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Also our quenched plaster. I just dry it out and throw it out. I
know there is gold in there.

G’day, Mark; To recover gold from very low content ores
commercial methods used in New Zealand first crush the material
finely, and then there are two possibilities:

  1. the crushed ore is put into a long trough containing a low
    concentration of cyanide solution in water - around 1%, and very
    fine bubbles of air are passed through the thin slurry not only
    to violently agitate it, but this also helps with gold solution.
    This dissolved gold can then be recovered by concentrating by
    evaporation of the filtered liquid and passing a DC current
    through it to plate off the gold on stainless electrodes. It
    can be peeled off the stainless when thick enough. This gives
    almost pure gold

  2. The crushed ore is stirred with mercury, or washed thinly
    over amalgamated copper plates, as it dissolves in the mercury.
    There are small plants on the West Coast of the South Island of
    NZ which make a living from washing ancient beach sand dunes in
    this manner, using an overshot water wheel to operate a stamping
    battery, then wash the crushed material down a steep slope
    containing bits of carpet to collect the larger bits, and then
    over the mercury coated copper plates. They scrape the thick
    yellowish amalgam paste off the plates and distill off the
    mercury in small, cheap iron retorts made by the local
    garage/blacksmith. The result is a lump of spongy gold, about
    18carat or so. I have seen both these methods used. Don’t know
    whether all that hassle would be worth it for used casting
    investments, though it might be if there was enough. At least,
    the processes can - and are - left to operate without much
    overseeing. So there you are. Cheers,

    / /    John Burgess, 

    / /
    / //\ @John_Burgess2
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