How long can you keep ferric chloride?

[Shea]

At room temperature,that is. I've had some sitting in a jar for a couple of years now. I'll buy new ferric chloride if I have to, but I'd rather not waste what I have left of the old stuff if I don't have to.

Which reminds me of another question -- how should I dispose of the stuff?

Shea

[Liam]

Cut off a bit of PCB. Write a line across it with an etch resist pen. See if it still works. It probably will.

Which reminds me of another question -- how should I dispose of the stuff?

Depends where you live as to the rules. I always work on the basis that anything that goes into landfill (i.e. the trash) will be quite well diluted and absorbed by all the fuller's earth cat litter I send them every fortnight.

Liam

[Mark Hammer]

Provided it isn't exposed to air, there's no reason why FeCl shouldn't last years in a glass jar or the plastic bottle it came in. I find the biggest risk is that any water in it evaporates and the stuff becomes so think that the sludge is not easily separated from the still-viable etchant. I've added some hot water to it in past (though I imagine distilled water is probably better) to thin it out and it still works like a charm. Even speedier in some instances.

Used etchant is a real nuisance but you can render it less harmful by mixing it with baking soda (sodium bicarbonate). It will produce a rust-colored foam that will dry crunchy hard and can simply be placed in a garbage bag at the curb without fear of contaminating the environment. Just keep in mind that the chemical reaction is very strong, VERY quick, and the volume increases about eightfold. No exaggeration. So you will want to mix it with baking soda in a much bigger container. Remember that moment in "Jaws" where the late Roy Scheider says "We're gonna need a bigger boat"? That's how I felt the first time I mixed the stuff together. Best to do it in small volumes toget used to it at first.

Also be aware that you DO NOT want to spill the stuff on clothes or surfaces. A real bugger to get out.

[Shea]

Thanks for the replies.

Although I've been keeping this in a jar with the lid screwed on, it has lost volume over time, which I guess means some water has evaporated out and slipped past the the lid. And the lid has started to rust. What I have left in the bottom of the jar looks like a yellow fluid with brown sludge in it. I might try to revive it with some hot water like Mark suggested, but I'm leaning towards getting rid of it and starting over with something new. At least with the volume being small, it should be easier to get rid of now. And I wonder if some rust from the lid has fallen into the solution, and I don't know what effect that would have on it.

This method looks promising: http://www.instructables.com/id/Stop-using-Ferric-Chloride-etchant!--A-better-etc

The guy talks about it like it's the greatest thing since sliced bread.

[Mark Hammer]

There are so many downsides to use of ferric chloride, that when people stumble onto something that can do the same job without the disadvantages they are jumping for joy, and right to do so.

Though I have not tried any alternate solutions myself (and shame on me for that!), like ammonium persulphate, they work well. So feel free to try them. Personally, I only stick with FeCl because I know it well, know where to buy the stuff in town, and don't do a huge volume of etching.