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Electrolytic plate-out of silver in the 1 ppm range

I'm currently carrying out electrolysis, trying to extract trace silver from a solution containing on average 1 ppm of silver. I deal with very large amounts of effluent so any extra silver I can extract after the method we currently use to extract silver is beneficial. I use current densities of approximately 0.01-0.15 amps/cm2, a copper cathode and stainless steel anode, fixed voltage, constant temp. and pressure. I test the solution before and after electrolysis and get varying results, most times a reduction in silver concentration but sometimes an increase. I also seem to get more of a black solid forming on my cathode which I presume is silver sulfide. I was hoping on some recommendations to improve my results and was wondering if there's anyway to target only the silver ions in solution.

Please help.

Lubini Nabutola
photographic film industry - London, Middlesex, England
2003

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You need very high agitation, and large cathode area to deposit silver at this low concentration. Even then, 1 ppm is very difficult to plate out with any efficiency. I suspect you should use ion exchange instead of electrolytic plate out when you are in this range. They can be combined, too: recover the silver on ion exchange resin then regenerate and back wash it and plate out from that mixture.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

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2004

Ion exchange surely is the best way to do it. If the solution is acid, several cationic exchangers should do the job. If it is photographic rinses, the silver is in thiosulphate complex, and you should use weak anionic resin like IRA-67. Silver thiosulphate can be stripped out of this resin with strong sodium chloride solution, and you will get a solution with several grams of silver per liter - which is very easily electrolyzed using graphite anode.

Using copper anode causes you to raise copper content in your solution, which is not a good idea if the stripped solution goes to sewer.

I once made an experiment using aluminium anode. We did reach a silver concentration of less than 0.1 mg/liter, but the silver deposition was black and sluggish. Because of poor efficiency, the cost of electricity was more than the value of silver.

Arsi Saukkola
metals recycling - Espoo, Finland