G’day. Since hydrofluoric acid is acknowledged to be one of the
acids most dangerous to humans, my advice is to stop looking for it
in in case you find some. Unless you have had some training in the
handling of HF, leave it it alone
However: In the hands of an expert it is no more dangerous than
anything else; my wife used to do clay analysis, using HF on a
daily basis for years and came to no harm. She is now 84.
You could perhaps obtain some sodium fluoride, or another salt of
fluorine, which when warmed with dilute sulphuric acid will produce
HF, but it will take days to etch away the quartz. Since such a
mixture will also dissolve glass and ceramics, you might have to
obtain a very high quality stainless steel vessel to contain the
reaction. (my wife had to use platinum beakers and crucibles) All
salts of hydrofluoric acid are very poisonous, and the vapour from
the fluoride/acid reaction is very bad indeed for lungs.
The alternative for releasing gold from quartz is to crush it, then
treat it with sodium or potassium cyanide solution, using continuous
agitation. Finally the gold is removed from this gold cyanide
solution by electroplating it on to stainless steel electrodes, from
which it is easily scraped off.
Cheers for now,
John Burgess; @John_Burgess2 of Mapua, Nelson NZ