CN108374095B - Method for recovering silver from silver-containing aqueous solution - Google Patents

Method for recovering silver from silver-containing aqueous solution Download PDF

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CN108374095B
CN108374095B CN201810107412.3A CN201810107412A CN108374095B CN 108374095 B CN108374095 B CN 108374095B CN 201810107412 A CN201810107412 A CN 201810107412A CN 108374095 B CN108374095 B CN 108374095B
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silver
solution
aqueous solution
inorganic
containing aqueous
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CN108374095A (en
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黄绍勇
邓成虎
江和明
刘永平
林东和
张剑
黄维
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Jiangxi Copper Co Ltd
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Jiangxi Copper Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B11/00—Obtaining noble metals
    • C22B11/04—Obtaining noble metals by wet processes
    • C22B11/042—Recovery of noble metals from waste materials
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
    • C22B7/006—Wet processes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Abstract

The invention discloses a method for recovering silver from a silver-containing aqueous solution containing inorganic oxysulfide, which comprises the steps of adjusting the pH of the silver-containing aqueous solution containing the inorganic oxysulfide to be more than 7, adding a reducing agent into the silver-containing aqueous solution to adjust the redox potential of the solution to be less than-300 mV to reduce the silver in the solution, then adding an inorganic polymer into the silver-containing aqueous solution to flocculate and precipitate the reduced silver, and recovering the silver. The method can efficiently recover silver from the silver-containing aqueous solution containing inorganic oxysulfide such as sodium sulfite and the like at a high recovery rate without complex operation, and has the advantages of good stability, low cost and the like.

Description

Method for recovering silver from silver-containing aqueous solution
Technical Field
The invention relates to the technical field of nonferrous metallurgy, in particular to a method for recovering silver from a silver-containing water solution.
Background
Silver and related products thereof have very wide application in the industries such as the photosensitive industry, the electronic and information industry, the electroplating industry, the chemical industry and the like, and most of raw materials for extracting the silver come from byproducts generated in the non-ferrous metal smelting process, such as copper (lead) anode mud and the like. In the treatment of these by-products, sodium sulfite is commonly used as a silver extraction reagent to introduce silver into the solution in the form of a stable complex, and then a reducing agent is used to reduce silver from the complex solution to obtain silver powder with higher purity. However, a large amount of silver-containing waste liquid with a low concentration is generated in this process, and it becomes a difficult problem to be solved to recover silver from the silver-containing waste liquid with high efficiency and low cost.
At present, methods for recovering silver from a silver-containing solution (waste liquid) mainly include various methods such as a precipitation method, an electrolysis method, a solvent extraction method, an ion exchange method, and an adsorption method. In general, various types of silver-containing waste liquids are treated to recover silver therefrom using a number of different methods or combinations of methods. For example, as a method for recovering silver from a fixing solution, there are a precipitation method, a substitution method, a hypochlorite method, a sodium borohydride method, a sodium dithionate method, an electrolytic method and the like (Ponga foot, noble metal metallurgy and further processing [ M)]Zhongnan university press, 2005.). among these, ① precipitation method is towards fixationAdding sodium sulfide into the solution to react silver with S2-The silver sulfide precipitate produced by the reaction is separated from the solution, then silver is recovered from the silver sulfide black precipitate by a method such as a nitric acid dissolution method, a roasting melting method, and an iron scrap replacement method, the precipitation method is simple and easy to implement, the silver recovery is complete, and the method is suitable for small-scale use, but the silver sulfide in the solution after silver precipitation is excessive, the fixing solution cannot be regenerated, therefore, the method is mainly used for silver-containing waste liquid with a relatively single metal ion type, the ② replacement method is a method using iron powder, zinc powder, and aluminum powder as reducing agents to reduce silver in the fixing solution to elemental silver, the method is highly efficient, but the replacement products contain silver powder, iron powder, silver sulfide, etc., the replacement metal is further purified, the replacement metal is dissolved into the solution, so that the fixing solution is not easily regenerated, the thiosulfate in the fixing solution is decomposed in an acidic medium, elemental sulfur and sulfur dioxide are produced, the hypochlorite method is a method using hypochlorite to decompose the silver-thiosulfate complex in the fixing solution, the silver-thiosulfate precipitate, the silver-sulfate precipitate is separated from the solution, because a large amount of thiosulfate is oxidized, the agent consumes a large amount of sodium sulfide, the sodium sulfate is adjusted to approximate to pH value of the silver-sodium sulfate-containing silver-sulfide solution in the fixing solution of the fixing solution after the fixing solution, the fixing solution is widely-containing silver-sodium borohydride-sodium sulfide solution, the sodium borohydride-containing silver-sodium sulfide-containing silver-sodium sulfide-containing solution, the sodium sulfide-containing silver-sodium sulfide-containing solution-sodium sulfide-sodium borohydride-containing solution is added in the fixing solution, the sodium borohydride-containing silver-containing solution-replacing-sodium borohydride-replacing method is added under the high-replacing method, the high-replacing method under the high-replacing2Under the conditions of (1), the concentration of silver in the stock solution containing 2.5 ~ 9.3.3 g/L of silver was reduced to 0.5 ~ 0.7.7 g/L, but the electrolysis method could not be carried out under the condition of low concentration, and the solution was dissolvedThe mass concentration of silver in the solution is controlled to be more than 200 mg/L.
The method for recovering silver from electroplating waste liquor includes electrolytic method, chloridizing precipitation method, zinc powder replacement method and active carbon adsorption method, etc. because it is usually cyanide-containing solution (silver concentration can be up to 10 ~ 12g/L, total cyanide concentration is 80 ~ 100 g/L), so that it can not be used under the acidic condition to prevent hydrogen cyanide from escaping, and the cyanide concentration in tail liquor must be up to related standard—+2 OH—- 2e = CNO—+ H2O，CNO—+ 2H2O = NH4 ++ CO3 2-，2CNO—+ 8OH—- 6e =2CO3 2-+ N2↑ + 4H2O). If the solution still contains a small amount of cyanide after electrolysis, then it is necessary to use ferrous sulfate to generate stable ferrocyanide.
The method of recovering silver from the silver-containing waste emulsion varies depending on its source. Among them, the waste emulsion for photosensitive film contains a large amount of organic substances, which need to be separated first to facilitate the recovery of silver, and the method can be roughly divided into two major types, i.e., fire process and wet process. The pyrogenic process comprises four working procedures of dehydration, drying, roasting and smelting; the wet process firstly heats the waste emulsion to 55 ℃, adds water for dilution, then adds protease for stirring to decompose the organic matter, then uses sulfuric acid for precipitation, then uses sodium thiosulfate solution for leaching, and finally obtains the crude silver by electrolysis. The method for recovering silver from silver-containing emulsifier in electric appliance element and mirror making plant is characterized by that the silver is mainly existed in the form of silver nitrate, and its treatment process is relatively simple, i.e. it adopts the processes of directly drying, smelting and electrolyzing to obtain pure silver, or uses nitric acid to dissolve silver in the pure silver, then makes silver nitrate.
Solvent extraction methods are widely used because of their good economical efficiency and operability, but there are problems in that an appropriate extraction agent needs to be selected in consideration of the characteristics of the solution and the comprehensive consideration of extraction capacity, extraction rate, durability, etc., and the used organic extraction agent needs to be disposed of. Adsorption methods using adsorbents such as activated carbon and ion exchange resin have problems such as a small adsorption capacity of the adsorbent, cumbersome post-adsorption treatment, difficulty in regenerating the adsorbent, and the need to properly dispose of the used adsorbent.
In addition to the above methods, many researchers have developed a variety of methods for the recovery of silver for different solution systems. For example, patent document CN1200407A discloses a method for extracting and recovering silver by mixing a raw material containing a sparingly soluble silver compound with S2-CN103305700A discloses a method for recovering silver from silver-containing waste water, said method is characterized by that the pH value of silver-containing waste water is controlled at 4 ~, after the silver-containing waste water is adsorbed and saturated by resin, it is desorbed by ammonia water, the low-concentration desorption liquid is circulated and used for desorption of resin, the high-concentration desorption liquid is separated by means of ultrafiltration device and desalting membrane device, the concentrated water after desalting membrane separation is added with reducing agent to obtain simple substance silver, and patent document CN1118015A discloses a method for recovering silver from silver waste liquid, said method is characterized by that one of iron, high-iron sulfate solution or polymeric ferric sulfate solution is added into silver-containing waste liquid, the volume ratio of iron-containing solution to silver-containing solution is (1.2 ~), silver is precipitated under normal temp., sodium sulfate is added into sodium sulfate solution, sodium sulfate solution or polymeric ferric sulfate solution, and the first solution is added into silver-containing solution, and sodium hydroxide solution, and the first precipitation method is added into silver-containing solution under the condition of normal temp. 1.2 ~, then the silver is precipitated, the silver-containing solution is obtained by heating, and the first precipitation method is characterized by adding sodium sulfateAdding sodium sulfate, and filtering to obtain filter residue and a second filtrate; and regulating the pH value of the second filtrate to be not less than 11 by using sodium hydroxide, adding formaldehyde, filtering to obtain silver powder and a third filtrate, adding hydrochloric acid into the third filtrate to regulate the pH value to be less than 1, and returning to the lead separation process. Patent document CN102010036A discloses a method for treating silver electrolysis waste liquid, which is to extract silver and copper from silver electrolysis waste liquid by applying a cyclone electrolysis technology, and make the treated liquid reach the standard of wastewater discharge and discharge. The method firstly feeds the silver electrolysis waste liquid into a series-connected cyclone electrolytic tank, and uses low current density and medium flow (circulation flow is 1 m)3/h~3m3H, current density 200A/m2~400A/m2Of) removing impurities; then the impurity-removed liquid is put in medium and low current density and medium flow (circulation flow 2 m)3/h~5m3H, current density 200A/m2~500A/m2) Extracting electrolytic silver powder under the condition; finally, the electrolyzed solution is subjected to deep purification (the circulation flow is 3 m)3/h~7m3H, current density 200A/m2~400A/m2) So that the treated waste liquid reaches the wastewater discharge standard.
Disclosure of Invention
When the by-product produced in the non-ferrous metal smelting process is treated, sodium sulfite is commonly used as an extraction reagent of silver, so that the silver enters the solution in the form of a stable complex, the silver-containing solution is acidified by using reagents such as inorganic acid, so that the silver is precipitated from the complex solution, the silver enters the precipitate after the acidification treatment, and the silver-containing precipitate is oxidized, purified and reduced to obtain the silver powder with higher purity. However, a large amount of silver-containing waste liquid with a low concentration is also generated in this process. Since a large amount of inorganic oxysulfide is contained in the waste liquid, the reduction of silver is not sufficiently performed, and even if the reduction is sufficient, the flocculation reaction of silver with a flocculant is insufficient due to the presence of inorganic oxysulfide, resulting in a low recovery rate of silver. Therefore, it is desired to develop a method capable of recovering silver from a silver-containing waste liquid containing inorganic sulfur oxides such as sodium sulfite at a high recovery rate. In view of the above circumstances, an object of the present invention is to provide a method capable of recovering silver from an aqueous silver-containing solution containing inorganic sulfur oxides such as sodium sulfite at a high recovery rate without requiring complicated operations.
The invention provides a method for recovering silver from a silver-containing aqueous solution, which comprises the following steps:
(1) adjusting the pH of the aqueous silver-containing solution containing inorganic sulfur oxide to 7 ~ 10;
(2) adding a reducing agent nano zero-valent iron into the silver-containing aqueous solution in the step (1) to keep the oxidation-reduction potential of the solution within the range of-500 mV ~ -300mV to reduce silver;
(3) adding an inorganic polymer into the silver-containing aqueous solution in the step (2) to flocculate and precipitate the reduced silver, and recovering the silver;
the inorganic sulfur oxide is at least one salt selected from sulfite and bisulfite.
Further, the mass concentration of the inorganic sulfur oxide in the inorganic sulfur oxide-containing aqueous solution containing silver is 180 ~ 300 g/L.
Further, the mass concentration of silver in the inorganic oxysulfide-containing silver-containing aqueous solution was 30 ~ 200 mg/L.
Furthermore, the mass concentration of the metal impurities in the silver-containing aqueous solution containing the inorganic oxysulfide is 5 ~ 20mg/L, 20 ~ 100mg/L and 10 ~ 100mg/L of copper.
Further, the inorganic polymer is polymeric ferric sulfate and polymeric aluminum chloride.
Further, the content of polymeric ferric sulfate in the silver-containing aqueous solution containing inorganic oxysulfide is within the range of 0.5 ~ 1g/L, and the content of polymeric aluminum chloride is within the range of 10 ~ 50 mg/L.
Compared with the prior art, the invention has the advantages and positive effects that:
the invention provides a method for recovering silver from a silver-containing aqueous solution, which can efficiently recover silver from the silver-containing aqueous solution containing inorganic oxysulfide such as sodium sulfite and the like with high recovery rate without complex operation; the method can adapt to the water quality with complex components and has the advantages of good stability, simple process and low cost.
Detailed Description
The reason why the reduction and flocculation reaction of silver in the silver-containing aqueous solution containing inorganic oxysulfide such as sodium sulfite hardly proceeds is that the inorganic oxysulfide such as sodium sulfite present in the silver-containing solution (waste liquid) forms a stable complex with silver. The applicant has found through extensive studies that silver in a silver-containing waste liquid can be sufficiently reduced by adjusting the pH of the waste liquid to a predetermined range and adding a reducing agent to maintain the oxidation-reduction potential of the solution at less than-300 mV, and that silver can be efficiently recovered by sufficiently flocculating the reduced silver by adding an inorganic polymer.
The invention provides a method for recovering silver from a silver-containing aqueous solution, which adopts the basic technical scheme that the method comprises the following steps:
(1) adjusting the pH of the aqueous silver-containing solution containing inorganic sulfur oxide to 7 or more;
preferably to a pH of 7 ~ 10, more preferably to a pH of 8 ~ 9;
(2) adding a reducing agent nano zero-valent iron into the silver-containing aqueous solution in the step (1) to keep the oxidation-reduction potential of the solution within the range of-500 mV ~ -300mV to reduce silver;
(3) and (3) adding an inorganic polymer into the silver-containing aqueous solution in the step (2) to flocculate and precipitate the reduced silver, and recovering the silver.
In the method of the present invention, the solution to be subjected to the silver recovery treatment is a silver-containing aqueous solution containing inorganic oxysulfide, and is derived from a leachate obtained by leaching silver with sodium sulfite as a leaching agent, and is acidified with an acidifying agent such as an inorganic acid to separate a silver precipitate, thereby obtaining a waste liquid.
The silver-containing aqueous solution to be treated for silver recovery may contain silver at any concentration, although the silver content is usually 30 ~ 200mg/L in the silver-containing aqueous solution after the silver leaching solution is acidified, the inorganic sulfur oxide is usually 180 ~ 300g/L in the silver-containing aqueous solution after the silver leaching solution is acidified, and the solution may contain impurities of compounds formed by sulfurous acid and metals, such as metal compounds of gold sulfite sodium, arsenic sulfite sodium, copper sulfite sodium, etc., and the mass concentration of the metal impurities is gold 5 ~ 20mg/L, arsenic 20 ~ 100mg/L, copper 10 ~ 100 mg/L.
The pH of the silver-containing aqueous solution to be treated by the present invention is adjusted to 7 or more, preferably to pH 7 ~ 10, more preferably to pH 8 ~ 9, the recovery rate of silver from the silver-containing aqueous solution containing inorganic oxysulfide can be dramatically improved by reducing silver with a reducing agent, and then flocculating-precipitating the reduced silver with an inorganic polymer, and when the pH exceeds 10, the reduction reaction does not proceed sufficiently even with the addition of a large excess of the reducing agent, the reducing agent utilization efficiency decreases, and the silver recovery rate decreases, on the other hand, when the pH is below 7, a large amount of the reducing agent needs to be added after the pH adjustment and the silver reduction efficiency decreases, and it should be noted that the pH of the waste liquid obtained after separating the silver precipitate after the acidification treatment of the leachate of silver (i.e., the silver-containing aqueous solution to be treated by the silver recovery treatment in the present invention) is about 3 ~ 6, and in order to adjust the pH of the silver-containing aqueous solution to 7 or more, a pH adjusting agent that is not limited, and sodium hydroxide is preferably used as an economically viable pH adjusting agent.
The nano zero-valent iron is not particularly limited, and generally has a particle size of 10 ~ 200nm, and in the present invention, silver in the solution can be efficiently reduced by adding the reducing agent, zero-valent nano iron, to adjust the oxidation-reduction potential of the solution to a range of-300 mV ~ -500 mV., wherein the oxidation-reduction potential of the solution is in the range of-300 mV ~ -500mV, and further preferably, the oxidation-reduction potential of the solution is in the range of-350 mV ~ -450 mV., wherein the addition of the reducing agent to adjust the oxidation-reduction potential of the solution to a value higher than-300 mV results in insufficient reduction of silver in the solution and low reduction efficiency of silver, and wherein the adjustment of the oxidation-reduction potential of the solution to a value lower than-500 mV requires the addition of a larger amount of reducing agent, which increases the cost, and wherein the treatment time during the reaction is generally about 15 ~ 60 minutes at room temperature.
The silver recovery method comprises adding an inorganic polymer to the silver-containing aqueous solution to flocculate and precipitate the reduced silver, thereby recovering silver, wherein the inorganic oxysulfide remains in the silver-containing aqueous solution, and the inorganic oxysulfide prevents the flocculation effect of the silver by the flocculant and prevents the flocculation of the silver, and the inorganic polymer is required to be added.
Example 1
Adjusting the pH value of a silver-containing aqueous solution containing inorganic oxysulfide to 7 by using sodium hydroxide, adding a reducing agent nano zero-valent iron into the silver-containing aqueous solution to adjust the oxidation-reduction potential of the solution to-300 mV, stirring and reacting for 30 minutes, then adding 500mg/L of inorganic polymer polymeric ferric sulfate into the silver-containing aqueous solution, stirring and reacting for 5 minutes, then adding 10mg/L of polymeric aluminum chloride, and stirring and reacting for 10 minutes. Wherein the pH value of the silver-containing aqueous solution containing inorganic oxysulfide is 5, the mass concentration of silver is 100mg/L, and the mass concentration of sodium bisulfite is 220 g/L. The recovery of silver was 98.5%.
Example 2
Adjusting the pH value of a silver-containing aqueous solution containing inorganic oxysulfide to 8 by using sodium hydroxide, adding a reducing agent nano zero-valent iron into the silver-containing aqueous solution to adjust the oxidation-reduction potential of the solution to-350 mV, stirring and reacting for 20 minutes, then adding 600mg/L of inorganic polymer polymeric ferric sulfate into the silver-containing aqueous solution, stirring and reacting for 10 minutes, then adding 20mg/L of polymeric aluminum chloride, and stirring and reacting for 5 minutes. Wherein the pH value of the silver-containing aqueous solution containing inorganic oxysulfide is 5, the mass concentration of silver is 100mg/L, and the mass concentration of sodium bisulfite is 220 g/L. The recovery of silver was 98.2%.
Example 3
Adjusting the pH value of a silver-containing aqueous solution containing inorganic oxysulfide to 9 by using sodium hydroxide, adding a reducing agent nano zero-valent iron into the silver-containing aqueous solution to adjust the oxidation-reduction potential of the solution to-400 mV, stirring and reacting for 40 minutes, adding 500mg/L of inorganic polymer polymeric ferric sulfate into the silver-containing aqueous solution, stirring and reacting for 10 minutes, then adding 20mg/L of polymeric aluminum chloride, and stirring and reacting for 5 minutes. Wherein the pH value of the silver-containing aqueous solution containing inorganic oxysulfide is 4, the mass concentration of silver is 100mg/L, and the mass concentration of sodium bisulfite is 220 g/L. The recovery of silver was 99.0%.
Example 4
Adjusting the pH value of a silver-containing aqueous solution containing inorganic oxysulfide to 8 by using sodium hydroxide, adding a reducing agent nano zero-valent iron into the silver-containing aqueous solution to adjust the oxidation-reduction potential of the solution to-350 mV, stirring and reacting for 20 minutes, then adding 800mg/L of inorganic polymer polymeric ferric sulfate into the silver-containing aqueous solution, stirring and reacting for 10 minutes, then adding 40mg/L of polymeric aluminum chloride, and stirring and reacting for 5 minutes. Wherein the pH value of the silver-containing aqueous solution containing inorganic oxysulfide is 5, the mass concentration of silver is 100mg/L, and the mass concentration of sodium bisulfite is 220 g/L. The recovery of silver was 98.4%.
Example 5
Adjusting the pH value of a silver-containing aqueous solution containing inorganic oxysulfide to 8 by using sodium hydroxide, adding a reducing agent nano zero-valent iron into the silver-containing aqueous solution to adjust the oxidation-reduction potential of the solution to-500 mV, stirring and reacting for 20 minutes, then adding 900mg/L of inorganic polymer polymeric ferric sulfate into the silver-containing aqueous solution, stirring and reacting for 10 minutes, then adding 20mg/L of polymeric aluminum chloride, and stirring and reacting for 5 minutes. Wherein the pH value of the silver-containing aqueous solution containing inorganic oxysulfide is 3, the mass concentration of silver is 30mg/L, and the mass concentration of sodium bisulfite is 180 g/L. The recovery of silver was 98.0%.
Example 6
Adjusting the pH value of a silver-containing aqueous solution containing inorganic oxysulfide to 9 by using sodium hydroxide, adding a reducing agent nano zero-valent iron into the silver-containing aqueous solution to adjust the oxidation-reduction potential of the solution to-400 mV, stirring and reacting for 30 minutes, then adding 1000mg/L of inorganic polymer polymeric ferric sulfate into the silver-containing aqueous solution, stirring and reacting for 10 minutes, then adding 30mg/L of polymeric aluminum chloride, and stirring and reacting for 10 minutes. Wherein the pH value of the silver-containing aqueous solution containing inorganic oxysulfide is 4, the mass concentration of silver is 200mg/L, and the mass concentration of sodium bisulfite is 300 g/L. The recovery of silver was 98.6%.
Example 7
Adjusting the pH value of a silver-containing aqueous solution containing inorganic oxysulfide to 8 by using sodium hydroxide, adding a reducing agent nano zero-valent iron into the silver-containing aqueous solution to adjust the oxidation-reduction potential of the solution to-500 mV, stirring and reacting for 30 minutes, then adding 700mg/L of inorganic polymer polymeric ferric sulfate into the silver-containing aqueous solution, stirring and reacting for 10 minutes, then adding 30mg/L of polymeric aluminum chloride, and stirring and reacting for 10 minutes. Wherein the pH value of the silver-containing aqueous solution containing inorganic oxysulfide is 5, the mass concentration of silver is 200mg/L, and the mass concentration of sodium bisulfite is 220 g/L. The recovery of silver was 98.7%.
The above embodiments are merely preferred embodiments of the present invention, and any simple modification, modification and substitution changes made to the above embodiments according to the technical spirit of the present invention are within the scope of the technical solution of the present invention.

Claims (5)

1. A method for recovering silver from an aqueous solution containing silver, characterized by: the method comprises the following steps:
(1) adjusting the pH of the aqueous silver-containing solution containing inorganic sulfur oxide to 7 ~ 10;
(2) adding a reducing agent nano zero-valent iron into the silver-containing aqueous solution in the step (1) to keep the oxidation-reduction potential of the solution within the range of-500 mV ~ -300mV to reduce silver;
(3) adding an inorganic polymer into the silver-containing aqueous solution in the step (2) to flocculate and precipitate the reduced silver, and recovering the silver;
the inorganic sulfur oxide is at least one salt of sulfite and bisulfite;
the inorganic polymer is polymeric ferric sulfate and polymeric aluminum chloride.
2. The method according to claim 1, wherein the concentration by mass of the inorganic sulfur oxide in the aqueous silver-containing solution is 180 ~ 300 g/L.
3. The method of claim 1, wherein the concentration of silver in the aqueous silver-containing solution containing inorganic oxysulfide is 30 ~ 200 mg/L.
4. The method of claim 1, wherein the concentration of the metal impurities in the aqueous silver solution containing inorganic oxysulfide is 5 ~ 20mg/L, 20 ~ 100mg/L and 10 ~ 100 mg/L.
5. The method of claim 1, wherein the ferric polysulfate is present in an amount of 0.5 ~ 1g/L and the aluminum polychloride is present in an amount of 10 ~ 50mg/L in the aqueous silver-containing solution containing inorganic sulfur oxide of step (3).
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