Elk City mining news. (Elk City, Idaho) 1903-1913, 1905-06-10
THE CYANIDE PROCESS.
Written by R. Stewart Browne in Min
ing and Scientific Press.

The following is from Cyanide Plant
Equipment" trade treatise from the
Redwood Manufacturers Co., San Fran
cisco, Cal. In this article Mr.. Browne,
who is the company's engineer, has
given in simple language description
of the cyanide process and attempted to
make plain to non-technical readers
some points governing the construction
of cyanide plants. To those familiar
with the process it presents no new
features, but to many others it will
prove of considerable interest:
The cyanide process is based on the
fact that dilute cyanide solution will
dissolve gold in the presence of oxygen.
This is explained in the following re-
action commonly known, as Ellsner's
equation.
Eau plus 4KCN plus o plus H2O
equals 2KAu(CN) 2 plus 2KOH.
Briefly stated, the process consists in
bringing an ore reduced to a suitable
degree of fineness in contact with a
cyanide solution; removing the solution
from time to time as the gold and silver
is dissolved, and replacing it with fresh
solution; precipitating the gold and sill
yer from the solution withdrawn; and,
finally, subjecting the ore to a wash
water and then discharging it. The
gold and silver is obtained in an impure
state mixed with base metals, and these
are removed by a simple refining pro-
cess.
The cyanide process is very flexible
one 1t may be used for the direct
treatment of ores after crushing, or in
connection with some other process such
as amalgamation, concentration, etc.
1t is only directly applicable to the
treatment of ores in which gold occurs
in an extremely fine state of division.
Coarse gold will dissolve in cyanide So
luton, but it may require very long
time to accomplish it. The process is,
therefore, necessarily limited to the
treatment of such ores as will yield a
satisfactory extraction in a reasonable
time. Fortunately, coarse gold may be
removed by amalgamation, and if, after
doing so, the tailings carry sufficient
value, the cyanide process may be used
for recovering the rest of it, or so much
as is practicable.
Sulphide minerals, such as pyrite,
yield up their gold to cyanide very slow
ly, so that when they are of sufficient
value it is customary to remove then
by concentration, and either treat then
separately or ship to smelter.
A certain class of ores require roast
ing to make them amenable, particularly
these in which tellurides and arsenides
occur. AS rule silver ore does MOI
yield high extraction, but by Chord
izing them the silver is converted intC
chloride, in which form it readily dis
solves in cyanide.
Anything of an acid nature will de
compose cyanide. Sulphides have ;
strong tendency to oxidize and form
acid salts. These will react with cyan
ide and destroy it. 1t is, therefore
necessary to neutralize them by adding
caustic soda or Stacked lime to the ore
the amount being determined by thu
acidity test.
The fact that oxygen is necessary IL
order for the cyanide to dissolve golt
has led to a number of patents being
taken out for processes in which air o
oxidizing compounds are either adde'
or forced into the ore to increase tn
extraction. 1t is worthy of note tina
none of these processes have becom
very widely adopted, the reason beinI
that if solutions are given sufficient ex
posture to the air they will absorb enoug
oxygen for the solution of gold, and thi
without the heavy cost entailed by tn
use of expensive reagents and heav
installations of machinery. However
any method that will cheaply aerate tn
ore or solution is of great benefit i
cyanide work.
We can divide the cyanide process in
to four operations: QD Crushing tn
ore; (2) dissolving the gold and silver
(3) precipitation; (4) refining.
CRUSHING THF ORE. The particula
mill to be used for crushing will hav
to be determined by the character @
the ore and the economic conditions
The selection of the proper mesh
crush through is one of the importar
details. 1t must be of such size tina
the gold, after passing through, wi
have been liberated from its matriz