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Sparex disposal REVISITED!


#1
Isn't what you're doing (that is,  taking the copper out of the
solution)  eliminating the need to get rid of the Sparex?  

G’day Laura (and any others who want to stop and listen.) OK,
lets start at the beginning. Gold and silver alloys which
jewellers use contain copper (they may contain very small amounts
of other things too, but let’s talk about the copper) When heated
strongly the copper in the alloys oxidises to copper oxide(s) -
one being red and the other is black; the dreaded firestain.
This is why we put the job in pickle, which is an acid that
dissolves copper oxides. The pickle in general use is 10%
sulphuric acid, or a solution of sodium bisulphate (sodium acid
sulphate) or alum - sodium, or potassium aluminium sulphate which
is slightly acid. The acid sulphate ions in all of these
combine with the copper oxide, converting it to copper sulphate,
and depleting the pickle of hydrogen ions (which made it acid)
Thus after a little while, the pickle needs renewing, for it is
no longer sufficiently acid (insufficient hydrogen ions present)
to do the job reasonably quickly. The copper stays in the
pickle and doesn’t interfere at all. Unless you put iron in it
which will precipitate the copper onto your silver. You should
regard the acid as being neutralised due to the removal of
hydrogen ions, and not by the build-up of copper in the solution.

Well, you can understand that the longer the pickle is in use,
the weaker it’s copper oxide removal powers will be, and the
darker the blue colour as the copper ions increase and the
hydrogen ions decrease.

So if you add washing soda or even baking soda (the former is
much cheaper) to spent pickle, it is completely neutralised when
bubbles no longer fizz up. A little more soda will precipitate
the copper as copper carbonate, a pale blue powder insoluble in
water. Swirl the liquid around and pour it off into a plastic
bucket of sawdust or shavings (cheaper than 'Kitty Litter!), and
when it has dried off, bag it and get it to the local rubbish
disposal, where it won’t cause further trouble. There’s too
little of it anyway, compared with everything else at the tip.

Silver oxide? Well, it takes a lot more than just heating in
air to make silver oxide - which, by the way, is a white powder
found virtually only in laboratories. Gold oxide? it is as rare
as hen’s teeth. It is quite a job to force gold to combine with
anything. One has to go a long way around to make gold compounds
other than gold choride. Which is why gold defeats the passage
of time.

I hope you don’t mind the lecture, or be offended by too much
detail above - which you already probably knew anyway. But
some of you might get something from it. And stop worrying
about pickle! Cheers,

   / \
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/ /| \ @John_Burgess2
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At sunny (not much lately) Nelson NZ