JP3223589B2 - Method for producing light calcium carbonate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing light calcium carbonate, and more particularly, to a method for producing light calcium carbonate having a Hunter brightness of 91 to 98%, which is useful as a filler for paper. The present invention relates to a method for producing light calcium carbonate which can eliminate calcium carbonate discarded as industrial waste from a calcium circulation system in pulp cooking.

[0002]

2. Description of the Related Art Alkaline pulp cooking comprises a cooking step and a cooking chemical liquid recovery step. In the above-mentioned cooking chemical liquid recovery step, taking the kraft cooking method (NaOH + Na ₂ S, which is the main component of the cooking chemical liquid) which is currently most widely used among the alkaline pulp cooking methods, the recovery boiler of the cooking chemical liquid is used. N by adjusting operations
a ₂ S is regenerated, and in a causticizing process, lime (CaO + CaCO ₃ + impurities) calcined and produced in a kiln is mixed with a kraft cooking chemical before regeneration, and NaOH is regenerated by the following chemical reaction formula. ₂ CO ₃ + CaO + H ₂ O → 2NaOH + CaCO ₃

[0003] CaCO ₃ produced by the above chemical reaction
Is thermally decomposed in a lime mud kiln (hereinafter, also simply referred to as a kiln) and regenerated into CaO. In such a cooking liquid recovery step, calcium consisting of CaO and CaCO ₃ is circulated through a causticizing step centering on the kiln, but from the viewpoint of calcium, the recovery step is a completely closed system. is there.

[0004] Also, impurities that accompany the pulp waste liquor from the cooking step and are mixed into calcium do not go out of the system at all if they are mixed into the calcium circulating system consisting of CaO and CaCO ₃ mainly in the kiln. . On the other hand, bricks stuck to the kiln come off (spalling)
Iron, such as rust, is mixed into the calcium circulation system to form impurities. All of these impurities are reduced the weight percentage physicians CaCO ₃ in the solid content to be supplied to the kiln.

[0005] impurities is increased, a decrease in production of CaO weight ratio physician is produced from CaCO ₃ when reduced reduction or pulping amount of CaCO _3, the fuel of the kiln is wasted. Therefore, in the actual operation, the amount of impurities in CaCO ₃ supplied to the kiln on a regular basis is actually measured, and impurities that are mixed in by periodically taking out a certain amount of CaCO ₃ containing impurities out of the system are also included. with the same time withdrawing the amount of CaCO ₃ corresponding to CaCO ₃ taken
Was added to the calcium circulatory system to keep the amount of impurities in the calcium circulatory system, especially the kiln, at a low level.

The following is taken out of the calcium circulatory system,
4 shows a general analysis result (weight) of discarded CaCO ₃ and impurities.・ CaCO ₃ (as CaO) 100 ・ Silica (as SiO ₂ ) 0.5-5 (as CaCO ₃ 100) ・ Iron, aluminum (as Fe ₂ O ₃ + Al ₂ O ₃ ) 5-15 (〃) ・ Magnesium ( 0.5 to 2 (as CaCO ₃ 100) ・ Others (such as carbon) 0 to 3 (〃)

[0007] CaCO ₃ and impurities which have the above composition and have been discarded hitherto have little toxicity to the human body. However, even this kind of waste is industrial waste, and the fact is that dumping must be voluntarily regulated in the current situation.

[0008] The above-mentioned impurity-containing C which has been removed from the calcium circulating system before being supplied to the kiln and has been discarded has been discarded.
Research on the effective use of aCO ₃ has been made in the past, and the technology used as an internal filler for neutral paper (Japanese Patent Application Laid-Open No. 61-179398) has been studied. Technology used as a wetting agent (US Pat. No. 3,269,941), treatment with an organic acid and / or an inorganic acid, adjusting the pH to 5 to 12 or mixing with bleaching mud to increase whiteness As a substitute for kaolin used as a filler and as a pigment for coated paper (German Published Patent Application No. 2,737,742)
Etc. have been proposed.

However, the CaCO ₃ produced by the above technique is
The amounts of various impurities such as coloring inorganic substances and coloring organic substances (mainly carbon) contained therein greatly vary depending on the operation state of the causticizing process, and the fluctuation results also increase the whiteness of CaCO _3. To go up and down,
When CaCO ₃ having such a large fluctuation in whiteness is used as a filler for paper, the whiteness of paper may be reduced. Therefore, none of the above-mentioned techniques of using CaCO ₃ containing impurities as a filler or a pigment for paper has yet been put to practical use.

[0010] Among the above-mentioned utilization techniques, although the method of using as a neutralizing agent for acid wastewater is certainly effective, the pH of the wastewater of a factory having a deinked waste paper pulp production facility becomes 6 to 7, Not only is there no need for neutralization, but CaCO ₃ supplied to the kiln has a slightly poor reactivity with acid wastewater due to the action of impurities, which can result in the formation of precipitates, which can cause troubles, etc. For this reason, this method has not been practically used.

As a method for removing impurities from the calcium circulating system, instead of removing the CaCO ₃ containing impurities supplied to the kiln, calcium is removed in the form of quick lime, and impurities are removed together with the quick lime out of the circulating system. There is also a method to extract it. In that case, quicklime contains little coloring organic matter.

[0012] As a technique relating to an effective utilization method of quick lime, C is obtained by slaking with water at a temperature of 75 ° C or less and then causticizing with green liquor obtained by alkali or kraft digestion.
Technology using aCO ₃ as a coating pigment (US Pat. No. 2,062,255), lime produced by a lime mud kiln at an alkaline pulp mill is sludged and then reacted with carbon dioxide gas or green liquor to produce Using CaCO ₃ as a filler for paper (US Pat. No. 3,268,387,
No. 3,268,388) has already been proposed.

However, all of these methods use CaC
O ₃ still contains impurities (colorable inorganic substances), and no technique has been proposed to eliminate coloring contamination of CaCO ₃ due to the color inorganic substances, so that it has not been put to practical use.

On the other hand, a technique for bleaching inorganic compounds mainly composed of calcium has also been studied, and a method of bleaching calcium sulfate in an acidic pH region using an oxidizing bleaching agent (Japanese Patent Application Laid-Open No. 55-60024). Is disclosed.
However, when such a method is applied, calcium carbonate is decomposed.
It is not a method that can be immediately adopted for the bleaching of calcium carbonate for eliminating coloring contamination of O ₃ .

[0015]

SUMMARY OF THE INVENTION In a method of extracting the above impurities from a calcium circulating system centering on a kiln and a processing method after the extraction, the present inventors have disclosed a CaO containing impurities produced by firing in a kiln. To remove the impurities to the outside of the system by extracting the impurities from the system, and to produce light calcium carbonate having a whiteness that can be used as a filler for paper using the impurities as a raw material. is there.

[0016] The present invention is also provided for extracting impurities from the calcium circulatory system. Light calcium carbonate is produced using CaO containing impurities after calcination, and then reduced bleaching is used as an internal filler for paper, thereby effectively utilizing light calcium carbonate together with impurities to reduce industrial waste from kilns. The purpose is to provide a technology that can be eliminated.

[0017]

SUMMARY OF THE INVENTION The present invention relates to a method for producing light calcium carbonate by mixing quick lime and water and then reacting it with carbon dioxide gas. Quick lime containing inorganic impurities is mixed with water, and then reacted with carbon dioxide gas. The produced light calcium carbonate is treated with a reducing bleach, and Hunter brightness (JIS P 812) is used.
The present invention relates to a method for producing light calcium carbonate, wherein 3) is adjusted to 91 to 98%.

The kiln of the present invention is installed in a recovery step of an alkaline pulp cooking liquor, especially a kraft cooking liquor, and is an apparatus for thermally decomposing CaCO ₃ by heating to produce CaO. Etc.
It is described in detail in "Craft pulp and non-wood pulp" issued on October 1, 1981 by Japan Association of Paper and Pulp Technology.

Usually, the production of light calcium carbonate is Ca
It is carried out by a method in which lime in which O is 80 to 99% by total weight is put in water, and carbon dioxide gas is blown into a liquid (emulsion) that is stirred and dispersed. As the carbon dioxide used for the reaction, kiln exhaust gas may be used (JP-A-63-30710).
No. 8, the specification).

On the other hand, lime calcined in a lime mud kiln is:
It contains 60 to 95% (by weight) of CaO. 60%
If it is less than 95%, the thermal efficiency of heavy oil or natural gas used as fuel in the kiln is lowered, which is not preferable. If it exceeds 95%, the calcined CaO becomes difficult to disperse and dissolve in water. 65-90% is most preferred.

The raw material CaO used in the present invention contains compounds such as silica, iron, aluminum, and magnesium. Hunter whiteness measured by finely pulverizing this lime is about 60 to 75%.

In the present invention, the lime containing the impurity is reacted with water to form a Ca (O) having a concentration of 5 to 20% by weight.
H) ₂ aqueous blowing carbon dioxide gas from 80 to 220 minutes,
Stop when the pH is between 7 and 8.5 to produce light calcium carbonate. When the Ca (OH) ₂ concentration, the blowing time of carbon dioxide gas and the pH are out of the above ranges, the shape of the light calcium carbonate changes, and for example, when used as a filler for paper,
It is not preferable because the wire life of the fourdrinier paper machine is shortened.

The light calcium carbonate thus produced has a Hunter whiteness of 84 to 87%. On the other hand, light filler calcium carbonate and light calcium carbonate produced by other methods are commonly used as an internal filler of paper produced using softwood bleached kraft pulp and hardwood bleached kraft pulp as a main raw material. 91-98%
belongs to. When paper is manufactured using light calcium carbonate having a hunter whiteness of 84 to 87% as a filler, the hunter whiteness is lower than that of ordinary paper, and the value of the paper is reduced. Therefore, the light calcium carbonate of the present invention is also difficult to use on paper unless bleached.

When bleaching light calcium carbonate, it is not preferable to use an acidic bleaching agent since light calcium carbonate is decomposed. When an alkaline bleaching agent is used, when an oxidizing bleaching agent such as hydrogen peroxide which performs bleaching at a pH of 8 to 11.5 is used, the whiteness hardly changes. Neither bleach can be used.

The bleaching agent which can be used in the present invention is a reducing bleaching agent. As the reducing bleach, for example, pH 5
So-called hydrosulfite of Na ₂ S ₂ O ₄ and ZnS ₂ O ₄ used at 10 and NaB used at pH 9 or more
H _4, Na ₂ SO ₃ , NaHSO ₃ , Rongalit and the like can be mentioned. These reducing bleaching agents are described in detail in "Pulping and Bleaching" issued on Jan. 1, 1986 by the Japan Association of Paper and Pulp Technology. Formamidine sulfinic acid (thiourea dioxide) is also suitable for the present invention.

In the present invention, for example, when hydrosulfite or formamidine sulfinic acid is used, various conditions are pH 9 to 10, addition rate is 0.05 to 0.5% by weight,
20-80 ° C (per weight of light calcium carbonate),
The bleaching time is between 10 and 60 minutes.

Under the above conditions, if the pH is lower than 6, light calcium carbonate is decomposed, and if the pH is higher than 10, the bleaching effect is undesirably reduced.

If the addition ratio is less than 0.05% by weight, a sufficient bleaching effect cannot be obtained, and if it exceeds 0.5% by weight, a further effect of increasing whiteness cannot be achieved.

If the reaction temperature is lower than 20 ° C., the bleaching action is slow and it is difficult to increase the whiteness.
If the temperature exceeds 0 ° C., the heat cost is undesirably increased.

Depending on the composition and amount of impurities contained in the light calcium carbonate, the bleaching is carried out by selecting the above-mentioned reducing bleach such as hydrosulfite and the bleaching conditions to maximize the hunter whiteness of the light calcium carbonate. 11%
Can also be raised. Hunter whiteness of light calcium carbonate after bleaching treatment is 84-87% to 91-98.
%, The whiteness of the paper is not reduced even when the light calcium carbonate is used as a filler for paper. If it is less than 91%, the whiteness of the paper is reduced as described above, which is not preferable.

When bleaching is carried out using a reducing bleaching agent according to the present invention, the upper limit of the increase in Hunter whiteness is 11%. Even if the bleaching conditions are strengthened, such as by adding more chemicals and raising the temperature, the hunter brightness does not increase beyond 11%, and only the cost increases. Therefore, the upper limit of hunter whiteness after bleaching of light calcium carbonate is 98%.

In order to make up for the deficiency of the calcium extracted from the kiln, it is common to supplement with a raw CaCO ₃ (limestone) containing 2 to 5% by weight of impurities. It is difficult to reduce the amount of impurities contained in CaCO ₃ circulated around the kiln to 5% by weight or less, but a method of replenishing the CaCO ₃ raw stone while extracting CaO from the kiln until it approaches 5% by weight is preferred for the present invention. .

As mentioned above, the present invention relates to the use of C
By taking out aO, impurities mixed with it in the calcium circulating system are extracted out of the system, and light calcium carbonate is produced using the impurity-containing CaO as a raw material,
The resulting calcium carbonate having a low whiteness is bleached by a selected bleaching method, that is, a reduction bleaching method, to produce light calcium carbonate having a whiteness that can be used as a paper filler. The invention also obviates the need to extract from the calcium circulating system in the alkaline pulp digestion process the calcium carbonate containing impurities, which was discarded as industrial waste, from the system.

Heretofore, 0.05 to ₃ kg of impurity-containing CaCO ₃ per ton of bleached kraft pulp has been dumped as industrial waste. If it is less than 0.05 kg, impurities are accumulated in the calcium circulation system centering on the kiln, and it is not preferable. If it exceeds 3 kg, CaCO ₃ is unnecessarily dumped, which is not preferable.

According to the present invention, an increase in impurities in lime is suppressed by removing CaO produced by firing in a kiln so that light calcium carbonate is produced in an amount of 0.05 kg or more per ton of bleached kraft pulp. Ca
Industrial waste based on CO ₃ can be eliminated.

When producing paper and paper products, it is common to use about 10 to 200 kg of light calcium carbonate as a paper filler per ton of bleached kraft pulp.
Light calcium carbonate (MAX 3 kg / about bleached kraft pulp) produced by extracting lime from a kiln to suppress impurities contained in CaCO ₃ to a low level can all be used for the paper.

In addition, even if the light calcium carbonate produced by the present invention is finely pulverized by a sand mill or the like and used as a pigment for coated paper, the whiteness of the coated paper does not decrease. Therefore, it can be used as a pigment.

The bleaching method of the present invention not only has a bleaching effect on light calcium carbonate produced from lime (CaO + impurities) from lime mud kilns, but also has the effect of light calcium carbonate produced by other methods. It is also effective for bleaching heavy calcium carbonate, talc and clay.

In the present invention, the hunter whiteness of the light calcium carbonate is 5 cm and 6 cm in depth and placed in a groove of 6 cm square. A mirror-finished metal plate is applied to apply pressure to fix the powder in the groove. Hunter whiteness was measured according to 8132. CaO after firing in a kiln was pulverized in a ball mill and then measured for whiteness in the same manner.

[0040]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but of course the present invention is not limited by these examples.

Production of Light Calcium Carbonate The apparatus used for producing light calcium carbonate is disclosed in Jpn.
No. 86792, which has a structure shown in FIG.

A blow valve 2 is attached to a lower portion of the reactor 1, and a punching plate 3 is attached to the upper portion of the blow valve 2 of the reactor 1. The punching plate 3 has a conical shape having an apex at the center of the reaction tank 1. On the other hand, a fresh water supply pipe 5 and a lime kiln exhaust gas supply pipe 6 are attached above the blow valve 2. In FIG. 1, reference numeral 7 denotes a suspension supply port, and 8 denotes a gas discharge port.

The suspension is supplied to the reactor 1 from the suspension supply port 7. At this time, since the suspension is stored in the lower portion A of the punching plate 3, the fresh water is supplied from the fresh water supply pipe 5 prior to the reaction, and the suspension in the portion A is pushed up with the fresh water and replaced with the fresh water. Exhaust gas is supplied from the exhaust gas supply pipe 6 and bubbled. On the other hand, the flue gas that floats through the clear water forms fine bubbles from a number of holes 4 of the punching plate 3 and slowly floats in the suspension. The contact completes the carbonation reaction. After the completion of the carbonation reaction, the blow valve 2 is opened to take out the suspension of the generated calcium carbonate. At this time, the calcium carbonate adhering to the many holes 4 of the punching plate 3 is washed away by the reverse flow of the calcium carbonate suspension.

The reactor used in this example has a capacity of 2
It is 2 m ³ , cylindrical at the top and conical at the bottom, the diameter of the cylinder is 2540 mm, and the height from the bottom of the cone to the top of the cylinder is 7400 mm. At the bottom of the reaction tank, a punching plate (aperture diameter: 25 mm, opening ratio: 6%) for dispersing the blown exhaust gas into fine particles in a Ca (OH) ₂ solution is attached.

The coloring inorganic matter from the kiln as an impurity
The amounts of CaO and water containing 5.2% are adjusted so that Ca (O
H) ₂ concentration put liquid 150 g / l to 20 m ³ the reactor, blowing exhaust lime mud kiln (CaO concentration 20% by volume) for 140 minutes, to stop the stopped reaction then blowing. The pH of the solution at this time was 7.5. The produced light calcium carbonate was sufficiently washed with water. The lime mud kiln is a long kiln (L130m × φ4m, manufactured by Ahlstrom Co., Ltd. (US)). As the CaO from the kiln, a CaO containing 85% by weight was used. In addition, the replenishment of the CaCO ₃ rough stone to the kiln was performed in the same amount as the withdrawn amount. The following two types of light calcium carbonate were produced on different days.

Light calcium carbonate (A): Hunter whiteness: 84.2% Average particle size: 3.2 μm

Light calcium carbonate (B): Hunter whiteness: 86.8% Average particle size: 3.2 μm

Manufacture of Paper Unbleached hardwood pulp (Kappa number: 18.30) was obtained from a Kamiya continuous digester using hardwood chips of domestic hardwood and softwood chips of 15% Douglas fir and 85% domestic pine as raw materials.
5) and softwood unbleached pulp (Kappa number 27) were produced. Then, Hunter brightness 8 was obtained by a multistage bleaching method comprising oxygen-chlorine-caustic soda-Na-hypo-chlorine dioxide.
4.0 hardwood bleached pulp (LBKP) and softwood bleached pulp (NBKP) were produced.

LBKP and NBKP were 65: 3 in absolute dry weight.
Mix at a ratio of 5 and the mixed pulp has a freeness of 340.
ml (CSF).

To this pulp, 10 parts by weight (per weight of absolutely dry pulp) of light calcium carbonate or heavy calcium carbonate of Examples and Comparative Examples were added, and the following chemicals were added.
Neutral paper of 44 g / m ² and 5.5% moisture was produced by a fourdrinier multi-cylinder dryer paper machine.

Sulfuric acid band: 0.5% Cationized starch (Kate F manufactured by Oji National Co., Ltd.): 1.0% Polyacrylamide (Harmade EX-360 manufactured by Harima Chemicals, Inc.): 0.4% Yield improver (NR-11 LH, manufactured by Kyoritsu Organic Co., Ltd.): 0.02% (all are based on absolute dry pulp weight)-Size pressed starch (Oji Constarch, Oji Ace A): 2 g / m ²

Example 1 0.1% by weight of Na ₂ S ₂ O ₄ was added to light calcium carbonate (A), and the concentration was 30% by weight, 40 ° C. and pH 7.5.
After bleaching for 0 minutes, it was sufficiently washed with water. Light calcium carbonate (A)
Was 0.2 kg / dry weight ton of bleached kraft pulp. The hunter whiteness of this light calcium carbonate is 9
1.8%. Paper was manufactured using the light calcium carbonate.

Example 2 Example 1 was the same as Example 1 except that formamidine sulfinic acid was used as the reducing bleach. The hunter whiteness of the obtained light calcium carbonate is 9
2.0%.

Example 3 0.45% by weight of formamidine sulfinic acid was added to light calcium carbonate (B), and the mixture was added at 75 ° C. and pH 9.5.
After bleaching for a minute, it was thoroughly washed with water. The production amount of the light calcium carbonate (B) was 3.5 kg / dry weight bleached kraft pulp. The hunter whiteness of this light calcium carbonate is 9
It was 7.4%. Paper was manufactured using the light calcium carbonate.

Comparative Example 1 Paper was produced without bleaching light calcium carbonate (A).
The production amount of the light calcium carbonate (A) was 0.04 kg / dry weight bleached kraft pulp.

Comparative Example 2 A paper was produced without bleaching light calcium carbonate (B).
The production amount of light calcium carbonate (B) was 0.04 kg / dry weight ton of bleached kraft pulp.

Comparative Example 3 Light calcium carbonate was purchased (Carpin Y Hunter whiteness 98%, manufactured by Yabashi Kogyo Co., Ltd.) to produce paper. In order to keep the impurities in CaCO ₃ into the kiln constant,
The CO ₃ was removed and dumped.

Comparative Example 4 Light calcium carbonate was purchased (LW manufactured by Yabashi Kogyo Co., Ltd.)
600 Hunter whiteness 92%) to produce paper. No removal of CaCO ₃ to be performed to keep the impurities in CaCO ₃ constant in the kiln was performed. Each of Examples and Comparative Examples continued for 40 days.

Examples and comparative examples were evaluated for the following items, and the evaluation results are shown in Table 1. And paper whiteness was evaluated by JIS P 8123, dumped CaCO ₃ weight bleached kraft pulp absolute dry per ton of dumping amount kg.・ The amount of impurities in CaCO ₃ is analyzed by the TAPPI test method. Limestone analysis T618hm-84
(Impurity amount (g) / (CaCO 3
₃ (g) + (impurity amount (g)) × 100 (%).

Each of the examples and comparative examples was continuously carried out for 40 days, during which the average value from the 35th day to the 40th day was calculated as CaC
Impurities in O ₃ (%).

As shown in Table 1, the whiteness of light calcium carbonate produced using CaO produced in a lime mud kiln is low, and therefore the whiteness of paper is reduced (target value 7).
9% or more), causing a decrease in quality (Comparative Examples 1 and 2). The purchased CaO and the light and heavy calcium carbonates do not reduce the whiteness of the paper, but depending on the use of such CaO, industrial waste discharged from the calcium circulating system in the alkaline pulp digestion method. Does not contribute to the achievement of the important object of the present invention of suppressing the generation of CaO. (Comparative Example 3)

Further, from the kiln, CaCO ₃ or CaO ₃
In addition, if impurities are not extracted, the amount of impurities in the lime increases. This indicates that Ca in the solids supplied to the kiln
The weight ratio of CO ₃ is reduced, which is not preferable. (Comparative Example 4)

On the other hand, in each of the embodiments of the present invention, light calcium carbonate which does not cause the quality deterioration due to the decrease in the whiteness of the paper is obtained, and therefore, is removed before entering the lime mud kiln. It is clear that the industrial waste derived from the impurity-containing CaCO ₃ can be eliminated and the impurities in CaCO ₃ in the calcium circulatory system can be kept low, and the result of the present invention is clear.

[0064]

[Table 1]

[0065]

As described above, the present invention is to obtain light-weight calcium carbonate having hunter whiteness that can be used as a filler for paper, and at the same time to eliminate calcium carbonate containing impurities which has been an industrial waste in alkaline pulp cooking. Can be.

[Brief description of the drawings]

FIG. 1 shows a cross-sectional view of a reactor used in the method for producing light calcium carbonate of the present invention.

[Explanation of symbols]

1: reaction tank, 2: blow valve, 3: punching plate, 4: fine hole, 5: fresh water supply pipe, 6: exhaust gas supply pipe, 7: suspension supply port, 8: gas discharge port

──────────────────────────────────────────────────続 き Continued from the front page (72) Inventor Kazuchi Sakamoto 1 Oji-cho, Kasugai-shi, Aichi Oji Paper Kasugai Mill Co., Ltd. (56) References JP-A-63-307108 (JP, A) JP-A-61 JP-A-183120 (JP, A) JP-A-58-151326 (JP, A) JP-B-41-11528 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) D21C 11/00- 11/14 C01F 11/18 D21H 17/67 D21H 19/38

Claims (1)

(57) [Claims] 1. A method for mixing light lime produced in a lime mud kiln in an alkaline pulp digestion method with water, followed by reaction with carbon dioxide gas to produce light calcium carbonate, and subsequently producing light calcium carbonate as a reducing bleach Hunter whiteness (JIS) characterized by bleaching using
P 8123) A method for producing light calcium carbonate in which the content is adjusted to 91 to 98%.