Method for producing first silver by using silver electrolyte purification residues

Abstract

The invention belongs to the technical field of silver electrolytic refining, and particularly relates to a method for producing first silver by using silver electrolyte purification residues, which comprises the following steps: firstly, slurrying the silver electrolytic purification residues by using pure water, adding an acid solution and an oxidizing agent after slurrying, oxidizing and leaching to obtain leached residues and leachate, separating silver from the leached residues by using a silver separation mother solution containing sodium sulfite, adjusting the pH value of the silver separation solution to 4-5 by using a sulfuric acid solution or acidic sulfur dioxide gas to produce crude silver chloride, purifying the crude silver chloride by using a hydrochloric acid solution and adding an oxidizing agent, washing the purified refined silver chloride to be neutral, and reducing by using hydrazine hydrate to produce 99.99% silver powder; and adjusting the leaching solution by using an alkaline solution to produce bismuth concentrate to recover bismuth, and precipitating copper in the solution after bismuth precipitation by using sodium sulfide to produce copper precipitation slag. The method is high in direct recovery rate of silver, simple in process, low in cost, high in comprehensive recovery value of byproducts, environmentally friendly, energy-saving and good in economic benefit.

Description

Technical Field

[0001] The invention belongs to the technical field of silver electrolytic refining, and in particular relates to a method for producing No. 1 silver by purifying slag with silver electrolyte. Background Art

[0002] During the silver electrolysis process, metal elements with a potential more negative than silver in the anode plate enter the electrolyte. The impurity elements in the electrolyte are continuously enriched as the electrolysis proceeds. When a certain concentration is reached, they will precipitate on the cathode and enter the silver powder, affecting the quality of the silver powder. The main metal elements are copper, lead, and bismuth. The methods for purifying the electrolyte during the silver electrolysis process include the method of scrapping the waste liquid and diluting the new liquid, and the method of purifying with silver oxide. The electrolyte purification method is now widely used. During the purification process, the metal elements copper, lead, and bismuth enter the silver oxide to form purified slag. When the copper, lead, and bismuth content in the purified slag reaches a certain mass fraction, the purified slag needs to be opened to recover the valuable metals.

[0003] At present, the commonly used methods for treating slag after silver electrolyte purification are: (1) pyrometallurgy → pyrometallurgy → silver anode plate → electrolytic refining → silver ingot; (2) acid leaching → silver chloride precipitation → silver reduction → silver anode plate → electrolytic refining → silver ingot. Both of these commonly used methods have problems such as long process, low silver recovery rate, long silver turnover, and capital backlog. Chinese patent application number 202311367035.4 discloses a slag treatment device and method after silver electrolysis purification. The slag after silver electrolysis purification uses pure water and nitric acid to leach copper and silver, and oxalic acid is used to precipitate copper. The solution after copper precipitation is used to make silver oxide, and the silver oxide is returned to the electrolyte for purification. However, this method only describes the recovery of silver and copper in the purified slag, and does not consider the open circuit and recovery of lead and bismuth in the purified slag. In the existing treatment methods, the pyrometallurgy has the problems of long process, low silver recovery rate, large amount of nitrogen oxides produced by wet nitric acid leaching, poor on-site environment, and poor quality of output silver powder.

[0004] Therefore, developing a silver electrolyte purification slag treatment method with high silver direct recovery rate, simple process, low cost and high comprehensive recovery value of by-products has become a technical problem that technical personnel in this field urgently need to solve. Summary of the invention

[0005] In view of this, in order to solve the problems existing in the prior art, the present invention provides a method for producing No. 1 silver by purifying slag with silver electrolyte.

[0006] A method for producing No. 1 silver by purifying slag with silver electrolyte, the specific steps comprising:

[0007] (1) Slurrying: Slurrying the silver electrolyte purification slag with pure water;

[0008] (2) Oxidative leaching: Add water to the purified slag of silver electrolyte after pulping in step (1) according to a certain liquid-solid ratio, add an acidic solution, raise the temperature and add an oxidant. After oxidative leaching, lower the temperature and filter to obtain a leaching solution and leaching residue;

[0009] (3) Silver separation with sodium nitrite: Pulp the leaching residue from step (2) with water, adjust the pH value with an alkaline solution, then add a mother liquor for silver separation. After heating and reacting, filter to obtain a silver separation solution and lead sulfate slag, and the lead sulfate slag is sent to lead smelting;

[0010] (4) Acidification and silver precipitation: Adjust the pH value of the silver separation solution from step (3) to acidic with an acidic solution or acidic gas to obtain crude silver chloride and a solution after silver precipitation. Adjust the pH value of the solution after silver precipitation to 9.5 with sodium hydroxide and then use it as the mother liquor for silver separation in step (3) for recycling;

[0011] (5) Oxidative purification: Pulp the crude silver chloride from step (4) with pure water, add an acidic solution, raise the temperature and add an oxidant. After reacting, filter to obtain refined silver chloride and a purified solution. Wash the refined silver chloride with hot water until it is neutral;

[0012] (6) Silver reduction: Pulp the refined silver chloride washed to neutral in step (5) with pure water, raise the temperature and then add a reducing agent until no bubbles are generated in the pulping solution. After stirring and reacting, filter to obtain silver powder and a solution after reduction. Wash the silver powder with hot water and then dry it, and cast it into silver ingots.

[0013] Furthermore, by mass percentage, the purified slag of silver electrolyte includes: 50 - 65% silver, 12 - 20% copper, 4 - 6% lead, and 0.5 - 1% bismuth.

[0014] It should be noted that the purified slag of silver electrolyte is an oxidized silver slag with excessive impurities of copper, lead, and bismuth after repeated use in the silver electrolysis process. To fully disclose the present invention, a method for producing the purified slag of silver electrolyte is now disclosed. Any method for obtaining the purified slag of silver electrolyte without creative work can be used for the preparation of the purified slag of silver electrolyte described in the present invention.

[0015] A method for preparing a purified slag of silver electrolyte includes the following steps:

[0016] S1. Add the silver-containing waste liquid generated during silver electrolysis, adjust the pH to 14 with sodium hydroxide, stir and react, and then filter to obtain oxidized silver slag and a filtrate;

[0017] S2. Pump the silver electrolyte with high impurities during silver electrolysis into a reaction kettle, add the oxidized silver slag obtained in step S1, adjust the pH to 6, raise the temperature to 65°C, and at the same time add sulfuric acid. Stir and react, and then filter to obtain a purified slag and a purified solution. The purified solution is returned to the silver electrolysis system;

[0018] S3. Put the purified slag obtained in step S2 into the wastewater generated in the silver electrolysis process, heat it to 65°C, then add sodium hydroxide to adjust the pH to 14, stir and react, and then filter to obtain regenerated silver oxide slag and the solution after silver precipitation;

[0019] S4. Repeat steps S2 and S3 for the regenerated silver oxide slag obtained in step S3. When the mass fractions of impurities such as copper, lead, and bismuth in the purified slag are greater than 15%, the purified slag is sent for the recovery of valuable metals through an open circuit.

[0020] Furthermore, the specific steps further include:

[0021] (7) Neutralize and precipitate bismuth: Add an alkaline solution to the leaching solution obtained in step (2), adjust the pH to 2 - 3, filter after reaction to obtain bismuth oxychloride and the solution after bismuth precipitation;

[0022] (8) Sulfide precipitation of copper: Add a certain amount of sodium sulfide to the solution after bismuth precipitation in step (7), filter after reaction to obtain copper precipitation slag and the solution after copper precipitation, and the solution after copper precipitation is sent for sewage treatment.

[0023] In some embodiments, the addition amount of sodium sulfide is 1.2 times the theoretical amount.

[0024] Thus, the present invention first uses the oxidation leaching technology to make bismuth and copper enter the leaching solution, while lead remains in the leaching residue in the form of lead sulfate and silver is converted into silver chloride, realizing the separation of lead and silver from bismuth and copper. Then, for the lead and silver in the leaching residue, taking advantage of the property that sodium sulfite can complex silver in silver chloride, silver is leached from the residue and lead remains in the residue, achieving the separation of lead and silver. Finally, by combining acidification silver precipitation and oxidation purification, the impurity elements carried in with silver refining in the process are further removed to produce qualified No. 1 silver. Moreover, for bismuth and copper entering the leaching solution, due to different hydrolysis pH values, bismuth is preferentially hydrolyzed to produce bismuth oxychloride, and then copper is recovered by the sulfide method.

[0025] Furthermore, in step (1), the mass ratio of the slurried silver electrolysis purification slag to the volume of pure water is 1:(0.5 - 1), the slurrying time is 2 - 3 h, and the temperature is normal temperature.

[0026] It should be noted that the slurrying process adopted in the present invention is mainly to completely disperse the materials without generating encapsulation, which is conducive to improving the leaching rates of copper and bismuth and the conversion rate of silver in subsequent oxidation leaching.

[0027] Furthermore, in step (2), the liquid - solid ratio of oxidation leaching is (4 - 6):1, the acidic solution is a 50 - 70 g / L hydrochloric acid solution, the heating temperature is 75 - 85°C, and the oxidant is one or more of sodium chlorate, hypochlorous acid, and hydrogen peroxide.

[0028] It should be noted that by using hydrochloric acid oxidative leaching, copper and bismuth can be converted into cupric chloride and bismuth chloride and enter the solution, while silver is converted into silver chloride. Hydrochloric acid oxidative leaching avoids the problem that metals in elemental state are insoluble in single acid leaching, which affects leaching and silver conversion.

[0029] Furthermore, in the step (3) of separating silver with sodium sulfite, the liquid-solid ratio is (8-10):1, the adjusted pH value is 8-10, and the mother liquor for silver separation is a sodium sulfite solution with a concentration of 210-250 g / L.

[0030] It should be noted that in the present invention, the main components of the leaching residue are lead sulfate and silver chloride. Under the alkaline condition with a pH value of 8-10, sodium sulfite can react with silver chloride to form [Ag(SO3)2] 3- complex ions, and silver enters the solution. Lead sulfate does not react with sodium sulfite and remains in the residue, thus realizing the effective separation of lead and silver. Moreover, the saturation solubility of the sodium sulfite solution is 270 g / L. If the concentration of sodium sulfite is too high during the silver separation process, crystallization will occur; if it is too low, the effective sulfite ions in the solution will be insufficient to provide enough silver separation ability. Therefore, the concentration of sodium sulfite in the mother liquor for silver separation is controlled at 210-250 g / L.

[0031] Furthermore, in step (4), the acidic solution is sulfuric acid, the acidic gas is sulfur dioxide, and the end-point pH is 4-5.

[0032] It should be noted that the [Ag(SO3)2] 3- complex ions in the solution release Ag + under the acidic condition with a pH of 4-5, and combine with Cl - in the solution to form a chloride precipitate, playing a role in preliminary purification.

[0033] Furthermore, in step (5), the liquid-solid ratio of the crude silver chloride slurried with pure water is (4-6):1, the acidic solution is a hydrochloric acid solution with a concentration of 50-70 g / L, the temperature is raised to 75-85 °C, the oxidant is one or more of sodium chlorate, hypochlorous acid, and hydrogen peroxide, and the filtration temperature is 50-60 °C.

[0034] It should be noted that oxidative purification can further remove the impurities in the crude silver chloride, meeting the standard of 99.99% silver.

[0035] Furthermore, in step (6), the liquid-solid ratio of the slurry is (4-6):1, the temperature is raised to 40-60 °C, and the reducing agent is hydrazine hydrate.

[0036] It should be noted that the liquid-solid ratio of (4-6):1 for the slurry ensures that all the silver chloride is dispersed, and when hydrazine hydrate is added, there is no encapsulation and no generation, which affects the quality of the reduced silver powder.

[0037] Compared with the prior art, the method for producing No. 1 silver by using silver electrolyte purification slag disclosed by the present invention slurries the silver electrolytic purification slag with pure water, adds an acidic solution after slurrying, oxidizes and leaches with an oxidant to obtain a leached residue and a leachate. The leached residue is separated from silver with a mother liquor containing sodium sulfite. The silver separation solution is adjusted to a pH of 4-5 with a sulfuric acid solution or acidic sulfur dioxide gas to produce crude silver chloride. The crude silver chloride is purified with a hydrochloric acid solution and an oxidant. The purified refined silver chloride is washed to neutrality and reduced with hydrazine hydrate to produce 99.99% silver powder. The leachate is adjusted with an alkaline solution to produce bismuth concentrate for recovering bismuth, and the solution after bismuth precipitation is used to precipitate copper with sodium sulfide to produce copper precipitation slag. This method adopts an all-wet process flow to produce No. 1 silver product from silver electrolyte with a short process and simplicity, and at the same time efficiently separates valuable metals in the silver electrolyte purification slag. The process of the present invention is simple, easy to operate, has a high direct silver recovery rate, and the valuable metal by-products have a high comprehensive recovery economic value, is environmentally friendly and energy-saving, produces no nitrogen oxides, and has good economic benefits. Brief Description of the Drawings

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0039] Figure 1 It is the process flow diagram of the method for producing No. 1 silver by using silver electrolyte purification slag of the present invention. Detailed Embodiments

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0041] The special term "embodiment" used here, any embodiment described as "exemplary" does not have to be construed as superior to or better than other embodiments. For the performance index tests in the embodiments of this application, unless otherwise specified, the conventional test methods in the art are adopted. It should be understood that the terms described in this application are only for describing special embodiments and are not used to limit the content disclosed in this application.

[0042] Unless otherwise specified, the technical and scientific terms used herein have the same meanings as those generally understood by those of ordinary skill in the technical field to which this application belongs; other test methods and technical means not specifically noted in this application refer to the experimental methods and technical means generally adopted by those of ordinary skill in the art.

[0043] In order to better illustrate the content of the present application, numerous specific details are given in the following specific embodiments. Those skilled in the art should understand that the present application can also be implemented without certain specific details. In the embodiments, some methods, means, instruments, equipment, etc. well-known to those skilled in the art are not described in detail in order to highlight the gist of the present application.

[0044] On the premise of no conflict, the technical features disclosed in the embodiments of the present application can be combined arbitrarily, and the obtained technical solutions belong to the content disclosed in the embodiments of the present application.

[0045] The present invention belongs to the technical field of silver electrolytic refining, and specifically relates to a method for producing No. 1 silver by using silver electrolyte purification slag. First, the silver electrolytic purification slag is slurried with pure water, and after slurrying, an acidic solution and an oxidant are added for oxidative leaching to obtain leaching residue and leaching solution. The leaching residue is separated by a silver separating mother liquor containing sodium sulfite, and the silver separating solution is adjusted to a pH of 4-5 with a sulfuric acid solution or acidic sulfur dioxide gas to produce crude silver chloride. The crude silver chloride is purified with a hydrochloric acid solution and an oxidant, and the purified refined silver chloride is washed to neutrality and reduced with hydrazine hydrate to produce 99.99% silver powder; the leaching solution is adjusted with an alkaline solution to produce bismuth concentrate for recovering bismuth, and copper is precipitated with sodium sulfide from the solution after bismuth precipitation to produce copper precipitation slag. The present invention has a high direct silver recovery rate, a simple process, low cost, high comprehensive recovery value of by-products, environmental protection and energy saving, and good economic benefits.

[0046] To better understand the present invention, the following embodiments are used to further specifically illustrate the present invention, but it should not be construed as a limitation of the present invention. For those skilled in the art, according to the above-mentioned invention content non-essential improvements and adjustments are also considered to fall within the scope of protection of the present invention. Example 1

[0047] 100 kg (dry basis) of silver electrolyte purification slag was put into a reaction kettle. The weight percentage components of the silver electrolyte purification slag were: silver 57%, copper 19%, lead 5%, bismuth 0.6%. 100 L of pure water was added according to a liquid-solid ratio of 1:1, and it was slurried for 2 hours. A 60 g / L hydrochloric acid solution was added according to a liquid-solid ratio of 4:1, the temperature was raised to 75 °C, 5 kg of sodium chlorate was added, and leaching was carried out for 3 hours. Solid-liquid separation was performed to obtain leachate and 87 kg (dry basis) of leached residue; 220 g / L sodium sulfite solution was mixed with the leached residue according to a liquid-solid ratio of 10:1 and leached for 4 hours. Solid-liquid separation was performed to obtain silver separation liquid and 8 kg (dry basis) of lead sulfate slag. The weight percentage components of the lead sulfate slag were: lead 64%, silver 0.15%; Analytical pure sulfuric acid was added to the silver separation liquid to adjust the pH to 4.5, and solid-liquid separation was performed to obtain 78 kg (dry basis) of crude silver chloride. After silver precipitation, the liquid was adjusted to pH 9.5 with sodium hydroxide and used as the mother liquor for the next silver separation in a cycle; 40 g / L hydrochloric acid solution was added to 78 kg (dry basis) of crude silver chloride according to a liquid-solid ratio of 4:1, the temperature was raised to 85 °C, 4.5 kg of sodium chlorate was added, and the reaction was carried out for 2 hours. Solid-liquid separation was performed to obtain 75.7 kg (dry basis) of refined silver chloride; 75.7 kg (dry basis) of refined silver chloride was slurried with pure water according to a liquid-solid ratio of 4:1, and hydrazine hydrate was added for reduction according to 1.5 times the theoretical amount to obtain 56.7 kg (dry basis) of silver powder. The composition of the silver powder is shown in Table 1; Sodium hydroxide solution was added to the leachate to control the pH = 3, and solid-liquid separation was performed to obtain 0.88 kg (dry basis) of bismuth oxychloride and the liquid after bismuth precipitation; 21 kg of sodium sulfide was added to the liquid after bismuth precipitation, and solid-liquid separation was performed to obtain 40 kg of copper precipitation slag.

[0048] Table 1 Composition of silver powder (%)

[0049] Ag Cu Fe Sb Bi Pb Se Te Pd 99.995 0.0008 0.0006 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001

[0050] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for producing No. 1 silver using silver electrolyte purification slag, characterized in that, The specific steps include: (1) Pulping: Pulping the purified residue of silver electrolyte with pure water; (2) Oxidative leaching: Adding water to the purified residue of silver electrolyte pulp obtained in step (1) according to a certain liquid-solid ratio, adding an acidic solution, heating up and adding an oxidant. After oxidative leaching, cooling and filtering to obtain a leaching solution and a leaching residue; (3) Separating silver with sodium nitrite: Pulping the leaching residue obtained in step (2) with water, adjusting the pH value with an alkaline solution, then adding a mother liquor for silver separation, heating up and reacting, and filtering to obtain a silver separation solution and a lead sulfate residue. The lead sulfate residue is sent to lead smelting; (4) Acidifying and precipitating silver: Adjusting the pH value of the silver separation solution obtained in step (3) to acidic with an acidic solution or an acidic gas to obtain crude silver chloride and a solution after silver precipitation. The solution after silver precipitation is adjusted to a pH value of 9.5 with sodium hydroxide and then recycled as the mother liquor for silver separation in step (3); (5) Oxidative purification: Pulping the crude silver chloride obtained in step (4) with pure water, adding an acidic solution, heating up and adding an oxidant. After reaction, filtering to obtain refined silver chloride and a purified solution. The refined silver chloride is washed with hot water until neutral; (6) Silver reduction: Pulping the refined silver chloride washed to neutral in step (5) with pure water, heating up and adding a reducing agent until no bubbles are generated in the pulp solution. After stirring and reacting, filtering to obtain silver powder and a solution after reduction. The silver powder is washed with hot water and then dried, and cast into silver ingots.

2. The method according to claim 1, wherein By mass percentage, the purified residue of silver electrolyte includes: 50 - 65% silver, 12 - 20% copper, 4 - 6% lead, and 0.5 - 1% bismuth.

3. The method according to claim 1, wherein The steps also include: (7) Neutralizing and precipitating bismuth: Adding an alkaline solution to the leaching solution obtained in step (2), adjusting the pH to 2 - 3, and filtering after reaction to obtain bismuth oxychloride and a solution after bismuth precipitation; (8) Sulfidizing and precipitating copper: Adding a certain amount of sodium sulfide to the solution after bismuth precipitation in step (7), filtering after reaction to obtain a copper precipitation residue and a solution after copper precipitation. The solution after copper precipitation is sent to sewage treatment.

4. The method according to claim 1, characterized in that, In step (1), the mass ratio of the purified residue of silver electrolysis to the volume of pure water for pulping is 1:(0.5 - 1), the pulping time is 2 - 3 h, and the temperature is at room temperature.

5. The method according to claim 1, wherein In step (2), the liquid-solid ratio for oxidative leaching is (4 - 6):1, the acidic solution is a 50 - 70 g / L hydrochloric acid solution, the heating-up temperature is 75 - 85 °C, and the oxidant is one or more of sodium chlorate, hypochlorous acid, and hydrogen peroxide.

6. The method according to claim 1, characterized in that, In step (3) of separating silver with sodium nitrite, the liquid-solid ratio is (8 - 10):1, the adjusted pH value is 8 - 10, and the mother liquor for silver separation is a 210 - 250 g / L sodium sulfite solution.

7. The method according to claim 1, wherein In step (4), the acidic solution is sulfuric acid, the acidic gas is sulfur dioxide, and the end-point pH is 4 - 5.

8. The method according to claim 1, wherein In step (5), the liquid-solid ratio of pulping the crude silver chloride with pure water is (4 - 6):1, the acidic solution is a 50 - 70 g / L hydrochloric acid solution, the heating-up temperature is 75 - 85 °C, the oxidant is one or more of sodium chlorate, hypochlorous acid, and hydrogen peroxide, and the filtering temperature is 50 - 60 °C.

9. The method according to claim 1, characterized in that, In step (6), the liquid-solid ratio for pulping is (4 - 6):1, heating up to 40 - 60 °C, and the reducing agent is hydrazine hydrate.

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