Process for preparing high-purity silver nitrate from crude silver powder

Abstract

The invention discloses a process for preparing high-purity silver nitrate from coarse silver powder, and belongs to the technical field of silver nitrate preparation, the technical scheme is characterized in that the process for preparing the high-purity silver nitrate from the coarse silver powder comprises the following steps: S1, washing, drying and grinding the coarse silver powder to obtain fine silver powder; s2, after the fine silver powder, electronic-grade nitric acid and water react, filtering is conducted, and a silver nitrate solution is obtained; s3, reacting the silver nitrate solution with an acidic sodium chloride solution to generate a silver chloride precipitate; s4, adding an acidic sodium chlorate solution into the silver chloride precipitate, and filtering after reaction to obtain silver chloride; s5, after silver chloride and an alkaline hydrazine hydrate solution react, filtering is conducted, and high-purity silver powder is obtained; s6, the high-purity silver powder reacts with electronic-grade nitric acid and water to prepare a dilute nitric acid solution; s7, the dilute nitric acid solution is subjected to evaporative crystallization to obtain high-purity silver nitrate, high-purity silver powder is obtained through a two-step impurity removal method and reduction of silver chloride, and then the high-purity silver powder reacts with electronic-grade nitric acid to obtain the high-purity silver nitrate.

Description

Technical Field

[0001] The invention relates to the field of preparation of silver nitrate, in particular to a process for preparing high-purity silver nitrate from coarse silver powder. Background Art

[0002] Pure silver nitrate, as an important fine chemical product, has attracted considerable attention due to its unique chemical properties and wide range of applications. High-purity silver nitrate is primarily used in the pharmaceutical industry, where dilute silver nitrate solutions are used as preventive antiseptics, such as for neonatal conjunctivitis, and for corroding hyperplastic granulation tissue. High-purity silver nitrate is an important analytical reagent for the determination of chlorides, bromides, iodides, cyanides, and thiocyanates. It is used as a catalyst, for example, in the hydrolysis and oxidation of silicones to generate hydrogen, and in the oxidation of various aldehydes. In the electronics industry, silver nitrate is used in electroplating and the preparation of conductive silver pastes. In the photosensitive material industry, silver nitrate is a key material in the photosensitive industry, where its purity directly affects photosensitivity. High-purity silver nitrate is a precursor for the preparation of Ag-TiO2 nanomaterials and nanosilver, with widespread applications in nanosilver catalysis, optics, biomedicine, new energy, and electronic devices. Among other applications, silver nitrate is also used in the manufacture of silver salts, porcelain coloring, and fingerprint verification.

[0003] The traditional silver nitrate production process mainly adopts the direct reaction of metallic silver and nitric acid. However, the silver nitrate products produced by the existing process cannot meet the process requirements of high-purity silver nitrate. The main disadvantages are as follows: (1) the quality of raw materials is not guaranteed. The quality of the three major raw materials (silver, nitric acid and water) for producing silver nitrate must meet the raw material standards for producing high-purity silver nitrate; (2) there is a lack of effective impurity removal means. Even if the raw materials are very pure, in order to reduce the content of metal impurities to trace amounts, high-purity silver nitrate cannot be produced without effective impurity removal means. In the existing process, commonly used impurity removers include silver carbonate, ferric hydroxide (ferric nitrate), aluminum hydroxide (aluminum nitrate), magnesium oxide, activated carbon, etc. The impurity removal of silver carbonate is mainly achieved by adjusting the pH value of the solution. When the pH value reaches a certain value, the impurities are removed from the solution. This impurity remover will not bring in impurity ions. Its preparation process is simple, but the disadvantage is that silver carbonate only The pH value can be adjusted to 6-7. At the same time, since silver nitrate will precipitate when the pH value is high, some impurity elements in the solution that require a higher pH value cannot be removed from the solution. Elements such as Hg, Ni, and Cd are difficult to remove. Ferric hydroxide (ferric nitrate) and aluminum hydroxide (aluminum nitrate) can adjust the pH value of the solution while the excess impurity remover can adsorb impurity ions in the solution, thereby further achieving the purpose of impurity removal. However, both impurity removers introduce impurity ions and are likely to bring in new pollution, making the final silver nitrate impure. Magnesium oxide impurity removal is also mainly achieved by adjusting the pH value, and it also has its shortcomings. Activated carbon impurity removal purifies the solution by adsorbing impurity ions in the solution, but the adsorption capacity of activated carbon for ionic impurities is limited (usually ≤10 mg / g), and it also has the disadvantage of incomplete impurity removal.

[0004] This shows that the existing impurity removers either do not remove impurities thoroughly or produce secondary pollution, resulting in low purity of silver nitrate. Summary of the Invention

[0005] In order to solve the problems in the prior art, the present invention provides a process for preparing high-purity silver nitrate from crude silver powder. This application adopts a two-step impurity removal method, first using an acidic sodium chloride solution to precipitate silver ions (silver chloride precipitation), then adding a strong oxidant to oxidize and remove impurities, after the impurity removal reaction is completed, using an alkaline hydrazine hydrate solution to reduce the silver chloride to obtain high-purity silver powder, and then adding electronic grade nitric acid to prepare a silver nitrate solution, which is then concentrated and crystallized to obtain high-purity silver nitrate.

[0006] The process for preparing high-purity silver nitrate from coarse silver powder provided by the present invention adopts the following technical solution: A process for preparing high-purity silver nitrate from coarse silver powder comprises the following steps: S1, washing, drying and grinding the coarse silver powder to obtain fine silver powder; S2, after the reaction of fine silver powder, electronic grade nitric acid and water is completed, filtering to obtain a silver nitrate solution; S3, reacting the silver nitrate solution with an acidic sodium chloride solution to generate a silver chloride precipitate; S4, adding acidic sodium chlorate solution to the silver chloride precipitate, filtering to obtain silver chloride after the reaction is completed; S5, reacting silver chloride and alkaline hydrazine hydrate solution, and filtering to obtain high-purity silver powder; S6. reacting high-purity silver powder with electronic-grade nitric acid and water to prepare a dilute nitric acid solution; S7. Evaporate and crystallize the dilute nitric acid solution to obtain high-purity silver nitrate.

[0007] By adopting the above technical solution, the present application washes, dries and grinds the coarse silver powder to obtain fine silver powder, ensuring that the raw material is initially cleaned to remove water-soluble impurities therein and the particle size is appropriate; the fine silver powder reacts with electronic-grade nitric acid and water and then is filtered to obtain a silver nitrate solution, thereby starting a subsequent purification process, reacting the silver nitrate solution with an acidic sodium chloride solution to generate a silver chloride precipitate to remove some impurities, and then reacting the silver chloride precipitate with an acidic sodium chlorate solution to further purify the silver chloride. In this process, sodium chlorate decomposes in a strong acid environment (pH < 0) to release new ecological oxygen and hypochlorous acid, which remove organic impurities (such as oils and fats), low-valent metal ions (such as divalent iron ions) and other impurities. The invention relates to a method for preparing silver powder by reacting silver chloride with alkaline hydrazine hydrate solution to obtain high-purity silver powder. The method comprises the following steps: first, reacting silver chloride with alkaline hydrazine hydrate solution to obtain high-purity silver powder; second, reacting silver chloride with electronic-grade nitric acid and water to obtain dilute nitric acid solution; and finally, evaporating and crystallizing the dilute nitric acid solution to obtain high-purity silver nitrate. The method effectively avoids the problems of unguaranteed raw material quality and lack of effective impurity removal methods in traditional processes, and can produce high-purity silver nitrate that meets process requirements.

[0008] Preferably, the molar ratio of silver ions to chloride ions in step S3 is 1:(2.1-2.3).

[0009] By adopting the above technical solution, excess chloride ions can ensure that lead and mercury form soluble complexes, thereby effectively reducing the content of lead and mercury in the silver powder, thereby improving the purity of the silver powder and reducing the impurity content.

[0010] Preferably, the pH value of the acidic sodium chloride is 2-3.

[0011] Preferably, the reaction temperature in step S3 is 35-40°C.

[0012] Preferably, in step S4, the solid-liquid ratio of the silver chloride precipitate to the acidic sodium chlorate solution is 1:(3.5-4.5) g / L.

[0013] Preferably, the reaction temperature in step S4 is 80-90°C.

[0014] Preferably, the molar ratio of silver chloride to hydrazine hydrate in step S5 is 2:1.

[0015] Preferably, the pH of the alkaline hydrazine hydrate solution is 9-10.

[0016] Preferably, the reaction temperature in step S5 is 60-80°C.

[0017] By adopting the above technical solution, the present application effectively reduces the impurity content in the silver powder by controlling the reaction temperature and the amount of reactants in the three processes of step S3, step S4, and step S5, thereby effectively improving the purity of the raw silver powder, solving the defect of unguaranteed raw material quality in the traditional process, and thus producing high-purity silver nitrate.

[0018] Preferably, in step S1 and step S6, the mass ratio of silver powder to electronic grade nitric acid and water is 1:(1.5-1.6):(0.5-0.6).

[0019] Preferably, the concentration of electronic grade nitric acid in step S1 and step S6 is 35-40 wt %, and the reaction temperature is 60-75° C.

[0020] Preferably, in step S7, the stirring rate is 155-165 r / min, the temperature is 60-70° C., and the stirring and heating are stopped after the crystal film appears.

[0021] In summary, the present invention has the following beneficial effects: 1. The water-soluble impurities can be removed by washing, drying and grinding the crude silver powder before reacting it with electronic-grade nitric acid and water to ensure the quality of the raw materials. The removal rate of copper, iron and lead impurities is greater than 99.5%.

[0022] 2. A silver nitrate solution is reacted with an excess of acidic sodium chloride solution to generate a silver chloride precipitate, and then a strong oxidant, acidic sodium chlorate, is added for oxidation and impurity removal. The dual-function impurity removal mechanism of excess chloride ion complexation and acidic sodium chlorate oxidation effectively reduces the impurity content in the silver powder. After the impurity removal reaction is completed, the silver chloride is reduced with an alkaline hydrazine hydrate solution to obtain high-purity silver powder. The molar ratio of silver chloride to hydrazine hydrate is precisely controlled to solve the problem of incomplete reduction, thereby providing raw material guarantee for the preparation of high-purity silver nitrate. The entire process can effectively remove impurities, avoiding the problem of incomplete impurity removal or secondary pollution caused by traditional impurity removers, thereby obtaining high-purity silver nitrate that can meet the use requirements of multiple fields such as medicine, analytical reagents, and catalysts.

[0023] 3. The fire hazard of most raw materials is classified as Class II or below. The fire hazard of sodium chlorate is Class A. However, the amount used in this application is small and it is in solution, which greatly reduces the requirements for engineering design. The present application uses an alkaline hydrazine hydrate solution to reduce silver chloride to obtain silver powder. This is also based on practical engineering applications. It reduces the difficulty of engineering design and production costs, making the preparation method of the present application easier to promote and use. If sodium borohydride is used in the reduction process of silver chloride, hydrogen will be generated, and a separate reaction room needs to be set up. The electrical equipment in the reaction room needs to be explosion-proof, which increases the difficulty of investment and design. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below with reference to the examples. All reagents without manufacturer's indication are conventional reagent products that can be obtained commercially.

[0025] Example 1 A process for preparing high-purity silver nitrate from coarse silver powder comprises the following steps: S1, the coarse silver powder is washed with deionized water several times to remove water-soluble impurities, and then dried and ground to obtain fine silver powder; S2, fine silver powder, electronic grade nitric acid and water in a mass ratio of 1:1.5:0.5, reacting at a temperature of 60°C. After the reaction is completed, filtering to obtain a silver nitrate solution, wherein the concentration of the electronic grade nitric acid is 35wt%; S3. Control the concentration of the silver nitrate solution to 50 g / L (deionized water can be added for adjustment), react the silver nitrate solution with an acidic sodium chloride solution (pH 2) at 35° C. to form a silver chloride precipitate, wherein the molar ratio of silver ions to chloride ions is 1:2.1; S4. Add acidic sodium chlorate solution to the silver chloride precipitate, wherein the solid-liquid ratio of the silver chloride precipitate to the acidic sodium chlorate solution is 1: 3.5 g / L, react at 80 ° C, filter after the reaction to obtain silver chloride; S5. After reacting silver chloride and an alkaline hydrazine hydrate solution (pH 9) at a temperature of 60° C., filtering to obtain high-purity silver powder, the purity of the silver powder is 99.6%, wherein the molar ratio of silver chloride to hydrazine hydrate is 2:1; S6. reacting high-purity silver powder with electronic-grade nitric acid (35 wt %) and water in a mass ratio of 1:1.5:0.5 at 60° C. to obtain a dilute nitric acid solution; S7. Evaporating and crystallizing the dilute nitric acid solution to obtain high-purity silver nitrate, the evaporation and crystallization parameters are a stirring rate of 155 r / min, a temperature of 60° C., controlling the crystal film to appear after a crystallization time of 9 hours, then stopping stirring and heating, and cooling and crystallizing. After the crystallization is completed, filtering and drying are performed to obtain high-purity silver nitrate, and the purity of the silver nitrate is 99.8%.

[0026] Example 2 A process for preparing high-purity silver nitrate from coarse silver powder comprises the following steps: S1, the coarse silver powder is washed with deionized water several times to remove water-soluble impurities, and then dried and ground to obtain fine silver powder; S2, reacting fine silver powder, electronic grade nitric acid and water in a mass ratio of 1:1.55:0.55 at a temperature of 70°C. After the reaction is completed, filtering to obtain a silver nitrate solution, wherein the concentration of the electronic grade nitric acid is 40wt%; S3. Control the concentration of the silver nitrate solution to 50 g / L (deionized water can be added for adjustment), react the silver nitrate solution with an acidic sodium chloride solution (pH 2) at 40° C. to generate a silver chloride precipitate, wherein the molar ratio of silver ions to chloride ions is 1:2.2; S4. Add acidic sodium chlorate solution to the silver chloride precipitate, wherein the solid-liquid ratio of the silver chloride precipitate to the acidic sodium chlorate solution is 1: 4g / L, react at 85℃, filter to obtain silver chloride after the reaction is completed; S5. Reacting silver chloride and an alkaline hydrazine hydrate solution (pH 10) at 60° C., and filtering to obtain high-purity silver powder, wherein the purity of the silver powder is 99.7%, wherein the molar ratio of silver chloride to hydrazine hydrate is 2:1; S6. Reacting high-purity silver powder with electronic-grade nitric acid (40 wt %) and water in a mass ratio of 1:1.55:0.55 at 70° C. to obtain a dilute nitric acid solution; S7. Evaporating and crystallizing the dilute nitric acid solution to obtain high-purity silver nitrate, the evaporation and crystallization parameters are a stirring rate of 160 r / min and a temperature of 60° C., controlling the crystal film to appear after a crystallization time of 9 hours, then stopping stirring and heating, and then cooling and crystallizing. After the crystallization is completed, filtering and drying are performed to obtain high-purity silver nitrate, and the purity of the silver nitrate is 99.9%.

[0027] Example 3 A process for preparing high-purity silver nitrate from coarse silver powder comprises the following steps: S1, the coarse silver powder is washed with deionized water several times to remove water-soluble impurities, and then dried and ground to obtain fine silver powder; S2, reacting fine silver powder, electronic grade nitric acid and water in a mass ratio of 1:1.6:0.6 at a temperature of 75°C. After the reaction is completed, filtering to obtain a silver nitrate solution, wherein the concentration of the electronic grade nitric acid is 40wt%; S3. Control the concentration of the silver nitrate solution to 50 g / L (deionized water can be added for adjustment), react the silver nitrate solution with an acidic sodium chloride solution (pH 3) at 40° C. to form a silver chloride precipitate, wherein the molar ratio of silver ions to chloride ions is 1:2.3; S4. Add acidic sodium chlorate solution to the silver chloride precipitate, wherein the solid-liquid ratio of the silver chloride precipitate to the acidic sodium chlorate solution is 1: 4.5 g / L, react at 90 ° C, filter after the reaction to obtain silver chloride; S5. Reacting silver chloride and an alkaline hydrazine hydrate solution (pH 9) at 60° C., and filtering to obtain high-purity silver powder, wherein the purity of the silver powder is 99.6%, wherein the molar ratio of silver chloride to hydrazine hydrate is 2:1; S6. reacting high-purity silver powder with electronic-grade nitric acid (40 wt %) and water in a mass ratio of 1:1.6:0.6 at 75° C. to obtain a dilute nitric acid solution; S7. Evaporating and crystallizing the dilute nitric acid solution to obtain high-purity silver nitrate, the evaporation and crystallization parameters are a stirring rate of 165 r / min, a temperature of 70° C., controlling the crystal film to appear after a crystallization time of 9 hours, then stopping stirring and heating, and cooling and crystallizing. After the crystallization is completed, filtering and drying are performed to obtain high-purity silver nitrate, and the purity of the silver nitrate is 99.9%.

[0028] Comparative Example 1 A process for preparing high-purity silver nitrate from crude silver powder differs from Example 1 in that step S4 is omitted, and the silver chloride precipitate is directly reacted with the alkaline hydrazine hydrate solution. The other steps are the same as those in Example 1.

[0029] Comparative Example 2 A process for preparing high-purity silver nitrate from crude silver powder is different from that in Example 1 in that the reaction temperature in step S4 is 60° C., and the rest is the same as in Example 1.

[0030] Comparative Example 3 A process for preparing high-purity silver nitrate from crude silver powder is different from that of Example 1 in that, in step S3, the molar ratio of silver ions to chloride ions is 1:1, and the rest is the same as that of Example 1.

[0031] Comparative Example 4 A process for preparing high-purity silver nitrate from crude silver powder, which differs from Example 1 in that, in step S5, silver chloride and alkaline ammonium formate solution (pH 9) are reacted at 60°C and then filtered to obtain silver powder, the purity of which is 97.8%, wherein the molar ratio of silver chloride to ammonium formate is 2:1, and the other steps are the same as in Example 1 Performance testing The high-purity silver nitrate obtained in the above examples and comparative examples was tested, and the test results are shown in the following table.

[0032] Table 1 Silver nitrate purity and impurity content test results From Table 1 above, we can see that: The purity of the silver nitrate obtained in Examples 1-3 of the present application is 99.8% or above, and the content of copper ions is ≤0.0003ppm, the content of iron particles is 0.0001ppm, the content of lead ions is ≤0.0003ppm, the content of chloride is ≤0.0002ppm, the content of sulfate is 0.0001ppm, and the content of hydrochloric acid non-precipitate is 0.01ppm. It can be seen that when the preparation method of the present application is used to first prepare high-purity silver powder and then prepare silver nitrate, not only the purity of the silver nitrate is high, but also the content of impurity ions in the silver nitrate is low, which can effectively meet the use requirements in multiple fields such as medicine, analytical reagents, and catalysts.

[0033] Compared with Example 1, when step S4 of oxidizing and removing impurities in silver chloride with acidic sodium chlorate is omitted, the purity of the silver nitrate obtained in Comparative Example 1 is significantly lower than that in Example 1, and the contents of copper ions, iron ions, and lead ions in the silver nitrate are doubled compared with those in Example 1, and the chloride, sulfate, and hydrochloric acid unprecipitated matter are also significantly increased compared with those in Example 1. It can be seen that the process of oxidizing and removing impurities from silver chloride and then reducing it to produce silver powder can effectively reduce the impurity content in the silver powder, thereby ensuring that the final silver nitrate has high purity while greatly reducing the impurity content, meeting the application effect of silver nitrate in different fields.

[0034] Comparative Example 2 Compared with Example 1, when the reaction temperature of step S4 is too low, the purity of silver nitrate decreases and the impurity content increases. It can be seen that when the reaction temperature is within the range of 80-90°C specified in this application, the purity of the final silver nitrate can be effectively guaranteed and the impurity content in the silver nitrate can be reduced.

[0035] Compared with Example 1, when the molar ratio of silver ions to chloride ions in step S3 is 1:1, the purity of the silver nitrate obtained in Comparative Example 3 is reduced and the impurity content is increased. The reason is that the dual-function impurity removal mechanism of excess chloride ions and acidic sodium chlorate can effectively improve the impurity removal effect. When the chloride ion content is not excessive, the impurities in the silver nitrate cannot effectively form soluble complexes, so they cannot be effectively removed in the later oxidation process, which leads to a significant increase in the impurity content in the silver nitrate.

[0036] Comparative Example 4 Compared with Example 1, when alkaline ammonium formate solution is used instead of alkaline hydrazine hydrate solution to reduce silver chloride, the purity of the finally obtained silver powder is low, the purity of silver nitrate is also reduced compared with Example 1, and the copper ion, iron ion, lead ion content, chloride, sulfate, and hydrochloric acid non-precipitate in the silver nitrate are all increased compared with Example 1. The reason is that the reducing property of the sodium formate solution is weak, resulting in low purity of the silver powder, and the impurity content in the silver powder will also increase, which in turn leads to a decrease in the purity of the finally obtained silver nitrate.

[0037] The embodiments of this specific implementation method are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A process for preparing high-purity silver nitrate from coarse silver powder, characterized in that: The following steps are involved: S1, washing, drying and grinding the coarse silver powder to obtain fine silver powder; S2, after the reaction of fine silver powder, electronic grade nitric acid and water is completed, filtering to obtain a silver nitrate solution; S3, reacting the silver nitrate solution with an acidic sodium chloride solution to generate a silver chloride precipitate; S4, adding acidic sodium chlorate solution to the silver chloride precipitate, filtering to obtain silver chloride after the reaction is completed; S5, reacting silver chloride and alkaline hydrazine hydrate solution, and filtering to obtain high-purity silver powder; S6. reacting high-purity silver powder with electronic-grade nitric acid and water to prepare a dilute nitric acid solution; S7. Evaporate and crystallize the dilute nitric acid solution to obtain high-purity silver nitrate.

2. The process for preparing high-purity silver nitrate from coarse silver powder according to claim 1, wherein: The molar ratio of silver ions to chloride ions in step S3 is 1:(2.1-2.3).

3. The process for preparing high-purity silver nitrate from coarse silver powder according to claim 1, wherein: The reaction temperature in step S3 is 35-40°C.

4. The process for preparing high-purity silver nitrate from coarse silver powder according to claim 1, wherein: In step S4, the solid-to-liquid ratio of the silver chloride precipitate to the acidic sodium chlorate solution is 1:(3.5-4.5) g / L.

5. The process for preparing high-purity silver nitrate from coarse silver powder according to claim 1, wherein: The reaction temperature in step S4 is 80-90°C.

6. The process for preparing high-purity silver nitrate from coarse silver powder according to claim 1, wherein: The molar ratio of silver chloride to hydrazine hydrate in step S5 is 2:

1.

7. The process for preparing high-purity silver nitrate from coarse silver powder according to claim 1, wherein: The reaction temperature in step S5 is 60-80°C.

8. The process for preparing high-purity silver nitrate from coarse silver powder according to claim 1, wherein: In step S1 and step S6, the mass ratio of silver powder to electronic grade nitric acid and water is 1:(1.5-1.6):(0.5-0.6).

9. The process for preparing high-purity silver nitrate from coarse silver powder according to claim 8, wherein: In step S1 and step S6, the concentration of electronic grade nitric acid is 35-40 wt %, and the reaction temperature is 60-75° C.

10. The process for preparing high-purity silver nitrate from coarse silver powder according to claim 1, characterized in that: In step S7, the stirring rate is 155-165 r / min, the temperature is 60-70° C., and the stirring and heating are stopped after the crystal film appears.

Images