Improvements in the Electrolytic Extraction of Zinc.
Year: 1892

page_text: Date of Application, 11th July, 1892
Complete Specification Left, 1st Apr., 1893-Accepted, 6th May, 1893
PROVISIONAL SPECIFICATION.
[Communicated from abroad by Messrs. SIEMENS & HALSKE, of Berlin, in the
German Empire, Electrical Engineers.]
Improvements in the Electrolytic Extraction of Zinc.
We, SIEMENS BROTHERS & Co. LIMITED of 12 Queen Anne's Gate, West-
minster in the County of Middlesex, Electrical Engineers, do hereby declare the
nature of this invention to be as follows:-
In the electrolytic extraction of zinc from a sulphate of zinc solution, prepared
according to any known method, the so called zinc sponge is formed that is to say,
a fine grey powder consisting mainly of zinc but which is difficult to melt, and
which renders the use of electrolysis practically impossible, partly on account of
its loose nature and partly on account of the difficulty of melting it. The cause of
the sponge formation both in neutral and in slightly acid solutions is not yet
accurately known, but a large number of phenomena tend to show that the traces
of hydride of zinc ZnH, appearing in the electrolysis, simultaneously with small
quantities of nascent hydrogen (H monatonic) cause a molecular alteration of the
separated zinc which constitutes the spongy aggregation.
The present invention relates to a process by means of which the formation of
zinc sponge during electrolysis is entirely prevented. The process is based upon
the prevention of the supposed action of the zinc hydride ZnH, and the nascent
hydrogen in causing the production of zinc sponge, by the addition of free halogens
or of halogen compounds, which bind the hydrogen by forming corresponding
halogen hydrates.
In practically carrying out this electrolytic extraction of zinc based upon this
method, the following process is employed.
The neutral or slightly acid zinc vitriol lye obtained from the ores by any known
method of extraction, has added thereto before the electrolysis
a, weak chlorine, bromine or iodine solution.
b, weak solutions of free hypochlorous or hypobromous acid; or by super-
saturating the same with
c, chlorine or bromine gas, whereby, as may be seen from the formulæ in the
subsequent chemical portion of this Specification, hypochlorous acid produced
Or by the addition of
d such chloric and bromic substitution products soluble in water of organic
bodies which on reduction to lower compounds, give up their chlorine or bromine
to nascent hydrogen, such as the halogen substitution product of glycerine
chlorhydrin soluble in water, and other glycols or:
e, additions are used consisting of combinations of the bodies mentioned under
a b c and d.
As the quantities of zinc hydride and nascent hydrogen that are produced in the
electrolysis are very small, the quantity of the halogens or halogen compounds to
be added to the bath, need also only be very small, so that the action of the free
chlorine &c. upon the substance of the cathode during the passage of the current
need not be considered. The useful effect is consequently not impaired.
It is only necessary with this process that the lye which is to be subjected to
electrolysis shall always show during the operation a distinct reaction of the free
halogen or of the active oxyhalogen body.
The zinc precipitated at the cathode under this process has, in contrast to the
grey zinc resulting from the other processes, a silvery colour and a distinctly
crystalline structure from the very moment the circuit is closed.
The chemical reactions that take place at the cathode in the above described
process will be readily seen from the following equations in which it is assumed

page_text: that the object is to remove or suppress the zine hydride ZnH₂ or nascent
hydrogen H as the disturbing cause of the formation of sponge.
If according to (a) there is present in the sulphate lye round the cathode, say,
free chlorine, it will act upon ZnH, and nascent H according to the formulæ :

page_text: free halogen enters into action the hydrogen of the hydrogen compounds of
the electrolysis, forming hydrochloric acid which in its turn reacts upon the
hypochlorous acid present, again producing chlorine, which latter again enters into
reaction in the sense of the above stated equations so that with a slight initial
excess of chlorine in the presence of hypochlorous acid, the chlorine can be in
large measure regenerated, as soon as the electrolytically separated hydrogen
produces hydrochloric acid in combining with the chlorine.
The process may be shortly stated by the following formulæ :
ẞ. HOCI + HCl = H³O + Cl,
which again acts upon ZnSO, with formation of HOCI:
ZnCl¸ +-H₂SO = ZnSO + HCl
4
COMPLETE SPECIFICATION.
Improvements in the Electrolytic Extraction of Zinc.
We, SIEMENS BROTHERS & Co. LIMITED, of 12 Queen Anne's Gate,
Westminster in the County of Middlesex, 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:
In the electrolytic extraction of zinc from a sulphate of zinc solution, prepared
according to any known method, the so called zinc sponge is formed that is to say,
a fine grey powder consisting mainly of zinc but which is difficult to melt, and
which renders the use of electrolysis practically impossible, partly on account of
its loose nature and partly on account of the difficulty of melting it. The cause of
the sponge formation both in neutral and in slightly acid solutions is not yet
accurately known, but a large number of phenomena tend to show that the traces
of hydride of zinc ZnH, appearing in the electrolysis simultaneously with
small quantities of nascent hydrogen (H monatonic) cause a molecular alteration
of the separated zinc which constitutes the spongy aggregation.
The present invention relates to a process by means of which the formation of
zinc sponge during electrolysis is entirely prevented. The process is based upon
the prevention of the supposed action of the zinc hydride ZnH, and the nascent
hydrogen in causing the production of zinc sponge by the addition of free halogens
or of halogen compounds, which bind the hydrogen by forming corresponding
halogen hydrates.
In practically carrying out this electrolytic extraction of zinc based upon this
method, the following process is employed.
The neutral or slightly acid zinc vitriol lye obtained from the ores by any known
method of extraction, has added thereto before the electrolysis
a, weak chlorine, bromine or iodine solution.
b, weak solutions of free hypochlorous or hypobromous acid; or by super-
saturating the same with
c, chlorine or bromine gas, whereby, as may be seen from the formulæ in the sub-
sequent chemical portion of this Specification, hypochlorous acid is produced.
Or by the addition of
d such chloric and bromic substitution products soluble in water of organic
bodies which on reduction to lower compounds, give up their chlorine or
bromine to nascent hydrogen, such as the halogen substitution product
of glycerine chlorhydrin soluble in water, and other glycols or:

page_text: If according to (d) an organic compound giving chlorine, for example mono-
chlorhydrin of glycerin be present then, in the presence of nascent hydrogen the
reaction will take place according to the following equation.
Mangahlarhedzin
Pronvleneglycol
chlorhydrin of glycerin be present then, in the presence of nascent hydrogen the
reaction will take place according to the following equation.
Monochlorhydrin
CH, Cl
Сион
CHOH + 2 H = HCl +
CH'OH
Propyleneglycol
CH,
CHOH
Сион
CH,OH
(There will generally be produced the next lower glycol.)
If according to (e) there are used as additions mixtures of the said bodies, the
action of the free chlorine as also that of the lightly bound oxygen in the case II
can take place simultaneously.
Generally speaking, the action of the additions may be stated to be that the
free halogen enters into action the hydrogen of the hydrogen compounds of the
electrolysis, forming hydrochloric acid which in its turn reacts upon the hypochlorous
acid present again producing chlorine, which latter again enters into reaction in the
sense of the above stated equations so that with a slight initial excess of chlorine
in the presence of hypochlorous acid, the chlorine can be in large measure
regenerated, as soon as the electrolytically separated hydrogen produces hydrochloric
acid in combining with the chlorine.
The process may be shortly stated by the following formulæ :
ZnCl2 + H2SO₁ = ZnSO̟ + HCl which enters into reaction according to p.
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 :-
In the electrolytical extraction of zinc from neutral or slightly acid sulphate of
zinc solutions, the method of preventing the formation of zinc sponge from such
solutions by mixing therewith free halogen compounds, or such other inorganic or
organic compounds (hypochlorous or hypobromous acids, or chlorhydrips of the
glycoles &c.) which under reduction, give off their halogens to the nascent hydrogen,
substantially as described.
ABEL & IMRAY,
Agents for Applicants.