WO2011004855A1

WO2011004855A1 - Method for manufacturing calcium carbonate by causticization using fired shells

Info

Publication number: WO2011004855A1
Application number: PCT/JP2010/061586
Authority: WO
Inventors: 小野　裕司; 雅人高山; 越智　隆; 一成加茂; 勇雄小野寺; 濱田　薫; 敬史堀崎; 睦寛廣瀬; 川崎　秀一; Tokuichi SATOH (佐藤徳一)
Original assignee: 日本製紙株式会社; 佐藤恭夫
Priority date: 2009-07-08
Filing date: 2010-07-08
Publication date: 2011-01-13

Abstract

Provided is a technique for improving the causticizing process in pulp production. A high-quality calcium carbonate can be produced efficiently by adding fired shells and a green liquor and by inducing a causticizing reaction during the causticizing process in pulp production.

Description

Method for producing causticized calcium carbonate using fired shells

The present invention relates to a method for producing calcium carbonate in a causticizing step of a pulp producing step by a sulfate method or a soda method. In particular, the present invention relates to a method for producing calcium carbonate in a causticizing step of a pulp manufacturing step by a sulfate method or a soda method using a baked shellfish including scallop shell.

The paper used for printing or writing usually contains a filler for the purpose of improving whiteness, opacity, smoothness, writing property, touch, printability and the like. This papermaking method includes so-called acidic papermaking in which talc, clay, titanium oxide or the like is used as a filler and the paper is made in the vicinity of pH = 4.5, and in a neutral to weakly alkaline region where pH = 7 to 8.5. There is neutral paper making.

中 Neutral paper is characterized by the fact that domestic calcium carbonate can be used as a filler in place of imported and expensive talc and clay. In addition, the paper made with acid has the disadvantage that the deterioration progresses with the lapse of time. Therefore, the neutral paper made by the neutral paper has been attracting attention in recent years. In addition to this, neutral paper has many advantages in terms of paper quality, cost, environmental measures, etc., so the transition to neutral papermaking is progressing, and the spread of this is in the future. Furthermore, looking at recent papers in terms of demand, commercial printing is expanding fields such as flyers, catalogs, pamphlets, direct mail, etc. In publishing printing, computers, multimedia, and game-related books are being developed as the information society evolves. , Magazines, photo books, mooks, comic papers are growing rapidly. Against this background, there is an increasing demand for paper cost reduction, and the paper used is required to be reduced in price and weight.

As described above, as the demand for cheap and light neutral paper increases, the positioning of calcium carbonate as a filler is very important. Calcium carbonate used as a filler for this neutral papermaking includes heavy calcium carbonate produced by mechanical pulverization of natural limestone dry or wet, and light calcium carbonate produced by chemical methods (precipitated calcium carbonate, synthetic Also called calcium carbonate).

However, heavy calcium carbonate obtained by pulverizing natural limestone with a pulverizer such as a ball mill produces sharp edges on the surface of the pulverized particles, and when used as a filler, the plastic wire is severely worn. Furthermore, the particle size distribution when pulverizing the starting limestone is very broad compared to light calcium carbonate produced under controlled reaction conditions. , Whiteness, opacity, smoothness, writing, touch, printability, etc. are insufficient.

On the other hand, light calcium carbonate produced by a chemical method is advantageous because of its low plastic wire wear, but as its production method,
(1) A method by a reaction between lime milk and a gas containing carbon dioxide generated from a lime baking apparatus,
(2) Method by reaction of ammonium carbonate and calcium chloride in the ammonia soda method,
(3) A method based on a reaction between lime milk and sodium carbonate, in which sodium hydroxide is produced by causticization of sodium carbonate,
It has been known. Among these methods, (2) and (3) are the reasons that the production method for obtaining the main product is changed to a new method, or that the content of impurities is high because the generated calcium carbonate is a byproduct. So, how to use it has not been studied much. On the other hand, (1) has a relatively simple reaction system, and extensive research has been conducted on methods for producing calcium carbonate suitable for various purposes, and many products are commercially available from lime makers. However, since this method has a very high manufacturing cost because calcium carbonate is the only product, it is difficult to use it for cheap paper, and its amount of use is greatly limited.

By the way, in the so-called causticizing step in the pulp manufacturing process by the sulfate method or the soda method, calcium carbonate is produced as a by-product when white liquor is produced by recovering and regenerating cooking chemicals. The causticized light calcium carbonate produced from the causticizing process is very inexpensive due to the by-product, and is advantageous for producing paper.

Generally, a causticizing process is known as a process of regenerating “white liquor” from “black liquor” in a pulp manufacturing process by a sulfate method or a soda method. “White liquor” is a cooking liquor used for producing pulp by cooking wood chips, and mainly contains sodium hydroxide and sodium sulfide. On the other hand, “black liquor” is a cooking waste liquid after cooking wood chips, and includes wood fibers, lignin, hemicellulose and the like. This “black liquor” is regenerated into “white liquor” by a causticizing process described below and reused as a cooking liquid for wood chips.

In the causticization process in the sulfate process or soda process pulp production, the recovered black liquor is burned in a boiler to obtain smelt, and the smelt is further dissolved to add quick lime to the supernatant liquid ("green liquor"). This is a step of preparing a “white liquor” which is a cooking solution of wood chips by adding sodium carbonate in the green liquor to convert it into sodium hydroxide and removing the resulting calcium carbonate. “Green liquor” is a strong alkaline aqueous solution mainly composed of sodium carbonate and sodium sulfide. When quick lime (CaO) is added to this green liquor, the quick lime reacts with water to produce calcium hydroxide (Ca (OH) _2. ) Is formed (soaking reaction). Furthermore, calcium hydroxide undergoes an exchange reaction with sodium carbonate (Na ₂ CO ₃ ) in the green liquor to produce water-insoluble calcium carbonate (CaCO ₃ ) (causticizing reaction).
(Salting reaction) CaO + H ₂ O → Ca (OH) ₂
(Causticization reaction) Ca (OH) ₂ + Na ₂ CO ₃ → CaCO ₃ ↓ + 2NaOH

That is, as a result of the causticizing reaction, a lime mud slurry comprising water-soluble sodium hydroxide, sodium sulfide, and water-insoluble calcium carbonate is obtained from “green liquor”. After solid-liquid separation, the filtrate is sent to the pulp cooking process as a “white liquor” containing sodium hydroxide, etc., and the lime mud cake separated on the filter surface is baked in a kiln or other firing furnace, It is regenerated into quicklime (calcium oxide) and recycled for use in the causticizing process.
CaCO ₃ → CaO + CO ₂

Calcium carbonate obtained from lime mud by the causticizing process is called causticized calcium carbonate, and this calcium carbonate can be extracted from the causticizing process and used as a papermaking material. Here, since the calcium carbonate produced | generated at a causticizing process is a by-product, it can be manufactured very cheaply. Moreover, by extracting calcium carbonate out of the system from the calcium circulation cycle of the causticization process that is a closed system, the system can be cleaned and the purity of the circulating lime can be increased. It is possible to improve the reactivity of the causticization reaction, improve the clarity of white liquor, and reduce waste.

For example, the following techniques are known as conventional techniques related to causticized light calcium carbonate by-produced in the causticizing process. That is, Patent Document 1 discloses a technique for obtaining high whiteness calcium carbonate by adding hydrosulfite to a slurry of causticized light calcium carbonate and then adding a phosphate. Patent Document 2 discloses a technique for obtaining calcium carbonate with high whiteness by adding hydrosulfite to a slurry of causticized light calcium carbonate and then adding a surfactant. However, in these techniques, since the coloring component remains in the causticized light calcium carbonate, when this is used for a filler or a pigment, there is a risk of recurrent color.

Patent Document 3 discloses a method of performing a causticizing reaction after agglomerating and removing impurities floating by blowing air into the green liquor. However, this technique requires special equipment such as a flotation separator, which not only increases costs, but also reduces the degree of sulfidation due to air oxidation of reducing sodium sulfide.

Furthermore, Patent Document 4 discloses that the calcium oxide added in the causticizing step as a clarification method of the green liquor is divided into two stages, and the calcium carbonate produced by the previous stage addition is removed from the system together with impurities, thereby A technique for obtaining highly white causticized light calcium carbonate by a reaction between the clarified green liquor and calcium oxide added at a later stage is disclosed. In this method, an excellent effect can be expected from the viewpoint of removing impurities, but an apparatus for separating and washing causticized light calories generated for each calcium oxide added in two stages is necessary.

In addition, in Patent Document 5, calcium oxide having a reduced sulfur content or calcium hydroxide that has been dehydrated with calcium oxide and green liquor generated in the causticizing step are mixed to perform a causticizing reaction. A method for obtaining calcium carbonate with high whiteness has been proposed.

JP 51-47597 JP 51-47598 JP-A-61-53112 JP-A-1-226719 JP 2004-231431 A

As described above, the causticizing step in pulp production recycles white liquor from black liquor by circulating substances in the system and is an extremely useful process from the viewpoint of environment and waste reduction.

However, when the lime milk slurry obtained in the causticizing step is subjected to solid-liquid separation, the dehydrating property is not sufficient and the moisture of the lime milk cake may not be sufficiently reduced. In other words, when the dehydration of lime mud is reduced due to fluctuations in the causticization process, or the filter used for solid-liquid separation is clogged, the moisture content of the lime mud cake increases, which not only hinders the dehydration process, When baking a lime mud cake with a kiln, a lot of fuel is needed, and energy efficiency falls.

Therefore, application of various dehydration accelerators has been proposed in order to improve the dewaterability of the lime mud slurry. For example, a method using a cationic polymer (Japanese Patent Laid-Open No. 57-48340), a method using polyoxyethylene alkylphenyl ether and polyoxyethylene polyoxypropylene alkyl ether in combination (Japanese Patent Laid-Open No. 62-121700), A method in which polyoxyethylene alkylphenyl ether and a nonionic surfactant such as polyoxyethylene polyoxypropylene condensate are used in combination (Japanese Patent Laid-Open No. 7-48793), 3 to 4 moles of ethylene oxide of a linear alcohol having 10 to 14 carbon atoms For example, a method using an adduct (Japanese Patent Laid-Open No. 2000-344518).

However, in the method using a cationic polymer, the lime mud slurry is aggregated, but the dehydration effect is not increased, and conversely, water may be entrapped in the aggregate to lower the dehydration rate. Also, a method of using polyoxyethylene alkylphenyl ether and polyoxyethylene polyoxypropylene alkyl ether in combination, a method of using nonionic surfactants such as polyoxyethylene alkylphenyl ether and polyoxyethylene polyoxypropylene condensate, and the number of carbon atoms In the process using ethylene oxide 3-4 mol adducts of 10-14 linear alcohols, these have a surface-active ability, which promotes foaming of the lime mud slurry, and poor sedimentation of lime mud due to entrained bubbles Further, the dehydration of the lime mud slurry is obstructed and the moisture content of the lime mud cake does not decrease, and a sufficient dehydration promoting effect cannot be obtained. Furthermore, the physical properties of the generated calcium carbonate change due to fluctuations in the causticization process, the moisture content of the lime mud cake in the dehydrator varies, and the lime mud cake moisture content is stable even when the above dehydration accelerator is added. In some cases, it was not possible to obtain a decrease in the.

Also, it is an important technical problem to reduce impurities such as dregs and grit in the causticizing process. That is, the purity of the circulating calcium can be increased by removing the dregs, which are impurities in the crude green liquor, from the system. In addition, in the caulking process slaker, green liquor and quicklime are mixed, and a two-stage reaction of a soothing reaction and a causticizing reaction is performed. At this time, unreacted coarse particles called grit are later It is important to suppress the generation amount of grit because it causes wear and deposition in the process. In general, the grid is discarded outside the system by the slaker clarifier, but a method of reducing the amount of grit generated is also strongly desired from the viewpoint of reducing the amount of waste.

Furthermore, the calcium carbonate obtained in the causticizing process is inexpensive, but it is extremely advantageous if it can be increased in whiteness and added value can be increased. The present inventors have studied on the technology for improving the quality of by-product calcium carbonate in order to use calcium carbonate produced as a by-product in the causticizing process as a raw material for papermaking. Have developed technologies for producing high-quality light calcium carbonate having a specific shape such as a shape, a needle shape, and a spot shape (Patent No. 3227421, Patent No. 3227422, JP-A No. 2000-264628, JP-A No. 2000- 264629, JP-A 2000-264630, JP-A 2001-199720, JP-A 2001-199721, JP-A 2002-284522, etc.). However, regarding calcium carbonate produced by these improved methods, the production process is part of the kraft pulp production process, so it is susceptible to fluctuations in the kraft pulp production process and the whiteness of the resulting light calcium carbonate is unstable. There was a problem of being.

In view of such a situation, an object of the present invention is to provide a technique for improving a causticizing process in pulp production. In particular, the present invention improves the dewaterability of lime mud in the causticization process, reduces the moisture content of the lime mud cake, reduces the amount of dregs generated, and produces causticized calcium carbonate with high whiteness. The technical challenge is to develop the technology to be used.

As a result of earnestly examining the technology for improving the causticizing process of pulp production, the present inventor has improved the dewaterability of lime mud and reduced the amount of dregs by adding calcium oxide derived from shells to the causticizing process as quick lime. Furthermore, the inventors have found that high whiteness of calcium carbonate can be realized, and have completed the present invention.

That is, the present invention includes, but is not limited to, the following aspects.
(1) A method for producing causticized light calcium carbonate, comprising mixing green liquor generated in a causticizing step in pulp production and a fired product of shells to perform a causticizing reaction to obtain light calcium carbonate.
(2) The method according to (1), wherein the shell is a scallop shell, an oyster shell, a clam shell, a swordfish shell, a sea shell, a tuna shell, or a snail shell.
(3) The method according to (1) or (2), wherein the shell is a scallop shell.
(4) The method according to any one of (1) to (3), wherein the iron content of the fired shell is 0.05% by weight or less in terms of Fe ₂ O ₃ .
(5) The method according to any one of (1) to (4), wherein the calcium carbonate is a papermaking material.
(6) Light calcium carbonate obtained by any of the methods (1) to (5).
(7) A method for producing coated paper, comprising coating calcium carbonate obtained by the method according to any one of (1) to (5) on a base paper.
(8) A coated paper obtained by coating calcium carbonate obtained by the method according to any one of (1) to (5) on a base paper.
(9) A method for producing paper, comprising internally adding calcium carbonate obtained by the method according to any one of (1) to (5) to paper.
(10) A paper internally added with calcium carbonate obtained by the method according to any one of (1) to (5).
(11) A method for producing a white liquor, which comprises obtaining a white liquor by performing a causticizing reaction between a green liquor generated in a causticizing step in pulp production and a shell baked product.
(12) A method for producing kraft pulp, which comprises obtaining a white liquor by performing a causticizing reaction between a green liquor generated in a causticizing step in pulp production and a shell baked product.

According to the present invention, the causticizing process in pulp production can be improved. In particular, according to the present invention, the dewaterability of lime mud is improved, the moisture content of the lime mud cake is reduced, and the amount of dregs generated is reduced. Further, according to the present invention, since the whiteness of calcium carbonate produced by the causticizing process is improved, high-value-added calcium carbonate useful for uses such as paper fillers and paper pigments can be produced.

FIG. 1 is a graph showing the particle size distribution of causticized light calcium carbonate measured by a laser diffraction method.

The present invention relates to a causticizing process in a pulp manufacturing process, particularly a causticizing process in a pulp manufacturing process by a sulfate method or a soda method. In the present invention, quick lime (baked shells) obtained by firing shells such as scallop shells is used as quick lime (calcium oxide) in the causticizing step. Accordingly, in the present invention, the causticizing reaction is performed by adding the shell baked product and the green liquor.

As described above, in the causticizing step of the pulp manufacturing process, by adding the calcined shellfish and green liquor and performing the causticizing reaction as in the present invention, the dewaterability of lime mud is improved and the amount of dregs generated Reduction and further increase in whiteness of calcium carbonate can be achieved. The details of the reason why such an effect is obtained by the present invention are not clear, and the present invention is not limited to this, but the following reason is presumed. That is, the dewaterability of the lime mud (lime mud) obtained by the present invention is improved, and the moisture content of the lime mud cake after the solid-liquid separation is reduced is due to the particle size distribution of the lime mud produced from quick lime derived from the shell. Since it is sharp, lime mud is difficult to close-pack and the voids in the lime mud increase, and it is estimated that the dewaterability is improved (see FIG. 1). In addition, the amount of grit generated by the present invention is reduced because quick lime produced by calcining limestone, which is a natural mineral, contains pebbled impurities, whereas quick lime produced by calcining shells is biological. This is probably because there are few pebble-like impurities and grit (unreacted coarse particles) hardly occurs. Furthermore, the whiteness of the causticized light calcium carbonate (lime mud) is improved by the present invention because the iron content in the quick lime produced by firing the shell is less than the quick lime derived from natural minerals. This is probably because there are few coloring components.

(Baked shellfish)
In the causticizing step of the present invention, baked shellfish including scallop shells is used as quick lime (calcium oxide). The baked shellfish is characterized by high calcium oxide purity and low impurities such as iron. As shown in Tables 1 and 3 of Examples, when comparing quick lime obtained by baking shells and quick lime obtained by baking natural limestone, quick lime obtained by baking shells has high calcium oxide purity, Fewer iron, sulfur, manganese, magnesium and aluminum.

In the fired shell of the present invention, the iron content relative to calcium oxide is preferably 0.05% by weight or less, more preferably 0.03% by weight or less in terms of Fe ₂ O ₃ . If the iron content of the shell baked product is 0.05% or more, the whiteness of causticized light calories may be reduced. If this is used as a papermaking raw material, it will adversely affect the whiteness of the paper, and the target There is a risk that the paper quality will not be obtained. The lower the iron content in calcium oxide, the more advantageous the whiteness of the causticized light calcium carbonate. In a general embodiment, the iron content of the fired shell is often 0.001% by weight or more in terms of Fe ₂ O ₃ .

The magnesium content of the fired product of the present invention is preferably 0.001 to 1.5% by weight, more preferably 1.0% by weight or less, in terms of elemental analysis oxide (MgO). Further, the sulfur content of the fired product of the present invention is preferably 0.001 to 1.0% by weight, more preferably 0.5% by weight or less, in terms of oxide (SO ₃ ) in elemental analysis. When the bio-derived calcium carbonate raw material has an iron content of 0.05% by weight or more, a magnesium content of 1.5% by weight or more, and a sulfur content of 1.0% or more, the whiteness of the causticized light calcium decreases. There is a risk. The lower the iron content in calcium oxide, the more advantageous the whiteness of the causticized light calcium carbonate. In a general embodiment, the iron content of the baked product of scallop shell, oyster shell, clam shell, swordfish shell, sea shell, tuna shell, snail shell is 0.001 in terms of Fe ₂ O _3. %, The magnesium content in terms of MgO is 0.001 or more, and the sulfur content in terms of SO ₃ is 0.001 or more.

In the present invention, the shell is a remnant of the shell and is mainly composed of calcium carbonate. Examples of the shell of the present invention include bivalves and snail shells, marine shells such as tuna and clams, brackish shellfish such as mussel and swordfish, freshwater shells such as snail and snail, and land shells such as snails. Shells and the like. However, shells of shellfish such as shrimp and crabs (shells), shells of brachiopods and the like do not fall under the shells of the present invention. Crustacean shells are secreted from crustacean organs, and brachiopod shells (mineral layers) are mainly composed of calcium phosphate. The shell is also suitable in that it has less variation between production areas than limestone, which is a natural mineral. In general, scallops and oysters are cultivated and consumed in large quantities, but most of the waste shells are landfilled and it is difficult to secure the landfill site. Therefore, if such a shell can be effectively used according to the present invention, it is preferable from the viewpoint of waste reduction and environmental protection.

Preferred shells in the present invention include scallop shells, oyster shells, clams shells, swordfish shells, hokki shells, tuna shells, snail shells, oyster shells, squid shells, clams shells, stupid shells, oyagi shells, purple shells, red shells, Sazae shells, abalone shells and the like are mentioned, and particularly preferable shells include oyster shells, clams shells, swordfish shells, hokki shells, tuna shells, snail shells and the like.

In the present invention, it is particularly preferable to use a scallop shell. In the present invention, the scallop shell is a remnant of scallops, which is a marine product, and is mainly composed of calcium carbonate. In addition, scallop shells are also suitable for having less variation between production areas than limestone, which is a natural mineral. In general, scallops are cultivated and consumed in large quantities, but most of the waste scallop shells are landfilled and it is difficult to secure the landfill site. Therefore, if such scallop shells can be effectively used according to the present invention, it is preferable from the viewpoint of waste reduction and environmental protection.

In general, shells have a structure in which calcium carbonate and proteins such as collagen are alternately laminated, and the calcium carbonate contained is said to be calcite type for scallops and oysters and aragonite type for clams. . Calcium carbonate, which constitutes scallop shells, is formed under normal temperature and pressure conditions due to the physiological action of shellfish, whereas limestone derived from natural minerals is crystallized for a very long time due to the action of the crust. As a result, the calcium carbonate in the shell is more reactive and has a smaller basic particle size than natural limestone. In general, the shell body consists mainly of calcium carbonate crystals and a protein called conchiolin. Site) and orthorhombic aragonite (aragonite). Therefore, when the shell is fired, a uniform particle size is obtained.

The firing of the shell may be performed under conditions that allow calcium oxide to be obtained from calcium carbonate, and the specific conditions are not particularly limited. In order to sufficiently fire the shell, the firing temperature is preferably 800 ° C. or higher, and particularly preferably about 1200 ° C. Further, the shell may be fired as it is, or may be fired after being pulverized in order to increase firing efficiency. In addition, general pretreatment such as washing with water may be performed. By firing the shell, proteins such as collagen joined to the calcium carbonate particles are burned and removed, and the calcium carbonate becomes calcium oxide.

The firing apparatus is not particularly limited, and a general firing apparatus can be used. For example, a Beckenbach furnace, a Merz furnace, a rotary kiln, a Kunii furnace, a KHD (Kerhardy) furnace, a Koma furnace, a karmatic An apparatus for converting calcium carbonate into calcium oxide, such as a furnace, a fluid firing furnace, a mixed baking furnace, and an electric furnace, can be suitably used.

(Causticization reaction)
In the causticizing step of the present invention, preferably, the shell content (calcium oxide) and the green liquor having an iron content of 0.05% by weight or less, more preferably 0.03% by weight or less in terms of Fe ₂ O ₃ are added. Mix, and perform causticizing reaction with stirring or kneading. In addition, in the causticizing step of the present invention, calcium hydroxide obtained by reducing the calcined shellfish with water can be added to the green liquor in the form of powder or slurry instead of adding calcium oxide to the green liquor. is there.

In the present invention, a shell baked product may be used as at least a part of the quicklime (calcium oxide) added in the causticizing step. Therefore, as quicklime added to the causticizing step, quicklime obtained by baking the lime milk produced in the causticizing step, quicklime introduced from outside the system, and the like can be used in combination with the shell calcined product. The ratio of the burned shellfish to the quicklime added to the causticizing step is not particularly limited, but in order to enjoy the effects of the present invention more than 30% of the quicklime is preferably the burned shellfish, % Or more is more preferably a shell baked product.

The causticizing reaction of the present invention can be carried out under general causticizing reaction conditions. JP-A-10-226974 (Patent No. 3227421), JP-A-10-292283 (Patent No. 3227422), JP-A-2000-264628, JP-A-2000-264629, JP-A-2000-264629 By applying the causticizing reaction conditions described in JP 2000-264630 A, JP 2001-199720 A, JP 2002-284522 A, etc. to the present invention, shape control of causticized light calcium carbonate, plastic wire wear It is also possible to improve the whiteness of causticized light calcium carbonate.

The reaction apparatus for the causticizing step is not particularly limited, and a known apparatus can be used. In particular, a reaction device called a slaker can be suitably used because it can react the green liquor and quicklime sufficiently mixed. Moreover, it is preferable to install one or a plurality of causticizing tanks after the slaker because each of the soaking reaction and the causticizing reaction can be easily controlled.

The lime milk slurry obtained by the causticizing process is separated into white liquor and lime mud cake by the solid-liquid separation process. This solid-liquid separation can be performed using a general apparatus. For example, a drum-type vacuum dehydration type lime mud filter can be suitably used. In addition, a commonly used lime mud filter, such as an Oliver filter, a Young filter, a precoat filter, or the like can be suitably used in the present invention. In general, the moisture content of the lime mud cake is usually 20% by weight to 40% by weight. However, according to the present invention, the dewaterability of the lime mud cake is improved. It can be reduced to:

(Causticized calcium carbonate)
The particle diameter of the causticized light calcium carbonate obtained in the present invention can be adjusted by wet or dry grinding as required. As a pulverizer, a general apparatus can be used. However, a wet batch pulverizer (attritor, etc.), a wet continuous pulverizer (sand grinder, etc.), a circulating pulverizer (SC mill, SC mill long, etc.) Etc.) can be preferably used.

The present invention improves the whiteness of the causticized light calcium carbonate produced by the causticizing reaction, thereby increasing the added value of the causticized light calcium carbonate and enabling the use of the causticized light calcium carbonate for various applications. Become. In addition, as a result of promoting the use of causticized light calcium carbonate, the amount of causticized light calcium carbonate extracted from the causticizing process is increased, and impurities easily accumulated in lime circulating in the causticizing process can be reduced. The load reduction of the kiln for baking can be achieved. Furthermore, if the entire amount of calcium carbonate can be extracted from the causticizing process, the kiln can be stopped, and the production cost of the white liquor that is the main product in the causticizing process can be greatly reduced.

The causticized light calcium carbonate obtained by the present invention has higher whiteness than the calcium carbonate obtained in the conventional causticizing process, and therefore can be used as a functional filler, and is particularly suitable as a papermaking material. is there. At that time, the obtained causticized light calcium carbonate may be pulverized and adjusted to a particle size suitable as a papermaking material.

By adding the causticized light calcium carbonate of the present invention to paper as a paper filler, the whiteness, opacity, printability, etc. of the filler-containing paper can be improved. The paper to which the causticized light calcium carbonate of the present invention is added is not particularly limited. Newspaper paper, medium paper, printing paper, book paper, securities paper, dictionary paper, kraft paper, bleached kraft paper, thin paper, rice It can be used for paper such as paper, Indian paper, paperboard and carbonless paper, and as a base paper for various coated paper such as art paper, lightweight coated paper and cast coated paper.

Moreover, since the causticized light calcium carbonate of the present invention has a high whiteness, it can be suitably used as a coating pigment for papermaking. Therefore, in one aspect, the present invention is a method for producing coated paper, which comprises coating calcium carbonate obtained by the causticizing step on a base paper. Furthermore, in one embodiment, the present invention is a coated paper containing calcium carbonate obtained by the causticizing process in a coating layer.

The causticized light calcium carbonate obtained by the present invention has a relatively narrow particle size distribution in addition to high whiteness as compared with the calcium carbonate obtained in the conventional causticizing process. In a preferred embodiment, the particle size of the calcium carbonate obtained by the present invention is 0.1 to 100 μm, more preferably 0.5 to 100 μm. In one embodiment, the present invention is light calcium carbonate itself obtained by the above method.

In another embodiment, the present invention is a method for producing white liquor, comprising mixing a green liquor generated in a causticizing step in pulp production with a shelled fired product and performing a causticizing reaction to obtain a white liquor. . In another aspect, the present invention is a method for producing kraft pulp using a white liquor obtained by a causticizing reaction between a green liquor generated in a causticizing step in pulp production and a shell fired product.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto. In the present specification, unless otherwise specified, the blending amount and the like are based on weight, and the numerical range is described as including the end points.

Experiment A: Production of causticized calcium carbonate using scallop shells
(1) Quick lime obtained by firing scallop shells The temperature of scallop shells (from Okhotsk Sea) is gradually raised to 1200 ° C using a high-temperature electric firing furnace (Kyoei Electric Furnace), and the firing time is 31 hours. Baked in.
(2) Quicklime obtained by calcining limestone As quicklime obtained by calcining limestone, quicklime (manufactured by Hokkaido Calcium) was used.
(3) Calcined calcium carbonate was calcined using a quick kiln (manufactured by Hitachi Zosen) with a calcining temperature of 1318 ° C. and a residence time of 4 hours to obtain a kiln calcined quick lime.

The scallop shell burned product and the natural limestone burned product produced as described above were subjected to elemental analysis by fluorescent X-rays. The results are shown in Table 1 below. As shown in Table 1, the scallop shell fired product had a lower iron content than the natural limestone fired product.

<Manufacture of causticized calcium carbonate>
[Example 1]
A causticizing reaction was performed using the above-mentioned quicklime (calcium oxide). Sintered scallop shells (quick lime derived from scallop shells) were added to the green liquor primary slaker at a rate of 0.4 t / hr and kiln calcined lime at a rate of 1.6 t / hr. In this example, the ratio of quick lime derived from scallop shell to kiln calcined lime is 20:80. The green liquor throughput was 150 m ³ / h, the NaOH concentration of the green liquor was 22.3 g / L, the Na ₂ S concentration was 26.0 g / L, and the Na ₂ CO ₃ concentration was 76.3 g / L. It was.

The causticizing reaction was carried out in an apparatus in which a green liquor primary-slaker (volume 180 m ³ ), a lime slaker (volume 40 m ³ ), and three tanks of causticizing tanks (volume of each tank 90 m ³ ) were connected in this order. The operating conditions of the green liquor primary slaker were a supply temperature of 93 ° C., a lime addition rate of 70 kg (calcium oxide) / m ³ (green liquor), and a reaction temperature of 102 ° C. The reaction temperature in the lime slaker and the three causticizing tanks was also 102 ° C. The average residence time was about 1 hour and 10 minutes for the green liquor primary-slaker, about 15 minutes for the lime-slaker, and about 35 minutes for each of the causticizing tanks (1 hour and 45 minutes for 3 tanks).

Next, the white liquor and lime mud were separated with a white liquor belt filter, the moisture content of the lime mud was improved with a mud filter, and the lime mud cake was baked with a lime kiln. At this time, grit was collected with a lime slaker and the amount of grid generated was measured. Moreover, the lime mud after a mud filter was extract | collected and the cake specific resistance, the water | moisture content, and the whiteness were measured by the below-mentioned method. The white liquor produced had a NaOH concentration of 76.9 g / L, a Na ₂ S concentration of 24.8 g / L, and a Na ₂ CO ₃ concentration of 20.5 g / L.

(Evaluation of filterability: cake resistivity)
The filterability of the obtained calcium carbonate was evaluated by the cake specific resistance of the lime milk cake. The cake specific resistance was calculated | required based on the following apparatus and method. The cake specific resistance is “the pressure difference required to filter a liquid with a viscosity of 1 kg / m / sec at 1 m / sec when a 1 kg cake is formed in a filtration area of 1 m ² ”. Means poor separation and poor separation and cleaning.
・ Equipment: Constant pressure slurry evaluation system (IKABUST JT-F; Chuo Kako)
Sample: About 20 mL slurry (concentration 10%)
・ Decompression degree: 0.4 MPa
-Filtration area: 9.62 cm ²

(Moisture of lime mud after mud filter)
The weight (W1) of the lime mud cake was measured and dried in a dryer at 105 ° C. for 6 hours. After standing to cool, the weight (W2) of the lime mud cake was measured, and the moisture content (%) of the lime mud cake was determined by the following formula.
Moisture content of lime mud cake (%) = {(W1-W2) / W1} × 100

(Whiteness of lime mud)
The dried powder was pelletized with a pressure tablet molding machine and measured with a spectrocolorimeter (CMS-35SPX, manufactured by Murakami Color Research Laboratory Co., Ltd.).

[Example 2]
The causticizing step was performed in the same manner as in Example 1 except that the scallop shell baked product was added to the green liquor primary slaker at a rate of 0.8 t / hr and kiln calcined lime at a rate of 1.2 t / hr. Manufactured. In this example, the ratio of quick lime derived from scallop shell to kiln calcined lime is 40:60.

[Example 3]
The causticizing step was carried out in the same manner as in Example 1 except that the fired scallop shell was added to the green liquor primary slaker at a rate of 1.2 t / hr and kiln calcined lime at a rate of 0.8 t / hr. Manufactured. In this example, the ratio of quick lime derived from scallop shell to kiln calcined lime is 60:40.

[Example 4]
A causticizing step was carried out in the same manner as in Example 1 except that the scallop shell baked product was added to the green liquor premaly slaker at a rate of 1.6 t / hr and kiln calcined lime at a rate of 0.4 t / hr. Manufactured. In this example, the ratio of quick lime derived from scallop shell to kiln calcined lime is 80:20.

[Example 5]
A causticizing step was performed in the same manner as in Example 1 except that the scallop shell baked product was charged into a green liquor primary slaker at 2.0 t / hr and no kiln calcined lime was used to produce calcium carbonate. In this example, the ratio of quick lime derived from scallop shell to kiln calcined lime is 100: 0.

[Comparative Example 1]
The calcium carbonate was manufactured by performing the causticizing process in the same manner as in Example 1 except that the scallop shell baked product was changed to quick lime manufactured by baking limestone.

[Comparative Example 2]
The calcium carbonate was manufactured by performing the causticizing process in the same manner as in Example 2 except that the scallop shell baked product was changed to quick lime manufactured by baking limestone.

[Comparative Example 3]
Causticizing step was performed in the same manner as in Example 1 except that only quick lime produced by firing limestone was used to produce calcium carbonate.

[Comparative Example 4]
Except for using only kiln calcined lime, a causticizing step was performed in the same manner as in Example 1 to produce calcium carbonate.

Table 2 shows the results of the above examples and comparative examples. As is clear from the test results shown in Table 2, by using the scallop shell calcined product as a quick lime source in the causticizing process of kraft pulp production, the moisture content of the lime mud cake is lowered and the dewaterability of the lime mud is improved. I was able to. In addition, the amount of grid generation is reduced by the present invention. Furthermore, according to this invention, since the usage-amount of kiln calcination lime decreases, the usage-amount of heavy oil for baking kilns can be suppressed. Thus, according to this invention, the operativity of the causticizing process was able to be improved.

Also, the whiteness of causticized light calcium carbonate (lime mud) was improved by using the scallop shell burned material. That is, the light calcium carbonate obtained by the present invention has a high whiteness and is extremely suitable as a papermaking material, particularly a papermaking filler or a coating pigment.

Furthermore, the particle size distribution of the causticized calcium carbonate obtained in Example 5 and Comparative Example 3 was measured with an X-ray diffraction type particle size distribution measuring machine. The results are shown in FIG. 1, and the causticized calcium carbonate obtained by using the scallop shell baked product according to the present invention has a sharp particle size distribution. That is, it was speculated that the causticized calcium carbonate obtained by the present invention has a high dehydration property because of its sharp particle size distribution.

Experiment B: Production of causticized calcium carbonate using various fired shells
(1) Baked shells Oyster shells, clams, shijimi shells, hokki shells, tuna shells, snail shells, egg shells, scallop shells (from Okhotsk and Sanriku) were tested as shells. These materials were pulverized with a crusher for 1 hour, and then fired in an electric furnace at 850 ° C. for 2 hours to obtain quick lime (calcium oxide) derived from a shell.
(2) Fired products of shellfish shells As comparative examples, fired products of shellfish shells (sea urchin shells, barnacle shells, snow crab shells) were tested. Crustacean shells were fired in the same manner as in (1) above to obtain powder containing quicklime.
(3) Quicklime obtained by calcining limestone As quicklime obtained by calcining limestone, quicklime produced by Hokkaido Calcifying Industry Co., Ltd. was used.
(4) Green liquor The green liquor was collected from the causticizing process of a kraft pulp manufacturing plant of Nippon Paper Industries Co., Ltd. The NaOH concentration of the green liquor was 12 g / L, the Na ₂ S concentration was 25 g / L, and the Na ₂ CO ₃ concentration was 95 g / L (all in terms of Na ₂ O).

<Test method>
(1) Alkaline analysis: Measured according to TAPPI 624hm-85, TAPPI 625 hm-85.
(2) Iron content in calcium oxide: measured according to JIS K 0119.
(3) Calcium carbonate content in calcium oxide: The amount of carbon dioxide was measured with a carbon-in-metal analyzer (Horiba Seisakusho EMIA-100), and the calcium carbonate content was calculated from the amount.
(4) Whiteness of produced calcium carbonate: The dried powder was pelleted with a pressure tablet molding machine and measured with a spectrocolorimeter (CMS-35SPX, manufactured by Murakami Color Research Laboratory Co., Ltd.).
(5) Average particle size of the produced calcium carbonate: The product was washed with water and filtered, diluted with water, and then measured with a laser diffraction particle size distribution meter (Cirrus model 715). The short diameter and long diameter were determined with a scanning electron microscope (JSM5300, manufactured by JEOL Ltd.) after the product was washed with water, filtered, dried.
(6) Form of produced calcium carbonate: The product was washed with water, filtered, dried, and then observed with a scanning electron microscope (JSM-5300, manufactured by JEOL Ltd.).
(7) Crystal system: Measured by X-ray diffraction RAD-2C manufactured by Rigaku.
(8) Wire wear measurement was performed with a Japan Filcon wear test apparatus. A COS-60 polyester wire manufactured by Nippon Filcon was used as the wire, and a wear test was conducted for 90 minutes under the conditions of a slurry concentration of 2% by weight and a load of 1250 g. The wire wear resistance of calcium carbonate was evaluated by the amount of wire wear before and after the wear test (the weight loss of the wire: mg).

<Manufacture of causticized calcium carbonate>
[Example 1]
A separable flask (volume 1 L) equipped with a stirrer (stirring speed 450 rpm, Kyoei Power Srirrer Type PS-2N) and a heating mantle heater was used as a causticizing reaction apparatus. 90 ml of hot water at 50 ° C. was poured into the flask, and then 60 g of Sanriku oyster shell calcined product was added to obtain a slaked lime slurry. Further, 630 mL of a green liquor at 50 ° C. was added every 2 hours to make caustic. Calcium carbonate produced from the reaction solution was collected by suction filtration, thoroughly washed with tap water, dehydrated, and dried in a blow dryer at 105 ° C. to obtain powdered calcium carbonate. Table 1 shows the measurement results of the whiteness and hue of calcium carbonate. Further, when the filtrate was analyzed, the sodium hydroxide concentration was 76.5 g / L and the sodium sulfide concentration was 25.2 g / L, which was suitable as a cooking liquid (white liquor) for producing kraft pulp. .

[Example 2]
Calcium carbonate was produced in the same manner as in Example 1 except that the fired clam shell was used. When the filtrate was analyzed, the sodium hydroxide concentration was 76.3 g / L and the sodium sulfide concentration was 25.1 g / L, which was suitable as a cooking liquid (white liquor) for kraft pulp production. .

[Example 3]
Calcium carbonate was produced in the same manner as in Example 1 except that the burnt seashell shell was used. When the filtrate was analyzed, the sodium hydroxide concentration was 76.4 g / L and the sodium sulfide concentration was 25.1 g / L, which was suitable as a cooking liquid (white liquor) for producing kraft pulp. .

[Example 4]
Calcium carbonate was produced in the same manner as in Example 1 except that the fired seashell shell was used. Further, when the filtrate was analyzed, the sodium hydroxide concentration was 76.0 g / L and the sodium sulfide concentration was 25.2 g / L, which was suitable as a cooking liquid (white liquor) for producing kraft pulp. .

[Example 5]
Calcium carbonate was produced in the same manner as in Example 1 except that the fired Sazae shell was used. Further, when the filtrate was analyzed, the sodium hydroxide concentration was 76.1 g / L and the sodium sulfide concentration was 25.2 g / L, which was suitable as a cooking liquid (white liquor) for producing kraft pulp. .

[Example 6]
Calcium carbonate was produced in the same manner as in Example 1 except that a fired snail shell was used. When the filtrate was analyzed, the sodium hydroxide concentration was 77.0 g / L and the sodium sulfide concentration was 25.3 g / L, which was suitable as a cooking liquid (white liquor) for producing kraft pulp. .

[Example 7]
Calcium carbonate was produced in the same manner as in Example 1 except that a baked product of Okhotsk scallop shell was used.

[Example 8]
Calcium carbonate was produced in the same manner as in Example 1 except that a fired product of Sanriku scallop shell was used.

[Comparative Example 1]
Calcium carbonate was produced in the same manner as in Example 1 except that the fired sea urchin shell was used.

[Comparative Example 2]
Calcium carbonate was produced in the same manner as in Example 1 except that a burned material of barnacle (arthropod / crustacea) shell was used.

[Comparative Example 3]
Calcium carbonate was produced in the same manner as in Example 1 except that a fired product of a snow crab (crustacea) shell was used.

[Comparative Example 4]
Calcium carbonate was produced in the same manner as in Example 1 except that limestone-derived quicklime was used.

Causticized light calcium carbonate made from fired shells has a whiteness of 6-8 points higher than the comparative example. The lower the content of iron, magnesium and sulfur in the calcium oxide used in the causticizing reaction, the higher the whiteness of the resulting calcium carbonate.

Experiment C: Production of paper coated with calcium carbonate Disperse the causticized light calcium carbonate sludge obtained in Example 1 of Experiment A in a dissolution tank to 72%, grind it with a sand grinder, and determine the particle size distribution by laser diffraction method. A causticized light calcium carbonate having an average particle size of 0.98 μm measured with a measuring instrument (Mastersizer 200, manufactured by Malvern) was obtained. 46.8 parts of this causticized light calcium carbonate, clay (26.2 parts of Capim DG (manufactured by Imerys), 18 parts of Contour 1500 (manufactured by Imerys), 9 parts of Hydraperth (manufactured by Keimin)) 2 parts, 9 parts of latex (F1755, manufactured by Asahi Kasei), 6.5 parts of starch (Etylex 2015, manufactured by Tate & Lyle), 2.8 parts of fluorescent dye (Brancophor UW-L, manufactured by Chemilla) are mixed, A paint was prepared.

It contains 45 parts of NBKP (conifer bleached kraft pulp), 25 parts of LBKP (hardwood bleached kraft pulp), 10 parts of DIP (deinked pulp), 20 parts of GP (groundwood pulp) and 21 parts of broke pulp. A base paper having a basis weight of 44.5 g / m ² was produced at a rate of 1 min.

The paint was coated with 845M / min at a coat weight of 10.4 g / ^{m 2} to 8.6g ^{/ m} 2, W surface (wire side) to the F surface of the base paper (felt side), 170 ° C. A coated paper was manufactured by performing a 2-nip HSNC (high temperature soft nip calender) process under the conditions of 190 kgf / cm and 190 ° C. and 220 kgf / cm.

On the other hand, as a comparative example, a coated paper was produced in the same manner as above except that the causticized light calcium carbonate sludge of Comparative Example 1 of Experiment A was used.

Table 4 shows the quality of the coated paper obtained. The coated paper coated with the causticized calcium carbonate of the present invention was excellent in whiteness and opacity.

Claims

A method for producing causticized light calcium carbonate, comprising mixing green liquor generated in a causticizing step in pulp manufacture and a fired shellfish and performing a causticizing reaction to obtain light calcium carbonate.
The method according to claim 1, wherein the shell is a scallop shell, an oyster shell, a clam shell, a swordfish shell, a sea shell, a tuna shell, or a snail shell.
The method according to claim 1 or 2, wherein the shell is a scallop shell.
The method according to any one of claims 1 to 3, wherein an iron content of the fired shell is 0.05% by weight or less in terms of Fe 2 O 3 .
The method according to any one of claims 1 to 4, wherein the calcium carbonate is a papermaking material.
Light calcium carbonate obtained by the method according to any one of claims 1 to 5.
A method for producing a coated paper, comprising coating calcium carbonate obtained by the method according to any one of claims 1 to 5 on a base paper.
A coated paper obtained by coating calcium carbonate obtained by the method according to any one of claims 1 to 5 on a base paper.
A method for producing paper, comprising internally adding calcium carbonate obtained by the method according to any one of claims 1 to 5 to the paper.
A paper internally added with calcium carbonate obtained by the method according to any one of claims 1 to 5.
A method for producing a white liquor, comprising obtaining a white liquor by performing a causticization reaction between a green liquor generated in a causticizing step in pulp production and a shell fired product.
A method for producing kraft pulp, which comprises obtaining a white liquor by performing a causticizing reaction between a green liquor generated in a causticizing step in pulp manufacture and a shell fired product.