Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
- 2Q26967
TITLE OF THE INVENTION
METHOD OF REMOVING COBALT FROM CHLORIDE SOLUTION
FIELD OF THE INVENTION
The present invention relates to a method of economi-
cally removing the cobalt contained in a nickel chloride
electrolyte or an exudate containing nickel chloride.
DESCRIPTION OF THE PRIOR ART
A method of producing electrolytic nickel is mainly
classified into an electrorefining method and an ele-
ctrowinning method.
The electrorefining method is a method of producing
electrolytic nickel by melting nickel and molding a nickel
matte and electrolizing the nickel matte as an anode in a
mixed bath of sulfate chloride ions.
The electrowinning method is a method of extracting
nickel by electrolysis from an electrolytic bath which is
obtained by refining the exudate obtained by the pressure
leach of the nickel in a nickel matte under pressurization
or refining the exudate obtained by the oxidative extraction
of the nickel in a nickel matte with chlorine. In both of
these methods, the cobalt in the nickel matte elutes into
the electrolytic bath or the exudate, so that if electro-
lysis is carried out in this state, the deposit on the
electrode has a high grade of cobalt. A purificati~n
process is therefore necessary to remove the cobalt so
2Q26967
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that the cobalt concentration in the electrolyte is not
more than 10 mg/~ and, in the production of high-purity
nickel, not more than 5 mg/J.
A method of removing cobalt adopted is different
depending upon whether the base is a sulfate bath or a
chloride bath.
In a sulfate bath, chlorine is blown into the
electrolyte so as to oxidize cobalt into trivalent cobalt,
and the trivalent cobalt is deposited, thereby being removed
as cobalt hydroxide. In this method, a part of the nickel
and the coexisting iron in the solution are also deposited
as hydroxides.
In a chloride bath, a solvent extraction method is
used, which requires an expansive equipment of a large
scale and fire-proof equipment relating with usage of
organic solvent, inconveniently leading to rise in the cost.
With the recent demand for economization in energy,
adoption of an electrowinning method in place of an ele-
ctrorefining method has been proposed. However, the
adoption of an electrowinning method necessitates a
solvent extracting method which requires a complicated
flow and the equipment therefor as a method of removing
cobalt, which inevitably leads to rise in the cost.
That is, when chlorine is blown into a sulfuric bath,
the reaction represented by the formula (1) is produced:
2026967
2Co + 6H2o + 3Ce2 ~2Co(OH)3 + 6HC,~ ... ~1)
As is clear from the formula (1), in order to proceed the
reaction to the right side and to deposit cobalt as a
hydroxide, it is necessary to remove HCV! produced. In order
to remove HCe, nickel carbonate is ordinarily added. The
nickel and iron in the solution also produce hydroxides and
deposit by the reaction similar to the reaction represented
by the formual (1) and produce a Co precipitate together
with the cobalt hydroxide. The Ni/Co in the Co precipitate
is 3.5 to 4Ø If the Ni/Co is large, the nickel loss in
the system increases and, hence, the amount of chlorine used
and the amount of neutralizer used increase, in other words,
the cost of treatment of the Co precipitate increases. The
further reduction of the Ni/Co in the Co precipitate is
therefore demanded.
The reaction represented by the formula (1) is only
effective with respect to a sulfate solution and is not
adaptable to a chloride solution or a solution having a
high C~ concentration. This is because when the ce
concentration is high, cobalt becomes a stable in the form
of a chlorocomplex, so that not only is the oxidation
reaction of cobalt into trivalent cobalt too difficult
to produce for adequate Co removal, but also the Ni/Co
in the Co precipitate greatly increases.
SUMMARY OF THE INVENTION
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Accordingly, it is an object of the present invention
to provide a method of removing the cobalt in a chloride
solution by chlorine so that the Ni/Co is not more than 2
and the Co concentration in the final solution is not more
than 10 ms/e-
To achieve this aim, a method according to the present
invention comprises the steps of: preparing a chloride
solution containing not more than 130 g/~ of nickel ions,
0.05 to 0.2 g/~ of divalent iron ions and cobalt ions' and
bringing the solution into the reaction with not less than
1 equivalent of chlorine with respect to the total amount of
iron ions and cobalt ions contained in the solution and
proceeding the reaction at pH of the solution between
3.9 and 4.1.
The above and other objects, features and advantages
of the present invention will become more apparent from the
following description when taken in conjunction with the
accompanying drawings in which a preferred embodiment of
the invention is shown by way of illustrative examples.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 shows the relationship between the concentration
of Co remaining in the final Co-removed solution and the
nickel concentration at the initiation of reaction;
Fig. 2 shows the relationship among the Ni/Co in the
Co precipitate, the reaction pH and the amount of coexistentFe;
and
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2~9-67
Fig. 3 shows the relationship among the Ni concentra-
tion, the time for blowing chlorine and the pH. DETAILED
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention will be explained with reference
to the accompanying drawings.
Fig. 1 shows the relationship between the concentration
of Co r~m~in;ng in the final Co-removed solution and the
nickel concentration at the initiation of reaction. The
relationship in Fig. 1 was obtained as follows. 8 ~ of a
reaction initiating solution in total was prepared in four
10-~ beakers by using a nickel chloride solution containing
0.7 g of cobalt and 180 g of nickel per of the nickel
chloride solution and pure water. While the temperature of
the solution was maintained at 51 to 55C and the pH thereof
was maintained at 4.1, chlorine was blown into the solution
at a rate of 12 to 14 g per hour under stirring, and the
concentration of Co ions rPm~;n;ng in the solution was
obtained by measuring samples after a predetermined time.
It is obvious from Fig. 1 that it is necessary to use a
reaction initiating solution having an Ni concentration of
not more than 130 g/~ in order to reduce the Co ions in the
solution to not more than 5 mg/.
Fig. 2 shows the influence of the amount of coexistent
Fe on the relationship between the Ni/Co in the Co precipitate
and the reaction pH. The result shown in Fig. 2 was
~QZ6967
obtained as follows. Three kinds of nickel chloride solu-
tions having Fe concentations of 0.01, 0.05 and 0.17 g/~,
respectively, an Ni concentration of 110 g/~ and a Co
concentration of 0.5 to 1.0 g/~ were prepared for testing.
Each of the nickel chloride solution was supplied to a
continuous cobalt removing bath having an actual volume of
1 m at a rate of 2.0 e/min. Chlorine gas was blown into
the solution for 24 hours so that the redox potential was
1,200 to 1,300 mV while maintaining the temperature of the
solution at 48 to 51C and the pH at a constant value. Each
of the Co precipitate obtained was analyzed to obtain the
Ni/Co. The Co concentration in the final Co-removed solu-
tion was 3 mg/e. The Co concentration was sufficiently
allowable for producing ultra high-purity electrolytic
nickel.
It is clear from Fig. 2 that addition of not less than
0-05 g/e of Fe greatly reduces the increase of the Ni/Co.
With the increase of pH, the Ni/Coin the Co precipitate
obtained increases. This is because with the increase in
pH, the redox potential on formation of trivalent Ni is
lowered.
The Ni/Co in the Co precipitate obtained in a conventional
sulfate bath is 3.5 to 4.0, as described above. To satisfy
this standard, the condition that pH ~ 4.1 and Fe ~ 0.01 g/e
or the condition that pH < 4.3 and Fe ~ 0.05 g/e is sufficient.
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However, it is naturally desirable that the Ni loss is as
small as possible, and in order to maintain the Ni/Co
stably at not more than 2 in a pH range of 3.9 to 4.1 in
accordance with the present invention, it is necessary to
maintain the Fe concentration in the reaction initiating
solution at not less than 0.05 g/~. Since too high an Fe
solution does not enhance the effect to that degree but
rather greatly increases the amount of deposit produced,
it is unfavorable to increase the Fe concentration more
than necessary.
Fig. 3 shows the relationship among the Ni concentration
in the solution, the time for blowing chlorine and the pH.
The relationship in Fig. 3 was obtained as follows. 8g
of a nickel chloride solution containing 0.69 g/e of cobalt
and 110 g/e of nickel was charged into a 10-e beaker while
maintaining the temperature of the solution at 51 to 55C.
The pH was maintained at a predetermined value, chlorine was
blown at a rate of 12 to 14 g per hour into the nickel
chloride solution under stirring. After a predetermined
time, the resulting solution was sampled and the concentra-
tion of the Co ions remaining in the solution was measured.
It is obvious from Fig. 3 that it is necessary to maintain
the pH in the range of 3.9to 4.3 in order to complete the
cobalt removing reaction within 3 hours. This is because
too high pH increases the amount of Ni in Co precipitate,
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while the removal of co is insufficient when
the pH is too low.
The amount of chlorine blown into the solution is
greatly different depending on the specifications of the
apparatus and the like used, but at least 1 equivalent of
chlorine is necessary with respect to the total amount of
Fe2+ and Co2+ contained in the chloride solution.
The Co2+ concentration in the thus-obtained chloride
solution is not more than 10 mg/~, which enables the chlo-
ride solution to be used as it is as an electrolytic bath.
Example
A chloride solution containing llO/Q g of Ni, 1.0 g/~
of Co, 0.15 g/~ of Fe2+, 0.003 g/Q of Pb, 3.5 g/~ of Na and
2.0 g/~ of SO4 was flown into a 1-m3 reaction tank from a
200-~ addition tank by a constant delivery pump at a rate of
2.0 Q/min. While the temperature of the solution was
maintained at 48 to 51C and the pH was maintained at 4.0 by
using 10 wt% of a nickel carbonate solution under stirring,
chlorine was blown into the solution at a rate of 0.07
Kg/Hr.
The slurry containing the cobalt ~recipltate produced was
supplied to a l-m3 relay tank through an overflow pipe, and
then supplied to a filter press by a pump for the purpose of
solid liquid separation.
The results of Example are shown in Table 1.
Z026967
Table 1
Quantity Grade
Ni Co _ _Fe
Chloride 120 110 1.0 0.15
solution __
Chlorine =0.062 i _ _ -
Co-removed 120 110 0.007 <0.0001
solution __
Co deposit 1682 23.1 17.5_ 2.6
The unit of quantity is g/~ in the case of a solution,
g/Hr in the case of a solid and Nm3/Hr in the case of a gas.
The unitofgrade is g/~ in the case of a solution and
% in the case of a solid. The Ni/Co in the Co precipitate
obtained was 1.32, and the Ni, Co, Fe and Pb concentrations
in the final Co-removed solution were llO g/e o . 005 g/~,
0.0001 g/e and 0.0001 g/~, respectively. It is obvious
that the thus-obtained Co-removed solution is usable as
an electrolytic bath for an electrowinning method as it is.
The redox potential in example was 1,200 to 1,300 mV.
According to the method of the present invention, it is
possible to sufficiently remove Co from a chloride solution
without using a solvent extraction method which requires an
expansive equipment of a large scale and fire-proof equipment
relating with usag of organic solvent. Thus, it is possible
to produce high-purity electrolytic nickel at a low cost.
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While there has been described what is at present
considered to be a preferred embodiment of the invention, it
will be understood that various modifications may be made
thereto, and it is intended that the appended claims cover
all such modifications as fall within the true spirit and
scope of the invention.
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