In reply to your question about refining sweeps using Nitric Acid. I
looked into refining sweeps myself a couple of years ago. I wanted to
do a comparison to the return I was getting from a refiner I was
using at the time.
From what I remember Nitric only removes the copper, silver & some
of the more unstable? metals. It leaves Palladium & Platinum behind
with the gold. This method may be OK for yellow gold sweeps.
The other method I looked into was to dissolve all the metals with
Aqua Regent & then precipitate the metals out of solution by adding
various chemicals.These acids, chemicals & fumes created were not
people friendly. I decided that it wasn’t worth the time it takes &
the risk to myself & anyone near.
The refiner I now use costs $150 Australian , per 10 oz, for a four
metal count return( Gold, Silver, Palladium, Platium) . I have been
getting around 50% gold from the original melted weight of the sweeps
which I’ve been very happy with.
There was also a metal refining system being sold which makes it
possible to refine sweeps yourself. Costing around $1000 Australian.
It will be interested to read other people’s ideas on refining & are
they happy with the returns they get. From the people I’ve talked to
most people seem to think they may have had just a tiny bit more gold
in their sweeps than they get back. Personally I think this is just
human nature not dishonest refiners but I hope to hear some comments.