acid in the second slag improves the reduction efficiency and utilization rate of the reducing agent carbon powder, thereby reducing the proportion of reducing agent hydrogen and making the composition of the reduction tail gas closer to that of the reformed gas. The carbon powder oxidation principle includes:

[0053]

[0054] Therefore, the residual sulfuric acid in the second slag can effectively promote the reduction reaction of the mixture after the reduction pyrolysis of the reducing agent carbon powder, thereby improving the reduction efficiency and carbon powder utilization. Since the reduction efficiency and carbon powder utilization are improved, the amount of hydrogen in the reducing agent is reduced, thereby improving production safety.

[0055] In this embodiment, the sulfuric acid in the second slag can also react with the lithium oxide in the pyrolysis mixture to obtain lithium sulfate that is easy to leach. The lithium in the second slag can also be converted into lithium hydroxide and lithium carbonate during the reduction process, thereby further improving the overall lithium recovery rate and realizing the waste utilization of the second slag and the synergistic recovery of battery recycled materials and the second slag.

[0056] In some embodiments, the mass ratio of the battery recyclables to the total residue is 2-5.6:1, the mass of the total residue is the sum of the masses of the first residue and the second residue, and the mass of the second residue is 40-70% of the mass of the total residue.

[0057] In this embodiment, since the lithium content in the battery recyclable is higher than that in the first slag, in order to effectively utilize the first slag as waste, and also to promote the control of subsequent electrolyte recovery after mixing and to improve the reduction reaction rate of the pyrolysis mixture, the lithium oxide content in the pre-baked material obtained by mixing the second slag and the pyrolysis mixture is 5-8%. That is, it is necessary to control the ratio of battery recyclable to first slag.

[0058] In some embodiments, the reduction exhaust gas is treated, specifically including:

[0059] The reduction tail gas is subjected to dust removal, washing, cooling, and transformation in sequence; at least part of the carbon monoxide and water in the reduction tail gas are converted into hydrogen and carbon dioxide through transformation; and the hydrogen and carbon dioxide obtained by transformation are separated and recovered. The carbon dioxide obtained by separation and recovery is returned to the carbonization and impurity removal cycle for reuse, and the hydrogen obtained by separation and recovery is used as a reducing agent for reduction roasting.

[0060] In this embodiment, after the reduction tail gas is treated by dust removal, washing, and cooling, the concentrations of hydrogen fluoride and phosphorus pentoxide in the discharged reduction tail gas are both no greater than 0.5 ppm. During the conversion process, at least a portion of the carbon monoxide and water in the reduction tail gas can be converted into hydrogen and carbon dioxide. The reaction equation includes: H2O + CO → H2 + CO2. Therefore, the composition of the resulting mixed gas can be controlled as follows: hydrogen content 20-45%, carbon monoxide content 0.3-0.8%, carbon dioxide content 22-39%, and water content 5-30%. Thus, by processing the reduction tail gas... The process allows the composition of the reduction tail gas to be similar to that of the reformed gas, thus creating favorable conditions for the combined treatment of the reduction tail gas and the reformed gas. At the same time, the hydrogen and carbon dioxide obtained from the subsequent conversion of the reduction tail gas are separated and recovered. The separated and recovered carbon dioxide can be returned to the carbonization and impurity removal cycle for reuse, thereby reducing raw material consumption and realizing the recycling of tail gas. Part of the separated and recovered hydrogen is directly returned to the reduction roasting as a reducing agent for recycling, and the other part is sent to the purification process. By adjusting the ratio of the two parts, the tail gas circulation balance is achieved, reducing the consumption of reducing agent hydrogen and further saving production costs.

[0061] Furthermore, in a preferred embodiment, the separation and recovery employs pressure swing adsorption (PSA), with a PSA temperature of 20-40°C and a pressure of 1.5-2.5 MPa. Controlling the temperature and pressure of PSA within these ranges allows for more thorough separation of hydrogen and carbon dioxide. Furthermore, based on temperature control during pyrolysis and the addition of the first slag, the content of hydrogen fluoride and phosphorus pentoxide in the reduction tail gas is reduced, thereby alleviating catalyst poisoning in subsequent reduction tail gas treatment and adsorbent poisoning in PSA. This also reduces the cost associated with frequent catalyst and adsorbent replacement. For example, the shift catalyst includes one or more of sodium silicate, ferric oxide, and copper oxide, and the adsorbent for PSA includes activated carbon and molecular sieve adsorbents.

[0062] In some embodiments, the carbon dioxide obtained from the separation and recovery is mixed with the carbon dioxide emitted from the evaporation and decomposition of lithium bicarbonate solution and then recovered and concentrated. A portion of the recovered and concentrated carbon dioxide is returned to carbonization for impurity removal, and another portion of the recovered and concentrated carbon dioxide is returned to reduction roasting as a protective gas.

[0063] In this embodiment, the recovery and concentration of carbon dioxide improves the carbon dioxide recycling rate, reduces the consumption of raw materials and protective gas nitrogen, and further reduces production costs. At the same time, the significant reduction in protective gas nitrogen consumption means that if the reduction tail gas is subsequently incinerated with pure oxygen, the nitrogen oxides in the flue gas can meet emission standards. This reduces the amount of nitrogen oxides that need to be reduced by SNCR, reduces the need for a supporting urea storage system, and further reduces production costs and investment.

[0064] In some embodiments, the evaporation decomposition temperature is 60-110°C and the evaporation decomposition pressure is (-0.05)-0.2 MPa.

[0065] In some embodiments, the mass ratio of the recovered, concentrated carbon dioxide returned to carbonization for impurity removal to the carbon dioxide returned to reduction roasting is 1.2-3.5:1. Within this parameter range, carbon dioxide can be fully utilized, thereby reducing production costs.

[0066] In some embodiments, the lithium carbonate obtained by evaporation and decomposition is subjected to slurry post-processing, which includes solid-liquid separation, drying, grinding and iron removal, thereby obtaining lithium carbonate with higher purity, such as battery-grade lithium carbonate.

[0067] In some embodiments, the reduction tail gas treatment further includes reforming methanol and water to obtain reformed gas, and mixing the reformed gas with the washed and cooled reduction tail gas for conversion; the reforming temperature is 150-350℃, and the reforming pressure is 1-2.6MPa; the reformed gas includes H2, CO, CO2 and H2O, wherein the H2 content is 50-75%.

[0068] In this embodiment, the reaction equation for the reforming process includes:

[0069] CH3OH→2H2+CO

[0070] CH3OH + H2O → 3H2 + CO2.

[0071] In some embodiments, the first filter residue is further subjected to acid leaching to obtain a second filter residue, a second filtrate, and hydrogen.

[0072] In this embodiment, since the first filter residue discharged after carbonization and impurity removal includes a small amount of nickel, cobalt, manganese metals and their compounds, sulfuric acid is used to contact it to generate a mixed solution of nickel sulfate, cobalt sulfate, and manganese sulfate, thereby enabling further recovery of nickel, cobalt, and manganese. Furthermore, the second filtrate can undergo gas-liquid separation to reduce gas-liquid entrainment. The hydrogen obtained from acid leaching and gas-liquid separation can be mixed with a portion of the recovered hydrogen for purification. The purified hydrogen can be returned to the reduction roasting process as a reducing agent for recycling, further improving the hydrogen recycling rate and achieving low-cost recovery of the first filter residue and hydrogen recycling.

[0073] In some embodiments, the pH of the acidic solution is 3-6.

[0074] Furthermore, in this embodiment, the input carbon dioxide gas pressure is controlled at 0.2-0.6 MPa, the carbon dioxide volume concentration is controlled at 80-99%, the carbonation and impurity removal temperature is controlled at 5-30°C, the carbonation and impurity removal pressure is controlled at 0.15-0.6 MPa, and the excess carbon dioxide coefficient during carbonation and impurity removal is controlled at 1.7-3.5. The excess carbon dioxide coefficient = carbonation inlet CO2 flow rate / theoretically required CO2 for lithium carbonate carbonation. By controlling the carbonation and impurity removal process conditions, impurities such as cobalt, nickel, and manganese in the roasted product can be removed. The carbonation and impurity removal process can also selectively convert lithium carbonate and / or lithium hydroxide in the roasted product into lithium bicarbonate, ensuring that the lithium carbonate content in the solution after carbonation does not exceed the saturation concentration.

[0075] In some embodiments, the acidic solution includes at least one of sulfuric acid and an acidic circulating mother liquor, wherein the acidic circulating mother liquor is obtained by centrifugation of the filtrate obtained after evaporation and decomposition of lithium bicarbonate solution. By controlling the pH of the acidic circulating mother liquor, its recycling is achieved, thereby improving the lithium recovery rate.

[0076] In some embodiments, the molar ratio of the reducing agent to the lithium salt in the pyrolysis mixture during reduction roasting is 2.1-2.3:1, the reduction roasting temperature is 500-800℃, and the reduction roasting time is 2.5-4.5 h. Controlling the parameters during reduction roasting within these ranges is more conducive to the conversion of lithium to lithium hydroxide / lithium carbonate, thereby improving lithium recovery rate. Furthermore, it allows for a reduction in hydrogen consumption while ensuring sufficient conversion of lithium to lithium hydroxide / lithium carbonate during reduction roasting, thus lowering production costs.

[0077] To better illustrate the working principle and technical effects of this application, three embodiments and five comparative examples are provided below.

[0078] Example 1

[0079] Step 1: Mix 25t of battery recycled material and 2.5t of first slag and then pyrolyze to obtain a pyrolysis mixture and pyrolysis tail gas. Recover the electrolyte from the pyrolysis tail gas. The pyrolysis temperature is 350℃ and the pyrolysis time is 3.2h. The first slag contains 0.5% lithium oxide. The lithium mass fraction of the battery recycled material, measured as lithium oxide, is 9%, the HF volume fraction in the pyrolysis tail gas is 3%, and the phosphide volume fraction is less than 0.5%.

[0080] The second step involves mixing the pyrolysis mixture with 2.5t of the second slag and then reducing and roasting it with hydrogen and carbon powder to obtain roasting products and reduction tail gas. The reduction temperature is 690℃, the reduction time is 4.5h, the mass ratio of battery recycled material to total slag is 5:1, and the lithium oxide content in the pre-roasted material is 7.58%. The molar ratio of reducing agent (hydrogen and carbon powder) to lithium salt in the pyrolysis mixture is 2.1:1.

[0081] The third step involves adding the reduction-calcination product to an acidic circulating mother liquor with a pH of 6 (an initial start-up sulfuric acid solution with a pH of 6) for carbonation and impurity removal, yielding a crude lithium bicarbonate solution. The carbonation and impurity removal process uses a CO2 volume concentration of 99%, a pressure of 0.35 MPa, a temperature of 30°C, and a CO2 excess coefficient of 1.7.

[0082] Simultaneously, the reduction tail gas undergoes dust removal, washing, and cooling in sequence. Then, at least a portion of the carbon monoxide and water in the washed and cooled reduction tail gas is converted into hydrogen and carbon dioxide through a transformation process. The hydrogen and carbon dioxide are then separated and recovered using pressure swing adsorption (PSA). The recovered carbon dioxide is returned to carbonization for impurity removal, while a portion of the recovered hydrogen is directly returned to the reduction roasting process. The remaining recovered hydrogen is purified and used for reduction roasting. The operating temperature of the PSA is 30℃, and the operating pressure is 0.8 MPa.

[0083] Lithium bicarbonate solution was evaporated and decomposed to obtain lithium carbonate slurry. The evaporation and decomposition temperature was 60℃ and the evaporation and decomposition pressure was -0.05MPa. Then, the lithium carbonate slurry was subjected to solid-liquid separation, drying, grinding and iron removal to obtain battery-grade lithium carbonate.

[0084] Carbon dioxide obtained from carbonization and evaporation decomposition is recovered and concentrated. A portion of the recovered and concentrated carbon dioxide is returned to carbonization, while the other portion is returned to reduction roasting. The mass ratio of CO2 returned to carbonization and carbon dioxide returned to reduction roasting is 1.2:1. Simultaneously, the first filter residue discharged from carbonization is acid-leached with sulfuric acid to obtain a second filter residue, a second filtrate, and hydrogen. The second filtrate is then subjected to gas-liquid separation. The hydrogen obtained from acid leaching and gas-liquid separation is mixed with hydrogen obtained from pressure swing adsorption and purified. The purified hydrogen is returned to reduction roasting, and this portion provides 35% of the total hydrogen required for reduction roasting.

[0085] Methanol and water are reformed at a temperature of 250°C and an operating pressure of 2.6 MPa. The reformed gas contains 75% hydrogen. The reformed gas is then mixed with the washed and cooled reduction tail gas for conversion.

[0086] Example 2

[0087] Step 1: Mix 25t of battery recycled material and 2.5t of first slag and then pyrolyze to obtain a pyrolysis mixture and pyrolysis tail gas. Recover the electrolyte from the pyrolysis tail gas. The pyrolysis temperature is 260℃ and the pyrolysis time is 6.3h. The first slag contains 0.5% lithium oxide. The lithium content in the battery recycled material, measured as lithium oxide, is 9%, the HF volume fraction in the pyrolysis tail gas is 3%, and the phosphide volume fraction is less than 0.5%.

[0088] The second step involves mixing the pyrolysis mixture with 2.5t of the second slag and then reducing and roasting it with hydrogen and carbon powder to obtain roasting products and reduction tail gas. The reduction temperature is 500℃, the reduction time is 4.5h, the mass ratio of battery recycled material to total slag is 5:1, and the lithium oxide content in the pre-roasted material is 7.58%. The molar ratio of reducing agent (hydrogen and carbon powder) to lithium salt in the pyrolysis mixture is 2.3:1.

[0089] The third step involves adding the reduction-calcination product to an acidic circulating mother liquor with a pH of 3 (an initial start-up sulfuric acid solution with a pH of 3) for carbonation and impurity removal, yielding a crude lithium bicarbonate solution. The CO2 volume concentration during carbonation and impurity removal is 89.5%, the carbonation pressure is 0.37 MPa, the carbonation temperature is 5°C, and the CO2 excess coefficient is 2.6.

[0090] Simultaneously, the reduction tail gas undergoes dust removal, washing, and cooling in sequence. Then, at least a portion of the carbon monoxide and water in the washed and cooled reduction tail gas is converted into hydrogen and carbon dioxide through a transformation process. The hydrogen and carbon dioxide are then separated and recovered using pressure swing adsorption (PSA). The recovered carbon dioxide is returned to carbonization for impurity removal, while a portion of the recovered hydrogen is directly returned to the reduction roasting process. The remaining recovered hydrogen is purified and used for reduction roasting. The operating temperature of the PSA is 30℃, and the operating pressure is 0.8 MPa.

[0091] The lithium bicarbonate solution was fed into an evaporation decomposition system to obtain lithium carbonate slurry. The evaporation decomposition temperature was 85℃ and the evaporation decomposition pressure was 0.03MPa. The lithium carbonate slurry was then subjected to solid-liquid separation, drying, grinding, and iron removal to obtain battery-grade lithium carbonate.

[0092] Carbon dioxide obtained from carbonization and evaporation decomposition is recovered and concentrated. A portion of the recovered and concentrated carbon dioxide is returned to carbonization, while the other portion is returned to reduction roasting. The mass ratio of CO2 returned to carbonization and carbon dioxide returned to reduction roasting is 3.5:1. Simultaneously, the first filter residue discharged from carbonization is acid-leached with sulfuric acid to obtain a second filter residue, a second filtrate, and hydrogen. The second filtrate is then subjected to gas-liquid separation. The hydrogen obtained from acid leaching and gas-liquid separation is mixed with hydrogen obtained from pressure swing adsorption and purified. The purified hydrogen is returned to reduction roasting, and this portion provides 43.5% of the total hydrogen required for reduction roasting.

[0093] Methanol and water are reformed at a temperature of 150°C and an operating pressure of 2.6 MPa. The reformed gas contains 50% hydrogen. The reformed gas is then mixed with the washed and cooled reduction tail gas for conversion.

[0094] Example 3

[0095] Step 1: Mix 25t of battery recycled material and 2.5t of first slag and then pyrolyze to obtain a pyrolysis mixture and pyrolysis tail gas. The electrolyte in the pyrolysis tail gas is recovered. The pyrolysis temperature is 292.5℃ and the pyrolysis time is 4.75h. The first slag contains 0.5% lithium oxide. The lithium content in the battery recycled material, measured as lithium oxide, is 9%.

[0096] The second step involves mixing the pyrolysis mixture with 2.5t of the second slag, followed by reduction roasting with hydrogen and carbon powder to obtain roasting products and reduction tail gas. The reduction temperature is 800℃, the reduction time is 2.5h, the mass ratio of battery recycled material to total slag is 5:1, and the lithium oxide content in the pre-roasted material is 7.58%. The molar ratio of reducing agent (hydrogen and carbon powder) to lithium salt in the pyrolysis mixture is 2.2:1.

[0097] The third step involves adding the reduction-calcined product to an acidic circulating mother liquor with a pH of 4.5 (an initial start-up sulfuric acid solution with a pH of 4.5) for carbonation and impurity removal, yielding a crude lithium bicarbonate solution. The carbonation process uses a CO2 volume concentration of 80%, a carbonation pressure of 0.37 MPa, a carbonation temperature of 17.5 °C, and a CO2 excess coefficient of 3.5.

[0098] Simultaneously, the reduction tail gas undergoes dust removal, washing, and cooling in sequence. Then, at least a portion of the carbon monoxide and water in the washed and cooled reduction tail gas is converted into hydrogen and carbon dioxide through a transformation process. The hydrogen and carbon dioxide are then separated and recovered using pressure swing adsorption (PSA). The recovered carbon dioxide is returned to carbonization for impurity removal, while a portion of the recovered hydrogen is directly returned to the reduction roasting process. The remaining recovered hydrogen is purified and used for reduction roasting. The operating temperature of the PSA is 30℃, and the operating pressure is 0.8 MPa.

[0099] The lithium bicarbonate solution was fed into an evaporation decomposition system to obtain lithium carbonate slurry. The evaporation decomposition temperature was 110℃ and the evaporation decomposition pressure was 0.2MPa. The lithium carbonate slurry was then subjected to solid-liquid separation, drying, grinding, and iron removal to obtain battery-grade lithium carbonate.

[0100] Carbon dioxide obtained from carbonization and evaporation decomposition is recovered and concentrated. A portion of the recovered and concentrated carbon dioxide is returned to carbonization, while the other portion is returned to reduction roasting. The mass ratio of CO2 returned to carbonization and reduction roasting is 2.35:1. Simultaneously, the first filter residue discharged from carbonization is leached with sulfuric acid to obtain a second filter residue, a second filtrate, and hydrogen. The second filtrate is then subjected to gas-liquid separation. The hydrogen obtained from acid leaching and gas-liquid separation is mixed with hydrogen obtained from pressure swing adsorption and purified. The purified hydrogen is returned to reduction roasting, and this portion provides 52% of the total hydrogen required for reduction roasting.

[0101] Methanol and water are reformed at a temperature of 350°C and an operating pressure of 2.6 MPa. The reformed gas contains 75% hydrogen. The reformed gas is then mixed with the washed and cooled reduction tail gas for conversion.

[0102] Comparative Example 1

[0103] The battery recycling capacity is 25t. Except for the first step of not adding 2.5t of first slag, the pyrolysis temperature is controlled at 320℃ and the pyrolysis time is controlled at 3.2h, the other parameters are the same as in Example 1, that is, no first slag is added during the pyrolysis process.

[0104] Comparative Example 2

[0105] The battery recycling capacity is 25t. Except for the fact that 2.5t of first slag is not added in the first pyrolysis process and 2.5t of second slag is not added in the second reduction roasting process, and the pyrolysis temperature is controlled at 375℃ and the pyrolysis time is controlled at 4h, the other parameters are the same as in Example 1.

[0106] Comparative Example 3

[0107] The battery recycling capacity is 25t. The CO2 obtained from decomposition is sent to the carbon dioxide recovery system for enrichment, and part of it is returned to the carbonization and impurity removal system, while the rest is vented. That is, only nitrogen is used as a protective gas in the reduction system. The reduction tail gas is incinerated, quenched, dusted, and washed before being vented. Methanol is used as a combustion aid. The other parameters are the same as in Example 1.

[0108] Comparative Example 4

[0109] The battery recycling capacity is 25t. Except for the first step of not adding the first slag, the second step of not adding the second slag, the pyrolysis temperature is controlled at 550℃, and the pyrolysis time is controlled at 8h, the other parameters are the same as in Example 1.

[0110] Comparative Example 5

[0111] The carbonization, evaporation, dephosphorization, defluorination, heavy metal removal, lithium precipitation, and crude carbon refining processes in Example 1 are replaced with leaching, phosphorus removal, defluorination, heavy metal removal, evaporation, and crude carbon refining processes. Other processes are the same as in Example 1.

[0112] Through Examples 1-3 and Comparative Examples 1-5, the corresponding technical and economic data tables were obtained, as detailed in Table 1.

[0113] Table 1. Comparison of technical and economic data between Examples 1-3 and Comparative Examples 1-5

[0114]

[0115]

[0116] As can be seen from Table 1, compared with Comparative Example 1, Examples 1-3 added the first residue during the pyrolysis process, which promoted the conversion of fluorine and phosphorus in the battery recycled material into hydrogen fluoride and phosphorus pentoxide, respectively, so that some of them would volatilize with the electrolyte during the pyrolysis process, thereby reducing the content of fluoride and phosphorus in the reduction tail gas.

[0117] Compared with Comparative Examples 2 and 4, the concentrations of HF and phosphorus pentoxide after washing and cooling of the reduction tail gas in Examples 1-3 are extremely low, which can reduce catalyst poisoning and adsorbent poisoning during subsequent reduction tail gas treatment, thereby reducing pollution.

[0118] Meanwhile, the formula for calculating lithium recovery rate is as follows:

[0119]

[0120] As shown in Table 1, the lithium recovery rates of Examples 1-3 are all superior to those of Comparative Examples 1, 2, and 5. Although the lithium recovery rates and battery-grade lithium carbonate production of Examples 1-3 are similar to those of Comparative Example 3, the nitrogen consumption and methanol usage in Comparative Example 3 are much higher than those of Examples 1-3, meaning that the cost of Comparative Example 3 is much higher than that of Examples 1-3. Comparing Examples 1-3 with Comparative Examples 1, 2, and 4, it can be seen that the electrolyte recovery amount of Examples 1-3 is significantly greater, and the electrolyte recovery amount decreases significantly with the increase of pyrolysis temperature. It is evident that under the pyrolysis conditions of this application, the electrolyte in the battery recycled material can be effectively recovered.

[0121] By adding a first slag during pyrolysis and controlling the pyrolysis temperature, the electrolyte in the battery recyclables can be effectively recovered, and the amount of fluorides and phosphides entering the reduction tail gas during the battery recyclables recovery process can be reduced. This significantly reduces the adverse effects of catalyst poisoning and adsorbent poisoning in the subsequent treatment of the reduction tail gas. At the same time, adding a first slag during pyrolysis and using purification processes such as carbonation to remove impurities, evaporation decomposition, and post-treatment can improve the lithium recovery rate in the production of lithium carbonate from battery recyclables. Moreover, by recycling and reusing the reduction tail gas while ensuring the overall lithium recovery rate, the consumption of production raw materials is effectively reduced. This achieves efficient, high-quality, and low-cost preparation and recycling of battery recyclables (including electrolyte and lithium), battery-grade lithium carbonate, and slag, demonstrating good economic efficiency.

[0122] The method for preparing lithium carbonate from battery recyclables provided in this application has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the core ideas of this application. It should be noted that those skilled in the art can make several improvements and modifications to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A method for preparing lithium carbonate from battery recycled materials, characterized in that, include: The battery recyclables and the first slag are obtained and mixed. The battery recyclables include lithium-containing cathode material and electrolyte. The first slag includes lithium ore slag, which is lithium ore slag with a lithium content of 0.05-0.5%, a sulfuric acid content of 0.05-1%, and a water content of 5-15%, obtained after leaching and filtering lithium ore. The mixed battery recyclables and the first slag were pyrolyzed at a temperature of 260-350℃ to obtain a pyrolyzed mixture. The pyrolysis mixture was reduced and roasted in the presence of a reducing agent to obtain roasting products and reduction tail gas. The roasted product is contacted with an acidic solution and carbon dioxide gas for carbonation and impurity removal to obtain a lithium bicarbonate solution and a first filter residue. The lithium bicarbonate solution is then evaporated and decomposed to obtain lithium carbonate.

2. The method for preparing lithium carbonate from battery recyclables as described in claim 1, characterized in that, The reducing agent is hydrogen and carbon powder.

3. The method for preparing lithium carbonate from battery recyclables as described in claim 2, characterized in that, The pyrolysis mixture is mixed with the second slag before reduction roasting. The second slag includes lithium ore slag, which is lithium ore slag obtained after leaching and filtration of lithium ore, with a lithium content of 0.05-0.5%, a sulfuric acid content of 0.05-1%, and a water content of 5-15%.

4. The method for preparing lithium carbonate from battery recyclables as described in claim 3, characterized in that, The mass ratio of the battery recycled material to the total residue is 2-5.6:1, the mass of the total residue is the sum of the masses of the first residue and the second residue, and the mass of the second residue is 40-70% of the mass of the total residue.

5. The method for preparing lithium carbonate from battery recyclables as described in claims 1-4, characterized in that, The treatment of the reduction exhaust gas specifically includes: The reduction tail gas is subjected to dust removal, washing, cooling, and conversion in sequence; at least part of the carbon monoxide and water in the reduction tail gas is converted into hydrogen and carbon dioxide through conversion; and the converted hydrogen and carbon dioxide are separated and recovered, the separated and recovered carbon dioxide is returned to the carbonization and impurity removal, and the separated and recovered hydrogen is returned to the reduction roasting.

6. The method for preparing lithium carbonate from battery recyclables as described in claim 5, characterized in that, The carbon dioxide obtained from the separation and recovery is mixed with the carbon dioxide emitted from the evaporation and decomposition of lithium bicarbonate solution for recovery and concentration. Part of the recovered and concentrated carbon dioxide is returned to carbonization for impurity removal, and the other part of the recovered and concentrated carbon dioxide is returned to reduction roasting.

7. The method for preparing lithium carbonate from battery recyclables as described in claim 4, characterized in that, The reduction exhaust gas treatment also includes: Methanol and water are reformed to obtain reformed gas, which is then mixed with washing and cooled reduction tail gas for conversion. The reforming temperature is 150-350℃, and the reforming pressure is 1-2.6MPa; The reformed gas includes H2, CO, CO2 and H2O, wherein the H2 content is 50-75%.

8. The method for preparing lithium carbonate from battery recyclables as described in claim 2, characterized in that, Also includes The first filter residue is acid-leached to obtain a second filter residue, a second filtrate, and hydrogen.

9. The method for preparing lithium carbonate from battery recyclables as described in claim 1, characterized in that, The pH value of the acidic solution is 3-6.

10. The method for preparing lithium carbonate from battery recyclables as described in claim 1, characterized in that, During the reduction roasting process, the molar ratio of the reducing agent to the lithium salt in the pyrolysis mixture is 2.1-2.3:1, the reduction roasting temperature is 500-800℃, and the reduction roasting time is 2.5-4.5h.

11. The method for preparing lithium carbonate from battery recyclables as described in claim 6, characterized in that, The mass ratio of carbon dioxide recovered and concentrated and returned to carbonization for purification to carbon dioxide returned to reduction roasting is 1.2-3.5:

1.

12. The method for preparing lithium carbonate from battery recyclables as described in claim 5, characterized in that, The separation and recovery are performed using pressure swing adsorption (PSA), with a temperature of 20-40℃ and a pressure of 0.8-2.5 MPa.

13. The method for preparing lithium carbonate from battery recyclables as described in claim 1, characterized in that, The acidic solution includes at least one of sulfuric acid and acidic circulating mother liquor, wherein the acidic circulating mother liquor is obtained by centrifugation of the filtrate obtained after evaporation and decomposition of lithium bicarbonate solution.

14. The method for preparing lithium carbonate from battery recyclables as described in claim 1, characterized in that, In the carbonization and impurity removal process, the carbon dioxide volume concentration is controlled at 80-99%, the temperature is controlled at 5-30℃, the pressure is controlled at 0.15-0.6MPa, and the excess carbon dioxide coefficient is controlled at 1.7-3.5.

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