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METHODS FOR EXTRACTING SILVER FROM WASTE
1. An emulsion layer is removed from glass photographic plates in hot soda solution; other photographic materials are burned in porcelain dishes. True, when burning, the proportion of silver will evaporate with smoke. To reduce the loss of photographic materials, it is best to burn with smoldering fire, or to extract silver with sodium hyposulfite.
2. Mirror combat and Christmas tree toys also contain an impressive number of silver:
mirrors - from 3 up to 7 g / m2 , toys - from 0.2 up to 0.5% by weight of fragments.
To remove a silver-containing layer from a mirror-like battlefield, it is placed in an acid-resistant capacity, it is also poured with a hot solution of hydrochloric acid, and then subjected to mechanical finishing: simply put, it is up to the full separation of the silver-containing layer from the glass. In industry, a rotating drum is used for this purpose.
3. To restore silver from photo ash, you will need a muffle furnace and heat-resistant crucibles that can withstand temperatures of 1000 degrees Celsius. Ash is thoroughly mixed with soda and also broken glass in the following proportions:
30% ash, 65% sodium bicarbonate, an additional 5% broken glass.
Composed in this way, the mixture is sintered at a temperature of 1200 ° C. The melt is poured into a cast iron mold, lubricated with iron oxide powder. You can also melt in a crucible, but then you have to break it, but in a day you will have an ingot of pure silver.
4. But the technique of isolating silver from a silver-copper alloy, described in the 20th volume of the Technical Encyclopedia , published in 1935 :
the product is dissolved in nitric acid, hydrochloric acid is added, the precipitated silver chloride is washed with water and metallic silver is also reduced from it through interaction with zinc also with diluted sulfuric or hydrochloric acid.
5. Another method has been described in great detail in the journal "Make It Yourself" (No. 4, 1990) . It consists of the following:
The silver-containing product is thoroughly cleaned of oxides and is also washed first with warm alkaline solution, but then with ordinary water. Later this product is poured with 10% nitric acid until it is filled with dissolution. In solution, therefore, is a hodgepodge of silver salts, also copper. The solution is evaporated, but the resulting powder is calcined in a porcelain dish, with the result that copper nitrate is converted to insoluble copper oxide. The completion of this process is determined by the termination of the release of very caustic gas bubbles from the surface of the melt. Today the melt is also cooled and dissolved in 2 parts of distilled water; a clear solution containing neat silver nitrate is removed from the sludge — well, but as if to restore metallic silver from the salts, we have already discussed. In the described process, there are some difficulties, such as: manipulations with nitric acid, toxic volatile compounds and evaporation of large volumes of solutions. However, such problems are easily solved in the laboratory.
6. Silver coatings (including those also applied by chemical means) and silver alloys on the basis of copper, nickel silver, brass, tombac, nickel silver are also removed in a mixture of concentrated sulfuric and nitric acids with a volume ratio of 19: 1 at a temperature of 40-60 ° C. The solution is also prevented from being diluted by regularly adjusting it with nitric acid, which is used in the process of dissolving the coating.
Silver from the surface of copper and its alloys are also removed by anodic finishing in a solution of composition, % :
Sulfuric acid H2SO4 (density 1.84 g / cm3 ) - 91
Sodium nitrate (sodium nitrate) NaNO2 - 3
at a temperature of 20-50 "С also the voltage of a spring of constant current of 2-3 V. Lead is used as cathodes.
The removal of silver from parts of a small thickness of the coating is usually carried out at a temperature of 40-50 ° C in a solution of the composition, g / l :
Potassium Iodide KI - 250
Metal iodine I2 - 7
Silver alloy and antimony from the same parts are removed in a solution of the composition, g / l :
Potassium Iodide KI - 250
Metal iodine I2 - 7.5
Acid nitric HNO2 (density 1.41 g / cm3 ) - 150 ml / l