Method for preparing cobalt phosphate pigment based on waste lithium batteries

Abstract

The invention relates to the technical field of lithium battery recovery, in particular to a method for preparing cobalt phosphate pigment based on waste lithium batteries. The method comprises the following steps: extracting lithium iron phosphate and lithium cobalt oxide powder from the waste lithium battery; preparing lithium iron phosphate into slurry, and treating with sulfuric acid to obtain mixed slurry A; adding lithium cobalt oxide into the slurry A, adjusting the pH value to 5.5-6.0, and filtering to obtain a leaching solution; adding ammonia water into the leachate to adjust the pH value to 7.5-8.5 to generate cobalt phosphate precipitate, and washing to obtain a precursor; calcining and grinding the precursor to obtain the cobalt phosphate pigment. According to the method, waste lithium batteries are used as raw materials, and the cobalt phosphate pigment is directly prepared by controlling components. Valuable components in the waste materials are utilized, the requirement for new resources is reduced, and the production process is shortened. A short-process treatment mode is adopted, so that cyclic utilization of resources is realized, and meanwhile, energy consumption and cost are reduced. The technology provides a new path for battery recovery, and shows technical and economic advantages.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery recycling, and particularly to a method for preparing cobalt phosphate pigment from waste lithium batteries. Background Art

[0002] With the rapid development of the new energy vehicle industry, the large-scale recycling and treatment of waste lithium-ion batteries have become the focus of global attention. At present, the mainstream recycling technologies in the industry mainly focus on the extraction of valuable metals such as cobalt, nickel, and lithium, and generally use pyrometallurgical smelting or hydrometallurgical processes.

[0003] However, metal purification requires multiple steps such as leaching, separation, and crystallization. The conversion cycle from raw materials to the final metal salt products is long (for example, the preparation of cobalt salts requires 5-7 processes). Moreover, the phosphorus element in lithium iron phosphate batteries is often discharged in the form of waste residue, and the phosphorus-iron-lithium synergy cannot be achieved. In addition, the output products are mostly basic chemical raw materials such as industrial-grade lithium carbonate and cobalt sulfate, and there is a lack of a direct conversion path for high-value-added end products. Summary of the Invention

[0004] The main purpose of this application is to provide a method for preparing cobalt phosphate pigment from waste lithium batteries, aiming to solve the technical problem of recovering cobalt resources from waste lithium batteries.

[0005] To achieve the above purpose, a method for preparing cobalt phosphate pigment from waste lithium batteries proposed in an embodiment of this application includes the following steps:

[0006] Obtain lithium iron phosphate powder and lithium cobaltate powder from waste lithium batteries;

[0007] Prepare the lithium iron phosphate powder into a slurry with water, then add sulfuric acid and mix for a hot leaching reaction to obtain a mixed slurry A;

[0008] Add the lithium cobaltate powder to the mixed slurry A, adjust the pH to 5.5-6.0, perform stirring treatment, and then filter to obtain a leachate;

[0009] Add ammonia water to the leachate to adjust the pH to 7.5-8.5 to generate cobalt phosphate precipitate, and obtain a precursor after washing;

[0010] Calcine and grind the precursor to prepare cobalt phosphate pigment.

[0011] In some embodiments, the mass ratio of the lithium iron phosphate powder to the water is 1:(3-7); the mass-volume ratio of the lithium iron phosphate powder to the sulfuric acid is 200g:(90-150mL).

[0012] In some embodiments, the reaction temperature of the hot leaching reaction is 60-90°C, and the reaction time is 0.5-2h.

[0013] In some embodiments, the mass of the lithium cobaltate powder is 10% - 50% of the mass of the lithium iron phosphate powder.

[0014] In some embodiments, the molar ratio of cobalt ions in the lithium cobaltate powder to phosphate radicals in the lithium iron phosphate powder is 1:(1.15 - 1.55).

[0015] In some embodiments, the concentration of the ammonia water is 5 - 15 wt%; the washing is carried out with water at 60 - 90 °C.

[0016] In some embodiments, the calcination temperature is 750 - 900 °C, the calcination time is 2 - 4 hours, and the particle size of the cobalt phosphate pigment after grinding is 600 - 2000 mesh.

[0017] In some embodiments, before adding ammonia water to adjust the pH of the leaching solution, it further includes the step of performing multi-stage cross-flow extraction for impurity removal on the leaching solution.

[0018] In some embodiments, the step of multi-stage cross-flow extraction for impurity removal uses extractant P204, and the number of extraction stages is 3 - 6.

[0019] In some embodiments, the lithium iron phosphate powder and the lithium cobaltate powder are obtained by processing waste lithium battery recycling materials, and the recycling materials include at least one of battery powder, electrode sheet powder, and positive electrode waste powder.

[0020] This technical solution uses waste lithium batteries as raw materials. Through the synergistic leaching process of lithium iron phosphate and lithium cobaltate waste powder, elements such as cobalt and phosphorus in waste batteries are directly converted into cobalt phosphate precursors, realizing the effective utilization of valuable components in waste resources and reducing the demand for primary mineral resources. The whole process adopts an integrated leaching - filtration - precipitation - calcination process flow. Ammonia water is used to adjust the pH value to the range of 7.5 - 8.5 to control the purity of cobalt phosphate precipitation, and cobalt phosphate pigment is directly prepared after the calcination step. This method omits multiple processes of metal separation, purification, and pigment synthesis in traditional processes, simplifying the production process.

[0021] Through this short process design, the intermediate separation steps are reduced, the equipment investment and operation complexity are lowered. Based on hydrometallurgy technology, this solution realizes the transformation from battery waste to a functional material - cobalt phosphate pigment product, expanding the application scope of traditional recycling limited to metal extraction. This provides a new idea for the battery recycling industry, that is, from "resource regeneration" to "functional material preparation", which helps to promote resource recycling and increase the added value of products. Description of the Drawings

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0023] Figure 1 is a schematic diagram of the preparation process flow of an embodiment of the present application;

[0024] Figure 2 is a schematic diagram of the preparation process flow of an embodiment of the present application.

[0025] The realization of the object of the present invention, its functional features and advantages will be further described in conjunction with the embodiments with reference to the drawings. Detailed Embodiments

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0027] Hereinafter, the non-aqueous sodium metal battery, the electrolyte, its preparation method and the electrical device of the present application will be specifically disclosed in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0028] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, 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, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise specified, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0029] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form a new technical solution.

[0030] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0031] If there is no special instruction, all steps of this application can be carried out sequentially or randomly, and preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0032] With the widespread application of lithium-ion batteries, the large-scale recycling and resource utilization of waste lithium batteries have become the focus of global attention. Traditional recycling methods mainly focus on the simple extraction and separation of metal elements, and generally have problems such as long process flow, high energy consumption, and high cost. For example, existing hydrometallurgical processes often use multi-stage acid leaching, complex extraction, and repeated purification steps, which not only limit the recovery efficiency of key metals such as cobalt and lithium, but also make it difficult to effectively remove impurities such as iron and aluminum, affecting the purity of the product. In addition, most recycling technologies only stay at the primary regeneration stage of metal raw materials and fail to convert the recycled products into high-value-added end products, resulting in low economic benefits of resource recycling. Especially in the context of the increasingly scarce cobalt resources, how to achieve efficient cobalt recovery and directly apply it to the field of high-performance materials has become a technical bottleneck that the industry urgently needs to break through.

[0033] A method for preparing cobalt phosphate pigment based on waste lithium batteries proposed in an embodiment of the present application includes the following steps:

[0034] S1. Obtain lithium iron phosphate powder and lithium cobaltate powder from waste lithium batteries;

[0035] S2. Prepare a slurry by mixing lithium iron phosphate powder with water, and then add sulfuric acid and conduct a hot leaching reaction to obtain a mixed slurry A;

[0036] S3. Add lithium cobaltate powder to the mixed slurry A, adjust the pH to 5.5 - 6.0, conduct a stirring treatment, and then filter to obtain a leaching solution;

[0037] S4. Add ammonia water to the leaching solution to adjust the pH to 7.5 - 8.5 to generate cobalt phosphate precipitate, and obtain a precursor after washing;

[0038] S5. Calcinate and grind the precursor to obtain cobalt phosphate pigment.

[0039] In this technical solution, the cathode materials, including lithium iron phosphate and lithium cobaltate, are recovered from waste lithium batteries and used as the cobalt source and phosphate source for synthesizing cobalt phosphate. This process directly utilizes the valuable metals (Co) and phosphate radicals in the battery waste, avoids the dependence on primary ores in traditional processes, reduces the raw material cost, and also reduces solid waste pollution.

[0040] First, add lithium cobaltate powder to the mixed slurry A and adjust the pH to the weakly acidic range (5.5 - 6.0). Under such acidic conditions, lithium cobaltate (LiCoO2) will release cobalt ions (Co 2+ ), (reaction formula: LiCoO2 + H + →Co 2+ +Li ++ H2O + O2), and these cobalt ions then combine with phosphate ions in the solution to form a cobalt phosphate precursor. Maintaining the pH value between 5.5 and 6.0 helps to inhibit the precipitation of impurity ions such as Fe 3+ and Al 3+ etc., thus reducing the co-precipitation phenomenon and improving the purity of the subsequent cobalt phosphate.

[0041] Next, the pH value of the leaching solution is adjusted to 7.5 - 8.5 by adding ammonia water to promote the formation of cobalt phosphate precipitation. This pH range is the optimal interval for the stable precipitation of cobalt phosphate, which can prevent the formation of by-products such as cobalt hydroxide (Co(OH)2).

[0042] This application adopts a hydrometallurgical process (including leaching and precipitation steps), replacing the traditional pyrometallurgical process and solid-phase synthesis method, greatly shortening the process flow and reducing energy consumption. In addition, this method also realizes the efficient recovery of cobalt in waste lithium batteries, while lithium is enriched in the filtrate in the form of lithium sulfate for further extraction and utilization, achieving the resource treatment of all components.

[0043] In some embodiments, the mass ratio of lithium iron phosphate powder to water is 1:(3 - 7); the mass-volume ratio of lithium iron phosphate powder to sulfuric acid is 200 g:(90 - 150 mL).

[0044] This technical solution involves preparing a slurry by mixing lithium iron phosphate powder and water at a mass ratio of 1:(3 - 7), that is, controlling the liquid-solid ratio between 3 and 7. Specifically, during operation, 90 mL to 150 mL of sulfuric acid is added to every 200 grams of lithium iron phosphate powder for hot leaching reaction. During this process, lithium iron phosphate reacts chemically with sulfuric acid (LiFePO4 + H2SO4 → FeSO4 + LiH2PO4 + H2O), thereby releasing phosphate ions (PO4 3- ) and lithium ions (Li + ). As an example, the mass ratio of lithium iron phosphate powder to water can be typical but non-limiting values such as 1:3, 1:4, 1:5, 1:6, 1:7, etc. The mass-volume ratio of lithium iron phosphate powder to sulfuric acid can be typical but non-limiting values such as 200 g:90 mL, 200 g:100 mL, 200 g:110 mL, 200 g:120 mL, 200 g:130 mL, 200 g:140 mL, 200 g:150 mL, etc.

[0045] By controlling the liquid-solid ratio of the slurry and the dosage of sulfuric acid, the dissolution of lithium iron phosphate can be further promoted, while avoiding the difficulty of subsequent neutralization treatment caused by excessive acid. This regulation not only improves the utilization rate of raw materials but also optimizes the efficiency and economy of the entire process flow.

[0046] In some embodiments, the reaction temperature of the hot dissolution reaction is 60-90 °C, and the reaction time is 0.5-2 h. In this embodiment, by setting the hot dissolution reaction conditions to a temperature of 60-90 °C and a time of 0.5-2 h, its core function is to achieve efficient dissolution of the target metals (Li, Fe, P) in lithium iron phosphate by optimizing the reaction kinetic parameters, while suppressing side reactions and impurity release. Further, the reaction temperature of the hot dissolution reaction is 80-85 °C.

[0047] In some embodiments, the mass of lithium cobaltate powder is 10%-50% of the mass of lithium iron phosphate powder. As an example, it can be typical but non-limiting values such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc. In the synthesis of cobalt phosphate (Co3(PO4)2), the stoichiometric ratio is Co 2+ :PO4 3- =1.5:1, that is, every 3 mol of Co 2+ requires 2 mol of PO4 3- . By adjusting the mass ratio of lithium cobaltate to lithium iron phosphate, the molar ratio of Co 2+ :PO4 3- is indirectly controlled to be close to the theoretical value (1.5:1). Through the ratio optimization of lithium cobaltate and lithium iron phosphate, the balance between resource recovery and product quality in this process is achieved.

[0048] In some embodiments, the molar ratio of cobalt ions in lithium cobaltate powder to phosphate groups in lithium iron phosphate powder is 1:(1.15-1.55). As an example, the end ratio of the two can be typical but non-limiting values such as 1:1.15, 1:1.2, 1:1.25, 1:1.3, 1:1.35, 1:1.4, 1:1.45, 1:1.5, 1:1.55, etc. When Co 2+ :PO4 3- =1:1.15-1.55 in the process, then the phosphate group (PO4 3- ) is always in excess. The excess phosphate group can cause almost all Co 2+ to participate in the reaction, avoiding unreacted cobalt ions remaining in the solution and improving the product yield. In addition, the excess phosphate group helps to optimize the morphology and particle size of cobalt phosphate crystals, making the final product particles more uniform and delicate.

[0049] In some embodiments, the concentration of the ammonia water is 5-15 wt%; the washing is carried out with water at 60-90 °C.

[0050] Using ammonia water within this concentration range to adjust the pH value helps to avoid excessive hydroxyl groups in the cobalt phosphate precipitate, preventing the rapid release of OH by high-concentration ammonia water - resulting in too high an instantaneous pH value, which in turn triggers Co2+ Hydroxylation reaction. An ammonia water concentration of 5-15 wt% can provide sufficient NH3 molecules to maintain the stability of the solution pH value, while reducing the introduction of excessive NH4 + ions and avoiding their competitive coordination with PO4 3- to reduce the possible defects that may occur during the crystallization process of cobalt phosphate.

[0051] In addition, washing with hot water at 60-90 °C can better remove the NH4 adsorbed on the product + , SO4 2- and other soluble impurities. This not only helps to improve the purity of the precursor, but also improves the quality of the final product. The washing process under such temperature conditions helps to improve the purity of the cobalt phosphate precursor, making the performance of the subsequently prepared functional materials more superior.

[0052] In some embodiments, the calcination temperature is 750-900 °C, the calcination time is 2-4 hours, and the particle size of the cobalt phosphate pigment after grinding is 600-2000 mesh.

[0053] By precisely controlling the calcination temperature within this range, cobalt phosphate will undergo a dehydration reaction and form a stable spinel structure (Co3(PO4)2), which endows the pigment with excellent high-temperature resistance characteristics. In addition, grinding the pigment into ultrafine powder (e.g., 600 mesh ≈ 25 μm) can significantly enhance the pigment dispersibility and coloring uniformity, meeting the application requirements of high-end pigments.

[0054] In some embodiments, before adding ammonia water to adjust the pH of the leaching solution, it further includes the step of performing multi-stage cross-flow extraction to remove impurities from the leaching solution. Multi-stage cross-flow extraction is a separation and purification technique used to remove unwanted elements from a solution containing target metal ions and other impurities. During this process, the feed solution passes through a series of extraction stages, and in each stage, fresh or partially used extractant is contacted with the feed solution. This contact method is called cross-flow, that is, the flow directions of the feed solution and the extractant are staggered between different stages, aiming to reduce the impurity content without losing too much of the target component. In this technical solution, it is achieved by mixing fresh organic phase with the leaching solution to be treated multiple times. As the process progresses, impurities such as copper, iron, and aluminum are gradually transferred to the extractant, while the target metal ions remain in the solution. After this process, the total content of impurities such as copper, iron, and aluminum can be reduced to below 10 ppm. The quality of the final product is improved.

[0055] In some embodiments, the step of multi-stage cross-flow extraction for impurity removal uses extractant P204, and the number of extraction stages is 3 to 6. Extractant P204, also known as Di(2-ethylhexyl)phosphoric acid, is mainly used for extracting metal ions such as copper, cobalt, nickel, etc. from aqueous solutions. P204 has good selectivity and extraction efficiency, and shows strong affinity for various metal ions especially under acidic conditions. The extraction impurity removal process selectively removes impurities, avoiding waste of resources caused by repeated purification. This process uses extractant P204 for 3 to 6 stages of cross-flow extraction to remove impurities such as iron, aluminum, copper, etc. in the leaching solution. Through 3-stage extraction, about 90% of the impurities can be removed; while for 5 to 6 stages of extraction, the impurity content can be further reduced to less than 1 ppm, meeting the purity requirements for high-end pigments.

[0056] As an example, for the step of multi-stage cross-flow extraction for impurity removal, the specific operation process is as follows: Mix the leaching solution and fresh extractant at a volume ratio of 1:1 to 1:1.5. The extractant can be P204 extractant with a mass concentration of 15% to 50%; after mixing evenly, separate the two phases after 4 to 10 minutes; retain the aqueous phase and send it to the next-stage treatment; repeat the above steps, each time using a new P204 organic phase to mix with the aqueous phase separated from the previous stage; according to the actual situation, 3 to 6 such operations can be selected. After each stage of extraction, the impurity content in the aqueous phase will gradually decrease, while the purity of the target metal ions will increase accordingly.

[0057] In some embodiments, the lithium iron phosphate powder and lithium cobalt oxide powder are obtained by processing waste lithium battery recycling materials, and the recycling materials include at least one of battery powder, electrode sheet powder, and positive electrode waste powder.

[0058] Battery powder refers to the fine powder obtained by physically or chemically crushing and decomposing waste lithium batteries. It may contain various components in the battery, such as cathode materials, anode materials, electrolyte residues, etc. Electrode sheet powder refers to the powder formed after the positive and negative electrode sheets inside the battery are pulverized. These electrode sheets are usually composed of current collectors (such as aluminum foil for the positive electrode and copper foil for the negative electrode) and the active substances coated on them. During the pulverization process, the current collector and the active substances are pulverized into powder together. Positive electrode waste powder refers to the powder recovered from the positive electrode part of waste lithium batteries, and its main components are positive electrode active materials, such as lithium iron phosphate (LiFePO4), lithium cobalt oxide (LiCoO2), etc., as well as auxiliary materials such as conductive agents and binders that may be mixed in. The materials obtained by recycling through the above method in this technical solution, especially the lithium iron phosphate and lithium cobalt oxide powders among them, will be further processed (such as leaching, precipitation, calcination, etc. steps) to prepare functional materials with specific uses, such as cobalt phosphate pigments. This method not only helps with resource recycling and reduces environmental pollution, but also can reduce raw material costs.

[0059] The following is an illustration with specific embodiments.

[0060] Example 1

[0061] This example provides a method for preparing cobalt phosphate pigment based on waste lithium batteries, including the following steps:

[0062] (1) Take 50 g of lithium iron phosphate powder and 200 g of lithium cobalt oxide powder in the electrode sheet powder (the components of both are shown in Table 1); (2) Configure the lithium iron phosphate powder and water into a slurry according to a mass ratio of 1:5, add 150 mL of sulfuric acid, and place it in a constant temperature water bath at 80 °C to heat and dissolve for 1.5 h to obtain a mixed slurry A;

[0063] (3) Add 50 g of lithium cobalt oxide powder to the mixed slurry A, adjust the pH value to 6.0, stir for 2 h to obtain a leaching solution and leaching residue, filter to obtain the leaching solution, and the composition of the leaching solution is shown in Table 2;

[0064] (4) Heat the leaching solution in a water bath at 50 °C, dropwise add ammonia water with a concentration of 10 wt%, adjust the system pH to 8.0 and stabilize for 1 h to generate cobalt phosphate precipitate, and obtain the precursor after washing with water;

[0065] (5) Place the obtained precursor in an oven to dry, then place it in a muffle furnace for calcination. The calcination temperature is 800 °C, and the calcination time is 3 hours. After the calcination is completed, take out the calcined product, continuously stir it with a ceramic rod at a high temperature state, wait until it cools to room temperature and take out the calcined product, and grind it to 600 meshes with a high-speed ball mill to obtain cobalt phosphate with a purity of 86.9%, and the conversion rate of cobalt phosphate reaches 91.4%.

[0066] Table 1 Composition analysis of lithium iron phosphate powder and lithium cobalt oxide powder

[0067]

[0068] Table 2 Composition of the leaching solution

[0069]

[0070] Example 2

[0071] The difference between Example 2 and Example 1 is that before adding ammonia water to adjust the pH of the leaching solution, it further includes the step of subjecting the leaching solution to multi-stage cross-flow extraction for impurity removal. The specific steps are as follows:

[0072] (1) Take 50 g of lithium iron phosphate powder and 200 g of lithium cobalt oxide powder in the electrode powder (the components of both are shown in Table 1);

[0073] (2) Prepare a slurry by mixing lithium iron phosphate powder and water at a mass ratio of 1:5, add 150 mL of sulfuric acid, and heat and dissolve it in a constant temperature water bath at 80 °C for 1.5 h to obtain a mixed slurry A;

[0074] (3) Add 50 g of lithium cobalt oxide powder to the mixed slurry A, adjust the pH value to 6.0, stir for 2 h to obtain a leaching solution and leaching residue, filter to obtain the leaching solution, and the composition of the leaching solution is shown in Table 2;

[0075] (4) Mix the leaching solution with a 30% mass concentration of P204 extractant at a volume ratio of 1:1, perform 3-stage cross-flow extraction to obtain an extract, and the composition of the extract is shown in Table 3,

[0076] (5) Heat the extract in a water bath at 50 °C, dropwise add ammonia water with a concentration of 10 wt%, adjust the system pH to 8.0 and stabilize for 1 h to form cobalt phosphate precipitate, and obtain a precursor after washing with water;

[0077] (6) Place the obtained precursor in an oven for drying, then place it in a muffle furnace for calcination. The calcination temperature is 800 °C, and the calcination time is 3 hours. After the calcination is completed, take out the calcined product, continuously stir it with a stainless steel rod at a high temperature state, wait until it cools to room temperature and take out the calcined product, and grind it to 600 with a high-speed ball mill to obtain cobalt phosphate with a purity of 99.11%, and the conversion rate of cobalt phosphate reaches 93.65%. It can be used as cobalt violet 50 pigment, showing a light cobalt violet - red tone.

[0078] Table 3 Composition of the extract

[0079]

[0080]

[0081] Example 3

[0082] Example 3 is different from Example 2 in that: the addition amount of lithium cobaltate powder is 100 g, and the number of stages of multi-stage cross-flow extraction is 5. Cobalt phosphate with a purity of 99.37% is finally obtained, and the conversion rate of cobalt phosphate reaches 92.11%.

[0083] Example 4

[0084] Example 4 is different from Example 2 in that: the addition amount of lithium cobaltate powder is 200 g, the addition amount of sulfuric acid is 210 mL, the hot melt-out time is 0.5 h, and the number of stages of multi-stage cross-flow extraction is 6. Cobalt phosphate with a purity of 99.13% is finally obtained, and the conversion rate of cobalt phosphate reaches 47.69%.

[0085] Comparative Example 1

[0086] Comparative Example 1 is different from Example 1 in that: in step (3), 50 g of lithium cobaltate powder is added to the mixed slurry A, and the pH value is not adjusted to 5.5 - 6.0. Cobalt phosphate with a purity of 63.71% is obtained, and the conversion rate of cobalt phosphate reaches 85.17%.

[0087] Comparative Example 2

[0088] Comparative Example 2 is different from Example 1 in that: in step (4), the pH of the system is adjusted to 9 by dropping 10 wt% ammonia water. Cobalt phosphate with a purity of 71.18% is obtained, and the conversion rate of cobalt phosphate reaches 85.05%.

[0089] Performance Test

[0090] 1. Purity Detection:

[0091] Use EDTA (ethylenediaminetetraacetic acid) as a complexing agent to titrate cobalt ions, measure the concentration of cobalt ions, and then calculate the purity.

[0092] 2. Calculation Method for the Conversion Rate of Cobalt Phosphate:

[0093] Calculate the maximum amount of cobalt phosphate that can be obtained theoretically (i.e., the theoretical yield) based on the amount of lithium cobaltate raw material input. Measure the mass of the actual output of cobalt phosphate obtained through experiments. Conversion rate (%) = (actual output / theoretical output) × 100%.

[0094] 3. Elemental Analysis Test

[0095] Use an inductively coupled plasma spectrometer (ICP, instrument model: PE Optima 7000DV) to test the metal element content in the material. First, weigh an appropriate amount of powder sample, add about 10 mL of aqua regia, and keep heating in a flat heating instrument environment at about 185 °C for 30 min to 50 min to fully digest the sample, and then perform on-machine testing.

[0096] 4. Chromaticity Test of Cobalt Phosphate Pigment

[0097] The cobalt phosphate pigment was dry-pressed into a disc-shaped sample, and the colorimetric test was carried out using Konica Minolta CM-3700D in Japan. The measured colorimetric data values are shown in Table 4, where the colorimetric data is characterized by Lab values. The range of the L value is 0 - 100, representing the lightness value; the range of the a value is -128 to +127, representing the range from green to red; the range of the b value is -128 to +127, representing the range from blue to yellow.

[0098] Performance Analysis

[0099] It was found from the raw material composition analysis in Table 1 that lithium cobaltate is rich in up to 59.48% cobalt and 6.94% lithium; while lithium iron phosphate mainly provides phosphorus (17.26%) and iron (30.17%), but its relatively high iron content needs to be removed through subsequent processes to improve the purity of the final product.

[0100] In terms of the comparison of the compositions of the leaching solution and the purified solution in Table 2 and Table 3, the initial leaching solution contains relatively high concentrations of the target metals cobalt, lithium, and phosphorus, but also contains significant amounts of impurities such as iron. After multi-stage cross-flow extraction treatment, the impurity content is reduced to <1 ppm, while maintaining the concentration stability of the target metals, indicating that this extraction process has high selectivity and purification ability, providing high-quality raw materials for the subsequent synthesis of cobalt phosphate.

[0101] The pH in step (3) of Comparative Example 1 was not controlled in the weakly acidic range (5.5 - 6.0), resulting in the co-precipitation of impurity ions such as Fe 3+ and Al 3+ with Co 2+ . These impurities are mixed into the cobalt phosphate, significantly reducing the product purity and the conversion rate of cobalt phosphate. The pH in step (4) of Comparative Example 2 was too high, and Co 2+ was easily combined with OH - to form cobalt hydroxide (Co(OH)2) precipitate, rather than the target product cobalt phosphate. This side reaction not only introduces impurities (such as Co(OH)2), but also consumes some cobalt ions, resulting in a decrease in purity and conversion rate.

[0102] The comparison of the example parameters reveals the influence of several key factors on the conversion rate and purity of cobalt phosphate. The optimal range of the lithium cobaltate addition amount should be 25% - 50% (the lithium cobaltate addition amounts in Examples 2, 3, and 4 are 50 g (25%), 100 g (50%), and 200 g (100%) respectively). Among them, Examples 2 and 3 maintain Co 2+ :PO4 3-The molar ratio is close to the theoretical value, thus achieving a high conversion rate. In Example 4, the addition amount of lithium cobaltate reached 200 g (100% of lithium iron phosphate), far exceeding the recommended range of 10%-50%. A large amount of unreacted cobalt ions remained in the solution, significantly reducing the conversion rate (the conversion rate was 47.69%). In addition, the extraction stage should be controlled between 3 and 5 stages, which can not only better remove impurities but also not overly affect the retention rate of cobalt. All examples can obtain high-purity cobalt phosphate products under the calcination conditions of 700-900 °C and form a stable spinel structure.

[0103] Table 4 Chromaticity Test Results of Cobalt Phosphate Pigments

[0104]

[0105]

[0106] The chromaticity characteristics of the commercial cobalt violet 50 pigment are specifically manifested as follows: the L value (brightness) is between 20 and 60, with medium brightness; the A value (red tone) is between 20 and 40; the B value (blue tone) is between -10 and -30. It can be seen from the data in Table 4 that the cobalt phosphate pigments prepared in Examples 1-4 of this application meet the standard requirements of the commercial cobalt violet 50 pigment in terms of chromaticity, indicating that the pigment has ideal color properties and is suitable for multiple industries such as painting, ceramic decoration, coloring of plastics and rubber products, and printing.

[0107] The above are only the preferred embodiments of this application, and do not limit the patent scope of this application. Any equivalent structural transformation made under the application concept of this application by using the content of the specification and drawings of this application, or directly / indirectly applied in other related technical fields, is included in the patent protection scope of this application.

Claims

1. A method for preparing cobalt phosphate pigment based on waste lithium batteries, characterized in that: The following steps are involved: Obtain lithium iron phosphate powder and lithium cobalt oxide powder from waste lithium batteries; The lithium iron phosphate powder and water are mixed into a slurry, and then sulfuric acid is added to mix and perform a thermal dissolution reaction to obtain a mixed slurry A; Adding the lithium cobalt oxide powder to the mixed slurry A, adjusting the pH to 5.5-6.0, stirring, and then filtering to obtain a leachate; Adding ammonia water to the leaching solution to adjust the pH to 7.5-8.5 to generate cobalt phosphate precipitate, and washing to obtain a precursor; The precursor is calcined and ground to obtain a cobalt phosphate pigment.

2. The method for preparing cobalt phosphate pigment based on waste lithium batteries according to claim 1, characterized in that: The mass ratio of the lithium iron phosphate powder to the water is 1:(3-7); the mass volume ratio of the lithium iron phosphate powder to the sulfuric acid is 200g:(90-150mL).

3. The method for preparing cobalt phosphate pigment based on waste lithium batteries according to claim 1 or 2, characterized in that: The reaction temperature of the thermal dissolution reaction is 60-90° C., and the reaction time is 0.5-2 h.

4. The method for preparing cobalt phosphate pigment based on waste lithium batteries according to claim 1, characterized in that: The mass of the lithium cobalt oxide powder is 10% to 50% of the mass of the lithium iron phosphate powder.

5. The method for preparing cobalt phosphate pigment based on waste lithium batteries according to claim 4, characterized in that: The molar ratio of cobalt ions in the lithium cobalt oxide powder to phosphate in the lithium iron phosphate powder is 1:(1.15-1.55).

6. The method for preparing cobalt phosphate pigment based on waste lithium batteries according to claim 1, characterized in that: The concentration of the ammonia water is 5-15wt%; the washing is performed with water at 60-90°C.

7. The method for preparing cobalt phosphate pigment based on waste lithium batteries according to claim 1, characterized in that: The calcination temperature is 750-900° C., the calcination time is 2-4 hours, and the particle size of the cobalt phosphate pigment after grinding is 600-2000 meshes.

8. The method for preparing cobalt phosphate pigment based on waste lithium batteries according to any one of claims 1 to 7, characterized in that: Before adding ammonia water to the leachate to adjust the pH, the method further includes subjecting the leachate to multipolar cross-current extraction to remove impurities.

9. The method for preparing cobalt phosphate pigment based on waste lithium batteries according to claim 8, characterized in that: The multi-stage cross-flow extraction and impurity removal step uses the extractant P204, and the number of extraction stages is 3 to 6.

10. The method for preparing cobalt phosphate pigment based on waste lithium batteries according to any one of claims 1 to 7, characterized in that: The lithium iron phosphate powder and the lithium cobalt oxide powder are obtained by processing recycled materials from waste lithium batteries, and the recycled materials include at least one of battery powder, pole piece powder and positive electrode waste powder.

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