A process for the purification of metallic silver

Abstract

The application discloses a kind of silver purification process, comprising the following steps: first, the silver material of the purity of more than 99% after crushing is added to the container containing nitric acid in proportion, stirring and dissolving to form solution A;Then sodium dihydrogen arsenate and disodium ethylenediaminetetraacetate are added to solution A in step one in proportion to form solution B;Second, the silver material of the purity of more than 99% after crushing is loaded into filter bag and put into electrolytic cell as anode, silver sheet is used as cathode, and solution B in step two is added as electrolyte for electrolysis;Then continue to supplement silver particles when two-thirds or so of silver particles in filter bag remain, electrolyze for 2h-2.5h, and obtain metal silver with purity of more than 99.9999% on the cathode;Finally, the metal silver in step four is taken out, washed, dried and stored, so that the purity of silver can meet the requirements of high-purity silver while directly using low-purity silver jewelry raw materials for electrolytic purification, greatly improving production efficiency.

Description

Technical Field

[0001] This application relates to the field of metallic silver preparation, and more specifically, to a process for purifying metallic silver. Background Technology

[0002] Silver is an important industrial raw material with a wide range of applications. High-purity silver has good electrical and thermal conductivity, making it an excellent conductor of electricity and heat.

[0003] With economic development, the requirements for silver purity are becoming increasingly stringent. Extremely high-purity silver has many important industrial applications, including in the production and processing of precious metal jewelry such as gold and silver. These processes involve various methods to create jewelry, inevitably leading to some loss and increase in impurities. Because precious metal jewelry typically contains a high amount of gold and silver, its recycling value is relatively high.

[0004] There are currently many methods for refining silver, such as electrolysis, chemical methods, ion exchange, and extraction. Among them, electrolysis is the most effective because it is environmentally friendly and highly efficient. Products obtained through electrolysis contain more than 99.0% silver, and after washing and drying, they can be melted and cast into ingots with a silver content of over 99.99%.

[0005] Current silver electrolysis uses a gold-silver alloy as the anode, encased in a diaphragm bag, with pure silver, titanium, or stainless steel sheets as the cathode, and silver nitrate solution as the electrolyte. It utilizes the different potentials of the elements to remove impurities and refine the silver. Impurities with higher potentials than silver do not dissolve and become anode sludge, while elements with lower potentials dissolve as ions and remain in the mother liquor. However, although high-purity silver (up to 99.9999%) has been achieved by controlling electrolysis parameters, it requires high-quality raw materials. Therefore, the recycling of precious metal jewelry mostly employs chemical smelting and purification methods. Further purification is required to increase the purity of silver, making the process complex. Summary of the Invention

[0006] In order to effectively simplify the steps of the silver refining process and obtain silver with the required purity, this application provides a silver refining process.

[0007] In a first aspect, this application provides a process for purifying metallic silver, employing the following technical solution: A process for purifying metallic silver includes the following steps: Step 1: Add the crushed silver material with a purity of 99% or higher to a container containing nitric acid in a certain proportion, stir to dissolve and form solution A; Step 2: Add sodium dihydrogen arsenate and disodium ethylenediaminetetraacetate to solution A in step 1 in a certain proportion to form solution B; Step 3: Place the crushed silver material with a purity of over 99% into a filter bag and put it into an electrolytic cell as the anode, use the silver sheet as the cathode, and add solution B from step 2 as the electrolyte for electrolysis. Step 4: When about two-thirds of the silver particles remain in the filter bag, continue to add silver particles. After electrolysis for 2-2.5 hours, metallic silver with a purity of over 99.9999% is obtained on the cathode. Step 5: Remove the silver metal from Step 4, wash it, dry it, and store it.

[0008] By adopting the above technical solution, sodium dihydrogen arsenate and disodium ethylenediaminetetraacetate are used as conductive salts to synergistically work with silver nitrate. This effectively improves current efficiency and electrolysis efficiency while reducing the precipitation of impurities in the electrolyte. Compared with existing electrolytic silver refining processes, this method can directly use crushed silver jewelry raw materials for electrolytic refining, and effectively ensure that the purity of the electrolytically refined silver meets the requirement of 99.9999% high-purity silver, greatly improving production efficiency.

[0009] Preferably, in step two, the mass ratio of sodium dihydrogen arsenate to disodium ethylenediaminetetraacetate is (2.4-3.2):1.

[0010] Preferably, the concentration of silver nitrate in solution B is 180 g / L-200 g / L, the concentration of sodium dihydrogen arsenate is 5.3 g / L-7.2 g / L, and the concentration of disodium ethylenediaminetetraacetate is 1.3 g / L-4.5 g / L. By adopting the above technical solution, and controlling the concentrations and mass ratios of silver nitrate, sodium dihydrogen arsenate, and disodium ethylenediaminetetraacetate in solution B, the synergistic effect between sodium dihydrogen arsenate, disodium ethylenediaminetetraacetate, and silver nitrate can be better improved, thereby further increasing the current efficiency and electrolysis efficiency in solution B during electrolysis.

[0011] Preferably, the pH value of the electrolyte in step three is 3.0-4.0.

[0012] Preferably, in step three, the electrolyte is subjected to periodic reverse electrolysis at a temperature of 20℃-40℃.

[0013] Preferably, the conditions for the periodic reverse electrolysis treatment are: a forward current density of 300 A / m 2 -450A / m 2 The high-level pulse duration is 15ms-30ms, and the low-level pulse duration is 1ms-10ms; the reverse current density is 120A / m. 2 -220A / m 2 The pulse width of the current has a high-level duration and a low-level duration of 1ms-4ms.

[0014] By adopting the above technical solution, the periodic reverse electrolysis method can effectively reduce impurity precipitation, while increasing the current density and cathode deposition rate. In addition, by controlling the pH value of the electrolyte at 3.0-4.0 and controlling the current intensity, the precipitation of impurity elements such as copper and lead at the cathode can be better reduced, thereby further improving the purity of silver.

[0015] Preferably, during electrolysis in step three, the cell voltage is 1-1.5V and the current density is 300-400A / ㎡.

[0016] By adopting the above technical solution and controlling the voltage and current within a specified range, the synergistic effect between sodium dihydrogen arsenate, disodium ethylenediaminetetraacetate, and silver nitrate can be further enhanced, thereby helping to improve electrolysis efficiency.

[0017] Preferably, the particle size of the silver material after crushing is 280-550 mesh.

[0018] Preferably, the silver material is at least one of silver bracelets, silver earrings, and silver necklaces.

[0019] By adopting the above technical solution, the recycled silver bracelets, silver earrings, and silver necklaces are used as silver materials and crushed to a specific particle size range, which can effectively shorten the purification time and thus better improve the purification efficiency of recycled silver materials in this application.

[0020] In summary, this application has the following beneficial effects: 1. By using sodium dihydrogen arsenate and disodium ethylenediaminetetraacetate as conductive salts to synergistically work with silver nitrate, the current efficiency and electrolysis efficiency can be effectively improved while reducing the precipitation of impurities in the electrolyte. Compared with the existing electrolytic purification process for silver, this method can directly use crushed silver jewelry raw materials for electrolytic purification, and can also effectively ensure that the purity of the electrolytically purified silver meets the requirement of 99.9999% high-purity silver, greatly improving production efficiency. 2. By controlling the concentrations of silver nitrate, sodium dihydrogen arsenate, and disodium ethylenediaminetetraacetate in solution B, as well as the mass ratio between these substances, the synergistic effect between sodium dihydrogen arsenate, disodium ethylenediaminetetraacetate, and silver nitrate can be better enhanced, thereby further increasing the current efficiency and electrolysis efficiency in solution B during electrolysis. 3. By using the periodic reverse electrolysis method, impurity precipitation can be effectively reduced, while increasing the current density and cathode deposition rate. In addition, by controlling the pH value of the electrolyte at 3.0-4.0 and controlling the current intensity, the precipitation of impurity elements such as copper and lead at the cathode can be better reduced, thereby further improving the purity of silver. 4. By controlling the voltage and current within a specified range, the synergistic effect between sodium dihydrogen arsenate, disodium ethylenediaminetetraacetate, and silver nitrate can be further enhanced, thereby improving electrolysis efficiency. Detailed Implementation

[0021] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0022] All raw materials used in the following examples and comparative examples are commercially available products. Example

[0023] Example 1 A process for purifying metallic silver includes the following steps: Step 1: After cleaning and degreasing, the 99% pure silver bracelet material is crushed and passed through a 220-mesh sieve to obtain silver particles with an average particle size of 220 mesh. A portion of the silver particles is added to a container containing nitric acid according to the reaction ratio and stirred to dissolve to form solution A. Step 2: Add sodium dihydrogen arsenate and disodium ethylenediaminetetraacetate to solution A from step 1 at a mass ratio of 2:1. Then add nitric acid and stir to form solution B with a pH of 4.5 and concentrations of silver nitrate, sodium dihydrogen arsenate, and disodium ethylenediaminetetraacetate of 170 g / L, 7.5 g / L, and 5 g / L, respectively. Step 3: Put the remaining silver particles from Step 1 into a filter bag and place it in an electrolytic cell as the anode, with a silver sheet as the cathode, and add solution B from Step 2 as the electrolyte. Electrolysis is carried out at a cell voltage of 2.5 V and a current density of 500 A / m². Step 4: When about two-thirds of the silver particles remain in the filter bag, continue to add silver particles and continue electrolysis for 2 hours, and obtain metallic silver on the cathode. Step 5: Remove the silver metal from Step 4, wash it, dry it, and store it.

[0024] Example 2 A silver purification process differs from Example 1 in that the electrolysis time in step four is 2.5 hours.

[0025] Example 3 A silver purification process differs from Example 2 in that the ratio of sodium dihydrogen arsenate to disodium ethylenediaminetetraacetate is 2.4:1.

[0026] Example 4 A silver purification process differs from Example 2 in that the ratio of sodium dihydrogen arsenate to disodium ethylenediaminetetraacetate is 3.6:1.

[0027] Example 5 A silver purification process differs from Example 2 in that the concentrations of silver nitrate, sodium dihydrogen arsenate, and disodium ethylenediaminetetraacetate are 180 g / L, 7.2 g / L, and 4.5 g / L, respectively.

[0028] Example 6 A silver purification process differs from Example 2 in that the concentrations of silver nitrate, sodium dihydrogen arsenate, and disodium ethylenediaminetetraacetate are 200 g / L, 5.3 g / L, and 1.3 g / L, respectively.

[0029] Example 7 A silver purification process differs from Example 2 in that the concentrations of silver nitrate, sodium dihydrogen arsenate, and disodium ethylenediaminetetraacetate are 180 g / L, 7.2 g / L, and 4.5 g / L, respectively.

[0030] Example 8 A silver purification process differs from Example 2 in that, in step two, nitric acid is added and stirred to achieve a pH of 4.0. Simultaneously, the electrolyte in step three undergoes periodic reverse electrolysis at 40°C, with a forward current density of 300 A / m. 2 The high-level pulse duration is 15ms, the low-level pulse duration is 1ms, and the reverse current density is 120A / m. 2 The pulse width is 1ms for both the high-level and low-level durations.

[0031] Example 9 A silver purification process differs from Example 2 in that, in step two, nitric acid is added and stirred to achieve a pH of 3.0. Simultaneously, the electrolyte in step three undergoes periodic reverse electrolysis at 20°C, with a forward current density of 450 A / m. 2 The high-level pulse duration is 30ms, the low-level pulse duration is 10ms, and the reverse current density is 220A / m. 2 The pulse width is 4ms for both the high-level and low-level durations.

[0032] Example 10 A silver refining process differs from Example 2 in that the cell voltage in step three is 1.5V, the current density is 400 A / m², and the average particle size of the silver material is 550 mesh.

[0033] Example 11 A silver refining process differs from Example 2 in that the cell voltage in step three is 1V, the current density is 300 A / m², and the average particle size of the silver material is 280 mesh.

[0034] Example 12 A silver refining process differs from Example 2 in that silver earrings are used instead of silver bracelets.

[0035] Example 13 A silver refining process differs from Example 2 in that a silver necklace is used instead of a silver bracelet.

[0036] Comparative Example Comparative Example 1 A purification process for metallic silver differs from Example 1 in that solution B in step two does not contain sodium dihydrogen arsenate.

[0037] Comparative Example 2 A purification process for metallic silver differs from Example 1 in that solution B in step two does not contain disodium ethylenediaminetetraacetate.

[0038] Comparative Example 3 A purification process for metallic silver differs from Example 1 in that solution B in step two does not contain sodium dihydrogen arsenate and disodium ethylenediaminetetraacetate.

[0039] Performance testing The purity values ​​of metallic silver purified in Examples 1-13 and Comparative Examples 1-3 were determined using GD-MS glow discharge mass spectrometry.

[0040] Table 1 - Summary of experimental data from Examples 1-13 and Comparative Examples 1-3 Example 1 99.99994% Example 2 99.99995% Example 3 99.99997% Example 4 99.99998% Example 5 99.99996% Example 6 99.99996% Example 7 99.99997% Example 8 99.99998% Example 9 99.99999% Example 10 99.99995% Example 11 99.99996% Example 12 99.99995% Example 13 99.99995% Comparative Example 1 99.9995% Comparative Example 2 99.9994% Comparative Example 3 99.9992% According to the comparison of the test data of Example 1 and Comparative Example 3 in Table 1, the purity of the metallic silver purified according to the technical solution of this application is greatly improved compared with the existing process of directly using low-purity silver jewelry for electrolytic purification. This can effectively improve the purity of electrolytic metallic silver, and also save the optimization steps before the purification of silver jewelry, thereby effectively improving production efficiency and having great economic value for the company's metallic silver purification production.

[0041] Furthermore, a comparison of the experimental data from Example 1 and Comparative Examples 1-3 in Table 1 shows that if the synergistic relationship between sodium dihydrogen arsenate and disodium ethylenediaminetetraacetate is disrupted in the electrolyte system, the interaction between the sodium dihydrogen arsenate and disodium ethylenediaminetetraacetate compound and silver nitrate cannot be achieved, resulting in a significant decrease in the purity of the metallic silver obtained after electrolytic purification. This indicates that both are indispensable, and it is thus concluded that the prerequisite for improving the purity of metallic silver in this application is the synergistic effect of both to obtain a more effective synergistic effect on the silver nitrate electrolyte.

[0042] According to the comparison of the detection data of Examples 2-7 in Table 3, it can be seen that by adjusting the addition ratio of sodium dihydrogen arsenate and disodium ethylenediaminetetraacetate or by controlling the concentrations of silver nitrate, sodium dihydrogen arsenate and disodium ethylenediaminetetraacetate, the purity of electrolytic metallic silver can be further improved to varying degrees based on Example 2, so as to further optimize the purification and production process of this application.

[0043] According to the comparison of the detection data of Examples 2 and 8-9 in Table 1, it can be seen that by adopting the periodic reverse electrolysis method to purify metallic silver based on the process of Example 2, and by controlling the relevant electrolysis parameters, the precipitation of impurities can be effectively reduced, the current density in the electrolyte can be increased, and the cathode deposition rate can be increased, thereby obtaining metallic silver with higher purity to a greater extent and achieving the purpose of improving purification efficiency.

[0044] According to the comparison of the detection data of Examples 2 and 10-11 in Table 3, it can be seen that by further controlling and adjusting the cell voltage, current density and average particle size of silver material during electrolysis, higher purity electrolytic silver can be obtained based on the process of Example 2, which is more conducive to optimizing the silver purification process of this application.

[0045] According to the comparison of the test data of Examples 2 and 12-13 in Table 3, when silver earrings or silver necklaces are used to replace the silver bracelet in Example 2, there is no difference in the purity of the metallic silver obtained by electrolysis of silver material. Therefore, the electrolytic metallic silver purification process of this application can be applied to the electrolytic purification of most silver jewelry, so as to facilitate people to efficiently purify different types of silver jewelry and has great economic benefits.

[0046] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A process for purifying metallic silver, comprising the following steps: Step 1: Add the crushed silver material with a purity of 99% or higher to a container containing nitric acid in a certain proportion, stir to dissolve and form solution A; Step 2: Add sodium dihydrogen arsenate and disodium ethylenediaminetetraacetate to solution A in step 1 in a certain proportion to form solution B; Step 3: Place the crushed silver material with a purity of over 99% into a filter bag and put it into an electrolytic cell as the anode, use the silver sheet as the cathode, and add solution B from step 2 as the electrolyte for electrolysis. Step 4: When two-thirds of the silver particles remain in the filter bag, continue to add silver particles. After electrolysis for 2-2.5 hours, metallic silver with a purity of over 99.9999% is obtained on the cathode. Step 5: Remove the silver metal from Step 4, wash it, dry it, and store it. In step two, the mass ratio of sodium dihydrogen arsenate to disodium ethylenediaminetetraacetate is (2.4-3.2):1; The pH value of the electrolyte in step three is 3.0-4.0; In step three, the electrolyte undergoes periodic reverse electrolysis at a temperature of 20℃-40℃. The conditions for the periodic reverse electrolysis treatment are: forward current density of 300 A / m 2 -450A / m 2 The high-level pulse duration is 15ms-30ms, and the low-level pulse duration is 1ms-10ms; the reverse current density is 120A / m. 2 -220A / m 2 The pulse width of the current has a high-level duration and a low-level duration of 1ms-4ms.

2. The silver refining process according to claim 1, characterized in that, The concentration of silver nitrate in solution B is 180 g / L-200 g / L, the concentration of sodium dihydrogen arsenate is 5.3 g / L-7.2 g / L, and the concentration of disodium ethylenediaminetetraacetate is 1.3 g / L-4.5 g / L.

3. The silver refining process according to claim 1, characterized in that, The silver material, after being crushed, has a particle size of 280-550 mesh.

4. The preparation method of a purification process for metallic silver according to claim 1, characterized in that, The silver material is at least one of silver bracelets, silver earrings, and silver necklaces.