Method for preparing high-purity sodium carbonate from fly ash

Abstract

The invention relates to the field of waste resource utilization and chemical material preparation, and discloses a method for preparing high-purity sodium carbonate from fly ash, which comprises the following steps: raw material pretreatment: carrying out component analysis, screening and acid pickling treatment on fly ash; multistage dissolution and selective precipitation: dissolving the pretreated fly ash in water, and adjusting the pH value and temperature of the solution for selective precipitation; multi-stage temperature control crystallization and purification: separating out sodium carbonate crystals through multiple times of crystallization and filtration; drying and finished product collection: drying and packaging the sodium carbonate crystals subjected to crystallization separation. Through accurate parameter monitoring, multi-stage temperature control crystallization, two-stage low-temperature drying and nitrogen purging treatment, efficient removal of sodium carbonate impurities is achieved, the purity and the product stability are improved, meanwhile, moisture absorption and caking are effectively prevented through improved drying and packaging measures, and it is ensured that the quality of finished products is kept stable in the storage and transportation process.

Description

Technical Field

[0001] The invention relates to the technical field of waste resource utilization and chemical material preparation, and in particular to a method for preparing high-purity sodium carbonate by utilizing fly ash. Background Art

[0002] As an important industrial basic chemical, sodium carbonate is widely used in glass, papermaking, detergent and other industries, which have high requirements for its purity. The traditional method of preparing high-purity sodium carbonate usually uses natural alkali mineral resources or chemical raw materials to extract sodium carbonate through dissolution, evaporation, crystallization and other methods.

[0003] Some existing methods for preparing high-purity sodium carbonate mainly purify sodium carbonate through multiple crystallizations and fine control of temperature, solution concentration and other operations. For example, some methods effectively separate impurities during multi-stage dissolution and cyclic crystallization, and improve the purity of sodium carbonate by staged cooling and refined dissolution steps. These methods can achieve higher sodium carbonate purity, are suitable for specific industrial applications, and some processes have higher production efficiency.

[0004] However, the existing technology still has problems in the preparation process of sodium carbonate, such as incomplete removal of impurities, easy moisture absorption and agglomeration of the product, and poor process stability. In particular, there is a lack of real-time monitoring means for the control of key parameters such as temperature, pH value, and sodium ion concentration, which makes it difficult to ensure purity and production stability. At the same time, there is a lack of effective anti-moisture absorption measures, which makes the finished product prone to agglomeration and moisture absorption and deterioration during storage and transportation, making it difficult to meet the needs of high-quality applications. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for preparing high-purity sodium carbonate using fly ash, which solves the problems of incomplete impurity removal, easy moisture absorption and agglomeration of the product, and unstable process control in the sodium carbonate preparation process in the prior art.

[0006] To achieve the above object, the present invention is implemented by the following technical scheme: A method for preparing high-purity sodium carbonate using fly ash, comprising the following steps: Raw material pretreatment: component analysis, screening and acid washing of fly ash; Multi-stage dissolution and selective precipitation: dissolving the pretreated fly ash in water and adjusting the pH and temperature of the solution for selective precipitation; Multi-stage temperature-controlled crystallization purification: Sodium carbonate crystals are separated through multiple crystallizations and filtration; Drying and finished product collection: Drying and packaging the sodium carbonate crystals after crystallization separation; Process parameter monitoring and optimization: Real-time monitoring and automatic adjustment of temperature, pH value and ion concentration throughout the entire process.

[0007] Preferably, the raw material pretreatment comprises the following steps: Component analysis: Use X-ray fluorescence spectroscopy or inductively coupled plasma mass spectrometry to detect the content of sodium carbonate, sodium sulfate, sodium chloride, heavy metals and insoluble impurities in fly ash; Screening: Use 60-mesh and 120-mesh screens to screen the fly ash in two stages to remove large particles of impurities; Acid washing treatment: Mix the screened fly ash with 0.1 mol / L dilute hydrochloric acid in proportion and stir to react to remove heavy metal impurities in the fly ash.

[0008] Preferably, the pickling treatment further comprises the following steps: Adding sodium hydroxide solution to adjust the pH value of the solution to 8-9 to precipitate heavy metal impurities; The precipitate was removed by centrifugation and washed several times with deionized water until the pH of the solution was neutral; Drying treatment: The washed fly ash was dried at 60°C for 12 hours.

[0009] Preferably, the multi-stage dissolution and selective precipitation comprises the following steps: Initial dissolution: Mix the pretreated fly ash with water in a ratio of 1:4 and stir to dissolve at 35-40°C for 30 minutes; pH and temperature adjustment: adjust the solution pH to 9-10 and control the temperature between 35-40°C to ensure the preferential dissolution of sodium carbonate; Calcium salt precipitation: Calcium chloride solution is gradually added to the solution to generate calcium sulfate precipitate, which is then removed by centrifugation.

[0010] Preferably, the calcium salt precipitation step further comprises adding 0.5 mol / L calcium chloride solution to the solution and stirring at 35-40° C. for 30 minutes to selectively precipitate sulfate ions in the solution.

[0011] Preferably, the multi-stage temperature-controlled crystallization purification comprises the following steps: First stage crystallization: the sodium carbonate enriched solution is cooled to 25°C and allowed to stand for 12 hours to allow sodium carbonate crystals to precipitate; Redissolution and step-by-step cooling crystallization: Dissolve crude sodium carbonate in deionized water at a ratio of 1:3, heat to 50°C to dissolve, gradually cool to 45°C and 30°C, and let stand to precipitate high-purity sodium carbonate crystals; Multi-stage crystallization cycle purification: Repeat the steps of redissolution and cooling crystallization until the purity of sodium carbonate reaches more than 98%.

[0012] Preferably, the purity of the crystals is detected by X-ray fluorescence spectroscopy after each crystallization in the multi-stage crystallization cycle purification.

[0013] Preferably, the drying and finished product collection comprises the following steps: Second stage low temperature drying: dry the sodium carbonate crystals at 60°C for 6 hours, then place them in a vacuum drying oven at 70°C with the vacuum pressure controlled below 0.1MPa and dry them for 3 hours; Nitrogen purging: The dried sodium carbonate crystals are purged with nitrogen to remove air and moisture.

[0014] Preferably, the sodium carbonate crystals after nitrogen purge are immediately sealed and packaged, and stored in a dry, light-proof environment to prevent moisture absorption and agglomeration.

[0015] Preferably, the process parameter monitoring and optimization comprises the following steps: The temperature, pH value and sodium ion concentration parameters are monitored and recorded in real time through the PLC control system; During the dissolution and precipitation process, the amount of sodium hydroxide and calcium chloride added is controlled by an automatic dosing system to accurately adjust the pH value of the solution; During the crystallization process, the cooling rate is automatically adjusted by the temperature control system to ensure crystal purity and particle uniformity.

[0016] The present invention provides a method for preparing high-purity sodium carbonate using fly ash. It has the following beneficial effects: 1. The present invention adopts a treatment method combining two-stage low-temperature drying and nitrogen purging to completely remove residual moisture and air in the crystals, avoid moisture absorption and agglomeration, and significantly improve the long-term storage stability and purity of the sodium carbonate product.

[0017] 2. The present invention adopts a multi-stage temperature-controlled crystallization and cyclic purification method, so that sodium carbonate is fully precipitated during the step-by-step cooling and dissolution process, thereby reducing the impurity content, improving the purity of the crystal, and making the final purity of sodium carbonate reach more than 98%, which is suitable for high-quality industrial applications.

[0018] 3. The present invention uses PLC control and automatic dosing system to accurately adjust the temperature, pH value and sodium ion concentration during the dissolution, precipitation and crystallization processes, achieves precise control of parameters, improves the purity of sodium carbonate and the uniformity of crystallization, and ensures the stability of product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a flow chart of the method. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the specification of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] Please see attached Figure 1 The embodiment of the present invention provides a method for preparing high-purity sodium carbonate using fly ash, comprising the following steps: Raw material pretreatment: Analyze the components, screen and pickle the fly ash, expand the provided content in detail, give its specific implementation method, describe the principle and the beneficial effects in detail, and the effects should be described at the end of each paragraph. Do not give the content of the rights section. The content of the rights section needs to be expanded separately later to avoid duplication of the expanded content; Multi-stage dissolution and selective precipitation: The pretreated fly ash is dissolved in water, and the pH value and temperature of the solution are adjusted for selective precipitation. By controlling the pH value and temperature, sodium carbonate is preferentially dissolved, and sulfate ions can be removed by calcium salt precipitation, achieving the enrichment of sodium carbonate and the preliminary separation of impurities, providing pure mother liquor for subsequent crystallization and purification; Multi-stage temperature-controlled crystallization and purification: Sodium carbonate crystals are separated through multiple crystallizations and filtrations. Through step-by-step cooling crystallization and multiple cycles of purification, efficient purification of sodium carbonate is achieved, other salt impurities are removed, and the purity of sodium carbonate is improved. At the same time, the mother liquor circulation improves the resource utilization efficiency and reduces the production cost; Drying and finished product collection: Dry and pack the sodium carbonate crystals after crystallization separation. Drying and blowing can ensure that the sodium carbonate crystals are completely dry, avoid agglomeration and moisture absorption and deterioration of the product during storage and transportation, and improve the storage stability of the finished product; Process parameter monitoring and optimization: Real-time monitoring and automatic adjustment of temperature, pH value and ion concentration are carried out throughout the entire process. Through process parameter monitoring and optimization, the stability and consistency of each step are ensured.

[0022] Please see attached Figure 1 In a preferred embodiment of the present invention, the raw material pretreatment comprises the following steps: Component analysis: Use X-ray fluorescence spectroscopy or inductively coupled plasma mass spectrometry to detect the content of sodium carbonate, sodium sulfate, sodium chloride, heavy metals and insoluble impurities in fly ash. Use X-ray fluorescence spectroscopy (XRF) or inductively coupled plasma mass spectrometry (ICP-MS) to quantitatively analyze the components of fly ash in order to accurately grasp the content of sodium carbonate, sodium sulfate, sodium chloride, heavy metal ions and insoluble impurities in fly ash. Through component analysis, the types and contents of the main components and impurities in fly ash can be accurately grasped, ensuring that subsequent operations have a scientific basis, reducing the blindness and errors in the setting of process parameters, and facilitating the final acquisition of high-purity sodium carbonate products; Screening: Use 60-mesh and 120-mesh screens to screen the fly ash in two stages to remove large impurities. Through the filtering effect of screens with different mesh sizes, particles of different sizes are separated. Large particles are not easy to dissolve and are easy to bring in impurities. Through the initial screening and fine screening steps, fine particles suitable for dissolution can be retained, improving the dissolution efficiency. It can provide a suitable particle size distribution for the subsequent dissolution and precipitation steps, so that sodium carbonate can be dissolved more evenly and quickly, improving the overall process efficiency and purity; Acid washing treatment: Mix the screened fly ash with 0.1 mol / L dilute hydrochloric acid in proportion and stir to react to remove heavy metal impurities in the fly ash. The purpose of acid washing is to dissolve the metal impurities in the fly ash into metal ions and precipitate or separate them, thereby reducing the heavy metal content in the finished product and improving the purity of sodium carbonate.

[0023] Please see attached Figure 1 In a preferred embodiment of the present invention, the pickling treatment further comprises the following steps: Add sodium hydroxide solution to adjust the pH value of the solution to 8-9 to precipitate heavy metal impurities. Transfer the fly ash solution after pickling to the reaction vessel, add 0.1 mol / L sodium hydroxide solution dropwise, stir the solution slowly, and monitor the pH value of the solution in real time during the addition of sodium hydroxide solution. When the pH value of the solution reaches 8-9, stop adding sodium hydroxide and continue stirring the reaction for 5 minutes to ensure that the metal ions are fully precipitated. When the pH value of the solution is 8-9, most of the heavy metal ions will be converted into insoluble hydroxide precipitates (such as iron hydroxide, lead hydroxide, etc.). These hydroxides have low solubility in neutral and weakly alkaline environments and can precipitate to avoid metal impurities remaining in the solution; The precipitate is removed by centrifugal separation and washed with deionized water several times until the pH value of the solution is neutral. The heavy metal hydroxide precipitate formed can be removed quickly and effectively by centrifugal separation to avoid interference from metal impurities in subsequent steps. Multiple water washings can further remove residual acidic components and avoid interference from acidic impurities in the sodium carbonate purification process during drying and dissolution, thereby improving the purity and stability of the subsequent sodium carbonate purification process; Drying treatment: The washed fly ash is dried at 60°C for 12 hours. Drying treatment at 60°C can quickly remove residual moisture in the sample, and the low-temperature drying condition avoids changes in the crystal structure or impurity reactions caused by high temperature. After drying treatment, the fly ash sample presents a stable particle state, avoiding the uneven dissolution caused by water evaporation in the subsequent steps, thereby ensuring that the fly ash sample has a stable dry state, avoiding the influence of residual moisture on the subsequent dissolution process, ensuring the uniformity and efficiency of the dissolution process, and laying the foundation for the efficient purification of sodium carbonate.

[0024] Please see attached Figure 1 In a preferred embodiment of the present invention, the multi-stage dissolution and selective precipitation comprises the following steps: Initial dissolution: Mix the pretreated fly ash with water at a ratio of 1:4, and stir and dissolve at 35-40°C for 30 minutes. Sodium carbonate has a high solubility in warm water and can dissolve quickly at 35-40°C. At the same time, most impurities (such as insoluble heavy metal oxides, sulfates, etc.) have a low solubility and can remain insoluble, so that the impurity content in the resulting crude solution is low, creating good conditions for the subsequent precipitation step; pH value and temperature adjustment: adjust the solution pH value to 9-10, and control the temperature between 35-40°C to ensure the preferential dissolution of sodium carbonate. Sodium carbonate has a higher solubility in an alkaline environment. Adjusting the pH value to 9-10 is conducive to the stable existence of sodium carbonate, but not conducive to the dissolution of acidic impurities (such as sulfate). Controlling the temperature within the range of 35-40°C further reduces the solubility of other salts, causing them to precipitate or remain insoluble at this temperature, thereby reducing the impurity content in the solution; Calcium salt precipitation: Calcium chloride solution is gradually added to the solution to generate calcium sulfate precipitation, and the precipitation is removed by centrifugation. The calcium ions in calcium chloride can react with sulfate ions in the solution to generate calcium sulfate precipitation. Since calcium sulfate has extremely low solubility in water, it is easy to form precipitation in the solution. These insoluble impurities can be removed by centrifugation, further reducing the impurity content in the solution.

[0025] Please see attached Figure 1In a preferred embodiment of the present invention, the calcium salt precipitation step further includes adding 0.5 mol / L calcium chloride solution to the solution and stirring at 35-40°C for 30 minutes to selectively precipitate sulfate ions in the solution. The calcium salt precipitation step is based on the chemical reaction principle of sulfate ions and calcium ions. Sulfate reacts with calcium ions to form calcium sulfate (CaSO4), which has an extremely low solubility (0.2 g / L at 25°C). By adding calcium chloride solution, sulfate ions in the solution can be selectively precipitated as calcium sulfate, avoiding sulfate ions from entering the final sodium carbonate product. In addition, by controlling the reaction temperature between 35 and 40°C, the formation of precipitation can be promoted, while reducing unnecessary reactions of other impurities, avoiding problems such as incomplete reactions or impurity dissolution, and providing a purer raw material basis for subsequent high-purity extraction of sodium carbonate crystals.

[0026] Please see attached Figure 1 In a preferred embodiment of the present invention, the multi-stage temperature-controlled crystallization purification comprises the following steps: First stage crystallization: the sodium carbonate enriched solution is cooled to 25°C and allowed to stand for 12 hours to allow sodium carbonate to crystallize. The solubility of sodium carbonate decreases as the temperature decreases, and the solubility decreases significantly at low temperatures. Therefore, sodium carbonate crystals can be effectively precipitated at 25°C, while most of the impurities in the solution remain dissolved, avoiding the mixing of impurities. Redissolution and step-by-step cooling crystallization: Dissolve crude sodium carbonate in deionized water at a ratio of 1:3, heat to 50°C to dissolve, gradually cool to 45°C and 30°C, and let stand to precipitate high-purity sodium carbonate crystals. The step-by-step cooling crystallization method utilizes the difference in the solubility of sodium carbonate at different temperatures. Sodium carbonate is gradually precipitated by segmented cooling, which can minimize the eutectic of impurities. Temperature control at each stage helps to accurately control the crystallization rate, reduce crystal structure defects, and significantly improve purity; Multi-stage crystallization cycle purification: Repeat the steps of re-dissolution and cooling crystallization until the purity of sodium carbonate reaches more than 98%. Multi-stage crystallization cycle purification makes the sodium carbonate crystals precipitated each time gradually become purer and the residual impurities in the mother liquor gradually decrease. Repeated cycles of crystallization can effectively reduce the impurity content and ensure the purity of the crystals.

[0027] Please see attached Figure 1In a preferred embodiment of the present invention, the purity of the crystal is detected by X-ray fluorescence spectroscopy after each crystallization of the multi-stage crystallization cycle purification. The X-ray fluorescence spectroscopy uses X-rays to excite elements in the sample to produce characteristic fluorescence, and the fluorescence intensity is proportional to the element content. XRF can accurately detect the sodium content and a small amount of impurity elements in the sodium carbonate crystals. It is a fast and non-destructive analysis method that helps to determine the purity of the crystals. Using XRF to detect the purity of the crystals after each cycle of purification can ensure that the effect of crystallization purification reaches the expected level. The crystallization parameters such as cooling time and temperature control are adjusted according to the test results, which effectively improves the accuracy and stability of purification.

[0028] Please see attached Figure 1 In a preferred embodiment of the present invention, drying and finished product collection comprises the following steps: Second stage low temperature drying: Dry the sodium carbonate crystals at 60°C for 6 hours, then place them in a vacuum drying oven at 70°C, control the vacuum pressure below 0.1MPa, and dry them for 3 hours. Normal pressure drying at 60°C can efficiently evaporate most of the moisture on the surface and inside of the crystals, and then further drying under vacuum conditions of 70°C and below 0.1MPa can more effectively remove residual moisture. The vacuum environment lowers the boiling point of water, making the moisture more volatile, thereby ensuring the thorough drying of the sodium carbonate crystals. The sodium carbonate crystals that have undergone the second stage drying process maintain a stable physical structure, which improves the purity and storage stability of the finished product; Nitrogen purging: Nitrogen is purged on the dried sodium carbonate crystals to remove air and moisture. Nitrogen is an inert gas that can effectively replace the air on the surface of the crystals to prevent the influence of moisture or carbon dioxide in the air on the sodium carbonate. The nitrogen protective layer formed after purging can prevent the crystals from contacting the outside air, making it difficult to absorb moisture and deteriorate during storage, and maintaining high purity.

[0029] Please see attached Figure 1 In a preferred embodiment of the present invention, the sodium carbonate crystals after nitrogen purge are immediately sealed and packaged, and stored in a dry, light-proof environment to prevent moisture absorption and agglomeration. The sealed packaging can effectively isolate the contact between moisture and carbon dioxide in the air and the sodium carbonate crystals, avoid moisture absorption by the crystals and the generation of by-products such as sodium bicarbonate (NaHCO3), thereby maintaining the purity and stability of the sodium carbonate.

[0030] Please see attached Figure 1 In a preferred embodiment of the present invention, process parameter monitoring and optimization includes the following steps: The temperature, pH value and sodium ion concentration parameters are monitored and recorded in real time through the PLC control system; Specifically: Install sensors in each operating unit of the preparation system to detect temperature, pH value and sodium ion concentration. Connect these sensors to the PLC system to achieve real-time data collection; the PLC system monitors the changes of various parameters in real time, and automatically alarms or prompts through set thresholds so that operators can adjust operating conditions in time; data is automatically recorded and stored in the database of the PLC system for subsequent analysis and process optimization, providing data support for improving and optimizing the process; During the dissolution and precipitation process, the amount of sodium hydroxide and calcium chloride added is controlled by the automatic dosing system to accurately adjust the pH value of the solution; specifically: the sodium hydroxide and calcium chloride solutions are connected to the automatic dosing system respectively, and the target range of the pH value is set (such as pH 9-10 during dissolution and the appropriate pH range during precipitation); during the dissolution and precipitation process, the PLC system monitors the pH value changes in real time and transmits the data to the automatic dosing system; when the pH value is lower or higher than the set range, the automatic dosing system automatically adjusts the dosing rate and dosage according to the instructions of the PLC system to ensure that the pH value returns to the set range; During the crystallization process, the temperature control system automatically adjusts the cooling rate to ensure the purity of the crystals and the uniformity of the particles. Specifically, a temperature sensor is installed in the crystallization equipment to monitor the solution temperature in real time and transmit the data to the temperature control system. According to the set crystallization curve, the temperature control system gradually lowers the temperature of the solution. The initial cooling rate is fast, and the cooling rate slows down when approaching the crystallization temperature to ensure that the crystals are gradually and evenly precipitated. The temperature control system adjusts the cooling rate in real time during the crystallization process to avoid crystal agglomeration or impurity entrainment caused by sudden temperature changes, thereby improving the purity and quality of the crystals.

[0031] In order to better understand the present invention, the above contents are described in detail below in conjunction with specific embodiments.

[0032] Embodiment 1: Innovative solution of the present invention Raw material pretreatment: Fly ash is screened and pickled.

[0033] Use 60-mesh and 120-mesh screens for two-stage screening to remove large particles of impurities.

[0034] The fly ash was acid-washed with 0.1 mol / L dilute hydrochloric acid to remove heavy metal impurities, and then the pH was adjusted to 8-9 with 0.1 mol / L sodium hydroxide solution, and washed with water several times until neutral and then dried.

[0035] Multi-stage dissolution and selective precipitation: Mix the pretreated fly ash with water in a ratio of 1:4, heat to 35-40°C, and stir to dissolve for 30 minutes.

[0036] Use the automatic dosing system to add sodium hydroxide solution and adjust the pH value of the solution to 9-10.

[0037] Add 0.5 mol / L calcium chloride solution and stir at 35-40°C for 30 minutes to generate calcium sulfate precipitate, which is then removed by centrifugation.

[0038] Multi-stage temperature controlled crystallization purification: First staged crystallization: The sodium carbonate enriched solution was cooled to 25°C, allowed to stand for 12 hours, and crude crystals were precipitated.

[0039] Redissolution and step-by-step cooling crystallization: Dissolve crude sodium carbonate in deionized water at a ratio of 1:3, heat to 50°C to dissolve, gradually cool to 45°C and 30°C, and let stand to precipitate high-purity sodium carbonate crystals.

[0040] Multi-stage crystallization cycle purification: The obtained crystals are tested by X-ray fluorescence spectroscopy (XRF). If it is confirmed that the purity has not reached 98%, they are dissolved again and the step-by-step cooling crystallization process is repeated.

[0041] Drying and finished product collection: Second stage drying: drying at 60°C under normal pressure for 6 hours, and then drying at 70°C and 0.1 MPa vacuum for 3 hours.

[0042] Nitrogen purging treatment to remove residual air and moisture, sealed packaging and stored in a dry, light-proof environment.

[0043] Process parameter monitoring and optimization: A PLC control system is used to monitor and adjust temperature, pH value and sodium ion concentration parameters in real time.

[0044] An automatic dosing system is used during the dissolution and precipitation process to precisely adjust the amount of sodium hydroxide and calcium chloride added to ensure a stable pH value.

[0045] During the crystallization process, a temperature control system is used to automatically adjust the cooling rate to ensure crystal purity and particle uniformity.

[0046] Embodiment 2: Conventional solution in the prior art Raw material pretreatment: Use single-stage screening to remove larger impurities only through a 60-mesh screen.

[0047] Failure to carry out acid washing and sodium hydroxide pH adjustment treatment results in difficulty in effectively removing heavy metal impurities.

[0048] Multi-stage dissolution and precipitation: Directly mix fly ash and water in a ratio of 1:5 and stir to dissolve at 30°C.

[0049] There is no pH adjustment control, no calcium chloride solution is added to precipitate impurities, and only sedimentation separation is relied upon, resulting in a large amount of impurities remaining in the solution.

[0050] Crystallization purification: Without precise temperature control, the solution was directly cooled to room temperature and filtered after standing for 10 hours.

[0051] There is no multi-stage crystallization cycle, only one cooling crystallization process, resulting in more impurities remaining and unstable purity.

[0052] Drying and finished product collection: Normal pressure drying is carried out at 60°C for 8 hours without nitrogen purging. The finished product is prone to moisture absorption and deterioration during packaging.

[0053] Process parameter monitoring: Without automatic dosing and PLC control system, it is difficult to achieve precise control of parameters through manual dosing and temperature monitoring.

[0054] Effect comparison summary: In the existing scheme, acid washing and sodium hydroxide pH adjustment are not adopted, resulting in poor impurity removal effect; automatic dosing and temperature control systems are not used, resulting in large parameter fluctuations during dissolution, precipitation and crystallization, and purity and quality are difficult to ensure; while the present invention, through multi-stage crystallization and real-time parameter monitoring, not only improves the purity of sodium carbonate, but also improves process stability and product quality, verifying the innovative effect of the present invention.

[0055] Example 3: Using different drying and purging conditions In Example 3, different drying temperatures and nitrogen purge parameters were tried to further verify the optimal process conditions.

[0056] Second stage drying: Under normal pressure, the initial drying was carried out at a low temperature of 50°C and the duration was extended to 8 hours.

[0057] The vacuum drying was carried out at 65°C and a low vacuum pressure of 0.05 MPa for 4 hours to ensure complete drying.

[0058] Nitrogen purge: The dried sodium carbonate crystals were purged with low-flow nitrogen and the purging time was extended to 15 minutes to ensure that the surface air was completely removed.

[0059] After purging, seal the package immediately and store under refrigerated conditions (below 20°C).

[0060] Example 4: Different crystallization control parameters In Example 4, different crystallization temperature controls and cycle numbers were tried to further verify the optimal crystallization parameters.

[0061] Multi-stage temperature controlled crystallization: First stage crystallization: Cool to 30°C, shorten the standing time to 8 hours, and observe the changes in crystal precipitation rate and purity.

[0062] Redissolution and step-by-step cooling crystallization: heat to 55°C to dissolve, then gradually cool to 40°C and 25°C, and let stand for 10 hours respectively.

[0063] Multi-stage crystallization cycle purification: Three cycles were used as purification conditions, and the crystal purity was detected by X-ray fluorescence spectroscopy after each crystallization until it reached a standard of more than 98%.

[0064] Effect comparison: Different crystallization temperature control and standing time have a significant impact on the morphology and purity of the crystals. In this example, a higher dissolution temperature (55°C) accelerates the dissolution process, while a longer standing time during step-by-step cooling improves the uniformity and purity of the crystals. By adjusting the crystallization parameters, the flexibility of the method of the present invention in temperature control and number of cycles is verified, providing more data support for the stable production of high-purity sodium carbonate.

[0065] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing high-purity sodium carbonate using fly ash, characterized in that: The following steps are involved: Raw material pretreatment: component analysis, screening and acid washing of fly ash; Multi-stage dissolution and selective precipitation: dissolving the pretreated fly ash in water and adjusting the pH and temperature of the solution for selective precipitation; Multi-stage temperature-controlled crystallization purification: Sodium carbonate crystals are separated through multiple crystallizations and filtration; Drying and finished product collection: Drying and packaging the sodium carbonate crystals after crystallization separation; Process parameter monitoring and optimization: Real-time monitoring and automatic adjustment of temperature, pH value and ion concentration throughout the entire process.

2. A method for preparing high-purity sodium carbonate using fly ash according to claim 1, characterized in that: The raw material pretreatment comprises the following steps: Component analysis: Use X-ray fluorescence spectroscopy or inductively coupled plasma mass spectrometry to detect the content of sodium carbonate, sodium sulfate, sodium chloride, heavy metals and insoluble impurities in fly ash; Screening: Use 60-mesh and 120-mesh screens to screen the fly ash in two stages to remove large particles of impurities; Acid washing treatment: Mix the screened fly ash with 0.1 mol / L dilute hydrochloric acid in proportion and stir to react to remove heavy metal impurities in the fly ash.

3. A method for preparing high-purity sodium carbonate using fly ash according to claim 2, characterized in that: The pickling treatment further comprises the following steps: Adding sodium hydroxide solution to adjust the pH value of the solution to 8-9 to precipitate heavy metal impurities; The precipitate was removed by centrifugation and washed several times with deionized water until the pH of the solution was neutral; Drying treatment: The washed fly ash was dried at 60°C for 12 hours.

4. A method for preparing high-purity sodium carbonate using fly ash according to claim 1, characterized in that: The multi-stage dissolution and selective precipitation comprises the following steps: Initial dissolution: Mix the pretreated fly ash with water in a ratio of 1:4 and stir to dissolve at 35-40°C for 30 minutes; pH and temperature adjustment: adjust the solution pH to 9-10 and control the temperature between 35-40°C to ensure the preferential dissolution of sodium carbonate; Calcium salt precipitation: Calcium chloride solution is gradually added to the solution to generate calcium sulfate precipitate, which is then removed by centrifugation.

5. A method for preparing high-purity sodium carbonate using fly ash according to claim 4, characterized in that: The calcium salt precipitation step further includes adding 0.5 mol / L calcium chloride solution to the solution and stirring at 35-40° C. for 30 minutes to selectively precipitate sulfate ions in the solution.

6. A method for preparing high-purity sodium carbonate using fly ash according to claim 1, characterized in that: The multi-stage temperature-controlled crystallization purification comprises the following steps: First stage crystallization: the sodium carbonate enriched solution is cooled to 25°C and allowed to stand for 12 hours to allow sodium carbonate crystals to precipitate; Redissolution and step-by-step cooling crystallization: Dissolve crude sodium carbonate in deionized water at a ratio of 1:3, heat to 50°C to dissolve, gradually cool to 45°C and 30°C, and let stand to precipitate high-purity sodium carbonate crystals; Multi-stage crystallization cycle purification: Repeat the steps of redissolution and cooling crystallization until the purity of sodium carbonate reaches more than 98%.

7. A method for preparing high-purity sodium carbonate using fly ash according to claim 6, characterized in that: After each crystallization in the multi-stage crystallization cycle purification, the purity of the crystal is detected by X-ray fluorescence spectroscopy.

8. The method for preparing high-purity sodium carbonate using fly ash according to claim 1, characterized in that: The drying and finished product collection comprises the following steps: Second stage low temperature drying: dry the sodium carbonate crystals at 60°C for 6 hours, then place them in a vacuum drying oven at 70°C with the vacuum pressure controlled below 0.1MPa and dry them for 3 hours; Nitrogen purging: The dried sodium carbonate crystals are purged with nitrogen to remove air and moisture.

9. A method for preparing high-purity sodium carbonate using fly ash according to claim 8, characterized in that: The sodium carbonate crystals after nitrogen purge are immediately sealed and packaged, and stored in a dry, light-proof environment to prevent moisture absorption and agglomeration.

10. The method for preparing high-purity sodium carbonate using fly ash according to claim 1, characterized in that: The process parameter monitoring and optimization comprises the following steps: The temperature, pH value and sodium ion concentration parameters are monitored and recorded in real time through the PLC control system; During the dissolution and precipitation process, the amount of sodium hydroxide and calcium chloride added is controlled by an automatic dosing system to accurately adjust the pH value of the solution; During the crystallization process, the cooling rate is automatically adjusted by the temperature control system to ensure crystal purity and particle uniformity.

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