Disposal depends in part on how much you have. Normally, for
jewelers, we’re talking about small quantities at any one time. If
you have a septic tank system, then what goes down it has to be
carefully limited because you don’t want to upset the biological
activity that keeps such systems working correctly. But if you are on
anything like the average municipal sewage system, then in almost all
cases, most of the above chemicals CAN go down the drain. The key is
that they must be very dilute. The easy answer to that is to pour
them into the toilet tank and flush. With amounts of around a cup of
material at a time, this is adequate dilution so the plumbing won’t
be harmed, and neither will the sewage system be affected.
Now, for specifics. Sodium bisulphate pickle, (rio pickle) mixed as
directed, can be poured in amounts of a cup or so, directly into the
sewer drain system via the toilet. It’s already used fairly dilute
chemically, so that’s fine. No fume hood needed.
Sodium Persulphate I cannot advise you on, since I’m not familier
with it’s use or disposal. What do you use it for?
Nitric acid, if concentrated, should be diluted first, around ten to
one with water (always remember to pour the acid into water, not the
other way around). If the initial acid is fuming, you might need a
fume hood, but most likely, unless it’s got annoying odor or fumes, a
simple mask or reasonable room ventillation should suffice. Once
diluted to 1 tenth the strength of concentrated acid, it too, like
the pickle, can go harmlessly into the toilet.
Same thing with ferric chloride. dispose of smaller quantities at a
time, or dilute it more, since it can affect plumbing more if
stronger, but hey, flush twice and you’re fine…
None of those three are at all harmfull to environmental issues with
municipal sewer systems. All three are adding ions that are already
common in the sewage stream and easily dealt with, so long as they
are properly diluted. There is no reason to mix your acid with bicarb
first to nuetralize. This may deal with the acidity/low ph, but then
simply is more if different materials for the sewage stream to deal
with. The normal mix of organic sludge materials in the sewage stream
reacts quite well to neutralize any excess acidity just as well as
anything you might do before disposal. Again, the key is dilution.
As to fume hoods, for the vast majority of jewelers, that would seem
an absurd suggestion. Few if any of us have such facilities in our
workshops. That doesn’t mean we lack ventillation. On the contrary,
good ventillation is important for many things we do (like soldering,
etc) But lab style fume hoods are overkill. In many cases, these are
intended not just to protect the worker from fumes, but also, and
importantly, to help prevent cross contamination of careful chemical
preparations. We don’t need this in typical jewelry work. A decent
vent fan will do fine. If you’re unsure, you can get respirator masks
and actual respirators that are rated for light acid mists. These
will give you all the protection you need from the above chemicals.
Your nose will tell you if you need it. It the odor is more than a
trace, or at all objectionable, you need better ventillation or a
There are, of course, some chemistries that need much more stringent
ventillation. Cyanide plating solutions are the prime example, but
also many of the organic solvents (turpentine, paint thinners, nail
polish removers, zylene, some alcohols, and a number of others. Here,
the danger is that they can in some cases be cumulative toxins and
carcinogens. For these, exposure limits should be as low as possible.
For things like pickle or similar strength acids (meaning pretty
dilute), noxious as they can seem, they are not actually as
dangerous since they are not cumulative, and so long as the fumes
aren’t strong, not actually damaging. Again, if it’s strong enough to
be bothersome at all, then you need to take steps. But if you can
only barely detect that it’s there, then you’re fine unless you are
unusually sensative to such things (most people aren’t).
Anyway, hope that helps.