Method for recovering sodium nitrate by CDI composite solventing-out technology

Abstract

The invention relates to the technical field of waste nitric acid treatment, and discloses a method for recovering sodium nitrate by a CDI composite solventing-out technology, which comprises the following steps: step 1, preparing an electrode plate; step 2, testing an electrode plate; 3, a CDI platform is built for analysis; step 4, carrying out secondary concentration on the water-absorbing gel; and step 5, solventing-out crystallization to obtain sodium nitrate crystals. The electric field is used for guiding ion migration in concentration through the CDI technology, compared with a traditional method, energy consumption is greatly reduced, the operation cost is lower when a large amount of waste water is treated, ethyl alcohol is selected as a solvating-out agent, due to the fact that ethyl alcohol is non-toxic and relatively low in cost, the economical efficiency of solvating-out operation is guaranteed, subsequent operation is simplified, and the method is suitable for industrial production. By optimizing the solvent proportion and the adding mode, the precipitation amount of sodium nitrate is increased to the maximum extent, the use amount and wastewater generated during treatment are reduced, and the beneficial effects of simple sodium nitrate recovery operation and lower cost are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of waste nitric acid treatment, in particular to a method for recovering sodium nitrate using a CDI composite dissolution technology. Background Art

[0002] Sodium nitrate is a kind of inorganic salt with the chemical formula NaNO3. It is a white solid powder and is also called Chilean saltpeter or Peruvian saltpeter (less common). The world's largest sodium nitrate mine is located in the Atacama Desert in Chile. It can be synthesized by the following chemical formula: NaOH(aq)+HNO3(aq)→NaNO3(aq)+H2O(l) Sodium nitrate is heated to 380°C and decomposes to produce sodium nitrite and oxygen. Sodium nitrate is oxidizing and can react with lead to produce sodium nitrite and lead oxide. It also oxidizes hydroiodic acid into iodine and forms nitric oxide at room temperature: When hydrogen ions are introduced into the sodium nitrate solution, it will exhibit the characteristics of nitric acid: Sodium nitrate is one of the components of pickling salt. It is colorless, transparent or white with a slight yellow rhombus crystal, slightly bitter, and easily deliquescent. When dissolved in water, the temperature of its solution decreases. The solution is neutral and oxidizing. Friction or collision with organic matter can cause combustion or explosion. It is toxic.

[0003] Existing technologies (such as traditional ion exchange, reverse osmosis or distillation, etc.) have some defects in recovering sodium nitrate and treating ions in water. For example, ion exchange usually requires the use of chemical agents to regenerate resins, which not only increases the complexity and cost of operations, but also imposes a burden on the environment. Reverse osmosis technology is susceptible to membrane contamination and requires regular chemical cleaning and maintenance, which will affect its long-term performance and economy. Summary of the invention

[0004] Technical issues solved:

[0005] In view of the shortcomings of the prior art, the present invention provides a method for recovering sodium nitrate using CDI composite dissolution technology, which has the advantages of simple operation, lower cost, more environmentally friendly and pollution-free recovery of sodium nitrate, and solves the problems of the above-mentioned technologies.

[0006] Technical solution:

[0007] To achieve the above object, the present invention provides the following technical solution: a method for recovering sodium nitrate by CDI composite dissolution technology, comprising the following steps:

[0008] Step 1: Prepare the electrode sheet: The porous carbon was subjected to scanning electron microscopy and specific surface area test. 2 / g, good pore size distribution: with microporous and mesoporous pore structures, the "porous carbon-commercial" material is used as the raw material for preparing the electrode sheet, and the loading material is configured according to the mass ratio of "porous carbon-commercial": carbon black: PTFE solution = 8:1:1, immersed in ethanol for 30 minutes, and bathed in 80℃ water until it is muddy, and evenly applied on both sides of the 5*5cm fully dried nickel foam, and dried and pressed into sheets;

[0009] Step 2, electrode sheet test: electrochemical tests: cyclic voltammetry, constant current charge and discharge, electrochemical impedance, the conclusion is that the electrode sheet has good electrochemical properties, cycle stability test: after ten times of adsorption-desorption, the capacity decays by 10-15%, and it can be used cyclically;

[0010] Step 3: Build a CDI platform for analysis: The device consists of a conductivity meter, a 500 mL beaker, a CDI module, a peristaltic pump, and a constant pressure source. The CDI method is used to concentrate a sodium nitrate stock solution with a mass concentration of less than 2% to 2% to obtain a concentrated solution 1;

[0011] Step 4: Secondary concentration using water-absorbing gel: using water-absorbing gel to secondary concentrate the concentrated solution 1 to 30% to obtain concentrated solution 2;

[0012] Step 5, dissolution crystallization to obtain sodium nitrate crystals: Sodium nitrate crystals are precipitated from the concentrated solution 2 using a dissolution crystallization method, an ethanol solution is added to the sodium nitrate solution, and after a water-absorbing material is added to the sodium nitrate solution that has reached a saturated precipitation amount, sodium nitrate crystals are further precipitated, and the water-absorbing material in step 2 is reused.

[0013] Preferably, the peristaltic pump in step three has a rotation speed of 30 r / min.

[0014] Preferably, the concentration of the stock solution in step three is less than 1%.

[0015] Preferably, in step three, a voltage of 1.2V is applied to the electrode sheet.

[0016] Preferably, in step three, the distance between the plates is 2 mm.

[0017] Preferably, in the step 4, the water-absorbing material is selected as follows: three water-absorbing materials of the same mass, namely, "Kexin", "Zhenghe" and "Yousuo", are placed in pure water for 3 hours, and the water absorption rate of the "Kexin" water-absorbing material can reach 550 times of its own.

[0018] Preferably, the water-absorbing material drying process is: drying the "trustworthy water-absorbing material" at 80°C for 24 hours.

[0019] Preferably, the concentration standard of the concentrated solution 1 in step 4 is: temperature of 30° C., pH=7, and mass concentration of 2%.

[0020] Preferably, the mass concentration of the sodium nitrate solution in step five is 40%.

[0021] Preferably, in step five, the mass ratio of anhydrous ethanol to solution is 7:1.

[0022] Compared with the prior art, the present invention provides a method for recovering sodium nitrate by using CDI composite dissolution technology, which has the following beneficial effects:

[0023] 1. The present invention uses electric field to guide ion migration in concentration through CDI technology. Compared with traditional methods, energy consumption is greatly reduced. When treating a large amount of wastewater, the operating cost is lower. The operation of the CDI system is relatively simple and easy to automate and integrate, reducing manual operation and related training costs. The recycling ability of the electrode material improves the economic efficiency of the long-term operation of the equipment and reduces the replacement and maintenance costs. The "trusted" water-absorbing material with high water absorption rate is selected so that it can quickly and effectively absorb water when the concentrated stock solution is processed, reducing the processing time and resource consumption. The optimal operating conditions are determined through experiments to achieve the highest efficiency of the secondary concentration process, which reduces the demand for equipment and energy consumption. The water-absorbing gel material can be reused, further reducing the material cost. Ethanol is selected as the solvent. Its non-toxicity and relatively low cost ensure the economy of the dissolution operation and simplify the subsequent operation. By optimizing the solvent ratio and the addition method, the precipitation amount of sodium nitrate is maximized, and the amount and wastewater generated during treatment are reduced. The mixing method of different concentrations and the strategy of adding absorbent materials allow the process to be flexibly adjusted to achieve the best effect when recovering sodium nitrate from waste liquid. By effectively integrating the three steps of concentration, secondary concentration and crystallization, the entire recovery process is simplified, the steps of multiple complex links in the traditional method are reduced, the complexity of the operation is reduced, the use of chemical drugs is reduced in the whole process, and compared with the traditional method, the investment is reduced, and the burden on the environment is reduced, achieving the beneficial effect of simple operation and lower cost for recovering sodium nitrate.

[0024] 2. The present invention utilizes an electric field to remove ions through CDI, thereby avoiding the use of chemical agents and reducing the risk of secondary pollution. In the dissolution and crystallization step, the selection of ethanol as a solvent is relatively environmentally friendly. Ethanol is non-toxic, easy to handle, and has strong degradation ability in the natural environment. It will not cause lasting impact on the environment after use. The process reduces dependence on chemical agents and avoids environmental pollution caused by improper use of chemicals. In particular, in the recovery and concentration process, physical methods are mainly relied on, such as electrochemical reactions of electrodes and physical adsorption of water-absorbing materials, which reduces the demand for chemical agents. The selected and developed water-absorbing materials can still show high water absorption capacity after multiple uses, which means that in the process of repeated use, the consumption of materials is reduced and the environmental burden brought by the production of new materials is reduced. Through efficient concentration and extraction steps, the amount of final waste liquid is significantly reduced, reducing the pollution to the water body after treatment and the treatment cost. The process of recovering sodium nitrate reduces energy consumption and resource waste by precisely controlling each step. The efficient secondary concentration and crystallization method ensures that as much sodium nitrate as possible is recovered, thereby minimizing the impact on the environment and achieving the beneficial effect of more environmentally friendly recovery without causing pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the steps of the present invention; DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments 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.

[0027] Embodiment 1

[0028] See also Figure 1 , process 1. CDI capacitor deionization device concentrates the stock solution

[0029] The sodium nitrate stock solution with a mass concentration of less than 2% was concentrated to 2% by using the CDI method to obtain a concentrated solution 1.

[0030] Preparation of electrode sheets

[0031] a. The porous carbon was subjected to SEM scanning electron microscopy and BET specific surface area tests, and the "porous carbon-commercial" material with a specific surface area of ​​2048m2 / / g, good pore size distribution, and microporous and mesoporous pore structure was used as the raw material for preparing electrode sheets.

[0032] b. Prepare the loading material according to the mass ratio of "porous carbon-commercial": carbon black: PTFE solution = 8:1:1, immerse in ethanol and ultrasonic for 30 minutes, bathe in 80℃ water until it becomes muddy, evenly apply it on both sides of 5*5cm fully dried nickel foam, and dry and press it into sheets.

[0033] Electrode test

[0034] a. Electrochemical tests such as cyclic voltammetry, constant current charge and discharge, and electrochemical impedance spectroscopy were performed, and the conclusion was that the electrode sheet had good electrochemical properties.

[0035] b. Cyclic stability test: After ten cycles of adsorption-desorption, the capacity decays by 10-15% and can be used cyclically.

[0036] Build a CDI platform for analysis

[0037] a. The device consists of a conductivity meter, a 500mL beaker, a CDI module, a peristaltic pump, and a constant pressure source.

[0038] Conclusion: When the speed of the cave pump is 30r / min, the mass concentration of the stock solution is lower than 1%, the voltage applied to the electrode is 1.2V, and the plate spacing is 2mm, the stock solution can be concentrated with high efficiency and energy saving.

[0039] Step 2. Secondary concentration of water-absorbing gel

[0040] The concentrated solution 1 was concentrated to 30% using the water-absorbing gel to obtain the concentrated solution 2.

[0041] Choice of absorbent material

[0042] The same mass of three absorbent materials, namely "Xin", "Zhenghe" and "Yousuo", were placed in pure water for 3 hours. The water absorption rate of the "Xin" absorbent material was 550 times that of itself, which was much higher than the other two.

[0043] Drying of absorbent materials

[0044] Dry the "water-absorbing material" at 80℃ for 24 hours.

[0045] Analytical experiments

[0046] a. Different concentrate temperatures

[0047] The same mass of "Xin" water-absorbing material was placed in concentrated solution 1 at different temperatures for 2 hours, and the mass of the water-absorbing material after swelling was the largest at 30°C.

[0048] b. Different pH values ​​of concentrate

[0049] The same mass of "Xin" water-absorbing material was placed in different pH concentrated solutions 1 for 2 hours, and the mass of the water-absorbing material after swelling was the largest when pH=7.

[0050] c. Different concentrations of concentrate

[0051] The same mass of "Xin" water-absorbing material was placed in sodium nitrate solution of different mass concentrations for 2 hours. The mass of the water-absorbing material after swelling was the largest when the mass concentration was 2%, and the higher the concentration, the worse the water absorption effect.

[0052] d. Reuse rate

[0053] The same mass of "Xin" absorbent material is placed in 2% mass concentration concentrated solution 1 for 2 hours, weighed to obtain its water absorption rate, and then dried. The dried absorbent material is used to repeatedly carry out the experiment, and the material can be reused 5-6 times.

[0054] Conclusion: When the temperature of the concentrated liquid 1 is 30°C, pH=7, and the mass concentration is 2%, the concentrated liquid 1 can be concentrated twice in an energy-saving and efficient manner.

[0055] Sodium nitrate crystals are obtained by dissolution and crystallization

[0056] Sodium nitrate crystals are precipitated from the concentrated solution 2 using a dissolution crystallization method.

[0057] Selection of solvent

[0058] Compared with commonly used organic solvents such as methanol, ethanol, and propanol, ethanol is non-toxic, moderately priced, and miscible with water in any proportion at room temperature, and sodium nitrate is difficult to dissolve in ethanol, which meets the requirements for solvent selection.

[0059] Analytical experiments

[0060] a. Different concentrations

[0061] A certain proportion of ethanol solution was added to sodium nitrate solutions of different mass concentrations. The higher the mass concentration, the higher the amount of sodium nitrate crystals precipitated. When the concentration was higher than 40%, the precipitation amount tended to be flat.

[0062] b. Different amounts of solvent added

[0063] Different amounts of anhydrous ethanol were added to sodium nitrate solutions with a mass concentration of 20%, 30%, 40%, and 60%. When the mass ratio of anhydrous ethanol to solution was 7:1, the amount of sodium nitrate crystal precipitation was the highest.

[0064] c. Mixing methods of different solutions and solvents

[0065] When adding ethanol to sodium nitrate solution, the recovery rate of sodium nitrate is higher than that of adding sodium nitrate solution to ethanol. The difference between ammonium nitrate solutions with different mass concentrations is 4%-19%.

[0066] d. Addition speed of different solvents

[0067] When the solvent is added to the sodium nitrate solution at different addition speeds, the amount of sodium nitrate crystals precipitated changes little. The addition speed mainly affects the rate of crystal nucleation and the particle size distribution of the crystals.

[0068] e. Addition of water-absorbing materials

[0069] After the water-absorbing material is added to the sodium nitrate solution that has reached the saturated precipitation amount, the sodium nitrate crystals are further precipitated, and the water-absorbing material in the second step is reused.

[0070] Conclusion: By adding ethanol to the sodium nitrate solution, the sodium nitrate crystals can be precipitated in an energy-saving and efficient manner when the mass concentration of the sodium nitrate solution is 40% and the alcohol-liquid ratio is 7:1. Adding water-absorbing materials can further precipitate sodium nitrate crystals.

[0071] Application of Capacitive Deionization (CDI) Technology

[0072] Low energy consumption: CDI technology uses an electric field to guide ion migration during concentration, which consumes significantly less energy than traditional methods. This means lower operating costs when treating large amounts of wastewater.

[0073] Simple operation process: The operation of the CDI system is relatively simple and easy to automate and integrate, reducing manual operation and related training costs.

[0074] Recyclability: The ability to recycle electrode materials improves the economic efficiency of long-term equipment operation and reduces replacement and maintenance costs.

[0075] Highly efficient water-absorbing gel secondary concentration

[0076] Material selection: Select "reliable" absorbent materials with high water absorption rate so that they can absorb water quickly and effectively when concentrated stock solution is processed, reducing processing time and resource consumption.

[0077] Temperature and pH optimization: The optimal operating conditions (such as 30°C and pH=7) were determined through experiments to achieve the highest efficiency of the secondary concentration process, which reduced the demand for equipment and energy consumption.

[0078] Recycling: The water-absorbent gel material can be reused (up to 5-6 times), further reducing material costs and improving overall economic benefits.

[0079] Choice of solution crystallization method

[0080] Economical solvent: Choosing ethanol as the solvent ensures the economic efficiency of the solvent dissolution operation due to its non-toxicity and relatively low cost. In addition, the subsequent operation is simplified.

[0081] Efficient precipitation: By optimizing the solvent ratio and addition method, the precipitation amount of sodium nitrate is maximized, reducing the amount used and the generation of wastewater during treatment.

[0082] Operational flexibility: The mixing methods of different concentrations and the strategy of adding absorbent materials make the process flexible to achieve the best results when recovering sodium nitrate from wastewater.

[0083] Simplification and integration of the overall process

[0084] Process optimization: By effectively integrating the three steps of concentration, secondary concentration and crystallization, the entire recovery process is simplified, reducing the steps of multiple complex links in the traditional method (such as evaporation, regeneration, etc.), and reducing the complexity of the operation.

[0085] Reduce the demand for chemicals: The entire process reduces the use of chemicals, which reduces investment compared to traditional methods and reduces the burden on the environment.

[0086] Use environmentally friendly materials and technologies

[0087] Capacitive Deionization (CDI) Technology: CDI is a relatively clean water treatment technology that does not produce harmful chemical waste compared to traditional chemical treatment methods. The technology uses electric fields to remove ions, avoiding the use of chemical agents and reducing the risk of secondary contamination.

[0088] Safe solvent: In the solvent crystallization step, ethanol is a relatively environmentally friendly choice. Ethanol is non-toxic, easy to handle, and has strong degradation ability in the natural environment, so it will not cause lasting impact on the environment after use.

[0089] Reduce the use of chemicals

[0090] This process reduces the reliance on chemicals and avoids environmental pollution caused by improper use of chemicals. In particular, the recovery and concentration process mainly relies on physical methods, such as electrochemical reactions of electrodes and physical adsorption of water-absorbing materials, which reduces the demand for chemicals.

[0091] Recycling and resource conservation

[0092] Reusable absorbent materials: The absorbent materials selected and developed can still show high water absorption capacity after multiple uses, which means that during the reuse process, the consumption of materials is reduced and the environmental burden caused by the production of new materials is reduced.

[0093] Reduction of wastewater volume: Through efficient concentration and extraction steps, the amount of final waste liquid is significantly reduced, reducing the pollution to the water body after treatment and the treatment cost.

[0094] Optimized process flow

[0095] Efficient concentration and crystallization: The process of sodium nitrate recovery reduces energy consumption and resource waste by precisely controlling each step. Efficient secondary concentration and crystallization methods ensure that as much sodium nitrate as possible is recovered, thereby minimizing the impact on the environment.

[0096] Avoiding the production of compounds: Since the entire process focuses on physical deionization and physical and chemical methods and does not involve complex chemical reactions, it avoids the production of potential harmful by-products, which is often a problem in traditional methods.

[0097] Environmental Compliance and Sustainable Development

[0098] Compliance with regulations: The recycling process meets stringent environmental standards and regulations, ensuring that there is no risk of contamination to the surrounding environment in large-scale industrial applications.

[0099] Supporting sustainable development: Through the efficient recycling of raw materials and the reduction of waste, the process clearly supports sustainable development goals and promotes environmentally friendly economic growth.

[0100] 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 alterations may be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for recovering sodium nitrate using CDI composite dissolution technology, characterized in that: The following steps are involved: Step 1: Prepare the electrode sheet: The porous carbon was subjected to scanning electron microscopy and specific surface area test. 2 / g, good pore size distribution: with microporous and mesoporous pore structures, the "porous carbon-commercial" material is used as the raw material for preparing the electrode sheet, and the loading material is configured according to the mass ratio of "porous carbon-commercial": carbon black: PTFE solution = 8:1:1, immersed in ethanol ultrasound for 30 minutes, bathed in 80℃ water until muddy, evenly spread on both sides of 5*5cm fully dried foam nickel, and dried and pressed into sheets; Step 2, electrode sheet test: electrochemical tests: cyclic voltammetry, constant current charge and discharge, electrochemical impedance, the conclusion is that the electrode sheet has good electrochemical properties, cycle stability test: after ten times of adsorption-desorption, the capacity decays by 10-15%, and it can be used cyclically; Step 3: Build a CDI platform for analysis: The device consists of a conductivity meter, a 500 mL beaker, a CDI module, a peristaltic pump, and a constant pressure source. The CDI method is used to concentrate a sodium nitrate stock solution with a mass concentration of less than 2% to 2% to obtain a concentrated solution 1; Step 4: Secondary concentration using water-absorbing gel: using water-absorbing gel to secondary concentrate the concentrated solution 1 to 30% to obtain concentrated solution 2; Step 5, dissolution crystallization to obtain sodium nitrate crystals: Sodium nitrate crystals are precipitated from the concentrated solution 2 using a dissolution crystallization method, an ethanol solution is added to the sodium nitrate solution, and after a water-absorbing material is added to the sodium nitrate solution that has reached a saturated precipitation amount, sodium nitrate crystals are further precipitated, and the water-absorbing material in step 2 is reused.

2. The method for recovering sodium nitrate by CDI composite dissolution technology according to claim 1, characterized in that: In step 3, the peristaltic pump has a rotation speed of 30 r / min.

3. The method for recovering sodium nitrate by CDI composite dissolution technology according to claim 1, characterized in that: The concentration of the stock solution in step 3 is less than 1%.

4. The method for recovering sodium nitrate by CDI composite dissolution technology according to claim 1, characterized in that: In the step 3, a voltage of 1.2V is applied to the electrode sheet.

5. The method for recovering sodium nitrate by CDI composite dissolution technology according to claim 1, characterized in that: In step 3, the distance between the plates is 2 mm.

6. The method for recovering sodium nitrate by CDI composite dissolution technology according to claim 1, characterized in that: Selection of water-absorbing materials in the step 4: Put the same mass of three water-absorbing materials, namely "Kexin", "Zhenghe" and "Yousuo", into pure water for 3 hours, and the water absorption rate of the "Kexin" water-absorbing material can reach 550 times of its own.

7. The method for recovering sodium nitrate by CDI composite dissolution technology according to claim 6, characterized in that: The water-absorbing material drying process is as follows: drying the "trustworthy water-absorbing material" at 80°C for 24 hours.

8. The method for recovering sodium nitrate by CDI composite dissolution technology according to claim 1, characterized in that: The concentration standard of the concentrated solution 1 in step 4 is: temperature of 30° C., pH=7, and mass concentration of 2%.

9. The method for recovering sodium nitrate by CDI composite dissolution technology according to claim 1, characterized in that: The mass concentration of the sodium nitrate solution in step 5 is 40%.

10. The method for recovering sodium nitrate by CDI composite dissolution technology according to claim 1, characterized in that: In the step 5, the mass ratio of anhydrous ethanol to the solution is 7:1.

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