Separation and detection methods

Abstract

This application relates to the field of materials testing technology and provides a separation and detection method suitable for the separation and detection of metallic magnetic foreign matter in lithium iron phosphate. The method includes the following steps: obtaining a primary concentrate from lithium iron phosphate slurry using a magnetic rod; placing the primary concentrate in an aqueous solution containing a viscous dispersant, using a magnet to attract and move it, separating the strongly magnetic metallic foreign matter; performing microscopic observation on the weakly magnetic impurities discharged after separation to distinguish the strongly magnetic metallic foreign matter from iron phosphide; and performing digestion treatment on the strongly magnetic metallic foreign matter and performing elemental quantitative analysis. This application achieves efficient separation of strongly magnetic metallic foreign matter from iron phosphide through a three-stage treatment method of primary screening, viscous dispersant separation, and digestion treatment, thereby improving the accuracy of the detection results. Microscopic observation further verifies and ensures the separation effect of strongly magnetic metallic foreign matter from the weakly magnetic impurity iron phosphide, thus contributing to the accuracy of the detection results.

Description

Technical Field

[0001] This application relates to the field of materials testing technology, and in particular to a separation testing method. Background Technology

[0002] Lithium iron phosphate, as a raw material for lithium batteries, has good electrochemical and thermal stability. However, a small amount of metallic magnetic foreign matter often exists in lithium iron phosphate materials. During charging and discharging, these metallic magnetic foreign matter can easily precipitate dendritic metals and pierce the separator, causing an internal short circuit in the battery and triggering thermal runaway.

[0003] In related technologies, when separating and detecting metallic magnetic foreign matter in lithium iron phosphate, inductively coupled plasma atomic emission spectrometry or scanning electron microscopy-energy dispersive spectroscopy are usually used. However, such detection methods are not conducive to improving the accuracy of the detection results. Summary of the Invention

[0004] In view of this, this application aims to propose a separation detection method to improve the accuracy of detection results.

[0005] To achieve the above objectives, the technical solution of this application is implemented as follows:

[0006] A separation and detection method suitable for separating and detecting metallic magnetic foreign matter in lithium iron phosphate, the method comprising the following steps:

[0007] Magnetic materials are adsorbed and enriched from lithium iron phosphate slurry using magnetic rods, and then washed to obtain a primary enrichment containing strongly magnetic metallic foreign matter and weakly magnetic impurities.

[0008] The primary enrichment is placed in an aqueous solution containing a viscous dispersant. A magnet is used to attract and move the enriched material, causing weakly magnetic impurities to separate from the magnet and be discharged under the resistance of the solution, while strongly magnetic metallic foreign matter is separated.

[0009] The weakly magnetic impurities discharged after separation are observed under a microscope, and the strong magnetic metal foreign matter is distinguished from iron phosphide by the optical characteristics of the particles; and / or, the strong magnetic metal foreign matter is digested and subjected to elemental quantitative analysis.

[0010] Furthermore, the step of using a magnetic rod to adsorb and enrich magnetic materials from lithium iron phosphate slurry, and then cleaning it to obtain a primary enriched product containing strongly magnetic metallic foreign matter and weakly magnetic impurities, includes: sealing the magnetic rod and demagnetizing the experimental environment and equipment; placing the sealed magnetic rod into a mixed slurry containing lithium iron phosphate powder and liquid, stirring for a preset time to allow the magnetic rod to adsorb magnetic materials; removing the magnetic rod with adsorbed magnetic materials, transferring it to a container, removing the sealing layer, and then cleaning the magnetic materials under magnetic field adsorption to obtain the primary enriched product.

[0011] Furthermore, the sealing process for the magnetic rod includes: placing the magnetic rod in a corrosion-resistant container, adding a strong oxidizing acid and heating it on an acid-removing hot plate, cooling it, and then using a magnet to attract it to the bottom of the corrosion-resistant container. The solution in the corrosion-resistant container is then transferred to a volumetric flask. The magnetic rod and the inner wall of the corrosion-resistant container are washed with pure water, and the washing solution is transferred to the volumetric flask. After making up the volume, elemental quantitative analysis is performed to verify that the concentration of each metal element is lower than a preset threshold. The magnetic rod is then cleaned, placed in a heat-shrink tubing that has been demagnetized, and heat-sealed.

[0012] Furthermore, the strong oxidizing acid is aqua regia.

[0013] Furthermore, the cleaning of the magnetic material under magnetic field adsorption includes:

[0014] Using a magnet, move it along a preset trajectory on the outside of the bottom of the container to attract and concentrate the pollutants. Then pour out the cleaning solution. Repeat this process several times.

[0015] Furthermore, the step of using a magnet to move along a preset trajectory on the outside of the bottom of the container, adsorbing the enriched material, and then pouring out the cleaning solution includes: the magnet adsorbing the material three times clockwise and three times counterclockwise on the outside of the bottom of the container as one round, with each round of adsorption taking 10±3s, and the material left to stand for no less than 3s after adsorption; when repeating the steps of adding water, adsorption, and pouring water, the amount of water added each time is 150±10mL.

[0016] Furthermore, the step of placing the primary concentrate in an aqueous solution containing a viscous dispersant and using a magnet to adsorb the weakly magnetic impurities, causing them to separate from the magnet under the resistance of the solution and be discharged, while separating the strongly magnetic metallic foreign matter, includes: adding ultrapure water to a container containing the primary concentrate and performing ultrasonic treatment; discarding the ultrasonicated liquid, adding an aqueous solution containing a viscous dispersant, using a magnet to move at the bottom of the container to adsorb the strongly magnetic metallic foreign matter, while simultaneously causing the weakly magnetic impurities and non-magnetic particles to leave the magnet's attraction area and be discharged along with the aqueous solution containing the viscous dispersant; repeating the discharge operation until no visible particles are found in the discharged solution.

[0017] Furthermore, the separation of the weakly magnetic impurities is subjected to microscopic observation to distinguish between strongly magnetic metallic foreign matter and iron phosphide by the optical characteristics of the particles. This includes: ultrasonically cleaning the weakly magnetic impurities with hydrochloric acid, washing them with water, filtering and drying them, and then observing them under a microscope; wherein, particles with smooth surfaces and reflective characteristics are identified as strongly magnetic metallic foreign matter, while particles with black spots are identified as iron phosphide.

[0018] Furthermore, the process of digesting the strongly magnetic metallic foreign matter and performing elemental quantitative analysis includes: digesting the strongly magnetic metallic foreign matter with a strong acid and adjusting the volume, and then using inductively coupled plasma atomic emission spectrometry to detect the content of one or more of the elements iron, chromium, and nickel.

[0019] Furthermore, the viscous dispersant is an aqueous solution of sodium carboxymethyl cellulose with a mass concentration between 0.1% and 0.3%.

[0020] Compared with related technologies, this application has the following advantages:

[0021] (1) The separation and detection method described in this application uses a magnetic rod to obtain the primary enrichment in lithium iron phosphate slurry, and treats the primary enrichment with a solution containing a viscous dispersant to remove weak magnetic impurities in the primary enrichment and separate strong magnetic metal foreign matter. Then, the strong magnetic metal foreign matter is digested. In this way, by adopting a three-stage treatment method of primary screening, viscous dispersant separation and digestion treatment, the strong magnetic metal foreign matter and iron phosphate are efficiently separated, which is beneficial to the accurate determination of strong magnetic metal foreign matter in lithium iron phosphate and thus improves the accuracy of detection results.

[0022] Meanwhile, by observing the separated weakly magnetic impurities under a microscope, it is possible to effectively detect whether the weakly magnetic impurities contain strongly magnetic metallic foreign objects, thereby further verifying and ensuring the separation effect of strongly magnetic metallic foreign objects from weakly magnetic iron phosphide impurities, which helps to ensure the accuracy of the detection results.

[0023] (2) By sealing the magnetic rod, direct contact between the magnetic rod and metallic magnetic foreign objects can be effectively avoided, thereby preventing impurities on the surface of the magnetic rod from mixing into the metallic magnetic foreign objects, and also effectively preventing the metallic magnetic foreign objects from adsorbing onto the magnetic rod and becoming difficult to collect. At the same time, demagnetizing the experimental environment and equipment can effectively prevent the environment from affecting the test results, thus helping to ensure the accuracy of the test data.

[0024] Cleaning the magnetic material after removing the sealing layer facilitates its detachment from the magnetic rod, ensuring the integrity of the primary concentrate collection. Furthermore, cleaning the magnetic material under magnetic field adsorption promotes the separation of lithium iron phosphate from the magnetic material, further ensuring both the integrity and purity of the primary concentrate collection.

[0025] (3) By placing the magnetic rod in a strong oxidizing acid and heating it on an acid-removing hot plate, impurities on the surface of the magnetic rod can be removed by the strong oxidizing acid. Furthermore, the cleanliness of the magnetic rod after cleaning can be effectively verified by elemental quantitative analysis. At the same time, heat-sealing the cleaned magnetic rod in a heat-shrink tubing can effectively ensure the cleanliness of the magnetic rod, which is conducive to ensuring the accuracy of subsequent test results.

[0026] (4) By selecting aqua regia as a strong oxidizing acid, the strong oxidizing acid can have both the coordination properties of hydrochloric acid and the oxidizing properties of nitric acid, thus being able to dissolve most metals and alloys that cannot be dissolved by a single acid. In this way, the metal on the surface of the magnetic rod can be dissolved, and impurities on the surface of the magnetic rod can be completely removed.

[0027] (5) By using a magnet to move along a preset trajectory, it is beneficial to adsorb magnetic materials in the container and effectively ensure the integrity of the magnetic material adsorption. Furthermore, by washing multiple times and moving the magnet along the preset trajectory, lithium iron phosphate that may be attached to the magnetic material can be removed, so as to effectively ensure the purity of the primary enrichment.

[0028] (6) By attaching the magnet to the bottom of the container, the magnetic material inside the container can be fixed, preventing the loss of magnetic material when the cleaning liquid is poured out. Furthermore, clockwise and counterclockwise rotation can effectively ensure that the magnetic material inside the container is attracted by the magnet, which is beneficial to ensuring the accuracy of subsequent test results.

[0029] (7) By ultrasonically treating the primary enrichment, the possible iron phosphate impurities and strong magnetic metal foreign matter can be dispersed in the solution, and the residual lithium iron phosphate attached to the surface of the magnetic material can be effectively removed, so that the lithium iron phosphate is separated from the magnetic material.

[0030] By adding an aqueous solution containing a viscous dispersant, it is possible to facilitate the adsorption of strongly magnetic metallic foreign objects by a magnet, while the weakly magnetic impurity iron phosphide, due to the viscous resistance of the aqueous solution containing the viscous dispersant, cannot be adsorbed by a magnet and remains suspended in the aqueous solution containing the viscous dispersant. This facilitates the separation of the weakly magnetic impurity iron phosphide from the strongly magnetic metallic foreign objects, thereby reducing the influence of iron phosphate on the test results and ensuring the accuracy of the test results.

[0031] (8) By ultrasonically cleaning the weakly magnetic impurities with hydrochloric acid, other impurities remaining on the weakly magnetic impurities can be effectively dissolved, while hydrochloric acid will not damage the metallic magnetic foreign matter. Water washing and filtration can effectively trap the metallic magnetic foreign matter, which is beneficial for verifying and ensuring the separation effect between the strongly magnetic metallic foreign matter and the weakly magnetic impurity iron phosphide.

[0032] (9) By using strong acid to dissolve the strong magnetic metal foreign matter, it is beneficial to dissolve the ionic magnetic elements and non-magnetic elements, while the strong magnetic metal foreign matter is adsorbed by the magnet, which helps to ensure the accuracy of the test results.

[0033] (10) By setting the viscous dispersant to an aqueous solution of sodium carboxymethyl cellulose, and ensuring its mass concentration is between 0.1% and 0.3%, it is beneficial to prevent the weakly magnetic impurity ferric phosphide from being adsorbed by a magnet and to remain suspended in the aqueous solution containing the viscous dispersant due to the viscous resistance of the solution. This also avoids the situation where the strong magnetic metal impurity remains suspended and cannot be adsorbed due to excessive viscous resistance of the solution, thus facilitating the separation of the strong magnetic metal foreign matter from the weakly magnetic impurity ferric phosphide, and consequently ensuring the accuracy of the detection results. Attached Figure Description

[0034] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0035] Figure 1 This is a microscopic imaging of a weakly magnetic impurity containing a strongly magnetic metallic foreign object, as described in the embodiments of this application.

[0036] Figure 2 This is a microscopic imaging of weakly magnetic impurities that do not contain strongly magnetic metallic foreign matter, as described in the embodiments of this application. Detailed Implementation

[0037] To make the technical solution and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0038] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0039] Furthermore, it should be noted that in the description of this application, if terms such as "upper," "lower," "inner," or "outer" appear, indicating orientation or positional relationship, these are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, if terms such as "first" or "second" appear, they are also used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0040] Furthermore, in the description of this application, unless otherwise expressly defined, the terms "installation," "connection," "joining," and "connector" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application in light of the specific circumstances.

[0041] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0042] The present application will now be described in detail through exemplary embodiments. However, it should be understood that, without further description, elements, structures, and features in one embodiment may be advantageously incorporated into other embodiments.

[0043] The embodiments of the first aspect of this application provide a separation and detection method suitable for separating and detecting metallic magnetic foreign matter in lithium iron phosphate, and the separation and detection method, through innovative design, can help improve the accuracy of separation and detection results.

[0044] In related technologies, when separating and detecting metallic magnetic foreign matter in lithium iron phosphate materials, inductively coupled plasma atomic emission spectrometry (ICP-OES) or scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) are commonly used. However, these metallic magnetic foreign matter may contain weakly magnetic impurities, such as iron phosphide. While trace amounts of iron phosphide have little impact on the electrochemical performance of the battery, the Fe content detected by ICP-OES may include Fe from the iron phosphide. Furthermore, SEM-EDS is only suitable for semi-quantitative methods. Therefore, using the above detection methods is not conducive to improving the accuracy of the detection results.

[0045] In view of this, to overcome the shortcomings of related technologies, the separation and detection method in this embodiment generally includes the following steps: using a magnetic rod to adsorb and enrich magnetic materials from lithium iron phosphate slurry, followed by washing to obtain a primary concentrate containing strongly magnetic metallic foreign matter and weakly magnetic impurities. The primary concentrate is placed in an aqueous solution containing a viscous dispersant, and adsorbed and moved by a magnet, causing the weakly magnetic impurities to separate from the magnet and be discharged under the resistance of the solution, thus separating the strongly magnetic metallic foreign matter. The strongly magnetic metallic foreign matter is then digested and subjected to elemental quantitative analysis.

[0046] Therefore, by using a magnetic rod to obtain the primary enrichment in lithium iron phosphate slurry, and then treating the primary enrichment with a solution containing a viscous dispersant to remove weakly magnetic impurities and separate strongly magnetic metallic foreign matter, the strongly magnetic metallic foreign matter is then digested. Thus, by employing a three-stage treatment method of primary screening, viscous dispersant separation, and digestion, the strongly magnetic metallic foreign matter is efficiently separated from iron phosphate, which is beneficial for the accurate determination of strongly magnetic metallic foreign matter in lithium iron phosphate and thus improves the accuracy of detection results.

[0047] In some exemplary embodiments, the separation and detection method includes the following steps: adsorbing and enriching magnetic materials from lithium iron phosphate slurry using a magnetic rod, followed by washing to obtain a primary concentrate containing strongly magnetic metallic foreign matter and weakly magnetic impurities. The primary concentrate is placed in an aqueous solution containing a viscous dispersant, and adsorbed and moved using a magnet, causing the weakly magnetic impurities to separate from the magnet and be discharged under the resistance of the solution, while the strongly magnetic metallic foreign matter is separated. The separated weakly magnetic impurities are observed under a microscope, and the optical characteristics of the particles are used to distinguish the strongly magnetic metallic foreign matter from iron phosphate.

[0048] Therefore, by observing the separated weakly magnetic impurities under a microscope, it is possible to effectively detect whether the weakly magnetic impurities contain strongly magnetic metallic foreign objects, and further verify and ensure the separation effect of strongly magnetic metallic foreign objects and weakly magnetic impurity iron phosphide, thereby helping to ensure the accuracy of the detection results.

[0049] Based on the above overview, it can be understood that, as a preferred embodiment of this separation and detection method, the method includes the following steps: First, magnetic materials are adsorbed and enriched from the lithium iron phosphate slurry using a magnetic rod, and then washed to obtain a primary concentrate containing strongly magnetic metallic foreign matter and weakly magnetic impurities. Second, the primary concentrate is placed in an aqueous solution containing a viscous dispersant, and adsorbed and moved using a magnet, causing the weakly magnetic impurities to separate from the magnet and be discharged under the resistance of the solution, thus separating the strongly magnetic metallic foreign matter. Then, the discharged weakly magnetic impurities are observed under a microscope, and the optical characteristics of the particles are used to distinguish the strongly magnetic metallic foreign matter from iron phosphide. Finally, the strongly magnetic metallic foreign matter is digested and subjected to elemental quantitative analysis.

[0050] This setup, through a three-stage treatment method involving primary screening, separation with a viscous dispersant, and digestion, achieves efficient separation of strongly magnetic metallic foreign matter from iron phosphide. It also further verifies and ensures the separation effect of strongly magnetic metallic foreign matter from weakly magnetic impurity iron phosphide, thereby helping to guarantee the accuracy of the test results.

[0051] It is worth noting that in this embodiment, a magnetic rod with a magnetic field strength ≥12000 GS is preferably selected, that is, a magnetic rod with a magnetic field strength greater than or equal to 12000 Gauss is selected. This setting can effectively ensure the adsorption capacity of the magnetic rod, so that the magnetic rod can effectively adsorb metallic magnetic foreign objects.

[0052] In some exemplary embodiments, the steps of using a magnetic rod to adsorb and enrich magnetic materials from a lithium iron phosphate slurry, followed by cleaning, to obtain a primary enrichment containing strongly magnetic metallic foreign matter and weakly magnetic impurities include: sealing the magnetic rod and demagnetizing the experimental environment and equipment; placing the sealed magnetic rod into a mixed slurry containing lithium iron phosphate powder and liquid, stirring the slurry for a preset time to allow the magnetic rod to adsorb the magnetic materials; removing the magnetic rod containing the adsorbed magnetic materials, transferring it to a container, removing the sealing layer, and then cleaning the magnetic materials under a magnetic field to obtain the primary enrichment.

[0053] Therefore, sealing the magnetic rod effectively prevents it from directly contacting metallic magnetic foreign objects, thus avoiding the contamination of impurities from the rod surface with these objects and preventing them from adsorbing onto the rod and becoming difficult to collect. Simultaneously, demagnetizing the experimental environment and equipment effectively prevents environmental influences on the test results, thereby ensuring the accuracy of the test data.

[0054] Meanwhile, cleaning the magnetic material after removing the sealing layer facilitates its detachment from the magnetic rod, ensuring the integrity of the primary concentrate collection. Furthermore, cleaning the magnetic material under magnetic field adsorption promotes the separation of lithium iron phosphate from the magnetic material, further ensuring both the integrity and purity of the primary concentrate collection.

[0055] It is worth noting that, as a specific implementation method of placing a sealed magnetic rod into a slurry containing lithium iron phosphate powder and liquid, and stirring the slurry for a preset time, this embodiment specifically includes the following steps: First, weigh lithium iron phosphate into a PE bottle, then add pure water and anhydrous ethanol to form a slurry of lithium iron phosphate powder and liquid. Then, place the magnetic rod into the PE bottle, tighten the cap, seal it, shake well, place it on a grinding mill, adjust the grinding mill speed, and rotate the PE bottle for a certain period of time. During the rotation, intermittently shake the PE bottle or change the rotation direction of the PE bottle to ensure that the magnetic rod and lithium iron phosphate are in full contact, thereby completing the stirring of the slurry and the adsorption of magnetic materials.

[0056] It is understandable that PE bottles refer to plastic bottles made primarily of polyethylene. By filling PE bottles with lithium iron phosphate, the good chemical stability, non-magnetic nature, and lack of introduction of other metallic impurities of PE facilitate the formation of a mixed slurry between the lithium iron phosphate powder and the liquid. Simultaneously, by adding pure water and anhydrous ethanol to the PE bottle, using pure water as a dispersion medium and anhydrous ethanol to reduce the agglomeration of the lithium iron phosphate powder, sufficient contact between the lithium iron phosphate powder and the magnetic rod is ensured. Furthermore, shaking the PE bottle or changing its rotation direction helps ensure that the magnetic rod fully contacts the lithium iron phosphate sample, preventing partial contact and ensuring the integrity of the primary enrichment collection.

[0057] The sealing process for the magnetic rod includes: placing the magnetic rod in a corrosion-resistant container, adding a strong oxidizing acid, heating it on an acid-removing hot plate, cooling it, and then using a magnet to attract it to the bottom of the corrosion-resistant container. The solution in the corrosion-resistant container is then transferred to a volumetric flask. The magnetic rod and the inner wall of the corrosion-resistant container are washed with pure water, and the washing solution is transferred to the volumetric flask. After making up to a fixed volume, elemental quantitative analysis is performed to verify that the concentrations of each metal element are below preset thresholds. The magnetic rod is then cleaned, placed in a demagnetized heat-shrink tubing, and heat-sealed.

[0058] Therefore, by placing the magnetic rod in a strong oxidizing acid and heating it on an acid-removing hot plate, impurities on the surface of the magnetic rod can be removed using the strong oxidizing acid. Furthermore, elemental quantitative analysis can effectively verify the cleanliness of the magnetic rod after cleaning. Simultaneously, heat-sealing the cleaned magnetic rod in heat-shrink tubing effectively ensures its cleanliness, which is beneficial for ensuring the accuracy of subsequent test results.

[0059] More specifically, in this embodiment, the sealing process for the magnetic rod includes the following steps: First, the magnetic rod is placed in a corrosion-resistant container, and a strong oxidizing acid is added. Second, the corrosion-resistant container is heated on an acid-removing hot plate, and after cooling, it is attracted to the bottom of the corrosion-resistant container using a magnet. Third, the solution in the corrosion-resistant container is transferred to a volumetric flask, and the magnetic rod and the inner wall of the container are rinsed multiple times with pure water, with all the cleaning solution transferred into the volumetric flask. Then, after the solution is brought to a final volume, the contents of iron, chromium, nickel, and zinc in the solution are detected using ICP-OES, ensuring that the contents of each element meet the requirements. This verifies that there are no residual impurities on the surface of the magnetic rod, thus avoiding sample contamination. Finally, the magnetic rod is rinsed with ultrapure water, placed in a heat-shrink tubing, and the ends of the heat-shrink tubing are sealed using a heat-sealing machine.

[0060] It is understood that in this embodiment, the corrosion-resistant container can be a PFA digestion vessel, that is, a container made of perfluoroalkoxy polymer (PFA) material, which has the characteristics of corrosion resistance and no impurity residue. Meanwhile, it is understood that ICP-OES, or inductively coupled plasma optical emission spectrometry, uses inductively coupled plasma as an excitation source to excite element atoms in the sample solution, causing them to emit characteristic spectra. By detecting the wavelength of the characteristic spectra, the element type is determined, and by detecting the spectral intensity, the element content is determined, enabling precise detection of trace element content.

[0061] Among them, aqua regia is preferred as the strong oxidizing acid. Therefore, by selecting aqua regia as the strong oxidizing acid, it can combine the coordination properties of hydrochloric acid and the oxidizing properties of nitric acid, thus being able to dissolve most metals and alloys that cannot be dissolved by a single acid. In this way, it can dissolve the metal on the surface of the magnetic rod, and at the same time, it can thoroughly remove impurities from the surface of the magnetic rod.

[0062] It is understood that aqua regia is a strong oxidizing mixed acid composed of concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 3:1. In this embodiment, the addition of a strong oxidizing acid refers to adding aqua regia diluted with concentrated aqua regia and ultrapure water in a certain proportion, while using aqua regia as the strong oxidizing acid.

[0063] The cleaning of magnetic materials under magnetic field adsorption includes: using a magnet to move along a preset trajectory on the outside of the bottom of the container, adsorbing the accumulated material, and then pouring out the cleaning solution, repeating this process multiple times.

[0064] Therefore, by using a magnet to move along a preset trajectory, it is beneficial to adsorb magnetic materials in the container and effectively ensure the integrity of the adsorption of magnetic materials. Furthermore, by repeatedly washing and moving the magnet along the preset trajectory, lithium iron phosphate that may be attached to the magnetic materials can be removed, thereby effectively ensuring the purity of the primary enrichment.

[0065] More specifically, in the specific implementation, firstly, use a magnetic block to remove the magnetic rod with heat-shrink tubing from the corrosion-resistant container after stirring, and transfer it to a clean beaker. Rinse one end of the heat-shrink tubing clean, and use tweezers to hold the tubing and cut the top of the tubing with ceramic scissors. Secondly, cut downwards along both ends of the heat-shrink tubing wall, fold the cut ends over, and slowly pull out the magnetic rod. Then, rinse the residue on the heat-shrink tubing into the beaker with ultrapure water. If any residue cannot be rinsed off, gently scrape it off with a ceramic scraper, ensuring that all magnetic impurities are transferred into the beaker. Avoid splashing water outside the beaker during the rinsing process. Finally, rinse the residue on the tweezers into the beaker as well.

[0066] The cleaning solution is then discarded after the magnet is moved along a preset trajectory on the outside of the bottom of the container to adsorb the accumulated matter. Specifically, the magnet is moved clockwise three times and counterclockwise three times on the outside of the bottom of the container to form one round, with each round taking 10±3 seconds. After adsorption, the container is left to stand for at least 3 seconds. When repeating the steps of adding water, adsorption, and discarding water, the amount of water added each time is 150±10 mL, that is, between 140 mL and 160 mL each time.

[0067] Therefore, by attaching a magnet to the bottom of the container, the magnetic material inside can be secured, preventing loss of magnetic material when the cleaning solution is poured out. Furthermore, rotating the container clockwise and counterclockwise effectively ensures that the magnetic material is attracted to the magnet, thus guaranteeing the accuracy of subsequent test results.

[0068] In this embodiment, the magnetic block is used to attract the water from the bottom of the beaker in three clockwise circles from the outside in, and then three counterclockwise circles, constituting one round. Each round of attraction lasts 10 seconds, followed by a 3-second pause. The water is then poured out without releasing the magnetic block. The magnetic block is then released, and 150 mL of water is added. The above steps are repeated until the water in the beaker is clear, thus completing the collection of the primary enrichment.

[0069] The above-mentioned method involves placing the primary concentrate in an aqueous solution containing a viscous dispersant, and using a magnet for adsorption. Weakly magnetic impurities are separated from the magnet by the resistance of the solution and are discharged, while strongly magnetic metallic foreign matter is separated. Specifically, this includes: adding ultrapure water to a container containing the primary concentrate and sonicating it; discarding the sonicated liquid; adding an aqueous solution containing a viscous dispersant; using a magnet to move along the bottom of the container to adsorb the strongly magnetic metallic foreign matter, while simultaneously causing weakly magnetic impurities and non-magnetic particles to detach from the magnet's attraction area and be discharged along with the aqueous solution containing the viscous dispersant; repeating the discharge process until no visible particles remain in the discharged solution.

[0070] Therefore, by ultrasonically treating the primary enrichment, any possible iron phosphate impurities and strongly magnetic metal foreign matter can be dispersed in the solution, and residual lithium iron phosphate adhering to the surface of the magnetic material can be effectively removed, thus separating lithium iron phosphate from the magnetic material.

[0071] Meanwhile, by adding an aqueous solution containing a viscous dispersant, it is beneficial for strongly magnetic metallic foreign objects to be adsorbed by a magnet, while weakly magnetic impurities such as iron phosphide cannot be adsorbed by a magnet and remain suspended in the aqueous solution containing the viscous dispersant due to the viscous resistance of the aqueous solution. This facilitates the separation of weakly magnetic impurities such as iron phosphide from strongly magnetic metallic foreign objects, thereby reducing the influence of iron phosphate on the test results and ensuring the accuracy of the test results.

[0072] Specifically, in this embodiment, the primary enrichment is placed in an aqueous solution containing a viscous dispersant. A magnet is used to attract the weakly magnetic impurities, causing them to separate from the magnet due to solution resistance and be discharged, while strongly magnetic metallic foreign matter is separated. The steps may include: First, adding ultrapure water to a beaker, sealing it with sealing film, and placing it in an ultrasonic cleaner. The water level in the ultrasonic cleaner must be above the height of the solution in the beaker to ensure the beaker does not tilt. Ultrasonication is performed for a certain time, and the above steps are repeated until the water in the beaker is clear. The ultrasonically treated liquid is then discarded. Second, an aqueous solution containing a viscous dispersant is added. A magnet is moved along the outer ring of the bottom of the beaker, and the time required for each ring is controlled. Then, while maintaining the magnet's attraction of the strongly magnetic metallic foreign matter, the viscous dispersant solution containing the weakly magnetic material is poured out. Finally, the area outside the magnetic attraction zone is rinsed with the aqueous solution containing the viscous dispersant to remove the weakly magnetic impurities until no particulate matter remains in the discharged solution.

[0073] The above-mentioned process involves microscopic observation of the separated weakly magnetic impurities to distinguish strongly magnetic metallic foreign matter from iron phosphide through the optical characteristics of the particles. Specifically, the weakly magnetic impurities are ultrasonically cleaned with hydrochloric acid, washed with water, filtered, dried, and then observed under a microscope.

[0074] Among them, particles with smooth surfaces and reflective characteristics were identified as strongly magnetic metallic foreign objects, while particles with black spots were identified as iron phosphide.

[0075] Therefore, ultrasonic cleaning of weakly magnetic impurities with hydrochloric acid can effectively dissolve other impurities remaining on the weakly magnetic impurities, while the hydrochloric acid will not damage the metallic magnetic foreign matter. Water washing and filtration can effectively retain the metallic magnetic foreign matter, which is beneficial for verifying and ensuring the separation effect between strongly magnetic metallic foreign matter and the weakly magnetic impurity iron phosphide.

[0076] In practice, firstly, the separated weakly magnetic material is washed with hydrochloric acid, sealed with a sealing film, and placed in an ultrasonic cleaner. After ultrasonic cleaning, ultrapure water is added as soon as possible to dilute the hydrochloric acid solution. Secondly, the magnetic block is tightly attached to the bottom of the beaker and slowly rotated several times. After settling, the solution is poured out while the magnetic block is still attached, and the beaker is washed repeatedly with ultrapure water. Then, a filter is connected, and the acid-washed particles are filtered out. After filtration is complete, the filter membrane is placed in a clean filter membrane box to air dry or dried at low temperature.

[0077] Therefore, by using air drying or low-temperature drying to dry the filter membrane and particulate matter, the oxidation of metallic magnetic foreign matter caused by high temperature can be avoided, which is beneficial to verifying and ensuring the accuracy of the test results.

[0078] Understandably, observing these particles under a microscope and noting their appearance—specifically, whether they contain bright particles—is used to distinguish strongly magnetic metallic foreign objects from iron phosphide. Specifically, strongly magnetic metallic foreign objects will exhibit a glossy surface after being digested with strong acid. Figure 1 As shown, this indicates that the separated weakly magnetic impurities contain strongly magnetic metallic foreign matter. Iron phosphide, after treatment with strong acid, only appears as black spots, combined with... Figure 2 As shown, this indicates that the separated weakly magnetic material does not contain strongly magnetic metallic foreign matter.

[0079] The process of digesting and quantitatively analyzing strongly magnetic metallic foreign objects includes: digesting the strongly magnetic metallic foreign objects with strong acid and adjusting the volume, and then using inductively coupled plasma atomic emission spectrometry to detect the content of one or more of the elements iron, chromium, and nickel in the digested solution.

[0080] Therefore, by using strong acid to dissolve strongly magnetic metallic foreign objects, it is beneficial to dissolve ionic magnetic elements and non-magnetic elements, while the strongly magnetic metallic foreign objects are attracted by magnets, thus helping to ensure the accuracy of the test results.

[0081] More specifically, the specific implementation involves the following steps: First, the separated strongly magnetic metallic foreign matter is placed in a PFA digestion vessel, and a mixture of aqua regia and ultrapure water is added. Second, the PFA digestion vessel is placed on an acid-removing hot plate for digestion. After cooling, the magnetic block is adsorbed onto the bottom of the PFA digestion vessel. Then, the solution in the PFA digestion vessel is transferred to a volumetric flask, and the inner wall of the PFA digestion vessel is rinsed several times with a small amount of pure water. The rinsing solution is then transferred to the corresponding glass volumetric flasks. Finally, the volume is adjusted to the required level in the glass volumetric flasks, and the elemental content after digestion is then analyzed using ICP-OES.

[0082] In some exemplary embodiments, the viscous dispersant is an aqueous solution of sodium carboxymethyl cellulose with a mass concentration between 0.1% and 0.3%.

[0083] Therefore, by setting the viscous dispersant to an aqueous solution of sodium carboxymethyl cellulose at a concentration between 0.1% and 0.3%, it is beneficial to prevent the weakly magnetic impurity ferric phosphide from being adsorbed by a magnet and to keep it suspended in the aqueous solution containing the viscous dispersant due to the viscous resistance of the solution. This also avoids the situation where the strongly magnetic metallic impurity remains suspended and cannot be adsorbed due to excessive viscous resistance of the solution, thus facilitating the separation of the strongly magnetic metallic foreign matter from the weakly magnetic impurity ferric phosphide, and consequently ensuring the accuracy of the detection results.

[0084] It is understood that the mass concentration of the viscous dispersant solution can be 0.1%, 0.15%, 0.2%, 0.25%, or 0.3%, etc. In this embodiment, the preferred mass concentration of the viscous dispersant solution is 0.2%. This setting effectively ensures the separation accuracy of strongly magnetic metallic foreign matter and weakly magnetic impurities, and guarantees the stability after separation. Specifically, please refer to Table 1 below:

[0085] Table 1

[0086]

[0087] As shown in Table 1, when the mass concentration of the viscous dispersant solution is 0.1%, P (phosphorus) is detected, indicating the presence of weakly magnetic impurities such as iron phosphide. However, in a viscous dispersant solution with a mass concentration of 0.2%, iron phosphide is almost entirely absent. Furthermore, in a viscous dispersant solution with a mass concentration of 0.3%, Cr (chromium), which was previously detected in solutions with mass concentrations of 0.1% or 0.2%, is also absent, indicating that the solution resistance is too high, resulting in the loss of some metallic magnetic foreign matter. Therefore, in this preferred embodiment, the mass concentration of the viscous dispersant solution is set to 0.2%.

[0088] It is worth noting that, regarding the separation and detection method of this embodiment, based on the above exemplary implementations, in specific implementation, as a preferred embodiment, it can be performed sequentially according to the following steps S1-S6, and the specific operation steps are as follows:

[0089] S1. First, place the magnetic rod in a corrosion-resistant PFA digestion vessel and add 20 mL of aqua regia diluted 1:1 with concentrated aqua regia and ultrapure water.

[0090] Next, heat the PFA digestion vessel on a 100°C acid-removing hot plate for half an hour. After cooling, use a magnet to attract the bottom of the PFA digestion vessel. Then, transfer the solution from the PFA digestion vessel to a volumetric flask, and rinse the magnetic rod and the inner wall of the container three times with about 5 mL of pure water. Transfer all the rinsing solution into the volumetric flask.

[0091] Then, after bringing the volume to 50 mL and shaking well, the contents of iron, chromium, nickel, and zinc in the solution were determined using ICP-OES, ensuring that the content of each element was less than 0.001 μg / mL. This was to verify that there were no residual impurities on the surface of the magnetic rod, thus avoiding sample contamination by the magnetic rod.

[0092] Finally, the magnetic rod was rinsed with ultrapure water, placed inside a heat shrink tubing, and then both ends of the tubing were sealed using a heat sealer. The experimental environment and equipment were then demagnetized. This completes the cleaning and sealing of the magnetic rod, as well as the demagnetization of the experimental environment and equipment.

[0093] S2. First, weigh 200 g of lithium iron phosphate into a 1000 mL PE bottle, then add 300 mL of pure water and 100 mL of anhydrous ethanol to form a mixed slurry of lithium iron phosphate powder and liquid.

[0094] Then, insert the magnetic rod into the PE bottle, tighten the cap, seal it, shake it well, place it on the grinding mill, adjust the grinding mill speed so that the actual speed of the PE bottle is 80±10 RPM, rotate for 30 minutes, and shake it no less than 3 times during the rolling process.

[0095] Specifically, the PE bottle can be shaken every 10 minutes or its rotation direction can be changed every 10 minutes to ensure full contact between the magnetic rod and the lithium iron phosphate. This stirs the mixture and allows the magnetic rod to adsorb magnetic substances, thus separating metallic magnetic foreign matter from the lithium iron phosphate raw material.

[0096] S3. First, use a magnetic block to remove the magnetic rod with heat shrink tubing from the corrosion-resistant container after stirring, transfer it to a 500 mL clean beaker, rinse one end of the heat shrink tubing clean, and use tweezers to hold the heat shrink tubing and cut the top of the heat shrink tubing with ceramic scissors.

[0097] Next, cut 1-2 cm downwards from both ends of the heat shrink tubing, fold the cut ends over, and slowly pull out the magnetic rod.

[0098] Next, rinse the material on the heat shrink tubing into the beaker with ultrapure water. If there is any material that cannot be rinsed off, gently scrape it off with a ceramic scraper, ensuring that all magnetic impurities are transferred into the beaker. Avoid splashing water outside the beaker during the rinsing process.

[0099] At the same time, rinse the substance on the tweezers into the beaker.

[0100] Finally, add water to the container and use a magnet to attract the water from the bottom of the container by rotating it clockwise three times and counterclockwise three times, completing one cycle. Each cycle takes 10±3 seconds, and the magnet should be left to stand for at least 3 seconds after attraction. Repeat the steps of adding water, attracting water, and pouring water out, adding 150±10 mL of water each time, until the water in the container becomes clear. This process yields the primary concentrate.

[0101] S4. First, add 50 mL of ultrapure water to the beaker, seal it with sealing film, and place it in an ultrasonic cleaner. The water level in the ultrasonic cleaner should be above the height of the solution in the beaker to ensure that the beaker does not tilt. Ultrasonicate for 5 minutes. Repeat the above steps until the water in the beaker is clear, and then pour out the liquid after ultrasonication.

[0102] Next, add 100 mL of a 0.2% sodium carboxymethyl cellulose aqueous solution, and use a magnet to move it around the bottom of the beaker 2.5 times along the outer ring, with each rotation taking 5 seconds.

[0103] Then, while keeping the magnet adsorbing the strongly magnetic metallic foreign object, pour out the viscous dispersant solution containing the weakly magnetic substance.

[0104] Finally, rinse the beaker with an aqueous solution containing a viscous dispersant, ensuring the area outside the magnetic adsorption zone is cleaned to remove weakly magnetic impurities until the discharged solution is free of particulate matter. This completes the separation of strongly magnetic metallic foreign matter from weakly magnetic impurities.

[0105] S5. First, clean the separated weakly magnetic material with hydrochloric acid, cover it with a sealing film, put it in an ultrasonic cleaner, and clean it for 120 seconds at 40 kHz / 50% power. After ultrasonic cleaning, add 100 mL of ultrapure water to dilute the hydrochloric acid solution as soon as possible.

[0106] Next, firmly attach the magnetic block to the bottom of the beaker and slowly rotate it about 15 times. Let it stand for 3 seconds, then firmly attach the magnetic block and pour out the solution. Wash the beaker repeatedly with ultrapure water 3-5 times.

[0107] Next, connect the filter and use a nylon microporous filter membrane with a pore size of 5μm and a diameter of 47mm to filter the acid-washed particles. Wait for the filtration to complete.

[0108] Then, place the filter membrane in a clean filter membrane box to air dry or dry at low temperature.

[0109] Finally, the dried filter membrane and particulate matter were observed under a microscope.

[0110] Among them, combined Figure 1 As shown, particles with smooth surfaces and reflective characteristics are identified as strongly magnetic metallic foreign objects, while particles with black spots are identified as iron phosphide. Figure 2 As shown. This is to verify the separation accuracy of strongly magnetic metallic foreign objects and weakly magnetic impurities, in order to ensure the accuracy of the test results.

[0111] S6. First, place the separated strong magnetic metal foreign matter into the PFA digestion vessel and add 20 mL of aqua regia and ultrapure water in a 1:1 ratio.

[0112] Next, the PFA digestion vessel was placed on a 90 ℃ acid-removing heating plate for 1 h for digestion. After cooling, the magnetic block was attached to the bottom of the PFA digestion vessel.

[0113] Then, transfer the solution in the PFA digestion vessel to a volumetric flask, and rinse the inner wall of the PFA digestion vessel three times with a small amount of pure water (about 5 mL). Transfer the rinsing solution into the corresponding glass volumetric flasks.

[0114] Finally, the volume was adjusted to 50 mL in a glass volumetric flask, and the elemental content after digestion was then analyzed using ICP-OES to complete the detection of metallic magnetic foreign matter in lithium iron phosphate.

[0115] Based on the above overview, to verify whether the recovery rate of strongly magnetic metallic foreign objects in a 0.2% (w / w) viscous dispersant solution meets the specified requirements, this application embodiment verifies this by setting up an iron powder recovery experiment and a blank experiment. It shows that strongly magnetic metallic foreign objects in a 0.2% (w / w) viscous dispersant solution can be attracted by a magnet, as detailed in Table 2 below:

[0116] Table 2

[0117]

[0118] As shown in Table 2, the recovery rate of strongly magnetic metal foreign objects is >80%, which meets the specified requirements.

[0119] Furthermore, to further verify whether the recovery rate of strongly magnetic metallic foreign matter in a 0.2% (w / w) viscous dispersant solution meets the specified requirements, this application embodiment adds iron powder to lithium iron phosphate and uses inductively coupled plasma atomic emission spectrometry (ICP-AES) to detect the iron powder elemental content. The specific detection results are shown in Table 3 below:

[0120] Table 3

[0121]

[0122] As shown in Table 3, the recovery rate of strongly magnetic metal foreign objects is >80%, which meets the specified requirements.

[0123] In the preferred embodiment of the separation and detection method described above, the specific setting and arrangement of the magnetic rod, strong oxidizing acid, viscous dispersant, etc. can still be referred to the descriptions in the above exemplary embodiments. Furthermore, in this preferred embodiment, the beneficial effects brought about by the design of the magnetic rod, strong oxidizing acid, and viscous dispersant can also be referred to the descriptions in the above exemplary embodiments.

[0124] The separation and detection method in this embodiment adopts the design described above. It utilizes a magnetic rod to collect primary enrichments in the lithium iron phosphate slurry, and then treats these primary enrichments with a solution containing a viscous dispersant to remove weakly magnetic impurities, thus separating strongly magnetic metallic foreign matter. This strongly magnetic metallic foreign matter is then digested. This three-stage process—primary screening, viscous dispersant separation, and digestion—achieves efficient separation of strongly magnetic metallic foreign matter from iron phosphate, facilitating accurate determination of such foreign matter in lithium iron phosphate and improving the accuracy of detection results. Furthermore, microscopic observation of the separated weakly magnetic impurities effectively detects whether they contain strongly magnetic metallic foreign matter, further verifying and ensuring the separation effect between the strongly magnetic metallic foreign matter and the weakly magnetic iron phosphate impurity, thereby guaranteeing the accuracy of the detection results.

[0125] The above descriptions are merely some embodiments of this application and are not intended to limit this application. The technical features or structures in the foregoing different embodiments can be arbitrarily combined to form other specific technical solutions as needed. For those skilled in the art, this application can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of the claims of this application.

Claims

1. A separation and detection method suitable for separating and detecting metallic magnetic foreign matter in lithium iron phosphate, characterized in that, The method includes the following steps: Magnetic materials are adsorbed and enriched from lithium iron phosphate slurry using magnetic rods, and then washed to obtain a primary enrichment containing strongly magnetic metallic foreign matter and weakly magnetic impurities. The primary enrichment is placed in an aqueous solution containing a viscous dispersant. A magnet is used to attract and move the enriched material, causing weakly magnetic impurities to separate from the magnet and be discharged under the resistance of the solution, while strongly magnetic metallic foreign matter is separated. The weakly magnetic impurities discharged after separation are observed under a microscope, and the strong magnetic metal foreign matter is distinguished from iron phosphide by the optical characteristics of the particles; and / or, the strong magnetic metal foreign matter is digested and subjected to elemental quantitative analysis.

2. The separation and detection method according to claim 1, characterized in that: The process involves using magnetic rods to adsorb and enrich magnetic materials from lithium iron phosphate slurry, followed by cleaning to obtain a primary enrichment containing strongly magnetic metallic foreign matter and weakly magnetic impurities, including: The magnetic rod was sealed, and the experimental environment and equipment were demagnetized. The sealed magnetic rod is placed into a mixture of lithium iron phosphate powder and liquid, and stirred for a preset time to allow the magnetic rod to adsorb magnetic material. The magnetic rod containing the magnetic material is removed, transferred to a container, and after the sealing layer is removed, the magnetic material is cleaned under magnetic field adsorption to obtain the primary enrichment.

3. The separation and detection method according to claim 2, characterized in that: The sealing process for the magnetic rod includes: Place the magnetic rod in a corrosion-resistant container, add a strong oxidizing acid, heat it on an acid-removing hot plate, and after cooling, use a magnet to attract the bottom of the corrosion-resistant container. Transfer the solution in the corrosion-resistant container to a volumetric flask, wash the magnetic rod and the inner wall of the corrosion-resistant container with pure water, and transfer the washing solution into the volumetric flask. After adjusting the volume, elemental quantitative analysis was performed to verify that the concentrations of each metal element were all below the preset threshold. Clean the magnetic rod, insert it into a demagnetized heat shrink tubing, and heat seal it.

4. The separation and detection method according to claim 3, characterized in that: The strong oxidizing acid is aqua regia.

5. The separation and detection method according to claim 2, characterized in that: The cleaning of the magnetic material under magnetic field adsorption includes: Using a magnet, move it along a preset trajectory on the outside of the bottom of the container to attract and concentrate the pollutants. Then pour out the cleaning solution. Repeat this process several times.

6. The separation and detection method according to claim 5, characterized in that: The process of using a magnet to move along a preset trajectory on the outside of the bottom of the container, adsorbing and accumulating the concentrate, and then discarding the cleaning solution includes: The magnet is attracted to the outside of the bottom of the container by three clockwise and three counterclockwise circles to complete one round. Each round of attraction takes 10±3 seconds, and the magnet should be left to stand for at least 3 seconds after attraction. When repeating the steps of adding water, adsorption, and pouring water, the amount of water added each time is 150±10mL.

7. The separation and detection method according to claim 1, characterized in that: The process involves placing the primary enrichment in an aqueous solution containing a viscous dispersant, using a magnet for adsorption, causing weakly magnetic impurities to separate from the magnet and be discharged under the resistance of the solution, while separating strongly magnetic metallic foreign matter, including: Add ultrapure water to the container containing the primary enrichment and then perform ultrasonic treatment; Discard the ultrasonicated liquid, add an aqueous solution containing a viscous dispersant, and use a magnet to move at the bottom of the container to attract strongly magnetic metallic foreign objects. At the same time, weakly magnetic impurities and non-magnetic particles are removed from the magnet's attraction area and discharged along with the aqueous solution containing the viscous dispersant. Repeat the discharge operation until there are no visible particles in the discharged solution.

8. The separation and detection method according to claim 1, characterized in that: The separated weakly magnetic impurities are then subjected to microscopic observation. The optical characteristics of the particles are used to distinguish strongly magnetic metallic foreign matter from iron phosphide, including: The weakly magnetic impurities were ultrasonically cleaned with hydrochloric acid, washed with water, filtered and dried, and then observed under a microscope. Among them, particles with smooth surfaces and reflective characteristics were identified as strongly magnetic metallic foreign objects, while particles with black spots were identified as iron phosphide.

9. The separation and detection method according to claim 1, characterized in that: The process of digesting the strongly magnetic metallic foreign matter and performing quantitative elemental analysis includes: After the strongly magnetic metallic foreign matter was digested with strong acid and brought to a constant volume, the content of one or more of the elements iron, chromium, and nickel was detected by inductively coupled plasma atomic emission spectrometry.

10. The separation and detection method according to any one of claims 1 to 9, characterized in that: The viscous dispersant is an aqueous solution of sodium carboxymethyl cellulose with a mass concentration between 0.1% and 0.3%.

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