A Process for Precipitating Precious Metals from Solutions.
Year: 1893

page_text: Date of Application, 2nd Sept., 1893
Complete Specification Left, 1st June, 1894-Accepted, 7th July, 1894
PROVISIONAL SPECIFICATION.
A Process for Precipitating Precious Metals from Solutions.
I, CARL MOLDENHAUER of 215 Gutleutstrasse Frankfort on Maine in the
Empire of Germany Chemist do hereby declare the nature of my invention to be
as follows:-
The present invention relates to a process consisting essentially in the employment
of aluminium for precipitating precious metals from cyanide solutions in the presence
of free alkalies or earthy alkalies being also applicable with advantage to sulphurized
solutions containing free alkali that is to say solutions which contain gold in the
form of sulphuret or hypo-sulphide of gold.
Zinc has heretofore been employed in practice by preference in precipitating
gold from the cyanide solutions obtained by leaching auriferous ores. The
employment of zinc for this purpose is found however to be attended with serious
disadvantages.
Now I have discovered that aluminium can be employed for this purpose in place
of zinc without the disadvantages attending the use of the latter.
Whilst zinc forms with the bound or free compound of cyanogen and alkali,
contained in the cyanide solution a combination according to the formula
2 AuKCy 2 + Zn — K 2 ZDCv 4 + 2 Au
aluminium separates the gold very quickly from the cyanogen solution without
entering into combination with the cyanogen but simply reacting with the caustic
alkali which is present at the same time.
The invention is carried out in practice as follows:
In leaching gold out of its ores with the aid of cyanide of potassium in the
presence of an oxidizing agent a solution is obtained according to the following
formula
6 Au + 12 KCy + 30 + 6 H20 = 6 AuKCy 2 + 6 KHO + 3H2O.
By introducing aluminium into this solution of cyanide of gold containing
free caustic alkali a chemical action is produced represented by the following
formula
+
6 An ±6 KCv + 6 HCy ± 6 KHO ♣ AL, O. -
6 Au 12 KCy + 6 HH 20 + Al₂ O₂.
6 Au 12 KCy + 6 HH 20 + Al₂ 03.
Thus by the action of aluminium the cyanide of potassium employed for leaching
the gold out of its ore is regenerated which is not the case when zinc is employed.
But the zinc does not confine itself to entering into combination with the
cyanogen of the cyanogene compounds of the gold but also acts upon the free
cyanide of potassium contained in the solution so that a great part of the latter is
consumed but this is not the case when aluminium is employed.

page_text: These results are of the greatest importance when the solution separated from the
gold is to be employed in subsequent gold extracting operations as the whole of the
cyanogen in the regenerated and liberated cyanide of potassium is enabled to renew
its action but the lyes resulting from the employment of zinc cannot be employed
with the same advantage in subsequent operations for the extraction of gold.
Numerous attempts have been made to regenerate the zinc but are found to be
inconvenient and costly..
It is consequently evident that an important saving in cyanide of potassium is
obtained by the employment of aluminium.
Aluminium acts in like manner in a sulphurized alkaline solution that is to say in
a solution containing the gold in the form of sulphuret of gold or hypo-sulphide of
gold. According to the following formula
6 AuNaS + 2 Al + 6 NaHO = 6 Au + 6 Na, S + Al 2 O 3 + 3H 2 O
it does not enter into combination with the sulphur in a solution of this description.
This great and important advantage attending the employment of aluminium is
combined with other advantages as follows:-
Aluminium is far less subject to oxidation than zinc so that it can be sent from
its place of production in the form in which it is to be used for the precipitation
whereas when zinc is employed it is considered to be an important advantage to
reduce it to the required form at the place where its is employed and immediately
before using it.
For the same reason the repeated employment of the aluminium is admissible for
continuous precipitation.
Finally the quantity of aluminium required for precipitating the same quantity
of precious metal is about four times less than the amount of zinc required to
produce the same effect.
I am aware that attempts have been made to employ aluminium for precipitating
precious metals from acid or neutral solutions but in this case it offers no advantages
as compared with zinc and iron.
On the other hand the practical precipitation of precious metals from alkaline
cyanide solutions or sulphurized solutions by means of aluminium was not known
neither was it known that by the employment of the same in the presence of free
alkali it was possible to obtain important advantages herein before set forth. Of
course in the place of pure aluminium also aluminium alloy and aluminium amalgam
can be used.
Dated the 2nd day of September 1893.
J. H. JOHNSON & Co.,
47, Lincoln's Inn Fields, London, W.C., Agents.
COMPLETE SPECIFICATION.
A Process for Precipitating Precious Metals from Solutions.
I, CARL MOLDENHAUER of 215 Gutleutstrasse Frankfort on Maine in the
Empire of 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 present invention relates to a process consisting essentially in the employment
of aluminium for precipitating precious metals from cyanide solutions in the
presence of free alkalies or earthy alkalies being also applicable with advantage to
sulphurized solutions containing free alkali that is to say, solutions which contain
gold in the form of sulphuret or hyposulphide of gold.
Zinc has heretofore been employed in practice by preference in precipitating
gold from the cyanide solutions obtained by leaching auriferous ores.
The

page_text: employment of zinc for this purpose is found however to be attended with serious
disadvantages.
Now I have discovered that aluminium can be employed for this purpose in place
of zinc without the disadvantages attending the use of zinc.
Whilst zinc forms with the bound or free compound of cyanogen and alkali.
contained in the cyanide solution a combination according to the formula :-
aluminium separates the gold very quickly from the cyanogen solution without
entering into combination with the cyanogen but simply reacting with the caustic
alkali which is present at the same time.
The invention is carried out in practice as follows:-
In leaching gold out of its ores with the aid of cyanide of potassium in the
presence of an oxidizing agent a solution is obtained according to the following
formula:
-
6 Au + 12 KCƑ + 3 O + 6 H₂O = 6 AuKCy 2 + 6 KHO + 3 H₂O.
6 Au + 12 KCy + 3 0 + 6 H₂O = 6 AuKCy 2 + 6 KHO + 3 H₂O.
6 Au + 12 KCƑ + 3 O + 6 H₂O = 6 AuKCy 2 + 6 KHO + 3 H₂O.
By introducing aluminium into this solution of cyanide of gold containing
free caustic alkali a chemical action is produced represented by the following-
formula:-
6 AuKCy 2 + 6 KHO + 2 Al + 3 H₂O =
6 Au + 6 KCy + 6 HCy + 6 KHO + Al,O,.
o Au + 12 Kɩy + 6 KH₂O + Al¿U.
Thus by the action of aluminium the cyanide of potassium employed for leaching
the gold out of its ore is regenerated which is not the case when zinc is employed.
But the zinc does not confine itself to entering into combination with the
cyanogen of the cyanogen compounds of the gold but also acts upon the free
cyanide of potassium contained in the solution so that a great part of the latter
is consumed but this is not the case when aluminium is employed.
These results are of the greatest importance when the solution separated from
the gold is to be employed in subsequent gold extracting operations as the whole
of the cyanogen in the regenerated and liberated cyanide of potassium is enabled
to renew its action but the lyes resulting from the employment of zinc cannot be
employed with the same advantage in subsequent operations for the extraction of
gold. Numerous attempts have been made to regenerate the zinc but are found to.
be inconvenient and costly.
It is consequently evident that an important saving in cyanide of potassium.
is obtained by the employment of aluminium.
Aluminium acts in like manner n a sulphurized alkaline solution that is to say in
a solution containing the gold in the form of sulphuret of gold or hyposulphide
of gold. According to the following formula :-
6 AuNaŊ + 2 Al + 6 NaHU = 6 Au + 6 NaS + ALU; + 3 H§O
6 AuNaS + 2 Al + 6 NaHO = 6 Au + 6 NaS + ALO; + 3 H§U
it does not enter into combination with the sulphur in a solution of this description.
This great and important advantage attending the employment of aluminium is
combined with other advantages as follows:-
--
Aluminium is far less subject to oxidation than is zinc so that it can be sent
from its place of production in the form in which it is to be used for the

page_text: precipitation, whereas, when zinc is employed it is considered to be an important
advantage to reduce it to the required form at the place where it is employed and
immediately before using it.
For the same reason the repeated employment of the aluminium is admissible
for continuous precipitation.
Finally the quantity of aluminium required for precipitating the same quantity
of precious metal is about four times less than the amount of zinc required to
produce the same effect.
I am aware that attempts have been made to employ aluminium for precipitating
precious metals from acid or neutral solutions but in this case it offers no advantages
as compared with zinc and iron.
On the other hand the practical precipitation of precious metals from alkaline
cyanide solutions or sulphurized solutions by means of aluminium was not known
neither was it known that by the employment of the same in the presence of free
alkali it was possible to obtain important advantages hereinbefore set forth.
Of course in carrying out this invention aluminium-alloy or aluminium-
amalgam can be used in place of pure aluminium.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
The process for precipitating gold or other precious metals from their solutions
by means of aluminium-aluminium alloy, or aluminium amalgam, substantially as
hereinbefore described.
Dated this 1st day of June 1894.