CN113186567A

CN113186567A - Silver purification method and silver product

Info

Publication number: CN113186567A
Application number: CN202110431478.XA
Authority: CN
Inventors: 李水湖
Original assignee: Shenzhen Jinlaili Gold Jewelry Co ltd
Current assignee: Shenzhen Jinlaili Gold Jewelry Co ltd
Priority date: 2021-04-21
Filing date: 2021-04-21
Publication date: 2021-07-30
Anticipated expiration: 2041-04-21
Also published as: CN113186567B

Abstract

The invention belongs to the technical field of silver purification, and particularly relates to a silver purification method and a silver product. The purification method comprises the following steps: crushing a clean recovered silver product with the purity of more than 99.0 percent, and placing the crushed recovered silver product into an anode titanium basket externally sleeved with a filter bag; placing the anode titanium blue in electrolyte, and taking a titanium plate as a cathode; the electrolyte contains sodium oxalate, polyacrylamide and 100g/L-150g/L AgNO₃(ii) a Adjusting the pH value of the electrolyte to 2.0-3.0, and carrying out periodic reverse electrolysis treatment at the temperature of 30-40 ℃; the metallic silver with the purity of more than 99.9999 percent is obtained on the cathode. The method can directly obtain high-purity silver from the silver product with the purity of more than 99.0 percent, avoid the generation of anode scrap and improve the recovery rate and the recovery efficiency of the silver.

Description

Silver purification method and silver product

Technical Field

The invention belongs to the technical field of silver purification, and particularly relates to a silver purification method and a silver product.

Background

At present, the purification methods of silver at home and abroad are more, such as an electrolytic method, a chemical method, an ion exchange method, an extraction method and the like, and although the purification methods can improve the purity of the metallic silver to a certain extent, the purity of the obtained silver is not high. In addition, it is difficult to obtain high-purity silver from a silver raw material having a low purity by the electrolytic method, and when a molten-cast electrode plate is used as an anode, it is necessary to treat a residual electrode. Therefore, in view of the above problems, there is a need for improvement in the existing purification techniques to meet the increasing economic demand.

Because the electrolytic method is green and environment-friendly and has high efficiency, the electrolytic preparation of high-purity silver is a mature process. For example, silver powder is prepared by an electrolytic method in the prior art, but only a purity of 99.99% is achieved. In another example, electrolytic methods are used to produce high purity silver, but only 99.999% purity is achieved. As another example, there is an electrolytic method for preparing high purity silver, and although high purity silver up to 99.9999% is obtained by controlling electrolysis parameters, it has high requirements for raw materials and requires silver having a purity of not less than 99.99% as an anode.

For the recovered silver products, such as silver bracelets, silver necklaces, silver earrings and other pure silver products, the prior art mostly adopts a chemical method for smelting and purifying, if high-purity silver needs to be prepared, the silver products need to be purified again, and the process is complex.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a silver purification method and a silver product, and aims to solve the problems of low recovery rate, low purification purity and complex process of the existing silver product.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method of purifying silver comprising the steps of:

(1) crushing a clean recovered silver product with the purity of more than 99.0 percent, and placing the crushed recovered silver product into an anode titanium basket externally sleeved with a filter bag;

(2) placing the anode titanium blue in an electrolytic tank, taking a titanium plate as a cathode, and introducing sodium oxalate, polyacrylamide and AgNO₃The electrolyte of (1);

(3) introducing nitric acid into the electrolytic bath to maintain the pH value of the electrolyte at 2.0-3.0, and then carrying out periodic reverse electrolysis treatment at the temperature of 30-40 ℃;

(4) and obtaining the metallic silver with the purity of more than 99.9999 percent on the cathode.

Further, in the electrolyte, the AgNO₃The concentration of the sodium oxalate is 100g/L-150g/L, the concentration of the sodium oxalate is 1g/L-5g/L, and the concentration of the polyacrylamide is 0.01g/L-0.03 g/L.

Further, the mass concentration ratio of the sodium oxalate to the polyacrylamide in the electrolyte is 50: 150.

further, the conditions of the periodic reverse electrolysis treatment are as follows: the forward current density is 500A/m²-650A/m²Duration of high level and duration of low level of current pulse widthRespectively 20ms-50ms and 1ms-10 ms; the reverse current density is 200A/m²-250A/m²The duration of the high level and the duration of the low level of the current pulse width are both 1ms-5 ms.

Further, in the periodic reverse electrolysis treatment process, the electrolyte is continuously introduced into the electrolytic cell and is continuously discharged from the electrolytic cell.

Further, the granularity of the silver product after being crushed is 150-600 meshes.

Further, the purity of the recovered silver product is between 99.0% and 99.9%.

Further, the recycled silver article comprises at least one of a silver bracelet, a silver earring, a silver necklace, and a silver ring.

And a silver product containing metallic silver purified by the above silver purification method.

The invention has the beneficial effects that:

compared with the prior art, the method directly purifies the recovered silver product, and takes sodium oxalate as conductive salt and complexing agent to improve current and current efficiency and electrolysis efficiency and reduce the precipitation of impurities; the polyacrylamide can promote the sedimentation of the anode mud, thereby improving the recovery rate of silver, finally purifying the low-purity silver to more than 99.9999 percent, wherein the recovery rate of the silver can reach more than 96 percent, and the current efficiency can reach as high as 99 percent. In addition, the invention also overcomes the problems that the high-purity silver prepared by the prior art needs to adopt silver with the purity of more than 99.99 percent as an anode and adopts a silver plate as the anode, so that a large amount of residual anodes exist and the purification process is complex.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the following embodiments further describe the present invention in detail. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The invention provides a silver purification method, which can directly purify a recovered silver product so as to realize the recovery and reuse of silver metal resources and reduce the waste of the metal silver resources.

In particular, the recycled silver article may be a silver jewelry, such as a silver bracelet, a silver earring, a silver finger ring, or the like. The method for purifying silver of the present invention can be applied to purification as long as the purity of silver in the recovered silver product is more than 99.0%.

More specifically, the purification method of silver of the present invention comprises the steps of:

(1) the method comprises the following steps of pretreating a recovered silver product, and then placing the pretreated silver product into an anode titanium basket, wherein a filter bag is sleeved outside the anode titanium basket.

Among them, the pretreatment of the recovered silver products includes washing, degreasing, and drying and crushing. By the cleaning and degreasing treatment, the influence of residual stains and other attached particle impurities on the purification effect can be reduced. And the recycled silver product is crushed, so that the purification time can be shortened, and the purification efficiency can be improved. Preferably, the crushed particle size of the silver product is 150-600 meshes. In some embodiments, the purity of the recovered silver product is between 99.0% and 99.9%.

(2) Placing the anode titanium blue in an electrolytic tank, taking a titanium plate as a cathode, and introducing electrolyte into the electrolytic tank, wherein the electrolyte contains sodium oxalate, polyacrylamide and 100-150 g/L AgNO₃。

Wherein, adopt electrolysis trough splendid attire electrolyte, and the electrolysis trough has electrolyte import and export, and the import is located the high level of electrolysis trough, and the export is located the low level of electrolysis trough, and the electrolysis trough has the bottom promptly and the top that sets up relatively with the bottom, and the bottom of electrolysis trough is located in the export, and the top of electrolysis trough is located in the import, and the export is closed before using. By controlling the concentration of sodium oxalate and polyacrylamide in the electrolyte, the sedimentation of anode mud can be promoted, the adsorption of polyacrylamide on a cathode can be avoided, and the silver recovery rate and the cathode current efficiency can be improved.

Specifically, the concentration of the sodium oxalate in the electrolyte is 1g/L-5 g/L; the concentration of the polyacrylamide in the electrolyte is 0.01g/L-0.03 g/L. Preferably, the mass concentration ratio of the sodium oxalate to the polyacrylamide in the electrolyte is 50: 150. sodium oxalate contained in the electrolyte is used as a conductive salt and a complexing agent, so that the precipitation of impurities can be reduced on the premise of improving the current efficiency and the electrolysis efficiency; and the polyacrylamide can promote the sedimentation of the anode mud so as to improve the recovery rate of silver.

(3) And introducing nitric acid into the electrolytic bath to adjust the pH value of the electrolyte to 2.0-3.0, and then carrying out periodic reverse electrolysis treatment at the temperature of 30-40 ℃.

Wherein, the conditions of the periodic reverse electrolysis are as follows: the forward current density is 500A/m²-650A/m²The high level time and the low level time of the current pulse width are respectively 20ms-50ms and 1ms-10 ms; the reverse current density is 200A/m²-250A/m²The duration of the high level and the duration of the low level of the current pulse width are both 1ms-5 ms. And continuously feeding the electrolyte and the nitric acid into the electrolytic cell during the electrolysis process, wherein the electrolyte and the nitric acid enter from an inlet of the electrolytic cell, are discharged from an outlet and are circulated back to the inlet for circular electrolysis. The periodic reverse electrolysis can reduce impurity precipitation, improve current density and improve cathode deposition rate. Free HNO in the electrolyte₃The conductivity of the electrolyte can be improved, but if the concentration is relatively high, chemical dissolution of silver occurs in the cathode, and a large amount of nitride is released, which affects the surrounding environment. The metal which is more active than silver is dissolved in the electrolyte in the electrolytic refining process, the pH is controlled within the range of 2.0-3.5, the precipitation of elements such as copper, Cu, Pd and the like at the cathode can be reduced by adopting large-current electrolysis, the purity of the metal silver is further improved, the electrolyte keeps flowing in the electrolytic process, on one hand, the concentration balance of each component in the electrolyte can be ensured, on the other hand, the uniform precipitation degree in the silver purification process can be improved, the silver deposited at the cathode has uniform compactness, and in addition, the current efficiency can be improved.

(4) Silver with the purity of more than 99.9999 percent is obtained on the cathode.

The embodiment of the invention can realize the electrolytic purification of the recovered silver product with the purity of 99-99.9 percent as the anode by the synergistic cooperation of all the parameters, and purify the metal silver until the purity reaches more than 99.9999 percent, the recovery rate of the silver reaches more than 96 percent, the current efficiency reaches 99 percent, the high-purity anode is not needed, and the residual anode does not appear.

In order to better illustrate the technical solution of the present invention, the following is further illustrated by a plurality of examples and comparative examples.

Example 1

A method of purifying silver comprising the steps of:

(1) the recovered silver jewelry (silver bracelets and silver earrings with the average purity of 99%) is cleaned and degreased, then crushed and sieved by a 200-mesh sieve to obtain silver particles with the average particle size of 200 meshes, the silver particles are placed in an anode titanium basket, and a filter bag is sleeved outside the anode titanium basket.

(2) Injecting electrolyte into an electrolytic cell, placing anode titanium blue into the electrolyte, taking a titanium plate as a cathode, wherein the electrolyte contains silver nitrate, sodium oxalate and polyacrylamide, and AgNO₃Is 100g/L, the concentration of sodium oxalate is 1g/L and the concentration of polyacrylamide is 0.02g/L, nitric acid is injected into an electrolytic cell until the pH value of the electrolyte is 2.5, periodic reverse electrolysis is adopted, wherein, the forward current density is 500A/m²The high level duration of the current pulse width is 20ms, and the low level duration is 1 ms; the reverse current density is 200A/m²The duration of the high level and the duration of the low level of the current pulse width are both 1ms, the electrolysis temperature is 30 ℃, and the circulating electrolysis is carried out according to the mode that the electrolyte enters from the inlet of the electrolytic cell and exits from the outlet of the electrolytic cell. When about two thirds of the silver particles in the anode titanium basket are left, the silver particles are supplemented through an automatic adding device.

(3) Electrolyzing for 2 hours to obtain metal silver at a cathode, stripping the metal silver from the cathode, washing and drying the metal silver obtained by glass stripping, and detecting and analyzing by a glow discharge mass spectrometry (hereinafter abbreviated as GD-MS) to obtain the metal silver with the purity of 99.99992 percent.

Example 2

A method of purifying silver comprising the steps of:

(1) the recovered silver jewelry (silver bracelets and silver rings, the average purity is 99%) is cleaned and degreased, then the jewelry is crushed and sieved by a 150-mesh sieve to obtain silver particles with the average particle size of 150 meshes, the silver particles are placed in an anode titanium basket, and a filter bag is sleeved outside the anode titanium basket.

(2) Injecting electrolyte into an electrolytic cell, placing anode titanium blue into the electrolyte, taking a titanium plate as a cathode, wherein the electrolyte contains silver nitrate, sodium oxalate and polyacrylamide, and AgNO₃The concentration of the sodium oxalate is 120g/L, the concentration of the sodium oxalate is 3g/L, the concentration of the polyacrylamide is 0.02g/L, nitric acid is injected into an electrolytic cell until the pH value of the electrolyte is 3, and periodic reverse electrolysis is adopted; wherein the forward current density is 550A/m²The duration of the current pulse width at high level is 30ms, the duration of the current pulse width at low level is 10ms, and the reverse current density is 220A/m²The duration of high level and the duration of low level of current pulse width are both 3ms, the electrolysis temperature is 35 ℃, and the circulating electrolysis is carried out according to the mode that the electrolyte enters from the inlet of the electrolytic cell and exits from the outlet of the electrolytic cell. When about two thirds of the silver particles in the anode titanium basket are left, the silver particles are supplemented through an automatic adding device.

(3) Electrolyzing for 3 hours to obtain metal silver at the cathode, then stripping the metal silver from the cathode, washing and drying the metal silver obtained by stripping the glass, and detecting and analyzing by GD-MS to obtain the metal silver with the purity of 99.99993%.

Example 3

A method of purifying silver comprising the steps of:

(1) the recovered silver jewelry (silver bracelets and silver earrings, the average purity is 99.9%) is cleaned and degreased, then crushed and sieved by a 150-mesh sieve to obtain silver particles with the average particle size of 150 meshes, the silver particles are placed in an anode titanium basket, and a filter bag is sleeved outside the anode titanium basket.

(2) Injecting electrolyte into an electrolytic cell, placing anode titanium blue into the electrolyte, taking a titanium plate as a cathode, wherein the electrolyte contains silver nitrate, sodium oxalate and polyacrylamide, and AgNO₃With the concentration of 150g/L, the concentration of sodium oxalate of 4g/L and the concentration of polyacrylamide of 0.03g/L, nitric acid is injected into the electrolytic bath until the pH value of the electrolyte is 3,periodic reverse electrolysis is adopted; wherein the forward current density is 650A/m²The high level duration of the current pulse width is 50ms, the low level duration is 10ms, and the reverse current density is 250A/m²The duration of the high level and the duration of the low level of the current pulse width are both 5ms, the electrolysis temperature is 40 ℃, and the circulating electrolysis is carried out according to the mode that the electrolyte enters from the inlet of the electrolytic cell and exits from the outlet of the electrolytic cell. When about two thirds of the silver particles in the anode titanium basket are left, the silver particles are supplemented through an automatic adding device.

(3) Electrolyzing for 3 hours to obtain metal silver at the cathode, then stripping the metal silver from the cathode, washing and drying the metal silver obtained by stripping the glass, and analyzing by GD-MS detection to obtain the metal silver with the purity of 99.99996%.

Comparative example 1

(1) The recovered silver jewelry (silver bracelets and silver earrings with the average purity of 99.9%) is subjected to oil removal and cleaning and then is subjected to melt casting to form an anode plate;

(2) putting silver powder with silver content of more than 99.999% into a container, adding nitric acid into the container according to the concentration and pH value of the generated silver nitrate, stirring and dissolving to form silver nitrate solution, wherein the concentration of the silver nitrate in the solution is 120g/L, and the pH value is 3.8;

(2) adding a silver nitrate solution into an electrolytic tank, taking the anode plate obtained in the step (1) as an anode, filling the anode plate into a filter bag, taking a titanium plate as a cathode, and taking the silver nitrate solution as an electrolyte for electrolysis; the current density is 400A/m²。

(3) When 1/3 is left in the volume of the anode plate, the electrolysis is stopped, the anode scrap is recovered, and the silver on the cathode is stripped, cleaned, dried and detected and analyzed by GD-MS, so that the purity of the obtained metallic silver is 99.99%.

Comparative example 2

(1) The recovered silver jewelry (silver bracelets and silver earrings, the average purity is 99%) is cleaned, degreased, crushed and sieved by a 200-mesh sieve to obtain silver particles with the average particle size of 200 meshes, the silver particles are placed in an anode titanium basket, and a filter bag is sleeved outside the anode titanium basket.

(2) Placing the anode titanium blue in electrolyte, and using a titanium plateThe electrolyte is used as a cathode, silver nitrate with the concentration of 100g/L is contained in the electrolyte, the pH value of the electrolyte is adjusted to be 2.5 by adopting nitric acid, periodic reverse electrolysis is adopted, wherein the forward current density is 500A/m²The duration of current pulse width at high level is 20ms, the duration of current pulse width at low level is 1ms, and the density of reverse current is 200A/m²The duration of the high level and the duration of the low level of the current pulse width are both 1ms, the electrolysis temperature is 30 ℃, and the circulating electrolysis is carried out according to the mode that the electrolyte enters from the inlet of the electrolytic cell and exits from the outlet of the electrolytic cell. When about two thirds of the silver particles in the anode titanium basket are left, the silver particles are supplemented through an automatic adding device.

(3) Electrolyzing for 2 hours to obtain metallic silver at the cathode, then stripping the metallic silver from the cathode, washing and drying the metallic silver obtained by glass stripping, and detecting and analyzing by GD-MS to obtain the metallic silver with the purity of 99.9993%.

Comparative example 3

(2) Placing anode titanium blue into electrolyte, taking a titanium plate as a cathode, wherein the electrolyte contains silver nitrate with the concentration of 100g/L, sodium oxalate with the concentration of 6g/L and polyacrylamide with the concentration of 0.03g/L, adjusting the pH value of the electrolyte to 2.5 by adopting nitric acid, adopting periodic reverse electrolysis, and realizing forward current density of 500A/m²The duration of current pulse width at high level is 20ms, the duration of current pulse width at low level is 1ms, and the density of reverse current is 200A/m²The duration of the high level and the duration of the low level of the current pulse width are both 1ms, the electrolysis temperature is 30 ℃, and the circulating electrolysis is carried out according to the mode that the electrolyte enters from the inlet of the electrolytic cell and exits from the outlet of the electrolytic cell. When about two thirds of the silver particles in the anode titanium basket are left, the silver particles are supplemented through an automatic adding device.

(3) Electrolyzing for 2 hours to obtain metal silver at the cathode, stripping the metal silver from the cathode, washing and drying the metal silver obtained by stripping the glass, and detecting and analyzing by GD-MS to obtain the metal silver with the purity of 99.9992%.

Comparative example 4

Referring to comparative example 3, the difference from comparative example 3 is that the concentration of sodium oxalate in the electrolyte is 4g/L, the concentration of polyacrylamide is 0.5g/L, and the purity of the cathode product, namely, metallic silver, is 99.996% by GD-MS detection analysis.

Comparative example 5

Referring to comparative example 3, the electrolyte does not contain polyacrylamide unlike comparative example 3, and the cathode product, metallic silver, is 99.999% pure by GD-MS detection.

Comparative example 6

Referring to comparative example 3, the electrolyte does not contain sodium oxalate, and the cathode product, namely, silver, has a purity of 99.997% through GD-MS detection analysis, which is different from comparative example 3.

Comparative example 7

(1) The recovered silver jewelry (silver bracelets and silver earrings, the average purity is 99%) is cleaned and degreased, then the jewelry is crushed and sieved by a sieve of 150 meshes to obtain silver particles with the average particle size of 150 meshes, the silver particles are placed in an anode titanium basket, and a filter bag is sleeved outside the anode titanium basket.

(2) Placing the anode titanium basket in electrolyte, taking a titanium plate as a cathode, wherein the electrolyte contains silver nitrate, sodium oxalate and polyacrylamide, and AgNO₃Has a concentration of 120g/L, a concentration of sodium oxalate of 3g/L and a concentration of polyacrylamide of 0.02g/L, adjusts the pH value of the electrolyte to 3 by using nitric acid, adopts direct current electrolysis, and has a current density of 500A/m²The electrolysis temperature is 35 ℃, and the circular electrolysis is carried out according to the mode that the electrolyte enters from the inlet of the electrolytic cell and exits from the outlet of the electrolytic cell. When about two thirds of the silver particles in the anode titanium basket are left, the silver particles are supplemented through an automatic adding device.

(3) Electrolyzing for 3 hours to obtain metal silver at the cathode, then stripping the metal silver from the cathode, washing and drying the metal silver obtained by stripping the glass, and analyzing by GD-MS detection to obtain the metal silver with the purity of 99.9997%.

Comparative example 8

(1) The recovered silver jewelry (silver bracelet and silver earring, average purity is 99.9%) is cleaned, degreased, then crushed and cast into an anode plate, and a filter bag is sleeved outside the anode plate.

(2) Placing the anode plate obtained in the step (1) in electrolyte, taking a titanium plate as a cathode, wherein the electrolyte contains silver nitrate, sodium oxalate and polyacrylamide, and AgNO₃Is 150g/L, the concentration of sodium oxalate is 5g/L and the concentration of polyacrylamide is 0.03g/L, nitric acid is injected into an electrolytic cell until the pH value of the electrolyte is 3, periodic reverse electrolysis is adopted, wherein the forward current density is 650A/m²The high level duration of the current pulse width is 50ms, the low level duration is 10ms, and the reverse current density is 250A/m²The duration of the high level and the duration of the low level of the current pulse width are both 5ms, the electrolysis temperature is 40 ℃, and the circulating electrolysis is carried out according to the mode that the electrolyte enters from the inlet of the electrolytic cell and exits from the outlet of the electrolytic cell. When the anode plate is left by about one third, the electrolysis is stopped.

(3) And obtaining metal silver at the cathode, stripping the metal silver from the cathode, washing and drying the metal silver obtained by glass stripping, and obtaining the metal silver with the purity of 99.99993% through GD-MS detection analysis.

It can be seen from examples 1 to 3 and comparative examples 1 and 8 that residual anodes appear when the recovered silver products are made into anode plates, and since the electrolyte does not contain sodium oxalate and polyacrylamide, the purity of the recovered silver products is only 4N grade after purification, while examples 1 to 3 do not have residual anodes, and the purity reaches 6N grade, and meanwhile, a fusion casting process is not needed, so that the recovery process is greatly simplified, the purification efficiency is high, and the energy consumption can be saved. Even if the recovered silver product is cast into an anode plate, and the electrolyte contains sodium oxalate and polyacrylamide, the purification can reach 6N grade, but due to casting and residual anode, on one hand, the purification time is longer, the purification efficiency is low, and on the other hand, continuous electrolytic purification cannot be realized.

It can be seen from examples 1 to 3 and comparative example 2 that since the electrolyte solution does not contain sodium oxalate and polyacrylamide, even if the recovered silver product is directly electrolyzed after being pulverized, although there is no anode scrap, the purity of the purified silver product only reaches 5N grade, and it is still difficult to achieve the high purity requirement of 6N grade.

It can be seen from examples 1 to 3 and comparative example 3 that when the concentration of sodium oxalate in the electrolyte reached 6g/L, the purity of the purified silver was reduced to 5N grade, indicating that the content of sodium oxalate in the electrolyte should not be too high.

It can be seen from examples 1 to 3 and comparative example 4 that when the concentration of polyacrylamide in the electrolyte reaches 0.5g/L, the purity of the purified silver is reduced to 4N grade, indicating that the content of polyacrylamide in the electrolyte should not be too high.

As can be seen from examples 1 to 3 and comparative examples 5 and 6, the purity of the purified silver is reduced without polyacrylamide or sodium oxalate in the electrolyte, and the reduction range of the purified silver without sodium oxalate is larger, and the purity is only 4N grade.

As can be seen from examples 1 to 3 and comparative example 7, the purity of the purified silver was 5N grade using direct current electrolysis without periodic reverse electrolysis.

In conclusion, the silver purification method provided by the invention has the effects of high purification purity, high purification efficiency and capability of realizing continuous electrolytic purification, and simultaneously solves the problems of anode scrap and complex purification process.

Various other modifications and changes may be made by those skilled in the art based on the above-described technical solutions and concepts, and all such modifications and changes should fall within the scope of the claims of the present invention.

Claims

1. A method of purifying silver, comprising the steps of:

crushing a clean recovered silver product with the purity of more than 99.0 percent, and placing the crushed recovered silver product into an anode titanium basket externally sleeved with a filter bag;

placing the anode titanium blue in an electrolytic tank, taking a titanium plate as a cathode, and introducing sodium oxalate, polyacrylamide and AgNO₃The electrolyte of (1);

introducing nitric acid into the electrolytic bath to maintain the pH value of the electrolyte at 2.0-3.0, and then carrying out periodic reverse electrolysis treatment at the temperature of 30-40 ℃;

and obtaining the metallic silver with the purity of more than 99.9999 percent on the cathode.

2. The method of purifying silver as claimed in claim 1, wherein said AgNO is present in said electrolyte₃The concentration of the sodium oxalate is 100g/L-150g/L, the concentration of the sodium oxalate is 1g/L-5g/L, and the concentration of the polyacrylamide is 0.01g/L-0.03 g/L.

3. The method for purifying silver according to claim 1, wherein the mass concentration ratio of the sodium oxalate to the polyacrylamide in the electrolyte is 50: 150.

4. the method for purifying silver according to claim 1, wherein the conditions of the periodic reverse electrolysis treatment are: the forward current density is 500A/m²-650A/m²The high level time and the low level time of the current pulse width are respectively 20ms-50ms and 1ms-10 ms; the reverse current density is 200A/m²-250A/m²The duration of the high level and the duration of the low level of the current pulse width are both 1ms-5 ms.

5. The method of purifying silver as claimed in claim 1, wherein the introduction of said electrolytic solution into said electrolytic cell and the discharge of said electrolytic solution from said electrolytic cell are continued during said periodic reverse electrolysis treatment.

6. The method of purifying silver as claimed in claim 1, wherein the crushed silver product has a particle size of 150 mesh to 600 mesh.

7. The method of purifying silver as claimed in any one of claims 1 to 6, wherein the purity of the recovered silver product is between 99.0% and 99.9%.

8. The method of purifying silver as claimed in any one of claims 1 to 6, wherein said recovered silver article comprises at least one of a silver bracelet, a silver earring, a silver necklace, and a silver ring.

9. A silver product containing metallic silver purified by the silver purification method according to any one of claims 1 to 8.