Improvements in the Treatment of Impure Bismuth for Refining the same.
Year: 1895

page_text: Date of Application, 21st Nov., 1895
Complete Specification Left, 20th Aug., 1895-Accepted, 26th Sept., 1896
PROVISIONAL SPECIFICATION.
Improvements in the Treatment of Impure Bismuth for Refining
the same.
We, BOLESLAS ZAHORSKI, Ph.D. Chemist FERDINAND HURter, Ph.D.
Chemist, and JOHN BROCK, Director of The United Alkali Company Limited,
all of G11 Exchange Buildings, Liverpool, in the County of Lancaster, do
hereby declare the nature of our invention to be as follows:-
Bismuth as usually obtained contains lead which it has hitherto been very
difficult to separate from the bismuth.
This invention has for its object to effect the separation of the bismuth from the
lead in a complete and ready manner and this we effect by electrolysis.
This may be carried out by making the impure bismuth the anode in an
electrolytic cell, for instance by casting the impure bismuth into plates of suitable
size, and using these plates as the said anodes. The cathodes may be plates of
carbon, but plates of pure bismuth, or of platinum, or of other suitable metal,
may be employed. As electrolyte a solution of nitric acid, obtained by mixing
about one part by volume of nitric acid of 14 specific gravity, with from 5 to
6 parts of water may be used, but we may also employ a solution of bismuth
nitrate, provided that it contains from 12 to 15% of free nitric acid.
There is no necessity to employ a diaphragm, but it is advisable to surround
the anodes of impure bismuth with a bag of muslin or other suitable material
offering no considerable resistance to the action so as to prevent small particles
of the impure metal, which are apt to break off the plate during the electrolysis,
from intermingling with the pure bismuth separated at the cathode.
The density of the current of electricity should be carefully adjusted, as if too
great a current density be used the anodes become covered with basic nitrate of
bismuth, which causes considerable resistance to the passage of the current, and
is difficult to redissolve in the electrolyte. We have found that if the current
does not exceed 30 ampères per square foot there is no danger of formation of
such basic nitrate.
The bismuth of the anode dissolves in the electrolyte together with the lead,
the bismuth being deposited at the cathode and the lead remaining in the
electrolyte. This electrolyte should be renewed from time to time, for when it
becomes too rich in lead, the bismuth deposited at the cathode is liable to be
contaminated with lead.
When the electrolyte has become too rich in lead it may be freed from it by
electrolysis as hereinafter described with regard to the electrolysis of impure
bismuth dissolved in nitric acid.
The bismuth is deposited on the cathode as a fine block powder if the current
density be too small, and so long as the electrolyte does not contain sufficient
bismuth. With a proper current density (say one about 30 ampères per square
foot) the bismuth soon becomes crystalline, but it does not adhere firmly to the
cathode plate but falls to the bottom of the cell, from whence it can be removed
from time to time. It should then be well washed with water to which a small
quantity of nitric acid has been added so as to remove from the bismuth all

page_text: traces of the solution containing lead nitrate. The bismuth is then dried and
fused.
Or we dissolve the impure bismuth in nitric acid and electrolyse this solution
between electrodes say of carbon. If the solution of the two metals contains a
sufficient excess of free nitric acid, the lead will be deposited on the anode as
lead-peroxide, whilst the bismuth deposits at the cathode as metallic bismuth.
In order to prevent the lead peroxide from falling and contaminating the
bismuth at the bottom of the cell, it is well to surround the anode with a muslin
bag, or the like.
The bismuth deposited can then be treated as herein before described.
Dated this 21st day of November 1895.
JOHNSONS & WILLCOX,
47 Lincoln's Inn Fields, London, W.C., Agents.
Improvements in the Treatment of Impure Bismuth for Refining
the same.
We, BOLESLAS ZAHORSKI, Ph.D. Chemist FERDINAND HURTER, Ph.D.
Chemist, and JOHN BROCK, Director of The United Alkali Company Limited,
all of G 11 Exchange Buildings Liverpool, in the County of Lancaster, 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:—
Bismuth, as usually obtained contains lead which it has hitherto been very
difficult to separate from the bismuth.
This invention has for its object to effect the separation of the bismuth from the
lead in a complete and ready manner and this we effect by electrolysis.
This may be carried out by making the impure bismuth the anode in an electro-
lytic cell; for instance, by casting the impure bismuth into plates of suitable size,
and using these plates as the said anodes. The cathodes may be plates of carbon,
but plates of pure bismuth, or of platinum, or of other suitable metal, may be
employed. As electrolyte a solution of nitric acid, obtained by mixing about
one part, by volume, of nitric acid of 1-4 specific gravity, with from to 6 parts,
by volume, of water may be used, but we may also employ a solution of bismuth
nitrate, provided that it contains from 12 to 15 per cent. of free nitric acid.
There is no necessity to employ a diaphragm, but it is advisable to surround
the anodes of impure bismuth by a bag or envelope of muslin, or other suitable
material, offering no considerable resistance to the electric current so as to
prevent small particles of the impure metal (which are apt to break off the plate
during the electrolysis) from mingling with the pure bismuth separated at the
cathode.
The density of the current of electricity should be carefully adjusted, as, if too
great a current density be used, the anodes become covered with basic nitrate
of bismuth, which causes considerable resistance to the passage of the electric
current, and is difficult to redissolve in the electrolyte. We have found that if
the current does not exceed 30 ampères per square foot there is no danger of the
formation of basic nitrate of bismuth.
We may carry out this invention as follows;-but we do not limit ourselves to
the precise details. We cast the impure bismuth to be treated into plates of
suitable thickness, and of the form shewn in Figure 1, the lugs A serving to
support the anodes in the electrolytic tank (one of which is shewn in sections at
right angles to each other in Figures 2 and 3) they receiving the electric current

page_text: by resting upon conductive strip D to which one of the poles of the generator is
connected.
As cathodes we use plates of, say, carbon of a size equal to that of the anode
plates. We use no diaphragms but suspend these plates in a tank or tanks B
tapered at the bottom and provided with a large stop-cock C.
Several tanks may be used in series and they are filled with the electrolyte,
which at the beginning of the process consists of dilute nitric acid, containing
from about 8 to 12 per cent. of real nitric acid (HNO3).
The bismuth deposits on the cathodes but does not adhere to them, and, when
the cathodes are shaken, it falls to the bottom of the tanks.
When a sufficient amount of bismuth has accumulated (say after 24 hours
working) the contents of the tanks are ruu off through the stopcock C and the
metallic bismuth is carried out by the liquid and can be separated by settling or
filtration.
The electrolyte is preferably kept in rapid circulation by causing it to flow from
tank to tank or otherwise.
We have found that if the current density exceed 30 ampères per square foot
of active bismuth surface the process does not work, and we prefer to employ
With proper
only 15 ampères per square foot of bismuth surface or thereabouts.
arrangements the potential difference will then not exceed three-quarters of a volt
per cell.
The current from the positive pole of the dynamo is conveyed into the aforesaid
copper bars or strips D fastened to the upper edge of the tank Figures 2 and 3,
the plates of impure bismuth resting by their lugs A on these copper bars or
strips D so as to receive the current. The cathodes are connected to the negative
pole of the dynamo by the connections D¹.
The nitric acid originally present in the electrolyte partially combines with lead
and bismuth during the working, and it is necessary to test the condition and add
nitric acid when necessary so as to have always about 8 per cent. of free acid
present.
The bismuth of the anode dissolves in the electrolyte together with the lead,
the bismuth being deposited at the cathode and the lead remaining in the
electrolyte. This electrolyte should be renewed from time to time, for when it
becomes too rich in lead, the bismuth deposited at the cathode is liable to be
contaminated with lead.
When the electrolyte has become too rich in lead, it may be freed from it by
electrolysis. We have however found it more convenient to treat the electrolyte,
when it contains too much lead, with metallic lead, so as to precipitate as metallic
bismuth any bismuth it may contain. The solution of lead nitrate thus obtained
may be utilized in any desired way.
The bismuth is deposited on the cathode as a fine black powder, if the current
density be too small, and so long as the electrolyte does not contain sufficient
bismuth. With a proper current density (say one of about 15 amperes and not
exceeding 30 amperes per square foot) the bismuth soon becomes crystalline, but
it does not adhere firmly to the cathode but falls to the bottom of the cell from
whence it can be removed from time to time as described. It should then be well
washed with water, to which a small quantity of nitric acid has been added
so as to remove from the bismuth all traces of the solution containing lead
uitrate. The bismuth is then dried and fused, and will be found of very good
quality.
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:-
In the treatment of impure bismuth, for refining it, employing the impure
bismuth as anode in an electrolytic tank, or in electrolytic tanks, with a solution
of or containing, nitric acid as electrolyte, and carbon, pure bismuth, platinum, or

page_text: other suitable material as cathode, substantially as and for the purpose herein before
described.
Dated this 20th day of August 1896.
JOHNSONS & WILLCOX,
47 Lincoln's Inn Fields, London, W.C., Agents.