Year: 1887

page_text: Date of Application, 29th Apr., 1887
Complete Left, 30th Jan., 1888
Complete Accepted, 2nd Mar., 1888
I ALEXANDER WATT of 29 Granfield Street, Battersea, Surrey, Consulting
Chemist, do hereby declare the nature of this invention to be as follows:-
The object of this invention is to effect the purification of crude or impure zinc
and the extraction of metallic zinc from its ores, more especially from calamine or
native carbonate of zinc, by means of electrolysis.
In carrying out my invention, I employ the impure zinc, however obtained, as an
anode, and place it in a solution, or electrolyte, composed of a vegetable acid.--I then
pass a current of electricity through the liquid, and the zinc becomes rapidly dissolved.
In a short time, zinc of great purity is deposited upon a cathode or negative electrode,
while the surface of the anodo assumes a discoloured, or even black appearance, duo
to the impurities with which the zinc is always more or less associated. After a time
theso impurities become dislodged, and fall to the bottom of the tank or vat, and may
be collected and separated in any well known manner.
The vegetable acid which I have found most useful, to effect my purpose, is acetic
acid, I would, however, remark that I do not intend to confine myself to this vegetable
acid, as others may be found which may be inore, or less available for the purpose.
Sometimes I may prefer to charge the acid solution with zinc in the first instance ;
this I may effect in the following manner :-
A porous cell, partly filled with a portion of the acid solution which is to form the
electrolyte, is immersed in the tank containing the acid solution, the liquid in both
vessels being on a level.-The negative pole of a dynamo-electric machine, or other
source of elasticity, having attached to it a strip of zinc or other suitable metal, or a
block of carbon, is immersed in the porous cell, and a stout plate or plates of zinc,
connected to the positive pole of the electric generator, is or are immersed in the bulk
of the liquid. After a time, the solution becomes sufficiently impregnated with the
metal under the action of the current, and is ready for use.
When the acid solution is employed direct as the electrolyte, there is a considerable
evolution of gases resulting from the decomposition which takes place, to check or
counteract which, I add to the solution carbonate of zinc or oxide of zinc until the
evolution of gas nearly ceases.

page_text: In treating certain ores of zinc, but more especially the native carbonate, or calamine,
for the purpose of extracting the metal therefrom, the ore, after being picked, finely
pulverized, and sifted, is digested in strong vegetable acid, say acetic acid, until a
concentrated solution of acetate of zinc, more or less impure from earthy matters, is
obtained. This solution is afterwards used as an electrolyte; plates of carbon,
platinum, or other metal insoluble in the vegetable acids being employed as anodes.
The cathodes or receiving plates are preferably also of carbon, but they may be of
any suitable metal. The separated zinc is then removed from the cathode, and is
made up in any convenient form for the market.
The impurities which remain after the treatment abovo described may in some cases
contain cadmium, antimony, and other metals of considerable commercial value, which
may be separated in any convenient manner.
Dated this 29th day of April 1007

page_text: Improvements in the Electrolytic Treatment of Zinc and its Ores.
I ALEXANDER WATT of 29
Chemist, do hereby declare the
same is to be performed, to be
the following statement :-
Granfield Street, Batterson, Surrey, Consulting
nature of this invention and in what manner the
particularly described and ascertained in and by
The object of this invention is to effect the purification of crude or impure zinc
and the extraction of inetallic zinc from its oros, moro especially from calamine or
native carbonato of zinc, by means of electrolysis, in a more efficient and practical
manner than heretofore.
In carrying out my invention, the crude or impure zinc, however obtained, may be
used as an anode or positive electrode, the electrolyte employed consisting of a solution
of a vegetable acid.-On a current of electricity being passed through the liquid, the
zinc is rapidly dissolved, and in a short time zinc of great purity is deposited on
the cathodo or negative electrode.
In some cases, the zinc may be previously dissolved or digested in a vegetablo acid,
with or without the aid of an electric current.
In treating certain ores of zinc, but more especially the native carbonate or calamine,
for the purpose of extracting the metal therefrom, the orc, after being picked, pulverized,
and sifted, is digested with a solution of a vegetable acid, and the solution thus obtained
is employed as an electrolyte.
In this case, plates of carbon, platinum, or other suitable metal, insoluble in the
vegetable acid, are used as the anode, and the cathodes or receiving plates may also be
of carbon, or of thin sheets of good zinc, or other suitable metal.
To effect the purification of crude or impure zinc, I first prepare in a suitable tank
or vat, or series of tanks or vats, a bath or solution of a vegetable acid, employing
for this purpose commercial acetic acid (containing about 15 per cent. of real acid),
which I mix with water in the proportion of about 1 part by measure of the acid, to
about 2 parts of water.
The tanks or vats are fitted with conducting rods of copper or brass, with connections
and leading wires for conveying a current of electricity from a dynamo-electric machine,
or other source of electricity, to the anodes and cathodes suspended from, or carried by
the conducting rods.-The anodes consist of slabs or thick plates of the impure zinc which
it is desired to purify, and may be cast with "lugs," so that they may be conveniently
suspended from the supporting or conducting rods.-For the cathodes, or plates which
are to receive the purified metal, plates of carbon may be used, but I prefer thin plates
of good sheet zinc.-These receiving plates may, however, also be made from sheet
copper, iron, or other suitable metal, but the surfaces should have a coating of plum-
bago, or be slightly greased to prevent the adhesion of the zinc deposited thereon.-
When the required series of anodes and cathodes have been suspended in the acid
liquor, the current of electricity is allowed to pass, and the electrolytic action at once

page_text: commences. In a short time, the liquid becomes impregnated with zinc, and the
metal deposits in a state of great purity upon the receiving plates in the form of a
bluish-white film. At the same time, the impure zinc anodes gradually assume a
discoloured or even blackish appearance, due to the metallic impurities with which
impure zinc is more or less contaminated, forming an insolublo film on their surfaces.
This film increases in thickness as the operation progresses, and the insoluble matters
eventually become dislodged, and fall from the anodes, in flakes or niasses, to the
bottom of the tank; or they may be removed mechanically by occasionally scouring
tho-plates with a hard brush. During the electro-chemical action, and until the acid
solution becomes well charged with zinc, a good deal of gas is liberated at the surface
of the plates, to check or moderate which, I introduce into the bath, in small quantities-
at a time, carbonate of zinc or oxide of zinc, until the evolution of gases nearly or
almost entirely ceases, when the deposition proceeds more favourably. I may stato
that the solution improves after a time by working, and the deposition of the metal
becomes more uniform than when the solution is newly prepared. When the cathodes
or receiving plates have become sufficiently coated with the purified zinc, they are
-removed from the baths, and replaced by fresh plates, and the zinc-coated plates
_are then rinsed and dried.-If the receiving plates used are of pure or nearly pure
zinc, they may be welted, and, with the deposit, cast into ingots in the usual way, but.
if copper or other metal is employed for the cathodes, the deposited zinc must_be
stripped off, with the aid of suitable tools, and the zinc then collected for melting.
Instead of employing a vegetable acid direct as the electrolyte as above described,
I may sometimes employ a solution of zinc formed with a vegetable acid for this
purpose, preferring the acetate of zinc, which I find most efficacious. To prepare the
-acetate of zinc solution, I place acetic acid, as before mentioned, in a suitable vessel
—or tank, and add to it, in small quantities at a time, either carbonate or oxide of zinc,
or clean scrap zinc, as zinc clippings, for example, and allow these, or either of them,
to digest in the acid, giving such agitation as may be necessary to hasten the solution.
of the zine, until the acid is sufficiently saturated with the metal; the solution is then
allowed to settle, and the clear liquor is afterwards drawn off for use as required.-To
make up an electrolytic bath for the purification of zinc from the zinc solution
obtained as above, I prefer to add to one part of the zinc solution, about two
parts of water, though the solution may be used in a more or less diluted state if
desired. The extraction of the zinc from the solution proceeds in the manner before
described, impure zine anodes, and pure or nearly pure zinc cathodes, or other suitable
_cathodes or receiving plates being used.
The electrolyte used for the purification of crude or impure zinc may also be
produced in the following manner-1 place a sufficient quantity of the vegetable
acid in a suitable vessel or tank, and I immerse in the liquid a porous cell, or a series
of porous cells, each of which I charge with a portion of the acid and solution, to a
height level with the bulk of the acid liquor in the larger vessel or tank. I then
-suspend in the large vessel a stout plate, or series of plates, of zinc of good quality,
and couple it or then with the positive pole of a dynamo electric machine, or other
source of electricity.-I next put into each porous cell, a strip or bar of zinc or block-
of carbon, or strip of any suitable metal, which I couple witli the negative pole of the
dynamo or other source of electricity, and the electric current is then passed through
the solutions. The electrolytic action at once commences, and the plates of zinc which
serve as anodes become rapidly dissolved under the combined influence of the acid
and the electric current, and the acid liquor, after a time, becomes sufficiently
saturated with zinc to be used as an electrolyte in the purification-of-zinc, as already
described.
In treating crude or impure zinc, I find that solutions prepared with vegetable acids
yield more favourable deposits of zinc than those obtained from solutions prepared
with the mineral acids; for example, it is well known that solutions of the sulphate
or chloride of zinc are very liable to yield deposits of a more or less granular character,
of a darkish grey colour, after the electro deposition has proceeded some time, and
that to obtain a perfectly homogeneous or reguline deposit of considerable thickness

page_text: is frequently a matter of great difficulty. From zinc solutions prepared with the
vegetable acids, however, the deposits are of a finer texture or grain, while the metal
has also a whiter appearance, and sometimes even a silvery lustre. Again, when zine
solutions prepared with the mineral acids are subjected to electrolysis, deposition of
the metal is invariably accompanied by more or less (and in some casos considerable)
liberation of hydrogen; whereas, when a well prepared solution of acctate of zinc is
employed as the electrolyte (a suitable current, say 3 to 5 amperes being also used),
no hydrogen whatever is set free at the negative electrode; consequently, in this
latter caso, there is neither waste of energy from this source, nor polarisation.-
Although I prefer to use acetic acid, more especially on the ground of economy, I
have obtained exceedingly satisfactory results from zinc solutions prepared with citric
acid, oxalic acid, and other vegetable acids. For all practical purposes in the
purification of zinc by electrolysis, however, ordinary commercial acetic acid is
preferred for preparing the necessary electrolyte.
When the bath, a solution used for the electrolytic purification of zinc has been
worked for a considerable time, a deposit, or "mud," accumulates at the bottom of the
tanks, which consists chiefly of the undissolved, metallic impurities derived from
the impure zinc employed as anodes during the operation. This deposit should be
removed from the tanks, when its presence is found to be objectionable, and the
constituent metals may be recovered by any well known means, and rendered
commercially available.
In treating zinc ores for the extraction of metallic zinc therefrom, by my process,
the ore is first to be finely ground and sifted, and then introduced, in small quantities
at a time, into a strong solution of the vegetable acid, say, commercial acetic acid
containing about 15 or 20 per cent. of real acid. From time to time the mass is
subjected to agitation to ensure the action of the acid on the pulverised ore.
The finely powdered ore is introduced gradually, in order to allow for the escape of
the liberated carbonic acid, without causing the contents of the tank to overflow, and
the supply of powdered ore is kept up until the required quantity (which may be
approximately estimated by previous calculation) has been introduced. The contents
of the tank will then be subjected to continuous agitation for some time, until the
liquor has become neutral, or nearly so, which can be ascertained by testing with
litmus paper or otherwise. When the solution is found to be sufficiently neutral for
the electrolytic bath (a [sight excess of acid not being objectionable), the contents of
the tank must be allowed to settle, and the clear liquor is afterwards drawn or pumped
off, for the extraction of the zinc, in the manner before described.
I would here remark that for the anode, I use carbon or platinum or other metal
which is insoluble in the acid, and for the cathode (by preference) a thin sheet of zinc
of good quality. The acetate of zinc (more or less impure) may be used in its con-
centrated condition, that is, just as it comes from the dissolving tank, or it may be
used more or less diluted with water, but I find that a "liquor," when it has a specific
gravity of about 1150 to 1160, water being 1000, yields very good results as an
electrolyte for the extraction of the metal.
As the metal becomes deposited upon the receiving plates, an equivalent proportion
of acetic acid is set free in the liquor, and in order, therefore, to prevent an accumula-
tion of free acid in the electrolyte, and to keep up the normal metallic.strength of
the solution as far as possible, and also to prevent polarisation, which an excess of
free acid would tend to set up, it is necessary that a continuous supply of fresh neutral
or nearly neutral zinc solution should constantly enter the baths, and also that a
corresponding proportion of the exhausted acid liquor should be removed from the
baths during the entire period when the electrolytic reduction of the zinc is going on.
To accomplish this, a system of circulation must be adopted, which may-be-effected
by any of the well-known methods applied in similar processes. The exhausted liquor
from the electrolytic tanks is conveyed into a suitable vessel or tank, and is there
re-saturated with zinc, from the ore in the manner above described.
In treating blende, or "black jack," (native sulphide of zinc) by my process, the ore
is first to be roasted in the usual way, to expel the sulphur, and the roasted oro is

page_text: afterwards pulverised and sifted. The finely powdered ore is then to be digested in
the vegetable acid, as before described.
Although I do not confine myself to any particular strength or density of solutions
of the vegetable acids, or of the solutions of zinc salts prepared from or with these
acids, I may state, generally, that I have found ordinary acetic acid of commerce,
containing about from 15 to 20 per cent of real acid, in its undiluted form, answers
well for dissolving zinc from its ores, or oxide obtained therefrom, after these ores
have undergone (when necessary) the process of calcination and subsequent pulverisa-
tion. I find, moreover, that the zinc extracted from its ores by the process herein
described, is of very good quality, while the metal deposits in a fair reguline condition,
and in all respects suitable for melting and casting into ingots as a useful article of
manufacture.
When the solutions of zinc are found to contain any considerable proportion of
lead, iron, etc.; these metals may be precipitated as sulphides by passing a stream
of sulphuretted hydrogen through the liquors while in an acid condition.
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 :-
1. In the purification of crude or impure zinc, and the extraction of zinc from its
ores by electrolysis, the use of vegetable acids, or solutions of salts of zinc, prepared
with such acids, as the electrolyte, substantially as and for the purpose described.
2. The process of purifying zinc and extracting zinc from its ores as above described,
and consisting in subjecting plates or bars of crude or impure zine, or the pulverised
zine ore, to the action of acetic or other vegetable acid, and causing the puro zine
held in solution, to be deposited on a cathode or negative electrode, by passing a
current of electricity through the solution, as set forth.
Dated this 30th day of January 1888.
NEWTON & SON,
Agents for the Applicant.