Improvements in the Recovery of Gold and Silver from their Solutions.
Year: 1896

page_text: Date of Application, 7th Aug., 1896
Complete Specification Left, 6th May, 1897-Accepted, 12th June, 1897
Improvements in the Recovery of Gold and Silver from their
Solutions.
We, CARL WILHELM HEINRICH GÖPNER, of Canalstrasse 46-48 Uhlenhorst,
Hamburg, Germany, Chemical Manufacturer, and HEINRICH LUDWIG DIEHL,
of Kl Grassbrook Vogelreth 8, Hamburg, Germany, Chemist, do hereby declare
the nature of this invention to be as follows:-
The leaching of auriferous ores or their tailings and slimes by solutions of
cyanide of potassium gives solutions, containing, in addition to an excess of
potassic cyanide, the dissolved gold as aurocyanide of potassium and sometimes a
auricyanide of potassium. If these very weak solutions are super-saturated at
ordinary temperature by acids, capable of decomposing the cyanide of potassium,
the, aurouscyanide or the auric cyanide are kept in solution by the hydrocyanic acid
produced.
According to the present invention the aurous or auric cyanides are precipitated
from the said solution by the following process:-
Cuprous oxide or copper compounds, belonging to the series of the protoxide,
preferably cuprous cyanide is added to the gold solution before the acidulation, or
these cuprous compounds are produced in the solution by the action of suitable
reducing agents (zinc-dust, dextrose &c.) on cupric oxide compounds-whereby
the copper compounds are dissolved in the solution with formation of a cuprous
potassic cyanide, soluble in water. If cuprous cyanide for instance is used in the
right proportion to form the soluble double compound with the free cyanide of
potassium contained in the solution, it will be entirely dissolved.
On now adding to the above solution an acid capable of decomposing cyanide
of potassium such as sulphuric acid, the free cyanide of potassium which may be
contained in the solution, as also the aurocyanide of potassium or the auricyanide of
'potassium, and the cuprous potassic cyanide will be entirely decomposed; hydro-
cyanic acid and sulphate of potassium are formed and kept in solution,
whilst the aurous cyanide or the auric cyanide and the copper cyanide are
precipitated.
The equation for the precipitation is probably :..
2 AuK(CN), Cu,(CN), x 4'SO.H₁ = Cu,Au₂(C.N), × 8 H.C.N × 4 SO,K,.
2 AuK(CN), Cu,(CN), x 4'SOH, = Cu,Au₂(C.N), × 8 H.C.N × 4 SO¿K,.
In practice it is convenient to take always an excess of cuprous cyanide in order
to obtain as complete a precipitation of the gold as possible. In this case the
precipitate consists of auro cuprous cyanide and cuprous cyanide.
The precipitate separates easily from the solution containing the hydrocyanic
acid, which may be drawn off almost entirely.
This is then slightly super-saturated with caustic alkali in order to recover a
solution of alkaline cyanide, which can always be used over again for the
extraction. A fresh quantity of alkaline gold cyanide solution is preferably
brought into contact with the precipitate remaining from the first operation in
the precipitating vat, which will then be entirely or partly dissolved in, this

page_text: (The amount of fresh cuprous cyanide to be added-if any depends upon its
excess in the first precipitate.) The process is repeated as before described until a
sufficient amount of gold has been accumulated in the precipitate from which the
metallic gold is then recovered.
If the cuprous compounds are replaced by cupric compounds in the above
process the precipitation of the gold is not so complete.
In the treatment with cyanide solutions of gold-ores containing copper (refractory
ores) or such gold ores to which from any cause copper compounds have been
added, copper is also dissolved. If the copper contained in such solutions is
sufficient to bring down the gold it is not necessary to add farther copper compounds
as described.
Silver contained in the ore together with the gold, and dissolved by the leaching
process will be recovered as well as the gold by the said process.
Instead of employing the above mentioned copper compounds. such silver
compounds may be used as are capable of forming with potassic cyanide, double
salts soluble in water, for instance cyanide of silver, nitrate of silver, sulphate of
silver, chloride of silver &c. If gold ores coutaining a comparatively high
percentage of silver are treated with cyanide solutions, it might be possible to
recover the gold without any further addition of silver or copper compounds to the
solutions in the above described manner.
Dated this 7th day of August 1896.
ABEL & IMRAY,
Agents for the Applicants.
COMPLETE SPECIFICATION.
Improvements in the Recovery of Gold and Silver from their
Solutions.
We, CARL WILHELM HEINRICH GÖPNER, of Canalstrasse 46-48, Uhlenhorst,
Hamburg, Germany, Chemical Manufacturer, and HEINRICH LUDWIG DIEHL
of Kl Grassbrook Vogelreth 8, Hamburg, Germany, Chemist, 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 the following
statement :-
The leaching of auriferous ores or tailings by solutions of potassium cyanide.
give solutions containing free alkali, the gold in solution as potassium aurocyanide
or sometimes as potassium auricyanide and a large excess of potassium cyanide.
When silver is present in the ores or tailings it is also found in the solution as a
cyanide.
This invention relates to the treatment of such solutions in such a manner as to
effect precipitation of the gold and silver cyanides and regeneration of the leaching
material.
For this purpose, the solution resulting from the leaching has added to it cuprous
cyanide which is acted on by the potassium cyanide forming soluble cuprous
potassic cyanide according to the equation::
There is then added an acid such as sulphuric acid capable of decomposing
potassium cyanide, whereupon the ingredients of the solution are decomposed
forming hydrocyɲanic acid and potassium sulphate which remain in solution
while auro or auri-cyanide and cuprous cyanide are precipitated as well as

page_text: silver cyanide when there is silver in the solution treated, according to the
equation :-
xAuK(CN), + yAgK(CN), + Cu,K¸(CN)¸ +·
6
22
-(H₂SO₂
In the practice of the process it is of advantage to add the cuprous cyanide in
excess, so as to render the precipitation of the gold as complete as possible, the
precipitate consisting then of auro-cuprous cyanide and cuprous cyanide.
The solution, decanted or otherwise separated from the precipitate, is slightly
supersaturated with caustic potassa so as to produce fresh potassium cyanide which
can be used again for leaching.
The reaction is according to the equation :-
In order to obtain gold in the precipitate in sufficient amount to render it suitable
for treatment to recover the gold, the precipitate from the first operation is
dissolved wholly or partially in a fresh quantity of the solution obtained by the
leaching, and fresh cuprous cyanide is added, if necessary, and then acid to effect a
fresh precipitation, and this may be repeated a number of times until sufficient
gold is accumulated.
When cuprous cyanide is added in considerable quantities in the first operation,
a number of successive precipitations may be effected without farther additions of
cuprous cyanide.
The process described is applicable where the solution obtained by leaching
already contains copper; but, in such case, the quantity of cuprous cyanide added
may be less than when no copper is present. When silver as well as gold is present
in the solution obtained from the leaching, the process may be modified as
follows: A soluble salt of silver such as the nitrate or sulphate is added to the
solution but not in such quantity as to effect precipitation. If nitrate of silver is
used the reaction may be expressed by the following equation.
(2y+)AgK(CN), + 2KNO,.
Or a silver salt insoluble in water such as the cyanide or the chloride may be
added but the quantity should be such that very little of it remains undissolved in
the solution. Acid is then added, and thus the silver as well as the gold is
precipitated as a cyanide, as appears from the equation
¡¤AuK(CN), + yAgK(CN), + *±³ H₂SO₁ = (x + y)HCN +
2

page_text: A mixture of a soluble salt, or insoluble silver compound with cuprous cyanide
may be used instead of simply a silver compound or cuprous cyanide.
In the leaching and and precipitation processes sodium cyanide may be used
instead of potassium cyanide, this being regenerated by adding soda instead of
potassa .to the solution separated from the precipitate. Also mixtures of sodium and
potassium cyanides may be used for leaching and may be regenerated from the
separated solution.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
1. The herein described process for precipitating gold and silver from their
cyanide solutions, by adding to these solutions cuprous cyanide or silver cyanide or
their mixture and then adding an acid..
2. The herein described process for the precipitation of gold and silver from
their cyanide solutions, by adding to said solutions a considerable quantity of
cuprous cyanide. then adding an acid to effect precipitation, dissolving the latter
by a fresh quantity of the cyanide solution obtained by leaching, and then adding
acid to effect successive precipitations from said solution..
ABEL & IMRAY,
Agents for the Applicants.