Elk City mining news. (Elk City, Idaho) 1903-1913, 1905-07-01

the water is completely expelled from
it, When this is done it becomes very
docile and may be worked by any meth
cd. For drying this class of ore the
best furnace is the revolving cylinder
of the White Howell type.
In treating tailings that have accu-
mulated in reservoirs it usually happens
that considerable quantities of slime are
found that have settled out from the
sands. A good way of treating such
is to pillow and harrow it up and then
mix it in with the sands in such quantl-
ties that it does not interfere too ser
iously with the percolation.
The fact that fine grinding gives an
increased extraction has led to numer-
GUS Investigations being made along this
line, with the result that quite number
of mills have adopted fine grinding. In
fine grinding mills the slime problem is
not so serious as it would seem, provid-
ed that the ore is siliceous. The admix-
ture of a large quantity of siliceous
material with slime renders filter press
ing comparatively easy matter. The
usual sequence of operations are fine
grinding, agitation with a cyanide solu-
ton, filter pressing, precipitation OF the
gold, washing of the cakes and finally
the discharging of the press. The sue
cess which has attended fine grinding
indicates that before long its adoption
will be widespread.
CYANIDING OF CoPPER-GoLD ORES. -
1t is we'll known fact that cyanide has
great affinity for certain copper COM
pounds, and the occurrence of an ap-
preciable amount of them in an ore may
make it impracticable to treat the ore
by the cyanide process. Sulphides which
have not undergone oxidation are not
appreciably attacked by cyanide, but
the oxides and carbonates are very SOL
uble.
There are two reasons why the pres
ence of copper is Objectionable first, it
causes a large loss of cyanide, it gives
a great deal of trouble in precipitation.
Gold and silver ores containing small
quantities of copper are now being
treated successfully by the cyanide pro-
cess, and making a commercial success,
but it requires very careful work, and
much of it is of delicate nature, re-
curing the services of an expert chem
list. Any lixiviation process which will
treat coppery gold-silver ores and give
a good extraction will solve one of the
most troublesome metallurgical prob
lens of the day.
1t is known that ammonia will rapidly
dissolve the oxides and carbonates of
copper, and, second, that if an alkaline
cyanide be added to the ammonia solu-
ton containing copper, solution con-
tanning the double salt, upro-ammonium
cyanide will be formed which will dis
solve gold and silver. These reactions
form the basis of several processes
which aim to treat copper-gold-silver
ores.
There is no question but that high
extraction can be obtained by the use
of the proper reagents. The weak point
is in the precipitation Of the metals. D.
Mosher, who has some patents covering
the process, employs boiling out meth
cd for recovering the ammonia and cop
per and then precipitates the precious
metals from the cyanide solution on zinc
shavings. He first teaches the ore with
a weak ammonia solution to remove a
greater portion of the copper. He then
follows with ammonia-cyanide to dis
solve the gold, silver and residuary cop
per, as in the ordinary cyanide process.
The fact that the cyanide is destroyed
by the copper does not decrease the ex-
traction of the precious metals, for the
cupro- ammonium cyanide that is formed
has an equal if not greater affinity fol
them, probably due to its powerful oxi-
dizing action.
The solutions coming from the leach
ing tanks pass through a continuous
still built on the heat exchange princi-
pie. Here the ammonia is driven of
and condensed in a receiver for further
use. The copper is precipitated in the
still as the black oxide. The outgoing
solution contains the cyanide, together
with the gold and silver. This is pre-
cipitated in the usual way and is made
ready for the teaching tanks again by
the addition of ammonia.
The important point in the process is,
Of course, the boiling out, and the ques-
ton of expense deserves careful consid-