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GOLD STRIPPING PROCESS.
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Sodium
cynide....(20z)
62.2070 gms.
Water
(1 pint)
0.56825 lit.
To one pint of this
solu. Add
1/2 fluid (14.20625 ml) once of 100 vol.hydrogen peroxide then
immerse the article to be stripped.the container should be
placed in a sink as
there may be
a suddenevolution
of heat with violent gassing. This
will increase
thestripping action.
After gassing leases,
add more
peroxide cautiously. If solu. Turns blue or is not clear,
more cyanide is
needed.
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Only
a few pieces
at a time should be stripped other
wise the
rapid action on a large amount of work in a large volume of slou.
Will cause boiling over.
4
au + 8 nacn + 2h2o2
4 naoh + 4 na [ au (cn)2 ].
A
better method,
although still requiring
a fair
amount of
attention on
the part
of the operator,
is to immerse
the gilt
articles in a 10 %
Aqueous
solu. Of nacn, 100
gm/lit. To
which has been added 20 ml/lit of 130 vol h2o2.
The
solu. Should be contained in a plain steel vessel
and this stood inside
a
trough or small vessel, as
heat is
developed during stripping and the liquid is opt to forth
over.
For
this reason, aloso, not more than one or two pieces of
work should be stripped at a time. Further small addition
of h2o2 may be
made when
ever the bath becomes sluggigh
in action. This
stripping solu.
Should be operated under an efficient fume
hood as it is highly toxic.
After sufficient time, the
mixture is allowed to settle doen
and clear the
solu. Is
separated. This solu. Is
run into the
precipitation tank containing zinc shavings or lead
coated zinc
as lead coated zinc precipitates gold
more rapidly
as a fine powder.
2na
[ au (cn)2 ]+zn
na2 [ znkn)4] +
2 au
I.e.
2[au(cn)2]+2n
[zn (cn)4] + 2 au]
The
precipitated gold
is treated with Sulpuric Acid
or Nitric
Acid to dissolve
any adhered zinc zinc is more
electropositive than gold & hence it easily displaces
gold from the complex ion.
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