A convenient method for recovering silver from silver sulfide
Simple methods for recovering silver from silver sulfide are:
1. Nitric acid oxidation
After the silver sulfide is wetted with water, it is dissolved by adding dilute nitric acid (acid: water = 1: 2 to 3). At this time, silver sulfide is decomposed by nitric acid and precipitates monomer sulfur. Then, it was filtered, and then brine was added to the AgNO 3 filtrate to form a silver chloride precipitate. After standing, the supernatant was removed, and then heated to boiling to cause the silver chloride to aggregate, and then filtered and washed. The washed silver chloride is added to the alkaline solution to reduce hydration:
AgCl+2NH 3 
Ag(NH 3 ) 2 +Cl -
4Ag(NH 3 ) 2 + +2N 2 H 2 4Ag↓+2N 2 +8NH 3 +4H 2 O
After the produced silver powder is filtered, washed with water and dried, it contains 99.5% of silver.
Second, the iron piece replacement method
To each 100g of silver sulfide, 250mL of concentrated hydrochloric acid and about 75g of thin iron piece are added, heated to boiling in a fume hood (with hydrogen sulfide release), and then moved to the asbestos mesh mat to continue heating, which is completely reduced to powder after about 1 hour of silver. The heating was decanted, the supernatant was washed, water was added and the residual iron pieces were picked up, filtered, washed with distilled water until dry without Cl.
Third, aluminum chip replacement method
The silver sulfide was placed a solution containing NaOH, was added aluminum scrap -4 object, i.e., the silver is reduced to metallic silver:
2Al+8NaOH+3Ag 2 S+2H 2 O 3Na 2 S+6Ag↓+Na 2 Al 2 O 4 +6H 2 O
The reduced metallic silver powder is filtered off, and after drying, a flux and an oxidizing agent are added for pyrometallurgical refining. This method has been applied to the industrial production of the Nipissing Mining Company in Ontario, Canada.
The waste fixer is regenerated after being silvered by sodium sulfide and can be returned to use. When the hydrogen sulfide method is employed, since hydrogen sulfide has a weak acid property and a reducing action, when a large amount of hydrogen sulfide is introduced into the fixing solution, sulfur is precipitated due to oxidation of hydrogen sulfide itself and destruction of sodium thiosulfate. The fixing solution becomes cloudy and cannot be returned to use. And hydrogen sulfide is highly toxic, so it should be avoided. For the same reason, some researchers believe that when using sodium sulfide, a certain amount of sodium hydroxide should be added to the fixing solution before adding sodium sulfide to make the fixing solution neutral or weakly alkaline (with stone). The paper is measured to increase the OH - ion concentration and to avoid the generation of a large amount of hydrogen sulfide by the sodium sulfide under weakly acidic conditions.
During the fixing process, the concentration of sodium thiosulfate decreases due to dilution and consumption. During the silver extraction process, the potassium strontium was destroyed and the acetic acid was neutralized. Therefore, after the fixing solution is silvered, it is necessary to add the medicine before returning to use. According to some testers, each 45L (10 gallons) should be supplemented with 2 to 4 kg of sodium thiosulfate and 300 to 400 g of potassium. And add an appropriate amount (usually around 400mL) glacial acetic acid, so that the fixing solution is weakly acidic.
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