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Treating wastewater from silver refining

September 16, 2008

I am chemically refining silver and have a problem treating my rinse water. I am using dry Sodium sulfide flake to precipitate copper and other heavy metals out. I am very sensitive to the Sulfide and its almost always an over treatment or under treatment. Any other suggestions for removing these heavy metals.
196 ppm Cu
54 ppm Zn
2 ppm Pb
4.38 ppm Cd
9.3 ppm Ni

Brian Smith
Employee - Newark, Delaware

Consider a liquid polythio carbonate product (PTC). IT can be fed directly from a drum or tote and introduced into the wastewater below the waters surface. It will have the same (or greater, depending on which type you use)precipitating benefits of the sodium sulfide. Ensure that the pH is maintained between 6-9 when adding. When the pH drops to the 4 range you will start to smell the sulfide (rotten egg smell) and as you continue to go lower you will continue to off-gas H2S.Try not to overfeed. Overfeeding causes a sulfide smell and higher operating costs. Use an ion specific controller (sulfide) to control the PTC feed (it actually measures excess sulfide in the wastewater.

Gordon Djani
- Greenville, South Carolina
September 17, 2008

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Mr. Djani's advice is excellent, and I concur.

However, if I'm not mistaken, what offgases when thiocarbonates, thiocarbamates, and similar compounds are acidified is carbon disulfide, not hydrogen sulfide.

Dave Wichern
Consultant - The Bronx, New York
September 24, 2008