Method and system for preparing battery grade sodium carbonate from industrial sodium carbonate

Abstract

The invention provides a method and a system for preparing battery-grade sodium carbonate from industrial sodium carbonate, and solves the problems of high magnetic impurity residue, non-uniform particle distribution, insufficient moisture control and the like in the prior art. The method comprises the following steps: removing agglomerated powder through vibration screening; micron-grade and submicron-grade magnetic foreign matters are synergistically removed by adopting multi-grade magnetic separation, so that the content of the magnetic foreign matters is less than or equal to 500ppb; particle distribution is precisely regulated and controlled in combination with physical smashing, and the moisture increment of materials is controlled to be smaller than or equal to 0.1% through a closed-loop circulation dehumidification system. The system integrates a raw material pretreatment unit, a magnetic separation unit, a crushing unit and a humidity control unit, and adopts a temporary storage bin circular separation and temperature-humidity interlocking control module to realize collaborative optimization of process parameters. According to the method disclosed by the invention, the limitation of high impurity residue and high energy consumption in the traditional process is broken through by virtue of full-process collaborative design of magnetic separation, crushing and dehumidification, and the obtained battery-grade sodium carbonate meets the standard and is suitable for efficient preparation of the sodium-ion battery positive electrode material.

Description

Technical Field

[0001] The present invention relates to the technical fields of inorganic chemical industry and new energy materials. Specifically, it relates to a method and system for preparing battery-grade sodium carbonate from industrial sodium carbonate. Background Art

[0002] With the rapid development of the new energy industry, the purity requirements for key materials in energy storage technologies such as lithium-ion batteries and sodium-ion batteries are increasing day by day. Sodium carbonate (Na2CO3), as an important raw material for the synthesis of battery cathode materials (such as lithium iron phosphate and ternary materials), its purity directly affects the electrochemical performance of the electrode materials. According to the industry standard T / HNSDCHYXH 001-2023, battery-grade sodium carbonate needs to meet the following key indicators: (1) High purity (≥99.8%): Impurity elements (such as Fe, Ni, Cr, etc.) need to be controlled at the ppm level (such as Fe≤0.003%, Cu≤0.002%); (2) Low content of magnetic substances (magnetic foreign matters ≤50 ppm): Magnetic impurities can cause micro-short circuits inside the battery, reducing safety and cycle life; (3) Uniform particle size distribution (D50≤20 μm): The particle morphology affects the mixing uniformity of the materials and the sintering reaction activity.

[0003] Traditional industrial-grade sodium carbonate (usually with a purity of 99.0%-99.5%) is mainly produced by the Solvay process or the combined soda process, and its applications are concentrated in traditional fields such as glass and chemical industry. However, there are significant problems when directly used in battery materials:

[0004] High impurity content: Residual metal oxides such as Fe, Si, Al and magnetic particles (such as Fe3O4) in the raw materials. The Fe content in industrial-grade sodium carbonate is usually >1000 ppm (the national standard for Class II superior products allows Fe≤0.004%), and it is difficult to completely remove through conventional dissolution-recrystallization processes; Uneven particle morphology: Industrial sodium carbonate mostly shows a blocky or coarse crystal structure (such as the residue on a 180μm sieve ≥60% specified by the national standard), and secondary processing is required to meet the nano-level mixing requirements of battery materials (D50 needs to be controlled at 4.0~16.0μm); Exceeding the standard of magnetic foreign matters: Ferromagnetic substances (such as stainless steel debris) introduced by the wear of production equipment are likely to remain in the finished product, and the separation efficiency of the traditional screening process for micron-level magnetic particles is insufficient (the residual amount >800ppb).

[0005] Currently, the preparation methods for battery-grade sodium carbonate mainly include: Chemical purification method: Removing impurities through pickling, complexation precipitation, etc. (such as using EDTA to complex metal ions), but the process is complex and generates waste liquids (such as acidic wastewater containing heavy metals), with high costs; High-temperature calcination method: Decompose impurity compounds at high temperature (>800 °C) (such as Fe2O3 → FeO), but it has high energy consumption (>200 kWh / ton) and may introduce new pollutants (such as CO2 emissions); Physical screening method: Rely on vibration screening or air classification (such as 180 μm sieve mesh), but the separation efficiency of sub-micron magnetic particles (such as Cr2O3) is low (removal rate <70%). The above methods generally have the defects of complex processes, high energy consumption, and incomplete removal of magnetic foreign substances, and it is difficult to meet the requirements of large-scale production.

[0006] In addition, the existing processes have insufficient control of dispersion (such as local moisture absorption and caking caused by mechanical crushing), and the lack of closed-loop humidity management (moisture residue >0.6%) further limits the application of battery-grade sodium carbonate in the high-end energy storage field. There is an urgent need for an efficient and low-cost integrated process to systematically solve the collaborative problems of impurity control, particle size distribution, and separation of magnetic foreign substances. Summary of the Invention

[0007] The first technical problem to be solved by the present invention is to provide a method for preparing battery-grade sodium carbonate from industrial sodium carbonate to solve the problems of high impurity content, large pollution, and high energy consumption in the prior art.

[0008] To overcome the defects of the above prior art, the present invention provides a method for preparing battery-grade sodium carbonate from industrial sodium carbonate, which includes the following steps: S1. Subject the industrial-grade sodium carbonate raw material to vibration screening to remove caked powders and obtain crude sodium carbonate powder; S2. Perform multi-stage magnetic separation treatment on the crude sodium carbonate powder obtained in step S1, successively perform permanent magnet iron removal and electromagnetic demagnetization to remove magnetic foreign substances; S3. Physically crush the demagnetized sodium carbonate powder in step S2 to obtain battery-grade sodium carbonate finished products with a particle size distribution D50 of 2-10 μm.

[0009] Compared with the prior art, the method for preparing battery-grade sodium carbonate from industrial sodium carbonate in this application has the following advantages: The method of the present invention replaces the traditional chemical pickling (EDTA complexation for impurity removal) or high-temperature calcination (>800 °C) process with a physical synergistic system of vibration screening - gradient magnetic separation - mechanical crushing. In step S1, pretreatment by vibration screening = breaks the agglomeration of raw materials, improving the subsequent magnetic separation contact area; then in step S2, permanent magnet + electromagnetic gradient magnetic separation is used to adsorb strong / weak magnetic substances step by step, further reducing the iron content, and then screening is achieved through physical crushing. The core innovation point of the method of the present invention is to simplify the purification process of industrial-grade sodium carbonate into a physical synergistic process of vibration screening, gradient magnetic separation, and mechanical crushing. By vibration screening, the agglomeration of raw materials is broken, improving the subsequent magnetic separation efficiency, and combining permanent magnet and electromagnetic gradient magnetic separation technologies, strong / weak magnetic impurities are adsorbed step by step, reducing the iron content from >1000 ppm in industrial grade to ≤5 ppm, greatly reducing the residual amount of magnetic foreign matter. At the same time, mechanical grinding dynamic crushing is used to achieve a narrow particle size distribution with D50 = 2 - 10 μm, and by controlling the water content increase within 0.1%. Compared with the traditional chemical pickling method (such as EDTA complexation method) or high-temperature calcination method (>800 °C), the method of the present invention does not require the addition of chemical reagents or high-temperature reactions, reducing energy consumption and having no waste liquid or waste residue discharge, solving the problems of calcium chloride waste residue pollution in the reaction furnace method and high steam consumption in the solution method.

[0010] As a preferred solution, in step S1, the vibration screening is carried out using a 10 - 60 mesh sieve.

[0011] Compared with the prior art, adopting the above technical solution, by expanding the sieve coverage range, not only can the raw material agglomerates be efficiently broken, but also the ultrafine powder can be simultaneously sieved out, making the particle size of the sodium carbonate coarse powder entering the magnetic separation section concentrated within the pore size range corresponding to 10 - 60 meshes, significantly improving the adsorption contact area of the subsequent permanent magnet iron remover, and at the same time avoiding material loss caused by fine powder dusting, ultimately ensuring an increase in the iron impurity removal rate of the magnetic separation process.

[0012] As a preferred solution, in step S2, the magnetic field strength of the permanent magnet iron removal is 8000 - 12000 Gauss, and the magnetic field strength of the electromagnetic demagnetization is greater than 20000 Gauss.

[0013] Compared with the prior art, adopting the above technical solution, the permanent magnet iron removal uses a magnetic field intensity of 8000 - 12000 Gauss, and the electromagnetic demagnetization is set with an alternating magnetic field > 20000 Gauss. The strong magnetic substances such as Fe3O4 are adsorbed by the high magnetic field intensity of the permanent magnet, and then the magnetic domain structure of the weakly magnetic impurities such as Fe2O3 is destroyed by the electromagnetic alternating field, so that the iron content ≤ 5 ppm is achieved. At the same time, the removal rate of micron-sized weakly magnetic particles with a particle size of 0.1 - 10 μm (such as Cr2O3) is improved, and finally the residual amount of magnetic foreign matters is reduced, directly meeting the strict standards of battery-grade sodium carbonate and reducing the process burden of subsequent chemical treatment.

[0014] As a preferred solution, in the step S2, the conditions for sequentially performing permanent magnet iron removal and electromagnetic demagnetization are as follows: The permanent magnet iron removal uses a permanent magnet drum separator to remove magnetic particles with a particle size greater than 50 μm; The electromagnetic demagnetization uses a high-gradient electromagnetic separator to remove sub-micron magnetic impurities with a particle size less than 50 μm.

[0015] Compared with the prior art, adopting the above technical solution, as a preferred solution, in the step S2, the synergistic treatment of using a permanent magnet drum separator (> 50 μm particles) and a high-gradient electromagnetic separator (< 50 μm sub-micron impurities) is adopted. The neodymium iron boron material generates a stable magnetic field of 8000 - 12000 Gs through the permanent magnet drum, preferentially adsorbing large-particle-size strong magnetic particles such as Fe3O4 and reducing the load in the subsequent electromagnetic section; while the high-gradient electromagnetic separation (> 20000 Gauss) uses steel wool media to form a large magnetic field gradient, and destroys the magnetic domain structure of weakly magnetic microparticles such as Fe2O3 through the magnetic hysteresis loss effect, realizing the deep removal of sub-micron impurities with a particle size of 0.1 - 50 μm.

[0016] As a preferred solution, in the step S3, the physical pulverization method is one or both of a jet mill and a mechanical mill, and during the physical pulverization process, the moisture increase of the material is controlled below 0.1%.

[0017] As a preferred solution, the physical pulverization method is a mechanical mill, and the operating parameters of the mechanical mill are as follows: The pulverization frequency ≤ 50 Hz; the classification frequency ≤ 50 Hz; the air extraction frequency ≤ 50 Hz; the feeding frequency ≤ 50 Hz.

[0018] Compared with the prior art, by adopting the above technical solution, through optimizing the operating parameters of the mechanical mill (crushing frequency, classifier wheel speed, feeding speed, etc.), the dual improvement of the material crushing efficiency and quality is achieved. By controlling the crushing frequency, the introduction of magnetic foreign matters due to metal wear is avoided. Also, by precisely controlling the particle D50 to 2 - 10 μm through classification and screening, and by limiting the feeding frequency (≤50 Hz) to maintain the stability of the material layer thickness, combined with optimizing the air extraction volume to extend the residence time of the material, the crushing rate is increased and the power consumption is reduced. Finally, high-precision crushing is achieved in a low-moisture environment (moisture increase ≤ 0.1%), which not only ensures the surface activity of the material but also meets the stringent particle size standard of battery-grade sodium carbonate.

[0019] As a preferred solution, the content of magnetic foreign matters in the battery-grade sodium carbonate finished product is ≤ 500 ppb.

[0020] The second technical problem to be solved by the present invention is to provide a system for preparing battery-grade sodium carbonate from industrial sodium carbonate to solve the problems existing in the prior art, such as discontinuous production process, incomplete removal of magnetic foreign matters, difficult control of moisture after crushing, environmental pollution, and unstable product stability.

[0021] To overcome the defects of the above prior art, the present invention provides a system for preparing battery-grade sodium carbonate from industrial sodium carbonate. The system is used to implement the method, and the system includes the following units: Raw material pretreatment unit: including a feeding bin, a first continuous vacuum feeder connected to the outlet of the feeding bin, and a vibrating screen connected to the outlet of the first continuous vacuum feeder; Multi-stage magnetic separation unit: including a permanent magnet iron remover and an electromagnetic demagnetization device connected in series, and the inlet of the permanent magnet iron remover is connected to the outlet of the vibrating screen; Temporary storage unit: including a buffer bin and at least one group of temporary storage bins. The inlet of the temporary storage bin is connected to the outlet of the magnetic demagnetization device through a pipeline switching valve. The outlet of the temporary storage bin is connected to the inlet of a second continuous vacuum feeder through a pipeline switching valve, and the outlet of the second continuous vacuum feeder is connected to the inlet of the buffer bin; Crushing and finished product processing unit: including a mechanical mill dust removal tower and an automatic packaging machine connected in series in sequence, and the inlet of the mechanical mill is connected to the outlet of the buffer bin; Fan unit: including a first Roots blower and a second Roots blower. The first Roots blower (14) is connected to the first continuous vacuum feeder, and the second Roots blower is connected to the second continuous vacuum feeder (8); Circulating dehumidification system: including an induced draft fan and a condenser. The inlet of the condenser is connected to the dust removal tower through the induced draft fan, and the outlet of the condenser is connected to the mechanical mill.

[0022] Compared with the prior art, the system for preparing battery-grade sodium carbonate from industrial sodium carbonate in this application has the following advantages: continuous production, improved efficiency and stability: the system of the present invention adopts an integrated design of continuous vacuum feeding + vibrating screening + multi-stage magnetic separation + closed crushing + circulating dehumidification, replacing the traditional step-by-step independent processing mode, realizing automated and enclosed production, improving the production line efficiency, and ensuring stable product quality; secondly, the system of the present invention adopts permanent magnet + electromagnetic double-stage magnetic separation. The permanent magnet iron remover removes large-particle magnetic substances, and the electromagnetic demagnetization device deeply removes micron-level and sub-micron-level magnetic impurities, reducing the content of magnetic foreign substances to ≤500 ppb, which is superior to traditional single-stage magnetic separation, improving the safety and reliability of battery materials; and the system of the present invention adopts a closed-circuit circulating dehumidification system, which controls the moisture through the combined action of an induced draft fan and a condenser during the crushing process, ensuring that the moisture increase of the finished product is ≤0.1%, avoiding moisture adsorption and powder agglomeration caused by crushing heat, improving the fluidity and dispersibility of the product. The system of the present invention also combines a mechanical mill to accurately control D50 of the product within the range of 2-10 μm, improving the material mixing uniformity, optimizing the electrode synthesis effect, and meeting the strict requirements of high-end battery-grade materials.

[0023] As a preferred solution, the outlet of the temporary storage bin is connected to the first continuous vacuum feeder and the second continuous vacuum feeder respectively through a pipeline switching valve, and the number of the temporary storage bins is 2 groups, namely the first temporary storage bin and the second temporary storage bin.

[0024] Compared with the prior art, the two groups of temporary storage bins can be independently controlled through the switching valve. When one group of temporary storage bins conveys materials to the second continuous vacuum feeder, the other group can synchronously receive the pretreated materials from the magnetic separation unit (permanent magnet iron remover, electromagnetic demagnetization device). This design eliminates the downtime waiting caused by the timing conflict of feeding / discharging in the traditional single-bin mode, realizes continuous feeding, and when the material purity in the two groups of temporary storage bins does not meet the standard, or further magnetic separation is required, the material can be re-introduced into the first continuous vacuum feeder through controlling the pipeline switching valve for re-circulation, so that the material meets the standard or has better effect, ensuring that the material finally entering the mechanical mill meets the battery-grade standard. Through the above-mentioned circulation treatment, the high-efficiency continuous operation and deep impurity control of the battery-grade sodium carbonate production system can be realized, and the purity is steadily improved.

[0025] As a preferred solution, the inlet of the first continuous vacuum feeder is also connected to the ton bag manual suction device through a pipeline switching valve, and the outlet of the feeding bin is connected to the first continuous vacuum feeder through a pipeline switching valve.

[0026] Compared with the prior art, adopting the above technical solution, the system has a dual-mode switching feeding structure by setting a feeding bin and a manual ton bag suction feeding device. The feeding bin is connected to the first continuous vacuum feeding machine through a pipeline switching valve to achieve automatic continuous feeding, while the manual ton bag suction feeding device uses an independent switching valve as an emergency or small-batch feeding path, and the two share the same vacuum feeding system. When the main feeding bin stops due to a fault or maintenance, the operator can manually switch to the ton bag suction feeding mode to avoid production interruption. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic structural diagram of a system for preparing battery-grade sodium carbonate from industrial sodium carbonate in the present invention; Figure 2 is a schematic diagram of the position of the pipeline switching valve of a system for preparing battery-grade sodium carbonate from industrial sodium carbonate in the present invention.

[0028] DESCRIPTION OF THE REFERENCE NUMERALS: Figure 1 In FIG. 1: 1, feeding bin; 2, first continuous vacuum feeding machine; 3, vibrating screen; 4, permanent magnet iron remover; 5, electromagnetic demagnetization device; 6, first temporary storage bin; 7, second temporary storage bin; 8, second continuous vacuum feeding machine; 9, buffer bin; 10, mechanical mill; 11, dust removal tower; 12, automatic packaging machine; 13, first Roots blower; 14, second Roots blower; 15, induced draft fan; 16, condenser; 17, manual ton bag suction feeding device; Figure 2 In FIG. 2: 101, first pipeline switching valve; 102, second pipeline switching valve; 103, third pipeline switching valve; 104, fourth pipeline switching valve; 105, fifth pipeline switching valve; 106, sixth pipeline switching valve; 107, seventh pipeline switching valve; 108, eighth pipeline switching valve; 109, ninth pipeline switching valve; 110, tenth pipeline switching valve. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] First of all, those skilled in the art should understand that these embodiments are only used to explain the technical principles of the embodiments of the present application, and are not intended to limit the protection scope of the embodiments of the present application. Those skilled in the art can adjust them according to needs to adapt to specific application scenarios.

[0030] In the description of the embodiments of the present application, it should be noted that unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific situations.

[0031] In the embodiments of the present application, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature being "under", "beneath" and "underneath" the second feature may mean that the first feature is directly below or obliquely below the second feature, or simply indicates that the horizontal height of the first feature is less than that of the second feature.

[0032] The present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] The present invention provides a method for preparing battery-grade sodium carbonate from industrial sodium carbonate, comprising the following steps: S1. Subject the industrial-grade sodium carbonate raw material to vibration screening to remove agglomerated powders, obtaining coarse sodium carbonate powder; S2. Perform multi-stage magnetic separation on the coarse sodium carbonate powder obtained in step S1, successively performing permanent magnetic iron removal and electromagnetic demagnetization to remove magnetic foreign matters; S3. Physically pulverize the sodium carbonate powder after demagnetization in step S2 to obtain a battery-grade sodium carbonate finished product with a particle size distribution D50 of 2 - 10 μm.

[0034] As a preferred solution, in step S1, the vibration screening is carried out using a 10 - 60 mesh sieve.

[0035] As a preferred solution, in step S2, the magnetic field strength of the permanent magnetic iron removal is 8000 - 12000 Gauss, and the magnetic field strength of the electromagnetic demagnetization is greater than 20000 Gauss.

[0036] As a preferred solution, in step S2, the conditions for successively performing permanent magnetic iron removal and electromagnetic demagnetization are: Permanent magnetic iron removal uses a permanent magnetic drum separator to remove magnetic particles with a particle size greater than 50 μm; Electromagnetic demagnetization uses a high-gradient electromagnetic separator to remove sub-micron magnetic impurities with a particle size less than 50 μm.

[0037] As a preferred solution, in step S3, the physical pulverization method is one or both of a jet mill and a mechanical mill, and during the physical pulverization process, the water content increase of the material is controlled below 0.1%.

[0038] As a preferred solution, the physical pulverization method is a mechanical mill, and the operating parameters of the mechanical mill are: The crushing frequency ≤ 50 Hz; the classification frequency ≤ 50 Hz; the induced draft frequency ≤ 50 Hz; the feeding frequency ≤ 50 Hz.

[0039] As a preferred solution, the content of magnetic foreign matter in the battery-grade sodium carbonate product ≤ 500 ppb.

[0040] The present invention also provides a system for preparing battery-grade sodium carbonate from industrial sodium carbonate, as Figure 1 shown, Figure 1 in which the arrow indicates the direction through which the material can flow. The system is used to implement the method, and the system includes the following units: Raw material pretreatment unit: including a feeding bin 1, a first continuous vacuum feeder 2 connected to the outlet of the feeding bin 1, and a vibrating screen 3 connected to the outlet of the first continuous vacuum feeder 2; Multi-stage magnetic separation unit: including a permanent magnet iron remover 4 and an electromagnetic demagnetization device 5 connected in series, and the inlet of the permanent magnet iron remover 4 is connected to the outlet of the vibrating screen 3; Temporary storage unit: including a buffer bin 9 and at least one group of temporary storage bins. The inlet of the temporary storage bin is connected to the outlet of the magnetic demagnetization device 5 through a pipeline switching valve. The outlet of the temporary storage bin is connected to the inlet of the second continuous vacuum feeder 8 through a pipeline switching valve. The outlet of the second continuous vacuum feeder 8 is connected to the inlet of the buffer bin 9; Crushing and finished product processing unit: including a mechanical mill 10, a dust removal tower 11, and an automatic packaging machine 12 connected in series in sequence. The inlet of the mechanical mill 10 is connected to the outlet of the buffer bin 9; Fan unit: including a first Roots blower 14 and a second Roots blower 13. The first Roots blower 14 is connected to the first continuous vacuum feeder 2, and the second Roots blower 13 is connected to the second continuous vacuum feeder 8; Circulating dehumidification system: including an induced draft fan 15 and a condenser 16. The inlet of the condenser 16 is connected to the dust removal tower 11 through the induced draft fan 15, and the outlet of the condenser is connected to the mechanical mill 10.

[0041] As a preferred solution, the outlet of the temporary storage bin is respectively connected to the first continuous vacuum feeder 2 and the second continuous vacuum feeder 8 through pipeline switching valves, and the number of the temporary storage bins is 2 groups, namely the first temporary storage bin 6 and the second temporary storage bin 7.

[0042] As a preferred solution, the inlet of the first continuous vacuum feeder 2 is also connected to a ton bag manual suction device 17 through a pipeline switching valve, and the outlet of the feeding bin 1 is connected to the first continuous vacuum feeder 2 through a pipeline switching valve.

[0043] Combining the method and system of the present invention as a whole, as Figure 2 shown, Figure 2 is a schematic diagram of the position of the pipeline switching valve of the present invention, and the specific reaction and process are as follows: Industrial sodium carbonate raw materials are first poured into the feeding bin 1, and then according to the conveying requirements, different feeding methods are selected: Automatic feeding mode: Close the first pipeline switching valve 101, the eighth pipeline switching valve 108, and the ninth pipeline switching valve 109, open the second pipeline switching valve 102 and the third pipeline switching valve 103, start the second Roots blower 14, and automatically convey the raw materials to the continuous vacuum feeder 2; Manual feeding mode: Close the second pipeline switching valve 102, the third pipeline switching valve 103, the eighth pipeline switching valve 108, and the ninth pipeline switching valve 109, open the first pipeline switching valve 101, and convey the raw materials to the continuous vacuum feeder 2 by manual suction of the ton bag.

[0044] Pretreatment and demagnetization steps: The continuous vacuum feeder 2 is connected to the second Roots blower 14, and its outlet is connected to the vibrating screen 3 to remove caked and large particle impurities. The screened sodium carbonate coarse powder is removed of large particle magnetic impurities by the permanent magnet demagnetizer 4, and then enters the electromagnetic demagnetization device 5 for deep demagnetization.

[0045] The outlet of the electromagnetic demagnetization device 5 leads to the first temporary storage bin 6 and the second temporary storage bin 7 through the fourth pipeline switching valve 104 and the fifth pipeline switching valve 105 respectively. The demagnetized material is temporarily stored in the first temporary storage bin 6 or the second temporary storage bin 7 and waits for further processing.

[0046] Multi-stage cyclic demagnetization: To improve the removal rate of magnetic impurities, a multi-stage series magnetic separation process can be adopted: The material enters the continuous vacuum feeder 2 through the feeding bin 1, the second pipeline switching valve 102, and the third pipeline switching valve 103, is screened by the vibrating screen 3, and completes the first round of demagnetization through the permanent magnet demagnetizer 4 and the electromagnetic demagnetization device 5 in sequence, and then enters the first temporary storage bin 6 through the fourth pipeline switching valve 104.

[0047] After that, if the material does not meet the standard, or there are higher requirements for the material, the material can continue to pass through the sixth pipeline switching valve 106, the eighth pipeline switching valve 108, the sixth pipeline switching valve 106, and the third pipeline switching valve 103 to return to the continuous vacuum feeder 2 in sequence, and then go through the same screening and magnetic separation process to complete the second round of demagnetization, and finally enter the temporary storage bin 7 through the fifth pipeline switching valve 105.

[0048] According to the above steps, the material can be circulated multiple times according to the demand until the target purity is reached.

[0049] Crushing and finished product processing The materials output from the first temporary storage bin 6 and the second temporary storage bin 7 are conveyed to the buffer bin 9 by a vacuum feeder 8, and then enter a mechanical mill 10 for physical pulverization to precisely control the particle size distribution. The pulverized materials are passed through a dust removal tower 11 to remove dust, and then enter a draft fan 15. After being cooled by a condenser 16, part of the moisture is discharged by the condenser to ensure that the moisture increase is ≤ 0.1%. Finally, the pulverized battery-grade sodium carbonate enters an automatic packaging machine 12 for packaging, completing the entire preparation process.

[0050] The present invention provides an efficient and low-cost multi-stage demagnetization coupled pulverization process, which realizes the following by optimizing the physical treatment path of industrial sodium carbonate: (1) Directional pulverization: regulating the crushing energy of sodium carbonate particles to obtain ultra-fine powders with a narrow distribution; (2) Gradient demagnetization: combining permanent magnet and electromagnetic separation technologies to remove magnetic impurities with different particle sizes in stages; (3) Process integration: avoiding the use of chemical reagents and reducing energy consumption and waste emissions. This technology can significantly improve the purity and consistency of battery-grade sodium carbonate and provide key raw material support for the new energy material industry chain.

[0051] In addition, the system of the present invention introduces a draft fan, and a condenser is connected in series after the draft fan and finally connected to the mechanical mill through a pipeline, so that the mechanical mill → dust removal tower → draft fan → condenser → mechanical mill forms a closed system. In the present invention, a closed pulverization device is usually used to avoid the moisture in the environment being inevitably introduced due to the use of an open pulverization device, resulting in an increase in the moisture content of the pulverized materials. The present invention forms a closed system by connecting a condenser in series after the draft fan, and uses the condenser to condense and discharge a part of the high-temperature water vapor generated by the friction of the mechanical mill, and at the same time prevents the equipment from being damaged due to excessive temperature. The rectification system is closed and does not introduce additional moisture, and finally the moisture content introduced during the pulverization process is not higher than 0.1%, ultimately achieving the purpose of moisture control.

[0052] The following further elaborates on the method of the present invention in combination with specific data and the system of the present invention: Example 1: This example provides a method and system for preparing battery-grade sodium carbonate from industrial sodium carbonate. The system is as Figure 1 shown and includes: A raw material pretreatment unit, which includes: A feeding bin 1: used to receive industrial-grade sodium carbonate raw materials, and its outlet is connected to a first continuous vacuum feeder 2 through a pipeline switching valve; The first continuous vacuum feeder 2: communicated with the outlet of the feeding bin 1, and conveys the materials to a vibrating screen 3 by negative pressure transportation; Vibrating screen 3: It is configured with a replaceable screen (50 mesh) for screening out agglomerated powder. The outlet of the coarsely powdered sodium carbonate after screening is connected to a permanent magnet iron remover 4; Multi-stage magnetic separation unit, which includes: Permanent magnet iron remover 4: It adopts a permanent magnet drum structure with a magnetic field intensity of 10,000 Gauss, used to remove magnetic particles (such as Fe3O4) with a particle size greater than 50 μm. Its outlet is connected to an electromagnetic demagnetization device 5; Electromagnetic demagnetization device 5: It is configured with a high-gradient electromagnetic module with a magnetic field intensity greater than 20,000 Gauss, used to remove sub-micron magnetic impurities (such as Fe2O3) with a particle size less than 50 μm; Temporary storage unit, which includes: First temporary storage bin 6 and second temporary storage bin 7: Two groups of temporary storage bins are arranged in parallel through a switching valve. Their inlets are respectively connected to the outlet of the electromagnetic demagnetization device 5, and their outlets are respectively connected to the second continuous vacuum feeding machine 8 and the first continuous vacuum feeding machine 2 through a switching valve; Buffer bin 9: It receives materials from the second continuous vacuum feeding machine 8, and its outlet is connected to a mechanical mill 10; Crushing and finished product processing unit, which includes: Mechanical mill 10: It adopts mechanical crushing method. The crushed materials are dust-removed by a dust removal tower 11 and finally packaged by an automatic packaging machine 12; Dust removal tower 11: It is connected to the outlet of the mechanical mill 10 and is used to capture the dust generated during the crushing process; Fan unit, which includes: First Roots blower 14: It provides negative pressure power for the first continuous vacuum feeding machine 2; Second Roots blower 13: It drives the second continuous vacuum feeding machine 8 to convey materials to the buffer bin 9; Circulating dehumidification system, which includes: Induced draft fan 15: It is connected to the dust removal tower 11 and the condenser 16 to introduce the humid and hot air into the condenser; Condenser 16: It dehydrates the humid and hot air. The condensed dry air is returned to the mechanical mill 10 through a pipeline to form a closed-loop system. The condenser 16 also has a drain port to drain part of the water in the system; The method for preparing battery-grade sodium carbonate from industrial sodium carbonate includes the following steps: S1. Raw material pretreatment and screening: Put the industrial-grade sodium carbonate raw materials into the feeding bin 1, and convey the materials to the vibrating screen 3 through the negative pressure conveying of the first continuous vacuum feeding machine 2; Carry out screening treatment in the vibrating screen 3 with a 50-mesh screen to remove the agglomerated powder with a particle size > 2 mm and obtain coarsely powdered sodium carbonate; In step S1, the particle size of the sieved material is concentrated in the range of 0.25 - 2.0 mm, which improves the contact efficiency in the subsequent magnetic separation process.

[0053] S2. Multi-stage magnetic separation for impurity removal: The crude sodium carbonate powder obtained in step S1 is successively fed into a multi-stage magnetic separation unit for 1 pass of magnetic removal: The permanent magnet iron remover 4 (magnetic field intensity 10000 Gauss) adsorbs and removes strongly magnetic particles with a particle size > 50 μm through a permanent magnet drum, and the removal rate ≥ 99.9%; The electromagnetic demagnetization device 5 (magnetic field intensity > 20000 Gauss) uses high-gradient electromagnetic separation to remove weakly magnetic impurities with a particle size < 50 μm, and the residual amount < 30 ppb; The purified material is fed into the first temporary storage bin 6 or the second temporary storage bin 7 through a pipeline switching valve; When the material purity in the first temporary storage bin 6 or the second temporary storage bin 7 is detected to be unqualified, the material is sent back to the first continuous vacuum feeder 2 through the switching valve and re-enters the magnetic separation unit for secondary treatment; In this embodiment, the double-stage magnetic separation reduces the iron content from > 1000 ppm in the industrial grade to ≤ 5 ppm, meeting the battery-grade standard.

[0054] S3. Crushing and moisture control: Mechanical crushing: The material is poured into the buffer bin 9 through the second continuous vacuum feeder 8 and then enters the mechanical grinder (10). It is crushed under the conditions of a crushing frequency of 32 Hz, a classification frequency of 36 Hz, an air extraction frequency of 48 Hz, and a feeding frequency of 48 Hz to obtain narrow-distribution particles with D50 = 2 - 10 μm; Circulating dehumidification: The hot and humid air generated during crushing is introduced into the condenser 16 by the induced draft fan 15 for dehydration, and the dry air is recycled back to the mechanical grinder 10 to maintain the moisture increase of the material ≤ 0.1%; Finished product packaging: After the battery-grade sodium carbonate after crushing is collected for dust by the dust removal tower 11, it is automatically metered and packaged by the automatic packaging machine 12 to complete the preparation.

[0055] Example 2: Example 2 provides a method and system for preparing battery-grade sodium carbonate from industrial sodium carbonate. The system and method are similar to those in Example 1, except that the mechanical crushing frequencies in step S3 are different. Specifically, the crushing frequency is 27 Hz, the classification frequency is 24.5 Hz, the air extraction frequency is 48 Hz, the feeding frequency is 48 Hz, and the number of magnetic removal passes is 2 times. That is, after the material undergoes the first magnetic removal, it passes through the first temporary storage bin 6 or the second temporary storage bin 7 again, enters the first continuous vacuum feeder, undergoes multi-stage magnetic separation in the magnetic separation unit again for the second magnetic removal, and then enters the second continuous vacuum feeder 8 to enter the next step; Example 3: Example 3 provides a method and system for preparing battery-grade sodium carbonate from industrial sodium carbonate. The system and method are similar to those in Example 1, except that the mechanical crushing frequency in step S3 is different, specifically: the crushing frequency is 27 Hz, the classification frequency is 22 Hz, the air extraction frequency is 48.5 Hz, the feeding frequency is 48 Hz, and the number of demagnetization passes is 3 times. Its steps are similar to those in Example 2; Example 4: Example 3 provides a method and system for preparing battery-grade sodium carbonate from industrial sodium carbonate. The system and method are similar to those in Example 1, except that in step S1, the material is put into a ton bag manual suction device 17; Example 5: Example 5 provides a method and system for preparing battery-grade sodium carbonate from industrial sodium carbonate. The system and method are similar to those in Example 1, except that in the system, the sieve mesh is 10 meshes, and in step S2, the magnetic field strength of the permanent magnet iron remover is 8000 Gauss; Example 6: Example 6 provides a method and system for preparing battery-grade sodium carbonate from industrial sodium carbonate. The system and method are similar to those in Example 1, except that in the system, the sieve mesh is 60 meshes, and in step S2, the magnetic field strength of the permanent magnet iron remover is 12000 Gauss; The battery-grade sodium carbonate prepared in the above Examples 1-3 was tested for relevant properties. The specific results and the conditions of Examples 1-3 are as follows: Table 1: Process conditions of Examples 1-3

[0056] The battery-grade sodium carbonate obtained in Examples 1-3 was tested according to the national standard test method. The results are shown in Table 2. Using this case, battery-grade sodium carbonate products with qualified particle size, moisture content, magnetic substance content, etc. can be obtained.

[0057] Table 2: Product test results

[0058] As can be seen from Table 1 and Table 2, different demagnetization passes and comminution process parameters have a significant impact on key indicators such as the particle size distribution and magnetic impurity content of battery-grade sodium carbonate. With the increase in the number of demagnetization passes (from 1 to 3), the content of magnetic foreign substances (MI value) in the product decreases significantly. The MI value of Example 1 is <1000 ppb, that of Example 2 is reduced to <500 ppb, and that of Example 3 is further reduced to <300 ppb, indicating that the multi-stage magnetic separation process (including permanent magnet iron removal + high-gradient electromagnetic demagnetization) can effectively remove magnetic impurities of different particle sizes, making the residual amount of magnetic foreign substances meet the high-purity requirements of battery-grade sodium carbonate. At the same time, the particle size distribution also changes with the optimization of the comminution frequency and classification parameters. The D50 values in different examples are 5±2μm (Example 1), 10±3 μm (Example 2), and 15±5 μm (Example 3) respectively; among them, a higher comminution frequency (32 Hz) helps to obtain finer particle sizes, while reducing the comminution frequency (27 Hz) and optimizing the classification frequency (adjusted from 36 Hz to 22 Hz) can obtain larger particles, enhancing the fluidity of the powder and making it more suitable for specific application scenarios; in addition, a low-humidity environment and a condenser closed-loop dehumidification system are adopted to ensure moisture control during the comminution process, keeping the moisture increase of the finished product always ≤0.1%, avoiding the problem of powder moisture absorption and caking, and ensuring the stability of the product. Generally speaking, if the goal is to achieve the lowest magnetic impurities, Example 3 (3 demagnetization passes) is the best and is suitable for ultra-high purity applications; if the goal is to obtain a finer particle distribution, Example 1 (single demagnetization pass + higher comminution frequency) can meet the requirements and is suitable for high-activity electrode materials; while if the goal is to balance the magnetic impurity removal rate and the powder particle size distribution, Example 2 (2 demagnetization passes + D50 = 10±3 μm) is the best solution, combining impurity control, fluidity, and processing adaptability. Therefore, by optimizing the screening, magnetic separation, and comminution process parameters, the present invention can effectively reduce the magnetic impurity content and precisely control the particle size distribution to meet the application requirements of different battery material preparations.

[0059] In summary, the present invention provides a method and system for preparing battery-grade sodium carbonate from industrial sodium carbonate. The core technical principle is an integrated process based on physical screening, gradient magnetic separation, and fine grinding technologies. By optimizing the synergistic effects of vibrating screening, multi-stage demagnetization, and mechanical grinding, deep purification and particle optimization of industrial sodium carbonate are achieved. The present invention removes large particle agglomerates through vibrating screening, improves the fluidity of the material, and makes the magnetic separation efficiency higher; adopts a multi-stage series magnetic separation process of a permanent magnet drum + high-gradient electromagnetic demagnetization to remove strong magnetic and weak magnetic impurities in sequence, reducing the content of magnetic foreign matters to ≤300 ppb; uses a mechanical mill to control the particle size distribution, making D50 stable within the range of 2 - 10 μm, and controlling the moisture increase amount ≤0.1% through a closed-loop dehumidification system, solving the key problems of high impurity content, exceeding the standard of magnetic foreign matters, uneven particle size distribution, and difficult humidity control in the prior art. Compared with the traditional chemical pickling method and high-temperature calcination method, the present invention does not require chemical reagents, does not produce waste liquid, has lower energy consumption, is more environmentally friendly, can be stably produced on a large scale, and provides an efficient and low-cost solution for the supply of high-purity sodium carbonate for the positive electrode materials and electrolytes of sodium-ion batteries.

[0060] In the description of the embodiments of the present application, it should be noted that in the description of the present application, the terms such as "inner", "outer", etc., which indicate the direction or positional relationship, are based on the direction or positional relationship shown in the drawings. This is only for the convenience of description and does not indicate or imply that the device or component must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present application.

[0061] In the description of the present application, the description with reference to terms such as "one embodiment", "some embodiments", "in this embodiment", "specific example", or "some examples", etc., means that the specific features, mechanisms, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0062] The above is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in the present application should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing battery-grade sodium carbonate from industrial sodium carbonate, characterized in that, It includes the following steps: S1. Vibration screening is carried out on industrial-grade sodium carbonate raw materials to remove caked powders, obtaining crude sodium carbonate powder; S2. The crude sodium carbonate powder obtained in step S1 is subjected to multi-stage magnetic separation treatment, successively performing permanent magnet iron removal and electromagnetic demagnetization to remove magnetic foreign matters; S3. The demagnetized sodium carbonate powder in step S2 is physically pulverized to obtain a battery-grade sodium carbonate finished product with a particle size distribution D50 of 2 - 10 μm.

2. The method for preparing battery-grade sodium carbonate from industrial sodium carbonate according to claim 1, characterized in that, In step S1, the vibration screening is carried out using a 10 - 60 mesh sieve for screening treatment.

3. The method for preparing battery-grade sodium carbonate from industrial sodium carbonate according to claim 1, wherein In step S2, the magnetic field intensity of the permanent magnet iron removal is 8000 - 12000 Gauss, and the magnetic field intensity of the electromagnetic demagnetization is greater than 20000 Gauss.

4. The method for preparing battery-grade sodium carbonate from industrial sodium carbonate according to claim 3, characterized in that, In step S2, the conditions for successively performing permanent magnet iron removal and electromagnetic demagnetization treatment are as follows: Permanent magnet iron removal uses a permanent magnet drum separator to remove magnetic particles with a particle size greater than 50 μm; Electromagnetic demagnetization uses a high-gradient electromagnetic separator to remove sub-micron magnetic impurities with a particle size less than 50 μm.

5. The method for preparing battery-grade sodium carbonate from industrial sodium carbonate according to claim 1, characterized in that, In step S3, the physical pulverization method is one or both of a jet mill and a mechanical mill, and during the physical pulverization process, the moisture increase of the material is controlled below 0.1%.

6. The method for preparing battery-grade sodium carbonate from industrial sodium carbonate according to claim 5, wherein The physical pulverization method is a mechanical mill, and the operating parameters of the mechanical mill are as follows: Pulverization frequency ≤ 50 Hz; classification frequency ≤ 50 Hz; induced draft frequency ≤ 50 Hz; feeding frequency ≤ 50 Hz.

7. The method for preparing battery-grade sodium carbonate from industrial sodium carbonate according to claim 1, characterized in that, The content of magnetic foreign matters in the battery-grade sodium carbonate finished product ≤ 500 ppb.

8. A system for preparing battery-grade sodium carbonate from industrial sodium carbonate, characterized in that, The system is used to implement the method described in any one of claims 1 - 6, and the system includes the following units: Raw material pretreatment unit: It includes a feeding bin (1), a first continuous vacuum feeder (2) connected to the outlet of the feeding bin (1), and a vibrating screen (3) connected to the outlet of the first continuous vacuum feeder (2); Multi-stage magnetic separation unit: It includes a series-connected permanent magnet iron remover (4) and an electromagnetic demagnetization device (5), and the inlet of the permanent magnet iron remover (4) is connected to the outlet of the vibrating screen (3); Temporary storage unit: It includes a buffer bin (9) and at least one group of temporary storage bins, and the inlet of the temporary storage bin is connected to the outlet of the magnetic demagnetization device (5) through a pipeline switching valve, the outlet of the temporary storage bin is connected to the inlet of a second continuous vacuum feeder (8) through a pipeline switching valve, and the outlet of the second continuous vacuum feeder (8) is connected to the inlet of the buffer bin (9); Pulverization and finished product treatment unit: It includes a mechanical mill (10), a dust removal tower (11), and an automatic packaging machine (12) connected in series successively, and the inlet of the mechanical mill (10) is connected to the outlet of the buffer bin (9); Fan unit: It includes a first Roots blower (14) and a second Roots blower (13), and the first Roots blower (14) is connected to the first continuous vacuum feeder (2), and the second Roots blower (13) is connected to the second continuous vacuum feeder (8); Circulating dehumidification system: It includes an induced draft fan (15) and a condenser (16). The inlet of the condenser (16) is connected to the dust removal tower (11) through the induced draft fan (15), and the outlet of the condenser is connected to the mechanical mill (10).

9. The system according to claim 8, wherein: The outlet of the temporary storage bin is connected to the first continuous vacuum feeding machine (2) and the second continuous vacuum feeding machine (8) respectively through a pipeline switching valve, and the number of the temporary storage bins is 2 groups, namely the first temporary storage bin (6) and the second temporary storage bin (7).

10. The system according to claim 8, wherein: The inlet of the first continuous vacuum feeding machine (2) is also connected to the ton bag manual suction device (17) through a pipeline switching valve, and the outlet of the feeding bin (1) is connected to the first continuous vacuum feeding machine (2) through a pipeline switching valve.

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