Originally Posted by thelovecollect
my only concern was the environmental impact of dumping spent fixer.. but if there are none...
Originally Posted by phototone
It you are a hobbiest, then you ecological impact will be minimal.
Actually spent fixer is the one photochemical substance (not counting bleach and some toners) where even a hobbyist can have substantial ecological impact, because the silver ions are one of the worst things you can do to the bacteria in your local waste water processing plant. It's a good idea to avoid this, even as a hobbyist.
Things you can do to get the fixer off your ecological conscience:
- Collect the fixer in a big tank and periodically bring it to either a professional photo lab (that is willing to collect it for you), a printing shop (ask before if they run photolithographic or similar processes that use fixer) or a reprocessing plant. In some countries (such as Germany) there are upper bounds on the amount you're allowed to give to them as a hobbyist, a friend of mine had problems when he collected about twenty gallons over the course of a year and then wanted to pass as a hobbyist.
- Put some iron wool in a bucket or canister and pour the spent fixer in there. The silver from the fixer will attach to the iron and fall out (I'm not a chemist, so I'm unfamiliar with the English proper terminology). Put the canister in a place with good ventilation outside your apartment. Keep it there for a couple of weeks, pour the remaining liquid into the toilet (harmless) and give the now blackened iron wool ro a reprocessing facility (or throw it away, it's not a good thing to do but it's substantially better than spent fixer in the toilet).
- Best solution: Put the fixer into a canister and add sodium dithionite, maybe three or four ounces for a gallon jug. Don't close the canister, put it in a well-ventilated location outside your apartment, as it will produce some sulphur dioxide which happens to stink. The silver will fall out to the bottom and some to the wall of the canister. After a week or so at room temperature filter the licquid through a coffee filter. The black stuff that remains in the filter and the canister is silver, the liquid can go into the toilet without any trouble. You can collect the silver and later take it to your next-door dental technician - a liter of spent 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. There is a guy on one of the German forums, an amateur with medium throughput, who does that every year.