IMPROVEMENTS IN THE PROCESS OF DECOMPOSING METALLIC HALOID SALTS BY ELECTROLYSIS
Year: 1884

page_text: I CARL HOEPFNER, Doctor of philosophy, of 47 Koeniggraetzerstrasse, Berlin
S.W. Prussia, German Empire do hereby declare the nature of said invention for
IMPROVEMENTS IN THE PROCESS OF DECOMPOSING METALLIC HALOID SALTS BY
ELECTROLYSIS" to be as follows:-
This invention relates to the decomposition of haloid salts of light and heavy
metals by electricity.
In the electrolysis of haloid salts of the light and heavy metals, especially in
that of alkaline salts the electricity has never been employed in a sufficiently
advantageous manner by reason of the difficulties resulting from polarization.
These difficulties or defects are obviated according to this invention which has
for its chief object to prevent polarization by using depolarizing substances at the
cathode and by causing the electrolyte to be kept in motion.
'
According to this method it has been found advantageous to select chlorides
amongst other substances to decompose the electrolyte and to use the chlorine
liberated therefrom for manifold purposes.
For instance, in order to prepare directly by electrolysis from any chloride such
as chloride of sodium, the chlorine required for the extraction of metals and for
other purposes, a conducting substance which cannot be attacked by chlorine, such
as carbon or manganese ore, is used as an anode in the solution of the chloride, this
solution of the chloride being caused to continually flow in and out whereby the
chlorine liberated is carried away.
According to the quantity of liquid flowing in, and the speed of such flow, the
said liquid becomes more or less saturated with chlorine. When the influx of
liquid is arrested the chlorine is evolved in the form of a gas and can easily be
collected. By heating the liquid the disengagement of gas is promoted.
In order to avoid the polarization, and current weakening evolution of hydrogen
at, the cathode, the latter, which may consist of lead, copper, iron, carbon or any
other conducting material, is covered with a substance which prevents polarization
from taking place. This depolarizing substance may be either solid or liquid. To
the latter form belong the strong. oxidizing acids such as nitric acid, manganic
acid, chromic acid and the solution of their salts, and particularly such substances
which are reduced by hydrogen; also the solutions of the oxysalts of iron,
...מ

page_text: manganese, mercury and the like as also the solutions of salts which liberate their
metals under the influence of an electric current such as chloride of gold, sulphate
of copper, plumbate of soda and the like. If the cathode is immersed in any of
the above liquids acting as an electrolyte, then no free hydrogen is evolved.
If solid substances are to be employed for the depolarization of the cathode they 5
should be such as are insoluble in water and can be reduced by the metals of the
alkalies and by hydrogen. To these substances belong insoluble chlorides, sulphates,
carbonates and other salts of the heavy metals, sulphides such as sulphide of lead,
iron pyrites or sulphide of iron, and particularly the oxides of the heavy metals.
Amongst the latter may be employed oxide of zinc, oxide of copper, tin, or oxide of 1
tin, manganese ore or oxide of manganese, magnetic iron or oxide of iron and
the like.
The most suitable substance is peroxide of lead or minium. When employing
solid depolarizing substances, a solution of common salt or of any other chloride
serves as electrolytic liquid for the cathode. As will be readily understood the 1
evolution of free hydrogen is now avoided; as in its nascent state it reduces the
oxide employed and forms water. The relative positions of the anode and cathode
and their size and form vary according to circumstances.
In apparatus suitable for carrying out this invention the cathode may have the
form of a hollow cylinder and is placed in a receptacle. In this cylinder is
arranged a membrane in which is placed the anode. The electrolyte for the
cathode is introduced through a pipe connecting the bottom of the receiver with a
reservoir and rises upwards subsequently leaving the apparatus in a reduced state
through another pipe which conveys it to a suitable vessel.
The anode is immersed in the liquid which is to be saturated with chlorine, and
the latter is introduced and runs out through suitable pipes.
When the electrodes are placed one above the other, the cathode lies on the
bottom of the receptacle which is provided at its upper part with an inlet aperture,
and at its upper and lower parts with outlet apertures. The upper outlet
aperture serves to permit the liquid to circulate while the lower outlet aperture is
used for the purpose of emptying the receptacle.
The chlorine generator which has the shape of an inverted funnel dips in the
electrolyte of the cathode, and is closed at its lower part by a membrane above
which is placed the anode. The liquid which has to be saturated with chloride
enters from the reservoir into the lower part of the inverted funnel by means of a
pipe and leaves the said funnel through another pipe. In all cases care must be
taken that the liquids of the two poles should not become mixed. This condition
can be safely fulfilled by using one, or preferably two, separating membranes.
A solution of common salt which is placed between the two membranes must be
renewed from time to time.
According to the depolarizing substances employed there is formed at the
cathode either a sodium salt such as carbonate of soda when carbonate of lead is
employed, or phosphate of soda when phosphate of lead is used and when
sulphides and oxides are employed either hydrate of soda or hydro sulphide of
soda are formed. These products are removed from time to time and employed for
various purposes.
It is of great importance that the soda lyes should be extracted directly, such
lyes when sufficient care is taken, being produced in a very pure state.
The parts of the apparatus which come in contact with the alkaline lyes of the
cathode are made for that purpose of iron or other resistant material; the parts in
which free chlorine enters must consist of material resisting the action of acids.
The membranes used are made of porous burnt clay, asbestos, stag hair,
parchment, paper, or other material resisting the action of acids.
Instead of producing free chlorine, a chlorinization (chloroning) may be effected
in such a manner that the substances which have to be saturated with chlorine at
the anode may be slowly conveyed with the chloride lyes thus produced. In this
manner it is possible to prepare chlorates, as the common salt lyes are conveyed to

page_text: the anode as an alkaline hydrate, and moreover it is possible to form chloride of
iron, of great importance in the extraction of metals, from chlorides; lastly organic
substances such as alcohol can also be treated in a similar manner.
This mode of production of chlorine at the anode has the advantage over that
heretofore employed, and according to which chlorine gas was passed into oxide of
iron or similar substances, that there is in the former method less expenditure of
chemical energy.
It is obvious that this method used for the production of chlorine is applicable
to other chlorides and thus rejected lyes containing oxide of iron and chloride of
manganese, chloride of calcium, and the like, can be rendered valuable. Likewise,
iodine can also be extracted from iodides bromine from bromides, caustic potash
from chloride of potassium, and so on.
It is not necessary to dwell upon the advantage of the above described method
for the production of chlorine over those heretofore employed and by means of which
chlorine was produced from manganese ore and hydrochloric acid because even if
these substances were cheaper than at the present time such advantages would bo
obvious.
This convenient mode of preparing chlorine is of the highest value where
manganèse ore and hydrochloric acid are high in price which is mostly the case in
gold producing countries Where power and common salt are at hand the pro-
duction of chlorine according to this invention can be easily obtained.
The common salt lyes obtained by this method are highly valuable for the
extraction of silver as it is well known that chloride of silver is soluble in
such lyes.
The lyes which contain gold and silver and are obtained by means of chlorine
water are deprived of their gold in such a manner that the gold is collected at
the cathode where the chloride of gold and the accompanying metallic salts are
reduced, and thus the polarization of the cathode is prevented.
In continuous circuits the chloride containing lyes are first saturated with
chlorine at the anode, then mixed with auriferous ore, and reduced at the cathode,
and then conveyed back again to the anode in order to absorb a fresh supply of
chlorine.
When auriferous lyes are not employed to prevent the polarization of the
cathode, the gold therefrom is precipitated by the electrolytic liquid of the cathode
which contains caustic alkalies, chloride of iron, sulphydrate of iron, or other
similar substances.
Compared with the above described preparation of soda lyes the method of
preparation heretofore employed was complicated and a good many valueless sub-
stances were produced, it also was not an economical method. The use of liquid
and solid depolarizing substances, and especially the latter, forms on that account a
more advantageous method than others, because, by its means, the expense of
electric power is very much smaller than in methods heretofore employed, and
valuable secondary products are obtained; the formation of injurious bubbles of
bydrogen-is prevented, the liquid is allowed to stand quietly, and the separation of
the alkaline from the neutral lyes is thereby ensured.
It is obvious that the above described method of depolarization is only valuable
for such solutions of salts by means of which polarization takes place especially at
the cathode, and applies only to haloid combinations which are soluble in water.
Dated this 23rd day of April 1884
HASELTINE, LAKE & Co.,
For the Applicant.

page_text: "
COMPLETE SPECIFICATION.
I, CARL HOEPFNER, Doctor of Philosophy, 47, Koeniggraetzerstrasse, Berlin,
S.W. Prussia, Germany do hereby declare the nature of my invention for
IMPROVEMENTS IN THE PROCESS OF DECOMPOSING METALLIC HALOID SALTS BY
ELECTROLYSIS" 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 decomposition of haloid salts of light and heavy
metals by electricity. In the electrolysis of haloid salts of the light and heavy
metals, especially those of the alkalies, the difficulties resulting from polarization
have hitherto bindered an advantageous application of electricity in the large
chemical industries.
These defects are obviated by the process described below, which consists chiefly
in preventing polarization by the use of depolarizing substances at the cathode, or
by circulation of the electrolyte.
According to this method it is possible, amongst other things, to decompose
chlorides in an advantageous manner and to utilize the chlorine present therein for
manifold purposes. For instance, in order to prepare directly by electrolysis and
from any chloride, such as chloride of sodium, the chlorine required for the
extraction of metals and for other purposes, a conducting substance which cannot
be attacked by chlorine, such as carbon or manganese-ore, is used as an anode in
the solution of the chloride, this solution being caused to continually flow in and
out at the same, whereby the chlorine liberated is carried away.
According to the quantity of liquid flowing in and the speed of such flow the
said liquid can be more or less saturated with chlorine.
When the influx of liquid is arrested, the chlorine is evolved in the form of a
gas and can easily be collected. By heating the liquid, the disengagement of gas
is promoted.
In order to avoid the polarizing and current-weakening separation of hydrogen,
at the cathode, the latter, which may consist of lead, copper, iron, carbon or any
other conducting material, is surrounded or covered with a substance which
prevents the polarization. These depolarizing substances may be either solid or
liquid. To the latter class belong the strongly oxidizing acids such as nitric acid,
manganic acid, chromic acid and the solution of their salts, and in general such
substances as are reduced by hydrogen; also the solutions of the oxysalts of iron,
manganese, mercury, and the like, as also the solutions of those salts, and hydrates
which, under the influence of an electric current, separate metal, such as chloride
of gold, sulphate of copper, plumbate of soda and the like. If the cathode is
immersed in any of the above liquids as an electrolyte, no free hydrogen is evolved.
The depolarization of the cathode can be effected with special advantage also by
means of solid substances, which are insoluble in water and can be reduced by a
metal of an alkali or by hydrogen. To this class of substances belong insoluble
chlorides, sulphates, carbonates and other salts of the heavy metals, also sulphides
such as sulphide of lead, iron pyrites or sulphide of iron, and particularly the oxides
of the heavy metals,

page_text: Amongst the latter may be employed oxide of zinc, oxide of copper, tin ore, or
oxide of tin, manganese-ore or oxide of manganese, magnetic iron or oxide of iron
and the like.
Peroxide of lead or minium, however, is especially suitable. The cathode, as
in secondary batteries, is covered with a layer of minium or any of the above
mentioned substances. When employing solid depolarizing substances, a solution
of common salt or of any other chloride serves as electrolytic liquid for the cathode.
As will be readily understood, the evolution of free hydrogen is now avoided, as in
its nascent state it reduces the oxide and forms water. The relative positions of
the anode and cathode and their size and form vary according to circumstances.
In the accompanying drawing two different arrangements of the apparatus to be
employed are shewn by way of example.
Figure 1 shows the electrodes arranged vertically one within the other, and
Figure 2 shows the electrodes arranged one above the other, this form being
most preferable when solid depolarizing substances are employed. The cathode,
with its minium covering, then lies below the anode, evolving chlorine.
As shewn in Figure 1, the cathode K, which has the form of a hollow cylinder,
is placed in a receptacle B in which is arranged a membrane or cell M Mi
surrounding the anode A. The electrolyte for the cathode is conducted through
a pipe a from the reservoir R into the lower part of the receptacle, and ascends,
passing from the apparatus in a reduced state through the pipe b which conveys it
to the vessel G.
The anode A is immersed in the liquid which is to be saturated with chlorine,
or chlorinized, and is introduced through the pipe d and runs out through the
pipe f
When the electrodes are placed one above the other, as shown in Figure 2, the
cathode K lies on the bottom of the receptacle B which is provided at its upper
part with an inlet aperture a and at its upper and lower parts with the outlet
apertures and c. The upper outlet aperture serves to permit the circulation,
while the lower one is used for the purpose of emptying the receptacle.
"
The chlorine generator G, which has the shape of a funnel, dips in the electrolyte
of the cathode, and is closed at its lower part by a membrane M above which the
anode is placed. The liquid which has to be chlorinized passes from the reservoir R
through the pipe d into the inverted funnel G below the anode, and leaves the
same through the pipe f.
In all cases, care must be taken that the liquids of the two poles do not mix.
This condition can be completely fulfilled by using one, or preferably two,
separating membranes or cells.
The solution of common salt, which is between the two membranes or cells
(Figure 1), is renewed from time to time.
:
According to the depolarizing substances employed, there is formed at the
cathode either a sodium salt, such as carbonate of soda when carbonate of lead is
employed, or phosphate of soda, when phosphate of lead is used, and when
sulphides and oxides are employed either hydro-sulphide of soda or hydroxide of
soda is formed. These products can be removed from time to time and employed
for various purposes.
.
The direct production of soda-lye, which, when sufficient care is taken, can be
obtained in a pure state, is of great importance.
The parts of the apparatus which come in contact with the alkaline lye of the
cathode are suitably made of iron or other resistant material; whilst the parts in
which free chlorine is present must consist of material resisting the action of acids.
The membranes or cells are made of porous burnt clay, asbestos, slag, hair,
parchment, paper or other material resisting the action of acids or alkalies. Instead
of producing free chlorine, an oxidation or a chlorinization can be effected by slowly
conveying, together with the chloride lye, the substance to be chlorinized past the
anode. In this manner it is possible to prepare oxy chlorates by admitting a
hydrate of an alkali to the common salt lyes at the anode, and moreover it is

page_text: possible to form from the chlorine compound chloride of iron, which is of great
importance in the extraction of metals; lastly organic substances, such as alcohol,
can also be chlorinized in this manner.
This chlorinization at the anode has the advantage over the former chlorinization
effected by introducing gasiform chlorine into protochloride of iron, that there is
less expenditure of chemical energy.
It is obvious that this method used for the production of chlorine is also
applicable to other chlorides, and especially rejected lyes, containing protochloride of
iron, protochloride of manganese, chloride of calcium, or the like, can be rendered
valuable. Likewise, iodine can be extracted from iodides, bromine from bromides,
caustic potash from chloride of potassium, and so on.
It is not necessary to point out more fully that the above described method for
the production of chlorine is preferable to that heretofore employed, according to
which chlorine was produced by manganese ore and bydrochloric acid, the prices
of which were high.
This convenient mode of preparing chlorine is of the highest value in cases
where the price of manganese-ore and hydrochloric acid is high, which is mostly
the case in gold-producing countries. The unhealthy mode of extracting gold by
amalgamation will soon be replaced by this cheap production of chlorine.
Where power and common salt are at hand, the production of chlorine according
to this invention can be easily carried out.
The common salt lyes containing chlorine, obtained by this method, are also
highly valuable for the extraction of silver, as it is well known that chloride of
silver is soluble in common salt.lye.
The lye containing gold and silver and obtained by means of chlorine water is
deprived of its gold by being conveyed to the cathode, where chloride of gold and
the metallic salts accompanying it are reduced, thereby effecting the depolarization
of the cathode.
In a continuous circuit, the chloride lye is first saturated with chlorine at the
anode, then mixed with auriferous ore and reduced at the cathode, and then con-
veyed back again to the anode in order to take up chlorine. When auriferous lye.
is not to be employed for the depolarization of the cathode, the gold can be
precipitated by the electrolytic liquid of the cathode, which contains caustic alkali,
protochloride of iron, or sulpho hydrate, etc.
Compared with the above described preparation of soda lye, the method of
preparation heretofore employed was complicated, and on account of many valueless
products being obtained it also was not economical.
The use of liquid and solid depolarizing substances, and especially the latter, is
very advantageous because, by these means, the expenditure of electric power is
decreased, valuable secondary products can be obtained, and the liquid is enabled
to stand quietly and a better separation of the alkaline from the neutral lye is
ensured while the injurious bubbles of hydrogen are prevented.
It is obvious that the above described method of depolarization is only valuable
for solutions of salts with which polarization at the cathode takes place at all, and
applies only to haloid combinations which are soluble in water.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is
First. In the electrolytic treatment of chlorides of the light and heavy metals
or of other baloid salts of the same, the employment of depolarizing substances in
the solid or liquid form at the cathode, in order to prevent the formation of free
hydrogen.
Second. In the electrolytic treatment of haloid salts, the employment of depo-
larizing substances at the cathode, in combination with the electrolyte circulating
at the anode.
Third. The process of direct extraction of halogens and of combinations of the
same, especially chlorine, chlorine containing liquids, perchlorides such as chloride

page_text: of iron, oxygen chlorates and organic chlorides, by electrolysis of common salt and
other haloid salts by means of depolarizing substances at the cathode and the
circulation of the electrolyte of the anode.
Fourth. The application of the electrolytic preparation of halogen to the
extraction of the precious and semi-precious metals, use being made of the
circulation of the electrolyte by which polarization is diminished at the anode.
Fifth. The process of the direct extraction of oxyhydrates and sulphohydrates
and their salts by electrolysis of common salt and other baloid salts, using
depolarizing substances at the cathode.
HASELTINE, LAKE & Co.,
For the Applicant.