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Dirk Rösler
25-Oct-2007, 22:23
I have been trying to figure out what to do with used fixer chemical other than pouring it down the drain.

Some web research showed (http://phototec.de/phorum/read.php?3,18224#msg-18256) that the following is the proposed, most environmentally (http://www.kodak.com/US/en/dpq/site/TKX/name/hseSilverManagement) acceptable (silver thiosulfate is toxic in minute concentrations) method of disposal:

Chemically, the key to the process is Na2O4S2 Sodium dithionite (http://en.wikipedia.org/wiki/Sodium_dithionite) (aka sodium hydrosulfite or sodium hydrosulphite), a white crystalline powder with a weak sulfurous odor. This substance will fall out the silver and separate it from the rest of the components, creating a benign liquid that can be poured into sewage.

This is how it is done: put the fixer into a canister and add the sodium dithionite, maybe around two table spoons per litre. Don't close the canister. Put it in a well-ventilated location at around room temperature, perhaps out on the balcony, as it will produce some sulphur dioxide which happens to smell (similar to Japanese onsen - enjoy!). The silver will fall out as a black sludge of colloid silver and silver sulfide to the bottom and some to the wall of the canister. After a week or so, pour off the excessive liquid and filter the rest through a coffee filter. The black stuff that remains in the filter and the canister is silver; dry the cake and collect it for further processing or disposal. The liquid can go into sewage without any trouble.

In theory, you can collect the resulting silver and later take it to your next-door dental technician - a liter of exhausted fixer contains some three to six grams of silver - who then can smelt it down into a ring for your loved one every year or two if you have enough throughput. You can also use nitric acid to dissolve it and coat your own photographic plates.

Sodium dithionite must be stored dry, otherwise it will decompose and corrode the container it is stored in. Don't inhale the dust (mask is recommended) and wear gloves, i.e. take the usual lab precautions. Obviously don't ingest the stuff either. Wash hands after handling. One kilogram of sodium dithionite should suffice for 80 liters of fixer.

You may have also heard of the steel wool method (http://photo.net/bboard/q-and-a-fetch-msg?msg_id=006io9), but my research shows two major disadvantages:

1) you cannot tell when the reaction has ended;

2) the fixer will never be exhaustively react with the steel wool unless
you keep adding fresh surface for the liquid to 'attack'. The reason is
that once the chemical reaction on the steel wool's surface has occurred, the
reactive parts of the surface are consumed and no longer reacts any further.

This limits the usefulness of the exercise - if you don't care you should not be bother with any of this at the first place.

Comments, corrections etc. welcome.

davidb
25-Oct-2007, 22:37
I take mine to the local university where it is recycled.

You might look into this as well.

Dirk Rösler
25-Oct-2007, 22:45
Trust me, I have 'exhausted' all those possibilities before deciding to get into those powders and things. This summary is meant for everyone who does not have access to alternatives and do the right thing anyway. There is not that much on the web on this.

Randy H
25-Oct-2007, 23:30
(silver thiosulfate is toxic in minute concentrations)

There is not that much on the web on this.


http://www.silvercouncil.org/html/faq.htm

Dirk Rösler
26-Oct-2007, 00:10
http://www.silvercouncil.org/html/faq.htm

So? Gotta love links thrown in without commentary...

Anyway, I have read most of it and it says neither you shouldn't or it is safe to dump it. So I have no idea what you are trying to tell us.

Randy H
26-Oct-2007, 00:28
So? Gotta love links thrown in without commentary...

Anyway, I have read most of it and it says neither you shouldn't or it is safe to dump it. So I have no idea what you are trying to tell us.

Comment: If you read the article, the silver thiosulfate is harmless. Totally.
(except for blue skin)
Words, words, words. More words,
The article pretty much speaks for itself. It is not a "commentary", just an informational piece from the the Silver Organization. And it is just one article among several. The EPA does have information on Silver Thiosulfate also. They concur. The dentist putting the silver fillings in your teeth is more likely to do harm than the silver in the fix.

Ole Tjugen
26-Oct-2007, 01:08
The article says that silver is harmless to humans, not that it is harmless to the environment. Or rather - it tries to say that silver/thiosulfate complexes are ahrmless, but there is a lot of missing and lightly skipped-over information. So what are they trying to avoid saying?

Anyway, even if Sodium dithionite is relatively harmless the byproducts of the reaction (SO2 gas) are highly toxic. IMO it's at best uninformed to recommend that method of treating used fixer!

As to "the steel wool method":


1) you cannot tell when the reaction has ended;
Sure you can. As long as there's still silver ions and solid iron present, it goes to completion.


2) the fixer will never be exhaustively react with the steel wool unless
you keep adding fresh surface for the liquid to 'attack'. The reason is
that once the chemical reaction on the steel wool's surface has occurred, the
reactive parts of the surface are consumed and no longer reacts any further.

Steel wool doesn't get "plated" like copper would, and starts with a very high surface-to-volume ratio. As long as there is more initial iron than total dissolved silver (weight-to-weight, since 2Ag+ + Fe -> 2Ag + Fe2+ ), you will get around 99.9% of the silver out of the solution.

jetcode
26-Oct-2007, 01:09
We have a hazardous chemical disposal site which manages "hobby" chemicals, there's silver reclamation products. There was an article on disposal by septic tanks floating around somewhere many moons ago.

Dirk Rösler
26-Oct-2007, 01:47
Comment: If you read the article, the silver thiosulfate is harmless. Totally.

Please supply a quote. The article is written by the photo industry. Everything in there is very carefully phrased - guess why?

Also why is it then collected for waste management in the real world? If it was harmless, that wouldn't be necessary...



IMO it's at best uninformed to recommend that method of treating used fixer!

Thanks for the input Ole. So looks like steel wool method is just as good? Sorry, I don't quite understand what you are saying with the above. You mean it's better to stay away from the reaction with sodium dithionite?

Ole Tjugen
26-Oct-2007, 02:34
The dithionite method works, and dithionite itself is "relatively harmless". But the reaction gives off SO2 gas, which is a lot more toxic than most people think! Look up toxicity data for sulfur dioxide...

The steel wool method works, works well, and is cheap and uses only safe ingredients. The products are iron thiosulfate and metallic silver (sludge), both of which are at least as harmless as the starting ingredients. Also, there are no toxic byproducts.

Randy H
26-Oct-2007, 03:30
From the GOV, not the photo industry.
"The effect of speciation on the acute and chronic toxicity of silver was compared using the fathead minnow as the test organism. Silver sulfide, silver thiosulfate and silver chloride were compared to the silver ion, added as silver nitrate. The tests were flow-through in soft water at 25C. Silver chloride was found to be 300 times less toxic, silver sulfide was 15,000 times less toxic, and silver thiosulfate was 17,500 times less toxic than silver nitrate.
Most existing silver criteria, objectives or regulated amounts are not based on the free ionic monovalent ion, which is acutely toxic to aquatic life. Instead they are based on total silver which includes the metal, complexes and precipitates, all of which are very much less toxic than the monovalent ion. Thus, these existing regulations and criteria are often overprotective. A method of measuring the biologically-available forms of silver is needed so that the criteria and the risk are correlated." http://www.env.gov.bc.ca/wat/wq/BCguidelines/silver/bcsilver-04.htm

Still, do what you feel comfortably safe with. No complaints from here for doing our part for the next-gen.
ME? Fix, (don't use stop) left-over dev is puored off into a 5-gallon bucket. and sits there. Usually evaporates within a week or so. Ailver left over? Never looked. Maybe I should. Perhaps I could retire :rolleyes: . Rinse is 20 gallon recycle through carbon filtered waterfall system.

Dirk Rösler
26-Oct-2007, 16:11
Thanks for comments, all.

jnantz
26-Oct-2007, 20:21
hi dirk:

i just have a waste hauler take away my spent photochemicals.
it doesn't cost very much money, and i feel better than turning a blind
eye to dumping it down the drain or ...

polished copper works well as an ionic transfer if you go that route ..
and you can probably get it from a hardware store (copper flashing ) ....

good luck!

john

Randy H
26-Oct-2007, 21:13
John, just a wild-a** thought here. Using the copper flashing as the transfer piece. Have you tried this? AND, would it retain enough of the silver to be re-polished and used as a photo-plate? IF it did, you could almost cut the copper to size before placing in solution. Hmmmm. I'll have to think on that one a while.

jnantz
26-Oct-2007, 21:52
John, just a wild-a** thought here. Using the copper flashing as the transfer piece. Have you tried this? AND, would it retain enough of the silver to be re-polished and used as a photo-plate? IF it did, you could almost cut the copper to size before placing in solution. Hmmmm. I'll have to think on that one a while.

before i started to use a waste hauler, i would polish a piece of copper ( to get copper ions "free")
and plate the silver out. did this for close to 10 years ...
it works well, but after you plate the black silver sludge out of solution, you still have to "deal" with that stuff.
dumping it in the trash is as bad as down the drain, and unfortunately
using a blow torch / crucible to purify the silver, yields nasty/ toxic fumes,
i have heard household bleach will also do the trick, but i fear the unknown,
so in the end it is easier to let the waste hauler take it all for 100$USD/few years, and have a clear conscience ...

Oren Grad
27-Oct-2007, 09:21
Dirk, if you can figure out the right power adapter, you might try one of these:

http://porters.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=PCS&Product_Code=221063&Product_Count=&Category_Code=

SamReeves
27-Oct-2007, 09:45
Usually your local garbage company will take the hazardous chems and dispose of them at their business site.

Randy H
27-Oct-2007, 10:48
Usually your local garbage company will take the hazardous chems and dispose of them at their business site.

Only in California. :rolleyes:

Dirk Rösler
28-Oct-2007, 18:28
Dirk, if you can figure out the right power adapter, you might try one of these:

http://porters.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=PCS&Product_Code=221063&Product_Count=&Category_Code=

Hi Oren, thanks. Pretty cool and inexpensive. Japan has pretty much the same mains power as the US, so an adapter may not even be needed.