From:Philip Oshel

Or, for those of us old enough to remember photomicroscopy by 
wet-chemistry methods, AgCl is used in film negatives and prints for 
recording images. And, photograph buffs collected their used 
developed, put a current through it, and collected the metallic 
silver. Not only made some money, but much less hazardous waste (and 
nowadays, less hazardous-waste costs).
Keep collecting the filters, ash them to get the Ag precipitate free 
of the paper, and reclaim the metal.
I don't have a recipe for doing this handy, but there would be plenty 
on the web, I'm sure.

>I would suggest you check with your safety department and/or your city's
>waste department. Silver salt is silver salt, and can not be disposed of
>down the sink, per the EPA.
>Chemically, by adding sodium chloride, the clear silver nitrate has been
>made into silver chloride, which is now white and which is not very soluble
>in water, hence the precipitation (turning visible). However, it is still a
>silver salt which cannot be disposed down the sink.
>Now, if you filter this through a filter paper, collect up the silver
>chloride on the filter paper, you should at that point be able to throw a
>away the clear water. You might wanted to have your safety department check
>the water first, to see if you did remove all the silver salts from the
>water. Safety department will send it out for analysis.
>Then, let the filter paper with the silver chloride dry overnight (in a hood
>is fine - dries faster and it's out of everyone's way). Put the dried filter
>paper into a zippable plastic bag. As you collect more filter papers with
>silver on it (such as from disposing solutions of silver stains like retic,
>GMS, PAMS, etc.) you can put these filter papers together in the same
>zippable plastic bag.
>These plastic bags with filter paper with silver chloride can be hauled away
>by your hazardous waste hauler. Now you are properly disposing silver
>nitrate via EPA rules, and you are not paying for disposal of water which is
>very heavy by weight.
>Another method for disposal of silver nitrate solutions is to add equal
>amount by volume of 1.0 N hydrocloric acid to the silver solution, and let
>it set overnight. Again, silver chloride will precipitate out, collect on
>the filter paper and dried as mentioned above, and the "water" part can now
>be disposed down the sink (if tested and OK'ed to go this).
>We take an old 1 gallon plastic alcohol bottle, pour all our silver staining
>solutions in it until it is 1/2 full, the pour the 1 N Hydrochoric acid to
>the top, let it set overnight, filter, etc. Then we reuse the plastic bottle
>for the next collection, as the some silver does stick to the inside plastic
>and turns black. There's no danger in this, it just looks ugly. After a few
>times of collecting and precipitating, we have the waste hauler dispose of
>the bottle too, and just start with a new plastic bottle. This bottle cannot
>go into the regular trash, as it is contaminated with silver, and the EPA
>won't like it in a regular land fill.
>We are a large institution, and are doing lots of silver stains a day, so we
>collect silver in large quantities. If you are a small institution, collect
>the silver solutions in a smaller bottle. Ammoniacal silver (such as used in
>the retic stain), if allowed to dry, can be explosive. So don't let the
>silver solutions dry out when you are collecting them. Add some water, if
>Peggy A. Wenk, HTL(ASCP)SLS
>William Beaumont Hospital
>Royal Oak, MI 48073
>-----Original Message-----
>[] On Behalf Of MaryAnn
>Sent: Friday, April 27, 2007 6:47 AM
>Subject: [Histonet] SILVER NITRATE
>Our Pathologists have used silver nitrate for years a 5% solution and then
>add NACL before discarding down the drain with water.  We only use it on
>large specimens, breast, lumpectomy etc.
>   MaryAnn Hancock
>Ahhh...imagining that irresistible "new car" smell?
>  Check outnew cars at Yahoo! Autos.
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Philip Oshel
Microscopy Facility Supervisor
Biology Department
024C Brooks Hall
Central Michigan University
Mt. Pleasant, MI 48859
voice: (989) 774-3576
dept. fax: (989) 774-3462

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