A method for purifying and preparing high-purity silver nitrate

Abstract

This invention relates to a method for purifying and preparing high-purity silver nitrate, comprising the following steps: (1) preparing an ammonia-methanol solution for later use; (2) assembling a Soxhlet extraction apparatus; (3) loading the powder to be purified into the filter paper tube of the extraction tube, adding methanol to the extraction flask, and adding the ammonia-methanol solution from step (1) to the constant pressure dropping funnel; (4) heating the extraction flask with a heating device to reflux the methanol, controlling the temperature not to exceed 68°C; adding the ammonia-methanol solution dropwise after each siphon until only solid residue remains in the filter paper tube, stopping the heating and cooling; (5) removing methanol by vacuum distillation, then filtering and washing to obtain crude silver nitrate; (6) dissolving the crude silver nitrate and filtering, concentrating the filtrate by vacuum distillation, crystallizing, filtering, washing, and drying. Utilizing the difference in solubility of silver nitrate and impurities in methanol, a high-efficiency and safe purification is achieved through the cyclic extraction method of Soxhlet extraction, filling the technological gap in deep purification using commercially available silver nitrate as raw material.

Description

Technical Field

[0001] This invention relates to the field of silver nitrate preparation technology, and more specifically, to a method for purifying and preparing high-purity silver nitrate. Background Technology

[0002] Silver nitrate (AgNO3) is an important inorganic compound widely used in photosensitive materials, coatings, silver mirror reactions, catalysts, and the manufacture of silver compounds. With the development of high-end manufacturing, the purity requirements for silver nitrate are increasingly stringent. Currently, silver nitrate is mainly produced by the reaction of elemental silver with nitric acid. The product often contains impurities such as copper, lead, and iron salts, as well as chlorides, which severely affect its purity.

[0003] Existing methods for preparing high-purity silver nitrate mostly use silver ingots, silver plates, or silver-containing waste as raw materials. High-purity elemental silver is obtained through alkaline washing, acid washing, smelting, and electrochemical treatment. This elemental silver is then reacted with nitric acid to generate a silver nitrate solution, followed by purification steps such as impurity removal, adsorption, filtration, and crystallization. For example, Chinese patent application CN120774453A discloses a method for producing high-purity silver nitrate. This method involves alkaline washing of silver ingots with sodium hydroxide solution, water washing, and nitric acid washing, followed by dissolution with nitric acid. Sodium sulfide is then added to adjust the pH value, followed by filtration through a precision filter. Finally, the solution is concentrated, crystallized, and dried to obtain the high-purity silver nitrate product. For example, Chinese patent application CN119038592A discloses a method for producing high-purity silver nitrate. The method first involves washing a silver plate with sodium hydroxide solution, washing it with water once, and washing it with nitric acid solution. Then, the silver plate is placed in a reaction vessel and reacted with nitric acid solution. Next, a composite impurity removal agent is added to obtain a primary filtrate, which is then adsorbed and filtered with nitric acid-modified carbon material to obtain a secondary filtrate. Finally, the filtrate is concentrated by vacuum evaporation, cooled and crystallized, filtered, and dried to obtain photographic-grade high-purity silver nitrate. For example, Chinese patent application CN119706915A discloses a method for preparing high-purity silver nitrate from silver-containing waste. The method involves using silver-containing waste as raw material, adjusting its pH value and adding a reducing agent solution to obtain crude silver powder; washing and filtering with dilute hydrochloric acid solution and pure water to obtain a filter cake, then melting the filter cake to obtain silver ingots; then obtaining national standard No. 1 silver ingots through a series of electrochemical treatments; using the above silver ingots as raw material to react with nitric acid solution, passing through ion exchange resin and precision filter, and then evaporating, crystallizing and drying to obtain high-purity silver nitrate with a purity of over 99.8%.

[0004] In summary, existing methods for preparing high-purity silver nitrate largely revolve around a complete process starting from elemental silver. After generating the silver nitrate solution, purification methods typically involve adding impurity-removing agents, resin adsorption, and high-precision filters. While these methods can achieve high purity, they are complex and costly; moreover, they lack specific solutions for further purification of commercially available silver nitrate products. Therefore, there is still significant room for improvement in existing technologies. Summary of the Invention

[0005] This invention aims to provide a method for purifying and preparing high-purity silver nitrate. By utilizing the difference in solubility of silver nitrate and impurities in methanol, combined with Soxhlet extraction and weak alkaline environment control, a highly efficient and safe purification process can be achieved.

[0006] To achieve the above objectives, this invention proposes a method for purifying and preparing high-purity silver nitrate, comprising the following steps: (1) Ammonia gas is introduced into methanol to prepare an ammonia-methanol solution for later use; (2) Assemble a Soxhlet extraction device, which includes an extraction flask, an extraction tube and a condenser tube. The extraction flask is connected to a thermometer and a constant pressure dropping funnel and is connected to the extraction tube. A heating device is provided below the extraction flask. A filter paper tube for containing materials is provided inside the extraction tube. (3) Load the powder to be purified into the filter paper tube of the extraction tube, add methanol to the extraction bottle, and add the ammonia methanol solution from step (1) to the constant pressure dropping funnel. (4) Turn on the cooling water and heating device. The heating device heats the extraction bottle to reflux methanol and controls the heating temperature to not exceed 68°C. During the Soxhlet extraction process, after each siphon, add ammonia methanol solution dropwise through a constant pressure dropping funnel until only solid residue remains in the filter paper tube in the extraction tube. Then stop heating and cool down. (5) The liquid in the extraction bottle was distilled under reduced pressure to remove methanol. The residue was filtered and washed to obtain crude silver nitrate. (6) After dissolving the crude silver nitrate, filter it, concentrate the filtrate by vacuum distillation, crystallize it, filter it, wash it and dry it to obtain high-purity silver nitrate.

[0007] In the extraction tube, methanol is used as a pure solvent to extract the powder to be purified. Silver nitrate is separated from the insoluble impurities by utilizing its higher solubility in methanol than in the impurities. Ammonia methanol solution is added dropwise after each siphon, and ammonia is replenished in time after each methanol cycle in the extraction bottle to keep the system in a stable weakly alkaline environment. This avoids the attenuation of the protective effect caused by the volatilization or consumption of ammonia due to a one-time addition, and achieves continuous inhibition of silver fulminate formation throughout the process.

[0008] This invention employs a Soxhlet extraction method, utilizing a cyclic process of repeated evaporation, condensation, leaching, and siphoning of methanol to achieve continuous leaching of crude silver nitrate with only a small amount of solvent, thus realizing efficient separation with low solvent consumption. Moreover, by using commercially available silver nitrate as raw material for the above purification, it eliminates the need to start from the entire process of silver elemental preparation, achieving deep purification of existing silver nitrate products and filling the technological gap in deep purification using commercially available silver nitrate as raw material.

[0009] According to the above scheme, the concentration of the ammonia methanol solution in step (1) is 1-3 mol / L.

[0010] According to the above scheme, step (3) also includes the step of processing the powder to be purified: take activated carbon, boil it with alkaline solution, then filter and wash it until neutral, and dry it for later use; mix the silver nitrate powder to be purified with the pretreated activated carbon evenly to obtain the powder to be purified.

[0011] The porous structure of activated carbon can adsorb trace amounts of insoluble impurities in methanol, preventing their accumulation in the system and thus avoiding secondary contamination of silver nitrate. After boiling in an alkaline solution, the acidic groups on the surface of the activated carbon are neutralized, preventing the introduction of acidic substances into the system and effectively preventing the formation of silver fulminate. Furthermore, the color difference between activated carbon and silver nitrate facilitates visual identification of the extraction endpoint.

[0012] According to the above scheme, in the step of treating the powder to be purified, the alkaline solution is a sodium hydroxide solution with a concentration of 1-3wt%, the boiling time is 20-60 minutes, and the drying temperature is 70℃; the amount of pretreated activated carbon added is 1%-5% of the mass of silver nitrate to be purified.

[0013] According to the above scheme, step (3) also includes the step of purging the reaction system with inert gas and keeping the inert gas sealed: connect an inert gas purging port to the extraction bottle, and set an inert gas sealing device at the top of the condenser tube; open the inert gas purging port, purge the reaction system with inert gas to replace the air in the system, and then close the purging port and keep the top of the condenser tube sealed with inert gas.

[0014] By purging with inert gas, the air inside the extraction bottle is removed. This prevents the formation of an explosive mixture between methanol vapor and oxygen, avoids the side reaction of oxygen promoting the reduction of silver nitrate by methanol, and prevents carbon dioxide from consuming the effective ammonia component in the ammonia-methanol solution. This ensures process safety and improves purification efficiency.

[0015] According to the above scheme, the heating rate in step (4) is 0.5-3℃ / min. By monitoring the heating temperature and heating rate throughout the process, the phenomenon of methanol rushing is effectively avoided, ensuring stable reflux and preventing local overheating from causing side reactions.

[0016] According to the above scheme, the amount of ammonia-methanol solution added after each siphon in step (5) is 2-10 drops. By dynamically replenishing ammonia, the system is kept in a weakly alkaline environment throughout the process, avoiding the attenuation of the protective effect caused by adding it all at once.

[0017] According to the above scheme, the vacuum distillation conditions in steps (5) and (6) are both -0.09 to -0.1 MPa and less than 45°C. By setting the distillation under low temperature and low pressure conditions, the thermal decomposition of silver nitrate is prevented, and the product yield is improved.

[0018] According to the above scheme, the washing in step (5) includes methanol washing and water washing; the methanol washing uses methanol at -5℃ to 0℃ and the number of washing times is 2-4 times; the water washing uses distilled water at 0-10℃ and the number of washing times is 1-3 times.

[0019] In step (5), silver nitrate is precipitated in solid form by vacuum distillation, followed by multiple washes with methanol at a low temperature of -5°C to 0°C. This significantly reduces the dissolution loss of solid silver nitrate during the washing process, effectively removing impurities while minimizing yield loss. By washing with distilled water at 0-10°C for 1-3 times, methanol and ammonia residues are effectively removed, avoiding the dissolution loss of silver nitrate caused by high-temperature washing.

[0020] According to the above scheme, in step (6), the crude silver nitrate is dissolved in distilled water at 0-5℃ and the crystallization temperature is 0-5℃; the drying is carried out by vacuum drying, the drying temperature is 40-60℃, the vacuum degree is -0.08 to -0.1MPa, and the drying time is 4-6 hours.

[0021] By using ice water at 0-5℃ for dissolution, selective dissolution is achieved by utilizing the property that silver oxide is difficult to dissolve in low-temperature water while silver nitrate maintains a high solubility, effectively separating silver nitrate from insoluble impurities such as silver oxide. Vacuum distillation is used to control the distillation temperature and remove most of the water, obtaining high-purity crystals while increasing the crystallization yield to over 90%. Low-temperature drying prevents the decomposition of silver nitrate, ensuring product purity and stability.

[0022] According to the above scheme, steps (3)-(6) are all completed in a light-protected environment.

[0023] By operating in complete darkness, the photolysis reaction of silver nitrate was effectively suppressed, ensuring product purity and yield.

[0024] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes the difference in solubility between silver nitrate and impurities in methanol, employing a Soxhlet extraction cyclic leaching method (evaporation, condensation, leaching, and siphoning) to achieve efficient and safe purification. This method uses commercially available silver nitrate as raw material, eliminating the need for a complete silver elemental preparation process, thus filling a technological gap in deep purification using commercially available silver nitrate as a raw material. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Example 1

[0026] In this embodiment, commercially available chemically pure silver nitrate was used as the raw material for the silver nitrate powder to be purified, with a nominal purity of 99.5%. Detection by inductively coupled plasma mass spectrometry (ICP-MS) and ion chromatography revealed that the actual purity of the raw material was 98.5%, with the main impurities being: copper nitrate 0.8%, lead nitrate 0.3%, ferric nitrate 0.2%, and chloride 0.1%. Those skilled in the art can also use other commercially available silver nitrates with equivalent purity and impurity profiles as raw materials. Anhydrous methanol with a purity ≥99.5% and a moisture content ≤0.05% was used. The activated carbon used was coconut shell-based or resin-based supercapacitor carbon conforming to the national standard "Activated Carbon for Supercapacitors" (GB / T 37386-2019), with a specific surface area ≥1800 m² / g.

[0027] This embodiment provides a method for purifying and preparing high-purity silver nitrate, including the following steps: (1) Take methanol and put it in a beaker, pass dry ammonia gas through it, stir to prepare an ammonia methanol solution with a concentration of 1 mol / L, seal it and protect it from light for later use; (2) Assemble a Soxhlet extraction device, which includes an extraction flask, an extraction tube and a condenser tube. The extraction flask is connected to a thermometer and a constant pressure dropping funnel and is connected to the extraction tube. A heating device is provided below the extraction flask. A filter paper tube for containing materials is provided inside the extraction tube. (3) Take 10g of activated carbon, add 1wt% sodium hydroxide solution, boil for 60 minutes, then filter and wash the filter cake repeatedly with distilled water until the washing liquid is neutral, place it in a drying oven at 70℃ and dry to constant weight; weigh 100g of silver nitrate powder to be purified (pass through an 80-mesh sieve), weigh 1g of pretreated activated carbon, and mechanically stir in a nitrogen atmosphere-protected operating box for 5 minutes until the mixture is uniform to obtain the powder to be purified; connect an inert gas purging port to the extraction bottle, and set an inert gas sealing device at the top of the condenser tube, open the inert gas purging port, purge the reaction system with inert gas to replace the air in the system, then close the purging port and keep the top of the condenser tube in an inert gas sealed state; put the powder to be purified into the filter paper tube of the extraction tube, add 500mL of methanol to the extraction bottle, and add 20mL of ammonia methanol solution from step (1) to the constant pressure dropping funnel; (4) Turn on the condenser and heating device, set the heating device heating rate to 0.5℃ / min, and slowly heat until the system temperature reaches 65±1℃. At this time, methanol begins to reflux. Maintain constant temperature reflux, and add 2 drops (about 0.1mL) of ammonia methanol solution through the constant pressure dropping funnel after each siphon. Continue extraction for about 10 hours until the material in the filter paper tube changes from white to gray-black, and only activated carbon remains. Stop heating and let it cool naturally to room temperature. (5) Transfer the extraction bottle to a vacuum distillation apparatus and distill about 300 mL of methanol under vacuum conditions of -0.09 MPa and 40 °C to obtain the distillation residue; filter the distillation residue under vacuum, wash the filter cake twice with methanol at 0 °C (15 mL each time), and then wash the filter cake once with distilled water at 5 °C (50 mL each time) to obtain crude silver nitrate. (6) Add crude silver nitrate to 120 mL of distilled water at 0 °C, stir thoroughly for 20 minutes until dissolved, remove solid impurities by vacuum filtration to obtain a clear aqueous solution of silver nitrate; distill the solution under reduced pressure at -0.09 MPa and 40 °C until a large amount of crystal film appears on the surface of the system; then cool to 2 °C, let stand to crystallize for 2 hours, filter under vacuum, wash the crystals once with 20 mL of ice-cold distilled water; place the crystals in a vacuum drying oven and dry under reduced pressure at 50 °C and -0.09 MPa for 5 hours until constant weight is obtained to obtain high-purity silver nitrate product.

[0028] Steps (3) to (6) are all completed in a dark environment.

[0029] The high-purity silver nitrate product was tested by ICP-MS and ion chromatography. The purity of the product was 99.992%, the total amount of metal impurities such as copper, lead and iron was not higher than 15 ppm, the chloride impurity (calculated as Cl⁻) content was not higher than 10 ppm, and silver fulminate was not detected. The product yield (calculated as silver) was 93.5%. Example 2

[0030] This embodiment is basically the same as Embodiment 1, except that: (1) In this embodiment, commercially available chemically pure silver nitrate was used as the raw material for the silver nitrate powder to be purified, with a nominal purity of 98%. Detection by inductively coupled plasma mass spectrometry (ICP-MS) and ion chromatography showed that the actual purity of the raw material was 97.8%, with the main impurities being: copper nitrate 0.9%, lead nitrate 0.6%, ferric nitrate 0.4%, and chloride 0.2%. (2) The process parameters for several steps have been adjusted: In step (1), the concentration of the ammonia-methanol solution is 2 mol / L; in step (3), the concentration of the sodium hydroxide solution is 2 wt%, the boiling time is 40 minutes, and 3 g of pretreated activated carbon is weighed and mixed with 100 g of silver nitrate to be purified; in step (4), the heating rate is 2℃ / min, and 5 drops of ammonia-methanol solution are added dropwise through a constant pressure dropping funnel after each siphon, and extraction is continued for about 8 hours; in step (5), the vacuum degree of vacuum distillation is -0.095 MPa, the filter cake is washed 3 times with methanol at -5℃, and washed 2 times with distilled water at 0℃; in step (6), the crude silver nitrate is dissolved in distilled water at 3℃, the vacuum degree of vacuum distillation is -0.095 MPa, the drying temperature is 40℃, and the drying time is 6 hours.

[0031] The high-purity silver nitrate product was tested by ICP-MS and ion chromatography. The purity of the product was 99.990%, the total amount of metal impurities such as copper, lead and iron was not higher than 20 ppm, the chloride impurity (calculated as Cl⁻) content was not higher than 10 ppm, and silver fulminate was not detected. The product yield (calculated as silver) was 92.8%. Example 3

[0032] This embodiment is basically the same as Embodiment 1, except that the process parameters for several steps have been adjusted: In step (1), the concentration of the ammonia-methanol solution is 3 mol / L; in step (3), the concentration of the sodium hydroxide solution is 3 wt%, the boiling time is 20 minutes, and 5 g of pretreated activated carbon is weighed and mixed with 100 g of silver nitrate to be purified; in step (4), the heating rate is 3℃ / min, and 10 drops of ammonia-methanol solution are added dropwise through a constant pressure dropping funnel after each siphon, and extraction is continued for about 7 hours; in step (5), the vacuum degree of vacuum distillation is -0.1 MPa, the filter cake is washed 4 times with methanol at -3℃, and washed 3 times with distilled water at 10℃; in step (6), the crude silver nitrate is dissolved in distilled water at 5℃, the vacuum degree of vacuum distillation is -0.1 MPa, the drying temperature is 40℃, and the drying time is 5 hours.

[0033] The high-purity silver nitrate product was tested by ICP-MS and ion chromatography. The purity of the product was 99.991%, the total amount of metal impurities such as copper, lead and iron was not higher than 15 ppm, the chloride impurity (calculated as Cl⁻) content was not higher than 10 ppm, and silver fulminate was not detected. The product yield (calculated as silver) was 93.4%.

[0034] In summary, this invention maintains a weakly alkaline environment by adding ammonia-methanol solution after each siphon, effectively inhibiting the formation of silver fulminate and the reduction reaction of methanol on silver nitrate, significantly improving product purity and yield, and providing an efficient and safe solution for the deep purification of commercially available silver nitrate.

[0035] The above description is only a preferred embodiment of the present invention. Therefore, all equivalent changes or modifications made to the structure, features and principles described in the claims of this patent application are included in the scope of this patent application.

Claims

1. A method for purifying and preparing high-purity silver nitrate, characterized in that, Includes the following steps: (1) Ammonia gas is introduced into methanol to prepare an ammonia-methanol solution for later use; (2) Assemble a Soxhlet extraction device, which includes an extraction flask, an extraction tube and a condenser tube. The extraction flask is connected to a thermometer and a constant pressure dropping funnel and is connected to the extraction tube. A heating device is provided below the extraction flask. A filter paper tube for containing materials is provided inside the extraction tube. (3) Load the powder to be purified into the filter paper tube of the extraction tube, add methanol to the extraction bottle, and add the ammonia methanol solution from step (1) to the constant pressure dropping funnel. (4) Turn on the cooling water and heating device. The heating device heats the extraction bottle to reflux methanol and controls the heating temperature to not exceed 68°C. During the Soxhlet extraction process, after each siphon, add ammonia methanol solution dropwise through a constant pressure dropping funnel until only solid residue remains in the filter paper tube in the extraction tube. Then stop heating and cool down. (5) The liquid in the extraction bottle was distilled under reduced pressure to remove methanol. The residue was filtered and washed to obtain crude silver nitrate. (6) After dissolving the crude silver nitrate, filter it, concentrate the filtrate by vacuum distillation, crystallize it, filter it, wash it and dry it to obtain high-purity silver nitrate.

2. The method for purifying and preparing high-purity silver nitrate according to claim 1, characterized in that, The concentration of the ammonia-methanol solution in step (1) is 1-3 mol / L.

3. The method for purifying and preparing high-purity silver nitrate according to claim 1, characterized in that, Step (3) also includes the step of processing the powder to be purified: take activated carbon, boil it with alkaline solution, then filter and wash it until neutral, and dry it for later use; mix the silver nitrate powder to be purified with the pretreated activated carbon evenly to obtain the powder to be purified.

4. The method for purifying and preparing high-purity silver nitrate according to claim 3, characterized in that, In the step of processing the powder to be purified, the alkaline solution is a sodium hydroxide solution with a concentration of 1-3 wt%, the boiling time is 20-60 minutes, and the drying temperature is 70℃; the amount of pretreated activated carbon added is 1%-5% of the mass of silver nitrate to be purified.

5. The method for purifying and preparing high-purity silver nitrate according to claim 1, characterized in that, Step (3) also includes the step of purging the reaction system with inert gas and keeping the inert gas sealed: an inert gas purging port is connected to the extraction bottle, and an inert gas sealing device is set at the top of the condenser tube; Open the inert gas purging port and purge the reaction system with inert gas to replace the air in the system. Then close the purging port and keep the top of the condenser tube sealed with inert gas.

6. The method for purifying and preparing high-purity silver nitrate according to claim 1, characterized in that, The heating rate in step (4) is 0.5-3℃ / min.

7. The method for purifying and preparing high-purity silver nitrate according to claim 1, characterized in that, The conditions for vacuum distillation in steps (5) and (6) are a vacuum degree of -0.09 to -0.1 MPa and a temperature of less than 45°C.

8. The method for purifying and preparing high-purity silver nitrate according to claim 1, characterized in that, The washing in step (5) includes methanol washing and water washing; the methanol washing uses methanol at -5℃ to 0℃ and the washing is performed 2-4 times; the water washing uses distilled water at 0-10℃ and the washing is performed 1-3 times.

9. The method for purifying and preparing high-purity silver nitrate according to claim 1, characterized in that, In step (6), crude silver nitrate is dissolved in distilled water at 0-5℃, and the crystallization temperature is 0-5℃. The drying is carried out under reduced pressure, with a drying temperature of 40-60℃, a vacuum degree of -0.08 to -0.1MPa, and a drying time of 4-6 hours.

10. The method for purifying and preparing high-purity silver nitrate according to claim 1, characterized in that, Steps (3)-(6) are all completed in a dark environment.