We tried using our CPAC ARU-700 electrolytic silver recovery unit to process the jewelry pickle waste (citric acid, pH = 3 to 4 with concentrations of copper =1950 ppm + other lower concentrations of metals including lead=13.9ppm, chromium=0.028ppm, cadmium=0.290ppm and zinc=181ppm). It didn’t work. We came to this conclusion by visual means (hardly any sludge left on the cathode) although I never had the effluent analytically tested after recovery.
This brings me to another dilemma we have with our pickle waste. We used to use sparex but due to the pH = 0-1 we changed to citric acid pH=3-4. The metals in the sparex waste could be precipitated using sodium hydroxide but this does not work with the metals dissolved in the citric acid. Any suggestions??
Flathead Valley Community College
Here's something I can't seem to get answered by the companies that put out small silver recovery units for college photography programs. I know they do a good job of capturing silver ion washed out of the photographic paper, but these people are putting waste from alternative processes through the thing as well.
Those other chemicals include silver nitrate, ferric ferrocyanide, ferric oxalate, potassium and sodium dichromates, a bunch of sulfites, ferrous sulfate, copper toner (not sure what form the copper is in) and thiourea. It might also be worth noting that the pH of these alternative process wastes can vary from basic to very acidic.
I am assuming the high concentration of silver in the silver nitrate will just wear out the cartridge faster. And I assume the sulfites and thiourea will just go through. But the metals I need some information about.. The electron potential table is not enough here. I need to know.
OH, and there are three basic types of units out there: electrolysis, metallic replacement, and precipitation. I think this unit is the first of these. But I also think the people I talked to there don't even really know.
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