JP2003286027A - Method for classifying heavy calcium carbonate aqueous slurry - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently and stably classifying or concentrating heavy calcium carbonate aqueous slurry and to provide a method for stably obtaining the heavy calcium carbonate having narrow grain size distribution in particular. <P>SOLUTION: In the method for feeding and classifying heave calcium carbonate aqueous slurry in a centrifuge, at a first separation operation, the heavy calcium carbonate aqueous slurry having 63 to 72 wt.% solid concentration and 160 to 700 mPa s B type viscosity is fed into the centrifuge, separation is performed so that 5 to 35 wt.% of fed heavy calcium carbonate is distributed in a heavy liquid and then a light liquid is recovered. At a second separation operation, recovered light liquid is adjusted to obtain the heavy calcium carbonate aqueous slurry having 10 to 29 wt.% solid concentration and 30 to 700 mPa s B type viscosity and then is fed into the centrifuge and separation is performed so that 50 to 95 wt.% of fed heavy calcium carbonate is distributed in the heavy liquid and then the heavy liquid is recovered. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for classifying a heavy calcium carbonate aqueous slurry, which is capable of efficient and stable classifying operation.

[0002]

2. Description of the Related Art Heavy calcium carbonate is widely used as white inorganic pigment for papermaking, like kaolin, light calcium carbonate and titanium oxide. When these white pigments are used, for example, for papermaking, the shape and size of the white pigments depend on optical properties such as glossiness, whiteness, opacity, and smoothness of the obtained paper, printing gloss, ink acceptability, and ink. Affects printability such as setability. Heavy-duty calcium carbonate is inexpensive as a white pigment for aqueous coating liquids for papermaking, especially for the production of coated papers, and the resulting coated papers have good fluidity of the aqueous coating liquids and enable high-concentration coating. It has various advantages such as high whiteness. On the other hand, heavy calcium carbonate has a drawback that the gloss of coated paper is hard to be expressed as compared with kaolin. It is believed that this is due to its particle size and shape, and in order to obtain a coated paper having high white paper gloss, the particle size of ground calcium carbonate has been made as small as possible.

However, in order to reduce the particle size of the heavy calcium carbonate, the amount of fine particles increases when mechanical pulverization is advanced in a bead mill or the like. For example, a large amount of adhesive is used to obtain the adhesive strength required during printing. Is required,
There is a problem that disadvantages other than white paper gloss increase, such as a decrease in opacity and a decrease in printing gloss.

In order to eliminate the above-mentioned demerits, a method of removing excessively small fine particles by classification and a crushing method so as not to generate excessive fine particles have been proposed. For example, in Japanese Unexamined Patent Publication No. 2000-34120, solid calcium having a solid content of 74
80% by weight, B-type viscosity (20 ° C, # 2 spindle, 6
(0 rpm) is 300 mPa · s or less, an aqueous slurry is centrifuged to collect a light liquid, and the obtained light liquid is diluted to a solid content concentration of 30 to 70% by weight to obtain a B type viscosity (20 ° C., # 2).
Spindle, 60 rpm) is adjusted to 100 mPa · s or less, and a heavy liquid is recovered by centrifugation to prepare a heavy calcium carbonate slurry having a narrow particle size distribution with less coarse particles and fine particles. . The above method
The purpose of the present invention is to provide a classification method in which a heavy liquid having a high solid content concentration is high at the time of classification in a centrifugal separator such as a decanter and does not solidify. Depending on the amount of solids to be concentrated in and the particle size of the heavy calcium carbonate supplied to the centrifuge,
There may be a problem that the heavy liquid is hardened and cannot be discharged from the centrifugal separator. In addition, when attempting to forcibly discharge the solidified heavy liquid by a mechanical force, a very large device may be required, or another problem such as wear of the metal of the discharge portion may occur.

Further, Japanese Patent Laid-Open No. 5-508606 proposes a method of classifying kaolin by a centrifuge, which lowers the solid content concentration (for example, 18% by weight or less), and more preferably the feed liquid. Temperature of 37.8 ℃
It has been reported that a kaolin slurry having a narrow particle size distribution can be obtained by increasing the above and classifying with a centrifugal separator. However, the above-mentioned proposal shows that lowering the viscosity of the liquid supplied to the centrifuge improves the classification efficiency, but regarding the problem of discharging heavy liquid with a large amount of solids, such a problem exists. There is no mention of one thing or its solution.

[0006]

DISCLOSURE OF THE INVENTION The object of the present invention is to classify a heavy calcium carbonate aqueous slurry in particle size, the particle size of heavy calcium carbonate to be used for classification, the centrifugal force to be applied, the concentration of heavy liquid and the concentration of heavy liquid. It is to provide a classification method capable of stable discharge of heavy liquid without the problem that the heavy liquid is hardened and cannot be discharged from the centrifuge due to the amount of solid content to be collected. A stable calcium carbonate having a narrow particle size distribution is provided.

[0007]

The first invention of the present invention is as follows:
An aqueous slurry of heavy calcium carbonate containing at least one of a viscosity modifier or a dispersant is continuously supplied to a centrifuge to give a centrifugal force of 200 to 4000 G to give a heavy liquid having a high solid content and a solid content. Is a method of separating into a light liquid having a low content, the solid concentration of heavy calcium carbonate is 63 to 72% by weight, and the B type viscosity is 160 to 700 mPa · s (20
C., 60 rpm) aqueous calcium carbonate slurry is fed to the centrifuge and 5 to 35 wt% of the heavy calcium carbonate fed to the centrifuge is separated so as to be distributed to the heavy liquid. It is a characteristic method for classifying a heavy calcium carbonate aqueous slurry.

In the second aspect of the present invention, an aqueous slurry of ground calcium carbonate containing at least one viscosity modifier or dispersant is continuously supplied to a centrifuge.
A method of applying a centrifugal force of 0 to 4000 G to separate a heavy liquid having a high solid content and a light liquid having a low solid content, wherein the solid content of heavy calcium carbonate is 10 to 29% by weight, and B type Viscosity is 30-700mPa · s (20 ℃, 60rp
m) an aqueous slurry of heavy calcium carbonate is fed to a centrifuge, and 50 to 95% by weight of the heavy calcium carbonate fed to the centrifuge is separated so as to be distributed to the heavy liquid. This is a method for classifying a heavy calcium carbonate aqueous slurry.

Furthermore, in the third aspect of the present invention, an aqueous slurry of ground calcium carbonate containing at least one viscosity modifier or dispersant is continuously supplied to a centrifuge.
Centrifugal force of 0 to 4000 G is applied to perform a two-step operation of separating into a heavy liquid having a high solid content and a light liquid having a low solid content, and in the first separation operation, a light liquid having a low solid content is recovered. Then, in the second-stage separation operation, the light liquid recovered in the first stage is used as it is, or after adjusting the concentration and viscosity, it is fed to a centrifuge to recover heavy liquid with a high solid content concentration. A method for classifying a slurry, wherein the solid calcium concentration of the heavy calcium carbonate is 63 to 7 in the first-stage separation operation.
2% by weight and B type viscosity of 160 to 700 mPa · s
An aqueous slurry of heavy calcium carbonate (20 ° C., 60 rpm) was fed to a centrifuge, and separated so that 5 to 35 wt% of the heavy calcium carbonate fed to the centrifuge was distributed to the heavy liquid. In the second-stage separation operation, an aqueous slurry of heavy calcium carbonate having a solid concentration of heavy calcium carbonate of 10 to 29% by weight and a B-type viscosity of 30 to 700 mPa · s (20 ° C., 60 rpm) is prepared. 5 of the heavy calcium carbonate supplied to the centrifuge and supplied to the centrifuge
A method for classifying a heavy calcium carbonate aqueous slurry, characterized in that 0 to 95% by weight is separated so as to be distributed in a heavy liquid.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION As the heavy calcium carbonate aqueous slurry to be supplied to the centrifuge in the present invention, natural limestone is pulverized by a dry pulverizer such as a roll mill, a jet mill, a dry ball mill and an impact pulverizer. If necessary, at least one of water and a dispersant or a viscosity modifier is added to a powder obtained by dry classification such as a vibrating screen or a cyclone to disperse heavy calcium carbonate, or What is obtained by wet-milling the slurry thus prepared using balls or beads such as an attritor, a ball mill and a sand mill is used. The heavy calcium carbonate aqueous slurry here is mainly composed of heavy calcium carbonate, and may contain a small amount of a pigment other than heavy calcium carbonate. Further, the viscosity modifier and the dispersant are not necessarily included in the wet pulverization, and may be added to the heavy calcium carbonate slurry prior to the separation operation by the centrifuge.

In the present invention, the average particle size of the heavy calcium carbonate supplied to the centrifuge is not particularly limited, but the average particle size is preferably 0.3 to 15 μm. Incidentally, if the average particle size is less than 0.3 μm, it may be difficult to produce a heavy liquid having a high solid content concentration in the classification according to the method of the present invention. Further, when the average particle diameter exceeds 15 μm, in classification in the method of the present invention, even if the centrifugal force is weakened, the heavy liquid having a high solid content concentration may be solidified, and the heavy liquid may not be discharged from the centrifugal separator. is there.

Examples of the viscosity modifier or dispersant used in the heavy calcium carbonate aqueous slurry include (A) a cationic surfactant, (B) an anionic surfactant,
(C) Nonionic surfactant can be mentioned. Examples of the cationic surfactant (A) include primary to tertiary amine salt type cationic low molecular or polymeric surfactants, and
Examples thereof include low-molecular-weight or high-molecular-weight ammonium salt type surfactants. Specific examples of the primary to tertiary amine salt type low molecular surfactants include higher alkyl amine salts, higher alkyl amine ethylene oxide adducts, higher alkyl amine ethylene oxide / propylene oxide adducts, solomine A type amine salts, Examples thereof include sapamin A-type amine salt, arcobel A-type amine salt, imidazoline-type amine salt, and the like. Specific examples of the quaternary ammonium salt-type low-molecular-weight surfactant include, for example, higher alkyltrimethylammonium salt and alkyldimethylbenzylammonium salt. , A sapamine-type quaternary ammonium salt, an imidazoline-type quaternary ammonium salt, an alkylviridium salt, and the like. Specific examples of the primary to tertiary amine salt type polymer surfactants include polyethyleneimine, polyalkylene polyamine salt, polyamine / dicyandiamide condensation salt, polydiallyl amine salt, and the like, and quaternary ammonium salt type. Specific examples of the polymer surfactant include, for example, polystyrene methylaminotrimethylammonium salt,
Polydiallyl dimethyl ammonium salt, trimethylaminoethyl (meth) acrylate ammonium salt, poly N
-Alkyl pyridine salt etc. can be illustrated.

Examples of (B) anionic surfactants include low molecular weight or high molecular weight surfactants having a carboxylate, a sulfate, a sulfonate and a phosphate as a functional group. Specific examples of the low molecular weight carboxylic acid salt include higher fatty acid salts such as sodium laurate, sodium stearate and sodium oleate, higher alcohol polyethylene oxide ether acetate, perfluoroalkyl carboxylate and the like. Specific examples of the high molecular weight carboxylic acid salt include, for example, polyacrylic acid salts, salts of polyacrylic acid-maleic acid copolymers, etc., carboxylic acid monomers alone or copolymers of at least two or more, or salts thereof. Examples thereof include copolymers of vinyl compounds and carboxylic acid monomers or salts thereof, and carboxymethyl cellulose. Specific examples of the low-molecular-weight sulfate ester salt include higher alcohol polyethylene oxide sulfate ester salt, sulfated oil, sulfated fatty acid ester, sulfated fatty acid, sulfated olefin, alkylphenol polyethylene oxide sulfate salt, and the like. Specific examples of the sulfonate include alkylbenzene sulfonate, α-olefin sulfonate, alkane polysulfonate, perfluoroalkyl sulfonate, igefone T type, and aerosol type. Specific examples of the polymer sulfonate include a formalin condensate of naphthalene sulfonate, a polystyrene sulfonate, a polyvinyl sulfonate, a polyaryl sulfonate, and a salt of a copolymer of acrylamide and acrylamide propane sulfonate. It can be illustrated. Specific examples of the copolymer type polymer surfactant include a copolymer composed of a carboxylic acid monomer and a sulfonic acid monomer or a salt thereof. Specific examples of the low molecular weight phosphoric acid ester salt include, for example, higher alcohol monophosphoric acid ester salt,
Examples thereof include higher alcohol polyethylene oxide phosphate ester salts, alkylphenol polyethylene oxide phosphate ester salts, and the like.

The nonionic polymer surfactant (C) includes polyethylene glycol type and polyhydric alcohol type nonionic surfactants. Specific examples of the polyethylene glycol type include, for example, higher alcohol ethylene oxide adducts and alkylphenols. Examples thereof include ethylene oxide adduct, fatty acid ethylene oxide adduct, polyhydric alcohol fatty acid ester ethylene oxide adduct, fatty acid amide ethylene oxide adduct, polypropylene glycol ethylene oxide adduct, and polyether modified silicone. Specific examples of the polyhydric alcohol type include fatty acid ester of glycerol, fatty acid ester of pentaerythritol, fatty acid ester of sorbitol and sorbitan, fatty acid ester of sucrose, alkyl ether of polyhydric alcohol, polyglycerin fatty acid ester or ethylene oxide thereof. Examples thereof include adducts, fatty acid amides of alkanolamines, and the like, and further examples include methyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol, polyalkylene oxide vinyl ether compounds, polyhydroxyl alkyl (meth) acrylate, and the like.

A dispersant or a viscosity modifier added to an aqueous slurry of heavy calcium carbonate to be subjected to wet grinding,
And, as the viscosity modifier added to the heavy calcium carbonate aqueous slurry after wet pulverization prior to the centrifugal separation operation, polymer type surfactants are preferable, and particularly preferable are polyacrylic acid or its salt, and polyacrylic acid. Examples thereof include a carboxylic acid monomer such as an acid-maleic acid copolymer or a salt thereof, or a copolymer of at least two of them or a salt thereof. The amount of these dispersants or viscosity modifiers added should be appropriately adjusted according to the particle size and particle size distribution of the ground calcium carbonate, the concentration and viscosity of the ground calcium carbonate aqueous slurry, and the desired degree of classification. However, it is generally adjusted in the range of 0.1 to 10% by weight with respect to the ground calcium carbonate.

The centrifuge used in the present invention continuously supplies an aqueous slurry of heavy calcium carbonate and continuously discharges a light liquid having a low solid content and a heavy liquid having a high solid content. Specifically, a liquid cyclone and a decanter centrifuge can be exemplified, and a decanter centrifuge can be preferably used. Further, the centrifugal force at that time is 200 to 4 depending on the particle size of the ground calcium carbonate to be subjected to the separation operation, the viscosity of the aqueous slurry thereof, the purpose of classification and concentration, and the like.
It is preferable to appropriately adjust in the range of 000 G, preferably in the range of 300 to 3500 G. If the centrifugal force is less than 200 G, it is difficult to perform classification or concentration operation.
When it exceeds 000 G, the heavy liquid is solidified or most of the solid content supplied to the centrifuge is separated into the heavy liquid side,
Classification operation becomes difficult.

Regarding the concentration and the B-type viscosity of the heavy calcium carbonate aqueous slurry supplied to the centrifuge, firstly, 5 to 35% by weight of the heavy calcium carbonate supplied to the centrifuge which is the first invention of the present invention. In the method for classifying a heavy calcium carbonate aqueous slurry that is separated so as to be distributed to a heavy liquid, the solid concentration of the heavy calcium carbonate is 63 to 72% by weight, and the B type viscosity is 160.
~ 700 mPas, preferably 310-700 mPas
It is important that it is s (20 ° C., 60 rpm). When the solid content concentration of the heavy calcium carbonate is less than 63% by weight or the B type viscosity is less than 160 mPa · s, the solid content easily moves to the heavy liquid side even with a weak centrifugal force and is separated to the heavy liquid side. It becomes difficult to separate the heavy liquid side solid content such as 5 to 35% by weight of the solid content supplied to the centrifuge. On the other hand, the solid concentration of heavy calcium carbonate is 72
If the content exceeds 10% by weight, coarse particles with a large particle size should be allowed to settle and classify due to centrifugal force, but since the solid content is high, the fine particles that do not want to settle are also coarse. Classification becomes difficult because the particles settle together with the particles. In addition, the B-type viscosity of the slurry is 700 mPa
・ If it exceeds s, it becomes difficult for the particles to settle down due to centrifugal force, and it becomes difficult to generate heavy liquid. Further, in order to separate 5 to 35% by weight of the heavy calcium carbonate supplied to the centrifuge so as to be distributed to the heavy liquid, the concentration and viscosity of the heavy calcium carbonate aqueous slurry should be adjusted to the above range. Then, the centrifugal force in the centrifugation operation is 200 to 4000.
G, preferably in the range of 300 to 3500 G, and the residence time under centrifugal force may be adjusted in the range of 5 seconds to 5 minutes.

Next, a method for classifying an aqueous slurry of heavy calcium carbonate in which 50 to 95% by weight of the heavy calcium carbonate supplied to the centrifuge which is the second invention of the present invention is separated so as to be distributed to the heavy liquid. In the case of the slurry,
The solid content concentration of the heavy calcium carbonate is 10 to 29% by weight, and the B type viscosity is 30 to 700 mPa · s, preferably 100 to 700 mPa · s (20 ° C., 60 rpm).
Is important. When the solid content concentration of the heavy calcium carbonate is less than 10% by weight, the amount of the processing liquid is increased when centrifuging a certain solid content, and the apparatus becomes too large, which is not economically preferable. On the other hand, if the solid content concentration of the heavy calcium carbonate exceeds 29%, fine particles that should not be originally distributed will be mixed in the heavy liquid, and the accuracy of classification will be deteriorated, which is not preferable. In addition, slurry B
If the mold viscosity is less than 30 mPa · s, the heavy liquid becomes too hard and it is difficult to discharge it from the centrifuge. On the contrary, if the mold viscosity exceeds 700 mPa · s, the centrifugal force makes it difficult for the particles to settle, and It becomes difficult to generate liquid. Further, in order to separate 50 to 95% by weight of the heavy calcium carbonate supplied to the centrifuge so as to be distributed to the heavy liquid, the concentration and viscosity of the heavy calcium carbonate aqueous slurry should be adjusted within the above range. Then, the centrifugal force in the centrifugal separation operation is 200
˜4000 G, preferably 300 to 3500 G, and the residence time under centrifugal force may be adjusted from 5 seconds to 5 minutes.

Furthermore, the third invention of the present invention is a combination of the first invention and the second invention, whereby the heavy calcium carbonate can be efficiently classified. That is, in the first-stage separation operation, the light liquid having a low solid content concentration is recovered, and in the second-stage separation operation, the light liquid recovered in the first stage is used as it is or after the concentration and viscosity are adjusted, it is centrifuged. In a method for classifying a heavy calcium carbonate slurry which is supplied to a machine to recover a heavy liquid having a high solid content concentration, in the first-stage separation operation, the solid content concentration of the heavy calcium carbonate is 63 to 7
2% by weight and B type viscosity of 160 to 700 mPa · s
A heavy calcium carbonate aqueous slurry (20 ° C., 60 rpm) was supplied to the centrifuge, and the heavy calcium carbonate supplied to the centrifuge was separated so that 5 to 35 wt% of the heavy calcium carbonate was distributed to the heavy liquid. In the two-stage separation operation, a heavy calcium carbonate aqueous slurry having a solid concentration of heavy calcium carbonate of 10 to 29% by weight and a B-type viscosity of 30 to 700 mPa · s (20 ° C., 60 rpm) is centrifuged. Of 50 to 95% by weight of the heavy calcium carbonate supplied to the centrifuge and distributed to the heavy liquid.

Here, in the first-stage separation operation, the light liquid from which the coarse particles having a large particle size have been removed is recovered, and in the second-stage separation operation, the one from which the coarse particles have been removed is used as the mother liquor. By recovering the heavy liquid from which the fine particles have been removed, it is possible to obtain ground calcium carbonate having a narrow particle size distribution. At this time,
The reason why the heavy calcium carbonate aqueous slurry supplied to the centrifuge has the above-mentioned concentration and viscosity is as described above. Further, in the first-stage separation operation, it is important to separate the heavy calcium carbonate supplied to the centrifuge so that 5 to 35 wt% of the heavy calcium carbonate is distributed to the heavy liquid. If the amount of ground calcium carbonate is less than 5% by weight, the removal of coarse particles will be insufficient. On the other hand, when the heavy calcium carbonate separated in the heavy liquid exceeds 35% by weight, the solid content in the recovered light liquid becomes too small. Also, in the second-stage separation operation, it is important to separate so that 50 to 95% by weight of the heavy calcium carbonate supplied to the centrifuge is distributed to the heavy liquid, and the separation is performed in the heavy liquid. If the amount of heavy calcium carbonate is less than 50% by weight, the solid content of the heavy liquid to be recovered is small, and the recovery rate of coarse calcium carbonate coarse particles having a narrow particle size distribution is too small. Further, when the amount of ground calcium carbonate separated in the heavy liquid exceeds 95% by weight, the removal of fine particles becomes insufficient. As described above, the amount of solids (heavy calcium carbonate) separated in the heavy liquid is adjusted by the centrifugal force in centrifugal separation, the residence time under centrifugal force, the concentration and viscosity of the heavy calcium carbonate aqueous slurry. It can be achieved by doing. In the present invention, the separation operation of the second step may be combined with the separation operation of the third step for the purpose of concentration, for example.

[0021]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.
Unless otherwise specified, parts and% in the examples represent parts by weight and% by weight, respectively.

The average particle size of the heavy calcium carbonate,
And the particle size distribution shown by D75 / D25 was measured by Sedigraph 5100 manufactured by Micromeritics.

<Example 1> A heavy calcium carbonate aqueous slurry (trade name: Hydrocarb 90 / manufactured by Bihoku Powder Differentiation Co., Ltd.) having an average particle size of 0.79 μm (which already contains a dispersant) prepared by wet pulverization. Water and polyacrylic acid type viscosity modifier (Product name: SN Thickener 615 / manufactured by San Nopco)
Was added to adjust the B-type viscosity to be 170 mPa · s (20 ° C., 60 rpm) at a calcium carbonate concentration of 68%. Then, this aqueous slurry was added to a decanter type centrifugal separator (rotation radius 0.077 m, effective volume 1.8).
Liter) at a rate of 150 liters / hour
Separation operation was performed by applying G centrifugal force. 20% of the supplied heavy calcium carbonate was distributed to the heavy liquid side. At this time, the concentration of heavy calcium carbonate in the heavy liquid was 84%,
Heavy liquid could be discharged smoothly and continuously.

<Example 2> A heavy calcium carbonate aqueous slurry (trade name: Hydrocarb 60 / Bihoku Powder Differentiation Co., Ltd.) having an average particle size of 1.29 μm (which already contains a dispersant) prepared by wet pulverization. Water and a viscosity modifier (trade name: SN Thickener 615 / manufactured by San Nopco) were added, and a B-type viscosity of 310 mPa · s (2
The temperature was adjusted to 0 ° C. and 60 rpm). Next, this aqueous slurry was supplied to a decanter type centrifuge (rotation radius 0.077 m, effective volume 1.8 liters) at 150 liters / hour and subjected to a centrifugal force of 2000 G to perform a separation operation. 25% of the supplied heavy calcium carbonate was distributed to the heavy liquid side. At this time, the heavy calcium carbonate concentration in the heavy liquid was 87%, and the heavy liquid could be discharged smoothly and continuously.

<Comparative Example 1> In Example 1, when the concentration of the heavy calcium carbonate in the aqueous heavy calcium carbonate slurry was adjusted to 68% with water alone without adding a viscosity modifier, the B-type viscosity was It was 32 mPa · s. When this was separated with a decanter type centrifuge under the same conditions as in Example 1, the current value of the main motor of the decanter exceeded the rated value, and the decanter automatically stopped.

<Comparative Example 2> In Example 2, water and a viscosity modifier were added so that the concentration of heavy calcium carbonate in the aqueous heavy calcium carbonate slurry was 55%, and the viscosity of B type was 180 mP.
It was adjusted to be a · s. Then, this aqueous slurry was separated by a decanter in the same manner as in Example 2 except that a centrifugal force of 700 G was applied. As a result, 40% of the supplied heavy calcium carbonate was distributed to the heavy liquid side.

<Example 3> Heavy calcium carbonate aqueous slurry (trade name: Setacurb HG / Bihoku Powder Differentiation Industry Co., Ltd.) prepared by wet pulverization and having an average particle size of 0.46 μm (which already contains a dispersant) was added to water. And viscosity modifier (Product name: Nopsanto R
/ Manufactured by San Nopco Co., Ltd. is added, and when the concentration of heavy calcium carbonate is 28%, the B-type viscosity is 35 mPa · s (20 ° C., 60 rp).
m) was adjusted. Then, the aqueous slurry was added to a decanter type centrifuge (rotation radius 0.077).
m, effective volume 1.8 liters) at a rate of 60 liters / hour and subjected to a separating operation by applying a centrifugal force of 2100G. 60% of the supplied heavy calcium carbonate was distributed to the heavy liquid side. At this time, the heavy calcium carbonate concentration in the heavy liquid was 58%, and the heavy liquid could be discharged smoothly and continuously.

Comparative Example 3 In Example 1, the concentration of the heavy calcium carbonate in the aqueous heavy calcium carbonate slurry was adjusted to 35% with water alone without adding a viscosity modifier, and the B type viscosity was It was 7 mPa · s. When this was separated with a decanter type centrifuge under the same conditions as in Example 3, the current value of the main motor of the decanter exceeded the rated value and the decanter automatically stopped.

Example 4 Water and the viscosity modifier used in Example 1 were added to the light liquid obtained in Example 1 to adjust the concentration of heavy calcium carbonate to 20% and the viscosity of B type to 33 mPa · s. did. Then, this aqueous slurry was separated under the same conditions as in Example 3 using a decanter type centrifuge. 65% of the supplied heavy calcium carbonate was distributed to the heavy liquid side. The concentration of heavy calcium carbonate in the heavy liquid at this time is 50%.
The heavy liquid could be discharged smoothly and continuously. When the particle size distribution of the heavy calcium carbonate separated on the heavy liquid side was measured, the average particle size was 0.75 μm, and the particle size D75 corresponding to 75% of the weight accumulated from the fine particles and the particle size corresponding to 25%. The ratio of D25 (D75 / D25) was 2.5. By the way, D75 / D25 of the heavy calcium carbonate before the separation operation with the centrifuge used in Example 1 was 4.1,
It can be seen that the particle size distribution is narrowed by the two-step separation operation.

[0030]

As is clear from the comparison between the examples and the comparative examples, the method of the present invention has good classification efficiency and can stably perform classification or concentration operation, and in particular, heavy carbonic acid having a narrow particle size distribution. It was a suitable classification method when preparing calcium.

Continued front page    F term (reference) 4D071 AA52 BA04 BA05 BA13 BB02                 4G076 AA16 AB09 BE20 BF10

Claims (3)

[Claims] 1. An aqueous slurry of heavy calcium carbonate containing at least one viscosity modifier or dispersant is continuously supplied to a centrifuge to give a centrifugal force of 200 to 4000 G, and a heavy solid having a high solid content concentration. A method for separating a liquid and a light liquid having a low solid content concentration, wherein the solid content concentration of heavy calcium carbonate is 63 to 72% by weight, and the B type viscosity is 160 to 700 m.
An aqueous slurry of heavy calcium carbonate of Pa · s (20 ° C., 60 rpm) is supplied to the centrifuge so that 5 to 35 wt% of the heavy calcium carbonate supplied to the centrifuge is distributed to the heavy liquid. A method for classifying an aqueous slurry of heavy calcium carbonate, characterized in that 2. An aqueous slurry of heavy calcium carbonate containing at least one viscosity modifier or dispersant is continuously supplied to a centrifuge to give a centrifugal force of 200 to 4000 G, and a heavy solid having a high solid content concentration. A method for separating a liquid and a light liquid having a low solid content concentration, wherein the solid content concentration of heavy calcium carbonate is 10 to 29% by weight, and the B type viscosity is 30 to 700 mP.
Aqueous slurry of heavy calcium carbonate (as (20 ° C, 60 rpm)) is supplied to the centrifuge so that 50 to 95% by weight of the heavy calcium carbonate supplied to the centrifuge is distributed to the heavy liquid. A method for classifying an aqueous slurry of heavy calcium carbonate, characterized in that 3. An aqueous slurry of heavy calcium carbonate containing at least one viscosity modifier or dispersant is continuously supplied to a centrifuge to give a centrifugal force of 200 to 4000 G, and a heavy solid having a high solid content concentration. The operation of separating the liquid and the light liquid having a low solid content concentration is performed in two stages. In the first stage separation operation, the light liquid having a low solid content concentration is recovered, and in the second stage separation operation,
A method for classifying a heavy calcium carbonate slurry, in which the light liquid recovered in the first step is supplied to a centrifuge after adjusting the concentration and viscosity as it is or the heavy liquid having a high solid content concentration is recovered. In the step separation operation, the solid content concentration of the heavy calcium carbonate was 63 to 72% by weight, and the B type viscosity was 16%.
An aqueous slurry of ground calcium carbonate of 0 to 700 mPa · s (20 ° C., 60 rpm) was supplied to the centrifuge, and 5 to 3 of the ground calcium carbonate supplied to the centrifuge.
5% by weight was separated so as to be distributed in the heavy liquid, and in the second-stage separation operation, the solid concentration of heavy calcium carbonate was 10 to 10.
29% by weight and B-type viscosity of 30 to 700 mPa · s
An aqueous slurry of heavy calcium carbonate (20 ° C., 60 rpm) is supplied to a centrifuge, and 50 to 95% by weight of the heavy calcium carbonate supplied to the centrifuge is separated so as to be distributed to the heavy liquid. A method for classifying a heavy calcium carbonate aqueous slurry, which comprises: