Note: Descriptions are shown in the official language in which they were submitted.
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SPECIFICATION
PROCESS FOR PRODUCING COBALT SOLUTION OF LOW
MANGANESE CONCENTRATION
BACK GROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a process for producing a cobalt
solution of low manganese concentration, more specifically a process for
producing a cobalt solution of low manganese concentration which can
increase direct recovery rate of cobalt by industrially advantageously
removing manganese from a cobalt solution containing manganese as an
impurity by the oxidative neutralization process.
DESCRIPTION OF THE PRIOR ART
Cobalt is a metal which has been widely used for industrial purposes as
a material for special alloys and magnetic materials. It is normally
occurring in the form of oxide or sulfide, and produced mostly as a
by-product of nickel and copper smelting. It is essential, therefore, to
separate impurities, e.g., nickel and copper, from a cobalt product.
In general, the first stage for producing cobalt is dissolution of a
cobalt-containing starting material in a mineral acid, e.g., hydrochloric or
sulfuric acid, to form the cobalt solution. A starting material for cobalt
contains a variety of impurities, and the cobalt solution will contain a
variety of impurities, accordingly. Cobalt is commonly recovered from the
solution as the metal by electrolysis, after the solution is treated to remove
impurities. Purity of the electrolysis-produced cobalt metal depends on
composition of the electrolyte, and it is necessary for production of
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high-purity cobalt metal to remove impurities from the cobalt solution.
At present, solvent extraction is used as a process for efficiently
separate nickel from cobalt. In the solvent extraction carried out in a
chloride bath, cobalt, which forms a stable chloro complex, is extracted in
the organic phase to be separated from nickel, and then back-extracted from
the organic phase with an aqueous solution of low chlorine ion
concentration, e.g., water.
However, manganese and copper are very similar to cobalt in behavior
in extraction and back extraction, with the result that the cobalt chloride
solution as the back extract produced in the solvent extraction process
contains manganese and copper.
Oxidative neutralization process is used to remove manganese and
copper from the cobalt chloride solution containing manganese and copper.
For example, the applicant of the present invention has proposed to
remove these impurities from a cobalt solution containing iron, manganese,
zinc, calcium and copper by the treatment process involving an oxidative
neutralization stage and extraction stage with phosphoric acid as the
solvent (Patent Document 1).
In the above treatment process, the cobalt chloride solution is
oxidized/neutralized while being controlled at an oxidation-reduction
potential of 600mV or more (based on an Ag/AgCl electrode), to remove iron,
manganese and copper. However, the oxidative neutralization process
involves a problem of coprecipitation with cobalt as the major component of
the solution partly oxidized/neutralized into the hydroxide as the impurities,
e.g., iron, manganese and copper, precipitate.
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Production of a cobalt solution of low impurity concentration, in
particular low manganese concentration, is accompanied by increased
quantity of cobalt in the precipitate. The impurity-containing precipitate is
separately treated after being discharged from the system, causing another
problem that the coprecipitated cobalt cannot be directly recovered.
Under these situations, there are demands for the processes which can
control coprecipitation with cobalt as impurities (e.g., iron, manganese and
copper) precipitate, in order to effectively remove manganese.
[Patent document 11
Japanese Patent Laid-open Publication No.2000-17347 (refer to the
claims)
SUMMARY OF THE INVENTION
The present invention
provides a process for producing a cobalt solution of low manganese
concentration which can increase direct recovery rate of cobalt by
industrially advantageously removing manganese from a cobalt solution
containing manganese as an impurity by the oxidative neutralization
process.
The inventors of the present invention have found, after having
extensively studied. precipitation behavior of manganese and cobalt in the
oxidation/neutralization reactions in the process for oxidative neutralization
of a cobalt chloride solution to achieve the object, that (1) the reaction to
form tetravalent manganese oxide proceeds in preference to the reaction to
form trivalent cobalt hydroxide in the solution in a low pH range of 3.0 or
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less and high oxidative atmosphere, i.e., in a high oxidation-reduction
potential range, and (2) cobalt hydroxide can be dissolved in preference to
manganese oxide, when a precipitate containing these compounds is
dissolved in hydrochloric acid, and that these phenomena can be utilized to
realize a high, direct recovery rate of cobalt and to produce a high-purity
cobalt solution, achieving the present invention.
The first aspect of the present invention is a process for producing a
cobalt solution of low manganese concentration, comprising 2 stages for
producing a cobalt solution of low manganese concentration by
incorporating an oxidant and neutralizer in a cobalt solution containing
manganese as an impurity, the first stage being for oxidative neutralization
of the cobalt solution controlled at an oxidation-reduction potential of
900mV or more (based on an Ag/AgCI electrode) and pH of 3 or less to
remove most of the manganese in the form of oxide precipitate having a
Co/Mn ratio of 0.3 to 1.0 by weight, and the second stage being for the
continued oxidative neutralization of the cobalt solution produced in the
first stage to remove a small quantity of the residual manganese in the form
of oxide precipitate and thereby to produce the high-purity cobalt solution
containing manganese at 0.05g/L or less, while keeping the same
oxidation-reduction potential and pH conditions for the cobalt solution.
The second aspect of the present invention is a process for producing a
cobalt solution of low manganese concentration, comprising 3 stages for
producing a cobalt solution of low manganese concentration by
incorporating an oxidant and neutralizer in a cobalt solution containing
manganese as an impurity, the first stage being for oxidative neutralization
of the cobalt solution controlled at an oxidation-reduction potential of
900mV or more (based on an Ag/AgC1 electrode) and pH of 3 or less to
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remove most of the manganese in the form of oxide precipitate having a
Co/Mn ratio of 0.3 to 1.0 by weight, the second stage being for the continued
oxidative neutralization of the cobalt solution produced in the first stage to
remove a small quantity of the residual manganese in the form of oxide
precipitate and thereby to produce the high-purity cobalt solution
containing manganese at 0.05g/L or less, while keeping the same
oxidation-reduction potential and pH conditions for the cobalt solution, and
the third stage being for dissolution of the precipitate containing the
separated manganese oxide and cobalt hydroxide in a mineral acid to keep
the solution at a pH of 0.05 to 2.0, and also for recycling the resulting
slurry
back to the first stage.
The third aspect of the present invention is the process of the first or
second aspect for producing a cobalt solution of low manganese
concentration, wherein the cobalt solution is oxidized/neutralized while
being controlled at an oxidation-reduction potential of 950 to 1050mV
(based on an Ag/AgCl electrode) and pH of 2.4 to 2.8.
The fourth aspect of the present invention is the process of the first or
second aspect for producing a cobalt solution of low manganese
concentration, wherein the cobalt solution containing manganese as an
impurity is a cobalt chloride solution.
The fifth aspect of the present invention is the process of the first or
second aspect for producing a cobalt solution of low manganese
concentration, wherein the oxidant is at least one type selected from the
group consisting of chlorine, hypochlorous acid and ozone.
The sixth aspect of the present invention is the process of the first or
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second aspect for producing a cobalt solution of low manganese concentration,
wherein the neutralizer is at least one type selected from the group
consisting of
hydroxide and carbonate of an alkali and alkali-earth metal, and cobalt
carbonate.
The seventh aspect of the present invention is the process of the
second aspect for producing a cobalt solution of low manganese concentration,
wherein said the solution is controlled at a pH of 0.1 to 1.5 in said third
stage.
In one embodiment, the invention relates to a process for producing
a cobalt solution of low manganese concentration by incorporating an oxidant
and
a neutralizer in a cobalt solution containing manganese as an impurity, the
process comprising three stages: the first stage being for oxidative
neutralization
of the cobalt solution controlled at an oxidation-reduction potential of 900mV
or
more, based on an Ag/AgCI, electrode and a pH of 3 or less, to remove most of
the manganese in the form of an oxide precipitate having a Co/Mn ratio of 0.3
to
1.0 by weight; the second stage being for the continued oxidative
neutralization of
the cobalt solution produced in the first stage to remove residual manganese
in
the form of an oxide precipitate containing the separated manganese oxide and
cobalt hydroxide and thereby to produce the high purity cobalt solution
containing
manganese at 0.05g/L or less, while keeping the same oxidation-reduction
potential and pH conditions for the cobalt solution; and the third stage being
for
preferential dissolution of cobalt hydroxide from the precipitate using a
mineral
acid to form a slurry, while keeping the liquid phase of the resulting slurry
at a pH
of 0.05 to 2.0 and also for recycling the resulting slurry back to the first
stage.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a graph showing the relationship between Mn concentration of the
final
solution and pH level for the oxidation/neutralization reaction of the cobalt
chloride
solution.
Figure 2 is a graph showing the relationship between Mn concentration of the
final
solution and oxidation-reduction potential (ORP) level for the
oxidation/neutralization reaction of the cobalt chloride solution.
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Figure 3 is a graph showing the relationship between Mn concentration of the
final
solution and Co/Mn weight ratio of the precipitate produced by the
oxidation/neutralization reaction of the cobalt chloride solution.
Figure 4 is a graph showing the effects of pH level on Co and Mn leaching
rates,
when the precipitate is treated with hydrochloric acid.
DETAILED DESCRIPTION OF THE PRIOR ART
The process of the present invention for producing a cobalt solution
of low manganese concentration is described in detail.
The present invention relates to a process for producing a cobalt
solution of low manganese concentration, comprising 2 stages for producing
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a cobalt solution of low manganese concentration by incorporating an
oxidant and neutralizer in a cobalt solution containing manganese as an
impurity, the first stage being for oxidative neutralization to remove most of
the manganese in the form of oxide precipitate and the second stage being
for the continued oxidative neutralization to remove a small quantity of the
residual manganese in the form of oxide precipitate. The process may
include, as required, the third stage for separating part of cobalt hydroxide
from the separated (removed) precipitate by preferential dissolution and
recycling it back to the first stage.
(1) First stage for removing most of manganese in the form of oxide
precipitate
This stage first sets a cobalt solution under specific conditions with
respect to oxidation-reduction potential and pH level, to remove most of
manganese in the form of oxide precipitate having a Co/Mn weight ratio in a
specific range.
Cobalt solutions containing manganese as an impurity include a
solution as a by-product of nickel or copper refining; solution resulting from
a mixed sulfide of nickel and cobalt as a starting material which is leached
and extracted with a solvent; cake containing iron which is removed as a
by-product of purifying the spent electrolyte discharged from electrolyte
refining stage of crude nickel; and solution produced from sulfide cake as a
starting material, which is recovered by treating the residual solution from
preferential reduction stage of nickel in the presence of hydrogen of elevated
pressure with hydrogen sulfide.
The oxidants useful for the present invention include chlorine,
hypochlorous acid and ozone, which have a sufficient oxidative power to
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oxidize the manganese ion to a valence number of +4. Chlorine is
particularly preferable, when the cobalt solution is a chloride-based one.
The neutralizer for the present invention is at least one type selected
from the group consisting of hydroxide and carbonate of an alkali and
alkali-earth metal, e.g., sodium hydroxide, potassium hydroxide and sodium
carbonate, and cobalt carbonate. Cobalt carbonate is more preferable,
when impurity accumulation in the cobalt solution causes a problem.
When chlorine and cobalt carbonate are used as the oxidant and
neutralizer, the divalent manganese in the solution is oxidized by chlorine,
and the reaction to precipitate the tetravalent manganese proceeds. This
reaction, however, is accompanied by oxidation of cobalt as the major
component of the solution into the trivalent state to form the hydroxide,
which coprecipitates with manganese oxide.
The present invention involves oxidation/neutralization of a cobalt
solution containing manganese as an impurity in the presence of an oxidant
and neutralizer, where manganese can be mostly removed in the form of
oxide precipitate, when the solution is controlled at an oxidation-reduction
potential of 900mV or more (based on an Ag/AgCl electrode) and pH of 3 or
less.
The reasons for the oxidation-reduction potential and pH ranges for the
cobalt solution are described by referring to Figs. 1 and 2.
A cobalt chloride solution containing Co at 80g/L and Mn at 0.45 or
0.38g/L as the starting solution was controlled at a given pH and
oxidation-reduction potential (ORP) level for the oxidation/neutralization in
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the presence of chlorine and cobalt carbonate as the oxidant and neutralizer,
to follow Mn concentration changes for 2 hours as reaction time.
The results are given in Figs. 1 and 2, where Fig.l shows the results
with the cobalt chloride solution containing Co at 80g/L and Mn at 0.45g/L
as the starting solution, and Fig.2 the results with the cobalt chloride
solution containing Co at 80g[L and Mn at 0.38g/L.
As shown, it is found that (1) decreasing pH or oxidation-reduction
potential level tends to hinder removal of manganese, and (2) it is necessary
to control the solution at a pH of 2.4 or more and ORP at 950mV or more, in
order to keep the reaction effluent (final solution) at an Mn concentration of
0.05g/L or less, desired for production of high-purity cobalt metal by
electrolysis.
Therefore, the present invention intending to remove manganese
controls the first stage at a pH of 2.4 or more and ORP at 950mV or more,
preferably at 2.4 to 2.8 and 950 to 1050mV, more preferably at 2.4 to 2.5
and 950 to 1000mV, while continuously charging chlorine and cobalt
carbonate. The first stage operating at a pH above 2.8 or ORP beyond the
above range is not economical, because of increased consumption of cobalt
carbonate or chlorine.
Next, the reasons for the desired oxidation/neutralization reaction to
remove most of manganese in the form of the oxide precipitate having a
Co/Mn ratio of 0.3 to 1.0 by weight are described by referring to Fig.3.
A cobalt chloride solution containing Co at 80g/L and Mn at 1.8g/L and
kept at a pH of 0.6 as the starting solution was subjected to the
oxidation/neutralization in the presence of continuously charged chlorine
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and cobalt carbonate while controlling the solution at a pH of 2.45, ORP of
950 to 1050mV and 50 C for 2 hours, to follow Mn concentration of the
reaction effluent (final solution) and Co/Mn weight ratio of the resulting
precipitate.
As a result, it is found that the precipitate has a higher Co/Mn weight
ratio as Mn concentration of the final solution decreases, and, for example,
the ratio of the resulting precipitate is 1.5 or more when Mn concentration
of the cobalt chloride solution is decreased to a level of 0.05g/L or less,
desired for production of high-purity cobalt metal by electrolysis.
It is also found that Mn concentration of the reaction effluent is around
0.15g/L and manganese removal rate is around 90%, in order to produce the
precipitate of limited coprecipitated cobalt quantity, or of Co/Mn ratio of
1.0
or less by weight.
Therefore, the optimum conditions for the first stage for the present
invention are determined from the relationship between manganese
precipitation rate (removal rate) and coprecipitated cobalt quantity, and it
is preferable to keep Co/Mn ratio of the resulting precipitate of limited
coprecipitated cobalt quantity at 1.0 or less by weight. Moreover, the
Co/Mn ratio of 0.3 or more by weight, which corresponds to a manganese
removal rate of 70% or more, is preferable in consideration of all of the
stages involving manganese removal. Therefore, the Co/Mn ratio of the
resulting precipitate is set at 0.3 to 1.0 by weight, preferably 0.3 to 0.8.
(2) Stage for producing a high-purity cobalt solution
The second stage for the present invention continues the
oxidation/neutralization reaction while controlling the cobalt solution,
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produced in the first stage, at a given oxidation-reduction potential and pH
level to remove a small quantity of the residual manganese in the form of
oxide precipitate and thereby to produce the high-purity cobalt solution
containing manganese at a specific level or less, as described above.
The second stage is controlled at a pH of 2.4 or more and ORP at
950mV or more, preferably at 2.4 to 2.8 and 950 to 1050mV, more preferably
at 2.4 to 2.5 and 950 to 1000mV, as is the case with the first stage. The
second stage operating at a pH above 2.8 or ORP above 1050mV is not
economical, because of increased consumption of cobalt carbonate or
chlorine.
The second stage conditions are set to decrease manganese
concentration of the solution to 0.05g/L or less, preferably 0.03g/L or less,
in
order to give a high-purity cobalt product, as described above. In the
second stage, quantity of manganese to be removed is small, because it has
been mostly removed in the first stage, and quantity of coprecipitated cobalt
decreases. In other words, coprecipitation of cobalt in the precipitate can
be controlled, when manganese is removed in 2 stages.
(3) Stage for recycling cobalt in the form of slurry
The third stage for the present invention is for separating part of cobalt
hydroxide from the precipitate by preferential dissolution and recycling it
back to the first stage directly in the form of slurry.
The cobalt hydroxide is preferentially dissolved out of the precipitate
separated in the second stage at a specific pH level. How the pH level is
determined is explained by referring to Fig.4.
The precipitate (Co concentration: 37.0%, Mn concentration: 17.0%),
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prepared in the second stage under the conditions of pH: 2.4 and ORP: 950
to 1050mV, was incorporated with hydrochloric acid to change its pH level,
to follow Co and Mn leaching rates.
As a result, it is found that manganese is little leached out of the
precipitate, while cobalt is preferentially leached out, until the pH level is
decreased to 0.1 or so, and that at least 50% of cobalt can be leached out at
a
pH of around 1.5.
Therefore, cobalt is dissolved out of the precipitate preferably at a pH of
0.05 to 2.0 in the third stage, particularly preferably 0.1 to 1.5. Most of
cobalt present in the precipitate is dissolved in the solution in the third
stage, and the resulting slurry containing undissolved manganese is
recycled back to the first stage. This allows cobalt to be effectively
utilized,
thereby directly contributing to improved yield of cobalt.
Cobalt hydroxide is leached out less at a higher pH level of the solution.
In this case, the recycled cobalt hydroxide precipitate works as a neutralizer
for the first stage for the present invention, decreasing cobalt carbonate
consumption. As a result, part of the precipitate formed in the second
stage can be directly utilized as a neutralizer for the first stage.
Several methods, e.g., precipitation with a sulfide and cementation with
cobalt metal, have been proposed to remove copper, when it is present in the
cobalt chloride solution. It can be removed efficiently by these
conventional techniques.
Moreover, electrolysis of the high-purity cobalt solution produced by the
above methods gives cobalt metal of high quality.
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EXAMPLES
The present invention is described by EXAMPLES, which by no means
limit the present invention. Weight of the precipitate prepared in each of
EXAMPLES is on a wet basis.
Cobalt chloride solution containing manganese:
The back-extract solution (Co concentration: 80.0g/L, Mn concentration:
1.85g/L, pH: 0.6) from the solvent extraction process was used as the cobalt
chloride solution.
EXAMPLE 1
The first aspect of the present invention, removing manganese in 2
stages, was verified using a reactor tank holding about 100L of the reaction
solution.
The solution was treated in the first stage for 2 hours, while it was
controlled at a pH of 2.45 and ORP of 950mV in the presence of
continuously charged chlorine gas and powdered cobalt carbonate. The
resulting precipitate was filtered to obtain 1.2kg of a precipitate having a
Co/Mn ratio of 0.40 by weight and 99L of a crude solution containing Mn at
0.45g/L. The first stage performed an Mn removal rate of 75.7% and Co
yield of 99.3% (precipitate lost from the system: 0.7%).
The crude solution produced in the first stage was passed to the second
stage, where it was treated under the same conditions as in the first stage
in the presence of continuously charged chlorine gas and powdered cobalt
carbonate. The precipitate produced in the second stage was filtered to
obtain 98L of a high-purity cobalt chloride solution containing Mn at
0.01g/L and 0.7kg of a precipitate having a Co/Mn ratio of 1.7 by weight.
The Mn and Co distribution rates in the precipitate produced in the second
stage were 23.8 and 0.9%, respectively, based on the Mn and Co amounts
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charged to the manganese removal process of the first stage.
Mn removal rate of 99.5% and direct Co yield of 98.4% were recorded by
the process.
EXAMPLE 2
The second aspect of the present invention, comprising removal of
manganese in 2 stages followed by a slurry recycling stage, was verified in a
similar manner. In the first stage, 100L of the solution was treated in the
first stage for 2 hours, while it was controlled at a pH of 2.45 and ORP of
950mV in the presence of continuously charged chlorine gas and powdered
cobalt carbonate, after it was incorporated with 1.3L of the slurry produced
in the second stage, and treated with and dissolved in hydrochloric acid to
be adjusted at a pH of 0.1
The resulting precipitate was filtered to obtain 1.8kg of a precipitate
having a Co/Mn ratio of 0.40 by weight and 100L of a crude solution
containing Mn at 0.45g[L. The first stage performed an Mn removal rate of
75.7% and Co yield of 99.2% (precipitate lost from the system: 0.8%).
The crude solution produced in the first stage was passed to the second
stage, where it was treated under the same conditions as in the first stage
in the presence of continuously charged chlorine gas and powdered cobalt
carbonate. The precipitate produced in the second stage was filtered to
obtain 99L of a high-purity cobalt chloride solution containing Mn at
0.01g[L and 1.1kg of a precipitate having a Co/Mn ratio of 1.7 by weight.
The Mn and Co distribution rates in the precipitate produced in the second
stage were 23.8 and 0.9%, respectively, based on the Mn and Co amounts
charged to the manganese removal process of the first stage.
Then, the precipitate produced in the second stage was passed to a
leaching tank, where it was treated with hydrochloric acid for 1 hour at a
pH of 0.1, to prepare the slurry to be recycled back to the first stage.
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Mn removal rate of 99.3% and direct Co yield of 99.2% were recorded by
the process.
COMPARATIVE EXAMPLE 1
Manganese was removed by a conventional process, where 100L of the
solution was treated for 4 hours, while it was controlled at a pH of 3.00 and
ORP of 900mV in the presence of continuously charged chlorine gas and
powdered cobalt carbonate. The resulting precipitate was filtered to obtain
98L of a high-purity cobalt chloride solution containing Mn at 0.01g/L and
6.1kg of a precipitate having a Co/Mn ratio of 2Ø
This process performed an Mn removal rate of 99.5% and direct Co
yield of 95.4% (precipitate lost from the system: 4.6%).
It is apparent, when the results of EXAMPLES are compared with
those of COMPARATIVE EXAMPLE, that the present invention can have a
greatly higher direct recovery rate of cobalt than the conventional process.
The present invention can remove manganese almost completely from a
cobalt chloride solution containing manganese as an impurity while
increasing a direct recovery rate of cobalt, and hence is of very high
industrial value.
