How to Recover Silver from Used Photo Emulsion

Silver is used in a number of applications other than coinage including photographic film, X-ray film, movie camera film, and computer chips. Among the methods used in recovering the silver used in these applications are electrolysis, metallic replacement, and precipitation, or a combination of some of these methods. Silver recovery can be as much as 98% of the original content and, with the price of silver at recent highs, the value of recovered silver more than pays for the cost of recovery.

Things You'll Need

• Mixing tank with agitator
• Exhaust vent
• Sodium hypochlorite
• Diluted nitric acid
• Distilled water
• Various pumps
• Commercial electrolytic extractors
• Ball mill
• Filtering unit

Instructions

1. Pour 20 gallons of distilled water into a mixing tank. Add 160 cc of concentrated sodium hypochlorite. Heat the mixture to just above room temperature. Place the silver-bearing film into the tank and turn on the agitator for 15 minutes.

2. Pump the silver emulsion which has settled to the bottom of the tank into an extractor until it has all been removed from the mixing tank. Operate the extractor until no more silver is deposited onto the cathode.

3. Collect by hand the silver granules that have been deposited on the cathode of the electrolytic extractor. Place the granules in a ball mill and pulverize them until they reach a 20 mesh consistency.

4. Place the pulverized silver granules into a tank which contains diluted nitric acid and which is equipped with a ventilator and hood for exhausting the fumes created by the chemical reaction in the tank. When the silver nitrate solution in the batch has reached a neutral pH, pump the solution into a Buchner-type filter unit containing a Watman paper filter.

5. Pump the filtered silver nitrate solution from the filtering unit into another electrolysis extractor where the silver will be deposited onto a cathode. Collect and dry the silver deposited on the cathode.

Tips & Warnings

• The silver finally collected will be 0.999 fine and will be suitable for a variety of end uses.

• Be careful in handling the chemicals involved as they are potentially harmful. Insure that the ventilation equipment is working properly as the fumes created by the chemical reactions are toxic.

References

• Silver Recycling in the United States in 2000
• Patent Storm