Improvements in the Method of Purifying Electrolytes Containing Zinc, relating to or connected with the Electro-metallurgic Production of Zinc.
Year: 1892

page_text: Date of Application, 5th Feb., 1892-Accepted, 2nd Apr., 1892
COMPLETE SPECIFICATION.
Improvements in the Method of Purifying Electrolytes Containing
Zinc, relating to or connected with the Electro-metallurgic
Production of Zinc.
I, GEORG NAHNSEN, of Christoph Strasse, Cologne, in the Province of
the Rhine, Kingdom of Prussia, Empire of Germany, Engineer 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 —
My invention relates to a new method of purifying electrolytes containing zinc,
and aims to remove as completely as possible the metallic impurities generally
found in said electrolytes.
I have found by experiments that these impurities cause very important and
noxious changes in the nature of the electrolytic precipitate, the latter becoming
of unequal structure and even of spongious appearance when the proportion of the
mentioned impurities surpasses a certain amount. I have found that when the
proportion of the zinc contained in the electrolyte to the impurities admixed
thereto copper, silver, arsenic, antimony, cadmium etc.-amounts to 10000.1 or
more, no influence is noticed; when the proportion decreases to 10000.5 hydrogen
gas is given off at 1000·1 granules arise upon the precipitate and at 1000-3 it
becomes spongious.
In order to remove the alien metals contained in the electrolyte, zinc has been
employed in the form of chips or of grains. This is utterly insufficient, the zinc
being soon covered with a dense layer of little solubility and in consequence
thereof rapidly deprived of its precipitating power.
Even a treatment of the mother-lye with zinc-powder prior to its precipitation
by means of lime is not sufficient. Though the results afforded thereby are much
more energetic and appropriate, still it does not insure a sufficient reliability in
working. The noxious impurities are of so powerful influence, even when present
only in very small quantities, that the slightest inattention may instantly disturb
the whole process.
The precipitation of the last traces of the alien metals depends in an important
measure on the time employed for this manipulation and on the quantity of zinc
powder suspended in the lye. The more the zinc powder has been utilized, the less
rapidly does the precipitation go on. I therefore employ several vats through
which the electrolyte is passed in succession, so that it gradually comes in contact
with zinc powder more and more pure, as of course the zinc powder in the first
vat will more rapidly become impure than that in the following vats.
My improved process is performed as follows:
When rough zinc or alloys of zinc have to be refined by using the same in
the baths as anodes, the lyes taken from the baths, which lyes are always
neutral or slightly basic owing to the formation of basic salts, are treated with
zinc powder in one vat or more, in order to remove the impurities contained in the
aid lyes. The latter are employed again for the baths only after having under-
gone this treatment. The lyes having passed through the baths and taken in
olution a small portion of the noxious metals admixed to the rough zinc, are
rought again into the vats containing zinc powder in order to be purified anew,
nd thus alternately made to remove a portion of the alien metals from the rough
inc, and to be freed of these impurities by the zinc powder.
When an insoluble anode is employed, whereby the electrolyte becomes acid, the

page_text: lyes are neutralized prior to purifying the same, either by the aid of ores
containing oxide of zinc, or carbonate or silicate of zinc, or by means of roasted
ore, such as blende etc., or of zinc ashes or any other raw material containing zinc
in such a form that it may be dissolved by the acid lyes until the latter are
completely neutralized. The neutralization being accomplished, the lyes pass
through the purifying apparatus, i.e. the vats containing zinc powder, where they
are freed of the impurities which they have taken from the raw material, and in
this purified state they are again brought into the baths.
When mother-lyes have to be treated, I precipitate the oxide of zinc contained
in the same by means of suitable chemicals, for instance lime or magnesia, and
this oxide of zinc serves to neutralize the electrolyte in exactly the same manner
as when treating other raw materials containing oxide of zinc. After the
neutralization the electrolyte is passed through the purifying apparatus and then
subjected to electrolysis again.
Though the treatment of the electrolyte is different according to the composition
of the raw material, yet this treatment is identical in each case in so far, as the
electrolyte is, prior to its admission to the baths, reduced to an entirely neutral
state and hereafter made to pass through a series of flat vats, in which zinc powder
is constantly agitated by means of a stirring mechanism. This precipitation is
effected not only in one vat, but in a series of the same placed one after the other,
so that the dissolved alien metals come in successive contact with zinc powder
of gradually increasing purity. This is at least the manner in which I prefer to
perform the process, but under special circumstances it may be sufficient to treat
the electrolyte with zinc powder in but one vat.
By my invention a most perfect utilization of the zinc powder is secured, as the
electrolyte, should it not be completely freed of the alien metals in the first vat, will
find in the following vats zinc powder of sufficient purity to be freed completely.
After the vats containing zinc powder I place, in the circuit through which the
electrolyte is made to circulate, a settling-vat, in which the small quantity of
particles suspended in the electrolyte and carried along by the same is allowed to
subside. The whole arrangement is such that the electrolyte must necessarily pass
in a slow, continuous current through the vats containing the zinc powder.
The quantity of zinc powder which it is necessary to employ depends of course on
the proportion of the impurities dissolved in the electrolyte. When these impurities
consist of copper only and amount to 1% of the entire quantity of zinc, 10 lbs. of
copper must be precipitated by means of zinc powder in the case of a daily
production of 1000 lbs. of zinc. In this case a daily addition of 11 lbs. of zinc
powder to the electrolyte would be required. It is preferable to introduce at the
beginning of the operation a larger quantity of zinc powder into each of the vats,
say 100 lbs. and to add the amount needed daily in the first of the series of
vats placed one after the other, thus 11 lbs. of zinc powder daily in the above
example.
३
If 1000 lbs. of zinc are produced daily in a refining establishment, and if 1%
of silver gets admixed to the electrolyte, a daily addition of about 5 oz. of zinc
powder will be sufficient. The addition of zinc powder necessary in each case
may be calculated according to the absolute quantity and to the chemical
equivalent of the metals admixed to the zinc and dissolved in the electrolyte.
If it is desired to remove the precipitated copper or silver etc., the daily supply
of zinc powder is introduced into the second vat, and not into the first vat as
described above, but the electrolyte rendered impure by copper or silver is made
to pass first through the first vat, as above, until all zine powder contained in the
same has been used up in precipitating copper or silver. The precipitate is then
allowed to subside and hereafter removed from the first vat. The latter being
charged again with 100 lbs. of fresh zinc powder the treatment is continued in the
above described manner.

page_text: 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 :-
In the electro-metallurgic production of zinc :
The hereinbefore described method of purifying and keeping pure the electrolyte
containing zinc, the entire electrolyte being in said method made to pass, prior to
its admission to the bath, through a vat or a series of vats, in which zinc powder is
introduced and agitated, for the purpose as described.
Dated, Berlin, this 2nd day of February 1892
GEORG NAHNSEN,
By Robert Deissler,
38, Alexander Strasse, Berlin, C., Germany, Agent for the Applicant.