From: "Jim O'Connor" <oconnor.jim77**At_Symbol_Here**GMAIL.COM>
Subject: Re: [DCHAS-L] silver recovery units
Date: July 3, 2013 12:29:35 PM EDT
Reply-To: DCHAS-L <DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU>
If you're talking about a 5 gallon plastic pail with rolled steel wool inside it works by metallic replacement. Iron is released into solution from the steel wool and metallic silver precipitates as a sludge on the bottom of the pail. Running low pH aqueous waste through the unit is probably dissolving the silver and steel wool, negating the value of the device. The effluent is supposed to be tested with silver test paper (it turns black) regularly to make sure the unit is not exhausted.
Sent from my iPhone
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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