Note: Descriptions are shown in the official language in which they were submitted.
The invention relates to a precipitation method for
precipitating metal from a solution by means of a precipitant.
In the precipitation of metal in the form of metal
precipitate from a solution of the metal mixed with another
metal as the precipitant, the so-called precipitation process,
substantially the same processes take place regardless of the
metals involved, in which an exchange of ions takes place bet-
ween a noble and a base metal in the electro-chemical series.
According to the "Lexicon der H~ttentechnik" by L~ger,
4th Edition, Volume 5, Deutsche Verlagsanstalt Stuttgart, page
733, 'iprecipitation" is defined as follows (translated from the
German):
"Precipitating a metal out of a solution by means of
a baser metal. The baser metal has a more negative potential
t~an the metal to be precipitated and releases positive ions
into solution, thus charging itself negatively and discharging
all cations having more positive potentials. Precipitation in
` the form of metal. The deciding factor is thus the difference -
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in potential between the various cations under the conditions
obtaining.~l
Major difficulties arise in the precipitation of the
widest variety of metals, in that the precipitated metal,coats
the surface of the metal used as the precipitant, thus impeding,
or even bringing to a halt, the electro-chemical reaction, i.e.
the exchange of ions. Other obstacles to the reaction are:
the formation of a layer of oxide upon the surface of the
metal precipitant, or the formation of a coating of very small
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gas bubbles on the surface of the metal precipitant arising from
electrolytic processes.
It is the purpose of this invention to overcome these
known difficulties in all types of precipitation process, and
thus to produce a definite improvement not only from the
economic standpoint but also from the standpoint of the yield
of metal, and therefore of the efficiency of the process as a
whole.
Accord.ing to the invention there is provided a
method for precipitating a metal from a solution of the metal
comprising
introducing into a solution of a first metal a more
basic metal to precipitate said first metal from said solution,
10 and - .
maintaining said more basic metal in motion effective
- to release precipitated metal deposited on individual ::
portions of said more basic metal. ~.
In particular the motion of the individual portions ~
of the more basic metal is preferably maintained by carrying -
out the precipitation in a vibration mill wherein the more
basic metal is subj~cted to a vibratory motion having a ~re- :
quency and amplitude such that individual portions of the more
~ basic metal are maintained in constant motion and the individual
: 20 portions of the more basic metal collide with each other. In
~- this way rubbing contact between the individual port~ons of the
more basic metal result in remo~al of deposits of the first -~ ;
metal precipitated from the solution onto the surface of the ~ -
more basic metal. -
In accordance with a broad aspect of the invention,
there lS provided a process for precipitating a metal from a : ; .
solution containing metal ions, said precipitating being carried
. out in a vibratory reactor which contains a precipitating agent
in the form of discrete particles of metal, and in which the .
solution is subjected to such frequency and amplitude that
deposits on the surface of the discrete particles of metal
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become permanently removed by movement oE the precipitated
metal, characterized in that the discrete particles consist of
zinc and the solution is a neutral zinc leaching solution which
in addition to zinc also contains polyvalent metal ions
selected from the group consisting of Cd, Co, Ni, Ag and Au
and which becomes free of these metal ions by precipitation.
The ~erm more basic metal as employed in this
specification is to be understood as referring to a metal higher
in the electrornotive series or more negative than the first
metal to be precipitated from solution. Thus iron is a more
basic metal than copper and is higher than copper in the
electromotive series, so that iron will precipitate copper from
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solution.
me more basic metal employed as the precipitating
agent is suitably employed in a non-powdery form, suitably in
the form of large lumps, pieces, fragments or granules or even
in t~e form of scraps of metal. Although the invention is not
limited to particular shapes or sizes of the pieces of more
basic metal, suitable pieces are found to be granules measuring
from about 2 to about 10 mm.
me method of the invention permits a much more rapid
precipitation than the prior art methods.
In one aspect the process of the invention can be
used for the precipitation of copper from a copper solution
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mixed with pieces of iron, the precipitated copper deposited
upon the pieces of iron being released by constant movement
thereof, and being removed Erom the decopperized solution by
vibrating the pieces of iron at a frequency and an amplitude
such that the said pieces of iron constantly come into
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colli~ion with each other.
The invention can be employed in other hydro-
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metallurgical processes for precipitating any metals in metal
form from solutions thereof using a more basic, electro-
chemically more negative metal, the more basic metal being
employed in the form of pieces of metal as the precipitant.
According to one advantageous embodiment, the inven~
tion is employed in zinc hydrometallurgy for the precipitation
oE metals nobler than zinc, for example Cu, Cd, Co, Ni, as
metal precipitates, from a zinc solution containing these metals
which is mixed with pieces of metallic zinc as the precipitant.
In another advantageous embodiment, the invention is
employed in noble-metal hydrometallurgy, for example for pre-
cipitating silver or gold, as metal precipitates, from cyanide
solutions thereof using mixes pieces of zinc as the precipitant.
In this different embodiment it is desirable to use a
vibration mill as the precipitation reactor.
The invention, together with the technological and
economical advantages attainable therewith, as compared with
~ . - .
existing processes, will be explained in greater detail, in -
- conjunction with a representative example from zinc hydro-
metallurgy.
In zinc hydrometallurgy it has hitherto be~n customary
; to remove foreign metals, such as Cu, Cd, Co and Ni, from the
neutral liquors produced, by adding to the liquors, in agitators,
metallic zinc powder and thus precipitating-out the said impu-
rities.
; This known method, however, has the particular dis-
`~ advantage, among others, that the zinc powder first of all has
to be produced, for example by spraying metallic zinc. Further-
more, the reaction between the precipitant powder and the
liquor is extremely slow and may take several hours, because
an immunizing layer of zinc oxide forms upon the particles of
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zinc, and this layer definitely inhibits the course of the
reaction.
In contrast to this prior method, the invention makes
use of larger non-powderous pieces of zinc instead of zinc
powder, the zinc may for example be added to the liquor in
the form of granules measuring from 2 and 10 mm, the entire
precipitation process can be conclucted using a vibration mill
as the precipitation reactor, in order to produce the intensive
vibration required to cause the zinc granules to come into
- 10 collision with each other.
In the method of the invention, this intensive vi-
bration of the pieces o~ the zinc, which can be achieved simply
and economically in a vibration mill, causes the surfaces of
the pieces of zinc coated with the precipitated nobler metal to ~ -
, . . .
; constantly collide with each other and to be rubbed bare, with
the result that the activity of the surfaces of the zinc are
maintained, so that the reaction by the exchange of ions con-
tinues.
The intenqive vibration of the precipitation reactor
containing the pieces of metal also produces intense tur~ulence
in the liquor, and this brings about a thorough mixing of the
solid and liquid phases in the boundary layer between the li-
quid and the pieces of more basic metal. As a result of this,
. ,~, ~
the ion concentration in the vicinity of the surface of the
m~re basic metal precipitant is substantially higher than it is
in conventional precipitation methods, and this speeds up still ~ `
further the transfer of material. Moreover, the hydrogen gas - -
released by the reaction into the liquor is in the form of very
small bubbles, and this considerably reduces its effect as a
reducing agent.
In æinc hydrometallurgy, for example, the invention
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improves the economics of the process by replacing expensive
zinc powder, used as the precipitant, by inexpensive zinc waste
and intermediate products, for example as dross and slag from
metallurgical processes. Some of the dross produced during the
smelting and casting of zinc cathodes made by electrolysis
consists only partly of metallic zinc~ Dross of this kind has
to be refined by segregating the zinc, the residue being
returned to the zinc-leaching operation where it is dissolved.
All of this costly processing becomes redundant and
may be eliminated if, according to the teaching of the inven-
tion, precipitation is carried out, not with zinc powder, but
with dross, waste, granular or lump metallic zinc in a vibrat-
~ ing container such as a precipitation reactor, since the ~-
; energy produced by the precipitation reactor imparts to the
content thereof a high energy potential such that the pieces
- of zinc constantly knock and rub violently against each other.
e surfaces thereof are thus kept free of contaminants or
immunizing coatings, be they in the form of oxides, deposits
of metal precipitate, or collections of gas bubbles. mis :
results in an accelerated transfer of material produced by the
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exchange of ions between the metal and the solution.
The final result of this is a considerable reduction
in the duration of the process and a better utilization of the
metallic substances used, the consumption thereof being reduced
a~most to the stoichiometric value, whereas in conventional
precipitation drums, this consumption may amount to up to 500% ;
of the stoichiometric value.
m e technological and economic advantages and possi-
I bilities demonstrated in the foregoing example taXen from zinc
- 30 metallurgy also apply to other applications of the principle of
the invention, in practically all precipitation processes in
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the field of hydrometallurgy.
The invention is explained hereinafter in greater de-
tail, in conjunction with two examples of precipitation
according to the prior art and two examples of precipitation
processes according to the invention.
EXAMPLE_I
Precipitation ~rocess according_to the prl r art:
A liquor was provided containing, in solution, metal
compounds obtained by chlorinating the volatilization product
from a complex iron ore the metal compounds having the follow-
.,
ing metal contents
25 g/1 Cu, 3 g/l Fe; 80 g/l zinc, l g/l Pbremainder Bi, Co, Cd, Ag about 200 mg/l.
About 30 m3 of the liquor, containing the dissolved
metals, is loaded into a precipitation drum having a capacity
of about lO0 m3, the drum being pear-shaped and set at an angle
for rotation about its axis, and having an acid-resistant
lining. About 50 t of Fe scrap is introduced into the drum
through a top opening. The load is moved for about 120 minutes
at a temperature of 50C by rotating the drum.
m e final liquor contains about 380 mg/l of Cu.
The scrap consumed in this batch process was about
215% of the stoichiometric amount of Fe.
TEXAMPLE II
Canventional preci~itation:
In zinc metallurgy, neutral leaching produces a
neutral liquor which contains, in addition to the dissolved
zinc oxides, various amounts of dissolved ions of electro-
chemically more noble metals, mainly Cu, Ni, Co and Cd~
.;
These foreign metals which, as compared with the zinc
metal to be recovered, are to be regarded as impurities, must
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be precipitated out of the liquor, since even small quantities
thereof would have an extremely detrimental effect upon the
subsequent electrolysis of the zinc.
These metallic impurities are precipitated with zinc
dust, since the said impurities are electro-chemically more
positive than the zinc.
Precipitation is carried out intermittently in a
stirring kettle, the zinc dust being added batch-wise. The
liquor introduced contains: 150 g/l Zn; 500 mg/l Cu:
- 10 400 mg/l Cd; 20 mg/l Ni; and 20 mg/l Co. ;
The liquor is subjected to the precipitation process 5
in the first stage at 95C, with additions of Zn dust, CUSO4 ~ ;
" and arsenic trioxide, the Cu, Co, Ni and As precipitate out
a precipitate, whereas the Cd remains in solution.
The period of residence in each precipitation stage is
l about 260 minutes. The consumption~of Zn dust is 530% of the
-, theoretical, stoichiometric amount of Zn.
' The purified neutral liquor contains as residual im- ;
;
~ purities:Cu 0.1 mg/l; Co 0.2 mg/l; Ni 0.05 mg/l; Cd 0.2
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` 20 mg/l.
EXAMPLE III
Precip t tion acc_rdinq to the invention:
` The copper solution of a neutral liquox of oxidic -
~i copper-ore concentrate is precipitated, using scrap iron as
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t~e precipitant. The precipitation process is carried out in
a test set-up with the aid of a vibrating mill, the r.p.m.
and amplitude of which are adjustable. The reactor is a heat-
:j ,
able satellite rigidly attached to the said vibrating mill and
having a capacity of 8.5 dm3. The charge of scrap iron pre-
cipitating agent is 65% of the volume of the reactor, i~e. 5.5
dm3. The amount of liquor is 45% of the volume of the reactor,
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i.e. 3 dm3.
Precipitation of the copper from the CuS04 solution
with scrap iron starts at a Cu content of 36 g/l. The amplitu-
de is 10 mm, the frequency of vibration 12.5 Hz. The treat-
ment temperature is 18C. The treatment time 180 seconds.
A residual Cu content of 40 mg/l Cu is found by ana-
lysis.
A parallel test carried out under strictly similar
conditions, but at a treatment temperature of 63C produces a
residual Cu content of 40 mg/l after only 32 seconds.
In both cases the scrap-iron consumption corresponds
to 1.2 times the stoichiometric amount of iron.
EX~MPLE IV
Precipitation accordinq to the invention
The precipitation of copper with granular zinc from a ~;~
neutral zinc liquor is carried out in the same test reactor on
the vibrating mill.
`~ With 150 g/l of zinc, the content of dissolved copper
at the start of the reaction amounts to about 500 mg/l.
Treatment temperature 95 C. pH value of the liquor 4.
The granular zinc used as the precipitant lies within
the 3 to 10 mm grain ~ixe. The treatment is carried out with
vibration at an amplitude of 10 mm and a frequency of 12.5 Hz.
~After a precipitating period of 32 seconds, analysis
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r~vealed a final copper content of less than 0.1 mg/l.
Applications of the principle of the method to other
- precipitation processes in the field of hydrometallurgy lie
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within the scope of the invention.
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