A couple idea. First off, review some basic chemistry before
thinking any pickle would somehow break down silver or copper
(elements, after all) into MAGNETIZED particles, since neither is a
magnetic metal. That would require turning the silver into another
metal that is magnetic. A good trick indeed (alchemy went out of
style some centuries ago). In strong pickle (sulphuric acid salt)
copper will dissolve. Silver itself will only slightly be attacked,
but not much dissolved. However, you mention it stripped enamel off
your sink. Most enamel sinks are, under the enamel, made of steel.
Could that be the source of your magnetic particles? Seems more
likely to me. Other sources would be anything else made of iron or
nickle that got into the pickle (tweezers?). But silver and copper
simply won’t have broken down into magnetic material. The blue color
is normal for dissolved copper. Any normally made pickle solution,
especially if strong, will dissolve copper, eventually becoming blue
in color. With peroxide added, this happens a lot faster, so a
peroxide containing pickle will rather quickly dissolve copper. But
not silver. Only a light etch on silver, and then the attack stops
after a surface film forms.
As to the pickle itself, well, add water. Hydrogen peroxide is not
itself very stable. It will mostly break down within a few days,
especially when exposed to air and light, leaving merely water. Even
a little remaining peroxide would still make the stuff an aggressive
pickle, so fully breaking down might take longer. But what you’d then
have is very concentrated sparex. All you need do is add enough
water, roughly the amount you might originally have used to mix up
normal pickle solution from that volume of dry chemical, and what
you’d then have is roughly the same as normal, but rather used (since
you say it’s now blue in color) pickle. If it then still works, it’s
usable as such. If you then wish to dispose of it, the usual disposal
methods would also apply. In general, this simply means diluting it a
lot, so it’s only mildly acidic, and then flushing it down the toilet
(assuming a municipal waste water system that then gets treated
downstream). In this situation, the only real concern is the copper
salts, which are a polutant if introduced into a waste water stream
that won’t be treated. So dumping it down the toilet if you’ve got a
septic tank, isn’t such a good idea.
Note that you don’t need to worry about neutralizing the acid in
pickle before dumping it. Simple dilution with water is enough. The
concern is heavy metals, like copper, contained in it.
The final concern, of course, is how to explain the damaged sink to
the rest of your household… (good luck with that… 
)
Peter
