JP2011073899A - Method for producing light calcium carbonate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing light calcium carbonate that can produce light calcium carbonate of good whiteness easier than conventional methods, using even low-grade limestone as a raw material. <P>SOLUTION: The light calcium carbonate is produced by wet-slaking quicklime with slaking water to obtain an aqueous slurry of slaked lime and then reacting the aqueous slurry of slaked lime with carbon dioxide. Before obtaining the aqueous slurry of slaked lime, a reducing agent is sprayed to the quicklime or added to the slaking water. The amount of the reducing agent to be added may be 0.005-1.0 mass% relative to the solid of the final light calcium carbonate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing light calcium carbonate (hereinafter, also simply referred to as “manufacturing method”), and more particularly, to a method for producing high white light calcium carbonate from limestone containing coloring impurities.

  Conventionally, calcium carbonate industrially uses limestone obtained by calcining limestone as a raw material, prepares a slaked lime aqueous slurry by wet digestion in which this reacts with water, and uses the obtained slaked lime aqueous slurry as carbon dioxide. It is produced as light calcium carbonate by reacting. This light calcium carbonate demand has increased mainly in the papermaking industry as the paper industry in recent years has shifted from acidic papermaking using talc as a filler to neutral and alkaline papermaking using calcium carbonate as a filler. It is what.

  However, the whiteness of light calcium carbonate produced as described above is easily affected by chemical components contained in the limestone raw material, and when using limestone with a high content of Mn and Fe as coloring components, There was a problem that the lightness of the light calcium carbonate produced became strong and the whiteness was significantly reduced.

As an improved technique relating to the production of this light calcium carbonate, for example, Patent Document 1 discloses a technique for bleaching the produced light calcium carbonate using a reducing bleach. sulphite _{(Na 2} S 2 _{O 4,} etc.), rongalite _{(NaHSO 2 · CH 2 O ·} H 2 O), formamidine sulfinic acid _{(H 2 NC (: NH)} SO 2 H) by the like, the addition As conditions, it is described that the addition rate is 0.05 to 0.5% by weight per light calcium carbonate weight, the temperature is 20 to 80 ° C., and the bleaching time is 10 to 60 minutes.

Japanese Patent Laid-Open No. 06-41892 (Claims, [0025], etc.)

  However, as in Patent Document 1, although there is a method for improving the whiteness of light calcium carbonate by bleaching after production, in this case, since a bleaching process is newly added after the production process, production There was a difficulty that the property would be lowered. Therefore, it has been desired to realize a technique for obtaining light calcium carbonate having better whiteness than ever before in a simpler manner.

  Accordingly, an object of the present invention is to provide a light calcium carbonate that can more easily obtain a high white light calcium carbonate with good whiteness even when a low-grade limestone raw material having a large content of coloring components is used. It is in providing the manufacturing method of.

  As a result of intensive studies, the present inventors have improved the optical properties of light calcium carbonate finally obtained by adding a reducing agent in the process of obtaining slaked lime from quick lime, and light carbonate with excellent whiteness. It was found that calcium can be used, and the present invention has been completed.

That is, the light calcium carbonate production method of the present invention is a method for producing light calcium carbonate by reacting the slaked lime aqueous slurry with carbon dioxide after adding digested water to wet lime to obtain wet slaked lime slurry, and then reacting the slaked lime aqueous slurry with carbon dioxide. In
Prior to obtaining the slaked lime aqueous slurry, a reducing agent is sprayed on the quicklime or added to the digested water.

  In the present invention, among the reducing agents, a reducing bleaching agent can be suitably used. Moreover, it is preferable that the addition amount of the said reducing agent shall be 0.005-1.0 mass% with respect to solid content of the light calcium carbonate finally obtained.

  According to the present invention, it is possible to obtain a high white light calcium carbonate with good whiteness more easily than in the past even when a low-grade limestone raw material containing a coloring component is used. it can. According to the production method of the present invention, since the reducing agent is added in the course of the existing light calcium carbonate production process, there is no need to provide a new treatment step, and an increase in treatment time can be prevented. No loss of productivity. Moreover, since a whitening effect can be heightened by adding a reducing agent before making quicklime react, whiteness can be raised with a slight reducing agent addition amount. Furthermore, according to the present invention, there can be obtained an advantage that low-grade limestone, which could not be used as a raw material for light calcium carbonate, can be effectively used.

Hereinafter, preferred embodiments of the present invention will be described in detail.
In the present invention, digested water is added to quick lime and wet digested to obtain a slaked lime aqueous slurry, and then the obtained slaked lime aqueous slurry and carbon dioxide are reacted to produce light calcium carbonate to obtain a slaked lime aqueous slurry. It is important to add a reducing agent during the process.

  When obtaining a slaked lime aqueous slurry by applying digested water to quick lime, it is possible to easily obtain light calcium carbonate with good whiteness even from low-grade limestone raw materials by adding a reducing agent before the reaction. Is possible. Here, in the present invention, the reducing agent may be added to the raw quicklime by spraying, or may be added to the digested water that acts on quicklime, and in any case, the effects of the present invention are obtained equally. be able to.

  The reducing agent that can be used in the present invention is not particularly limited, and any reducing agent may be used as long as it can cause a reducing action. Specifically, for example, hydrogen, hydrogen compounds such as hydrogen iodide and sodium borohydride, lower oxides such as sulfur dioxide and sulfite, or salts of lower oxygen acids, sodium sulfide, sodium polysulfide, ammonium sulfide, etc. Low-valence metals such as sulfur compounds, alkali metals, magnesium, calcium, aluminum, zinc, etc., or their amalgams, iron (II), tin (II), titanium (III), chromium (II) Examples thereof include organic salts having a low oxidation stage such as metal salts, aldehydes, saccharides, formic acid, and oxalic acid. Among them, particularly, a reducing bleaching agent can be suitably used. Specific examples include sulfur dioxide, sodium hydrogen sulfite, hydrosulfite (sodium dithionite) and the like.

  Moreover, as addition amount of the reducing agent in this invention, it is 0.005-1.0 mass% with respect to solid content of the light calcium carbonate finally obtained, especially 0.01-0.1 mass%. It is preferable. If the amount of the reducing agent used is less than 0.005% by mass, sufficient whiteness may not be obtained, and even if it exceeds 1.0% by mass, no further effect can be obtained. In the present invention, there is a great merit in that light calcium carbonate with good whiteness can be obtained with such a small amount of addition.

  In this invention, what is necessary is just to add a reducing agent in the preparation process of the said slaked lime aqueous slurry, About other points, it can implement according to a conventional method, and it does not restrict | limit in particular. In the present invention, the reducing agent can be used by appropriately mixing with a commonly used additive such as a chelating agent or a pH adjuster (alkali metal compound, etc.). The same whitening effect as when used can be obtained.

  As a raw material of quicklime used in the present invention, not only high-grade limestone with few impurities that are usually used, but also low-grade limestone with a high content of coloring components such as Mn and Fe can be used. Specifically, for example, low-grade limestone containing 0.02% by mass or more, particularly 0.1 to 0.3% by mass of coloring impurities other than CaO when used as quick lime as a raw material. It is possible to use. Moreover, in this invention, there is no restriction | limiting in particular as water used for the wet digestion of the quicklime obtained from this limestone, Industrial water, well water, groundwater, etc. can be used.

  Furthermore, in this invention, the carbonation reaction of the slaked lime aqueous slurry obtained by wet digestion can be performed by the method used normally, Preferably it is 50-200 g / liter of slaked lime density | concentration, More preferably, it is 60-150 g / liter of slaked lime. Carbon dioxide-containing gas having a carbon dioxide concentration of 5 to 40% by volume, particularly 10 to 35% by volume, is added to the aqueous slurry at a rate of 1 to 12 liters per minute, especially 3 to 10 liters per kg of slaked lime. A method of blowing at a reaction start temperature of 30 to 70 ° C., particularly 35 to 60 ° C. is used.

  As a particularly suitable aqueous slaked lime slurry, the residue generated by wet digestion is removed so as to be 1% by mass or less, preferably 0.5% by mass or less based on the aqueous slurry, and the viscosity is measured by a B-type viscometer. The measured value is adjusted to 250 cP or less, preferably 200 cP or less. If there is too much residue, the carbonation reaction will be uneven and the particle size and shape may be uneven. If the viscosity is higher than 250 cP, columnar or needle-shaped aragonite will be mixed during the carbonation reaction. The viscosity of the calcium carbonate aqueous slurry increases, and clogging of the sieve is likely to occur during sieving. Here, the viscosity is a value measured at 60 rpm using a Brookfield viscometer, that is, a B-type viscometer after adjusting the slaked lime aqueous slurry to 25 ° C.

  The carbon dioxide used in the present invention is not limited to a genuine one, but a mixed gas containing it, for example, limestone fired exhaust gas such as limestone fired kiln exhaust gas, lime fired exhaust gas such as lime kiln exhaust gas of a pulp production plant, It may be in the form of power generation boiler exhaust gas, garbage incineration exhaust gas, or the like.

  According to the production method of the present invention, high white light calcium carbonate having an ISO whiteness of 96.5 to 99.0% according to JIS P8148 can be obtained.

Hereinafter, the present invention will be described in more detail with reference to examples.
(Conventional example)
Light calcium carbonate was produced from quick lime obtained from low-grade limestone containing 0.16% by mass of coloring impurities. First, 2 kg of this quicklime was digested with 30 liters of digested water at 60 ° C. to obtain a slaked lime aqueous slurry having a slaked lime concentration of 74 g / liter. A pure gas having a carbon dioxide concentration of 99.9% by volume is blown into this slaked lime aqueous slurry at a reaction start temperature of 60 ° C. at a rate of 2 liters per minute in a standard state per kg of slaked lime to perform a carbonation reaction. A light calcium carbonate was obtained. After removing the residue from the obtained light calcium carbonate using a 325 mesh sieve, formamidine sulfinic acid as a reducing bleach was added to the light calcium carbonate in the addition amount shown in the following table. did.

Example 1
Light calcium carbonate was obtained in the same manner as in the conventional example except that the reducing bleaching agent was not added to the obtained light calcium carbonate but sprayed on quick lime.

(Example 2)
A light calcium carbonate was obtained in the same manner as in the conventional example except that the reducing bleaching agent was not added to the obtained light calcium carbonate but added to the digested water.

  About each obtained light calcium carbonate, ISO whiteness based on JIS P8148 was measured using CMS-35SPX by Murakami Color Research Laboratory as an ISO whiteness measuring apparatus. The results are also shown in the table below.

＊１）最終的に得られる軽質炭酸カルシウムの固形分に対する添加量である。

* 1) The amount added to the solid content of light calcium carbonate finally obtained.

  As shown in the above table, in each Example in which the reducing bleach was added to quick lime or digested water in advance, a smaller amount was added compared to the conventional example added to the light calcium carbonate finally obtained. However, it can be seen that light calcium carbonate having high whitening effect and high whiteness is obtained.

(Example 3)
Light calcium carbonate was obtained in the same manner as in Example 2 except that hydrosulfite as a reducing bleaching agent was added in the amount shown in the following table instead of formamidine sulfinic acid as a reducing bleaching agent. It was.

Example 4
Light calcium carbonate was obtained in the same manner as in Example 2 except that hydrazine as a reducing agent was added in the amount shown in the following table instead of formamidinesulfinic acid as a reducing bleach.

(Comparative example)
Light calcium carbonate was obtained in the same manner as in Example 2 except that hydrogen peroxide as an oxidizing bleaching agent was added in the addition amount shown in the following table instead of formamidinesulfinic acid as a reducing bleaching agent. It was.

  About each obtained light calcium carbonate, ISO whiteness based on JIS P8148 was measured using CMS-35SPX by Murakami Color Research Laboratory as an ISO whiteness measuring apparatus. The results are also shown in the table below.

＊２）無データを示す。

* 2) Indicates no data.

  As shown in the above table, a whitening effect is obtained in each example using a reducing bleach or a reducing agent, whereas a whitening effect is seen in a comparative example using an oxidized bleach. I understand that there is no.

Claims (3)

In a method for producing light calcium carbonate by reacting the slaked lime aqueous slurry and carbon dioxide after adding digested water to wet lime to obtain wet slaked lime slurry,
Prior to obtaining the slaked lime aqueous slurry, a reducing agent is sprayed on the quick lime or added to the digested water.   The method for producing light calcium carbonate according to claim 1, wherein a reducing bleach is used as the reducing agent.   The method for producing a light calcium carbonate according to claim 1 or 2, wherein the addition amount of the reducing agent is 0.005 to 1.0 mass% with respect to the solid content of the light calcium carbonate finally obtained.