Process for the Electrolytic Decomposition of Compounds of Metals and Sulphur.
Year: 1892

page_text: Date of Application, 22nd Oct., 1892
Complete Specification Left, 18th July, 1893-Accepted, 19th Aug., 1893
[Communicated from abroad by Messrs. SIEMENS & HALSKE, of Markgrafen-
strasse, Berlin, in the German Empire.]
Process for the Electrolytic Decomposition of Compounds of Metals
and Sulphur.
We, SIEMENS BROTHERS & Co., LIMITED, of 12 Queen Anne's Gate,
Westminster, Electrical Engineers, do hereby declare the nature of this invention
to be as follows:-
This invention relates to an improved process for the electrolytic decomposition
of metallic sulphides and other compounds of metals and sulphur and it consists
essentially in treating natural or artificially produced sulphides, that will form
soluble double salts with the alkaline sulphides, with such alkaline sulphides,
sulphhydrates or polysulphurets, to form a solution, and in subjecting the same when
in this condition to electrolytic action.
Those metals which are principally applicable to this process are antimony and
arsenic, which occur in nature in large quantities as sulphur compounds, and we
will proceed to describe the application of the invention to these substances.
The finely ground ore containing sulphide of arsenic or of antimony is passed
from the grinding mill into an extraction vessel containing a stirring apparatus
and charged with a solution of an alkaline sulp-hydrate which is capable of
dissolving the sulphur compounds of antimony and arsenic from their ores
according to the following formulæ.

page_text: The extracted antimony will consequently be completely precipitated, and at the
same time a lye will be obtained which is capable of taking up fresh quantities of
antimony and arsenic.
This lye is led through pipes from the several cathode compartments to the
stirring vessel, where it is mixed with fresh ores.
The nature of the electrolyte that circulates in the anode compartments is
dependent upon the ore residues resulting from the extraction of the antimony or
arsenic.
If these contain gold, silver, copper, mercury, bismuth, zinc, cobalt, nickel, the
anode electrolyte may be an alkaline chloride (NaCl, KCÍ, NH,C1) which during
the electrolysis developes chlorine either in gascous form, or dissolved in the lye,
and which is brought together in a second stirring apparatus with the solid ore
residues retained in the filter, so that the above mentioned metals are dissolved from
the gangue, from which the solution is separated in a second filter tank. The
solution of Cu, Au, Ag Bi, Zn Co Ni Hg is treated with the sulphuretted hydrogen
escaping from the extraction vessel according to equation I, for separating therefrom
the said metals.
The further separation and treatment is effected according to known methods.
If there are no metals worth treating in the ore residues, the generated chlorine
can be otherwise utilised, for example for bleaching purposes; or an electrolyte
may be chosen for the anode compartments by which an oxidising process may be
carried out, suitable for the particular local conditions such for instance as for the
oxidation of ferrous sulphate to ferric sulphate.
These secondary electro chemical processes form however no part of the present
invention.
The quantities of alkaline sulphides and of chlorine required for the above
described process, as also for making good the losses thereof that will result in
practice, are prepared in an electrolytic vessel by the decomposition of alkaline
chlorides, and by the introduction of sulphuretted hydrogen into the cathode
compartments.
The above described process is applicable, as already stated, not only to the
sulphides or sulphurets of arsenic and antimony occurring in nature, but also to
sulphur, antimony and arsenic compounds that are produced artificially, such for
example as by precipitations from aqueous solutions. In this way, for instance,
the by products obtained in copper smelting works can readily be so treated as to
precipitate therefrom the arsenic and antimony in the form of sulphurets, which
are then subjected to the above electrolytic process.
If the said by products shew a large percentage of sulphur the metal compounds
can be directly dissolved by treatment with the alkaline sulphides.
The above described process can be employed for obtaining all other, metals,
besides arsenic and antimony, the sulphides of which form with alkaline, sulphides,
sulph hydrates and poly sulphates, soluble sulphur, compounds, and which occur.in
nature in sufficiently large quantities, as sulphur, compounds, or, which can, be
produced as such artificially without great loss.
The principal ones of such metals are gold, platinum, tellurium, molybdenum,
tiu &c.

page_text: The extraction and precipitation of the said metals can be effected either at
ordinary temperature, or under heating.
Dated this 22nd day of October 1892.
ABEL & IMKAI,
Agents for the Applicants.
Process for the Electrolytic Decomposition of Compounds of Metals
and Sulphur.
We SIEMENS BROTHERS & CO. LIMITED of 12 Queen Anne's Gate, Westminster,
Electrical Engineers 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 an improved process for the electrolytic decomposition
of metallic sulphides and other compounds of metals and sulphur, and it consists
essentially in treating natural or artificially produced sulphides, that will form
soluble double salts with the alkaline sulphides, with such alkaline sulphides, sulph-
hydrates or polysulphurets, to form a solution, and in subjecting the same when in
this condition to electrolytic action.
Those metals which are principally applicable to this process are antimony and
arsenic, which occur in nature in large quantities as sulphur compounds, and we
will proceed to describe the application of the invention to these substances,
referring for this purpose to the accompanying diagrammatic drawing.
The finely ground ore containing sulphide of arsenic or of antimony is passed
from the grinding mill A into an extraction vessel B containing a stirring
apparatus and charged with a solution of an alkaline sulph-hydrate which is
capable of dissolving the sulphur compounds of antimony and arsenic from their
ores according to the following formulæ
As,S,+6 NH, SH = (As,S, 3 (NH),S) + 3 H,S.
The lye obtained is separated from the solid residues in a filtering tank D', and
after collecting in a reservoir C it is passed into the cathode compartment of an
electrolytic precipitating apparatus D which is divided by diaphragms into several
negative and positive compartments a and b. The diaphragms should be such as to
offer a minimum resistance to the passage of the current, but to prevent as much as
possible the diffusion of the two electrolytes contained respectively in the positive
and negative electrode compartments. This is best effected by rapid circulation
and by the use of diaphragms of colloid materials such as sheet asbestos boiled in
gelatine and the like."
The positive compartments of this depositing vessel are closed gas tight, for
the purpose hereinafter mentioned, and they contain insoluble anodes such as
carbon, platinum &c., while the negative compartments are open and generally
contain metal plates, such as copper and antimony, as cathodes.

page_text: ¨ (As̟„S¸ 3 (NH¸)„S) + 6 H = As₂ + 6 NH, HS.
The extracted antimony will consequently be completely deposited, and at the
same time a lye will be obtained which is capable of taking up fresh quantities of
antimony and arsenic.
This lye is led through pipes 1, 2, 3, 4, 5 from the several cathode compartments
to the extraction vessel B, where it is mixed with fresh ores.
The nature of the electrolyte that circulates in the anode compartments is
dependent upon the ore residues resulting from the extraction of the antimony or
arsenic. If these contain gold, silver, copper, mercury, bismuth, zinc, cobalt,
nickel, the anode electrolyte may be an alkaline chloride (NaCl, KCI, NH,CI)
which during the electrolysis developes chlorine either in gaseous form, or dissolved
in the lye, and which is brought together in a second extraction apparatus E with
the solid ore residues retained in the filter D', so that the above mentioned metals
are dissolved from the gangue, from which the solution is separated in a second
filter tank F. The solution of Cu, Au, Ag, Bi, Zn, Co, Ni, Hg is treated with the
sulphuretted hydrogen escaping from the extraction vessel according to equation I,
for separating therefrom the said metals.
The further separation and treatment is effected according to known methods.
If there are no metals worth treating in the ore residues, the generated chlorine
can be otherwise utilised, for example for bleaching purposes; or an electrolyte
may be chosen for the anode compartments by which an oxidising process may be
carried out, suitable for the particular local conditions, such for instance as for the
oxidation of ferrous sulphate to ferric sulphate.
These secondary electro-chemical processes form however no part of the present
invention.
The quantities of alkaline sulphides and of chlorine required for the above
described process, as also for making good the losses thereof that will result in
practice, are prepared in an electrolytic vessel H by the decomposition of alkaline
chlorides, and by the introduction of sulphuretted hydrogen into the cathode
compartments.
The above described process is applicable, as already stated, not only to the
sulphides or sulphurets of arsenic 'and antimony occurring in nature, but also to
sulphur-, antimony- and arsenic compounds that are produced artificially, such for
example as by precipitations from aqueous solutions. In this way, for instance,
the by-products obtained in copper sinelting works can readily be so treated as to
precipitate therefrom the arsenic and antimony in the form of sulphurets, which are
then subjected to the above electrolytic process.
If the said by-products shew a large percentage of sulphur, the metal compounds
can be directly dissolved by treatment with the alkaline sulphides.
The above described process can be employed for obtaining all other metals,
besides arsenic and antimony, the sulphides of which form with alkaline sulphides,
sulph-hydrates and poly-sulphurets, soluble sulphur compounds, and which occur in
nature in sufficiently large quantities, as sulphur compounds, or which can be
produced as such artificially without great loss.
The principal ones of such metals are gold, platinum; tellurium, molybdenum,
tin &c.

page_text: The extraction and deposition of the said metals can be effected either at
ordinary temperature or under heating.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the, same is to be performed we declare that what we
claim is:
Process for the electrolytic separation of antimony and arsenic from their
sulphur compounds wherein the latter are dissolved in sulph-hydrates with genera-
tion of sulphuretted hydrogen, which sulph-hydrates are then subjected to
electrolysis only in the cathode compartments of the electrolytic bath, whereby the
sulph-hydrates are regenerated and are employed for further extractions, a
secondary process being carried out at the anode according to which, by the
utilisation of the sulphuretted hydrogen given off by the extraction process, any
foreign metals contained in the ores such as Au, Ag, Cu, Hg, Bi, Ni, Co, Zn are
obtained substantially as described.
Deted this 10th 1 of 1 1000
ABEL & IMRAY,
Agents for the Applicants.