An Improved Method or Process for the Extraction of Precious Metals from their Ores.
Year: 1895

page_text: Date of Application, 29th July, 1895-Accepted, 31st Aug., 1895
COMPLETE SPECIFICATION.
An Improved Method or Process for the Extraction of Precious
Metals from their Ores.
I, ARNOLD VON SIEMENS, of 94 Markgrafenstrasse, Berlin, in the Empire of
Germany, 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 :-
This invention relates to the extraction of precious metals from their ores and
has for its object to obtain those metals free from other inferior metals present in
the ore.
If the ore contains besides the precious metals-gold, silver, platinum-a con-
siderable quantity of other metals, the extracting process is usually carried out in
such a manner that the baser metals are removed or remain in the residue, and a
solution is obtained of the precious metals; this is especially the case when treating
the ores with chlorine.
The removal of the inferior or baser metals is frequently a difficult operation
but was considered necessary on account of the known methods not being such
as would allow the precious metals to be obtained from the final solution sepa-
rately from other metals contained therein, so that a mixture would have resulted
from which the precious metals would have to be extracted by a separate
process.
It is however, possible to extract by the aid of electrolysis, the precious metals
from a lye containing in addition other metals, it being only necessary to so control
the electromotive force of the decomposing cell that the inferior metals are allowed
to remain dissolved, while the precious metals are caused to separate with practically
sufficient speed.
When a solution containing several metals is subjected to electrolysis and the
E.M.F. of the decomposing cell gradually increased, the metals will be precipitated
in the order of the places they occupy in the electromotive force series, that is
to say, that metal which is most electropositive will be deposited first, then the
next one in the series, and so on. Therefrom it results that the precious metals
being of the highest electropositive order, will first separate out whilst the
inferior metals will not be deposited until the E.M.F. of the cell has been further
increased.
If therefore the E.M.F. is kept below that limit at which inferior metals com-
mence to separate, the precious metals alone will be deposited, and if the operation
is continued for a sufficient length of time all of the latter will come out.
It is obvious that by this method it is also possible to separate the precious
metals from each other, but as for this purpose the E.M.F. would have to be
regulated within such narrow limits as to make it a rather troublesome operation,
and as, on the other hand, it is desired to obtain all the precious metals present
in the ore, it will practically be sufficient to extract all of them in one operation.
The E.M.F. to be applied is dependent upon different circumstances, viz. the
nature of the acids with which the different metals are combined, the degree of
concentration of the solution, and the nature of the different metals. It is practically
sufficient to find by experiment the limits of the E.M.F. for the special lye which
is obtained from the metallurgical process, so as to operate within these limits for
the purpose of separating the precious metals alone. The limits of the E.M.F.,
however, must be determined anew, when from any cause the constitution of the lye
is altered.

page_text: For instance in operating with a lye which contains five grains of each of the
chlorides of gold, copper and iron in one pint, and using a lead cathode, a coal
anode and a current density of 12 amp. for each two square yards, the limits of
E.M.F. would be between 12 and 1.4 volts. Mere traces of copper and iron will
be precipitated within these limits whilst gold will separate completely and with
sufficient speed.
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 :-
In the process of extracting by electrolysis the precious metals from a lye
containing besides these metals inferior metals, the application of so low an E.M.F.
in the decomposing cell that substantially the precious metals only are deposited.
Dated this 29th day of July 1895.
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HASELTINE, LAKE & Co.,
45 Southampton Buildings, London, W.C., Agents for the Applicant.