Silver purification method

Abstract

The invention discloses a silver purification method which comprises the following steps: (1) taking a crude silver plate containing more than or equal to 95% of Ag as an anode and a titanium sheet as a cathode, respectively putting the anodes and the cathodes into an anode chamber and a cathode chamber of a cation diaphragm electrolytic cell, introducing an electrolyte containing nitric acid, silver nitrate and an impurity complexing agent into the anode chamber, introducing an acidic silver nitrate electrolyte into the cathode, the impurity complexing agent is one of ethylene diamine tetraacetic acid disodium salt, 1-hydroxyethylidene-1, 1-diphosphonic acid and diethylene triamine penta (methylene phosphonic acid); (2) electrolysis is started, direct current is introduced, electrolysis is started, high-purity silver is separated out from a cathode, and the purity of the high-purity silver is larger than or equal to 99.99%; compared with other conventional silver electrolysis methods, the method has the advantages that the requirement for impurities of the anode crude silver raw material is lower, the crude silver does not need to be subjected to fire refining pretreatment, and the cost is lower.

Description

Technical Field

[0001] This invention relates to the technical field of precious metal purification processes, and in particular to a method for purifying silver. Background Technology

[0002] High-purity silver, due to its excellent electrical and thermal conductivity, antibacterial properties, and corrosion resistance, is widely used in many high-end fields such as electronics and semiconductors, new energy, medical and health, and aerospace. With the rapid development of emerging fields such as photovoltaics, electronics, semiconductors, new energy vehicles, humanoid robots, and medical and optical equipment, the global high-purity silver market is expected to expand at a compound annual growth rate of 15%, and the demand gap for high-purity silver will continue to widen.

[0003] Currently, silver purification methods mainly include electrolysis, chemical reduction, pyrometallurgical refining, extraction, and ion exchange. For example, invention patent CN120421525A synthesized high-purity silver powder with good dispersibility, pore structure, and specific surface area through chemical reduction, but this method suffers from drawbacks such as high reagent consumption, long process, and the generation of large amounts of waste liquid. Invention patent CN116574915A synthesized high-purity silver powder with a purity ≥99.999wt% using pyrometallurgical refining, but this method suffers from drawbacks such as high energy consumption and large equipment investment. Invention patent CN1136322C discloses a method for extracting and recovering silver, which synthesizes high-purity silver through extraction, back-extraction, and reduction steps, but the extraction method suffers from drawbacks such as complex process and long process. Among these methods for refining silver, electrolysis has become the mainstream method for purifying crude silver due to its advantages such as short process, simple operation, low energy consumption, high product purity, and stable process. For example, invention patent CN115074783B synthesized 6N grade high-purity silver powder through electrolysis, but it requires 4N grade No. 1 silver ingots as raw materials, which places stringent requirements on the purity of the raw materials. Therefore, there is an urgent need for a simple, low-cost, and efficient method for refining silver. Summary of the Invention

[0004] The purpose of this invention is to provide a method for purifying silver in response to the above-mentioned situation. This method utilizes a cation membrane to selectively couple impurities through selective complexation, thereby achieving green and efficient purification of crude silver.

[0005] The specific solution of this invention is: a method for purifying silver, comprising the following steps:

[0006] (1) Using a crude silver plate containing Ag≥95% as the anode and a titanium sheet as the cathode, they are placed in the anode chamber and cathode chamber of a cation membrane electrolytic cell, respectively. An electrolyte containing nitric acid, silver nitrate and impurity complexing agent is introduced into the anode chamber, and an acidic silver nitrate electrolyte is introduced into the cathode. The impurity complexing agent is one of ethylenediaminetetraacetic acid disodium salt, hydroxyethylidene diphosphate, and diethylenetriaminepentamethylidene phosphonic acid.

[0007] (2) Start electrolysis: Apply DC current to start electrolysis. High-purity silver is deposited at the cathode. The purity of the high-purity silver is ≥99.99%.

[0008] Furthermore, in the electrolyte of the anode chamber in step (1) of the present invention, the concentration of AgNO3 is 80-250 g / L, the concentration of HNO3 is 1-15 g / L, and the concentration of impurity complexing agent is 1-30 g / L.

[0009] Furthermore, in step (1) of this invention, the concentration of AgNO3 in the cathode chamber electrolyte is 80-150 g / L, and the concentration of HNO3 is 1-15 g / L.

[0010] Furthermore, in step (2) of this invention, the cathode current density during electrolysis is 50–1000 A / m. 2 .

[0011] The present invention has the following beneficial effects:

[0012] (1) The present invention uses an impurity complexing agent to selectively complex Cu in the electrolyte. 2+ Pb 2+ Fe 3+ Bi 3+ Sb 3+ Impurity ions are removed, altering their ionic form and diffusion rate. This, combined with the effects of the coupled electric field and the selective action of the ion membrane, reduces the distribution of impurity elements near the cathode, thereby improving the purity of electrolytic silver products.

[0013] (2) Compared with other conventional silver electrolysis methods, this method has more lenient requirements for impurities in the crude silver raw material at the anode, and does not require pyrometallurgical refining pretreatment of the crude silver, thus having a lower cost advantage. Detailed Implementation

[0014] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0015] A method for purifying silver includes the following steps:

[0016] (1) Using a crude silver plate containing Ag≥95% as the anode and a titanium sheet as the cathode, they are placed in the anode chamber and cathode chamber of a cation membrane electrolytic cell, respectively. An electrolyte containing nitric acid, silver nitrate, and an impurity complexing agent is introduced into the anode chamber, and an acidic silver nitrate electrolyte is introduced into the cathode. The impurity complexing agent is one of ethylenediaminetetraacetic acid disodium salt, hydroxyethylidene diphosphate, and diethylenetriaminepentamethylidene phosphonic acid. Further, in the electrolyte of the anode chamber in step (1) of the present invention, the concentration of AgNO3 is 80-250 g / L, the concentration of HNO3 is 1-15 g / L, and the concentration of the impurity complexing agent is 1-30 g / L. Further, in the electrolyte of the cathode chamber in step (1) of the present invention, the concentration of AgNO3 is 80-150 g / L, and the concentration of HNO3 is 1-15 g / L.

[0017] (2) Start electrolysis: Apply direct current to start electrolysis. High-purity silver is deposited at the cathode, with a purity ≥99.99%. Furthermore, in step (2) of this invention, the cathode current density during electrolysis is 50-1000 A / m. 2 .

[0018] The specific implementation method is as follows:

[0019] Example 1

[0020] Using a crude silver plate containing ≥95% Ag as the anode and a titanium sheet as the cathode, the plates were placed in the anode and cathode chambers of a cation exchange membrane electrolyzer, respectively. An electrolyte solution with an AgNO3 concentration of 250 g / L, an HNO3 concentration of 15 g / L, and an impurity complexing agent (disodium ethylenediaminetetraacetate) concentration of 30 g / L was introduced into the anode chamber. An electrolyte solution with an AgNO3 concentration of 150 g / L and an HNO3 concentration of 15 g / L was introduced into the cathode chamber. The cathode current density was 800 A / m. 2 Under these conditions, the power supply was turned on for electrolytic refining, and the high-purity silver obtained from the cathode had a purity of 99.997%.

[0021] Example 2

[0022] Using a crude silver plate containing ≥95% Ag as the anode and a titanium sheet as the cathode, the two plates were placed in the anode and cathode chambers of a cation exchange membrane electrolytic cell, respectively. An electrolyte solution with AgNO3 concentration of 80 g / L, HNO3 concentration of 5 g / L, and ethylenediaminetetraacetic acid disodium salt concentration of 1 g / L was introduced into the anode chamber. An electrolyte solution with AgNO3 concentration of 80 g / L and HNO3 concentration of 5 g / L was introduced into the cathode chamber. The cathode current density was 200 A / m. 2 Under these conditions, the power supply is turned on for electrolytic refining, and the high-purity silver obtained at the cathode has a purity of 99.998%.

[0023] Example 3

[0024] Using a crude silver plate containing ≥95% Ag as the anode and a titanium sheet as the cathode, the two plates were placed in the anode and cathode chambers of a cation exchange membrane electrolyzer, respectively. An electrolyte solution with an AgNO3 concentration of 200 g / L, an HNO3 concentration of 10 g / L, and an impurity complexing agent hydroxyethylidene diphosphate concentration of 15 g / L was introduced into the anode chamber. An electrolyte solution with an AgNO3 concentration of 100 g / L and an HNO3 concentration of 10 g / L was introduced into the cathode chamber. The cathode current density was 400 A / m. 2 Under these conditions, the power supply is turned on for electrolytic refining, and the high-purity silver obtained at the cathode has a purity of 99.999%.

[0025] Example 4

[0026] Using a crude silver plate containing ≥95% Ag as the anode and a titanium sheet as the cathode, the two plates were placed in the anode and cathode chambers of a cation exchange membrane electrolytic cell, respectively. An electrolyte solution with an AgNO3 concentration of 150 g / L, an HNO3 concentration of 5 g / L, and an impurity complexing agent (disodium ethylenediaminetetraacetate) concentration of 5 g / L was introduced into the anode chamber. An electrolyte solution with an AgNO3 concentration of 100 g / L and an HNO3 concentration of 5 g / L was introduced into the cathode chamber. The cathode current density was 200 A / m. 2 Under these conditions, the power supply is turned on for electrolytic refining, and the high-purity silver obtained at the cathode has a purity of 99.998%.

[0027] Example 5

[0028] Using a crude silver plate containing ≥95% Ag as the anode and a titanium sheet as the cathode, the plates were placed in the anode and cathode chambers of a cation exchange membrane electrolyzer, respectively. An electrolyte solution with an AgNO3 concentration of 200 g / L, an HNO3 concentration of 5 g / L, and a diethylenetriaminepentamethylphosphonic acid (DMI) complexing agent concentration of 30 g / L was introduced into the anode chamber. An electrolyte solution with an AgNO3 concentration of 150 g / L and an HNO3 concentration of 5 g / L was introduced into the cathode chamber. The cathode current density was 600 A / m. 2 Under these conditions, the power supply is turned on for electrolytic refining, and the high-purity silver obtained at the cathode has a purity of 99.999%.

[0029] Example 6

[0030] Using a crude silver plate containing ≥95% Ag as the anode and a titanium sheet as the cathode, the plates were placed in the anode and cathode chambers of a cation exchange membrane electrolytic cell, respectively. An electrolyte solution with AgNO3 concentration of 100 g / L, HNO3 concentration of 1 g / L, and ethylenediaminetetraacetic acid disodium salt (EDTA) concentration of 1 g / L was introduced into the anode chamber. An electrolyte solution with AgNO3 concentration of 80 g / L and HNO3 concentration of 1 g / L was introduced into the cathode chamber. The cathode current density was 50 A / m. 2 Under these conditions, the power supply is turned on for electrolytic refining, and the high-purity silver obtained at the cathode has a purity of 99.999%.

[0031] The above scheme, through the use of impurity complexing agents, can selectively complex Cu in the electrolyte. 2+ Pb 2+ Fe 3+ Bi 3+ Sb 3+ This method modifies the ionic form and diffusion rate of impurity ions, coupled with the effects of the electric field and the selectivity of the ion-exchange membrane, reducing the distribution of impurity elements near the cathode and thus improving the purity of electrolytic silver products. Compared with other conventional silver electrolysis methods, this method has more lenient requirements on the impurities in the crude silver raw material at the anode, eliminates the need for pyrometallurgical refining pretreatment of the crude silver, and has a lower cost advantage.

Claims

1. A method for purifying silver, characterized in that, Includes the following steps: (1) Using a crude silver plate containing Ag≥95% as the anode and a titanium sheet as the cathode, they are placed in the anode chamber and cathode chamber of a cation membrane electrolytic cell, respectively. An electrolyte containing nitric acid, silver nitrate and impurity complexing agent is introduced into the anode chamber, and an acidic silver nitrate electrolyte is introduced into the cathode. The impurity complexing agent is one of ethylenediaminetetraacetic acid disodium salt, hydroxyethylidene diphosphate, and diethylenetriaminepentamethylidene phosphonic acid. (2) Start electrolysis: Apply DC current to start electrolysis. High-purity silver is deposited at the cathode. The purity of the high-purity silver is ≥99.99%.

2. The method for purifying silver according to claim 1, characterized in that, In the electrolyte of the anode chamber in step (1), the concentration of AgNO3 is 80-250 g / L, the concentration of HNO3 is 1-15 g / L, and the concentration of impurity complexing agent is 1-30 g / L.

3. The method for purifying silver according to claim 1, characterized in that, In step (1), the concentration of AgNO3 in the cathode electrolyte is 80-150 g / L, and the concentration of HNO3 is 1-15 g / L.

4. The method for purifying silver according to claim 1, characterized in that, In step (2), the cathode current density during electrolysis is 50–1000 A / m. 2 .