Note: Descriptions are shown in the official language in which they were submitted.
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NOVEL MANUFACTURING METHOD OF ARAGONITE CALCIUM CARBONATE
[Technical Field]
The present invention is to provide methods of
manufacture of aragonite-type precipitated calcium carbonate
with increased yield and particle size according to the
carbonation method.
[Background Art]
Precipitated calcium carbonate is synthesized according
to various methods including the carbonation method in which
carbon dioxide is blown into the suspension of calcium
hydroxide and reacted, solution process in which the aqueous
solution of calcium chloride is reacted with caustic soda and
the aqueous solution of sodium carbonate, precipitation method
in which the solution of calcium bicarbonate made by blowing
carbon dioxide to calcium carbonate is heated and precipitated,
etc. Industrially, the method of carbonation is applied.
Such precipitated calcium carbonate is an inorganic
material which is not readily soluble in pure water, has a
proper specific gravity, high whiteness, incombustibility,
etc., and is applicable extensively as inorganic filler in
various areas of industry such as rubber, paint, plastic,
paper, cosmetics, toothpaste, etc.
There are three representative polymorphs of calcium
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carbonate: calcite which is stable at a room temperature is
cubic or spindle shaped; aragonite which is meta-stable is
navicular or needle shaped; and unstable vaterite is spherical
mostly.
Particularly, aragonite-type sedimentary calcium
carbonate is expected to be a new functional inorganic
material that can grant mechanical functionality and optical
functionality in that it is of needle shape having a very
large aspect ratio (the ratio of length with respect to size
of a crystal), and it is possible not only to increase
strength but also to improve whiteness and to control
opaqueness owing to the complicated surface structure of a
needle shape when it is used as a filler for rubbers, plastics,
or coating materials, or as an industrial raw material for the
pigments for paper, etc.
Further, the needle-shaped aragonite having the
appearance of 0.05-/_cm fine hair is expected to have an affect
of increasing its strength if it is mixed with a conformation
control thermoplastic resin or polypropylene resin as a filler
in that the absorptivity may be increased as the specific
surface area is increased, and the needle shape having a
length of 50 - 60 gm has a superior impact resistance. However,
it has been known that aragonite has been a meta-stable phase
which has existed stably in the temperature region below 75K,
and therefore, it has been difficult to synthesize it,
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especially when it has a large particle size, as the rate of
transition of thermodynamically more stable calcite has been
fast.
[Disclosure]
[Technical Problem]
The present invention is devised in order to solve the above-
described problems. As a result of repeating studies to
improve the yield of aragonite according to the carbonation
reaction, the inventors of the present invention found out
that it was possible to increase the particle size of
aragonite-type precipitated calcium carbonate and to
manufacture 100%-pure single-phase aragonite-type precipitated
calcium carbonate by making aragonite-type calcium carbonate
seeds in the slurry form firstly, and performing the
carbonation reaction repeatedly and continuously by using the
above seeds when synthesizing sedimentary calcium carbonate
according to the carbonation reaction, and that it was
possible to provide new methods of manufacture of aragonite-
type calcium carbonate in which the aspect ratio was
controlled.
It is another object of the present invention to provide
methods of manufacture of 100% aragonite by making seeds
according to the methods of manufacture of the present
invention and controlling the particle size and aspect ratio
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by adding the carbonation reaction by using the above seeds.
[Technical Solution]
The present invention is illustrated in more detail below:
The present invention is devised from the findings that,
in the method of manufacture of aragonite according to the
carbonation.process, it is possible to control the particle
size and aspect ratio in that aragonite having a very large
particle size may be obtained by repeating the carbonation
reaction, and it is possible to manufacture practically 100%-
pure single-phase aragonite.
In other words, the present invention provides methods of
manufacture of new aragonite-type sedimentary calcium
carbonate having a practically 100% purity, large particle
size, and increased aspect ratio comprising the steps of:
making aragonite-type sedimentary calcium carbonate seeds
by using calcium hydroxide, magnesium chloride, and carbon
dioxide;
growing the seeds by having calcium hydroxide, magnesium
chloride, and lowly concentrated carbon dioxide come in
contact with the slurry containing the above seeds at a flow
rate of 70 mt/min; and
repeating the above step of growing the seeds more than
once.
Aragonite manufactured according to the method of
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manufacture of the present invention in the form of a calcium
carbonate slurry containing seeds shows 100% yield as a result
of analysis using XRD, and it is seen that aragonite having an
average particle diameter of about 40 - 50 /cm is manufactured
as the particle size is increased nearly twice if the above
carbonation reaction is repeated more than twice as a result
of measuring SEM images.
Accordingly, the present invention is characterized by
injecting carbon dioxide to the above seeds at a low flow rate,
and by the method of manufacture of aragonite with increased
average particle diameter as well as aspect ratio by repeating
the carbonation reaction more than twice.
More concretely, in the method of manufacture of
aragonite according to the carbonation reaction by using the
suspension of calcium hydroxide, magnesium chloride, and
carbon dioxide, the present invention is comprised of the
steps of:
a) manufacturing aragonite seeds by mixing 0.2 - 0.6 M
suspension of calcium hydroxide and 0.4 - 0.8 M magnesium
chloride, and inserting carbon dioxide at a flow rate of 100
ml/minute while mixing at 60 - 90 ~ inserting
b) manufacturing aragonite-type precipitated calcium carbonate
by mixing and inputting 0.2 - 0.6 M calcium hydroxide and 0.4
- 0.8 M magnesium chloride while supplying continuously carbon
dioxide to the seeds manufactured in the above, and inputting
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lowly concentrated carbon dioxide at 60 - 90 C at a flow rate
of 10 - 70 ml/minute; and
c) manufacturing aragonite-type sedimentary calcium
carbonate by repeating the above step b) more than once.
In the present invention, the method of manufacture of
aragonite is further comprised of the step of washing,
filtering, and drying after the above step c). It is
preferable to use ethyl alcohol during the processes of
washing and filtering, and to progress the process of drying
at 60 - 90'Cfor 10 - 15 hours.
In the present invention, it is preferable that carbon
dioxide in the above step b) is inserted at a flow rate of 10
- 70 d/minute, more preferably, at a flow rate of 50 mt/minute,
in order to increase the particle size as well as aspect ratio
by reducing the rate of production of the initial nucleus.
Accordingly, in the present invention, the particle size of
aragonite manufactured is affected by the rate of flow-in of
the above carbon dioxide, and it is shown that the best
results are obtained when carbon dioxide is inputted at a flow
rate in the range of 10 - 70 d/minute. Moreover, if carbon
dioxide is passed at a flow rate in the above range,
remarkable effects of manufacturing practically 100%-pure
single-phase aragonite are obtained. The reason for limiting
the contents of magnesium chloride and calcium hydroxide in
the present invention is that the yield of aragonite is most
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superior when they are within the above ranges.
Figure 1 is a flow chart showing the processes of manufacture
of aragonite according to the present invention. According to
the method of manufacture of aragonite shown in Figure 1 of
the present invention, seeds are manufactured in the step of
the first carbonation reaction, the second carbonation
reaction is progressed by inputting calcium hydroxide and
magnesium chloride and passing lowly concentrated (low-rate)
carbon dioxide, terminating the reaction by performing the
same reaction once more under the same conditions as those of
the second carbonation reaction, filtering, washing, drying,
and analyzing.
[Brief Description of the Drawings]
A more complete appreciation of this invention, and many of
the attendant advantages thereof, will be readily apparent as
the same becomes better understood by reference to the
following detailed description when considered in conjunction
with the accompanying drawings, wherein:
Figure 1 is a flow chart showing the processes of manufacture
of aragonite according to the present invention;
Figure 2 is a graph showing the XRD data of pure single-phase
aragonite according to Preferred Embodiment 1 of the present
invention;
Figure 3 shows two photographs to compare the sizes of seeds
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and particles after the second growth according to Preferred
Embodiment 2 of the present invention; and
Figure 4 is a graph showing the sizes and shapes of particles
according to the flow rate of carbon dioxide during the growth
reaction.
[Description of Preferred Embodiments of the Invention]
The present invention is illustrated in terms of a few
preferred embodiments below:
[Preferred Embodiment 1]
Manufacture of the seeds of aragonite-type sedimentary
calcium carbonate
The seeds of aragonite-type precipitated calcium
carbonate were manufactured by adding 0.8 M magnesium chloride
(Junsei Company) to 0.4 M suspension of calcium hydroxide
(Sigma Company) in a 1.5-liter reactor, inserting carbon
dioxide to the mixture at a flow rate of 100 mk/minute, and
reacting the mixture at 80 Cfor 2 hours.
Primary aragonite growth reaction
The seeds of aragonite-type sedimentary calcium carbonate
were manufactured by adding again 0.4 M suspension of calcium
hydroxide and 0.8 M magnesium chloride (Junsei Company) to the
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above seed slurry, inserting carbon dioxide to the mixture at
a flow rate of 50 mi/minute, and reacting the mixture at 80- C
for 2 hours.
As a result of diffraction analysis using XRD, it was
found that thus manufactured aragonite was of needle shape,
and all components produced according to the reaction time,
except for a minute amount of aragonite formed as aragonite
came in contact with air in the early stage, were obtained in
the form of 100%-pure single-phase aragonite. That is, as
shown in Figure 2, it was seen that it was possible to
manufacture very superior and practically 100%-pure aragonite-
type precipitated calcium carbonate by reducing the content of
carbon dioxide in the primary growth reaction since the
content of calcite (C component) produced as an impurity of
aragonite produced during the process of polymerization of the
seeds was not at all increased as a result of the reaction by
flowing lowly concentrated carbon dioxide at a flow rate of 50
mt/minute. It was, therefore, seen that it was very critical
to use a small amount of carbon dioxide in order to
manufacture pure aragonite-type calcium carbonate since it was
seen that the content of calcite was increased somewhat when
carbon dioxide was flowed in at a flow rate of 100 ml/minute
during the primary growth reaction.
[Preferred Embodiment 2]
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Manufacture of the seeds of aragonite-type precipitated
calcium carbonate The seeds of aragonite-type precipitated
calcium carbonate were manufactured by adding 0.8 M magnesium
chloride (Junsei Company) to 0.4 M suspension of calcium
hydroxide (Sigma Company) in a 1.5-liter reactor, inputting
carbon dioxide to the mixture at a flow rate of 100 0/minute,
and reacting the mixture at 80- C for 2 hours..
Primary aragonite growth reaction
The seeds of aragonite-type sedimentary calcium carbonate
were manufactured by adding again 0.4 M suspension of calcium
hydroxide and 0.8 M magnesium chloride (Junsei Company) to the
above seed slurry, inserting carbon dioxide to the mixture at
a flow rate of 50 mt/minute, and reacting the mixture at 80- C
for 2 hours.
Secondary aragonite growth reaction
The seeds of aragonite-type precipitated calcium
carbonate were manufactured by adding 0.4 M suspension of
calcium hydroxide and 0.8 M magnesium chloride (Junsei
Company) to the aragonite slurry obtained in the above primary
growth reaction, inserting carbon dioxide to the mixture at a
flow rate of 50 0/minute, and reacting the mixture at 80 Cfor
2 hours.
As seen in Figure 3, it was seen that aragonite
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manufactured according to the present invention by using seeds
had very large particle size as well as aspect ratio during
the growth reaction after the seed reaction compared to
aragonite obtained through the secondary reaction without
using seeds, as a result of observation of their SEM images.
[Comparative Examples 1 and 2]
Aragonite was manufactured in the same method as that in
Preferred Embodiment 1 except that carbon dioxide was inputted
at flow rates of 100 0/minute and 500 mt/minute in the primary
growth reaction and the secondary growth reaction,
respectively. As seen in Figure 4, no definite aragonite-type
needle-shaped crystals were formed, and crystals were not
formed readily and the particle size was reduced as the flow
rate of carbon dioxide was increased.
[Industrial Applicability]
Therefore, it is seen that based on findings that it is
possible to manufacture needle-shaped practically single-phase
100%-pure aragonite-type sedimentary calcium carbonate by
performing repeatedly a multiple number of growth reaction for
growing particles along with the seed reaction as in the
present invention, it is possible to manufacture particulate
aragonite-type precipitated calcium carbonate having more
diversified, economical, and wide application areas by
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applying the methods of manufacture according to the present
invention.
While certain present preferred embodiments of the
invention have been shown and described, it is to be
distinctly understood that the invention is not limited
thereto but may be otherwise variously embodied and practiced
within the scope of the following claims.
