A method for preparing pure silver from silver chloride

Abstract

The present application discloses a method for preparing pure silver from silver chloride, which relates to the technical field of precious metal recovery methods. The method comprises the following steps: adding ammonia water to silver chloride solid until all the silver chloride is dissolved, adding a reducing agent to the silver ammonia solution in portions, heating and stirring until the solution is clear, performing solid-liquid separation by centrifugation or static filtration, washing the separated reduced silver, drying it, detecting the contents of copper, lead, iron, antimony, bismuth, palladium, and selenium therein, and selecting a washing solution for impurity removal, washing, and drying according to the exceeded impurity elements to obtain high-purity silver powder. The method of the present application can directly utilize silver chloride containing multiple components to prepare pure silver with a silver content of more than 99.99%, and has a small loss of silver amount and low impurity content, providing good guidance for the recovery and treatment of silver chloride.

Description

Technical Field

[0001] The present application relates to a method for preparing pure silver from silver chloride, belonging to the technical field of precious metal recovery methods. Background Art

[0002] As an important industrial raw material, silver has relatively stable physical and chemical properties, good electrical and thermal conductivity, and is ductile. It has been widely used in electronic and electrical materials, photosensitive materials, chemical and chemical engineering materials. With the increasing consumption of silver and silver alloys, the amount of silver-containing waste generated each year is also increasing. From the perspective of resource recycling and the recycling value of silver, recovering silver and other metals from silver-containing waste has significant economic and social benefits.

[0003] A considerable amount of silver chloride solid is generated during the refining, detection, and processing of precious metals. Such silver chloride often contains a large amount of solid insoluble substances, solid suspended substances, and various metal ions, with a complex composition and is not easy to recycle.

[0004] Chinese Patent CN1122836A discloses a method for recovering silver from silver chloride waste liquid: adding an alkali solution to the silver chloride waste liquid, adjusting the solution to be alkaline, filtering, and then adding ascorbic acid solid or aqueous solution. After conversion, the silver precipitate is filtered and washed with water to obtain product silver, and the silver recovery rate is above 98%.

[0005] Common recovery methods use reducing agents to reduce or use pyrometallurgical smelting to obtain crude silver with a low silver content, and cannot provide a method for directly using silver chloride with a high impurity content as a raw material to produce pure silver. Therefore, the present application provides a method for directly using silver chloride with a high impurity content as a raw material to produce pure silver. Summary of the Invention

[0006] The object of the present invention is to provide a method for preparing pure silver from silver chloride. This method uses silver chloride with a complex composition as a raw material to prepare pure silver. By using this method for treatment, pure silver with a silver content of more than 99.99% can be obtained, and the silver loss is small and the impurity content is low, providing a good guiding role for the recovery and treatment of silver chloride.

[0007] To achieve the above object, the present application is realized through the following technical solutions: A method for preparing pure silver from silver chloride, comprising the following steps:

[0008] (S1) Add ammonia water to silver chloride solid until all the silver chloride is dissolved, and collect the silver ammonia solution by centrifugation or filtration;

[0009] (S2) Add a reducing agent to the silver ammonia solution, heat and stir until the solution is clear, and centrifuge or let it stand still and filter to obtain the first filtrate and the first reduced silver;

[0010] (S3) Add a reducing agent to the first filtrate, heat and stir until the solution becomes clear, and obtain a second filtrate and second reduced silver by centrifugation or static filtration;

[0011] (S4) Wash the second reduced silver to obtain first washed silver; take a sample of the first washed silver for detection, soak it in different washing solutions according to the detection results, centrifuge or filter and wash, collect the second washed silver, and dry it to obtain high-purity silver powder.

[0012] Specifically, in step (S4), the washing solution is one or more of ammonium bifluoride solution, glacial acetic acid solution or EDTA solution.

[0013] Specifically, it further includes a step of washing the silver chloride solid before step (S1).

[0014] Specifically, in steps (S2) and (S3), the reducing agent is any one of sodium metabisulfite, sodium sulfite or hydrazine hydrate.

[0015] Specifically, in step (S2), the addition amount of the reducing agent is 0.01 - 0.1 times the silver content in silver chloride; in step (S3), the addition amount of the reducing agent is 0.8 - 0.9 times the silver content in silver chloride.

[0016] Specifically, in steps (S2) and (S3), the heating temperature is 75 - 95 °C, the stirring time is 1.5 - 2.5 hours, and the static time is 50 - 70 min.

[0017] Specifically, in step (S4), the soaking time is 1 - 4 h.

[0018] Specifically, the silver content in the high-purity silver powder is not less than 99.99%.

[0019] Preferably, add an excessive amount of sodium metabisulfite, sodium sulfite or hydrazine hydrate to the second filtrate, heat to 75 - 95 °C, stir for 1.5 - 2.5 h until the solution becomes clear, stand for 50 - 70 min, filter and wash to separate, and obtain silver and some base metals for standby.

[0020] The beneficial effects of this application include but are not limited to:

[0021] 1. According to a method for preparing pure silver from silver chloride provided by this application, pure silver can be directly prepared from silver chloride with high impurity content, and pure silver with a purity of more than 99.99% can be obtained. Moreover, the silver loss is small and the impurity content is low, which provides a good guiding role for the recovery and treatment of silver chloride and is suitable for large-scale promotion and application.

[0022] 2. A method for preparing pure silver from silver chloride provided by the present application. Before treating silver chloride, most of the soluble metal ions, nitrate ions in the silver chloride solid are separated from the silver chloride by washing, so as to improve the subsequent treatment speed and the purity of the obtained silver.

[0023] 3. A method for preparing pure silver from silver chloride provided by the present application. The reduced silver is obtained by adding the reducing agent in batches. First, a small amount of reducing agent is added to reduce the metal impurities that may be less active than silver. Then, an insufficient amount of reducing agent is added to reduce most of the silver, and the insufficient amount of reducing agent makes part of the silver ions still exist in the solution, ensuring that other impurities will not be reduced and enter the silver powder, so as to increase the impurity content in the silver.

[0024] 4. A method for preparing pure silver from silver chloride provided by the present application. The first washed silver is sampled and detected for the contents of copper, lead, iron, antimony, bismuth, palladium, and selenium. The washing solution is selected for impurity removal according to the exceeded impurity elements. If iron exceeds the standard, the silver is soaked in ammonium bifluoride solution for impurity removal. If copper exceeds the standard, EDTA solution is selected for impurity removal. If lead exceeds the standard, acetic acid solution is selected for impurity removal. The impurity removal is precise, the purity of the product silver is improved, the silver content reaches more than 99.99%, it is suitable for long-term use and can be popularized and applied to the washing and impurity removal of electrolytic silver powder.

[0025] 5. A method for preparing pure silver from silver chloride provided by the present application. An excessive amount of reducing agent is added to the filtrate after the pure silver is reduced, and the silver and part of the base metals are obtained for standby, preventing the loss of excessive metal ions in the filtrate and reducing the difficulty of subsequent sewage treatment. Specific Embodiments

[0026] The present invention will be further described below in conjunction with specific embodiments. It should be pointed out here that the following embodiments cannot be understood as limiting the protection scope of the present invention. Those of ordinary skill in the art make some simple substitutions or adjustments according to the content of the present invention, which are all within the protection scope of the present invention. Unless otherwise specified, the raw materials in the embodiments of the present application are all purchased through commercial channels.

[0027] Example 1

[0028] (S1) The silver chloride solid with a silver content of 30% is washed with pure water, and ammonia water composed of concentrated ammonia water and water with a volume ratio of 1:9 is added until all the silver chloride is dissolved, and the silver ammonia solution is filtered and collected;

[0029] (S2) Hydrazine hydrate with 0.01 times the silver content in the silver chloride is added to the silver ammonia solution, heated to 75 °C, stirred for 1.5 h until the solution is clear, left standing for 50 min, and filtered to obtain the first filtrate and the first reduced silver;

[0030] (S3) Add hydrazine hydrate which is 0.8 times the silver content in silver chloride to the first filtrate, heat to 75 °C, stir for 1.5 h until the solution becomes clear, let it stand for 50 min, filter to obtain the second filtrate and the second reduced silver;

[0031] (S4) Wash the second reduced silver to obtain the first washed silver; when sampling and testing the first washed silver shows that the iron impurity content exceeds the standard, soak it in ammonium bifluoride solution for 4 h, filter and wash, collect the second washed silver, and dry the second washed silver to obtain high-purity silver powder.

[0032] Example 2

[0033] (S1) Wash the silver chloride solid with a silver content of 70% with pure water, and add ammonia water composed of concentrated ammonia water and water with a volume ratio of 1:9 until all the silver chloride dissolves, and filter to collect the silver ammonia solution;

[0034] (S2) Add sodium sulfite which is 0.1 times the silver content in silver chloride to the silver ammonia solution, heat to 95 °C, stir for 2.5 h until the solution becomes clear, centrifuge for 70 min, filter to obtain the first filtrate and the first reduced silver;

[0035] (S3) Add sodium sulfite which is 0.9 times the silver content in silver chloride to the first filtrate, heat to 95 °C, stir for 2.5 h until the solution becomes clear, centrifuge for 70 min, filter to obtain the second filtrate and the second reduced silver;

[0036] (S4) Wash the second reduced silver to obtain the first washed silver; when sampling and testing the first washed silver shows that the copper content exceeds the standard, soak the first washed silver in an EDTA solution for 1 h, and centrifuge and wash to collect the second washed silver; dry the second washed silver to obtain high-purity silver powder.

[0037] Example 3

[0038] (S1) Wash the silver chloride solid with a silver content of 60% with pure water, and add ammonia water composed of concentrated ammonia water and water with a volume ratio of 1:9 until all the silver chloride dissolves, and filter to collect the silver ammonia solution;

[0039] (S2) Add sodium metabisulfite which is 0.06 times the silver content in silver chloride to the silver ammonia solution, heat to 80 °C, stir for 2 h until the solution becomes clear, let it stand for 60 min, filter to obtain the first filtrate and the first reduced silver;

[0040] (S3) Add sodium metabisulfite which is 0.85 times the silver content in silver chloride to the first filtrate, heat to 80 °C, stir for 2 h until the solution becomes clear, let it stand for 60 min, filter to obtain the second filtrate and the second reduced silver;

[0041] (S4) Wash the second reduced silver to obtain the first washed silver; sample and test the first washed silver. When the test results show that the impurity content does not exceed the standard, dry the first washed gold to obtain high-purity silver powder.

[0042] Example 4

[0043] (S1) Wash the silver chloride solid with a silver content of 55% with pure water, and add ammonia water composed of concentrated ammonia water and water with a volume ratio of 1:9 until all the silver chloride is dissolved, and filter to collect the silver ammonia solution;

[0044] (S2) Add sodium sulfite 0.06 times the silver content in the silver chloride to the silver ammonia solution, heat to 84 °C, stir for 1.8 h until the solution is clear, centrifuge for 68 min, filter to obtain the first filtrate and the first reduced silver;

[0045] (S3) Add sodium sulfite 0.89 times the silver content in the silver chloride to the first filtrate, heat to 86 °C, stir for 2.0 h until the solution is clear, let stand for 56 min, filter to obtain the second filtrate and the second reduced silver;

[0046] (S4) Wash the second reduced silver to obtain the first washed silver; sample and test the first washed silver. When the test results show that the lead content exceeds the standard, soak it in an acetic acid solution for 10 h, filter and wash, and collect the second washed silver; dry the second washed silver to obtain high-purity silver powder.

[0047] Comparative Example 1

[0048] (S1) Add ammonia water composed of concentrated ammonia water and water with a volume ratio of 1:9 to the silver chloride solid with a silver content of 60% until all the silver chloride is dissolved, and filter to collect the silver ammonia solution;

[0049] (S2) Add sodium metabisulfite 0.06 times the silver content in the silver chloride to the silver ammonia solution, heat to 80 °C, stir for 2 h until the solution is clear, let stand for 60 min, filter to obtain the first filtrate and the first reduced silver;

[0050] (S3) Add sodium metabisulfite 0.85 times the silver content in the silver chloride to the first filtrate, heat to 80 °C, stir for 2 h until the solution is clear, let stand for 60 min, filter to obtain the second filtrate and the second reduced silver;

[0051] (S4) Wash the second reduced silver to obtain the first washed silver; soak the first washed silver in an ammonium bifluoride solution for 10 h, filter and wash, and collect the second washed silver; dry the second washed silver to obtain high-purity silver powder.

[0052] Comparative Example 2

[0053] (S1) Wash the silver chloride solid with a silver content of 60% with pure water, and add ammonia water composed of concentrated ammonia water and water with a volume ratio of 1:9 until all the silver chloride is dissolved, and then filter to collect the silver ammonia solution;

[0054] (S2) Add sodium metabisulfite which is 0.9 times the silver content in the silver chloride to the silver ammonia solution, heat to 80 °C, stir for 2 h until the solution is clear, let it stand for 60 min, and then filter to obtain the first filtrate and the first reduced silver;

[0055] (S3) Wash the first reduced silver to obtain the first washed silver; soak the first washed silver in an ammonium bifluoride solution for 10 h, filter and wash it, and collect the second washed silver; dry the second washed silver to obtain high-purity silver powder.

[0056] Comparative Example 3

[0057] (S1) Wash the silver chloride solid with a silver content of 60% with pure water, and add ammonia water composed of concentrated ammonia water and water with a volume ratio of 1:9 until all the silver chloride is dissolved, and then filter to collect the silver ammonia solution;

[0058] (S2) Add sodium metabisulfite which is 0.06 times the silver content in the silver chloride to the silver ammonia solution, heat to 80 °C, stir for 2 h until the solution is clear, let it stand for 60 min, and then filter to obtain the first filtrate and the first reduced silver;

[0059] (S3) Add sodium metabisulfite which is 0.98 times the silver content in the silver chloride to the first filtrate, heat to 80 °C, stir for 2 h until the solution is clear, let it stand for 60 min, and then filter to obtain the second filtrate and the second reduced silver;

[0060] (S4) Wash the second reduced silver to obtain the first washed silver; soak the first washed silver in an ammonium bifluoride solution for 10 h, filter and wash it, and collect the second washed silver; dry the second washed silver to obtain high-purity silver powder.

[0061] The examples 1-4 and comparative examples 1-3 were respectively analyzed according to GB / T25934.1-2010, and the specific data are shown in Table 1.

[0062] Serial number Ag purity (%) Example 1 99.994 Example 2 99.989 Example 3 99.995 Example 4 99.994 Comparative Example 1 99.994 Comparative Example 2 99.955 Comparative Example 3 99.922

[0063] Table 1

[0064] The results show that the silver purity finally obtained by using the method defined in this application is higher than 99.99%. Among them, the silver purity prepared by the steps adopted in Example 3 is the best.

[0065] The difference between Comparative Example 1 and Example 3 is that there is no step of washing the silver chloride solid in step (S1), and the remaining steps are the same as those in Example 3. Washing the silver chloride solid can remove the nitrate ions, most of the metal ions such as iron, copper, and lead contained in it in advance. In the case of not washing, a small amount of reducing agent added first may not be able to reduce some impurities, resulting in an increase in the content of iron, copper, and lead carried out by the reduced silver powder. Although it does not affect the final purity of silver, it increases the difficulty of subsequent washing treatment.

[0066] The difference between Comparative Example 2 and Example 3 is that an excessive amount of reducing agent is not added at one time, and the remaining steps are the same as those in Example 3, which will cause metals less reactive than silver to exist in the reduced silver, resulting in an increase in the silver impurity content.

[0067] The difference between Comparative Example 3 and Example 3 is that an excessive amount of reducing agent is added in step (S3), and the remaining steps are the same as those in Example 3. Excessive reduction will cause the reduction of other metals and an increase in the impurity content.

[0068] The above data show that the method of the present application can realize the recovery of silver chloride to prepare pure silver, and the obtained silver content is higher than 99.99%, the silver loss is small, and the impurity content is low, which provides a good guiding role for the recovery and treatment of silver chloride. Among them, the method of selecting a detergent according to the impurity content is also applicable to the washing of electrolytic silver powder and is suitable for large-scale popularization and application.

[0069] As described above, only the embodiments of the present application are given. The protection scope of the present application is not limited by these specific embodiments, but is determined by the claims of the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the technical idea and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing pure silver from silver chloride, characterized in that, it comprises the following steps: (S1) Add ammonia water to solid silver chloride until all the silver chloride is dissolved, and collect the silver ammonia solution by centrifugation or filtration; (S2) Add a reducing agent to the silver ammonia solution, heat and stir until the solution is clear, then centrifuge or let it stand and filter to obtain a first filtrate and a first reduced silver; the addition amount of the reducing agent is 0.01 - 0.1 times the silver content in silver chloride; (S3) Add a reducing agent to the first filtrate, heat and stir until the solution is clear, then centrifuge or let it stand and filter to obtain a second filtrate and a second reduced silver; the addition amount of the reducing agent is 0.8 - 0.9 times the silver content in silver chloride; (S4) Wash the second reduced silver to obtain a first washed silver; Immerse the first washed silver in a washing solution, then centrifuge or filter and wash it, collect the second washed silver, and dry it to obtain high - purity silver powder.

2. The method for preparing pure silver from silver chloride according to claim 1, characterized in that, in step (S4), the washing solution is one or more of ammonium bifluoride solution, glacial acetic acid solution or EDTA solution.

3. The method for preparing pure silver from silver chloride according to claim 1, characterized in that, in step (S1), the ammonia water is an aqueous solution containing 20% - 30% ammonia.

4. The method for preparing pure silver from silver chloride according to claim 1, characterized in that, it further comprises a step of washing the silver chloride solid before step (S1).

5. The method for preparing pure silver from silver chloride according to claim 1, characterized in that, the silver content in the silver chloride is 30% - 70%.

6. The method for preparing pure silver from silver chloride according to claim 1, characterized in that, in steps (S2) and (S3), the reducing agent is any one of sodium metabisulfite, sodium sulfite or hydrazine hydrate.

7. The method for preparing pure silver from silver chloride according to claim 1, characterized in that, in steps (S2) and (S3), the heating temperature is 75 - 95 °C, the stirring time is 1.5 - 2.5 hours, and the standing time is 50 - 70 min.

8. The method for preparing pure silver from silver chloride according to claim 1, characterized in that, in step (S4), the soaking time is 1 - 4 h.

9. The method for preparing pure silver from silver chloride according to claim 1, characterized in that, the silver content in the high - purity silver powder is not less than 99.99%.