Note: Descriptions are shown in the official language in which they were submitted.
CA 02475667 2004-07-21
77486-18
SPECIFICATION
COBALT CARBONATE OF LOW ALKALI METAL CONTENT,
METHOD FOR PRODUCING THE SAME AND COBALT OXIDE PRODUCED
FROM THE SAME
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to cobalt carbonate
of a low alkali metal content, a method for producing the
same and cobalt oxide produced from the same, more
specifically a method for producing cobalt carbonate of a
low alkali metal content at a low cost in high productivity,
and cobalt oxide of a low alkali metal content and high
performance produced from the cobalt carbonate.
DESCRIPTION OF THE PRIOR ART
Cobalt oxide has been used as a pigment for
potteries and a colorant for glass products. Recently, a
demand of the cobalt oxide has been growing rapidly as a
ceramic material for electronic device parts, e.g., those
for condensers, varistors and thermistors, and as a material
for lithium ion batteries and organic synthesis catalysts.
When the cobalt oxide is used for the above-mentioned
purposes, in particular for the electronic device and the
battery, an alkali metal is cited as an impurity which
causes various problems, e.g., abnormal sintering, reduced
electronic resistance and deteriorated electromagnetic
properties, while they are produced or in service. In
particular, it is highly desirable to contain no sodium.
It is difficult for a common method used for
removing the alkali metal, e.g., by wet washing or
1
CA 02475667 2010-11-01
77486-18
evaporation under heating, to remove efficiently and
sufficiently the alkali metal from cobalt oxide containing
an alkali metal. Therefore, a cobalt salt as a starting
material for cobalt oxide is pretreated to reduce alkali
metal content. Several methods for producing a cobalt salt
of low alkali metal content have been proposed, and the
representative ones are described below. They have been
contributing to production of cobalt oxide of low alkali
metal content, but each involves its own disadvantages.
(1) Precipitation of highly filterable cobalt
basic carbonate is produced from an aqueous cobalt salt
solution using a sodium-free carbonate of an alkali, e.g.,
ammonium bicarbonate or ammonium carbonate. This method can
produce .cobalt oxide of low ammonium content by washing the
precipitate, which is highly filterable, and subsequent
calcination to reduce ammonium content. However, the method
involves disadvantages of high production cost, because
ammonium bicarbonate used as a reactant is relatively
expensive, and,'in particular, high cost for waste solution
treatment because ammonium ions are massively present in the
solution.
(2) Production of cobalt hydroxide from an aqueous
cobalt salt solution using an alkali metal hydroxide, and
subsequent removal of impurities, e.g., an alkali metal,
from the resulting precipitate by repeated washing (refer
to, e.g., Japanese Patent Publication No. 55-62814). This
method involves a disadvantage of low productivity resulting
from difficulties in washing and filtration on a commercial
scale because the precipitate is of. very fine cobalt
hydroxide particles, very. difficult to filtrate and settle.
(3) Precipitation of cobalt basic carbonate (also referred to as basic
cobalt carbonate) produced from an aqueous cobalt salt solution using sodium
2
CA 02475667 2004-07-21
77486-18
carbonate or sodium bicarbonate, and subsequent washing the
resulting precipitate with a sodium hydroxide solution and
then with water, to produce cobalt basic carbonate of low
sodium content (refer to, e.g., Japanese Patent Publication
No. 7-196323). This method can remove sodium by washing a
water-insoluble double salt e.g., sodium cobaltate
dicarbonate (Na2[Co(CO3)2]=4H2O), which is precipitated as a
by-product in the case of high carbonate ion content in a
solution, with a sodium hydroxide solution to decompose the
salt and thereby to produce cobalt carbonate of low sodium
content. However, it involves disadvantages of increased
costs, e.g., those resulting from an additional step of
alkali washing needed before a water-washing step, which is
normally adopted, and those associated with use of sodium
hydroxide or the like.
As discussed above, cobalt carbonate, e.g., cobalt
basic carbonate, is a more preferable starting compound for
cobalt oxide of low sodium content than cobalt hydroxide,
because it is highly filterable and can be easily treated by
water-washing. Moreover, a carbonate of an alkali metal is
preferable than a carbonate of an alkali., because it can
avoid problems associated with waste water treatment.
Under these circumstances, there are demands for
methods for producing cobalt carbonate of low alkali metal
content at a low cost in high productivity, and for cobalt
oxide of low alkali metal content and high performance
produced from the cobalt carbonate. The term cobalt
carbonate used in this specification means a cobalt
carbonate compound in the broad sense, including cobalt
basic carbonate having hydroxide group in addition to
carbonate group.
3
CA 02475667 2011-09-13
77486-18
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for producing
cobalt carbonate of low alkali metal content at a low cost in high
productivity in
consideration of the problems involved in the conventional techniques. It is
another
object of the present invention to provide cobalt oxide of low alkali metal
content and
high performance produced from the cobalt carbonate.
The inventors of the present invention have found, after having
extensively studied, in particular, cobalt carbonate for a method for
producing cobalt
oxide to attain the above objects, that cobalt carbonate of low alkali metal
content can
be produced at a low cost in high productivity when specific reaction
conditions are
adopted, and have achieved the present invention.
A first aspect of the present invention provides a method for producing
cobalt carbonate of low alkali metal content, which comprises reacting an
aqueous
cobalt salt solution with a carbonate of an alkali metal to produce the cobalt
carbonate under at least one of the following conditions:
(1) a reaction temperature is controlled at 25 C or lower, and
(2) an aqueous solution of an alkali metal carbonate containing of an
alkali metal hydroxide in an amount of 5 to 40g/L is used as the carbonate of
an alkali
metal. The temperature in the first aspect may be controlled at 14 to 18 C.
In a first major embodiment of the first aspect, a sodium salt is used as
the carbonate of an alkali metal.
4
CA 02475667 2010-11-01
77486-18
In the first aspect, the alkali metal content may
be 0.7% by weight or less, and the cobalt carbonate may be
basic.
In a second major embodiment of the method, sodium
bicarbonate is used as the carbonate of an alkali metal.
In a third major embodiment of the method, the
reaction temperature is controlled at 10 to 20 C.
In a fourth major embodiment of the method, sodium
hydroxide is used as the hydroxide of an alkali metal.
The second aspect of the present invention
provides cobalt carbonate of low alkali metal content
produced by the method.
A third aspect of the present invention provides
cobalt oxide of low alkali metal content produced from the
cobalt carbonate.
The method of the present invention can produce
cobalt carbonate of low alkali metal content at a low cost
in high productivity, and cobalt oxide produced from the
cobalt carbonate contains an alkali metal at a low content
and exhibits high performance. As such, they have very high
industrial values.
DETAILED DESCRIPTION OF THE INVENTION
Cobalt carbonate of low alkali metal content, the
method for producing the same and cobalt oxide produced from
the same of the present invention are described in more
detail below.
5
CA 02475667 2010-11-01
77486-18
The method of the present invention produces
cobalt carbonate of low alkali metal content by a reaction
of a .carbonate of an alkali metal with a cobalt salt in the
form of an aqueous solution, wherein (1) a reaction
temperature is controlled at 25 C or lower, and/or (2) an
aqueous solution of carbonate of an alkali metal containing
5a
CA 02475667 2004-07-21
77486-18
a hydroxide of alkali metal in an amount of 5 to 40g/L is
used as the carbonate of an alkali metal. The cobalt
carbonate of low alkali metal content is used for producing
cobalt oxide.
1. Method for producing cobalt carbonate
The method of the present invention produces
cobalt carbonate by the reaction of a carbonate of an alkali
metal with a cobalt salt in the form of an aqueous solution,
while satisfying at least one of the conditions (1) and (2):
(1) a reaction temperature is controlled at 25 C
or lower, and
(2) an aqueous solution of carbonate of an alkali
metal containing a hydroxide of an alkali metal at a
concentration of 5 to 40g/L is used as the carbonate of an
alkali metal.
More specifically, the method of the present
invention produces cobalt carbonate by the reaction of a
carbonate of an alkali metal with a cobalt salt in the form
of an aqueous solution, wherein (A) a reaction temperature
is controlled at 25 C or lower, (B) an aqueous solution of
carbonate of an alkali metal containing a hydroxide of an
alkali metal at 5 to 40g/L is used as the carbonate of an
alkali metal, or (C) an aqueous solution of carbonate of an
alkali metal containing a hydroxide of an alkali metal at 5
to 40g/L is used as the carbonate of an alkali metal and, at
the same time, reaction temperature is controlled at 25 C or
lower.
Each of controlling reaction temperature at 25 C
or lower, and using an
6
CA 02475667 2004-07-21
aqueous solution of carbonate of an alkali metal containing a hydroxide of
an alkali metal at 5 to 40g/L as the carbonate of an alkali metal has an
essential meaning for the method of the present invention for producing
cobalt carbonate. Each leads to a solution for producing cobalt carbonate of
low alkali metal content in high productivity on a commercial scale, which
is a technical theme for the conventional techniques.
By contrast, the conventional method for producing cobalt carbonate
cannot give cobalt carbonate of low alkali metal content by a simple
procedure for the following technical problems. For example, some of the
conventional methods react a cobalt salt, e.g., cobalt chloride, nitrate or
sulfate, in the form of aqueous solution with sodium carbonate or
bicarbonate incorporated in the solution to produce cobalt carbonate in the
form of precipitate. The resulting cobalt carbonate contains sodium at 1 to
4% by weight, which cannot be removed by water-washing.
The high content of sodium conceivably results from a water-insoluble
double salt of alkali metal, e.g., sodium cobaltate dicarbonate
(Na2[Co(CO3)2] - 4H20) partly formed in the system to contaminate the
product precipitate of cobalt carbonate. The reaction mechanism for
producing the double salt conceivably involves the Co ion which forms the
Co-carbonate complex ion in a solution of high carbonate ion concentration
and also forms a double salt of the complex ion with a monovalent cation,
e.g., that of sodium.
It is therefore essential to allow the cobalt carbonate producing reaction
as the major reaction to preferentially proceed while controlling the double
salt producing reaction, for which each of controlling reaction temperature
at 25 C or lower, and using an aqueous solution of carbonate of an alkali
7
CA 02475667 2004-07-21
metal containing a hydroxide of alkali metal at a given content as the
carbonate of an alkali metal is effective.
The method for controlling the reaction for the above production
method is not limited. For example, the reaction can be controlled by
incorporating an aqueous solution containing a cobalt salt at a given
content with an aqueous solution containing a carbonate of an alkali metal
at a given content in a given mixing ratio, or by controlling addition rate of
an aqueous solution of carbonate of an alkali metal in such a way to control
the reaction solution at a given pH level.
For the former approach, content of the carbonate of an alkali metal in
the aqueous solution of cobalt salt is not limited, but preferably 1.0 to 1.5
chemical equivalents required for transforming cobalt in the aqueous
solution into CoCO3 in order to recover cobalt at a high rate. For the latter
approach, pH level of the reaction solution is not limited, but preferably 6.5
to 8.0 in order to recover cobalt at a high rate.
The carbonate of an alkali metal for the above production method is not
limited. For example, sodium or potassium is used as the alkali metal. In
particular, sodium carbonate and sodium bicarbonate are preferable for
their inexpensiveness. Sodium bicarbonate is more preferable, because it
is low in alkalinity, and hence excellent in pH controllability for the
reaction to keep sodium content at a low level more easily.
(1) Production Method (A)
Production Method (A) involves a procedure to control reaction
temperature at 25 C or lower, wherein reaction temperature is controlled at
25 C or lower, preferably 10 to 20 C, more preferably 14 to 18 C. More
8
CA 02475667 2004-07-21
specifically, decreasing reaction temperature retards the double salt
producing reaction more than the cobalt carbonate producing reaction as the
major reaction. Therefore, it is decreased to room temperature or below to
control production of the double salt. The reaction system operating at
above 25 C cannot give cobalt carbonate of sufficiently low alkali metal
content for electronic device and battery materials because of its
insufficient
effect of controlling the double salt producing reaction. Decreasing
reaction temperature increases the effect of controlling the double salt
producing reaction. However, it is 10 C or higher for the present invention,
because decreasing the level excessively is accompanied by increased cooling
system cost.
(2) Production Method (B)
Production Method (B) involves a procedure which uses an aqueous
solution of carbonate of an alkali metal containing a hydroxide of an alkali
metal at 5 to 40g/L as the carbonate of an alkali metal. More specifically,
incorporation of a hydroxide of an alkali metal brings favorable effects,
e.g.,
increasing OH ion in the reaction solution while decreasing CO32- ion
content, and triggering the reaction for producing the hydroxide
simultaneously with that for producing the carbonate, the former
proceeding faster than the latter, thereby accelerating production of the
hydroxide and carbonate while controlling production of the double salt to
decrease alkali metal content.
In Production Method (B), a hydroxide of an alkali metal is
incorporated in the aqueous solution of carbonate of an alkali metal at 5 to
40g/L, preferably 20 to 40g/L, more preferably 20 to 30g/L. At below 5g/L,
the effect of decreasing sodium content of the cobalt carbonate product may
be insufficient. At above 40gIL, on the other hand, cobalt hydroxide may
9
CA 02475667 2004-07-21
be the major component of the precipitate produced, because the reaction for
producing the hydroxide will prevail over that for producing the carbonate.
As a result, the precipitate is composed of finer particles, to have
deteriorated filterability and washability.
Reaction temperature for the above method is not limited, and it is
carried out at a reaction solution temperature of room temperature or
higher. The hydroxide of an alkali metal for the above method is not
limited. For example, sodium or potassium is used as the alkali metal.
Sodium hydroxide is particularly preferable because of its inexpensiveness.
(3) Production Method (C)
Production Method (C) is a combination of Production Methods (A) and
(B), involving a procedure which uses an aqueous solution of carbonate of
an alkali metal containing a hydroxide of an alkali metal at 5 to 40gIL as
the carbonate of an alkali metal, and another procedure to control reaction
temperature at 25 C or lower. Each of these procedures is carried out
under the conditions similar to those for Production Method (A) or (B).
2. Cobalt carbonate
Cobalt carbonate of the present invention is the one containing an
alkali metal at a low content, produced by one of Production Methods (A) to
(C) described above. The cobalt carbonate precipitate produced is
separated into the solid and reaction filtrate by centrifugal separation or
the
like, and the solid is washed with water and then dehydrated.
Cobalt carbonate of the present invention contains an alkali metal at
0.3% or less and 0.1% or less, both by weight, when produced by Production
Method (A) or (C) operating at 25 and 20 C, respectively, and 0.7% or less
and 0.3% or less, both by weight, when produced by Production Method (B)
CA 02475667 2004-07-21
operating under the preferable conditions for the latter. By contrast, cobalt
carbonate produced by the conventional method operating at 30 to 70 C
contains an alkali metal at 1 to 4% by weight.
As discussed above, the production method of the present invention
gives cobalt carbonate of lower alkali metal content.
3. Cobalt oxide
Cobalt oxide of low alkali metal content of the present invention is
produced from the cobalt carbonate as the starting compound, which is
produced by the method described above and calcined. It contains an
alkali metal at a lower content than the one produced by the conventional
method, and is suitable as materials for electronic device and battery, for
which materials containing an alkali metal, e.g., sodium, is unsuitable.
The method for producing the cobalt oxide is not limited. It is
produced by calcination of the cobalt carbonate, preferably heated at 350 C
or higher in air. At a calcination temperature below 350 C, the carbonate
may be decomposed insufficiently and left undecomposed in the product.
EXAMPLES
The present invention is described in more detail by EXAMPLES and
COMPARATIVE EXAMPLES, which by no means limit the present
invention. Cobalt carbonate was analyzed for metal and moisture contents
by the following procedures in EXAMPLES and COMPARATIVE
EXAMPLES.
(1) Analysis of metal contents
The dehydration-treated sample was dried at 105 C for 24 hours, and
analyzed by ICP emission spectrometry.
11
CA 02475667 2004-07-21
(2) Analysis of moisture content
The dehydration-treated sample was dried at 105 C for 24 hours, and
measured for weight difference before and after the drying treatment.
(EXAMPLE i)
Cobalt carbonate was prepared by Production Method (A), and
evaluated for its sodium content.
First, 20L of a 140g/L aqueous solution of sodium bicarbonate as the
carbonate of an alkali metal was put in a reaction tank, to which 20L of a
50g/L aqueous solution of cobalt chloride was added in 30 minutes for the
reaction, while reaction temperature was kept at 18 C with stirring. The
carbonate of the alkali metal was added to the aqueous cobalt salt solution
at 1.0 chemical equivalent required for transforming cobalt into CoCO3.
The reaction was allowed to continue for 20 minutes, and the resultant
slurry was centrifugally separated into cobalt carbonate (solid) and reaction
filtrate (liquid). The separated cobalt carbonate was repulp-washed with
water and centrifugally dehydrated again. It was analyzed for sodium
content. The result is given in Table 1.
(EXAMPLE 2)
Cobalt carbonate was prepared by Production Method (A), and
evaluated for its sodium content.
First, IL of a 50gIL aqueous solution of cobalt chloride was put in a
reaction tank, to which a 100g/L aqueous solution of sodium carbonate
(reagent grade) as the carbonate of an alkali metal was added for the
reaction, which was allowed to proceed for 4 hours while reaction
temperature was kept at 14 C with stirring, where the reaction solution
was adjusted at a final pH level of 7.7.
The resultant slurry was separated into cobalt carbonate (solid) and
12
CA 02475667 2004-07-21
reaction filtrate (liquid) by filtration under a vacuum. The separated
cobalt carbonate was repulp-washed with water and dehydrated again by
filtration under a vacuum. It was analyzed for sodium content. The
result is given in Table 1.
(EXAMPLE 3)
Cobalt carbonate was prepared by Production Method (A), and
evaluated for its sodium content.
It was prepared in the same manner as in EXAMPLE 2, except that a
73g/L aqueous solution of sodium bicarbonate (reagent grade) was used as
the carbonate of an alkali metal and the reaction solution was adjusted at a
final pH level of 6.9. The resultant cobalt carbonate was analyzed for
sodium content. The result is given in Table 1.
(EXAMPLE 4)
Cobalt carbonate was prepared by Production Method (A), and
evaluated for its sodium content.
It was prepared in the same manner as in EXAMPLE 1, except that
reaction temperature was controlled at 25 C . The resultant cobalt
carbonate was analyzed for sodium content. The result is given in Table 1.
(EXAMPLE 5)
Cobalt carbonate was prepared by Production Method (C), and
evaluated for its sodium and moisture content.
First, a 100g/L aqueous solution of sodium carbonate (reagent grade) as
the carbonate of an alkali metal was incorporated with sodium hydroxide to
10g/L. Next, the above aqueous solution containing the alkali metal was
pumped into a 1L reactor together with a 50g/L aqueous solution of cobalt
chloride (reagent grade), and the reaction was allowed to proceed while
13
CA 02475667 2004-07-21
reaction temperature was kept at 18 C with stirring. These aqueous
solutions were pumped in such a way to keep the residence time at 1 hour
and reaction solution pH level at 7.5.
The resultant slurry was separated into cobalt carbonate (solid) and
reaction filtrate (liquid) by filtration under a vacuum. The separated
cobalt carbonate was washed with sprayed water and dehydrated again by
filtration under a vacuum. It was analyzed for sodium content. The
result is given in Table 1.
(EXAMPLES 6 to 9)
Cobalt carbonate was prepared by Production Method (B) in each of
EXAMPLES 6 to 9, and evaluated for its sodium and moisture contents.
First, a 100g/L aqueous solution of sodium carbonate (reagent grade) as
the carbonate of an alkali metal was incorporated with sodium oxide to 5, 10,
20 or 40g/L. Next, the above aqueous solution containing the alkali metal
was pumped into a 1L reactor together with a 50g/L aqueous solution of
cobalt chloride (reagent grade), and the reaction was allowed to proceed
while reaction temperature was kept at 70 C with stirring. These aqueous
solutions were pumped in such a way to keep the residence time at 1 hour
and reaction solution pH level at 7.5.
The resultant slurry was separated into cobalt carbonate (solid) and
reaction filtrate (liquid) by filtration under a vacuum. The separated
cobalt carbonate was washed with sprayed water and dehydrated again by
filtration under a vacuum. It was analyzed for sodium, cobalt and
moisture contents. The result is given in Table 2.
(COMPARATIVE EXAMPLE 1)
Cobalt carbonate was prepared in the same manner as in EXAMPLE 6,
except that sodium hydroxide was incorporated in the aqueous sodium
14
CA 02475667 2004-07-21
carbonate solution to 50g/L as the aqueous carbonate solution containing
the alkali metal. The resulting cobalt carbonate showed deteriorated
filterability. It was analyzed for sodium, cobalt and moisture contents.
The result is given in Table 2.
(COMPARATIVE EXAMPLE 2)
Cobalt carbonate was prepared in the same manner as in EXAMPLE 6,
except that sodium hydroxide was not incorporated in the aqueous sodium
carbonate solution as the aqueous carbonate solution containing the alkali
metal. It was analyzed for sodium, cobalt and moisture contents. The
result is given in Table 2
CA 02475667 2004-07-21
Table 1
Production Reaction Slurry pH during Na content of
Method temperature the reaction process cobalt carbonate
( C) (% by weight)
EXAMPLE 1 (A) 1.8 - 0.01
EXAMPLE 2 (A) 14 7.7 0.02
EXAMPLE 3 (A) 14 6.9 0.01
EXAMPLE 4 (A) 25 0.30
EXAMPLE .5 (C) 18 0.02
Table 2
Production NaOH Reaction Na, Co and moisture
Method content of temperature contents of cobalt
the aqueous ( C) carbonate
Na2CO3 /o b wei ht)
solution Na Co moisture
contents*
EXAMPLE 6 (B) 5 70 0.68 49.0 26.0
EXAMPLE 7 (B) 10 70 0.52 51.2 25.9
EXAMPLE 8 (B) 20 70 0.22 51.8 27.7
EXAMPLE 9 (B) 40 70 0.13 52.5 50.4
COMPARATIVE (B) 50 70 0.13 52.8 62.5*
EXAMPLE 1
COMPARATIVE - 0 70 0.92 50.3 22.4
EXAMPLE 2
* Cobalt carbonate showed deteriorated filterability when it contained
moisture at 60%
or more.
16
CA 02475667 2004-07-21
As shown in Table 1, cobalt carbonate prepared in each of EXAMPLES
1 to 4 by Production Method (A) and in EXAMPLE 5 by Production Method
(C) at a reaction temperature for the present invention contained sodium at
a low level.
As shown in Table 2, cobalt carbonate prepared in each of EXAMPLES
6 to 9 by Production Method (B) using the aqueous solution of carbonate of
an alkali metal incorporated with sodium hydroxide at a given content for
the present invention contained sodium at a low level. By contrast, cobalt
carbonate prepared in each of COMPARATIVE EXAMPLES 1 and 2 using
the aqueous solution of carbonate of an alkali metal incorporated with
sodium hydroxide at a content out of the range for the present invention
showed unsatisfactory result with respect to sodium content or moisture
content (which relates to filterability).
As discussed above, cobalt oxide produced from cobalt carbonate of low
alkali metal content of the present invention, produced by the method of the
present invention, contains an alkali metal at a sufficiently low content to
be suitable as materials for electronic device and battery, in particular for
purposes for which materials containing an alkali metal, e.g., sodium, is
unsuitable.
17
