Production method of ultra-low salt high-purity sodium carbonate for sodium ion battery

Abstract

The application belongs to the technical field of inorganic compound preparation, and discloses a production method of ultra-low-salt high-purity sodium carbonate for sodium ion batteries. The application is unique in washing and purifying industrial sodium bicarbonate crystal slurry, obtaining ultra-purity sodium bicarbonate, and directly calcining the ultra-purity sodium bicarbonate to obtain sodium carbonate. The obtained sodium carbonate is ultra-low-salt high-purity sodium carbonate without washing, the purity of the product is more than 99.9%, the content of chloride ions in the product is less than 20 ppm (the content of NaCl is less than 33 ppm), other indexes can also meet the chemical purity standard requirements of GB / T 639-2008 "Chemical Reagent Sodium Carbonate", and the obtained product can be used in the fields of sodium ion batteries and reagent-grade sodium carbonate, and enters the high-end soda market, greatly improving the competitiveness and market influence of enterprises.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of inorganic compound preparation, and relates to a production method of sodium carbonate, in particular to a production method of ultra-low-salt high-purity sodium carbonate for sodium ion batteries. BACKGROUND

[0002] The main secondary batteries on the market mainly include nickel-hydrogen batteries, nickel-chromium batteries, lead-acid batteries, lithium batteries, and polymer lithium batteries. In recent years, lithium ions have been widely used in the field of batteries due to their high standard potential, high energy density, and large specific capacity. Sodium, potassium, and lithium are all alkali metals in Group IA of the periodic table, and their physical and chemical properties are similar. In theory, they can all be used as metal ion carriers for secondary batteries. As a substitute for lithium, sodium has the advantages of low cost and large reserves, and has begun to show its advantages in the field of sodium batteries. As an important raw material for sodium ion batteries, the purity of soda ash is also becoming higher and higher, especially the salt content in soda ash, which requires the content of chloride ions to be ≤100 ppm, or even lower to 10-20 ppm.

[0003] According to the quality grade, sodium carbonate can be divided into industrial-grade sodium carbonate, reagent-grade sodium carbonate, and battery-grade ammonium carbonate. The production process of industrial soda ash mainly includes the ammonia soda method (Solvay method), the underground circulation method for producing soda ash, the combined soda method (Hou's soda production method), or the method of directly producing soda ash from natural soda. The ammonia soda method (Solvay method) and the underground circulation method for producing soda ash both use sodium chloride, limestone, and ammonia as raw materials. The brine is refined, ammonia is absorbed, and carbonization (CO2 is obtained by calcining limestone) is performed to obtain NaHCO 3， After filtration, calcination, and other processes, sodium carbonate is obtained; the combined soda method (Hou's soda production method) uses ammonia gas and water to react with carbon dioxide to form ammonium bicarbonate, which is then reacted with sodium chloride to produce sodium bicarbonate and ammonium chloride (as a nitrogen fertilizer). Sodium bicarbonate is then filtered, calcined, and other processes to obtain sodium carbonate; the method of directly producing soda ash from natural soda uses ore dissolution, clarification, and evaporation crystallization to obtain sodium bicarbonate, which is then filtered, calcined, and other processes to obtain sodium carbonate. The salt content in Class I industrial soda ash is required to be controlled below 0.3wt%, which cannot meet the requirements of sodium carbonate for sodium ion batteries. The industry mainly uses the method of purifying source brine, washing monohydrate soda or light soda, and recrystallization to prepare low-salt sodium carbonate. However, the impurity content in the refined brine is still high, which cannot reach the expected purity. During washing and recrystallization, the solubility of sodium carbonate is high, which easily causes a large amount of solid loss and increases the energy consumption of the system. After washing monohydrate soda, the water is saturated, which easily causes scarring of the system and affects normal production. Moreover, the solubility of sodium carbonate changes slightly with temperature, and the effect of recrystallization is poor, the energy consumption is high, the system water balance is destroyed, and the cost is greatly increased.

[0004] Therefore, it is urgent to develop a convenient, feasible, low loss and simple process to reduce the impurity content in sodium carbonate and produce high-purity sodium carbonate. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a production method of ultra-low salt high-purity sodium carbonate for sodium ion batteries. In order to avoid the problems of high solubility of sodium carbonate, large specific surface area of impurities and difficult removal of impurities, the present application creatively adopts the method of calcining ultra-low salt high-purity sodium carbonate after washing sodium bicarbonate slurry. By using the principle of elutriation and crystal growth, the fine grains in the sodium bicarbonate slurry are washed away to increase the supersaturation of the solution, so that the production rate of the crystals and the production capacity of the equipment are improved, thereby increasing the average particle size of the crystals and reducing the specific surface area of the sodium bicarbonate crystals, greatly improving the solid washing effect and prolonging the crystallization time. After the washing of sodium bicarbonate is completed, the ultra-low salt high-purity sodium carbonate is directly calcined. The obtained ultra-low salt high-purity sodium carbonate has a greatly reduced impurity content, a simple and easy-to-operate process and low energy consumption. At the same time, the production process of sodium carbonate can be combined to fully utilize the washing water and avoid other pollution.

[0006] The present application is realized by the following technical solutions:

[0007] A production method of ultra-low salt high-purity sodium carbonate for sodium ion batteries, comprising the following steps: centrifuging sodium bicarbonate slurry produced by an alkali production process to remove most of the water and a large amount of Cl - After the washing and filtration, the fine grains in the sodium bicarbonate slurry are washed away to increase the supersaturation of the solution, so that the production rate of the crystals and the production capacity of the equipment are improved, thereby increasing the average particle size of the crystals and reducing the specific surface area of the sodium bicarbonate crystals, greatly improving the solid washing effect. The filter cake after the washing of the belt filter is sent to a slurry mixing tank by a belt for slurry mixing and crystal growth. After centrifugal separation, the wet material is sent to the slurry mixing tank by a screw for slurry mixing, and then centrifuged by a centrifugal machine. The obtained wet material is sent to a calcining furnace by a wet material screw for calcination. After calcination, the product is ultra-low salt high-purity sodium carbonate without purification. The purity of the product is above 99.9%, and the content of chloride ions in the product is below 20 ppm.

[0008] Further improved schemes of the present application are as follows:

[0009] The washing and purification includes three washing procedures, specifically a first washing procedure, a second washing procedure and a third washing procedure.

[0010] Further, the first washing process is as follows: the sodium bicarbonate crystal slurry is thickened to a crystallization content of 30-50%, and then centrifugally separated in a centrifugal machine; washing water is added in the centrifugal machine to wash part of the salt and impurities in the crystals, so as to obtain wet sodium bicarbonate. The adding speed of the washing water is 1-3 m 3 / h.

[0011] Further, the sodium bicarbonate crystal slurry is derived from the ammonia soda method (Solvay method), the downhole circulating method for producing pure alkali, the combined alkali method (Hou's alkali production method), or the process for directly producing pure alkali from natural alkali.

[0012] Further, the mass percentage of NaCl in the sodium bicarbonate crystal slurry is ≤0.7%, the mass percentage of SO4 2- is ≤0.1%, the mass percentage of water insoluble substance is ≤0.1%, the mass percentage of iron element is ≤0.1%, and the mass percentage of potassium element is ≤0.1%.

[0013] Further, the second washing process is as follows: the wet sodium bicarbonate, from which most of the water and a large amount of Cl - and other impurities are removed through thickening and centrifugal separation, is sent to a vacuum belt filter, multiple washing water (3-10 washing water) is added on the belt filter for washing and suction filtration, the fine grains in the sodium bicarbonate crystal slurry are washed away to increase the supersaturation of the solution and the average particle size of the crystals, the specific surface area of the sodium bicarbonate crystals is reduced, and the solid washing effect is greatly improved.

[0014] Further, the water content of the wet sodium bicarbonate is <15%, and 3-10 washing water is designed to be added on the belt filter, so that the number of washing times can be selected according to the purity requirement of the product, and the production flexibility is increased.

[0015] Further, the third washing process is as follows: the filter cake after the belt filter washing is sent to a slurry mixing barrel containing a stirrer through a belt, clean washing water is added for slurry mixing, the crystals grow, and after centrifugal separation, the wet material is sent to the next slurry mixing barrel through a screw conveyor for slurry mixing, and then centrifugally separated in a centrifugal machine to obtain ultra-low salt high-purity wet sodium bicarbonate.

[0016] Further, the water content of the filter cake is <8%, and the solid-liquid ratio in the slurry mixing barrel is (1-4):1. Two slurry mixing barrels and two centrifugal machines are used in series, and the number of washing times can be selected according to the production needs, so as to realize flexible production and reduce the production energy consumption.

[0017] Further, the calcination process is as follows: the obtained ultra-pure wet sodium bicarbonate is sent to a calcination device, the product after calcination is cooled through a powder flow cooler, and then packaged to obtain ultra-low salt high-purity sodium carbonate.

[0018] Further, the mass percentage of NaCl in the ultra-pure wet sodium bicarbonate is ≤0.01%, the mass percentage of SO4 2-The mass percentage of the quality is less than or equal to 0.01%, the mass percentage of water insoluble is less than or equal to 0.01%, the mass percentage of iron element is less than or equal to 0.005%, and the mass percentage of potassium element is less than or equal to 0.02%.

[0019] Further, the calcination is electric calcination, steam calcination or rotary kiln calcination, and the temperature of the calcination is 280-340 DEG C.

[0020] Compared with the prior art, the present application has the following advantages:

[0021] The sodium ion battery grade sodium carbonate requires low sodium carbonate impurities, especially low chloride ion content, that is, it must be ultra-low salt high-purity sodium carbonate. The present application breaks the traditional method of producing ultra-low salt high-purity sodium carbonate by washing with sodium carbonate or secondary washing and secondary crystallization of sodium carbonate, avoiding the problems of high solubility of sodium carbonate, large specific surface area of impurities, difficult removal, complex production process and difficult control. The sodium bicarbonate crystal slurry is washed several times and then calcined to produce ultra-low salt high-purity sodium carbonate. This method improves the supersaturation of the solution by washing away the fine crystals, thereby increasing the average particle size of the crystals and reducing the specific surface area of the sodium bicarbonate crystals. The solid washing effect is greatly improved. After the sodium bicarbonate is washed to the required standard, it is directly calcined to produce ultra-low salt high-purity sodium carbonate. The product produced by this method has a purity of more than 99.9% and a chloride ion content of less than 20 ppm. Other indicators also meet the chemical purity standard of GB / T 639-2008 "Chemical Reagents Sodium Carbonate". The process is simple and easy to operate, and the energy consumption is low. At the same time, the production process of sodium carbonate can be combined to fully utilize the washing water and not cause other pollution.

[0022] The present application utilizes the fact that the solubility of sodium bicarbonate is lower than that of sodium carbonate under the same conditions to produce ultra-low salt high-purity sodium carbonate by washing and calcining sodium bicarbonate. In this process, the sodium bicarbonate is washed by process water to obtain ultra-pure sodium bicarbonate, and the washing is carried out until the mass percentage of NaCl is less than or equal to 0.01%, the mass percentage of SO4 is less than or equal to 0.01%, the mass percentage of Fe is less than or equal to 0.005%, and the mass percentage of K is less than or equal to 0.02%. 2 The mass percentage of the quality is less than or equal to 0.01%, the mass percentage of water insoluble is less than or equal to 0.01%, the mass percentage of iron element is less than or equal to 0.005%, and the mass percentage of potassium element is less than or equal to 0.02%.

[0023] Thirdly, the present application is based on the industrial sodium carbonate production process, only the washing, calcination, drying and other devices need to be added, and flexible production can be realized according to the production needs, while the quality of sodium carbonate products is greatly improved, and the industrial chain is prolonged. Moreover, without changing the existing alkali production process main device of the company, the washing water is recycled by using the original alkali production system, the system water balance is maintained, the washing water is circulated in the system, no resource waste is caused, no waste liquid is discharged, and the salt in the washing water can be used for production. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Process flow chart of the present application. Embodiment

[0025] The present application will be described in detail below with specific examples.

[0026] In the present application, the titer is a special unit for the concentration of solution in the production of sodium carbonate, and the titer = molar concentration of solute in solution x valence x 20. Example

[0027] A production method of ultra-low salt high-purity sodium carbonate for sodium ion batteries: after obtaining ammonia salt water (ammonia salt water concentration is 1.13:1, temperature is 40℃) by refining brine ammonia absorption in the ammonia alkali method or underground circulating alkali production process, carbonation is carried out to obtain sodium bicarbonate slurry (main impurities are NaCl, Na2SO4, water insoluble substance, iron, KCl, etc., wherein Cl - content is 0.7%, SO4 2- content is 0.1%, water insoluble substance content is 0.08%, iron content is 0.09%, and potassium content is 0.1%).

[0028] The sodium bicarbonate slurry is thickened in a thickener to a crystalline content of 30-50%, and then the wet sodium bicarbonate (water content is less than 8%) after centrifugal separation is sent to a vacuum belt filter (length: width = 15:1, 8 channels of washing water are opened), and the belt filter is washed by soft water negative pressure in 8 stages (washing water temperature is 45℃, vacuum degree is 0.06MPa). The filter cake after belt filter washing is sent to a slurry tank by a belt for slurry adjustment (slurry solid-liquid ratio is 3:1), and then the wet material is sent to the slurry tank for slurry adjustment by a screw (slurry solid-liquid ratio is 3:1) after centrifugal separation. The separated material is calcined by a steam calcining furnace using medium-pressure superheated steam as a heat source (pressure is 2.8Mpa, temperature is 285 o C), and then the calcined product is cooled by a powder flow cooler and packaged to obtain ultra-low salt high-purity sodium carbonate for sodium ion batteries. Example

[0029] A production method of ultra-low salt high-purity sodium carbonate for sodium ion batteries: sodium carbonate solution (alkali concentration is 70-88tt) in the natural alkali direct production of soda process is carbonated with CO2 to generate sodium bicarbonate slurry (main impurities are NaCl, Na2SO4, water insoluble substance, iron, KCl, etc., wherein Cl - content is 0.6%, SO4 2- content is 0.08%, water insoluble substance content is 0.07%, iron content is 0.088%, and potassium content is 0.09%).

[0030] The sodium bicarbonate crystal slurry is thickened in a thickener to a crystallization content of 30-50%, and is centrifugally separated by a centrifuge, and a soft water pipe is connected to the centrifuge for washing (2 cubic meters of washing water per hour). Then, the wet sodium bicarbonate (water content less than 8%) after centrifugal separation is sent to a vacuum belt filter (length: width = 15:1, 5 washing water channels are opened), and soft water negative pressure is supplied to the belt filter for 5-stage washing (washing water temperature 40℃, vacuum degree 0.06MPa). The filter cake after belt filter washing is sent to a slurry adjusting barrel for slurry adjustment (slurry solid-liquid ratio 2.8:1), and then is centrifugally separated. After centrifugal separation, the wet material is sent to a slurry adjusting barrel for slurry adjustment (slurry solid-liquid ratio 2.8:1) by a screw conveyor, and then is centrifugally separated (after washing, the loss rate of solid material is 5%). The wet sodium bicarbonate after centrifugal separation is calcined by a steam calcining furnace using medium-pressure superheated steam as a heat source (pressure 2.6Mpa, temperature 280 o C), and is cooled by a powder flow cooler after calcination. The sodium ion battery grade ultra-low salt high-purity sodium carbonate is obtained after packaging. Embodiment

[0031] A production method of sodium ion battery grade ultra-low salt high-purity sodium carbonate: sodium chloride solution and ammonium bicarbonate in a soda ash production process by a double alkali method are subjected to a double decomposition reaction to obtain sodium bicarbonate crystal slurry (main impurities are NaCl, Na2SO4, water insoluble substance, iron, KCl, etc., wherein Cl - content is 0.7%, SO4 2- content is 0.09%, water insoluble substance content is 0.08%, iron content is 0.09%, and potassium content is 0.085%).

[0032] The sodium bicarbonate crystal slurry is thickened in a thickener to a crystallization content of 30-50%, and is centrifugally separated by a centrifuge to obtain wet sodium bicarbonate (water content less than 8%). The wet material is sent to a vacuum belt filter (length: width = 15:1, 10 washing water channels are opened), and soft water negative pressure is supplied to the belt filter for 10-stage washing (washing water temperature 40℃, vacuum degree 0.06MPa). After washing, the loss rate of solid material is 5%. The filter cake after belt filter washing is sent to an electric calcining furnace (temperature 290℃), and is cooled by a powder flow cooler after calcination. The sodium ion battery grade ultra-low salt high-purity sodium carbonate is obtained after packaging.

[0033] The product detection results of Examples 1-3 are as follows:

[0034] Test item GB / T 639-2008 "Chemical Reagent Sodium Carbonate" for chemical purity Example 1 Example 2 Example 3 Sodium carbonate / % ≥99.8% 99.93 99.92 99.92 Chloride / % ≤0.005% 0.0015 0.0011 0.0013 Sulfur compounds / % ≤0.01% 0.0024 0.0009 0.0019 Silica / % ≤0.013% 0.0032 0.0022 0.0018 Lead / % ≤0.001% 0.0001 0.0001 0.0001 Aluminium / % ≤0.01% 0.0055 0.0062 0.0045 Magnesium / % ≤0.005% 0.0042 0.0043 0.0036 Iron / % ≤0.001% 0.0008 0.0008 0.0007 Potassium / % ≤0.02% 0.0072 0.0061 0.0069

[0035] As shown in the above table, the purity of the sodium ion battery grade sodium carbonate obtained by the present application reaches more than 99.9wt%, the chloride content is less than 0.002wt%, and other indexes can meet the chemical purity standard requirements of GB / T 639-2008 "Chemical Reagents Sodium Carbonate".

[0036] The above embodiments are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent transformation or modification according to the spirit and essence of the present application should be covered within the protection scope of the present application.

Claims

1. A method for producing ultra-low salt high-purity sodium carbonate for sodium ion batteries, characterized in that: The following steps are involved: After washing and purifying the sodium bicarbonate slurry, calcining is performed. No purification is required after calcination, and the obtained product is ultra-low salt high-purity sodium carbonate; The mass percentage of NaCl in the sodium bicarbonate slurry is ≤0.7%, SO4 2- The mass percentage content is ≤0.1%, the mass percentage content of water-insoluble matter is ≤0.1%, the mass percentage content of iron element is ≤0.1%, and the mass percentage content of potassium element is ≤0.1%; The washing and purification includes three washing steps, specifically the first washing step, the second washing step and the third washing step; The specific process of the first washing step is: thickening the sodium bicarbonate slurry to a crystal content of 30-50%, entering the centrifuge for centrifugal separation, and adding washing water to the centrifuge to wash the salt and impurities in the crystals to obtain wet sodium bicarbonate; The specific process of the second washing step is as follows: the wet sodium bicarbonate obtained in the first washing step is sent to a vacuum belt filter, multiple wash waters are added to the belt filter, and washing and filtering are performed; The specific process of the third washing process is as follows: the filter cake obtained in the second washing process is conveyed to a slurry mixing barrel containing a stirrer via a belt, clean washing water is added for slurry mixing, crystals grow, and after centrifugal separation, the wet material is conveyed to the next slurry mixing barrel via an auger for slurry mixing, and then centrifuged in a centrifuge to obtain ultra-low salt high-purity wet sodium bicarbonate; The mass percentage of NaCl in the low-salt high-purity sodium bicarbonate is ≤0.01%, SO4 2- The mass percentage content is ≤0.01%, the mass percentage content of water-insoluble matter is ≤0.01%, the mass percentage content of iron element is ≤0.005%, and the mass percentage content of potassium element is ≤0.02%; The calcination temperature is 280-340°C.

2. The method for producing ultra-low salt high-purity sodium carbonate for sodium ion batteries according to claim 1, wherein: The sodium bicarbonate slurry is derived from an ammonia-soda process, an underground circulating soda ash production process, a combined soda process or a natural soda direct soda ash production process.

3. The method for producing ultra-low salt high-purity sodium carbonate for sodium ion batteries according to claim 1, characterized in that: The moisture content of the wet sodium bicarbonate obtained in the first washing step is less than 15%, and the belt filter is designed to add 3-10 washing waters.

4. The method for producing ultra-low salt high-purity sodium carbonate for sodium ion batteries according to claim 1, wherein: The moisture content of the filter cake obtained in the second washing process is less than 8%, and the solid-liquid ratio in the slurry mixing barrel is (1-4):

1.

5. The method for producing ultra-low salt high-purity sodium carbonate for sodium ion batteries according to claim 1, characterized in that: The calcination process is as follows: the high-purity moist sodium bicarbonate obtained by washing is sent to a calcination device, the calcined product is cooled by a powder flow cooler, and then packaged to obtain ultra-low salt high-purity sodium carbonate.

6. The method for producing ultra-low salt high-purity sodium carbonate for sodium ion batteries according to claim 1 or 5, characterized in that: The calcination is carried out in an electric calciner, a steam calciner or a rotary kiln.

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