A process for producing ultra-low salt high-purity soda ash by stirring and washing method

Abstract

The invention discloses a process for producing ultra-low salt high-purity soda ash by a stirring and washing method, comprising the following process steps: (1) sodium chloride solution and ammonium bicarbonate are subjected to double decomposition reaction to obtain baking soda slurry; (2) the baking soda slurry is placed in a thickener to thicken to a crystal content of 30-50%, and then centrifuged and dehydrated by a centrifuge; (3) it is sent to a belt filter for washing, and (4) the wet material after unloading is sent to an electric calcining furnace through a feed auger, cooled by a powder flow cooler after calcination, and packaged to obtain ultra-low salt high-purity soda ash for sodium ion batteries. The washing water distributed above the baking soda filter cake is fully stirred and mixed with the filter cake by a stirring device to form a slurry again. Without increasing the number of washing steps, the impurities adsorbed on the surface of the baking soda crystal can be fully dissolved in the washing, thereby improving the washing operation effect of the baking soda solid, reducing the water content of the baking soda entering the calcining kiln, thereby achieving the effect of reducing costs and improving quality, and then obtaining high-purity soda ash.

Description

Technical Field

[0001] The invention relates to a preparation technology of ultra-low salt high-purity soda ash for sodium ion batteries, and in particular to a process for producing ultra-low salt high-purity soda ash by a stirring and washing method. Background Art

[0002] The main secondary batteries on the market include nickel-metal hydride batteries, nickel-chromium batteries, lead-acid batteries, lithium batteries, polymer lithium batteries, etc. Lithium ions have been widely used in the battery field in recent years due to their advantages such as high standard potential, high energy density, and large specific capacity. Sodium, potassium, and lithium are all alkali metal elements of Group IA of the periodic table, with similar physical and chemical properties. In theory, they can all be used as metal ion carriers for secondary batteries. As an alternative resource to lithium, sodium has begun to show its advantages of low cost and large reserves, and has received more and more attention in the battery field.

[0003] Sodium carbonate is also called soda ash, which is divided into heavy soda ash and light soda ash. The importance of sodium carbonate to sodium-ion batteries is the same as that of lithium carbonate to lithium-ion batteries. With the rapid development of the electronics industry, as an important raw material for sodium-ion batteries, the purity requirements of soda ash are getting higher and higher, especially the salt content in soda ash. During the production process of soda ash companies, customers generally require the salt content of soda ash products to be controlled at around 0.3wt%, but sodium-ion battery-grade soda ash requires a chloride ion content of ≤100ppm, or even lower to 10-20ppm.

[0004] At present, the production processes of soda ash include the ammonia-soda method (Solvay process), the combined alkali method (Hou's alkali process) and the underground circulation method. The main method is to make ammonia brine from refined brine through an ammonia absorption process, which is then carbonized with carbon dioxide gas to produce sodium bicarbonate, and the sodium bicarbonate crystals are calcined to make soda ash. To prepare high-purity ultra-low salt soda ash, the source refined brine is purified, mainly through the two-alkali method, and flocculants are added. However, the impurity content in the brine refined by this method is still high and cannot reach the expected purity, so further purification is required. Washing monohydrate or light soda ash to prepare high-purity ultra-low salt soda ash will cause a large solid loss and increase system energy consumption because the solubility of soda ash is greater than that of sodium bicarbonate; and the monohydrate is saturated with water after washing, which can easily lead to scarring of the system and affect normal production.

[0005] On the other hand, technicians further refine the soda ash obtained by production to obtain higher purity soda ash. The traditional method of refining soda ash mainly utilizes the industrial-grade soda ash produced to carry out physical washing or chemical method to remove impurities such as chloride ions, calcium and magnesium, and then obtains soda ash with higher purity through processes such as recrystallization and drying. However, this type of method generally has complicated procedures, and the method of washing soda ash has a high solid loss rate, while increasing energy consumption, or destroying the system water balance, greatly increasing costs, and the high-purity soda ash acquisition rate is low. Therefore, it is urgent to develop a convenient and feasible method with low loss rate and simple and easy-to-operate process to reduce the impurity content in soda ash and produce high-purity soda ash.

[0006] Because the solubility of sodium bicarbonate is lower than that of sodium carbonate under the same conditions, sodium bicarbonate is washed with water and then calcined to produce ultra-low salt and high-purity soda ash.

[0007] However, in the soda ash production process, the belt vacuum filter is a device that vacuum filters the baking soda slurry to separate the solid and liquid, and washes it during the solid-liquid separation process to remove some impurities, thereby achieving the purpose of improving the quality of soda ash.

[0008] The belt vacuum filter is an efficient separation device that uses filter cloth as the filter medium, fully utilizes the gravity of the material, and relies on vacuum negative pressure as the power to achieve solid-liquid separation. The equipment continuously completes the filtration, filter cake washing, slag unloading, and filter cloth cleaning during the production process as the belt runs; the equipment can adapt to materials of different concentrations, and the mother liquor and filter cake washing liquid can be collected in sections. It has the advantages of large production capacity, high filtration efficiency, good washing effect, and low moisture content in the filter cake.

[0009] The equipment is arranged in the filter cloth working area, slurry cloth area, vacuum filtration area, and filter cake washing area along the horizontal length direction (such as Figure 1As shown). The baking soda slurry overflows from the cloth trough onto the filter cloth. The mother liquor in the slurry, under the action of its own weight and the vacuum suction under the filter cloth, penetrates the filter cloth and enters the vacuum groove under the filter cloth. The baking soda filter cake separated from the mother liquor above the filter cloth moves to the washing area together with the filter cloth. In the washing area, the washing water is evenly distributed on the filter cake from the water distributor above the filter cake. Under the action of its own gravity and the vacuum suction under the filter cloth, the washing water penetrates the filter cake and the filter cloth and enters the vacuum groove under the filter cloth. In the process of washing water penetrating the filter cake, the washing water washes the surface of the baking soda material crystals to remove the impurities of the baking soda filter cake and improve the product quality. In order to ensure the quality of the product output, it is generally washed 2-3 times, that is, 2-3 levels of washing devices are installed in the washing area. The moisture content of the washed filter cake is generally less than 16%. The washed filter cake moves to the unloading area along with the filter cloth, and the filter cake is scraped off the filter cloth by a scraper and enters the lower hopper to enter the next process; the unloading belt moves to the filter belt washing area below the belt filter, and the washing water is used to rinse the two sides of the filter cloth to wash away the baking soda remaining on the surface of the filter cloth. The washed filter cloth passes through the power device and the correction device and returns to the slurry spreading area, where it is spread again, and the filter cloth completes a continuous cycle operation.

[0010] In the filter cake washing area, in order to wash the baking soda solids, the usual practice is to lay a water distribution board on the moving filter cake (baking soda solids). After the washing water overflows from the washing tank and falls on the water distribution board, it flows evenly from the edge of the water distribution board to the top of the filter cake. The washing water above the filter cake, under the action of gravity and the vacuum suction under the filter cloth, washes the filter cake layer with the washing water. In this process of washing, the washing water achieves a washing effect on the surface of the filter cake (such as Figure 2 After washing the filter cake, the washing water passes through the filter cloth and enters the vacuum tank below the filter cloth.

[0011] In the process of washing the filter cake with washing water, the baking soda filter cake is fixed. The washing water quickly penetrates from top to bottom under the action of gravity and vacuum. The washing water does not fully contact and stay on the surface of the filter cake particles, and the washing effect is not obvious. In order to achieve a certain washing effect, the washing times can only be increased, the length of the filter cloth can be increased, and a repeated washing device can be added to the washing area. Generally, when the washing device is increased to three levels, the chloride ion content in the soda ash is less than 0.25% (wet basis), and it is difficult to reduce it. If the number of washing stages is increased, the washing effect is not obvious, the product quality is not improved much, and the filter cake loss increases (washing will dissolve part of the product, and some fine crystals will pass through the filter cloth and enter the washing water), affecting the product output. That is, increasing the number of washing stages will not improve the product quality, but will affect the production line capacity. Summary of the invention

[0012] The invention provides a process for producing ultra-low salt high-purity soda ash by a stirring and washing method. Under the same conditions, the solubility of sodium bicarbonate is lower than that of sodium carbonate, and the sodium bicarbonate is washed with water and then calcined to produce ultra-low salt high-purity soda ash. During washing, a stirring device is used to fully stir and mix the washing water distributed above the baking soda filter cake with the filter cake to form a slurry again. Impurities adsorbed on the surface of the baking soda crystal can be fully dissolved in the washing process without increasing the number of washing steps, thereby improving the washing operation effect of the baking soda solid, reducing the water content of the baking soda entering the calcining kiln, thereby achieving the effect of reducing cost and improving quality, and further obtaining high-purity soda ash.

[0013] The technical solution disclosed in the present invention is as follows: A process for producing ultra-low salt high-purity soda ash by a stirring and washing method, comprising the following process steps:

[0014] (1) Sodium chloride solution and ammonium bicarbonate undergo double decomposition reaction to obtain baking soda slurry;

[0015] (2) Place the baking soda slurry in a thickener and thicken it to a crystal content of 30-50%, and then centrifuge it for dehydration;

[0016] (3) Send to the filter machine for washing,

[0017] in,

[0018] A: The baking soda filter cake moves with the filter cloth to the washing area of ​​the filter machine. While the water distributor above it distributes washing water, it enters the stirring device. Under the stirring action of the stirring device, the filter cake and washing water form a slurry on the filter cloth again and are evenly distributed on the filter cloth;

[0019] B: The mixed washing slurry evenly distributed on a flat beach moves to the vacuum filtration area along with the filter cloth. The washing water in the slurry, under the action of its own weight and the vacuum suction under the filter cloth, penetrates the filter cloth and enters the vacuum groove under the filter cloth.

[0020] C: The mixed washing slurry is dehydrated on the filter cloth to form a filter cake, which moves with the filter cloth to the next washing area or enters the drying area or unloading area to enter the next unloading operation;

[0021] (4) The wet material after unloading is fed into an electric calcining furnace through a feeding auger, cooled by a powder flow cooler after calcination, and packaged to obtain ultra-low salt high-purity soda ash for sodium ion batteries.

[0022] Based on the above scheme, preferably, in step (3), the moving speed of the filter cake is 0.03-0.6 m / s, the rotation speed of the stirring device is 1-400 rpm, the volume ratio of the filter cake and the washing water to form a slurry on the filter cloth again is 100:20-100:100, and the absolute air pressure is 20-100 kPa.

[0023] Based on the above scheme, preferably, in step (3), the moving speed of the filter cake is 0.08-0.15 m / s, the rotation speed of the stirring device is 50-150 rpm, the volume ratio of the filter cake and the washing water to form a slurry on the filter cloth again is 100:30-100:50, and the absolute air pressure is 50-80 kPa.

[0024] Based on the above solution, preferably, in step (3), the minimum distance between the end of the stirring blade of the stirring device and the surface of the filter cloth is 1-2 mm.

[0025] Based on the above scheme, preferably, the number of washing zones in step (3) is not more than 3.

[0026] Based on the above scheme, preferably, the temperature of the electric calcining furnace in step (4) is 290±20°C.

[0027] Based on the above solution, preferably, the belt filter in step (3) comprises:

[0028] filter cloth, and

[0029] A water distributor is arranged above the filter cloth, the water distributor comprises a water distribution trough and a water distribution plate, the upper end of the rear end plate of the water distribution trough is higher than the front end plate to form an overflow port or an overflow port is arranged on the front end plate, the rear end of the water distribution plate is connected to the front end surface of the front end plate, and the front end extends downward;

[0030] The stirring device is arranged in front of the water distributor, and includes a stirring shaft and a cover plate covering the stirring shaft, the height of the front end of the cover plate is higher than the height of the rear end of the cover plate, the rear end of the cover plate is fixedly connected with a flat plate, the front end of the water distribution plate extends to below the front end of the cover plate, and a plurality of stirring blades are fixedly installed in the radial direction of the stirring shaft;

[0031] The vacuum groove is located below the filter cloth, and its projection in the vertical direction is located in front of the flattening plate. The vacuum groove is connected to the vacuum system.

[0032] Based on the above solution, preferably, one end of the stirring blade is fixedly connected to the stirring shaft, and the other end has a grip.

[0033] On the basis of the above scheme, as a preferred embodiment, the water distributor, the stirring device and the vacuum tank constitute a set of washing devices, and 1-3 washing devices can be set in the washing area of ​​a filter cloth.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. The present invention washes and purifies sodium bicarbonate slurry to obtain ultra-pure sodium bicarbonate, which is then directly calcined and produced. The obtained sodium carbonate does not need to be washed, that is, ultra-low salt high-purity soda ash. The product purity is above 99.9%, the chloride ion content in the product is lower than 20ppm, and other indicators can also meet the chemical purity standard requirements of GB / T 639-2008 "Chemical Reagent Sodium Carbonate". The obtained product can be used in the fields of sodium ion batteries, reagent-grade soda ash, etc., enter the high-end soda ash market, and greatly improve the competitiveness and market influence of enterprises.

[0036] Second, taking advantage of the fact that the solubility of sodium bicarbonate is lower than that of sodium carbonate under the same conditions, the sodium bicarbonate is washed with water and then calcined to produce ultra-low salt high-purity soda ash. During the washing process, the stirring washing method is used to improve the washing effect of the baking soda solid, reduce the water content of the baking soda entering the calcining kiln, thereby achieving the effect of reducing costs and improving quality, and then obtaining high-purity soda ash.

[0037] 3. In the conventional filter cake washing method, the filter cake is fixed and the washing water directly rinses through the filter cake from top to bottom. This method is changed to a method in which the washing water and the filter cake are mechanically beaten and fully mixed. The washing water is in full contact with the crystal surface of the filter cake material and stirred intimately, and the impurities adsorbed on the crystal surface are fully eluted. Compared with the direct elution method, the washing effect is doubled. Under the same conditions, the amount of washing water and the number of washing stages are reduced, and the amount of filter cake washing dissolution loss is reduced.

[0038] 4. When stirred by the agitator, the washing slurry is more easily evenly distributed on the filter cloth. The surface of the filter cake is flat and cooperates with the flat plate of the stirring device, so that the thickness of the filter cake after passing through the flat plate is consistent, and the surface of the filter cake is flat. The pressure difference between the upper and lower surfaces of the filter cake and the filter cloth is consistent, and the mother liquor in the filter cake is evenly and efficiently filtered out and separated, thereby reducing the moisture content of the baking soda filter cake entering the calcining kiln.

[0039] 5. The direction of rotation of the stirring shaft is consistent with the moving direction of the filter cloth, which can offset the resistance of the stirring scrubber to the movement of the filter cloth and will not increase the wear of the filter cloth or filter belt due to resistance.

[0040] 6. The shape and speed of the stirring shaft can be adjusted according to the stirring effect of the material to maintain the material moving speed and stirring, beating and washing effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the structure of the existing baking soda cloth, washing, drying and unloading;

[0042] Figure 2 It is a schematic diagram of the existing baking soda filter cake washing;

[0043] Figure 3 This is a schematic diagram of washing baking soda filter cake of the present invention;

[0044] Figure 4It is a structural schematic diagram of a stirring device;

[0045] Figure 5 It is a system block diagram of the present invention. DETAILED DESCRIPTION

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings and other implementation methods can be obtained based on these drawings without creative work.

[0047] like Figure 3-4 As shown, the belt vacuum filter stirring washing method comprises the following steps:

[0048] A: The baking soda filter cake moves to the washing area with the filter cloth (moving speed 0.03-0.6m / s, optimal 0.08-0.15m / s), and enters the stirring device while the water distributor above it distributes washing water. Under the stirring of the stirring device (speed of 1-400 rpm, optimal 50-150 rpm), the filter cake and washing water (volume ratio 100:20-100:100, optimal volume ratio 100:30-100:50) form slurry on the filter cloth again and are evenly distributed on the filter cloth; among them, the minimum distance between the end of the stirring blade of the stirring device and the surface of the filter cloth is 1-2mm to prevent the stirring shaft from wearing or damaging the filter cloth.

[0049] B: The mixed washing slurry evenly distributed on a flat beach moves to the vacuum filtration area with the filter cloth. The washing water in the slurry, under the action of its own weight and the vacuum suction force under the filter cloth (the air absolute pressure is 20-100kPa, and the optimal air absolute pressure is 50-80kPa), passes through the filter cloth and enters the vacuum groove under the filter cloth. This pressure can keep the filter cake thickness uniform and the surface flat, ensuring the vacuum dehydration effect of the subsequent filter cake in the suction drying area;

[0050] C: The mixed washing slurry is dehydrated on the filter cloth to form a filter cake, which is moved with the filter cloth to the next washing device to repeat the ab operation, or enters the drying area or the unloading area to enter the next unloading operation.

[0051] The washing device specifically comprises:

[0052] A water distributor is arranged above the filter cloth, the water distributor comprises a water distribution trough and a water distribution plate, the upper end of the rear end plate of the water distribution trough is higher than the front end plate to form an overflow port or an overflow port is arranged on the front end plate, the rear end of the water distribution plate is connected to the front end surface of the front end plate, and the front end extends downward;

[0053] The stirring device is arranged in front of the water distributor, and includes a stirring shaft and a cover plate covering the stirring shaft. The height of the front end of the cover plate is higher than the height of the rear end of the cover plate. The rear end of the cover plate is fixedly connected with a flat plate. The front end of the water distribution plate extends to below the front end of the cover plate. A plurality of stirring blades are fixedly installed in the radial direction of the stirring shaft. One end of the stirring blade is fixedly connected to the stirring shaft, and the other end has a gripper.

[0054] The vacuum groove is located below the filter cloth, and its projection in the vertical direction is located in front of the flattening plate. The vacuum groove is connected to the vacuum system.

[0055] The water distributor, stirring device and vacuum tank constitute a set of washing devices. 1-3 levels of washing devices can be set in the washing area of ​​a filter cloth.

[0056] Specific washing process:

[0057] Conventional washing method

[0058] In normal washing, the baking soda filter cake on the filter cloth is 2000mm wide and 25mm thick. The ratio of filter cake to washing water is 2:1 (volume ratio), the vacuum degree is 60kPa, the filter cloth moving speed is 10cm / s, the moisture content of the filter cake after the first-stage washing is 16-17%, and the chloride ion content is 0.42%; after the third-stage washing, the chloride ion content of the filter cake can be reduced to 0.25%.

[0059] Embodiment 1

[0060] The stirring, mixing and washing device of the present invention is installed on a vacuum belt filter, and the width of the baking soda filter cake on the filter cloth is 2000 mm and the thickness is 25 mm. The ratio of the filter cake to the washing water is 10:3 (volume ratio), the vacuum degree is 40 kPa, the filter cloth moving speed is 10 cm / s, and the baking soda filter cake and the washing water are mixed, stirred and slurried. The stirring shaft speed is 120 rpm, and the filter cake is evenly spread on the filter cloth after being leveled by the stirrer leveling plate. The thickness is uniform, the thickness is 24 mm, the surface is flat, the filter cake chloride ion content is 0.25% (wet basis), and the baking soda filter cake moisture content is 12%.

[0061] Embodiment 2

[0062] The stirring, mixing and washing device of the present invention is installed on a vacuum belt filter, and the width of the baking soda filter cake on the filter cloth is 2000 mm and the thickness is 45 mm. The ratio of the filter cake to the washing water is 10:4 (volume ratio), the vacuum degree is 40 kPa, the filter cloth moving speed is 10 cm / s, and the baking soda filter cake and the washing water are mixed, stirred and slurried. The stirring shaft speed is 120 rpm, and the filter cake is evenly spread on the filter cloth after being leveled by the stirrer leveling plate. The thickness is uniform, the thickness is 43 mm, the surface is flat, the filter cake chloride ion content is 0.15% (wet basis), and the baking soda filter cake moisture content is 13%.

[0063] Embodiment 3

[0064] The two-stage stirring, mixing and washing device of the present invention is installed on the vacuum belt filter, the width of the baking soda filter cake on the filter cloth is 2000mm, the thickness is 45mm, the vacuum degree is 40kPa, and the filter cloth moving speed is 10cm / s. The ratio of the filter cake to the washing water of the first-stage washing device is 10:4 (volume ratio), and the ratio of the filter cake to the washing water of the second-stage washing device is 10:3 (volume ratio). After the baking soda filter cake and the washing water are mixed, stirred and slurried, the stirring shaft speed is 120 rpm, and the filter cake is evenly distributed on the filter cloth with a uniform thickness of 42mm and a flat surface. The chloride ion content of the filter cake is 0.06% (wet basis), and the moisture content of the baking soda filter cake is 12%.

[0065] Embodiment 4

[0066] The three-stage stirring and mixing washing device of the present invention is installed on the vacuum belt filter, the width of the baking soda filter cake on the filter cloth is 2000mm, the thickness is 45mm, the vacuum degree is 40kPa, and the filter cloth moving speed is 10cm / s. The ratio of the filter cake to the washing water of the first-stage washing device is 10:4 (volume ratio), the ratio of the filter cake to the washing water of the second-stage washing device is 10:3 (volume ratio), and the ratio of the filter cake to the washing water of the third-stage washing device is 10:3 (volume ratio). After the baking soda filter cake and the washing water are mixed, stirred and slurried, the stirring shaft speed is 120 rpm, and the filter cake is evenly distributed on the filter cloth with a uniform thickness of 40mm and a flat surface. The chloride ion content of the filter cake is 0.02% (wet basis), and the moisture content of the baking soda filter cake is 12%.

[0067] like Figure 5 As shown, the process of producing ultra-low salt high-purity soda ash for sodium ion batteries using the washing method described above is as follows:

[0068] 1. Sodium chloride solution and ammonium bicarbonate undergo double decomposition reaction to obtain sodium bicarbonate slurry (the main impurities are NaCl, Na2SO4, water-insoluble matter, iron, KCl, etc., among which Cl - ≤0.7%, SO4 2- ≤0.1%, water-insoluble matter ≤0.1%, iron content ≤0.1%, potassium content ≤0.1%).

[0069] 2. Place the sodium bicarbonate slurry in a thickener to thicken it to a crystal content of 30-50%, and then centrifuge it for dehydration.

[0070] 3. Send to the filter machine for washing.

[0071] 4. The washed wet material is fed into an electric calcining furnace (temperature 290°C) via a feed auger, cooled by a powder flow cooler after calcination, and packaged to obtain ultra-low salt high-purity soda ash for sodium ion batteries.

[0072] The test results of the soda ash produced by the conventional washing method and the soda ash produced after washing using Examples 1-4 are as follows:

[0073] Test items GB / T 639-2008 "Chemical Reagent Sodium Carbonate" Chemically Pure Conventional washing (three-stage washing) Embodiment 1 Embodiment 2 Embodiment 3 Embodiment 4 Sodium carbonate / % ≥99.8% 99.92 99.93 99.92 99.93 99.95 chloride / % ≤0.005% 0.0014 0.0015 0.0011 0.0011 0.0010 Sulfur compounds / % ≤0.01% 0.0025 0.0024 0.0019 0.0019 0.0009 Silicon dioxide / % ≤0.013% 0.0030 0.0032 0.0022 0.0021 0.0017 lead / % ≤0.001% 0.0001 0.0001 0.0001 0.0001 0.0001 aluminum / % ≤0.01% 0.0055 0.0055 0.0062 0.0055 0.0050 magnesium / % ≤0.005% 0.0045 0.0042 0.0043 0.0040 0.0038 iron / % ≤0.001% 0.0008 0.0008 0.0008 0.0008 0.0007 Potassium / % ≤0.02% 0.0075 0.0072 0.0061 0.0060 0.0055

[0074] As can be seen from the above table, the purity of the sodium ion battery-grade soda ash obtained by the present invention reaches more than 99.9wt%, the chloride content is lower than 0.002wt%, and other indicators can meet the chemical purity standard requirements of GB / T 639-2008 "Chemical Reagent Sodium Carbonate".

[0075] It should be noted that the above embodiments can be freely combined as needed. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered as the protection scope of the present invention.

Claims

1. A process for producing ultra-low salt high-purity soda ash by a stirring and washing method, characterized in that: The process steps include: (1) Sodium chloride solution and ammonium bicarbonate undergo double decomposition reaction to obtain baking soda slurry; (2) Place the baking soda slurry in a thickener and thicken it to a crystal content of 30-50%, and then centrifuge it for dehydration; (3) Send to the filter machine for washing, in, A: The baking soda filter cake moves with the filter cloth to the washing area of ​​the filter machine. While the water distributor above it distributes washing water, it enters the stirring device. Under the stirring action of the stirring device, the filter cake and washing water form a slurry on the filter cloth again and are evenly distributed on the filter cloth; B: The evenly distributed mixed washing slurry moves to the vacuum filtration area along with the filter cloth. The washing water in the slurry, under the action of its own weight and the vacuum suction under the filter cloth, passes through the filter cloth and enters the vacuum slot under the filter cloth. C: The mixed washing slurry is dehydrated on the filter cloth to form a filter cake, which moves with the filter cloth to the next washing area or enters the drying area or unloading area to enter the next unloading operation; (4) The wet material after unloading is fed into an electric calcining furnace through a feeding auger, cooled by a powder flow cooler after calcination, and packaged to obtain ultra-low salt high-purity soda ash for sodium ion batteries; In step (3), the moving speed of the filter cake is 0.03-0.6 m / s, the rotation speed of the stirring device is 1-400 rpm, the volume ratio of the filter cake and the washing water to form a slurry on the filter cloth again is 100:20-100:100, the absolute air pressure is 20-100 kPa, and the number of washing zones in step (3) is not more than 3.

2. The process for producing ultra-low salt high-purity soda ash by the stirring and washing method as claimed in claim 1, characterized in that: In step (3), the moving speed of the filter cake is 0.08-0.15 m / s, the rotation speed of the stirring device is 50-150 rpm, the volume ratio of the filter cake and the washing water to form a slurry on the filter cloth again is 100:30-100:50, and the absolute air pressure is 50-80 kPa.

3. The process for producing ultra-low salt high-purity soda ash by the stirring and washing method as claimed in claim 1, characterized in that: In step (3), the minimum distance between the end of the stirring blade of the stirring device and the surface of the filter cloth is 1-2 mm.

4. The process for producing ultra-low salt high-purity soda ash by the stirring and washing method as claimed in claim 1, characterized in that: In step (4), the temperature of the electric calcining furnace is 290±20°C.

5. The process for producing ultra-low salt high-purity soda ash by the stirring and washing method as claimed in claim 1, characterized in that: The belt filter in step (3) comprises: filter cloth, and A water distributor is arranged above the filter cloth, the water distributor comprises a water distribution trough and a water distribution plate, the upper end of the rear end plate of the water distribution trough is higher than the front end plate to form an overflow port or an overflow port is arranged on the front end plate, the rear end of the water distribution plate is connected to the front end surface of the front end plate, and the front end extends downward; The stirring device is arranged in front of the water distributor, and includes a stirring shaft and a cover plate covering the stirring shaft, the height of the front end of the cover plate is higher than the height of the rear end of the cover plate, the rear end of the cover plate is fixedly connected with a flat plate, the front end of the water distribution plate extends to below the front end of the cover plate, and a plurality of stirring blades are fixedly installed in the radial direction of the stirring shaft; The vacuum groove is located below the filter cloth, and its projection in the vertical direction is located in front of the flattening plate. The vacuum groove is connected to the vacuum system.

6. The process for producing ultra-low salt high-purity soda ash by the stirring and washing method as claimed in claim 5, characterized in that: One end of the stirring blade is fixedly connected to the stirring shaft, and the other end is provided with a gripper.

7. The process for producing ultra-low salt high-purity soda ash by the stirring and washing method as claimed in claim 5, characterized in that: The water distributor, stirring device and vacuum tank constitute a set of washing devices. One to three washing devices can be arranged in the washing area of ​​a filter cloth.

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