Method for preparing battery sodium carbonate from industrial sodium carbonate based on crystallization-nanofiltration coupling

Abstract

The invention discloses a method for preparing battery sodium carbonate from industrial sodium carbonate based on crystallization-nanofiltration coupling, and belongs to the technical field of inorganic chemical industry and battery material purification. The content of chloride ions, divalent ions (Ca < 2 + > and Mg < 2 + >) and magnetic foreign matters in industrial sodium carbonate is high; the traditional process is high in energy consumption and large in wastewater generation amount; in order to solve the problems of insufficient product purity, particle distribution and moisture control, the battery sodium carbonate is prepared through the cooperation of multiple procedures of dissolution, adsorption, nanofiltration impurity removal, crystallization, drying, magnetic separation and the like. Wherein divalent ions are selectively separated by adopting a nanofiltration membrane, and a DTB crystallizer is combined to control the crystal form, so that the purity of the final product is greater than or equal to 99.95%, the chloride ion content is less than or equal to 0.005%, the magnetic foreign matter content is less than or equal to 500ppb, and the water content is less than or equal to 0.03%. The system integrates the nanofiltration unit, the crystallizer and the magnetic separation device, and energy consumption is reduced by 30%. The method is suitable for efficient preparation of the sodium-ion battery positive electrode material.

Description

Technical Field

[0001] This invention belongs to the field of inorganic chemical engineering and battery material purification technology, specifically relating to a method for preparing battery sodium carbonate from industrial sodium carbonate based on crystallization-nanofiltration coupling. Background Technology

[0002] Battery-grade sodium carbonate must meet stringent requirements: purity ≥99.8%, chloride ion ≤0.005% (superior grade), magnetic impurities ≤50ppm, and total calcium and magnesium ≤0.007%. Industrial-grade sodium carbonate (purity 99.0%~99.5%) contains more impurities (such as NaCl 0.42~0.44%, Fe >1000ppm), and traditional purification methods have significant limitations. For example, chemical purification methods (such as acid washing and complexation) generate large amounts of waste liquid and are costly; high-temperature calcination methods have high energy consumption (>200 kWh / ton) and may introduce new pollutants; physical sieving methods have a low removal rate for submicron-sized magnetic particles (<70%); and recrystallization methods have high steam consumption (3.5t / t of product) and a purity of only 99.6%.

[0003] Existing patent CN120348961A employs a physical method of magnetic separation-crushing-dehumidification, but focuses on controlling magnetic foreign matter and is insufficient in removing chloride ions; CN202310497740.X uses monohydrate alkali reduction for purification, but the process is lengthy and relies on multiple crystallizations. This invention combines nanofiltration membrane selective separation with crystallization optimization to achieve high-efficiency purification at low cost and low energy consumption. Through crystallization-nanofiltration coupling technology, this invention achieves efficient and green production of battery-grade sodium carbonate, with product performance superior to industry standards (such as those of Lanke and New Materials), and significantly reduced costs and energy consumption. The system has high integration and is suitable for upgrading existing industrial soda ash production lines. Summary of the Invention

[0004] To address the problems of high chloride ion, divalent ion (Ca²⁺, Mg²⁺), and magnetic impurities content in industrial sodium carbonate; high energy consumption and large wastewater generation in traditional processes; and insufficient product purity, particle distribution, and moisture control, this invention provides...

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A method for preparing battery-grade sodium carbonate from industrial sodium carbonate based on crystallization-nanofiltration coupling.

[0007] Step 1, raw material dissolution: Prepare an aqueous solution of industrial grade sodium carbonate with a purity ≥99.2% into a 25~30wt% sodium carbonate solution, heat to 40~50℃ and stir until completely dissolved;

[0008] Step 2, Adsorption and Filtration: Add activated carbon (0.1-0.5 wt%) to the completely dissolved solution from Step 1 to adsorb organic impurities, and remove solid particles through a precision filter (pore size ≤ 5 μm);

[0009] Step 3, nanofiltration for impurity removal: Under operating conditions of 2.5 MPa and 40°C, the solution is passed through a nanofiltration membrane with a molecular weight cutoff of 200 Da to remove divalent ions (Ca²⁺, Mg²⁺) and chloride ions, with a rejection rate ≥98%;

[0010] Step 4, Evaporation and Crystallization: The clarified liquid after nanofiltration enters the DTB crystallizer and is evaporated and crystallized at 70~80℃ to obtain crystal slurry, and the crystal growth is controlled to be cubic crystal system;

[0011] Step 5, centrifugal separation: The crystal slurry is dehydrated by a centrifuge (G=1000) to obtain a wet sodium carbonate filter cake;

[0012] Step 6, Drying and Magnetic Separation: The wet sodium carbonate filter cake is dried in a fluidized bed (moisture content ≤ 0.03%), and then magnetic foreign matter is removed by multi-stage magnetic separation to make the magnetic impurity content ≤ 500 ppb, thus obtaining battery sodium carbonate.

[0013] The multi-stage magnetic separation includes permanent magnet iron removal combined with electromagnetic demagnetization to remove submicron-sized magnetic particles.

[0014] The magnetic field strength of the permanent magnet demagnetization is 8000~12000 Gauss; the magnetic field strength of the electromagnetic demagnetization is >20000 Gauss.

[0015] The pH range of the nanofiltration membrane in step 3 is 2 to 11.

[0016] The nanofiltration membrane is made of polyamide composite material and has a membrane area of ​​2000 m².

[0017] In step 4, the crystal growth is controlled to maintain a crystal grain size of 2~10μm in the cubic crystal system.

[0018] A system for preparing battery sodium carbonate from industrial sodium carbonate based on crystallization-nanofiltration coupling includes a raw material dissolving tank, an activated carbon adsorption tower, a precision filter, a nanofiltration unit, a DTB crystallizer, a centrifuge, a fluidized bed dryer, a multi-stage magnetic separator, and a packaging machine.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] This invention achieves precise impurity removal through nanofiltration membranes (replacing chemical precipitation or resin adsorption), combined with DTB crystallizer control of crystal morphology and multi-stage magnetic separation to remove magnetic foreign matter, realizing synergistic optimization of the entire process and a process yield exceeding 95%. Product purity is improved: Na₂CO₃ ≥ 99.95%, Cl⁻ ≤ 0.005%, Fe ≤ 0.0001%, total calcium and magnesium ≤ 0.005%; energy consumption is reduced: electricity consumption per ton of product is 160 kWh, a 30% reduction compared to recrystallization; it is environmentally friendly: wastewater reuse rate is 90%, with no chemical waste liquid; and it has a cost advantage: production costs are 15% lower than resin adsorption methods. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 Process flow diagram. Detailed Implementation

[0023] To gain a deeper understanding of this invention, we will provide a comprehensive and detailed description. However, this invention has various implementations and is not limited to the specific examples listed herein. These examples are presented to enhance a full understanding of the disclosure of this invention.

[0024] The nanofiltration membrane selected in the following examples is a polyamide composite material with a membrane area of ​​2000 m² and a pH range of 2 to 11.

[0025] Example 1:

[0026] Step 1: The raw material is industrial-grade Na2CO3 (purity 98.9%, NaCl 0.62%, Fe 0.0006%). The industrial-grade Na2CO3 is dissolved in deionized water (conductivity ≤5μS / cm) to prepare a 28wt% solution.

[0027] Step 2: Add activated carbon (0.1~0.5wt%) to the solution that has been completely dissolved in Step 1 to adsorb organic impurities, and remove solid particles through a precision filter (pore size ≤5μm);

[0028] Step 3, the nanofiltration step operates at a pressure of 2.5 MPa and a temperature of 40°C, with a Ca²⁺ and Mg²⁺ rejection rate of 98.5%.

[0029] Step 4, the crystallization step uses a DTB crystallizer (Φ4000×12000mm, 316L material), and the evaporation temperature is 85℃;

[0030] Step 5: The crystal slurry is dehydrated by a centrifuge (G=1000) to obtain a wet sodium carbonate filter cake;

[0031] Step 6: After the wet sodium carbonate filter cake is dried in a fluidized bed with a moisture content of ≤0.02%, permanent magnet iron removal (12000 Gauss) + electromagnetic demagnetization (20000 Gauss) is performed. The product specifications are: Na2CO3 99.73%, Cl⁻ 0.005%, Fe 0.00009%, and magnetic foreign matter 400ppb.

[0032] Example 2:

[0033] Step 1: The raw material is industrial-grade Na2CO3 (purity 99.4%, NaCl 0.43%, Fe 0.0003%). The industrial-grade Na2CO3 is dissolved in deionized water (conductivity ≤5 μS / cm) to prepare a 28wt% solution.

[0034] Step 2: Add activated carbon (0.1~0.5wt%) to the solution that has been completely dissolved in Step 1 to adsorb organic impurities, and remove solid particles through a precision filter (pore size ≤5μm);

[0035] Step 3, the nanofiltration step operates at a pressure of 2.5 MPa and a temperature of 40°C, with a Ca²⁺ and Mg²⁺ rejection rate of 98.5%.

[0036] Step 4, the crystallization step uses a DTB crystallizer (Φ4000×12000mm, 316L material), and the evaporation temperature is 75℃;

[0037] Step 5: The crystal slurry is dehydrated by a centrifuge (G=1000) to obtain a wet sodium carbonate filter cake;

[0038] Step 6: After the wet sodium carbonate filter cake is dried in a fluidized bed with a moisture content of ≤0.02%, permanent magnet iron removal (12000 Gauss) + electromagnetic demagnetization (20000 Gauss) is performed. The product specifications are: Na2CO3 99.96%, Cl⁻ 0.004%, Fe 0.00008%, and magnetic foreign matter 400ppb.

[0039] Contents not described in detail in this specification are prior art known to those skilled in the art. Although illustrative specific embodiments of the invention have been described above to facilitate understanding by those skilled in the art, it should be understood that the invention is not limited to the scope of the specific embodiments. Various modifications are readily apparent to those skilled in the art as long as they fall within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of this invention are protected.

Claims

1. A method for preparing battery sodium carbonate from industrial sodium carbonate based on crystallization-nanofiltration coupling, characterized in that: Includes the following steps: Step 1, raw material dissolution: Prepare a 25~30wt% sodium carbonate aqueous solution from industrial grade sodium carbonate with a purity ≥99.2%, and heat and stir until completely dissolved; Step 2, Adsorption and Filtration: Add activated carbon to the completely dissolved solution from Step 1 to adsorb organic impurities, and remove solid particles through a precision filter; Step 3, nanofiltration for impurity removal: Under operating conditions of 2.5 MPa and 40°C, the solution is passed through a nanofiltration membrane with a molecular weight cutoff of 200 Da to remove divalent ions and chloride ions, with a rejection rate of ≥98%; Step 4, Evaporation and Crystallization: The clarified liquid after nanofiltration enters the DTB crystallizer and is evaporated and crystallized at 70~80℃ to obtain crystal slurry, and the crystal growth is controlled to be cubic crystal system; Step 5, centrifugal separation: The crystal slurry is dehydrated by a centrifuge to obtain a wet sodium carbonate filter cake; Step 6, Drying and Magnetic Separation: The wet sodium carbonate filter cake is dried in a fluidized bed (moisture content ≤ 0.03%), and then magnetic foreign matter is removed by multi-stage magnetic separation to make the magnetic impurity content ≤ 500 ppb, thus obtaining battery sodium carbonate.

2. The method for preparing battery sodium carbonate from industrial sodium carbonate based on crystallization-nanofiltration coupling according to claim 1, characterized in that: The multi-stage magnetic separation includes permanent magnet iron removal combined with electromagnetic demagnetization to remove submicron-sized magnetic particles.

3. The method for preparing battery sodium carbonate from industrial sodium carbonate based on crystallization-nanofiltration coupling according to claim 2, characterized in that: The magnetic field strength of the permanent magnet demagnetization is 8000~12000 Gauss; the magnetic field strength of the electromagnetic demagnetization is >20000 Gauss.

4. The method for preparing battery sodium carbonate from industrial sodium carbonate based on crystallization-nanofiltration coupling according to claim 1, characterized in that: The pH range of the nanofiltration membrane in step 3 is 2 to 11.

5. The method for preparing battery sodium carbonate from industrial sodium carbonate based on crystallization-nanofiltration coupling according to claim 4, characterized in that: The nanofiltration membrane is made of polyamide composite material and has a membrane area of ​​2000 m².

6. The method for preparing battery sodium carbonate from industrial sodium carbonate based on crystallization-nanofiltration coupling according to claim 1, characterized in that: In step 4, the crystal growth is controlled to maintain a crystal grain size of 2~10μm in the cubic crystal system.

7. A system for preparing battery sodium carbonate from industrial sodium carbonate based on crystallization-nanofiltration coupling, characterized in that: It includes raw material dissolving tanks, activated carbon adsorption towers, precision filters, nanofiltration units, DTB crystallizers, centrifuges, fluidized bed dryers, multi-stage magnetic separation devices, and packaging machines.

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