Improvements in the Process of Recovering Precious Metals from their Ores.
Year: 1892

page_text: Date of Application, 25th Jan., 1892
Complete Specification Left, 24th Oct., 1892-Accepted, 26th Nov., 1892
PROVISIONAL SPECIFICATION.
Improvements in the Process of Recovering Precious Metals from
their Ores.
1, CARL MOLDENHAUER of Frankfort-on-the-Main, Germany, Chemical
Engineer, do hereby declare the nature of this invention to be as follows:-
This invention relates to the process of extracting gold from its ores by means of
a solution of cyanide of an alkali or alkaline earth, and has for its object to render
the process more expeditious and considerably cheaper.
In extracting gold from its ores by means of a solution of cyanide of potassium
sodium, barium, etc., the simultaneous oxidation of the gold is necessary and this
has hitherto been effected by the action of the air upon the gold which is rendered
oxidisable thereby by the action of the cyanide solution.
Instead of depending upon the agency of the air for the oxidising action, I oxidise
the gold by means of ferricyanide of potassium or another ferricyanogen salt of an
alkali or of an earth-alkali in an alkaline solution.
In this case, the oxidation is very much more energetic and consequently a con-
siderably smaller quantity of the solvent is required.
Thus, by the addition of ferricyanide of potassium or other ferricyanides to the
cyanide of potassium solution, as much as 80% of potassium cyanide may be saved.
It may be remarked that the ferricyanide of potassium alone will not dissolve the
gold and does not therefore come under the category of a solvent hitherto employed
in processes of extraction.
It does not therefore render unnecessary the employment of the simple.cyanide
as a solvent but only reduces the amount required owing to the capacity of the
ferricyanide to rapidly oxidise the gold in the presence of the simple salt.
Consequently the cyanogen of the latter is not used to form the gold cyanide
compound.
I may also employ permanganate of potash as the oxidiser instead of the ferri-
cyanide ; this is not however unaffected by the cyanide of potassium present, but
takes up a portion of it which is, of course, lost to the dissolving process whereas
cyanide and ferricyanide of potassium are mutually inactive at the ordinary
temperature.
In some cases, permanganate and other artificial oxidising agents for the most
part, or absolutely, unattackable by the cyanide of potassium may be advantageously
employed for commencing the solvent action in order to economise the solvent.
The process is carried out preferably in a ball mill lined with porcelain, wood, or
other substance, unattackable by the chemicals employed.
DL:. 05th da Tanu 1900
COMPLETE SPECIFICATION.
0 Improvements in the Process of Recovering Precious Metals from
their Ores.
1, CARL MOLDENHAUER, of Frankfort-on-the-Main, Germany, Chemical
Engineer, do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by
5 the following statement :--
This invention relates to the process of extracting gold from its ores by means of

page_text: a solution of cyanide of an alkali or alkaline earth and has for its object to render
the process more expeditious and considerably cheaper.
In extracting gold from its ores by means of a solution of cyanide of potassium,
sodium, barium, etc., the simultaneous oxidation of the gold is necessary and this has
hitherto been effected by the action of the air upon the gold which is rendered
oxidisable thereby, by the artion of the cyanide solution.
Instead of depending upon the agency of the air for the oxidising action, I oxidise the
gold by means of ferricyanide of potassium or another ferricyanogen salt of an alkali
or of an earth alkali. In either case, the ferricyanogen salt is employed in alkaline
solution, the result being that the oxidation is very much more energetic and con-
sequently a considerably smaller quantity of the solvent is required. Thus by the
addition of ferricyanide of potassium or other ferricyanogen salt in alkaline solution,
to the cyanide of potassium solution as much as 80% of the potassium cyanide may
be saved. The proportions preferred are from to 2 parts of ferricyanide to 1 part
of cyanide.
It may be remarked that the ferricyanide of potassium alone will not dissolve the
gold and does not therefore come under the category of a solvent hitherto employed
in processes of extraction.. It does not therefore render unnecessary the employment
of the simple cyanide as a solvent, but only reduces the amount required, owing to
the capacity of the ferricyanide to rapidly oxidise the gold in the presence of the
simple cyanide. Consequently the cyanogen of the ferricyanide is not used to form
the gold cyanide compound.
I may also employ permanganate of potash as the oxidiser instead of the
ferricyanide. This not, however, unaffected by the cyanide of potassium present,
but takes up a portion of it which is of course lost to the dissolving process, whereas
cyanide and ferricyanide of potassium are mutually inactive at the ordinary
temperature. The permanganate of potash is also added in solution and in the
same proportions as before, viz. :-from to 2 parts of permanganate to 1 part of
cyanide.
In lieu of permanganate of potash, other oxidising agents such as other per-
manganates, manganates, hypochlorites, peroxide of manganese, or peroxide of lead,
may be employed in the herein described process as a substitute for and in the same
proportions as the ferricyanide of potassium.
Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed. I declare that what I
claim is :-
1. In the process of extracting gold from its ores by means of a solution of potassium
cyanide or other similar salt of cyanogen, the addition to the cyanide solution of
potassium ferricyanide, or other ferricyanogen salt, in alkaline solution as and for
the purpose specified.
2. In the process of extracting gold from its ores by means of a solution of potassium
cyanide or other similar salt of cyanogen, the addition to the cyanide solution of a
permanganate, manganate, or hypochlorite, or of peroxide of manganese or of
peroxide of lead, substantially as and for the purpose specified.
Dated this 24th day of October 1892.
*7401 JATO CON T
C.
MOLDENHAUER,
By A. M. & Wm. Clark,
53, Chancery Lane, London, Chartered Patent Agents.