Year: 1888

page_text: 1 ALEXANDER WATT of 29 Granfield Street, Battersea, Surrey, Consulting Chemist
do hereby declare the nature of this invention to be as follows :-
This invention relates to the treatment of zinc or its ores by electrolysis,
either for the purpose of refining impure zinc, or of obtaining the pure zinc from
the ore.
In the specification filed in respect of my application for patent dated April 29th
1887, No. 6294, I set forth the use of vegetable acids for preparing the bath or solution
in which the electrolytic action takes place.
I have found in some samples of zinc, whether commercial or in the ore, which
have been submitted to me for treatment by the process described in my said specifi-
cation, that lead is present in varying proportions.
Lead is soluble in some vegetable acids, acetic acid for example, and I have found
in such cases that the lead present in the electrolytic solution or bath injuriously
affects the electro deposition of the zinc.
Now the object of my present invention is to obviate this difficulty by converting
the lead into an insoluble salt.
In carrying out my invention, I employ for the electrolytic solution or bath, a com-
bination of vegetable and mineral acids (by preference acetic and sulphuric acids) in
a more or less dilute condition.
The principal effect of the sulphuric acid is to convert the lead into sulphate, which
is insoluble in the vegetable acid, and which deposits at the bottom of the tank or
vat in which the solution is prepared or used. The lead thus becomes harmless so far
as the electro deposition of the zinc is concerned.
The mixture of the two acids also, in some cases, yields better results in the electro-
lytic treatment of zinc than are obtained when either a vegetable or a mineral acid
is used separately, as the zinc is less liable to form trees or irregularities of a
similar nature.
"
"

page_text: In some cases I employ solutions of zinc prepared with vegetable acids (acetic acid
by preference) mixed with sulphate of zinc, in which case I find that if any lead be
present in the solution, or in the impure zinc employed as anodes in the process of
electrolytic refining of zinc, that the lead does not become deposited with the zinc
upon the cathode or receiving plate.
The mode of procedure which I prefer is to first prepare a mixture of the vegetable.
and mineral acids moderately dilute, and in this I digest a suitable quantity of
powdered zine ore, oxide of zinc or other product, from which it is desired to
extract the zinc, until the acid mixture becomes sufficiently saturated, when the whole
is allowed to settle, and the clear liquor is afterwards drawn or pumped off for use as
an electrolyte for the extraction of the metal.-When refining impure zinc by my
process, I prepare a mixture of the vegetable and mineral acids (acetic and sulphuric
acids, by preference) in a suitably dilute condition, which may be used as the electro-
lyte direct. I then employ impure zinc as anodes in the electrolytic bath thus formed,
and pass a current of electricity in the usual way, when the acid liquor soon becomes
charged with zinc which finally deposits upon the receiving plate or cathode, as is well
understood. If preferred, a dilnte solution of the corresponding salts of zinc, say
acetate and sulphate of zinc, for example, may be used as the electrolyte.
Dated this 5th day of March 1888.

page_text: Improvements in the Treatment of Zinc and its Ores.
I ALEXANDER WATT of 29 Granfield Street, Battersea, Surrey, Consulting 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:
This invention relates to the treatment of zinc or its ores by electrolysis either for
the purpose of refining impure zinc or of obtaining the zinc from the ore.
In the specification of my patent dated April 29th 1887 No. 6294 I set forth the
use of vegetable acids for preparing the bath or solution in which the electrolytic
action takes place.
I have found in some samples of zinc (whether commercial or in the ore) which
have been submitted to me for treatment by the process described in my said specifi-
cation that lead is present in varying proportions.
Lead is soluble in some vegetable acids, acetic acid for example and I have found in
such cases that the lead present in the electrolyte or solution injuriously affects the
electro deposition of the zinc.
Now the object of my present invention is to overcome this difficulty and also to
treat zinc in any form to obtain pure zinc therefrom.
In carrying out my invention I employ for the electrolyte or bath a combination
of a vegetable and a mineral acid (acetic and sulphuric acids) in a more or less
dilute condition.
The principal effect of the sulphuric acid is to convert the lead into an insoluble
sulphate which deposits at the bottom of the tank or vat in which the solution is
prepared or used; the lead is thus rendered barmless so far as the electro deposition
of the zinc is concerned.
In the production of pure zinc from impure metal by my process I first prepare
a zinc bath or electrolyte from mixed solutions of acetate and sulphate of zine, for
which purpose I take about 1 part of a solution of acetate of zinc of the specific
gravity of say about 1160 (water being 1000) and about 2 parts of a solution of
sulphate of zinc of specific gravity of about 1290 and add water to these mixed
solutions until the bulk of the diluted solution acquires a specific gravity of 1050
or thereabouts which forms a good working solution. The exact proportions and
the precise density of the solution are not however material. If preferred larger
or smaller proportions of the acetate of zinc solution may be used but the pro-
portions given yield very good results. Or I may make the zine solution by
electrolysis using an impure zinc as the anode, carbon as the cathode and an
electrolyte of mixed dilute vegetable and mineral (acetic and sulphuric) acids.
The zinc solution is placed for the purpose of electrolysis in a tank or series of
tanks made of any suitable material.
In working the above solution for the purification of zinc the impure zinc in the
form of slabs or plates is used as anodes and thin sheets of the best commercial

page_text: zine for the cathodes. Copper, iron, or other suitable metal may also be used
the cathodes or receiving plates in which case the surfaces should be slightly
greased or covered with plumbago to prevent the deposited metal adhering thereto
so that it can be stripped off for the purpose of being melted in the usual way.
In extracting zinc from its ores, calamine or native carbonate of zinc is first
ground to a powder and then sifted and the fine powder thus obtained is gradually
added to an acid solution of mixed acetic and sulphuric acids. The proportions of
the acids which 1 find most suitable for my purpose are say 1 part commercial
15% acetic acid and 2 parts of dilute sulphuric acid (1 part acid to about 7 parts
water). The mixture is well agitated until the solution of zinc becomes neutral to
litmus paper. It is necessary to add the powdered ore to the acids gradually and to
employ a deep vessel or tank otherwise the effervesence which ensues from the libera-
tion of carbonic acid may cause the contents of the vessel to overflow. If preferred
the powdered calamine may be treated first with acetic acid in its commercial form
or more or less diluted as desired, and after the resulting liquor has been run off to
a separate vessel with dilute sulphuric acid and the resulting liquors from the two
operations after allowing the sedimentary matters to deposit, may be mixed in such
proportions as may be desired say from th to rd of the acetate solution to
rds or ths of the sulphate solution. The more or less concentrated solution
obtained is afterwards diluted with water until the diluted liquid attains a specific
gravity of about 1100 (water being 1000) or thereabouts. This diluted solution is then
transferred to the electrolytic tanks by means of pumps or otherwise. The depositing
tanks are furnished with conducting rods from which are suspended the anodes
and cathodes in the usual way. It is best to place these electrodes about two
inches apart which is a good working distance. The electric current is then allowed to
pass from a dynamo or other source of electricity and the process allowed to proceed
as usual, the operation being kept up as far as practicable without intermission
until the cathodes or receiving plates have acquired such a thickness of the deposited
metal as may render it advisable to remove them when fresh receiving plates will be
provided. The deposited metal will be stripped off the receiving plates and melted
or otherwise treated for commercial purposes. When the cathodes are of commercially
pure zine they will be melted down with the deposited metal as the impurities con-
tained in the cathode (only a very small percentage) will be so far diluted as to be
rendered practically harmless. As to the strength of current which will be necessary
for the electrolytic reduction of the zinc from solutions obtained direct from its ores
this will necessarily depend upon the density of the working solution, the tem-
peratures, the conductivity of the anodes &c. but I have found that a current from
4 to 6 amperes per square foot of cathode surface yields very satisfactory results and
does not cause the liberation of hydrogen at the negative electrodes.
In treating blende or native sulphide of zinc the ore is first to be roasted to expel
the sulphur, in the usual way, and is then ground to a fine powder, which, after sifting
is ready for use. The powdered ore is then added gradually as before to a solution
of acetic and sulphuric acids, in about the same proportion and strength as before
mentioned.
impure zinc or in
which will dissolve
the lead can then
Whenever lead is present in appreciable quantities either in the
the ore, the zinc or ore will be first treated with the acetic acid
the lead as well as the zinc.-The solution will be drawn off and
be recovered therefrom, after which the zinc or ore will be treated with sulphuric acid,
and the two solutions will be mixed together to form the electrolyte as before
described.
To deprive the acetate solution of any lead which it may have taken up, I throw
down the lead by immersing or suspending in the solution sheets of zinc or scrap
zinc the latter material being the most economical-until the whole of the lead is
deposited from its solution in the metallic state as will be well understood. The lead
thus reduced may afterwards be collected and melted by ordinary methods and thus
rendered available as a valuable by-product in the electrolytic treatment by this
process of blende and other zinc ores containing lead in appreciable quantities. When

page_text: the zinc solution is freed from the lead, it is in a fit condition to be used after
dilution as before described, as an electrolyte for the extraction of the zinc by this
process.
When the lead is only in a small percentage, it would not pay to recover it in
which case the sulphuric acid in the mixed solution will convert it into an insoluble
sulphate which will be deposited in the vessel as before described.
In working the invention on an extensive scale, it will be necessary, in order to
keep the solution in as uniform a condition as possible, that the liquid in each tank
should be kept in a continual state of circulation, which may be effected by any of the
methods ordinarily adopted for similar purposes, by which the partially exhausted
and acid liquors of the tanks are allowed to gradually flow out the tanks, while a
corresponding quantity of fresh neutral liquor is allowed to flow into them from a
head tank charged therewith.
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
1. The use in combination of vegetable and mineral acids (acetic and sulphuric
acids) in a more or less diluted state, in the preparation of a zinc solution or electrolyte
for the treatment of impure zinc or zinc ores as set forth.
2. The use of acetate and sulphate of zinc in the preparation of an electrolyte for
the treatment of impure zinc by electrolysis, as set forth.
3. The method herein described of treating zinc ores containing appreciable
quantities of lead so that the lead may be recovered as a valuable by product as set
forth.
Dated this 7th day of January 1880