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METHODS OF EXTRACTION OF SILVER FROM WASTE
1. The emulsion layer is removed from the glass photographic plates in a hot soda solution, other photo materials are burned in porcelain utensils. True, when burning, the proportion of silver will evaporate with smoke. To reduce losses, it is best to burn photographic materials with smoldering fire, or to remove silver with sodium hyposulfite.
2. Mirror battle and Christmas toys similarly contain an impressive number of silver:
mirrors - from 3 to 7 g / m2 , toys - from 0.2 to 0.5% of the mass of the fragments.
To remove the silver-containing layer from a mirror battle, it is placed in an acid-proof container, it is poured over with a hot solution of hydrochloric acid, and also subjected to mechanical finishing: in simple terms, they are moved up to the filled section of the silver-containing layer from the glass. In industry, a rotary drum is used for this purpose.
3. For the resumption of silver from the ash of photographic materials, you will need a muffle furnace also with heat-resistant crucibles capable of withstanding the 1000 degree temperature. The ash is thoroughly mixed with soda and broken glass in the following proportions:
30% ash, 65% sodium bicarbonate additionally 5% broken glass.
The batch thus formed is sintered at a temperature of 1200 ° C. The melt is poured into a cast iron mold, lubricated with a powder of iron oxide. you can also cool the melt in a crucible, but then it will have to be broken, but on days you will have an ingot of pure silver.
4. And here is a technique for the isolation of 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 silver metal is also reduced therefrom by reacting with zinc with dilute sulfuric or hydrochloric acid.
5. Another method was described in great detail in the magazine Do-It-Yourself (No. 4, 1990) . It consists of the following:
The silver-containing product is thoroughly cleaned of oxides also washed first with a warm alkaline solution, but then with ordinary water. Later this product is poured with 10% nitric acid until its dissolved solution is filled. In solution, therefore, there is a hodgepodge of silver salts also of copper. The solution is evaporated, but the resulting powder is calcined in a porcelain dish, whereby copper nitrate is converted to insoluble copper oxide. The completion of this process is determined by stopping the release of highly corrosive gas from the surface of the melt. Now the melt is cooled also dissolved in 2 parts of distilled water; a transparent solution containing neat silver nitrate is removed from the sludge - well, but as if to restore silver from the salts, we have already discussed. In the described process, there are some difficulties, such as: manipulation of nitric acid, toxic volatile compounds, and evaporation of impressive volumes of solutions. However, such problems are easily resolved in the laboratory.
6. Silver coatings (including those applied also chemically) also silver alloys on bases of copper, nickel silver, brass, tombac, and cupronickel 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 C. The solution is protected from dilution and is also regularly corrected by its nitric acid, which is used in the dissolution process of the coating.
Silver from the surface of copper and its alloys is also removed by an anodic finish in a solution of the composition, % :
Sulfuric acid H2SO4 (density 1.84 g / cm3 ) - 91
Sodium nitrate (sodium nitrate) NaNO2 - 3
at a temperature of 20-50 "C, also the voltage of the source of a constant current of 2-3 V. As lead cathodes.
The removal of silver from parts of low coating thickness is usually carried out at a temperature of 40-50 ° C in a solution of the composition, g / l :
Potassium iodide KI-250
Iodine I2 - 7
The silver alloy is also antimony with the same parts removed in the solution of the composition, g / l :
Potassium iodide KI-250
Iodine I2 - 7,5
Nitric acid HNO2 (density 1.41 g / cm3 ) - 150 ml / l